砷暴露下p50抑制细胞自噬进而上调HIF-1α表达的新发现及机制研究

Arsenic has dual effects in carcinogenic and cancer therapy, which has attracted a great deal of attention and is the hot research spots in the field of environmental health and pharmacology. NFκB consists of five members–NFκB1 (p50), NFκB2 (p52), Rel A (p65), Rel B, and c-Rel. Whereas the p50/p65 heterodimer is the dominant form of NFκB, acting as a transcription factor and regulating downstream gene expression, the p50/p50 homodimer alone does not act as transcription factor for regulating NFκB downstream gene expression. For this reason, the biological functions of p50 are much less frequently studied. Through funding support from National Natural Science Foundation of China, we have carried out the studies related to this topic and have made the first discovery regarding the regulatory effect of p50 on GADD45 protein degradation in NFκB transcription-independent manner. Accumulating results from our subsequent studies demonstrate that the regulatory effect of p50 on p53 protein translation and C-Myc protein degradation, as well as SOD protein transcription are all exclusively dependent on NFκB transcriptional activity. Our published studies demonstrate that low-dose arsenite promotes cell cycle progression, proliferation, and.transformation via the NFκB transcription-dependent induction of Cyclin D1, whereas relatively high doses of arsenite treatment lead to cell apoptosis through the p50-dependent and NFκB transcription-independent induction of GADD45α and p53. Thus, we anticipate that p50-mediated NFκB transcription-dependent and -independent pathways might be a switch for the determination of cell death and survival, which also accounts for the abilities of different concentrations of arsenic to either promote or cure cancer (dual biological effects of arsenite.treatment). Therefore, fully understanding the molecular mechanisms that control the p50-mediated downstream new gene expression and their novel function will provide key information for understanding of nature of arsenic carcinogenic effect as well as for using p50 and its downstream components as targets for cancer prevention and therapy. Our most recent studies have uncovered a novel function of p50 in exhibiting up-regulating HIF-1α protein expression in arsenic exposure, whereas autophagic response due to arsenic exposure contributed to p50-regulated HIF-1α protein expression. Therefore, we will elucidate the molecular mechanism underlying p50 up-regulation of HIF1α in arsenic exposure and its relationship with the dual biological function of arsenic treatment. Success of this proposal will enhance our understanding of the molecular basis of the NFκB transcription-independent novel function of p50. Better insight into this novel function of p50 will enable us to design more effective therapeutic strategies to use arsenite or other new reagents that target p50.

砷化物是一类兼具促癌及治癌双重特性的环境致癌物与抗癌药物，其机制研究是环境卫生等领域的热点。在前期国家自然科学基金项目资助下，我们发现了砷化物可通过调控依赖于p50的p53蛋白翻译等过程而诱发细胞凋亡。然而砷化物展现双重效应的分子机制还远未阐述清楚。我们最新的研究发现砷暴露下p50通过抑制细胞自噬的发生进而促进了HIF-1α的表达。已有研究表明，HIF-1α是一类具有致癌及通过细胞凋亡抑癌的多功能基因，细胞自噬在不同微环境下对癌症的发生发展也起促进或抑制双重功能，因此我们推测新发现对于砷化物效应研究至关重要，但相关机制尚不清楚。本研究旨在阐明砷暴露下p50抑制细胞自噬的分子机制，明确细胞自噬与HIF-1α之间的相互作用关系并进行分子机制研究，进一步揭示其与砷化物双重生物学功能之间的关系。这不仅能够加深我们对p50生物学功能的认识，更有助于砷化物暴露疾病预防及指导砷剂临床安全使用。

砷化物是一类兼具促癌及治癌双重特性的环境致癌物与抗癌药物，其机制研究是环境卫生等领域的热点。在前期国家自然科学基金项目资助下，我们发现了砷化物可通过调控依赖于p5 0的p53蛋白翻译等过程而诱发细胞凋亡。然而砷化物展现双重效应的分子机制还远未阐述清楚 。我们最新的研究发现砷暴露下p50通过抑制细胞自噬的发生进而促进了HIF-1α的表达。已有研究表明，HIF-1α是一类具有致癌及通过细胞凋亡抑癌的多功能基因，细胞自噬在不同微环境下对癌症的发生发展也起促进或抑制双重功能，因此我们推测新发现对于砷化物效应研究至 关重要，但相关机制尚不清楚。本研究利用生物信息技术、细胞生物学技术及分子生物学手段，通过对p50 上调 miR-494 的分子机制研究、miR-494 致 Atg7 表达下调的分子机制研究、系统阐明砷暴露下 p50 抑制细胞自噬促进 HIF-1α 表达的分子机制等重要内容的探索，最终揭示了砷化物毒理新机制：砷化物暴露下，p50 上调 miR-494表达，使 Atg7 表达下调从而抑制细胞自噬的发生，进而抑制了HIF-1α 蛋白的自噬依赖性降解，促进 HIF-1α 蛋白的稳定及表达，最终在砷化物致细胞凋亡或致癌等过程中发挥重要作用。该研究进展不仅加深了我们对NFKB家族中不具有独立转录活性的p50的特有生物学功能的认识，更有助于砷化物暴露疾病预防及指导砷剂临床安全使用。