Abstract: The NF-κB family of transcription factors is activated in response to many stimuli, including pro-inflammatory cytokines, environmental stresses and, in the case of B and T lymphocytes, by antigenic stimulation1,2. Bcl10 is essential for NF-κB activation by T- and B-cell receptors. T and B lymphocytes from Bcl10-deficient mice fail to activate NF-κB in response to antigen-receptor stimulation and, as a consequence, are unable to proliferate3. Bcl10 overexpression is sufficient to activate NF-κB, a process that requires the NF-κB essential modulator NEMO (also known as IKK-γ), which is the regulatory subunit of the IκB kinase complex4. However, the cellular mechanism by which Bcl10 activates the NF-κB pathway remains unclear. Here we show that Bcl10 targets NEMO for lysine-63-linked ubiquitination. Notably, a mutant form of NEMO that cannot be ubiquitinated inhibited Bcl10-induced NF-κB activation. Paracaspase and a ubiquitin-conjugating enzyme (UBC13) were both required for Bcl10-induced NEMO ubiquitination and subsequent NF-κB activation. Furthermore, short interfering RNAs that reduced the expression of paracaspase and UBC13 abrogated the effects of Bcl10. Thus, the adaptor protein Bcl10 promotes activation of NF-κB transcription factors through paracaspase- and UBC13-dependent ubiquitination of NEMO.

Abstract: Background: Many studies have shown that fish oil supplementation inhibits tumor necrosis factor-α (TNF-α) production in mice and human subjects; however, the mechanisms remain unclear. Nuclear factor-κB (NF-κB) is a transcription factor that plays an important role in controlling the expression of pro-inflammatory genes including TNF-α. Activation of NF-κB has been shown to mediate the maximal expression of TNF-α in human monocytes. NF-κB is kept in an inactive form in the cytoplasm by IκB, the inhibitory subunit of NF-κB complex. Phosphorylation and subsequent degradation of IκB lead to NF-κB activation.Objectives: The effect of eicosapentaenoic acid (EPA), a major n-3 fatty acid in fish oil, on the lipopolysaccharide (LPS)-induced expression of TNF-α and activation of NF-κB were investigated. The mechanism underlying EPA modulation of NF-κB activation was also studied.Methods: Human monocytic THP-1 cells were pre-incubated with EPA and stimulated with LPS. The levels of secreted TNF-α were determined b...

Abstract: Nuclear factor kappa B (NF-kappaB) is a transcription factor pivotal for the development of inflammation. A dysregulation of NF-kappaB has been shown to play an important role in many chronic inflammatory diseases including rheumatoid arthritis, inflammatory bowel disease and psoriasis. Although classical NF-kappaB, a heterodimer composed of the p50 and p65 subunits, has been well studied, little is known about gene regulation by other hetero- and homodimeric forms of NF-kappaB. While p65 possesses a transactivation domain, p50 does not. Indeed, p50/p50 homodimers have been shown to inhibit transcriptional activity. We have recently shown that Interleukin-10 exerts its anti-inflammatory activity in part through the inhibition of NF-kappaB by blocking IkappaB kinase activity and by inhibiting NF-kappaB already found in the nucleus. Since the inhibition of nuclear NF-kappaB could not be explained by an increase of nuclear IkappaB, we sought to further investigate the mechanisms involved in the inhibition of NF-kappaB by IL-10. We show here that IL-10 selectively induced nuclear translocation and DNA-binding of p50/p50 homodimers in human monocytic cells. TNF-alpha treatment led to a strong translocation of p65 and p50, whereas pretreatment with IL-10 followed by TNF-alpha blocked p65 translocation but did not alter the strong translocation of p50. Furthermore, macrophages of p105/p50-deficient mice exhibited a significantly decreased constitutive production of MIP-2alpha and IL-6 in comparison to wild type controls. Surprisingly, IL-10 inhibited high constitutive levels of these cytokines in wt macrophages but not in p105/p50 deficient cells. Our findings suggest that the selective induction of nuclear translocation and DNA-binding of the repressive p50/p50 homodimer is an important anti-inflammatory mechanism utilized by IL-10 to repress inflammatory gene transcription.

Abstract: In addition to marshalling immune and inflammatory responses, transcription factors of the NF-κB family control cell survival. This control is crucial to a wide range of biological processes, including B and T lymphopoiesis, adaptive immunity, oncogenesis and cancer chemoresistance. During an inflammatory response, NF-κB activation antagonizes apoptosis induced by tumor necrosis factor (TNF)-α, a protective activity that involves suppression of the Jun N-terminal kinase (JNK) cascade. This suppression can involve upregulation of the Gadd45-family member Gadd45β/Myd118, which associates with the JNK kinase MKK7/JNKK2 and blocks its catalytic activity. Upregulation of XIAP, A20 and blockers of reactive oxygen species (ROS) appear to be important additional means by which NF-κB blunts JNK signaling. These recent findings might open up entirely new avenues for therapeutic intervention in chronic inflammatory diseases and certain cancers; indeed, the Gadd45β-MKK7 interaction might be a key target for such intervention.

Abstract: Numerous studies have indicated that inflammatory cytokines play a major role in osteoclastogenesis, leading to the bone resorption that is frequently associated with cancers and other diseases. Gene deletion studies have shown that receptor activator of NF-kappaB ligand (RANKL) is one of the critical mediators of osteoclastogenesis. How RANKL mediates osteoclastogenesis is not fully understood, but an agent that suppresses RANKL signaling has potential to inhibit osteoclastogenesis. In this report, we examine the ability of curcumin (diferuloylmethane), a pigment derived from turmeric, to suppress RANKL signaling and osteoclastogenesis in RAW 264.7 cells, a murine monocytic cell line. Treatment of these cells with RANKL activated NF-kappaB, and preexposure of the cells to curcumin completely suppressed RANKL-induced NF-kappaB activation. Curcumin inhibited the pathway leading from activation of IkappaBalpha kinase and IkappaBalpha phosphorylation to IkappaBalpha degradation. RANKL induced osteoclastogenesis in these monocytic cells, and curcumin inhibited both RANKL- and TNF-induced osteoclastogenesis and pit formation. Curcumin suppressed osteoclastogenesis maximally when added together with RANKL and minimally when it was added 2 days after RANKL. Whether curcumin inhibits RANKL-induced osteoclastogenesis through suppression of NF-kappaB was also confirmed independently, as RANKL failed to activate NF-kappaB in cells stably transfected with a dominant-negative form of IkappaBalpha and concurrently failed to induce osteoclastogenesis. Thus overall these results indicate that RANKL induces osteoclastogenesis through the activation of NF-kappaB, and treatment with curcumin inhibits both the NF-kappaB activation and osteoclastogenesis induced by RANKL.

Abstract: In addition to their roles in desensitization and signaling of seven-membrane-spanning receptors, β-arrestins have been more recently implicated in regulating non-seven-membrane-spanning receptor pathways. By using a yeast two-hybrid screen, we identified the inhibitor of NF-κB, IκBα, as a binding partner of β-arrestin 1. Both β-arrestin 1 and 2 interact with IκBα in transfected cells as assessed by immunoprecipitation experiments. Additionally, upstream kinases known to regulate the function of IκBα, such as IκB kinase α and β and NF-κB-inducing kinase, were also shown to interact with β-arrestin. Overexpression of either β-arrestin 1 or β-arrestin 2 led to marked inhibition of NF-κB activity, as measured by reporter gene activity. Inhibition of NF-κB activity was independent of the type of stimulus used for NF-κB activation. Conversely, suppression of β-arrestin 1, but not β-arrestin 2, expression by using RNA interference led to a 3-fold increase in tumor necrosis factor-stimulated NF-κB activity as measured by NF-κB mobility-shift analysis. These data uncover a role of β-arrestins in the regulation of NF-κB-mediated gene regulation.

Abstract: The nuclear factor–kappa B (NF-κB) family of transcription factors plays a seminal role in inflammation, apoptosis, development, and cancer. Modulation of NF-κB–mediated gene expression in response to diverse signals is coordinated by the IκB kinase (IKK) complex. We identified ELKS, an essential regulatory subunit of the IKK complex. Silencing ELKS expression by RNA interference blocked induced expression of NF-κB target genes, including the NF-κB inhibitor I κ B α and proinflammatory genes such as cyclo-oxygenase 2 and interleukin 8 . These cells were also not protected from apoptosis in response to cytokines. ELKS likely functions by recruiting IκBα to the IKK complex and thus serves a regulatory function for IKK activation.

Abstract: NF-κB is a heterodimeric transcription activator consisting of the DNA binding subunit p50 and the transactivation subunit p65/RelA NF-κB prevents cell death caused by tumor necrosis factor (TNF) and other genotoxic insults by directly inducing antiapoptotic target genes We report here that the tumor suppressor PTEN, which functions as a negative regulator of phosphatidylinositol (PI)-3 kinase/Akt-mediated cell survival pathway, is down regulated by p65 but not by p50 Moreover, a subset of human lung or thyroid cancer cells expressing high levels of endogenous p65 showed decreased expression of PTEN that could be rescued by specific inhibition of the NF-κB pathway with IκB overexpression as well as with small interfering RNA directed against p65 Importantly, TNF, a potent inducer of NF-κB activity, suppressed PTEN gene expression in IKKβ+/+ cells but not in IKKβ−/− cells, which are deficient in the NF-κB activation pathway These findings indicated that NF-κB activation was necessary and sufficient for inhibition of PTEN expression The promoter, RNA, and protein levels of PTEN are down-regulated by NF-κB The mechanism underlying suppression of PTEN expression by NF-κB was independent of p65 DNA binding or transcription function and involved sequestration of limiting pools of transcriptional coactivators CBP/p300 by p65 Restoration of PTEN expression inhibited NF-κB transcriptional activity and augmented TNF-induced apoptosis, indicating a negative regulatory loop involving PTEN and NF-κB PTEN is, thus, a novel target whose suppression is critical for antiapoptosis by NF-κB

Abstract: Interleukin-1β (IL-1β) is a potent and pleiotropic inflammatory cytokine that is highly produced in the CNS under conditions of damage, disease, or stress. This cytokine acts on CNS glia to effect inflammatory responses, mediated in part via activation of the nuclear factor-κB (NF-κB) transcription factor, and consequent induction of numerous cytokines. Neurons as well as astrocytes in the hippocampus also express the type 1 IL-1 receptor, indicating that this cytokine can influence neuronal function directly, yet IL-1β does not induce production of cytokines in neurons as it does in glia. In contrast, IL-1β regulates synaptic function of hippocampal neurons. Here we demonstrate that different signaling pathways mediate IL-1β actions in neurons as compared with astrocytes. IL-1β activates the p38 mitogen-activated protein kinase (MAPK) signaling pathway and induces the activation of CREB in hippocampal neurons, in contrast to the activation of NF-κB in hippocampal astrocytes, demonstrating cell type-specific signaling responses to IL-1 in the brain and yielding distinct functional responses.

Abstract: The Kaposi's sarcoma-associated herpesvirus (KSHV, also called human herpesvirus 8) has been linked to KS and primary effusion lymphoma (PEL) in immunocompromised individuals. We report that PEL cell lines have constitutive active alternative NF-kappa B pathway and demonstrate high-level expression of NF-kappa B2/p100 precursor and its processed subunit p52. To elucidate the mechanism of activation of the alternative NF-kappa B pathway in PEL cells, we have investigated the role of KSHV-encoded viral Fas-associated death domain-like IL- beta 1-converting enzyme inhibitory protein (vFLIP) K13. We demonstrate that stable expression of K13, but not other FLIPs, in a variety of cell lines constitutively up-regulates p100/NF-kappa B2 expression and leads to its processing into the p52 subunit. K13-induced up-regulation and processing of p100 critically depends on the I kappa B kinase (IKK)alpha/IKK1 subunit of the IKK complex, whereas IKK beta/IKK2, receptor-interacting protein, and NF-kappa B-inducing kinase are dispensable for this process. Silencing of endogenous K13 expression by siRNA inhibits p100 processing and cellular proliferation. Our results demonstrate for the first time, to our knowledge, that KSHV vFLIP K13 is required for the growth and proliferation of PEL cells and alternative NF-kappa B pathway plays a key role in this process. Therapeutic agents targeting the alternative NF-kappa B pathway may have a role in the treatment of KSHV-associated lymphomas.

Abstract: Nuclear factor-κB (NF-κB) and c-Jun NH2-terminal kinase (JNK) are activated simultaneously under a variety of stress conditions. They also share several common signaling pathways for their activation in response to cytokines or growth factors. Recent studies, however, demonstrated a new form of interplay between these two allies. Inhibition of NF-κB by ikk β or rela gene deficiency sensitizes stress responses through enhanced or prolonged activation of JNK. Conversely, sustained activation of NF-κB inhibits cytokine-induced JNK activation. The mechanisms of how NF-κB and JNK become rivals for each other are under extensive debate.

Abstract: Atherosclerosis is a chronic inflammatory disease affecting arterial vessels. Strategies to reduce the inflammatory responses of endothelial cells and macrophages may slow lesion development and prevent complications such as plaque rupture. The human protease human neutrophil elastase (HNE), oxidized low density lipoprotein, LPS, and TNF-α were chosen as model stimuli of arterial wall inflammation and led to production of the chemokine IL-8 in endothelial cells. To counteract the activity of HNE, we have examined the effects of adenoviral gene delivery of the anti-elastases elafin, previously demonstrated within human atheroma, and murine secretory leukocyte protease inhibitor (SLPI), a related molecule, on the inflammatory responses of human endothelial cells and macrophages to atherogenic stimuli. We developed a technique of precomplexing adenovirus with cationic lipid to augment adenoviral infection efficiency in endothelial cells and to facilitate infection in macrophages. Elafin overexpression protected endothelial cells from HNE-induced IL-8 production and cytotoxicity. Elafin and murine SLPI also reduced endothelial IL-8 release in response to oxidized low density lipoprotein, LPS, and TNF-α and macrophage TNF-α production in response to LPS. This effect was associated with reduced activation of the inflammatory transcription factor NF-κB, through up-regulation of IκBα, in both cell types. Our work suggests a novel and extended anti-inflammatory role for these HNE inhibitors working as effectors of innate immunity to protect tissues against maladaptive inflammatory responses. Our findings indicate that elafin and SLPI may be gene therapy targets for the treatment of atheroma.

Abstract: Atherosclerosis is a slowly evolutive age-linked disease of large arteries, characterized by a local lipid deposition associated with a chronic inflammatory response, leading potentially to acute plaque rupture, thrombosis and ischemic heart disease. Atherogenesis is a complex sequence of events associating first expression of adhesion molecules, recruitment of mononuclear cells to the endothelium, local activation of leukocytes and inflammation, lipid accumulation and foam cell formation. Low density lipoproteins (LDLs) become atherogenic after undergoing oxidation by vascular cells, that transform them into highly bioreactive oxidized LDL (oxidized LDLs). Oxidized LDLs are involved in foam cell formation, and trigger proatherogenic events such as overexpression of adhesion molecules, chemoattractant agents growth factors and cytokines involved in the inflammatory process, cell proliferation and apoptosis. Moreover, this toxic effect of oxidized LDLs plays probably a role in plaque erosion/rupture and su...

Abstract: High levels of free heme are found in pathological states of increased hemolysis, such as sickle cell disease, malaria, and ischemia reperfusion. The hemolytic events are often associated with an inflammatory response that usually turns into chronic inflammation. We recently reported that heme is a proinflammatory molecule, able to induce neutrophil migration, reactive oxygen species generation, and IL-8 expression. In this study, we show that heme (1-50 microM) delays human neutrophil spontaneous apoptosis in vitro. This effect requires heme oxygenase activity, and depends on reactive oxygen species production and on de novo protein synthesis. Inhibition of ERK and PI3K pathways abolished heme-protective effects upon human neutrophils, suggesting the involvement of the Ras/Raf/MAPK and PI3K pathway on this effect. Confirming the involvement of these pathways in the modulation of the antiapoptotic effect, heme induces Akt phosphorylation and ERK-2 nuclear translocation in neutrophils. Futhermore, inhibition of NF-kappa B translocation reversed heme antiapoptotic effect. NF-kappa B (p65 subunit) nuclear translocation and I kappa B degradation were also observed in heme-treated cells, indicating that free heme may regulate neutrophil life span modulating signaling pathways involved in cell survival. Our data suggest that free heme associated with hemolytic episodes might play an important role in the development of chronic inflammation by interfering with the longevity of neutrophils.

Abstract: The NF-κB/IκB signaling pathway is a critical regulator of cell survival in cancer. Here, we report that combined down-regulation of growth arrest- and DNA-damage-inducible proteins (GADD)45α and γ expression by NF-κB is an essential step for various cancer types to escape programmed cell death. We demonstrate that inhibition of NF-κB in cancer cells results in GADD45α- and γ-dependent induction of apoptosis and inhibition of tumor growth. Inhibition of GADD45α and γ in cancer cells by small interfering RNA abrogates apoptosis induction by the inhibitor of NF-κB and blocks c-Jun N-terminal kinase activation, whereas overexpression of GADD45α and γ activates c-Jun N-terminal kinase and induces apoptosis. These results establish an unambiguous role for the GADD45 family as an essential mediator of cell survival in cancer cells with implications for cancer chemotherapy and novel drug discovery.

Abstract: Nuclear factor (NF)-κB is a key player in the control of both innate and adaptive immunity. NF-κB proteins are present in the cytoplasm in association with inhibitory proteins called inhibitors of κB (IκBs). On activation by a large plethora of inducers, the IκB proteins are phosphorylated, ubiquitinated, and subsequently degraded in the proteasomes. Degradation of IκBs allows translocation of NF-κB into the nucleus and bind to their cognate DNA binding sites to regulate the transcription of large numbers of genes including antimicrobial peptides, cytokines, chemokines, stress response proteins, and antiapoptotic proteins. NF-κB activity is essential for lymphocyte survival, activation, and mounting normal immune responses. Constitutive activation of NF-κB pathways is often associated with inflammatory diseases like rheumatoid arthritis, inflammatory bowel disease, multiple sclerosis, and asthma. Better understanding of the regulation of NF-κB will provide a platform for development of specific therapeutic agents targeted towards the inflammatory diseases. As most transcription factors, the mammalian NF-κB family has multiple members including RelA (p65), NF-κB1 (p50; p105), NF-κB2 (p52; p100), c-Rel, and RelB1,2 (fig 1). These proteins have a structurally conserved N-terminal 300-amino acid region, which contains the dimerisation, nuclear localisation, and DNA binding domains (see fig 1). The c-Rel, RelB, and RelA proteins also have a C-terminal non-homologous transactivation domain that strongly activates transcription from NF-κB binding sites. On the other hand, the other Rel proteins, such as p50 homodimers, lack the transcription activation domain but still bind to κB-consensus sites and therefore function as transcription repressors.3 The p50 and p52 proteins are generated by proteolytic processing of their precursors, p105 and p100, respectively.4 All members of the NF-κB family except RelB can form homodimers, as well as heterodimers with one another. The most prevalent activated form of NF-κB is the heterodimer of subunit p65 associated with either …

Abstract: Toll-like receptors (TLRs) recognize conserved products of microbial pathogens to initiate the innate immune response. TLR4 signaling is triggered upon binding of lipopolysaccharides (LPS) from gram-negative bacteria. Using comparative gene expression profiling, we demonstrate a master regulatory role of IκB kinase (IKK)/NF-κB signaling for immediate-early gene induction after LPS engagement in precursor B cells. IKK/NF-κB signaling controls a large panel of gene products associated with signaling and transcriptional activation and repression. Intriguingly, the induction of AP-1 activity by LPS in precursor B cells and primary dendritic cells fully depends on the IKK/NF-κB pathway, which promotes expression of several AP-1 family members, including JunB, JunD, and B-ATF. In pre-B cells, AP-1 augments induction of a subset of primary NF-κB targets, as shown for chemokine receptor 7 (CCR7) and immunoglobulin κ light chain. Thus, our data illustrate that NF-κB orchestrates immediate-early effects of LPS signaling and controls secondary AP-1 activation to mount an appropriate biological response.

Abstract: Caffeic acid phenethyl ester (CAPE), which is derived from the propolis of honeybee hives, has been shown to reveal anti-inflammatory properties. Since T-cells play a key role in the onset of several inflammatory diseases, we have evaluated the immunosuppressive activity of CAPE in human T-cells, discovering that this phenolic compound is a potent inhibitor of early and late events in T-cell receptor-mediated T-cell activation. Moreover, we found that CAPE specifically inhibited both interleukin (IL)-2 gene transcription and IL-2 synthesis in stimulated T-cells. To further characterize the inhibitory mechanisms of CAPE at the transcriptional level, we examined the DNA binding and transcriptional activities of nuclear factor (NF)-κB, nuclear factor of activated cells (NFAT), and activator protein-1 (AP-1) transcription factors in Jurkat cells. We found that CAPE inhibited NF-κB-dependent transcriptional activity without affecting the degradation of the cytoplasmic NF-κB inhibitory protein, IκBα. However, both NF-κB binding to DNA and transcriptional activity of a Gal4-p65 hybrid protein were clearly prevented in CAPE-treated Jurkat cells. Moreover, CAPE inhibited both the DNA-binding and transcriptional activity of NFAT, a result that correlated with its ability to inhibit phorbol 12-myristate 13-acetate plus ionomycin-induced NFAT1 dephosphorylation. These findings provide new insights into the molecular mechanisms involved in the immunomodulatory and anti-inflammatory activities of this natural compound.