Translational Control in Cr(VI) Carcinogenesis

项目摘要 Cr（VI）是一种常见的环境致癌物，可导致人类肺癌和其他癌症。 尽管大量的研究工作，以了解Cr（VI）的分子和细胞机制， 致癌作用，这些机制的关键方面仍然在很大程度上未知;关键分子的鉴定 迫切需要监管机构和程序、行动机制以及预防战略。 已经取得了显着的进展，突出了mRNA翻译和蛋白质的功能重要性， 在癌症发展和进展中的作用。然而，铬（VI）致癌作用的翻译控制， 尚未被调查。我们最近证明，慢性低剂量Cr（VI）暴露于人肺中， 支气管上皮细胞可以诱导肿瘤干细胞样特性、细胞转化和肿瘤 通过上调组蛋白-赖氨酸甲基转移酶（包括G9 a、SUV 39 H1和EZH 2）形成。 值得注意的是，我们发现慢性Cr（VI）暴露可以激活mTOR激酶，导致磷酸化， （失活）翻译阻遏物4 E-BP 1，从而促进加帽mRNA的募集， eIF 4F翻译起始复合物（eIF 4 E + eIF 4G + eIF 4A）的核糖体亚基，用于在 多核糖体此外，我们发现，在慢性Cr（VI）暴露时，EZH 2 mRNA被积极翻译， 在转录水平上没有变化的多聚核糖体。重要的是，靶向抑制mTOR激酶可以抑制 EZH 2 mRNA在多核糖体中的翻译，并导致Cr（VI）转化细胞的生长抑制。基于 根据这些发现，该研究的中心假设是帽依赖性mRNA的激活 需要mTOR激酶的翻译机制来选择性上调赋予Cr（VI）- 诱发肿瘤发生。为了检验这一假设，提出了两个具体目标。目标1将确定 在Cr（VI）诱导的肿瘤发生中使用分子， 细胞、生物化学和药理学方法，以及遗传工程小鼠模型， 临床联合方案。目的2将表征mTOR激活帽的分子机制， 使用多聚核糖体分析方法系统地鉴定一种依赖于翻译的Cr（VI）致癌性， 一组选择性募集到多聚核糖体并在Cr（VI）转化的人中翻译的关键mRNA 支气管上皮细胞，随后表征其在Cr（VI）诱导的 致瘤性我们的研究将探讨铬（VI）诱导致癌的创新概念 通过mTOR/4 E-BP 1介导的翻译起始过程的失调。阐明这一进程将 提供了新的见解的生物学和临床意义的翻译调控铬（VI）致癌。 这项研究将有额外的好处，确定铬（VI）诱导的免疫调节目标， 潜在的预防或介入治疗。

PROJECT SUMMARY Cr(VI) is a common and well-recognized environmental carcinogen that causes lung and other cancers in human. Despite considerable research effort to understand the molecular and cellular mechanisms of Cr(VI) carcinogenesis, crucial facets of these mechanisms remain largely unknown; identification of the key molecular regulators and processes, the mechanisms of action, and strategies for prevention are urgently needed. Remarkable progress has been made that highlights the functional importance of mRNA translation and protein synthesis in cancer development and progression. However, translational control of Cr(VI) carcinogenesis has not yet been investigated. We recently demonstrated that chronic low dose Cr(VI) exposure in human lung bronchial epithelial cells can induce cancer stem cell (CSC)-like properties, cell transformation and tumor formation through upregulation of histone-lysine methyltransferases including G9a, SUV39H1 and EZH2. Notably, we found that chronic Cr(VI) exposure can activate mTOR kinase leading to phosphorylation (inactivation) of the translational repressor 4E-BP1, and thereby promote the recruitment of capping mRNAs and ribosomal subunits to the eIF4F translation initiation complex (eIF4E+eIF4G+eIF4A) for active translation in polysomes. Furthermore, we found that on chronic Cr(VI) exposure, the EZH2 mRNA is actively translated in polysomes with no changes in its transcriptional level. Importantly, targeted inhibition of mTOR kinase can inhibit translation of EZH2 mRNA in polysomes and result in growth inhibition of Cr(VI)-transformed cells. Based on these findings, the central hypothesis of the proposed study is that the activation of cap-dependent mRNA translation machinery by mTOR kinase is required to selectively upregulate key oncoproteins that confer Cr(VI)- induced tumorigenesis. To test this hypothesis, two specific aims are proposed. Aim 1 will define the role of mTOR-activated translation machinery in Cr(VI)-induced tumorigenesis using a combination of molecular, cellular, biochemical, and pharmacologic approaches, as well as genetically engineered mouse models with clinical association schemes. Aim 2 will characterize the molecular mechanism of mTOR-activated cap- dependent translation in Cr(VI) carcinogenicity using a polysome profiling approach to systematically identify a set of key mRNAs that are selectively recruited to polysomes and translated in Cr(VI)-transformed human bronchial epithelial cells, followed by characterization of their functional importance in Cr(VI)-induced tumorigenicity. Our proposed study will investigate the innovative concept that Cr(VI) induces carcinogenesis through dysregulation of the mTOR/4E-BP1-mediated translation initiation process. Elucidating this process will provide novel insights into the biology and clinical relevance of translational regulation in Cr(VI) carcinogenesis. This research will have the added benefit of identifying Cr(VI)-induced translationally-regulated targets for potential preventive or interventional therapy.