Role Of Peptidylarginine Deiminase 2 (Pad2) In Epithelial Carcinogenesis And Tumor-Associated Inflammation
Mohanan Nair Padmini, Sunish
Numerous recent studies have shown that epigenetic modifications play a significant role in cancer pathogenesis. The PADs are a family of epigenetic enzymes that catalyze citrullination, a reaction by which PADs convert peptidyl-arginine to neutral citrulline, leading to the disruption of protein-protein interactions. Our lab has found that PAD2 has a critical role in breast cancer progression. The goal of this thesis research was to further elucidate the role of PAD2 in epithelial carcinogenesis using PAD2 overexpression tumor cell lines and a MMTV-FLAG-hPAD2 transgenic mouse model. We also aimed to evaluate how PAD2 may play a direct role in regulating chronic inflammation via macrophage extracellular chromatin trap release ("ETosis"). Interestingly, we found that 40% of the MMTV-FLAG-hPAD2 overexpressing transgenic mice developed proliferative skin lesions after five months of age. The tumors expressed the transgenic form of FLAG-hPAD2 and showed increased expression for inflammatory cytokines such as IL6 and IL8. As the next step we conducted a two-stage chemical carcinogenesis study to further evaluate the predilection of MMTV-FLAG-hPAD2 mice to develop more invasive skin tumors and compare the histopathology of these tumors with the WT tumors. We found that a higher percentage of MMTV-FLAG-hPAD2 mice developed skin papillomas and the transgenic tumors were more invasive. Furthermore, hPAD2 expression levels were highly positively correlated with chemokine levels and negatively correlated with the cell adhesion markers suggesting the role of PAD2 in assisting epithelial-mesenchymal transition. We had previously shown that PAD4 isozyme in neutrophils is involved in chromatin decondensation and extracellular chromatin trap release. In this thesis research we provide evidence on how PAD2 is involved in macrophage extracellular trap (MET) release. Using in vitro macrophage culture models, we found that PAD2 is critical in functional MET release and that METs contain high levels of histone H4 citrulline 3 (H4Cit3) modification. Using human tongue SCC tissue, we show that CD68+ macrophage associated ETs exist in tumor tissue and are highly positive for citrullinated histones. Additionally, we show that PAD2-rich macrophages associated with chronic subclinical inflammation in adipose tissue also release METs suggesting the significant role of PAD2 in chronic inflammation via MET release. Collectively, these studies provide strong experimental evidence establishing PAD2 as a potential oncogene, a therapeutic target for immunomodulation and a regulator of obesity and tumor associated inflammation.
Peptidylarginine deiminase 2 (PAD2); Cancer progression; Extracellular chromatin traps (ETosis)
Coonrod, Scott A.
August, Avery; Fischbach, Claudia; Weiss, Robert S.
Ph.D. of Veterinary Medicine
Doctor of Philosophy
dissertation or thesis