Purification and partial characterization of a 17 beta-estradiol-binding macromolecule in the human pancreas

Studies have been performed in order to investigate the presence of estrogen-binding proteins in the human pancreas that may provide the biochemical basis for tissue-specific treatment of pancreatic carcinoma with estrogen-based cytotoxic drugs. Using in vitro techniques, an estrogen-binding macromolecule has been purified from pancreatic cytosol. With estradiol a ligand, Kd was calculated to be 1.7 X 10(-7) M, and this protein was found to constitute about 4% of the total protein content in the cytosol. No metabolism of estradiol was detected under the in vitro conditions used. Competition experiments indicated that, besides estradiol, the protein also had some affinity for estrone and estriol but not for testosterone, progesterone, or dexamethasone. The protein was purified to homogeneity using chromatography on concanavalin A and hydroxylapatite followed by preparative polyacrylamide gel electrophoresis. The purified protein, still able to bind, [3H]-estradiol, gave one single protein-staining band when analyzed using different electrophoretic systems. The steroid-protein and did not bind to phosphocellulose or DNA-cellulose and did not show any similarities to steroid receptor proteins. The complex has a Strokes' radius of 52 A and a sedimentation coefficient of 3S. The biological significance of the macromolecule is known, but the protein is probably synthesized in the pancreas since no similar protein could be detected in serum. Studies are now being carried out to investigate whether this novel protein in the human pancreas may interact with complexes between cytotoxic agents and estrogens and provide the basis for tissue-specific treatment of pancreatic carcinoma.