Arginine methylation coordinates with phosphorylation to regulate NADP ⁺ synthesis

NADK is the sole cytosolic enzyme responsible for synthesizing NADP ⁺ from NAD ⁺ within cells. The homeostasis of NAD ⁺ /NADP ⁺ is controlled by NADK, usually dysregulated in various cancers, yet the precise underlying regulatory mechanisms remain largely unknown. In this study, we discover that PRMT6 methylates NADK at R39, R41, and R45, resulting in the suppression of NADK kinase activity and NADP ⁺ synthesis. Mutations of these sites promote cancer cell proliferation and tumor growth. PRMT6-mediated methylation of NADK coordinates with Akt-mediated phosphorylation to regulate NADK, which stimulates its activity to increase NADP ⁺ production through relief of an autoinhibitory function inherent to its amino terminus. PRMT6 also inhibits NADK activity in a phosphorylation-independent manner. Furthermore, NADK methylation is upregulated by RB1/E2F pathway in high-fat diet mice. Downregulation of NADK methylation in HCC enhances NADP ⁺ production to promote cancer development. Our findings illuminate the molecular regulatory mechanisms governing NAD ⁺ /NADP ⁺ homeostasis, suggesting that the PRMT6-NADK axis emerges as a direct player in high energy state. Furthermore, our research suggests potential therapeutic targets through chemical and genetic interventions.