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.TP53基因编码转录因子p53，该因子可结合一系列不同的靶基因以响应应激刺激。p53的激活可引发高度特异性的转录应答，但学界对p53如何调控启动子选择性的机制仍知之甚少。本文报道，p53的序列特异性结合活性受其靶基因及结合伙伴肽基精氨酸脱亚胺酶4（PADI4）调控。PADI4可通过酶促反应将肽基精氨酸转化为肽基瓜氨酸，这一过程被称为瓜氨酸化。本研究证实，PADI4可在体外对p53的C端区域进行瓜氨酸化修饰，并在体内验证了两处瓜氨酸化位点（R306、R363）。染色质免疫沉淀测序（ChIP-seq）结果显示，PADI4的表达会使p53的结合偏好从一部分经典结合位点转向与ETS转录因子相关的靶基因。使用瓜氨酸化特异性p53抗体进行的染色质组学分析进一步验证了这一结论。本研究结果将瓜氨酸化与p53功能关联起来，并阐明了PADI4这类染色质修饰因子如何调控p53的转录应答。