Deciphering the role of miR-631 in the pathogenesis of oral squamous cell carcinoma

Abstract

Oral squamous cell carcinoma (OSCC) is a malignant neoplasm originating from the epithelial cells of the oral cavity. The Asian population has the highest incidence of OSCC and despite advances in its treatment, the five-year survival rate for OSCC remains low, emphasizing the need for more effective therapeutic strategies. In our laboratory, we have aimed to identify potential tumor suppressor microRNAs (miRs) that could serve as therapeutic targets in OSCC. Tumor suppressor miRs are often epigenetically silenced through promoter hypermethylation, and their expression can be reactivated by DNA methyltransferase (DNMT) inhibitors such as 5-Azacytidine. A previous microRNA microarray analysis from our laboratory has identified 50 miRs upregulated in 5-Azacytidine treated cells from an OSCC cell line SCC131. Of these, miR-631, which has no previously known roles in OSCC, was selected for further investigation. We have found that miR-631 suppresses OSCC cell proliferation and directly targets the 3’UTR of an oncogene RAB11A. This interaction has resulted in reduced RAB11A expression at both transcript and protein levels. A sodium bisulfite sequencing analysis has demonstrated that the upregulation of miR-631 in SCC131 cells following 5-Azacytidine treatment is attributed to demethylation of its gene MIR631 promoter. RAB11A has exhibited reduced transcript and protein levels upon 5-Azacytidine treatment, correlating with the increased expression of miR-631. We have demonstrated that miR-631 inhibits proliferation and anchorage-independent growth of OSCC cells in soft agar, in part, by targeting RAB11A. Additionally, miR-631 promotes apoptosis of OSCC cells, in part, by targeting RAB11A. An inverse correlation in levels of miR-631 and RAB11A has been observed across multiple cancer cell lines and in a majority of OSCC patient samples, underscoring the biological significance of their interaction. Furthermore, the reduction in tumor volume and weight of the OSCC xenografts in nude mice by a synthetic miR-631 mimic has suggested the tumor suppressor role of miR-631. Further, we have demonstrated that miR-631 and RAB11A interaction reduces the Wnt signaling in OSCC. Based on our results, we suggest that miR-631 functions as a tumor suppressor and holds promise as a potential therapeutic agent for treating OSCC, and perhaps other cancers.