SIRT4 Controls Acetyl-CoA Synthesis to Promote Stemness and Invasiveness of Hepatocellular Carcinoma through Deacetylating MCCC2

SIRT4 is well-known as a tumor suppressor by controlling several metabolic pathways, although it is highly expressed in certain cancers including hepatocellular carcinoma (HCC). Here, we reported that SIRT4 was highly expressed in the voltage-gated calcium channel α2δ1 subunit-positive HCC tumor-initiating cells (TIC), and was upregulated by α2δ1-mediated calcium signaling. Moreover, the expression of SIRT4 in HCC tissues was predictive of poor prognosis of the patients. Interestingly, SIRT4 was functionally sufficient and indispensable to promote TIC properties and invasiveness of HCC cells by directly deacetylating the leucine catabolism pathway enzyme-3-methylcrotonyl-CoA carboxylase 2 (MCCC2) at K269, leading to the formation of a stable MCCC1/MCCC2 complex with robust MCCC enzymatic activity to produce more acetyl-CoA, which resulted in increased H3K27 acetylation and stem cell-like properties at doses≤2 µM. However, 10 µM acetyl-CoA was neither able to enhance H3K27 acetylation, nor to promote stem cell-like properties, while forced expression of SIRT4 in α2δ1⁺ cells resulted in retardation of tumor growth <i>in vivo</i>. Thus, SIRT4 serves as an oncogene to promote stemness and invasiveness by controlling the production of acetyl-CoA, linking α2δ1-mediated calcium signaling to SIRT4-mediated epigenetic reprogramming of HCC TICs which hold significant potential for the development of novel therapeutic strategies targeting TICs, and the dual roles of SIRT4 in HCC might be dependent on the production levels of acetyl-CoA.