Substitution of arginine for cysteine 643 of the glucocorticoid receptor reduces its steroid-binding affinity and transcriptional activity.

To investigate the mechanism for glucocorticoid resistance in leukemic cells, we sequenced the coding region of glucocorticoid receptor (GR) gene in ten Japanese leukemic cells. We identified a novel heterozygous mutation (C643R) in the ligand-binding domain in P30/OHK cells. Western blot analysis for COS-7 cells transfected with the wild-type or C643R mutant GR plasmid revealed similar protein expression levels. In the ligand-binding assay, the dissociation constant of the C643R GR was six-fold higher than that of the wild-type GR. Moreover, the C643R GR showed no transcriptional activity in the luciferase reporter assay.