miR-185-5p rewires cisplatin resistance by restoring miR-203a-3p expression via downregulation of SOX9.

Chemotherapeutic drug resistance is a challenge for the effective treatment of OSCC. There are a couple of studies on the involvement of microRNAs (miRNAs) in chemoresistance of oral squamous cell carcinoma (OSCC), but the exact molecular events in many cases are not clearly understood. In this work, we intend to track down key miRNA(s) and unveil their regulatory molecular mechanisms in imparting chemoresistance in this lethal cancer. We analyzed gene and miRNA array profiles of drug-resistant OSCC cells, predicted miRNA targets, performed enrichment analysis, and validated our findings in cisplatin-sensitive and cisplatin-resistant SCC9 and H357 OSCC cells. We evaluated the anticancer and chemosensitivity roles of selected miRNA by adopting several molecular assays like qRT-PCR, MTT assay, wound healing assay, fluorescence imaging by DCFHDA, AO/EB staining, DAPI, and γ-H2AX accumulation assay. We also validated the miRNA-target binding by qRT-PCR and luciferase reporter assay. Among the enriched miRNAs, we found miR-185-5p downregulated in cisplatin-resistant OSCC cells as a signature miRNA modulating chemoresistance. The upregulation of miR-185-5p by mimic transfection restores cisplatin sensitivity by decreasing cell viability in a dose-dependent manner and increasing ROS-induced DNA damage and apoptosis. miR-185-5p overexpression increases miR-203a-3p expression through negative regulation of SOX9. siRNA-mediated silencing of the SOX9 also shows similar results. Mechanistically, miR-185-5p dependent miR-203a-3p expression decreases cisplatin efflux and cisplatin-induced DNA damage repair by regulating ABCC1, ABCB1, RRM2, and RAN. This study will pave the way for employing this miR-185-5p as a combination therapeutic strategy to combat cisplatin resistance in oral cancer.