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Fibrinmonomer binding to macrophages mediated by fibrin-binding fibronectin fragments
Abstract:
Binding of 125-I-fibrinmonomer to peritoneal macrophages was investigated in dependence of plasma fibronectin and of its thrombin- or plasmin-derived fragments. Plasma fibronectin failed to enhance cell binding of 125-I-fibrinmonomer. In contrast, 30kD-fragments derived from the N-termini of the fibronectin subunits improved binding considerably. The association with the cell surface was completely inhibited by EDTA, 2-5 mM putrescine and to about 40 per cent by 0.1 mM dansylcadaverine suggesting that a transamidase-catalyzed cross-linking reaction was involved. Thrombin-derived 200kD-remnants of the fibronectin subunit chains failed to mediate cell binding of 125-I-fibrinmonomer provided they had been deprived of residual thrombin activity. Otherwise they were active and their activity was inhibited by the thrombin inhibitor hirudin. Plasmin-derived 200 kD-fragments were inactive as well.
Insights
Specific fibronectin fragments, not plasma fibronectin itself, enhance fibrinmonomer binding to macrophages. This interaction involves a transamidase-catalyzed cross-linking reaction, highlighting fragment-specific roles in cell adhesion.
Area of Science:
- Biochemistry
- Cell Biology
- Immunology
Background:
- Fibronectin is a key extracellular matrix protein involved in cell adhesion and wound healing.
- Understanding fibronectin's interaction with immune cells like macrophages is crucial for inflammatory and repair processes.
Purpose of the Study:
- To investigate the binding of iodinated fibrinmonomer (125-I-fibrinmonomer) to peritoneal macrophages.
- To determine the role of plasma fibronectin and its fragments (thrombin- or plasmin-derived) in this binding process.
Main Methods:
- Incubation of peritoneal macrophages with 125-I-fibrinmonomer in the presence of plasma fibronectin or its fragments.
- Assessment of cell binding using radiolabeled fibrinmonomer.
- Inhibition studies using EDTA, putrescine, dansylcadaverine, and hirudin to elucidate the binding mechanism.
Main Results:
- Plasma fibronectin did not enhance 125-I-fibrinmonomer binding to macrophages.
- 30kD N-terminal fibronectin fragments significantly improved 125-I-fibrinmonomer binding.
- Binding was inhibited by EDTA, putrescine, and dansylcadaverine, indicating involvement of a transamidase-catalyzed cross-linking reaction.
- Thrombin-derived 200kD fibronectin fragments mediated binding only if residual thrombin activity was present, inhibited by hirudin.
- Plasmin-derived 200 kD fragments were inactive.
Conclusions:
- Specific N-terminal fibronectin fragments, not intact plasma fibronectin, are responsible for enhancing fibrinmonomer binding to macrophages.
- The binding mechanism involves a transamidase-catalyzed cross-linking reaction.
- Fragment activity is dependent on their origin (thrombin- vs. plasmin-derived) and enzymatic activity.