REGULATION OF OXIDATIVE-STRESS-RESPONSIVE GENES: INVOLVEMENT OF CYP1A1 AND RELATIONSHIP WITH GLUTATHIONE AND APOPTOSIS
The regulation of oxidative-stress-responsive genes has been studied in the context of the aromatic hydrocarbon [Ah] receptor-regulated gene battery, tyrosine kinase pathways, and a mouse model exhibiting endogenous oxidative stress. Mice homozygous for a null allele of the [Ah] battery gene, cytochrome P450 1A1 (Cyp1a1) are viable and develop normally. Tyrphostin AG879, a tyrosine kinase inhibitor, was discovered to specifically block electrophile response element (EPRE)-mediated, and to a lesser extent Ah response element (AHRE)-mediated, transactivation of the Cyp1a1 and Nqo1 genes in mouse hepatoma Hepa-1 cells. Mice homozygous for the radiation-induced 14CoS albino deletion die as neonates, as a result of disruption of the gene encoding fumarylacetoacetate hydrolase (FAH), which catalyzes the last step in tyrosine catabolism. Absence of FAH leads to the accumulation of reactive intermediates in the tyrosine degradation pathway, which is manifest in the expression of EPRE- regulated oxidative-stress-responsive genes at birth. Neonatal lethality in the 14CoS/14CoS mouse is prevented by treatment with 2-(2-nitro-4-trifluoromethyl-benzyol)-1,3-cyclohexanedione (NTBC), a potent inhibitor of the tyrosine catabolic pathway. Adult 14CoS/14CoS mice treated with NTBC are “rescued” from death but still exhibit a significant oxidative stress response in the liver and kidney, as measured by expression of NQO1 mRNA, as well as the oxidative-stress-responsive genes glutamate cysteine ligase (structural and regulatory subunits, GCLS and GCLR), and heme oxygenase-1 (HO1) mRNA. Rescued mice also have decreased levels of reduced glutathione (GSH) relative to controls. Withholding NTBC from 14CoS/14CoS mice results in apoptosis of the liver, and further depletion of GSH; the degree of oxidative stress response, seem unrelated to the GSH levels and apoptosis response observed. Hepatic expression of NAD(P)H:quinone oxidoreductase-1 (NQO1), a Phase II oxidative-stress-responsive enzyme, is unaltered, suggesting that an endogenous Ah receptor ligand is metabolized by other P450 enzymes in Cyp1a1(-/-) mice. Results with AG879 suggest that a common regulatory pathway exists to activate [Ah] battery genes through distinct DNA recognition sequences. While the regulation of [Ah] battery and other EPRE-responsive genes may be involved with apoptosis, and protection from oxidative stress, this regulatory scheme affords little, if any, protection from oxidative stress and apoptosis in the 14CoS/14CoS mouse.
School:University of Cincinnati
School Location:USA - Ohio
Source Type:Master's Thesis
Keywords:oxidative stress glutathione antioxidant response element 14cos mouse
Date of Publication:01/01/2000