Negative Regulation of NIP45 Function by Peptidylarginine Deminase 4

IL-4 production in Th2 lymphocytes is regulated by the nuclear factor of activated T-cells (NFAT) and NFAT-interacting protein 45kDa (NIP45). Recently, we showed that arginine methylation of NIP45 modulates its interaction with NFAT and augments IL-4 transcription. Here we report that NIP45 methylation is negatively regulated by peptidylarginine-deiminase 4 (PAD4) via deimination of arginine residues and generation of the atypical amino acid citrulline. NIP45 loses its ability to become methylated after deimination by PAD4. Ectopic expression of PAD4 impairs the association of NIP45 with NFAT and profoundly inhibits IL-4 promoter activity. Whereas, knockdown of PAD4 expression in Th2 cells by a PAD4-directed shRNA-expressing retrovirus leads to elevated IL-4 production. Interestingly, a PAD4 variant is association with rheumatoid arthritis (RA) in a Japanese population. Indeed, many autoantibodies in RA are directed against citrullinated proteins. It has been proposed that PAD4 is linked to RA because citrullination of peptides leads to a breakdown of self-tolerance to self-antigens. Our data suggest that PAD4 may also influence RA development through regulation of the cytokine milieu. Modification of NIP45 by PAD4 provides a novel negative regulatory mechanism whereby NFAT and NIP45 control IL-4 and potentially other cytokines production.