Macrophage surface component gp160: sensitivity to plasmin and other proteases

Area of Science:

• Immunology
• Biochemistry
• Cell Biology

Background:

• Macrophages play a key role in inflammatory processes.
• Increased plasminogen activator secretion by activated macrophages suggests exposure to plasmin.
• A surface protein, gp160, is known to be sensitive to trypsin cleavage.

Purpose of the Study:

• To investigate the interaction of plasmin with macrophage surface proteins.
• To determine if plasmin cleaves gp160 and to characterize the resulting fragments.
• To assess the specificity of plasmin cleavage on macrophage surface components.

Main Methods:

• Incubation of 125I-labeled guinea pig peritoneal macrophages with purified plasmin.
• Analysis of surface protein cleavage by gel electrophoresis.
• Comparison of plasmin-generated fragments with trypsin-generated fragments.
• Testing cleavage by other inflammatory proteases: thrombin, collagenase, elastases, cathepsin G, and urokinase.

Main Results:

• Plasmin specifically cleaves the macrophage surface protein gp160.
• Plasmin generates fragments fr85 and fr71, which comigrate with trypsin fragments, indicating similar cleavage sites.
• No other detectable 125I-labeled surface proteins were cleaved by plasmin.
• Plasmin showed specificity, as other tested proteases did not cleave gp160.
• Measurable cleavage of gp160 occurred at plasmin concentrations as low as 50 μg/ml within 30 minutes.

Conclusions:

• Macrophages possess a surface protein, gp160, that is specifically cleaved by plasmin.
• The cleavage sites for plasmin and trypsin on gp160 are closely related or identical.
• This interaction highlights a specific enzymatic activity of plasmin on macrophages, potentially relevant in inflammatory conditions.