P2-01-07: Proto-Oncogene PELP1 Promotes Metastasis through miR-200 Dependent Pathway.

Background: Endocrine therapy is the most important component of adjuvant therapy for patients with early stage estrogen receptor (ER)-positive breast cancer. Despite positive effects of hormonal therapy, initial or acquired resistance to endocrine therapies frequently occurs and tumor recurs as advanced metastatic disease. Accumulating evidence suggests that ER-coregulators play an essential role in cancer progression and that metastatic tumors have increased expression of coregulators. Proline glutamic acid rich protein (PELP1) is an ER coregulator, its expression is upregulated during breast cancer progression to metastasis. PELP1 is an independent prognostic predictor of shorter breast cancer specific survival and its elevated expression positively associates with markers of poor outcome. The objective of this study is to examine the mechanism and significance of PELP1 mediated signaling in breast cancer metastasis. Methods: To examine the significance of PELP1 in metastasis, we have used two ER+Ve (ZR75, MCF7) and one ER-ve MDA-MB 231 models cell that either stably express PELP1 or PELP1 shRNA. MCF7 and ZR75 cells were used as controls. Role of PELP1 on metastasis was studied using Boyden chamber, wound healing, invasion, MMP and reporter gene assays. Epithelial to Mesenchymal Transition (EMT) real time qPCR Array (Super array) was used to identify PELP1 target genes. Whole genome based microarray analysis was performed to identify PELP1 regulated microRNAs. miRNA mimetics and antamiRs were used to establish the mechanism. Nude mice based assays were performed to study the role of PELP1 on in vivo metastasis. Results: Boyden chamber and wound healing assays showed PELP1 down regulation substantially affect migration of both ER+ve and ER-ve cells and showed alterations in the expression of the EMT markers. Focused microarray studies identified PELP1 modulate expression of eight genes involved in the EMT (including Snail, Twist, ZEB1 and MMPs). In xenograft assays, overexpression of PELP1 in non-metastatic cells increases their propensity for metastasis in vivo, while PELP1 knockdown in metastatic model cells decreased in vivo metastatic potential. Whole genome microRNA array analysis revealed that miR 200a and miR141 were upregulated in cells expressing PELP1-shRNA compared to control shRNA expressing cells. Accordingly, over expression of PELP1 in low metastatic model cells decreased expression of miR200a and miR141. Mechanistic studies showed PELP1 down regulate expression of metastasis suppressive microRNAs (miR200a and miR141) by promoting chromatin modifications. Ectopic expression of miR200a and miR141 mimetic decreased PELP1 mediated metastatic functions. Conclusions: These results suggest that PELP1 play a role in breast cancer metastasis by promoting cell motility/EMT by modulating microRNA expression and blockage of PELP1 axis has potential to reduce metastasis potential of breast cancer cells. Understanding how NR coregulator PELP1 plays a role in metastasis will be useful in maximizing treatment opportunities for metastatic breast cancer. This study is funded by DOD grant. Citation Information: Cancer Res 2011;71(24 Suppl):Abstract nr P2-01-07.