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Endogenously expressed estrogen receptor and coactivator AIB1 interact in MCF-7 human breast cancer cells
M K Tikkanen1, D J Carter, A M Harris
1The Hospital of Loimaa, 32201 Loimaa, Finland.
Abstract:
Coactivators are believed to mediate estrogen-induced gene responses via interaction with estrogen receptors (ER). Currently, a major challenge is to determine the importance of each coactivator in a specific cell type and promoter context in response to a particular ligand. The potential of ER to interact with a growing list of coactivators has been shown in a variety of in vitro and gene transfer assays, yet very few data have demonstrated the interaction of endogenous coactivators with ER in intact cells. We report here a ligand-specific interaction of endogenous human ER (hER) and the AIB1 coactivator in MCF-7 human breast cancer cells by using immunoprecipitation analyses. Complexes between endogenously expressed hER and AIB1 were detected in estradiol-treated cells and to a much lesser extent in cells treated with the partial agonist, monohydroxytamoxifen. We were unable to detect an hER-SRC-1 complex in our immunoprecipitations from MCF-7 cells. The in vitro-binding affinity for mouse ER interaction with AIB1 was estimated to be 40-120 nM. We conclude that AIB1 is a major coactivator for hER in MCF-7 human breast cancer cells.
Insights
Estrogen receptor (ER) coactivators are crucial for gene regulation. This study identifies AIB1 as a key coactivator interacting with endogenous human ER in breast cancer cells, particularly with estradiol.
Area of Science:
- Molecular Biology
- Endocrinology
- Cancer Research
Background:
- Coactivators mediate estrogen receptor (ER)-induced gene expression.
- Determining coactivator importance in specific cellular contexts remains challenging.
- In vivo evidence for endogenous coactivator-ER interactions is limited.
Purpose of the Study:
- To investigate ligand-specific interactions between endogenous human ER (hER) and coactivators in intact breast cancer cells.
- To identify key coactivators involved in ER-mediated signaling in MCF-7 cells.
Main Methods:
- Immunoprecipitation analyses were employed to detect protein complexes.
- MCF-7 human breast cancer cells were treated with estradiol and monhydroxytamoxifen.
- In vitro binding affinity assays were performed.
Main Results:
- A ligand-specific interaction between endogenous hER and the AIB1 coactivator was detected in MCF-7 cells.
- hER-AIB1 complexes were observed with estradiol and to a lesser extent with monhydroxytamoxifen.
- No hER-SRC-1 complex was detected, and the in vitro binding affinity of mouse ER with AIB1 was 40-120 nM.
Conclusions:
- AIB1 is a major coactivator for hER in MCF-7 human breast cancer cells.
- The interaction is ligand-dependent, highlighting differential coactivator recruitment.
- This provides in vivo evidence for AIB1's role in ER signaling within breast cancer cells.