Abstract 24: Integrin αIIb Tail Participates in Inside-Out αIIbß3 Activation by Providing a Steric Lever Arm for Talin
Increases in ligand binding to integrins (“activation”) play critical roles in platelet and leukocyte function. Integrin activation requires talin and kindlin binding to integrin β cytoplasmic tails. Much research has focused on the conserved GFFKR motif in integrin αIIb tails for its importance in keeping integrins inactive and integrin β cytoplasmic tails and their interacting partners. However, the roles of αIIb tail distal of GFFKR motif are unexplored. Here, we examine the role of αIIb tail distal of GFFKR in talin-mediated inside-out integrin activation, αIIbβ3 outside-in signaling and αIIbβ3-talin interactions. Deletion of amino acid residues after the GFFKR motif in αIIb tail abolished talin-induced inside-out αIIbβ3 activation without affecting αIIbβ3-talin interaction or outside-in αIIbβ3 signaling in modeled cell systems, measured by cell spreading and Src phosphorylation. Addition of non-homologous or non-specific amino acids to the GFFKR motif restored the capacity of talin to activate αIIbβ3 in modeled cells. Moreover, thrombin-stimulated αIIbβ3 activation in megakaryocytic leukemia cells (CMK cells) are similarly abolished by truncation after GFFKR and restored by adding non-specific sequences. Furthermore, Molecular modeling indicates that β3-bound talin sterically clashes with the αIIb tail in the αIIbβ3 complexes, potentially disfavoring the α-β interactions that keep αIIbβ3 inactive. Thus, the αIIb tail sequences distal of GFFKR participate in talin-mediated inside-out αIIbβ3 activation through its steric clashes with β3-bound talin.
Author Disclosures: F. Ye: None. A. Li: None. Q. Guo: None. W. Hu: None.
- © 2014 by American Heart Association, Inc.