S. Roux et al., MUTATION OF ISOLEUCINE-747 BY A THREONINE ALTERS THE LIGAND RESPONSIVENESS OF THE HUMAN GLUCOCORTICOID RECEPTOR, Molecular endocrinology, 10(10), 1996, pp. 1214-1226
Mutation of isoleucine 747 to threonine in the C-terminal part of the
ligand-binding domain (LBD) of the human glucocorticoid receptor (GR)
alters the ligand specificity for transactivation. Natural glucocortic
oids such as cortisol or corticosterone were completely inactive with
the mutant I7477, whereas synthetic steroids like dexamethasone effici
ently stimulated GR I747T-mediated transactivation. However, the corre
sponding ligand dose-response curve for dexamethasone-induced transact
ivation was shifted to higher concentrations when compared with that o
btained with the wild type GR. Neither this shift nor the inability of
cortisol to activate the I747T mutant was due to an altered in vitro
ligand-binding affinity, in the canonical three-dimensional structure
of nuclear receptor LBDs, isoleucine 747 is in the direct vicinity of
residues that contribute to the ligand-binding pocket. Moreover, it is
located in the C-terminal LBD region, which harbors the conserved cor
e of the activation function AF-2 and undergoes a ligand-induced trans
conformation, required to generate the surface interacting with putati
ve transcriptional intermediary factors/coactivators of AF-2. The phen
otype of I747T mutant is discussed in view of the possible consequence
s of the mutation on the various events which, according to the model,
lead to a transcriptionally competent AF-2.