TPL-2 Inhibits IFN-β Expression via an ERK1/2-TCF-FOS Axis in TLR4-Stimulated Macrophages.

Louise Blair,Stephen Smale,Erwin F Wagner,Michael J Pattison,Latifa Bakiri,Stamatia Papoutsopoulou,Steven C Ley,Probir Chakravarty

doi:10.4049/jimmunol.2100213

Abstract

TPL-2 kinase plays an important role in innate immunity, activating ERK1/2 MAPKs in myeloid cells following TLR stimulation. We investigated how TPL-2 controls transcription in TLR4-stimulated mouse macrophages. TPL-2 activation of ERK1/2 regulated expression of genes encoding transcription factors, cytokines, chemokines, and signaling regulators. Bioinformatics analysis of gene clusters most rapidly induced by TPL-2 suggested that their transcription was mediated by the ternary complex factor (TCF) and FOS transcription factor families. Consistently, TPL-2 induced ERK1/2 phosphorylation of the ELK1 TCF and the expression of TCF target genes. Furthermore, transcriptomic analysis of TCF-deficient macrophages demonstrated that TCFs mediate approximately half of the transcriptional output of TPL-2 signaling, partially via induced expression of secondary transcription factors. TPL-2 signaling and TCFs were required for maximal TLR4-induced FOS expression. Comparative analysis of the transcriptome of TLR4-stimulated Fos -/- macrophages indicated that TPL-2 regulated a significant fraction of genes by controlling FOS expression levels. A key function of this ERK1/2-TCF-FOS pathway was to mediate TPL-2 suppression of type I IFN signaling, which is essential for host resistance against intracellular bacterial infection.

Highlights

To gain some insight into the potential impact of TPL-2 signaling on the biological response of macrophages to LPS stimulation, the genes regulated by TPL-2 catalytic activity were analyzed for process and pathway enrichment using the MetaCore program (Supplemental Fig. 1B)
Our previous analyses of the TPL-2 phosphoproteome demonstrated that ∼85% of protein phosphorylations regulated by TPL-2 catalytic activity are dependent on ERKs 1 and 2 (ERK1/2) activation [10]
Consistent with this, RNAseq analyses in this study revealed a strong correlation between the effect of an MKK1/2 inhibitor on WT cells and Map3k8D270A mutation, indicating that most TPL-2regulated changes in transcription in response to TLR4 activation were mediated via ERK1/ 2 activation

Summary

Introduction

RNA-seq determined that LPS induction of cluster 1 genes was significantly reduced by Nfkb1SSAA mutation [11], which prevents signal-induced proteolysis of p105 and prevents TPL-2 activation of MKK1/ 2 and their substrates ERK1/2 (Fig. 1C). Analysis of the RNA-seq data revealed that Map3k8D270A mutation significantly reduced the mRNA abundance of the TCF-regulated immediate early genes Egr1, Egr3, and Nr4A1 following LPS stimulation of macrophages (Fig. 2D), which was confirmed by quantitative RT-PCR (qRT-PCR) (Fig. 2E).

Results

Conclusion