The number of receptors for factor VII correlates with the ability of cultured cells to initiate coagulation

Abstract

Previously, we showed that cells derived from nonvascular tissues initiate clotting primarily by markedly increasing the activity of coagulation factor VII. Cells derived from vascular tissue do not normally exhibit this property (tissue factor activity). In this study, we have characterized the relationship between the tissue factor activity of cultured cells derived from normal tissues and the number of receptors they possess for coagulation factor VII. Only cultured nonvascular cells expressed tissue factor activity or possessed receptors for 125I-factor VII. Fetal lung cells, the nonvascular tissue with the largest amount of procoagulant and tissue factor activity, possessed the most receptors for 125I-factor VII (880,000/cell). Bovine corneal endothelial cells, the nonvascular tissue possessing the fewest number of receptors (2,400/cell), had the least amount of procoagulant or tissue factor activity. The affinity of nonvascular cells for 125I-factor VII varied for the cells studied (K(d) ≃ 1.3-90 x 10-10 M). Vascular cells expressed no tissue factor activity, nor did they bind 125I-factor VII. 125I-factor VII and unlabeled factor VII bound to cells had identical procoagulant activities. These results indicate that the ability of cultured cells to initiate coagulant may be regulated in part by the number of receptors they possess for factor VII.