Abstract LB-101: Combined p53 dynamics and post-translational modifications determine subsequent protein expression and cell fate

Abstract

Abstract The tumor suppressor protein p53 is activated by a diverse repertoire of cellular stresses (e.g. oncogenic signalling, DNA damage) and as a transcription factor induces the expression of response pathways genes (including cell cycle arrest, senescence, apoptosis). While p53 is frequently lost during tumorigenesis, approximately 50% of human tumors retain intact p53, potentially rendering them sensitive to p53-induced cell death during radiotherapy. Recent single cell analysis from our lab has shown that irradiation of cells does not cause a simple sustained accumulation of p53, but rather, induces pulsatile p53 dynamic that oscillates at 5-hour periods resulting from a p53-Mdm2 negative feedback loop, leading to reversible cell cycle arrest. Disrupting this feedback loop by small molecules results in sustained p53 dynamics, leading to irreversible apoptosis or senescence. Moreover, extensive work by others has shown that post-translational modifications (PTM) on p53 also govern the cell fate decision process. Here we show that aside from differences in p53 dynamics following irradiation, multiple PTMs on p53 also differ, with the latter causing quantitative changes of p53 binding to interactions proteins and subsequent alterations in promoter binding. In contrast, p53 dynamics govern broad transcription dynamics of target genes. For example, pulsatile p53 dynamics result in several distinct patterns of mRNA transcription including a cluster of oscillating p53 target genes. However, these oscillatory mRNA dynamics are lost at the protein level. The only p53 target protein that oscillates is the Mdm2 negative regulator of p53, while all other targets gradually accumulate over time. Furthermore, sustained p53 dynamics over 24h results in far greater accumulation of nearly all target proteins compared to pulsatile p53 dynamics, which likely explains the differences in the reversibility of cell fate decisions. The results described here uncover a link between p53 dynamics and p53 PTMs providing an overall mechanistic cell fate selection process by p53, which have important implications both for understanding of cell signalling processing as well as improving p53-mediated therapies. Citation Format: Dan Lu, Kristina Holton, Antonina Hafner, Caroline DeHart, Jacek Sikora, Houjiang Zhou, Ashwini Jambhekar, Neil Kelleher, Jeremy Gunawardena, Galit Lahav. Combined p53 dynamics and post-translational modifications determine subsequent protein expression and cell fate [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2019; 2019 Mar 29-Apr 3; Atlanta, GA. Philadelphia (PA): AACR; Cancer Res 2019;79(13 Suppl):Abstract nr LB-101.