| HOME | HELP | FEEDBACK | SUBSCRIPTIONS | ARCHIVE | SEARCH | TABLE OF CONTENTS |
BRIEF REPORT |
Division of Endocrinology and Metabolism (E.C., G.P.C.), Biomedical Research Foundation of the Academy of Athens, Athens 11527, Greece; Section on Pediatric Endocrinology (E.C., T.I., S.B., K.Z., G.P.C., T.K.), Program in Reproductive and Adult Endocrinology, Eunice Kennedy Shriver National Institute of Child Health and Human Development, National Institutes of Health, Bethesda, Maryland 20892; and Centro de Endocrinologia (W.J.), Cali, Colombia
Address all correspondence and requests for reprints to: Evangelia Charmandari, M.D., Division of Endocrinology and Metabolism, Biomedical Research Foundation of the Academy of Athens, 4 Soranou tou Efessiou Street, Athens 11527, Greece. E-mail: evangelia.charmandari{at}googlemail.com.
| Abstract |
|---|
|
|
|---|
C) substitution at position 1201 (exon 2) of the hGR gene, which resulted in aspartic acid to histidine substitution at amino acid position 401 in the amino-terminal domain of the hGR
. We investigated the molecular mechanisms of action of the natural mutant receptor hGR
D401H.
Methods-Results: Compared with the wild-type hGR
, the mutant receptor hGR
D401H demonstrated a 2.4-fold increase in its ability to transactivate the glucocorticoid-inducible mouse mammary tumor virus promoter in response to dexamethasone but had similar affinity for the ligand (dissociation constant = 6.2 ± 0.6 vs. 6.1 ± 0.6 nM) and time to nuclear translocation (14.75 ± 0.25 vs. 14.25 ± 1.13 min). The mutant receptor hGR
D401H did not exert a dominant positive or negative effect upon the wild-type receptor, it preserved its ability to bind to glucocorticoid response elements, and displayed a normal interaction with the glucocorticoid receptor-interacting protein 1 coactivator.
Conclusions: The mutant receptor hGR
D401H enhances the transcriptional activity of glucocorticoid-responsive genes. The presence of the D401H mutation may predispose subjects to obesity, hypertension, and other manifestations of the metabolic syndrome.
| Introduction |
|---|
|
|
|---|
|
C) substitution at position 1201 in exon 2 of the gene, which resulted in aspartic acid to histidine substitution at amino acid position 401 in the amino-terminal domain of the hGR
(nuclear receptor subfamily 3, group C, member 1 isoform
; protein identification: NP000167). No other mutations or polymorphisms were identified. We investigated the molecular mechanisms of action of the natural mutant receptor hGR
D401H. | Materials and Methods |
|---|
|
|
|---|
The plasmids used included pRShGR
, pRShGR
D401H, pRShGR
N363S, pRShGR
F737L, pF25GFP-hGR
, pF25GFP-hGR
D401H, pBK/CMV-hGR
, pBK/CMV-hGR
D401H, pGEX4T3-GRIP1 (1–1462), pGEX4T3-GRIP1 (596–774), pGEX4T3-GRIP1 (740–1217), pRSV-erbA–1, pMMTV-luc, and pSV40-β-gal (7–11).
Transactivation assays
CV-1 cells were cotransfected with pRShGR
pRShGR
N363S, pRShGR
F737L, or pRShGR
D401H (0.05 µg/well), pMMTV-luc (0.5 µg/well), and pSV40-β-gal (0.1 µg/well). In further experiments, cells were cotransfected with pMMTV-luc, pSV40-β-gal, a constant amount of pRShGR
, and progressively increasing concentrations of pRShGR
D401H. A control plasmid was added in appropriate quantities to maintain a constant amount of DNA in each well. Cells were exposed to dexamethasone for 24 h, and luciferase and β-galactosidase activities were determined in the cell lysates (7, 8, 9, 10, 11). Luciferase activity was divided by β-galactosidase activity to account for transfection efficiency.
Western blot analyses
CV-1 and COS-7 cells were transfected with pRShGR
or pRShGR
D401H (15 µg/flask). Western blot analyses were performed as previously described (7, 8, 9, 10, 11).
Dexamethasone-binding assays
Dexamethasone-binding assays were performed on peripheral blood mononuclear cells obtained from the patient and a control subject. Ligand-binding assays were also performed on COS-7 cells transfected with pRShGR
or pRShGR
D401H (1.5 µg/well) (7, 8, 9, 10, 11).
Nuclear translocation studies
HeLa cells were transfected with pF25GFP-hGR
or pF25GFP-hGR
D401H (2 µg/dish). In further experiments, cells were transfected with equal amounts of pF25GFP-hGR
and pRShGR
D401H (1.5 µg/dish). Nuclear translocation studies were performed as previously described (7, 8, 9, 10, 11).
Chromatin immunoprecipitation (ChIP) assays
HCT-116 cells, in which the mouse mammary tumor virus (MMTV) promoter was stably integrated within chromatin, were transiently transfected with pRShGR
or pRShGR
D401H (10 µg/dish). ChIP assays were performed as previously described (8, 9, 10, 11).
Glutathione-S-transferase (GST) pull-down assays
In vitro transcription/translation reactions were used to produce 35S-labeled hGR
and hGR
D401H in rabbit reticulocyte lysate by using pBK/CMV-hGR
and pBK/CMV-hGR
D401H, respectively, as templates. The in vitro interaction between hGR
-related plasmids and GST-fused GR-interacting protein 1 (GRIP1) proteins was tested as previously described (7, 8, 9, 10, 11).
| Results |
|---|
|
|
|---|
D401H displays increased transcriptional activity compared with the wild-type hGR
Compared with the wild-type hGR
, the mutant receptor hGR
D401H demonstrated a 2.4-fold increase in its ability to transactivate the glucocorticoid-inducible MMTV promoter in response to dexamethasone (10–12 to 10–5 M) (Fig. 1C
). This effect of hGR
D401H was similar to that of hGR
N363S, a polymorphism known to be associated with glucocorticoid hypersensitivity, but opposite to the effect of hGR
F737L, a natural mutant receptor associated with glucocorticoid resistance (7, 8, 9, 10, 11). The concentration of dexamethasone required to achieve 50% of transactivation was 10–8 M for the mutant receptor and 14.5 x 10–8 M for the wild-type receptor.
The mutant receptor hGR
D401H does not exert a dominant positive or negative effect upon the wild-type hGR
Cotransfection with a constant amount of hGR
and progressively increasing concentrations of hGR
D401H indicated that the mutant receptor hGR
D401H had an additive rather than a dominant positive or negative effect upon the wild-type receptor (Fig. 1D
).
The mutant receptor hGR
D401H demonstrates normal affinity for the ligand
The apparent dissociation constant of hGR
D401H was similar to that of hGR
in COS-7 cells transfected with the respective plasmids [6.2 ± 0.6 vs. 6.1 ± 0.6 nM; P = not significant (NS)]. Furthermore, there was no difference in the affinity of hGR
for the ligand between the patient and the control subject in peripheral blood mononuclear cells (dissociation constant, 8.95 ± 2.3 vs. 8.39 ± 3.11 nM; P = NS). No difference in the number of dexamethasone-binding sites was noted between the wild-type and mutant receptor in both assays.
Western blot analyses demonstrated no differences in the expression of hGR
and hGR
D401H proteins in CV-1 or COS-7 cells, indicating that the aforementioned results did not reflect differences at the protein expression level.
The mutant receptor hGR
D401H demonstrates normal subcellular localization and nuclear translocation
In the absence of dexamethasone, both the wild-type and mutant receptors were primarily localized in the cytoplasm of cells. No significant differences were observed between hGR
and hGR
D401H in the time required for nuclear translocation after exposure to dexamethasone (10–6 M) (14.75 ± 0.25 vs. 14.25 ± 1.13 min; P = NS) (Fig. 2
, A and B). Coexpression of hGR
and hGR
D401H at a 1:1 ratio had no apparent effect on the nuclear translocation of the wild-type hGR
(Fig. 2C
).
|
D401H preserves its ability to bind to DNA in vivo
In ChIP assays, both hGR
and hGR
D401H coprecipitated with MMTV glucocorticoid response elements similarly in a ligand-dependent fashion, suggesting that hGR
D401H preserves its ability to bind to DNA (Fig. 2D
).
The mutant receptor hGR
D401H interacts with the GRIP1 coactivator in vitro through both its activation function (AF)-1 and AF-2 domains
GRIP1 contains two sites that bind to steroid receptors: one site interacts with the AF-2 of hGR
in a ligand-dependent fashion, whereas the other site interacts with the AF-1 of hGR
in a ligand-independent fashion (12). In GST pull-down assays, like the wild-type receptor, hGR
D401H interacted with the GRIP1 coactivator through both its AF-1 and AF-2 domains (Fig. 2D
).
| Discussion |
|---|
|
|
|---|
-mediated transactivation of glucocorticoid-responsive genes but did not affect the affinity of the receptor for the ligand, its cytoplasmic to nucleus translocation, its ability to bind to DNA, or its interaction with the GRIP1 coactivator. Furthermore, the mutant receptor hGR
D401H had an additive rather than a dominant positive or negative effect upon the wild-type receptor. Our findings suggest that, even at a heterozygotic state, the D401H mutation enhances the transcriptional activity of hGR
and may predispose carriers to an adverse metabolic profile, which, along with other important determinants, such as environmental, dietary, and socioeconomic factors, may lead to visceral obesity, hypertension, dyslipidemia, and metabolic syndrome-related atherosclerotic cardiovascular disease. Interindividual variations in tissue sensitivity to glucocorticoids have been described within the normal population and have been partly attributed to polymorphisms in the hGR gene. Several polymorphisms of the hGR gene have been reported (4). The N363S polymorphism is associated with higher sensitivity to glucocorticoids in vivo, increased insulin response to exogenous dexamethasone administration, higher body mass index and waist to hip ratio, elevated cholesterol and triglyceride concentrations, lower bone mineral density in trabecular bone, and higher incidence of coronary artery disease independent of weight (4, 13, 14, 15).
A frequent BclI restriction fragment length polymorphism is also associated with increased sensitivity to glucocorticoids, hypertension, visceral adiposity, and increased insulin concentrations in obese women (4, 16).
A third polymorphism, the ER22/23EK, is associated with relative glucocorticoid resistance, lower fasting insulin concentrations and improved insulin sensitivity, lower total and low-density lipoprotein cholesterol concentrations, and lower C-reactive protein concentrations (4, 17, 18). In line with this favorable metabolic profile, the ER22/23EK polymorphism is significantly higher in the oldest half of the population and is associated with increased survival. Furthermore, at older age, carriers of this polymorphism have lower risk of dementia and fewer white matter lesions in the brain compared with noncarriers (4).
We believe that the D401H mutation in our patient is producing a mixed glucocorticoid resistance and hypersensitivity phenotype with tissue selectivity. Therefore, the presence of resistance at the regulatory centers of the hypothalamic-pituitary-adrenal (HPA) axis is associated with hypercortisolism, whereas the presence of hypersensitivity at the vasculature, central adipose tissue, and liver is associated with hypertension, central adiposity, and dyslipidemia. Interestingly, the N363S polymorphism was also associated with a paradoxically hyperresponsive HPA axis at the Trier social stress test, suggesting that this point mutation caused glucocorticoid resistance at the level of feedback regulation of the HPA axis (19).
Like most polymorphic variants, the D401H mutation is located at the amino-terminal domain of the receptor, in close proximity to the major transactivation domain AF-1. Given that modification of AF-1 by phosphorylation may enhance or repress the transcriptional activity of hGR
in a gene- and tissue-specific manner, it is possible that the D401H mutation causes a tissue-specific effect on AF-1 activity (20). This hGR gene mutation has not been previously described, and its prevalence in Colombia or other countries has not been determined. Therefore, it is essential that it should be included in population studies aiming to detect hGR variants associated with glucocorticoid hypersensitivity.
In clinical practice, glucocorticoids are used widely to treat a number of pathological conditions, as well as for replacement therapy purposes. The effects of glucocorticoid treatment may vary considerably between patients and may be partly attributed to polymorphisms in the hGR gene. Therefore, when the presence of these hGR gene variants is known in a patient, the dose of glucocorticoids should be adjusted accordingly to ensure optimal therapy and minimal adverse effects (4).
We conclude that the D401H mutation enhances the hGR
-mediated transactivation of glucocorticoid-responsive genes in a tissue-specific manner, and may predispose subjects to obesity, hypertension, and metabolic syndrome-related atherosclerotic cardiovascular disease.
| Footnotes |
|---|
Disclosure Statement: The authors have nothing to disclose.
First Published Online September 30, 2008
1 E.C. and T.K. contributed equally to this project. ![]()
Abbreviations: AF, Activation function; ChIP, chromatin immunoprecipitation; GR, glucocorticoid receptor; GRIP1, glucocorticoid receptor-interacting protein 1; GST, glutathione-S-transferase; hGR, human glucocorticoid receptor; HPA, hypothalamic-pituitary-adrenal; MMTV, mouse mammary tumor virus; NS, not significant.
Received April 24, 2008.
Accepted September 22, 2008.
| References |
|---|
|
|
|---|
by interfering with formation of active coactivator complexes. Mol Endocrinol 19:52–64
R477H and hGR
G679S associated with generalized glucocorticoid resistance. J Clin Endocrinol Metab 91:1535–1543
| |||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
| HOME | HELP | FEEDBACK | SUBSCRIPTIONS | ARCHIVE | SEARCH | TABLE OF CONTENTS |
| Endocrinology | Endocrine Reviews | J. Clin. End. & Metab. |
| Molecular Endocrinology | Recent Prog. Horm. Res. | All Endocrine Journals |