Chemotactic factor-induced recruitment and activation of Tec family kinases in human neutrophils - Implication of phosphatidylinositol 3-kinases

The importance of the tyrosine phosphorylation cascades in the initiation and regulation of the functional responsiveness of human neutrophils is well established. On the other hand, the link between the G protein-coupled receptors (to which the receptors for chemotactic factors belong) and the activation of tyrosine kinases is very poorly characterized. Based on previous observations indicating that the stimulation of tyrosine phosphorylation was sensitive to inhibition by the phosphatidylinositol 3-kinase inhibitor wortmannin and the recent description of pleckstrin homology domain-containing tyrosine kinases (the Tee family), we have examined the potential implication of the latter in the responses of human neutrophils to chemotactic factors. The results obtained indicate firstly that several members of the Tee family of tyrosine kinases are expressed in human neutrophils, including Tee, Btk, and Bmx. Stimulation of the cells with fMet-Leu-Phe led to a rapid activation of Tee as indicated by its translocation to a membrane fraction and to increases in its in situ level of tyrosine phosphorylation and its capacity to tyrosine phosphorylate itself or an exogenous substrate (SAM68-GST) in in vitro kinase assays. The activation of Tee was inhibited by pertussis toxin as well as by wortmannin. The results of this study provide direct evidence for the implication of Tee family kinases in the responses of human neutrophils to chemotactic factors. They also suggest that one of the links between G protein-coupled receptors and tyrosine kinases depends on the activation of phosphatidylinositol 3-kinase and the generation of phosphatidylinositol 3,4,5-trisphosphate.