Differential Hormone-Dependent Transcriptional Activation and -Repression by Naturally Occurring Human Glucocorticoid Receptor Variants
Pieter de Lange,
Jan W. Koper,
Nannette A. T. M. Huizenga,
Albert O. Brinkmann,
Frank H. de Jong,
Michael Karl,
George P. Chrousos and
Steven W. J. Lamberts
Department of Internal Medicine III (P.d.L., J.W.K., N.A.T.M.H.,
F.H.d.J., S.W.J.L.) Department of Endocrinology and Reproduction
(A.O.B.) Erasmus University 3015 GD Rotterdam, The
Netherlands
Developmental Endocrinology Branch (M.K.,
G.P.C.) National Institute of Child Health and Human
Development National Institutes of Health Bethesda, Maryland
20892
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ABSTRACT
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The molecular mechanisms underlying primary
glucocorticoid resistance or hypersensitivity are not well understood.
Using transfected COS-1 cells as a model system, we studied gene
regulation by naturally occurring mutants of the glucocorticoid
receptor (GR) with single-point mutations in the regions encoding the
ligand-binding domain or the N-terminal domain reflecting different
phenotypic expression. We analyzed the capacity of these GR variants to
regulate transcription from different promoters, either by binding
directly to positive or negative glucocorticoid-response elements on
the DNA or by interfering with protein-protein interactions. Decreased
dexamethasone (DEX) binding to GR variants carrying mutations in the
ligand-binding domain correlated well with decreased capacity to
activate transcription from the mouse mammary tumor virus (MMTV)
promoter. One variant, D641V, which suboptimally activated MMTV
promoter-mediated transcription, repressed a PRL promoter element
containing a negative glucocorticoid-response element with wild type
activity. DEX-induced repression of transcription from elements of the
intercellular adhesion molecule-1 promoter via nuclear factor-
B by
the D641V variant was even more efficient compared with the wild type
GR. We observed a general DEX-responsive AP-1-mediated transcriptional
repression of the collagenase-1 promoter, even when receptor variants
did not activate transcription from the MMTV promoter. Our findings
indicate that different point mutations in the GR can affect separate
pathways of gene regulation in a differential fashion, which can
explain the various phenotypes observed.
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INTRODUCTION
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In man, response to glucocorticoids may vary considerably. Some
individuals are quite sensitive to these steroid hormones, whereas
others are relatively resistant. Hypersensitivity to glucocorticoids
may be manifested by the development of cushingoid features after
low-dose treatment (1). In primary glucocorticoid resistance, negative
feedback of cortisol on the hypothalamic-pituitary-adrenal axis is
decreased. The set point of this axis is set at a higher level with
higher plasma concentrations of ACTH and cortisol (2, 3, 4, 5). The diurnal
rhythm of cortisol secretion remains intact, and the system also
remains sensitive to external stressors such as acute hypoglycemia (2, 6). The elevated cortisol levels do not cause signs or symptoms of
Cushings syndrome, due to reduced response to cortisol in all target
tissues.
In a number of reports, glucocorticoid resistance in humans has been
correlated with mutations in the gene encoding the glucocorticoid
receptor (GR) (7, 8, 9, 10). The receptor is expressed throughout the body
and plays a key role in both positive and negative regulation of gene
expression (11, 12, 13, 14). Because glucocorticoids play an important role in
normal development and in maintenance of basal and stress-related
homeostasis, including regulation of various metabolic processes,
central nervous system functions, and restraint of the
inflammatory/immune reaction, altered GR function may have widespread
consequences (2, 15).
Analysis of a number of healthy volunteers indicated the existence of
two N-terminal GR receptor variants with a normal dissociation constant
(16), carrying either an arginine to lysine change at position 23 of
the protein (R23K) or an asparagine to serine change at codon 363
(N363S). In three individuals the R23K variant was accompanied by signs
and symptoms of glucocorticoid resistance, whereas four other
individuals with the same mutation were asymptomatic. The N363S variant
was present in several members of a family with glucocorticoid
resistance. The glucocorticoid-resistant members also had a GR gene
microdeletion resulting in functional knock-out of the allele not
containing the mutation. This variant had a normal capacity to activate
transcription in a transfection assay (9). It was later reported to be
present in two glucocorticoid-resistant small cell lung tumor cell
lines (17, 18). Our recent studies suggest that the N363S variant is
present in about 6% of the normal Dutch population and might be
accompanied by an increased sensitivity to glucocorticoids (1).
Furthermore, three different variant human GR forms with altered amino
acids in their C termini have been reported to date: 1) a heterozygous
isoleucine to asparagine change at codon 559 (I559N), which abolished
detectable ligand binding and was found in a patient who presented with
hypertension and oligospermia (10); 2) a homozygous aspartic acid to
valine change at codon 641 (D641V), the dissociation constant of which
was 3 times higher relative to the wild type receptor, occurring in a
patient with severe hypertension and hypokalemia (7); and 3) a
homozygous valine to isoleucine change at codon 729 (V729I), with a
2-fold higher dissociation constant relative to the wild type receptor,
which was found in a young boy with isosexual precocity as a result of
increased levels of adrenal androgens (8). These mutations are
indicated in Fig. 1A
. No mutations in the region
involved in DNA binding have yet been reported in humans. The natural,
non-ligand-binding ß-isoform of the GR (human GRß), the presence of
which has not yet been related to disease, does not activate
transcription in transfection assays (9). To obtain more insight into
its mode of action, this isoform has been included in this
investigation.

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Figure 1. Human GR Variants and Their Expression
A, Amino acid alterations reported in the hGR associated with
glucocorticoid resistance (7 8 10 16 ). B, Western Immunoblot
analysis of the GR receptor variants. The expression of the indicated
receptor variants was measured by transfecting COS-1 cells. hGRß is a
naturally occurring splice variant of the wild type GR (see Refs. 9 and
47). Size markers are ß-galactosidase (123 kDa) and BSA (80 kDa).
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GR acts through several distinct mechanisms to activate or repress
transcription. It can either bind directly to a specific DNA sequence,
termed a positive or a negative (n) glucocorticoid response element
(GRE) (19, 20), or it can interact with other transcription factors
such as AP-1 (21, 22) and nuclear factor (NF)-
B (23, 24, 25) without
itself being bound to DNA. GR variants may achieve a differential
interaction with the transcription machinery and any of these factors.
Furthermore, the abundance and activity of components of the
transcription machinery and the interacting factors may differ among
individuals. As a first step toward explaining more precisely the
varying phenotypic expression of the GR variants in primary
glucocorticoid resistance, we examined their capacity to activate or
repress transcription from several different promoters in COS-1
cells.
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RESULTS
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Expression of the Human (h) GR Mutant Constructs
First, we investigated whether transfection of expression plasmids
containing the different GR variants as well as the naturally occurring
splice variant hGRß resulted in comparable intracellular levels of
receptor protein. COS-1 cells were used in this and subsequent
experiments because these cells contain little, if any, endogenous GR
protein (Fig. 1B
, pTZ control lane). Immunoblot analysis of lysates
from COS-1 cells transfected with the GR variants showed that all GR
constructs were properly expressed (Fig. 1B
).
Activation of Transcription by hGR Variants
The R23K and N363S variants had a capacity to activate mouse
mammary tumor virus (MMTV)-driven transcription similar to that of the
wild type GR (see Table 1
, column MMTV. The potency of
the wild type GR to regulate transcription from the various promoters
is set as 1). I559N did not activate transcription (Ref. 10 and Table 1
), whereas the concentration of dexamethasone (DEX) required for
half-maximal stimulation of LUC activity by the V729I variant was
12-fold higher (Fig. 2
), similar to what has been
published previously (8). The overall relative potency of the V729I
variant to activate transcription from the MMTV promoter compared with
the wild type GR at the suboptimal ligand concentrations was 0.08
(Table 1
). The D641V variant was even less potent than the V729I
variant (Fig. 2
), with an overall relative potency of 0.04 (Table 1
).
The hGRß-form, which is known not to activate transcription, was used
as a negative control (Fig. 2
).
Negative GRE-Mediated Repression of Transcription by the hGR
Variants
An expression construct containing a region of the PRL promoter
designated PRL3 (-247 to -214), comprising an nGRE fused upstream of
a thymidine kinase (tk) promoter-LUC fusion gene (PRL3-tk-LUC), was
cotransfected with the variant GR plasmids. At different ligand
concentrations, repression of LUC transcription by the receptor
variants was determined. In the presence of 10-7
M DEX, the wild type GR repressed transcription by 55%
(Fig. 3
). The capacity of the N-terminal variants (R23K
and N363S) to repress transcription was comparable to the wild type GR
(Table 1
). The I559N and hGRß variants did not repress transcription
(Table 1
). Surprisingly, the D641V variant repressed nearly as
efficiently as did the wild type GR (Fig. 3
). The overall relative
potency of repression by D641V was 0.52 (Table 1
). V729I, however, did
not repress at 10-9 M DEX, whereas the wild
type GR and D641V significantly repressed PRL3-tk-LUC transcription to
76% at this concentration (Fig. 3
). At higher ligand concentrations,
V729I repressed at wild type levels with an overall relative potency of
0.95 (Table 1
).
Nuclear Factor (NF)-
B Transcriptional Repression by the hGR
Variants
Without added p65 plasmid, the intercellular adhesion molecule
(ICAM)-1 promoter had a basal activity that could not be repressed by
active GR (data not shown), due to the virtual absence of endogenous
NF-
B in COS-1 cells. A 6-fold induction of ICAM-1-LUC expression was
observed when a p65 expression plasmid was cotransfected (data not
shown). In the presence of 10-7 M DEX, the
wild type GR repressed p65-induced expression by 57% (Fig. 4
). The R23K and N363S variants repressed to a similar
extent as did the wild type GR, but the I559N variant did not repress
p65-induced expression (Table 1
). To study subtle differences between
the capacities of the variants to inactivate NF-
B, repression of the
ICAM 1 promoter was also studied at lower ligand concentrations. The
D641V variant repressed better than did the wild type GR (Fig. 4
); the
overall relative potency to repress the ICAM-1 promoter compared with
the wild type GR at the measured ligand concentrations was 4.6 (Table 1
). The V729I variant was slightly less effective compared with the
wild type GR (Fig. 4
), with a relative potency value of 0.3 (Table 1
).
Human GRß did not repress at all ligand concentrations (Table 1
).
Because the D641V variant repressed transcription from the ICAM-1
promoter more efficiently compared with the wild type GR, it might
interact more efficiently with the p65 protein to prevent the
interaction of the p65 protein with the ICAM-1 promoter. We studied
repression by lower concentrations of the variants at 1.0
nM DEX, as this ligand concentration was most
discriminative (Fig. 4
). At receptor concentrations that were up to 5
times lower, we observed the same relative levels of repression of the
ICAM-1 promoter (not shown). C476W/R479Q, an artificial GR variant that
retained its full capacity to bind hormone (21), did not repress
NF-
B activity at all; it even seemed to increase the activation of
the ICAM-1 promoter at 10-8 M and
10-7 M DEX (Fig. 4
).
Repression of AP-1 by the GR Variants
Repression of AP-1-mediated transcription from the collagenase
-517/+63 promoter by the GR variants in the presence of increasing
amounts of DEX was measured. In the presence of 10-7
M DEX, the wild type GR inactivated AP-1 by 84% (Fig. 5
). The R23K and N363S variants repressed similarly as
the wild type GR (Table 1
). The I559N and hGRß variants displayed a
weak, hormone-dependent repression. The I559N variant repressed by 50%
at 10-7 M DEX (Fig. 5A
) with an overall
relative potency compared with the wild type GR of 0.002 (Table 1
).
Human GRß repressed by 40% at 10-7 M DEX
with an overall relative potency compared with the wild type GR of
0.001 (Table 1
).
The C476W/R479Q variant did not repress, as has been shown before (21).
At 1, 10, and 100 nM DEX, this variant even induced
expression from the collagenase promoter (Fig. 5B
). At
10-7 M DEX, the D641V and V729I variants
repressed as efficiently as did the wild type GR. However, these
variants showed a shift in their dose-response curves (Fig. 5B
), with
overall relative potencies of 0.16 and 0.12, respectively
(Table 1
).
 |
DISCUSSION
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To obtain insight in what might be the functional significance of
naturally occurring point mutations of the human GR gene, we set up
transfection assays using different reporter constructs, the promoters
of which were either positively or negatively regulated by GR.
There were no indications for reduced function of the R23K variant
receptor because it activated MMTV transcription equally well as the
wild type GR. The R23K amino acid substitution is well outside the
1-region of the transcriptional activation domain, which
ranges from position 77 to 262 of the GR protein as determined in an
in vitro system similar to the one used here (26); this
explains the unaltered in vitro capacity of this variant to
activate transcription. Carriers of the R23K variant receptor showed a
variety of phenotypes, ranging from asymptomatic to severely
glucocorticoid resistant. Thus, the presence of the mutation per
se could not be correlated directly with glucocorticoid resistance
(16). If it is a functional mutation, this would imply that at least
one additional factor is involved in the resulting phenotype. Carriers
of the N363S variant receptor showed a significantly higher increase of
peripheral insulin levels in response to DEX than controls, suggesting
increased sensitivity (1). At present it is not known which molecular
mechanism underlies this observation.
Different modes of GR-mediated transcriptional repression have been
reported (19, 20, 21, 22, 23, 24, 25), one of which requires binding of the receptor to an
nGRE (19, 20). Different nGREs lack extensive homologies, but each nGRE
is related to the GRE consensus element implicated in receptor binding
and enhancer activity at positive GREs (20). The nGRE-bound GR does not
activate, but represses, transcription of the downstream gene, as is
shown to be the case for the POMC promoter (19) and the PRL promoter
(20). The fact that the N-terminal amino acid alterations are
positioned outside the
1-region does not necessarily
imply that the capacity of the N-terminal GR variants to repress
transcription by binding to an nGRE is unaltered. It is well known that
the GR DNA-binding domain is involved in nGRE binding (20). The
variants tested here have amino acid alterations residing well outside
the DNA-binding domain. Since the effects of the N-terminal variants on
PRL3tkLUC expression and MMTV- directed transcription did not differ
from those of the wild type GR, there are no indications for disruption
of conformation, or diminished binding to DNA due to the altered amino
acids. Results of this study suggest that repression by binding to the
PRL nGRE requires hormone binding because the I559N variant, which has
a very low, if any, ligand affinity, completely failed to repress
transcription from the thymidine kinase promoter, most likely as a
result of failure of this variant to translocate into the nucleus. The
V729I variant repressed the PRL promoter relatively less efficiently at
low ligand concentrations (Fig. 3
), which could be anticipated from the
similarly less efficient transcriptional activation of the MMTV
promoter by this variant (Fig. 2
), as both types of gene regulation are
mediated by direct binding of the GR to response elements on the DNA.
The D641V variant (7) showed a strongly reduced potency to activate
MMTV-driven transcription compared with wild type GR (Fig. 2
). These
data are in line with the clinical observations concerning the
propositus, who had a 7-fold elevation of free serum cortisol levels
(7). However, this variant repressed transcription from the PRL
promoter nearly at wild type levels (Fig. 3
). This suggests that a
different conformation of the GR is achieved when it is bound to an
nGRE or that a different conformation is necessary for repression. The
point mutation has an influence on the effective conformation for
transcriptional activation, but not for this type of transcriptional
repression.
GR has also been reported by several groups to play a role in
repressing transcription regulated by NF-
B (23, 24, 25).
NF-
B-responsive elements are required for the function of many
cytokine promoters as well as other genes, including ICAM-1 (27, 28). A
major form of NF-
B is composed of a dimer of p50 and p65 (RelA)
subunits, and this complex is retained in the cytoplasm by repressor
molecules that contain ankyrin repeat motifs (27, 28, 29). Recently it was
shown that a large fraction of the NF-
B protein can be kept from
entering the nucleus by interacting with I
B
, the transcription of
which is stimulated by active GR (24, 25). COS-1 cells lack endogenous
I
B
activity (23), indicating that in this system NF-
B is
inactivated by a direct interaction with GR, a mechanism that has been
postulated previously (23). The I559N and hGRß receptor variants did
not inactivate NF-
B at all. The capacity of the D641V variant to
repress transcription was increased, whereas the V729I variant
repressed slightly less efficiently as compared with the wild type GR
(Fig. 4
). At lower receptor concentrations, this difference in
repression was maintained. This indicates that the binding capacities
of the point mutants to p65 have not altered, but the conformation of
the p65-GR complex differs depending on the GR variant.
The transcription factor AP-1, consisting of heterodimers of the
various members of the Fos and Jun protein families, may play an
essential role in converting extracellular signals into changes of the
expression of specific genes involved in inflammation as well as cell
growth and differentiation (for review see Refs. 30, 31). AP-1
proteins share the bZIP-motif that allows the formation of homodimeric
complexes with DNA. This motif is part of the target required for
repression (32). Both the Fos and Jun proteins are at the receiving end
of signal transduction pathways from the cell membrane to the nucleus.
GR synergizes with Jun homodimers to activate AP-1 regulated promoters,
whereas it represses transcription induced by Fos-Jun heterodimers
without abolishing their binding to DNA (33, 34). Unliganded GR is
associated with heat shock protein (hsp) 90 in the form of a
heterohexamer containing the receptor, two molecules of hsp 90, and one
molecule each of hsp 70, hsp 56, and hsp 26 (35, 36, 37, 38). The receptor is
thus kept in a ligand-friendly conformation. Ligand binding stimulates
receptor activation, dissociation from hsp 90 (39, 40), and nuclear
translocation, prerequisites for both activation and repression of
transcription. The general inactivation of AP-1 we observed suggests
that weak association of the ligand with the receptor is sufficient for
dissociation of the heat shock proteins and subsequent binding of the
receptor to AP-1. It has been shown that transcriptional repression of
the collagenase promoter also occurs upon heat shock-induced nuclear
import of GR in transfected CV-1 cells, even without addition of
hormone (40). A receptor variant isolated from the human leukemic cell
line ICR27TK.3 (41), carrying a leucine to phenylalanine change at
position 753, which showed 14% hormone binding relative to the wild
type GR, was 100-fold less active in transcriptional activation and did
not reach wild type levels at 10-7 M DEX.
However, it had full DEX-responsive AP-1-repressing activity. In
addition, heat shock treatment of cells transfected with this variant
resulted in full repression in the absence of ligand (22). This
suggests that, in contrast to transcriptional activation, stably bound
ligand is not necessary for transcriptional repression once the
receptor is in the nucleus. The I559N and the hGRß variants have an
intact DNA-binding domain, which has been shown to be essential for
inactivation of AP-1, more so than is the hormone binding domain (21).
Interaction of GR with AP-1 in the cytoplasm would explain why certain
receptor variants such as I559N and hGRß may repress the collagenase
promoter without stable ligand binding. It has been shown that the
in vivo AP-1 footprint does not disappear in the presence of
glucocorticoids (33), which would imply that the putative cytoplasmic
GR/AP-1 complex does migrate into the nucleus and binds to AP-1
response elements but has lost its capacity to activate transcription.
Because we have no indication for a more efficient repression of AP-1
by any of the GR variants we tested compared with the wild type GR, it
is conceivable that the complex resides on the target promoter after
inactivation by these variants. As is the case for MMTV transcriptional
activation, the reduced transcriptional repression by the variants can
directly be associated with their reduced ligand binding capacity.
The observed hormone-dependent induction of activity of the ICAM-1
promoter as well as the collagenase promoter by the C467W/R479Q variant
is puzzling. Because this induction was not seen in the absence of
receptor (data not shown), the activation is somehow brought about
directly by this receptor variant. It could be that this variant in its
active state forms a complex with factors such as p65 or AP-1, thereby
allowing a better interaction with the regulatory elements on the DNA
rather than preventing it.
From the differential response of NF-
B and AP-1 to the variant
receptors, one can conclude that different GR mutations may cause
strong phenotypic differences due to the differential association of
the GR mutants with several factors, which can either act as
coactivators (42) or corepressors (43, 44). Recently, a protein
representing the human homolog of the yeast E2 ubiquitin-conjugating
enzyme, Ubc9, has been reported to interact with the wild type GR but
not with the inactive artificial GR mutant C476W/R479Q (44).
Furthermore, differences in phenotype between persons carrying the same
receptor variant may be due to individual differences in the abundance
and activity of the GR-associating factors.
Taken together, our data point toward an explanation as to why certain
point mutations that reduce or even impair the transcriptional
activation capacity of GR are not lethal to the subjects. Future
research will focus on factors associating with the receptor
(e.g. coactivators, corepressors as well as the hGRß
isoform), determining the fine-tuning of gene regulation that results
in the observed variety of phenotypes.
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MATERIALS AND METHODS
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Materials
Dexamethasone was purchased from Pharmacin (Zwijn-drecht,
The Netherlands). 12-O-Tetradecanoylphorbol-13-acetate (TPA)
and D-luciferin were purchased from Sigma (St. Louis, MO).
The Renaissance chemiluminescence Western blotting kit was obtained
from Dupont NEN (Boston, MA).
Reporter Genes and Expression Vectors
Constructions of the majority of GR expression plasmids used in
this study were previously described: pRShGR
and pRShGRß (26),
which were kindly provided by Dr. Ronald Evans (The Salk Institute, La
Jolla, CA), pRShGRSer363 (9), pRShGRAsn559 (10), and pRShGRVal641 (7).
The pRShGRIle729 expression plasmid (8) was a kind gift from Dr. Carl
Malchoff (Farmington, CT). pRShGRTrp476Gln479, containing a GR variant
generated by Taq polymerase errors during site-directed
mutagenesis, which neither activates nor represses transcription (21),
was used as a control. In this receptor variant, one of the
coordinating cysteine residues in the second Zn-cluster of the DNA
binding domain at position 476 was converted into a tryptophan;
furthermore, it contains an arginine to glutamine change at position
479. This plasmid was a kind gift from Dr. Andrew Cato
(Forschungszentrum, Karlsruhe, Germany). Construction of the plasmids
pRShGRLys23 and pRShGRVal641-II is described in the following
section.
The mouse mammary tumor virus-luciferase (MMTV-LUC) reporter plasmid
was kindly provided by Organon (Oss, The Netherlands). The human
collagenase 1-luciferase reporter plasmid (COLL-LUC) was a kind gift
from Dr. Andrew Cato. The p65 expression plasmid was a kind gift from
Prof. Carl Scheidereit (Max-Delbrück Center for Molecular
Medicine, Berlin, Germany). The human intercellular adhesion molecule
1-luciferase (ICAM-1-LUC) reporter plasmid pHBLUC1.3 was kindly
provided by Dr. Christian Stratowa (Bender & Co, GmbH, Vienna,
Austria), and the bovine PRL-luciferase reporter plasmid (PRL3-tk-LUC)
was a kind gift from Dr. Sam Okret (Huddinge Hospital, Huddinge,
Sweden).
Construction of GR Plasmids
pRShGRLys23 was generated by overlap extension PCR (46), to
replace the guanosine (G) residues at cDNA positions 198 and 200 for
adenosine (A) residues using the primers: 5'-CCATTCACCACATTGGTGTG-3'
(outer forward primer, positioned 28 nucleotides (nt) 5' of the unique
KpnI site), 5'-TTGCCTGACAGTAAACTGTG-3' [outer reverse
primer, cDNA nt position 10251045, numbering according to Hollenberg
et al. (47)], 5'-CACATCTCCCTTTTCCTGCG-3' (overlapping
reverse primer, cDNA nt position 186206), 5'-TTGCCTGACAGTAAACTGTG-3'
(overlapping forward primer, cDNA nt position 191211), and the
pRShGR
expression vector as a template. The G to A change at
position 198 does not give rise to an amino acid change, and the G to A
change at position 200 changes the arginine residue at codon 23 to a
lysine residue. The thymine (T) residue at position 192 was replaced by
a G residue to generate a CfoI restriction site, without
altering the encoded amino acid residue. The resulting fragment was
digested with KpnI and SalI and was inserted into
Bluescript plasmid (Stratagene, La Jolla, CA) digested with the same
enzymes. The fragment was fully sequenced to confirm the presence of
the desired point mutations and to exclude additional point mutations.
After digestion of the recombinant plasmid with KpnI and
SalI, the recombinant fragment was ligated back into
pRShGR
. The expression vector obtained was confirmed by sequencing
and was designated pRShGRLys23.
The pRShGRVal641-II plasmid was constructed as follows: The
ClaI/XhoI fragment from the original
pRShGRVal641 plasmid was inserted into Bluescript plasmid digested
with the same enzymes. Similarly, the ClaI/XhoI
fragment from pRShGR
was inserted into Bluescript plasmid. This
latter plasmid was digested with ClaI/SauI and
replaced with the ClaI/SauI recombinant fragment
containing the desired A to T change at cDNA position 2054 without any
further alterations. The ClaI/XhoI GR fragment
containing the single-point mutation was finally inserted to replace
the wild type fragment of pRShGR
. The resulting plasmid was
designated pRShGRVal641-II.
In the previous sections, GR variants encoded by these plasmids have
been referred to by their amino acid alterations, indicated by single
letter code.
Cell Culture and Transfections
Monkey kidney (COS-1) cells were maintained in DMEM-Hams F-12
tissue culture medium (Life Technologies, Gaithersburg, MD)
supplemented with 5% charcoal dextran-treated FCS (Life Technologies).
For transcription regulation studies, cells were plated at 1.0 x
105 cells per well (10 cm2), grown for 24
h, and transfected overnight by calcium phosphate precipitation, as
described previously (48). For MMTV-LUC and COLL-LUC measurements,
cells were transfected with 250 ng GR expression plasmid and 250 ng
reporter plasmid per well. For PRL3-tk-LUC and ICAM 1-LUC measurements,
500 ng GR expression plasmid and 1250 ng reporter plasmid were added;
in the ICAM-1 studies 75 ng p65 expression plasmid were also added. pTZ
carrier DNA was added to a total amount of 5 µg DNA/well. After
transfection, experimental media were added. After an incubation period
of 24 h, cells were harvested for the LUC assay, as described
previously (49).
Western Immunoblot Analysis
Whole-cell lysate was prepared by resuspending the cell pellet
from a well (10 cm2) in 200 µl 40 mM
Tris-HCl, pH 7.4 (Boehringer, Mannheim, Germany), 1 mM
EDTA, 10% (vol/vol) glycerol, 1% (vol/vol) Triton X-100, 0.5%
(wt/vol) sodium deoxycholate, 0.08% (wt/vol) SDS (all from Merck,
Amsterdam, The Netherlands), 0.6 mM
phenylmethylsulfonylfluoride (Sigma), and 0.5 mM bacitracin
(Aldrich, Axel, The Netherlands) at 4 C. The lysate was centrifuged (10
min, 1700 x g), and GR protein was immunoprecipitated
from the supernatant using monoclonal antibody F52 (50) coupled to goat
anti-mouse agarose beads. Immunoprecipitated GR protein was used for
Western immunoblot analysis, essentially as described previously (48).
The polyclonal rabbit antiserum 57 (Affinity Bioreagents, Golden, CO)
was used as the primary antibody to identify the GR in a
chemiluminescence protein detection method, performed as described by
the manufacturer (Dupont NEN).
 |
ACKNOWLEDGMENTS
|
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The authors are grateful to the Netherlands Organization for
Scientific Research (NWO) for supporting their research: P.d.L. and
N.A.T.M.H. were supported by Grant 95010-608.
 |
FOOTNOTES
|
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Address requests for reprints to: P. de Lange, Ph.D., Department of Internal Medicine III, Room Bd277, Erasmus University, Dijkzigt University Hospital, 40 Dr. Molewaterplein, 3015 GD Rotterdam, The Netherlands.
Received for publication February 24, 1997.
Accepted for publication March 27, 1997.
 |
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