title: Translocation of the Csk homologous kinase (Chk/Hyl) controls activity of CD36-anchored Lyn tyrosine kinase in thrombin-stimulated platelets.
abstract: Chk/Hyl is a recently isolated non-receptor tyrosine kinase with greatest homology to a ubiquitous negative regulator of Src family kinases, Csk. To understand the significance of co-expression of Chk and Csk in platelets, we examined the subcellular localization of each protein. Chk, but not Csk, was completely translocated from the Triton X-100-soluble to the Triton X-100-insoluble cytoskeletal fraction within 10 s of thrombin stimulation. Chk and Lyn, but not Csk and c-Src, co-fractionated in the higher density lysate fractions of resting platelets, with Chk being found to localize close to CD36 (membrane glycoprotein IV)-anchored Lyn. The kinase activity of co-fractionated Lyn was suppressed 3-fold. In vitro phosphorylation assays showed that Chk suppressed Lyn activity by phosphorylating its C-terminal negative regulatory tyrosine. Upon stimulation of platelets with thrombin, the rapid and complete translocation of Chk away from Lyn caused concomitant activation of Lyn. This activation was accompanied by dephosphorylation of Lyn at its C-terminal negative regulatory tyrosine in cooperation with a protein tyrosine phosphatase. These results suggest that Chk, but not Csk, may function as a translocation-controlled negative regulator of CD36-anchored Lyn in thrombin-induced platelet activation.
authors.affiliation: Department of Cell Differentiation, Institute of Molecular Embryology and Genetics, Kumamoto University School of Medicine, Honjo, Japan.
authors.forename: A
authors.initials: A
authors.lastname: Hirao
authors.forename: I
authors.initials: I
authors.lastname: Hamaguchi
authors.forename: T
authors.initials: T
authors.lastname: Suda
authors.forename: N
authors.initials: N
authors.lastname: Yamaguchi
mesh_terms: D000818:Animals; D000911:Antibodies, Monoclonal / Q000378:metabolism; D001692:Biological Transport; D001792:Blood Platelets / Q000201:enzymology*; D018955:CD36 Antigens / Q000378:metabolism*; D019556:COS Cells; D002462:Cell Membrane / Q000201:enzymology; D003599:Cytoskeleton / Q000378:metabolism; D004789:Enzyme Activation; D006801:Humans; D046911:Macromolecular Substances; D008533:Megakaryocytes / Q000201:enzymology*; D008958:Models, Molecular; D010766:Phosphorylation; D015539:Platelet Activation / Q000187:drug effects*; D011505:Protein-Tyrosine Kinases / Q000276:immunology / Q000378:metabolism*; D016392:Proto-Oncogene Proteins pp60(c-src); D013917:Thrombin / Q000494:pharmacology*; D019061:src-Family Kinases / Q000378:metabolism*
chemical_list: D000911:Antibodies, Monoclonal; D018955:CD36 Antigens; D046911:Macromolecular Substances; D011505:Protein-Tyrosine Kinases; C085377:MATK protein, human; D016392:Proto-Oncogene Proteins pp60(c-src); C060902:lyn protein-tyrosine kinase; D019061:src-Family Kinases; D013917:Thrombin