Response to interferons and antibacterial innate immunity in the absence of tyrosine-phosphorylated STAT1.

Andrea Majoros,Claus Vogl,George R Stark,Christian Schindler,Ekaterini Platanitis,Hyeonjoo Cheon,Mathias Müller,Veronika Sexl,Priyank Shukla,Robert Schreiber,Thomas Decker,Daniel Szappanos

doi:10.15252/embr.201540726

Abstract

Signal transducer and activator of transcription 1 (STAT1) plays a pivotal role in the innate immune system by directing the transcriptional response to interferons (IFNs). STAT1 is activated by Janus kinase (JAK)‐mediated phosphorylation of Y701. To determine whether STAT1 contributes to cellular responses without this phosphorylation event, we generated mice with Y701 mutated to a phenylalanine (Stat1Y701F). We show that heterozygous mice do not exhibit a dominant‐negative phenotype. Homozygous Stat1Y701F mice show a profound reduction in Stat1 expression, highlighting an important role for basal IFN‐dependent signaling. The rapid transcriptional response to type I IFN (IFN‐I) and type II IFN (IFNγ) was absent in Stat1Y701F cells. Intriguingly, STAT1Y701F suppresses the delayed expression of IFN‐I‐stimulated genes (ISG) observed in Stat1−/− cells, mediated by the STAT2/IRF9 complex. Thus, Stat1Y701F macrophages are more susceptible to Legionella pneumophila infection than Stat1−/− macrophages. Listeria monocytogenes grew less robustly in Stat1Y701F macrophages and mice compared to Stat1−/− counterparts, but STAT1Y701F is not sufficient to rescue the animals. Our studies are consistent with a potential contribution of Y701‐unphosphorylated STAT1 to innate antibacterial immunity.

Highlights

Signal transducer and activator of transcription 1 (STAT1) plays a pivotal role in the innate immune system by directing the transcriptional response to interferons (IFNs)
We first examined heterozygous Stat1Y701F/+ mice. Importance of this genetic configuration stems from human patients, where Stat1Y701C heterozygosity was classified as an autosomal dominant cause of Mendelian susceptibility to mycobacterial disease (MSMD) [15,16]
In order to further characterize the mechanism by which STAT1Y701F represses STAT1-independent, STAT2/IRF9-dependent gene expression during the late IFN-I response, we considered a dominant-negative effect of the mutant at the level of Janus kinase (JAK)-mediated tyrosine phosphorylation

Summary

Introduction

Signal transducer and activator of transcription 1 (STAT1) plays a pivotal role in the innate immune system by directing the transcriptional response to interferons (IFNs). STAT1 is activated by Janus kinase (JAK)-mediated phosphorylation of Y701. To determine whether STAT1 contributes to cellular responses without this phosphorylation event, we generated mice with Y701 mutated to a phenylalanine (Stat1Y701F). Homozygous Stat1Y701F mice show a profound reduction in Stat expression, highlighting an important role for basal IFN-dependent signaling. STAT1Y701F suppresses the delayed expression of IFN-I-stimulated genes (ISG) observed in Stat1À/À cells, mediated by the STAT2/IRF9 complex. Listeria monocytogenes grew less robustly in Stat1Y701F macrophages and mice compared to Stat1À/À counterparts, but STAT1Y701F is not sufficient to rescue the animals. Our studies are consistent with a potential contribution of Y701-unphosphorylated STAT1 to innate antibacterial immunity

Objectives

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Conclusion