Modulation of mannose receptor activity by proteolysis

Area of Science:

• Immunology
• Cell Biology
• Biochemistry

Background:

• Macrophages possess a cell surface receptor crucial for clearing extracellular glycoproteins.
• This mannose receptor's activity is impaired in inflammatory conditions due to increased extracellular proteases.
• Understanding receptor regulation during inflammation is vital for immune response studies.

Purpose of the Study:

• To investigate the structural and activity changes of the macrophage mannose receptor upon trypsin treatment.
• To elucidate the mechanism behind activation-associated receptor down-regulation.
• To determine if trypsin proteolysis contributes to reduced glycoprotein clearance during inflammation.

Main Methods:

• Treatment of intact macrophages and purified receptor with trypsin (1 µg/ml for 3 h).
• Analysis of receptor fragments using SDS-PAGE and Coomassie Blue staining.
• Assessment of ligand-binding activity and immunoreactivity of receptor fragments.
• Surface labeling with Na125I to track protein domains.

Main Results:

• Trypsin treatment generated a 140 kDa trypsin-resistant fragment from the mannose receptor.
• This 140 kDa fragment lost its ligand-binding capability.
• A smaller 35 kDa fragment was further degraded, and the 140 kDa fragment retained immunoreactivity and some iodinated residues.

Conclusions:

• The macrophage mannose receptor undergoes proteolytic cleavage by trypsin at the cell surface.
• This process releases the ligand-binding domain and produces a membrane-associated 140 kDa fragment.
• Trypsin-mediated down-regulation of mannose receptor activity may play a role in controlling glycoprotein clearance during inflammation.