The p50 subunit of NF-kappa B associates with the NF-IL6 transcription factor

Activation of the TSG-6 gene by NF-IL6 requires two adjacent NF-IL6 binding sites

Tumor necrosis factor (TNF)-stimulated gene 6 (TSG-6) encodes a protein expressed during inflammation. We have previously shown that transcription factors of the NF-IL6 and AP-1 families cooperatively modulate activation of the TSG-6 gene by TNF or interleukin 1 (IL-1) through a promoter region that contains an NF-IL6 site (-106 to -114) and an AP-1 element (-126 to -119). In this study we report the identification of an additional NF-IL6 site (NF-IL6*) located at positions -92 to -83. Footprinting and electrophoretic mobility shift assay suggested that NF-IL6 binds with higher affinity to the newly identified NF-IL6* site than to the earlier identified promoter-distal NF-IL6 site and that the two sites cooperate in binding NF-IL6. TNF and IL-1 stimulate specific binding of nuclear proteins to the NF-IL6* site more efficiently than to the promoter-distal NF-IL6 site. Moreover, a mutation in the NF-IL6* site abolished transactivation of the TSG-6 promoter by NF-IL6 despite the presence of the intact promoter-distal NF-IL6 site. A mutation in the promoter-distal NF-IL6 site also greatly decreased activation of the TSG-6 promoter by NF-IL6. We conclude that the two NF-IL6 sites are functionally interdependent in the activation of the TSG-6 gene.

Structure of the NF-kappa B transcription factor: a holistic interaction with DNA

An unexpected mode of binding to DNA is revealed in two crystal structures of a transcription factor that is essential for many signalling pathways in eukaryotic cells.

Transcriptional regulation of the intercellular adhesion molecule-1 gene by inflammatory cytokines in human endothelial cells. Essential roles of a variant NF-kappa B site and p65 homodimers

Intercellular adhesion molecule-1 (ICAM-1) is greatly up-regulated on endothelial cells at sites of inflammation and is involved in leukocyte attachment and extravasation. Previously, we had shown that the ICAM-1 gene expression in human umbilical vein endothelial cells (HUVECs) was transcriptionally regulated by tumor necrosis factor-alpha (TNF-alpha) (Wertheimer, S. J., Myers, C. L., Wallace, R. W., and Parks, T. P. (1992) J. Biol. Chem. 267, 12030-12035). In the present investigation, TNF-alpha-induced transcription was found to be initiated exclusively at two sites, 40 and 41 base pairs upstream of the translation start site. Deletion analysis of the 5' regulatory region of the ICAM-1 gene revealed a 92-base pair sequence which was both necessary and sufficient to confer TNF-alpha responsiveness to a linked luciferase reporter gene in transient transfection assays. This TNF-alpha-responsive region contained a variant NF-kappa B site at -187 to -178, which when mutated, completely abolished ICAM-1 promoter activation by TNF-alpha, interleukin-1 beta, and lipopolysaccharide. Two inducible nuclear protein complexes bound to the ICAM-1 kappa B and were identified as the NF-kappa B p65 homodimer and p65/p50 heterodimer. Overexpression of p65, but not p50, transactivated the ICAM-1 promoter in a kappa B site-dependent manner in HUVECs. In addition, p65-mediated transactivation was suppressed by co-expression of p50. Our results suggest that cytokine activation of the ICAM-1 promoter in HUVECs may critically depend on p65 homodimers binding to a variant kappa B site.

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.

Specification of C/EBP function during Drosophila development by the bZIP basic region

The biologically relevant interactions of a transcription factor are those that are important for function in the organism. Here, a transgenic rescue assay was used to determine which molecular functions of Drosophila CCAAT/enhancer binding protein (C/EBP), a basic region-leucine zipper transcription factor, are required for it to fulfill its essential role during development. Chimeric proteins that contain the Drosophila C/EBP (DmC/EBP) basic region, a heterologous zipper, and a heterologous activation domain could functionally substitute for DmC/EBP. Mammalian C/EBPs were also functional in Drosophila. In contrast, 9 of 25 single amino acid substitutions in the basic region disrupted biological function. Thus, the conserved basic region specifies DmC/EBP activity in the organism.

A labile transcriptional repressor modulates endotoxin tolerance

Tolerance to bacterial lipopolysaccharide (LPS, endotoxin) is an adaptive cellular process whereby exposure to endotoxin induces a subsequent hyporesponsive state characterized by decreased levels of LPS-induced cytokine mRNA and protein. We demonstrate, in a human promonocytic cell line, THP-1, that endotoxin tolerance is manifested by decreased LPS-induced interleukin 1 beta (IL-1 beta) transcription. Inhibition of protein synthesis reverses the tolerant phenotype by inducing transcription of IL-1 beta in the absence of a second stimulus. These results indicate that a labile protein contributes to the endotoxin-tolerant phenotype, and that this factor acts in a dominant repressive manner to inhibit the activity of existing transcription factors. We provide further data that cellular expression of I kappa B-alpha correlates with downregulated IL-1 beta gene expression during endotoxin tolerance, implicating I kappa B-alpha as a potential candidate for the labile repressor identified herein.

Regulatory elements and transcription factors controlling basal and cytokine-induced expression of the gene encoding intercellular adhesion molecule 1

The gene encoding intercellular adhesion molecule 1 (ICAM-1) is transcriptionally induced in response to inflammatory and immunomodulatory cytokines. To investigate the mechanisms controlling ICAM-1 gene expression, we have identified regulatory DNA sequences responsible for maintaining basal and mediating induced transcription in response to tumor necrosis factor alpha (TNF-alpha) and interferon gamma (IFN-gamma). Regulatory elements centered 115, 60, and 40 bp upstream from the ICAM-1 transcription start site were implicated in cytokine-independent gene expression. Regulatory elements dedicated to TNF-alpha and IFN-gamma were identified 190 and 90 bp, respectively, upstream from the ICAM-1 transcription start site. A combination of mutagenesis and DNA-binding assays revealed that the TNF-alpha response element is composite, consisting of binding sites for both C/EBP and NF-kappa B. The IFN-gamma response element behaved as a simple regulatory element that selectively binds to an IFN-gamma-inducible activity composed, at least in part, of p91. These observations provide a framework for understanding how extracellular signals dynamically regulate the adhesive properties of mammalian cells.

Transcription factors NF-IL6 and CREB recognize a common essential site in the human prointerleukin 1 beta gene

A site located between -2782 and -2729 of the human prointerleukin-1 beta (IL1B) gene functions as a strong lipopolysaccharide (LPS)-responsive enhancer independent of the previously identified enhancer located between -2896 and -2846 (F. Shirakawa, K. Saito, C.A. Bonagura, D.L. Galson, M. J. Fenton, A. C. Webb, and P. E. Auron, Mol. Cell. Biol. 13:1332-1344, 1993). Although these two enhancers appear to function cooperatively in the native sequence context, they function independently as LPS-responsive elements upon removal of an interposed silencer sequence. The new enhancer is not induced by dibutyryl cyclic AMP (dbcAMP) alone but is superinduced by costimulation with LPS-dbcAMP. This pattern of induction depends upon the nature of the sequence, a composite NF-IL6-cAMP response element (CRE) binding site. This pseudosymmetrical sequence is shown to contrast with a classical symmetric CRE which responds to dbcAMP but not LPS. DNA binding studies using in vivo nuclear extract, recombinant proteins, and specific antibodies show that LPS induces the formation of two different complexes at the enhancer: (i) an NF-IL6-CREB heterodimer and (ii) a heterodimer consisting of NF-IL6 and a non-CREB, CRE-binding protein. Cotransfection studies using NF-IL6 and CREB expression vectors show that NF-IL6 transactivates the enhancer in the presence of LPS, whereas CREB acts either positively or negatively, depending upon its cAMP-regulated phosphorylation state. Our data demonstrate that the newly identified enhancer is a specialized LPS-responsive sequence which can be modulated by cAMP as a result of the involvement of NF-IL6-CRE-binding protein heterodimers.

Transcription factors NF-IL6 and CREB recognize a common essential site in the human prointerleukin 1 beta gene

A site located between -2782 and -2729 of the human prointerleukin-1 beta (IL1B) gene functions as a strong lipopolysaccharide (LPS)-responsive enhancer independent of the previously identified enhancer located between -2896 and -2846 (F. Shirakawa, K. Saito, C.A. Bonagura, D.L. Galson, M. J. Fenton, A. C. Webb, and P. E. Auron, Mol. Cell. Biol. 13:1332-1344, 1993). Although these two enhancers appear to function cooperatively in the native sequence context, they function independently as LPS-responsive elements upon removal of an interposed silencer sequence. The new enhancer is not induced by dibutyryl cyclic AMP (dbcAMP) alone but is superinduced by costimulation with LPS-dbcAMP. This pattern of induction depends upon the nature of the sequence, a composite NF-IL6-cAMP response element (CRE) binding site. This pseudosymmetrical sequence is shown to contrast with a classical symmetric CRE which responds to dbcAMP but not LPS. DNA binding studies using in vivo nuclear extract, recombinant proteins, and specific antibodies show that LPS induces the formation of two different complexes at the enhancer: (i) an NF-IL6-CREB heterodimer and (ii) a heterodimer consisting of NF-IL6 and a non-CREB, CRE-binding protein. Cotransfection studies using NF-IL6 and CREB expression vectors show that NF-IL6 transactivates the enhancer in the presence of LPS, whereas CREB acts either positively or negatively, depending upon its cAMP-regulated phosphorylation state. Our data demonstrate that the newly identified enhancer is a specialized LPS-responsive sequence which can be modulated by cAMP as a result of the involvement of NF-IL6-CRE-binding protein heterodimers.

Identification of a C/EBP-Rel complex in avian lymphoid cells

Protein-protein interactions between the CCAAT box enhancer-binding proteins (C/EBP) and the Rel family of transcription factors have been implicated in the regulation of cytokine gene expression. We have used sequence-specific DNA affinity chromatography to purify a complex from avian T cells that binds to a consensus C/EBP motif. Our results provide evidence that Rel-related proteins are components of the C/EBP-DNA complex as a result of protein-protein interactions with the C/EBP proteins. A polyclonal antiserum raised against the Rel homology domain of v-Rel and antisera raised against two human RelA-derived peptides specifically induced a supershift of the C/EBP-DNA complex in mobility shift assays using the affinity-purified C/EBP. In addition, several kappa B-binding proteins copurified with the avian C/EBP complex through two rounds of sequence-specific DNA affinity chromatography. The kappa B-binding proteins are distinct from the C/EBP proteins that directly contact DNA containing the C/EBP binding site. The identification of a protein complex that binds specifically to a consensus C/EBP site and contains both C/EBP and Rel family members suggests a novel mechanism for regulation of gene expression by Rel family proteins.

An interaction between the DNA-binding domains of RelA(p65) and Sp1 mediates human immunodeficiency virus gene activation

Induction of human immunodeficiency virus type 1 (HIV-1) gene expression in stimulated T cells has been attributed to the activation of the transcription factor NF-kappa B. The twice-repeated kappa B sites within the HIV-1 long terminal repeat are in close proximity to three binding sites for Sp1. We have previously shown that a cooperative interaction of NF-kappa B with Sp1 is required for the efficient stimulation of HIV-1 transcription. In this report, we define the domains of each protein responsible for this effect. Although the transactivation domains seemed likely to mediate this interaction, we find, surprisingly, that this interaction occurs through the putative DNA-binding domains of both proteins. Sp1 specifically interacted with the amino-terminal region of RelA(p65). Similarly, RelA bound directly to the zinc finger region of Sp1. This interaction was specific and resulted in cooperative DNA binding to the kappa B and Sp1 sites in the HIV-1 long terminal repeat. Furthermore, the amino-terminal region of RelA did not associate with several other transcription factors, including MyoD, E12, or Kox15, another zinc finger protein. These findings suggest that the juxtaposition of DNA-binding sites promotes a specific protein interaction between the DNA-binding regions of these transcription factors. This interaction is required for HIV transcriptional activation and may provide a mechanism to allow for selective activation of kappa B-regulated genes.

NF-IL6 and AP-1 cooperatively modulate the activation of the TSG-6 gene by tumor necrosis factor alpha and interleukin-1

Tumor necrosis factor alpha (TNF-alpha) and interleukin-1 (IL-1) activate transcription of the TSG-6 gene in normal human fibroblasts through a promoter region (-165 to -58) that encompasses an AP-1 and a NF-IL6 site. We show by deletion analysis and substitution mutagenesis that both sites are necessary for activation by TNF-alpha. Activation by IL-1 requires the NF-IL6 site and is enhanced by the AP-1 site. These results suggest that the NF-IL6 and AP-1 family transcription factors functionally cooperate to mediate TNF-alpha and IL-1 signals. Consistent with this possibility, IL-1 and TNF-alpha markedly increase the binding of Fos and Jun to the AP-1 site, and NF-IL6 activates the native TSG-6 promoter. Activation by NF-IL6 requires an intact NF-IL6 site and is modulated by the ratio of activator to inhibitor NF-IL6 isoforms that are translated from different in-frame AUGs. However, the inhibitor isoform can also bind to the AP-1 site and repress AP-1 site-mediated transcription. The finding that the inhibitor isoform antagonizes activation of the native TSG-6 promoter by IL-1 and TNF-alpha suggests that NF-IL6 has a physiologic role in these cytokine responses. Thus, the functionally distinct NF-IL6 isoforms cooperate with Fos and Jun to positively and negatively regulate the native TSG-6 promoter by TNF-alpha and IL-1.

NF-IL6 and AP-1 cooperatively modulate the activation of the TSG-6 gene by tumor necrosis factor alpha and interleukin-1

Tumor necrosis factor alpha (TNF-alpha) and interleukin-1 (IL-1) activate transcription of the TSG-6 gene in normal human fibroblasts through a promoter region (-165 to -58) that encompasses an AP-1 and a NF-IL6 site. We show by deletion analysis and substitution mutagenesis that both sites are necessary for activation by TNF-alpha. Activation by IL-1 requires the NF-IL6 site and is enhanced by the AP-1 site. These results suggest that the NF-IL6 and AP-1 family transcription factors functionally cooperate to mediate TNF-alpha and IL-1 signals. Consistent with this possibility, IL-1 and TNF-alpha markedly increase the binding of Fos and Jun to the AP-1 site, and NF-IL6 activates the native TSG-6 promoter. Activation by NF-IL6 requires an intact NF-IL6 site and is modulated by the ratio of activator to inhibitor NF-IL6 isoforms that are translated from different in-frame AUGs. However, the inhibitor isoform can also bind to the AP-1 site and repress AP-1 site-mediated transcription. The finding that the inhibitor isoform antagonizes activation of the native TSG-6 promoter by IL-1 and TNF-alpha suggests that NF-IL6 has a physiologic role in these cytokine responses. Thus, the functionally distinct NF-IL6 isoforms cooperate with Fos and Jun to positively and negatively regulate the native TSG-6 promoter by TNF-alpha and IL-1.

C/EBP beta regulation of the tumor necrosis factor alpha gene

Activated macrophages contribute to chronic inflammation by the secretion of cytokines and proteinases. Tumor necrosis factor alpha (TNF alpha) is particularly important in this process because of its ability to regulate other inflammatory mediators in an autocrine and paracrine fashion. The mechanism(s) responsible for the cell type-specific regulation of TNF alpha is not known. We present data to show that the expression of TNF alpha is regulated by the transcription factor C/EBP beta (NF-IL6). C/EBP beta activated the TNF alpha gene promoter in cotransfection assays and bound to it at a site which failed to bind the closely related protein C/EBP alpha. Finally, a dominant-negative version of C/EBP beta blocked TNF alpha promoter activation in myeloid cells. Our results implicate C/EBP beta as an important regulator of TNF alpha by myelomonocytic cells.

Identification of a C/EBP-Rel complex in avian lymphoid cells

Protein-protein interactions between the CCAAT box enhancer-binding proteins (C/EBP) and the Rel family of transcription factors have been implicated in the regulation of cytokine gene expression. We have used sequence-specific DNA affinity chromatography to purify a complex from avian T cells that binds to a consensus C/EBP motif. Our results provide evidence that Rel-related proteins are components of the C/EBP-DNA complex as a result of protein-protein interactions with the C/EBP proteins. A polyclonal antiserum raised against the Rel homology domain of v-Rel and antisera raised against two human RelA-derived peptides specifically induced a supershift of the C/EBP-DNA complex in mobility shift assays using the affinity-purified C/EBP. In addition, several kappa B-binding proteins copurified with the avian C/EBP complex through two rounds of sequence-specific DNA affinity chromatography. The kappa B-binding proteins are distinct from the C/EBP proteins that directly contact DNA containing the C/EBP binding site. The identification of a protein complex that binds specifically to a consensus C/EBP site and contains both C/EBP and Rel family members suggests a novel mechanism for regulation of gene expression by Rel family proteins.

An interaction between the DNA-binding domains of RelA(p65) and Sp1 mediates human immunodeficiency virus gene activation

Induction of human immunodeficiency virus type 1 (HIV-1) gene expression in stimulated T cells has been attributed to the activation of the transcription factor NF-kappa B. The twice-repeated kappa B sites within the HIV-1 long terminal repeat are in close proximity to three binding sites for Sp1. We have previously shown that a cooperative interaction of NF-kappa B with Sp1 is required for the efficient stimulation of HIV-1 transcription. In this report, we define the domains of each protein responsible for this effect. Although the transactivation domains seemed likely to mediate this interaction, we find, surprisingly, that this interaction occurs through the putative DNA-binding domains of both proteins. Sp1 specifically interacted with the amino-terminal region of RelA(p65). Similarly, RelA bound directly to the zinc finger region of Sp1. This interaction was specific and resulted in cooperative DNA binding to the kappa B and Sp1 sites in the HIV-1 long terminal repeat. Furthermore, the amino-terminal region of RelA did not associate with several other transcription factors, including MyoD, E12, or Kox15, another zinc finger protein. These findings suggest that the juxtaposition of DNA-binding sites promotes a specific protein interaction between the DNA-binding regions of these transcription factors. This interaction is required for HIV transcriptional activation and may provide a mechanism to allow for selective activation of kappa B-regulated genes.

Signals and nuclear factors that regulate the expression of interleukin-4 and interleukin-5 genes in helper T cells

Mouse thymoma line EL-4 cells produce cytokines such as interleukin (IL)-2, IL-3, IL-4, IL-10, and granulocyte-macrophage colony-stimulating factor in response to phorbol 12-myristate 13-acetate (PMA). EL-4 cells also produce low levels of IL-5 when stimulated by PMA alone; however, cAMP greatly augments PMA-dependent IL-5 production. A transient transfection assay revealed that two signals, PMA and cAMP, are required for optimal activation of the IL-5 promoter. In contrast, cAMP almost completely inhibited the PMA-dependent activation of the endogenous IL-2 gene, as well as the transfected IL-2 promoter. These results indicate that the IL-5 gene is positively regulated by cAMP in a manner opposite to that for the IL-2 gene. One of the nuclear factors (NFs) that regulates the response of the IL-5 promoter to cAMP and PMA has properties similar to NF for activated t cell. The P sequence of the IL-4 gene, defined as a responsive element for PMA and calcium ionophore (A23187), shares sequence similarity with the NF kappa B and the NF-activated T cell binding sites. We attempted to determine whether NF(P), a nuclear factor specific for the P sequence, is related to NF-kappa B and nuclear factor for activated T cell (NF-AT). In electromobility shift assays both NF-kappa B (P65 or P65/P50 heterodimer) and NF-AT bound to the P sequence. However, sequence specificity of NF-AT was more similar to that of NF(P), and only a small amount of P65 was detected in NF(P). These results indicate that a component or components of NF-AT have the potential to reconstitute NF(P), whereas NF-kappa B alone does not account for NF(P) in Jurkat crude extract. Taken together, these results suggest that NF-AT-like factors are involved in the regulation of IL-4 and IL-5 genes.

Transcriptional inhibition of the interleukin-8 gene by interferon is mediated by the NF-kappa B site

The cytokine interleukin-8 (IL-8) is an important mediator of neutrophil, lymphocyte, and basophil chemotaxis and activation. Earlier we demonstrated that beta interferon (IFN-beta) can inhibit tumor necrosis factor (TNF)-induced IL-8 gene expression at the transcriptional level, apparently by a novel mechanism. To define the cis-acting elements and trans-acting factors involved in this inhibition, DNA constructs containing portions of the 5'-flanking region of the IL-8 gene were linked to the chloramphenicol acetyltransferase (CAT) reporter gene and transfected into human diploid FS-4 fibroblasts. The region spanning positions -98 to +44 was sufficient to confer both inducibility by TNF and inhibition by simultaneous treatment with IFN-beta. Inhibition of TNF- or IL-1-induced CAT activity by IFN-beta or IFN-alpha was also observed when a DNA fragment containing only the NF-IL-6 and NF-kappa B sites (positions -94 to -70) was placed upstream of the homologous or a heterologous minimal promoter. A construct containing three copies of the NF-kappa B element in front of the CAT gene also was inducible by TNF, and this stimulatory effect too was inhibited by IFN-beta, indicating that the NF-kappa B element is sufficient to confer inhibition by IFN-beta. This inhibitory effect was specific for the NF-kappa B site of the IL-8 gene since it was less marked with constructs containing three copies of the NF-kappa B site from the HLA-B7 gene. Gel shift assays with a probe containing the NF-kappa B and NF-IL-6 binding sites of the IL-8 gene (positions -101 to -63) showed that IFN-beta treatment did not block the activation of NF-kappa B proteins or their ability to bind to the NF-kappa B site. However, nuclear extracts from cells treated with TNF in the presence of IFN-beta gave rise to an additional band that appears to contain protein components from the NF-kappa B and NF-IL-6 families. NF-kappa B site-mediated suppression of IL-8 gene expression by IFN-beta represents a hitherto unknown mechanism and target of IFN action.

Transcriptional inhibition of the interleukin-8 gene by interferon is mediated by the NF-kappa B site

The cytokine interleukin-8 (IL-8) is an important mediator of neutrophil, lymphocyte, and basophil chemotaxis and activation. Earlier we demonstrated that beta interferon (IFN-beta) can inhibit tumor necrosis factor (TNF)-induced IL-8 gene expression at the transcriptional level, apparently by a novel mechanism. To define the cis-acting elements and trans-acting factors involved in this inhibition, DNA constructs containing portions of the 5'-flanking region of the IL-8 gene were linked to the chloramphenicol acetyltransferase (CAT) reporter gene and transfected into human diploid FS-4 fibroblasts. The region spanning positions -98 to +44 was sufficient to confer both inducibility by TNF and inhibition by simultaneous treatment with IFN-beta. Inhibition of TNF- or IL-1-induced CAT activity by IFN-beta or IFN-alpha was also observed when a DNA fragment containing only the NF-IL-6 and NF-kappa B sites (positions -94 to -70) was placed upstream of the homologous or a heterologous minimal promoter. A construct containing three copies of the NF-kappa B element in front of the CAT gene also was inducible by TNF, and this stimulatory effect too was inhibited by IFN-beta, indicating that the NF-kappa B element is sufficient to confer inhibition by IFN-beta. This inhibitory effect was specific for the NF-kappa B site of the IL-8 gene since it was less marked with constructs containing three copies of the NF-kappa B site from the HLA-B7 gene. Gel shift assays with a probe containing the NF-kappa B and NF-IL-6 binding sites of the IL-8 gene (positions -101 to -63) showed that IFN-beta treatment did not block the activation of NF-kappa B proteins or their ability to bind to the NF-kappa B site. However, nuclear extracts from cells treated with TNF in the presence of IFN-beta gave rise to an additional band that appears to contain protein components from the NF-kappa B and NF-IL-6 families. NF-kappa B site-mediated suppression of IL-8 gene expression by IFN-beta represents a hitherto unknown mechanism and target of IFN action.

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.

Multiple regulatory elements in the interleukin-6 gene mediate induction by prostaglandins, cyclic AMP, and lipopolysaccharide

Induction of interleukin-6 (IL-6) gene expression is mediated by numerous agents involving all major signal transduction pathways. We have compared the effects of prostaglandins and their second messenger cyclic AMP (cAMP) with the effect of lipopolysaccharide (LPS) on IL-6 gene expression. We demonstrate that secretion of IL-6 is induced by cAMP in murine monocytic PU5-1.8 cells, even though to a lesser extent than by LPS. Nevertheless, cAMP and prostaglandins of the E series in the presence of theophylline induce transcription of the IL-6 promoter more strongly than LPS, suggesting distinctive effects of cAMP and LPS on posttranscriptional events. Mutations within four regulatory elements, namely, the multiple response element (MRE), AP-1, NF-IL6, and NF-kappa B sites, significantly reduce, but do not completely abrogate, inducibility by cAMP and prostaglandin E1, whereas alterations of four additional sites have no effects. LPS-induced promoter activity, however, is almost completely abolished by mutations in the NF-kappa B site, suggesting that a single regulatory element is crucial for inducibility by LPS. Stimulation by cAMP is correlated with the binding of inducible factors to the AP-1, NF-IL6, and NF-kappa B elements, whereas factors binding to the MRE are constitutively expressed. Recombinant cAMP response element-binding protein binds to the MRE, indicating a potential role for this factor in the cAMP response. Our results suggest that cAMP and prostaglandins act through multiple, partially redundant regulatory elements to induce IL-6 expression in monocytic cells. Nuclear events that overlap partially with the LPS response but also exhibit distinctive features are involved.

Multiple regulatory elements in the interleukin-6 gene mediate induction by prostaglandins, cyclic AMP, and lipopolysaccharide

Induction of interleukin-6 (IL-6) gene expression is mediated by numerous agents involving all major signal transduction pathways. We have compared the effects of prostaglandins and their second messenger cyclic AMP (cAMP) with the effect of lipopolysaccharide (LPS) on IL-6 gene expression. We demonstrate that secretion of IL-6 is induced by cAMP in murine monocytic PU5-1.8 cells, even though to a lesser extent than by LPS. Nevertheless, cAMP and prostaglandins of the E series in the presence of theophylline induce transcription of the IL-6 promoter more strongly than LPS, suggesting distinctive effects of cAMP and LPS on posttranscriptional events. Mutations within four regulatory elements, namely, the multiple response element (MRE), AP-1, NF-IL6, and NF-kappa B sites, significantly reduce, but do not completely abrogate, inducibility by cAMP and prostaglandin E1, whereas alterations of four additional sites have no effects. LPS-induced promoter activity, however, is almost completely abolished by mutations in the NF-kappa B site, suggesting that a single regulatory element is crucial for inducibility by LPS. Stimulation by cAMP is correlated with the binding of inducible factors to the AP-1, NF-IL6, and NF-kappa B elements, whereas factors binding to the MRE are constitutively expressed. Recombinant cAMP response element-binding protein binds to the MRE, indicating a potential role for this factor in the cAMP response. Our results suggest that cAMP and prostaglandins act through multiple, partially redundant regulatory elements to induce IL-6 expression in monocytic cells. Nuclear events that overlap partially with the LPS response but also exhibit distinctive features are involved.

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.

The bZIP transactivator of Epstein-Barr virus, BZLF1, functionally and physically interacts with the p65 subunit of NF-kappa B

The Epstein-Barr virus (EBV) BZLF1 (Z) immediate-early transactivator initiates the switch between latent and productive infection in B cells. The Z protein, which has homology to the basic leucine zipper protein c-Fos, transactivates the promoters of several replicative cycle proteins. Transactivation efficiency of the EBV BMRF1 promoter by Z is cell type dependent. In B cells, in which EBV typically exists in a latent form, Z activates the BMRF1 promoter inefficiently. We have discovered that the p65 component of the cellular factor NF-kappa B inhibits transactivation of several EBV promoters by Z. Furthermore, the inhibitor of NF-kappa B, I kappa B alpha, can augment Z-induced transactivation in the B-cell line Raji. Using glutathione S-transferase fusion proteins and coimmunoprecipitation studies, we demonstrate a direct interaction between Z and p65. This physical interaction, which requires the dimerization domain of Z and the Rel homology domain of p65, can be demonstrated both in vitro and in vivo. Inhibition of Z transactivation function by NF-kappa B p65, or possibly by other Rel family proteins, may contribute to the inefficiency of Z transactivator function in B cells and may be a mechanism of maintaining B-cell-specific viral latency.

The bZIP transactivator of Epstein-Barr virus, BZLF1, functionally and physically interacts with the p65 subunit of NF-kappa B

The Epstein-Barr virus (EBV) BZLF1 (Z) immediate-early transactivator initiates the switch between latent and productive infection in B cells. The Z protein, which has homology to the basic leucine zipper protein c-Fos, transactivates the promoters of several replicative cycle proteins. Transactivation efficiency of the EBV BMRF1 promoter by Z is cell type dependent. In B cells, in which EBV typically exists in a latent form, Z activates the BMRF1 promoter inefficiently. We have discovered that the p65 component of the cellular factor NF-kappa B inhibits transactivation of several EBV promoters by Z. Furthermore, the inhibitor of NF-kappa B, I kappa B alpha, can augment Z-induced transactivation in the B-cell line Raji. Using glutathione S-transferase fusion proteins and coimmunoprecipitation studies, we demonstrate a direct interaction between Z and p65. This physical interaction, which requires the dimerization domain of Z and the Rel homology domain of p65, can be demonstrated both in vitro and in vivo. Inhibition of Z transactivation function by NF-kappa B p65, or possibly by other Rel family proteins, may contribute to the inefficiency of Z transactivator function in B cells and may be a mechanism of maintaining B-cell-specific viral latency.

The expression of the interleukin 6 gene is induced by the human immunodeficiency virus 1 TAT protein

Human immunodeficiency virus 1 (HIV1) infection is associated with severe psoriasis, B cell lymphoma, and Kaposi's sarcoma. A deregulated production of interleukin 6 (IL-6) has been implicated in the pathogenesis of these diseases. The molecular mechanisms underlying the abnormal IL-6 secretion of HIV1-infected cells may include transactivation of the IL-6 gene by HIV1. To test this hypothesis, we used the pIL6Pr-chloramphenicol acetyltransferase (CAT) plasmid, an IL-6 promoter-CAT construct, as a target of the transactivating function of the HIV1 TAT protein. By cotransfecting the pIL6Pr-CAT and the tat-expressing pSVT8 plasmid in MC3 B-lymphoblastoid or in HeLa epithelial cells, we observed that TAT transactivates the human IL-6 promoter. These results were confirmed when pIL6Pr-CAT was transfected in MC3 or HeLa cells that constitutively expressed the tat gene in a sense (pSVT8 cells) or antisense (pSVT10 cells) orientation. 5' deletion plasmids of pIL6Pr-CAT, in which regions at -658, -287, and -172 were inserted 5' to the cat gene, were transiently transfected in pSVT10 and pSVT8 cells and showed that TAT-induced activation of the IL-6 promoter required a minimal region located between -287 and -54 bp. Moreover, experiments with plasmids carrying the -658, -287, and -172 bp regions of the IL-6 promoter inserted downstream to a TAR-deleted HIV1-LTR identified the sequence of -172 to -54 as the minimal region of the IL-6 promoter required for TAT to transactivate the TAR-deleted HIV1-LTR. By DNA-protein binding experiments, tat-transfected cells expressed a consistent increase in kappa B and nuclear factor (NF)-IL-6 binding activity. Accordingly, the pDRCAT and IL-1REK9CAT, carrying tandem repeats of NF-kappa B or NF-IL6 binding motifs, respectively, were activated in TAT-expressing cells. The biological relevance of the TAT-induced IL-6 secretion was addressed by generating 7TD1 cells, an IL-6-dependent mouse cell line, stably expressing the tat gene. These tat-positive cells expressed the endogenous IL-6 gene, secreted high amounts of murine IL-6, and grew efficiently in the absence of exogenous IL-6. Moreover, the tat-positive 7TD1 cells sustained the growth of parental 7TD1 cells and showed a dramatic increase in their tumorigenic potency. These results suggest that TAT protein may play a role in the pathogenesis of some HIV1-associated diseases by modulating the expression of host cellular genes.

Evidence for a non-alpha-helical DNA-binding motif in the Rel homology region

The Rel family of transcription factors serve as terminal messengers in a variety of developmental and receptor-mediated signaling pathways. These proteins are related by a domain of approximately 280 amino acids, the Rel homology region, which mediates dimerization and sequence-specific binding to DNA. Here we report the use of photocrosslinking and site-directed mutagenesis to identify specific contact partners in a Rel protein-DNA interface. Within the Rel homology region of NF-kappa B p50 (also known as KBF1), two amino acid residues were identified by photocrosslinking to adjacent bases in a beta-interferon regulatory element. Secondary structure analysis suggests that the DNA-binding motif of the Rel homology region comprises a beta-turn-beta structure, in contrast to the alpha-helical motifs so commonly observed in transcription factors.

MGSA/GRO transcription is differentially regulated in normal retinal pigment epithelial and melanoma cells

We have characterized constitutive and cytokine-regulated MGSA/GRO alpha, -beta, and -gamma gene expression in normal retinal pigment epithelial (RPE) cells and a malignant melanoma cell line (Hs294T) to discern the mechanism for MGSA/GRO constitutive expression in melanoma. In RPE cells, constitutive MGSA/GRO alpha, -beta, and -gamma mRNAs are not detected by Northern (RNA) blot analysis although nuclear runoff experiments show that all three genes are transcribed. In Hs294T cells, constitutive MGSA/GRO alpha expression is detectable by Northern blot analysis, and the level of basal MGSA/GRO alpha transcription is 8- to 30-fold higher than in RPE cells. In contrast, in Hs294T cells, basal MGSA/GRO beta and -gamma transcription is only twofold higher than in RPE cells and no beta or gamma mRNA is detected by Northern blot. These data suggest that the constitutive MGSA/GRO alpha mRNA in Hs294T cells is due to increased basal MGSA/GRO alpha gene transcription. The cytokines interleukin-1 (IL-1) and tumor necrosis factor alpha (TNF alpha) significantly increase the mRNA levels for all three MGSA/GRO isoforms in Hs294T and RPE cells, and both transcriptional and posttranscriptional mechanisms are operational. Nuclear runoff assays indicate that in RPE cells, a 1-h IL-1 treatment induces a 10- to 20-fold increase in transcription of MGSA/GRO alpha, -beta and -gamma but only a 2-fold increase in Hs294T cells. Similarly, chloramphenicol acetyltransferase (CAT) reporter gene analysis using the MGSA/GRO alpha, -beta, and -gamma promoter regions demonstrates that IL-1 treatment induces an 8- to 14-fold increase in CAT activity in RPE cells but only a 2-fold increase in Hs294T cells. The effect of deletion or mutation of the MGSA/GRO alpha NF-kappa B element, combined with data from gel mobility shift analyses, indicates that the NF-kappa B p50/p65 heterodimer in RPE cells plays an important role in IL-1- and TNF alpha-enhanced gene transcription. In Hs294T cells, gel shift analyses indicate that IL-1 and TNF alpha induce NF-kappa B complex formation; however, transactivation does not occur, suggesting that subtle differences in the NF-kappa B complexes may result in the inability of the cytokines IL-1 and TNF alpha to activate transcription of the MGSA/GRO genes. IL-1 and TNF alpha posttranscriptionally regulate MGSA/GRO mRNA levels in both cell types. In Hs294T cells, IL-1 increases the half-life of MGSA/GRO alpha from 15 min to 6 h (a 24-fold increase in half-life). These data indicate that IL-1 and TNF alpha transcriptionally and posttranscriptionally regulate MGSA/GRO alpha, -beta, and -gamma mRNA levels in RPE cells, while in Hs294T cells, the major effect of IL-1 and TNF alpha is on mRNA stability.

Fos and Jun repress transcription activation by NF-IL6 through association at the basic zipper region

NF-IL6 and AP-1 family transcription factors are coordinately induced by interleukin-6 (IL-6) in a cell-type-specific manner, suggesting that they mediate IL-6 signals in the nucleus. We show that the basic leucine zipper (bZIP) region of NF-IL6 mediates a direct association with the bZIP regions of Fos and Jun in vitro. This interaction does not depend on the presence of their cognate recognition DNA elements or the posttranslational modification of either partner. NF-IL6 homodimers can bind to both NF-IL6 and AP-1 sites, whereas Fos and Jun cannot bind to most NF-IL6 sites. Cross-family association with Fos or with Jun alters the DNA binding specificity of NF-IL6 and reduced its binding to NF-IL6 sites. NF-IL6 isoforms that differ in the site of translation initiation have distinct transcriptional activities. Activation of a reporter gene linked to the NF-IL6 site by NF-IL6 is repressed by Fos and by Jun in transient transfection assays. Thus, association with AP-1 results in repression of transcription activation by NF-IL6. The repression is NF-IL6 site dependent and may have a role in determining the promoter and cell type specificity in IL-6 signaling.

Physical association and functional antagonism between the p65 subunit of transcription factor NF-kappa B and the glucocorticoid receptor

Glucocorticoids, which are widely used as antiinflammatory agents, downregulate the expression of the interleukin 6 gene and of additional cytokine genes involved in inflammatory responses. Conversely, the transcription factor NF-kappa B, a member of the Rel family of transcription factors, has been implicated in the induction of multiple genes involved in the early processes of immune and inflammatory responses. This prompted us to investigate whether one of the mechanisms by which glucocorticoids exert their antiinflammatory activities is through inhibition of gene activation mediated by NF-kappa B. We report that, in intact cells, activation of the interleukin 6 promoter by a combination of the factor NF-IL6 and the p65 subunit of NF-kappa B is inhibited by dexamethasone (ligand)-activated glucocorticoid receptor. Conversely, activation of the mouse mammary tumor virus promoter by a combination of dexamethasone and glucocorticoid receptor is inhibited by overexpression of p65. Furthermore, we provide evidence for physical association between glucocorticoid receptor and p65 in protein crosslinking and coimmunoprecipitation experiments, using either in vitro translated proteins or those present in cell extracts. These studies suggest that direct interactions between NF-kappa B and glucocorticoid receptor may partly account for the antiinflammatory properties of glucocorticoids in vivo.

MGSA/GRO transcription is differentially regulated in normal retinal pigment epithelial and melanoma cells

We have characterized constitutive and cytokine-regulated MGSA/GRO alpha, -beta, and -gamma gene expression in normal retinal pigment epithelial (RPE) cells and a malignant melanoma cell line (Hs294T) to discern the mechanism for MGSA/GRO constitutive expression in melanoma. In RPE cells, constitutive MGSA/GRO alpha, -beta, and -gamma mRNAs are not detected by Northern (RNA) blot analysis although nuclear runoff experiments show that all three genes are transcribed. In Hs294T cells, constitutive MGSA/GRO alpha expression is detectable by Northern blot analysis, and the level of basal MGSA/GRO alpha transcription is 8- to 30-fold higher than in RPE cells. In contrast, in Hs294T cells, basal MGSA/GRO beta and -gamma transcription is only twofold higher than in RPE cells and no beta or gamma mRNA is detected by Northern blot. These data suggest that the constitutive MGSA/GRO alpha mRNA in Hs294T cells is due to increased basal MGSA/GRO alpha gene transcription. The cytokines interleukin-1 (IL-1) and tumor necrosis factor alpha (TNF alpha) significantly increase the mRNA levels for all three MGSA/GRO isoforms in Hs294T and RPE cells, and both transcriptional and posttranscriptional mechanisms are operational. Nuclear runoff assays indicate that in RPE cells, a 1-h IL-1 treatment induces a 10- to 20-fold increase in transcription of MGSA/GRO alpha, -beta and -gamma but only a 2-fold increase in Hs294T cells. Similarly, chloramphenicol acetyltransferase (CAT) reporter gene analysis using the MGSA/GRO alpha, -beta, and -gamma promoter regions demonstrates that IL-1 treatment induces an 8- to 14-fold increase in CAT activity in RPE cells but only a 2-fold increase in Hs294T cells. The effect of deletion or mutation of the MGSA/GRO alpha NF-kappa B element, combined with data from gel mobility shift analyses, indicates that the NF-kappa B p50/p65 heterodimer in RPE cells plays an important role in IL-1- and TNF alpha-enhanced gene transcription. In Hs294T cells, gel shift analyses indicate that IL-1 and TNF alpha induce NF-kappa B complex formation; however, transactivation does not occur, suggesting that subtle differences in the NF-kappa B complexes may result in the inability of the cytokines IL-1 and TNF alpha to activate transcription of the MGSA/GRO genes. IL-1 and TNF alpha posttranscriptionally regulate MGSA/GRO mRNA levels in both cell types. In Hs294T cells, IL-1 increases the half-life of MGSA/GRO alpha from 15 min to 6 h (a 24-fold increase in half-life). These data indicate that IL-1 and TNF alpha transcriptionally and posttranscriptionally regulate MGSA/GRO alpha, -beta, and -gamma mRNA levels in RPE cells, while in Hs294T cells, the major effect of IL-1 and TNF alpha is on mRNA stability.

Fos and Jun repress transcription activation by NF-IL6 through association at the basic zipper region

NF-IL6 and AP-1 family transcription factors are coordinately induced by interleukin-6 (IL-6) in a cell-type-specific manner, suggesting that they mediate IL-6 signals in the nucleus. We show that the basic leucine zipper (bZIP) region of NF-IL6 mediates a direct association with the bZIP regions of Fos and Jun in vitro. This interaction does not depend on the presence of their cognate recognition DNA elements or the posttranslational modification of either partner. NF-IL6 homodimers can bind to both NF-IL6 and AP-1 sites, whereas Fos and Jun cannot bind to most NF-IL6 sites. Cross-family association with Fos or with Jun alters the DNA binding specificity of NF-IL6 and reduced its binding to NF-IL6 sites. NF-IL6 isoforms that differ in the site of translation initiation have distinct transcriptional activities. Activation of a reporter gene linked to the NF-IL6 site by NF-IL6 is repressed by Fos and by Jun in transient transfection assays. Thus, association with AP-1 results in repression of transcription activation by NF-IL6. The repression is NF-IL6 site dependent and may have a role in determining the promoter and cell type specificity in IL-6 signaling.

NF-kappa B site-mediated negative regulation of the HIV-1 promoter by CCAAT/enhancer binding proteins in brain-derived cells

Several transcription regulatory elements that interact with cellular DNA-binding proteins have been identified in the HIV-1 long terminal repeat (LTR). We have identified two sequence motifs in the U3 region of the LTR that are similar to the consensus 9-bp DNA-binding element of the CCAAT/enhancer-binding protein (C/EBP) family of transcription factors. One of the sequences (promoter-proximal) mapped immediately upstream of the NF-kappa B element, whereas the other (promoter-distal) completely overlapped the upstream stimulatory factor (USF) binding site. In this study, we investigated the role of the enhancer-proximal consensus C/EBP binding sequence in the expression of the HIV-1 LTR. In cotransfection assays we found that although this sequence is a functional C/EBP-responsive element, the regulation of the HIV promoter by C/EBP is very complex. C/EBP isoforms inhibited the phorbol 12-myristate 13-acetate (PMA)-stimulated HIV-1 promoter activity in human glioblastoma U138MG and neuroblastoma SHSY5Y cells, but not in HeLa epithelial cells, and this inhibition required the NF-kappa B element. C/EBP also downregulated the HIV NF-kappa B element-containing SV40 early promoter activity, regardless of the presence of the flanking C/EBP-binding sequences, in the two brain-derived cells. In electrophoretic mobility shift assays with nuclear extracts from HeLa and U138MG cells, purified C/EBP markedly increased the complex formation between endogenous proteins and the NF-kappa B DNA probe without detectable association with the complex. However, with extracts from U138MG cells but not from HeLa cells, a slow migrating complex was observed. Our data suggest that the C/EBP family of transcription factors can downregulate the HIV-1 promoter activity in CNS-derived cells through the NF-kappa B binding elements.

Cyclic AMP-independent ATF family members interact with NF-kappa B and function in the activation of the E-selectin promoter in response to cytokines

We previously reported that NF-kappa B and a complex we referred to as NF-ELAM1 play a central role in cytokine-induced expression of the E-selectin gene. In this study we identify cyclic AMP (cAMP)-independent members of the ATF family binding specifically to the NF-ELAM1 promoter element. The NF-ELAM1 element (TGACATCA) differs by a single nucleotide substitution from the cAMP-responsive element consensus sequence. We demonstrate that this sequence operates in a cAMP-independent manner to induce transcription and thus define it as a non-cAMP-responsive element (NCRE). We show that ATFa is a component of the NF-ELAM1 complex and its overexpression activates the E-selectin promoter. In addition, ATFa, ATF2, and ATF3 interact directly with NF-kappa B in vitro, linking two unrelated families of transcription factors in a novel protein-protein interaction. Furthermore, we demonstrate that the ability of overexpressed NF-kappa B to transactivate the E-selectin promoter in vivo is dependent on the NF-ELAM1 complex. Our results suggest that a direct interaction between ATFs and NF-kappa B is, at least in part, the mechanism by which these factors specifically regulate E-selectin promoter activity.

Transcription factors NF-IL6 and NF-kappa B synergistically activate transcription of the inflammatory cytokines, interleukin 6 and interleukin 8

Single binding sites for transcription factors NF-IL6 and NF-kappa B are present in the promoter of the interleukin (IL) 6 gene. Previous studies of internally deleted promoter mutants demonstrated that these two sites are important for the transcriptional regulation of this gene. In this report, we describe the synergistic activation of the IL-6 promoter by transcription factors NF-IL6 and NF-kappa B. Cotransfection of NF-IL6 with the NF-kappa B p65 subunit resulted in strong synergistic activation of an IL-6 promoter-reporter construct. Both the NF-IL6 and NF-kappa B binding sites in the IL-6 promoter were required for synergistic activation. Similar synergistic activation was observed in the IL-8 promoter, which also contains both NF-IL6 and NF-kappa B binding sites. Furthermore, we demonstrated that NF-IL6 and the NF-kappa B p65 subunit directly associated via the basic leucine-zipper domain of NF-IL6 and the Rel homology domain of p65. Since the promoters of many other genes involved in the inflammatory and acute-phase responses also contain binding sites for NF-IL6 and NF-kappa B, the cooperation between these two factors may have an important role in these responses. We also discuss the possible interplay between various viral gene products and these two factors in the process of viral infection and constitutive cytokine production.

Cyclic AMP-independent ATF family members interact with NF-kappa B and function in the activation of the E-selectin promoter in response to cytokines

We previously reported that NF-kappa B and a complex we referred to as NF-ELAM1 play a central role in cytokine-induced expression of the E-selectin gene. In this study we identify cyclic AMP (cAMP)-independent members of the ATF family binding specifically to the NF-ELAM1 promoter element. The NF-ELAM1 element (TGACATCA) differs by a single nucleotide substitution from the cAMP-responsive element consensus sequence. We demonstrate that this sequence operates in a cAMP-independent manner to induce transcription and thus define it as a non-cAMP-responsive element (NCRE). We show that ATFa is a component of the NF-ELAM1 complex and its overexpression activates the E-selectin promoter. In addition, ATFa, ATF2, and ATF3 interact directly with NF-kappa B in vitro, linking two unrelated families of transcription factors in a novel protein-protein interaction. Furthermore, we demonstrate that the ability of overexpressed NF-kappa B to transactivate the E-selectin promoter in vivo is dependent on the NF-ELAM1 complex. Our results suggest that a direct interaction between ATFs and NF-kappa B is, at least in part, the mechanism by which these factors specifically regulate E-selectin promoter activity.

Characterization of a functional NF-kappa B site in the human interleukin 1 beta promoter: evidence for a positive autoregulatory loop

The -300 region of the interleukin 1 beta (IL-1 beta) promoter contains a functional NF-kappa B binding site composed of the decamer sequence 5'-GGGAAAATCC-3'. Probes representing the -300 region or the NF-kappa B site alone interacted with NF-kappa B proteins present in phorbol myristate acetate-, lipopolysaccharide-, or Sendai virus-induced myeloid cell extracts as well as recombinant NFKB1 (p50) and RelA (p65); furthermore, NF-kappa B protein-DNA complex formation was dissociated in vitro by the addition of recombinant I kappa B alpha. Mutation of the NF-kappa B site in the context of the IL-1 beta promoter reduced the responsiveness of the IL-1 beta promoter to various inducers, including phorbol ester, Sendai virus, poly(rI-rC), and IL-1 beta. A 4.4-kb IL-1 beta promoter fragment linked to a chloramphenicol acetyltransferase reporter gene was also preferentially inducible by coexpression of individual NF-kappa B subunits compared with a mutated IL-1 beta promoter fragment. When multiple copies of the IL-1 beta NF-kappa B site were linked to an enhancerless simian virus 40 promoter, this element was able to mediate phorbol ester- or lipopolysaccharide-inducible gene expression. In cotransfection experiments, RelA (p65) and c-Rel (p85) were identified as the main subunits responsible for the activation of the IL-1 beta NF-kappa B site; also, combinations of NFKB1 (p50) and RelA (p65) or c-Rel and RelA were strong transcriptional activators of reporter gene activity. The presence of a functional NF-kappa B binding site in the IL-1 beta promoter suggests that IL-1 positively autoregulates its own synthesis, since IL-1 is a strong inducer of NF-kappa B binding activity. Thus, the IL-1 beta gene may be considered as an important additional member of the family of cytokine genes regulated in part by the NF-kappa B/rel family of transcription factors.

NF-kappa B subunit-specific regulation of the interleukin-8 promoter

Interleukin-8 (IL-8), a chemotactic cytokine for T lymphocytes and neutrophils, is induced in several cell types by a variety of stimuli including the inflammatory cytokines IL-1 and tumor necrosis factor alpha TNF-alpha. Several cis elements, including a binding site for the inducible transcription factor NF-kappa B, have been identified in the regulatory region of the IL-8 gene. We have examined the ability of various NF-kappa B subunits to bind to, and activate transcription from, the IL-8 promoter. A nuclear complex was induced in phorbol myristate acetate-treated Jurkat T cells which bound specifically to the kappa B site of the IL-8 promoter and was inhibited by addition of purified I kappa B alpha to the reaction mixture. Only antibody to RelA (p65), but not to NFKB1 (p50), NFKB2 (p50B), c-Rel, or RelB was able to abolish binding, suggesting that RelA is a major component in these kappa B binding complexes. Gel mobility shift analysis with in vitro-translated and purified proteins indicated that whereas the kappa B element in the human immunodeficiency virus type 1 long terminal repeat bound to all members of the kappa B/Rel family examined, the IL-8 kappa B site bound only to RelA and to c-Rel and NFKB2 homodimers, but not to NFKB1 homodimers or heterodimers of NFKB1-RelA. Transient transfection analysis demonstrated a kappa B-dependent expression of the IL-8 promoter in a human fibrosarcoma cell line (8387) and in Jurkat T lymphocytes. Cotransfection with various NF-kappa B subunits indicated that RelA and c-Rel, but neither NFKB1 nor heterodimeric NFKB1-RelA, was able to activate transcription from the IL-8 promoter. Furthermore, cotransfection of NFKB1 and RelA, although able to support activation from the human immunodeficiency virus type 1 long terminal repeat, failed to activate expression from the IL-8 promoter. Antisense oligonucleotides to RelA, but not NFKB1, inhibited phorbol myristate acetate-induced IL-8 production in Jurkat T lymphocytes. These data demonstrate the differential ability of members of the kappa B/Rel family to bind to, and activate transcription from, the IL-8 promoter. Furthermore, while providing a novel example of a kappa B-regulated promoter in which the classical NF-kappa B complex is unable to activate transcription from the kappa B element, these data provide direct evidence for the role of RelA in regulation of IL-8 gene expression.

Macrophage nitric oxide synthase gene: two upstream regions mediate induction by interferon gamma and lipopolysaccharide

The promoter region of the mouse gene for macrophage-inducible nitric oxide synthase (mac-NOS; EC 1.14.13.39) has been characterized. A putative TATA box is 30 base pairs upstream of the transcription start site. Computer analysis reveals numerous potential binding sites for transcription factors, many of them associated with stimuli that induce mac-NOS expression. To localize functionally important portions of the regulatory region, we constructed deletion mutants of the mac-NOS 5' flanking region and placed them upstream of a luciferase reporter gene. The macrophage cell line RAW 264.7, when transfected with a minimal promoter construct, expresses little luciferase activity when stimulated by lipopolysaccharide (LPS), interferon gamma (IFN-gamma), or both. Maximal expression depends on two discrete regulatory regions upstream of the putative TATA box. Region I (position -48 to -209) increases luciferase activity approximately 75-fold over the minimal promoter construct. Region I contains LPS-related responsive elements, including a binding site for nuclear factor interleukin 6 (NF-IL6) and the kappa B binding site for NF-kappa B, suggesting that this region regulates LPS-induced expression of the mac-NOS gene. Region II (position -913 to -1029) alone does not increase luciferase expression, but together with region I it causes an additional 10-fold increase in expression. Together the two regions increase expression 750-fold over activity obtained from a minimal promoter construct. Region II contains motifs for binding IFN-related transcription factors and thus probably is responsible for IFN-mediated regulation of LPS-induced mac-NOS. Delineation of these two cooperative regions explains at the level of transcription how IFN-gamma and LPS act in concert to induce maximally the mac-NOS gene and, furthermore, how IFN-gamma augments the inflammatory response to LPS.

Characterization of a functional NF-kappa B site in the human interleukin 1 beta promoter: evidence for a positive autoregulatory loop

The -300 region of the interleukin 1 beta (IL-1 beta) promoter contains a functional NF-kappa B binding site composed of the decamer sequence 5'-GGGAAAATCC-3'. Probes representing the -300 region or the NF-kappa B site alone interacted with NF-kappa B proteins present in phorbol myristate acetate-, lipopolysaccharide-, or Sendai virus-induced myeloid cell extracts as well as recombinant NFKB1 (p50) and RelA (p65); furthermore, NF-kappa B protein-DNA complex formation was dissociated in vitro by the addition of recombinant I kappa B alpha. Mutation of the NF-kappa B site in the context of the IL-1 beta promoter reduced the responsiveness of the IL-1 beta promoter to various inducers, including phorbol ester, Sendai virus, poly(rI-rC), and IL-1 beta. A 4.4-kb IL-1 beta promoter fragment linked to a chloramphenicol acetyltransferase reporter gene was also preferentially inducible by coexpression of individual NF-kappa B subunits compared with a mutated IL-1 beta promoter fragment. When multiple copies of the IL-1 beta NF-kappa B site were linked to an enhancerless simian virus 40 promoter, this element was able to mediate phorbol ester- or lipopolysaccharide-inducible gene expression. In cotransfection experiments, RelA (p65) and c-Rel (p85) were identified as the main subunits responsible for the activation of the IL-1 beta NF-kappa B site; also, combinations of NFKB1 (p50) and RelA (p65) or c-Rel and RelA were strong transcriptional activators of reporter gene activity. The presence of a functional NF-kappa B binding site in the IL-1 beta promoter suggests that IL-1 positively autoregulates its own synthesis, since IL-1 is a strong inducer of NF-kappa B binding activity. Thus, the IL-1 beta gene may be considered as an important additional member of the family of cytokine genes regulated in part by the NF-kappa B/rel family of transcription factors.