Arginine methylation coordinates with phosphorylation to control NADP+ synthesis

The NAD(H)/NADP(H) ratio is essential for maintaining cellular redox homeostasis. NAD kinase (NADK) is the sole cytosolic enzyme responsible for converting NAD + to NADP + . Dysregulation of NADK has been linked to aging and cancer; however, the underlying regulatory mechanisms remain poorly understood. Here, we show that NADP + synthesis is markedly suppressed in mice fed a high-fat diet. Mechanistically, NADK undergoes PRMT6-mediated arginine methylation at residues R39, R41, and R45, which inhibits its kinase activity and reduces NADP + production. Mutations at these sites enhance cancer cell proliferation and tumor growth. PRMT6-dependent methylation antagonizes Akt-mediated phosphorylation to inhibit NADK activity by promoting an autoinhibitory function within its N-terminal region, thereby inhibiting NADP + synthesis. In addition, PRMT6 can suppress NADK activity in a phosphorylation-independent manner. NADK methylation is further upregulated by the RB1/E2F pathway in response to a high-fat diet. In hepatocellular carcinoma, reduced NADK methylation elevates NADP + levels and facilitates tumor progression. Collectively, these findings elucidate a regulatory mechanism governing NAD(H)/NADP(H) homeostasis and identify the PRMT6–NADK axis as a critical mediator of cellular adaptation to high-fat diets and increased adiposity.