Interleukin-2-inducible T Cell Kinase (Itk) Network Edge Dependence for the Maturation of iNKT Cell

Qian Qi,Margherita Cantorna,Mingcan Xia,Avery August,Sanhong Yu,Yuting Bai

doi:10.1074/jbc.m110.148205

Abstract

Invariant natural killer T (iNKT) cells are a unique subset of innate T lymphocytes that are selected by CD1d. They have diverse immune regulatory functions via the rapid production of interferon-γ (IFN-γ) and interleukin-4 (IL-4). In the absence of signaling nodes Itk and Txk, Tec family non-receptor tyrosine kinases, mice exhibit a significant block in iNKT cell development. We now show here that although the Itk node is required for iNKT cell maturation, the kinase domain edge of Itk is not required for continued maturation iNKT cells in the thymus compared with Itk-null mice. This rescue is dependent on the expression of the Txk node. Furthermore, this kinase domain independent edge rescue correlates with the increased expression of the transcription factors T-bet, the IL-2/IL-15 receptor β chain CD122, and suppression of eomesodermin expression. By contrast, α-galactosyl ceramide induced cytokine secretion is dependent on the kinase domain edge of Itk. These findings indicate that the Itk node uses a kinase domain independent edge, a scaffolding function, in the signaling pathway leading to the maturation of iNKT cells. Furthermore, the findings indicate that phosphorylation of substrates by the Itk node is only partially required for maturation of iNKT cells, while functional activation of iNKT cells is dependent on the kinase domain/activity edge of Itk.

Highlights

The Kinase Domain Edge of Itk Is Required for Generating Normal Numbers of Thymic Invariant natural killer T (iNKT) Cells—To determine if the kinase domain edge of Itk is required for the development of iNKT cells, we compared the iNKT population in WT, ItkϪ/Ϫ, Itk/Txk double knock-out (DKO) mice and mice carrying a mutant ITK lacking its kinase domain instead of WT Itk in Itk null or Itk/Txk (DKO) mice (Tg(Lck-Itk⌬Kin)/ItkϪ/Ϫ and Tg(Lck-Itk⌬Kin)/Itk/Txk DKO [22])
We found that the absence of Itk results in a reduction in the percent of iNKT cells in the thymus, and expression of the kinase-deleted mutant of Itk could rescue this percentage to WT levels (Fig. 1A)
The numbers of thymic iNKT cells was significantly reduced in Itk/Txk DKO mice compared with ItkϪ/Ϫ mice (Fig. 1B), and these numbers were not rescued by expression of the kinase domain-deleted mutant (Fig. 1, A and B)

Summary

Introduction

While the percentage of thymic iNKT cells in Itk/Txk DKO was similar to that seen in the ItkϪ/Ϫ mice (i.e. reduced compared with WT mice), this percentage was not rescued by expression of the kinase-deleted mutant (Fig. 1A). The numbers of thymic iNKT cells was significantly reduced in Itk/Txk DKO mice compared with ItkϪ/Ϫ mice (Fig. 1B), and these numbers were not rescued by expression of the kinase domain-deleted mutant (Fig. 1, A and B).

Results

Conclusion