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Vol. 60, Issue 5, 972-980, November 2001
Signaling and
H2O2 Scavenging
Department of Internal Medicine (S.H.K., J.M.S., H.K.C., H.K.R.,
M.S.), Department of Anatomy (O.-Y.K.), Chungnam National University,
Taejon, Korea; Korea Research Institute of Bioscience and Biotechnology
(Y.-H.L., D.-Y.Y., K.-K.L.), Yusong, Taejon, Korea; and Department of
Food and Nutrition, College of Home Economics (Y.S.H., M.A.B., K.H.K.),
Chonnam National University, Kwang-Ju, Korea
The antithyroid drug, methimazole (MMI) is used to treat patients
with Graves' hyperthyroidism. The major action of MMI is to inhibit
synthesis of thyroid hormone in the thyroid gland. However, MMI also
has antioxidant and immunomodulatory effects on thyrocytes and/or
immune cells. This study identifies novel antioxidant and
immunomodulatory effects of MMI involving the interferon-
(IFN-
) signaling pathway in thyroid cells. MMI inhibits transcription of the intercellular adhesion molecule-1 (ICAM-1) gene by
modulating the function of transcription factor STAT1 (signal
transducer and activator of transcription 1), which binds to the
IFN-
activated site of the ICAM-1 promoter. Furthermore, MMI rapidly
eliminates H2O2 produced by IFN-
treatment
in thyroid cells and thus inhibits the
H2O2-mediated phosphorylation of tyrosine 701 in STAT1. MMI also eliminates H2O2
in vitro. MMI facilitates electron transfer from NADPH to
H2O2 using thioredoxin or glutathione, fulfilling a role similar to peroxiredoxin or glutathione peroxidase, respectively. MMI prevents the IFN-
and
H2O2-mediated reversible inactivation of
phosphatases. These effects inhibit full activation of the
IFN-
-induced Janus kinase(JAK)/STAT signaling pathway in FRTL-5
thyroid cells. These results may in part explain the antioxidant and
immunomodulatory effects of MMI in thyroid cells of Graves' disease patients.
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