Suppression of p53 response by blocking p53-Mediator binding with a stapled peptide

DNA-binding transcription factors (TFs) have been challenging to target with molecular probes. Many TFs function in part through interaction with Mediator; we sought to block p53 function by disrupting the p53-Mediator interaction. Through rational design and activity-based screening, we characterized a stapled peptide, with functional mimics of both p53 activation domains, that selectively disrupted p53- and Mediator-dependent transcription in vitro. This “bivalent peptide” also suppressed p53 transcriptional response in human cancer cells. Our strategy circumvents the TF and instead targets the TF-Mediator interface, with desired transcriptional outcomes. Different TFs target Mediator through different subunits, suggesting this strategy could be generalizable. Overall design: Examination of polII (pol II Ser5 3E8) TSS occupancy by ChIPseq with and without the inhibitory peptide in the presense of the p53 activator Nutlin3a.