Expression and Editing of MicroRNA-376 Cluster in Human Glioblastomas: Role in Tumor Growth and Invasion

Abstract

In the human brain, microRNAs (miRNAs) from the miRNA-376 cluster undergo programmed ¿seed¿ sequence modifications by adenosine-to-inosine editing. Editing is mediated by a family of editing enzymes, adenosine deaminases acting on RNA, the activity of which has been shown to be disrupted in several cancers including gliomas. In this study, by sequencing of miRNAs from miRNA-376 cluster, we show that their overall editing frequencies are subject to reduction in human gliomas compared to normal brain tissue. In high-grade gliomas, specifically in glioblastomas (GBMs), where the expression of this miRNA cluster is only moderately reduced, miRNA-376a* aberrantly accumulates entirely in the unedited form. Using miRNA overexpression and knockdown techniques in glioma cell lines, we demonstrate that the unedited miRNA-376a* is a functional sequence variant that promotes glioma cell migration and invasion in vitro and in an orthotopic xenograft model. Strikingly, the edited miRNA-376a* suppresses these malignant features. The effects of the unedited miRNA-376a* are mediated by its sequence-dependent ability to target STAT3 and concomitant inability to target AMFR in glioma cells. Thus, the tumor-dependent introduction of single base difference in miRNA-376a* sequence dramatically alters the selection of its target genes and redirects its function from inhibiting to promoting glioma cell invasion. These findings uncover a novel mechanism of miRNA deregulation in cancer due to altered adenosine-to-inosine editing and identify unedited miRNA-376a* as a potential therapeutic target in GBMs.