The Dual Regulation Of Autophagy By RMP Depends On The Status Of P53 In Hepatic Malignancy

PART1The dual regulation of autophagy by RMP depends on the status of p53 in hepatic malignancyHepatic malignancy is a severe threat to human health, and the burden continues to increase every year. Liver cancer, which is a common malignant tumor in adult, is the sixth most frequently diagnosed cancer worldwide but the third leading cause of cancer death. Among primary liver cancers, hepatocellular carcinoma (HCC) represents the major histological subtype, accounting for 70% to 85% of the total liver cancer burden worldwide. Hepatoblastoma is the most common pediatric liver malignancy. It is reported that Wnt signaling pathway and Hedgehog signaling pathway are affected in hepatoblastoma. However, the mechanism of hepatic malignancy development remains unclear. Here, we provided evidence that RMP was up-regulated in hepatic malignancy and promoted the proliferation, colony formation while inhibited senescence of hepatic malignant tumor cells. Interestingly, RMP played a dual role in the regulation of autophagy in these cells. RNA Interference of RMP could dramatically up-regulate the expression of wild-type 53 and mutant p53. And immunoprecipitaion assays suggested that RMP might promote the interaction of MDM2 and p53, and ultimately promote the degradation of p53 via ubiquitin-proteasome pathway. However, nuclear p53 was not activated by knockdown of RMP, for the expression of downstream targets genes of p53 was not affected. Furthermore, cytoplasm and nucleus extraction showed that cytoplasmic p53 rather than nuclear p53 increased. It has confirmed that cytoplasmic wild-type p53 can inhibit autophagy and mutant p53 usually acts like an oncogene. Thus, RMP may dual regulate autophagy in a p53-dependent manner.PART2p53 status determines the role of autophagy in the regulation of apoptosis induced by proteasome inhibitor.Autophagy is the major degradation pathway by which cytoplasmic materials are delivered to and degraded in lysosome. It is not also an elimination of damaged or superfluous cell components, but also serves as a dynamic recycling system that provides energy for cellular renovation and homeostasis. However, autophagy can do the opposite-it can also active apoptosis and kill cells. Therefore, the relationship between autophagy and apoptosis has an important role in pathophysiological processes. Proteasome inhibitors can active autophagy and induce apoptosis almost simultaneously. We confirmed that using MG132 in hepatic malignant tumor cells. Nevertheless, pre-activate autophagy by incubating in EBSS, an autophagy inducer, did not affect the apoptosis induced by MG132 in the same way. We determined the expression of molecules associated with autophagy and apoptosis. Autophagy induction positively adjusted apoptosis susceptibility in wild type p53 cells. Meanwhile, autophagy attenuated apoptosis mediated by MG132 in cells with mutant p53 and reversed the degradation of mutp53 protein triggered by MG132. Furthermore, Lyso-Tracker and RT-PCR assay suggested that MG132 induced the degradation of mutp53 through multiple mechanisms.