Molybdate-sensitive and molybdate-resistant activation-labile glucocorticoid-receptor mutants of the human lymphoid...

The basis for the glucocorticoid resistance of three (3R7, 3R43 and 4R4) genetically independent mutants derived from the glucocorticoid-sensitive human lymphoid cell line CEM-C7 was examined. Each mutant contained significant, albeit reduced, amounts of steroid binding activity measured in both whole and broken cell assays. These activities were of similar high affinity and specificity to that seen in the sensitive parent, suggesting that the steroid binding portion of the receptors in these mutants was normal. However, nuclear translocation of steroid-receptor (SR) complexes was defective in all three clones. Analysis of SR complex activation by DEAE-cellulose chromatography established that receptors from the mutant clones were extremely labile under conditions which would activate normal SR complexes. Such lability was not exhibited by the unoccupied or occupied but unactivated forms of these receptors, indicating that all three were "activation labile" (act1). SR complexes of clones 3R7 and 4R4 were completely protected by the inclusion of molybdate during attempted activation and were classified as act1:molybdate-sensitive. However, SR complexes of clone 3R43 were unstable during attempted activation, even in the presence of 50 mM molybdate, and were thus classified as act1:molybdate-resistant. Our results suggest that while the act1 phenotype may predominate among spontaneously derived glucocorticoid-resistant mutants derived from CEM-C7, this phenotype may be the consequence of at least two different mutations.