Glucocorticoid Receptors in Rat Thymocytes: INTERACTIONS WITH THE ANTIGLUCOCORTICOID CORTEXOLONE AND MECHANISM OF ITS ACTION

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Abstract The antiglucocorticoid cortexolone competes with triamcinolone acetonide (TA) for binding to specific receptors in rat thymocytes, and prevents the inhibitory action of TA on 2-deoxy[14C]glucose uptake and on the uptake and incorporation of [3H]uridine in these cells. Different sedimentation profiles were noted for the active glucocorticoid-receptor complex and the hormone antagonist-receptor complex. Thymocytes incubated with [3H]TA at 0° or 37° and extracted with a high salt buffer (0.15 m KCl) yielded a single receptor complex sedimenting at ∼4 S. At 0° and extraction with a low salt buffer, most of the [3H]TA was associated with the 27,000 x g supernatant and complexes sedimenting at ∼3.5 S and ∼7 S were observed in a 5 to 20% sucrose gradient. At 37° and low salt extraction, the [3H]TA was bound to a 27,000 x g pellet (containing 98% cellular DNA) from which it could be extracted with high salt to yield a ∼4 S complex. In contrast, cortexolone yielded a single receptor complex, ∼3.5 S, at both 0° and 37° after extraction of thymocytes with either the low or high salt buffer. Moreover, if the 37° low salt pellet is re-extracted with the high salt buffer, additional [3H]TA-receptor complex could be isolated but this was not the case for the [3H]cortexolone-receptor complex. When the [3H]TA receptor enters the nucleus it is firmly bound to an intranuclear molecule, whereas the cortexolone-receptor when taken up by the nucleus does not bind to an acceptor molecule. It is concluded that the lack of activity of the cortexolone-receptor complex is the result of a conformational change which allows for its uptake by the nucleus but decreases its affinity for a nuclear acceptor site and therefore does not mediate a biological response.