Gene/Protein Disease Symptom Drug Enzyme Compound
Pivot Concepts:   Target Concepts:
Query: UNIPROT:P16104 (H2AX)
 3,930 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Mammalian ATR and ATM checkpoint kinases modulate chromatin structures near DNA breaks by phosphorylating a serine residue in the carboxy-terminal tail SQE motif of histone H2AX. Histone H2A is similarly regulated in Saccharomyces cerevisiae. The phosphorylated forms of H2AX and H2A, known as gamma-H2AX and gamma-H2A, are thought to be important for DNA repair, although their evolutionarily conserved roles are unknown. Here, we investigate gamma-H2A in the fission yeast Schizosaccharomyces pombe. We show that formation of gamma-H2A redundantly requires the ATR/ATM-related kinases Rad3 and Tel1. Mutation of the SQE motif to AQE (H2A-AQE) in the two histone H2A genes caused sensitivity to a wide range of genotoxic agents, increased spontaneous DNA damage, and impaired checkpoint maintenance. The H2A-AQE mutations displayed a striking synergistic interaction with rad22Delta (Rad52 homolog) in ionizing radiation (IR) survival. These phenotypes correlated with defective phosphorylation of the checkpoint proteins Crb2 and Chk1 and a failure to recruit large amounts of Crb2 to damaged DNA. Surprisingly, the H2A-AQE mutations substantially suppressed the IR hypersensitivity of crb2Delta cells by a mechanism that required the RecQ-like DNA helicase Rqh1. We propose that gamma-H2A modulates checkpoint and DNA repair through large-scale recruitment of Crb2 to damaged DNA. This function correlates with evidence that gamma-H2AX regulates recruitment of several BRCA1 carboxyl terminus domain-containing proteins (NBS1, 53BP1, MDC1/NFBD1, and BRCA1) in mammals.
 ...
PMID:Histone H2A phosphorylation controls Crb2 recruitment at DNA breaks, maintains checkpoint arrest, and influences DNA repair in fission yeast. 1522 25

DNA damage that is not repaired with high fidelity can lead to chromosomal aberrations or mitotic cell death. To date, it is unclear what factors control the ultimate fate of a cell receiving low levels of DNA damage (i.e. survival at the risk of increased mutation or cell death). We investigated whether DNA damage could be introduced into human cells at a level and frequency that could evade detection by cellular sensors of DNA damage. To achieve this, we exposed cells to equivalent doses of ionizing radiation delivered at either a high dose rate (HDR) or a continuous low dose rate (LDR). We observed reduced activation of the DNA damage sensor ataxia-telangiectasia mutated (ATM) and its downstream target histone H2A variant (H2AX) following LDR compared with HDR exposures in both cancerous and normal human cells. This lack of DNA damage signaling was associated with increased amounts of cell killing following LDR exposures. Increased killing by LDR radiation has been previously termed the "inverse dose rate effect," an effect for which no clear molecular processes have been described. These LDR effects could be abrogated by the preactivation of ATM or simulated in HDR-treated cells by inhibiting ATM function. These data are the first to demonstrate that DNA damage introduced at a reduced rate does not activate the DNA damage sensor ATM and that failure to activate ATM-associated repair pathways contributes to the increased lethality of continuous LDR radiation exposures. This inactivation may reflect one strategy by which cells avoid accumulating mutations as a result of error-prone DNA repair and may have a broad range of implications for carcinogenesis and, potentially, the clinical treatment of solid tumors.
 ...
PMID:Evasion of early cellular response mechanisms following low level radiation-induced DNA damage. 1537 58

While the role of ATP-dependent chromatin remodeling in transcription is well established, a link between chromatin remodeling and DNA repair has remained elusive. We have found that the evolutionarily conserved INO80 chromatin remodeling complex directly participates in the repair of a double-strand break (DSB) in yeast. The INO80 complex is recruited to a HO endonuclease-induced DSB through a specific interaction with the DNA damage-induced phosphorylated histone H2A (gamma-H2AX). This interaction requires Nhp10, an HMG-like subunit of the INO80 complex. The loss of Nhp10 or gamma-H2AX results in reduced INO80 recruitment to the DSB. Finally, components of the INO80 complex show synthetic genetic interactions with the RAD52 DNA repair pathway, the main pathway for DSB repair in yeast. Our findings reveal a new role of ATP-dependent chromatin remodeling in nuclear processes and suggest that an ATP-dependent chromatin remodeling complex can read a DNA repair histone code.
 ...
PMID:INO80 and gamma-H2AX interaction links ATP-dependent chromatin remodeling to DNA damage repair. 1560 67

DNA repair must take place within the context of chromatin, and it is therefore not surprising that many aspects of both chromatin components and proteins that modify chromatin have been implicated in this process. One of the best-characterized chromatin modification events in DNA-damage responses is the phosphorylation of the SQ motif found in histone H2A or the H2AX histone variant in higher eukaryotes. This modification is an early response to the induction of DNA damage, and occurs in a wide range of eukaryotic organisms, suggesting an important conserved function. One function that histone modifications can have is to provide a unique binding site for interacting factors. Here, we review the proteins and protein complexes that have been identified as H2AS129ph (budding yeast) or H2AXS139ph (human) binding partners and discuss the implications of these interactions.
 ...
PMID:Histone H2A phosphorylation in DNA double-strand break repair. 1597 30

H2AX is a core histone H2A variant that contains an absolutely conserved serine/glutamine (SQ) motif within an extended carboxy-terminal tail. H2AX phosphorylation at the SQ motif (gamma-H2AX) has been shown to increase dramatically upon exogenously introduced DNA double-strand breaks (DSBs). In this study, we use quantitative in situ approaches to investigate the spatial patterning and cell cycle dynamics of gamma-H2AX in a panel of normally growing (unirradiated) mammalian cell lines and cultures. We provide the first evidence for the existence of two distinct yet highly discernible gamma-H2AX focal populations: a small population of large amorphous foci that colocalize with numerous DNA DSB repair proteins and previously undescribed but much more abundant small foci. These small foci do not recruit proteins involved in DNA DSB repair. Cell cycle analyses reveal unexpected dynamics for gamma-H2AX in unirradiated mammalian cells that include an ATM-dependent phosphorylation that is maximal during M phase. Based upon similarities drawn from other histone posttranslational modifications and previous observations in haplo-insufficient (H2AX-/+) and null mice (H2AX-/-), gamma-H2AX may contribute to the fidelity of the mitotic process, even in the absence of DNA damage, thereby ensuring the faithful transmission of genetic information from one generation to the next.
 ...
PMID:ATM-dependent DNA damage-independent mitotic phosphorylation of H2AX in normally growing mammalian cells. 1603 Feb 61

In eukaryotic cell nuclei, DNA associates with the core histones H2A, H2B, H3 and H4 to form nucleosomal core particles. DNA binding to histones is regulated by posttranslational modifications of N-terminal tails (e.g., acetylation and methylation of histones). These modifications play important roles in the epigenetic control of chromatin structure. Recently, evidence that biotinidase and holocarboxylase synthetase (HCS) catalyze the covalent binding of biotin to histones has been provided. The primary aim of this study was to identify biotinylation sites in histone H2A and its variant H2AX. Secondary aims were to determine whether acetylation and methylation of histone H2A affect subsequent biotinylation and whether biotinidase and HCS localize to the nucleus in human cells. Biotinylation sites were identified using synthetic peptides as substrates for biotinidase. These studies provided evidence that K9 and K13 in the N-terminus of human histones H2A and H2AX are targets for biotinylation and that K125, K127 and K129 in the C-terminus of histone H2A are targets for biotinylation. Biotinylation of lysine residues was decreased by acetylation of adjacent lysines but was increased by dimethylation of adjacent arginines. The existence of biotinylated histone H2A in vivo was confirmed by using modification-specific antibodies. Antibodies to biotinidase and HCS localized primarily to the nuclear compartment, consistent with a role for these enzymes in regulating chromatin structure. Collectively, these studies have identified five novel biotinylation sites in human histones; histone H2A is unique among histones in that its biotinylation sites include amino acid residues from the C-terminus.
 ...
PMID:Lysine residues in N-terminal and C-terminal regions of human histone H2A are targets for biotinylation by biotinidase. 1610 83

A variant of histone H2A, H2AX, is phosphorylated on Ser139 in response to DNA double-strand breaks (DSBs), and clusters of the phosphorylated form of H2AX (gamma-H2AX) in nuclei of DSB-induced cells show foci at breakage sites. Here, we show phosphorylation of H2AX in a cell cycle-dependent manner without any detectable DNA damage response. Western blot and immunocytochemical analyses with the anti-gamma-H2AX antibody revealed that H2AX is phosphorylated at M phase in HeLa cells. In ataxia-telangiectasia cells lacking ATM kinase activity, gamma-H2AX was scarcely detectable in the mitotic chromosomes, suggesting involvement of ATM in M-phase phosphorylation of H2AX. Single-cell gel electrophoresis assay and Western blot analysis with the anti-phospho-p53 (Ser15) antibody indicated that H2AX in human M-phase cells is phosphorylated independently of DSB and DNA damage signaling. Even in the absence of DNA damage, phosphorylation of H2AX in normal cell cycle progression may contribute to maintenance of genomic integrity.
 ...
PMID:Phosphorylation of histone H2AX at M phase in human cells without DNA damage response. 1615 2

One of the earliest marks of a double-strand break (DSB) in eukaryotes is serine phosphorylation of the histone variant H2AX at the carboxy-terminal SQE motif to create gammaH2AX-containing nucleosomes. Budding-yeast histone H2A is phosphorylated in a similar manner by the checkpoint kinases Tel1 and Mec1 (ref. 2; orthologous to mammalian ATM and ATR, respectively) over a 50-kilobase region surrounding the DSB. This modification is important for recruiting numerous DSB-recognition and repair factors to the break site, including DNA damage checkpoint proteins, chromatin remodellers and cohesins. Multiple mechanisms for eliminating gammaH2AX as DNA repair completes are possible, including removal by histone exchange followed potentially by degradation, or, alternatively, dephosphorylation. Here we describe a three-protein complex (HTP-C, for histone H2A phosphatase complex) containing the phosphatase Pph3 that regulates the phosphorylation status of gammaH2AX in vivo and efficiently dephosphorylates gammaH2AX in vitro. gammaH2AX is lost from chromatin surrounding a DSB independently of the HTP-C, indicating that the phosphatase targets gammaH2AX after its displacement from DNA. The dephosphorylation of gammaH2AX by the HTP-C is necessary for efficient recovery from the DNA damage checkpoint.
 ...
PMID:A phosphatase complex that dephosphorylates gammaH2AX regulates DNA damage checkpoint recovery. 1643 2

Chromatin changes within the context of DNA repair remain largely obscure. Here we show that DNA damage induces monoubiquitylation of histone H2A in the vicinity of DNA lesions. Ultraviolet (UV)-induced monoubiquitylation of H2A is dependent on functional nucleotide excision repair and occurs after incision of the damaged strand. The ubiquitin ligase Ring2 is required for the DNA damage-induced H2A ubiquitylation. UV-induced ubiquitylation of H2A is dependent on the DNA damage signaling kinase ATR (ATM- and Rad3-related) but not the related kinase ATM (ataxia telangiectasia-mutated). Although the response coincides with phosphorylation of variant histone H2AX, H2AX was not required for H2A ubiquitylation. Together our data show that monoubiquitylation of H2A forms part of the cellular response to UV damage and suggest a role of this modification in DNA repair-induced chromatin remodeling.
 ...
PMID:DNA damage triggers nucleotide excision repair-dependent monoubiquitylation of histone H2A. 1670 7

Exposure to ionizing radiation (IR) results in the formation of DNA double strand breaks, resulting in the activation of phosphatidylinositol 3'-kinase-like kinases ATM, ATR and DNK-PKcs. A physiologically important downstream target is the minor histone H2A variant, H2AX, which is rapidly phosphorylated on Ser 139 of the carboxyl tail after IR. Recent work suggests that phosphorylated H2AX (gamma-H2AX) plays an important role in the recruitment and/or retention of DNA repair and checkpoint proteins such as BRCA1, MRE11/RAD50/NBS1 complex, MDC1 and 53BP1. H2AX-/- mouse embryonic fibroblasts are radiation sensitive and demonstrate deficits in repairing DNA damage compared to their wildtype counterparts. Cells treated with peptide inhibitors of gamma-H2AX demonstrate increased radiosensitivity following radiation compared with untreated irradiated cells. Analysis of the kinetics of gamma-H2AX clearance after IR or other DNA damaging agents reveals a correlation between increased gamma-H2AX persistence and unrepaired DNA damage and cell death. These data highlight the potential of post-translational modifications of chromatin as a therapeutic target for enhancing the efficacy of radiotherapy. Therapies that either block gamma-H2AX foci formation by inhibiting upstream kinase activity or that directly inhibit H2AX function may interfere with DNA damage repair processes and warrant further investigation as potential radiosensitizing agents. Agents that increase persistence of gamma-H2AX after IR are likely to increase unrepaired DNA damage.
 ...
PMID:gamma-H2AX as a therapeutic target for improving the efficacy of radiation therapy. 1671 57


<< Previous 1 2 3 4 5 6 7 8 9 10 Next >>