Regulation of E2F1 by PAD4 mediated citrullination

Peptidyl arginine deiminase (PAD) 4 is a nuclear enzyme that converts arginine residues to citrulline. PAD4 activity has been implicated in inflammatory disease and cancer, although its mechanism of action, particularly the identity of functionally relevant targets, remains unclear. Moreover, there are no known reader domains specifically recognising citrulline modifications. E2F transcription factors play a central role in regulating gene expression during cellular proliferation but in addition participate in diverse biological processes. Furthermore, it is known that arginine methylation provides an important level of control in dictating the biological consequence of E2F1 activity. Here, we show that E2F1 is citrullinated by PAD4 on functionally important arginine residues. Citrullination of E2F1 assists its chromatin association, specifically to cytokine genes in granulocyte cells, and regulates binding of the bromodomain reader BRD4 to an acetylated domain inE2F1. Accordingly, the combined inhibition of PAD4 and BRD4 impedes the chromatin association of E2F1 and the activation of cytokine gene expression. When administered as a combination therapy in the murine collagen-induced arthritis model, small molecule inhibitors of PAD4 and BRD4 provide an effective approach for preventing collagen-induced arthritis. Our results shed light on a new E2F-dependent pathway that mediates the inflammatory effect of PAD4 and, for the first time, establish the interplay between citrullination and acetylation as a regulatory interface for driving inflammatory gene expression. Moreover, the results highlight a novel therapeutic approach for treating chronic inflammatory diseases