The influence of various proteases and inhibitors on steroid hormone receptors in rat liver and kidney

Abstract

The influence of various proteolytic enzymes and protease inhibitors on hormone-receptor binding, in rat liver and kidney, was studied in relation to the known polymorphism of steroid receptors on various chromatographic systems. Liver-cytososl-bound [ 3H]corticosterone or [ 3H]cortisol was decreased as: papain > trypsin > chymotrypsin and this was also true of kidney-bound [ 3H]progesterone, although chymotrypsin was as effective as trypsin when renal aldosterone receptor was considered. Leupeptin almost completely eliminated [ 3H]cortisol binding to liver cytosol without altering [ 3H]aldosterone binding in the kidney. Whereas lima bean trypsin inhibitor or ε-aminocaproyl did not alter gluco- or mineralocorticoid binding, both inhibitors increased [ 3H]estradiol binding in the liver which was decreased by leupeptin; conversely, leupeptin increased liver testosterone binding which was decreased by ε-aminocaproyl and was not affected by trypsin inhibitor. The resolution of liver glucocorticoid receptor (GR) into GR 1-GR 4 and of mineralocorticoid receptor (MR) from the kidney into MR 1-MR 4 could be eliminated with high doses of proteases but was unaffected by a large excess of protease inhibitors added during cytosol preparation. Additional peaks of bound steroid could sometimes be observed during mild proteolysis prior to chromatography vs separation in total absence of a protease. The resolution of GR and MR into various subcomponents would therefore appear to be an inherent property of the receptor required to discriminate sense from nonsense or antisense.