Indoleamine 2,3-dioxygenase activity and L-tryptophan transport in human breast cancer cells

The activity and expression of indoleamine 2,3-dioxygenase together with L-tryptophan transport has been examined in cultured human breast cancer cells. MDA-MB-231 but not MCF-7 cells expressed mRNA for indoleamine 2,3-dioxygenase. Kynurenine production by MDA-MB-231 cells, which was taken as a measure of enzyme activity, was markedly stimulated by interferon-gamma (1000 units/ml). Accordingly, L-tryptophan utilization by MDA-MB-231 cells was enhanced by interferon-gamma. 1-Methyl-DL-tryptophan (1 mM) inhibited interferon-gamma induced kynurenine production by MBA-MB-231 cells. Kynurenine production by MCF-7 cells remained at basal levels when cultured in the presence of interferon-gamma. L-Tryptophan transport into MDA-MB-231 cells was via a Na(+)-independent, BCH-sensitive pathway. It appears that system L (LAT1/CD98) may be the only pathway for l-tryptophan transport into these cells. 1-Methyl-D,L-tryptophan trans-stimulated l-tryptophan efflux from MDA-MB-231 cells and thus appears to be a transported substrate of system L. The results suggest that system L plays an important role in providing indoleamine-2,3-dioxygenase with its main substrate, L-tryptophan, and suggest a mechanism by which estrogen receptor-negative breast cancer cells may evade the attention of the immune system.     

L-leucine transport in human breast cancer cells (MCF-7 and MDA-MB-231): kinetics, regulation by estrogen and molecular identity of the transporter

The transport of L-leucine by two human breast cancer cell lines has been examined. L-leucine uptake by MDA-MB-231 and MCF-7 cells was via a BCH-sensitive, Na+ -independent pathway. L-leucine uptake by both cell lines was inhibited by L-alanine, D-leucine and to a lesser extent by L-lysine but not by L-proline. Estrogen (17beta-estradiol) stimulated L-leucine uptake by MCF-7 but not by MDA-MB-231 cells. L-leucine efflux from MDA-MB-231 and MCF-7 cells was trans-stimulated by BCH in a dose-dependent fashion. The effect of external BCH on L-leucine efflux from both cell types was almost abolished by reducing the temperature from 37 to 4 degrees C. There was, however, a significant efflux of L-leucine under zero-trans conditions which was also temperature-sensitive. L-glutamine, L-leucine, D-leucine, L-alanine, AIB and L-lysine all trans-stimulated L-leucine release from MDA-MB-231 and MCF-7 cells. In contrast, D-alanine and L-proline had little or no effect. The anti-cancer agent melphalan inhibited L-leucine uptake by MDA-MB-231 cells but had no effect on L-leucine efflux. Quantitative real-time PCR revealed that LAT1 mRNA was approximately 200 times more abundant than LAT2 mRNA in MCF-7 cells and confirmed that MDA-MB-231 cells express LAT1 but not LAT2 mRNA. LAT1 mRNA levels were higher in MCF-7 cells than in MDA-MB-231 cells. Furthermore, LAT1 mRNA was more abundant than CD98hc mRNA in both MDA-MB-231 and MCF-7 cells. The results suggest that system L is the major transporter for L-leucine in both MDA-MB-231 and MCF-7 cells. It is possible that LAT1 may be the major molecular correlate of system L in both cell types. However, not all of the properties of system L reflected those of LAT1/LAT2/CD98hc.     

Induction of indoleamine 2,3-dioxygenase by interferon-gamma in human lens epithelial cells: Apoptosis through the formation of 3-hydroxykynurenine

Interferon-gamma (IFN-γ) is known to cause apoptosis of lens epithelial cells and cataract formation, but the molecular mechanisms underlying these effects are unknown. IFN-γ induces the expression of indoleamine 2,3-dioxygenase (IDO) and thereby enhances the production of kynurenines from l-tryptophan. The present study was designed to investigate the role of IDO and kynurenines in the IFN-γ-mediated apoptosis of lens epithelial cells and to determine the signaling pathways involved. IFN-γ stimulated the synthesis of IDO and activated the JAK–STAT1 signaling pathway in human lens epithelial cells (HLE-B3) in a dose-dependent manner. Meanwhile, fludarabine, an inhibitor of STAT1 activation, blocked IFN-γ-mediated IDO expression. N-Formylkynurenine, kynurenine (Kyn) and 3-hydroxykynurenine (3OHKyn) were detected in cells, with 3OHKyn concentrations being higher than those of the other kynurenines. The intracellular production of kynurenines was completely blocked by 1-methyl-dl-tryptophan (MT), an inhibitor of IDO. Kyn- and 3OHKyn-modified proteins were detected in IFN-γ-treated cells. The induction of IDO by IFN-γ in HLE-B3 cells caused increases in intracellular ROS, cytosolic cytochrome c and caspase-3 activity, along with a decrease in protein-free thiol content. These changes were accompanied by apoptosis. At equimolar concentrations, 3OHKyn caused higher levels of apoptosis than the other kynurenines in HLE-B3 cells. MT and a kynurenine 3-hydroxylase inhibitor (Ro61-8048) effectively inhibited IFN-γ-mediated apoptosis in HLE-B3 cells. Our results show that the induction of IDO by IFN-γ is JAK–STAT1 pathway-dependent and that this induction causes 3OHKyn-mediated apoptosis in HLE-B3 cells. These data suggest that IDO-mediated kynurenine formation could play a role in cataract formation related to chronic inflammation.     

Inhibition of indoleamine 2,3-dioxygenase and tryptophan 2,3-dioxygenase by β-carboline and indole derivatives

β-Carboline derivatives inhibited both indoleamine 2,3-dioxygenase and tryptophan 2,3-dioxygenase activities from various sources. Among them, norharman is most potent for both enzymes from mammalian sources. Kinetic studies revealed that norharman is uncompetitive (K_i = 0.12 mm) with l-tryptophan for rabbit intestinal indoleamine 2,3-dioxygenase, and linearly competitive (K_i = 0.29 mm) with l-tryptophan for mouse liver tryptophan 2,3-dioxygenase. In addition, some β-carbolines selectively inhibited one enzyme or the other. Pseudomonad tryptophan 2,3-dioxygenase was inhibited by a different spectrum of β-carbolines. Such a selective inhibition by the structure of substrate analogs is more evident by the use of indole derivatives. Indole-3-acetamide, indole-3-acetonitrile and indole-3-acrylic acid exhibited a potent inhibition for mammalian tryptophan 2,3-dioxygenase, while they moderately inhibited the pseudomonad enzyme. However, they showed no inhibition for indoleamine 2,3-dioxygenase. These results suggest the difference of the structures of the active sites among these enzymes from various sources.     

l-Leucine transport in human breast cancer cells (MCF-7 and MDA-MB-231): kinetics, regulation by estrogen and molecular identity of the transporter

The transport of l-leucine by two human breast cancer cell lines has been examined. l-Leucine uptake by MDA-MB-231 and MCF-7 cells was via a BCH-sensitive, Na⁺-independent pathway. l-Leucine uptake by both cell lines was inhibited by l-alanine, d-leucine and to a lesser extent by l-lysine but not by l-proline. Estrogen (17β-estradiol) stimulated l-leucine uptake by MCF-7 but not by MDA-MB-231 cells. l-Leucine efflux from MDA-MB-231 and MCF-7 cells was trans-stimulated by BCH in a dose-dependent fashion. The effect of external BCH on l-leucine efflux from both cell types was almost abolished by reducing the temperature from 37 to 4 °C. There was, however, a significant efflux of l-leucine under zero-trans conditions which was also temperature-sensitive. l-Glutamine, l-leucine, d-leucine, l-alanine, AIB and l-lysine all trans-stimulated l-leucine release from MDA-MB-231 and MCF-7 cells. In contrast, d-alanine and l-proline had little or no effect. The anti-cancer agent melphalan inhibited l-leucine uptake by MDA-MB-231 cells but had no effect on l-leucine efflux. Quantitative real-time PCR revealed that LAT1 mRNA was approximately 200 times more abundant than LAT2 mRNA in MCF-7 cells and confirmed that MDA-MB-231 cells express LAT1 but not LAT2 mRNA. LAT1 mRNA levels were higher in MCF-7 cells than in MDA-MB-231 cells. Furthermore, LAT1 mRNA was more abundant than CD98hc mRNA in both MDA-MB-231 and MCF-7 cells. The results suggest that system L is the major transporter for l-leucine in both MDA-MB-231 and MCF-7 cells. It is possible that LAT1 may be the major molecular correlate of system L in both cell types. However, not all of the properties of system L reflected those of LAT1/LAT2/CD98hc.     

Upregulation of interferon-induced indoleamine 2,3-dioxygenase in human macrophage cultures by lipopolysaccharide, muramyl tripeptide, and interleukin-1

The tryptophan decyclizing enzyme indoleamine 2,3-dioxygenase (IDO) was induced in human monocyte-derived macrophages (MDM) treated with human recombinant interferon-β (IFN-β) or interferon-γ (IFN-γ). Treated cells exhibited dose-dependent increases in IDO when assayed 48 hr after treatment. Cells exposed to IFN-γ were observed to exhibit consistently higher peak levels of IDO when compared with cells incubated in the presence of IFN-β. When IFN-β-treated cells were incubated in the presence of specified amounts of bacterial lipopolysaccharide (LPS) or liposome-encapsulated muramyl tripeptide (MTP), peak IDO activity increased such that enzyme activity was comparable to maximal activity observed with IFN-γ-treated cells. LPS and MTP also upregulated IFN-γ-mediated IDO activity when suboptimal amounts of IFN-γ were used. When macrophages were costimulated with various concentrations of human recombinant interleukin 1α (IL-1α), along with either maximum-stimulating amounts of IFN-β or suboptimal amounts of IFN-γ, IDO activity was upregulated in a manner similar to results obtained using the microbial products as stimuli. While neither IL-1α or IL-1β was detected in culture supernatants from macrophages treated with either LPS or MTP (alone or in combination with IFN), IL-1α was detected in cell lysates of macrophages treated with these upregulators. Although neutralizing antibody to IL-1α abolished the upregulatory effect of exogenous IL-1α, it had no effect on upregulation by LPS or MTP. This suggests that although LPS and MTP may induce production of cell-associated IL-1α, upregulation of IDO activity by these agents is independent of IL-1α production and may be mediated through distinct pathways.     

Inhibition of increased indoleamine 2,3-dioxygenase activity attenuates Toxoplasma gondii replication in the lung during acute infection

The regulation of local L-tryptophan concentrations by tryptophan-degrading enzyme, indoleamine 2,3-dioxygenase (IDO) induced by various stimuli such as interferon-γ (IFN-γ) is one of the key mechanisms in antimicrobial effect. Recently, IDO is also focused on an immunosuppressive mechanism shared by several different immune cell types. Here, we show that inhibition of increased IDO activity maybe involved in the antiparasitic mechanism during Toxoplasma gondii (T. gondii) infection in vivo. In this study, we investigated the role of IDO by using IDO-gene-deficient (IDO KO) mice and by administering a competitive enzyme inhibitor, 1-methyl-D,L-tryptophan (1MT), to wild-type mice following T. gondii infection. Although depletion of lung l-tryptophan did not occur in IDO KO mice after T. gondii infection, the increased mRNA expression of T. gondii surface antigen gene 2 (SAG2) and the inflammatory cytokines in the lung were drastically reduced in the IDO KO mice following infection. We also found that complete depletion of lung l-tryptophan was observed in wild-type mice after infection, but not in mice treated with 1MT. At the same time, 1MT suppressed the increased mRNA expression of SAG2. Taken together, we observed that the inflammatory damage was significantly decreased by the administration of 1MT in the lung after infection. Inhibition of the IDO activity or the elimination of IDO's substrate may be an effective therapy against microbial diseases.     

Functional and molecular characteristics of system L in human breast cancer cells

The functional and molecular properties of system L in human mammary cancer cells (MDA-MB-231 and MCF-7) have been examined. All transport experiments were conducted under Na(+)-free conditions. alpha-Aminoisobutyric acid (AIB) uptake by MDA-MB-231 and MCF-7 cells was almost abolished by BCH (2-amino-2-norbornane-carboxylic acid). AIB uptake by MDA-MB-231 cells was also inhibited by L-alanine (83.6%), L-lysine (75.6%) but not by L-proline. Similarly, L-lysine and L-alanine, respectively, reduced AIB influx into MCF-7 cells by 45.3% and 63.7%. The K(m) of AIB uptake into MDA-MB-231 and MCF-7 cells was, respectively, 1.6 and 8.8 mM, whereas the V(max) was, respectively, 9.7 and 110.0 nmol/mg protein/10 min. AIB efflux from MDA-MB-231 and MCF-7 cells was trans-stimulated by BCH, L-glutamine, L-alanine, L-leucine, L-lysine and AIB (all at 2 mM). In contrast, L-glutamate, L-proline, L-arginine and MeAIB had no effect. The interaction between L-lysine and AIB efflux was one of low affinity. The fractional release of AIB from MDA-MB-231 cells was trans-accelerated by D-leucine and D-tryptophan but not by D-alanine. MDA-MB-231 and MCF-7 cells expressed LAT1 and CD98 mRNA. MCF-7 cells also expressed LAT2 mRNA. The results suggest that AIB transport in mammary cancer cells under Na(+)-free conditions is predominantly via system L which acts as an exchange mechanism. The differences in the kinetics of AIB transport between MDA-MB-231 and MCF-7 cells may be due to the differential expression of LAT2.     

Identification of genes modulated by interferon gamma in breast cancer cells

Interferon gamma (IFNγ) plays a context-dependent dual tumor-suppressor and pro-tumorigenic roles in cancer. IFNγ induces morphological changes in breast cancer (BC) cells with or without estrogen receptor alpha (ERα) expression. However, IFNγ-regulated genes in BC cells remain unexplored. Here, we performed a cDNA microarray analysis of MCF-7 (ERα+) and MDA-MB-231 (HER2-/PR-/ERα-) cells with and without IFNγ treatment. We identified specific IFNγ?modulated genes in each cell type, and a small group of genes regulated by IFNγ common in both cell types. IFNγ treatment for an extended time mainly repressed gene expression shared by both cell types. Nonetheless, some of these IFNγ-repressed genes were seemingly deregulated in human mammary tumor samples, along with decreased IFNGR1 (an IFNγ receptor) expression. Thus, IFNγ signaling-elicited anti-tumor activities may be mediated by the downregulation of main IFNγ target genes in BC; however, it may be deregulated by the tumor microenvironment in a tumor stage-dependent manner.     

Interplay between interferon-stimulated gene 15/ISGylation and interferon gamma signaling in breast cancer cells

Interferon-stimulated gene 15 (ISG15) is a ubiquitin-like protein that conjugates to its target proteins to modify them through ISGylation, but the relevance of ISG15 expression and its effects have been not completely defined. Herein, we examined the interplay between ISG15/ISGylation and the interferon-gamma (IFN-γ) signaling pathway in mammary tumors and compared it with that in normal mammary tissues. Our results indicated that mammary tumors had higher levels of ISG15 mRNA and ISG15 protein than the adjacent normal mammary tissue. Furthermore, the expression of IFN-γ signaling components was altered in breast cancer. Interestingly, IFN-γ treatment induced morphological changes in MCF-7 and MDA-MB-231 breast cancer cell lines due to cytoskeletal reorganization. This cellular process seems to be related to the increase in ISGylation of cytoplasmic IQ Motif Containing GTPase Activating Protein 1 (IQGAP1). Interactome analysis also indicated that IFN-γ signaling and the ISGylation system are associated with several proteins implicated in cytoskeletal remodeling, including IQGAP1. Thus, ISG15 may present a potential biomarker for breast cancer, and IFN-γ signaling and protein ISGylation may participate in the regulation of the cytoskeleton in breast cancer cells.     

Different anticancer effects of Saxifragifolin A on estrogen receptor-positive and estrogen receptor-negative breast cancer cells

BackgroundBreast cancer is the leading cause of cancer-related death among women worldwide. For treating breast cancer, numerous natural products have been considered as chemotherapeutic drugs.Hypothesis/purposeThe present study aims to investigate the apoptotic effect of Saxifragifolin A (Saxi A) isolated from Androsace umbellata in two different human breast cancer cells which are ER-positive MCF-7 cells and ER-negative MDA-MB-231 cells, and examine the molecular basis for its anticancer actions.Study designThe inhibitory effects of Saxi A on cell survival were examined in MCF-7 cells and MDA-MB-231 cells in vitro.MethodsMTT assays, Annexin V/PI staining analysis, ROS production assay, Hoechst33342 staining and Western blot analysis were performed.ResultsOur results showed that MDA-MB-231 cells were more sensitive to Saxi A-induced apoptosis than MCF-7 cells. Saxi A induced apoptosis in MDA-MB-231 cells through ROS-mediated and caspase-dependent pathways, whereas treatment with Saxi A induced apoptosis in MCF-7 cells in a caspase-independent manner. In spite of Saxi A-induced activation of MAPKs in both breast cancer cell lines, only p38 MAPK and JNK mediated Saxi A-induced apoptosis. In addition, cell survival of shERα-transfected MCF-7 cells was decreased, while MDA-MB-231 cells that overexpress ERα remained viable.ConclusionSaxi A inhibits cell survival in MCF-7 cells and MDA-MB-231 cells through different regulatory pathway, and ERα status appears to be important for regulating Saxi A-induced apoptosis in breast cancer cells. Thus, Saxi A may have a potential therapeutic use for treating breast cancer.     

Troglitazone enhances tamoxifen-induced growth inhibitory activity of MCF-7 cells

Peroxisome proliferator-activated receptor γ (PPARγ) ligands have been identified as a potential source of therapy for human cancers. However, PPARγ ligands have a limitation for breast cancer therapy, since estrogen receptor α (ER_α) negatively interferes with PPARγ signaling in breast cancer cells. Here we show that ER_α inhihits PPARγ transactivity and ER_α-mediated inhibition of PPARγ transactivity is blocked by tamoxifen, an estrogen receptor blocker. The activation of ER_α with 17-β-estradiol blocked PPRE transactivity induced by troglitazone, a PPARγ ligand, indicating the resistance of ER_α-positive breast cancer cells to troglitazone. Indeed, troglitazone inhibited the growth of ER_α-negative MDA-MB-231 cells more than that of ER_α-positive MCF-7 cells. Combination of troglitazone with tamoxifen led to a marked increase in growth inhibition of ER_α-positive MCF-7 cells compared to either agent alone. Our data indicates that troglitazone enhances the growth inhibitory activity of tamoxifen in ER_α-positive MCF-7 cells.     

乳腺癌细胞中人血小板衍生生长因子受体β启动子的基础活性研究

目的:探讨低迁移表型的乳腺癌细胞MCF-7和高迁移表型的乳腺癌细胞MDA-MB-231中血小板衍生生长因子β启动子的基础活性及转录调控差异。方法:Real-Time PCR,Weastern blot等技术检测PDGFRβ在2株细胞中的转录和表达差异。双荧光报告系统检测PDGFRβ启动子各缺失突变片段在2株细胞中的活性,筛选差异片段。生物信息学预测启动子区可能存在的转录因子。凝胶迁移实验研究转录因子在两株乳腺癌细胞中对PDGFRβ启动子的调节活性。结果:两株细胞中都有PDGFRβ的内源性表达,且在MDA-MB-231中表达较高。在2株细胞中找到了人PDGFRB 启动子的重要活性调节区,(+539bp,+1457bp)在2株细胞中均呈负调控,(+54bp,+539bp)在两株细胞中均呈正调控,(-983bp,+54bp)在MDA-MB-231中呈显著正调控,在MCF-7中没有活性。转录因子AP1的转录活性和与DNA的结合活性在MDA-MB-231中均高于MCF-7。结论:不同迁移表型的乳腺癌细胞中PDGFRβ存在不同的表达调控机制,PDGFRβ启动子活性片段(-983bp,+54bp)在两株细胞中存在显著活性差异。转录因子AP-1在两株细胞中有表达水平和结合活性差异。     

Benzyl isothiocyanate causes FoxO1-mediated autophagic death in human breast cancer cells

Benzyl isothiocyanate (BITC), a constituent of edible cruciferous vegetables, inhibits growth of breast cancer cells but the mechanisms underlying growth inhibitory effect of BITC are not fully understood. Here, we demonstrate that BITC treatment causes FoxO1-mediated autophagic death in cultured human breast cancer cells. The BITC-treated breast cancer cells (MDA-MB-231, MCF-7, MDA-MB-468, BT-474, and BRI-JM04) and MDA-MB-231 xenografts from BITC-treated mice exhibited several features characteristic of autophagy, including appearance of double-membrane vacuoles (transmission electron microscopy) and acidic vesicular organelles (acridine orange staining), cleavage of microtubule-associated protein 1 light chain 3 (LC3), and/or suppression of p62 (p62/SQSTM1 or sequestosome 1) expression. On the other hand, a normal human mammary epithelial cell line (MCF-10A) was resistant to BITC-induced autophagy. BITC-mediated inhibition of MDA-MB-231 and MCF-7 cell viability was partially but statistically significantly attenuated in the presence of autophagy inhibitors 3-methyl adenine and bafilomycin A1. Stable overexpression of Mn-superoxide dismutase, which was fully protective against apoptosis, conferred only partial protection against BITC-induced autophagy. BITC treatment decreased phosphorylation of mTOR and its downstream targets (P70s6k and 4E-BP1) in cultured MDA-MB-231 and MCF-7 cells and MDA-MB-231 xenografts, but activation of mTOR by transient overexpression of its positive regulator Rheb failed to confer protection against BITC-induced autophagy. Autophagy induction by BITC was associated with increased expression and acetylation of FoxO1. Furthermore, autophagy induction and cell growth inhibition resulting from BITC exposure were significantly attenuated by small interfering RNA knockdown of FoxO1. In conclusion, the present study provides novel insights into the molecular circuitry of BITC-induced cell death involving FoxO1-mediated autophagy.     

The effect of cancer procoagulant on expression of metastatic and angiogenic markers in breast cancer and embryonic stem cell lines

Cancer procoagulant is present only in malignant tumours and the undifferentiated tissues of human placenta. Its possible role in angiogenesis and metastasis was investigated. Cancer procoagulant increased the steady-state mRNA level of L1 cell adhesion molecule (L1CAM) in MCF-7 breast cancer cells and E14 mouse embryonic stem cells (MESCs), while an increase in angiogenin mRNA was observed in MDA-MB-231 breast cancer cells. Furthermore, production of vascular endothelial growth factor (VEGF) protein in MCF-7 breast cancer cells and E14 MESCs, but decreased in MDA-MB-231 breast cancer cells. We conclude that cancer procoagulant could potentially play a part in angiogenesis in cancer and vascular development during embryonic development.     

Inhibition of indoleamine 2,3 dioxygenase activity by H2O2

Indoleamine 2,3-dioxygenase is the first and rate limiting enzyme of the kynurenine pathway of tryptophan metabolism, has potent effects on cell proliferation and mediates antimicrobial, antitumorogenic, and immunosuppressive effects. As a potent cytotoxic effector, the mechanisms of indoleamine 2,3-dioxygenase inhibition deserve greater attention. The work presented here represents the first systematic study exploring the mechanisms by which low levels of hydrogen peroxide (10-100 microM) inhibit indoleamine 2,3-dioxygenase in vitro. Following brief peroxide exposure both enzyme inhibition and structural changes were observed. Loss of catalysis was accompanied by oxidation of several cysteine residues to sulfinic and sulfonic acids, observed by electrospray and MALDI mass spectrometry. Enzyme activity could in part be preserved in the presence of sulfhydryl containing compounds, particularly DTT and methionine. However, these structural alterations did not prevent substrate (l-tryptophan) binding. Some enzyme activity could be recovered in the presence of thioredoxin, indicating that the inhibitory effect of H(2)O(2) is at least partially reversible in vitro. We present evidence that cysteine oxidation represents one mechanism of indoleamine 2,3-dioxygenase inhibition.     

LPS-induced NF-κB expression in THP-1Blue cells correlates with neopterin production and activity of indoleamine 2,3-dioxygenase

Neopterin production is induced in human monocyte-derived macrophages and dendritic cells upon stimulation with Th1-type cytokine interferon-γ (IFN-γ). In parallel, IFN-γ induces the tryptophan-(trp)-degrading enzyme indoleamine 2,3-dioxygenase (IDO) and triggers the formation of reactive oxygen species (ROS). Translocation of the signal transduction element nuclear factor-κB (NF-κB) is induced by ROS and accelerates the pro-inflammatory response by activation of other pro-inflammatory pathways. Therefore, a close relationship between NF-κB expression, the production of neopterin and the degradation of trp can be assumed, although this has not been demonstrated so far. In the present in vitro study we compared the influence of lipopolysaccharide (LPS) on NF-κB activation, neopterin formation and the degradation of trp in THP-1Blue cells, which represent the human myelomonocytic cell line THP-1 stably transfected with an NF-κB inducible reporter system.In cells stimulated with LPS, a significant induction of NF-κB was observed, and this was paralleled by an increase of kynureunine (kyn) and neopterin concentrations and a decline of trp. The increase of the kyn to trp quotient indicates accelerated IDO activity. Higher LPS concentrations and longer incubation of cells were associated with higher activities of all three biochemical pathways and significant correlations existed between NF-κB activation, neopterin release and trp degradation (all p < 0.001). We conclude that there is a parallel induction of NF-κB, neopterin formation and trp degradation in monocytic THP-1 cells, which is elicited by pro-inflammatory triggers like LPS during innate immune responses.