Abstract P4-06-01: Significance and Therapeutic Potential of PELP1 in ER-Negative Breast Cancers

Background: During the past 20 years, studies have extensively focused on the role of estrogen receptor (ER) and progesterone receptor (PR) in breast cancer. Even through ER and PR explain the biology of ER-positive tumors, it remain unknown as to what drives ER-negative metastatic tumors. Recent advances implicated potential importance of several additional nuclear receptor (NRs) including ERRα, AR, GR, and PPAR in breast cancer. NR action is complex, requires functional interactions with coregulators, and deregulation of coregulators occur during cancer progression. As a modulator of multiple NR functions, coregulators are likely to play a role in breast cancer progression to metastasis. Recent studies indicated that metastatic tumors have increased expression of corgulators. Proline glutamic acid rich protein (PELP1) is a NR coregulator, and its expression is upregulated during breast cancer progression. The objective of this study is to examine whether proto-oncogene PELP1 contributes to metastatic potential of ER-negative breast cancer cells and to test whether blocking of PELP1 signaling axis will have therapeutic effect. Methods: We have used two ER-negative model cells; (1) MDA-MB231 cells that facilitate study of bone and lungs metastasis of breast cancer cells using Nude mice models, (2) 4T1 cells, a clinically relevant model of spontaneous breast cancer metastasis that facilitate tumor growth studies using syngenic mice. To establish the significance of PELP1 axis, we have established clones stably expressing PELP1-shRNA (MDA-MB231- PELP1 shRNA, 4T1-PELP1 shRNA). Proliferation was measured using CellTiter-Glo assays. Role of PELP1 on metastasis was studied using Boyden chamber, wound healing, invasion and MMP assays. Epithelial to Mesenchymal Transition (EMT) real time qPCR Array (Super array) was used to identify PELP1 target genes and targets were validated using ChIP assays. Nude mice based assays were performed to study the role of PELP1 on in vivo metastasis. Results: MDA-MB231 and 4T1 cells expressing PELP1-shRNA showed decreased PELP1 expression (∼75% of endogenous levels) and exhibited decreased propensity to proliferate in in vitro growth assays. Boyden chamber and wound healing assays showed PELP1 down regulation substantially affect migratory potential of MDA-MB231 and 4T1 cells. PELP1 shRNA model cells showed alterations in the expression of the EMT markers. EMT array studies identified eight genes involved in the EMT (including MMPs, E-cadherin, MTA1) as PELP1 potential target genes and ChIP studies showed PELP1 recruitment to these gene promoters. Overexpression of PELP1 in nonmetastatic cells increases their propensity for metastasis in vivo, while, PELP1 knockdown in metastatic model cells decreased their metastatic potential. Nanopartiles delivering PELP1-siRNA significantly affected the growth and metastatic potential of ER-ve cells. Conclusions: These results suggest that PELP1 play a role in ER-ve breast cancer metastasis by promoting cell motility and EMTand blockage of PELP1 axis reduces metastasis potential of ER-negative breast cancer cells. Understanding how NR coregulator PELP1play a role in metastasis will be useful in maximizing treatment opportunities for metastatic breast cancer. This study is funded by Komen grant KG091267. Citation Information: Cancer Res 2010;70(24 Suppl):Abstract nr P4-06-01.