LIFE01200604005 Shri Somnath Ghosh - Homi Bhabha National ...

CHAPTER 3
RESULTS
3.3.1.3 ATM foci in gamma and carbon irradiated cells
ATM, an important DNA damage response protein to ionizing radiation and a part of irradiation
induced foci (IRIF), is mainly involved in cell cycle arrest and repair. It gets activated after DNA
dsb by phosphorylation at ser 1981 and activates many key cellular proteins that include H2AX,
BRCA1, Chk1/2 and p53. Phospho ATM foci and intensity were scored at 4 hours after gamma
or carbon irradiation. At 4 hours after gamma irradiation, 88% cells showed pATM foci with the
average foci per cell was 6.5±4.4, as against 25% control cells (3.4±1.67) (Fig.3.3.1.3A, B).
Like γ-H2AX foci, small number of ATM foci 4 hours after gamma irradiation indicates that by
4 hours most of the repair have taken place. However, at 4 hours after carbon ion irradiation only
52 % of the cells showed the foci but the average pATM foci per cell (21±10) was much higher
as compared to 4 hours after gamma (Fig.3.3.1.3A, B). Total intensity levels of phospho ATM
matched with the number of foci observed (Fig.3.3.1.3C).
3.3.1.4 ATR foci in gamma and carbon irradiated cells
ATR, another important DNA damage sensor, which is known to respond late to the IR induced
damage, was also looked for its activation at 4 hours. After gamma irradiation, 53% of the cells
showed ATR foci (2.8±1.64), as against no foci in any of the control-unirradiated cells. On the
other hand, 4 hours after carbon ion irradiation although only 10% of cells showed the foci, the
average foci per cell (7±4.5) were thrice that of gamma irradiated cells (Fig.3.3.1.4A, B). Total
intensity levels of phospho ATR matched with the number of foci observed (Fig.3.3.1.4C).
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