Characterization of the 5' flanking region and gene encoding the mouse interferon-gamma receptor

Epigenetic reprogramming around IFN1 and IFNy2 promoters in rainbow trout cells inoculated with infectious pancreatic necrosis virus (IPNV)

Infectious pancreatic necrosis virus (IPNV) has proven to effectively evade the host antiviral responses. This study clarifies whether the modulation of the antiviral immune response exerted by IPNV involves epigenetic mechanisms. An in-silico characterization of the rainbow trout IFN1 and IFNγ2 promoters was performed, identifying the islands or sequences rich in CpG dinucleotides and the putative transcription factor binding sites (TBS) for both gene promoters. RTS11 cells (rainbow trout monocyte/macrophage) were infected with IPNV, and the course of viral infection was followed up to 48 h post infection (hpi). Infected cells showed increased IFN1 and IFNγ2 transcriptional expression at 6 and 24 hpi, respectively. IPNV infection caused increases and decreases in global IFNγ2 promoter methylation at 6 and 24 hpi, respectively. The CpG dinucleotides at positions -392 and + 38 of this promoter were the most sensitive to methylation changes. The IFN1 promoter remained fully unmethylated during the course of the infection, similar to the control. The changes in the methylation pattern observed for the IFNγ2 promoter were coincident with the changes in DNA methyltransferase (DNMT) expression levels, increasing at 6 hpi and decreasing below basal level at 24 hpi. Similarly, the H4 histones associated with the IFN1 and IFNγ2 promoters were hyperacetylated at 6 hpi, subsequently decreasing their acetylation below basal levels at 24 hpi, in both promoters. Coincidentally with the above, overexpression of histone acetyltransferase (HAT) was observed at 6 hpi and of histone deacetylase (HDAC) at 24 hpi, with return to baseline of HAT. These results suggest that IPNV would epigenetically modulate the expression of IFN1 by changing acetylation levels of the histones H4 associated with its promoter. Also, the modulation of the expression of IFNy2 would be by switching methylation/demethylation levels of its promoter, in addition to changes in acetylation levels of histones H4 associated with this promoter. This study is the first to demonstrate the effect of epigenetic reprogramming after IPNV infection in salmonid cells, demonstrating that promoter methylation/demethylation level and changes in the histone code associated with promoters may play a role in the modulation of the immune response induced by the virus.

Genomic structure and characterization of mRNA expression pattern of porcine interferon gamma receptor 1 gene

Interferon gamma receptor (IFNGR) plays an important role in the biological effects of IFN-γ. In this study, porcine IFNGR1 cDNA was cloned and two transcripts both having a coding region of 1413 bp were identified. Porcine IFNGR1 cDNA shares 62.95%, 63.73%, 72.90% and 81.10% identity in nucleotide sequence; and 45.64%, 46.69%, 58.04% and 72.55% homology in amino acid sequence to those of rat, mouse, human and cattle, respectively. The porcine IFNGR1 genomic structure consists of seven exons and six introns and is located on porcine chromosome 1. The mRNA expression of porcine IFNGR1 gene is detected in all tissues examined, with strong expression in spleen and liver tissues and weak expression in cerebrum, cerebellum and uterus tissues, respectively. A different developmental pattern in IFNGR1 mRNA expression between Laiwu and Duroc breeds was revealed by real-time quantitative RT-PCR: in Duroc pigs, a significantly higher expression was found in the tissues of heart (P<0.05), liver (P<0.01), kidney (P<0.01) and skeletal muscle (P<0.05) of adult pigs compared to piglets. In porcine reproductive and respiratory syndrome virus (PRRSV)-infected Dapulian pigs, compared to the uninfected ones, the expression level of IFNGR1 mRNA in spleen was significantly up-regulated (P<0.05), whereas its expression in the lymph node was significantly down-regulated (P<0.05); in PRRSV-infected Duroc × Yorkshire × Landrace commercial pigs, however, the differences both in spleen and lymph node tissues were not significant.

Modulation of gamma interferon receptor 1 by Mycobacterium tuberculosis: a potential immune response evasive mechanism

Mycobacterium tuberculosis inhibits gamma interferon (IFN-gamma)-mediated antimycobacterial action by adopting diverse mechanisms. IFN-gamma binds to its receptor, IFN-gammaR, in order to initiate proper signaling. We have observed reduced surface expression levels of IFN-gamma receptor 1 (IFN-gammaR1) in untreated pulmonary tuberculosis patients compared to those in healthy individuals (P < 0.01). Following antitubercular therapy, the expression of IFN-gammaR1 was restored in these patients. To delineate the mechanism by which M. tuberculosis modulates IFN-gammaR1, in vitro experiments were designed, wherein the down modulation of IFN-gammaR1 surface expression was observed for CD14+ cells in peripheral blood mononuclear cells (PBMCs) cocultured with live M. tuberculosis compared to that for uninfected cells (P < 0.01). No modulation of IFN-gammaR1 expression was observed for CD14+ cells in PBMCs infected with Mycobacterium smegmatis. A time-dependent decrease in IFN-gammaR1 mRNA expression was observed for PBMCs infected with M. tuberculosis. Similar down modulation of IFN-gammaR1 protein and mRNA expression in phorbol myristate acetate-differentiated THP-1 cells (pdTHP-1) by M. tuberculosis was observed (P < 0.01). Using reporter gene analysis of 5' deletion constructs of the IFN-gammaR1 gene (IFNGR1) promoter, the decrease in IFN-gammaR1 mRNA in M. tuberculosis-infected pdTHP-1 cells was shown to be due to the decreased transcription of IFNGR1. By immunoblotting and electrophoretic mobility shift assays, the down regulation of stimulating protein 1 (Sp1) expression and its recruitment on the phorbol ester-responsive element of the IFNGR1 promoter in M. tuberculosis-infected pdTHP-1 cells was observed. This down regulation of Sp1 in pdTHP-1 cells cocultured with M. tuberculosis may be responsible for the down regulation of IFN-gammaR1 expression, thereby potentially altering its receptivity to IFN-gamma.

Cholera toxin potentiates influences of IFN-gamma through activation of NF-kappaB and release of tumor necrosis factor-alpha

Cholera toxin (Ctx) is a potent adjuvant in the mucosal immune system. Previous studies have indicated that Ctx induces intestinal interferon-gamma (IFN-gamma) production and that adjuvant properties require activation of the IFN-gamma receptor (IFNGR). Thus, we hypothesized that Ctx potentiates IFN-gamma responses in intestinal epithelia. Initial studies suggested that Ctx enhances IFN-gamma-mediated barrier disruption in cultured intestinal epithelia. This response was attributable to liberation of a soluble mediator into conditioned supernatants, subsequently identified as tumor necrosis factor-alpha (TNF-alpha). Extensions of these findings revealed that the Ctx A subunit induces transcriptional activation of proinflammatory genes in addition to TNF-alpha (interleukin-8 [IL- 8], intracellular adhesion molecule-1 [ICAM-1], and IL-6) and that such transactivation is mediated by the transcriptional regulator NF-kappaB. We conclude that Ctx elicits a proinflammatory phenotype in intestinal epithelia and that potentiation of IFN-gamma-mediated barrier disruption by TNF-alpha may contribute to the overall adjuvant properties of Ctx.

Toll-like receptor 2 stimulation decreases IFN-gamma receptor expression in mouse RAW264.7 macrophages

Interferon-gamma (IFN-gamma) is a key cytokine in the immune defense against mycobacteria. IFN-gamma activates macrophages to resist the growth of mycobacteria and induces expression of MHC class II molecules required for antigen presentation. Macrophages infected with mycobacteria or stimulated by the interaction of mycobacterial products with toll-like receptor 2 (TLR2) have reduced responses to IFN-gamma. Previous research has shown that infection of mouse macrophages with Mycobacterium avium causes decreased expression of the IFN-gamma receptor (IFNGR). In the present study, we show that TLR2 stimulation of RAW264.7 macrophages with a synthetic lipoprotein, Pam3CSK4, also causes rapid decrease in expression of IFNGR-1 protein, with little change in IFNGR-2 protein levels. The decrease in IFNGR-2 expression in TLR2-stimulated cells required receptor internalization and proteasomal degradation. The level of IFNGR-1 mRNA also decreased in TLR2-stimulated RAW264.7 cells and M. avium-infected cells. The decrease in IFNGR-1 mRNA was shown to be due to decreased transcription. In spite of the decrease in IFNGR-2 receptor expression, activation of Stat1 activation by an optimal dose of IFN-gamma was identical between control and TLR2-stimulated RAW264.7 cells. However, at low suboptimal doses of IFN-gamma, Stat1 activation was decreased in TLR2-stimulated cells.

Interferon-gamma receptor polymorphisms determine strain differences in accessibility of activated lymphocyte NK-triggering antigens to recognition by self-reactive NK cells

The "NK-triggering-antigen regulator" (Nktar) gene is a locus identified in the C57BL/6 genome which regulates the ability of unlabeled activated Con A blasts to compete for recognition of labeled syngeneic Con A blasts by BALB/c NK cells. Linkage analysis on Con A blasts from (BALB/c x CByB6F1) N2 backcross progeny for (1) relative level of competitive inhibition of BALB/c NK lysis of syngeneic Con A blasts and (2) genotypes at polymorphic microsatellite markers distributed throughout the mouse genome mapped the Nktar gene locus to a 5-cM region of chromosome 10 containing the interferon-gamma receptor (Ifngr) gene locus. N2 Con A blasts exhibited an inverse relationship between (a) their cell surface density of IFN-gammaR molecules detected by FACS with monoclonal anti-CD119 and (b) their cold target inhibition of BALB/c NK self-reactivity. Con A blasts from Ifngr(-/-) knockout mice showed a relatively high level of inhibition of BALB/c NK self-lysis and a relatively low level of class I MHC, which were both reversed by transient transfection with the Ifngr gene. Sequencing studies showed that Balb/c Ifngr encodes a Gly(69) whereas C57BL/6 Ifngr encodes Glu(69) due to a difference at nucleotide 284. Sequencing studies of N2 progeny demonstrated 100% concordance between their Nktar inhibitory phenotype and their Ifngr genotype. These findings demonstrate that the Nktar and Ifngr loci are identical. They further indicate that polymorphisms related to the Ifngr locus and affecting expression of cell surface IFN-gammaR may underlie genetic differences in the availability of NK-triggering antigens (NKTAgs) to recognition by self-reactive BALB/c NK cells by differentially affecting the ability of IFN-gammaR molecules to mediate up-regulation of NKTAg-masking class I molecules.

Comparative Genomic Analysis of the Interferon/Interleukin-10 Receptor Gene Cluster

Interferons and interleukin-10 are involved in key aspects of the host defence mechanisms. Human chromosome 21 harbors the interferon/interleukin-10 receptor gene cluster linked to theGART gene. This cluster includes both components of the interferon α/β-receptor (IFNAR1 and IFNAR2) and the second components of the interferon γ-receptor (IFNGR2) and of the IL-10 receptor (IL10R2). We report here the complete gene content of this GART–cytokine receptor gene cluster and the use of comparative genomic analysis to identify chicken IFNAR1, IFNAR2, andIL10R2. We show that the large-scale structure of this locus is conserved in human and chicken but not in the pufferfish Fugu rubripes. This establishes that the receptor components of these host defense mechanisms were fixed in an ancestor of the amniotes. The extraordinary diversification of the interferon ligand family during the evolution of birds and mammals has therefore occured in the context of a fixed receptor structure.

[The sequence data described in this paper have been submitted to GenBank under accession nos.AF039904, AF039905, AF039906, AF039907, AF045606, AF082664, AF082665,AF082666, AF082667, and AF083221.]

A new mouse mutation causing male sterility and histoincompatibility

Male sterility and histoincompatibility, mshi, is an autosomal recessive mutation in BALB/cBy mice that causes reduced testis size and sterility in homozygous males. The testes of homozygous mutants are highly disorganized and appear to have a block in the regulation of male germ cell proliferation. No heterozygous effect is detectable. Reproduction is unaffected in females carrying the mutation. The mutation also affects histocompatibility; most homozygous males and females reject sex-matched skin grafts from BALB/cBy mice. We used an intercross between BALB/cBy and CAST/Ei to map the mshi mutation to the proximal end of Chromosome (Chr) 10. The most likely gene order places the mutation between D10Mit80 and D10Mit16, near the interferon gamma receptor locus, Ifgr, which may be a candidate gene for this mutation.

Characterization of the promoter of the human KAL gene, responsible for the X-chromosome-linked Kallmann syndrome

We report on the first characterization of the human KAL promoter (pKAL), based on the analysis of a 2-kb fragment of the 5' flanking region. As determined by primer extension, transcription of the human KAL gene is initiated at two different sites in the quail embryonic neuroretina QNR/D cell line. The promoter region is G+C rich and contains a CCAAT box, two binding sites for the SP1 transcription factor and two AP2-binding sites, but no TATA box. It also shares a motif with several neural-specific genes. The ability of four deletion mutants to drive transcription of the heterologous chloramphenicol acetyltransferase (CAT)-encoding gene was determined in transfection experiments. The mutant containing the KAL sequence from nt +2 to -435 demonstrated a tissue-specific, although weak, transcriptional activity only in the quail embryonic neuroretina K2 and QNR/D cell lines. Longer constructs did not confer any activity. Therefore, we suggest that this 437-bp segment of pKAL constitutes a neural-specific promoter which could be negatively controlled by upstream sequences.