Receptor for glucocorticoids in RPMI 3460 melanoma cells

We are investigating the role of steroid hormones in the biological behavior of malignant melanoma. We have recently shown that the growth of RPMI 3460 Syrian hamster melanoma cells in monolayer culture is retarded by the synthetic glucocorticoid dexamethasone. This paper reports the identification of a macromolecule with properties of a glucocorticoid receptor in cytosis prepared from these cells. Sucrose density gradient analyses on six separate cell batches consistently demonstrated substantial levels of saturable [3H]dexamethasone binding [concentration = 195 +/- 47 (S.E.) fmol/mg cytosol protein] in the 7S region of the gradients. Similar analyses failed to detect saturable binding for other classes of steroid hormones. Scatchard plots of [3H]dexamethasone binding to the receptor were linear, indicating a single class of high-affinity sites (Kd = 2.3 +/- 0.78 x 10(-9) M for three cell batches). Steroid competition experiments confirmed the glucocorticoid specificity of the binding molecule; competitors in descending order of effectiveness were glucocorticoids, mineralocorticoid, progestins, estrogen, and androgen. Combined hormone receptor and growth studies with RPMI 3460 cells can help to define the mechanism of glucocorticoid action in malignant melanoma and may ultimately help establish the value of steroid hormones as therapeutic agents for this disease.