Evidence for the selective association of a subpopulation of GPIIb-IIIa with the actin cytoskeletons of thrombin-activated platelets.
Activation of blood platelets triggers a series of responses leading to the formation and retraction of blood clots. Among these responses is the establishment of integrin-mediated transmembrane connections between extracellular matrix components and the actin cytoskeleton of the platelet. Here we report that a specific subpopulation of the major platelet integrin, glycoprotein IIb-IIIa (GPIIb-IIIa) (also referred to as alpha IIb beta 3 integrin), becomes incorporated into the detergent-insoluble actin cytoskeleton of platelets during the platelet activation response. The cytoskeletal association of GPIIb-IIIa is independent of platelet aggregation and fibrin sedimentation and is sensitive to cytochalasin D treatment. As determined by Western immunoblot analysis, approximately 22% of the total cellular GPIIb-IIIa becomes associated with the actin cytoskeleton upon thrombin activation in a manner that is independent of the detection of talin, alpha-actinin, or vinculin in the complex. We found that the cytoskeleton-associated GPIIb-IIIa is derived from an intracellular source since it is not available for lactoperoxidase-catalyzed radioiodination before platelet activation. Two intracellular sources of GPIIb-IIIa are present in resting platelets: GPIIb-IIIa associated with the alpha-granule secretory compartment as well as surface-inaccessible domains of the surface-connected canalicular system. Interestingly, alpha-granule secretion, which occurs in thrombin-activated platelets and results in the translocation of intracellular GPIIb-IIIa to the plasma membrane, appears to be required for the cytoskeleton incorporation of GPIIb-IIIa that we observe. Collectively, our data provide evidence that a subpopulation of GPIIb-IIIa derived from an intracellular source is selectively linked to the actin cytoskeleton of platelets upon thrombin activation in the absence of platelet aggregation.
Department of Biology, University of Utah, Salt Lake City 84112.
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ME
Bertagnolli
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MC
Beckerle
D000199:Actins / Q000097:blood*; D000595:Amino Acid Sequence; D001792:Blood Platelets / Q000378:metabolism*; D015153:Blotting, Western; D003599:Cytoskeleton / Q000378:metabolism*; D006801:Humans; D066298:In Vitro Techniques; D008969:Molecular Sequence Data; D015539:Platelet Activation / Q000502:physiology; D010980:Platelet Membrane Glycoproteins / Q000378:metabolism*; D013917:Thrombin
D000199:Actins; D010980:Platelet Membrane Glycoproteins; D013917:Thrombin