The Roles of PCB-regulated TR-binding Proteins during brain development.

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Environmental chemicals (ECs) such as Polychlorinated biphenyls (PCBs), dibenzo-p-dioxin (PCDDs) and dibenzofurans (PCDFs) were exerted abnormalities on brain development. We recently reported that low-dose bydroxylated-PCB whose toxicity equivalent factor (TEF) is almost negligible, suppressed TH receptor (TR)-mediated transcription by dissociation of TR from TH response element (TRE).#1. In the present study, we investigated effects of several ECs on TR-mediated transcription.TCDD and PCDFs did not affect on TR-mediated transcription and various effects of PCBs were observed. The degree of TR dissociation from TRE is correlated with that of suppression by ECs. These results suggest that PCBs effects are caused through TR-DNA binding domain (DBD), thus we performed transient transfection assay with chimeric receptors. The suppressions by PCBs were observed on chimeric receptors containing TR-DBD mediated transcription. Furthermore, the proteins contained TR-DBD dissociated from TRE. We also have reported that the magnitude of dissociation of TR from TRE by each congener was correlated with that of suppression. These findings led us to propose a hypothesis that ECs may act on DNA binding domain on TR.Thus, the toxic effects of these compounds on the development of central nerve system might be exerted through several different mechanisms. Especially PCBs affects TR-mediated transcription through DBD.#2. To screen above mentioned findings, we develop a novel in vitro DNA-protein binding assay. This assay is based on a fluorescence-labeled DNAs and GST-fused proteins. After washing steps, immunological reaction was performed seconds.#3. To investigate the roles of PCB on TR, we cloned a novel nuclear protein, using Sos-Ras Yeast Two-hybrid screening, and the functional examinations are under investigation.In conclusion, we propose that the toxicity index should be rearranged based on several critical factors.