Development of bioassay system for evaluating the (anti-) thyroid hormone-like activity by various environmental contaminants

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It had been reported that reproductive and immune systems were affected in wildlife containing high concentrations of dioxins and/or polychlorinated biphenyls (PCBs). Recently the organohalogen compounds which have structural similarities with thyroid hormone have been used widely as flame retardants and some of them are detected in environmental samples. From these facts, it has been suspected that these organohalogen compounds may affect on wildlife as well as human beings as environmental contaminants. In this work, we constructed the bioassay system using transcriptional activation by thyroid hormone receptor as biomarkers. First, we established human cell line in which thyroid hormone receptor α gene was stable transfected and designated HeLaTR cells. Then DR4-SV-Luc plasmid in which thyroid hormone response element (DR4) was inserted upstream of luciferase gene was transfected into HeLaTR cells transiently in the presence or absence of T3. Luciferase activities were determined us … More ing cell lysate and it was found that T3 increased luciferase activity four to five fold. After addition of various organohalogen compounds such as environmental contaminants to this bioassay system, luciferase activities in each cell lysates were determined to evaluate the effects on thyroid hormone system by organohalogen compounds. One hydroxylated PCB, which was the metabolite of PCB turned to reduce the luciferase activity which was induced by T3 in HeLaTR cells. In contrast, dioxin, hexacyclododecane which is used for flame retardant, and nitrofen which had been used for pesticide augmented the luciferase activities induced by T3. Diiodobiphenyl (DIB) which is used for photoconductor of cellular phone could induce luciferase activity and augment the T3 action. Furthermore, DIB could augment the transcriptional activation by estrogen receptor through estrogen response element. We also determined the gene expression profile after addition of T3 into HeLaTR cells by DNA microarray, and showed that apoptosis signal through 4-1BB was activated after addition of T3. Less