GW182 Proteins Directly Recruit Cytoplasmic Deadenylase Complexes to miRNA Targets

miRNAs are posttranscriptional regulators of gene expression that associate with Argonaute and GW182 proteins to repress translation and/or promote mRNA degradation. miRNA-mediated mRNA degradation is initiated by deadenylation, although it is not known whether deadenylases are recruited to the mRNA target directly or by default, as a consequence of a translational block. To answer this question, we performed a screen for potential interactions between the Argonaute and GW182 proteins and subunits of the two cytoplasmic deadenylase complexes. We found that human GW182 proteins recruit the PAN2-PAN3 and CCR4-CAF1-NOT deadenylase complexes through direct interactions with PAN3 and NOT1, respectively. These interactions are critical for silencing and are conserved in D. melanogaster. Our findings reveal that GW182 proteins provide a docking platform through which deadenylase complexes gain access to the poly(A) tail of miRNA targets to promote their deadenylation, and they further indicate that deadenylation is a direct effect of miRNA regulation.