Abstract BACKGROUND: Triple-negative breast cancer (TNBC) represents a significant challenge in global breast cancer prevention and treatment due to its aggressive behavior, poor prognosis, and the absence of molecular markers for targeted therapy. There is an urgent need to elucidate its progression mechanisms and identify effective therapeutic targets. This study aimed to investigate the role and mechanism of the tumor promoting factor CYBA (Cytochrome B-245 Alpha Chain) in TNBC progression. Methods: The expression of CYBA in normal tissues, tumor tissues, and adjacent tissues, as well as its correlation with prognosis, was evaluated by analyzing public databases, performing qRT-PCR and Western blot asssays, and conducting immunohistochemistry (IHC). The impact of CYBA on the proliferation of TNBC was assessed using CCK-8 assays, EDU incorporation assays, and subcutaneous xenograft models in nude mice. The role of CYBA of TNBC metastasis was assessed by scratch assay, transwell assay and tail vein injection lung metastasis models. The mechanisms underlying the biological effects of CYBA were investigated through the integrated analysis of LC-MS/MS and RNA-seq data, combined with Western blot validation, immunofluorescence (IF) and immunoprecipitation (CoIP). Results: In patients with breast cancer and TNBC subtypes, those with high CYBA expression exhibited significantly shorter overall survival (OS) and recurrence-free survival (RFS) compared to those with low expression. In vitro and in vivo studies have confirmed that elevated CYBA expression promotes TNBC cell proliferation and metastasis. Drug sensitivity assays revealed that CYBA -overexpressing tumor cells demonstrated resistance to paclitaxel and carboplatin. Mechanistically, CYBA is co-localized in the cytoplasm and interacts with the deubiquitinase USP16, which inhibits CYBA degradation and stabilizes its expression via the deubiquitination pathway, thereby exerting its oncogenic function. Conclusion: USP16 stabilizes the expression of the tumor promoter CYBA through deubiquitination. High expression of CYBA in TNBC is associated with tumor progression, poor prognosis, and resistance to chemotherapy. Targeting the USP16/CYBA axis or inhibiting CYBA expression may represent a therapeutic potential strategy for TNBC. Citation Format: N. Zhang, Y. Huang, S. Zhang, Y. Qin, X. Zeng. Deubiquitinase USP16 stabilizes CYBA expression and promotes progression and chemoresistance in triple-negative breast cancer chemoresistance in triple-negative breast cancer abstract. In: Proceedings of the San Antonio Breast Cancer Symposium 2025; 2025 Dec 9-12; San Antonio, TX. Philadelphia (PA): AACR; Clin Cancer Res 2026;32(4 Suppl):Abstract nr PS2-12-21.
Zhang et al. (Tue,) studied this question.