Abstract
Thyroid hormones are a critical role in cardiac function and brain development, and the act of thyroid hormones is mediated through the activation of nuclear thyroid hormone receptors (TRs). Although in vitro reporter gene assays are widely used to detect endocrine disruptors, a TR-responsive reporter gene assay has not been established except for a few human cell-based bioassays. In the previous study, we developed yeast-based TR responsive reporter gene assays. In this study, we investigated whether thyroid hormones and anti-thyroid hormone compounds were effectively detectable using four yeast-based reporter gene assays for TRα and TRβ in human and Xenopus tropicalis.
In 96-wells plates, yeasts were incubated with the various concentrations of test substances for 16 hours. The antagonistic activities of chemicals were examined by competition between the chemical and thyroid hormone simultaneously added at the following concentrations. To distinguish antagonist activity from the cytotoxicity, the CYC yeast strains established in W303a and corresponding mutants for each receptor that constitutively expressed the lacZ reporter were used for comparisons.
In both of TRα and TRβ assays in human and Xenopus tropicalis, β-galactosidase activity was induced by thyroid hormones in a dose-dependent manner. All anti-thyroid hormone compounds tested in this study inhibited thyroid hormone-induced in human TR assays, but some compounds had no antagonistic effects in the assays for Xenopus tropicalis. Further studies are needed to determine whether other compounds can be evaluated in our assays.
