ATR and cancer: Therefore, on the basis of our previous results and to further validate the connection between AEP and ATR in DNA damage signaling and chromosome stability, we hypothesized that the increase in ATR levels in AEP-deficient cancer cells (Figs. 2C, 3C, I-K and Supplementary Fig. 3E) could lead to increased pChek1 and pP53 levels, thus explaining the G2/M arrest observed in AEP-deficient cancer cells (Fig. 1H).