Intra-laboratory validation of yeast-based reporter gene assays for human thyroid hormone receptors

Thyroid hormones (THs) function by activating TH receptors (THRα and THRβ) on the target cells. Several chemicals adversely affect human health and ecosystems by disrupting TH signaling. Multiple assays for thyroid disruption have been reviewed for validation, especially with respect to assay reliability, sensitivity, efficiency, and technical criteria in the OECD Test Guidelines framework. The reporter gene assay is a sensitive method used to observe cellular events associated with signal transduction and gene expression. Some mammalian cell-based THR reporter gene assays have been developed optimized, and verified. In contrast, yeast-based reporter gene assays offer a cost-effective and rapid approach compared to mammalian-based assays and are considered advantageous for detecting direct or indirect interactions between test chemicals and the receptor of interest. In this study, the previously developed yeast-based reporter gene assays for human-derived THRα and THRβ were validated using several test substances, including THs and TH-disrupting chemicals, to establish scientific confidence. Our results showed that the yeast-based THRs reporter gene assays had high repeatability and the use of a fluorescent substrate improved the detection of TH disruption caused by several chemicals. Although inter-laboratory studies are needed to verify the acceptance and data interpretation criteria, our assays can provide information on the potential of chemicals to interfere with THR transactivation as animal-free in vitro assays.