A Feedback Circuitry between Polycomb Signaling and Fructose-1, 6-Bisphosphatase Enables Hepatic and Renal Tumorigenesis

Abstract Suppression of gluconeogenesis elevates glycolysis and is commonly observed in tumors derived from gluconeogenic tissues including liver and kidney, yet the definitive regulatory mechanism remains elusive. Here, we screened an array of transcription regulators and identified the enhancer of zeste homolog 2 (EZH2) as a key factor that inhibits gluconeogenesis in cancer cells. Specifically, EZH2 repressed the expression of a rate-limiting gluconeogenic enzyme fructose-1, 6-bisphosphatase 1 (FBP1) and promoted tumor growth primarily through FBP1 suppression. Furthermore, EZH2 was upregulated by genotoxins that commonly induce hepatic and renal tumorigenesis. Genotoxin treatments augmented EZH2 acetylation, leading to reduced association between EZH2 and its E3 ubiquitin ligase SMURF2. Consequently, EZH2 became less ubiquitinated and more stabilized, promoting FBP1 attenuation and tumor formation. Intriguingly, FBP1 physically interacted with EZH2, competed for EZH2 binding, and dissembled the polycomb complex. Therefore, FBP1 suppresses polycomb-initiated transcriptional responses and constitutes a double-negative feedback loop indispensable for EZH2-promoted tumorigenesis. Finally, EZH2 and FBP1 levels were inversely correlated in tumor tissues and accurately predicted patient survival. This work reveals an unexpected cross-talk between epigenetic and metabolic events, and identifies a new feedback circuitry that highlights EZH2 inhibitors as liver and kidney cancer therapeutics. Significance: A novel feedback loop involving EZH2 and suppression of the gluconeogenesis enzyme FBP1 promotes hepatocellular cancer growth. See related commentary by Leithner, p. 657