DYSTROPHIN-RELATED PROTEIN IN THE PLATELET MEMBRANE SKELETON - INTEGRIN-INDUCED CHANGE IN DETERGENT-INSOLUBILITY AND CLEAVAGE BY CALPAIN IN AGGREGATING PLATELETS

The platelet membrane is lined with a membrane skeleton that associates with transmembrane adhesion receptors and is thought to play a role in regulating the stability of the membrane, distribution and function of adhesive receptors, and adhesive receptor-induced transmembrane signaling, When platelets are lysed with Triton X-100, cytoplasmic actin filaments can be sedimented by centrifugation at low g-forces (15,600 x g) but the membrane skeleton requires 100,000 x g. The present study shows that DRP (dystrophin-related protein) sediments from lysed platelets along with membrane skeleton proteins, Sedimentation results from association with the membrane skeleton because DRP was released into the detergent-soluble fraction when actin filaments were depolymerized, Interaction of fibrinogen with the integrin alpha(IIb)beta(3) induces platelet aggregation, transmembrane signaling, and the formation of integrin-rich cytoskeletal complexes that can be sedimented from detergent lysates at low g-forces. Like other membrane skeleton proteins, DRP redistributed from the high-speed pellet to the integrin-rich low-speed pellet of aggregating platelets, One of the signaling enzymes that is activated following alpha(IIb)beta(3)-ligand interactions in a platelet aggregate is calpain; DRP was cleaved by calpain to generate a similar to 140-kDa fragment that remained associated with the low-speed detergent-insoluble fraction. These studies show that DRP is part of the platelet membrane skeleton and indicate that DRP participates in the cytoskeletal reorganizations resulting from signal transmission between extracellular adhesive ligand and the interior of the cell.