Protein Tyrosine Phosphatase CD148-Mediated Inhibition of T-Cell Receptor Signal Transduction Is Associated with Reduced LAT and Phospholipase Cγ1 Phosphorylation

Abstract

In this study, we investigate the role of the receptor-like protein tyrosine phosphatase CD148 in T-cell activation. Overexpression of CD148 in the Jurkat T-cell line inhibited activation of the transcription factor nuclear factor of activated T cells following T-cell receptor (TCR) stimulation but not following stimulation through a heterologously expressed G protein-coupled receptor, the human muscarinic receptor subtype 1. Using a tetracycline-inducible expression system, we show that the TCR-mediated activation of both the Ras and calcium pathways was inhibited by expression of CD148 at levels that approximate those found in activated primary T cells. These effects were dependent on the phosphatase activity of CD148. Analysis of TCR-induced protein tyrosine phosphorylation demonstrated that most phosphoproteins were unaffected by CD148 expression. However, phospholipase Cγ1 (PLCγ1) and LAT were strikingly hypophosphorylated in CD148-expressing cells following TCR stimulation, whereas the phosphorylation levels of Slp-76 and Itk were modestly reduced. Based on these results, we propose that CD148 negatively regulates TCR signaling by interfering with the phosphorylation and function of PLCγ1 and LAT.

ACKNOWLEDGMENTS

We thank G. Koretzky, J. Bolen, M. Tomlinson, and H. Bujard for reagents; L. Kane and M. Kuhne for critical reading of the manuscript; and members of the Weiss lab for helpful suggestions.

J. E. Baker is a research associate and A. Weiss is an investigator of the Howard Hughes Medical Institute.