Role Of NF-κB-inducing Kinase Research Articles

Proliferation, Plasticity, and Migration: Exploring the synergistic relationship between eosinophils and TH2 cells in development of HES-like syndrome

Abstract Aberrancies in eosinophil proliferation, activation and chemotaxis can lead to acute eosinophilic leukemia, paraneoplastic eosinophilia associated with T cell lymphoma and carcinomas, and Hypereosinophilic Syndrome (HES), respectively. HES is an idiopathic disease affecting humans and veterinary patients characterized by persistent eosinophilia (>1,500 cells/uL) and eosinophilic infiltration of solid organs leading to increased morbidity and mortality. Previous studies have demonstrated the role of NF-κB inducing kinase, NIK, an upstream regulator of the noncanonical NF-κB signaling pathway, in development of a HES-like syndrome due to aberrant TH2 polarization in the Nik−/−murine model. However, the intricacies of eosinophilic granulopoiesis, eosinophil/neutrophil plasticity, and chemotactic ability has not been assessed during development of HES-like syndrome in Nik−/−mice. Here we show that loss of NIK potentially enhances eosinophilic chemotaxis to CCL11, enhances eosinophilic/neutrophilic plasticity, and affects granulopoiesis in the bone marrow and spleen beginning at the level of eosinophilic metamyelocytes, despite potentially decreasing the proliferative potential of these cells. Taken together, these results suggest that NIK and the noncanonical NF-κB signaling pathway plays a role in dictating the hematopoietic and chemotactic potential of eosinophils and highlights a synergistic relationship with TH2 cells and their respective cytokines during development of HES-like syndrome in Nik−/−mice. Overall, these findings warrant further study to better characterize the synergistic relationship described above to better understand development of HES and HES-like diseases. Virginia-Maryland College of Veterinary Medicine and the Institute for Critical Technology and Applied Science

NF-κB-Inducing Kinase Governs the Mitochondrial Respiratory Capacity, Differentiation, and Inflammatory Status of Innate Immune Cells.

NF-κB-inducing kinase (NIK), which is essential for the activation of the noncanonical NF-κB pathway, regulates diverse processes in immunity, development, and disease. Although recent studies have elucidated important functions of NIK in adaptive immune cells and cancer cell metabolism, the role of NIK in metabolic-driven inflammatory responses in innate immune cells remains unclear. In this study, we demonstrate that murine NIK-deficient bone marrow-derived macrophages exhibit defects in mitochondrial-dependent metabolism and oxidative phosphorylation, which impair the acquisition of a prorepair, anti-inflammatory phenotype. Subsequently, NIK-deficient mice exhibit skewing of myeloid cells characterized by aberrant eosinophil, monocyte, and macrophage cell populations in the blood, bone marrow, and adipose tissue. Furthermore, NIK-deficient blood monocytes display hyperresponsiveness to bacterial LPS and elevated TNF-α production ex vivo. These findings suggest that NIK governs metabolic rewiring, which is critical for balancing proinflammatory and anti-inflammatory myeloid immune cell function. Overall, our work highlights a previously unrecognized role for NIK as a molecular rheostat that fine-tunes immunometabolism in innate immunity, and suggests that metabolic dysfunction may be an important driver of inflammatory diseases caused by aberrant NIK expression or activity.

NIK/MAP3K14 Regulates Mitochondrial Dynamics and Trafficking to Promote Cell Invasion

Although the role of NF-κB-inducing kinase (NIK) in immunity is well established, its relevance in cancer is just emerging. Here we describe novel functions for NIK in regulating mitochondrial dynamics and motility to promote cell invasion. We show that NIK is localized to mitochondria in cancer cell lines, exvivo tumor tissue, and mouse embryonic fibroblasts (MEFs). NIK promotes mitochondrial fission, velocity, and directional migration, resulting in subcellular distribution of mitochondria to the periphery of migrating cells. Moreover, NIK is required for recruitment of Drp1 to mitochondria, forms a complex with Drp1, and regulates Drp1 phosphorylation at Ser-616 and dephosphorylation at Ser-637. Consistent with a role for NIK in regulating mitochondrial dynamics, we demonstrate that Drp1 is required for NIK-dependent, cytokine-induced invasion. Importantly, using MEFs, we demonstrate that the established downstream mediators of NIK signaling, IκB kinase α/β (IKKα/β) and NF-κB, are not required for NIK to regulate cell invasion, Drp1 mitochondrial localization, or mitochondrial fission. Our results establish a new paradigm for IKK-independent NIK signaling and significantly expand the current dogma that NIK is predominantly cytosolic and exclusively regulates NF-κB activity. Overall, these findings highlight the importance of NIK in tumor pathogenesis and invite new therapeutic strategies that attenuate mitochondrial dysfunction through inhibition of NIK and Drp1.

NF-kappaΒ-inducing kinase regulates stem cell phenotype in breast cancer.

Breast cancer stem cells (BCSCs) overexpress components of the Nuclear factor-kappa B (NF-κB) signaling cascade and consequently display high NF-κB activity levels. Breast cancer cell lines with high proportion of CSCs exhibit high NF-κB-inducing kinase (NIK) expression. The role of NIK in the phenotype of cancer stem cell regulation is poorly understood. Expression of NIK was analyzed by quantitative RT-PCR in BCSCs. NIK levels were manipulated through transfection of specific shRNAs or an expression vector. The effect of NIK in the cancer stem cell properties was assessed by mammosphere formation, mice xenografts and stem markers expression. BCSCs expressed higher levels of NIK and its inhibition through small hairpin (shRNA), reduced the expression of CSC markers and impaired clonogenicity and tumorigenesis. Genome-wide expression analyses suggested that NIK acts on ERK1/2 pathway to exert its activity. In addition, forced expression of NIK increased the BCSC population and enhanced breast cancer cell tumorigenicity. The in vivo relevance of these results is further supported by a tissue microarray of breast cancer samples in which we observed correlated expression of Aldehyde dehydrogenase (ALDH) and NIK protein. Our results support the essential involvement of NIK in BCSC phenotypic regulation via ERK1/2 and NF-κB.

NIK promotes tissue destruction independently of the alternative NF-κB pathway through TNFR1/RIP1-induced apoptosis.

NF-κB-inducing kinase (NIK) is well-known for its role in promoting p100/NF-κB2 processing into p52, a process defined as the alternative, or non-canonical, NF-κB pathway. Here we reveal an unexpected new role of NIK in TNFR1-mediated RIP1-dependent apoptosis, a consequence of TNFR1 activation observed in c-IAP1/2-depleted conditions. We show that NIK stabilization, obtained by activation of the non-death TNFRs Fn14 or LTβR, is required for TNFα-mediated apoptosis. These apoptotic stimuli trigger the depletion of c-IAP1/2, the phosphorylation of RIP1 and the RIP1 kinase-dependent assembly of the RIP1/FADD/caspase-8 complex. In the absence of NIK, the phosphorylation of RIP1 and the formation of RIP1/FADD/caspase-8 complex are compromised while c-IAP1/2 depletion is unaffected. In vitro kinase assays revealed that recombinant RIP1 is a bona fide substrate of NIK. In vivo, we demonstrated the requirement of NIK pro-death function, but not the processing of its substrate p100 into p52, in a mouse model of TNFR1/LTβR-induced thymus involution. In addition, we also highlight a role for NIK in hepatocyte apoptosis in a mouse model of virus-induced TNFR1/RIP1-dependent liver damage. We conclude that NIK not only contributes to lymphoid organogenesis, inflammation and cell survival but also to TNFR1/RIP1-dependent cell death independently of the alternative NF-κB pathway.

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

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

NF-κB-Inducing Kinase Regulates Cyclooxygenase 2 Gene Expression in Macrophages by Phosphorylation of PU.1

Selective expression of cyclooxygenase 2 (COX-2) by macrophages could have an important role in the pathobiology of inflammation. We reported a functional synergism between PU.1 and other transcription factors that contributes to COX-2 gene expression in macrophages. PU.1 resides in the nuclear compartment and is activated by phosphorylation to bind to cognate DNA elements containing a 5'-GGAA/T-3' motif, but the involved kinase has not been discovered. We tested the hypothesis that NF-kappaB-inducing kinase (NIK) regulates COX-2 gene expression in macrophages through inducible phosphorylation of PU.1. Our initial experiments showed an in vitro protein-protein binding interaction between myc-NIK and GST-PU.1. Purified myc-NIK had a strong in vitro kinase activity for purified GST-PU.1, and this activity and production of COX-2 protein is blocked by treatment with a nonspecific kinase inhibitor, 5,6-dichloro-1-beta-D-ribofuranosylbenzimidazole. We used short interfering RNA to develop a stable NIK knockdown macrophage cell line that had an approximately 50% decrease in COX-2 protein production and decreased generation of PGD(2), and this was correlated with decreased binding of activated PU.1 to the COX-2 promoter in response to treatment with endotoxin. These findings suggest a novel role for NIK in mediating COX-2 gene expression in endotoxin-treated macrophages by a mechanism that involves phosphorylation of PU.1.

NFκB-Inducing Kinase Deficiency Results in the Development of a Subset of Regulatory T Cells, which Shows a Hyperproliferative Activity upon Glucocorticoid-Induced TNF Receptor Family-Related Gene Stimulation

CD4+CD25+ regulatory T cells (T(reg)) play an important role in maintaining immunologic tolerance. Glucocorticoid-induced TNFR family-related gene (GITR) expressed preferentially at high levels on T(reg) has been shown to be a key player of regulating T(reg)-mediated suppression. A recent study reports that NF-kappaB-inducing kinase (NIK) expression in thymic stroma is important for the normal production of T(reg) but not for its suppression capacity. In this report, we have shown that T(reg) from NIK-deficient mice display hyperproliferative activities upon GITR stimulation through an IL-2-independent mechanism. Furthermore, high dose IL-2, anti-CD28 stimulation, or GITR ligand-transduced bone marrow-derived dendritic cells used as APC (culture conditions which drive T(reg) proliferation in vitro) could not ablate this difference in proliferative activity between NIK-deficient and wild-type T(reg). Additional experiments have shown NIK-deficient mice have a higher ratio of CD4+CD25+CD62L(low) T(reg) both in thymus and periphery than their wild-type littermates. This CD62(low) subset is responsible for the hyperproliferative activity upon GITR stimulation. These data suggest a novel role of NIK in controlling the development and expansion of CD4+CD25+ regulatory T cells.

Will the Real NIK Function Please Stand Up?

The nuclear factor-κB (NF-κB)-inducing kinase (NIK) was originally identified as a MAP kinase kinase kinase (MAPKKK, MEKK) that phosphorylated IκB kinase (IKK) α and activated NF-κB. Subsequently, NIK-deficient mouse studies revealed that NIK is not essential for cytokine-dependent IKK activiation. A naturally occurring NIK gene mutation results in alymphoplasia ( aly ) in mice, which leads to defective antibody responses, and the aly phenotype resembles the nfkb2 -deficient phenotype. The 100-kD NFkB2 precursor protein is cleaved to a mature 52-kD protein that heterodimerizes with Rel proteins members of the NF-κB family to form a functional transcription factor. Overexpression of NIK and p100 in different cell lines promoted the accumulation of mature p52 protein, suggesting a role for NIK in the processing of p100. The presence of p52 required the kinase activity of NIK, was independent of IKK phosphorylation, and was blocked by proteasomal inhibitors. NIK phosphorylation of p100 at Ser 866 and Ser 870 was essential for the subsequent ubiquitination of p100 and processing to p52. Assays done with NIK from aly -/- and aly -/+ mice revealed that the amounts of NFkB2 proteins were the same but that p52 was barely detectable in aly -/- cells. Additionally, cells overexpressing the NIK aly allele were completely defective for p100 processing. Thus, the real function of NIK may be to regulate the maturation of p52, instead of activating NF-κB from inactive cytoplasmic complexes. G. Xiao, E. W. Harhaj, S.-C. Sun, NF-κB-inducing kinase regulates the processing of NF-κB2 p100. Mol. Cell 7 , 401-409 (2001). [Online Journal]