Hepatitis B Virus X Interacting Protein (HBXIP)

HBXIP encodes a protein that specifically complexes with the C-terminus of hepatitis B virus X protein (HBx). The function of this protein is to negatively regulate HBx activity and thus to alter the replication life cycle of the virus.The deduced 91-amino acid protein has a calculated molecular mass of 9.6 kD. It contains a putative leucine zipper motif and may form an amphipathic helix. HBXIP also has 2 putative threonine phosphorylation sites. Northern blot analysis detected a 0.7-kb transcript in all tissues tested, with highest expression in skeletal and cardiac muscle.HBXIP expression in differentiated hepatocellular carcinoma cells reduced wildtype HBV replication to levels observed following infection with an HBX-minus virus.