CYTOPLASMIC RETENTION OF THE P53 TUMOR-SUPPRESSOR GENE-PRODUCT IS OBSERVED IN THE HEPATITIS-B VIRUS-X GENE-TRANSFECTED CELLS

It has been suggested that hepatitis B virus (HBV) X gene activates X gene expression by disrupting the function of p53 tumor suppressor gen e (Takada et al., 1996). To find out their connection, effect of X pro tein expression on the nuclear localization of p53 protein in human he patoma cells was examined by the immunofluorescent double-staining tec hnique. The location of transiently-expressed p53 protein was examined in X gene-transfected cells, where X protein was detected in the cyto plasm. The nuclear location of transiently-expressed p53 protein was c hanged to the cytoplasm by X protein co-expression. Endogenous p53 pro tein was also observed in the cytoplasm by X protein expression. The t ranscriptional activation domain of X protein and the carboxy-terminal region of p53 protein were found mutually responsible for the cytopla smic retention of p53 in X gene-transfected cells. Therefore, the cyto plasmic retention of p53 protein may be closely correlated to the func tion of X protein expressed in transfected cells.