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Shawn P. Murphy - One of the best experts on this subject based on the ideXlab platform.

  • Regulation of major histocompatibility complex Class II Gene expression in trophoblast cells
    Reproductive biology and endocrinology : RB&E, 2004
    Co-Authors: Shawn P. Murphy, Jason C. Choi, Renae Holtz
    Abstract:

    Trophoblast cells are unique because they are one of the few mammalian cell types that do not express major histocompatibility complex (MHC) Class II antigens, either constitutively or after exposure to IFN-γ. The absence of MHC Class II antigen expression on trophoblast cells has been postulated to be one of the essential mechanisms by which the semi-alloGeneic fetus evades immune rejection reactions by the maternal immune system. Consistent with this hypothesis, trophoblast cells from the placentas of women suffering from chronic inflammation of unknown etiology and spontaneous recurrent miscarriages have been reported to aberrantly express MHC Class II antigens. The lack of MHC Class II antigen expression on trophoblast cells is due to silencing of expression of the Class II transactivator (CIITA), a transacting factor that is essential for constitutive and IFN-γ-inducible MHC Class II Gene transcription. Transfection of trophoblast cells with CIITA expression vectors activates both MHC Class II and Class Ia antigen expression, which confers on trophoblast cells both the ability to activate helper T cells, and sensitivity to lysis by cytotoxic T lymphocytes. Collectively, these studies strongly suggest that stringent silencing of CIITA (and therefore MHC Class II) Gene expression in trophoblast cells is critical for the prevention of immune rejection responses against the fetus by the maternal immune system. The focus of this review is to summarize studies examining the novel mechanisms by which CIITA is silenced in trophoblast cells. The elucidation of the silencing of CIITA in trophoblast cells may shed light on how the semi-alloGeneic fetus evades immune rejection by the maternal immune system during pregnancy.

  • Repression of MHC Class II Gene transcription in trophoblast cells by novel single-stranded DNA binding proteins.
    Molecular reproduction and development, 1997
    Co-Authors: Shawn P. Murphy, Sandra O. Gollnick, Tamas Pazmany, Patricia Maier, Galina Elkin, Thomas B. Tomasi
    Abstract:

    The maintenance of the fetus during pregnancy has been attributed to the absence of major histocompatibility complex (MHC) Class II antigens on fetal trophoblastic cells that make contact with the maternal immune system. However, the mechanism(s) by which Class II Genes are regulated in trophoblast cells is unclear. We have identified a negative regulatory element (IAαNRE) in the promoter of the mouse Class II Gene IAα that represses IAα transcription in trophoblast cells. IAαNRE, located from −839 to −828, binds transacting factors from rat, mouse and human trophoblast cells, but not from 18 other cell lines tested. These results indicate that IAαNRE binding proteins (IAαNRE BPs) are conserved in species with hemochordial placentas, and suggest that IAαNRE binding activity is restricted primarily to trophoblast cells. Interestingly, the IAαNRE BPs bind to the IAαNRE antisense strand in a sequence-specific manner. IAαNRE represses transcription from the IAα promoter in a position-dependent manner, and has a minor down-regulatory effect on the activity of the SV40 promoter/enhancer. Our results demonstrate that MHC Class II Gene transcription is repressed in fetal trophoblast cells by sequence-specific, single-stranded DNA binding proteins, and suggest a possible mechanism by which the conceptus is protected from immune rejection during pregnancy.

Jack L. Strominger - One of the best experts on this subject based on the ideXlab platform.

  • A zinc finger protein that represses transcription of the human MHC Class II Gene, DPA.
    Journal of immunology (Baltimore Md. : 1950), 1996
    Co-Authors: Thomas Scholl, M. B. Stevens, Sanjeev Mahanta, Jack L. Strominger
    Abstract:

    The proximal promoters of all MHC Class II Genes contain a sequence element, the 19-bp X box, that is conserved in both sequence and position. Extensive analysis using a wide variety of approaches has demonstrated that the integrity of the X box is essential for transcription initiation from all Class II Genes studied. However, the X box is now recognized to contain two subregions, termed X1 and X2. Radiolabeled oligonucleotides corresponding to the X2 box of the MHC Class II Genes DPA and DQB were used to screen B cell and T cell expression libraries. A novel cDNA, termed XBR (X box repressor), encoding a putative zinc finger protein that binds specifically to the DPA X2 box was isolated from a human T cell line. The XBR Gene encodes a 7-kb message that is ubiquitously transcribed, although at higher levels in tissues of the lymphocytic compartment. Southern blots indicate that this Gene is single copy in primates and contains regions that are highly divergent in other species. Overexpression of XBR in a B cell line resulted in a dramatic reduction of transcription from a reporter Gene construct driven by the DPA promoter, but not from similar constructs with mutations in the X2 box. Similarly, overexpression of XBR reduced induction of reporter Gene activity driven from the DPA promoter in HeLa cells treated with IFN-gamma. XBR may, therefore, mediate transcriptional repression, thus preventing inappropriate MHC Class II expression. XBR function may in part explain the dominant trans-acting repression of MHC Class II expression reported in cell fusion experiments.

  • a factor that regulates the Class II major histocompatibility complex Gene dpa is a member of a subfamily of zinc finger proteins that includes a drosophila developmental control protein
    Molecular and Cellular Biology, 1994
    Co-Authors: Minoru Sugawara, Thomas Scholl, Paul D Ponath, Jack L. Strominger
    Abstract:

    A novel DNA sequence element termed the J element involved in the regulated expression of Class II major histocompatibility complex Genes was recently described. To study this element and its role in Class II Gene regulation further, a cDNA library was screened with oligonucleotide probes containing both the S element and the nearby J element of the human DPA Gene. Several DNA clones were obtained by this procedure, one of which, clone 18, is reported and characterized here. It encodes a protein predicted to contain 688 amino acid residues, including 11 zinc finger motifs of the C2H2 type in the C-terminal region, that are Kruppel-like in the conservation of the H/C link sequence connecting them. The 160 N-terminal amino acids in the nonfinger region of clone 18 are highly homologous with similar regions of several other human, mouse, and Drosophila sequences, defining a subfamily of Kruppel-like zinc finger proteins termed TAB (tramtrack [ttk]-associated box) here. One of the Drosophila sequences, ttk, is a developmental control Gene, while a second does not contain a zinc finger region but encodes a structure important in oocyte development. An acidic activation domain is located between the N-terminal conserved region of clone 18 and its zinc fingers. This protein appears to require both the S and J elements, which are separated by 10 bp for optimal binding. Antisense cDNA to clone 18 inhibited the expression of a reporter construct containing the DPA promoter, indicating its functional importance in the expression of this Class II Gene.

Jeremy M. Boss - One of the best experts on this subject based on the ideXlab platform.

  • Characterization of the RFX complex and the RFX5(L66A) mutant: implications for the regulation of MHC Class II Gene expression.
    Biochemistry, 2007
    Co-Authors: Colin W. Garvie, Jason R. Stagno, Sarah L. Reid, Ashina Singh, Erik Harrington, Jeremy M. Boss
    Abstract:

    Major histocompatability complex Class II (MHCII) molecules are an essential component of the mammalian adaptive immune response. The expression of MHCII Genes is regulated by a cell-specific multiprotein complex, termed the MHCII enhanceosome. The heterotrimeric RFX complex is the key DNA-binding component of the MHCII enhanceosome. The RFX complex is comprised of three proteins, RFXB, RFXAP, and RFX5, all of which are required for DNA binding and activation of MHCII Gene expression. Static light scattering and chemical cross-linking of the three RFX proteins show that RFXB and RFXAP are monomers and that RFX5 dimerizes through two separate domains. One of these domains, the oligomerization domain, promotes formation of a dimer of dimers of RFX5. In addition, we show that the RFX complex forms a 2:1:1 complex of RFX5.RFXAP.RFXB, which can associate with a further dimer of RFX5 to form a 4:1:1 complex through the oligomerization domain of RFX5. On the basis of these studies, we propose DNA-binding models for the interaction between the RFX complex and the MHCII promoter including a DNA looping model. We also provide direct evidence that the RFX5(L66A) point mutation prevents dimerization of the RFX complexes and propose a model for how this results in a loss of MHCII Gene expression.

  • Methylation of Class II trans-activator promoter IV: a novel mechanism of MHC Class II Gene control.
    Journal of immunology (Baltimore Md. : 1950), 2000
    Co-Authors: Ann C. Morris, Wendi E. Spangler, Jeremy M. Boss
    Abstract:

    Inhibition of Class II trans -activator (CIITA) expression prevents embryonic trophoblast cells from up-regulating MHC Class II Genes in response to IFN-γ. This is thought to be one mechanism of maternal tolerance to the fetal allograft. The CIITA Gene is regulated by four distinct promoters; promoter III directs constitutive (B cell) expression, and promoter IV regulates IFN-γ-inducible expression. Using in vivo genomic footprinting, promoter-reporter analysis, Southern blot analysis, and RT-PCR, we have examined the cause of CIITA silencing in a trophoblast-derived cell line. We report here that methylation of promoter IV DNA at CpG sites in Jar cells prevents promoter occupancy and IFN-γ-inducible transcription. The inhibition of CpG methylation in Jar cells by treatment with 5-aza-2′-deoxycytidine restores IFN-γ inducibility to CIITA. This is the first description of an epiGenetic mechanism involved in regulation of CIITA and MHC Class II Gene expression.

  • MHC Class II Gene silencing in trophoblast cells is caused by inhibition of CIITA expression.
    American journal of reproductive immunology (New York N.Y. : 1989), 1998
    Co-Authors: Ann C. Morris, James L. Riley, William H. Fleming, Jeremy M. Boss
    Abstract:

    PROBLEM: Major histocompatibility complex (MHC) Class II molecule expression is specifically suppressed on fetal trophoblasts, even in response to interferon (IFN)-γ, a potent inducer of MHC Class II Genes. The suppression of Class II induction has been suggested to play a role in preventing rejection of the fetal allograft. The mechanism of this suppression is unknown. METHOD OF STUDY: Human trophoblast cell lines were examined for expression of MHC Class II transcription factors and for activity of the IFN-γ signaling pathway. Additionally, trophoblast cells were transfected with a vector expressing the Class II transactivator, CIITA, and assayed for Class II expression. RESULTS: The MHC Class II transcription factors RFX and X2BP and the IFN-γ signaling pathway components are expressed constitutively and are functional in trophoblasts. However, CIITA expression was absent in trophoblasts and could not be induced by IFN-γ. Transfection of CIITA into trophoblast cells resulted in derepression of Class II Gene expression. CONCLUSIONS: The lack of induction of MHC Class II Genes in response to IFN-γ in trophoblast cells is caused neither by the absence of factors that bind Class II promoters, nor by a lesion in the IFN-γ signaling pathway, but results from a specific inhibition of the CIITA Gene.

Viktor Steimle - One of the best experts on this subject based on the ideXlab platform.

  • pml promotes mhc Class II Gene expression by stabilizing the Class II transactivator
    Journal of Cell Biology, 2012
    Co-Authors: Tobias Ulbricht, Viktor Steimle, Mohammad Alzrigat, Almut Horch, Nina Reuter, Anna Von Mikecz, Eberhard Schmitt, Oliver H Kramer, Thomas Stamminger
    Abstract:

    Promyelocytic leukemia (PML) nuclear bodies selectively associate with transcriptionally active genomic regions, including the Gene-rich major histocompatibility (MHC) locus. In this paper, we have explored potential links between PML and interferon (IFN)-γ–induced MHC Class II expression. IFN-γ induced a substantial increase in the spatial proximity between PML bodies and the MHC Class II Gene cluster in different human cell types. Knockdown experiments show that PML is required for efficient IFN-γ–induced MHC II Gene transcription through regulation of the Class II transactivator (CIITA). PML mediates this function through protection of CIITA from proteasomal degradation. We also show that PML isoform II specifically forms a stable complex with CIITA at PML bodies. These observations establish PML as a coregulator of IFN-γ–induced MHC Class II expression.

  • cIIta leucine rich repeats control nuclear localization in vivo recruitment to the major histocompatibility complex mhc Class II enhanceosome and mhc Class II Gene transactivation
    Molecular and Cellular Biology, 2000
    Co-Authors: Sandra B Hake, Walter Reith, Krzysztof Masternak, Claudia Kammerbauer, Christian Janzen, Viktor Steimle
    Abstract:

    The major histocompatibility complex (MHC) Class II transactivator CIITA plays a pivotal role in the control of the cellular immune response through the quantitative regulation of MHC Class II expression. We have analyzed a region of CIITA with similarity to leucine-rich repeats (LRRs). CIITA LRR alanine mutations abolish both the transactivation capacity of full-length CIITA and the dominant-negative phenotype of CIITA mutants with N-terminal deletions. We demonstrate direct interaction of CIITA with the MHC Class II promoter binding protein RFX5 and could also detect novel interactions with RFXANK, NF-YB, and -YC. However, none of these interactions is influenced by CIITA LRR mutaGenesis. On the other hand, chromatin immunoprecipitation shows that in vivo binding of CIITA to the MHC Class II promoter is dependent on LRR integrity. LRR mutations lead to an impaired nuclear localization of CIITA, indicating that a major function of the CIITA LRRs is in nucleocytoplasmic translocation. There is, however, evidence that the CIITA LRRs are also involved more directly in MHC Class II Gene transactivation. CIITA interacts with a novel protein of 33 kDa in a manner sensitive to LRR mutaGenesis. CIITA is therefore imported into the nucleus by an LRR-dependent mechanism, where it activates transcription through multiple protein-protein interactions with the MHC Class II promoter binding complex.

  • Complementation cloning of mammalian transcriptional regulators: the example of MHC Class II Gene regulators.
    Current opinion in genetics & development, 1995
    Co-Authors: Viktor Steimle, Bernard Mach
    Abstract:

    Abstract Cloning by complementation of mutant cell lines is a powerful way in which to identify and isolate important regulatory Genes on the basis of functional assays. The recent cloning of two essential regulators of major histocompatibility complex (MHC) Class II Gene expression has not only advanced our understanding of the complex mechanisms controlling these Genes, but also helps to illustrate the feasibility of this approach for the of mammalian Gene regulation.

  • developmental extinction of major histocompatibility complex Class II Gene expression in plasmocytes is mediated by silencing of the transactivator Gene cIIta
    Journal of Experimental Medicine, 1994
    Co-Authors: Paolo Silacci, Walter Reith, Viktor Steimle, A Mottet, Bernard Mach
    Abstract:

    Constitutive major histocompatibility complex (MHC) Class II Gene expression is tightly restricted to antigen presenting cells and is under developmental control. Cells of the B cell lineage acquire the capacity to express MHC Class II Genes early during ontogeny and lose this property during terminal differentiation into plasma cells. Cell fusion experiments have suggested that the extinction of MHC Class II expression in plasma cells is due to a dominant repression, but the underlying mechanisms are not understood. CIITA was recently identified as an MHC Class II transactivator that is essential for MHC Class II expression in B lymphocytes. We show here that inactivation of MHC Class II Genes in plasmocytes is associated with silencing of the CIITA Gene. Moreover, experimentally induced expression of CIITA in plasmocytes leads to reexpression of MHC Class II molecules to the same level as that observed on B lymphocytes. We therefore conclude that the loss of MHC Class II expression observed upon terminal differentiation of B lymphocytes into plasmocytes results from silencing of the transactivator Gene CIITA.

Josef Bryja - One of the best experts on this subject based on the ideXlab platform.

  • Association between the DQA MHC Class II Gene and Puumala virus infection in Myodes glareolus, the bank vole
    Infection Genetics and Evolution, 2008
    Co-Authors: Julie Deter, Josef Bryja, Maxime Galan, Yannick Chaval, Heikki Henttonen, Juha Laakkonen, Liina Voutilainen, Olli Vapalahti, Antti Vaheri, Alexis Ribas Salvador
    Abstract:

    Puumala virus (PUUV) is a hantavirus specifically harboured by the bank vole, Myodes (earlier Clethrionomys) glareolus. It causes a mild form of hemorrhagic fever with renal syndrome (HFRS) in humans, called Nephropathia epidemica (NE). The clinical severity of NE is variable among patients and depends on their major histocompatibility complex (MHC) Genetic background. In this study we investigated the potential role of Class II MHC Gene polymorphism in the susceptibility/resistance to PUUV in the wild reservoir M. glareolus. We performed an association study between the exon 2 of the DQA Gene and PUUV antibodies considering a natural population of bank voles. Because immune Gene polymorphism is likely to be driven by multiple parasites in the wild, we also screened bank voles for other potential viral and parasitic infections. We used multivariate analyses to explore DQA polymorphism/PUUV associations while considering the potential antagonist and/or synergistic effects of the whole parasite community. Our study suggests links between Class II MHC characteristics and viral infections including PUUV and Cowpox virus. Several alleles are likely to be involved in the susceptibility or in the resistance of bank voles to these infections. Alternatively, heterozygosity does not seem to be associated with PUUV or any other parasite infections. This result thus provides no evidence in favour of the hypothesis of selection through overdominance. Finally this multivariate approach reveals a strong antagonism between ectoparasitic mites and PUUV, suggesting direct or indirect immunoGenetic links between infections by these parasites. Other datasets are now required to confirm these results and to test whether the associations vary in space and/or time.

  • Analysis of major histocompatibility complex Class II Gene in water voles using capillary electrophoresis-single stranded conformation polymorphism
    Molecular Ecology Notes, 2005
    Co-Authors: Josef Bryja, Maxime Galan, Nathalie Charbonnel, Jean-francois Cosson
    Abstract:

    Analysis of a single strand conformation polymorphism (SSCP) using capillary electrophoresis (CE) is a novel method to study polymorphism of DNA sequences in large scale population studies. We optimized CE-SSCP analysis to study the major histocompatibility complex (MHC) Class II alpha Gene (DQA) polymorphism. Short-chain linear polyacrylamide (6%) as sieving matrix, TrisCl (pH 8.5) as buffer for sample dilution, and 27 ° C, 9 kV as electrophoresis parameters were suitable for sufficient resolution of all alleles. We found that almost 25% of clones contained a PCR (polymerase chain reaction) artefact and strict criteria have to be applied when using cloning and sequencing to analyse the allelic diversity of MHC Genes