NF-κB subunits RelA and c-Rel selectively control CD4+ T cell function in multiple sclerosis and cancer

The outcome of cancer and autoimmunity is often dictated by the effector functions of CD4+ conventional T cells (Tconv). Although activation of the NF-κB signaling pathway has long been implicated in Tconv biology, the cell-autonomous roles of the separate NF-κB transcription-factor subunits are unknown. Here, we dissected the contributions of the canonical NF-κB subunits RelA and c-Rel to Tconv function. RelA, rather than c-Rel, regulated Tconv activation and cytokine production at steady-state and was required for polarization toward the TH17 lineage in vitro. Accordingly, RelA-deficient mice were fully protected against neuroinflammation in a model of multiple sclerosis due to defective transition to a pathogenic TH17 gene-expression program. Conversely, Tconv-restricted ablation of c-Rel impaired their function in the microenvironment of transplanted tumors, resulting in enhanced cancer burden. Moreover, Tconv required c-Rel for the response to PD-1-blockade therapy. Our data reveal distinct roles for canonical NF-κB subunits in different disease contexts, paving the way for subunit-targeted immunotherapies.

Co-imaging of RelA and c-Rel reveals features of NF-κB signaling for ligand discrimination

Individual cell sensing of external cues has evolved through the temporal patterns in signaling. Since nuclear factor κB (NF-κB) signaling dynamics have been examined using a single subunit, RelA, it remains unclear whether more information might be transmitted via other subunits. Using NF-κB double-knockin reporter mice, we monitored both canonical NF-κB subunits, RelA and c-Rel, simultaneously in single macrophages by quantitative live-cell imaging. We show that signaling features of RelA and c-Rel convey more information about the stimuli than those of either subunit alone. Machine learning is used to predict the ligand identity accurately based on RelA and c-Rel signaling features without considering the co-activated factors. Ligand discrimination is achieved through selective non-redundancy of RelA and c-Rel signaling dynamics, as well as their temporal coordination. These results suggest a potential role of c-Rel in fine-tuning immune responses and highlight the need for approaches that will elucidate the mechanisms regulating NF-κB subunit specificity.

c-Rel-dependent Chk2 signaling regulates the DNA damage response limiting hepatocarcinogenesis

BACKGROUND AND AIMS

Hepatocellular carcinoma (HCC) is a leading cause of cancer-related death. The NF-κB transcription factor family subunit c-Rel is typically protumorigenic; however, it has recently been reported as a tumor suppressor. Here, we investigated the role of c-Rel in HCC.

APPROACH AND RESULTS

Histological and transcriptional studies confirmed expression of c-Rel in human patients with HCC, but low c-Rel expression correlated with increased tumor cell proliferation and mutational burden and was associated with advanced disease. In vivo , global ( Rel-/- ) and epithelial specific ( RelAlb ) c-Rel knockout mice develop more tumors, with a higher proliferative rate and increased DNA damage, than wild-type (WT) controls 30 weeks after N-diethylnitrosamine injury. However, tumor burden was comparable when c-Rel was deleted in hepatocytes once tumors were established, suggesting c-Rel signaling is important for preventing HCC initiation after genotoxic injury, rather than for HCC progression. In vitro , Rel-/- hepatocytes were more susceptible to genotoxic injury than WT controls. ATM-CHK2 DNA damage response pathway proteins were suppressed in Rel-/- hepatocytes following genotoxic injury, suggesting that c-Rel is required for effective DNA repair. To determine if c-Rel inhibition sensitizes cancer cells to chemotherapy, by preventing repair of chemotherapy-induced DNA damage, thus increasing tumor cell death, we administered single or combination doxorubicin and IT-603 (c-Rel inhibitor) therapy in an orthotopic HCC model. Indeed, combination therapy was more efficacious than doxorubicin alone.

CONCLUSION

Hepatocyte c-Rel signaling limits genotoxic injury and subsequent HCC burden. Inhibiting c-Rel as an adjuvant therapy increased the effectiveness of DNA damaging agents and reduced HCC growth.

Detrimental NFKB1 missense variants affecting the Rel-homology domain of p105/p50

Most of the currently known heterozygous pathogenic NFKB1 (Nuclear factor kappa B subunit 1) variants comprise deleterious defects such as severe truncations, internal deletions, and frameshift variants. Collectively, these represent the most frequent monogenic cause of common variable immunodeficiency (CVID) identified so far. NFKB1 encodes the transcription factor precursor p105 which undergoes limited proteasomal processing of its C-terminal half to generate the mature NF-κB subunit p50. Whereas p105/p50 haploinsufficiency due to devastating genetic damages and protein loss is a well-known disease mechanism, the pathogenic significance of numerous NFKB1 missense variants still remains uncertain and/or unexplored, due to the unavailability of accurate test procedures to confirm causality. In this study we functionally characterized 47 distinct missense variants residing within the N-terminal domains, thus affecting both proteins, the p105 precursor and the processed p50. Following transient overexpression of EGFP-fused mutant p105 and p50 in HEK293T cells, we used fluorescence microscopy, Western blotting, electrophoretic mobility shift assays (EMSA), and reporter assays to analyze their effects on subcellular localization, protein stability and precursor processing, DNA binding, and on the RelA-dependent target promoter activation, respectively. We found nine missense variants to cause harmful damage with intensified protein decay, while two variants left protein stability unaffected but caused a loss of the DNA-binding activity. Seven of the analyzed single amino acid changes caused ambiguous protein defects and four variants were associated with only minor adverse effects. For 25 variants, test results were indistinguishable from those of the wildtype controls, hence, their pathogenic impact remained elusive. In summary, we show that pathogenic missense variants affecting the Rel-homology domain may cause protein-decaying defects, thus resembling the disease-mechanisms of p105/p50 haploinsufficiency or may cause DNA-binding deficiency. However, rare variants (with a population frequency of less than 0.01%) with minor abnormalities or with neutral tests should still be considered as potentially pathogenic, until suitable tests have approved them being benign.

c-Rel Is Required for IL-33-Dependent Activation of ILC2s

Group 2 innate lymphoid cells (ILC2s) are emerging as important cellular regulators of homeostatic and disease-associated immune processes. The cytokine interleukin-33 (IL-33) promotes ILC2-dependent inflammation and immunity, with IL-33 having been shown to activate NF-κB in a wide variety of cell types. However, it is currently unclear which NF-κB members play an important role in IL-33-dependent ILC2 biology. Here, we identify the NF-κB family member c-Rel as a critical component of the IL-33-dependent activation of ILC2s. Although c-Rel is dispensable for ILC2 development, it is critical for ILC2 function in the lung, with c-Rel-deficient (c-Rel-/- ) mice present a significantly reduced response to papain- and IL-33-induced lung inflammation. We also show that the absence of c-Rel reduces the IL-33-dependent expansion of ILC2 precursors and lower levels of IL-5 and IL-13 cytokine production by mature ILC2s in the lung. Together, these results identify the IL-33-c-Rel axis as a central control point of ILC2 activation and function.

NF-κB c-Rel Is Dispensable for the Development but Is Required for the Cytotoxic Function of NK Cells

Natural Killer (NK) cells are cytotoxic lymphocytes critical to the innate immune system. We found that germline deficiency of NF-κB c-Rel results in a marked decrease in cytotoxic function of NK cells, both in vitro and in vivo, with no significant differences in the stages of NK cell development. We found that c-Rel binds to the promoters of perforin and granzyme B, two key proteins required for NK cytotoxicity, and controls their expression. We generated a NK cell specific c-Rel conditional knockout to study NK cell intrinsic role of c- Rel and found that both global and conditional c-Rel deficiency leads to decreased perforin and granzyme B expression and thereby cytotoxic function. We also confirmed the role of c-Rel in perforin and granzyme B expression in human NK cells. c-Rel reconstitution rescued perforin and granzyme B expressions in c-Rel deficient NK cells and restored their cytotoxic function. Our results show a previously unknown role of c-Rel in transcriptional regulation of perforin and granzyme B expressions and control of NK cell cytotoxic function.

c-Rel orchestrates energy-dependent epithelial and macrophage reprogramming in fibrosis

Fibrosis is a common pathological feature of chronic disease. Deletion of the NF-κB subunit c-Rel limits fibrosis in multiple organs, although the mechanistic nature of this protection is unresolved. Using cell-specific gene-targeting manipulations in mice undergoing liver damage, we elucidate a critical role for c-Rel in controlling metabolic changes required for inflammatory and fibrogenic activities of hepatocytes and macrophages and identify Pfkfb3 as the key downstream metabolic mediator of this response. Independent deletions of Rel in hepatocytes or macrophages suppressed liver fibrosis induced by carbon tetrachloride, while combined deletion had an additive anti-fibrogenic effect. In transforming growth factor-β1-induced hepatocytes, c-Rel regulates expression of a pro-fibrogenic secretome comprising inflammatory molecules and connective tissue growth factor, the latter promoting collagen secretion from HMs. Macrophages lacking c-Rel fail to polarize to M1 or M2 states, explaining reduced fibrosis in RelΔLysM mice. Pharmacological inhibition of c-Rel attenuated multi-organ fibrosis in both murine and human fibrosis. In conclusion, activation of c-Rel/Pfkfb3 in damaged tissue instigates a paracrine signalling network among epithelial, myeloid and mesenchymal cells to stimulate fibrogenesis. Targeting the c-Rel-Pfkfb3 axis has potential for therapeutic applications in fibrotic disease.

The c-Rel-c-Myc axis controls metabolism and proliferation of human T leukemia cells

Genome-wide association studies have established that human REL is a susceptibility gene for lymphoid cancers and inflammatory diseases. REL is the hematopoietic member of the nuclear factor-κB (NF-κB) family and is frequently amplified in human lymphomas. However, the mechanism through which REL and its encoded protein c-Rel affect human lymphoma is largely unknown. Using both loss-of-function and gain-of-function approaches, we studied the roles of REL gene in human Jurkat leukemia cells. Compared with control Jurkat cells, REL knockout cells exhibited significant defects in cell growth and mitochondrial respiration. Genome-wide transcriptome analyses revealed that T cells lacking c-Rel had selective defects in the expression of inflammatory and metabolic genes including c-Myc. We found that c-Rel controlled the expression of c-Myc through its promotor, and expressing c-Myc in c-Rel-deficient lymphoma cells rescued their proliferative and metabolic defects. Thus, the human c-Rel-c-Myc axis controls lymphoma growth and metabolism and could be a therapeutic target for lymphomas.

Constitutive expression of c-REL in uveal melanoma patients: correlation with clinicopathological parameters and patient outcome

PURPOSE

Uveal melanoma (UM) is the most common intraocular cancer with a high mortality rate that requires new research in the field of prevention and treatment. c-REL is a member of the nuclear factor κB (NF-κB) transcription factor family and an emerging regulator of tumorigenesis. Therefore, the objective of the study is to evaluate the constitutive expression of c-REL in uveal melanoma patients and its prognostic significance.

METHODS

Detection of c-REL expression was carried out by immunohistochemistry in all 75 patients, and qRT-PCR performed on 58 fresh cases of uveal melanoma along with IL-6 status. Immunoblot was performed to validate immunohistochemistry results. Expression of c-REL protein correlated with clinicopathological parameters and overall survival of patients.

RESULTS

Immunohistochemistry results revealed nuclear expression of the c-REL protein (56%) in our cases. Out of 75 cases, 31 cases showed nuclear expression, and 11 cases had cytoplasmic expression. qRT-PCR showed upregulation of the REL gene in 56.89% cases at the transcriptional level. There was a statistically significant difference in the overall survival of patients with c-REL nuclear immunopositivity (p = 0.0048). On multivariate analysis, scleral invasion and c-REL nuclear expression found to be an independent prognostic factor (p < 0.05) CONCLUSIONS: To the best of our knowledge, this was the first study reporting the expression of the c-REL protein in uveal melanoma. Strong nuclear immunoexpression of c-Rel suggests NFκB pathway activation which might be involved in the progression of the disease. Differential expression of c-REL protein may be used as an attractive target for the development of anticancer strategies.

A Matter of Choice: Inhibition of c-Rel Shifts Neuronal to Oligodendroglial Fate in Human Stem Cells

The molecular mechanisms underlying fate decisions of human neural stem cells (hNSCs) between neurogenesis and gliogenesis are critical during neuronal development and neurodegenerative diseases. Despite its crucial role in the murine nervous system, the potential role of the transcription factor NF-κB in the neuronal development of hNSCs is poorly understood. Here, we analyzed NF-κB subunit distribution during glutamatergic differentiation of hNSCs originating from neural crest-derived stem cells. We observed several peaks of specific NF-κB subunits. The most prominent nuclear peak was shown by c-REL subunit during a period of 2–5 days after differentiation onset. Furthermore, c-REL inhibition with pentoxifylline (PTXF) resulted in a complete shift towards oligodendroglial fate, as demonstrated by the presence of OLIG2⁺/O4⁺-oligodendrocytes, which showed PDGFRα, NG2 and MBP at the transcript level. In addition c-REL impairment further produced a significant decrease in neuronal survival. Transplantation of PTXF-treated predifferentiated hNSCs into an ex vivo oxidative-stress-mediated demyelination model of mouse organotypic cerebellar slices further led to integration in the white matter and differentiation into MBP⁺ oligodendrocytes, validating their functionality and therapeutic potential. In summary, we present a human cellular model of neuronal differentiation exhibiting a novel essential function of NF-κB-c-REL in fate choice between neurogenesis and oligodendrogenesis which will potentially be relevant for multiple sclerosis and schizophrenia.

PACT-mediated PKR activation acts as a hyperosmotic stress intensity sensor weakening osmoadaptation and enhancing inflammation

The inability of cells to adapt to increased environmental tonicity can lead to inflammatory gene expression and pathogenesis. The Rel family of transcription factors TonEBP and NF-κB p65 play critical roles in the switch from osmoadaptive homeostasis to inflammation, respectively. Here we identified PACT-mediated PKR kinase activation as a marker of the termination of adaptation and initiation of inflammation in Mus musculus embryonic fibroblasts. We found that high stress-induced PACT-PKR activation inhibits the interaction between NF-κB c-Rel and TonEBP essential for the increased expression of TonEBP-dependent osmoprotective genes. This resulted in enhanced formation of TonEBP/NF-κB p65 complexes and enhanced proinflammatory gene expression. These data demonstrate a novel role of c-Rel in the adaptive response to hyperosmotic stress, which is inhibited via a PACT/PKR-dependent dimer redistribution of the Rel family transcription factors. Our results suggest that inhibiting PACT-PKR signaling may prove a novel target for alleviating stress-induced inflammatory diseases.

Alternative and canonical NF-kB pathways DNA-binding hierarchies networks define Hodgkin lymphoma and Non-Hodgkin diffuse large B Cell lymphoma respectively

PURPOSE

Despite considerable evidence that supports the NF-kB role in the immune system and lymphomagenesis, it is unclear whether specific NF-kB dimers control a particular set of genes that account for their biological functions. Our previous work showed that Hodgkin Lymphoma (HL) is unique, among germinal center (GC)-derived lymphomas, with respect to its dependency on Rel-B to survive. In contrast, diffuse large B-Cell lymphoma (DLBCL) including both Activated B-Cell-Like and Germinal Center B-Cell-Like, requires cREL and Rel-A to survive and it is not affected by Rel-B depletion. These findings highlighted the activity of specific NF-kB subunits in different GC-derived lymphomas.

METHODS

Sequenced chromatin immunoprecipitated DNA fragments (ChIP-Seq) analysis revealed an extensive NF-kB DNA-binding network in DLBCL and HL. The ChIP-Seq data was merged with microarray analysis following the Rel-A, Rel-B or cRel knockdown to determine effectively regulated genes.

RESULTS

Downstream target analysis showed enrichment for cell cycle control, among other signatures. Rel-B and cRel controlled different genes within the same signature in HL and DLBCL, respectively. BCL2 was exclusively controlled by Rel-B in HL. Both mRNA and protein levels decreased following Rel-B depletion meanwhile there was no change upon cRel knock-down. BCL2 exogenous expression partially rescued the death induced by decreased Rel-B in HL cells.

CONCLUSION

The Rel-B hierarchical network defined HL and the cRel hierarchical network characterized DLBCL. Each Rel member performs specific functions in distinct GC-derived lymphomas. This result should be considered for the development of targeted therapies that are aimed to selectively inhibit individual NF-kB dimers.

Circadian control of p75 neurotrophin receptor leads to alternate activation of Nrf2 and c-Rel to reset energy metabolism in astrocytes via brain-derived neurotrophic factor

Circadian clock genes regulate energy metabolism partly through neurotrophins in the body. The low affinity neurotrophin receptor p75^NTR is a clock component directly regulated by the transcriptional factor Clock:Bmal1 complex. Brain-derived neurotrophic factor (BDNF) is expressed in the brain and plays a key role in coordinating metabolic interactions between neurons and astrocytes. BDNF transduces signals through TrkB and p75^NTR receptors. This review highlights a novel molecular mechanism by which BDNF via circadian control of p75^NTR leads to daily resetting of glucose and glycogen metabolism in brain astrocytes to accommodate their functional interaction with neurons. Astrocytes store glycogen as an energy reservoir to provide active neurons with the glycolytic metabolite lactate. Astrocytes predominantly express the truncated receptor TrkB.T1 which lacks an intracellular receptor tyrosine kinase domain. TrkB.T1 retains the capacity to regulate cell morphology through regulation of Rho GTPases. In contrast, p75^NTR mediates generation of the bioactive lipid ceramide upon stimulation with BDNF and inhibits PKA activation. As ceramide directly activates PKCζ, we discuss the importance of the TrkB.T1-p75^NTR-ceramide-PKCζ signaling axis in the stimulation of glycogen and lipid synthesis and activation of RhoA. Ceramide-PKCζ-casein kinase 2 signaling activates Nrf2 to support oxidative phosphorylation via upregulation of antioxidant enzymes. In the absence of p75^NTR, TrkB.T1 functionally interacts with adenosine A_2AR and dopamine D1R receptors to enhance cAMP-PKA signaling and activate Rac1 and NF-κB c-Rel, favoring glycogen hydrolysis, gluconeogenesis and aerobic glycolysis. Thus, diurnal changes in p75^NTR levels in astrocytes resets energy metabolism via BDNF to accommodate their metabolic interaction with neurons.

Inhibition of lipopolysaccharide-induced tissue factor expression in monocytes by urinary trypsin inhibitor in vitro and in vivo

Tissue factor (TF) plays a critical role in the pathogenesis of disseminated intravascular coagulation (DIC) observed in patients with septic shock. Urinary trypsin inhibitor (UTI), a multivalent protease inhibitor, is currently used for treatment of patients with septic shock. This study was undertaken to determine whether UTI reduces LPS-induced coagulation abnormalities by inhibiting lipopolysaccharide (LPS)-induced expression of TF by monocytes. UTI inhibited LPS-induced increases in both TF activities andTF mRNA expression in monocytes without affecting the viability. Although activation of nuclear factor-κB (NF-κB), activator protein-1 (AP-1) and extracellular signal-regulated kinase (ERK)1/2 were shown to be critically involved in LPS-induced increases in TF activities in isolated monocytes, UTI inhibited phosphorylation of ERK1/2 and decreased expression of early growth response factor-1 (Egr-1) induced by LPS without affecting the activation of NF-κB and AP-1. UTI inhibited both the expression of TF mRNA in whole blood, increases in TF activities in mononuclear cells, and increases in serum levels of fibrin and fibrinogen degradation products (E) in rats given LPS without affecting the number of monocytes in the peripheral blood. Taken together these results strongly suggested that UTI might reduce LPS-induced coagulation abnormalities in rats by inhibiting TF expression in monocytes through inhibition of Egr-1 expression.

A haplotype variant of the human chromogranin A gene (CHGA) promoter increases CHGA expression and the risk for cardiometabolic disorders

The acidic glycoprotein chromogranin A (CHGA) is co-stored/co-secreted with catecholamines and crucial for secretory vesicle biogenesis in neuronal/neuroendocrine cells. CHGA is dysregulated in several cardiovascular diseases, but the underlying mechanisms are not well established. Here, we sought to identify common polymorphisms in the CHGA promoter and to explore the mechanistic basis of their plausible contribution to regulating CHGA protein levels in circulation. Resequencing of the CHGA promoter in an Indian population (n = 769) yielded nine single-nucleotide polymorphisms (SNPs): G-1106A, A-1018T, T-1014C, T-988G, G-513A, G-462A, T-415C, C-89A, and C-57T. Linkage disequilibrium (LD) analysis indicated strong LD among SNPs at the -1014, -988, -462, and -89 bp positions and between the -1018 and -57 bp positions. Haplotype analysis predicted five major promoter haplotypes that displayed differential promoter activities in neuronal cells; specifically, haplotype 2 (containing variant T alleles at -1018 and -57 bp) exhibited the highest promoter activity. Systematic computational and experimental analyses revealed that transcription factor c-Rel has a role in activating the CHGA promoter haplotype 2 under basal and pathophysiological conditions (viz. inflammation and hypoxia). Consistent with the higher in vitro CHGA promoter activity of haplotype 2, individuals carrying this haplotype had higher plasma CHGA levels, plasma glucose levels, diastolic blood pressure, and body mass index. In conclusion, these results suggest a functional role of the CHGA promoter haplotype 2 (occurring in a large proportion of the world population) in enhancing CHGA expression in haplotype 2 carriers who may be at higher risk for cardiovascular/metabolic disorders.

Molecular mechanisms of signaling via the docosanoid neuroprotectin D1 for cellular homeostasis and neuroprotection

Docosahexaenoic acid, enriched in the brain and retina, generates docosanoids in response to disruptions of cellular homeostasis. Docosanoids include neuroprotectin D1 (NPD1), which is decreased in the CA1 hippocampal area of patients with early-stage Alzheimer's disease (AD). We summarize here how NPD1 elicits neuroprotection by up-regulating c-REL, a nuclear factor (NF)-κB subtype that, in turn, enhances expression of BIRC3 (baculoviral inhibitor of apoptosis repeat-containing protein 3) in the retina and in experimental stroke, leading to neuroprotection. Elucidating the mechanisms of action of docosanoids will contribute to managing diseases, including stroke, AD, age-related macular degeneration, traumatic brain injury, Parkinson's disease, and other neurodegenerations.

MCPIP1, alias Regnase-1 binds and cleaves mRNA of C/EBPβ

CCAAT/enhancer-binding protein beta (C/EBPβ) is a transcription factor controlling a broad range of genes essential for homeostasis, including genes related to immune functions, inflammation, metabolism and growth. Monocyte chemoattractant protein-1-induced protein 1 (MCPIP1) also called as Regnase-1 is an RNase and has been shown to decrease the stability of short-lived transcripts coding for inflammation-related proteins, including IL-1β, IL-6, IL-2, IL-8, IL-12b, IER-3, c-Rel. We found previously that the half-life of the C/EBPβ transcript is regulated by MCPIP. To understand the mechanism driving down-regulation of C/EBPβ by MCPIP1, we applied an in vitro cleavage assay, followed by a luciferase-reporter assay and RNA immunoprecipitation (RIP). We demonstrated that MCPIP1 recognizes regions of the 3’UTR of C/EBPβ mRNA and promotes its decay by introducing direct endonucleolytic cleavage.

c-Rel is dispensable for the differentiation and functional maturation of M cells in the follicle-associated epithelium

M cells reside within the follicle-associated epithelium (FAE) overlying the gut-associated lymphoid tissues. These unique phagocytic epithelial cells enable the mucosal immune system to sample antigens within the lumen of the intestine. The differentiation of M cells from uncommitted precursors in the FAE is dependent on the production of receptor activator of nuclear factor-κB ligand (RANKL) by subepithelial stromal cells. The ligation of a variety of cell surface receptors activates the nuclear factor-κB (NF-κB) family of transcription factors which in-turn induce the transcription of multiple target genes. RANKL-stimulation can stimulate the nuclear translocation of the NF-κB subunit c-Rel. We therefore used c-Rel-deficient mice to determine whether the differentiation and functional maturation of M cells in the Peyer's patches was dependent on c-Rel. Our data show that c-Rel-deficiency does not influence the expression of RANKL or RANK in Peyer's patches, or the induction of M-cell differentiation in the FAE. RANKL-stimulation in the differentiating M cells induces the expression of SpiB which is essential for their subsequent maturation. However, SpiB expression in the FAE was also unaffected in the absence of c-Rel. As a consequence, the functional maturation of M cells was not impaired in the Peyer's patches of c-Rel-deficient mice. Although our data showed that the specific expression of CCL20 and ubiquitin D in the FAE was not impeded in the absence of c-Rel, the expression of ubiquitin D was dramatically reduced in the B cell-follicles of c-Rel-deficient mice. Coincident with this, we also observed that the status of follicular dendritic cells in the B cell-follicles was dramatically reduced in Peyer's patches from c-Rel-deficient mice. Taken together, our data show that c-Rel is dispensable for the RANKL-mediated differentiation and functional maturation of M cells.

Deficiency of Nuclear Factor-κB c-Rel Accelerates the Development of Autoimmune Diabetes in NOD Mice

The nuclear factor-κB protein c-Rel plays a critical role in controlling autoimmunity. c-Rel-deficient mice are resistant to streptozotocin-induced diabetes, a drug-induced model of autoimmune diabetes. We generated c-Rel-deficient NOD mice to examine the role of c-Rel in the development of spontaneous autoimmune diabetes. We found that both CD4(+) and CD8(+) T cells from c-Rel-deficient NOD mice showed significantly decreased T-cell receptor-induced IL-2, IFN-γ, and GM-CSF expression. Despite compromised T-cell function, c-Rel deficiency dramatically accelerated insulitis and hyperglycemia in NOD mice along with a substantial reduction in T-regulatory (Treg) cell numbers. Supplementation of isogenic c-Rel-competent Treg cells from prediabetic NOD mice reversed the accelerated diabetes development in c-Rel-deficient NOD mice. The results suggest that c-Rel-dependent Treg cell function is critical in suppressing early-onset autoimmune diabetogenesis in NOD mice. This study provides a novel natural system to study autoimmune diabetes pathogenesis and reveals a previously unknown c-Rel-dependent mechanistic difference between chemically induced and spontaneous diabetogenesis. The study also reveals a unique protective role of c-Rel in autoimmune diabetes, which is distinct from other T-cell-dependent autoimmune diseases such as arthritis and experimental autoimmune encephalomyelitis, where c-Rel promotes autoimmunity.

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.

Regulation pattern of fish irf4 (the gene encoding IFN regulatory factor 4) by STAT6, c-Rel and IRF4

Interferon regulatory factor 4 (IRF4) plays pivotal roles in both innate and adaptive immune responses in mammals. In fish, there are two homologues of irf4, irf4a and irf4b. In this study, we examined the regulatory patterns of zebrafish irf4a and irf4b by STAT6 and c-Rel. Firstly, expression of irf4a and irf4b was monitored in several tissues at mRNA level. By infection with SVCV, irf4a and irf4b were upregulated in both kidney and spleen, and were immediately induced by treatment with poly I:C in ZF4 cells. Moreover, the activation of irf4a promoter was regulated by overexpression of stat6 and c-rel in a cooperation manner, which could be inhibited by mutation of the putative binding sites of STAT6 and c-Rel in irf4a promoter region. However, irf4b promoter was activated slightly only by STAT6 but not c-Rel. Furthermore, overexpression of irf4a inhibited the activation of its own promoter under induction of STAT6 and c-Rel, which was the result of that IRF4a bound to STAT6 and c-Rel directly. In addition, cellular location analysis showed that IRF4a was located only in nuclear region. These data indicate that fish irf4a can also be upregulated by STAT6 and c-Rel.

The VEGF-Receptor Inhibitor Axitinib Impairs Dendritic Cell Phenotype and Function

Inhibitors of VEGF receptor (VEGFR) signaling such as sorafenib and sunitinib that are currently used in the treatment of malignant diseases have been shown to affect immunological responses by inhibition of the function of antigen presenting cells and T lymphocytes. The VEGFR-inhibitor axitinib has recently been approved for second line therapy of metastatic renal cell carcinoma. While there is some evidence that axitinib might interfere with the activation of T cells, not much is known about the effects of axitinib on dendritic cell (DC) phenotype and function. We here show that the addition of axitinib during the final Toll-like receptor-4-induced maturation step of monocyte-derived human DCs results in a reduced DC activation characterized by impaired expression of activation markers and co-stimulatory molecules such as CD80, CD83 and CD86. We further found a decreased secretion of interleukin-12 which was accompanied by reduced nuclear expression of the transcription factor cRel. In addition, we found a dose-dependent reduced activation of p38 and STAT3 in axitinib-exposed DCs, whereas the expression was not affected. The dysfunction of axitinib-exposed DCs was further underlined by their impaired induction of allogeneic T cell proliferation in a mixed lymphocyte reaction assay and inhibition of DC migration. Our results demonstrate that axitinib significantly affects DC differentiation and function primarily via the inhibition of the nuclear factor kappa B signaling pathway leading to impaired T cell activation. This will be of importance for the design of future vaccination protocols and therapeutic approaches aiming at combining different treatment strategies, eg such as programmed death-1 inhibitors with axitinib.

Triptolide reverses hypoxia-induced epithelial-mesenchymal transition and stem-like features in pancreatic cancer by NF-κB downregulation

Pancreatic ductal adenocarcinoma (PDA) is one of the most lethal malignancies characterized by an intense tumor stroma with hypoperfused regions, a significant inflammatory response and pronounced therapy resistance. New therapeutic agents are urgently needed. The plant-derived agent triptolide also known as "thunder god vine" has a long history in traditional Chinese medicine for treatment of rheumatoid arthritis and cancer and is now in a clinical phase II trial for establishing the efficacy against a placebo. The authors mimicked the situation in patient tumors by induction of hypoxia in experimental models of pancreatic cancer stem cells (CSCs) and evaluated the therapeutic effect of triptolide. Hypoxia led to induction of colony and spheroid formation, aldehyde dehydrogenase 1 (ALDH1) and NF-κB activity, migratory potential and a switch in morphology to a fibroblastoid phenotype, as well as stem cell- and epithelial-mesenchymal transition-associated protein expression. Triptolide efficiently inhibited hypoxia-induced transcriptional signaling and downregulated epithelial-mesenchymal transition (EMT) and CSC features in established highly malignant cell lines, whereas sensitive cancer cells or nonmalignant cells were less affected. In vivo triptolide inhibited tumor take and tumor growth. In primary CSCs isolated from patient tumors, triptolide downregulated markers of CSCs, proliferation and mesenchymal cells along with upregulation of markers for apoptosis and epithelial cells. This study is the first to show that triptolide reverses EMT and CSC characteristics and therefore may be superior to current chemotherapeutics for treatment of PDA.

Galectin-3 modulates Th17 responses by regulating dendritic cell cytokines

Galectin-3 is a β-galactoside-binding animal lectin with diverse functions, including regulation of T helper (Th) 1 and Th2 responses. Current data indicate that galectin-3 expressed in dendritic cells (DCs) may be contributory. Th17 cells have emerged as critical inducers of tissue inflammation in autoimmune disease and important mediators of host defense against fungal pathogens, although little is known about galectin-3 involvement in Th17 development. We investigated the role of galectin-3 in the induction of Th17 immunity in galectin-3-deficient (gal3(-/-)) and gal3(+/+) mouse bone marrow-derived DCs. We demonstrate that intracellular galectin-3 negatively regulates Th17 polarization in response to the dectin-1 agonist curdlan (a β-glucan present on the cell wall of fungal species) and lipopolysaccharide, agents that prime DCs for Th17 differentiation. On activation of dectin-1, gal3(-/-) DCs secreted higher levels of the Th17-axis cytokine IL-23 compared with gal3(+/+) DCs and contained higher levels of activated c-Rel, an NF-κB subunit that promotes IL-23 expression. Levels of active Raf-1, a kinase that participates in downstream inhibition of c-Rel binding to the IL23A promoter, were impaired in gal3(-/-) DCs. Modulation of Th17 by galectin-3 in DCs also occurred in vivo because adoptive transfer of gal3(-/-) DCs exposed to Candida albicans conferred higher Th17 responses and protection against fungal infection. We conclude that galectin-3 suppresses Th17 responses by regulating DC cytokine production.

Regulation of Transcriptional Networks by PKC Isozymes: Identification of c-Rel as a Key Transcription Factor for PKC-Regulated Genes

BACKGROUND

Activation of protein kinase C (PKC), a family of serine-threonine kinases widely implicated in cancer progression, has major impact on gene expression. In a recent genome-wide analysis of prostate cancer cells we identified distinctive gene expression profiles controlled by individual PKC isozymes and highlighted a prominent role for PKCδ in transcriptional activation.

PRINCIPAL FINDINGS

Here we carried out a thorough bioinformatics analysis to dissect transcriptional networks controlled by PKCα, PKCδ, and PKCε, the main diacylglycerol/phorbol ester PKCs expressed in prostate cancer cells. Despite the remarkable differences in the patterns of transcriptional responsive elements (REs) regulated by each PKC, we found that c-Rel represents the most frequent RE in promoters regulated by all three PKCs. In addition, promoters of PKCδ-regulated genes were particularly enriched with REs for CREB, NF-E2, RREB, SRF, Oct-1, Evi-1, and NF-κB. Most notably, by using transcription factor-specific RNAi we were able to identify subsets of PKCδ-regulated genes modulated by c-Rel and CREB. Furthermore, PKCδ-regulated genes condensed under the c-Rel transcriptional regulation display significant functional interconnections with biological processes such as angiogenesis, inflammatory response, and cell motility.

CONCLUSION/SIGNIFICANCE

Our study identified candidate transcription factors in the promoters of PKC regulated genes, in particular c-Rel was found as a key transcription factor in the control of PKCδ-regulated genes. The deconvolution of PKC-regulated transcriptional networks and their nodes may greatly help in the identification of PKC effectors and have significant therapeutics implications.

The increased transcriptional response and translocation of a Rel/NF-κB homologue in scallop Chlamys farreri during the immune stimulation

The Rel/NF-κB transcription factors can function as key regulators to modulate the expression of immune-related genes in response to immune challenge or environmental stress. In the present study, a gene coding Rel/NF-κB homologue was identified from scallop Chlamys farreri (designated CfRel). Its deduced protein comprised 359 amino acids, and contained a conserved N-terminal Rel homology domain (RHD) and an IPT domain. There was an NF-κB/Rel/dorsal domain signature sequence in the RHD domain. The mRNA transcripts of CfRel could be detected in all the tested tissues including adductor muscle, mantle, gill, gonad, haemocytes, kidney and hepatopancreas, with the highest expression level in hepatopancreas. After LPS stimulation, there were two peaks of CfRel mRNA expression level in haemocytes at 6 h (25.25-fold, P < 0.05) and 24 h (59.66-fold, P < 0.05) respectively, while the mRNA expression of CfRel was only up-regulated at 3 h after PGN stimulation (2.35-fold, P < 0.05). By Western blotting technique, CfRel protein was observed in the cytoplasm and nucleus of scallop haemocytes, and its concentration in the haemocyte nucleus increased significantly at 3 h and 12 h after LPS stimulation. The noticeable NF-κB transcription activity of CfRel protein was determined by NF-κB luciferase reporter assays (122.43%, P < 0.05), and it decreased significantly (17.61%, P < 0.05) after the coexpression of scallop IκB protein. These results collectively suggested that CfRel mRNA transcripts and protein were induced by immune stimulation, and CfRel protein could extricate itself from IκB protein and transfer into the haemocyte nucleus to modulate the immune response in scallop.

Depletion of c-Rel from cytokine gene promoters is required for chromatin reassembly and termination of gene responses to T cell activation

The role of the Nuclear Factor κB (NF-κB) transcription factor family in T cell function has been well described. The c-Rel family member is of particular importance in initiating T cell responses to antigen and regulating activation of inflammatory cytokine genes, including the Interleukin-2 (IL-2) and Granulocyte macrophage colony stimulating factor (GM-CSF) genes. c-Rel is required for chromatin remodeling of these gene promoters, which involves depletion of histones from the promoters in response to T cell activating signals. These chromatin remodeling events precede transcriptional activation of the genes. The subsequent down-regulation of cytokine gene expression is important in the termination of an immune response and here we examine this process at the murine GM-CSF and IL-2 genes. We show that the cytokine mRNA levels rapidly return to basal levels following stimulus removal and this is associated with reassembly of histones onto the promoter. Histone reassembly at the GM-CSF and IL-2 promoters occurs concomitantly with depletion of RelA, c-Rel and RNA polymerase II from the promoters. Furthermore we show that transcriptional down-regulation and chromatin reassembly is dependent on depletion of c-Rel from the nucleus, and that this is regulated by the nuclear translocation of the NF-κB inhibitor, IκBα. The nuclear activation of c-Rel therefore not only regulates the initiation of GM-CSF and IL-2 gene activation in response to T cell activation, but also the termination of these gene responses following the removal of the activating signal.

Irreversible EGFR inhibitor EKB-569 targets low-LET γ-radiation-triggered rel orchestration and potentiates cell death in squamous cell carcinoma

EKB-569 (Pelitinib), an irreversible EGFR tyrosine kinase inhibitor has shown potential therapeutic efficiency in solid tumors. However, cell-killing potential in combination with radiotherapy and its underlying molecular orchestration remain to be explored. The objective of this study was to determine the effect of EKB-569 on ionizing radiation (IR)-associated NFκB-dependent cell death. SCC-4 and SCC-9 cells exposed to IR (2Gy) with and without EKB-569 treatment were analyzed for transactivation of 88 NFκB pathway molecules, NFκB DNA-binding activity, translation of the NFκB downstream mediators, Birc1, 2 and 5, cell viability, metabolic activity and apoptosis. Selective targeting of IR-induced NFκB by EKB-569 and its influence on cell-fate were assessed by overexpressing (p50/p65) and silencing (ΔIκBα) NFκB. QPCR profiling after IR exposure revealed a significant induction of 74 NFκB signal transduction molecules. Of those, 72 were suppressed with EKB-569. EMSA revealed a dose dependent inhibition of NFκB by EKB-569. More importantly, EKB-569 inhibited IR-induced NFκB in a dose-dependent manner, and this inhibition was sustained up to at least 72 h. Immunoblotting revealed a significant suppression of IR-induced Birc1, 2 and 5 by EKB-569. We observed a dose-dependent inhibition of cell viability, metabolic activity and apoptosis with EKB-569. EKB-569 significantly enhanced IR-induced cell death and apoptosis. Blocking NFκB improved IR-induced cell death. Conversely, NFκB overexpression negates EKB-569 -induced cell-killing. Together, these pre-clinical data suggest that EKB-569 is a radiosensitizer of squamous cell carcinoma and may mechanistically involve selective targeting of IR-induced NFκB-dependent survival signaling. Further pre-clinical in-vivo studies are warranted.

Nod2 downregulates TLR2/1 mediated IL1β gene expression in mouse peritoneal macrophages

Nod2 is a cytosolic pattern recognition receptor. It has been implicated in many inflammatory conditions. Its signaling has been suggested to modulate TLR responses in a variety of ways, yet little is known about the mechanistic details of the process. We show in this study that Nod2 knockdown mouse peritoneal macrophages secrete more IL1β than normal macrophages when stimulated with peptidoglycan (PGN). Muramyl dipeptide (MDP, a Nod2 ligand) + PGN co-stimulated macrophages have lower expression of IL1β than PGN (TLR2/1 ligand) stimulated macrophages. MDP co-stimulation have similar effects on Pam3CSK4 (synthetic TLR2/1 ligand) mediated IL1β expression suggesting that MDP mediated down regulating effects are receptor dependent and ligand independent. MDP mediated down regulation was specific for TLR2/1 signaling as MDP does not affect LPS (TLR4 ligand) or zymosan A (TLR2/6 ligand) mediated IL1β expression. Mechanistically, MDP exerts its down regulating effects by lowering PGN/Pam3CSK4 mediated nuclear cRel levels. Lower nuclear cRel level were observed to be because of enhanced transporting back rather than reduced nuclear translocation of cRel in MDP + PGN stimulated macrophages. These results demonstrate that Nod2 and TLR2/1 signaling pathways are independent and do not interact at the level of MAPK or NF-κB activation.

c-Rel controls multiple discrete steps in the thymic development of Foxp3+ CD4 regulatory T cells

The development of natural Foxp3⁺ CD4 regulatory T cells (nTregs) proceeds via two steps that involve the initial antigen dependent generation of CD25⁺GITR^hiFoxp3⁻CD4⁺ nTreg precursors followed by the cytokine induction of Foxp3. Using mutant mouse models that lack c-Rel, the critical NF-κB transcription factor required for nTreg differentiation, we establish that c-Rel regulates both of these developmental steps. c-Rel controls the generation of nTreg precursors via a haplo-insufficient mechanism, indicating that this step is highly sensitive to c-Rel levels. However, maintenance of c-Rel in an inactive state in nTreg precursors demonstrates that it is not required for a constitutive function in these cells. While the subsequent IL-2 induction of Foxp3 in nTreg precursors requires c-Rel, this developmental transition does not coincide with the nuclear expression of c-Rel. Collectively, our results support a model of nTreg differentiation in which c-Rel generates a permissive state for foxp3 transcription during the development of nTreg precursors that influences the subsequent IL-2 dependent induction of Foxp3 without a need for c-Rel reactivation.

c-Rel deficiency increases caspase-4 expression and leads to ER stress and necrosis in EBV-transformed cells

LMP1-mediated activation of nuclear factor of kappaB (NF-κB) is critical for the ligand independent proliferation and cell survival of in vitro EBV-transformed lymphoblastoid cell lines (LCLs). Previous experiments revealed that a majority of LMP1-dependent responses are regulated by NF-κB. However, the extent that individual NF-κB family members are required for these responses, in particular, c-Rel, whose expression is restricted to mature hematopoietic cells, remains unclear. Here we report that low c-Rel expression in LCLs derived from a patient with hyper-IgM syndrome (Pt1), resulted in defects in proliferation and cell survival. In contrast to studies that associated loss of NF-κB with increased apoptosis, Pt1 LCLs failed to initiate apoptosis and alternatively underwent autophagy and necrotic cell death. Whereas the proliferation defect appeared linked to a c-Rel-associated decrease in c-myc expression, identified pro-survival and pro-apoptotic targets were expressed at or near control levels consistent with the absence of apoptosis. Ultrastructural examination of Pt1 LCLs revealed a high level of cellular and ER stress that was further supported by gene expression profiling showing the upregulation of several genes involved in stress and inflammation. Apoptosis-independent cell death was accompanied by increased expression of the inflammatory marker, caspase-4. Using gene overexpression and siRNA knockdown we demonstrated that levels of c-Rel directly modulated expression of caspase-4 as well as other ER stress genes. Overall, these findings reveal the importance of c-Rel in maintaining LCL viability and that decreased expression results in ER stress and a default response leading to necrotic cell death.

Foxp3 interacts with c-Rel to mediate NF-κB repression

Expression of the lineage-specific DNA-binding factor Foxp3 controls the development and function of naturally occurring regulatory T cells. Foxp3 has been shown to interact with a multitude of transcriptional regulators including NFAT, NF-κB (p65), Runx1 and RORγt, as well as the histone modification enzymes TIP60, HDAC7 and HDAC9. The sum of these interactions is believed to cause the change in the transcriptional program of regulatory T cells. Here we show that Foxp3 directly or as part of a multimeric complex engages with the NF-κB component c-Rel. We demonstrate that the N-terminal region of Foxp3 is required for the binding of c-Rel, but not NFAT. Conversely, deletion of the forkhead domain causes a loss of interaction with NFAT, but not c-Rel. Our findings are of particular interest, as c-Rel is crucial for the induction of Foxp3 in regulatory T cells during thymic development, but has to be repressed in mature regulatory T cells to maintain their suppressive phenotype.

Anti-apoptotic effect of hyperglycemia can allow survival of potentially autoreactive T cells

Thymocyte development is a tightly controlled multi-step process involving selective elimination of self-reactive and non-functional T cells by apoptosis. This developmental process depends on signaling by Notch, IL-7 and active glucose metabolism. In this study, we explored the requirement of glucose for thymocyte survival and found that in addition to metabolic regulation, glucose leads to the expression of anti-apoptotic genes. Under hyperglycemic conditions, both mouse and human thymocytes demonstrate enhanced survival. We show that glucose-induced anti-apoptotic genes are dependent on NF-κB p65 because high glucose is unable to attenuate normal ongoing apoptosis of thymocytes isolated from p65 knockout mice. Furthermore, we demonstrate that in vivo hyperglycemia decreases apoptosis of thymocytes allowing for survival of potentially self-reactive thymocytes. These results imply that hyperglycemic conditions could contribute to the development of autoimmunity through dysregulated thymic selection.

Tissue and developmental expression of SRAM, an unconventional Rel-family protein

Previously we have reported the purification and cDNA cloning of a novel Rel/Ankyrin-family protein named SRAM from the flesh fly, Sarcophaga peregrina. Rel proteins generally translocate into the nucleus upon immune stimuli by dissociating from an inhibitory ankyrin domain, while SRAM is unique in terms of its constitutive nuclear localization with its internal ankyrin domain accompanied, at least in a Sarcophaga cell line and fat body cells. Although SRAM had been originally identified as a sole factor that binds to the κB motif of the inducible Sarcophaga lectin gene promoter, its transcriptional activity remained controversial. Moreover, homologues of SRAM have not been found in any other established model organisms including Drosophila. Here we report that the developmental expression of SRAM was up-regulated at the early stages of embryogenesis and metamorphosis. Furthermore, SRAM expression was prominent in the digestive tracts of the third instar larvae. We argue the hypothesis that SRAM has evolved as a quite unconventional Rel-family protein in Sarcophaga.

A feed-forward circuit controlling inducible NF-κB target gene activation by promoter histone demethylation

Activation of transcription from a silenced state is crucial to achieve specific gene expression in many biological contexts. Methylation of lysine 9 on histone H3 (H3K9) is widely associated with transcriptional silencing, and its disappearance is linked to the activation of several inflammatory genes by NF-κB. Here we describe that this event is controlled by a feed-forward circuit catalyzed by the activity of the histone demethylase Aof1 (also known as Lsd2/Kdm1b). We find that Aof1 is required for removal of dimethyl H3K9 at specific promoters, and thereby it controls stimulus-induced recruitment of NF-κB and gene expression. However, Aof1 is itself recruited by interaction with the c-Rel subunit of NF-κB, which is found at low levels associated with promoters in unstimulated cells. Thus, at these tightly regulated genes, NF-κB functions both as a transcriptional activator and as an upstream targeting signal that marks promoters to be derepressed by histone demethylation.

The type III effectors NleE and NleB from enteropathogenic E. coli and OspZ from Shigella block nuclear translocation of NF-kappaB p65

Many bacterial pathogens utilize a type III secretion system to deliver multiple effector proteins into host cells. Here we found that the type III effectors, NleE from enteropathogenic E. coli (EPEC) and OspZ from Shigella, blocked translocation of the p65 subunit of the transcription factor, NF-kappaB, to the host cell nucleus. NF-kappaB inhibition by NleE was associated with decreased IL-8 expression in EPEC-infected intestinal epithelial cells. Ectopically expressed NleE also blocked nuclear translocation of p65 and c-Rel, but not p50 or STAT1/2. NleE homologues from other attaching and effacing pathogens as well OspZ from Shigella flexneri 6 and Shigella boydii, also inhibited NF-kappaB activation and p65 nuclear import; however, a truncated form of OspZ from S. flexneri 2a that carries a 36 amino acid deletion at the C-terminus had no inhibitory activity. We determined that the C-termini of NleE and full length OspZ were functionally interchangeable and identified a six amino acid motif, IDSY(M/I)K, that was important for both NleE- and OspZ-mediated inhibition of NF-kappaB activity. We also established that NleB, encoded directly upstream from NleE, suppressed NF-kappaB activation. Whereas NleE inhibited both TNFalpha and IL-1beta stimulated p65 nuclear translocation and IkappaB degradation, NleB inhibited the TNFalpha pathway only. Neither NleE nor NleB inhibited AP-1 activation, suggesting that the modulatory activity of the effectors was specific for NF-kappaB signaling. Overall our data show that EPEC and Shigella have evolved similar T3SS-dependent means to manipulate host inflammatory pathways by interfering with the activation of selected host transcriptional regulators.

Nuclear factor-kappaB modulates regulatory T cell development by directly regulating expression of Foxp3 transcription factor

Naturally derived regulatory T (Treg) cells are characterized by stable expression of the transcription factor Foxp3 and characteristic epigenetic imprinting at the Foxp3 gene locus. Here, we found that enhancing nuclear factor (NF)-kappaB activity via a constitutive active inhibitor of kappaB kinase beta (IKKbeta) transgene in T cells led to increased number of Foxp3(+) cells in the thymus and can rescue Foxp3 expression in thymocytes deficient in other pleiotropic signaling molecules. Enhancing the signal strength of the NF-kappaB pathway also induced Foxp3 expression in otherwise conventionally selected T cells. NF-kappaB directly promoted the transcription of Foxp3, and upon T cell receptor (TCR) stimulation, c-Rel, a NF-kappaB family member, bound to Foxp3 enhancer region, which is specifically demethylated in natural Treg cells. Hence, NF-kappaB signaling pathway is a key regulator of Foxp3 expression during natural Treg cell development.

Aging-dependent upregulation of IL-23p19 gene expression in dendritic cells is associated with differential transcription factor binding and histone modifications

Age-associated changes in immune response increase the risk of infection and promote inflammation and autoimmunity in older adults. The newly discovered cytokine IL-23 contributes to the maintenance and expansion of Th-17 cells, which promote proinflammatory responses. Our preliminary findings suggested that Th-17 responses are increased in aged mice. IL-23 consists of p40 and p19 subunits. Expression of the p19 subunit is regulated at the transcriptional level by NF-kappaB p65 and c-Rel transcription factors. Using bone-marrow-derived dendritic cells (DCs) from C57BL/6 mice, we show that IL-23 protein production and p19 subunit mRNA levels are significantly increased in DCs from aged mice after activation with TLR ligands (LPS + R848) when compared with DCs of young adult mice. We found that the increase in p19 expression in aged cells is associated with chromatin remodeling characterized by di- and tri-methylation of histone H3K4 and binding of mainly c-Rel at the p19 promoter. In young DCs, the promoter is tri-methylated only at H3K4 and bound by both p65 and c-Rel. C-Rel knockdown restores p65 binding in aged cells but does not activate p19 expression, suggesting that c-Rel is critical for p19 expression. In addition, p65 knockdown significantly increases c-Rel binding and p19 expression in young DCs to levels close to those detected in old cells. Furthermore, the decrease in p65 binding at the p19 promoter in old DCs was specific to the p19 gene since p65 binding to the IL-12p40 promoter was not significantly different between old and young DCs. Our results demonstrate that selective changes in H3K4 methylation, and c-Rel and p65 binding at the p19 promoter occur in DCs and contribute to the upregulation of the p19 subunit expression and IL-23 protein production observed in aged mice. This suggests epigenetic and transcriptional mechanisms contribute to dysregulated inflammatory and autoimmune responses associated with aging.

Ser484 and Ser494 in REL are the major sites of IKK phosphorylation in vitro: evidence that IKK does not directly enhance GAL4-REL transactivation

Human c-Rel (REL) is a member of the NF-kappa B family of transcription factors, and one of its primary physiological roles is in the regulation of B-cell proliferation and survival. Although REL is primarily regulated by cytoplasmic-nuclear translocation through interaction with I kappa B inhibitors, REL also undergoes several posttranslational modifications that have been proposed to modulate its transcriptional activation activity. For example, phosphorylation of C-terminal sequences of REL has been proposed to increase its transactivation activity. In this report, we have used immune complex kinase assays to identify Ser484 and Ser494 as the primary sites of IKK alpha- and IKK beta-mediated in vitro phosphorylation in the C-terminal transactivation domain of REL. However, in cotransfection studies in A293 cells we have failed to detect IKK beta-mediated phosphorylation of these sites on REL in vivo, nor does IKK beta appear to interact with REL in these cells. Ser-to-Ala mutation of Ser484 and Ser494 does not affect IKK's ability to enhance GAL4-REL transactivation in reporter gene assays in A293 cells. We also show that the previously reported effects of overexpressed IKK and tumor necrosis factor treatment on GAL4-REL transactivation are due to IKK-mediated activation of the endogenous NF-kappa B pathway, which increases transcription from kappa B sites in the promoter of a commonly used GAL4 expression vector. Taken together, these results do not support a role for IKK-mediated phosphorylation as means for regulating the activity of REL in vivo.

The Th2 transcription factor c-Maf inhibits IL-12p35 gene expression in activated macrophages by targeting NF-kappaB nuclear translocation

The inflammatory response of macrophages to infectious agents is a highly dynamic and orchestrated process involving the release of a variety of inflammatory mediators, including interleukin-12 (IL-12), as a consequence of the recognition of the pathogens. Regulation of IL-12 gene expression by the anti-inflammatory cytokine IL-10 represents a major homeostatic process underlying host-pathogen and host-self interactions. Our group first reported that the Th2-specific transcription factor c-Maf is expressed also in macrophages treated with lipopolysaccharide (LPS) and IL-10. When overexpressed, c-Maf can potently suppress IL-12 production. However, c-Maf does not appear to be a physiologic regulator of IL-12p40 gene transcription because p40 production is not dysregulated in c-Maf-deficient macrophages. In this study, we investigated the role of c-Maf in regulation of the transcription of the p35 gene, which encodes the chain that is rate limiting in the synthesis of the heterodimeric IL-12. We report that c-Maf is a physiologic modulator of IL-12p35 gene expression and IL-12p70 production. We identify a novel NF-kappaB element within the proximal p35 promoter and show that c-Maf inhibits p35 transcription by antagonizing the effects of NF-kappaB, especially c-Rel, on p35 activation. It does so not by directly interacting with the target DNA but by interfering with the nuclear localization of NF-kappaB c-Rel. This study contributes to our understanding of the molecular basis of the homeostatic regulation of IL-12 production by c-Maf, which plays a dual role both in the function of antigen-presenting cells (APCs) and in T helper cell differentiation.

Functional conservation of Rel binding sites in drosophilid genomes

Evolutionary constraints on gene regulatory elements are poorly understood: Little is known about how the strength of transcription factor binding correlates with DNA sequence conservation, and whether transcription factor binding sites can evolve rapidly while retaining their function. Here we use the model of the NFKB/Rel-dependent gene regulation in divergent Drosophila species to examine the hypothesis that the functional properties of authentic transcription factor binding sites are under stronger evolutionary constraints than the genomic background. Using molecular modeling we compare tertiary structures of the Drosophila Rel family proteins Dorsal, Dif, and Relish and demonstrate that their DNA-binding and protein dimerization domains undergo distinct rates of evolution. The accumulated amino acid changes, however, are unlikely to affect DNA sequence recognition and affinity. We employ our recently developed microarray-based experimental platform and principal coordinates statistical analysis to quantitatively and systematically profile DNA binding affinities of three Drosophila Rel proteins to 10,368 variants of the NFKB recognition sequences. We then correlate the evolutionary divergence of gene regulatory regions with differences in DNA binding affinities. Genome-wide analyses reveal a significant increase in the number of conserved Rel binding sites in promoters of developmental and immune genes. Significantly, the affinity of Rel proteins to these sites was higher than to less conserved sites and was maintained by the conservation of the DNA binding site sequence (static conservation) or in some cases despite significantly diverged sequences (dynamic conservation). We discuss how two types of conservation may contribute to the stabilization and optimization of a functional gene regulatory code in evolution.

TCR/CD28-stimulated actin dynamics are required for NFAT1-mediated transcription of c-rel leading to CD28 response element activation

TCR/CD28 engagement triggers the initiation of a variety of signal transduction pathways that lead to changes in gene transcription. Although reorganization of the actin cytoskeleton is required for T cell activation, the molecular pathways controlled by the actin cytoskeleton are ill defined. To this end, we analyzed TCR/CD28-stimulated signaling pathways in cytochalasin D-treated T cells to determine the cytoskeletal requirements for T cell activation. Cytochalasin D treatment impaired T cell activation by causing a reduction in TCR/CD28-mediated calcium flux, and blocked activation of two regulatory elements within the IL-2 promoter, NFAT/AP-1 and CD28RE/AP. Treatment had no effect on signaling leading to the activation of either AP-1 or NF-kappaB. Significantly, we found that NFAT1 is required for optimal c-rel up-regulation in response to TCR/CD28 stimulation. In fact, NFAT1 could be detected bound at the c-rel promoter in response to TCR/CD28 stimulation, and targeting of NFAT1 using RNA interference in human CD4(+) T cells abrogated c-rel transcription. Overall, these findings establish that disrupting actin cytoskeletal dynamics impairs TCR/CD28-mediated calcium flux required for NFAT1-mediated c-rel transcription and, thus, activation of the CD28RE/AP.

Despite inhibition of nuclear localization of NF-kappa B p65, c-Rel, and RelB, 17-beta estradiol up-regulates NF-kappa B signaling in mouse splenocytes: the potential role of Bcl-3

NF-kappaB plays a major role in regulating the immune system. Therefore, alterations in NF-kappaB activity have profound effects on many immunopathologies, including inflammation, autoimmunity, and lymphoid neoplasia. We investigated the effects of estrogen (17beta-estradiol) on NF-kappaB in C57BL/6 mice since estrogen is a natural immunomodulator and we have recently reported that estrogen up-regulates several NF-kappaB-regulated proteins (inducible NO synthase, IFN-gamma, and MCP-1). We found that in vivo estrogen treatment had differential effects on NF-kappaB family members. Estrogen profoundly blocked the nuclear translocation of p65, c-Rel, and Rel-B, partially blocked p52, but permitted translocation of p50. Despite blockade of both the classical (p65/p50) and alternative (RelB/p52) NF-kappaB activation pathways, estrogen induced constitutive NF-kappaB activity and increased the levels of cytokines regulated by NF-kappaB (IL-1 alpha, IL-1 beta, IL-10, and IFN-gamma). Studies involving a NF-kappaB inhibitor confirmed a positive regulatory role of NF-kappaB on these cytokines. Remarkably, estrogen selectively induced B cell lymphoma 3 (Bcl-3), which is known to associate with p50 to confer transactivation capabilities, thereby providing a potential link between observed p50 DNA-binding activity and estrogen up-regulation of NF-kappaB transcriptional activity. Chromatin immunoprecipitation assays confirmed that Bcl-3 bound to the promoter of the NF-kappaB-regulated inducible NO synthase gene in cells from estrogen-treated mice. Estrogen appeared to act at the posttranscriptional level to up-regulate Bcl-3 because mRNA levels in splenocytes from placebo- and estrogen-treated mice were comparable. The novel findings of differential regulation of NF-kappaB proteins by estrogen provide fresh insight into potential mechanisms by which estrogen can regulate NF-kappaB-dependent immunological events.

Expression of antimicrobial peptide genes encoding Enbocin and Gloverin isoforms in the silkworm, Bombyx mori

Antimicrobial peptides, Enbocin and Gloverin isoforms from the silkworm Bombyx mori, were analyzed for expression of these peptide genes. Tissue-specific expression of Enbocin and Bmgloverin isoform genes was observed mainly in the fat body upon injection of Escherichia coli. Peptidoglycan and lipopolysaccharide triggered expression of these genes in vivo. On the other hand, lipid A activated Bmgloverin isoform genes but not Enbocin isoform genes. These results illustrate the fact that expression of Enbocin and Bmgloverin isoform genes is inducible by bacteria and that the effects of bacterial cell wall components on the activation of these peptide genes are not necessarily the same. In addition, selective activation of the Enbocin2, Bmgloverin2, and Bmgloverin4 genes by BmRelB rather than BmRelA was observed, providing additional evidence for the occurrence of selective activation of antimicrobial peptide genes by a Rel protein. These results suggest complex regulatory mechanisms in insect antimicrobial peptide genes by bacterial cell wall components.

Normal or stress-induced fibroblast senescence involves COX-2 activity

Cyclooxygenase-2 (COX-2) is an inducible enzyme of the prostaglandin biosynthesis pathway. It is involved in many stress responses, and its activity can produce oxidative damage, suggesting it could participate in senescence. In this study, COX-2 expression is shown to increase during senescence of normal human dermal or prostatic fibroblasts, and the ensuing prostaglandin E(2) (PGE(2)) production to increase about 10-fold. Enhancing this COX-2 activity by supplying exogenous arachidonic acid accelerates the occurrence of the major markers of senescence, cell-size increase, spreading, senescence-associated-beta-galactosidase (SA-beta-Gal) activity and growth plateau. Conversely, blocking this COX-2 activity with the specific inhibitor NS398 partially inhibited the occurrence of these markers. COX-2 expression and PGE(2) production are also increased about 10-fold during both NF-kappaB- or H(2)O(2)-induced senescence. Using NS398 or small interferent RNA specifically targeting COX-2 attenuated the appearance of the SA-beta-Gal activity and growth arrest in both stress situations. Taken together, these findings indicate that COX-2 is highly up-regulated during both normal and stress-induced fibroblast senescence and contributes to the establishment of the senescent characteristics.

TLR stimulation modifies BLyS receptor expression in follicular and marginal zone B cells

Through their differential interactions with B lymphocyte stimulator (BLyS) and a proliferation-inducing ligand (APRIL), the three BLyS family receptors play central roles in B cell survival and differentiation. Recent evidence indicates BLyS receptor levels shift following BCR ligation, suggesting that activation cues can alter overall BLyS receptor profiles and thus ligand sensitivity. In this study, we show that TLR stimuli also alter BLyS receptor expression, but in contrast to BCR ligation, TLR9 and TLR4 signals, preferentially increase transmembrane activator calcium modulator and cyclophilin ligand interactor (TACI) expression. Although both of these TLRs act through MyD88-dependent mechanisms to increase TACI expression, they differ in terms of their downstream mediators and the B cell subset affected. Surprisingly, only TLR4 relies on c-Rel and p50 to augment TACI expression, whereas TLR9 does not. Furthermore, although all follicular and marginal zone B cells up-regulate TACI in response to TLR9 stimulation, only marginal zone B cells and a subset of follicular B cells respond to TLR4. Finally, we find that both BLyS and APRIL enhance viability among quiescent and BCR-stimulated B cells. However, although BLyS enhances viability among TLR stimulated B cells, APRIL does not, suggesting that TACI but not BLyS receptor 3 may share survival promoting pathways with TLRs.

MALT1 directs B cell receptor-induced canonical nuclear factor-kappaB signaling selectively to the c-Rel subunit

NF-kappaB (Rel) transcription factors control physiological and pathological immune cell function. The scaffold proteins Bcl-10 and MALT1 couple antigen-receptor signals to the canonical NF-kappaB pathway and are pivotal in lymphomagenesis. Here we found that Bcl-10 and MALT1 differentially regulated B cell receptor-induced activation of RelA and c-Rel. Bcl-10 was essential for recruitment of the kinase IKK into lipid rafts for the activation of RelA and c-Rel, for blocking apoptosis and for inducing division after B cell receptor ligation. In contrast, MALT1 participated in survival signaling but was not involved in IKK recruitment or activation and was dispensable for RelA induction and proliferation. MALT1 selectively activated c-Rel to control a distinct subprogram. Our results provide mechanistic insights into B cell receptor-induced survival and proliferation signals and demonstrate the selective control of c-Rel in the canonical NF-kappaB pathway.

Leptin induces tissue factor expression in human peripheral blood mononuclear cells: a possible link between obesity and cardiovascular risk?

BACKGROUND

Obesity is a major modifiable risk factor for cardiovascular disease. Leptin, the hormone synthesized and released primarily by adipose tissue and found increased in obese individuals, has been implicated in the regulation of inflammation and arterial and venous thrombosis.

OBJECTIVE

To investigate the role of tissue factor (TF), the pivotal agonist of the clotting cascade, as a link between obesity and cardiovascular disease.

METHODS AND RESULTS

In 15 obese patients, plasma levels of leptin and TF as well as TF expression in resting and endotoxin-stimulated mononuclear leukocytes (MN) were increased when compared with healthy donors. In a selected sample of obese patients, loss of body weight led to decreased circulating leptin levels, accompanied by a reduction in plasma TF as well as in TF expression, both in resting and endotoxin-stimulated MN. In subsequent in vitro experiments, leptin was incubated with MN from healthy subjects. Leptin induced TF activity and antigen in a dose-dependent fashion, as assessed by clotting assay and ELISA, respectively. Increased migration of c-Rel/p65 into the nucleus, as determined by EMSA, and development of TF mRNA in monocytes, as assessed by RT-PCR, were observed. Experiments with mitogen-activated protein kinase (MAPK) inhibitors, indicated the involvement of p38 and ERK1/2 pathways.

CONCLUSIONS

The presence of TF-expressing MN in blood from obese subjects and the in vitro induction of TF by pharmacologic concentrations of leptin in MN from healthy subjects suggest that TF expression by leptin-stimulated monocytes may contribute to the cardiovascular risk associated with obesity.

Genome-Wide Analysis of Gene Expression in T Cells to Identify Targets of the NF-κB Transcription Factor c-Rel

It is well established that the NF-kappaB family of transcription factors serves a major role in controlling gene expression in response to T cell activation, but the genome-wide roles of individual family members remain to be determined. c-Rel, a member of the NF-kappaB family, appears to play a specific role in T cell function because T cells from c-Rel(-/-) animals are defective in their response to immune signals. We have used expression profiling to identify sets of genes that are affected by either deletion or overexpression of c-Rel in T cells. Very few of these genes exhibit a strong requirement for c-Rel; rather, c-Rel appears to modulate the expression of a large number of genes in these cells. The sets of c-Rel-affected genes are significantly enriched for genes containing consensus NF-kappaB/Rel sites in their proximal promoter regions. In addition, their promoters contain a higher average density of NF-kappaB/Rel sites compared with all genes represented on the microarrays. A transcriptional module comprised of two closely spaced c-Rel consensus sites is found with higher frequency in the c-Rel-affected gene sets and may represent an important control module for genes regulated by c-Rel or other NF-kappaB family members. We confirmed the importance of these findings on a subgroup of genes by using quantitative PCR to monitor gene expression as well as in vitro c-Rel/DNA binding assays and luciferase reporter assays. The c-Rel-regulated genes identified here support a role for c-Rel in inflammatory responses as well as in the promotion of cell growth and survival.

Cutting Edge: TFII-I controls B cell proliferation via regulating NF-kappaB

The multifunctional transcription factor TFII-I physically and functionally interacts with Bruton's tyrosine kinase in murine B cells. However, the downstream functions of TFII-I in B cells are unknown. Toward achieving this goal, we established stable posttranscriptional silencing of TFII-I in WEHI-231 immature murine B cells, which undergoes growth arrest and apoptosis either upon anti-IgM or TGF-beta signaling. In this study, we show that TFII-I promotes growth arrest of cells in a signal-dependent manner. Unlike control cells, B cells exhibiting loss of TFII-I function fail to undergo arrest upon signaling due to up-regulation of c-Myc expression and concomitant down-regulation of both p21 and p27. Loss of TFII-I is also associated with simultaneous increase in nuclear c-rel and decrease in p50 homodimer binding. Thus, besides controlling c-myc transcription, TFII-I controls B cell proliferation by regulating both nuclear translocation of c-rel and DNA-binding activity of p50 NF-kappaB.