P28^GANK Enhances Oxidative Stress Tolerance Of HCC Cells By Promoting Detoxifying Enzymes Expression

Part I p28^GANK Enhances Oxidative Stress Tolerance of HCC cell lines by Promoting Detoxifying Enzymes ExpressionTolerance to oxidative stress of cancer cells determines their survival advantage with active proliferation during the pathogenesis and development of hepatocelluar carcinoma (HCC), and also cancer cells' drug resistance in chemotherapy. So finding out critical molecular targets that regulate the oxidative stress tolerance of HCC cells is significant for HCC therapy. p28^GANK is one onco-protein highly expressed in HCC. Our previous study revealed that interfering p28^GANK expression in HCC cell lines induces apoptosis via elevating intracellular ROS level. In the present study, we investigated the expression of p28^GANK under oxidative stress conditions and examined its protential role in modulating HCC cells' tolerance to oxidative stress. Our results confirmed that p28^GANK expression is upregulated both in H₂O₂-induced moderate oxidative stress in HCC cell lines and in DEN-induced oxidative stress in rat HCC model. Furthermore, we demonstrated that p28^GANK protects HCC cells from oxidative stress-induced cell death probably through enhancing ROS-detoxifying enzymes expression, resulting in reduction of intracellular ROS accumulation. In addition, p28^GANK may pomotes cell survival via activating PI3K/AKT pathway under oxidative stress. Part II The oncoprotein p28^GANK establishes a positive feedback loop inβ-catenin signalingGANKYRIN (also known as PSMD10 or p28^GANK) is a novel oncoprotein highly expressed in hepatocellular carcinoma (HCC) and interacts with multiple proteins leading to degradation of tumor suppressor proteins, Rb and p53. p53 was reported to downregulateβ-catenin, but whether p28^GANK is involved in regulation ofβ-catenin is elusive. Herein we report that both growth factors and Ras upregulated p28^GANK expression thrsough the activation of the PI3K-AKT pathway. The induced p28^GANK expression subsequently enhanced the transcription activity ofβ-catenin, and this effect was observed in p53-deficient cells, suggesting a p53-independent mechanism for p28^GANK regulation ofβ-catenin activation. p28^GANK overexpression also increased release of freeβ-catenin into cytoplasm. Interestingly, exogenous expression of p28^GANK resulted in elevated expression of the endogenous protein. The present study also suggested that bothβ-catenin and c-Myc were transcriptional activators of p28^GANK and p28^GANK overexpression correlated with c-Myc, cyclin D1 andβ-catenin was detected in primary human HCC. In aggregate, these results suggest a positive feedback loop for p28^GANK expression, which may play a critical role in tumorigenesis and progression of HCC.