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Estrogen Receptor Characterization in a Transplantable Mouse Mammary Tumor¹

Department of Cell Biology, Baylor College of Medicine, Houston, Texas 77030

The estrogen receptor was characterized in a new transplantable mammary tumor line (MXT) which was induced by urethan treatment in C57BL x DBAf F₁ mice. The tumor is a ductal papillary carcinoma that is ovarian dependent. Treatment of ovariectomized mice with estradiol benzoate results in rapid growth of the tumor. Cytoplasmic and nuclearbound estrogen receptors were measured by the charcoal adsorption exchange assay and by the [³H]estradiol exchange assay, respectively. Tumor cytosol contained relatively large quantities of receptors, 8 to 9 fmoles/mg wet weight, which were depleted from the cytoplasmic compartment after an injection of 2 µg of estradiol. This depletion was accompanied by concomitant and stoichiometric accumulation of receptors by the nuclear fraction. Thus an apparent cytoplasmic-to-nuclear translocation was demonstrated. The affinity of both cytoplasmic and nuclear receptors was similar to that reported by others ( 1 nM). Receptor binding was specific for estrogens, and other steroids showed no competitive inhibition at concentrations up to 10^–7 M. These results demonstrate that this tumor line contains relatively large quantities of estrogen receptors that are similar to those found in normal tissue. This finding in a tumor that is transplantable makes it an ideal model system for the study of growth control by estrogens in neoplastic tissue.

¹ Supported by American Cancer Society Grant BC-92 and National Cancer Institute Grant CA-11944.

² To whom requests for reprints should be addressed.

Received 4/ 7/77. Accepted 6/10/77.

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