Dual roles of USP1 in HELLS deubiquitination and SUMOylation drive EMT and FOLFOX-based chemoresistance.

Although the FOLFOX strategy has demonstrated benefits for tumor patients at advanced stages, chemoresistance remains a significant challenge to therapeutic efficacy. Thus, identifying strategies to overcome chemoresistance and enhance chemotherapy sensitivity is critical for optimizing HAIC-FOLFOX treatment. Comprehensive investigations of deubiquitinating enzymes (DUBs) across multiple bioinformatics cohorts and a local hepatocellular carcinoma (HCC) cohort identified ubiquitin-specific protease 1 (USP1) as a key regulator of HCC progression, correlating with poor survival outcomes. Functional assays demonstrated that USP1 overexpression promotes aggressive phenotypes in HCC cells, including enhanced proliferation, migration, and epithelial-mesenchymal transition (EMT), whereas USP1 inhibitor ML323 suppresses these effects and increases sensitivity to oxaliplatin and fluorouracil (5-FU), the primary agents in FOLFOX, both in vitro and in vivo. Mechanistic studies revealed that USP1 interacted with and stabilized the chromatin-remodeling factor lymphoid-specific helicase (HELLS) through deubiquitinating, thereby facilitating EMT and homologous recombination repair (HRR), thereby driving chemoresistance. Furthermore, USP1 promoted HELLS SUMOylation by stabilizing PIAS1, an E3 SUMO ligase, through deubiquitination and prevention of its ubiquitin-mediated degradation. Importantly, inhibition of SUMOylation significantly attenuated the aggressive effects mediated by USP1. In conclusion, this study highlights the USP1/PIAS1/HELLS deubiquitinating and SUMOylation axis as a critical driver of aggressiveness and DNA damage repair responses in HCC cells, offering a promising therapeutic strategy to suppress HCC progression and enhance the efficacy of FOLFOX-based chemotherapy.