Negative regulation of TCR signaling by NF-kappaB2/p100

Targeting NF-κB signaling in B cells as a potential new treatment modality for ANCA-associated vasculitis

B lineage cells are critically involved in ANCA-associated vasculitis (AAV), evidenced by alterations in circulating B cell subsets and beneficial clinical effects of rituximab (anti-CD20) therapy. This treatment renders a long-term, peripheral B cell depletion, but allows for the survival of long-lived plasma cells. Therefore, there is an unmet need for more reversible and full B lineage cell targeting approaches. To find potential novel therapeutic targets, RNA sequencing of CD27+ memory B cells of patients with active AAV was performed, revealing an upregulated NF-κB-associated gene signature. NF-κB signaling pathways act downstream of various B cell surface receptors, including the BCR, CD40, BAFFR and TLRs, and are essential for B cell responses. Here we demonstrate that novel pharmacological inhibitors of NF-κB inducing kinase (NIK, non-canonical NF-κB signaling) and inhibitor-of-κB-kinase-β (IKKβ, canonical NF-κB signaling) can effectively inhibit NF-κB signaling in B cells, whereas T cell responses were largely unaffected. Moreover, both inhibitors significantly reduced B cell proliferation, differentiation and production of antibodies, including proteinase-3 (PR3) autoantibodies, in B lineage cells of AAV patients. These findings indicate that targeting NF-κB, particularly NIK, may be an effective, novel B lineage cell targeted therapy for AAV and other autoimmune diseases with prominent B cell involvement.

Amelioratory effect of neoandrographolide on myocardial ischemic-reperfusion injury by its anti-inflammatory and anti-apoptotic activities

In the present study, we aimed to evaluate the cardioprotective effect of neoandrographolide (Neo) on myocardial ischemia/reperfusion injury (I/R) models and explore its possible mechanism. We randomly and equally divided male mice into sham-operation, I/R, and I/R + Neo groups. H9C2 cell line and primary neonatal rat cardiomyocytes were induced into the simulated I/R's status and used to further validate the Neo's role in vitro. Heart systolic function, indexes of myocardial injury (IMI), infarct size, pathological change, cell apoptosis, inflammatory cytokines, and indexes related to apoptotic and NF-κB signaling pathways were analyzed in vivo or in vitro after the Neo treatment. Compared to the I/R group, Neo significantly suppressed IMI, infarct size, inflammatory cell infiltration, cell apoptosis, inflammatory cytokines, bax, cleaved caspase-3, P-IKBa, and P-NF-κB protein expressions, and the translocation of NF-kB subunit p65 from the cytoplasm to the nucleus in vivo or in vitro. Still, ejected fraction, fractional shortening, and the bcl-2 protein expression were notably increased after the Neo treatment. Neo could be developed into a new drug for treating myocardial I/R by inhibiting myocardial inflammation and apoptosis, which was closely related to suppressing the activation of bax/bcl-2 and NF-κB signaling pathways.

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.

Elevated fibroblast growth factor-inducible 14 expression transforms proneural-like gliomas into more aggressive and lethal brain cancer

High-grade gliomas (HGGs) are aggressive, treatment-resistant, and often fatal human brain cancers. The TNF-like weak inducer of apoptosis (TWEAK)/fibroblast growth factor-inducible 14 (Fn14) signaling axis is involved in tissue repair after injury and constitutive signaling has been implicated in the pathogenesis of numerous solid cancers. The Fn14 gene is expressed at low levels in the normal, uninjured brain but is highly expressed in primary isocitrate dehydrogenase wild-type and recurrent HGGs. Fn14 signaling is implicated in numerous aspects of glioma biology including brain invasion and chemotherapy resistance, but whether Fn14 overexpression can directly promote tumor malignancy has not been reported. Here, we used the replication-competent avian sarcoma-leukosis virus/tumor virus A system to examine the impact of Fn14 expression on glioma development and pathobiology. We found that the sole addition of Fn14 to an established oncogenic cocktail previously shown to generate proneural-like gliomas led to the development of highly invasive and lethal brain cancer with striking biological features including extensive pseudopalisading necrosis, constitutive canonical and noncanonical NF-κB pathway signaling, and high plasminogen activator inhibitor-1 (PAI-1) expression. Analyses of HGG patient datasets revealed that high human PAI-1 gene (SERPINE1) expression correlates with shorter patient survival, and that the SERPINE1 and Fn14 (TNFRSF12A) genes are frequently co-expressed in bulk tumor tissues, in tumor subregions, and in malignant cells residing in the tumor microenvironment. These findings provide new insights into the potential importance of Fn14 in human HGG pathobiology and designate both the NF-κB signaling node and PAI-1 as potential targets for therapeutic intervention. MAIN POINTS: This work demonstrates that elevated levels of the TWEAK receptor Fn14 in tumor-initiating, neural progenitor cells leads to the transformation of proneural-like gliomas into more aggressive and lethal tumors that exhibit constitutive NF-κB pathway activation and plasminogen activator inhibitor-1 overexpression.

Combined immunodeficiency caused by a novel homozygous NFKB1 mutation

BACKGROUND

Genetic faults in several components of the nuclear factor-κB pathway cause immunodeficiency. Most defects lead to combined immunodeficiency with a range of severity. Heterozygous mutations in NFKB1 were associated with common variable immunodeficiency, however, homozygous mutations have not been described.

OBJECTIVE

We studied the molecular basis of combined immunodeficiency in a patient who presented with failure to thrive, persistent EBV viremia and hepatitis, pneumocystis jirovecii pneumonitis, and generalized lymphadenopathy.

METHODS

Whole genome and exome sequencing followed by Sanger confirmation were performed to identify the genetic defect. Molecular and cellular techniques were used to assess the variant impact on the nuclear factor-κB pathway and lymphocyte function.

RESULTS

Genetic analysis revealed a novel homozygous mutation in NFKB1, c.2878G>A, p.Gly960Arg (G960R). This affected p105 phosphorylation and p50 formation on antigen and cytokine stimulation, as well as attenuating nuclear signal transmission. As a result, both T- and B-cell maturation and function were perturbed. The number of memory CD4⁺ T cells were reduced, while CD8⁺ T cells consisted predominately of expanded differentiated populations. The function of T cells were diminished as shown by reduced responses to mitogens as well as diminished cytokine secretion. B-cell maturation was also affected, with decreased IgD⁺CD27⁺ memory B cells while transitional B cells were increased, likely contributing to the reduced ability to produce specific antibodies.

CONCLUSION

Homozygous G960R mutation in NFKB1 leads to a severe clinical presentation of combined immunodeficiency. This was associated with blockade of nuclear factor-κB pathway signaling, resulting in aberrations in T- and B-cell maturation and function.

miRNA-129/FBW7/NF-κB, a Novel Regulatory Pathway in Inflammatory Bowel Disease

F-box and WD repeat domain-containing protein 7 (FBW7) has been documented to be implicated in nuclear factor κB (NF-κB) signaling and inflammation, but its role in the pathogenesis of inflammatory bowel disease (IBD) remains unknown. FBW7 was increased both in colon tissues from IBD patients and trinitrobenzene sulphonic acid (TNBS)-induced colitis mice. Immunoprecipitation assay identified that FBW7 as a novel inhibitor of κBα (IκBα)-binding partner. FBW7 upregulation promoted IκBα ubiquitin-dependent degradation, NF-κB activation, and subsequent intestinal inflammation in intestinal epithelial cells, whereas inhibition of FBW7 produced the opposite effects. Computational analysis revealed that microRNA-129 (miR-129) directly targets at 3' UTR of FBW7. The miR-129-suppressed proteasome pathway mediated the degradation of IκBα by negatively regulating FBW7. The in vivo study demonstrated that upregulation of miR-129 ameliorated intestinal inflammation in TNBS-induced colitis mice through inhibition of the NF-κB signaling pathway. In conclusion, FBW7 is a novel E3 ubiquitin ligase for IκBα and thereby leads to NF-κB activation and inflammation. miR-129 negatively regulates FBW7 expression, resulting in secondary inhibition of the NF-κB pathway and amelioration of intestinal inflammation. Our findings provide new insight into the development of therapeutic strategies for the treatment of IBD.

Role of NF-kappaB2-p100 in regulatory T cell homeostasis and activation

The immunological roles of the nuclear factor-kappaB (NF-κB) pathway are mediated via the canonical components in immune responses and via non-canonical components in immune organogenesis and homeostasis, although the two components are capable of crosstalk. Regulatory CD4 T cells (Tregs) are homeostatically functional and represent an interesting potential meeting point of these two NF-κB components. We show that mice deficient in the non-canonical NF-κB component gene Nfkb2 (p100) had normal thymic development and suppressive function of Tregs. However, they had enhanced frequencies of peripheral 'effector-phenotype' Tregs (eTregs). In bi-parental chimeras of wild-type (WT) and Nfkb2-/- mice, the Nfkb2-/- genotype was over-represented in Tregs, with a further increase in the relative prominence of eTregs. Consistent with distinct properties of eTregs, the Nfkb2-/- genotype was more prominent in Tregs in extra-lymphoid tissues such as liver in the bi-parental chimeras. The Nfkb2-/- Tregs also displayed greater survival, activation and proliferation in vivo. These Nfkb2-/- Tregs showed higher nuclear NF-κB activity mainly comprising of RelB-containing dimers, in contrast to the prominence of cRel- and RelA-containing dimers in WT Tregs. Since p100 is an inhibitor of RelB activation as well as a participant as cleaved p52 in RelB nuclear activity, we tested bi-parental chimeras of WT and Relb-/- mice, and found normal frequencies of Relb-/- Tregs and eTregs in these chimeric mice. Our findings confirm and extend recent data, and indicate that p100 normally restrains RelB-mediated Treg activation, and in the absence of p100, p50-RelB dimers can contribute to Treg activation.

Preventing abnormal NF-κB activation and autoimmunity by Otub1-mediated p100 stabilization

NF-κB, a family of transcription factors regulating diverse biological processes including immune responses, is activated by canonical and noncanonical pathways based on degradation of IκBα and processing of the IκB-like protein p100, respectively. Although p100 responds to noncanonical NF-κB stimuli for processing, it does not undergo degradation, but rather becomes accumulated, along with canonical NF-κB activation. We show here that the stability of p100 is tightly controlled by a deubiquitinase, Otub1. Otub1 deficiency not only promotes signal-induced p100 processing and noncanonical NF-κB activation but also causes steady-state p100 degradation, leading to aberrant NF-κB activation in the canonical pathway. B-cell-conditional deletion of Otub1 results in B-cell hyperplasia, antibody hyper-production, and lupus-like autoimmunity. Otub1-deficient B cells display aberrantly activated phenotypes and overproduce the cytokine IL-6, contributing to autoimmunity induction. Thus, maintenance of p100 stability by Otub1 serves as an unusual mechanism of NF-κB regulation that prevents autoimmunity.

NF-κB pathway and the Goldilocks principle: Lessons from human disorders of immunity and inflammation

Nuclear factor κ-light-chain-enhancer of activated B cells (NF-κB) signaling pathways play a key role in various cell processes related to host immunity. The last few years have seen an explosion of disorders associated with NF-κB components from core members of the canonical and noncanonical cascades to adaptor protein and ubiquitination-related enzymes. Disease phenotypes have extended beyond susceptibility to infections and include autoimmunity, lymphoproliferation, atopy, and inflammation. Concurrently, studies are unveiling a tightly regulated system marked by extensive cross-talk between the canonical and noncanonical pathways, as well as among the NF-κB and other signaling pathways. As the rate of discovery in the realm of NF-κB defects accelerates, this review presents a timely summary of major known defects causing human disease, as well as diagnostic, therapeutic, and research challenges and opportunities.

Noncanonical NF-κB in Cancer

The NF-κB pathway is a critical regulator of immune responses and is often dysregulated in cancer. Two NF-κB pathways have been described to mediate these responses, the canonical and the noncanonical. While understudied compared to the canonical NF-κB pathway, noncanonical NF-κB and its components have been shown to have effects, usually protumorigenic, in many different cancer types. Here, we review noncanonical NF-κB pathways and discuss its important roles in promoting cancer. We also discuss alternative NF-κB-independent functions of some the components of noncanonical NF-κB signaling. Finally, we discuss important crosstalk between canonical and noncanonical signaling, which blurs the two pathways, indicating that understanding the full picture of NF-κB regulation is critical to deciphering how this broad pathway promotes oncogenesis.

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.

Genetics of Cutaneous T Cell Lymphoma: From Bench to Bedside

OPINION STATEMENT

Cutaneous T cell lymphomas (CTCLs) are non-Hodgkin lymphomas of skin homing T cells. Although early-stage disease may be limited to the skin, tumor cells in later stage disease can populate the blood, the lymph nodes, and the visceral organs. Unfortunately, there are few molecular biomarkers to guide diagnosis, staging, or treatment of CTCL. Diagnosis of CTCL can be challenging and requires the synthesis of clinical findings, histopathology, and T cell clonality studies; however, none of these tests are entirely sensitive or specific for CTCL. Treatment of CTCL is often empiric and is not typically based on specific molecular alterations, as is common in other cancers. In part, limitations in diagnosis and treatment selection reflect the limited insight into the genetic basis of CTCL. Recent next-generation sequencing has revolutionized our understanding of the mutational landscape in this disease. These analyses have uncovered ultraviolet radiation and recombination activating gene (RAG) endonucleases as important mutagens. Furthermore, these studies have revealed potentially targetable oncogenic mutations in the T cell receptor complex, NF-κB, and JAK-STAT signaling pathways. Collectively, these somatic mutations drive lymphomagenesis via cancer-promoting changes in proliferation, apoptosis, and T cell effector function. We expect that these genetic findings will launch a new era of precision medicine in CTCL.

Disease-modifying effects of orally bioavailable NF-B inhibitors in dystrophin-deficient muscle

Duchenne muscular dystrophy (DMD) is a devastating muscle disease characterized by progressive muscle deterioration and replacement with an aberrant fatty, fibrous matrix. Chronic upregulation of nuclear factor κB (NF-κB) is implicated as a driver of the dystrophic pathogenesis. Herein, 2 members of a novel class of NF-κB inhibitors, edasalonexent (formerly CAT-1004) and CAT-1041, were evaluated in both mdx mouse and golden retriever muscular dystrophy (GRMD) dog models of DMD. These orally bioavailable compounds consist of a polyunsaturated fatty acid conjugated to salicylic acid and potently suppress the pathogenic NF-κB subunit p65/RelA in vitro. In vivo, CAT-1041 effectively improved the phenotype of mdx mice undergoing voluntary wheel running, in terms of activity, muscle mass and function, damage, inflammation, fibrosis, and cardiac pathology. We identified significant increases in dysferlin as a possible contributor to the protective effect of CAT-1041 to sarcolemmal damage. Furthermore, CAT-1041 improved the more severe GRMD phenotype in a canine case study, where muscle mass and diaphragm function were maintained in a treated GRMD dog. These results demonstrate that NF-κB modulation by edasalonexent and CAT-1041 is effective in ameliorating the dystrophic process and these compounds are candidates for new treatments for DMD patients.

A new molecular paradigm in mycosis fungoides and Sézary syndrome

Mycosis Fungoides (MF) and Sézary Syndrome (SS) are clonal proliferations of mature T-cells manifesting as lymphoproliferative disorders in which the neoplastic cells show a strong propensity for skin-homing. While the predominant site of presentation in MF is the skin, the peripheral blood carries a significant tumor burden in Sézary Syndrome such that it resembles a "leukemic" disease. While the genetic basis of these diseases has been studied using different approaches in the previous years, recent genome-wide studies employing massively parallel sequencing techniques now offer new insights into the molecular pathogenesis of these diseases. In this chapter, we discuss the recent findings elucidating the genomic landscape of MF and SS. The pathways targeted by mutational alterations are discussed and a model for understanding the pathogenesis of these diseases is proposed. It is anticipated that prognostic stratification and therapeutic targeting based on mutational signatures will be achieved in the near future based on the improved understanding of the molecular pathogenesis of these diseases.

TNFR2 expression by CD4 effector T cells is required to induce full-fledged experimental colitis

There is now compelling evidence that TNFR2 is constitutively expressed on CD4(+) Foxp3(+) regulatory T cells (Tregs) and TNF-TNFR2 interaction is critical for the activation, expansion and functional stability of Tregs. However, we showed that the expression of TNFR2 was also up-regulated on CD4(+) Foxp3(-) effector T cells (Teffs) upon TCR stimulation. In order to define the role of TNFR2 in the pathogenic CD4 T cells, we compared the effect of transferred naïve CD4 cells from WT mice and TNFR2(-/-) mice into Rag 1(-/-) recipients. Transfer of TNFR2-deficient Teff cells failed to induce full-fledged colitis, unlike WT Teffs. This was due to defective proliferative expansion of TNFR2-deficient Teff cells in the lymphopenic mice, as well as their reduced capacity to express proinflammatory Th1 cytokine on a per cell basis. In vitro, the proliferative response of TNFR2 deficient naïve CD4 cells to anti-CD3 stimulation was markedly decreased as compared with that of WT naïve CD4 cells. The hypoproliferative response of TNFR2-deficient Teff cells to TCR stimulation was associated with an increased ratio of p100/p52, providing a mechanistic basis for our findings. Therefore, this study clearly indicates that TNFR2 is important for the proliferative expansion of pathogenic Teff cells.

TCR signaling to NF-κB and mTORC1: Expanding roles of the CARMA1 complex

Naïve T-cell activation requires signals from both the T-cell receptor (TCR) and the costimulatory molecule CD28. A central mediator of the TCR and CD28 signals is the scaffold protein CARMA1, which functions by forming a complex with partner proteins, Bcl10 and MALT1. A well-known function of the CARMA1 signaling complex is to mediate activation of IκB kinase (IKK) and its target transcription factor NF-κB, thereby promoting T-cell activation and survival. Recent evidence suggests that CARMA1 also mediates TCR/CD28-stimulated activation of the IKK-related kinase TBK1, which plays a role in regulating the homeostasis and migration of T cells. Moreover, the CARMA1 complex connects the TCR/CD28 signals to the activation of mTORC1, a metabolic kinase regulating various aspects of T-cell functions. This review will discuss the mechanism underlying the activation of the CARMA1-dependent signaling pathways and their roles in regulating T-cell functions.

Genomic landscape of cutaneous T cell lymphoma

Cutaneous T cell lymphoma (CTCL) is a non-Hodgkin lymphoma of skin-homing T lymphocytes. We performed exome and whole genome DNA sequence and RNA sequencing on purified CTCL and matched normal cells. The results implicate mutations in 17 genes in CTCL pathogenesis, including genes involved in T cell activation and apoptosis, NFκB signaling, chromatin remodeling, and DNA damage response. CTCL is distinctive in that somatic copy number variants (SCNVs) comprise 92% of all driver mutations (mean of 11.8 pathogenic SCNVs vs. 1.0 somatic single nucleotide variants per CTCL). These findings have implications for novel therapeutics.

Stimulus-selective crosstalk via the NF-κB signaling system reinforces innate immune response to alleviate gut infection

Tissue microenvironment functions as an important determinant of the inflammatory response elicited by the resident cells. Yet, the underlying molecular mechanisms remain obscure. Our systems-level analyses identified a duration code that instructs stimulus specific crosstalk between TLR4-activated canonical NF-κB pathway and lymphotoxin-β receptor (LTβR) induced non-canonical NF-κB signaling. Indeed, LTβR costimulation synergistically enhanced the late RelA/NF-κB response to TLR4 prolonging NF-κB target gene-expressions. Concomitant LTβR signal targeted TLR4-induced newly synthesized p100, encoded by Nfkb2, for processing into p52 that not only neutralized p100 mediated inhibitions, but potently generated RelA:p52/NF-κB activity in a positive feedback loop. Finally, Nfkb2 connected lymphotoxin signal within the intestinal niche in reinforcing epithelial innate inflammatory RelA/NF-κB response to Citrobacter rodentium infection, while Nfkb2^−/− mice succumbed to gut infections owing to stromal defects. In sum, our results suggest that signal integration via the pleiotropic NF-κB system enables tissue microenvironment derived cues in calibrating physiological responses.

DOI:http://dx.doi.org/10.7554/eLife.05648.001

The innate immune system is the body's first line of defense against infection and disease. Innate immune cells are found in every tissue type, poised to respond immediately to damaged, stressed, or infected host cells. When innate immune cells recognize any injury or infection, one of the first things they do is trigger the inflammatory response. Fluid and other immune cells then move from the blood into the injured tissues. This movement can cause redness and swelling. But the response helps to establish a physical barrier against the spread of infection, promotes the elimination of both invading microbes and damaged host cells, and encourages the repair of the tissue.

Inflammation is tightly controlled. If the response is too weak, it could leave an individual prone to serious infection. On the other hand, excessive inflammation can severely damage healthy cells and tissues. Inflammation is regulated differently in different tissue types, and the environment within the tissue itself influences the activity of local innate immune cells and the inflammatory response. However, the molecular mechanisms responsible for receiving and interpreting the signals derived from the host tissue remain unknown.

Now, Banoth et al., have revealed that the integration of inflammation-provoking signals, such as injury or infection and cues from the tissue environment occurs via the so-called ‘NF-κB signaling system’. NF-κB is a protein found in almost all cell types, and when activated it is able to switch on the expression of many different genes. Banoth et al. explain that signal integration via the NF-κB system enables cues from the tissue environment to tune a cell's responses. Further experiments confirmed the importance of this signal integration by showing how a signal coming from intestinal tissue can influence the activity of innate immune cells and inflammation in the gut.

These findings suggest that a breakdown in the NF-κB signaling system's ability to integrate multiple signals, including those derived from the tissue environment, may be responsible for many inflammatory disorders, and in particular those that involve the gut. Future work is now needed to explore this possibility.

DOI:http://dx.doi.org/10.7554/eLife.05648.002

IKKα is required for the homeostasis of regulatory T cells and for the expansion of both regulatory and effector CD4 T cells

It was reported that TNF receptor type II signaling, which has the capacity to stimulate CD4+ forkhead box P3+ (Foxp3+) regulatory T cells (Tregs), activated the noncanonical NF-κB pathway in an IKKα-dependent manner. Therefore, we studied the role of IKKα in the homeostasis of Treg population. To this end, we generated a mouse strain with conditional knockout of IKKα in CD4 cells (Ikkα(f/f):CD4.Cre) that showed a >60% reduction in the number of Tregs in the thymus and peripheral lymphoid tissues, whereas the number of Foxp3- effector T cells (Teffs) remained at a normal level. The function of Tregs deficient in IKKα was examined using Rag1(-/-) mice cotransferred with naive CD4 cells (nCD4s). Although wild-type (WT) Tregs inhibited colitis induced by transfer of WT nCD4s, IKKα-deficient Tregs failed to do so, which was associated with their inability to reconstitute Rag1(-/-) mice. Furthermore, nCD4s deficient in IKKα also failed to reconstitute Rag1(-/-) mice and were defective in proliferative responses in vitro and in vivo. Thus, our study reveals a novel role of IKKα in the maintenance of a normal Treg population and in the control of expansion of CD4 T cells. These properties of IKKα may be exploited as therapeutic strategies in the treatment of major human diseases.

p100, a precursor of NF-κB2, inhibits c-Rel and reduces the expression of IL-23 in dendritic cells

Nuclear factor κB regulates various genes involved in the immune response, inflammation, cell survival, and development. NF-κB activation is controlled by proteins possessing ankyrin repeats, such as IκBs. A precursor of the NF-κB2 (p52) subunit, p100, contains ankyrin repeats in its C-terminal portion and has been found to act as a cytoplasmic inhibitor of RelA in the canonical pathway of NF-κB activation. Here, we demonstrate that p100 also suppresses c-Rel function in dendritic cells. Expression of the p19 and p40 subunits of IL-23, a c-Rel-dependent cytokine, was enhanced in p100-deficient cells, although expression of a RelA-dependent cytokine, TNF-α, was reduced. Nuclear translocation of c-Rel was enhanced in p100-deficient cells. p100, and not the processed p52 form, associated with c-Rel in the steady state and dissociated immediately after lipopolysaccharide stimulation in wild-type dendritic cells. Four hours after the stimulation, p100 was newly synthesized and associated with c-Rel again. In cells expressing both c-Rel and RelA, c-Rel is preferentially suppressed by p100.

Combined immune deficiency in a patient with a novel NFKB2 mutation

NFKB2 encodes the p100/p52 protein, a critical mediator of the canonical and noncanonical NFkB signaling pathways. Here we report the comprehensive immune evaluation of a child with a novel NFKB2 mutation and provide evidence that aberrant NFKB2 signaling not only causes humoral immune deficiency, but also interferes with the TCR-mediated proliferation of T cells. These observations expand the known phenotype associated with NFKB2 mutations.

T cell-intrinsic function of the noncanonical NF-κB pathway in the regulation of GM-CSF expression and experimental autoimmune encephalomyelitis pathogenesis

The noncanonical NF-κB pathway induces processing of the NF-κB2 precursor protein p100, and thereby mediates activation of p52-containing NF-κB complexes. This pathway is crucial for B cell maturation and humoral immunity, but its role in regulating T cell function is less clear. Using mutant mice that express a nonprocessible p100, NF-κB2(lym1), we show that the noncanonical NF-κB pathway has a T cell-intrinsic role in regulating the pathogenesis of a T cell-mediated autoimmunity, experimental autoimmune encephalomyelitis (EAE). Although the lym1 mutation does not interfere with naive T cell activation, it renders the Th17 cells defective in the production of inflammatory effector molecules, particularly the cytokine GM-CSF. We provide evidence that p52 binds to the promoter of the GM-CSF-encoding gene (Csf2) and cooperates with c-Rel in the transactivation of this target gene. Introduction of exogenous p52 or GM-CSF to the NF-κB2(lym1) mutant T cells partially restores their ability to induce EAE. These results suggest that the noncanonical NF-κB pathway mediates induction of EAE by regulating the effector function of inflammatory T cells.

A cell-intrinsic requirement for NF-κB-inducing kinase in CD4 and CD8 T cell memory

NF-κB-inducing kinase [(NIK), MAP3K14] is an essential kinase linking a subset of TNFR family members to the noncanonical NF-κB pathway. To assess the cell-intrinsic role of NIK in murine T cell function, we generated mixed bone marrow chimeras using bone marrow from NIK knockout (KO) and wild-type (WT) donor mice and infected the chimeras with lymphocytic choriomeningitis virus (LCMV). The chimeras possess an apparently normal immune system, including a mixture of NIK KO and WT T cells, and the virus was cleared normally. Comparison of the NIK KO and WT CD4 and CD8 T cell responses at 8 d post infection revealed modest but significant differences in the acute response. In both CD4 and CD8 compartments, relatively fewer activated (CD44(hi)) NIK KO T cells were present, but within the CD44(hi) population, a comparable percentage of the activated cells produced IFN-γ in response to ex vivo stimulation with antigenic LCMV peptides, although IL-7R expression was reduced in the NIK KO CD8 T cells. Assessment of the LCMV-specific memory at 65 d post infection revealed many more LCMV-specific WT memory T cells than NIK KO memory T cells in both the CD4 and the CD8 compartments, although the small number of surviving NIK KO memory T cells responded to secondary challenge with virus. These results demonstrate a cell-intrinsic requirement for NIK in the generation and/or maintenance of memory T cells in response to acute viral infection.

SCF(Fbw7) modulates the NFkB signaling pathway by targeting NFkB2 for ubiquitination and destruction

The NFkB/Rel family of proteins play critical roles in a variety of cellular processes. Thus, their physiological activation is tightly controlled. Recently, the NFkB2/p100 precursor has been characterized as the fourth IkB type of suppressor for NFkB. However, the molecular mechanism(s) underlying regulated destruction of NFkB2 remains largely unknown. Here, we report that, unlike other IkBs, ubiquitination and destruction of NFkB2 are governed by SCF(Fbw7) in a GSK3-dependent manner. In Fbw(7-/-) cells, elevated expression of NFkB2/p100 leads to a subsequent reduction in NFkB signaling pathways and elevated sensitivity to TNFa-induced cell death. Reintroducing wild-type Fbw7, but not disease-derived mutant forms of Fbw7, rescues NFkB activity. Furthermore, T cell-specific depletion of Fbw7 also leads to reduced NFkB activity and perturbed T cell differentiation. Therefore, our work identifies Fbw7 as a physiological E3 ligase controlling NFkB20s stability. It further implicates that Fbw7 might exert its tumor-suppressor function by regulating NFkB activity.

Impact of NF-κB gene polymorphism on allograft outcome in Hispanic renal transplant recipients

BACKGROUND

The dimeric NF-κB transcription factors play critical roles in diverse cellular processes including adaptive and innate immunity, cell differentiation, proliferation and apoptosis. It regulates the expression of numerous genes that play a key role in the inflammatory response during kidney allograft rejection. This study aims to determine the association of NF-κB gene polymorphisms with allograft outcomes in the Hispanic renal transplant recipients.

METHODS

A total of 607 Hispanic renal transplant recipients at St. Vincent Medical Center between 2001 and 2010 were included in this study. The NF-κB genotypes were studied along with clinical data. In the case of NF-κB genotypes, the following single nucleotide polymorphisms (SNPs) were included: NF-κB1 (rs3774959, rs3774932, rs3774937, rs230526, rs230519), NF-κB2 (rs1056890, rs7897947, rs12769316) and NF-κB inducing kinase (NIK) (rs9908330, rs7222094). The association of each genotype with renal allograft survival and acute rejection was evaluated.

RESULTS

NF-κB1 (rs3774937) CC genotype showed protective association with allograft rejection (OR=0.66, 95% CI=0.44-0.99, p=0.04). There was a significant increase in allograft survival time associated with the NF-κB1 (rs3774959) A allele (OR=0.76, 95% CI=0.60-0.98, p=0.03) while GG genotype was associated with a higher risk of graft failure (OR=1.51, 95% CI=1.02-2.21, p=0.03). There were no associations between polymorphic markers in NF-κB2 and NIK genes with allograft survival or acute rejection. Among non-genetic factors, we found that the use of tacrolimus, a deceased donor, delayed graft function and acute rejection were associated with allograft failure.

CONCLUSION

The result of present study suggests that NF-κB1 gene polymorphisms may determine the incidence of acute rejection or graft survival among Hispanic allograft recipients.

Mesenchymal stem cells promote the sustained expression of CD69 on activated T lymphocytes: roles of canonical and non-canonical NF-κB signalling

Mesenchymal stem cells (MSCs) are known to induce the conversion of activated T cells into regulatory T cells in vitro. The marker CD69 is a target of canonical nuclear factor kappa-B (NF-κB) signalling and is transiently expressed upon activation; however, stable CD69 expression defines cells with immunoregulatory properties. Given its enormous therapeutic potential, we explored the molecular mechanisms underlying the induction of regulatory cells by MSCs. Peripheral blood CD3⁺ T cells were activated and cultured in the presence or absence of MSCs. CD4⁺ cell mRNA expression was then characterized by microarray analysis. The drug BAY11-7082 (BAY) and a siRNA against v-rel reticuloendotheliosis viral oncogene homolog B (RELB) were used to explore the differential roles of canonical and non-canonical NF-κB signalling, respectively. Flow cytometry and real-time PCR were used for analyses. Genes with immunoregulatory functions, CD69 and non-canonical NF-κB subunits (RELB and NFKB2) were all expressed at higher levels in lymphocytes co-cultured with MSCs. The frequency of CD69⁺ cells among lymphocytes cultured alone progressively decreased after activation. In contrast, the frequency of CD69⁺ cells increased significantly following activation in lymphocytes co-cultured with MSCs. Inhibition of canonical NF-κB signalling by BAY immediately following activation blocked the induction of CD69; however, inhibition of canonical NF-κB signalling on the third day further induced the expression of CD69. Furthermore, late expression of CD69 was inhibited by RELB siRNA. These results indicate that the canonical NF-κB pathway controls the early expression of CD69 after activation; however, in an immunoregulatory context, late and sustained CD69 expression is promoted by the non-canonical pathway and is inhibited by canonical NF-κB signalling.

Lessons from mathematically modeling the NF-κB pathway

Mathematical modeling has proved to be a critically important approach in the study of many complex networks and dynamic systems in physics, engineering, chemistry, and biology. The nuclear factor κB (NF-κB) system consists of more than 50 proteins and protein complexes and is both a highly networked and dynamic system. To date, mathematical modeling has only addressed a small fraction of the molecular species and their regulation, but when employed in conjunction with experimental analysis has already led to important insights. Here, we provide a personal account of studying how the NF-κB signaling system functions using mathematical descriptions of the molecular mechanisms. We focus on the insights gained about some of the key regulatory components: the control of the steady state, the signaling dynamics, and signaling crosstalk. We also discuss the biological relevance of these regulatory systems properties.

NF-κB–inducing kinase plays an essential T cell–intrinsic role in graft-versus-host disease and lethal autoimmunity in mice

NF-κB–inducing kinase (NIK) is an essential upstream kinase in noncanonical NF-κB signaling. NIK-dependent NF-κB activation downstream of several TNF receptor family members mediates lymphoid organ development and B cell homeostasis. Peripheral T cell populations are normal in the absence of NIK, but the role of NIK during in vivo T cell responses to antigen has been obscured by other developmental defects in NIK-deficient mice. Here, we have identified a T cell–intrinsic requirement for NIK in graft-versus-host disease (GVHD), wherein NIK-deficient mouse T cells transferred into MHC class II mismatched recipients failed to cause GVHD. Although NIK was not necessary for antigen receptor signaling, it was absolutely required for costimulation through the TNF receptor family member OX40 (also known as CD134). When we conditionally overexpressed NIK in T cells, mice suffered rapid and fatal autoimmunity characterized by hyperactive effector T cells and poorly suppressive Foxp3(+) Tregs. Together, these data illuminate a critical T cell–intrinsic role for NIK during immune responses and suggest that its tight regulation is critical for avoiding autoimmunity.

Classical NF-kappaB activation negatively regulates noncanonical NF-kappaB-dependent CXCL12 expression

Ligation of the lymphotoxin-β receptor (LTβR) by LIGHT (lymphotoxin-related inducible ligand that competes for glycoprotein D binding to herpes virus entry mediator on T cells (TNFSF14)) activates the noncanonical (NC) NF-κB (nuclear factor-κB) pathway and up-regulates CXCL12 gene expression by human umbilical vein endothelial cells (HUVEC). In contrast, TNF only activates classical NF-κB signaling and does not up-regulate CXCL12. To determine whether cross-talk between the classical and NC pathways affects CXCL12 expression, we investigated the effects of TNF on LIGHT signaling in HUVEC. We show here that TNF inhibits both basal and LIGHT-induced CXCL12 expression. Negative regulation by TNF requires the classical NF-κB pathway as inhibition of basal and induced CXCL12 was reversed in HUVEC-expressing dominant negative IκB (inhibitor of NF-κB) kinase (IKK)β (IKKβ(K44M)). TNF did not inhibit the NC NF-κB pathway activation as LIGHT-induced p100 processing to p52 was intact; however, TNF either alone or together with LIGHT up-regulated p100 and RelB expression and induced the nuclear localization of p100-RelB complexes. Enhanced p100 and RelB expression was inhibited by IKKβ(K44M), which led us to question whether the IκB function of elevated p100 mediates the inhibition of CXCL12 expression by TNF. We retrovirally transduced HUVEC to express p100 at a level similar to that up-regulated by TNF; however, basal and LIGHT-induced CXCL12 expression was normal in the transduced cells. In contrast, ectopic RelB expression recapitulated the effects of TNF on NC signaling and inhibited basal and LIGHT-induced CXCL12 expression by HUVEC. Our findings therefore demonstrate that TNF-induced classical NF-κB signaling up-regulates RelB expression that inhibits both basal and NC NF-κB-dependent CXCL12 expression.

TACI induces cIAP1-mediated ubiquitination of NIK by TRAF2 and TANK to limit non-canonical NF-kappaB signaling

B-cell-activating factor of the TNF family (BAFF) is a critical factor for B-cell survival and maturation through non-canonical nuclear factor kappaB (NF-kappaB) pathway, a NF-kappaB inducing kinase (NIK)-dependent pathway for the processing of NF-kappaB2 p100 to generate p52. While BAFF acts primarily through BAFF receptor (BAFF-R), the transmembrane activator and CAML interactor (TACI), the other receptor for BAFF, is thought to serve as a negative regulator for B-cell responses. However, how TACI regulates NF-kappaB2 activity is largely unknown. In this study, we showed that constitutive activation of TACI signaling suppressed BAFF-R-mediated NF-kappaB2 p100 processing with the up-regulation of cellular inhibitors of apoptosis 1 (cIAP1) and TNF receptor associated factor (TRAF)-associated NF-kappaB activator (TANK). The ubiquitination of NIK by cIAP1 was inhibited by the expression of TRAF2 with physical binding to cIAP1. TANK deficiency by small interfering RNA (siRNA) impaired TACI-dependent inhibition of NF-kappaB2 p100 processing. TANK also inhibited TRAF2-mediated cIAP1 inactivation. Moreover, the recruitment of TRAF2 to TACI induced the ubiquitination of NIK. Taken together, the regulation of NIK by TACI through the interaction of TANK/TRAF2/cIAP1 plays a pivotal role in the suppression of non-canonical NF-kappaB signaling.

Kinetic control of negative feedback regulators of NF-kappaB/RelA determines their pathogen- and cytokine-receptor signaling specificity

Mammalian signaling networks contain an abundance of negative feedback regulators that may have overlapping ("fail-safe") or specific functions. Within the NF-kappaB signaling module, IkappaB alpha is known as a negative feedback regulator, but the newly characterized inhibitor IkappaB delta is also inducibly expressed in response to inflammatory stimuli. To examine IkappaB delta's roles in inflammatory signaling, we mathematically modeled the 4-IkappaB-containing NF-kappaB signaling module and developed a computational phenotyping methodology of general applicability. We found that IkappaB delta, like IkappaB alpha, can provide negative feedback, but each functions stimulus-specifically. Whereas IkappaB delta attenuates persistent, pathogen-triggered signals mediated by TLRs, the more prominent IkappaB alpha does not. Instead, IkappaB alpha, which functions more rapidly, is primarily involved in determining the temporal profile of NF-kappaB signaling in response to cytokines that serve intercellular communication. Indeed, when removing the inducing cytokine stimulus by compound deficiency of the tnf gene, we found that the lethality of ikappab alpha(-/-) mouse was rescued. Finally, we found that IkappaB delta provides signaling memory owing to its long half-life; it integrates the inflammatory history of the cell to dampen NF-kappaB responsiveness during sequential stimulation events.

Analysis of genes isolated from plated hemocytes of the Pacific oyster, Crassostreas gigas

A complementary deoxyribonucleic acid library was constructed from hemocytes of Crassostrea gigas that had been plated on poly-lysine plates for 24 h. From this library, 2,198 expressed sequence tags (ESTs) of greater than or equal to 100 bp were generated and analyzed. A large number of genes that potentially could be involved in the physiology of the oyster hemocyte were uncovered. They included proteins involved in cytoskeleton rearrangement, proteases and antiproteases, regulators of transcription and translation, cell death regulators, receptors and their associated protein factors, lectins, signal transduction proteins, and enzymes involved in eicosanoid and steroid synthesis and xenobiotic metabolism. Based on their relationship with innate immunity, the expression of selected genes was analyzed by quantitative polymerase chain reaction in gills from bacterial-challenged oysters. Several genes observed in the library were significantly upregulated by bacterial challenge including interleukin 17, astacin, cystatin B, the EP4 receptor for prostaglandin E, the ectodysplasin receptor, c-jun, and the p100 subunit of nuclear factor-kB. Using a similar approach, we have been analyzing the genes expressed in trout macrophages. While there are significant differences between the types of genes present in vertebrate macrophages compared with oyster hemocytes, there are some striking similarities including proteins involved in cytoskeletal rearrangement, proteases and antiproteases, and genes involved in certain signal transduction pathways underlying immune processes such as phagocytosis. Finally, C. virginica homologs of some of the C. gigas genes uncovered in the ESTs were obtained by aligning the ESTs reported here, against the assembled C. virginica ESTs at the National Center for Biotechnology Information.

Cell Defence and Survival

Central to immune defence mechanisms is the role of transcription factor nuclear factor kappa B (NF-kB). This is a complex biochemical topic with ever more controls revealed. NF-kB determines the production of proinflammatory cytokines and chemokines. Pharmacologists step in with possible means of control. Other systems involved in defence include the cyclooxygenase 2 (Cox-2) enzyme and perioxisome proliferator-activated receptors. Insulin receptor activation needs to be seen in context. The mTOR system directs uptake of nutrients by cells. mTOR is suppressed by rapamycin, whose usage is now quite considerable in the control of transplant rejection.

A novel mutation in the Nfkb2 gene generates an NF-kappa B2 "super repressor"

The noncanonical NF-kappaB pathway regulates the development and function of multiple organs and cell lineages. We have generated mice harboring a novel mutation in Nfkb2 that prevents the processing of the inhibitory precursor, p100, into the active subunit, p52. Mutant mice express a complex phenotype with abnormalities in a variety of tissues, and with a spectrum that is more severe than in mice carrying a targeted deletion of Nfkb2. Signaling through the noncanonical pathway is ablated due to the absence of p52, resulting in disorganized splenic architecture and disrupted B cell development. The inhibitory precursor form of NF-kappaB2 interacts with RelA, preventing activation of RelA dimers in response to both canonical and noncanonical stimuli, which in combination with p52 deficiency, results in defective lymph node formation and bone homeostasis. These findings demonstrate a key role for NF-kappaB2 in the regulation of RelA activation and suggest overlap in the function of NF-kappaB members in canonical and noncanonical pathway signaling.