Identification and characterization of LAMP-1 as an activation-dependent platelet surface glycoprotein.
Platelets normally circulate in a quiescent state. When activated, they undergo biochemical and morphological changes which greatly alter their function and contribute to their role in thrombosis and hemostasis. We have identified, cloned, and sequenced a cDNA from a human unbilical vein endothelial cell library that encodes a 110-kDa integral membrane protein. This protein is present on the surface of activated but not resting platelets and has previously been identified as lysosomal-associated membrane protein 1 (LAMP-1). Half-maximal surface expression of platelet LAMP-1 was induced by concentrations of thrombin that resulted in lysosome enzyme release, not alpha-, or dense granule release. Also consistent with lysosome enzyme studies, there was little surface expression of LAMP-1 in response to the weak agonists ADP and epinephrine. In addition, sucrose density gradient fractionation of platelet granules showed colocalization of LAMP-1 with the lysosomal enzyme, beta-galactosidase, and not with markers of alpha- or dense granules. While we found virtually no LAMP-1 on the resting platelet surface (0-90 molecules/cell), we estimated a mean of 1175 LAMP-1 molecules on the thrombin-activated platelet surface. The translocation of this heavily glycosylated protein to the platelet surface upon stimulation may play a role in the adhesive, prothrombic nature of these cells.
Febbraio
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Department of Medicine, Cornell University Medical College, New York, New York 10021.
Silverstein
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D015703:Antigens, CD; D001792:Blood Platelets / Q000378:metabolism*; D015152:Blotting, Northern; D015153:Blotting, Western; D015815:Cell Adhesion Molecules / Q000378:metabolism; D002451:Cell Compartmentation; D003001:Cloning, Molecular; D015870:Gene Expression; D006801:Humans; D066298:In Vitro Techniques; D051907:Lysosomal Membrane Proteins; D008247:Lysosomes / Q000378:metabolism*; D008562:Membrane Glycoproteins / Q000378:metabolism*; D008970:Molecular Weight; D015539:Platelet Activation; D010980:Platelet Membrane Glycoproteins / Q000378:metabolism*; D013917:Thrombin / Q000494:pharmacology
D015703:Antigens, CD; D015815:Cell Adhesion Molecules; D051907:Lysosomal Membrane Proteins; D008562:Membrane Glycoproteins; D010980:Platelet Membrane Glycoproteins; D013917:Thrombin