The Experts below are selected from a list of 1863 Experts worldwide ranked by ideXlab platform

Dimitris Thanos - One of the best experts on this subject based on the ideXlab platform.

  • The transcriptional code of human IFN-beta gene expression.
    Biochimica et biophysica acta, 2010
    Co-Authors: Ethan Ford, Dimitris Thanos
    Abstract:

    Activation of interferon-beta transcription is a highly ordered process beginning with the delivery of NF-kappaB to the IFN-beta enhancer through a process involving stochastic interchromosomal interactions between the IFN-beta enhancer and specialized Alu elements. NF-kappaB delivery is followed by the binding of ATF-2/c-Jun and IRF proteins in a highly cooperative fashion. The assembled "Enhanceosome" then recruits PCAF/GCN5 which acetylates the histone tails of the adjacent nucleosomes. The transcriptional coactivator CBP, which binds in a complex with the RNA polymerase II holoenzyme is recruited by the Enhanceosome replacing PCAF/GCN5. Next, SWI/SNF, which is part of the holoenzyme complex, induces a conformational change in a nucleosome positioned over the transcriptional start site allowing TFIID to bind, which promotes the sliding of this nucleosome to a new downstream position. At this point the full pre-initiation complex is assembled and transcription commences. This detailed picture of the IFN-beta transcription program gathered through years of rigorous studies, now serves as a paradigm for understanding complex transcriptional switches in eukaryotic systems.

  • The transcriptional code of human IFN-β gene expression
    Biochimica et Biophysica Acta, 2010
    Co-Authors: Ethan Ford, Dimitris Thanos
    Abstract:

    Activation of interferon-beta transcription is a highly ordered process beginning with the delivery of NF-kappaB to the IFN-beta enhancer through a process involving stochastic interchromosomal interactions between the IFN-beta enhancer and specialized Alu elements. NF-kappaB delivery is followed by the binding of ATF-2/c-Jun and IRF proteins in a highly cooperative fashion. The assembled "Enhanceosome" then recruits PCAF/GCN5 which acetylates the histone tails of the adjacent nucleosomes. The transcriptional coactivator CBP, which binds in a complex with the RNA polymerase II holoenzyme is recruited by the Enhanceosome replacing PCAF/GCN5. Next, SWI/SNF, which is part of the holoenzyme complex, induces a conformational change in a nucleosome positioned over the transcriptional start site allowing TFIID to bind, which promotes the sliding of this nucleosome to a new downstream position. At this point the full pre-initiation complex is assembled and transcription commences. This detailed picture of the IFN-beta transcription program gathered through years of rigorous studies, now serves as a paradigm for understanding complex transcriptional switches in eukaryotic systems.

  • virus infection induces nf κb dependent interchromosomal associations mediating monoallelic ifn β gene expression
    Cell, 2008
    Co-Authors: Effie Apostolou, Dimitris Thanos
    Abstract:

    Transcriptional activation of the IFN-β gene by virus infection requires the cooperative assembly of an Enhanceosome. We report that the stochastic and monoallelic expression of the IFN-β gene depends on interchromosomal associations with three identified distinct genetic loci that could mediate binding of the limiting transcription factor NF-κB to the IFN-β enhancer, thus triggering Enhanceosome assembly and activation of transcription from this allele. The probability of a cell to express IFN-β is dramatically increased when the cell is transfected with any of these loci. The secreted IFN-β protein induces high-level expression of the Enhanceosome factor IRF-7, which in turn promotes Enhanceosome assembly and IFN-β transcription from the remaining alleles and in other initially nonexpressing cells. Thus, the IFN-β enhancer functions in a nonlinear fashion by working as a signal amplifier.

  • Modifying gene expression programs by altering core promoter chromatin architecture.
    Cell, 2002
    Co-Authors: Stavros Lomvardas, Dimitris Thanos
    Abstract:

    Transcriptional activation of the IFN-β gene in response to virus infection requires the assembly of an Enhanceosome, which instructs a recruitment program of chromatin modifiers/remodelers and general transcription factors to the promoter. This program culminates with sliding of a nucleosome blocking the core promoter to a downstream position, a prerequisite for transcriptional activation. We show that delivery of this nucleosome to the same downstream position to create an accessible IFN-β core promoter prior to Enhanceosome assembly results in major changes in the gene expression program with regard to the temporal pattern and the signal specificity of the transcriptional response. Thus, the identity of a gene expression program is achieved and maintained by the dynamic interplay between specific Enhanceosomes and specific local chromatin structure.

  • Coordination of a Transcriptional Switch by HMGI(Y) Acetylation
    Science (New York N.Y.), 2001
    Co-Authors: Nikhil V. Munshi, Menie Merika, Theodora Agalioti, Guoying Chen, Stavros Lomvardas, Dimitris Thanos
    Abstract:

    Dynamic control of interferon-beta (IFN-beta) gene expression requires the regulated assembly and disassembly of the Enhanceosome, a higher-order nucleoprotein complex formed in response to virus infection. The Enhanceosome activates transcription by recruiting the histone acetyltransferase proteins CREB binding protein (CBP) and p300/CBP-associated factors (PCAF)/GCN5, which, in addition to modifying histones, acetylate HMGI(Y), the architectural component required for Enhanceosome assembly. We show that the accurate execution of the IFN-beta transcriptional switch depends on the ordered acetylation of the high-mobility group I protein HMGI(Y) by PCAF/GCN5 and CBP, which acetylate HMGI(Y) at distinct lysine residues on endogenous promoters. Whereas acetylation of HMGI(Y) by CBP at lysine-65 destabilizes the Enhanceosome, acetylation of HMGI(Y) by PCAF/GCN5 at lysine-71 potentiates transcription by stabilizing the Enhanceosome and preventing acetylation by CBP.

Walter Reith - One of the best experts on this subject based on the ideXlab platform.

  • NLRC5 exclusively transactivates MHC class I and related genes through a distinctive SXY module.
    PLoS genetics, 2015
    Co-Authors: Kristina Ludigs, Walter Reith, Queralt Seguín-estévez, Sylvain Lemeille, Isabel Ferrero, Giorgia Rota, Sonia T. Chelbi, Chantal Mattmann, H. Robson Macdonald, Greta Guarda
    Abstract:

    MHC class II (MHCII) genes are transactivated by the NOD-like receptor (NLR) family member CIITA, which is recruited to SXY enhancers of MHCII promoters via a DNA-binding “Enhanceosome” complex. NLRC5, another NLR protein, was recently found to control transcription of MHC class I (MHCI) genes. However, detailed understanding of NLRC5’s target gene specificity and mechanism of action remained lacking. We performed ChIP-sequencing experiments to gain comprehensive information on NLRC5-regulated genes. In addition to classical MHCI genes, we exclusively identified novel targets encoding non-classical MHCI molecules having important functions in immunity and tolerance. ChIP-sequencing performed with Rfx5−/− cells, which lack the pivotal Enhanceosome factor RFX5, demonstrated its strict requirement for NLRC5 recruitment. Accordingly, Rfx5-knockout mice phenocopy Nlrc5 deficiency with respect to defective MHCI expression. Analysis of B cell lines lacking RFX5, RFXAP, or RFXANK further corroborated the importance of the Enhanceosome for MHCI expression. Although recruited by common DNA-binding factors, CIITA and NLRC5 exhibit non-redundant functions, shown here using double-deficient Nlrc5−/−CIIta−/− mice. These paradoxical findings were resolved by using a “de novo” motif-discovery approach showing that the SXY consensus sequence occupied by NLRC5 in vivo diverges significantly from that occupied by CIITA. These sequence differences were sufficient to determine preferential occupation and transactivation by NLRC5 or CIITA, respectively, and the S box was found to be the essential feature conferring NLRC5 specificity. These results broaden our knowledge on the transcriptional activities of NLRC5 and CIITA, revealing their dependence on shared Enhanceosome factors but their recruitment to distinct enhancer motifs in vivo. Furthermore, we demonstrated selectivity of NLRC5 for genes encoding MHCI or related proteins, rendering it an attractive target for therapeutic intervention. NLRC5 and CIITA thus emerge as paradigms for a novel class of transcriptional regulators dedicated for transactivating extremely few, phylogenetically related genes.

  • New Functions of the Major Histocompatibility Complex Class II-Specific Transcription Factor RFXANK Revealed by a High-Resolution Mutagenesis Study
    Molecular and cellular biology, 2005
    Co-Authors: Michal Krawczyk, Krzysztof Masternak, Madeleine Zufferey, Emmanuèle Barras, Walter Reith
    Abstract:

    The transcription factors RFX and CIITA are major players in regulation of the expression of all classical and nonclassical major histocompatibility complex class II (MHC-II) genes. RFX nucleates the formation of a multiprotein complex, called the MHC-II Enhanceosome, on MHC-II promoters. Assembly of this Enhanceosome is an obligatory step for recruitment of the coactivator CIITA and thus for activation of MHC-II gene transcription. We have analyzed the function of the ankyrin repeat-containing protein RFXANK, which forms the heterotrimeric RFX complex together with RFX5 and RFXAP. We discovered that ANKRA2, the closest paralogue of RFXANK, can substitute for RFXANK in the activation of MHC-II genes and that this ability is mediated by its ankyrin repeat domain (ARD). This finding provided the basis for a high-resolution structure-function analysis of the ARD of RFXANK, which allowed us to map the RFX5 interaction domain and residues critical for assembly of the RFX complex. We also found that mutations in the fourth ankyrin repeat of RFXANK abolish assembly of the Enhanceosome on MHC-II promoters in vivo but not in vitro, suggesting a new role of RFXANK in facilitating promoter occupation in the context of chromatin.

  • the s box of major histocompatibility complex class ii promoters is a key determinant for recruitment of the transcriptional co activator ciita
    Journal of Biological Chemistry, 2004
    Co-Authors: Annick Muhlethalermottet, Krzysztof Masternak, Michal Krawczyk, Charalambos Spilianakis, Androniki Kretsovali, Joseph Papamatheakis, Walter Reith
    Abstract:

    Tightly regulated expression of major histocompatibility complex (MHC) class II genes is critical for the immune system. A conserved regulatory module consisting of four cis-acting elements, the W, X, X2 and Y boxes, controls transcription of MHC class II genes. The X, X2, and Y boxes are bound, respectively, by RFX, CREB, and NF-Y to form a MHC class II-specific Enhanceosome complex. The latter constitutes a landing pad for recruitment of the transcriptional co-activator CIITA. In contrast to the well defined roles of the X, X2, and Y boxes, the role of the W region has remained controversial. In vitro binding studies have suggested that it might contain a second RFX-binding site. We demonstrate here by means of promoter pull-down assays that the most conserved subsequence within the W region, called the S box, is a critical determinant for tethering of CIITA to the Enhanceosome complex. Binding of CIITA to the Enhanceosome requires both integrity of the S box and a remarkably stringent spacing between the S and X boxes. Even a 1-2-base pair change in the native S-X distance is detrimental for CIITA recruitment and promoter function. In contrast to current models, binding of RFX to a putative duplicated binding site in the W box is thus not required for either CIITA recruitment or promoter activity. This paves the way for the identification of novel factors mediating the contribution of the S box to the activation of MHC class II promoters.

  • CIITA and the MHCII Enhanceosome in the Regulation of MHCII Expression
    Current Genomics, 2003
    Co-Authors: Salomé Landmann, Krzysztof Masternak, Jean-marc Waldburger, Annick Mühlethaler-mottet, Walter Reith
    Abstract:

    Major Histocompatibility Complex class II (MHCII) molecules direct the development, activation and homeostasis of CD4+ T cells. Given these key functions it is not surprising that the absence of MHCII expression results in a severe primary immunodeficiency disease called MHCII deficiency or the Bare Lymphocyte Syndrome (BLS). The genetic defects responsible for BLS lie in genes encoding transcription factors required for MHCII expression. Four different MHCII regulatory genes encoding RFXANK, RFX5, RFXAP and CIITA have been identified. The first three are subunits of RFX, a ubiquitously expressed factor that binds cooperatively with other proteins to MHCII and related promoters to form a highly stable macromolecular nucleoprotein complex referred to as the MHCII Enhanceosome. This Enhanceosome serves as a landing pad for the MHCII transactivator CIITA. CIITA is a non-DNA binding coactivator that serves as the master control factor for MHCII expression. The highly regulated expression pattern of CIITA ultimately dictates the cell type specificity, induction and level of MHCII expression. The Enhanceosome and CIITA collaborate in activating transcription by promoting histone hyperacetylation and by recruiting components of the general transcription machinery. In this review we summarize what is known about the molecular basis of BLS and what this has taught us about the mechanisms regulating transcription of MHCII and related genes. Particular attention is devoted to the structure, function and mode of action of the MHCII Enhanceosome and CIITA. In addition, we focus on the highly regulated and cell type specific expression of CIITA.

  • Promoter-specific functions of CIITA and the MHC class II Enhanceosome in transcriptional activation
    The EMBO journal, 2002
    Co-Authors: Krzysztof Masternak, Walter Reith
    Abstract:

    Transcription of the major histocompatibility complex class II family of genes is regulated by conserved promoter elements and two gene-specific trans-activators, RFX and CIITA. RFX binds DNA and nucleates the assembly of an Enhanceosome, which recruits CIITA through protein--protein interactions. Transcriptional activation is a complex, multi-step process involving chromatin modification and recruitment of the transcription apparatus. To examine the roles of the Enhanceosome and CIITA in these processes, we analysed the level of promoter-associated hyperacetylated histones H3 and H4, TBP, TFIIB and RNA poly merase II in cells lacking RFX or CIITA. We compared four genes co-regulated by RFX and CIITA (HLA-DRA, HLA-DPB, HLA-DMB and Ii) and found that the Enhanceosome and CIITA make variable, promoter-dependent contributions to histone acetylation and transcription apparatus recruitment. CIITA is generally implicated at multiple levels of the activation process, while the Enhanceosome contributes in a CIITA-independent manner only at certain promoters. Our results support the general notion that the impact of a particular activator on transcription in vivo may vary depending on the promoter and the chromatin context.

Tom Maniatis - One of the best experts on this subject based on the ideXlab platform.

  • An atomic model of the interferon-beta Enhanceosome.
    Cell, 2007
    Co-Authors: Daniel Panne, Tom Maniatis, Stephen C. Harrison
    Abstract:

    Transcriptional activation of the interferon-beta (IFN-beta) gene requires assembly of an Enhanceosome containing ATF-2/c-Jun, IRF-3/IRF-7, and NFkappaB. These factors bind cooperatively to the IFN-beta enhancer and recruit coactivators and chromatin-remodeling proteins to the IFN-beta promoter. We describe here a crystal structure of the DNA-binding domains of IRF-3, IRF-7, and NFkappaB, bound to one half of the enhancer, and use a previously described structure of the remaining half to assemble a complete picture of Enhanceosome architecture in the vicinity of the DNA. Association of eight proteins with the enhancer creates a continuous surface for recognizing a composite DNA-binding element. Paucity of local protein-protein contacts suggests that cooperative occupancy of the enhancer comes from both binding-induced changes in DNA conformation and interactions with additional components such as CBP. Contacts with virtually every nucleotide pair account for the evolutionary invariance of the enhancer sequence.

  • Ordered Recruitment of Chromatin Modifying and General Transcription Factors to the IFN-β Promoter
    Cell, 2000
    Co-Authors: Theodora Agalioti, Junming Yie, Tom Maniatis, Stavros Lomvardas, Bhavin S. Parekh, Dimitris Thanos
    Abstract:

    Summary SAGA complex, together with the CBP/p300 proteins, bear intrinsic histone acetyltransferase activities and Here, we show that the IFN-b Enhanceosome activates function as coactivators of transcription after their retranscription by directing the ordered recruitment of cruitment to promoters via their interaction with numerchromatin modifying and general transcription factors ous DNA binding proteins, and in several cases, the to the IFN-b promoter. The Enhanceosome is assem- histone acetyltransferase activity of these complexes bled in the nucleosome-free enhancer region of the

  • assembly of a functional beta interferon Enhanceosome is dependent on atf 2 c jun heterodimer orientation
    Molecular and Cellular Biology, 2000
    Co-Authors: James V Falvo, Bhavin S. Parekh, Ernest Fraenkel, Tom Maniatis
    Abstract:

    Heterodimeric transcription factors, including the basic region-leucine zipper (bZIP) protein ATF-2–c-jun, are well-characterized components of an Enhanceosome that mediates virus induction of the human beta interferon (IFN-β) gene. Here we report that within the IFN-β Enhanceosome the ATF-2–c-jun heterodimer binds in a specific orientation, which is required for assembly of a complex between ATF-2–c-jun and interferon regulatory factor 3 (IRF-3). We demonstrate that correct orientation of the ATF-2–c-jun binding site is required for virus induction of the IFN-β gene and for IRF-3-dependent activation of a composite ATF-2– c-jun–IRF site in the IFN-β promoter. We also show that in vitro the DNA-bound ATF-2–c-jun heterodimer adopts a fixed orientation upon the binding of IRF-3 at an adjacent site in the IFN-β enhancer and that the DNA-binding domain of IRF-3 is sufficient to mediate this effect. In addition, we show that the DNA-binding domain of ATF-2 is necessary and sufficient for selective protein-protein interactions with IRF-3. Strikingly, in vivo chromatin immunoprecipitation experiments with IFN-β reporter constructs reveal that recruitment of IRF-3 to the IFN-β promoter upon virus infection is dependent on the orientation of the ATF-2–c-jun heterodimer binding site. These observations demonstrate functional and physical cooperativity between the bZIP and IRF transcription factor families and illustrate the critical role of heterodimeric transcription factors in formation of the IFN-β Enhanceosome.

  • Efficient recruitment of TFIIB and CBP-RNA polymerase II holoenzyme by an interferon-β Enhanceosome in vitro
    Proceedings of the National Academy of Sciences of the United States of America, 1998
    Co-Authors: Tae Kook Kim, Tae Hoon Kim, Tom Maniatis
    Abstract:

    The transcriptional activity of an in vitro assembled human interferon-β gene Enhanceosome is highly synergistic. This synergy requires five distinct transcriptional activator proteins (ATF2/c-JUN, interferon regulatory factor 1, and p50/p65 of NF-κB), the high mobility group protein HMG I(Y), and the correct alignment of protein-binding sites on the face of the DNA double helix. Here, we investigate the mechanisms of Enhanceosome-dependent transcriptional synergy during preinitiation complex assembly in vitro. We show that the stereospecific assembly of the Enhanceosome is critical for the efficient recruitment of TFIIB into a template-committed TFIID-TFIIA-USA (upstream stimulatory activity complex) and for the subsequent recruitment of the RNA polymerase II holoenzyme complex. In addition, we provide evidence that recruitment of the holoenzyme by the Enhanceosome is due, at least in part, to interactions between the Enhanceosome and the transcriptional coactivator CREB, cAMP responsive element binding protein (CBP). These studies reveal a unique role of Enhanceosomes in the cooperative assembly of the transcription machinery on the human interferon-β promoter.

  • The Mechanism of Transcriptional Synergy of an In Vitro Assembled Interferon-β Enhanceosome
    Molecular cell, 1997
    Co-Authors: Tae Kook Kim, Tom Maniatis
    Abstract:

    Abstract A functional interferon-β gene Enhanceosome was assembled in vitro using the purified recombinant transcriptional activator proteins ATF2/c-JUN, IRF1, and p50/p65 of NF-κB. Maximal levels of transcriptional synergy between these activators required the specific interactions with the architectural protein HMG I(Y) and the correct helical phasing of the binding sites of these proteins on the DNA helix. Analyses of the in vitro assembled Enhanceosome revealed that the transcriptional synergy is due, at least in part, to the cooperative assembly and stability of the complex. Reconstitution experiments showed that the formation of a stable Enhanceosome-dependent preinitiation complex requires cooperative interactions between the Enhanceosome; the general transcription factors TFIID, TFIIA, and TFIIB; and the cofactor USA. These studies provide a direct biochemical demonstration of the importance of the structure and function of natural multicomponent transcriptional enhancer complexes in gene regulation.

Mariann Bienz - One of the best experts on this subject based on the ideXlab platform.

  • Bcl9 and Pygo synergise downstream of Apc to effect intestinal neoplasia in FAP mouse models.
    Nature communications, 2019
    Co-Authors: Juliusz Mieszczanek, Laurens M. Van Tienen, Ashraf E. K. Ibrahim, Douglas J. Winton, Mariann Bienz
    Abstract:

    Bcl9 and Pygo are Wnt Enhanceosome components that effect β-catenin-dependent transcription. Whether they mediate β-catenin-dependent neoplasia is unclear. Here we assess their roles in intestinal tumourigenesis initiated by Apc loss-of-function (ApcMin), or by Apc1322T encoding a partially-functional Apc truncation commonly found in colorectal carcinomas. Intestinal deletion of Bcl9 extends disease-free survival in both models, and essentially cures Apc1322T mice of their neoplasia. Loss-of-Bcl9 synergises with loss-of-Pygo to shift gene expression within Apc-mutant adenomas from stem cell-like to differentiation along Notch-regulated secretory lineages. Bcl9 loss also promotes tumour retention in ApcMin mice, apparently via relocating nuclear β-catenin to the cell surface, but this undesirable effect is not seen in Apc1322T mice whose Apc truncation retains partial function in regulating β-catenin. Our results demonstrate a key role of the Wnt Enhanceosome in β-catenin-dependent intestinal tumourigenesis and reveal the potential of BCL9 as a therapeutic target during early stages of colorectal cancer.

  • Bcl9 and Pygo synergise downstream of Apc to effect intestinal neoplasia in FAP mouse models
    Nature Publishing Group, 2019
    Co-Authors: Juliusz Mieszczanek, Laurens M. Van Tienen, Ashraf E. K. Ibrahim, Douglas J. Winton, Mariann Bienz
    Abstract:

    BCL9 and Pygo are components of Wnt Enhanceosome, which facilitates β-catenin-dependent transcription. Here, the authors show that deletion of Bcl9 and Pygo suppresses tumorigenesis and extends disease free survival in two different colorectal cancer models, suggesting a strategy for drugging β-catenin signalling in this cancer

  • Constitutive scaffolding of multiple Wnt Enhanceosome components by Legless/BCL9
    eLife, 2017
    Co-Authors: Laurens M. Van Tienen, Juliusz Mieszczanek, Marc Fiedler, Trevor J. Rutherford, Mariann Bienz
    Abstract:

    In every animal, different cells must be able to communicate with each other to make sure that the body is correctly formed and maintained. Animal cells have many ways of communicating, but one important and well-studied mechanism involves a signaling molecule called Wnt that is released by some cells and received by others. The Wnt molecule and its effects are similar in all animals, and over-active Wnt signaling in humans contributes to a number of diseases including various cancers. The Wnt signal is carried from the surface of the receiving cell to the DNA in its nucleus via a protein called β-catenin. The β-catenin protein then helps to switch on a large number of genes. However, to do this β-catenin must interact with an assembly of other proteins collectively called the Wnt Enhanceosome. There are still many unknowns about how exactly β-catenin cooperates with the Enhanceosome. Now, van Tienen et al. investigated one component of the Wnt/β-catenin pathway called BCL9/B9L: a large protein that contains a number of flexible regions. First, a biochemical technique called BioID was used with human embryonic kidney cells to determine the proteins that BCL9/B9L encounters during a 12-hour period. This technique can detect when two proteins come close together, even if the interaction is weak or does not last very long. The BioID experiments showed that BCL9/B9L is close to two proteins in the Wnt Enhanceosome in addition to β-catenin, and other techniques were used to confirm that one of these proteins contacts BCL9/B9L directly. The experiments also showed that BCL9/B9L acted as a tether to bring β-catenin close to the protein within the Enhanceosome that binds to the DNA. Importantly, BCL9/B9L interacted with the Enhanceosome both in the presence and absence of Wnt, indicating that the assembly is ready to switch genes on as soon as β-catenin reaches the DNA. Next, van Tienen et al. confirmed that the parts of BCL9/B9L that bind to the Enhanceosome are important for its activity by using a gene-editing technology called CRISPR/Cas9 to essentially delete them both in the human cells and in fruit flies. Unexpectedly, the BioID experiments also revealed that BCL9/B9L binds to proteins that transmit signals from molecules other than Wnt, in particular from hormones such as estrogen and androgen. Future experiments could explore if, and how, BCL9/B9L integrates these signals from hormones with the signal from Wnt. A better understanding of this process might have important implications for the treatment of certain cancers, such as breast and prostate cancers that can be driven by over-active hormone signals.

  • constitutive scaffolding of multiple wnt Enhanceosome components by legless bcl9
    eLife, 2017
    Co-Authors: Laurens M. Van Tienen, Juliusz Mieszczanek, Marc Fiedler, Trevor J. Rutherford, Mariann Bienz
    Abstract:

    In every animal, different cells must be able to communicate with each other to make sure that the body is correctly formed and maintained. Animal cells have many ways of communicating, but one important and well-studied mechanism involves a signaling molecule called Wnt that is released by some cells and received by others. The Wnt molecule and its effects are similar in all animals, and over-active Wnt signaling in humans contributes to a number of diseases including various cancers. The Wnt signal is carried from the surface of the receiving cell to the DNA in its nucleus via a protein called β-catenin. The β-catenin protein then helps to switch on a large number of genes. However, to do this β-catenin must interact with an assembly of other proteins collectively called the Wnt Enhanceosome. There are still many unknowns about how exactly β-catenin cooperates with the Enhanceosome. Now, van Tienen et al. investigated one component of the Wnt/β-catenin pathway called BCL9/B9L: a large protein that contains a number of flexible regions. First, a biochemical technique called BioID was used with human embryonic kidney cells to determine the proteins that BCL9/B9L encounters during a 12-hour period. This technique can detect when two proteins come close together, even if the interaction is weak or does not last very long. The BioID experiments showed that BCL9/B9L is close to two proteins in the Wnt Enhanceosome in addition to β-catenin, and other techniques were used to confirm that one of these proteins contacts BCL9/B9L directly. The experiments also showed that BCL9/B9L acted as a tether to bring β-catenin close to the protein within the Enhanceosome that binds to the DNA. Importantly, BCL9/B9L interacted with the Enhanceosome both in the presence and absence of Wnt, indicating that the assembly is ready to switch genes on as soon as β-catenin reaches the DNA. Next, van Tienen et al. confirmed that the parts of BCL9/B9L that bind to the Enhanceosome are important for its activity by using a gene-editing technology called CRISPR/Cas9 to essentially delete them both in the human cells and in fruit flies. Unexpectedly, the BioID experiments also revealed that BCL9/B9L binds to proteins that transmit signals from molecules other than Wnt, in particular from hormones such as estrogen and androgen. Future experiments could explore if, and how, BCL9/B9L integrates these signals from hormones with the signal from Wnt. A better understanding of this process might have important implications for the treatment of certain cancers, such as breast and prostate cancers that can be driven by over-active hormone signals.

  • An ancient Pygo-dependent Wnt Enhanceosome integrated by Chip/LDB-SSDP
    eLife, 2015
    Co-Authors: Marc Fiedler, Juliusz Mieszczanek, Trevor J. Rutherford, Michael Graeb, Christopher M. Johnson, Mariann Bienz
    Abstract:

    In animals, cells have to be able to communicate with neighboring cells in order to generate and maintain the different tissues and organs. One ancient method of cell communication that is used in all animals is the Wnt signaling pathway. In this pathway, a cell secretes a protein called Wnt, which binds to a Wnt receptor present on the surface of another cell. This triggers a cascade of signals inside the second cell that leads to the activation of proteins called TCF factors. These proteins bind to regions of DNA called enhancers to trigger the expression of particular genes that control the development of the animal. Hyperactive Wnt signaling in humans can result in cancer, so Wnt signaling is tightly controlled to avoid this. One of the proteins that regulates Wnt signaling is called Groucho and it interacts with TCF to prevent it from activating genes in the absence of a Wnt signal. However, when Wnt is present, a protein called Pygo overcomes this repression by Groucho to activate TCF, but it is not clear how this works. Fiedler, Graeb, Mieszczanek et al. discovered that Pygo directly binds to a protein complex called Chip/LDB-SSDP (or ChiLS for short). ChiLS is able to associate with TCF enhancers through its association with Groucho. Fiedler, Graeb, Mieszczanek et al. observed that ChiLS can also interact with a number of other proteins that control body formation. This enables ChiLS to integrate multiple signals that regulate the activity of TCF factors. Fiedler, Graeb, Mieszczanek et al. named this complex the ‘Wnt Enhanceosome’ because it serves to activate the expression of genes in response to Wnt signaling. Fiedler, Graeb, Mieszczanek et al. analyzed the role of the Wnt Enhanceosome during the development of the fly wing and the embryo's midgut. Many genes that are required to form these organs were switched on by the Wnt Enhanceosome. This study shows that ChiLS and Pygo are core components of a large complex of proteins that regulate animal development. The next challenge is to study how the components of this complex work together to regulate the enhancers in response to different signals.

Charles Després - One of the best experts on this subject based on the ideXlab platform.

  • The BTB/POZ Domain of the Arabidopsis Disease Resistance Protein NPR1 Interacts with the Repression Domain of TGA2 to Negate Its Function
    The Plant Cell, 2009
    Co-Authors: Patrick Boyle, Amanda Rochon, Heather Shearer, Jhadeswar Murmu, Jee Yan Chu, Pierre R. Fobert, Charles Després
    Abstract:

    TGA2 and NONEXPRESSER OF PR GENES1 (NPR1) are activators of systemic acquired resistance (SAR) and of the SAR marker gene pathogenesis-related-1 (PR-1) in Arabidopsis thaliana. TGA2 is a transcriptional repressor required for basal repression of PR-1, but during SAR, TGA2 recruits NPR1 as part of an Enhanceosome. Transactivation by the Enhanceosome requires the NPR1 BTB/POZ domain. However, the NPR1 BTB/POZ domain does not contain an autonomous transactivation domain; thus, its molecular role within the Enhanceosome remains elusive. We now show by gel filtration analyses that TGA2 binds DNA as a dimer, tetramer, or oligomer. Using in vivo plant transcription assays, we localize the repression domain of TGA2 to the N terminus and demonstrate that this domain is responsible for modulating the DNA binding activity of the oligomer both in vitro and in vivo. We confirm that the NPR1 BTB/POZ domain interacts with and negates the molecular function of the TGA2 repression domain by excluding TGA2 oligomers from cognate DNA. These data distinguish the NPR1 BTB/POZ domain from other known BTB/POZ domains and establish its molecular role in the context of the Arabidopsis PR-1 gene Enhanceosome.

  • the btb poz domain of the arabidopsis disease resistance protein npr1 interacts with the repression domain of tga2 to negate its function
    The Plant Cell, 2009
    Co-Authors: Patrick Boyle, Amanda Rochon, Heather Shearer, Jhadeswar Murmu, Jee Yan Chu, Pierre R. Fobert, Charles Després
    Abstract:

    TGA2 and NONEXPRESSER OF PR GENES1 (NPR1) are activators of systemic acquired resistance (SAR) and of the SAR marker gene pathogenesis-related-1 (PR-1) in Arabidopsis thaliana. TGA2 is a transcriptional repressor required for basal repression of PR-1, but during SAR, TGA2 recruits NPR1 as part of an Enhanceosome. Transactivation by the Enhanceosome requires the NPR1 BTB/POZ domain. However, the NPR1 BTB/POZ domain does not contain an autonomous transactivation domain; thus, its molecular role within the Enhanceosome remains elusive. We now show by gel filtration analyses that TGA2 binds DNA as a dimer, tetramer, or oligomer. Using in vivo plant transcription assays, we localize the repression domain of TGA2 to the N terminus and demonstrate that this domain is responsible for modulating the DNA binding activity of the oligomer both in vitro and in vivo. We confirm that the NPR1 BTB/POZ domain interacts with and negates the molecular function of the TGA2 repression domain by excluding TGA2 oligomers from cognate DNA. These data distinguish the NPR1 BTB/POZ domain from other known BTB/POZ domains and establish its molecular role in the context of the Arabidopsis PR-1 gene Enhanceosome.