Cancer Stem Cells from Tumor Cell Lines Activate the DNA Damage Response Pathway after Ionizing Radiation More Efficiently Than Noncancer Stem Cells

Figure 3

ATM and PARP1 are present and activated in cancer stem cells before and after ionizing radiation. (a) Representative immunoblot showing overall expression of ATM and phospho ATM (pATM) in SP and ML cultures before and 3 h after exposure to ionizing radiation (IR). (b) Representative immunoblot showing overall expression of PARP1 and cleaved PARP1 (cPARP1) in HeLa SP and HeLa ML cultures before and 3 h after exposure to IR. (c) HeLa SP cultures had a higher level of ATM protein than HeLa ML cultures without exposure to IR. After exposure to IR, ATM expression increased in both cultures. (d) HeLa SP cultures had a higher level of pATM than HeLa ML cultures without exposure to IR. After exposure to IR, only HeLa ML cultures had an increase of pATM. (e) HeLa SP and HeLa ML cultures exhibited no differences in the level of PARP1 protein before and after exposure to IR. (f) HeLa SP cultures had a higher level of cPARP1 than HeLa ML before exposure to IR. After exposure to IR, both cultures had a decreased level of cPARP1; however, HeLa SP continued to express cPARP1. β-Actin and GAPDH were used as loading control. The relative level of these proteins to β-Actin and GAPDH was analyzed by densitometry. The normalized level of proteins was expressed as error of the mean (SEM) at least two independent experiments.

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