Mapping miRNA regulation of MGAT3 reveals upregulation as the dominant mode of action

Abstract

SummaryEndogenous, short, non-coding RNA, known as miRNA, enable tight control of protein expression within the cell, strongly impacting low abundance proteins including glycosylation enzymes. Herein we use our high-throughput miRFluR assay to map the miRNA regulatory landscape of MGAT3, the enzyme biosynthesizing bisecting GlcNAc inN-linked glycans. We find that MGAT3 is predominantly upregulated by miRNA, contradicting the conventional role of miRNAs as downregulators of protein expression. Validation of our data confirmed upregulation of MGAT3 and bisecting GlcNAc by both miRNA mimics and endogenous miRNAs. The identified binding site on MGAT3 for our strongest upregulator, miR-92a-1-5p, displays non-canonical interactions, deviating from conventional seed-pairing rules. Upregulation requires AGO2, but not the downregulatory RISC component TNRC6A, indicating unique complexes. MGAT3 is only the second protein identified that is predominantly upregulated by miRNA. Overall, our data underscores the prevalence of miRNA-mediated upregulation and reveals potential mechanisms governing up- and downregulation.