Elsevier

DNA Repair

Volume 3, Issues 8–9, August–September 2004, Pages 959-967
DNA Repair

Review
H2AX: the histone guardian of the genome

https://doi.org/10.1016/j.dnarep.2004.03.024Get rights and content

Abstract

At close hand to one’s genomic material are the histones that make up the nucleosome. Standing guard, one variant stays hidden doubling as one of the core histones. But, thanks to its prime positioning, a variation in the tail of H2AX enables rapid modification of the histone code in response to DNA damage. A role for H2AX phosphorylation has been demonstrated in DNA repair, cell cycle checkpoints, regulated gene recombination events, and tumor suppression. In this review, we summarize what we have learned about this marker of DNA breaks, and highlight some of the questions that remain to be elucidated about the physiological role of H2AX. We also suggest a model in which chromatin restructuring mediated by H2AX phosphorylation serves to concentrate DNA repair/signaling factors and/or tether DNA ends together, which could explain the pleotropic phenotypes observed in its absence.

Section snippets

Introduction: the tale of a tail

Just as the nucleic acid base is the fundamental repeating unit of DNA, the nucleosome forms the basic building block of chromatin. Within each nucleosome, 147 base-pairs of DNA are wrapped 1.7 times around a central core of eight histone protein molecules (an octamer consisting of two copies each of H2A, H2B, H3, and H4 histones) that form a 100 kDa protein complex [1]. Each core histone contains a “globular domain,” which is necessary for histone–histone and histone–DNA contacts, as well as a

γ-H2AX marks the spot

The presence of two evolutionary conserved pathways, homologous end joining (NHEJ) and homologous recombination (HR), for the repair of DNA double strand breaks (DSBs) highlights the threat to genomic integrity caused by free DNA ends [8]. A role for H2AX in the DNA damage response was first suggested by William Bonner and co-workers who used two-dimensional gel analysis to show that phosphorylated H2AX formed rapidly following exposure of cells to ionizing radiation [5]. The phosphorylation

Who rings the H2AX serine 139 bell?

Following the generation of DSBs a rapid kinase-based signaling pathway is activated that coordinates DNA repair with the induction cell-cycle checkpoints [22], [23]. The principal mediators in this pathway are the phosphatidylinositol-3 kinase-like family of kinases (PIKK). At least four PIKK family members are involved in the transduction of the signal that originates at broken DNA: ataxia telangiectasia mutated (ATM) ATM-and Rad3-related (ATR) ATM related kinase (ATX), and DNA dependent

Race to the break

The recruitment of DNA damage signaling and repair proteins to sites of genomic damage constitutes a primary event triggered by DNA damage. Many components of the DNA damage response, including ATM, BRCA1, 53BP1, MDC1, RAD51, and the MRE11/RAD50/NBS1 (MRN) complex [12], [21], [32], [33], [34], [35], [36] form ionizing radiation induced foci (IRIF) that co-localize with γ-H2AX foci. These nuclear micro-domains are thought to contain hundreds to thousands of molecules that accumulate in the

The H2AX syndrome

Hereditary diseases affecting the cellular response to DSBs include ataxia telangiectasia (defective ATM), Nijmegen breakage syndrome (defective Nbs1) and Bloom’s syndrome (defective BLM). The hallmarks of these disorders are growth defects, immunodeficiency, hypogonadism, hypersensitivity to specific DNA damaging agents, chromosomal fragility, and cancer predisposition. Mouse models in which specific components of the DSB repair/signaling pathway are disrupted recapitulate most of the

Role of H2AX in DNA repair

The first experiment that demonstrated a role for H2AX in DNA repair was a genetic study performed in Saccharomyces cerevisiae [51]. Elimination of the unique C-terminal H2A serine residue in yeast led to an impairment in NHEJ [51]. More recently, it was shown that in S. cerevisiae H2A Ser 129 is critical for the efficient repair of DSBs during DNA replication [52]. The analysis of H2AX-deficient ES cells and mice showed that H2AX is not essential for NHEJ or HR in mammalian cells, but does

Role of H2AX in genomic stability and cell cycle checkpoints

Genomic instability is a general term used to describe a genetic propensity for an increase in chromosomal pathology secondary to inaccurate repair or deficiency in cell cycle checkpoints. Typically, the instability can be visualized as chromosomal breaks, translocations, or aneuploidy. H2AX-deficient mouse embryo fibroblasts and T cells contain chromosomal breaks and translocations. However, H2AX−/− B-cells do not show such aberrations, presumably because the apoptotic machinery eliminates B

Role of H2AX in growth

Like other mouse models of genomic instability, H2AX deficient mice are small in size [39]. This growth defect is distributed proportionally throughout the entire organism. Similarly, H2AX−/− mouse embryonic fibroblasts (MEFs) exhibit impaired growth and senesce after only 3–4 passages in culture [39], a phenotype partially alleviated by p53 deficiency [49]. In human cells, senescence is associated with telomere erosion that follows every cell division [55]. Moreover, a number of proteins

Role of H2AX in meiosis

Meiosis is a cellular differentiation program during which physiological DSBs are created and repaired, giving rise to recombination events between parental chromosomes. Meiotic recombination takes place in the prophase stage within the first of two meiotic divisions, and is triggered by DSBs generated by the Spo11 transesterase [58]. When the distribution of γ-H2AX is analyzed in mouse spermatocytes, it shows two distinct patterns of staining [19]. On the one hand, there is a Spo11-dependent

Role of H2AX tumor suppression

There is mounting evidence that genomic instability is a cause and not just a consequence of cancer development [8]. Although chromosomes in cells from H2AX deficient mice contain frequent breaks and translocations, there is little or no increase in tumor development in H2AX−/− mice [49], [50]. Apparently, H2AX−/− cells are protected from malignant transformation by the activity of DNA damage sensors, like p53. Such ‘gatekeepers’ [64] proteins provide a safeguard against genomic instability by

Role of H2AX in immune receptor rearrangements

During lymphocyte development, T and B cells undergo the process of somatic gene rearrangement known as Variable Diversity Joining (V(D)J) recombination to produce the primary antigen receptor repertoire. Antigen receptor diversification in lymphocytes is initiated by the RAG-1/2 endonuclease, which introduces DSBs adjacent to the antigen receptor segments (V, D, and J segments) [65]. The subsequent juxtaposition and ligation of V(D)J ends requires ubiquitously expressed proteins (Ku80, Ku70,

Model for H2AX function

We speculate that the pleotropic phenotypes observed in the absence of H2AX- chromosomal instability and radiation sensitivity in mitotic cells, abnormalities in XY pairing and transcriptional inactivation in spermatocytes, defects in G2/M checkpoint control, and reduced levels of class-switching are all due to two complementary structural functions provided by the phosphorylation marks on H2AX: a role in (1) the focal assembly and retention of factors in chromatin regions near the damaged site

Implications for human disease

The histone H2AX gene, located 11 Mb telomeric to ATM at 11q23.3, is in a region commonly deleted or translocated in several human hematological malignancies and solid tumors [75]. Heterozygous deletion of chromosome bands 11q22-q23 is detected at a particularly high frequency in B cell chronic lymphocytic leukemia (B-CLL), mantle cell lymphoma (MCL), and T cell prolymphocytic leukemia (T-PLL), and is associated with rapid disease progression and poor survival in B-CLL [75], [76]. Since somatic

References (77)

  • O. Fernandez-Capetillo et al.

    H2AX is required for chromatin remodeling and inactivation of sex chromosomes in male mouse meiosis

    Dev. Cell

    (2003)
  • I.M. Ward et al.

    Accumulation of checkpoint protein 53BP1 at DNA breaks involves its binding to phosphorylated histone H2AX

    J. Biol. Chem.

    (2003)
  • J. Kobayashi et al.

    NBS1 localizes to gamma-H2AX foci through interaction with the FHA/BRCT domain

    Curr. Biol.

    (2002)
  • E.C. Friedberg et al.

    Database of mouse strains carrying targeted mutations in genes affecting biological responses to DNA damage. Version 5

    DNA Repair

    (2003)
  • A. Celeste et al.

    H2AX haploinsufficiency modifies genomic stability and tumor susceptibility

    Cell

    (2003)
  • C.H. Bassing et al.

    Histone H2AX. A dosage-dependent suppressor of oncogenic translocations and tumors

    Cell

    (2003)
  • A. Smogorzewska et al.

    DNA ligase IV-dependent NHEJ of deprotected mammalian telomeres in G1 and G2

    Curr. Biol.

    (2002)
  • N. Hunter et al.

    The single-end invasion: an asymmetric intermediate at the double-strand break to double-holliday junction transition of meiotic recombination

    Cell

    (2001)
  • A.J. Solari

    The behavior of the XY pair in mammals

    Int. Rev. Cytol.

    (1974)
  • M. Muramatsu et al.

    Class switch recombination and hypermutation require activation-induced cytidine deaminase (AID), a potential RNA editing enzyme

    Cell

    (2000)
  • P. Revy et al.

    Activation-induced cytidine deaminase (AID) deficiency causes the autosomal recessive form of the Hyper-IgM syndrome (HIGM2)

    Cell

    (2000)
  • J.P. Manis et al.

    IgH class switch recombination to IgG1 in DNA-PKcs-deficient B cells

    Immunity

    (2002)
  • K. Hiom et al.

    Assembly of a 12/23 paired signal complex: a critical control point in V(D)J recombination

    Mol. Cell

    (1998)
  • A. Agrawal et al.

    RAG1 and RAG2 form a stable postcleavage synaptic complex with DNA containing signal ends in V(D)J recombination

    Cell

    (1997)
  • K. Luger et al.

    Crystal structure of the nucleosome core particle at 2.8 Å resolution

    Nature

    (1997)
  • M.H. West et al.

    Histone 2A, a heteromorphous family of eight protein species

    Biochemistry

    (1980)
  • C. Mannironi et al.

    H2A.X. a histone isoprotein with a conserved C-terminal sequence, is encoded by a novel mRNA with both DNA replication type and polyA 3′ processing signals

    Nucleic Acids Res.

    (1989)
  • A. Zweidler

    Complexity and variability of the histone complement

    Life Sci. Res. Rep.

    (1976)
  • R.S. Wu et al.

    Histones and their modifications

    CRC Crit. Rev. Biochem.

    (1986)
  • K.K. Khanna et al.

    DNA double-strand breaks: signaling, repair and the cancer connection

    Nat. Genet.

    (2001)
  • E.P. Rogakou et al.

    Megabase chromatin domains involved in DNA double-strand breaks in vivo

    J. Cell Biol.

    (1999)
  • O.A. Sedelnikova et al.

    Quantitative detection of (125)IdU-induced DNA double-strand breaks with gamma-H2AX antibody

    Radiat. Res.

    (2002)
  • F. d’Adda di Fagagna et al.

    A DNA damage checkpoint response in telomere-initiated senescence

    Nature

    (2003)
  • K. Rothkamm et al.

    Pathways of DNA double-strand break repair during the mammalian cell cycle

    Mol. Cell Biol.

    (2003)
  • S.K. Mahadevaiah et al.

    Recombinational DNA double-strand breaks in mice precede synapsis

    Nat. Genet

    (2001)
  • S. Petersen et al.

    AID is required to initiate Nbs1/gamma-H2AX focus formation and mutations at sites of class switching

    Nature

    (2001)
  • H.T. Chen et al.

    Response to RAG-mediated VDJ cleavage by NBS1 and gamma-H2AX

    Science

    (2000)
  • J. Rouse et al.

    Interfaces between the detection, signaling, and repair of DNA damage

    Science

    (2002)
  • Cited by (0)

    View full text