Targeting Ubiquitin-specific Protease 5 Overcomes Chemoresistance via Negatively Regulating p53 in Gastric Cancer

Background: Resistance to chemotherapy is a major obstacle in the clinical management of gastric cancer, and the mechanisms underlying chemoresistance remain largely unknown. Aims: This study aimed to investigate the involvement of ubiquitin-specific protease 5 (USP5), a deubiquitinating enzyme, in gastric cancer chemoresistance Methods: USP5 expression was analyzed in fifty paired gastric cancer and adjacent normal tissues, chemo-sensitive and chemo-resistant gastric cancer lines using quantitative ELISA. The role of USP5 was determined using loss-of-function and gainof- function methods. USP5-mediated downstream effectors were analyzed using biochemical methods focusing on p53. Results: USP5 expression was comparable in tumors and normal in the majority of the cohort. Following chemotherapy treatment, USP5 expression significantly increased in gastric cancer cells, while p53 levels remained unaltered. Overexpression of USP5 amplified growth and migration while decreasing apoptosis induced by serum withdrawal across multiple gastric cancer cell lines. Conversely, USP5 knockdown effectively heightened gastric cancer sensitivity to paclitaxel and 5-FU treatments, particularly targeting chemo-resistant gastric cancer cells by inhibiting proliferation and migration and inducing apoptosis. Additionally, USP5 knockdown increased levels of p53 but not MDM2, increased p53 activity and increased transcription of p53 target genes. In contrast, USP5 overexpression decreased the level and activity of p53 and inhibited transcription of p53 target genes. The anti-proliferative, anti-migratory, and pro-apoptotic effects of USP5 were significantly diminished upon p53 depletion, highlighting the interplay between p53 and USP5 in regulating gastric cancer cell activities. Additionally, USP5 inhibition suppressed chemo-resistant gastric cancer cell migration via suppressing epithelial-mesenchymal transition (EMT) and RhoA activity. Conclusion: Targeting USP5 inhibition has emerged as a promising alternative therapeutic approach to overcoming chemoresistance in gastric cancer. Additionally, our study sheds light on the novel role of USP5 as a regulator of p53 in gastric cancer.