Mitochondrial ACSS1 regulates the oncometabolite 2-hydroxyglutarate and De Novo Pyrimidine biosynthesis under nutrient-deprived conditions in lymphoma

The mitochondrial Acetyl-CoA synthetase short-chain family member 1 (ACSS1) converts acetate, an energy source in nutrient-deprived conditions, to mitochondrial acetyl-CoA. However, the specific mechanism behind this process remains unknown. Here, we show that ACSS1 is overexpressed in patients with mantle cell lymphoma (MCL), diffuse large B cell lymphoma (DLBCL), chronic lymphocytic leukemia (CLL), and Ibrutinib (IBR)-resistant cell lines. The mitochondrial stress test showed reduced oxygen consumption in ACSS1 knockdown (KD) cell lines. 13C-acetate stable isotope tracing revealed that ACSS1 knockdown (KD) in MCL cell lines attenuates the flux of mitochondrial acetate to acetyl-CoA, acetylcarnitine, and TCA cycle intermediates, including glutamine and aspartate, which are precursors for de novo pyrimidine synthesis. Consistently, there was a decrease in the labeling of glutamate, aspartate, dihydroorotate, and orotate pools in KD cell lines. Pathway analysis revealed the enrichment of de novo pyrimidine synthesis metabolites and depleting ACSS1 impaired cell growth and potential vulnerability of IBR-resistant MCL cells. Further, we discovered that acetate is used to synthesize 2-hydroxyglutarate in an ACSS1-dependent manner, and it is involved in histone methylation. These results highlight a metabolic phenotype in MCL cells, showing their ability to metabolize acetate in nutrient-deprived conditions and provide new insights into the role of ACSS1 in cancer metabolism. SignificanceThe enzyme ACSS1 catalyzes the conversion of acetate, an energy source in nutrient-deprived conditions, to mitochondrial acetyl-CoA. Our results show that ACSS1 may affect cancer metabolism, particularly in MCL. Studies using MCL cell lines showed that reducing ACSS1 activity affects acetate utilization for various metabolic pathways and influences the production of oncometabolite D-2-hydroxyglutarate. Additionally, reducing ACSS1 activity affects the expression of cyclin D1 and inhibits cell growth, highlighting the potential significance of ACSS1 in cancer metabolism.