|
||
The Journal of Cell Biology, Vol 118, 901-909, Copyright © 1992 by The Rockefeller University Press
ARTICLES |
R Flaumenhaft, M Abe, P Mignatti and DB Rifkin
Department of Cell Biology, New York University Medical Center, New York 10016.
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.
This article has been cited by other articles:
|
|