RelB cellular regulation and transcriptional activity are regulated by p100

Revisiting Neuroblastoma: Nrf2, NF-κB and Phox2B as a Promising Network in Neuroblastoma

Neuroblastoma is the most common solid extracranial tumor during childhood; it displays extraordinary heterogeneous clinical courses, from spontaneous regression to poor outcome in high-risk patients due to aggressive growth, metastasizing, and treatment resistance. Therefore, the identification and detailed analysis of promising tumorigenic molecular mechanisms are inevitable. This review highlights the abnormal regulation of NF-κB, Nrf2, and Phox2B as well as their interactions among each other in neuroblastoma. NF-κB and Nrf2 play a key role in antioxidant responses, anti-inflammatory regulation and tumor chemoresistance. Recent studies revealed a regulation of NF-κB by means of the Nrf2/antioxidant response element (ARE) system. On the other hand, Phox2B contributes to the differentiation of immature sympathetic nervous system stem cells: this transcription factor regulates the expression of RET, thereby facilitating cell survival and proliferation. As observed in other tumors, we presume striking interactions between NF-κB, Nrf2, and Phox2B, which might constitute an important crosstalk triangle, whose decompensation may trigger a more aggressive phenotype. Consequently, these transcription factors could be a promising target for novel therapeutic approaches and hence, further investigation on their regulation in neuroblastoma shall be reinforced.

NF-κB in biology and targeted therapy: new insights and translational implications

NF-κB signaling has been discovered for nearly 40 years. Initially, NF-κB signaling was identified as a pivotal pathway in mediating inflammatory responses. However, with extensive and in-depth investigations, researchers have discovered that its role can be expanded to a variety of signaling mechanisms, biological processes, human diseases, and treatment options. In this review, we first scrutinize the research process of NF-κB signaling, and summarize the composition, activation, and regulatory mechanism of NF-κB signaling. We investigate the interaction of NF-κB signaling with other important pathways, including PI3K/AKT, MAPK, JAK-STAT, TGF-β, Wnt, Notch, Hedgehog, and TLR signaling. The physiological and pathological states of NF-κB signaling, as well as its intricate involvement in inflammation, immune regulation, and tumor microenvironment, are also explicated. Additionally, we illustrate how NF-κB signaling is involved in a variety of human diseases, including cancers, inflammatory and autoimmune diseases, cardiovascular diseases, metabolic diseases, neurological diseases, and COVID-19. Further, we discuss the therapeutic approaches targeting NF-κB signaling, including IKK inhibitors, monoclonal antibodies, proteasome inhibitors, nuclear translocation inhibitors, DNA binding inhibitors, TKIs, non-coding RNAs, immunotherapy, and CAR-T. Finally, we provide an outlook for research in the field of NF-κB signaling. We hope to present a stereoscopic, comprehensive NF-κB signaling that will inform future research and clinical practice.

The Role of the Nuclear Factor-Kappa B (NF-κB) Pathway in SARS-CoV-2 Infection

COVID-19 is a global health threat caused by severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) and is associated with a significant increase in morbidity and mortality. The present review discusses nuclear factor-kappa B (NF-κB) activation and its potential therapeutical role in treating COVID-19. COVID-19 pathogenesis, the major NF-κB pathways, and the involvement of NF-κB in SARS-CoV-2 have been detailed. Specifically, NF-κB activation and its impact on managing COVID-19 has been discussed. As a central player in the immune and inflammatory responses, modulating NF-κB activation could offer a strategic avenue for managing SARS-CoV-2 infection. Understanding the NF-κB pathway's role could aid in developing treatments against SARS-CoV-2. Further investigations into the intricacies of NF-κB activation are required to reveal effective therapeutic strategies for managing and combating the SARS-CoV-2 infection and COVID-19.

An EZH2-NF-κB regulatory axis drives expression of pro-oncogenic gene signatures in triple negative breast cancer

The histone methyltransferase EZH2 has been studied most extensively in the context of PRC2-dependent gene repression. Accumulating evidence indicates non-canonical functions for EZH2 in cancer contexts including promoting paradoxical gene expression through interactions with transcription factors, including NF-κB in triple negative breast cancer (TNBC). We profile EZH2 and NF-κB factor co-localization and positive gene regulation genome-wide, and define a subset of NF-κB targets and genes associated with oncogenic functions in TNBC that is enriched in patient datasets. We demonstrate interaction between EZH2 and RelA requiring the recently identified transactivation domain (TAD) which mediates EZH2 recruitment to, and activation of certain NF-κB-dependent genes, and supports downstream migration and stemness phenotypes in TNBC cells. Interestingly, EZH2-NF-κB positive regulation of genes and stemness does not require PRC2. This study provides new insight into pro-oncogenic regulatory functions for EZH2 in breast cancer through PRC2-independent, and NF-κB-dependent regulatory mechanisms.

Alternative Splicing of RIOK3 Engages the Noncanonical NFκB Pathway during Rift Valley Fever Virus Infection

Although the noncanonical NFκB pathway was originally identified as a cellular pathway contributing to lymphoid organogenesis, in the past 20 years, its involvement in innate immunity has become more appreciated. In particular, the noncanonical NFκB pathway has been found to be activated and even exploited by some RNA viruses during infection. Intriguingly, activation of this pathway has been shown to have a role in disrupting transcription of type 1 interferon (IFN), suggesting a rationale for why this response could be co-opted by some viruses. Rift Valley fever virus (RVFV) is a trisegmented ambisense RNA virus that poses a considerable threat to domestic livestock and human health. Previously, we showed the atypical kinase RIOK3 is important for mounting an IFN response to RVFV infection of human epithelial cells, and shortly following infection with RVFV (MP12 strain), RIOK3 mRNA is alternatively spliced to its X2 isoform that encodes a truncated RIOK3 protein. Alternative splicing of RIOK3 mRNA has an inhibitory effect on the IFN response but also stimulates an NFκB-mediated inflammatory response. Here, we demonstrate alternative splicing of RIOK3 mRNA is associated with activation of the noncanonical NFκB pathway and suggest this pathway is co-opted by RVFV (MP12) to enhance viral success during infection.

Aberrant accumulation of NIK promotes tumor growth by dysregulating translation and post-translational modifications in breast cancer

BACKGROUND

In vivo investigations with cancer cells have powerful tools to discover cancer progression mechanisms and preclinical candidate drugs. Among these in vivo experimental models, the establishment of highly malignancy cell lines with xenograft has been frequently used. However, few previous researches targeted malignancy-related genes whose protein levels translationally changed. Therefore, this study aimed to identify malignancy-related genes which contributed to cancer progression and changed at the protein level in the in vivo selected cancer cell lines.

METHODS

We established the high malignancy breast cancer cell line (LM05) by orthotopic xenograft as an in vivo selection method. To explore the altered genes by translational or post-translational regulation, we analyzed the protein production by western blotting in the highly malignant breast cancer cell line. Functional analyses of the altered genes were performed by in vitro and in vivo experiments. To reveal the molecular mechanisms of the regulation with protein level, we evaluated post-translational modification by immunoprecipitation. In addition, we evaluated translational production by click reaction-based purification of nascent protein.

RESULTS

As a result, NF-κB inducing kinase (NIK) increased at the protein level and promoted the nuclear localization of NF-κB2 (p52) and RelB in the highly malignant breast cancer cell line. The functional analyses indicated the NIK upregulation contributed to tumor malignancy via cancer-associated fibroblasts (CAFs) attraction and partially anti-apoptotic activities. Additionally, the immunoprecipitation experiment revealed that the ubiquitination of NIK decreased in LM05 cells. The decline in NIK ubiquitination was attributed to the translational downregulation of cIAP1.

CONCLUSIONS

Our study identified a dysregulated mechanism of NIK production by the suppression of NIK post-modification and cIAP1 translation. The aberrant NIK accumulation promoted tumor growth in the highly malignant breast cancer cell line.

Effects of Helicobacter pylori adhesin HopQ binding to CEACAM receptors in the human stomach

Helicobacter pylori has developed several strategies using its diverse virulence factors to trigger and, at the same time, limit the host's inflammatory responses in order to establish a chronic infection in the human stomach. One of the virulence factors that has recently received more attention is a member of the Helicobacter outer membrane protein family, the adhesin HopQ, which binds to the human Carcinoembryonic Antigen-related Cell Adhesion Molecules (CEACAMs) on the host cell surface. The HopQ-CEACAM interaction facilitates the translocation of the cytotoxin-associated gene A (CagA), an important effector protein of H. pylori, into host cells via the Type IV secretion system (T4SS). Both the T4SS itself and CagA are important virulence factors that are linked to many aberrant host signaling cascades. In the last few years, many studies have emphasized the prerequisite role of the HopQ-CEACAM interaction not only for the adhesion of this pathogen to host cells but also for the regulation of cellular processes. This review summarizes recent findings about the structural characteristics of the HopQ-CEACAM complex and the consequences of this interaction in gastric epithelial cells as well as immune cells. Given that the upregulation of CEACAMs is associated with many H. pylori-induced gastric diseases including gastritis and gastric cancer, these data may enable us to better understand the mechanisms of H. pylori's pathogenicity.

SYTL5 Promotes Papillary Thyroid Carcinoma Progression by Enhancing Activation of the NF-κB Signaling Pathway

The function and mechanism of SYTL5 in papillary thyroid carcinoma (PTC) are still unclear. In this research, we found that SYTL5 was significantly overexpressed in PTC tissues compared with normal thyroid tissues. SYTL5 downregulation significantly weakened the proliferative, migratory, and invasive abilities of PTC cells. In addition, upregulated SYTL5 could promote cancer progression by activating the NF-κB signaling pathway. RAC1b expression is positively associated with SYTL5, and overexpressed RAC1b abrogated the antitumor effect after SYTL5 inhibition. In conclusion, our findings identify the oncogenic role of SYTL5 in PTC by activation of the NF-κB signaling pathway, thus facilitating PTC development and progression.

Inhibitory feedback control of NF-κB signalling in health and disease

Cells must adapt to changes in their environment to maintain cell, tissue and organismal integrity in the face of mechanical, chemical or microbiological stress. Nuclear factor-κB (NF-κB) is one of the most important transcription factors that controls inducible gene expression as cells attempt to restore homeostasis. It plays critical roles in the immune system, from acute inflammation to the development of secondary lymphoid organs, and also has roles in cell survival, proliferation and differentiation. Given its role in such critical processes, NF-κB signalling must be subject to strict spatiotemporal control to ensure measured and context-specific cellular responses. Indeed, deregulation of NF-κB signalling can result in debilitating and even lethal inflammation and also underpins some forms of cancer. In this review, we describe the homeostatic feedback mechanisms that limit and ‘re-set’ inducible activation of NF-κB. We first describe the key components of the signalling pathways leading to activation of NF-κB, including the prominent role of protein phosphorylation and protein ubiquitylation, before briefly introducing the key features of feedback control mechanisms. We then describe the array of negative feedback loops targeting different components of the NF-κB signalling cascade including controls at the receptor level, post-receptor signalosome complexes, direct regulation of the critical ‘inhibitor of κB kinases’ (IKKs) and inhibitory feedforward regulation of NF-κB-dependent transcriptional responses. We also review post-transcriptional feedback controls affecting RNA stability and translation. Finally, we describe the deregulation of these feedback controls in human disease and consider how feedback may be a challenge to the efficacy of inhibitors.

RelB and Neuroinflammation

Neuroinflammation within the central nervous system involves multiple cell types that coordinate their responses by secreting and responding to a plethora of inflammatory mediators. These factors activate multiple signaling cascades to orchestrate initial inflammatory response and subsequent resolution. Activation of NF-κB pathways in several cell types is critical during neuroinflammation. In contrast to the well-studied role of p65 NF-κB during neuroinflammation, the mechanisms of RelB activation in specific cell types and its roles during neuroinflammatory response are less understood. In this review, we summarize the mechanisms of RelB activation in specific cell types of the CNS and the specialized effects this transcription factor exerts during neuroinflammation.

Targeting NF-κB with Nanotherapy in a Mouse Model of Adult T-Cell Leukemia/Lymphoma

Adult T-cell leukemia/lymphoma (ATLL) is an aggressive, clonal malignancy of mature T cells caused by human T-cell leukemia virus type 1. Although it is a rare tumor type, it serves as an excellent model of a virus driven process that transforms cells and engenders a highly malignant tumor that is extraordinarily difficult to treat. The viral transcriptional transactivator (Tax) in the HTLV-1 genome directly promotes tumorigenesis, and Tax-induced oncogenesis depends on its ability to constitutively activate NF-κB signaling. Accordingly, we developed and evaluated a nano-delivery system that simultaneously inhibits both canonical (p65) and noncanonical (p100) NF-κB signaling pathways locally in tumors after systemic administration. Our results demonstrate that siRNA is delivered rapidly to ATLL tumors after either i.p. or i.v. injection. The siRNA treatment significantly reduced both p65 and p100 mRNA and protein expression. Anti-NF-κB nanotherapy significantly inhibited tumor growth in two distinct tumor models in mice: a spontaneous Tax-driven tumor model, and a Tax tumor cell transplant model. Moreover, siRNA nanotherapy sensitized late-stage ATLL tumors to the conventional chemotherapeutic agent etoposide, indicating a pleiotropic benefit for localized siRNA nanotherapeutics.

Quantitative assessment of NFκB transcription factor activity

The Nuclear Factor Kappa B (NFκB) pathway is an important signalling pathway in the immune system. Single gene defects in the NFκB pathway are described in a number of immunodeficiency diseases. These conditions provide a unique opportunity to investigate the mechanisms of NFκB function and how genetic mutations that disrupt this function lead to human disease. Here we describe a robust method for quantifying small differences in the functional activity of the NFκB pathway. Peripheral blood mononuclear cells from healthy donors were stimulated over several days, with a combination of anti-IgM antibody and multimeric CD40 ligand. Nuclear proteins were thereafter extracted and tested for the ability of activated transcription factors, to bind known NFκB DNA binding motifs. Repeatability experiments showed that the DNA binding Activity can be quantified with an average inter and intra assay coefficient of variation of less than 10% (RelB and p52) and less than 15% (p50 and RelA). In healthy individuals there is a significant increase in the DNA binding activity of NFκB transcription factors in response to stimulation, although the magnitude of this response varies across individuals. The kinetics of the DNA binding activity also differs between the canonical and non-canonical transcription factors. P50 and RelA DNA binding activity responds within hours of stimulation, whilst RelB and p52 response was delayed to more than a day after stimulation. Activation of NFκB signalling in response to B cell specific stimulation, can be precisely measured to distinguish individuals with differences in the functional activity of this pathway. This test may prove to be an important biomarker for investigating the functional impact of genetic variants on NFκB signalling.

17β-Estradiol Promotes Trained Immunity in Females Against Sepsis via Regulating Nucleus Translocation of RelB

Sepsis is more common among males than females, and the unequal estrogen levels have been suspected to play a vital role in gender differences. Recently, trained immunity is reported to be a novel strategy for the innate immune system to fight infection. However, it has not been clarified whether β-glucan-induced trained immunity causes different responses to early sepsis between male and female mice. In this study, sepsis was induced in mice by intraperitoneal injection of Escherichia coli (E. coli). The changes of inflammatory cytokines expression, and macrophage polarization in male, female, and ovariectomized C57BL/6 mice in sepsis model were investigated. For in vitro studies, different macrophages were treated with LPS. The function of estradiol (E2) on macrophage cell lines was verified and the mechanism of E2 affecting trained immunity was explored. We demonstrated that β-glucan-induced trained immunity was more resistant to sepsis in female than male mice. Macrophage polarization toward the M1 phenotype, which exhibited enhanced trained immunity, was related to the difference in sepsis resistance between female and male mice. Moreover, ovariectomized (OVX) mice manifested serious sepsis consequences with a weaker trained immunity effect than female mice. Female bone marrow-derived macrophages (BMDMs) were also apt to be polarized to the M1 phenotype in response to trained immunity in vitro. Furthermore, E2 promoted trained immunity in macrophage cell lines J774 and RAW264.7. E2 was also verified to facilitate trained immunity in primary BMDMs from female and male mice. Mechanistically, we found that E2 inhibited the nuclear translocation of RelB, which is a member of non-canonical pathway of NFκB and contributes to macrophage polarization to change the intensity of trained immunity. This study is the first to indicate the role of E2 in the trained immunity induced by β-glucan to protect against E. coli-induced sepsis via the non-canonical NFκB pathway. These results improve our understanding of the molecular mechanisms governing trained immunity in gender differences.

Classic and Novel Signaling Pathways Involved in Cancer: Targeting the NF-κB and Syk Signaling Pathways

The nuclear factor kappa B (NF-κB) consists of a family of transcription factors involved in the regulation of a wide variety of biological responses. Growing evidence support that NF-κB plays a major role in oncogenesis as well as its well-known function in the regulation of immune responses and inflammation. Therefore, we made a review of the diverse molecular mechanisms by which the NF-κB pathway is constitutively activated in different types of human cancers and the potential role of various oncogenic genes regulated by this transcription factor in cancer development and progression. We also discussed various pharmacological approaches employed to target the deregulated NF-κB signaling pathway and their possible therapeutic potential in cancer therapy. Moreover, Syk (Spleen tyrosine kinase), non-receptor tyrosine kinase which mediates signal transduction downstream of a variety of transmembrane receptors including classical immune-receptors like the B-cell receptor (BCR), which can also activate the inflammasome and NF-κB-mediated transcription of chemokines and cytokines in the presence of pathogens would be discussed as well. The highlight of this review article is to summarize the classic and novel signaling pathways involved in NF-κB and Syk signaling and then raise some possibilities for cancer therapy.

A detrimental role of RelB in mature oligodendrocytes during experimental acute encephalomyelitis

Background

Multiple sclerosis (MS) is an autoimmune demyelinating disease of the central nervous system (CNS). It is firmly established that overactivation of the p65 (RelA) nuclear factor kappa B (NF-κB) transcription factor upregulates expression of inflammatory mediators in both immune and non-immune resident CNS cells and promotes inflammation during MS. In contrast to p65, NF-κB family member RelB regulates immune cell development and can limit inflammation. Although RelB expression is induced during inflammation in the CNS, its role in MS remains unknown.

Methods

To examine the role of RelB in non-immune CNS cells, we generated mice with RelB specifically deleted in astrocytes (RelB^ΔAST), oligodendrocytes (RelB^ΔOLIGO), or neural progenitor-derived cells (RelB^ΔNP). We used experimental autoimmune encephalomyelitis (EAE), an accepted mouse model of MS, to assess the effect of RelB deletion on disease outcomes and performed analysis on the histological, cellular, and molecular level.

Results

Despite being a negative regulator of inflammation, conditional knockout of RelB in non-immune resident CNS cells surprisingly decreased the severity of EAE. This protective effect was recapitulated by conditional deletion of RelB in oligodendrocytes but not astrocytes. Deletion of RelB in oligodendrocytes reduced disease severity, promoted survival of mature oligodendrocytes, and correlated with increased activation of p65 NF-κB.

Conclusions

These findings suggest that RelB fine tunes inflammation and cell death/survival during EAE. Importantly, our data points out the detrimental role RelB plays in controlling survival of mature oligodendrocytes, which could be explored as a viable option to treat MS in the future.

Electronic supplementary material

The online version of this article (10.1186/s12974-019-1548-7) contains supplementary material, which is available to authorized users.

NF-κB as the mediator of metformin's effect on ageing and ageing-related diseases

Ageing can be defined as the progressive failure of repair and maintenance systems with a consequent accumulation of cellular damage in nucleic acids, proteins, and lipids. These various types of damage promote ageing by driving cellular senescence and apoptosis. The nuclear factor-kappa B (NF-kB) pathway is one of the key mediators of ageing and this pathway is activated by genotoxic, oxidative and inflammatory stress, and regulates expression of cytokines, growth factors, and genes that regulate apoptosis, cell-cycle progression, and inflammation. Therefore, NF-kB is increased in a variety of tissues with ageing, thus the inhibition of NF-kB leads to delayed onset of ageing-related symptoms and pathologies such as diabetes, atherosclerosis, and cancer. Metformin is often used as an anti-diabetic medication in type 2 diabetes throughout the world and appears to be a potential anti-ageing agent. Owing to its antioxidant, anticancer, cardio-protective and anti-inflammatory properties, metformin has become a potential candidate drug, improving in the context of ageing and ageing-related diseases. An inappropriate NF-kB activation is associated with diseases and pathologic conditions which can impair the activity of genes involved in cell senescence, apoptosis, immunity, and inflammation. Metformin, inhibiting the expression of NF-kB gene, eliminates the susceptibility to common diseases. This review underlines the pleiotropic effects of metformin in ageing and different ageing-related diseases and attributes its effects to the modulation of NF-kB.

Allograft Inflammatory Factor-1 Governs Hematopoietic Stem Cell Differentiation Into cDC1 and Monocyte-Derived Dendritic Cells Through IRF8 and RelB in vitro

The multistep differentiation process from hematopoietic stem cells through common myeloid progenitors into committed dendritic cell (DC) subsets remains to be fully addressed. These studies now show that Allograft Inflammatory Factor-1 (AIF1) is required for differentiation of classical DC type 1 (cDC1) subsets and monocyte-derived DC (Mo-DC). Phenotypic studies found that AIF1 expression increased in committed subsets differentiating from common myeloid progenitors (CMP). However, silencing AIF1 expression in hematopoietic stem progenitors restrained the capacity to differentiate into Mo-DC and cDC1 cell subsets under GM-CSF or Flt3-L stimuli conditions, respectively. This was further marked by restrained expression of IRF8, which is critical for development of Mo-DC and cDC1 subsets. As a result, absence of AIF1 restrained the cells at the Lin⁻CD117⁺FcγR⁻CD34⁺ CMP stage. Further biochemical studies revealed that abrogating AIF1 resulted in inhibition of the NFκB family member RelB expression and p38 MAPK phosphorylation during differentiation of Mo-DC. Lastly, protein binding studies identified that AIF1 interacts with protein kinase C (PKC) to influence downstream signaling pathways. Taken together, this is the first report showing a novel role of AIF1 as a calcium-responsive scaffold protein that supports IRF8 expression and interacts with PKC to drive NFκB-related RelB for successfully differentiating hematopoietic progenitor cells into cDC and Mo-DC subsets under Flt3-L and GM-CSF stimuli, respectively.

The Alternative NF-κB Pathway in Regulatory T Cell Homeostasis and Suppressive Function

CD4⁺Foxp3⁺ regulatory T cells (Tregs) are essential regulators of immune responses. Perturbation of Treg homeostasis or function can lead to uncontrolled inflammation and autoimmunity. Therefore, understanding the molecular mechanisms involved in Treg biology remains an active area of investigation. It has been shown previously that the NF-κB family of transcription factors, in particular, the canonical pathway subunits, c-Rel and p65, are crucial for the development, maintenance, and function of Tregs. However, the role of the alternative NF-κB pathway components, p100 and RelB, in Treg biology remains unclear. In this article, we show that conditional deletion of the p100 gene, nfkb2, in Tregs, resulted in massive inflammation because of impaired suppressive function of nfkb2-deficient Tregs. Surprisingly, mice lacking RelB in Tregs did not exhibit the same phenotype. Instead, deletion of both relb and nfkb2 rescued the inflammatory phenotype, demonstrating an essential role for p100 as an inhibitor of RelB in Tregs. Our data therefore illustrate a new role for the alternative NF-κB signaling pathway in Tregs that has implications for the understanding of molecular pathways driving tolerance and immunity.

Novel nonsense gain-of-function NFKB2 mutations associated with a combined immunodeficiency phenotype

NF-κB signaling through its NFKB1-dependent canonical and NFKB2-dependent noncanonical pathways plays distinctive roles in a diverse range of immune processes. Recently, mutations in these 2 genes have been associated with common variable immunodeficiency (CVID). While studying patients with genetically uncharacterized primary immunodeficiencies, we detected 2 novel nonsense gain-of-function (GOF) NFKB2 mutations (E418X and R635X) in 3 patients from 2 families, and a novel missense change (S866R) in another patient. Their immunophenotype was assessed by flow cytometry and protein expression; activation of canonical and noncanonical pathways was examined in peripheral blood mononuclear cells and transfected HEK293T cells through immunoblotting, immunohistochemistry, luciferase activity, real-time polymerase chain reaction, and multiplex assays. The S866R change disrupted a C-terminal NF-κΒ2 critical site affecting protein phosphorylation and nuclear translocation, resulting in CVID with adrenocorticotropic hormone deficiency, growth hormone deficiency, and mild ectodermal dysplasia as previously described. In contrast, the nonsense mutations E418X and R635X observed in 3 patients led to constitutive nuclear localization and activation of both canonical and noncanonical NF-κΒ pathways, resulting in a combined immunodeficiency (CID) without endocrine or ectodermal manifestations. These changes were also found in 2 asymptomatic relatives. Thus, these novel NFKB2 GOF mutations produce a nonfully penetrant CID phenotype through a different pathophysiologic mechanism than previously described for mutations in NFKB2.

Regulation of cell signaling pathways by dietary agents for cancer prevention and treatment

Although it is widely accepted that better food habits do play important role in cancer prevention and treatment, how dietary agents mediate their effects remains poorly understood. More than thousand different polyphenols have been identified from dietary plants. In this review, we discuss the underlying mechanism by which dietary agents can modulate a variety of cell-signaling pathways linked to cancer, including transcription factors, nuclear factor κB (NF-κB), signal transducer and activator of transcription 3 (STAT3), activator protein-1 (AP-1), β-catenin/Wnt, peroxisome proliferator activator receptor- gamma (PPAR-γ), Sonic Hedgehog, and nuclear factor erythroid 2 (Nrf2); growth factors receptors (EGFR, VEGFR, IGF1-R); protein Kinases (Ras/Raf, mTOR, PI3K, Bcr-abl and AMPK); and pro-inflammatory mediators (TNF-α, interleukins, COX-2, 5-LOX). In addition, modulation of proteasome and epigenetic changes by the dietary agents also play a major role in their ability to control cancer. Both in vitro and animal based studies support the role of dietary agents in cancer. The efficacy of dietary agents by clinical trials has also been reported. Importantly, natural agents are already in clinical trials against different kinds of cancer. Overall both in vitro and in vivo studies performed with dietary agents strongly support their role in cancer prevention. Thus, the famous quote "Let food be thy medicine and medicine be thy food" made by Hippocrates 25 centuries ago still holds good.

Lymphotoxin β receptor signalling executes Helicobacter pylori-driven gastric inflammation in a T4SS-dependent manner

OBJECTIVE

Lymphotoxin β receptor (LTβR) signalling has been implicated in inflammation-associated tumour development in different tissues. We have analysed the role of LTβR and alternative NF-κB signalling in Helicobacter pylori-mediated gastric inflammation and pathology.

DESIGN

We analysed several ligands and receptors of the alternative NF-κB pathway, RelB, p52 nuclear translocation and target genes in tissue samples of H. pylori-infected patients with different degrees of gastritis or early gastric tumours by in situ hybridisation, immunohistochemistry, Western blot and real-time PCR analyses. Molecular mechanisms involved in LTβR activation by H. pylori were assessed in vitro using human gastric cancer cell lines and distinct H. pylori isolates. The effects of blocking or agonistically activating LTβR on gastric pathology during challenge with a human pathogenic H. pylori strain were studied in a mouse model.

RESULTS

Among the tested candidates, LT was significantly increased and activated alternative NF-κB signalling was observed in the gastric mucosa of H. pylori-infected patients. H. pyloriinduced LTβR-ligand expression in a type IV secretion system-dependent but CagA-independent manner, resulting in activation of the alternative NF-κB pathway, which was further enhanced by blocking canonical NF-κB during infection. Blocking LTβR signalling in vivo suppressed H. pylori-driven gastritis, whereas LTβR activation in gastric epithelial cells of infected mice induced a broadened pro-inflammatory chemokine milieu, resulting in exacerbated pathology.

CONCLUSIONS

LTβR-triggered activation of alternative NF-κB signalling in gastric epithelial cells executes H. pylori-induced chronic gastritis, representing a novel target to restrict gastric inflammation and pathology elicited by H. pylori, while exclusively targeting canonical NF-κB may aggravate pathology by enhancing the alternative pathway.

RAC1b overexpression stimulates proliferation and NF-kB-mediated anti-apoptotic signaling in thyroid cancer cells

Overexpression of tumor-associated RAC1b has been recently highlighted as one of the most promising targets for therapeutic intervention in colon, breast, lung and pancreatic cancer. RAC1b is a hyperactive variant of the small GTPase RAC1 and has been recently shown to be overexpressed in a subset of papillary thyroid carcinomas associated with unfavorable outcome. Using the K1 PTC derived cell line as an in vitro model, we observed that both RAC1 and RAC1b were able to induce a significant increase on NF-kB and cyclin D1 reporter activity. A clear p65 nuclear localization was found in cells transfected with RAC1b-WT, confirming NF-kB canonical pathway activation. Consistently, we observed a RAC1b-mediated decrease in IκBα (NF-kB inhibitor) protein levels. Moreover, we show that RAC1b overexpression stimulates G1/S progression and protects thyroid cells against induced apoptosis, the latter through a process involving the NF-kB pathway. Present data support previous findings suggesting an important role for RAC1b in the development of follicular cell-derived thyroid malignancies and point out NF-kB activation as one of the molecular mechanisms associated with the pro-tumorigenic advantage of RAC1b overexpression in thyroid carcinomas.

Interplay of Murine Gammaherpesvirus 68 with NF-kappaB Signaling of the Host

Herpesviruses establish a chronic infection in the host characterized by intervals of lytic replication, quiescent latency, and reactivation from latency. Murine gammaherpesvirus 68 (MHV68) naturally infects small rodents and has genetic and biologic parallels with the human gammaherpesviruses (gHVs), Kaposi's sarcoma-associated herpesvirus and Epstein-Barr virus. The murine gammaherpesvirus model pathogen system provides a platform to apply cutting-edge approaches to dissect the interplay of gammaherpesvirus and host determinants that enable colonization of the host, and that shape the latent or lytic fate of an infected cell. This knowledge is critical for the development of novel therapeutic interventions against the oncogenic gHVs. The nuclear factor kappa B (NF-κB) signaling pathway is well-known for its role in the promotion of inflammation and many aspects of B cell biology. Here, we review key aspects of the virus lifecycle in the host, with an emphasis on the route that the virus takes to gain access to the B cell latency reservoir. We highlight how the murine gammaherpesvirus requires components of the NF-κB signaling pathway to promote replication, latency establishment, and maintenance of latency. These studies emphasize the complexity of gammaherpesvirus interactions with NF-κB signaling components that direct innate and adaptive immune responses of the host. Importantly, multiple facets of NF-κB signaling have been identified that might be targeted to reduce the burden of gammaherpesvirus-associated diseases.

Non-canonical NF-κB pathway activation predicts outcome in borderline oestrogen receptor positive breast carcinoma

Background:

NF-κB signalling appears deregulated in breast tumours. The purpose of this study was to determine whether the non-canonical NF-κB pathway, is activated in oestrogen receptor positive (ER+) breast cancer, to identify any correlation between its activity and the clinico-pathological phenotype and to explore whether NF-κB2 and RelB subunits and/or any of their target genes might be used as a predictive marker.

Methods:

Two independent cohorts of ER+ early breast cancer patients treated with adjuvant endocrine therapy were included in the study. Activation of RelB and NF-κB2 subunits was determined in a training set of 121 patients by measuring DNA-binding activities in nuclear extracts from fresh frozen specimens by an ELISA-based assay. Samples of 15 ER− breast cancer patients were also included in the study. In a large validation cohort of 207 patients, nuclear immunostaining of RelB and NF-κB2 on formalin-fixed paraffin-embedded specimens was performed. Statistical correlation within clinico-pathological factors, disease-free survival (DFS) and overall survival (OS) was evaluated. Publicly available gene expression and survival data have been interrogated aimed to identify target genes.

Results:

Activation of NF-κB2 and RelB was found in 53.7 and 49.2% of the 121 ER+ tumours analysed, with similar levels to ER− breast tumours analysed in parallel for comparisons. In the validation cohort, we obtained a similar proportion of cases with activation of NF-κB2 and RelB (59.9 and 32.4%), with a 39.6% of co-activation. Multiplexing immunofluorescence in breast cancer tissue confirmed an inverse spatial distribution of ER with NF-κB2 and RelB nuclear expression in tumour cells. Interestingly, NF-κB2 and RelB mRNA expression was inversely correlated with ER gene (ESR1) levels (P<0.001, both) and its activation was significantly associated with worse DFS (P=0.005 and P=0.035, respectively) in ER+ breast cancer. Moreover, the co-activation of both subunits showed a stronger association with early relapse (P=0.002) and OS (P=0.001). Finally, higher expression of the non-canonical NF-κB target gene myoglobin was associated with a poor outcome in ER+ breast cancer (DFS, P<0.05).

Conclusions:

The non-canonical NF-κB pathway activation is inversely associated with oestrogen receptor expression in ER+ breast cancer and predicts poor survival in this subgroup. The myoglobin gene expression has been identified as a possible surrogate marker of the non-canonical NF-κB pathway activation in these tumours.

Roles of NF-κB in Cancer and Inflammatory Diseases and Their Therapeutic Approaches

Nuclear factor-κB (NF-κB) is a transcription factor that plays a crucial role in various biological processes, including immune response, inflammation, cell growth and survival, and development. NF-κB is critical for human health, and aberrant NF-κB activation contributes to development of various autoimmune, inflammatory and malignant disorders including rheumatoid arthritis, atherosclerosis, inflammatory bowel diseases, multiple sclerosis and malignant tumors. Thus, inhibiting NF-κB signaling has potential therapeutic applications in cancer and inflammatory diseases.

Signaling via the NFκB system

The nuclear factor kappa B (NFκB) family of transcription factors is a key regulator of immune development, immune responses, inflammation, and cancer. The NFκB signaling system (defined by the interactions between NFκB dimers, IκB regulators, and IKK complexes) is responsive to a number of stimuli, and upon ligand-receptor engagement, distinct cellular outcomes, appropriate to the specific signal received, are set into motion. After almost three decades of study, many signaling mechanisms are well understood, rendering them amenable to mathematical modeling, which can reveal deeper insights about the regulatory design principles. While other reviews have focused on upstream, receptor proximal signaling (Hayden MS, Ghosh S. Signaling to NF-κB. Genes Dev 2004, 18:2195-2224; Verstrepen L, Bekaert T, Chau TL, Tavernier J, Chariot A, Beyaert R. TLR-4, IL-1R and TNF-R signaling to NF-κB: variations on a common theme. Cell Mol Life Sci 2008, 65:2964-2978), and advances through computational modeling (Basak S, Behar M, Hoffmann A. Lessons from mathematically modeling the NF-κB pathway. Immunol Rev 2012, 246:221-238; Williams R, Timmis J, Qwarnstrom E. Computational models of the NF-KB signalling pathway. Computation 2014, 2:131), in this review we aim to summarize the current understanding of the NFκB signaling system itself, the molecular mechanisms, and systems properties that are key to its diverse biological functions, and we discuss remaining questions in the field. WIREs Syst Biol Med 2016, 8:227-241. doi: 10.1002/wsbm.1331 For further resources related to this article, please visit the WIREs website.

The non-canonical NF-κB pathway is induced by cytokines in pancreatic beta cells and contributes to cell death and proinflammatory responses in vitro

AIMS/HYPOTHESIS

Activation of the transcription factor nuclear factor (NF)-κB by proinflammatory cytokines plays an important role in beta cell demise in type 1 diabetes. Two main signalling pathways are known to activate NF-κB, namely the canonical and the non-canonical pathways. Up to now, studies on the role of NF-κB activation in beta cells have focused on the canonical pathway. The aim of this study was to investigate whether cytokines activate the non-canonical pathway in beta cells, how this pathway is regulated and the consequences of its activation on beta cell fate.

METHODS

NF-κB signalling was analysed by immunoblotting, promoter reporter assays and real-time RT-PCR, after knockdown or overexpression of key genes/proteins. INS-1E cells, FACS-purified rat beta cells and the human beta cell line EndoC-βH1 exposed to cytokines were used as models.

RESULTS

IL-1β plus IFN-γ induced stabilisation of NF-κB-inducing kinase and increased the expression and cleavage of p100 protein, culminating in the nuclear translocation of p52, the hallmark of the non-canonical signalling. This activation relied on different crosstalks between the canonical and non-canonical pathways, some of which were beta cell specific. Importantly, cytokine-mediated activation of the non-canonical pathway controlled the expression of 'late' NF-κB-dependent genes, regulating both pro-apoptotic and inflammatory responses, which are implicated in beta cell loss in early type 1 diabetes.

CONCLUSIONS/INTERPRETATION

The atypical activation of the non-canonical NF-κB pathway by proinflammatory cytokines constitutes a novel 'feed-forward' mechanism that contributes to the particularly pro-apoptotic effect of NF-κB in beta cells.

Chimeric Vaccine Stimulation of Human Dendritic Cell Indoleamine 2, 3-Dioxygenase Occurs via the Non-Canonical NF-κB Pathway

A chimeric protein vaccine composed of the cholera toxin B subunit fused to proinsulin (CTB-INS) was shown to suppress type 1 diabetes onset in NOD mice and upregulate biosynthesis of the tryptophan catabolic enzyme indoleamine 2, 3-dioxygenase (IDO1) in human dendritic cells (DCs). Here we demonstrate siRNA inhibition of the NF-κB-inducing kinase (NIK) suppresses vaccine-induced IDO1 biosynthesis as well as IKKα phosphorylation. Chromatin immunoprecipitation (ChIP) analysis of CTB-INS inoculated DCs showed that RelB bound to NF-κB consensus sequences in the IDO1 promoter, suggesting vaccine stimulation of the non-canonical NF-κB pathway activates IDO1 expression in vivo. The addition of Tumor Necrosis Factor Associated Factors (TRAF) TRAF 2, 3 and TRAF6 blocking peptides to vaccine inoculated DCs was shown to inhibit IDO1 biosynthesis. This experimental outcome suggests vaccine activation of the TNFR super-family receptor pathway leads to upregulation of IDO1 biosynthesis in CTB-INS inoculated dendritic cells. Together, our experimental data suggest the CTB-INS vaccine uses a TNFR-dependent signaling pathway of the non-canonical NF-κB signaling pathway resulting in suppression of dendritic cell mediated type 1 diabetes autoimmunity.

p52 Overexpression Increases Epithelial Apoptosis, Enhances Lung Injury, and Reduces Survival after Lipopolysaccharide Treatment

Although numerous studies have demonstrated a critical role for canonical NF-κB signaling in inflammation and disease, the function of the noncanonical NF-κB pathway remains ill-defined. In lung tissue from patients with acute respiratory distress syndrome, we identified increased expression of the noncanonical pathway component p100/p52. To investigate the effects of p52 expression in vivo, we generated a novel transgenic mouse model with inducible expression of p52 in Clara cell secretory protein-expressing airway epithelial cells. Although p52 overexpression alone did not cause significant inflammation, p52 overexpression caused increased lung inflammation, injury, and mortality following intratracheal delivery of Escherichia coli LPS. No differences in cytokine/chemokine expression were measured between p52-overexpressing mice and controls, but increased apoptosis of Clara cell secretory protein-positive airway epithelial cells was observed in transgenic mice after LPS stimulation. In vitro studies in lung epithelial cells showed that p52 overexpression reduced cell survival and increased the expression of several proapoptotic genes during cellular stress. Collectively, these studies demonstrate a novel role for p52 in cell survival/apoptosis of airway epithelial cells and implicate noncanonical NF-κB signaling in the pathogenesis of acute respiratory distress syndrome.

TNF induced inhibition of Cirbp expression depends on RelB NF-κB signalling pathway

The circadian clock is required for the rhythmic expression of a plethora of genes that orchestrate metabolism, sleep-wake behaviour and the immune response to pathogens. The cold-inducible RNA binding protein (CIRBP) is required for high amplitude expression of clock genes. Moreover, CIRBP protects the expression of clock genes from the inhibitory effects of tumour necrosis factor (TNF). However, since TNF represses Cirbp expression, the protective effect of CIRBP is lost. Here, we show that the TNF effect on Cirbp requires the non-canonical NF-κB signalling pathway. While a knock down of RelA does not alter the effects of TNF on Cirbp, a knock down of RelB represses this effect. In addition, the data indicate that p50 and p52 are required in the TNF induced inhibition of Cirbp. These results show that Cirbp expression in TNF treated cells is regulated via the non-canonical NF-κB pathway.

B-Cell Activating Factor as a Cancer Biomarker and Its Implications in Cancer-Related Cachexia

B-cell activating factor (BAFF) is a cytokine and adipokine of the TNF ligand superfamily. The main biological function of BAFF in maintaining the maturation of B-cells to plasma cells has recently made it a target of the first FDA-approved selective BAFF antibody, belimumab, for the therapy of systemic lupus erythematosus. Concomitantly, the role of BAFF in cancer has been a subject of research since its discovery. Here we review BAFF as a biomarker of malignant disease activity and prognostic factor in B-cell derived malignancies such as multiple myeloma. Moreover, anti-BAFF therapy seems to be a promising approach in treatment of B-cell derived leukemias/lymphomas. In nonhematologic solid tumors, BAFF may contribute to cancer progression by mechanisms both dependent on and independent of BAFF's proinflammatory role. We also describe ongoing research into the pathophysiological link between BAFF and cancer-related cachexia. BAFF has been shown to contribute to inflammation and insulin resistance which are known to worsen cancer cachexia syndrome. Taking all the above together, BAFF is emerging as a biomarker of several malignancies and a possible hallmark of cancer cachexia.

The Transitional Endoplasmic Reticulum ATPase p97 Regulates the Alternative Nuclear Factor NF-κB Signaling via Partial Degradation of the NF-κB Subunit p100

Partial degradation of the p100 subunit to generate p52 subunit is a hallmark of the alternative NF-κB pathway, which has been implicated in cancer. Here, we uncovered a role of the p97-Npl4-Ufd1 complex in mediating p100-to-p52 processing and therefore positively regulating the alternative NF-κB pathway. We observed an elevation of p97 mRNA levels in lymphoma patients, which positively correlates with NFKB2 expression, a downstream target gene of the alternative NF-κB pathway. Moreover, NFKB2 mRNA levels were aberrantly down-regulated in patients with inclusion body myopathy associated with Paget's disease of the bone and frontotemporal dementia (IBMPFD), a disease caused by mutation of p97. Inactivation of p97 or depletion of the p97-Npl4-Ufd1 complex inhibits the processing of p100 into p52, decreasing transcription of the downstream target genes. Further analyses reveal that the p97-Npl4-Ufd1 complex interacts with F-box and WD repeats protein SCF(βTrCP) complex to regulate the partial degradation of p100, a process involving K48- and K11-linked ubiquitination. In line with this, in LPS-induced lung damage mice model, generation of p52 is significantly decreased in p97-KD mice compared with mock mice. Finally, abrogation of p97 ATPase activity by its specific inhibitor DBeQ, efficiently decreased proliferation of lymphoma cells. Collectively, our study revealed a regulatory role of the p97-Npl4-Ufd1 complex in regulating p100 partial degradation, highlighting the potential of p97 as a drug target for cancers with aberrant activation of the alternative NF-κB pathway.

RELB Alters Proliferation of Human Pluripotent Stem Cells via IMP3- and LIN28-Mediated Modulation of the Expression of IGF2 and Other Cell-Cycle Regulators

The molecular mechanisms that orchestrate the exit from pluripotency, cell cycle progression, and lineage-specific differentiation in human pluripotent stem cells (hPSCs) are poorly understood. RELB, a key protein in the noncanonical nuclear factor-kappaB (NFκB) signaling pathway, was previously implicated in controlling the switch between human embryonic stem cell (hESC) proliferation and differentiation. Here, we show that RELB enhances the proliferation of hESCs and human-induced pluripotent stem cells (hiPSCs) without affecting their pluripotency. We demonstrate that RELB does this by interacting with two RNA-binding proteins LIN28A and IMP3 (IGF2 mRNA-binding protein 3); further, these interactions control mRNA levels and protein expression of insulin-like growth factor 2 (IGF2) and key cell-cycle genes. Finally, after stress, these proteins co-localize in stress granules in hESCs and iPSCs. Our data identify RELB as a novel regulator of hPSC proliferation, and suggest a new function for RELB, in addition to its widely accepted role as a transcription factor, that involves recruitment of IMP3 and LIN28 to the cytosolic mRNA translation-control domains for post-transcriptional modulation of IGF2 and cell-cycle gene expression.

TRAF protein function in noncanonical NF-κB signaling

Nuclear factor-κB (NF-κB) signaling is classified into the canonical and noncanonical pathways. We describe in this chapter the methods used to study the noncanonical pathway, including derivation of primary cells, pathway stimulation, and immunoblotting.

Noncanonical NF-κB activation and SDF-1 expression in human endothelial cells

NF-κB is a family of transcription factors regulated through two distinct signaling cascades, the classical and the Noncanonical NF-κB pathways. Noncanonical NF-κB plays important roles in the immune system, as it is necessary for lymphoid organogenesis and B-cell survival and differentiation, as well as osteoclastogenesis. In the last few years, there has been an increased number of studies focusing on both identifying the upstream events that regulate the noncanonical NF-κB pathway as well as determining the physiological roles of noncanonical NF-κB in normal and disease pathologies, such as cancer and autoimmune diseases. Dysregulation of noncanonical NF-κB has now been associated with the pathogenesis of several types of lymphomas and autoimmune diseases and is believed to contribute to chronic inflammatory diseases, including ulcerative colitis. These studies suggest that targeting the Noncanonical pathway, similar to classical NF-κB, may have some therapeutic potential in the future; however, there is still quite a bit about the regulation of the noncanonical signaling that remains to be defined. In this chapter we describe the use of HUVEC, as an in vitro model for examining noncanonical NF-κB signaling in response to different stimuli. We demonstrate two different methods to measure noncanonical NF-κB activation: the processing of p100 to p52, and noncanonical NF-κB-dependent gene expression of CXCL12. The first method examines a key regulatory requirement for noncanonical NF-κB activation, by which p100 undergoes proteolytic cleavage to relieve the inhibition of NF-κB dimers for nuclear translocation and activation of gene transcription. The latter demonstrates the downstream effects of activated noncanonical NF-κB in response to stimuli.

IKK-induced NF-κB1 p105 proteolysis is critical for B cell antibody responses to T cell-dependent antigen

Jacque et al. investigate the functions of NF-κB1 p105 and its associated NF-κB–binding partners in B cells, using a mutant mouse strain that carries a form of the NF-κB1 precursor that is resistant to IKK-induced proteolysis. They identify a critical B cell–intrinsic role for this IKK signaling pathway in the antigen-induced survival and differentiation of follicular mature B cells.

The importance of IκB kinase (IKK)–induced proteolysis of NF-κB1 p105 in B cells was investigated using Nfkb1^SSAA/SSAA mice, in which this NF-κB signaling pathway is blocked. Nfkb1^SSAA mutation had no effect on the development and homeostasis of follicular mature (FM) B cells. However, analysis of mixed bone marrow chimeras revealed that Nfkb1^SSAA/SSAA FM B cells were completely unable to mediate T cell–dependent antibody responses. Nfkb1^SSAA mutation decreased B cell antigen receptor (BCR) activation of NF-κB in FM B cells, which selectively blocked BCR stimulation of cell survival and antigen-induced differentiation into plasmablasts and germinal center B cells due to reduced expression of Bcl-2 family proteins and IRF4, respectively. In contrast, the antigen-presenting function of FM B cells and their BCR-induced migration to the follicle T cell zone border, as well as their growth and proliferation after BCR stimulation, were not affected. All of the inhibitory effects of Nfkb1^SSAA mutation on B cell functions were rescued by normalizing NF-κB activation genetically. Our study identifies critical B cell-intrinsic functions for IKK-induced NF-κB1 p105 proteolysis in the antigen-induced survival and differentiation of FM B cells, which are essential for T-dependent antibody responses.

Imaging of nuclear factor κB activation induced by ionizing radiation in human embryonic kidney (HEK) cells

Ionizing radiation modulates several signaling pathways resulting in transcription factor activation. Nuclear factor kappa B (NF-κB) is one of the most important transcription factors that respond to changes in the environment of a mammalian cell. NF-κB plays a key role not only in inflammation and immune regulation but also in cellular radiation response. In response to DNA damage, NF-κB might inhibit apoptosis and promote carcinogenesis. Our previous studies showed that ionizing radiation is very effective in inducing biological damages. Therefore, it is important to understand the radiation-induced NF-κB signaling cascade. The current study aims to improve existing mammalian cell-based reporter assays for NF-κB activation by the use of DD-tdTomato which is a destabilized variant of red fluorescent protein tdTomato. It is demonstrated that exposure of recombinant human embryonic kidney cells (HEK/293 transfected with a reporter constructs containing NF-κB binding sites in its promoter) to ionizing radiation induces NF-κB-dependent DD-tdTomato expression. Using this reporter assays, NF-κB signaling in mammalian cells was monitored by flow cytometry and fluorescence microscopy. Activation of NF-κB by the canonical pathway was found to be quicker than by the genotoxin- and stress-induced pathway. X-rays activate NF-κB in HEK cells in a dose-dependent manner, and the extent of NF-κB activation is higher as compared to camptothecin.

Regulation of NF-κB by TNF family cytokines

The NF-κB family of inducible transcription factors is activated in response to a variety of stimuli. Amongst the best-characterized inducers of NF-κB are members of the TNF family of cytokines. Research on NF-κB and TNF have been tightly intertwined for more than 25 years. Perhaps the most compelling examples of the interconnectedness of NF-κB and the TNF have come from analysis of knock-out mice that are unable to activate NF-κB. Such mice die embryonically, however, deletion of TNF or TNFR1 can rescue the lethality thereby illustrating the important role of NF-κB as the key regulator of transcriptional responses to TNF. The physiological connections between NF-κB and TNF cytokines are numerous and best explored in articles focusing on a single TNF family member. Instead, in this review, we explore general mechanisms of TNF cytokine signaling, with a focus on the upstream signaling events leading to activation of the so-called canonical and noncanonical NF-κB pathways by TNFR1 and CD40, respectively.

NFKB1 -94 insertion/deletion polymorphism and cancer risk: a meta-analysis

Previous studies on the associations of the NFKB1 -94 insertion/deletion polymorphism with cancer risk have produced conflicting results. The purpose of this meta-analysis is to define the effect of the NFKB1 -94 insertion/deletion polymorphism on cancer risk. A search of the literature by PubMed was performed to identify studies based on the predetermined inclusion criteria. Twenty-three studies consisting of 6,494 cases and 9,884 controls were identified and analyzed. Overall, significant association was observed between the polymorphism and cancer risk under all genetic models. Subgroup analysis according to ethnicity and cancer type also detected significant association. The NFKB1 -94 insertion/deletion polymorphism was associated with cancer risk in Asian population (dominant model: OR=1.52, 95 % CI=1.17-1.98; recessive model: OR=1.50, 95 % CI=1.26-1.79; II vs. DD: OR=1.90, 95 % CI=1.37-2.65; ID vs. DD: OR=1.32, 95 % CI=1.05-1.66; I vs. D: OR=1.37, 95 % CI=1.17-1.60), but not in Caucasian population. In addition, significant associations in OC, HCC, and OSCC were observed, but significant associations were not found in BC and LC. The current meta-analysis suggested that NFKB1 -94 insertion/deletion polymorphism may influence cancer risk in Asian population.

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.

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.

Atypical IκB proteins - nuclear modulators of NF-κB signaling

Nuclear factor κB (NF-κB) controls a multitude of physiological processes such as cell differentiation, cytokine expression, survival and proliferation. Since NF-κB governs embryogenesis, tissue homeostasis and the functions of innate and adaptive immune cells it represents one of the most important and versatile signaling networks known. Its activity is regulated via the inhibitors of NF-κB signaling, the IκB proteins. Classical IκBs, like the prototypical protein IκBα, sequester NF-κB transcription factors in the cytoplasm by masking of their nuclear localization signals (NLS). Thus, binding of NF-κB to the DNA is inhibited. The accessibility of the NLS is controlled via the degradation of IκBα. Phosphorylation of the conserved serine residues 32 and 36 leads to polyubiquitination and subsequent proteasomal degradation. This process marks the central event of canonical NF-κB activation. Once their NLS is accessible, NF-κB transcription factors translocate into the nucleus, bind to the DNA and regulate the transcription of their respective target genes. Several studies described a distinct group of atypical IκB proteins, referred to as the BCL-3 subfamily. Those atypical IκBs show entirely different sub-cellular localizations, activation kinetics and an unexpected functional diversity. First of all, their interaction with NF-κB transcription factors takes place in the nucleus in contrast to classical IκBs, whose binding to NF-κB predominantly occurs in the cytoplasm. Secondly, atypical IκBs are strongly induced after NF-κB activation, for example by LPS and IL-1β stimulation or triggering of B cell and T cell antigen receptors, but are not degraded in the first place like their conventional relatives. Finally, the interaction of atypical IκBs with DNA-associated NF-κB transcription factors can further enhance or diminish their transcriptional activity. Thus, they do not exclusively act as inhibitors of NF-κB activity. The capacity to modulate NF-κB transcription either positively or negatively, represents their most important and unique mechanistic difference to classical IκBs. Several reports revealed the importance of atypical IκB proteins for immune homeostasis and the severe consequences following their loss of function. This review summarizes insights into the physiological processes regulated by this protein class and the relevance of atypical IκB functioning.

TWEAK and cIAP1 regulate myoblast fusion through the noncanonical NF-κB signaling pathway

The fusion of mononucleated muscle progenitor cells (myoblasts) into multinucleated muscle fibers is a critical aspect of muscle development and regeneration. We identified the noncanonical nuclear factor κB (NF-κB) pathway as a signaling axis that drives the recruitment of myoblasts into new muscle fibers. Loss of cellular inhibitor of apoptosis 1 (cIAP1) protein led to constitutive activation of the noncanonical NF-κB pathway and an increase in the number of nuclei per myotube. Knockdown of essential mediators of NF-κB signaling, such as p100, RelB, inhibitor of κB kinase α, and NF-κB-inducing kinase, attenuated myoblast fusion in wild-type myoblasts. In contrast, the extent of myoblast fusion was increased when the activity of the noncanonical NF-κB pathway was enhanced by increasing the abundance of p52 and RelB or decreasing the abundance of tumor necrosis factor (TNF) receptor-associated factor 3, an inhibitor of this pathway. Low concentrations of the cytokine TNF-like weak inducer of apoptosis (TWEAK), which preferentially activates the noncanonical NF-κB pathway, also increased myoblast fusion, without causing atrophy or impairing myogenesis. These results identify roles for TWEAK, cIAP1, and noncanonical NF-κB signaling in the regulation of myoblast fusion and highlight a role for cytokine signaling during adult skeletal myogenesis.

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.