NNMT/1‐MNA Promote Cell‐Cycle Progression of Breast Cancer by Targeting UBC12/Cullin‐1‐Mediated Degradation of P27 Proteins

Abstract Cell cycle dysregulation is a defining feature of breast cancer. Here, 1‐methyl‐nicotinamide (1‐MNA), metabolite of nicotinamide N‐methyltransferase(NNMT) is identified, as a novel driver of cell‐cycle progression in breast cancer. NNMT, highly expressed in breast cancer tissues, positively correlates with tumor grade, TNM stage, Ki‐67 index, and tumor size. Ablation of NNMT expression dramatically suppresses cell proliferation and causes cell‐cycle arrest in G0/G1 phase. This phenomenon predominantly stems from the targeted action of 1‐MNA, resulting in a specific down‐regulation of p27 protein expression. Mechanistically, 1‐MNA expedites the degradation of p27 proteins by enhancing cullin‐1 neddylation, crucial for the activation of Cullin‐1‐RING E3 ubiquitin ligase(CRL1)—an E3 ubiquitin ligase targeting p27 proteins. NNMT/1‐MNA specifically up‐regulates the expression of UBC12, an E2 NEDD8‐conjugating enzyme required for cullin‐1 neddylation. 1‐MNA showes high binding affinity to UBC12, extending the half‐life of UBC12 proteins via preventing their localization to lysosome for degradation. Therefore, 1‐MNA is a bioactive metabolite that promotes breast cancer progression by reinforcing neddylation pathway‐mediated p27 degradation. The study unveils the link between NNMT enzymatic activity with cell‐cycle progression, indicating that 1‐MNA may be involved in the remodeling of tumor microenvironment.