Tissue-specific induction of murine glutathione transferase mRNAs by butylated hydroxyanisole

Abstract

Three murine liver glutathione transferase (GT, EC 2.5.1.18) have been cloned and sequenced. Two of the cDNA clones, pGT875 and pGT55, encode the murine class-mu GT isoenzymes, GT8.7 and GT9.3, respectively. These two cDNA clones share 85% DNA sequence identity with one another, and the GT8.7 sub-unit encoded by pGT875 shares 92% protein sequence identity with the class-mu rat-3 (Yb1) GT subunit. The third cDNA clone, pGT41, encodes a class-alpha GT subunit that shares 96% protein sequence identity with a mouse Ya gene, 95% identity with a rat-1 (Ya) GT subunit, and 70% identity with the rat-2 (Yc) subunit. These cDNA clones and an oligonucleotide derived from the sequence of a rat class-pi cDNA clone were used to measure the induction of the mu, alpha, and pi classes of GT mRNA in different tissues of mice that were fed the dietary antioxidant 2(3)-tert-butyl hydroxyanisole (BHA). These tissues included liver, intestinal mucosa, kidney, lung, spleen, and brain. Class-mu GT mRNAs that hybridize with pGT875 are most abundant in liver and intestinal mucosa but are also found in kidney and lung, and at low levels in brain and spleen. Class-alpha GT mRNAs are most abundant in BHA-induced and uninduced intestinal mucosa, kidney, and induced liver, and were not found in spleen and brain. Class-mu and -alpha GT mRNA levels increased 15- and 50-fold, respectively, in the liver and 15- and 100-fold in intestinal mucosa in response to BHA induction. BHA increases class-mu mRNAs less than 5-fold in the kidney and lung. Class-pi mRNAs were found in all the tissues examined but were much less responsive to BHA induction. The expression of two cytochrome P-450 mRNAs increased 3-5-fold in liver and intestine after BHA induction. Oligonucleotides from divergent portions of the pGT875 and pGT55 cDNA clones have been used to examine the expression of specific mRNAs from individual class-mu GT genes; these experiments suggest that the GT mRNAs expressed in BHA-induced tissues are also expressed in the uninduced tissue. Measurements of transcription rates in isolated nuclei showed that increased GT mRNA levels are due to increased rates of transcription.