Human progesterone receptor shows differential sensitivity to carboxyl group modifying agents when bound to agonist and antagonist ligands.

BACKGROUND: Modulation of human uterine progesterone receptor (PR) in relation to its binding to synthetic steroids with known agonist (R5020) and antagonist (triamcinolone acetonide, T.A.) properties was studied in the presence of the specific carboxyl group modifiers, N,N'-dicyclohexylcarbodiimide (DCCD) and 1-ethyl-3-carbodiimide hydrochloride (EDC). METHODS: Uterine cytosol was treated with DCCD or EDC. The amounts of total bound were detected using the steroid binding measurements. The formation and transformation of progesterone-receptor complexes (PRc) were analyzed using sedimentation rate analysis. RESULTS: Our studies show that the modification of the COOH group differentially influences the properties of mammalian PR binding with either R5020 or T.A. DCCD and EDC affect the steroid binding of PR by decreasing the binding sites, not by the changing the affinity. CONCLUSION: Our studies indicate the importance of the carboxyl group in steroid binding by PR. This implies that both aspartic acid and glutamic acid residues, which have the carboxyl group, may play an important role when PR binds with steroid ligands.