Published online before print February 12, 2004, doi: 10.1161/01.RES.0000122043.11286.57
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Submitted on September 22, 2003
Revised on January 30, 2004
Accepted on February 3, 2004
Thromboxane A2 Receptor Agonists Antagonize the Proangiogenic Effects of Fibroblast Growth Factor-2. Role of Receptor Internalization, Thrombospondin-1, and 
v
3
Anthony W. Ashton *;
From the Departments of Medicine (Cardiology) and Molecular Pharmacology (A.W.A, A.H., J.A.W.), the Albert Einstein College of Medicine, Yeshiva University, Bronx, NY; and Center for Experimental Therapeutics (Y.C.), University of Pennsylvania, Philadelphia, Pa.
* To whom correspondence should be addressed. E-mail: ashton{at}aecom.yu.edu.
Thromboxane (TX) A2 is released from multiple cell types and is a prime mediator of the pathogenesis of many vascular events, including angiogenesis. Endothelial cells express TXA2 receptors (TP) but the effects of TP stimulation on angiogenesis remain controversial. In this study, we show that stimulation of endothelial cell TXA2 receptors (TP) impairs ligand-induced FGF receptor internalization and consequently abrogates FGF-2-induced endothelial cell migration in vitro and angiogenesis in vivo. Prevention of FGF-2-induced angiogenesis was associated with expression of the TP
isoform. The deficit in FGFR1 internalization was mediated through activation of TP preventing the FGF-2-mediated decrease in p53 expression, thus enhancing thrombospondin-1 (TSP-1) release from EC and reducing FGFR1 internalization. Once released TSP-1 interacted with the 
v3 integrin on the EC surface. On stimulation, FGFR1 and v3 were found to associate in a complex. We determined that complex formation was important for receptor internalization as conditions that inhibit FGFR1 internalization, such as inappropriate ligation of v3 by either TSP-1 or a neutralizing antibody, disrupted the complex. These results establish a novel role for isoform specific regulation of angiogenesis by TP, provide the first functional significance for the existence of two TP isoforms in humans, and clarify the mechanism by which TP signaling regulates FGFR1 kinetics and signaling.
Key words: thromboxane • angiogenesis • FGFR1 internalization • integrin
v3
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