DDIT3, OTUB2, and ASS1 regulate arginine biosynthesis in colorectal cancer cells under arginine deficiency

Argininosuccinate synthetase 1 (ASS1) is a rate-limiting enzyme in arginine biosynthesis, and its stability is regulated by TRAF2-mediated ubiquitination. Here, we report OTUB2 as a major deubiquitinase to stabilize ASS1, resulting increased arginine biosynthesis in colorectal cancer (CRC) cells; OTUB2 expression is elevated in CRC tissue, and patients with high OTUB2 expression exhibit shorter overall survival. As such, ectopic expression of OTUB2 promotes growth of CRC cells and xenograted tumors and accelerates cell migration and lung metastasis. Moreover, arginine deprivation induces marked expression of OTUB2 in CRC cells; mechanistically, arginine deprivation can activate AMPK, which in turn phosphorylates DDIT3, resulting its disassociation from C/EBPα and subsequent translocation into the cytoplasm and leading to increased binding of C/EBPα to the proximal promoter region of OTUB2 gene. Together, these data uncover a signaling pathway constituted of AMPK- DDIT3-C/EBPα-OTUB2-ASS1 to sense arginine deficiency and stimulate a metabolic compensatory pathway to sustain arginine homeostasis in CRC cells.