Receptor characteristics of the rat mammary carcinoma cell line 64-24.

Saturable binding of androgens, glucocorticoids, and triiodothyronine was found in the 64-24 hormone-responsive rat mammary carcinoma cell line. Androgen receptors had a dissociation content (Kd) for methyltrienolone of 3.4 X 10(-10) M and a binding capacity of approximately 10,000 sites/cell in whole cells. 5 alpha-[3H]dihydrotestosterone (DHT) was specifically taken up into approximately 2,150 nuclear sites with an affinity of 8.3 X 10(-10) M when nuclei were isolated from whole cells incubated with [3H]DHT. Sucrose gradient centrifugation of cytosol prepared from these cells revealed a displaceable [3H]DHT-binding component which migrated at 8S. Sedimentation analysis with high salt gradients of nuclear extracts from cells incubated with [3H]DHT revealed a peak of radioactivity in the 4S region which was abolished by coincubation of the cells with excess nonradioactive methyltrienolone. Receptors for [3H]dexamethasone were more abundant (approximately 50,000 sites/cell) in whole cells and had a Kd of 7.5 X 10(-9) M, but the number of nuclear binding sites was similar to that for androgens. Specificity studies using unlabeled steroids showed that each of the two classes of steroid receptors had greater affinities for their appropriate hormones. High affinity receptors for estrogens and progestins were not detectable in these cells. Triiodothyronine receptors were demonstrable but at a very low binding capacity (1,100 sites/cell). The Kd of these receptors was 0.6 X 10(-10) M. Cytogenetic studies revealed 44 chromosomes/mitosis with several unique markers. These receptor and karyotypic features suggest that the 64-24 cells may be useful in studying androgen action on breast cancer independently of estrogen or progestin influence, as well as the effects of thyroid hormone and glucocorticoids on breast cancer cells.