Regulation Of Autophagy By Apoptosis Stimulating Protein Of P53(ASPP2) Genes

Hepatocellular carcinoma is one of the most common cancers in the world. Infection by hepatitis B and C viruses, exposure to aflatoxin B1, and cirrhosis of any etiology is considered as the major risk factor for the development of HCC. The ability to diagnose and treat of HCC is limited. To date, surgery offers the major HCC treatment, but improvement of long-term survival is urgently needed. The poor prognosis of HCC is largely due to the high recurrence after operation and resistance to chemotherapy. Therefore, It is necessary to identify new clues for understanding of hepatocarcinogenesis and to explore new targets for the diagnosis of HCC and the development of effective therapeutic strategies.ASPP2 is the first identified member in ASPP(apoptosis stimulating proteins of p53) family of proteins, which regulate apoptosis through interaction with p53 and its family members. ASPP2 plays a vital role in tumorgenesis and tumor progress in various cancers. Our group has demonstrated in the previous studies that slience of ASPP2 expression promotes tumor growth and metastasis in hepatocellular carcinoma. It has been reported that ASPP2 might bind with ATG6(Beclin1) in a proteomic analysis of the autophagy interaction network. Here we investigate the regulation of autophagy by ASPP2 in HCC.Autophagy is a regulated lysosomal degradation pathway. It is a process of bulk degradation of proteins and organelles in cytoplasm. Autophagy widely exists in the normal physiological process. According to some reports, autophagy has duel functions in cellular response. But the physiological function of autophagy is to maintain the intracellular homeostatisis. Autophagy is a rapid adaptive response of cells to exogenous stress including nutrition deprivation, oxidative stress, cytoplasmic components damage, and so on. Recent studies have suggested that autophagy plays an important role in the development and progress of cancer.Firstly, we observe the autophagy phemonenon by Transmission electron microscopy, GFP-LC3 dots analysis, Western blotting and RT-PCR in HCC cells with ASPP2 knock-down or ASPP2 overexpression. The results show that ASPP2 can inhibit autophagy in HCC. Secondly, we investigate the mechanisms of autophagy regulated by ASPP2 with Western blotting, RNA interference and Co-IP. The results verify that ASPP2 regulates autophagy through the AMPK/mTOR dependent pathway. Meanwhile, ASPP2 can bind to Beclin-1 and inhibits Beclin-induced autophagy. In the third section we explore the effects of ASPP2-regulated autophagy on cell growth, lipid metabolism and ATP storage. The results show that depletion of ASPP2 decreases lipid storage and attenuates ATP depletion by activating autophagy during nutrition deprivation and favours survival of HCC cells. In order to determine whether ASPP2 deletion contributes to chemoresistance of hepatoma cells through activating autophagy, we examine the chemoresistance of hepatoma cells in vitro and in vivo. The results indicate that autophagy induced by silence of ASPP2 contributes to the chemoresistance of HCC. In the final section, the expression of ASPP2 and Beclin-1 were analysed in 99 HCC tissues and compared with the clinicopathological features of the patients. A significant negative correlation between the expression and Beclin-1 is observed(P=0.013). HCC with absence of ASPP2 expression and high level of Beclin-1 expression levels are more frequently found in tumor with large size(P=0.023) and high grade of AJCC stage(P=0.044). The results indicate that ASPP2 negatively regulates Beclin-1, which might be involved in the progress of HCC.In conclusion, we demonstrate the decreased ASPP2 expression in HCC facilitates the survival of tumor cells through activation of autophagy under starvation, which is involved in the growth of tumor cells and chemoresistance of tumor cells. The results provide a new insight in the development of anti-cancer therapy.