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

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.

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。

p50是NFκB家族的一员，由于缺乏转录激活单元而不具直接转录活性，致使人们对其生物学功能知之甚少。我们利用基因敲除及表达重建技术发现p50在砷暴露时具有上调原癌基因c-Myc蛋白表达的新功能，但p50并不影响c-Myc的mRNA水平，有别于经典的NFκB活性参与的调控机制。而后我们筛选发现p50能够抑制c-Myc蛋白降解的关键E3泛素连接酶FBW7 的表达，推测其可能参与调控了这一生物学过程，但相关调控机制及所介导的生物学功能仍是未解之谜。通过该项目资助，系统证实了p50抑制c-Myc蛋白降解的新生物学功能，鉴定了FBW7系介导砷暴露下p50抑制c-Myc蛋白降解的中间信号分子，揭示了p50抑制FBW7表达是通过抑制转录调控因子E2F1表达进而抑制FBW7的基因转录而实现的，阐明了p50调控FBW7的分子机制，明确了p50/c-Myc及其中间信号分子FBW7有显著促进细胞凋亡的生物学功能，并发现了p50/c-Myc新信号通路与早期发现的p50/GADD45α信号通路的交叉反应，进一步拓展了砷暴露下p50调控的生物学功能及分子机制调控网络。本课题的研究不仅加深了我们对p50功能的全面认识，而且对靶向p50/c-Myc新通路及中间信号分子的抗癌药物研发与砷剂临床安全有效使用提供了理论依据。