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Division of Vascular Surgery, Department of Surgery, New York Presbyterian Hospital and Weill Medical College of Cornell University, New York, New York
Submitted 9 June 2004 ; accepted in final form 4 February 2005
The matrix protein fibronectin (FN) is a potent agoinst of vascular smooth muscle cell (SMC) migration. The role of rapamycin and the mammalian target of rapamycin (mTOR) in matrix protein-induced migration has not yet been defined. In these studies, we found that rapamycin (10 nM) markedly diminished chemotaxis of E47 cells (a cell line derived from human atherosclerotic plaques) and rat aortic SMCs toward FN as well as type I collagen and laminin; however, a period of preincubation >20 h was required. Subsequently, we showed that treatment with FN induced a rapid activation of mTOR as well as its downstream effector, S6 kinase (S6K). Moreover, FN-induced activation of both proteins was inhibited by preincubation with rapamycin for only 30 min. We then explored the upstream signaling pathway through which FN might mediate mTOR activation. A blocking antibody to 
v
3 inhibited FN-induced mTOR/S6K activation as well as E47 cell chemotaxis, implicating v3 as the integrin receptor responsible for initiating FN-induced migration. Moreover, preincubation of E47 cells with wortmannin or LY-294002 blocked FN-induced mTOR/S6K activation, demonstrating that phosphatidylinositol 3-kinase (PI3K) plays a critical role in this rapamycin-sensitive signaling pathway. It has been previously suggested that rapamycin's effect on migration maybe related to enhancement of p27kip1. However, treatment of E47 cells with rapamycin did not alter the level of p27kip1 in the presence or absence of FN. Taken together, our data demonstrate that rapamycin inhibits FN-induced SMC migration through a pathway that involves at least v3-integrin, PI3K, mTOR, and S6K.
S6 kinase; phosphatidylinositol 3-kinase; integrin; p27kip1; extracellular matrix proteins
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