Integrin αII b tail distal of GFFKR participates in inside-out αII b β3 activation.
BACKGROUND
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. Research has focused on the conserved GFFKR motif in integrin αII b tails, integrin β cytoplasmic tails and the binding partners of β tails. However, the roles of αII b tail distal of GFFKR motif are unexplored.


OBJECTIVE
To investigate the role of αII b tail distal of GFFKR in talin-mediated inside-out integrin signaling.


METHODS
We used model cell systems to examine the role of αII b tail distal of GFFKR in bidirectional αII b β3 signaling and αII b β3 -talin interactions.


RESULTS
Deletion of amino acid residues after the GFFKR motif in αII b tail moderately decreased β3 (D723R)-induced activation, abolished talin-induced αII b β3 activation in model cells, and inhibited agonist-induced αII b β3 activation in megakaryocytic cells. Furthermore, residues in αII b tail distal of GFFKR did not affect outside-in αII b β3 signaling or αII b β3 -talin interaction. Addition of non-homologous or non-specific amino acids to the GFFKR motif restored αII b β3 activation in model cells and in megakaryocytic cells. Molecular modeling indicates that β3 -bound talin sterically clashes with the αII b tail in the αII b β3 complexes, potentially disfavoring the α-β interactions that keep αII b β3 inactive.


CONCLUSIONS
The αII b tail sequences distal of GFFKR participate in talin-mediated inside-out αII b β3 activation through its steric clashes with β3 -bound talin.
Department of Pancreatic Surgery, West China Hospital, Sichuan University, Chengdu, China.
A
A
Li
Q
Q
Guo
C
C
Kim
W
W
Hu
F
F
Ye
D020816:Amino Acid Motifs; D000818:Animals; D016466:CHO Cells; D006224:Cricetinae; D003412:Cricetulus; D003599:Cytoskeleton / Q000378:metabolism; D006801:Humans; D039661:Integrin beta3 / Q000737:chemistry*; D016086:Lentivirus / Q000378:metabolism; D008024:Ligands; D008533:Megakaryocytes / Q000166:cytology; D008565:Membrane Proteins / Q000737:chemistry; D008856:Microscopy, Fluorescence; D008958:Models, Molecular; D009363:Neoplasm Proteins / Q000737:chemistry; D040201:Platelet Membrane Glycoprotein IIb / Q000737:chemistry*; D011485:Protein Binding; D017434:Protein Structure, Tertiary; D015398:Signal Transduction; D055672:Static Electricity; D016608:Talin / Q000737:chemistry
C475301:FERMT1 protein, human; D039661:Integrin beta3; D008024:Ligands; D008565:Membrane Proteins; D009363:Neoplasm Proteins; D040201:Platelet Membrane Glycoprotein IIb; D016608:Talin
Integrin αIIbβ3; cell adhesion; kindlin-2 protein, human; signal transduction; talin