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Minactivin: a human monocyte product which specifically inactivates urokinase-type plasminogen activators
Abstract:
Culture supernatants from monolayers of human peripheral monocytes strongly inhibited colorimetric assays of urokinase in which plasmin was measured by esterolysis. This inhibitory activity of monocyte culture supernatant was enhanced after culture with muramyl dipeptide. Inhibition was specific for plasminogen activators of Mr 52 000 and 36 000, as shown by three methods: (1) inhibition of plasminogen-dependent fibrinolysis; (2) inhibition at the level of plasminogen activation in a colorimetric assay; (3) the irreversible loss of plasminogen-activating activity, as evidenced by electrophoresis, after preincubation with culture media. The factor responsible for this inactivation (which we propose to call minactivin) had an apparent Mr of 66 000 on Sephacryl S300 gel chromatography and interacted with enzyme in a biphasic manner: a rapid partial inhibition (reversible by sodium dodecyl sulphate) was followed by slow inactivation (irreversible by sodium dodecyl sulphate). It is proposed that secretion of minactivin by monocytes may contribute to regulation of extracellular proteolysis at sites of tissue injury.
Insights
Human monocytes secrete a novel inhibitor, minactivin, that regulates urokinase and plasminogen activators. This finding offers insights into controlling extracellular proteolysis in tissue injury.
Area of Science:
- Biochemistry
- Immunology
- Cell Biology
Background:
- Monocytes play a role in regulating extracellular proteolysis.
- Plasminogen activators are crucial enzymes in tissue remodeling and injury.
- Urokinase is a key plasminogen activator involved in various physiological and pathological processes.
Purpose of the Study:
- To investigate the inhibitory activity of human peripheral monocyte culture supernatants on urokinase.
- To characterize the factor responsible for this inhibition and its mechanism of action.
- To explore the potential role of this factor in regulating extracellular proteolysis.
Main Methods:
- Colorimetric assays to measure urokinase and plasmin activity.
- Plasminogen-dependent fibrinolysis assays.
- Electrophoresis to assess the effect on plasminogen activator activity.
- Sephacryl S300 gel chromatography for factor purification and characterization.
Main Results:
- Monocyte culture supernatants exhibited strong inhibition of urokinase activity, enhanced by muramyl dipeptide.
- The inhibitory activity was specific for plasminogen activators of Mr 52,000 and 36,000.
- A novel inhibitory factor, termed minactivin (Mr 66,000), was identified, causing biphasic inhibition (rapid reversible and slow irreversible).
Conclusions:
- Human monocytes secrete minactivin, a novel inhibitor of urokinase and other plasminogen activators.
- Minactivin's interaction with enzymes suggests a regulatory role in extracellular proteolysis.
- Monocyte-derived minactivin may contribute to controlling proteolysis at sites of tissue injury.