BackgroundPenetration of the mammary gland basement membrane by cancer cells is a crucial first step in tumor invasion. Using a mouse model of ductal carcinoma in situ, we previously found that inhibition of peptidylarginine deiminase 2 (PAD2, aka PADI2) activity appears to maintain basement membrane integrity in xenograft tumors. The goal of this investigation was to gain insight into the mechanisms by which PAD2 mediates this process.MethodsFor our study, we modulated PAD2 activity in mammary ductal carcinoma cells by lentiviral shRNA-mediated depletion, lentiviral-mediated PAD2 overexpression, or PAD inhibition and explored the effects of these treatments on changes in cell migration and cell morphology. We also used these PAD2-modulated cells to test whether PAD2 may be required for EGF-induced cell migration. To determine how PAD2 might promote tumor cell migration in vivo, we tested the effects of PAD2 inhibition on the expression of several cell migration mediators in MCF10DCIS.com xenograft tumors. In addition, we tested the effect of PAD2 inhibition on EGF-induced ductal invasion and elongation in primary mouse mammary organoids. Lastly, using a transgenic mouse model, we investigated the effects of PAD2 overexpression on mammary gland development.ResultsOur results indicate that PAD2 depletion or inhibition suppresses cell migration and alters the morphology of MCF10DCIS.com cells. In addition, we found that PAD2 depletion suppresses the expression of the cytoskeletal regulatory proteins RhoA, Rac1, and Cdc42 and also promotes a mesenchymal to epithelial-like transition in tumor cells with an associated increase in the cell adhesion marker, E-cadherin. Our mammary gland organoid study found that inhibition of PAD2 activity suppresses EGF-induced ductal invasion. In vivo, we found that PAD2 overexpression causes hyperbranching in the developing mammary gland.ConclusionTogether, these results suggest that PAD2 plays a critical role in breast cancer cell migration. Our findings that EGF treatment increases protein citrullination and that PAD2 inhibition blocks EGF-induced cell migration suggest that PAD2 likely functions within the EGF signaling pathway to mediate cell migration.Electronic supplementary materialThe online version of this article (doi:10.1186/s12885-017-3354-x) contains supplementary material, which is available to authorized users.

Aims Clear cell stromal tumour of the lung (CCST‐L) is a rare, recently recognised neoplasm which has been found to express TFE3 and harbour YAP1::TFE3 fusions. Initial data suggested a benign process; however, a single reported case gave rise to distant metastases. We sought to describe the clinicopathological and molecular features of additional cases of CCST‐L. Methods and Results Pathology and molecular archives were searched for cases of CCST‐L or tumours with YAP1::TFE3 fusions. Clinical features were noted. Available slides, including immunohistochemical studies, were re‐reviewed for diagnosis confirmation and assessment of pathological features. Results of molecular studies were also recorded. Four tumours were identified, all occurring in women (median age = 61 years, range = 24–69). Median tumour size was 4.4 cm (range = 1–9.5 cm); three tumours were unifocal and one was multifocal. Tumours were composed of epithelioid to spindled cells with eosinophilic to clear cytoplasm and grew in sheets, vague nests and short fascicles. Nuclear atypia was predominately mild; however, two cases showed scattered atypical cells. Mitotic activity was generally low, although one case showed a mitotic count of 6/2 mm2. All tumours expressed TFE3 and harboured YAP1::TFE3 fusions. One case was unresectable and was treated with chemotherapy, and two underwent complete resection. One patient died of disease 7 months following diagnosis, while a second patient was alive with no evidence of disease after 43 months. Follow‐up was not available for two cases. Conclusion CCST‐L expresses TFE3, harbours YAP1::TFE3 fusions and at least rare cases behave in an aggressive manner.

Peptidylarginine deiminases (PADIs) enzymes are calcium-dependent enzymes that post-translationally convert positively charged protein arginine residues to a neutrally charged citrulline in a process known as citrullination or deimination. This loss of charge can alter the tertiary structure of proteins and affect protein-protein and protein-DNA interactions. We, and others, have found that PADI-mediated histone tail citrullination alters chromatin structure and regulates gene expression. For example, we found that PADI2 interacts with estrogen receptor (ERα) and that PADI2-mediated citrullination of histone H3 arginine 26 residues at ERα binding sites regulates target gene expression. In addition, we also found that PADI2 is often co-expressed with HER2 in both breast cancer cell lines and in tumor tissue. Our molecular studies suggest that PADI2 activates HER2 expression via histone citrullination at the HER2 gene locus and that HER2 signaling appears to induce PADI2 expression, thus potentially forming an oncogenic positive feedback loop with HER2. These findings suggest an important role for PADI2 in breast cancer progression. This prediction is supported by our finding that PADI2 expression is upregulated in cancer cells and that depletion of PADI2 from breast cancer cells results in reduced tumorigenicity. In addition, we found that transgenic overexpression of PADI2 promotes carcinogenesis and that the PADI inhibitor, Cl-Amidine, slows tumor growth in mouse models of breast cancer. Furthermore, we found that Cl-Amidine also maintains basement membrane integrity in xenograft tumors, preventing initiation of metastasis. Together, these findings suggest that PADI2 represents a novel therapeutic target and biomarker for early stage breast cancer. Citation Format: Sachi Horibata, John L. McElwee, David Sadegh, Katherine Rogers, Dalton McLean, Scott A. Coonrod. Peptidylarginine deiminase 2 as a novel therapeutic target for breast cancer. [abstract]. In: Proceedings of the 106th Annual Meeting of the American Association for Cancer Research; 2015 Apr 18-22; Philadelphia, PA. Philadelphia (PA): AACR; Cancer Res 2015;75(15 Suppl):Abstract nr 2271. doi:10.1158/1538-7445.AM2015-2271