DNA-PK phosphorylates histone H2AX during apoptotic DNA fragmentation in mammalian cells

Short-term culture and gammaH2AX flow cytometry determine differences in individual radiosensitivity in human peripheral T lymphocytes

Histone H2AX, a subfamily of histone H2A, is phosphorylated and forms proteinaceous repair foci at the sites of DNA double-strand breaks in response to genotoxic insults, such as ionizing radiation. This process is believed to play a key role in the repair of DNA damage. In this study, we established a flow cytometry (FCM) system for measuring radiation-induced phosphorylated histone H2AX (gammaH2AX) in cultured human T lymphocytes to evaluate individual radiation sensitivity in vitro. Irradiation of short-term ( approximately 7 days) cultured T lymphocytes exhibited significant interindividual, but not interexperimental, differences in the cellular content of gammaH2AX 6 hr after 4 Gy of X-irradiation in three independent experiments using peripheral blood lymphocytes from six healthy donors. However, these differences were not as marked in uncultured lymphocytes, or lymphocytes that were cultured for a prolonged period ( approximately 13 days). The variation of gammaH2AX focus formation in lymphocytes of individuals was reproducible, with differences reaching about 1.5-fold following 7 days of culture. Therefore, the FCM-based gammaH2AX measurement appeared to reflect both the temporal course and the amount of DNA damage within the irradiated lymphocytes. Further, we confirmed that the differences in residual lymphocyte subsets were not involved in individual radiosensitivity. These results suggest that the FCM-based gammaH2AX assay using cultured T lymphocytes might be useful for the rapid and reliable assessment of individual radiation sensitivity involved in DNA damage repair.

Prevention of aneuploidy by S-adenosyl-methionine in human cells treated with sodium arsenite

Alterations in methyl group's metabolism affect availability of S-adenosyl-L-methionine (SAM); these modifications can be originated by enzyme polymorphisms, nutritional deficiencies, and exposure to chemical agents. There are several types of chemicals that interfere with methyl groups, among them is arsenic. It deserves special attention because it modifies a number of cell functions that influence the development of diseases such as cancer. Since part of arsenic's toxicity is influenced by changes on SAM availability, in a previous study we investigated whether exogenous addition of SAM to cells treated with sodium arsenite (NaAsO(2)) has an effect on its genotoxicity. Results demonstrated that SAM reduces the frequency of cells presenting micronuclei (MN) and tubulin-cytoskeleton defects after treatment with NaAsO(2). MN are fragments of the cell nucleus that may contain whole chromosomes or chromosome fragments depending on whether they derive either from the aneugenic or from the clastogenic action of chemicals. Therefore one question generated by these results was whether SAM reduced only the frequency MN resulting from aneugenic damage. To answer this question, in the present work we used an all-centromere DNA probe to distinguish the type of MN reduced by SAM after treatment with NaAsO(2) and vinblastine. In addition, the capacity of SAM to reduce clastogenicity was also evaluated. Results show that SAM decreases the frequency of cells with MN containing whole chromosomes in cultures treated either with NaAsO(2) or with vinblastine; however, induction of double-strand breaks by NaAsO(2) was not prevented by SAM.

Chromosomal Instability and Delayed Apoptosis in Long-Term T-Lymphocyte Cultures Irradiated with Carbon Ions and X Rays

In this study, we examined genomic instability induced by 250 kV X rays and 100 MeV/nucleon carbon ions in long-term lymphocyte cultures from two healthy donors. Two biological end points, delayed apoptosis and chromosomal instability, were studied in descendants of cells irradiated with three different doses of the particular radiation up to 22 population doublings. The delayed apoptosis showed no clear dependence on radiation dose, culture time or radiation quality. A persistent significant increase in the rate of apoptosis up to 36 days after X irradiation was observed for a dose of 4 Gy in donor 1 only. For both donors and radiations, de novo aberration yields were significantly increased in comparison to control values up to day 36. For both radiations, chromosome-type aberrations were seen more frequently than chromatid-type aberrations in both donors up to 22 days postirradiation. In both donors, carbon ions were more effective than X rays with respect to the induction of chromosome instability. A dose of 0.25 Gy of carbon ions corresponding to 1.4 ion traversals per cell nucleus was effective in the induction of instability in our cell system.