MicroRNA-Offset RNA Alters Gene Expression and Cell Proliferation

MicroRNA-offset RNAs (moRs) were first identified in simple chordates and subsequently in mouse and human cells by deep sequencing of short RNAs. MoRs are derived from sequences located immediately adjacent to microRNAs (miRs) in the primary miR (pri-miR). Currently moRs are considered to be simply a by-product of miR biosynthesis that lack biological activity. Here we show for the first time that a moR is biologically active. We demonstrate that endogenous or over-expressed moR-21 significantly alters gene expression and inhibits the proliferation of vascular smooth muscle cells (VSMC). In addition, we find that miR-21 and moR-21 may regulate different genes in a given pathway and can oppose each other in regulating certain genes. We report that there is a "seed region" of moR-21 as well as a "seed match region" in the target gene 3'UTR that are indispensable for moR-21-mediated gene down-regulation. We further demonstrate that moR-21-mediated gene repression is Argonaute 2 (Ago2) dependent. Taken together, these findings provide the first evidence that microRNA offset RNA alters gene expression and is biologically active.