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Analysis of Estrogen Receptor -Sp1 Interactions in Breast Cancer Cells by Fluorescence Resonance Energy Transfer

Departments of Veterinary Physiology and Pharmacology (KK., S.S.), and Veterinary Anatomy and Public Health (R.Ba., R.Bu.), Texas A&M University, College Station, Texas 77843; and Institute of Biosciences and Technology (S.S.), Texas A&M University System Health Science Center, Houston, Texas 77030-3303

Address all correspondence and requests for reprints to: Stephen Safe, Department of Veterinary Physiology and Pharmacology, Texas A&M University, 4466 TAMU, Veterinary Research Building 409, College Station, Texas 77843-4466. E-mail: ssafe{at}cvm.tamu.edu.

Estrogen-dependent regulation of several genes associated with cell cycle progression, proliferation, and nucleotide metabolism in breast cancer cells is associated with interactions of estrogen receptor (ER)/Sp1 with GC-rich promoter elements. This study investigates ligand-dependent interactions of ER and Sp1 in MCF-7 breast cancer cells using fluorescence resonance energy transfer (FRET). Chimeric ER and Sp1 proteins fused to cyan fluorescent protein or yellow fluorescent protein were transfected into MCF-7 cells, and a FRET signal was induced after treatment with 17ß-estradiol, 4'-hydroxytamoxifen, or ICI 182,780. Induction of FRET by these ER agonists/antagonists was paralleled by their activation of gene expression in cells transfected with a construct (pSp1₃) containing three tandem Sp1 binding sites linked to a luciferase reporter gene. In contrast, interactions between ER and Sp1DBD [a DNA binding domain (DBD) deletion mutant of Sp1] are not observed, and this is consistent with the critical role of the C-terminal DBD of Sp1 for interaction with ER. Results of the FRET assay are consistent with in vitro studies on ER/Sp1 interactions and transactivation, and confirm that ER and Sp1 interact in living breast cancer cells.

NURSA Molecule Pages Link:

Nuclear Receptors:   ERα

Ligands:   17β-Estradiol  |  4-Hydroxytamoxifen

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