A p53 Oscillator Model of DNA Break Repair Control

The transcription factor p53 is an important regulator of cell fate. Mutations in p53 gene are associated with many cancers. In response to signals such as DNA damage, p53 controls the transcription of a series of genes that cause cell cycle arrest during which DNA damage is repaired, or triggers programmed cell death that eliminates possibly cancerous cells wherein DNA damage might have remained unrepaired. Previous experiments showed oscillations in p53 level in response to DNA damage, but the mechanism of oscillation remained unclear. Here we examine a model where the concentrations of p53 isoforms are regulated by Mdm22, Arf, Siah, and β-catenin. The extent of DNA damage is signalled through the switch-like activity of a DNA damage sensor, the DNA-dependent protein kinase Atm. This switch is responsible for initiating and terminating oscillations in p53 concentration. The strength of the DNA damage signal modulates the number of oscillatory waves of p53 and Mdm22 but not the frequency or amplitude of oscillations–a result that recapitulates experimental findings. A critical finding was that the phosphorylated form of Nbs11, a member of the DNA break repair complex Mre11-Rad50-Nbs11 (MRN), must augment the activity of ∗Corresponding Author :Herbert M Sauro, Keck Graduate Institute, 535 Watson Drive, Claremont, CA 91711, Phone: (909) 607 0377, Fax: (909) 607 8086, E-mail: [email protected]