Cooperative Interaction of Nck and Lck Orchestrates Optimal TCR Signaling.

Frederike A Hartl,Prapat Suriyaphol,Sutatip Pongcharoen,Susana Minguet,Esmeralda Beck-Garcia,Stefan Günther,Liz Cerqueira,Piyamaporn Wipa,Wolfgang W A Schamel,Burkhart Schraven,Jatuporn Ngoenkam,Pankaj Mishra,Pussadee Paensuwan

doi:10.3390/cells10040834

Abstract

The T cell antigen receptor (TCR) is expressed on T cells, which orchestrate adaptive immune responses. It is composed of the ligand-binding clonotypic TCRαβ heterodimer and the non-covalently bound invariant signal-transducing CD3 complex. Among the CD3 subunits, the CD3ε cytoplasmic tail contains binding motifs for the Src family kinase, Lck, and the adaptor protein, Nck. Lck binds to a receptor kinase (RK) motif and Nck binds to a proline-rich sequence (PRS). Both motifs only become accessible upon ligand binding to the TCR and facilitate the recruitment of Lck and Nck independently of phosphorylation of the TCR. Mutations in each of these motifs cause defects in TCR signaling and T cell activation. Here, we investigated the role of Nck in proximal TCR signaling by silencing both Nck isoforms, Nck1 and Nck2. In the absence of Nck, TCR phosphorylation, ZAP70 recruitment, and ZAP70 phosphorylation was impaired. Mechanistically, this is explained by loss of Lck recruitment to the stimulated TCR in cells lacking Nck. Hence, our data uncover a previously unknown cooperative interaction between Lck and Nck to promote optimal TCR signaling.

Highlights

The T cell antigen receptor (TCR) is a multimeric transmembrane protein, exclusively expressed on the surface of T cells
proline-rich sequence (PRS) prevent recruitment of non-catalytic region of tyrosine kinase (Nck) to the TCR resulting in impaired ZAP70 recruitment and phosphorylation, which suggests that the early recruitment of Nck to the TCR modulates
Binding in cells lacking Nck (Supplementary Figure S2A,B). These results suggest that endogenous Nck might help to stabilize the open TCR conformation and thereby, facilitate the exposure of the receptor kinase (RK) motif for Lck recruitment, of the PRS for Nck binding, and of the immunoreceptor tyrosine-based activation motif (ITAM) of CD3ε for subsequent phosphorylation by Lck [4,10,22]

Summary

Introduction

The T cell antigen receptor (TCR) is a multimeric transmembrane protein, exclusively expressed on the surface of T cells. It is composed of the ligand-binding clonotypic. TCRαβ heterodimer and the noncovalently associated invariant CD3 signal-transducing complex [1]. This CD3 complex includes the CD3εγ, CD3εδ, and ζζ signal transduction chains [2]. Binding of the TCR’s ligand (major histocompatibility complex bound to an antigenic peptide; pMHC) selects and stabilizes the TCR in active conformations that were hardly visited in the absence of ligand binding (reviewed in) [8,9]

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