Abstract
This study molecularly elucidates the basis for the dominant negative mechanism of the glucocorticoid receptor (GR) isoform hGRbeta, whose overexpression is associated with human glucocorticoid resistance. Using a series of truncated hGRalpha mutants and sequential mutagenesis to generate a series of hGRalpha/beta hybrids, we find that the absence of helix 12 is neither necessary nor sufficient for the GR dominant negative phenotype. Moreover, we have localized the dominant negative activity of hGRbeta to two residues and found that nuclear localization, in addition to heterodimerization, is a critical feature of the dominant negative activity. Molecular modeling of wild-type and mutant hGRalpha and hGRbeta provides structural insight and a potential physical explanation for the lack of hormone binding and the dominant negative actions of hGRbeta.