Biomedical Sciences ETDs

Nicole Marjon

Publication Date

5-1-2015

Abstract

The steroid hormone, estrogen (17β-estradiol or E2), is involved in numerous and varied physiological processes. Until recently, all E2-dependent effects were thought to be propagated exclusively through the classical estrogen receptors (ERs), ERα and ERβ. However, in double ERα/β knockout mice, select E2-dependent effects remain, suggesting the existence of additional E2 receptors, such as the G protein-coupled estrogen receptor (GPER) 1. E2 plays a central role in the progression of breast cancer, and inhibiting E2 signaling in women with breast cancer increases long-term survival. The role of GPER in breast cancer is largely unknown. E2 stimulation of GPER activates the mitogen activated protein kinase (MAPK) cascade as well as phosphoinositide 3-kinase (PI3K), suggesting a role for GPER in proliferation and cell survival. Additionally, GPER is responsible for E2-dependent proliferation in select breast cancer cells in vitro. Clinically, GPER expression is correlated with increased size of the primary tumor and occurrence of distant metastasis. Although these data implicate GPER in breast carcinogenesis, its role in vivo, where tumor cells exist in a complex microenvironment, remains unclear. Therefore, this study focuses on the in vivo effects of GPER on mammary tumorigenesis. GPER KO mice were bred with MMTV-PyMT mice, a model of mammary carcinogenesis, to determine the effects of GPER expression on tumor development and progression. Tumor latency and extent of hyperplasia was unaffected, suggesting GPER does not play a role in early tumor development. However, in late stage tumorigenesis, GPER KO mice displayed smaller tumors and decreased metastases, demonstrating a role for GPER in tumor growth and progression. To distinguish the effects of GPER in the tumor parenchyma and microenvironment, GPER expressing PyMT tumor epithelial cells (WT/PyMT) or GPER KO PyMT cells (KO/PyMT) were each orthotopically transplanted into GPER WT and GPER KO recipient mice, and analyzed for tumor growth and metastasis. WT/PyMT tumor size was unaffected by the microenvironment, whereas KO/PyMT tumors were larger in KO recipient mice compared to WT recipient mice. With respect to metastasis, WT/PyMT mice metastasized more frequently in WT compared with KO mice, while KO/PyMT cell metastasis was unaffected by the microenvironment. These data suggest GPER expression in the tumor microenvironment and epithelium differentially regulates tumor growth and metastasis. Finally, because GPER expression regulates tumor progression, the effects of administering a GPER-selective agonist or antagonist in the PyMT model were determined. While the GPER-selective agonist G-1 did not affect tumor size or metastasis, the GPER-selective antagonist G36 decreased E2-mediated metastasis. Together, these data are the first in vivo demonstration of GPER augmenting tumor growth and progression. Further, pharmacologically inhibiting GPER decreases metastasis, suggesting GPER could be a viable candidate for targeted therapy in breast cancer.

Keywords

Breast Cancer, G protein-coupled estrogen receptor, metastasis, microenvironment, small molecule therapy

Sponsors

Department of Defense, National Institutes of Health

Document Type

Dissertation

Language

English

Degree Name

Biomedical Sciences

Level of Degree

Doctoral

Department Name

Biomedical Sciences Graduate Program

First Committee Member (Chair)

Hathaway, Helen

Second Committee Member

Royce, Melanie

Third Committee Member

Mold, Carolyn

Fourth Committee Member

Bisoffi, Marco

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