Alymphoplasia is caused by a point mutation in the mouse gene encoding Nf-kappa b-inducing kinase

Dendritic cell maturation in cancer

Dendritic cells (DCs) are specialized antigen-presenting cells that are present at low abundance in the circulation and tissues; they serve as crucial immune sentinels by continually sampling their environment, migrating to secondary lymphoid organs and shaping adaptive immune responses through antigen presentation. Owing to their ability to orchestrate tolerogenic or immunogenic responses to a specific antigen, DCs have a pivotal role in antitumour immunity and the response to immune checkpoint blockade and other immunotherapeutic approaches. The multifaceted functions of DCs are acquired through a complex, multistage process called maturation. Although the role of inflammatory triggers in driving DC maturation was established decades ago, less is known about DC maturation in non-inflammatory contexts, such as during homeostasis and in cancer. The advent of single-cell technologies has enabled an unbiased, high-dimensional characterization of various DC states, including mature DCs. This approach has clarified the molecular programmes associated with DC maturation and also revealed how cancers exploit these pathways to subvert immune surveillance. In this Review, we discuss the mechanisms by which cancer disrupts DC maturation and highlight emerging therapeutic opportunities to modulate DC states. These insights could inform the development of DC-centric immunotherapies, expanding the arsenal of strategies to enhance antitumour immunity.

NF-κB-Inducing Kinase Is Essential for Effective c-Rel Transactivation and Binding to the Il12b Promoter in Macrophages

This study investigates the role of NIK in activating specific inflammatory genes in macrophages, focusing on the effect of a mutation in NIK found in alymphoplasia (aly/aly) mice. Mouse peritoneal macrophages from aly/aly mice showed a severe defect in the production of some pro-inflammatory cytokines, such as IL-12. This effect seemed to take place at the transcriptional level, as shown by the reduced transcription of Il12b and Il12a in aly/aly macrophages after exposure to the TLR4 agonist LPS. Immunoprecipitation studies showed that the binding of NIK to c-Rel was not efficient in RAW 264.7 cells over-expressing the aly/aly mutation. In addition, the shuttling of c-Rel to the nucleus was shown to be impaired in aly/aly macrophages in response to LPS. When looking more specifically at the regulation of the Il12b promoter, we found that c-Rel bound to the NF-kB consensus sequence in macrophages from WT mice 1 hr. after LPS challenge, whereas in aly/aly macrophages, the transcription factor bound to the promoter was p65. These findings indicate that NIK is essential for efficient c-Rel activation and proper inflammatory responses. NIK dysfunction could lead to weakened immune responses, and targeting this pathway may help in developing therapies for immune-related conditions.

The Ins and Outs of Thymic Epithelial Cell Differentiation and Function

The thymus is an essential component of the immune system responsible for producing T cells. It is anatomically divided into two main regions: the outer cortex and the inner medulla. This chapter summarizes our current understanding of thymic stromal cell functions, with a particular focus on the interactions between these cells and T cells. This exploration aims to shed light on the pathogenesis of immune disorders, including autoimmunity.

NIK Is a Mediator of Inflammation and Intimal Hyperplasia in Endothelial Denudation-Induced Vascular Injury

Neointimal hyperplasia is the main cause of vascular graft failure in the medium term. NFκB is a key mediator of inflammation that is activated during neointimal hyperplasia following endothelial injury. However, the molecular mechanisms involved in NFκB activation are poorly understood. NFκB may be activated through canonical (transient) and non-canonical (persistent) pathways. NFκB-inducing kinase (NIK, MAP3K14) is the upstream kinase of the non-canonical pathway. We have now explored the impact of NIK deficiency on neointimal hyperplasia following guidewire-induced endothelial cell injury and on local inflammation by comparing NIK activity-deficient alymphoplasia mice (NIKaly/aly) with control wild-type (NIK+/+) mice. Guidewire-induced endothelial cell injury caused neointimal hyperplasia and luminal stenosis and upregulated the local expression of NIK and the NFκB target chemokines monocyte chemoattractant protein-1 (MCP-1/CCL2) and chemokine ligand 5 (RANTES/CCL5). Immunohistochemistry disclosed the infiltration of the media and intima by F4/80 positive macrophages. The intima/media ratio and percentage of stenosis were milder in the NIKaly/aly than in the NIK+/+ mice. Additionally, the gene expression for MCP-1 and RANTES was lower and F4/80+ cell infiltration was milder in the NIKaly/aly than in the NIK+/+ mice. Finally, circulating MCP-1 levels were lower in the NIKaly/aly than in the NIK+/+ mice, reflecting milder systemic inflammation. In conclusion, NIK is a driver of vascular wall inflammation and stenosis following guidewire-induced endothelial cell injury. NIK targeting may be a novel therapeutic approach to limit arterial stenosis following endothelial cell injury.

Fibrotic progression from acute cellular rejection is dependent on secondary lymphoid organs in a mouse model of chronic lung allograft dysfunction

Chronic lung allograft dysfunction (CLAD) remains one of the major limitations to long-term survival after lung transplantation. We modified a murine model of CLAD and transplanted left lungs from BALB/c donors into B6 recipients that were treated with intermittent cyclosporine and methylprednisolone postoperatively. In this model, the lung allograft developed acute cellular rejection on day 15 which, by day 30 after transplantation, progressed to severe pleural and peribronchovascular fibrosis, reminiscent of changes observed in restrictive allograft syndrome. Lung transplantation into splenectomized B6 alymphoplastic (aly/aly) or splenectomized B6 lymphotoxin-β receptor-deficient mice demonstrated that recipient secondary lymphoid organs, such as spleen and lymph nodes, are necessary for progression from acute cellular rejection to allograft fibrosis in this model. Our work uncovered a critical role for recipient secondary lymphoid organs in the development of CLAD after pulmonary transplantation and may provide mechanistic insights into the pathogenesis of this complication.

NF-κB Inducing Kinase Attenuates Colorectal Cancer by Regulating Noncanonical NF-κB Mediated Colonic Epithelial Cell Regeneration

BACKGROUND & AIMS

Dysregulated colonic epithelial cell (CEC) proliferation is a critical feature in the development of colorectal cancer. We show that NF-κB-inducing kinase (NIK) attenuates colorectal cancer through coordinating CEC regeneration/differentiation via noncanonical NF-κB signaling that is unique from canonical NF-kB signaling.

METHODS

Initial studies evaluated crypt morphology/functionality, organoid generation, transcriptome profiles, and the microbiome. Inflammation and inflammation-induced tumorigenesis were initiated in whole-body NIK knockout mice (Nik-/-) and conditional-knockout mice following administration of azoxymethane and dextran sulfate sodium.

RESULTS

Human transcriptomic data revealed dysregulated noncanonical NF-kB signaling. In vitro studies evaluating Nik-/- crypts and organoids derived from mature, nondividing CECs, and colonic stem cells exhibited increased accumulation and stunted growth, respectively. Transcriptomic analysis of Nik-/- cells revealed gene expression signatures associated with altered differentiation-regeneration. When assessed in vivo, Nik-/- mice exhibited more severe colitis with dextran sulfate sodium administration and an altered microbiome characterized by increased colitogenic microbiota. In the inflammation-induced tumorigenesis model, we observed both increased tumor burdens and inflammation in mice where NIK is knocked out in CECs (NikΔCEC). Interestingly, this was not recapitulated when NIK was conditionally knocked out in myeloid cells (NikΔMYE). Surprisingly, conditional knockout of the canonical pathway in myeloid cells (RelAΔMYE) revealed decreased tumor burden and inflammation and no significant changes when conditionally knocked out in CECs (RelAΔCEC).

CONCLUSIONS

Dysregulated noncanonical NF-κB signaling is associated with the development of colorectal cancer in a tissue-dependent manner and defines a critical role for NIK in regulating gastrointestinal inflammation and regeneration associated with colorectal cancer.

Functions of MAP3Ks in antiviral immunity

Immune signal transduction is crucial to the body's defense against viral infection. Recognition of pathogen-associated molecular patterns by pattern recognition receptors (PRRs) activates the transcription of interferon regulators and nuclear factor-κB (NF-κB); this promotes the release of interferons and inflammatory factors. Efficient regulation of type I interferon and NF-κB signaling by members of the mitogen-activated protein (MAP) kinase kinase kinase (MAP3K) family plays an important role in antiviral immunity. Elucidating the specific roles of MAP3K activation during viral infection is essential to develop effective antiviral therapies. In this review, we outline the specific regulatory mechanisms of MAP3Ks in antiviral immunity and discuss the feasibility of targeting MAP3Ks for the treatment of virus-induced diseases.

Filling a nick in NIK: extending the half-life of a NIK inhibitor through structure-based drug design

Inhibition of NF-κB inducing kinase (NIK) has been pursued as a promising therapeutic target for autoimmune disorders due to its highly regulated role in key steps of the NF-κB signaling pathway. Previously reported NIK inhibitors from our group were shown to be potent, selective, and efficacious, but had higher human dose projections than desirable for immunology indications. Herein we report the clearance-driven optimization of a NIK inhibitor guided by metabolite identification studies and structure-based drug design. This led to the identification of an azabicyclo[3.1.0]hexanone motif that attenuated in vitro and in vivo clearance while maintaining NIK potency and increasing selectivity over other kinases, resulting in a greater than ten-fold reduction in predicted human dose.

NF-κB-inducing kinase maintains mitochondrial efficiency and systemic metabolic homeostasis

NF-κB-inducing kinase (NIK) is an essential upstream inducer of noncanonical NF-κB signaling and a critical regulator of immunity and inflammation. Our recent work has demonstrated that NIK regulates mitochondrial respiration and adaptive metabolic responses in cancer and innate immune cells. However, it is not clear whether NIK also has roles in regulating systemic metabolism. In this study, we demonstrate that NIK has local and systemic effects on developmental and metabolic processes. Our findings show that NIK-deficient mice exhibit reduced adiposity, as well as elevated energy expenditure both basally, and under the stress of a high-fat diet. Moreover, we identify NF-κB-independent and -dependent functions for NIK in white adipose tissue metabolism and development. Specifically, we found that in an NF-κB-independent manner NIK is required for maintaining mitochondrial fitness, as NIK-deficient adipocytes have impaired mitochondrial membrane potential and spare respiratory capacity. In addition to mitochondrial exhaustion, NIK-deficient adipocytes and ex vivo adipose tissue exhibit a compensatory upregulation of glycolysis to meet bioenergetic demands. Finally, while NIK regulation of mitochondrial metabolism in preadipocytes is NF-κB-independent, we demonstrate that NIK has a complementary role in adipocyte differentiation that requires activation of RelB and the noncanonical NF-κB pathway. Collectively, these data demonstrate that NIK has critical roles in local and systemic development and metabolism. Our findings establish NIK as an important regulator of organelle, cell, and systemic metabolic homeostasis, suggesting that metabolic dysfunction may be an important and unappreciated component of immune disorders and inflammatory diseases arising from NIK deficiency.

Critical Roles of NF-κB Signaling Molecules in Bone Metabolism Revealed by Genetic Mutations in Osteopetrosis

The nuclear factor-κB (NF-κB) transcription factor family consists of five related proteins, RelA (p65), c-Rel, RelB, p50/p105 (NF-κB1), and p52/p100 (NF-κB2). These proteins are important not only for inflammation and the immune response but also for bone metabolism. Activation of NF-κB occurs via the classic and alternative pathways. Inflammatory cytokines, such as tumor necrosis factor (TNF)-α and interleukin (IL)-1β, activate the former, and cytokines involved in lymph node formation, such as receptor activator of NF-κB ligand (RANKL) and CD40L, activate the latter. p50 and p52 double-knockout mice revealed severe osteopetrosis due to the total lack of osteoclasts, which are specialized cells for bone resorption. This finding suggests that the activation of NF-κB is required for osteoclast differentiation. The NF-κB signaling pathway is controlled by various regulators, including NF-κB essential modulator (NEMO), which is encoded by the IKBKG gene. In recent years, mutant forms of the IKBKG gene have been reported as causative genes of osteopetrosis, lymphedema, hypohidrotic ectodermal dysplasia, and immunodeficiency (OL-EDA-ID). In addition, a mutation in the RELA gene, encoding RelA, has been reported for the first time in newborns with high neonatal bone mass. Osteopetrosis is characterized by a diffuse increase in bone mass, ranging from a lethal form observed in newborns to an asymptomatic form that appears in adulthood. This review describes the genetic mutations in NF-κB signaling molecules that have been identified in patients with osteopetrosis.

IKKα-Mediated Noncanonical NF-κB Signaling Is Required To Support Murine Gammaherpesvirus 68 Latency In Vivo

Noncanonical NF-κB signaling is activated in B cells via the tumor necrosis factor (TNF) receptor superfamily members CD40, lymphotoxin β receptor (LTβR), and B-cell-activating factor receptor (BAFF-R). The noncanonical pathway is required at multiple stages of B cell maturation and differentiation, including the germinal center reaction. However, the role of this pathway in gammaherpesvirus latency is not well understood. Murine gammaherpesvirus 68 (MHV68) is a genetically tractable system used to define pathogenic determinants. Mice lacking the BAFF-R exhibit defects in splenic follicle formation and are greatly reduced for MHV68 latency. We report a novel approach to disrupt noncanonical NF-κB signaling exclusively in cells infected with MHV68. We engineered a recombinant virus that expresses a dominant negative form of IκB kinase α (IKKα), named IKKα-SA, with S176A and S180A mutations that prevent phosphorylation by NF-κB-inducing kinase (NIK). We controlled for the transgene insertion by introducing two all-frame stop codons into the IKKα-SA gene. The IKKα-SA mutant but not the IKKα-SA.STOP control virus impaired LTβR-mediated activation of NF-κB p52 upon fibroblast infection. IKKα-SA expression did not impact replication in primary fibroblasts or in the lungs of mice following intranasal inoculation. However, the IKKα-SA mutant was severely defective in the colonization of the spleen and in the establishment of latency compared to the IKKα-SA.STOP control and wild-type (WT) MHV68 at 16 days postinfection (dpi). Reactivation was undetectable in splenocytes infected with the IKKα-SA mutant, but reactivation in peritoneal cells was not impacted by IKKα-SA. Taken together, the noncanonical NF-κB signaling pathway is essential for the establishment of latency in the secondary lymphoid organs of mice infected with the murine gammaherpesvirus pathogen MHV68. IMPORTANCE The latency programs of the human gammaherpesviruses Epstein-Barr virus (EBV) and Kaposi sarcoma-associated herpesvirus (KSHV) are associated with B cell lymphomas. It is critical to understand the signaling pathways that are used by gammaherpesviruses to establish and maintain latency in primary B cells. We used a novel approach to block noncanonical NF-κB signaling only in the infected cells of mice. We generated a recombinant virus that expresses a dominant negative mutant of IKKα that is nonresponsive to upstream activation. Latency was reduced in a route- and cell type-dependent manner in mice infected with this recombinant virus. These findings identify a significant role for the noncanonical NF-κB signaling pathway that might provide a novel target to prevent latent infection of B cells with oncogenic gammaherpesviruses.

Transcriptional and epigenetic regulation in thymic epithelial cells

The thymus is required for the development of both adaptive and innate-like T cell subsets. There is keen interest in manipulating thymic function for therapeutic purposes in circumstances of autoimmunity, immunodeficiency, and for purposes of immunotherapy. Within the thymus, thymic epithelial cells play essential roles in directing T cell development. Several transcription factors are known to be essential for thymic epithelial cell development and function, and a few transcription factors have been studied in considerable detail. However, the role of many other transcription factors is less well understood. Further, it is likely that roles exist for other transcription factors not yet known to be important in thymic epithelial cells. Recent progress in understanding of thymic epithelial cell heterogeneity has provided some new insight into transcriptional requirements in subtypes of thymic epithelial cells. However, it is unknown whether progenitors of thymic epithelial cells exist in the adult thymus, and consequently, developmental relationships linking putative precursors with differentiated cell types are poorly understood. While we do not presently possess a clear understanding of stage-specific requirements for transcription factors in thymic epithelial cells, new single-cell transcriptomic and epigenomic technologies should enable rapid progress in this field. Here, we review our current knowledge of transcription factors involved in the development, maintenance, and function of thymic epithelial cells, and the mechanisms by which they act.

Lymph node formation and B cell homeostasis require IKK-α in distinct endothelial cell-derived compartments

Global inactivation of IκB kinase (IKK)-α results in defective lymph node (LN) formation and B cell maturation, and loss of IKK-α-dependent noncanonical NF-κB signaling in stromal organizer and hematopoietic cells is thought to underlie these distinct defects. We previously demonstrated that this pathway is also activated in vascular endothelial cells (ECs). To determine the physiologic function of EC-intrinsic IKK-α, we crossed Ikkα^F/F mice with Tie2-cre or Cdh5-cre mice to ablate IKK-α in ECs. Notably, the compound defects of global IKK-α inactivation were recapitulated in Ikkα^Tie2 and Ikkα^Cdh5 mice, as both lacked all LNs and mature follicular and marginal zone B cell numbers were markedly reduced. However, as Tie2-cre and Cdh5-cre are expressed in all ECs, including blood forming hemogenic ECs, IKK-α was also absent in hematopoietic cells (HC). To determine if loss of HC-intrinsic IKK-α affected LN development, we generated Ikkα^Vav mice lacking IKK-α in only the hematopoietic compartment. While mature B cell numbers were significantly reduced in Ikkα^Vav mice, LN formation was intact. As lymphatic vessels also arise during development from blood ECs, we generated Ikkα^Lyve1 mice lacking IKK-α in lymphatic ECs (LECs) to determine if IKK-α in lymphatic vessels impacts LN development. Strikingly, while mature B cell numbers were normal, LNs were completely absent in Ikkα^Lyve1 mice. Thus, our findings reveal that IKK-α in distinct EC-derived compartments is uniquely required to promote B cell homeostasis and LN development, and we establish that LEC-intrinsic IKK-α is absolutely essential for LN formation.

A T cell-intrinsic function for NF-κB RelB in experimental autoimmune encephalomyelitis

NF-kappaB (NF-κB) is a family of transcription factors with pleiotropic functions in immune responses. The alternative NF-κB pathway that leads to the activation of RelB and NF-κB2, was previously associated with the activation and function of T cells, though the exact contribution of these NF-κB subunits remains unclear. Here, using mice carrying conditional ablation of RelB in T cells, we evaluated its role in the development of conventional CD4⁺ T (Tconv) cells and their function in autoimmune diseases. RelB was largely dispensable for Tconv cell homeostasis, activation and proliferation, and for their polarization toward different flavors of Thelper cells in vitro. Moreover, ablation of RelB had no impact on the capacity of Tconv cells to induce autoimmune colitis. Conversely, clinical severity of experimental autoimmune encephalomyelitis (EAE), a mouse model of multiple sclerosis (MS) was significantly reduced in mice with RelB-deficient T cells. This was associated with impaired expression of granulocyte–macrophage colony-stimulating factor (GM-CSF) specifically in the central nervous system. Our data reveal a discrete role for RelB in the pathogenic function of Tconv cells during EAE, and highlight this transcription factor as a putative therapeutic target in MS.

Combined immunodeficiency with autoimmunity caused by a homozygous missense mutation in inhibitor of nuclear factor 𝛋B kinase alpha (IKKα)

[Figure: see text].

BYHWD Alleviates Inflammatory Response by NIK-Mediated Repression of the Noncanonical NF-κB Pathway During ICH Recovery

Intracerebral hemorrhage (ICH) is a life-threatening type of stroke that lacks effective treatments. The inflammatory response following ICH is a vital response that affects brain repair and organism recovery. The nuclear factor κB (NF-κB) signaling pathway is considered one of the most important inflammatory response pathways and one of its response pathways, the noncanonical NF-κB signaling pathway, is known to be associated with persistent effect and chronic inflammation. NF-κB–inducing kinase (NIK) via the noncanonical NF-κB signaling plays a key role in controlling inflammation. Here, we investigated potential effects of the traditional Chinese medicine formula Buyang Huanwu Decoction (BYHWD) on inflammatory response in a rat model of ICH recovery by inhibiting the NIK-mediated the noncanonical NF-κB signaling pathway. In the first part, rats were randomly divided into three groups: the sham group, the ICH group, and the BYHWD group. ICH was induced in rats by injecting collagenase (type VII) into the right globus pallidus of rats' brain. For the BYHWD group, rats were administered BYHWD (4.36 g/kg) once a day by intragastric administration until they were sacrificed. Neurological function was evaluated in rats by a modified neurological severity score (mNSS), the corner turn test, and the foot-fault test. The cerebral edema showed the degree of inflammatory response by sacrificed brain water content. Western blot and real-time quantitative reverse transcription PCR tested the activity of inflammatory response and noncanonical NF-κB signaling. In the second part, siRNA treatment and assessment of inflammation level as well as alterations in the noncanonical NF-κB signaling were performed to determine whether the effect of BYHWD on inflammatory response was mediated by suppression of NIK via the noncanonical NF-κB signaling pathway. We show that BYHWD treated rats exhibited: (i) better health conditions and better neural functional recovery; (ii) decreased inflammatory cytokine and the edema; (iii) reduced expression of NIK, a key protein in unregulated the noncanonical NF-κB signaling pathways; (iv) when compared with pretreated rats with NIK targeting (NIK siRNAs), showed the same effect of inhibiting the pathway and decreased inflammatory cytokine. BYHWD can attenuate the inflammatory response during ICH recovery in rats by inhibiting the NIK-mediated noncanonical NF-κB signaling pathway.

Targeting NF-κB-Inducing Kinase (NIK) in Immunity, Inflammation, and Cancer

NF-κB-inducing kinase (NIK), the essential upstream kinase, which regulates activation of the noncanonical NF-κB pathway, has important roles in regulating immunity and inflammation. In addition, NIK is vital for maintaining cellular health through its control of fundamental cellular processes, including differentiation, growth, and cell survival. As such aberrant expression or regulation of NIK is associated with several disease states. For example, loss of NIK leads to severe immune defects, while the overexpression of NIK is observed in inflammatory diseases, metabolic disorders, and the development and progression of cancer. This review discusses recent studies investigating the therapeutic potential of NIK inhibitors in various diseases.

Fibroblasts as a source of self-antigens for central immune tolerance

Fibroblasts are one of the most common but also neglected types of stromal cells, the heterogeneity of which underlies the specific function of tissue microenvironments in development and regeneration. In the thymus, autoreactive T cells are thought to be negatively selected by reference to the self-antigens expressed in medullary epithelial cells, but the contribution of other stromal cells to tolerance induction has been poorly examined. In the present study, we report a PDGFR⁺ gp38⁺ DPP4^- thymic fibroblast subset that is required for T cell tolerance induction. The deletion of the lymphotoxin β-receptor in thymic fibroblasts caused an autoimmune phenotype with decreased expression of tissue-restricted and fibroblast-specific antigens, offering insight into the long-sought target of lymphotoxin signaling in the context of the regulation of autoimmunity. Thus, thymic medullary fibroblasts play an essential role in the establishment of central tolerance by producing a diverse array of self-antigens.

NF-κB-inducing kinase contributes to normal development of cortical thymic epithelial cells: its possible role in shaping a proper T-cell repertoire

Nuclear factor (NF)-κB-inducing kinase (NIK) is known to be a critical regulator of multiple aspects of the immune response. Although the role of NIK in the development of medullary thymic epithelial cells (mTECs) has been well documented, the impact of NIK on the differentiation and function of cortical thymic epithelial cells (cTECs) remains ambiguous. To investigate the possible involvement of NIK in cTEC differentiation, we have compared the gene expression and function of cTECs from a NIK-mutant mouse, alymphoplasia (aly/aly) with those of cTECs from wild-type (WT) mice. Flow cytometric analyses revealed that expression levels of MHC class II, but not MHC class I or other TEC markers, were higher in aly/aly cells than in WT cells. Notably, the proportion of MHC class IIhi+ cTECs was elevated in aly/aly mice. We also demonstrated that expression of Ccl5 mRNA in the MHC class IIhi+ subset of aly/aly cTECs was decreased compared with that in WT cells, implying an abnormal pattern of gene expression in aly/aly cTECs. Analyses of bone marrow chimera using aly/aly or aly/+ mice as hosts suggested that Vβ usage and CD5 expression on WT T-cells were altered when they matured in aly/aly thymi. These results collectively indicate that NIK may be involved in controlling the function of cTEC in selecting a proper T-cell repertoire.

4-1BB costimulation promotes CAR T cell survival through noncanonical NF-κB signaling

Clinical response to chimeric antigen receptor (CAR) T cell therapy is correlated with CAR T cell persistence, especially for CAR T cells that target CD19⁺ hematologic malignancies. 4-1BB-costimulated CAR (BBζ) T cells exhibit longer persistence after adoptive transfer than do CD28-costimulated CAR (28ζ) T cells. 4-1BB signaling improves T cell persistence even in the context of 28ζ CAR activation, which indicates distinct prosurvival signals mediated by the 4-1BB cytoplasmic domain. To specifically study signal transduction by CARs, we developed a cell-free, ligand-based activation and ex vivo culture system for CD19-specific CAR T cells. We observed greater ex vivo survival and subsequent expansion of BBζ CAR T cells when compared to 28ζ CAR T cells. We showed that only BBζ CARs activated noncanonical nuclear factor κB (ncNF-κB) signaling in T cells basally and that the anti-CD19 BBζ CAR further enhanced ncNF-κB signaling after ligand engagement. Reducing ncNF-κB signaling reduced the expansion and survival of anti-CD19 BBζ T cells and was associated with a substantial increase in the abundance of the most pro-apoptotic isoforms of Bim. Although our findings do not exclude the importance of other signaling differences between BBζ and 28ζ CARs, they demonstrate the necessary and nonredundant role of ncNF-κB signaling in promoting the survival of BBζ CAR T cells, which likely underlies the engraftment persistence observed with this CAR design.

Map3k14 as a Regulator of Innate and Adaptive Immune Response during Acute Viral Infection

The replication of virus in secondary lymphoid organs is crucial for the activation of antigen-presenting cells. Balanced viral replication ensures the sufficient availability of antigens and production of cytokines, and both of which are needed for virus-specific immune activation and viral elimination. Host factors that regulate coordinated viral replication are not fully understood. In the study reported here, we identified Map3k14 as an important regulator of enforced viral replication in the spleen while performing genome-wide association studies of various inbred mouse lines in a model of lymphocytic choriomeningitis virus (LCMV) infection. When alymphoplasia mice (aly/aly, Map3k14^aly/aly, or Nik^aly/aly), which carry a mutation in Map3k14, were infected with LCMV or vesicular stomatitis virus (VSV), they display early reductions in early viral replication in the spleen, reduced innate and adaptive immune activation, and lack of viral control. Histologically, scant B cells and the lack of CD169⁺ macrophages correlated with reduced immune activation in Map3k14^aly/aly mice. The transfer of wildtype B cells into Map3k14^aly/aly mice repopulated CD169⁺ macrophages, restored enforced viral replication, and resulted in enhanced immune activation and faster viral control.

The Role of Endothelial Cells and TNF-Receptor Superfamily Members in Lymphoid Organogenesis and Function During Health and Inflammation

Lymph nodes (LNs) are crucial for the orchestration of immune responses. LN reactions depend on interactions between incoming and local immune cells, and stromal cells. To mediate these cellular interactions an organized vascular network within the LN exists. In general, the LN vasculature can be divided into two components: blood vessels, which include the specialized high endothelial venules that recruit lymphocytes from the bloodstream, and lymphatic vessels. Signaling via TNF receptor (R) superfamily (SF) members has been implicated as crucial for the development and function of LNs and the LN vasculature. In recent years the role of cell-specific signaling of TNFRSF members in different endothelial cell (EC) subsets and their roles in development and maintenance of lymphoid organs has been elucidated. Here, we discuss recent insights into EC-specific TNFRSF member signaling and highlight its importance in different EC subsets in LN organogenesis and function during health, and in lymphocyte activation and tertiary lymphoid structure formation during inflammation.

Molecular dynamics simulation and QM/MM calculation reveal the selectivity mechanism of type I 1/2 kinase inhibitors: the effect of intramolecular H-bonds and conformational restriction for improved selectivity

Understanding the selectivity mechanisms of inhibitors towards highly similar proteins is extremely important work on the way to a new drug. Here, we aim to reveal the selectivity mechanisms of type I 1/2 kinase inhibitors towards p21-activated kinase (PAK4) and mitogen-activated protein kinase kinase kinase 14 (MAP3K14, NIK). PAK4, belonging to the serine/threonine protein kinases, is involved in cell signaling pathways and controls cellular functions and has received attention as an attractive drug target. The high sequence identity between PAK4 and NIK makes it challenging to design selective PAK4 inhibitors. In this work, computational methods including protein comparison, molecular docking, QM/MM, molecular dynamics simulations, and density functional theory (DFT) calculation were employed to explore the binding mechanisms of selective inhibitors against NIK and PAK4. The simulation results revealed the crucial factors accounting for selective inhibition of PAK4 over NIK, including different protein-ligand interactions, the positions and conformations of key residues, and the ligands flexibilities. This study will shed light on understanding the selectivity mechanisms of PAK4 and NIK inhibitors.

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.

A NIK-SIX signalling axis controls inflammation by targeted silencing of non-canonical NF-κB

The non-canonical NF-κB signalling cascade is essential for lymphoid organogenesis, B cell maturation, osteoclast differentiation, and inflammation in mammals1,2; dysfunction of this system is associated with human diseases, including immunological disorders and cancer3-6. Although expression of NF-κB-inducing kinase (NIK, also known as MAP3K14) is the rate-limiting step in non-canonical NF-κB pathway activation2,7, the mechanisms by which transcriptional responses are regulated remain largely unknown. Here we show that the sine oculis homeobox (SIX) homologue family transcription factors SIX1 and SIX2 are integral components of the non-canonical NF-κB signalling cascade. The developmentally silenced SIX proteins are reactivated in differentiated macrophages by NIK-mediated suppression of the ubiquitin proteasome pathway. Consequently, SIX1 and SIX2 target a subset of inflammatory gene promoters and directly inhibit the trans-activation function of the transcription factors RELA and RELB in a negative feedback circuit. In support of a physiologically pivotal role for SIX proteins in host immunity, a human SIX1 transgene suppressed inflammation and promoted the recovery of mice from endotoxic shock. In addition, SIX1 and SIX2 protected RAS/P53-driven non-small-cell lung carcinomas from inflammatory cell death induced by SMAC-mimetic chemotherapeutic agents (small-molecule activators of the non-canonical NF-κB pathway). Our findings identify a NIK-SIX signalling axis that fine-tunes inflammatory gene expression programs under both physiological and pathological conditions.

NIK as a Druggable Mediator of Tissue Injury

NF-κB-inducing kinase (NIK, MAP3K14) is best known as the apical kinase that triggers non-canonical NF-κB activation and by its role in the immune system. Recent data indicate a role for NIK expressed by non-lymphoid cells in cancer, kidney disease, liver injury, glucose homeostasis, osteosarcopenia, vascular calcification, hematopoiesis, and endothelial function. The spectrum of NIK-associated disease now ranges from immunodeficiency (when NIK is defective) to autoimmunity, cancer, sterile inflammation, fibrosis, and metabolic disease when NIK is overactive. The development of novel small-molecule NIK inhibitors has paved the way to test NIK targeting to treat disease in vivo, and may eventually lead to NIK targeting in the clinic. In addition, NIK activators are being explored for specific conditions such as myeloid leukemia.

Lymphatic endothelial cells regulate B-cell homing to lymph nodes via a NIK-dependent mechanism

B cells home to the lymph nodes (LNs) via high endothelial venules (HEVs) under the guidance of chemokines, particularly CXCL13. However, as CXCL13 is not directly made in HEVs, the molecular mechanism mediating B-cell homing to LNs has remained unclear. We show here that nuclear factor (NF)-κB-inducing kinase (NIK), a kinase mediating activation of the noncanonical NF-κB pathway, functions in lymphatic endothelial cells (LECs) to regulate B-cell homing to LNs. LEC-conditional deletion of NIK in mice did not affect the integrity or global function of lymphatic vessels but caused a severe reduction in the frequency of B cells in LNs. The LEC-specific NIK deficiency did not affect the survival of B cells or the frequency of B cells in the spleen. B-cell adoptive transfer studies revealed that the LEC-specific NIK deletion impairs the ability of LNs to recruit B cells. We further show that NIK mediates expression of the chemokines CXCL13 and CCL19 in LECs. Although CCL19 is also expressed in blood endothelial cells (BECs), CXCL13 is not produced in BECs. These results suggest that NIK regulates naive B-cell homing to LNs via mediating production of the B-cell homing chemokine CXCL13 in LECs.

Inhibitory-κB Kinase (IKK) α and Nuclear Factor-κB (NFκB)-Inducing Kinase (NIK) as Anti-Cancer Drug Targets

The cellular kinases inhibitory-κB kinase (IKK) α and Nuclear Factor-κB (NF-κB)-inducing kinase (NIK) are well recognised as key central regulators and drivers of the non-canonical NF-κB cascade and as such dictate the initiation and development of defined transcriptional responses associated with the liberation of p52-RelB and p52-p52 NF-κB dimer complexes. Whilst these kinases and downstream NF-κB complexes transduce pro-inflammatory and growth stimulating signals that contribute to major cellular processes, they also play a key role in the pathogenesis of a number of inflammatory-based conditions and diverse cancer types, which for the latter may be a result of background mutational status. IKKα and NIK, therefore, represent attractive targets for pharmacological intervention. Here, specifically in the cancer setting, we reflect on the potential pathophysiological role(s) of each of these kinases, their associated downstream signalling outcomes and the stimulatory and mutational mechanisms leading to their increased activation. We also consider the downstream coordination of transcriptional events and phenotypic outcomes illustrative of key cancer 'Hallmarks' that are now increasingly perceived to be due to the coordinated recruitment of both NF-κB-dependent as well as NF-κB⁻independent signalling. Furthermore, as these kinases regulate the transition from hormone-dependent to hormone-independent growth in defined tumour subsets, potential tumour reactivation and major cytokine and chemokine species that may have significant bearing upon tumour-stromal communication and tumour microenvironment it reiterates their potential to be drug targets. Therefore, with the emergence of small molecule kinase inhibitors targeting each of these kinases, we consider medicinal chemistry efforts to date and those evolving that may contribute to the development of viable pharmacological intervention strategies to target a variety of tumour types.

Poly IC pretreatment suppresses B cell-mediated lupus-like autoimmunity through induction of Peli1

Noncanonical NF-κB pathway is essential for the B cell activation and antibody production, which centralize the critical role of B cells in regulating the pathogenesis of systemic lupus erythematosus (SLE). We have previously demonstrated that Pellino1 (Peli1) negatively regulates noncanonical NF-κB activation and lupus autoimmunity. Here, we showed that poly IC is a potent inducer of Peli1 protein in mouse splenic B cells in dose- and time-dependent manners, and poly IC-induced Peli1 protein dramatically suppressed the activation of noncanonical NF-κB pathway. In addition, poly IC-pretreated B cells failed to induce lupus-like disease in BM12 CD4+ T cell-immunized mice. Accordingly, the induction of antibody-producing plasma cells and germinal center B cells, as well as the production of autoantibodies were significantly impaired in immunized μMT mice that were transferred with poly IC-pretreated B cells. Our findings demonstrate that poly IC-induced Peli1 negatively regulates the noncanonical NF-κB pathway in the context of restraining the pathogenesis of lupus-like disease.

STIM- and Orai-mediated calcium entry controls NF-κB activity and function in lymphocytes

The central role of Ca²⁺ signaling in the development of functional immunity and tolerance is well established. These signals are initiated by antigen binding to cognate receptors on lymphocytes that trigger store operated Ca²⁺ entry (SOCE). The underlying mechanism of SOCE in lymphocytes involves TCR and BCR mediated activation of Stromal Interaction Molecule 1 and 2 (STIM1/2) molecules embedded in the ER membrane leading to their activation of Orai channels in the plasma membrane. STIM/Orai dependent Ca²⁺ signals guide key antigen induced lymphocyte development and function principally through direct regulation of Ca²⁺ dependent transcription factors. The role of Ca²⁺ signaling in NFAT activation and signaling is well known and has been studied extensively, but a wide appreciation and mechanistic understanding of how Ca²⁺ signals also shape the activation and specificity of NF-κB dependent gene expression has lagged. Here we discuss and interpret what is known about Ca²⁺ dependent mechanisms of NF-kB activation, including what is known and the gaps in our understanding of how these signals control lymphocyte development and function.

Peli1 negatively regulates noncanonical NF-κB signaling to restrain systemic lupus erythematosus

Systemic lupus erythematosus (SLE) is characterized by uncontrolled secretion of autoantibodies by plasma cells. Although the functional importance of plasma cells and autoantibodies in SLE has been well established, the underlying molecular mechanisms of controlling autoantibody production remain poorly understood. Here we show that Peli1 has a B cell-intrinsic function to protect against lupus-like autoimmunity in mice. Peli1 deficiency in B cells induces autoantibody production via noncanonical NF-κB signaling. Mechanically, Peli1 functions as an E3 ligase to associate with NF-κB inducing kinase (NIK) and mediates NIK Lys48 ubiquitination and degradation. Overexpression of Peli1 inhibits noncanonical NF-κB activation and alleviates lupus-like disease. In humans, PELI1 levels negatively correlate with disease severity in SLE patients. Our findings establish Peli1 as a negative regulator of the noncanonical NF-κB pathway in the context of restraining the pathogenesis of lupus-like disease.

Enhanced Antibody Responses in a Novel NOG Transgenic Mouse with Restored Lymph Node Organogenesis

Lymph nodes (LNs) are at the center of adaptive immune responses. Various exogenous substances are transported into LNs and a series of immune responses ensue after recognition by antigen–specific lymphocytes. Although humanized mice have been used to reconstitute the human immune system, most lack LNs due to deficiency of the interleukin (IL)-2Rγ gene (cytokine common γ chain, γc). In this study, we established a transgenic strain, NOG-pRORγt-γc, in the NOD/shi-scid-IL-2Rγ^null (NOG) background, in which the γc gene was expressed in a lymph-tissue inducer (LTi) lineage by the endogenous promoter of RORγt. In this strain, LN organogenesis was normalized and the number of human T cells substantially increased in the periphery after reconstitution of the human immune system by human hematopoietic stem cell transplantation. The distribution of human T cells differed between NOG-pRORγt-γc Tg and NOG-non Tg mice. About 40% of human T cells resided in LNs, primarily the mesenteric LNs. The LN-complemented humanized mice exhibited antigen-specific immunoglobulin G responses together and an increased number of IL-21⁺–producing CD4⁺ T cells in LNs. This novel mouse strain will facilitate recapitulation of human immune responses.

NF-κB inducing kinase is a therapeutic target for systemic lupus erythematosus

NF-κB-inducing kinase (NIK) mediates non-canonical NF-κB signaling downstream of multiple TNF family members, including BAFF, TWEAK, CD40, and OX40, which are implicated in the pathogenesis of systemic lupus erythematosus (SLE). Here, we show that experimental lupus in NZB/W F1 mice can be treated with a highly selective and potent NIK small molecule inhibitor. Both in vitro as well as in vivo, NIK inhibition recapitulates the pharmacological effects of BAFF blockade, which is clinically efficacious in SLE. Furthermore, NIK inhibition also affects T cell parameters in the spleen and proinflammatory gene expression in the kidney, which may be attributable to inhibition of OX40 and TWEAK signaling, respectively. As a consequence, NIK inhibition results in improved survival, reduced renal pathology, and lower proteinuria scores. Collectively, our data suggest that NIK inhibition is a potential therapeutic approach for SLE.

Nuclear Factor-kappaB in Autoimmunity: Man and Mouse

NF-κB (nuclear factor-kappa B) is a transcription complex crucial for host defense mediated by innate and adaptive immunity, where canonical NF-κB signaling, mediated by nuclear translocation of RelA, c-Rel, and p50, is important for immune cell activation, differentiation, and survival. Non-canonical signaling mediated by nuclear translocation of p52 and RelB contributes to lymphocyte maturation and survival and is also crucial for lymphoid organogenesis. We outline NF-κB signaling and regulation, then summarize important molecular contributions of NF-κB to mechanisms of self-tolerance. We relate these mechanisms to autoimmune phenotypes described in what is now a substantial catalog of immune defects conferred by mutations in NF-κB pathways in mouse models. Finally, we describe Mendelian autoimmune syndromes arising from human NF-κB mutations, and speculate on implications for understanding sporadic autoimmune disease.

Molecular insights into the mechanisms of M-cell differentiation and transcytosis in the mucosa-associated lymphoid tissues

Microfold cells (M cells), which are located in the follicle-associated epithelium (FAE) covering mucosal lymphoid follicles, are specialized epithelial cells that initiate mucosal immune responses. These cells take luminal antigens and transport them via transcytosis across the FAE to the antigen-presenting cells underneath. Several intestinal pathogens exploit M cells as their portal for entry to invade the host and cause disease conditions. Recent studies have revealed that the uptake of antigens by M cells is essential for efficient antigen-specific IgA production and that this process likely maintains the homeostasis of mucosal tissues. The present article reviews recent advances in understanding the molecular mechanism of M-cell differentiation and describes the molecules expressed by M cells that are associated with antigen uptake and/or the transcytosis process. Current efforts to augment M-cell-mediated uptake for use in the development of effective mucosal vaccines are also discussed.

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

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

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.

Dysregulated homeostasis of target tissues or autoantigens - A novel principle in autoimmunity

Monogenic autoimmune disorders provide a powerful tool for our understanding of the principles of autoimmunity due to the obvious impact of a single gene on the disease. So far, approximately 100 single gene defects causing murine monogenic autoimmune disorders have been reported and the functional characterization of these genes will provide significant progress in understanding the nature of autoimmunity. According to their function, genes leading to monogenic autoimmune disorders can be categorized into two groups. An expectable first group contains genes involved in the homeostasis of the immune system, including homeostasis of immune organs and immune cells. Intriguingly, the second group consists of genes functionally involved in the homeostasis of target tissues or autoantigens. According to our novel hypothesis, we propose that autoimmunity represents a consequence of a dysregulated homeostasis of the immune system and/or its targets including autoantigens and target tissues. In this review we refer to both aspects of homeostasis in autoimmunity with a highlight on the role of the homeostasis of target tissues and autoantigens.

Structure-Based Design of Tricyclic NF-κB Inducing Kinase (NIK) Inhibitors That Have High Selectivity over Phosphoinositide-3-kinase (PI3K)

We report here structure-guided optimization of a novel series of NF-κB inducing kinase (NIK) inhibitors. Starting from a modestly potent, low molecular weight lead, activity was improved by designing a type 11/2 binding mode that accessed a back pocket past the methionine-471 gatekeeper. Divergent binding modes in NIK and PI3K were exploited to dampen PI3K inhibition while maintaining NIK inhibition within these series. Potent compounds were discovered that selectively inhibit the nuclear translocation of NF-κB2 (p52/REL-B) but not canonical NF-κB1 (REL-A/p50).

Late-phase synthesis of IκBα insulates the TLR4-activated canonical NF-κB pathway from noncanonical NF-κB signaling in macrophages

The nuclear factor κB (NF-κB) transcription factors coordinate the inflammatory immune response during microbial infection. Pathogenic substances engage canonical NF-κB signaling through the heterodimer RelA:p50, which is subjected to rapid negative feedback by inhibitor of κBα (IκBα). The noncanonical NF-κB pathway is required for the differentiation of immune cells; however, cross-talk between both pathways can occur. Concomitantly activated noncanonical signaling generates p52 from the p100 precursor. The synthesis of p100 is induced by canonical signaling, leading to the formation of the late-acting RelA:p52 heterodimer. This cross-talk prolongs inflammatory RelA activity in epithelial cells to ensure pathogen clearance. We found that the Toll-like receptor 4 (TLR4)-activated canonical NF-κB signaling pathway is insulated from lymphotoxin β receptor (LTβR)-induced noncanonical signaling in mouse macrophage cell lines. Combined computational and biochemical studies indicated that the extent of NF-κB-responsive expression of Nfkbia, which encodes IκBα, inversely correlated with cross-talk. The Nfkbia promoter showed enhanced responsiveness to NF-κB activation in macrophages compared to that in fibroblasts. We found that this hyperresponsive promoter engaged the RelA:p52 dimer generated during costimulation of macrophages through TLR4 and LTβR to trigger synthesis of IκBα at late time points, which prevented the late-acting RelA cross-talk response. Together, these data suggest that, despite the presence of identical signaling networks in cells of diverse lineages, emergent cross-talk between signaling pathways is subject to cell type-specific regulation. We propose that the insulation of canonical and noncanonical NF-κB pathways limits the deleterious effects of macrophage-mediated inflammation.

Epithelia Use Butyrophilin-like Molecules to Shape Organ-Specific γδ T Cell Compartments

Many body surfaces harbor organ-specific γδ T cell compartments that contribute to tissue integrity. Thus, murine dendritic epidermal T cells (DETCs) uniquely expressing T cell receptor (TCR)-Vγ5 chains protect from cutaneous carcinogens. The DETC repertoire is shaped by Skint1, a butyrophilin-like (Btnl) gene expressed specifically by thymic epithelial cells and suprabasal keratinocytes. However, the generality of this mechanism has remained opaque, since neither Skint1 nor DETCs are evolutionarily conserved. Here, Btnl1 expressed by murine enterocytes is shown to shape the local TCR-Vγ7(+) γδ compartment. Uninfluenced by microbial or food antigens, this activity evokes the developmental selection of TCRαβ(+) repertoires. Indeed, Btnl1 and Btnl6 jointly induce TCR-dependent responses specifically in intestinal Vγ7(+) cells. Likewise, human gut epithelial cells express BTNL3 and BTNL8 that jointly induce selective TCR-dependent responses of human colonic Vγ4(+) cells. Hence, a conserved mechanism emerges whereby epithelia use organ-specific BTNL/Btnl genes to shape local T cell compartments.

Mitogen-Activated Protein Kinase 14 Promotes AKI

An improved understanding of pathogenic pathways in AKI may identify novel therapeutic approaches. Previously, we conducted unbiased liquid chromatography-tandem mass spectrometry-based protein expression profiling of the renal proteome in mice with acute folate nephropathy. Here, analysis of the dataset identified enrichment of pathways involving NFκB in the kidney cortex, and a targeted data mining approach identified components of the noncanonical NFκB pathway, including the upstream kinase mitogen-activated protein kinase kinase kinase 14 (MAP3K14), the NFκB DNA binding heterodimer RelB/NFκB2, and proteins involved in NFκB2 p100 ubiquitination and proteasomal processing to p52, as upregulated. Immunohistochemistry localized MAP3K14 expression to tubular cells in acute folate nephropathy and human AKI. In vivo, kidney expression levels of NFκB2 p100 and p52 increased rapidly after folic acid injection, as did DNA binding of RelB and NFκB2, detected in nuclei isolated from the kidneys. Compared with wild-type mice, MAP3K14 activity-deficient aly/aly (MAP3K14^aly/aly) mice had less kidney dysfunction, inflammation, and apoptosis in acute folate nephropathy and less kidney dysfunction and a lower mortality rate in cisplatin-induced AKI. The exchange of bone marrow between wild-type and MAP3K14^aly/aly mice did not affect the survival rate of either group after folic acid injection. In cultured tubular cells, MAP3K14 small interfering RNA targeting decreased inflammation and cell death. Additionally, cell culture and in vivo studies identified the chemokines MCP-1, RANTES, and CXCL10 as MAP3K14 targets in tubular cells. In conclusion, MAP3K14 promotes kidney injury through promotion of inflammation and cell death and is a promising novel therapeutic target.

Expanding the Interactome of the Noncanonical NF-κB Signaling Pathway

NF-κB signaling is a central pathway of immunity and integrates signal transduction upon a wide array of inflammatory stimuli. Noncanonical NF-κB signaling is activated by a small subset of TNF family receptors and characterized by NF-κB2/p52 transcriptional activity. The medical relevance of this pathway has recently re-emerged from the discovery of primary immunodeficiency patients that have loss-of-function mutations in the MAP3K14 gene encoding NIK. Nevertheless, knowledge of protein interactions that regulate noncanonical NF-κB signaling is sparse. Here we report a detailed state-of-the-art mass spectrometry-based protein-protein interaction network including the noncanonical NF-κB signaling nodes TRAF2, TRAF3, IKKα, NIK, and NF-κB2/p100. The value of the data set was confirmed by the identification of interactions already known to regulate this pathway. In addition, a remarkable number of novel interactors were identified. We provide validation of the novel NIK and IKKα interactor FKBP8, which may regulate processes downstream of noncanonical NF-κB signaling. To understand perturbed noncanonical NF-κB signaling in the context of misregulated NIK in disease, we also provide a differential interactome of NIK mutants that cause immunodeficiency. Altogether, this data set not only provides critical insight into how protein-protein interactions can regulate immune signaling but also offers a novel resource on noncanonical NF-κB signaling.

Emerging Roles for Noncanonical NF-κB Signaling in the Modulation of Inflammatory Bowel Disease Pathobiology

Crohn's disease and ulcerative colitis are common and debilitating manifestations of inflammatory bowel disease (IBD). IBD is characterized by a radical imbalance in the activation of proinflammatory and anti-inflammatory signaling pathways in the gut. These pathways are controlled by NF-κB, which is a master regulator of gene transcription. In IBD patients, NF-κB signaling is often dysregulated resulting in overzealous inflammation. NF-κB activation occurs through 2 distinct pathways, defined as either canonical or noncanonical. Canonical NF-κB pathway activation is well studied in IBD and is associated with the rapid, acute production of diverse proinflammatory mediators, such as COX-2, IL-1β, and IL-6. In contrast to the canonical pathway, the noncanonical or "alternative" NF-κB signaling cascade is tightly regulated and is responsible for the production of highly specific chemokines that tend to be associated with less acute, chronic inflammation. There is a relative paucity of literature regarding all aspects of noncanonical NF-ĸB signaling. However, it is clear that this alternative signaling pathway plays a considerable role in maintaining immune system homeostasis and likely contributes significantly to the chronic inflammation underlying IBD. Noncanonical NF-κB signaling may represent a promising new direction in the search for therapeutic targets and biomarkers associated with IBD. However, significant mechanistic insight is still required to translate the current basic science findings into effective therapeutic strategies.

Mouse Models of Primary Sjogren's Syndrome

Sjogren's syndrome (SjS) is a chronic autoimmune disorder characterized by immune cell infiltration and progressive injury to the salivary and lacrimal glands. As a consequence, patients with SjS develop xerostomia (dry mouth) and keratoconjunctivitis sicca (dry eyes). SjS is the third most common rheumatic autoimmune disorder, affecting 4 million Americans with over 90% of patients being female. Current diagnostic criteria for SjS frequently utilize histological examinations of minor salivary glands for immune cell foci, serology for autoantibodies, and dry eye evaluation by corneal or conjunctival staining. SjS can be classified as primary or secondary SjS, depending on whether it occurs alone or in association with other systemic rheumatic conditions, respectively. Clinical manifestations typically become apparent when the disease is relatively advanced in SjS patients, which poses a challenge for early diagnosis and treatment of SjS. Therefore, SjS mouse models, because of their close resemblance to the human SjS, have been extremely valuable to identify early disease markers and to investigate underlying biological and immunological dysregulations. However, it is important to bear in mind that no single mouse model has duplicated all aspects of SjS pathogenesis and clinical features, mainly due to the multifactorial etiology of SjS that includes numerous susceptibility genes and environmental factors. As such, various mouse models have been developed in the field to try to recapitulate SjS. In this review, we focus on recent mouse models of primary SjS xerostomia and describe them under three categories of spontaneous, genetically engineered, and experimentally induced models. In addition, we discuss future perspectives highlighting pros and cons of utilizing mouse models and current demands for improved models.

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.

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.

NF-κB-inducing kinase is essential for B-cell maintenance in mice

NF-κB-inducing kinase (NIK) is a key mediator of the noncanonical NF-κB signaling pathway, which is critical for normal B-cell development and function. It is well established that the complete deletion of NIK in mice results in defective B cells and impaired secondary lymphoid organogenesis. To address the role of NIK deficiency specifically in B cells, we generated a new mouse strain for the conditional deletion of this kinase. Deletion of NIK during B-cell development results in a drastic reduction of mature B cells from the transitional 2 stage on, while B-1 B cells are less affected. Moreover, deletion of NIK in the germinal centers decreases the numbers of germinal center B cells and impairs the ability of NIK-deficient B cells to develop into class-switched cells in vivo. This new mouse strain will be helpful for studying the role of NIK in different cell types of the body.

Cell intrinsic role of NF-κB-inducing kinase in regulating T cell-mediated immune and autoimmune responses

NF-κB inducing kinase (NIK) is a central component of the noncanonical NF-κB signaling pathway. Although NIK has been extensively studied for its function in the regulation of lymphoid organ development and B-cell maturation, the role of NIK in regulating T cell functions remains unclear and controversial. Using T cell-conditional NIK knockout mice, we here demonstrate that although NIK is dispensable for thymocyte development, it has a cell-intrinsic role in regulating the homeostasis and function of peripheral T cells. T cell-specific NIK ablation reduced the frequency of effector/memory-like T cells and impaired T cell responses to bacterial infection. The T cell-conditional NIK knockout mice were also defective in generation of inflammatory T cells and refractory to the induction of a T cell-dependent autoimmune disease, experimental autoimmune encephalomyelitis. Our data suggest a crucial role for NIK in mediating the generation of effector T cells and their recall responses to antigens. Together, these findings establish NIK as a cell-intrinsic mediator of T cell functions in both immune and autoimmune responses.