Whole genome sequencing data mining efforts have revealed numerous histone mutations in a wide range of cancer types. These occur in all four core histones in both the tail and globular domains and remain largely uncharacterized. Here we used two high-throughput approaches, a DNA-barcoded mononucleosome library and a humanized yeast library, to profile the biochemical and cellular effects of these mutations. We identified cancer-associated mutations in the histone globular domains that enhance fundamental chromatin remodeling processes, histone exchange and nucleosome sliding, and are lethal in yeast. In mammalian cells, these mutations upregulate cancer-associated gene pathways and inhibit cellular differentiation by altering expression of lineage-specific transcription factors. This work represents a comprehensive functional analysis of the histone mutational landscape in human cancers and leads to a model in which histone mutations that perturb nucleosome remodeling may contribute to disease development and/or progression.

The diphosphoinositol polyphosphates (PP-IPs) are a central group of eukaryotic second messengers. They regulate numerous processes, including cellular energy homeostasis and adaptation to environmental stresses. To date, most of the molecular details in PP-IP signalling have remained elusive, due to a lack of appropriate methods and reagents. Here we describe the expedient synthesis of methylene-bisphosphonate PP-IP analogues. Their characterization revealed that the analogues exhibit significant stability and mimic their natural counterparts very well. This was further confirmed in two independent biochemical assays, in which our analogues potently inhibited phosphorylation of the protein kinase Akt and hydrolytic activity of the Ddp1 phosphohydrolase. The non-hydrolysable PP-IPs thus emerge as important tools and hold great promise for a variety of applications.

Recent studies have implicated the nucleosome acidic patch in the activity of ATP-dependent chromatin remodeling machines. We employed a photocrosslinking-based nucleosome profiling technology-'photoscanning'-to identify a conserved basic motif within the catalytic subunit of ISWI remodelers, SNF2h, which engages this nucleosomal epitope. This region of SNF2h is essential for chromatin remodeling activity in a reconstituted biochemical system and in cells. Our studies suggest that the basic motif in SNF2h plays a critical role in anchoring the remodeler to the nucleosomal surface. We also examine the functional consequences of several cancer-associated histone mutations that map to the nucleosome acidic patch. Kinetic studies employing physiologically relevant heterotypic nucleosomal substrates ('Janus' nucleosomes) indicate that these cancer mutations can disrupt regularly spaced chromatin structure by inducing ISWImediated unidirectional nucleosome sliding. These results imply a potential mechanistic link between oncogenic histones and alterations to the chromatin landscape. Users may view, print, copy, and download text and data-mine the content in such documents, for the purposes of academic research, subject always to the full Conditions of use:

As a central component of the DNA damage checkpoint pathway, the conserved protein kinase Chk1 mediates cell cycle progression when DNA damage is generated. Msc1 was identified as a multicopy suppressor capable of facilitating survival in response to DNA damage of cells mutant for chk1. We demonstrate that loss of msc1 function results in an increased rate of chromosome loss and that an msc1 null allele exhibits genetic interactions with mutants in key kinetochore components. Multicopy expression of msc1 robustly suppresses a temperature-sensitive mutant (cnp1-1) in the centromere-specific histone H3 variant CENP-A, and localization of CENP-A to the centromere is compromised in msc1 null cells. We present several lines of evidence to suggest that Msc1 carries out its function through the histone H2A variant H2A.Z, encoded by pht1 in fission yeast. Like an msc1 mutant, a pht1 mutant also exhibits chromosome instability and genetic interactions with kinetochore mutants. Suppression of cnp1-1 by multicopy msc1 requires pht1. Likewise, suppression of the DNA damage sensitivity of a chk1 mutant by multicopy msc1 also requires pht1. We present the first genetic evidence that histone H2A.Z may participate in centromere function in fission yeast and propose that Msc1 acts through H2A.Z to promote chromosome stability and cell survival following DNA damage.

The DNA damage checkpoint pathway governs how cells regulate cell cycle progression in response to DNA damage. A screen for suppressors of a fission yeast chk1 mutant defective in the checkpoint pathway identified a novel Schizosaccharomyces pombe protein, Msc1. Msc1 contains 3 plant homeodomain (PHD) finger motifs, characteristically defined by a C 4 HC 3 consensus similar to RING finger domains. PHD finger domains in viral proteins and in the cellular protein kinase MEKK1 (mitogen-activated protein kinase/extracellular signal-regulated kinase kinase kinase 1) have been implicated as ubiquitin E3 protein ligases that affect protein stability. The close structural relationship of PHD fingers to RING fingers suggests that other PHD domain-containing proteins might share this activity. We show that each of the three PHD fingers of Msc1 can act as ubiquitin E3 ligases, reporting for the first time that PHD fingers from a nuclear protein exhibit E3 ubiquitin ligase activity. The function of the PHD fingers of Msc1 is needed to rescue the DNA damage sensitivity of a chk1⌬ strain. Msc1 co-precipitates Rhp6, the S. pombe homologue of the human ubiquitin-conjugating enzyme Ubc2. Strikingly, deletion of msc1 confers complete suppression of the slow growth phenotype, UV and hydroxyurea sensitivities of an rhp6 deletion strain and restores deficient histone H3 methylation observed in the rhp6⌬ mutant. We speculate that the target of the E3 ubiquitin ligase activity of Msc1 is likely to be a chromatin-associated protein.The DNA damage checkpoint pathway governs how cells regulate cell cycle progression in response to DNA damage (1). The fission yeast gene msc1 was found in a genetic screen as a multicopy suppressor of chk1 (2). Msc1 is similar to the mammalian protein RBP2 that binds the tumor suppressor retinoblastoma (3) as well as to PLU-1, encoded by a gene that is up-regulated in breast cancer cells (4). Database searches indicate that there are also homologues of Msc1 in Caenorhabditis elegans and Drosophila, but no apparent homologue with the same domain structure exists in Saccharomyces cerevisiae. Both RBP2 and PLU-1 associate with proteins that have roles in regulating gene transcription and chromatin structure (5-8).Msc1 contains Jumonji N and Jumonji C domains, three plant homeodomain (PHD) 2 fingers, and a C 2 C 5 zinc finger. The PHD finger is a motif defined by seven cysteines and a histidine arranged in a C 4 HC 3 consensus. The PHD domain was first identified in a homeodomain protein involved in plant root development (9). Since then more than 400 eukaryotic proteins have been identified containing PHD fingers. Most of these proteins are nuclear and are thought to play roles in gene expression (10).The solution structure of the PHD finger of the KAP-1 corepressor shows that the zinc ligation scheme and cross-brace topology of the anti-parallel ␤-sheets are very similar to the structure of the RING (really interesting new gene) finger (11). Many proteins with RING fingers can act as E3 ubiquitin ligases in t...