Emmy P. Rogakou

DNA Double-stranded Breaks Induce Histone H2AX Phosphorylation on Serine 139

When mammalian cell cultures or mice are exposed to ionizing radiation in survivable or lethal amounts, novel mass components are found in the histone H2A region of two-dimensional gels. Collectively referred to as γ, these components are formed in vivo by several procedures that introduce double-stranded breaks into DNA. γ-Components, which appeared to be the only major novel components detected by mass or 32PO4incorporation on acetic acid-urea-Triton X-100-acetic acid-urea-cetyltrimethylammonium bromide or SDS-acetic acid-urea-cetyltrimethylammonium bromide gels after exposure of cells to ionizing radiation, are shown to be histone H2AX species that have been phosphorylated specifically at serine 139. γ-H2AX appears rapidly after exposure of cell cultures to ionizing radiation; half-maximal amounts are reached by 1 min and maximal amounts by 10 min. At the maximum, approximately 1% of the H2AX becomes γ-phosphorylated per gray of ionizing radiation, a finding that indicates that 35 DNA double-stranded breaks, the number introduced by each gray into the 6 × 109 base pairs of a mammalian G1 genome, leads to the γ-phosphorylation of H2AX distributed over 1% of the chromatin. Thus, about 0.03% of the chromatin appears to be involved per DNA double-stranded break. This value, which corresponds to about 2 × 106 base pairs of DNA per double-stranded break, indicates that large amounts of chromatin are involved with each DNA double-stranded break. Thus, γ-H2AX formation is a rapid and sensitive cellular response to the presence of DNA double-stranded breaks, a response that may provide insight into higher order chromatin structures.

A critical role for histone H2AX in recruitment of repair factors to nuclear foci after DNA damage.

BACKGROUND The response of eukaryotic cells to double-strand breaks in genomic DNA includes the sequestration of many factors into nuclear foci. Recently it has been reported that a member of the histone H2A family, H2AX, becomes extensively phosphorylated within 1-3 minutes of DNA damage and forms foci at break sites. RESULTS In this work, we examine the role of H2AX phosphorylation in focus formation by several repair-related complexes, and investigate what factors may be involved in initiating this response. Using two different methods to create DNA double-strand breaks in human cells, we found that the repair factors Rad50 and Rad51 each colocalized with phosphorylated H2AX (gamma-H2AX) foci after DNA damage. The product of the tumor suppressor gene BRCA1 also colocalized with gamma-H2AX and was recruited to these sites before Rad50 or Rad51. Exposure of cells to the fungal inhibitor wortmannin eliminated focus formation by all repair factors examined, suggesting a role for the phosphoinositide (PI)-3 family of protein kinases in mediating this response. Wortmannin treatment was effective only when it was added early enough to prevent gamma-H2AX formation, indicating that gamma-H2AX is necessary for the recruitment of other factors to the sites of DNA damage. DNA repair-deficient cells exhibit a substantially reduced ability to increase the phosphorylation of H2AX in response to ionizing radiation, consistent with a role for gamma-H2AX in DNA repair. CONCLUSIONS The pattern of gamma-H2AX foci that is established within a few minutes of DNA damage accounts for the patterns of Rad50, Rad51, and Brca1 foci seen much later during recovery from damage. The evidence presented strongly supports a role for the gamma-H2AX and the PI-3 protein kinase family in focus formation at sites of double-strand breaks and suggests the possibility of a change in chromatin structure accompanying double-strand break repair.

Quantitative Detection of 125IdU-Induced DNA Double-Strand Breaks with γ-H2AX Antibody

Abstract Sedelnikova, O. A., Rogakou, E. P., Panyutin, I. G. and Bonner, W. M. Quantitative Detection of 125IdU-Induced DNA Double-Strand Breaks with γ-H2AX Antibody. Radiat. Res. 158, 486–492 (2002). When mammalian cells are exposed to ionizing radiation and other agents that introduce DSBs into DNA, histone H2AX molecules in megabase chromatin regions adjacent to the breaks become phosphorylated within minutes on a specific serine residue. An antibody to this phosphoserine motif of human H2AX (γ-H2AX) demonstrates that γ-H2AX molecules appear in discrete nuclear foci. To establish the quantitative relationship between the number of these foci and the number of DSBs, we took advantage of the ability of 125I, when incorporated into DNA, to generate one DNA DSB per radioactive disintegration. SF-268 and HT-1080 cell cultures were grown in the presence of 125IdU and processed immunocytochemically to determine the number of γ-H2AX foci. The numbers of 125IdU disintegrations per cell were measured by exposing the same immunocytochemically processed samples to a radiation-sensitive screen with known standards. Under appropriate conditions, the data yielded a direct correlation between the number of 125I decays and the number of foci per cell, consistent with the assumptions that each 125I decay yields a DNA DSB and each DNA DSB yields a visible γ-H2AX focus. Based on these findings, we conclude that γ-H2AX antibody may form the basis of a sensitive quantitative method for the detection of DNA DSBs in eukaryotic cells.

Yeast histone 2A serine 129 is essential for the efficient repair of checkpoint‐blind DNA damage

Cells maintain genomic stability by the coordination of DNA‐damage repair and cell‐cycle checkpoint control. In replicating cells, DNA damage usually activates intra‐S‐phase checkpoint controls, which are characterized by delayed S‐phase progression and increased Rad53 phosphorylation. We show that in budding yeast, the intra‐S‐phase checkpoint controls, although functional, are not activated by the topoisomerase I inhibitor camptothecin (CPT). In a CPT‐hypersensitive mutant strain that lacks the histone 2A (H2A) phosphatidylinositol‐3‐OH kinase (PI(3)K) motif at Ser 129 (h2a‐s129a), the hypersensitivity was found to result from a failure to process full‐length chromosomal DNA molecules during ongoing replication. H2A Ser 129 is not epistatic to the RAD24 and RAD9 checkpoint genes, suggesting a non‐checkpoint role for the H2A PI(3)K site. These results suggest that H2A Ser 129 is an essential component for the efficient repair of DNA double‐stranded breaks (DSBs) during replication in yeast, particularly of those DSBs that do not induce the intra‐S‐phase checkpoint.