Functionally distinct NF-kappa B binding sites in the immunoglobulin kappa and IL-2 receptor alpha chain genes

Transient interactions modulate the affinity of NF-κB transcription factors for DNA

The dimeric nuclear factor kappa B (NF-κB) transcription factors (TFs) regulate gene expression by binding to a variety of κB DNA elements with conserved G:C-rich flanking sequences enclosing a degenerate central region. Toward defining mechanistic principles of affinity regulated by degeneracy, we observed an unusual dependence of the affinity of RelA on the identity of the central base pair, which appears to be noncontacted in the complex crystal structures. The affinity of κB sites with A or T at the central position is ~10-fold higher than with G or C. The crystal structures of neither the complexes nor the free κB DNAs could explain the differences in affinity. Interestingly, differential dynamics of several residues were revealed in molecular dynamics simulation studies, where simulation replicates totaling 148 μs were performed on NF-κB:DNA complexes and free κB DNAs. Notably, Arg187 and Arg124 exhibited selectivity in transient interactions that orchestrated a complex interplay among several DNA-interacting residues in the central region. Binding and simulation studies with mutants supported these observations of transient interactions dictating specificity. In combination with published reports, this work provides insights into the nuanced mechanisms governing the discriminatory binding of NF-κB family TFs to κB DNA elements and sheds light on cancer pathogenesis of cRel, a close homolog of RelA.

Distinct use of super-enhancer elements controls cell type-specific CD25 transcription and function

The IL-2 receptor α chain (IL-2Rα/CD25) is constitutively expressed on double-negative (DN2/DN3 thymocytes and regulatory T cells (Tregs) but induced by IL-2 on T and natural killer (NK) cells, with Il2ra expression regulated by a STAT5-dependent super-enhancer. We investigated CD25 regulation and function using a series of mice with deletions spanning STAT5-binding elements. Deleting the upstream super-enhancer region mainly affected constitutive CD25 expression on DN2/DN3 thymocytes and Tregs, with these mice developing autoimmune alopecia, whereas deleting an intronic region decreased IL-2-induced CD25 on peripheral T and NK cells. Thus, distinct super-enhancer elements preferentially control constitutive versus inducible expression in a cell type-specific manner. The mediator-1 coactivator colocalized with specific STAT5-binding sites. Moreover, both upstream and intronic regions had extensive chromatin interactions, and deletion of either region altered the super-enhancer structure in mature T cells. These results demonstrate differential functions for distinct super-enhancer elements, thereby indicating previously unknown ways to manipulate CD25 expression in a cell type-specific fashion.

The TNFα/TNFR2 axis mediates natural killer cell proliferation by promoting aerobic glycolysis

Natural killer (NK) cells are predominant innate lymphocytes that initiate the early immune response during infection. NK cells undergo a metabolic switch to fuel augmented proliferation and activation following infection. Tumor necrosis factor-alpha (TNFα) is a well-known inflammatory cytokine that enhances NK cell function; however, the mechanism underlying NK cell proliferation in response to TNFα is not well established. Here, we demonstrated that upon infection/inflammation, NK cells upregulate the expression of TNF receptor 2 (TNFR2), which is associated with increased proliferation, metabolic activity, and effector function. Notably, IL-18 can induce TNFR2 expression in NK cells, augmenting their sensitivity toward TNFα. Mechanistically, TNFα-TNFR2 signaling upregulates the expression of CD25 (IL-2Rα) and nutrient transporters in NK cells, leading to a metabolic switch toward aerobic glycolysis. Transcriptomic analysis revealed significantly reduced expression levels of genes involved in cellular metabolism and proliferation in NK cells from TNFR2 KO mice. Accordingly, our data affirmed that genetic ablation of TNFR2 curtails CD25 upregulation and TNFα-induced glycolysis, leading to impaired NK cell proliferation and antiviral function during MCMV infection in vivo. Collectively, our results delineate the crucial role of the TNFα-TNFR2 axis in NK cell proliferation, glycolysis, and effector function.

The CpG Dinucleotide Adjacent to a κB Site Affects NF-κB Function through Its Methylation

NF-κB is an important transcription factor that plays critical roles in cell survival, proliferation, inflammation, and cancers. Although the majority of experimentally identified functional NF-κB binding sites (κB sites) match the consensus sequence, there are plenty of non-functional NF-κB consensus sequences in the genome. We analyzed the surrounding sequences of the known κB sites that perfectly match the GGGRNNYYCC consensus sequence and identified the nucleotide at the -1 position of κB sites as a key contributor to the binding of the κB sites by NF-κB. We demonstrated that a cytosine at the -1 position of a κB site (-1C) could be methylated, which thereafter impaired NF-κB binding and/or function. In addition, all -1C κB sites are located in CpG islands and are conserved during evolution only when they are within CpG islands. Interestingly, when there are multiple NF-κB binding possibilities, methylation of -1C might increase NF-κB binding. Our finding suggests that a single nucleotide at the -1 position of a κB site could be a critical factor in NF-κB functioning and could be exploited as an additional manner to regulate the expression of NF-κB target genes.

Disturbed canonical nuclear factor of κ light chain signaling in B cells of patients with common variable immunodeficiency

BACKGROUND

Most patients with common variable immunodeficiency (CVID) present with severely reduced switched memory B-cell counts, and some display an increase of CD21^low B-cell counts (CVID 21low), whereas others do not (CVID 21norm). Altered B-cell receptor (BCR) signaling might contribute to the defective memory formation observed in patients with CVID.

OBJECTIVE

We sought to investigate canonical nuclear factor of κ light chain (NF-κB) signaling in B cells from patients with CVID as a central pathway in B-cell differentiation.

METHODS

Degradation of inhibitor of κBα (IκBα) and p65 phosphorylation, nuclear translocation of p65, and regulation of target genes and cell function were investigated after different modes of B-cell stimulation.

RESULTS

BCR-mediated canonical NF-κB signaling was impaired in all mature naive CVID-derived B cells. This impairment was more profound in naive B cells from CVID 21low patients than CVID 21norm patients and most pronounced in CD21^low B cells. The signaling defect translated into reduced induction of Bcl-xL and IκBα, 2 bona fide target genes of the canonical NF-κB pathway. CD40 ligand- and Toll-like receptor 9-mediated signaling were less strongly altered. Signaling in CD21^low B cells but not CD21⁺ B cells of patients with HIV was similarly affected.

CONCLUSION

Combined with the previous description of disturbed Ca²⁺ signaling, the discovery of NF-κB signaling defects, especially in CVID 21low patients, suggests a broad underlying signaling defect affecting especially BCR-derived signals. Given the immune phenotype of monogenic defects affecting Ca²⁺ and NF-κB signaling, the latter is more likely to contribute to the humoral deficiency. The strongly disturbed BCR signaling of CD21^low B cells is characteristic for this cell type and independent of the underlying disease.

Dysregulation of plasma amino acid levels in HIV-infection and cancer and its relevance for the immune system

T cells have a weak membrane transport actitivity for cystine but strong transport activity for cysteine. Even moderate variations of the cysteine concentration affect T cell functions in spite of the high concentration of cystine in cultures with physiological amino acid concentrations. The IL-2 dependent DNA synthesis and the activation of cytotoxic T cells are positively regulated by cysteine, while the activity of the transcription factor NFkB and the production of IL-2 are stimulated by active oxygen species and inhibited by cysteine or GSH. Macrophages, in contrast to T cells, take up more cystine than they need and release the excess after intracellular reduction as cysteine into the extracellular space. This "cysteine pumping activity" of macrophages raises intracellular GSH levels and DNA synthesis of T cells in the vicinity. The difference between the cystine transport activities of T cells and macrophages, therefore, enables T cells to switch between prooxidant and antioxidant states. The "cysteine pump" favors selectively the antigen-specific T cells that are about to be stimulated by antigen-presenting macrophages. The capacity of macrophages to take up cystine and to release cysteine is inhibited, however, by elevated extracellular glutamate concentrations. Elevated plasma glutamate levels have been found in several pathological conditions including cancer and HIV-infection. In HIV-infected patients, the hyperglutamataemia is aggravated by hypocystinaemia and hypocysteinaemia. Our studies, therefore, suggest that the cysteine supply is impaired in several pathological conditions with immunodeficiencies including AIDS. N-acetyl-cysteine (NAC) is a safe and well established drug that may be considered for the treatment of patients with HIV-infection.

Transcriptional regulation via the NF-kappaB signaling module

Stimulus-induced nuclear factor-kappaB (NF-kappaB) activity, the central mediator of inflammatory responses and immune function, comprises a family of dimeric transcription factors that regulate diverse gene expression programs consisting of hundreds of genes. A family of inhibitor of kappaB (IkappaB) proteins controls NF-kappaB DNA-binding activity and nuclear localization. IkappaB protein metabolism is intricately regulated through stimulus-induced degradation and feedback re-synthesis, which allows for dynamic control of NF-kappaB activity. This network of interactions has been termed the NF-kappaB signaling module. Here, we summarize the current understanding of the molecular structures and biochemical mechanisms that determine NF-kappaB dimer formation and the signal-processing characteristics of the signaling module. We identify NF-kappaB-kappaB site interaction specificities and dynamic control of NF-kappaB activity as mechanisms that generate specificity in transcriptional regulation. We discuss examples of gene regulation that illustrate how these mechanisms may interface with other transcription regulators and promoter-associated events, and how these mechanisms suggest regulatory principles for NF-kappaB-mediated gene activation.

Both integrated and differential regulation of components of the IL-2/IL-2 receptor system

Interleukin-2 was discovered in 1976 as a T-cell growth factor. It was the first type I cytokine cloned and the first for which a receptor component was cloned. Its importance includes its multiple actions, therapeutic potential, and lessons for receptor biology, with three components differentially combining to form high, intermediate, and low-affinity receptors. IL-2Ralpha and IL-2Rbeta, respectively, are markers for double-negative thymocytes and regulatory T-cells versus memory cells. gamma(c), which is shared by six cytokines, is mutated in patients with X-linked severe-combined immunodeficiency. We now cover an under-reviewed area-the regulation of genes encoding IL-2 and IL-2R components, with an effort to integrate/explain this knowledge.

Notch1 augments NF-kappaB activity by facilitating its nuclear retention

Notch1 specifically upregulates expression of the cytokine interferon-gamma in peripheral T cells through activation of NF-kappaB. However, how Notch mediates NF-kappaB activation remains unclear. Here, we examined the temporal relationship between Notch signaling and NF-kappaB induction during T-cell activation. NF-kappaB activation occurs within minutes of T-cell receptor (TCR) engagement and this activation is sustained for at least 48 h following TCR signaling. We used gamma-secretase inhibitor (GSI) to prevent the cleavage and subsequent activation of Notch family members. We demonstrate that GSI blocked the later, sustained NF-kappaB activation, but did not affect the initial activation of NF-kappaB. Using biochemical approaches, as well as confocal microscopy, we show that the intracellular domain of Notch1 (N1IC) directly interacts with NF-kappaB and competes with IkappaBalpha, leading to retention of NF-kappaB in the nucleus. Additionally, we show that N1IC can directly regulate IFN-gamma expression through complexes formed on the IFN-gamma promoter. Taken together, these data suggest that there are two 'waves' of NF-kappaB activation: an initial, Notch-independent phase, and a later, sustained activation of NF-kappaB, which is Notch dependent.

A negative regulatory element-dependent inhibitory role of ITF2B on IL-2 receptor alpha gene

Despite the fact that the negative regulatory element (NRE) within the upstream regulatory region of human IL-2 receptor alpha (IL-2Ralpha) gene has been identified two decades ago, mechanisms of the NRE function on the gene are hitherto unknown. In this paper, we report for the first time that the immunoglobulin transcription factor 2B (ITF2B) encoded by transcription factor 4 (TCF4) gene is a NRE binding protein. The full-length TCF4 cDNA clone was obtained from a HTLV-1 transformed human peripheral T cell MACHERMAKER cDNA library with NRE as the bait in yeast one-hybrid system. The NRE binding ability of ITF2B was further confirmed in chromatin-immunoprecipitation assay. Competitive RT-PCR-based promoter activity assay showed that over-expression of ITF2B protein inhibited the expression of IL-2Ralpha gene in Jurkat cells in an NRE-dependent manner. The function of ITF2B on the inhibition of both the IL-2Ralpha and the 5'LTR activity of HIV-1 shed light on the essence of NRE binding protein as a potential target for immune therapy and treatment in AIDS patients.

Smad-dependent cooperative regulation of interleukin 2 receptor alpha chain gene expression by T cell receptor and transforming growth factor-beta

The interleukin 2 receptor alpha chain (IL-2Ralpha) is a component of high affinity IL-2 receptors and thus critically regulates T cell growth and other lymphoid functions. Five positive regulatory regions together control lineage-restricted and activation-dependent IL-2Ralpha induction in response to antigen and IL-2. We now show that TGF-beta cooperates with T cell receptor (TCR) signaling to increase IL-2Ralpha gene expression. Moreover, we identify a sixth positive regulatory region that regulates IL-2Ralpha expression in cells treated with anti-CD3 + anti-CD28 as well as TGF-beta and show that this region contains binding sites for Smad3, AP-1, and cAMP-responsive element-binding protein/ATF proteins. The importance of Smad complexes is indicated by impaired IL-2Ralpha induction by TGF-beta in CD4+ T cells from both Smad3-/- and Smad4-/- mice. Thus, we have identified a novel positive regulatory region in the IL-2Ralpha gene that mediates TGF-beta-dependent induction of the gene. These findings have implications related to IL-2Ralpha expression on activated T cells and regulatory T cells.

Cellular FLIP (long form) regulates CD8+ T cell activation through caspase-8-dependent NF-kappa B activation

Cellular FLIP long form (c-FLIP(L)) was originally identified as an inhibitor of Fas (CD95/Apo-1). Subsequently, additional functions of c-FLIP(L) were identified through its association with receptor-interacting protein (RIP)1 and TNFR-associated factor 2 to activate NF-kappaB, as well as by its association with and activation of caspase-8. T cells from c-FLIP(L)-transgenic (Tg) mice manifest hyperproliferation upon activation, although it was not clear which of the various functions of c-FLIP(L) was involved. We have further explored the effect of c-FLIP(L) on CD8(+) effector T cell function and its mechanism of action. c-FLIP(L)-Tg CD8(+) T cells have increased proliferation and IL-2 responsiveness to cognate Ags as well as to low-affinity Ag variants, due to increased CD25 expression. They also have a T cytotoxic 2 cytokine phenotype. c-FLIP(L)-Tg CD8(+) T cells manifest greater caspase activity and NF-kappaB activity upon activation. Both augmented proliferation and CD25 expression are blocked by caspase inhibition. c-FLIP(L) itself is a substrate of the caspase activity in effector T cells, being cleaved to a p43(FLIP) form. p43(FLIP) more efficiently recruits RIP1 than full-length c-FLIP(L) to activate NF-kappaB. c-FLIP(L) and RIP1 also coimmunoprecipitate with active caspase-8 in effector CD8(+) T cells. Thus, one mechanism by which c-FLIP(L) influences effector T cell function is through its activation of caspase-8, which in turn cleaves c-FLIP(L) to allow RIP1 recruitment and NF-kappaB activation. This provides a partial explanation of why caspase activity is required to initiate proliferation of resting T cells.

Synergistic activation of the CMV promoter by NF-kappaB P50 and PKG

Several DNA binding NF-kappaB subunits are substrates for cGMP-dependent kinase (PKG) and their transactivation from cognate sites is induced by phosphorylation. This includes p50, which does not have a transcriptional activation domain and therefore needs to bind to other proteins to mediate gene expression. Here, we describe the synergistic transactivation by p50 and PKG from the CMV promoter. This is caused not only by phosphorylation of p50, leading to increased DNA binding, but also by PKG-dependent activation of CRE sites in the promoter. One of the CRE sites is located directly adjacent to a NF-kappaB site and is essential for p50-mediated induction of transcription. According to the binding of CREB to p50 in pull-down assays and according to the inhibition of p50-dependent transactivation by dominant-negative CREB, this reflects the formation of a transcription factor complex containing CREB and p50. The nuclear translocation of NF-kappaB is insufficient to distinguish among the multitude of promoters that harbor cognate recognition sites. The phosphorylation of multiple transcription factors by an upstream kinase, such as PKG, can lead to the formation of transcription factor complexes and differential transactivation from a subset of NF-kappaB sites. These interactions may be relevant for the activation of viral gene expression.

STAT4 is required for interleukin-12-induced chromatin remodeling of the CD25 locus

Signal transducer and activator of transcription 4 (STAT4) is a critical mediator of interleukin-12 (IL-12)-stimulated inflammatory immune responses. Despite extensive analysis of the immune responses of STAT4-deficient mice, there is still very little understood about STAT4-dependent gene induction. IL-12 stimulated increases in IL-2 receptor alpha chain gene (CD25) mRNA levels and surface expression require STAT4. In this report, we utilize chromatin immunoprecipitation assays to analyze IL-12-stimulated and STAT4-dependent changes in chromatin remodeling of the CD25 gene. Gene activation requires binding of STAT4 to the PRRIII upstream regulatory element, the recruitment of the CREB-binding protein (CBP), and chromatin remodeling including increased acetylation and decreased methylation of histones within the CD25 promoter. Evidence suggests that STAT4 also facilitates binding of other factors to the CD25 promoter including c-Jun. Thus, these results provide a model for STAT4-dependent gene induction and a mechanism for cytokine-induced expression of the CD25 gene.

Nuclear factor kappa B decoy oligodeoxynucleotides prevent endotoxin-induced fatal liver failure in a murine model

Endotoxin syndrome is a systemic inflammatory response mediated by inflammatory cytokines. Nuclear factor kappa B (NF-kappa B) is the dominant regulator of the production of these cytokines by inflammatory cells. The aim of this study was to assess the efficacy of in vivo transfer of synthetic double-stranded oligodeoxynucleotides (ODN) with high affinity against NF-kappa B (NF-kappa B/decoy/ODN) as a therapeutic strategy for treating endotoxin-induced fatal liver injury. Liver injury was induced by administration of lipopolysaccharide (LPS) to Propionibacterium acnes-primed BALB/C mice. NF-kappa B/decoy/ODN was transferred into the portal vein using a fusigenic liposome with hemagglutinating virus of Japan. NF-kappa B/decoy/ODN was preferentially transferred to Kupffer cells, and activation of NF-kappa B after the LPS challenge was suppressed, leading to decreased inflammatory cytokine production. As a result, the massive necrosis and hepatocyte apoptosis observed in the control mice was dramatically attenuated and the survival rate improved. In conclusion, NF-kappa B/decoy/ODN transfer in vivo effectively suppressed endotoxin-induced fatal liver injury in mice.

TNF-alpha and IFN-gamma regulate the expression of the NOD2 (CARD15) gene in human intestinal epithelial cells

BACKGROUND & AIMS

NOD2, a member of the NOD1/Apaf-1 family, was recently identified as the first susceptibility gene for Crohn's disease. The aim of this report was to describe the regulation and functional significance of NOD2 expression in intestinal epithelial cells.

METHODS

Expression of NOD2 messenger RNA was determined by reverse-transcription polymerase chain reaction (RT-PCR); NOD2 protein was detected by Western blot. Promoter activity was assessed by reporter gene assays and DNA-binding of NF-kappaB by electrophoretic mobility shift assays. IL-8 production was investigated by RT-PCR and enzyme-linked immunosorbent assay.

RESULTS

TNF-alpha induced an up-regulation of NOD2 in epithelial cell lines (HT-29, SW620, SW948, HeLa S3) and in primary colonic epithelial cells. A synergism was seen by cotreatment with IFN-gamma. Two NF-kappaB binding sites were identified in the promoter. Deletion of either site or overexpression of dominant negative IkappaBalpha led to reduced levels of TNF-alpha/IFN-gamma-stimulated reporter gene activity. The identified kappaB3 site was bound by NF-kappaB as determined by gelshift assays. Elevated amounts of NOD2 protein were also found in colonic epithelial cells from patients with IBD. LPS induced high levels of IL-8 production in SW620 cells overexpressing NOD2.

CONCLUSIONS

TNF-alpha(/IFN-gamma) treatment up-regulates the expression of the NOD2 gene in intestinal epithelial cells and subsequently increases their LPS susceptibility. Together with the mutation-derived truncation and functional change of the NOD2 protein, this could be part of the complex pathophysiology of barrier disruption as it is observed in inflammatory bowel diseases.

NF-kappa B1 is required for optimal CD4+ Th1 cell development and resistance to Leishmania major

The NF-kappaB family of transcription factors regulates the expression of a wide range of immune response genes involved in immunity to pathogens. However, the need for individual family members in regulating innate and adaptive immune responses in vivo has yet to be clearly defined. We investigated the role of NF-kappaB1 in the induction of protective IL-12-dependent Th1 cell responses following infection with the intracellular protozoan parasite Leishmania major. Whereas wild-type C57BL/6 mice controlled parasite replication, NF-kappaB1 knockout (KO) mice were susceptible to infection, developing chronic unresolving lesions associated with persistent parasites. There was a profound defect in Ag-specific CD4(+) T cell proliferation and IFN-gamma production in infected KO mice, although innate responses-including IL-12 production and control of intracellular parasite replication by macrophages-were intact. In vitro polyclonal stimulation of purified naive KO T cells revealed an intrinsic defect in CD4(+) T cell proliferation associated with reduced IL-2 receptor expression, but operating independently of APC function and IL-2 production. Critically, the frequency of proliferating KO CD4(+) T cells secreting IFN-gamma matched that of wild-type cells, suggesting that NF-kappaB1 was not required for efficient transcription of the IFN-gamma gene. Taken together, these results identify a novel role for NF-kappaB1 in CD4(+) T cell proliferation and the development of Th1 cell responses required for protective immunity against intracellular pathogens.

The kappa B DNA sequence from the HIV long terminal repeat functions as an allosteric regulator of HIV transcription

NF-kappaB is an inducible transcription factor involved in the immune response, inflammation, and viral transcription. To address how the two NF-kappaB and three Sp1 binding sites of the human immunodeficiency virus (HIV) long terminal repeat (LTR) control multiple activator assembly and transcription, we first observed and compared unique conformations between the crystallographic structure of the NF-kappaB p50.p65 heterodimer bound to the uPA-kappaB target site to that of the p50.p65.HIV-kappaB complex. Next, cooperativity between two NF-kappaB molecules bound to tandem HIV-kappaB sequences was measured as well as that of NF-kappaB and transcription factor Sp1 when bound to adjacent sites. The cooperativity of hybrid HIV-LTR enhancers was measured with the 3' kappaB site converted to uPA-kappaB or to interferon beta gene enhancer kappaB. The hybrids were defective in transcriptional activator assembly and less active transcriptionally. These functional differences correlate with observed conformational differences and demonstrate that distinct kappaB DNA sequences function as allosteric regulators in a gene-specific manner.

The basis for TCR-mediated regulation of the IL-2 receptor alpha chain gene: role of widely separated regulatory elements

The interleukin-2 receptor alpha (IL-2Ralpha) chain is a component of high-affinity IL-2 receptors and thus is a key regulator of lymphocyte proliferation. Lineage-restricted and activation-dependent IL-2Ralpha transcription is controlled by four upstream positive regulatory regions (PRRs) and one downstream PRR. We now demonstrate that T-cell receptor (TCR) responsiveness requires both upstream sequences and an intronic region, PRRIV, previously identified as an IL-2 response element. Whereas IL-2 responsiveness requires Stat5 and HMG-I(Y) binding, TCR responsiveness of PRRIV requires two AP-1- and two NFAT-binding sites that bind Jun, Fos and NFAT family members in vitro and in vivo. Moreover, IL-2Ralpha induction is impaired in T lymphocytes from transgenic mice expressing a dominant-negative c-jun construct, or following treatment with cyclosporin A. Thus, our data indicate an important role for both AP-1 and NFAT proteins for TCR-induced IL-2Ralpha expression and establish that both upstream and intronic sequences mediate TCR responsiveness of the IL-2Ralpha gene. Moreover, our data reveal a previously unappreciated link between the TCR-mediated up-regulation of the IL-2 and IL-2Ralpha genes.

Control of IL-2Ralpha gene expression: structural changes within the proximal enhancer/core promoter during T-cell development

During T-cell development in thymus, CD25, the IL-2 receptor alpha chain (IL-2Ralpha) is already expressed in early double-negative (DN) thymocytes where commitment to T-cell lineage has been established, but subsequently IL-2Ralpha is dramatically down-regulated for the remainder of T-cell development. The loss of IL-2Ralpha expression after expression of the pre-TCR alpha:beta complex on the cell surface is essential for the later specific responses of mature T cells. Using appropriate mouse models and DMS genomic footprinting, we showed that the TATA box in the core promoter region of the murine IL-2Ralpha locus was occupied only in DN CD25+ T cells. Further, by chromatin immunoprecipitation assays, we evidenced that down-regulation of IL-2Ralpha transcription correlated with (i) loss of the basal transcriptional machinery; (ii) dissociation of histone acetylase p300 and BRG1, a member of the ATP-dependent chromatin remodeling complex SWI/SNF; and (iii) histone N-termini dephosphorylation plus deacetylation. In contrast, occupancy of the proximal enhancer region (positive regulatory region I) was not detected by in vivo genomic footprinting though constitutive accessibility of the promoter region for DNase I digestion both in the DN and double-positive stages correlated with the constitutive association of CBP and PCAF to the IL-2Ralpha core promoter. These results exemplify one mechanism by which a promoter enables transcription to switch on and off during T-cell differentiation.

Structure of NF-kappaB p50/p65 heterodimer bound to the PRDII DNA element from the interferon-beta promoter

Upon viral infection, NF-kappaB translocates to the nucleus and activates the IFN-beta gene by binding to the PRDII element. Strikingly, NF-kappaB loses its ability to activate the IFN-beta gene when the PRDII element is substituted by closely related sites. We report here the crystal structure of NF-kappaB p50/p65 heterodimer bound to the PRDII element from the IFN-beta promoter. The structure reveals an unexpected alteration in configuration, in which the p50 specificity domain moves by as much as approximately 9 A when compared to NF-kappaB heterodimer bound to the immunoglobulin kappaB site (Ig-kappaB) while maintaining the same base-specific contacts with the DNA. Taken together, the structure offers new insights into the allosteric effects of closely related DNA sites on the configuration of NF-kappaB and its transcriptional selectivity.

Selected contribution: Association of gender-related LMP2 inactivation with autoimmune pathogenesis

Recent results in an animal model of autoimmune diabetes, the nonobese diabetic (NOD) mouse, suggest a hypothesis to explain the role of major histocompatibility complex (MHC) in autoimmunity. The genome MHC region contains immune response genes that are important for T cell education and antigen presentation by MHC molecules. Two such genes encoding the LMP2 and LMP7 proteasome subunits are located in this high-risk MHC genomic region. Proteasome containing the LMP2 subunit is essential for T cell education and proteolytically activates transcription factor nuclear factor-kappaB. Splenocytes of NOD mouse with marked female specificity for disease expression are defective in LMP2 expression. The spontaneous defective LMP2 expression in NOD mice, which is gender biased toward female cohorts, is restricted to select lymphoid and myeloid cells and is developmentally controlled with lowered LMP2 protein and heightened tumor necrosis factor-alpha-induced apoptosis. These defects are apparent only after approximately 7 wk of age. These data suggest a proteasome role in autoimmune progression, and a gender developmental and lineage restriction of LMP2 expression may contribute to the diverse autoimmune characteristics preferentially observed in female NOD mice.

Antisense phosphorothioate oligonucleotides to the p65 subunit of NF-kappaB abrogate fulminant septic shock induced by S. typhimurium in mice

The aim of this study was to characterize the functional relevance of the transcription factor NF-kappaB in the pathogenesis of septic shock. BALB/c mice were infected with two wild-type (WT 1, WT 2) strains of S. typhimurium that induce NF-kappaB or an escape variant that lacks this ability (P21) at a dose of 1 x 109/animal, respectively. Furthermore, wild-type infected mice were treated with antisense oligonucleotides directed against NF-kappaB 24 h before and 3 or 6 h after infection, while mismatched oligonucleotides were used as controls. Subsequently, the clinical course, histological and immunological alterations were monitored. Infection with WT 1 and WT 2 strains led to lethal septic shock within 24-36 h. In contrast, infection with the P21 variant was not followed by fulminant septic shock. Treatment with specific antisense oligonucleotides against the p65 subunit of NF-kappaB 24 h before infection prevented the development of fulminant, lethal septic shock and was associated with a significant increase of survival. After 20 h, markedly depressed serum levels of interferon (IFN)-gamma and interleukin (IL)-6 but not IL-10 and tumour necrosis factor (TNF)-alpha were observed in p65 antisense-treated compared to mismatched-treated animals. These data show that the ability of S. typhimurium to induce lethal septic shock is critically dependent on their capacity to induce NF-kappaB.

The basis for IL-2-induced IL-2 receptor alpha chain gene regulation: importance of two widely separated IL-2 response elements

The interleukin-2 receptor alpha (IL-2Ralpha) chain is an essential component of high-affinity IL-2 receptors. Accordingly, IL-2Ralpha expression helps to regulate T cell growth and other lymphoid functions. Lineage-restricted and activation-dependent IL-2Ralpha transcription is controlled by three upstream positive regulatory regions (PRRs). We now describe an additional IL-2 response element, PRRIV, within intron 1, in humans and mice. PRRIV activity requires GAS motifs that bind Stat5 proteins and additional upstream HMG-I(Y) binding sites. Moreover, IL-2 induces the binding of HMG-I(Y), Stat5a, and Stat5b in vivo to PRRIV and PRRIII, which also functions as an IL-2 response element. Thus, the IL-2 inducibility of the IL-2Ralpha gene is unexpectedly mediated by two widely separated regulatory Stat5-dependent elements, located both upstream and downstream of the transcription initiation sites.

NF-kappa B/Rel participation in the lymphokine-dependent proliferation of T lymphoid cells

Proliferative responses of lymphoid cells to IL-2 and IL-4 depend on activation of the cells, but the mechanism(s) by which activation enhances cellular competence to respond to cytokines is not fully understood. The NF-kappaB/Rel family represents one signal transduction pathway induced during such activation. We show in this study that inhibition of NF-kappaB through the expression of an IkappaBalpha (inhibitory protein that dissociates from NF-kappaB) mutant refractory to signal-induced degradation (IkappaBalpha(DeltaN)) interfered with the acquisition of competence to proliferate in response to IL-4 as well as IL-2. Thymocytes and T cells from IkappaBalpha(DeltaN) transgenic mice expressed normal levels of IL-2R subunits. However, transgenic cells exhibited a dramatic defect in Stat5A activation treatment with IL-2, and a similar defect was observed for IL-4-induced Stat5. In contrast, T lymphoid cells with inhibition of NF-kappaB showed normal insulin receptor substrate-2 phosphorylation and only a modest decrease in Stat6 activation and insulin receptor substrate-1 phosphorylation after IL-4 stimulation. These results indicate that the NF-kappaB/Rel/IkappaBalpha system can regulate cytokine receptor capacitation through effects on the induction of downstream signaling by the Stat transcription factor family.

Autoantibodies to TNFalpha in HIV-1 infection: prospects for anti-cytokine vaccine therapy

Tumor necrosis factor alpha (TNFalpha) is a proinflammatory cytokine principally involved in the activation of lymphocytes in response to viral infection. TNFalpha also stimulates the production of other cytokines, activates NK cells and potentiates cell death and/or lysis in certain models of viral infection. Although TNFalpha might be expected to be a protective component of an antiviral immune response, several lines of evidence suggest that TNFalpha and other virally-induced cytokines actually may contribute to the pathogenesis of HIV infection. Based on the activation of HIV replication in response to TNFalpha, HIV appears to have evolved to take advantage of host cytokine activation pathways. Antibodies to TNFalpha are present in the serum of normal individuals as well as in certain autoimmune disorders, and may modulate disease progression in the setting of HIV infection. We examined TNFalpha-specific antibodies in HIV-infected non-progressors and healthy seronegatives; anti-TNFalpha antibody levels are significantly higher in GRIV seropositive slow/non-progressors (N = 120, mean = 0.24), compared to seronegative controls (N= 12, mean = 0.11). TNFalpha antibodies correlated positively with viral load, (P = 0.013, r = 0.282), and CD8+ cell count (P = 0.03, r = 0.258), and inversely with CD4+ cell count (P = 0.003, r = - 0.246), percent CD4+ cells (P = 0.008, r = -0.306), and CD4 :CD8 ratio (P = 0.033, r = - 0.251). TNFalpha antibodies also correlated positively with antibodies to peptides corresponding to the CD4 binding site of gp160 (P = 0.001, r = 0.384), the CD4 identity region (P = 0.016, r = 0.29), the V3 loop (P = 0.005, r = 0.34), and the amino terminus of Tat (P = 0.001, r = 0.395); TNFalpha antibodies also correlated positively with antibodies to Nef protein (P = 0.008, r = 0.302). The production of anti-TNFalpha antibodies appears to be an adaptive response to HIV infection and suggests the potential utility of modified cytokine vaccines in the treatment of HIV infections as well as AIDS-related and unrelated autoimmune and CNS disorders.

Identification and characterization of nuclear factor kappaB binding sites in the murine bcl-x promoter

Signal transduction pathways that mediate neuronal commitment to apoptosis involve the nuclear factor kappaB (NF-kappaB) transcription factor. Bcl-X(L) is a potent regulator of apoptosis in the CNS and is highly expressed in the developing and adult brain. We identified three putative NF-kappaB DNA binding sequences clustered upstream of the brain-specific transcription start site in the upstream promoter region. Recombinant p50/p50 and NF-kappaB proteins from nuclear extracts bound to these sites as determined by electrophoretic mobility shift assay and biotin-oligonucleotide/streptavidin affinity assays. NF-kappaB overexpression, coupled with bcl-x promoter/reporter assays using a series of murine bcl-x promoter and deletion mutants, has identified the downstream 1.1 kb of the bcl-x promoter as necessary for basal promoter activity and induction by NF-kappaB. The mutagenic removal of NF-kappaB binding sites individually or in combination revealed altered response patterns to p49/p65 and p50/p65 overexpression. These results support the hypothesis that NF-kappaB can act to enhance Bcl-X(L) expression via highly selective interactions, where NF-kappaB binding and bcl-x promoter activation are dependent on both DNA binding site sequence and NF-kappaB subunit composition. Our data suggest that molecular events associated with NF-kappaB promote regulation of neuronal apoptosis in the developing or injured CNS.

Characterisation of NF-kappa B complexes in Theileria parva-transformedT cells

Transformation of T cells by the intracellular parasite Theileria parva is accompanied by constitutive I-kappa B degradation and NF-kappa B activation, a process which is essential to prevent the spontaneous apoptosis of these parasite-transformed cells. NF-kappa B-mediated responses are regulated by selective combinations of NF-kappa B proteins as homo- or heterodimers and by distinct kappa B motifs. We characterised the NF-kappa B complexes induced by T. parva infection in TpM(803) T cells. By western blot, we demonstrated that all members of the NF-kappa B/Rel family of proteins translocate to the nucleus of infected cells. Using two different kappa B oligonucleotides (kappa B-1 and kappa B-2), both containing the decameric consensus kappa B motif (GGGACTTTCC), clearly distinct patterns of DNA binding activities could be demonstrated in electrophoretic mobility shift assays. Supershift analysis and UV cross-linking assays showed that complexes binding to kappa B-1 consisted of p50, p65 and RelB homo and/or heterodimers. We could also detect an association of ATF-2 and c-Fos with one of the complexes. The HIV-derived kappa B-2 oligo only bound p50 and p65. Additionally, several agents known to inhibit a wide range of NF-kappa B activation pathways had no inhibitory effect on the activation of NF-kappa B DNA binding in TpM(803) T cells.

The role of the proteasome in autoimmunity

Type 1 diabetes is believed to be caused by T cell-mediated autoimmunity, with a prediabetic state characterized by the production of autoantibodies specific for proteins expressed by pancreatic beta cells. The non-obese diabetic (NOD) mouse is a spontaneous model of Type 1 diabetes with a strong genetic component that maps to the major histocompatibility complex (MHC) region of the genome. A specific proteasome defect has now been identified in NOD mouse lymphocytes that results from down-regulation of expression of the proteasome subunit LMP2, which is encoded by a gene in the MHC genomic region. This defect both prevents the proteolytic processing required for the production and activation of the transcription factor nuclear factor-kappaB (NF-kappaB), which plays an important role in immune and inflammatory responses, in addition to increasing the susceptibility of the affected cells to apoptosis induced by tumor necrosis factor-alpha (TNF-alpha). The proteasome dysfunction is both tissue- and developmental stage-specific and likely contributes to disease pathogenesis and tissue targeting.

Binding of HMG-I(Y) imparts architectural specificity to a positioned nucleosome on the promoter of the human interleukin-2 receptor alpha gene

Transcriptional induction of the interleukin-2 receptor alpha-chain (IL-2Ralpha) gene is a key event regulating T-cell-mediated immunity in mammals. In vivo, the T-cell-restricted protein Elf-1 and the general architectural transcription factor HMG-I(Y) cooperate in transcriptional regulation of the human IL-2Ralpha gene by binding to a specific positive regulatory region (PRRII) in its proximal promoter. Employing chromatin reconstitution analyses, we demonstrate that the binding sites for both HMG-I(Y) and Elf-1 in the PRRII element are incorporated into a strongly positioned nucleosome in vitro. A variety of analytical techniques was used to determine that a stable core particle is positioned over most of the PRRII element and that this nucleosome exhibits only a limited amount of lateral translational mobility. Regardless of its translational setting, the in vitro position of the nucleosome is such that DNA recognition sequences for both HMG-I(Y) and Elf-1 are located on the surface of the core particle. Restriction nuclease accessibility analyses indicate that a similarly positioned nucleosome also exists on the PRRII element in unstimulated lymphocytes when the IL-2Ralpha gene is silent and suggest that this core particle is remodeled following transcriptional activation of the gene in vivo. In vitro experiments employing the chemical cleavage reagent 1,10-phenanthroline copper (II) covalently attached to its C-terminal end demonstrate that HMG-I(Y) protein binds to the positioned PRRII nucleosome in a direction-specific manner, thus imparting a distinct architectural configuration to the core particle. Together, these findings suggest a role for the HMG-I(Y) protein in assisting the remodeling of a critically positioned nucleosome on the PRRII promoter element during IL-2Ralpha transcriptional activation in lymphocytes in vivo.

The role of Stat5a and Stat5b in signaling by IL-2 family cytokines

The activation of Stat5 proteins (Stat5a and Stat5b) is one of the earliest signaling events mediated by IL-2 family cytokines, allowing the rapid delivery of signals from the membrane to the nucleus. Among STAT family proteins, Stat5a and Stat5b are the two most closely related STAT proteins. Together with other transcription factors and co-factors, they regulate the expression of the target genes in a cytokine-specific fashion. In addition to their activation by cytokines, activities of Stat5a and Stat5b, as well as other STAT proteins, are negatively controlled by CIS/SOCS/SSI family proteins. The outcome of Stat5 activation in regulating expression of target genes varies, depending upon the complexity of the promoter region of target genes and the other signaling pathways that are activated by each cytokine as well. Here, we mainly focus on the IL2-/IL-2 receptor system, as it is one of the best-studied systems that depend on Stat5-mediated signals. We will summarize what we have learned about the molecular mechanisms of how Stat5 is activated by IL-2 family cytokines from in vitro biochemical studies as well as the role that is played by Stat5 in each of the cytokine signaling pathways from in vivo gene-targeting analyses. Oncogene (2000).

In vivo identification of lymphocyte subsets exhibiting transcriptionally active NF-kappaB/Rel complexes

To analyze the NF-kappaB/Rel activity pattern in a living organism, we previously generated transgenic mice carrying a kappaB-dependent lacZ gene. In situ analysis of both primary and secondary lymphoid organs revealed a strong NF-kappaB transcriptional activity in antigen-presenting cells, some endothelial cells and sinus lining cells of the lymph node capsula with very little activity in lymphocytes and thymocytes. Using fluorescein-di-beta-D-galactopyranoside (FDG) as a vital substrate for the beta-galactosidase, we re-examined by flow cytometry the NF-kappaB/Rel transcriptional activity in our mouse model. We report here that such constitutive NF-kappaB/Rel activity was significantly detected in thymocytes at the CD44+CD25(-) stage. This constitutive activity extended with CD25 expression to the majority of the CD44(-)CD25(+) thymocytes and was then restricted to a few mature T cells. In the spleen, constitutive NF-kappaB/Rel activity was found in most B cells, unlike T cells which were largely negative. Virgin IgD(+) B cells expressed higher levels of NF-kappaB transcriptional activity than other B cell types. Altogether, these results suggest that NF-kappaB/Rel complexes are key players in the in vivo differentiation of IgD(+) B lymphocytes and possibly CD25(+) thymocytes.

NF-kappaB p65 (RelA) homodimer uses distinct mechanisms to recognize DNA targets

BACKGROUND

The NF-kappaB family of dimeric transcription factors regulates the expression of several genes by binding to a variety of related DNA sequences. One of these dimers, p65(RelA), regulates a subclass of these targets. We have shown previously that p65 binds to the 5'-GGAA T TTTC-3' sequence asymmetrically. In that complex one subunit base specifically interacts with the preferred 5' half site and the other subunit binds non-specifically to the 3' half site.

RESULTS

Here we describe the crystal structures of two new p65-DNA complexes. One complex contains a pseudosymmetric 5'-GGAA T TTCC-3' DNA sequence taken from the enhancer of the gene encoding interleukin 8 (IL-8) and the other contains the asymmetric 5'-GGAA T TCCC-3' target DNA taken from the enhancer of the gene encoding type VII collagen. As expected, the global positioning of the dimer on both DNA targets is roughly symmetric, however, the hydrogen-bonding patterns at the protein-DNA interfaces differ significantly. One of the p65 monomers in complex with the asymmetric DNA binds to an extra base pair located immediately upstream of the 5'-GGAA-3' half site. We also show that p65 binds to these targets with almost equal affinity and that different residues have variable roles in binding different kappaB targets.

CONCLUSIONS

Taken together, these structures reveal that p65 exhibits the unique capability to specifically bind DNA targets of variable lengths from four to ten base pairs. Also, the small protein segment Arg41-Ser42-Ala43 is at least partially responsible for flexibility in DNA-binding modes.

Essential role of human leukocyte antigen-encoded proteasome subunits in NF-kappaB activation and prevention of tumor necrosis factor-alpha-induced apoptosis

The multisubunit proteasome complex is the principal mediator of nonlysosomal protein degradation. The proteasome subunit varies minimally between cells with the exception of LMP2, LMP7, and LMP10 subunits in rodent and human cells. LMP2 and LMP7 subunits are encoded by the human lymphocyte antigen region, and they optimize proteolytic mediated antigen presentation. The proteasome is also important for the function of transcription factor nuclear factor-kappaB (NF-kappaB). It is required for NF-kappaB subunits p50 and p52 generation and catalyzes degradation of phosphorylated IkappaBalpha. These proteasome-mediated reactions have now been shown to be defective in T2 cells, a human lymphocyte cell line that lacks both LMP2 and LMP7. Although T2 cells contain normal expression of p100 and p105, the abundance of p50 and p52 was greatly reduced. Tumor necrosis factor-alpha (TNF-alpha) induced normal phosphorylation of IkappaBalpha but failed to induce degradation of phosphorylated IkappaBalpha. Both DNA binding assays and luciferase assays revealed that TNF-alpha-induced NF-kappaB activation is defective in T2 cells. Unlike parental cells, T2 cells were susceptible to TNF-alpha-induced apoptosis. These data indicate human leukocyte antigen-linked proteasome subunits are essential for NF-kappaB activation and protection of cells from TNF-alpha-induced apoptosis.

Cytokine-induced nuclear factor kappa B activation promotes the survival of developing neurons

Ciliary neurotrophic factor (CNTF), leukemia inhibitory factor (LIF), cardiotrophin-1 (CT-1), and interleukin 6 (IL-6) comprise a group of structurally related cytokines that promote the survival of subsets of neurons in the developing peripheral nervous system, but the signaling pathways activated by these cytokines that prevent neuronal apoptosis are unclear. Here, we show that these cytokines activate NF-kappaB in cytokine-dependent developing sensory neurons. Preventing NF-kappaB activation with a super-repressor IkappaB-alpha protein markedly reduces the number of neurons that survive in the presence of cytokines, but has no effect on the survival response of the same neurons to brain-derived neurotrophic factors (BDNF), an unrelated neurotrophic factor that binds to a different class of receptors. Cytokine-dependent sensory neurons cultured from embryos that lack p65, a transcriptionally active subunit of NF-kappaB, have a markedly impaired ability to survive in response to cytokines, but respond normally to BDNF. There is increased apoptosis of cytokine- dependent neurons in p65(-/)- embryos in vivo, resulting in a reduction in the total number of these neurons compared with their numbers in wild-type embryos. These results demonstrate that NF-kappaB plays a key role in mediating the survival response of developing neurons to cytokines.

Defective function of the proteasome in autoimmunity: involvement of impaired NF-kappaB activation

Type 1 diabetes (also known as insulin-dependent diabetes mellitus or juvenile-onset diabetes) is usually caused by T cell-mediated autoimmunity, with a prediabetic state characterized by the production of autoantibodies specific for proteins expressed by pancreatic beta cells. The nonobese patient with diabetes (NOD) mouse is a spontaneous model of type 1 diabetes with a strong genetic component that maps to the major histocompatibility complex (MHC) region of the genome. A specific proteasome defect has been identified in NOD mouse in select lymphocytic and monocytic lineages that results from down-regulation of expression of the proteasome subunit LMP2, which is encoded by a gene in the MHC genomic region. This defect prevents the proteolytic processing required for the production and activation of the transcription factor nuclear factor-kappaB (NF-kappaB), which plays important roles in immune and inflammatory responses, as well as increases the susceptibility of the affected cells to apoptosis induced by tumor necrosis factor-alpha (TNF-alpha). The novel role of the proteasome in dysfunction in autoimmunity is presented and documented to be both tissue and developmental stage specific. We propose a role of the proteasome as a step in disease pathogenesis and tissue targeting.

NOD mice are defective in proteasome production and activation of NF-kappaB

The nonobese diabetic (NOD) mouse is an animal model of human type I diabetes with a strong genetic component that maps to the major histocompatibility complex (MHC) of the genome. We have identified in NOD lymphocytes a specific proteasome defect that results from the lack of the LMP2 subunit. The pronounced proteasome defect results in defective production and activation of the transcription factor NF-kappaB, which plays an important role in immune and inflammatory responses as well as in preventing apoptosis induced by tumor necrosis factor alpha. The defect in proteasome function in NOD mouse splenocytes was evident from impaired NF-kappaB subunit p50 and p52 generation by proteolytic processing and impaired degradation of the NF-kappaB-inhibitory protein IkappaBalpha. An obligatory role of MHC-linked proteasome subunits in transcription factor processing and activation has been established in a spontaneous-disease model and mutant cells similarly lacking the MHC-encoded subunit. These data suggest that NOD proteasome dysfunction is due to a tissue- and developmental-stage-specific defect in expression of the MHC-linked Lmp2 gene, resulting in altered transcription factor NF-kappaB activity, and that this defect contributes to pathogenesis in NOD mice. These observations are consistent with the diverse symptomatology of type I diabetes and demonstrate clear sex-, tissue-, and age-specific differences in the expression of this error which parallel the initiation and disease course of insulin-dependent (type I) diabetes mellitus.

p75-mediated NF-kappaB activation enhances the survival response of developing sensory neurons to nerve growth factor

We have investigated whether the transcription factor NF-kappaB plays a role in regulating neuronal survival by manipulating NF-kappaB activation in the nerve growth factor (NGF)-dependent sensory neurons of the embryonic mouse trigeminal ganglion. Overexpression of either the p65 or the p50 NF-kappaB subunits resulted in NF-kappaB activation and promoted in vitro survival as effectively as NGF. Expression of a superrepressor IkappaB-alpha protein prevented NF-kappaB activation in p65/p50-overexpressing neurons and caused the neurons to die as rapidly as NGF-deprived neurons. NGF treatment also activated NF-kappaB, and preventing this activation with superrepressor IkappaB-alpha reduced the NGF survival response. Antibodies that block binding of NGF to the p75 receptor prevented NGF-induced NF-kappaB activation and reduced the NGF survival response to the same extent as superrepressor IkappaB-alpha. Trigeminal neurons cultured from p65(-/-) embryos showed a reduced survival response to NGF compared with neurons from wild-type embryos and there was increased apoptosis of neurons in the trigeminal ganglia of p65(-/-) embryos in vivo. However, as with p75-deficient sensory neurons, p65-deficient sensory neurons showed a normal survival response to BDNF. These results reveal a role for NF-kappaB in regulating neuronal survival during embryonic development and suggest that in addition to the well-established Trk receptor tyrosine kinase signaling cascade, NGF enhances neuronal survival by signaling via a p75-mediated pathway.

Characterization of phenotype and cytokine profiles of T cell lines derived from vitreous humour in ocular inflammation in man

Intermediate uveitis (IU) and Fuchs' heterochromic cyclitis (FHC) are two chronic ocular inflammatory disorders. They differ considerably in ocular morbidity, which is higher in IU. T cell lines were derived from the vitreous humour (VH) and peripheral blood (PB) of 10 patients with IU and four patients with FHC. There was a predominance of CD8+ in all the lines. However, there was a significantly higher percentage of CD4+ T cells in the T cell lines derived from VH of IU (32.0 +/- 8.6%) compared with FHC patients (19. 2 +/- 8.9%) (P = 0.04). The VH-derived T cell lines (VDTC) produced significantly higher levels of IL-2, interferon-gamma (IFN-gamma) and IL-10, but not IL-4, compared with PB-derived T cell lines (PBDTC) in both entities. There was significantly higher IL-2 production by VDTC from IU when compared with FHC patients (1810 +/- 220 pg/ml versus 518 +/- 94 pg/ml; P = 0.009), which could account for the more aggressive clinical features of this condition. In contrast IL-10 production was significantly higher by the VDTC from FHC compared with IU patients. The high IL-10 production by T cells infiltrating VH of FHC patients could down-regulate the inflammatory responses, thereby contributing to the benign clinical course seen in these patients. The accumulation of T cells with differing cytokine profiles in the VH suggests an important role for these cytokines in the pathogenesis of these chronic uveitides.

In Vivo Inhibition of NF-κB in T-Lineage Cells Leads to a Dramatic Decrease in Cell Proliferation and Cytokine Production and to Increased Cell Apoptosis in Response to Mitogenic Stimuli, But Not to Abnormal Thymopoiesis

To understand the role of NF-κB complexes in T cell development and activation, we have generated transgenic mice in which RelA and c-Rel complexes were selectively inhibited in the T-lineage cells by specific expression of a trans-dominant form of IκBα. Transgene expression did not affect the thymic development, but led to lowered numbers of splenic T cells and to a dramatic decrease in the ex vivo proliferative response of splenic T lymphocytes. Analysis of IL-2 and IL-2Rα expression demonstrated that the perturbation of the proliferation response was not attributable to an abnormal expression of these genes. In contrast, expression of IL-4, IL-10, and IFN-γ was strongly inhibited in the transgenic T cells. The proliferative deficiency of the transgenic T cells was associated with an increased apoptosis. These results point out the involvement of NF-κB/Rel family proteins in growth signaling pathways by either regulating proteins involved in the IL-2 signaling or by functionally interfering with the cell cycle progression.

Activation of NF-kappaB in Mycobacterium tuberculosis- induced interleukin-2 receptor expression in mononuclear phagocytes

Soluble interleukin-2 receptor-alpha (IL-2Ralpha) has been reported to be increased in the sera of patients with advanced tuberculosis, and levels decline after therapy in accordance with improvement of radiologic findings. We investigated expression of the IL-2Ralpha in bronchoalveolar lavage (BAL) cells in active pulmonary tuberculosis, and evaluated the mechanism Mycobacterium tuberculosis induces in the IL-2Ralpha using the THP-1 mononuclear phagocyte cell line. We found IL-2Ralpha expression to be increased in BAL cells from involved sites of active pulmonary tuberculosis. Expression of the alpha-chain of IL-2Ralpha on peripheral blood monocytes (PBM) was induced by M. tuberculosis by flow cytometry evaluation. Northern analysis demonstrated increased IL-2Ralpha gene expression after stimulation with M. tuberculosis which was further induced by interferon-gamma (IFN-gamma). The IL-2Ralpha promoter containing the nuclear factor kappa B (NF-kappaB) site was transcriptionally induced by M. tuberculosis and this NF-kappaB site could confer inducibility to a heterologous herpes thymidine kinase (TK) promoter by M. tuberculosis. Electrophoretic mobility shift assays (EMSAs) revealed specific binding of nuclear protein to the NF-kappaB site upon induction with M. tuberculosis. Using antibodies against the p50 and p65 subunits of NF-kappaB in EMSAs, the involvement of both p50 and p65 proteins was further demonstrated. Functional expression of the IL-2Ralpha on mononuclear phagocytes in M. tuberculosis infection may play an important immunomodulatory role in the host response.

Interleukin-2 (IL-2) regulates the accessibility of the IL-2-responsive enhancer in the IL-2 receptor alpha gene to transcription factors

Interleukin-2 (IL-2) responsiveness of T lymphocytes is controlled through transcription of the IL-2 receptor (IL-2R) alpha subunit by antigen and by IL-2 itself. IL-2 induces IL-2Ralpha transcription via an IL-2-responsive enhancer (IL-2rE), whose activity depends on the cooperative binding of IL-2-induced STAT5 to two sites and of constitutively active Elf-1 to a third one. Here we describe the changes in IL-2rE chromatin that occur in normal T lymphocytes upon activation of IL-2Ralpha expression. In cells induced to transiently express IL-2Ralpha with concanavalin A (which mimics antigen), none of the IL-2rE sites is occupied despite the presence of Elf-1 and STAT1, which bind to the IL-2rE in vitro. The two STAT binding sites are occupied rapidly upon IL-2 stimulation, concomitantly with STAT5 activation. Occupation of the Elf-1 binding site is delayed, although Elf-1 concentration and binding activity are not modified by IL-2. Digestion of T-cell chromatin with DNase I and micrococcal nuclease shows that IL-2 induces the appearance of nuclease-hypersensitive sites flanking the IL-2rE. Thus IL-2, in addition to activating STAT5, appears to regulate IL-2Ralpha transcription by making IL-2Ralpha chromatin accessible to transcription factors.

AP-1 and NF-kappaB regulation in rheumatoid arthritis and murine collagen-induced arthritis

OBJECTIVE

To determine the expression and regulation of nuclear transcription factors AP-1 and NF-kappaB in rheumatoid arthritis and in collagen-induced arthritis in mice.

METHODS

AP-1 and NF-kappaB expression and function were determined in RA, OA and normal synovial tissue by electrophoretic mobility shift assay (EMSA) and immunohistochemistry. The kinetics of transcription factor expression were then examined in collagen-induced arthritis (CIA) in mice. EMSAs were performed with the nuclear extracts obtained from paws of CIA mice from 10 to 45d after immunization to determine AP-1 and NF-kappaB binding activity. The expression of collagenase-3 (MMP13) and stromelysin (MMP3) mRNA was examined by northern blot analysis.

RESULTS

Immunohistochemistry showed that NF-kappaB expression was increased in both RA and OA synovial intimal lining. AP-1 components Jun and Fos were also present in the intimal lining and was significantly greater in RA than OA. The DNA binding activities of both AP-1 and NF-kappaB were significantly higher RA patients compared with OA. In CIA, AP-1 and NF-kappaB expression increased by day 20, which was 1-2 weeks before onset of clinical arthritis. However, collagenase and stromelysin gene expression did not increase until day 35.

CONCLUSION

The DNA binding activity of AP-1 and NF-kappaB are markedly increased in both CIA and RA. In CIA, activation of AP-1 and NF-kappaB precede both clinical arthritis and metalloproteinase gene expression. NF-kappaB expression correlated better than AP-1 with metalloproteinase expression.

Signaling Pathways Mediated by the TNF- and Cytokine-Receptor Families Target a Common cis-Element of the IFN Regulatory Factor 1 Promoter

CD40 activation of B cells is strongly influenced by the presence of cytokines. However, the molecular basis for the interplay between these distinct stimuli is not clearly delineated. IFN regulatory factor 1 (IRF-1) is a transcription factor activated by either CD40 or cytokines. We have found that these different sets of signals target a common cis-acting element in the promoter of this gene, the IRF-1 gamma-activated site (GAS). Targeting of the IRF-1 GAS is not confined to activation via CD40 but extends to other stimuli that mimic the CD40 signaling cascade, like TNF-α and EBV. In contrast to induction of STATs by cytokines, the IRF-1 GAS-binding complex activated by CD40, TNF-α, or EBV contains Rel proteins, specifically p50 and p65. In this system, simultaneous exposure to CD40L together with either IL-4 or IFN-γ does not lead to the activation of novel Rel/STAT complexes. Given the importance of IRF-1 in a variety of biologic functions from proliferation to apoptosis, our findings support the notion that modulation of IRF-1 levels may be a critical control point in B cell activation.

Bladder carcinoma cell line KU-19-19-derived cytokines support proliferation of growth factor-dependent hematopoietic cell lines: modulation by phorbol ester, interferon-gamma and interleukin-1 beta

The human bladder carcinoma cell line KU-19-19 synthesizes and secretes hematopoietic growth factors. Conditioned medium (CM) from KU-19-19 stimulated the [3H]thymidine incorporation of growth factor-dependent hematopoietic cell lines. ELISA documented high amounts of granulocyte colony-stimulating factor (G-CSF; > 5 ng/ml); also granulocyte-macrophage CSF (GM-CSF), macrophage-CSF (M-CSF), stem cell factor (SCF), IL-6, and IL-8 were detected in KU-19-19 CM. Pretreatment with phorbol ester, IL-1 beta, or IFN-gamma increased the level of G-CSF, GM-CSF, and M-CSF in KU-19-19 CM. Thus, KU-19-19 represents a reliable source for purification of G-CSF and can easily be used to support proliferation of growth factor-dependent cell lines. The ability to respond to different stimuli suggests that several regulatory pathways may be involved in cytokine production of this bladder carcinoma cell line.

Crystal structure of p50/p65 heterodimer of transcription factor NF-kappaB bound to DNA

The NF-kappaB p50/p65 heterodimer is the classical member of the Rel family of transcription factors which regulate diverse cellular functions such as immune response, cell growth, and development. Other mammalian Rel family members, including the proteins p52, proto-oncoprotein c-Rel, and RelB, all have amino-terminal Rel-homology regions (RHRs). The RHR is responsible for the dimerization, DNA binding and cytosolic localization of these proteins by virtue of complex formation with inhibitor kappaB proteins. Signal-induced removal of kappaB inhibitors allows translocation of dimers to the cell nucleus and transcriptional regulation of kappaB DNA-containing genes. NF-kappaB specifically recognizes kappaB DNA elements with a consensus sequence of 5'-GGGRNYYYCC-3' (R is an unspecified purine; Y is an unspecified pyrimidine; and N is any nucleotide). Here we report the crystal structure at 2.9 A resolution of the p50/p65 heterodimer bound to the kappaB DNA of the intronic enhancer of the immunoglobulin light-chain gene. Our structure reveals a 5-base-pair 5' subsite for p50, and a 4-base-pair 3' subsite for p65. This structure indicates why the p50/p65 heterodimer interface is stronger than that of either homodimer. A comparison of this structure with those of other Rel dimers reveals that both subunits adopt variable conformations in a DNA-sequence-dependent manner. Our results explain the different behaviour of the p50/p65 heterodimer with heterologous promoters.