IRF3 Research Articles

Chicken interferon consensus sequence-binding protein (ICSBP) and interferon regulatory factor (IRF) 1 genes reveal evolutionary conservation in the IRF gene family.

Members of the IRF family mediate transcriptional responses to interferons (IFNs) and to virus infection. So far, proteins of this family have been studied only among mammalian species. Here we report the isolation of cDNA clones encoding two members of this family from chicken, interferon consensus sequence-binding protein (ICSBP) and IRF-1. The predicted chicken ICSBP and IRF-1 proteins show high levels of sequence similarity to their corresponding human and mouse counterparts. Sequence identities in the putative DNA-binding domains of chicken and human ICSBP and IRF-1 were 97% and 89%, respectively, whereas the C-terminal regions showed identities of 64% and 51%; sequence relationships with mouse ICSBP and IRF-1 are very similar. Chicken ICSBP was found to be expressed in several embryonic tissues, and both chicken IRF-1 and ICSBP were strongly induced in chicken fibroblasts by IFN treatment, supporting the involvement of these factors in IFN-regulated gene expression. The presence of proteins homologous to mammalian IRF family members, together with earlier observations on the occurrence of functionally homologous IFN-responsive elements in chicken and mammalian genes, highlights the conservation of transcriptional mechanisms in the IFN system, a finding that contrasts with the extensive sequence and functional divergence of the IFNs.

The Sequence and Genomic Organization of the Human Type 2 Angiotensin II Receptor

A human genomic DNA library was screened utilizing a human angiotensin II type 2 receptor (hAT2R) cDNA as a probe. Several positive clones were isolated and characterized. A comparison of the hAT2R cDNA sequence with the hAT2R genomic clone sequence suggests that the hAT2R gene is composed of three exons and spans at least 5 kb. Exons 1 and 2 encode for 5′ untranslated mRNA sequence and exon 3 harbors the entire uninterrupted open reading frame of the hAT2R. Sequence analysis of the 5′-flanking region of the hAT2R gene demonstrates that it contains the typical sequence motifs found in many eukaryotic promoters. Interestingly, however, this promoter region also includes an interferon consensus sequence binding protein site (ICSBP) and a putative embryonal, long terminal repeat binding protein (ELF) site. The presence of these novel putative transcription factor binding sites suggests that this gene may be regulated in a unique manner.

Differential expression of interferon regulatory factor 1 (IRF-1), IRF-2, and interferon consensus sequence binding protein genes in lipopolysaccharide (LPS)-responsive and LPS-hyporesponsive macrophages.

Macrophages secrete interferon (IFN), as well as other cytokines, following lipopolysaccharide (LPS) stimulation. The interferon regulatory factors (IRFs) comprise a family of DNA-binding proteins that have been implicated in the transcriptional regulation of IFN and certain IFN-inducible genes. We therefore characterized basal and LPS-inducible levels of IRF-1, IRF-2, and interferon consensus sequence binding protein (ICSBP) mRNA in LPS-responsive macrophages and compared the expression of these genes in macrophages that typify two murine models of LPS hyporesponsiveness. In the first model, the LPS-hyporesponsive phenotype of the C3H/HeJ mouse is genetically determined and maps to the Lps locus on mouse chromosome 4. In the second model, normally LPS-responsive macrophages acquire a transient LPS-hyporesponsive phenotype following a prior exposure to LPS, a phenomenon referred to as "endotoxin tolerance." Using reverse transcription PCR, we detected basal levels of IRF-1 mRNA in LPS-responsive (Lpsn) macrophages that were approximately 15 times higher than those found in LPS-hyporesponsive (Lpsd) macrophages. Conversely, Lpsd macrophages expressed basal levels of IRF-2 mRNA that were approximately 18 times higher than those expressed in Lpsn macrophages. LPS stimulation resulted in a dose- and time-dependent accumulation of IRF-1, IRF-2, and ICSBP mRNA only in Lpsn macrophages. Cycloheximide inhibited the accumulation of LPS-stimulated IRF-2 and ICSBP mRNA, but not IRF-1 mRNA, thus designating IRF-1 an immediate-early, LPS-inducible gene. Finally, macrophages rendered tolerant to endotoxin expressed elevated but nonmaximal mRNA levels for all three transcription factors that are not reinduced upon secondary challenge with LPS. Thus, the IRFs may represent yet an additional molecular pathway in the complex response to LPS.

Molecular interactions between interferon consensus sequence binding protein and members of the interferon regulatory factor family.

Interferon (IFN) consensus sequence binding protein (ICSBP) is a transcription factor expressed mostly in the cells of the immune system. ICSBP belongs to the IFN regulatory factor (IRF) family, which also includes IRF-1, IRF-2, and the IFN-alpha-stimulated gene factor 3 gamma (ISGF3 gamma). We show here that ICSBP forms a complex with IRF-1 or IRF-2 both in vivo and in vitro and, in the presence or absence of the target DNA, with the IFN-stimulated response element (ISRE). Further, electrophoretic mobility shift assays show that this interaction greatly enhances the otherwise very low binding affinity of ICSBP to the ISRE. We show, on the other hand, that ICSBP inhibits binding of the IFN-alpha-stimulated gene factor 3 gamma to the ISRE. Through these interactions ICSBP is likely to exert complex modulatory functions in the regulation of IFN-stimulated genes.

Regulation of IFN-gamma-induced nuclear expression of IFN consensus sequence binding protein in murine peritoneal macrophages.

IFNs are well characterized macrophage-activating agents. Their varied effects are largely mediated via the induction of many genes, whose products act in concert to induce macrophage differentiation. Homologous DNA sequences have been found upstream of the promoter in many of these IFN-inducible genes and bind a family of trans-acting proteins. Interferon consensus sequence binding protein (ICSBP) is one member of this family of interferon regulatory factors (IRF) and is structurally related within the DNA-binding domain to the other members, IRF-1, IRF-2, and ISGF3 gamma. ISCBP mRNA levels become elevated in response to IFN-gamma; however, little is known about the regulation of ICSBP expression at the protein level. In this study, anti-ICSBP peptide Abs were used to quantify and localize ICSBP in murine peritoneal exudate macrophages. Western blot analysis of cytoplasmic and nuclear extracts from treated and control cells revealed ICSBP to be induced by IFN-gamma and not by IFN-alpha and to exist primarily in the nucleus. The regulation of ICSBP induction by IFN-gamma was consistent with the characteristics found at the mRNA level; inhibition by IFN-alpha or glucocorticoids and the requirement for protein kinase C (as determined pharmacologically). The time course of IFN-gamma-induced ICSBP showed an induction of protein that required approximately 12 h to reach maximal levels. Induced ICSBP was relatively stable, exhibiting a half-life of approximately 48 h. Indirect immunofluorescence also demonstrated ICSBP to be an IFN-gamma-inducible protein that is strongly localized to the nucleus.

IFN consensus sequence binding protein (ICSBP) is a conditional repressor of IFN inducible promoters.

IFN stimulated genes (ISGs) contain common DNA motif termed IFN consensus sequence (ICS) at their promoters that enable IFN responsiveness. Different transcription factors capable of interacting with the ICS have been described. Previously, we reported the cloning of a factor capable of binding to the ICS (ICSBP) that demonstrates similarity at DNA the binding domain with three other ICS binding factor, i.e. IRF-1, IRF-2 and ISGF3 gamma. ICSBP is expressed constitutively in hematopoietic cells and its expression is further induced by IFN-gamma. This is a negative trans-acting regulator of ISGs; however, its effect is attenuated following prolonged exposures of cells to both types of IFNs. In this communication, we show that short exposures of cells to IFNs (priming) are sufficient to alleviate ICSBP mediated repression. Further, exposure of primed cells to the synthetic dsRNA (polyl-polyC) results in total abrogation of ICSBP repression. In an attempt to unravel the molecular mechanism governing this conditional repression of ICSBP, the direct involvement of transcriptional activator IRF-1 is demonstrated. We postulate that constitutive expression of ICSBP in hematopoietic cells is mediating submaximal expression of ISGs such as MHC class I. Our data demonstrate that IRF-1 competes with ICSBP for the binding to the ISRE element, resulting in the alleviation of ICSBP repression. Thus, the magnitude of ISGs expression is a result of a fine balance between positive and negative regulators.

Interferon consensus sequence-binding protein, a member of the interferon regulatory factor family, suppresses interferon-induced gene transcription.

We previously isolated a cDNA clone encoding interferon consensus sequence-binding protein (ICSBP), a member of the interferon regulatory factor (IRF) family, that binds to the interferon (IFN)-stimulated response element (ISRE) of many IFN-regulated genes. In this investigation, we studied the functional role of ICSBP by transient cotransfection of ICSBP cDNA with IFN-responsive reporter genes into the human embryonal carcinoma cell line N-Tera2. These cells were shown not to express ICSBP or IRF-2, thus allowing functional analysis of transfected cDNAs. Cotransfection of ICSBP into cells treated with retinoic acid or any of the IFNs (alpha, beta, or gamma) repressed expression of a chloramphenicol acetyltransferase reporter driven by the major histocompatibility complex class I gene promoter. Similarly, ICSBP repressed expression of chloramphenicol acetyltransferase reporters driven by the ISREs of the 2'-5' oligoadenylate synthetase, guanylate-binding protein, and ISG-15 genes in IFN-treated cells. The repression was dependent on the presence of the ISRE in the reporter. Deletion analysis showed that the putative N-terminal DNA binding domain of ICSBP by itself is capable of mediating the repression. Using the same cotransfection conditions as for ICSBP, a similar repression of these reporters was observed with IRF-2. Finally, ICSBP repressed the IRF-1-mediated induction of major histocompatibility complex class I and IFN-beta reporters in the absence of IFN or retinoic acid. Taken together, these results suggest that ICSBP is a negative regulatory factor capable of repressing transcription of target genes induced by IFN, retinoic acid, or IRF-1.

Interferon Consensus sequence-Binding Protein, a Member of the Interferon Regulatory Factor Family, Suppresses Interferon-Induced Gene Transcription

We previously isolated a cDNA clone encoding interferon consensus sequence-binding protein (ICSBP), a member of the interferon regulatory factor (IRF) family, that binds to the interferon (IFN)-stimulated response element (ISRE) of many IFN-regulated genes. In this investigation, we studied the functional role of ICSBP by transient cotransfection of ICSBP cDNA with IFN-responsive reporter genes into the human embryonal carcinoma cell line N-Tera2. These cells were shown not to express ICSBP or IRF-2, thus allowing functional analysis of transfected cDNAs. Cotransfection of ICSBP into cells treated with retinoic acid or any of the IFNs (alpha, beta, or gamma) repressed expression of a chloramphenicol acetyltransferase reporter driven by the major histocompatibility complex class I gene promoter. Similarly, ICSBP repressed expression of chloramphenicol acetyltransferase reporters driven by the ISREs of the 2'-5' oligoadenylate synthetase, guanylate-binding protein, and ISG-15 genes in IFN-treated cells. The repression was dependent on the presence of the ISRE in the reporter. Deletion analysis showed that the putative N-terminal DNA binding domain of ICSBP by itself is capable of mediating the repression. Using the same cotransfection conditions as for ICSBP, a similar repression of these reporters was observed with IRF-2. Finally, ICSBP repressed the IRF-1-mediated induction of major histocompatibility complex class I and IFN-beta reporters in the absence of IFN or retinoic acid. Taken together, these results suggest that ICSBP is a negative regulatory factor capable of repressing transcription of target genes induced by IFN, retinoic acid, or IRF-1.

Human interferon consensus sequence binding protein is a negative regulator of enhancer elements common to interferon-inducible genes.

The promoter regions of many interferon-inducible genes share a short DNA sequence motif, termed the interferon consensus sequence (ICS) to which several regulatory proteins bind. A murine cDNA which encodes an ICS binding protein has been reported (M-ICSBP). The cloning of the human homologue of ICSBP (H-ICSBP) is described. H-ICSBP shares high sequence homology with its murine cognate. The derived sequence of H-ICSBP reveals restricted homology within the first 120 amino acids to three other interferon regulatory factors, IRF-1, IRF-2, and ISGF3 gamma. Truncated ICSBP lacking the first 33 amino-terminal amino acids fails to bind to the ICS, indicating that at least part of the DNA binding domain is located within the well conserved amino terminus. H-ICSBP is expressed exclusively in cell lines of hematopoietic origin. The results of transient transfection assays carried out either in hematopoietic or nonhematopoietic cells suggest that ICSBP acts as a negative regulatory factor on ICS-containing promoters. Furthermore, either interferon-gamma (IFN-gamma) or IFN-beta can alleviate the repression mediated by ICSBP. Therefore, ICSBP may be involved in maintaining submaximal transcriptional activity of IFN-inducible genes in hematopoietic cells. IFN treatment would then alleviate repression allowing maximal transcriptional activity of these genes.

Mechanisms of tumor necrosis factor action.

Tumor necrosis factor (TNF) is able to induce a great diversity of cellular responses via modulating the expression of a number of different genes. The multitude of TNF activities may be explained by both structural and functional heterogeneity in TNF receptors as well as by a diversification of postreceptor signal transduction pathways. Purification of TNF receptors has revealed two major, distinct binding proteins (TR60 and TR80). TR60 seems to be an essential component for TNF signaling; the functional role of TR80 remains to be elucidated. The pathway of postreceptor signal transduction involves phospholipase A2, a phosphatidylcholine-specific phospholipase C, protein kinase C, and other serine/threonine and tyrosine-specific protein kinases with as yet unknown function. At the receiving end of TNF signaling, induction of gene expression is mediated through activation of nuclear transcription factors, such as NFkB, AP-1, IRF-1, and NF-GMa.

Modulation of interferon consensus sequence binding protein mRNA in murine peritoneal macrophages. Induction by IFN-gamma and down-regulation by IFN-alpha, dexamethasone, and protein kinase inhibitors.

IFN play a central role in the activation of macrophages by inducing the expression of several proteins which, in turn, result in increased functional capabilities. Homologous interferon responsive sequences have been found in many IFN-inducible genes, and the gene for a protein that binds these sequences (interferon consensus sequence binding protein, ICSBP) has recently been cloned. In this study, the regulation of ICSBP mRNA induction by IFN-gamma was characterized in murine thioglycolate-elicited peritoneal macrophages. Northern blot analysis revealed two ICSBP mRNA species from these cells. Steady-state levels of both of these species were elevated by IFN-gamma at doses consistent with many IFN-gamma-induced macrophage functional responses. ICSBP mRNA levels increased within 1 h of IFN-gamma treatment, peaked between 4 and 6 h, and subsequently declined to approach baseline levels by approximately 24 h. IFN-alpha, at a concentration shown previously to modulate macrophage surface markers and functions, had no effect on ICSBP message levels alone, but antagonized the IFN-gamma-induction of ICSBP mRNA. IFN-gamma-induction of ICSBP mRNA is resistant to cycloheximide but sensitive to protein kinase inhibitors (H7, H8, HA-1004, staurosporine) at doses that suggest that protein kinase C is a likely target. ICSBP mRNA induction is also inhibited by dexamethasone, a synthetic glucocorticoid, well known as an anti-inflammatory drug capable of influencing gene expression in macrophages. The characterization of ICSBP mRNA regulation should help identify functions for this putative IFN trans-acting factor in macrophage activation.

Structure-activity relationships of cephem analogs

Abstract

Fertility in 47,XXX and 45,X patients.

Female patients with a sex chromosome abnormality may be fertile. In patients with a 47,XXX cell line there appears to be an increased risk of a cytogenetically abnormal child but the extent of this risk cannot yet be determined; it is probably lower in the non-mosaic 47,XXX patient than the mosaic 46,XX/47,XXX one. Patients with a 45,X cell line rarly become pregnant, and when they do they appear to have a high risk of an abnormal child or repeated unsuccessfuly pregnancies; this risk is certainly exaggerated by the method of reporting; when the poor reproductive perforamcne is first identified leading to the recognition of the maternal cytogenetic fault, the reproductive failure rate is naturally high; when the maternal fault is first identified and the reproductive history then established far better results are evident.