Structure and dynamics of the estrogen receptor |
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Authors: | G L Greene M F Press |
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Affiliation: | 1. Bond Life Sciences Center, University of Missouri, Columbia, MO, 65211, USA;2. Biomedical Sciences, University of Missouri, Columbia, MO, 65211, USA;3. Thompson Center for Autism and Neurobehavioral Disorders, Columbia, MO, 65211, USA;4. Department of Physiological Sciences, University of Florida, Gainesville, FL, 32610, USA;1. Department of Pharmacology, Toxicology and Therapeutics, School of Medicine, University of Kansas Medical Center, Kansas City, KS 66160, USA;2. Institute of Zoology, Chinese Academy of Sciences, Beijing 100101, China;3. Department of Chemistry, South University of Science and Technology of China, Shenzhen, Guangdong 518055, China;4. Department of Biology, South University of Science and Technology of China, Shenzhen, Guangdong 518055, China;1. National Institute of Food and Drug Safety Evaluation, Ministry of Food and Drug Safety, Chungcheongbuk-do 28159, Republic of Korea;2. Dongguk University Research Institute of Biotechnology & Medical Converged Science, Dongguk University, Gyeonggi 10325, Republic of Korea |
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Abstract: | To evaluate the structure and function of estrogen receptor (ER) in various mammalian systems, the cytosolic forms of receptor from calf uterus and from MCF-7 human breast cancer cells have been purified to virtual homogeneity by sequential selective adsorption to estradiol-Sepharose and heparin-Sepharose. In both cases, the purified steroid-receptor complex appears to exist as an activated 5S homo- or heterodimer of mol. wt 65,000 (4S) steroid-binding subunits. Purified ER has high affinity for DNA and serves as a substrate for phosphorylation by a purified rat brain kinase. Several monoclonal antibodies prepared against affinity-purified MCF-7 cytosol ER have been used to localize receptor by an indirect immunoperoxidase technique in fixed, frozen sections of human breast tumors, human uterus, rabbit uterus and in other mammalian reproductive tissues and cancers, as well as in fixed MCF-7 cell cultures and in paraffin-embedded sections of breast tumors and human endometrium. In all cases, we have observed only nuclear localization of immunoreactive receptor in tissues and whole cells, even under conditions in which virtually all of the receptor is found in a low-salt extract (cytosol) of the target cells. Treatment of cells or tissues in vivo or in vitro with estradiol alters the intensity but not the distribution of specific staining for ER. By immunoelectron microscopy, receptor was localized in the euchromatin, but not in the marginated heterochromatin or nucleoli of MCF-7 nuclei and epithelial and stromal nuclei of postmenopausal human endometrium. These observations suggest that the majority of the unoccupied receptor may actually reside in the nucleus, rather than in the cytoplasm as previously thought. Thus, hormone action may involve binding of the steroid directly to receptor loosely associated with nuclear components, followed by conversion of the steroid-receptor complex to an activated form which becomes more tightly associated with chromatin. |
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