Abstract A11: Crosstalk Between Mtorc1 and Estrogen Receptor in Breast Cancer

Abstract Approximately two thirds of all breast cancer cases are estrogen receptor (ER) positive, which underscores the dependence of cancer cells on estrogen for growth and survival. However, resistance to endocrine therapy develops in most cases. mTORC1 (the mechanistic target of rapamycin complex 1) is a critical node of estrogen signaling in the cell, however the mechanism of estrogen activation of mTORC1 is not well understood. We have previously demonstrated that mTORC1 promotes growth factor-mediated ER activation by phosphorylating ERα on Ser167. This phosphorylation, which is mediated by the mTORC1 effector kinase S6K1, is important for ERα dimerization, DNA binding and transcriptional activity, is associated with endocrine resistance and correlates with therapy response. Moreover, ERα promotes expression of S6K1, generating a feed-forward positive activation loop. Our current efforts are focused on fully understanding the nature and mechanism of the relationship between mTORC1 and estrogen pathways. Our data indicate that mTOR, raptor and ER form a complex whereby ER directly interacts with raptor. Moreover, this interaction is stimulated by estrogen as seen by co-immunoprecipitation analysis. We additionally found that ER and raptor co-localize to the nucleus upon estrogen stimulation, where they interact as detected by both immunofluorescence and cellular fractionation experiments. Our current efforts are focused on understanding the role of this interaction and the mechanism of estrogen mediated localization of raptor to the nucleus. We are also investigating the role of raptor and estrogen receptor interaction in endocrine therapy treatment and resistance. Citation Format: Anya Alayev, Rachel S. Salamon, Marina K. Holz. Crosstalk between mTORC1 and estrogen receptor in breast cancer. [abstract]. In: Proceedings of the AACR Special Conference: Targeting the PI3K-mTOR Network in Cancer; Sep 14-17, 2014; Philadelphia, PA. Philadelphia (PA): AACR; Mol Cancer Ther 2015;14(7 Suppl):Abstract nr A11.