E2F1 and hepatocellular carcinoma: In addition, in two ISX-inducible hepatoma cells (SK-Hep1 and Huh 7), the mRNA of E2F1 and protein of total E2F1, cell cycle-associated phosphorylated E2F1 (332serine), and cyclin D1–a positive marker of an ISX downstream gene–all were shown to increase 5.6–24.8-fold in a time-dependent manner after the induction of ISX by doxycycline (Dox.; 1 μg/ml) (Figure 1C, 1D and 1E).