Subcellular localisation of the X protein in HBV infected hepatocytes

Hepatitis B virus X protein (HBx) is a multi-functional protein that exerts its effects primarily by acting as a transcriptional transactivator of vir al and multiple host cell genes. HBx is thought to be essential for maintai ning viral replication and has been implicated in the development of hepato cellular carcinoma in patients chronically infected with hepatitis B virus. Very little is known about its functional mechanisms and although interact ions with several nuclear and cytoplasmic proteins have been demonstrated i n vitro, there is no clear consensus as to where HBx localises in infected hepatocytes, In this study, the expression and intracellular distribution o f HBx were examined in human liver biopsies using an anti-HBx rabbit polycl onal antiserum. HBx was detected in a high proportion (69%) of samples from patients with chronic HBV infection. Detection of HBx correlated with the absence of cirrhosis and the presence of serum e-antigen. HBx was detected predominantly in the cytoplasm; however, it was also found in the nuclei of up to 20% of positively stained hepatocytes, either exclusively nuclear or localised both in the nucleus and cytoplasm within the same cell. Furtherm ore, the intracellular distribution of HBx was analysed in transfected Huh- 7 cells by confocal microscopy, using the monoclonal antibody 16F1. In thes e experiments, a substantial nuclear detection was confirmed in a significa nt proportion of HBx expressing cells. The data indicate a high functional significance of nuclear HBx, consistent with the concept that transactivati on may involve interactions with nuclear proteins. J. Med. Virol. 64:419-42 6, 2001. (C) 2001 Wiley-Liss, Inc.