Unravelling the complexities of the NF-κB signalling pathway using mouse knockout and transgenic models

Loss of Nfkb1 leads to early onset aging

NF-κB is a major regulator of age-dependent gene expression and the p50/NF-κB1 subunit is an integral modulator of NF-κB signaling. Here, we examined Nfkb1-/- mice to investigate the relationship between this subunit and aging. Although Nfkb1-/- mice appear similar to littermates at six months of age, by 12 months they have a higher incidence of several observable age-related phenotypes. In addition, aged Nfkb1-/- animals have increased kyphosis, decreased cortical bone, increased brain GFAP staining and a decrease in overall lifespan compared to Nfkb1+/+. In vitro, serially passaged primary Nfkb1-/- MEFs have more senescent cells than comparable Nfkb1+/+ MEFs. Also, Nfkb1-/- MEFs have greater amounts of phospho-H2AX foci and lower levels of spontaneous apoptosis than Nfkb1+/+, findings that are mirrored in the brains of Nfkb1-/- animals compared to Nfkb1+/+. Finally, in wildtype animals a substantial decrease in p50 DNA binding is seen in aged tissue compared to young. Together, these data show that loss of Nfkb1 leads to early animal aging that is associated with reduced apoptosis and increased cellular senescence. Moreover, loss of p50 DNA binding is a prominent feature of aged mice relative to young. These findings support the strong link between the NF-κB pathway and mammalian aging.

Catalytic subunits of the phosphatase calcineurin interact with NF-κB-inducing kinase (NIK) and attenuate NIK-dependent gene expression

Nuclear factor (NF)-κB-inducing kinase (NIK) is a serine/threonine kinase that activates NF-κB pathways, thereby regulating a wide variety of immune systems. Aberrant NIK activation causes tumor malignancy, suggesting a requirement for precise regulation of NIK activity. To explore novel interacting proteins of NIK, we performed in vitro virus screening and identified the catalytic subunit Aα isoform of serine/threonine phosphatase calcineurin (CnAα) as a novel NIK-interacting protein. The interaction of NIK with CnAα in living cells was confirmed by co-immunoprecipitation. Calcineurin catalytic subunit Aβ isoform (CnAβ) also bound to NIK. Experiments using domain deletion mutants suggested that CnAα and CnAβ interact with both the kinase domain and C-terminal region of NIK. Moreover, the phosphatase domain of CnAα is responsible for the interaction with NIK. Intriguingly, we found that TRAF3, a critical regulator of NIK activity, also binds to CnAα and CnAβ. Depletion of CnAα and CnAβ significantly enhanced lymphotoxin-β receptor (LtβR)-mediated expression of the NIK-dependent gene Spi-B and activation of RelA and RelB, suggesting that CnAα and CnAβ attenuate NF-κB activation mediated by LtβR-NIK signaling. Overall, these findings suggest a possible role of CnAα and CnAβ in modifying NIK functions.

IKK-related genetic diseases: probing NF-κB functions in humans and other matters

The transcription factor NF-κB plays a key role in numerous physiological processes such as inflammation, immunity, cell proliferation or control of cell death. Its activation is tightly controlled by a kinase complex, IκB kinase (IKK), composed of three core proteins: IKK1/IKKα, IKK2/IKKβ and NEMO/IKKγ. The first two are structurally related kinases whereas the third one is a regulatory subunit exhibiting affinity for upstream activators modified by polyubiquitin chains. Over the years, several inherited diseases caused by mutations of each of the three subunits of IKK have been identified in humans together with diseases caused by mutations of several of its substrates. They are associated with very specific and complex phenotypes involving a broad range of abnormalities such as impaired innate and acquired immune response, perturbed skin development and defects of the central nervous system. Here, we summarize the diverse clinical, cellular and molecular manifestations of IKK-related genetic diseases and show that studying patient-related mutations affecting the IKK subunits and some of their substrates offers the opportunity to understand the various functions of NF-κB in humans, complementing studies performed with mouse models. This analysis also provides glimpses about putative functions of IKK subunits that may be NF-κB-independent.

Nfkb1 suppresses DNA alkylation-induced tumor formation

NF-κB proteins play a complex role in modulating carcinogenesis following DNA damage. Previous work identified p50/NF-κB1 as a necessary factor in the cytotoxic response to alkylation damage. Recently, these findings were extended to demonstrate that in the setting of alkylation damage, this NF-κB subunit acts as a haploinsufficient tumor suppressor that prevents hematologic malignancy formation.

Roles of the NF-κB Pathway in B-Lymphocyte Biology

NF-κB was originally identified as a family of transcription factors that bind the enhancer of the immunoglobulin κ light-chain gene. Although its function in the regulation of immunoglobulin κ light-chain gene remains unclear, NF-κB plays critical roles in development, survival, and activation of B lymphocytes. In B cells, many receptors, including B-cell antigen receptor (BCR), activate NF-κB pathway, and the molecular mechanism of receptor-mediated activation of IκB kinase (IKK) complex has been partially revealed. In addition to normal B lymphocytes, NF-κB is also involved in the growth of some types of B-cell lymphomas, and many oncogenic mutations involved in constitutive activation of the NF-κB pathway were recently identified in such cancers. In this review, we first summarize the function of NF-κB in B-cell development and activation, and then describe recent progress in understanding the molecular mechanism of receptor-mediated activation of the IKK complex, focusing on the roles of the ubiquitin system. In the last section, we describe oncogenic mutations that induce NF-κB activation in B-cell lymphoma.

NFκB-activated astroglial release of complement C3 compromises neuronal morphology and function associated with Alzheimer's disease

Abnormal NFκB activation has been implicated in Alzheimer's disease (AD). However, the signaling pathways governing NFκB regulation and function in the brain are poorly understood. We identify complement protein C3 as an astroglial target of NFκB and show that C3 release acts through neuronal C3aR to disrupt dendritic morphology and network function. Exposure to Aβ activates astroglial NFκB and C3 release, consistent with the high levels of C3 expression in brain tissue from AD patients and APP transgenic mice, where C3aR antagonist treatment rescues cognitive impairment. Therefore, dysregulation of neuron-glia interaction through NFκB/C3/C3aR signaling may contribute to synaptic dysfunction in AD, and C3aR antagonists may be therapeutically beneficial.

Loss of c-REL but not NF-κB2 prevents autoimmune disease driven by FasL mutation

FASL/FAS signaling imposes a critical barrier against autoimmune disease and lymphadenopathy. Mutant mice unable to produce membrane-bound FASL (FasL(Δm/Δm)), a prerequisite for FAS-induced apoptosis, develop lymphadenopathy and systemic autoimmune disease with immune complex-mediated glomerulonephritis. Prior to disease onset, FasL(Δm/Δm) mice contain abnormally high numbers of leukocytes displaying activated and elevated NF-κB-regulated cytokine levels, indicating that NF-κB-dependent inflammation may be a key pathological driver in this multifaceted autoimmune disease. We tested this hypothesis by genetically impairing canonical or non-canonical NF-κB signaling in FasL(Δm/Δm) mice by deleting the c-Rel or NF-κB2 genes, respectively. Although the loss of NF-κB2 reduced the levels of inflammatory cytokines and autoantibodies, the impact on animal survival was minor due to substantially accelerated and exacerbated lymphoproliferative disease. In contrast, a marked increase in lifespan resulting from the loss of c-REL coincided with a striking reduction in classical parameters of autoimmune pathology, including the levels of cytokines and antinuclear autoantibodies. Notably, the decrease in regulatory T-cell numbers associated with loss of c-REL did not exacerbate autoimmunity in FasL(Δm/Δm)c-rel(-/-) mice. These findings indicate that selective inhibition of c-REL may be an attractive strategy for the treatment of autoimmune pathologies driven by defects in FASL/FAS signaling that would be expected to circumvent many of the complications caused by pan-NF-κB inhibition.

The oral iron chelator deferasirox inhibits NF-κB mediated gene expression without impacting on proximal activation: implications for myelodysplasia and aplastic anaemia

The myelodysplastic syndromes (MDS) are a group of disorders characterized by ineffective haematopoiesis, bone marrow dysplasia and cytopenias. Failure of red cell production often results in transfusion dependency with subsequent iron loading requiring iron chelation in lower risk patients. Consistent with previous reports, we have observed haematopoietic improvement in a cohort of patients treated with the oral iron chelator deferasirox (DFX). It has been postulated that MDS patients have a pro-inflammatory bone marrow environment with increased numbers of activated T cells producing elevated levels of tumour necrosis factor (TNF), which is detrimental to normal haematopoiesis. We demonstrate that DFX inhibits nuclear factor (NF)-κB dependent transcription without affecting its proximal activation, resulting in reduced TNF production from T cells stimulated in vitro. These results suggest that the haematopoietic improvement observed in DFX-treated patients may reflect an anti-inflammatory effect, mediated through inhibition of the transcription factor NF-κB and support the therapeutic targeting of this pathway, which is aberrantly activated in a large proportion of haematological malignancies.

The NF-κB genomic landscape in lymphoblastoid B cells

The nuclear factor κB (NF-κΒ) subunits RelA, RelB, cRel, p50, and p52 are each critical for B cell development and function. To systematically characterize their responses to canonical and noncanonical NF-κB pathway activity, we performed chromatin immunoprecipitation followed by high-throughput DNA sequencing (ChIP-seq) analysis in lymphoblastoid B cell lines (LCLs). We found a complex NF-κB-binding landscape, which did not readily reflect the two NF-κB pathway paradigms. Instead, 10 subunit-binding patterns were observed at promoters and 11 at enhancers. Nearly one-third of NF-κB-binding sites lacked κB motifs and were instead enriched for alternative motifs. The oncogenic forkhead box protein FOXM1 co-occupied nearly half of NF-κB-binding sites and was identified in protein complexes with NF-κB on DNA. FOXM1 knockdown decreased NF-κB target gene expression and ultimately induced apoptosis, highlighting FOXM1 as a synthetic lethal target in B cell malignancy. These studies provide a resource for understanding mechanisms that underlie NF-κB nuclear activity and highlight opportunities for selective NF-κB blockade.

Nfkb1 is a haploinsufficient DNA damage-specific tumor suppressor

NF-κB proteins play a central and subunit-specific role in the response to DNA damage. Previous work identified p50/NF-κB1 as being necessary for cytotoxicity in response to DNA alkylation damage. Given the importance of damage-induced cell death for the maintenance of genomic stability, we examined whether Nfkb1 acts as a tumor suppressor in the setting of alkylation damage. Hprt mutation analysis demonstrates that Nfkb1(-/-) cells accumulate more alkylator-induced, but not ionizing radiation (IR)-induced, mutations than similarly treated wild-type cells. Subsequent in vivo tumor induction studies reveal that following alkylator treatment, but not IR, Nfkb1(-/-) mice develop more lymphomas than similarly treated Nfkb1(+/+) animals. Heterozygous mice develop lymphomas at an intermediate rate and retain functional p50 in their tumors, indicating that Nfkb1 acts in a haploinsufficient manner. Analysis of human cancers, including therapy-related myeloid neoplasms, demonstrates that NFKB1 mRNA expression is downregulated compared with control samples in multiple hematological malignancies. These data indicate that Nfkb1 is a haploinsufficient, pathway-specific tumor suppressor that prevents the development of hematologic malignancy in the setting of alkylation damage.

Helper T-cell differentiation in graft-versus-host disease after allogeneic hematopoietic stem cell transplantation

Allogeneic hematopoietic stem cell transplantation (allo-HSCT) is an effective therapeutic option for many malignant diseases. However, the efficacy of allo-HSCT is limited by the occurrence of destructive graft-versus-host disease (GVHD). Since allogeneic T cells are the driving force in the development of GVHD, their activation, proliferation, and differentiation are key factors to understanding GVHD pathogenesis. This review focuses on one critical aspect: the differentiation and function of helper T (Th) cells in acute GVHD. We first summarize well-established subsets including Th1, Th2, Th17, and T-regulatory cells; their flexibility, plasticity, and epigenetic modification; and newly identified subsets including Th9, Th22, and T follicular helper cells. Next, we extensively discuss preclinical findings of Th-cell lineages in GVHD: the networks of transcription factors involved in differentiation, the cytokine and signaling requirements for development, the reciprocal differentiation features, and the regulation of microRNAs on T-cell differentiation. Finally, we briefly summarize the recent findings on the roles of T-cell subsets in clinical GVHD and ongoing strategies to modify T-cell differentiation for controlling GVHD in patients. We believe further exploration and understanding of the immunobiology of T-cell differentiation in GVHD will expand therapeutic options for the continuing success of allo-HSCT.

IκBε is a key regulator of B cell expansion by providing negative feedback on cRel and RelA in a stimulus-specific manner

The transcription factor NF-κB is a regulator of inflammatory and adaptive immune responses, yet only IκBα was shown to limit NF-κB activation and inflammatory responses. We investigated another negative feedback regulator, IκBε, in the regulation of B cell proliferation and survival. Loss of IκBε resulted in increased B cell proliferation and survival in response to both antigenic and innate stimulation. NF-κB activity was elevated during late-phase activation, but the dimer composition was stimulus specific. In response to IgM, cRel dimers were elevated in IκBε-deficient cells, yet in response to LPS, RelA dimers also were elevated. The corresponding dimer-specific sequences were found in the promoters of hyperactivated genes. Using a mathematical model of the NF-κB-signaling system in B cells, we demonstrated that kinetic considerations of IκB kinase-signaling input and IκBε's interactions with RelA- and cRel-specific dimers could account for this stimulus specificity. cRel is known to be the key regulator of B cell expansion. We found that the RelA-specific phenotype in LPS-stimulated cells was physiologically relevant: unbiased transcriptome profiling revealed that the inflammatory cytokine IL-6 was hyperactivated in IκBε(-/-) B cells. When IL-6R was blocked, LPS-responsive IκBε(-/-) B cell proliferation was reduced to near wild-type levels. Our results provide novel evidence for a critical role for immune-response functions of IκBε in B cells; it regulates proliferative capacity via at least two mechanisms involving cRel- and RelA-containing NF-κB dimers. This study illustrates the importance of kinetic considerations in understanding the functional specificity of negative-feedback regulators.

NF-κB control of T cell development

The NF-κB signal transduction pathway is best known as a major regulator of innate and adaptive immune responses, yet there is a growing appreciation of its importance in immune cell development, particularly of T lineage cells. In this Review, we discuss how the temporal regulation of NF-κB controls the stepwise differentiation and antigen-dependent selection of conventional and specialized subsets of T cells in response to T cell receptor and costimulatory, cytokine and growth factor signals.

NF-κB mediated regulation of adult hippocampal neurogenesis: relevance to mood disorders and antidepressant activity

Adult hippocampal neurogenesis is a peculiar form of process of neuroplasticity that in recent years has gained great attention for its potential implication in cognition and in emotional behavior in physiological conditions. Moreover, a vast array of experimental studies suggested that adult hippocampal neurogenesis may be altered in various neuropsychiatric disorders, including major depression, where its disregulation may contribute to cognitive impairment and/or emotional aspects associated with those diseases. An intriguing area of interest is the potential influence of drugs on adult neurogenesis. In particular, several psychoactive drugs, including antidepressants, were shown to positively modulate adult hippocampal neurogenesis. Among molecules which could regulate adult hippocampal neurogenesis the NF-κB family of transcription factors has been receiving particular attention from our and other laboratories. Herein we review recent data supporting the involvement of NF-κB signaling pathways in the regulation of adult neurogenesis and in the effects of drugs that are endowed with proneurogenic and antidepressant activity. The potential implications of these findings on our current understanding of the process of adult neurogenesis in physiological and pathological conditions and on the search for novel antidepressants are also discussed.

The regulation of IL-10 expression

Interleukin (IL)-10 is an important immunoregulatory cytokine and an understanding of how IL-10 expression is controlled is critical in the design of immune intervention strategies. IL-10 is produced by almost all cell types within the innate (including macrophages, monocytes, dendritic cells (DCs), mast cells, neutrophils, eosinophils and natural killer cells) and adaptive (including CD4(+) T cells, CD8(+) T cells and B cells) immune systems. The mechanisms of IL-10 regulation operate at several stages including chromatin remodelling at the Il10 locus, transcriptional regulation of Il10 expression and post-transcriptional regulation of Il10 mRNA. In addition, whereas some aspects of Il10 gene regulation are conserved between different immune cell types, several are cell type- or stimulus-specific. Here, we outline the complexity of IL-10 production by discussing what is known about its regulation in macrophages, monocytes, DCs and CD4(+) T helper cells.

Crosstalk between the type 1 interferon and nuclear factor kappa B pathways confers resistance to a lethal virus infection

Nuclear factor kappa B (NF-κB) and type 1 interferon (T1-IFN) signaling are innate immune mechanisms activated upon viral infection. However, the role of NF-κB and its interplay with T1-IFN in antiviral immunity is poorly understood. We show that NF-κB is essential for resistance to ectromelia virus (ECTV), a mouse orthopoxvirus related to the virus causing human smallpox. Additionally, an ECTV mutant lacking an NF-κB inhibitor activates NF-κB more effectively in vivo, resulting in increased proinflammatory molecule transcription in uninfected cells and organs and decreased viral replication. Unexpectedly, NF-κB activation compensates for genetic defects in the T1-IFN pathway, such as a deficiency in the IRF7 transcription factor, resulting in virus control. Thus, overlap between the T1-IFN and NF-κB pathways allows the host to overcome genetic or pathogen-induced deficiencies in T1-IFN and survive an otherwise lethal poxvirus infection. These findings may also explain why some pathogens target both pathways to cause disease.

Resolvin D1 reverts lipopolysaccharide-induced TJ proteins disruption and the increase of cellular permeability by regulating IκBα signaling in human vascular endothelial cells

Tight Junctions (TJ) are important components of paracellular pathways, and their destruction enhances vascular permeability. Resolvin D1 (RvD1) is a novel lipid mediator that has treatment effects on inflammatory diseases, but its effect on inflammation induced increase in vascular permeability is unclear. To understand whether RvD1 counteracts the lipopolysaccharide (LPS) induced increase in vascular cell permeability, we investigated the effects of RvD1 on endothelial barrier permeability and tight junction reorganization and expression in the presence or absence of LPS stimulation in cultured Human Vascular Endothelial Cells (HUVECs). Our results showed that RvD1 decreased LPS-induced increased in cellular permeability and inhibited the LPS-induced redistribution of zo-1, occludin, and F-actin in HUVECs. Moreover, RvD1 attenuated the expression of IκBα in LPS-induced HUVECs. The NF-κB inhibitor PDTC enhanced the protective effects of RvD1 on restoration of occludin rather than zo-1 expression in LPS-stimulated HUVECs. By contrast, the ERK1/2 inhibitor PD98059 had no effect on LPS-induced alterations in zo-1 and occludin protein expressions in HUVECs. Our data indicate that RvD1 protects against impairment of endothelial barrier function induced by LPS through upregulating the expression of TJ proteins in HUVECs, which involves the IκBα pathway but not the ERK1/2 signaling.

Activation of the transcriptional function of the NF-κB protein c-Rel by O-GlcNAc glycosylation

The transcription factor nuclear factor κB (NF-κB) rapidly reprograms gene expression in response to various stimuli, and its activity is regulated by several posttranslational modifications, including phosphorylation, methylation, and acetylation. The addition of O-linked β-N-acetylglucosamine (a process known as O-GlcNAcylation) is an abundant posttranslational modification that is enhanced in conditions such as hyperglycemia and cellular stress. We report that the NF-κB subunit c-Rel is modified and activated by O-GlcNAcylation. We identified serine 350 as the site of O-GlcNAcylation, which was required for the DNA binding and transactivation functions of c-Rel. Blocking the O-GlcNAcylation of this residue abrogated c-Rel-mediated expression of the cytokine-encoding genes IL2, IFNG, and CSF2 in response to T cell receptor (TCR) activation, whereas increasing the extent of O-GlcNAcylation of cellular proteins enhanced the expression of these genes. TCR- or tumor necrosis factor (TNF)-induced expression of other NF-κB target genes, such as NFKBIA (which encodes IκBα) and TNFAIP3 (which encodes A20), occurred independently of the O-GlcNAcylation of c-Rel. Our findings suggest a stimulus-specific role for hyperglycemia-induced O-GlcNAcylation of c-Rel in promoting T cell-mediated autoimmunity in conditions such as type 1 diabetes by enhancing the production of T helper cell cytokines.

Defective immune responses in mice lacking LUBAC-mediated linear ubiquitination in B cells

The linear ubiquitin chain assembly complex (LUBAC) plays a crucial role in activating the canonical NF-κB pathway, which is important for B-cell development and function. Here, we describe a mouse model (B-HOIP(Δlinear)) in which the linear polyubiquitination activity of LUBAC is specifically ablated in B cells. Canonical NF-κB and ERK activation, mediated by the tumour necrosis factor (TNF) receptor superfamily receptors CD40 and TACI, was impaired in B cells from B-HOIP(Δlinear) mice due to defective activation of the IKK complex; however, B-cell receptor (BCR)-mediated activation of the NF-κB and ERK pathways was unaffected. B-HOIP(Δlinear) mice show impaired B1-cell development and defective antibody responses to thymus-dependent and thymus-independent II antigens. Taken together, these data suggest that LUBAC-mediated linear polyubiquitination is essential for B-cell development and activation, possibly via canonical NF-κB and ERK activation induced by the TNF receptor superfamily, but not by the BCR.

RelB: an outlier in leukocyte biology

RelB is one of the more unusual members of the NF-κB family. This family, arguably the best known group of transcription regulators, regulates an astonishing array of cell types and biological processes. This includes regulation of cell growth, differentiation and death by apoptosis, and the development and function of the innate and adaptive-immune system. RelB is best known for its roles in lymphoid development, DC biology, and noncanonical signaling. Within the last few years, however, surprising functions of RelB have emerged. The N-terminal leucine zipper motif of RelB, a motif unique among the NF-κB family, may associate with more diverse DNA sequences than other NF-κB members. RelB is capable of direct binding to the AhR that supports the xenobiotic-detoxifying pathway. RelB can regulate the circadian rhythm by directly binding to the BMAL partner of CLOCK. Finally, RelB also couples with bioenergy NAD(+) sensor SIRT1 to integrate acute inflammation with changes in metabolism and mitochondrial bioenergetics. In this review, we will explore these unique aspects of RelB, specifically with regard to its role in immunity.

Electroacupuncture Could Regulate the NF-κB Signaling Pathway to Ameliorate the Inflammatory Injury in Focal Cerebral Ischemia/Reperfusion Model Rats

The activated nuclear factor-KappaB signaling pathway plays a critical role in inducing inflammatory injury. It has been reported that electroacupuncture could be an effective anti-inflammatory treatment. We aimed to explore the complex mechanism by which EA inhibits the activation of the NF- κ B signal pathway and ameliorate inflammatory injury in the short term; the effects of NEMO Binding Domain peptide for this purpose were compared. Focal cerebral I/R was induced by middle cerebral artery occlusion for 2 hrs. Total 380 male Sprague-Dawley rats are in the study. The neurobehavioral scores, infarction volumes, and the levels of IL-1 β and IL-13 were detected. NF- κ B p65, I κ B α , IKK α , and IKK β were analyzed and the ability of NF- κ B binding DNA was investigated. The EA treatment and the NBD peptide treatment both reduced infarct size, improved neurological scores, and regulated the levels of IL-1 β and IL-13. The treatment reduced the expression of IKK α and IKK β and altered the expression of NF- κ B p65 and I κ B α in the cytoplasm and nucleus; the activity of NF- κ B was effectively reduced. We conclude that EA treatment might interfere with the process of NF- κ B nuclear translocation. And it also could suppress the activity of NF- κ B signaling pathway to ameliorate the inflammatory injury after focal cerebral ischemia/reperfusion.

Crystal structure of a human IκB kinase β asymmetric dimer

Phosphorylation of inhibitor of nuclear transcription factor κB (IκB) by IκB kinase (IKK) triggers the degradation of IκB and migration of cytoplasmic κB to the nucleus where it promotes the transcription of its target genes. Activation of IKK is achieved by phosphorylation of its main subunit, IKKβ, at the activation loop sites. Here, we report the 2.8 Å resolution crystal structure of human IKKβ (hIKKβ), which is partially phosphorylated and bound to the staurosporine analog K252a. The hIKKβ protomer adopts a trimodular structure that closely resembles that from Xenopus laevis (xIKKβ): an N-terminal kinase domain (KD), a central ubiquitin-like domain (ULD), and a C-terminal scaffold/dimerization domain (SDD). Although hIKKβ and xIKKβ utilize a similar dimerization mode, their overall geometries are distinct. In contrast to the structure resembling closed shears reported previously for xIKKβ, hIKKβ exists as an open asymmetric dimer in which the two KDs are further apart, with one in an active and the other in an inactive conformation. Dimer interactions are limited to the C-terminal six-helix bundle that acts as a hinge between the two subunits. The observed domain movements in the structures of IKKβ may represent trans-phosphorylation steps that accompany IKKβ activation.

Molecular characterization and expression analysis of IκB from Haliotis discus discus

Innate immune system relies on the recognition of pathogen associated molecular patterns present in the microbes by the pattern recognition receptors leading to the activation of signaling cascade and subsequent synthesis of cytokines. NF-κB is a major stimulus activated transcription factor, which regulates the expression of a diverse array of genes. IκB is an inhibitor of NF-κB, retaining NF-κB in an inactive state in the cytoplasm. In this study, we have reported the characterization of first abalone IκB (HdIκB). The cDNA possessed an ORF of 1200 bp coding for a protein of 400 amino acids with molecular mass of 45 kDa and isoelectric point of 4.7. HdIκB protein possessed a conserved phosphorylation site (58)DSGIFS(63) in the N-terminal region, six ankyrin repeats, and a PEST sequence in the C-terminal region. A casein kinase II phosphorylation site could also be observed in the PEST sequence. Constitutive expression of HdIκB revealed its physiological significance since NF-κB is known to be activated by various stimuli. Elevated expression of HdIκB transcripts could be observed in abalones challenged with various mitogens and live microbes. This novel characterization of abalone IκB would further be a positive approach in the affirmation of evolutionary conservation and significance of this protein as a repressor/inhibitor of a pleiotropic transcription factor like NF-κB.

MicroRNA-146a acts as a guardian of the quality and longevity of hematopoietic stem cells in mice

During inflammation and infection, hematopoietic stem and progenitor cells are stimulated to proliferate and differentiate into mature immune cells, especially of the myeloid lineage. MicroRNA-146a (miR-146a) is a critical negative regulator of inflammation. Deletion of miR-146a produces effects that appear as dysregulated inflammatory hematopoiesis, leading to a decline in the number and quality of hematopoietic stem cells (HSCs), excessive myeloproliferation, and, ultimately, to HSC exhaustion and hematopoietic neoplasms. At the cellular level, the defects are attributable to both an intrinsic problem in the miR-146a-deficient HSCs and extrinsic effects of lymphocytes and nonhematopoietic cells. At the molecular level, this involves a molecular axis consisting of miR-146a, signaling protein TRAF6, transcriptional factor NF-κB, and cytokine IL-6. This study has identified miR-146a to be a critical regulator of HSC homeostasis during chronic inflammation in mice and provided a molecular connection between chronic inflammation and the development of bone marrow failure and myeloproliferative neoplasms. DOI:http://dx.doi.org/10.7554/eLife.00537.001.

TNFR1 signaling kinetics: spatiotemporal control of three phases of IKK activation by posttranslational modification

TNFα is a pleotropic cytokine that plays a central role in the inflammatory response by activating the NF-κB signaling pathway, and is targeted in a range of chronic inflammatory diseases, underscoring the therapeutic importance of understanding its underlying molecular mechanisms. Although K63-linked ubiquitination of RIP1 by TRAF2/5 and cIAP1/2 was thought to serve as a scaffold to activate the NF-κB pathway, the recent accumulation of conflicting results has challenged the necessity of these proteins in NF-κB activation. In addition, several serine/threonine kinases have been implicated in TNFα-induced IKK activation; however, the targeted disruption of these kinases had no effect on transient IKK activation. The recent discovery of RIP1-dependent and -independent activation of the early and delayed phases of IKK and TRAF2 phosphorylation-dependent activation of the prolonged phase of IKK offers a reconciliatory model for the interpretation of contradictory results in the field. Notably, the TNFα-induced inflammatory response is not exclusively controlled by the NF-κB pathway but is subject to regulatory crosstalk between NF-κB and other context-dependent pathways. Thus further elucidation of these spatiotemporally-coordinated signaling mechanisms has the potential to provide novel molecular targets and therapeutic strategies for NF-κB intervention.

Mitochondria and reactive oxygen species: physiology and pathophysiology

The air that we breathe contains nearly 21% oxygen, most of which is utilized by mitochondria during respiration. While we cannot live without it, it was perceived as a bane to aerobic organisms due to the generation of reactive oxygen and nitrogen metabolites by mitochondria and other cellular compartments. However, this dogma was challenged when these species were demonstrated to modulate cellular responses through altering signaling pathways. In fact, since this discovery of a dichotomous role of reactive species in immune function and signal transduction, research in this field grew at an exponential pace and the pursuit for mechanisms involved began. Due to a significant number of review articles present on the reactive species mediated cell death, we have focused on emerging novel pathways such as autophagy, signaling and maintenance of the mitochondrial network. Despite its role in several processes, increased reactive species generation has been associated with the origin and pathogenesis of a plethora of diseases. While it is tempting to speculate that anti-oxidant therapy would protect against these disorders, growing evidence suggests that this may not be true. This further supports our belief that these reactive species play a fundamental role in maintenance of cellular and tissue homeostasis.

Two coordinated mechanisms underlie tumor necrosis factor alpha-induced immediate and delayed IκB kinase activation

Tumor necrosis factor alpha (TNF-α)-induced NF-κB activation has been believed to depend on TRAF2- and cIAP1-mediated RIP1 ubiquitination. However, recent findings have challenged the notion that these proteins play essential roles in NF-κB activation. Here, by assessing the kinetics and amplitude of IκB kinase (IKK) activation, we report that TNF-α-induced immediate and robust activation of IKK requires K63-linked and linearly linked ubiquitination of RIP1 and that in the absence of RIP1 expression, TRAF2 and cIAP1 cooperatively induce delayed IKK activation by recruiting LUBAC to TNFR1. Knockdown of HOIP (a component of LUBAC) in RIP1-deficient cells completely impairs the recruitment and activation of IKK but does not affect K63-linked ubiquitination of TRAF2 and recruitment of TAK1 to TNFR1, suggesting that the K63-linked ubiquitin chain is not capable of recruiting IKK in vivo. We also demonstrate that TRAF2 and cIAP1 together, but not either one alone, directly catalyze linearly linked ubiquitination of RIP1. Importantly, in embryonic hepatocytes, TNF-α activates NF-κB through a RIP1-independent pathway. Thus, our findings clarify molecular details of this important signaling mechanism by providing evidence for the existence of two phases of IKK activation: the immediate phase, induced by TRAF2/cIAP1-mediated ubiquitination of RIP1, and the delayed phase, activated by TRAF2/cIAP1-dependent recruitment of LUBAC.

A functional genomics screen for microRNA regulators of NF-kappaB signaling

BACKGROUND

The nuclear factor-KappaB (NF-κB) pathway is conserved from fruit flies to humans and is a key mediator of inflammatory signaling. Aberrant regulation of NF-κB is associated with several disorders including autoimmune disease, chronic inflammation, and cancer, making the NF-κB pathway an attractive therapeutic target. Many regulatory components of the NF-κB pathway have been identified, including microRNAs (miRNAs). miRNAs are small non-coding RNAs and are common components of signal transduction pathways. Here we present a cell-based functional genomics screen to systematically identify miRNAs that regulate NF-κB signaling.

RESULTS

We screened a library of miRNA mimics using a NF-κB reporter cell line in the presence and absence of tumor necrosis factor (+/- TNF). There were 9 and 15 hits in the -TNF and +TNF screens, respectively. We identified putative functional targets of these hits by integrating computational predictions with NF-κB modulators identified in a previous genome-wide cDNA screen. miR-517a and miR-517c were the top hits, activating the reporter 86- and 126-fold, respectively. Consistent with these results, miR-517a/c induced the expression of endogenous NF-κB targets and promoted the nuclear localization of p65 and the degradation of IκB. We identified TNFAIP3 interacting protein1 (TNIP1) as a target and characterized a functional SNP in the miR-517a/c binding site. Lastly, miR-517a/c induced apoptosis in vitro, which was phenocopied by knockdown of TNIP1.

CONCLUSIONS

Our study suggests that miRNAs are common components of NF-κB signaling and miR-517a/c may play an important role in linking NF-κB signaling with cell survival through TNIP1.

A novel IRAK1-IKKε signaling axis limits the activation of TAK1-IKKβ downstream of TLR3

IRAK1 is involved in the regulation of type I IFN production downstream of TLR3. Previous work indicated that IRAK1 negatively regulates TRIF-mediated activation of IRF3 and IRF7. We report that IRAK1 limits the activation of the TLR3-NF-κB pathway. Following TLR3 stimulation, IRAK1-deficient macrophages produced increased levels of IL-6 and IFN-β compared with wild type macrophages. Pharmacological inhibition of TAK1 reduced this increase in IFN-β, together with the heightened activation of IRF3 and p65 found in TLR3-ligand stimulated IRAK1-deficient macrophages. Recently, IKKε and TANK-binding kinase 1 (TBK1) were reported to limit activation of the NF-κB pathway downstream of IL-1R, TNFR1, and TLRs. We show that TBK1 has a positive role in the TLR3-NF-κB pathway, because we detected reduced levels of IL-6 and reduced activation of p65 in TBK1-deficient macrophages. In contrast, we show that IKKε limits the activation of the TLR3-NF-κB pathway. Furthermore, we show that IRAK1 is required for the activation of IKKε downstream of TLR3. We report impaired activation of ERK1/2 in IRAK1- and IKKε-deficient macrophages, a novel finding for both kinases. Importantly, this work provides novel mechanistic insight into the regulation of the TLR3-signaling pathway, providing strong evidence that an IRAK1-IKKε-signaling axis acts to limit the production of both type I IFNs and proinflammatory cytokines by regulating TAK1 activity.

Targeting IκB proteins for HIV latency activation: the role of individual IκB and NF-κB proteins

Latently infected cell reservoirs represent the main barrier to HIV eradication. Combination antiretroviral therapy (cART) effectively blocks viral replication but cannot purge latent provirus. One approach to HIV eradication could include cART to block new infections plus an agent to activate latent provirus. NF-κB activation induces HIV expression, ending latency. Before activation, IκB proteins sequester NF-κB dimers in the cytoplasm. Three canonical IκBs, IκBα, IκBβ, and IκBε, exist, but the IκB proteins' role in HIV activation regulation is not fully understood. We studied the effects on HIV activation of targeting IκBs by single and pairwise small interfering RNA (siRNA) knockdown. After determining the relative abundance of the IκBs, the relative abundance of NF-κB subunits held by the IκBs, and the kinetics of IκB degradation and resynthesis following knockdown, we studied HIV activation by IκB knockdown, in comparison with those of known HIV activators, tumor necrosis factor alpha (TNF-α), tetradecanoyl phorbol acetate (TPA), and trichostatin A (TSA), in U1 monocytic and J-Lat 10.6 lymphocytic latently infected cells. We found that IκBα knockdown activated HIV in both U1 and J-Lat 10.6 cells, IκBβ knockdown did not activate HIV, and, surprisingly, IκBε knockdown produced the most HIV activation, comparable to TSA activation. Our data show that HIV reactivation can be triggered by targeting two different IκB proteins and that IκBε may be an effective target for HIV latency reactivation in T-cell and macrophage lineages. IκBε knockdown may offer attractive therapeutic advantages for HIV activation because it is not essential for mammalian growth and development and because new siRNA delivery strategies may target siRNAs to HIV latently infected cells.

NF-κB is required for cnidocyte development in the sea anemone Nematostella vectensis

The sea anemone Nematostella vectensis (Nv) is a leading model organism for the phylum Cnidaria, which includes anemones, corals, jellyfishes and hydras. A defining trait across this phylum is the cnidocyte, an ectodermal cell type with a variety of functions including defense, prey capture and environmental sensing. Herein, we show that the Nv-NF-κB transcription factor and its inhibitor Nv-IκB are expressed in a subset of cnidocytes in the body column of juvenile and adult anemones. The size and distribution of the Nv-NF-κB-positive cnidocytes suggest that they are in a subtype known as basitrichous haplonema cnidocytes. Nv-NF-κB is primarily cytoplasmic in cnidocytes in juvenile and adult animals, but is nuclear when first detected in the 30-h post-fertilization embryo. Morpholino-mediated knockdown of Nv-NF-κB expression results in greatly reduced cnidocyte formation in the 5 day-old animal. Taken together, these results indicate that NF-κB plays a key role in the development of the phylum-specific cnidocyte cell type in Nematostella, likely by nuclear Nv-NF-κB-dependent activation of genes required for cnidocyte development.

Anti-inflammatory therapy in type 1 diabetes

Type 1 diabetes (T1D) is a multi-factorial, organ-specific autoimmune disease in genetically susceptible individuals, which is characterized by a selective and progressive loss of insulin-producing β-cells. Cells mediating innate as well as adaptive immunity infiltrate pancreatic islets, thereby generating an aberrant inflammatory process called insulitis that can be mirrored by a pathologic autoantibody production and autoreactive T-cells. In tight cooperation with infiltrating innate immune cells, which secrete high levels of pro-inflammatory cytokines like IL-1β, TNFα, and INFγ effector T-cells trigger the fatal destruction process of β-cells. There is ongoing discussion on the contribution of inflammation in T1D pathogenesis, ranging from a bystander reaction of autoimmunity to a dysregulation of immune responses that initiate inflammatory processes and thereby actively promoting β-cell death. Here, we review recent advances in anti-inflammatory interventions in T1D animal models and preclinical studies and discuss their mode of action as well as their capacity to interfere with T1D development.

Pleiotropic cellular functions of PARP1 in longevity and aging: genome maintenance meets inflammation

Aging is a multifactorial process that depends on diverse molecular and cellular mechanisms, such as genome maintenance and inflammation. The nuclear enzyme poly(ADP-ribose) polymerase 1 (PARP1), which catalyzes the synthesis of the biopolymer poly(ADP-ribose), exhibits an essential role in both processes. On the one hand, PARP1 serves as a genomic caretaker as it participates in chromatin remodelling, DNA repair, telomere maintenance, resolution of replicative stress, and cell cycle control. On the other hand, PARP1 acts as a mediator of inflammation due to its function as a regulator of NF-κB and other transcription factors and its potential to induce cell death. Consequently, PARP1 represents an interesting player in several aging mechanisms and is discussed as a longevity assurance factor on the one hand and an aging-promoting factor on the other hand. Here, we review the molecular mechanisms underlying the various roles of PARP1 in longevity and aging with special emphasis on cellular studies and we briefly discuss the results in the context of in vivo studies in mice and humans.

A novel small molecule, HK-156, inhibits lipopolysaccharide-induced activation of NF-κB signaling and improves survival in mouse models of sepsis

AIM

To characterize a small molecule compound HK-156 as a novel inhibitor of the nuclear factor κB (NF-κB) signaling pathway.

METHODS

THP-1 monocytes and HEK293/hTLR4A-MD2-CD14 cells were tested. HK-156 and compound 809, an HK-156 analogue, were synthesized. A luciferase assay was used to evaluate the transcriptional activity of NF-κB. The levels of cytokines were measured with cytokine arrays, ELISA and quantitative PCR. An electrophoretic mobility shift assay (EMSA), immunofluorescence, Western blot and mass spectrometry were used to investigate the molecular mechanisms underlying the actions of the agent. BALB/c mice challenged with lipopolysaccharide (LPS, 15 mg/kg, ip) were used as a mouse experimental endotoxemia model.

RESULTS

In HEK293hTLR4/NF-κB-luc cells treated with LPS (1000 ng/mL), HK-156 inhibited the transcriptional activity of NF-κB in a concentration-dependent manner (IC₅₀=6.54 ± 0.37 μmol/L). Pretreatment of THP-1 monocytes with HK-156 (5, 10 and 20 μmol/L) significantly inhibited LPS-induced release and production of TNF-α and IL-1β, attenuated LPS-induced translocation of NF-κB into the nucleus and its binding to DNA, and suppressed LPS-induced phosphorylation and degradation of IκBα, and phosphorylation of IKKβ and TGFβ-activated kinase (TAK1). Meanwhile, HK-156 (5, 10 and 20 μmol/L) slightly suppressed LPS-induced activation of p38. The effect of HK-156 on LPS-induced activation of NF-κB signaling was dependent on thiol groups of cysteines in upstream proteins. In mouse models of sepsis, pre-injection of HK-156 (50 mg/kg, iv) significantly inhibited TNFα production and reduced the mortality caused by the lethal dose of LPS.

CONCLUSION

HK-156 inhibits LPS-induced activation of NF-κB signaling by suppressing the phosphorylation of TAK1 in vitro, and exerts beneficial effects in a mouse sepsis model. HK-156 may therefore be a useful therapeutic agent for treating sepsis.

c-Rel: shaping CD4 regulatory T cell development in unexpected ways

In the thymus, sequential antigen and cytokine receptor signals direct the stepwise differentiation of multi-potential CD4+CD8+ thymic precursors into Foxp3+ CD4 regulatory T cells (Tregs). In this Point of View article we discuss our recent findings about how the c-Rel transcription factor orchestrates this developmental process.

The c-Rel Transcription Factor in Development and Disease

c-Rel is a member of the nuclear factor κB (NF-κB) transcription factor family. Unlike other NF-κB proteins that are expressed in a variety of cell types, high levels of c-Rel expression are found primarily in B and T cells, with many c-Rel target genes involved in lymphoid cell growth and survival. In addition to c-Rel playing a major role in mammalian B and T cell function, the human c-rel gene (REL) is a susceptibility locus for certain autoimmune diseases such as arthritis, psoriasis, and celiac disease. The REL locus is also frequently altered (amplified, mutated, rearranged), and expression of REL is increased in a variety of B and T cell malignancies and, to a lesser extent, in other cancer types. Thus, agents that modulate REL activity may have therapeutic benefits for certain human cancers and chronic inflammatory diseases.

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.

Depletion of c-Rel from cytokine gene promoters is required for chromatin reassembly and termination of gene responses to T cell activation

The role of the Nuclear Factor κB (NF-κB) transcription factor family in T cell function has been well described. The c-Rel family member is of particular importance in initiating T cell responses to antigen and regulating activation of inflammatory cytokine genes, including the Interleukin-2 (IL-2) and Granulocyte macrophage colony stimulating factor (GM-CSF) genes. c-Rel is required for chromatin remodeling of these gene promoters, which involves depletion of histones from the promoters in response to T cell activating signals. These chromatin remodeling events precede transcriptional activation of the genes. The subsequent down-regulation of cytokine gene expression is important in the termination of an immune response and here we examine this process at the murine GM-CSF and IL-2 genes. We show that the cytokine mRNA levels rapidly return to basal levels following stimulus removal and this is associated with reassembly of histones onto the promoter. Histone reassembly at the GM-CSF and IL-2 promoters occurs concomitantly with depletion of RelA, c-Rel and RNA polymerase II from the promoters. Furthermore we show that transcriptional down-regulation and chromatin reassembly is dependent on depletion of c-Rel from the nucleus, and that this is regulated by the nuclear translocation of the NF-κB inhibitor, IκBα. The nuclear activation of c-Rel therefore not only regulates the initiation of GM-CSF and IL-2 gene activation in response to T cell activation, but also the termination of these gene responses following the removal of the activating signal.

Context-Dependent Regulation of Autophagy by IKK-NF-κB Signaling: Impact on the Aging Process

The NF-κB signaling system and the autophagic degradation pathway are crucial cellular survival mechanisms, both being well conserved during evolution. Emerging studies have indicated that the IKK/NF-κB signaling axis regulates autophagy in a context-dependent manner. IKK complex and NF-κB can enhance the expression of Beclin 1 and other autophagy-related proteins and stimulate autophagy whereas as a feedback response, autophagy can degrade IKK components. Moreover, NF-κB signaling activates the expression of autophagy inhibitors (e.g., A20 and Bcl-2/xL) and represses the activators of autophagy (BNIP3, JNK1, and ROS). Several studies have indicated that NF-κB signaling is enhanced both during aging and cellular senescence, inducing a proinflammatory phenotype. The aging process is also associated with a decline in autophagic degradation. It seems that the activity of Beclin 1 initiation complex could be impaired with aging, since the expression of Beclin 1 decreases as does the activity of type III PI3K. On the other hand, the expression of inhibitory Bcl-2/xL proteins increases with aging. We will review the recent literature on the control mechanisms of autophagy through IKK/NF-κB signaling and emphasize that NF-κB signaling could be a potent repressor of autophagy with ageing.

It takes two to tango: IκBs, the multifunctional partners of NF-κB

The inhibitory IκB proteins have been discovered as fundamental regulators of the inducible transcription factor nuclear factor-κB (NF-κB). As a generally excepted model, stimulus-dependent destruction of inhibitory IκBs and processing of precursor molecules, both promoted by components of the signal integrating IκB kinase complex, are the key events for the release of various NF-κB/Rel dimers and subsequent transcriptional activation. Intense research of more than 20 years provides evidence that the extending family of IκBs act not simply as reversible inhibitors of NF-κB activation but rather as a complex regulatory module, which assures feedback regulation of the NF-κB system and either can inhibit or promote transcriptional activity in a stimulus-dependent manner. Thus, IκB and NF-κB/Rel family proteins establish a complex interrelationship that allows modulated NF-κB-dependent transcription, tailored to the physiological environment.

NF-κB: where did it come from and why?

The vast majority of research on nuclear factor κB (NF-κB) signaling in the past 25 years has focused on its roles in normal and disease-related processes in vertebrates, especially mice and humans. Recent genome and transcriptome sequencing efforts have shown that homologs of NF-κB transcription factors, inhibitor of NF-κB (IκB) proteins, and IκB kinases are present in a variety of invertebrates, including several in phyla simpler than Arthropoda, the phylum containing insects such Drosophila. Moreover, many invertebrates also contain genes encoding homologs of upstream signaling proteins in the Toll-like receptor signaling pathway, which is well-known for its downstream activation of NF-κB for innate immunity. This review describes what we now know or can infer and speculate about the evolution of the core elements of NF-κB signaling as well as the biological processes controlled by NF-κB in invertebrates. Further research on NF-κB in invertebrates is likely to uncover information about the evolutionary origins of this key human signaling pathway and may have relevance to our management of the responses of ecologically and economically important organisms to environmental and adaptive pressures.

NF-κB subunit specificity in hemopoiesis

Although the diverse functions served by the nuclear factor-κB (NF-κB) pathway in virtually all cell types are typically employed to deal with stress responses, NF-κB transcription factors also play key roles in the development of hemopoietic cells. This review focuses on how NF-κB transcription factors control various aspects of thymic T-cell and myeloid cell differentiation that include its roles in hemopoietic precursors, conventional αβ T cells, CD4(+) regulatory T cells, natural killer T cells, γδ T cells, macrophages, and dendritic cells.

ERK inhibition enhances TSA-induced gastric cancer cell apoptosis via NF-κB-dependent and Notch-independent mechanism

AIMS

To analyze the combined impact of the histone deacetylase inhibitor (HDACI) Trichostatin A (TSA) and the extracellular-signal-regulated kinase 1/2 (ERK1/2) inhibitor PD98059 on gastric cancer (GC) cell line SGC7901 growth.

MAIN METHODS

SGC7901 cells were treated with TSA, PD98059 or with a TSA-PD98059 combination. Effects of drug treatment on tumor cell proliferation, apoptosis, cell cycle progression, and cell signaling pathways were investigated by MTS assay, flow cytometry, Western blotting, chromatin immunoprecipitation (ChIP) assay, electrophoretic mobility shift assay (EMSA), and luciferase reporter assay, respectively.

KEY FINDINGS

PD98059 enhanced TSA-induced cell growth arrest, apoptosis and activation of p21(WAF1/CIP1), but reversed TSA-induced activation of ERK1/2 and nuclear factor-κB (NF-κB). TSA alone up-regulated Notch1 and Hes1, and down-regulated Notch2, but PD98059 did not affect the trends of Notch1 and Notch2 induced by TSA. Particularly, PD98059 did potentiate the ability of TSA to down-regulate phospho-histone H3 protein, but increased levels of the acetylated forms of histone H3 bound to the p21(WAF1/CIP1) promoter, leading to enhanced expression of p21(WAF1/CIP1) in SGC7901 cells.

SIGNIFICANCE

PD98059 synergistically potentiates TSA-induced GC growth arrest and apoptosis by manipulating NF-κB and p21(WAF1/CIP1) independent of Notch. Therefore, concomitant administration of HDACIs and ERK1/2 inhibitors may be a promising treatment strategy for individuals with GC.

The critical role of TAK1 in accentuated epithelial to mesenchymal transition in obliterative bronchiolitis after lung transplantation

Therapies to limit or reverse fibrosis have proven unsuccessful, highlighting the need for a greater understanding of basic mechanisms that drive fibrosis and, in particular, the link between fibrosis and inflammation. It has been shown that pro-fibrotic transforming growth factor β1 (TGF-β1)-driven epithelial-to-mesenchymal transition (EMT) can be accentuated by tumor necrosis factor α (TNF-α). TGF-β-activated kinase 1 (TAK1) is activated by both TGF-β1 and TNF-α, activating both nuclear factor kappa-light-chain-enhancer of activated B cells and mitogen-activated protein kinase signaling pathways. In this study, we evaluated the potential for TAK1 to modulate the synergistic effect between TGF-β1 and TNF-α in driving EMT. Co-stimulation with TGF-β1 and TNF-α induced an accentuated and extended phosphorylation of TAK1 compared to either alone. TAK1 signaled downstream via nuclear factor kappa-light-chain-enhancer of activated B cells, and Jun N-terminal kinase-2, but independent of Jun N-terminal kinase-1, extracellular signal-regulated kinase-1/2, or p38 mitogen-activated protein kinase signaling to drive EMT in bronchial epithelial cells. Blocking either TAK1 or Jun N-terminal kinase-2 inhibited EMT. TAK1 phosphorylation was increased in the airway epithelium of patients with fibrotic airway disease. These data identify factors leading to and affected by accentuated and extended TAK1 phosphorylations potential novel therapeutic targets in inflammation-driven fibrotic diseases.

c-mip down-regulates NF-κB activity and promotes apoptosis in podocytes

The mechanisms of podocyte disorders in cases of idiopathic nephrotic syndrome (INS) are complex and remain incompletely elucidated. The abnormal regulation of NF-κB may play a key role in the pathophysiology of these podocyte diseases, but at present, NF-κB has not been thoroughly investigated. In this study, we report that induction of c-mip in podocytes of patients with INS is associated with a down-regulation of RelA, a potent antiapoptotic factor that belongs to the NF-κB family. Overexpression of c-mip in differentiated podocytes promotes apoptosis by inducing caspase-3 activity and up-regulating the proapoptotic protein Bax, whereas the overall levels of the antiapoptotic protein Bcl-2 was concomitantly decreased. The associated overexpression of RelA prevented the proapoptotic effects of c-mip. In addition, the targeted induction of c-mip in podocytes in vivo inhibited the expression of the RelA protein and increased the Bax/Bcl-2 ratio. The expression of both c-mip and active caspase-3 increased in focal and segmental glomerulosclerosis biopsies, and both proteins displayed a close spatial relationship. These results suggest that alterations in NF-κB activity might result from the up-regulation of c-mip and are likely to contribute to podocyte disorders in cases of INS.

A systematic survey of the response of a model NF-κB signalling pathway to TNFα stimulation

White's lab established that strong, continuous stimulation with tumour necrosis factor-α (TNFα) can induce sustained oscillations in the subcellular localisation of the transcription factor nuclear factor κB (NF-κB). But the intensity of the TNFα signal varies substantially, from picomolar in the blood plasma of healthy organisms to nanomolar in diseased states. We report on a systematic survey using computational bifurcation theory to explore the relationship between the intensity of TNFα stimulation and the existence of sustained NF-κB oscillations. Using a deterministic model developed by Ashall et al. in 2009, we find that the system's responses to TNFα are characterised by a supercritical Hopf bifurcation point: above a critical intensity of TNFα the system exhibits sustained oscillations in NF-kB localisation. For TNFα below this critical value, damped oscillations are observed. This picture depends, however, on the values of the model's other parameters. When the values of certain reaction rates are altered the response of the signalling pathway to TNFα stimulation changes: in addition to the sustained oscillations induced by high-dose stimulation, a second oscillatory regime appears at much lower doses. Finally, we define scores to quantify the sensitivity of the dynamics of the system to variation in its parameters and use these scores to establish that the qualitative dynamics are most sensitive to the details of NF-κB mediated gene transcription.