Sp1 increases expression of cyclooxygenase-2 in hypoxic vascular endothelium - Implications for the mechanisms of aortic aneurysm and heart failure

Cyclooxygenase-2 (COX-2) catalyzes prostaglandin synthesis from arachidonic acid and is expressed locally in aortic aneurysm and heart failure. Cellul ar hypoxia is also found in these conditions. We have previously shown that cox-2 is transcriptionally regulated by hypoxia in human umbilical vein en dothelial cells (HUVEC) in culture via the transactivation factor NF-kappa B p65, leading to increased production of prostaglandin E-2, an inhibitor o f vascular smooth muscle cell proliferation. Sp1 is a transactivation facto r known to be important in the regulation of cytokine expression in associa tion with NF-kappa B. We hypothesized that Sp1 is involved in the induction of cox-2 in hypoxic HUVEC, Electrophoretic mobility shift assays with hypo xic HUVEC nuclear protein showed that both Spl and the related protein Sp3 specifically bound to the cox-2 promoter. Immunoblotting demonstrated that hypoxia increased the nuclear localization of Sp1 but did not change the Sp 3 content in HUVEC. Overexpression of Sp1 through transfection of HUVEC enh anced cox-2 promoter activity as measured by reporter gene expression and b y the production of COX-2. The specificity of the results was confirmed by mutation of the Sp1-binding site in the cox-2 promoter construct and by rep roducibility in an Sp-deficient Drosophila SL2 cell line. The regulatory ro le of Spl discovered in this work supports the concept that a mechanistic l ink exists between vascular cellular hypoxia and mediators of inflammation associated with aortic aneurysm and heart failure.