Eck receptor protein tyrosine kinase-signal transduction and functions.

Receptor protein tyrosine kinases (RPTKs) are of fundamental importance in processes such as cell proliferation, survival and differentiation. The Eph subfamily is the largest subfamily of RPTKs with 13 members having been discovered to date. Eck was the first member of this subfamily for which a ligand was characterized. B61, a cytokine-inducible gene product originally isolated from tumor necrosis factor-alpha (TNF-$\alpha$) stimulated endothelial cells, was recently shown to be the ligand for the Eck RPTK. In this study, using the yeast two-hybrid system, two molecules that are involved in transducing signals from activated Eck RPTK were identified. The first was the p85 subunit of phosphatidylinositol 3-kinase (PI 3-kinase). It was shown that the p85 subunit bound activated Eck RPTK via its C terminal SH2 domain. Activation of Eck by its ligand, B61, stimulated PI 3-kinase activity in vascular smooth muscle cells. The second molecule that identified was a novel gene product. It was designated Src like adapter protein (SLAP) based on its striking homology to SH3 and SH2 domains of the Src family of kinases and the absence of a catalytic tyrosine kinase domain. These two molecules are the first reports of any signaling intermediates engaged by the activated Eck RPTK. Endothelial cells were found to express the Eck RPTK which is the counterreceptor for B61. Further, it was shown that B61 could act as an angiogenic factor in vivo and a chemoattractant for endothelial cells in vitro. The Eck RPTK was activated by TNF-$\alpha$ through induction of B61, and an antibody to B61 attenuated angiogenesis induced by TNF-$\alpha$ but not by basic fibroblast growth factor. This finding suggests the existence of an autocrine or paracrine loop involving activation of the Eck RPTK by its inducible ligand after an inflammatory stimulus, the net effect of which would be to promote angiogenesis, a hallmark of chronic inflammation. These are the first functions ascribed to any member of this large family of receptor tyrosine kinases.PhDPathologyUniversity of Michigan, Horace H. Rackham School of Graduate Studieshttp://deepblue.lib.umich.edu/bitstream/2027.42/104685/1/9542926.pdfDescription of 9542926.pdf : Restricted to UM users only