Characterization of prostaglandin endoperoxide synthase from a human cell line

Immunohistochemical localization of prostaglandin H synthase in the female reproductive tract and endometriosis

Prostaglandin H synthase, also known as cyclooxygenase, is an essential enzyme in prostaglandin synthesis. Using a monoclonal antibody and immunohistochemical techniques, we studied the localization of this enzyme in the female reproductive tract and in endometriosis. In the uterus, prostaglandin H synthase was primarily localized to endometrial epithelium with surface epithelium containing more immunoreactive prostaglandin H synthase than glandular epithelium. Fallopian tube secretory epithelial cells also contained prostaglandin H synthase while ciliated epithelial cells did not. Cervical epithelium and myometrial cells did not contain prostaglandin H synthase. A higher percentage of glands in endometriosis and adenomyosis, as compared with eutopic endometrium, contained prostaglandin H synthase suggesting that these tissues are also capable of prostaglandin synthesis. These findings may have important physiologic significance in the mechanisms of embryo implantation, in menstruation, and in the pathophysiologic features of endometriosis.

Arachidonic acid and other fatty acids directly activate potassium channels in smooth muscle cells

Arachidonic acid, as well as fatty acids that are not substrates for cyclooxygenase and lipoxygenase enzymes, activated a specific type of potassium channel in freshly dissociated smooth muscle cells. Activation occurred in excised membrane patches in the absence of calcium and all nucleotides. Therefore signal transduction pathways that require such soluble factors, including the NADPH-dependent cytochrome P450 pathway, do not mediate the response. Thus, fatty acids directly activate potassium channels and so may constitute a class of signal molecules that regulate ion channels.

Isolation of the cDNA for human prostaglandin H synthase

Prostaglandin H Synthase (PGHS, cyclooxygenase) is a 67 kd protein which catalyzes the first step in prostaglandin synthesis. The primary amino acid sequence and the molecular mechanisms regulating expression are unknown. We report here isolation of a cDNA clone for the enzyme from human vascular endothelial cells for use in such studies. High titre, polyclonal antiserum against PGHS was developed in rabbits. The antiserum was monospecific, reacted with cyclooxygenase on Western blots at a limiting dilution of 1:500,000 and immunoprecipitated cyclooxygenase synthesized by in vitro translation of PGHS messenger RNA. It was used to screen a lambda gt11 cDNA expression library from human endothelial cells. Three positive clones were isolated. Following plaque purification, one clone reacted strongly with two other polyclonal antisera independently raised against highly purified cyclooxygenase and the aspirin-acetylated enzyme. Western blot analysis confirmed production of a large approximately 180 kd fusion protein of cyclooxygenase and beta-galactosidase. The cDNA insert of approximately 2.2 kilo base pairs was excised and subcloned into plasmid pUC8. A 24 nucleotide DNA probe, synthesized according to the amino acid sequence of the aspirin-acetylation site of cyclooxygenase, hybridized strongly with the 2.2 kbp cDNA insert. It is concluded that the 2.2 kbp cDNA insert represents a cDNA clone for human cyclooxygenase, which also expresses the aspirin-acetylation site. This is the first reported isolation of the cDNA for this enzyme, and will facilitate further studies on the primary sequence and on the regulation of the enzyme at the molecular level.