[show abstract][hide abstract] ABSTRACT: Lung cancer remains one of the leading causes of cancer-related deaths worldwide with a 5-year survival rate of less than 20%. One approach to improving survival is the identification of biomarkers to detect early stage disease. In this study, we investigated the potential of the stem cell and progenitor cell marker, Musashi1 (Msi1), as a diagnostic marker and potential therapeutic target for lung cancer. Functional studies in A549 bronchioalveolar carcinoma and NCI-H520 squamous cell carcinoma cells revealed that Msi1 was enriched in spheroid cultures of tumor cells and in the CD133+ cell population. Downregulation of Msi1 by lentivirus-mediated expression of an Msi1 shRNA reduced spheroid colony proliferation. Growth inhibition was associated with reduced nuclear localization of β-catenin and inhibition of the processing of intracellular Notch. In primary lung cancer, Msi1 protein expression was elevated in 86% of 202 tissue microarray specimens, and Msi1 mRNA was increased in 80% of 118 bronchoscopic biopsies, including metastatic disease, but was rarely detected in adjacent normal lung tissue and in non-malignant diseased tissue. Msi1 was expressed in a diffuse pattern in most tumor subtypes, except in squamous cell carcinomas, where it appeared in a focal pattern in 50% of specimens. Thus, Msi1 is a sensitive and specific diagnostic marker for all lung cancer subtypes.
[show abstract][hide abstract] ABSTRACT: Our previous data suggested that the human basic helix-loop-helix transcription factor achaete-scute homologue-1 (hASH1) may stimulate both proliferation and migration in the lung. In the CNS, cyclin-dependent kinase 5 (Cdk5) and its activator p35 are important for neuronal migration that is regulated by basic helix-loop-helix transcription factors. Cdk5/p35 may also play a role in carcinogenesis. In this study, we found that the neuronal activator p35 was commonly expressed in primary human lung cancers. Cdk5 and p35 were also expressed by several human lung cancer cell lines and coupled with migration and invasion. When the kinase activity was inhibited by the Cdk5 inhibitor roscovitine or dominant-negative (dn) Cdk5, the migration of lung cancer cells was reduced. In neuroendocrine cells expressing hASH1, such as a pulmonary carcinoid cell line, knocking down the gene expression by short hairpin RNA reduced the levels of Cdk5/p35, nuclear p35 protein, and migration. Furthermore, expression of hASH1 in lung adenocarcinoma cells normally lacking hASH1 increased p35/Cdk5 activity and enhanced cellular migration. We were also able to show that p35 was a direct target for hASH1. In conclusion, induction of Cdk5 activity is a novel mechanism through which hASH1 may regulate migration in lung carcinogenesis.
Molecular biology of the cell 06/2012; 23(15):2856-66. · 5.98 Impact Factor
[show abstract][hide abstract] ABSTRACT: Lung cancer is the leading cause of cancer-related deaths in the world. Achaete-scute complex homolog-1 (Ascl1) is a member of the basic helix-loop-helix (bHLH) transcription factor family that has multiple functions in the normal and neoplastic lung such as the regulation of neuroendocrine differentiation, prevention of apoptosis and promotion of tumor-initiating cells. We now show that Ascl1 directly regulates matrix metalloproteinase-7 (MMP-7) and O(6)-methylguanine-DNA methyltransferase (MGMT). Loss- and gain-of-function experiments in human bronchial epithelial and lung carcinoma cell lines revealed that Ascl1, MMP-7 and MGMT are able to protect cells from the tobacco-specific nitrosamine NNK-induced DNA damage and the alkylating agent cisplatin-induced apoptosis. We also examined the role of Ascl1 in NNK-induced lung tumorigenesis in vivo. Using transgenic mice which constitutively expressed human Ascl1 in airway lining cells, we found that there was a delay in lung tumorigenesis. We conclude that Ascl1 potentially enhances DNA repair through activation of MMP-7 and MGMT which may impact lung carcinogenesis and chemoresistance. The study has uncovered a novel and unexpected function of Ascl1 which will contribute to better understanding of lung carcinogenesis and the broad implications of transcription factors in tobacco-related carcinogenesis.
PLoS ONE 01/2012; 7(12):e52832. · 3.73 Impact Factor
[show abstract][hide abstract] ABSTRACT: Clara cells are non-ciliated, secretory bronchiolar epithelial cells that serve to detoxify harmful inhaled substances. Clara cells also function as stem/progenitor cells for repair in the bronchioles. Clara cell secretory protein (CCSP) is specifically expressed in pulmonary Clara cells and is widely used as a Clara cell marker. In addition CCSP promoter is commonly used to direct gene expression into the lung in transgenic models. The discovery of CCSP immunoreactivity in plasma membranes of airway lining cells prompted us to explore the possibility of enriching Clara cells by flow cytometry. We established a novel and simple method for the isolation of CCSP-expressing cell Clara cells using a combination of mechanical and enzymatic dissociation followed by flow cytometry sorting technology. We showed that ∼25% of dissociated cells from whole lung expressed CCSP. In the resulting preparation, up to 98% of cells expressed CCSP. Notably, we found that several common stem cell markers including CD44, CD133, Sca-1 and Sox2 were expressed in CCSP(+) cells. Moreover, CCSP(+) cells were able to form spheroid colonies in vitro with 0.97‰ efficiency. Parallel studies in vivo confirmed that a small population of CCSP(-)expressing cells in mouse airways also demonstrates stem cell-like properties such as label retention and harboring rare bronchioalveolar stem cells (BASCs) in terminal bronchioles (TBs). We conclude that CCSP(+) cells exhibit a number of stem cell-like features including stem cell marker expression, bronchosphere colony formation and self-renewal ability. Clara cell isolation by flow cytometry sorting is a useful method for investigating the function of primary Clara cells in stem cell research and mouse models.
PLoS ONE 01/2012; 7(8):e43008. · 3.73 Impact Factor
[show abstract][hide abstract] ABSTRACT: Smoking is the leading cause of preventable cancer deaths in the United States. Nicotine replacement therapies (NRT) have been developed to aid in smoking cessation, which decreases lung cancer incidence. However, the safety of NRT is controversial because numerous preclinical studies have shown that nicotine enhances tumor cell growth in vitro and in vivo. We modeled NRT in mice to determine the effects of physiologic levels of nicotine on lung tumor formation, tumor growth, or metastasis. Nicotine administered in drinking water did not enhance lung tumorigenesis after treatment with the tobacco carcinogen, 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone (NNK). Tumors that develop in this model have mutations in K-ras, which is commonly observed in smoking-related, human lung adenocarcinomas. In a transgenic model of mutant K-ras-driven lung cancer, nicotine did not increase tumor number or size and did not affect overall survival. Likewise, in a syngeneic model using lung cancer cell lines derived from NNK-treated mice, oral nicotine did not enhance tumor growth or metastasis. These data show that nicotine does not enhance lung tumorigenesis when given to achieve levels comparable with those of NRT, suggesting that nicotine has a dose threshold, below which it has no appreciable effect. These studies are consistent with epidemiologic data showing that NRT does not enhance lung cancer risk in former smokers.
Cancer Prevention Research 11/2011; 4(11):1743-51. · 4.89 Impact Factor
[show abstract][hide abstract] ABSTRACT: Achaete-scute homolog-1 (ASH1) is pivotal for the development of pulmonary neuroendocrine (NE) cells. We examined human ASH1 (hASH1) expression across a comprehensive panel of human lung cancer cell lines, primary human lung tumors and normal fetal and post-natal lungs. While hASH1 was a cardinal feature of NE carcinomas, a subgroup of non-NE lung cancers also exhibited expression of this factor. Twenty lung cancer cell lines out of 33 were positive for hASH1 mRNA by reverse transcription PCR, including 6/6 small cell carcinomas (SCLC), 5/5 carcinoids, 6/7 non-SCLC with NE features, and 3/14 other non-SCLC. Among human primary tumors, 2/2 SCLC, 5/5 pulmonary carcinoids, and 10/41 non-SCLC (only 4 of which had NE features) were positive for hASH1 by immunohistochemistry and RNA-RNA in situ hybridization. In normal human fetal lung, the expression of hASH1 and the neural marker synaptophysin was highly concordant in neuroepithelial bodies and solitary NE cells, while the rest of the epithelium was negative. In childhood and adulthood, the markers became progressively discordant, with a majority of hASH1-immunoreactive foci (69%) being negative for synaptophysin in adults, potentially representing dormant NE cell progenitors. We conclude that hASH1 provides an early indication of NE program in human lung.
Lung cancer (Amsterdam, Netherlands) 06/2011; 75(1):58-65. · 3.14 Impact Factor
[show abstract][hide abstract] ABSTRACT: K-ras mutations are associated with smoking-induced lung cancer and poor clinical outcomes. In mice, K-ras mutations are sufficient to induce lung tumors, which require phosphoinoside-3-kinase (PI3K) and further downstream, mammalian target of rapamycin (mTOR) activation. However, the roles of individual Akt isoforms that link PI3K and mTOR are unknown. Here, we show that deletion of Akt1 but not Akt2 or Akt3 prevents lung tumorigenesis in a tobacco carcinogen-induced model and a genetic model. Akt1 deletion prevented tumor initiation as well as tumor progression, coincident with decreased Akt signaling in tumor tissues. In contrast, deletion of Akt3 increased tumor multiplicity in the carcinogen model and increased tumor size in the genetic model. Fibroblasts lacking Akt1 are resistant to transformation by mutant K-ras and stimulation by epidermal growth factor. Human lung cancer cells with mutant K-ras and diminished Akt1 levels fail to grow in vivo. These data suggest that Akt1 is the primary Akt isoform activated by mutant K-ras in lung tumors, and that Akt3 may oppose Akt1 in lung tumorigenesis and lung tumor progression. Given that Akt inhibitors in clinical development as cancer therapeutics are not isoform selective, these studies support specific targeting of Akt1 to mitigate the effects of mutant K-ras in lung cancer.
[show abstract][hide abstract] ABSTRACT: Late stage or aggressive cancers exhibit metastatic growth at multiple sites, and the characterization of treatment response in various organs to drugs with potentially wide-ranging efficacy is needed. Tumor cells that induce angiogenesis are a common characteristic of metastatic disease, and clinically, antiangiogenic therapies have shown value in the setting of advanced cancer. However, recent preclinical studies have suggested that exposure to antiangiogenic drugs can increase tumor invasiveness and metastasis, making it important to determine which contexts antiangiogenic therapy is most appropriate. We describe here the effects of cediranib, a receptor tyrosine kinase inhibitor, in a model of advanced prostate cancer metastatic to skeleton and brain. Treatment with cediranib decreased metastatic tumor burden in the brain and bone, decreased cerebral vasogenic edema, and improved survival, despite increasing the invasive histology of brain metastases. Short-duration cediranib treatment given at the time of tumor cell dissemination was sufficient to inhibit the establishment and subsequent growth of bone metastases, although brain metastases were subject to rebound growth after the discontinuation of cediranib. Distinct growth patterns at different organ sites in the same animal showed that certain tumor microenvironments such as bone may be most amenable to interventions by anti-vascular endothelial growth factor (VEGF) therapies. In addition, anti-VEGF treatment may be of utility in decreasing the rapid growth of solid brain metastases and vasogenic edema in patients with advanced cancer, leading to reduced morbidity and associated clinical benefit.
Cancer Research 10/2010; 70(21):8662-73. · 8.65 Impact Factor
[show abstract][hide abstract] ABSTRACT: The basic helix-loop-helix transcription factor achaete-scute homologue-1 (ASH1) plays a critical role in regulating the neuroendocrine (NE) phenotype in normal and neoplastic lung. Transgenic (TG) mice that constitutively express human ASH1 (hASH1) under control of the Clara cell 10-kDa protein (CC10) promoter in non-NE airway lining cells display progressive epithelial hyperplasia and bronchiolar metaplasia or bronchiolization of the alveoli (BOA). However, little is known about the involvement of hASH1 in regeneration of the conducting airway. In this study, we investigated the impact of hASH1 on airway cell injury and repair in the TG mice following an intraperitoneal injection of naphthalene, which specifically ablates bronchiolar Clara cells and induces pulmonary NE cell hyperplasia. We discovered an overall attenuation of NE maturation coupled with increased proliferation in TG mice during post-naphthalene repair. In addition, BOA lesions revealed enhanced epithelial cell proliferation while preserving Clara cell markers CC10 and the principal naphthalene-metabolizing enzyme cytochrome P4502F2. These data suggest that ASH1 may play an important role in maintaining a progenitor phenotype that promotes renewal of both NE and epithelial cells. Moreover, ASH1 may propagate a stem cell microenvironment in BOA where epithelium becomes resistant to naphthalene toxicity.
[show abstract][hide abstract] ABSTRACT: Secretoglobin (SCGB) 3A2, also called uteroglobin-related protein (UGRP) 1, is a downstream target for a homeodomain transcription factor NKX2-1, which is critical for the development of lung, thyroid and ventral forebrain. Both SCGB3A2 and NKX2-1 are expressed in airway epithelial cells and the latter also in alveolar Type II cells. NKX2-1 has been used clinically for diagnosis of human pulmonary tumors. Recently, the expression of SCGB3A2 was reported in human carcinomas, suggesting the use of this protein as a tumor marker. In this study, 28 lung tumors from aging B6;129 mice and nine lung adenocarcinomas from CC10TAg transgenic mice that express SV40 large T antigen under the mouse Scgb1a1 (CC10) gene promoter, were subjected to histopathological and immunohistochemical analyses for the expression of NKX2-1 and SCGB3A2. NKX2-1 was expressed in all types of tumors albeit more focally in carcinomas. In contrast, SCGB3A2 normally expressed in Clara cells, was negative in Type II cell hyperplasias and adenomas. However, it was expressed in alveolar Type II cell carcinomas and Clara cell adenocarcinomas. In these carcinomas, SCGB3A2 expression was observed in the portion of the tumor where NKX2-1 expression was reduced or almost abolished. As a comparison, the expression of SCGB3A2 and NKX2-1 from 23 human non-small cell lung carcinoma specimens was also examined. The results demonstrate that SCGB3A2 is a useful marker for diagnosis of pulmonary tumors both in mice and humans.
Lung cancer (Amsterdam, Netherlands) 05/2010; 71(1):42-8. · 3.14 Impact Factor
[show abstract][hide abstract] ABSTRACT: Musashi1 (Msi1) is a conserved RNA-binding protein that regulates the Notch and Wnt pathways, and serves as a stem cell marker in the breast and other tissues. It is unknown how Msi1 relates to other breast cancer markers, whether it denotes tumor initiating cells (TICs), and how it affects gene expression and tumor cell survival in breast cancer cells.
Msi1 expression was analyzed in 20 breast cancer cell lines and in 140 primary breast tumors by western blotting and immunohistochemistry, respectively. Lentivirus RNA interference was used to reduce Msi1 expression in breast cancer cell lines MCF-7 and T47D grown as spheroid cultures and to assess stem cell gene expression and the growth of these cell lines as xenografts. In normal human breast tissue, Msi1 was expressed in 10.6% of myoepithelum and 1.2% of ductal epithelium in the terminal ductal lobular unit (TDLU), whereas, less than 0.05% of ductal epithelium and myoepithelium in large ducts outside the TDLU expressed Msi1. Msi1 was expressed in 55% of the breast cancer cell lines and correlated with ErbB2 expression in 50% of the cell lines. Msi1 was expressed in 68% of primary tumors and in 100% of lymph node metastases, and correlated with 5 year survival. Msi1 was enriched in CD133+ MCF-7 and T47D cells and in spheroid cultures of these cells, and Msi1 'knockdown' (KD) with a lentivirus-expressed shRNA decreased the number and size of spheroid colonies. Msi1 KD reduced Notch1, c-Myc, ErbB2 and pERK1/2 expression, and increased p21CIP1 expression, which is consistent with known Msi1 target mRNAs. Msi1 KD also reduced the expression of the somatic and embryonic stem cell markers, CD133, Bmi1, Sox2, Nanog and Oct4. Xenografts of MCF-7 and T47D Msi1 KD cells resulted in a marked reduction of tumor growth, reduced Msi1 and Notch1 expression and increased p21CIP1 expression.
Msi1 is a negative prognostic indicator of breast cancer patient survival, and is indicative of tumor cells with stem cell-like characteristics. Msi1 KD reduces tumor cell survival and tumor xenograft growth, suggesting that it may represent a novel target for drug discovery.
Molecular Cancer 01/2010; 9:221. · 5.13 Impact Factor
[show abstract][hide abstract] ABSTRACT: Matrilysin-1 (also called matrix metalloproteinase-7) is expressed in injured lung and in cancer but not in normal epithelia. Bronchiolization of the alveoli (BOA), a potential precursor of lung cancer, is a histologically distinct type of metaplasia that is composed of cells resembling airway epithelium in the alveolar compartment. We demonstrate that there is increased expression of matrilysin-1 in human lesions and BOA in the CC10-human achaete-scute homolog-1 transgenic mouse model. Forced expression of the matrilysin-1 gene in immortalized human normal airway epithelial BEAS-2B and HPLD1 cells, which do not normally express matrilysin-1, promoted cellular migration, suggesting a functional link for BOA formation via bronchiolar cell migration. In addition, matrilysin-1 stimulated proliferation and inhibited Fas-induced apoptosis, while a knockdown by RNA interference decreased cell growth, migration, and increased sensitivity to apoptosis. Western blotting demonstrated increased levels of phospho-p38 and phospho-Erk1/2 kinases after matrilysin-1 expression. Gene expression analysis uncovered several genes that were related to cell growth, migration/movement, and death, which could potentially facilitate bronchiolization. In vivo, the formation of BOA lesions was reduced when CC10-human achaete-scute homolog-1 mice were crossed with matrilysin-1 null mice and was correlated with reduced matrilysin-1 expression in BOA. We conclude that matrilysin-1 may play an important role in the bronchiolization of alveoli by promoting proliferation, migration, and attenuation of apoptosis involving multiple genes in the MAP kinase pathway.
American Journal Of Pathology 09/2009; 175(2):592-604. · 4.52 Impact Factor
[show abstract][hide abstract] ABSTRACT: Protein Gene Product 9.5 (PGP9.5) is highly expressed in nervous tissue. Recently PGP9.5 expression has been found to be upregulated in the pulmonary epithelium of smokers and in non-small cell lung cancer, suggesting that it also plays a role in carcinogen-inflicted lung epithelial injury and carcinogenesis. We investigated the expression of PGP9.5 in mice in response to two prominent carcinogens found in tobacco smoke: Naphthalene and 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone (NNK). By immunostaining, we found that PGP9.5 protein was highly expressed throughout the airway epithelium in the days immediately following a single injection of naphthalene. In contrast, PGP9.5 was exclusively confined to neurons and neuroendocrine cells in the control and NNK-exposed lungs. Furthermore, we investigated the expression of PGP9.5 mRNA in the lungs by quantitative RT-PCR (qPCR). PGP9.5 mRNA expression was highly upregulated in the days immediately following naphthalene injection and gradually returning to that of control mice 5 days after naphthalene injection. In contrast, exposure to NNK did not result in a significant increase in PGP9.5 mRNA 10 weeks after exposure. No increased expression of two other neuroendocrine markers was found in the non-neuroendocrine epithelial cells after naphthalene exposure. In contrast, immunostaining for the cell cycle regulator p27(Kip1), which has previously been associated with PGP9.5 in lung cancer cells, revealed transient downregulation of p27(Kip1) in naphthalene exposed airways compared to controls, indicating that the rise in PGP9.5 in the airway epithelium is related to downregulation of p27(Kip1). This study is the first to specifically identify the carcinogen naphthalene as an inducer of PGP9.5 expression in non-neuroendocrine epithelium after acute lung injury and further strengthens the accumulating evidence of PGP9.5 as a central player in lung epithelial damage and early carcinogenesis.
[show abstract][hide abstract] ABSTRACT: Squamous cell carcinoma accounts for 20% of all human lung cancers and is strongly linked to cigarette smoking. It develops through premalignant changes that are characterized by high levels of keratin 14 (K14) expression in the airway epithelium and evolve through basal cell hyperplasia, squamous metaplasia and dysplasia to carcinoma in situ and invasive carcinoma. In order to explore the impact of K14 in the pulmonary epithelium that normally lacks both squamous differentiation and K14 expression, human keratin 14 gene hK14 was constitutively expressed in mouse airway progenitor cells using a mouse Clara cell specific 10 kDa protein (CC10) promoter. While the lungs of CC10-hK14 transgenic mice developed normally, we detected increased expression of K14 and the molecular markers of squamous differentiation program such as involucrin, loricrin, small proline-rich protein 1A, transglutaminase 1 and cholesterol sulfotransferase 2B1. In contrast, wild-type lungs were negative. Aging CC10-hK14 mice revealed multifocal airway cell hyperplasia, occasional squamous metaplasia and their lung tumors displayed evidence for multidirectional differentiation. We conclude that constitutive expression of hK14 initiates squamous differentiation program in the mouse lung, but fails to promote squamous maturation. Our study provides a novel model for assessing the mechanisms of premalignant lesions in vivo by modifying differentiation and proliferation of airway progenitor cells.
[show abstract][hide abstract] ABSTRACT: Pten is a negative regulator of the Akt pathway, and its inactivation is believed to be an etiological factor in many tumor types. Pten+/- mice are susceptible to a variety of spontaneous tumor types, depending on strain background. Pten+/- mice, in lung tumor-sensitive and -resistant background strains, were treated with a tobacco carcinogen, 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone (NNK), to determine whether allelic Pten deletion can cooperate with NNK in carcinogenesis in lung or other tissues. In lung tumor-resistant C57BL/6 Pten+/- or +/+ mice, NNK treatment did not lead to any lung tumors and did not increase the incidence or severity of tumors previously reported for this strain. In contrast, in a lung tumor-susceptible pseudo-A/J strain, there was a dose-dependent increase in lung tumor size in Pten+/- compared with +/+ mice, although there was no increase in multiplicity. No other tumor types were observed in pseudo-A/J Pten+/- mice regardless of NNK treatment. Lung tumors from these Pten+/- mice had K-ras mutations, retained Pten expression and had similar Akt pathway activation as lung tumors from +/+ mice. Therefore, deletion of a single copy of Pten does not substantially add to the lung tumor phenotype conferred by mutation of K-ras by NNK, and there is likely no selective advantage for loss of the second Pten allele in lung tumor initiation.
Neoplasia (New York, N.Y.) 09/2008; 10(8):866-72. · 5.48 Impact Factor
[show abstract][hide abstract] ABSTRACT: The Gynecologic Oncology Group (GOG) performed a detailed analysis of p53 overexpression in previously-untreated women with invasive early or advanced stage epithelial ovarian cancer (EOC).
Women were eligible for the study if they provided a tumor block for translational research and participated in either GOG-157, a randomized phase III trial of three versus (vs.) six cycles of paclitaxel+carboplatin in high-risk, early stage EOC, or GOG-111, a randomized phase III trial of cyclophosphamide+cisplatin vs. paclitaxel+cisplatin in suboptimally-resected, advanced stage EOC. The N-terminal DO-7 p53 antibody was used to examine the expression of the major normal and mutant p53-isoforms. p53 overexpression was defined as >or=10% tumor cells exhibiting nuclear staining.
p53 was overexpressed in 51% (73/143) and 66% (90/136) of cases in the GOG-157 and GOG-111 cohorts, respectively. In the GOG-157 cohort, p53 overexpression was not associated with any clinical characteristics or overall survival (OS) but was associated with worse progression-free survival (PFS) (logrank test: p=0.013; unadjusted Cox modeling: p=0.015). In the GOG-111 cohort, p53 overexpression was associated with GOG performance status (p=0.018) and grade (p=0.003), but not with age, stage, cell type or with tumor response and disease status after primary chemotherapy, PFS or OS. Adjusted Cox regression modeling demonstrated that p53 overexpression was not an independent prognostic factor for PFS or OS in either cohort.
p53 overexpression assessed by DO-7 immunostaining is common in early and advanced stage EOC, but has limited prognostic value in women treated with surgical staging and platinum-based combination chemotherapy.
[show abstract][hide abstract] ABSTRACT: The basic helix-loop-helix protein achaete-scute homolog-1 (ASH1) is involved in lung neuroendocrine (NE) differentiation and tumor promotion in SV40 transgenic mice. Constitutive expression of human ASH-1 (hASH1) in mouse lung results in hyperplasia and remodeling that mimics bronchiolization of alveoli (BOA), a potentially premalignant lesion of human lung carcinomas. We now show that this is due to sustained cellular proliferation in terminal bronchioles and resistance to apoptosis. Throughout the airway epithelium the expression of anti-apoptotic Bcl-2 and c-Myb was increased and Akt/mTOR pathway activated. Moreover, the expression of matrix metalloproteases (MMPs) including MMP7 was specifically enhanced at the bronchiolo-alveolar duct junction and BOA suggesting that MMPs play a key role in this microenvironment during remodeling. We also detected MMP7 in 70% of human BOA lesions. Knockdown of hASH1 gene in human lung cancer cells in vitro suppressed growth by increasing apoptosis. We also show that forced expression of hASH1 in immortalized human bronchial epithelial cells decreases apoptosis. We conclude that the impact of hASH1 is not limited to cells with NE phenotype. Rather, constitutive expression of hASH1 in lung epithelium promotes remodeling through multiple pathways that are commonly activated during lung carcinogenesis. The collective results suggest a novel model of BOA formation via hASH1-induced suppression of the apoptotic pathway. Our study yields a promising new preclinical tool for chemoprevention of peripheral lung carcinomas.
[show abstract][hide abstract] ABSTRACT: Naphthalene exposure kills lung airway epithelial (Clara) cells, but is rapidly followed by Clara cell reconstitution coincident with proliferation of pulmonary neuroendocrine cells (PNEC). Although a role for mature PNEC in the reconstitution process has been excluded, the reconstituting progenitor cells have been suggested to enter a transient neuroendocrine (NE) differentiation phase before differentiating to Clara cells. Furthermore, these progenitors were suggested to be the target population for transformation to a NE tumor; small cell lung cancer (SCLC). Although the NE phenotype is central to SCLC oncogenesis, the relevance of NE differentiation to post naphthalene reconstitution remains to be determined. The Growth factor independent-1 (Gfi1) transcription factor is expressed in SCLC and is required for the NE differentiation of PNEC. Gfi1(-/-) mice display a 70% reduction in airway cells that express NE markers, and cells that stain for NE markers show weak expression of some markers. Therefore, to determine the relevance of the NE phenotype to post-naphthalene reconstitution, we examined post-naphthalene reconstitution in Gfi1(-/-) mice. Our analyses indicate that the post-naphthalene regeneration process includes both airway epithelial proliferation and apoptosis. Gfi1 deletion lowered both airway epithelial proliferation and apoptosis; however, the post-naphthalene rate of increase in growth and apoptosis was not significantly different between Gfi1(-/-) mice and wild-type littermates. Moreover, the timing and extent of CC10+ cell regeneration was unaffected by Gfi1 deletion. These data suggest that neither Gfi1 nor the NE phenotype play a dominant role in the regeneration process. However, the few Gfi1(-/-) cells capable of NE differentiation show a significant reduction in post-naphthalene proliferation. The modest proliferation seen in Gfi1(-/-) NE cells is consistent with the previously proposed role for Gfi1 in controlling neuroendocrine cancer growth.
[show abstract][hide abstract] ABSTRACT: Human and murine preneoplastic lung lesions induced by tobacco exposure are characterized by increased activation of the Akt/mammalian target of rapamycin (mTOR) pathway, suggesting a role for this pathway in lung cancer development. To test this, we did studies with rapamycin, an inhibitor of mTOR, in A/J mice that had been exposed to the tobacco-specific carcinogen 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone (NNK).
Tumorigenesis was induced by i.p. injection of NNK, and rapamycin was administered 1 or 26 weeks after NNK administration. Biomarkers associated with mTOR inhibition were assessed in lung and/or surrogate tissues using immunohistochemistry and immunoblotting. Rapamycin levels were measured using mass spectroscopy.
Rapamycin was administered on a daily (5 of 7 days) regimen beginning 26 weeks after NNK decreased tumor size, proliferative rate, and mTOR activity. Multiplicity was not affected. Comparing this regimen with an every-other-day (qod) regimen revealed that rapamycin levels were better maintained with qod administration, reaching a nadir of 16.4 ng/mL, a level relevant in humans. When begun 1 week after NNK, this regimen was well tolerated and decreased tumor multiplicity by 90%. Tumors that did develop showed decreased phenotypic progression and a 74% decrease in size that correlated with decreased proliferation and inhibition of mTOR.
Tobacco carcinogen-induced lung tumors in A/J mice are dependent upon mTOR activity because rapamycin markedly reduced the development and growth of tumors. Combined with the Food and Drug Administration approval of rapamycin and broad clinical experience, these studies provide a rationale to assess rapamycin in trials with smokers at high risk to develop lung cancer.
Clinical Cancer Research 04/2007; 13(7):2281-9. · 7.84 Impact Factor