The roles of p53 and MYC dynamics in regulating heterogeneous cell fate responses to genotoxic stress

Project Summary Our long-term goal is to understand how dynamic regulation of signal transduction systems control cellular stress responses. The focus of this proposal is on identifying the mechanisms by which dynamic expression of the transcription factors p53 and MYC coordinately regulate apoptosis and senescence in response to genotoxic stress. Proper regulation of p53 and MYC are of undeniable importance in human health, as their mutation predisposes human cells to cancer. While the regulation and functions of p53 and MYC have been extensively studied, exactly how they generate variable cell fate outcomes in individual cells of a population responding to the same stress remains poorly understood. Our recent studies have shown that the dynamics of p53, the temporal pattern of p53 accumulation and degradation, serves an integral function for controlling MYC levels and cell fate responses to DNA damage. We have shown p53 dynamics to be highly variable between individual cells, but it remains to be determined how such variability contributes to heterogeneous responses to DNA damaging agents, which is critical for understanding tumor cell heterogeneity and evasion of therapies. To answer this question, we will combine time-lapse fluorescence microscopy to quantify p53 and MYC dynamics with quantitative analysis of key transcriptional targets at the single cell level to determine the temporal regulation of the triggering of apoptosis and senescence in response to DNA damage. We will apply this analysis to three conditions: 1.) non-transformed cells expressing normal p53 and MYC, 2.) transformed cells in which MYC expression is elevated over a range of concentrations, and 3.) transformed cells expressing a p53 gain-of-function hotspot mutation. This work will show how p53 and MYC dynamics control initiation of terminal cell fates in physiological and pathological conditions, and it will serve as the basis for approaches to reduce heterogeneous responses to DNA damaging compounds. These results will provide novel insight into the basic functioning of one of the most important stress response pathways in human cells, and are likely to inform innovative therapeutic strategies based on improved timing of the delivery of therapies. More broadly, this study is likely to provide general insights into the growing list of other important signaling pathways that use dynamic regulation.