Cell-Intrinsic Role for NF-kappa B-Inducing Kinase in Peripheral Maintenance but Not Thymic Development of Foxp3+ Regulatory T Cells in Mice

Susan E Murray,Alexandre Salgado Basso

doi:10.1371/journal.pone.0076216

Susan E Murray, Alexandre Salgado Basso

Open Access

https://doi.org/10.1371/journal.pone.0076216

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Journal: PloS one	Publication Date: Sep 20, 2013
Citations: 24	License type: CC BY 4.0

Affiliation: Oregon Health & Science University

Abstract

NF-κB inducing kinase (NIK, MAP3K14) is a key signaling molecule in non-canonical NF-κB activation, and NIK deficient mice have been instrumental in deciphering the immunologic role of this pathway. Global ablation of NIK prevents lymph node development, impairs thymic stromal development, and drastically reduces B cells. Despite altered thymic selection, T cell numbers are near normal in NIK deficient mice. The exception is CD4+ regulatory T cells (Tregs), which are reduced in the thymus and periphery. Defects in thymic stroma are known to contribute to impaired Treg generation, but whether NIK also plays a cell intrinsic role in Tregs is unknown. Here, we compared intact mice with single and mixed BM chimeric mice to assess the intrinsic role of NIK in Treg generation and maintenance. We found that while NIK expression in stromal cells suffices for normal thymic Treg development, NIK is required cell-intrinsically to maintain peripheral Tregs. In addition, we unexpectedly discovered a cell-intrinsic role for NIK in memory phenotype conventional T cells that is masked in intact mice, but revealed in BM chimeras. These results demonstrate a novel role for NIK in peripheral regulatory and memory phenotype T cell homeostasis.

Highlights

NF-κB is an evolutionarily conserved intracellular signaling pathway that acts as a critical immune sensor
Using Foxp3 as a specific Treg suppression assay CD4+RFP+ cells (Tregs) marker, we found that the proportion of Tregs among CD4 single positive cells (SP4) was decreased in NF-κB inducing kinase (NIK) KO thymus (Figure 1A and B)
The proportion of CD25+Foxp3- Treg precursors was significantly decreased in NIK KO thymus (Figure 1A and F), CD25 expression was equivalent between NIK KO and WT Foxp3+ cells (Figure 1A and G)

Summary

Introduction

NF-κB is an evolutionarily conserved intracellular signaling pathway that acts as a critical immune sensor. Canonical NFκB mediates cellular responses to myriad danger and inflammatory signals including pattern recognition receptors, antigen receptors, and cytokine and chemokine receptors This pathway is activated rapidly—within minutes of receptor ligation —by virtue of rapid phosphorylation and degradation of inhibitory IκB proteins that retain the transcriptionally active NFκB subunits in the cytosol. Non-canonical NF-κB is activated more slowly, as it requires new protein synthesis, and it is not dependent on IκB degradation [1] Instead, it relies on accumulation of NF-κB inducing kinase (NIK) and subsequent phosphorylation of IKKα, which induces partial proteasomal degradation of the NF-κB2 subunit. Unlike the canonical pathway, activation of non-canonical NF-κB is restricted to a subset of TNF receptor family members (TNFR). We recently found that CD4+ regulatory T cells overexpressing NIK have impaired suppressive function [12]

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