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Mechanism and prognostic value of indoleamine 2,3-dioxygenase 1 expressed in hepatocellular carcinoma.

ABSTRACT: Indoleamine 2,3-dioxygenase 1 (IDO1) is a tryptophan-metabolizing enzyme that is widely distributed in normal or malignant tissues and contributes to immunologic tolerance and immune escape. However, in hepatocellular carcinoma (HCC), the characteristics and mechanism of IDO1 expression have not been well defined. In this study, IDO1 expression in tumor cells (T-IDO1) was frequently detected (109/112) by immunohistochemistry in formalin-fixed paraffin-embedded specimens from HCC patients, and the expression patterns were mostly focal (102/109). Expression of T-IDO1 was significantly associated with the infiltration of CD8+ T cells (P = .043), as well as younger age (<50 years old, P = .02). It was also found that IDO1 had diffuse expression in inflammatory cells in all specimens, which were defined as antigen-presenting cells. Significant correlations among IDO1, IFNG, and CD8A transcriptional levels were observed in freshly resected HCC specimens; moreover, no constitutive IDO1 expression was detected in HCC cell lines until stimulated by interferon-? through the JAK2-STAT1 signaling pathway, but not type I interferon. Survival analyses showed that increased T-IDO1 and CD8+ T cell infiltration were significantly associated with superior overall survival (OS) (T-IDO1, P = .003; CD8+ T cells, P = .004), and T-IDO1 expression is an independent prognosis factor in both OS and disease-free survival (OS, P = .007; disease-free survival, P = .044). These findings indicated that T-IDO1 expression in HCC is common and is dominantly driven by the host antitumor immune response, which is a favorable prognostic factor in HCC.

SUBMITTER: Li S

PROVIDER: S-EPMC6272112 | biostudies-literature | 2018 Dec

REPOSITORIES: biostudies-literature

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Mechanism and prognostic value of indoleamine 2,3-dioxygenase 1 expressed in hepatocellular carcinoma.

Li Shaolong S Han Xue X Lyu Ning N Xie Qiankun Q Deng Haijing H Mu Luwen L Pan Tao T Huang Xin X Wang Xia X Shi Yuanyuan Y Zhao Ming M

Cancer science 20181105 12

Indoleamine 2,3-dioxygenase 1 (IDO1) is a tryptophan-metabolizing enzyme that is widely distributed in normal or malignant tissues and contributes to immunologic tolerance and immune escape. However, in hepatocellular carcinoma (HCC), the characteristics and mechanism of IDO1 expression have not been well defined. In this study, IDO1 expression in tumor cells (T-IDO1) was frequently detected (109/112) by immunohistochemistry in formalin-fixed paraffin-embedded specimens from HCC patients, and th ...[more]

PMID: 30264546

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Project description:Indoleamine 2,3-dioxygenase catalyzes the O(2)-dependent oxidation of L-tryptophan (L-Trp) to N-formylkynurenine (NFK) as part of the kynurenine pathway. Inhibition of enzyme activity at high L-Trp concentrations was first noted more than 30 years ago, but the mechanism of inhibition has not been established. Using a combination of kinetic and reduction potential measurements, we present evidence showing that inhibition of enzyme activity in human indoleamine 2,3-dioxygenase (hIDO) and a number of site-directed variants during turnover with L-tryptophan (L-Trp) can be accounted for by the sequential, ordered binding of O(2) and L-Trp. Analysis of the data shows that at low concentrations of L-Trp, O(2) binds first followed by the binding of L-Trp; at higher concentrations of L-Trp, the order of binding is reversed. In addition, we show that the heme reduction potential (E(m)(0)) has a regulatory role in controlling the overall rate of catalysis (and hence the extent of inhibition) because there is a quantifiable correlation between E(m)(0) (that increases in the presence of L-Trp) and the rate constant for O(2) binding. This means that the initial formation of ferric superoxide (Fe(3+)-O(2)(•-)) from Fe(2+)-O(2) becomes thermodynamically less favorable as substrate binds, and we propose that it is the slowing down of this oxidation step at higher concentrations of substrate that is the origin of the inhibition. In contrast, we show that regeneration of the ferrous enzyme (and formation of NFK) in the final step of the mechanism, which formally requires reduction of the heme, is facilitated by the higher reduction potential in the substrate-bound enzyme and the two constants (k(cat) and E(m)(0)) are shown also to be correlated. Thus, the overall catalytic activity is balanced between the equal and opposite dependencies of the initial and final steps of the mechanism on the heme reduction potential. This tuning of the reduction potential provides a simple mechanism for regulation of the reactivity, which may be used more widely across this family of enzymes.

Dataset Information

Mechanism and prognostic value of indoleamine 2,3-dioxygenase 1 expressed in hepatocellular carcinoma.

Publications

Mechanism and prognostic value of indoleamine 2,3-dioxygenase 1 expressed in hepatocellular carcinoma.

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