title: Reduced constitutive 8-oxoguanine-DNA glycosylase expression and impaired induction following oxidative DNA damage in the tuberin deficient Eker rat.
abstract: The Tsc-2 tumor suppressor gene encodes the protein tuberin, a multi-functional protein with sequence homology to the GTPase activating protein (GAP) for Rap1. Mutations in the Tsc-2 gene are associated with the development of renal tumors. The Eker rat (Tsc-2(EK/+)) bears a mutation in one allele of the Tsc-2 gene, which predisposes these animals to renal cancer. Treatment of wild-type (Tsc-2(+/+)) and mutant (Tsc-2(EK/+)) Eker rats with 2,3,5-tris-(glutathion-S-yl)hydroquinone (TGHQ; 7.5 micro mol/kg. i.v.), a potent redox active and nephrotoxic metabolite of hydroquinone increases the incidence of renal tumors only in animals carrying the mutant Tsc-2(EK/+) allele. We now show that the constitutive expression of 8-oxoguanine-DNA glycosylase (OGG1) in Tsc-2(EK/+) rats is three-fold lower than in wild-type Tsc-2(+/+) rats. Moreover, treatment of wild-type and mutant Eker rats with TGHQ greatly increases 8-oxo-deoxyguanosine (8-oxo-dG) levels within the outer stripe of the outer medulla. Tsc-2(EK/+) rats, with lower constitutive renal OGG1 expression, experience substantially higher levels of 8-oxo-dG than do wild type Tsc-2(+/+) rats. Interestingly, whereas OGG1 expression was rapidly (4 h) induced in Tsc-2(+/+) rats following exposure to TGHQ, it was significantly reduced in Tsc-2(EK/+) rats. The combination of the higher constitutive expression of OGG1 in Tsc-2(+/+) rats, and its rapid induction in response to TGHQ treatment, coupled to the initial decrease in OGG1 expression in Tsc-2(EK/+) rats, results in Tsc-2(EK/+) OGG1 protein levels just 5% of those seen in Tsc-2(+/+) rats 8 h after treatment. Coincidentally, 8-oxo-dG levels in Tsc-2(+/+) rats 8 h after treatment with TGHQ are just 5% of those that occur in Tsc-2(EK/+) rats. The results indicate that the Tsc-2 gene influences constitutive OGG1 expression and the ability of OGG1 to respond to an oxidative stress, consistent with the proposal that Tsc-2 is an acute-phase response gene. In keeping with this view, acute TGHQ-induced cytotoxicity was greater in Tsc-2(EK/+) rats than in Tsc-2(+/+) rats. The mechanism(s) coupling tuberin expression to the regulation of OGG1 are not known and are under investigation.
authors.affiliation: Center for Molecular and Cellular Toxicology, Division of Pharmacology and Toxicology, College of Pharmacy, The University of Texas at Austin, Austin, TX 78712-1074, USA.
authors.forename: Samy L
authors.initials: SL
authors.lastname: Habib
authors.forename: Minh N
authors.initials: MN
authors.lastname: Phan
authors.forename: Sonal K
authors.initials: SK
authors.lastname: Patel
authors.forename: Donghui
authors.initials: D
authors.lastname: Li
authors.forename: Terrence J
authors.initials: TJ
authors.lastname: Monks
authors.forename: Serrine S
authors.initials: SS
authors.lastname: Lau
mesh_terms: D000818:Animals; D002851:Chromatography, High Pressure Liquid; D004249:DNA Damage; D043382:DNA-Formamidopyrimidine Glycosylase; D004563:Electrochemistry; D005455:Fluorescent Antibody Technique; D005978:Glutathione / Q000031:analogs & derivatives* / Q000494:pharmacology; D006873:Hydroquinones / Q000494:pharmacology; D007668:Kidney / Q000187:drug effects; D008297:Male; D009699:N-Glycosyl Hydrolases / Q000378:metabolism*; D018384:Oxidative Stress; D051381:Rats; D011922:Rats, Mutant Strains; D012097:Repressor Proteins / Q000235:genetics / Q000502:physiology*; D000077005:Tuberous Sclerosis Complex 2 Protein; D025521:Tumor Suppressor Proteins
chemical_list: D006873:Hydroquinones; D012097:Repressor Proteins; D000077005:Tuberous Sclerosis Complex 2 Protein; D025521:Tumor Suppressor Proteins; C078765:2,3,5-(triglutathion-S-yl)hydroquinone; D009699:N-Glycosyl Hydrolases; D043382:DNA-Formamidopyrimidine Glycosylase; D005978:Glutathione