INTERACTION OF PLATELET FACTOR-4 WITH CULTURED VASCULAR ENDOTHELIAL-CELLS

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  • 1 May 1989
    • journal article
    • research article
    • Vol. 73  (6) , 1534-1539
Abstract
Platelets secrete a low-molecular weight protein, platelet factor four (PF-4), which binds to and neutralizes heparin and related sulfated glycosaminoglycans (GAGs). To examine the interactions of PF-4 with the GAGs present on endothelial cell surfaces, we incubated 125I-PF-4 with cell suspensions derived from confluent monolayers of cultured bovine aortic endothelium. Binding of 125I-PF04 was inhibited by a 100-fold excess of nonradioactive PF4 and varied with duration and temperature of incubation. At 4.degree. C, binding reached equilibrium at 20 minutes with kd = 2.87 .mu.mol/L and Bmax of 63.83 pmol/105 cells. Binding capacity was reduced 83.4% by brief incubation of endothelial cells with trypsin and 46.67% by incubation with Flavobacterium heparinase, but was unchanged by chondroitin-ABCase treatment. At 37.degree. CV, PF-4 was internalized by confluent monolayer of bovine aortic endothelial cells primarily through low affinity-adsorptive endocytosis. The internalized PF-4 was degraded to amino acids and small peptides with 50% conversion after 18-hour incubation. These studies demonstrate that a secreted platelet protein can bind to and enter endothelial cells. Binding may explain the rapid clearance of released PF4 from plasma and could have important local effects on endothelial structure and function.