Abstract P5-04-05: Loss of REST in breast cancer promotes tumor progression through estrogen sensitization, MMP24 and CEMIP overexpression
Authors: Vargheese Aditya M. , Cloud Ashley S. , Gunewardena Sumedha , Shimak Raeann M. , Ganeshkumar Sornakala , Kumaraswamy Easwari , Jensen Roy A. , Chennathukuzhi Vargheese M. 
Published: March 2022

Abstract
Breast cancer is the most common malignancy in women and is the second leading cause of cancer-related deaths. Breast cancer is both pathologically and genetically heterogeneous, making early detection and treatment difficult. A subset of breast cancers expresses normal levels of REST (Repressor Element 1 Silencing Transcription factor) mRNA but lacks functional REST protein. Loss of REST function is seen in ~20% of breast cancers and is associated with a more aggressive phenotype and poor prognosis. Despite the frequent loss of REST, little is known about the role of REST in the molecular pathogenesis of breast cancer. TCGA data was analyzed for the expression of REST and its target genes in breast cancer patient samples. MCF7, an estrogen and progesterone receptor positive breast cancer cell line, and MDA-MB-231, a triple-negative breast cancer cell line were used for in vitro studies to understand the function of REST. To evaluate the role of REST in the regulation of hormone receptor pathways, RNA sequencing was carried out on total RNA from MCF7 cells after siRNA knockdown of REST followed by treatment of hormones estrogen and progesterone. Chromatin Immunoprecipitation and PCR were performed on REST knockdown cells to evaluate gene regulation by REST and understand its tumor suppressor role in breast cancer. We show that REST directly regulates CEMIP (Cell Migration-Inducing and Hyaluronan-Binding Protein, KIAA1199) and MMP24 (Matrix Metallopeptidase 24), genes known to have roles in invasion and metastasis. REST knockdown in breast cancer cell lines leads to significant upregulation of CEMIP and MMP24. In addition, we found that REST binds to RE-1 sites (Repressor Element-1) within the genes and influences their transcriptional regulation. Aberrant expression of CEMIP and MMP24 results in CD44 dependent cell signaling that promotes cell proliferation and survival. We also found that the estrogen receptor signaling pathway is activated in the absence of REST regardless of hormone treatment. Our studies show that REST plays a significant role in altering the estrogen signaling pathway in hormone-sensitive breast cancers. REST transcriptionally regulates genes known to affect cell invasion and metastasis. Importantly, we demonstrate that loss of REST promotes aggressive breast cancer and see REST as an attractive therapeutic target.
Citation Format: Aditya M. Vargheese, Ashley S. Cloud, Sumedha Gunewardena, Raeann M. Shimak, Sornakala Ganeshkumar, Easwari Kumaraswamy, Roy A. Jensen, Vargheese M. Chennathukuzhi. Loss of REST in breast cancer promotes tumor progression through estrogen sensitization, MMP24 and CEMIP overexpression [abstract]. In: Proceedings of the 2021 San Antonio Breast Cancer Symposium; 2021 Dec 7-10; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2022;82(4 Suppl):Abstract nr P5-04-05.