Targeted citrullination enables p53 binding to non-canonical sites

TP53 encodes for the transcription factor p53, which binds to a diverse set of target genes in response to stress. Activation of p53 results in highly specific transcriptional responses, but the regulation of promoter selectivity by p53 is poorly understood. Here we report that sequence-specific binding of p53 is regulated by its target gene and binding partner PADI4. PADI4 enzymatically converts peptidyl-arginine to peptidyl-citrulline in a process known as citrullination. We show that PADI4 citrullinates p53 at the C-terminus in vitro, and we confirm two citrullination events in vivo (R306, R363). ChIP-seq reveals that PADI4 expression causes a redirection of p53 away from a subset of canonical binding sites to target genes associated with ETS transcription factors. Chromatin profiling using citrullination-specific p53 antibodies supports this conclusion. These findings link citrullination to p53 function and illustrate how chromatin modifiers like PADI4 can direct the p53 transcriptional response.