NF-kappaB-inducing Kinase Research Articles

Immunological link between periodontitis and type 2 diabetes deciphered by single-cell RNA analysis.

Type 2 diabetes mellitus (DM) is a complex metabolic disorder that causes various complications, including periodontitis (PD). Although a bidirectional relationship has been reported between DM and PD, their immunological relationship remains poorly understood. Therefore, this study aimed to compare the immune response in patients with PD alone and in those with both PD and DM (PDDM) to expand our knowledge of the complicated connection between PD and DM. Peripheral blood mononuclear cells were collected from 11 healthy controls, 10 patients with PD without DM, and six patients with PDDM, followed by analysis using single-cell RNA sequencing. The differences among groups were then compared based on intracellular and intercellular perspectives. Compared to the healthy state, classical monocytes exhibited the highest degree of transcriptional change, with elevated levels of pro-inflammatory cytokines in both PD and PDDM. DM diminished the effector function of CD8+ T and natural killer (NK) cells as well as completely modified the differentiation direction of these cells. Interestingly, a prominent pathway, RESISTIN, which is known to increase insulin resistance and susceptibility to diabetes, was found to be activated under both PD and PDDM conditions. In particular, CAP1+ classical monocytes from patients with PD and PDDM showed elevated nuclear factor kappa B-inducing kinase activity. Overall, this study elucidates how the presence of DM contributes to the deterioration of T/NK cell immunity and the immunological basis connecting PD to DM.

Febuxostat attenuates aluminum chloride-induced hepatorenal injury in rats with the impact of Nrf2, Crat, Car3, and MNK-mediated apoptosis

Aluminum (Al) is a ubiquitous xenobiotic with known toxicity for both humans and animals. Our study was conducted to investigate the protective role of febuxostat (Feb) against aluminum chloride (AlCl3)-induced hepatorenal injury in rats. Hepatorenal injury was induced by oral administration of AlCl3 (40 mg/kg b.w.), for 2 months. Twenty-four male Sprague–Dawley rats were randomly allocated into four groups (six rats/group). The first group received the vehicle thought the experiment. The second group was considered as a control positive group. The third and fourth groups received oral treatment of Feb (10 mg/kg.b.w.) and (15 mg/kg.b.w.), respectively with AlCl3, concurrently for 2 months. Twenty-four hours, after the last treatment, serum biochemical, molecular, histopathology, and immunohistochemical studies were evaluated. Our findings showed that rats intoxicated with Alcl3 had disturbed biochemical picture. In addition, intoxication with AlCl3 increased oxidative stress and apoptosis, as demonstrated by an increase in malodialdeyde (MDA), carnitine o-acetyltransferase (Crat), and carbonic anhydrase (Car3) with a decrease in glutathione (GSH), MAP kinase-interacting serine/threonine kinase (MNK) and nuclear factor-erythroid 2-related factor 2 (Nrf2) mRNA expression. Furthermore, the levels of tumor necrosis factor-alpha (TNF-α) and the levels of caspase-3 were elevated with sever hepatic and renal pathological changes. Conversely, Feb (15 mg/kg.b.w.) could improve the serum biochemical indices and repressed MDA, Crat, and Car3 levels, whereas it increased GSH, MNK, and Nrf2 levels. Feb inhibited the apoptotic effect of AlCl3 in the liver and kidney by decreasing caspase-3 and TNF-α expression. The protective effect of Feb against AlCl3 toxicity was confirmed by histopathological findings. Moreover, molecular docking studies supported the anti-inflammatory effect of Feb due to its significant binding interactions with cyclooxygenase-1 (COX-1), NF-kappa-B-inducing kinase (NIK), and mitogen-activated protein kinases-p38 (MAPK-p38). The findings suggest that Feb system Feb can avert Alcl3-induced hepatotoxicity and nephrotoxicity by enhancing the antioxidant defense system, and inhibiting the inflammatory cascade and apoptosis.

Analysis of the binding pattern of NIK inhibitors by computational simulation

NF-kappaB-Inducing Kinase (NIK) is a key kinase in the activation of the NF-κB non-classical signalling pathway, which has been shown to be over-activated in patients with inflammatory diseases, immune disorders and malignancies and solid tumours inducing activation of the NF-κB non-classical signalling pathway. The design of ATP-competitive small molecule inhibitors against NIK has been a hot topic in the last decade, and many efficient NIK inhibitors have been identified. In this work, I aim to unravel the mechanism of NIK inhibition by different representative NIK type I 1/2 kinase inhibitors, using ADME, molecular docking, molecular dynamics simulation, MM-PBSA analysis and 3D-QSAR analysis. This work contributes to the understanding of the efficiency of NIK inhibitor binding by revealing the basis of the efficiency of NIK inhibitors, the difference in binding modes between different inhibitors and the overall effect on NIK. Communicated by Ramaswamy H. Sarma

Aspirin alleviates the symptoms of immunoglobulin A nephropathy via suppressing platelets-mediated non-canonical NF-κB activation in B cells

Purpose: Antiplatelet aggregation drugs, such as aspirin, can alleviate pathological renal damage in immunoglobulin A (IgA) nephropathy, although the precise mechanism is unclear.
 Methods: The serum levels of platelet factor 4 (PF4), IgA, and platelet-activating factor (PAF) were assessed by enzyme-linked immunosorbent assay in IgA nephropathy patients and TANK-binding kinase 1 (TBK1)-/- tumor necrosis factor (TNF)-/- mice. The deposition of IgA in glomeruli was detected by immunofluorescence. Phorbol-12-myristate-13-acetate (PMA) induced platelets activation was examined by the cell counting kit 8 assay. B cells were further stimulated with lipopolysaccharides (LPS) or plus platelets supernatant, or combined with nuclear factor kappa-B (NF-κB) inducing kinase (NIK) inhibitor, NIK SMI1.
 Results: Increased serum IgA and proportion of activated platelets were observed in IgA nephropathy patients. TBK1-/-TNF-/- mice had significant increased urinary protein and serum creatinine, and IgA deposition in glomeruli. Up-regulated serum PF4 and PAF were observed in both the IgA nephropathy patients and TBK1-/-TNF-/- mice. Aspirin suppressed the deposition of IgA in glomeruli of TBK1-/-TNF-/- mice with down-regulated platelets activation. Platelets supernatant could promote the proliferation of B cells with up-regulated IgA and sCD40L secretion and up-regulated P52 and RelB expression, which could be inhibited by NIK SMI1 administration.
 Conclusion: TBK1-/-TNF-/- mice demonstrate IgA nephropathy phenotype, which could be alleviated by aspirin administration via inhibiting platelets induced non-canonical NF-κB activation mediated IgA production in B cells.

Constitutive activation of nuclear factor kappa B-inducing kinase counteracts apoptosis in cells with rearranged mixed lineage leukemia gene.

Constitutive activation of nuclear factor kappa B-inducing kinase counteracts apoptosis in cells with rearranged mixed lineage leukemia gene.

Bovine lactoferrin free of lipopolysaccharide can induce a proinflammatory response of macrophages.

BackgroundLactoferrin (LF) is an 80 kDa glycoprotein which is known for its effects against bacteria, viruses and other pathogens. It also has a high potential in nutrition therapy and welfare of people and a variety of animals, including piglets. The ability to bind lipopolysaccharide (LPS) is one of the described anti-inflammatory mechanisms of LF. Previous studies suggested that cells can be stimulated even by LPS-free LF. Therefore, the aim of our study was to bring additional information about this possibility. Porcine monocyte derived macrophages (MDMF) and human embryonic kidney (HEK) cells were stimulated with unpurified LF in complex with LPS and with purified LF without bound LPS.ResultsBoth cell types were stimulated with unpurified as well as purified LF. On the other hand, neither HEK0 cells not expressing any TLR nor HEK4a cells transfected with TLR4 produced any pro-inflammatory cytokine transcripts after stimulation with purified LF. This suggests that purified LF without LPS stimulates cells via another receptor than TLR4. An alternative, TLR4-independent, pathway was further confirmed by analyses of the NF-kappa-B-inducing kinase (NIK) activation. Western blot analyses showed NIK which activates different NFκB subunits compared to LF-LPS signaling via TLR4. Though, this confirmed an alternative pathway which is used by the purified LF free of LPS. This stimulation of MDMF led to low, but significant amounts of pro-inflammatory cytokines, which can be considered as a positive stimulation of the immune system.ConclusionOur results suggest that LF’s ability is not only to bind LPS, but LF itself may be a stimulant of pro-inflammatory pathways.

Mangiferin, a novel nuclear factor kappa B-inducing kinase inhibitor, suppresses metastasis and tumor growth in a mouse metastatic melanoma model

Advanced metastatic melanoma, one of the most aggressive malignancies, is currently without reliable therapy. Therefore, new therapies are urgently needed. Mangiferin is a naturally occurring glucosylxanthone and exerts many beneficial biological activities. However, the effect of mangiferin on metastasis and tumor growth of metastatic melanoma remains unclear. In this study, we evaluated the effect of mangiferin on metastasis and tumor growth in a mouse metastatic melanoma model. We found that mangiferin inhibited spontaneous metastasis and tumor growth. Furthermore, mangiferin suppressed the nuclear translocation of nuclear factor kappa B (NF-κB) and expression of phosphorylated NF-κB-inducing kinase (NIK), inhibitor of kappa B kinase (IKK), and inhibitor of kappa B (IκB) and increases the expression of IκB protein in vivo. In addition, we found that mangiferin inhibited the expression of matrix metalloproteinases (MMPs) and very late antigens (VLAs) in vivo. Mangiferin treatment also increased the expression of cleaved caspase-3, cleaved Poly ADP ribose polymerase-1 (PARP-1), p53 upregulated modulator of apoptosis (PUMA), p53, and phosphorylated p53 proteins, and decreased the expression of Survivin and Bcl-associated X (Bcl-xL) proteins in vivo. These results indicate that mangiferin selectivity suppresses the NF-κB pathway via inhibition of NIK activation, thereby inhibiting metastasis and tumor growth. Importantly, the number of reported NIK selective inhibitors is limited. Taken together, our data suggest that mangiferin may be a potential therapeutic agent with a new mechanism of targeting NIK for the treatment of metastatic melanoma.

Mangiferin induces apoptosis in multiple myeloma cell lines by suppressing the activation of nuclear factor kappa B-inducing kinase

Mangiferin is a naturally occurring glucosyl xanthone, which induces apoptosis in various cancer cells. However, the molecular mechanism underlying mangiferin-induced apoptosis has not been clarified thus far. Therefore, we examined the molecular mechanism underlying mangiferin-induced apoptosis in multiple myeloma (MM) cell lines. We found that mangiferin decreased the viability of MM cell lines in a concentration-dependent manner. We also observed an increased number of apoptotic cells, caspase-3 activation, and a decrease in the mitochondrial membrane potential. In addition, mangiferin inhibited the nuclear translocation of nuclear factor kappa B (NF-κB) and expression of phosphorylated inhibitor kappa B (IκB) and increased the expression of IκB protein, whereas no changes were observed in the phosphorylation levels of extracellular signal-regulated kinase 1/2 (ERK1/2), c-Jun N-terminal protein kinase 1/2 (JNK1/2), and mammalian target of rapamycin (mTOR). The molecular mechanism responsible for mangiferin-induced inhibition of nuclear translocation of NF-κB was a decrease in the expression of phosphorylated NF-κB-inducing kinase (NIK). Moreover, mangiferin decreased the expression of X-linked inhibitor of apoptosis protein (XIAP), survivin, and Bcl-xL proteins. Knockdown of NIK expression showed results similar to those observed with mangiferin treatment. Our results suggest that mangiferin induces apoptosis through the inhibition of nuclear translocation of NF-κB by suppressing NIK activation in MM cell lines. Our results provide a new insight into the molecular mechanism of mangiferin-induced apoptosis. Importantly, since the number of reported NIK inhibitors is limited, mangiferin, which targets NIK, may be a potential anticancer agent for the treatment of MM.

Abstract B36: NF-kappaB-dependent and -independent roles for NIK in regulating GBM cell invasion

Abstract The aggressive invasion of GBM cells into healthy brain tissue is a major factor contributing to the therapy resistance and poor prognosis of this malignancy. Our recent results demonstrated that the alternative, or noncanonical, NF-kappaB signaling pathway, predominates in the aggressive mesenchymal subtype of GBM. Additionally, NF-kappaB-inducing kinase (NIK), a key upstream activator of noncanonical NF-kappaB signaling, robustly promotes GBM cell invasion and pathogenesis. We demonstrate that expression of NIK is increased in response to exposure to collagen, a major extracellular matrix (ECM) protein present in GBM tumors, with NIK protein levels continuing to increase during invasion in 3D collagen matrices. Interestingly, NIK expression levels correlates with induction of membrane type-1 matrix metalloproteinase (MT1-MMP), a critical enzyme in many invasive tumors, functioning to degrade the basement membrane and ECM during cell migration and invasion. We provide evidence that NIK promotes MT1-MMP activation through increased phosphorylation at membrane protrusions and elevated enzymatic activity. Notably, the activation of MT1-MMP and the pro-invasive effects of NIK persist in the absence of the downstream NF-kappaB transcription factors RelA/p65 and RelB. Together, these data demonstrate a novel ability of NIK to promote GBM cell migration and invasion that is independent of NF-kappaB transcriptional activation functions. The results underscore the therapeutic potential of targeting noncanonical NF-kappaB signaling in these highly invasive tumors. Citation Format: Camille L. Duran, Linda Herrera de Lechuga, Dong W. Lee, Kayla J. Bayless, Raquel Sitcheran. NF-kappaB-dependent and -independent roles for NIK in regulating GBM cell invasion. [abstract]. In: Proceedings of the AACR Special Conference: Advances in Brain Cancer Research; May 27-30, 2015; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2015;75(23 Suppl):Abstract nr B36.

Novel drug targets for personalized precision medicine in relapsed/refractory diffuse large B-cell lymphoma: a comprehensive review.

Diffuse large B-cell lymphoma (DLBCL) is a clinically heterogeneous lymphoid malignancy and the most common subtype of non-Hodgkin’s lymphoma in adults, with one of the highest mortality rates in most developed areas of the world. More than half of DLBLC patients can be cured with standard R-CHOP regimens, however approximately 30 to 40 % of patients will develop relapsed/refractory disease that remains a major cause of morbidity and mortality due to the limited therapeutic options.Recent advances in gene expression profiling have led to the identification of at least three distinct molecular subtypes of DLBCL: a germinal center B cell-like subtype, an activated B cell-like subtype, and a primary mediastinal B-cell lymphoma subtype. Moreover, recent findings have not only increased our understanding of the molecular basis of chemotherapy resistance but have also helped identify molecular subsets of DLBCL and rational targets for drug interventions that may allow for subtype/subset-specific molecularly targeted precision medicine and personalized combinations to both prevent and treat relapsed/refractory DLBCL. Novel agents such as lenalidomide, ibrutinib, bortezomib, CC-122, epratuzumab or pidilizumab used as single-agent or in combination with (rituximab-based) chemotherapy have already demonstrated promising activity in patients with relapsed/refractory DLBCL. Several novel potential drug targets have been recently identified such as the BET bromodomain protein (BRD)-4, phosphoribosyl-pyrophosphate synthetase (PRPS)-2, macrodomain-containing mono-ADP-ribosyltransferase (ARTD)-9 (also known as PARP9), deltex-3-like E3 ubiquitin ligase (DTX3L) (also known as BBAP), NF-kappaB inducing kinase (NIK) and transforming growth factor beta receptor (TGFβR).This review highlights the new insights into the molecular basis of relapsed/refractory DLBCL and summarizes the most promising drug targets and experimental treatments for relapsed/refractory DLBCL, including the use of novel agents such as lenalidomide, ibrutinib, bortezomib, pidilizumab, epratuzumab, brentuximab-vedotin or CAR T cells, dual inhibitors, as well as mechanism-based combinatorial experimental therapies. We also provide a comprehensive and updated list of current drugs, drug targets and preclinical and clinical experimental studies in DLBCL. A special focus is given on STAT1, ARTD9, DTX3L and ARTD8 (also known as PARP14) as novel potential drug targets in distinct molecular subsets of DLBCL.Electronic supplementary materialThe online version of this article (doi:10.1186/s12943-015-0474-2) contains supplementary material, which is available to authorized users.

The role of NFkappaB inducing kinase (NIK) in the pathogenicity of EAE

Question: NIK knockout mice have been shown to be resistant in the mouse model of multiple sclerosis, experimental autoimmune encephalomyelitis (EAE). As the knockout mice harbor various deficiencies in the immune cell compartment as well as in the structure of lymphoid tissue, it is not possible to use them to study the cell-specific role of NIK. Of special interest is the analysis of the function of NIK in T-cells, which are one of the main players in this disease. To overcome this issue, we generated a conditional NIKfl/fl mouse where we can analyze the role of NIK specifically in T-cells in the pathogenicity of EAE.

Cell-Intrinsic Role for NF-kappa B-Inducing Kinase in Peripheral Maintenance but Not Thymic Development of Foxp3+ Regulatory T Cells in Mice

NF-κB inducing kinase (NIK, MAP3K14) is a key signaling molecule in non-canonical NF-κB activation, and NIK deficient mice have been instrumental in deciphering the immunologic role of this pathway. Global ablation of NIK prevents lymph node development, impairs thymic stromal development, and drastically reduces B cells. Despite altered thymic selection, T cell numbers are near normal in NIK deficient mice. The exception is CD4+ regulatory T cells (Tregs), which are reduced in the thymus and periphery. Defects in thymic stroma are known to contribute to impaired Treg generation, but whether NIK also plays a cell intrinsic role in Tregs is unknown. Here, we compared intact mice with single and mixed BM chimeric mice to assess the intrinsic role of NIK in Treg generation and maintenance. We found that while NIK expression in stromal cells suffices for normal thymic Treg development, NIK is required cell-intrinsically to maintain peripheral Tregs. In addition, we unexpectedly discovered a cell-intrinsic role for NIK in memory phenotype conventional T cells that is masked in intact mice, but revealed in BM chimeras. These results demonstrate a novel role for NIK in peripheral regulatory and memory phenotype T cell homeostasis.

SAT0051 NF-KAPPAB inducing kinase (NIK) is a key regulator of angiogenesis: Implications for the role of non-canonical NF-KAPPAB signaling in synovial inflammation

BackgroundIn rheumatoid arthritis (RA) synovial tissue (ST), (pathological) angiogenesis can be observed already in the earliest phase of disease, which may be critical in the switch from acute to chronic...

NF-kappaB inducing kinase (NIK) is a key regulator of inflammation-induced angiogenesis

Background In rheumatoid arthritis (RA) synovial tissue (ST) angiogenesis can be observed already in the earliest phase of disease. The chemokine CXCL12, which is induced via the non-canonical nuclear factor-kappaB (NF-kB) pathway, plays an important role in angiogenesis, lymphocyte transendothelial migration, and the homing of endothelial progenitor cells. Therefore, the non-canonical pathway, with its key mediator NF-kB inducing kinase (NIK), may play an important role in pathological angiogenesis and the perpetuation of synovial inflammation in RA.

HTLV-1感染症とmiRNA

Although human T cell leukemia virus type I (HTLV-I) is undoubtedly involved in the immortalization and leukemogenesis of infected cells, mechanistic underpinnings of its molecular pathophysiology in long latent period of Adult T-cell leukemia (ATL) remain to be elucidated. One of the most significant recent advances in biomedical research has been the discovery of small noncoding RNAs designated microRNA (miRNA), which affect the field of virology including HTLV-1 research. Mounting evidence indicates that viruses use these miRNAs to manipulate both cellular and viral gene expression. Viral infection also can exert a profound impact on the cellular miRNA expression profile. Some studies have demonstrated that some deregulations of miRNA are involved in the pathogenesis of HTLV-1. Furthermore, global analyses of ATL patient samples have provided a conceptual progress that Polycomb family induces miR-31 silencing, resulting in overexpression of NF- kappaB inducing kinase (NIK) following NF-kappaB activation. Given that miRNAs act as pleiotropic molecules essential in all cellular events, deregulation of miRNA signature caused by HTLV-1 infection strongly involves the imbalance of molecular network of lymphocytes. Recognition and understanding of the widespread molecular applicability of miRNAs will increasingly have much effect on the development of novel strategies to treat the HTLV-1-associated diseases. Here we discuss our current knowledge of viral miRNAs and virally influenced cellular miRNAs and their relationship to ATL.

Allosteric Regulation of the Ubiquitin:NIK and Ubiquitin:TRAF3 E3 Ligases by the Lymphotoxin-β Receptor

The lymphotoxin-beta receptor (LTbetaR) activates the NF-kappaB2 transcription factors, p100 and RelB, by regulating the NF-kappaB-inducing kinase (NIK). Constitutive proteosomal degradation of NIK limits NF-kappaB activation in unstimulated cells by the ubiquitin:NIK E3 ligase comprised of subunits TNFR-associated factors (TRAF)3, TRAF2, and cellular inhibitor of apoptosis (cIAP). However, the mechanism releasing NIK from constitutive degradation remains unclear. We found that insertion of a charge-repulsion mutation in the receptor-binding crevice of TRAF3 ablated binding of both LTbetaR and NIK suggesting a common recognition site. A homologous mutation in TRAF2 inhibited cIAP interaction and blocked NIK degradation. Furthermore, the recruitment of TRAF3 and TRAF2 to the ligated LTbetaR competitively displaced NIK from TRAF3. Ligated LTbetaR complexed with TRAF3 and TRAF2 redirected the specificity of the ubiquitin ligase reaction to polyubiquitinate TRAF3 and TRAF2, leading to their proteosomal degradation. Stimulus-dependent degradation of TRAF3 required the RING domain of TRAF2, but not of TRAF3, implicating TRAF2 as a key E3 ligase in TRAF turnover. The combined action of competitive displacement of NIK and TRAF degradation halted NIK turnover, and promoted its association with IKKalpha and signal transmission. These results indicate the LTbetaR modifies the ubiquitin:NIK E3 ligase, and also acts as an allosteric regulator of the ubiquitin:TRAF E3 ligase.

Activation of Noncanonical NF-κB Signaling by the Oncoprotein Tio

NF-kappaB transcription factors are key regulators of cellular proliferation and frequently contribute to oncogenesis. The herpesviral oncoprotein Tio, which promotes growth transformation of human T cells in a recombinant herpesvirus saimiri background, potently induces canonical NF-kappaB signaling through membrane recruitment of the ubiquitin ligase tumor necrosis factor receptor-associated factor 6 (TRAF6). Here, we show that, in addition to Tio-TRAF6 interaction, the Tio-induced canonical NF-kappaB signal requires the presence of the regulatory subunit of the inhibitor of kappaB kinase (IKK) complex, NF-kappaB essential modulator (NEMO), and the activity of its key kinase, IKKbeta, to up-regulate expression of endogenous cellular inhibitor of apoptosis 2 (cIAP2) and interleukin 8 (IL-8) proteins. Dependent on TRAF6 and NEMO, Tio enhances the expression of the noncanonical NF-kappaB proteins, p100 and RelB. Independent of TRAF6 and NEMO, Tio mediates stabilization of the noncanonical kinase, NF-kappaB-inducing kinase (NIK). Concomitantly, Tio induces efficient processing of the p100 precursor molecule to its active form, p52, as well as DNA binding of nuclear p52 and RelB. In human T cells transformed by infection with a Tio-recombinant virus, sustained expression of p100, RelB, and cIAP2 depends on IKKbeta activity, yet processing to p52 remains largely unaffected by IKKbeta inhibition. However, long term inhibition of IKKbeta disrupts the continuous growth of the transformed cells and induces cell death. Hence, the Tio oncoprotein triggers noncanonical NF-kappaB signaling through NEMO-dependent up-regulation of p100 precursor and RelB, as well as through NEMO-independent generation of p52 effector.

Processing of the NF-κB2 precursor p100 to p52 is critical for RANKL-induced osteoclast differentiation

Gene targeting of the p50 and p52 subunits of NF-kappaB has shown that NF-kappaB plays a critical role in osteoclast differentiation. However, the molecular mechanism by which NF-kappaB regulates osteoclast differentiation is still unclear. To address this issue, we analyzed alymphoplasia (aly/aly) mice in which the processing of p100 to p52 does not occur owing to an inactive form of NF-kappaB-inducing kinase (NIK). Aly/aly mice showed a mild osteopetrosis with significantly reduced osteoclast numbers. RANKL-induced osteoclastogenesis from bone marrow cells of aly/aly mice also was suppressed. RANKL still induced the degradation of I kappaB alpha and activated classical NF-kappaB, whereas processing of p100 to p52 was abolished by the aly/aly mutation. Moreover, RANKL-induced expression of NFATc1 was impaired in aly/aly bone marrow. Overexpression of constitutively active IKK alpha or p52 restored osteoclastogenesis in aly/aly cells. Finally, transfection of either wild-type p100, p100 Delta GRR that cannot be processed to p52, or p52 into NF-kappaB 2-deficient cells followed by RANKL treatment revealed a strong correlation between the number of osteoclasts induced by RANKL and the ratio of p52 to p100 expression. Our data provide a new finding for a previously unappreciated role for NF-kappaB in osteoclast differentiation.

The pivotal role of the alternative NF-κB pathway in maintenance of basal bone homeostasis and osteoclastogenesis

The alternative NF-kappaB pathway consists predominantly of NF-kappaB-inducing kinase (NIK), IkappaB kinase alpha (IKKalpha), p100/p52, and RelB. The hallmark of the alternative NF-kappaB signaling is the processing of p100 into p52 through NIK, thus allowing the binding of p52 and RelB. The physiologic relevance of alternative NF-kappaB activation in bone biology, however, is not well understood. To elucidate the role of the alternative pathway in bone homeostasis, we first analyzed alymphoplasic (aly/aly) mice, which have a defective NIK and are unable to process p100, resulting in the absence of p52. We observed increased bone mineral density (BMD) and bone volume, indicating an osteopetrotic phenotype. These mice also have a significant defect in RANKL-induced osteoclastogenesis in vitro and in vivo. NF-kappaB DNA-binding assays revealed reduced activity of RelA, RelB, and p50 and no binding activity of p52 in aly/aly osteoclast nuclear extracts after RANKL stimulation. To determine the role of p100 itself without the influence of a concomitant lack of p52, we used p100(-/-) mice, which specifically lack the p100 inhibitor but still express p52. p100(-/-) mice have an osteopenic phenotype owing to the increased osteoclast and decreased osteoblast numbers that was rescued by the deletion of one allele of the relB gene. Deletion of both allele of relB resulted in a significantly increased bone mass owing to decreased osteoclast activity and increased osteoblast numbers compared with wild-type (WT) controls, revealing a hitherto unknown role for RelB in bone formation. Our data suggest a pivotal role of the alternative NF-kappaB pathway, especially of the inhibitory role of p100, in both basal and stimulated osteoclastogenesis and the importance of RelB in both bone formation and resorption.

TNF Superfamily: A Growing Saga of Kidney Injury Modulators

Members of the TNF superfamily participate in kidney disease. Tumor necrosis factor (TNF) and Fas ligand regulate renal cell survival and inflammation, and therapeutic targeting improves the outcome of experimental renal injury. TNF-related apoptosis-inducing ligand (TRAIL and its potential decoy receptor osteoprotegerin are the two most upregulated death-related genes in human diabetic nephropathy. TRAIL activates NF-kappaB in tubular cells and promotes apoptosis in tubular cells and podocytes, especially in a high-glucose environment. By contrast, osteoprotegerin plays a protective role against TRAIL-induced apoptosis. Another family member, TNF-like weak inducer of apoptosis (TWEAK induces inflammation and tubular cell death or proliferation, depending on the microenvironment. While TNF only activates canonical NF-kappaB signaling, TWEAK promotes both canonical and noncanonical NF-kappaB activation in tubular cells, regulating different inflammatory responses. TWEAK promotes the secretion of MCP-1 and RANTES through NF-kappaB RelA-containing complexes and upregulates CCl21 and CCL19 expression through NF-kappaB inducing kinase (NIK-) dependent RelB/NF-kappaB2 complexes. In vivo TWEAK promotes postnephrectomy compensatory renal cell proliferation in a noninflammatory milieu. However, in the inflammatory milieu of acute kidney injury, TWEAK promotes tubular cell death and inflammation. Therapeutic targeting of TNF superfamily cytokines, including multipronged approaches targeting several cytokines should be further explored.