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J. Biol. Chem., Vol. 281, Issue 36, 25915-25925, September 8, 2006

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Matrix Metalloproteinase-2 Expression by Vascular Smooth Muscle Cells Is Mediated by Both Stimulatory and Inhibitory Signals in Response to Growth Factors^*

From the Department of Cell Biology, University of Oklahoma Health Sciences Center, Oklahoma City, Oklahoma 73104

In response to growth factors, vascular smooth muscle cells (VSMCs) undergo a phenotypic modulation from a contractile, non-proliferative state to an activated, migratory state. This transition is characterized by changes in their gene expression profile, particularly by a significant down-regulation of contractile proteins. Platelet-derived growth factor (PDGF)-BB has long been known to initiate VSMC de-differentiation and mitogenesis. Insulin-like growth factor (IGF)-I, on the other hand, has differing effects depending on the model studied. Here, we report that both IGF-I and PDGF-BB stimulated VSMC de-differentiation of rat heart-derived SMCs in culture, although only PDGF-BB was capable of inducing proliferation. Although both PDGF-BB and IGF-I stimulation resulted in decreased smooth muscle -actin expression and increased matrix metalloproteinase (MMP)-2 expression, the response to IGF-I was significantly more rapid. The increased MMP-2 expression in response to both growth factors was due to increased transcription rates and was dependent on the action of phosphatidylinositol 3-kinase (PI3K) and its downstream effector, Akt. Both PDGF-BB and IGF-I activated PI3K/Akt to similar degrees; however, only PDGF-BB concomitantly stimulated an inhibitory signaling pathway that antagonized the effects of Akt but did not alter the extent or duration of Akt activation. Together, these findings suggest that changes in MMP-2 expression are part of the program of VSMC phenotypic modulation and that both PDGF-BB and IGF-I, despite their different abilities to induce proliferation in this model, are capable of inducing VSMC activation.

Received for publication, December 19, 2005 , and in revised form, July 19, 2006.

^* This work was supported by the Oklahoma Center for the Advancement of Science and Technology and by National Institutes of Health Grants HL-62268 and GM-63638. The costs of publication of this article were defrayed in part by the payment of page charges. This article must therefore be hereby marked "advertisement" in accordance with 18 U.S.C. Section 1734 solely to indicate this fact.

¹ To whom correspondence should be addressed: Dept. of Cell Biology, BMSB 566, University of Oklahoma Health Sciences Center, 940 Stanton L. Young Blvd., Oklahoma City, OK 73104. Tel.: 405-271-2377; Fax: 405-271-3548; E-mail: eric-howard{at}ouhsc.edu.

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