title: Liver glutathione S-transferase expression is decreased by 3,5,3-triiodothyronine in hypothyroid but not in euthyroid mice.
abstract: As previously reported, the activity of liver glutathione S-transferases, an important family of enzymes for detoxification processes, is regulated by thyroid hormone levels. Here, we specifically studied glutathione S-transferase α (Gsta) gene expression in livers of mice. First, in wild-type (WT) mice, hypothyroidism was induced by 5 weeks of a diet containing 5-propyl-2-thiouracil plus water containing metimazole, whereas hyperthyroidism was induced by daily injections of 50 μg (100 g body weight)(-1) of 3,3, 5-triiodo-L-thyronine (L-T(3)) for 15 days. Importantly, hypothyroidism induced liver Gsta mRNA (>500%) and protein levels (70%; P < 0.01), indicating an important role of baseline thyroid hormone levels to repress this gene; however, surprisingly, no differences were seen in hyperthyroid mice. To further investigate Gsta repression by T(3), we used animals expressing a naturally occurring mutation of the gene for thyroid hormone receptor (TR)-β (Δ337T), which prevents T(3) binding and causes a general resistance to thyroid hormone. At baseline, homozygous animals showed increased Gsta levels (mRNA 3.5 times, protein 1.3 times) similar to those found in hypothyroid animals. After a T(3) suppression test, we found a blunted response of liver Gsta after the lower doses of T(3) in homozygous animals, as expected. However, after the highest dose of T(3), we observed a decrease in Gsta expression (80%), similar to normal animals, explained by a higher expression of TR-α1 (60%; P < 0.01) and a lower expression of Src1 (steroid coactivator receptor) in the mutant animals (50% decrease). In summary, a decrease in Gsta expression caused by T(3) was observed only in the hypothyroid state. In addition, an essential role of TR-β1 is to mediate Gsta suppression in response to T(3) and, in the absence of a functional TR-β, there is a compensatory action of TR-α1 that depends on low levels of Src1.
authors.affiliation: Laboratório de Endocrinologia Molecular, Instituto de Biofísica Carlos Chagas Filho, Federal University of Rio de Janeiro, Rio de Janeiro, Brazil.
authors.forename: Larissa C
authors.initials: LC
authors.lastname: Faustino
authors.forename: Rachel M
authors.initials: RM
authors.lastname: Pires
authors.forename: Ana Claudia
authors.initials: AC
authors.lastname: Lima
authors.forename: Aline
authors.initials: A
authors.lastname: Cordeiro
authors.forename: Luana L
authors.initials: LL
authors.lastname: Souza
authors.forename: Tânia M
authors.initials: TM
authors.lastname: Ortiga-Carvalho
mesh_terms: D000818:Animals; D005260:Female; D005982:Glutathione Transferase / Q000096:biosynthesis / Q000235:genetics* / Q000378:metabolism*; D006980:Hyperthyroidism / Q000097:blood / Q000235:genetics; D007037:Hypothyroidism / Q000097:blood* / Q000201:enzymology / Q000235:genetics*; D007453:Iodide Peroxidase / Q000235:genetics / Q000378:metabolism; D008099:Liver / Q000187:drug effects / Q000201:enzymology*; D008297:Male; D051379:Mice; D008810:Mice, Inbred C57BL; D008817:Mice, Mutant Strains; D017354:Point Mutation; D012333:RNA, Messenger / Q000235:genetics; D037021:Thyroid Hormone Receptors alpha / Q000235:genetics / Q000378:metabolism; D037042:Thyroid Hormone Receptors beta / Q000235:genetics / Q000378:metabolism; D013972:Thyrotropin / Q000097:blood* / Q000235:genetics; D014284:Triiodothyronine / Q000097:blood* / Q000494:pharmacology
chemical_list: D012333:RNA, Messenger; D037021:Thyroid Hormone Receptors alpha; D037042:Thyroid Hormone Receptors beta; D014284:Triiodothyronine; D013972:Thyrotropin; D007453:Iodide Peroxidase; C507436:selenodeiodinase type 1, mouse; D005982:Glutathione Transferase