The EDC4-XRN1 axis controls P-body dynamics to link mRNA decapping with decay

ABSTRACT Deadenylation-dependent mRNA decapping and decay is the major cytoplasmic mRNA turnover pathway in eukaryotes. Many mRNA decapping and decay factors associate with each other via protein-protein interaction motifs. For example, the decapping enzyme DCP2 and the 5’-3’ exoribonuclease XRN1 interact with enhancer of mRNA decapping protein 4 (EDC4), a large scaffold that has been reported to stimulate mRNA decapping. mRNA decapping and decay factors are also found in processing bodies (P-bodies), evolutionarily conserved ribonucleoprotein (RNP) granules that are often enriched with mRNAs targeted for decay, such as microRNA (miRNA)-targeted mRNAs, yet paradoxically are not required for mRNA decay to occur. In this study, we show that disrupting the interaction between XRN1 and EDC4 or altering their stoichiometry leads to an inhibition of mRNA decapping, with miRNA-targeted mRNAs being stabilized in a translationally repressed state. Importantly, we demonstrate that this concomitantly leads to larger P-bodies that are directly responsible for preventing mRNA decapping under these conditions. Finally, we demonstrate that P-bodies act to support cell viability and prevent stress granule formation under conditions when XRN1 is limiting. Taken together, these data demonstrate that the interaction between XRN1 and EDC4 regulates P-body dynamics to properly coordinate mRNA decapping with 5’-3’ decay in human cells. HIGHLIGHTS XRN1-EDC4 interaction couples mRNA decapping with mRNA decay. Disrupting XRN1-EDC4 contact generates larger P-bodies that, in turn, inhibit decapping. P-bodies support cellular fitness in the absence of XRN1.