1-3-dihydroxy-4-4-5-5-tetramethyl-2-(4-carboxyphenyl)tetrahydroimidazole and 2-2--(hydroxynitrosohydrazono)bis-ethanamine

Expression of heme oxygenase-1 (HO-1) in mammalian cells contributes to resistance to various types of free radical damage. Nitric oxide (NO) induces HO-1 in many cell types, but the specific contribution of transcriptional or post-transcriptional effects to this induction have remained unresolved. Here we show that the extent of HO-1 mRNA expression in IMR-90 and HeLa cells depends on the rate of NO delivery, and that the induction occurs more slowly in HeLa than in human fibroblast (IMR-90) cells. We used a specific NO scavenger (2-(4-carboxylphenyl)-4,4,5,5-tetramethylimidazolin-1-oxyl 3-oxide) that completely prevented the inducible expression of HO-1 by NO, pointing to direct signaling action of NO in this induction. By inhibiting transcription during the NO exposure, we have confirmed that NO treatment activates a mechanism that stabilizes HO-1 mRNA. The increase in the HO-1 mRNA half-life in IMR-90 cells was directly correlated with increasing rates of NO release. We also show here that the stabilization of the HO-1 message does not require de novo protein synthesis. Collectively, these results show that stabilization of HO-1 mRNA can be finely tuned to the NO exposure, and that the effect in human fibroblasts is mediated by a pre-existing protein.

Topics: Benzoates; Cell Line; Dactinomycin; Gene Expression Regulation, Enzymologic; HeLa Cells; Heme Oxygenase (Decyclizing); Heme Oxygenase-1; Humans; Imidazoles; Kinetics; Membrane Proteins; Nitric Oxide; Nitric Oxide Donors; Nitrogen Oxides; Nitroso Compounds; Protein Biosynthesis; Puromycin; RNA, Messenger; Spermine; Transcription, Genetic

Two retrograde signals influence the chick embryo's isthmo-optic nucleus, which projects to the retina: a slow-acting survival signal due to uptake of neurotrophic factors, and a fast-acting death signal initiated by calcium entry into isthmo-optic terminals due to electrical activity. The latter signal also affects dendritic reorganization. Since nitric oxide synthase is present in isthmo-optic terminals and their retinal target cells, we have tested its possible role in the fast-acting signal. Intraocular injection of nitric oxide antagonists led within 6-12 h to a reduction in the number of dying isthmo-optic neurons and slowed dendritic reorganization. Surprisingly, nitric oxide agonists had a similar fast effect on neuronal death. Although the mechanism appears to be complex, nitric oxide is involved in mediating the fast-acting retrograde signal.

Topics: Animals; Arginine; Benzoates; Cell Division; Cell Survival; Chick Embryo; Dendrites; Imidazoles; Nerve Growth Factors; Neurons; Nitric Oxide; Nitric Oxide Synthase; Nitroso Compounds; Optic Nerve; Presynaptic Terminals; Signal Transduction