CELL-CYCLE REGULATION OF NUCLEAR-LOCALIZATION OF HEPATITIS-B VIRUS CORE PROTEIN

The hepatitis B virus (HBV) core protein has been found in the nucleus , the cytoplasm, or both of HBV-infected hepatocytes. However, the mec hanism that regulates the subcellular localization of the HBV core pro tein is still unclear. In this report, we demonstrate that nuclear loc alization of the HBV core protein is cell cycle-regulated in two diffe rent cell lines. The amount of the core protein in the nucleus was inc reased during the G1 phase, reduced to an undetectable level during th e S phase, and increased again when the cells were confluent and cease d to grow. Thus, the nuclear localization of the core protein during H BV infection can be at least partially attributed to liver injury and regeneration, which cause the hepatocytes to enter cell cycles. Based on the observation that the cytoplasmic core protein was phosphorylate d and the nuclear core protein was not, we speculate that nuclear loca lization of the HBV core protein is negatively regulated by phosphoryl ation during the cell cycle.