PAD2-Mediated Histone Citrullination Drives Tumor Progression by Enhancing Cell Proliferation and Modifying the Microenvironment in Pancreatic Cancer.

Histone citrullination is catalyzed by peptidyl-arginine deiminases (PAD) that play a role in gene regulation and several specific inhibitors have been developed. However, the clinical significance, molecular mechanisms of histone citrullination and PADs and effects of PAD inhibitors in pancreatic ductal adenocarcinoma (PDAC) remain unclear. This study aimed to investigate the role and potential molecular mechanisms of PADs in PDAC. Histone citrullination was upregulated and strongly associated with nuclear expression of PAD2, a one of the PAD family, in human PDAC tissues, correlating with aggressiveness and poor prognosis. PAD2 overexpression increased PDAC cell proliferation, whereas its knockdown had the opposite effect in vitro. PAD2 was recruited to the promoter regions of PRUNE1 and E2F1, resulting in the activation of their mRNA expression via increasing histone citrullination and chromatin accessibility. PAD2 overexpression enhanced tumorigenicity, and increased PRUNE1 expression and M2 tumor-associated macrophage (M2 TAM) infiltration in vivo. PAD2 inhibitor suppressed the growth and tumorigenicity of PAD2-expressing PDAC mice models by reducing PRUNE1 expression and M2 macrophage infiltration. Pad2 knockdown and PAD inhibitor treatment showed similar effects in syngeneic mouse models. The triple-high expression of nuclear PAD2, PRUNE1, and the M2 TAM marker CD206 may serve as independent adverse prognostic factors for human PDAC. Conclusively, PAD2-mediated histone citrullination drives PDAC progression by epigenetically regulating downstream target genes and influencing the tumor microenvironment. The PAD2-PRUNE1-M2 TAM axis presents a promising therapeutic target and prognostic indicator for PDAC. Implications: Elevated PAD2 expression promotes PDAC progression by epigenetically activating PRUNE1 and enhancing M2 macrophage polarization.