A 3' cis-acting element is involved in tumor necrosis factor-alpha gene expression in astrocytes

The impact of astrocytic NF-κB on healthy and Alzheimer's disease brains

Astrocytes play a role in healthy cognitive function and Alzheimer's disease (AD). The transcriptional factor nuclear factor-κB (NF-κB) drives astrocyte diversity, but the mechanisms are not fully understood. By combining studies in human brains and animal models and selectively manipulating NF-κB function in astrocytes, we deepened the understanding of the role of astrocytic NF-κB in brain health and AD. In silico analysis of bulk and cell-specific transcriptomic data revealed the association of NF-κB and astrocytes in AD. Confocal studies validated the higher level of p50 NF-κB and phosphorylated-p65 NF-κB in glial fibrillary acidic protein (GFAP)+-astrocytes in AD versus non-AD subjects. In the healthy mouse brain, chronic activation of astrocytic NF-κB disturbed the proteomic milieu, causing a loss of mitochondrial-associated proteins and the rise of inflammatory-related proteins. Sustained NF-κB signaling also led to microglial reactivity, production of pro-inflammatory mediators, and buildup of senescence-related protein p16INK4A in neurons. However, in an AD mouse model, NF-κB inhibition accelerated β-amyloid and tau accumulation. Molecular biology studies revealed that astrocytic NF-κB activation drives the increase in GFAP and inflammatory proteins and aquaporin-4, a glymphatic system protein that assists in mitigating AD. Our investigation uncovered fundamental mechanisms by which NF-κB enables astrocytes' neuroprotective and neurotoxic responses in the brain.

Suppression of prolactin signaling by pyrrolidine dithiocarbamate is alleviated by N-acetylcysteine in mammary epithelial cells

Prolactin is the key hormone to stimulate milk synthesis in mammary epithelial cells. It signals through the Jak2-Stat5 pathway to induce the expression of β-casein, a milk protein which is often used as a marker for mammary differentiation. Here we examined the effect of pyrrolidine dithiocarbamate (PDTC) on prolactin signaling. Our results show that PDTC downregulates prolactin receptor levels, and inhibits prolactin-induced Stat5 tyrosine phosphorylation and β-casein expression. This is not due to its inhibitory action on NF-κB since application of another NF-κB inhibitor, BAY 11-7082, and overexpression of I-κBα super-repressor do not lead to the same results. Instead, the pro-oxidant activity of PDTC is involved as inclusion of the antioxidant N-acetylcysteine restores prolactin signaling. PDTC triggers great extents of activation of ERK and JNK in mammary epithelial cells. These do not cause suppression of prolactin signaling but confer serine phosphorylation of insulin receptor substrate-1, thereby perturbing insulin signal propagation. As insulin facilitates optimal β-casein expression, blocking insulin signaling by PDTC might pose additional impediment to β-casein expression. Our results thus imply that lactation will be compromised when the cellular redox balance is dysregulated, such as during mastitis.

Dynamic changes in chromatin conformation at the TNF transcription start site in T helper lymphocyte subsets

Tumor necrosis factor (TNF) is one of the key primary response genes in the immune system that can be activated by a variety of stimuli. Previous analysis of chromatin accessibility to DNaseI demonstrated open chromatin conformation of the TNF proximal promoter in T cells. Here, using chromatin probing with restriction enzyme EcoNI and micrococcal nuclease we show that in contrast to the proximal promoter, the TNF transcription start site remains in a closed chromatin configuration in primary T helper (Th) cells, but acquires an open state after activation or polarization under Th1 and Th17 conditions. We further demonstrate that transcription factor c-Jun plays a pivotal role in the maintenance of open chromatin conformation at the transcription start site of the TNF gene.

Inhibition of nuclear factor-kappa B activation decreases survival of Mycobacterium tuberculosis in human macrophages

Nuclear factor-kappa B (NFκB) is a ubiquitous transcription factor that mediates pro-inflammatory responses required for host control of many microbial pathogens; on the other hand, NFκB has been implicated in the pathogenesis of other inflammatory and infectious diseases. Mice with genetic disruption of the p50 subunit of NFκB are more likely to succumb to Mycobacterium tuberculosis (MTB). However, the role of NFκB in host defense in humans is not fully understood. We sought to examine the role of NFκB activation in the immune response of human macrophages to MTB. Targeted pharmacologic inhibition of NFκB activation using BAY 11-7082 (BAY, an inhibitor of IκBα kinase) or an adenovirus construct with a dominant-negative IκBα significantly decreased the number of viable intracellular mycobacteria recovered from THP-1 macrophages four and eight days after infection. The results with BAY were confirmed in primary human monocyte-derived macrophages and alveolar macrophages. NFκB inhibition was associated with increased macrophage apoptosis and autophagy, which are well-established killing mechanisms of intracellular MTB. Inhibition of the executioner protease caspase-3 or of the autophagic pathway significantly abrogated the effects of BAY. We conclude that NFκB inhibition decreases viability of intracellular MTB in human macrophages via induction of apoptosis and autophagy.

Higher-order chromatin regulation and differential gene expression in the human tumor necrosis factor/lymphotoxin locus in hepatocellular carcinoma cells

The three-dimensional context of endogenous chromosomal regions may contribute to the regulation of gene clusters by influencing interactions between transcriptional regulatory elements. In this study, we investigated the effects of tumor necrosis factor (TNF) signaling on spatiotemporal enhancer-promoter interactions in the human tumor necrosis factor (TNF)/lymphotoxin (LT) gene locus, mediated by CCCTC-binding factor (CTCF)-dependent chromatin insulators. The cytokine genes LTα, TNF, and LTβ are differentially regulated by NF-κB signaling in inflammatory and oncogenic responses. We identified at least four CTCF-enriched sites with enhancer-blocking activities and a TNF-responsive TE2 enhancer in the TNF/LT locus. One of the CTCF-enriched sites is located between the early-inducible LTα/TNF promoters and the late-inducible LTβ promoter. Depletion of CTCF reduced TNF expression and accelerated LTβ induction. After TNF stimulation, via intrachromosomal dynamics, these insulators mediated interactions between the enhancer and the LTα/TNF promoters, followed by interaction with the LTβ promoter. These results suggest that insulators mediate the spatiotemporal control of enhancer-promoter associations in the TNF/LT gene cluster.

Suppression of local inflammation contributes to the neuroprotective effect of ginsenoside Rb1 in rats with cerebral ischemia

Local inflammation accounts for the progression of cerebral ischemic insult. Ginsenoside Rb1 (GRb1) is a natural product extracted from Panax ginseng C.A. Meyer. It has been reported to have beneficial effects in cerebral ischemia and to inhibit the inflammatory cascade in sepsis. In this study, to determine whether modulating local inflammation contributed to the neuroprotection of GRb1, male Sprague-Dawley rats were treated with GRb1 or vehicle intranasally for 1 week before being subjected to temporary occlusion of the right middle cerebral artery and reperfusion. Neuroprotection of GRb1 was evaluated with a focus on the key elements of central nervous system (CNS) inflammation, such as inflammatory cells, proinflammatory cytokines, and transcriptional factor. GRb1 reduced infarction volume by 57% (n=6, P<0.01) and significantly alleviated the neurological deficit (n=12, modified neurological severity scores [mNSS]: 6.6±1.1 vs. 8.6±1.1, P<0.05). GRb1 depressed the activation of microglia in the penumbra by 15%-27% from 24 h to 72 h after reperfusion and its further convention into phagocytic microglia/macrophages. In GRb1 group, the peak mRNA level of tumor necrosis factor α (TNF-α) mRNA was decreased by 35% 12 h after reperfusion, whereas the protein level was significantly reduced by 43%-57%. Downregulation by GRb1 of both interleukin (IL)-6 gene and protein after GRb1 administration was also observed. GRb1 partially inhibited the activation of nuclear factor-κB (NF-κB) pathway from 6 h to 72 h after ischemia and reperfusion onset, as determined by the expression of total and phosphorylated NF-κB/p65, inhibitor protein of κB (IκB)-α, and IκB-kinase complex (IKK)-α. All these results indicate that suppression of local inflammation after cerebral ischemia might be one mechanism that contributes to the neuroprotection of GRb1.

Transcriptional control of the TNF gene

The cytokine TNF is a critical mediator of immune and inflammatory responses. The TNF gene is an immediate early gene, rapidly transcribed in a variety of cell types following exposure to a broad range of pathogens and signals of inflammation and stress. Regulation of TNF gene expression at the transcriptional level is cell type- and stimulus-specific, involving the recruitment of distinct sets of transcription factors to a compact and modular promoter region. In this review, we describe our current understanding of the mechanisms through which TNF transcription is specifically activated by a variety of extracellular stimuli in multiple cell types, including T cells, B cells, macrophages, mast cells, dendritic cells, and fibroblasts. We discuss the role of nuclear factor of activated T cells and other transcription factors and coactivators in enhanceosome formation, as well as the contradictory evidence for a role for nuclear factor kappaB as a classical activator of the TNF gene. We describe the impact of evolutionarily conserved cis-regulatory DNA motifs in the TNF locus upon TNF gene transcription, in contrast to the neutral effect of single nucleotide polymorphisms. We also assess the regulatory role of chromatin organization, epigenetic modifications, and long-range chromosomal interactions at the TNF locus.

Activation-dependent intrachromosomal interactions formed by the TNF gene promoter and two distal enhancers

Here we provide a mechanism for specific, efficient transcription of the TNF gene and, potentially, other genes residing within multigene loci. We identify and characterize highly conserved noncoding elements flanking the TNF gene, which undergo activation-dependent intrachromosomal interactions. These elements, hypersensitive site (HSS)-9 and HSS+3 (9 kb upstream and 3 kb downstream of the TNF gene, respectively), contain DNase I hypersensitive sites in naive, T helper 1, and T helper 2 primary T cells. Both HSS-9 and HSS+3 inducibly associate with acetylated histones, indicative of chromatin remodeling, bind the transcription factor nuclear factor of activated T cells (NFAT)p in vitro and in vivo, and function as enhancers of NFAT-dependent transactivation mediated by the TNF promoter. Using the chromosome conformation capture assay, we demonstrate that upon T cell activation intrachromosomal looping occurs in the TNF locus. HSS-9 and HSS+3 each associate with the TNF promoter and with each other, circularizing the TNF gene and bringing NFAT-containing nucleoprotein complexes into close proximity. TNF gene regulation thus reveals a mode of intrachromosomal interaction that combines a looped gene topology with interactions between enhancers and a gene promoter.

FcepsilonR1 and toll-like receptors mediate synergistic signals to markedly augment production of inflammatory cytokines in murine mast cells

Mast cells mediate both IgE-dependent allergic reactions and protective responses against acute infections, possibly through the activation of Toll-like receptors (TLRs). We find that antigen interacts synergistically with TLR2 and TLR4 ligands to markedly enhance production of cytokines in murine mast cell lines. However, the TLR ligands neither stimulated degranulation and release of arachidonic acid nor influenced such responses to antigen, probably because these ligands failed to generate a necessary calcium signal. The enhanced cytokine production could be attributed to synergistic activation of mitogen-activated protein kinases in addition to the engagement of a more effective repertoire of transcription factors for cytokine gene transcription. The synergistic interactions of TLR ligands and antigen might have relevance to the exacerbation of IgE-mediated allergic diseases by infectious agents.

Bi-functional effects of ATP/P2 receptor activation on tumor necrosis factor-alpha release in lipopolysaccharide-stimulated astrocytes

Neuroinflammation is associated with a variety of CNS pathologies. Levels of tumor necrosis factor-alpha (TNF-alpha), a major proinflammatory cytokine, as well as extracellular ATP, are increased following various CNS insults. Here we report on the relationship between ATP/P2 purinergic receptor activation and lipopolysaccharide (LPS)-induced TNF-alpha release from primary cultures of rat cortical astrocytes. Using ELISA, we confirmed that treatment with LPS stimulated the release of TNF-alpha in a concentration and time dependent manner. ATP treatment alone had no effect on TNF-alpha release. LPS-induced TNF-alpha release was attenuated by 1 mm ATP, a concentration known to activate P2X7 receptors. Consistent with this, 3'-O-(4-Benzoyl)benzoyl-ATP (BzATP), a P2X7 receptor agonist, also attenuated LPS-induced TNF-alpha release. This reduction in TNF-alpha release was not due to loss of cell viability. Adenosine and 2-chloroadenosine were ineffective, suggesting that attenuation of LPS-induced TNF-alpha release by ATP was not due to ATP breakdown and subsequent activation of adenosine/P1 receptors. Interestingly, treatment of astrocyte cultures with 10 microm or 100 microm ATP potentiated TNF-alpha release induced by a submaximal concentration of LPS. UTP and 2methylthioADP (2-MeSADP), P2Y receptor agonists, also enhanced this LPS-induced TNF-alpha release. Our observations demonstrate opposing effects of ATP/P2 receptor activation on TNF-alpha release, i.e. P2X receptor activation attenuates, whereas P2Y receptor activation potentiates TNF-alpha release in LPS-stimulated astrocytes. These observations suggest a mechanism whereby astrocytes can sense the severity of damage in the CNS via ATP release from damaged cells and can modulate the TNF-alpha mediated inflammatory response depending on the extracellular ATP concentration and corresponding type of astrocyte ATP/P2 receptor activated.

IL-18 translational inhibition restricts IFN-gamma expression in crescentic glomerulonephritis

BACKGROUND

Interleukin-18 (IL-18), a potent inducer of interferon gamma (IFN-gamma) production, is a cytokine involved in the cell-mediated immune response that is expressed during inflammatory and pathologic conditions. IFN-gamma plays a role in the development of some models of glomerulonephritis (GN); however, the role of IL-18 in the production of IFN-gamma during these pathologies has not been studied.

METHODS

Rat IL-18 cDNA was isolated and the regulation of IL-18 gene expression was studied. IFN-gamma and IL-18 expression were determined in anti-glomerular basement membrane (GBM) antibody (Ab)-induced GN. Recombinant active IL-18 (rIL-18) was used to further identify its effect on IFN-gamma production during this GN. Glomerular injury and levels of IFN-gamma were assayed in Wistar Kyoto (WKY) rats with anti-GBM GN in the presence or absence of rIL-18.

RESULTS

Rat IL-18, similar to the mouse clone, requires processing by the IL-1beta converting enzyme to become activated. A rat IL-18 5'-untranslated region (UTR) translational inhibitor was identified that strongly inhibited the synthesis of IL-18. This translational inhibitor with different lengths (180 and 130 bp) was highly expressed during GN and correlated with minimal IFN-gamma mRNA expression. Injection of recombinant active IL-18 in WKY rats with anti-GBM GN was associated with an increase of glomerular IFN-gamma levels, proliferating cell nuclear antigen (PCNA)-ED1+ cells, and PCNA-CD8+ cells, with worsening of glomerular injury.

CONCLUSION

These data suggest that the translational control of IL-18 expression by its 5'-UTR limits the production of IL-18, resulting in restricted expression of mRNA and protein IFN-gamma in this model of GN. Furthermore, it was suggested that possible IL-18/IFN-gamma induction of local proliferation of macrophages and CD8+ cells might be an important mechanism for amplifying CD8+-mediated macrophage-dependent GN.

Myotrophin-kappaB DNA interaction in the initiation process of cardiac hypertrophy

To investigate how cardiac hypertrophy and heart failure develop, we isolated and characterized a candidate initiator, the soluble 12-kDa protein myotrophin, from rat and human hearts. Myotrophin stimulates protein synthesis and myocardial cell growth associated with increased levels of hypertrophy marker genes. Recombinant myotrophin from the cloned gene showed structural/functional motifs, including ankyrin repeats and putative phosphorylation sites for protein kinase C (PKC) and casein kinase II. One repeat, homologous with I kappaB, interacts with rel/NF-kappaB in vitro. We analyzed the interaction of recombinant myotrophin and nuclear extracts prepared from neonatal and adult cardiomyocytes; gel mobility shift assay showed that myotrophin bound to kappaB DNA. To define PKC's role in myotrophin-induced myocyte growth, we incubated neonatal rat myocytes (normal and stretch) with specific inhibitors and found that myotrophin inhibits [3H]leucine incorporation into myocytes and different hypertrophic gene expression in neonatal myocytes. Using confocal microscopy, we observed that a basal level of myotrophin was present in both cytoplasm and nucleus under normal conditions, but under cyclic stretch, myotrophin levels became elevated in the nucleus. Myotrophin gene levels were upregulated when myocytes underwent cyclic stretch or were treated with tumor necrosis factor-alpha (TNF-alpha) or interleukin-1beta and also when excised beating hearts were exposed to high pressure. Our data showed that the myotrophin-kappaB interaction was increased with age in spontaneously hypertensive rats (SHRs) only. Our data provide evidence that myotrophin-kappaB DNA interaction may be an important step in initiating cardiac hypertrophy.

Identification of new regulatory sequences far upstream of the mouse monocyte chemoattractant protein-1 gene

We systematically searched for sequences influencing the expression of the mouse monocyte chemoattractant protein-1 (MCP-1) gene (Scya2) by mapping DNase I hypersensitive sites (HS) in the chromatin of mesangial cells in a 40-kb interval around the gene. We found nine HS located between -24 kb and +12.7 kb. Three HS coincided with previously known regulatory sequences (HS-2.4, HS-1.0, and HS-0.2). We tested two of the previously unknown HS located far upstream of Scya2 (HS-19.4 and HS-16.3) in transfection experiments using luciferase reporter constructs and mouse mesangial cells as recipients. In transient transfections, both HS had a moderate effect on basal promoter activity as well as promoter activity stimulated by tumor necrosis factor-alpha. In stable transfection experiments, we found much higher activity. A DNA fragment containing HS-19.4 and HS-16.3 caused a considerable increase in the number of stably integrated luciferase copies. We determined the nucleotide sequence of the 5' flanking region to -28.6 kb. Computer-assisted sequence analysis did not yield evidence of an additional gene. These HS are located within the 5' flanking region of a gene cluster consisting of Scya2 (MCP-1), Scya7 (MCP-3), Scya11 (eotaxin), Scya12 (MCP-5), and Scya8 (MCP-2). This report represents the first comprehensive chromatin analysis of the mouse MCP-1 locus leading to the identification of a complex regulatory region located far upstream of Scya2.

Triflusal posttreatment inhibits glial nuclear factor-kappaB, downregulates the glial response, and is neuroprotective in an excitotoxic injury model in postnatal brain

BACKGROUND AND PURPOSE

Nuclear factor-kappaB (NF-kappaB) and the signal transducer and activator of transcription 3 (STAT3) are important transcription factors regulating inflammatory mechanisms and the glial response to neural injury, determining lesion outcome. In this study we evaluate the ability of triflusal (2-acetoxy-4-trifluoromethylbenzoic acid), an antiplatelet agent inhibitor of NF-kappaB activation, to improve lesion outcome after excitotoxic damage to the immature brain.

METHODS

Postnatal day 9 rats received an intracortical injection of the excitotoxin N-methyl-D-aspartate (NMDA) and oral administration of triflusal (30 mg/kg) either as 3 doses before NMDA injection (pretreatment) or as a single dose 8 hours after NMDA injection (posttreatment). After survival times of 10 and 24 hours, brains were processed for toluidine blue staining, tomato lectin histochemistry, and glial fibrillary acidic protein, NF-kappaB, and STAT3 immunocytochemistry.

RESULTS

NMDA-lesioned animals that were not treated with triflusal showed activation of NF-kappaB in neuronal cells at first and in glial cells subsequently. Animals that received pretreatment with triflusal showed a strong downregulation of neuronal and glial NF-kappaB but a similar development of the glial response and an equivalent lesion volume compared with nontreated animals. In contrast, animals receiving triflusal posttreatment showed increased early neuronal NF-kappaB but a reduction in the subsequent glial NF-kappaB, accompanied by important downregulation of the microglial and astroglial response and a drastic reduction in the lesion size. STAT3 activation was not affected by triflusal treatment.

CONCLUSIONS

Triflusal posttreatment diminishes glial NF-kappaB, downregulates the glial response, and improves the lesion outcome, suggesting a neuroprotective role of this compound against excitotoxic injury in the immature brain.

ICAM-1-induced expression of proinflammatory cytokines in astrocytes: involvement of extracellular signal-regulated kinase and p38 mitogen-activated protein kinase pathways

ICAM-1 is a transmembrane glycoprotein of the Ig superfamily involved in cell adhesion. ICAM-1 is aberrantly expressed by astrocytes in CNS pathologies such as multiple sclerosis, experimental allergic encephalomyelitis, and Alzheimer's disease, suggesting a possible role for ICAM-1 in these disorders. ICAM-1 has been shown to be important for leukocyte diapedesis through brain microvessels and subsequent binding to astrocytes. However, other functional roles for ICAM-1 expression on astrocytes have not been well elucidated. Therefore, we investigated the intracellular signals generated upon ICAM-1 engagement on astrocytes. ICAM-1 ligation by a mAb to rat ICAM-1 induced mRNA expression of proinflammatory cytokines such as IL-1alpha, IL-1beta, IL-6, and TNF-alpha. Examination of cytokine protein production revealed that ICAM-1 ligation results in IL-6 secretion by astrocytes, whereas IL-1beta and IL-1alpha protein is expressed intracellularly in astrocytes. The involvement of mitogen-activated protein kinases (MAPKs) in ICAM-1-mediated cytokine expression in astrocytes was tested, as the MAPK extracellular signal-regulated kinase (ERK) was previously shown to be activated upon ICAM-1 engagement. Our results indicate that ERK1/ERK2, as well as p38 MAPK, are activated upon ligation of ICAM-1. Studies using pharmacological inhibitors demonstrate that both p38 MAPK and ERK1/2 are involved in ICAM-1-induced IL-6 expression, whereas only ERK1/2 is important for IL-1alpha and IL-1beta expression. Our data support the role of ICAM-1 on astrocytes as an inflammatory mediator in the CNS and also uncover a novel signal transduction pathway through p38 MAPK upon ICAM-1 ligation.

The differential regulation of group II(A) and group V low molecular weight phospholipases A(2) in cultured rat astrocytes

In astrocytes, cytokines stimulate the release of secretory phospholipase A(2) (sPLA(2)) activity and group II(A) sPLA(2) expression. This paper reports that two sPLA(2) isoforms, group II(A) and group V, are in fact expressed by astrocytes. Our studies showed that tumor necrosis factor alpha (TNFalpha) enhanced the mRNA of both isoforms, but the time courses of enhancement differed; group V was induced much faster than group II(A). Moreover, TNFalpha stimulated both the NF-kappaB and mitogen-activated protein (MAP) kinase (extracellular signal-regulated kinase, c-Jun NH(2)-terminal kinase, and p38 MAP kinase) signaling pathways in astrocytes. Interestingly, PI 3-kinase activity also was enhanced by TNFalpha, and NF-kappaB pathway was involved in mediating its effect. Specific inhibitors were used to show that both extracellular signal-regulated kinase and p38 MAP kinase may contribute to the effect of TNFalpha and that blocking phosphatidylinositol 3-kinase activity fully reversed the effect of TNFalpha. Furthermore, in astrocytes, TNFalpha-induced release of sPLA(2) activity was partially reversed by thyroid hormone and almost abolished by growth factors. This phenomenon was accompanied by a less marked increase in both group II(A) and group V sPLA(2) mRNA. In the presence of growth factors, the increase in group V mRNA was inhibited early and transiently, in contrast to what was observed with group II(A), which was more persistently inhibited. Although a transcriptional effect of thyroid hormone or growth factors in astrocytes cannot be definitively excluded, both types of factor interfered with sPLA(2) expression in a manner suggesting the existence of regulation of post-transcriptional events.

Binding of octamer factors to a novel 3'-positive regulatory element in the mouse interleukin-5 gene

The development of eosinophilia is regulated by interleukin (IL)-5. The biological specificity of eosinophilia suggests a tight and independent regulation of IL-5 expression. A number of regulatory regions in the 5'-end of the IL-5 gene have been described; many of them are involved in the regulation of other genes, and it is not clear how the specific expression of IL-5 is regulated. In this study, we report the finding of a novel 3'-regulatory element. Data base analysis of a 2-kilobase fragment of the 3'-end of the mouse IL-5 gene revealed the presence of a 40-base pair-long repetitive sequence that consists of four direct repeats of ATGAATGA distributed in a symmetrical manner. This sequence, named mouse downstream regulatory element-1 (mDRE1), was shown to be protected in DNase I footprinting assays in vitro. Electrophoretic mobility shift assays using specific antibodies identified the transcription factors Oct-1 and Oct-2 as responsible for the formation of the specific complexes with mDRE1 and nuclear extracts from both EL4 and primary T-cells. Competition electrophoretic mobility shift assays with oligonucleotides containing different numbers of ATGAATGA repeats showed that Oct-1 and Oct-2 bind to different motifs in the mDRE1 sequence. Deletion of mDRE1 from a 9.5-kilobase IL-5 gene construct significantly decreased the expression of the luciferase reporter gene, suggesting that it plays a positive role in the expression of the IL-5 gene.

Inhibition of human immunodeficiency virus (HIV-1) replication in SupT1 cells transduced with an HIV-1 LTR-driven PKR cDNA construct

Current strategies against the human immunodeficiency virus type 1 (HIV-1), including nucleoside analogues and protease inhibitors, have limited effectiveness as shown by the evolution of resistant retroviral strains and the presence of latent HIV-1 reservoirs. Therefore, it is necessary to look beyond anti-retroviral strategies and to rely on the body's immune system to inhibit HIV-1 replication. In this study, we approach the inhibition of HIV-1 replication by upregulation of the antiviral pathway that is natural to mammalian cells. Vectors were constructed which were capable of transferring the antiviral enzyme, p68 kinase (PKR), into target SupT1 lymphoblastoid cells under HIV-1 LTR transcriptional regulation via a retroviral-mediated shuttle system. We report a significant inhibition of HIV-1 replication in HIV-1 LTR-PKR cDNA transduced clones (105-10 : 239 and 106-4 : 560) expressing different PKR levels as measured by inhibition of HIV-1 induced syncytia formation and HIV-1 reverse transcriptase activity. Whereas the expression of PKR in parental vector transduced clone (N2-20P) is down-regulated 48 h after HIV-1 infection, the two transduced clones (one with PKR in the forward orientation and one in the reverse orientation) demonstrate increased PKR expression through 96 h post-infection, concomitant with an increase in eIF-2alpha phosphorylation and an increase in NF-kappaB activity at 72 h postinfection. These results demonstrate that the overexpression of PKR can inhibit HIV-1 replication and confirm the involvement of PKR in the IFN-associated antiviral pathway against HIV-1 infection. Finally, the treatment of the transduced clone 106-4 : 560 with AZT resulted in complete inhibition of HIV-1 replication.

Neuronal death and survival in two models of hypoxic-ischemic brain damage

Two unilateral hypoxic-ischemia (HI) models (moderate and severe) in immature rat brain have been used to investigate the role of various transcription factors and related proteins in delayed neuronal death and survival. The moderate HI model results in an apoptotic-like neuronal death in selectively vulnerable regions of the brain while the more severe HI injury consistently produces widespread necrosis resulting in infarction, with some necrosis resistant cell populations showing evidence of an apoptotic type death. In susceptible regions undergoing an apoptotic-like death there was not only a prolonged induction of the immediate early genes, c-jun, c-fos and nur77, but also of possible target genes amyloid precursor protein (APP751) and CPP32. In contrast, increased levels of BDNF, phosphorylated CREB and PGHS-2 were found in cells resistant to the moderate HI insult suggesting that these proteins either alone or in combination may be of importance in the process of neuroprotection. An additional feature of both the moderate and severe brain insults was the rapid activation and/or proliferation of glial cells (microglia and astrocytes) in and around the site of damage. The glial response following HI was associated with an upregulation of both the CCAAT-enhancer binding protein alpha (microglia only) and NFkappaB transcription factors.

Activation of nuclear factor-kappaB in the rat brain after transient focal ischemia

Nuclear factor-kappaB (NF-kappaB) becomes activated under inflammatory conditions and triggers induction of gene expression. Here, activation of NF-kappaB was studied after transient middle cerebral artery occlusion in the rat. Expression of p65 and p50, protein subunits of NF-kappaB, was examined by Western blotting, and immunohistochemistry for p65 was carried out. Double-labelling with specific markers for astroglia and microglia was used for cell type identification. Neurons located within and surrounding the ischemic core were identified during the first 24 h post-ischemia by using an antibody against 72-kDa heat shock protein. NF-kappaB binding activity was evaluated at different times post-ischemia with electrophoretic mobility gel shift assays. The results showed constitutive expression of p65 and p50, and NF-kappaB binding activity. Basal p65 was seen in certain neurons and resting astrocytes. Constitutive NF-kappaB binding activity was attributable to one main protein complex possibly formed in neurons and astrocytes, although two minor complexes were also detected. At 1 day post-ischemia selective induction of p65 was seen in neurons located in a penumbra-like area. At this time, however, no disturbances of basal NF-kappaB binding activity were found. Western blotting showed delayed induction of p65 several days after ischemia, whereas no changes were detected for p50. From 4 days post-ischemia, a substantial increase in the amount of p65 was detected due to induction in reactive astrocytes and microglia/macrophages. This was correlated with a robust enhancement of NF-kappaB binding activity with formation of three major specific complexes binding DNA. It is proposed that the highly inducible NF-kappaB complexes resulted from induction of p65 and activation of NF-kappaB in post-ischemic reactive glia.

Transcriptional regulation of intercellular adhesion molecule-1 in astrocytes involves NF-kappaB and C/EBP isoforms

ICAM-1 is an inducible cell surface protein that is involved in cell extravasation into inflamed tissues as well as immune responses. ICAM-1 expression is upregulated by proinflammatory cytokines such as TNF-alpha and IL-1beta in numerous cell types including the astrocyte, which functions as an immune effector cell in the central nervous system (CNS). We investigated the mechanism by which the ICAM-1 gene is transcriptionally regulated in astrocytes in response to TNF-alpha and IL-1beta. Human ICAM-1 promoter constructs linked to the reporter gene luciferase were transiently transfected into astrocytes, stimulated with TNF-alpha and IL-1beta, and ICAM-1 promoter activity examined. We determined that binding sites for both NF-kappaB (-186 bp region) and C/EBP (-198 bp region) are involved in TNF-alpha and IL-1beta-mediated ICAM-1 upregulation. Electrophoretic mobility shift assays using antibodies against NF-kappaB and C/EBP isoforms showed that p65 homodimers and p65/p50 heterodimers bind to the NF-kappaB site, and C/EBPdelta homodimers and C/EBPbeta/delta heterodimers bind to the C/EBP site. Transient transfection assays demonstrated that overexpression of p65 could transactivate the promoter activity of ICAM-1 reporter constructs. p50 overexpression had no effect on the basal levels of ICAM-1 transcription, but inhibited, in a dose dependent manner, p65 mediated transcription. Overexpression of C/EBPbeta slightly inhibited basal levels of ICAM-1 promoter activity, however, when C/EBPbeta and p65 were cotransfected, C/EBPbeta completely abolished the transactivating effects of p65. These results demonstrate that cytokine-induced ICAM-1 expression in astrocytes is regulated by interactions between NF-kappaB and C/EBP transcription factors.

FcεRI-Mediated Induction of TNF-α Gene Expression in the RBL-2H3 Mast Cell Line: Regulation by a Novel NF-κB-Like Nuclear Binding Complex

Using rat basophilic leukemia (RBL-2H3) cells as a model, we investigated how aggregation of the high affinity receptor for IgE (FcεRI) regulates TNF-α gene expression. Antigenic stimulation of RBL-2H3 cells led to an increase in newly synthesized TNF-α mRNA that was dependent on continuous receptor aggregation and did not require de novo protein synthesis. Kinetic analysis showed that maximal levels were achieved at 60 min and waned by 180 min of stimulation. Concomitant with the transcriptional activation of the TNF-α gene, the rapid appearance and disappearance of a previously uncharacterized nuclear NF-κB DNA binding activity, comprised of two distinct protein complexes, were observed. These protein complexes bound to NF-κB sites within the TNF-α gene and contained novel proteins (three species of Mr between 90,000–110,000) distinct from the classical proteins in NF-κB complexes. The induced NF-κB binding activity required continuous receptor stimulation and induced NF-κB-dependent reporter gene expression. Consistent with a role for the novel NF-κB nuclear binding activity in TNF-α gene expression, deletion of several 5′ κB elements in the TNF-α promoter abolished all measurable FcεRI-dependent induction of a reporter construct. Pharmacologic agents that inhibited the NF-κB binding activity also inhibited TNF-α mRNA expression. Our results demonstrate that a novel NF-κB-like nuclear binding activity plays an important role in regulation of the rapid and transient transcriptional activation of the TNF-α gene via FcεRI.

Interrelationships between astrocyte function, oxidative stress and antioxidant status within the central nervous system

Astrocytes have, until recently, been thought of as the passive supporting elements of the central nervous system. However, recent developments suggest that these cells actually play a crucial and vital role in the overall physiology of the brain. Astrocytes selectively express a host of cell membrane and nuclear receptors that are responsive to various neuroactive compounds. In addition, the cell membrane has a number of important transporters for these compounds. Direct evidence for the selective co-expression of neurotransmitters, transporters on both neurons and astrocytes, provides additional evidence for metabolic compartmentation within the central nervous system. Oxidative stress as defined by the excessive production of free radicals can alter dramatically the function of the cell. The free radical nitric oxide has attracted a considerable amount of attention recently, due to its role as a physiological second messenger but also because of its neurotoxic potential when produced in excess. We provide, therefore, an in-depth discussion on how this free radical and its metabolites affect the intra and intercellular physiology of the astrocyte(s) and surrounding neurons. Finally, we look at the ways in which astrocytes can counteract the production of free radicals in general by using their antioxidant pathways. The glutathione antioxidant system will be the focus of attention, since astrocytes have an enormous capacity for, and efficiency built into this particular system.