A Gain-of-function Polymorphism in a G-protein Coupling
Domain of the Human
1-Adrenergic Receptor*
Deborah A.
Mason,
J. Donald
Moore,
Stuart A.
Green, and
Stephen B.
Liggett
From the Departments of Medicine and Pharmacology, University of
Cincinnati College of Medicine, Cincinnati, Ohio 45267
 |
ABSTRACT |
The
1-adrenergic receptor
(
1AR) is a key cell surface signaling protein expressed
in the heart and other organs that mediates the actions of
catecholamines of the sympathetic nervous system. A polymorphism in the
intracellular cytoplasmic tail near the seventh transmembrane-spanning
segment of the human
1AR has been identified in a cohort
of normal individuals. At amino acid position 389, Gly or Arg can be
found (allele frequencies 0.26 and 0.74, respectively), the former
previously considered as the human wild-type
1AR. Using
site-directed mutagenesis to mimic the two variants, CHW-1102 cells
were permanently transfected to express the Gly-389 and Arg-389
receptors. In functional studies with matched expression, the Arg-389
receptors had slightly higher basal levels of adenylyl cyclase
activities (10.7 ± 1.2 versus 6.1 ± 0.4 pmol/min/mg). However, maximal isoproterenol-stimulated levels were
markedly higher for the Arg-389 as compared to the Gly-389
receptor (63.3 ± 6.1 versus 20.9 ± 2.0 pmol/min/mg). Agonist-promoted [35S]guanosine
5'-O-(thiotriphosphate) binding was also increased with the
Arg-389 receptor consistent with enhanced coupling to Gs
and increased adenylyl cyclase activation. In agonist competition studies carried out in the absence of guanosine
5'-(
,
-imido)triphosphate, high affinity binding could not be
resolved with the Gly-389 receptor, whereas Arg-389 displayed an
accumulation of the agonist high affinity receptor complex
(RH = 26%). Taken together, these data indicate
that this polymorphic variation of the human
1AR results
in alterations of receptor-Gs interaction with functional signal transduction consequences, consistent with its localization in a
putative G-protein binding domain. The genetic variation of
1AR at this locus may be the basis of interindividual
differences in pathophysiologic characteristics or in the response to
therapeutic
AR agonists and antagonists in cardiovascular and other diseases.
 |
INTRODUCTION |
The
1-adrenergic receptor
(
1AR)1 is a
member of the adrenergic family of G-protein-coupled receptors, with
epinephrine and norepinephrine being endogenous agonists. Like other
members of the G-protein-coupled receptor superfamily, the amino
terminus is extracellular, the protein is predicted to traverse the
cell membrane seven times, and the carboxyl terminus is intracellular. In the adrenergic receptor family, agonists bind in a pocket formed by
the transmembrane-spanning domains, and G-protein binding and activation occur at intracellular domains of the loops and tail, typically near the membrane (1).
1ARs couple to the
stimulatory G-protein, Gs, activating adenylyl cyclase, as
well as to non-cAMP pathways such as the activation of ion channels
(2).
1ARs are expressed on a number of cell types
including cardiomyocytes where they serve to increase cardiac inotropy
and chronotropy, adipocytes where they mediate lypolysis, and
juxtaglomerular cells of the kidney where they regulate renin
secretion. It has been known for decades that these responses, as well
as those of the
2AR, are somewhat variable in the human
population (3, 4). Indeed, we have recently found and characterized
several
2AR polymorphisms that have altered signaling
phenotypes compared with wild-type receptor (5-7). This finding has
prompted us to examine the
1AR coding sequence for
variability in the human population. Here we report a common single
nucleotide polymorphism resulting in a Gly to Arg switch at
intracellular amino acid 389, within a region important for G-protein
coupling. The resulting phenotype of the Arg-389 receptor is one of
enhanced receptor-Gs interaction, functionally manifested
as increased activation of the adenylyl cyclase effector.
 |
MATERIALS AND METHODS |
Nomenclature--
The wild-type sequence of the intronless human
1AR gene is considered that reported by Frielle et
al. (8) (GenBankTM accession number
J03019). In the current report the adenine of the initiator ATG of the
coding block is designated as nucleotide 1, and amino acid 1 is the
encoded methionine. The receptor consists of 477 amino acids.
Polymorphism Detection--
Genomic DNA was extracted from blood
or banked tissue from normal individuals by standard techniques (9).
The study was approved by the University of Cincinnati Institutional
Review Board. PCR reactions were established to produce overlapping
products spanning 1131 base pairs of the coding region starting from
nucleotide 300 of the second transmembrane-spanning domain past the
stop codon into the 3'-untranslated region. A consistent deviation from
the published sequence was noted at nucleotide 951 where guanine was
found in all subjects instead of adenine and likely represents a
sequencing error in the original report. Both codons encode for Leu at
amino acid 317. At nucleotide 1165, a guanine ("wild-type") or
cytosine was found (Fig. 1A),
altering the encoded amino acid from Gly to Arg at amino acid position
389. The primers used to amplify the 488-base pair fragment where this
polymorphism at position 1165 was detected were:
5'-CAGGAAACAGCTATGACCACTGGAGCCGCCTCTTCGTCTTCTTCAACTG-3' (sense)
and 5'-TGGGCTTCGAGTTCACCTGCTATC-3' (antisense). The sense primer
contains a 5' M13 forward primer sequence, so that dye primer chemistry
using the universal primer could be utilized in the sequencing
reactions. PCRs consisted of ~500 ng of DNA, each dNTP at 62.5 nM, 100 pmol of each primer, 0.5 µl of Pwo polymerase (Roche Molecular Biochemicals), 10% of the supplied buffer, and 5%
Me2SO in a final volume of 50 µl. Cycling conditions
started at 98 °C for 5 min, followed by 98 °C for 45 s,
60 °C for 1 min, and 72 °C for 1 min for 35 cycles, and a final
extension of 72 °C for 7 min in a Perkin-Elmer 9600 thermocycler.
Automated sequencing was carried out with an Applied Biosystems
sequencer using dye primer chemistry. At nucleotide 1165, the G to C
transition results in a loss of a BsmF1 restriction
endonuclease site. Additional samples were thus studied with the
polymorphism identified by the absence or presence of digestion of the
aforementioned PCR product with BsmF1 (Fig.
1B).

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Fig. 1.
Genetic variance of the human
1AR at nucleotide 1165, amino acid
389. A, PCR fragments generated from genomic DNA were
sequenced as described under "Materials and Methods." The G in the
indicated position of codon 389 results in a Gly (left-hand
sequence), whereas a C encodes for Arg (right-hand
sequence). Shown are representative chromatograms from two individuals
homozygous for the two alleles. B, PCR fragments were
digested with the restriction endonuclease BsmF1, which
fails to digest the Arg-389 product because of the G to C transition.
Homo., homozygous; control, no enzyme in the
reaction.
|
|
Constructs and Cell Transfection--
Site-directed mutagenesis
was carried out by methods previously described (5) to mimic the
Arg-389 polymorphism. Arg-389 and Gly-389
1AR cDNAs
were subcloned into the mammalian expression vector pBC12BI (10).
CHW-1102 fibroblasts (CHW cells) were permanently transfected with the
Gly-389 and Arg-389
1AR constructs by calcium phosphate
precipitation as described previously (11). Positive clones were
selected based upon resistance to 300 µg/ml G418. Cultures were
maintained at 37 °C in a 5% CO2 atmosphere in
Dulbecco's modified Eagle's medium with 10% fetal calf serum, 100 units/ml penicillin, 100 µg/ml streptomycin, and 80 µg/ml G418.
COS-7 cells were transiently transfected with the
1AR
constructs and rat G
s in pCDNA1 for
[35S]GTP
S binding studies. These transient
transfections were performed by the DEAE-dextran/chloroquine method as
described previously (12).
Radioligand Binding--
Confluent monolayers of CHW cells were
washed three times with phosphate-buffered saline, lysed in a hypotonic
buffer (5 mM Tris, 2 mM EDTA, pH 7.4), detached
by scraping with a rubber policeman, and centrifuged at 42,000 × g for 10 min. Crude membranes were resuspended in buffer (75 mM Tris, 12.5 mM MgCl2, 2 mM EDTA, pH 7.4) and saturation binding experiments
performed with 125I-CYP as described (12), with nonspecific
binding defined by co-incubation with 1 µM propranolol.
Reactions for these and other radioligand experiments were terminated
by dilution and vacuum filtration over glass fiber filters. One-site
agonist competition binding studies were carried out with 40 pM 125I-CYP, 100 µM GTP, and
varying concentrations of isoproterenol, epinephrine, or norepinephrine
for 2 h at 25 °C. To assess high and low affinity agonist
receptor binding, membranes were prepared as described above, except
two additional centrifugations were included before the addition of
reaction buffer to assure the removal of endogenous GTP. Membranes were
incubated with 40 pM 125I-CYP and 18 concentrations of isoproterenol in the presence or absence of the
nonhydrolyzable GTP analog Gpp(NH)p at 100 µM for 1 h at 37 °C. Competition data were fit to one-site and two-site models by an iterative least squares technique as described previously (13). A two-site model was considered valid if by F-test the fit was
statistically better (p < 0.05) than that obtained
with a one-site model.
Adenylyl Cyclase Activity Measurements--
Membranes were
incubated with 30 mM Tris, pH 7.4, 2.0 mM
MgCl2, 0.8 mM EDTA, 120 µM ATP,
60 µM GTP, 2.8 mM phosphoenolpyruvate, 2.2 µg of myokinase, 100 µM cAMP, and 1 µCi of
[
-32P]ATP for 30 min at 37 °C as described (11).
[32P]cAMP was separated from [
-32P]ATP
by chromatography over alumina columns. A [3H]cAMP
standard included in the stop buffer accounted for individual column
recovery. Activities were determined in the presence of vehicle
(basal), the indicated concentrations of agonists, or 100 µM forskolin.
[35S]GTP
S Binding--
Transiently transfected
COS cells were washed three times with phosphate-buffered saline, lysed
in hypotonic buffer (5 mM HEPES, 1 mM EDTA, pH
8), detached by scraping with a rubber policeman, and centrifuged for
10 min at 42,000 × g. Pellets were resuspended in the
same buffer and centrifuged two additional times.
[35S]GTP
S binding was carried out by a modification of
the method of Befort et al. (14). The reaction consisted of
membranes in 10 mM HEPES, pH 7.40, 5 mM
MgCl2, 100 mM NaCl, 1 mM EDTA
buffer, with 1.0 µM GDP and 180 pM
[35S]GTP
S in the presence of water (basal), 100 µM unlabeled GTP
S (to define nonspecific binding), or
10 µM isoproterenol for 2.5 h at 30 °C. Unbound
[35S]GTP
S was separated using vacuum filtration over
glass fiber filters that were washed twice with 10 mM Tris buffer.
Miscellaneous--
Protein concentrations were determined by the
copper bicinchoninic acid method (15). Curve fitting was carried out
using PRISM software (GraphPad, San Diego, CA). Statistical comparisons were made by paired or unpaired t tests, as appropriate,
with significance considered when p < 0.05. Data are
presented as mean ± S.E. of the indicated number of independent experiments.
 |
RESULTS |
Sequencing results from DNA derived from 30 individuals from a
defined healthy cohort revealed variance in the examined
1AR region (encompassing the coding block from the
second transmembrane domain to the last amino acid in the carboxyl
terminus of the receptor) in only one location (Fig. 1), at nucleotide
1165, where guanine or cytosine could be found, resulting in a Gly or
Arg at amino acid 389. Using BsmF1 restriction digests,
additional genotyping at this locus was carried out for a total of 50 samples. While the wild-type human
1AR had previously
been reported (8) as Gly at amino acid 389, we found a higher frequency
of Arg in our normal population. The allele frequencies were 0.74 for
Arg and 0.26 for Gly.
To ascertain whether the Arg in this position conferred a distinct
phenotype compared with the Gly-389 receptor (which we (11) and others
(16) had previously characterized), site-directed mutagenesis was
carried out to mimic Arg-389, and the two cDNAs were subcloned into
mammalian expression vectors. The final constructs were identical
except for the single nucleotide difference. These constructs were used
to establish permanent lines of transfected CHW cells, which
endogenously lack
AR expression. As indicated, studies were carried
out on several clonal lines from each transfection at matched levels of
receptor expression. Radioligand binding studies (Table
I) revealed essentially identical
dissociation binding constants for 125I-CYP. Competition
binding studies with isoproterenol, epinephrine, and norepinephrine in
the presence of GTP showed no differences between the two receptors in
binding affinities for these agonists.
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Table I
Radioligand binding parameters of the two polymorphic 1ARs
Studies were carried out in the presence of 100 µM GTP.
ISO, isoproterenol; NE, norepinephrine; EPI, epinephrine.
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Basal, isoproterenol-, and forskolin-stimulated adenylyl cyclase
activities were determined using membranes from lines expressing Gly-389 at 159 ± 14 fmol/mg and Arg-389 at 151 ± 13 fmol/mg
(Fig. 2A). As shown, basal
activities were slightly higher with the Arg-389 receptor than with the
Gly-389 receptor (10.7 ± 1.2 versus 6.1 ± 0.4 pmol/min/mg, n = 4, p < 0.02). The
most dramatic differences, however, were seen with agonist stimulation.
Maximal isoproterenol-stimulated activities were higher with the
Arg-389 receptor than with the Gly-389 receptor (63.3 ± 6.1 versus 20.9 ± 2.0 pmol/min/mg, n = 4, p < 0.01). Similarly, expressing the responses as
-fold increases over basal levels, the Arg-389 receptor displayed a
greater stimulation of adenylyl cyclase than the Gly-389 receptor (6.1- ± 0.3-fold versus 3.3- ± 0.1-fold). In contrast,
stimulation of adenylyl cyclase by forskolin was not consistently
different between the lines (104 ± 11 versus 120 ± 10 pmol/min/mg). Thus, normalizing the data to the extent of
stimulation of adenylyl cyclase by forskolin still revealed a
significantly greater agonist stimulation by the Arg-389 variant than
the Gly-389 variant (Fig. 2B). The EC50 values
for isoproterenol stimulation of adenylyl cyclase for Gly-389 and
Arg-389 receptors were not different (115 ± 5 versus
132 ± 5 nM). Results from an additional set of
studies carried out on other lines at higher expression levels are
shown in Fig. 2, C and D (expression was 246 ± 32 and 255 ± 11 fmol/mg for Gly-389 and Arg-389,
respectively). Again, the maximal extent of stimulation by agonist was
greater with the Arg-389 variant. These differences in adenylyl cyclase
stimulation between the two polymorphic receptors were also observed in
responses to epinephrine and norepinephrine (data not shown).

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Fig. 2.
Functional coupling of the Gly-389 and
Arg-389 receptors to adenylyl cyclase. Shown are the results from
studies with clonal lines expressing each receptor at matched levels
and the data presented as absolute activities (A) and
normalized to the stimulation by forskolin (B). The results
of similar studies with two other clonal lines are shown in
panels C and D. The Arg-389 demonstrated small
increases in basal activities and marked increases in
agonist-stimulated activities compared with the Gly-389 receptor. See
"Results" for details. Shown are the mean results from four
independent experiments carried out with each line. Absent error bars
denote that standard errors were smaller than the plotting
symbol.
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|
To investigate the basis of these differences between the two
receptors, studies were undertaken to assess interactions between agonist, receptor, and Gs with [35S]GTP
S
binding experiments and agonist competition studies in the absence and
presence of Gpp(NH)p. For [35S]GTP
S binding, we found
that adequate signals were reproducibly obtained with high levels of
transient receptor expression (~10 pmol/mg) in COS-7 cells, which
were co-transfected with G
s. Results of these studies
are shown in Fig. 3. Maximal
isoproterenol-stimulated [35S]GTP
S binding was found
to be greater in membranes bearing the Arg-389 versus the
Gly-389 receptor, consistent with the adenylyl cyclase studies, which
also showed enhanced agonist-stimulated function with the Arg-389
receptor.

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Fig. 3.
[35S]GTP S binding to the
two polymorphic 1ARs. COS-7
cells were transfected as described under "Materials and Methods."
Binding in the presence of 10 µM isoproterenol was
greater (p < 0.05) with the Arg-389 than with the
Gly-389 receptor. Because of day-to-day variation in the absolute
levels of binding, data are presented as a percentage of binding to the
wild-type (Gly389) receptor (mean absolute values were
7.7 ± 1.4 × 105 dpm/mg for Gly-389). Basal
levels of binding were not different between the two receptors.
nt, nontransfected cells.
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A well recognized characteristic of agonist binding to receptors such
as the
2AR is the increase in high affinity binding states, indicative of receptor/G-protein interactions (17-19). Interestingly, we have previously reported (13) that in competition studies carried out in the absence of Gpp(NH)p, agonist-promoted accumulation of a
1AR (Gly-389) high affinity fraction
is not readily resolved. This result is likely because of the similar affinities of the high and low affinity sites consistent with relatively less free energy transfer during signal transduction. We
wondered whether the Arg-389 receptor would in fact have enhanced agonist-promoted high affinity binding, because this receptor has
increased functional coupling to Gs. Isoproterenol
competition studies were thus carried out in parallel, in the absence
and presence of Gpp(NH)p, with washed membranes from CHW cells
expressing each receptor. These results are provided in Fig.
4 and Table II. As shown, the displacement curves in
the absence of a guanine nucleotide from the Gly-389 experiments were
relatively steep (mean pseudo-Hill coefficient, 0.87 ± 0.03) and
were best resolved statistically to a one-site model. Gpp(NH)p had no
effect on agonist competition with the Gly-389 receptor (Fig. 4). In
contrast, the displacement curves obtained with the Arg-389 receptor in
the absence of Gpp(NH)p had mean pseudo-Hill coefficients of 0.73 ± 0.03, and the data were best resolved with a two-site model (composite p value < 0.001). The percentage of
receptors in the high affinity state with the Arg-389 receptor was
26 ± 1% (Fig. 4 and Table II). As shown, with this receptor the
presence of Gpp(NH)p in the reaction resulted in the expected rightward
shift, with monophasic, steep curves consistent with a single low
affinity agonist interaction.

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Fig. 4.
Agonist competition curves from studies of
the Gly-389 and Arg-389 receptors. Experiments were carried out
with CHW membranes in the absence and presence of Gpp(NH)p. The Gly-389
data obtained in the absence of a guanine nucleotide was best fit to a
one-site model, and the binding was unaffected by Gpp(NH)p. In
contrast, studies with Arg-389 resulted in two-site fits with high and
low affinity components (see text and Table II) when carried out in the
absence of Gpp(NH)p, and curves were right-shifted and represented
single-site binding in its presence. Results shown are the mean data
from five independent experiments. Absent error bars denote that
standard errors were less than the plotting symbol. (Because these
experiments were performed at a higher temperature, the
Ki values for isoproterenol with Gpp(NH)p are
~4-fold higher than those obtained in the experiments shown in Table
I.)
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Table II
Results of agonist (isoproterenol) competition binding studies in the
absence and presence of Gpp(NH)p with the Gly-389 and Arg-389
1ARs
The Gly-389 receptor could not be fit to a two-site model with greater
significance than a one-site model (see text for details), and thus
high and low affinity binding parameters were not obtained.
RH, percent of receptors in high affinity states;
NA, not applicable.
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 |
DISCUSSION |
These findings reveal in the normal human population the presence
of two
1AR genetic variants with significant differences in functional signaling. For purposes of consistency, and because of
the fact that a number of structure/function studies have been published using the Gly-389 receptor (13, 20), we prefer to continue to
designate this receptor as the "wild-type" human
1AR, although the Arg variant appears to be more common.
This is analogous to the precedent that has been set with the common
2AR polymorphisms (5, 6). The site of the variability is
~9 amino acids from the seventh transmembrane-spanning domain, in the
intracellular portion of the tail prior to the proposed palmitoylated
cysteine(s) (Fig. 5). This region is
sometimes referred to as the fourth intracellular loop, but in this
report will be termed the proximal portion of the cytoplasmic tail. By
analogy with
2AR (21, 22),
2AR (23), and
other G-protein-coupled receptors, this region is considered important
for receptor coupling to its cognate G-protein, Gs. Indeed,
the difference between the Arg-389 and Gly-389
receptors is in functional coupling. Receptor-promoted binding of
GTP
S to G
s, another indicator of agonist-initiated
coupling to Gs, was similarly different between the two
polymorphic
1ARs. Consistent with these findings,
agonist-promoted accumulation of the high affinity state in washed
membrane preparations in the absence of a guanine nucleotide was
detected with the Arg-389 receptor but could not be resolved in studies
with the Gly-389 receptor. Based on the multistate model
(18, 19) of receptor/G-protein interactions, as well as the above
results, an elevated basal activity of adenylyl cyclase
(i.e. spontaneous toggling to R* in the absence of agonist)
should also be expected with the Arg-389 receptor if it has a greater
efficiency of stabilizing the active conformation in the presence of
agonist, which in fact was the case. The differences in basal
activities that we observed were small but consistent, and the
magnitude likely results from the relatively low ("physiologic")
levels of expression utilized in the functional studies. As such, we
consider the functional phenotype as shown in Fig. 2, A and
C, to be indicative of signaling in cells that endogenously
express the two polymorphic
1ARs.

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Fig. 5.
Alignment of amino acid residues of the
proximal cytoplasmic tail of the
1AR from various species. Note the
conservation at the position of the human Gly-Arg polymorphism. Amino
acid numbers are from the human receptor.
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|
The residues in this region of the
1AR among other
species are shown in Fig. 5. The amino acid analogous to position 389 of the human, as well as the surrounding residues, are highly conserved
in species sequenced to date, with the only deviation at position 389 being found in the human, where Gly was originally reported. Whereas we
know nothing regarding genetic variability in these other species, the
high degree of consistency in this region, its importance in G-protein
coupling, and the nonconservative (size and charge) nature of the Gly
to Arg substitution are consistent with this variation having
functional consequences.
As introduced earlier,
1AR are expressed on a number of
cell types in the body. In the heart,
1AR represent the
predominant
AR subtype and is expressed on myocytes of the atria and
ventricles, where they act to increase the force and frequency of
contraction in response to sympathetic stimulation. It is intriguing to
consider the potential role of the
1AR polymorphisms at
position 389 in regulating cardiac function under pathologic
conditions. As left ventricular failure develops,
1AR
expression and function decrease in human heart failure (24, 25). This
response is thought to be a protective mechanism, sparing the heart
from sustained sympathetic stimulation in the face of limited metabolic
reserves. In earlier phases of the disease, maintenance of
1AR function may contribute to improved ventricular
function. Given the above circumstances, the dramatic differences in
function between the two
1AR polymorphisms suggest that
the pathophysiology of congestive heart failure may be influenced by
the
1AR genotype. Indeed, there is unexplained
interindividual variation in the progression of heart failure as well
as the cardiac response to infused
-agonists used therapeutically
during acute decompensation (26-28). Interestingly,
AR antagonists
(
-blockers) are utilized in the chronic treatment of heart failure,
the presumed basis of which is minimization of the aforementioned
consequences of long term sympathetic stimulation. There is, however,
significant interindividual variation in the clinical response to
-blockers in patients with heart failure (29). Based on our current
results, it might be predicted that individuals bearing the Arg-389
receptor would be most responsive to
-blocker therapy because they
would have a genetically determined
1AR that achieves a
greater stimulation of adenylyl cyclase. A similar scenario might be
present in the treatment of essential hypertension with
-blockers,
where responders could be predicted by
1AR genotyping.
These pharmacogenetic concepts will need to be explicitly tested in
human studies. While we are unaware of therapeutic agents specifically
targeting adipocyte
1ARs, the different functional
properties of the two
1ARs may be the basis of these
polymorphisms acting as disease modifiers in obesity. Finally, we have
yet to delineate the frequencies of these
1AR polymorphisms in various disease groups. Given that both polymorphisms are common in the general population, however, it is unlikely that
either represents the primary basis of disease. These polymorphisms may, however, represent small risk factors in common, multifactorial diseases such as heart failure, hypertension, and obesity.
In conclusion, we have found polymorphic variation of the human
1AR at amino acid 389, where Gly (previously
considered wild-type) or Arg can be found. This variation alters
receptor-Gs coupling, manifested as significant differences
between the two receptors in agonist-stimulated adenylyl cyclase
activation. Such variation may represent a genetic basis for
interindividual differences in disease susceptibility or phenotype, or
the response to agents targeting the
1AR.
 |
FOOTNOTES |
*
This work was supported by National Institutes of Health
Grants HL52318 and HL41496.The costs of publication of this
article were defrayed in part by the
payment of page charges. The article must therefore be hereby marked
"advertisement" in
accordance with 18 U.S.C. Section
1734 solely to indicate this fact.
To whom correspondence should be addressed: University of
Cincinnati College of Medicine, 231 Bethesda Ave., Cincinnati, OH 45267-0564. Tel.: 513-558-4831; Fax: 513-558-0835; E-mail:
Stephen.Liggett{at}UC.Edu.
 |
ABBREVIATIONS |
The abbreviations used are:
AR,
-adrenergic receptor;
Arg-389,
1AR polymorphism with
Arg at amino acid 389;
Gly-389,
1AR polymorphism with
Gly at amino acid 389;
125I-CYP, 125I-labeled
cyanopindolol;
Gpp(NH)p, guanosine 5'-(
,
-imido)triphosphate;
GTP
S, guanosine 5'-O-(thiotriphosphate);
PCR, polymerase
chain reaction.
 |
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