Citrullination of AKT2 Catalyzed by PAD1 Facilitates the Maintenance of Stemness Characteristics of Ovarian Cancer Stem‐Like Cells in Ovarian Cancer

The presence of ovarian cancer stem-like cells (OCSLCs) is a crucial driving force for malignant progression, metastasis, and tumor recurrence of ovarian cancer (OC). However, the mechanisms underlying activation and maintenance of OCSLC stemness remain unclear. Here, it is identified an increased expression of peptidylarginine deiminase 1 (PAD1) in OC cells, particularly within the CD133⁺ subset or cisplatin-resistant cells, which is positively associated with the upregulation of stemness-related markers and maintenance of stemness in OCSLCs. Mechanistically, PAD1 specifically binds to the kinase domain of AKT2 and catalyzes citrullination at R202. Citrullination subsequently promotes AKT2 phosphorylation at S474 and T309, the two critical residues for AKT2 kinase activity. As a major driver of OC malignancy, the activation of AKT2 leads to an increased expression of CCAAT/Enhancer Binding Protein Beta (CEBPβ), thereby promoting CEBPβ enrichment to the promoters of a subset of stemness-related genes. Moreover, PAD1 gene silencing, inhibition of AKT2 citrullination, and AKT2 mutation all decrease the tumor-initiating ability of OC cells both in vitro and in vivo. Importantly, treatment with a PAD1 inhibitor can resensitize cisplatin-resistant OC cells to cisplatin treatment, suggesting that targeting PAD1/AKT2/CEBPβ signaling axis in OCSLCs may be highly effective in preventing OC progression.