All eukaryotic cells divide a finite number of times, although the mechanistic basis of this replicative aging remains unclear. Replicative aging is accompanied by a reduction in histone protein ...levels, and this is a cause of aging in budding yeast. Here we show that nucleosome occupancy decreased by 50% across the whole genome during replicative aging using spike-in controlled micrococcal nuclease digestion followed by sequencing. Furthermore, nucleosomes became less well positioned or moved to sequences predicted to better accommodate histone octamers. The loss of histones during aging led to transcriptional induction of all yeast genes. Genes that are normally repressed by promoter nucleosomes were most induced, accompanied by preferential nucleosome loss from their promoters. We also found elevated levels of DNA strand breaks, mitochondrial DNA transfer to the nuclear genome, large-scale chromosomal alterations, translocations, and retrotransposition during aging.
Chromosomal double-strand breaks (DSBs) are resected by 5' nucleases to form 3' single-stranded DNA substrates for binding by homologous recombination and DNA damage checkpoint proteins. Two ...redundant pathways of extensive resection have been described both in cells and in vitro, one relying on Exo1 exonuclease and the other on Sgs1 helicase and Dna2 nuclease. However, it remains unknown how resection proceeds within the context of chromatin, where histones and histone-bound proteins represent barriers for resection enzymes. Here we identify the yeast nucleosome-remodelling enzyme Fun30 as a factor promoting DSB end resection. Fun30 is the major nucleosome remodeller promoting extensive Exo1- and Sgs1-dependent resection of DSBs. The RSC and INO80 chromatin-remodelling complexes and Fun30 have redundant roles in resection adjacent to DSB ends. ATPase and helicase domains of Fun30, which are needed for nucleosome remodelling, are also required for resection. Fun30 is robustly recruited to DNA breaks and spreads along the DSB coincident with resection. Fun30 becomes less important for resection in the absence of the histone-bound Rad9 checkpoint adaptor protein known to block 5' strand processing and in the absence of either histone H3 K79 methylation or γ-H2A, which mediate recruitment of Rad9 (refs 9, 10). Together these data suggest that Fun30 helps to overcome the inhibitory effect of Rad9 on DNA resection.
Recent developments in next-generation sequencing have enabled whole-genome profiling of nucleosome organizations. Although several algorithms for inferring nucleosome position from a single ...experimental condition have been available, it remains a challenge to accurately define dynamic nucleosomes associated with environmental changes. Here, we report a comprehensive bioinformatics pipeline, DANPOS, explicitly designed for dynamic nucleosome analysis at single-nucleotide resolution. Using both simulated and real nucleosome data, we demonstrated that bias correction in preliminary data processing and optimal statistical testing significantly enhances the functional interpretation of dynamic nucleosomes. The single-nucleotide resolution analysis of DANPOS allows us to detect all three categories of nucleosome dynamics, such as position shift, fuzziness change, and occupancy change, using a uniform statistical framework. Pathway analysis indicates that each category is involved in distinct biological functions. We also analyzed the influence of sequencing depth and suggest that even 200-fold coverage is probably not enough to identify all the dynamic nucleosomes. Finally, based on nucleosome data from the human hematopoietic stem cells (HSCs) and mouse embryonic stem cells (ESCs), we demonstrated that DANPOS is also robust in defining functional dynamic nucleosomes, not only in promoters, but also in distal regulatory regions in the mammalian genome.
Cancers have long been recognized to be not only genetically but also epigenetically distinct from their tissues of origin. Although genetic alterations underlying oncogene upregulation have been ...well studied, to what extent epigenetic mechanisms, such as DNA methylation, can also induce oncogene expression remains unknown.
Here, through pan-cancer analysis of 4174 genome-wide profiles, including whole-genome bisulfite sequencing data from 30 normal tissues and 35 solid tumors, we discover a strong correlation between gene-body hypermethylation of DNA methylation canyons, defined as broad under-methylated regions, and overexpression of approximately 43% of homeobox genes, many of which are also oncogenes. To gain insights into the cause-and-effect relationship, we use a newly developed dCas9-SunTag-DNMT3A system to methylate genomic sites of interest. The locus-specific hypermethylation of gene-body canyon, but not promoter, of homeobox oncogene DLX1, can directly increase its gene expression.
Our pan-cancer analysis followed by functional validation reveals DNA hypermethylation as a novel epigenetic mechanism for homeobox oncogene upregulation.
The solutions of stress and displacement of a circular opening excavated in brittle and strain-softening rock mass incorporating rockbolts effectiveness and seepage force are presented in this study. ...The evolution equation is reconstructed for the strength parameters that incorporate these factors. Based on the evolution equation, an improved numerical method and stepwise procedure are presented which are compatible with the Mohr–Coulomb (M–C) and the generalized Hoek–Brown (H–B) failure criteria, respectively. Then given three interaction mechanisms between rockbolts and surrounding rock, solutions for stress and displacement are proposed in line with the improved numerical method and numerical stepwise procedure. The proposed approach can be reduced to Fahimifar and Soroush’s (Tunn Undergr Space Technol 20:333–343,
2005
) solutions for special cases. The proposed method was validated by field monitoring data and FLAC results of Yanzidong tunnel. Examples under the M–C and generalized H–B failure criteria for rock mass are generated through MATLAB programming. Moreover, parametric studies are conducted to highlight the influence of rockbolts effectiveness in combination with seepage force on the stress and displacement of very good, average, and very poor surrounding rock. Results show that in this case, stress confinement is higher and tunnel convergences are lower than the corresponding stresses and displacements obtained in non-reinforced tunnels. Displacement and plastic radius are also higher than those without considering seepage force.
Naive CD4+ T cells can be converted to Foxp3+ T regulatory cells (Tregs) in the periphery (iTregs), where induction of Foxp3 gene expression is central to Treg differentiation. OX40 signaling is ...known to inhibit Foxp3 expression and Treg induction, but the underlying mechanisms remain poorly defined. Here, we found that OX40 costimulation activates two distinct molecular pathways to suppress Foxp3 expression in freshly activated naive CD4+ T cells. Specifically, OX40 upregulates BATF3 and BATF, which produce a closed chromatin configuration to repress Foxp3 expression in a Sirt1/7-dependent manner. Moreover, OX40 can also activate the AKT-mTOR pathway, especially in the absence of BATF3 and BATF, to inhibit Foxp3 induction, and this is mediated by phosphorylation and nuclear exclusion of the transcription factor Foxo1. Taken together, our results provide key mechanistic insights into how OX40 inhibits Foxp3 expression and Treg induction in the periphery.
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•OX40 costimulation upregulates BATF3 and BATF expression in activated CD4+ T cells•BATF proteins are potent repressors of Foxp3 expression•Suppression function of BATF proteins is dependent on histone deacetylases Sirt1/7•OX40 also activates the AKT-mTOR pathway to suppress Foxp3 expression
Zhang et al. show that OX40 inhibits Foxp3 expression by upregulating BATF and BATF3 expression in activating CD4+ T cells, and BATF proteins close the Foxp3 locus by recruiting the histone deacetylases Sirt1/7. Additionally, OX40 activates the AKT-mTOR pathway to inhibit Foxp3 expression in the absence of the BATF proteins.
Sirtuin proteins regulate diverse cellular pathways that influence genomic stability, metabolism and ageing. SIRT7 is a mammalian sirtuin whose biochemical activity, molecular targets and ...physiological functions have been unclear. Here we show that SIRT7 is an NAD(+)-dependent H3K18Ac (acetylated lysine 18 of histone H3) deacetylase that stabilizes the transformed state of cancer cells. Genome-wide binding studies reveal that SIRT7 binds to promoters of a specific set of gene targets, where it deacetylates H3K18Ac and promotes transcriptional repression. The spectrum of SIRT7 target genes is defined in part by its interaction with the cancer-associated E26 transformed specific (ETS) transcription factor ELK4, and comprises numerous genes with links to tumour suppression. Notably, selective hypoacetylation of H3K18Ac has been linked to oncogenic transformation, and in patients is associated with aggressive tumour phenotypes and poor prognosis. We find that deacetylation of H3K18Ac by SIRT7 is necessary for maintaining essential features of human cancer cells, including anchorage-independent growth and escape from contact inhibition. Moreover, SIRT7 is necessary for a global hypoacetylation of H3K18Ac associated with cellular transformation by the viral oncoprotein E1A. Finally, SIRT7 depletion markedly reduces the tumorigenicity of human cancer cell xenografts in mice. Together, our work establishes SIRT7 as a highly selective H3K18Ac deacetylase and demonstrates a pivotal role for SIRT7 in chromatin regulation, cellular transformation programs and tumour formation in vivo.
Super-enhancers are large clusters of enhancers that activate gene expression. Broad trimethyl histone H3 lysine 4 (H3K4me3) often defines active tumor suppressor genes. However, how these epigenomic ...signatures are regulated for tumor suppression is little understood. Here we show that brain-specific knockout of the H3K4 methyltransferase MLL4 (a COMPASS-like enzyme, also known as KMT2D) in mice spontaneously induces medulloblastoma. Mll4 loss upregulates oncogenic Ras and Notch pathways while downregulating neuronal gene expression programs. MLL4 enhances DNMT3A-catalyzed DNA methylation and SIRT1/BCL6-mediated H4K16 deacetylation, which antagonize expression of Ras activators and Notch pathway components, respectively. Notably, Mll4 loss downregulates tumor suppressor genes (e.g., Dnmt3a and Bcl6) by diminishing broad H3K4me3 and super-enhancers and also causes widespread impairment of these epigenomic signatures during medulloblastoma genesis. These findings suggest an anti-tumor role for super-enhancers and provide a unique tumor-suppressive mechanism in which MLL4 is necessary to maintain broad H3K4me3 and super-enhancers at tumor suppressor genes.
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•Brain-specific Mll4 loss in mice results in spontaneous medulloblastoma•MLL4 upregulates DNMT3A-catalyzed DNA methylation to repress Ras activators•MLL4 enhances SIRT1/BCL6-mediated H4K16 deacetylation to downregulate Notch pathways•MLL4 establishes broad H3K4me3 and super-enhancers to activate tumor suppressor genes
Dhar et al. show that MLL4 suppresses medulloblastoma by establishing super-enhancers and broad H3K4me3 to activate multiple mechanisms that lead to activation of tumor suppressor genes and repression of oncogenes.
Histone acetylation, including acetylated H3K14 (H3K14ac), is generally linked to gene activation. Monomethylated histone H3 lysine 4 (H3K4me1), together with other gene-activating marks, denotes ...active genes. In contrast to usual gene-activating functions of H3K14ac and H3K4me1, we here show that the dual histone modification mark H3K4me1-H3K14ac is recognized by ZMYND8 (also called RACK7) and can function to counteract gene expression. We identified ZMYND8 as a transcriptional corepressor of the H3K4 demethylase JARID1D. ZMYND8 antagonized the expression of metastasis-linked genes, and its knockdown increased the cellular invasiveness in vitro and in vivo. The plant homeodomain (PHD) and Bromodomain cassette in ZMYND8 mediated the combinatorial recognition of H3K4me1-H3K14ac and H3K4me0-H3K14ac by ZMYND8. These findings uncover an unexpected role for the signature H3K4me1-H3K14ac in attenuating gene expression and reveal a metastasis-suppressive epigenetic mechanism in which ZMYND8’s PHD-Bromo cassette couples H3K4me1-H3K14ac with downregulation of metastasis-linked genes.
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•ZMYND8 acts as a JARID1D corepressor for JARID1D-mediated gene repression•PHD-Bromo in ZMYND8 reads H3K4me1-H3K14ac and H3K4me0-H3K14ac•ZMYND8 has an anti-metastasis function•H3K4me1-H3K14ac is associated with repression of metastasis-linked genes
Li et al. reveal that ZMYND8 recognizes the dual histone mark H3K4me1-H3K14ac and acts as a transcriptional corepressor of the H3K4 demethylase JARID1D. ZMYND8-mediated recognition of H3K4me1-H3K14ac and JARID1D-catalyzed H3K4 demethylation cooperate to antagonize the expression of metastasis-linked genes.
DNA replication-coupled nucleosome assembly is essential to maintain genome integrity and retain epigenetic information. Multiple involved histone chaperones have been identified, but how nucleosome ...assembly is coupled to DNA replication remains elusive. Here we show that replication protein A (RPA), an essential replisome component that binds single-stranded DNA, has a role in replication-coupled nucleosome assembly. RPA directly binds free H3-H4. Assays using a synthetic sequence that mimics freshly unwound single-stranded DNA at replication fork showed that RPA promotes DNA-(H3-H4) complex formation immediately adjacent to double-stranded DNA. Further, an RPA mutant defective in H3-H4 binding exhibited attenuated nucleosome assembly on nascent chromatin. Thus, we propose that RPA functions as a platform for targeting histone deposition to replication fork, through which RPA couples nucleosome assembly with ongoing DNA replication.
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