Recent insights into Groucho co-repressor recruitment and function.
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ABSTRACT:
SUBMITTER: Kaul AK
PROVIDER: S-EPMC4422819 | biostudies-other | 2015
REPOSITORIES: biostudies-other
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Project description:Groucho (Gro) is a Drosophila co-repressor that regulates the expression of a large number of genes, many of which are involved in developmental control. Previous studies have shown that its central region is essential for function even though its three domains are poorly conserved and intrinsically disordered. Using these disordered domains as affinity reagents, we have now identified multiple embryonic Gro-interacting proteins. The interactors include protein complexes involved in chromosome organization, mRNA processing, and signaling. Further investigation of the interacting proteins using a reporter assay showed that many of them modulate Gro-mediated repression either positively or negatively. The positive regulators include components of the spliceosomal subcomplex U1 small nuclear ribonucleoprotein (U1 snRNP). A co-immunoprecipitation experiment confirms this finding and suggests that a sizable fraction of nuclear U1 snRNP is associated with Gro. The use of RNA-seq to analyze the gene expression profile of cells subjected to knockdown of Gro or snRNP-U1-C (a component of U1 snRNP) showed a significant overlap between genes regulated by these two factors. Furthermore, comparison of our RNA-seq data with Gro and RNA polymerase II ChIP data led to a number of insights, including the finding that Gro-repressed genes are enriched for promoter-proximal RNA polymerase II. We conclude that the Gro central domains mediate multiple interactions required for repression, thus functioning as a regulatory hub. Furthermore, interactions with the spliceosome may contribute to repression by Gro.
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Project description:Extracellular signals are transduced to the cell nucleus by effectors that bind to enhancer complexes to operate transcriptional switches. For example, the Wnt enhanceosome is a multiprotein complex associated with Wnt-responsive enhancers through T cell factors (TCF) and kept silent by Groucho/TLE co-repressors. Wnt-activated β-catenin binds to TCF to overcome this repression, but how it achieves this is unknown. Here, we discover that this process depends on the HECT E3 ubiquitin ligase Hyd/UBR5, which is required for Wnt signal responses in Drosophila and human cell lines downstream of activated Armadillo/β-catenin. We identify Groucho/TLE as a functionally relevant substrate, whose ubiquitylation by UBR5 is induced by Wnt signaling and conferred by β-catenin. Inactivation of TLE by UBR5-dependent ubiquitylation also involves VCP/p97, an AAA ATPase regulating the folding of various cellular substrates including ubiquitylated chromatin proteins. Thus, Groucho/TLE ubiquitylation by Hyd/UBR5 is a key prerequisite that enables Armadillo/β-catenin to activate transcription.
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Project description:T-box proteins are conserved transcription factors that play crucial roles in development of all metazoans; and, in humans, mutations affecting T-box genes are associated with a variety of congenital diseases and cancers. Despite the importance of this transcription factor family, very little is known regarding how T-box factors regulate gene expression. The Caenorhabditis elegans genome contains 21 T-box genes, and their characterized functions include cell fate specification in a variety of tissues. The C. elegans Tbx1 sub-family member MLS-1 functions during larval development to specify the fate of non-striated uterine muscles; and, in mls-1 mutants, uterine muscles are transformed to a vulval muscle fate. Here we demonstrate that MLS-1 function depends on binding to the Groucho-family co-repressor UNC-37. MLS-1 interacts with UNC-37 via a conserved eh1 motif, and the MLS-1 eh1 motif is necessary for MLS-1 to specify uterine muscle fate. Moreover, unc-37 loss-of-function produces uterine muscle to vulval muscle fate transformation similar to those observed in mls-1 mutants. Based on these results, we conclude that MLS-1 specifies uterine muscle fate by repressing target gene expression, and this function depends on interaction with UNC-37. Moreover, we suggest that MLS-1 shares a common mechanism for transcriptional repression with related T-box factors in other animal phyla.
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Project description:Gene expression is regulated by the complex interaction between transcriptional activators and repressors, which function in part by recruiting histone-modifying enzymes to control accessibility of DNA to RNA polymerase. The evolutionarily conserved family of Groucho/Transducin-Like Enhancer of split (Gro/TLE) proteins act as co-repressors for numerous transcription factors. Gro/TLE proteins act in several key pathways during development (including Notch and Wnt signaling), and are implicated in the pathogenesis of several human cancers. Gro/TLE proteins form oligomers and it has been proposed that their ability to exert long-range repression on target genes involves oligomerization over broad regions of chromatin. However, analysis of an endogenous gro mutation in Drosophila revealed that oligomerization of Gro is not always obligatory for repression in vivo. We have used chromatin immunoprecipitation followed by DNA sequencing (ChIP-seq) to profile Gro recruitment in two Drosophila cell lines. We find that Gro predominantly binds at discrete peaks (<1 kilobase). We also demonstrate that blocking Gro oligomerization does not reduce peak width as would be expected if Gro oligomerization induced spreading along the chromatin from the site of recruitment. Gro recruitment is enriched in "active" chromatin containing developmentally regulated genes. However, Gro binding is associated with local regions containing hypoacetylated histones H3 and H4, which is indicative of chromatin that is not fully open for efficient transcription. We also find that peaks of Gro binding frequently overlap the transcription start sites of expressed genes that exhibit strong RNA polymerase pausing and that depletion of Gro leads to release of polymerase pausing and increased transcription at a bona fide target gene. Our results demonstrate that Gro is recruited to local sites by transcription factors to attenuate rather than silence gene expression by promoting histone deacetylation and polymerase pausing.
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Project description:Groucho-related genes (GRGs) are transcriptional co-repressors that are crucial for many developmental processes. Several essential pancreatic transcription factors are capable of interacting with GRGs; however, the in vivo role of GRG-mediated transcriptional repression in pancreas development is still not well understood. In this study, we used complex mouse genetics and transcriptomic analyses to determine that GRG3 is essential for β cell development, and in the absence of Grg3 there is compensatory upregulation of Grg4Grg3/4 double mutant mice have severe dysregulation of the pancreas gene program with ectopic expression of canonical liver genes and Foxa1, a master regulator of the liver program. Neurod1, an essential β cell transcription factor and predicted target of Foxa1, becomes downregulated in Grg3/4 mutants, resulting in reduced β cell proliferation, hyperglycemia, and early lethality. These findings uncover novel functions of GRG-mediated repression during pancreas development.
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Project description:Histone deacetylase 3 (HDAC3) and nuclear receptor co-repressor (NCoR1/2) are epigenetic regulators that play a key role in gene expression and metabolism. HDAC3 is a class I histone deacetylase that functions as a transcriptional co-repressor, modulating gene expression by removing acetyl groups from histones and non-histone proteins. NCoR1, on the other hand, is a transcriptional co-repressor that interacts with nuclear hormone receptors, including peroxisome proliferator-activated receptor gamma (PPARγ) and liver X receptor (LXR), to regulate metabolic gene expression. Recent research has revealed a functional link between HDAC3 and NCoR1 in the regulation of metabolic gene expression. Genetic deletion of HDAC3 in mouse models has been shown to improve glucose intolerance and insulin sensitivity in the liver, skeletal muscle, and adipose tissue. Similarly, genetic deletion of NCoR1 has improved insulin resistance and reduced adiposity in mouse models. Dysregulation of this interaction has been associated with the development of cardio-metabolic diseases such as cardiovascular diseases, obesity and type 2 diabetes, suggesting that targeting this pathway may hold promise for the development of novel therapeutic interventions. In this review, we summarize the current understanding of individual functions of HDAC3 and NCoR1/2 and the co-repressor complex formation (HDAC3/NCoR1/2) in different metabolic tissues. Further studies are needed to thoroughly understand the mechanisms through which HDAC3, and NCoR1/2 govern metabolic processes and the implications for treating metabolic diseases.
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Project description:Transcriptional repressors function primarily by recruiting co-repressors, which are accessory proteins that antagonize transcription by modifying chromatin structure. Although a repressor could function by recruiting just a single co-repressor, many can recruit more than one, with Drosophila Brinker (Brk) recruiting the co-repressors CtBP and Groucho (Gro), in addition to possessing a third repression domain, 3R. Previous studies indicated that Gro is sufficient for Brk to repress targets in the wing, questioning why it should need to recruit CtBP, a short-range co-repressor, when Gro is known to be able to function over longer distances. To resolve this we have used genomic engineering to generate a series of brk mutants that are unable to recruit Gro, CtBP and/or have 3R deleted. These reveal that although the recruitment of Gro is necessary and can be sufficient for Brk to make an almost morphologically wild-type fly, it is insufficient during oogenesis, where Brk must utilize CtBP and 3R to pattern the egg shell appropriately. Gro insufficiency during oogenesis can be explained by its downregulation in Brk-expressing cells through phosphorylation downstream of EGFR signaling.
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Project description:The Drosophila Groucho (Gro) protein was the founding member of the family of transcriptional co-repressor proteins that now includes the transducin-like enhancer of split (TLE) and Grorelated gene (Grg) proteins in vertebrates. Gro family proteins do not bind DNA directly, but are recruited by a diverse profile of transcription factors, including members of the Hes, Runx, Nkx, LEF1/Tcf, Pax, Six and c-Myc families. The primary structure of Gro proteins includes five identifiable regions, of which the most highly conserved are the amino-terminal glutamine-rich Q domain and the carboxy-terminal WD-repeat domain. The Q domain contains two coiled-coil motifs that facilitate oligomerization into tetramers and binding to some transcription factors. The WD domain folds to form a beta-propeller, which mediates protein-protein interactions. Many transcription factors interact with the WD domain via a short peptide motif that falls into either of two classes: WRPW and related tetrapeptides; and the 'eh1' motif (FxIxxIL). Gro family proteins are broadly expressed during development and in the adult. They have essential functions in many developmental pathways (including Notch and Wnt signaling) and are implicated in the pathogenesis of some cancers. The molecular mechanisms through which Gro proteins act to repress transcription are not yet well understood. It is becoming clear that Gro proteins have different modes of action in vivo dependent on biological context and these include direct and indirect modification of chromatin structure at target genes.
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