Mechanism of microRNA‑30b‑5p enhancing the response of MDA‑MB‑231 cells to cisplatin by regulating RAP1B expression

The present study investigated the role of hsa‑microRNA (miR)‑30b‑5p in potentiating cisplatin‑induced cytotoxicity in triple‑negative breast cancer (TNBC) MDA‑MB‑231 cells via Ras‑related protein Rap‑1b (RAP1B) regulation. Expression levels of hsa‑miR‑30b‑5p and RAP1B were examined in multiple breast cell lines, including normal breast epithelial cells (MCF‑10A) and breast cancer cell lines (MCF‑7, MDA‑MB‑231 and MDA‑MB‑468). MDA‑MB‑231 cells were divided into control, miR‑30b‑5p mimic, cisplatin (DDP), miR‑30b‑5p mimic + DDP and miR‑30b‑5p mimic + overexpressed RAP1B + DDP groups. Reverse transcription‑quantitative PCR (RT‑qPCR) demonstrated significantly lower miR‑30b‑5p expression in MDA‑MB‑231 compared with MCF‑10A normal breast epithelial cells (P<0.001), which was rescued by miR‑30b‑5p mimics. Cell Counting Kit‑8 assays revealed that miR‑30b‑5p overexpression or DDP alone suppressed cell viability (P<0.001), with combined treatment showing synergistic inhibition (P<0.001). Flow cytometry demonstrated increased apoptosis in miR‑30b‑5p mimic and DDP groups, further amplified by their combination (P<0.001). Luciferase reporter and RNA pull‑down‑qPCR assays confirmed miR‑30b‑5p directly targets RAP1B 3'‑untranslated region (UTR) via sequence‑specific binding. RNA pull‑down demonstrated molecular association between miR‑30b‑5p and RAP1B mRNA, while the luciferase reporter assay confirmed 3'‑UTR‑specific interaction. Western blotting and RT‑qPCR showed miR‑30b‑5p mimics downregulated RAP1B (P<0.001), reversed by RAP1B overexpression. In the rescue experiment, RAP1B overexpression partially reversed the pro‑apoptotic effect of miR‑30b‑5p under cisplatin treatment, supporting the hypothesis that RAP1B mediates the effect of miR‑30b‑5p on the cisplatin response (P<0.001). These findings indicate that miR‑30b‑5p potentiates cisplatin‑induced cytotoxicity in TNBC by suppressing RAP1B, suggesting a novel therapeutic strategy to overcome chemoresistance.