Endothelial heme oxygenase-1 induction by hypoxia. Modulation by inducible nitric-oxide synthase and S-nitrosothiols.
The stress protein heme oxygenase-1 (HO-1) is induced in endothelial cells exposed to nitric oxide (NO)-releasing agents, and this process is finely modulated by thiols (Foresti, R., Clark, J. E., Green, C. J., and Motterlini R. (1997) J. Biol. Chem. 272, 18411-18417). Here, we report that up-regulation of HO-1 in aortic endothelial cells by severe hypoxic conditions (pO(2) </= 2 mm Hg) is preceded by increased inducible NO synthase and NO synthase activity. This effect is accompanied by oxidation of intracellular glutathione and formation of S-nitrosothiols. Incubation of cells with a selective inhibitor of inducible NO synthase (S-(2-aminoethyl)-isothiourea) or a NO scavenger ([2-(4-carboxyphenyl)-4,4,5, 5-tetramethylimidazoline-1-oxyl-3-oxide]) significantly attenuated the increase in heme oxygenase activity caused by reduced oxygen availability. A series of antioxidant agents did not prevent the elevation in heme oxygenase activity by hypoxia; however, the precursor of glutathione synthesis and thiol donor, N-acetylcysteine, completely abolished HO-1 induction. We also found that the hypoxia-mediated increase in endothelial heme oxygenase activity was potentiated by the presence of S-nitrosoglutathione. These results indicate that intracellular interaction of thiols with NO is an important determinant in the mechanism leading to HO-1 induction by reduced oxygen levels. We suggest that in addition to oxidative stress, HO-1 gene expression can be regulated by redox reactions involving NO and S-nitrosothiols (nitrosative stress), emphasizing a versatile role for the heme oxygenase pathway in the cellular adaptation to a variety of stressful conditions.
Motterlini
R
R
Vascular Biology Unit, Department of Surgical Research, Northwick Park Institute for Medical Research, Harrow, Middlesex HA1 3UJ, United Kingdom. r.motterlini@ic.ac.uk
Foresti
R
R
Bassi
R
R
Calabrese
V
V
Clark
J E
JE
Green
C J
CJ
D000818:Animals; D002417:Cattle; D002478:Cells, Cultured; D004730:Endothelium, Vascular / Q000378:metabolism*; D004790:Enzyme Induction; D006419:Heme Oxygenase (Decyclizing) / Q000378:metabolism*; D051547:Heme Oxygenase-1; D000860:Hypoxia; D008623:Mercaptoethanol; D019001:Nitric Oxide Synthase / Q000378:metabolism*; D052247:Nitric Oxide Synthase Type II; D009603:Nitroso Compounds / Q000378:metabolism*; D026403:S-Nitrosothiols
D009603:Nitroso Compounds; D026403:S-Nitrosothiols; D008623:Mercaptoethanol; C032635:S-nitrosomercaptoethanol; D019001:Nitric Oxide Synthase; D052247:Nitric Oxide Synthase Type II; D006419:Heme Oxygenase (Decyclizing); D051547:Heme Oxygenase-1