We investigate the role of urea cycle dysregulation on cancer genome by perturbing the UC enzymes (over expression or knock-down) in different cancer cell lines.

The urea cycle (UC) is the main pathway by which mammals dispose waste nitrogen. We find that specific alterations in the expression of most UC enzymes occurs in many tumors, leading to a general metabolic hallmark termed UC dysregulation (UCD). UCD elicits nitrogen diversion towards carbamoyl-phosphate synthetase2, aspartate transcarbamylase and dihydrooratase (CAD) activation and enhances pyrimidine synthesis, resulting in detectable changes in nitrogen metabolites in both patient tumors and bio-fluids. The accompanying excess of pyrimidine vs purine nucleotides results in a genomic signature consisting of transversion mutations at the DNA, RNA and protein levels. This mutational bias is associated with more hydrophobic tumor antigens and with a better response to immune checkpoint inhibitors, independent of mutational load. Taken together, our findings demonstrate that UCD is a common feature of tumors, which profoundly impacts carcinogenesis, mutagenesis and immunotherapy response.