NOTCH1 and cancer: 15) and references therein). We report here that PLK1 promotes NOTCH1 down-modulation to the G2-M transition; conversely, NOTCH1 remains active during a DNA damage–induced G2 arrest. Our data show that NOTCH1 has pleiotropic effects in DNA damage-arrested cells, and also in those contexts where NOTCH1 is known to play a tumor suppressor function, cancer cells might still be dependent on specific NOTCH1 signals to sustain their cancerous phenotype.