Inhibition of NF-kappaB in T cells blocks lymphoproliferation and partially rescues autoimmune disease in gld/gld mice

Impact of loss of NF-κB1, NF-κB2 or c-REL on SLE-like autoimmune disease and lymphadenopathy in Fas(lpr/lpr) mutant mice

Defects in apoptosis can cause autoimmune disease. Loss-of-function mutations in the 'death receptor' FAS impair the deletion of autoreactive lymphocytes in the periphery, leading to progressive lymphadenopathy and systemic lupus erythematosus-like autoimmune disease in mice (Fas(lpr/lpr) (mice homozygous for the lymphoproliferation inducing spontaneous mutation)) and humans. The REL/nuclear factor-κB (NF-κB) transcription factors regulate a broad range of immune effector functions and are also implicated in various autoimmune diseases. We generated compound mutant mice to investigate the individual functions of the NF-κB family members NF-κB1, NF-κB2 and c-REL in the various autoimmune pathologies of Fas(lpr/lpr) mutant mice. We show that loss of each of these transcription factors resulted in amelioration of many classical features of autoimmune disease, including hypergammaglobulinaemia, anti-nuclear autoantibodies and autoantibodies against tissue-specific antigens. Remarkably, only c-REL deficiency substantially reduced immune complex-mediated glomerulonephritis and extended the lifespan of Fas(lpr/lpr) mice. Interestingly, compared with the Fas(lpr/lpr) animals, Fas(lpr/lpr)nfkb2(-/-) mice presented with a dramatic acceleration and augmentation of lymphadenopathy that was accompanied by severe lung pathology due to extensive lymphocytic infiltration. The Fas(lpr/lpr)nfkb1(-/-) mice exhibited the combined pathologies caused by defects in FAS-mediated apoptosis and premature ageing due to loss of NF-κB1. These findings demonstrate that different NF-κB family members exert distinct roles in the development of the diverse autoimmune and lymphoproliferative pathologies that arise in Fas(lpr/lpr) mice, and suggest that pharmacological targeting of c-REL should be considered as a strategy for therapeutic intervention in autoimmune diseases.

Loss of c-REL but not NF-κB2 prevents autoimmune disease driven by FasL mutation

FASL/FAS signaling imposes a critical barrier against autoimmune disease and lymphadenopathy. Mutant mice unable to produce membrane-bound FASL (FasL(Δm/Δm)), a prerequisite for FAS-induced apoptosis, develop lymphadenopathy and systemic autoimmune disease with immune complex-mediated glomerulonephritis. Prior to disease onset, FasL(Δm/Δm) mice contain abnormally high numbers of leukocytes displaying activated and elevated NF-κB-regulated cytokine levels, indicating that NF-κB-dependent inflammation may be a key pathological driver in this multifaceted autoimmune disease. We tested this hypothesis by genetically impairing canonical or non-canonical NF-κB signaling in FasL(Δm/Δm) mice by deleting the c-Rel or NF-κB2 genes, respectively. Although the loss of NF-κB2 reduced the levels of inflammatory cytokines and autoantibodies, the impact on animal survival was minor due to substantially accelerated and exacerbated lymphoproliferative disease. In contrast, a marked increase in lifespan resulting from the loss of c-REL coincided with a striking reduction in classical parameters of autoimmune pathology, including the levels of cytokines and antinuclear autoantibodies. Notably, the decrease in regulatory T-cell numbers associated with loss of c-REL did not exacerbate autoimmunity in FasL(Δm/Δm)c-rel(-/-) mice. These findings indicate that selective inhibition of c-REL may be an attractive strategy for the treatment of autoimmune pathologies driven by defects in FASL/FAS signaling that would be expected to circumvent many of the complications caused by pan-NF-κB inhibition.

Regulation and function of NF-kappaB transcription factors in the immune system

The mammalian Rel/NF-kappaB family of transcription factors, including RelA, c-Rel, RelB, NF-kappaB1 (p50 and its precursor p105), and NF-kappaB2 (p52 and its precursor p100), plays a central role in the immune system by regulating several processes ranging from the development and survival of lymphocytes and lymphoid organs to the control of immune responses and malignant transformation. The five members of the NF-kappaB family are normally kept inactive in the cytoplasm by interaction with inhibitors called IkappaBs or the unprocessed forms of NF-kappaB1 and NF-kappaB2. A wide variety of signals emanating from antigen receptors, pattern-recognition receptors, receptors for the members of TNF and IL-1 cytokine families, and others induce differential activation of NF-kappaB heterodimers. Although work over the past two decades has shed significant light on the regulation of NF-kappaB transcription factors and their functions, much progress has been made in the past two years revealing new insights into the regulation and functions of NF-kappaB. This recent progress is covered in this review.

Rel/NF-kappaB family member RelA regulates NK1.1- to NK1.1+ transition as well as IL-15-induced expansion of NKT cells

Development of NKT cells was shown to depend on lymphotoxin (LT) and IL-15 signaling pathways as well as on cytokine receptor common gamma chain. After positive selection, NKT-cell precursors transit through progressive maturation stages including proliferative expansion within the NK1.1(-) window. The transcription factors that integrate different signaling pathways into different stages of NKT-cell development are not well characterized. Here, we show that the Rel/NF-kappaB family member RelA regulates the NK1.1(-) to NK1.1(+) transition during NKT-cell development. RelA is also required for both IL-15- and IL-7-induced proliferation of CD44(hi)NK1.1(-) NKT-cell precursors. Activation of the invariant NKT-cell receptor induces both IL-15 receptor alpha and gamma chains' expression in an NF-kappaB-dependent manner, suggesting a molecular mechanism by which NF-kappaB regulates NKT-cell development. NF-kappaB also regulates TCR-induced expression of LT-alpha and LT-beta within NKT cells. In contrast to previous reports, however, we show that LT signaling is dispensable for thymic NKT-cell development but is essential for their colonization of peripheral organs such as liver.

Dissection of the NF-kappaB signalling cascade in transgenic and knockout mice

Studies in transgenic and knockout mice have made a major contribution to our current understanding of the physiological functions of the NF-kappaB signalling cascade. The generation and analysis of mice with targeted modifications of individual components of the NF-kappaB pathway tremendously advanced our knowledge of the roles of the NF-kappaB proteins themselves, and also of the many activators and negative regulators of NF-kappaB. These studies have highlighted the complexity of the NF-kappaB system, by revealing the multiple interactions, redundancies, but also diverse functions, performed by the different molecules participating in the regulation of NF-kappaB signalling. Furthermore, inhibition or enforced activation of NF-kappaB in transgenic mice has uncovered the critical roles that NF-kappaB plays in the pathogenesis of various diseases such as liver failure, diabetes and cancer.

Coordination of NF-kappaB and NFAT antagonism by the forkhead transcription factor Foxd1

Forkhead transcription factors play critical roles in the maintenance of immune homeostasis. In this study, we demonstrate that this regulation most likely involves intricate interactions between the forkhead family members and inflammatory transcription factors: the forkhead member Foxd1 coordinates the regulation of the activity of two key inflammatory transcription factors, NF-AT and NF-kappaB, with Foxd1 deficiency resulting in multiorgan, systemic inflammation, exaggerated Th cell-derived cytokine production, and T cell proliferation in autologous MLRs. Foxd1-deficient T cells possess increased activity of both NF-AT and NF-kappaB: the former correlates with the ability of Foxd1 to regulate casein kinase 1, an NF-AT inhibitory kinase; the latter with the ability of Foxd1 to regulate Foxj1, which regulates the NF-kappaB inhibitory subunit IkappaB beta. Thus, Foxd1 modulates inflammatory reactions and prevents autoimmunity by directly regulating anti-inflammatory regulators of the NF-AT pathway, and by coordinating the suppression of the NF-kappaB pathway via Foxj1. These findings indicate the presence of a general network of forkhead proteins that enforce T cell quiescence.

NF-kappaB couples protein kinase B/Akt signaling to distinct survival pathways and the regulation of lymphocyte homeostasis in vivo

Protein kinase B (PKBalpha/Akt1) a PI3K-dependent serine-threonine kinase, promotes T cell viability in response to many stimuli and regulates homeostasis and autoimmune disease in vivo. To dissect the mechanisms by which PKB inhibits apoptosis, we have examined the pathways downstream of PKB that promote survival after cytokine withdrawal vs Fas-mediated death. Our studies show that PKB-mediated survival after cytokine withdrawal is independent of protein synthesis and the induction of NF-kappaB. In contrast, PKB requires de novo gene transcription by NF-kappaB to block apoptosis triggered by the Fas death receptor. Using gene-deficient and transgenic mouse models, we establish that NF-kappaB1, and not c-Rel, is the critical signaling molecule downstream of the PI3K-PTEN-PKB signaling axis that regulates lymphocyte homeostasis.

Neuronal activation of NF-kappaB contributes to cell death in cerebral ischemia

The transcription factor NF-kappaB is a key regulator of inflammation and cell survival. NF-kappaB is activated by cerebral ischemia in neurons and glia, but its function is controversial. To inhibit NF-kappaB selectively in neurons and glial cells, we have generated transgenic mice that express the IkappaBalpha superrepressor (IkappaBalpha mutated at serine-32 and serine-36, IkappaBalpha-SR) under transcriptional control of the neuron-specific enolase (NSE) and the glial fibrillary acidic protein (GFAP) promoter, respectively. In primary cortical neurons of NSE-IkappaBalpha-SR mice, NF-kappaB activity was partially inhibited. To assess NF-kappaB activity in vivo after permanent middle cerebral artery occlusion (MCAO), we measured the expression of NF-kappaB target genes by real-time polymerase chain reaction (PCR). The induction of c-myc and transforming growth factor-beta2 by cerebral ischemia was inhibited by neuronal expression of IkappaBalpha-SR, whereas induction of GFAP by MCAO was reduced by astrocytic expression of IkappaBalpha-SR. Neuronal, but not astrocytic, expression of the NF-kappaB inhibitor reduced both infarct size and cell death 48 hours after permanent MCAO. In summary, the data show that NF-kappaB is activated in neurons and astrocytes during cerebral ischemia and that NF-kappaB activation in neurons contributes to the ischemic damage.

Modulation of Th1 Activation and Inflammation by the NF- B Repressor Foxj1

Forkhead transcription factors play key roles in the regulation of immune responses. Here, we identify a role for one member of this family, Foxj1, in the regulation of T cell activation and autoreactivity. Foxj1 deficiency resulted in multiorgan systemic inflammation, exaggerated Th1 cytokine production, and T cell proliferation in autologous mixed lymphocyte reactions. Foxj1 suppressed NF-kappaB transcription activity in vitro, and Foxj1-deficient T cells possessed increased NF-kappaB activity in vivo, correlating with the ability of Foxj1 to regulate IkappaB proteins, particularly IkappaBbeta. Thus, Foxj1 likely modulates inflammatory reactions and prevents autoimmunity by antagonizing proinflammatory transcriptional activities. These results suggest a potentially general role for forkhead genes in the enforcement of lymphocyte quiescence.

NF kappa B controls the balance between Fas and tumor necrosis factor cell death pathways during T cell receptor-induced apoptosis via the expression of its target gene A20

Activation-induced cell death (AICD), a term originally coined for the anti-CD3-induced apoptosis of T cell hybridomas and thymocytes, is predominantly driven by death receptors and has been involved in the control of autoreactive T cells in the periphery. In the Do-11.10 T cell hybridoma model of AICD, activation of the T cell receptor (TCR) results in Fas-dependent apoptosis. Here, we show that inhibition of the transcription factor nuclear factor kappa B (NF kappa B) in Do-11.10 cells resulted in increased sensitivity to TCR-mediated apoptosis, correlating with defective induction of the anti-apoptotic NF kappa B target gene A20. Stable expression of the zinc finger protein A20 in NF kappa B-negative Do-11.10 cells rescued the phenotype. TCR activation in NF kappa B-deficient Do-11.10 cells resulted predominantly in tumor necrosis factor (TNF) receptor 2 (TNFR2)-dependent bystander cell death rather than classical Fas-dependent AICD. Strikingly, A20 blocked TNF-mediated apoptosis and simultaneously restored TCR-induced Fas-dependent AICD. In addition, NF kappa B downstream of TNFR was required for up-regulation of Fas expression by endogenous TNF secreted in response to TCR stimulation. Together, these results suggest that NF kappa B can play both pro- and anti-apoptotic roles during AICD. We propose that NF kappa B controls the balance between Fas and TNF cell death pathways during AICD via the expression of the zinc finger protein A20.

Differential requirement for Rel/nuclear factor kappa B family members in natural killer T cell development

Natural killer T (NKT) cells have been implicated in diverse immune responses ranging from suppression of autoimmunity to tumor rejection. Thymus-dependent NKT cells are positively selected by the major histocompatibility complex class I-like molecule CD1d, but the molecular events downstream of CD1d are still poorly understood. Here, we show that distinct members of the Rel/nuclear factor (NF)-kappa B family of transcription factors were required in both hematopoietic and nonhematopoietic cells for normal development of thymic NKT cells. Activation of NF-kappa B via the classical I kappa B alpha-regulated pathway was required in a cell autonomous manner for the transition of NK-1.1-negative precursors that express the TCR V alpha 14-J alpha 18 chain to mature NK-1.1-positive NKT cells. The Rel/NF-kappa B family member RelB, on the other hand, had to be expressed in radiation resistant thymic stromal cells for the generation of early NK-1.1-negative NKT precursors. Moreover, NF-kappa B-inducing kinase (NIK) was required for both constitutive thymic DNA binding of RelB and the specific induction of RelB complexes in vitro. Thus, distinct Rel/NF-kappa B family members in hematopoietic and nonhematopoietic cells regulate NKT cell development with a unique requirement for NIK-mediated activation of RelB in thymic stroma.

Egr1 promotes growth and survival of prostate cancer cells. Identification of novel Egr1 target genes

In the majority of aggressive tumorigenic prostate cancer cells, the transcription factor Egr1 is overexpressed. We provide new insights of Egr1 involvement in proliferation and survival of TRAMP C2 prostate cancer cells by the identification of several new target genes controlling growth, cell cycle progression, and apoptosis such as cyclin D2, P19ink4d, and Fas. Egr1 regulation of these genes, identified by Affymetrix microarray, was confirmed by real-time PCR, immunoblot, and chromatin immunoprecipitation assays. Furthermore we also showed that Egr1 is responsible for cyclin D2 overexpression in tumorigenic DU145 human prostate cells. The regulation of these genes by Egr1 was demonstrated using Egr1 antisense oligonucleotides that further implicated Egr1 in resistance to apoptotic signals. One mechanism was illustrated by the ability of Egr1 to inhibit CD95 (Fas/Apo) expression, leading to insensitivity to FasL. The results provide a mechanistic basis for the oncogenic role of Egr1 in TRAMP C2 prostate cancer cells.

RelB is required for Peyer's patch development: differential regulation of p52-RelB by lymphotoxin and TNF

Targeted disruption of the Rel/NF-kappaB family members NF-kappaB2, encoding p100/p52, and RelB in mice results in anatomical defects of secondary lymphoid tissues. Here, we report that development of Peyer's patch (PP)-organizing centers is impaired in both NF-kappaB2- and RelB-deficient animals. IL-7-induced expression of lymphotoxin (LT) in intestinal cells, a crucial step in PP development, is not impaired in RelB-deficient embryos. LTbeta receptor (LTbetaR)-deficient mice also lack PPs, and we demonstrate that LTbetaR signaling induces p52-RelB and classical p50-RelA heterodimers, while tumor necrosis factor (TNF) activates only RelA. LTbetaR-induced binding of p52-RelB requires the degradation of the inhibitory p52 precursor, p100, which is mediated by the NF-kappaB-inducing kinase (NIK) and the IkappaB kinase (IKK) complex subunit IKKalpha, but not IKKbeta or IKKgamma. Activation of RelA requires all three IKK subunits, but is independent of NIK. Finally, we show that TNF increases p100 levels, resulting in the specific inhibition of RelB DNA binding via the C-terminus of p100. Our data indicate an important role of p52-RelB heterodimers in lymphoid organ development downstream of LTbetaR, NIK and IKKalpha.

Induction of immune tolerance by dendritic cells: implications for preventative and therapeutic immunotherapy of autoimmune disease

Dendritic cells (DC) have a key role in controlling the immune response, by determining the outcome of antigen presentation to T cells. Through costimulatory molecules and other factors, DC are involved in the maintenance of peripheral tolerance through modulation of the immune response. This modulation occurs both constitutively, and in inflammation, in order to prevent autoimmunity and to control established immune responses. Dendritic cell control of immune responses may be mediated through cytokine or cell-contact dependent mechanisms. The molecular and cellular basis of these controls is being understood at an increasingly more complex level. This understanding is reaching a level at which DC-based therapies for the induction of immune regulation in autoimmunity can be tested in vivo. This review outlines the current state of knowledge of DC in immune tolerance, and proposes how DC might control both T cell responses, and themselves, to prevent autoimmunity and maintain peripheral tolerance.