镍暴露下MEG3/p62/c-Myc潜在新通路的发现及分子机制研究

Decades of both epidemiological research and in vitro and in vivo laboratory studies have consistently reported an association between xenobiotic nickel exposure and lung cancer. Although most people experience nickel exposure through inhaling ambient pollution, some breathe a more localized concentration in their work environments. So, the International Agency for Research on Cancer (IARC) classified nickel compounds as Group 1 carcinogens: substances confirmed as carcinogenic to humans. Since nickel compounds do not show a high affinity for DNA, it has been suggested that nongenotoxic mechanism(s) might be responsible for their carcinogenic activity. Nonetheless, there is no evidence that a single nickel-inducible factor can drive transformation of human bronchial cells to the best of our knowledge, while the identification of nickel-induced lung carcinogenic driver is highly significant for us not only understanding nickel lung carcinogenic effect, but also being used as a prognostic biomarker and/or as a therapeutic target. Our preliminary data indicate that reduced abundance of maternally-expressed gene 3 (MEG3) was sufficient for malignant transformation of normal human bronchial epithelial cell (NHBEC). Our demonstration that MEG3 inhibition can independently transform HBECs provides the basis of our central hypothesis that MEG3 downregulation drives transformation and tumorigenecity of NHBEC after nickel exposure. Here we propose to elucidate the molecular mechanisms that underlie our novel findings that MEG3 downregulation is a crucial driver for nickel-induced malignant transformation of HBECs. Our investigations will focus on the potential pathway of p62/c-Myc caused by MEG3 inhibition and/or nickel exposure both in vitro and in vivo. Our proposed studies—which are designed to specifically elucidate the downstream effectors(such as p62,c-Myc), mechanisms, and in vivo functions of MEG3 downregulation—should help us to better understand the biological role of MEG3 and shed light on its potential as a prognostic biomarker and/or a therapeutic target in nickel-exposed clinical settings.

流行病学调查及动物实验结果证实镍化物暴露导致肺癌。镍致DNA突变能力较弱，调控基因表达可能是其主要致癌方式,然而已有发现均集中在起间接作用的促癌基因，未有直接作用的致癌靶基因的突破。我们的初步研究表明：镍暴露显著下调MEG3的表达，而仅敲低（knock-down）MEG3表达即可模拟镍暴露导致正常人肺支气管上皮细胞（NHBEC）恶性转化；敲低MEG3模拟的镍致癌能力可能通过上调SQSTM1（p62）而实现，同时敲低p62亦下调癌基因c-Myc的表达。因此我们提出假说：镍暴露通过激活MEG3/p62/c-Myc这一潜在新通路，直接诱导NHBEC恶性转化而导致肺癌的发生。本课题拟利用原发动物模型等技术手段，揭示新通路的生物学功能并阐明具体调控机制，进而证实新假说。预期成果不仅有助于了解MEG3这一镍化物直接致癌靶基因的生物学功能，而且能够加深我们对镍化物致癌机制的认识，服务于镍暴露危害防治。

流行病学调查及动物实验结果证实镍化物暴露导致肺癌。镍致DNA突变能力较弱，调控基因表达可能是其主要致癌方式,然而已有发现均集中在起间接作用的促癌基因，未有直接作用的致癌靶基因的突破。我们的初步研究表明：镍暴露显著下调MEG3的表达，而仅敲低（knock-down）MEG3表达即可模拟镍暴露导致正常人肺支气管上皮细胞（NHBEC）恶性转化；敲低MEG3模拟的镍致癌能力可能通过上调SQSTM1（p62）而实现，同时敲低p62亦下调癌基因c-Myc的表达。因此我们提出假设：镍暴露通过激活MEG3/p62/c-Myc这一潜在新通路，直接诱导NHBEC恶性转化而导致肺癌的发生。本课题拟利用细胞生物学、分子生物学及生物信息学等技术手段，揭示新通路的生物学功能并阐明具体调控机制，进而证实新假说。通过研究，我们发现：镍化物暴露下，下调肺支气管上皮细胞中MEG3的表达，进而通过与其结合的p62蛋白，抑制p62蛋白的降解而致p62蛋白积累，而p62蛋白可与STAT5结合，通过促进其蛋白降解抑制其表达并降低对miR-33b的转录活性，减少肺支气管上皮细胞中miR-33b的水平，减弱了miR-33b对c-Myc翻译的抑制作用，增强c-Myc的蛋白水平，促进肺支气管上皮细胞恶性转化；同时初步发现异丹叶大黄素具有上调MEG3潜在抑制镍化物致癌效应的潜能。本研究的结果不仅有助于了解MEG3这一镍化物直接致癌靶基因的生物学功能，而且能够加深我们对镍化物致癌机制的认识，服务于镍暴露危害防治。