A point mutation in the integrin beta 3 cytoplasmic domain (S752-->P) impairs bidirectional signaling through alpha IIb beta 3 (platelet glycoprotein IIb-IIIa).
Agonist-induced inside-out signaling results in an increased affinity of integrin alpha IIb beta 3 (platelet glycoprotein IIb-IIIa) for soluble ligands (fibrinogen [Fg] and PAC1). Ligand binding to integrins initiates outside-in signaling that leads to cellular responses such as cell spreading and focal adhesion formation. A point mutation in the beta 3 cytoplasmic domain (S752-->P) is associated with blocked inside-out alpha IIb beta 3 signaling in a variant Glanzmann's thrombasthenia. This mutation was introduced into beta 3 and cotransfected into Chinese hamster ovary cells with a chimeric alpha subunit consisting of the alpha IIb extracellular and transmembrane domains and the alpha 6B cytoplasmic domain. The substitution of the alpha IIb cytoplasmic domain with that of alpha 6 led to activation of alpha IIb beta 3 to bind PAC1, mimicking inside-out signaling. This effect was reversed by the S752-->P mutation, indicating a disruption of inside-out signaling by the mutation. In addition, transfectants expressing this beta 3 variant showed reduced alpha IIb beta 3-mediated cell spreading on immobilized Fg, focal adhesion, and fibrin clot retraction, suggesting an impairment in outside-in alpha IIb beta 3 signaling. Therefore, a single point mutation in the beta 3 cytoplasmic domain impaired bidirectional signaling through alpha IIb beta 3.
Chen
Y P
YP
Department of Vascular Biology, Scripps Research Institute, La Jolla, CA 92037.
O'Toole
T E
TE
Ylänne
J
J
Rosa
J P
JP
Ginsberg
M H
MH
D000818:Animals; D016466:CHO Cells; D002448:Cell Adhesion; D006224:Cricetinae; D003593:Cytoplasm / Q000378:metabolism; D005340:Fibrinogen / Q000378:metabolism; D006801:Humans; D039661:Integrin beta3; D016023:Integrins / Q000737:chemistry / Q000235:genetics* / Q000502:physiology; D008855:Microscopy, Electron, Scanning; D010980:Platelet Membrane Glycoproteins / Q000502:physiology*; D017354:Point Mutation; D015398:Signal Transduction; D013915:Thrombasthenia / Q000235:genetics; D014162:Transfection
D039661:Integrin beta3; D016023:Integrins; D010980:Platelet Membrane Glycoproteins; D005340:Fibrinogen