cyclic-gmp and 7-(3-(3-hydroxy-4-(4--iodophenoxy)-1-butenyl)-7-oxabicyclo(2.2.1)heptan-2-yl)-5-heptenoic-acid

The thromboxane receptor (TPr) and multiple TPr ligands, including thromboxane A(2) (TxA(2)) and prostaglandin H(2), are elevated during vascular and atherothrombotic diseases. How TPr stimulation causes vascular injury remains poorly defined. This study was conducted to investigate the mechanism by which TPr stimulation leads to vascular injury.. Exposure of bovine aortic endothelial cells to either [1S-(1α,2β(5Z),3α(1E,3R),4α]-7-[3-(3-hydroxy-4-(d'-iodophenoxy)-1-butenyl)-7-oxabicyclo-[2.2.1] heptan-2-yl]-5'-heptenoic acid (IBOP) or U46619, 2 structurally related TxA(2) mimetics, for 24 hours markedly increased the release of superoxide anions (O(2)(·-)) and peroxynitrite (ONOO(-)) but reduced cyclic GMP, an index of nitric oxide bioactivity. IBOP also significantly suppressed activity of endothelial nitric oxide synthase (eNOS), increased enzyme-inactive eNOS monomers, and reduced levels of tetrahydrobiopterin, an essential eNOS cofactor. IBOP- and U46619-induced increases in O(2)(·-) were accompanied by the membrane translocation of the p67(phox) subunit of NAD(P)H oxidase. Pharmacological or genetic inhibition of either NAD(P)H oxidase or TPr abolished IBOP-induced O(2)(·-) formation. Furthermore, TPr activation significantly increased protein kinase C-ζ (PKC-ζ) in membrane fractions and PKC-ζ phosphorylation at Thr410. Consistently, PKC-ζ inhibition abolished TPr activation-induced membrane translocation of p67(phox) and O(2)(·-) production. Finally, exposure of isolated mouse aortae to IBOP markedly increased O(2)(·-) in wild-type but not in those from gp91(phox) knockout mice.. We conclude that TPr activation via PKC-ζ-mediated NAD(P)H oxidase activation increases both O(2)(·-) and ONOO(-), resulting in eNOS uncoupling in endothelial cells.

Topics: 15-Hydroxy-11 alpha,9 alpha-(epoxymethano)prosta-5,13-dienoic Acid; Animals; Apoptosis; Biopterins; Bridged Bicyclo Compounds, Heterocyclic; Cattle; Cell Survival; Cells, Cultured; Cyclic GMP; Cytochrome P-450 Enzyme System; Endothelial Cells; Enzyme Activation; Enzyme Inhibitors; Fatty Acids, Unsaturated; Intramolecular Oxidoreductases; Mice; Mice, Inbred C57BL; Mice, Knockout; NADPH Oxidases; Nitric Oxide; Nitric Oxide Synthase Type III; Oxidative Stress; Peroxynitrous Acid; Phosphoproteins; Phosphorylation; Protein Kinase C; Protein Processing, Post-Translational; Protein Transport; Receptors, Immunologic; Receptors, Thromboxane A2, Prostaglandin H2; RNA Interference; Signal Transduction; Superoxides; Time Factors; Tyrosine

Human embryonic kidney (HEK)293 cells stably transfected with the His-tagged thromboxane receptor alpha (TPalpha) was used to study the phosphorylation and desensitization of the receptor induced by 8-bromo-cyclic GMP (8-Br-cGMP), sodium nitroprusside (SNP), or S-nitroso-glutathione (SNG). These agents are known to activate cGMP-dependent protein kinase (PKG). Pretreatment of cells with these agents attenuated significantly agonist I-BOP induced Ca(2+) release. These agents also induced dose-dependent phosphorylation of the TPalpha as demonstrated by increased (32)P-labeling of the receptor from cells prelabeled with (32)Pi. To facilitate the identification of the intracellular domains involved in phosphorylation, glutathione S-transferase (GST)-intracellular domain fusion proteins were used as substrates for the purified PKG. It was found that only the GST-C-terminal tail fusion protein could serve as a substrate for the PKG. To identify the specific serine/threonine residues in the C-terminal tail being phosphorylated, various alanine mutants of these serine/threonine residues were checked for their ability to serve as substrates. It was found that the Ser-331 of the C-terminal tail was primarily involved in the PKG-mediated phosphorylation. That Ser-331 is a predominant site of phosphorylation was supported by in vivo studies in which HEK293 cells expressing the S331A mutant receptor showed little phosphorylation induced by any of the above three agents. Furthermore, HEK293 cells expressing the S331A mutant receptor pretreated with any of the above three agents became responsive to the agonist I-BOP-induced Ca(2+) release. These results indicate that Ser-331 of the TPalpha is the primary site responsible for the phosphorylation and the desensitization of the receptor induced by agents that activate the PKG.

Topics: Base Sequence; Binding Sites; Bridged Bicyclo Compounds, Heterocyclic; Cell Line; Cyclic GMP; Cyclic GMP-Dependent Protein Kinases; DNA Primers; Enzyme Activation; Fatty Acids, Unsaturated; Glutathione; Humans; In Vitro Techniques; Mutagenesis, Site-Directed; Nitroprusside; Nitroso Compounds; Phosphorylation; Receptors, Thromboxane; Recombinant Fusion Proteins; S-Nitrosoglutathione; Serine