E2F1 and hepatocellular carcinoma: Although E2f2, E2f3 and E2f4 protein expression levels are mostly unaltered, we found that E2f1 expression increases in TKO HCC compared with control livers (Fig. 6a; an average of 2.61-fold induction for E2f1 compared with controls, 1.07- for E2f2, 1.3- for E2f3 and 0.84-fold induction for E2f4).