Molecular basis of estrogen-induced cyclooxygenase type 1 upregulation in endothelial cells

Estrogen upregulates cyclooxygenase-1 (COX-1) expression in endothelial cells. To determine the basis of this process, studies were performed in ovine endothelial cells transfected with the human COX-1 promoter fused to luciferase. Estradiol (E-2) caused activation of the COX-1 promoter with maximal stimulation at 10(-8) mol/L E-2, and the response was mediated by either ER alpha or ER beta. Mutagenesis revealed a primary role for a putative Sp1 binding motif at -89 (relative to the ATG codon) and lesser involvement of a consensus Sp1 site at -111. Electrophoretic mobility shift assays yielded a single complex with the site at -89, and supershift analyses implicated AP-2 alpha and ER alpha, and not Sp1, in protein-DNA complex formation. In endothelial cells with minimal endogenous ER, the transfection of ER alpha mutants lacking the DNA binding domain or primary nuclear localization signals caused 4-fold greater stimulation of promoter activity with E-2 than wild-type ER alpha. In contrast, mutant ER alpha lacking the A-B domains was inactive. Thus, estrogen-mediated upregulation of COX-1 in endothelium is uniquely independent of direct ER alpha-DNA binding and instead entails protein-DNA interaction involving AP-2 alpha and ER alpha at a proximal regulatory element. In addition, the process may be initiated by cytoplasmic ER alpha, and critical receptor elements reside within the amino terminus.