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The amino-terminal 29- and 72-Kd fragments of fibronectin mediate selective monocyte recruitment
Abstract:
Proteolytic fragments of fibronectin (Fn) can possess properties not inherent to intact Fn. Previously, only mixtures of low molecular weight Fn fragments, and the 120-Kd fibroblastic cell-binding segment, but not intact Fn, were shown to be selectively chemotactic for human monocytes (MOs). In order to determine if other structural domains of Fn were responsible, we tested six Fn fragments. The amino-terminal 72-Kd fragment at 1.5 microns was about 75% as potent as zymosan-activated serum (ZAS). Its amino-terminal 29-Kd degradation product at 1.0 micron was about one third as potent as ZAS. Checkerboard analysis confirmed chemotaxis. Complexing gelatin to 72-Kd fragments reduced MO chemotaxis by 28% to 30%. Reducing disulfide bonds in 29- and 72-Kd segments had no effect. A synthetic peptide containing the thrombin cleavage site between the 29- and 50-Kd segments of the 72-Kd fragment was chemotactic. The 50-, 190/170-, 35-, and 160/150/120-Kd fragments, and intact Fn were not chemotactic for MOs. The data suggest that the 72-Kd fragment and its 29-Kd subfragment are additional Fn fragments that mediate selective MO chemotaxis. We speculate that proteinases present at inflammatory sites can liberate such fragments that selectively recruit MOs.
Insights
Certain fibronectin (Fn) fragments, specifically the 72-Kd and its 29-Kd subfragment, are chemotactic for human monocytes (MOs). These fragments may recruit MOs during inflammation.
Area of Science:
- Biochemistry
- Immunology
- Cell Biology
Background:
- Proteolytic fragments of fibronectin (Fn) exhibit distinct properties compared to intact Fn.
- Previous studies identified low molecular weight Fn fragments and the 120-Kd segment as chemotactic for human monocytes (MOs).
Purpose of the Study:
- To investigate other structural domains of Fn responsible for monocyte (MO) chemotaxis.
- To identify specific Fn fragments that selectively recruit MOs.
Main Methods:
- Tested six different Fn fragments for their chemotactic potential on human MOs.
- Utilized checkerboard analysis to confirm chemotaxis and assessed the impact of gelatin complexation and disulfide bond reduction.
Main Results:
- The amino-terminal 72-Kd Fn fragment and its 29-Kd degradation product demonstrated significant MO chemotaxis.
- Chemotaxis was confirmed via checkerboard analysis; gelatin complexation reduced chemotaxis, while disulfide bond reduction had no effect.
- A synthetic peptide from the 72-Kd fragment's thrombin cleavage site was also chemotactic.
Conclusions:
- The 72-Kd Fn fragment and its 29-Kd subfragment are identified as novel mediators of selective MO chemotaxis.
- Proteinases at inflammatory sites may release these Fn fragments to recruit MOs, suggesting a role in inflammatory processes.