HCT-116 wild type and p53−/− cells revealed that CREB was bound to the PPM1D promoter region in the absence of stress and independent of the presence of p53, which further supports a role of CREB in basal PPM1D transcriptional regulation (19). Like p53, CREB also regulates PPM1D transcription after IR exposure. This was illustrated by the finding that the amount of CREB bound to the PPM1D promoter region increased two hours after IR. Surprisingly, results from experiments with mutated reporter constructs suggested that even though both p53 and CREB regulate PPM1D, they appear to do so independently (19). Thus, CREB facilitates the transcription of PPM1D basally and after DNA damage independently of p53.
