microRNA-99a-5p induces cellular senescence in gemcitabine-resistant bladder cancer by targeting SMARCD1

Patients with advanced bladder cancer are generally treated with a combination of chemotherapeutics, including gemcitabine, but the effect is limited due to acquisition of drug resistance. Thus, in this study, we investigated the mechanism of gemcitabine resistance. First, gemcitabine-resistant cells were established and resistance confirmed in vitro and in vivo. Small RNA sequencing analyses were performed to search for miRNAs involved in gemcitabine resistance. miR-99a-5p, selected as a candidate miRNA, was downregulated compared to its parental cells. In gain-of-function studies, miR-99a-5p inhibited cell viabilities and restored sensitivity to gemcitabine. RNA sequencing analysis was performed to find the target gene of miR-99a-5p. SMARCD1 was selected as a candidate gene. Dual-luciferase reporter assays showed that miR-99a-5p directly regulated SMARCD1. Loss-of-function studies conducted with si-RNAs revealed suppression of cell functions and restoration of gemcitabine sensitivity. miR-99a-5p overexpression and SMARCD1 knockdown also suppressed gemcitabine-resistant cells in vivo. Furthermore, β-galactosidase staining showed that miR-99a-5p induction and SMARCD1 suppression contributed to cellular senescence. In summary, tumor-suppressive miR-99a-5p induced cellular senescence in gemcitabine-resistant bladder cancer cells by targeting SMARCD1.