CD40 regulates the processing of NF-kappaB2 p100 to p52

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.

Activation of GSK-3 disrupts cholinergic homoeostasis in nucleus basalis of Meynert and frontal cortex of rats

The cholinergic impairment is an early marker in Alzheimer's disease (AD), while the mechanisms are not fully understood. We investigated here the effects of glycogen synthase kinse-3 (GSK-3) activation on the cholinergic homoeostasis in nucleus basalis of Meynert (NBM) and frontal cortex, the cholinergic enriched regions. We activated GSK-3 by lateral ventricular infusion of wortmannin (WT) and GF-109203X (GFX), the inhibitors of phosphoinositol-3 kinase (PI3-K) and protein kinase C (PKC), respectively, and significantly decreased the acetylcholine (ACh) level via inhibiting choline acetyl transferase (ChAT) rather than regulating acetylcholinesterase (AChE). Neuronal axonal transport was disrupted and ChAT accumulation occurred in NBM and frontal cortex accompanied with hyperphosphorylation of tau and neurofilaments. Moreover, ChAT expression decreased in NBM attributing to cleavage of nuclear factor-κB/p100 into p52 for translocation into nucleus to lower ChAT mRNA level. The cholinergic dysfunction could be mimicked by overexpression of GSK-3 and rescued by simultaneous administration of LiCl or SB216763, inhibitors of GSK-3. Our data reveal the molecular mechanism that may underlie the cholinergic impairments in AD patients.

The non-canonical NF-κB pathway in immunity and inflammation

The nuclear factor-κB (NF-κB) family of transcription factors is activated by canonical and non-canonical signalling pathways, which differ in both signalling components and biological functions. Recent studies have revealed important roles for the non-canonical NF-κB pathway in regulating different aspects of immune functions. Defects in non-canonical NF-κB signalling are associated with severe immune deficiencies, whereas dysregulated activation of this pathway contributes to the pathogenesis of various autoimmune and inflammatory diseases. Here we review the signalling mechanisms and the biological function of the non-canonical NF-κB pathway. We also discuss recent progress in elucidating the molecular mechanisms regulating non-canonical NF-κB pathway activation, which may provide new opportunities for therapeutic strategies.

The aryl hydrocarbon receptor repressor - More than a simple feedback inhibitor of AhR signaling: Clues for its role in inflammation and cancer

The aryl hydrocarbon receptor repressor (AhRR) was first described as a specific competitive repressor of aryl hydrocarbon receptor (AhR) activity based on its ability to dimerize with the AhR nuclear translocator (ARNT) and through direct competition of AhR/ARNT and AhRR/ARNT complexes for binding to dioxin-responsive elements (DREs). Like AhR, AhRR belongs to the basic Helix-Loop-Helix/Per-ARNT-Sim (bHLH/PAS) protein family but lacks functional ligand-binding and transactivation domains. Transient transfection experiments with ARNT and AhRR mutants examining the inhibitory mechanism of AhRR suggested a more complex mechanism than the simple mechanism of negative feedback through sequestration of ARNT to regulate AhR signaling. Recently, AhRR has been shown to act as a tumor suppressor gene in several types of cancer cells. Furthermore, epidemiological studies have found epigenetic changes and silencing of AhRR associated with exposure to cigarette smoke and cancer development. Additional studies from our laboratories have demonstrated that AhRR represses other signaling pathways including NF-κB and is capable of regulating inflammatory responses. A better understanding of the regulatory mechanisms of AhRR in AhR signaling and adverse outcome pathways leading to deregulated inflammatory responses contributing to tumor promotion and other adverse health effects is expected from future studies. This review article summarizes the characteristics of AhRR as an inhibitor of AhR activity and highlights more recent findings pointing out the role of AhRR in inflammation and tumorigenesis.

YOD1/TRAF6 association balances p62-dependent IL-1 signaling to NF-κB

The ubiquitin ligase TRAF6 is a key regulator of canonical IκB kinase (IKK)/NF-κB signaling in response to interleukin-1 (IL-1) stimulation. Here, we identified the deubiquitinating enzyme YOD1 (OTUD2) as a novel interactor of TRAF6 in human cells. YOD1 binds to the C-terminal TRAF homology domain of TRAF6 that also serves as the interaction surface for the adaptor p62/Sequestosome-1, which is required for IL-1 signaling to NF-κB. We show that YOD1 competes with p62 for TRAF6 association and abolishes the sequestration of TRAF6 to cytosolic p62 aggregates by a non-catalytic mechanism. YOD1 associates with TRAF6 in unstimulated cells but is released upon IL-1β stimulation, thereby facilitating TRAF6 auto-ubiquitination as well as NEMO/IKKγ substrate ubiquitination. Further, IL-1 triggered IKK/NF-κB signaling and induction of target genes is decreased by YOD1 overexpression and augmented after YOD1 depletion. Hence, our data define that YOD1 antagonizes TRAF6/p62-dependent IL-1 signaling to NF-κB.

DOI:http://dx.doi.org/10.7554/eLife.22416.001

Targeting IKK and NF-κB for Therapy

In addition to regulating immune responses, the NF-κB family of transcription factors also promotes cellular proliferation and survival. NF-κB and its activating kinase, IKK, have become appealing therapeutic targets because of their critical roles in the progression of many diseases including chronic inflammation and cancer. Here, we discuss the conditions that lead to pathway activation, the effects of constitutive activation, and some of the strategies used to inhibit NF-κB signaling.

Structural Basis for the Activation of IKK1/α

Distinct signaling pathways activate the NF-κB family of transcription factors. The canonical NF-κB-signaling pathway is mediated by IκB kinase 2/β (IKK2/β), while the non-canonical pathway depends on IKK1/α. The structural and biochemical bases for distinct signaling by these otherwise highly similar IKKs are unclear. We report single-particle cryoelectron microscopy (cryo-EM) and X-ray crystal structures of human IKK1 in dimeric (∼150 kDa) and hexameric (∼450 kDa) forms. The hexamer, which is the representative form in the crystal but comprises only ∼2% of the particles in solution by cryo-EM, is a trimer of IKK1 dimers. While IKK1 hexamers are not detectable in cells, the surface that supports hexamer formation is critical for IKK1-dependent cellular processing of p100 to p52, the hallmark of non-canonical NF-κB signaling. Comparison of this surface to that in IKK2 indicates significant divergence, and it suggests a fundamental role for this surface in signaling by these kinases through distinct pathways.

TRAF3 as a powerful and multitalented regulator of lymphocyte functions

This review summarizes the current state of knowledge regarding the roles of the signaling adapter protein tumor necrosis factor receptor (TNFR)-associated factor 3 in regulating the functions of B and T lymphocytes. In B lymphocytes, TNFR-associated factor 3 inhibits signaling by TNFR superfamily receptors, Toll-like receptors, and interleukin-6R. In contrast, signaling to B cells by the virally encoded oncogenic protein latent membrane protein 1 is promoted by TNFR-associated factor 3. An important B cell-specific role for TNFR-associated factor 3 is the inhibition of homeostatic survival, directly relevant to the common occurrence of TNFR-associated factor 3 mutations in human B cell malignancies. TNFR-associated factor 3 was recently found to be a resident nuclear protein in B cells, where it interacts with and inhibits gene expression mediated by the cAMP response element-binding protein transcription complex, including expression of the prosurvival protein myeloid leukemia cell differentiation protein 1. In T lymphocytes, TNFR-associated factor 3 is required for normal signaling by the T cell antigen receptor, while inhibiting signaling by the interleukin-2 receptor. Cytoplasmic TNFR -associated factor 3 restrains nuclear factor-κB2 activation in both T and B cells. Clinical implications and future directions for the study of this context-dependent signaling regulator are discussed.

The NF-κB subunit RelB controls p100 processing by competing with the kinases NIK and IKK1 for binding to p100

The heterodimer formed by the nuclear factor κB (NF-κB) subunits p52 and RelB is the product of noncanonical signaling in which the key event is the proteolytic processing of p100 to generate p52. The kinases NF-κB-inducing kinase (NIK) and inhibitor of κB kinase 1 (IKK1; also known as IKKα) are activated during noncanonical signaling and play essential roles in p100 processing. In resting cells, RelB remains associated with unprocessed p100 as a transcriptionally inert p100:RelB complex, which is part of a larger assembly with other NF-κB factors known as the "kappaBsome." We investigated how these two different RelB-containing complexes with opposing effects on target gene transcription are formed. We found that RelB controls the extent of both p100 processing and kappaBsome formation during noncanonical signaling. Within an apparently "transitional" complex that contains RelB, NIK, IKK1, and p100, RelB and the NIK:IKK1 complex competed with each other for binding to a region of p100. A fraction of p100 in the transitional complex was refractory to processing, which resulted in the formation of the kappaBsome. However, another fraction of p100 protein underwent NIK:IKK1-mediated phosphorylation and processing while remaining bound to RelB, thus forming the p52:RelB heterodimer. Our results suggest that changes in the relative concentrations of RelB, NIK:IKK1, and p100 during noncanonical signaling modulate this transitional complex and are critical for maintaining the fine balance between the processing and protection of p100.

TNF-α augments RANKL-dependent intestinal M cell differentiation in enteroid cultures

Microfold (M) cells are phagocytic intestinal epithelial cells in the follicle-associated epithelium of Peyer's patches that transport particulate antigens from the gut lumen into the subepithelial dome. Differentiation of M cells from epithelial stem cells in intestinal crypts requires the cytokine receptor activator of NF-κB ligand (RANKL) and the transcription factor Spi-B. We used three-dimensional enteroid cultures established with small intestinal crypts from mice as a model system to investigate signaling pathways involved in M cell differentiation and the influence of other cytokines on RANKL-induced M cell differentiation. Addition of RANKL to enteroids induced expression of multiple M cell-associated genes, including Spib, Ccl9 [chemokine (C-C motif) ligand 9], Tnfaip2 (TNF-α-induced protein 2), Anxa5 (annexin A5), and Marcksl1 (myristoylated alanine-rich protein kinase C substrate) in 1 day. The mature M cell marker glycoprotein 2 (Gp2) was strongly induced by 3 days and expressed by 11% of cells in enteroids. The noncanonical NF-κB pathway was required for RANKL-induced M cell differentiation in enteroids, as addition of RANKL to enteroids from mice with a null mutation in the mitogen-activated protein kinase kinase kinase 14 (Map3k14) gene encoding NF-κB-inducing kinase failed to induce M cell-associated genes. While the cytokine TNF-α alone had little, if any, effect on expression of M cell-associated genes, addition of TNF-α to RANKL consistently resulted in three- to sixfold higher levels of multiple M cell-associated genes than RANKL alone. One contributing mechanism is the rapid induction by TNF-α of Relb and Nfkb2 (NF-κB subunit 2), genes encoding the two subunits of the noncanonical NF-κB heterodimer. We conclude that endogenous activators of canonical NF-κB signaling present in the gut-associated lymphoid tissue microenvironment, including TNF-α, can play a supportive role in the RANKL-dependent differentiation of M cells in the follicle-associated epithelium.

Transcription factors of the alternative NF-κB pathway are required for germinal center B-cell development

The NF-κB signaling cascade relays external signals essential for B-cell growth and survival. This cascade is frequently hijacked by cancers that arise from the malignant transformation of germinal center (GC) B cells, underscoring the importance of deciphering the function of NF-κB in these cells. The NF-κB signaling cascade is comprised of two branches, the canonical and alternative NF-κB pathways, mediated by distinct transcription factors. The expression and function of the transcription factors of the alternative pathway, RELB and NF-κB2, in late B-cell development is incompletely understood. Using conditional deletion of relb and nfkb2 in GC B cells, we here report that ablation of both RELB and NF-κB2, but not of the single transcription factors, resulted in the collapse of established GCs. RELB/NF-κB2 deficiency in GC B cells was associated with impaired cell-cycle entry and reduced expression of the cell-surface receptor inducible T-cell costimulator ligand that promotes optimal interactions between B and T cells. Analysis of human tonsillar tissue revealed that plasma cells and their precursors in the GC expressed high levels of NF-κB2 relative to surrounding lymphocytes. Accordingly, deletion of nfkb2 in murine GC B cells resulted in a dramatic reduction of antigen-specific antibody-secreting cells, whereas deletion of relb had no effect. These results demonstrate that the transcription factors of the alternative NF-κB pathway control distinct stages of late B-cell development, which may have implications for B-cell malignancies that aberrantly activate this pathway.

Angiotensin II promotes the inflammatory response to CD40 ligation via TRAF-2

A plethora of evidence supports a link between inflammation and atherogenesis. Both the vasoactive peptide angiotensin II (ANG II) as well as the CD40/CD154 signaling pathway exhibit proinflammatory properties with a direct influence on atherogenesis. We therefore tested the hypothesis that ANG II interacts with CD40/CD154 in human vascular smooth muscle cells (SMC). ANG II did not increase expression of CD40 in human SMC. However, when SMC were prestimulated with ANG II and thereafter stimulated with CD154, the ligand for CD40, the release of IL-6 as a marker of inflammatory activation was augmented compared to cells not primed with ANG II. TNF receptor-associated factor 2 (TRAF-2), an important adaptor protein involved in CD40 signaling, but not TRAF-5 or -6, was increased by ANG II via activation of the angiotensin II type 1 (AT1) receptor subtype. These results suggest that a signaling pathway downstream of CD40 may be altered by ANG II prestimulation. Thus, ANG II can also indirectly cause inflammatory activation of vascular SMC. The data show a novel link between the proatherogenic vasoactive peptide ANG II and cell—cell contact-mediated inflammatory pathways and implicate options for the prevention and therapy of atherosclerotic disease.

The Ubiquitination of NF-κB Subunits in the Control of Transcription

Nuclear factor (NF)-κB has evolved as a latent, inducible family of transcription factors fundamental in the control of the inflammatory response. The transcription of hundreds of genes involved in inflammation and immune homeostasis require NF-κB, necessitating the need for its strict control. The inducible ubiquitination and proteasomal degradation of the cytoplasmic inhibitor of κB (IκB) proteins promotes the nuclear translocation and transcriptional activity of NF-κB. More recently, an additional role for ubiquitination in the regulation of NF-κB activity has been identified. In this case, the ubiquitination and degradation of the NF-κB subunits themselves plays a critical role in the termination of NF-κB activity and the associated transcriptional response. While there is still much to discover, a number of NF-κB ubiquitin ligases and deubiquitinases have now been identified which coordinate to regulate the NF-κB transcriptional response. This review will focus the regulation of NF-κB subunits by ubiquitination, the key regulatory components and their impact on NF-κB directed transcription.

Noncanonical NF-κB Signaling in Health and Disease

Noncanonical NF-κB signaling differs from canonical NF-κB signaling by being activated through different cell surface receptors, cytoplasmic adaptors, and NF-κB dimers. Under normal physiological conditions, this noncanonical pathway has been implicated in diverse biological processes, including lymphoid organogenesis, B cell maturation, osteoclast differentiation, and various functions of other immune cells. Recently, dysfunction of this pathway has also been causally associated with numerous immune-mediated pathologies and human malignancies. Here, we summarize the core elements as well as the recently identified novel regulators of the noncanonical NF-κB signaling pathway. The involvement of this pathway in different pathologies and the potential therapeutic options that are currently envisaged are also discussed.

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.

A roadmap of constitutive NF-κB activity in Hodgkin lymphoma: Dominant roles of p50 and p52 revealed by genome-wide analyses

Background

NF-κB is widely involved in lymphoid malignancies; however, the functional roles and specific transcriptomes of NF-κB dimers with distinct subunit compositions have been unclear.

Methods

Using combined ChIP-sequencing and microarray analyses, we determined the cistromes and target gene signatures of canonical and non-canonical NF-κB species in Hodgkin lymphoma (HL) cells.

Results

We found that the various NF-κB subunits are recruited to regions with redundant κB motifs in a large number of genes. Yet canonical and non-canonical NF-κB dimers up- and downregulate gene sets that are both distinct and overlapping, and are associated with diverse biological functions. p50 and p52 are formed through NIK-dependent p105 and p100 precursor processing in HL cells and are the predominant DNA binding subunits. Logistic regression analyses of combinations of the p50, p52, RelA, and RelB subunits in binding regions that have been assigned to genes they regulate reveal a cross-contribution of p52 and p50 to canonical and non-canonical transcriptomes. These analyses also indicate that the subunit occupancy pattern of NF-κB binding regions and their distance from the genes they regulate are determinants of gene activation versus repression. The pathway-specific signatures of activated and repressed genes distinguish HL from other NF-κB-associated lymphoid malignancies and inversely correlate with gene expression patterns in normal germinal center B cells, which are presumed to be the precursors of HL cells.

Conclusions

We provide insights that are relevant for lymphomas with constitutive NF-κB activation and generally for the decoding of the mechanisms of differential gene regulation through canonical and non-canonical NF-κB signaling.

Electronic supplementary material

The online version of this article (doi:10.1186/s13073-016-0280-5) contains supplementary material, which is available to authorized users.

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.

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.

Biological rational for sequential targeting of Bruton tyrosine kinase and Bcl-2 to overcome CD40-induced ABT-199 resistance in mantle cell lymphoma

The aggressive biological behavior of mantle cell lymphoma (MCL) and its short response to current treatment highlight a great need for better rational therapy. Herein, we investigate the ability of ABT-199, the Bcl-2-selective BH3 mimetic, to kill MCL cells. Among MCL cell lines tested (n = 8), only three were sensitive (LD50 < 200 nM). In contrast, all primary MCL samples tested (n = 11) were highly sensitive to ABT-199 (LD50 < 10 nM). Mcl-1 and Bcl-xL both confer resistance to ABT-199-specific killing and BCL2/(BCLXL+MCL1) mRNA ratio is a strong predictor of sensitivity. By mimicking the microenvironment through CD40 stimulation, we show that ABT-199 sensitivity is impaired through activation of NF-kB pathway and Bcl-x(L) up-regulation. We further demonstrate that resistance is rapidly lost when MCL cells detach from CD40L-expressing fibroblasts. It has been reported that ibrutinib induces lymphocytosis in vivo holding off malignant cells from their protective microenvironment. We show here for two patients undergoing ibrutinib therapy that mobilized MCL cells are highly sensitive to ABT-199. These results provide evidence that in situ ABT-199 resistance can be overcome when MCL cells escape from the lymph nodes. Altogether, our data support the clinical application of ABT-199 therapy both as a single agent and in sequential combination with BTK inhibitors.

Impairment of Mature B Cell Maintenance upon Combined Deletion of the Alternative NF-κB Transcription Factors RELB and NF-κB2 in B Cells

BAFF is critical for the survival and maturation of mature B cells. BAFF, via BAFFR, activates multiple signaling pathways in B cells, including the alternative NF-κB pathway. The transcription factors RELB and NF-κB2 (p100/p52) are the downstream mediators of the alternative pathway; however, the B cell-intrinsic functions of these NF-κB subunits have not been studied in vivo using conditional alleles, either individually or in combination. We in this study report that B cell-specific deletion of relb led to only a slight decrease in the fraction of mature splenic B cells, whereas deletion of nfkb2 caused a marked reduction. This phenotype was further exacerbated upon combined deletion of relb and nfkb2 and most dramatically affected the maintenance of marginal zone B cells. BAFF stimulation, in contrast to CD40 activation, was unable to rescue relb/nfkb2-deleted B cells in vitro. RNA-sequencing analysis of BAFF-stimulated nfkb2-deleted versus normal B cells suggests that the alternative NF-κB pathway, in addition to its critical role in BAFF-mediated cell survival, may control the expression of genes involved in the positioning of B cells within the lymphoid microenvironment and in the establishment of T cell-B cell interactions. Thus, by ablating the downstream transcription factors of the alternative NF-κB pathway specifically in B cells, we identify in this study a critical role for the combined activity of the RELB and NF-κB2 subunits in B cell homeostasis that cannot be compensated for by the canonical NF-κB pathway under physiological conditions.

Identification and characterization of tumor necrosis factor receptor (TNFR)-associated factor 3 from humphead snapper, Lutjanus sanguineus

Tumor necrosis factor receptor (TNFR)-associated factor 3(TRAF3) is a key regulator in TNFR and Toll-like receptor (TLRs)/RIG-I-like receptors (RLRs) signal pathway. Here, a TRAF3 gene (Ls-TRAF3, GenBank Accession No: KJ789921) is cloned from humphead snapper (Lutjanus sanguineus). The Ls-TRAF3 cDNA contains an open reading frame of 1788 bp, which encodes a polypeptide of 595 amino acids. The deduced amino acid of Ls-TRAF3 possesses a RING finger, two TRAF-type zinc fingers, a coiled-coil and a MATH domain. Ls-TRAF3 protein shares high identities with other known TRAF3 proteins. In healthy fish, Ls-TRAF3 transcripts were broadly expressed in all examined tissues with highest expression levels in spleen, liver and head kidney. Quantitative real-time PCR (qRT-PCR) analysis revealed that Ls-TRAF3 could be induced by bacteria or viral PAMP poly I:C stimulation in vivo. Here, we also showed Ls-TRAF3 that, positively regulated IRF3 and Mx upon poly I:C stimuli, whereas prevented production of proinflammatory cytokine IL-6 after LPS injection. Moreover, over-expression of wide type (WT) Ls-TRAF3 and truncated forms, including ΔZinc finger 1, ΔZinc finger 2 and Δcoiled-coil suppressed NF-κB activity significantly, whereas the inhibitory effect of NF-κB was partially impaired when the RING finger or MATH domain deletion, suggesting the latter was more important for downstream signal transduction. Taken together, these results implicated that Ls-TRAF3 might play regulatory roles in immune response to pathogen invasion.

XEDAR activates the non-canonical NF-κB pathway

Members of the tumor necrosis factor receptor (TNFR) superfamily are involved in a number of physiological and pathological responses by activating a wide variety of intracellular signaling pathways. The X-linked ectodermal dysplasia receptor (XEDAR; also known as EDA2R or TNFRSF27) is a member of the TNFR superfamily that is highly expressed in ectodermal derivatives during embryonic development and binds to ectodysplasin-A2 (EDA-A2), a member of the TNF family that is encoded by the anhidrotic ectodermal dysplasia (EDA) gene. Although XEDAR was first described in the year 2000, its function and molecular mechanism of action is still largely unclear. XEDAR has been reported to activate canonical nuclear factor κB (NF-κB) signaling and mitogen-activated protein (MAP) kinases. Here we report that XEDAR is also able to trigger the non-canonical NF-κB pathway, characterized by the processing of p100 (NF-κB2) into p52, followed by nuclear translocation of p52 and RelB. We provide evidence that XEDAR-induced p100 processing relies on the binding of XEDAR to TRAF3 and TRAF6, and requires the kinase activity of NIK and IKKα. We also show that XEDAR stimulation results in NIK accumulation and that p100 processing is negatively regulated by TRAF3, cIAP1 and A20.

Desflurane preconditioning protects human umbilical vein endothelial cells against anoxia/reoxygenation by upregulating NLRP12 and inhibiting non-canonical nuclear factor-κB signaling

Volatile anesthetics modulate endothelial cell apoptosis and inhibit nuclear factor-κB (NF-κB) signaling. In this study, we aimed to assess whether desflurane preconditioning protects human umbilical vein endothelial cells (HUVECs) agaist anoxia/reoxygenation (A/R) injury. HUVECs were pre-conditioned with desflurane (1.0 MAC) for 30 min, followed by a 15-min washout, then exposed to 60 min anoxia and 60 min reoxygenation (A/R), and incubated with 10 ng/ml tumor necrosis factor (TNF)-α for 60 min. HUVEC viability and apoptosis were measured by MTT assay and annexin V staining, and immunoblot analysis was used to measure the levels of Smac and cellular inhibitor of apoptosis 1 (cIAP1). NF-κB activation was assessed using the NF-κB signaling pathway real‑time PCR array, and the levels of NF-κB inducing kinase (NIK), p52, IκB kinase (IKK)α, p100, RelB and NLR family, pyrin domain containing 12 (NLRP12) were assessed by immunoblot analysis. Desflurane preconditioning attenuated the effects of A/R and/or A/R plus TNF-α on cell viability, decreasing the levels of Smac and enhancing the levels of of cIAP1 (P<0.05). Preconditioning with desflurane also enhanced the mRNA levels of interleukin (IL)-10 and NLRP12 in the cells exposed to A/R by 2.40- and 2.16‑fold, respectively. The HUVECs exposed to A/R had greater levels of NIK and p100 and reduced levels of p52 and IKKα. Desflurance preconditioning further increased p100 levels, decreased the level of NIK, further decreased p52 levels and further reduced IKKα levels. A/R in combination with TNF-α increased the NIK, IKKα, p100 and RelB levels, and this increase was significantly attenuated by desflurance preconditioning (all P<0.05). Desflurane preconditioning enhanced HUVEC survival and protected the cells against A/R injury, and our results suggested that this process involved the upregulation of NLRP12 and the inhibition of non-canonical NF-κB signaling.

Conditional Deletion of NF-κB-Inducing Kinase (NIK) in Adult Mice Disrupts Mature B Cell Survival and Activation

NF-κB-inducing kinase (NIK) is a primary regulator of the noncanonical NF-κB signaling pathway, which plays a vital role downstream of BAFF, CD40L, lymphotoxin, and other inflammatory mediators. Germline deletion or inactivation of NIK in mice results in the defective development of B cells and secondary lymphoid organs, but the role of NIK in adult animals has not been studied. To address this, we generated mice containing a conditional allele of NIK. Deletion of NIK in adult mice results in decreases in B cell populations in lymph nodes and spleen, similar to what is observed upon blockade of BAFF. Consistent with this, B cells from mice in which NIK is acutely deleted fail to respond to BAFF stimulation in vitro and in vivo. In addition, mice with induced NIK deletion exhibit a significant decrease in germinal center B cells and serum IgA, which is indicative of roles for NIK in additional pathways beyond BAFF signaling. Our conditional NIK-knockout mice may be broadly useful for assessing the postdevelopmental and cell-specific roles of NIK and the noncanonical NF-κB pathway in mice.

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.

BAFF activation of the ERK5 MAP kinase pathway regulates B cell survival

B cell activating factor (BAFF) stimulation of the BAFF receptor (BAFF-R) is essential for the homeostatic survival of mature B cells. Earlier in vitro experiments with inhibitors that block MEK 1 and 2 suggested that activation of ERK 1 and 2 MAP kinases is required for BAFF-R to promote B cell survival. However, these inhibitors are now known to also inhibit MEK5, which activates the related MAP kinase ERK5. In the present study, we demonstrated that BAFF-induced B cell survival was actually independent of ERK1/2 activation but required ERK5 activation. Consistent with this, we showed that conditional deletion of ERK5 in B cells led to a pronounced global reduction in mature B2 B cell numbers, which correlated with impaired survival of ERK5-deficient B cells after BAFF stimulation. ERK5 was required for optimal BAFF up-regulation of Mcl1 and Bcl2a1, which are prosurvival members of the Bcl-2 family. However, ERK5 deficiency did not alter BAFF activation of the PI3-kinase-Akt or NF-κB signaling pathways, which are also important for BAFF to promote mature B cell survival. Our study reveals a critical role for the MEK5-ERK5 MAP kinase signaling pathway in BAFF-induced mature B cell survival and homeostatic maintenance of B2 cell numbers.

Novel inhibitors are cytotoxic for myeloma cells with NFkB inducing kinase-dependent activation of NFkB

NFkB activity is critical for survival and proliferation of normal lymphoid cells and many kinds of B-cell tumors, including multiple myeloma (MM). NFkB activating mutations, which are apparent progression events, enable MM tumors to become less dependent on bone marrow signals that activate NFkB. Mutations that activate NFkB-inducing kinase (NIK) protein are the most prevalent among the many kinds of NFkB mutations in MM tumors. NIK is the main activating kinase of the alternative NFkB pathway, although over-expression of NIK also can activate the classical pathway. Two NIK inhibitors and an isomeric control were tested with human myeloma cell lines. These specific NIK inhibitors are selectively cytotoxic for cells with NIK-dependent activation of NFkB. Combination therapy targeting NIK and IKKbeta (as a main kinase of the classical NFkB pathway) represents a promising treatment strategy in MM. NIK inhibitors can also be useful tool for assessing the role of NIK and alternative NFkB pathway in different cells.

STAT3 cooperates with the non-canonical NF-κB signaling to regulate pro-labor genes in the human placenta

INTRODUCTION

Our recent studies have shown that constitutively activated non-canonical RelB/NF-κB2 (p52) in the human placenta positively regulates the pro-labor genes CRH and COX-2. STAT3 regulates NF-κB2 (p100) processing to active p52, and in turn, nuclear activation of RelB/p52, by directly binding to p100/p52 in a variety of cancer cells. In the current study, we tested the hypothesis that STAT3 is involved in regulation of pro-labor genes by associating with RelB/p52 heterodimers in the human placenta.

METHODS

We used a variety of techniques including immunohistochemical staining, gene silencing, ectopic expression, chromatin immunoprecipitation, Western blot, RT-qPCR, and immunofluorescence assays in primary culture of cytotrophoblast and placental tissues.

RESULTS

We found that knockdown of STAT3 led to down-regulation of both CRH and COX-2 in a dose-dependent manner. By using chromatin immunoprecipitation, we further showed that interaction of RelB with the CRH or COX-2 gene promoters decreased when STAT3 was depleted. Immunofluorescence demonstrated co-localization of STAT3 with RelB or p100/p52 in both the cytoplasm and nucleus of term cytotrophoblasts.

DISCUSSION

Collectively, these results suggest that STAT3 constitutes part of the RelB/p52-containing activator complex that positively regulates pro-labor genes in the human placenta.

Transcription factor c-Rel plays a crucial role in driving anti-CD40-mediated innate colitis

Genetic and environmental factors, including the commensal microbiota, have a crucial role in the development of inflammatory bowel disease. Aberrant activation of the transcription factor NF-κB is associated with chronic intestinal inflammation in mice and humans. Recently, an emerging family of innate lymphoid cells (ILCs) has been identified at mucosal sites contributing to the maintenance of gut homeostasis and intestinal immunopathology. Here, we show that the NF-κB protein c-Rel regulates the inflammatory potential of colonic IFN-γ(+)Thy1(+) ILCs to induce anti-CD40-mediated colitis in rag1(-/-) mice. Stimulation of dendritic cells (DCs) with anti-CD40 or CD40L led to translocation of c-Rel into the nucleus resulting in induction of expression of interleukin-12 (IL-12) and IL-23, key regulators of innate cell-induced colitis. While c-Rel deficiency completely abrogated anti-CD40-induced colitis, adoptively transferred wild-type DCs were able to induce pronounced colonic inflammation in rag1(-/-)rel(-/-) mice. In summary, these results suggest that the expression of c-Rel in DCs is essential for initiating anti-CD40-mediated intestinal pathogenesis.

MicroRNA-30c-2-3p negatively regulates NF-κB signaling and cell cycle progression through downregulation of TRADD and CCNE1 in breast cancer

Nuclear Factor kappa B (NF-κB) signaling is frequently deregulated in a variety of cancers and is constitutively active in estrogen receptor negative (ER-) breast cancer subtypes. These molecular subtypes of breast cancer are associated with poor overall survival. We focused on mechanisms of NF-κB regulation by microRNAs (miRNAs), which regulate eukaryotic gene expression at the post-transcriptional level. In a previous genome-wide miRNA screen, we had identified miR-30c-2-3p as one of the strongest negative regulators of NF-κB signaling. Here we have uncovered the underlying molecular mechanisms and its consequences in breast cancer. In vitro results show that miR-30c-2-3p directly targets both TNFRSF1A-associated via death domain (TRADD), an adaptor protein of the TNFR/NF-κB signaling pathway, and the cell cycle protein Cyclin E1 (CCNE1). Ectopic expression of miR-30c-2-3p downregulated essential cytokines IL8, IL6, CXCL1, and reduced cell proliferation as well as invasion in MDA-MB-231 breast cancer cells. RNA interference (RNAi) induced silencing of TRADD phenocopied the effects on invasion and cytokine expression caused by miR-30c-2-3p, while inhibition of CCNE1 phenocopied the effects on cell proliferation. We further confirmed the tumor suppressive role of this miRNA using a dataset of 781 breast tumors, where higher expression was associated with better survival in breast cancer patients. In summary we have elucidated the mechanism by which miR-30c-2-3p negatively regulates NF-κB signaling and cell cycle progression in breast cancer.

Methods to assess the activation of the alternative (noncanonical) NF-κB pathway by non-death TNF receptors

The alternative or noncanonical NF-κB pathway regulates the generation of p52-containing NF-κB dimers (e.g., p52/RelB) through a partial degradation (called processing) of the precursor p100 into p52. This pathway is activated by a subset of non-death TNF receptor members, which ultimately activate two kinases: NIK (NF-κB-Inducing Kinase) and IKKα (Inhibitor of κB Kinase alpha). These kinases create a phosphodegron for the E3 ligase SCF-β-TrCP that covalently binds K48-linked polyubiquitin chain onto p100 prior to its proteasomal processing. The resulting p52-containing complexes translocate into the nucleus to activate target genes involved in secondary lymphoid organ development, B cell survival or in osteoclastogenesis. We describe in this chapter straightforward methods to monitor the activation of the alternative NF-κB pathway. These methods uncover cytosolic and nuclear biochemical modifications of key proteins of the alternative NF-κB pathway required prior to the transcription of NF-κB target genes.

Systematic detection of noncanonical NF-κB activation

In unstimulated cells, NF-κB dimers usually exist as latent complexes in the cytoplasm with the IκB (inhibitor of NF-κB) proteins or IκB-like protein p100, the precursor of NF-κB2 mature form p52. Accordingly, there are two major mechanisms leading to NF-κB activation: inducible degradation of IκBs and processing of p100 to generate p52 (selective degradation of the C-terminal IκB-like sequence of p100), which are termed the canonical and noncanonical NF-κB pathways, respectively. While activation of the canonical NF-κB pathway plays critical roles in a wide range of biological processes, the noncanonical NF-κB pathway has important but more restricted roles in both normal and pathological processes. Systematic detection of the noncanonical NF-κB pathway activation is very important for understanding the physiological role of this pathway in biological processes, and for the diagnosis, prevention, and treatment of related diseases. We describe here the methods we employ to detect noncanonical NF-κB activation in cells and tissues. These methods are immunoblotting, co-immunoprecipitation, immunofluorescence, immunohistochemistry, chromatin immunoprecipitation (ChIP) analysis, and electrophoretic mobility shift assay (EMSA). Noncanonical NF-κB-induced gene expression changes can be determined by gene array analysis and quantitative real-time PCR.

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.

Quantitative dissection and modeling of the NF-κB p100-p105 module reveals interdependent precursor proteolysis

The mechanisms that govern proteolytic maturation or complete destruction of the precursor proteins p100 and p105 are fundamental to homeostasis and activation of NF-κB; however, they remain poorly understood. Using mass-spectrometry-based quantitative analysis of noncanonical LTβR-induced signaling, we demonstrate that stimulation induces simultaneous processing of both p100 and p105. The precursors not only form hetero-oligomers but also interact with the ATPase VCP/p97, and their induced proteolysis strictly depends on the signal response domain (SRD) of p100, suggesting that the SRD-targeting proteolytic machinery acts in cis and in trans. Separation of cellular pools by isotope labeling revealed synchronous dynamics of p105 and p100 proteolysis. The generation of p50 and p52 from their precursors depends on functional VCP/p97. We have developed quantitative mathematical models that describe the dynamics of the system and predict that p100-p105 complexes are signal responsive.

Activation of NF-κB by the Kaposi's sarcoma-associated herpesvirus K15 protein involves recruitment of the NF-κB-inducing kinase, IκB kinases, and phosphorylation of p65

Kaposi's sarcoma herpesvirus (KSHV) (or human herpesvirus 8) is the cause of Kaposi's sarcoma, primary effusion lymphoma (PEL), and the plasma cell variant of multicentric Castleman's disease (MCD). The transmembrane K15 protein, encoded by KSHV, has been shown to activate NF-κB and the mitogen-activated protein kinases (MAPKs) c-jun-N-terminal kinase (JNK) and extracellular signal-regulated kinase (Erk) as well as phospholipase C gamma (PLCγ) and to contribute to KSHV-induced angiogenesis. Here we investigate how the K15 protein activates the NF-κB pathway. We show that activation of NF-κB involves the recruitment of NF-κB-inducing kinase (NIK) and IKK α/β to result in the phosphorylation of p65/RelA on Ser536. A K15 mutant devoid in NIK/IKK recruitment fails to activate NF-κB but remains proficient in the stimulation of both NFAT- and AP1-dependent promoters, showing that the structural integrity of the mutant K15 protein has not been altered dramatically. Direct recruitment of NIK represents a novel way for a viral protein to activate and manipulate the NF-κB pathway.

IMPORTANCE

KSHV K15 is a viral protein involved in the activation of proinflammatory and angiogenic pathways. Previous studies reported that K15 can activate the NF-κB pathway. Here we show the molecular mechanism underlying the activation of this signaling pathway by K15, which involves direct recruitment of the NF-κB-inducing kinase NIK to K15 as well as NIK-mediated NF-κB p65 phosphorylation on Ser536. K15 is the first viral protein shown to activate NF-κB through direct recruitment of NIK. These results indicate a new mechanism whereby a viral protein can manipulate the NF-κB pathway.

HAX1 regulates E3 ubiquitin ligase activity of cIAPs by promoting their dimerization

HS-1-associated protein X-1 (HAX1) is a multi-functional protein which was first identified as a Hematopoietic cell specific Lyn Substrate 1 (HS1)-binding protein. Although the roles of HAX1 in apoptosis have been unraveled and HAX1 has been proposed to be involved in several diseases, additional roles of HAX1 are still being identified. Here, we demonstrated that HAX1 directly interacted with cellular Inhibitor of Apoptosis Proteins (cIAPs), ubiquitin E3 ligases which regulate the abundance of cellular proteins, via ubiquitin-dependent proteasomal degradation. We showed that HAX1 promotes auto-ubiquitination and degradation of cIAPs by facilitating the intermolecular homodimerization of RING finger domain. Moreover, HAX1 regulates the non-canonical Nuclear Factor-κB (NF-κB) signaling pathway by modulating the stability of NF-κB-Inducing Kinase (NIK), which is one of the substrates of cIAPs. Taken together, these results unveil a novel role of HAX1 in the non-canonical NF-κB pathway, and provide an important clue that HAX1 is a potential therapeutic target for the treatment of cancer.

Autosomal-dominant B-cell deficiency with alopecia due to a mutation in NFKB2 that results in nonprocessable p100

Most genetic defects that arrest B-cell development in the bone marrow present early in life with agammaglobulinemia, whereas incomplete antibody deficiency is usually associated with circulating B cells. We report 3 related individuals with a novel form of severe B-cell deficiency associated with partial persistence of serum immunoglobulin arising from a missense mutation in NFKB2. Significantly, this point mutation results in a D865G substitution and causes a failure of p100 phosphorylation that blocks processing to p52. Severe B-cell deficiency affects mature and transitional cells, mimicking the action of rituximab. This phenotype appears to be due to disruption of canonical and noncanonical nuclear factor κB pathways by the mutant p100 molecule. These findings could be informative for therapeutics as well as immunodeficiency.

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.

Hepatitis B virus polymerase suppresses NF-κB signaling by inhibiting the activity of IKKs via interaction with Hsp90β

Nuclear factor-κB (NF-κB) plays a central role in the regulation of diverse biological processes, including immune responses, development, cell growth, and cell survival. To establish persistent infection, many viruses have evolved strategies to evade the host’s antiviral immune defenses. In the case of hepatitis B virus (HBV), which can cause chronic infection in the liver, immune evasion strategies used by the virus are not fully understood. It has recently been reported that the polymerase of HBV (Pol) inhibits interferon-β (IFN-β) activity by disrupting the interaction between IKKε and the DDX3. In the current study, we found that HBV Pol suppressed NF-κB signaling, which can also contribute to IFN-β production. HBV Pol did not alter the level of NF-κB expression, but it prevented NF-κB subunits involved in both the canonical and non-canonical NF-κB pathways from entering the nucleus. Further experiments demonstrated that HBV Pol preferentially suppressed the activity of the IκB kinase (IKK) complex by disrupting the association of IKK/NEMO with Cdc37/Hsp90, which is critical for the assembly of the IKK complex and recruitment of the IKK complex to the tumor necrosis factor type 1 receptor (TNF-R1). Furthermore, we found that HBV Pol inhibited the NF-κB-mediated transcription of target genes. Taken together, it is suggested that HBV Pol could counteract host innate immune responses by interfering with two distinct signaling pathways required for IFN-β activation. Our studies therefore shed light on a potential therapeutic target for persistent infection with HBV.

TWEAK-Fn14 Cytokine-Receptor Axis: A New Player of Myocardial Remodeling and Cardiac Failure

Tumor necrosis factor (TNF) has been firmly established as a pathogenic factor in heart failure, a significant socio-economic burden. In this review, we will explore the role of other members of the TNF/TNF receptor superfamily (TNFSF/TNFRSF) in cardiovascular diseases (CVDs) focusing on TWEAK and its receptor Fn14, new players in myocardial remodeling and heart failure. The TWEAK/Fn14 pathway controls a variety of cellular activities such as proliferation, differentiation, and apoptosis and has diverse biological functions in pathological mechanisms like inflammation and fibrosis that are associated with CVDs. Furthermore, it has recently been shown that the TWEAK/Fn14 axis is a positive regulator of cardiac hypertrophy and that deletion of Fn14 receptor protects from right heart fibrosis and dysfunction. We discuss the potential use of the TWEAK/Fn14 axis as biomarker for CVDs as well as therapeutic target for future treatment of human heart failure based on supporting data from animal models and in vitro studies. Collectively, existing data strongly suggest the TWEAK/Fn14 axis as a potential new therapeutic target for achieving cardiac protection in patients with CVDs.

Negative effects of progesterone receptor isoform-A on human placental activity of the noncanonical NF-κB signaling

CONTEXT

Progesterone (P4)contributes to the maintenance of human pregnancy, in part by inhibiting activity of the human pro-labor genes CRH and cyclooxygenase-2 (COX-2). However, the molecular mechanisms underlying the action of P4 remain poorly defined. We have shown that in human placenta, the constitutively activated noncanonical nuclear factor (NF)-κB pathway positively regulates CRH and COX-2, which is further stimulated by glucocorticoid receptor signaling.

OBJECTIVE

We investigated the role of P4 receptor (PR) in the regulation of nuclear activity of v-rel avian reticuloendotheliosis viral oncogene homolog B (RelB)/NF-κB2 and, in turn, expression of placental CRH and COX-2.

METHODS

We used a variety of techniques including gene silencing, ectopic expression, chromatin immunoprecipitation, Western blot, quantitative RT-PCR, and immunohistochemical staining assays in human placental tissues and primary culture of human cytotrophoblast.

RESULTS

We identified PR isoform-A (PR-A) as the only isoform of PR produced in human placenta. PR-A levels were lower in term placenta than in midterm placenta. Depletion of PR-A by short interfering RNA derepressed inhibition of CRH and COX-2 by P4 and the synthetic progestin 17α-hydroxyprogesterone caproate. Overexpression of PR-A inhibited transcription of CRH and COX-2, which was further downregulated by treatment with P4 or 17α-hydroxyprogesterone caproate. Such an inhibition was mediated by a negative functional interaction of PR-A with the activity of RelB/NF-κB2.

CONCLUSION

P4 inhibits the pro-labor genes CRH and COX-2 via PR-A repression of the noncanonical NF-κB signaling in human placenta. Characterization of these pathways may identify potential drug targets for prevention of preterm birth.

TWEAK/Fn14 Axis: A Promising Target for the Treatment of Cardiovascular Diseases

Cardiovascular diseases (CVD) are the first cause of mortality in Western countries. CVD include several pathologies such as coronary heart disease, stroke or cerebrovascular accident, congestive heart failure, peripheral arterial disease, and aortic aneurysm, among others. Interaction between members of the tumor necrosis factor (TNF) superfamily and their receptors elicits several biological actions that could participate in CVD. TNF-like weak inducer of apoptosis (TWEAK) and its functional receptor and fibroblast growth factor-inducible molecule 14 (Fn14) are two proteins belonging to the TNF superfamily that activate NF-κB by both canonical and non-canonical pathways and regulate several cell functions such as proliferation, migration, differentiation, cell death, inflammation, and angiogenesis. TWEAK/Fn14 axis plays a beneficial role in tissue repair after acute injury. However, persistent TWEAK/Fn14 activation mediated by blocking experiments or overexpression experiments in animal models has shown an important role of this axis in the pathological remodeling underlying CVD. In this review, we summarize the role of TWEAK/Fn14 pathway in the development of CVD, focusing on atherosclerosis and stroke and the molecular mechanisms by which TWEAK/Fn14 interaction participates in these pathologies. We also review the role of the soluble form of TWEAK as a biomarker for the diagnosis and prognosis of CVD. Finally, we highlight the results obtained with other members of the TNF superfamily that also activate canonical and non-canonical NF-κB pathway.

Thymic medullary epithelium and thymocyte self-tolerance require cooperation between CD28-CD80/86 and CD40-CD40L costimulatory pathways

A critical process during thymic development of the T cell repertoire is the induction of self-tolerance. Tolerance in developing T cells is highly dependent on medullary thymic epithelial cells (mTEC), and mTEC development in turn requires signals from mature single-positive thymocytes, a bidirectional relationship termed thymus crosstalk. We show that CD28-CD80/86 and CD40-CD40L costimulatory interactions, which mediate negative selection and self-tolerance, upregulate expression of LTα, LTβ, and receptor activator for NF-κB in the thymus and are necessary for medullary development. Combined absence of CD28-CD80/86 and CD40-CD40L results in profound deficiency in mTEC development comparable to that observed in the absence of single-positive thymocytes. This requirement for costimulatory signaling is maintained even in a TCR transgenic model of high-affinity TCR-ligand interactions. CD4 thymocytes maturing in the altered thymic epithelial environment of CD40/CD80/86 knockout mice are highly autoreactive in vitro and are lethal in congenic adoptive transfer in vivo, demonstrating a critical role for these costimulatory pathways in self-tolerance as well as thymic epithelial development. These findings demonstrate that cooperativity between CD28-CD80/86 and CD40-CD40L pathways is required for normal medullary epithelium and for maintenance of self-tolerance in thymocyte development.

TWEAK/Fn14 and Non-Canonical NF-kappaB Signaling in Kidney Disease

The incidence of acute kidney injury (AKI) and chronic kidney disease (CKD) is increasing. However, there is no effective therapy for AKI and current approaches only slow down, but do not prevent progression of CKD. TWEAK is a TNF superfamily cytokine. A solid base of preclinical data suggests a role of therapies targeting the TWEAK or its receptor Fn14 in AKI and CKD. In particular TWEAK/Fn14 targeting may preserve renal function and decrease cell death, inflammation, proteinuria, and fibrosis in mouse animal models. Furthermore there is clinical evidence for a role of TWEAK in human kidney injury including increased tissue and/or urinary levels of TWEAK and parenchymal renal cell expression of the receptor Fn14. In this regard, clinical trials of TWEAK targeting are ongoing in lupus nephritis. Nuclear factor-kappa B (NF-κB) activation plays a key role in TWEAK-elicited inflammatory responses. Activation of the non-canonical NF-κB pathway is a critical difference between TWEAK and TNF. TWEAK activation of the non-canonical NF-κB pathways promotes inflammatory responses in tubular cells. However, there is an incomplete understanding of the role of non-canonical NF-κB activation in kidney disease and on its contribution to TWEAK actions in vivo.

TRAF3 enforces the requirement for T cell cross-talk in thymic medullary epithelial development

Induction of self-tolerance in developing T cells depends on medullary thymic epithelial cells (mTECs), whose development, in turn, requires signals from single-positive (SP) thymocytes. Thus, the absence of SP thymocytes in Tcra(-/-) mice results in a profound deficiency in mTECs. Here, we have probed the mechanism that underlies this requirement for cross-talk with thymocytes in medullary development. Previous studies have implicated nonclassical NF-κB as a pathway important in the development of mTECs, because mice lacking RelB, NIK, or IKKα, critical components of this pathway, have an almost complete absence of mTECs, with resulting autoimmune pathology. We therefore assessed the effect of selective deletion in TEC of TNF receptor-associated factor 3 (TRAF3), an inhibitor of nonclassical NF-κB signaling. Deletion of TRAF3 in thymic epithelial cells allowed RelB-dependent development of normal numbers of AIRE-expressing mTECs in the complete absence of SP thymocytes. Thus, mTEC development can occur in the absence of cross-talk with SP thymocytes, and signals provided by SP T cells are needed to overcome TRAF3-imposed arrest in mTEC development mediated by inhibition of nonclassical NF-κB. We further observed that TRAF3 deletion is also capable of overcoming all requirements for LTβR and CD40, which are otherwise necessary for mTEC development, but is not sufficient to overcome the requirement for RANKL, indicating a role for RANKL that is distinct from the signals provided by SP thymocytes. We conclude that TRAF3 plays a central role in regulation of mTEC development by imposing requirements for SP T cells and costimulation-mediated cross-talk in generation of the medullary compartment.

Bidirectional regulation of NF-κB by reactive oxygen species: a role of unfolded protein response

Nuclear factor-κB (NF-κB) is a transcription factor that plays a crucial role in coordinating innate and adaptive immunity, inflammation, and apoptotic cell death. NF-κB is activated by various inflammatory stimuli including peptide factors and infectious microbes. It is also known as a redox-sensitive transcription factor activated by reactive oxygen species (ROS). Over the past decades, various investigators focused on the role of ROS in the activation of NF-κB by cytokines and lipopolysaccharides. However, recent studies also suggested that ROS have the potential to repress NF-κB activity. Currently, it is not well addressed how ROS regulate activity of NF-κB in a bidirectional fashion. In this paper, we summarize evidence for positive and negative regulation of NF-κB by ROS, possible redox-sensitive targets for NF-κB signaling, and mechanisms underlying biphasic and bidirectional influences of ROS on NF-κB, especially focusing on a role of ROS-mediated induction of endoplasmic reticulum stress.