Dysregulation of cell cycle checkpoints is a cancer hallmark, with ubiquitination-controlled protein stability playing a pivotal role. Although p21, a key cyclin-dependent kinase inhibitor, is tightly regulated by ubiquitin-mediated degradation, the key upstream modulators of its ubiquitination remain incompletely defined. Here, we identify poly(ADP-ribose) glycohydrolase (PARG) as a regulator of p21 stability in gastric cancer (GC) cells. We show that PARG expression is markedly upregulated in GC tissues and correlates with poor patient prognosis. Functional assays revealed that genetic depletion of PARG triggers G2/M phase arrest and impairs GC cell proliferation. Mechanistically, we demonstrate that PARG loss enhances p21 PARylation, which disrupts its association with E3 ubiquitin ligase, thereby reducing K48-linked ubiquitination and leading to p21 protein stabilization. Moreover, we identify lysine residues K161 and K163 as critical sites for PARG-mediated regulation of p21 ubiquitination. Our findings reveal a posttranslational regulatory axis in which PARG governs cell cycle progression by modulating the PARylation-dependent ubiquitination of p21. These results broaden the understanding of p21 regulation in cancer and highlight PARG as a potential therapeutic target for GC treatment.
Keywords: Cell biology; Drug screens; Gastric cancer; Gastroenterology; Oncology; Ubiquitin-proteosome system.