Abstract 897: PEA-15 regulates epithelial-mesenchymal transition and invasive behavior through its phosphorylation in triple-negative breast cancer
Authors: Park Jihyun , Cohen Evan N. , Chauhan Gaurav , Lee Jangsoon , Ueno Naoto T. , Tripathy Debu , Reuben James M. , Bartholomeusz Chandra 
Published: July 2017

Abstract
Triple-negative breast cancer (TNBC) is an aggressive subtype with no proven active targeted therapies available. Patients with TNBC have a very poor prognosis because the disease often metastasizes. Newer approaches to preventing metastasis and inhibiting tumor growth, are crucial to improving prognosis for these patients. Previously it has been shown that PEA-15 binds to ERK, preventing ERK from being translocated to the nucleus and hence blocking its activity. Our previous studies showed that overexpression of wild type PEA-15 inhibited ERK activity and reduced tumor volume in a TNBC xenograft model. We also showed that PEA-15 being unphosphorylated at both Ser104 and Ser116 inhibited ovarian cancer cell tumorigenicity. However, the function and impact of PEA-15 phosphorylation on TNBC is not well understood. From these observations, we hypothesized that unphosphorylated PEA-15 will prevent metastasis in TNBC through the inhibition of EMT. To study the effect of the phosphorylation status of PEA-15 on metastasis in TNBC, we established stable cell lines overexpressing nonphosphorylatable (PEA-15-AA) and phosphomimetic (PEA-15-DD) mutants in MDA-MB-468 cells. The clonogenic growth of PEA-15-AA was significantly reduced by 80% compared with vector control, PEA-15-V. Anchorage-independent growth of PEA-15-AA was inhibited by 60% compared with PEA-15-V (P&lt;0.05). PEA15-AA upregulated the expression of E-cadherin, a key epithelial molecular marker and decreased expression of vimentin suggesting that PEA-15-AA reverses EMT. Moreover, compared with PEA-15-V, migration and invasion of PEA-15-AA were significantly reduced. To determine the mechanism of how PEA-15 regulates EMT and metastasis, we performed RT-PCR immune and metastasis arrays. We found that expression levels of IL-6, IL-8 and PDGF-BB were greatly decreased in PEA-15-AA. Upon stimulation of the PEA-15-AA with these cytokines, mesenchymal characteristics were partially rescued indicating that PEA-15-AA may inhibit the expression of these cytokines, thereby reversing EMT. Further, to determine the in vivo effect of PEA-15-AA, we injected stable transfectants of MDA-MB-468 cells into the mammary fat pad of NOD/SCID mice. The PEA-15-DD-injected group showed an increase (P&lt;0.05) in tumor volume compared with PEA-15-V and PEA-15-AA groups. Additionally, immunohistochemical data revealed that vimentin and p-β-catenin (Ser675) expression was greatly decreased in PEA-15-AA tissues, suggesting that PEA-15-AA has antitumor effects. Further studies are warranted to evaluate the impact of PEA-15 phosphorylation on metastasis in vivo using mice bearing highly metastatic human breast tumor and determine the mechanism underlying decreased cytokine expression in PEA-15-AA. Together, this study highlights the potential for overexpression of unphosphorylated PEA-15 as an approach for TNBC-targeted therapy.
Citation Format: Jihyun Park, Evan N. Cohen, Gaurav Chauhan, Jangsoon Lee, Naoto T. Ueno, Debu Tripathy, James M. Reuben, Chandra Bartholomeusz. PEA-15 regulates epithelial-mesenchymal transition and invasive behavior through its phosphorylation in triple-negative breast cancer [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2017; 2017 Apr 1-5; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2017;77(13 Suppl):Abstract nr 897. doi:10.1158/1538-7445.AM2017-897