Control of estradiol-directed gene transactivation by an intracellular estrogen-binding protein and an estrogen response element-binding protein.
New World primates exhibit a form of resistance to estrogens that is associated with overexpression of an estrogen response element (ERE)-binding protein (ERE-BP) and an intracellular estradiol (E(2))-binding protein (IEBP). Both proteins suppress E(2)-mediated transcription when overexpressed in estrogen receptor-alpha (ERalpha)-positive cells. Although ERE-BP acts as a competitor for ERE occupancy by liganded ERalpha, the function of IEBP and its human homolog, heat-shock protein 27 (hsp27), is less clear. In data presented here, we have used E(2)-responsive human MCF-7 breast cancer cells to show that IEBP/hsp27 can regulate estrogen signaling as a cytosolic decoy for E(2) and as a protein chaperone for ERalpha. Furthermore, co-immunoprecipitation, colocalization, yeast two-hybrid, and glutathione S-transferase pull-down analyses indicate that IEBP/hsp27 also interacts with ERE-BP to form a dynamic complex that appears to cycle between the cytoplasm and nucleus during normal estrogen signaling. Overexpression of either IEBP/hsp27 or ERE-BP in MCF-7 cells resulted in abnormal subcellular distribution of the IEBP/hsp27 and ERE-BP, with concomitant dysregulation of ERE occupancy as determined by chromatin immunoprecipitation. We hypothesize that IEBP/hsp27 and ERE-BP not only cause hormone resistance in New World primates but are also crucial to normal estrogen signaling in human cells. This appears to involve a physical association between the two proteins to form a complex that is able to interact with both E(2) and ERalpha in cytosolic and nuclear compartments.
Chen
Hong
H
Division of Endocrinology, Metabolism, and Lipids, Department of Medicine, Emory University School of Medicine, Atlanta, Georgia 30322, USA.
Hewison
Martin
M
Adams
John S
JS
D000595:Amino Acid Sequence; D001667:Binding, Competitive; D001943:Breast Neoplasms / Q000378:metabolism; D048708:Cell Growth Processes / Q000502:physiology; D045744:Cell Line, Tumor; D002843:Chromatin / Q000378:metabolism; D004958:Estradiol / Q000235:genetics / Q000378:metabolism*; D047628:Estrogen Receptor alpha / Q000378:metabolism*; D055551:HSP27 Heat-Shock Proteins; D006360:Heat-Shock Proteins / Q000378:metabolism*; D006801:Humans; D018832:Molecular Chaperones; D008969:Molecular Sequence Data; D009363:Neoplasm Proteins / Q000378:metabolism*; D012313:RNA / Q000737:chemistry / Q000235:genetics; D020218:Response Elements; D020133:Reverse Transcriptase Polymerase Chain Reaction; D016415:Sequence Alignment; D015398:Signal Transduction; D015533:Transcriptional Activation; D014162:Transfection
D002843:Chromatin; D047628:Estrogen Receptor alpha; D055551:HSP27 Heat-Shock Proteins; C057725:HSPB1 protein, human; D006360:Heat-Shock Proteins; D018832:Molecular Chaperones; D009363:Neoplasm Proteins; D004958:Estradiol; D012313:RNA