The c-rel protooncogene product represses NF-kappa B p65-mediated transcriptional activation of the long terminal repeat of type 1 human immunodeficiency virus

Activation of the Anti-Oxidative Stress Response Reactivates Latent HIV-1 Through the Mitochondrial Antiviral Signaling Protein Isoform MiniMAVS

The mitochondrial antiviral signaling protein (MAVS) is part of the cell's innate immune mechanism of defense. MAVS mRNA is bicistronic and can give rise to a full length-MAVS and a shorter isoform termed miniMAVS. In response to viral infections, viral RNA can be sensed by the cytosolic RNA sensors retinoic acid-inducible gene I (RIG-I) and/or melanoma differentiation-associated protein 5 (MDA5) and activate NF-κB through interaction with MAVS. MAVS can also sense cellular stress and activate an anti-oxidative stress (AOS) response through the activation of NF-κB. Because NF-κB is a main cellular transcription factor for HIV-1, we wanted to address what role MAVS plays in HIV-1 reactivation from latency in CD4 T cells. Our results indicate that RIG-I agonists required full length-MAVS whereas the AOS response induced by Dynasore through its catechol group can reactivate latent HIV-1 in a MAVS dependent manner through miniMAVS isoform. Furthermore, we uncover that PKC agonists, a class of latency-reversing agents, induce an AOS response in CD4 T cells and require miniMAVS to fully reactivate latent HIV-1. Our results indicate that the AOS response, through miniMAVS, can induce HIV-1 transcription in response to cellular stress and targeting this pathway adds to the repertoire of approaches to reactivate latent HIV-1 in 'shock-and-kill' strategies.

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

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

Regulation of B-cell function by NF-kappaB c-Rel in health and disease

B cells mediate humoral immune response and contribute to the regulation of cellular immune response. Members of the Nuclear Factor kappaB (NF-κB) family of transcription factors play a major role in regulating B-cell functions. NF-κB subunit c-Rel is predominantly expressed in lymphocytes, and in B cells, it is required for survival, proliferation, and antibody production. Dysregulation of c-Rel expression and activation alters B-cell homeostasis and is associated with B-cell lymphomas and autoimmune pathologies. Based on its essential roles, c-Rel may serve as a potential prognostic and therapeutic target. This review summarizes the current understanding of the multifaceted role of c-Rel in B cells and B-cell diseases.

Tat predominantly associates with host promoter elements in HIV-1-infected T-cells - regulatory basis of transcriptional repression of c-Rel

HIV-1 Tat is a multifunctional regulatory protein that, in addition to its primary function of transactivating viral transcription, also tends to modulate cellular gene expression, for which the molecular mechanism remains to be clarified. We have reported earlier nuclear factor kappa B (NFκB) enhancer binding activity of Tat and proposed this DNA binding activity as a possible molecular basis for Tat-mediated regulation of cellular gene expression in infected cells. In the present study, we analyzed the genome-wide occupancy of Tat protein on host cell chromatin in HIV-1-infected T-cells to investigate a potential role of Tat on cellular gene expression. The results obtained identify a spectrum of binding sites of Tat protein on the chromatin and reveal that Tat is also recruited on a number of cellular gene promoters in HIV-1-infected T-cells, indicating its possible involvement in the regulation of gene expression of such cellular genes. Tat was identified as a repressor of one such validated gene, c-Rel, because it downregulates the expression of c-Rel in both Tat expressing and HIV-1-infected T-cells. The results also show that Tat downregulates c-Rel promoter activity by interacting with specific NFκB sites on the c-Rel promoter, thus providing a molecular basis of Tat-mediated regulation of cellular gene expression. Thus, in the present study, we have not only identified recruitment sites of Tat on the chromatin in HIV-1-infected T-cells, but also report for the first time that c-Rel is downregulated in HIV-1-infected cells specifically by interaction of Tat with NFκB binding sites on the promoter.

Plakoglobin as a regulator of desmocollin gene expression

Desmosomes are cell adhesion junctions required for the normal development and maintenance of mammalian tissues and organs such as the skin, skin appendages and the heart. The goal of the present study was to investigate how desmocollins (DSC), transmembrane components of desmosomes, are regulated at the transcriptional level. We hypothesized that differential expression of the Dsc2 and Dsc3 genes is a prerequisite for normal development of skin appendages. We demonstrate that plakoglobin (Pg) in conjunction with Lef-1 differentially regulates the proximal promoters of these two genes. Specifically, we found that Lef-1 acts as a switch activating Dsc2 and repressing Dsc3 in the presence of Pg. Interestingly, we also determined that NFκB pathway components, down-stream effectors of the Eda/EDAR signaling cascade, can activate Dsc2 expression. We hypothesize that Lef-1 and Eda/EDAR/NFκB signaling contribute to a shift in Dsc isoform expression from Dsc3 to Dsc2 in placode keratinocytes. It is tempting to speculate that this shift is required for invasive growth of placode keratinocytes into the dermis, a crucial step in skin appendage formation.

Molecular mechanisms of HIV-1 infection in neonatal target cells

HIV-1-infected neonates and infants have a higher viral load and progress to symptomatic AIDS more rapidly than their own infected mothers, as well as other infected adults, with differences in clinical manifestations, recurrent bacterial infections and CNS disorders. Two major reasons have been attributed to this differential HIV pathogenesis and disease; the relative immaturity of the neonate’s immune system and it’s inability to contain the highly replicating and mutating HIV-1, and the more efficient replication of HIV-1 in neonatal cells than in adult target cells. In this context, it has been demonstrated that HIV-1 replicates more efficiently in neonatal (cord) blood monocytes/macrophages and T lymphocytes – including naive and memory T lymphocytes – compared with adult blood cells. We have also determined the mechanisms of the differential HIV-1 replication in cord versus adult blood monocytes/macrophages and T lymphocytes (naive and memory), finding that it was influenced at the level of HIV-1 gene expression. The increased HIV-1 gene expression in neonatal versus adult target cells was regulated by differential expression of host factors, transcription factors (NF-κB, E2F, HAT-1, TFIIE, Cdk9 and Cyclin T1), signal transducers (STAT3 and STAT5A) and cytokines (IL-1β, IL-6 and IL-10). We also showed that nuclear extracts from cord cells interacted with HIV-1 long terminal repeat cis-acting sequences, including NF-κB, NFAT, AP1 and NF-IL6, to a greater extent when compared with adult peripheral blood mononuclear cell nuclear extracts. Additionally, shRNA of retroviral origin for STAT3 and IL-6 downregulated both their own gene expression as well as that of HIV-1, indicating that these factors influenced the differential expression of HIV-1 genes in cord cells compared with adult cells. In addition, HIV-1 integration plays an important role in differential HIV-1 replication and gene expression in neonatal versus adult cells by integrating into more actively transcribed genes in neonates compared with adults. We characterized 468 HIV-1 integration sites within cord and adult blood T lymphocytes and monocytes/macrophages, including genes coding for cellular components, and those involved with maintenance of the intracellular environment, enzyme regulation, cellular metabolism, catalytic activity and cation transport, as well as several potential transcription factor binding sites at the sites of integration. Additionally, the genes at the integration sites, transcription factors and transcription binding sites were expressed at higher levels in cord than adult target cells. In summary, the increased HIV-1 gene expression and replication in neonatal target cells due to differential expression of host factors all contribute to an increased viral load and faster disease progression in neonates and infants when compared with similar situations in adult patients. Based on these findings, it may be possible to identify new viral and host targets for use in developing strategies for the treatment and prevention of HIV-1.

c-Rel is a transcriptional repressor of EPHB2 in colorectal cancer

The receptor tyrosine kinase EPHB2 has recently been identified as a TCF4 transcriptional target that controls the intestinal epithelial architecture through repulsive interactions with Ephrin-B ligands. Many reports have demonstrated that most human colorectal cancers lose EPHB2 expression despite constitutive Wnt activation. Therefore, we investigated the mechanisms that cause EPHB2 down-regulation in colorectal cancer. In this study, we demonstrate that DNA hypermethylation was not responsible for the frequent loss of EPHB2 expression in colorectal cancer. Cloning and functional characterization of the EPHB2 gene 5'-flanking region revealed a potential negative regulatory element in the distal regulatory region. In vitro electrophoretic gel mobility shift and in vivo chromatin immunoprecipitation assays demonstrated that c-Rel directly binds to the putative element. Inhibiting c-Rel activity or knocking down c-Rel expression by RNA interference in colon cancer cells was sufficient to induce EPHB2 expression. Furthermore, transient transfection assays demonstrated that c-Rel over-expression repressed endogenous EPHB2 expression in colon cancer cells. We demonstrate for the first time that c-Rel acts as a transcriptional repressor of EPHB2 and plays an active role in EPHB2 down-regulation in colorectal cancers.

OHMM: a Hidden Markov Model accurately predicting the occupancy of a transcription factor with a self-overlapping binding motif

Background

DNA sequence binding motifs for several important transcription factors happen to be self-overlapping. Many of the current regulatory site identification methods do not explicitly take into account the overlapping sites. Moreover, most methods use arbitrary thresholds and fail to provide a biophysical interpretation of statistical quantities. In addition, commonly used approaches do not include the location of a site with respect to the transcription start site (TSS) in an integrated probabilistic framework while identifying sites. Ignoring these features can lead to inaccurate predictions as well as incorrect design and interpretation of experimental results.

Results

We have developed a tool based on a Hidden Markov Model (HMM) that identifies binding location of transcription factors with preference for self-overlapping DNA motifs by combining the effects of their alternative binding modes. Interpreting HMM parameters as biophysical quantities, this method uses the occupancy probability of a transcription factor on a DNA sequence as the discriminant function, earning the algorithm the name OHMM: Occupancy via Hidden Markov Model. OHMM learns the classification threshold by training emission probabilities using unaligned sequences containing known sites and estimating transition probabilities to reflect site density in all promoters in a genome. While identifying sites, it adjusts parameters to model site density changing with the distance from the transcription start site. Moreover, it provides guidance for designing padding sequences in gel shift experiments. In the context of binding sites to transcription factor NF-κB, we find that the occupancy probability predicted by OHMM correlates well with the binding affinity in gel shift experiments. High evolutionary conservation scores and enrichment in experimentally verified regulated genes suggest that NF-κB binding sites predicted by our method are likely to be functional.

Conclusion

Our method deals specifically with identifying locations with multiple overlapping binding sites by computing the local occupancy of the transcription factor. Moreover, considering OHMM as a biophysical model allows us to learn the classification threshold in a principled manner. Another feature of OHMM is that we allow transition probabilities to change with location relative to the TSS. OHMM could be used to predict physical occupancy, and provides guidance for proper design of gel-shift experiments. Based upon our predictions, new insights into NF-κB function and regulation and possible new biological roles of NF-κB were uncovered.

Determinants of the establishment of human immunodeficiency virus type 1 latency

Recent research has emphasized the notion that human immunodeficiency virus type 1 (HIV-1) latency is controlled by a restrictive histone code at, or DNA methylation of, the integrated viral promoter (long terminal repeat [LTR]). The present concept of HIV-1 latency has essentially been patterned from the principles of cellular gene regulation. Here we introduce an experimental system that allows for the qualitative and quantitative kinetic study of latency establishment and maintenance at the population level. In this system, we find no evidence that HIV-1 latency establishment is the consequence of downregulation of initial active infection followed by the establishment of a restrictive histone code at the viral LTR. Latent infection was established following integration of the virus in the absence of viral gene expression (silent integration) and was a function of the NF-kappaB activation level in the host cell at the time of infection. In the absence of a role for epigenetic regulation, we demonstrate that transcriptional interference, a mechanism that has recently been suggested to add to the stabilization of HIV-1 latency, is the primary mechanism to govern latency maintenance. These findings provide direct experimental evidence that the high number of viral integration events (>90%) found in actively expressed genes of CD4(+) memory T cells from highly active antiretroviral therapy-suppressed patients represent indeed latent infection events and that transcriptional interference may be the primary mechanism to control HIV-1 latency in vivo. HIV-1 latency may thus not be governed by the principles of cellular gene regulation, and therapeutic strategies to deplete the pool of latently HIV-1-infected cells should be reconsidered.

Differential HIV-1 integration targets more actively transcribed host genes in neonatal than adult blood mononuclear cells

We have recently shown an increased HIV-1 replication and gene expression in neonatal (cord) blood mononuclear cells compared with adult cells, which could be due to HIV-1 integration as it targets active host genes. Here we have characterized 468 HIV-1 integration sites within cord and adult blood T-lymphocytes and monocyte-derived macrophages (MDM) from five donors. Several functional classes of genes were identified by gene ontology to be over represented, including genes for cellular components, maintenance of intracellular environment, enzyme regulation, cellular metabolism, catalytic activity and cation transport. Numerous potential transcription factor binding sites at the sites of integration were identified. Furthermore, the genes at the site of integration, transcription factors which potentially bind upstream of the HIV-1 promoter and factors that assist HIV-1 integration were found to be expressed at higher levels in cord than adult cells. Taken together, these results suggest HIV-1 integration occurred in a more actively transcribed genes in neonatal cells compared with adult cells, which may help explain a higher level of HIV-1 gene expression and replication in neonatal compared with adult cells.

HIV-1 latency in actively dividing human T cell lines

Background

Eradication of HIV-1 from an infected individual cannot be achieved by current drug regimens. Viral reservoirs established early during the infection remain unaffected by anti-retroviral therapy and are able to replenish systemic infection upon interruption of the treatment. Therapeutic targeting of viral latency will require a better understanding of the basic mechanisms underlying the establishment and long-term maintenance of HIV-1 in resting memory CD4 T cells, the most prominent reservoir of transcriptional silent provirus. However, the molecular mechanisms that permit long-term transcriptional control of proviral gene expression in these cells are still not well understood. Exploring the molecular details of viral latency will provide new insights for eventual future therapeutics that aim at viral eradication.

Results

We set out to develop a new in vitro HIV-1 latency model system using the doxycycline (dox)-inducible HIV-rtTA variant. Stable cell clones were generated with a silent HIV-1 provirus, which can subsequently be activated by dox-addition. Surprisingly, only a minority of the cells was able to induce viral gene expression and a spreading infection, eventhough these experiments were performed with the actively dividing SupT1 T cell line. These latent proviruses are responsive to TNFα treatment and alteration of the DNA methylation status with 5-Azacytidine or genistein, but not responsive to the regular T cell activators PMA and IL2. Follow-up experiments in several T cell lines and with wild-type HIV-1 support these findings.

Conclusion

We describe the development of a new in vitro model for HIV-1 latency and discuss the advantages of this system. The data suggest that HIV-1 proviral latency is not restricted to resting T cells, but rather an intrinsic property of the virus.

Regulation of HIV-1 latency by T-cell activation

HIV-infected patients harbor approximately 10(5)-10(6) memory CD4 T-cells that contain fully integrated but transcriptionally silent HIV proviruses. While small in number, these latently infected cells form a drug-insensitive reservoir that importantly contributes to the life-long persistence of HIV despite highly effective antiviral therapy. In tissue culture, latent HIV proviruses can be activated when their cellular hosts are exposed to select proinflammatory cytokines or their T-cell receptors are ligated. However, due to a lack of potency and/or dose-limiting toxicity, attempts to purge virus from this latent reservoir in vivo with immune-activating agents, such as anti-CD3 antibodies and IL-2, have failed. A deeper understanding of the molecular underpinnings of HIV latency is clearly required, including determining whether viral latency is actively reinforced by transcriptional repressors, defining which inducible host transcription factors most effectively antagonize latency, and elucidating the role of chromatin in viral latency. Only through such an improved understanding will it be possible to identify combination therapies that might allow complete purging of the latent reservoir and to realize the difficult and elusive goal of complete eradication of HIV in infected patients.

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

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

An HIV-1 encoded peptide mimics the DNA binding loop of NF-kappaB and binds thioredoxin with high affinity

Pro-fs is a human immunodeficiency virus type 1 (HIV-l)-encoded putative selenoprotein, predicted by a theoretical analysis of the viral genome; it is potentially expressed by a -1 frameshift from the protease coding region. Pro-fs has significant sequence similarity to the DNA binding loop of nuclear factor kappa B (NF-kappaB), which is known to bind thioredoxin (Trx). We hypothesize that the putative HIV-1 pro-fs gene product functions by mimicry of NF-kappaB via binding to Trx. The hypothesis was tested in vitro by co-immunoprecipitation and GST-pull down assays, using a purified mutant pro-fs protein, in which the two potential selenocysteine residues were mutated to cysteines, in order to permit expression in bacteria. Both experiments showed that pro-fs binds to human wild type Trx (Trx-wt) with high affinity. Mutation of the two conserved cysteine residues in the Trx active site redox center to serine (Ser) (Trx-CS) weakened but failed to abolish the interaction. In pro-fs-transfected 293T cells, using confocal microscopy and fluorescence resonance energy transfer (FRET), we have observed that pro-fs localizes in cell nuclei and forms oligomers. Upon stimulation by phorbol 12-myristate 13-acetate (PMA), Trx translocates into cell nuclei. Significant FRET efficiency was detected in the nuclei of PMA-stimulated 293T cells co-expressing fluorescence-tagged pro-fs and Trx-wt or Trx-CS. These results indicate that in living cells the double cysteine mutant of pro-fs binds to both Trx and Trx-CS with high affinity, suggesting that Trx-pro-fs binding is a structurally-specific interaction, involving more of the Trx molecule than just its active site cysteine residues. These results establish the capacity for functional mimicry of the Trx binding ability of the NF-kappaB/Rel family of transcription factors by the putative HIV-1 pro-fs protein.

Reductions in I kappa B epsilon and changes in NF-kappa B activity during B lymphocyte differentiation

The levels and stability of IkappaBepsilon have been examined in unstimulated and stimulated splenic B cells and compared with that of IkappaBalpha and IkappaBbeta. Primary murine splenic B cells but not T cells were found to contain high levels of IkappaBepsilon protein, equivalent to levels of the abundant IkappaBalpha. Most agents that activate IkappaBalpha and IkappaBbeta degradation do not induce rapid degradation of IkappaBepsilon. Interestingly, however, the levels of IkappaBepsilon, but not of IkappaBalpha or IkappaBbeta, are dramatically reduced upon the stimulation of B cells both in vivo and in vitro. Since IkappaBepsilon exhibits substrate specificity for NF-kappaB Rel homodimers, this suggested the possibility that changes in NF-kappaB-responsive genes might also occur during this transition. Consistent with this hypothesis, we found that a NF-kappaB reporter construct sensitive to p65/RelA homodimers is activated at the time that IkappaBepsilon levels decline following B cell stimulation. In IgG(+) B cell lines, which contain low levels of IkappaBepsilon, this same reporter construct was inactive, suggesting that the increases in Rel homodimer activity that accompany B cell stimulation are transient. However, there are differences in the level of expression of NF-kappaB-responsive genes in these IgG(+) B cell lines compared with their IgM(+) counterparts. From these data, we conclude that there are transient changes in NF-kappaB activity due to reductions in IkappaBepsilon, which might contribute to long-term, persistent changes that accompany B cell differentiation. We propose an important role for IkappaBepsilon in the differential regulation of nuclear NF-kappaB activity in stimulated B cells.

Bis-anthracycline antibiotics inhibit human immunodeficiency virus type 1 transcription

The increasing numbers of human immunodeficiency virus type 1 (HIV-1) strains that exhibit resistance to antiretroviral agents used at present require the development of new effective antiretroviral compounds. Tat transactivation was recognized early on as an attractive target for drug interference. To screen for and analyze the effects of compounds that interfere with Tat transactivation, we developed several cell-based reporter systems in which enhanced green fluorescence protein is a direct and quantitative marker of HIV-1 expression or Tat-dependent long terminal repeat activity. Using these reporter cell lines, we found that the bis-anthracycline WP631, a recently developed DNA intercalator, efficiently inhibits HIV-1 expression at subcytotoxic concentrations. WP631 also abrogated acute HIV-1 replication in peripheral blood mononuclear cells infected with various primary virus isolates. We demonstrate that WP631-mediated HIV-1 inhibition is caused by the inhibition of Tat transactivation. The data presented suggest that WP631 could serve as a lead compound for a new type of HIV-1 inhibitor.

Regulation of c-Rel nuclear localization by binding of Ca2+/calmodulin

The NF-kappa B/Rel family of transcription factors participates in the control of a wide array of genes, including genes involved in embryonic development and regulation of immune, inflammation, and stress responses. In most cells, inhibitory I kappa B proteins sequester NF-kappa B/Rel in the cytoplasm. Cellular stimulation results in the degradation of I kappa B and modification of NF-kappa B/Rel proteins, allowing NF-kappa B/Rel to translocate to the nucleus and act on its target genes. Calmodulin (CaM) is a highly conserved, ubiquitously expressed Ca(2+) binding protein that serves as a key mediator of intracellular Ca(2+) signals. Here we report that two members of the NF-kappa B/Rel family, c-Rel and RelA, interact directly with Ca(2+)-loaded CaM. The interaction with CaM is greatly enhanced by cell stimulation, and this enhancement is blocked by addition of I kappa B. c-Rel and RelA interact with CaM through a similar sequence near the nuclear localization signal. Compared to the wild-type protein, CaM binding-deficient mutants of c-Rel exhibit increases in both nuclear accumulation and transcriptional activity on the interleukin 2 and granulocyte macrophage colony-stimulating factor promoters in the presence of a Ca(2+) signal. Conversely, for RelA neither nuclear accumulation nor transcriptional activity on these promoters is increased by mutation of the sequence interacting with CaM. Our results suggest that CaM binds c-Rel and RelA after their release from I kappa B and can inhibit nuclear import of c-Rel while letting RelA translocate to the nucleus and act on its target genes. CaM can therefore differentially regulate the activation of NF-kappa B/Rel proteins following stimulation.

Ribosomal protein S19 expression during erythroid differentiation

The gene encoding ribosomal protein S19 (RPS19) has been shown to be mutated in 25% of the patients affected by Diamond-Blackfan anemia (DBA), a congenital erythroblastopenia. As the role of RPS19 in erythropoiesis is still to be defined, we performed studies on RPS19 expression during terminal erythroid differentiation. Comparative analysis of the genomic sequences of human and mouse RPS19 genes enabled the identification of 4 conserved sequence elements in the 5' region. Characterization of transcriptional elements allowed the identification of the promoter in the human RPS19 gene and the localization of a strong regulatory element in the third conserved sequence element. By Northern blot and Western blot analyses of murine splenic erythroblasts infected with the anemia-inducing strain Friend virus (FAV cells), RPS19 mRNA and protein expression were shown to decrease during terminal erythroid differentiation. We anticipate that these findings will contribute to further development of our understanding of the contribution of RPS19 to erythropoiesis.

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

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

Molecular mechanisms in lymphocyte activation and growth

Transcription factor NF-kappaB is biochemically coupled to the T cell antigen receptor (TCR) and activated transiently during an adaptive immune response. The author's laboratory is investigating the signal-dependent regulation of NF-kappaB, its downstream gene targets, and its function in lymphocyte biology. Our studies have revealed novel enzymatic checkpoints in the NF-kappaB signaling pathway and constitutive repressors of NF-kappaB that might be clinically applicable for therapeutic control of the immune system. We have also found that the Tax transforming protein encoded by human T cell leukemia virus type 1 (HTLV1) binds to and persistently activates an inducible protein kinase in the TCR/NF-kappaB axis. This viral/host interaction appears to trigger the inappropriate expression of NF-kappaB and the development of HTLV1-associated disease.

Molecular mechanisms in lymphocyte activation and growth

Transcription factor NF-kappaB is biochemically coupled to the T cell antigen receptor (TCR) and activated transiently during an adaptive immune response. The author's laboratory is investigating the signal-dependent regulation of NF-kappaB, its downstream gene targets, and its function in lymphocyte biology. Our studies have revealed novel enzymatic checkpoints in the NF-kappaB signaling pathway and constitutive repressors of NF-kappaB that might be clinically applicable for therapeutic control of the immune system. We have also found that the Tax transforming protein encoded by human T cell leukemia virus type 1 (HTLV1) binds to and persistently activates an inducible protein kinase in the TCR/NF-kappaB axis. This viral/host interaction appears to trigger the inappropriate expression of NF-kappaB and the development of HTLV1-associated disease.

Nuclear factor-kappaB (NF-kappaB) regulates proliferation and branching in mouse mammary epithelium

The nuclear factor-kappaB (NF-kappaB) family of transcription factors has been shown to regulate proliferation in several cell types. Although recent studies have demonstrated aberrant expression or activity of NF-kappaB in human breast cancer cell lines and tumors, little is known regarding the precise role of NF-kappaB in normal proliferation and development of the mammary epithelium. We investigated the function of NF-kappaB during murine early postnatal mammary gland development by observing the consequences of increased NF-kappaB activity in mouse mammary epithelium lacking the gene encoding IkappaBalpha, a major inhibitor of NF-kappaB. Mammary tissue containing epithelium from inhibitor kappaBalpha (IkappaBalpha)-deficient female donors was transplanted into the gland-free mammary stroma of wild-type mice, resulting in an increase in lateral ductal branching and pervasive intraductal hyperplasia. A two- to threefold increase in epithelial cell number was observed in IkappaBalpha-deficient epithelium compared with controls. Epithelial cell proliferation was strikingly increased in IkappaBalpha-deficient epithelium, and no alteration in apoptosis was detected. The extracellular matrix adjacent to IkappaBalpha-deficient epithelium was reduced. Consistent with in vivo data, a fourfold increase in epithelial branching was also observed in purified IkappaBalpha-deficient primary epithelial cells in three-dimensional culture. These data demonstrate that NF-kappaB positively regulates mammary epithelial proliferation, branching, and functions in maintenance of normal epithelial architecture during early postnatal development.

Analysis of the NF-kappa B and PI 3-kinase/Akt survival pathways in nerve growth factor-dependent neurons

Nerve growth factor (NGF) readdition to NGF-deprived neurons can halt Jun N-terminal kinase (JNK) activation, cytochrome c release, and cell death through mechanisms that may involve phosphatidylinositol (PI) 3-kinase, Akt, and nuclear factor kappa B (NF-kappaB). We found that expression of the NF-kappaB protein c-Rel in NGF-deprived neurons blocks cytochrome c release but does not inhibit c-Jun phosphorylation. Conversely, inhibition of NF-kappaB in NGF-maintained neurons promotes cytochrome c release and cell death. In contrast to c-Rel, activated PI 3-kinase and Akt inhibit c-Jun phosphorylation but have only a small effect on cytochrome c release. Finally, although c-Rel can protect neurons from death caused by inhibitors of PI 3-kinase or Akt, NF-kappaB function is not critical for Akt-promoted survival. These results suggest that the PI 3-kinase/Akt and NF-kappaB survival pathways target distinct cell death events in neurons.

CpG stimulation of primary mouse B cells is blocked by inhibitory oligodeoxyribonucleotides at a site proximal to NF-kappaB activation

Bacterial DNA and CpG-oligodeoxyribonucleotides (ODN) are powerful B cell activators, inducing apoptosis protection, cell cycle entry, proliferation, costimulatory molecule expression, immunoglobulin (Ig) and interleukin-6 (IL-6) secretion. However, proximal events in B cell activation by ODN are only partially characterized, including the translocation of NF-kappaB to the nucleus. In this paper, we provide evidence that CpG-ODN-induced cell cycle entry and apoptosis protection are blocked by SN50 or gliotoxin and thus require NF-kappaB activation. NF-kappaB activation occurred within 30 minutes of stimulation of murine B cells with a phosphorothioate (S) CpG-ODN and persisted for up to 40 hours, with p50, p65, and c-Rel as the major components. Similar to other NF-kappaB inducers, CpG-ODN caused an early IkappaBalpha and IkappaBbeta degradation plus cleavage of the p50 precursor and subsequent NF-kappaB nuclear translocation. A group of closely related S-ODN, which specifically blocked CpG-induced B cell activation at submicromolar concentrations, also prevented NF-kappaB DNA binding and transcriptional activation. These inhibitory S-ODN differed from stimulatory S-ODN by having 2-3 G substitutions in the central motif. As inhibitory S-ODN did not directly interfere with the NF-kappaB DNA binding but prevented CpG-induced NF-kappaB nuclear translocation of p50, p65, and c-Rel and blocked p105, IkappaBalpha, and IkappaBbeta degradation, we concluded that their putative target must lie upstream of inhibitory kinase (IKK) activation.

The maturation of dendritic cells results in postintegration inhibition of HIV-1 replication

Maturation of dendritic cells (DC) is known to result in decreased capacity to produce HIV due to postentry block of its replicative cycle. In this study, we compared the early phases of this cycle in immature DC (iDC) and mature DC (mDC) generated from monocytes cultured with GM-CSF and IL-4, trimeric CD40 ligand (DC(CD40LT)), or monocyte-conditioned medium (DC(MCM)) being added or not from day 5. Culture day 8 cells exposed to X4 HIV-1(LAI) or R5 HIV-1(Ba-L) were analyzed by semiquantitative R-U5 PCR, which detects total HIV DNA. CXC chemokine receptor 4(low) (CXCR4(low)) CCR5(+) iDC harbored similar viral DNA amounts when exposed to either strain. HIV-1(LAI) entered more efficiently into DC(CD40LT) or DC(MCM) with up-regulated CXCR4. CCR5(low) DC(CD40LT) still allowed entry of HIV-1(Ba-L), whereas CCR5(-) DC(MCM) displayed reduced permissivity to this virus. Comparing amounts of late (long terminal repeat (LTR)-gag PCR) and total (R-U5 PCR) viral DNA products showed that HIV-1(Ba-L) reverse transcription was more efficient than that of HIV-1(LAI), but was not affected by DC maturation. Southern blot detection of linear, circular, and integrated HIV DNA showed that maturation affected neither HIV-1 nuclear import nor integration. When assessing virus transcription by exposing iDC to pNL4-3.GFP or pNL4-3.Luc viruses pseudotyped with the G protein of vesicular stomatitis virus (VSV-G), followed by culture with or without CD40LT or MCM, GFP and luciferase activities decreased by 60-75% in mDC vs iDC. Thus, reduced HIV replication in mDC is primarily due to a postintegration block occurring mainly at the transcriptional level. We could not relate this block to altered expression and nuclear localization of NF-kappa B proteins and SP1 and SP3 transcription factors.

The role of NF-kappaB as a survival factor in environmental chemical-induced pre-B cell apoptosis

Polycyclic aromatic hydrocarbons (PAH) are ubiquitous environmental chemicals that suppress the immune system at multiple levels, including at the level of B cell development in the bone marrow microenvironment. Specifically, PAH induce preB cell apoptosis in primary bone marrow cultures and in cocultures of an early preB cell line (BU-11) and a bone marrow stromal cell line (BMS2). Previous studies focused on the molecular mechanisms through which PAH induce stromal cells to deliver an apoptosis signal to adjacent preB cells. Apoptosis signaling within the preB cell itself was not investigated. Here, the role of NF-kappaB, a lymphocyte survival factor, in PAH-induced preB cell apoptosis was assessed. Analysis of DNA-binding proteins extracted from the nuclei of untreated BU-11 cells indicated DNA-binding complexes comprising NF-kappaB subunits p50, c-Rel, and/or Rel A. NF-kappaB down-regulation with previously described inhibitors induced BU-11 cell apoptosis, demonstrating that the default apoptosis pathway blocked by NF-kappaB is functional at this early stage in B cell development. Similarly, exposure of BU-11/BMS2 cocultures to 7,12-dimethylbenz[a]anthracene (DMBA), a prototypic PAH, down-regulated nuclear Rel A and c-Rel before overt apoptosis. Finally, ectopic expression of Rel A or c-Rel rescued BU-11 cells from DMBA-induced apoptosis. These results extend previous observations by demonstrating that 1) NF-kappaB is a survival factor at an earlier stage of B cell development than previously appreciated and 2) NF-kappaB down-regulation is likely to be part of the molecular mechanism resulting in PAH-induced preB cell apoptosis. These results suggest nonclonally restricted, PAH-mediated suppression of B lymphopoiesis.

Dynamic expression and activity of NF-kappaB during post-natal mammary gland morphogenesis

The Rel/NF-kappaB family of transcription factors has been implicated in such diverse cellular processes as proliferation, differentiation, and apoptosis. As each of these processes occurs during post-natal mammary gland morphogenesis, the expression and activity of NF-kappaB factors in the murine mammary gland were examined. Immunohistochemical and immunoblot analyses revealed expression of the p105/p50 and RelA subunits of NF-kappaB, as well as the major inhibitor, IkappaBalpha, in the mammary epithelium during pregnancy, lactation, and involution. Electrophoretic mobility shift assay (EMSA) demonstrated that DNA-binding complexes containing p50 and RelA were abundant during pregnancy and involution, but not during lactation. Activity of an NF-kappaB-dependent luciferase reporter in transgenic mice was highest during pregnancy, decreased to near undetectable levels during lactation, and was elevated during involution. This highly regulated pattern of activity was consistent with the modulated expression of p105/p50, RelA, and IkappaBalpha.

Mesenchymal expression of nuclear factor-kappaB inhibits epithelial growth and branching in the embryonic chick lung

It is becoming increasingly recognized that the ubiquitous, inducible transcription factor nuclear factor-kappaB (NF-kappaB) is involved in developmental processes. For example, NF-kappaB acts as a mediator of epithelial-mesenchymal interactions in the developing chick limb. We investigated the role of NF-kappaB in directing the branching morphogenesis of the developing chick lung, a process which relies on epithelial-mesenchymal communication. High level expression of relA was found in the mesenchyme surrounding the nonbranching structures of the lung but was not detected either in the mesenchyme surrounding the branching structures of the distal lung or in the developing lung epithelium. Specific inhibition of mesenchymal NF-kappaB in lung cultures resulted in increased epithelial budding. Conversely, expression of a trans-dominant activator of NF-kappaB in the lung mesenchyme repressed budding. Ectopic expression of RelA was sufficient to inhibit the ability of the distal mesenchyme to induce epithelial bud formation. Cellular proliferation in the mesenchyme was inhibited by hyperactivation of NF-kappaB in the mesenchyme of lung cultures. Interestingly, increased NF-kappaB activity in the mesenchyme also decreased the proliferation of the associated epithelium, while inhibition of NF-kappaB activity increased cellular proliferation in lung cultures. Expression patterns of several genes which are known to influence lung branching morphogenesis were altered in response to changes in mesenchymal NF-kappaB activity, including fgf10, bmp-4, and tgf-beta1. Thus NF-kappaB represents the first transcription factor reported to function within the lung mesenchyme to limit growth and branching of the adjacent epithelium.

SEK1/MKK4, c-Jun and NFKappaB are differentially activated in forebrain neurons during postnatal development and injury in both control and p75NGFR-deficient mice

The common neurotrophin receptor (p75NGFR) can signal in vitro through activation of the c-Jun N-terminal kinase (JNK) pathway and nuclear translocation of NFKappaB. Activation of JNK and its substrate c-Jun can lead to apoptosis. We investigated these activities in vivo by comparing immunoreactivity for phosphorylated(p) SEK-1 (or MKK4, which activates JNK), c-Jun (ser63, ser73) and nuclear translocation of NFKappaB-p50 in tissue sections through the forebrain of control and p75NGFR-deficient mice. During postnatal development, SEK1p-immunoreactivity was detectable in p75NGFR-positive cholinergic neurons and p75NGFR-negative neurons throughout the forebrain in control mice. During development, few cells contained c-Junp, although many neurons contained c-Jun. No obvious c-Jun immunostaining was present in the adult forebrain. At any age, NFKappaB-p50 immunoreactivity was seen in nuclei of most cells throughout the forebrain. Following fimbria fornix transection in adult mice, few basal forebrain neurons contained SEK1p while many axotomized choline acetyltransferase (ChAT)-positive neurons contained c-Junp and nuclear NFKappaB-p50. The immunostaining patterns of SEK1p, c-Junp and NFKB during development and following injury were largely similar in p75NGFR-deficient mice. During development, cells throughout the forebrain had TdT-mediated dUTP-biotin nick end labelling (TUNEL)-labelling (a potential marker for apoptosis), however, their presence was not predicted by number of neurons stained for SEK1p or c-Junp. These results suggest that the expected activation of the JNK pathway by p75NGFR, as well as the expected relationship between SEK1 and downstream activation of c-Jun do not occur in the mammalian forebrain. Also, these results suggest that this activation does not necessarily lead to cell death.

Differential regulation of vascular smooth muscle nuclear factor kappa-B by G alpha q-coupled and cytokine receptors

NF kappaB has been implicated as a downstream effector of G alphaq-coupled receptor signaling, but whether these and cytokine receptors activate NF kappaB similarly remains unclear. Stimulation of rat vascular smooth muscle cell G alphaq-coupled P2Y nucleotide receptors with UTP induces luciferase transcription from a sensitive and specific NF kappaB dependent promoter. However, these responses are only;15% of that to the reference cytokine IL-1 beta. IL-1 beta is a powerful stimulator of I kappaB alpha degradation, RelA nuclear import, and isoform specific NF kappaB enhancer binding in vitro, responses that are not detectable after P2Y receptor stimulation. Expression of two trans -dominant NF kappaB polypeptides suppresses induction of the NF kappaB reporter and also IL-1 beta stimulated monocyte chemoattractant-1 mRNA, which is not induced by UTP. In contrast, UTP induces higher expression of the endogenous COX-2 and IL-6 mRNAs than does IL-1 beta, implying that G alphaq-coupled receptor evokes additional NF kappaB-independent transcription factors in regulating these two genes. P2Y receptors are as effective as the reference growth factor PDGF-BB at inducing CREB, AP-1, SRE and NFAT transcription, which are largely unaffected by IL-1 beta treatment. NF kappaB is less efficiently activated then several other transcriptional effectors of G alphaq-coupled receptor signaling in vascular smooth muscle cells, and is instead preferentially activated by inflammatory cytokines.

Transcription factor nuclear factor-kappa B is activated in neurons after focal cerebral ischemia

Nuclear factor-kappa B (NF-kappaB) is a multisubunit transcription factor that when activated induces the expression of genes encoding acute-phase proteins, cell adhesion molecules, cell surface receptors, and cytokines. NF-kappaB is composed of a variety of protein subunits of which p50-and p65-kDa (RelA) are the most widely studied. Under resting conditions, these subunits reside in the cytoplasm as an inactive complex bound by inhibitor proteins, IkappaB alpha and IkappaB beta. On activation, IkappaB is phosphorylated by IkappaB kinase and ubiquitinated and degraded by the proteasome; simultaneously, the active heterodimer translocates to the nucleus where it can initiate gene transcription. In the periphery, NF-kappaB is involved in inflammation through stimulation of the production of inflammatory mediators. The role of NF-kappaB in the brain is unclear. In vitro, NF-kappaB activation can be either protective or deleterious. The role of NF-kappaB in ischemic neuronal cell death in vivo was investigated. Adult male rats were subjected to 2 hours of focal ischemia induced by middle cerebral artery occlusion (MCAO). At 2, 6, and 12 hours after reperfusion, the expression and transactivation of NF-kappaB in ischemic versus nonischemic cortex and striatum were determined by immunocytochemistry and by electrophoretic mobility gel-shift analysis. At all time points studied, p50 and p65 immunoreactivity was found exclusively in the nuclei of cortical and striatal neurons in the ischemic hemisphere. The contralateral nonischemic hemisphere showed no evidence of nuclear NF-kappaB immunoreactivity. Double immunofluorescence confirmed expression of p50 in nuclei of neurons. Increased NF-kappaB DNA-binding activity in nuclear extracts prepared from the ischemic hemisphere was further substantiated by electrophoretic mobility gel-shift analysis. Because the activation of NF-kappaB by many stimuli can be blocked by antioxidants in vitro, the effect of the antioxidant, LY341122, previously shown to be neuroprotective, on NF-kappaB activation in the MCAO model was evaluated. No significant activation of NF-kappaB was found by electrophoretic mobility gel-shift analysis in animals treated with LY341122. These results demonstrate that transient focal cerebral ischemia results in activation of NF-kappaB in neurons and supports previous observations that neuroprotective antioxidants may inhibit neuronal death by preventing the activation of NF-kappaB.

Identification by in vivo genomic footprinting of a transcriptional switch containing NF-kappaB and Sp1 that regulates the IkappaBalpha promoter

In unstimulated cells, NF-kappaB transcription factors are retained in the cytoplasm by inhibitory IkappaB proteins. Upon stimulation by multiple inducers including cytokines or viruses, IkappaBalpha is rapidly phosphorylated and degraded, resulting in the release of NF-kappaB and the subsequent increase in NF-kappaB-regulated gene expression. IkappaBalpha gene expression is also regulated by an NF-kappaB autoregulatory mechanism, via NF-kappaB binding sites in the IkappaBalpha promoter. In previous studies, tetracycline-inducible expression of transdominant repressors of IkappaBalpha (TD-IkappaBalpha) progressively decreased endogenous IkappaBalpha protein levels. In the present study, we demonstrate that expression of TD-IkappaBalpha blocked phorbol myristate acetate-phytohemagglutinin or tumor necrosis factor alpha-induced IkappaBalpha gene transcription and abolished NF-kappaB DNA binding activity, due to the continued cytoplasmic sequestration of RelA(p65) by TD-IkappaBalpha. In vivo genomic footprinting revealed stimulus-responsive protein-DNA binding not only to the -63 to -53 kappaB1 site but also to the adjacent -44 to -36 Sp1 site of the IkappaBalpha promoter. In vivo protection of both sites was inhibited by tetracycline-inducible TD-IkappaBalpha expression. Prolonged NF-kappaB binding and a temporal switch in the composition of NF-kappaB complexes bound to the -63 to -53 kappaB1 site of the IkappaBalpha promoter were also observed; with time after induction, decreased levels of transcriptionally active p50-p65 and increased p50-c-Rel heterodimers were detected at the kappaB1 site. Mutation of either the kappaB1 site or the Sp1 site abolished transcription factor binding to the respective sites and the inducibility of the IkappaBalpha promoter in transient transfection studies. These observations provide the first in vivo characterization of a promoter proximal transcriptional switch involving NF-kappaB and Sp1 that is essential for autoregulation of the IkappaBalpha promoter.

Nerve growth factor-dependent activation of NF-kappaB contributes to survival of sympathetic neurons

Neurotrophins activate multiple signaling pathways in neurons. However, the precise roles of these signaling molecules in cell survival are not well understood. In this report, we show that nerve growth factor (NGF) activates the transcription factors NF-kappaB and AP-1 in cultured sympathetic neurons. Activated NF-kappaB complexes were shown to consist of heterodimers of p50 and Rel proteins (RelA, as well as c-Rel), and NF-kappaB activation was found to occur independently of de novo protein synthesis but in a manner that required the action of the proteasome complex. Treatment with the NF-kappaB inhibitory peptide SN50 in the continuous presence of NGF resulted in dose-dependent induction of cell death. Under the conditions used, SN50 was shown to selectively inhibit NF-kappaB activation but not the activation of other cellular transcription factors such as AP-1 and cAMP response element-binding protein. Cells treated with SN50 exhibited morphological and biochemical hallmarks of apoptosis, and the kinetics of cell killing were accelerated relative to death induced by NGF withdrawal. Finally, experiments were conducted to test directly whether NF-kappaB could act as a survival factor for NGF-deprived neurons. Microinjection of cells with an expression plasmid encoding NF-kappaB (c-Rel) resulted in enhanced neuronal survival after withdrawal of NGF, whereas cells that were transfected with a vector encoding a mutated derivative of c-Rel lacking the transactivation domain underwent cell death to the same extent as control cells. Together, these findings suggest that the activation of NF-kappaB/Rel transcription factors may contribute to the survival of NGF-dependent sympathetic neurons.

Binding of c-Rel to STAT5 target sequences in HTLV-I-transformed T cells

The type I human T-cell leukemia virus (HTLV-I) induces abnormal growth and subsequent transformation of T cells, which is associated with the development of an acute T-cell malignancy termed adult T-cell leukemia. A characteristic of HTLV-I-transformed T cells is the constitutive nuclear expression of NF-kappaB/Rel family of transcription factors, which appears to be essential for the growth of these transformed cells. Although NF-kappaB/Rel factors are known to induce the expression of T-cell growth factor interleukin (IL)-2, it is unclear how they participate in the IL-2-independent growth of HTLV-I-transformed cells. In this study, we show that certain NF-kappaB/Rel members, predominantly c-Rel, interact with enhancer sequences for STAT5, a key transcription factor mediating IL-2-induced T-cell proliferation. Reporter gene assays reveal that the binding of c-Rel to the STAT5 site present in the Fc gammaR1 gene leads to potent transactivation of this enhancer. Binding of c-Rel to the Fc gammaR1 STAT site also occurs in human peripheral blood T cells immortalized with HTLV-I in vitro and is correlated with enhanced levels of proliferation of these cells. These results raise the possibility that NF-kappaB/Rel may participate in the growth control of HTLV-I-transformed T cells by regulating genes driven by both kappaB and certain STAT enhancers.

Nerve growth factor-dependent activation of NF-kappaB contributes to survival of sympathetic neurons

Neurotrophins activate multiple signaling pathways in neurons. However, the precise roles of these signaling molecules in cell survival are not well understood. In this report, we show that nerve growth factor (NGF) activates the transcription factors NF-kappaB and AP-1 in cultured sympathetic neurons. Activated NF-kappaB complexes were shown to consist of heterodimers of p50 and Rel proteins (RelA, as well as c-Rel), and NF-kappaB activation was found to occur independently of de novo protein synthesis but in a manner that required the action of the proteasome complex. Treatment with the NF-kappaB inhibitory peptide SN50 in the continuous presence of NGF resulted in dose-dependent induction of cell death. Under the conditions used, SN50 was shown to selectively inhibit NF-kappaB activation but not the activation of other cellular transcription factors such as AP-1 and cAMP response element-binding protein. Cells treated with SN50 exhibited morphological and biochemical hallmarks of apoptosis, and the kinetics of cell killing were accelerated relative to death induced by NGF withdrawal. Finally, experiments were conducted to test directly whether NF-kappaB could act as a survival factor for NGF-deprived neurons. Microinjection of cells with an expression plasmid encoding NF-kappaB (c-Rel) resulted in enhanced neuronal survival after withdrawal of NGF, whereas cells that were transfected with a vector encoding a mutated derivative of c-Rel lacking the transactivation domain underwent cell death to the same extent as control cells. Together, these findings suggest that the activation of NF-kappaB/Rel transcription factors may contribute to the survival of NGF-dependent sympathetic neurons.

The ability of CD40L, but not lipopolysaccharide, to initiate immunoglobulin switching to immunoglobulin G1 is explained by differential induction of NF-kappaB/Rel proteins

Antibodies of the immunoglobulin G1 class are induced in mice by T-cell-dependent antigens but not by lipopolysaccharide (LPS). CD40 engagement contributes to this preferential isotype production by activating NF-kappaB/Rel to induce germ line gamma1 transcripts, which are essential for class switch recombination. Although LPS also activates NF-kappaB, it poorly induces germ line gamma1 transcripts. Western blot analyses show that CD40 ligand (CD40L) induces all NF-kappaB/Rel proteins, whereas LPS activates predominantly p50 and c-Rel. Electrophoretic mobility shift assays show that in CD40L-treated cells, p50-RelA and p50-RelB dimers are the major NF-kappaB complexes binding to the germ line gamma1 promoter, whereas in LPS-treated cells, p50-c-Rel and p50-p50 dimers are the major binding complexes. Transfection of expression plasmids for NF-kappaB/Rel fusion proteins (forced dimers) indicates that p50-RelA and p50-RelB dimers activate the germ line gamma1 promoter and that p50-c-Rel and p50-p50 dimers inhibit this activation by competitively binding to the promoter without activating the promoter. Therefore, germ line gamma1 transcription depends on the composition of NF-kappaB/Rel proteins.

Cyclic AMP signaling and gene regulation

Cyclic adenosine monophosphate (cAMP) is a ubiquitous second messenger produced in cells in response to hormones and nutrients. The production of cAMP is dependent upon the actions of many different proteins that affect its synthesis and degradation. An important function of cAMP is to activate the phosphorylating enzyme, protein kinase A. The key roles of cAMP and protein kinase A in the phosphorylation and regulation of enzyme substrates involved in intermediary metabolism are well known. A newly discovered role for protein kinase A is in the phosphorylation and activation of transcription factors that are critical for the control of the transcription of genes in response to elevated levels of cAMP.

Both PU.1 and Nuclear Factor-κB Mediate Lipopolysaccharide-Induced HIV-1 Long Terminal Repeat Transcription in Macrophages

We recently reported that LPS stimulation of monocytic cells leads to the activation of PU.1, a member of the Ets family of transcription factors. Phosphorylation of PU.1 by protein kinase CK2 was found to up-regulate its trans-activation function, but not its DNA binding activity. Previous studies suggested that Ets proteins could bind to NF-κB motifs at the tetrameric core sequence TTCC. In macrophages, LPS-inducible HIV-1 gene expression is mediated in part by binding of NF-κB to identical tandem binding sites located within the long terminal repeat (LTR). Thus, we performed additional studies to determine whether PU.1 also played a role in regulating HIV-1 gene expression in macrophages. Our functional studies revealed that activation of the HIV-1 LTR in LPS-stimulated cells requires both NF-κB and PU.1. Extensive mutagenesis of the HIV-1 LTR revealed that PU.1-dependent activation requires the Ets motif within the upstream NF-κB site, whereas NF-κB itself binds to the downstream site. We also found that insertion of five additional nucleotides between the NF-κB sites abolished LPS inducibility, suggesting a direct interaction between factors that bind these sites. Lastly, we found that mutation of PU.1 at serine 148, which prevents its phosphorylation by CK2, blocked its ability to activate the HIV-1 LTR in response to LPS. These effects were promoter specific because PU.1 did not affect LPS-inducible activation of a distinct NF-κB-dependent promoter. While these data do not demonstrate direct binding of PU.1 to the HIV-1 LTR, they illustrate a novel role for PU.1 in activation of the HIV-1 LTR by LPS.

Inhibition of phosphodiesterase type IV suppresses human immunodeficiency virus type 1 replication and cytokine production in primary T cells: involvement of NF-kappaB and NFAT

Rolipram, a phosphosdiesterase type IV-specific inhibitor, prevented p24 antigen release from anti-CD3-activated human immunodeficiency virus (HIV)-infected T cells and CD4(+)-cell depletion associated with viral replication in a dose-responsive manner but minimally inhibited T-cell proliferation. Moreover, rolipram reduced the production of tumor necrosis factor alpha (TNF-alpha) and interleukin-10 (IL-10) by HIV-infected T cells. The transcriptional ability of a luciferase reporter gene under control of the HIV long terminal repeat, induced by phorbol myristic acetate plus ionomycin or by TNF-alpha, in primary T and Jurkat cells was also inhibited by rolipram. Rolipram inhibited NF-kappaB and NFAT activation induced by T-cell activation in Jurkat and primary T cells, as measured by transient transfection of reporter genes and electrophoretic mobility shift assays. Exogenous addition of TNF-alpha in the presence of rolipram restored NF-kappaB but not NFAT activation or p24 release. Addition of dibutyryl-cyclic AMP (dBcAMP) mimicked the effects of rolipram on p24 antigen release, NF-kappaB activation, and TNF-alpha secretion, but it did not affect NFAT activation or IL-10 production. The protein kinase A inhibitor KT5720 prevented the inhibition of TNF-alpha secretion but not that of HIV type 1 (HIV-1) replication caused by rolipram. Our data indicate that blockade of phosphodiesterase type IV could be of benefit against HIV-1 disease by modulating cytokine secretion and transcriptional regulation of HIV replication, and they suggest an important role of NFAT in HIV replication in primary T cells. Some of those activities cannot be ascribed solely to its ability to increase cAMP.

NF-κB Transcription Factors Are Involved in Normal Erythropoiesis

NF-κB/Rel designates a widely distributed family of transcription factors involved in immune and acute phase responses. Here, the expression and function of NF-κB factors in erythroid proliferation and differentiation were explored. In an erythroleukemia cell line, TF-1, high levels of p105/p50, p100/p52, p65, and IκBα were detected 24 hours after growth factor deprivation. In response to granulocyte-macrophage colony-stimulating factor (GM-CSF) stimulation, significant induction of p52 expression was observed. GM-CSF also induced nuclear translocation of both p52 and p65. No induction of NF-κB factors was observed with erythropoietin stimulation of TF-1 cells. Overexpression of p52 and p65 in TF-1 cells by transient transfection resulted in significant induction of a κB-TATA-luciferase reporter plasmid, showing that these factors are functional in vivo in erythroid cells. To determine whether NF-κB factors may play a role in normal erythropoiesis, levels of these factors were determined in burst-forming unit-erythroid (BFU-E)–derived cells at different stages of differentiation. The NF-κB factors p105/p50, p100/p52, and p65 were highly expressed in early BFU-E–derived precursors, which are rapidly proliferating, and declined during maturation. Furthermore, nuclear levels of NF-κB factors p50, p52, and p65 were higher in less mature precursors (day 10 BFU-E–derived cells) compared with more differentiated (day 14) erythroblasts. In nuclear extracts from day 10 BFU-E–derived cells, p50, p52, and p65 were able to form complexes, which bound to κB sites in the promoters of both the c-myb and c-mycgenes, suggesting that c-myb and c-myc may be among the κB-containing genes regulated by NF-κB factors in normal erythroid cells. Taken together, these data show that NF-κB factors are modulated by GM-CSF and suggest they function to regulate specific κB containing genes involved in erythropoiesis.

NF-κB Transcription Factors Are Involved in Normal Erythropoiesis

NF-κB/Rel designates a widely distributed family of transcription factors involved in immune and acute phase responses. Here, the expression and function of NF-κB factors in erythroid proliferation and differentiation were explored. In an erythroleukemia cell line, TF-1, high levels of p105/p50, p100/p52, p65, and IκBα were detected 24 hours after growth factor deprivation. In response to granulocyte-macrophage colony-stimulating factor (GM-CSF) stimulation, significant induction of p52 expression was observed. GM-CSF also induced nuclear translocation of both p52 and p65. No induction of NF-κB factors was observed with erythropoietin stimulation of TF-1 cells. Overexpression of p52 and p65 in TF-1 cells by transient transfection resulted in significant induction of a κB-TATA-luciferase reporter plasmid, showing that these factors are functional in vivo in erythroid cells. To determine whether NF-κB factors may play a role in normal erythropoiesis, levels of these factors were determined in burst-forming unit-erythroid (BFU-E)–derived cells at different stages of differentiation. The NF-κB factors p105/p50, p100/p52, and p65 were highly expressed in early BFU-E–derived precursors, which are rapidly proliferating, and declined during maturation. Furthermore, nuclear levels of NF-κB factors p50, p52, and p65 were higher in less mature precursors (day 10 BFU-E–derived cells) compared with more differentiated (day 14) erythroblasts. In nuclear extracts from day 10 BFU-E–derived cells, p50, p52, and p65 were able to form complexes, which bound to κB sites in the promoters of both the c-myb and c-mycgenes, suggesting that c-myb and c-myc may be among the κB-containing genes regulated by NF-κB factors in normal erythroid cells. Taken together, these data show that NF-κB factors are modulated by GM-CSF and suggest they function to regulate specific κB containing genes involved in erythropoiesis.

Discrimination between RelA and RelB transcriptional regulation by a dominant negative mutant of IkappaBalpha

RelA and RelB belong to the nuclear factor-kappaB (NF-kappaB-Rel) transcription factor family. Both proteins are structurally and functionally related, but their intracellular and tissue distributions are different. In resting cells, RelB is found mostly in the nucleus, whereas RelA is sequestered in the cytosol by protein inhibitors, among which IkappaBalpha is the dominant form in lymphocytes. Upon cellular activation IkappaBalpha is proteolyzed, allowing RelA dimers to enter the nucleus and activate target genes. To study the selectivity of gene regulation by RelA and RelB, we generated T cell lines stably expressing a dominant negative mutant of IkappaBalpha. We show that selective inhibition of RelA-NF-kappaB decreased induction of NFKB1, interleukin-2, and interleukin-2Ralpha genes but not c-myc. Transcription driven by the IkappaBalpha promoter was blocked by the transgenic IkappaBalpha; however, wild type IkappaBalpha was expressed in the transgenic cell clones but with much slower kinetics than that in control cells. Wild type IkappaBalpha expression was concomitant with RelB up-regulation, suggesting that RelB could be involved in transcription of IkappaBalpha through binding to an alternative site. These results indicate that RelB and RelA have both distinct and overlapping effects on gene expression.

Bcl-Xshort is elevated following severe global ischemia in rat brains

Hippocampal CA1 neurons are highly susceptible to short periods of transient global ischemia. We have previously reported in a rat model of transient forebrain global ischemia that activation and nuclear localization of NF-kB occurs in the CA1 neurons at 24 and 72 h post reperfusion. Events following NF-kB activation would ultimately determine whether damaged cells will undergo programmed cell death. We have selected bcl-x gene expression for study because there is increasing evidence that proteins encoded by the bcl-2 gene family (bcl-2, bcl-x, bax etc) play a role in the regulation of programmed cell death. We have observed that the bcl-x gene promoter contains a putative consensus sequence for NF-kB/CS4 responsive activation. We also can show that other members of the bcl-2 multigene family contain the NF-kB/CS4 sequence in their five prime regulatory regions. In this study, we show that NF-kB p50 and NF-kB p65 act in synergy to transactivate the bcl-x promoter in co-transfected 293 cells. We also report that following ischemia and NF-kB activation, bcl-x messenger RNA levels increase in the CA1 hippocampal region. As a result of this transcriptional increase, surprisingly, it is bcl-xs, the apoptotic form of bcl-x, that is elevated. These results suggest that activation of NF-kB can lead to increased expression of bcl-x as manifested by the increase in the short form of bcl-x.

Global cerebral ischemia activates nuclear factor-kappa B prior to evidence of DNA fragmentation

The oxidative stress responsive transcription factor nuclear factor-kappa B (NF-kappa B) consists of a p50 (50 kDa) and p65/RelA (65 kDa) component and can be activated in vitro by TNF alpha, IL1 beta, hydrogen peroxide and oxygen radicals. All of the above factors are also known to be elevated at certain times after transient global ischemia. The present study was performed to determine if NF-kappa B was activated in vivo by transient global forebrain ischemia. Adult male rats were subjected to 30 min of 4-vessel occlusion (4-VO) and sacrificed at selected post-ischemic time points. Levels of NF-kappa B p50 and p65 subunits were determined by immunocytochemistry, Western blot and electrophoretic mobility-shift analysis. The enhancer complex was also confirmed by immuno-gel-shift analysis. Specific labeling of DNA strand breaks and DNA fragmentation was examined in situ by means of the terminal deoxynucleotidyl transferase-mediated dUTP nick end labeling (TUNEL) method. Western blot analysis of hippocampus showed induction of p50 and p65. A time course of NF-kappa B induction in hippocampus showed a p50-specific band at 6 h that increased in intensity over 12, 48 h and then decreased by 96 h post-ischemia. Immunocytochemistry revealed at 24 h post-ischemia that p65 and p50 immunoreactivity was present in neuronal nuclei of hippocampal CA1 neurons as well as all other hippocampal regions and several other forebrain regions which were not vulnerable to transient forebrain ischemia. At 72 h post-ischemia, nuclear NF-kappa B immunoreactivity had disappeared in all brain areas except in hippocampal CA1 neurons which were degenerating. No evidence for DNA fragmentation as revealed by TUNEL staining could be observed at 24 h. However, at 72 h, hippocampal CA1 neurons were heavily labeled. The results of this study demonstrate that global forebrain ischemia causes a transient activation of NF-kappa B in many forebrain regions. NF-kappa B remains persistently activated in the vulnerable hippocampal CA1 sector. Because of the persistent activation of NF-kappa B in these neurons, the possibility exists that NF-kappa B has a role in programmed cell death in hippocampal CA1 neurons.

Induction of nuclear factor kappa B/Rel nuclear activity in human peripheral blood T lymphocytes by anti-HLA class I monoclonal antibodies

Monoclonal antibodies against either monomorphic or polymorphic determinants of class I antigen induced in PBMC and highly purified T lymphocytes the nuclear activity of NF-kappa B/Rel complexes. These included both p50/p50 and p50/p65 dimers, recognized by specific antibodies in EMSA. The induced complexes were detectable in extracts of cells incubated with anti-class I monoclonal antibody (mAb) for 1.5 h; the induction was maximal at 5 h, persistent at 16 h and no longer observed at 40 h. The mAb failed to induce NF-kappa B/Rel nuclear activity in cells incubated in the presence of 3,4-dichloroisocoumarin, an inhibitor of I kappa B-alpha degradation. Together, these results suggest that class I triggering can induce the activity of NF-kappa B/Rel nuclear activity in peripheral blood T lymphocytes, thereby modulating the expression of genes regulated by these transcription factors.

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

Members of the nuclear factor (NF)-kappaB/Rel family transcription factors are induced during thymic selection and in mature T lymphocytes after ligation of the T cell antigen receptor (TCR). Despite these findings, disruption of individual NF-kappaB/Rel genes has revealed no intrinsic defect in the development of mature T cells, perhaps reflecting functional redundancy. To circumvent this possibility, the T cell lineage was targeted to express a trans-dominant form of IkappaBalpha that constitutively represses the activity of multiple NF-kappaB/Rel proteins. Transgenic cells expressing this inhibitor exhibit a significant proliferative defect, which is not reversed by the addition of exogenous interleukin-2. Moreover, mitogenic stimulation of splenocytes leads to increased apoptosis of transgenic T cells as compared with controls. In addition to deregulated T cell growth and survival, transgene expression impairs the development of normal T cell populations as evidenced by diminished numbers of TCRhi CD8 single-positive thymocytes. This defect was significantly amplified in the periphery and was accompanied by a decrease in CD4(+) T cells. Taken together, these in vivo findings indicate that the NF-kappaB/Rel signaling pathway contains compensatory components that are essential for the establishment of normal T cell subsets.

Regulation of the interleukin-2 CD28-responsive element by NF-ATp and various NF-kappaB/Rel transcription factors

The CD28 costimulatory signal enhances antigen-mediated induction of interleukin-2 (IL-2) gene transcription through activation of an enhancer termed the CD28-responsive element (CD28RE). Although various nuclear proteins have been shown to bind to CD28RE, their in vivo functions in the regulation of this enhancer remain elusive. In this report, we show that CD28RE binds distinct transcription factors in cells treated with different mitogenic stimuli. Stimulation of the T-cell receptor (TCR) complex in the absence of a CD28 costimulatory signal induces a member of the nuclear factor of the activated T cells, NF-ATp; however, this treatment fails to activate the CD28RE enhancer activity. Significant activation of CD28RE was detected when the cells were treated with both the TCR stimulators and an anti-CD28 monoclonal antibody (anti-CD28), which induces the NF-kappaB/Rel enhancer binding proteins in addition to NF-ATp. The costimulatory activity of anti-CD28 can be further enhanced by a phorbol ester. Kinetic analyses demonstrate that activation of endogenous IL-2 gene transcription is correlated with the binding of CD28RE by NF-ATp and different NF-kappaB/Rel species. Transient-transfection studies reveal that expression of either NF-ATp or the p50-RelA NF-kappaB heterodimer leads to the potent transactivation of both the CD28RE enhancer and the intact IL-2 promoter in mitogen-stimulated cells. Remarkably, coexpression of these two families of enhancer-binding proteins in Jurkat T cells results in the transactivation of the CD28RE enhancer even in the absence of any cellular stimuli. Together, these results suggest that activation of IL-2 gene transcription by the TCR- and CD28-mediated signals involves the interaction of CD28RE with NF-ATp and various NF-kappaB/Rel transcription factors.

Physical interactions between Ets and NF-kappaB/NFAT proteins play an important role in their cooperative activation of the human immunodeficiency virus enhancer in T cells

The transcriptional regulatory elements of many inducible T-cell genes contain adjacent or overlapping binding sites for the Ets and NF-kappaB/NFAT families of transcription factors. Similar arrays of functionally important NF-kappaB/NFAT and Ets binding sites are present in the transcriptional enhancers of human immunodeficiency viruses types 1 and 2 (HIV-1 and HIV-2), suggesting that this pattern of nuclear protein binding sites reflects an evolutionarily conserved mechanism for regulating inducible T-cell gene expression that has been co-opted during HIV evolution. Despite these findings, the molecular mechanisms by which Ets and NF-kappaB/NFAT proteins cooperatively regulate inducible T-cell gene expression remained unknown. In the studies described in this report, we demonstrated a physical interaction between multiple Ets and NF-kappaB/NFAT proteins both in vitro and in activated normal human T cells. This interaction is mediated by the Ets domain of Ets proteins and the C-terminal region of the Rel homology domains of NF-kappaB/NFAT proteins. In addition, the Ets-NF-kappaB/NFAT interaction requires the presence of DNA binding sites for both proteins, as it is abolished by the DNA intercalating agents propidium iodide and ethidium bromide and enhanced by the presence of synthetic oligonucleotides containing binding sites for Ets and NF-kappaB proteins. A dominant-negative mutant of NF-kappaB p50 that binds DNA but fails to interact with Ets proteins inhibits the synergistic activation of the HIV-1 and HIV-2 enhancers by NF-kappaB (p50 + p65) and Ets-1, suggesting that physical interaction between Ets and NF-kappaB proteins is required for the transcriptional activity of the HIV-1 and HIV-2 enhancers. Taken together, these findings suggest that evolutionarily conserved physical interactions between Ets and NF-kappaB/NFAT proteins are important in regulating the inducible expression of T-cell genes and viruses. These interactions represent a potential target for the development of novel immunosuppressive and antiviral therapies.

Global ischemia activates nuclear factor-kappa B in forebrain neurons of rats

BACKGROUND AND PURPOSE

After global ischemia, brain levels of hydrogen peroxide, oxygen radicals, and the cytokines tumor necrosis factor-alpha (TNF-alpha) and interleukin-1 beta (IL-1 beta) are increased. Oxygen radicals, TNF-alpha, and IL-1 beta are known to activate nuclear factor-kappa B (NF-kappa B) in vitro. The present study was performed to determine whether NF-kappa B was activated in vivo by global ischemia in hippocampal CA1 neurons.

METHODS

Adult male rats were subjected to 30 minutes of four-vessel occlusion and killed 72 hours later. Levels of NF-kappa B p50 and p65 subunits in hippocampus were determined by immunocytochemistry, Western blot, and gel-shift analysis. Specific labeling of DNA strand breaks was demonstrated by means of an Apoptag apoptosis detection kit.

RESULTS

Labeling of DNA strand breaks was present at 72 hours. Chromatin compaction and segregation, a characteristic of apoptosis, was observed in sections stained with hematoxylin and eosin. NF-kappa B p50 and p65 immunoreactivity localized only to nuclei of CA1 neurons at 72 hours after reperfusion. Induction of the activated p50 and p65 subunits was confirmed by Western blot and electromobility shift analysis. The results demonstrate that NF-kappa B is activated selectively in hippocampal CA1 neurons at 72 hours after four-vessel occlusion, which is at the approximate time of CA1 neuronal cell death.

CONCLUSIONS

Transient forebrain ischemia resulted in a marked activation of nuclear NF-kappa B in the highly vulnerable CA1 sector. Intense nuclear localization of NF-kappa B was associated only with dying neurons; regions of the hippocampus that were not vulnerable to four-vessel occlusion did not exhibit nuclear NF-kappa B localization. The elevation of NF-kappa B in degenerating CA1 neurons may be associated mechanistically with apoptotic or necrotic cell death.