Basic fibroblast growth factor-induced activation of latent transforming growth factor beta in endothelial cells: regulation of plasminogen activator activity.
Exposure of bovine aortic or capillary endothelial cells to basic FGF (bFGF) for 1 h resulted in an approximately sixfold increase in plasminogen activator (PA) activity by 18 h that returned nearly to basal levels by 36 h. We hypothesized that the decrease in PA activity following bFGF stimulation was mediated by transforming growth factor beta (TGF-beta) formed from its inactive precursor. Conditioned medium collected from endothelial cells 36 h after a 1-h exposure to bFGF, but not control medium, inhibited basal levels of PA activity when transferred to confluent monolayers of bovine aortic endothelial cells. Antibody to TGF-beta neutralized the inhibitory activity of this conditioned medium, indicating that the medium contained active TGF-beta. Northern blot analysis and quantitation of acid activatable latent TGF-beta in conditioned medium demonstrated that bFGF exposure did not increase the amount of transcription or secretion of latent TGF-beta by the endothelial cells. Both aprotinin, an inhibitor of plasmin, and anti-urokinase type PA IgG blocked the generation of active TGF-beta in cultures exposed to bFGF. These results demonstrated that plasmin generated by uPA activity is required for the activation of latent TGF-beta in endothelial cell cultures treated with bFGF. Activation of TGF-beta by endothelial cells exposed to bFGF appears to limit both the degree and duration of PA stimulation. Thus, in bFGF-stimulated endothelial cell cultures, PA levels are controlled by a negative feedback loop: PA, whose expression is stimulated by bFGF, contributes to the formation of TGF-beta, which in turn opposes the effects of bFGF by limiting PA synthesis and activity. These studies suggest a role for TGF-beta in reversing the invasive stage of angiogenesis and contributing to the formation of quiescent capillaries.
Flaumenhaft
R
R
Department of Cell Biology, New York University Medical Center, New York 10016.
Abe
M
M
Mignatti
P
P
Rifkin
D B
DB
D000818:Animals; D007611:Aprotinin / Q000494:pharmacology; D002417:Cattle; D002478:Cells, Cultured; D003470:Culture Media; D004730:Endothelium, Vascular / Q000166:cytology / Q000187:drug effects / Q000378:metabolism*; D005341:Fibrinolysin / Q000378:metabolism; D016222:Fibroblast Growth Factor 2 / Q000494:pharmacology*; D010960:Plasminogen Activators / Q000096:biosynthesis / Q000378:metabolism*; D016212:Transforming Growth Factor beta / Q000096:biosynthesis / Q000378:metabolism*; D014568:Urokinase-Type Plasminogen Activator / Q000378:metabolism
D003470:Culture Media; D016212:Transforming Growth Factor beta; D016222:Fibroblast Growth Factor 2; D007611:Aprotinin; D010960:Plasminogen Activators; D005341:Fibrinolysin; D014568:Urokinase-Type Plasminogen Activator