Abstract: In various cancers, abnormal USP9X expression is involved in tumor genesis, progression, apoptosis, and metastasis. However, the relationship between USP9X abnormal expression and cisplatin resistance in nasopharyngeal carcinoma (NPC) cells remains unclear. Using qRT-PCR and western blot, we detected the expressions of USP9X and β-catenin in NPC cells. The effects of USP9X on cell cisplatin resistance, proliferation, apoptosis, and metastasis were examined by CCK-8 assay, flow cytometry, wound-healing assay, and Transwell chamber assay. Co-IP assay, qRT-PCR, and western blot were performed to explore the detailed molecular mechanism of USP9X-β-catenin and its effect on the protein levels of MDR1, MRP2, Bcl-2, Bax, MMP2, and MMP9. We found that USP9X and β-catenin expressions in cisplatin-resistance cell lines (HNE1/DDP) were much higher than cisplatin-sensitive cell lines (HNE1) at both mRNA and protein levels. Co-IP assay demonstrated that USP9X was immunoprecipitated with β-catenin in NPC cells. Knockdown of USP9X was able to partially reverse cisplatin-resistance, increased cisplatin-induced apoptosis, and decreased the capacities of proliferation, migration, and invasion. Overexpression of USP9X can increase cisplatin resistance in NPC cells. Moreover, knockdown of USP9X expression can significantly reduce the expressions of MDR1, MRP2, Bcl-2, MMP2, and MMP9, but significantly increased the expression of Bax. These findings indicate that USP9X high expression plays a significant part in cisplatin-resistance of NPC. This study elucidated the possible mechanism of cisplatin resistance in NPC cells and may have implications for the therapeutic reversal of cisplatin resistance.
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