EFFECT OF HEPATITIS-B VIRUS X-PROTEIN ON THE EXPRESSION OF RETINOBLASTOMA GENE-PRODUCT

Hepatitis B virus X protein (HBX) was studied for its capacity to form a specific complex with the retinoblastoma tumour suppressor protein (pRB), and for its effect on the expression of pRB. HEX was synthesize d by in vitro transcription and translation in the presence of [S-35]m ethionine. The synthesized HEX was assayed for its binding to a glutat hione-S-transferase (GST)-pRB fusion protein bound to Sepharose beads. The in vivo binding was investigated by a co-immunoprecipitation and Western blot analysis of the cell extract from a CMV-HBX-transfected h epatoblastoma cell line, Hep G2 cells. These experiments demonstrated that HEX was unable to form a detectable complex with pRB. However, th e level of pRB increased considerably in Hep G2 cells transfected with CMV-HBX clone. The alteration of pRB expression by HEX could be a mec hanism, contributing to the development of hepatocellular carcinoma (H CC) in human.