title: Catalytically inactive heme oxygenase-2 mutant is cytoprotective.
abstract: Heme oxygenase (HO) catalyzes the rate-limiting step in heme degradation, producing iron, carbon monoxide, and bilirubin/biliverdin. HO consists of two isozymes: HO-1, which is an oxidative stress-response protein, and HO-2, which is constitutively expressed. HO-2 accounts for most HO activity within the nervous system. Its posttranslational modifications and/or interactions with other proteins make HO-2 a unique regulator of cellular homeostasis. Our previous results revealed that brain infarct volume was enlarged in HO-2 knockout mice. A similar neuroprotective role of HO-2 was shown using primary cortical neurons. To better understand the neuroprotective mechanism of HO-2, we used a catalytically inactive mutant, HO-2H45A, and investigated its cellular effects in response to hemin and hydrogen peroxide-induced cytotoxicity. We observed that HO-2WT overexpression in the HEK293 cell lines became less sensitive to hemin, whereas the inactive mutant HO-2H45A was more sensitive to hemin as compared to control. Interestingly, HO-2WT- and HO-2H45A-overexpressing cells were both protected against H2O2-induced oxidative stress and had less oxidatively modified proteins as compared to control cells. These data indicate that when HO-2 cannot metabolize the prooxidant heme, more cytotoxicity is found, whereas, interestingly, the catalytically inactive HO-2H45A was also able to protect cells against oxidative stress injury. These results suggest the multiplicity of action of the HO-2 protein itself.
authors.affiliation: Department of Anesthesiology/Critical Care Medicine, Johns Hopkins University School of Medicine, Neuro. Res. Div., 720 Rutland Ave., Ross Research Bldg. 365, Baltimore, MD 21205, USA.
authors.forename: Yun-Sook
authors.initials: YS
authors.lastname: Kim
authors.forename: Sylvain
authors.initials: S
authors.lastname: Doré
mesh_terms: D019943:Amino Acid Substitution; D002478:Cells, Cultured; D019610:Cytoprotection / Q000502:physiology*; D006419:Heme Oxygenase (Decyclizing) / Q000096:biosynthesis / Q000235:genetics*; D006427:Hemin / Q000494:pharmacology; D006801:Humans; D006861:Hydrogen Peroxide / Q000494:pharmacology; D007668:Kidney / Q000196:embryology; D018384:Oxidative Stress / Q000187:drug effects*; D014162:Transfection
chemical_list: D006427:Hemin; D006861:Hydrogen Peroxide; D006419:Heme Oxygenase (Decyclizing); C105245:heme oxygenase-2