Estrogen Receptor Characterization in a Transplantable Mouse Mammary Tumor

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 nuclear-bound 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 othrs (~ 1 nM). Receptor binding was specific for estrogens, and Other steroids showed no competitive inhibition at concentrations up to 10^-7M. 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.