Protein Arginine Deiminase 2 and 4 (PAD2 & PAD4) are independent predictors of good prognosis in colorectal cancer
Objective: Protein arginine deiminase (PADs) are a family of enzymes that catalyse the post translational modification (PTM) of proteins. In this study the prognostic significance of PAD2 and PAD4 in colorectal cancer (CRC) was assessed. Design: PAD2 and PAD4 expression was assessed immunohistochemically in a cohort of CRC patients. Association between PAD expression with clinicopathology, protein expression and outcome was determined. Results: CRC tissues expressed variable levels of PAD2 which was mainly localised in the cytoplasm and correlated with patient survival (p=0.005); high expression increased survival time from 43.5 to 67.6 months. Expression of cytoplasmic PAD2 correlated with expression of nuclear β catenin, PAD4 and alpha-enolase. In contrast expression of nuclear PAD2 correlated with a decrease in survival (p=0.010), with high expression decreasing survival from 76.4 to 42.9 months. CRC tissues expressed variable levels of PAD4 in both the nucleus and cytoplasm. Expression of cytoplasmic PAD4 correlated with survival (p=0.001) with high expression increasing survival time from 48.1 to 71.8 months. Expression of cytoplasmic PAD4 correlated with expression of, nuclear β catenin, alpha-enolase (p≤ 0.0001, p=0.002) and the apoptotic related protein, Bcl-2. Expression of nuclear PAD4 also correlated with survival (p=0.011) with high expression of nuclear PAD4 increasing survival time from 55.4 to 74 months. Expression of nuclear PAD4 correlated with p53, alpha-enolase and Bcl-2. Multivariate analysis showed that TNM stage and cytoplasmic PAD2 and PAD4 remained independent prognostic factors in CRC. Conclusion: Both PAD2 and PAD4 are good prognostic factors in CRC.