p53 regulates its own activator: transcriptional co-activator PC4, a new p53-responsive gene.

The tumour suppressor protein p53 regulates the expression of several genes that mediate cell cycle arrest, apoptosis, DNA repair and other cellular responses. Recently, we have shown that human transcriptional co-activator PC4 is a unique activator of p53 function. In the present study, we report that PC4 is a p53-inducible gene. Bioinformatics analysis reveals multiple p53-binding sites in the PC4 promoter. We have found that indeed p53 binds to all the identified sites in vitro and in vivo with varying affinities. p53 acts as an activator of PC4 transcription. Both PC4 mRNA and protein levels increase in response to stimuli that result in p53 induction. Furthermore, PC4 enhances p53 recruitment to the PC4 promoter. Our results thus establish the first report of a positively regulated feedback loop to control p53 function.