ASS1 and cancer: Indeed, independent of arginine importance, cancer cells become more proliferative when ASS1 is silenced because of the increased cytosolic availability of its substrate, aspartate, for pyrimidine synthesis by CAD (carbamoyl-phosphate synthase 2, aspartate transcarbamylase and dihydroorotase) (Rabinovich et al., 2015; Moreno-Morcillo et al., 2017).