title: Distinct protective mechanisms of HO-1 and HO-2 against hydroperoxide-induced cytotoxicity.
abstract: Heme oxygenases (HO-1 and HO-2) catalyze the NADPH-cytochrome P(450) reductase (CPR)-dependent degradation of heme into iron, carbon monoxide, and biliverdin, which is reduced into bilirubin. Under basal conditions, HO-1 is often undetected and can be induced by numerous stress conditions. Although HO-2 is constitutively expressed, its activity appears to be regulated by post-translational modifications. HO activity has been associated with cellular protection, by which it degrades heme, a prooxidant, into bioactive metabolites. Under given circumstances, overexpression of HO-1 can render cells more sensitive to free radicals. Here, we investigated the properties of human HO isoforms that protect against oxidative stress. Considering that CPR can be a limiting factor for optimal HO activity, we tested stable HO-1 and HO-2 cell lines that derived from the CPR cells. Results indicate that the HO-1 and HO-2 cells are more resistant than controls to hemin and to the organic tert-butyl hydroperoxide, t-BuOOH. However, HO-1 cells are less resistant than HO-2 cells to hydrogen peroxide (H(2)O(2)). The levels of oxidatively modified proteins of HO-1 and HO-2 cells in response to t-BuOOH toxicity are identical, but the level of oxidatively modified proteins of HO-2 cells is less than that of HO-1 cells in response to H(2)O(2) toxicity. Performing subcellular fractionations revealed that HO-2 and CPR are found together in the microsomal fractions, whereas HO-1 is partially present in the microsome and also found in other fractions, such as the cytosol. These same findings were observed in non-transfected primary neurons where HO-1 proteins were chemically induced with 15-deoxy-Delta(12,14)-prostaglandin J(2) (15dPGJ(2)). The differences in subcellular localization of HO-1 and HO-2 could explain some of the discrepancies in their cellular activity and enzymatic protective mechanisms.
authors.affiliation: Department of Anesthesiology/Critical Care Medicine, Johns Hopkins University, School of Medicine, Baltimore, MD 21205, USA.
authors.forename: Yun-Sook
authors.initials: YS
authors.lastname: Kim
authors.forename: Hean
authors.initials: H
authors.lastname: Zhuang
authors.forename: Raymond C
authors.initials: RC
authors.lastname: Koehler
authors.forename: Sylvain
authors.initials: S
authors.lastname: Doré
mesh_terms: D003600:Cytosol / Q000201:enzymology; D006419:Heme Oxygenase (Decyclizing) / Q000235:genetics / Q000378:metabolism*; D051547:Heme Oxygenase-1; D006427:Hemin / Q000494:pharmacology; D006801:Humans; D006861:Hydrogen Peroxide / Q000009:adverse effects*; D007527:Isoenzymes; D008565:Membrane Proteins; D008861:Microsomes / Q000201:enzymology; D009251:NADPH-Ferrihemoprotein Reductase; D009474:Neurons / Q000201:enzymology; D010084:Oxidation-Reduction; D018384:Oxidative Stress; D015230:Prostaglandin D2 / Q000031:analogs & derivatives* / Q000494:pharmacology; D013347:Subcellular Fractions; D020122:tert-Butylhydroperoxide / Q000494:pharmacology
chemical_list: C477819:15-deoxyprostaglandin J2; D007527:Isoenzymes; D008565:Membrane Proteins; D006427:Hemin; D020122:tert-Butylhydroperoxide; D006861:Hydrogen Peroxide; C496541:HMOX1 protein, human; D006419:Heme Oxygenase (Decyclizing); D051547:Heme Oxygenase-1; C105245:heme oxygenase-2; D009251:NADPH-Ferrihemoprotein Reductase; D015230:Prostaglandin D2