In vivo evidence of interaction between interferon-stimulated gene factors and the interferon-stimulated response element

The important roles of type I interferon and interferon-inducible genes in systemic lupus erythematosus

Systemic lupus erythematosus (SLE) is a severe autoimmune disease that causes multiple-organ dysfunction mainly affecting women in their childbearing years. Type I IFN synthesis is usually triggered by viruses, and its production is tightly regulated and limited in time in health individuals. However, many patients with systemic autoimmune diseases including SLE have signs of aberrant production of type I interferon (IFN) and display an increased expression of IFN-inducible genes. Continuous type I IFNs derived from activated plasmacytoid dendritic cells (pDCs) by interferogenic immune complexes (ICs) and migration of these cells to tissues both break immune tolerance and promote an on-going autoimmune reaction in human body. By the means of detecting type I IFNs and IFN-inducible genes, it can help with diagnosis and evaluation of SLE in early stage and more efficiently. Anti-IFN-α monoclonal antibodies in SLE patients were recently reported and is now being investigated in phase II clinical trails. In this review, we focus on recent research progress in type I IFN and IFN-inducible genes. Possible mechanisms behind the dysregulated type I IFN system in SLE and how they contribute to the development of an autoimmune process, and act as a biomarker and therapeutic target will be reviewed.

Plasma membrane biophysical properties linked to the antiproliferative effect of interferon-alpha

The relationship of plasma membrane biophysical properties to the anti-proliferative effect of interferon-alpha (IFN-alpha) was investigated in Daudi lymphoblasts cell lines with sensitivity to growth inhibition, parallel clonal variants selected for resistance, and one revertant subclone. Lateral mobility of surface differentiation antigens (I2, CD19, CD20, and sIgM-kappa) were measured by fluorescence recovery after photobleaching (FRAP). The mean diffusion coefficients, D, values for two clones of IFN-alpha resistant Daudi cells were significantly higher (D = 8.1-11 x 10(-10) cm2/sec) than for parental sensitive cells (D = 4.9-7.4 x 10(-10) cm2/sec). Microviscosity of the plasma membranes were probed by electron spin resonance (ESR) spectrometry. These results also indicate a greater degree of molecular motional freedom in resistant cells. Treatment of sensitive lymphoblasts with IFN-alpha (100-400 U/10(6) cells) for 5-30 min consistently increased mean values of D and the degree of spin-probe motional freedom, whereas no significant differences were detected in resistant cells. The effect of IFN-alpha on the membrane potential (Em) of Daudi cells was quantitated by flow cytometry using a voltage-sensitive oxonol dye. Membrane potential of all clones was similar (-50 to -56 mV). Treatment with IFN-alpha for 8-10 min caused hyperpolarization in the sensitive cells (deltaEm up to 45 mV), but only minimal hyperpolarization in the resistant ones (deltaEm up to 7 mV). We concluded that sensitivity to IFN-alpha and treatment with IFN-alpha are related to the biophysical status of plasma membranes.

Host defense responses to infection by Mycobacterium tuberculosis. Induction of IRF-1 and a serine protease inhibitor

Alveolar macrophages and newly recruited monocytes are targets of infection by Mycobacterium tuberculosis. Therefore, we examined the expression of interferon regulatory factor 1 (IRF-1), which plays an important role in host defense against M. tuberculosis, in undifferentiated and differentiated cells. Infection induced IRF-1 in both. IRF-1 from undifferentiated, uninfected monocytic cell lines was modified during extraction to produce specific species that were apparently smaller than intact IRF-1. After infection by M. tuberculosis or differentiation, intact IRF-1 was recovered. Subcellular fractions were assayed for the ability to modify IRF-1 or inhibit its modification. A serine protease on the cytoplasmic surface of an organelle or vesicle in the "lysosomal/mitochondrial" fraction from undifferentiated cells was responsible for the modification of IRF-1. Thus, the simplest explanation of the modification is cleavage of IRF-1 by the serine protease. Recovery of intact IRF-1 correlated with induction of a serine protease inhibitor that was able to significantly reduce the modification of IRF-1. The inhibitor was present in the cytoplasm of M. tuberculosis-infected or -differentiated cells. It is likely that induction of both IRF-1 and the serine protease inhibitor in response to infection by M. tuberculosis represent host defense mechanisms.

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 interferon-stimulable response elements of two human genes detect overlapping sets of transcription factors

We have previously reported three types of DNA-protein complexes, formed specifically with the interferon-stimulable response elements (ISRE) in the 5' flanking DNA of the interferon-inducible 6-16 and 9-27 genes, a type-I interferon-inducible early complex involving factor E (ISGF3), M and G complexes induced more slowly in response to type-I and type-II interferons, respectively and C1/C2, a constitutive complex(s). Similar complexes have been reported by others. The operationally defined band-shift complexes M, G and C1/C2 are shown here to be heterogeneous and to differ in their factor content, depending on the ISRE probe. With a 9-27 ISRE probe the M, G and C1/C2 complexes all contain the gamma subunit of ISGF3, which is present constitutively but is induced in response to IFN-alpha (to yield M) or IFN-gamma (to yield G). In contrast, a 6-16 ISRE probe forms band-shift complexes with IFN-alpha-inducible and IFN-gamma-inducible IRF1 and IRF2. With a 6-16 ISRE probe, therefore, M and G each correspond to two complexes which co-migrate in band-shift assays, one corresponding to IRF1, the other to IRF2. With this probe, the constitutive complex C1/C2 corresponds predominantly to IRF2. Consistent with this, IRF1 and IRF2 have lower affinity for the 9-27 ISRE than the 6-16 ISRE, whereas the reverse is true for E (ISGF3) and its gamma subunit. Relatively small differences in affinity appear sufficient to determine whether or not a band-shift complex is detected. In the case of IRF1 and IRF2, the different affinities for the 6-16 and 9-27 probes are dominated by a dinucleotide sequence in the centre of the 14-nucleotide 'core' ISRE. In contrast, preferential binding of E (ISGF3) by the 39-nucleotide 9-27 ISRE-containing sequence, although ISRE dependent, appears to be mediated by sequences 3' of the 'core' ISRE. Accordingly, these complexes can be simultaneously assayed using a hybrid probe consisting of the 5' flanking region and 'core' ISRE sequences from the 6-16 gene and sequences immediately 3' of the 'core' 9-27 ISRE sequence. No evidence was obtained for a modulatory role in factor binding for a pseudo-ISRE sequence close to ISRE in the 9-27 gene. The precise roles of IRF1 and IRF2 in the induction of IFN-beta and the control of interferon-inducible gene expression remain to be established.(ABSTRACT TRUNCATED AT 400 WORDS)

Interferon-gamma potentiates the antiviral activity and the expression of interferon-stimulated genes induced by interferon-alpha in U937 cells

Binding of type I interferon (IFN-alpha/beta) to specific receptors results in the rapid transcriptional activation, independent of protein synthesis, of IFN-alpha-stimulated genes (ISGs) in human fibroblasts and HeLa and Daudi cell lines. The binding of ISGF3 (IFN-stimulated gene factor 3) to the conserved IFN-stimulated response element (ISRE) results in transcriptional activation. This factor is composed of a DNA-binding protein (ISGF3 gamma), which normally is present in the cytoplasm, and other IFN-alpha-activated proteins which preexist as latent cytoplasmic precursors (ISGF3 alpha). We have found that ISG expression in the monocytic U937 cell line differs from most cell lines previously examined. U937 cells express both type I and type II IFN receptors, but only IFN-alpha is capable of inducing antiviral protection in these cells. Pretreatment with IFN-gamma potentiates the IFN-alpha-induced protection, but IFN-gamma alone does not have any antiviral activity. ISG15 mRNA accumulation in U937 cells is not detectable before 6 h of IFN-alpha treatment, peaks at 24 h, and requires protein synthesis. Although IFN-gamma alone does not induce ISG expression, IFN-gamma pretreatment markedly increases and hastens ISG expression and transcriptional induction. Nuclear extracts assayed for the presence of ISRE binding factors by electrophoretic mobility shift assays show that ISGF3 is induced by IFN-alpha within 6 h from undetectable basal levels in untreated U937 cells. Activation of ISGF3 alpha, the latent component of ISGF3, occurs rapidly. However, the increase in ISGF3 activity ultimately correlates with the accumulation of ISGF3 gamma induced by IFN-alpha or IFN-gamma.(ABSTRACT TRUNCATED AT 250 WORDS)

Transcriptional regulation of interferon-stimulated genes

Interferons (IFN) stimulate the expression of a number of genes following interaction with specific high-affinity plasma membrane receptors. The products of these genes either singly or coordinately mediate the antiviral, growth inhibitory or immunoregulatory activities attributed to IFN. While the gene products in some cases have been well characterized, other IFN-regulated genes encode proteins whose functions have yet to be elucidated. A feature common to all IFN-stimulated genes characterized thus far is the presence of a DNA element which constitutes an IFN-responsive enhancer, usually present in the 5' upstream region of the genes. This element, termed interferon-stimulated response element (ISRE) binds a nuclear factor(s) translocated from the cytoplasm to the nucleus following IFN-receptor-triggered signal transduction. The binding of these factors to the ISRE represents the initiating event in stimulating RNA-polymerase-II-mediated transcription from IFN-responsive genes. Depending on the nature of the cells responding to IFN and the genes involved, induced transcription may be prolonged or rapidly terminated. The rapid termination of transcription is dependent in some cases on IFN-induced protein synthesis and also involves factor binding to the ISRE. Recent progress in detailing these events will be discussed including IFN-receptor interactions, signal-transduction pathways, comparing and contrasting IFN-regulated genes and elucidation of IFN-regulated factors.

Signal transduction and transcriptional regulation of interferon-alpha-stimulated genes

Interferon-alpha (IFN-alpha) stimulates the expression of a number of genes in a pathway that begins with binding to specific high-affinity plasma membrane receptors. All IFN-alpha-stimulated genes cloned thus far are characterized by the presence of a DNA element, termed Interferon-Stimulated Response Element (ISRE), usually in the 5' upstream region of the genes. The ISRE binds a nuclear factor(s) following IFN-receptor triggered signal transduction and provides a convenient assay for the rapid phase of IFN-alpha signal transduction. This phase utilizes a phospholipase A2-generated second messenger which modulates ISRE-binding factors. Expression cloning has resulted in the identification of two specific ISRE-binding proteins that are candidates as signal recipients. Further advances in our understanding of the molecular mechanisms of IFN action may come through the use of yeast genetics. The human p68 kinase expressed in yeast has a growth inhibitory phenotype and provides a useful alternative system for analyzing components of the IFN-stimulated pathways.

Interleukin-6 induces the (2'-5') oligoadenylate synthetase gene in M1 cells through an effect on the interferon-responsive enhancer

Interleukin-6 (IL-6) activates (2'-5') A synthetase (2'-5' AS) gene expression in differentiating myeloleukemic M1 cells. Antibodies to type I interferon (IFN) inhibit 2'-5' AS induction but not differentiation. Analysis of the mechanism of 2'-5' AS induction shows that it does not result from increased IFN formation, but from a synergism between IL-6 and endogenously secreted IFN. IL-6 can activate expression of a CAT construct fused to the interferon response sequence (IRS) of the 2'-5' AS gene. In extracts of IL-6-treated M1 cells, changes in protein binding to IRS DNA can be demonstrated. One of the effects of IL-6 on M1 cells is, therefore, to induce DNA binding factors, some of which act on the same enhancer sequence as IFNs, resulting in a synergistic gene activation. M1 variants resistant to differentiation by IL-6 have lost the ability to induce the 2'-5' AS gene.

Constitutive in vitro binding of nuclear proteins to the 5'-flanking region of 6-16, a human gene inducible by alpha, beta-interferons

Proteins in nuclear extracts of HeLa cells that constitutively bound in vitro to three regions upstream of the interferon-inducible gene 6-16 were separated partially by chromatography on DEAE-Sepharose. Region one, a CCAAT box in the non-coding strand at position --63 to --67, was protected from DNase digestion by the bound protein(s) and was required for transcription in vitro. Region two, a tandem duplication sequence at position --89 to --168 contains two copies of a sequence essential for strong induction of the 6-16 gene by interferon in vitro. Region three, a palindromic sequence at position --449 to --465, not necessary for induction of 6-16 by interferon, was also protected from DNase digestion by nuclear protein(s). Templates with or without regions of two and three were transcribed equally well in extracts from interferon-treated or untreated cells.