Vascular endothelium forms a multifunctional interface between the circulating blood and the peripheral tissues. It is a metabolically active component of the vessel wall, serving as a source of multiple interacting factors that are important for normal homeostasis. Endothelial cells can undergo adaptive changes in function that are critical to normal physiological processes and the pathogenesis of vascular disease. The underlying assumption behind these studies has been that a crucial initial step in endothelial dysfunction consists of increased production of platelet-derived growth factor by endothelium. Regulation of PDGF expression by endothelial cells occurs in part at the transcriptional level. Efficient basal expression of both the PDGF A- and B-chain genes in endothelial cells requires the concerted action of a select group of DNA-binding proteins acting upon cis-elements present in the promoters. Induced expression of these genes probably involves the interaction of additional regulatory factors with these basal components. Specific transcriptional regulatory elements were identified in both the A- and B-chain promoters important in basal expression of these genes in endothelial cells. Three of these elements in the B-chain promoter and one in the A-chain promoter may bind novel nuclear proteins. A recognition element was identified in the PDGF A-chain core promoter that is necessary for induction of the gene by a model agonist, as well as by the more physiologically relevant stimulus, laminar fluid shear stress. This response element contains overlapping Sp1 and Egr-1 elements and is found in other genes that are induced by these stimuli in endothelial cells. Activation of the pleiotropic mediator Egr-1 could help coordinate the expression of numerous endothelial products that are important in endothelial dysfunction. Egr-1 may be one of a select set of transcription factors that convert quiescent endothelial cells into dysfunctional vascular elements. To understand both basal and induced transcriptional regulation of the A- and B-chain genes in endothelium, three approaches are proposed:
SPECIFIC AIM 1 : Characterize the interactions between the novel nuclear proteins and the corresponding elements in the PDGF A- and B-chain promoters;
SPECIFIC AIM 2 : Clone the nuclear binding proteins and characterize these transcription factors;
SPECIFIC AIM 3 : Determine how relevant PDGF agonists, such as inflammatory cytokines and physical forces, increase transcription of the PDGF genes. These studies should help to better define the molecular mechanisms regulating PDGF gene expression and provide new insights into the role of this growth factor in the pathophysiology of the vasculature.
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