Interferon gamma regulates binding of two nuclear protein complexes in a macrophage cell line

Tetanus antigen modulates the gene expression profile of aluminum phosphate adjuvant in spleen lymphocytes in vivo

Adjuvants play an important role in stimulation of the immune response to antigens. Very little is known about the molecular mechanisms of this stimulation. Here we address this issue by studying gene expression profiles from spleen lymphocytes after in vivo immunization of mice with a clinically relevant vaccine, tetanus toxoid formulated with aluminum phosphate as adjuvant (TT(ADJ)), or the adjuvant alone (ADJ). The Th1/Th2 response to TT(ADJ) was obtained from a combination of up- and downstream markers to conventional cytokines, which were in good agreement with cytokine protein levels. A clustering algorithm revealed that ADJ elicited expression of 47 genes active in cytotoxic lymphocytes, inflammation, oncogenesis, stress, toxicity and cell cycle regulation. In TT(ADJ) these adjuvant-elicited genes were expressed at lower levels and a compensatory onset of protective and inhibitory genes was observed. We conclude that the antigen, to a larger extent than previously recognized, modulates the molecular mechanism of the aluminum phosphate adjuvant and that the identified genes may serve as predictive biomarkers in the development of new adjuvants and vaccines.

Protein inhibitor of activated signal transducer and activator of transcription (STAT)-1 (PIAS-1) regulates the IFN-gamma response in macrophage cell lines

Macrophage cell lines exhibit different responses to IFN-gamma depending on their maturation stage. We investigated the mechanisms underlying the differential IFN-gamma responsiveness in the less mature P388.D1 and in mature RAW264.7 cells. A reduction in the binding activity of the signal transducer and activator of transcription-1 (STAT-1) to different STAT binding elements (SBEs) was observed in P388.D1. This reduced binding activity was not due to an impaired STAT-1 activation. Studies on the expression of a negative regulator of cytokine signalling, protein-inhibiting activated STAT-1 (PIAS-1), showed that this protein was expressed constitutively at high levels in P388.D1. Forced expression of a PIAS-1 homologue, the Gu binding protein (GBP), inhibited the STAT-1-mediated gene activation in RAW264.7 cells, whereas a construct expressing the 5' portion of GBP in the antisense orientation reverts the IFN-gamma-resistant phenotype of P388.D1. Thus, our results indicate that PIAS-1 may account for the differential IFN-gamma responsiveness in macrophage cell lines at different stages of maturation.

Administration of pentoxifylline during allergen sensitization dissociates pulmonary allergic inflammation from airway hyperresponsiveness

Asthma, a chronic inflammatory disease characterized by intermittent, reversible airflow obstruction and airway hyperresponsiveness (AHR), is classically characterized by an excess of Th2 cytokines (IL-13, IL-4) and depletion of Th1 cytokines (IFN-gamma, IL-12). Recent studies indicating an important role for Th1 immunity in the development of AHR with allergic inflammation suggest that Th1/Th2 balance may be important in determining the association of AHR with allergic inflammation. We hypothesized that administration of pentoxifylline (PTX), a phosphodiesterase inhibitor known to inhibit Th1 cytokine production, during allergen (OVA) sensitization and challenge would lead to attenuation of AHR in a murine model of allergic pulmonary inflammation. We found that PTX treatment led to attenuation of AHR when administered at the time of allergen sensitization without affecting other hallmarks of pulmonary allergic inflammation. Attenuation of AHR with PTX treatment was found in the presence of elevated bronchoalveolar lavage fluid levels of the Th2 cytokine IL-13 and decreased levels of the Th1 cytokine IFN-gamma. PTX treatment during allergen sensitization leads to a divergence of AHR and pulmonary inflammation following allergen challenge.

NF-κB/Rel Transcription Factors: c-Rel Promotes Airway Hyperresponsiveness and Allergic Pulmonary Inflammation

The NF-κB/Rel family of transcription factors induces many genes involved in immune and inflammatory responses. Mice with germline deletions of individual NF-κB/Rel subunits have different phenotypes, suggesting that the NF-κB/Rel transcription factors have different functions. We tested whether c-Rel promotes allergic asthma using a murine model of allergen-induced pulmonary inflammation and airway hyperresponsiveness. Our investigation focused on c-Rel, which is expressed in lymphoid cells and is important for lymphocyte activation. In response to allergen sensitization and challenge, c-Rel-deficient mice did not develop increases in pulmonary inflammation, bronchoalveolar lavage fluid eosinophilia, or total serum IgE. c-Rel deficiency also prevented the induction of airway hyperresponsiveness. Allergen-treated wild-type mice had increased DNA binding to an NF-κB consensus site. Chemokine expression was altered in allergen-treated c-Rel-deficient mice. Monocyte chemoattractant protein-1, which is regulated by NF-κB, was decreased in allergen-treated c-Rel-deficient mice relative to wild-type controls. The increase in NF-κB/Rel transcription factors after allergen challenge in wild-type mice and the decrease in allergen reactivity found in c-Rel-deficient mice indicate that c-Rel promotes allergic inflammation. Alteration of pulmonary chemokine expression in c-Rel-deficient mice may inhibit allergen-induced pulmonary inflammation and airway hyperresponsiveness.

Mutations in the human 5-lipoxygenase gene

Our data demonstrate the presence of a naturally occurring family of alleles in the core promoter of the 5-LO gene, which is characterized by the deletion or addition of consensus Sp1 (-GGGCGG) and Egr-1 (-GCGGGGGCG-) binding motifs. Each of the variant alleles can bind Sp1 and Egr-1 protein, as indicated by EMSA and supershift analysis with nuclear extracts. In addition, preliminary data from CAT reporter assays indicate that these alleles are less effective than the wild-type allele in initiating 5-LO gene expression. Whether patients harboring the various alleles identified herein have different capacities to transcribe the 5-LO gene and the importance of such potential regulation to the clinical expression of 5-LO have yet to be determined.

In vivo class II transactivator expression in mice is induced by a non-interferon-gamma mechanism in response to local injury

BACKGROUND

Tissue injury induces MHC class II expression, which could be important in the recognition of that tissue as an allograft. The class II transcriptional activator (CIITA) is the major regulator of basal and induced MHC class II expression and is essential for antigen presentation. The role of CIITA in the induction of class II by tissue injury is unknown. In this study, we examined CIITA induction in the course of acute ischemic or toxic renal injury in mice, including the role of interferon (IFN)-gamma and of the transcription factor, interferon regulatory factor (IRF)-1.

METHODS

Kidneys were injured by ischemia or by gentamicin toxicity and were then studied for changes in gene expression using Northern blot, reverse transcriptase-polymerase chain reaction, radioimmunoassay, and tissue staining. We compared wild-type (WT) mice to IFN-gamma knockout (GKO) or IRF-1 knockout mice.

RESULTS

Ischemic injury induced CIITA and class II expression in the kidney, in WT and GKO mice. Gentamicin injury also induced both CIITA and class II expression, independent of IFN-gamma, in WT and GKO mice. After ischemic injury, the induction of class II protein levels and CIITA and class II mRNA levels were induced, to a lesser degree, in IRF-1 knockout mice.

CONCLUSIONS

These data indicate that CIITA is induced by tissue injury, and probably accounts for class II induction during tissue injury. CIITA induction by injury is largely IFN-gamma independent but requires IRF-1. The similarities of the pattern of CIITA and class II induction in ischemic and toxic injury suggest that this is a stereotyped response of injured tissue and not a consequence of a particular mechanism of injury.

Naturally occurring mutations in the human 5-lipoxygenase gene promoter that modify transcription factor binding and reporter gene transcription

Five lipoxygenase (5-LO) is the first committed enzyme in the metabolic pathway leading to the synthesis of the leukotrienes. We examined genomic DNA isolated from 25 normal subjects and 31 patients with asthma (6 of whom had aspirin-sensitive asthma) for mutations in the known transcription factor binding regions and the protein encoding region of the 5-LO gene. A family of mutations in the G + C-rich transcription factor binding region was identified consisting of the deletion of one, deletion of two, or addition of one zinc finger (Sp1/Egr-1) binding sites in the region 176 to 147 bp upstream from the ATG translation start site where there are normally 5 Sp1 binding motifs in tandem. Reporter gene activity directed by any of the mutant forms of the transcription factor binding region was significantly (P < 0.05) less effective than the activity driven by the wild type transcription factor binding region. Electrophoretic mobility shift assays (EMSAs) demonstrated the capacity of wild type and mutant transcription factor binding regions to bind nuclear extracts from human umbilical vein endothelial cells (HUVECs). These data are consistent with a family of mutations in the 5-LO gene that can modify reporter gene transcription possibly through differences in Sp1 and Egr-1 transactivation.

Evidence for the in vivo role of class II transactivator in basal and IFN-gamma induced class II expression in mouse tissue

The class II transactivator (CIITA) is a protein that induces the transcription of MHC class II genes. We studied the expression of CIITA in vivo, comparing steady state levels of CIITA and class II mRNA in various mouse tissues. Many tissues in normal mice contained mRNA for CIITA, correlating with class II mRNA. The basal expression of CIITA and class II mRNA in mice with disrupted IFN-gamma genes (GKO mice) was similar to that in wild-type mice. Injection of rIFN-gamma strongly induced CIITA and class II mRNA: CIITA mRNA increased at 2 hr and declined to baseline by 48 hr, whereas class II mRNA increased at 24 hr and returned to baseline at 7 days. Proinflammatory stimuli that induce IFN-gamma production (allogeneic cells and LPS) induce CIITA and class II expression in wild-type mice, but not in GKO mice. CIITA induction by IFN-gamma was partially sensitive to cycloheximide, suggesting that another protein is required for CIITA induction. The data suggest that CIITA is a major regulator of basal and induced class II expression in vivo.

Differential expression of inducible NO synthase in two murine macrophage cell lines

Although primary macrophages and most murine macrophage cell lines such as RAW 264.7 cells respond to interferon-gamma (IFN-gamma) and/or lipopolysaccharide (LPS) by producing large amounts of nitrite, i.e. the oxidation product of nitric oxide (NO) produced by inducible NO synthase (iNOS), other cell lines like P388.D1 cells do not produce significant amounts. To gain insight into the signalling pathway that leads to the induction of iNOS activity, we compared iNOS expression in RAW 264.7 and P388.D1 cells. We showed that IFN-gamma binds to each cell line with a similar affinity. Furthermore, no differences in iNOS gene structure were detectable by Southern blot analysis. Even though no significant nitrite secretion was found in the supernatant of P388:D1 cells stimulated with IFN-gamma and/or LPS, iNOS mRNA expression was induced. In addition, IFN-gamma induced the interferon regulatory factor-1 (IRF-1) gene and activated the binding of this factor to its target sequence in the iNOS gene. This binding was recently shown to be necessary for iNOS expression. However, in P388.D1 cells, we were unable to detect the corresponding iNOS protein. These results indicate a deficiency in P388.D1 cells which appears to be restricted to the signalling pathway controlling iNOS protein synthesis. This deficiency does not affect the overall IFN-gamma biological response, but rather a convergent post-transcriptional step common to IFN-gamma and LPS.

Identification of a transcription factor that binds to the S box of the I-A beta gene of the major histocompatibility complex

Class II genes of the MHC show a striking homology upstream of the transcription start site that is composed of three conserved sequences (S, X and Y boxes, each separated by 15-20 bp). The presence of the S-box sequence in the mouse MHC class II gene I-A Beta was examined for its influence on the expression of this gene. Deletion or mutation of the S box decreased the induction of chloramphenicol acetyltransferase (CAT) activity in B lymphocytes by 32%. In macrophages, deletion or mutation of the S box abolished interferon-gamma (IFN-gamma) inducibility of CAT activity. Using a gel-retardation assay, we have identified a nuclear factor whose binding site overlaps the 7-mer conserved sequence of the S box. This factor is present in lymphocytes, macrophages, mastocytes and fibroblasts. Surprisingly, binding of this nuclear factor to DNA was induced by IFN-gamma in bone-marrow-derived macrophages, but not in macrophage-like cell lines. The binding site for this factor was defined by DNase I footprinting and partially purified by using an affinity column containing double-stranded oligonucleotides containing a sequence of the S box. A prominent protein of 43 kDa was found that bound specifically to the S-box sequence.

A unique palindromic element mediates gamma interferon induction of mig gene expression

To define the molecular mechanisms involved in the action of gamma interferon (IFN-gamma), we have analyzed the transcriptional regulation of the mig (monokine induced by gamma interferon) gene, a member of the platelet factor 4-interleukin-8 cytokine family that is expressed in murine macrophages specifically in response to IFN-gamma. Analysis of mig/CAT chimeric constructs transiently transfected into the RAW 264.7 mouse monocytic cell line revealed a unique IFN-gamma-responsive element (gamma RE-1). The sequence of this cis regulatory element defined by deletion analysis contains an imperfect inverted repeat extending 27 bp. Examination of mig/CAT constructs with mutations in gamma RE-1 revealed that the palindromic positions in the element were essential for activity. Consistent with its function as an enhancer, a single copy of gamma RE-1 conferred IFN-gamma inducibility to a heterologous (herpes simplex virus thymidine kinase) promoter. Exonuclease III protection assays demonstrated symmetrical protection of a mig promoter fragment centered about the gamma RE-1 palindromic sequence. Using the gel electrophoretic mobility shift assay, we identified a factor (gamma RF-1) present in nuclear extracts prepared from IFN-gamma-stimulated RAW 264.7 cells which binds to gamma RE-1. The activation of gamma RF-1 occurred rapidly (within 1 min) in response to IFN-gamma and was independent of protein synthesis. Similar to the expression of mig mRNA, the formation of gamma RF-1 was selectively induced by IFN-gamma and not IFN-alpha. The regulation of gene expression through gamma RF-1 and gamma RE-1 may explain the preferential activation of a subset of interferon-inducible genes by IFN-gamma.

A unique palindromic element mediates gamma interferon induction of mig gene expression

To define the molecular mechanisms involved in the action of gamma interferon (IFN-gamma), we have analyzed the transcriptional regulation of the mig (monokine induced by gamma interferon) gene, a member of the platelet factor 4-interleukin-8 cytokine family that is expressed in murine macrophages specifically in response to IFN-gamma. Analysis of mig/CAT chimeric constructs transiently transfected into the RAW 264.7 mouse monocytic cell line revealed a unique IFN-gamma-responsive element (gamma RE-1). The sequence of this cis regulatory element defined by deletion analysis contains an imperfect inverted repeat extending 27 bp. Examination of mig/CAT constructs with mutations in gamma RE-1 revealed that the palindromic positions in the element were essential for activity. Consistent with its function as an enhancer, a single copy of gamma RE-1 conferred IFN-gamma inducibility to a heterologous (herpes simplex virus thymidine kinase) promoter. Exonuclease III protection assays demonstrated symmetrical protection of a mig promoter fragment centered about the gamma RE-1 palindromic sequence. Using the gel electrophoretic mobility shift assay, we identified a factor (gamma RF-1) present in nuclear extracts prepared from IFN-gamma-stimulated RAW 264.7 cells which binds to gamma RE-1. The activation of gamma RF-1 occurred rapidly (within 1 min) in response to IFN-gamma and was independent of protein synthesis. Similar to the expression of mig mRNA, the formation of gamma RF-1 was selectively induced by IFN-gamma and not IFN-alpha. The regulation of gene expression through gamma RF-1 and gamma RE-1 may explain the preferential activation of a subset of interferon-inducible genes by IFN-gamma.

The MHC class II E beta promoter: a complex arrangement of positive and negative elements determines B cell and interferon-gamma (IFN-gamma) regulated expression

The 5' proximal region of the E beta gene was studied with respect to B lymphoid expression and responsiveness to cytokines, revealing a complex array of general and cell type specific cis-elements and factors. Full lymphoid activity and response to interferon-gamma (IFN-gamma) is generated by the concerted action of the MHC boxes (H, X and Y) and additional elements. Combinatorial interactions between elements and their cognate factors are indicated by several lines of evidence. Thus, mutations within the X box in the promoter context are strongly deleterious to both B lymphoid activity and IFN-gamma regulation. However, the X box alone has minimal lymphoid activity upon heterologous promoters. Data from deletion, insertion and site directed mutagenesis demonstrate that sequences extending approximately 35 bp 5' of the X box (designated as Cytokine Response Sequence--CRS) have a dual role: they are required for cytokine-regulated expression as well as serving as an enhancer element for cell-specific constitutive expression. A region that carries X and CRS permits both lymphoid activity and IFN-gamma response. In contrast, sequences that include X and the downstream Y box are constitutively active in all cell types tested. Combination of the sequences both upstream and downstream of the X box results in a tissue-specific and cytokine-regulated enhancer of full strength. In vivo competition studies show that titratable trans-acting factors, shared by Class I and Class II promoters, mediate the CRS-dependent IFN-gamma response. We report here the identification of novel nuclear complexes that bind to the CRS and recognize sites which correlate with its negative or positive elements. One of these complexes is present in B lymphoid cells only. Three other CRS complexes that are upregulated by either IFN-alpha and IFN-gamma are competed by a non-Class II, IFN-alpha stimulated response element (ISRE), providing evidence for the functional interconnection of these cytokines.

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.

Identification of cis-acting regulatory elements controlling interleukin-4 gene expression in T cells: roles for NF-Y and NF-ATc

Activity of the murine interleukin-4 (IL-4) promoter was localized to several cis-acting elements present within the first 300 bp from the transcriptional initiation site. Five repeated elements, P0 to P4, that share the common consensus ATTTTCCNNT were located between -40 and -250, and each was shown to interact with the T-cell-specific factor NF(P). These distinct P sites appear functionally interchangeable and cooperatively confer cyclosporin A-sensitive and ionomycin-inducible promoter activity. NF(P) may be closely related to the cytoplasmic component of NF-AT (nuclear factor of activated T cells), a T-cell-specific factor essential for IL-2 gene transcription, as judged from indistinguishable molecular weights and protease fragmentation patterns of UV-photolabeled factors. Also, we identified an element in the IL-4 promoter with homology to the Y box common to all major histocompatibility complex class II gene promoters. Our data show that the IL-4 promoter Y box -114CTGATTGG-107 significantly enhances overall promoter activity, since point mutations within this element diminish promoter activity by 85%. The factor binding this region is indistinguishable from the cloned nuclear factor NF-Y, as judged from interactions with specific anti-NF-Y monoclonal and polyclonal antibodies. Last, we point out the presence of two sites that share sequence identity to the OAP region of the ARRE-1 site within the IL-2 promoter (K. S. Ullman, W. M. Flanagan, C. A. Edwards, and G. R. Crabtree, Science 254:558-562, 1991). These regions, -85GTGTAATA-78 and -245GTGTAATT-238, reside adjacent to the NF(P) binding sites P1 and P4 and bind a distinct nuclear factor.

Identification of cis-acting regulatory elements controlling interleukin-4 gene expression in T cells: roles for NF-Y and NF-ATc

Activity of the murine interleukin-4 (IL-4) promoter was localized to several cis-acting elements present within the first 300 bp from the transcriptional initiation site. Five repeated elements, P0 to P4, that share the common consensus ATTTTCCNNT were located between -40 and -250, and each was shown to interact with the T-cell-specific factor NF(P). These distinct P sites appear functionally interchangeable and cooperatively confer cyclosporin A-sensitive and ionomycin-inducible promoter activity. NF(P) may be closely related to the cytoplasmic component of NF-AT (nuclear factor of activated T cells), a T-cell-specific factor essential for IL-2 gene transcription, as judged from indistinguishable molecular weights and protease fragmentation patterns of UV-photolabeled factors. Also, we identified an element in the IL-4 promoter with homology to the Y box common to all major histocompatibility complex class II gene promoters. Our data show that the IL-4 promoter Y box -114CTGATTGG-107 significantly enhances overall promoter activity, since point mutations within this element diminish promoter activity by 85%. The factor binding this region is indistinguishable from the cloned nuclear factor NF-Y, as judged from interactions with specific anti-NF-Y monoclonal and polyclonal antibodies. Last, we point out the presence of two sites that share sequence identity to the OAP region of the ARRE-1 site within the IL-2 promoter (K. S. Ullman, W. M. Flanagan, C. A. Edwards, and G. R. Crabtree, Science 254:558-562, 1991). These regions, -85GTGTAATA-78 and -245GTGTAATT-238, reside adjacent to the NF(P) binding sites P1 and P4 and bind a distinct nuclear factor.

The response of gamma interferon activation factor is under developmental control in cells of the macrophage lineage

Gamma interferon activation factor (GAF) rapidly induces transcriptional activation of gamma interferon (IFN-gamma)-responsive genes. Conversion of the GAF from a latent cytoplasmic to an activated, DNA-binding form is an immediate step in the cellular response to IFN-gamma. The amount of IFN-gamma-activated GAF, measured by exonuclease III protection or gel shift assays, increased strongly upon monocytic differentiation of U937 cells. Activated GAF contained the IFN-responsive 91-kDa protein as its DNA-binding activity in gel shift or exonuclease III assays could be inhibited through direct addition of specific antiserum, and it was not present in p91-immunodepleted extracts. There was a differentiation-induced increase in the amount of nonphosphorylated (latent) p91. Transcription rate measurement demonstrated a strong induction of the p91 gene during monocytic differentiation of U937 cells. The amount of p91 which was rapidly phosphorylated in response to IFN-gamma was found to be much higher in the differentiated cells and suggested a differentiation-controlled increase in the signaling leading to p91 phosphorylation. Concomitantly with a better GAF response, transcriptional activation of IFN-gamma-induced genes and the expression of GAF-dependent, transfected reporter plasmids increased in differentiated U937 monocytes. The promonocyte-monocyte transition also affected the IFN-alpha-responsive transcription factor ISGF-3. Differentiated U937 cells contained more of both the alpha-component p91 and the gamma-component p48, which constitutes the DNA-binding subunit of the complex. Our study thus provides evidence that the synthesis of specific transcription factors can be a regulated event to control the cytokine responsiveness of cells during development.

The response of gamma interferon activation factor is under developmental control in cells of the macrophage lineage

Gamma interferon activation factor (GAF) rapidly induces transcriptional activation of gamma interferon (IFN-gamma)-responsive genes. Conversion of the GAF from a latent cytoplasmic to an activated, DNA-binding form is an immediate step in the cellular response to IFN-gamma. The amount of IFN-gamma-activated GAF, measured by exonuclease III protection or gel shift assays, increased strongly upon monocytic differentiation of U937 cells. Activated GAF contained the IFN-responsive 91-kDa protein as its DNA-binding activity in gel shift or exonuclease III assays could be inhibited through direct addition of specific antiserum, and it was not present in p91-immunodepleted extracts. There was a differentiation-induced increase in the amount of nonphosphorylated (latent) p91. Transcription rate measurement demonstrated a strong induction of the p91 gene during monocytic differentiation of U937 cells. The amount of p91 which was rapidly phosphorylated in response to IFN-gamma was found to be much higher in the differentiated cells and suggested a differentiation-controlled increase in the signaling leading to p91 phosphorylation. Concomitantly with a better GAF response, transcriptional activation of IFN-gamma-induced genes and the expression of GAF-dependent, transfected reporter plasmids increased in differentiated U937 monocytes. The promonocyte-monocyte transition also affected the IFN-alpha-responsive transcription factor ISGF-3. Differentiated U937 cells contained more of both the alpha-component p91 and the gamma-component p48, which constitutes the DNA-binding subunit of the complex. Our study thus provides evidence that the synthesis of specific transcription factors can be a regulated event to control the cytokine responsiveness of cells during development.

The mouse Eb meiotic recombination hotspot contains a tissue-specific transcriptional enhancer

A meiotic recombination hotspot exists within the second intron of the mouse major histocompatibility complex (MHC) gene, Eb. In the present study, a small fragment from the intron which contains two potential transcriptional regulatory elements was cloned into an expression vector and its effect on transcription was tested. This fragment was found to contain tissue-specific transcriptional enhancer activity. An octamer-like sequence and a B motif may contribute to this enhancer activity. Similar regulatory sequences with the same orientation and distance from one another are found in another mouse MHC recombination hotspot.

The HXY box regulatory element modulates expression of the murine IA antigen-associated invariant chain in L fibroblasts

The murine invariant chain (Ii) gene has been shown to be interferon-gamma (IFN-gamma)-inducible in a number of nonlymphoid cell types. In mouse L cells, steady-state levels of Ii mRNA are barely detectable in untreated cells but increase sharply upon IFN-gamma treatment. In IFN-gamma treated L cells, transcription starts 23, 28, 38, and 40 bases downstream of the TATA box. To identify cis-acting elements regulating expression of the Ii gene, reporter plasmids containing deletions of the Ii promoter have been constructed and transfected into mouse L cells. Deletion of the H box results in a 50-100% increase in basal expression. Deletion of both the H and X boxes increases basal expression by 200-300% above that seen in constructs containing all three elements. A 25% decrease in basal level expression is seen for constructs that lack the Y-box element when compared to constructs containing the Y-box element but not the H- and X-box elements. DNase I footprinting analysis demonstrates protection of the H, X, and Y boxes as well as a nonconserved region between the H and X boxes. Mobility-shift experiments detect a factor specifically interacting with the Y box. Although the H-, X-, and Y-box elements interact with nuclear protein and are regulatory elements in L cells, these elements do not appear to play a role in IFN-gamma induction suggesting that other regulatory mechanisms must account for IFN-gamma's induction of the Ii in L cells.

Delineation of a previously unrecognized cis-acting element required for HLA class II gene expression

The cis-acting DNA sequences that control expression of the HLA-DPA and HLA-DQB promoters have been investigated in detail. A set of recombinant plasmids containing 5' promoter deletions as well as site-directed mutants of the DPA and DQB genes were fused to a reporter gene and transfected into human B and interferon gamma (IFN-gamma)-inducible cells. A previously unrecognized cis element, which is essential both for transcription induced by IFN-gamma in several cell types and for constitutive class II expression in B cells, in addition to the well known X and Y boxes, has been defined. This sequence, which spans nucleotides -107 to -98 and -146 to -137 of the DPA and DQB promoters, respectively, has been called the J element. Some evidence for function of a fourth element, the S element, is also presented.

Human X-box-binding protein 1 is required for the transcription of a subset of human class II major histocompatibility genes and forms a heterodimer with c-fos

A complementary DNA encoding a member of the leucine-zipper class of proteins (human X-box-binding protein, hXBP-1) that binds to the 3' end of the conserved X box (X2) of the HLA-DRA major histocompatibility complex gene was recently described. Further gel-retardation analysis has demonstrated that hXBP-1 also binds to HLA-DPB X2 but not to other X2 sequences. Transient transfection of a mammalian expression vector with the hXBP-1 cDNA inserted in the antisense orientation represses the surface expression of HLA-DR and HLA-DP in Raji cells. Cotransfection of the antisense hXBP-1 vector with a HLA-DRA/chloramphenicol acetyltransferase (but not a HLA-DQB/chloramphenicol acetyltransferase) reporter plasmid decreases chloramphenicol acetyltransferase activity in Raji cells and in gamma-interferon-treated HeLa cells relative to cells cotransfected with a control antisense vector. Moreover, hXBP-1 is shown to form a stable heterodimer with the product of the c-fos protooncogene. These data suggest that the hXBP-1 c-fos heterodimer is critical for the transcription of a subset of the human class II major histocompatibility complex genes and that the regulatory mechanisms for the different class II genes are distinct.

The same CCAAT box-binding factor binds to the promoter of two coordinately regulated major histocompatibility complex class II genes

Using competition mobility shift, methylation interference, and proteolytic clipping DNA binding assays, we demonstrate that the protein binding the major histocompatibility complex A beta CCAAT box is indistinguishable from the protein previously named NF-Y, which binds the major histocompatibility complex E alpha CCAAT box. Although the two CCAAT boxes share the same 10-base core sequence, termed the Y box, their flanking sequences, known to be important for binding, are very different.

Transcription factors induced by interferons alpha and gamma

Factors induced by interferons (IFNs) bind to the IFN-stimulated response elements (ISREs) of many genes. In human cells treated with type I (alpha, beta) IFN, factor E is induced in about 1 min and factor M after about 1 hr. Factor G is induced after about 1 hr in cells treated with type II (gamma) IFN. G and M have very similar positions in bandshift assays, sensitivities to cycloheximide, footprints on an ISRE and relative affinities for different ISREs. Four different patterns of expression were observed in different cell lines: E,M and G strongly induced; M and G strongly but E weakly; only E and M induced; only E induced. Transcription in response to IFN alpha is initiated by E and probably maintained by M since, in fibroblasts, M is present maximally when transcription is most active and declines together with transcription. In Bristol-8 cells, where induction of M is not detected, transcription is still induced by IFN alpha and still declines in its continued presence, suggesting that M is not essential for either process. A variant ISRE with two G-to-C mutations binds E especially weakly but M and G strongly. The mutations don't change the response of a reporter gene to IFN gamma but do abolish its response to IFN alpha, suggesting that the binding of M is not sufficient for the latter. G probably acts positively, since its appearance correlates well with induction of transcription by IFN gamma. A 39-bp ISRE from the 9-27 gene binds E much better than M or G. Conversely, a 39-bp ISRE from the 6-16 gene binds M and G much better than E. Different patterns of expression of E, M, and G and different affinities of these factors for alternative ISREs may play a part in modulating the relative responses of genes to type I and type II IFNs in vivo.

Loss of a DNA-protein complex correlates with extinguished major histocompatibility complex class II expression in a human B cell

An E beta DNA protein complex termed complex A, whose binding activity has recently been shown to correlate with both constitutive and regulated class II expression in murine cell lines, is also present in a human B cell, Raji. The DNA involved in complex A, which includes three previously defined transcriptional motifs, W, X, and Y, is a cis-acting transcription element in Raji cells. Both complex A binding activity and transcriptional activity of its target sequence are absent in an Ia- mutant subclone of Raji, RJ 2.2.5. This cell line, whose defect is complemented by a locus on mouse chromosome 16, reexpresses both class II and complex A upon transfection with mouse genomic DNA. We suggest that factors that form complex A or that regulate complex A formation account for the molecular lesion in this cell line.