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Elevated insulin-like growth factor-I receptor (IGF-IR) levels in primary breast tumors associated with BRCA1 mutations
Abstract
The insulin-like growth factors (IGFs) play a pivotal role in breast cancer. Inherited predisposition to breast and ovarian cancer is associated with germline BRCA1/BRCA2 mutations. To evaluate the impact of BRCA1 mutations on IGF-IR gene expression, we performed an immunohistochemical analysis of IGF-IR in primary breast tumors from BRCA1 mutation carriers and non-carriers. Results obtained revealed a significant elevation in IGF-IR levels in tumors from BRCA1 mutation carriers compared with non-carriers. To assess the potential inhibitory role of BRCA1 on IGF-IR levels, we infected the BRCA1-deficient HCC1937 cell line with a BRCA1-encoding adenoviral vector. Results of Western blots showed that BRCA1 induced a large reduction in endogenous IGF-IR levels. Furthermore, results of chromatin immunoprecipitation assays indicated that the mechanism of action of BRCA1 involves interaction with Sp1, a potent transactivator of the IGF-IR gene. In conclusion, our data suggests that the IGF-IR gene is a physiologically relevant downstream target for BRCA1 action.
... Most BRCA1 tumors phenocopy TNBC (100). In line with BRCA1-mediated repression of the IGF1R promoter (112,113), BRCA1-mutant tumors show elevated IGFIR and IGF1 levels, leading to reduced apoptosis, and enhanced survival (113)(114)(115). Importantly, inhibition of the IGF1R/PI3K/AKT pathway decreases proliferation in BRCA1-deficient cells (116). ...
... Most BRCA1 tumors phenocopy TNBC (100). In line with BRCA1-mediated repression of the IGF1R promoter (112,113), BRCA1-mutant tumors show elevated IGFIR and IGF1 levels, leading to reduced apoptosis, and enhanced survival (113)(114)(115). Importantly, inhibition of the IGF1R/PI3K/AKT pathway decreases proliferation in BRCA1-deficient cells (116). ...
... This expression may be a result of ER-driven growth through IGF1R rather than a causative link between IGF1R and the luminal lineage; nevertheless, the presence of IGF1R may still affect cell signaling and perhaps cell lineage. In addition to luminal tumors, IGF1R actively promotes tumor growth and survival in p53 and BRCA1-mutant tumors, which usually emulate the basal-like subtype (113)(114)(115). Although basal-like breast cancers are defined by basal and myoepithelial marker expression (148), they present with a luminal progenitor gene signature (148)(149)(150)(151)(152). In support of this luminal link, recent studies suggest BRCA1-associated basal-like tumors derive from a luminal progenitor cell of origin rather than a basally positioned cell (150,153). ...
Insulin-like growth factor (IGF) signaling is fundamental for growth and survival. A large body of evidence (laboratory, epidemiological, and clinical) implicates the exploitation of this pathway in cancer. Up to 50% of breast tumors express the activated form of the IGF1 receptor (IGF1R). Breast cancers are categorized into subtypes based upon hormone and ERRB2 receptor expression and/or gene expression profiling. Even though IGF1R influences tumorigenic phenotypes and drug resistance across all breast cancer subtypes, it has specific expression and function in each. In some subtypes, IGF1R levels correlate with a favorable prognosis, while in others it is associated with recurrence and poor prognosis, suggesting different actions based upon cellular and molecular contexts. In this review, we examine IGF1R expression and function as it relates to breast cancer subtype and therapy-acquired resistance. Additionally, we discuss the role of IGF1R in stem cell maintenance and lineage differentiation and how these cell fate influences may alter the differentiation potential and cellular composition of breast tumors.
... Further evidence suggests that additional factors, including breast cancer-associated factor 1 (BRCA1), high-mobility group A1, estrogen receptor a (ERa) and ATM kinase, associate with Sp1 (see Table 2) and modulate IGF1R transcription [97,198,201]. BRCA1 has been shown to play a role in suppressing Sp1-mediated regulation of IGF1R, which has significant implications for the development and [199,200,262]. The interaction between Brca1 and Sp1 is stimulated by IGF1 [199,262]. ...
... BRCA1 has been shown to play a role in suppressing Sp1-mediated regulation of IGF1R, which has significant implications for the development and [199,200,262]. The interaction between Brca1 and Sp1 is stimulated by IGF1 [199,262]. BRCA1 directly interacts with Sp1 through amino acids 260-802, but the region of Sp1 that binds Brca1 has yet to be identified [115]. It was later established that individuals with the BRCA1 mutation have increased levels of IGF1R compared to patients lacking the BRCA1 mutation [199]. ...
... BRCA1 directly interacts with Sp1 through amino acids 260-802, but the region of Sp1 that binds Brca1 has yet to be identified [115]. It was later established that individuals with the BRCA1 mutation have increased levels of IGF1R compared to patients lacking the BRCA1 mutation [199]. This suggests that individuals with the BRCA1 mutation are probably able to maintain increased IGF1R transcription in the presence or absence of IGF1 stimulation, due to a lack of Sp1dependent transcriptional inhibition. ...
Transcription factor Sp1 was, for many years, viewed as a basal transcription factor and relegated to the regulation of so-called housekeeping genes. Sp1's role in recruiting the general transcription machinery in the absence of a TATA box increased its importance in gene regulation, particularly in light of recent estimates that the majority of mammalian genes lack a TATA box. In this review, we briefly address the history of Sp1, the founding member of the Sp family of transcription factors. We review the evidence suggesting Sp1 is highly regulated by post-translational modifications that both positively and negatively affect Sp1's activity on a wide array of genes. Sp1 is overexpressed in many cancers and is associated with poor prognosis. Targeting Sp1 in cancer treatment has been suggested; however, our review of the literature on Sp1-dependent regulation of genes that contribute to the "hallmarks of cancer", described by Hanahan and Weinberg, illustrates the extreme complexity of Sp1 functions. Sp1 both activates and suppresses the expression of a number of essential oncogenes and tumor suppressors, as well as genes involved in essential cellular functions, including proliferation, differentiation, DNA damage response, apoptosis, senescence, and angiogenesis. Sp1 is also implicated in inflammation and genomic instability, as well as epigenetic silencing. Based on the seemingly opposing effects of Sp1, a more complete understanding of the function of Sp1 in cancer is needed to validate its potential as a therapeutic target. This article is protected by copyright. All rights reserved.
... A bidirectional link between the IGF1 and BRCA1 signaling pathways was suggested by studies showing that cellular levels of BRCA1 are upregulated by ambient concentrations of IGF1 (23). In addition, immunohistochemical analyses of IGF1R levels in a collection of primary breast tumors derived from BRCA1 mutation carriers and non-carriers revealed a higher score in BRCA1-associated tumors compared to sporadic tumors (24). Non-tumorous breast tissue of 185delAG BRCA1 mutation carriers had a higher IGF1R score than tissue derived from non-carriers. ...
... Electrophoretic mobility shift assays using the in vitro translated BRCA1 protein revealed no BRCA1 binding to the IGF1R promoter sequence (21). Coherent with the failure of mutant BRCA1 to suppress IGF1R gene transcription, immunohistochemical analyses of primary breast tumors derived from a cohort of 185delAG BRCA1 mutation carrier patients revealed almost twofold higher IGF1R levels than in sporadic breast tumors (24). Of clinical relevance, loss-of-function mutation of tumor suppressor p53 in human cancer may affect the capacity of BRCA1 to inhibit the IGF1R gene (33). ...
The insulin-like growth factor-1 receptor (IGF1R) emerged in recent years as a promising therapeutic target in oncology. Identification of potential biomarkers capable of predicting response to IGF1R-targeted therapy is of cardinal importance. Tumor suppressor BRCA1 has important roles in multiple pathways, including gene transcription, DNA damage repair, and control of apoptosis. Early studies have identified the IGF1R gene as a downstream target for inhibitory regulation by wild-type, but not mutant, BRCA1. The aim of the present study was to evaluate the hypothesis that the mutational status of BRCA1 may influence the ability of IGF1R-directed therapies to efficiently inhibit the IGF1R axis. Using breast cancer-derived cell lines expressing a wild-type or a mutant BRCA1, we demonstrate that the capacity of MK-0646, a monoclonal antibody antagonist to the human IGF1R, to inhibit insulin-like growth factor-1-stimulated IGF1R and downstream mediators’ phosphorylation was impaired in mutant BRCA1-expressing cell lines. In addition, the antibody was able to reduce proliferation of wild-type BRCA1-expressing cells but had a reduced inhibitory effect in mutant BRCA1-expressing cells. In summary, our data indicate that the mutational status of BRCA1 must be taken into account when selecting patients for IGF1R targeting protocols.
... BRCA1 has been shown to directly affect the IGF-1R pathway [12] and studies have suggested that BRCA1/2 deficient breast cancer cells are associated with elevated expression of Insulin like growth factor-1 receptor (IGF-1R) [13][14][15]. IGF-1R are widely expressed on normal and neoplastic cells [13,[16][17][18][19][20], and an IGF-1 autocrine loop was described in ovarian and breast cancer cells [21][22][23]. Inhibition of the IGF-1 pathway suppresses ovarian cancer cell survival in vitro [22,24,25] and in vivo in xenograft models [26], and its expression is associated with cancer progression [17,27]. ...
... *p value <0.05 and has been shown to directly interact with IGF signaling such that variants in this pathway may modify risk of cancer in women carrying BRCA mutations [12]. Transcriptional suppression of the IGF-1R gene by BRCA1 has also been reported in breast and endometrial cancer, and loss-of-function mutation of BRCA1 leads to amplification [44][45][46] and constitutive activation of the IGF-1R pathway in breast cancer [13][14][15]. The data presented in this manuscript suggests an interaction between the two pathways, as demonstrated by the enhanced protein levels of IGF-1R, p-IGF-1R, p-IRS-1, p-AKT and p-S6 in ovarian and breast cancer cells having loss-of-function mutations of BRCA1. ...
Background
Impairment of homologous recombination (HR) is found in close to 50 % of ovarian and breast cancer. Tumors with BRCA1 mutations show increased expression of the Insulin-like growth factor type 1 receptor (IGF-1R). We previously have shown that inhibition of IGF-1R results in growth inhibition and apoptosis of ovarian tumor cells. In the current study, we aimed to investigate the correlation between HR and sensitivity to IGF-1R inhibition. Further, we hypothesized that IGF-1R inhibition might sensitize HR proficient cancers to Poly ADP ribose polymerase (PARP) inhibitors.
Methods
Using ovarian and breast cancer cellular models with known BRCA1 status, we evaluated their HR functionality by RAD51 foci formation assay. The 50 % lethal concentration (LC50) of Insulin-like growth factor type 1 receptor kinase inhibitor (IGF-1Rki) in these cells was assessed, and western immunoblotting was performed to determine the expression of proteins involved in the IGF-1R pathway. Moreover, IGF-1R inhibitors were added on HR proficient cell lines to assess mRNA and protein expression of RAD51 by qPCR and western blot. Also, we explored the interaction between RAD51 and Insulin receptor substance 1 (IRS-1) by immunoprecipitation. Next, combination effect of IGF-1R and PARP inhibitors was evaluated by clonogenic assay.
Results
Cells with mutated/methylated BRCA1 showed an impaired HR function, and had an overactivation of the IGF-1R pathway. These cells were more sensitive to IGF-1R inhibition compared to HR proficient cells. In addition, the IGF-IR inhibitor reduced RAD51 expression at mRNA and protein levels in HR proficient cells, and sensitized these cells to PARP inhibitor.
Conclusion
Targeting IGF-1R might lead to improved personalized therapeutic approaches in cancer patients with HR deficiency. Targeting both PARP and IGF-1R might increase the clinical efficacy in HR deficient patients and increase the population of patients who may benefit from PARP inhibitors.
... In contrast, mutant BRCA1 proteins lack transcriptional activity and are impaired in their ability to suppress the IGF1R promoter, with resulting increases in IGF1R mRNA and IGF binding in mammary tumors. Consistent with the postulate that mutant BRCA1 may lead to deregulated IGF1R expression, a recent immunohistochemical analysis revealed significantly elevated IGF1R levels in primary breast tumors derived from BRCA1 mutation carriers, compared to sporadic tumors (50). ...
... As discussed above, our studies provided evidence for functional and physical interactions between the IGF signaling pathways and tumor suppressors p53 and BRCA1. We demonstrated that IGF1R gene transcription rate is dependent on a number of stimulatory nuclear proteins and is also modulated by negative transcriptional regulators, including p53/p63/p73 (45,75) and BRCA1 (46)(47)(48)(49)(50). The level of expression of the IGF1R gene is ultimately determined by complex interactions between stimulatory and inhibitory transcription factors. ...
Epidemiological as well as clinical and experimental data identified the insulin-like growth factors (IGF1, IGF2) as important players in gynecological cancers in general, and endometrial tumors in particular. The IGF1 receptor (IGF1R), which mediates the proliferative and anti-apoptotic activities of both ligands, emerged in recent years as a promising therapeutic target in oncology. However, most clinical trials conducted so far led to mixed results, emphasizing the need to identify biomarkers that can predict responsiveness to anti-IGF1R-targeted therapies. This article will review recent data regarding the role and expression of IGF system components in endometrial cancer. In addition, we will review data on the interplay between the IGF signaling pathway and tumor suppressors p53 and breast cancer susceptibility gene-1 (BRCA1). Anti-oncogenes p53 and BRCA1 play a key role in the etiology of gynecological cancers and, therefore, their interaction with IGF1R is of high relevance in translational terms. A better understanding of the complex mechanisms underlying the regulation of the IGF system will improve our ability to develop effective treatment modalities for endometrial tumors.
... The luciferase assays corroborate the results obtained by Western blots and ChIP assays. We have previously shown using EMSA and ChIP that both Sp1 and ER bind to the IGF-IR promoter and stimulate gene transcription, whereas no ER binding was seen in C4 cells [60]. In addition, we have reported that Sp1 increased IGF-IR promoter activity with a 5.8-fold higher potency in MC7 than in C4 cells [60]. ...
... We have previously shown using EMSA and ChIP that both Sp1 and ER bind to the IGF-IR promoter and stimulate gene transcription, whereas no ER binding was seen in C4 cells [60]. In addition, we have reported that Sp1 increased IGF-IR promoter activity with a 5.8-fold higher potency in MC7 than in C4 cells [60]. Taken together, there is a remarkable consistency between the various technological approaches used to identify IGF-IR promoter-binding transcription factors. ...
The insulin-like growth factor I receptor (IGF-IR) has been implicated in the etiology of breast cancer. Overexpression of the IGF-IR gene is a typical feature of most primary breast cancers, whereas low IGF-IR levels are seen at advanced stages. Hence, evaluation of IGF-IR levels might be important for assessing prognosis. In the present study, we employed a proteomic approach based on DNA affinity chromatography followed either by mass spectroscopy (MS) or Western blot analysis to identify transcription factors that may associate with the IGF-IR promoter in estrogen receptor (ER)-positive and ER-depleted breast cancer cells. A biotinylated IGF-IR promoter fragment was bound to streptavidin magnetic beads and incubated with nuclear extracts of breast cancer cells. IGF-IR promoter-binding proteins were eluted with high salt and analyzed by MS and Western blots. Among the proteins that were found to bind to the IGF-IR promoter we identified zinc finger transcription factors Sp1 and KLF6, ER-, p53, c-jun, and poly (ADP-ribosylation) polymerase. Furthermore, chromatin immune-precipitation (ChIP) analysis confirmed the direct in vivo binding of some of these transcription factors to IGF-IR promoter DNA. The functional relevance of binding data was assessed by cotransfection experiments with specific expression vectors along with an IGF-IR promoter reporter. In summary, we identified nuclear proteins that are potentially responsible for the differential expression of the IGF-IR gene in ER-positive and ER-depleted breast cancer cells.
... The luciferase assays corroborate the results obtained by Western blots and ChIP assays. We have previously shown using EMSA and ChIP that both Sp1 and ER bind to the IGF-IR promoter and stimulate gene transcription, whereas no ER binding was seen in C4 cells [60]. In addition, we have reported that Sp1 increased IGF-IR promoter activity with a 5.8-fold higher potency in MC7 than in C4 cells [60]. ...
... We have previously shown using EMSA and ChIP that both Sp1 and ER bind to the IGF-IR promoter and stimulate gene transcription, whereas no ER binding was seen in C4 cells [60]. In addition, we have reported that Sp1 increased IGF-IR promoter activity with a 5.8-fold higher potency in MC7 than in C4 cells [60]. Taken together, there is a remarkable consistency between the various technological approaches used to identify IGF-IR promoter-binding transcription factors. ...
The insulin-like growth factor I receptor (IGF-IR) has been implicated in the etiology of breast cancer. Overexpression of the IGF-IR gene is a typical feature of most primary breast cancers, whereas low IGF-IR levels are seen at advanced stages. Hence, evaluation of IGF-IR levels might be important for assessing prognosis. In the present study, we employed a proteomic approach based on DNA affinity chromatography followed either by mass spectroscopy (MS) or Western blot analysis to identify transcription factors that may associate with the IGF-IR promoter in estrogen receptor (ER)-positive and ER-depleted breast cancer cells. A biotinylated IGF-IR promoter fragment was bound to streptavidin magnetic beads and incubated with nuclear extracts of breast cancer cells. IGF-IR promoter-binding proteins were eluted with high salt and analyzed by MS and Western blots. Among the proteins that were found to bind to the IGF-IR promoter we identified zinc finger transcription factors Sp1 and KLF6, ER-, p53, c-jun, and poly (ADP-ribosylation) polymerase. Furthermore, chromatin immune-precipitation (ChIP) analysis confirmed the direct in vivo binding of some of these transcription factors to IGF-IR promoter DNA. The functional relevance of binding data was assessed by cotransfection experiments with specific expression vectors along with an IGF-IR promoter reporter. In summary, we identified nuclear proteins that are potentially OPEN ACCESS Cancers 2010, 2 234 responsible for the differential expression of the IGF-IR gene in ER-positive and ER-depleted breast cancer cells.
... An association between somatic IGF1R expression and BRCA1 status in breast cancer has been described. 44 Immunohistochemical analyses of 36 primary breast tumour specimens (11 tumours from patients with 185_186delAG BRCA1 mutation and 25 specimens from patients who tested negative for four common BRCA1 and BRCA2 mutations) showed that IGF1R expression was twice as high in tumours from BRCA1 mutation carriers as it was in tumours from non-BRCA1 mutation carriers (ie, sporadic tumours). Additionally, surrounding healthy breast tissue from the BRCA1 mutation carriers showed higher IGF1R levels than similar tissue from non-carriers. ...
... Additionally, surrounding healthy breast tissue from the BRCA1 mutation carriers showed higher IGF1R levels than similar tissue from non-carriers. 44 The capacity of wild-type, but not mutant, BRCA1 to inhibit IGF1R biosynthesis might provide an explanation for the lower IGF1R levels seen in tumours from non-BRCA1 mutation carriers, and for the reduced mitogenic activity in wild-type BRCA1-expressing cells (fi gure 1). Voskuil and colleagues 45 showed that concentrations of some IGF system components, including IGF1R mRNA, in healthy and malignant breast tissues were higher in individuals with a strong family history of breast cancer (usually asso ciated with BRCA1 or BRCA2 mutations) than in individuals with no such history. ...
The insulin-like growth factor (IGF) system has a direct effect on cellular proliferation and survival, and interacts with genetic and environmental factors implicated in causing cancer. Experimental, clinical, and epidemiological evidence show that the IGF signalling pathways are important mediators in the biochemical and molecular chain of events that lead from a phenotypically normal cell to one harbouring neoplastic traits. BRCA1 and BRCA2 have an important role in the development of hereditary and sporadic breast and ovarian cancer. Recent evidence suggests that risk of cancer conferred by BRCA mutations can be modified by genetic and environmental factors, including ambient concentrations of IGF-1 and polymorphisms in IGF system components. This Review addresses interactions between the IGF and BRCA1 signalling pathways, and emphasises the convergence of IGF-1-mediated cell survival, proliferative pathways, and BRCA1-mediated tumour protective pathways. Understanding the complex interactions between these signalling pathways might improve our understanding of basic molecular oncology processes and help to identify new molecular targets, predictive biomarkers, and approaches for optimising cancer therapies.
... Consistent with this finding, BRCA1 deficiency leads to increased expression of various IGF system members in multiple experimental systems, including BRCA1-deficient mice, primary mammary tumors and cultured human cells 41 . IGF1R levels in tumors from patients carrying BRCA1 mutations were elevated when compared to tumors from sporadic (non-familial) breast cancer patients 42 (Figure 3). In addition, expression of the IGF1 ligand was markedly enhanced in tumors of BRCA1 mutation carriers in comparison with matched sporadic tumors 43 . ...
The insulin-like growth factor-1 hormonal axis has emerged in recent years as a promising therapeutic target in oncology. Empirical support to this view was provided by pre-clinical studies showing that insulin-like growth factor-1 receptor expression and activation constitute fundamental prerequisites for breast cancer development. Unfortunately, the vast majority of phase III clinical trials using monoclonal antibodies against the receptor have been disappointing. As a result of these negative outcomes there is an urgent need to identify predictive biomarkers that may identify potential responders. The present review article is aimed at providing an overview of the role of the insulin-like growth factor-1 axis in breast cancer. Circulating insulin-like growth factor-1 constitutes a risk factor for a number of malignancies, including breast cancer, and various members of the insulin-like growth factor-1 system are produced by the tumoral cells or by stromal cells. In addition, we provide evidence that the mechanism of action of insulin-like growth factor-1 involves interactions with the estrogen receptor as well as with the breast cancer gene-1. Finally, lifestyle factors that are related to insulin-like growth factor-1, such as obesity, have been suggested to have an effect on breast cancer.
... Specifically, binding of BRCA1 to Sp1 prevents Sp1 from binding the IGF1R promoter region, leading to reduction in IGF1R levels and ensuing decrease in IGF1-mediated proliferation. In agreement with the inability of mutant BRCA1 to suppress IGF1R transcription, primary breast tumors derived from BRCA1 mutation carrier patients expressed significantly higher levels of IGF1R than sporadic breast tumors (47). ...
The breast and ovarian cancer susceptibility gene (BRCA1) is a tumor suppressor whose mutation has been associated with the development of breast, ovarian and, probably, other malignancies at young ages. The BRCA1 gene product participates in multiple biological pathways including the DNA damage response, transcriptional control, cell growth and apoptosis. Inactivating germline mutations of the BRCA1 gene can be detected in a substantial portion of families with inherited breast and/or ovarian cancer. While the genomic and cancer-related actions of BRCA1 have been extensively investigated, not much information exists regarding the cellular and circulating factors involved in regulation of BRCA1 expression and action. The present review article dissects the emerging role of BRCA1 as an important regulator of various endocrine and metabolic axes. Experimental and clinical evidence links BRCA1 with a number of peptide and steroid hormones. Furthermore, comprehensive analyses identified complex interactions between the insulin/insulin-like growth factor-1 (IGF1) signaling axis and BRCA1. The correlation between metabolic disorders, including diabetes and the metabolic syndrome, and BRCA1 mutations, are discussed in this article.
... Malignant cells display augmented numbers of IGF1R on their cell surface as well as increased IGF1R mRNA levels [32]. Examination of various tumors (including breast, ovarian, prostate, colon, hematopoietic, rhabdomyosarcoma, renal, etc.), shows an abundant expression of IGF1R, suggesting that upregulation of the IGF1R gene constitutes a common paradigm in different types of cancer [33][34][35]. The molecular mechanisms that are responsible for IGF1R gene expression are described in the next section. ...
... The antiapoptotic properties induced by IGF-IR activation contribute to tumorigenesis and are one of the traits of cancer [86]. Accordingly, a high IGF-IR expression in human lung and breast tumors has been reported [87][88][89]. In addition, resistance to tumor progression is a central component contributing to the extended life span seen in animals with GHR absence. ...
The Ecuadorian cohort of subjects with LS has taught us valuable lessons since the late 80’s. We have learned about migration of Sephardic Jews to our country, their isolation in remote hamlets and further inbreeding. These geographical, historical and social determinants induced dissemination of a growth hormone (GH) receptor mutation which widely occurred in those almost inaccessible villages. Consequently, the world’s largest Laron syndrome (LS) cohort emerged in Loja and El Oro, two of the southern provinces of Ecuador. We have been fortunate to study these patients since 1987. New clinical features derived from GH insensitivity, their growth patterns as well as treatment with exogenous insulin-like growth factor I (IGF-I) have been reported. Novel biochemical characteristics in the field of GH insensitivity, IGFs, IGF binding proteins (BP) and their clinical correlates have also been described. In the last few years, studies on the morbidity and mortality of Ecuadorian LS adults surprisingly demonstrated that despite obesity, they had lower incidence of diabetes and cancer than their relatives. These events were linked to their metabolic phenotype of elevated but ineffective GH concentrations and low circulating IGF-I and IGFBP-3. It was also noted that absent GH counter-regulation induces a decrease in insulin resistance (IR), which results in low but highly efficient insulin levels which properly handle metabolic substrates. We propose that the combination of low IGF-I signaling, decreased IR, and efficient serum insulin concentrations are reasonable explanations for the diminished incidence of diabetes and cancer in these subjects.
... Malignant cells display augmented numbers of IGF1R on their cell surface as well as increased IGF1R mRNA levels [32]. Examination of various tumors (including breast, ovarian, prostate, colon, hematopoietic, rhabdomyosarcoma, renal, etc.), shows an abundant expression of IGF1R, suggesting that upregulation of the IGF1R gene constitutes a common paradigm in different types of cancer [33][34][35]. The molecular mechanisms that are responsible for IGF1R gene expression are described in the next section. ...
Introduction: The insulin-like growth factors (IGF) are a family of secreted peptide hormones with important roles in different cellular and organism functions. The biological activities of the IGFs are mediated by the IGF1 receptor (IGF1R), a cell-surface, tyrosine kinase-containing heterotetramer that is linked to numerous cytoplasmic signaling cascades. The IGF1R displays potent anti-apoptotic, pro-survival capacities and plays a key role in malignant transformation. Research has identified the IGF1R as a candidate therapeutic target in cancer.
Areas covered: We offer a synopsis of ongoing efforts to target the IGF axis for therapeutic purposes. Our review includes a digest of early experimental work that led to the identification of IGF1R as a candidate therapeutic target in oncology.
Expert opinion: Targeting of the IGF axis has yielded disappointing results in phase III trials, but it is important to learn from this to improve future trials in a rational manner. The potential of anti-IGF1R antibodies and small molecular weight inhibitors, alone or in combination with chemotherapy or other biological agents, should be investigated further in randomized studies. Moreover, the implementation of predictive biomarkers for patient selection will improve the outcome of future trials. Emerging personalized medicine could have a major impact on IGF1R targeting.
... IGF1R is a pro-protein convertase substrate essential for mammary gland development and milk production (Yee & Wood, 2008). Expression of IGF1R is upregulated in breast cancer and has been associated with cancer initiation, evasion of apoptosis, motility, proliferation and resistance to cancer therapy (Aaltonen et al., 2014;Frasca et al., 2008;Haupt, Ro, & Schwartz, 2010;Klinakis et al., 2009;Maor et al., 2007). Our previous study demonstrated the appearance of cytochrome P450Z1 (CYP4Z1) autoantibodies in the sera of breast cancer patients (Nunna, Jalal, & Bureik, 2017), while CYP4Z1 has a significantly higher expression in cancerous breast tissue (Rieger et al., 2004), indicating CYP4Z1 as an early diagnostic marker of breast cancer initiation. ...
We evaluated the carcinogenic capacity of Bisphenol A (BPA) treatment at low nano molar concentrations (8.73 and 17.47 nM) on both normal breast epithelial cells (MCF- 10A) and breast cancer cells (MCF-7) and found that the highest DNA damage occurred 6 hours after BPA treatment. In MCF-10A cells the IGF1R protein, a breast cancer marker was significantly increased upon BPA treatment while its mRNA expression remained unchanged but it was converse in MCF-7 cells. BPA treatment at the lower dose also resulted in higher expression of (NF-κB) RelA in both cell lines, but only in MCF-7 cells at the higher dose. Through homology modeling we predicted the structure of SPCA1/2 and detected strong BPA binding within the catalytic domain. We report that 6 hour BPA treatment in nano molar range causes detectable DNA damage; inhibits and reduces cellular SPCA1/2 protein that subsequently results in dysregulated Ca2+ dependent IGF1R to trigger tumorigenic changes. BPA treatment also increased the early breast cancer marker CYP4Z1 expression, compared to mock but not significantly, in MCF-10A cells.
... A functional interaction between the BRCA genes and IGF-I system was confirmed by mechanistic studies. The IGF-I signalling pathway regulates BRCA1 gene expression and wild-type BRCA1 strongly reduces the synthesis of IGF-I receptors [24][25][26]. A recent review emphasized the convergence of IGF-I-mediated cell survival, proliferative pathways, and BRCA-mediated tumor protective pathway. ...
Background:
Insulin-like growth factor I (IGF-I) and other markers of insulin resistance (IRm) might influence the penetrance of BRCA gene mutation. In a demonstration project on BRCA mutation carriers we tested the effect of the 'Mediterranean diet', with moderate protein restriction, on serum levels of IGF-I and IRm.
Methods:
BRCA mutation carriers, with or without breast cancer, aged 18⁻70 years and without metastases were eligible. After the baseline examinations, women were randomized to an active dietary intervention or to a control group. The intervention group attended six full days of life-style intervention activities (cookery classes followed by lunch, sessions of walking for 45 min and nutritional conferences) over the next six months.
Results:
213 BRCA mutation carriers completed the six-month study. Women in the intervention group (110) showed major changes in all the parameters under study. They significantly lost weight (p < 0.001), fat mass (p = 0.002), with reduced hip circumference (p = 0.01), triglycerides (p = 0.02) and IGF-I (p = 0.02) compared with controls. They also had a significantly higher levels of insulin-like growth factor-binding protein 3 (IGFI-BP3) (p = 0.03) and a lower IGF-I/IGFI-BP3 ratio (p = 0.04). The reduction of serum levels of IGF-I was significantly associated with the reduction in the consumption of animal products (p = 0.04).
Conclusions:
Women in the intervention group showed significant improvements in IGF-I and in other IRm that might influence the penetrance of BRCA mutations.
... These results encourage the expanded use of this therapy to a subgroup of breast cancer containing EGFR amplifications [35]. Furthermore, the insulinlike growth factor type 1 receptor (IGF-1R) is involved in tumorigenesis and shown to exhibit hyper-activation in BRCA1-mutation-associated breast cancers [36][37][38]. Preclinical studies have shown BRCA1-deficient breast and ovarian cancer cell lines to be particularly vulnerable to IGF-1R inhibitors (IGF-1Ri), and PARPi/IGF-1Ri combination therapy resulted in a synergistic cytotoxic effect on these cells [39]. However, despite these promising preclinical results, this approach has yet to be implemented in a clinical setting. ...
Opinion statement:
The single agent activity of PARP inhibitors (PARPi) in germline BRCA mutated (gBRCAm) breast and ovarian cancer suggests untapped potential for this new class of drug in breast cancer. The US Food and Drug Administration has approved three PARPi (olaparib, rucaparib, and niraparib) so far to treat certain ovarian cancers, including those with gBRCAm and olaparib for treatment of gBRCAm breast cancers. Several PARPi are now under clinical development for breast cancer in the various treatment settings. Recently, two phase III trials of olaparib (OlympiaD) and talazoparib (EMBRACA) demonstrated 3-month progression-free survival improvement with PARPi compared to physician's choice single agent chemotherapy in metastatic gBRCAm breast cancer. To date, PARPi seems less efficacious in metastatic breast cancer patients than those with BRCA mutated platinum-sensitive recurrent ovarian cancer, perhaps reflecting the biologic heterogeneity and low somatic BRCA mutation rate in breast cancer. The use of PARPi is gradually evolving, including combination strategies with chemotherapy, targeted agents, radiotherapy, or immunotherapy in women with and without gBRCAm. The role of predictive biomarkers, including molecular signatures and homologous recombination repair deficiency scores based on loss of heterozygosity and other structural genomic aberrations, will be crucial to identify a subgroup of patients who may have benefit from PARPi. An improved understanding of the mechanisms underlying PARPi clinical resistance will also be important to enable the development of new approaches to increase efficacy. This is a field rich in opportunity, and the coming years should see a better understanding of which breast cancer patients we should treat with PARPi and where these agents should come in over the course of treatment.
... These studies demonstrate that IGF-IR is overexpressed in ERPBC and associates to recurrence and resistance to anti-estrogen therapy; however, in an apparent contradiction, metastases express low levels of IGF-IR and correlate with lethality in discrete cell types [31]. Similarly, in families with inherited tendency towards breast and ovarian cancer associated to the BRCA1 mutation, a significant elevation of IGF-IR in tumors of those carrying the mutation was found, if compared to non-carriers [32]. Results from this study demonstrated that mechanisms involve transactivation of the IGF-IR gene. ...
Along with its inherent properties in growth promotion, cell division and regeneration, growth hormone (GH) exerts a variety of miscellaneous and widespread actions on the human body after binding to its receptor (GHR). Indeed, GH influences the metabolism of carbohydrates, lipids and proteins; shapes body composition, influences cardiovascular profile, quality of life, and induces other direct and indirect physiologic effects. Besides this salutary actions, GH and its derived peptide insulin-like growth factor-I (IGF-I), main product of the GH/GHR interaction, have been implicated in the genesis of diseases such as cancer and insulin-resistant diabetes. The effects of these peptides are difficult to discern in healthy individuals but can be better evaluated in disease states in which their action in target tissues is abnormal. In consequence, we selected acromegaly and Laron syndrome due to GH receptor deficiency (GHRD) as models for excess and absence of GH action, and focused in the role of GH/GHR signaling in the genesis of cancer and diabetes.
Considering that malignancy has been linked at epidemiological level to type 2 diabetes and high body mass index, suggesting that hyperinsulinemia is an independent contributor to cancer genesis and progression, we propose that the GH-derived IGF-I is also an independent influence for progression to neoplasia since its absence associates with less DNA damage, diminished mutagenesis and efficient apoptosis. Regarding development of type 2 diabetes, we support the notion that GH, by influencing insulin sensitivity via its counter-regulatory properties on carbohydrate metabolism, is an important contributor for development of this disease.
... Furthermore, BRCA1 reduces expression levels of insulin-like growth factor 1 receptor (IGF1R) and its ligand IGF1 [102,103]. Accordingly, BRCA1 germline mutation carriers are exposed to higher serum E2 levels (particularly in luteal phase) [104,105], exhibit a higher activity of ERα and elevated IGF1R expression levels in estrogen-stimulated cells [106], and show intratumoral accumulation of IGF1 [107] combined with a decrease in IGF1 serum concentrations (likely due to increased binding to IGF1R) [100]. While an excess supply of E2 and also IGF1/2 upregulates BRCA1 expression in a compensative manner in BRCA1 wild-type cells [108,109], this mechanism is impaired in mutation carriers. ...
Altered metabolism in tumor cells has been a focus of cancer research for as long as a century but has remained controversial and vague due to an inhomogeneous overall picture. Accumulating genomic, metabolomic, and lastly panomic data as well as bioenergetics studies of the past few years enable a more comprehensive, systems-biologic approach promoting deeper insight into tumor biology and challenging hitherto existing models of cancer bioenergetics. Presenting a compendium on breast cancer-specific metabolome analyses performed thus far, we review and compile currently known aspects of breast cancer biology into a comprehensive network, elucidating previously dissonant issues of cancer metabolism. As such, some of the aspects critically discussed in this review include the dynamic interplay or metabolic coupling between cancer (stem) cells and cancer-associated fibroblasts, the intratumoral and intertumoral heterogeneity and plasticity of cancer cell metabolism, the existence of distinct metabolic tumor compartments in need of separate yet simultaneous therapeutic targeting, the reliance of cancer cells on oxidative metabolism and mitochondrial power, and the role of pro-inflammatory, pro-tumorigenic stromal conditioning. Comprising complex breast cancer signaling networks as well as combined metabolomic and genomic data, we address metabolic consequences of mutations in tumor suppressor genes and evaluate their contribution to breast cancer predisposition in a germline setting, reasoning for distinct personalized preventive and therapeutic measures. The review closes with a discussion on central root mechanisms of tumor cell metabolism and rate-limiting steps thereof, introducing essential strategies for therapeutic targeting.
... Breast cancer gene 1 (BRCA1) suppresses the IGF-IR promoter [73,74]. Overexpression of IGF-I and IGF-IR is observed in BRCA1-deficient tumors that is associated with increased cell survival and reduced cell apoptosis [13]. ...
Breast cancer is the most common cancer and the second leading cause of cancer-related deaths among women worldwide. Although patients are often diagnosed in the early and curable stages, the treatment of metastatic breast cancer remains a major clinical challenge. The combination of chemotherapy with new targeting agents, such as bevacizumab, is helpful in improving patient survival; however, novel treatment strategies are required to improve clinical outcomes. The insulin-like growth factor-I receptor (IGF-IR) is a tyrosine kinase cell surface receptor which is involved in the regulation of cell growth and metabolism. Previous studies have shown that activation of the IGF-IR signaling pathway promotes proliferation, survival, and metastasis of breast cancer cells. Additionally, overexpression of IGF-IR is associated with breast cancer cell resistance to anticancer therapies. Recently, IGF-IR has been introduced as a marker of stemness in breast cancer cells and there is also accumulating evidence that IGF-IR contributes to the establishment and maintenance of breast cancer epithelial-mesenchymal transition (EMT). Therefore, pharmacological or molecular targeting of IGF-IR could be a promising strategy, in the treatment of patients with breast cancer, particularly in order to circumvent the therapeutic resistance and targeting breast cancer stem/progenitors. Currently, many strategies have been developed for targeting IGF-IR, some have entered clinical trials and some are in preclinical stages for breast cancer therapy. In this review, we will first discuss on the biology of IGF-IR in an attempt to find the role of this receptor in breast cancer and then discuss about therapeutic strategies to target this receptor.
... Wild-type BRCA1 reduce the promoter activity of IGF1R whereas mutated BRCA1 lead to enhance IGF1R promoter activity and expression of protein. BRCA1 and BRCA2 carries have an increased level of IGF1R compared with those with sporadic cancers [55,56]. WT1 gene which product is a zinc-finger transcription factor is associated with the etiology of Wilms tumor a kind of pediatric kidney cancer [57]. ...
Renal cell carcinoma (RCC) incidence is highest in highly developed countries and it is the seventh most common neoplasm diagnosed. RCC management include nephrectomy and targeted therapies. Type 1 insulin-like growth factor (IGF-1) pathway plays an important role in cell proliferation and apoptosis resistance. IGF-1 and insulin share overlapping downstream signaling pathways in normal and cancer cells. IGF-1 receptor (IGF1R) stimulation may promote malignant transformation promoting cell proliferation, dedifferentiation and inhibiting apoptosis. Clear cell renal cell carcinoma (ccRCC) patients with IGF1R overexpression have 70 % increased risk of death compared to patients who had tumors without IGF1R expression. IGF1R signaling deregulation may results in p53, WT, BRCA1, VHL loss of function. RCC cells with high expression of IGF1R are more resistant to chemotherapy than cells with low expression. Silencing of IGF1R increase the chemosensitivity of ccRCC cells and the effect is greater in VHL mutated cells. Understanding the role of IGF-1 signaling pathway in RCC may result in development of new targeted therapeutic interventions. First preclinical attempts with anti-IGF-1R monoclonal antibodies or fragment antigen-binding (Fab) fragments alone or in combination with an mTOR inhibitor were shown to inhibit in vitro growth and reduced the number of colonies formed by of RCC cells.
... In this mouse model, combined PI3K and PARP inhibition was superior to either agent alone to induce durable remissions of established tumors. phosphoinositide 3-kinase | DNA damage | breast cancer | Parp-inhibition | tumor metabolism T riple-negative breast cancers, including BRCA1-linked breast cancers, frequently show activation of the PI3K pathway as a result of overexpression of epidermal growth factor receptor (EGFR) (1,2) or insulin-like growth factor 1 receptor (IGFR) (3), and inhibition of the EGFR (1,2,4) and/or the PI3K/Nrf2 axis (5) prevents cancers arising from BRCA1 mutant mammary epithelial cells (MECs). In addition, activating mutations of PIK3CA, or loss of the inhibitory lipid phosphatases PTEN (phosphatase and tensin homolog) and INPP4B (inositol polyphosphate 4-phosphatase type II) (6,7), suggest that the PI3K pathway is contributing to tumor growth and survival. ...
Significance
Mutations in the PI3K pathway are highly prevalent in cancers, and isoform-specific and pan-PI3K inhibitors have entered clinical trials in both solid and hematologic malignancies. The PI3K δ-specific inhibitor idelalisib (in combination with rituximab) was recently approved for the treatment of chronic lymphocytic leukemia. However, identifying tumor types and biological mechanisms that predict for response to PI3K inhibitors as single agents or in combination has been a challenge. Our data indicate that PI3K inhibitors induce DNA damage in tumors that have defects in DNA damage-repair pathways and that they do so by impairing the production of Rib phosphate and amino acids needed for deoxynucleotide synthesis.
... A manifestation of the mechanistic interplay between BRCA1/BRCA2 and the IGF axis is seen in the clinics. Immunohistochemical analysis of IGF1R levels in breast tumor specimens derived from BRCA1/BRCA2 mutation carriers, compared to matched sporadic breast cancer patients, revealed higher IGF1R levels in tumors of BRCA mutation carriers (99). Furthermore, evidence in support of a complex interplay between the IGF1 axis and tumor suppressor BRCA1 was provided by studies showing that IGF1 increases BRCA1 gene expression and enhances BRCA1 promoter activity (100). ...
Clinical, epidemiological and experimental evidence indicate that the insulin-like growth factors (IGFs) are important mediators in the biochemical chain of events that lead from a phenotypically normal to a neoplastic cell. The IGF1 receptor (IGF1R), which mediates the biological actions of IGF1 and IGF2, exhibits potent pro-survival and anti-apoptotic activities. The IGF1R is highly expressed in most types of cancer and is regarded as a promising therapeutic target in oncology. P53 is a transcription factor with tumor suppressor activity that is usually activated in response to DNA damage and other forms of cellular stress. On the basis of its protective activities, p53 is commonly regarded as the guardian of the genome. We provide evidence that the IGF signaling axis and p53 genome protection pathways are tightly interconnected. Wild type, but not mutant, p53 suppresses IGF1R gene transcription, leading to abrogation of the IGF signaling network, with ensuing cell cycle arrest. Gain-of-function, or loss-of-function, mutations of p53 in tumor cells may disrupt its inhibitory activity, thus generating oncogenic molecules capable of transactivating the IGF1R gene. The interplay between the IGF1 and p53 pathways is also of major relevance in terms of metabolic regulation, including glucose transport and glycolysis. A better understanding of the complex physical and functional interactions between these important signaling pathways will have major basic and translational relevance.
... For example, BRCA1 can inhibit Progesterone Receptor (PR) activity in the PR-positive T47D cells [7,8] and repress estrogen receptor-alpha activity in MCF-7 cells [9]. BRCA1 may also be a potential regulator of the insulin-like growth factor 1 receptor in HCC1937 cells [10]. In addition, the Epidermal Growth Factor Receptor (EGFR) is a member of the ErbB family of receptor tyrosine kinases that is a potential link between genetic and environmental interactions [11]. ...
... BRCA1 deficiency leads to increased expression of several IGF system members in multiple experimental systems, including BRCA1-deficient mice, primary mammary tumors, and cultured human cells [64]. IGF1R levels in tumors from patients carrying BRCA1 mutations have been shown to be elevated compared with the levels in tumors from sporadic (non-familial) breast cancer patients [65]. In addition, IGF-1 protein expression is significantly upregulated in tumors of BRCA1 and BRCA2 mutation carriers [66] in comparison with matched sporadic tumors [67]. ...
... Indeed, extensive crosstalk between ER and IGF1R is now well-established from several in vitro studies, which demonstrate a synergistic effect of IGF1R and ER on the proliferation of human breast cancer cells [46,47]. Even if some studies did not find any significant results [35,48,49], IGF1R positivity was generally related to favorable prognostic features in ER-positive breast cancer, including low histological grade [19]. On the contrary, strong IGF1R expression was associated with aggressive features in triple negative breast cancer, such as high histological grade [40]. ...
Background
Dogs spontaneously develop invasive mammary carcinoma with a high prevalence of the triple-negative (TN) subtype (lack of ER-Estrogen Receptor and PR-Progesterone Receptor expression, lack of HER2-Human Epidermal Growth Factor Receptor 2 overexpression), making this animal model relevant for investigating new therapeutic pathways. Insulin-like growth factor Type-1 receptor (IGF1R) is frequently overexpressed in primary human breast cancers, with a growing role in the TN phenotype. The purpose of this study was to investigate the Dog as a candidate model for IGF1R-overexpressing mammary carcinoma.
Methods
150 bitches with canine mammary carcinoma (CMC) and a known 2-year follow-up were retrospectively included. IGF1R expression was assessed by immunohistochemistry (IHC) using a similar scoring system as for HER2 in breast cancer. The prognostic value of the IGF1R expression was assessed in terms of overall and specific survival as well as disease-free interval (DFI).
Results
47 CMC (31 %) were classified as luminal and 103 (69 %) as triple-negative (TN-CMC). 41 % of CMC overexpressed IGF1R (IHC score 3+) of which 76 % were TN-CMC and 62 % grade III. IGF1R overexpression was associated with aggressive features including lymphovascular invasion, histological grade III, low ER expression and the TN phenotype. Univariate and multivariate analyses revealed that IGF1R overexpression was associated with shorter overall and specific survivals and shorter DFI in TN-CMC.
Conclusions
IGF1R overexpression is common and related to a poor outcome in canine invasive mammary carcinoma, particularly in the triple negative subtype, as in human breast cancer. Preclinical studies using the Dog as a spontaneous animal model could be considered to investigate new therapies targeting IGF1R in triple-negative breast cancer.
... All of these are direct effects with E2 binding to ER and acting as a co-repressor and BRCA1 binding to the IGF-IR promoter and suppressing transcription of IGF-IR mRNA. Breast tumors from BRCA1 mutation carriers have elevated IGF-IR and IGF-I levels [49,50]. BRCA1 also has important independent actions on DNA damage response [51], stem and progenitor cell fate [34], cell cycle regulation [52] and telomerase activity [53] among others. ...
Since its identification 20 years ago, the biological basis for the high breast cancer risk in women who have germline BRCA1 mutations has been an area of intense study for three reasons. First, BRCA1 was the first gene shown to associate with breast cancer risk, and therefore serves as model for understanding genetic susceptibility.
Second, the type of breast cancer that occurs in these women has specific features that have engendered new hypotheses about
the cancer biology. Third, it is hoped that understanding the origins of this disease may provide the means to prevent disease.
Resolving this question has proven extremely challenging because the biology controlled by BRCA1 is complex. Our working model
is that the high frequency of basal-like breast cancer in BRCA1 mutation carriers is the result of a self-perpetuating triad
of cellular phenotypes consisting of: (i) intrinsic defects in DNA repair and centrosome regulation that lead to genomic instability
and increases spontaneous transformation; (ii) aberrant lineage commitment; and (iii) increased proliferation due to in large
part to increased IGF-1 activity. We propose that the last is key and is a potential entree for preventing breast cancer in
BRCA1 mutation carriers.
... Both in vitro and in vivo models, as well as clinical and epidemiological data have indicated the role of the IGF-1 system in BrCa via many diverse endocrine, paracrine and autocrine signaling pathways [16,17]. Although some of these findings are conflicting, many components of the IGF-1 system are known to be altered during BrCa establishment and progression [9,16,18]. ...
IGF-1 is a potent mitogen of major importance in the mammary gland. IGF-1 binding to the cognate receptor, IGF-1R, triggers a signaling cascade leading to proliferative and anti-apoptotic events. Although many of the relevant molecular pathways and intracellular cascades remain to be elucidated, a growing body of evidence points to the important role of the IGF-1 system in breast cancer development, progression and metastasis. IGF-1 is a point of convergence for major signaling pathways implicated in breast cancer growth. In this review, we provide an overview and concise update on the function and regulation of IGF-1 as well as the role it plays in breast malignancies.
... Therefore, delivery of IGF-1R-targeting siRNA in a mouse model of gastric cancer or RNAi-based xenografts may be a promising area of future study. Overexpression of IGF-1R has been regarded as a typical hallmark of numerous human cancers, and various tumor suppressors, including p53 family proteins (14,15), breast cancer 1 (16,17), Von Hippel-Lindau protein (18), Wilms' tumor 1 (19,20), have been shown to negatively regulate IGF-1R transcription (4). These results imply that IGF-1R may be a therapeutic target for human cancers. ...
The oncoprotein insulin‑like growth factor‑1 receptor (IGF‑1R) has previously been shown to promote tumorigenesis. Overexpression of IGF‑1R is considered to be a critical prerequisite for malignant transformation in numerous human cancers. Therefore, targeting IGF‑1R for cancer therapy has gained a lot of interest. In the present study, an RNA interference (RNAi)‑mediated IGF‑1R gene silencing approach was conducted in BGC823 gastric cancer cells. The tumorigenic and malignant properties of the cells were assessed, in response to reduced IGF‑1R expression. Notably, IGF‑1R depletion not only inhibited gastric cancer cell growth, resulted in G1 cell cycle arrest and consequently led to apoptosis, but also suppressed cancer cell motility and invasion. The findings of the present study are the first, to the best of our knowledge, to suggest that RNAi‑based IGF‑1R silencing may be a potential and promising therapeutic strategy for gastric cancer treatment.
... It has also been found that AA women tend to have more ER (À) tumors [37], p53 mutations [38], and c-met (stem cell factor/hepatocyte growth factor receptor) [39]. Maor et al. [40] showed an association between higher IGF1R levels and BRCA1 mutation carriers. This could be a possible mechanistic explanation for the lower IGF1R levels observed in tumors derived from non-BRCA1 mutation carriers. ...
... It has also been found that AA women tend to have more ER (À) tumors [37], p53 mutations [38], and c-met (stem cell factor/hepatocyte growth factor receptor) [39]. Maor et al. [40] showed an association between higher IGF1R levels and BRCA1 mutation carriers. This could be a possible mechanistic explanation for the lower IGF1R levels observed in tumors derived from non-BRCA1 mutation carriers. ...
... However, BRCA1 was capable of binding Sp1, hence preventing the zinc finger from binding and transactivating the IGF1R gene. Consistent with the inability of mutant BRCA1 to suppress IGF1R transcription, primary breast tumors derived from BRCA1 mutation carrier patients expressed significantly higher IGF1R levels than sporadic breast tumors [43]. Additionally, BRCA1 transcriptional action depends on the cellular status of p53 and physical interactions between BRCA1 and p53 were demonstrated by co-IP [44]. ...
... The present study reports the following associations between BRCA1 and IGF1R status in ovarian cancer cells: i) IGF1R expression is increased in non-BRCA1-mutated ovarian cancer; ii) BRCA1 inactivation (BRCA1 mutation and promoter hypermethylation) markedly increases the expression of IGF1R; and iii) BRCA1 knockdown is an effective method to activate the IGF1R gene. These results indicated that BRCA1 may be a potential regulator of IGF1R in ovarian cancer, although, a comparable phenomenon has been observed in breast cancer (11,12). Notably, the activation effect of BRCA1 was primarily observed in cells originating from ovarian cancer, however, 293T cells were insensitive to the overexpression or knockdown of BRCA1. ...
Breast cancer 1 (BRCA1) and insulin-like growth factor 1 receptor (IGF1R) are critical in ovarian cancer progression. However, the crosstalk between the BRCA1 and IGF1R signaling pathways in ovarian cancer remains largely unknown. The effects of BRCA1 on IGF1R were assessed in 121 serous ovarian cancer patients (BRCA1 mutation, n=30; non-BRCA1 mutation, n=32; hypermethylated BRCA1 promoter, n=28; and non-methylation, n=31). BRCA1 promoter methylation was analyzed via bisulfite sequencing using primers focused on the core promoter region. The expression levels of BRCA1 and IGF1R were assessed by immunohistochemistry and real-time polymerase chain reaction. Knockdown and overexpression of BRCA1 were achieved using a lentiviral vector in 293T and SKOV3 ovarian cancer cells, and primary non-mutated and BRCA1-mutated ovarian cancer cells. The present study demonstrated that IGF1R expression is increased in non-BRCA1-mutated ovarian cancer when compared with adjacent normal tissue. Furthermore, IGF1R levels are additionally significantly elevated in BRCA1 inactivation ovarian cancer (BRCA1 mutation or hypermethylated BRCA1 promoter). In addition, BRCA1 knockdown was found to be an effective method of activating IGF1R expression in non-BRCA1-mutated ovarian cancer cells. The observations of the current study indicate that BRCA1 may be a potential trigger that is involved in the transcriptional regulation of IGF1R in the development of ovarian cancer.
... Importantly, increased IGF1R-mediated signaling has been related to resistance to anti-HER2 therapies including trastuzumab [38] and has been proposed as a possible therapeutic target [14] and a prognostic marker [39] in HER2-positive tumors. More recently, accumulating data implicate IGFR pathway in the pathogenesis of triplenegative tumors [15,40], as well as in tumors with BRCA1 mutations [41,42]. We found that IGF2R was inversely correlated with all other components of the IGFR pathway ( Figure 4) and that low IGF2R expression, combined with high IGF1R-alpha expression, were able to define a distinct subgroup of patients with better prognosis. ...
Introduction:
We sought to determine the level of protein expression of the critical components of the insulin-like growth factor receptor (IGFR) pathway and to evaluate their prognostic significance across the different early breast cancer subtypes.
Patients and methods:
Archival tumor tissue from 1,021 women with early, node positive breast cancer, who were prospectively evaluated within two randomized clinical trials, was used to construct tissue microarrays that were stained for hormone receptors (HR), Ki67, HER2, epidermal growth factor receptor (EGFR) and cytokeratins 5/6, to classify tumors into five immunophenotypical subgroups. Immunohistochemical (IHC) expression of IGF1R-alpha and beta subunits, IGF2R and IGF-binding protein 2 (IGFBP2) was assessed using the immunoreactive score (IRS). Repeated internal cross-validation was performed to examine the statistical validity of the cut off points for all biomarkers.
Results:
After a median follow-up time of 105.4 months, overall 370 women (36.2%) had relapsed and 270 (26.4%) had died. Tumors expressing IGF1R-alpha above the median IRS were significantly more frequently HR positive (luminal A+B+HER2), as compared to HER2-enriched and triple negative ones (p<0.001 for both comparisons). IGF2R was overexpressed significantly more frequently in HR negative tumors (p = 0.001) and had an inverse correlation with all other biomarkers. Patients with luminal A and B tumors with high IGF1R-alpha and negative EGFR expression (N = 190) had significantly higher 4-year survival rates, as compared to the rest (log-rank p = 0.046), as did patients with luminal A and B tumors with high IGF1R-alpha and low IGF2R expression, as compared to the rest (N = 91), (log-rank p = 0.035). After adjustment for significant variables, patients in the latter group had a relative 45% reduction in the risk of death, as compared to the rest (p = 0.035).
Conclusion:
Aberrant expression of components of the IGF1R pathway is associated with better clinical outcomes in women with luminal A and B, node positive, early breast cancer.
... Additionally, other studies demonstrated that estrogen deficiency in ovariectomized rats is followed by reduced UCP1 expression [25] while other studies have demonstrated that IGF-1 can induce UCP-1 expression in vitro and in vivo models [26,27]. Indeed, several lines of evidence have demonstrated that both experimental mouse models and humans that are deficient in BRCA1 have abnormally high levels of estrogen/IGF-1 signaling and production [28][29][30][31][32][33]. In particular, experimental and epidemiological studies have demonstrated that loss of BRCA1 function can lead to the loss of the normal restraint on estrogen receptor signaling [34][35][36] and also an increase in estrogen production through increased expression of aromatase, an enzyme responsible for a key step in the biosynthesis of estrogens [37]. ...
A major challenge to breast cancer research is the identification of alterations in the architecture and composition of the breast that are associated with breast cancer progression. The aim of the present investigation was to characterize the mammary adipose phenotype from Brca1 mutant mice in the expectation that this would shed light on the role of the mammary tissue environment in the early stages of breast tumorigenesis. We observed that histological sections of mammary tissue from adult Brca1 mutant mice abnormally display small, multilocular adipocytes that are reminiscent of brown adipose tissue (BAT) as compared to wildtype mice. Using a marker for BAT, the uncoupling protein 1 (UCP1), we demonstrated that these multilocular adipose regions in Brca1 mutant mice stain positive for UCP1. Transcriptionally, UCP1 mRNA levels in the Brca1 mutant mice were elevated greater than 50-fold compared to age-matched mammary glands from wildtype mice. Indeed, BAT has characteristics that are favorable for tumor growth, including high vascularity. Therefore, we also demonstrated that the multilocular brown adipose phenotype in the mammary fat pad of Brca1 mutant mice displayed regions of increased vascularity as evidenced by a significant increase in the protein expression of CD31, a marker for angiogenesis. This Brca1 mutant mouse model should provide a physiologically relevant context to determine whether brown adipose tissue can play a role in breast cancer development.
... For example, BRCA1 can inhibit progesterone receptor (PR) activity in the PRpositive human breast cancer cell line T47D [17,18] and repress estrogen receptor-alpha activity in MCF-7 cells [19]. BRCA1 may also be a potential regulator of the insulin-like growth factor 1 receptor in human breast cancer cell line HCC1937 [20]. However, to date, there have been few reports about the interactions between BRCA1 and EGFR in ovarian cancer. ...
Both BRCA1 and epidermal growth factor receptor (EGFR) play a critical role in ovarian cancer progression. However, the crosstalk between BRCA1 and EGFR signaling pathways in ovarian cancer remains largely unknown.
The effect of BRCA1 on EGFR was assessed in 146 serous ovarian cancer patients (28 pairs of BRCA1-mutated or not, 23 pairs of BRCA2-mutated or not, and 22 pairs with hypermethylated BRCA1 promoter or not). BRCA1 promoter methylation was analyzed by bisulfite sequencing using primers flanking the core promoter region. Expression levels of BRCA1 and EGFR were assessed by immunohistochemistry and real-time PCR. The knockdown and overexpression of BRCA1 were achieved using a lentiviral vector in 293 T cells, SKOV3 ovarian cancer cells, and primary non-mutated and BRCA1-mutated ovarian cancer cells.
EGFR expression was increased in all cancer tissues compared to normal tissues. Additionally, EGFR expression was higher in normal tissues of BRCA1-mutated patients, and was further increased in cancer tissues; EGFR levels were also significantly elevated in ovarian cancer with promoter hypermethylation-mediated inactivation of BRCA1. BRCA1 knockdown was an effective way to activate EGFR expression in ovarian cancer cells.
These results indicate that BRCA1 may be a potential trigger in transcriptional regulation of EGFR in the development of ovarian cancer.
... Milk directly stimulates insulin production or release [18], and it is associated with higher plasma levels of IGF-I [19]. Consistently, mechanistic studies hypothesized a functional interaction between the BRCA1 and the IGF-I systems relevant to BC biology and showed that BRCA1 gene expression is regulated by the IGF-I signalling pathway [20][21][22][23]. ...
High serum levels of insulin-like growth factor I (IGF-I) are associated with an increased risk of sporadic breast cancer (BC). Furthermore, insulin and markers of insulin resistance, such as abdominal obesity, high blood glucose, high serum testosterone and metabolic syndrome, may affect both BC incidence and prognosis. We hypothesized that all these factors might be relevant also for hereditary BC, due to a deleterious mutation of BRCA genes. Epidemiological observation suggested that weight, energy intake (usually associated with higher bio-availability of growth factors) and physical activity may be relevant in BRCA mutation carriers. Mechanistic studies hypothesized a functional interaction between BRCA genes and the IGF-I system. We have provided some evidence that high serum levels of IGF-I are associated with a significantly increased penetrance. We are recruiting a larger cohort of BRCA mutation carriers in order to test potential modulators of penetrance and prognosis. Within this cohort, we have planned a randomized controlled trial to test whether moderate calorie and protein restriction, together with physical activity, decrease IGF-I. Eligible study subjects are women with or without BC, aged 18-70, with a proven deleterious BRCA mutation, and without metastases. All the women will receive recommendations for the dietary prevention of cancer. The women will be then randomized into an active life-style intervention group and into a control group that will receive only the baseline recommendations. We expect to significantly reduce IGF-I in the intervention group. This trial and the subsequent cohort follow-up might open up primary prevention options for genetic BC.
Background
Cancer is widely regarded as a complex disease primarily driven by genetic mutations. A critical concern and significant obstacle lies in discerning driver genes amid an extensive array of passenger genes.
Findings
We present a new method termed DriverMP for effectively prioritizing altered genes on a cancer-type level by considering mutated gene pairs. It is designed to first apply nonsilent somatic mutation data, protein‒protein interaction network data, and differential gene expression data to prioritize mutated gene pairs, and then individual mutated genes are prioritized based on prioritized mutated gene pairs. Application of this method in 10 cancer datasets from The Cancer Genome Atlas demonstrated its great improvements over all the compared state-of-the-art methods in identifying known driver genes. Then, a comprehensive analysis demonstrated the reliability of the novel driver genes that are strongly supported by clinical experiments, disease enrichment, or biological pathway analysis.
Conclusions
The new method, DriverMP, which is able to identify driver genes by effectively integrating the advantages of multiple kinds of cancer data, is available at https://github.com/LiuYangyangSDU/DriverMP. In addition, we have developed a novel driver gene database for 10 cancer types and an online service that can be freely accessed without registration for users. The DriverMP method, the database of novel drivers, and the user-friendly online server are expected to contribute to new diagnostic and therapeutic opportunities for cancers.
Emerging evidence links the growth hormone (GH)-insulin-like growth factor-1 (IGF1) endocrine axis to cancer development. While this putative correlation is of major translational relevance, most clinical and epidemiological reports to date found no causal linkage between GH therapy and enhanced cancer risk. Thus, it is generally agreed that GH therapy constitutes a safe pharmacological intervention. The present review focuses on a number of issues in the area of GH-IGF1 action in cancer development. Emphasis is given to the idea that GH and IGF1 do not conform to the definition of oncogenic factors. Specifically, these hormones, even at high pharmacological doses, are unable to induce malignant transformation. However, the GH-IGF1 axis is capable of 'pushing' already transformed cells through the various phases of the cell cycle. Viral and cellular oncogenes require an intact IGF1 signaling pathway in order to elicit transformation; in other words, oncogenic agents adopt the IGF1 pathway. This universal mechanism of action of oncogenes has broad implications in oncology. Our review provides an in-depth analysis of the interplay between the GH-IGF1 axis and cancer genes, including tumor suppressors p53 and BRCA1. Finally, the safety of GH therapy in both children and adults needs further long-term follow-up studies.
Breast tumors display tremendous heterogeneity in part due to varying molecular alterations, divergent cells of origin, and differentiation. Understanding where and how this heterogeneity develops is likely important for effective breast cancers eradication. Insulin-like growth factor (IGF) signaling is critical for normal mammary gland development and function, and has an established role in tumor development and resistance to therapy. Here we demonstrate that constitutive activation of the IGF1 receptor (IGF1R) influences lineage differentiation during mammary tumorigenesis. Transgenic IGF1R constitutive activation promotes tumors with mixed histologies, multiple cell lineages and an expanded bi-progenitor population. In these tumors, IGF1R expands the luminal-progenitor population while influencing myoepithelial differentiation. Mammary gland transplantation with IGF1R-infected mammary epithelial cells (MECs) resulted in hyperplastic, highly differentiated outgrowths and attenuated reconstitution. Restricting IGF1R constitutive activation to luminal versus myoepithelial lineage-sorted MECs resulted in ductal reconstitutions co-expressing high IGF1R levels in the opposite lineage of origin. Using in vitro models, IGF1R constitutively activated MCF10A cells showed increased mammosphere formation and CD44+/CD24-population, which was dependent upon Snail and NFκB signaling. These results suggest that IGF1R expands luminal progenitor populations while also stimulating myoepithelial cell differentiation. This ability to influence lineage differentiation may promote heterogeneous mammary tumors, and have implications for clinical treatment.
T-cell acute lymphoblastic leukemia (T-ALL) is an aggressive cancer, characterized by an uncontrolled expansion and accumulation of T-cell progenitors. During leukemic progression, immature T cells grow abnormally and occupy the bone marrow compartment, thereby interfering with the production of normal blood cells. Pediatric T-ALL is curable with intensive chemotherapy, but there are significant, long-term side effects and ~20% of patients suffer relapse for which there are limited treatment options. Adult T-ALL in contrast is largely incurable and refractory/relapsed disease is common despite multi-agent chemotherapy (5-year overall survival of ~40%), and thus new therapeutic targets are needed.
We have reported previously on the role of insulin-like growth factor (IGF) signaling in T-ALL, and shown that it exerts potent phenotypes in both leukemia stem cell and bulk tumor cell populations. Modulators of IGF signaling may thus prove useful in improving outcomes in patients with T-ALL. In this review, we summarize the most recent findings relating to IGF signaling in T-ALL and outline therapeutic options using clinically relevant IGF signaling modulators.
Ovarian cancer has a poor prognosis especially due to late diagnosis, intrinsic resistance to some therapeutic drugs, increased interest in finding novel DNA – binding and transcription factor agents as a probable chemotherapy in treating ovarian the gynecological cancer. Based on many previous reports it is evident that the expression of various cellular genes are been regulated by Sp1 the transcription factor, but still a better understanding is required, about its role in developing and progressing the human cancer. Sp1 is been found playing dual role such as the activation as well as suppression of the cellular genes either converting into an oncogene or performing biological activity such as proliferation, differentiation, DNA damage response, apoptosis and angiogenesis. There are even proofs, which suggest that Sp1 has homologous forms of proteins named as Sp2 and Sp3, which also support Sp1 in contributing the progression of tumor cells. These typical characters of Sp1 and its interesting facts related to biological functions are yet to be explained clearly. Thus, in this current review, we briefly explain the role, characters and proteins associated with Sp1 family of transcription factor do contribute as a “hallmarks of cancer”. We also review the evidence suggesting that Sp1 is highly over – expressing the genes, which pay ways in promoting ovarian cancer. Thus, we conclude that targeting Sp1 one of the best diagnostic tool to detect ovarian cancer in early stages or promoting Sp1 as best therapeutic agent would be a best resolution to reduce the incidence of ovarian cancer.
Sp1 protein binds to GC/GT-rich promoter elements through zinc finger motifs present at their C-terminal domains and regulates expression of multiple genes in normal tissues and tumors. Sp1 protein plays a critical role in the growth and metastasis of gastrointestinal cancers by regulating expression of cell cycle genes and VEGF. However, Sp1 is involved much in growth-related signal transduction pathways, and its overexpression has both positive and negative effects on proliferation of cells. In addition to growth control, Sp1 is intricate in apoptosis and angiogenesis; therefore, Sp1 is involved in several aspects of tumorigenesis. Consistent with a role of Sp1 in cancer, it interacts with oncogenes and tumor suppressors and alters their expression. Effects of changes in Sp1 factor are context-dependent and are paradoxical. Sp1 proteins have been recognized as an essential cancer drug target.
It is increasingly evident that not only breast cancer cells, but also the tissue embedding these cells: the tumor microenvironment, plays an important role in tumor progression, metastasis formation and treatment sensitivity. This review focuses on the current knowledge of processes by which the microenvironment affects breast cancer, including formation of the metastatic niche, metabolic stimulation, stimulation of tumor cell migration, immune modulation, angiogenesis and matrix remodeling. The number of drugs targeting key factors in these processes is expanding, and the available clinical data is increasing. Therefore current strategies for intervention and prediction of treatment response are outlined. At present, targeting the formation of the metastatic niche and metabolic stimulation by the breast cancer microenvironment, is already showing clinical efficacy. Intervening in the stimulation of tumor cell migration and immune modulation by the microenvironment is an upcoming field of great research interest. In contrast, targeting microenvironmental angiogenesis or matrix remodeling appears to be of limited clinical relevance in breast cancer treatment so far. Further research is warranted to optimize intervention strategies and develop predictive tests for the relevance of targeting involved factors within the microenvironment in order to optimally personalize breast cancer treatment.
Background
The Klotho gene was originally identified as an anti-aging gene in 1997. Recent studies have demonstrated aberrant expression of Klotho in a number of cancers, including breast cancer, lung cancer, hepatocellular carcinoma (HCC), and so on.
Methods
A literature search focusing on dysregulation of Klotho and its possible mechanisms in cancer was performed.
Results and conclusions
Downregulation of Klotho was found in several cancers, such as pancreatic cancer, HCC, and other tumors. Epigenetic modulation, such as promoter methylation and histone deacetylation, also contributed to the dysregulation of Klotho in cancers. Downregulation of Klotho resulted in promoted proliferation and reduced apoptosis of cancer cells. The relevant mechanisms include the fibroblast growth factor signaling, the insulin-like growth factor 1 receptor pathway, and the Wnt/β-catenin signaling pathway. Furthermore, the Klotho protein hopefully provides new insights into cancer target treatment.
Purpose
Triple negative breast cancer (TNBC) is biologically characterised by heterogeneous presence of molecular pathways underlying it. Insulin-like growth factor receptor-1 (IGF-1R) expression and vascular endothelial growth factor-A (VEGF-A) have been identified as key factors in these pathways in TNBC. In this study, we aimed at in vivo PET imaging the effect of heat shock protein (Hsp) 90 inhibition by means of NVP-AUY922 on these pathways, with zirconium-89 (89Zr) labelled antibodies targeting IGF-1R and VEGF-A.
Materials and methods
In vitro NVP-AUY922 effects on cellular IGF-1R expression and VEGF-A secretion were determined in MCF-7 and MDA-MB-231 cell lines. Moreover human TNBC bearing MDA-MB-231 mice received 50 mg/kg NVP-AUY922 or vehicle q3d intraperitoneally for 21 days. PET scans with 89Zr-MAB391 and 89Zr-bevacizumab for visualisation of IGF-1R and VEGF-A were performed before and during treatment. Ex vivo biodistribution and correlative tissue analyses were performed.
Results
NVP-AUY922 treatment reduced IGF-1R expression and VEGF-A excretion in both cell lines. Hsp90 inhibition lowered tumour uptake on 89Zr-MAB391-PET by 37.3% (P < 0.01) and on 89Zr-bevacizumab-PET by 44.4% (P < 0.01). This was confirmed by ex vivo biodistribution with a reduction of 41.3% injected dose (ID)/g for 89Zr-MAB391 and 37.8% ID/g for 89Zr-bevacizumab, while no differences were observed for other tissues. This coincided with reduced IGF-1R expression and mean vessel density in the NVP-AUY922 treated tumours.
Conclusion
89Zr-MAB391 and 89Zr-bevacizumab PET reflect effect of Hsp90 inhibitors and can therefore potentially be used to monitor therapeutic effects of Hsp90 inhibitor therapy in TNBC.
Several lines of evidence indicate that sequence alterations within microRNA (miRNA)-binding sites can modify the binding to its target gene resulting in altered expression patterns. We hypothesized that a single nucleotide polymorphism (SNP) located in the miR-515-5p binding site of igf-1r gene may alter IGF-1R regulation, with consequent effects on breast cancer risk in BRCA1 mutation carriers. Computational prediction revealed that the rs28674628 SNP in the igf-1r 3' UTR is located within a predicted binding site for miR-515-5p. The effect of this SNP on breast cancer risk was evaluated by genotyping 115 Jewish Ashkenazi carriers of the 185delAG mutation in the BRCA1 gene using the Sequenom platform followed by Kaplan-Meier analysis. Additional data set of 378 Jewish BRCA1 carriers was analyzed to validate our results. MiRNA transfection, Western blot analysis, luciferase reporter assay, real time PCR, and immunohistochemistry were performed to assess direct regulation of igf-1r by miR-515-5p. We show direct regulation of IGF-1R by miR-515-5p. We identified that disrupting miR-515-5p and igf-1r 3' UTR binding by SNP may cause elevated IGF-1R protein levels. Interestingly, miR-515-5p is downregulated in tumor tissue compared to its non-neoplastic surrounding tissue while IGF-1R levels are elevated. This igf-1r SNP was found to be significantly associated with age at diagnosis of breast cancer in Jewish Ashkenazi BRCA1 mutation carriers. These findings support the hypothesis that a SNP located in igf-1r gene may alter miRNA regulation of IGF-1R, with a putative effect on BRCA1 penetrance and breast cancer risk.
Chemoresistance and metastasis are the main reasons for the failure of current treatments with sarcoma patients. Novel biomarkers are required to predict metastasis and response to treatment. The oncogene MTDH/AEG1 and the long noncoding RNA (lincRNA) HOTAIR are two novel factors involved in drug resistance and metastasis in various types of solid tumors. However, the correlation between MTDH/AEG-1 and HOTAIR expression with metastasis and drug resistance in sarcoma is unknown.
Expression of MTDH protein or HOTAIR was detected by Western blotting or qRT-PCR, respectively, in primary and metastatic sarcoma patient tissue samples.
High individual or co-expression of MTDH/AEG1 and HOTAIR was observed in three of four primary and six of eight metastatic sarcoma patient tumor samples. High level expression of both of MTDH/AEG1 and HOTAIR in the primary tumor correlated with a likelihood to metastasize. MTDH expression was lower in samples pre-treated with irradiation and/or chemotherapy as compared to those that had not been treated. HOTAIR expression seemed to correlate with the percent necrosis seen in different sarcoma samples.
High levels of both MTDH/AEG-1 and HOTAIR in primary sarcoma are correlated with a high probability of metastasis. By contrast, reduced expression of both MTDH/AEG-1 and HOTAIR is correlated with a good response to treatment in terms of necrosis, suggesting that levels of MTDH and HOTAIR are potential biomarkers for treatment efficacy. Whether we can predict disease progression in sarcoma remains to be seen. Additional study is needed to better define the best clinical application of MTDH/AEG-1 and HOTAIR expression with metastasis and outcome.
Unlabelled:
There is a need to improve treatments for metastatic breast cancer. Here, we show the activation of the phosphoinositide 3-kinase (PI3K) and mitogen-activated protein kinase (MAPK) pathways in a MMTV-CreBrca1(f/f)Trp53(+/-) mouse model of breast cancer. When treated with the pan-class IA PI3K inhibitor NVP-BKM120, tumor doubling was delayed from 5 to 26 days. NVP-BKM120 reduced AKT phosphorylation, tumor cell proliferation, and angiogenesis. Resistant tumors maintained suppression of AKT phosphorylation but exhibited activation of the MAPK pathway at the "pushing margin." Surprisingly, PI3K inhibition increased indicators of DNA damage, poly-ADP-ribosylation (PAR), and γ-H2AX, but decreased Rad51 focus formation, suggesting a critical role of PI3K activity for Rad51 recruitment. The PARP inhibitor olaparib alone attenuated tumor growth modestly; however, the combination of NVP-BKM120 and olaparib delayed tumor doubling to more than 70 days in the mouse model and more than 50 days in xenotransplants from human BRCA1-related tumors, suggesting that combined PI3K and PARP inhibition might be an effective treatment of BRCA1-related tumors.
Significance:
Current treatment options for triple-negative breast cancer are limited to chemotherapeutic regimens that have considerable toxicity and are not curative. We report here that the combination of a PI3K inhibitor with a PARP inhibitor provides in vivo synergy for treatment of an endogenous mouse model for BRCA1-related breast cancers, making this a candidate combination to be tested in human clinical trials.
The IGF1-R displays potent antiapoptotic, prosurvival activities and has an important role in cell cycle progression. In addition,
activation of the IGF1-R signaling pathway is a crucial prerequisite for malignant transformation. Overexpression of the IGF1-R
has been identified as a typical hallmark of many, but definitely not all, types of tumors. The level of expression of the
IGF1-R gene is determined by the concerted action of positively acting and negatively acting transcription factors. Loss-of-function mutation of tumor suppressors, a characteristic feature of many human cancers, leads to IGF1-R expression, with ensuing activation
of cell-surface receptors by circulating and/or locally produced IGF-1 and IGF-2.
Insulin-like growth factors (IGFs), which include insulin-like growth factor I (IGF-I) and insulin-like growth factor II (IGF-II)
are mitogenic and anti-apoptotic growth factors that regulate cellular proliferation, differentiation and cell death. The
mitogenic and anti-apoptotic properties of IGF-I and IGF-II affect both normal and cancerous cells. The effects of the IGFs
on cell growth and apoptosis are mediated through binding to a tyrosine kinase receptor, the insulin-like growth factor-I
receptor (IGF-IR). The IGF-IIR (the cation-independent mannose-6-phosphate receptor – M6P-R) is a single transmembrane glycoprotein
that mediates the uptake and processing of M6P-containing cytokines, enzymes and peptide hormones and is involved in diverse
functions related to lysosome biogenesis. IGF-II also binds the insulin receptor isoform-A (IR-A), with high affinity and
can trigger mitogenic activity. IR and IGF-IR form hybrid heterodimeric receptors that bind insulin and IGFs. However, the
role of the hybrid receptors in physiology and carcinogenesis is not fully understood and remains an area of active investigation.
IGF-I receptor (IGFR) content and its prognostic significance were evaluated in human breast cancer specimens using a sensitive and specific radioimmunoassay (V. Pezzino et al., Metabolism, 40: 861, 1991). The prognostic significance of IGFR expression was investigated by two dif ferent approaches: (a) detectable IGFR content was measured in 82% of specimens in a consecutive series of 184 human breast cancers and in 32% of 19 normal breast tissues. The average IGFR content in breast cancer was nearly 10-fold higher than the value observed in normal breast tissue (7.6. ± 0.8 versus 0.8 ± 0.1 ng/0.1 mg protein, mean ± SEM; P < 0.001). IGFR content was positively correlated with estrogen (ER) and insulin receptor content (r = 0.269 and 0.515, respectively, Pearson correlation) but not with progesterone receptors (PR). No significant correlation was observed between IGFR content and a variety of tumor parameters (tu mor size, lymph node involvement, grade) and host characteristics (age, body mass index, menopausa! status); (ft) IGFR content was measured in a noncontinuous series of 265 primary breast cancer specimens subdivided into 136 high-risk and 129 low-risk specimens on the basis of being either negative (ER-/PR-/aneuploid/high S-phase) or positive (ER+/PR+/ diploid/low S-phase) for four well-established prognostic factors. IGFR levels were significantly higher in the low-risk group (6.4 ± 0.4 ng/0.1 mg protein, mean ± SEM) than in the high-risk group (3.6 ± 0.5: /' < 0.0001,
The ligands, receptors and related signaling proteins of the insulin-like growth factor family are involved in the regulation of breast-cancer cell growth. We investigated the expression pattern of insulin-like growth factor-I receptor (IGF-IR), insulin receptor (IR) and insulin receptor substrate-1 (IRS-1), a core downstream signaling protein, in 69 primary breast-cancer specimens of different grades and in 21 control tissues by immunohistochemistry. In addition, cell proliferation (percentage of Ki67+ nuclei) and estrogen receptor (ER) expression were determined. IGF-IR, IRS-1 and IR were expressed mainly in epithelial cells. IRS-1 and IGF-IR were expressed at high levels in control tissues and in well and moderately differentiated carcinomas but at low levels in poorly differentiated breast cancers. IR expression did not show a significant correlation with the differentiation grade of the tissues investigated. Statistical analysis (ROC analysis for tumor grade) demonstrated that down-regulation of IGF-IR and IRS-1 correlated better with tumor progression than reduction of ER expression or increase in cell proliferation, IGF-IR showing the best correlation, followed by IRS-1 and, less significant, ER and Ki67. Our findings clearly show that progression of breast cancer is accompanied by a reduction of IGF-IR/IRS-1 expression and that IGF-IR/IRS-1 expression inversely correlates with high proliferation rate in dedifferentiated breast cancers. The strong correlation of IGF-IR and IRS-1 down-regulation with tumor progression suggests the use of IGF-IR and IRS-1 as a novel set of marker proteins for tumor grading. Int. J. Cancer 89:506–513, 2000. © 2000 Wiley-Liss, Inc.
A strong candidate for the 17q-linked BRCA1 gene, which influences susceptibility to breast and ovarian cancer, has been identified
by positional cloning methods. Probable predisposing mutations have been detected in five of eight kindreds presumed to segregate
BRCA1 susceptibility alleles. The mutations include an 11-base pair deletion, a 1-base pair insertion, a stop codon, a missense
substitution, and an inferred regulatory mutation. The BRCA1 gene is expressed in numerous tissues, including breast and ovary,
and encodes a predicted protein of 1863 amino acids. This protein contains a zinc finger domain in its amino-terminal region,
but is otherwise unrelated to previously described proteins. Identification of BRCA1 should facilitate early diagnosis of
breast and ovarian cancer susceptibility in some individuals as well as a better understanding of breast cancer biology.
We analysed 50 probands with a family history of breast and/or ovarian cancer for germline mutations in the coding region of the BRCA1 candidate gene, using single-strand conformation polymorphism (SSCP) analysis on PCR-amplified genomic DNA. A total of eight putative disease-causing alterations were identified: four of these are frameshifts and two are nonsense mutations. In addition, we found two missense mutations, one of which changes the final cysteine of the BRCA1 zinc finger motif to glycine. These data are consistent with a tumour suppressor model, and support the notion that this candidate gene is in fact BRCA1. The heterogeneity of mutations, coupled with the large size of the gene, indicates that clinical application of BRCA1 mutation testing will be technically challenging.
Fibroblast cell lines were established from mouse embryos homozygous for a targeted disruption of the Igf1r gene, encoding the type 1 receptor for insulin-like growth factor I (IGF-I) and from their wild-type littermates. The cells from the wild-type embryos (W cells) grow in serum-free medium supplemented with platelet-derived growth factor, epidermal growth factor, and IGF-I, whereas the cells from Igf1r(-/-) embryos (R- cells) do not, although they grow at a reduced rate in 10% fetal calf serum. The simian virus 40 (SV40) large T antigen, expressed from a transfected plasmid, can transform W cells, which form foci in monolayer cultures and colonies in soft agar (anchorage-independent growth). In contrast, the SV40 large tumor antigen, although normally expressed from the transfected template, is unable to transform R- cells, which remain contact-inhibited and fail to grow in soft agar. The transformed phenotype is restored if the R- cells carrying the SV40 large tumor antigen are stably transfected with a plasmid expressing the human IGF-I receptor. These results demonstrate that signaling via the IGF-I receptor is an indispensable component of the SV40 transformation pathway. This conclusion is further supported from the results of antisense RNA experiments with tumor cell lines showing that interference with the function of the IGF-I receptor has a profound effect on anchorage-independent growth, even under conditions that only modestly affect growth in monolayers.
Mutations in BRCA1 account for 45% of families with high incidence of breast cancer and for 80-90% of families with both breast and ovarian cancer. BRCA1 protein includes an amino-terminal zinc finger motif as well as an excess of negatively charged amino acids near the C terminus. In addition, BRCA1 contains two nuclear localization signals and localizes to the nucleus of normal cells. While these features suggest a role in transcriptional regulation, no function has been assigned to BRCA1. Here, we show that the C-terminal region, comprising exons 16-24 (aa 1560-1863) of BRCA1 fused to GAL4 DNA binding domain can activate transcription both in yeast and mammalian cells. Furthermore, we define the region comprising exons 21-24 (aa 1760-1863) as the minimal transactivation domain. Any one of four germ-line mutations in the C-terminal region found in patients with breast or ovarian cancer (Ala-1708-->Glu, Gln-1756 C+, Met-1775-->Arg, Tyr-1853 ->Stop), had markedly impaired transcription activity. Together these data underscore the notion that one of the functions of BRCA1 may be the regulation of transcription.
The familial breast-ovarian tumor suppressor gene product BRCA1 was found to be a component of the RNA polymerase II holoenzyme by several criteria. BRCA1 was found to copurify with the holoenzyme over multiple chromatographic steps. Other tested transcription activators that could potentially contact the holoenzyme were not stably associated with the holoenzyme as determined by copurification. Antibody specific for the holoenzyme component hSRB7 specifically purifies BRCA1. Immunopurification of BRCA1 complexes also specifically purifies transcriptionally active RNA polymerase II and transcription factors TFIIF, TFIIE, and TFIIH. Moreover, a BRCA1 domain, which is deleted in about 90% of clinically relevant mutations, participates in binding to the holoenzyme complex in cells. These data are consistent with recent data identifying transcription activation domains in the BRCA1 protein and link the BRCA1 tumor suppressor protein with the transcription process as a holoenzyme-bound protein.
In this study, we tested the hypothesis that insulin-like growth factor-1 (IGF-1) modulates apoptosis in human breast cancer cells, HBL100, induced by diverse chemotherapeutic drugs. IGF-1 increased cell survival of HBL100 cells treated with 5-fluorouracil (antimetabolite), methotrexate (antimetabolite), tamoxifen (antiestrogen/antiproliferative), or camptothecin (topoisomerase 1 inhibitor) and after serum withdrawal. Elevated cell survival was not due to an increase in cell proliferation by IGF-1, but rather to an inhibition of apoptosis. Evidence for death by apoptosis was supported by cellular morphology and DNA fragmentation. There were no changes observed in Bcl-2 protein or bax mRNA levels. Extracellular matrix (ECM) is known to influence the apoptotic response of cells; therefore, the antiapoptotic effect of IGF-1 on breast cancer cells was examined using different ECMs: laminin, collagen IV, or Matrigel. IGF-1 protected cells from apoptosis induced by methotrexate on all ECMs tested, providing the first evidence that IGF-1 protects against apoptosis in three-dimensional culture systems. These data provide the rationale to search for drugs that lower serum IGF-1 in an effort to improve the efficacy of chemotherapeutic drugs for the treatment of breast cancer.
The insulin-like growth factor-I receptor (IGF-IR) plays a critical role in cell growth regulation and transformation. The radiosensitivity of NIH 3T3 fibroblasts overexpressing either wild-type or mutant IGF-IR was examined. High levels of wild-type IGF-IR conferred radioresistance, and mutational analysis revealed that this effect correlated with the transforming capacity but not the mitogenic activity of the receptor. The radioresistant phenotype was reversed when the cells were incubated with antisense oligonucleotides targeted to IGF-IR mRNA, demonstrating that IGF-IR directly influences radioresistance. The clinical significance of these findings was examined in an immunohistochemical analysis of primary breast tumors, revealing that high levels of IGF-IR in tumor samples were highly correlated with ipsilateral breast tumor recurrence (IBTR) following lumpectomy and radiation therapy (P = 0.001). Subgroup analysis revealed that, for early breast tumor relapses (within 4 years of initial breast tumor diagnosis), elevated levels of IGF-IR were strongly associated with IBTR (P = 0.004) but IGF-IR expression was not prognostic for IBTR from breast cancer patients with late relapses (P was not significant). These studies provide evidence for the influence of IGF-IR on cellular radioresistance and response to therapy and raise the possibility that the radiocurability of selected tumors may be improved by pharmaceutical strategies directed toward the IGF-IR.
The ligands, receptors and related signaling proteins of the insulin-like growth factor family are involved in the regulation of breast-cancer cell growth. We investigated the expression pattern of insulin-like growth factor-I receptor (IGF-IR), insulin receptor (IR) and insulin receptor substrate-1 (IRS-1), a core downstream signaling protein, in 69 primary breast-cancer specimens of different grades and in 21 control tissues by immunohistochemistry. In addition, cell proliferation (percentage of Ki67(+) nuclei) and estrogen receptor (ER) expression were determined. IGF-IR, IRS-1 and IR were expressed mainly in epithelial cells. IRS-1 and IGF-IR were expressed at high levels in control tissues and in well and moderately differentiated carcinomas but at low levels in poorly differentiated breast cancers. IR expression did not show a significant correlation with the differentiation grade of the tissues investigated. Statistical analysis (ROC analysis for tumor grade) demonstrated that down-regulation of IGF-IR and IRS-1 correlated better with tumor progression than reduction of ER expression or increase in cell proliferation, IGF-IR showing the best correlation, followed by IRS-1 and, less significant, ER and Ki67. Our findings clearly show that progression of breast cancer is accompanied by a reduction of IGF-IR/IRS-1 expression and that IGF-IR/IRS-1 expression inversely correlates with high proliferation rate in dedifferentiated breast cancers. The strong correlation of IGF-IR and IRS-1 down-regulation with tumor progression suggests the use of IGF-IR and IRS-1 as a novel set of marker proteins for tumor grading.
The breast cancer and ovarian cancer susceptibility gene BRCA1 encodes a nucleoprotein whose mutations or aberrant expression is associated with both inherited and sporadic cancers. Studies over the last 6 years have suggested that BRCA1 may function as a scaffold in the assembly of a multi-protein complex, which plays a role in gene transcription, DNA damage repair, and transcription-coupled DNA damage repair. In this review, we discuss the implications drawn from the studies of BRCA1-interacting proteins and the cellular signaling pathways that may be involved in controlling the functions of BRCA1.
Extensive studies of BRCA1- and BRCA2-associated breast tumours have been carried out in the few years since the identification of these familial breast cancer predisposing genes. The morphological studies suggest that BRCA1 tumours differ from BRCA2 tumours and from sporadic breast cancers. Recent progress in immunohistochemistry and molecular biology techniques has enabled in-depth investigation of molecular pathology of these tumours. Studies to date have investigated issues such as steroid hormone receptor expression, mutation status of tumour suppressor genes TP53 and c-erbB2, and expression profiles of cell cycle proteins p21, p27 and cyclin D1. Despite relative paucity of data, strong evidence of unique biological characteristics of BRCA1-associated breast cancer is accumulating. BRCA1-associated tumours appear to show an increased frequency of TP53 mutations, frequent p53 protein stabilization and absence of imunoreactivity for steroid hormone receptors. Further studies of larger number of samples of both BRCA1- and BRCA2-associated tumours are necessary to clarify and confirm these observations.
The breast cancer tumor-suppressor gene, BRCA1, encodes a protein with a BRCT domain-a motif that is found in many proteins that are implicated in DNA damage response and in genome stability. Phosphorylation of BRCA1 by the DNA damage-response proteins ATM, ATR and hCds1/Chk2 changes in response to DNA damage and at replication-block checkpoints. Although cells that lack BRCA1 have an abnormal response to DNA damage, the exact role of BRCA1 in this process has remained unclear. Here we show that BRCA1 is essential for activating the Chk1 kinase that regulates DNA damage-induced G2/M arrest. Thus, BRCA1 controls the expression, phosphorylation and cellular localization of Cdc25C and Cdc2/cyclin B kinase-proteins that are crucial for the G2/M transition. We show that BRCA1 regulates the expression of both Wee1 kinase, an inhibitor of Cdc2/cyclin B kinase, and the 14-3-3 family of proteins that sequesters phosphorylated Cdc25C and Cdc2/cyclin B kinase in the cytoplasm. We conclude that BRCA1 regulates key effectors that control the G2/M checkpoint and is therefore involved in regulating the onset of mitosis.
In Ashkenazi (East European) Jews, three predominant mutations in BRCA1 (185delAG and 5382insC) and BRCA2 (6174delT) account for the majority of germline mutations in high‐risk breast and/or ovarian cancer families. Among non‐Ashkenazi Jews, the 185delAG, Tyr978Ter, and a handful of “private” mutations have been reported anecdotally within both genes. In this study we attempted to determine the spectrum of BRCA1 and BRCA2 mutations in high‐risk Jewish individuals, non‐carriers of any of the predominant Jewish mutations. We employed multiplex PCR and denaturing gradient gel electrophoresis (DGGE) analysis for BRCA2, and combined denaturing high performance liquid chromatography (DHPLC) and protein truncation test (PTT) for BRCA1, complemented by DNA sequencing. We screened 47 high‐risk Jewish individuals, 26 Ashkenazis, and 21 non‐Ashkenazis. Overall, 13 sequence alterations in BRCA1 and eight in BRCA2 were detected: nine neutral polymorphisms and 12 missense mutations, including five novel ones. The novel missense mutations did not co‐segregate with disease in BRCA1 and were detected at rates of 6.25% to 52.5% in the general population for BRCA2. Our findings suggest that except for the predominant mutations in BRCA1 and BRCA2 in Jewish individuals, there are only a handful of pathogenic mutations within these genes. It may imply novel genes may underlie inherited susceptibility to breast/ovarian cancer in Jewish individuals. Hum Mutat 16:491–501, 2000. © 2000 Wiley‐Liss, Inc.
The functions of most of the 12 subunits of the RNA polymerase II (Pol II) enzyme are unknown. In this study, we demonstrate that two of the subunits, hRPB2 and hRPB10α, mediate the regulated stimulation of transcription. We find that the transcriptional coactivator BRCA1 interacts directly with the core Pol II complex in vitro. We tested whether single subunits from Pol II would compete with the intact Pol II complex to inhibit transcription stimulated by BRCA1. Excess purified Pol II subunits hRPB2 or hRPB10α blocked BRCA1- and VP16-dependent transcriptional activation in vitro with minimal effect on basal transcription. No other Pol II subunits tested inhibited activated transcription in these assays. Furthermore, hRPB10α, but not hRPB2, blocked Sp1-dependent activation.
Loss of heterozygosity data from familial tumors suggest that BRCA1, a gene that confers susceptibility to ovarian and early-onset
breast cancer, encodes a tumor suppressor. The BRCA1 region is also subject to allelic loss in sporadic breast and ovarian
cancers, an indication that BRCA1 mutations may occur somatically in these tumors. The BRCA1 coding region was examined for
mutations in primary breast and ovarian tumors that show allele loss at the BRCA1 locus. Mutations were detected in 3 of 32
breast and 1 of 12 ovarian carcinomas; all four mutations were germline alterations and occurred in early-onset cancers. These
results suggest that mutation of BRCA1 may not be critical in the development of the majority of breast and ovarian cancers
that arise in the absence of a mutant germline allele.
The mutations 185delAG, 188del11, and 5382insC in the BRCA1 gene and 6174delT in the BRCA2 gene were analyzed in 199 Ashkenazi and 44 non-Ashkenazi Jewish unrelated patients with breast and/or ovarian cancer. Of the Jewish Ashkenazi women with ovarian cancer, 62% (13/21) had one of the target mutations, as did 30% (13/43) of women with breast cancer alone diagnosed before the age 40 years and 10% (15/141) of those with breast cancer diagnosed after the age 40 years. Age at ovarian cancer diagnosis was not associated with carrier status. Of 99 Ashkenazi patients with no family history of breast and/or ovarian cancer, 10% carried one of the mutations; in two of them the mutation was proved to be paternally transmitted. One non-Ashkenazi Jewish ovarian cancer patient from Iraq carried the 185delAG mutation. Individual mutation frequencies among breast cancer Ashkenazi patients were 6.7% for 185delAG, 2.2% for 5382insC, and 4.5% for 6174delT, among ovarian cancer patients; 185delAG and 6174delT were about equally common (33% and 29%, respectively), but no ovarian cancer patient carried the 5382insC. More mutations responsible for inherited breast and ovarian cancer probably remain to be found in this population, since 79% of high-incidence breast cancer families and 35% of high-incidence breast/ovarian cancer families had none of the three known founder mutations. 25 refs., 3 figs., 6 tabs.
In Ashkenazi (East European) Jews, three predominant mutations in BRCA1 (185delAG and 5382insC) and BRCA2 (6174delT) account for the majority of germline mutations in high-risk breast and/or ovarian cancer families. Among non-Ashkenazi Jews, the 185delAG, Tyr978Ter, and a handful of “private” mutations have been reported anecdotally within both genes. In this study we attempted to determine the spectrum of BRCA1 and BRCA2 mutations in high-risk Jewish individuals, non-carriers of any of the predominant Jewish mutations. We employed multiplex PCR and denaturing gradient gel electrophoresis (DGGE) analysis for BRCA2, and combined denaturing high performance liquid chromatography (DHPLC) and protein truncation test (PTT) for BRCA1, complemented by DNA sequencing. We screened 47 high-risk Jewish individuals, 26 Ashkenazis, and 21 non-Ashkenazis. Overall, 13 sequence alterations in BRCA1 and eight in BRCA2 were detected: nine neutral polymorphisms and 12 missense mutations, including five novel ones. The novel missense mutations did not co-segregate with disease in BRCA1 and were detected at rates of 6.25% to 52.5% in the general population for BRCA2. Our findings suggest that except for the predominant mutations in BRCA1 and BRCA2 in Jewish individuals, there are only a handful of pathogenic mutations within these genes. It may imply novel genes may underlie inherited susceptibility to breast/ovarian cancer in Jewish individuals. Hum Mutat 16:491–501, 2000. © 2000 Wiley-Liss, Inc.
BACKGROUND
The expression of steroid receptors is a common feature of both male and female breast carcinomas and is also one of the most important prognostic factors for patients with this disease. Steroid receptor levels in BRCA1-related breast carcinoma have reportedly been low. Little data on steroid receptor levels have been reported with regard to BRCA2.METHODS
Steroid receptor levels were analyzed in 27 breast carcinomas associated with BRCA1 mutations, 14 associated with BRCA2 mutations, and 32 from individuals who had hereditary breast carcinoma but no detectable mutations of either BRCA1 or BRCA2. Breast carcinomas from 32 consecutive male patients, 6 of whom had mutations of BRCA2, were also examined for steroid receptors. Estrogen receptor (ER) and progesterone receptor (PgR) analyses were performed with radioligand or enzyme immunoassay techniques on tumor cytosol preparations. Germline mutation screening and detection were performed using the protein truncation test, single strand conformation polymorphism, and direct sequencing on DNA from normal tissue.RESULTSThe BRCA1-related tumors expressed significantly lower levels of ER than tumors from the other hereditary groups. The PgR levels were significantly lower in the BRCA1-related cases than in the hereditary cases not related to BRCA1 or BRCA2, but not significantly lower than in the BRCA2-related cases. Fourteen of 32 (44%) of the hereditary tumors not related to BRCA1 or BRCA2 had PgR levels exceeding 100 fmol/mg of protein. The tumors from male patients with BRCA2-related disease did not have receptor levels that differed from those in non-BRCA2-related tumors.CONCLUSIONSBRCA1- and BRCA2-related breast tumors were distinct in their expression of steroid receptors. Moreover, a subgroup of tumors not related to BRCA1 or BRCA2 manifested a strongly positive PgR phenotype rarely seen in BRCA1- and BRCA2-related tumors. These characteristics may be of relevance to the treatment and follow-up of high risk individuals in these families and may help identify a homogenous category of hereditary breast carcinomas not related to BRCA1 or BRCA2 in which new susceptibility genes may be sought. Cancer 1998;83:310-319. © 1998 American Cancer Society.
The insulin-like growth factor (IGF) family of ligands, receptors, and binding proteins can regulate breast cancer cell proliferation in vitro, and interruption of these pathways inhibits IGF-mediated cell proliferation. If the IGF family members are key regulators of breast cancer growth and progression in vivo, we would expect their expression to be an indicator of the prognosis of the disease. Thus, measurement of IGF expression may provide an indicator of the growth effect within a tumor, and provide new targets for treatment of the disease. In this review we will summarize the data generated thus far indicating that IGF family members are indicators of prognosis of breast cancer, and that measurement of the whole IGF family in concert may provide useful information for treatment strategies of breast cancer.
Once it was recognized that breast tumor growth was stimulated by estrogens, successfultherapeutic strategies based on depriving the tumor of this hormone were developed. Sincethe growth stimulatory properties of the estrogens are governed by the estrogen receptor (ER),4understanding the mechanisms that activate ER are highly relevant. In addition to estrogens,peptide growth factors can also activate the ER. The insulin-like growth factors (IGFs) arepotent mitogens for ER-positive breast cancer cell lines. This review will examine the evidencefor interaction between these two pathways. The IGFs can activate the ER, while ERtranscriptionally regulates genes required for IGF action. Moreover, blockade of ER function can inhibitIGF-mediated mitogenesis and interruption of IGF action can similarly inhibit estrogenicstimulation of breast cancer cells. Taken together, these observations suggest that the twogrowth regulatory pathways are tightly linked and that a further understanding of the mechanismof this crosstalk could lead to new therapeutic strategies in breast cancer.
The first step of the action of IGF1 and IGF2 (IGFs) is their binding to membrane receptors. IGF binding sites have been characterized by competitive binding and cross-linking techniques in human breast cancer cell lines as well as in human breast cancers and in human benign breast diseases. IGF2 is a good competitor of125I-IGF1 binding to IGF1-R; insulin competes but with a potency 1/100 lower than the IGF1 potency. Chemical cross-linking experiments revealed that the apparent molecular weight of the IGF1-binding sites is 130,000. Alpha IR-3, a murine monoclonal antibody against the IGF1-R, blocks IGF1-binding to this receptor. This antibody inhibits the IGF1-stimulated growth of breast cancer cells. Therefore, the IGF1 specific binding sites correspond to the previously described type 1 IGF receptors (IGF1-R) in normal tissues. Cross-linking experiments with labeled IGF2 resulted in a major band of apparent Mr 260,000–270,000 that was inhibited by unlabeled IGF2 but not by insulin, and corresponds to the type 2 IGF receptor; a second band of apparent Mr 130,000 was inhibited by excess IGFs and insulin (Type I receptor). The alpha-IR3 inhibition of the IGF2 mitogenic activity suggest that IGF1-R partially mediates the growth effect of IGF2 in these cells.
We and others have demonstrated that most breast cancer cell lines contain IGF1-R. This is also the case in breast cancer biopsies in which histo-autoradiographic analyses allowed the localization of IGF1-R on the epithelial component. IGF1-R concentrations were positively correlated to estradiol and progesterone receptor concentrations. In our experience, the presence of IGF1-R is associated with a better prognosis. Finally, IGF1-R are found less frequently and at lower concentrations in benign breast diseases. These results suggest that IGF1-R could be a marker of the proliferative epithelial component within the tumor.
The insulin-like growth factor I receptor (IGF-I-R) gene is expressed in most body tissues. The levels of IGF-I-R mRNA, however, are regulated by a number of physiological conditions (development, differentiation, and hormonal milieu) as well as in certain pathological states (diabetes and tumors). To understand the molecular mechanisms which control the transcription of the IGF-I-R gene, we have cloned the promoter of the rat receptor gene and have characterized its activity by transient expression assays. Different fragments of the 5'-flanking region (subcloned upstream of a luciferase reporter gene) were transfected into buffalo rat liver 3A cells (a cell line with a low number of IGF-I binding sites) and Chinese hamster ovary cells (a cell line with a higher number of cell-surface receptors). In both cell lines, most of the promoter activity was located in the proximal 416 base pairs of 5'-flanking region. However, further dissection of this proximal fragment revealed a cell type-specific pattern of promoter activity. Thus, in buffalo rat liver 3A cells, subfragments of this region each contributed to total activity, suggesting that contiguous cis-elements can act together to activate transcription. In Chinese hamster ovary cells, on the other hand, subfragments of the proximal promoter region partially substituted for the proximal 416 base pairs of 5'-flanking region. Coexpression studies using an IGF-I-R promoter reporter construct together with an Sp1 expression vector (under the control of an ADH promoter) were performed in SL2 cells, a Drosophila cell line which lacks endogenous Sp1. The results obtained showed that Sp1 can trans-activate the IGF-I-R promoter in vivo. Transient transfection assays were complemented with gel-retardation assays and DNase I footprinting experiments, which showed that transcription factor Sp1 is potentially an important regulator of IGF-I-R gene expression.
We isolated genomic fragments containing the 5' region of the human type I insulin-like growth factor receptor gene. A unique transcription start site was identified, defining a 1038 bp 5'-untranslated region. No TATA or CCAAT elements were identified in the proximal 480 nucleotides of 5'-flanking region. The region surrounding the transcription start site was similar to a recently described "initiator" sequence. The 5'-flanking and 5'-untranslated regions were highly GC-rich, with numerous potential Sp1 binding sites. A potential AP-2 binding site was identified in the 5'-flanking region and a potential thyroid response element was identified in the 5'-untranslated region. The 5' region of the human gene was very similar to that of the rat gene, with conservation of many of the potential regulatory elements.
The insulin-like growth factor I (IGF-I) receptor mediates signal transduction by the IGFs and plays a critical role in growth and development. The proximal promoter region of the rat IGF-I receptor gene contains multiple Sp1 consensus-binding sites (GC boxes). Various promoter fragments fused to a luciferase reporter gene were transiently cotransfected together with an Sp1 expression vector into Drosophila Schneider cells, which lack endogenous Sp1. A proximal promoter fragment containing 476 nucleotides of 5'-flanking region and 640 nucleotides of 5'-untranslated region was strongly activated by Sp1 (an average of 116-fold), and progressive 5'-deletions of the promoter that sequentially removed GC boxes reduced Sp1 activation to 15-fold over basal promoter activity. DNase I footprinting studies with purified Sp1 protein revealed four GC boxes in the 5'-flanking region of the promoter and one homopurine/homopyrimidine motif (CT element) in the 5'-untranslated region that bound Sp1. Mutation of the CT element reduced Sp1 activation by 70%. Taken together, these results demonstrate that Sp1 can regulate expression of the IGF-I receptor promoter by acting both on GC boxes in the 5'-flanking region of the promoter and on a CT element in the 5'-untranslated region.
Evidence from several experimental systems has shown that the insulin-like growth factors (IGFs) can stimulate breast cancer proliferation. Since IGF action is mediated by interaction with specific cell surface receptors, interruption of these signalling pathways could result in inhibition of cellular growth. In all extracellular fluids, the IGFs are associated with high affinity binding proteins, the IGFBPs can bind the IGFs and prevent receptor activation, and thus might have a role in a targeted approach to breast cancer therapy. Here we present our studies using IGFBP-1 to inhibit growth of the breast cancer cell line MCF-7.
I. Introduction THE insulin-like growth factors (IGFs) and their receptors and binding proteins constitute a family of cellular modulators that play essential roles in the regulation of growth and development. The IGF ligands include three structurally related peptides: insulin, IGF-I, and IGF-II. Unlike insulin, IGF-I and IGF-II are expressed ubiquitously, albeit in a highly regulated manner (see reviews in Refs. 1-5). The biological functions of the IGFs are mediated by a family of transmembrane receptors, which includes the insulin, IGF-I, and IGF-II/mannose-6-phosphate (M-6-P) receptors. While the IGF-I receptor is the primary mediator of IGF action, the insulin and IGF-II/M-6-P receptors may also mediate some of these functions (Fig. 1) (6, 7). The biological actions of the IGFs are modulated by a family of at least six IGF-binding proteins (IGFBPs) that are found in the circulation and in extracellular compartments and are produced by most tissues. The IGFBPs are capable of inhibiting or enhancing I...
Inherited mutations in BRCA1 predispose to breast and ovarian cancer, but the role of BRCA1 in sporadic breast and ovarian cancer has previously been elusive. Here, we show that retroviral transfer of the wild-type BRCA1 gene inhibits growth in vitro of all breast and ovarian cancer cell lines tested, but not colon or lung cancer cells or fibroblasts. Mutant BRCA1 has no effect on growth of breast cancer cells; ovarian cancer cell growth is not affected by BRCA1 mutations in the 5' portion of the gene, but is inhibited by 3' BRCA1 mutations. Development of MCF-7 tumours in nude mice is inhibited when MCF-7 cells are transfected with wild-type, but not mutant, BRCA1. Most importantly, among mice with established MCF-7 tumours, peritoneal treatment with a retroviral vector expressing wild-type BRCA1 significantly inhibits tumour growth and increased survival.
This chapter focuses on the role of the insulin-like growth factor system in human cancer. The normal process of growth and differentiation results from the genetically programmed action of a number of different cellular and extracellular factors. Derangement in the function of one or more of those agents can result in a pathologic phenotype, including neoplastic growth. A family of growth factors shown to be intimately involved in the regulation of cell growth as well as in cellular transformation is the insulin-like growth factor (IGF) family. IGF-I and IGF-II are mitogenic polypeptides produced in the largest amounts by the liver and secreted into the circulation, where they mediate the effects of growth hormone (GH) on longitudinal growth. In addition to ligands and receptors, the IGF system comprises a third category of molecules, which bind IGFs in the circulation and in extracellular compartments. Six IGF-binding proteins (IGFBPs) have been characterized to date. Binding of IGFs to the IGF-I receptor induces receptor autophosphorylation. The cell cycle consists of four major phases: (1) the presynthetic phase, G; (2) the phase of DNA synthesis, S; (3) the premitotic phase, G; and (4) mitosis, M. IGF-I, IGF-II, and insulin are chemotactic agents for the human melanoma cell line A2058, as assayed in a modified Boyden chamber. The chapter also gives selected examples of IGF involvement in human cancer. The wealth of information generated in the IGF field, as well as continued research efforts, both basic and clinic, promise to produce rational therapeutic approaches for those cancers in which the IGF system is involved.
The tumor suppressor genes BRCA1 and BRCA2, which confer increased susceptibility to breast and (or) ovarian cancer, were recently identified. Mutation analysis of BRCA1 has demonstrated significant allelic heterogeneity; however, some distinct mutations have been detected in unrelated individuals. The most notable is the 185delAG mutation, which occurs at an estimated frequency of approximately 1% in individuals of Ashkenazi Jewish descent [1]. Although consensus has not been reached regarding clinical testing for mutations in BRCA1, a tiered strategy may be appropriate, in which direct testing for the more common mutations is one component. Specific alleles can be detected by using PCR-mediated site-directed mutagenesis (PSM), which alters the PCR products derived from either the wild-type or mutant allele to create or destroy a restriction endonuclease recognition site. Recognition sites are introduced by a base substitution in one of the primers. The alleles are then resolved by electrophoresis of the digested PCR products. We have applied this technique to the detection of four BRCA1 mutations: 185delAG, 5382insC, E1250X, and R1443X. Another mutation, 1294de140, can be resolved from the wild-type allele by high-resolution gel electrophoresis alone. The PSM technique is sensitive, does not require radioactivity, and is specific for individual mutations.
The mutations 185delAG, 188del11, and 5382insC in the BRCA1 gene and 6174delT in the BRCA2 gene were analyzed in 199 Ashkenazi and 44 non-Ashkenazi Jewish unrelated patients with breast and/or ovarian cancer. Of the Jewish Ashkenazi women with ovarian cancer, 62% (13/21) had one of the target mutations, as did 30% (13/43) of women with breast cancer alone diagnosed before the age 40 years and 10% (15/141) of those with breast cancer diagnosed after the age 40 years. Age at ovarian cancer diagnosis was not associated with carrier status. Of 99 Ashkenazi patients with no family history of breast and/or ovarian cancer, 10% carried one of the mutations; in two of them the mutation was proved to be paternally transmitted. One non-Ashkenazi Jewish ovarian cancer patient from Iraq carried the 185delAG mutation. Individual mutation frequencies among breast cancer Ashkenazi patients were 6.7% for 185delAG, 2.2% for 5382insC, and 4.5% for 6174delT, among ovarian cancer patients; 185delAG and 6174delT were about equally common (33% and 29%, respectively), but no ovarian cancer patient carried the 5382insC. More mutations responsible for inherited breast and ovarian cancer probably remain to be found in this population, since 79% of high-incidence breast cancer families and 35% of high-incidence breast/ovarian cancer families had none of the three known founder mutations.
Insulin-like growth factors (IGFs) play an important role in normal cellular growth and development and have been implicated in the regulation of tumour growth. Two receptors are recognized, IGFR-1 and IGFR-2, of which one, IGFR-1, is a transmembrane heterodimer structurally similar to the insulin receptor. Studies using ligand-binding assays have suggested that the proportion of human breast carcinomas expressing IGFR-1 varies between 39 and 93 per cent and all suggest a lower level of IGFR-1 expression in benign mammary epithelia. As there is this variation between studies and since no study appears to have examined the immunohistochemical localization of IGFR-1 within breast tissue, a series of 79 infiltrating ductal carcinomas, 11 infiltrating lobular carcinomas, three cases of pure ductal carcinoma in situ (DCIS), seven fibroadenomas, and eight normal breast specimens have been studied utilizing the monoclonal antibody alpha IR3. IGFR-1 localized to the epithelial component of 90 per cent of the carcinomas, with only cytoplasmic (21 per cent), only membrane (5 per cent), or a mixture of both cytoplasmic and membrane (64 per cent) staining patterns. In some tumours, distinct basolateral distribution of the receptor was observed. Invasive lobular carcinoma showed significantly less labelling than ductal (P = 0.0009). There was a significant correlation between the level of IGFR-1 immunostaining with both oestrogen receptor (P < 0.001) and progesterone receptor (P = 0.0018) positivity within the malignant group. All normal mammary epithelium showed strong labelling, which was often at an intensity matching that of the most strongly labelled carcinoma and occasionally visualized as basolateral staining of the luminal cells. Weak to moderate staining of endothelial cells was also observed. It is concluded that IGFR-1 immunoreactivity is found in the majority of breast carcinomas, where it correlates most closely with oestrogen receptor status. The high intensity labelling of normal cells seen in this study contrasts with the low levels inferred from ligand-binding-based techniques and emphasizes the importance of the morphological approach in the investigation of novel molecules.
The breast cancer specific tumour suppressor protein, BRCA1 (refs 1,2), activates transcription when linked with a DNA-binding domain and is a component of the RNA polymerase II (Pol II) holoenzyme. We show here that RNA helicase A (RHA) protein links BRCA1 to the holoenzyme complex. The region of BRCA1 which interacts with RHA and, thus, the holoenzyme complex, corresponds to subregions of the BRCT domain of BRCA1 (ref. 9). This interaction was shown to occur in yeast nuclei, and expression in human cells of a truncated RHA molecule which retains binding to BRCA1 inhibited transcriptional activation mediated by the BRCA1 carboxy terminus. These data are the first to identify a specific protein interaction with the BRCA1 C-terminal domain and are consistent with the model that BRCA1 functions as a transcriptional coactivator.
The expression of steroid receptors is a common feature of both male and female breast carcinomas and is also one of the most important prognostic factors for patients with this disease. Steroid receptor levels in BRCA1-related breast carcinoma have reportedly been low. Little data on steroid receptor levels have been reported with regard to BRCA2.
Steroid receptor levels were analyzed in 27 breast carcinomas associated with BRCA1 mutations, 14 associated with BRCA2 mutations, and 32 from individuals who had hereditary breast carcinoma but no detectable mutations of either BRCA1 or BRCA2. Breast carcinomas from 32 consecutive male patients, 6 of whom had mutations of BRCA2, were also examined for steroid receptors. Estrogen receptor (ER) and progesterone receptor (PgR) analyses were performed with radioligand or enzyme immunoassay techniques on tumor cytosol preparations. Germline mutation screening and detection were performed using the protein truncation test, single strand conformation polymorphism, and direct sequencing on DNA from normal tissue.
The BRCA1-related tumors expressed significantly lower levels of ER than tumors from the other hereditary groups. The PgR levels were significantly lower in the BRCA1-related cases than in the hereditary cases not related to BRCA1 or BRCA2, but not significantly lower than in the BRCA2-related cases. Fourteen of 32 (44%) of the hereditary tumors not related to BRCA1 or BRCA2 had PgR levels exceeding 100 fmol/mg of protein. The tumors from male patients with BRCA2-related disease did not have receptor levels that differed from those in non-BRCA2-related tumors.
BRCA1- and BRCA2-related breast tumors were distinct in their expression of steroid receptors. Moreover, a subgroup of tumors not related to BRCA1 or BRCA2 manifested a strongly positive PgR phenotype rarely seen in BRCA1- and BRCA2-related tumors. These characteristics may be of relevance to the treatment and follow-up of high risk individuals in these families and may help identify a homogeneous category of hereditary breast carcinomas not related to BRCA1 or BRCA2 in which new susceptibility genes may be sought.
Three founder mutations in the cancer-associated genes BRCA1 and BRCA2 occur frequently enough among Ashkenazi Jews to warrant consideration of genetic testing outside the setting of high-risk families with multiple cases of breast or ovarian cancer. We estimated the prevalence of these founder mutations in BRCA1 and BRCA2 in the general population of Ashkenazi Jews according to age at testing, personal cancer history, and family cancer history. We compared the results of anonymous genetic testing of blood samples obtained in a survey of >5,000 Jewish participants from the Washington, DC, area with personal and family cancer histories obtained from questionnaires completed by the participants. In all subgroups defined by age and cancer history, fewer mutations were found in this community sample than in clinical series studied to date. For example, 11 (10%) of 109 Jewish women who had been given a diagnosis of breast cancer in their forties carried one of the mutations. The most important predictor of mutation status was a previous diagnosis of breast or ovarian cancer. In men and in women never given a diagnosis of cancer, family history of breast cancer before age 50 years was the strongest predictor. As interest in genetic testing for BRCA1 and BRCA2 in the Jewish community broadens, community-based estimates such as these help guide those seeking and those offering such testing. Even with accurate estimates of the likelihood of carrying a mutation and the likelihood of developing cancer if a mutation is detected, the most vexing clinical problems remain.
Cross-talk between insulin-like growth factor (IGF)- and estrogen receptor (ER)-signaling pathways results in synergistic growth. We show here that estrogen enhances IGF signaling by inducing expression of three key IGF-regulatory molecules, the type 1 IGF receptor (IGFR1) and its downstream signaling molecules, insulin receptor substrate (IRS)-1 and IRS-2. Estrogen induction of IGFR1 and IRS expression resulted in enhanced tyrosine phosphorylation of IRS-1 after IGF-I stimulation, followed by enhanced mitogen-activated protein kinase activation. To examine whether these pathways were similarly activated in vivo, we examined MCF-7 cells grown as xenografts in athymic mice. IRS-1 was expressed at high levels in estrogen-dependent growth of MCF-7 xenografts, but withdrawal of estrogen, which decreased tumor growth, resulted in a dramatic decrease in IRS-1 expression. Finally, we have shown that high IRS-1 expression is an indicator of early disease recurrence in ER-positive human primary breast tumors. Taken together, these data not only reinforce the concept of cross-talk between IGF- and ER-signaling pathways, but indicate that IGF molecules may be critical regulators of estrogen-mediated growth and breast cancer pathogenesis.
Breast cancer, one of the most common serious malignancies affecting women, occurs in hereditary and sporadic forms. Hereditary breast cancer accounts for 5-10% of all cases and has some distinctive clinical features compared with sporadic breast cancer. The recently identified genes BRCA1 and BRCA2 appear to account for the majority of hereditary breast cancer in US and European populations. Both of these genes have already been localized and isolated; however, the exact functions of their proteins are not clear yet. The detection of LOH in the 17q21 and 13q12-q13 regions, where the BRCA1 and BRCA2 genes are located, indicates that BRCA1 and BRCA2 act as tumor suppressor genes. The list of identified germline mutations in BRCA1 and BRCA2 is still growing, and mutation carriers have a substantial lifetime risk of both breast and ovarian cancer. However, it is still undetermined whether BRCA1 and BRCA2 play similar important roles in sporadic breast cancer. This paper reviews the current advances in BRCA1/BRCA2 research: the structure of their genes and proteins, their mutation frequencies, their possible roles in both hereditary and sporadic breast cancers, and their functions in transcriptional regulation and DNA repair.
The type 1 insulin-like growth factor receptor (IGF-IR) plays an important role in both normal and abnormal growth. It is particularly important in anchorage-independent growth. Impairment of its function causes apoptosis of tumor cells and inhibition of tumor growth in experimental animals. However, the IGF-IR can also induce differentiation, and eventually cell death, of certain types of cells. Its major substrates, IRS-1 and Shc, determine whether the IGF-IR will transform cells or will cause their differentiation.
The insulin-like growth factor I receptor (IGF-I-R) has an important role in breast cancer etiology. The receptor is overexpressed by most breast cancers, where it functions as a potent antiapoptotic agent. BRCA1 is a tumor suppressor gene that is mutated in a large fraction of familial breast and ovarian cancers. Cotransfection of Saos-2, MCF7, and CHO cells with IGF-I-R promoter constructs driving luciferase reporter genes, and with a BRCA1 expression vector, suppressed promoter activity in a dose-dependent manner. Functional interactions between BRCA1 and Sp1 in the regulation of the IGF-I-R gene were studied in Schneider cells, a Drosophila cell line which lacks endogenous Sp1. In these cells BRCA1 suppressed 45% of the Sp1-induced trans-activation of the IGF-I-R promoter. These results suggest that BRCA1 is capable of suppressing the IGF-I-R promoter in a number of cell lines, thus resulting in low levels of receptor mRNA and protein. Mutant versions of BRCA1 lacking trans-activational activity can potentially derepress the IGF-I-R promoter. Activation of the overexpressed receptor by locally produced or circulating IGFs may be a crucial step in breast and ovarian cancer progression.
The functions of most of the 12 subunits of the RNA polymerase II (Pol II) enzyme are unknown. In this study, we demonstrate that two of the subunits, hRPB2 and hRPB10alpha, mediate the regulated stimulation of transcription. We find that the transcriptional coactivator BRCA1 interacts directly with the core Pol II complex in vitro. We tested whether single subunits from Pol II would compete with the intact Pol II complex to inhibit transcription stimulated by BRCA1. Excess purified Pol II subunits hRPB2 or hRPB10alpha blocked BRCA1- and VP16-dependent transcriptional activation in vitro with minimal effect on basal transcription. No other Pol II subunits tested inhibited activated transcription in these assays. Furthermore, hRPB10alpha, but not hRPB2, blocked Sp1-dependent activation.
The insulin-like growth factor-I receptor (IGF-IR) is a transmembrane tyrosine kinase regulating various biological processes such as proliferation, survival, transformation, differentiation, cell-cell and cell-substrate interactions. Different signaling pathways may underlie these pleiotropic effects. The specific pathways engaged depend on the number of activated IGF-IRs, availability of intracellular signal transducers, the action of negative regulators, and is influenced by extracellular modulators. Experimental and clinical data implicate the IGF-IR in breast cancer etiology. There is strong evidence linking hyperactivation of the IGF-IR with the early stages of breast cancer. In primary breast tumors, the IGF-IR is overexpressed and hyperphosphorylated, which correlates with radio-resistance and tumor recurrence. In vitro, the IGF-IR is often required for mitogenesis and transformation, and its overexpression or activation counteract effects of various pro-apoptotic treatments. In hormone-responsive breast cancer cells, IGF-IR function is strongly linked with estrogen receptor (ER) action. The IGF-IR and the ER are co-expressed in breast tumors. Moreover, estrogens stimulate the expression of the IGF-IR and its major signaling substrate IRS-1, while antiestrogens downregulate IGF-IR signaling, mainly by decreasing IRS-1 expression and function. On the other hand, overexpression of IRS-1 promotes estrogen-independence for growth and transformation. In ER-negative breast cancer cells, usually displaying a more aggressive phenotype, the levels of the IGF-IR and IRS-1 are often low and IGF is not mitogenic, yet the IGF-IR is still required for metastatic spread. Consequently, IGF-IR function in the late stages of breast cancer remains one of the most important questions to be addressed before rational anti-IGF-IR therapies are developed.
Background: In Jewish individuals of Ashkenazi (East European) decent, three predominant mutations, 185 delAG and 5382insC (BRCA1) and 6174delT (BRCA2), seem to account for a substantial portion of germline mutations in high-risk breast/ovarian cancer families. Among non-Ashkenazi Jews, the 185delAG and the Tyr978X mutations, as well as several 'private' mutations have been reported within the BRCA1 gene. Objective: Assessing the occurrence rate of the Tyr978X BRCA1 germline mutation in Jewish non-Ashkenazi individuals: high-risk familial cases, unselected ovarian cancer patients and the general average risk Jewish Iraqi population. In addition, finding proof that this is a founder mutation. Methods: PCR amplification of the relevant fragment of the BRCA1 gene from constitutional DNA followed by restriction enzyme digest that differentiates the wild type from the mutant allele. In addition, BRCA1-linked markers were used for haplotype analysis. Results: The Tyr978X BRCA1 mutation was detected in 3/289 (1%) of the average-risk Jewish Iraqi population, in 7/408 (1.7%) high-risk Jewish non-Ashkenazi individuals (representing 332 unrelated families) and in 1/81 (1.2%) of unselected Jewish non-Ashkenazi ovarian cancer patients. Allelotyping using BRCA1-linked markers revealed an identical allelic pattern in all mutation carriers with the intragenic markers. Conclusions: Our findings suggest that this mutation is prevalent in Iraqi Jews, represents a founder mutation, and should be incorporated into the panel of mutations analyzed in high-risk families of the appropriate ethnic background. Copyright 2001 S. Karger AG, Basel
A large number of diverse functions have been attributed to the BRCA1 and BRCA2 breast cancer susceptibility genes. Here we review recent progress in the field.
The insulin-like growth factor-I receptor (IGF-IR) plays a critical role in transformation. The expression of the IGF-IR gene is negatively regulated by a number of transcription factors, including the WT1 and p53 tumor suppressors. Previous studies have suggested both physical and functional interactions between the WT1 and p53 proteins. The potential functional interactions between WT1 and p53 in control of IGF-IR promoter activity were addressed by transient coexpression of vectors encoding different isoforms of WT1, together with IGF-IR promoter-luciferase reporter constructs, in p53-null osteosarcoma-derived Saos-2 cells, wild-type p53-expressing kidney tumor-derived G401 cells, and mutant p53-expressing, rhabdomyosarcoma-derived RD cells. Similar studies were also performed to compare p53-expressing Balb/c-3T3 and clonally derived p53-null, (10)1 fibroblasts and the colorectal cancer cell line HCT116 +/+, which expresses a wild-type p53 gene, and its HCT116 -/- derivative, in which the p53 gene has been disrupted by homologous recombination. WT1 splice variants lacking a KTS insert between zinc fingers 3 and 4 suppressed IGF-IR promoter activity in the absence of p53 or in the presence of wild-type p53. WT1 variants that contain the KTS insert are impaired in their ability to bind to the IGF-IR promoter and are unable to suppress IGF-IR promoter. In the presence of mutant p53, WT1 cannot repress the IGF-IR promoter. Coimmunoprecipitation experiments showed that p53 and WT1 physically interact, whereas electrophoretic mobility shift assay studies revealed that p53 modulates the ability of WT1 to bind to the IGF-IR promoter. In summary, the transcriptional activity of WT1 proteins and their ability to function as tumor suppressors or oncogenes depends on the cellular status of p53.
The insulin-like growth factor-I receptor (IGF-IR) plays a critical role in breast tumorigenesis and is overexpressed in most primary tumors. BRCA1 is a transcription factor involved in numerous cellular processes, including DNA damage repair, cell growth, and apoptosis. Consistent with its tumor suppressor role, we demonstrated that BRCA1 repressed the activity of co-transfected IGF-IR promoter reporter constructs in a number of breast cancer-derived cell lines. Results of electrophoretic mobility shift assay showed that BRCA1 did not exhibit any specific binding to the IGF-IR promoter, although it prevented binding of Sp1. Co-immunoprecipitation experiments demonstrated that BRCA1 action was associated with specific interaction with Sp1 protein. Furthermore, using a series of glutathione S-transferase-tagged BRCA1 fragments, we mapped the Sp1-binding domain to a segment located between aa 260 and 802. In summary, our data suggest that the IGF-IR gene is a novel downstream target for BRCA1 action.