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

The platelet membrane is lined with a membrane skeleton that associate s 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 si gnaling, 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 stud y shows that DRP (dystrophin-related protein) sediments from lysed pla telets along with membrane skeleton proteins, Sedimentation results fr om association with the membrane skeleton because DRP was released int o the detergent-soluble fraction when actin filaments were depolymeriz ed, Interaction of fibrinogen with the integrin alpha(IIb)beta(3) indu ces platelet aggregation, transmembrane signaling, and the formation o f integrin-rich cytoskeletal complexes that can be sedimented from det ergent 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 t hat 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-sp eed detergent-insoluble fraction. These studies show that DRP is part of the platelet membrane skeleton and indicate that DRP participates i n the cytoskeletal reorganizations resulting from signal transmission between extracellular adhesive ligand and the interior of the cell.