Passenger strand miRNA miR-31* regulates the phenotypes of oral cancer cells by targeting RhoA

Objectives: MicroRNAs (miRNAs) are endogenous small non-coding RNAs that negatively regular target gene expression by RNA interference. The processing of the pre-miRNA hairpin generates a miRNA duplex, which consists of a miRNA (guide strand) and a miRNA* (passenger strand). miR-31 is an oncogenic miRNA and is up-regulated in oral squamous cell carcinoma (OSCC). miR-31* shows a high level of conservation across species and, based on this, this study hypothesized that miR-31* is a functional miRNA. Materials and Methods: The expression of miR-31 and miR-31* in OSCC tissues and oral cells were analyzed. Functional studies were performed on OSCC cells. Results: miR-31* is up-regulated in OSCC tissues, but its expression is less abundant than miR-31. miR-31* decreases the proliferation and migration of both SAS and Fadu cells. Furthermore, miR-31* targets the 3'UTR of RhoA and is able to down-regulate RhoA expression. Knockdown of RhoA expression is known to decrease the proliferation and migration of OSCC cells. However, up-regulation of both miR-31 and miR-31* by delivery of pre-mir-31 does still enhance OSCC oncogenicity. Conclusion: miR-31* is a functional miRNA involving in regulating RhoA, and the activity of miR-31*'s activity seems to counteract the functions of miR-31 during OSCC tumorigenesis. (C) 2012 Elsevier Ltd. All rights reserved.