Effects of HBV X gene and arsenic trioxide on the expression of p53 in cultured HepG2 cells

Background Hepatitis B virus（HBV）X protein（HBx）and p53 could mutually down-regulate at transcriptional level andHBx could bind with p53 protein within its transactivation domain and inhibit the function of p53 protein.In recent years,effects of arsenic trioxide（AsO）on the expression of p53 protein have been widely studied,while little is known aboutthe activity of p53 protein.This study was undertaken to delineate the effect of HBV X gene and AsOon p53 proteinexpression（level and activity）in HepG2 cells by small hairpin RNA（shRNA）-mediated RNA interference（RNAi）technique.Methods Cell line HepG2 and cells with stable expression of HBV X gene（HepG2-X）were treated with 2 μmol/L AsO,with corresponding untreated cells serving as controls.Cell lysates and nuclear extracts were extracted.Total level andthe relative activity of p53 protein were detected by modified enzyme-linked immunosorbent assay（ELISA）.HBV X genesequence-specific shRNA expression vector（pXi-1 and pXi-2）and sequence-unrelated control（pXi-3）were transfectedinto HepG2-X.Single cell clone with stable expression of shRNA was selected and exposed to propagating culture.Theeffect of AsOon p53 protein expression and activity was re-observed.Results Total p53 protein level was up-regulated and its relative activity ratio was enhanced by AsOin HepG2 andHepG2-X cells.The total p53 protein level induced by AsOwas up-regulated by HBV X gene expression,while itsrelative activity was significantly suppressed.The suppression was removed after HBV X gene expression wasrepressed by shRNA.Conclusions AsOup-regulates p53 protein expression and enhance its activity.HBV X up-regulates AsOinduced-p53 protein expression while suppresses its activity.