Two cis-DNA elements involved in myeloid-cell-specific expression and gamma interferon (IFN-gamma) activation of the human high-affinity Fc gamma receptor gene: a novel IFN regulatory mechanism

IFN-gamma-induced upregulation of Fcgamma-receptor-I during activation of monocytic cells requires the PKR and NFkappaB pathways

Interferon (IFN)-gamma is a potent activator of macrophages, increasing the cells capacity to perform specific functions during inflammation and immune response. In this report we use IFN-gamma-induced upregulation of the high affinity receptor for IgG (FcgammaRI/CD64) in the human monocytic cell line U-937 as a model for monocytic activation. We show that upregulation of FcgammaRI is dependent on signals mediated by the dsRNA-dependent kinase PKR, and the transcription factor NFkappaB. Silencing of PKR expression by siRNA or inhibition of PKR by 2-aminopurine (2-AP) potently blocks the IFN-gamma-induced transcriptional activation of the FcgammaRI promoter. We find that the serine 727 phosphorylation of Stat1, required for full IFN-gamma-induced FcgammaRI promoter activity, is dependent on PKR. We further show that IFN-gamma induction of FcgammaRI upregulation is dependent on the NFkappaB pathway, as evidenced by inhibition of NFkappaB using a phosphorylation defective IkappaBalpha (S32A/S36A) mutant, or inhibiting the IkappaB-kinase (IKK) by treatment with BMS345541. Our results suggest that IFN-gamma-induced increase of FcgammaRI expression requires the integration of two signalling events: PKR-dependent Stat1 serine 727 phosphorylation, and activation of NFkappaB.

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.

The Pmed1 gene promoter of human Fc gamma RIIIA can function as a NK/T cell-specific restriction element, which involves binding of Sp1 transcription factor

The low-affinity receptor for IgG (human FcgammaRIIIA) is selectively expressed by a subset of T lymphocytes, NK cells, and macrophages. To understand the mechanisms underlying this pattern of cell type-specific expression, we initially identified alternative promoters, Pmed1/2 and Pprox, in the 5' end of the FcgammaRIIIA gene. In this study, we focused on the Pmed1 promoter and demonstrated this 93-bp region to be highly specific in governing restriction to NK/T cell lines. This property of Pmed1 is context independent and can extend to a disparate promoter. Deletion analysis defined a contribution of two separate elements located to the 5' 21-bp (-942/-922) and 3' 72-bp (-921/-850) regions of Pmed1 in conferring NK/T cell specificity. The 5' part of Pmed1 contains binding sites for Sp1 and NK element-recognizing factors and substitution mapping studies revealed a critical requirement of the Sp1-I site. The importance of Sp1 protein to regulate maximal Pmed1 promoter activity was further established by EMSAs and cotransfection experiments in Sp1-null Drosophila SL2 cells. Our data suggest that Sp1 can contribute, in part, to NK/T cell restriction and further indicate that the FcgammaRIIIA Pmed1 sequence might be useful to direct the NK/T cell-specific expression of heterologous genes.

Transcriptional mechanisms regulating myeloid-specific genes

Myeloid blood cells comprise an important component of the immune system. Proper control of both lineage- and stage-specific gene expression is required for normal myeloid cell development and function. In recent years, a relatively small number of critical transcriptional regulators have been identified that serve important roles both in myeloid cell development and regulation of lineage-restricted gene expression in mature myeloid cells. This review summarizes our current understanding of the regulation of lineage- and stage-restricted transcription during myeloid cell differentiation, how critical transcriptional regulators control myeloid cell development, and how perturbations in transcription factor function results in the development of leukemia.

Characterization of the human Fc gamma RIIB gene promoter: human zinc-finger proteins (ZNF140 and ZNF91) that bind to different regions function as transcription repressors

Expression of the human low-affinity Fc receptors for IgG (human Fc gamma RII) is differentially regulated. We report here the characterization of the promoter structure of the human Fc gamma RIIB gene and the isolation of the promoter region-binding proteins by a yeast one-hybrid assay. The minimal 154-bp region upstream from the transcription start site of the human Fc gamma RIIB gene was shown to possess promoter activity in a variety of cells. An electrophoretic mobility shift assay indicated that multiple nuclear factors in cell extracts bind to the two regions [F2-3 (-110 to -93) and F4-3 (-47 to -31)] of the human Fc gamma RIIB gene promoter. Mutation analysis indicated that GGGAGGAGC (-105 to -97) and AATTTGTTTGCC (-47 to -36) sequences are responsible for binding to nuclear factors respectively. By using GGGAGGAGC and AATTTGTTTGCC as bait sequences, we cloned two zinc-finger proteins (ZNF140 and ZNF91) that bind to the F2-3 and F4-3 regions within the promoter of the human Fc gamma RIIB gene respectively. When the ZNF140 and ZNF91 were transfected with reporter plasmid, both showed repressor activity with additive effects. Thus, these results indicate that these cloned ZNF140 and ZNF91 proteins function as repressors for the human Fc gamma RIIB transcription.

Up-regulation of gut-enriched krüppel-like factor by interferon-gamma in human colon carcinoma cells

Interferon-gamma (IFN-gamma) induces growth arrest and apoptosis of tumor cells but the mechanisms for these functions are unknown. Recently, gut-enriched krüppel-like factor (GKLF) was found to possess similar biological properties. Treatment of HT-29 cells with IFN-gamma inhibited cell proliferation and induced apoptosis, the effect was found to associate with GKLF expression. IFN-gamma stimulates GKLF mRNA and protein levels in a dose- and time-dependent manner and this process is independent of p53, occurs rapidly and does not require de novo protein synthesis indicating that GKLF is an immediate-early IFN-gamma-responsive gene. Moreover, overexpression of GKLF results in similar effect as IFN-gamma suggesting that GKLF may function as a downstream target of IFN-gamma.

Interleukin-10 (IL-10) Selectively Enhances CIS3/SOCS3 mRNA Expression in Human Neutrophils: Evidence for an IL-10–Induced Pathway That Is Independent of STAT Protein Activation

We have recently shown that, in human neutrophils, interleukin-10 (IL-10) fails to induce specific DNA-binding activities to the gamma-interferon response region (GRR), a regulatory element located in the FcγRI gene promoter, which is required for transcriptional activation by IL-10 and interferon γ (IFNγ) in monocytic cells. In this study, we report that IL-10 is also unable to induce the binding of STAT1 or STAT3 to the serum-inducible element (hSIE/m67), despite the fact that both proteins are expressed in neutrophils. Whereas IFNγ and granulocyte colony-stimulating factor (G-CSF) are efficient inducers of STAT1 and STAT3 tyrosine phosphorylation in polymorphonuclear neutrophils (PMN), IL-10 fails to trigger STAT1 and STAT3 tyrosine and serine phosphorylation, therefore explaining its inability to induce the FcγRI expression in these cells. By contrast, we demonstrate that IL-10 alone represents an efficient stimulus of CIS3/SOCS3 mRNA expression in neutrophils. CIS3/SOCS3 belongs to the recently cloned cytokine-inducible SH2-containing protein (CIS) gene family (which also includes CIS1, CIS2, CIS4, CIS5, and JAB) that is believed to be, at least in part, under the control of STAT transcription factors and whose products are potential modulators of cytokine signaling. Moreover, IL-10 synergizes with lipopolysaccharide (LPS) in upregulating CIS3/SOCS3 mRNA expression in PMN through a mechanism that involves mRNA stabilization. In contrast to CIS3/SOCS3, mRNA transcripts encoding other family members are unaffected by IL-10 in neutrophils. Finally, transfection of CIS3/SOCS3 in murine M1 myeloid cells suppresses LPS-induced growth arrest, macrophage-like differentiation, and nitric oxide synthesis, but not IL-6 mRNA expression. Collectively, our data suggest that, in neutrophils, the activation of STAT1 and STAT3 phosphorylation is neither required for CIS3/SOCS3 induction by IL-10 nor involved in the regulatory effects of IL-10 on cytokine production.

The Transcription Factors Elf-1 and GATA-1 Bind to Cell-Specific Enhancer Elements of Human High-Affinity IgE Receptor α-Chain Gene

Key regulatory regions necessary for the expression of the gene encoding FcεRI α-chain, a component of the high-affinity IgE receptor primarily responsible for IgE-dependent allergic response, were investigated. Two regions, −74/−69 and −55/−47, which contained binding motifs for proteins belonging to the Ets family and the GATA family, respectively, were shown to be necessary for the activation of the α-chain promoter. Both the regulatory elements enhanced the promoter activity only in α-chain-producing cells PT18 and RBL-2H3 (mast cell lines), indicating that the elements required specific trans-acting proteins present in the α-chain-producing cells. EMSA using nuclear extracts and in vitro-translated proteins revealed that Elf-1 and GATA-1 bound to the enhancer elements. This is the first report describing the regulation in the expression of the FcεRI α-chain.

How cells respond to interferons

Interferons play key roles in mediating antiviral and antigrowth responses and in modulating immune response. The main signaling pathways are rapid and direct. They involve tyrosine phosphorylation and activation of signal transducers and activators of transcription factors by Janus tyrosine kinases at the cell membrane, followed by release of signal transducers and activators of transcription and their migration to the nucleus, where they induce the expression of the many gene products that determine the responses. Ancillary pathways are also activated by the interferons, but their effects on cell physiology are less clear. The Janus kinases and signal transducers and activators of transcription, and many of the interferon-induced proteins, play important alternative roles in cells, raising interesting questions as to how the responses to the interferons intersect with more general aspects of cellular physiology and how the specificity of cytokine responses is maintained.

Antagonistic Action of IFN-β and IFN-γ on High Affinity Fcγ Receptor Expression in Healthy Controls and Multiple Sclerosis Patients

Monocyte-macrophage activation by IFN-γ is characterized by a pronounced increase of high affinity Fc receptors for IgG (FcγRI), capable of triggering respiratory burst, phagocytosis, Ab-dependent cytotoxicity, and release of proinflammatory cytokines. In view of the antagonism of IFN-β on IFN-γ action, of interest in the chronic inflammatory disorder multiple sclerosis, we examined the possible effect of IFN-β on IFN-γ induction of FcγRI gene expression. We found that IFN-β significantly down-regulated IFN-γ-induced FcγRI surface expression in peripheral blood monocytes from healthy donors, in a dose- and time-dependent manner. This down-regulation of FcγRI surface levels did not correspond to a decrease in FcγRI mRNA, suggesting a posttranscriptional effect of IFN-β. Down-regulation of FcγRI surface expression correlated with diminished cellular signaling through FcγRI, since the IFN-γ-induced increase in Fcγ receptor-triggered respiratory burst was nearly completely abrogated by simultaneous addition of IFN-β. Finally, the same antagonism between both IFNs on FcγRI surface expression was observed in peripheral blood monocytes derived from multiple sclerosis patients; inhibition by IFN-β was even increased (82 ± 11%), as compared with healthy controls (67 ± 4%). These results may partially help explain the beneficial effect of IFN-β in multiple sclerosis.

Human IgG Fc receptors

Human IgG receptors constitute a family of glycoprotein complexes consisting of ligand-binding, and associated signaling chains. Three leukocyte classes (Fc gamma RI, II, and III) and one separate endothelial Fc gamma R class (FcRB) are defined which are expressed on hematopoietic and endothelial cells. Upon interaction with IgG, Fc gamma R initiate a plethora of signaling cascades involving receptor signaling motifs, and protein tyrosine kinases and phosphatases. These cascades ultimately culminate in activation or deactivation of effector cells, resulting in initiation or down-modulation of cellular processes. Recent evidence points to a crucial in vivo role of Fc gamma R in both initiation and regulation of inflammatory and cytotoxic responses. These Fc gamma R-mediated immune responses can be exploited to develop novel immunotherapies.

Protein-DNA interactions in interferon-gamma signaling

The ability to rapidly activate new genes is essential for the biological effects mediated by IFN-gamma. Studies directed at understanding how these genes are induced by this ligand led to the identification of the STAT family of transcription factors. STATs are rapidly activated at the receptor, whereupon they translocate to the nucleus and bind to a unique enhancer found in the promoter of target genes. The ability to identify this IFN-gamma response element and the proteins that bind it was critical for the elucidation of this pathway. These techniques are the focus of this review.

Role of PU.1 in hematopoiesis

The ETS-family transcription factor PU.1 is expressed in hematopoietic tissues, with significant levels of expression in the monocytic and B lymphocytic lineages. PU.1 is identical to the Spi-1 proto-oncogene which is associated with the generation of spleen focus-forming virus-induced erythroleukemias. An extensive body of in vitro gene regulatory studies has implicated PU.1 as an important, versatile regulator of B lymphoid- and myeloid-specific genes. The first half of the review is designed to coalesce data generated from studies examining the two PU.1 "knockout" animals, which have prompted a reevaluation of the proposed function of PU.1 during hematopoiesis. During hematopoiesis, PU.1 is required for development along the lymphoid and myeloid lineages but needs to be downregulated during erythropoiesis. These unique functional characteristics of PU.1 will be exemplified by contrasting the function of PU.1 with other transcription factors required during fetal hematopoiesis. The second half of this review will reexamine the functional characteristics of PU.1 deduced from traditional biochemical and transactivation assays in light of recent experiments examining the functional behavior of PU.1 in an embryonic stem cell in vitro differentiation system. Working models of how PU.1 regulates promoter and enhancer regions in the B cell and myeloid lineage will be presented and discussed.

Inhibition of NF-kappaB and HIV-1 long terminal repeat transcriptional activation by inducible nitric oxide synthase 2 activity

In the human lymphoblastoid T cell line JJhan-5.1, stably transfected with a human immunodeficiency virus-1 long terminal repeat luciferase vector, the level of luciferase activity is dependent on activation of the nuclear factor kappaB (NF-kappaB) transcription factor. Tumor necrosis factor-induced luciferase activity was not modified in JJhan-5.1 cells co-cultivated with murine adenocarcinoma EMT-6 cells but was strongly decreased when nitric oxide (NO) synthase 2 expression was induced in these cells. Two NO synthase inhibitors counteracted this inhibitory effect. Tumor necrosis factor-alpha binding to JJhan-5.1 cells was not modified after incubation with EMT-6 cells. Viability and protein synthesis in JJhan-5.1 cells were also unchanged. Induction of NF-kappaB DNA binding activity was inhibited when EMT-6 cells expressed NO synthase 2 activity. Aminoguanidine, which completely abolished nitrite production, prevented this inhibition. NF-kappaB activation was also strongly inhibited by S-nitrosoglutathione but was marginally affected by N-(2-aminoethyl)-N-(2-hydroxy-2-nitrosohydrazino)-1, 2-ethylenediamine. Taken together, these results indicated that NO-related species, released by EMT-6 effector cells and probably different from NO itself, inhibited NF-kappaB activation in human lymphoblastoid target cells. Consequently, transcriptional activity of a long terminal repeat-driven luciferase gene construct was markedly diminished.

High Affinity Receptor for IgG (FcγRI/CD64) Gene and STAT Protein Binding to the IFN-γ Response Region (GRR) Are Regulated Differentially in Human Neutrophils and Monocytes by IL-10

Since IL-10 has been shown to up-regulate the expression of the high affinity receptor for IgG (FcγRI/CD64) in human monocytes, we examined whether the cytokine exerts a similar action toward polymorphonuclear neutrophils (PMN). Unexpectedly, we found that in neutrophils, IL-10 failed to induce either the mRNA accumulation or the surface expression of FcγRI. Consistent with these findings, stimulation of PMN with IFN-γ, but not with IL-10, resulted in the induction of specific DNA-binding activities to the IFN-γ response region (GRR), a regulatory element located in the FcγRI gene promoter, required for transcriptional activation. In electrophoretic mobility shift assays (EMSAs), we confirmed that in PBMC, IL-10 induces the binding to the GRR of both STAT1 and STAT3, two members of the STAT family. In neutrophils, however, these activators did not bind to the GRR in response to IL-10, despite the fact that both STAT1 and STAT3 are expressed in these cells. On the other hand, IFN-γ was an efficient inducer of STAT1 binding to the GRR in both PMN and PBMC. The lack of inducible GRR-binding activity in IL-10-treated PMN could not be ascribed to a lack of IL-10R, and did not appear to reflect an inhibitory effect of the cytokine. Taken together, our data suggest that IL-10 is unable to induce FcγRI gene expression in neutrophils because the intracellular signaling pathway triggered by the cytokine is impaired at the level of, or upstream of, STAT1 and/or STAT3 activation.

Synergism between multiple virus-induced factor-binding elements involved in the differential expression of interferon A genes

Comparative transfection analysis of murine interferon A4 and interferon A11 promoter constructs transiently transfected in mouse L929 and human HeLa S3 cells infected with Newcastle disease virus showed that the second positive regulatory domain I-like domain (D motif), located between nucleotides -57 and -46 upstream of the transcription start site, contributes to the activation of virus-induced transcription of the interferon (IFN)-A4 gene promoter by cooperating with the positive regulatory domain I-like and TG-like domains previously described. Electrophoretic mobility shift assay performed with the virus-inducible fragments containing these motifs indicated that the binding activity that we have denoted as virus-induced factor (Génin, P., Bragança, J., Darracq, N., Doly, J., and Civas, A. (1995) Nucleic Acids Res. 23, 5055-5063) is different from interferon-stimulated gene factor 3. It binds to the D motif but not to the virus-unresponsive form of the D motif disrupted by a G-57 --> C substitution. We show that the low levels of IFN-A11 gene expression are caused essentially by the lack of two inducible enhancer domains disrupted by the A-78 --> G and the G-57 --> C substitutions. These data suggest a model taking account of the differential regulation of IFN-A gene family members. They also suggest that virus-induced factor may correspond to the primary transcription factor directly activated by virus that is involved in the initiation of IFN-A gene transcription.

Inhibition of nitric oxide synthase expression and activity in macrophages by 3-hydroxyanthranilic acid, a tryptophan metabolite

Indoleamine 2,3-dioxygenase (IDO) and nitric oxide synthase (NOS) type II are induced in macrophages by interferon (IFN)-gamma and lipopolysaccharide (LPS). Nitric oxide has been previously shown to inhibit IDO activity. We studied whether metabolites of tryptophan via the IDO pathway could alter NOS II activity. In RAW 264.7 cells, the phenolic antioxidant 3-hydroxyanthranilic acid (OH-AA), but not anthranilic acid, inhibited citrulline synthesis by NOS II at sub-millimolar concentrations, when added 1 h before IFN-gamma and LPS. OH-AA inhibited NOS II activity in cytosolic extracts, suggesting a direct action of OH-AA on NOS II protein. Moreover, expression of NOS II mRNA and activation of the nuclear factor kappa B (NF-kappa B) in RAW 264.7 cells were decreased by a pretreatment with OH-AA, but not anthranilic acid, before addition of IFN-gamma and LPS. This pretreatment also inhibited activation of NF-kappa B in response to TNF-alpha in lymphoblastoid J.Jhan5-1 cells. Finally, expression of a long terminal repeat of the human immunodeficiency virus (HIV-LTR)-driven luciferase reporter gene, controlled by NF-kappa B activation, was severely decreased by OH-AA or 3-hydroxykynurenine in J.Jhan5-1 cells. Other tryptophan derivatives were inactive. These data identify OH-AA as an aminophenolic tryptophan derivative inhibiting NF-kappa B activation and impairing both NOS II expression and activity in a millimolar concentration range.

GAS elements: a few nucleotides with a major impact on cytokine-induced gene expression

Gamma interferon activation site (GAS) elements are short stretches of DNA, originally defined as a requirement for the rapid transcriptional induction of genes in response to interferon-gamma (IFN-gamma). The protein complex binding to GAS sequences in IFN-gamma-treated cells, the gamma interferon activation factor (GAF), is a dimer of Stat1, the prototype of a family of cytokine-responsive transcription factors, the signal transducers and activators of transcription. To date, seven different Stats are known (excluding alternatively spliced or processed forms), six of which recognize the same small palindromic consensus sequence TTCN2-4 GAA that defines a GAS element. Because one or several Stats take part in nuclear signaling in response to most cytokines or growth factors, the GAS sequence has changed from being viewed as a specific site for IFN-activated GAF to becoming the general nuclear end of the Jak-Stat signaling pathways. This review focuses on the identification and definition of GAS elements, their interaction with Stat transcription factors, and their contribution to the specificity of cytokine-induced gene expression.

Human proteinase-3 expression is regulated by PU.1 in conjunction with a cytidine-rich element

Human proteinase-3 is one of three serine proteinases present in the azurophil granules of polymorphonuclear leukocytes along with elastase and cathepsin G. Proteinase-3 gene expression is confined to the promyelocytic stage of polymorphonuclear leukocyte maturation. The present investigation identifies elements responsible for this highly controlled tissue- and developmental-specific expression of proteinase-3. Within the first 200 base pairs of the proteinase-3 promoter, two elements were identified as important for expression, these elements at -101 and -190 confer the majority of the activity. The element at -101 has a PU.1 consensus. It binds a myeloid nuclear protein of approximately 45 kDa that "supershifts" with PU.1 antibody and is competed by the CD11b PU.1 element. The element at -190 has a core sequence of CCCCGCCC (CG element). The cytidines but not the guanidine are essential for promoter activity. The CG element binds a second nuclear protein with a molecular mass of approximately 40 kDa that is found in cells of myeloid lineage as well as non-myeloid HeLa cells. However, the proteinase-3 promoter is not active in HeLa cells which suggests that the CG element alone is not sufficient for proteinase-3 gene expression. Maturation of promyelocytic cells results in an inhibition of proteinase-3 gene expression and a reduction in nuclear protein binding to the PU.1 and CG elements. Similar elements occur in the elastase and cathepsin G promoters. Using the elastase and cathepsin G PU.1 and CG-like elements as probes results in identical band-shift patterns to that obtained with proteinase-3 PU.1 and CG elements. These data suggest that there is cooperative interaction between a PU.1 and a CG element with a consensus of CCCCXCCC and that they are important control elements for tissue- and developmental-specific expression of azurophil serine proteinases of polymorphonuclear leukocytes.

Interferon regulatory factor-2 directs transcription from the gp91phox promoter

Repressor elements in the gp91(phox) promoter are necessary to restrict tissue-specific transcription to mature phagocytes. Deletion of these elements leads to significant promoter activity in cell lines such as HEL and K562 that do not normally express gp91(phox). The -100 to +12 base pair gp91(phox) promoter region is sufficient to direct maximal de-repressed transcription in these cells. However, promoter activity is dramatically decreased following a 16-base pair truncation that deletes an interferon-stimulated response element. This element interacts with IRF-1 and IRF-2, members of the interferon regulatory factor family of transcription factors. In addition, this promoter region is bound by a factor with properties similar to BID, a DNA-binding protein that also interacts with three upstream sites within the gp91(phox) promoter. Transient transfection studies using mutated promoters indicate that both the IRF and BID binding sites are required for maximal gp91(phox) promoter activity. Overexpression of IRF-1 or IRF-2 in K562 cells leads to transactivation of gp91(phox) promoter constructs, which is dependent on the presence of an intact IRF binding site. IRF-2 predominates in macrophages that express the gp91(phox) gene as well as in HEL and K562 cells. We conclude that IRF-2 and BID activate gp91(phox) promoter activity in the absence of transcriptional repression.

Granulocyte colony-stimulating factor induces the binding of STAT1 and STAT3 to the IFNgamma response region within the promoter of the Fc(gamma)RI/CD64 gene in human neutrophils

Granulocyte colony-stimulating factor (G-CSF) has been recently shown to induce the high-affinity Fc receptor for IgG (Fc(gammaRI)/CD64) in human polymorphonuclear neutrophils (PMN). To elucidate the molecular mechanisms whereby G-CSF exerts this effect, we examined whether the cytokine induces the binding of transcription factors to the IFNgamma response region (GRR), a well characterized regulatory element in the Fc(gammaRI) promoter that is responsible for the transcriptional induction of this gene. Using electrophoretic mobility shift assays, we show that in human PMN, G-CSF activates a GRR-binding complex which contains members of the signal transducer and activator of transcription (STAT) family of proteins, namely STAT1 and STAT3. In keeping with this result, treatment of neutrophils with G-CSF led to tyrosine phosphorylation of STAT3, as determined by immunoprecipitation followed by immunoblotting with antiphosphotyrosine antibodies. This is the first demonstration that in human neutrophils, the induction by G-CSF of Fc(gammaRI) gene expression may be mediated by the binding of STAT1 and STAT3 to the GRR sequence.

Delta-9-tetrahydrocannabinol: an inhibitor of STAT1 alpha protein tyrosine phosphorylation

Tyrosine-phosphorylated signal transducer and activator of transcription 1 alpha (STAT1 alpha) is a 91-kDa protein responsible for interferon-gamma (IFN-gamma)-dependent transcription. The present study demonstrates that activation by IFN-gamma of murine macrophages resulted in tyrosine phosphorylation of STAT1 alpha identified by immunoprecipitation. The tyrosine phosphorylation of STAT1 alpha was found highly sensitive to treatment by delta-9 tetrahydrocannabinol (THC), a major marijuana component. Subsequently, the isoform formation of p91 due to tyrosine phosphorylation was reduced in THC-treated macrophages. Although inhibition by THC of the tyrosine phosphorylation of STAT1 alpha induced by IFN-gamma was in a THC concentration-related manner, the tyrosine phosphorylation of other proteins induced by lipopolysaccharide/IFN-gamma treatment of macrophages appeared insensitive to THC treatment. Our data suggest that blockade by THC of tyrosine phosphorylation of STAT1 alpha may be an important mechanism involved in the broad immunosuppressive effects of THC.

Stat1 depends on transcriptional synergy with Sp1

STAT (signal transducer and activator of transcription) proteins combine with cytokine receptors and receptor-associated kinases in distinct protein/protein interactions that are critical for STAT-dependent signal transduction events, but the nature of any subsequent STAT interactions with DNA-binding proteins in the nucleus is less certain. Based on assays of DNA/protein binding and activity of transfected reporter plasmids, we determined that occupation of contiguous DNA-binding sites for Stat1 (the first member of the STAT family) and the transcriptional activator Sp1 are both required for full activation of the intercellular adhesion molecule-1 gene by interferon-gamma. Thus, Stat1 binding to DNA cannot by itself be equated with biologic actions of Stat1. In co-immunoprecipitation experiments, we also obtained evidence of direct and selective Stat1/Sp1 interaction (in primary culture cells without overexpression), further indicating that Stat1/Sp1 synergy confers an element of specificity in the pathway leading to cytokine-activated transcription and cytokine-dependent immunity and inflammation.

PU. 1 is not essential for early myeloid gene expression but is required for terminal myeloid differentiation

We have previously shown using gene targeting that PU.1 is essential for the development of lymphoid and myeloid lineages during fetal liver hematopoiesis. We now show that PU.1 is required for the maturation of yolk sac-derived myeloid progenitors and for the differentiation of ES cells into macrophages. The role of PU.1 in regulating target genes, thought to be critical in the development of monocytes and granulocytes, has been analyzed. Early genes such as GM-CSFR, G-CSFR, and myeloperoxidase are expressed in PU.1-/- embryos and differentiated PU.1-/- ES cells. However, the expression of genes associated with terminal myeloid differentiation (CD11b, CD64, and M-CSFR) is eliminated in differentiated PU.1-/- ES cells. Development of macrophages is restored with the introduction of a PU.1 cDNA regulated by its own promoter. The PU.1-/- ES cells represent an important model for analyzing myeloid cell development.

A human Fc gamma RI/CD64 transgenic model for in vivo analysis of (bispecific) antibody therapeutics

The human high-affinity IgG receptor, hFc gamma RI (CD64), is exclusively expressed on myeloid cells, where it serves an important role as a (cytotoxic) trigger molecule. To establish an in vivo model for analysis of the role of hFc gamma RI in immunity, we developed a novel transgenic mouse model. The human Fc gamma RIA gene, with endogenous regulatory sequences, was used to generate two lines of transgenic FVB/N mice. Immunohistochemical and flow cytometric studies showed that hFc gamma RI expression was restricted to myeloid cells. Monocytes, macrophages, and polymorphonuclear neutrophils (PMN) expressed physiologic hFc gamma RI levels, whereas lymphocytes and mast cells lacked expression. Human Fc gamma RI expression was regulated in vivo by the cytokines IFN-gamma (exactly as in humans) and IL-10. The transgenic receptor proved functional and bound human tumor cells via anti-hFc gamma RI-based bispecific antibodies. hFc gamma RI could, furthermore, be efficiently targeted in vivo by CD64 antibodies. These data demonstrate that the hFc gamma RI transgenic mouse model closely parallels the situation in humans. This mouse model seems useful for in vivo evaluation of the therapeutic potential of novel bispecific reagents in tumor and infection models.

Transcription factors in interferon signaling

Interferons (IFNs) comprise a family of polypeptides that exhibit diverse biological effects such as inhibition of cell growth and protection against viral infection. These activities are based mainly on the transcriptional induction of cellular genes by both type I (IFN-alpha and IFN-beta) and type II (IFN-gamma) interferons. Several of these IFN-induced early response genes have been cloned and common elements within their promoters defined. Transcription factors, such as interferon-stimulated gene factor-3, IFN-gamma activation factor and FcRF gamma, that bind to these enhancers subsequently have been isolated and their components identified. This review shall provide an overview of the DNA response elements, the components of the IFN-induced transcription factors and their mechanism of action.

The human low affinity immunoglobulin G Fc receptor III-A and III-B genes. Molecular characterization of the promoter regions

The human Fc receptor with low affinity for IgG (Fc gamma RIII, CD16) is encoded by two nearly identical genes, Fc gamma RIII-A and Fc gamma RIII-B, resulting in tissue-specific expression of alternative membrane-anchored isoforms. The transmembrane CD16 receptor forms a heteromeric structure with the Fc epsilon RI (gamma) and/or CD3 (zeta) subunits on the surface of activated monocytes/macrophages, NK cells, and a subset of T cells. The expression of the glycosylphosphatidylinositol-anchored CD16 isoform encoded by the Fc gamma RIII-B gene is restricted to polymorphonuclear leukocytes and can be induced by Me2SO differentiation of HL60 cells. We have isolated and sequenced genomic clones of the human Fc gamma RIII-A and Fc gamma RIII-B genes, located their transcription initiation sites, identified a different organization of their 5' regions, and demonstrated four distinct classes of Fc gamma RIII-A transcripts (a1-a4) compared with a single class of Fc gamma RIII-Bb1 transcripts. Both CD16 promoters (positions -198 to -10) lack the classical "TATA" positioning consensus sequence but confer transcriptional activity when coupled to the human lysozyme enhancer. Both promoters also display different tissue-specific transcriptional activities reflecting the expected gene expression of Fc gamma RIII-A and Fc gamma RIII-B in NK cells versus polymorphonuclear leukocytes. Within the -198/-10 fragments, the sequences of the two CD16 genes have been identified to differ in 10 positions. It is suggested that these nucleotide differences might contribute to cell type-specific transcription of Fc gamma RIII genes.

Transcriptional regulation of the interferon-gamma-inducible tryptophanyl-tRNA synthetase includes alternative splicing

We have investigated the transcriptional control elements of the human interferon (IFN)-gamma-induced tryptophanyl-tRNA synthetase (hWRS) gene and characterized the transcripts. Transcription leads to a series of mRNAs with different combinations of the first exons. The full-length mRNA codes for a 55-kDa protein (hWRS), but a mRNA lacking exon II is present in almost as high amounts as the full-length transcript. This alternatively spliced mRNA is probably translated into a 48-kDa protein starting from Met48 in exon III. The predicted 48-kDa protein corresponds exactly to an IFN-gamma-inducible protein previously detected by two-dimensional gel electrophoresis. By isolation of genomic clones and construction of plasmids containing hWRS promoter fragments fused to the secreted alkaline phosphatase reporter gene we have mapped a promoter region essential for IFN-mediated gene activation. This region contains IFN-stimulated response elements (ISRE) as well as a Y-box and a gamma-activated sequence (GAS) element. IFN-gamma inducibility of hWRS depends on ongoing protein synthesis, suggesting that so far undescribed transcription factors apart from the latent GAS-binding protein p91 contribute to gene activation. This could be interferon-regulatory factor-1, which binds ISRE elements.

Signal transduction and activation of gene transcription by interferons

Advances in the field of interferon research have identified a signal transduction pathway that initiates at a cell surface receptor and culminates at target genes in the nucleus. The binding of interferon to a transmembrane receptor stimulates the concomitant activation of tyrosine kinases of the Janus kinase (JAK) family. Subsequently, latent cytoplasmic transcription factors are activated by tyrosine phosphorylation and function as signal transducers and activators of transcription (STATs). The STATs form homomeric or heteromeric protein complexes that translocate to the nucleus to bind to specific DNA sequences in the promoters of stimulated genes. The discovery of this regulated pathway in the interferon system served as a paradigm for receptor to nucleus signal transmission by a variety of cytokines.

Interferon response pathways--a paradigm for cytokine signalling?

Considerable progress has been made in the past few years elucidating the molecular mechanisms of cytokine signalling. The interferons (IFNs) have provided a singular system allowing the detailed characterization of a specific cytokine signalling pathway. Studies on the IFN signal transduction pathway have identified protein tyrosine kinases (PTKs) that phosphorylate signal transducers (STATs) which then bind to DNA promoter sequences and activate gene transcription. Related work has shown that JAKs and STATs are also activated in response to a variety of the cytokines. Thus the novel type of signal transduction pathway identified for the IFNs promises to be more widely utilized than anticipated.

Growth hormone induces the tyrosine phosphorylation and nuclear accumulation of components of the ISGF3 transcription factor complex

Growth hormone induced the accumulation of the stat91 and p84 subunits of the transcription factor complex ISGF3 in nuclear fractions of 3T3-F442A cells. Nuclear levels of p84 and stat91 peaked 30-60 min after addition of growth hormone. Growth hormone also induced the tyrosine phosphorylation of two proteins, with similar sizes to stat91 and p84, in both nuclear and cytosolic fractions. The time course of growth hormone-induced tyrosine phosphorylation of these proteins paralleled the nuclear accumulation of stat91 and p84. Immunoprecipitation with stat91-specific antibodies confirmed that growth hormone induced the tyrosine phosphorylation of stat91 and an associated protein of M(r) = 120 kDa. These findings suggest a mechanism for the modulation of specific gene transcription by growth hormone.

Receptor to nucleus signaling via tyrosine phosphorylation of the p91 transcription factor

Recent studies on signal transduction stimulated by interferons have defined pathways that link cell surface receptors to target genes in the nucleus. After interferon binding, nonreceptor tyrosine kinases are activated that phosphorylate components of latent DNA-binding factors in the cytoplasm. These phosphorylated factors form multimeric complexes that translocate to the nucleus and bind to specific DNA sequences in the promoters of induced genes. A 91-kD factor (p91 or Stat 91) is activated by interferons and serves as a subunit partner in the composition of diverse transcription factors.

Complementation by the protein tyrosine kinase JAK2 of a mutant cell line defective in the interferon-gamma signal transduction pathway

Interferons (IFNs) alpha/beta (type I) and gamma (type II) bind to distinct cell surface receptors, inducing transcription of overlapping sets of genes by intracellular pathways that have recently attracted much attention. Previous studies using cell lines selected for their inability to respond to IFN-alpha (ref. 4) have shown that the protein kinase Tyk2 plays a central role in the IFN alpha/beta response. Here we report the isolation of the cell line gamma 1A, selected for its inability to express IFN-gamma-inducible cell-surface markers, that is deficient in all aspects of the IFN-gamma response tested, but responds normally to IFNs alpha and beta. The mutant cells can be complemented by the expression of another member of the JAK family of protein tyrosine kinases, JAK2 (refs 6-9). Unlike IFNs alpha and beta, IFN-gamma induces rapid tyrosine phosphorylation of JAK2 in wild-type cells, and JAK2 immunoprecipitates from these cells show tyrosine kinase activity. These responses are absent in gamma 1A cells. JAK2 is therefore required for the response to IFN-gamma but not to IFNs alpha and beta.

The protein tyrosine kinase JAK1 complements defects in interferon-alpha/beta and -gamma signal transduction

We have produced a cell line which lacks the protein tyrosine kinase JAK1 and is completely defective in interferon response. Complementation of this mutant with JAK1 restored the response, establishing the requirement for JAK1 in both the interferon-alpha/beta and -gamma signal transduction pathways. The reciprocal interdependence between JAK1 and Tyk2 activities in the interferon-alpha pathway, and between JAK1 and JAK2 in the interferon-gamma pathway, may reflect a requirement for these kinases in the correct assembly of interferon receptor complexes.

Transcription factor p91 interacts with the epidermal growth factor receptor and mediates activation of the c-fos gene promoter

Transcription factor p91 contains a SH2 domain and is activated by tyrosine phosphorylation. Here we demonstrate that epidermal growth factor (EGF) induces rapid tyrosine phosphorylation and nuclear translocation of p91. Through its SH2 domain, p91 directly interacts with the EGF receptor in a ligand-dependent manner. p91 is a necessary component of an EGF-induced DNA-binding factor that recognizes a previously identified regulatory element, SIE (c-sis-inducible element), in the c-fos gene promoter. Activated p91 stimulates SIE-dependent transcription in vitro. Cotransfection of an SIE-containing reporter with a p91 expression vector shows that p91 is a positive transcriptional regulator of the c-fos gene promoter. These studies suggest that EGF uses a direct signaling pathway to control nuclear transcriptional events.

Early events in signalling by interferons

The heterogeneity of the biological responses to alpha/beta and gamma interferons, the degree of overlap, synergy and antagonism appear to reflect functional interactions between these two signalling pathways. Recent biochemical and genetic experimental approaches have identified some of the effector proteins involved in interferon signalling, and have advanced our understanding of the crosstalk between these signalling networks.