Figure 5.

ATM inhibition after end resection leads to HR deficiency and increases radiosensitization after PARP inhibition. (A) Upper panel: Schematic representation of the inducible I-SceI-expressing vector pDSRed-I-SceI-GR. Addition of triamcinolone (TA) leads to the nuclear localization of the I-SceI enzyme. Lower panel: HeLa cells harboring the pGC reporter were transfected with pDSRed-I-SceI-GR. Twenty-four hours later, MRE11 or ATM was inhibited either 2 h prior to TA treatment (pre) or 2 , 6 or 12 h after TA (post). GFP⁺ cells were evaluated 48 h after I-SceI-transfection as an indication of HR efficiency. (B) Radiosensitivity of exponentially growing A549 cells was measured by colony forming assay after inhibition of ATM (10-μM KU55933) and/or PARP (1-μM Olaparib) either prior to (-pre) or after (-post) the indicated X-ray doses. Error bars represent the SEM of three independent experiments.