Hepatitis B virus X protein (HBx) has been found to be overexpressed in liver cancer tissues.492 It acts as a transcriptional co-activator through direct interaction with various proteins, such as the TATA-binding protein, RPB5 subunit of RNA polymerase II, TF IIH, TF IIB, and the proteins of basic domain-leucine zipper (bZIP) family, including the cyclic AMP-response element (CRE)-binding protein (CREB).493 HBx interacts with the co-activators CBP/p300 and cooperates with CBP/p300 in the CREB-mediated activation. This evidence concerns the gene CREB1 and liver cancer.