Abstract 3250: Prostaglandin E2 receptor EP1 suppresses breast cancer metastasis
Authors: Reader Jocelyn C. , Ma Xinrong , Kundu Namita , Goloubeva Olga , Fulton Amy 
Published: August 2015

Cyclooxygenases (COX-1 and COX-2) catalyze the formation of prostaglandins and play a role in the pathogenesis of breast cancer. Prostaglandin E2 (PGE2), the chief COX product in tumors, is the predominant protumorigenic prostanoid and mediates biological effects by binding to each of four EP receptors (EP1-4). Each receptor is coupled to different intracellular signaling pathways; and EP1 is coupled to calcium mobilization and PKC activation. Our published studies indicate that EP1 was detected in the cytoplasm and nucleus of benign ducts and malignant cells in invasive ductal carcinomas, and overall survival for women with tumors negative for nuclear EP1 was significantly worse than for women with any nuclear EP1 expression. Pharmacologic antagonism or reduction of EP1 expression increased metastatic capacity in a murine model of metastatic breast cancer. These data support our hypothesis that EP1 functions as a metastasis suppressor.

We now report that murine metastatic mammary tumor cell lines 410.4 and 66.1 have decreased EP1 mRNA expression compared to the non-metastatic cell line 410. Western blot analysis of total and subcellular fractions of EpH4 (normal, immortalized mammary epithelial) and malignant 410, 410.4 and 66.1 cell lines demonstrates that EP1 protein is present in the total and cytoplasmic fractions for all cell lines examined. Nuclear EP1 is detected in EpH4 and non-metastatic 410 cells; however, very little to no nuclear protein is detected in metastatic cell lines 410.4 and 66.1. The absence of nuclear EP1 in metastatic cell lines is consistent with the prognostic data that overall survival for women with tumors negative for nuclear EP1 was significantly worse.

Previously, we determined that reduction of EP1 expression leads to increased metastatic capacity; therefore, we investigated the effect of EP1 overexpression on lung colonization in 410.4 and 66.1 cells via tail vein injection in a syngeneic murine model of breast cancer. In 410.4 cells, EP1 overexpression leads to a 57%-97% decrease in metastasis, and in 66.1 cells EP1 overexpression resulted in a 10% - 38% decrease in lung tumor burden compared to vector control mice. The inverse correlation between EP1 expression and metastatic capacity supports our hypothesis that EP1 functions as a metastasis suppressor. We explored potential mechanisms leading to the alteration in the metastatic behavior in response to manipulation of the expression of EP1. We previously published that an EP1 antagonist altered adhesion to laminin in 410.4 cells. Overexpression of EP1 altered the expression of several integrin receptors in 410.4 and 66.1 cell lines including integrins alpha-V, alpha-6 and alpha-3. Also, overexpression of EP1 led to altered adhesion of these cells to several extracellular matrices including fibronectin, collagen, laminin and fibrinogen. Alteration of the adhesive properties of these cells by EP1 could contribute to the metastasis suppressor function of the EP1 receptor.

Citation Format: Jocelyn C. Reader, Xinrong Ma, Namita Kundu, Olga Goloubeva, Amy Fulton. Prostaglandin E2 receptor EP1 suppresses breast cancer metastasis. [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 3250. doi:10.1158/1538-7445.AM2015-3250