title: Identification of lysosome-associated membrane protein-2 as an activation-dependent platelet surface glycoprotein.
abstract: Platelets undergo biochemical and morphologic changes when stimulated that greatly alter their function and contribute to their role in thrombosis and hemostasis. We recently identified and cloned the cDNA for a platelet surface glycoprotein expressed on activated, not resting cells. We found that this protein, lysome-associated membrane protein-1 (LAMP-1), is an integral membrane protein of the lysosome that translocated to the surface membrane when platelets were stimulated by a strong agonist. We now show with immunofluorescence flow cytometry that LAMP-2, a lysosomal membrane protein that shares approximately 30% homology with LAMP-1, is also expressed preferentially on the surface of activated platelets. Equilibrium binding studies with 125I-anti-LAMP-2 IgG showed approximately 1,100 binding sites per thrombin-stimulated platelet and less than 50 per resting platelet. Sucrose gradient ultracentrifugation fractionation of resting platelet sonicates showed that LAMP-2 colocalized with LAMP-1 and with lysosomal enzymes, and not with thrombospondin or serotonin, which are markers of the two other platelet granule compartments, alpha-granules and dense granules. LAMP-2 surface expression was minimal in response to platelet stimulation by weak agonists such as epinephrine and ADP. These data show that LAMP-2, like LAMP-1, translocates from the lysosomal membrane compartment to the surface membrane when platelets are activated. Regulated surface expression of these heavily glycosylated proteins may play a role in the adhesive, prothrombotic phenotype of these cells.
authors.affiliation: Department of Medicine, Cornell University Medical College, New York, NY 10021.
authors.forename: R L
authors.initials: RL
authors.lastname: Silverstein
authors.forename: M
authors.initials: M
authors.lastname: Febbraio
mesh_terms: D000911:Antibodies, Monoclonal / Q000378:metabolism; D015703:Antigens, CD; D001792:Blood Platelets / Q000737:chemistry; D006801:Humans; D051907:Lysosomal Membrane Proteins; D008562:Membrane Glycoproteins / Q000737:chemistry* / Q000276:immunology / Q000378:metabolism; D015394:Molecular Structure; D015539:Platelet Activation / Q000502:physiology*; D011485:Protein Binding
chemical_list: D000911:Antibodies, Monoclonal; D015703:Antigens, CD; D051907:Lysosomal Membrane Proteins; D008562:Membrane Glycoproteins