DNA damage response induced by oxidative stress in G0 cells and cells that re-initiated the cell cycle
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In response to DNA damage, cells activate a signaling cascade known as the DNA damage response (DDR). DDR can modulate the cell cycle to give the cell prolonged time for DNA repair or to induce apoptosis. Cells residing in G0 phase, out of cell cycle, are deprived of canonical cell cycle checkpoints. G0 cells can be quiescent or terminally differentiated and they are less prone to DNA-damaging factors than cycling cells. Research on quiescent stem cells and terminally differentiated cells, demonstrated their attenuated DDR. To further explore this subject we investigated the role of cell cycle exit and re-entry in DDR induced by oxidative stress. We chemically induced quiescence, differentiation and cell cycle re-entry and studied cell viability, intracellular reactive oxygen species (ROS) production, DNA damage and repair, apoptosis, autophagy and distribution of cells in cell cycle phases. We showed that G0 cells, both quiescent and differentiating were more resistant to DNA damage and apoptosis evoked by oxidative stress than cycling cells. These cells showed similar DNA repair kinetics and distribution of cells in cell cycle phases to cycling cells. Unlike quiescent cells, which reduced the level of intracellular ROS, differentiating cells increased intracellular ROS level in oxidative stress. To further confirm that attenuated DDR was specific to G0, we made quiescent cells re-enter cell cycle and measured the activation of DDR pathways. DDR of cells that re-initiated cell cycle was similar to normally cycling cells followed oxidative stress, including intracellular ROS production, sensitivity to DNA damage and apoptosis. However, autophagy decreased upon cell cycle re-entry. Our results demonstrate that the manipulation of cell cycle status influences DDR: attenuates it in G0 and restores upon cell cycle re-entry. Our study strengthens the conception of DDR regulation via G0 phase induction and cell cycle re-initiation.
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