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.
Bertagnolli
M E
ME
Department of Biology, University of Utah, Salt Lake City 84112.
Beckerle
M C
MC
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