Regulated Association Between the Tyrosine Kinase Emt/Itk/Tsk and Phospholipase-Cγ1 in Human T Lymphocytes

Abstract

AbstractThe Emt/Itk/Tsk tyrosine kinase is involved in intracellular signaling events induced by several lymphocyte surface receptors. Modulation of TCR/CD3-induced phospholipase-Cγ1 (PLCγ1) activity by the tyrosine kinase Emt/Itk/Tsk has been demonstrated based on studies of Itk-deficient murine T lymphocytes. Here we report a TCR/CD3-regulated association between Emt and PLCγ1 in both normal and leukemic T cells. In addition, this association was enhanced following independent ligation of the CD2, CD4, or CD28 costimulatory molecules, but not of CD5 or CD6 surface receptors, correlating to the induced tyrosine phosphorylation of Emt. Before Ab-induced T cell activation, we found that the Emt-SH3 domain was crucial for the constitutive Emt/PLCγ1 association; however, upon TCR/CD3 engagement, the Emt-SH2 domain was more efficient in mediating the enhanced Emt/PLCγ1 interaction. Furthermore, the PLCγ1-SH3 domain, but not the two PLCγ1-SH2 domains, contributed to formation of the protein complex. Thus, we describe a regulated interaction between Emt and PLCγ1, and based on our studies with individual Emt and PLCγ1 SH2/SH3 domains, we propose a mechanism for this association.