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.
