Tec kinase signaling in T cells is regulated by phosphatidylinositol 3-kinase and the Tec pleckstrin homology domain.

Tec, the prototypical member of the Tec family of tyrosine kinases, is abundantly expressed in T cells and other hemopoietic cell types. Although the functions of Itk and Txk have recently been investigated, little is known about the role of Tec in T cells. Using antisense oligonucleotide treatment to deplete Tec protein from primary T cells, we demonstrate that Tec plays a role in TCR signaling leading to IL-2 gene induction. Interestingly, Tec kinases are the only known family of tyrosine kinases containing a pleckstrin homology (PH) domain. Using several PH domain mutants overexpressed in Jurkat T cells, we show that the Tec PH domain is required for Tec-mediated IL-2 gene induction and TCR-mediated Tec tyrosine phosphorylation. Furthermore, we show that Tec colocalizes with the TCR after TCR cross-linking, and that both the Tec PH and Src homology (SH) 2 domains play a role in this association. Wortmannin, a phosphatidylinositol 3-kinase inhibitor, abolishes Tec-mediated IL-2 gene induction and Tec tyrosine phosphorylation, and partially suppresses Tec colocalization with the activated TCR. Thus, our data implicate the Tec kinase PH domain and phosphatidylinositol 3-kinase in Tec signaling downstream of the TCR.