Project description:Genome-wide mapping of TIP60 complex subunits in K562 cells. The objectives of this study are to describe TIP60 genome wide localization, confirm MBTD1 co-localization with already known unique subunits and observe the impact of MBTD1 on TIP60 complex targeting to chromatin. The TIP60 acetyltransferase complex is a key regulator of genome expression and stability. Here, we identified MBTD1 as a new stable subunit of the complex and revealed interesting insights about TIP60 function during the repair of DNA double strand breaks. MBTD1 binds H4K20me1/2, helping TIP60 association to specific promoters but also the DNA repair process by homologous recombination. While pro-end joining factor 53BP1 engages chromatin through simultaneous binding of H4K20me2 and H2AK15ub, TIP60 regulates the resolution of 53BP1 foci after DNA damage through a related bivalent mechanism. MBTD1 competes with 53BP1 for the H4K20me2 mark, affecting its retention at the break cooperatively with H4 acetylation by TIP60. In addition, we show that H2AK15ub deposition by RNF168 inhibits chromatin acetylation by TIP60, whereas H2AK15 can also be acetylated by TIP60 in vivo, therefore blocking its ubiquitylation. Altogether, these results uncover an intricate mechanism orchestrated by the TIP60 complex to regulate 53BP1-dependent repair pathway selection, through incompatible bivalent binding/action on chromatin.
Project description:Background Tip60 (KAT5) is the histone acetyltransferase (HAT) of the mammalian Tip60/NuA4 complex. While Tip60 is important for early mouse development and mouse embryonic stem cell (mESC) pluripotency, the function of Tip60 as reflected in a genome-wide context is not yet well understood. Results Gel filtration of nuclear mESCs extracts indicate incorporation of Tip60 into large molecular complexes and exclude the existence of large quantities of âfreeâ Tip60 within the nuclei of ESCs. Thus, monitoring of Tip60 binding to the genome should reflect the behaviour of Tip60-containing complexes. The genome-wide mapping of Tip60 binding in mESCs by chromatin immunoprecipitation (ChIP) coupled with high-throughput sequencing (ChIP-seq) shows that the Tip60 complex is present at promoter regions of predominantly active genes that are bound by RNA polymerase II (Pol II) and contain the H3K4me3 histone mark. The coactivator HAT complexes, Tip60- and Mof (KAT8)-containing (NSL and MSL), show a global overlap at promoters, whereas distinct binding profiles at enhancers suggest different regulatory functions of each essential HAT complex. Interestingly, Tip60 enrichment peaks at about 200 bp downstream of the transcription start sites suggesting a function for the Tip60 complexes in addition to histone acetylation. The comparison of genome-wide binding profiles of Tip60 and c-Myc, a somatic cell reprogramming factor that binds predominantly to active genes in mESCs, demonstrate that Tip60 and c-Myc co-bind at 50â60 % of their binding sites. We also show that the Tip60 complex binds to a subset of bivalent developmental genes and defines a set of mESC-specific enhancer as well as super-enhancer regions. Conclusions Our study suggests that the Tip60 complex functions as a global transcriptional co-activator at most active Pol II promoters, co-regulates the ESC-specific c-Myc network, important for ESC self-renewal and cell metabolism and acts at a subset of active distal regulatory elements, or super enhancers, in mESCs. Genome- wide binding of Tip60 co-activator complexes
Project description:The Tip60 (also known as Kat5) lysine acetyltransferase functions broadly as a transcriptional co-activator that acetylates histones. In contrast, Tip60 functions in embryonic stem cells (ESCs) both to silence genes that promote differentiation and to activate genes required for proliferation. The mechanism by which Tip60 functions as a repressor is unknown. Here we show that the class II histone deacetylase Hdac6 co-purifies with Tip60-p400 complex from ESCs and is necessary for complete silencing of most differentiation genes targeted by Tip60. In contrast to differentiated cells, where Hdac6 is mainly cytoplasmic and does not interact with Tip60, Hdac6 is largely nuclear in ESCs and neural stem cells (NSCs) and interacts with Tip60-p400 in both cell types. Hdac6 is enriched at promoters bound by Tip60-p400 in ESCs, but while Tip60 binds on both sides of transcription start sites (TSSs), Hdac6 binding overlaps with only the downstream Tip60 peak. Surprisingly, Hdac6 does not deacetylate histones at these sites, but rather is required for Tip60 binding. These data suggest that nuclear exclusion of Hdac6 during differentiation plays a major role in modulation of Tip60-p400 function. We determined the genome-wide localization of Tip60 and Hdac6 in mouse ES cells, and examined genomic binding profiles of Tip60 and Hdac6 upon indicated knockdown by ChIP-seq. We examined genomic binding profiles of p400 upon indicated knockdown by ChIP-seq.
Project description:Background Tip60 (KAT5) is the histone acetyltransferase (HAT) of the mammalian Tip60/NuA4 complex. While Tip60 is important for early mouse development and mouse embryonic stem cell (mESC) pluripotency, the function of Tip60 as reflected in a genome-wide context is not yet well understood. Results Gel filtration of nuclear mESCs extracts indicate incorporation of Tip60 into large molecular complexes and exclude the existence of large quantities of “free” Tip60 within the nuclei of ESCs. Thus, monitoring of Tip60 binding to the genome should reflect the behaviour of Tip60-containing complexes. The genome-wide mapping of Tip60 binding in mESCs by chromatin immunoprecipitation (ChIP) coupled with high-throughput sequencing (ChIP-seq) shows that the Tip60 complex is present at promoter regions of predominantly active genes that are bound by RNA polymerase II (Pol II) and contain the H3K4me3 histone mark. The coactivator HAT complexes, Tip60- and Mof (KAT8)-containing (NSL and MSL), show a global overlap at promoters, whereas distinct binding profiles at enhancers suggest different regulatory functions of each essential HAT complex. Interestingly, Tip60 enrichment peaks at about 200 bp downstream of the transcription start sites suggesting a function for the Tip60 complexes in addition to histone acetylation. The comparison of genome-wide binding profiles of Tip60 and c-Myc, a somatic cell reprogramming factor that binds predominantly to active genes in mESCs, demonstrate that Tip60 and c-Myc co-bind at 50–60 % of their binding sites. We also show that the Tip60 complex binds to a subset of bivalent developmental genes and defines a set of mESC-specific enhancer as well as super-enhancer regions. Conclusions Our study suggests that the Tip60 complex functions as a global transcriptional co-activator at most active Pol II promoters, co-regulates the ESC-specific c-Myc network, important for ESC self-renewal and cell metabolism and acts at a subset of active distal regulatory elements, or super enhancers, in mESCs.
Project description:Stem cells establish cortical polarity and divide asymmetrically to simultaneously maintain themselves and generate differentiating offspring cells. Several chromatin modifiers have been identified as stemness factors in mammalian pluripotent stem cells, but whether these factors control stem cell polarity and asymmetric division has not been investigated so far. We addressed this question in Drosophila neural stem cells called neuroblasts. We identified the Tip60 chromatin remodeling complex and its interaction partner Myc to regulate target genes required for neuroblast maintenance. Knockdown of members of this complex results in loss of cortical polarity, symmetric neuroblast division and premature differentiation through nuclear entry of the transcription factor Prospero. We found that aPKC is the key target gene of Myc and the Tip60 complex subunit Domino regulating neuroblast polarity. Our transcriptome analysis further showed that Domino regulates the expression of mitotic spindle genes which were identified before as direct Myc targets. Our findings reveal an evolutionarily conserved functional link between Myc, the Tip60 complex and the molecular network controlling cell polarity and asymmetric cell division.
Project description:In this study, we characterize the fusion protein produced by the ZMYND11-MBTD1 translocation in acute myeloid leukemia. We express the fusion protein and necessary controls in K562 Cells. The fusion protein assembles ZMYND11 factor with the full acetyltransferase NuA4/TIP60 complex. The fusion protein leads to mislocalization NuA4/TIP60 complex in gene bodies, thereby increasing H4ac in specific gene targets. Finally, chromatin aberration is linked to aberrant gene expression and spliced isoforms.
Project description:The Tip60 (also known as Kat5) lysine acetyltransferase functions broadly as a transcriptional co-activator that acetylates histones. In contrast, Tip60 functions in embryonic stem cells (ESCs) both to silence genes that promote differentiation and to activate genes required for proliferation. The mechanism by which Tip60 functions as a repressor is unknown. Here we show that the class II histone deacetylase Hdac6 co-purifies with Tip60-p400 complex from ESCs and is necessary for complete silencing of most differentiation genes targeted by Tip60. In contrast to differentiated cells, where Hdac6 is mainly cytoplasmic and does not interact with Tip60, Hdac6 is largely nuclear in ESCs and neural stem cells (NSCs) and interacts with Tip60-p400 in both cell types. Hdac6 is enriched at promoters bound by Tip60-p400 in ESCs, but while Tip60 binds on both sides of transcription start sites (TSSs), Hdac6 binding overlaps with only the downstream Tip60 peak. Surprisingly, Hdac6 does not deacetylate histones at these sites, but rather is required for Tip60 binding. These data suggest that nuclear exclusion of Hdac6 during differentiation plays a major role in modulation of Tip60-p400 function.
Project description:The histone lysine acetyltransferase TIP60 is the main enzyme that catalyzes histone H4 acetylation in cells. Domains on TIP60 regulate its enzymatic activity from different aspects. Here we use a CRISPR-Cas9 tiling screen to scan for essential domains on TIP60 protein and found that the Tudor-knot domain is essential for cell survival and intercellular H4 acetylation. We performed in-vitro biochemical assays and demonstrated Tudor-knot domain is not a histone reader. And deficiency of the Tudor-knot domain has mild effects on TIP60 intracellular localization, as well as the TIP60 complex’s constitution. But Tudor-knot deficiency significantly reduces TIP60 HAT activity both in vivo and in vitro. By comparing the catalytic efficiency of nucleosome substrate and histone octamer substrate, as well as TIP60 protein alone or TIP60 complex, we found the nucleosomal structure and other TIP60 complex components are required for Tudor-knot relative HAT activity regulation. We propose that the Tudor-knot domain function to increase nucleosome accessibility. Finally, we show that the Tudor-knot domain is required for TIP60-dependent transcription regulation. Altogether, our study reveals a mechanism that the Tudor-knot domain that regulates TIP60-dependent transcription through the regulation of TIP60 substrate catalytic efficiency.
Project description:The histone lysine acetyltransferase TIP60 is the main enzyme that catalyzes histone H4 acetylation in cells. Domains on TIP60 regulate its enzymatic activity from different aspects. Here we use a CRISPR-Cas9 tiling screen to scan for essential domains on TIP60 protein and found that the Tudor-knot domain is essential for cell survival and intercellular H4 acetylation. We performed in-vitro biochemical assays and demonstrated Tudor-knot domain is not a histone reader. And deficiency of the Tudor-knot domain has mild effects on TIP60 intracellular localization, as well as the TIP60 complex’s constitution. But Tudor-knot deficiency significantly reduces TIP60 HAT activity both in vivo and in vitro. By comparing the catalytic efficiency of nucleosome substrate and histone octamer substrate, as well as TIP60 protein alone or TIP60 complex, we found the nucleosomal structure and other TIP60 complex components are required for Tudor-knot relative HAT activity regulation. We propose that the Tudor-knot domain function to increase nucleosome accessibility. Finally, we show that the Tudor-knot domain is required for TIP60-dependent transcription regulation. Altogether, our study reveals a mechanism that the Tudor-knot domain that regulates TIP60-dependent transcription through the regulation of TIP60 substrate catalytic efficiency.
Project description:Proper regulation of chromatin structure is necessary for the maintenance of cell type-specific gene expression patterns. The embryonic stem cell (ESC) expression pattern governs self-renewal and pluripotency. Here, we present an RNAi screen in mouse ESCs of 1008 loci encoding chromatin proteins. We identified 68 proteins that exhibit diverse phenotypes upon knockdown (KD), including seven subunits of the Tip60-p400 complex. Phenotypic analyses revealed that Tip60-p400 is necessary to maintain characteristic features of ESCs. We show that p400 localization to the promoters of both silent and active genes is dependent upon histone H3 lysine 4 trimethylation (H3K4me3). Furthermore, the Tip60-p400 KD gene expression profile is enriched for developmental regulators and significantly overlaps with that of the transcription factor Nanog. Depletion of Nanog reduces p400 binding to target promoters without affecting H3K4me3 levels. Together, these data indicate that Tip60-p400 integrates signals from Nanog and H3K4me3 to regulate gene expression in ESCs. Experiment Overall Design: We identified genes encoding subunits of the Tip60-p400 complex in an RNAi screen of chromatin proteins in mouse embryonic stem cells (ESCs), which upon depletion resulted in a dramatic phenotype. To investigate the role of this complex in gene expression in ESCs, we performed expression profiling upon depletion of the catalytic subunits. We performed 4 biological replicates of p400 or Tip60 knockdown and compared them to biological replicates of control EGFP knockdown. The p400 (Ep400) experiment was performed as competitive two-color hybridizations on one 4x44K array with dye swaps and the Tip60 (Htatip) experiment was performed as single color hybridizations on two 4x44K arrays. Note: the Tip60 KD replicate 3 was excluded from downstream analysis of differential expression, because the intensity profile was an outlier in diagnostic analyses