Symmetric Arginine Dimethylation Is Selectively Required for mRNA Splicing and the Initiation of Type I and Type III Interferon Signaling.

Alternative splicing is well understood to enhance proteome diversity as cells respond to stimuli. However, mechanistic understanding for how the spliceosome processes precursor messenger RNA (mRNA) transcripts to achieve template diversification is incomplete. We use recently developed enzymatic inhibitors of protein arginine methyltransferase 5 (PRMT5) and human naive T lymphocyte activation as a model system to uncover a precise set of mRNA transcripts that require symmetric arginine dimethylation. This methylation-dependent splicing selectivity is associated with a limited set of signaling pathways that are affected when PRMT5 is inhibited. Specifically, we identify a conserved role for symmetric arginine dimethylation in the induction of antiviral type I and type III interferon signaling following T cell receptor and pattern recognition receptor stimulation in human T lymphocytes and undifferentiated human THP-1 monocytes. Altogether, these findings reveal a mechanism by which cells may be enabled to precisely modulate transcript heterogeneity to orchestrate specific functional outcomes.

SETD7 Controls Intestinal Regeneration and Tumorigenesis by Regulating Wnt/ß-Catenin and Hippo/YAP Signaling.

Intestinal tumorigenesis is a result of mutations in signaling pathways that control cellular proliferation, differentiation, and survival. Mutations in the Wnt/ß-catenin pathway are associated with the majority of intestinal cancers, while dysregulation of the Hippo/Yes-Associated Protein (YAP) pathway is an emerging regulator of intestinal tumorigenesis. In addition, these closely related pathways play a central role during intestinal regeneration. We have previously shown that methylation of the Hippo transducer YAP by the lysine methyltransferase SETD7 controls its subcellular localization and function. We now show that SETD7 is required for Wnt-driven intestinal tumorigenesis and regeneration. Mechanistically, SETD7 is part of a complex containing YAP, AXIN1, and ß-catenin, and SETD7-dependent methylation of YAP facilitates Wnt-induced nuclear accumulation of ß-catenin. Collectively, these results define a methyltransferase-dependent regulatory mechanism that links the Wnt/ß-catenin and Hippo/YAP pathways during intestinal regeneration and tumorigenesis.

(R)-PFI-2 is a potent and selective inhibitor of SETD7 methyltransferase activity in cells.

SET domain containing (lysine methyltransferase) 7 (SETD7) is implicated in multiple signaling and disease related pathways with a broad diversity of reported substrates. Here, we report the discovery of (R)-PFI-2-a first-in-class, potent (Ki (app) = 0.33 nM), selective, and cell-active inhibitor of the methyltransferase activity of human SETD7-and its 500-fold less active enantiomer, (S)-PFI-2. (R)-PFI-2 exhibits an unusual cofactor-dependent and substrate-competitive inhibitory mechanism by occupying the substrate peptide binding groove of SETD7, including the catalytic lysine-binding channel, and by making direct contact with the donor methyl group of the cofactor, S-adenosylmethionine. Chemoproteomics experiments using a biotinylated derivative of (R)-PFI-2 demonstrated dose-dependent competition for binding to endogenous SETD7 in MCF7 cells pretreated with (R)-PFI-2. In murine embryonic fibroblasts, (R)-PFI-2 treatment phenocopied the effects of Setd7 deficiency on Hippo pathway signaling, via modulation of the transcriptional coactivator Yes-associated protein (YAP) and regulation of YAP target genes. In confluent MCF7 cells, (R)-PFI-2 rapidly altered YAP localization, suggesting continuous and dynamic regulation of YAP by the methyltransferase activity of SETD7. These data establish (R)-PFI-2 and related compounds as a valuable tool-kit for the study of the diverse roles of SETD7 in cells and further validate protein methyltransferases as a druggable target class.