Regulation of macrophage receptor-bound plasmin by autoproteolysis.

TitleRegulation of macrophage receptor-bound plasmin by autoproteolysis.
Publication TypeJournal Article
Year of Publication1994
AuthorsFalcone DJ, Borth W, McCaffrey TA, Mathew J, McAdam K
JournalJ Biol Chem
Date Published1994 Dec 23
Keywordsalpha-2-Antiplasmin, Catalysis, Cell Line, Cell Membrane, Fibrinolysin, Humans, Hydrolysis, Iodine Radioisotopes, Macrophages, Phenylmethylsulfonyl Fluoride, Plasminogen, Receptors, Cell Surface, Receptors, Urokinase Plasminogen Activator, Urokinase-Type Plasminogen Activator

The activation of plasminogen by macrophage is regulated by their expression of receptors for urokinase and plasmin(ogen). In these studies we have examined plasmin(ogen) binding to adherent human THP-1 macrophage. Plasmin bound to the THP-1 cells in a time- and dose-dependent manner (Kd 15.8 +/- 6.2 nM; Bmax 1.4 +/- 0.3 x 10(6)/cell). The lysine analog epsilon-aminocaproic acid competitively inhibited plasmin binding. The fraction of membrane-bound plasmin, however, became increasingly resistant to displacement with epsilon-aminocaproic acid. Over a 24-h period, membrane-bound plasmin activity fell 80% despite the presence of catalytically active plasmin in the incubation media. The loss of receptor-bound plasmin activity was not due to proteolytic alterations of its receptor since 125I-Lys-plasminogen bound to THP-1 cells pretreated with plasmin with similar affinity as to untreated cells. Following a 24-h incubation of 125I-Lys-plasminogen or 125I-plasmin with THP-1 cells, several degradative fragments were apparent in their conditioned media. The smaller degradative fragments (28 and 36 kDa) lacked cell binding activity and were demonstrated to be active by casein-zymography. A 48-kDa fragment bound to cells in a lysine-dependent manner but was not active. In contrast, phenylmethylsulfonyl fluoride-inactivated 125I-plasmin retained its binding activity over 24 h, and degradative fragments were not present in the conditioned media. The binding of 125I-Lys-plasmin(ogen) to THP-1 cells was also examined in the presence of excess alpha 2 plasmin inhibitor. Despite the absence of fluid-phase plasmin activity, membrane-bound 125I-Lys-plasmin(ogen) decreased over 24 h. At 24 h a radiolabeled 48-kDa fragment was observed in the conditioned media and together with 125I-Lys-plasmin(ogen) was bound to cells. Unlike 125I-Lys-plasmin, the 48-kDa fragment did not form a complex with alpha 2 plasmin inhibitor. Thus, autoproteolysis of receptor-bound plasmin results in fragments with truncated physiologic properties that possess either cell binding or catalytic activities. We propose that autoproteolysis is a mechanism for regulating membrane-bound plasmin activity.

Alternate JournalJ Biol Chem
PubMed ID7528219
Grant ListP01 HL46403 / HL / NHLBI NIH HHS / United States
R01-HL40819 / HL / NHLBI NIH HHS / United States
R29 HL42606 / HL / NHLBI NIH HHS / United States
Related Faculty: 
Domenick J. Falcone, Ph.D.

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