Microarray analyses uncover UBE1L as a candidate target gene for lung cancer chemoprevention

Retinoids, natural and synthetic derivatives of vitamin A, are active in cancer therapy and chemoprevention. We reported previously that all-trans-retinoic acid (RA) treatment prevented carcinogen-induced transformation of immortalized human bronchial epithelial (HBE) cells. To identify cancer chemopreventive mechanisms, immortalized (BEAS-2B), carcinogen-transformed (BEAS-2B(NNK)), and RA-chemoprevented (BEAS-2B(NNK/RA)) HBE cells were used to conduct microarray analyses independently. Species increased in chemoprevented as compared with immortalized HBE cells (group I) and those augmented in chemoprevented as compared with transformed HBE cells (group II) included known RA-target genes as well as previously unrecognized RA-target genes in HBE cells. Unexpectedly, both groups were also enriched for interferon-stimulated genes. One interferon-stimulated gene of particular interest was UBE1L, the ubiquitin-activating enzyme E1-like protein. UBE1L expression was also induced after prolonged RA-treatment of immortalized HBE cells. UBE1L mRNA was shown previously as repressed in certain lung cancer cell lines, directly implicating UBE1L in lung carcinogenesis. Notably, UBE1L immunoblot expression was reduced in a subset of malignant as compared with adjacent normal lung tissues that were examined. Immunohistochemical analyses were performed using a new assay developed to detect this species using rabbit polyclonal anti-UBE1L antibodies independently raised against the amino- or carboxyl-termini of UBE1L. Studies done on paraffin-embedded and fixed tissues revealed abundant UBE1L, but low levels of cyclin D1 expression in the normal human bronchial epithelium, indicating an inverse relationship existed between these species. To study this further, cotransfection into HBE cells of wild-type or mutant UBE1L species was accomplished. In a dose-dependent manner, wild-type but not mutant UBE1L species repressed cyclin D1 expression. This implicated UBE1L in a retinoid chemoprevention mechanism involving cyclin D1 repression described previously. Taken together, these findings directly implicate UBE1L as a candidate-pharmacologic target for lung cancer chemoprevention. These findings also provide a mechanistic basis for the tumor suppressive effects of UBE1L through cyclin D1 repression.     

Specific chemopreventive agents trigger proteasomal degradation of G1 cyclins: implications for combination therapy.

PURPOSE: There is a need to identify cancer chemoprevention mechanisms. We reported previously that all-trans-retinoic acid (RA) prevented carcinogenic transformation of BEAS-2B immortalized human bronchial epithelial cells by causing G(1) arrest, permitting repair of genomic DNA damage. G(1) arrest was triggered by cyclin D1 proteolysis via ubiquitin-dependent degradation. This study investigated which chemopreventive agents activated this degradation program and whether cyclin E was also degraded. EXPERIMENTAL DESIGN: This study examined whether: (a) cyclin E protein was affected by RA treatment; (b) cyclin degradation occurred in derived BEAS-2B-R1 cells that were partially resistant to RA; and (c) other candidate chemopreventive agents caused cyclin degradation. RESULTS: RA treatment triggered degradation of cyclin E protein, and ALLN, a proteasomal inhibitor, inhibited this degradation. Induction of the retinoic acid receptor beta, growth suppression, and cyclin degradation were each inhibited in BEAS-2B-R1 cells. Transfection experiments in BEAS-2B cells indicated that RA treatment repressed expression of wild-type cyclin D1 and cyclin E, but ALLN inhibited this degradation. Mutation of threonine 286 stabilized transfected cyclin D1, and mutations of threonines 62 and 380 stabilized transfected cyclin E, despite RA treatment. Specific chemopreventive agents triggered cyclin degradation. Nonclassical retinoids (fenretinide and retinoid X receptor agonists) and a synthetic triterpenoid (2-cyano-3,12-dioxooleana-1,9-dien-28-oic acid) each suppressed BEAS-2B growth and activated this degradation program. However, a vitamin D3 analog (RO-24-5531), a cyclooxygenase inhibitor (indomethacin), and a peroxisome proliferator-activated receptor gamma agonist (rosiglitazone) each suppressed BEAS-2B growth, but did not cause cyclin degradation. BEAS-2B-R1 cells remained responsive to nonclassical retinoids and to 2-cyano-3,12-dioxooleana-1,9-dien-28-oic acid. CONCLUSIONS: Specific chemopreventive agents activate cyclin proteolysis. Yet, broad resistance did not occur after acquired resistance to a single agent. This provides a therapeutic rationale for combination chemoprevention with agents activating non-cross-resistant pathways.     

Cyclin D1 proteolysis: a retinoid chemoprevention signal in normal, immortalized, and transformed human bronchial epithelial cells

BACKGROUND: Retinoids (derivatives of vitamin A) are reported to reduce the occurrence of some second primary cancers, including aerodigestive tract tumors. In contrast, beta-carotene does not reduce the occurrence of primary aerodigestive tract cancers. Mechanisms explaining these effective retinoid and ineffective carotenoid chemoprevention results are poorly defined. Recently, the all-trans-retinoic acid (RA)-induced proteolysis of cyclin D1 that leads to the arrest of cells in G1 phase of the cell cycle was described in human bronchial epithelial cells and is a promising candidate for such a mechanism. In this study, we have investigated this proteolysis as a common signal used by carotenoids or receptor-selective and receptor-nonselective retinoids. METHODS: We treated cultured normal human bronchial epithelial cells, immortalized human bronchial epithelial cells (BEAS-2B), and transformed human bronchial epithelial cells (BEAS-2BNNK) with receptor-selective or receptor-nonselective retinoids or with carotenoids and studied the effects on cell proliferation by means of tritiated thymidine incorporation and on cyclin D1 expression by means of immunoblot analysis. We also examined whether calpain inhibitor I, an inhibitor of the 26S proteasome degradation pathway, affected the decline (i.e., proteolysis) of cyclin D1. RESULTS: Receptor-nonselective retinoids were superior to the carotenoids studied in mediating the decline in cyclin D1 expression and in suppressing the growth of bronchial epithelial cells. Retinoids that activated retinoic acid receptor beta or retinoid X receptor pathways preferentially led to a decrease in the amount of cyclin D1 protein and a corresponding decline in growth. The retinoid-mediated degradation of cyclin D1 was blocked by cotreatment with calpain inhibitor I. CONCLUSIONS: Retinoid-dependent cyclin D1 proteolysis is a common chemoprevention signal in normal and neoplastic human bronchial epithelial cells. In contrast, carotenoids did not affect cyclin D1 expression. Thus, the degradation of cyclin D1 is a candidate intermediate marker for effective retinoid-mediated cancer chemoprevention in the aerodigestive tract.     

A proof-of-principle clinical trial of bexarotene in patients with non-small cell lung cancer.

PURPOSE: Bexarotene is a rexinoid (selective retinoid X receptor agonist) that affects proliferation, differentiation, and apoptosis in preclinical studies. The relationship between bexarotene levels and biomarker changes in tumor tissues has not been previously studied. EXPERIMENTAL DESIGN: BEAS-2B human bronchial epithelial (HBE) cells, retinoid-resistant BEAS-2B-R1 cells, A427, H226, and H358 lung cancer cells were treated with bexarotene. Proliferation and biomarker expression were assessed. In a proof-of-principle clinical trial, bexarotene tumor tissue levels and intratumoral pharmacodynamic effects were assessed in patients with stages I to II non-small cell lung cancer. Bexarotene (300 mg/m(2)/day) was administered p.o. for 7 to 9 days before resection. RESULTS: Bexarotene-induced dosage-dependent repression of growth, cyclin D1, cyclin D3, total epidermal growth factor receptor (EGFR), and phospho-EGFR expression in BEAS-2B, BEAS-2B-R1, A427, and H358, but not H226 cells. Twelve patients were enrolled, and 10 were evaluable. Bexarotene treatment was well tolerated. There was nonlinear correlation between plasma and tumor bexarotene concentrations (r(2) = 0.77). Biomarker changes in tumors were observed: repression of cyclin D1, total EGFR and proliferation in one case; repression of cyclin D3, total and phospho-EGFR in another. The cases with multiple biomarker changes had high tumor bexarotene (107-159 ng/g). A single biomarker change was detected in one case with low tumor bexarotene. CONCLUSION: Bexarotene represses proliferation and biomarker expression in responsive, but not resistant HBE and lung cancer cells. Similar biomarker changes occur in lung tumors when therapeutic intratumoral bexarotene levels are achieved. This proof-of-principle trial approach is useful to uncover pharmacodynamic mechanisms in vivo and relate these to intratumoral pharmacokinetic effects.     

Cyclin D1 as a target for chemoprevention

Lung cancer is the leading cause of cancer mortality. Chemoprevention is an attractive strategy to combat this major public health problem. Pre-clinical and clinical studies have identified diverse candidate chemopreventive agents that affect cellular proliferation, differentiation, apoptosis and tumor angiogenesis, among other pathways. These pharmacological agents are undergoing testing through use of pre-clinical models and clinical trials. These studies have uncovered cyclin D1 as a chemoprevention target and a surrogate marker of chemopreventive response in the lung. Chemoprevention of tobacco-carcinogen transformed human bronchial epithelial (HBE) cells appears to be due at least partly to degradation of cyclin D1. These studies of cultured HBE cells were extended to the in vivo setting by examination of preneoplastic bronchial lesions that established the frequent aberrant expression of cyclin D1 in lung carcinogenesis. Certain retinoids, natural and synthetic derivatives of vitamin A, repress cyclin D1, but activation of the epidermal growth factor receptor (EGFR) induces cyclin D1. Retinoids and specific chemopreventive agents can activate the proteasome-dependent degradation of cyclin D1 and also repress EGFR expression, thereby reducing cyclin D1 levels. These actions oppose the mitogenic effects of cyclin D1. This is hypothesized to trigger G1 arrest and thereby permit repair of carcinogenic damage of genomic DNA. These and other pre-clinical and clinical studies that will be reviewed here indicate that cyclin D1 and perhaps other cyclins are attractive pharmacological targets for lung cancer chemoprevention.     

Malignant transformation of human bronchial epithelial cells with the tobacco-specific nitrosamine, 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone

Sufficient evidence has demonstrated that cigarette smoking is causally associated with various types of human cancers. In the United States, about 90% of deaths from lung cancer among men and 79% of those among women are associated with smoking. Tobacco-specific nitrosamines are formed from nicotine and related tobacco alkaloids and are the most carcinogenic compounds of tobacco smoke. The most potent N-nitrosamine contained in tobacco smoke is 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone, NNK. In the our study, the oncogenic transforming effects of graded doses of NNK were examined using papillomavirus-immortalized human bronchial epithelial cells. Growth kinetics, saturation density, resistance to serum-induced terminal differentiation, anchorage independent growth and tumorigenicity in nude mice were used to investigate the various stages of transformation in bronchial epithelial cells. We show here that immortalized human bronchial epithelial cells in culture can be malignantly transformed by treatment with NNK (100 microg/ml or 400 microg/ml) for 7 days. Transformed cells produced progressively growing subcutaneous tumors upon inoculation into nude mice. Immunofluorescence staining for keratin expression confirmed the epithelial nature of the tumor cells. Increased expression of p16, beta-catenin and PCNA in the established cell lines were detected by immunofluorescence staining and quantified by confocal microscopy. These data suggested that NNK can induce malignant transformation of human bronchial epithelial cells, and the tumor cell lines established are useful models in investigating the carcinogenic mechanism(s) of NNK.     

Overexpressed Raf-1 and phosphorylated cyclic adenosine 3'-5'-monophosphatate response element-binding protein are early markers for lung adenocarcinoma

BACKGROUND: Pulmonary adenocarcinoma (PAC) is the leading type of lung cancer and has a high mortality. The tobacco carcinogen nicotine-derived nitrosamine 4-(N-methyl-N-nitrosamino)-1-(3-pyridyl)-1-butanone (NNK) stimulates the proliferation of human PAC cells and small airway epithelial cells through beta-1 adrenorecptor-mediated transactivation of the epidermal growth factor receptor (EGFR). METHODS: Using the NNK hamster PAC model and human PAC tissue arrays with matched and unmatched normal lung tissues, the authors tested the hypothesis that Raf-1, an effector of the EGFR, and P-CREB, an effector of the beta-adrenoreceptor, are overexpressed in a significant subset of human PACs and are early markers of PAC development. Western blots from respiratory epithelial cells and microadenomas harvested by laser-capture microdissection from hamster lungs accompanied by immunostains were used to monitor the expression levels of Raf-1 and P-CREB after 5 weeks, 10 weeks, and 20 weeks of NNK treatment. Expression levels of these markers in human PAC tissue arrays were assessed by immunostains. Reverse-phase proteomics, Western blot analysis, and immunoprecipitation in immortalized human small-airway epithelial cells and in a human PAC cell line in the presence and absence of dominant-negative Raf were used to determine Raf dependence of extracellular signal-regulated kinase 1 and 2 (ERK1/2) activation in response to NNK or isoproterenol. RESULTS: The data showed a time-dependent increase in the expression of Raf-1 and P-CREB after NNK treatment in small-airway epithelial cells and microadenomas of hamsters. The majority of human lung adenocarcinomas simultaneously overexpressed Raf-1 and P-CREB. Dominant-negative Raf completely abrogated ERK1/2 activation by NNK and isoproterenol. CONCLUSIONS: The current results indicated that RAF-1 and P-CREB may contribute to the development of a significant subset of human lung adenocarcinomas and may offer promising targets for early detection and treatment.     

Apo-10'-lycopenoic acid inhibits lung cancer cell growth in vitro, and suppresses lung tumorigenesis in the A/J mouse model in vivo

High intake of lycopene has been associated with a lower risk of a variety of cancers including lung cancer. We recently showed that lycopene can be converted to apo-10'-lycopenoids [Hu et al. (2006). J. Biol. Chem., 281, 19327-19338] in mammalian tissues both in vitro and in vivo, raising the question of whether apo-10'-lycopenoids have biological activities against lung carcinogenesis. In the present study, we report that apo-10'-lycopenoic acid inhibited the growth of NHBE normal human bronchial epithelial cells, BEAS-2B-immortalized normal bronchial epithelial cells and A549 non-small cell lung cancer cells. This inhibitory effect of apo-10'-lycopenoic acid was associated with decreased cyclin E, inhibition of cell cycle progression from G(1) to S phase and increased cell cycle regulators p21 and p27 protein levels. In addition, apo-10'-lycopenoic acid transactivated the retinoic acid receptor beta (RARbeta) promoter and induced the expression of RARbeta. We further examined the effect of apo-10'-lycopenoic acid treatment on 4-(N-methyl-N-nitrosamino)-1-(3-pyridal)-1-butanone (NNK)-induced lung tumorigenesis in the A/J mouse model. We found that the lung tumor multiplicity was decreased dose dependently from an average of 16 tumors per mouse in the NNK injection alone group, to an average of 10, 7 and 5 tumors per mouse in groups injected with NNK and supplemented with 10, 40 and 120 mg/kg diet of apo-10'-lycopenoic acid, respectively. These observations demonstrate that apo-10'-lycopenoic acid is a biological active metabolite of lycopene and suggest that apo-10'-lycopenoic acid is a potential chemopreventive agent against lung tumorigenesis.     

Neoplastic transformation of a human bronchial epithelial cell line by a recombinant retrovirus encoding viral Harvey ras

Activated ras oncogenes have previously been implicated in the pathogenesis of human lung carcinomas. A v-Ha-ras-containing retrovirus, Zip-ras, was generated by inserting the coding region of the v-Ha-ras oncogene into the Zip-NeoSV(X) [Cepko et al., Cell 37:1053-1062, 1984] retroviral vector. Amphotrophic Zip-ras retrovirus was used to infect an SV40 large T antigen-positive immortalized cell line, BEAS-2B, derived from normal bronchial epithelial cells, the predominant progenitor cells of human lung carcinomas. Zip-ras-infected BEAS-2B cells selected for G418 resistance formed anaplastic carcinomas in 12 of 15 athymic nude mice (latency 3 wk), whereas Zip-NeoSV(X)-infected BEAS-2B control cultures inoculated into 12 nude mice formed no tumors after a minimum of 7 mo. Tumor cell lines were established and demonstrated to be of human epithelial origin and to express v-Ha-ras p21 protein. A common feature of the tumor cell lines was an increase in ploidy. The increased efficiency of neoplastic transformation by v-Ha-ras of cell lines as compared with our previous results with normal bronchial epithelial cells [Yoakum et al., Science 227:1174-1179, 1985] is consistent with the hypothesis that the "immortalization" step is rate-limiting in in vitro human epithelial cell carcinogenesis.     

肺癌细胞抑癌蛋白PTEN下调机制的研究

目的:探讨肺癌细胞中抑癌蛋白PTEN低表达的相关机制。方法:Western blot方法检测肺癌细胞和正常人肺上皮细胞BEAS-2BPTEN蛋白的表达;用放线菌酮(1μg/mL)处理人肺腺癌细胞A549和正常人肺上皮细胞BEAS-2B阻断细胞翻译后,Western blot方法检测不同时相PTEN蛋白的表达。RT-PCR检测肺癌细胞与正常肺上皮细胞PTEN mRNA水平;放线菌素D(1μg/mL)处理肺癌细胞与正常肺上皮细胞阻断新生RNA合成,RT-PCR检测不同时相PTEN mRNA的水平。结果:Western blot结果显示,肺癌细胞中PTEN蛋白表达与正常肺上皮细胞比较有不同程度的降低(0.38～1.32倍);使用放线菌酮处理A549和BEAS-2B后,24h内A549及BEAS-2B细胞PTEN蛋白表达无明显改变。RT-PCR结果显示肺癌细胞中PTEN mRNA与正常人肺上皮细胞相比明显降低(0.41～0.68倍);放线菌素D处理显示肺癌细胞PTEN mRNA降解速率比正常肺上皮细胞降解速率明显加快。结论:肺癌细胞中抑癌蛋白PTEN低表达的主要原因是其mRNA降解加速,这为进一步研究PTEN蛋白低表达的详细分子机制提供了线索。     

Chemopreventive effects of deguelin, a novel Akt inhibitor, on tobacco-induced lung tumorigenesis

Tobacco carcinogens induce Akt activation and lung carcinogenesis. We previously demonstrated that deguelin, a natural plant product, specifically inhibits the proliferation of premalignant and malignant human bronchial epithelial cells by blocking Akt activation. To evaluate the ability of deguelin to block tobacco carcinogen-induced lung tumorigenesis, we evaluated the in vivo effects of deguelin on Akt activation and lung tumorigenesis in transgenic mice in which Akt expression was induced by tamoxifen and in 4-(methylnitrosoamino)-1-(3-pyridyl)-1-butanone (NNK)/benzo(a)pyrene (BaP)-treated A/J mice. Deguelin suppressed Akt activation in vivo, as measured by immunohistochemistry and immunoblotting, and statistically significantly reduced NNK/BaP-induced lung tumor multiplicity, volume, and load in A/J mice, as monitored by microcomputed tomography image analysis, with no detectable toxicity. These results indicate that deguelin warrants consideration as a chemopreventive agent for early-stage lung carcinogenesis in a clinical lung cancer chemoprevention trial.     

贫铀诱发人支气管上皮细胞恶性转化

背景与目的：实验研究和流行病学调查结果表明,铀可广泛地影响人体健康,但其远期效应,特别是致癌性,还缺乏明确的结论。本文模拟人吸入贫铀（depleted uranium,DU)气溶胶的情形,研究难溶性贫铀诱发人支气管上皮细胞恶性转化及肺癌相关基因表达谱。方法：用难溶性贫铀氧化物（dUO2)作用腺病毒-12/SV40病毒永生化的人支气管上皮细胞（BEAS-2B）,通过观察不同代龄细胞的倍增时间,血清抗性,半固体琼脂克隆形成率及裸鼠成瘤性,鉴定细胞的恶性转化特性;用213个肺癌相关基因的芯片对贫铀诱发的转化BEAS-2B细胞的基因表达谱进行检测。结果：贫铀作用后的第5代BEAS-2B细胞倍增时间明显缩短,血清抗性显著增强;第10代细胞具有锚着独立性生长特性（半固体琼脂克隆形成）;第15代裸鼠体内成瘤。二甲亚砜（DMSO）对贫铀诱发的BEAS-2B细胞恶性转化有明显保护效果。213个肺癌相关基因的芯片检测结果表明,转化细胞中有70多个基因的表达水平发生明显改变,其中10余个基因表达水平明显下降。结论：贫铀在体外具有致癌性。     

The function of IGF-IR in NNK-mediated lung tumorigenesis

The type I insulin-like growth factor receptor (IGF-IR) is associated with many different types of cancer and it has been found to be involved in many aspects of the malignant phenotype, such as mitogenesis, survival, transformation and metastasis. This receptor has been observed to be overexpressed in the majority of lung cancer cell lines and human lung tumor biopsies. Two doxycycline-inducible transgenic mouse models in which the human IGF-IR was overexpressed in either the Clara cells or the type II alveolar cells of the lung were used in this study to examine the interaction between the nicotine derivative, nitrosamine 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone (NNK) and the IGF-IR. NNK was injected into both of the transgenic mouse models that overexpress human IGF-IR in the lung tissue in order to determine whether IGF-IR overexpression would affect NNK-induced tumorigenesis. No significant differences in the overall tumor burden were found between mice overexpressing the IGF-IR transgene that were treated with NNK and those that were not, however NNK-treated mice expressing high levels of IGF-IR transgene developed larger tumors than mice expressing high levels of IGF-IR transgene that did not receive NNK injections. In addition, endogenous murine IGF-IR was found to be expressed at high levels in the tumors that developed in the wild type, NNK injected mice suggesting that NNK induces lung tumors through inducing endogenous IGF-IR expression.     

甲醛对人支气管上皮细胞系染色体不稳定性的研究

背景与目的： 为探讨染色体不稳定性与细胞恶性转化之间的关系,揭示化学致癌的机制,本研究以甲醛为诱导剂,研究化学致癌物甲醛作用于人支气管上皮细胞系后,对人支气管上皮细胞染色体稳定性的影响。 材料与方法： 用甲醛作为诱导剂,以液体染毒方式处理细胞,检测染毒后细胞的LC50,以低剂量（20% LC50）对细胞进行诱导并筛选诱导克隆。然后采用细胞遗传学方法（G带染色法）考察染毒后甲醛诱导的人支气管上皮细胞系（BEAS-2B）染色体畸变的情况。 结果： 甲醛作用后,诱导细胞的核型由2倍体转化为近2倍体、非整倍体和多倍体等核型同时存在。诱导细胞染色体稳定性降低,呈现大量染色体畸变,包括染色体丢失、内复制、易位、断裂、双/三着丝粒,同时伴有大量非稳定性畸变。 结论： 甲醛可影响BEAS-2B细胞染色体的稳定性,使其发生畸变并最终使细胞向恶性化方向发展。     

Retinoid targeting of different D-type cyclins through distinct chemopreventive mechanisms

D-type cyclins (cyclins D1, D2, and D3) promote G1-S progression and are aberrantly expressed in cancer. We reported previously that all-trans-retinoic acid chemo-prevented carcinogenic transformation of human bronchial epithelial (HBE) cells through proteasomal degradation of cyclin D1. Retinoic acid is shown here to activate distinct mechanisms to regulate different D-type cyclins in HBE cells. Retinoic acid increased cyclin D2, decreased cyclin D3 and had no effect on cyclin D1 mRNA expression. Retinoic acid decreased cyclin D1 and cyclin D3 protein expression. Repression of cyclin D3 protein preceded that of cyclin D3 mRNA. Proteasomal inhibition prevented the early cyclin D3 degradation by retinoic acid. Threonine 286 (T286) mutation of cyclin D1 stabilized cyclin D1, but a homologous mutation of cyclin D3 affecting threonine 283 did not affect cyclin D3 stability, despite retinoic acid treatment. Lithium chloride and SB216763, both glycogen synthase kinase 3 (GSK3) inhibitors, inhibited retinoic acid repression of cyclin D1, but not cyclin D3 proteins. Notably, phospho-T286 cyclin D1 expression was inhibited by lithium chloride, implicating GSK3 in these effects. Expression of cyclin D1 and cyclin D3 was deregulated in retinoic acid-resistant HBE cells, directly implicating these species in retinoic acid response. D-type cyclins were independently targeted using small interfering RNAs. Repression of each D-type cyclin suppressed HBE growth. Repression of all D-type cyclins cooperatively suppressed HBE growth. Thus, retinoic acid repressed cyclin D1 and cyclin D3 through distinct mechanisms. GSK3 plays a key role in retinoid regulation of cyclin D1. Taken together, these findings highlight these cyclins as molecular pharmacologic targets for cancer chemoprevention.     

SIRT1 in B[a]P-induced lung tumorigenesis

Benzo[a]pyrene (B[a]P) is a carcinogen in cigarette smoke. We found that B[a]P induced SIRT1 in human bronchial epithelial BEAS-2B cell. SIRT1 was overexpressed in the lung of B[a]P-exposed mice and in human lung cancer biopsies. SIRT1 up-regulated TNF-α and β-catenin and down-regulated the membrane fraction of E-cadherin. In addition, SIRT1 promoted invasion, migration and tumorigenesis of BEAS-2B cells in nude mice upon B[a]P exposure. Thus, SIRT1 is involved in B[a]P-induced transformation associated with activation of the TNF-α/β-catenin axis and is as a potential therapeutic target for lung cancer.