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. 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.