Absence of interactions between histidine-rich glycoprotein and heparin-like compounds on cultured porcine aortic endothelial cells

Abstract

A role of histidine-rich glycoprotein in controlling heparin-like compounds on the endothelial cell surface is yet unclear. Incubation of purified porcine ¹²⁵I-histidine-rich glycoprotein retaining heparin neutralizing activity with cultured porcine aortic endothelial cells resulted in only unsaturable binding that is not inhibited by excess unlabeled histidine-rich glycoprotein. This binding was not inhibited by excess unlabeled purified porcine antithrombin III or protamine sulfate and by prior treatment of endothelial cells with heparitinase. On the other hand, displacement of ¹²⁵I-antithrombin III specifically bound to endothelial cells by unlabeled histidine-rich glycoprotein was much less potent than that by unlabeled antithrombin III. The endothelial cell-mediated acceleration of thrombin inactivation by antithrombin III was diminished by protamine sulfate, but was not affected by histidine-rich glycoprotein even at a histidine-rich glycoprotein/antithrombin III molar of -7:1. These data indicate that histidine-rich glycoprotein neither binds to endothelial cell surface heparan sulfate nor interferes with the interaction of this compound with antithrombin III, suggesting that it may not play an important role in the modulation of anticoagulant activity of endothelial cells.