Investigation of estrogen receptor functionality in hamster melanoma

The biology of hamster melanoma, HM1, was assessed congenitally athymic mice after administration of estradiol. Chronic treatment with this steroid hormone delayed tumor appearance in females, inhibited tumor growth in both sexes and reduced the number of lung metastatic lesions in males. Cytosol and nuclear estrogen receptors were characterized in HM1 cells. Specific binding in both fractions was saturable and indicative of high affinity sites with a mean Kd of 0.22 nM in the cytosol and 1.5 nM in the nucleus. Sucrose density-gradient centrifugation of 3H-estradiol-labelled cytosol demonstrated a peak in the 8S-9S region, which was completely suppressible by excess diethylstilbesterol. To determine whether the estrogen receptor in HM1 cells was functional, athymic mice received 2.5 μg estradiol or vehicle s.c. and were necroscopied 1, 2, 6 and 24 hr later. Nuclear estrogen receptor content was maximal one hr after injection of estradiol and declined to control levels by 24 hr. This effect was accompanied by a rapid reduction in cytosol estrogen receptor content which returned to control levels by 24 hr. A physiologic dose of estradiol, 0.1 μg, injected one hr prior to necroscopy, produced maximal changes in cytosol and nuclear estrogen receptor content