E2F1 and hepatocellular carcinoma: Clinical analysis also showed a significant correlation of mRNA and protein levels between E2F1 and ISX; however, both ISX and E2F1 mRNA expressions were negatively correlated with RB1 expression in the HCC patients, a finding that highlights the positive cell cycle regulation and oncogenic activity of the ISX–E2F1 axis in HCC (Figure 6B, Tables 1 and 2).