Transformation of calf uterine progesterone receptor: analysis of the process when receptor is bound to progesterone and RU38486.

Effects of different transforming agents were examined on the sedimentation characteristics of calf uterine progesterone receptor (PR) bound to the synthetic progestin [3H]R5020 or the known progesterone antagonist [3H]RU38486 (RU486). [3H]R5020-receptor complexes [progesterone-receptor complexes (PRc)] sedimented as fast migrating 8S moieties in 8-30% linear glycerol gradients containing 0.15 M KCl and 20 mM Na2MoO4. Incubation of cytosol containing [3H]PRc at 23 degrees C for 10-60 min, or at 0 degrees C with 0.15-0.3 M KCl or 1-10 mM ATP, caused a gradual transformation of PRc to a slow sedimenting 4S form. This 8S to 4S transformation was molybdate sensitive. In contrast, the [3H]RU486-receptor complex exhibited only the 8S form. Treatment with all three activation agents caused a decrease in the 8S form but no concomitant transformation of the [3H]RU486-receptor complex into the 4S form. PR in the calf uterine cytosol incubated at 23 or at 0 degrees C with 0.3 M KCl or 10 mM ATP could be subsequently complexed with [3H]R5020 to yield the 4S form of PR. However, the cytosol PR transformed in the absence of any added ligand failed to bind [3H]RU486. Heat treatment of both [3H]R5020- and [3H]RU486-receptor complexes caused an increase in DNA-cellulose binding, although the extent of this binding was lower when RU486 was bound to receptors. An aqueous two-phase partitioning analysis revealed a significant change in the surface properties of PR following both binding to ligand and subsequent transformation. The partition coefficient (Kobsd) of the heat-transformed [3H]R5020-receptor complex increased about 5-fold over that observed with PR at 0 degrees C.(ABSTRACT TRUNCATED AT 250 WORDS)