Correlation between antigenic and functional expression of tissue factor on the surface of cultured human endothelial cells following stimulation by lipopolysaccharide endotoxin

Abstract

Previous studies indicated that E. coli lipopolysaccharide (LPS) induces human umbilical vein endothelial cells (HUVEC) to express tissue factor activity. Using a radiolabeled anti-tissue factor monoclonal antibody to assess cell-surface tissue factor apoprotein antigen and a two-stage amidolytic assay to assess functional tissue factor activity, we have investigated the temporal relationship between antigenic expression and functional expression of tissue factor on the surface of LPS-stimulated HUVEC. Maximum tissue factor apoprotein antigenic expression on the surface of LPS-stimulated HUVEC was achieved in four hours after LPS treatment, while maximum functional tissue factor activity occurred after 6 hours. Specific binding of radiolabelled human factor VIIa to LPS-stimulated HUVEC paralleled the time course of the expression of tissue factor functional activity. Thus, these data indicate that the presence of newly-synthesized tissue factor apoprotein antigen on the cell surface is insufficient by itself for maximal factor VIIa binding to occur, and provide presumptive evidence for the posttranslational processing of tissue factor apoprotein on the cell surface prior to its acquisition of ligand binding function.