The migration of THP-1 monocytes through a porous membrane, in response to monocyte chemotactic protein-1, was blocked when the membranes were coated with extracellular matrix. Inhibition of plasminogen binding to annexin II on RAW264.7 macrophages significantly impaired their ability to activate plasminogen and degrade -glucosamine–labeled extracellular matrices. Likewise, plasmin binding to human monocyte-derived macrophages and THP-1 monocytes was inhibited (50% and 35%, respectively) when cells were preincubated with anti–annexin II IgG. Preincubation of RAW264.7 macrophages with monoclonal anti–annexin II IgG inhibited (35%) their binding of 125I-Lys-plasminogen. Ligand blots demonstrated that annexin II comigrates with one of several proteins in lysates and membranes derived from RAW264.7 macrophages that bind plasminogen.
Calcium-dependent binding of annexin II to RAW264.7 macrophages was shown using flow cytometry and Western blot analysis of EGTA eluates. These studies identified the plasminogen binding protein annexin II on the surface of macrophages and determined its role in their ability to degrade and migrate through extracellular matrices. Genetic evidence demonstrates the importance of plasminogen activation in the migration of macrophages to sites of injury and inflammation, their removal of necrotic debris, and their clearance of fibrin.
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