Pyrimidine synthase CAD deamidates and inactivates p53

p53, a critical tumor suppressor, regulates the cell cycle in response to DNA damage and metabolic changes. While p53 stability and activity are predominantly governed by post-translational modifications, the role of deamidation in modulating p53 function remains unclear. This study demonstrates that 6-diazo-5-oxo-L-norleucine (DON) inhibits CAD, a glutamine amidotransferase, to block p53 deamidation, thereby activating the p53 signaling pathway and suppressing tumor cell proliferation. Metabolomic analyses confirmed that DON inhibits CAD-mediated pyrimidine biosynthesis, but this metabolic disruption is not the primary driver of p53 activation. CAD deamidates p53 at N235 and N239, impairing its transcriptional activity and promoting tumor growth. DON restores p53 function by inhibiting CAD's deamidase activity. Clinical data revealed elevated CAD expression in tumors with wild-type TP53, correlating with poor patient survival. Our findings uncover a novel mechanism by which CAD suppresses p53 activity via deamidation and propose that DON treatment may benefit cancer patients with wild-type TP53 and high CAD expression. Overall design: To investigate the impact of DON on gene expression in HCT116 cells, we treated the cells with DON, using DMSO as a control. RNA sequencing (RNA-seq) was then performed, followed by data analysis to compare the differential expression of genes between the two groups.