title: Mechanism of arylating quinone toxicity involving Michael adduct formation and induction of endoplasmic reticulum stress.
abstract: Quinones permeate our biotic environment, contributing to both homeostasis and cytotoxicity. All quinones generate reactive oxygen species through redox cycling, while partially substituted quinones also undergo arylation (Michael adduct formation) yielding covalent bonds with nucleophiles such as cysteinyl thiols. In contrast to reactive oxygen species, the role of arylation in quinone cytotoxicity is not well understood. We found that the arylating quinones, including unsubstituted 1,4-benzoquinone (1,4-BzQ) and partially substituted vitamin E congener gamma-tocopherol quinone (gamma-TQ), were cytotoxic, with gamma-TQ > 1,4-BzQ, whereas the fully substituted nonarylating vitamin E congener alpha-tocopherol quinone was not. In vitro, both arylating quinones formed Michael adducts with the thiol nucleophile N-acetylcysteine (NAC) at rates where 1,4-BzQ > gamma-TQ. In cultured cells, concurrent addition of NAC eliminated 1,4-BzQ caused toxicity, but preincubation was required for the same NAC detoxification effect on gamma-TQ. These data clearly established the role of arylation in quinone toxicity and revealed that arylating quinone structure affects cytotoxicity by governing detoxification through the rate of adduct formation. Furthermore, arylating quinones induced endoplasmic reticulum (ER) stress by activating the pancreatic ER kinase (PERK) signaling pathway including elF2alpha, ATF4, and C/EBP homologous protein (CHOP). Detoxification by NAC greatly attenuates CHOP induction in arylating quinone-treated cells, suggesting that ER stress is a cellular mechanism for arylating quinone cytotoxicity.
authors.affiliation: Department of Molecular and Cellular Biochemistry, Ohio State University, Columbus, OH 43210, USA.
authors.forename: Xinhe
authors.initials: X
authors.lastname: Wang
authors.forename: Beena
authors.initials: B
authors.lastname: Thomas
authors.forename: Rakesh
authors.initials: R
authors.lastname: Sachdeva
authors.forename: Linnea
authors.initials: L
authors.lastname: Arterburn
authors.forename: Lucy
authors.initials: L
authors.lastname: Frye
authors.forename: Patrick G
authors.initials: PG
authors.lastname: Hatcher
authors.forename: David G
authors.initials: DG
authors.lastname: Cornwell
authors.forename: Jiyan
authors.initials: J
authors.lastname: Ma
mesh_terms: D016475:3T3 Cells; D000111:Acetylcysteine / Q000494:pharmacology; D000818:Animals; D016227:Benzoquinones / Q000737:chemistry / Q000378:metabolism / Q000633:toxicity; D019556:COS Cells; D002460:Cell Line; D002522:Chlorocebus aethiops; D004721:Endoplasmic Reticulum / Q000187:drug effects* / Q000378:metabolism*; D008658:Inactivation, Metabolic; D051379:Mice; D018384:Oxidative Stress / Q000187:drug effects; D011809:Quinones / Q000737:chemistry / Q000378:metabolism / Q000633:toxicity*; D015398:Signal Transduction; D013438:Sulfhydryl Compounds / Q000737:chemistry / Q000378:metabolism
chemical_list: D016227:Benzoquinones; D011809:Quinones; D013438:Sulfhydryl Compounds; C004532:quinone; D000111:Acetylcysteine