Pre-clinical and clinical studies on the role of RBM3 in muscle-invasive bladder cancer: longitudinal expression, transcriptome-level effects and modulation of chemosensitivity

Background: The response to neoadjuvant cisplatin-based chemotherapy (NAC) in muscle-invasive bladder cancer (MIBC) is impaired in up to 50% of patients due to chemoresistance, with no predictive biomarkers in clinical use. RNA-binding motif protein 3 (RBM3) has emerged as a putative modulator of chemotherapy response but has a hitherto unrecognized role in MIBC. Methods: Tumour-specific RBM3 protein expression was assessed via immunohistochemistry in paired transurethral resection of the bladder (TURB) specimens, cystectomy specimens and lymph node metastases from 145 patients. The effect of RBM3 suppression on chemosensitivity was examined in RT4 and T24 cells in vitro. RNA-sequencing was applied to compare gene expression profiles between siRBM3-treated and control cells. Findings: RBM3 protein expression was significantly higher in TURB compared to cystectomy specimens but showed consistency between primary tumours and lymph node metastases. High tumour-specific RBM3 expression was significantly associated with a reduced risk of recurrence in NAC treated patients. In T24 cells, which displayed higher RBM3 levels than RT4 cells, RBM3 silencing conferred a decreased sensitivity to cisplatin and gemcitabine. RNA-sequencing revealed potential involvement of RBM3 in facilitating cell cycle progression, in particular G1/S-phase transition, and initiation of DNA replication. Interpretation: The presented data highlight the predictive value of RBM3 in MIBC, which could, if prospectively validated, improve treatment stratification of patients with this aggressive disease. Overall design: n = 3 T24 control vs. n = 3 T24 siRNA targetting RBM3.