Expression of relB transcripts during lymphoid organ development: specific expression in dendritic antigen-presenting cells

Critical and distinct roles of cell type-specific NF-κB2 in lung cancer

Different from the well-studied canonical NF-κB member RelA, the role of the noncanonical NF-κB member NF-κB2 in solid tumors, and lung cancer in particular, is poorly understood. Here we report that in contrast to the tumor-promoting role of RelA, NF-κB2 intrinsic to lung epithelial and tumor cells had no marked effect on lung tumorigenesis and progression. On the other hand, NF-κB2 limited dendritic cell number and activation in the lung but protected lung macrophages and drove them to promote lung cancer through controlling activation of noncanonical and canonical NF-κB, respectively. NF-κB2 was also required for B cell maintenance and T cell activation. The antitumor activity of lymphocyte NF-κB2 was dominated by the protumor function of myeloid NF-κB2; thus, NF-κB2 has an overall tumor-promoting activity. These studies reveal a cell type-dependent role for NF-κB2 in lung cancer and help understand the complexity of NF-κB action and lung cancer pathogenesis for better design of NF-κB-targeted therapy against this deadliest cancer.

RelB and Neuroinflammation

Neuroinflammation within the central nervous system involves multiple cell types that coordinate their responses by secreting and responding to a plethora of inflammatory mediators. These factors activate multiple signaling cascades to orchestrate initial inflammatory response and subsequent resolution. Activation of NF-κB pathways in several cell types is critical during neuroinflammation. In contrast to the well-studied role of p65 NF-κB during neuroinflammation, the mechanisms of RelB activation in specific cell types and its roles during neuroinflammatory response are less understood. In this review, we summarize the mechanisms of RelB activation in specific cell types of the CNS and the specialized effects this transcription factor exerts during neuroinflammation.

Cellular Specificity of NF-κB Function in the Nervous System

Nuclear Factor Kappa B (NF-κB) is a ubiquitously expressed transcription factor with key functions in a wide array of biological systems. While the role of NF-κB in processes, such as host immunity and oncogenesis has been more clearly defined, an understanding of the basic functions of NF-κB in the nervous system has lagged behind. The vast cell-type heterogeneity within the central nervous system (CNS) and the interplay between cell-type specific roles of NF-κB contributes to the complexity of understanding NF-κB functions in the brain. In this review, we will focus on the emerging understanding of cell-autonomous regulation of NF-κB signaling as well as the non-cell-autonomous functional impacts of NF-κB activation in the mammalian nervous system. We will focus on recent work which is unlocking the pleiotropic roles of NF-κB in neurons and glial cells (including astrocytes and microglia). Normal physiology as well as disorders of the CNS in which NF-κB signaling has been implicated will be discussed with reference to the lens of cell-type specific responses.

RelB-Deficient Dendritic Cells Promote the Development of Spontaneous Allergic Airway Inflammation

RelB is a member of the NF-κB family, which is essential for dendritic cell (DC) function and maturation. However, the contribution of RelB to the development of allergic airway inflammation (AAI) is unknown. Here, we identify a pivotal role for RelB in the development of spontaneous AAI that is independent of exogenous allergen exposure. We assessed AAI in two strains of RelB-deficient (RelB^-/-) mice: one with a targeted deletion and one expressing a major histocompatibility complex transgene. To determine the importance of RelB in DCs, RelB-sufficient DCs (RelB^+/+ or RelB^-/-) were adoptively transferred into RelB^-/- mice. Both strains had increased pulmonary inflammation compared with their respective wild-type (RelB^+/+) and heterozygous (RelB^+/-) controls. RelB^-/- mice also had increased inflammatory cell influx into the airways, levels of chemokines (CCL2/3/4/5/11/17 and CXCL9/10/13) and T-helper cell type 2-associated cytokines (IL-4/5) in lung tissues, serum IgE, and airway remodeling (mucus-secreting cell numbers, collagen deposition, and epithelial thickening). Transfer of RelB^+/- CD11c⁺ DCs into RelB^-/- mice decreased pulmonary inflammation, with reductions in lung chemokines, T-helper cell type 2-associated cytokines (IL-4/5/13/25/33 and thymic stromal lymphopoietin), serum IgE, type 2 innate lymphoid cells, myeloid DCs, γδ T cells, lung Vβ13⁺ T cells, mucus-secreting cells, airway collagen deposition, and epithelial thickening. These data indicate that RelB deficiency may be a key pathway underlying AAI, and that DC-encoded RelB is sufficient to restore control of this inflammation.

Phytosterols Synergize With Endotoxin to Augment Inflammation in Kupffer Cells but Alone Have Limited Direct Effect on Hepatocytes

INTRODUCTION

Phytosterols are implicated in the development of parenteral nutrition-associated liver disease. A newly proposed mechanism for phytosterol-mediated parenteral nutrition-associated liver disease is through phytosterol-facilitated hepatic proinflammatory cytokine release following exposure to intestinally derived bacteria. Whether the proinflammatory effects are liver cell specific is not known.

AIM

To determine if phytosterols cause inflammation in hepatocytes or Kupffer cells independently or require costimulation by lipopolysaccharide (LPS).

METHODS

In an in vivo study, neonatal piglets on parenteral nutrition for 11 days received an 8-hour infusion of LPS. In the in vitro studies, neonatal piglet Kupffer cells and hepatocytes were treated with media, media + 1% soy oil, or media + 1% soy oil + 100µM phytosterols. After 24-hour incubation, cells were treated with farnesoid X receptor (FXR) agonist obeticholic acid or liver X receptor (LXR) agonist GW3965 and challenged with LPS or interleukin 1β.

RESULTS

LPS administration in piglets led to transient increases in proinflammatory cytokines and suppression of the transporters bile salt export pump and ATP-binding cassette transporter G5. In hepatocytes, phytosterols did not activate inflammation. Phytosterol treatment alone did not activate inflammation in Kupffer cells but, combined with LPS, synergistically increased interleukin 1β production. FXR and LXR agonists increased transporter expression in hepatocytes. GW3965 suppressed proinflammatory cytokine production in Kupffer cells, but obeticholic acid did not.

CONCLUSIONS

LPS suppresses transporters that control bile acid and phytosterol clearance. Phytosterols alone do not cause inflammatory response. However, with costimulation by LPS, phytosterols synergistically maximize the inflammatory response in Kupffer cells.

Rel B-modified dendritic cells possess tolerogenic phenotype and functions on lupus splenic lymphocytes in vitro

Systemic lupus erythematosus (SLE) is an autoimmune disease that is characterized by high morbidity and mortality and its treatment remains challenging. Dendritic cells (DCs) have been shown to participate in the initiation and perpetuation of lupus pathogenesis and the DCs that can induce tolerogenicity appear as potential cell‐based therapy in this condition. In this study, we examined the in vitro tolerogenic properties of bone‐marrow derived DCs (BMDCs) in the murine lupus setting. We used lentiviral transduction of RelB‐silencing short hairpin RNA to modify the expression of RelB, a key transcription factor regulating DC maturation, in BMDCs from MRL/MpJ mice. Tolerogenic properties of RelB‐modified DCs were compared with scrambled control (SC) ‐modified DCs. RelB expression was found to be significantly reduced in RelB‐modified DCs derived from MRL/MpJ mice, wild‐type of the same genetic background as MRL/lpr lupus‐prone mice. These MRL/MpJ RelB‐modified DCs displayed semi‐mature phenotype with expression of lower levels of co‐stimulatory molecules compared with SC‐modified DCs. RelB‐modified DCs were found to be low producers of interleukin‐12p70 (IL‐12p70) and could induce hyporesponsiveness of splenic T cells from MRL/MpJ and MRL/lpr mice. Furthermore, they down‐regulated interferon‐γ expression and induced IL‐10‐producing T cells in MRL/MpJ splenocytes, and attenuated interferon‐γ and IL‐17 expression in MRL/lpr splenic CD4⁺ lymphocytes. Splenocytes primed by RelB‐modified DCs demonstrated antigen‐specific suppressive effects on allogeneic splenocytes. In conclusion, RelB‐silencing in DCs generates DCs of tolerogenic properties with immunomodulatory function and appears as potential option of cell‐targeted therapy.

Deficiency of transcription factor RelB perturbs myeloid and DC development by hematopoietic-extrinsic mechanisms

RelB is an NF-κB family transcription factor activated in the noncanonical pathway downstream of NF-κB-inducing kinase (NIK) and TNF receptor family members including lymphotoxin-β receptor (LTβR) and CD40. Early analysis suggested that RelB is required for classical dendritic cell (cDC) development based on a severe reduction of cDCs in Relb-/- mice associated with profound myeloid expansion and perturbations in B and T cells. Subsequent analysis of radiation chimeras generated from wild-type and Relb-/- bone marrow showed that RelB exerts cell-extrinsic actions on some lineages, but it has remained unclear whether the impact of RelB on cDC development is cell-intrinsic or -extrinsic. Here, we reevaluated the role of RelB in cDC and myeloid development using a series of radiation chimeras. We found that there was no cell-intrinsic requirement for RelB for development of most cDC subsets, except for the Notch2- and LTβR-dependent subset of splenic CD4+ cDC2s. These results identify a relatively restricted role of RelB in DC development. Moreover, the myeloid expansion in Relb-/- mice resulted from hematopoietic-extrinsic actions of RelB. This result suggests that there is an unrecognized but critical role for RelB within the nonhematopoietic niche that controls normal myelopoiesis.

Bortezomib for the prevention and treatment of graft-versus-host disease after allogeneic hematopoietic stem cell transplantation

Allogeneic hematopoietic stem cell transplantation is the standard treatment for a variety of benign and malignant conditions. However, graft-versus-host disease (GvHD) continues to present a major barrier to the success and wide applicability of this procedure. Although current GvHD prevention and treatment regimens exclusively target T cells, bortezomib, a reversible proteasome inhibitor, possesses unique immune regulatory activities that span a wide variety of cellular processes of T and dendritic cells essential for the development of GvHD. Herein, we review the current understanding of the effects of bortezomib in vitro and in animal models and summarize the clinical data relevant to its use in the prevention and treatment of GvHD. We conclude with an outline of the remaining challenges and opportunities to optimize bortezomib's potential role in this setting.

Club Cell-16 and RelB as Novel Determinants of Arterial Stiffness in Exacerbating COPD Patients

Background

Exacerbations of chronic obstructive pulmonary disease (COPD) are acute events of worsened respiratory symptoms that may increase the risk of cardiovascular disease (CVD), a leading cause of mortality amongst COPD patients. The utility of lung-specific inflammatory mediators such as club cell protein-16 (CC-16) and surfactant protein D (SPD) and that of a novel marker of CV outcomes in COPD- RelB- in predicting adverse cardiovascular events during exacerbation is not known.

Methods

Thirty-eight subjects with COPD admitted to the hospital for severe exacerbation were included in this analysis. Clinical, physiological and arterial stiffness measurements were performed within 72 hours of admission; this was followed by measurements taken every 3 days until hospital discharge, then once a week until 30 days after discharge, and then again at 90 and 180 days. Plasma concentrations of inflammatory mediators were measured from peripheral venous blood taken at admission, and at days 15, 30, 90 and 180.

Results

CC-16 and RelB concentrations were increased at day 15 of exacerbations whereas SPD concentrations were decreased. The course of change in CC-16 and RelB levels over time was inversely associated with that of carotid-femoral pulse wave velocity, the gold-standard measure of arterial stiffness. Increases in CC-16 could predict a decreased number of subsequent exacerbations during follow-up.

Conclusions

Lung-specific (CC-16) and novel (RelB) biomarkers are associated with systemic cardiovascular changes over time. CC-16 can predict subsequent exacerbations in subjects with severe COPD and may be an important biomarker of pulmonary and systemic stress in COPD.

Visualization of RelB expression and activation at the single-cell level during dendritic cell maturation in Relb-Venus knock-in mice

RelB is activated by the non-canonical NF-κB pathway, which is crucial for immunity by establishing lymphoid organogenesis and B-cell and dendritic cell (DC) maturation. To elucidate the mechanism of the RelB-mediated immune cell maturation, a precise understanding of the relationship between cell maturation and RelB expression and activation at the single-cell level is required. Therefore, we generated knock-in mice expressing a fusion protein between RelB and fluorescent protein (RelB-Venus) from the Relb locus. The Relb(Venus/Venus) mice developed without any abnormalities observed in the Relb(-/-) mice, allowing us to monitor RelB-Venus expression and nuclear localization as RelB expression and activation. Relb(Venus/Venus) DC analyses revealed that DCs consist of RelB(-), RelB(low) and RelB(high) populations. The RelB(high) population, which included mature DCs with projections, displayed RelB nuclear localization, whereas RelB in the RelB(low) population was in the cytoplasm. Although both the RelB(low) and RelB(-) populations barely showed projections, MHC II and co-stimulatory molecule expression were higher in the RelB(low) than in the RelB(-) splenic conventional DCs. Taken together, our results identify the RelB(low) population as a possible novel intermediate maturation stage of cDCs and the Relb(Venus/Venus) mice as a useful tool to analyse the dynamic regulation of the non-canonical NF-κB pathway.

Alterations in the expression of the NF-κB family member RelB as a novel marker of cardiovascular outcomes during acute exacerbations of chronic obstructive pulmonary disease

BACKGROUND

Chronic obstructive pulmonary disease (COPD) exacerbations are acute events of worsened respiratory symptoms and enhanced inflammation partly mediated by NF-κB activation. RelB, an NF-κB family member, suppresses cigarette smoke-induced inflammation but its expression in COPD is unknown. Moreover, there is no information on its association with clinical features of COPD. The objectives of this study were to assess RelB expression relative to markers of inflammation as well as its association with cardiovascular and pulmonary features of COPD patients at stable-state and exacerbation.

METHODS

Data from 48 COPD patients were analyzed. Blood samples were collected from stable-state and exacerbating patients. After RNA isolation, quantitative real-time polymerase chain reaction (qRT-PCR) was performed to assess RelB, Cox-2, IL-8 and IL-1β mRNA expression and their associations with measured clinical variables.

RESULTS

Of the 48 COPD subjects, 18 were in stable-state and 30 were in exacerbation. RelB mRNA expression was lower than that of Cox-2, IL-8, and IL-1β in all cases (all p<0.001, except for IL-8 at exacerbation (p = 0.22)). Cox-2, IL-8 and IL-1β were significantly associated with clinical features of patients in both stable-state and at exacerbation. There was no association with RelB expression and any clinical features in COPD subjects at stable-state. RelB mRNA levels were significantly associated with cardiovascular events such as systolic blood pressure during exacerbation.

CONCLUSIONS

RelB mRNA expression is lower than that of the other inflammatory mediators. Expression of Cox-2, IL-8 and IL-1β were related to clinical features in both stable-state and at exacerbation. However, RelB expression was associated with clinical features of patients only during exacerbation, suggesting that RelB may represent a novel marker of health outcomes, in particular cardiovascular, during exacerbation in COPD.

Tumor-induced STAT3 signaling in myeloid cells impairs dendritic cell generation by decreasing PKCβII abundance

A major mechanism by which cancers escape control by the immune system is by blocking the differentiation of myeloid cells into dendritic cells (DCs), immunostimulatory cells that activate antitumor T cells. Tumor-dependent activation of signal transducer and activator of transcription 3 (STAT3) signaling in myeloid progenitor cells is thought to cause this block in their differentiation. In addition, a signaling pathway through protein kinase C βII (PKCβII) is essential for the differentiation of myeloid cells into DCs. We found in humans and mice that breast cancer cells substantially decreased the abundance of PKCβII in myeloid progenitor cells through a mechanism involving the enhanced activation of STAT3 signaling by soluble, tumor-derived factors (TDFs). STAT3 bound to previously undescribed negative regulatory elements within the promoter of PRKCB, which encodes PKCβII. We also found a previously undescribed counter-regulatory mechanism through which the activity of PKCβII inhibited tumor-dependent STAT3 signaling by decreasing the abundance of cell surface receptors, such as cytokine and growth factor receptors, that are activated by TDFs. Together, these data suggest that a previously unrecognized cross-talk mechanism between the STAT3 and PKCβII signaling pathways provides the molecular basis for the tumor-induced blockade in the differentiation of myeloid cells, and suggest that enhancing PKCβII activity may be a therapeutic strategy to alleviate cancer-mediated suppression of the immune system.

RelB: an outlier in leukocyte biology

RelB is one of the more unusual members of the NF-κB family. This family, arguably the best known group of transcription regulators, regulates an astonishing array of cell types and biological processes. This includes regulation of cell growth, differentiation and death by apoptosis, and the development and function of the innate and adaptive-immune system. RelB is best known for its roles in lymphoid development, DC biology, and noncanonical signaling. Within the last few years, however, surprising functions of RelB have emerged. The N-terminal leucine zipper motif of RelB, a motif unique among the NF-κB family, may associate with more diverse DNA sequences than other NF-κB members. RelB is capable of direct binding to the AhR that supports the xenobiotic-detoxifying pathway. RelB can regulate the circadian rhythm by directly binding to the BMAL partner of CLOCK. Finally, RelB also couples with bioenergy NAD(+) sensor SIRT1 to integrate acute inflammation with changes in metabolism and mitochondrial bioenergetics. In this review, we will explore these unique aspects of RelB, specifically with regard to its role in immunity.

Control of RelB during dendritic cell activation integrates canonical and noncanonical NF-κB pathways

The NF-κB protein RelB controls dendritic cell (DC) maturation and may be targeted therapeutically to manipulate T cell responses in disease. Here we report that RelB promoted DC activation not as the expected RelB-p52 effector of the non-canonical NF-κB pathway, but as a RelB-p50 dimer regulated by canonical IκBs, IκBα and IκBε. IκB control of RelB minimized spontaneous maturation but enabled rapid pathogen-responsive maturation. Computational modeling of the NF-κB signaling module identified control points of this unexpected cell-type-specific regulation. Fibroblasts that were engineered accordingly showed DC-like RelB control. Canonical pathway control of RelB regulated pathogen-responsive gene expression programs. This work illustrates the potential utility of systems analyses in guiding the development of combination therapeutics for modulating DC-dependent T cell responses.

Steady state migratory RelB+ langerin+ dermal dendritic cells mediate peripheral induction of antigen-specific CD4+ CD25+ Foxp3+ regulatory T cells

Tolerance to self-antigens expressed in peripheral organs is maintained by CD4(+) CD25(+) Foxp3(+) Treg cells, which are generated as a result of thymic selection or peripheral induction. Here, we demonstrate that steady-state migratory DCs from the skin mediated Treg conversion in draining lymph nodes of mice. These DCs displayed a partially mature MHC II(int) CD86(int) CD40(hi) CCR7(+) phenotype, used endogenous TGF-β for conversion and showed nuclear RelB translocation. Deficiency of the alternative NF-κB signaling pathway (RelB/p52) reduced steady-state migration of DCs. These DCs transported and directly presented soluble OVA provided by s.c. implanted osmotic minipumps, as well as cell-associated epidermal OVA in transgenic K5-mOVA mice to CD4(+) OVA-specific TCR-transgenic OT-II T cells. The langerin(+) dermal DC subset, but not epidermal Langerhans cells, mediated conversion of naive OT-II×RAG-1(-/-) T cells into proliferating CD4(+) CD25(+) Foxp3(+) Tregs. Thus, our data suggest that steady-state migratory RelB(+) TGF-β(+) langerin(+) dermal DCs mediate peripheral Treg conversion in response to epidermal antigen in skin-draining lymph nodes.

A single NFκB system for both canonical and non-canonical signaling

Two distinct nuclear factor κB (NFκB) signaling pathways have been described; the canonical pathway that mediates inflammatory responses, and the non-canonical pathway that is involved in immune cell differentiation and maturation and secondary lymphoid organogenesis. The former is dependent on the IκB kinase adaptor molecule NEMO, the latter is independent of it. Here, we review the molecular mechanisms of regulation in each signaling axis and attempt to relate the apparent regulatory logic to the physiological function. Further, we review the recent evidence for extensive cross-regulation between these two signaling axes and summarize them in a wiring diagram. These observations suggest that NEMO-dependent and -independent signaling should be viewed within the context of a single NFκB signaling system, which mediates signaling from both inflammatory and organogenic stimuli in an integrated manner. As in other regulatory biological systems, a systems approach including mathematical models that include quantitative and kinetic information will be necessary to characterize the network properties that mediate physiological function, and that may break down to cause or contribute to pathology.

Redox control in mammalian embryo development

The development of an embryo constitutes a complex choreography of regulatory events that underlies precise temporal and spatial control. Throughout this process the embryo encounters ever changing environments, which challenge its metabolism. Oxygen is required for embryogenesis but it also poses a potential hazard via formation of reactive oxygen and reactive nitrogen species (ROS/RNS). These metabolites are capable of modifying macromolecules (lipids, proteins, nucleic acids) and altering their biological functions. On one hand, such modifications may have deleterious consequences and must be counteracted by antioxidant defense systems. On the other hand, ROS/RNS function as essential signal transducers regulating the cellular phenotype. In this context the combined maternal/embryonic redox homeostasis is of major importance and dysregulations in the equilibrium of pro- and antioxidative processes retard embryo development, leading to organ malformation and embryo lethality. Silencing the in vivo expression of pro- and antioxidative enzymes provided deeper insights into the role of the embryonic redox equilibrium. Moreover, novel mechanisms linking the cellular redox homeostasis to gene expression regulation have recently been discovered (oxygen sensing DNA demethylases and protein phosphatases, redox-sensitive microRNAs and transcription factors, moonlighting enzymes of the cellular redox homeostasis) and their contribution to embryo development is critically reviewed.

Transcriptional regulation of thymus organogenesis and thymic epithelial cell differentiation

Transcriptional regulatory networks are the central regulatory mechanisms that control organ identity, patterning, and differentiation. In the case of the thymus, several key transcription factors have been identified that are critical for various aspects of thymus organogenesis and thymic epithelial cell (TEC) differentiation. The thymus forms from the third pharyngeal pouch endoderm during embryogenesis. Organ development progresses from initial thymus cell fate specification, through multiple stages of TEC differentiation and cortical (cTEC) and medullary (mTEC) formation. Transcription factors have been identified for each of these stages: a Hoxa3-dependent cascade at initial fate specification, Foxn1 for early (and later) TEC differentiation, and NF-kappaB for mTEC differentiation. As important as these factors are, their interrelationships are not understood, and many more transcription factors are likely required for complete thymus organogenesis to occur. In this chapter, we review the literature on these known genes, as well as identify gaps in our knowledge for future studies.

Signal transduction involving the dmp1 transcription factor and its alteration in human cancer

Dmp1 (cyclin D-interacting myb-like protein 1; also called Dmtf1) is a transcription factor that has been isolated in a yeast two-hybrid screen through its binding property to cyclin D2. Dmp1 directly binds to and activates the Arf promoter and induces Arf-p53-dependent cell cycle arrest in primary cells. D-type cyclins usually inhibit Dmp1-mediated transcription in a Cdk-independent fashion; however, Dmp1 shows synergistic effects with D-cyclins on the Arf promoter. Ras or Myc oncogene-induced tumor formation is accelerated in both Dmp1^+/− and Dmp1^−/− mice with no significant differences between Dmp1^+/− and Dmp1^−/−. Thus, Dmp1 is haplo-insufficient for tumor suppression. Tumors from Dmp1^−/− or Dmp1^+/− mice often retain wild-type Arf and p53, suggesting that Dmp1 is a physiological regulator of the Arf-p53 pathway. The Dmp1 promoter is activated by oncogenic Ras-Raf signaling, while it is repressed by physiological mitogenic stimuli, overexpression of E2F proteins, and genotoxic stimuli mediated by NF-κB. The human DMP1 gene (hDMP1) is located on chromosome 7q21 and is hemizygously deleted in approximately 40% of human lung cancers, especially those that retain normal INK4a/ARF and P53 loci. Thus, hDMP1 is clearly involved in human carcinogenesis, and tumors with hDMP1 deletion may constitute a discrete disease entity.

The presence of capsule in Cryptococcus neoformans influences the gene expression profile in dendritic cells during interaction with the fungus

The aim of this investigation was to study the effect of polysaccharide capsule on the gene expression in dendritic cells (DC) during their interaction with Cryptococcus neoformans. To this end, we used an encapsulated virulent strain of C. neoformans and a cap59 gene-disrupted acapsular avirulent strain derived from the same genetic background. DC were exposed to encapsulated and acapsular C. neoformans strains for 4 h and 18 h, and their transcriptional profiles were analyzed using the Affymetrix mouse gene chip U74Av2. A large number of DC genes were up-regulated after treatment with the acapsular strain. In particular, we observed the up-regulation of the genes involved in DC maturation, such as cell surface receptors, cytokines, and chemokines (interleukin-12 [IL-12], IL-2, IL-1alpha, IL-1beta, IL-6, IL-10, tumor necrosis factor alpha, CCR7, CCL17, CCL22, CCL3, CCL4, CCL7, and CXCL10), membrane proteins, and the genes involved in antigen processing and presentation as well as cell cycle or apoptosis. The chemokine gene expression data were confirmed by real-time reverse transcription-PCR, while the expression of cytokine genes was correlated with their secretion. A completely different pattern of gene expression was observed for DC treated with an encapsulated strain of C. neoformans. In particular, no significant induction was observed in the expression of the genes mentioned above. Moreover, a number of genes, such as those coding for chemokines, were down-regulated. These results suggest that the polysaccharide capsule shrouding the cell wall of C. neoformans plays a fundamental role in inducing DC response, highlighting the molecular basis of the true nature of immune silencing exerted by capsular material.

Vitamin D receptor-mediated suppression of RelB in antigen presenting cells: a paradigm for ligand-augmented negative transcriptional regulation

The immunological effects of vitamin D receptor (VDR) ligands include inhibition of dendritic cell (DC) maturation, suppression of T-helper type 1 (Th1) T-cell responses and facilitation of antigen-specific immune tolerance in vivo. While studying the molecular profile of DCs cultured in the presence of 1alpha,25(OH)D3 or synthetic D3 analogs we observed that expression of the NF-kappaB family member RelB, which plays an essential role in DC differentiation and maturation, is selectively suppressed by VDR ligands. Further in vitro and in vivo studies of VDR-mediated RelB suppression indicated that the mechanism for this effect involves direct binding of VDR/RXR alpha to a defined region of the relB promoter and assembly of a negative regulatory complex containing HDAC3, HDAC1, SMRT and, most likely, other factors. Interestingly, promoter engagement by VDR and HDAC3, but not the other identified components, is enhanced by addition of a VDR ligand and inhibited by a pro-maturational stimulus (LPS) that results in RelB upregulation. Promoter assays in a panel of cell lines suggest that the VDR ligand-dependent component of relB suppression may occur selectively in antigen presenting cells. Cell type-specific, ligand-enhanced negative transcriptional regulation represents a potentially novel paradigm for VDR-controlled genes. In this report we review the experimental data to support such a mechanism for relB regulation in DCs and present a model for the process.

The role and regulation of the nuclear factor kappa B signalling pathway in human labour

Within the discipline of reproductive biology, our understanding of one of the most fundamental biological processes is lacking--the cellular and molecular mechanisms that govern birth. This lack of understanding limits our ability to reduce the incidence of labour complications. The incidence of labour complications including: preterm labour; cervical incompetence; and post-date pregnancies has not diminished in decades. The key to improving the management of human labour and delivery is an understanding of how the multiple processes that are requisite for a successful labour and delivery are coordinated to achieve a timely birth. Processes of human labour include the formation of: contraction associated proteins; inflammatory mediators (e.g. cytokines); uterotonic phospholipid metabolites (e.g. prostaglandins); and the induction of extracellular matrix (ECM) remodelling. Increasingly, it is becoming evident that labour onset and birth are the result of cross-talk between multiple components of an integrated network. This hypothesis is supported by recent data implicating various upstream regulatory pathways in the control of key labour-associated processes, including the activity of enzymes involved in the formation of prostaglandins and extracellular matrix remodelling, and mediators of inflammation. Clearly, the biochemical pathways involved in the formation of these mediators represent potential sites for intervention that may translate to therapeutic interventions to delay or prevent preterm labour and delivery. Available data strongly implicate the nuclear factor-kappaB (NF-kappaB) family as candidate upstream regulators of multiple labour-associated processes. Not only do these data warrant further detailed analysis of the involvement of these pathways in the process of human labour but also promise new insights into the key mechanisms that trigger birth and the identification of new therapeutic interventions that will improve the management of labour.

Regulation of RelB expression during the initiation of dendritic cell differentiation

The transcription factor RelB is required for proper development and function of dendritic cells (DCs), and its expression is upregulated early during differentiation from a variety of progenitors. We explored this mechanism of upregulation in the KG1 cell line model of a DC progenitor and in the differentiation-resistant KG1a subline. RelB expression is relatively higher in untreated KG1a cells but is upregulated only during differentiation of KG1 by an early enhancement of transcriptional elongation, followed by an increase in transcription initiation. Restoration of protein kinase CbetaII (PKCbetaII) expression in KG1a cells allows them to differentiate into DCs. We show that PKCbetaII also downregulated constitutive expression of NF-kappaB in KG1a-transfected cells and restores the upregulation of RelB during differentiation by increased transcriptional initiation and elongation. The two mechanisms are independent and sensitive to PKC signaling levels. Conversely, RelB upregulation was inhibited in primary human monocytes where PKCbetaII expression was knocked down by small interfering RNA targeting. Altogether, the data show that RelB expression during DC differentiation is controlled by PKCbetaII-mediated regulation of transcriptional initiation and elongation.

Transcriptional control of B cell activation

The developmental program that commits a hematopoietic stem cell to the B lymphocyte lineage employs transcriptional regulators to enable the assembly of an antigen receptor complex with a useful specificity and with signalling competence. Once a naive IgM+ B cell is generated, it must correctly integrate signals from the antigen receptor with those from cytokine receptors and co-receptors delivering T cell help. The B cell responds through the regulated expression of genes that implement specific cell expansion and differentiation, secretion of high levels of high-affinity antibody, and generation of long-term memory. The transcriptional regulators highlighted in this chapter are those for which genetic evidence of function in IgM+ B cells in vivo has been provided, often in the form of mutant mice generated by conventional or conditional gene targeting. A critical developmental step is the maturation of bone marrow emigrant "transitional" B cells into the mature, long-lived cells of the periphery, and a number of the transcription factors discussed here impact on this process, yielding B cells with poor mitogenic responses in vitro. For mature B cells, it is clear that not only the nature, but the duration and amplitude of an activating signal are major determinants of the transcription factor activities enlisted, and so the ultimate outcome. The current challenge is the identification of the target genes that are activated to implement the correct response, so that we may more precisely and safely manipulate B cell behavior to predictably and positively influence humoral immune responses.

Resveratrol inhibits phenotypic and functional maturation of murine bone marrow-derived dendritic cells

This study investigated the effects of resveratrol, a natural polyphenol found in grapes and grape products such as wine and having a wide range of biological and pharmacological activities effecting on the phenotypic and functional maturation of bone marrow (BM)-derived dendritic cells (DC). Resveratrol inhibited the expression of costimulatory molecules (CD80 and CD86), and major histocompatibility complex (MHC) classes I and II significantly, and had the same effect dose-dependently on DC. Resveratrol also significantly suppressed the ability of BM-DC to produce intracellular IL-12 p40/p70 and secretory IL-12 p70 in response to lipopolysaccharides (LPS) stimulation. Resveratrol-treated DC were highly efficient in antigen capture via mannose receptor-mediated endocytosis. Also, they were poor stimulators of naïve allogeneic T-cell proliferation and induced lower levels of IL-2 in responding T cells. These results indicate the immunosuppressive properties of resveratrol, which may be therapeutically useful in controlling chronic immune and/or inflammatory diseases through the down-regulation of DC differentiation and maturation.

RelB regulates human dendritic cell subset development by promoting monocyte intermediates

In humans, epithelial Langerhans cells (LCs) and monocyte-derived/interstitial dendritic cells (DCs) constitute 2 myeloid DC sublineages. Molecular mechanisms involved in their development from common myeloid progenitors remain poorly defined. Here we demonstrate that the nuclear factor-κB (NF-κB) transcription factor RelB regulates the generation of monocytic CD14+CD11b+ precursors of interstitial DCs from human hematopoietic progenitors. RelB overexpression promoted, whereas endogenous RelB inhibition (by p100ΔN) blocked, precursor cell development along this DC subset pathway. RelB inhibition specifically arrested precursor progression from CD14loCD11b- to CD14+CD11b+ stages. Precursors were still capable of LC and granulocyte differentiation but were defective in macrophage–colony-stimulating factor (M-CSF)–dependent monocyte/macrophage differentiation. RelB inhibition markedly differed from classical NF-κB signaling inhibition because IκBα superrepressor (IκBα-SR), but not p100ΔN, impaired LC/DC differentiation, DC adhesion, and progenitor cell proliferation. Although RelB up-regulation and nuclear translocation are regarded as hallmarks of human myeloid DC maturation, ectopic RelB overexpression failed to promote DC maturation. Our results suggest that RelB regulates human monopoiesis and monocyte-derived DC subset development.

To die or not to die: the function of the transcription factor NF-kappaB in embryos exposed to stress

BACKGROUND

Cytokines operating in the embryo and embryonic microenvironment determine, to a significant extent, whether pregnancy is completed successfully or results in embryonic loss or maldevelopment. They act as activators of specific transcription factors, which control cell responses such as cell proliferation differentiation and apoptosis. One such transcription factor is the nuclear factor-kappaB (NF-kappaB), which is presently seen as a key molecule controlling the apoptosis process. In the light of evidence that a majority of embryopathic stresses, regardless of their nature, first disturb the apoptotic process, it is conceivable, that NF-kappaB may play an important role in regulating the resistance of embryos to embryopathic stresses. In this brief review, we discuss such a possibility based on data characterizing expression and function of NF-kappaB in the embryo and extraembryonic tissues during normal embryogenesis as well as after exposure to various embryopathic stresses.

METHODS

Critical review of existing data.

RESULTS

Data summarized in this review suggest that (a) practically all NF-kappaB/Rel family members are expressed in embryonic, trophoblast and uterine cells in a developmental stage- and cell type-specific manner; (b) NF-kappaB-mediated anti-apoptotic signaling in embryonic cells seems to be indispensable for proper development during the organogenesis stage, (c) NF-kappaB activity in stress-targeted embryonic and extraembryonic structures directly correlates with their ability to resist stress-induced process of embryo loss and maldevelopment.

CONCLUSION

Data presented in this review suggest that NF-kappaB may act as a protector of embryos exposed to embryopathic stresses, possibly, because of the ability of NF-kappaB to prevent the induction of programmed cell death as well as to activate cell proliferation.

Induced dendritic cell differentiation of chronic myeloid leukemia blasts is associated with down-regulation of BCR-ABL

Although differentiation of leukemic blasts to dendritic cells (DC) has promise in vaccine strategies, the mechanisms underlying this differentiation and the differences between leukemia and normal progenitor-derived DC are largely undescribed. In the case of chronic myeloid leukemia (CML), understanding the relationship between the induction of DC differentiation and the expression of the BCR-ABL oncogene has direct relevance to CML biology as well as the development of new therapeutic approaches. We now report that direct activation of protein kinase C (PKC) by the phorbol ester PMA in the BCR-ABL(+) CML cell line K562 and primary CML blasts induced nonterminal differentiation into cells with typical DC morphology (cytoplasmic dendrites), characteristic surface markers (MHC class I, MHC class II, CD86, CD40), chemokine and transcription factor expression, and ability to stimulate T cell proliferation (equivalent to normal monocyte-derived DC). PKC-induced differentiation was associated with down-regulation of BCR-ABL mRNA expression, protein levels, and kinase activity. This down-regulation appeared to be signaled through the mitogen-activated protein kinase pathway. Therefore, PKC-driven differentiation of CML blasts into DC-like cells suggests a potentially novel strategy to down-regulate BCR-ABL activity, yet raises the possibility that CML-derived DC vaccines will be less effective in presenting leukemia-specific Ags.

Antigen presentation by murine dendritic cells is nuclear factor-kappa B dependent both in vitro and in vivo

Antigen presentation is a key rate-limiting step in the immune response. Dendritic cells (DCs) have been reported to be the most potent antigen-presenting cells for naïve T cells, but little is known about the biochemical pathways that regulate this function. We here demonstrate that mature murine DC can be infected with adenovirus at high efficiency (>95%) and that an adenovirus transferring the endogenous inhibitor IkappaBalpha blocks nuclear factor-kappa B (NF-kappaB) function in murine DC. This result indicates that antigen presentation in the mixed leucocyte reaction is NF-kappaB dependent, confirming data with human DC in vitro. However, the importance of this finding depends on verifying that this is true also in vivo. Using delayed type hypersensitivity with allogeneic cells, we show that NF-kappaB inhibition had a marked immunosuppressive effect in vivo. These results thus establish NF-kappaB as an effective target for blocking DC antigen presentation and hence inhibiting T-cell-dependent immune responses. This finding has potential implications for the development of therapeutic agents for use in various pathological conditions of the immune system, including allergy and autoimmunity, and also in transplantation.

Modification of in vivo and in vitro T- and B-cell-mediated immune responses by the Pseudomonas aeruginosa quorum-sensing molecule N-(3-oxododecanoyl)-L-homoserine lactone

N-3-(oxododecanoyl)-L-homoserine lactone (OdDHL), a quorum-sensing molecule of Pseudomonas aeruginosa, plays an important role in the pathogenesis of the organism through its control of virulence factor expression. Several reports have suggested that OdDHL can also directly modulate host immune responses. However, the nature of the modulation is controversial, with different reports suggesting promotion of either humoral (Th2-mediated) or inflammatory (Th1-mediated) responses. This report describes a series of studies which demonstrate for the first time that in vivo administration of OdDHL can modulate the course of an antibody response, with an increase in ovalbumin (OVA)-specific immunogloblulin G1 (IgG1) but not IgG2a in OdDHL-treated OVA-immunized BALB/c mice compared to levels for controls. In vitro stimulation of lymphocytes from both Th1-biased C57Bl/6 and T-cell receptor transgenic mice and Th2-biased BALB/c mice in the presence of OdDHL demonstrated that OdDHL inhibits in vitro cytokine production in response to both mitogen and antigen, with gamma interferon (IFN-gamma) tending to be more inhibited than interleukin-4 (IL-4). In vitro mitogen or antigen restimulation of cells from mice treated with OdDHL in vivo shows effects on cytokine production which depend on the underlying immune bias of the mouse strain used, with a relative increase of IFN-gamma in Th1-biased C57Bl/6 mice and a relative increase of IL-4 in Th2-biased BALB/c mice. Thus, the mode of action of OdDHL on T-cell cytokine production is likely to be a relatively nonspecific one which accentuates an underlying immune response bias rather than one which specifically targets either Th1 or Th2 responses.

Disruption of B-cell homeostatic control mediated by the BLV-Tax oncoprotein: association with the upregulation of Bcl-2 and signaling through NF-kappaB

Transactivating proteins associated with complex onco-retroviruses including human T-cell leukemia virus-1 (HTLV-1) and bovine leukemia virus (BLV) mediate transformation using poorly understood mechanisms. To gain insight into the processes that govern tumor onset and progression, we have examined the impact of BLV-Tax expression on ovine B-cells, the targets of BLV in experimentally infected sheep, using B-cell clones that are dependent on CD154 and gammac-common cytokines. Tax was capable of mediating progression of B-cells from cytokine dependence to cytokine independence, indicating that the transactivator can over-ride signaling pathways typically controlled by cytokine receptor activation in B-cells. When examined in the presence of both CD154 and interleukin-4, Tax had a clear supportive role on B-cell growth, with an impact on B-cell proliferation, cell cycle phase distribution, and survival. Apoptotic B-cell death mediated by growth factor withdrawal, physical insult, and NF-kappaB inhibition was dramatically reduced in the presence of Tax. Furthermore, the expression of Tax was associated with higher Bcl-2 protein levels, providing rationale for the rescue signals mediated by the transactivator. Finally, Tax expression in B-cells led to a dramatic increase of nuclear RelB/p50 and p50/p50 NF-kappaB dimers, indicating that cellular signaling through NF-kappaB is a major contributory mechanism in the disruption of B-cell homeostasis. Although Tax is involved in aspects of pathogenesis that are unique to complex retroviruses, the viral strategies associated with this transactivating oncoprotein may have wide-ranging effects that are relevant to other B-cell malignancies.

NIK-dependent RelB activation defines a unique signaling pathway for the development of V alpha 14i NKT cells

A defect in RelB, a member of the Rel/nuclear factor (NF)-kappa B family of transcription factors, affects antigen presenting cells and the formation of lymphoid organs, but its role in T lymphocyte differentiation is not well characterized. Here, we show that RelB deficiency in mice leads to a selective decrease of NKT cells. RelB must be expressed in an irradiation-resistant host cell that can be CD1d negative, indicating that the RelB expressing cell does not contribute directly to the positive selection of CD1d-dependent NKT cells. Like RelB-deficient mice, aly/aly mice with a mutation for the NF-kappa B-inducing kinase (NIK), have reduced NKT cell numbers. An analysis of NK1.1 and CD44 expression on NKT cells in the thymus of aly/aly mice reveals a late block in development. In vitro, we show that NIK is necessary for RelB activation upon triggering of surface receptors. This link between NIK and RelB was further demonstrated in vivo by analyzing RelB+/- x aly/+ compound heterozygous mice. After stimulation with alpha-GalCer, an antigen recognized by NKT cells, these compound heterozygotes had reduced responses compared with either RelB+/- or aly/+ mice. These data illustrate the complex interplay between hemopoietic and nonhemopoietic cell types for the development of NKT cells, and they demonstrate the unique requirement of NKT cells for a signaling pathway mediated by NIK activation of RelB in a thymic stromal cell.

The role of relB in regulating the adaptive immune response

Dendritic cells (DCs), which represent a key type of antigen-presenting cell (APC), are important for the development of innate and adaptive immunity. DCs are involved in T cell activation in at least two main ways: priming via direct processing/presentation of soluble antigen taken up from the microenvironment (conventional priming), and processing/presentation of antigen released from other cells (cross-priming). relB, a component of the NF-kappaB complex of transcription factors, is a critical regulator of the differentiation of DCs. In mice, lack of relB impairs DCs derived from bone marrow both in number and function. Here relB (-/-) bone marrow chimera mice is used to study the APC function of residual DCs in presentation of soluble antigen and cross-priming. It is found that the DCs in these mice are profoundly deficient in their ability to both prime and cross-prime T cell responses. It was concluded that the relB gene is involved in regulating the APC function of DCs in vivo.

Ikappa B kinase 2 but not NF-kappa B-inducing kinase is essential for effective DC antigen presentation in the allogeneic mixed lymphocyte reaction

Although dendritic cells (DCs) are the most potent antigen-presenting cells involved in numerous physiologic and pathologic processes, little is known about the signaling pathways that regulate DC activation and antigen-presenting function. Recently, we demonstrated that nuclear factor (NF)-kappaB activation is central to that process, as overexpression of IkappaBalpha blocks the allogeneic mixed lymphocyte reaction (MLR), an in vitro model of T-cell activation. In this study, we investigated the role of 2 putative NF-kappaB-inducing components, NF-kappaB-inducing kinase (NIK), and IkappaB kinase 2 (IKK2). Using an adenoviral gene transfer method to efficiently express dominant-negative (dn) forms of these molecules in monocyte-derived DCs, we found that IKK2dn but not NIKdn inhibited the allogeneic MLR. When DCs were fixed, this inhibitory effect of IKK2dn was lost, suggesting that IKK2 is involved in T-cell-derived signals that enhance DC antigen presentation during the allogeneic MLR period and does not have an effect on viability or differentiation state of DCs prior to coculture with T cells. One such signal is likely to be CD40 ligand (CD40L), as IKK2dn blocked CD40L but not lipopolysaccharide (LPS)-induced NF-kappaB activation, cytokine production, and up-regulation of costimulatory molecules and HLA-DR in DCs. In summary, our results demonstrate that IKK2 is essential for DC activation induced by CD40L or contact with allogeneic T cells, but not by LPS, whereas NIK is not required for any of these signals. In addition, our results support IKK2 as a potential therapeutic target for the down-regulation of unwanted immune responses that may occur during transplantation or autoimmunity.

Cross-priming is under control of the relB gene

Cross-priming is an important mechanism of intercell transfer of antigenic material leading to the specific activation of cytotoxic T lymphocytes. Dendritic cells (DCs) are considered the central antigen-presenting cell in cross-priming. Here we decided to probe the role of the relB gene, a regulator of DC differentiation, in the in vivo cross-priming of a model tumour antigen, TAP(-/-) murine embryo cells (MEC), expressing human adenovirus type 5 early region 1. To this end, we used relB(-/-) mutant mice to generate bone marrow (BM) chimeras as these possess few residual DC but are capable of initiating CD4+ and CD8+ T-cell responses in vivo. Our results show that relB(-/-) BM chimeras are unable to cross-prime CD8+ T cells, suggesting that the relB gene regulates cross-priming.

NF-kappaB family of transcription factors: central regulators of innate and adaptive immune functions

Transcription factors of the Rel/NF-kappaB family are activated in response to signals that lead to cell growth, differentiation, and apoptosis, and these proteins are critical elements involved in the regulation of immune responses. The conservation of this family of transcription factors in many phyla and their association with antimicrobial responses indicate their central role in the regulation of innate immunity. This is illustrated by the association of homologues of NF-kappaB, and their regulatory proteins, with resistance to infection in insects and plants (M. S. Dushay, B. Asling, and D. Hultmark, Proc. Natl. Acad. Sci. USA 93:10343-10347, 1996; D. Hultmark, Trends Genet. 9:178-183, 1993; J. Ryals et al., Plant Cell 9:425-439, 1997). The aim of this review is to provide a background on the biology of NF-kappaB and to highlight areas of the innate and adaptive immune response in which these transcription factors have a key regulatory function and to review what is currently known about their roles in resistance to infection, the host-pathogen interaction, and development of human disease.

RelB-p50 NF-kappa B complexes are selectively induced by cytomegalovirus immediate-early protein 1: differential regulation of Bcl-x(L) promoter activity by NF-kappa B family members

The NF-kappa B/Rel family has been implicated in control of transcription of the Bcl-x(L) gene, a target which mediates cell survival signals. The cytomegalovirus (CMV) immediate-early protein 1 (IE1) was previously shown to induce NF-kappa B activity. Here, we report that in both vascular smooth muscle cells (SMCs) and NIH 3T3 cells, surprisingly, IE1 failed to induce Bcl-x(L) promoter activity, although it induced activity of E8-CAT, a reporter construct driven by two copies of the NF-kappa B element upstream of the c-myc promoter (upstream regulatory element [URE]). Thus, the subunit nature of the NF-kappa B/Rel factors induced by IE1 was examined using immunofluorescence and immunoblotting. IE1 was found to selectively induce nuclear RelB and p50 in SMCs and NIH 3T3 cells. An increase in RelB protein mediated by IE1 could, in part, be related to an increase in steady-state relB mRNA levels. Consistent with this subunit identification, IE1 was unable to induce E8-CAT activity in relB(-/-) murine embryonic fibroblast cells. In cotransfection analysis of SMCs and NIH 3T3 cells, RelB and p50 proteins failed to induce Bcl-x(L) promoter activity while inducing E8-CAT. Furthermore, the NF-kappa B element of the Bcl-x(L) promoter only weakly bound RelB-p50 complexes compared to the URE NF-kappa B element. Overall, these findings demonstrate in SMCs and NIH 3T3 cells that the CMV IE1 protein selectively induces RelB and p50, which fail to activate the Bcl-x(L) promoter, indicating a strong specificity of binding and activity for the RelB member of the NF-kappa B family. Furthermore, our results implicate RelB in CMV infection of cells such as vascular SMCs.

Nuclear RelB+ cells are found in normal lymphoid organs and in peripheral tissue in the context of inflammation, but not under normal resting conditions

Differentiated dendritic cells (DC) have been identified by the presence of nuclear RelB (nRelB) and HLA-DR, and the absence of CD20 or high levels of CD68, in lymph nodes and active rheumatoid arthritis synovial tissue. The current studies aimed to identify conditions in which nRelB is expressed in human tissues, by single and double immunohistochemistry of formalin-fixed peripheral and lymphoid tissue. Normal peripheral tissue did not contain nRelB+ cells. nRelB+ DC were located only in T- or B-cell areas of lymphoid tissue associated with normal organs or peripheral tissues, including tonsil, colon, spleen and thymus, or in association with T cells in inflamed peripheral tissue. Inflamed sites included skin delayed-type hypersensitivity reaction, and a wide range of tissues affected by autoimmune disease. Nuclear RelB+-HLA-DR- follicular DC were located in B-cell follicles in lymphoid organs and in lymphoid-like follicles of some tissues affected by autoimmune disease. Lymphoid tissue T-cell areas also contained nRelB(-)-HLA-DR+ cells,some of which expressed CD123 and/or CD68. Nuclear RelB+ cells are found in normal lymphoid organs and in peripheral tissue in the context of inflammation, but not under normal resting conditions.

RelB cellular regulation and transcriptional activity are regulated by p100

RelB mediates the constitutive nuclear pool of NF-kappaB transcriptional activity in myeloid and lymphoid cells, which is believed to be secondary to its weak interaction with the classical NF-kappaB inhibitor proteins, the IkappaBs. In other cell types, RelB is located in the cytosol, thus suggesting that RelB is also regulated by an inhibitory protein(s). In this study, it is demonstrated that RelB is associated in the cytosol with p100 but not with IkappaBalpha, IkappaBbeta, IkappaBepsilon, nor p105. Its cytosolic control is not affected by stimuli that lead to RelA nuclear translocation, and RelB nuclear localization is prevented by p100, but not by p105 or IkappaBalpha. Structure function analysis p100-RelB interactions indicates that p100 amino acids 623-900 are required for effective interaction and repression of nuclear translocation and RelB driven NF-kappaB-dependent transcription. Moreover, this carboxyl-portion of p100 contains a nuclear export signal(s), which is required for effective retrieval of RelB from the nucleus. Finally, overexpression of NF-kappaB-inducing kinase, a kinase that has recently been shown to induce p100 processing, possibly through IKKalpha activation, causes nuclear translocation of RelB protein. Thus, these studies indicate that p100 is a bone fide inhibitor of RelB and that this transcription factor may be regulated by NF-kappaB-inducing kinase and/or IKKalpha.

RelB reduces thymocyte apoptosis and regulates terminal thymocyte maturation

Thymocyte maturation is controlled by successive developmental checkpoints connected to the acquisition of a functional T cell receptor (TCR). During thymocyte selection, engagement of the TCR regulates the fine balance between death and survival signals. At the final stages of single-positive (SP) thymocyte maturation, the coupling of the TCR changes from death- to proliferation-inducing signals, a competence required for optimal effector functions in the periphery. We show here that in RelB mutant thymuses, thymocyte differentiation of CD24(-) SP cells is partially impaired. Competitive bone marrow reconstitution experiments show that this defect is constitutive to the lymphoid compartment. This is accompanied by an increased proportion of apoptotic thymocytes and a drastically reduced proliferation upon activation with anti-CD3 antibody/PMA stimulation. Thus, the RelB protein contributes to the quality of cell signaling in thymocytes by providing anti-apoptotic signals. These results suggest that in addition to its major role on the activation of antigen-presenting cell function, the RelB protein is intrinsically required for terminal thymocyte differentiation and activation.

NF-kappaB cis-acting motifs of the human immunodeficiency virus (HIV) long terminal repeat regulate HIV transcription in human macrophages

The role of NF-kappaB in the reactivation of human immunodeficiency virus (HIV) from latency in CD4 T lymphocytes is well documented. However, its role in driving HIV transcription in human macrophages, which contain a constitutive nuclear pool of NF-kappaB, is less well understood. In this study we have investigated the role that the constitutive pool of NF-kappaB and the NF-kappaB cis-acting motifs of the HIV long terminal repeat (LTR) play in regulating HIV transcription in human monocytic cells and primary macrophages. Inhibition of the constitutive nuclear pool of NF-kappaB (RelA and RelB) in the promonocytic U937 cell line using dominant-negative IkappaBalpha significantly decreases HIV replication. Moreover, it is demonstrated that in the differentiated monocytic cell line THP1, which contains a constitutive nuclear pool of NF-kappaB (RelB),an HIV provirus containing mutations of the kappaB cis-acting sites in the LTR is transcriptionally impaired. Reduction of the constitutive pool of NF-kappaB in human macrophages by an adenovirus vector expressing a dominant-negative IkappaBalpha also reduces HIV transcription. Lastly, mutation of the NF-kappaB cis-acting sites in the LTR of an R5 HIV provirus completely abrogates the first cycle of HIV transcription. These studies indicate that the cis-acting NF-kappaB motifs of the HIV LTR are critical in initiating HIV transcription in human macrophages and suggest that the constitutive nuclear pool of NF-kappaB is important in regulating HIV transcription in these cells.

Transcription of the RelB gene is regulated by NF-kappaB

RelA and RelB are two members of the NF-kappaB family that differ structurally and functionally. While RelA is regulated through its cytosolic localization by inhibitor proteins or IkappaB and not through transcriptional mechanisms, the regulation of RelB is poorly understood. In this study we demonstrate that stimuli (TNF or LPS) lead within minutes to the nuclear translocation of RelA, but require hours to result in the nuclear translocation of RelB. The delayed nuclear translocation of RelB correlates with increases in its protein synthesis which are secondary to increases in RelB gene transcription. RelA is alone sufficient to induce RelB gene transcription and to mediate the stimuli-driven increase in RelB transcription. Cloning and characterization of the RelB 5' untranslated gene region indicates that RelB transcription is dependent on a TATA-less promoter containing two NF-kappaB binding sites. One of the NF-kappaB sites is primarily involved in the binding of p50 while the other one in the binding and transactivation by RelA and also RelB. Lastly, it is observed that p21, a protein involved in cell cycle control and oncogenesis known to be regulated by NF-kappaB, is upregulated at the transcriptional level by RelB. Thus, RelB is regulated at least at the level of transcription in a RelA and RelB dependent manner and may exert an important role in p21 regulation.

Notch-1 regulates NF-kappaB activity in hemopoietic progenitor cells

We investigated the interaction between two elements critical for differentiation of hemopoietic cells, the Notch-1 receptor and the transcription factor NF-kappaB. These factors were studied in hemopoietic progenitor cells (HPC) using Notch-1 antisense transgenic (Notch-AS-Tg) mice. DNA binding of NF-kappaB as well as its ability to activate transcription was strongly decreased in HPC from Notch-AS-Tg mice. NF-kappaB-driven transcriptional activity was completely restored after transduction of the cells with retroviral constructs containing activated Notch-1 gene. HPC from Notch-AS-Tg mice have decreased levels of several members of the NF-kappaB family, p65, p50, RelB, and c-Rel and this is due to down-regulation of the gene expression. To investigate functional consequences of decreased NF-kappaB activity in transgenic mice, we studied LPS-induced proliferation of B cells and GM-CSF-dependent differentiation of dendritic cells from HPC. These two processes are known to be closely dependent on NF-kappaB. B cells from Notch-AS-Tg mice had almost 3-fold lower response to LPS than B cells isolated from control mice. Differentiation of dendritic cells was significantly affected in Notch-AS-Tg mice. However, it was restored by transduction of activated Notch-1 into HPC. Taken together, these data indicate that in HPC NF-kappaB activity is regulated by Notch-1 via transcriptional control of NF-kappaB.

The chicken RelB transcription factor has transactivation sequences and a tissue-specific expression pattern that are distinct from mammalian RelB

Rel/NF-kappaB proteins are eukaryotic transcription factors that control the expression of genes involved in a large variety of cellular processes. Rel proteins share a highly conserved DNA-binding/dimerization domain called the Rel Homology (RH) domain. We have constructed and characterized a composite cDNA encoding most of the chicken RelB transcription factor. The predicted chicken RelB protein has a high degree of sequence similarity to other vertebrate RelB proteins within the RH domain, but is much less conserved outside this domain. Chicken RelB does not bind DNA as a homodimer, but forms DNA-binding heterodimers with NF-kappaB p50 or p52. Overexpressed chicken RelB localizes to the nucleus in chicken embryo fibroblasts, and the nonconserved C-terminal sequences of chicken RelB contain a transactivation domain that functions in chicken and mouse fibroblasts. Thus, chicken RelB has functional properties similar to other vertebrate RelB proteins. However, Western blotting of diverse chicken tissues indicates that chicken RelB is more widely expressed than mammalian RelB.

Essential role of RelB in germinal center and marginal zone formation and proper expression of homing chemokines

High levels of the Rel/NF-kappaB family member RelB are restricted to specific regions of thymus, lymph nodes, and Peyer's patches. In spleen, RelB is expressed in periarteriolar lymphatic sheaths, germinal centers (GCs), and the marginal zone (MZ). In this study, we report that RelB-deficient (relB(-/-)) mice, in contrast to nfkb1(-/-), but similar to nfkb2(-/-) mice, are unable to form GCs and follicular dendritic cell networks upon Ag challenge in the spleen. RelB is also required for normal organization of the MZ and its population by macrophages and B cells. Reciprocal bone marrow transfers demonstrate that RelB expression in radiation-resistant stromal cells, but not in bone marrow-derived hemopoietic cells, is required for proper formation of GCs, follicular dendritic cell networks, and MZ structures. However, the generation of MZ B cells requires RelB in hemopoietic cells. Expression of TNF ligand/receptor family members is only moderately altered in relB(-/-) splenocytes. In contrast, expression of homing chemokines is strongly reduced in relB(-/-) spleen with particularly low mRNA levels of the chemokine B lymphocyte chemoattractant. Our data indicate that activation of p52-RelB heterodimers in stromal cells downstream of TNF/lymphotoxin is required for normal expression of homing chemokines and proper development of spleen microarchitecture.