Figure 5. Model of regulation of p53 stabilization by USF1 in response to stress.

USF1 prevents MDM2-mediated p53 degradation under stress conditions, thereby ensuring the stability and tumor suppressor activity of the p53 protein. Left Panel, in the absence of stress, p53 is targeted to proteasomal degradation after binding to MDM2, maintaining cell proliferation. Right Panel, under DNA-damage context, USF1 counteracts MDM2 function by interacting with p53 thereby increasing its transcriptional activity to control transient cell cycle arrest and DNA repair processes. In the absence of USF1, p53 stabilization is abolished abrogating cell cycle control in response to DNA damage and thereby favoring genomic instability.