Abstract 1316: Estrogen receptor-α dictates the subcellular localization of ERK5 to control differential proliferation and invasion programs of breast cancer cells.
Authors: Madak Erdogan Zeynep , Bergamaschi Anna , Ventrella Rosa , Lu Hailing , Katzenellenbogen Benita S. 
Published: August 2014

Abstract
Mitogen activated protein kinases (MAPKs) are key players in relaying extracellular signals to the cell nucleus and are often overexpressed in aggressive and endocrine-resistant breast cancers. Our previous studies (Madak-Erdogan et al. Mol Cell Biol 31:226,2011) revealed that one such kinase, ERK2, was recruited to distal enhancers of estradiol(E2)-regulated genes together with estrogen receptor alpha (ERα) and collaborated with ERα to regulate gene expression and cell proliferation programs in response to hormone. In the current study, we identified ERK5, a close relative of ERK2, as a factor that is recruited to the transcription start site (TSS) of E2-stimulated genes. Use of dominant negative and constitutively active forms, as well as small molecule inhibitors of ERK5 and MEK5, revealed that activation of ERK5 by upstream kinase MEK5 and activity of ERK5 itself was required for recruitment of the kinase to the chromatin. Immunofluorescence studies demonstrated that ERK5 localized to transcription factories in the nucleus upon cell treatment with E2. Inhibitors of ERK5 completely abrogated E2-dependent cell proliferation and colony formation for all of the ERα-positive breast cancer cell lines studied. In contrast to what we observed in ERα-positive cells, in ERα-negative breast cancer cell lines we did not detect any nuclear ERK5; instead, we found ERK5 localized to the actin cytoskeleton, especially to sites where substantial remodeling takes place. Upon expression of ERα in these ERα-negative cells, we observed re-localization of ERK5 to the nucleus and a decrease in actin reorganization associated with reduced cell motility and invasion. Abrogation of ERα expression using siRNA in ERα-positive cell lines caused loss of nuclear ERK5 and relocalized this kinase to the actin cytoskeleton. Our studies with tamoxifen resistant cell lines revealed that ERK5 localization to the nucleus was reduced and localization to the actin cytoskeleton increased as resistance progressed, suggesting a correlation between ERα activity, ERK5 localization and motility of breast cancer cells. Our data reveal that ERα elicits nuclear localization of ERK5, diminishing ERK5 localization to regions of high actin remodeling, thereby possibly accounting for the generally lower metastatic potential that is characteristic of many ERα-positive breast cancer cells.
(Supported by grants T32 ES007326 and P50 AT006268 from NIH, and a grant from The Breast Cancer Research Foundation.)
Citation Format: Zeynep Madak Erdogan, Anna Bergamaschi, Rosa Ventrella, Hailing Lu, Benita S. Katzenellenbogen. Estrogen receptor-α dictates the subcellular localization of ERK5 to control differential proliferation and invasion programs of breast cancer cells. [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 1316. doi:10.1158/1538-7445.AM2013-1316