CRE-LIKE RESPONSE ELEMENT REGULATES EXPRESSION OF RAT ALPHA(2D)-ADRENERGIC RECEPTOR GENE IN VASCULAR SMOOTH-MUSCLE

Contractile and binding studies indicate that alpha(2)-adrenergic rece ptors (ARs) are differentially expressed by vascular smooth muscle cel ls (SMCs) according to vascular segment (artery, arteriole, vein). In the present study, alpha(2D)-AR mRNA was two- to threefold higher in v ena cava than in aorta. To understand vascular regulation of alpha(2D) -AR expression in these cells, we sequenced 2.8 kb of the 5' flanking region of the alpha(2D)-AR gene. Notable features include two potentia l TATA boxes, an adenosine 3',5'-cyclic monophosphate response element (CRE)-like binding element, and an Sp1 element. Comparison of the rat and human genes revealed an overall homology of 74% over the 1.87-kb sequence 5' to the translation initiator methionine, including complet e homology at the distal TATA, CRE-like, and Sp1 sites. alpha(2D)-AR t ranscription starts from the guanine nucleotide 18 base pair downstrea m from the distal TATA box. Reporter gene constructs demonstrated stro ng alpha(2D)-AR promoter activity, but with several differences in con struct activity, in both rat aorta and vena cava SMCs. Analysis of an essential promoter fragment revealed two regions protected by aorta an d vena cava SMC nuclear proteins. The core sequences of these protecte d regions are TGACGCTA and TATAA. The former CRE-like element conferre d specific binding of both aorta and vena cava nuclear proteins. In ad dition, promoter activity was increased 300% by forskolin or 8-bromoad enosine 3',5'-cyclic monophosphate, indicating that the CRE-like eleme nt may regulate alpha(2D)-AR expression in vascular tissue.