<総説>線溶系の調節機構 : とくにα_2-Macroglobulinとその受容体について

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Fibrinolytic promotion factors are regulated by two processes: one is dependent on a complex formation between these factors and α_2-macrogulobulin (α_2M), the other does not depend on complex formation. 1. With the complex formation: Here, the important roles of α_2M are specially referred to. In addition to the role of α_2M as a protease inhibitor, a further role has been proposed for α_2M as a binding protein of four major classes of proteases (serine, cysteine, aspartic and metalloproteases) and non-proteolytic amines, peptides, and proteins. A protease, as tissue plasminogen activator (tPA), trapped by α_2M suffers an apparent decrease in activity compared with free tPA, but the activity is preserved and protected from the specific inhibitor, as plasminogen activator inhibitor-1 (PAI-1). Plasmin trapped by α_2M, however, is not able to dissolve fibrin. The reason for this phenomenon appears to be that the fibrin molecule is too big to be attacked by the active center of plasmin in α_2M, although the plasmin still reserves the activity. The binding of α_2M to methyl-amine or protease activates α_2M and takes part in a conformational change. The α_2M protese complex, however, exposes the recognition site of the α_2M to the specific receptor and is rapidly removed from circulating blood. The α_2M specific receptor (α_2MR) is a identical with low density lipoprotein (LDL) receptor-related protein (LRP) : LRP/α_2MR. In addition, α_2M is an acute phase reactant and seems to trap various enzymes and products induced from inflammatory processes. Therefore, the most important role of α_2M is considered to be as a scavenger in circulating blood. 2. The second process of regulation of fibrinolytic promotion factors directly depends on LRP/α_2MR: Plasmiongen activator (PA) such as tPA or urokinase (uPA) forms a complex with PA-1. This complex is trapped by LRP/α_2MR, which is exprssed on the cell surface of the liver, and is removed rapidly from circulating blood. The tPA, which does not form a complex with PAI-1, trapped by LRP/α_2MR, is removed rapidly from circulating blood. The tPA, which does not form a complex with PAI-1, binds with PAI-1 already bound with vitronectin on the cell surface of liver. After the binding between tPA and PAI-1-vitronectin, the tPA-PAI-1 complex separates the vitronectin and the complex is also trapped by LRP/α_2MR.The regulation of Pro-uPA proceeds as follows: pro-uPA binds uPA receptor (uPAR), PAI-1 binds the pro-uPA and forms a uPAR-pro-uPA-PAI-1 complex. The complex binds LRP/α_2MR and is internalized in liver cells.
北海道医療大学の論文
1995-06-30

<総説>線溶系の調節機構 : とくにα_2-Macroglobulinとその受容体について

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