Increased peptidylarginine deiminases expression during the macrophage differentiation and participated inflammatory responses.

OBJECTIVE: To investigate the expression of peptidylarginine deiminases (PADIs) during macrophage differentiation and its role in inflammatory responses. METHODS: The protein expression of PADI2, PADI4, and citrullinated histone 3 in U937 cells, differentiated macrophages, and macrophages stimulated with lipopolysaccharides (LPS) were analyzed by Western blotting. Three PADI inhibitors were used for assessing their effects on the secretion of proinflammatory cytokines in macrophages. The differential expressed citrullinated proteins during macrophage differentiation were probed by self-prepared anti-citrullinated protein antibodies, and the reactive bands were sent for proteomic analyses. Transfection studies were conducted to search for the functions of specific proteins. A specific protein was cloned and citrullinated for its protein binding study. RESULTS: The expression of PADI2 and PADI4 markedly increased during macrophage differentiation, whereas the formation of citrullinated histone 3 increased after stimulated with lipopolysaccharides. Three PADI inhibitors suppressed the LPS mediated proinflammatory cytokines secretion, but did not affect the expression of PADI2 and PADI4. Plasminogen activator inhibitor-2 (PAI-2) was citrullinated during macrophage differentiation. The expression of PAI-2 increased during macrophage differentiation and further increased after stimulated with LPS. Suppressed PAI-2 expression decreased the expression and secretion of proinflammatory cytokines. Decreased PADI2 expression also suppressed the expression of PAI-2 and protein levels of citrullinated PAI-2. The citrullination of PAI-2 inhibited its binding ability to proteasome subunit beta type-1 (PSMB1). CONCLUSION: PADI2 and PADI4 protein levels increased during the macrophage differentiation resulting in protein citrullination, including PAI-2. The increased expression of PAI-2 promoted inflammatory response, and the citrullination of PAI-2 impaired its binding to PSMB1. Therefore, protein citrullination could play a critical role in macrophage differentiation and function.

Peptidyl arginine deiminase 2 (Padi2) is expressed in Sertoli cells in a specific manner and regulated by SOX9 during testicular development.

Peptidyl arginine deiminases (PADIs) are enzymes that change the charge of proteins through citrullination. We recently found Padi2 was expressed exclusively in fetal Sertoli cells. In this study, we analyzed the transcriptional regulation of Padi2 and the role of PADI2 in testicular development. We showed SOX9 positively regulated Padi2 transcription and FOXL2 antagonized it in TM3 cells, a model of Sertoli cells. The responsive region to SOX9 and FOXL2 was identified within the Padi2 sequence by reporter assay. In fetal testes from Sox9 knockout (AMH-Cre:Sox9flox/flox) mice, Padi2 expression was greatly reduced, indicating SOX9 regulates Padi2 in vivo. In vitro analysis using siRNA suggested PADI2 modified transcriptional regulation by SOX9. However, Padi2-/- XY mice were fertile and showed no apparent reproductive anomalies. Although, PADI2 is known as an epigenetic transcriptional regulator through H3 citrullination, no significant difference in H3 citrullination between wildtype and Padi2-/- XY gonads was observed. These results suggest Padi2 is a novel gene involved in testis development that is specifically expressed in Sertoli cells through the regulation by SOX9 and FOXL2 and PADI2 supports regulation of target genes by SOX9. Analysis of the Padi2-/- XY phenotype suggested a redundant factor compensated for PADI2 function in testicular development.

Induction of peptidylarginine deiminase 2 and 3 by dibutyryl cAMP via cAMP-PKA signaling in human astrocytoma U-251MG cells.

Peptidylarginine deiminases (PADs) are posttranslational modification enzymes that citrullinate (deiminate) protein arginine residues in a calcium-dependent manner, yielding citrulline residues. Enzymatic citrullination abolishes positive charges of native protein molecules, inevitably causing significant alterations in their structure and function. Previously, we reported the abnormal accumulation of citrullinated proteins and an increase of PAD2 content in hippocampi of patients with Alzheimer disease. In this study, we investigated PAD expression by using dibutyryl cAMP (dbcAMP) in human astrocytoma U-251MG cells. Under normal culture conditions, PAD2 and PAD3 mRNA expression is detectable with quantitative PCR in U-251MG cells. The addition of dbcAMP in a dose-dependent manner significantly increased this mRNA expression and protein levels. Moreover, PAD enzyme activity also increased significantly and dose-dependently. Furthermore, the expression of PAD2 and PAD3 mRNA was inhibited by the cAMP-dependent PKA inhibitor KT5720, suggesting that such expression of dbcAMP-induced PAD2 and PAD3 mRNA is mediated by the cAMP-PKA signaling pathway in U-251MG cells. This is the first report to document the PAD2 and PAD3 mRNA expression induced by dbcAMP and to attribute the induction of these genes to mediation by the cAMP-PKA signaling pathway in U-251MG cells. © 2016 Wiley Periodicals, Inc.