Fructose-1,6-Bisphosphate Aldolase B Depletion Promotes Hepatocellular Carcinogenesis Through Activating Insulin Receptor Signaling and Lipogenesis

Abstract

Background and aims: Insulin receptor (IR) transduces cell surface signal through phosphoinositide 3-kinase (PI3K)-AKT pathways or translocates to the nucleus and binds to the promoters to regulate genes associated with insulin actions, including de novo lipogenesis (DNL). Chronic activation of IR signaling drives malignant transformation, but the underlying mechanisms remain poorly defined. Down-regulation of fructose-1,6-bisphosphate aldolase (ALDO) B in hepatocellular carcinoma (HCC) is correlated with poor prognosis. We aim to study whether and how ALDOB is involved in IR signaling in HCC.

Approach and results: Global or liver-specific ALDOB knockout (L-ALDOB^-/- ) mice were used in N-diethylnitrosamine (DEN)-induced HCC models, whereas restoration of ALDOB expression was achieved in L-ALDOB^-/- mice by adeno-associated virus (AAV). ¹³ C₆ -glucose was employed in metabolic flux analysis to track the de novo fatty acid synthesis from glucose, and nontargeted lipidomics and targeted fatty acid analysis using mass spectrometry were performed. We found that ALDOB physically interacts with IR and attenuates IR signaling through down-regulating PI3K-AKT pathways and suppressing IR nuclear translocation. ALDOB depletion or disruption of IR/ALDOB interaction in ALDOB mutants promotes DNL and tumorigenesis, which is significantly attenuated with ALDOB restoration in L-ALDOB^-/- mice. Notably, attenuated IR/ALDOB interaction in ALDOB-R46A mutant exhibits more significant tumorigenesis than releasing ALDOB/AKT interaction in ALDOB-R43A, whereas knockdown IR sufficiently diminishes tumor-promoting effects in both mutants. Furthermore, inhibiting phosphorylated AKT or fatty acid synthase significantly attenuates HCC in L-ALDOB^-/- mice. Consistently, ALDOB down-regulation is correlated with up-regulation of IR signaling and DNL in human HCC tumor tissues.

Conclusions: Our study reports a mechanism by which loss of ALDOB activates IR signaling primarily through releasing IR/ALDOB interaction to promote DNL and HCC, highlighting a potential therapeutic strategy in HCC.