The transcriptional function of the hepatitis B virus X protein and its role in hepatocarcinogenesis (Review)

The hepatitis B virus (HBV) encodes a 16.5 kDa multifunctional protein term ed pX or HBx, required for transcription of the viral genome and implicated in the development of hepatocellular carcinoma (HCC) in chronic HBV-infect ed patients. However, the mechanism of pX-mediated hepatocarcinogenesis rem ains unknown. pX is a multifunctional protein exhibiting a number of activi ties affecting transcription, cell growth, and apoptotic cell death. Althou gh pX does not directly bind DNA, pX is regarded as a promiscuous transacti vator, acting via a dual mechanism: in the cytoplasm, pX activates mitogeni c signaling cascades; in the nucleus, pX interacts directly with members of the bZip class of transcription factors and with specific components of th e basal transcriptional apparatus. The focus of this review is to describe the transactivation function of pX and its role in hepatocarcinogenesis.