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Investigation of Hormone-Receptor Interactions by Means of Fluorescence Labeling¹

Department of Biochemistry, Scripps Clinic and Research Foundation, La Jolla, California 92037 [W. B. D., R. J. B., M. L. H.]; Department of Pathology, University of California, San Diego, La Jolla, California 92037 [P. N. B.]; Burroughs Corporation, Fort Lauderdale, Florida 33302 [J. L.]; and Department of Chemistry and Biochemistry, Southern Illinois University, Carbondale, Illinois 62901 [C. Y. M., V. M. K.]

Fluorescent-labeled hormones can be used to study hormone-receptor interactions by means of fluorescence polarization, visualization by fluorescence microscopy, or separation methods, e.g., dextran-coated charcoal. Subcellular fragments, single cells, and tissue preparations are amenable to study; in this work rat uterine cytosol was used unless otherwise noted.

Estrone labeled with fluorescein at position 17 gives 50% inhibition in the radiometric dextran-coated charcoal assay at 8.3 x 10^-7 M as compared to 3.4 and 3.5 x 10^-8 M for diethylstilbestrol and estradiol, respectively.

Scatchard plots from fluorescence polarization are hyperbolic and consistent with two classes of binding sites having association constants 5.6 x 10¹⁰ and 6.4 x 10⁷ M^-1. Binding by high-affinity sites, which were present at about 3 times the concentration of "specific" sites (radiometric dextran-coated charcoal assay), was abrogated by estradiol or diethylstilbestrol.

Kinetic measurements showed that binding sites that can be blocked by excess estradiol or diethylstilbestrol are those that are both slowly associating and slowly dissociating.

Staining of tissues by estrone labeled with fluorescein at position 17 as seen in the fluorescence microscope showed specificity. In normal rat uterus only epithelial cells were stained. In one human infiltrating ductal carcinoma only the malignant ductoid elements stained, while in another there was essentially no staining.

¹ Presented at the John E. Fogarty International Center Conference on Hormones and Cancer, March 29 to 31, 1978, Bethesda, Md. Supported by Research Contract N01-CB-43905 from the National Cancer Institute, Research Grant GB-31611 from the National Science Foundation, and PHS Research Grant No. 23980 from the National Institute of General Medical Sciences.

² Present address: University of Oregon Medical Center, Portland, Oreg.