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LIFE01200604005 Shri Somnath Ghosh - Homi Bhabha National ...

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CHAPTER 3<br />

RESULTS<br />

3.1.6 Radiation induced foci of DNA damage response proteins ATM and BRCA1<br />

ATM, an important DNA damage response protein to ionizing radiation and a part of irradiation<br />

induced foci (IRIF), is mainly involved in cell cycle arrest and repair. It gets activated after DNA<br />

double strand break by phosphorylation at ser 1981 and activates many key cellular proteins that<br />

include H2AX, BRCA1, Chk1/2 and p53. Phospho ATM foci and intensity were looked at 4<br />

hours after irradiation. All the cells either exposed to 10 Gy (23±3 foci per cell) or fractionated<br />

irradiation (25±2.8 foci per cell) showed ATM foci but only 10% of cells exposed to 2 Gy<br />

showed ATM foci and the number of foci per cell was 2±0.08 (Fig. 3.1.6A). The intensity of<br />

phosphorylation of ATM was quantified by ImageJ software, was significantly higher in the<br />

fractionated group as compared to any of the treatment groups (control, 2Gy or 10Gy )<br />

BRCA1, which is phosphorylated by ATM, is a part of IRIF and shares many downstream<br />

substrates of ATM. 4 hours after irradiation, A549 cells that had been exposed to 2 Gy acute<br />

dose did not show any BRCA1 foci where as 55 % of cells that had been exposed to fractionated<br />

irradiation showed BRCA1 foci and the number of foci per cells was 24±4. 22% of cells that had<br />

been exposed to 10 Gy acute showed BRCA1 foci and the number of foci per cell was 15±2.1<br />

(Fig. 3.1.6B). The intensity of phosphorylation of BRCA1 as determined by ImageJ software<br />

was significantly higher in the fractionated group as compared to any of the treatment groups<br />

(control, 2Gy or 10Gy).<br />

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