title: Activation of Syk protein tyrosine kinase through interaction with integrin beta cytoplasmic domains.
abstract: Syk protein tyrosine kinase is essential for immune system development and function [1]and for the maintenance of vascular integrity [2,3]. In leukocytes, Syk is activated by binding to diphosphorylated immune receptor tyrosine-based activation motifs (pITAMs)[1]. Syk can also be activated by integrin adhesion receptors [4,5], but the mechanism of its activation is unknown. Here we report a novel mechanism for Syk's recruitment and activation, which requires that Syk bind to the integrin beta3 cytoplasmic tail. We found that both Syk and the related kinase ZAP-70 bound the beta3 cytoplasmic tail through their tandem SH2 domains. However, unlike Syk binding to pITAMs, this interaction was independent of tyrosine phosphorylation and of the phosphotyrosine binding function of Syk's tandem SH2 domains. Deletion of the four C-terminal residues of the beta3 cytoplasmic tail [beta3(759X)] decreased Syk binding and disrupted its physical association with integrin alphaIIbbeta3. Furthermore, cells expressing alphaIIbbeta3(759X) failed to exhibit Syk activation or lamellipodia formation upon cell adhesion to the alphaIIbbeta3 ligand, fibrinogen. In contrast, FAK phosphorylation and focal adhesion formation were unimpaired by this mutation. Thus, the direct binding of Syk kinase to the integrin beta3 cytoplasmic tail is a novel and functionally significant mechanism for the regulation of this important non-receptor tyrosine kinase.
authors.affiliation: Department of Vascular Biology, The Scripps Research Institute, La Jolla, CA 92037, USA.
authors.forename: D G
authors.initials: DG
authors.lastname: Woodside
authors.forename: A
authors.initials: A
authors.lastname: Obergfell
authors.forename: L
authors.initials: L
authors.lastname: Leng
authors.forename: J L
authors.initials: JL
authors.lastname: Wilsbacher
authors.forename: C K
authors.initials: CK
authors.lastname: Miranti
authors.forename: J S
authors.initials: JS
authors.lastname: Brugge
authors.forename: S J
authors.initials: SJ
authors.lastname: Shattil
authors.forename: M H
authors.initials: MH
authors.lastname: Ginsberg
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D015703:Antigens, CD / Q000235:genetics / Q000378:metabolism*; D016466:CHO Cells; D018797:Cell Cycle Proteins; D006224:Cricetinae; D003593:Cytoplasm / Q000378:metabolism; D004789:Enzyme Activation; D004792:Enzyme Precursors / Q000378:metabolism*; D051416:Focal Adhesion Protein-Tyrosine Kinases; D039661:Integrin beta3; D016023:Integrins / Q000235:genetics / Q000378:metabolism*; D047908:Intracellular Signaling Peptides and Proteins; D008969:Molecular Sequence Data; D010766:Phosphorylation; D010980:Platelet Membrane Glycoproteins / Q000235:genetics / Q000378:metabolism*; D011505:Protein-Tyrosine Kinases / Q000378:metabolism*; D011518:Proto-Oncogene Proteins / Q000378:metabolism; D051567:Proto-Oncogene Proteins c-vav; D000072377:Syk Kinase; D051746:ZAP-70 Protein-Tyrosine Kinase; D018909:src Homology Domains
chemical_list: D015703:Antigens, CD; D018797:Cell Cycle Proteins; D004792:Enzyme Precursors; D039661:Integrin beta3; D016023:Integrins; D047908:Intracellular Signaling Peptides and Proteins; D010980:Platelet Membrane Glycoproteins; D011518:Proto-Oncogene Proteins; D051567:Proto-Oncogene Proteins c-vav; D011505:Protein-Tyrosine Kinases; D051416:Focal Adhesion Protein-Tyrosine Kinases; D000072377:Syk Kinase; D051746:ZAP-70 Protein-Tyrosine Kinase