Inhibition Of IκBα Degradation Research Articles

The proteasome inhibitor MG132 reduces immobilization-induced skeletal muscle atrophy in mice

BackgroundSkeletal muscle atrophy is a serious concern for the rehabilitation of patients afflicted by prolonged limb restriction. This debilitating condition is associated with a marked activation of NFκB activity. The ubiquitin-proteasome pathway degrades the NFκB inhibitor IκBα, enabling NFκB to translocate to the nucleus and bind to the target genes that promote muscle atrophy. Although several studies showed that proteasome inhibitors are efficient to reduce atrophy, no studies have demonstrated the ability of these inhibitors to preserve muscle function under catabolic condition.MethodsWe recently developed a new hindlimb immobilization procedure that induces significant skeletal muscle atrophy and used it to show that an inflammatory process characterized by the up-regulation of TNFα, a known activator of the canonical NFκB pathway, is associated with the atrophy. Here, we used this model to investigate the effect of in vivo proteasome inhibition on the muscle integrity by histological approach. TNFα, IL-1, IL-6, MuRF-1 and Atrogin/MAFbx mRNA level were determined by qPCR. Also, a functional measurement of locomotors activity was performed to determine if the treatment can shorten the rehabilitation period following immobilization.ResultsIn the present study, we showed that the proteasome inhibitor MG132 significantly inhibited IκBα degradation thus preventing NFκB activation in vitro. MG132 preserved muscle and myofiber cross-sectional area by downregulating the muscle-specific ubiquitin ligases atrogin-1/MAFbx and MuRF-1 mRNA in vivo. This effect resulted in a diminished rehabilitation period.ConclusionThese finding demonstrate that proteasome inhibitors show potential for the development of pharmacological therapies to prevent muscle atrophy and thus favor muscle rehabilitation.

IκBα glutathionylation and reduced histone H3 phosphorylation inhibit eotaxin and RANTES

Airway smooth muscle cells (ASMCs) secrete eotaxin and RANTES (regulated on activation, normal T-cell expressed and secreted) in response to tumour necrosis factor (TNF)-α, which is inhibited by the nuclear factor (NF)-κB inhibitor dimethylfumarate (DMF). NF-κB/IκB (inhibitor of NF-κB) glutathionylation and changes in chromatin remodelling can inhibit NF-κB activity. In this study, we determined whether NF-κB/IκB glutathionylation and reduced histone H3 phosphorylation might underlie the inhibitory effect of DMF on NF-κB activity, and eotaxin and RANTES secretion. Primary human ASMCs were treated with DMF, diamide and/or glutathione (GSH) ethylester (OEt) prior to TNF-α stimulation and were subsequently analysed by ELISA, electrophoretic mobility shift assay, immunofluorescence, co-immunoprecipitation or immunoblotting. DMF reduced intracellular GSH and induced IκBα glutathionylation (IκBα-SSG), which inhibited IκBα degradation, NF-κB p65 nuclear entry and NF-κB/DNA binding. In addition, DMF inhibited the phosphorylation of histone H3, which was possibly mediated by the inhibitory effect of DMF on mitogen- and stress-activated protein kinase (MSK)-1. However, p38 mitogen-activated protein kinase (MAPK), extracellular signal-regulated kinase MAPK and MAPK phosphatase-1, upstream of MSK-1, were not inhibited by DMF. Importantly, DMF-mediated effects on NF-κB, histone H3, eotaxin and RANTES were reversed by addition of GSH-OEt. Our data suggest that DMF inhibits NF-κB-dependent eotaxin and RANTES secretion by reduction of GSH with subsequent induction of IκBα-SSG and inhibition of histone H3 phosphorylation. Our findings offer new potential drug targets to reduce airway inflammation in asthma.

Abstract 847: Resolvin D1 stimulates efferocytosis through p50/p50-mediated suppression of tumor necrosis factor-α

Abstract Phagocytosis of apoptotic neutrophils by macrophages, called efferocytosis, is critical to resolution of inflammation as this process prevents the exposure of surrounding tissues at the inflammatory site to the toxic contents of lytic cells. Docosahexaenoic acid-derived resolvin D1 (RvD1), endogenously generated during resolution of inflammation, is known to stimulate efferocytosis, but little is known about the mechanism of its action. In the present study, we found that lipopolysaccharide (LPS; 200 μg/ml) suppressed efferocytosis by murine macrophage-like RAW264.7 cells, and RvD1 (50 nM) restored the phagocytic ability of these cells by down-regulating TNF-α expression. The inhibitory effect of RvD1 on LPS-induced TNF-α expression was associated with enhanced nuclear localization of p50/p50 homodimer and concomitant reduction in the nuclear levels of p65/p50 heterodimer. RvD1 triggered extracellular signal-regulated kinase (ERK)- and Akt-mediated nuclear factor κB1 (NF-κB1) p105 degradation and subsequently translocation of p50/p50 homodimer to nucleus in RAW264.7 cells. In contrast, LPS-induced nuclear translocation and DNA binding of p65/p50 heterodimer were attenuated by RvD1 treatment through inhibition of IκBα degradation. siRNA knockdown of NF-κB p50 abolished RvD1-mediated suppression of TNF-α expression and resulted in impaired efferocytosis, suggesting that the replacement of p65/p50 with p50/p50 homodimer is an essential event for RvD1-mediated stimulation of efferocytosis. In a murine peritonitis model, intraperitoneal administration of RvD1 (300 ng) abrogated zymosan A (30 mg/kg)-induced TNF-α production, thereby reactivating efferocytosis. In addition, RvD1 significantly reduced polymorphonuclear leukocyte infiltration while it increased monocyte infiltration. Taken together, these findings indicate that RvD1 expedites resolution of inflammation via p50/p50-mediated repression of TNF-α production. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 102nd Annual Meeting of the American Association for Cancer Research; 2011 Apr 2-6; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2011;71(8 Suppl):Abstract nr 847. doi:10.1158/1538-7445.AM2011-847

Inhibitory effect of Physalis alkekengi L. var. franchetii extract and its chloroform fraction on LPS or LPS/IFN-γ-stimulated inflammatory response in peritoneal macrophages

The aerial parts of the plant Physalis alkekengi L. var. franchetii (PA) are traditionally used in folk medicine to treat cough, middle ear infection, sore throat, abscesses, and urinary problems. However, the cellular mechanisms underlying PA's possible anti-inflammatory effects are unknown. We examined the effect of a methanol extract of PA on the production of nitric oxide (NO), inducible NO synthase (iNOS), cyclooxygenase (COX)-2, tumor necrosis factor (TNF)-α, and interleukin (IL)-6. We also examined the extract's effect on the activity of IκBα, mitogen-activated protein kinases (MAPKs) and STAT1 in macrophages stimulated by lipopolysaccharide (LPS) or LPS/interferon-γ (IFN-γ). We further fractioned the extract into chloroform and water to investigate which fraction possessed anti-inflammatory activity. We found that the PA methanol extract significantly reduced the production of NO, iNOS, COX-2, TNF-α, and IL-6. The extract also inhibited LPS-induced IκBα degradation and MAPK activation as well as LPS/IFN-γ-induced STAT1 activation, effects observed at a higher concentration than that required to suppress iNOS. The chloroform fraction possessed the anti-inflammatory activity of PA by inhibiting the expression of iNOS, TNF-α and IL-6 through downregulation of IκBα degradation and MAPK activation. Our findings indicate that the PA methanol extract contains different anti-inflammatory compounds, some of which suppressed iNOS expression and some of which inhibited IκBα degradation and MAPK activity. Further research is warranted to identify these anti-inflammatory components of PA and validate its use in animal studies.

Azadirachtin Interacts with Retinoic Acid Receptors and Inhibits Retinoic Acid-mediated Biological Responses

Considering the role of retinoids in regulation of more than 500 genes involved in cell cycle and growth arrest, a detailed understanding of the mechanism and its regulation is useful for therapy. The extract of the medicinal plant Neem (Azadirachta indica) is used against several ailments especially for anti-inflammatory, anti-itching, spermicidal, anticancer, and insecticidal activities. In this report we prove the detailed mechanism on the regulation of retinoic acid-mediated cell signaling by azadirachtin, active components of neem extract. Azadirachtin repressed all trans-retinoic acid (ATRA)-mediated nuclear transcription factor κB (NF-κB) activation, not the DNA binding but the NF-κB-dependent gene expression. It did not inhibit IκBα degradation, IκBα kinase activity, or p65 phosphorylation and its nuclear translocation but inhibited NF-κB-dependent reporter gene expression. Azadirachtin inhibited TRAF6-mediated, but not TRAF2-mediated NF-κB activation. It inhibited ATRA-induced Sp1 and CREB (cAMP-response element-binding protein) DNA binding. Azadirachtin inhibited ATRA binding with retinoid receptors, which is supported by biochemical and in silico evidences. Azadirachtin showed strong interaction with retinoid receptors. It suppressed ATRA-mediated removal of retinoid receptors, bound with DNA by inhibiting ATRA binding to its receptors. Overall, our data suggest that azadirachtin interacts with retinoic acid receptors and suppresses ATRA binding, inhibits falling off the receptors, and activates transcription factors like CREB, Sp1, NF-κB, etc. Thus, azadirachtin exerts anti-inflammatory and anti-metastatic responses by a novel pathway that would be beneficial for further anti-inflammatory and anti-cancer therapies.

San‐Huang‐Xie‐Xin‐Tang Protects against Activated Microglia‐ and 6‐OHDA‐Induced Toxicity in Neuronal SH‐SY5Y Cells

San-Huang-Xie-Xin-Tang (SHXT), composed of Coptidis rhizoma, Scutellariae radix and Rhei rhizoma, is a traditional Chinese herbal medicine used to treat gastritis, gastric bleeding and peptic ulcers. This study investigated the neuroprotective effects of SHXT on microglia-mediated neurotoxicity using co-cultured lipopolysaccharide (LPS)-activated microglia-like BV-2 cells with neuroblastoma SH-SY5Y cells. Effects of SHXT on 6-hydroxydopamine (6-OHDA)-induced neurotoxicity were also examined in SH-SY5Y cells. Results indicated SHXT inhibited LPS-induced inflammation of BV-2 cells by downregulation of iNOS, NO, COX-2, PGE2, gp91phox, iROS, TNF-α, IL-1β, inhibition of IκBα degradation and upregulation of HO-1. In addition, SHXT increased cell viability and down regulated nNOS, COX-2 and gp91phox of SH-SY5Y cells co-cultured with LPS activated BV-2 cells. SHXT treatment increased cell viability and mitochondria membrane potential (MMP), decreased expression of nNOS, COX-2, gp91phox and iROS, and inhibited IκBα degradation in 6-OHDA-treated SH-SY5Y cells. SHXT also attenuated LPS activated BV-2 cells- and 6-OHDA-induced cell death in differentiated SH-SY5Y cells with db-cAMP. Furthermore, SHXT-inhibited nuclear translocation of p65 subunit of NF-κB in LPS treated BV-2 cells and 6-OHDA treated SH-SY5Y cells. In conclusion, SHXT showed protection from activated microglia- and 6-OHDA-induced neurotoxicity by attenuating inflammation and oxidative stress.

Mangiferin attenuates osteoclastogenesis, bone resorption, and RANKL‐induced activation of NF‐κB and ERK

Osteolytic bone diseases such as osteoporosis have a common pathological feature in which osteoclastic bone resorption outstrips bone synthesis. Osteoclast formation and activation are regulated by receptor activator of nuclear factor κB ligand (RANKL). The induction of RANKL-signaling pathways occurs following the interaction of RANKL to its cognate receptor, RANK. This specific binding drives the activation of downstream signaling pathways; which ultimately induce the formation and activation of osteoclasts. In this study, we showed that a natural immunomodulator, mangiferin, inhibits osteoclast formation and bone resorption by attenuating RANKL-induced signaling. Mangiferin diminished the expression of osteoclast marker genes, including cathepsin K, calcitonin receptor, DC-STAMP, and V-ATPase d2. Mechanistic studies revealed that mangiferin inhibits RANKL-induced activation of NF-κB, concomitant with the inhibition of IκB-α degradation, and p65 nuclear translocation. In addition, mangiferin also exhibited an inhibitory effect on RANKL-induced ERK phosphorylation. Collectively, our data demonstrates that mangiferin exhibits anti-resorptive properties, suggesting the potential application of mangiferin for the treatment and prevention of bone diseases involving excessive osteoclastic bone resorption.

Lauroside B, a Megastigmane Glycoside from Laurus Nobilis (Bay Laurel) Leaves, Induces Apoptosis in Human Melanoma Cell Lines by Inhibiting NF-κB Activation

Malignant melanoma is a highly aggressive tumor that frequently resists chemotherapy, so the search for new agents for its treatment is of great importance. In the present study, the antiproliferative propensity against human melanoma cell lines of lauroside B (1), a megastigmane glycoside isolated from Laurus nobilis (bay laurel) leaves, was investigated. This compound suppressed the proliferation of three human melanoma cell lines, namely, A375, WM115, and SK-Mel-28. The 1-induced inhibition of human melanoma cell proliferation was due to the induction of apoptosis, as demonstrated by FACS analysis with annexin V/PI staining and confirmed by activation of caspase-3 and by the cleavage of poly(ADP-ribose) polymerase (PARP). Growing evidence implicates NF-κB as an important contributor to metastasis and increased chemoresistance of melanoma. Thus, it was hypothesized that 1-induced apoptosis could be associated with suppression of NF-κB activation. The results showed that exposure of human melanoma cells to 1 inhibited IκB-α degradation and constitutive NF-κB DNA-binding activity as well as the expression, regulated by NF-κB, of two antiapoptotic genes, XIAP and c-FLIP. Induction of apoptosis by 1 in human aggressive melanoma cell lines has a potential high biological value.

Anti-inflammatory activity of ethylacetate fraction of Cliona celata

We evaluated the ability of the ethylacetate fraction of marine sponge, Cliona celata (ECC), harvested from Korean seaside to regulate the expression of inducible nitric oxide synthase (iNOS) in lipopolysaccharide (LPS)-stimulated murine macrophage-like RAW264.7 cells. ECC dose-dependently inhibited both the expression of iNOS protein and mRNA, resulting in decreased production of nitric oxide (NO), with an IC50 of 80.5 μg/mL. To investigate action mechanism by which ECC inhibits NO production and iNOS expression, we examined the activation of IκB in LPS-stimulated RAW264.7 cells. ECC clearly inhibited translocation of nuclear factor-κB (NF-κB) p65 subunits from cytosol to nucleus, which correlated with its inhibitory effects on IκB-α phosphorylation and degradation. Furthermore, ECC potently suppressed both the reporter gene expression and DNA-binding activity of NF-κB, which was associated with decreased p65 protein levels in the nucleus. Here, we show for the first time that ECC inhibits NF-κB activation through the inhibition of IκB degradation.

Preventive effect of silymarin in cerebral ischemia–reperfusion-induced brain injury in rats possibly through impairing NF-κB and STAT-1 activation

Silymarin and silibinin are bioactive components isolated from Silybum marianum. They have been reported to exhibit anti-oxidative and anti-inflammatory effects. Many studies revealed that drugs with potent anti-inflammatory potential can protect animals against inflammation-associated neurodegenerative disease, e.g., stroke. In this current work we established an animal model of acute ischemic stroke injury by inducing cerebral ischemic/reperfusion (CI/R) in rats to elucidate whether silymarin or silibinin can protect animals from CI/R injury. Pretreatment with silymarin, but not silibinin, dose-dependently (1-10μg/kg, i.v.) reduced CI/R-induced brain infarction by 16-40% and improved neurological deficits in rats with a stroke. Elevated pathophysiological biomarkers for CI/R-induced brain injury, including lipid peroxidation, protein nitrosylation, and oxidative stress, were all reduced by silymarin. In addition, expression of inflammation-associated proteins (e.g., inducible nitric oxide synthase, cyclooxygenase-2 and myeloperoxidase), and transcriptional factors (e.g., nuclear factor (NF)-kappa B and signal transducer and activator of transcription (STAT)-1), as well as production of proinflammatory cytokine (e.g., interleukin-1β and tumor necrosis factor-α) was all significantly prevented by silymarin. Furthermore, an in vitro study on microglial BV2 cells showed that silymarin could inhibit nitric oxide and superoxide anion production, possibly by interfering with NF-κB nuclear translocation/activation. Likewise, silymarin pretreatment also inhibited IκB-α degradation and NF-κB nuclear translocation in brain tissues of ischemic rats. Our results reveal that silymarin, but not its active component silibinin, protected rats against CI/R-induced stroke injury by amelioration of the oxidative and nitrosative stresses and inflammation-mediated tissue injury through impeding the activation of proinflammatory transcription factors (e.g., NF-κB and STAT-1) in the upregulation of proinflammatory proteins and cytokines in stroke-damaged sites. In conclusion, silymarin displays beneficial effects of preventing inflammation-related neurodegenerative disease, e.g., stroke, which needs further investigation and clinical evidences.

S1767 NOD1 is Essential Signal Transducer in Human Gastric Epithelial Cells Infected With Helicobacter pylori

BACKGROUND/AIM Nucleotide binding oligomerization domain (Nod) proteins are members of a family that includes the apoptosis regulator APAF1. Nod proteins have been implicated in the induction of NF-κB activity and in the activation of caspases. Helicobacter pylori (H. pylori) infection is reported to express TLR 4, TLR-5 and TLR-9 in gastric epithelial cells. However, TLR-4 and TLR-5 are not recognized as important role in H. pylori infection. This implicated that another signal transducer different from TLR pathway may affect NFκB activation in cag PAI (+) H. pylori infection. The purpose of this study was to investigate whether cag PAI (+) H. pylori infection affects NF-κB activation and IL-8 production through Nod1 and to evaluate the transepithelial neutrophil migration induced by H. pylori infection. METHODS Stable transfection of Dominant Negative (DN) Nod1 in AGS cell line was established followed by NF-κB activation and IL-8 production by H. pylori HP 99 infection was assessed. The role of cag PAI was examined comparing wild type H. pylori strain with cag PAI knock-down CagAand CagEH. pylori strain. To assess the production of IL-8, we examined mRNA expression using RT-PCR, and IL-8 secretion using ELISA. To assess the inhibition of NF-κB activation, we examined degradation and phosphorylation of IκBα using western blot and EMSA. To examine the role of cag PAI, we examined the production of IL-8 and the inhibition of NF-κB activation in the cag PAI knock-down CagAand CagEH. pylori infection in the same manner with wild type. We established the neutrophil migration model induced by H. pylori infection in polarized DN Nod1 Caco-2 cell line and evaluated transepithelial neutrophil migration as to the cag PAI status. RESULTS Stable transfection of DN Nod1 followed by cag PAI (+) H. pylori inhibited IL-8 mRNA expression and IL-8 production. In addition, cag PAI (+) H. pylori inhibited IκB-α degradation and IκB-α phosphorylation. IL-8 mRNA expression and IL-8 production by CagA-and CagEH. pylori were significantly decreased compared with those by wild type H. pylori. IκB-α degradation and IκB-α phosphorylation by CagA-and CagEH. pylori were significantly decreased compared with those by wild type H. pylori. NF-κB expression by CagA-and CagEH. pylori was significantly decreased compared with that by wild type H. pylori. Transepithelial neutrophil migration was more prominent in wild type H. pylori than CagAand CagEH. pylori CONCLUSION Signaling through Nod1 plays an essential role in the upregulated expression of IL-8 in human epithelial cells infected with H. pylori.

1α,25-Dihydroxyvitamin D 3 inhibits transcriptional potential of nuclear factor kappa B in breast cancer cells

1α,25-Dihydroxyvitamin D 3 (VD 3), the biologically active form of vitamin D, may have either pro- or anti-inflammatory activities because of its diverse actions on nuclear factor kappa B (NF-κB). Previous studies indicated that VD 3 can either activate or inhibit NF-κB via Akt-induced IκBα phosphorylation and increase in IκBα synthesis respectively. At present, the relevant contribution of each mechanism has not been fully explored. We observed a VD 3-mediated NF-κB inhibitory effect in vitamin D receptor (VDR)-positive MCF-7 breast cancer cells. We showed that VD 3 induced VDR-dependent IκBα expression but still able to lead on transient NF-κB p65 nuclear translocation through Akt-induced IκBα phosphorylation. Upon TNFα stimulation, VD 3 was not capable to inhibit IκBα degradation, p65 nuclear translocation and p65/p50-DNA binding. Here, we found that VD 3 strongly repressed p65 transactivation in MCF-7 cells using Gal4-p65 chimeras system. VDR was required for the VD 3-mediated transrepression and mutations in VDR affected its suppressive ability. We also demonstrated that neither inhibition of p65 phosphorylation nor acetylation was responsible for the transrepression. In fact, we found that treatment of MCF-7 cells with histone deacetylase inhibitors abrogated VD 3-induced p65 transrepression. In addition, knockdown of two nuclear corepressors HDAC3 and SMRT relieved p65 transactivation and particular TNFα-triggered gene expression. In conclusion, the reduction of gene activation by VD 3 in breast cancer cells was caused by the interference of the transactivation potential of NF-κB p65 subunit. Our studies provide a scientific background for rational use of vitamin D in the prevention and treatment of inflammatory diseases.

Scutellarin protects against lipopolysaccharide-induced acute lung injury via inhibition of NF-κB activation in mice

This paper investigates the effect of natural scutellarin on acute lung injury (ALI) induced by Escherichia coli endotoxin lipopolysaccharide (LPS) in mice and its mechanism of action. Mouse ALI was induced by the injection of LPS (15 mg/kg) via the tail vein, and mice were intraperitoneally injected with 50 and 25 mg/kg of scutellarin before the LPS injection. The lung index, serum , and tumor necrosis factor-alpha (TNF-α) levels were determined using kits. The lung lesions were examined by light microscope. The mRNA levels of TNF-α, inducible nitric oxide synthase (iNOS), and FasL in pulmonary tissues were detected by RT-PCR. c-Fos, c-Jun, IκB, and iNOS proteins were detected by the western blotting method. Pretreatment with 25 and 50 mg/kg of scutellarin significantly reduced lung injury induced by LPS, which expressed in the decrease in lung morphological lesions, serum , TNF-α levels, lactate dehydrogenase release, and total protein in the lavage fluid of bronchoalveolar of the lung. The mRNA level of TNF-α, iNOS, the protein content of c-Fos, iNOS, and the activation of NF-κB in pulmonary tissues were all inhibited, while the lung glutathione level increased. In conclusion, scutellarin has protective action against LPS-induced lung damage in mice, and its underlying mechanism might be the inhibition of IκBα degradation and the expression of TNF-α mRNA.

NCX 4040, a Nitric Oxide-Donating Aspirin, Exerts Anti-Inflammatory Effects through Inhibition of IκB-α Degradation in Human Monocytes

NO-donating aspirins consist of aspirin to which a NO-donating group is covalently linked via a spacer molecule. NCX 4040 and NCX 4016 are positional isomers with respect to the -CH(2)ONO(2) group (para and meta, respectively) on the benzene ring of the spacer. Because positional isomerism is critical for antitumor properties of NO-donating aspirins, we aimed to compare their anti-inflammatory effects with those of aspirin in vitro. Thus, we assessed their impacts on cyclooxygenase-2 activity (by measuring PGE(2) levels), protein expression, and cytokine generation(IL-1beta, IL-18, TNF-alpha, and IL-10) in human whole blood and isolated human monocytes stimulated with LPS. Interestingly, we found that micromolar concentrations of NCX 4040, but not NCX 4016 or aspirin, affected cyclooxygenase-2 expression and cytokine generation. We compared the effects of NCX 4040 with those of NCX 4016 or aspirin on IkappaB-alpha stabilization and proteasome activity in the LPS-stimulated human monocytic cell line THP1. Differently from aspirin and NCX 4016, NCX 4040, at a micromolar concentration range, inhibited IkappaB-alpha degradation. In fact, NCX 4040 caused concentration-dependent accumulation of IkappaB-alpha and its phosphorylated form. This effect was not reversed by 1H-[1,2,4]oxadiazolo[4,3-a]quinoxalin-1-one, an inhibitor of guanylyl cyclase, thus excluding the contribution of NO-dependent cGMP generation. In contrast, IkappaB-alpha accumulation by NCX 4040 may involve an inhibitory effect on proteasome functions. Indeed, NCX 4040 inhibited 20S proteasome activity when incubated with intact cells but not in the presence of cell lysate supernatants, thus suggesting an indirect inhibitory effect. In conclusion, NCX 4040 is an inhibitor of IkappaB-alpha degradation and proteasome function, and it should be taken into consideration for the development of novel anti-inflammatory and chemopreventive agents.

Proteasomal inhibition upregulates the endogenous MAPK deactivator MKP-1 in human airway smooth muscle: Mechanism of action and effect on cytokine secretion

Asthma is a chronic inflammatory condition. Inhibition of the ubiquitin–proteasome system offers promise as a anti-inflammatory strategy, being responsible for the degradation of key proteins involved in crucial cellular functions, including gene expression in inflammation (e.g. inhibitory IκB-α and the endogenous MAPK deactivator — MKP-1). As MKP-1 inhibits MAPK-mediated pro-remodeling functions in human airway smooth muscle (ASM; a pivotal immunomodulatory cell in asthma) in this study we investigate the effect of the proteasome inhibitor MG-132 on MKP-1 and evaluate the anti-inflammatory effect of MG-132 on cytokine secretion from ASM cells. Examining the time-course of induction of MKP-1 mRNA and protein by MG-132 (10μM) we show that MKP-1 mRNA was first detected at 30min, increased to significant levels by 4h, resulting in a 12.6±1.5-fold increase in MKP-1 mRNA expression by 24h (P<0.05). MKP-1 protein levels corroborate the mRNA results. Investigating the effect of MG-132 on secretion of the cytokine IL-6 we show that while short-term pretreatment with MG-132 (30min) partially reduced TNFα-induced IL-6 via inhibition of IκB-α degradation and the NF-κB pathway, longer-term proteasome inhibition (up to 24h) robustly upregulated MKP-1 and was temporally correlated with repression of p38-mediated IL-6 secretion from ASM cells. Moreover, utilizing a cytokine array we show that MG-132 represses the secretion of multiple cytokines implicated in asthma. Taken together, our results demonstrate that MG-132 upregulates MKP-1 and represses cytokine secretion from ASM and highlight the potential of the proteasome as a therapeutic target in asthma.

Eriobotryae Folium Extract Suppresses LPS-Induced iNOS and COX-2 Expression by Inhibition of NF-κB and MAPK Activation in Murine Macrophages

Eriobotryae folium (EF), the dried leaves of Eriobotrya japonica (Thunb.) Lindl. has been traditionally used to treat various diseases such as chronic bronchitis, cough, inflammation, skin diseases, and diabetes. In this study, we examined the effects of Eriobotryae folium extract (EFE) on lipopolysaccharide (LPS)-induced production of nitric oxide (NO) and prostaglandin E2(PGE2) in RAW264 murine macrophage cells. EFE suppressed LPS-induced NO and PGE2 production in a dose-dependent manner. Consistent with these observations, EFE reduced the LPS-induced expressions of inducible nitric oxide synthase (iNOS) and cyclooxygenase-2 (COX-2) at both protein and mRNA levels. Furthermore, EFE significantly inhibited LPS-induced NF-kappaB binding activity, which was associated with the inhibition of IkappaB-alpha degradation. EFE also attenuated LPS-induced phosphorylation of mitogen-activated protein kinases (MAPKs) including extracellular signal-regulated kinase (ERK), p38 MAPK and c-Jun N-terminal kinase (JNK). These results suggest that the anti-inflammatory properties of EF might result from inhibition of iNOS and COX-2 expression through the downregulation of NF-kappaB activation and MAPK phosphorylation in LPS-stimulated RAW264 cells.

Carabrol suppresses LPS-induced nitric oxide synthase expression by inactivation of p38 and JNK via inhibition of I-κBα degradation in RAW 264.7 cells

Carabrol, isolated from Carpesium macrocephalum, showed anti-inflammatory potential in LPS-induced RAW 264.7 murine macrophages. In present study, carabrol demonstrated the inhibitory activity on pro-inflammatory cytokines such as IL-1β, IL-6 and TNF-α. In addition, mRNA and protein levels of iNOS and COX-2 were reduced by carabrol. Molecular analysis revealed that these suppressive effects were correlated with the inactivation of p38 and JNK via inhibition of NF-κB activation. Immunoblotting showed that carabrol suppressed LPS-induced degradation of I-κBα and decreased nuclear translocation of p65. Taken together, these results suggest that carabrol can be a modulator of pro-inflammatory signal transduction pathway in RAW 264.7 cells.

Pollen-Derived E1-Phytoprostanes Signal via PPAR-γ and NF-κB-Dependent Mechanisms

In a humid milieu such as mucosal surfaces, pollen grains do not only release allergens but also proinflammatory and immunomodulatory lipids, termed pollen-associated lipid mediators. Among these, the E(1)-phytoprostanes (PPE(1)) were identified to modulate dendritic cell (DC) function: PPE(1) inhibit the DC's capacity to produce IL-12 and enhance DC mediated T(H)2 polarization of naive T cells. The mechanism(s) by which PPE(1) act on DC remained elusive. We thus analyzed candidate signaling elements and their role in PPE(1)-mediated regulation of DC function. Aqueous birch pollen extracts induced a marked cAMP response in DC that could be blocked partially by EP2 and EP4 antagonists. In contrast, PPE(1) hardly induced cAMP and the inhibitory effect on IL-12 production was mostly independent of EP2 and EP4. Instead, PPE(1) inhibited the LPS-induced production of IL-12 p70 by a mechanism involving the nuclear receptor PPAR-gamma. Finally, PPE(1) efficiently blocked NF-kappaB signaling in DCs by inhibiting IkappaB-alpha degradation, translocation of p65 to the nucleus, and binding to its target DNA elements. We conclude that pollen-derived PPE(1) modulate DC function via PPAR-gamma dependent pathways that lead to inhibition of NFkappaB activation and result in reduced DC IL-12 production and consecutive T(H)2 polarization.

Inhibition of IL-1β-mediated inflammatory responses by the IκBα super-repressor in human fibroblast-like synoviocytes

The IL-1β-NF-κB axis is a key pathway in the pathogenesis of rheumatoid arthritis (RA) and is central in the production of proinflammatory mediators in the inflamed synovium. Therefore, we examined whether fibroblast-like synoviocytes (FLS) could be spared from IL-1β-induced toxicity by an overexpressing IκB super-repressor. Infection of FLS with Ad-IκBα (S32A, S36A), an adenovirus-containing mutant IκBα, inhibited IL-1β-induced nuclear translocation and DNA binding of NF-κB. In addition, Ad-IκBα (S32A, S36A) prevented IL-1β-induced inflammatory responses; namely, the production of chemokines, such as ENA-78 and RANTES, and activation of MMP-1 and MMP-3. Finally, increased cellular proliferation of FLS after IL-1β treatment was significantly reduced by Ad-IκBα (S32A, S36A). However, Ad-IκBβ (S19A, S23A), the IκBβ mutant, was not effective in preventing IL-1β toxicity. These results suggest that inhibition of IκBα degradation is a potential target for the prevention of joint destruction in patients with RA.

Saucerneol D, a naturally occurring sesquilignan, inhibits LPS-induced iNOS expression in RAW264.7 cells by blocking NF-κB and MAPK activation

We evaluated the ability of saucerneol D (SD), a tetrahydrofuran-type sesquilignan isolated from Saururus chinensis, to regulate the expression of inducible nitric oxide synthase (iNOS) in lipopolysaccharide (LPS)-stimulated murine macrophage-like RAW264.7 cells. SD consistently inhibited nitric oxide (NO) production in a dose-dependent manner, with an IC 50 of 2.62 µM, and also blocked LPS-induced iNOS expression. SD potently suppressed both the reporter gene expression and DNA-binding activity of nuclear factor-κB (NF-κB). In addition, SD inhibited IκB-α degradation in a concentration- and time-dependent manner. SD also inhibited LPS-induced activation of various mitogen-activated protein kinases, including extracellular signal-regulated kinase 1/2 (ERK1/2) and c-Jun NH 2-terminal kinase (JNK). These findings suggest that SD may inhibit LPS-induced iNOS expression by blocking NF-κB and MAPK activation.