The Effect of Grp78 Inhibition on Tissue Factor Gene Expression, Procoagulant Activity, and Factor Xa Generation.

In vivo biopanning with phage displayed peptide libraries has generated a group of peptide probes which bind selectively to the surface of atherosclerotic plaque endothelium. The highest affinity peptide, EKO130, binds to the 78 kDa glucose regulated protein (Grp78). Grp78 has been demonstrated to play a role in numerous pathological processes as well as a possible role in the local cell surface regulation of the coagulation cascade. The goal of this study is to determine the role of Grp78 in coagulation including plasma clotting, factor Xa (Xa) generation, and tissue factor (TF) gene expression. siRNA mediated inhibition of Grp78 results in a marked increase in TF gene expression in bEND.3 endothelial cells and RAW macrophage-like cells. Antibody mediated inhibition of cell surface Grp78 results in increased TF procoagulant activity and TF-dependent Xa generation in both the endothelial and macrophage cell types. These studies are consistent with results from another laboratory demonstrating that Grp78 over-expression inhibits TF mediated initiation and support of the coagulation protease cascade. Thus, our work indicates that Grp78 suppresses TF at both the functional and molecular level by inhibiting both its thrombogenic potential and gene expression.