| Co-Investigator(Kenkyū-buntansha) |
NAGAYA Takashi Nagoya Univ., Res. Inst. Environ. Med., Research Associate, 環境医学研究所, 助手 (80262913)
SEO Hisao Nagoya Univ., Res.Inst.Environ.Med., Professor, 環境医学研究所, 教授 (40135380)
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| Research Abstract |
Thyroid follicular cells synthesize thyroid hormones. This process requires thyroid-specific gene products, thyroglobulin (TG) and thyroperoxidase (TPO). Expression of both genes is regulated by thyroid-enriched transcription factors, Pax-8 and TTF-1. Thyroid hormone synthesis is regulated by TSH.Production of H_2O_2, which is necessary for iodide oxidation at the step of iodide incorporation into TG, is also regulated by TSH.In various cells, it was demonstrated that reactive oxygen intermediates (ROIs) such as H_2O_2 act as an intracellular signal-transducing molecule to regulate cellular function and proliferation. Based on these findings, we postulated that H_2O_2 or other ROIs, generated in response to TSH, might play a role in regulating the function of thyroid cells. We therefore investigated effects of antioxidants, which scavenge ROIs, on expression of Pax-8, TTF-1, TG and TPO, and on proliferation of rat thyroid FRTL-5 cells. Pyrrolidine dithiocarbamate (PDTC) is a metal-chelating compound that exerts pro-oxidant or antioxidant effects. Treatment of the cells with PDTC resulted in a decrease in Pax-8 mRNA and its DNA-binding. This decrease was associated with a reduction in TPO mRNA.TTF-1 and TG mRNA was not affected by PDTC.PDTC also decreased DNA-binding of p53, a tumor suppressor protein, and increased cell proliferation. These changes were not observed by another antioxidant, N-acetyl-L-cysteine, suggesting that the metal-chelating property of PDTC is responsible for its effects. Indeed, intracellular copper level was increased by PDTC.Bathocuproinedisulfonic acid, a n* cell-permeable chelator of Cu^<1+>, abrogated the copper increase by PDTC and its effects on Pax-8 and TPO expression as well as on p*binding. These results indicate that the intracellular level of redox-active copper is crucial for Pax-8 and TPO expression and for proliferation of thyroid follicular cells.
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