Activation and Partial Proteolysis of Variant Glucocorticoid Receptors, Studied by Two‐Phase Partitioning

In cultured lines of mouse lymphoma cells, resistance to glucocorticoids is frequently associated with the occurrence of glucocorticoid receptors with an abnormally low affinity (nt − ) C an abnormally high affinity (nt i ) for nucleiand 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 coefficeint in aqueous dextran/poly(ethylene glycol) two‐phase systems. We have found that none of teh receptor variants is defective in the activation step per se , and that only the nt i receptors are abnormal in partition properties. Partial proteolysis of wild‐type and nt − receptors with α‐chymotrypsin products forms which are indistinguishable from the nt i receptors with respect to partition coefficeints, Upon α‐chymotrypsin treatment the wild‐type receptors attain DNA‐binding properties identical to those of the nt i receptors, while the nt − receptors, in spite of some increase in DNA affinity, still bind less firmly to DNA than the α‐chymotrypsin‐treated wild‐type receptors, α‐Chymotrypsin treatment of the various receptor types also produces and increase in the inding 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. We conclude that the increased DNA affinity of the nt i receptors is due to a gross change in teh structure of the receptors, while the decreased DNA affinity of the nt − receptors is caused by more subtle alterations in the polyanion binding domain of the receptors.