Bassing, C.H. et al. Increased ionizing radiation sensitivity and genomic instability in the absence of histone H2AX. Proc. Natl. Acad. Sci. USA 99, 8173-8178

Howard Hughes Medical Institute, Department of Genetics, Children's Hospital, Boston, MA 02115, USA.
Proceedings of the National Academy of Sciences (Impact Factor: 9.67). 07/2002; 99(12):8173-8. DOI: 10.1073/pnas.122228699
Source: PubMed


In mammalian cells, DNA double-strand breaks (DSBs) cause rapid phosphorylation of the H2AX core histone variant (to form gamma-H2AX) in megabase chromatin domains flanking sites of DNA damage. To investigate the role of H2AX in mammalian cells, we generated H2AX-deficient (H2AX(Delta)/Delta) mouse embryonic stem (ES) cells. H2AX(Delta)/Delta ES cells are viable. However, they are highly sensitive to ionizing radiation (IR) and exhibit elevated levels of spontaneous and IR-induced genomic instability. Notably, H2AX is not required for NHEJ per se because H2AX(Delta)/Delta ES cells support normal levels and fidelity of V(D)J recombination in transient assays and also support lymphocyte development in vivo. However, H2AX(Delta)/Delta ES cells exhibit altered IR-induced BRCA1 focus formation. Our findings indicate that H2AX function is essential for mammalian DNA repair and genomic stability.

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    • "Our recent study has also shown that SUV39H2 methylates histone H2AX on lysine 134 and subsequently enhances the phosphorylation of H2AX on serine 139 [18]. Phosphorylated histone H2AX (γ-H2AX) is associated with activation of DNA-damage repair pathways and enhanced radio and chemoresistance of cancer cells [21] [22] [23] [24] [25]. Here, we hypothesized that an SUV39H2-dependent pathway might play a role in survival and proliferation of ALL cells and that targeting the gene would result in antileukemic activity. "
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    ABSTRACT: Although recent progress in understanding the biology and optimizing the treatment of acute lymphoblastic leukemia (ALL) has improved cure rates of childhood ALL to nearly 90%, the cure rate in adult ALL remains less than 50%. The poor prognosis in adult ALL has in part been attributed to larger proportion of high-risk leukemia showing drug resistance. Thus, identifying novel therapeutic targets in ALL is needed for further improvements in treatment outcomes of adult ALL. Genetic aberration of chromatin-modifying molecules has been recently reported in subtypes of ALL, and targeting components of chromatin complexes has shown promising efficacy in preclinical studies. Suppressor of variegation 3-9 homologue 2 (SUV39H2), also known as KMT1B, is a SET-domain-containing histone methyltransferase that is upregulated in solid cancers, but its expression is hardly detectable in normal tissues. Here, we show that SUV39H2 is highly expressed in ALL cells but not in blood cells from healthy donors and also that SUV39H2 mRNA is expressed at significantly higher levels in bone marrow or blood cells from patients with ALL obtained at diagnosis compared with those obtained at remission (P = .007). In four ALL cell lines (Jurkat and CEM derived from T-ALL and RS4;11 and REH derived from B-ALL), SUV39H2 knockdown resulted in a significant decrease in cell viability (~77%, P < .001), likely through induction of apoptosis. On the other hand, SUV39H2 overexpression made cells more resistant to chemotherapy. We conclude that SUV39H2 is a promising therapeutic target and further investigation of this therapeutic approach in ALL is warranted.
    Translational oncology 07/2015; DOI:10.1016/j.tranon.2015.07.003 · 2.88 Impact Factor
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    • "Due to the essential roles of DDR/DNA repair factors during meiosis, germ cells must coordinate chromatin remodeling and DDR/DNA repair events during the normal developmental process. Phosphorylated H2AX at Ser139 (γH2AX) mediates somatic DDR (Bassing et al., 2002; Celeste et al., 2002) and has an essential function in the male germline. H2AX knockout mice lack MSCI (Fernandez-Capetillo et al., 2003); MDC1, a binding partner of γH2AX (Goldberg et al., 2003; Lou et al., 2003; Stewart et al., 2003), is required for the spreading of γH2AX to the chromosomewide domain and initiation of MSCI (Ichijima et al., 2011). "
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    ABSTRACT: Meiosis is precisely regulated by the factors involved in DNA damage response in somatic cells. Among them, phosphorylation of H2AX on Serine 139 (γH2AX) is an essential signal for the silencing of unsynapsed sex chromosomes during male meiosis. However, it remains unknown how adjacent H2AX phosphorylation on Tyrosine 142 (pTyr142) is regulated in meiosis. Here we investigate the meiotic functions of BAZ1B (WSTF), the only known Tyr142 kinase in somatic cells, using mice possessing a conditional deletion of BAZ1B. Although BAZ1B deletion causes ectopic γH2AX signals on synapsed autosomes during the early pachytene stage, BAZ1B is dispensable for fertility and critical events during spermatogenesis. BAZ1B deletion does not alter events on unsynapsed axes and pericentric heterochromatin formation. Furthermore, BAZ1B is dispensable for localization of the ATP-dependent chromatin remodeling protein SMARCA5 (SNF2h) during spermatogenesis despite the complex formation between BAZ1B and SMARCA5, known as the WICH complex, in somatic cells. Notably, pTyr142 is regulated independently of BAZ1B and is dephosphorylated on the sex chromosomes during meiosis in contrast with the presence of adjacent γH2AX. Dephosphorylation of pTyr142 is regulated by MDC1, a binding partner of γH2AX. These results reveal the distinct regulation of two adjacent phosphorylation sites of H2AX during meiosis, and suggest that another kinase mediates Tyr142 phosphorylation. © 2015. Published by The Company of Biologists Ltd.
    Biology Open 05/2015; 4(7). DOI:10.1242/bio.011734 · 2.42 Impact Factor
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    • "To test this hypothesis, we used RNA sequencing (RNA-seq) approaches to interrogate the transcriptomes of H2A.X KO ESCs and control ESCs (Figure 2A and Figure S2). To avoid potential long-term culture effects, we generated H2A.X KO ESCs from H2A.X floxed/floxed ESCs (Bassing et al., 2002) via Cre-mediated deletion and used them immediately (passage five to seven) for the ensuing analyses. The efficiency of the H2A.X allele deletion was demonstrated by PCR approaches (Figure S2A). "
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    ABSTRACT: For future application of induced pluripotent stem cell (iPSC) technology, the ability to assess the overall quality of iPSC clones will be an important issue. Here we show that the histone variant H2A.X is a functional marker that can distinguish the developmental potentials of mouse iPSC lines. We found that H2A.X is specifically targeted to and negatively regulates extraembryonic lineage gene expression in embryonic stem cells (ESCs) and prevents trophectoderm lineage differentiation. ESC-specific H2A.X deposition patterns are faithfully recapitulated in iPSCs that support the development of "all-iPS" animals via tetraploid complementation, the most stringent test available of iPSC quality. In contrast, iPSCs that fail to support all-iPS embryonic development show aberrant H2A.X deposition, upregulation of extraembryonic lineage genes, and a predisposition to extraembryonic differentiation. Thus, our work has highlighted an epigenetic mechanism for maintaining cell lineage commitment in ESCs and iPSCs that can be used to distinguish the quality of iPSC lines.
    Cell Stem Cell 09/2014; 15(3):281–294. DOI:10.1016/j.stem.2014.06.004 · 22.27 Impact Factor
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