TNF stimulates expression of mouse MHC class I genes by inducing an NF kappa B-like enhancer binding activity which displaces constitutive factors

A T lymphocyte-specific transcription complex containing RUNX1 activates MHC class I expression

MHC class I expression is subject to both tissue-specific and hormonal regulatory mechanisms. Consequently, levels of expression vary widely among tissues, with the highest levels of class I occurring in the lymphoid compartment, in T cells and B cells. Although the high class I expression in B cells is known to involve the B cell enhanceosome, the molecular basis for high constitutive class I expression in T cells has not been explored. T cell-specific genes, such as TCR genes, are regulated by a T cell enhanceosome consisting of RUNX1, CBFbeta, LEF1, and Aly. In this report, we demonstrate that MHC class I gene expression is enhanced by the T cell enhanceosome and results from a direct interaction of the RUNX1-containing complex with the class I gene in vivo. T cell enhanceosome activation of class I transcription is synergistic with CIITA-mediated activation and targets response elements distinct from those targeted by CIITA. These findings provide a molecular basis for the high levels of MHC class I in T cells.

Inhibition of cytokine-induced IkappaB kinase activation as a mechanism contributing to the anti-atherogenic activity of tilianin in hyperlipidemic mice

Tilianin has been shown to down-regulate TNF-alpha induced expression of vascular cell adhesion molecules in endothelial cells. In this study, we examined the anti-atherogenic effects and molecular mechanism of tilianin in vitro and in vivo. Male low-density lipoprotein receptor null mice (Ldlr-/-) fed a high cholesterol diet showed significant increases in the size of atherosclerotic lesions, as well as increased plasma levels of total cholesterol, triglycerides, and the pro-inflammatory cytokines TNF-alpha and IL-1beta, when compared with Ldlr-/- mice fed a normal diet. Mice fed the high cholesterol diet supplemented with tilianin showed significantly reduced lesion sizes and reductions in cytokine levels, without significant changes in serum cholesterol levels. Primary cultured peritoneal macrophages from Ldlr-/- mice showed increased level of TNF-alpha andIL-1beta mRNA in response to treatment with lipopolysaccharide; these increases were inhibited by co-treatment with tilianin. Moreover, tilianin inhibited NF-kappaB activation, as determined by electrophoretic mobility shift and NF-kappaB promoter assays. Upstream of NF-kappaB activation, tilianin inhibited IkappaB kinase activation and the subsequent phosphorylation and degradation of IkappaBalpha protein. These results suggest that tilianin ameliorates atherosclerosis by inhibiting the production of the NF-kappaB-dependent pro-inflammatory cytokines, TNF-alpha and IL-1beta, via the inhibition of IkappaB kinase activity.

cis-Acting Element-specific Transcriptional Activity of Differentially Phosphorylated Nuclear Factor-κB

Phosphorylation of nuclear factor-kappa B (NF-kappa B) subunits emerges as a mechanism by which transcriptional activity of nuclear NF-kappa B complexes is regulated in an inhibitor kappa B-independent fashion. As the main transactivator, the p65 subunit of NF-kappa B has an outstanding position in the hierarchy of NF-kappa B proteins. p65 is a multiply phosphorylated protein with phosphorylation sites in the C-terminal transactivation domain and the N-terminal Rel homology domain (RHD). In this study, we describe two previously non-reported phospho-acceptor sites within the p65 RHD. We show that differential phosphorylation of serine residues within the RHD modulates transcriptional activity in a cis-acting element and promoter-specific context, thus leading to a phosphorylation state-dependent gene expression profile. RelA(-/-) mouse embryonic fibroblasts reconstituted with wild-type p65 or p65 phosphorylation-deficient mutants showed a distinctive expression profile of synthetic kappa B-dependent reporters as well as endogenous genes. Hypophosphorylated p65 did not display cis-acting element-specific changes in DNA binding or dimerization behavior. This study shows for the first time that site-specific phosphorylation can target a transcription factor to a particular subset of genes.

NF-kappaB is essential for epithelial-mesenchymal transition and metastasis in a model of breast cancer progression

The transcription factor NF-kappaB is activated in a range of human cancers and is thought to promote tumorigenesis, mainly due to its ability to protect transformed cells from apoptosis. To investigate the role of NF-kappaB in epithelial plasticity and metastasis, we utilized a well-characterized in vitro/in vivo model of mammary carcinogenesis that depends on the collaboration of the Ha-Ras oncoprotein and TGF-beta. We show here that the IKK-2/IkappaBalpha/NF-kappaB pathway is required for the induction and maintenance of epithelial-mesenchymal transition (EMT). Inhibition of NF-kappaB signaling prevented EMT in Ras-transformed epithelial cells, while activation of this pathway promoted the transition to a mesenchymal phenotype even in the absence of TGF-beta. Furthermore, inhibition of NF-kappaB activity in mesenchymal cells caused a reversal of EMT, suggesting that NF-kappaB is essential for both the induction and maintenance of EMT. In line with the importance of EMT for invasion, blocking of NF-kappaB activity abrogated the metastatic potential of mammary epithelial cells in a mouse model system. Collectively, these data provide evidence of an essential role for NF-kappaB during distinct steps of breast cancer progression and suggest that the cooperation of Ras- and TGF-beta-dependent signaling pathways in late-stage tumorigenesis depends critically on NF-kappaB activity.

Activation of the NF-kappaB pathway in human cytomegalovirus-infected cells is necessary for efficient transactivation of the major immediate-early promoter

We previously demonstrated that human cytomegalovirus (HCMV) infection induced the activation of the cellular transcription factor NF-kappaB. Here, we investigate the mechanism for the HCMV-induced NF-kappaB activation and the role that the induced NF-kappaB plays in transactivation of the major immediate-early promoter (MIEP) and production of immediate-early (IE) proteins. Using a dominant-negative inhibitor of NF-kappaB, the IkappaB-superrepressor, we demonstrated that active NF-kappaB is critical for transactivation of the HCMV MIEP. Investigation of the mechanisms of NF-kappaB activation following HCMV infection showed a rapid and sustained decrease in the inhibitors of NF-kappaB, IkappaBalpha and IkappaBbeta. Because the IkappaB kinases (IKKs) regulate the degradation of the IkappaBs, virus-mediated changes in the IKKs were examined next. Using dominant-negative forms of the IKKs, we showed significant decreases in transactivation of the MIEP in the presence of these mutants. In addition, protein levels of members of the IKK complex and IKK kinase activity were upregulated throughout the time course of infection. Lastly, the role NF-kappaB plays in HCMV IE mRNA and protein production during infection was examined. Using aspirin and MG-132, we demonstrated that production of IE protein and mRNA was significantly decreased and delayed in infected cells treated with these drugs. Together, the results of these studies suggest that virus-mediated NF-kappaB activation, through the dysregulation of the IKK complex, plays a primary role in the initiation of the HCMV gene cascade in fibroblasts and may provide new targets for therapeutic intervention.

Involvement of Rel/NF-kappa B transcription factors in senescence

Senescence is now established as a genetically controlled phenomenon that alters different cell functions, including proliferation, apoptosis, resistance to stress, and energetic metabolism. Underlying changes in gene expression are governed by some transcription factors, whose expression or activity must change with senescence as well. Transcription factors of the Rel/NF-kappa B family are good candidates to participate in the establishment of senescence. Arguments range from correlation between cell functions controlled by these factors and cell functions altered during senescence, to phenotypes resulting from in vitro manipulations of Rel/NF-kappa B activity.

KR‐31378 ameliorates atherosclerosis by blocking monocyte recruitment in hypercholestrolemic mice

The recruitment of monocytes into the artery wall is a crucial early step in atherogenesis. A novel compound, KR-31378, has been shown to be a neuroprotective agent for ischemia-reperfusion damage in rat brain via its potent antioxidant and antiapoptotic actions. Here, we report the effects of this compound on atherogenesis and possible mechanisms of action. In Ldlr knockout mice fed with a high-fat, high-cholesterol diet, treatment with KR-31378 significantly inhibited fatty streak formation and macrophage accumulation. To address the possibility that KR-31378 may influence the initial stages of atherogenesis, we examined its effect on the adhesion and migration of monocytes to endothelial cells stimulated with tumor necrosis factor-alpha. KR-31378 decreased the adhesion in a dose-dependent manner. The observed decreases in cell adhesion and migration correlated with KR-31378-mediated down-regulation of vascular cell adhesion molecule-1 (VCAM-1) and interleukin (IL)-8. Nuclear factor-kappaB (NF-kappaB) is known to regulate the expression of adhesive and chemotactic molecules including VCAM-1 and IL-8. Indeed, transient transfection experiments, electrophoretic mobility shift assay, and IkappaB degradation assay showed that KR-31378 decreased NF-kappaB activation. These results indicate that KR-31378 potently reduces fatty streak formation by inhibiting NF-kappaB-dependent cellular adhesion and chemotactic molecule expression, which are crucial to monocyte infiltration into the arterial wall during the early stages of atherogenesis.

Identification of an autoregulatory feedback pathway involving interleukin-1alpha in induction of constitutive NF-kappaB activation in pancreatic cancer cells

We previously reported that NF-kappaB is constitutively activated in most human pancreatic cancer tissues and cell lines but not in normal pancreatic tissues and immortalized pancreatic ductal epithelial cells. IkappaBalphaM-mediated inhibition of constitutive NF-kappaB activity in human pancreatic cancer cells suppressed tumorigenesis and liver metastasis in an orthotopic nude mouse model, suggesting that constitutive NF-kappaB activation plays an important role in pancreatic tumor progression and metastasis. However, the underlying mechanism by which NF-kappaB is activated in pancreatic cancer remains to be elucidated. In this study, we found that an autocrine mechanism accounts for the constitutive activation of NF-kappaB in metastatic human pancreatic cancer cell lines. Further investigation showed that interleukin-1alpha was the primary cytokine secreted by these cells that activates NF-kappaB. Neutralization of interleukin-1alpha activity suppressed the constitutive activation of NF-kappaB and the expression of its downstream target gene, urokinase-type plasminogen activator, in metastatic pancreatic cancer cell lines. Our results demonstrate that regulation of interleukin-1alpha expression is primarily dependent on AP-1 activity, which is in part induced by signaling pathways that are epidermal growth factor receptor-dependent and -independent. In conclusion, our findings suggest a possible mechanism for the constitutive activation of NF-kappaB in metastatic human pancreatic cancer cells and a possible missing mechanistic link between inflammation and cancer.

Jun oncoproteins do not function as primary transcription factors for the mouse major histocompatibility complex class I H-2 genes in fibroblasts

There are several reports in the literature focusing on regulation of major histocompatibility complex (MHC) class I genes by transcription factors of the jun family. The methods employed in these reports differed in various respects, and their results are inconsistent. In mouse Lewis lung carcinoma, B16-melanoma and F9-teratocarcinoma cell lines, c-jun was characterized as a transcriptional activator of the murine MHC class I H2-Kb gene, while c-jun was identified as a direct transcriptional repressor of the swine class I PD1 gene, and c-jun stably transfected clones of mouse L-fibroblasts markedly reduced their H-2 class I gene expression. In this study, we attempted to reproduce this last effect by means of transient transfection coupled to Northern hybridization, upon transfecting L-fibroblasts with expression vectors for all jun family members as well as with an array of c-jun-derived dominant negative mutants. No change in H-2 class I expression could be identified. Next, we derived two additional fibroblastic cell lines from the fibrosarcoma of the H2-Kk/v-jun transgenic mouse and transfected them with the two most potent c-jun dominant negative mutants, again without eliciting any change in H-2 class I mRNA level. We conclude that the negative regulation of H-2 class I genes by c-jun in cells of the fibroblastic lineage is not a primary effect.

The inverted CCAAT motif is an indispensable element of the enhancer B of the mouse major histocompatibility I H2-Kb gene

We have identified a strong binding of nuclear proteins derived from Ltk(-) fibroblasts to the enhancer B of the mouse MHC class I H2-K(b) gene. The inverted CCAAT motif and its adjacent upstream sequences have been revealed as protein-binding sites by electrophoretic mobility-shift, methylation interference, and DNase I footprint assays. Specific mutations in the inverted CCAAT motif as well as in the 5'-flanking cytosine pentanucleotide abrogated the formation of the major DNA-protein complex. Transcription of the chloramphenicol acetyltransferase (CAT) reporter gene driven by the H2-K(b) promoter in the Ltk(-) cell line was reduced substantially when a two-nucleotide mutation was introduced into the CCAAT element (CCAATCgcAT). The indicated two-nucleotide mutation decreased transcription initiated from both the homologous and a heterologous promoter. Furthermore, cotransfected MHC class II transactivator (CIITA) elevated the transcription of the reporter gene under the control of the H2-K(b) upstream sequences in the NIH 3T3 cell line. The intact enhancer B involving both the inverted CCAAT motif and the site alpha was found to play an indispensable role in the CIITA-mediated gene transactivation. The band-shift assay with the enhancer B probe revealed forming of a protein complex in a cooperative manner, which was again prevented by mutations in either element. Our results suggest an essential role of the inverted CCAAT element in the constitutive as well as inducible transcription of the mouse MHC class I genes.

Gene array identification of Epstein Barr virus-regulated cellular genes in EBV-converted Burkitt lymphoma cell lines

Epstein Barr virus (EBV) is associated with various B-cell neoplasms such as post-transplant lymphoproliferative disease or Burkitt lymphoma. B-lymphocyte reprogramming by EBV involves the control of numerous cellular genes. To identify such EBV-deregulated genes, we have compared the gene expression profile of EBV-negative Burkitt lymphoma cell lines (BL) (BL2, BL30, BL70) with their EBV-converted counterpart (BL2-B95, BL30-B95, BL70-B95) by cDNA array. Statistical analysis of the results was made using Ward's cluster analysis method. Results showed that the expression of up to 26% of the 1176 cellular genes analyzed may be modified in EBV-converted BL cells. Within this set of genes, a subset of genes markedly regulated in EBV-converted BL cells was defined as those for which expression in EBV+ cells was increased or decreased more than 2-fold. Expression of various genes was modulated in agreement with their previously reported regulation by EBV or by transcription factors activated by EBV. Numerous genes were newly identified as modulated in EBV-converted BL cells. Some of these results were verified by both semiquantitative RT-PCR and Western blotting, and were consistent with functional studies. Functional classification of EBV-regulated genes gave a comprehensive picture of cellular reprogramming by EBV in BL, by pointing out cellular modules such as cell cycle, apoptosis, and signal transduction pathways, including BCR and TNF receptor family and interferon pathways. Furthermore, and perhaps most importantly, cDNA array results point to three families of transcription factors, Rel/NF-kappaB, STAT1, and Ets-related proteins Spi-B, Elf-1, and Ets-1 as putative cellular targets of EBV.

Nuclear transcription factors in the hippocampus

In the mammalian hippocampus, there is a trisynaptic loop that has been often referred to in studies on learning and memory mechanisms and their physiological correlate, the long-term potentiation (LTP). The three sets of synapses are formed by the fibers of perforant pathway terminating on granule cells and by the mossy fibers and Schaeffer collaterals making connections with the pyramidal cells. Each of the three types of synapses can develop LTP. LTP is accompanied by changes in gene expression and it is the nuclear transcription, involving specific transcription factors, that is the starting point for the series of biological amplifications and consolidations both necessary for such sustained changes. The transcription factors are proteins that control gene expression, development and functional formation in every eukaryotic cell. Two categories of transcription factors have been defined to date: general factors that comprise at least 20 proteins to form multiple preinitiation complex at the TATA box (TATA rich sequence) or regulatory factors that bind to promoter or enhancer regions at specific sites on the DNA close to, or distant from, the TATA box. Transcription factors have been divided into five different major classes according to unique protein motifs. These include basic domain, zinc-finger, helix-turn-helix, beta-Scaffold factors with minor groove contacts and other transcription factors not specifically classified. Much evidence has been accumulating in favor of the participation of several transcription factors in the consolidation of memory in the mammalian hippocampus following a spatial memory task. It is, therefore, of great importance that the involvement of transcription factors in de novo protein synthesis relevant to the synaptic mechanisms that mediate the formation of long-term memory should be summarized and discussed. No specific correlation between transduction of extracellular signals and expression of nuclear transcription factors, however, has been demonstrated to date.

Inhibition of tumor necrosis factor-alpha -induced nuclear translocation and activation of NF-kappa B by dehydroxymethylepoxyquinomicin

We previously designed and synthesized an NF-kappaB inhibitor, dehydroxymethylepoxyquinomicin (DHMEQ), that showed anti-inflammatory activity in vivo. In the present study we looked into its mechanism of inhibition. DHMEQ inhibited tumor necrosis factor-alpha (TNF-alpha)- and 12-O-tetradecanoylphorbol-13-acetate-induced transcriptional activity of NF-kappaB in human T cell leukemia Jurkat cells. It also inhibited the TNF-alpha-induced DNA binding of nuclear NF-kappaB but not the phosphorylation and degradation of IkappaB. Moreover, DHMEQ inhibited the TNF-alpha-induced nuclear accumulation of p65, a component of NF-kappaB. It also inhibited TNF-alpha-induced nuclear transport of green fluorescent protein-tagged p65. On the other hand, DHMEQ did not inhibit the nuclear transport of Smad2 and large T antigen. Also, it did not inhibit TNF-alpha-induced activation of JNK but synergistically induced apoptosis with TNF-alpha in Jurkat cells. Taken together, these data indicate that DHMEQ is a unique inhibitor of NF-kappaB acting at the level of nuclear translocation.

Transcription factor NF-IL6 (C/EBPbeta) activates the expression of the mouse MHC class I H2-Kb gene in response to TNF-alpha via the intragenic downstream regulatory element

The 5'-enhancer-deleted genomic construct of the H2-K(b) gene, stably integrated into the genome of L(tk-) fibroblasts, retains full competence to be induced by tumor necrosis factor-alpha (TNF-alpha) treatment. The only defined regulatory region in this construct is the intragenic downstream regulatory element (H2DRE). Computational inspection uncovered two potential NF-IL6 (C/EBPbeta) binding motifs within the H2DRE. Chloramphenicol acetyltransferase (CAT) reporter gene assay revealed that NF-IL6 is able to elevate transcription from H2DRE. Moreover, transient transfection of an NF-IL6 expression vector increased both constitutive and TNF-alpha-induced mRNA levels of endogenous H2 class I genes, and transfection of an NF-IL6 dominant negative construct decreased the expression of endogenous H2 class I genes in a dose-dependent manner. Using the electrophoretic mobility shift assay (EMSA) and antibody supershift assay, we were able to qualify the two computationally identified NF-IL6 binding motifs as one high-affinity and one low-affinity binding site. We conclude that the H2-K(b) gene belongs to target genes of the NF-IL6 (C/EBPbeta) in the course of the cellular response to TNF-alpha, and we discuss some consequences of this conclusion in a general framework of inducible expression of the H2-K(b) gene.

Induction of macrophage-inflammatory protein-3alpha gene expression by TNF-dependent NF-kappaB activation

Macrophage-inflammatory protein-3alpha (MIP-3alpha), also designated as liver and activation-regulated chemokine (LARC), Exodus, or CCL20, is a recently identified CC chemokine that is expected to play a crucial role in the initiation of immune responses. In this study, we describe that MIP-3alpha expression is under the direct control of NF-kappaB, a key transcription factor of immune and inflammatory responses. Overexpression of the p65/RelA subunit of NF-kappaB significantly increased the MIP-3alpha mRNA level. MIP-3alpha transcription was stimulated by TNF, and this stimulation was inhibited by an NF-kappaB inhibitor, I-kappaBalpha superrepressor. Analysis of the human MIP-3alpha promoter demonstrated a functional NF-kappaB site responsible for its expression. We also show that MIP-3alpha expression is induced in LPS-treated mouse livers that were primed with Propionibacterium acnes, which developed massive liver injury with infiltration of inflammatory cells. This induction was fully dependent on the TNF signaling cascade, because it was not observed in the livers of TNFR1-deficient mice. Furthermore, pretreatment with gliotoxin, an inhibitor of NF-kappaB activity, abrogated the P. acnes/LPS-induced MIP-3alpha expression of wild-type mice. These results clearly demonstrate that MIP-3alpha gene expression is dependent on NF-kappaB activity in vitro, and indicate that the TNFR1-mediated TNF signaling cascade that leads to NF-kappaB activation plays an essential role in MIP-3alpha expression in the murine liver injury model.

Interferon regulatory factor-1 is required for interferon-gamma-induced MHC class I genes in astrocytes

Recent studies have shown that the role of the transcription factor interferon regulatory factor-1 (IRF-1) in the expression of major histocompatibility complex (MHC) class I molecules is tissue-specific. Our previous studies indicated a role for IRF-1 in expression of MHC class I genes in cultured astrocytes in response to interferon-gamma (IFN-gamma). However, the requirement for IRF-1 in MHC class I expression has not been directly analyzed in neural tissue. To further ascertain the importance of IRF-1 in the induction of MHC class I genes in astrocytes in response to IFN-gamma, we analyzed astrocytes from mice with a targeted disruption of the IRF-1 gene (IRF-1(-/-) mice). As expected, astrocytes from wild type (IRF-1(+/+)) mice showed a coordinate increase in both IRF-1 and MHC class I gene expression in response to IFN-gamma. To the contrary, astrocytes from IRF-1(-/-) mice had greatly reduced MHC class I mRNA expression. MHC class I gene promoter activity in astrocytes was controlled entirely through a single enhancer, the MHC-IRF-E, to which IRF-1 bound in response to IFN-gamma in wild type but not in IRF-1(-/-) mouse astrocytes. In vivo, astrocytes in brains of wild type mice readily responded to IFN-gamma to express MHC class I molecules. This correlated with increased MHC class I mRNA in the brain. In contrast, brains of IRF-1(-/-) mice showed no MHC class I gene induction following exposure to IFN-gamma indicating that all cells in the central nervous system (CNS) including astrocytes with the potential to express MHC class I molecules were dependent on IRF-1. These studies conclusively demonstrate a major role for IRF-1/MHC-IRF-E interactions in controlling MHC class I gene expression in astrocytes in response to IFN-gamma.

The transporter associated with antigen processing: function and implications in human diseases

The adaptive immune systems have evolved to protect the organism against pathogens encountering the host. Extracellular occurring viruses or bacteria are mainly bound by antibodies from the humoral branch of the immune response, whereas infected or malignant cells are identified and eliminated by the cellular immune system. To enable the recognition, proteins are cleaved into peptides in the cytosol and are presented on the cell surface by class I molecules of the major histocompatibility complex (MHC). The transport of the antigenic peptides into the lumen of the endoplasmic reticulum (ER) and loading onto the MHC class I molecules is an essential process for the presentation to cytotoxic T lymphocytes. The delivery of these peptides is performed by the transporter associated with antigen processing (TAP). TAP is a heterodimer of TAP1 and TAP2, each subunit containing transmembrane domains and an ATP-binding motif. Sequence homology analysis revealed that TAP belongs to the superfamily of ATP-binding cassette transporters. Loss of TAP function leads to a loss of cell surface expression of MHC class I molecules. This may be a strategy for tumors and virus-infected cells to escape immune surveillance. Structure and function of the TAP complex as well as the implications of loss or downregulation of TAP is the topic of this review.

The histone acetyltransferase activity of PCAF cooperates with the brahma/SWI2-related protein BRG-1 in the activation of the enhancer A of the MHC class I promoter

Major histocompatibility complex (MHC) class I proteins are an essential component of the immune system allowing the organism to protect from viral infections and neoplastic transformation. Expression of the MHC class I genes is regulated by a variety of cis-regulatory promoter elements among which the enhancer A is of particular importance. This enhancer is synergistically activated through AP-1/ATF and NF-kappa B transcription factors. NF-kappa B recruits the histone acetyltransferase (HAT) p300/CREB-binding protein (CBP) to the multiprotein complex bound to the enhancer A. Here we present evidence that acetylation and deacetylation processes are involved in the activation of the enhancer A. The p300/CBP associated factor PCAF, but not p300/CBP, counteracts the repression of the enhancer A mediated by the histone deacetylase HDAC1. Furthermore, overexpression of PCAF results in an increase in the acetylation of histone H4 bound to the enhancer A and HDAC1 counteracts the PCAF-mediated H4 acetylation. The activation function of PCAF requires the p300/CBP binding motif indicating that PCAF might be recruited to the enhancer A through an association with p300/CBP. Moreover, PCAF and the Brahma/SWI2-related protein BRG-1, which is a key factor of the human ATP-dependent chromatin remodelling complex SWI/SNF, synergistically up-regulate the enhancer A. Synergistic activation requires the HAT domain of PCAF. Taken together our data suggest that members of two different groups of chromatin modifying complexes are involved in the activation of the enhancer A of the MHC class I promoter.

Oscillating fluid flow inhibits TNF-alpha -induced NF-kappa B activation via an Ikappa B kinase pathway in osteoblast-like UMR106 cells

Fluid flow plays an important role in load-induced bone remodeling. However, the molecular mechanism of flow-induced signal transduction in osteoblasts remains unclear. In endothelial cells, fluid flow alters activation of NF-kappaB resulting in changes in expression of cell adhesion molecules. To test the hypothesis that fluid flow alters NF-kappaB activation and expression of cell adhesion molecules in osteoblastic cells, we examined the effect of oscillating fluid flow (OFF) on tumor necrosis factor (TNF)-alpha-induced NF-kappaB activation in rat osteoblast-like UMR106 cells. We found that OFF inhibits NF-kappaB-DNA binding activities, especially TNF-alpha-induced p50-p65 heterodimer NF-kappaB activation and TNF-alpha-induced intercellular adhesion molecule-1 mRNA expression. The inhibitory effects of OFF on both TNF-alpha-induced NF-kappaB activation and intercellular adhesion molecule-1 mRNA expression were shear stress-dependent and also increased with OFF exposure duration, indicating that OFF has potent effects on mechanotransduction pathways. OFF also inhibited TNF-alpha-induced IkappaBalpha degradation and TNF-alpha-induced IkappaB kinase (IKK) activity in a shear stress-dependent manner. These results demonstrate that IKK is an initial target molecule for OFF effects on osteoblastic cells. Thus, OFF inhibits TNF-alpha-induced IKK activation, leading to a decrease in phosphorylation and degradation of inhibitory IkappaBalpha, which in turn results in the decrease of TNF-alpha-induced NF-kappaB activation and potentially the transcription of target genes.

Influenza A virus NS1 protein prevents activation of NF-kappaB and induction of alpha/beta interferon

The alpha/beta interferon (IFN-alpha/beta) system represents one of the first lines of defense against virus infections. As a result, most viruses encode IFN antagonistic factors which enhance viral replication in their hosts. We have previously shown that a recombinant influenza A virus lacking the NS1 gene (delNS1) only replicates efficiently in IFN-alpha/beta-deficient systems. Consistent with this observation, we found that infection of tissue culture cells with delNS1 virus, but not with wild-type influenza A virus, induced high levels of mRNA synthesis from IFN-alpha/beta genes, including IFN-beta. It is known that transactivation of the IFN-beta promoter depends on NF-kappaB and several other transcription factors. Interestingly, cells infected with delNS1 virus showed high levels of NF-kappaB activation compared with those infected with wild-type virus. Expression of dominant-negative inhibitors of the NF-kappaB pathway during delNS1 virus infection prevented the transactivation of the IFN-beta promoter, demonstrating a functional link between NF-kappaB activation and IFN-alpha/beta synthesis in delNS1 virus-infected cells. Moreover, expression of the NS1 protein prevented virus- and/or double-stranded RNA (dsRNA)-mediated activation of the NF-kappaB pathway and of IFN-beta synthesis. This inhibitory property of the NS1 protein of influenza A virus was dependent on its ability to bind dsRNA, supporting a model in which binding of NS1 to dsRNA generated during influenza virus infection prevents the activation of the IFN system. NS1-mediated inhibition of the NF-kappaB pathway may thus play a key role in the pathogenesis of influenza A virus.

MHC class I gene expression and regulation

Major histocompatibility complex (MHC) is a conglomerate of genes that play an important role in recognition of self and nonself. These genes are under tight control. In this review we have discussed the transcription processes regulating MHC gene expression. Various biological or chemical modulators can modulate MHC gene expression. The promoter region of class I genes can be activated through several pathways. Hence, these genes are not typical "domestic" genes. Extensive studies on regulation of MHC class I expression, using transfection techniques and transgenic animal models, have resulted in identification of various cis-acting sequences involved in positive and negative regulation of class I genes. Work is in progress to identify the transacting proteins that bind to these sites and to delineate the mechanisms that regulate constitutive and inducible expression of class I genes in normal and diseased cells. It has been seen that various biological molecules (IFN, GM-CSF, IL-2) and other chemicals up-regulate the MHC expression. If the exact mechanisms are known by which the expression of class I genes is up regulated, the efforts can be made to balance the beneficial and toxic effects of biological molecules with one another, which may facilitate the use of combination of these molecules in subpharmacological doses (to eliminate toxicity) for early and better management of neoplastic diseases, as it is well-known that during malignancy MHC gene expression is down-regulated. In the future, the use of transgenic and knockout mice will be useful in acquiring a better understanding, which may further help in cancer therapy.

Polyomavirus enhancer-binding protein 2/core binding factor/acute myeloid leukemia factors contribute to the cell type-specific activity of the CD11a integrin gene promoter

The CD11a/CD18 leukocyte integrin (LFA-1; also known as alphaL/beta2) mediates leukocyte transendothelial migration during immune and inflammatory responses and participates in lymphoma metastasis. CD11a/CD18 leukocyte-restricted expression is controlled by the CD11a gene promoter, which confers tissue-specific expression to reporter genes in vitro and in vivo. DNase I protection analysis of the CD11a proximal gene promoter revealed DNA-protein interactions centered at position -110 (CD11a-110). Disruption of CD11a-110 reduced CD11a promoter activity in a cell type-specific manner, as it reduced its activity by 70% in Jurkat lymphoid cells, whereas the effect was considerably lower in K562 and HepG2 cells. Electrophoretic mobility shift assays showed evidence of cell type-specific differences in CD11a-110 binding and indicated its specific recognition by members of the polyomavirus enhancer-binding protein 2/core binding factor (CBF)/acute myeloid leukemia (AML) family of transcription factors. AML1B/CBFbeta transactivated the CD11a promoter, with AML1B/CBFbeta-mediated transactivation being completely dependent on the integrity of the CD11a-110 element. Therefore, CBF/AML factors play a role in the cell type-restricted transcription of the CD11a integrin gene through recognition of CD11a-110. The involvement of CBF/AML factors in CD11a expression raises the possibility that CD11a/CD18 expression might be deregulated in acute myeloid and B-lineage acute lymphoblastic leukemias, thus contributing to their altered adhesion and metastatic potential.

Invasive Shigella flexneri activates NF-kappa B through a lipopolysaccharide-dependent innate intracellular response and leads to IL-8 expression in epithelial cells

The pathogenesis of Shigella flexneri infection centers on the ability of this organism to invade epithelial cells and initiate an intense inflammatory reaction. Because NF-kappa B is an important transcriptional regulator of genes involved in inflammation, we investigated the role of this transcription factor during S. flexneri infection of epithelial cells. Infection of HeLa cells with invasive S. flexneri induced NF-kappa B DNA-binding activity; noninvasive S. flexneri strains did not lead to this activation. The pathway leading to NF-kappa B activation by invasive S. flexneri involved the kinases, NF-kappa B-inducing kinase, I kappa B kinase-1, and I kappa B kinase-2. NF-kappa B activation was linked to inflammation, because invasive S. flexneri activated an IL-8 promoter-driven reporter gene, and the kappa B site within this promoter was indispensable for its induction. Microinjection of bacterial culture supernatants into HeLa cells suggested that LPS is responsible for NF-kappa B activation by S. flexneri infection. In conclusion, the eukaryotic transcription factor NF-kappa B was activated during S. flexneri infection of epithelial cells, which suggests a role for this transcriptional regulator in modulating the immune response during infection in vivo.

Structural characterisation of the mouse nuclear oxysterol receptor genes LXRalpha and LXRbeta

Oxysterols are important regulatory molecules of diverse biological processes such as cholesterol homeostasis, bile acid synthesis and apoptosis. Recent findings led to the suggestion that some of these functions are mediated by the nuclear receptors LXRalpha and LXRbeta owing to their potential to bind a group of naturally occurring oxysterols as their ligands. In this report, we compare the genomic structure and the promoter regions of the two mouse LXR genes. In addition, we show evidence for the presence of a processed, but truncated LXRbeta pseudogene in the mouse genome. RACE-PCR on mouse liver cDNA demonstrates the presence of more than one defined transcription initiation site for both genes. The LXRalpha and LXRbeta promoter regions are GC-rich and contain a number of putative Sp1 binding sites but lack obvious TATA and CAAT boxes. A database search revealed several sequence motifs in the LXR promoter regions that resemble known transcription factor binding sites. Most striking is the identification of one potential NFkappaB and seven potential Ets-protein binding sites in the LXRbeta promoter, suggesting an important role for this receptor in the haematopoietic/immune system.

The transporter associated with antigen processing TAP: structure and function

The transport of antigenic peptides from the cytosol to the lumen of the endoplasmic reticulum (ER) is an essential process for presentation to cytotoxic T-lymphocytes. The transporter associated with antigen processing (TAP) is responsible for the intracellular translocation of peptides across the membrane of the ER. Efficient assembly of MHC-peptide complex requires the formation of a macromolecular transport and chaperone complex composed of TAP, tapasin and MHC class I molecules. Therefore, structure and function of TAP is important for the understanding of the immune surveillance.

Activators and target genes of Rel/NF-kappaB transcription factors

The vertebrate transcription factor NF-kappaB is induced by over 150 different stimuli. Active NF-kappaB, in turn, participates in the control of transcription of over 150 target genes. Because a large variety of bacteria and viruses activate NF-kappaB and because the transcription factor regulates the expression of inflammatory cytokines, chemokines, immunoreceptors, and cell adhesion molecules, NF-kappaB has often been termed a 'central mediator of the human immune response'. This article contains a complete listing of all NF-kappaB inducers and target genes described to date. The collected data argue that NF-kappaB functions more generally as a central regulator of stress responses. In addition, NF-kappaB activation blocks apoptosis in several cell types. Coupling stress responsiveness and anti-apoptotic pathways through the use of a common transcription factor may result in increased cell survival following stress insults.

Activators and target genes of Rel/NF-kappaB transcription factors

The vertebrate transcription factor NF-kappaB is induced by over 150 different stimuli. Active NF-kappaB, in turn, participates in the control of transcription of over 150 target genes. Because a large variety of bacteria and viruses activate NF-kappaB and because the transcription factor regulates the expression of inflammatory cytokines, chemokines, immunoreceptors, and cell adhesion molecules, NF-kappaB has often been termed a 'central mediator of the human immune response'. This article contains a complete listing of all NF-kappaB inducers and target genes described to date. The collected data argue that NF-kappaB functions more generally as a central regulator of stress responses. In addition, NF-kappaB activation blocks apoptosis in several cell types. Coupling stress responsiveness and anti-apoptotic pathways through the use of a common transcription factor may result in increased cell survival following stress insults.

SELEX and missing phosphate contact analyses reveal flexibility within the AP-2[alpha] protein: DNA binding complex

The AP-2 family of transcription factors are defined by the presence of a novel DNA binding domain, termed a 'basic helix-span-helix' motif. The AP-2 genes regulate important aspects of vertebrate embryogenesis and have also been linked to the control of cell proliferation and tumorigenesis, but the cellular targets that the AP-2 proteins control are largely undefined. In particular, since only a limited number of sequences have previously been utilized to define the nature of the AP-2 binding site, the range of DNA sequences recognized by the AP-2 proteins remains unknown. We have therefore utilized a SELEX analysis to identify multiple new AP-2[alpha] binding sites. Moreover, we have devised a novel missing phosphate and nucleotide competition analysis to characterize the residues in the binding site required for AP-2[alpha] protein:DNA contact. These studies suggest that the AP-2[alpha] protein:DNA complex is flexible and indicate that AP-2[alpha] can bind three related sequence motifs: GCC N3 GGC, GCC N4 GGC and GCC N3/4 GGG. The availability of these more refined consensus sequences should assist in the identification of target genes for this critical transcription factor.

Reduced phosphorylation of p50 is responsible for diminished NF-kappaB binding to the major histocompatibility complex class I enhancer in adenovirus type 12-transformed cells

Reduced cell surface levels of major histocompatibility complex class I antigens enable adenovirus type 12 (Ad12)-transformed cells to escape immunosurveillance by cytotoxic T lymphocytes (CTL), contributing to their tumorigenic potential. In contrast, nontumorigenic Ad5-transformed cells harbor significant cell surface levels of class I antigens and are susceptible to CTL lysis. Ad12 E1A mediates down-regulation of class I transcription by increasing COUP-TF repressor binding and decreasing NF-kappaB activator binding to the class I enhancer. The mechanism underlying the decreased binding of nuclear NF-kappaB in Ad12-transformed cells was investigated. Electrophoretic mobility shift assay analysis of hybrid NF-kappaB dimers reconstituted from denatured and renatured p50 and p65 subunits from Ad12- and Ad5-transformed cell nuclear extracts demonstrated that p50, and not p65, is responsible for the decreased ability of NF-kappaB to bind to DNA in Ad12-transformed cells. Hypophosphorylation of p50 was found to correlate with restricted binding of NF-kappaB to DNA in Ad12-transformed cells. The importance of phosphorylation of p50 for NF-kappaB binding was further demonstrated by showing that an NF-kappaB dimer composed of p65 and alkaline phosphatase-treated p50 from Ad5-transformed cell nuclear extracts could not bind to DNA. These results suggest that phosphorylation of p50 is a key step in the nuclear regulation of NF-kappaB in adenovirus-transformed cells.

Defective induction of the transcription factor interferon-stimulated gene factor-3 and interferon alpha insensitivity in human trophoblast cells

During pregnancy, trophoblast cells of the placenta contact maternal immune cells and yet are protected from attack. One mechanism that may account for this is that trophoblasts show altered expression of major histocompatibility complex (MHC) antigens. The gene for human leukocyte antigen G (HLA-G), a nonclassical gene, is expressed at high levels in trophoblast. Unlike other MHC class I genes, the HLA-G gene lacks an interferon (IFN) response element. Moreover, we demonstrate here that IFN, which regulates classical MHC class I genes in other cell types, does not affect these genes in trophoblast, owing to inactivation of an IFNalpha signaling pathway. Trophoblast cells (JEG-3 and JAR) were found to be selectively refractory to IFN. Specifically, although IFNalpha induced the transcription factors STAT1, STAT2, and IFN regulatory factor-1, and a protective response against encephalomyocarditis virus, it failed to protect the cells from vesicular stomatitis virus, activate a transfected MHC class I gene promoter, and induce the transcription factor IFN-stimulated gene factor (ISGF)-3. The lack of ISGF3 DNA-binding activity apparently was due to diminished p48/ISGF3gamma subunit activity since ISGF3 DNA-binding activity and IFNalpha induction of MHC class I promoter activity were reconstituted by p48/ISGF3gamma supplementation. These data indicate that a specific IFN signaling pathway is inactive in JEG-3 trophoblast cells because of altered activity of p48/ISGF3gamma, and they suggest IFN insensitivity as a mechanism that may help promote feto-placental survival.

Regulation of transgene expression in genetic immunization

The use of mammalian gene expression vectors has become increasingly important for genetic immunization and gene therapy as well as basic research. Essential for the success of these vectors in genetic immunization is the proper choice of a promoter linked to the antigen of interest. Many genetic immunization vectors use promoter elements from pathogenic viruses including SV40 and CMV. Lymphokines produced by the immune response to proteins expressed by these vectors could inhibit further transcription initiation by viral promoters. Our objective was to determine the effect of IFN-gamma on transgene expression driven by viral SV40 or CMV promoter/enhancer and the mammalian promoter/enhancer for the major histocompatibility complex class I (MHC I) gene. We transfected the luciferase gene driven by these three promoters into 14 cell lines of many tissues and several species. Luciferase assays of transfected cells untreated or treated with IFN-gamma indicated that although the viral promoters could drive luciferase production in all cell lines tested to higher or lower levels than the MHC I promoter, treatment with IFN-gamma inhibited transgene expression in most of the cell lines and amplification of the MHC I promoter-driven transgene expression in all cell lines. These data indicate that the SV40 and CMV promoter/enhancers may not be a suitable choice for gene delivery especially for genetic immunization or cancer cytokine gene therapy. The MHC I promoter/enhancer, on the other hand, may be an ideal transgene promoter for applications involving the immune system.

Evolution of the human immunodeficiency virus type 1 long terminal repeat promoter by conversion of an NF-kappaB enhancer element into a GABP binding site

Human immunodeficiency virus type 1 (HIV-1) transcription is regulated by the viral Tat protein and cellular factors, of which the concentration and activity may depend on the cell type. Viral long terminal repeat (LTR) promoter sequences are therefore optimized to suit the specific nuclear environment of the target host cell. In long-term cultures of a Tat-defective, poorly replicating HIV-1 mutant, we selected for a faster-replicating virus with a 1-nucleotide deletion in the upstream copy of two highly conserved NF-kappaB binding sites. The variant enhancer sequence demonstrated a severe loss of NF-kappaB binding in protein binding assays. Interestingly, we observed a new binding activity that is specific for the variant NF-kappaB sequence and is present in the nuclear extract of unstimulated cells that lack NF-kappaB. These results suggest that inactivation of the NF-kappaB site coincides with binding of another transcription factor. Fine mapping of the sequence requirements for binding of this factor revealed a core sequence similar to that of Ets binding sites, and supershift assays with antibodies demonstrated the involvement of the GABP transcription factor. Transient transfection experiments with LTR-chloramphenicol acetyltransferase constructs indicated that the variant LTR promoter is specifically inhibited by GABP in the absence of Tat, but this promoter was dramatically more responsive to Tat than the wild-type LTR. Introduction of this GABP site into the LAI virus yielded a specific gain of fitness in SupT1 cells, which contain little NF-kappaB protein. These results suggest that GABP potentiates Tat-mediated activation of LTR transcription and viral replication in some cell types. Conversion of an NF-kappaB into a GABP binding site is likely to have occurred also during the worldwide spread of HIV-1, as we noticed the same LTR modification in subtype E isolates from Thailand. This typical LTR promoter configuration may provide these viruses with unique biological properties.

Control of genes by mammalian retroposons

Available data on possible genetic impacts of mammalian retroposons are reviewed. Most important is the growing number of established examples showing the involvement of retroposons in modulation of expression of protein-coding genes transcribed by RNA polymerase II (Pol II). Retroposons contain conserved blocks of nucleotide sequence for binding of some important Pol II transcription factors as well as sequences involved in regulation of stability of mRNA. Moreover, these mobile genes provide short regions of sequence homology for illegitimate recombinations, leading to diverse genome rearrangements during evolution. Therefore, mammalian retroposons representing a significant fraction of noncoding DNA cannot be considered at present as junk DNA but as important genetic symbionts driving the evolution of regulatory networks controlling gene expression.

The Role of Enhancer A in the Locus-Specific Transactivation of Classical and Nonclassical HLA Class I Genes by Nuclear Factor κB

HLA class I expression is tightly controlled at the transcriptional level by several conserved regulatory elements in the proximal promoter region. In this study, the two putative κB motifs of enhancer A (κB1 and κB2) of the classical and nonclassical HLA class I genes were investigated for their binding properties of transcription factors and tested for their contribution to the NF-κB-induced route of transactivation. It was shown that NF-κB-induced transactivation through enhancer A is most important for the HLA-A locus, which contains two NF-κB binding sites. Although the enhancer A of HLA-B contains only one NF-κB binding site (κB1), there was still a moderate transactivation by NF-κB. Since HLA-F, which also possesses one NF-κB binding site but lacks protein binding to its κB2 site, was not transactivated by NF-κB, the NF-κB-mediated transactivation through the κB1 motif in HLA-B is most probably facilitated by binding of the transcription factor Sp1 to the upstream κB2 site. Thus, transcriptional regulation of HLA class I genes by NF-κB is restricted to the HLA-A and HLA-B loci.

MHC class I expression in murine skin: developmentally controlled and strikingly restricted intraepithelial expression during hair follicle morphogenesis and cycling, and response to cytokine treatment in vivo

Hair bulb keratinocytes generate one of the few "immune privileged" tissue compartments of the mammalian organism by suppressing classical MHC class I (MHC Ia) antigens. Expression of non-classical MHC class I (MHC Ib) antigens in the follicle has been found, but only in its distal epithelium. Here, we have defined when during murine hair follicle morphogenesis these peculiar MHC Ia and Ib expression patterns are established, how they change during the murine hair cycle, and how different MHC I modulatory agents alter follicular MHC Ia and Ib expression in vivo. During neonatal hair follicle morphogenesis in C57BL/6 mice, distal follicle keratinocytes began to express MHC Ia (H2b) only late in development. The MHC Ib antigens, Qa-1 and Qa-2, did not become visible until the initiation of follicle cycling, with Qa-1 expression being more widespread than that of Qa-2. H2b, Qa-1, and TAP-1 immunoreactivity on previously negative keratinocytes of the proximal anagen hair bulb was upregulated by intradermal injection of the proinflammatory cytokine interferon-gamma, but not by tumor necrosis factor-alpha or interleukin-1beta. Injection of the reportedly MHC class I downregulating agents interleukin-10, insulin-like growth factor-1, transforming growth factor-beta, alpha-melanocyte stimulating hormone, or dexamethasone, however, all failed to downregulate constitutive or interferon-gamma-induced follicular MHC Ia expression. This shows that the hair follicle is a previously unrecognized site of Qa-1 expression and that interferon-gamma is a key regulator of follicular MHC I expression in vivo. It also suggests that the developmental and immunologic controls of MHC I expression by follicle keratinocytes differ from those of other epithelial cells.

The Regulation of Murine H-2Dd Expression by Activation Transcription Factor 1 and cAMP Response Element Binding Protein

Resistance to radiation leukemia virus (RadLV)-induced leukemia is correlated with an increase in H-2Dd expression on the thymocyte surface. It has been shown that elevated H-2Dd expression on infected thymocytes is a result of elevated mRNA transcription and that the transcriptional increase is correlated with elevated levels of a DNA binding activity, H-2 binding factor 1 (H-2 BF1), which recognizes the 5′-flanking sequence (5′-TGACGCG-3′) of the H-2Dd gene. Recently, it has been shown that the activation transcription factor 1 (ATF-1) homodimer is one form of the H-2 BF1 complex. Here we demonstrate that the cAMP response element binding protein (CREB) homodimer and the heterodimer of CREB/ATF-1 also recognize the cis regulatory motif and are two additional forms of the H-2 BF1 complex. The levels of mRNA encoding ATF-1 and CREB were both increased in RadLV-infected thymocytes that showed increased levels of H-2 mRNA. Also, all three H-2 BF1 binding activities, ATF-1 homodimer, CREB homodimer, and ATF-1/CREB heterodimer, were increased in RadLV-infected thymocytes that expressed high levels of H-2Dd Ag on the cell surface. Transfection experiments demonstrated that ATF-1 and CREB activated a reporter plasmid containing the H-2 BF1 motif. These observations strongly suggest that both ATF-1 and CREB are involved in the regulation of H-2 gene expression following RadLV infection of mouse thymocytes.

DNA damaging agents induce expression of Fas ligand and subsequent apoptosis in T lymphocytes via the activation of NF-kappa B and AP-1

Apoptosis induced by DNA damage and other stresses can proceed via expression of Fas ligand (FasL) and ligation of its receptor, Fas (CD95). We report that activation of the two transcription factors NF-kappa B and AP-1 is crucially involved in FasL expression induced by etoposide, teniposide, and UV irradiation. A nondegradable mutant of I kappa B blocked both FasL expression and apoptosis induced by DNA damage but not Fas ligation. These stimuli also induced the stress-activated kinase pathway (SAPK/JNK), which was required for the maximal induction of apoptosis. A 1.2 kb FasL promoter responded to DNA damage, as well as coexpression with p65 Rel or Fos/Jun. Mutations in the relevant NF-kappa B and AP-1 binding sites eliminated these responses. Thus, activation of NF-kappa B and AP-1 contributes to stress-induced apoptosis via the expression of FasL.

Characterization and functional analysis of the promoter of RAGE, the receptor for advanced glycation end products

The receptor for advanced glycation end products, RAGE, is a member of the immunoglobulin superfamily of cell surface molecules differentially expressed on a range of cell types. Ligation of RAGE perturbs homeostatic mechanisms and, potentially, provides a basis for cellular dysfunction in pathologic situations in which its ligands accumulate. To understand factors underlying RAGE expression, we cloned the 5'-flanking region of the RAGE gene and characterized putative regulatory motifs. Analysis of the putative promoter region revealed the presence of three potential NF-kappaB-like and two SP1 binding sites. Transient transfection of vascular endothelial and smooth muscle cells using chimeric 5'-deletion constructs linked to luciferase reporter revealed that the region -1543/-587 contributed importantly to both basal and stimulated expression of the RAGE gene. This region of the RAGE gene contained three putative NF-kappaB-like binding sites and was responsible for increased luciferase activity observed when endothelial or smooth muscle cells were stimulated with lipopolysaccharide. DNase I footprinting assays and electrophoretic mobility shift assay revealed that two of the three NF-kappaB-like binding sites (1 and 2) were likely functional and responsive to stimuli. Upon simultaneous mutation of NF-kappaB-like sites 1 and 2, both basal promoter expression and response to stimulation with LPS, as measured by relative luciferase activity, were significantly diminished. These results point to NF-kappaB-dependent mechanisms regulating cellular expression of RAGE and suggest a means of linking RAGE to the inflammatory response.

Activation transcription factor 1 involvement in the regulation of murine H-2Dd expression

Resistance to radiation leukemia virus-induced leukemia is correlated with an increase in H-2D expression on the thymocyte surface. Recently, it has been shown that elevated H-2Dd expression on the infected thymocyte is a result of elevated mRNA transcription and that the transcriptional increase is correlated with elevated levels of a DNA binding activity, H-2 binding factor 1 (H-2 BF1), which recognizes the 5'-flanking sequences (5'-TGACGCG-3') of the H-2Dd gene. This target for transcription factor binding has been found to be identical in the 5'-regulatory region of 12 rodent class I genes, nine of which have been shown to be functional genes. Furthermore, this cis-element is found 5' of 20 primate class I genes (15 human genes), seven of which are known to be functional. Here, we demonstrate that activation transcription factor 1 (ATF-1) is one component of H-2 BF1. In addition, the levels of ATF-1 mRNA in uninfected and radiation leukemia virus-infected thymocytes parallel those of H-2Dd mRNA, and therefore, it is suggested that ATF-1 up-regulates the transcription of the H-2Dd gene after radiation leukemia virus infection of thymocytes. Transfection experiments also demonstrate that ATF-1 activates a reporter plasmid that contains the H-2 BF1 motif, but not a reporter lacking this motif. This is the first demonstration of the interaction of ATF-1 with 5'-regulatory sequences of major histocompatibility complex class I genes.

Regulation of the hepatic CYP 2E1 gene during chronic alcohol exposure: lack of an ethanol response element in the proximal 5'-flanking sequence

Chronic exposure to ethanol is known to cause a dramatic increase in the level of CYP 2E1 apoprotein. More recently it has been demonstrated that under certain conditions the mRNA encoding cytochrome P450 2E1(CYP 2E1) is inducible; however, the mechanisms by which these increases occur are not well understood. In the current study, DNase I footprinting assays performed on the first kilobase of the CYP 2E1 5'-flanking sequences resulted in the identification of 13 sequence-specific protected regions using rat liver nuclear extracts isolated from either control or ethanol-treated animals. No differences were observed in the DNase I footprint patterns produced by the two different nuclear extracts. In addition, analysis by electrophoretic mobility shift assays (EMSA) revealed that with one exception, there were no differences in the level of binding complexes between the two extracts. However, EMSA analysis with an oligonucleotide to one footprint site (designated Site C) revealed that in nuclear extracts isolated from ethanol-treated animals there was a 2.9-fold increase in this binding complex when compared to control nuclear extracts. This site was previously shown to contain an HNF-1alpha binding site, and here we demonstrate that bacterially expressed HNF-1alpha in footprint assays bind Site C sequences and that HNF-1alpha transactivates the CYP 2E1 promoter in co-transfection experiments with HNF-1alpha expression plasmid and plasmids containing CYP 2E1 promoter sequences coupled to the chloramphenicol acetyl transferase gene. Furthermore, in contrast to the increase observed by EMSA in Site C binding, no increase was detected in the CYP 2E1 transcriptional rate supported by nuclear extracts from ethanol-treated animals over controls using in vitro transcription assays, suggesting that the increase by ethanol in CYP 2E1 transcription is not mediated through the HNF-1alpha site.

Induction of MHC class I expression by the MHC class II transactivator CIITA

Major histocompatibility complex (MHC) class I-deficient cell lines were used to demonstrate that the MHC class II transactivator (CIITA) can induce surface expression of MHC class I molecules. CIITA induces the promoter of MHC class I heavy chain genes. The site alpha DNA element is the target for CIITA-induced transactivation of class I. In addition, interferon-gamma (IFNgamma)-induced MHC class I expression also requires an intact site alpha. The G3A cell line, which is defective in CIITA induction, does not induce MHC class I antigen and promoter in response to IFNgamma. Trans-dominant-negative forms of CIITA reduce class I MHC promoter function and surface antigen expression. Collectively, these data argue that CIITA has a role in class I MHC gene induction.

Site alpha is crucial for two routes of IFN gamma-induced MHC class I transactivation: the ISRE-mediated route and a novel pathway involving CIITA

The constitutive and cytokine-induced levels of major histocompatibility (MHC) class I expression are tightly controlled at the transcriptional level. In this study, it is shown that the cis-acting regulatory element site alpha of the MHC class I promoter is essential for the IFN gamma-induced transactivation of MHC class I gene expression through the ISRE. Moreover, it was discovered that the class II transactivator (CIITA), which is itself under the control of the IFN gamma induction pathway, strongly transactivates MHC class I gene expression and exerts its activity through site alpha. Therefore, site alpha is a crucial regulatory element, mediating the classic route of IFN gamma induction via the ISRE as well as a novel route of MHC class I transactivation involving CIITA.

Identification of a cis-acting element in the class I major histocompatibility complex gene promoter responsive to activation by retroviral sequences

The infection of cells with Moloney murine leukemia virus (M-MuLV) causes an increase in specific cellular gene products, including the major histocompatibility complex (MHC) class I antigens. This upregulation occurs through a transactivation process mediated by the long terminal repeat (LTR) of M-MuLV, and we show here that the gene activation response to the LTR requires at least one specific cis element within the MHC proximal promoter region. Nested deletions of MHC class I H-2Kb gene promoter sequence were subcloned into a chloramphenicol acetyltransferase (CAT) reporter vector and then transiently introduced into BALB/c-3T3 cells expressing M-MuLV or cotransfected into BALB/c-3T3 cells with a vector containing subgenomic portions of the virus, including the LTR. CAT activity assays demonstrated that a minimal H-2Kb gene promoter (-64 to +12) contained elements sufficient for this transactivation. DNase I footprinting assays located a protein-binding site in the region of -64 to -34 bp from the transcriptional start site, and point mutation analysis confirmed the location of this cis-acting element, designated the let response element (LRE), and defined a binding motif. This LRE is distinct from binding sites for currently known transcription factors in the class I MHC gene promoter and is conserved in the promoters of human and murine MHC class I genes. Mutation of the LRE resulted in dramatic reduction in both DNA-protein binding activity in electrophoretic mobility shift assay and in the ability of the mutated promoter to respond to retroviral transactivation. Addition of the LRE to a heterologous promoter conferred the ability to respond to retroviral transactivation.

Major histocompatibility complex (MHC) class I gene expression in single neurons of the central nervous system: differential regulation by interferon (IFN)-gamma and tumor necrosis factor (TNF)-alpha

This study examined the effect of the pro-inflammatory cytokines interferon-gamma (IFN-gamma) and tumor necrosis factor-alpha (TNF-alpha) on the induction of MHC class I-related genes in functionally mature brain neurons derived from cultures of dissociated rat hippocampal tissue. Patch clamp electrophysiology combined with single cell RT-PCR demonstrated that approximately 50% of the untreated neurons contained mRNA for MHC class I heavy chains, while, with few exceptions, the cells failed to transcribe beta2-microglobulin and TAP1/TAP2 gene transcripts. No constitutive expression of MHC class I protein was detectable by confocal laser microscopy on the surface of neurons. All neurons transcribed the alpha-chain of the interferon-type II receptor (binding IFN-gamma) along with the p55 receptor for TNF-alpha. Sustained exposure to IFN-gamma resulted in transcription of beta2-microglobulin and TAP1/TAP2 genes and MHC class I surface expression in a minor part of the neurons, but did not alter their electrophysiological activities as assessed by whole cell electrophysiology. Suppression of neuronal electric activity by the sodium channel blocker tetrodotoxin drastically increased to almost 100% IFN-gamma-mediated induction of MHC class I chains, of both TAP transporters, and of membrane expression of MHC class I protein. The effect of tetrodotoxin is at least partly reverted by the neurotransmitter glutamate. In contrast to IFN-gamma, treatment with TNF-alpha did neither upregulate TAP1/TAP2 nor beta2-microglobulin gene expression, but induced MHC class I heavy chain gene transcription in all neurons. Consequently, no MHC class I molecules were detectable on the membranes of TNF-alpha-treated neurons.

Cellular responses to interferon-gamma

Interferons are cytokines that play a complex and central role in the resistance of mammalian hosts to pathogens. Type I interferon (IFN-alpha and IFN-beta) is secreted by virus-infected cells. Immune, type II, or gamma-interferon (IFN-gamma) is secreted by thymus-derived (T) cells under certain conditions of activation and by natural killer (NK) cells. Although originally defined as an agent with direct antiviral activity, the properties of IFN-gamma include regulation of several aspects of the immune response, stimulation of bactericidal activity of phagocytes, stimulation of antigen presentation through class I and class II major histocompatibility complex (MHC) molecules, orchestration of leukocyte-endothelium interactions, effects on cell proliferation and apoptosis, as well as the stimulation and repression of a variety of genes whose functional significance remains obscure. The implementation of such a variety of effects by a single cytokine is achieved by complex patterns of cell-specific gene regulation: Several IFN-gamma-regulated genes are themselves components of transcription factors. The IFN-gamma response is itself regulated by interaction with responses to other cytokines including IFN-alpha/beta, TNF-alpha, and IL-4. Over 200 genes are now known to be regulated by IFN-gamma and they are listed in a World Wide Web document that accompanies this review. However, much of the cellular response to IFN-gamma can be described in terms of a set of integrated molecular programs underlying well-defined physiological systems, for example the induction of efficient antigen processing for MHC-mediated antigen presentation, which play clearly defined roles in pathogen resistance. A promising approach to the complexity of the IFN-gamma response is to extend the analysis of the less understood IFN-gamma-regulated genes in terms of molecular programs functional in pathogen resistance.

The induction of class I and II major histocompatibility complex by allogeneic stimulation is dependent on the transcription factor interferon regulatory factor 1 (IRF-1): observations in IRF-1 knockout mice

Hosts undergoing allograft rejection show increased MHC expression locally in the graft and systemically in the normal host organs, mediated principally by IFN-gamma. The transcription factor IRF-1 has been implicated in the regulation of MHC expression by IFNs in vitro as well as in the regulation of production of some cytokines. We investigated the role of IRF-1 in vivo in the systemic regulation of MHC expression in hosts undergoing rejection of allogeneic tumors by comparing MHC induction in mice with normal IRF-1 genes (wild type or WT mice) with mice with disrupted IRF-1 genes (IRF-1 knockout or IRF-1 KO mice). We assessed MHC product expression by immunohistology and by radiolabeled antibody binding to tissue homogenates, and MHC mRNA levels by Northern blotting. By immunohistology in mice undergoing allogeneic stimulation by the ascites tumor cells, kidneys of WT mice showed massive class I and II induction, but kidneys from IRF-1 KO mice showed almost no class I and II induction. Allograft rejection also increased class I and II product levels by radiolabeled antibody binding and steady state mRNA levels, but again IRF-1 KO mice showed severe impairment of MHC induction. Similar impaired MHC class I and II induction was seen in heart and spleen, but in liver the IRF-1 mice showed impaired class I induction but unimpaired class II induction. The results indicate that IRF-1 has an essential role in both class I and class II MHC induction in allogeneic responses, but that a component of IRF-1 independent MHC induction is also demonstrable in some tissues. The reduction in MHC induction by allogeneic stimulation probably reflects decreased response to IFN-gamma and other cytokines as well as some reduction in the amount of cytokines produced.

Tumor necrosis factor alpha induces the adenovirus early 3 promoter by activation of NF-kappaB

The early transcription unit 3 (E3) of human adenoviruses encodes proteins which appear to subvert host defense mechanisms. For example, the E3/19K protein inhibits the transport of major histocompatibility complex (MHC) class I molecules to the cell surface and thereby prevents cell lysis by cytotoxic T cells. Tumor necrosis factor alpha (TNF) stimulates expression of MHC molecules on the cell surface of normal cells but not of E3(+) cells, rather, a further reduction of MHC expression is evident. This was attributed to the increased expression of E3/19K upon TNF treatment, an effect also observed for other E3 proteins. We investigated the mechanism of the TNF-mediated up-regulation of E3 products. We show that TNF stimulates expression of a luciferase reporter gene driven by the E3 promoter. Mutation of individual transcription factor binding sites within the E3 promoter reveals the importance of the NF-kappaB binding site kappa2 for TNF inducibility. Electrophoretic mobility shift assays using antibodies directed against various members of the NF-kappaB family demonstrate that stimulation by TNF is mediated by the p50-p65 NF-kappaB complex. TNF inducibility does not depend on coexpression of E1A and can be observed during infection. Interestingly, the E3 promoter seems to be the only early promoter responsive to TNF and the only adenovirus promoter containing an NF-kappaB site. The implications of this regulatory mechanism for the adenovirus life cycle and its pathogenesis are discussed.

Enhancement of immunoreactivity for NF-kappa B in the hippocampal formation and cerebral cortex of Alzheimer's disease

The distribution of nuclear factor-kappa B (NF-kappa B) was investigated immunohistochemically in the hippocampal formation, entorhinal cortex, middle temporal gyrus and visual cortex of Alzheimer's disease (AD) and control postmortem cases using a polyclonal antibody against the NF-kappa B p65 subunit. In AD cases, prominent staining for NF-kappa B was seen in neurons and their processes, neurofibrillary tangles and dystrophic neurites. In control cases, only weak staining of some neurons was obtained. The neuronal staining observed in AD was strongest in the hippocampal formation and entorhinal cortex, less in the middle temporal gyrus and least in the visual cortex. There was no difference between AD and control cases in the staining of glial cells and vascular walls. These results suggest that enhanced expression of neuronal NF-kappa B occurs in areas affected by AD pathology.