The effect of fractionated doses of γ-irradiation (2Gy per fraction over 5 days), as delivered in cancer radiotherapy, was compared with acute doses of 10 and 2Gy, in A549 cells. A549 cells were found to be relatively more radioresistant if the 10Gy dose was delivered as a fractionated regimen. Microarray analysis showed upregulation of DNA repair and cell cycle arrest genes in the cells exposed to fractionated irradiation. There was intense activation of DNA repair pathway-associated genes (DNA-PK, ATM, Rad52, MLH1 and BRCA1), efficient DNA repair and phospho-p53 was found to be translocated to the nucleus of A549 cells exposed to fractionated irradiation. MCF-7 cells responded differently in fractionated regimen. Silencing of the Rad52 gene in fractionated group of A549 cells made the cells radiosensitive. The above result indicated increased radioresistance in A549 cells due to the activation of Rad52 gene.
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