PADI4 ChIP-chip from MCF-7 cells

Peptidylarginine deiminase IV (PADI4) catalyzes the conversion of positively charged arginine and methylarginine residues to neutrally charged citrulline residues on histone tails. This activity has been linked to the repression of gene transcription on a limited number of genes. To broaden our knowledge of the regulatory potential of PADI4, we utilized chromatin immunoprecipitation coupled with promoter tiling array (ChIP-chip) to more comprehensively investigate the range of PADI4 target genes across the genome in MCF-7 cells. Results showed that PADI4 is enriched in the gene promoter regions near the transcription start sites (TSSs) and, surprisingly, this pattern of binding is primarily associated with actively transcribed genes. Computational analysis found Elk-1, a member of the ETS oncogene family, to be highly enriched around PADI4 binding sites and coimmunoprecipitation analysis then confirmed that Elk-1 physically associates with PADI4. The expression of two well characterized Elk-1 target genes, c-fos and egr-1, was then found to be inhibited following treatment of MCF-7 cells with a PADI4 specific inhibitor. The inhibitor also significantly reduced levels of acetylation at H4 lysine 5 at these promoters suggesting that the activating function of PADI4 at these target genes is mediated, in part, by interplay between histone citrullination and HAT-mediated acetylation. These findings greatly expand our knowledge of the role of PADI4 in gene regulation by defining a new role for PADI4 catalyzed histone citrullination in mediating gene transactivation. Two PADI4 ChIP-chip biological replicates from MCF-7 human breast cancer cells are included.