The decision to live or die in response to DNA damage controlled by differential regulation of p53 pathway dynamics

The tumor suppressor protein, p53, and its downstream effectors play a central role in mediating process of cellular repair or cell death in response to a wide variety of cellular stress. Cell fate varies, depending on the type of stress, its level and the genetic background of individual cell types. By using quantitative time-lapse microscopy to track dynamics of individual cells in real time, we investigate cell-type variation in stress response, in particular DNA damage response, and how it is differentially regulated by p53 pathway dynamics. We induced DNA damage in selected cultured cell lines by using common DNA-damaging drugs, including cisplatin and etoposide. At low dosage the majority of cells entered cell-cycle arrest with continuous oscillation of p53 level at the nucleus, while at high dosage cells tended to die rapidly with fast elevation of p53 upon drug addition. Contrary to common hypothesis, the alternative cell fate of arrest (i.e. to live) and death did not appear to correlate with the absolute level of p53 or its continuous pulsing dynamics. Our data so far pointed to the regulatory module in the p53 DNA damage response pathway that controls its initial elevation as a likely decision maker. Based on the single-cell kinetic data, we used kinetic modeling to determine quantitative characteristics of the p53 pathway that correlate with cell fate choice of life or death, and identify essential variables as well as modules in the p53 pathway that are key to the decision-making process.