ZRANB1 promotes cell proliferation and lymph node metastasis through SF3B3-mediated alternative splicing of CHEK2 in urothelial bladder cancer

Urothelial bladder cancer (UBC) poses a considerable threat to public health, and its clinical management is limited by high recurrence rates and a tendency for progression. While dysregulation of the ubiquitin‒proteasome system (UPS) is a hallmark of tumorigenesis, the specific landscape of deubiquitinating enzymes (DUBs) in UBC remains largely underexplored. Multiple transcriptomic datasets were used for a comprehensive screening of ubiquitination-related genes in UBC, and ZRANB1 was identified as a potential oncogenic DUB, whose expression was validated using immunohistochemistry. High ZRANB1 expression was correlated with advanced pathological T stage, lymph node metastasis, and poor overall survival. The oncogenic role of ZRANB1 was assessed by proliferation, migration, and invasion assays in vitro, as well as in subcutaneous xenograft and lymph node metastasis models in vivo. Using immunoprecipitation coupled with mass spectrometry, we revealed that ZRNAB1 acted as a DUB to prevent the UPS-dependent degradation of SF3B3. The ZRANB1-SF3B3 axis subsequently modulates the alternative splicing of the cell cycle checkpoint kinase CHEK2, specifically inhibiting the production of the exon 4-skipped isoform (CHEK2-e4-). We demonstrated that while full-length CHEK2 is permissive for growth, the CHEK2-e4- isoform exerts a potent tumour-suppressive effect. This study reveals a novel post-translational mechanism linking the UPS to the RNA splicing machinery in UBC. ZRANB1 promotes tumorigenesis by stabilizing SF3B3 to prevent the generation of the tumour-suppressive CHEK2-e4- isoform, suggesting that ZRANB1 is a promising prognostic biomarker and therapeutic target.