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HOP interacts with enhancer of polycomb1 (Epc1). A, yeast one to one match experiment to confirm the interaction of HOP and Epc1. The pGBKT7-human HOP plasmid was co-transfected with pACT2-human EPC1 full into S. cerevisiae, and the interaction was seen by 5-bromo-4chloro-3-indolyl-D-galactopyranoside staining. B, immunoprecipitation analysis to show the physical interaction of HOP and EPC1 in mammalian cells. pCMV-human-flag-EPC1 constructs with either pcDNA3.1 (mock) or pcDNA3.1-mouse Hop-myc (Hop-myc) was transiently transfected into 293T cells and immunoprecipitated (IP) with-Myc antibody. After separation on SDS-polyacrylamide gel, EPC1 was detected with-FLAG antibody. C, co-localization of HOP and EPC1 in the nucleus. pcDNA3.1-HOP-V5/His and pCMV-myc-Epc1 were co-transfected to COS7, and fluorescent immunocytochemistry was done. Localizations of Epc1 (panel a) and Hop (panel b) as well as the nucleus (panel c) were seen. Merged image of panels a and b is provided in panel d.
Source publication
Homeodomain only protein, Hop, is an unusual small protein that modulates target gene transcription without direct binding
to DNA. Here we show that Hop interacts with Enhancer of Polycomb1 (Epc1), a homolog of a Drosophila polycomb group gene product that regulates transcription, to induce the skeletal muscle differentiation. Yeast two-hybrid
assa...
Contexts in source publication
Context 1
... confirm the interaction further, in vivo interaction assay in yeast was performed with pGBKT7-HOP and pACT2-Epc1. HOP did show a strong association with Epc1, although it had no apparent interaction with an empty pACT2 vector (Fig. 1A). To test if the interaction takes place in mammalian cells, we performed immunoprecipitation and found that Hop success- fully recruited Epc1 (Fig. ...
Context 2
... in vivo interaction assay in yeast was performed with pGBKT7-HOP and pACT2-Epc1. HOP did show a strong association with Epc1, although it had no apparent interaction with an empty pACT2 vector (Fig. 1A). To test if the interaction takes place in mammalian cells, we performed immunoprecipitation and found that Hop success- fully recruited Epc1 (Fig. ...
Context 3
... next tried to see the subcellular localization of Epc1 in relation to that of Hop by immunofluorescent staining. After transient transfection of both pCMV-myc-Epc1 and pcDNA3.1-HOP-V5/His, COS7 cells were stained with anti- Epc1 polyclonal and anti-V5 monoclonal antibodies. As shown in Fig. 1C, the majority of Epc1 (Fig. 1C, panel a) and Hop (Fig. 1C, panel b) was co-localized in the nucleus of COS7 cells, as demarcated by 4,6-diamidino-2-phenylindole nucleus staining (Fig. 1C, panel c). The merged image is shown in Fig. 1C, panel ...
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... next tried to see the subcellular localization of Epc1 in relation to that of Hop by immunofluorescent staining. After transient transfection of both pCMV-myc-Epc1 and pcDNA3.1-HOP-V5/His, COS7 cells were stained with anti- Epc1 polyclonal and anti-V5 monoclonal antibodies. As shown in Fig. 1C, the majority of Epc1 (Fig. 1C, panel a) and Hop (Fig. 1C, panel b) was co-localized in the nucleus of COS7 cells, as demarcated by 4,6-diamidino-2-phenylindole nucleus staining (Fig. 1C, panel c). The merged image is shown in Fig. 1C, panel ...
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... next tried to see the subcellular localization of Epc1 in relation to that of Hop by immunofluorescent staining. After transient transfection of both pCMV-myc-Epc1 and pcDNA3.1-HOP-V5/His, COS7 cells were stained with anti- Epc1 polyclonal and anti-V5 monoclonal antibodies. As shown in Fig. 1C, the majority of Epc1 (Fig. 1C, panel a) and Hop (Fig. 1C, panel b) was co-localized in the nucleus of COS7 cells, as demarcated by 4,6-diamidino-2-phenylindole nucleus staining (Fig. 1C, panel c). The merged image is shown in Fig. 1C, panel ...
Context 6
... transfection of both pCMV-myc-Epc1 and pcDNA3.1-HOP-V5/His, COS7 cells were stained with anti- Epc1 polyclonal and anti-V5 monoclonal antibodies. As shown in Fig. 1C, the majority of Epc1 (Fig. 1C, panel a) and Hop (Fig. 1C, panel b) was co-localized in the nucleus of COS7 cells, as demarcated by 4,6-diamidino-2-phenylindole nucleus staining (Fig. 1C, panel c). The merged image is shown in Fig. 1C, panel ...
Context 7
... COS7 cells were stained with anti- Epc1 polyclonal and anti-V5 monoclonal antibodies. As shown in Fig. 1C, the majority of Epc1 (Fig. 1C, panel a) and Hop (Fig. 1C, panel b) was co-localized in the nucleus of COS7 cells, as demarcated by 4,6-diamidino-2-phenylindole nucleus staining (Fig. 1C, panel c). The merged image is shown in Fig. 1C, panel ...
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... immunohistochem- istry with E13.5 to E17.5 embryo sections. Strong positive immuno- reactivity was detected in E13.5 heart (Fig. 3D, panel a), which dis- appeared completely by premixing the excess blocking peptides (Fig. 3D, panel b). However, Epc1 expres- sion in the heart (arrow in Fig. 3D, panel c, at E13.5) was gradually decreased by aging (Fig. 3D, panel d, E15.5, and Fig. 3D, panel e, E17.5 day). Interestingly, skeletal muscles such as tongue were gradually increased by aging (arrow in Fig. 3D, panel e), suggesting the differences in the expression patterns in both types of sarcomeric muscles. Epc1 was also well expressed in the endo- thelium, spinal ganglia, and cartilage. Although ...
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Citations
... A physical interaction between HOPX and Epc 1 was found in yeast and mammalian cells. For example, myogenin is activated and myotube formation is stimulated in H9c2 cells following co-transfection of HOPX and Epc 1, and Epc 1-mediated skeletal muscle differentiation was disrupted in HOPX-knockout mice [43]. ...
Simple Summary
Homeobox (HOX) genes encode homeodomain proteins that regulate a wide range of molecular pathways. The homeodomain is highly conserved and binds to DNA. One exception is homeodomain-only protein (HOPX) that lacks DNA-binding capacity. HOPX plays a crucial role in development and its functional impairment is associated with a variety of diseases, including cancer. Loss of HOPX function occurs in a wide range of cancer types, where it functions as a tumor suppressor gene. Understanding the molecular mechanisms by which HOPX regulates carcinogenesis will likely lead to the development of new therapeutic approaches.
Abstract
Homeobox genes are master regulators of morphogenesis and differentiation by acting at the top of genetic hierarchies and their deregulation is associated with a variety of human diseases. They usually contain a highly conserved sequence that codes for the homeodomain of the protein, a specialized motif with three α helices and an N-terminal arm that aids in DNA binding. However, one homeodomain protein, HOPX, is unique among its family members in that it lacks the capacity to bind DNA and instead functions by interacting with transcriptional regulators. HOPX plays crucial roles in organogenesis and is expressed in both embryonic and adult stem cells. Loss of HOPX expression is common in cancer, where it functions primarily as a tumor suppressor gene. In this review, we describe the function of HOPX in development and discuss its role in carcinogenesis.
... In the single case of EPC1-PHC2 fusion identified in CHE, the translocation results in the fusion of the highly conserved enhancer of polycomb A (EPcA) domain of EPC1 with PHC2 [64]. In yeast, a truncated Epc1 construct consists solely of the EPcA domain revealed to be essential for nuclear localization of Epc1 and interaction with Hop, a transcriptional regulator [78]. EPC1 rearrangements were previously found in ossifying fibromyxoid tumors (OFMT) and endometrial stromal sarcoma, but their oncogenesis is primarily unknown [79]. ...
Introduction
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Areas covered
This review will discuss the various vascular tumors for which recurrent gene fusions have been identified. The gene fusions and the presumed molecular mechanisms underlying tumorigenesis are shown, and potential implications for targeted therapies discussed The identification of these gene fusions in vascular tumors has improved diagnostic accuracy, especially since several of these fusions can be easily detected using surrogate immunohistochemical markers.
Expert opinion
The identification of gene fusions in a subset of vascular tumors over the past decade has improved diagnostic accuracy, and has provided the pathologists with novel diagnostic tools to accurately diagnose these often difficult tumors. Moreover, the increased understanding of the underlying molecular mechanisms can guide the development of targeted therapeutic strategies.
... SNPs in this region are found between B6 and C3H/HeJ and B6 and BALB/cJ. This locus contains a number of interesting candidate genes potentially relating to organismal fitness, including Epc1, a transcription factor linked to DNA repair, muscle differentiation and cancer suppression [42,43]. It is also the only gene within the locus whose expression has a suggestive Gxθ association with the locus itself (P = 0.014). ...
Background
The majority of quantitative genetic models used to map complex traits assume that alleles have similar effects across all individuals. Significant evidence suggests, however, that epistatic interactions modulate the impact of many alleles. Nevertheless, identifying epistatic interactions remains computationally and statistically challenging. In this work, we address some of these challenges by developing a statistical test for polygenic epistasis that determines whether the effect of an allele is altered by the global genetic ancestry proportion from distinct progenitors.
Results
We applied our method to data from mice and yeast. For the mice, we observed 49 significant genotype-by-ancestry interaction associations across 14 phenotypes as well as over 1,400 Bonferroni-corrected genotype-by-ancestry interaction associations for mouse gene expression data. For the yeast, we observed 92 significant genotype-by-ancestry interactions across 38 phenotypes. Given this evidence of epistasis, we test for and observe evidence of rapid selection pressure on ancestry specific polymorphisms within one of the cohorts, consistent with epistatic selection.
Conclusions
Unlike our prior work in human populations, we observe widespread evidence of ancestry-modified SNP effects, perhaps reflecting the greater divergence present in crosses using mice and yeast.
... The first and second MBT domains are reported to accommodate transcription factor YY1 in vitro (Alfieri et al., 2013), whereas the fourth MBT domain harboring the semi-aromatic cage is responsible for histone mark readout (Eryilmaz et al., 2009). EPC1 contains EPcA, EpcB, and EPcC domains at the N terminus (Kee et al., 2007). The C terminus of EPC1 was reported to interact with transcriptional repressor RFP (ret finger protein) (Tezel et al., 2002). ...
MBTD1, a H4K20me reader, has recently been identified as a component of the NuA4/TIP60 acetyltransferase complex, regulating gene expression and DNA repair. NuA4/TIP60 inhibits 53BP1 binding to chromatin through recognition of the H4K20me mark by MBTD1 and acetylation of H2AK15, blocking the ubiquitination mark required for 53BP1 localization at DNA breaks. The NuA4/TIP60 non-catalytic subunit EPC1 enlists MBTD1 into the complex, but the detailed molecular mechanism remains incompletely explored. Here, we present the crystal structure of the MBTD1-EPC1 complex, revealing a hydrophobic C-terminal fragment of EPC1 engaging the MBT repeats of MBTD1 in a site distinct from the H4K20me binding site. Different cellular assays validate the physiological significance of the key residues involved in the MBTD1-EPC1 interaction. Our study provides a structural framework for understanding the mechanism by which MBTD1 recruits the NuA4/TIP60 acetyltransferase complex to influence transcription and DNA repair pathway choice.
... Furthermore, Hopx knock-out mice show delays in hamstring muscle healing after injury, and skeletal myoblasts isolated from mice exhibit impaired differentiation [42]. In the skin, Takeda et al. found that Hopx+Lgr5+Shh-stem cells could escape catagen-induced apoptosis, and give rise to K6+ telogen-phase niche cells, thus do favor of regulating stem cell homeostasis of the hair follicle [43]. ...
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... The first and second MBT domains are reported to accommodate transcription factor YY1 in vitro (Alfieri et al., 2013), whereas the fourth MBT domain harboring the semi-aromatic cage is responsible for histone mark readout (Eryilmaz et al., 2009). EPC1 contains EPcA, EpcB and EPcC domains at the N-terminus (Kee et al., 2007). The C-terminus of EPC1 was reported to interact with transcriptional repressor RFP (Tezel et al., 2002). ...
MBTD1 has recently been identified to join the NuA4/TIP60 acetyltransferase complex to regulate gene expression and DNA repair. MBTD1 competes with 53BP1 for recognition of the H4K20me mark, while MBTD1-associated TIP60 carries out the acetylation of H2AK15 and thereby blocks the ubiquitylation-dependent association of 53BP1 to the sites of DNA double strand breaks. Interestingly, the non-catalytic subunit EPC1 has been shown to enlist MBTD1 into the dynamic NuA4/TIP60 acetyltransferase complex, but the detailed molecular mechanism remains unexplored. Here, we present the crystal structure of the MBTD1-EPC1 complex that sheds light on the molecular mechanism by which MBTD1 recognizes EPC1. Mutational analysis coupled with functional evaluations in human cell lines validate the physiological significance of the key residues involved in the MBTD1-EPC1 association. Overall, our study provides a structural framework for understanding the mechanism by which MBTD1 recruits the NuA4/TIP60 acetyltransferase complex to influence transcription and DNA repair pathway choice.
... The genes that were downregulated compared to the control and then upregulated under TP treatment were CCK, HOPX, and PGF. These genes are involved in protein metabolism [41], differentiation [42][43][44], and hypertrophy [45]. ...
Muscle wasting or atrophy is extensively associated with human systemic diseases including diabetes, cancer, and kidney failure. Accumulating evidence from transcriptional profiles has noted that a common set of genes, termed atrogenes, is modulated in atrophying muscles. However, the transcriptional changes that trigger the reversion or attenuation of muscle atrophy have not been characterized at the molecular level until now. Here, we applied cDNA microarrays to investigate the transcriptional response of androgen-sensitive Levator ani muscle (LA) during atrophy reversion. Most of the differentially expressed genes behaved as atrogenes and responded to castration-induced atrophy. However, seven genes (APLN, DUSP5, IGF1, PIK3IP1, KLHL38, PI15, and MKL1) did not respond to castration but instead responded exclusively to testosterone replacement. Considering that almost all proteins encoded by these genes are associated with the reversion of atrophy and may function as regulators of cell proliferation/growth, our results provide new perspectives on the existence of anti-atrogenes.
... It appears that the mechanisms that control Hopx expression and Hopx regulation of downstream mediators are epigenitically controlled. For example, skeletal muscle differentiation was induced by the direct interaction of HOPX with enhancer of polycomb 1, a component of a histone acetyltransferase complex, by potentiating its function to activate gene transcription by histone acetylation (23). A functional role of HOPX as a tumor suppressor has also been shown in multiple cancers, including colorectal cancer, where in vitro and in vivo cellular proliferation was suppressed by Hopx gene transfection (22,26,51,(53)(54)(55). ...
Intestinal ischemia is an abdominal emergency with a mortality rate >50%, leading to epithelial barrier loss and subsequent sepsis. Epithelial renewal and repair after injury depend on intestinal epithelial stem cells (ISC) that reside within the crypts of Lieberkühn. Two ISC populations critical to epithelial repair have been described: 1) Active ISC (aISC; highly proliferative; Lgr5+, Sox9+) and 2) reserve ISC (rISC; less proliferative; Hopx+). 8-10 week-old Yorkshire-cross pigs were subjected to 1-4 hours of ischemia and an hour of reperfusion or recovery by reversible mesenteric vascular occlusion. This study was designed to evaluate whether ISC expressing biomarkers of aISCs or rISCs show differential resistance to ischemic injury and different contributions to the subsequent repair and regenerative responses. Our data demonstrate that following 3-4 hours ischemic injury aISC undergo apoptosis, whereas rISC are preserved. Furthermore, these rISC are retained ex vivo in spheroids in which cell populations are enriched in the rISC biomarker Hopx. These cells appear to go on to provide a proliferative pool of cells during the recovery period. Taken together, these data indicate that Hopx+ cells are resistant to injury and are the likely source of epithelial renewal following prolonged ischemic injury. It is therefore possible that targeting reserve stem cells will lead to new therapies for patients with severe intestinal injury.
... Many PcG null mutations of one of the orthologs in mice can survive to later embryonic stages; some of them are even viable, showing very mild phenotypes [94] (see Tables 2-5). Furthermore, analyzing the mouse phenotypes of late lethal PcG mutations, it became obvious that although these factors play profound role in homeotic regulation [158,159], their epigenetic repressor functions are also important in hematopoiesis [160][161][162][163] (reviewed in [164] and [165]), neuronal [154,166] (reviewed in [167]) cardiac [168][169][170] and skeletal muscle differentiation [171], as well as in the maintenance of germ cell fate [172][173][174][175]. ...
Originally two types of Polycomb Repressive Complexes (PRCs) were described, canonical PRC1 (cPRC1) and PRC2. Recently, a versatile set of complexes were identified and brought up several dilemmas in PRC mediated repression. These new class of complexes were named as non-canonical PRC1s (ncPRC1s). Both cPRC1s and ncPRC1s contain Ring finger protein (RING1, RNF2) and Polycomb group ring finger catalytic (PCGF) core, but in ncPRCs, RING and YY1 binding protein (RYBP), or YY1 associated factor 2 (YAF2), replaces the Chromobox (CBX) and Polyhomeotic (PHC) subunits found in cPRC1s. Additionally, ncPRC1 subunits can associate with versatile accessory proteins, which determine their functional specificity. Homozygous null mutations of the ncPRC members in mice are often lethal or cause infertility, which underlines their essential functions in mammalian development. In this review, we summarize the mouse knockout phenotypes of subunits of the six major ncPRCs. We highlight several aspects of their discovery from fly to mice and emerging role in target recognition, embryogenesis and cell-fate decision making. We gathered data from stem cell mediated in vitro differentiation assays and genetically engineered mouse models. Accumulating evidence suggests that ncPRC1s play profound role in mammalian embryogenesis by regulating gene expression during lineage specification of pluripotent stem cells.
