NF-kappaB family of transcription factors: central regulators of innate and adaptive immune functions

MicroRNA-302b augments host defense to bacteria by regulating inflammatory responses via feedback to TLR/IRAK4 circuits

MicroRNAs (miRNAs) have been implicated in a spectrum of physiological and pathological conditions, including immune responses. miR-302b has been implicated in stem cell differentiation but its role in immunity remains unknown. Here we show that miR-302b is induced by TLR2 and TLR4 through ERK-p38-NF-κB signaling upon Gram-negative bacterium Pseudomonas aeruginosa infection. Suppression of inflammatory responses to bacterial infection is mediated by targeting IRAK4, a protein required for the activation and nuclear translocation of NF-κB. Through negative feedback, enforced expression of miR-302b or IRAK4 siRNA silencing inhibits downstream NF-κB signaling and airway leukocyte infiltration, thereby alleviating lung injury and increasing survival in P. aeruginosa-infected mice. In contrast, miR-302b inhibitors exacerbate inflammatory responses and decrease survival in P. aeruginosa-infected mice and lung cells. These findings reveal that miR-302b is a novel inflammatory regulator of NF-κB activation in respiratory bacterial infections by providing negative feedback to TLRs-mediated immunity.

MicroRNA roles in the NF- κB signaling pathway during viral infections

NF- κ B signaling network is a crucial component of innate immunity. miRNAs are a subtype of small noncoding RNAs, involved in regulation of gene expression at the posttranscriptional level. Increasing evidence has emerged that miRNAs play an important role in regulation of NF- κ B signaling pathway during viral infections. Both host and viral miRNAs are attributed to modulation of NF- κ B activity, thus affecting viral infection and clearance. Understandings of the mechanisms of these miRNAs will open a direction for development of novel antivirus drugs.

Triptolide improves early survival of mesenchymal stem cells transplanted into rat myocardium

OBJECTIVE

To investigate whether triptolide can prolong the survival of rat mesenchymal stem cells (MSCs) transfected with the mouse hyperpolarization-activated cyclic nucleotide-gated channel 4 (mHCN4) gene in the myocardium.

METHODS

Grafted cell survival was determined using a sex-mismatched cell transplantation model and analysis of Y chromosome-specific Sry gene expression from hearts harvested at different time points after cell transplantation. ELISA and RT-PCR were used to measure protein and mRNA levels, respectively, of nuclear factor (NF)-κB, IL-1β, IL-6 and TNF-α.

RESULTS

Donor cell numbers decreased over time. Pretreatment with triptolide improved graft survival both 24 (29.3 ± 0.9%) and 72 h (17.5 ± 1.2%) after transplantation of MSCs and resulted in a 2.5-fold increase in the total cell number 72 h after cell transplantation. The mRNA expression and protein content of NF-κB, IL-1β, IL-6 and TNF-α were significantly reduced in the triptolide-treated group compared with the control groups. In addition, triptolide downregulated Bax but upregulated Bcl-2 in the injected region.

CONCLUSIONS

Transient treatment with triptolide may significantly improve the early survival of MSCs in vivo. The mechanism underlying this effect involves attenuating the inflammatory response via inhibition of the NF-κB signaling pathway.

Mechanisms of DNA damage response to targeted irradiation in organotypic 3D skin cultures

DNA damage (caused by direct cellular exposure and bystander signaling) and the complex pathways involved in its repair are critical events underpinning cellular and tissue response following radiation exposures. There are limited data addressing the dynamics of DNA damage induction and repair in the skin particularly in areas not directly exposed. Here we investigate the mechanisms regulating DNA damage, repair, intracellular signalling and their impact on premature differentiation and development of inflammatory-like response in the irradiated and surrounding areas of a 3D organotypic skin model. Following localized low-LET irradiation (225 kVp X-rays), low levels of 53BP1 foci were observed in the 3D model (3.8±0.28 foci/Gy/cell) with foci persisting and increasing in size up to 48 h post irradiation. In contrast, in cell monolayers 14.2±0.6 foci/Gy/cell and biphasic repair kinetics with repair completed before 24 h was observed. These differences are linked to differences in cellular status with variable level of p21 driving apoptotic signalling in 2D and accelerated differentiation in both the directly irradiated and bystander areas of the 3D model. The signalling pathways utilized by irradiated keratinocytes to induce DNA damage in non-exposed areas of the skin involved the NF-κB transcription factor and its downstream target COX-2.

NF-κB activation induced by hepatitis A virus and Newcastle disease virus occurs by different pathways depending on the structural pattern of viral nucleic acids

NF-κB is activated by hepatitis B virus and hepatitis C virus and is assumed to contribute to viral persistence, leading to the development of hepatocellular cancer by inhibition of apoptosis mediated by cytotoxic T cells. Whether hepatitis A virus (HAV), which does not cause chronic infection, activates NF-κB is a topic of controversy. Here, we confirm that HAV activates NF-κB and show that HAV enhances the activation of NF-κB by poly(I-C), but it inhibits the activation of NF-κB by Newcastle disease virus (NDV), a paramyxovirus. In addition, HAV inhibits NF-κB activation induced by overexpressed MAVS (mitochondrial antiviral signaling protein). We conclude from these findings that NF-κB induction occurs in cells infected with HAV by dsRNA, independently of mitochondrial-transduced RIG-I/MDA-5 signaling, whereas the induction of NF-κB in cells infected by NDV is mediated by RIG-I signaling, independenly of viral dsRNA. This is supported by experiments in which the different RNA inducers of RIG-I and MDA-5 are sequestered and which also show that poly(I-C) and HAV, but not NDV, are functionally equivalent in inducing NF-κB activity. Furthermore, we demonstrate that HAV interferes with the protein kinase R (PKR) activity and PKR activation induced by dsRNA, and that HAV-induced activation of NF-κB therefore does not take place via the PKR-induced pathway. As assumed for hepatitis B and C virus infections, NF-κB activation could attenuate the effects of cytotoxic T cells and may contribute to prolonged as well as relapsing courses of hepatitis A.

Mycobacteria bypass mucosal NF-kB signalling to induce an epithelial anti-inflammatory IL-22 and IL-10 response

The mechanisms by which mycobacteria subvert the inflammatory defence to establish chronic infection remain an unresolved question in the pathogenesis of tuberculosis. Using primary epithelial cells, we have analysed mycobacteria induced epithelial signalling pathways from activation of TLRs to cytokine secretion. Mycobacterium bovis bacilli Calmette-Guerin induced phosphorylation of glycogen synthase kinase (GSK)3 by PI3K-Akt in the signalling pathway downstream of TLR2 and TLR4. Mycobacteria did not suppress NF-κB by activating the peroxisome proliferator-activated receptor γ. Instead the pro-inflammatory NF-κB was bypassed by mycobacteria induced GSK3 inhibition that promoted the anti-inflammatory transcription factor CREB. Mycobacterial infection did not thus induce mucosal pro-inflammatory response as measured by TNFα and IFNγ secretion, but led to an anti-inflammatory IL-10 and IL-22 production. Apart from CREB, MAP3Ks p38 and ERK1/2 activated the transcription factor AP-1 leading to IL-6 production. Interestingly, blocking of TLR4 before infection decreased epithelial IL-6 secretion, but increased the CREB-activated IL-10 production. Our data indicate that mycobacteria suppress epithelial pro-inflammatory production by suppressing NF-κB activation thereby shifting the infection towards an anti-inflammatory state. This balance between the host immune response and the pathogen could determine the outcome of infection.

Methanol Extract of Artemisia apiacea Hance Attenuates the Expression of Inflammatory Mediators via NF- κ B Inactivation

Artemisia apiacea Hance is one of the most widely used herbs for the treatment of malaria, jaundice, and dyspeptic complaint in oriental medicine. This study investigated the effects of methanol extracts of A. apiacea Hance (MEAH) on the induction of inducible nitric oxide synthase (iNOS) and proinflammatory mediators by lipopolysaccharide (LPS) in Raw264.7 macrophage cells and also evaluated the in vivo effect of MEAH on carrageenan-induced paw edema in rats. MEAH treatment in Raw264.7 cells significantly decreased LPS-inducible nitric oxide production and the expression of iNOS in a concentration-dependent manner, while MEAH (up to 100 μg/mL) had no cytotoxic activity. Results from immunoblot analyses and ELISA revealed that MEAH significantly inhibited the expression of cyclooxygenase-2, tumor necrosis factor-α, interleukin-1β, and interleukin-6 in LPS-activated cells. As a plausible molecular mechanism, increased degradation and phosphorylation of inhibitory-κBα and nuclear factor-κB accumulation in the nucleus by LPS were partly blocked by MEAH treatment. Finally, MEAH treatment decreased the carrageenan-induced formation of paw edema and infiltration of inflammatory cells in rats. These results demonstrate that MEAH has an anti-inflammatory therapeutic potential that may result from the inhibition of nuclear factor-κB activation, subsequently decreasing the expression of proinflammatory mediators.

PTEN functions as a melanoma tumor suppressor by promoting host immune response

Cancer cells acquire several traits that allow for their survival and progression, including the ability to evade the host immune response. However, the mechanisms by which cancer cells evade host immune responses remain largely elusive. Here we study the phenomena of immune evasion in malignant melanoma cells. We find that the tumor suppressor phosphatase and tensin homolog (PTEN) is an important regulator of the host immune response against melanoma cells. Mechanistically, PTEN represses the expression of immunosuppressive cytokines by blocking the phosphatidylinositide 3-kinase (PI3K) pathway. In melanoma cells lacking PTEN, signal transducer and activator of transcription 3 activates the transcription of immunosuppressive cytokines in a PI3K-dependent manner. Furthermore, conditioned media from PTEN-deficient, patient-derived short-term melanoma cultures and established melanoma cell lines blocked the production of the interleukin-12 (IL-12) in human monocyte-derived dendritic cells. Inhibition of IL-12 production was rescued by restoring PTEN or using neutralizing antibodies against the immunosuppressive cytokines. Furthermore, we report that PTEN, as an alternative mechanism to promote the host immune response against cancer cells, represses the expression of programmed cell death 1 ligand, a known repressor of the host immune response. Finally, to establish the clinical significance of our results, we analyzed malignant melanoma patient samples with or without brisk host responses. These analyses confirmed that PTEN loss is associated with a higher percentage of malignant melanoma samples with non-brisk host responses compared with samples with brisk host responses. Collectively, these results establish that PTEN functions as a melanoma tumor suppressor in part by regulating the host immune response against melanoma cells and highlight the importance of assessing PTEN status before recruiting melanoma patients for immunotherapies.

Identification of trans-sialidases as a common mediator of endothelial cell activation by African trypanosomes

Understanding African Trypanosomiasis (AT) host-pathogen interaction is the key to an "anti-disease vaccine", a novel strategy to control AT. Here we provide a better insight into this poorly described interaction by characterizing the activation of a panel of endothelial cells by bloodstream forms of four African trypanosome species, known to interact with host endothelium. T. congolense, T. vivax, and T. b. gambiense activated the endothelial NF-κB pathway, but interestingly, not T. b. brucei. The parasitic TS (trans-sialidases) mediated this NF-κB activation, remarkably via their lectin-like domain and induced production of pro-inflammatory molecules not only in vitro but also in vivo, suggesting a considerable impact on pathogenesis. For the first time, TS activity was identified in T. b. gambiense BSF which distinguishes it from the subspecies T. b. brucei. The corresponding TS were characterized and shown to activate endothelial cells, suggesting that TS represent a common mediator of endothelium activation among trypanosome species with divergent physiopathologies.

KPNB1, XPO7 and IPO8 mediate the translocation ofNF-κB/p65 into the nucleus

NF-κB/p65 is retained in the cytoplasm until it is activated in response to stress. Nuclear import of p65 is regulated by importin α in a nuclear localization signal (NLS)-dependent manner. However, the role of importin β family members in the nuclear translocation of p65 is largely unclear. In this study, using high-content siRNA screening, we identified three of 17 importin β family members that are involved in the nuclear import of p65. Our data showed that knockdown of KPNB1, XPO7 and IPO8 reduced the amount of nuclear p65 following tumor necrosis factor-α (TNF-α) stimulation, resulting in lower NF-κB activity. KPNB1 was the major importin β receptor for p65 import, and this import was dependent on the NLS of p65. However, NLS-mutated p65 still entered the nucleus and bound to XPO7 and IPO8. Interestingly, among the six members of the importin α family, KPNA2 was most important for p65 import. Taken together, our results show that the import of p65 mainly relies on the canonical KPNA2/KPNB1 pathway; however, p65 is also imported by an alternative pathway that is independent of its NLS. Redundant importin receptors are likely to maintain the important function of p65 according to need.

The complexity of NF-κB signaling in inflammation and cancer

The NF-κB family of transcription factors has an essential role in inflammation and innate immunity. Furthermore, NF-κB is increasingly recognized as a crucial player in many steps of cancer initiation and progression. During these latter processes NF-κB cooperates with multiple other signaling molecules and pathways. Prominent nodes of crosstalk are mediated by other transcription factors such as STAT3 and p53 or the ETS related gene ERG. These transcription factors either directly interact with NF-κB subunits or affect NF-κB target genes. Crosstalk can also occur through different kinases, such as GSK3-β, p38, or PI3K, which modulate NF-κB transcriptional activity or affect upstream signaling pathways. Other classes of molecules that act as nodes of crosstalk are reactive oxygen species and miRNAs. In this review, we provide an overview of the most relevant modes of crosstalk and cooperativity between NF-κB and other signaling molecules during inflammation and cancer.

Kupffer cell stimulation in the isolated perfused rat liver triggers nuclear factor-κB DNA binding activity

Activation of transcription factor NF-kappaB (electrophoretic mobility shift assay) was investigated in the isolated perfused rat liver infused with 0.5 mg of colloidal carbon/ml for 5-20 min, in relation to carbon phagocytosis and carbon-induced O(2) consumption. Experiments were carried out in control rats and in animals treated with the Kupffer cell inactivator gadolinium chloride (GdCl(3)). Carbon uptake and carbon-induced O(2) consumption by perfused livers exhibited a linear increase as a function of the perfusion time, leading to constant O(2)/carbon uptake ratios, with low (0.04-0.15%) fractional sinusoidal lactate dehydrogenase release in the 5-20 min perfusion time studied. NF-kappaB DNA binding activity showed a maximal enhancement at 10 min of carbon perfusion, a response that was sustained at a lower extent at 15 and 20 min of carbon stimulation. After 10 min of carbon infusion, NF-kappaB activation, carbon-induced O(2) consumption, and carbon uptake were diminished by 84%, 94%, and 64% by GdCl(3) treatment (P < 0.05), respectively. It is concluded that the respiratory burst of carbon-stimulated Kupffer cells triggers NF-kappaB activation in the isolated perfused liver, a response that is elicited under optimal conditions of Kupffer cell function and organ viability.

Effect of chelerythrine against endotoxic shock in mice and its modulation of inflammatory mediators in peritoneal macrophages through the modulation of mitogen-activated protein kinase (MAPK) pathway

A quaternary benzo [c] alkaloid chelerythrine (CHE), which is a traditional herbal prescription, has been used for the treatment of various inflammatory diseases. To gain insight into the anti-inflammatory effect and molecular mechanisms underlying the anti-inflammatory activity of CHE, we used experimentally induced mice endotoxic shock moled and lipopolysaccharide (LPS)-induced murine peritoneal macrophages to examine the anti-inflammatory function of CHE. CHE displayed significant anti-inflammatory effects in experimentally induced mice endotoxic shock model in vivo through inhibition of LPS-induced tumor necrosis factor-alpha (TNF-α) level and nitric oxide (NO) production in serum. Additionally, our data suggest that CHE treatment inhibits LPS-induced TNF-α level and NO production in LPS-induced murine peritoneal macrophages through selective inhibition of p38 mitogen-activated protein kinase (MAPK) and extracellular signal-regulated protein kinases 1 and 2 (ERK1/2) activation. Moreover, the effects of CHE on NO and cytokine TNF-α production can possibly be explained by the role of p38 MAPK and ERK1/2 in the regulation of inflammatory mediators expression.

Michael F, Cox AD, Moraes TF, Gray-Owen SD. Neisseria gonorrhoeae-derived heptose elicits an innate immune response and drives HIV-1 expression

Clinical and epidemiological synergy exists between the globally important sexually transmitted infections, gonorrhea and HIV. Neisseria gonorrhoeae, which causes gonorrhea, is particularly adept at driving HIV-1 expression, but the molecular determinants of this relationship remain undefined. N. gonorrhoeae liberates a soluble factor that potently induces expression from the HIV-1 LTR in coinfected cluster of differentiation 4-positive (CD4(+)) T lymphocytes, but this factor is not a previously described innate effector. A genome-wide mutagenesis approach was undertaken to reveal which component(s) of N. gonorrhoeae induce HIV-1 expression in CD4(+) T lymphocytes. A mutation in the ADP-heptose biosynthesis gene, hldA, rendered the bacteria unable to induce HIV-1 expression. The hldA mutant has a truncated lipooligosaccharide structure, contains lipid A in its outer membrane, and remains bioactive in a TLR4 reporter-based assay but did not induce HIV-1 expression. Mass spectrometry analysis of extensively fractionated N. gonorrhoeae-derived supernatants revealed that the LTR-inducing fraction contained a compound having a mass consistent with heptose-monophosphate (HMP). Heptose is a carbohydrate common in microbes but is absent from the mammalian glycome. Although ADP-heptose biosynthesis is common among Gram-negative bacteria, and heptose is a core component of most lipopolysaccharides, N. gonorrhoeae is peculiar in that it effectively liberates HMP during growth. This N. gonorrhoeae-derived HMP activates CD4(+) T cells to invoke an NF-κB-dependent transcriptional response that drives HIV-1 expression and viral production. Our study thereby shows that heptose is a microbial-specific product that is sensed as an innate immune agonist and unveils the molecular link between N. gonorrhoeae and HIV-1.

Nitric oxide and KLF4 protein epigenetically modify class II transactivator to repress major histocompatibility complex II expression during Mycobacterium bovis bacillus Calmette-Guerin infection

Pathogenic mycobacteria employ several immune evasion strategies such as inhibition of class II transactivator (CIITA) and MHC-II expression, to survive and persist in host macrophages. However, precise roles for specific signaling components executing down-regulation of CIITA/MHC-II have not been adequately addressed. Here, we demonstrate that Mycobacterium bovis bacillus Calmette-Guérin (BCG)-mediated TLR2 signaling-induced iNOS/NO expression is obligatory for the suppression of IFN-γ-induced CIITA/MHC-II functions. Significantly, NOTCH/PKC/MAPK-triggered signaling cross-talk was found critical for iNOS/NO production. NO responsive recruitment of a bifunctional transcription factor, KLF4, to the promoter of CIITA during M. bovis BCG infection of macrophages was essential to orchestrate the epigenetic modifications mediated by histone methyltransferase EZH2 or miR-150 and thus calibrate CIITA/MHC-II expression. NO-dependent KLF4 regulated the processing and presentation of ovalbumin by infected macrophages to reactive T cells. Altogether, our study delineates a novel role for iNOS/NO/KLF4 in dictating the mycobacterial capacity to inhibit CIITA/MHC-II-mediated antigen presentation by infected macrophages and thereby elude immune surveillance.

Glutamine on Intestinal Inflammation: A Mechanistic Perspective

Intestinal inflammation is associated with various pathological diseases, such as gastritis from Helicobacter pylori infection, Crohn's and colitis in inflammatory bowel disease, and colorectal cancer. Thus, treatment with anti-inflammatory substances in these inflammation-associated diseases is critical. Increasingly compelling evidence indicates that glutamine is an anti-inflammatory compound candidate because it can influence the long-term outcome of the inflammatory diseases with in a low-risk way. However, before recommending its use in clinical practice, it is important to elucidate the molecular mechanism by which glutamine exerts its roles in modulating intestinal inflammation. In this study, we review the current knowledge on the detailed regulation pathway used by glutamine in its proinflammatory regulation, with a special emphasis on intestinal inflammation. These regulation pathways include nuclear factor kappa B (NF-κB), signal transducer and activator of transcription (STAT), mitogen-activated protein kinases (MAPK), phosphoinositide-3-kinases (PI3K)/PI3K-protein kinase B (Akt), activating protein-1 (AP-1), nitric oxide synthases (NOS)-nitric oxide (NO), peroxisome proliferator-activated receptor-Γ (PPARγ), heat shock factor-1 (HSF-1)- heat shock proteins (HSP) and glutathione (GSH) - reactive oxygen species (ROS). Although some regulatory pathways, such as PI3K/PI3K-Akt, GSH-ROS and AP-1, need to be further investigated, this review provides useful information to utilize glutamine as an immunonutritional or pharmaconutritional drug, not only for inflammation-associated diseases in the intestine, but also possibly for other inflammatory-associated diseases, i.e. arthritis, asthma, type 2 diabetes, etc.

Vascular endothelial growth factor induces growth of uterine cervix and immune cell recruitment in mice

Knowledge of uterine cervical epithelial biology and factors that influence its events may be critical in understanding the process of cervical remodeling (CR). Here, we examine the impact of exogenous vascular endothelial growth factor (VEGF) on uterine cervical epithelial growth in mice (nonpregnant and pregnant) treated with VEGF agents (recombinant and inhibitor) using a variety of morphological and molecular techniques. Exogenous VEGF altered various uterine cervical epithelial cellular events, including marked induction of growth, edema, increase in inter-epithelial paracellular space, and recruitment of immune cells to the outer surface of epithelial cells (cervical lumen). We conclude that VEGF induces multiple alterations in the uterine cervical epithelial tissues that may play a role in local immune surveillance and uterine cervical growth during CR.

Epidermal growth factor protects squamous cell carcinoma against cisplatin-induced cytotoxicity through increased interleukin-1β expression

The expression of cytokines, such as IL-1β, and the activation of the epidermal growth factor receptor (EGFR) are crucial regulators in the process of carcinogenesis. The correlation between growth factor and activated cytokine signals in the control of tumor development is a critical issue to be clarified. In our study, we found that the IL-1β gene and protein expression were induced by EGF in squamous cell carcinoma. To clarify the mechanism involved in EGF-regulated IL-1β expression, we examined the transcriptional activity and mRNA stability of IL-1β in EGF-treated cells. We found that EGF induced the expression of IL-1β and was mediated through transcriptional activation, but not through mRNA stability. The involvement of Akt and NF-κB signaling pathways in the EGF-induced IL-1β gene expression was confirmed by knockdown of RelA and Akt in cells or treating cells with Akt and NF-κB inhibitors, LY294002 and parthenolide, respectively. The expression of dominant negative IκB also repressed the activation of NF-κB and inhibited EGF-induced IL-1β expression. Using immunofluorescence staining assay, the EGF-stimulated nuclear translocation of NF-κB (p65) was inhibited by pre-treating cells with LY294002 and parthenolide. Furthermore, EGF increased the binding of NF-κB to the NF-κB binding site of the IL-1β promoter through the activation of the Akt/NF-κB pathway, which resulted in activating IL-1β promoter activity. The expression and secretion of IL-1β induced by EGF considerably reduced chemotherapeutic drug cisplatin-induced cell death. These results showed that EGF enhanced the expression of IL-1β, which was mediated by the Akt/NF-κB pathway. The activation of EGF signaling and increase of IL-1β contributed to chemotherapeutic resistance of cancer cells, suggesting that the expression of IL-1β may be used as a biomarker to evaluate successful cancer treatment.

Hepatitis C virus mediated changes in miRNA-449a modulates inflammatory biomarker YKL40 through components of the NOTCH signaling pathway

Liver disease due to hepatitis C virus (HCV) infection is an important health problem worldwide. HCV induced changes in microRNAs (miRNA) are shown to mediate inflammation leading to liver fibrosis. Gene expression analyses identified dysregulation of miRNA-449a in HCV patients but not in alcoholic and non-alcoholic liver diseases. By sequence analysis of the promoter for YKL40, an inflammatory marker upregulated in patients with chronic liver diseases with fibrosis, adjacent binding sites for nuclear factor of Kappa B/P65 and CCAAT/enhancer-binding protein alpha (CEBPα) were identified. P65 interacted with CEBPα to co-operatively activate YKL40 expression through sequence specific DNA binding. In vitro analysis demonstrated that tumor necrosis factor alpha (TNFα) mediated YKL40 expression is regulated by miRNA-449a and its target NOTCH1 in human hepatocytes.NOTCH1 facilitated nuclear localization of P65 in response to TNFα. Further, HCV patients demonstrated upregulation of NOTCH1 along with downregulation of miRNA-449a. Taken together it is demonstrated that miRNA-449a plays an important role in modulating expression of YKL40 through targeting the components of the NOTCH signaling pathway following HCV infection. Therefore, defining transcriptional regulatory mechanisms which control inflammatory responses and fibrosis will be important towards developing strategies to prevent hepatic fibrosis especially following HCV recurrence in liver transplant recipients.

Functional characterization of TNF-α in grass carp head kidney leukocytes: induction and involvement in the regulation of NF-κB signaling

Tumor necrosis factor-alpha (TNF-α) is a potent regulatory cytokine, which serves as a key mediator of inflammation, immunity and apoptosis in mammals. Identification, expression and regulatory effects of TNF-α have been reported in various fish species, showing the structural and functional similarity or discrepancy between each other. In this study, TNF-α was identified from grass carp (Ctenopharyngodon idella) and the deduced grass carp TNF-α (gcTNF-α) protein possessed the TNF family signature motifs, a protease cleavage site, a transmembrane domain and two conserved cysteine residues. Further studies showed that gcTNF-α expression was induced with a rapid kinetics by immune challenge in vitro and in vivo. To characterize the function of gcTNF-α, recombinant gcTNF-α (rgcTNF-α) was prepared by using the Escherichia coli expression system. It was shown to enhance the mRNA expression of gcTNF-α and gcIL-1β in head kidney leukocytes (HKLs), confirming the biological activity of rgcTNF-α. In the same model, NF-κB inhibitor (PDTC) was able to attenuate rgcTNF-α-induced gcTNF-α mRNA expression, implying the involvement of NF-κB pathway in fish TNF-α action. This notion was reinforced by the finding that rgcTNF-α could induce the phosphorylation of IκBα in a time-dependent oscillation in HKLs, indicating a dynamical variation of NF-κB activity as seen in mammals. In addition, rgcTNF-α could up-regulate the expression of two TNF receptor-associated factors (TRAF), TRAF1 and TRAF2, in a time- and dose-dependent manner, suggesting that gcTNF-α may function as a regulator of fish NF-κB pathway. These results for the first time reveal the link of gcTNF-α to the NF-κB pathway and provide a better understanding of TNF-α signaling in teleost immunity.

Potential of in vitro reconstituted 3D human airway epithelia (MucilAir™) to assess respiratory sensitizers

Respiratory sensitizers are considered as substances of higher risk, at the same level as carcinogens, mutagens and toxic chemicals for reproduction. Presently, there is no validated assay for identifying the respiratory sensitizers. Based on a fully differentiated and functional in vitro cell model of the human airway epithelium, MucilAir™, we attempt to develop such assay. To this end, we invented a novel method, using Dextran as carrier, for applying the water insoluble chemicals to the apical surface of the airway epithelia. Using the Dextran carrier method, we successfully tested some reference chemical compounds known to cause respiratory sensitisation in human beings, including MDI, TMA and HCPt. Interestingly, these chemical sensitizers differentially up-regulated the releases of certain cytokines and chemokines involved in allergic responses. We believe that based on MucilAir™ an in vitro assay could be developed for identification and characterization of the respiratory sensitizers.

Enterotoxigenic Escherichia coli prevents host NF-κB activation by targeting IκBα polyubiquitination

The NF-κB pathway regulates innate immune responses to infection. NF-κB is activated after pathogen-associated molecular patterns are detected, leading to the induction of proinflammatory host responses. As a countermeasure, bacterial pathogens have evolved mechanisms to subvert NF-κB signaling. Enterotoxigenic Escherichia coli (ETEC) causes diarrheal disease and significant morbidity and mortality for humans in developing nations. The extent to which this important pathogen subverts innate immune responses by directly targeting the NF-κB pathway is an understudied topic. Here we report that ETEC secretes a heat-stable, proteinaceous factor that blocks NF-κB signaling normally induced by tumor necrosis factor (TNF), interleukin-1β, and flagellin. Pretreating intestinal epithelial cells with ETEC supernatant significantly blocked the degradation of the NF-κB inhibitor IκBα without affecting IκBα phosphorylation. Data from immunoprecipitation experiments suggest that the ETEC factor functions by preventing IκBα polyubiquitination. Inhibiting clathrin function blocked the activity of the secreted ETEC factor, suggesting that this yet-uncharacterized activity may utilize clathrin-dependent endocytosis to enter host cells. These data suggest that ETEC evades the host innate immune response by directly modulating NF-κB signaling.

Chromatinized Protein Kinase C-θ: Can It Escape the Clutches of NF-κB?

We recently provided the first description of a nuclear mechanism used by Protein Kinase C-theta (PKC-θ) to mediate T cell gene expression. In this mode, PKC-θ tethers to chromatin to form an active nuclear complex by interacting with proteins including RNA polymerase II, the histone kinase MSK-1, the demethylase LSD1, and the adaptor molecule 14-3-3ζ at regulatory regions of inducible immune response genes. Moreover, our genome-wide analysis identified many novel PKC-θ target genes and microRNAs implicated in T cell development, differentiation, apoptosis, and proliferation. We have expanded our ChIP-on-chip analysis and have now identified a transcription factor motif containing NF-κB binding sites that may facilitate recruitment of PKC-θ to chromatin at coding genes. Furthermore, NF-κB association with chromatin appears to be a prerequisite for the assembly of the PKC-θ active complex. In contrast, a distinct NF-κB-containing module appears to operate at PKC-θ targeted microRNA genes, and here NF-κB negatively regulates microRNA gene transcription. Our efforts are also focusing on distinguishing between the nuclear and cytoplasmic functions of PKCs to ascertain how these kinases may synergize their roles as both cytoplasmic signaling proteins and their functions on the chromatin template, together enabling rapid induction of eukaryotic genes. We have identified an alternative sequence within PKC-θ that appears to be important for nuclear translocation of this kinase. Understanding the molecular mechanisms used by signal transduction kinases to elicit specific and distinct transcriptional programs in T cells will enable scientists to refine current therapeutic strategies for autoimmune diseases and cancer.

The role of NF-κB activation during protection against Leishmania infection

Members of the nuclear factor-κB (NF-κB) family of transcription factors regulate a variety of molecules involved in host defense against pathogens. A prominent role of NF-κB in innate and adoptive immunity is based on the regulation of inducible transcription of various genes whose products are essential components of the immune response such as cytokines, chemokines, and adhesion molecules. Since the discovery of the five members of the NF-κB transcription factor family, RelA, c-Rel, RelB, p50 and p52, considerable progress has been made toward better understanding how the different NF-κB homo- and heterodimers regulate such distinct subsets of target genes. All of the NF-κB molecules are activated by various infectious stimuli; however, there are still open questions related to the selective functions of individual NF-κB family members during a coordinated immune response to infection. Diverse parasites such as Toxoplasma gondii, Leishmania donovani, Leishmania major, and Trichuris muris have been reported to activate NF-κB signaling cascades, and a number of distinct parasite-derived molecules may actively interfere with the pathways that lead to NF-κB activation. In this review, we provide an overview on the role of NF-κB activation in leishmaniasis and discuss how individual NF-κB family members might perform their distinct and non-overlapping functions in the regulation of protective immunity to Leishmania infection.

Association between the SUMO4 M55V (A163G) polymorphism and susceptibility to type 1 diabetes: a meta-analysis

OBJECTIVE

The aim of this study was to determine whether the SUMO4 M55V (A163G) polymorphism confers susceptibility to type 1 diabetes (T1D).

METHODS

A meta-analysis was conducted on the association between the SUMO4 M55V polymorphism and T1D using; (1) allelic contrast (G vs. A), and the (2) recessive (GG vs. GA+AA), (3) dominant (GG+GA vs. AA), and (4) additive models (GG vs. AA).

RESULTS

Thirteen separate studies were considered in the meta-analysis, which in total included 5915 patients and 6660 controls, and five European and eight Asian sample populations. Europeans had a higher prevalence of the G allele than Asians (50.4% vs. 30.2%). Meta-analysis of the SUMO4 M55V polymorphism showed an association between T1D and the SUMO4 G allele in all study subjects (OR=1.236, 95% CI=1.112-1.373, p=7.9×10(-6)), and stratification by ethnicity indicated a highly significant association between the SUMO4 G allele and T1D in Asians (OR=1.303, 95% CI=1.169-1.452, p=1.78×10(-7)) and a marginal association with T1D in Europeans (OR=1.177, 95% CI=1.000-1.386, p=0.050). Furthermore, significant associations were found between the SUMO4 M55V polymorphism and T1D and all study subjects, Europeans, and Asians using the dominant model (OR=1.239, 95% CI=1.144-1.342, p=1.4×10(-8); OR=1.156, 95% CI=1.051-1.271, p=0.003; OR=1.461, 95% CI=1.262-1.691, p=3.8×10(-8), respectively).

CONCLUSIONS

This meta-analysis indicates that the SUMO4 M55V polymorphism confers susceptibility to T1D in Asians and Europeans.

Involvement of interleukin-1β mediated nuclear factor κB signalling pathways to down-regulate prostate-specific antigen and cell proliferation in LNCaP prostate cancer cells

Involvement of NF-κB (nuclear factor κB) mediated by IL-1β (interleukin-1β) on cell proliferation and PSA (prostate-specific antigen) production of LNCaP prostate cell lines and the possible cross-talk with Akt (also known as protein kinase B) signalling pathway has been investigated. NF-κB and Akt were analysed by Western blotting from LNCaP cells treated by IL-1β before proliferation and PSA production were measured. IL-1β inhibited proliferation and decreased PSA production. The Akt pathway was not sensitive, whereas NF-κB phosphorylation occurred as a result of treatment. PSA production and proliferation of LNCaP cells were down-regulated by NF-κB mediated by IL-1β promoting anti-apoptotic signalling and co-suppressor factors of PSA expression. IL-1β through NF-κB activation provides a rationale for therapeutic approaches in the anticancer treatment of prostate.

Regulation of NF-κB by ubiquitination and degradation of the IκBs

The nuclear factor-κB (NF-κB) signaling pathway is a busy ground for the action of the ubiquitin-proteasome system; many of the signaling steps are coordinated by protein ubiquitination. The end point of this pathway is to induce transcription, and to this end, there is a need to overcome a major obstacle, a set of inhibitors (IκBs) that bind NF-κB and prohibit either the nuclear entry or the DNA binding of the transcription factor. Two major signaling steps are required for the elimination of the inhibitors: activation of the IκB kinase (IKK) and degradation of the phosphorylated inhibitors. IKK activation and IκB degradation involve different ubiquitination modes; the latter is mediated by a specific E3 ubiquitin ligase SCF(β-TrCP) . The F-box component of this E3, β-TrCP, recognizes the IκB degron formed following phosphorylation by IKK and thus couples IκB phosphorylation to ubiquitination. SCF(β-TrCP) -mediated IκB ubiquitination and degradation is a very efficient process, often resulting in complete degradation of the key inhibitor IκBα within a few minutes of cell stimulation. In vivo ablation of β-TrCP results in accumulation of all the IκBs and complete NF-κB inhibition. As many details of IκB-β-TrCP interaction have been worked out, the development of β-TrCP inhibitors might be a feasible therapeutic approach for NF-κB-associated human disease. However, we may still need to advance our understanding of the mechanism of IκB degradation as well as of the diverse functions of β-TrCP in vivo.

The interactions between pristine graphene and macrophages and the production of cytokines/chemokines via TLR- and NF-κB-related signaling pathways

Graphene may have attractive properties for some biomedical applications, but its potential adverse biological effects, in particular, possible modulation of immune responses, require further investigation. Macrophages are one of the most important effector cells of the innate immune system, and play pivotal roles in the response to graphene exposure. We have previously reported that exposure of macrophages to high concentrations of graphene triggers cell death via MAPK- and TGF-related pathways. However, little is known about the influence of exposure to low concentrations of graphene on the function of macrophages. In the present investigation, we demonstrate the biological effects of sub-cytotoxic concentrations of commercial pristine graphene on both primary murine macrophages and immortalized macrophages. Graphene significantly stimulates the secretion of Th1/Th2 cytokines including IL-1α, IL-6, IL-10, TNF-α and GM-CSF as well as chemokines such as MCP-1, MIP-1α, MIP-1β and RANTES, probably by activating TLR-mediated and NF-κB-dependent transcription. Furthermore, these graphene-induced factors alter the morphology of naïve macrophages by remodeling their actin assembly, decreasing their ability to adhere to the extracellular matrix, and attenuating their phagocytosis. This negative feedback of the immune response of macrophages by graphene-induced factors may play an important role in the prevention of their over-activation after graphene exposure. These findings shed light on the interaction of graphene and macrophages in vitro. Further research is needed to systematically assess the biological responses of graphene, both to improve its safety and to contribute to the design of new biological applications.

The involvement of heat shock protein and cytochrome P450 genes in response to UV-A exposure in the beetle Tribolium castaneum

Sunlight is an important environmental factor that affects all living organisms on Earth. Ultraviolet A (UV-A) is one of the many frequency bands found in sunlight. Many animals use UV-A to attain visual cues, for example, in foraging and mate selection. However, UV-A can also induce damage, such as oxidative stress, DNA lesions and apoptosis. In the present study, we investigated the effects of UV-A on the survival, fecundity and expression profiles of several stress-responsive genes belonging to the heat shock protein (Hsp) and the cytochrome CYP6BQ families from the adult red flour beetle, Tribolium castaneum (Herbst) (Coleoptera: Tenebrionidae). The results showed that short-term UV-A exposure (365 nm, <4h) did not influence the survival or fecundity of the beetles; however, Hsp27, Hsp68, Hsp83, CYP6BQ4 and CYP6BQ8 mRNA levels significantly increased during the first 2h of UV-A exposure. Among them, Hsp68 was the most highly up-regulated, increasing by 8.9-fold. These results indicate that these genes may participate in the defense against harmful UV-A radiation. In addition, we investigated the potential transcription factor binding motifs (TFBMs) in the promoter sequences of genes induced in similar pattern from the Hsp and P450 gene families; the results indicated that, these motifs are highly homologous to environmental stress transcription factor binding sites in mammals. Our experiments revealed that UV-A irradiation could influence the expression profile of stress-responsive genes, such as Hsps and P450s, which have universal TFBMs, and that these genes may be involved in reducing the ecological challenges posed by irradiation.

Porcine reproductive and respiratory syndrome virus nonstructural protein 2 contributes to NF-κB activation

Background

Nuclear factor-kappaB (NF-κB) is an inducible transcription factor that plays a key role in inflammation and immune responses, as well as in the regulation of cell proliferation and survival. Previous studies by our group and others have demonstrated that porcine reproductive and respiratory syndrome virus (PRRSV) infection could activate NF-κB in MARC-145 cells and alveolar macrophages. The nucleocapsid (N) protein was identified as an NF-κB activator among the structural proteins encoded by PRRSV; however, it remains unclear whether the nonstructural proteins (Nsps) contribute to NF-κB activation. In this study, we identified which Nsps can activate NF-κB and investigated the potential mechanism(s) by which they act.

Results

By screening the individual Nsps of PRRSV strain WUH3, Nsp2 exhibited great potential to activate NF-κB in MARC-145 and HeLa cells. Overexpression of Nsp2 induced IκBα degradation and nuclear translocation of NF-κB. Furthermore, Nsp2 also induced NF-κB-dependent inflammatory factors, including interleukin (IL)-6, IL-8, COX-2, and RANTES. Compared with the Nsp2 of the classical PRRSV strain, the Nsp2 of highly pathogenic PRRSV (HP-PRRSV) strains that possess a 30 amino acid (aa) deletion in Nsp2 displayed greater NF-κB activation. However, the 30-aa deletion was demonstrated to not be associated with NF-κB activation. Further functional domain analyses revealed that the hypervariable region (HV) of Nsp2 was essential for NF-κB activation.

Conclusions

Taken together, these data indicate that PRRSV Nsp2 is a multifunctional protein participating in the modulation of host inflammatory response, which suggests an important role of Nsp2 in pathogenesis and disease outcomes.

Differential regulation of primary and memory CD8 T cell immune responses by diacylglycerol kinases

The manipulation of signals downstream of the TCR can have profound consequences for T cell development, function, and homeostasis. Diacylglycerol (DAG) produced after TCR stimulation functions as a secondary messenger and mediates the signaling to Ras-MEK-Erk and NF-κB pathways in T cells. DAG kinases (DGKs) convert DAG into phosphatidic acid, resulting in termination of DAG signaling. In this study, we demonstrate that DAG metabolism by DGKs can serve a crucial function in viral clearance upon lymphocytic choriomeningitis virus infection. Ag-specific CD8(+) T cells from DGKα(-/-) and DGKζ(-/-) mice show enhanced expansion and increased cytokine production after lymphocytic choriomeningitis virus infection, yet DGK-deficient memory CD8(+) T cells exhibit impaired expansion after rechallenge. Thus, DGK activity plays opposing roles in the expansion of CD8(+) T cells during the primary and memory phases of the immune response, whereas consistently inhibiting antiviral cytokine production.

Listeria monocytogenes infection in macrophages induces vacuolar-dependent host miRNA response

Listeria monocytogenes is a Gram-positive facultative intracellular pathogen, causing serious illness in immunocompromised individuals and pregnant women. Upon detection by macrophages, which are key players of the innate immune response against infection, L. monocytogenes induces specific host cell responses which need to be tightly controlled at transcriptional and post-transcriptional levels. Here, we ask whether and how host miRNAs, which represent an important mechanism of post-transcriptional regulation in a wide array of biological processes, are altered by a model pathogen upon live infection of murine bone marrow derived macrophages. We first report that L. monocytogenes subverts the host genome-wide miRNA profile of macrophages in vitro. Specifically, we show that miR-155, miR-146a, miR-125a-3p/5p and miR-149 were amongst the most significantly regulated miRNAs in infected macrophages. Strikingly, these miRNAs were highly upregulated upon infection with the Listeriolysin-deficient L. monocytogenes mutant Δhly, that cannot escape from the phagosome thus representing a vacuolar-contained infection. The vacuolar miRNA response was significantly reduced in macrophages deficient for MyD88. In addition, miR-146a and miR-125a-3p/5p were regulated at transcriptional levels upon infection, and miR-125a-3p/5p were found to be TLR2 responsive. Furthermore, miR-155 transactivation in infection was regulated by NF-κB p65, while miR-146a and miR-125a-3p/5p expression was unaffected in p65-deficient primary macrophages upon L. monocytogenes infection. Our results demonstrate that L. monocytogenes promotes significant changes in the miRNA expression profile in macrophages, and reveal a vacuolar-dependent miRNA signature, listeriolysin-independent and MyD88-dependent. These miRNAs are predicted to target immune genes and are therefore most likely involved in regulation of the macrophage innate immune response against infection at post-transcriptional levels.

NF-κB signaling in the brain of autistic subjects

Autism is a neurodevelopmental disorder characterized by problems in communication, social skills, and repetitive behavior. Recent studies suggest that apoptotic and inflammatory mechanisms may contribute to the pathogenesis of this disorder. Nuclear factor-κB (NF-κB) is an important gene transcriptional factor involved in the mediation of inflammation and apoptosis. This study examined the activities of the NF-κB signaling pathway in the brain of autistic subjects and their age-matched controls. The NF-κB activation is also determined in the brain of BTBR mice, which is a promising animal model for study of pathogenic mechanisms responsible for autism. Our results showed that the level of IKKα kinase, which phosphorylates the inhibitory subunit IκBα, is significantly increased in the cerebellum of autistic subjects. However, the expression and phosphorylation of IκBα are not altered. In addition, our results demonstrated that the expression of NF-κB (p65), and the phosphorylation/activation of NF-κB (p65) at Ser536 are not significantly changed in the cerebellum and cortex of both autistic subjects and BTBR mice. Our findings suggest that the NF-κB signaling pathway is not disregulated in the brain of autistic subjects and thus may not be significantly involved in the processes of abnormal inflammatory responses suggested in autistic brain.

Blocking TREM-1 signaling prolongs survival of mice with Pseudomonas aeruginosa induced sepsis

TREM-1 is a recently discovered receptor expressed on neutrophils and macrophages. Blocking of TREM-1 signaling improves the survival of mice with bacterial sepsis. However, the precise mechanism by which TREM-1 modulates the inflammatory responses is poorly defined. In this study, we investigated the role of TREM-1 in Pseudomonas aeruginosa-induced peritonitis. Our results showed that TREM-1 was not expressed on lymphocytes but emerged on the cell surface of neutrophils and peritoneal macrophages. Blockade of TREM-1 signaling significantly prolonged survival of mice with P. aeruginosa-induced peritonitis. However, blocking TREM-1 signaling had no effect on macrophage phagocytosis in vitro. Interestingly, the expression of the costimulatory molecules CD40 and CD86 on macrophages was significantly decreased after blocking TREM-1 signaling. Furthermore, interfering with TREM-1 engagement led to significant reduction of pro-inflammatory mediators such as IL-1, TNF-α, MCP-1 and IFN-γ. Therefore, our results showed that TREM-1 could be a potential therapeutic target for bacterial sepsis.

Novel IkB kinase inhibitors for treatment of nuclear factor-kB-related diseases

INTRODUCTION

NF-kB is a key regulator of inflammation and immunity in cancer development. The IkB kinase (IKK) is a multisubunit complex containing catalytic subunits termed IKK-α, -β and -γ. It is well known that many pro-inflammatory stimuli require the IKK-β subunit for NF-kB activation.

AREAS COVERED

NF-kB affects the progression of inflammation-related diseases,such as myocardial ischemia, bronchial asthma, arthritis, cancer and other diseases. We review the characteristics and effects of these inhibitors on inflammatory and other diseases.

EXPERT OPINION

Various synthesized IKK inhibitors have been developed and they will be used clinically in the near future.

Involvement of ERK1/2/NF-κB signal transduction pathway in TF/FVIIa/PAR2-induced proliferation and migration of colon cancer cell SW620

Our previous study has demonstrated that TF/FVIIa and protease-activated receptor 2 (PAR2) are closely related to the proliferation and migration of colon cancer cell line SW620. However, the detailed signaling cascades and underlying molecular mechanisms remain unclear. This study has investigated whether extracellular signal-regulated kinase 1 and 2 (ERK1/2) and nuclear factor kappaB (NF-κB) signaling pathways are involved in the events. The results revealed that PAR2-activating peptide (PAR2-AP) or FVIIa elicited time-dependent upregulation of ERK1/2 phosphorylation in SW620 cells, and the effect of FVIIa was significantly attenuated by anti-TF antibody. PAR2-AP or FVIIa also increased NF-κB (p65/RelA) levels among cell nuclear proteins and simultaneously decreased IκB-α levels in the cytoplasmic proteins. Such effects of FVIIa can be inhibited with anti-PAR2 or anti-TF antibodies. While ERK1/2 inhibitor (U0126) intervened with the regulatory effects of PAR2-AP and FVIIa on IκB-α/NF-κB (p65/Rel) expression in the cells, NF-κB inhibitor (PDTC) partially blocked the enhancing effects of PAR2-AP and FVIIa on the proliferating and migratory ability of SW620 cells. Furthermore, the regulatory effects of PAR2-AP and FVIIa on expressions of certain proteins (IL-8, caspase-7, and TF) were also significantly abolished by PDTC. Collectively, the data in this study suggest that the interaction between FVIIa and TF induces PAR2 activation, thereby triggers the ERK1/2 and IκB-α/NF-κB signal transduction pathway to regulate the gene expression of IL-8, TF, and caspase-7, and ultimately promotes SW620 cell proliferation and migration.

Japanese encephalitis virus induces matrix metalloproteinase-9 in rat brain astrocytes via NF-κB signalling dependent on MAPKs and reactive oxygen species

BACKGROUND AND PURPOSE

Japanese encephalitis virus (JEV) is a member of the family Flaviviridae and JEV infection is a major cause of acute encephalopathy in children, which destroys cells in the CNS, including astrocytes and neurons. However, the detailed mechanisms underlying the inflammatory action of JEV are largely unclear.

EXPERIMENTAL APPROACH

The effect of JEV on the expression of matrix metalloproteinase (MMP)-9 was determined by gelatin zymography, Western blot analysis, real-time PCR and promoter assay. The involvement of the NADPH oxidase and reactive oxygen species (ROS), MAPKs, and the transcription factor NF-κB in these responses was investigated by using selective pharmacological inhibitors and transfection with appropriate siRNAs.

KEY RESULTS

JEV induced the expression of the pro-form of MMP-9 in rat brain astrocytes (RBA-1 cells). In RBA-1 cells, JEV induced MMP-9 expression and promoter activity, which was inhibited by pretreatment with inhibitors of NADPH oxidase (diphenylene iodonium chloride or apocynin), MAPKs (U0126, SB203580 or SP600125) and a ROS scavenger (N-acetylcysteine), or transfection with siRNAs of p47(phox) , ERK1, JNK2 and p38. In addition, JEV-induced MMP-9 expression was reduced by pretreatment with an inhibitor of NF-κB (helenalin) or transfection with p65 siRNA. Moreover, JEV-stimulated NF-κB activation was inhibited by pretreatment with the inhibitors of NADPH oxidase and MAPKs.

CONCLUSIONS AND IMPLICATIONS

MMP-9 expression induced by JEV infection of RBA-1 cells was mediated through the generation of ROS and activation of p42/p44 MAPK, p38 MAPK and JNK1/2, leading to NF-κB activation.

Emodin suppresses lipopolysaccharide-induced pro-inflammatory responses and NF-κB activation by disrupting lipid rafts in CD14-negative endothelial cells

BACKGROUND AND PURPOSE

Emodin [1,3,8-trihydroxy-6-methylanthraquinone] has been reported to exhibit vascular anti-inflammatory properties. However, the corresponding mechanisms are not well understood. The present study was designed to explore the molecular target(s) of emodin in modifying lipopolysaccharide (LPS)-associated signal transduction pathways in endothelial cells.

EXPERIMENTAL APPROACH

Cultured primary human umbilical vein endothelial cells (HUVECs; passages 3-5) were pre-incubated with emodin (1-50 µg·mL(-1) ). LPS-induced expression of pro-inflammatory cytokines [interleukin (IL)-1β, IL-6] and chemokines (IL-8; CCL2/MCP-1) were determined by reverse transcription-PCR and elisa. Nuclear factor-κB (NF-κB) activation, inhibitor of κB (IκB)α degradation and Toll-like receptor-4 (TLR-4) were detected by immunocytochemistry and Western blotting. Cholesterol depletion [by methyl β-cyclodextrin (MBCD), a specific cholesterol binding agent] and cholesterol replenishment were further used to investigate the roles of lipid rafts in activation of HUVECs.

KEY RESULTS

Emodin inhibited, concentration-dependently, the expression of LPS-induced pro-inflammatory cytokines (IL-1β, IL-6) and chemokines (IL-8, CCL2) and, in parallel, inhibited NF-κB activation and IκBα degradation in HUVECs. However, emodin did not inhibit the NF-κB activation and IκBα degradation induced by IL-1β. The cholesterol binding agent, MBCD, inhibited LPS-induced NF-κB activation in passaged HUVECs [which also lack the LPS receptor, membrane CD14 (mCD14)], showing that lipid rafts played a key role in LPS signalling in mCD14-negative HUVECs. Moreover, emodin disrupted the formation of lipid rafts in cell membranes by depleting cholesterol.

CONCLUSIONS AND IMPLICATIONS

Lipid rafts were crucial in facilitating inflammatory responses of mCD14-negative HUVECs to LPS. Emodin disrupted lipid rafts through depleting cholesterol and, consequently, inhibited inflammatory responses in endothelial cells.

14-Deoxyandrographolide desensitizes hepatocytes to tumour necrosis factor-alpha-induced apoptosis through calcium-dependent tumour necrosis factor receptor superfamily member 1A release via the NO/cGMP pathway

BACKGROUND AND PURPOSE

Andrographis paniculata (AP) has been found to display hepatoprotective effect, although the mechanism of action of the active compounds of AP in this context still remains unclear. Here, we evaluated the hepatoprotective efficacy of 14-deoxyandrographolide (14-DAG), a bioactive compound of AP, particularly its role in desensitization of hepatocytes to tumour necrosis factor-alpha (TNF-alpha)-induced signalling of apoptosis.

EXPERIMENTAL APPROACH

TNF-alpha-mediated ligand receptor interaction in hepatocytes in the presence of 14-DAG was studied in vitro in primary hepatocyte cultures, with the help of co-immunoprecipitation, confocal microscopy and FACS analysis. Events associated with 14-DAG-induced TNFRSF1A release from hepatocytes were determined using immunoblotting, biochemical assay and fluorimetric studies. Pulse-chase experiments with radiolabelled TNF-alpha and detection of apoptotic nuclei by terminal transferase-mediated dUTP nick-end labelling were performed under in vivo conditions.

KEY RESULTS

14-DAG down-regulated the formation of death-inducing signalling complex, resulting in desensitization of hepatocytes to TNF-alpha-induced apoptosis. Pretreatment of hepatocytes with 14-DAG accentuated microsomal Ca-ATPase activity through induction of NO/cGMP pathway. This resulted in enhanced calcium influx into microsomal lumen with the formation of TNFRSF1A-ARTS-1-NUCB2 complex in cellular vesicles. It was followed by the release of full-length 55 kDa TNFRSF1A and a reduction in the number of cell surface TNFRSF1A, which eventually caused diminution of TNF-alpha signal in hepatocytes.

CONCLUSION AND IMPLICATION

Taken together, the results demonstrate for the first time that 14-DAG desensitizes hepatocytes to TNF-alpha-mediated apoptosis through the release of TNFRSF1A. This can be used as a strategy against cytokine-mediated hepatocyte apoptosis in liver dysfunctions.

Nonstructural protein 1α subunit-based inhibition of NF-κB activation and suppression of interferon-β production by porcine reproductive and respiratory syndrome virus

Induction of type I interferon (IFN-α/β) is an early antiviral response of the host, and porcine reproductive and respiratory syndrome virus (PRRSV) has been reported to downregulate the IFN response during infection in cells and pigs. We report that the PRRSV nonstructural protein 1α (Nsp1α) subunit of Nsp1 is a nuclear-cytoplasmic protein distributed to the nucleus and contains a strong suppressive activity for IFN-β production that is mediated through the retinoic acid-inducible gene I (RIG-I) signaling pathway. Nsp1α suppressed the activation of nuclear factor (NF)-κB when stimulated with dsRNA or tumor necrosis factor (TNF)-α, and NF-κB suppression was RIG-I-dependent. The suppression of NF-κB activation was associated with the poor production of IFN-β during PRRSV infection. The C-terminal 14 amino acids of the Nsp1α subunit were critical in maintaining immunosuppressive activity of Nsp1α for both IFN-β and NF-κB, suggesting that the newly identified zinc finger configuration comprising of Met180 may be crucial for inhibitory activities. Nsp1α inhibited IκB phosphorylation and as a consequence NF-κB translocation to the nucleus was blocked, leading to the inhibition of NF-κB stimulated gene expression. Our results suggest that PRRSV Nsp1α is a multifunctional nuclear protein participating in the modulation of the host IFN system.

Ubiquitination and degradation of the inhibitors of NF-kappaB

The key step in NF-kappaB activation is the release of the NF-kappaB dimers from their inhibitory proteins, achieved via proteolysis of the IkappaBs. This irreversible signaling step constitutes a commitment to transcriptional activation. The signal is eventually terminated through nuclear expulsion of NF-kappaB, the outcome of a negative feedback loop based on IkappaBalpha transcription, synthesis, and IkappaBalpha-dependent nuclear export of NF-kappaB (Karin and Ben-Neriah 2000). Here, we review the process of signal-induced IkappaB ubiquitination and degradation by comparing the degradation of several IkappaBs and discussing the characteristics of IkappaBs' ubiquitin machinery.

The influence of donepezil and EGb 761 on the innate immunity of human leukocytes: effect on the NF-κB system

Ginkgo biloba special extract EGb 761 and donepezil are drugs used in Alzheimer therapy. The influence of donepezil and EGb 761 on two mechanisms of innate immunity, natural antiviral resistance of human leukocytes ex vivo and NF-κB activation, was studied. Correlation between the innate immunity of leukocytes and NF-κB activation was investigated. The effect of the two drugs on resistance of human leukocytes to vesicular stomatitis virus (VSV) infection was also assessed. Two groups of healthy blood donors (n=30) were distinguished: one with resistant leukocytes (n=15) and one (n=15) with leukocytes sensitive to VSV. The degree of natural resistance of human peripheral blood leukocytes (PBLs) was determined by studying the kinetics of VSV replication. NF-κB activation was assayed by immunocytochemical staining. Efficiency of donepezil and EGb 761 was determined by a special regression model. The toxicity of the preparations to PBLs and the cell lines L(929) and A(549) and their effect on the different viruses was established. Results showed that donepezil used in concentrations of 10-50 μg/ml and EGb761 of 25-100 μg/ml stimulated resistance of human leukocytes. At the same concentrations both preparations decreased activation of transcriptional factor NF-κB. Correlation between innate immunity of PBLs and NF-κB activation was observed. Comparison of the effects of these two drugs showed that EGb 761 is more effective in stimulating leukocyte resistance. Donepezil and EGb 761 regulated innate immunity of human leukocytes by stimulating resistance and modulating NF-κB activation. The natural drug was more efficient in stimulating innate antiviral immunity of human leukocytes.