Activation of rat alveolar macrophage-derived latent transforming growth factor beta-1 by plasmin requires interaction with thrombospondin-1 and its cell surface receptor, CD36.
Transforming growth factor-beta-1 (TGF-beta1) is secreted by cells in a latent form (L-TGF-beta1) noncovalently bound to a latency-associated peptide. Activated alveolar macrophages obtained from rat lungs after bleomycin-induced pulmonary injury released increased amounts of active TGF-beta1 as well as plasmin, a protease, and thrombospondin-1 (TSP-1), a trimeric glycoprotein. Previously we had demonstrated that plasmin was critical to the activation of L-TGF- beta1. In the present study we demonstrated that TSP-1 is also important for the activation of L-TGF- beta1 because the activation can be inhibited by anti-TSP-1 monoclonal antibody. Proteins obtained from alveolar macrophage cell lysates immunoprecipitated with antibodies specific for TSP-1 were identified on immunoblots as LAP and TGF-beta1, indicating that TSP-1/L-TGF-beta1 complexes are present on alveolar macrophages. However, in the presence of plasmin both latency-associated peptide and TGF-beta1 were decreased in the same cell lysates, indicating that L-TGF-beta1 associated with TSP-1 is released by plasmin. Using immunofluorescence and antibodies to TGF-beta1 and CD36, a receptor for TSP-1, there was colocalization of TGF-beta1 with CD36. Because TSP-1 but not TGF-beta1 is a natural ligand for CD36, these findings suggest that the L-TGF-beta1 in a complex with TSP-1 localizes to the macrophage cell surface when TSP-1 interacts with its receptor, CD36. Furthermore, the association of TSP-1/L-TGF-beta1 complex with CD36 is necessary to the activation of L-TGF-beta1 because antibodies to CD36 prevent the colocalization of TGF-beta1 with CD36 as observed by immunofluorescence and inhibit activation of the L-TGF-beta1 by explanted alveolar macrophages. These findings suggest that activation of L-TGF-beta1 by plasmin occurs at the cell surface of activated alveolar macrophages and requires a TSP-1/CD36 interaction.
Yehualaeshet
T
T
Departments of Medicine, Manitoba Institute of Cell Biology, University of Manitoba, Winnipeg, Manitoba, Canada.
O'Connor
R
R
Green-Johnson
J
J
Mai
S
S
Silverstein
R
R
Murphy-Ullrich
J E
JE
Khalil
N
N
D000818:Animals; D000911:Antibodies, Monoclonal / Q000494:pharmacology; D000964:Antimetabolites, Antineoplastic / Q000494:pharmacology; D001761:Bleomycin / Q000494:pharmacology; D015153:Blotting, Western; D018955:CD36 Antigens / Q000276:immunology / Q000378:metabolism*; D002478:Cells, Cultured; D004797:Enzyme-Linked Immunosorbent Assay; D005260:Female; D005341:Fibrinolysin / Q000378:metabolism* / Q000502:physiology; D019084:Fluorescent Antibody Technique, Indirect; D016676:Macrophages, Alveolar / Q000187:drug effects / Q000378:metabolism*; D011233:Precipitin Tests; D011506:Proteins / Q000378:metabolism; D051381:Rats; D017207:Rats, Sprague-Dawley; D048008:TNF Receptor-Associated Factor 3; D019700:Thrombospondin 1 / Q000276:immunology / Q000378:metabolism*; D016212:Transforming Growth Factor beta / Q000378:metabolism*
D000911:Antibodies, Monoclonal; D000964:Antimetabolites, Antineoplastic; D018955:CD36 Antigens; D011506:Proteins; D048008:TNF Receptor-Associated Factor 3; D019700:Thrombospondin 1; D016212:Transforming Growth Factor beta; D001761:Bleomycin; D005341:Fibrinolysin