The genomic structure of the chicken ICSBP gene and its transcriptional regulation by chicken interferon

Structural and expression studies of interferon regulatory factor 8 in Japanese flounder, Paralichthys olivaceus

Interferon regulatory factor 8 (IRF8) plays a role in both innate and adaptive systems in mammals. In this study, the gene and promoter sequences of Japanese flounder, Paralichthys olivaceus, (Po) IRF8 were cloned, and its expression in response to polyinosinic:polycytidylic acid (poly I:C) and lymphocystis disease virus (LCDV) challenges was studied in vivo. The PoIRF8 gene spans over 3.3 kb with a structure of 9 exon-8 intron and encodes 420 amino acids. The putative protein shows the highest sequence identity (69.5-89.0%) to fish IRF8 and possesses a DNA-binding domain (DBD), an IRF-association domain (IAD) and a nuclear localization signal (NLS) of vertebrate IRF8. Phylogenetic analysis classified PoIRF8 into the cluster of fish IRF8 within vertebrate IRF8 group of IRF4 subfamily. A number of transcription factor binding sites were identified in the 2348-bp 5' flanking region of PoIRF8 gene, including those of transcription factors for type Ⅰ and type Ⅱ interferon (IFN) inducible genes and genes regulating the development and function of lymphomyeloid cells in mammals. The PoIRF8 transcripts were expressed in all examined tissues of healthy flounders, with higher levels observed in the immune relevant tissues. They were up-regulated by both poly I:C and LCDV treatments in the spleen, head kidney, gills and muscle in an early phase of immune responses, with initiation and peak time points of induction prior to type Ⅰ IFN and Mx. Relative to LCDV, the induction by poly I:C was quicker in all four tissues. These results indicate an involvement of PoIRF8 in the host's antiviral responses and a functional conservation of IRF8 between fish and mammals.

PU.1 and ICSBP control constitutive and IFN-gamma-regulated Tlr9 gene expression in mouse macrophages

Macrophages are activated by unmethylated CpG-containing DNA (CpG DNA) via TLR9. IFN-gamma and LPS can synergize with CpG DNA to enhance proinflammatory responses in murine macrophages. Here, we show that LPS and IFN-gamma up-regulated Tlr9 mRNA in murine bone marrow-derived macrophages (BMM). The ability of LPS and IFN-gamma to induce Tlr9 mRNA expression in BMM was dependent on the presence of the growth factor, CSF-1, which is constitutively present in vivo. However, there were clear differences in mechanisms of Tlr9 mRNA induction. LPS stimulation rapidly removed the CSF-1 receptor (CSF-1R) from the cell surface, thereby blocking CSF-1-mediated transcriptional repression and indirectly inducing Tlr9 mRNA expression. By contrast, IFN-gamma activated the Tlr9 promoter directly and only marginally affected cell surface CSF-1R expression. An approximately 100-bp proximal promoter of the murine Tlr9 gene was sufficient to confer basal and IFN-gamma-inducible expression in RAW264.7 cells. A composite IFN regulatory factor (IRF)/PU.1 site upon the major transcription start site was identified. Mutation of the binding sites for PU.1 or IRF impaired basal promoter activity, but only the IRF-binding site was required for IFN-gamma induction. The mRNA expression of the IRF family member IFN consensus-binding protein [(ICSBP)/IRF8] was coregulated with Tlr9 in macrophages, and constitutive and IFN-gamma-inducible Tlr9 mRNA expression was reduced in ICSBP-deficient BMM. This study therefore characterizes the regulation of mouse Tlr9 expression and defines a molecular mechanism by which IFN-gamma amplifies mouse macrophage responses to CpG DNA.

A novel interferon regulatory factor (IRF), IRF-10, has a unique role in immune defense and is induced by the v-Rel oncoprotein

The cloning and functional characterization of a novel interferon regulatory factor (IRF), IRF-10, are described. IRF-10 is most closely related to IRF-4 but differs in both its constitutive and inducible expression. The expression of IRF-10 is inducible by interferons (IFNs) and by concanavalin A. In contrast to that of other IRFs, the inducible expression of IRF-10 is characterized by delayed kinetics and requires protein synthesis, suggesting a unique role in the later stages of an antiviral defense. Accordingly, IRF-10 is involved in the upregulation of two primary IFN-gamma target genes (major histocompatibility complex [MHC] class I and guanylate-binding protein) and interferes with the induction of the type I IFN target gene for 2',5'-oligo(A) synthetase. IRF-10 binds the interferon-stimulated response element site of the MHC class I promoter. In contrast to that of IRF-1, which has some of the same functional characteristics, the expression of IRF-10 is not cytotoxic for fibroblasts or B cells. The expression of IRF-10 is induced by the oncogene v-rel, the proto-oncogene c-rel, and IRF-4 in a tissue-specific manner. Moreover, v-Rel and IRF-4 synergistically cooperate in the induction of IRF-10 in fibroblasts. The level of IRF-10 induction in lymphoid cell lines by Rel proteins correlates with Rel transformation potential. These results suggest that IRF-10 plays a role in the late stages of an immune defense by regulating the expression some of the IFN-gamma target genes in the absence of a cytotoxic effect. Furthermore, IRF-10 expression is regulated, at least in part, by members of the Rel/NF-kappa B and IRF families.

ICSBP/IRF-8: its regulatory roles in the development of myeloid cells

Interferon (IFN) consensus sequence binding protein (ICSBP)/IFN regulatory factor (IRF)-8 is an IFNgamma-inducible transcription factor of the IRF family and regulates transcription through multiple target DNA elements, such as IFN-stimulated response element (ISRE), Ets/IRF composite element, and IFN-gamma activation site (GAS). ICSBP(-/-) mice are immunodeficient and susceptible to various pathogens. They have defects in the macrophage function, including the ability to induce interleukin-12 (IL-12) p40 and some IFN-gamma-responsible genes. In addition, ICSBP(-/-) mice develop a chronic myelogenous leukemia (CML)-like syndrome, where a systemic expansion of granulocytes is followed by a fatal blast crisis. ICSBP(-/-) mice harbor an increased number of myeloid progenitor cells, and the -/- progenitors preferentially give rise to granulocytes, although they cannot efficiently generate another descendant of the myeloid lineage, macrophages. Studies with myeloid progenitor cells have shown that ICSBP drives their differentiation toward macrophage, whereas it inhibits granulocyte differentiation. Furthermore, myeloid cells from ICSBP(-/-) mice are resistant to apoptosis. These results illustrate the mechanism by which the loss of ICSBP leads to immunodeficiency and CML-like syndrome and suggest ICSBP's critical role in the development of myeloid cells.

Interferon regulatory factor 4 contributes to transformation of v-Rel-expressing fibroblasts

The avian homologue of the interferon regulatory factor 4 (IRF-4) and a novel splice variant lacking exon 6, IRF-4DeltaE6, were isolated and characterized. Chicken IRF-4 is expressed in lymphoid organs, less in small intestine, and lungs. IRF-4DeltaE6 mRNA, though less abundant than full-length IRF-4, was detected in lymphoid tissues, with the highest levels observed in thymic cells. IRF-4 is highly expressed in v-Rel-transformed lymphocytes, and the expression of IRF-4 is increased in v-Rel- and c-Rel-transformed fibroblasts relative to control cells. The expression of IRF-4 from retrovirus vectors morphologically transformed primary fibroblasts, increased their saturation density, proliferation, and life span, and promoted their growth in soft agar. IRF-4 and v-Rel cooperated synergistically to transform fibroblasts. The expression of IRF-4 antisense RNA eliminated formation of soft agar colonies by v-Rel and reduced the proliferation of v-Rel-transformed cells. v-Rel-transformed fibroblasts produced interferon 1 (IFN1), which inhibits fibroblast proliferation. Infection of fibroblasts with retroviruses expressing v-Rel resulted in an increase in the mRNA levels of IFN1, the IFN receptor, STAT1, JAK1, and 2',5'-oligo(A) synthetase. The exogenous expression of IRF-4 in v-Rel-transformed fibroblasts decreased the production of IFN1 and suppressed the expression of several genes in the IFN transduction pathway. These results suggest that induction of IRF-4 expression by v-Rel likely facilitates transformation of fibroblasts by decreasing the induction of this antiproliferative pathway.

DNA binding and transcription activation by chicken interferon regulatory factor-3 (chIRF-3)

Interferon regulatory factors (IRFs) are a family of transcription factors involved in the cellular response to interferons and viral infection. Previously we isolated an IRF from a chicken embryonic liver cDNA library. Using a PCR-based binding site selection assay, we have characterised the binding specificity of chIRF-3. The optimal binding site (OBS) fits within the consensus interferon-stimulated response element (ISRE) but the specificity of chIRF-3 binding allows less variation in nucleotides outside the core IRF-binding sequence. A comparison of IRF-1 and chIRF-3 binding to ISREs in electrophoretic mobility shift assays confirmed that the binding specificity of chIRF-3 was clearly distinguishable from IRF-1. The selection assay also showed that chIRF-3 is capable of binding an inverted repeat of two half OBSs separated by 10-13 nt. ChIRF-3 appears to bind both the OBS and inverted repeat sites as a dimer with the protein-protein interaction requiring a domain between amino acids 117 and 311. In transfection experiments expression of chIRF-3 strongly activated a promoter containing the OBS. The activation domain was mapped to between amino acids 138 and 221 and a domain inhibitory to activation was also mapped to the C-terminal portion of chIRF-3.

Cloning and promoter analysis of the chicken interferon regulatory factor-3 gene

Interferon regulatory factors (IRFs) are a family of DNA-binding proteins involved in mediating the cellular response to interferons (IFNs) and viral infection. Although extensively studied in mammals, IRFs of other vertebrates have been less well characterized. Previously, we cloned chicken interferon regulatory factor-3 (chIRF-3) mRNA, which is rapidly and transiently induced by double-stranded (ds)RNA. The chIRF-3 mRNA encodes a protein distinct from any known mammalian IRF. Here, we show that chIRF-3 is activated additively by type I and type II IFNs. To delineate the sequence elements required to regulate chIRF-3 expression, we cloned chlRF-3 and 0.48 kb of 5' flanking sequence. Computer analysis of the proximal promoter revealed three putative binding sites for nuclear factor (NF)-kappaB, two overlapping interferon-stimulated response elements (ISREs), and an interferon gamma activating sequence (GAS). The presence of both GAS and ISRE consensus sequences in the chIRF-3 promoter is unique among IRF family members. Both type I and II IFNs, as well as dsRNA and IRF-1, trans-activate the promoter in short-term transfection experiments. Mutational analysis of the promoter demonstrated that the putative NF-kappaB binding sites are needed for stimulation by dsRNA but not by either type I or type II IFN and that both the overlapping ISREs and GAS are required for full induction by type I or type II IFN.

Sequence comparison of avian interferon regulatory factors and identification of the avian CEC-32 cell as a quail cell line

Interferon (IFN) regulatory factor-1 (IRF-1) is a well-characterized member of the IRF family. Previously, we have cloned cDNA of several members of the chicken IRF (ChIRF) family and studied the function of ChIRF-1 in the avian cell line CEC-32. The IRF-1 proteins from primary chicken embryo fibroblasts (CEF) and CEC-32 cells differed in their electrophoretic mobility. To characterize the different forms of IRF-1 in avian cells, we compared the sequences of IRF-1 cDNA from CEC-32 cells, primary CEF, and quail fibroblasts (QEF). The deduced amino acid sequences of IRF-1 cDNA from chicken and quail show high similarity. Comparison of genomic sequences of IRF-1 and IFN consensus sequence binding protein (ICSBP) also confirm the relatedness of the members of the IRF family in quail and chicken. Based on these data, it is concluded that the avian fibroblast cell line CEC-32 is derived from quail. This conclusion is further supported by deoxynucleotide sequence comparison of a DNA fragment in an avian MHC class II gene and by fluorescence in situ hybridization (FISH) using the vertebrate telomeric (TTAGGG) repeat. Chromosome morphology and the lack of interstitial hybridization signals in macrochromosomes suggest that the CEC-32 cell line has probably been derived from Japanese quail.

Interferon consensus sequence-binding protein is constitutively expressed and differentially regulated in the ocular lens

Interferon signaling is mediated by STATs and interferon regulatory factor (IRF) families of transcription factors. Ten distinct IRFs have been described and most are expressed in a variety of cells except for interferon consensus sequence-binding protein (ICSBP) and lymphoid-specific IRF/Pip that are thought to be exclusively expressed in lymphoid cells. We show here for the first time that ICSBP is constitutively and inducibly expressed in the mouse lens. In contrast to lymphoid cells with exclusive expression of ICSBP in the nucleus, ICSBP is present in both the cytoplasm and nucleus of the lens cell. However, ICSBP in the nucleus is of lower apparent molecular weight. We further show that the ICSBP promoter is constitutively bound by lens nuclear factors and that its activation requires binding of additional factors including STAT1. Furthermore, transcriptional activation of ICSBP gene by interferon gamma is accompanied by selective nuclear localization of ICSBP in proliferating epithelial cells but not in the nuclei of nondividing cells in the lens fiber compartment. Constitutive and inducible expression of ICSBP in the ocular lens and differential regulation of its subcellular localization in the developing lens suggest that ICSBP may have nonimmunity related functions and that the commonly held view that it is lymphoid-specific be modified.