Deubiquitinase USP45 stabilizes RTCB and DDX1, promoting tumorigenesis and chemoresistance

The RNA Ligase RTCB and DEAD-box helicase DDX1 regulate critical processes including MicroRNA maturation and DNA repair, with emerging roles in tumorigenesis and chemoresistance. However, their post-translational regulatory mechanisms remain elusive. Here, we identify the Deubiquitinase USP45 as a central coordinator that interacts and co-localizes with RTCB and DDX1. USP45 directly removes polyubiquitin chains from both proteins, thereby stabilizing RTCB and DDX1 in a substrate-specific manner. Notably, USP45-mediated DDX1 deubiquitination requires RTCB, whereas RTCB deubiquitination is DDX1-independent, revealing an asymmetric regulatory hierarchy. Functionally, USP45 cooperates with RTCB and DDX1 to regulate tumor-associated phenotypes in both cellular and murine models, including promoting cell proliferation through RTCB-dependent DDX1 deubiquitination and enhancing chemoresistance through both RTCB- and DDX1-driven pathways. Clinical bioinformatics analyses further reveal that elevated expression of USP45, RTCB, and DDX1 correlates with poor patient survival. Our findings establish the USP45-RTCB-DDX1 axis as a dual driver of oncogenesis and chemoresistance via specific RTCB/DDX1 post-translational stabilization, nominating USP45 inhibition as a therapeutic strategy to suppress Cancer progression and overcome treatment resistance.