title: Involvement of the beta3 E749ATSTFTN756 region in stabilizing integrin alphaIIbbeta3-ligand interaction.
abstract: Platelet integrin alphaIIbbeta3 must be activated via intracellular mechanisms before it binds soluble ligands, and it is thought to be activated at its extracellular site by surface-bound ligands. Integrin activation is associated with rearrangement of the cytoskeleton and phosphorylation of proteins that become localized in focal contacts. In these processes, the cytoplasmic tail of the beta-subunit plays a central role. We introduced peptides homologous to the E749ATSTFTN756 domain (E-N peptide) and the T755NITYRGT762 domain (T-T peptide) of beta3 in streptolysin O-permeabilized platelets and analyzed the initial interaction with soluble fibronectin, fibrinogen and PAC-1 after stimulation with thrombin. E-N peptide left the initial binding of fibronectin intact but interfered with stable receptor occupancy. E-N peptide also inhibited fibrinogen binding, thereby reducing the formation of large aggregates. Strikingly, E-N peptide did not disturb the binding of PAC-1, which is known to reflect activation of the integrin. E-N peptide also inhibited tyrosine phosphorylation of focal adhesion kinase, a response known to be dependent on alphaIIbbeta3. T-T peptide did not affect these processes. In a model for outside-in integrin activation, E-N peptide disrupted the binding of CHO cells expressing alphaIIbbeta3 to surface-bound ligand. Again, T-T peptide had no effect. We conclude that the E749ATSTFTN756 region of the beta3-tail stabilizes the binding of soluble and surface-bound ligand to integrin alphaIIbbeta3 via a mechanism that involves the phosphorylation of FAK.
authors.affiliation: Laboratory for Thrombosis and Haemostasis, Department of Haematology, University Medical Center Utrecht, NL-3508 GA Utrecht, the Netherlands.
authors.forename: P E M H
authors.initials: PE
authors.lastname: Litjens
authors.forename: G
authors.initials: G
authors.lastname: Gorter
authors.forename: J
authors.initials: J
authors.lastname: Ylänne
authors.forename: J-W N
authors.initials: JW
authors.lastname: Akkerman
authors.forename: G
authors.initials: G
authors.lastname: van Willigen
mesh_terms: D000818:Animals; D001792:Blood Platelets / Q000166:cytology / Q000378:metabolism; D016466:CHO Cells; D002460:Cell Line; D006224:Cricetinae; D003593:Cytoplasm / Q000378:metabolism; D003599:Cytoskeleton / Q000378:metabolism; D005340:Fibrinogen / Q000737:chemistry; D005353:Fibronectins / Q000737:chemistry / Q000378:metabolism; D051417:Focal Adhesion Kinase 1; D051416:Focal Adhesion Protein-Tyrosine Kinases; D006801:Humans; D008024:Ligands; D010455:Peptides / Q000737:chemistry; D010766:Phosphorylation; D019039:Platelet Glycoprotein GPIIb-IIIa Complex / Q000737:chemistry* / Q000378:metabolism; D011485:Protein Binding; D017434:Protein Structure, Tertiary; D011505:Protein-Tyrosine Kinases / Q000378:metabolism; D013917:Thrombin / Q000737:chemistry; D013997:Time Factors; D014443:Tyrosine / Q000378:metabolism
chemical_list: D005353:Fibronectins; D008024:Ligands; D010455:Peptides; D019039:Platelet Glycoprotein GPIIb-IIIa Complex; D014443:Tyrosine; D005340:Fibrinogen; D011505:Protein-Tyrosine Kinases; D051417:Focal Adhesion Kinase 1; D051416:Focal Adhesion Protein-Tyrosine Kinases; C496050:PTK2 protein, human; D013917:Thrombin