Oestrogen-Binding Components in Human Renal Cell Carcinoma

Abstract

Specific binding of [3H]estradiol-17.beta. by the cytosol fraction of human renal cell carcinoma was studied. The binding reaction displayed marked ligand specificity and high affinity of binding. Unlabeled estradiol, estriol and estrone inhibited the binding of [3H]estradiol-17.beta. to the cytosol binding sites; all other steroids tested were weak or insignificant competitors for the estrogen binding sites. Scatchard analyses suggested the existence of a single class of binding sites. The dissociation constant of the estradiol-binder complex was 2.51 .+-. 0.75 .times. 10-9 mol/l. The number of binding sites was limited (17.5 .+-. 3.8 fmol/mg of cytosol protein). Sucrose gradient centrifugation revealed these binding components to be macromolecules, displaying a complex sedimentation pattern (peaks at 3.5 S, 4 S, 5.7 S and, in addition, high molecular weight aggregates) or sedimenting in the 4 S region alone. By agar gel electrophoresis it could be demonstrated that the estradiol binding components migrated into the receptor region of the gel. Binding of [3H]estradiol-17.beta. to these entities was reduced when the cytosol was heated (60 min at 45.degree. C) prior to reaction with labeled hormone. Since the specific binding components exhibit properties of estradiol receptors in target tissues, a direct effect of estradiol on human renal cell carcinoma is suggested.