Effects of ATP and pyrophosphate on properties of glucocorticoid-receptor complexes from rat thymus cells

Cytosols from rat thymus cells incubated with glucocorticoid contain nonactivated and activated receptors and mero-receptor complexes, in relative amounts that depend on the incubation conditions. These forms can be separated by a rapid minicolumn chromatographic technique based on their differential affinities for DNA, DEAE, and hydroxylapatite. We have used this method to examine the effects of ATP, pyrophosphate (PPi), and related compounds on cytosolic complexes. In addition to ATP, already known to promote activation at 0 degrees C, PPi, ADP, and other triphosphates at millimolar concentrations promoted activation of nonactivated complexes. AMP and Pi had little effect. ATP and PPi at millimolar concentrations also reduced binding of activated complexes to DNA. Characterization of the ATP- and PPi-activated complexes by gel filtration and ion exchange chromatography revealed two DNA-binding forms. One was essentially identical (Stokes radius of approximately 5.4 nm, elution from DEAE at approximately 50 mM KCl) to the normal activated complex obtained directly from cells incubated at 37 degrees C. The other had a Stokes radius of approximately 3.1 nm and had no affinity for DEAE. Analysis by minicolumns and gel filtration showed that ATP and PPi prevented formation of mero-receptor complexes, a process which occurs relatively rapidly in untreated thymus cytosols. These compounds did not alter properties of preformed mero-receptor. The accumulation of 3.1-nm complexes in thymus cytosols in which formation of mero-receptor is prevented suggests that this form is an intermediate, normally short-lived, in the conversion of 5.4 nm complexes to mero-receptor.