Coordination of PAD4 and HDAC2 in the regulation of p53-target gene expression

Histone Arg methylation and Lys acetylation have been found to cooperatively regulate the expression of p53-target genes. Peptidylarginine deiminase 4 (PAD4) is an enzyme that citrullinates histone arginine and monomethyl-arginine residues thereby regulating histone Arg methylation. We have recently found that PAD4 serves as a p53 corepressor to regulate histone Arg methylation at the p53-target gene p21/WAF1/CIP1 promoter. However, it has not been tested whether histone Arg citrullination coordinates with other histone modifications to repress transcription. Here, we show that histone deacetylase (HDAC2) and PAD4 interact with p53 through distinct domains and simultaneously associate with the p21 promoter to regulate gene expression. After DNA damage, PAD4 and HDAC2 dissociate from several p53-target gene promoters (for example, p21, GADD45, and PUMA) with a concomitant increase in histone Lys acetylation and Arg methylation at these promoters. Furthermore, PAD4 promoter association and histone Arg modifications are regulated by p53 and HDAC activity. In contrast, HDAC2 promoter association and histone Lys acetylation are affected by p53 and PAD4 activity at minor degrees. Importantly, PAD4 inhibitor Cl-amidine and HDAC inhibitor suberoylanilide hydroxamic acid show additive effects in inducing p21, GADD45, and PUMA expression and inhibiting cancer cell growth in a p53-dependent manner. Our results unveil an important crosstalk between histone deacetylation and citrullination, suggesting that a combination of PAD4 and HDAC2 inhibitors as a potential strategy for cancer treatment.