Analysis of Tissue-Type Plasminogen Activator Receptor (t-PAR) in Human Endothelial Cells

Abstract

Vascular endothelial cells regulate the fibrinolytic system in blood by expressing cell-surface receptors for plasminogen and plasminogen activators (PAs) as well as secreting PAs and their inhibitors. Although several receptors for plasminogen and PAs have been identified in many cell types, little is known about tissue-type PA (t-PA)-specific receptor (t-PAR) on endothelial cells except a few reports. By using suspended human umbilical vein endothelial cells (HUVEC), which are free from the formation of extracellular matrix (ECM)--where type-1 plasminogen activator inhibitor (PAI-1) preferably accumulates and interacts with t-PA with high affinity--we demonstrated a relatively low affinity binding site for t-PA on the cells and identified a novel t-PAR. The isolation and characterization of HUVEC-derived t-PAR was performed in the present study. A 20-kDa t-PAR was successively isolated and purified by high performance liquid chromatography system from HUVEC which specifically binds t-PA and not plasminogen forming a 90-kDa complex with t-PA. When t-PA binds the immobilized t-PAR stoichiometrically 1:1, the enzymatic activity of t-PA was enhanced 90-fold. Thus, it is suggested that the t-PAR may function as a t-PA-enhancing molecule expressed on the surface of endothelial cells.

Role of Tissue Plasminogen Activator Receptor LRP in Hippocampal Long-Term Potentiation

“…Several previous studies have suggested the presence of tPA binding protein on the cell surface that might serve as a docking receptor for tPA (Pittman et al, 1989;Verrall and Seeds, 1989;Hajjar et al, 1994;Fukao and Matsuo, 1998). However, our current study suggests that tPA is rapidly endocytosed by LRP after its binding to the receptor, suggesting that LRP likely functions as an endocytosis/signaling receptor as opposed to a docking receptor.…”

“…Both LRP and a mannose receptor have been shown to bind tPA (Otter et al, 1991;Bu et al, 1992b). In addition, several studies have described various tPA binding receptors on the cell surface of both endothelial and neuronal cells (Pittman et al, 1989;Verrall and Seeds, 1989;Hajjar et al, 1994;Fukao and Matsuo, 1998). However, only binding to LRP is inhibited by RAP (Bu et al, 1998).…”