CHARACTERIZATION OF LNK - AN ADAPTER PROTEIN EXPRESSED IN LYMPHOCYTES

Stimulation of the T cell antigen receptor (TCR) activates a set of no n-receptor protein tyrosine kinases that assist in delivering signals to the cell interior. Among the presumed substrates for these kinases, adaptor proteins, which juxtapose effector enzyme systems with the an tigen receptor complex, figure prominently. Previous studies suggested that Lnk, a 38-kDa protein consisting of a single SH2 domain and a re gion containing potential tyrosine phosphorylation sites, might serve to join Grb2, phospholipase C-gamma 1, and phosphatidylinositol 3-kina se to the TCR. To elucidate the physiologicalroles of Lnk in T cell si gnal transduction, we isolated the mouse Lnk cDNA, characterized the s tructure of the mouse Lnk gene, and generated transgenic mice that ove rproduce Lnk in thymocytes. Here we report that although Lnk becomes p hosphoryIated during T cell activation, it plays no limiting role in t he TCR signaling process. Moreover, we have distinguished p38(Lnk) fro m the more prominent 36-kDa tyrosine phosphoproteins that appear in ac tivated T cells. Together these studies suggest that Lnk participates in signaling from receptors other than antigen receptors in lymphocyte s.