Smooth muscle cell replication has a major role in atherosclerosis and hypertension as well as in vascular graft failures, yet much is still unclear about the factors that elicit this response in normally quiescent, contractile smooth muscle cells. Even less is known about the molecular processes that define the changes that these cells must undergo when they transition from a growth-arrested phenotype to a proliferative phenotype. We have identified two genes of unknown function that are dramatically down-regulated when quiescent smooth muscle cells are stimulated with serum. We propose to further study the regulation of these genes by growth-stimulatory signals. In addition, by DNA sequencing of isolated cDNA clones and microinjection of recombinant proteins as well as DNA transfection analysis we hope to elucidate the function of these growth-arrest associated genes. We have also identified the adenosine analog, 2-aminopurine as a potent inhibitor of smooth muscle cell proliferation. It appears to specifically block a critical step in the late G1/early S phase that is necessary for DNA synthesis. 2-aminopurine is a specific inhibitor of protein kinases and we propose experiments to test the hypothesis that 2-aminopurine specifically inhibits an as yet unidentified protein kinase that plays an important role in G0 to S-phase transition in vascular smooth muscle cells. Finally, we have isolated and sequenced a full-length cDNA that encodes a novel serum-inducible mRNA of unknown function. Of particular interest, is the finding that this gene is specifically induced by fibroblast growth factor and transforming growth factor-beta but is not induced by platelet-derived growth factor. We propose to define important cis- and trans-regulatory elements that mediate the growth- factor specific response for this gene. Experiments are also proposed to delineate the function of this gene. A better understanding of the function and regulation of this gene will provide new insight into the response of smooth muscle cells to different growth factors. Elucidation of the control of vascular smooth muscle cell growth will provide new therapeutic approaches to solve the important problem of atherosclerosis and coronary restenosis after vascular surgery.
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