Abstract
Development of acquired antihormone resistance exposes a vulnerability in breast cancer: estrogen-induced apoptosis. Triphenylethylenes (TPEs), which are structurally similar to 4-hydroxytamoxifen (4OHT), were used for mechanistic studies of estrogen-induced apoptosis. These TPEs all stimulate growth in MCF-7 cells, but unlike the planar estrogens they block estrogen-induced apoptosis in the long-term estrogen-deprived MCF7:5C cells. To define the conformation of the TPE:estrogen receptor (ER) complex, we employed a previously validated assay using the induction of transforming growth factor α (TGFα) mRNA in situ in MDA-MB 231 cells stably transfected with wild-type ER (MC2) or D351G ER mutant (JM6). The assays discriminate ligand fit in the ER based on the extremes of published crystallography of planar estrogens or TPE antiestrogens. We classified the conformation of planar estrogens or angular TPE complexes as “estrogen-like” or “antiestrogen-like” complexes, respectively. The TPE:ER complexes did not readily recruit the coactivator steroid receptor coactivator-3 (SRC3) or ER to the PS2 promoter in MCF-7 and MCF7:5C cells, and molecular modeling showed that they prefer to bind to the ER in an antagonistic fashion, i.e., helix 12 not sealing the ligand binding domain (LBD) effectively, and therefore reduce critical SRC3 binding. The fully activated ER complex with helix 12 sealing the LBD is suggested to be the appropriate trigger to initiate rapid estrogen-induced apoptosis.
Footnotes
- Received August 30, 2013.
- Accepted March 7, 2014.
This work was supported by the Department of 1090 Defense Breast Program [Grant W81XWH-06-1-0590] Center of Excellence; the Susan G. Komen for the Cure Foundation [Grant SAC100009]; the Lombardi Comprehensive Cancer 1095 Center Support Grant (CCSG) Core Grant; the National Institutes of Health National Cancer Institute [Grant P30-CA051008]; and National Research Council (CNCS)-Executive Agency for Higher Education, Research, Development and Innovation (UEFISCDI) (Romania) [Grant PN II-RU PD_502/2010].
The views and opinions of the authors do not reflect those of the US Army or the Department of Defense.
This work was presented as a poster at the following conferences: Obiorah I, Sengupta S, Curpan R, Jordan VC (2012) Defining the conformation of the estrogen receptor complex that controls estrogen-induced apoptosis in breast cancer. Lombardi Research Days at Georgetown University Medical Center; 2012 March 7; Washington, DC; and Obiorah I, Sengupta S, Curpan R, Jordan VC (2012) Defining the conformation of the estrogen receptor complex that controls estrogen-induced apoptosis in breast cancer. AACR Annual Meeting; 2012 April 6–13; Chicago, IL.
↵This article has supplemental material available at molpharm.aspetjournals.org.
- Copyright © 2014 by The American Society for Pharmacology and Experimental Therapeutics
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