title: Calcium-dependent properties of CIB binding to the integrin alphaIIb cytoplasmic domain and translocation to the platelet cytoskeleton.
abstract: The alphaIIbbeta3 integrin receives signals in agonist-activated platelets, resulting in its conversion to an active conformation that binds fibrinogen, thereby mediating platelet aggregation. Fibrinogen binding to alphaIIbbeta3 subsequently induces a cascade of intracellular signalling events. The molecular mechanisms of this bi-directional alphaIIbbeta3-mediated signalling are unknown but may involve the binding of proteins to the integrin cytoplasmic domains. We reported previously the sequence of a novel 22-kDa, EF-hand-containing, protein termed CIB (calcium- and integrin-binding protein) that interacts specifically with the alphaIIb cytoplasmic domain in the yeast two-hybrid system. Further analysis of numerous tissues and cell lines indicated that CIB mRNA and protein are widely expressed. In addition, isothermal titration calorimetry indicated that CIB binds to an alphaIIb cytoplasmic-domain peptide in a Ca(2+)-dependent manner, with moderate affinity (K(d), 700 nM) and 1:1 stoichiometry. In aggregated platelets, endogenous CIB and alphaIIbbeta3 translocate to the Triton X-100-insoluble cytoskeleton in a parallel manner, demonstrating that the cellular localization of CIB is regulated, potentially by alphaIIbbeta3. Thus CIB may contribute to integrin-related functions by mechanisms involving Ca(2+)-modulated binding to the alphaIIb cytoplasmic domain and changes in intracellular distribution.
authors.affiliation: Department of Pharmacology, The University of North Carolina at Chapel Hill, CB# 7365, Chapel Hill, NC 27599, USA.
authors.forename: D D
authors.initials: DD
authors.lastname: Shock
authors.forename: U P
authors.initials: UP
authors.lastname: Naik
authors.forename: J E
authors.initials: JE
authors.lastname: Brittain
authors.forename: S K
authors.initials: SK
authors.lastname: Alahari
authors.forename: J
authors.initials: J
authors.lastname: Sondek
authors.forename: L V
authors.initials: LV
authors.lastname: Parise
mesh_terms: D000595:Amino Acid Sequence; D001665:Binding Sites; D001693:Biological Transport, Active; D001792:Blood Platelets / Q000378:metabolism* / Q000648:ultrastructure; D002118:Calcium / Q000378:metabolism*; D002135:Calcium-Binding Proteins; D002151:Calorimetry; D002352:Carrier Proteins / Q000378:metabolism*; D003593:Cytoplasm / Q000378:metabolism*; D003599:Cytoskeleton / Q000378:metabolism*; D003902:Detergents; D006801:Humans; D008969:Molecular Sequence Data; D017830:Octoxynol; D019039:Platelet Glycoprotein GPIIb-IIIa Complex / Q000378:metabolism*; D016133:Polymerase Chain Reaction; D011485:Protein Binding; D011487:Protein Conformation; D012995:Solubility
chemical_list: C109198:CIB1 protein, human; D002135:Calcium-Binding Proteins; D002352:Carrier Proteins; D003902:Detergents; D019039:Platelet Glycoprotein GPIIb-IIIa Complex; D017830:Octoxynol; D002118:Calcium