Purified alpha 2-macroglobulin receptor/LDL receptor-related protein binds urokinase.plasminogen activator inhibitor type-1 complex. Evidence that the alpha 2-macroglobulin receptor mediates cellular degradation of urokinase receptor-bound complexes.

A Nykjaer,C.M Petersen,B Møller,P.H Jensen,S.K Moestrup,T.L Holtet,M Etzerodt,H.C Thøgersen,M Munch,P.A Andreasen

doi:10.1016/s0021-9258(18)42072-8

Abstract

Complexes between 125I-labeled urokinase-type plasminogen activator (uPA) and plasminogen activator inhibitor type-1 (PAI-1) bound to purified alpha 2-macroglobulin (alpha 2M) receptor (alpha 2MR)/low density lipoprotein receptor-related protein (LRP). No binding was observed when using uPA. The magnitude of uPA.PAI-1 binding was comparable with that of the alpha 2MR-associated protein (alpha 2MRAP). Binding of uPA.PAI-1 was blocked by natural and recombinant alpha 2MRAP, and about 80% inhibited by complexes between tissue-type plasminogen activator (tPA) and PAI-1, and by a monoclonal anti-PAI-1 antibody. In human monocytes, uPA.PAI-1, like uPA and its amino-terminal fragment, bound to the urokinase receptor (uPAR). Degradation of uPAR-bound 125I-uPA.PAI-1 was 3-4-fold enhanced as compared with uncomplexed uPAR-bound uPA. The inhibitor-enhanced uPA degradation was blocked by r alpha 2MRAP and inhibited by polyclonal anti-alpha 2MR/LRP antibodies. This is taken as evidence for mediation of internalization and degradation of uPAR-bound uPA.PAI-1 by alpha 2MR/LRP.

Highlights

Complexes between ‘261-labeluedrokinase-typeplasminogenactivator(uPA)andplasminogen activator inhibitor type-1 (PAI-1) bound to purified az-macroglobulin receptor/lowdensity lipoprotein receptor-related protein (LRP)
UPA*PAI-1was 3-4-fold enhanced as compared with uncomplexeduPAR-bounduPAT. he inhibitor-enhanced uPA degradationwas blocked byrazMRAP and inhibited by polyclonalanti-azMR/LRPantibodies. This is taken as evidence for mediation oifnternalization and degradation of uPAR-bound uPA-PAI-1 by azMR/LRP
Binding of uPA does not involve the serine proteinase domain [18]and the16-kDa amino-terminalfragment (ATF)binds as well as pro-uPA and uPA [19]. uPAR is expressed on numerous cell types including monocytes [20, 21], T-lymphocyte-deriveindterleukin-2-activated killer (LAK) cells [21], and several established cell lines [22]

Summary

Introduction

Complexes between ‘261-labeluedrokinase-typeplasminogenactivator(uPA)andplasminogen activator inhibitor type-1 (PAI-1) bound to purified az-macroglobulin (azM) receptor (azMR)/lowdensity lipoprotein receptor-related protein (LRP). This is taken as evidence for mediation oifnternalization and degradation of uPAR-bound uPA-PAI-1 by azMR/LRP. A2MR/LRP is located largely in coated pits [12] and receptor-active a2M is readily internalized and degraded, e.g. in monocytes [12] and JAR choriocarcinoma cells [13].

Results

Conclusion