[Show abstract][Hide abstract] ABSTRACT: Drug resistance is a major challenge in cancer therapeutics. Abundant evidence indicates that DNA repair systems are enhanced after repetitive chemotherapeutic treatments, rendering cancers cells drug-resistant. Flap endonuclease 1 (FEN1) plays critical roles in DNA replication and repair and in counteracting replication stress, which is a key mechanism for many chemotherapeutic drugs to kill cancer cells. FEN1 was previously shown to be upregulated in response to DNA damaging agents. However, it is unclear about the transcription factors that regulate FEN1 expression in human cancer. More importantly, it is unknown whether up-regulation of FEN1 has an adverse impact on the prognosis of chemotherapeutic treatments of human cancers.
To reveal regulation mechanism of FEN1 expression, we search and identify FEN1 transcription factors or repressors and investigate their function on FEN1 expression by using a combination of biochemical, molecular, and cellular approaches. Furthermore, to gain insights into the impact of FEN1 levels on the response of human cancer to therapeutic treatments, we determine FEN1 levels in human breast cancer specimens and correlate them to the response to treatments and the survivorship of corresponding breast cancer patients.
We observe that FEN1 is significantly up-regulated upon treatment of chemotherapeutic drugs such as mitomycin C (MMC) and Taxol in breast cancer cells. We identify that the transcription factor/repressor YY1 binds to the FEN1 promoter and suppresses the expression of FEN1 gene. In response to the drug treatments, YY1 is dissociated from the FEN1 promoter region leading over-expression of FEN1. Overexpression of YY1 in the cells results in down-regulation of FEN1 and sensitization of the cancer cells to MMC or taxol. Furthermore, we observe that the level of FEN1 is inversely correlated with cancer drug and radiation resistance and with survivorship in breast cancer patients.
Altogether, our current data indicate that YY1 is a transcription repressor of FEN1 regulating FEN1 levels in response to DNA damaging agents. FEN1 is up-regulated in human breast cancer and its levels inversely correlated with cancer drug and radiation resistance and with survivorship in breast cancer patients.
BMC Cancer 12/2015; 15(1):1043. DOI:10.1186/s12885-015-1043-1 · 3.32 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Of all breast cancer patients, about 70% are ER+ and 10% are ER+/HER2+. The ER+/HER2+ patients have a worse outcome compared to ER+/HER2- patients. Currently there is a lack of effective prognosis biomarkers for the prediction of outcome in ER+/HER2+ patients. Genome-wide differences in ER binding between the endocrine-responsive and endocrine-resistant cells were discovered using ChIP-seq, and combined with gene expression microarray data to identify direct ER target genes. These genes were correlated to survival outcome using publicly available breast cancer patient cohorts. We found the expression of the gene SERPINA1 to have a significant predictive value for the overall survival (OS) of ER+ patients in the TCGA cohort, and validated this finding in the Curtis cohort. SERPINA1 also has a significant predictive value for the OS of ER+/HER2+ patients in the TCGA cohort, with validation in the Bild cohort. The expression of SERPINA1 can be suppressed by fulvestrant and HER2 siRNA. Our results indicate that ER is constitutively activated, resulting in an E2-independent ER binding to the SERPINA1 gene and upregulation of SERPINA1 expression. Importantly, results of survival correlation suggests that high expression of SERPINA1 could be predictive for a better clinical outcome of ER+ and ER+/HER2+ patients.
[Show abstract][Hide abstract] ABSTRACT: Progression or recurrence due to resistance to aromatase inhibitors (AIs) is a significant clinical problem for a considerable number of patients with breast cancer. Programmed cell death 4 (PDCD4), a tumor suppressor protein, is targeted for degradation during tumor progression. In the current study, we aimed to examine PDCD4 expression and regulation in AI-resistant breast cancer cells, and its association with survival in patients with estrogen receptor (ER)-positive breast cancer. We determined PDCD4 expression levels in AI-resistant breast cancer cell lines and ER-positive breast cancer tumors, investigated the regulation of PDCD4 in AI-resistant breast cancer cell lines, and carried out a Kaplan-Meier survival analysis in two independent cohorts that included a total of 420 patients with ER-positive breast cancer. We found that PDCD4 expression was down-regulated in AI-resistant breast cancer cells, and this down-regulation was inversely correlated with activation of HER2 signaling. Moreover, lower expression of PDCD4 was significantly associated with HER2 positive status in ER-positive breast tumors. Down-regulation of PDCD4 was mediated through up-regulation of HER2 via the mitogen-activated protein kinase (MAPK), protein kinase B (PKB/AKT), and miR-21 in AI-resistant breast cancer cells. MiR-21 inhibitor and the ER down-regulator fulvestrant induced PDCD4 expression and decreased cell proliferation in AI-resistant breast cancer cells. Furthermore, forced overexpression of PDCD4 resensitized AI-resistant cells to AI or hormone deprivation. Finally, we identified that down-regulation of PDCD4 was associated with a lower rate of disease-free survival in patients with ER-positive breast cancer and high histologic grade of breast tumors. In summary, our study shows that expression of PDCD4 is down-regulated by HER2 signaling in AI-resistant breast cancer. Down-regulation of PDCD4 is associated with AI resistance and a poor prognosis in patients with ER-positive breast cancer.
Breast Cancer Research and Treatment 05/2015; 152(1). DOI:10.1007/s10549-015-3446-8 · 4.20 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: COH29, a novel antimetabolite drug developed at City of Hope Cancer Center, has anticancer activity that stems primarily from the inhibition of human ribonucleotide reductase (RNR). This key enzyme in deoxyribonucleotide biosynthesis is the target of established clinical agents such as hydroxyurea (HU) and gemcitabine because of its critical role in DNA replication and repair. Herein we report that BRCA-1-defective human breast cancer cells are more sensitive than wild-type BRCA-1 counterparts to COH29 in vitro and in vivo. Microarray gene expression profiling showed that COH29 reduces expression of DNA repair pathway genes, suggesting that COH29 interferes with these pathways. It is well-established that BRCA1 plays a role in DNA damage repair, especially homologous recombination (HR) repair, to maintain genome integrity. In BRCA1-defective HCC1937 breast cancer cells, COH29 induced more double-strand breaks (DSB) and DNA-damage response (DDR) than in HCC1937+BRCA1 cells. By EJ5- and DR-GFP reporter assay, we found COH29 could inhibit NHEJ efficiency and that no HR activity was detected in HCC1937 cells, suggesting the repression of the NHEJ repair pathway may be involved in COH29-induced DSB in BRCA1-deficient HCC1937 cells. Furthermore, we observed accumulation of nuclear Rad51 foci in COH29-treated HCC1937+BRCA1 cells, suggesting BRCA1 plays a crucial role in repairing/recovering drug-induced DNA damage by recruiting Rad51 to damage sites. In summary, we have described additional biological effects of the RNR inhibitor COH29 that potentially strengthen its utility as an anticancer agent.
The American Society for Pharmacology and Experimental Therapeutics.
[Show abstract][Hide abstract] ABSTRACT: Acquired resistance through genetic mutations is a major obstacle in targeted cancer therapy, but the underlying mechanisms are poorly understood. Here we studied mechanisms of acquired resistance of chronic myeloid leukemia (CML) to tyrosine kinase inhibitors (TKIs) by examining genome-wide gene expression changes in KCL-22 CML cells versus their resistant KCL-22M cells that acquire T315I BCR-ABL mutation following TKI exposure. Although T315I BCR-ABL is sufficient to confer resistance to TKIs in CML cells, surprisingly we found that multiple drug resistance pathways were activated in KCL-22M cells along with reduced expression of a set of myeloid differentiation genes. Forced myeloid differentiation by all-trans-retinoic acid (ATRA) effectively blocked acquisition of BCR-ABL mutations and resistance to the TKIs imatinib, nilotinib or dasatinib in our previously described in vitro models of acquired TKI resistance. ATRA induced robust expression of CD38, a cell surface marker and cellular NADase. High levels of CD38 reduced intracellular nicotinamide adenine dinucleotide (NAD+) levels and blocked acquired resistance by inhibiting the activity of the NAD+-dependent SIRT1 deacetylase that we have previously shown to promote resistance in CML cells by facilitating error-prone DNA damage repair. Consequently, ATRA treatment decreased DNA damage repair and suppressed acquisition of BCR-ABL mutations. This study sheds novel insight into mechanisms underlying acquired resistance in CML, and suggests potential benefit of combining ATRA with TKIs in treating CML, particularly in advanced phases.
[Show abstract][Hide abstract] ABSTRACT: Triple negative breast cancer (TNBC) has higher rates of recurrence and distant metastasis, and poorer outcome as compared to non-TNBC. Aberrant activation of WNT signaling has been detected in TNBC, which might be important for triggering oncogenic conversion of breast epithelial cell. Therefore, we directed our focus on identifying the WNT ligand and its underlying mechanism in TNBC cells.
We performed large-scale analysis of public microarray data to screen the WNT ligands and the clinical significance of the responsible ligand in TNBC. WNT5B was identified and its overexpression in TNBC was confirmed by immunohistochemistry staining, Western blot and ELISA. ShRNA was used to knockdown WNT5B expression (shWNT5B). Cellular functional alteration with shWNT5B treatment was determined by using wound healing assay, mammosphere assay; while cell cycle and apoptosis were examined by flowcytometry. Mitochondrial morphology was photographed by electron microscope. Biological change of mitochondria was detected by RT-PCR and oxygen consumption assay. Activation of WNT pathway and its downstream targets were evaluated by liciferase assay, immunohistochemistry staining and immunoblot analysis. Statistical methods used in the experiments besides microarray analysis was two-tailed t-test.
WNT5B was elevated both in the tumor and the patients' serum. Suppression of WNT5B remarkably impaired cell growth, migration and mammosphere formation. Additionally, G0/G1 cell cycle arrest and caspase-independent apoptosis was observed. Study of the possible mechanism indicated that these effects occurred through suppression of mitochondrial biogenesis, as evidenced by reduced mitochondrial DNA (MtDNA) and compromised oxidative phosphorylation (OXPHOS). In Vivo and in vitro data uncovered that WNT5B modulated mitochondrial physiology was mediated by MCL1, which was regulated by WNT/beta-catenin responsive gene, Myc. Clinic data analysis revealed that both WNT5B and MCL1 are associated with enhanced metastasis and decreased disease-free survival.
All our findings suggested that WNT5B/MCL1 cascade is critical for TNBC and understanding its regulatory apparatus provided valuable insight into the pathogenesis of the tumor development and the guidance for targeting therapeutics.
BMC Cancer 02/2014; 14(1):124. DOI:10.1186/1471-2407-14-124 · 3.32 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Aromatase inhibitors (AIs) are important drugs for treating postmenopausal patients with hormone receptor-positive breast cancer. However, acquired resistance to AI therapies is a significant problem. Our study has revealed that the histone deacetylase inhibitor LBH589 treatment abrogated growth of AI-resistant cells in vitro and in vivo, causing cell cycle G2/M arrest and induced apoptosis. LBH589 treatment also reduced the level of NF-κB1 which is overexpressed when AI resistance develops. Analyzing paired tumor specimens from 12 patients, we found that NF-κB1 expression was increased in recurrent AI-resistant tumors as compared to the paired primary tumors before AI treatment. This finding was consistent with up-regulated NF-κB1 expression seen in a collection of well-established AI-resistant cell lines. Furthermore, knockdown of NF-κB1 expression significantly suppressed the proliferation of AI-resistant cells. Treatment of AI-resistant cell lines with LBH589 suppressed NF-κB1 mRNA and protein expression. In addition, LBH589 treatment abrogated growth of AI-resistant tumors in mice, and was associated with significantly decreased levels of NF-κB1 in tumors. In all, our findings strongly support further investigation of LBH589 as a novel therapeutic strategy for patients with AI-resistant breast cancer, in part by suppressing the NF-κB1 pathway.
Breast Cancer Research and Treatment 11/2012; 137(1). DOI:10.1007/s10549-012-2332-x · 4.20 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Lymph node metastasis is an important indicator of oncologic outcome for patients with rectal cancer. Identifying predictive biomarkers of lymph node metastasis could therefore be clinically useful.
The aim of this study was to assess whether chromosomal copy number alterations can assist in predicting persistent lymph node metastasis in patients with locally advanced rectal cancer treated with preoperative chemoradiation therapy.
This is a nonrandomized, prospective phase II study.
This study took place in a multi-institutional setting.
Ninety-five patients with stage II (cT3-4, cN0) or stage III (any cT, cN1-2) rectal cancer were included.
Patients were treated with preoperative chemoradiation therapy followed by total mesorectal excision. Pretreatment biopsy tumor DNA and surgical margin control DNA were extracted and analyzed by oligonucleotide array-based comparative genomic hybridization. Chromosomal copy number alterations were correlated with persistent lymph node metastasis. Finally, a model for predicting persistent lymph node metastasis was built.
The primary outcomes assessed were whether chromosomal copy number alterations are associated with persistent lymph node metastasis in patients with rectal cancer and the accuracy of oligonucleotide array-based comparative genomic hybridization for predicting lymph node metastasis.
Twenty-five of 95 (26%) patients had lymph node metastasis after chemoradiation. Losses of 28 chromosomal regions, most notably in chromosome 4, were significantly associated with lymph node metastasis. Our predictive model contained 65 probes and predicted persistent lymph node metastasis with 68% sensitivity, 93% specificity, and positive and negative predictive values of 77% and 89%. The use of this model accurately predicted lymph node status (positive or negative) after chemoradiation therapy in 82 of 95 patients (86%).
The patient cohort was not completely homogeneous, which may have influenced their clinical outcome. In addition, although we performed rigorous, statistically sound internal validation, external validation will be important to further corroborate our findings.
Copy number alterations can help identify patients with rectal cancer who are at risk of lymph node metastasis after chemoradiation.
Diseases of the Colon & Rectum 06/2012; 55(6):677-85. DOI:10.1097/DCR.0b013e31824f873f · 3.20 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Gene set analysis has enhanced the microarray data analysis field with biological insights. The first introduced and widely used Over-representation analysis (ORA) method, has the limitation of the requirement of a predetermined differentially expressed genes list. To overcome this limitation, distribution based analysis (DBA) methods were developed with different analysis steps and null hypothesis. To understand the advantages and limitations of these methods, we present a comprehensive survey and evaluate the performance for nine commonly used gene set analysis tools. Methods testing self-contained hypothesis generally have better sensitivity and specificity than methods testing competitive hypothesis. But most of the methods have bias towards larger gene sets with self-contained methods more severe. Therefore, better sensitivity and specificity is obtained at the tradeoff of bigger bias in self-contained methods, and vice versa in competitive methods. We propose a combined performance plot to compare these methods, among which GSA demonstrated superiority over others.
[Show abstract][Hide abstract] ABSTRACT: Both genetic and environmental factors are implicated in type 1 diabetes (T1D). Because environmental factors can trigger epigenetic changes, we hypothesized that variations in histone post-translational modifications (PTMs) at the promoter/enhancer regions of T1D susceptible genes may be associated with T1D. We therefore evaluated histone PTM variations at known T1D susceptible genes in blood cells from T1D patients versus healthy nondiabetic controls, and explored their connections to T1D. We used the chromatin immunoprecipitation-linked to microarray approach to profile key histone PTMs, including H3-lysine 4 trimethylation (H3K4me3), H3K27me3, H3K9me3, H3K9 acetylation (H3K9Ac), and H4K16Ac at genes within the T1D susceptible loci in lymphocytes, and H3K4me3, H3K9me2, H3K9Ac, and H4K16Ac at the insulin-dependent diabetes mellitus 1 region in monocytes of T1D patients and healthy controls separately. We screened for potential variations in histone PTMs using computational methods to compare datasets from T1D and controls. Interestingly, we observed marked variations in H3K9Ac levels at the upstream regions of HLA-DRB1 and HLA-DQB1 within the insulin-dependent diabetes mellitus 1 locus in T1D monocytes relative to controls. Additional experiments with THP-1 monocytes demonstrated increased expression of HLA-DRB1 and HLA-DQB1 in response to interferon-γ and TNF-α treatment that were accompanied by changes in H3K9Ac at the same promoter regions as that seen in the patient monocytes. These results suggest that the H3K9Ac status of HLA-DRB1 and HLA-DQB1, two genes highly associated with T1D, may be relevant to their regulation and transcriptional response toward external stimuli. Thus, the promoter/enhancer architecture and chromatin status of key susceptible loci could be important determinants in their functional association to T1D susceptibility.
[Show abstract][Hide abstract] ABSTRACT: Nonalcoholic fatty liver disease (NAFLD) includes various hepatic pathologies ranging from hepatic steatosis to non-alcoholic steatohepatitis (NASH), fibrosis and cirrhosis. Estrogen provides a protective effect on the development of NAFLD in women. Therefore, postmenopausal women have a higher risk of developing NAFLD. Hepatic steatosis is an early stage of fatty liver disease. Steatosis can develop to the aggressive stages (nonalcoholic steatohepatitis, fibrosis and cirrhosis). Currently, there is no specific drug to prevent/treat these liver diseases. In this study, we found that white button mushroom (WBM), Agaricus Bisporus, has protective effects against liver steatosis in ovariectomized (OVX) mice (a model of postmenopausal women). OVX mice were fed a high fat diet supplemented with WBM powder. We found that dietary WBM intake significantly lowered liver weight and hepatic injury markers in OVX mice. Pathological examination of liver tissue showed less fat accumulation in the livers of mice on WBM diet; moreover, these animals had improved glucose clearance ability. Microarray analysis revealed that genes related to the fatty acid biosynthesis pathway, particularly the genes for fatty acid synthetase (Fas) and fatty acid elongase 6 (Elovl6), were down-regulated in the liver of mushroom-fed mice. In vitro mechanistic studies using the HepG2 cell line showed that down-regulation of the expression of FAS and ELOVL6 by WBM extract was through inhibition of Liver X receptor (LXR) signaling and its downstream transcriptional factor SREBP1c. These results suggest that WBM is protective against hepatic steatosis and NAFLD in OVX mice as a model for postmenopausal women.
PLoS ONE 10/2011; 6(10):e26654. DOI:10.1371/journal.pone.0026654 · 3.23 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Rectal cancer response to chemoradiation (CRT) varies from no response to a pathologic complete response (pCR). Identifying predictive biomarkers of response would therefore be useful. We assessed whether chromosomal copy number alterations (CNAs) can assist in predicting pCR. Pretreatment tumor biopsies and paired normal surgical tissues from the proximal resection margin were collected from 95 rectal cancer patients treated with preoperative CRT and total mesorectal excision in a prospective Phase II study. Tumor and control DNA were extracted, and oligonucleotide array-based comparative genomic hybridization (aCGH) was used to identify CNAs, which were correlated with pCR. Ingenuity pathway analysis (IPA) was then used to identify functionally relevant genes in aberrant regions. Finally, a predictive model for pCR was built using support vector machine (SVM), and leave-one-out cross validation assessed the accuracy of aCGH. Chromosomal regions most commonly affected by gains were 20q11.21-q13.33, 13q11.32-23, 7p22.3-p22.2, and 8q23.3-q24.3, and losses were present at 18q11.32-q23, 17p13.3-q11.1, 10q23.1, and 4q32.1-q32.3. The 25 (26%) patients who achieved a pCR had significantly fewer high copy gains overall than non-pCR patients (P = 0.01). Loss of chromosomal region 15q11.1-q26.3 was significantly associated with non-pCR (P < 0.00002; Q-bound < 0.0391), while loss of 12p13.31 was significantly associated with pCR (P < 0.0003; Q-bound < 0.097). IPA identified eight genes in the imbalanced chromosomal regions that associated with tumor response. SVM identified 58 probes that predict pCR with 76% sensitivity, 97% specificity, and positive and negative predictive values of 91% and 92%. Our data indicate that chromosomal CNAs can help identify rectal cancer patients more likely to develop a pCR to CRT.
Genes Chromosomes and Cancer 09/2011; 50(9):689-99. DOI:10.1002/gcc.20891 · 3.84 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Previous studies in our laboratory demonstrated that blueberry (BB) extract exhibited antitumor activity against MDA-MB-231 triple negative breast cancer (TNBC) cells and decreased metastatic potential in vitro. The current study tested 2 doses of whole BB powder, 5 and 10% (wt:wt) in the diet, against MDA-MB-231 tumor growth in female nude mice. In this study, tumor volume was 75% lower in mice fed the 5% BB diet and 60% lower in mice fed the 10% BB diet than in control mice (P ≤ 0.05). Tumor cell proliferation (Ki-67) was lower in the 5 and 10% BB-fed mice and cell death (Caspase 3) was greater in the 10% BB-fed mice compared to control mice (P ≤ 0.05). Gene analysis of tumor tissues from the 5% BB-fed mice revealed significantly altered expression of genes important to inflammation, cancer, and metastasis, specifically, Wnt signaling, thrombospondin-2, IL-13, and IFNγ. To confirm effects on Wnt signaling, analysis of tumor tissues from 5% BB-fed mice revealed lower β-catenin expression and glycogen synthase kinase-3β phosphorylation with greater expression of the β-catenin inhibitory protein adenomatous polyposis coli compared to controls. A second study tested the ability of the 5% BB diet to inhibit MDA-MB-231-luc-D3H2LN metastasis in vivo. In this study, 5% BB-fed mice developed 70% fewer liver metastases (P = 0.04) and 25% fewer lymph node metastases (P = 0.09) compared to control mice. This study demonstrates the oral antitumor and metastasis activity of whole BB powder against TNBC in mice.
Journal of Nutrition 08/2011; 141(10):1805-12. DOI:10.3945/jn.111.140178 · 4.23 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: As a first step towards discovery of genes expressed from only one allele in the CNS, we used a tiling array assay for DNA sequences that are both methylated and unmethylated (the MAUD assay). We analyzed regulatory regions of the entire mouse brain transcriptome, and found that approximately 10% of the genes assayed showed dual DNA methylation patterns. They include a large subset of genes that display marks of both active and silent, i.e., poised, chromatin during development, consistent with a link between differential DNA methylation and lineage-specific differentiation within the CNS. Sixty-five of the MAUD hits and 57 other genes whose function is of relevance to CNS development and/or disorders were tested for allele-specific expression in F(1) hybrid clonal neural stem cell (NSC) lines. Eight MAUD hits and one additional gene showed such expression. They include Lgi1, which causes a subtype of inherited epilepsy that displays autosomal dominance with incomplete penetrance; Gfra2, a receptor for glial cell line-derived neurotrophic factor GDNF that has been linked to kindling epilepsy; Unc5a, a netrin-1 receptor important in neurodevelopment; and Cspg4, a membrane chondroitin sulfate proteoglycan associated with malignant melanoma and astrocytoma in human. Three of the genes, Camk2a, Kcnc4, and Unc5a, show preferential expression of the same allele in all clonal NSC lines tested. The other six genes show a stochastic pattern of monoallelic expression in some NSC lines and bi-allelic expression in others. These results support the estimate that 1-2% of genes expressed in the CNS may be subject to allelic exclusion, and demonstrate that the group includes genes implicated in major disorders of the CNS as well as neurodevelopment.
PLoS ONE 11/2010; 5(11):e13843. DOI:10.1371/journal.pone.0013843 · 3.23 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Resistance to endocrine therapy agents has presented a clinical obstacle in the treatment of hormone-dependent breast cancer. Our laboratory has initiated a study of microRNA regulation of signaling pathways that may result in breast cancer progression on aromatase inhibitors (AI). Microarray analysis of hormone refractory cell lines identified 115 differentially regulated microRNAs, of which 49 microRNAs were believed to be hormone-responsive. A group of microRNAs were inversely expressed in the AI-resistant lines versus LTEDaro and tamoxifen-resistant. We focused our work on hsa-miR-128a which was hormone-responsive and selectively up-regulated in the letrozole-resistant cell lines. Human miR-128a was predicted to target the TGFβ signaling pathway and indeed sensitivity to TGFβ was compromised in the letrozole-resistant cells, as compared to parental MCF-7aro. Human miR-128a was shown to negatively target TGFβRI protein expression by binding to the 3'UTR region of the gene. Inhibition of endogenous miR-128a resulted in resensitization of the letrozole-resistant lines to TGFβ growth inhibitory effects. These data suggest that the hormone-responsive miR-128a can modulate TGFβ signaling and survival of the letrozole-resistant cell lines. To our knowledge, this is the first study to address the role of microRNA regulation as well as TGFβ signaling in AI-resistant breast cancer cell lines. We believe that in addition to estrogen-modulation of gene expression, hormone-regulated microRNAs may provide an additional level of post-transcriptional regulation of signaling pathways critically involved in breast cancer progression and AI-resistance.
Breast Cancer Research and Treatment 11/2010; 124(1):89-99. DOI:10.1007/s10549-009-0716-3 · 4.20 Impact Factor