Activation and partial proteolysis of variant glucocorticoid receptors, studied by two-phase partitioning.

In cultured lines of mouse lymphoma cells, resistant to glucocorticoids is frequently associated with the occurrence of glucocorticoid receptors with an abnormally low affinity (nt-) or an abnormally high affinity (nti) for nuclei and DNA. We have investigated whether the abnormal affinities for DNA are correlated with alterations in charge and surface properties of the receptors, that would be revealed through the partition coefficient in aqueous dextran/poly(ethylene glycol) two-phase systems. We have found that none of the receptor variants is defective in the activation step per se, and that only the nti receptors are abnormal in partition properties. Partial proteolysis of wild-type and nt- receptors with alpha-chymotrypsin produces forms which are indistinguishable from the nti receptors with respect to partition coefficients. Upon alpha-chymotrypsin treatment the wild-type receptors attain DNA-binding properties identical to those of the nti receptors, while the nt- receptors, in spite of some increase in DNA affinity, still bind less firmly to DNA than the alpha-chymotrypsin-treated wild-type receptors. alpha-Chymotrypsin treatment of the various receptor types also produces an increase in the binding to dextran sulphate, but the dextran sulphate affinity is higher and varies less between different receptor types than the DNA affinity. Trypsin-treated receptors were found to be devoid of affinity for DNA and dextran sulphate.