Sulfhydryl sensitivity and [ 125I]-16α-iodo-17β-estradiol binding of estrogen receptor in ovarian epithelial carcinomas

Abstract

We find that estrophilin from either the cytosolic or nuclear fractions of ovarian epithelial carcinomas (OVCA) binds irreversibly to controlled-pore glass beads (CPG). The CPG-adsorbed estrophilin releases [ 3H]-estradiol at 4°C in the presence of 1.25 mM AgNO 3; estradiol binding capacity from the nuclear fraction is restored by 10 mM dithiothreitol. The number of available estradiol binding sites in cytosol that are sensitive to AgNO 3 correlate with (a) the number of estradiol-inhibitable binding sites found in the 8S region in low-salt sucrose gradients ( r = 0.9) but not with (b) estradiol-inhibitable binding in the 4S region ( r = 0.3) and thus, as expected, only poorly with (c) estimates of available cytoplasmic estrogen binding sites using a standard dextran-coated charcoal analysis ( r = 0.7). Total estrogen binding extracted from the nuclear fraction with 0.5 M KCl and adsorbed to hydroxylapatite agreed with the sulfhydryl blocking reagent sensitive moiety ( r = 0.9). Estrophilin from OVCA cytosol or nuclear fractions bound [ 125I]-16α-iodo-estradiol indistinguishably from [ 3H]-estradiol. The two forms of radiolabelled-estradiol yielded equivalent data that demonstrated a shift in the estrogen binding moiety from the 8S region to the 4–5S region when 0.5 M KCl was added to gradient analyses of OVCA cytosols. From these observations we conclude that the estrophilin found in OVCA is similar to that found in normal and cancerous tissues of other female reproductive organs and that this estrophilin can bind a biologically active radiohalogenated estrogen potentially useful for imaging or treating these tumors.