Perturbation of the T lymphocyte lineage in transgenic mice expressing a constitutive repressor of nuclear factor (NF)-kappaB

Bcl10/Malt1 signaling is essential for TCR-induced NF-kappaB activation in thymocytes but dispensable for positive or negative selection

During T cell development in the thymus, high-affinity/avidity TCR engagement induces negative selection by apoptosis, while lower affinity/avidity TCR interactions lead to positive selection and survival of thymocytes. Yet, the mechanisms that discriminate between positive and negative selection are not fully understood. One major regulator of survival and apoptosis in lymphoid cells is the transcription factor NF-kappaB. Several reports have indicated key roles for NF-kappaB in positive and negative selection. In peripheral T cells, TCR ligation activates NF-kappaB through a selective pathway that involves protein kinase Ctheta, Bcl10, and Malt1. While protein kinase Ctheta is dispensable for thymic TCR signaling, the molecular roles of Bcl10 and Malt1 in thymocytes have not been investigated. In the present study, we show that both Bcl10 and Malt1 are essential for TCR signaling in thymocytes as a genetic disruption of either molecule blocks TCR-induced NF-kappaB activation in these cells. To investigate the function of this pathway in thymic selection, we introduced the Bcl10 or Malt1 mutations into three well-established TCR transgenic mouse models. Surprisingly, using several in vivo or in vitro assays, we were unable to demonstrate a role for TCR-induced NF-kappaB activation in either positive or negative selection. Thus, while TCR signaling to NF-kappaB controls the activation of mature T cells, we suggest that this pathway is not involved in the positive or negative selection of thymocytes.

Targeting the NF-kappaB signaling pathway in Notch1-induced T-cell leukemia

T-cell acute lymphoblastic leukemia (T-ALL), unlike other ALL types, is only infrequently associated with chromosomal aberrations, but it was recently shown that most individuals with T-ALL carry activating mutations in the NOTCH1 gene. However, the signaling pathways and target genes responsible for Notch1-induced neoplastic transformation remain undefined. We report here that constitutively active Notch1 activates the NF-kappaB pathway transcriptionally and via the IkappaB kinase (IKK) complex, thereby causing increased expression of several well characterized target genes of NF-kappaB in bone marrow hematopoietic stem cells and progenitors. Our observations demonstrate that the NF-kappaB pathway is highly active in established human T-ALL and that inhibition of the pathway can efficiently restrict tumor growth both in vitro and in vivo. These findings identify NF-kappaB as one of the major mediators of Notch1-induced transformation and suggest that the NF-kappaB pathway is a potential target of future therapies of T-ALL.

ERK5 Activates NF-κB in Leukemic T Cells and Is Essential for Their Growth In Vivo

MAPK cascades play a central role in the cellular response to the environment. The pathway involving the MAPK ERK5 mediates growth factor- and stress-induced intracellular signaling that controls proliferation or survival depending upon the cell context. In this study, we show that reducing ERK5 levels with a specific small hairpin RNA 5 (shERK5) reduced cell viability, sensitized cells to death receptor-induced apoptosis, and blocked the palliative effects of phorbol ester in anti-Fas Ab-treated cells. shERK5 decreased nuclear accumulation of the NF-kappaB p65 subunit, and conversely, ectopic activation of ERK5 led to constitutive nuclear localization of p65 and increased its ability to trans activate specific reporter genes. Finally, the T lymphoma cell line EL-4, upon expression of shERK5, proliferated in vitro, but failed to induce s.c. tumors in mice. Our results suggest that ERK5 is essential for survival of leukemic T cells in vivo, and thus represents a promising target for therapeutic intervention in this type of malignancy.

Unravelling the complexities of the NF-κB signalling pathway using mouse knockout and transgenic models

The nuclear factor-kappaB (NF-kappaB) signalling pathway serves a crucial role in regulating the transcriptional responses of physiological processes that include cell division, cell survival, differentiation, immunity and inflammation. Here we outline studies using mouse models in which the core components of the NF-kappaB pathway, namely the IkappaB kinase subunits (IKKalpha, IKKbeta and NEMO), the IkappaB proteins (IkappaBalpha, IkappaBbeta, IkappaBvarepsilon and Bcl-3) and the five NF-kappaB transcription factors (NF-kappaB1, NF-kappaB2, c-Rel, RelA and RelB), have been genetically manipulated using transgenic and knockout technology.

NF-kappaB regulation of endothelial cell function during LPS-induced toxemia and cancer

The transcription factor NF-kappaB is an important regulator of homeostatic growth and inflammation. Although gene-targeting studies have revealed important roles for NF-kappaB, they have been complicated by component redundancy and lethal phenotypes. To examine the role of NF-kappaB in endothelial tissues, Tie2 promoter/enhancer-IkappaBalpha(S32A/S36A) transgenic mice were generated. These mice grew normally but exhibited enhanced sensitivity to LPS-induced toxemia, notable for an increase in vascular permeability and apoptosis. Moreover, B16-BL6 tumors grew significantly more aggressively in transgenic mice, underscoring a new role for NF-kappaB in the homeostatic response to cancer. Tumor vasculature in transgenic mice was extensive and disorganized. This correlated with a marked loss in tight junction formation and suggests that NF-kappaB plays an important role in the maintenance of vascular integrity and response to stress.

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

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

POLKADOTS are foci of functional interactions in T-Cell receptor-mediated signaling to NF-kappaB

Stimulation of the T-cell receptor (TCR) results in the activation of several transcription factors, including NF-kappaB, that are crucial for T-cell proliferation and gain of effector functions. On TCR engagement, several proteins within the TCR-directed NF-kappaB signaling pathway undergo dynamic spatial redistribution, but the significance of these redistribution events is largely unknown. We have previously described TCR-induced cytoplasmic structures called POLKADOTS (punctate and oligomeric killing or activating domains transducing signals) that are enriched in the NF-kappaB signaling intermediate, Bcl10. We now show that these structures are formed only under conditions that promote efficient NF-kappaB activation. Furthermore, POLKADOTS formation is dependent on functional domains of specific NF-kappaB signal transducers. Through use of a photoactivatable GFP, we demonstrate that POLKADOTS contain both a highly stable and a rapidly equilibrating protein component. FRET analyses show that POLKADOTS are sites of enriched interactions between Bcl10 and partner signaling proteins. These observations strongly suggest that POLKADOTS are focal sites of dynamic information exchange between cytosolic intermediates in the process of TCR activation of NF-kappaB.

RelA regulates the survival of activated effector CD8 T cells

Nuclear factor of kappa B (NF-kappaB) transcription factors are critical regulators of T-cell activation and survival. The relative contribution of individual NF-kappaB members to these processes remains elusive. We investigated the role of RelA in the regulation of CD8 T-cell activation. We overexpressed, in mature CD8 T cells, a transactivation domain-deficient RelA molecule (p65TAD). We show that p65TAD forms homo- and heterodimers with p50 that bind kappaB sites and selectively inhibit RelA-dependent transactivation. Expression of p65TAD does not affect initial activation or cell cycle progression but induces the death of activated CD8 T cells in vitro and in vivo. However, the long-term survival of resting effector CD8 T cells seems not to be affected by p65TAD expression. Collectively, our results indicate that RelA is a critical regulator of survival of proliferating CD8 T cells but may be dispensable for the survival of resting effector T cells.

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

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

The Anti-Death Machinery in IKK/NF-κB Signaling

The most extensively studied function of NF-kappaB is its ability to promote cell survival through induction of target genes, whose products inhibit various aspects of the apoptotic machinery in both normal and malignant cells. Recent studies, however, indicate that NF-kappaB activation can also suppress programmed necrosis through induction of genes encoding anti-oxidant proteins. Since tumor cells often use NF-kappaB pathway as a shield to escape the killing of conventional anti-cancer therapies, intervention of IKK/NF-kappaB signaling would be a promising option to improve the efficacy of cancer treatment.

3-Phosphoinositide-dependent protein kinase-1-mediated IkappaB kinase beta (IkkB) phosphorylation activates NF-kappaB signaling

The IkappaB kinase (IKK)/NF-kappaB and phosphatidylinositol 3-OH-kinase/3-phosphoinositide-dependent protein kinase-1 (PDK1)/Akt pathways regulate various cellular functions, especially cell survival. These two pathways are often activated in many tumors and are thought to be associated with tumor progression. However, the cross-talk between them remains unclear. Here we show that PDK1 can activate IKK/NF-kappaB signaling in addition to Akt signaling to promote cell survival. Screening kinases that could modulate NF-kappaB activity revealed that expression of an upstream Akt kinase PDK1 up-regulates NF-kappaB transcriptional activity. We found that PDK1 directly phosphorylates IKKbeta at the Ser(181) residue in the activation loop, leading to NF-kappaB nuclear translocation and NF-kappaB-dependent anti-apoptotic gene expression. IKKalpha is not required for PDK1-mediated NF-kappaB activation because NF-kappaB activation was observed in IKKalpha(-/-) mouse embryonic fibroblast (MEF) cells as in wild type MEF cells. Akt, which was previously reported to activate IKKalpha, did not participate in the PDK1-dependent IKKbeta or NF-kappaB activation. The siRNA-mediated PDK1 gene silencing attenuated NF-kappaB activity and increased TRAIL-mediated cytotoxicity. Moreover, expression of constitutively active IKKbeta overcame the PDK1 siRNA-mediated susceptibility to TRAIL. These results indicate that PDK1 is a critical regulator of cell survival by modulating the IKK/NF-kappaB pathway in addition to the Akt pathway.

Increased GILZ expression in transgenic mice up-regulates Th-2 lymphokines

GILZ (glucocorticoid-induced leucine zipper), a gene induced by dexamethasone, is involved in control of T lymphocyte activation and apoptosis. In the present study, using Gilz transgenic mice (TG), which overexpress GILZ in the T-cell lineage, we demonstrate that Gilz is implicated in T helper-2 (Th-2) response development. After in vitro stimulation by CD3/CD28 antibodies, peripheral naive CD4+ T cells from TG mice secrete more Th-2 cytokines such as interleukin-4 (IL-4), IL-5, IL-13, and IL-10, and produce less Th-1 cytokines such as interferon-gamma (IFN-gamma) than wild-type mice (WT). CD4+ TG lymphocytes up-regulated Th-2 cytokine expression in the specific response to ovalbumin chicken egg (OVA) antigen immunization. Up-regulation correlated with increased expression of GATA-3 and signal transducer and activator of transcription 6 (Stat6), Th-2-specific transcription factors and decreased expression of T-bet, a transcription factor involved in Th-1 differentiation. Finally, in TG mice delayed-type hypersensitivity, a Th-1 response, was inhibited and bleomycin-induced pulmonary fibrosis, a Th-2 mediated disease, was more severe. These results indicate that Gilz contributes to CD4+ commitment toward a Th-2 phenotype and suggest this contribution may be another mechanism accounting for glucocorticoid immunomodulation.

Reciprocal regulation of airway rejection by the inducible gas-forming enzymes heme oxygenase and nitric oxide synthase

Obliterative bronchiolitis (OB) develops insidiously in nearly half of all lung transplant recipients. Although typically preceded by a CD8⁺ T cell–rich lymphocytic bronchitis, it remains unresponsive to conventional immunosuppression. Using an airflow permissive model to study the role of gases flowing over the transplanted airway, it is shown that prolonged inhalation of sublethal doses of carbon monoxide (CO), but not nitric oxide (NO), obliterate the appearance of the obstructive airway lesion. Induction of the enzyme responsible for the synthesis of CO, heme oxygenase (Hmox) 1, increased carboxyhemoglobin levels and suppressed lymphocytic bronchitis and airway luminal occlusion after transplantation. In contrast, zinc protoporphyrin IX, a competitive inhibitor of Hmox, increased airway luminal occlusion. Compared with wild-type allografts, expression of inducible NO synthase (iNOS), which promotes the influx of cytoeffector leukocytes and airway graft rejection, was strikingly reduced by either enhanced expression of Hmox-1 or exogenous CO. Hmox-1/CO decreased nuclear factor (NF)-κB binding activity to the iNOS promoter region and iNOS expression. Inhibition of soluble guanylate cyclase did not interfere with the ability of CO to suppress OB, implicating a cyclic guanosine 3′,5′-monophosphate–independent mechanism through which CO suppresses NF-κB, iNOS transcription, and OB. Prolonged CO inhalation represents a new immunosuppresive strategy to prevent OB.

Opposing Roles for RelB and Bcl-3 in Regulation of T-Box Expressed in T Cells, GATA-3, and Th Effector Differentiation

CD4+ T cells with a block in the NF-kappaB signaling pathway exhibit decreases in Th1 responses and diminished nuclear levels of multiple transactivating NF-kappaB/Rel/IkappaB proteins. To determine the lineage-intrinsic contributions of these transactivators to Th differentiation, T cells from mice deficient in specific subunits were cultured in exogenous cytokines promoting either Th1 or Th2 differentiation. RelB-deficient cells exhibited dramatic defects in Th1 differentiation and IFN-gamma production, whereas no consistent defect in either Th1 or Th2 responses was observed with c-Rel-deficient cells. In sharp contrast, Bcl-3-null T cells displayed no defect in IFN-gamma production, but their Th2 differentiation and IL-4, IL-5, and IL-13 production were significantly impaired. The absence of RelB led to a dramatic decrease in the expression of T-box expressed in T cells and Stat4. In contrast, Bcl-3-deficient cells exhibited decreased GATA-3, consistent with evidence that Bcl-3 can transactivate a gata3 promoter. These data indicate that Bcl-3 and RelB exert distinct and opposing effects on the expression of subset-determining transcription factors, suggesting that the characteristics of Th cell responses may be regulated by titrating the stoichiometry of transactivating NF-kappaB/Rel/IkappaB complexes in the nuclei of developing helper effector cells.

Control of lymphocyte development by nuclear factor-kappaB

The evolutionarily conserved nuclear factor-kappaB family of transcription factors is known to have a crucial role in rapid responses to stress and pathogens, inducing transcription of many genes that are essential for host defence. Now, studies of mice that are deficient in nuclear factor-kappaB-family members (or deficient in the activation of these factors) reveal that nuclear factor-kappaB is extensively involved in the development of T cells and B cells. And, as we review here, although these factors have several roles, their primary cell-autonomous function is to ensure lymphocyte survival at various developmental stages. This function is subverted in numerous diseases and can lead, for example, to survival of self-reactive lymphocytes or tumour cells.

Endotoxin-induced acute lung injury requires interaction with the liver

Clinical and laboratory data indicate that the liver plays an important role in the incidence, pathogenesis, and outcome of acute lung injury/acute respiratory distress syndrome. To distinguish direct effects of endotoxin on the lungs from liver-dependent effects during the early phase of the response to endotoxemia, we used an in situ perfused piglet preparation in which only the ventilated lung or both the lung and liver could be included in a blood perfused circuit. We monitored pulmonary vascular resistance, oxygenation, neutrophil count, lung edema as reflected by wet-dry weights of lung tissue, perfusate concentrations of TNF-alpha, IL-6, and 8-isoprostane (a marker of oxidative stress), and activation of the transcription factor (NF-kappaB) in lung tissue before and for 2 h after endotoxin. When only the lung was perfused, endotoxin caused pulmonary hypertension and neutropenia; but oxygenation was maintained; TNF-alpha, IL-6, and 8-isoprostane levels were minimally elevated; and there was no lung edema. When both the liver and lung were perfused, endotoxin caused marked hypoxemia, large increases in perfusate TNF-alpha, IL-6, and 8-isoprostane concentrations, and severe lung edema. NF-kappaB activation in the lung was greatest when the liver was in the perfusion circuit. We conclude that the direct effects of endotoxemia on the lungs include vasoconstriction and leukocyte sequestration, but not lung injury. Intense activation of the inflammatory response and oxidative injury that results in pulmonary edema and hypoxemia (acute lung injury) requires interaction of the lungs with the liver.

Prevention of NF-kappaB activation in vivo by a cell-permeable NF-kappaB inhibitor peptide

The NF-kappaB/Rel transcription factor family plays a central role in coordinating the expression of a variety of genes that regulate stress responses, immune cell activation, apoptosis, proliferation, differentiation, and oncogenic transformation. Interventions that target the NF-kappaB pathway may be therapeutic for a variety of pathologies, especially immune/inflammatory diseases. Using membrane translocating sequence (MTS) technology, we developed a cell-permeable dominant inhibitor of NF-kappaB activation, termed IkappaBalpha-(DeltaN)-MTS. This molecule contains a 12-amino acid MTS motif attached to the COOH-terminal region of a nondegradable inhibitor protein [IkappaBalpha-(DeltaN)]. The recombinant protein enters cells and localizes in the cytoplasm. Delivery of the IkappaBalpha-(DeltaN)-MTS to cell lines and primary cells inhibited nuclear translocation of NF-kappaB proteins induced by cell activation. The protein also effectively inhibited NF-kappaB activation in vivo in two different animal models: NF-kappaB activation in response to skin wounding in mice and NF-kappaB activation in lungs after endotoxin treatment in sheep. Inhibition of NF-kappaB by the IkappaBalpha-(DeltaN)-MTS in the endotoxin model attenuated physiological responses to endotoxemia. These data demonstrate that activation of NF-kappaB can be inhibited using a recombinant protein designed to penetrate into cells. This technology may provide a new approach to NF-kappaB pathway-targeted therapies.

Peripheral survival of naïve CD8+ T cells

Maintenance of a sufficient population of naive CD8+ T cells in the peripheral lymphoid compartment is critical for immunocompetence. Peripheral T cell number is a function of T cell generation, survival, and death. Homeostasis, a critical balance between survival and death, must exist to prevent either lymphopenia or lymphocytosis. In the current review, we discuss known requirements for the survival of naive peripheral CD8+ T cells as well as mechanisms of death when survival signals are lost. We also discuss associations between survival and homeostasis-driven proliferation, and highlight the gaps in our knowledge of these critical processes.

Commitment toward the natural T (iNKT) cell lineage occurs at the CD4+8+ stage of thymic ontogeny

T lineage commitment occurs in a discrete, stage-specific manner during thymic ontogeny. Intrathymic precursor transfer experiments and the identification of CD4(+)8+ double-positive (DP), V alpha 14J alpha 18 natural T (iNKT) cells suggest that commitment to this lineage might occur at the DP stage. Nevertheless, this matter remains contentious because others failed to detect V alpha 14J alpha 18-positive iNKT cells that are CD4(+)8+. In resolution to this issue, we demonstrate that retinoic acid receptor-related orphan receptor gamma (ROR gamma)0/0 thymi, which accumulate immature single-positive (ISP) thymocytes that precede the DP stage, do not rearrange V alpha 14-to-J alpha 18 gene segments, suggesting that this event occurs at a post-ISP stage. Mixed radiation bone marrow chimeras revealed that RORgamma functions in an iNKT cell lineage-specific manner. Further, introgression of a Bcl-x(L) transgene into ROR gamma(0/0) mice, which promotes survival and permits secondary rearrangements of distal V alpha and J alpha gene segments at the DP stage, rescues V alpha 14-to-J alpha 18 recombination. Similarly, introgression of a rearranged V alpha 14J alpha 18 transgene into ROR gamma(0/0) mice results in functional iNKT cells. Thus, our data support the "T cell receptor-instructive (mainstream precursor) model" of iNKT cell lineage specification where V alpha 14-to-J alpha 18 rearrangement, positive selection, and iNKT cell lineage commitment occur at or after the DP stage of ontogeny.

Signaling pathways in Th2 development

In order for an immune response to be successful, it must be of the appropriate type and magnitude. Intracellular residing pathogens require a cell-mediated immune response, whereas extracellular pathogens evoke a humoral immune response. T-helper (Th) cells orchestrate the immune response and are divided into two subsets, Th1 and Th2 cells. Here, we discuss the mechanisms of Th2 development with a focus on signal transduction pathways that influence Th2 differentiation.

Transplantation Tolerance in NF-κB-Impaired Mice Is Not Due to Regulation but Is Prevented by Transgenic Expression of Bcl-xL

NF-kappaB is a key regulator of transcription after TCR and costimulatory receptor ligation. To determine the role of T cell-intrinsic NF-kappaB activation in acute allograft rejection, we used IkappaBalphaDeltaN-Tg mice (H-2b) that express an inhibitor of NF-kappaB restricted to the T cell compartment. We have previously shown that these mice permanently accept fully allogeneic (H-2d) cardiac grafts and secondary donor skin grafts, and that splenocytes from these tolerant mice have reduced alloreactivity when restimulated in vitro. These results were compatible with either deletion or suppression of allospecific T cells as possible mechanisms of tolerance. The aim of this study was to investigate the mechanism of transplant tolerance in these mice. IkappaBalphaDeltaN-Tg mice did not have increased numbers or function of CD4+ CD25+ regulatory T cells either before or after cardiac transplantation. In addition, tolerance could not be transferred to fresh NF-kappaB-competent T cells and was not permissive for linked suppression to skin grafts sharing donor and third-party alloantigens, suggesting that dominant suppression is not the mechanism by which IkappaBalphaDeltaN-Tg mice achieve tolerance. In contrast, overexpression of the antiapoptotic protein Bcl-xL in T cells from IkappaBalphaDeltaN-Tg mice resulted in effective rejection of cardiac allografts and correlated with an increased frequency of splenocytes producing IFN-gamma in response to alloantigen. Together, these results suggest that the death of alloreactive T cells may be partly responsible for the transplantation tolerance observed in mice with defective T cell-intrinsic NF-kappaB activation.

Suppression of nuclear translocation of nuclear factor-kappaB and nuclear factor of activated T cells by Younggaechulgam-tang

Younggaechulgam-tang (YGCGT) is known to suppress inflammatory and autoimmune responses, and it has clinically been used among Oriental medical doctors in South Korea. We investigated YGCGT-mediated changes in downstream T cell signal transduction. The expression levels of nuclear factor-kappaB (NFkappaB) subunit RelA and nuclear factor of activated T cells (NFATc1) in cytoplasm and nucleus were examined by western blot analysis. Interlukin-2 (IL-2) expression in MOLT-4 cells activated by phytohemagglutinin (PHA) was determined by reverse transcription-polymerase chain reaction (RT-PCR) and Western blot analysis. IL-2 secretion was measured by an enzyme-linked immunosorbent assay (ELISA). PHA-induced translocation of Rel A and NFATcl to the nucleus were markedly reduced by YGCGT treatment. Furthermore, IL-2 mRNA and protein levels and IL-2 secretion were significantly diminished by YGCGT treatment. In conclusion, YGCGT treatment of T cells inhibits selectively nuclear translocation of RelA and NFATc1, resulting in diminished production of IL-2. These results suggest that YGCGT may have potential as immunosuppressive drugs with improved efficacy and reduced side effects.

Transcriptional regulation of interleukin 2 in SLE T cells

Interleukin-2 (IL-2) is a central cytokine required for the activation of T, B, and NK cells. It propagates the immune response and terminates it by promoting the activation induced cell death of T cells. IL-2 production is altered in T cells of patients with systemic lupus erythematosus (SLE). The consequence of reduced IL-2 production in SLE is decreased immune response to infectious agents. Decreased IL-2 production by SLE T cells is the result of transcriptional repression of the IL-2 gene. This article will review the defective transcription regulation of IL-2 in SLE T cells, which is the result of decreased expression of the enhancers NF-kappa B and AP1 and the increased expression of the transcriptional repressor CREM.

Deficient translocation of c-Rel is associated with impaired Th1 cytokine production in T cells from atopic dermatitis patients

Decreased production of T helper type 1 (Th1) cytokines, such as interferon-gamma (IFN-gamma) or interleukin-2 (IL-2), is a hallmark of atopic diseases. While accessory signals from antigen-presenting cells may be missing, T cells themselves may be suppressed in their ability to produce substantial amounts of Th1 cytokines. We show, in this study, that T cell receptor (TCR)-activated T cells from atopic dermatitis (AD) patients proliferate less than control T cells and produce lower amounts of IFN-gamma and IL-2, but comparable amounts of IL-4. Because mice lacking the nuclear factor kappa B (NF-kappaB) transcription factors - p65 or c-Rel - show reduced Th1, but undisturbed Th2 responses, we investigated the role of c-Rel and p65 for Th1 cytokine production in T cells from healthy and severe AD patients. TCR-activated primary T cells from healthy donors treated with c-Rel antisense oligonucleotides produced lower levels of IL-2 and IFN-gamma and proliferated less efficiently than the corresponding control T cells. Moreover, transfection of primary T cells with c-Rel or p65 enhanced proliferation and production of IL-2 and IFN-gamma. Nuclear extracts of activated primary T cells from AD donors bound weakly to NF-kappaB-specific oligonucleotides, compared to extracts from healthy control T cells. Western blotting studies revealed that nuclear, but not cytosolic, extracts from T cells of AD patients lacked significant amounts of c-Rel and p65. T cell clones derived from AD patients failed to sufficiently translocate c-Rel and p65 into the nucleus following activation. Thus, impaired nuclear translocation of c-Rel and p65 may determine an impaired Th1 cytokine response in AD.

Linking JNK signaling to NF-kappaB: a key to survival

In addition to marshalling immune and inflammatory responses, transcription factors of the NF-kappaB family control cell survival. This control is crucial to a wide range of biological processes, including B and T lymphopoiesis, adaptive immunity, oncogenesis and cancer chemoresistance. During an inflammatory response, NF-kappaB activation antagonizes apoptosis induced by tumor necrosis factor (TNF)-alpha, a protective activity that involves suppression of the Jun N-terminal kinase (JNK) cascade. This suppression can involve upregulation of the Gadd45-family member Gadd45beta/Myd118, which associates with the JNK kinase MKK7/JNKK2 and blocks its catalytic activity. Upregulation of XIAP, A20 and blockers of reactive oxygen species (ROS) appear to be important additional means by which NF-kappaB blunts JNK signaling. These recent findings might open up entirely new avenues for therapeutic intervention in chronic inflammatory diseases and certain cancers; indeed, the Gadd45beta-MKK7 interaction might be a key target for such intervention.

Decrease of Bcl-xL and augmentation of thymocyte apoptosis in GILZ overexpressing transgenic mice

Glucocorticoids promote thymocyte apoptosis and modulate transcription of numerous genes. GILZ (glucocorticoid-induced leucine zipper), being one of them, is strongly up-regulated in the thymus. To elucidate its function we generated transgenic mice overexpressing it specifically in the T-cell lineage and characterized its influence on thymus function. In young adult transgenic mice CD4(+)CD8(+) thymocyte number was significantly decreased and ex vivo thymocyte apoptosis was increased. Apoptotic pathway analysis detected reduced antiapoptotic B-cell leukemia XL (Bcl-xL) expression and increased activation of caspase-8 and caspase-3. Time-course experiments showed that in wild-type (WT) thymocytes GILZ up-regulation was followed by sequential Bcl-xL decreased expression and activation of caspase-8 and of caspase-3. Moreover, GILZ delivered inside WT thymocytes by a fusion protein with the transactivator of transcription (TAT) peptide decreased Bcl-xL and promoted their apoptosis. In aged mice perturbation of thymic subset numbers was amplified over time, as demonstrated by a further decrease in CD4(+)CD8(+) cells and increases in CD4(+)CD8(-), CD4(-)CD8(-), and CD8(+)CD4(-) cell counts. These results support the hypothesis that GILZ participates in the regulation of thymocyte apoptosis by glucocorticoids.

Cellular FLIP long form-transgenic mice manifest a Th2 cytokine bias and enhanced allergic airway inflammation

Cellular FLIP long form (c-FLIP(L)) is a caspase-defective homologue of caspase-8 that blocks apoptosis by death receptors. The expression of c-FLIP(L) in T cells can also augment extracellular signal-regulated kinase phosphorylation after TCR ligation via the association of c-FLIP(L) with Raf-1. This contributes to the hyperproliferative capacity of T cells from c-FLIP(L)-transgenic mice. In this study we show that activated CD4(+) T cells from c-FLIP(L)-transgenic mice produce increased amounts of Th2 cytokines and decreased amounts of Th1 cytokines. This correlates with increased serum concentrations of the Th2-dependent IgG1 and IgE. The Th2 bias of c-FLIP(L)-transgenic CD4(+) T cells parallels impaired NF-kappa B activity and increased levels of GATA-3, which contribute, respectively, to decreased IFN-gamma and increased Th2 cytokines. The Th2 bias of c-FLIP(L)-transgenic mice extends to an enhanced sensitivity to OVA-induced asthma. Taken together, these results show that c-FLIP(L) can influence cytokine gene expression to promote Th2-driven allergic reaction, in addition to its traditional role of blocking caspase activation induced by death receptors.

NF-kappa B controls cell fate specification, survival, and molecular differentiation of immunoregulatory natural T lymphocytes

Ontogenetic, homeostatic, and functional deficiencies within immunoregulatory natural T (iNKT) lymphocytes underlie various inflammatory immune disorders including autoimmunity. Signaling events that control cell fate specification and molecular differentiation of iNKT cells are only partly understood. Here we demonstrate that these processes within iNKT cells require classical NF-kappaB signaling. Inhibition of NF-kappaB signaling blocks iNKT cell ontogeny at an immature stage and reveals an apparent, novel precursor in which negative selection occurs. Most importantly, this block occurs due to a lack of survival signals, as Bcl-x(L) overexpression rescues iNKT cell ontogeny. Maturation of immature iNKT cell precursors induces Bcl-2 expression, which is defective in the absence of NF-kappaB signaling. Bcl-x(L) overexpression also rescues this maturation-induced Bcl-2 expression. Thus, antiapoptotic signals relayed by NF-kappaB critically control cell fate specification and molecular differentiation of iNKT cells and, hence, reveal a novel role for such signals within the immune system.

Nuclear factor-kappaB: its role in health and disease

Nuclear factor-kappaB (NF-kappaB) is a major transcription factor that plays an essential role in several aspects of human health including the development of innate and adaptive immunity. The dysregulation of NF-kappaB is associated with many disease states such as AIDS, atherosclerosis, asthma, arthritis, cancer, diabetes, inflammatory bowel disease, muscular dystrophy, stroke, and viral infections. Recent evidence also suggests that the dysfunction of NF-kappaB is a major mediator of some human genetic disorders. Appropriate regulation and control of NF-kappaB activity, which can be achieved by gene modification or pharmacological strategies, would provide a potential approach for the management of NF-kappaB related human diseases. This review summarizes the current knowledge of the physiological and pathophysiological functions of NF-kappaB and its possible role as a target of therapeutic intervention

Modulation of gene expression by alloimmune networks following murine heart transplantation

The objective of our study was to analyze gene expression profiles in a complex in vivo model of solid organ transplantation, and to investigate the effects of single-gene deletions on alloimmunity. Using algorithms to generate dendrograms and self-organizing maps, we differentiated the alloimmune profiles of 16 transgenic knockout mouse strains, and identified subsets of genes that correlate with the duration of graft survival and provide candidates for prognostic and diagnostic indicators following transplantation in our model system.

Cutting Edge: The Ontogeny and Function of Va14Ja18 Natural T Lymphocytes Require Signal Processing by Protein Kinase Cθ and NF-κB

The rapid and robust immunoregulatory cytokine response of Va14Ja18 natural T (iNKT) cells to glycolipid Ags determines their diverse functions. Unlike conventional T cells, iNKT lymphocyte ontogeny absolutely requires NF-kappa B signaling. However, the precise role of NF-kappa B in iNKT cell function and the identity of upstream signals that activate NF-kappa B in this T cell subset remain unknown. Using mice in which iNKT cell ontogeny has been rescued despite inhibition of NF-kappa B signaling, we demonstrate that iNKT cell function requires NF-kappa B in a lymphocyte-intrinsic manner. Furthermore, the ontogeny of functional iNKT cells requires signaling through protein kinase C theta, which is dispensable for conventional T lymphocyte development. The unique requirement of protein kinase C theta implies that signals emanating from the TCR activate NF-kappa B during iNKT cell development and function. Thus, we conclude that NF-kappa B signaling plays a crucial role at distinct levels of iNKT cell biology.

NF-kB inhibitor blocks B cell development at two checkpoints

Members of the NF-kB transcription factor family are differentially expressed in the B cell lineage. Disruption of individual or two NF-kB subunits exhibits distinct defects in B lymphocyte development, activation, and survival. However, the role each NF-kB plays during B cell development has been obscured by molecular compensation. To address this issue, a trans-dominant form of IkBα was transduced into bone marrow cells to act as a pan-inhibitor of NF-kB using a retroviral system. While the development of T-lymphocytes and myeloid cell lineages was not grossly affected by the transduced IkBα gene, a significant reduction in the number and percentage of B lineage cells was apparent in IkBα transduced chimeric mice. IkBα expression decreased the percentage of pre-B and immature B cell subsets in the bone marrow and further impaired the development of follicular mature B cells and marginal zone B cells in the periphery. Introduction of the Bcl-X transgene completely restored the pre-B and immature B cell pool in the bone marrow. However, despite a significant improvement of overall viability of the B cell lineage, Bcl-X expression was insufficient to overcome the maturation block resulting from NF-kB inhibition. Together, our study suggests that NF-kB activity is required for two distinct checkpoints during B cell development: one is for pre-B/immature B cell viability, the other is to provide both survival and maturation signals to ensure the proper development of follicular mature B cells.

Expression of NF-kappaB in prostate cancer lymph node metastases

INTRODUCTION

Nuclear factor-kappaB (NF-kappaB) is a transcription factor that transactivates genes involved in the regulation of cell growth, apoptosis, angiogenesis, and metastasis. Our aim was to assess NF-kappaB expression in lymph node (LN) metastases of prostate cancer.

METHODS

Immunohistochemical staining was performed using the p65 anti-NF-kappaB antibody. Seventy-seven paraffin-embedded LN specimens obtained from 54 prostate cancer patients were analyzed. Of the 54 patients, 32 had positive LN metastases, while 22 showed no evidence of metastasis and were considered as controls. The overall percentage of NF-kappaB-nuclear localization was assessed, as well as the intensity of staining.

RESULTS

Nuclear localization of NF-kappaB was significantly greater in the metastatic LN group compared to controls. In patients with positive-LN metastases, 84.4% showed >10% nuclear staining in tumor cells. Moreover, 64.4% of the malignant LN specimens had >10% nuclear staining in lymphocytes compared to 0% in controls. Intensity of cytoplasmic and nuclear staining was higher in the metastatic LN group than in controls (P < 0.01).

CONCLUSIONS

Nuclear localization/activation of NF-kappaB is up-regulated in prostate cancer LN metastasis. Such up-regulation of NF-kappaB activity is observed in the tumor cells as well as in the surrounding lymphocytes.

Cellular origin of ionizing radiation-induced NF-kappaB activation in vivo and role of NF-kappaB in ionizing radiation-induced lymphocyte apoptosis

PURPOSE

To investigate the cellular origin of ionizing radiation (IR)-induced NF-kappaB activation in vivo and the role of NF-kappaB in IR-induced lymphocyte apoptosis.

MATERIALS AND METHODS

NF-kappaB activities were analysed by gel shift/supershift assay in isolated murine T- and B-cells, macrophages (MPhi) and tissues from normal and T- and B-cell-deficient Rag1 mice with or without exposure to IR. IR-induced lymphocyte apoptosis was determined by analysis of 3,3'-dihexyloxacarbocyanine iodide (DiOC(6)) uptake, annexin-V staining and the sub-G0/1 population, or by TUNEL assay.

RESULTS

The results showed that IR activated NF-kappaB in lymphocytes, including both T- and B-cells, but failed to do so in MPhi. Furthermore, T- and B-cell-deficient Rag1 mice exposed to IR exhibited a significant reduction in NF-kappaB activation as compared with normal mice. Although NF-kappaB1 (p50) gene knockout or NF-kappaB decoy oligonucleotide treatment specifically inhibited IR-induced lymphocyte NF-kappaB activation, they had no significant effect on IR-induced lymphocyte apoptosis.

CONCLUSIONS

This finding suggests that lymphocytes are the main cellular origin of IR-induced NF-kappaB activation in vivo. However, NF-kappaB activation has no significant effect on IR-induced lymphocyte apoptosis.

Combined deficiency in IkappaBalpha and IkappaBepsilon reveals a critical window of NF-kappaB activity in natural killer cell differentiation

Nuclear factor kappaB (NF-kappaB) transcription factors are key regulators of immune, inflammatory, and acute-phase responses and are also implicated in the control of cell proliferation and apoptosis. While perturbations in NF-kappaB activity impact strongly on B- and T-cell development, little is known about the role for NF-kappaB in natural killer (NK) cell differentiation. Inhibitors of NF-kappaB (IkappaBs) act to restrain NF-kappaB activation. We analyzed the cell-intrinsic effects of deficiencies in 2 IkappaB members (IkappaBalpha and IkappaBepsilon) on NK cell differentiation. Neither IkappaBalpha nor IkappaBepsilon deficiency had major effects on NK cell generation, while their combined absence led to NF-kappaB hyperactivation, resulting in reduced NK cell numbers, incomplete NK cell maturation, and defective interferon gamma (IFN-gamma) production. Complementary analysis of transgenic mice expressing an NF-kappaB-responsive reporter gene showed increased NF-kappaB activity at the stage of NK cell development corresponding to the partial block observed in IkappaBalpha x IkappaBepsilon-deficient mice. These results define a critical window in NK cell development in which NF-kappaB levels may be tightly controlled.

Suppression of Staphylococcal Enterotoxin B-induced Toxicity by a Nuclear Import Inhibitor

Staphylococcal enterotoxin B and related toxins that target T cells have the capacity to elicit systemic inflammation, tissue injury, and death. Genes that encode mediators of inflammation can be globally inhibited by blocking the nuclear import of stress-responsive transcription factors. Here we show that cell-permeant peptides targeting Rch1/importin alpha/karyopherin alpha 2, a nuclear import adaptor protein, are delivered to T cells where they inhibit the staphylococcal enterotoxin B-induced production of inflammatory cytokines ex vivo in cultured primary spleen cells and in vivo. The systemic production of tumor necrosis factor alpha, interferon gamma, and interleukin-6 was attenuated in mice either by a cell-permeant cyclized form of SN50 peptide or by a transgene whose product suppresses the nuclear import of transcription factor nuclear factor kappa B in T cells. The extent of liver apoptosis and hemorrhagic necrosis was also reduced, which correlated with significantly decreased mortality rates. These findings highlight nuclear import inhibitors as a potentially useful countermeasure for staphylococcal enterotoxin B and other toxins that trigger harmful systemic inflammatory responses.

X-linked ectodermal dysplasia and immunodeficiency caused by reversion mosaicism of NEMO reveals a critical role for NEMO in human T-cell development and/or survival

X-linked ectodermal dysplasia and immunodeficiency (XL-EDA-ID) is an X-linked recessive disease caused by a mutation in the nuclear factor-kappaB (NF-kappaB) essential modulator (NEMO). Here we report an XL-EDA-ID patient with atypical features of very few naive-phenotype T cells and defective mitogen-induced proliferation of peripheral blood mononuclear cells (PBMCs). The patient's NEMO defect was diagnosed by flow cytometric analysis of intracellular NEMO staining. Specific cell lineages (monocytes and neutrophils) expressed reduced levels of NEMO, but 2 populations of T, B, and NK cells were detected with normal and reduced expression of NEMO. Genomic analysis revealed that duplication of a 4.4-kb sequence ranging from intron 3 to exon 6 caused the reduced expression of NEMO. Polymorphism analysis showed that the patient's B- and T-cell lines with reduced and normal expression of NEMO had the same X chromosome, indicating that the somatic mosaicism was not due to fetomaternal transfusion but was most likely due to postzygotic reversion. This XLEDA-ID case adds to our understanding of NEMO biology, indicating that NEMO is critical for T-cell development and/or survival in humans as well as in mice.

Complex and dynamic redistribution of NF-kappaB signaling intermediates in response to T cell receptor stimulation

The central zone of the supramolecular activation cluster (c-SMAC) is a zone of T cell receptor (TCR) enrichment that forms at a T cell/antigen-presenting cell (APC) junction in response to antigen stimulation. We demonstrate that there is a surprisingly complex relocalization process that brings PKC and Bcl10, two intermediates in TCR activation of NF-kappaB, to the cytoplasmic face of the c-SMAC. TCR activation causes enrichment of PKC at the c-SMAC, followed by Bcl10 relocalization to punctate cytoplasmic structures, often at sites distant from the c-SMAC. These Bcl10 structures then undergo further relocalization, becoming enriched at the c-SMAC. TCR activation of NF-kappaB therefore involves the dynamic relocalization of multiple signaling intermediates, with distinct phases proximal to and distant from the c-SMAC.

To be, or not to be: NF-kappaB is the answer--role of Rel/NF-kappaB in the regulation of apoptosis

During their lifetime, cells encounter many life or death situations that challenge their very own existence. Their survival depends on the interplay within a complex yet precisely orchestrated network of proteins. The Rel/NF-kappaB signaling pathway and the transcription factors that it activates have emerged as critical regulators of the apoptotic response. These proteins are best known for the key roles that they play in normal immune and inflammatory responses, but they are also implicated in the control of cell proliferation, differentiation, apoptosis and oncogenesis. In recent years, there has been remarkable progress in understanding the pathways that activate the Rel/NF-kappaB factors and their role in the cell's decision to either fight or surrender to apoptotic challenge. Whereas NF-kappaB is most commonly involved in suppressing apoptosis by transactivating the expression of antiapoptotic genes, it can promote programmed cell death in response to certain death-inducing signals and in certain cell types. This review surveys our current understanding of the role of NF-kappaB in the apoptotic response and focuses on many developments since this topic was last reviewed in Oncogene 4 years ago. These recent findings shed new light on the activity of NF-kappaB as a critical regulator of apoptosis in the immune, hepatic, epidermal and nervous systems, on the mechanisms through which it operates and on its role in tissue development, homoeostasis and cancer.

IkappaBalpha/IkappaBepsilon deficiency reveals that a critical NF-kappaB dosage is required for lymphocyte survival

In most cells, the NF-kappaB transcription factor is sequestered in the cytoplasm by interaction with inhibitory proteins, the IkappaBs. Here, we show that combined IkappaBalpha/IkappaBepsilon deficiency in mice leads to neonatal death, elevated kappaB binding activity, overexpression of NF-kappaB target genes, and disruption of lymphocyte production. In IkappaBalpha/IkappaBepsilon-deficient fetuses, B220+IgM+ B cells and single-positive T cells die by apoptosis. In adults, IkappaBalpha-/-IkappaBepsilon-/- reconstituted chimeras exhibit a nearly complete absence of T and B cells that is not rescued by cotransfer with wild-type bone marrow. These findings demonstrate that IkappaBs tightly control NF-kappaB activity in vivo and that increased NF-kappaB activity intrinsically impairs lymphocyte survival. Because reduction or rise of NF-kappaB activity leads to similar dysfunction, they also reveal that only a narrow window of NF-kappaB activity is tolerated by lymphocytes.

A hypermorphic IkappaBalpha mutation is associated with autosomal dominant anhidrotic ectodermal dysplasia and T cell immunodeficiency

X-linked anhidrotic ectodermal dysplasia with immunodeficiency (XL-EDA-ID) is caused by hypomorphic mutations in the gene encoding NEMO/IKKgamma, the regulatory subunit of the IkappaB kinase (IKK) complex. IKK normally phosphorylates the IkappaB-inhibitors of NF-kappaB at specific serine residues, thereby promoting their ubiquitination and degradation by the proteasome. This allows NF-kappaB complexes to translocate into the nucleus where they activate their target genes. Here, we describe an autosomal-dominant (AD) form of EDA-ID associated with a heterozygous missense mutation at serine 32 of IkappaBalpha. This mutation is gain-of-function, as it enhances the inhibitory capacity of IkappaBalpha by preventing its phosphorylation and degradation, and results in impaired NF-kappaB activation. The developmental, immunologic, and infectious phenotypes associated with hypomorphic NEMO and hypermorphic IKBA mutations largely overlap and include EDA, impaired cellular responses to ligands of TIR (TLR-ligands, IL-1beta, and IL-18), and TNFR (TNF-alpha, LTalpha1/beta2, and CD154) superfamily members and severe bacterial diseases. However, AD-EDA-ID but not XL-EDA-ID is associated with a severe and unique T cell immunodeficiency. Despite a marked blood lymphocytosis, there are no detectable memory T cells in vivo, and naive T cells do not respond to CD3-TCR activation in vitro. Our report highlights both the diversity of genotypes associated with EDA-ID and the diversity of immunologic phenotypes associated with mutations in different components of the NF-kappaB signaling pathway.

Exacerbated inflammatory responses in transgenic mice expressing an inhibitor of apoptosis protein (OpIAP)

Members of the inhibitor of apoptosis protein family are involved not only in suppressing apoptosis, but also in signal transduction, cell division, and are associated with some types of cancers. Here we show that transgenic expression of the inhibitor of apoptosis protein OpIAP in murine T lymphocytes leads to a significant increase in T-cell receptor-induced cell activation, proliferation and cytokine production. Transgenic T lymphocytes expressing OpIAP have a lower proliferation threshold in response to T-cell receptor stimulation. Unstimulated OpIAP transgenic T lymphocytes show elevated nuclear levels of NF-kappaB transcription factor that increase after in vivo antigen peptide treatment. OpIAP transgenic animals present an exacerbated inflammatory response in an experimental contact hypersensitivity model, suggesting increased T-cell activation in vivo. These data indicate a new role for the inhibitor of apoptosis proteins in T-lymphocyte activation and proliferation.

Mature T cells depend on signaling through the IKK complex

The transcription factor NF-kappaB is implicated in various aspects of T cell development and function. The IkappaB kinase (IKK) complex, consisting of two kinases, IKK1/alpha and IKK2/beta, and the NEMO/IKKgamma regulatory subunit, mediates NF-kappaB activation by most known stimuli. Adoptive transfer experiments had demonstrated that IKK1 and IKK2 are dispensable for T cell development. We show here that T lineage-specific deletion of IKK2 allows survival of naive peripheral T cells but interferes with the generation of regulatory and memory T cells. T cell-specific ablation of NEMO or replacement of IKK2 with a kinase-dead mutant prevent development of peripheral T cells altogether. Thus, IKK-induced NF-kappaB activation, mediated by either IKK1 or IKK2, is essential for the generation and survival of mature T cells, and IKK2 has an additional role in regulatory and memory T cell development.

TCR-mediated Notch signaling regulates proliferation and IFN-gamma production in peripheral T cells

Notch genes encode membrane receptors that regulate cell fate decisions in metazoa. Notch receptors and ligands are expressed in developing lymphoid tissue and mature lymphocytes and the role of Notch signaling in early T and B cell development has been studied extensively. However, its contribution to mature T cell function is unknown. TCR-mediated T cell activation is a fundamental process of the adaptive immune system that has been studied for decades; however, the details of this process are incompletely understood. In this study, we present evidence that Notch is required for TCR-mediated activation of peripheral T cells. Inhibition of Notch activation dramatically decreases T cell proliferation in both CD4 and CD8 cells and blocks both NF-kappaB activity and IFN-gamma production in peripheral T cells. Our data reveal a new, nondevelopmental function of Notch as a previously unknown key link in peripheral T cell activation and cytokine secretion.

Antiapoptotic function of NF-kappaB in T lymphocytes is influenced by their differentiation status: roles of Fas, c-FLIP, and Bcl-xL

Inducible protection from apoptosis in vivo controls the size of cell populations. An important question in this respect is how differentiation affects mechanisms of apoptosis regulation. Among mature T lymphocytes, the NF-kappaB/Rel transcription factors are coupled to receptors that control cell population sizes by concurrently regulating survival and multiplication. In the present study, we used a transgenic inhibitor of NF-kappaB/Rel signaling to investigate the role of this pathway in proliferation and death of mature T cells in vivo. The results indicate that NF-kappaB integrates two critical yet distinct molecular pathways preventing apoptosis affected by the death receptor Fas, coordinately regulating levels of FLIP and Bcl-x(L) in primary T cells. Surprisingly, NF-kappaB blockade preferentially impacted naive as compared to memory T cells. The Fas/FasL pathway was linked to these findings by evidence that the abnormalities imposed by NF-kappaB inhibition were ameliorated by Fas deficiency, particularly for the CD4(+) lineage. Moreover, levels of an inhibitor of Fas-mediated apoptosis, c-FLIP, were diminished in cells expressing the transgenic inhibitor. NF-kappaB was also linked to T cell survival in vivo by mediating induction of Bcl-x(L): restoration of Bcl-x(L) levels reversed the preferential deficit of naive T cells, differentially impacting the CD4 and CD8 subsets. These results show that promoting survival and effective multiplication are central roles for NF-kappaB in T lymphoid homeostasis in vivo, but this effect and its underlying mechanisms are influenced by the developmental state of the lymphocyte.

Iron tetrakis (N-methyl-4'-pyridyl) porphyrinato inhibits proliferative activity of thymocytes by blocking activation of p38 mitogen-activated protein kinase, nuclear factor-kappaB, and interleukin-2 secretion

Iron tetrakis (N-methyl-4'-pyridyl) porphyrinato (FeTMPyP) has been demonstrated to be a potent scavenger of reactive oxygens and to have antiinflammatory activities. However, the effects of FeTMPyP on the function of T cells have not been illustrated. The objective of this study was to determine whether treatment of thymocytes with FeTMPyP inhibited the proliferative activity in response to various mitogens and, if so, to further characterize the mechanism of FeTMPyP immune modulation. The results indicate that treatment of thymocytes with FeTMPyP resulted in dose-dependent inhibition of thymocyte proliferation stimulated by concanawalin (Con) A-, Interleukin (IL)-1beta; or lipopdy socchande-exposed macrophage supernatant. FeTMPyP treatment also inhibited Con A- or IL-1beta-induced DNA-binding activity of NF-kappaB and IL-2 secretion by thymocytes. Both the p38 MAP kinase inhibitor SB203580 and the extracellular signal-regulated protein kinases inhibitor PD98059 blocked proliferative activity in Con A-stimulated thymocytes, while SB203580 but not PD98059 blocked nuclear factor (NF)-kappaB activation. FeTMPyP inhibited the activation and phosphorylation of p38 mitogen-activated protein kinase (MAPK) in response to Con A. These data suggest that FeTMPyP downregulates the proliferative activity by inhibition of p38 MAPK activation, NF-kappaB activation, and IL-2 secretion during mitogenic stimulation of thymocytes. Therefore, further studies concerning the effects of FeTMPyP on the human diseases associated with both inflammatory disorders and immunologic overactivation are warranted.

T cell-intrinsic requirement for NF-kappa B induction in postdifferentiation IFN-gamma production and clonal expansion in a Th1 response

NF-kappaB/Rel transcription factors are linked to innate immune responses and APC activation. Whether and how the induction of NF-kappaB signaling in normal CD4(+) T cells regulates effector function are not well-understood. The liberation of NF-kappaB dimers from inhibitors of kappaB (IkappaBs) constitutes a central checkpoint for physiologic regulation of most forms of NF-kappaB. To investigate the role of NF-kappaB induction in effector T cell responses, we targeted inhibition of the NF-kappaB/Rel pathway specifically to T cells. The Th1 response in vivo is dramatically weakened when T cells defective in their NF-kappaB induction (referred to as IkappaBalpha(DeltaN) transgenic cells) are activated by a normal APC population. Analyses in vivo, and IL-12-supplemented T cell cultures in vitro, reveal that the mechanism underlying this T cell-intrinsic requirement for NF-kappaB involves activation of the IFN-gamma gene in addition to clonal expansion efficiency. The role of NF-kappaB in IFN-gamma gene expression includes a modest decrease in Stat4 activation, T box expressed in T cell levels, and differentiation efficiency along with a more prominent postdifferentiation step. Further, induced expression of Bcl-3, a trans-activating IkappaB-like protein, is decreased in T cells as a consequence of NF-kappaB inhibition. Together, these findings indicate that NF-kappaB induction in T cells regulates efficient clonal expansion, Th1 differentiation, and IFN-gamma production by Th1 lymphocytes at a control point downstream from differentiation.

Distinctions between c-Rel and other NF-kappaB proteins in immunity and disease

c-Rel is a proto-oncogene first identified as the cellular counterpart of the v-Rel oncogene derived from the avian reticuloendotheliosis retrovirus (REV-T). It was subsequently discovered that c-Rel belongs to the NF-kappaB/Rel transcription factor family whose members share a common DNA recognition motif and similar signaling pathways. Despite the similarities, however, each NF-kappaB/Rel member possesses unique properties with regard to tissue expression pattern, response to receptor signals and target gene specificity. These differences are fairly evident from the non-redundant phenotypes exhibited by individual NF-kappaB/Rel knockout mice. Hence the work described in this review will compare and contrast the various physiological functions of c-Rel to those of other NF-kappaB members, particularly with respect to the regulation of proliferation, survival and effector functions in multiple hematopoietic and immunological cell types. The study of c-Rel knockout mice in several disease models will also be discussed as they reveal an important role for c-Rel in response to allergens, auto-antigens, allo-antigens and pathogenic infection.

Characterization of transcriptional regulation during negative selection in vivo

Negative selection is the process whereby immature thymocytes expressing TCRs with high affinity for self-peptide:MHC complexes are induced to undergo apoptosis. The transcriptional events that occur as a result of TCR signaling during negative selection are not well-characterized. Using oligonucleotide arrays, we have identified 33 genes that exhibit changes in RNA levels in CD4(+)CD8(+) thymocytes during negative selection in vivo. Of 18 genes that have been further characterized, 13 are regulated in response to stimulation with Ag or anti-CD3 and anti-CD28 Abs ex vivo, indicating that these genes are regulated independently of activation of the peripheral immune system. These data also support the idea that anti-CD3/CD28-mediated thymocyte apoptosis is a valid model for negative selection in vivo. A detailed examination of the regulation of many of the identified genes in response to treatment with dexamethasone or gamma-radiation or in response to anti-CD3/anti-CD28 stimulation in the presence of pharmacological inhibitors of mitogen-activated protein kinase kinase kinase 1, p38 mitogen-activated protein kinase, phosphatidylinositol 3-kinase, calcineurin, and cyclin-dependent kinase 2 has facilitated the elucidation of a map of the transcriptional events that occur downstream of the TCR. These studies support a model whereby similar signal transduction pathways are activated by stimuli that induce positive and negative selection and are consistent with the idea that the balance between opposing proapoptotic and antiapoptotic pathways determines cell fate. The data presented in this study also suggest that calcineurin functions to amplify TCR signals by promoting sustained increases in the levels of specific transcripts.