Abstract
The Transplantable B‐16 melanotic melanoma carried in syngeneic C57B1/6J female mice and the Syrian hamster melanoma cell line, RPMI 3460, were utilized to determine whether steroid‐hormone receptors are present in animal melanomas. In the B‐16 melanoma, a cytoplasmic‐estrogen receptor is detectable, but there is no evidence for androgen or progestin receptors. Some tumors contain a glucocorticoid‐binding macromolecule. Sucrosedensity gradient centrifugation of cytosol after incubation with [^3^H]‐estradiol revealed an 8S peak that was suppressed by excess radioinert diethylstilbesterol. Binding varied from 5–35 fmoles per mg cytosol protein. Scatchard analysis of [^3^H]‐estradiol binding in cytosol yielded a single class of high‐affinity binding sites; the dissociation constant is 6 × 10^−10^ M. The receptor molecule is shown to be estrogen‐specific by ligand competition assays. In contrast to B‐16 melanoma, no estrogen, androgen, or progestin receptor can be found in the Syrian hamster melanoma cell line. However, a substantial level of specific binding is observed using [^3^H]‐dexamethasone. Sucrose‐gradient centrifugation of cytosol from this cell line after incubation with [^3^H]‐dexamethasone revealed a 7S peak that was suppressed by excess radioinert dexamethasone. Scatchard analysis indicated a single class of high affinity sites with a dissociation constant of 2 × 10^−9^ M. Binding levels from 70–610 fmoles per mg cytosol protein were observed. The Syrian hamster melanoma cells also exhibit a biological response to glucocorticoids: Dexamethasone causes both an inhibition of growth and a decrease in final‐cell density in these cells.