E2F1 and E2F2-Mediated Repression of CPT2 Establishes a Lipid-Rich Tumor-Promoting Environment.

Abstract

Lipid metabolism rearrangements in nonalcoholic fatty liver disease (NAFLD) contribute to disease progression. NAFLD has emerged as a major risk for hepatocellular carcinoma (HCC), where metabolic reprogramming is a hallmark. Identification of metabolic drivers might reveal therapeutic targets to improve HCC treatment. Here, we investigated the contribution of transcription factors E2F1 and E2F2 to NAFLD-related HCC and their involvement in metabolic rewiring during disease progression. In mice receiving a high-fat diet (HFD) and diethylnitrosamine (DEN) administration, <i>E2f1</i> and <i>E2f2</i> expressions were increased in NAFLD-related HCC. In human NAFLD, E2F1 and E2F2 levels were also increased and positively correlated. <i>E2f1</i> ^-/- and <i>E2f2</i> ^-/- mice were resistant to DEN-HFD-induced hepatocarcinogenesis and associated lipid accumulation. Administration of DEN-HFD in <i>E2f1</i> ^-/- and <i>E2f2</i> ^-/- mice enhanced fatty acid oxidation (FAO) and increased expression of <i>Cpt2</i>, an enzyme essential for FAO, whose downregulation is linked to NAFLD-related hepatocarcinogenesis. These results were recapitulated following <i>E2f2</i> knockdown in liver, and overexpression of <i>E2f2</i> elicited opposing effects. E2F2 binding to the <i>Cpt2</i> promoter was enhanced in DEN-HFD-administered mouse livers compared with controls, implying a direct role for E2F2 in transcriptional repression. In human HCC, <i>E2F1</i> and <i>E2F2</i> expressions inversely correlated with <i>CPT2</i> expression. Collectively, these results indicate that activation of the E2F1-E2F2-CPT2 axis provides a lipid-rich environment required for hepatocarcinogenesis. SIGNIFICANCE: These findings identify E2F1 and E2F2 transcription factors as metabolic drivers of hepatocellular carcinoma, where deletion of just one is sufficient to prevent disease. GRAPHICAL ABSTRACT: http://cancerres.aacrjournals.org/content/canres/81/11/2874/F1.large.jpg.