title: Integrin cytoplasmic tyrosine motif is required for outside-in alphaIIbbeta3 signalling and platelet function.
abstract: Integrins not only bind adhesive ligands, they also act as signalling receptors. Both functions allow the integrin alphaIIbbeta3 to mediate platelet aggregation. Platelet agonists activate alphaIIbbeta3 (inside-out signalling) to allow the binding of soluble fibrinogen. Subsequent platelet aggregation leads to outside-in alphaIIbbeta3 signalling, which results in calcium mobilization, tyrosine phosphorylation of numerous proteins including beta3 itself, increased cytoskeletal reorganisation and further activation of alphaIIbbeta3. Thus, outside-in signals enhance aggregation, although the mechanisms and functional consequences of specific signalling events remain unclear. Here we describe a mouse that expresses an alphaIIbbeta3 in which the tyrosines in the integrin cytoplasmic tyrosine motif have been mutated to phenylalanines. These mice are selectively impaired in outside-in alphaIIbbeta3 signalling, with defective aggregation and clot-retraction responses in vitro, and an in vivo bleeding defect which is characterized by a pronounced tendency to rebleed. These data provide evidence for an important role of outside-in signalling in platelet physiology. Furthermore, they identify the integrin cytoplasmic tyrosine motif as a key mediator of beta-integrin signals and a potential target for new therapeutic agents.
authors.affiliation: COR Therapeutics, Inc., South San Francisco, California 94080, USA.
authors.forename: D A
authors.initials: DA
authors.lastname: Law
authors.forename: F R
authors.initials: FR
authors.lastname: DeGuzman
authors.forename: P
authors.initials: P
authors.lastname: Heiser
authors.forename: K
authors.initials: K
authors.lastname: Ministri-Madrid
authors.forename: N
authors.initials: N
authors.lastname: Killeen
authors.forename: D R
authors.initials: DR
authors.lastname: Phillips
mesh_terms: D020816:Amino Acid Motifs; D000818:Animals; D001760:Bleeding Time; D001777:Blood Coagulation; D001792:Blood Platelets / Q000502:physiology*; D003001:Cloning, Molecular; D003593:Cytoplasm / Q000378:metabolism; D005340:Fibrinogen / Q000378:metabolism; D066298:In Vitro Techniques; D051379:Mice; D010766:Phosphorylation; D010974:Platelet Aggregation / Q000502:physiology; D019039:Platelet Glycoprotein GPIIb-IIIa Complex / Q000235:genetics / Q000378:metabolism*; D017354:Point Mutation; D015398:Signal Transduction; D014443:Tyrosine / Q000378:metabolism*
chemical_list: D019039:Platelet Glycoprotein GPIIb-IIIa Complex; D014443:Tyrosine; D005340:Fibrinogen