Characterization and comparison of the estrogen and androgen receptors from the R-3327 rat prostatic adenocarcinoma.

Abstract

Abstract The estrogen and androgen receptors found in the high-speed supernatant (cytosol) fraction of the Dunning R-3327 rat prostatic adenocarcinoma have been characterized and their properties compared. [ 3 H]-17β-Estradiol is bound to a macromolecule which sediments at 8.3 S after sucrose density gradient centrifugation in low salt buffer, whereas [ 3 H]-R1881 (methyltrienolone, a synthetic androgen) binds to a macromolecule sedimenting at 7.8 S. Competitive binding studies distinguish the two receptors and indicate that they are unique and distinct proteins. The dissociation constants for 17β-estradiol and R-1881 binding to their receptors are 8 × 10 −10 and 3 × 10 −9 , respectively. Both Scatchard plots are linear, suggesting a single class of high-affinity binding sites for each receptor. Steroid binding for both receptors was saturable and of low capacity. Estrogen receptor levels varied from barely detectable to 300 fmol/mg cytosol protein and androgen receptor levels ranged from barely detectable to 300 fmol/mg cytosol protein depending on tumor pathology. Tumors with large amounts of fibrous stroma had low receptor levels, whereas those tumors that were mostly epithelial in nature contained significantly higher levels of the receptors. Both the estrogen and androgen binding proteins satisfy criteria which clearly distinguish them from other (plasma) steroid binding proteins and classify them as true steroid hormone receptors.