Sirtuin 4 Depletion Promotes Hepatocellular Carcinoma Tumorigenesis Through Regulating Adenosine-Monophosphate-Activated Protein Kinase Alpha/Mammalian Target of Rapamycin Axis in Mice.

ABSTRACT

Sirtuin 4 (SIRT4) has been reported to play a vital role in the maintenance of glutamine catabolism and adenosine triphosphate (ATP) homeostasis, but its character in hepatocellular carcinomas (HCCs) remains obscure. In this study, we observed low expression of SIRT4 in both HCC cell lines and HCCs from patients. Decreased disease-free survival time is associated with low tumor levels of SIRT4 in patients. Deficiency of SIRT4 facilitated liver tumor development and lung metastasis in xenografts and knockout (KO) mice by promoting colony formation and migration of hepatoma cells and enhancing sphere formation of HCCs. Mechanistically, SIRT4 deletion augmented mammalian target of rapamycin (mTOR) signaling by inactivating adenosine-monophosphate (AMP)-activated protein kinase alpha (AMPKα) through regulation of glutamine catabolism and subsequent AM)/liver kinase B1 (LKB1) axis. Blockage of mTOR by rapamycin or inhibition of glutaminolysis abolished the discrepancy in tumorigenic capacity between SIRT4-depleted hepatoma cells and control cells. Suppression of LKB1 or promotion of AMP by metformin also abrogated the hyperproliferative phenotype caused by SIRT4 loss, which further confirmed that the LKB1/AMPKα/mTOR axis is required in SIRT4-deficiency-promoted HCC tumorigenesis. Conclusion: SIRT4 could exert its tumor suppressive function in HCC by inhibiting glutamine metabolism and thereby increasing the adenosine diphosphate (ADP)/AMP levels to phosphorylate AMPKα by LKB1, which blocks the mTOR signaling pathway.