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

The chemokines CXCL8 and CXCL12: molecular and functional properties, role in disease and efforts towards pharmacological intervention

Chemokines are an indispensable component of our immune system through the regulation of directional migration and activation of leukocytes. CXCL8 is the most potent human neutrophil-attracting chemokine and plays crucial roles in the response to infection and tissue injury. CXCL8 activity inherently depends on interaction with the human CXC chemokine receptors CXCR1 and CXCR2, the atypical chemokine receptor ACKR1, and glycosaminoglycans. Furthermore, (hetero)dimerization and tight regulation of transcription and translation, as well as post-translational modifications further fine-tune the spatial and temporal activity of CXCL8 in the context of inflammatory diseases and cancer. The CXCL8 interaction with receptors and glycosaminoglycans is therefore a promising target for therapy, as illustrated by multiple ongoing clinical trials. CXCL8-mediated neutrophil mobilization to blood is directly opposed by CXCL12, which retains leukocytes in bone marrow. CXCL12 is primarily a homeostatic chemokine that induces migration and activation of hematopoietic progenitor cells, endothelial cells, and several leukocytes through interaction with CXCR4, ACKR1, and ACKR3. Thereby, it is an essential player in the regulation of embryogenesis, hematopoiesis, and angiogenesis. However, CXCL12 can also exert inflammatory functions, as illustrated by its pivotal role in a growing list of pathologies and its synergy with CXCL8 and other chemokines to induce leukocyte chemotaxis. Here, we review the plethora of information on the CXCL8 structure, interaction with receptors and glycosaminoglycans, different levels of activity regulation, role in homeostasis and disease, and therapeutic prospects. Finally, we discuss recent research on CXCL12 biochemistry and biology and its role in pathology and pharmacology.

Red sea bream interleukin (IL)-1β and IL-8 expression, subcellular localization, and antiviral activity against red sea bream iridovirus (RSIV)

Interleukin-1 beta (IL-1β) is transcribed by monocytes, macrophages, and dendritic cells in response to activation of toll-like receptors (TLRs) by pathogen-associated molecular patterns (PAMPs) or cytokine signalling and causes a rapid inflammatory response to infection. IL-8, also known as chemokine C-X-C motif ligand (CXCL)-8, is regulated by IL-1β and affects the chemotaxis of macrophages and neutrophils upon pathogen infection. In healthy red sea bream, rsbIL-1β is most highly distributed in the liver, and rsbIL-8 is most highly distributed in the head kidney. In response to RSIV infection, rsbIL-1β and rsbIL-8 mRNA are significantly upregulated in the kidney and spleen. This may be because the primary infection targets of RSIV are the kidney and spleen. In the gills, both genes were significantly upregulated at 7 days after RSIV infection and may be accompanied by a cytokine storm. In the liver, both genes were significantly downregulated at most observation points, which may be because the immune cells such as macrophages and dendritic cells expressing rsbIL-1β or rsbIL-8 migrated to other tissues because the degree of RSIV infection was relatively low. Using a GFP fusion protein, it was confirmed that rsbIL-1β and rsbIL-8 were localized to the cytoplasm of Pagrus major fin (PMF) cells. RsbIL-1β overexpression induced the expression of interferon gamma (IFN-γ), myxovirus-resistance protein (Mx) 1, IL-8, IL-10, TNF-α, and MyD88, while rsbIL-8 overexpression induced the expression of IFN-γ, Mx1, rsbIL-1β and TNF-α. In addition, overexpression of both genes significantly reduced the genome copies of RSIV and significantly reduced the viral titers. Therefore, rsbIL-1β and rsbIL-8 in red sea bream play an antiviral role against RSIV through their normal signalling.

RANKL Impairs the TLR4 Pathway by Increasing TRAF6 and RANK Interaction in Macrophages

High serum levels of osteoprotegerin (OPG) are found in patients with obesity, type 2 diabetes, sepsis, or septic shock and are associated with a high mortality rate in stroke. The primary known function of OPG is to bind to the receptor activator of NF-κB ligand (RANKL), and by doing so, it inhibits the binding between RANKL and its receptor (RANK). TLR4 signaling in macrophages involves TRAF6 recruitment and contributes to low-grade chronic inflammation in adipose tissue. LPS is a classical activator of the TLR4 pathway and induces the expression of inflammatory cytokines in macrophages. We have previously observed that in the presence of RANKL, there is no LPS-induced activation of TLR4 in macrophages. In this study, we investigated the crosstalk between RANK and TLR4 pathways in macrophages stimulated with both RANKL and LPS to unveil the role of OPG in inflammatory processes. We found that RANKL inhibits TLR4 activation by binding to RANK, promoting the binding between TRAF6 and RANK, lowering TLR4 activation and the expression of proinflammatory mediators. Furthermore, high OPG levels aggravate inflammation by inhibiting RANKL. Our findings elect RANKL as a candidate for drug development as a way to mitigate the impact of obesity-induced inflammation in patients.

Inteurleukin-8 gene variations and the susceptibility to schizophrenia

The relevance of Interleukin-8 (IL-8) cytokine alteration in the peripheral and central system has been widely shown in psychosis while variation in the IL-8 gene remains largely unexplored and to the best of our knowledge, IL-8 polymorphisms have never been specifically targeted in Schizophrenia (Scz). Thus, we set out to search a potential correlation between rs4073, rs2227306 and rs1126647 polymorphisms in IL-8 gene and the development of Scz in a sample of the Tunisian population in a candidate gene approach. Targeted polymorphisms were analysed in 206 patients and 195 controls using PCR-RFLP method. Among all analysed polymorphisms, only rs1126647 showed a significant risk for Scz. After stratification analysis, we noted a significant association of TT genotype and T allele at rs1126647 with paranoid form, and more specifically with female sex. We find that the rare haplotypes at rs4073-rs2227306-rs1126647 of TTT, ACT and TCT, each containing the risk allele rs1126647T, were associated with increased risk for paranoid Scz while only the TCT combination constituted a risk factor for Scz more generally. Our findings support that IL-8 gene may be involved in susceptibility to Scz but this still preliminary and needs to be strengthened by further independent analyses.

Dynamic mRNP Remodeling in Response to Internal and External Stimuli

Signal transduction and the regulation of gene expression are fundamental processes in every cell. RNA-binding proteins (RBPs) play a key role in the post-transcriptional modulation of gene expression in response to both internal and external stimuli. However, how signaling pathways regulate the assembly of RBPs with mRNAs remains largely unknown. Here, we summarize observations showing that the formation and composition of messenger ribonucleoprotein particles (mRNPs) is dynamically remodeled in space and time by specific signaling cascades and the resulting post-translational modifications. The integration of signaling events with gene expression is key to the rapid adaptation of cells to environmental changes and stress. Only a combined approach analyzing the signal transduction pathways and the changes in post-transcriptional gene expression they cause will unravel the mechanisms coordinating these important cellular processes.

EPHB6 controls catecholamine biosynthesis by up-regulating tyrosine hydroxylase transcription in adrenal gland chromaffin cells

EPHB6 is a member of the erythropoietin-producing hepatocellular kinase (EPH) family and a receptor tyrosine kinase with a dead kinase domain. It is involved in blood pressure regulation and adrenal gland catecholamine (CAT) secretion, but several facets of EPHB6-mediated CAT regulation are unclear. In this study, using biochemical, quantitative RT-PCR, immunoblotting, and gene microarray assays, we found that EPHB6 up-regulates CAT biosynthesis in adrenal gland chromaffin cells (AGCCs). We observed that epinephrine content is reduced in the AGCCs from male Ephb6-KO mice, caused by decreased expression of tyrosine hydroxylase, the rate-limiting enzyme in CAT biosynthesis. We demonstrate that the signaling pathway from EPHB6 to tyrosine hydroxylase expression in AGCCs involves Rac family small GTPase 1 (RAC1), MAP kinase kinase 7 (MKK7), c-Jun N-terminal kinase (JNK), proto-oncogene c-Jun, activator protein 1 (AP1), and early growth response 1 (EGR1). On the other hand, signaling via extracellular signal-regulated kinase (ERK1/2), p38 mitogen-activated protein kinase, and ELK1, ETS transcription factor (ELK1) was not affected by EPHB6 deletion. We further report that EPHB6's effect on AGCCs was via reverse signaling through ephrin B1 and that EPHB6 acted in concert with the nongenomic effect of testosterone to control CAT biosynthesis. Our findings elucidate the mechanisms by which EPHB6 modulates CAT biosynthesis and identify potential therapeutic targets for diseases, such as hypertension, caused by dysfunctional CAT biosynthesis.

IL-8 signaling is involved in resistance of lung carcinoma cells to erlotinib

A signaling pathway that is frequently deregulated in human carcinomas and has been explored as a therapeutic target involves the activation of the epidermal growth factor receptor (EGFR). Inhibition of EGFR via the small molecule inhibitors erlotinib and gefitinib commonly results in tumor resistance, even in patients with EGFR-mutant tumors that initially show substantial clinical responses. This study was designed to broaden our understanding of the molecular mechanisms of acquired resistance to erlotinib in lung cancer cells bearing wild type or mutated EGFR. We report here that generation of erlotinib-resistant lung cancer cells in vitro resulted in a phenotypic alteration reminiscent of an epithelial-mesenchymal transition (EMT) concomitant with a robust upregulation of the IL-8/IL-8R axis. Our results also demonstrate that upregulation of p38 MAPK signaling is responsible for the enhanced IL-8 secretion in the erlotinib-resistant tumor cells. Blockade of IL-8 signaling effectively reduced mesenchymal features of the resistant cells and also markedly enhanced their susceptibility to erlotinib. These results provide a rationale for the development of new therapeutic approaches involving blockade of IL-8 signaling for the management of acquired resistance to EGFR inhibition in patients with lung cancer.

A model of the onset of the senescence associated secretory phenotype after DNA damage induced senescence

Cells and tissues are exposed to stress from numerous sources. Senescence is a protective mechanism that prevents malignant tissue changes and constitutes a fundamental mechanism of aging. It can be accompanied by a senescence associated secretory phenotype (SASP) that causes chronic inflammation. We present a Boolean network model-based gene regulatory network of the SASP, incorporating published gene interaction data. The simulation results describe current biological knowledge. The model predicts different in-silico knockouts that prevent key SASP-mediators, IL-6 and IL-8, from getting activated upon DNA damage. The NF-κB Essential Modulator (NEMO) was the most promising in-silico knockout candidate and we were able to show its importance in the inhibition of IL-6 and IL-8 following DNA-damage in murine dermal fibroblasts in-vitro. We strengthen the speculated regulator function of the NF-κB signaling pathway in the onset and maintenance of the SASP using in-silico and in-vitro approaches. We were able to mechanistically show, that DNA damage mediated SASP triggering of IL-6 and IL-8 is mainly relayed through NF-κB, giving access to possible therapy targets for SASP-accompanied diseases.

LPS Cooperates with Poly-L-Arginine to Promote IL-6 and IL-8 Release via the JNK Signaling Pathway in NCI-H292 Cells

Objective. Herein, we aimed to study the mechanism whereby poly-L-arginine (PLA) and lipopolysaccharide (LPS) can synergistically induce the release of interleukin-6 (IL-6) and IL-8 in NCI-H292 cells. Methods. NCI-H292 cells were divided into control, PLA, LPS, and PLA+LPS groups. At various time points, the phosphorylation of JNK in each group was measured by western blotting. Additionally, the productions of IL-6 and IL-8 were assessed using an enzyme-linked immunosorbent assay (ELISA). The effects of SP600125, an inhibitor of the JNK pathway, on the increase of p-JNK, IL-6, and IL-8 were also studied. Results. Our results showed that either PLA or LPS treatment alone can significantly increase the phosphorylation level of JNK in NCI-H292 cells. Of interest was the combined use of PLA and LPS that has a synergistic effect on the phosphorylation of JNK, as well as synergistically inducing the release of IL-6 and IL-8 in NCI-H292 cells. Furthermore, SP600125 significantly inhibited the activation of JNK signal, as well as reducing the productions of IL-6 and IL-8 in response to PLA+LPS stimulation. Conclusions. The JNK signaling pathway contributes to the release of IL-6 and IL-8, which is stimulated by the synergistic actions of PLA+LPS in NCI-H292 cells.

Transcriptional and posttranscriptional regulation of CXCL8/IL-8 gene expression induced by connective tissue growth factor

Connective tissue growth factor (CTGF), a CCN family member, is a secreted protein regulating cellular functions, including fibrosis, apoptosis, adhesion, migration, differentiation, proliferation, angiogenesis, and chondrogenesis. CTGF increases proinflammatory factor production; however, inflammatory cytokine regulation by CTGF is poorly understood. The aim of this study was to identify novel biological functions and elucidate the functional mechanisms of CTGF. Specifically, the study focused on the ability of CTGF-primed monocytes to secrete interleukin 8 (CXCL8/IL-8) and determined the signaling pathways involved in CTGF-induced CXCL8/IL-8 gene regulation during inflammation. We transfected wild-type or mutant CXCL8/IL-8 promoter-derived luciferase reporter constructs into 293T cells to examine the effect of CTGF on the CXCL8/IL-8 promoter. The results showed that the activator protein-1 and nuclear factor κB binding sites of the CXCL8/IL-8 promoter are essential for CTGF-induced CXCL8/IL-8 transcription. Moreover, the CTGF-induced activation of p38 mitogen-activated protein kinase (MAPK), c-Jun-N-terminal kinase, and extracellular signal-regulated kinase (ERK) is involved in this process. In addition, adenosine-uridine-rich elements (AREs) of the CXCL8/IL-8 3'-untranslated region (3'-UTR) reduce CXCL8/IL-8 mRNA stability. To investigate whether CTGF regulates CXCL8/IL-8 gene expression at the posttranscriptional level, we transfected 293 cells with serial luciferase constructs containing different segments of the CXCL8/IL-8 3'-UTR and then stimulated the cells with CTGF. The results suggested that CTGF stabilized luciferase mRNA and increased luciferase activity by regulating the CXCL8/IL-8 3'-UTR. Moreover, the p38 MAPK pathway may contribute to CTGF-induced CXCL8/IL-8 mRNA stabilization.

Regulation of mRNA turnover in cystic fibrosis lung disease

Cystic fibrosis (CF) is an autosomal recessive disease due to mutations in the cystic fibrosis transmembrane conductance regulator (CFTR) gene, F508del-CFTR being the most frequent mutation. The CF lung is characterized by a hyperinflammatory phenotype and is regulated by multiple factors that coordinate its pathophysiology. In CF the expression of CFTR as well as proinflammatory genes are regulated at the level of messenger RNA (mRNA) stability, which subsequently affect translation. These mechanisms are mediated by inflammatory RNA-binding proteins as well as small endogenous noncoding microRNAs, in coordination with cellular signaling pathways. These regulatory factors exhibit altered expression and function in vivo in the CF lung, and play a key role in the pathophysiology of CF lung disease. In this review, we have described the role of mRNA stability and associated regulatory mechanisms in CF lung disease. WIREs RNA 2017, 8:e1408. doi: 10.1002/wrna.1408 For further resources related to this article, please visit the WIREs website.

Synergistic effects of lipopolysaccharide and interferon-γ in inducing interleukin-8 production in human monocytic THP-1 cells is accompanied by up-regulation of CD14, Toll-like receptor 4, MD-2 and MyD88 expression

Lipopolysaccharide (LPS) and interferon (IFN)-γ synergistically induced interleukin-8 (IL-8) production in human monocytic THP-1 cells. IFN-γ-primed THP-1 cells produced higher levels of IL-8 on stimulation with LPS than non-primed cells and the level correlated with duration of priming up to 24 h, although the level of IL-8 induced was most comparable to that induced by co-stimulation with LPS and IFN-γ . Unstimulated THP-1 cells were shown by flow cytometry to be practically devoid of membrane CD14 (mCD14). LPS and IFN-γ enhanced mCD14 and Toll-like receptor (TLR) 4 expression in THP-1 cells, respectively, and co-stimulation with LPS and IFN-γ induced higher levels of mCD14 and TLR4 expression than stimulation with either agent alone. LPS and IFN-γ alone each augmented MD-2 and MyD88 mRNA expression in THP-1 cells, and co-stimulation with LPS and IFN-γ markedly enhanced MD-2 and MyD88 mRNA expression in the cells compared to those with either LPS or IFN-γ alone. Anti-CD 14 and anti-TLR4 monoclonal antibodies almost completely inhibited IL-8 production induced by LPS plus IFN-γ in THP-1 cells. These findings suggest that combined stimulation of THP-1 cells with LPS and IFN-γ up-regulate mCD14, TLR4, MD-2 and MyD88 expression by these cells, which might be involved in synergistic IL-8 production by the cells.

Environment-induced epigenetic reprogramming in genomic regulatory elements in smoking mothers and their children

Epigenetic mechanisms have emerged as links between prenatal environmental exposure and disease risk later in life. Here, we studied epigenetic changes associated with maternal smoking at base pair resolution by mapping DNA methylation, histone modifications, and transcription in expectant mothers and their newborn children. We found extensive global differential methylation and carefully evaluated these changes to separate environment associated from genotype-related DNA methylation changes. Differential methylation is enriched in enhancer elements and targets in particular "commuting" enhancers having multiple, regulatory interactions with distal genes. Longitudinal whole-genome bisulfite sequencing revealed that DNA methylation changes associated with maternal smoking persist over years of life. Particularly in children prenatal environmental exposure leads to chromatin transitions into a hyperactive state. Combined DNA methylation, histone modification, and gene expression analyses indicate that differential methylation in enhancer regions is more often functionally translated than methylation changes in promoters or non-regulatory elements. Finally, we show that epigenetic deregulation of a commuting enhancer targeting c-Jun N-terminal kinase 2 (JNK2) is linked to impaired lung function in early childhood.

Substance P Enhances Keratocyte Migration and Neutrophil Recruitment through Interleukin-8

Keratocytes, the resident cells of the corneal stroma, are responsible for maintaining turnover of this tissue by synthesizing extracellular matrix components. When the cornea is injured, the keratocytes migrate to the wounded site and participate in the stromal wound healing. The neuropeptide substance P (SP), which is also known to be produced by non-neuronal cells, has previously been implicated in epithelial wound healing after corneal injury. Corneal scarring, which occurs in the stroma when the process of wound healing has malfunctioned, is one of the major causes of preventable blindness. This study aimed to elucidate the potential role of SP in keratocyte migration and therefore in stromal wound healing. We report that the expression and secretion of SP in human keratocytes are increased in response to injury in vitro. Moreover, SP enhances the migration of keratocytes by inducing the actin cytoskeleton reorganization and focal adhesion formation through the activation of the phosphatidylinositide 3-kinase and Ras-related C3 botulinum toxin substrate 1/Ras homolog gene family, member A pathway. Furthermore, SP stimulation leads to upregulated expression of the proinflammatory and chemotactic cytokine interleukin-8 (IL-8), which also contributes significantly to SP-enhanced keratocyte migration and is able to attract neutrophils. In addition, the preferred SP receptor, the neurokinin-1 receptor, is necessary to induce keratocyte migration and IL-8 secretion. In conclusion, we describe new mechanisms by which SP enhances migration of keratocytes and recruits neutrophils, two necessary steps in the corneal wound-healing process, which are also likely to occur in other tissue injuries.

Vigilant keratinocytes trigger pathogen-associated molecular pattern signaling in response to streptococcal M1 protein

The human skin exerts many functions in order to maintain its barrier integrity and protect the host from invading microorganisms. One such pathogen is Streptococcus pyogenes, which can cause a variety of superficial skin wounds that may eventually progress into invasive deep soft tissue infections. Here we show that keratinocytes recognize soluble M1 protein, a streptococcal virulence factor, as a pathogen-associated molecular pattern to release alarming inflammatory responses. We found that this interaction initiates an inflammatory intracellular signaling cascade involving the activation of the mitogen-activated protein kinases extracellular signal-regulated kinase (ERK), p38, and Jun N-terminal protein kinase and the subsequent induction and mobilization of the transcription factors NF-κB and AP-1. We also determined the imprint of the inflammatory mediators released, such as interleukin-8 (IL-8), growth-related oncogene alpha, migration inhibitory factor, extracellular matrix metalloproteinase inducer, IL-1α, IL-1 receptor a, and ST2, in response to streptococcal M1 protein. The expression of IL-8 is dependent on Toll-like receptor 2 activity and subsequent activation of the mitogen-activated protein kinases ERK and p38. Notably, this signaling seems to be distinct for IL-8 release, and it is not shared with the other inflammatory mediators. We conclude that keratinocytes participate in a proinflammatory manner in streptococcal pattern recognition and that expression of the chemoattractant IL-8 by keratinocytes constitutes an important protective mechanism against streptococcal M1 protein.

Rhesus macaque θ-defensin RTD-1 inhibits proinflammatory cytokine secretion and gene expression by inhibiting the activation of NF-κB and MAPK pathways

The anti‐inflammatory effects of θ‐defensin RTD‐1 are mediated by cell signaling pathways that down‐regulate expression of pro‐inflammatory cytokines.

θ‐Defensins are pleiotropic, macrocyclic peptides that are expressed uniquely in Old World monkeys. The peptides are potent, broad‐spectrum microbicides that also modulate inflammatory responses in vitro and in animal models of viral infection and polymicrobial sepsis. θ‐Defensins suppress proinflammatory cytokine secretion by leukocytes stimulated with diverse Toll‐like receptor (TLR) ligands. Studies were performed to delineate anti‐inflammatory mechanisms of rhesus θ‐defensin 1 (RTD‐1), the most abundant θ‐defensin isoform in macaque granulocytes. RTD‐1 reduced the secretion of tumor necrosis factor‐α (TNF‐α), interleukin (IL)‐1β, and IL‐8 in lipopolysaccharide (LPS)‐stimulated human blood monocytes and THP‐1 macrophages, and this was accompanied by inhibition of nuclear factor κB (NF‐κB) activation and mitogen‐activated protein kinase (MAPK) pathways. Peptide inhibition of NF‐κB activation occurred following stimulation of extracellular (TLRs 1/2 and 4) and intracellular (TLR9) receptors. Although RTD‐1 did not inhibit MAPK in unstimulated cells, it induced phosphorylation of Akt in otherwise untreated monocytes and THP‐1 cells. In the latter, this occurred within 10 min of RTD‐1 treatment and produced a sustained elevation of phosphorylated Akt (pAkt) for at least 4 h. pAkt is a negative regulator of MAPK and NF‐κB activation. RTD‐1 inhibited IκBα degradation and p38 MAPK phosphorylation, and stimulated Akt phosphorylation in LPS‐treated human primary monocytes and THP‐1 macrophages. Specific inhibition of phosphatidylinositol 3‐kinase (PI3K) blocked RTD‐1‐stimulated Akt phosphorylation and reversed the suppression of NF‐κB activation by the peptide. These studies indicate that the anti‐inflammatory properties of θ‐defensins are mediated by activation of the PI3K/Akt pathway and suppression of proinflammatory signals in immune‐stimulated cells.

Transcription of Interleukin-8: How Altered Regulation Can Affect Cystic Fibrosis Lung Disease

Interleukin-8 (IL-8) is a neutrophil chemokine that is encoded on the CXCL8 gene. Normally CXCL8 expression is repressed due to histone deacetylation, octamer-1 binding to the promoter and the inhibitory effect of nuclear factor-κB repressing factor (NRF). However, in response to a suitable stimulus, the human CXCL8 gene undergoes transcription due to its inducible promoter that is regulated by the transcription factors nuclear factor-κB (NF-κB), activating protein (AP-1), CAAT/enhancer-binding protein β (C/EBPβ, also known as NF-IL-6), C/EBP homologous protein (CHOP) and cAMP response element binding protein (CREB). CXCL8 mRNA is then stabilised by the activity of p38 mitogen-activated protein kinase (p38 MAPK). Cystic fibrosis (CF) lung disease is characterised by a neutrophil-dominated airway inflammatory response. A major factor contributing to the large number of neutrophils is the higher than normal levels of IL-8 that are present within the CF lung. Infection and inflammation, together with intrinsic alterations in CF airway cells are responsible for the abnormally high intrapulmonary levels of IL-8. Strategies to inhibit aberrantly high CXCL8 expression hold therapeutic potential for CF lung disease.

L-Ascorbyl-2-phosphate attenuates NF-κB signaling in SZ95 sebocytes without affecting IL-6 and IL-8 secretion

Acne is the most common inflammatory skin disease. Interleukin-1 (IL-1) is at the beginning of the cytokine signaling cascade and may be involved in the pathogenesis of this disorder. It activates redox-sensitive transcription factors, which induce IL-6 and IL-8 expression. Interestingly, l-ascorbyl-2-phosphate (APS) was shown to have beneficial effects in patients with acne vulgaris. The mechanism of action of this agent remains unknown. Here, we investigated if APS attenuates IL-1β- or TNF-α-mediated IL-6 and IL-8 expression in SZ95 sebocytes, whereas TNF-α was used as control. We also explored NF-κB activation which is known to orchestrate IL-1β- and TNF-α-mediated cytokine expression in many cell types. Both IL-1β and TNF-α increased IL-6 and IL-8 mRNA expression in SZ95 sebocytes. However, only IL-1β induced IL-6 and IL-8 secretion. IL-1β but not TNF-α activated NF-κB canonical signaling as demonstrated by Iκ-Bα phosphorylation and degradation as well as by nuclear accumulation of NF-κB/p65. Concomitant treatment of SZ95 sebocytes with APS attenuated the effect of IL-1β and TNF-α on IL-6 and IL-8 gene expression as well as on IL-1β-mediated NF-κB signaling. In contrast, APS failed to reduce IL-1β-mediated IL-6 and IL-8 secretion, presumably by maintained IL-1β-mediated p38 activation, which is known to control IL-8 secretion. Our findings shed light into the impact of IL-1β on the inflammatory cytokine response and its molecular mechanisms in human sebocytes. Our data further suggest that the beneficial effect of APS in acne patients involves attenuation of NF-κB signaling but not reduction of IL-6 or IL-8 secretion.

Enterococcus faecalis lipoteichoic acid suppresses Aggregatibacter actinomycetemcomitans lipopolysaccharide-induced IL-8 expression in human periodontal ligament cells

Periodontitis is caused by multi-bacterial infection and Aggregatibacter actinomycetemcomitans and Enterococcus faecalis are closely associated with inflammatory periodontal diseases. Although lipopolysaccharide (LPS) of A. actinomycetemcomitans (Aa.LPS) and lipoteichoic acid of E. faecalis (Ef.LTA) are considered to be major virulence factors evoking inflammatory responses, their combinatorial effect on the induction of chemokines has not been investigated. In this study, we investigated the interaction between Aa.LPS and Ef.LTA on IL-8 expression in human periodontal ligament (PDL) cells. Aa.LPS, but not Ef.LTA, substantially induced IL-8 expression at the protein and mRNA levels. Interestingly, Ef.LTA suppressed Aa.LPS-induced IL-8 expression without affecting the binding of Aa.LPS to Toll-like receptor (TLR) 4. Ef.LTA reduced Aa.LPS-induced phosphorylation of mitogen-activated protein kinases, including ERK, JNK and p38 kinase. Furthermore, Ef.LTA inhibited the Aa.LPS-induced transcriptional activities of the activating protein 1, CCAAT/enhancer-binding protein and nuclear factor-kappa B transcription factors, all of which are known to regulate IL-8 gene expression. Ef.LTA augmented the expression of IL-1 receptor-associated kinase-M (IRAK-M), a negative regulator of TLR intracellular signaling pathways, in the presence of Aa.LPS at both the mRNA and protein levels. Small interfering RNA silencing IRAK-M reversed the attenuation of Aa.LPS-induced IL-8 expression by Ef.LTA. Collectively, these results suggest that Ef.LTA down-regulates Aa.LPS-induced IL-8 expression in human PDL cells through up-regulation of the negative regulator IRAK-M.

Cyr61 is involved in neutrophil infiltration in joints by inducing IL-8 production by fibroblast-like synoviocytes in rheumatoid arthritis

Introduction

It is well known that neutrophils play very important roles in the development of rheumatoid arthritis (RA) and interleukin (IL)-8 is a critical chemokine in promoting neutrophil migration. We previously showed that increased production of Cyr61 by fibroblast-like synoviocytes (FLS) in RA promotes FLS proliferation and Th17 cell differentiation, thus Cyr61 is a pro-inflammatory factor in RA pathogenesis. In this study, we explored the role of Cyr61 in neutrophil migration to the joints of RA patients.

Methods

RA FLS were treated with Cyr61 and IL-8 expression was analyzed by real-time PCR and ELISA. The migration of neutrophils recruited by the culture supernatants was determined by the use of a chemotaxis assay. Mice with collagen-induced arthritis (CIA) were treated with anti-Cyr61 monoclonal antibodies (mAb), or IgG1 as a control. Arthritis severity was determined by visual examination of the paws and joint destruction was determined by hematoxylin-eosin (H&E) staining. Signal transduction pathways in Cyr61-induced IL-8 production were investigated by real-time PCR, western blotting, confocal microscopy, luciferase reporter assay or chromatin immunoprecipitation (ChIP) assay.

Results

We found that Cyr61 induced IL-8 production by RA FLS in an IL-1β and TNF-α independent pathway. Moreover, we identified that Cyr61-induced IL-8-mediated neutrophil migration in vitro. Using a CIA animal model, we found that treatment with anti-Cyr61 mAb led to a reduction in MIP-2 (a counterpart of human IL-8) expression and decrease in neutrophil infiltration, which is consistent with an attenuation of inflammation in vivo. Mechanistically, we showed that Cyr61 induced IL-8 production in FLS via AKT, JNK and ERK1/2-dependent AP-1, C/EBPβ and NF-κB signaling pathways.

Conclusions

Our results here reveal a novel role of Cyr61 in the pathogenesis of RA. It promotes neutrophil infiltration via up-regulation of IL-8 production in FLS. Taken together with our previous work, this study provides further evidence that Cyr61 plays a key role in the vicious cycle formed by the interaction between infiltrating neutrophils, proliferated FLS and activated Th17 cells in the development of RA.

Activation of NF-κB by the Kaposi's sarcoma-associated herpesvirus K15 protein involves recruitment of the NF-κB-inducing kinase, IκB kinases, and phosphorylation of p65

Kaposi's sarcoma herpesvirus (KSHV) (or human herpesvirus 8) is the cause of Kaposi's sarcoma, primary effusion lymphoma (PEL), and the plasma cell variant of multicentric Castleman's disease (MCD). The transmembrane K15 protein, encoded by KSHV, has been shown to activate NF-κB and the mitogen-activated protein kinases (MAPKs) c-jun-N-terminal kinase (JNK) and extracellular signal-regulated kinase (Erk) as well as phospholipase C gamma (PLCγ) and to contribute to KSHV-induced angiogenesis. Here we investigate how the K15 protein activates the NF-κB pathway. We show that activation of NF-κB involves the recruitment of NF-κB-inducing kinase (NIK) and IKK α/β to result in the phosphorylation of p65/RelA on Ser536. A K15 mutant devoid in NIK/IKK recruitment fails to activate NF-κB but remains proficient in the stimulation of both NFAT- and AP1-dependent promoters, showing that the structural integrity of the mutant K15 protein has not been altered dramatically. Direct recruitment of NIK represents a novel way for a viral protein to activate and manipulate the NF-κB pathway.

IMPORTANCE

KSHV K15 is a viral protein involved in the activation of proinflammatory and angiogenic pathways. Previous studies reported that K15 can activate the NF-κB pathway. Here we show the molecular mechanism underlying the activation of this signaling pathway by K15, which involves direct recruitment of the NF-κB-inducing kinase NIK to K15 as well as NIK-mediated NF-κB p65 phosphorylation on Ser536. K15 is the first viral protein shown to activate NF-κB through direct recruitment of NIK. These results indicate a new mechanism whereby a viral protein can manipulate the NF-κB pathway.

MKK7 mediates miR-493-dependent suppression of liver metastasis of colon cancer cells

The prognosis of advanced colon cancer patients is profoundly affected by the presence or absence of liver metastasis. miR-493 functions as a potent suppressor of liver metastasis, and low-level miR-493 expression in human primary colon cancer is associated with an elevated incidence of liver metastasis. We previously showed that IGF1R is a target gene of miR-493, and that the inhibition of IGF1R partly explains how miR-493 suppresses liver metastasis. However, major functional targets that mediate the antimetastatic activity of miR-493 remain elusive. Here, we extended our search for target genes and identified MKK7, a mitogen-activated protein kinase kinase, as a novel target of miR-493. miR-493 inhibits MKK7 expression by targeting the binding site at the 3′-UTR of the mkk7 gene. MKK7 was expressed in six out of seven colon cancer cell lines examined but not in non-transformed colon epithelial cells, and its expression was required for the activating phosphorylation of JNK. RNA interference-mediated inhibition of MKK7 resulted in marked suppression of liver metastasis of colon cancer cells. A significant decrease of metastasized cells by the MKK7 knockdown was observed, even at early stages of the metastatic settlement, in accordance with a time course of the miR-493-mediated inhibition of the metastasis. Immunohistochemical examination in human primary colon tumors revealed that the occurrence of liver metastasis is associated with elevated levels of MKK7. Thus, MKK7 is a major functional target of miR-493, and its suppression thwarts liver metastasis of colon cancer cells.

Prevention of F-actin assembly switches the response to SCF from chemotaxis to degranulation in human mast cells

Following antigen/IgE-mediated aggregation of high affinity IgE-receptors (FcεRI), mast cells (MCs) degranulate and release inflammatory mediators leading to the induction of allergic reactions including anaphylaxis. Migration of MCs to resident tissues and sites of inflammation is regulated by tissue chemotactic factors such as stem cell factor (SCF (KIT ligand)). Despite inducing similar early signaling events to antigen, chemotactic factors, including SCF, produce minimal degranulation in the absence of other stimuli. We therefore investigated whether processes regulating MC chemotaxis are rate limiting for MC mediator release. To investigate this issue, we disrupted actin polymerization, a requirement for MC chemotaxis, with latrunculin B and cytochalasin B, then examined chemotaxis and mediator release in human (hu)MCs induced by antigen or SCF. As expected, such disruption minimally affected early signaling pathways, but attenuated SCF-induced human mast cell chemotaxis. In contrast, SCF, in the absence of other stimuli, induced substantial degranulation in a concentration-dependent manner following actin disassembly. It also moderately enhanced antigen-mediated human mast cell degranulation which was further enhanced in the presence of SCF. These observations suggest that processes regulating cell migration limit MC degranulation as a consequence of cytoskeletal reorganization.

Contrasting roles of mitogen-activated protein kinases in cellular entry and replication of hepatitis C virus: MKNK1 facilitates cell entry

The human kinome comprises over 800 individual kinases. These contribute in multiple ways to regulation of cellular metabolism and may have direct and indirect effects on virus replication. Kinases are tempting therapeutic targets for drug development, but achieving sufficient specificity is often a challenge for chemical inhibitors. While using inhibitors to assess whether c-Jun N-terminal (JNK) kinases regulate hepatitis C virus (HCV) replication, we encountered unexpected off-target effects that led us to discover a role for a mitogen-activated protein kinase (MAPK)-related kinase, MAPK interacting serine/threonine kinase 1 (MKNK1), in viral entry. Two JNK inhibitors, AS601245 and SP600125, as well as RNA interference (RNAi)-mediated knockdown of JNK1 and JNK2, enhanced replication of HCV replicon RNAs as well as infectious genome-length RNA transfected into Huh-7 cells. JNK knockdown also enhanced replication following infection with cell-free virus, suggesting that JNK actively restricts HCV replication. Despite this, AS601245 and SP600125 both inhibited viral entry. Screening of a panel of inhibitors targeting kinases that may be modulated by off-target effects of AS601245 and SP600125 led us to identify MKNK1 as a host factor involved in HCV entry. Chemical inhibition or siRNA knockdown of MKNK1 significantly impaired entry of genotype 1a HCV and HCV-pseudotyped lentiviral particles (HCVpp) in Huh-7 cells but had only minimal impact on viral RNA replication or cell proliferation and viability. We propose a model by which MKNK1 acts to facilitate viral entry downstream of the epidermal growth factor receptor (EGFR) and extracellular signal-regulated kinase (ERK), both of which have been implicated in the entry process.

Diversity in sequence-dependent control of GRO chemokine mRNA half-life

Neutrophil trafficking to sites of injury or infection is regulated, in part, by the closely related GRO family of chemokines (CXCL1, -2, and -3). Expression of the GRO chemokine genes is known to be determined by transcriptional bursts in response to proinflammatory stimulation, but post-transcriptional mechanisms that regulate mRNA half-life are now recognized as important determinants. mRNA half-life is regulated via distinct sequence motifs and sequence-specific, RNA-binding proteins, whose function is subject to regulation by extracellular proinflammatory stimuli. Moreover, such mechanisms exhibit cell-type and stimulus dependency. We now present evidence that in nonmyeloid cells, GRO2 and GRO3 isoforms exhibit at least two patterns of mRNA instability that are distinguished by differential sensitivity to specific mRNA-destabilizing proteins and stimulus-mediated prolongation of mRNA half-life, respectively. Although the 3' UTR regions of GRO2 and GRO3 mRNAs contain multiple AREs, GRO2 has eight AUUUA pentamers, whereas GRO3 has seven. These confer quantitative differences in half-life and show sensitivity for TTP and KSRP but not SF2/ASF. Moreover, these AUUUA determinants do not confer instability that can be modulated in response to IL-1α. In contrast, IL-1α-sensitive instability for GRO2 and GRO3 is conferred by sequences located proximal to the 3' end of the 3'UTR that are independent of the AUUUA sequence motif. These regions are insensitive to TTP and KSRP but show reduced half-life mediated by SF2/ASF. These sequence-linked, post-transcriptional activities provide substantial mechanistic diversity in the control of GRO family chemokine gene expression.

Anti-inflammatory effects of moxifloxacin on rat airway smooth muscle cells exposed to allergen: Inhibition of extracellular-signal-regulated kinase and nuclear factor-κB activation and of interleukin-8 and eotaxin synthesis

BACKGROUND AND OBJECTIVE

Moxifloxacin (MXF) has been shown to possess immunomodulatory properties in addition to its antimicrobial effects. We investigated the effects of MXF on cytokine secretion and signal transduction mechanisms in naive control and allergen-exposed airway smooth muscle cell (ASMC) stimulated with tumour necrosis factor (TNF)-α.

METHODS

An animal model was established. ASMC was derived from rat airway tissue and cultured in vitro, then incubated with 10 ng/mL of TNF-α. Interleukin (IL)-8 and eotaxin secretion were measured by enzyme-linked immunosorbent assay, and activation of extracellular-signal-regulated kinase (ERK)1/2 and nuclear factor (NF)-κB p65 was measured by western blotting, with or without the addition of MXF (20 µg/mL) and/or dexamethasone (DXM) (10(-6)  M).

RESULTS

Baseline IL-8 and eotaxin secretion did not differ between control and allergen-exposed cells. Stimulation with TNF-α increased IL-8 and eotaxin secretion, with increased IL-8 secretion by allergen-exposed compared with naive control ASMC, post-TNF-α stimulation (P = 0.001). Baseline phosphorylation of ERK1/2 (p-ERK1/2) and NF-κB p65 was higher in allergen-exposed than in control ASMC. TNF-α increased p-ERK1/2 and NF-κB p65 levels, with higher levels in allergen-exposed ASMC, post-TNF-α stimulation (P < 0.001). MXF and the combination of MXF with DXM suppressed the secretion of IL-8 and eotaxin, but DXM alone did not affect IL-8, post-TNF-α stimulation (P > 0.05). MXF, DXM and the combination of MXF with DXM inhibited TNF-α-stimulated p-ERK1/2 and NF-κB p65 levels by 34, 40 and 62%, and 33, 38 and 64%, respectively.

CONCLUSIONS

MXF suppressed the secretion of pro-inflammatory cytokines by allergen-exposed rat ASMC, partly by inhibiting NF-κB and ERK activation. DXM may have additional or synergistic effects with MXF.

Cyclin-dependent kinase 6 phosphorylates NF-κB P65 at serine 536 and contributes to the regulation of inflammatory gene expression

Nuclear factor kappa-B (NF-κB) activates multiple genes with overlapping roles in cell proliferation, inflammation and cancer. Using an unbiased approach we identified human CDK6 as a novel kinase phosphorylating NF-κB p65 at serine 536. Purified and reconstituted CDK6/cyclin complexes phosphorylated p65 in vitro and in transfected cells. The physiological role of CDK6 for basal as well as cytokine-induced p65 phosphorylation or NF-κB activation was revealed upon RNAi-mediated suppression of CDK6. Inhibition of CDK6 catalytic activity by PD332991 suppressed activation of NF-κB and TNF-induced gene expression. In complex with a constitutively active viral cyclin CDK6 stimulated NF-κB p65-mediated transcription in a target gene specific manner and this effect was partially dependent on its ability to phosphorylate p65 at serine 536. Tumor formation in thymi and spleens of v-cyclin transgenic mice correlated with increased levels of p65 Ser536 phosphorylation, increased expression of CDK6 and upregulaton of the NF-κB target cyclin D3. These results suggest that aberrant CDK6 expression or activation that is frequently observed in human tumors can contribute through NF-κB to chronic inflammation and neoplasia.

Mechanisms of the anti-inflammatory effects of glucocorticoids: genomic and nongenomic interference with MAPK signaling pathways

Glucocorticoids (GCs) are steroid hormones produced by the adrenal gland and regulated by the hypothalamus-pituitary-adrenal axis. GCs mediate effects that mostly result in transcriptional regulation of glucocorticoid receptor target genes. Mitogen-activated protein kinases (MAPKs) comprise a family of signaling proteins that convert extracellular stimuli into the activation of intracellular transduction pathways via phosphorylation of a cascade of substrates. They modulate a variety of physiological cell processes, such as proliferation, apoptosis, and development. However, when MAPKs are improperly activated by proinflammatory and/or extracellular stress stimuli, they contribute to the regulation of proinflammatory transcription factors, thus perpetuating activation of the inflammatory cascade. One of the mechanisms by which GCs exert their anti-inflammatory effects is negative interference with MAPK signaling pathways. Several functional interactions between GCs and MAPK signaling have been discovered and studied. Some of these interactions involve the GC-mediated up-regulation of proteins that in turn interfere with the activation of MAPK, such as glucocorticoid-induced-leucine zipper, MAPK phosphatase-1, and annexin-1. Other mechanisms include activated GR directly interacting with components of the MAPK pathway and negatively regulating their activation. The multiple interactions between GCs and MAPK pathways and their potential biological relevance in mediating the anti-inflammatory effects of GCs are reviewed.

Glutathione-S-transferase M1 regulation of diesel exhaust particle-induced pro-inflammatory mediator expression in normal human bronchial epithelial cells

Background

Diesel exhaust particles (DEP) contribute substantially to ambient particulate matter (PM) air pollution in urban areas. Inhalation of PM has been associated with increased incidence of lung disease in susceptible populations. We have demonstrated that the glutathione S-transferase M1 (GSTM1) null genotype could aggravate DEP-induced airway inflammation in human subjects. Given the critical role airway epithelial cells play in the pathogenesis of airway inflammation, we established the GSTM1 deficiency condition in primary bronchial epithelial cells from human volunteers with GSTM1 sufficient genotype (GSTM1+) using GSTM1 shRNA to determine whether GSTM1 deficiency could exaggerate DEP-induced expression of interleukin-8 (IL-8) and IL-1β proteins. Furthermore, the mechanisms underlying GSTM1 regulation of DEP-induced IL-8 and IL-1β expression were also investigated.

Methods

IL-8 and IL-1β protein levels were measured using enzyme-linked immunosorbent assay. GSTM1 deficiency in primary human bronchial epithelial cells was achieved using lentiviral GSTM1 shRNA particles and verified using real-time polymerase chain reaction and immunoblotting. Intracellular reactive oxygen species (ROS) production was evaluated using flow cytometry. Phosphorylation of protein kinases was detected using immunoblotting.

Results

Exposure of primary human bronchial epithelial cells (GSTM1+) to 25-100 μg/ml DEP for 24 h significantly increased IL-8 and IL-1β protein expression. Knockdown of GSTM1 in these cells further elevated DEP-induced IL-8 and IL-1β expression, implying that GSTM1 deficiency aggravated DEP-induced pro-inflammatory response. DEP stimulation induced the phosphorylation of extracellular signal-regulated kinase (ERK) and Akt, the downstream kinase of phosphoinositide 3-kinase (PI3K), in GSTM1+ bronchial epithelial cells. Pharmacological inhibition of ERK kinase and PI3K activity blocked DEP-induced IL-8 and IL-1β expression. DEP-induced ERK and Akt phosphorylation could be increased by GSTM1 knockdown. In addition, pretreatment of HBEC with the antioxidant N-acetyl cysteine significantly inhibited DEP-induced ERK and Akt phosphorylation, and subsequent IL-8 and IL-1β expression.

Conclusion

GSTM1 regulates DEP-induced IL-8 and IL-1β expression in primary human bronchial epithelial cells by modulation of ROS, ERK and Akt signaling.

Altered stability of mRNAs associated with glaucoma progression in human trabecular meshwork cells following oxidative stress

PURPOSE

The goals of this study were to determine if oxidative stress on human trabecular meshwork (HTM) cells influences the stability of key mRNAs containing AU rich elements (AREs) known to be associated with glaucoma progression, and if the presence of topographic cue alters the stability of these mRNAs.

METHODS

HTM cells were treated with 300 μM hydrogen peroxide (H(2)O(2)) for 1 hour in the presence of 5 μg/mL actinomycin D and compared with untreated cells. The selected mRNAs (IL-6, IL-8, myocilin, SPARC [secreted protein, acidic and rich in cysteine], matrix metalloproteinase [MMP]-3, and MMP-9) from the cells were analyzed by using relative quantitative PCR. Immunohistochemistry for Hu antigen R (HuR) was performed in addition to Western blots of HuR. HTM cells were also grown on topographically patterned surfaces, and IL-6 mRNA was analyzed by quantitative PCR.

RESULTS

H(2)O(2) increased IL-6 mRNA stability 0.145 (0.095-0.27) to 0.345 (0.2-0.48) (normalized ratio, median [interquartile range]) (n = 5), while IL-8 mRNA was increased from 0.565 (0.408-0.6) to 0.775 (0.486-0.873) (n = 5). These differences were statistically significant (P = 0.0313, for both IL-6 and IL-8; Wilcoxon signed-rank test). The mRNAs of myocilin, SPARC, and MMP-3, which do not have AREs, were more stable after actinomycin D treatment and were not altered with oxidation. Western blot and immunohistochemistry demonstrated that H(2)O(2) treatment induces the translocation of HuR from the nucleus to the cytoplasm. Nanopatterned surfaces did not alter IL-6 mRNA stability.

CONCLUSIONS

Oxidative stress stabilizes IL-6 and IL-8 mRNAs significantly. The decay of certain mRNAs associated with glaucoma may be altered in the trabecular meshwork of glaucoma patients.

Networks controlling mRNA decay in the immune system

The active control of mRNA degradation has emerged as a key regulatory mechanism required for proper gene expression in the immune system. An adenosine/uridine (AU)-rich element (ARE) is at the heart of a first regulatory system that promotes the rapid degradation of a multitude of cytokine and chemokine mRNAs. AREs serve as binding sites for a number of regulatory proteins that either destabilize or stabilize the mRNA. Several kinase pathways regulate the activity of ARE-binding proteins and thereby coordinate the expression of their target mRNAs. Small regulatory micro (mi)-RNAs represent a second system that enhances the degradation of several mRNAs encoding important components of signal transduction cascades that are activated during adaptive and innate immune responses. Specific miRNAs are important for the differentiation of T helper cells, class switch recombination in B cells, and the maturation of dendritic cells. Excitement in this area of research is fueled by the discovery of novel RNA elements and regulatory proteins that exert control over specific mRNAs, as exemplified by an endonuclease that was found to directly cleave interleukin-6 mRNA. Together, these systems make up an extensive regulatory network that controls decay rates of individual mRNAs in a precise manner and thereby orchestrates the dynamic expression of many factors essential for adaptive and innate immune responses. In this review, we provide an overview of relevant factors regulated at the level of mRNA stability, summarize RNA-binding proteins and miRNAs that control their degradation rates, and discuss signaling pathways operating within this regulatory network.

The myxobacterial compounds spirangien a and spirangien M522 are potent inhibitors of IL-8 expression

Elevated expression of interleukin-8 (IL-8) has been implicated in inflammatory diseases, in tumor growth, and in angiogenesis. The aim of this study was to identify natural or synthetic compounds that suppress IL-8 production in response to interleukin-1 (IL-1), the natural inflammatory stimulus of the IL-8 gene. We therefore developed an IL-1-inducible cell-based screening assay by stable integration of an IL-8 reporter gene into HeLa S3 cells. The screening of heterogeneous compound libraries revealed several compounds that displayed an inhibitory effect on the reporter gene expression. Following hit validation, we focused on the most efficient compound, spirangien A, and its chemical derivate spirangien M522. Detailed analysis shows that both compounds are potent inhibitors of the endogenous IL-8 gene transcription. Furthermore, both compounds decelerate the phosphorylation and degradation of IκBα, the key regulator of the IL-1-stimulated NF-κB signaling pathway. Our study has identified the two spirangiens A and M522 as potent inhibitors of IL-1/NF-κB-mediated IL-8 gene expression.

Identification and functional characterization of novel phosphorylation sites in TAK1-binding protein (TAB) 1

TAB1 was defined as a regulatory subunit of the protein kinase TAK1, which functions upstream in the pathways activated by interleukin (IL)-1, tumor necrosis factor (TNF), toll-like receptors (TLRs) and stressors. However, TAB1 also functions in the p38 MAPK pathway downstream of TAK1. We identified amino acids (aa) 452/453 and 456/457 of TAB1 as novel sites phosphorylated by TAK1 as well as by p38 MAPK in intact cells as well as in vitro. Serines 452/453 and 456/457 were phosphorylated upon phosphatase blockade by calyculin A, or in response to IL-1 or translational stressors such as anisomycin and sorbitol. Deletion or phospho-mimetic mutations of aa 452–457 of TAB1 retain TAB1 and p38 MAPK in the cytoplasm. The TAB1 mutant lacking aa 452–457 decreases TAB1-dependent phosphorylation of p38 MAPK. It also enhances TAB1-dependent CCL5 secretion in response to IL-1 and increases activity of a post-transcriptional reporter gene, which contains the CCL5 3′ untranslated region. These data suggest a complex role of aa 452–457 of TAB1 in controlling p38 MAPK activity and subcellular localization and implicate these residues in TAK1- or p38 MAPK-dependent post-transcriptional control of gene expression.

Cell type- and stimulus-specific mechanisms for post-transcriptional control of neutrophil chemokine gene expression

mRNAs encoding inflammatory chemokines that recruit neutrophils frequently exhibit short half-lives that serve to limit their expression under inappropriate conditions but are often prolonged to ensure adequate levels during inflammatory response. Extracellular stimuli that modulate the stability of such mRNAs may be the same as the transcriptional activator, as is the case with TLR ligands, or may cooperate with independent transcriptional stimuli, as with IL-17, which extends the half-life of TNF-induced transcripts. These different stimuli engage independent signaling pathways that target different instability mechanisms distinguished by dependence on different regulatory nucleotide sequence motifs within the 3'UTRs, which involve that action of different mRNA-binding proteins. The selective use of these pathways by different stimuli and in distinct cell populations provides the potential for tailoring of chemokine expression patterns to meet specific needs in different pathophysiologic circumstances.

EGFRvIII promotes glioma angiogenesis and growth through the NF-κB, interleukin-8 pathway

Sustaining a high growth rate requires tumors to exploit resources in their microenvironment. One example of this is the extensive angiogenesis that is a typical feature of high-grade gliomas. Here, we show that expression of the constitutively active mutant epidermal growth factor receptor, ΔEGFR (EGFRvIII, EGFR*, de2-7EGFR) is associated with significantly higher expression levels of the pro-angiogenic factor interleukin (IL)-8 in human glioma specimens and glioma stem cells. Furthermore, the ectopic expression of ΔEGFR in different glioma cell lines caused up to 60-fold increases in the secretion of IL-8. Xenografts of these cells exhibit increased neovascularization, which is not elicited by cells overexpressing wild-type (wt)EGFR or ΔEGFR with an additional kinase domain mutation. Analysis of the regulation of IL-8 by site-directed mutagenesis of its promoter showed that ΔEGFR regulates its expression through the transcription factors nuclear factor (NF)-κB, activator protein 1 (AP-1) and CCAAT/enhancer binding protein (C/EBP). Glioma cells overexpressing ΔEGFR showed constitutive activation and DNA binding of NF-κB, overexpression of c-Jun and activation of its upstream kinase c-Jun N-terminal kinase (JNK) and overexpression of C/EBPβ. Selective pharmacological or genetic targeting of the NF-κB or AP-1 pathways efficiently blocked promoter activity and secretion of IL-8. Moreover, RNA interference-mediated knock-down of either IL-8 or the NF-κB subunit p65, in ΔEGFR-expressing cells attenuated their ability to form tumors and to induce angiogenesis when injected subcutaneously into nude mice. On the contrary, the overexpression of IL-8 in glioma cells lacking ΔEGFR potently enhanced their tumorigenicity and produced highly vascularized tumors, suggesting the importance of this cytokine and its transcription regulators in promoting glioma angiogenesis and tumor growth.

An NF-κB-independent and Erk1/2-dependent mechanism controls CXCL8/IL-8 responses of airway epithelial cells to cadmium

Airway epithelial cells in the lung are the first line of defense against pathogens and environmental pollutants. Inhalation of the environmental pollutant cadmium has been linked to the development of lung cancer and chronic obstructive pulmonary disease, which are diseases characterized by chronic inflammation. To address the role of airway epithelial cells in cadmium-induced lung inflammation, we investigated how cadmium regulates secretion of interleukin 8 (IL-8) by airway epithelial cells. We show that exposure of human airway epithelial cells to subtoxic doses of cadmium in vitro promotes a characteristic inflammatory cytokine response consisting of IL-8, but not IL-1β or tumor necrosis factor-alpha. We also found that intranasal delivery of cadmium increases lung levels of the murine IL-8 homologs macrophage inflammatory protein-2 and keracinocyte-derived chemokine and results in an influx of Gr1+ cells into the lung. We determined that inhibition of the nuclear factor-κB (NF-κB) pathway had no effect on cadmium-induced IL-8 secretion by human airway epithelial cells, suggesting that IL-8 production was mediated through an NF-κB-independent pathway. Mitogen-activated protein kinases (MAPKs) are often involved in proinflammatory signaling. Cadmium could activate the main MAPKs (i.e., p38, JNK, and Erk1/2) in human airway epithelial cells. However, only pharmacological inhibition of Erk1/2 pathway or knockdown of the expression of Erk1 and Erk2 using small interfering RNAs suppressed secretion of IL-8 induced by cadmium. Our findings identify cadmium as a potent activator of the proinflammatory cytokine IL-8 in lung epithelial cells and reveal for the first time the role of an NF-κB-independent but Erk1/2-dependent pathway in cadmium-induced lung inflammation.

A flexible approach to studying post-transcriptional gene regulation in stably transfected mammalian cells

The study of post-transcriptional regulation is constrained by the technical limitations associated with both transient and stable transfection of chimeric reporter plasmids examining the activity of 3'-UTR cis-acting elements. We report the adaptation of a commercially available system that enables consistent stable integration of chimeric reporter cDNA into a single genomic site in which transcription is induced by tetracycline. Using this system, we demonstrate the tight control afforded by this system and its suitability in mapping the regulatory function of defined cis-acting elements in the human TNF 3'-UTR, as well as the distinct effects of serum starvation on transiently transfected and stably integrated chimeric reporter genes.

c-Jun N-terminal kinase phosphorylates DCP1a to control formation of P bodies

Cytokines and stress-inducing stimuli signal through c-Jun N-terminal kinase (JNK) using a diverse and only partially defined set of downstream effectors. In this paper, the decapping complex subunit DCP1a was identified as a novel JNK target. JNK phosphorylated DCP1a at residue S315 in vivo and in vitro and coimmunoprecipitated and colocalized with DCP1a in processing bodies (P bodies). Sustained JNK activation by several different inducers led to DCP1a dispersion from P bodies, whereas IL-1 treatment transiently increased P body number. Inhibition of TAK1-JNK signaling also affected the number and size of P bodies and the localization of DCP1a, Xrn1, and Edc4. Transcriptome analysis further identified a central role for DCP1a in IL-1-induced messenger ribonucleic acid (mRNA) expression. Phosphomimetic mutation of S315 stabilized IL-8 but not IκBα mRNA, whereas overexpressed DCP1a blocked IL-8 transcription and suppressed p65 NF-κB nuclear activity. Collectively, these data reveal DCP1a as a multifunctional regulator of mRNA expression and suggest a novel mechanism controlling the subcellular localization of DCP1a in response to stress or inflammatory stimuli.

Parthenolide inhibits ERK and AP-1 which are dysregulated and contribute to excessive IL-8 expression and secretion in cystic fibrosis cells

Background

Excessive secretion of IL-8 characterizes cystic fibrosis (CF). This has been attributed to excessive activation of epithelial cell I-κB Kinase and/or NFκB. Maximum IL-8 production requires 3 cooperative mechanisms: 1) release of the promoter from repression; 2) activation of transcription by NFκB and AP-1; 3) stabilization of mRNA by p38-MAPK. Little is known about regulation of IL-8 by MAPKs or AP-1 in CF.

Methods

We studied our hypothesis in vitro using 3-cellular models. Two of these models are transformed cell lines with defective versus normal cystic fibrosis transmembrane conductance regulator (CFTR) expression: an antisense/sense transfected cell line and the patient derived IB3-1/S9. In the third series of studies, we studied primary necropsy human tracheal epithelial cells treated with an inhibitor of CFTR function. All cell lines were pretreated with parthenolide and then stimulated with TNFα and/or IL-1β.

Results

In response to stimulation with TNFα and/or IL-1β, IL-8 production and mRNA expression was greater in CF-type cells than in non-CF controls. This was associated with enhanced phosphorylation of p38, ERK1/2 and JNK and increased activation of AP-1. Since we previously showed that parthenolide inhibits excessive IL-8 production by CF cells, we evaluated its effects on MAPK and AP-1 activation and showed that parthenolide inhibited ERK and AP-1 activation. Using a luciferase promoter assay, our studies showed that parthenolide decreased activation of the IL-8 promoter in CF cells stimulated with TNFα/IL-1β.

Conclusions

In addition to NFκB MAPKs ERK, JNK and p38 and the transcription factor AP-1 are also dysregulated in CF epithelial cells. Parthenolide inhibited both NFκB and MAPK/AP-1 pathways contributing to the inhibition of IL-8 production.

Plasma membrane cholesterol plays a critical role in the Salmonella-induced anti-inflammatory response in intestinal epithelial cells

Our recent study demonstrated that a phosphatidylinositol-3 kinase (PI3K)/Akt-dependent anti-inflammatory pathway was activated by Salmonella in intestinal epithelial cells. Salmonella virulence is dependent on the ability of the bacterium to invade nonphagocytic host cells and then survive and replicate within modified Salmonella-containing vacuoles where cholesterol accumulates. In addition, cholesterol in membrane lipid rafts is frequently a platform for the activation of downstream signaling pathways, including the PI3K/Akt pathway. However, the role of plasma membrane cholesterol in the Salmonella-induced anti-inflammatory response in intestinal epithelial cells has not been elucidated. Here, we show that the effect of plasma membrane cholesterol depletion on the inhibition of Akt activation allows sustained ERK activation and the subsequent upregulation of IL-8 expression. These results demonstrate that plasma membrane cholesterol plays a critical role in the PI3K-dependent anti-inflammatory pathway activated by Salmonella in intestinal epithelial cells.