Abstract
We developed an antagonist assay system for estrogen receptor using the yeast two-hybrid system with which the yeast toxicity test is incorporated. The principle of the yeast antagonist test for estrogen receptor is measuring the inhibition of expression of β-galactosidase by the competition reaction between test chemical substance and β-estradiol when added in the medium at 300pM as a ligand for receptor. The yeast toxicity test, which measures the residual activity of β-galactosidase using a test chemical alone, is designed to indicate the toxicity of a test chemical to yeast. Thus, we can distinguish general toxicity and antagonist activity for estrogen receptor by comparing both results. The yeast antagonist test for estrogen receptor was applied to examine the antagonist activities for estrogen receptor of triphenyltin chloride (TPT) and tributyltin chloride (TBT) . The results showed that EC50 value was 32nM with the -S9 test of TPT, and 250nM with the + S9 test. TBT showed antagonist activities for estrogen receptor with the - S9 test only, and EC50 value was 560nM. TPT and TBT showed no toxic effect over the tested concentration range in this study. An estrogen receptor binding test (ER-ELISA) also showed that TPT and TBT are positive. These results suggested that the imposex promotion in the rock shell might be induced by antagonist action for estrogen receptor of organotin compounds.
