USP49 promotes the malignancy of triple-negative breast cancer cells by regulating PKMYT1 ubiquitination and stability.

Triple-negative breast cancer (TNBC) is an aggressive subtype of breast cancer (BC) that lacks effective targeted therapies. PKMYT1, a membrane-associated kinase involved in G2/M cell cycle regulation, is overexpressed in BC and associated with poor prognosis. However, the post-translational mechanisms regulating PKMYT1 stability remain largely unknown. In this study, we identified USP49 as a key deubiquitinase regulating PKMYT1 protein stability. Bioinformatic analysis of publicly available TNBC transcriptomic datasets revealed that USP49 is significantly overexpressed in TNBC tissues and correlates with unfavorable clinical outcomes. Consistently, USP49 expression was elevated in multiple TNBC cell lines. Functional assays demonstrated that USP49 knockdown reduced cell viability and colony formation, disrupted cell cycle progression, increased apoptosis, and suppressed migration and invasion. Mechanistically, USP49 was shown to interact with PKMYT1, limiting its ubiquitination and subsequent degradation. Overexpression of PKMYT1 restored the malignant phenotypes of USP49-deficient TNBC cells. Collectively, these findings uncover a novel USP49-PKMYT1 regulatory axis that drives TNBC progression.