Synthesis and secretion of thrombospondin by cultured human endothelial cells

Abstract

Thombospondin, the major glycoprotein released from α-granules of thrombinstimulated platelets, is a disulfide-bonded trimer of 160 kilodalton subunits and apparently functions as a platelet lectin. Because cultured human umbilical vein endothelial cells synthesize and secrete a glycoprotein (GP-160) which is a disulfide-bonded multimer of 160 Walton subunits, the possibility that GP-160 is thrombospondin was investigated. Tritiated GP-160 could be immunoisolated from [3H]leucine-labeled endothelial cell postculture medium using a rabbit antiserum to human platelet thrombospondin. Thrombospondin and GP-160 comigrated in two different two-dimensional electrophoretic systems. Both proteins are disulfidebonded trimers of acidic 160-kdalton subunits. A competitive radioimmunoassay for binding of 125 l-thrombospondin to the rabbit antibodies indicated that 49 µg of thrombospondin antigen per 106 confluent endothelial cells accumulated in postculture medium over 24 h. Thus, endothelial cells secrete large amounts of a glycoprotein that is identical or very similar to platelet thrombospondin. © 1982, Rockefeller University Press., All rights reserved.