title: Calcium-and integrin-binding protein regulates focal adhesion kinase activity during platelet spreading on immobilized fibrinogen.
abstract: Platelet spreading on the subendothelium in response to vascular injury is fundamental to the regulation of physiologic hemostasis. Previously, we have shown that, when bound to glycoprotein IIb (GPIIb), calcium- and integrin-binding protein (CIB) regulates platelet spreading on immobilized fibrinogen (Fg). In this study, we investigated the signaling events that occur downstream of CIB in the absence of signaling that occurs as a result of granular secretion. Using Chinese hamster ovary (CHO) cells as a model, we demonstrate that CIB induces cell migration. Immunofluorescence analysis of CIB localization indicates that endogenous CIB accumulates in areas of focal adhesions, and its overexpression up-regulates the formation of focal adhesion complexes compared with control cells. Immunoprecipitation analysis indicates that CIB associates with focal adhesion kinase (FAK), a key regulator in focal complex formation, and up-regulates its activity. Overexpression of dominant-negative FAK, FRNK, along with CIB in CHO cells completely inhibits CIB-induced cell migration. Further, confirmation of these data in the platelet system indicates that CIB and FAK associate throughout all stages of platelet spreading but only on Fg binding to GPIIb/IIIa. Taken together, our results suggest that CIB regulates platelet spreading through the regulation of FAK activation.
authors.affiliation: Department of Biological Sciences, University of Delaware, Newark, DE 19716, USA. unaik@udel.edu
authors.forename: Meghna U
authors.initials: MU
authors.lastname: Naik
authors.forename: Ulhas P
authors.initials: UP
authors.lastname: Naik
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D001792:Blood Platelets / Q000166:cytology / Q000502:physiology*; D016466:CHO Cells; D002135:Calcium-Binding Proteins; D002352:Carrier Proteins / Q000378:metabolism / Q000502:physiology*; D002465:Cell Movement; D006224:Cricetinae; D005340:Fibrinogen / Q000378:metabolism*; D051417:Focal Adhesion Kinase 1; D051416:Focal Adhesion Protein-Tyrosine Kinases; D006801:Humans; D015539:Platelet Activation; D019039:Platelet Glycoprotein GPIIb-IIIa Complex / Q000378:metabolism; D011505:Protein-Tyrosine Kinases / Q000096:biosynthesis / Q000378:metabolism*; D015398:Signal Transduction; D014471:Umbilical Veins / Q000166:cytology; D015854:Up-Regulation
chemical_list: C109198:CIB1 protein, human; D002135:Calcium-Binding Proteins; D002352:Carrier Proteins; D019039:Platelet Glycoprotein GPIIb-IIIa Complex; D005340:Fibrinogen; D011505:Protein-Tyrosine Kinases; D051417:Focal Adhesion Kinase 1; D051416:Focal Adhesion Protein-Tyrosine Kinases; C496050:PTK2 protein, human