The endothelial cell nitric oxide synthase: is it really constitutively expressed?

During the past two years, the enzyme responsible for production of endothelium-derived nitric oxide, the endothelial cell NO synthase (ecNOS) has been cloned and the gene encoding this enzyme isolated, cloned and its structure characterized. This research has provided direction for a variety of studies of regulation of the ecNOS. Several features of the ecNOS are compatible with a constitutively expressed, poorly regulated gene, including absence of a TATA box and numerous SP-1 sites. The promoter also contains a number of putative binding domains which suggest that it may be regulated by a variety of transcription factor mediated signals. In this review we will discuss evidence to support the concept that the ecNOS is a constitutively expressed gene subject to a modest degree of regulation by important physiological influences.