砷暴露下NFκB1(p50)新功能—抑制c-Myc蛋白降解的发现及分子机制研究

p50是NFκB家族的一员，因缺乏转录激活单元而不具直接的转录活性，人们对其生物学功能知之甚少。我们前期研究发现：p50在砷暴露时不仅为原癌基因c-myc表达所必需，而且具有上调c-myc蛋白水平的新功能，但p50并不影响c-myc的mRNA水平，有别于NFκB参与的经典调控机制；泛素连接酶FBW7E3是调节c-Myc蛋白降解的关键酶，p50则能够抑制FBW7的表达、进而抑制c-Myc蛋白的降解，但相关作用机制及其所介导的生物学功能尚未明确。因此，我们拟利用基因敲除、基因表达重建、ChIP，RNA-IP，同位素示踪等技术，阐明砷暴露时p50调控c-Myc 表达的分子机制，并揭示这一新信号通路的潜在生物学意义。本课题不仅能加深我们对p50功能的全面认识，而且有助于研发针对p50/c-Myc信号通路及中间信号分子的靶向抗癌药物，并为砷剂在临床的安全有效使用提供理论依据。

NFκB is a well-known transcription factor in regulation of multiple functions, and most of them are shown rely on transcriptional activity of the p65/RelA subunit. But due to lack transcriptional activation domain, the roles of another ubiquitously expressed subunit, NFκB1 (p50), remains largely unknown. Here we found a novel biological-function of p50, regulating oncogenic c-myc protein accumulation upon arsenite treatment. As our prelimitary results, p50 is required for c-Myc expression after arsenite exposure. Depletion (p50-/-) of p50 significantly blocked arsenite-induced c-Myc expression, and the effects could be restored by adenovivus infection which expressed HA-p50. Subsequent studies suggested that the c-myc mRNA are at comparable levels between WT and p50-/- cells. Whereas p50 attenuated c-Myc protein degradation, demonstrating the major reason of p50 increased c-Myc-expression through suppression of c-Myc degradation. Moreover, we identified p50 was important for down-regulation of Fbw7 expression, which is an important E3 ligase component for c-Myc ubiquination and degradation, but related molecular mechanism of this process and mediated roles of p50 in regulation of bio-function still unclear.The information gained from these studies will also enable us to explore the potential contribution of the p50/c-Myc pathway in preventing cells from abnormal cell growth and carcinogenesis due to arsenite exposure.Furthermore, we also reveal a new function of p50, and in turn, provide information for the use p50,c-Myc or FBW7 as targets for cancer chemoprevention andtherapy. Thus, the studies will have a significant impact in cancer prevention and therapy.