title: Calcium Integrin Binding Protein Associates with Integrins αVβ3and αIIbβ3Independent of β3Activation Motifs.
abstract: The Calcium Integrin Binding protein (CIB) has been identified as interacting specifically with the cytoplasmic tail of the integrin αIIbdomain to induce receptor activation and integrin αIIbβ3mediated cell adhesion to extracellular proteins. In K562 cells stably expressing mutated integrin αVβ3, or chimeric αVβ3carrying αIIbcytoplasmic tail, we report that the interaction of CIB with β3integrins is not αIIbβ3specific but binds αIIbas well as αVcytoplasmic tail domains. A double mutation of two proline residues to alanine residues in the αIIbcytoplasmic domain, previously shown to disturb its conformation, inhibits chimeric αV/αIIbβ3-CIB interaction. This demonstrates that αIIbcytoplasmic domain loop-like conformation is required for interaction with CIB. Moreover, mutations of β3cytoplasmic domain residues Tyr-747 and/or Tyr-759 to phenylalanine residues (Y747F, Y759F, and Y747,759F) as well as residues Ser-752 to proline or alanine (S752P and S752A), do not affect the αIIbβ3or αVβ3interaction with CIB. Since tyrosine residues Tyr-747 and/or Tyr-759 are the sites of tyrosine phosphorylation of β3subunit, these results suggest that the β3integrin-CIB interaction occurs through a β3-phosphorylation independent mechanism. Likewise, ablation of conformation-dependent affinity change in β3Ser752Pro mutation had no affect on CIB-β3interaction. In summary, our results demonstrate that the αIIb-subunit integrin and CIB interaction is non-exclusive and requires the loop-like αIIb-cytoplasmic domain conformation. An interaction of CIB with αV-containing integrins provides an additional role for this molecule in keeping with its expression outside of platelets.
authors.affiliation: Department of Cell and Developmental Biology, State University of New York Upstate Medical University, Syracuse, USA.
authors.forename: Innocent H
authors.initials: IH
authors.lastname: Yamodo
authors.forename: Scott D
authors.initials: SD
authors.lastname: Blystone
keywords: Activation; Cytoskeleton; Hematopoietic; Integrin; Leukocyte; Signaling