Abstract
Indoleamine 2,3-dioxygenase (IDO) catalyzes the initial and rate-limiting step in the degradation of tryptophan and is strongly induced in interferon-gamma (IFNgamma)-stimulated dendritic cells (DCs). IDO has recently been established as a key enzyme in T-cell suppression-mediated immune tolerance to tumors. STAT1 phosphorylation appears to play an important role in the control of IDO expression by IFNgamma, but the precise regulatory mechanism remains obscure. Here we present a novel mechanism of IFNgamma-induced IDO expression in bone marrow-derived dendritic cells. In addition, we demonstrate that curcumin, an active component of turmeric, significantly inhibited the induction of IDO expression and activity by IFNgamma. We found that curcumin suppressed STAT1 activation by directly inhibiting Janus-activated kinase 1/2 and protein kinase Cdelta phosphorylation in bone marrow-derived DCs, suppressing the subsequent translocation and binding of STAT1 to the GAS element of the IRF-1 promoter. Coincident with these inhibitory effects on IFNgamma-induced IDO expression, curcumin reversed IDO-mediated suppression of T-cell responses. Our results, thus, suggest that down-regulation of IDO in DCs is an important immunomodulatory property of curcumin that may be exploited therapeutically in the control of cancers.
Publication types
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Research Support, Non-U.S. Gov't
MeSH terms
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Active Transport, Cell Nucleus / drug effects
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Active Transport, Cell Nucleus / immunology
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Animals
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Bone Marrow Cells / enzymology
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Bone Marrow Cells / immunology
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Cell Nucleus / enzymology
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Cell Nucleus / immunology
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Cucumis* / immunology
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Dendritic Cells / enzymology*
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Dendritic Cells / immunology
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Gene Expression Regulation, Enzymologic / drug effects*
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Gene Expression Regulation, Enzymologic / immunology
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Immune Tolerance / drug effects
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Immune Tolerance / physiology
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Indoleamine-Pyrrole 2,3,-Dioxygenase / biosynthesis*
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Indoleamine-Pyrrole 2,3,-Dioxygenase / immunology
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Interferon Regulatory Factor-1 / immunology
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Interferon Regulatory Factor-1 / metabolism
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Interferon-gamma / immunology
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Interferon-gamma / metabolism*
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Interferon-gamma / pharmacology
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Janus Kinase 1 / immunology
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Janus Kinase 1 / metabolism*
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Janus Kinase 2 / immunology
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Janus Kinase 2 / metabolism*
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Mice
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Neoplasms / enzymology
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Neoplasms / immunology
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Phosphorylation / immunology
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Protein Kinase C-delta / immunology
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Protein Kinase C-delta / metabolism*
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Response Elements / immunology
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STAT1 Transcription Factor / immunology
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STAT1 Transcription Factor / metabolism*
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T-Lymphocytes / immunology
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T-Lymphocytes / metabolism
Substances
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Indoleamine-Pyrrole 2,3,-Dioxygenase
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Interferon Regulatory Factor-1
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STAT1 Transcription Factor
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Stat1 protein, mouse
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Interferon-gamma
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Jak1 protein, mouse
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Jak2 protein, mouse
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Janus Kinase 1
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Janus Kinase 2
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Protein Kinase C-delta