Ubiquitination mediated cisplatin resistance in bladder cancer.

Bladder cancer (BCa) patients frequently develop resistance to platinum-based therapies, particularly cisplatin. The link between chemoresistance and glycolysis has been well documented. Emerging evidence suggests that Rac family small GTPase 3 ( RAC3 ) may play significant roles in cisplatin resistance. This study investigated the underlying molecular mechanisms. Clinical specimens (cisplatin-sensitive/resistant BCa tissues and matched adjacent normal tissues) were collected from hospital. Cisplatin-resistant cell lines [T24-derived cisplatin-resistant cells (T24-DDP) and 5637-derived cisplatin-resistant cells (5637-DDP)] were generated through stepwise dose escalation. RAC3 , Myc-binding protein 2 (MYCBP2 ), P21-activated kinase 1 ( PAK1 ), Ki-67, and glycolysis markers were analyzed by quantitative PCR, immunohistochemistry, and Western blot. RAC3 ubiquitination was assessed via co-immunoprecipitation. Cell viability, apoptosis, and glycolytic metabolism were evaluated using the cell counting kit-8 assay, terminal deoxynucleotidyl transferase deoxyuridine triphosphate/flow cytometry, and ATP/lactate assays, respectively. Glycolytic flux was measured by extracellular acidification rate. Additionally, BCa xenograft models were established for in-vivo detection. Elevated RAC3 expression and glycolytic activity were observed in BCa tissues, with further augmentation in cisplatin-resistant tumors. RAC3 overexpression promoted cell viability, glycolysis, invasion, and migration in cisplatin-treated T24 and 5637 cells. Conversely, RAC3 knockdown exerted the opposite effects and restored cisplatin sensitivity in resistant T24-DDP and 5637-DDP cells. Notably, the sensitizing effect of RAC3 knockdown was reversed by PAK1 overexpression. Furthermore, MYCBP2 regulated RAC3 stability, as MYCBP2 overexpression enhanced RAC3 ubiquitination, suppressed glycolysis, and sensitized resistant cells to cisplatin. These effects were abrogated by the proteasome inhibitor MG132, confirming proteasome-dependent degradation of RAC3 . MYCBP2 -mediated ubiquitination of RAC3 modulates the PAK1 /pyruvate dehydrogenase E1 subunit alpha axis to regulate glycolytic activity, ultimately determining cisplatin sensitivity in BCa.