Comparison of estrogen receptors in hormone-dependent and hormone-independent Grunder strain mouse mammary tumors.

Hormone-dependent (HD) Grunder strain mouse mammary carcinomas contain a 65-kDa estrogen receptor (ER) with minor amounts of 50- and 35-kDa components which apparently still contain the intact hormone-binding (COOH-terminal) domain. When the HD tumors lose their hormonal dependence during serial transplantation, the hormone-independent (HI) transplants show an increase in 50- and 35-kDa components relative to 65-kDa ER. In HI transplants of three of five tumor lines studied (TSl 85, 86, and 106), the 65-kDa receptor was entirely replaced by 50- and 35-kDa receptors, whereas in the two other lines (TSl 101 and 104) there usually were about equal amounts of 65- and 50-kDa ERs. No difference was found between ERs of HD and HI tumors in affinity for estradiol, steroid specificity, or immunoreactivity for the monoclonal antibody JS34/32. Estrogen stimulation of HI tumors did not increase the concentration of progesterone receptor in the tumor tissue, indicating that ER in these tumors was not functional in enhancing progesterone receptor. Incubation of 65-kDa ER with HI tumor cytosol or combined homogenization of HD and HI tumor tissue did not cause degradation of 65-kDa ER. alpha-Chymotrypsin-like protease activity generally was lower in HI than in HD tumor cytosols, indicating that the lower molecular size of ER in HI tumors cannot be attributed to the increased level of this protease activity.