Detection of thyroid hormone receptor-binding activities of chemicals using a yeast two-hybrid assay

Abstract

The adverse effects of chemicals exerted via estrogen receptors (ER) and androgen receptors (AR) have been studied extensively in recent years. However, those occurring via thyroid hormone receptors (TR) have not been studied enough. We examined the TR-binding activities of thyronine derivatives and alkylphenol derivatives (bisphenol A, parabens and antioxidants with o-t-butylphenol residue) using a yeast two-hybrid assay. In this assay system, the TR-binding activity of 3,5,3′-triiodo-L-thyronine (T3) was detectable at concentrations as low as 3.0 × 10-8 M and reached a plateau at 1.0 × 10-6 M. The concentration of T3 producing 10% of the activity stimulated at 1.0 × 10-6 M (10% relative effective concentration, REC10) was 2.1 × 10-8 M. 3,5,3′,5′-tetraiodo-L-thyronine (T4), 3,3′,5′-triiodo-L-thyronine (rT3) and 3, 5-diiodo-L-thyronine (T2) also exhibited TR-binding activities. The REC10 values of these chemicals were 4.2 × 10-8, 5.0 × 10-7 and 1.0 × 10-5 M, respectively. o-Isopropylphenol and o-t-butylphenol exhibited TR-binding activities with REC10 values of 3.1 × 10-4 and 4.8 × 10 -5 M, respectively, whereas t-butylbenzene, isopropylbenzene and the other chemicals tested had no detectable TR-bindng activity. These results suggest that a phenolic hydroxyl group and the ortho-substituents may play important roles in the TR-binding activities of these chemicals. This assay system will be a useful tool for screening the TR-binding activities of chemicals.