Ubiquitin-specific protease 15 contributes to gastric cancer progression by regulating the Wnt/β-catenin signaling pathway

BACKGROUND Ubiquitin-specific protease 15 (USP15) is an important member of the ubiquitin-specific protease family, the largest deubiquitinase subfamily, whose expression is dysregulated in many types of cancer. However, the biological function and the underlying mechanisms of USP15 in gastric cancer (GC) progression have not been elucidated. AIM To explore the biological role and underlying mechanisms of USP15 in GC progression. METHODS Bioinformatics databases and western blot analysis were utilized to determine the expression of USP15 in GC. Immunohistochemistry was performed to evaluate the correlation between USP15 expression and clinicopathological characteristics of patients with GC. A loss- and gain-of-function experiment was used to investigate the biological effects of USP15 on GC carcinogenesis. RNA sequencing, immunofluorescence, and western blotting were performed to explore the potential mechanism by which USP15 exerts its oncogenic functions. RESULTS USP15 was up-regulated in GC tissue and cell lines. The expression level of USP15 was positively correlated with clinical characteristics (tumor size, depth of invasion, lymph node involvement, tumor-node-metastasis stage, perineural invasion, and vascular invasion), and was related to poor prognosis. USP15 knockdown significantly inhibited cell proliferation, invasion and epithelial-mesenchymal transition (EMT) of GC in vitro, while overexpression of USP15 promoted these processes. Knockdown of USP15 inhibited tumor growth in vivo. Mechanistically, RNA sequencing analysis showed that USP15 regulated the Wnt signaling pathway in GC. Western blotting confirmed that USP15 silencing led to significant down-regulation of beta-catenin and Wnt/beta-catenin downstream genes (c-myc and cyclin D1), while overexpression of USP15 yielded an opposite result and USP15 mutation had no change. Immunofluorescence indicated that USP15 promoted nuclear translocation of beta-catenin, suggesting activation of the Wnt/beta-catenin signaling pathway, which may be the critical mechanism promoting GC progression. Finally, rescue experiments showed that the effect of USP15 on gastric cancer progression was dependent on Wnt/beta-catenin pathway. CONCLUSION USP15 promotes cell proliferation, invasion and EMT progression of GC via regulating the Wnt/beta-catenin pathway, which suggests that USP15 is a novel potential therapeutic target for GC.