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 challenged by high recurrence rates and tendency to progression. While dysregulation of the ubiquitin-proteasome system (UPS) is a hallmark of tumourigenesis, the specific landscape of deubiquitinating enzymes (DUBs) in UBC remains largely underexplored. Multiple transcriptomic datasets were applied for a comprehensive screening of ubiquitination-related genes in UBC. And ZRANB1 was identified as a potential oncogenic DUB molecule, whose expression was validated using immunohistochemistry. High ZRANB1 expression was correlated with advanced pathological T stages, 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 subcutaneous xenograft and lymph node metastasis models in vivo. By conducting 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 uncovers a novel post-translational mechanism linking the UPS to RNA splicing machinery in UBC. ZRANB1 promotes tumourigenesis by stabilizing SF3B3 to prevent the generation of the tumour-suppressive CHEK2-e4- isoform, suggesting ZRANB1 is a promising prognostic biomarker and therapeutic target.