The Activity and Stability of p56Lck and TCR Signaling Do Not Depend on the Co-Chaperone Cdc37.

Sarah Kowallik,Luca Simeoni,Burkhart Schraven,Andreas Kritikos,Christoph Thurm,Matthias Kästle

doi:10.3390/ijms22010126

Abstract

Lymphocyte-specific protein tyrosine kinase (Lck) is a pivotal tyrosine kinase involved in T cell receptor (TCR) signaling. Because of its importance, the activity of Lck is regulated at different levels including phosphorylation of tyrosine residues, protein–protein interactions, and localization. It has been proposed that the co-chaperone Cdc37, which assists the chaperone heat shock protein 90 (Hsp90) in the folding of client proteins, is also involved in the regulation of the activity/stability of Lck. Nevertheless, the available experimental data do not clearly support this conclusion. Thus, we assessed whether or not Cdc37 regulates Lck. We performed experiments in which the expression of Cdc37 was either augmented or suppressed in Jurkat T cells. The results of our experiments indicated that neither the overexpression nor the suppression of Cdc37 affected Lck stability and activity. Moreover, TCR signaling proceeded normally in T cells in which Cdc37 expression was either augmented or suppressed. Finally, we demonstrated that also under stress conditions Cdc37 was dispensable for the regulation of Lck activity/stability. In conclusion, our data do not support the idea that Lck is a Cdc37 client.

Highlights

The lymphocyte-specific protein tyrosine kinase p56Lck is one of the most well studied member of the Src-family kinases (SFKs), playing an essential role in the initiation of T cell receptor (TCR) signaling [1,2]
16 h after transfection, JE6 cells were lysed and the levels of total Lymphocyte-specific protein tyrosine kinase (Lck) as well as the levels of Lck phosphorylated on the regulatory sites, Y394 and Y505, were assessed by immunoblotting
Even though heat shock protein 90 (Hsp90) has been proposed to regulate the pool of constitutively active Lck [17,18,20], its co-chaperone appears to be dispensable in this process

Summary

Introduction

The lymphocyte-specific protein tyrosine kinase p56Lck is one of the most well studied member of the Src-family kinases (SFKs), playing an essential role in the initiation of T cell receptor (TCR) signaling [1,2]. Lck phosphorylates tyrosine residues within the immunoreceptor tyrosine-based activation motifs (ITAMs), which are located in the intracellular tails of TCR-associated CD3 chains (for more comprehensive reviews, see [2,10,11]). This event allows the recruitment of the tyrosine kinase zeta chain of T cell receptor-associated protein kinase 70 (Zap-70) to the phosphorylated ITAMs, followed by Zap-70 phosphorylation and activation by Lck. Signaling is further propagated upon Zap-70-mediated phosphorylation of the transmembrane adaptor molecule linker for activation of T cells (LAT), culminating in T cell activation. Lck-deficient mice display a severe block of T cell development [14], impaired T cell activation [13,15], and defective T cell homeostasis [15]

Methods

Results

Conclusion