Induction of interleukin-8 synthesis integrates effects on transcription and mRNA degradation from at least three different cytokine- or stress-activated signal transduction pathways

MOZ and MOZ-CBP cooperate with NF-kappaB to activate transcription from NF-kappaB-dependent promoters

OBJECTIVE

Monocytic zinc finger (MOZ) maintains hematopoietic stem cells and, upon fusion to the coactivator CREB-binding protein (CBP), induces acute myeloid leukemia (AML). Leukemic stem cells in AML often exhibit excessive signal-dependent activity of the transcription factor nuclear factor (NF)-kappaB. Because aberrant interaction between NF-kappaB and coactivators represents an alternative mechanism for enhancing NF-kappaB activity, we evaluated whether MOZ and MOZ-CBP cooperate with NF-kappaB to activate transcription from NF-kappaB-dependent promoters.

METHODS

The ability of MOZ, MOZ mutants, and MOZ-CBP to enhance expression of NF-kappaB-dependent promoters was tested in reporter studies. The interaction between MOZ and NF-kappaB was evaluated by both coimmunoprecipitation and glutathione S-transferase pulldown assays.

RESULTS

MOZ activates transcription from the NF-kappaB-dependent interleukin-8 promoter; interestingly, this effect is markedly enhanced by CBP. Although MOZ has less potent transcriptional activity than MOZ-CBP, both proteins cooperate with steroid receptor coactivator-1 to activate transcription. MOZ also induces multiple NF-kappaB-dependent viral promoters. Importantly, MOZ associates in a protein complex with the p65 subunit of NF-kappaB and interacts directly with p65 in vitro. Transcriptional activity of MOZ requires its C-terminal domain, which is absent from MOZ-CBP, indicating that the transcriptional activity of MOZ-CBP derives from its CBP sequence.

CONCLUSIONS

MOZ interacts with the p65 subunit of NF-kappaB and enhances expression of NF-kappaB-dependent promoters. The more potent transcriptional activity of MOZ-CBP derives from its CBP sequence. Thus, interaction between NF-kappaB and MOZ-CBP may play an important role in the pathogenesis of certain acute myeloid leukemias.

Modulation of bcl-xL in tumor cells regulates angiogenesis through CXCL8 expression

In this paper, we investigated whether bcl-xL can be involved in the modulation of the angiogenic phenotype of human tumor cells. Using the ADF human glioblastoma and the M14 melanoma lines, and their derivative bcl-xL-overexpressing clones, we showed that the conditioned medium of bcl-xL transfectants increased in vitro endothelial cell functions, such as proliferation and morphogenesis, and in vivo vessel formation in Matrigel plugs, compared with the conditioned medium of control cells. Moreover, the overexpression of bcl-xL induced an increased expression of the proangiogenic interleukin-8 (CXCL8), both at the protein and mRNA levels, and an enhanced CXCL8 promoter activity. The role of CXCL8 on bcl-xL-induced angiogenesis was validated using CXCL8-neutralizing antibodies, whereas down-regulation of bcl-xL through antisense oligonucleotide or RNA interference strategies confirmed the involvement of bcl-xL on CXCL8 expression. Transient overexpression of bcl-xL led to extend this observation to other tumor cell lines with different origin, such as colon and prostate carcinoma. In conclusion, our results showed that CXCL8 modulation by bcl-xL regulates tumor angiogenesis, and they point to elucidate an additional function of bcl-xL protein.

p38 MAPK signaling in oral-related diseases

Multiple dental diseases are characterized by chronic inflammation, due to the production of cytokines, chemokines, and prostanoids by immune and non-immune cells. Membrane-bound receptors provide a link between the extracellular environment and the initiation of intracellular signaling events that activate common signaling components, including p38 mitogen-activated protein kinase (MAPK), extracellular signal-regulated kinase (ERK), c-Jun N-terminal kinase (JNK), and nuclear factor (NF)-kappaB. Although ERK pathways regulate cell survival and are responsive to extracellular mitogens, p38 MAPK, JNK, and NF-kappaB are involved in environmental stress responses, including inflammatory stimuli. Over the past decade, significant advances have been made relative to our understanding of the fundamental intracellular signaling mechanisms that govern inflammatory cytokine expression. The p38 MAPK pathway has been shown to play a pivotal role in inflammatory cytokine and chemokine gene regulation at both the transcriptional and the post-transcriptional levels. In this review, we present evidence for the significance of p38 MAPK signaling in diverse dental diseases, including chronic pain, desquamative disorders, and periodontal diseases. Additional information is presented on the molecular mechanisms whereby p38 signaling controls post-transcriptional gene expression in inflammatory states.

Signal transduction mechanisms of CD137 ligand in human monocytes

Bidirectional signalling, i.e. simultaneous signalling through a receptor as well as its cell surface-bound ligand has been identified for several members of the TNF and TNF receptor family members. Reverse signalling through the ligands offers the advantage of an immediate feed-back and a more precise fine tuning of biological responses. Little is known about the molecular nature of reverse signalling through the ligands. CD137 ligand, member of the TNF family is expressed on monocytes and induces activation, migration, prolongation of survival and proliferation of monocytes. Here we show that reverse signalling by CD137 ligand is mediated by protein tyrosine kinases, p38 mitogen activated protein kinase (MAPK), extracellular signal-regulated kinase (ERK)1,2, MAP/ERK kinase (MEK), Phosphoinositide-3-kinase (PI3-K) and protein kinase A (PKA) but not by protein kinase C (PKC). This study also shows that reverse signalling relies on the same signal transduction molecules as signalling through classical receptors and is in its nature not different from it.

Functional analysis of KSRP interaction with the AU-rich element of interleukin-8 and identification of inflammatory mRNA targets

mRNA stability is a major determinant of inflammatory gene expression. Rapid degradation of interleukin-8 (IL-8) mRNA is imposed by a bipartite AU-rich element (ARE) in the 3' untranslated region (R. Winzen et al., Mol. Cell. Biol. 24:4835-4847, 2004). Small interfering RNA-mediated knockdown of the ARE-binding protein KSRP resulted in stabilization of IL-8 mRNA or of a beta-globin reporter mRNA containing the IL-8 ARE. Rapid deadenylation was impaired, indicating a crucial role for KSRP in this step of mRNA degradation. The two IL-8 ARE domains both contribute to interaction with KSRP, corresponding to the importance of both domains for rapid degradation. Exposure to the inflammatory cytokine IL-1 has been shown to stabilize IL-8 mRNA through p38 mitogen-activated protein (MAP) kinase and MK2. IL-1 treatment impaired the interaction of KSRP with the IL-8 ARE in a manner dependent on p38 MAP kinase but apparently independent of MK2. Instead, evidence that TTP, a target of MK2, can also destabilize the IL-8 ARE reporter mRNA is presented. In a comprehensive approach to identify mRNAs controlled by KSRP, two criteria were evaluated by microarray analysis of (i) association of mRNAs with KSRP in pulldown assays and (ii) increased amounts in KSRP knockdown cells. According to both criteria, a group of 100 mRNAs is controlled by KSRP, many of which are unstable and encode proteins involved in inflammation. These results indicate that KSRP functions as a limiting factor in inflammatory gene expression.

Differential regulation of iron chelator-induced IL-8 synthesis via MAP kinase and NF-kappaB in immortalized and malignant oral keratinocytes

Background

Interleukin-8 (IL-8) is a cytokine that plays an important role in tumor progression in a variety of cancer types; however, its regulation is not well understood in oral cancer cells. In the present study, we examined the expression and mechanism of IL-8 in which it is involved by treating immortalized (IHOK) and malignant human oral keratinocytes (HN12) cells with deferoxamine (DFO).

Methods

IL-8 production was measured by an enzyme-linked immunoabsorbent assay and reverse transcriptase-polymerase chain reaction (RT-PCR) analysis. Electrophoretic mobility shift assays was used to determine NF-κB binding activity. Phosphorylation and degradation of the I-κB were analyized by Western blot.

Results

IHOK cells incubated with DFO showed increased expression of IL-8 mRNA, as well as higher release of the IL-8 protein. The up-regulation of DFO-induced IL-8 expression was higher in IHOK cells than in HN12 cells and was concentration-dependent. DFO acted additively with IL-1β to strongly up-regulate IL-8 in IHOK cells but not in HN12 cells. Accordingly, selective p38 and ERK1/2 inhibitors for both kinases abolished DFO-induced IL-8 expression in both IHOK and HN12 cells. Furthermore, DFO induced the degradation and phosphorylation of IκB, and activation of NF-κB. The IL-8 inducing effects of DFO were mediated by a nitric oxide donor (S-nitrosoglutathione), and by pyrrolidine dithiocarbamate, an inhibitor of NF-κB, as well as by wortmannin, which inhibits the phosphatidylinositol 3-kinase-dependent activation of NAD(P)H oxidase.

Conclusion

This results demonstrate that DFO-induced IL-8 acts via multiple signaling pathways in immortalized and malignant oral keratinocytes, and that the control of IL-8 may be an important target for immunotheraphy against human oral premalignant lesions.

Platelet-derived growth factor-induced stabilization of cyclooxygenase 2 mRNA in rat smooth muscle cells requires the c-Src family of protein-tyrosine kinases

Cyclooxygenases (COXs) are crucial rate-limiting enzymes required for the biosynthesis of prostaglandins. COX-2 is an inducible isoform of this enzyme, which is believed to play important roles in the development of atherosclerotic vascular disease. We found that COX-2 expression rapidly increases in response to various signaling events, including activation of the platelet-derived growth factor (PDGF) pathway. Activation of PDGF receptor (PDGFR) in rat aortic vascular smooth muscle cells leads to c-Src-dependent stabilization of COX-2 mRNA requiring an AU-rich region within the 3'-untranslated region of this transcript. This regulation correlates with tyrosine phosphorylation of the RNA-associated protein, CUG-binding protein 2 (CUGBP2), which appears to enhance its interaction with COX-2 mRNA. Site-directed mutagenesis of putative tyrosine phosphorylation sites in CUGBP2 identified tyrosine 39 as a c-Src target, and a CUGBP2 with a mutated tyrosine 39 displayed an attenuated ability to bind COX-2 mRNA. We further show that silencing of CUGBP2 with specific small interference RNAs significantly reduces PDGF-dependent induction of COX-2 at both mRNA and protein levels. Furthermore, forced expression of CUGBP2 or constitutively active c-Src leads to stabilization of co-expressed COX-2 mRNA. Finally, in vitro RNA decay assay demonstrates that CUGBP2 is functionally required for the stabilization of COX-2 mRNA. Therefore, our data suggest that tyrosine phosphorylation of CUGBP2 is an important underlying mechanism for the ability of PDGFR/c-Src signaling to control the stability of COX-2 mRNA.

Transcriptional regulation of deoxynivalenol-induced IL-8 expression in human monocytes

The trichothecene mycotoxin deoxynivalenol (DON), commonly present in contaminated grains worldwide, induces expression of the chemokine interleukin (IL)-8 in human monocytes. The purpose of this study was to test the hypothesis that DON modulates transcriptional and posttranscriptional regulation of IL-8 expression in the U937 human monocyte model. When U937 cells were transfected with a wild-type IL-8 promoter luciferase construct (-162/+44 IL-8 LUC) and incubated with DON (1 mug/ml) or the positive control, lipopolysaccharide (LPS) (1 mug/ml), there was a significant increase in luciferase expression. Mutation of the nuclear factor-kappaB (NF-kappaB) binding site significantly impaired both DON- and LPS-induced luciferase expression. In contrast, mutating the activator protein-1 binding site resulted in significantly increased DON- and LPS-induced luciferase expression. CCAAT/enhancer-binding protein beta, octamer-1, or NF-kappaB repressing factor binding site mutations did not affect DON-induced luciferase activity. Consistent with reporter studies, the NF-kappaB inhibitor caffeic acid phenethyl ester completely ablated both DON-induced IL-8 mRNA and protein expression. When NF-kappaB subunit binding to a specific IL-8 promoter probe was evaluated by enzyme-linked immunosorbent assay (ELISA), DON was observed to increase p65 binding by 21-fold, have no effect on p50 binding and decrease p52 binding. DON was not found to stabilize IL-8 mRNA in U937 cells. Taken together, these data suggest that DON-induced IL-8 expression is likely to be mediated at the transcriptional level by NF-kappaB, specifically p65, but does not appear to involve mRNA stabilization.

Prostaglandin E2 induces the expression of IL-1alpha in colon cancer cells

PGE(2) has been shown to exert pro-oncogenic effects in colorectal neoplasia through producing autocrine or paracrine growth factors. In the present study, we demonstrate that PGE(2) induced the expression of IL-1alpha in colon cancer cells, which plays critical roles in tumor metastasis and neoangiogenesis in a variety of cancers. PGE(2) increased the levels of both IL-1alpha mRNA and protein, suggesting a positive feedback loop between the IL-1 pathway and PGE(2) signaling. Mechanistically, PGE(2) induced the expression of IL-1alpha at both transcriptional and posttranscriptional levels. PGE(2) stimulated the transcriptional activity of the IL-1alpha promoter and significantly stabilized IL-1alpha mRNA. Moreover, we show that IL-1alpha enhanced colorectal neoplasia, stimulating cell migration and neoangiogenesis. Knockdown of the expression of IL-1alpha by small-interfering RNA resulted in a reduction of vascular endothelial growth factor secretion in colon cancer cells and an inhibition of tube formation by HUVECs. Thus, our results suggest that PGE(2) induces the expression of proinflammatory cytokine IL-1alpha, which may potentially enhance the proneoplastic actions of the cyclooxygenase-2/PGE(2) signaling pathway.

Functional consequences of alteration of N-linked glycosylation sites on the neurokinin 1 receptor

The neurokinin 1 receptor (NK1R), a G protein-coupled receptor involved in diverse functions including pain and inflammation, has two putative N-linked glycosylation sites, Asn-14 and Asn-18. We studied the role of N-linked glycosylation in the functioning of the NK1R by constructing three receptor mutants: two single mutants (Asn --> Gln-14 and Asn --> Gln-18) and a double mutant, lacking both glycosylation sites. Using a lentiviral transfection system, the mutants were stably transfected into NCM 460 cells, a nontransformed human colonic epithelial cell line. We observed that the magnitude of glycosylation as estimated by changes in gel migration depends on the number of glycosylation sites available, with the wild-type receptor containing the greatest amount of glycosylation. All mutant receptors were able to bind to substance P and neurokinin A ligand with similar affinities; however, the double mutant, nonglycosylated NK1R showed only half the B(max) of the wild-type NK1R. In terms of receptor function, the ablation of both N-linked glycosylation sites did not have a profound effect on the receptors' abilities to activate the MAP kinase families (p42/p44, JNK, and p38), but did affect SP-induced IL-8 secretion. All mutants were able to internalize, but the kinetics of internalization of the double mutant receptor was more rapid, when compared with wild-type NK1R. Therefore, glycosylation of NK1R may stabilize the receptor in the plasma membrane. These results contribute to the ongoing elucidation of the role of glycosylation in G protein-coupled receptors and the study of the neurokinin receptors in particular.

Role of NF-kappaB in transcriptional regulation of the phagocyte NADPH oxidase by tumor necrosis factor-alpha

Macrophages play an important role in the pathogenesis of chronic inflammatory disease. Activation of these phagocytes induces the production of proinflammatory cytokines, such as IL-1 and TNF-alpha and the generation of reactive oxygen species (ROS), such as superoxide anion (O2*-). Recently, we found that TNF-alpha treatment of human monocytic cells (MonoMac1) and isolated human monocytes resulted in up-regulation of the NADPH oxidase gene, neutrophil cytosolic factor 2 (NCF2). These results suggested that TNF-alpha, produced by activated macrophages, could serve as an autocrine/paracrine regulator of the oxidase, resulting in increased and/or prolonged production of O2*-. To gain a better understanding of the mechanisms involved in NADPH oxidase regulation by TNF-alpha, we evaluated transcriptional regulation of oxidase genes in MonoMac1 cells and human monocytes. We show that TNF-alpha-treated cells have increased levels of mRNA and up-regulated expression of NADPH oxidase subunits p47(phox), p67(phox), and gp91(phox), as well as increased oxidase activity. Pharmacological inhibitors of NF-kappaB activation blocked TNF-alpha-induced up-regulation of NCF1, NCF2, and CYBB message, which correlated with a reduction in expression of the corresponding oxidase proteins and decreased O2*- production. These data demonstrate that the increase in and/or maintenance of O2*- production in TNF-alpha-treated MonoMac1 cells and monocytes are a result, in part, of transcriptional up-regulation of three essential NADPH oxidase genes via the NF-kappaB pathway. This novel finding supports a model, whereby TNF-alpha-dependent activation of NF-kappaB up-regulates phagocyte NADPH oxidase activity, leading to enhanced ROS production and further NF-kappaB activation, potentially contributing to sustained oxidant production in chronic inflammation.

Introns regulate the rate of unstable mRNA decay

The expression of neutrophil-specific chemokines is known to be regulated via adenine-uridine-rich sequence elements in the 3'-untranslated regions of their mRNAs that confer a high degree of mRNA instability. Although the presence of intron sequences in eukaryotic genes is known to enhance expression, the effect of intron content on the rate of mature, translatable mRNA degradation has not been demonstrated. In this study, we have determined the effects of intron content on the rate of decay of the chemokine CXCL1 (KC) mRNA. The half-life of KC mRNA was markedly prolonged when the primary transcript was obtained from a genomic clone containing three introns as compared with the half-life observed with sequence-identical KC mRNA derived from an intron-free cDNA construct. The effect of intron content was achieved with a single intron, and neither the intron sequences nor the intron positions were critical determinants of the outcome. The intron content produced the same effect when expressed in multiple cell types and when the sequences were stably integrated into the genome. The differential decay rates were not a consequence of differential nuclear to cytoplasmic transport. The intron content of the primary transcript did not influence the rate of KC mRNA translation and did not modulate the ability of interleukin-1 stimulation to stabilize the otherwise unstable mRNA. The intron effect on mRNA decay was seen with mRNAs containing two distinct instability determinants. These findings document that intron content marks the mRNA sequence leading to enhanced stability that is particularly evident in short lived ARE-containing mRNAs.

Inhibition of T-cell inflammatory cytokines, hepatocyte NF-kappaB signaling, and HCV infection by standardized Silymarin

BACKGROUND & AIMS

Chronic hepatitis C is a serious global medical problem necessitating effective treatment. Because standard of care with pegylated interferon plus ribavirin therapy is costly, has significant side effects, and fails to cure about half of all infections, many patients seek complementary and alternative medicine to improve their health, such as Silymarin, derived from milk thistle (Silybum marianum). Milk thistle's clinical benefits for chronic hepatitis C are unsettled due to variability in standardization of the herbal product.

METHODS

In the current study, we focused on the anti-inflammatory and antiviral properties of a standardized Silymarin extract (MK-001).

RESULTS

MK-001 inhibited expression of tumor necrosis factor-alpha in anti-CD3 stimulated human peripheral blood mononuclear cells and nuclear factor kappa B-dependent transcription in human hepatoma Huh7 cells. Moreover, MK-001 dose dependently inhibited infection of Huh7 and Huh7.5.1 cells by JFH-1 virus. MK-001 displayed both prophylactic and therapeutic effects against HCV infection, and when combined with interferon-alpha, inhibited HCV replication more than interferon-alpha alone. Commercial preparations of Silymarin also displayed antiviral activity, although the effects were not as potent as MK-001. Antiviral effects of the extract were attributable in part to induction of Stat1 phosphorylation, while interferon-independent mechanisms were suggested when the extract was biochemically fractionated by high-performance liquid chromatography. Silybin A, silybin B, and isosilybin A, isosilybin B elicited the strongest anti-NF-kappaB and anti-HCV actions. These effects were independent of MK-001-induced cytotoxicity.

CONCLUSIONS

The data indicate that Silymarin exerts anti-inflammatory and antiviral effects, and suggest that complementary and alternative medicine-based approaches may assist in the management of patients with chronic hepatitis C.

Chemokine and chemoattractant receptor expression: post-transcriptional regulation

The magnitude and character of the inflammatory process are determined in part via the trafficking of leukocytes into sites of injury and infection, and this process depends on proper control of the expression of genes encoding chemoattractant peptides and their receptors. Although these controls operate at multiple mechanistic levels, recent evidence indicates that post-transcriptional events governing the half-life of select mRNAs are important determinants. Adenine-uridine rich elements (AREs) located within 3' untranslated regions (UTRs) confer constitutive mRNA instability and in some cases, stabilization following stimulation by ligands of the Toll-IL-1 receptor (TIR) family. Although the importance of AREs in determining activity and mRNA half-life is well-recognized, the mechanistic scope and diversity remain poorly understood. Using the mouse KC or CXCL1 gene as a model, we have demonstrated that the abundance of mRNA and protein produced during an inflammatory response depends on multiple mechanistically distinct AREs present in the 3' UTR of the mRNA. The mRNA encoding the receptor for N-terminal formyl-methionine-containing peptides is also unstable and subject to stabilization in response to TIR ligands. These two models can, however, be readily distinguished from one another on the basis of specific stimulus sensitivity and the signaling pathways, through which such stimuli couple to the control of mRNA decay. These models demonstrate the substantial diversity operative in the post-transcriptional regulation of inflammatory gene expression.

Cloning and characterisation of p38 MAP kinase from Atlantic salmon A kinase important for regulating salmon TNF-2 and IL-1beta expression

p38 mitogen-activated protein kinase is activated by environmental stress and cytokines and plays a role in transcriptional regulation and inflammatory responses. In this study, three distinct Atlantic salmon p38 (As-p38) cDNAs were cloned, which all translated into 361 amino acid proteins. The As-p38 protein sequences possessed showed >85% identity to the mammalian homolog, p38alpha. All three contained the conserved phosphorylation motif TGY located in the activation loop of the kinase. Salmon p38 showed ubiquitous tissue distribution, including expression in the immune organs head kidney and spleen. A higher p38 mRNA expression was detected in the ovary compared to other organs suggesting that p38 may perform specific functions within this organ. Western blot analysis with an antibody specific for phosphorylated p38 showed that ectopically expressed As-p38 variants were activated in CHSE-214 cells in response to chemical stress. Furthermore, lipopolysaccharide, CpG oligonucleotides and recombinant trout IL-1beta induced endogenous phosphorylation of p38 in salmon head kidney macrophages in a dose-dependent manner. The importance of p38 for regulation of salmon innate immunity was further demonstrated by the ability of the p38 specific inhibitor SB203580 to completely abolish LPS-stimulated TNF-2 and IL-1beta mRNA expression in the macrophages.

Signaling in Lipopolysaccharide-Induced Stabilization of Formyl Peptide Receptor 1 mRNA in Mouse Peritoneal Macrophages

To identify the TLR4-initiated signaling events that couple to formyl peptide receptor (FPR)1 mRNA stabilization, macrophages were treated with LPS along with a selection of compounds targeting several known signaling pathways. Although inhibitors of protein tyrosine kinases, MAPKs, and stress-activated kinases had little or no effect on the response to LPS, LY294002 (LY2) and parthenolide (an IkappaB kinase inhibitor) were both potent inhibitors. LY2 but not parthenolide blocked the LPS-induced stabilization of FPR1 mRNA. Although both LY2 and wortmannin effectively blocked PI3K activity, wortmannin had little effect on FPR1 expression and did not modulate the decay of FPR1 mRNA. Moreover, although LY2 was demonstrated to be a potent inhibitor of PI3K activity, a structural analog of LY2, LY303511 (LY3), which did not inhibit PI3K, was equally effective at preventing LPS-stimulated FPR1 expression. The mammalian target of rapamycin activity (measured as phospho-p70S6 kinase) was activated by LPS but not significantly blocked by LY2. In addition, although rapamycin blocked mTOR activity, it did not inhibit FPR1 mRNA expression. Finally, the mechanisms involved in stabilization of FPR1 by LPS could be distinguished from those involved in stabilization of AU-rich mRNAs because the prolonged half-life of FPR1 mRNA was insensitive to the inhibition of p38 MAPK. These findings demonstrate that LY2/LY3 targets a novel TLR4-linked signaling pathway that selectively couples to the stabilization of FPR1 mRNA.

IRAK-4 mutation (Q293X): rapid detection and characterization of defective post-transcriptional TLR/IL-1R responses in human myeloid and non-myeloid cells

Innate immunodeficiency has recently been reported as resulting from the Q293X IRAK-4 mutation with consequent defective TLR/IL-1R signaling. In this study we report a method for the rapid allele-specific detection of this mutation and demonstrate both cell type specificity and ligand specificity in defective IL-1R-associated kinase (IRAK)-4-deficient cellular responses, indicating differential roles for this protein in human PBMCs and primary dermal fibroblasts and in LPS, IL-1beta, and TNF-alpha signaling. We demonstrate transcriptional and post-transcriptional defects despite NF-kappaB signaling and intact MyD88-independent signaling and propose that dysfunctional complex 1 (IRAK1/TRAF6/TAK1) signaling, as a consequence of IRAK-4 deficiency, generates specific defects in MAPK activation that could underpin this patient's innate immunodeficiency. These studies demonstrate the importance of studying primary human cells bearing a clinically relevant mutation; they underscore the complexity of innate immune signaling and illuminate novel roles for IRAK-4 and the fundamental importance of accessory proinflammatory signaling to normal human innate immune responses and immunodeficiencies.

Regulation of CXCL-8 (interleukin-8) induction by double-stranded RNA signaling pathways during hepatitis C virus infection

Hepatitis C virus (HCV) infection induces the alpha-chemokine interleukin-8 (CXCL-8), which is regulated at the levels of transcription and mRNA stability. In the current study, CXCL-8 regulation by double-stranded (ds)RNA pathways was analyzed in the context of HCV infection. A constitutively active mutant of the retinoic acid-inducible gene I (RIG-I), RIG-N, activated CXCL-8 transcription. Promoter mutagenesis experiments indicated that NF-kappaB and interferon (IFN)-stimulated response element (ISRE) binding sites were required for the RIG-N induction of CXCL-8 transcription. IFN-beta promoter stimulator 1 (IPS-1) expression also activated CXCL-8 transcription, and mutations of the ISRE and NF-kappaB binding sites reduced and abrogated CXCL-8 transcription, respectively. In the presence of wild-type RIG-I, transfection of JFH-1 RNA or JFH-1 virus infection of Huh7.5.1 cells activated the CXCL-8 promoter. Expression of IFN regulatory factor 3 (IRF-3) stimulated transcription from both full-length and ISRE-driven CXCL-8 promoters. Chromatin immunoprecipitation assays demonstrated that IRF-3 and NF-kappaB bound directly to the CXCL-8 promoter in response to virus infection and dsRNA transfection. RIG-N stabilized CXCL-8 mRNA via the AU-rich element in the 3' untranslated region of CXCL-8 mRNA, leading to an increase in its half-life following tumor necrosis factor alpha induction. The data indicate that HCV infection triggers dsRNA signaling pathways that induce CXCL-8 via transcriptional activation and mRNA stabilization and define a regulatory link between innate antiviral and inflammatory cellular responses to virus infection.

Moxifloxacin but not ciprofloxacin or azithromycin selectively inhibits IL-8, IL-6, ERK1/2, JNK, and NF-κB activation in a cystic fibrosis epithelial cell line

Cystic fibrosis (CF) is associated with severe neutrophilic airway inflammation. We showed that moxifloxacin (MXF) inhibits IL-8 and MAPK activation in monocytic and respiratory epithelial cells. Azithromycin (AZM) and ciprofloxacin (CIP) are used clinically in CF. Thus we now examined effects of MXF, CIP, and AZM directly on CF cells. IB3, a CF bronchial cell line, and corrected C38 cells were treated with TNF-α, IL-1β, or LPS with or without 5–50 μg/ml MXF, CIP, or AZM. IL-6 and IL-8 secretion (ELISA), MAPKs ERK1/2, JNK, p38, and p65 NF-κB (Western blot) activation were measured. Baseline IL-6 was sixfold higher in IB3 than C38 cells but IL-8 was similar. TNF-α and IL-1β increased IL-6 and IL-8 12- to 67-fold with higher levels in IB3 than C38 cells post-TNF-α ( P < 0.05). Levels were unchanged following LPS. Baseline phosphorylated form of ERK1/2 (p-ERK1/2), JNK, and NF-κB p65 were higher in IB3 than C38 cells (5-, 1.4-, and 1.4-fold), and following TNF-α increased, as did the p-p38, by 1.6- to 2-fold. MXF (5–50 μg/ml) and CIP (50 μg/ml), but not AZM, suppressed IL-6 and IL-8 secretion by up to 69%. MXF inhibited TNF-α-stimulated MAPKs ERK1/2, 46-kDa JNK, and NF-κB up to 60%, 40%, and 40%, respectively. In contrast, MXF did not inhibit p38 activation, implying a highly selective pretranslational effect. In conclusion, TNF-α and IL-1β induce an exaggerated inflammatory response in CF airway cells, inhibited by MXF more than by CIP or AZM. Clinical trials are recommended to assess efficacy in CF and other chronic lung diseases.

The role of sphingosine 1-phosphate in the TNF-alpha induction of IL-8 gene expression in lung epithelial cells

Tumor necrosis factor-alpha (TNF-alpha) is an important cytokine involved in the pathogenesis of inflammatory diseases of the lung. Interleukin-8 (IL-8), a C-X-C chemokine, is induced by TNF-alpha and initiates injury by acting as a chemoattractant for neutrophils and other immune cells. Although sphingolipids such as ceramide and sphingosine 1-phosphate (S1-P) have been shown to serve as signaling molecules in the TNF-alpha inflammatory response, their role in the TNF-alpha induction of IL-8 gene expression in lung epithelial cells is not known. We investigated the role of sphingolipids in the TNF-alpha induction of IL-8 gene expression in H441 lung epithelial cells. We found that TNF-alpha induced IL-8 mRNA levels by increasing gene transcription, and the stability of IL-8 mRNA was not affected. Exogenous S1-P but not ceramide or sphingosine increased IL-8 mRNA levels and IL-8 secretion. Dimethylsphingosine, an inhibitor of sphingosine kinase, partially inhibited TNF-alpha induction of IL-8 mRNA levels indicating the importance of intracellular increases in S1-P in the IL-8 induction. S1-P induction of IL-8 mRNA was due to an increase in gene transcription, and the stability of IL-8 mRNA was not affected. S1-P induction of IL-8 mRNA was associated with an increase in the binding activity of AP-1 but the activities of NF-kappaB and NF IL-6 were unchanged. S1-P induced the phosphorylation of ERK, p38 and JNK MAPKs. Pharmacological inhibitors of ERK and p38 but not JNK partly inhibited S1-P induction of IL-8 mRNA levels. These data show that increases in the intracellular S1-P partly mediate TNF-alpha induction of IL-8 gene expression in H441 lung epithelial cells via ERK and p38 MAPK signaling pathways and increased AP-1 DNA binding.

Release of interleukins and other inflammatory cytokines by human adipose tissue is enhanced in obesity and primarily due to the nonfat cells

The white adipose tissue, especially of humans, is now recognized as the central player in the mild inflammatory state that is characteristic of obesity. The question is how the increased accumulation of lipid seen in obesity causes an inflammatory state and how this is linked to the hypertension and type 2 diabetes that accompanies obesity. Once it was thought that adipose tissue was primarily a reservoir for excess calories that were stored in the adipocytes as triacylglycerols. In times of caloric deprivation these stored lipids were mobilized as free fatty acids and the insulin resistance of obesity was attributed to free fatty acids. It is now clear that in humans the expansion of adipose tissue seen in obesity results in more blood vessels, more connective tissue fibroblasts, and especially more macrophages. There is an enhanced secretion of some interleukins and inflammatory cytokines in adipose tissue of the obese as well as increased circulating levels of many cytokines. The central theme of this chapter is that human adipose tissue is a potent source of inflammatory interleukins plus other cytokines and that the majority of this release is due to the nonfat cells in the adipose tissue except for leptin and adiponectin that are primarily secreted by adipocytes. Human adipocytes secrete at least as much plasminogen activator inhibitor-1 (PAI-1), MCP-1, interleukin-8 (IL-8), and IL-6 in vitro as they do leptin but the nonfat cells of adipose tissue secrete even more of these proteins. The secretion of leptin, on the other hand, by the nonfat cells is negligible. The amount of serum amyloid A proteins 1 & 2 (SAA 1 & 2), haptoglobin, nerve growth factor (NGF), macrophage migration inhibitory factor (MIF), and PAI-1 secreted by the adipocytes derived from a gram of adipose tissue is 144%, 75%, 72%, 37%, and 23%, respectively, of that by the nonfat cells derived from the same amount of human adipose tissue. However, the release of IL-8, MCP-1, vascular endothelial growth factor (VEGF), TGF-beta1, IL-6, PGE(2), TNF-alpha, cathepsin S, hepatocyte growth factor (HGF), IL-1beta, IL-10, resistin, C-reactive protein (CRP), and interleukin-1 receptor antagonist (IL-1Ra) by adipocytes is less than 12% of that by the nonfat cells present in human adipose tissue. Obesity markedly elevates the total release of TNF-alpha, IL-6, and IL-8 by adipose tissue but only that of TNF-alpha is enhanced in adipocytes. However, on a quantitative basis the vast majority of the TNF-alpha comes from the nonfat cells. Visceral adipose tissue also releases more VEGF, resistin, IL-6, PAI-1, TGF-beta1, IL-8, and IL-10 per gram of tissue than does abdominal subcutaneous adipose tissue. In conclusion, there is an increasing recognition that adipose tissue is an endocrine organ that secretes leptin and adiponectin along with a host of other paracrine and endocrine factors in addition to free fatty acids.

An antiapoptotic protein, c-FLIPL, directly binds to MKK7 and inhibits the JNK pathway

Inhibition of NF-kappaB activation increases susceptibility to tumor necrosis factor (TNF)alpha-induced cell death, concurrent with caspases and prolonged c-Jun N-terminal kinase (JNK) activation, and reactive oxygen species (ROS) accumulation. However, the detailed mechanisms are unclear. Here we show that cellular FLICE-inhibitory protein (c-FLIP) is rapidly lost in NF-kappaB activation-deficient, but not wild-type fibroblasts upon TNFalpha stimulation, indicating that NF-kappaB normally maintains the cellular levels of c-FLIP. The ectopic expression of the long form of c-FLIP (c-FLIPL) inhibits TNFalpha-induced prolonged JNK activation and ROS accumulation in NF-kappaB activation-deficient fibroblasts. Conversely, TNFalpha induces prolonged JNK activation and ROS accumulation in c-Flip-/- fibroblasts. Moreover, c-FLIPL directly interacts with a JNK activator, MAP kinase kinase (MKK)7, in a TNFalpha-dependent manner and inhibits the interactions of MKK7 with MAP/ERK kinase kinase 1, apoptosis-signal-regulating kinase 1, and TGFbeta-activated kinase 1. This stimuli-dependent interaction of c-FLIPL with MKK7 might selectively suppress the prolonged phase of JNK activation. Taken that ROS promote JNK activation and activation of the JNK pathway may promote ROS accumulation, c-FLIPL might block this positive feedback loop, thereby suppressing ROS accumulation.

Combined Effect of 25-Hydroxycholesterol and IL-1β on IL-8 Production in Human Colon Carcinoma Cell Line (Caco-2)

Interleukin-1 beta (IL-1beta) is an important mediator in intestinal inflammation. IL-1beta promotes IL-8 production, which can be modulated by a number of factors, including oxidative stress. Interestingly, oxysterols, which are thought to contribute to inflammation in atherosclerotic plaques, are also produced by intestinal epithelial cells. Thus, we investigated the effect of oxysterols, including 25-hydroxycholesterol and 7beta-hydroxycholesterol, on IL-1beta-induced IL-8 production in Caco-2 cells (a human colon carcinoma cell line). Pre-treatment of Caco-2 cells with 25-hydroxycholesterol significantly enhanced IL-1beta-induced IL-8 expression at both mRNA and protein levels. However, 7beta-hydroxycholesterol showed very little effect on IL-8 production. Furthermore, pre-treatment with 25-hydroxycholesterol, followed by IL-1beta stimulation, enhanced IL-8 promoter activity beyond that observed with IL-1beta alone. These results suggest that 25-hydroxycholesterol enhances IL-1beta-induced IL-8 production, possibly by enhancing promoter activity.

Low-Density Lipoprotein Modified by Macrophage-Derived Lysosomal Hydrolases Induces Expression and Secretion of IL-8 Via p38 MAPK and NF-κB by Human Monocyte-Derived Macrophages

OBJECTIVE

Modified lipoproteins induce inflammatory reactions in the atherosclerotic arterial wall. We have previously found that macrophages in atherosclerotic lesions secrete lysosomal hydrolases that can modify low-density-lipoprotein (LDL) in vitro to generate "hydrolase-modified LDL" (H-LDL). Here, we studied whether H-LDL exerts inflammatory effects on cultured human macrophages.

METHODS AND RESULTS

Using cytokine cDNA arrays, we found that H-LDL induced expression of IL-8, but not of the anti-inflammatory cytokines IL-10 and transforming growth factor (TGF)-beta, in human monocyte-derived macrophages. H-LDL induced rapid phosphorylation of the p38 mitogen-activated protein kinase (MAPK), nuclear translocation of 2 transcription factors, nuclear factor kappaB (NF-kappaB) and activator protein 1 (AP-1), and time-dependent secretion of IL-8 from the macrophages. Inhibition of MAPKs and of transcription factors showed that p38 MAPK and NF-kappaB, but not ERK1/2, JNK, or AP-1, were crucial for the H-LDL-induced IL-8 secretion from the macrophages.

CONCLUSIONS

The results show that by activating p38 MAPK and NF-kappaB, macrophage hydrolases modify LDL into biologically active particles capable of triggering the secretion of IL-8 in macrophages. Thus, activated hydrolase-secreting macrophages in atherosclerotic lesions may sustain a proatherogenic extracellular environment by hydrolyzing LDL and triggering it to act in an autocrine or paracrine fashion to induce IL-8 secretion by the plaque macrophages.

Activations of mitogen-activated protein kinase and nuclear factor-kappaB by mechanical stretch result in ventilation-induced lung injury

Mechanical ventilation is an important therapeutic technique for patients with respiratory failure. Nonetheless, it may cause or worsen lung injury. The specific triggers for cytokine release and the cellular origins of the inflammatory mediators in ventilation-induced lung injury (VILI) have yet to be defined. With the development of cytomechanics, we can study the lung cell response to mechanical strain. The initial step is mechanosensation, including stretch-activated ionchannels and the ECM-integrin-cytoskeleton pathway. Several intracellular signaling pathways then are activated and eventually result in increased transcription of specific genes. Mitogen-activated protein kinase cascade, nuclear factor(NF)-kappaB, PKC are all activated by mechanical stretch. But the mechanisms regulating lung stretch-induced cytokine production are still unclear. I hypotheses mechanical stretch initiate specific genes transcription, then the cytokines stimulate the cell again. This formed a positive feed back loop, which caused VILI. These studies may lead to the identification of new targets for therapeutic interventions and help to develop less aggressive ventilation strategies for patients with acute respiratory failure.

A p38alpha selective mitogen-activated protein kinase inhibitor prevents periodontal bone loss

In the oral microbial environment, Gram-negative bacterial derived lipopolysaccharide (LPS) can initiate inflammatory bone loss as seen in periodontal diseases. p38 Mitogen-activated protein kinase (MAPK) signaling is critical to inflammatory cytokine and LPS-induced cytokine expression, which may contribute toward periodontal bone loss. The purpose of this proof-of-principle study was to evaluate the ability of an orally active p38alpha MAPK inhibitor (SD-282) to reduce periopathogenic LPS-induced alveolar bone loss in an experimental rat model. Five groups of Sprague-Dawley rats received one of the following treatments: LPS injected to the palatal gingiva adjacent to the maxillary molars three times per week for 8 weeks, LPS plus two doses of SD-282 (15 or 45 mg/kg) twice daily by oral gavage, or control groups given drug vehicle (1% polyethylene glycol) or SD-282 (45 mg/kg) only. Baseline and 8-week alveolar bone loss was assessed by microcomputed tomography (microCT) and histological examination. LPS induced severe bone loss over this time period, whereas control groups were unchanged from baseline measurements. Both doses of SD-282 showed significant protection from LPS-induced bone loss. Bone area and volumetric analysis of maxillas by microCT indicated significant loss of bone volume with LPS treatment, which was blocked with the p38 inhibitor. Histological examination indicated significantly fewer tartate-resistant acid phosphatase-positive osteoclasts and a significant decrease in interleukin (IL)-6, IL-1beta, and tumor necrosis factor alpha expression in p38 inhibitor-treated groups compared with LPS groups by immunostaining. Results from this in vivo study suggest that orally active p38 MAPK inhibitors can reduce LPS-induced inflammatory cytokine production and osteoclast formation and protect against LPS-stimulated alveolar bone loss.

Relationships between hepatitis C virus replication and CXCL-8 production in vitro

The chemokine CXCL-8 (interleukin-8) is induced by many viruses, including hepatitis C virus (HCV). In the current study, we examined CXCL-8 levels in the context of acute and chronic HCV replication in vitro. Two different small interfering RNAs were used to silence CXCL-8 mRNA and protein expression in Huh7 and BB7 replicon cells. HCV RNA synthesis in BB7 cells was inhibited by CXCL-8 knockdown. Furthermore, antibody neutralization of endogenous CXCL-8 activity inhibited HCV replication, while addition of recombinant human CXCL-8 stimulated NS5A protein expression. Moreover, CXCL-8 protein levels correlated positively with HCV RNA levels in four independent subgenomic and genomic replicon lines (R = 0.41, P = 0.0013). However, CXCL-8 mRNA levels correlated inversely with CXCL-8 protein and HCV RNA levels in all replicon lines and in Huh7 cells. Transient replication assays with strongly permissive and weakly permissive Huh7 cells and three independent subgenomic replicons with various replicative capacities revealed that CXCL-8 protein levels were higher in weakly than in strongly permissive cells. The JFH-1 subgenomic replicon, which replicated to high levels in both strongly and weakly permissive Huh7 cells, induced CXCL-8 protein to high levels in both cell types. The data indicate that in the replicon system, CXCL-8 protein levels are positively associated with chronic HCV replication and that CXCL-8 removal inhibits HCV replication. During acute HCV replication, CXCL-8 production may be inhibitory to viruses with low replicative capacity. The data underscore the complex regulation of CXCL-8 mRNA and protein expression and further suggest that in addition to contributing to HCV pathology via proinflammatory actions, CXCL-8 may have opposing antiviral and proviral effects depending on the level of HCV replication, the cellular context, and whether the infection is acute or chronic.

The type III pseudomonal exotoxin U activates the c-Jun NH2-terminal kinase pathway and increases human epithelial interleukin-8 production

Microbial interactions with host cell signaling pathways are key determinants of the host cell response to infection. Many toxins secreted by bacterial type III secretion systems either stimulate or inhibit the host inflammatory response. We investigated the role of type III secreted toxins of the lung pathogen Pseudomonas aeruginosa in the inflammatory response of human respiratory epithelial cells to infection. Using bacteria with specific gene deletions, we found that interleukin-8 production by these cells was almost entirely dependent on bacterial type III secretion of exotoxin U (ExoU), a phospholipase, although other bacterial factors are involved. ExoU activated the c-Jun NH(2)-terminal kinase pathway, stimulating the phosphorylation and activation of mitogen-activated kinase kinase 4, c-Jun NH(2)-terminal kinase, and c-Jun. This in turn increased levels of transcriptionally competent activator protein-1. Although this pathway was dependent on the lipase activity of ExoU, it was independent of cell death. Activation of mitogen-activated kinase signaling by ExoU in this fashion is a novel mechanism by which a bacterial product can initiate a host inflammatory response, and it may result in increased epithelial permeability and bacterial spread.

Rotavirus activates JNK and p38 signaling pathways in intestinal cells, leading to AP-1-driven transcriptional responses and enhanced virus replication

Rotavirus infection is known to regulate transcriptional changes in many cellular genes. The transcription factors NF-kappaB and AP-1 are activated by rotavirus infection, but the upstream processes leading to these events are largely unidentified. We therefore studied the activation state during rotavirus infection of c-Jun NH2-terminal kinase (JNK) and p38, which are kinases known to activate AP-1. As assessed by Western blotting using phospho-specific antibodies, infection with rhesus rotavirus (RRV) or exposure to UV-psoralen-inactivated RRV (I-RRV) resulted in the activation of JNK in HT-29, Caco-2, and MA104 cells. Activation of p38 during RRV infection was observed in Caco-2 and MA104 cells but not in HT-29 cells, whereas exposure to I-RRV did not lead to p38 activation in these cell lines. Rotavirus strains SA11, CRW-8, Wa, and UK also activated JNK and p38. Consistent with the activation of JNK, a corresponding increase in the phosphorylation of the AP-1 component c-Jun was shown. The interleukin-8 (IL-8) and c-jun promoters contain AP-1 binding sequences, and these genes have been shown previously to be transcriptionally up-regulated during rotavirus infection. Using specific inhibitors of JNK (SP600125) and p38 (SB203580) and real-time PCR, we showed that maximal RRV-induced IL-8 and c-jun transcription required JNK and p38 activity. This highlights the importance of JNK and p38 in RRV-induced, AP-1-driven gene expression. Significantly, inhibition of p38 or JNK in Caco-2 cells reduced RRV growth but not viral structural antigen expression, demonstrating the potential importance of JNK and p38 activation for optimal rotavirus replication.

The Yersinia enterocolitica effector YopP inhibits host cell signalling by inactivating the protein kinase TAK1 in the IL-1 signalling pathway

The mechanism by which YopP simultaneously inhibits mitogen-activated protein kinase (MAPK) and nuclear factor-kappaB pathways has been elusive. Ectopic expression of YopP inhibits the activity and ubiquitination of a complex consisting of overexpressed TGF-beta-activated kinase 1 (TAK1) and its subunit TAK1-binding protein (TAB)1, but not of MEK kinase 1. YopP, but not the catalytically inactive mutant YopP(C172A), also suppresses basal and interleukin-1-inducible activation of endogenous TAK1, TAB1 and TAB2. YopP does not affect the interaction of TAK1, TAB1 and TAB2 but inhibits autophosphorylation of TAK1 at Thr 187 and phosphorylation of TAB1 at Ser 438. Glutathione S-transferase-tagged YopP (GST-YopP) binds to MAPK kinase (MAPKK)4 and TAB1 but not to TAK1 or TAB2 in vitro. Furthermore, YopP in synergy with a previously described negative regulatory feedback loop inhibits TAK1 by MAPKK6-p38-mediated TAB1 phosphorylation. Taken together, these data strongly suggest that YopP binds to TAB1 and directly inhibits TAK1 activity by affecting constitutive TAK1 and TAB1 ubiquitination that is required for autoactivation of TAK1.

Roles of p38 and ERK MAP kinases in IL-8 expression in TNF-α- and dexamethasone-stimulated human periodontal ligament cells

Orthodontic tooth movement is recognized as a pro-inflammatory stressor of human periodontal ligament (hPDL) cells. However, the cell-signaling pathways linking interleukin-8 (IL-8), intercellular adhesion molecule-1 (ICAM-1), pro-inflammatory cytokines, and dexamethasone in hPDL cells have not been well elucidated. In this study, we investigated the role of mitogen-activated protein (MAP) kinases in dexamethasone- and TNF-alpha-induced IL-8 and ICAM-1 expression in hPDL cells. IL-8 production was measured by enzyme-linked immunosorbent assay (ELISA) and reverse transcriptase-polymerase chain reaction (RT-PCR) analysis. MAP kinase activation and IkappaB degradation were determined by Western blot analysis, and ICAM-1 expression was determined by RT-PCR and FACS analysis. TNF-alpha increased IL-8 mRNA expression and protein secretion in a dose- and time-dependent manner. Dexamethasone suppressed TNF-alpha-induced IL-8 production in a dose-dependent manner. In addition, dexamethasone inhibited TNF-alpha-induced phosphorylation of p38 MAP kinase and extracellular-regulated kinases (ERKs), IkappaB degradation, and NF-kappaB activation. Selective inhibitors for ERKs and p38 attenuated TNF-alpha-induced IL-8 and ICAM-1 expression in the presence and absence of dexamethasone, indicating that MAP kinases play a role in the response of hDPL cells to TNF-alpha. Furthermore, these results suggest that inflammatory cytokine- and dexamethasone-induced IL-8 and ICAM-1, produced via a MAP kinase pathway, may serve as an important mediator of PDL immunoregulation involved in bone remodeling during orthodontic tooth movement.

Saccharomyces boulardii inhibits ERK1/2 mitogen-activated protein kinase activation both in vitro and in vivo and protects against Clostridium difficile toxin A-induced enteritis

Saccharomyces boulardii (Sb), a probiotic yeast, protects against intestinal injury and inflammation caused by a wide variety of enteric pathogens, including Clostridium difficile. Given the broad range of protective effects of Sb in multiple gastrointestinal disorders, we hypothesize that Sb modulates host signaling pathways involved in intestinal inflammatory responses. In this study, we found that Sb culture supernatant (SbS) inhibits interleukin-8 production induced by C. difficile toxin A or IL-1beta in human colonocyte NCM460 cells in a dose-dependent fashion. Furthermore, SbS inhibited IL-1beta and toxin A induced Erk1/2 and JNK/SAPK but not p38 activation in NCM460 cells. To test whether this inhibition also occurs in vivo, we used a previously established mouse ileal loop model. On its own, SbS had no significant effect on basal fluid secretion or intestinal histology. However, Erk1/2 activation was significantly inhibited by SbS in toxin A exposed mouse ileal mucosa. In control loops, toxin A increased fluid secretion (2.2-fold), histological score (3.3-fold), and levels of the chemokine KC (4.5-fold). SbS pretreatment completely normalized toxin A mediated fluid secretion (p < 0.01), and histopathologic changes (p < 0.01) and substantially inhibited toxin A-associated KC increases (p < 0.001). In summary, the probiotic yeast S. boulardii inhibits C. difficile toxin A-associated enteritis by blocking the activation of Erk1/2 MAP kinases. This study indicates a new mechanism whereby Sb protects against intestinal inflammation and supports the hypothesis that Sb modulates host inflammatory signaling pathways to exert its beneficial effects.

Induction of IL-8 expression by human herpesvirus 8 encoded vFLIP K13 via NF-kappaB activation

Human herpesvirus 8 (HHV-8) encodes a viral FLICE inhibitory protein (vFLIP), called K13, with homology to the prodomain of caspase 8. K13 has been postulated to protect virally infected cells against death receptor-induced apoptosis. We report that K13 leads to constitutive upregulation of IL-8 secretion by transcriptional upregulation of its promoter. K13-induced IL-8 promoter activation is dependent on an intact NF-kappaB-binding site and is associated with increased binding of classical NF-kappaB pathway subunits p65, c-Rel and p50, respectively. IL-8 production is defective in K13 mutants defective in classical NF-kappaB activation and is blocked by genetic and pharmacological inhibitors of this pathway. In contrast, K13 failed to activate the JNK/AP-1 pathway and deletion of AP-1-binding site in the IL-8 promoter or use of a specific JNK inhibitor had only a partial effect on K13-induced IL-8 promoter activation. Collectively, above results demonstrate that K13 is a major mediator of IL-8 production and therapeutic agents targeting K13-induced NF-kappaB pathway may have a role in the treatment of conditions in which HHV-8-induced IL-8 production plays a pathogenic role.

CpG DNA modulates interleukin 1beta-induced interleukin-8 expression in human bronchial epithelial (16HBE14o-) cells

Background

Recognition of repeat unmethylated CpG motifs from bacterial DNA through Toll-like receptor (TLR-9) has been shown to induce interleukin (IL)-8 expression in immune cells. We sought to investigate the role of CpG oligodeoxynucleotides (ODN) on a human bronchial epithelial cells.

Methods

RT-PCR and Western blot analysis were used to determine expression of TLR-9 in human bronchial epithelial cells (16HBE14o-). Cells were treated with CpG ODN in the presence or absence of IL-1β and IL-8 protein was determined using ELISA. In some cases cells were pretreated with chloroquine, an inhibitor of TLR-9 signaling, or SB202190, an inhibitor of the mitogen activated protein kinase p38, prior to treatment with IL-1β and CpG. TLR9 siRNA was used to silence TLR9 prior to treatment with IL-1β and CpG. IκBα and p38 were assessed by Western blot, and EMSA's were performed to determine NF-κB activation. To investigate IL-8 mRNA stability, cells were treated with IL-1β in the absence or presence of CpG for 2 h and actinomycin D was added to induce transcriptional arrest. Cells were harvested at 15 min intervals and Northern blot analysis was performed.

Results

TLR-9 is expressed in 16HBE14o- cells. CpG synergistically increased IL-1β-induced IL-8 protein abundance, however treatment with CpG alone had no effect. CpC (a control ODN) had no effect on IL-1β-induced IL-8 levels. In addition, CpG synergistically upregulated TNFα-induced IL-8 expression. Silencing TLR9 using siRNA or pretreatment of cells with chloroquine had little effect on IL-1β-induced IL-8 levels, but abolished CpG-induced synergy. CpG ODN had no effect on NF-κB translocation or DNA binding in 16HBE14o- cells. Treatment with CpG increased phosphorylation of p38 and pretreatment with the p38 inhibitor SB202190 attenuated the synergistic increase in IL-8 protein levels. Analysis of the half-life of IL-8 mRNA revealed that IL-8 mRNA had a longer half-life following the co-treatment of CpG and IL-1β compared to treatment with IL-1β alone.

Conclusion

Together, these data demonstrate that CpG modulates IL-8 synthesis in the presence of a pro-inflammatory mediator utilizing TLR9 and post-transcriptional mechanisms involving the activation of p38 and stabilization of IL-8 mRNA.

IL-21 enhances SOCS gene expression and inhibits LPS-induced cytokine production in human monocyte-derived dendritic cells

Dendritic cells (DCs) play an important role in innate and adaptive immune responses. In addition to their phagocytic activity, DCs present foreign antigens to naïve T cells and regulate the development of adaptive immune responses. Upon contact with DCs, activated T cells produce large quantities of cytokines such as interferon-gamma (IFN-gamma) and interleukin (IL)-21, which have important immunoregulatory functions. Here, we have analyzed the effect of IL-21 and IFN-gamma on lipopolysaccharide (LPS)-induced maturation and cytokine production of human monocyte-derived DCs. IL-21 and IFN-gamma receptor genes were expressed in high levels in immature DCs. Pretreatment of immature DCs with IL-21 inhibited LPS-stimulated DC maturation and expression of CD86 and human leukocyte antigen class II (HLAII). IL-21 pretreatment also dramatically reduced LPS-stimulated production of tumor necrosis factor alpha, IL-12, CC chemokine ligand 5 (CCL5), and CXC chemokine ligand 10 (CXCL10) but not that of CXCL8. In contrast, IFN-gamma had a positive feedback effect on immature DCs, and it enhanced LPS-induced DC maturation and the production of cytokines. IL-21 weakly induced the expression Toll-like receptor 4 (TLR4) and translation initiation region (TIR) domain-containing adaptor protein (TIRAP) genes, whereas the expression of TIR domain-containing adaptor-inducing IFN-beta (TRIF), myeloid differentiation (MyD88) 88 factor, or TRIF-related adaptor molecule (TRAM) genes remained unchanged. However, IL-21 strongly stimulated the expression of suppressor of cytokine signaling (SOCS)-1 and SOCS-3 genes. SOCS are known to suppress DC functions and interfere with TLR4 signaling. Our results demonstrate that IL-21, a cytokine produced by activated T cells, can directly inhibit the activation and cytokine production of myeloid DCs, providing a negative feedback loop between DCs and T lymphocytes.

Effect of Ligustrazine on liver injury after burn trauma

This study was designed to investigate the effect of Ligustrazine on burn-induced liver injury as well as the activation of nuclear factor kappaB (NF-kappaB) in severely burned rats. Sprague-Dawley rats were divided into three groups: (1) sham group, rats who underwent sham burn; (2) control group, rats given third-degree burns over 30% total body surface area (TBSA) and lactated Ringer solution for resuscitation; (3) Ligustrazine group, rats given burn and lactated Ringer's solution with Ligustrazine inside for resuscitation. Liver injury was assessed at 24 h post-burn by serum levels of aspartate aminotransferase (AST) and alanine aminotransferase (ALT), as well as liver wet/dry weight ratio. Liver myeloperoxidase (MPO) activity was also analyzed. Hepatic NF-kappaB activity was examined by electrophoretic mobility shift assay (EMSA). Burn results in hepatic dysfunction and increased hepatic NF-kappaB activity, elevated liver wet/dry ratio and hepatic MPO activity. Ligustrazine inhibited these changes and alleviated burn-mediated hepatic dysfunction. The data indicated that Ligustrazine has a protective effect on burn-induced liver injury and possible mechanism may be attributed to its inhibitory action on the activation of NF-kappaB following burn trauma.

Regulation of monocyte chemoattractant protein 1 (MCP-1) release by explants of human visceral adipose tissue

BACKGROUND

Monocyte chemoattractant protein-1 (MCP-1) is a chemokine involved in monocyte recruitment during inflammation whose plasma level is elevated in obesity.

OBJECTIVE

The present studies were designed to examine the release of MCP-1 in primary culture by explants of visceral adipose tissue from morbidly obese women.

RESULTS

Most of the MCP-1 released by adipose tissue explants was derived from the nonfat cells in adipose tissue. The release of MCP-1 by adipose tissue explants was upregulated almost five-fold between 3 and 48 h of incubation. Approximately half of this upregulation was due to the release of endogenous tumor necrosis factor alpha (TNFalpha) and IL-1beta based on the ability of a combination of a soluble TNFalpha receptor (etanercept) and a blocking antibody against IL-1beta to reduce MCP-1 release. The release of MCP-1 over 48 h was unaffected by insulin or dexamethasone but significantly reduced by the combination of both agents. MCP-1 release was reduced by 60% in the presence of an inhibitor of the nuclear factor kappaB (NF-kappaB) pathway. There were no significant effects of inhibitors of p44/42 mitogen-activated protein kinase (ERK), Jun N-terminal kinase (JNK) and p38 mitogen-activated protein kinase (p38 MAPK) pathways on MCP-1 release. However, inhibition of MCP-1 release in the presence of inhibitors of both the p38 MAPK and NF-kappaB pathways was greater than that seen with only the NF-kappaB inhibitor.

DISCUSSION

The present data shows that MCP-1 formation is upregulated over a 48-h incubation of primary explants of visceral adipose tissue. Half of this upregulation is dependent upon endogenous TNFalpha and Il-1beta and involves the p38 MAPK and NF-kappaB pathways.

Variants of the paramyxovirus Simian virus 5 with accelerated or delayed viral gene expression activate proinflammatory cytokine synthesis

Our previous results have shown that the parainfluenza virus SV5 is a poor inducer of proinflammatory cytokines interleukin-8 (IL-8) and macrophage chemoattractant protein 1 (MCP-1). By contrast, an engineered P/V mutant rSV5-P/V-CPI- and a naturally-occurring variant WF-PIV (Wake Forest-Parainfluenza Virus) are both potent activators of IL-8 and MCP-1. In the present study, we addressed the question of why rSV5-WT is such a poor inducer of host cytokine responses relative to the two SV5 variants, and we used the CC chemokine RANTES as a measure of host responses. Time course experiments showed high-level secretion of IL-6 and RANTES following infections of human A549 lung epithelial cells with the P/V-CPI- mutant and WF-PIV. By contrast, SV5-WT induced very low cytokine responses, with the notable exception of moderate induction of RANTES. The mechanism of RANTES induction by the two SV5 variants shared common properties, since RANTES secretion from infected cells had similar kinetics, depended on virus replication, correlated with increased RANTES mRNA levels and promoter activation, and was reduced by inhibitors of the p38 MAPK, ERK, and PI3K pathways. Despite the similar mechanisms of RANTES induction, the two SV5 variants differed dramatically in their growth and gene expression kinetics. By comparison to the P/V mutant rSV5-P/V-CPI- which has accelerated viral gene expression, WF-PIV infection showed a prolonged delay in viral replication, and infected cells did not show high-level viral RNA and protein expression until approximately 12-24 hpi. Sequence analysis revealed that the N, P, V, and M genes from WF-PIV differed by 3, 8, 5, and 10 amino acids compared to rSV5-WT, respectively. Chimeric viruses harboring the WF-PIV P/V or M genes in the context of the other rSV5 genes had growth properties similar to rSV5-WT but had a RANTES-inducing phenotype similar to that of the bone fide WF-PIV virus. Our data indicate a role for both the P/V and the M gene products as determinants of RANTES induction in response to SV5 infection.

Posttranscriptional mechanisms regulating the inflammatory response

The inflammatory response is a complex physiologic process that requires the coordinate induction of cytokines, chemokines, angiogenic factors, effector-enzymes, and proteases. Although transcriptional activation is required to turn on the inflammatory response, recent studies have revealed that posttranscriptional mechanisms play an important role by determining the rate at which mRNAs encoding inflammatory effector proteins are translated and degraded. Most posttranscriptional control mechanisms function to dampen the expression of pro-inflammatory proteins to ensure that potentially injurious proteins are not overexpressed during an inflammatory response. Here we discuss the factors that regulate the stability and translation of mRNAs encoding pro-inflammatory proteins.

Rho GTPases as therapeutic targets for the treatment of inflammatory diseases

Diseases related to inflammation are a major cause of morbidity and mortality throughout the world and affect the functions of several tissues. The pathophysiology of these diseases involves release of many pro-inflammatory cytokines, such as TNF and IL-1, in addition to anti-inflammatory molecules. Recent studies have demonstrated that neuroimmune interactions are important in the initiation and progress of inflammatory processes. TNF, IL-1 and neuropeptides such as substance P and neurotensin stimulate the release of chemokines, in particular IL-8, a potent neutrophil chemoattractant. Expression of IL-8 is regulated mainly by the transcription factors NF-kappaB, activating protein-1 and CCAAT/enhancer-binding proteins. Recent exciting results indicate that the Rho family of small GTP-binding proteins plays an important role in the expression of NF-kappaB-dependent genes and migration of leukocytes. These results suggest that these proteins may represent a potential therapeutic target to treat several inflammatory states.

Human mucosa/submucosa interactions during intestinal inflammation: involvement of the enteric nervous system in interleukin-8 secretion

Interleukin-8 (IL-8) is a key chemokine upregulated in various forms of intestinal inflammation, especially those induced by bacteria such as Clostridium difficile (C. difficile). Although interactions between different mucosal and submucosal cellular components have been reported, whether such interactions are involved in the regulation of IL-8 secretion during C. difficile infection is unknown. Moreover, whether the enteric nervous system, a major component of the submucosa, is involved in IL-8 secretion during an inflammatory challenge remains to be determined. In order to investigate mucosa/submucosa interactions that regulate IL-8 secretion, we co-cultured human intestinal mucosa and submucosa. In control condition, IL-8 secretion in co-culture was lower than the sum of the IL-8 secretion of both tissue layers cultured alone. Contrastingly, IL-8 secretion increased in co-culture after mucosal challenge with toxin B of C. difficile through an IL-1 beta-dependent pathway. Moreover, we observed that toxin B of C. difficile increased IL-8 immunoreactivity in submucosal enteric neurones in co-culture and in intact preparations of mucosa/submucosa, through an IL-1 beta-dependent pathway. IL-1 beta also increased IL-8 secretion and IL-8 mRNA expression in human neuronal cell lines (NT2-N and SH-SY5Y), through p38 and ERK1/2 MAP kinase-dependent pathways. Our results demonstrate that mucosa/submucosa interactions regulate IL-8 secretion during inflammatory processes in human through IL-1 beta-dependent pathways. Finally we observed that human submucosal neurones synthesize IL-8, whose production in neurones is induced by IL-1 beta via MAPK-dependent pathways.

RNA-binding protein HuR is required for stabilization of SLC11A1 mRNA and SLC11A1 protein expression

The solute carrier family 11 member 1 (SLC11A1, formerly NRAMP1) gene is associated with infectious and autoimmune diseases and plays an important role in macrophage activation. Human SLC11A1 mRNA contains an AU-rich element (ARE) within the 3' untranslated region; however, its role in the regulation of SLC11A1 gene expression has not been elucidated. Here we analyze the expression of SLC11A1 in human monocytes and HL-60 cells and then use HL-60 cells as a model to determine whether RNA-binding protein HuR is associated with the ARE and involved in SLC11A1 mRNA turnover. Our results demonstrate a binding of HuR to the SLC11A1 ARE in phorbol myristate acetate (PMA)-differentiated cells dramatically increased compared to that in undifferentiated cells. Interestingly, PMA-induced accumulation of cytoplasmic HuR occurs in parallel with an increase in the binding of HuR to SLC11A1 ARE and with an increase in the SLC11A1 mRNA level. This suggests that HuR's cytoplasmic localization plays an important role in the regulation of SLC11A1 expression. We also observe that down-regulation of HuR expression by RNA interference (RNAi) results in a decrease in SLC11A1 expression which can be restored by the addition of recombinant HuR protein to the RNAi-treated cells. Finally, we show that HuR overexpression in HL-60 cells significantly increases the SLC11A1 mRNA stability. Taken together, our data demonstrate that HuR is a key mediator of posttranscriptional regulation and expression of the SLC11A1 gene.

hKSR-2 inhibits MEKK3-activated MAP kinase and NF-kappaB pathways in inflammation

Kinase suppressor of ras (KSR) and MEKK3 (MAP kinase kinase kinase) are integral members of the MAP kinase pathway. We have recently identified a new isoform of the KSR family named human kinase suppressor of ras-2 (hKSR-2), and demonstrated that hKSR-2 negatively regulates Cot, a MAP3K family member which is important in inflammation and oncogenesis [P.L. Channavajhala, L. Wu, J.W. Cuozzo, J.P. Hall, W. Liu, L.L. Lin, Y. Zhang, J. Biol. Chem. 278 (2003) 47089-47097]. In this report, we provide evidence that hKSR-2 also regulates the activity of MEKK3 (another MAP3K family member) in HEK-293T cells. We demonstrate that hKSR-2 is a negative regulator of MEKK3-mediated activation of MAP kinase (specifically ERK and JNK) and NF-kappaB pathways, and concurrently inhibits MEKK3-mediated interleukin-8 production. We find that while hKSR-2 blocks MEKK3 activation, it has little to no effect on other members of the MAP3K family, including MEKK4, TAK1, and Ras-Raf, suggesting that its effects are selective.

MAPK signalling pathways as molecular targets for anti-inflammatory therapy--from molecular mechanisms to therapeutic benefits

Excessive inflammation is becoming accepted as a critical factor in many human diseases, including inflammatory and autoimmune disorders, neurodegenerative conditions, infection, cardiovascular diseases, and cancer. Cerebral ischemia and neurodegenerative diseases are accompanied by a marked inflammatory reaction that is initiated by expression of cytokines, adhesion molecules, and other inflammatory mediators, including prostanoids and nitric oxide. This review discusses recent advances regarding the detrimental effects of inflammation, the regulation of inflammatory signalling pathways in various diseases, and the potential molecular targets for anti-inflammatory therapy. Mitogen-activated protein kinases (MAPKs) are a family of serine/threonine protein kinases that mediate fundamental biological processes and cellular responses to external stress signals. Increased activity of MAPK, in particular p38 MAPK, and their involvement in the regulation of the synthesis of inflammation mediators at the level of transcription and translation, make them potential targets for anti-inflammatory therapeutics. Inhibitors targeting p38 MAPK and JNK pathways have been developed, and preclinical data suggest that they exhibit anti-inflammatory activity. This review discusses how these novel drugs modulate the activity of the p38 MAPK and JNK signalling cascades, and exhibit anti-inflammatory effects in preclinical disease models, primarily through the inhibition of the expression of inflammatory mediators. Use of MAPK inhibitors emerges as an attractive strategy because they are capable of reducing both the synthesis of pro-inflammatory cytokines and their signalling. Moreover, many of these drugs are small molecules that can be administered orally, and initial results of clinical trials have shown clinical benefits in patients with chronic inflammatory disease.

Death receptor-mediated apoptosis in human malignant glioma cells: modulation by the CD40/CD40L system

CD40, a TNF-R-related cell surface receptor, is shown here to be expressed by glioma cells in vitro and in vivo. Glioma cell lines expressing low levels of CD40 at the cell surface resist cytotoxic effects of CD40L. CD40 gene transfer sensitizes glioma cells to CD40L. Inhibition of protein synthesis potentiates cell death which involves CD40 clustering and caspases 8 and 3 processing. CD40-transfected LN-18 cells acquire resistance to CD95L. In contrast, subtoxic concentrations of CD40L strongly sensitize these cells for TNF-alpha-induced apoptosis. Bispecific CD40xCD95 antibodies specifically kill glioma cells, disclosing the property of endogenous CD40 to facilitate death signalling.

Functionally independent AU-rich sequence motifs regulate KC (CXCL1) mRNA

Certain pro-inflammatory chemokine mRNAs containing adenine/uridine-rich sequence elements (AREs) in their 3' untranslated regions (3'-UTRs) are known to exhibit constitutive instability and sensitivity to proinflammatory stimuli resulting in the stabilization of the message. Using tetR-regulated transcription we now show that the 3'-UTR of the mouse CXCL1 (KC) mRNA contains at least two ARE motifs that are structurally and functionally distinct. A fragment of 77 nucleotides containing 4 clustered AUUUA pentamers located at the 5'-end of the KC 3'-UTR is only modestly unstable yet promotes markedly enhanced, post-transcriptional protein production in response to either interleukin-1alpha (IL-1alpha) or lipopolysaccharide (LPS), suggesting translational regulation. In contrast, a fragment containing 3 isolated AUUUA pentamers corresponding to the residual 3' 400 nucleotides of the KC 3'-UTR confers both instability and is stabilized in response to IL-1alpha. Although the clustered AUUUA pentamers in the upstream region are required for stimulus sensitivity, mutation of all three pentamers in the downstream region has little or no effect on either instability or stimulus sensitivity. The upstream region is comparably stabilized in response to either IL-1alpha or LPS, whereas the AUUUA-independent downstream determinant is differentially more sensitive to IL-1alpha. Finally, using UV-induced RNA cross-linking, these functionally independent sequences exhibit different patterns of interaction with RNA-binding proteins. Collectively, these findings document the presence of multiple independent determinants of KC mRNA function and demonstrate that these operate via distinct mechanisms.

The role of interleukin-8 and its receptors in gliomagenesis and tumoral angiogenesis

Interleukin-8 (IL-8, or CXCL8), which is a chemokine with a defining CXC amino acid motif that was initially characterized for its leukocyte chemotactic activity, is now known to possess tumorigenic and proangiogenic properties as well. In human gliomas, IL-8 is expressed and secreted at high levels both in vitro and in vivo, and recent experiments suggest it is critical to glial tumor neovascularity and progression. Levels of IL-8 correlate with histologic grade in glial neoplasms, and the most malignant form, glioblastoma, shows the highest expression in pseudopalisading cells around necrosis, suggesting that hypoxia/anoxia may stimulate expression. In addition to hypoxia/anoxia stimulation, increased IL-8 in gliomas occurs in response to Fas ligation, death receptor activation, cytosolic Ca(2+), TNF-alpha, IL-1, and other cytokines and various cellular stresses. The IL-8 promoter contains binding sites for the transcription factors NF-kappaB, AP-1, and C-EBP/NF-IL-6, among others. AP-1 has been shown to mediate IL-8 upregulation by anoxia in gliomas. The potential tumor suppressor ING4 was recently shown to be a critical regulator of NF-kappaB-mediated IL-8 transcription and subsequent angiogenesis in gliomas. The IL-8 receptors that could contribute to IL-8-mediated tumorigenic and angiogenic responses include CXCR1 and CXCR2, both of which are G-protein coupled, and the Duffy antigen receptor for cytokines, which has no defined intracellular signaling capabilities. The proangiogenic activity of IL-8 occurs predominantly following binding to CXCR2, but CXCR1 appears to contribute as well through independent, small-GTPase activity. A precise definition of the mechanisms by which IL-8 exerts its proangiogenic functions requires further study for the development of effective IL-8-targeted therapies.

ERK1/2 regulates epidermal chemokine expression and skin inflammation

Resident cell populations of the skin contribute to the inflammatory response by producing an array of chemokines, which attract leukocytes from the circulation. TNF-alpha is a major inducer of proinflammatory mediators in keratinocytes. We have recently observed that epidermal growth factor receptor (EGFR) signaling affects TNF-alpha-driven chemokine expression in epidermal keratinocytes, and its functional impairment increases the levels of crucial chemoattractants such as CCL2/MCP-1, CCL5/RANTES, and CXCL10/IFN-gamma-inducible protein-10. In this study, we report evidence that EGFR-dependent ERK1/2 activity is implicated in this mechanism. Abrogation of ERK1/2 activity with specific inhibitors increased chemokine expression in keratinocytes by enhancing mRNA stabilization. In mouse models, inflammatory response to irritants and T cell-mediated contact hypersensitivity were both aggravated when elicited in a skin area previously treated with an EGFR or a MAPK kinase 1/2 inhibitor. In contrast, impairment of p38alpha beta MAPK phosphorylation markedly attenuated these responses. Our data indicate that EGFR-dependent ERK1/2 activity in keratinocytes takes part to a homeostatic mechanism regulating inflammatory responses, and emphasize the distinct role of MAPKs as potential targets for manipulating inflammation in the skin.

Analysis of differentially expressed genes in nitric oxide-exposed human monocytic cells

In this study we examined the gene expression pattern of *NO-dependent genes in U937 and Mono Mac 6 monocytes exposed to the synthetic NO-donor DPTA-NO using microarray technology. cDNA microarray data were validated by Northern blot analysis and quantitative real-time PCR. This approach allowed the identification of 17 *NO-sensitive genes that showed at least a twofold difference in expression, in both U937 cells and Mono Mac 6 cells exposed to 500 microM DPTA-NO for 4 h. NO-stimulated genes belong to various functional groups, including transcription factors, signaling molecules, and cytokines. Among the selected genes, 11 (ATF-4, c-maf, SGK-1, PBEF, ATPase 8, NADH dehydrogenase 4, STK6, TRAF4-associated factor 1, molybdopterin synthase, CKS1, and CIDE-B) have not been previously reported to be sensitive to *NO. Because several *NO-stimulated genes are transcription factors, we analyzed the mRNA expression profile in U937 cells exposed to DPTA-NO for 14 h. We found that long-term *NO treatment influenced transcription rates of a rather limited set of genes, including CIDE-B, BNIP3, p21/Cip1, molybdopterin synthase, and TRAF4-associated factor 1. To accelerate formation of nitrosating species, U937 cells were exposed to DPTA-NO along with suboptimal concentrations of 2-phenyl-4,4,5,5-tetramethylimidazole-1-oxyl 3-oxide (PTIO). PTIO-mediated increase in nitrosating species remarkably enhanced *NO-dependent induction of IL-8, p21/Cip1, and MKP-1 and built a specific gene expression profile.