The Role Of Myeloid Cell Leukemia-1 In HBx-or Free Fatty Acid-induced Apoptosis

Background & Aims:Many studies provide strong evidence of the critical role of hepatitis B virus X(HBx) in human hepatocarcinogenesis.Although the association of HBx with apoptosis has been widely investigated,the exact role of HBx in modulating apoptotic process remains controversial.Here,we examined whether HBx exerts its apoptosis- promoting effects via dysregulation of Mcl-1 expression.Methods:Apoptotic cell death and the expression of Bcl-2 family proteins were determined in HBx-expressing hepatic cell lines and HBx transgenic mice. Immunohistochemistry and immunoblotting were performed to evaluate the expression of Mcl-1 in hepatocellular carcinoma(HCC) samples with or without hepatitis B virus(HBV) infection.Results:Ectopic expression of HBx rendered cell susceptible to death signals in response to cisplatin,which relied on the loss of Mcl-1.Caspase-3 inhibitors,but not JNK,P38,GSK-3βor proteasome inhibitors,effectively abrogated HBx-enhanced Mcl-1 degradation as well as cell apoptosis.Antioxidant treatment demonstrated that reactive oxygen species(ROS) triggered caspase-3-mediated Mcl-1 turnover in this model.Moreover,HBx sensitized cells to ROS-induced apoptotic killing also through activating caspase-3/Mcl-1 signaling.This pathway may be a general signal,as it was also observed in HBx transgenic mice in which HBx-primed Mcl-1 degradation and hepatocyte apoptosis were enhanced during liver ischemia/reperfusion(I/R),and was further supported by immunohistochemical and immunoblot data in HBV-related HCCs.Conclusions:We suggested that ROS/caspase-3/Mcl-1 pathway plays a dominant role in HBx-promoted cell apoptosis,which may shed a new light on the molecular mechanism of HBx-mediated hepatocarcinogenesis. Background & Aims:Non-alcoholic fatty liver disease(NAFLD) is the most common liver disease and affects millions of people worldwide.Elevated serum free fatty acids(FFAs) and hepatocyte lipoapoptosis are features of non-alcoholic fatty liver disease.It is well established that free fatty acid(FFA)-induced lipotoxicity plays a pivotal role in the pathogenesis of NAFLD.However,the mechanism by which FFAs mediate lipoapoptosis remains unclear.Here,we explored whether the antiapoptotic Bcl-2 family member Mcl-1 plays a role in FFAs-mediated hepatocyte lipoapoptosis.Methods:Multiple hepatocyte cell lines were treated in culture with monounsaturated fatty acids and saturated fatty acids.Apoptotic cell death,caspase activity and the expression of antiapoptotic Bcl-2 family members were determined using Western blot and caspase activity assay.Results:Apoptosis was greater during exposure to palmitic acid versus oleic acid. Protein levels of Mcl-1,but not Bcl-xL or Bcl-2 were decreased during palmitic acid-induced apoptosis in a time-dependent manner.Mcl-1 overexpression dramatically prevented palmitic acid-induced apoptosis.Conversely,Mcl-1 downregulation further enhanced palmitic acid toxicity.Neither antioxidant nor pancaspase inhibitor was able to abrogated palmitic acid-enhanced Mcl-1 downregulation.Importantly,JNK activation was enhanced during exposure to palmitic acid and Inhibition of JNK,pharmacologically,effectively blocked hepatocyte lipoapoptosis triggered by palmitic acid.Conclusions:We suggested that JNK/Mcl-1 pathway plays a major role in palmitic acid-mediated hepatocyte lipoapoptosis,which may provide novel insights into the pathogenesis of NAFLD.