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. n = 3 T24 control vs. n = 3 T24 siRNA targetting RBM3.

背景：肌层浸润性膀胱癌（muscle-invasive bladder cancer, MIBC）患者接受新辅助顺铂基化疗（neoadjuvant cisplatin-based chemotherapy, NAC）后，多达50%的患者因化疗耐药导致疗效受损，目前临床尚无可用的预测生物标志物。RNA结合基序蛋白3（RNA-binding motif protein 3, RBM3）已被证实为化疗应答的潜在调节因子，但在MIBC中的作用迄今尚未明确。
方法：本研究对145例患者的配对经尿道膀胱肿瘤切除术（transurethral resection of the bladder, TURB）标本、膀胱切除术标本及淋巴结转移灶，采用免疫组化法检测肿瘤特异性RBM3蛋白的表达水平。在体外实验中，于RT4与T24细胞系中探究RBM3敲低对化疗敏感性的影响。通过RNA测序对比靶向RBM3的小干扰RNA（siRBM3）处理组与对照组的基因表达谱。
结果：与膀胱切除术标本相比，TURB标本中的RBM3蛋白表达水平显著更高，但原发肿瘤与淋巴结转移灶的RBM3表达水平具有一致性。高肿瘤特异性RBM3表达与接受NAC治疗患者的复发风险降低显著相关。在RBM3表达水平高于RT4细胞的T24细胞中，RBM3沉默可降低其对顺铂与吉西他滨的敏感性。RNA测序结果显示，RBM3可能参与促进细胞周期进程，尤其是G1/S期转换及DNA复制起始。
解读：本研究数据证实了RBM3在MIBC中的预测价值，若经前瞻性验证，可助力该侵袭性疾病患者的治疗分层。本实验包含3例T24对照组样本与3例靶向RBM3的小干扰RNA处理的T24细胞样本。