RAPID SIGNALING OF CONVENTIONAL AND UNCONVENTIONAL ESTROGEN RECEPTORS TO THE ACTIN CYTOSKELETON AND CELL MOVEMENT

Female sex steroid estrogen is the fundamental regulator of normal breast development. In addition to this, clinical data showed that aromatase inhibitors reduces early distant metastasis and improves disease-free survival indicating that estrogen may facilitate the progression of breast cancer. Cell migration is required for cancer spread, invasion, and metastasis. Cell migration requires the integration of events that induce changes in cell structure such as protrusion, polarization and traction toward the direction of migration. These actions are driven by actin remodeling. These events are dependent on the rapid activation of FAK and Moesin, a member of ERM (Ezrin, Radixin and Moesin) family. However, the mechanistic basis of estrogens on endothelial and breast tumor cell motility or invasion remains unclear. The main focus of this thesis is to study the role of conventional and unconventional estrogen receptors in cell movement in different cell settings. First we used human umbilical vein endothelial cells and ER negative MDA MB468 cells to study the mechanistic basis of cell movement in non cancerous human vein endothelial cells and breast cancer MDA-MB 468 cells, these two cells enable us to provide insights into how steroids induces metastasis in breast cancer cells. The first part of my thesis focuses on exploring the regulatory actions of estrogen on PAI-1 in human endothelial cells and to characterize the signaling steps through which these actions are enacted. Here we have shown that estrogen through various signaling intermediates from membrane to nucleus, to induce the expression of PAI-1. Our lab have shown previously that estrogen is the powerful modulator of cell movement in ER positive T47D breast cancer cells. The interesting point is that, PAI-1 besides being important player in fibrinolysis, also demonstrated to have other roles such as actin remodeling. Actin remodeling is the crucial event. The fundamental goal of this second part of Thesis are to explore the dynamics and regulatory controls of actin based processes in an effort to further understand the molecular events governing invasion and cell movement. Within this context, the work presented here focuses on the role of unconventional estrogen receptors such as G-Protein Coupled Estrogen Receptor (GPER) in ER negative breast tumor MDA MB468 cell line. Previous studies have shown with debate that, apart from endogenous ER receptors, GPER is an unconventional estrogen receptor which is used by sex steroids such as estrogen. Previous studies have also shown that estrogen exerts trace effect in the cells without ER, so we hypothesized that, this trace effect could be the presence of unconventional GPER in ER negative breast cancer cells. These findings described in this thesis provide new mechanisms of action of estrogens through conventional and unconventional estrogen receptors to the actin cytoskeleton and cell movement, which may be important for vascular function and heamostasis in endothelial cells and invasion and metastasis in breast cancer cells.