Chromatographic separation on phosphocellulose of activated and nonactivated forms of steroid-receptor complex. Purification of the activated complex.

Steroid-receptor complexes formed at low temperature and ionic strength are unable to bind to target cell nuclei. After a temporary exposure to high ionic strength and/or temperature they become activated (i.e., able to bind to nuclei). However, there exists an equilibrium between activated and nonactivated complexes; thus, mixtures of both populations are obtained. In this paper it is shown that activated [3H]triamcinolone acetonide-rat liver receptor complexes bind strongly to phosphocellulose, whereas nonactivated complexes do not. Thus, it is chromatographically possible to isolate these two populations of complexes. The experimental conditions of the separation have been established. The most important feature is that upon prolonged exposure to phosphocellulose, nonactivated complexes become progressively activated. The separation on phosphocellulose has at least three potential applications. A first application is the possibility of measuring the concentration of activated complexes in incubates. However, when activated complexes were titrated with rat liver nuclei in excess or assayed through binding to phosphocellulose, slightly different results were obtained. This discrepancy was due on one hand to the difficulty of obtaining binding of all the activated complexes and on the other hand to the second activation of some of the complexes during their exposure to phosphocellulose. A second application was the possibility of obtaining a homogeneous population of activated complexes. This was actually achieved, since the complexes eluted from phosphocellulose were demonstrated to be 90--100% activated. The use of such homogeneous preparations simplifies considerably studies on binding of steroid-receptor complexes to nuclear acceptors (nuclei, chromatin, DNA). A third application is the use of phosphocellulose for the purification of receptor. Cytosol containing nonactivated complexes was filtered through phosphocellulose the complexes present in the breakthrough of the column were then activated and bound to phosphocellulose in a second chromatography. Advantage was also taken of the "amphoteric" behavior of the receptor that binds to both anionic (phosphocellulose) and cationic (diethylaminoethylcellulose) resins. Purification (940fold) with 24% yield could be obtained in preparations taking less than 2 days. The partially purified receptor was a heavy aggregate (greater than 12 S) that could be dissociated into 4S subunits by exposure to 0.3 M K C1. It has kept its property of interacting with nuclear acceptor. Preliminary experiments have shown that this technique could be of general application for steroid hormone receptors: activation enhanced binding to phosphocellulose of progesterone, aldosterone, and estradiol receptors.