Abstract 1305: Activation of G-protein coupled estrogen receptor (GPER) inhibits ELT-3 uterine leiomyoma cell proliferation.

Uterine leiomyomas are ovarian hormone-responsive tumors originating in the smooth muscle layer of the uterus called the myometrium. These benign tumors require surgery or other clinical intervention in ∼25% of all premenopausal women in the United States. Despite the high frequency and clinical impact of these tumors, the pathogenesis of uterine leiomyomas is not understood. The estrogen-responsive growth of uterine leiomyomas has been well established, however the role of G protein-coupled estrogen receptor (GPER) in leiomyoma cell regulation has not been studied. The membrane bound estrogen receptor GPER, formerly known as GPR30, is a 7-transmembrane G protein-coupled receptor that is activated by 17β-estradiol (E2). A role for GPER has been previously established in cancers that originate in E2-dependent tissues such as the breast and uterus. Other reports show that GPER is expressed in myometrial cells and activation of GPER modulates myometrial contraction suggesting an important regulatory role for this receptor in the myometrium. Based on these reports, we hypothesized that GPER regulates uterine leiomyoma cells and may represent a putative therapeutic target for this tumor type. The Eker rat model-derived uterine leiomyoma (ELT-3) cell line was used as a model system to study GPER in uterine leiomyoma cells. First, the expression of GPER in uterine leiomyoma cells was determined using RNA and protein samples from ELT-3 cells and real-time PCR and immunoblot analysis. Our findings indicate that GPER transcript and protein were expressed in ELT-3 cells. To determine if activation of GPER regulated uterine leiomyoma cell proliferation, ELT-3 cells were treated with G1, a GPER-specific ligand, or vehicle control and counted 5 days after treatment. Data from these experiments indicated that G1 treatment, and potentially GPER activation, reduced the number of cells over time compared to vehicle control. GPER activation is known to result in the accumulation of pERK and intracellular free Ca2+ and such accumulation is used as a biomarker for GPER activation. Upon G1 treatment, pERK and intracellular free Ca2+ were elevated compared to vehicle treatment in ELT-3 cells suggesting that GPER is functional in uterine leiomyoma cells and is activated by G1. In an effort to determine the mechanism of inhibition of uterine leiomyoma cell proliferation by G1 treatment, we hypothesized that treatment of estrogen-stimulated ELT-3 cells with G1 would inhibit the characteristic E2-induced proliferation of this cell type. Growth curve experiments were performed and data obtained in these experiments suggested that G1 treatment resulted in the inhibition of E2-induced ELT-3 cell proliferation. Taken together, these data suggest that GPER is an important regulator of uterine leiomyoma cell proliferation and is a putative target for novel molecular therapeutics for this tumor type. Citation Format: Maryann Castillo, Angelique M. Wimbley, Jacob J. Mayfield, Jenifer C. Lascano, Kevin D. Houston. Activation of G-protein coupled estrogen receptor (GPER) inhibits ELT-3 uterine leiomyoma cell proliferation. [abstract]. In: Proceedings of the 104th Annual Meeting of the American Association for Cancer Research; 2013 Apr 6-10; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2013;73(8 Suppl):Abstract nr 1305. doi:10.1158/1538-7445.AM2013-1305