A platelet alpha granule membrane protein that is associated with the plasma membrane after activation. Characterization and subcellular localization of platelet activation-dependent granule-external membrane protein.

Abstract

We have identified and purified a platelet integral membrane protein (140,900 mol wt), using the KC4 monoclonal antibody specific for activated platelets, that is internal in resting platelets but exposed on activated platelets (Hsu-Lin S.-C., C. L. Berman, B. C. Furie, D. August, and B. Furie, 1984, J. Biol. Chem. 259: 9121-9126.). The expression ofthe protein on the platelet surface is secretion-dependent. This protein has been named platelet activation-dependent granule-external membrane (PADGEM) protein. PADGEM protein is distinct from the surface glycoproteins of resting platelets, but identical to the S12 antigen, GMP-140. Using immunofluorescent staining, resting platelets failed to stain for PADGEM protein with the KC4 antibody, but after permeabilization showed a punctate staining of the cell interior. Thrombin-stimulated intact platelets stained with a peripheral rim pattern thus demonstrating the translocation of PADGEM protein from an internal location to the cell surface. PADGEM protein expression on the platelet surface at varying thrombin concentrations correlated with alpha granule release, as measured by the secretion of platelet factor 4. Further evidence for an alpha granule localization of PADGEM protein was provided by nitrogen cavitation of resting platelets followed by metrizamide density gradient centrifugation; PADGEM protein codistributed with platelet factor 4. Using immunoelectron microscopy, the protein was localized to the alpha granule in frozen ultrathin sections of resting platelets labeled using rabbit anti-PADGEM protein antibodies, whereas in thrombin-activated platelets, the plasma membrane was labeled. These studies indicate that PADGEM protein is a component of the alpha granule membrane of resting platelets and is incorporated into the plasma membrane upon activation and secretion.

Expression of Selectin Families and Their Ligand Sialyl Lewis X in the Muscles of Inflammatory Myopathies. An Immunohistochemical Study.

“…However, the most strong immunoreactivity of P-selectin shown in inflammatory myopathies suggested the importance of this molecule in the mechanisms of leukodiapedesis. P-selectin is originally stored in Weibel-Palade body of vascular endothelial cells and in ocgranules of platelets and is translocated to the surface membrane immediately after the activating stimuli such as thrombin (17). So the expression of P-selectin is much faster than Eselectin.…”

Gray platelet syndrome. Dissociation between abnormal sorting in megakaryocyte alpha-granules and normal sorting in Weibel-Palade bodies of endothelial cells.

“…However, the transmembrane protein P-selectin, also called CD62, PADGEM, or GMP. 140 (8,9), is expressed along the membranes ofintracellular vesicles in gray platelets and fuse normally with the cell surface after activation (10), as in normal platelets (8, 9, 1 1 ).…”

A Balance of Opposing Signals within the Cytoplasmic Tail Controls the Lysosomal Targeting of P-selectin

“…P-selectin is a type I membrane protein originally found within the secretory organelles of endothelial cells and platelets (21)(22)(23). Following the stimulation of these cells with thrombin or other agonists, it is redistributed to the plasma membrane (24 -26) and then rapidly internalized (27)(28)(29)(30)(31).…”