Regulation of von Willebrand factor binding to the platelet glycoprotein Ib-IX by a membrane skeleton-dependent inside-out signal.
The platelet receptor for von Willebrand factor (vWF), glycoprotein Ib-IX (GPIb-IX), mediates initial platelet adhesion and activation. We show here that the receptor function of GPIb-IX is regulated intracellularly via its link to the filamin-associated membrane skeleton. Deletion of the filamin binding site in GPIb(alpha) markedly enhances ristocetin- (or botrocetin)-induced vWF binding and allows GPIb-IX-expressing cells to adhere to immobilized vWF under both static and flow conditions. Cytochalasin D (CD) that depolymerizes actin also enhances vWF binding to wild type GPIb-IX. Thus, vWF binding to GPIb-IX is negatively regulated by the filamin-associated membrane skeleton. In contrast to native vWF, binding of the isolated recombinant vWF A1 domain to wild type and filamin binding-deficient mutants of GPIb-IX is comparable, suggesting that the membrane skeleton-associated GPIb-IX is in a state that prevents access to the A1 domain in macromolecular vWF. In platelets, there is a balance of membrane skeleton-associated and free forms of GPIb-IX. Treatment of platelets with CD increases the free form and enhances vWF binding. CD also reverses the inhibitory effects of prostaglandin E1 on vWF binding to GPIb-IX. Thus, GPIb-IX-dependent platelet adhesion is doubly controlled by vWF conformation and a membrane skeleton-dependent inside-out signal.
Department of Pharmacology, University of Illinois, College of Medicine, Chicago, Illinois 60612, USA.
G D
GD
Englund
R J
RJ
Bodnar
Z
Z
Li
Z M
ZM
Ruggeri
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X
Du
D000818:Animals; D001665:Binding Sites; D001792:Blood Platelets / Q000502:physiology*; D016466:CHO Cells; D002448:Cell Adhesion; D002462:Cell Membrane / Q000502:physiology*; D003285:Contractile Proteins / Q000378:metabolism; D006224:Cricetinae; D064448:Filamins; D006801:Humans; D008840:Microfilament Proteins / Q000378:metabolism; D016296:Mutagenesis; D019038:Platelet Glycoprotein GPIb-IX Complex / Q000737:chemistry / Q000378:metabolism*; D010980:Platelet Membrane Glycoproteins; D011994:Recombinant Proteins / Q000737:chemistry / Q000378:metabolism; D017384:Sequence Deletion; D014162:Transfection; D014841:von Willebrand Factor / Q000737:chemistry / Q000378:metabolism*
D003285:Contractile Proteins; D064448:Filamins; D008840:Microfilament Proteins; D019038:Platelet Glycoprotein GPIb-IX Complex; D010980:Platelet Membrane Glycoproteins; D011994:Recombinant Proteins; C032193:glycoprotein receptor GPIb-IX; D014841:von Willebrand Factor