title: Detection of both type 1 and type 2 plasminogen activator inhibitors in human monocytes.
abstract: Increasing evidence suggests the involvement of leukocytes in the fibrinolytic system. Monocytes secrete pro-urokinase (Grau, Thromb Res 1989; 53: 145) and it has been shown that these cells have specific receptors for urokinase and plasminogen (Miles, Thromb Haemostas 1987; 58: 936). The aim of this study was to analyse the presence of plasminogen activator inhibitor(s) in platelet-free suspensions of human peripheral blood monocytes and polymorphonuclear leukocytes (PMN). SDS-PAGE and reverse fibrin autography showed an inhibitory band of 50 kDa in the monocyte extracts (Triton X-100) but not in the PMN extracts. Urokinase (u-PA) was mixed with increasing amounts of monocyte extract for 10 min and the mixtures were added to 125I-fibrin coated wells containing plasminogen. A dose-dependent decrease in the u-PA fibrinolytic activity was observed. The amount of inhibition increased when the monocyte releasates were preincubated with u-PA (40% inhibition after 5 min preincubation and 80% after 15 min), indicating a direct interaction between this activator and an inhibitor(s). After SDS-PAGE of monocyte extracts, immunoblotting and peroxidase staining identified both PAI1 and PAI2, with an apparent molecular weight of 47-50 kDa. Monocyte-associated PAI1 formed complexes with single chain t-PA with a molecular mass 50 kDa higher than the molecular mass of the free PAI1. However, a significant amount of PAI1 remained unbound to t-PA. This inactive PAI1 could have come from a rapid inactivation of the primary active PAI1. These PAI1 and PAI2 detected in human monocytes may be transcendent in the regulation of the fibrinolytic system.
authors.affiliation: Servei d'Hematologia, Hospital de la Santa Creu i Sant Pau, Barcelona, Spain.
authors.forename: J C
authors.initials: JC
authors.lastname: Castellote
authors.forename: E
authors.initials: E
authors.lastname: Grau
authors.forename: M A
authors.initials: MA
authors.lastname: Linde
authors.forename: N
authors.initials: N
authors.lastname: Pujol-Moix
authors.forename: M L
authors.initials: ML
authors.lastname: Rutllant
mesh_terms: D004591:Electrophoresis, Polyacrylamide Gel; D005342:Fibrinolysis / Q000502:physiology; D006801:Humans; D015151:Immunoblotting; D008854:Microscopy, Electron; D009000:Monocytes / Q000378:metabolism*; D015849:Plasminogen Inactivators / Q000097:blood*; D013379:Substrate Specificity
chemical_list: D015849:Plasminogen Inactivators