Abstract
Processing of microRNAs (miRNAs) from their precursors to their biologically active mature forms is regulated during development and cancer. We show that mouse pri- or pre-miR-151 can bind to and compete with mature miR-151-5p and miR-151-3p for binding sites contained within the complementary regions of the E2f6 mRNA 3' untranslated region (UTR). E2f6 mRNA levels were directly regulated by pri- or pre-miR-151. Conversely, miR-151-mediated repression of ARHGDIA mRNA was dependent on the level of mature miR-151 because only the mature miRNA binds the 3' UTR. Thus, processing of miR-151 can have different effects on separate mRNA targets within a cell. A bioinformatics pipeline revealed additional candidate regions where precursor miRNAs can compete with their mature miRNA counterparts. We validated this experimentally for miR-124 and the SNAI2 3' UTR. Hence, miRNA precursors can serve as post-transcriptional regulators of miRNA activity and are not mere biogenesis intermediates.