BCLB,Methylated In Hepatocellular Carcinoma,is A Starvation Stress Sensor Inducing Apoptosis And Autophagy Through AMPK-mTOR Signaling Cascade

Hepatocellular carcinoma(HCC)is one of the most common cancers and the third most common cause of tumor-related death.Recently,more and more reports indicate that epigenetic disruption of tumor suppressor genes(TSGs),especially DNA methylation,play a key role in HCC development.Purpose:We studied the inactivation of BCLB through promoter methylation,and explored its functions in the pathogenesis of these cancers.Methods:BCLB methylation was evaluated by methylation specific PCR and bisulfite genome sequencing.BCLB expression was determined by semi-quantitative RT-PCR and immunohistochemistry.The effects of BCLB on the migration,aopoptosis and autophagy of tumor cells were tested.Results:BCLB was hypermethylated in all the HCC tumor cell lines with silenced or reduced expression,also in most of the HCC tumors.Only 44.8%(47/105)of HCC tumors showed high expression,while the percentage in para-normal tissues were91.4%(96/105).BCLB protein expression in para-normal tissues was significantly higher than in tumors(p=0.04).Negative BCLB protein expression was significantly correlated higher HBV infection(p=0.036),higher AFP level(p=0.048),bigger tumor size(p=0.006)and worse tumor TNM stage(p=0.022).Besides,negative BCLB expression indicated poor 5-year overall survival rate and disease-free survival rate(p=0.032,p=0.027,respectively).Restoring BCLB expression promoted cell autophagy and apoptosis induced by starvation,through AMPKa-mTOR pathway.Also reexpress BCLB inhibited tumor cell migration and inhibited tumor formation or growth in vivo.Conclusions:BCLB might act as a candidate tumor suppressor and is regulated by promotor hypermethylation.Restoring BCLB expression promoted cell autophagy induced by starvation,and inhibited tumor cell migration tumor formation or growth in vivo.