PADI2 (peptidyl arginine deiminase 2) is a calcium-dependent enzyme that catalyzes the conversion of protein-bound arginine residues to citrulline, a post-translational modification called citrullination or deimination 1. This process changes the protein charge from positive to neutral, affecting protein folding, stability, and function 2. PADI2 can translocate to the nucleus and citrullinate both cytoplasmic and nuclear proteins, particularly histone H3 at arginine residue 26 32. The enzyme plays critical roles in transcriptional regulation through chr1 remodeling and RNA polymerase II modification 1. In cancer contexts, PADI2 exhibits dual roles: it promotes prostate cancer progression by stabilizing androgen receptor signaling and facilitating castration-resistant prostate cancer development 3, while serving as a potential therapeutic target in lung cancer, particularly in non-smokers 4. PADI2 also contributes to drug resistance mechanisms in hepatocellular carcinoma through macrophage extracellular trap formation 5. Additionally, PADI2 serves as a biomarker in Duchenne muscular dystrophy, with plasma levels decreasing following therapeutic intervention 6. The gene's expression is regulated by Sp1 and Sp3 transcription factors through GC-rich promoter elements 7.