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

SummaryObjectivesMicroRNAs (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 MethodsThe expression of miR-31 and miR-31∗ in OSCC tissues and oral cells were analyzed. Functional studies were performed on OSCC cells.ResultsmiR-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.ConclusionmiR-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.