The involvement of NF-kappa B in beta-interferon gene regulation reveals its role as widely inducible mediator of signal transduction

Characterization of mechanisms involved in transrepression of NF-kappa B by activated glucocorticoid receptors

Glucocorticoids are potent immunosuppressants which work in part by inhibiting cytokine gene transcription. We show here that NF-kappa B, an important regulator of numerous cytokine genes, is functionally inhibited by the synthetic glucocorticoid dexamethasone (DEX). In transfection experiments, DEX treatment in the presence of cotransfected glucocorticoid receptor (GR) inhibits NF-kappa B p65-mediated gene expression and p65 inhibits GR activation of a glucocorticoid response element. Evidence is presented for a direct interaction between GR and the NF-kappa B subunits p65 and p50. In addition, we demonstrate that the ability of p65, p50, and c-rel subunits to bind DNA is inhibited by DEX and GR. In HeLa cells, DEX activation of endogenous GR is sufficient to block tumor necrosis factor alpha or interleukin 1 activation of NF-kappa B at the levels of both DNA binding and transcriptional activation. DEX treatment of HeLa cells also results in a significant loss of nuclear p65 and a slight increase in cytoplasmic p65. These data reveal a second mechanism by which NF-kappa B activity may be regulated by DEX. We also report that RU486 treatment of wild-type GR and DEX treatment of a transactivation mutant of GR each can significantly inhibit p65 activity. In addition, we found that the zinc finger domain of GR is necessary for the inhibition of p65. This domain is also required for GR repression of AP-1. Surprisingly, while both AP-1 and NF-kappa B can be inhibited by activated GR, synergistic NF-kappa B/AP-1 activity is largely unaffected. These data suggest that NF-kappa B, AP-1, and GR interact in a complex regulatory network to modulate gene expression and that cross-coupling of NF-kappa B and GR plays an important role in glucocorticoid-mediated repression of cytokine transcription.

HIV type 1 protease activation of NF-kappa B within T lymphoid cells

NF-kappa B is a nuclear protein of the rel oncogene family capable of enhancing transcription of several cellular genes, including IL-2 and the IL-2 receptor, and viral genes transcribed from the HIV-1 LTR. It has been reported that HIV-1 protease may cleave the NF-kappa B precursor to its active form in vitro. In this study the effects of HIV protease on NF-kappa B precursor activation were examined in Jurkat T cells by introducing a protease expression vector into the cells. Increased NF-kappa B activity was observed and this increased activity was blocked by a specific inhibitor of the viral protease. Viral transcription, as measured using LTR-CAT assays, was only slightly enhanced in the HIV-protease expressing cells, while secretion of IL-2 and expression of the IL-2 receptor were not affected. The limited activation of NF-kappa B by HIV protease appears unlikely to have a significant effect on virus expression or T cell function.

Characterization of the CD48 gene demonstrates a positive element that is specific to Epstein-Barr virus-immortalized B-cell lines and contains an essential NF-kappa B site

Epstein-Barr virus (EBV) infection of mature, resting B cells drives them to become lymphoblasts expressing high levels of cell surface molecules, such as CD48, characteristically expressed on normal activated B cells. Here, we report on the identification of an enhancer element in the CD48 gene which reproducibly confers strong transcriptional activity only in EBV-positive B-lymphoblastoid cell lines. The element is not activated upon infection of established EBV-negative B-cell lines, indicating that EBV fails to drive these cells to a fully lymphoblastoid phenotype. An NF-kappa B binding site is an essential component of the element but alone is not sufficient to account for the activity or the specificity of the element. We have detected a specific nuclear protein complex that binds to the element and show that NF-kappa B1 (p50) is a part of this complex. The EBV-encoded latent membrane protein 1 is capable of transactivating the isolated CD48 NF-kappa B site but not the intact element, suggesting that the latent membrane protein 1-driven activation of NF-kappa B/Rel must interact with other regulatory pathways to control expression of cellular genes as EBV drives resting B cells into the cell cycle.

Targeted disruption of the p50 subunit of NF-kappa B leads to multifocal defects in immune responses

NF-kappa B, a heterodimeric transcription factor composed of p50 and p65 subunits, can be activated in many cell types and is thought to regulate a wide variety of genes involved in immune function and development. Mice lacking the p50 subunit of NF-kappa B show no developmental abnormalities, but exhibit multifocal defects in immune responses involving B lymphocytes and nonspecific responses to infection. B cells do not proliferate in response to bacterial lipopolysaccharide and are defective in basal and specific antibody production. Mice lacking p50 are unable effectively to clear L. monocytogenes and are more susceptible to infection with S. pneumoniae, but are more resistant to infection with murine encephalomyocarditis virus. These data support the role of NF-kappa B as a vital transcription factor for both specific and nonspecific immune responses, but do not indicate a developmental role for the factor.

Identification of the rel family members required for virus induction of the human beta interferon gene

We have carried out experiments to determine which members of the rel family of transcription factors are involved in virus induction of the beta interferon (IFN-beta) gene. First, we examined the inducibility of artificial DNA binding sites that preferentially interact with different homo- or heterodimeric combinations of rel proteins in vitro. We found that only those sites capable of binding the p50/p65 heterodimer are virus inducible. Second, we analyzed a series of mutant rel DNA-binding sites in the context of the intact IFN-beta promoter. We found a correlation between (i) sites capable of binding both the p50/p65 heterodimer and the high-mobility-group protein HMG I(Y) and (ii) virus inducibility. Third, cotransfection of the IFN-beta gene enhancer/promoter with plasmids capable of expressing several different rel proteins revealed that only the combination of p50 and p65 efficiently activated transcription. Finally, we have used antibodies directed against different rel proteins to show that virus-inducible protein-DNA complexes assembled on the IFN-beta enhancer in vitro contain both p50 and p65. We conclude that the p50/p65 heterodimer is responsible for the NF-kappa B-dependent activation of the IFN-beta gene promoter in response to virus infection.

Inhibition of human immunodeficiency virus type 1 replication by a Tat-activated, transduced interferon gene: targeted expression to human immunodeficiency virus type 1-infected cells

We have examined the feasibility of using interferon (IFN) gene transfer as a novel approach to anti-human immunodeficiency virus type 1 (HIV-1) therapy in this study. To limit expression of a transduced HIV-1 long terminal repeat (LTR)-IFNA2 (the new approved nomenclature for IFN genes is used throughout this article) hybrid gene to the HIV-1-infected cells, HIV-1 LTR was modified. Deletion of the NF-kappa B elements of the HIV-1 LTR significantly inhibited Tat-mediated transactivation in T-cell lines, as well as in a monocyte line, U937. Replacement of the NF-kappa B elements in the HIV-1 LTR by a DNA fragment derived from the 5'-flanking region of IFN-stimulated gene 15 (ISG15), containing the IFN-stimulated response element, partially restored Tat-mediated activation of LTR in T cells as well as in monocytes. Insertion of this chimeric promoter (ISG15 LTR) upstream of the human IFNA2 gene directed high levels of IFN synthesis in Tat-expressing cells, while this promoter was not responsive to tumor necrosis factor alpha-mediated activation. ISG15-LTR-IFN hybrid gene inserted into the retrovirus vector was transduced into Jurkat and U937 cells. Selected transfected clones produced low levels of IFN A (IFNA) constitutively, and their abilities to express interleukin-2 and interleukin-2 receptor upon stimulation with phytohemagglutinin and phorbol myristate acetate were retained. Enhancement of IFNA synthesis observed upon HIV-1 infection resulted in significant inhibition of HIV-1 replication for a period of at least 30 days. Virus isolated from IFNA-producing cells was able to replicate in the U937 cells but did not replicate efficiently in U937 cells transduced with the IFNA gene. These results suggest that targeting IFN synthesis to HIV-1-infected cells is an attainable goal and that autocrine IFN synthesis results in a long-lasting and permanent suppression of HIV-1 replication.

The Ikaros gene encodes a family of functionally diverse zinc finger DNA-binding proteins

We previously described the lymphocyte-restricted Ikaros gene encoding a zinc finger DNA-binding protein as a potential regulator of lymphocyte commitment and differentiation. Here, we report the isolation of four additional Ikaros transcripts, products of alternate splicing that encode functionally diverse proteins. The Ikaros proteins contain unique combinations of zinc finger modules that dictate their overall sequence specificity and affinity. The Ik-1 and Ik-2 proteins can both bind, albeit with different affinities, to the same recognition sequences present in a number of lymphocyte-specific regulatory elements. The Ik-3 and the Ik-4 proteins interact only with a subset of these motifs. The Ik-1 and Ik-2 proteins can strongly stimulate transcription, whereas Ik-3 and Ik-4 are weak activators. Significantly, the transcription activation potential of the Ikaros proteins correlates with their subcellular localization. Upon ectopic expression of the Ikaros isoforms in nonlymphoid cells, Ik-1 and Ik-2 localize to the nucleus, whereas Ik-3 and Ik-4 are predominantly found in the cytoplasm. The Ikaros isoforms are expressed differentially in lymphocytes: Ik-1 and Ik-2 mRNAs are the predominating forms, and Ik-4 is present in significant amounts only in early T-cell progenitors, whereas Ik-3 and Ik-5 transcripts are expressed at relatively low levels throughout lymphocyte development. The ability of the Ikaros gene to generate functionally diverse proteins that may participate in distinct regulatory pathways substantiates its role as a master regulator during lymphocyte development.

The Ikaros gene encodes a family of functionally diverse zinc finger DNA-binding proteins

We previously described the lymphocyte-restricted Ikaros gene encoding a zinc finger DNA-binding protein as a potential regulator of lymphocyte commitment and differentiation. Here, we report the isolation of four additional Ikaros transcripts, products of alternate splicing that encode functionally diverse proteins. The Ikaros proteins contain unique combinations of zinc finger modules that dictate their overall sequence specificity and affinity. The Ik-1 and Ik-2 proteins can both bind, albeit with different affinities, to the same recognition sequences present in a number of lymphocyte-specific regulatory elements. The Ik-3 and the Ik-4 proteins interact only with a subset of these motifs. The Ik-1 and Ik-2 proteins can strongly stimulate transcription, whereas Ik-3 and Ik-4 are weak activators. Significantly, the transcription activation potential of the Ikaros proteins correlates with their subcellular localization. Upon ectopic expression of the Ikaros isoforms in nonlymphoid cells, Ik-1 and Ik-2 localize to the nucleus, whereas Ik-3 and Ik-4 are predominantly found in the cytoplasm. The Ikaros isoforms are expressed differentially in lymphocytes: Ik-1 and Ik-2 mRNAs are the predominating forms, and Ik-4 is present in significant amounts only in early T-cell progenitors, whereas Ik-3 and Ik-5 transcripts are expressed at relatively low levels throughout lymphocyte development. The ability of the Ikaros gene to generate functionally diverse proteins that may participate in distinct regulatory pathways substantiates its role as a master regulator during lymphocyte development.

NF-kappa B-independent activation of beta-interferon expression in mouse F9 embryonal carcinoma cells

We have examined the behaviour of the beta-interferon promoter in mouse F9 embryonal carcinoma cells. In undifferentiated cells, the beta-interferon promoter is not responsive to dsRNA or to Sendai virus. In cells stimulated to differentiate into parietal endoderm by treatment with retinoic acid, the beta-interferon promoter responds to both inducers, but only Sendai virus can activate the transcription factor NF-kappa B previously thought to be essential for beta-interferon induction. Differentiated F9 cells therefore present an unprecedented situation in which induction of the beta-interferon gene does not require NF-kappa B. In addition to these differences, induction by dsRNA, but not by Sendai virus, is significantly enhanced by a pretreatment with interferon (priming). These observations suggest that paramyxo-viruses can participate in beta-interferon induction in a manner that is distinct from a simple generator of dsRNA. Analysis of the promoter requirements for induction in differentiated F9 cells suggests that induction is brought about by a novel mechanism using the currently identified regulatory domains.

A striking similarity in the organization of the E-selectin and beta interferon gene promoters

Transcription of the endothelial leukocyte adhesion molecule 1 (E-selectin or ELAM-1) gene is induced by the inflammatory cytokines interleukin-1 beta and tumor necrosis factor alpha (TNF-alpha). In this report, we identify four positive regulatory domains (PDI to PDIV) in the E-selectin promoter that are required for maximal levels of TNF-alpha induction in endothelial cells. In vitro DNA binding studies reveal that two of the domains contain novel adjacent binding sites for the transcription factor NF-kappa B (PDIII and PDIV), a third corresponds to a recently described CRE/ATF site (PDII), and a fourth is a consensus NF-kappa B site (PDI). Mutations that decrease the binding of NF-kappa B to any one of the NF-kappa B binding sites in vitro abolished cytokine-induced E-selectin gene expression in vivo. Previous studies demonstrated a similar correlation between ATF binding to PDII and E-selectin gene expression. Here we show that the high-mobility-group protein I(Y) [HMG I(Y)] also binds specifically to the E-selectin promoter and thereby enhances the binding of both ATF-2 and NF-kappa B to the E-selectin promoter in vitro. Moreover, mutations that interfere with HMG I(Y) binding decrease the level of cytokine-induced E-selectin expression. The organization of the TNF-alpha-inducible element of the E-selectin promoter is remarkably similar to that of the virus-inducible promoter of the human beta interferon gene in that both promoters require NF-kappa B, ATF-2, and HMG I(Y). We propose that HMG I(Y) functions as a key architectural component in the assembly of inducible transcription activation complexes on both promoters.

The cellular transcription factor USF cooperates with varicella-zoster virus immediate-early protein 62 to symmetrically activate a bidirectional viral promoter

The mechanisms governing the function of cellular USF and herpesvirus immediate-early transcription factors are subjects of considerable interest. In this regard, we identified a novel form of coordinate gene regulation involving a cooperative interplay between cellular USF and the varicella-zoster virus immediate-early protein 62 (IE 62). A single USF-binding site defines the potential level of IE 62-dependent activation of a bidirectional viral early promoter of the DNA polymerase and major DNA-binding protein genes. We also report a dominant negative USF-2 mutant lacking the DNA-binding domain that permits the delineation of the biological role of both USF-1 and USF-2 in this activation process. The symmetrical stimulation of the bidirectional viral promoter by IE 62 is achieved at concentrations of USF-1 (43 kDa) or USF-2 (44 kDa) already existing in cells. Our observations support the notion that cellular USF can intervene in and possibly target promoters for activation by a herpesvirus immediate-early protein.

Inhibition by N-acetyl-L-cysteine of interleukin-6 mRNA induction and activation of NF kappa B by tumor necrosis factor alpha in a mouse fibroblastic cell line, Balb/3T3

Redox-based modulation plays a role in transcriptional control of gene expression. In the present study, we investigated the possible role of reactive oxygen species in the induction of interleukin-6 (IL-6) mRNA and in increases in NF kappa B binding activity by tumor necrosis factor (TNF) alpha using a mouse fibroblastic cell line, Balb/3T3. Expression of IL-6 mRNA is known to be dependent upon NF kappa B that binds to the 5'-flanking region of the IL-6 gene. We found that: (i) TNF alpha increased IL-6 mRNA levels and this increase was inhibited by N-acetyl-L-cysteine (NAC), a scavenger of reactive oxygen species. (ii) NF kappa B binding activity in this cell line was also increased by TNF alpha, and the increase was inhibited in the presence of NAC. (iii) The treatment of cells with low doses of hydrogen peroxide increased the NF kappa B binding activity. (iv) Expression of a reporter gene in which the chloramphenicol acetyltransferase (CAT) gene was under the control of NF kappa B binding sites was induced by hydrogen peroxide. These results suggest that the induction of IL-6 mRNA is regulated by a mechanism involving reactive oxygen species and that NF kappa B, whose activity is sensitive to the cellular redox state, plays an important role in this induction in a fibroblastic cell line, Balb/3T3, stimulated with TNF alpha.

A striking similarity in the organization of the E-selectin and beta interferon gene promoters

Transcription of the endothelial leukocyte adhesion molecule 1 (E-selectin or ELAM-1) gene is induced by the inflammatory cytokines interleukin-1 beta and tumor necrosis factor alpha (TNF-alpha). In this report, we identify four positive regulatory domains (PDI to PDIV) in the E-selectin promoter that are required for maximal levels of TNF-alpha induction in endothelial cells. In vitro DNA binding studies reveal that two of the domains contain novel adjacent binding sites for the transcription factor NF-kappa B (PDIII and PDIV), a third corresponds to a recently described CRE/ATF site (PDII), and a fourth is a consensus NF-kappa B site (PDI). Mutations that decrease the binding of NF-kappa B to any one of the NF-kappa B binding sites in vitro abolished cytokine-induced E-selectin gene expression in vivo. Previous studies demonstrated a similar correlation between ATF binding to PDII and E-selectin gene expression. Here we show that the high-mobility-group protein I(Y) [HMG I(Y)] also binds specifically to the E-selectin promoter and thereby enhances the binding of both ATF-2 and NF-kappa B to the E-selectin promoter in vitro. Moreover, mutations that interfere with HMG I(Y) binding decrease the level of cytokine-induced E-selectin expression. The organization of the TNF-alpha-inducible element of the E-selectin promoter is remarkably similar to that of the virus-inducible promoter of the human beta interferon gene in that both promoters require NF-kappa B, ATF-2, and HMG I(Y). We propose that HMG I(Y) functions as a key architectural component in the assembly of inducible transcription activation complexes on both promoters.

The cellular transcription factor USF cooperates with varicella-zoster virus immediate-early protein 62 to symmetrically activate a bidirectional viral promoter

The mechanisms governing the function of cellular USF and herpesvirus immediate-early transcription factors are subjects of considerable interest. In this regard, we identified a novel form of coordinate gene regulation involving a cooperative interplay between cellular USF and the varicella-zoster virus immediate-early protein 62 (IE 62). A single USF-binding site defines the potential level of IE 62-dependent activation of a bidirectional viral early promoter of the DNA polymerase and major DNA-binding protein genes. We also report a dominant negative USF-2 mutant lacking the DNA-binding domain that permits the delineation of the biological role of both USF-1 and USF-2 in this activation process. The symmetrical stimulation of the bidirectional viral promoter by IE 62 is achieved at concentrations of USF-1 (43 kDa) or USF-2 (44 kDa) already existing in cells. Our observations support the notion that cellular USF can intervene in and possibly target promoters for activation by a herpesvirus immediate-early protein.

Stimulation of HIV type 1 gene expression and induction of NF-kappa B (p50/p65)-binding activity in tumor necrosis factor alpha-treated human fetal glial cells

In vitro, HIV-1 infection of human fetal glial cells initiates a noncytopathic, productive infection that results in a long-term persistence during which the viral genome remains latent. The cytokines tumor necrosis factor alpha (TNF-alpha) and interleukin 1 beta (IL-1 beta) reactivate HIV-1 gene expression in these cells, leading to production of infectious virus. Here we show that treatment of human fetal glial cells with TNF-alpha and IL-1 beta increase expression of the reporter gene chloramphenicol acetyltransferase (CAT) when placed under the control of the HIV-1 5' LTR. We also show that treatment of human fetal glial cells with TNF-alpha leads to increased binding of the nuclear transcription factor NF-kappa B (p50/p65) to a consensus kappa B-binding site present in the HIV-1 5'LTR. Our results suggest that TNF-alpha stimulation of HIV-1 gene expression in primary cultures of human fetal glial cells is mediated by an increase in binding of NF-kappa B (p50/p65) to the HIV-1 LTR. This is the first report documenting NF-kappa B-binding activity in primary cultures of human fetal glial cells.

Lipofection of synthetic oligodeoxyribonucleotide having a palindromic sequence of AACGTT to murine splenocytes enhances interferon production and natural killer activity

A synthetic 22-mer oligodeoxyribonucleotide having an AACGTT palindrome, AAC-22, induced interferon (IFN) production and augmented the natural killer (NK) activity in murine splenocytes, whereas its analogue, ACC-22, having an ACCGGT palindrome, did not. The binding of AAC-22 to splenocytes was not different from that of ACC-22. Lipofection of AAC-22 to splenocytes remarkably enhanced IFN production and NK cell activity, whereas that of ACC-22 caused little enhancement. These results strongly suggest that the prerequisite for IFN production is not the binding of AAC-22 to the cell surface receptors, but its penetration into the spleen cells.

Signal transduction mechanisms in mesenchymal cells

Mesenchymal cells are continually stimulated by a wide spectrum of biological mediators. These mediators bind to receptors on the cell surface and initiate a cascade of signaling events. The initial signal transduction pathways known to be stimulated in mesenchymal cells included phospholipase C, phospholipase D, phospholipase A2, adenylate cyclase, receptor tyrosine kinases, and receptor serine/threonine kinases. These pathways are reviewed and specific applications for therapeutic intervention in wound healing and regenerative therapy in the periodontium are discussed.

Blockage of NF-kappa B signaling by selective ablation of an mRNA target by 2-5A antisense chimeras

Activation of 2-5A-dependent ribonuclease by 5'-phosphorylated, 2',5'-linked oligoadenylates, known as 2-5A, is one pathway of interferon action. Unaided uptake into HeLa cells of 2-5A linked to an antisense oligonucleotide resulted in the selective ablation of messenger RNA for the double-stranded RNA (dsRNA)-dependent protein kinase PKR. Similarly, purified, recombinant human 2-5A-dependent ribonuclease was induced to selectively cleave PKR messenger RNA. Cells depleted of PKR activity were unresponsive to activation of nuclear factor-kappa B (NF-kappa B) by the dsRNA poly(I):poly(C), which provides direct evidence that PKR is a transducer for the dsRNA signaling of NF-kappa B.

Viral induction of the human beta interferon promoter: modulation of transcription by NF-kappa B/rel proteins and interferon regulatory factors

Multiple regulatory domains within the -100 region of the beta interferon (IFN-beta) promoter control the inducible response of the IFN gene to virus infection. In this study, we demonstrate that the formation of NF-kappa B-specific complexes on the positive regulatory domain II (PRDII) precedes the onset of detectable IFN-beta transcription in Sendai virus-infected cells. By using NF-kappa B subunit-specific antibodies, a temporal shift in the composition of NF-kappa B subunits in association with the PRDII domain is detected as a function of time after virus infection. Furthermore, a virus-induced degradation of I kappa B alpha (MAD3) protein is observed between 2 and 8 h after infection; at later times, de novo synthesis of I kappa B alpha restores I kappa B alpha to levels found in uninduced cells and correlates with the down regulation of IFN-beta transcription. In cotransfection experiments using various NF-kappa B subunit expression plasmids and two copies of PRDII/NF-kappa B linked to a chloramphenicol acetyltransferase reporter gene, we demonstrate that expression of p65, c-Rel, or p50 or combinations of p50-p65 and p65-c-Rel differentially stimulated PRDII-dependent transcription. Coexpression of I kappa B alpha completely abrogated p65-, c-Rel-, or p65-p50-induced gene activity. When the entire IFN-beta promoter (-281 to +19) was used in coexpression studies, synergistic stimulation of IFN-beta promoter activity was obtained when NF-kappa B subunits were coexpressed together with the IFN regulatory factor 1 (IRF-1) transcription factor. Overexpression of either I kappa B or the IRF-2 repressor was able to abrogate inducibility of the IFN-beta promoter. Thus, multiple regulatory events--including differential activation of DNA-binding NF-kappa B heterodimers, degradation of I kappa B alpha, synergistic interaction between IRF-1 and NF-kappa B, and decreased repression by I kappa B and IRF-2--are all required for the transcriptional activation of the IFN-beta promoter.

Double-stranded RNA-dependent protein kinase activates transcription factor NF-kappa B by phosphorylating I kappa B

The induction of interferon (IFN) genes by viruses or double-stranded RNA (dsRNA) requires the assembly of a complex set of transcription factors on responsive DNA elements of IFN gene promoters. One of the factors necessary for regulating IFN-beta gene transcription is nuclear factor NF-kappa B, the activation of which is triggered by dsRNA. It has previously been suggested that the dsRNA-activated p68 protein kinase (PKR) may act as an inducer-receptor, transducing the signal from dsRNA to NF-kappa B through phosphorylation of the inhibitor I kappa B. We present direct evidence that PKR can phosphorylate I kappa B-alpha (MAD-3) and activate NF-kappa B DNA binding activity in vitro. We further show that dsRNA induces an unusual phosphorylated form of I kappa B-alpha. The expression of a transdominant mutant PKR is able to perturb the dsRNA-mediated signaling pathway in vivo, suggesting a role for this kinase in IFN-beta gene induction.

Apo CIII gene transcription is regulated by a cytokine inducible NF-kappa B element

Overproduction of Apo CIII causes elevated plasma triglyceride levels in transgenic animals and is associated with hypertriglyceridemia in humans. The regulation of apo CIII production is likely to play an important role in controlling plasma triglyceride levels. As an initial step in determining the role of transcriptional regulation in the production of apo CIII and in triglyceride metabolism, we have begun to characterize the activity of specific transcriptional regulatory elements in the CIII promoter. In the current study, we have identified and characterized an NF-kappa B regulatory element located 150 nucleotides upstream from the transcriptional start site of the apo CIII gene. Purified NF-kappa B, as well as an NF-kappa B protein in HepG2 cell nuclear extracts, bound specifically to this sequence element. The hepatic protein was induced by phorbol ester (PMA), and reacted with antibodies to the p50 and p65 subunits of NF-kappa B. The NF-kappa B element conferred PMA and IL1-beta inducible transcriptional activity to a heterologous promoter/reporter construct when transfected into HepG2 cells. Analysis of the full length CIII promoter demonstrated that the inducible activity of the NF-kappa B element was suppressed by sequences in the apo CIII enhancer element located approximately 500 nucleotides upstream of the NF-kappa B binding site. A deletion removing the enhancer restored the PMA inducible activity of the NF-kappa B binding site. These results indicate that apo CIII gene expression is regulated by NF-kappa B, and suggest that apo CIII production may be modulated by cellular signals, like inflammatory cytokines, that activate NF-kB.

Constitutive production of alpha and beta interferons in mutant human cell lines

Alpha and beta interferons control expression of a selectable marker in the human hypoxanthine phosphoribosyltransferase-negative cell line 2fTGH, in which transcription of gpt is regulated by the upstream region of an interferon-responsive human gene. Selection of mutagenized 2fTGH cells in hypoxanthine-aminopterin-thymidine medium yielded mutants in one recessive (C1) and two dominant (C2 and C3) complementation groups. The mutants constitutively expressed low levels of beta interferon (C1), alpha interferon (C2), or both (C3).

Positive and negative regulation of IL-2 gene expression: role of multiple regulatory sites

Interleukin 2 (IL-2) is an important lymphokine required in the process of T cell activation, proliferation, clonal expansion and differentiation. The IL-2 gene displays both T cell specific and inducible expression: it is only expressed in CD4+ T cells after antigenic or mitogenic stimulation. Several cis-acting regulatory sites are required for induction of the IL-2 gene after stimulation. In this study, we have analysed the function of these cis-acting regulatory sites in the context of the native IL-2 enhancer and promoter sequence. The results of this study suggest that the NFAT (-276 to -261), the distal octamer (-256 to -248) and the proximal octamer (-75 to -66) sites not only act as enhancers of IL-2 gene transcription in the presence of cellular stimulation, but also have a silencing effect on IL-2 gene expression in resting cells. Two other sites display disparate effects on IL-2 gene expression in different T leukemia cell lines: the distal purine box (-291 to -277) and the proximal purine box sites (-145 to -128). Finally, the AP-1 (-186 to -176) and the kappa B sites (-206 to -195) respond to different cellular activation in EL4 cells. The AP-1 site mediated the response to PMA stimulation while the kappa B site responded to IL-1 stimulation. These data suggest that the regulation of IL-2 gene expression is a complex process and multiple cis-acting regulatory sites interact to exert different effects in T cells representative of alternative stages of differentiation.

Structure and regulation of the human interferon regulatory factor 1 (IRF-1) and IRF-2 genes: implications for a gene network in the interferon system

Interferon regulatory factor 1 (IRF-1) and IRF-2 are structurally similar DNA-binding factors which were originally identified as regulators of the type I interferon (IFN) system; the former functions as a transcriptional activator, and the latter represses IRF-1 function by competing for the same cis elements. More recent studies have revealed new roles of the two factors in the regulation of cell growth; IRF-1 and IRF-2 manifest antioncogenic and oncogenic activities, respectively. In this study, we determined the structures and chromosomal locations of the human IRF-1 and IRF-2 genes and further characterized the promoters of the respective genes. Comparison of exon-intron organization of the two genes revealed a common evolutionary structure, notably within the exons encoding the N-terminal portions of the two factors. We confirmed the chromosomal mapping of the human IRF-1 gene to 5q31.1 and newly assigned the IRF-2 gene to 4q35.1, using fluorescence in situ hybridization. The 5' regulatory regions of both genes contain highly GC-rich sequences and consensus binding sequences for several known transcription factors, including NF-kappa B. Interestingly, one IRF binding site was found within the IRF-2 promoter, and expression of the IRF-2 gene was affected by both transient and stable IRF-1 expression. In addition, one potential IFN-gamma-activated sequence was found within the IRF-1 promoter. Thus, these results may shed light on the complex gene network involved in regulation of the IFN system.

An upstream protein interacts with a distinct protein that binds to the cap site of the human interleukin 1 beta gene

Interleukin 1 beta (IL-1 beta) is a proinflammatory cytokine that exhibits a wide variety of biological activities. Genomic sequences that mediate the induction of human IL-1 beta gene transcription by lipopolysaccharide and phorbol esters are located more than 2,700 bp upstream of the transcriptional start site (cap site). These upstream elements require additional cap site-proximal (CSP) sequences which are necessary for basal transcription of the human IL-1 beta gene. In addition, these CSP sequences have been shown to mediate both cell type-specific expression of this gene, and trans-activation by some viral proteins. In this study, we report the identification of a novel nuclear protein, termed NF beta C, that binds to a DNA sequence which spans the cap site of the human IL-1 beta gene (positions -12 to +8). We have also identified a second region (positions -305 to -280) containing a putative NF-kappa B binding site. We show here that this region can bind three distinct nuclear proteins. One protein is similar or identical to NF-kappa B, a second protein (termed NF beta B) binds a distinct sequence that substantially overlaps the 5' half of the NF kappa B binding sequence, and a third protein (termed NF beta D) binds a distinct sequence that substantially overlaps the 3' half of the NF kappa B binding sequence. Unlike NF kappa B, NF1 beta B and NF beta D are present in nuclear extracts prepared from unstimulated monocytic cells. Although the NF beta D and NF beta C binding sequences share no significant similarity, each sequence can specifically compete for the binding of either protein to DNA, whereas oligonucleotides containing only the NF kappa B or NF beta B motifs do not compete for the binding of NF beta C or NF beta D. This suggests that NF beta C and NF beta D can specifically interact in vitro, possibly through a common subunit.

Structure and regulation of the human interferon regulatory factor 1 (IRF-1) and IRF-2 genes: implications for a gene network in the interferon system

Interferon regulatory factor 1 (IRF-1) and IRF-2 are structurally similar DNA-binding factors which were originally identified as regulators of the type I interferon (IFN) system; the former functions as a transcriptional activator, and the latter represses IRF-1 function by competing for the same cis elements. More recent studies have revealed new roles of the two factors in the regulation of cell growth; IRF-1 and IRF-2 manifest antioncogenic and oncogenic activities, respectively. In this study, we determined the structures and chromosomal locations of the human IRF-1 and IRF-2 genes and further characterized the promoters of the respective genes. Comparison of exon-intron organization of the two genes revealed a common evolutionary structure, notably within the exons encoding the N-terminal portions of the two factors. We confirmed the chromosomal mapping of the human IRF-1 gene to 5q31.1 and newly assigned the IRF-2 gene to 4q35.1, using fluorescence in situ hybridization. The 5' regulatory regions of both genes contain highly GC-rich sequences and consensus binding sequences for several known transcription factors, including NF-kappa B. Interestingly, one IRF binding site was found within the IRF-2 promoter, and expression of the IRF-2 gene was affected by both transient and stable IRF-1 expression. In addition, one potential IFN-gamma-activated sequence was found within the IRF-1 promoter. Thus, these results may shed light on the complex gene network involved in regulation of the IFN system.

Proteins that interact with PKR

The in vitro activities of recombinant gene products of the vaccinia virus E3L and K3L genes have been compared. These proteins are both potent inhibitors of the dsRNA activated protein kinase (PKR) as assayed in cell-free translation systems or with purified PKR. The two gene products function at similar molar concentrations. Both proteins are expressed early in vaccinia virus infection suggesting that vaccinia virus maintains redundant mechanisms for the down regulation of PKR. The K3L gene product can be shown to be associated with PKR in vaccinia virus infected cells. The activities of the vaccinia virus PKR inhibitors are compared with other viral protein inhibitors of PKR. A variety of cellular proteins have also been identified by their ability to inhibit PKR activity or to prevent PKR activation. These cellular PKR interacting proteins have been uncovered from the studies of viral strategies to prevent PKR activation, as well as from studies looking at the effects of growth control, growth factors or oncogene expression on PKR activity. A picture emerges of PKR fulfilling a complex regulatory role in cell function with the regulation of its activity as part of a complex cascade interfacing with the signal transduction/cell cycle control machinery.

Constitutive expression of TNF-alpha and -beta genes in mouse embryo: roles of cytokines as regulator and effector on development

1. Using the RT/PCR method, we examined mRNA expression of several inflammatory factors in mouse embryos during mid-late embryonal development. mRNAs of tumor necrosis factor (TNF)-alpha, TNF-beta, their receptors (TNF-RI, TNF-RII), transforming growth factor (TGF)-beta, were expressed constitutively in most of the embryonic tissues. 2. While mRNAs of other factors, interleukin (IL)-1 alpha, IL-1 beta, IL-3, IL-6, granurocyte-colony stimulating factor (G-CSF), leukaemia inhibitory factor (LIF), and interferon (IFN)-gamma were only limitedly expressed. 3. The mRNAs of several complement components (C2, C3, C4, C5) and receptors (CR1, CR2) were also detected. Among them, the expression of C3 and CR1 were prominent. These results strongly support our idea that inflammation-like system play an important role to regulate embryogenesis.

Induction of type I interferon genes and interferon-inducible genes in embryonal stem cells devoid of interferon regulatory factor 1

Overexpression of interferon regulatory factor 1 (IRF-1) can induce expression of the interferon (IFN) beta gene, at least in certain cells. A role of IRF-1 in the activation of IFN-alpha genes has also been claimed. We have generated embryonal stem cells in which both IRF-1 alleles were disrupted. In undifferentiated embryonal stem cells, virus-induced levels of IFN-alpha RNA were similar for wild-type and IRF-1%, and there was little induction of IFN-beta RNA in either cell type. In 8-day differentiated cells, the levels of virus-induced IFN-beta RNA, but not of IFN-alpha RNA, were about 10-fold higher than in undifferentiated cells and only slightly higher in wild-type than in IRF-1% cells. Thus, although IRF-1 at high levels may elicit or augment induction of IFN genes under certain circumstances, it is not essential for IFN gene induction by virus. Lack of IRF-1 had no effect on the IFN-induced expression levels of the IFN-inducible genes tested; however, there was little or no constitutive expression of (2'-5')oligoadenylate synthetase in IRF-1% embryonal stem cells, in contrast to wild-type cells.

The role of tumor necrosis factor in viral disease

Tumor Necrosis Factor (TNF) is one of the many cytokines that comprise a complex intertwined network of biological response modifiers that takes on extreme significance as the host response to infectious diseases. Soluble factors such as Interleukin-2 and Interferon-gamma released by T cells and Interleukin-1, Interleukin-6 and TNF released by monocytes have been shown to play key roles in proliferation, activation and differentiation of immune cells. It has also become evident that development of treatment modalities for infectious diseases is complicated by the complexity of this cytokine network. In the last decade numerous reports have presented data, often conflicting, which clearly demonstrate a role for TNF in the response to infections caused by viruses. This review summarizes this rapidly growing volume of data, discussing consistencies and discrepancies as appropriate. By better understanding the role of TNF in the host immune response, it may be possible to modulate this complex network for the benefit of the host in its battle against viral infection.

NF-kappa B p100 (Lyt-10) is a component of H2TF1 and can function as an I kappa B-like molecule

NF-kappa B is an important transcription factor regulating expression of genes involved in immune function, inflammation, and cellular growth control. NF-kappa B activity is induced by numerous stimuli, such as phorbol esters, B- and T-cell mitogens, the cytokines tumor necrosis factor and interleukin-1, and serum growth factors. The standard model for the induction of NF-kappa B activity involves the release of the transcription factor from a cytoplasmic inhibitor termed I kappa B, allowing translocation of NF-kappa B to the nucleus. I kappa B contains multiple copies of the so-called ankyrin repeat, which are apparently necessary for its function. Subunits comprising NF-kappa B and related binding activities are members of the Rel multigene family. Two such subunits, p50 and p52 (also called p50B), are proteolytically processed from precursors of 105 kDa (also called p105 and NFKB1) and 100 kDa (also called p100, NFKB2, and Lyt-10), respectively. Both contain N-terminal Rel-homologous domains as well as multiple copies of C-terminal ankyrin repeats. We show here that NF-kappa B p100 is a component of the previously identified DNA-binding activity H2TF1. In addition, we show that p100 is localized in the cytoplasm in HeLa cells, where it is associated with c-Rel, p50, or p65 (RelA). In transient-transfection assays, p100 represses the ability of NF-kappa B p65 to activate a kappa B-containing reporter construct. Transfection of p100 also results in a loss of nuclear p65 DNA binding to a kappa B probe, as measured by an electrophoretic mobility shift assay, and a loss of nuclear p65 immunoreactivity, as measured by immunoblotting. This loss of nuclear p65 is paralleled by a gain of p65 DNA-binding activity and immunoreactivity in the cytoplasm. We interpret these data as demonstrating that p100 functions as an I kappa B-like molecule to sequester Rel family members in the cytoplasm. Proteolytic processing of p100 to the activator p52 is predicted to generate several new forms of Rel family heterodimers and therefore represents a form of regulation of NF-kappa B activity distinct from the classic I kappa B pathway.

Inhibition of phorbol ester-induced cellular adhesion by competitive binding of NF-kappa B in vivo

Adhesive interactions between cells are essential for the organization and function of differentiated tissues and organs and are mediated by inducible cell surface glycoproteins. In normal tissues, cell adhesion molecules contribute to immune regulation, inflammation, and embryogenesis. Additionally, they play an important role in a variety of pathogenic processes. Cell adhesion molecule expression can be induced by stimuli known to activate NF-kappa B, a ubiquitous transcription factor found in a variety of cell types. To investigate the role of NF-kappa B in cell adhesion molecule expression, we treated HL-60 cells with a double-stranded oligonucleotide which specifically inhibits NF-kappa B-mediated transcription. This treatment resulted in the inhibition of phorbol 12-myristate 13-acetate (PMA)-induced cellular adhesion, morphological changes, and the expression of leukocyte integrin CD11b. In a similar fashion, expression of intercellular adhesion molecule 1 on human endothelial cells induced by PMA was specifically inhibited by the NF-kappa B antagonist. We suggest that NF-kappa B activation is a necessary event for the PMA-induced differentiation of HL-60 cells and the expression of certain activation is a necessary event for the PMA-induced differentiation of HL-60 cells and the expression of certain adhesion molecules. Furthermore, the inhibition of transcription factor functions by this generally applicable mechanism can be used to define their role in cellular differentiation and function.

NF-kappa B p100 (Lyt-10) is a component of H2TF1 and can function as an I kappa B-like molecule

NF-kappa B is an important transcription factor regulating expression of genes involved in immune function, inflammation, and cellular growth control. NF-kappa B activity is induced by numerous stimuli, such as phorbol esters, B- and T-cell mitogens, the cytokines tumor necrosis factor and interleukin-1, and serum growth factors. The standard model for the induction of NF-kappa B activity involves the release of the transcription factor from a cytoplasmic inhibitor termed I kappa B, allowing translocation of NF-kappa B to the nucleus. I kappa B contains multiple copies of the so-called ankyrin repeat, which are apparently necessary for its function. Subunits comprising NF-kappa B and related binding activities are members of the Rel multigene family. Two such subunits, p50 and p52 (also called p50B), are proteolytically processed from precursors of 105 kDa (also called p105 and NFKB1) and 100 kDa (also called p100, NFKB2, and Lyt-10), respectively. Both contain N-terminal Rel-homologous domains as well as multiple copies of C-terminal ankyrin repeats. We show here that NF-kappa B p100 is a component of the previously identified DNA-binding activity H2TF1. In addition, we show that p100 is localized in the cytoplasm in HeLa cells, where it is associated with c-Rel, p50, or p65 (RelA). In transient-transfection assays, p100 represses the ability of NF-kappa B p65 to activate a kappa B-containing reporter construct. Transfection of p100 also results in a loss of nuclear p65 DNA binding to a kappa B probe, as measured by an electrophoretic mobility shift assay, and a loss of nuclear p65 immunoreactivity, as measured by immunoblotting. This loss of nuclear p65 is paralleled by a gain of p65 DNA-binding activity and immunoreactivity in the cytoplasm. We interpret these data as demonstrating that p100 functions as an I kappa B-like molecule to sequester Rel family members in the cytoplasm. Proteolytic processing of p100 to the activator p52 is predicted to generate several new forms of Rel family heterodimers and therefore represents a form of regulation of NF-kappa B activity distinct from the classic I kappa B pathway.

Tumor necrosis factor alpha mediates a T cell receptor-independent induction of the gene regulatory factor NF-kappa B in T lymphocytes

We investigated the molecular basis of the ability of DCEK experimental antigen-presenting cells (APCs) to induce the nuclear form of the transcription factor NF-kappa B in T lymphocytes without engagement of the T cell receptor. We found that NF-kappa B induction did not require contact between the APCs and T lymphocytes and could be achieved by medium conditioned by the APCs. The APCs were found to express low levels of mRNA for TNF alpha. The addition of antibody against TNF alpha blocked the ability of APCs to induce NF-kappa B. These observations were extended by the finding that NF-kappa B was also induced in T lymphocytes separated by a membrane from a mixture of T lymphocytes, splenic APCs and antigen by a TNF alpha-dependent mechanism. Together, these findings suggest that induction of NF-kappa B in antigenically stimulated or 'bystander' T cells may take place through stimulation by TNF alpha as well as in response to T cell receptor occupancy.

Inhibition of phorbol ester-induced cellular adhesion by competitive binding of NF-kappa B in vivo

Adhesive interactions between cells are essential for the organization and function of differentiated tissues and organs and are mediated by inducible cell surface glycoproteins. In normal tissues, cell adhesion molecules contribute to immune regulation, inflammation, and embryogenesis. Additionally, they play an important role in a variety of pathogenic processes. Cell adhesion molecule expression can be induced by stimuli known to activate NF-kappa B, a ubiquitous transcription factor found in a variety of cell types. To investigate the role of NF-kappa B in cell adhesion molecule expression, we treated HL-60 cells with a double-stranded oligonucleotide which specifically inhibits NF-kappa B-mediated transcription. This treatment resulted in the inhibition of phorbol 12-myristate 13-acetate (PMA)-induced cellular adhesion, morphological changes, and the expression of leukocyte integrin CD11b. In a similar fashion, expression of intercellular adhesion molecule 1 on human endothelial cells induced by PMA was specifically inhibited by the NF-kappa B antagonist. We suggest that NF-kappa B activation is a necessary event for the PMA-induced differentiation of HL-60 cells and the expression of certain activation is a necessary event for the PMA-induced differentiation of HL-60 cells and the expression of certain adhesion molecules. Furthermore, the inhibition of transcription factor functions by this generally applicable mechanism can be used to define their role in cellular differentiation and function.

Mechanisms of transcriptional synergism between distinct virus-inducible enhancer elements

The high mobility group protein HMG I(Y) and the transcription factor NF-kappa B are required for the activity of positive regulatory domain II (PRDII), a virus-inducible regulatory element of the human interferon-beta gene promoter. In this paper we provide evidence that HMG I(Y) is also required for the activity of PRDIV, a regulatory element that synergizes with PRDII. In this case, HMG I(Y) stimulates binding of activating transcription factor 2 (ATF-2) and the assembly of inducible complexes containing ATF-2 and c-Jun. Remarkably, HMG I(Y) also specifically interacts with the leucine zipper/basic region of ATF-2, and ATF-2 in turn interacts with NF-kappa B. We therefore propose that the HMG I(Y) plays a critical structural role in establishing transcriptional synergy between PRDII and PRDIV by promoting the activities and/or binding of NF-kappa B and ATF-2 and by facilitating their interaction.