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Vol. 29, Issue 11, 1467-1472, November 2001
Department of Pharmacology and Toxicology, University of Kansas Medical Center, Kansas City, Kansas (J.S., Y.L., S.H., C.D.K.); and XenoTech LLC, Kansas City, Kansas (A.M.)
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Abstract |
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 Top
 Abstract
 Introduction
Experimental Procedures
Results
Discussion
References
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Identification and characterization of the pregnane X receptor
(PXR) as a key regulator of cytochrome P450 3A (CYP3A)
gene expression has led to an increased understanding of the molecular basis of many drug-drug interactions. Mice lacking PXR (PXR-KO) were
used in the present study to delineate the role of PXR in regulating
hepatomegaly and regulating the activity of CYP3A, organic anion transporting polypeptide-2 (Oatp2), and
Cyp7a1 (cholesterol 7
-hydroxylase) gene products in
vivo. Pregnenolone-16-carbonitrile (PCN) produced hepatomegaly in
the wild-type mice but not in the PXR-KO mice. PCN increased both the
number of proliferating cell nuclear antigen immuno-positive
nuclei and apparent cell size in the wild-type mice but not in the
PXR-KO mice. To determine the role PXR plays in regulating CYP3A
activity, 6
-hydroxylation of testosterone and the duration of the
loss of righting reflex following administration of the muscle-relaxant
zoxazolamine were measured. PCN increased the level of testosterone
6-hydroxylation and decreased the duration of the loss of
righting-reflex time following zoxazolamine administration in wild-type
mice, but did not effect either of these parameters in PXR-KO mice. PCN
increased the hepatic uptake of [3H]digoxin, an Oatp2
substrate, in wild-type mice but not in the PXR-KO mice. Similarly, PCN
decreased bile acid excretion in wild-type mice but not in the PXR-KO
mice. Taken together, these data demonstrate a pivotal role for PXR in
the regulation of drug-induced hepatomegaly and in the metabolism
(CYP3A), transport (Oatp2), biosynthesis (Cyp7a1), and excretion of xenobiotics and bile acids in vivo.
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Introduction |
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Top
Abstract
Introduction
Experimental Procedures
Results
Discussion
References
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The
pregnane X receptor (PXR1; NR1I2) is the
molecular target of many xenobiotics including the synthetic steroid
pregnenolone-16-carbonitrile (PCN) and mediates the
xenobiotic-inducible transcription of CYP3A family members
across species (Bertilsson et al., 1998
; Blumberg et al., 1998; Kliewer
et al., 1998; Lehmann et al., 1998; Jones et al., 2000; Xie et al.,
2000a). Recent research has led to the idea that in addition to serving
as a broad specificity "xenosensor", PXR function is also activated
by lithocholic acid, thereby regulating the expression of
Cyp3a11, organic anion transporting polypeptide (Oatp2), and Cyp7a1 genes in mice in a coordinate
manner (Staudinger et al., 2001).
For many years it has been known that pretreatment of rodents with
certain steroids produces protection from various forms of toxicants.
Subsequently, it was shown that these "catatoxic" or protective
steroids exert their effect by accelerating the metabolism of the
toxicant (Selye, 1971). A screen designed to identify additional
protective compounds revealed that PCN is one of the most potent
catatoxic chemicals (Selye, 1970). It was later shown that the
protective nature of PCN probably involves the stimulation of
transcription and activity of the CYP3A subfamily of the
cytochrome P450 family of monooxygenases in rodents (Newman and
Guzelian, 1983; Schuetz et al., 1984), which are highly expressed in
liver and intestine. CYP3A family members encode broad
specificity heme-containing monooxygenases that catalyze the oxidation
of a wide variety of structurally dissimilar compounds. In humans, the
CYP3A enzymes are collectively responsible for the oxidation of greater
than 60% of all clinically prescribed drugs, as well as many steroids
and bile acids (Guzelian, 1988; Maurel, 1996).
Early research on PCN revealed its ability to induce hepatomegaly in
rodents (Garg et al., 1970). Subsequent reports indicated that this
marked increase in liver size was due to increases in both cell number
(hyperplasia) and cell size (hypertrophy) (Japundzic et al., 1974).
This research raises questions about the role of PXR in mediating these
two processes.
The Oatp2 gene-product, in part, mediates the hepatic uptake of cardiac
glycosides, such as ouabain and digoxin in rodents (Abe et al., 1998;
Reichel et al., 1999). Insights regarding the involvement of drug
transporter systems in the regulation of drug disposition came when it
was noted that newborn mammals exhibit a marked sensitivity to ouabain,
a nonmetabolized cardiac glycoside, when compared with adults
(Klaassen, 1972, 1973). This increased susceptibility of newborn rats
to ouabain appeared to be due to the inability of the liver of newborn
animals to concentrate ouabain. Additionally, pretreatment of both
newborn and adult rodents with PCN markedly increases hepatic uptake
and biliary excretion of ouabain (Klaassen, 1974a,b). PCN treatment
also markedly enhanced the uptake of
[3H]digoxin, an Oatp2 substrate, in isolated
hepatocytes (Eaton and Klaassen, 1979). This research strongly implies
the existence of a xenobiotic-inducible drug transporter system
separate from the xenobiotic-inducible drug-metabolizing systems and
suggests that these two systems could in principle be coregulated.
PCN treatment has been shown to enhance cholesterol turnover (Honohan
and Parkinson, 1975), decrease cholesterol hydroxylase activity (Mason
and Boyd, 1978), and decrease biliary bile acid excretion (Turley and
Dietschy, 1984). More recent evidence reveals that both
Cyp7a1 transcription and cholesterol 7-hydroxylase activities are dramatically reduced following administration of PCN in
rodents (Li et al., 1990; Stahlberg, 1995). These data suggest a role
for the PXR in the regulation of Cyp7a1 transcription, although it is not currently clear whether this is a direct or an
indirect effect.
In this study, wild-type mice and mice lacking functional PXR (PXR-KO)
were used to examine specific functional endpoints following PCN
treatment. As an indication of cell proliferation, the presence of
proliferating cell nuclear antigen (PCNA) immunoreactivity was
measured. The number of cells per high power visual field (light
microscopy, 400× magnification) was determined as a reflection of cell
size. As a measure of CYP3A activity, both testosterone 6-hydroxylation and zoxazolamine-induced paralysis time were measured. Hepatic uptake of [3H]digoxin and
bile acid excretion into bile were measured as markers for Oatp2 and
cholesterol 7-hydroxylase activities, respectively. Taken together,
these experiments demonstrate that, in addition to regulating the
transcription of CYP3A, Oatp2, and
Cyp7a1, PXR activation by PCN regulates the activity of
their gene-products in vivo. Thus, PXR is involved in regulating both
xenobiotic homeostasis and bile acid homeostasis in vivo, and these two
processes appear to be coupled, at least in part, by PXR activation.
Furthermore, these experiments demonstrate a pivotal role for PXR in
mediating PCN-induced hepatomegaly through induction of cellular
hypertrophy and hyperplasia.
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Experimental Procedures |
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Top
Abstract
Introduction
Experimental Procedures
Results
Discussion
References
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Maintenance and Treatment of PXR-KO and Wild-Type Mouse
Populations.
Generation of the PXR-KO mice was previously described (Staudinger et
al., 2001). Adult male wild-type mice and PXR-KO mice were maintained
on standard laboratory chow and were allowed food and water ad libitum.
All mice were treated once a day i.p. with either vehicle (corn oil) or
PCN at the indicated doses for 4 days.
Hepatocyte Proliferation and Cell Size Following PCN Treatment.
Four mice were randomly allocated per treatment group. Livers from mice
pretreated with corn oil or PCN were removed and weighed on the morning
of day 5 following 4 days of treatment. Portions of the liver were
fixed and immunostained for the presence of PCNA, as described
previously (Hood et al., 1999). The cell size was determined by
counting the total number of nuclei in a given field at 400×
magnification following hematoxylin and eosin staining. The slides were
blinded and randomized, and the nuclei were counted in 15 to 20 fields/treatment group. The data are expressed as cells per high power field.
RNA Isolation and Northern Blot Analysis.
Total RNA was isolated from liver using a commercially available
reagent (Trizol; Invitrogen, Carlsbad, CA) according to the manufacturer's instructions. Total RNA (10 µg) was resolved on a 1%
agarose/2.2 M formaldehyde-denaturing gel and transferred to a nylon
membrane (Hybond N+; Amersham Pharmacia Biotech,
Inc., Piscataway, NJ). Blots were hybridized with
32P-labeled cDNAs corresponding to the rodent
cDNA sequences for Cyp3a11 (bases 69-1609; GenBank no. NM 007818),
Oatp2 (bases 1-240; GenBank no. AB031814), Cyp7a1 (bases 235-460;
GenBank no. J05460), and -actin (CLONTECH, Palo Alto, CA). Northern
blots were scanned, and band intensities were quantified using
ImagQuant software (Molecular Dynamics, Sunnyvale, CA).
Preparation of Microsomes.
Liver microsomes were prepared as previously described (Pearce et al.,
1996). Briefly, 3 ml of homogenization buffer (50 mM Tris-HCl, pH 7.4, 150 mM KCl, and 2 mM EDTA)/gram of liver on ice was used to homogenize
samples using a motor driven liver homogenizer and a Teflon pestle. The
liver homogenates were centrifuged at 12,000g for 20 min at
4°C. The resulting fraction was centrifuged at 104,000g
for 60 min at 4°C. The pellets were fully resuspended in ice-cold
wash buffer (150 mM KCl and 10 mM EDTA, pH 7.4) and centrifuged again
at 104,000g for 60 min at 4°C. The pellets were resuspended in 0.4 ml of 0.25 M sucrose/gram of starting liver weight
and frozen at 
80°C.
Protein Concentration and High-Pressure Liquid
Chromatography Testosterone 6-Hydroxylation Assay.
The protein concentration of isolated microsomal preparations was
determined with the bicinchoninic acid protein assay reagent kit
(Pierce, Rockford, IL), as described by the manufacturer. Microsomal
testosterone 6-hydroxylase activities were determined as described
previously (Pearce et al., 1996).
Zoxazolamine Paralysis.
All mice were injected i.p. with 112 mg/kg zoxazolamine in 2% Tween 80 in 0.9% saline solution. Paralysis time was measured as the time
between loss and return of the righting reflex (Selye, 1971).
[3H]Digoxin Uptake.
Hepatic uptake of [3H]digoxin was assayed as
previously described (Klaassen, 1972). Briefly, each experimental group
was administered a digoxin solution at a dose of 1 mg/kg i.v. dissolved
in 10% ethanol and 5% glucose with 10 µCi/kg
[3H]digoxin. Livers were removed after 5 min,
and a portion of the tissue was digested in 10% (w/v) tissue and gel
solubilizer (Packard Instruments, Meriden, CT) at 60°C until
dissolved. A 200-µl aliquot was removed and placed in a scintillation
vial with 15 ml of scintillation fluid (Research Product International
Corp., Mount Prospect, IL) and quantified in a scintillation counter.
Biliary Bile Acid Excretion. Mice were anesthetized using pentobarbital (60 mg/kg). The bile duct was exposed using a midline incision and cannulated with polyethylene tubing (PE-90). Bile samples were collected for 30 to 60 min. The animal's body temperature was maintained at 37°C throughout the procedure. Bile acid concentrations were determined using the bile acids kit (Sigma Diagnostics, St. Louis, MO). Briefly, bile was diluted in fetal bovine serum, and biliary bile acid concentration was determined using a standard curve generated using a bile acid calibrator set (Sigma Diagnostics; cat no. 450-11).
Statistical Analysis. Differences between liver mass, messenger RNA levels, the numbers of PCNA positive nuclei, cells per field, and enzymatic activities in vehicle and PCN-treated animals were determined using a one-way analysis of variance followed by the Duncan's multiple range posthoc test.
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Results |
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Top
Abstract
Introduction
Experimental Procedures
Results
Discussion
References
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PXR Is Required for PCN-Induced Hepatomegaly.
Acute treatment of rodents with PCN causes an increase in liver mass
and is thought to be due to increases in cellular hypertrophy and
hyperplasia (Japundzic et al., 1974). To determine the role of PXR in
this process, liver and body weight were quantified in the wild-type
and PXR-KO mice following treatment with PCN. As expected, the
wild-type mice exhibited approximately a 40% increase in the relative
liver weight (grams of liver per 100 g of total body weight) from
4.5 ± 0.1 to 6.3 ± 0.4, whereas the PXR-KO mice did not
exhibit any increase following PCN treatment (Fig.
1A). The wild-type mice exhibited about a
10-fold increase in the percentage of total PCNA immunopositive nuclei
following PCN treatment from 0.7 ± 0.2 to 11.4 ± 1.0, whereas the PXR-KO mice did not (Fig. 1B). When cell size was
determined using the number of cells per high power field, a decrease
of about 23% from 69.7 ± 1.2 to 53.6 ± 0.6 in the number
of cells per field was observed in PCN-treated wild-type mice,
indicating an increase in cell size; however, this effect was totally
absent in the PXR-KO mice (Fig. 1C). Photomicrographs of representative
liver sections stained with anti-PCNA antibodies and hematoxylin reveal
both an increase in cell division and cell size in the PCN-treated wild-type mice but not in the PXR-KO mice (Fig.
2). These results are similar to those
published by Xie et al. (2001a), except hepatomegaly was observed in
the PXR-null mice expressing the constitutively active human SXR/PXR
transgene under the control of the albumin promoter.
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PXR Regulates the Expression and Activity of Cyp3a11.
Because PXR has been shown to mediate PCN-inducible transcription of
rodent CYP3A family members (Bertilsson et al., 1998; Blumberg et al., 1998; Kliewer et al., 1998; Lehmann et al., 1998; Schuetz et al., 1998; Goodwin et al., 1999), the expression of Cyp3a11 in wild-type mice and PXR-KO mice was examined.
Wild-type mice exhibited a 6-fold increase in the hepatic expression of Cyp3a11 following PCN treatment (Fig.
3A). Surprisingly, the vehicle treated
PXR-KO mice exhibited a 3-fold increase in the basal expression level
of Cyp3a11 when compared with their wild-type vehicle
treated littermates (Fig. 3B). Induction of Cyp3a11
expression following PCN treatment was totally absent in the PXR-KO
mice. These results are consistent with those previously published
(Staudinger et al., 2001).
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) and activity (Eberhart et al., 1992) of hepatic
CYP3A family members, it was of interest to measure CYP3A
activity as reflected by testosterone 6-hydroxylation. Wild-type
mice treated with PCN exhibited a 5- to 7-fold increase in liver
microsomal testosterone 6-hydroxylation, whereas the PXR-KO mice
exhibited no such increase in testosterone 6-hydroxylation following
PCN treatment (Fig. 4A). Notably, the
basal level of testosterone 6-hydroxylation was increased
approximately 2-fold in the vehicle treated PXR-KO liver microsomes
when compared with testosterone 6-hydroxylation levels in the
vehicle treated wild-type liver microsomes.
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). Therefore, it was of interest to measure zoxazolamine-induced paralysis time following PCN administration in
wild-type and PXR-KO mice in an effort to dissect the possible role of
PXR in mediating PCN-inducible resistance to the classic cytochrome
P450 substrate and muscle relaxant zoxazolamine. The vehicle treated
wild-type mice were paralyzed for approximately 26 min following
administration of zoxazolamine, whereas the PCN-treated wild-type mice
were paralyzed for approximately 2 min following zoxazolamine
administration (Fig. 4B). The PXR-KO mice were paralyzed for 6 to 8 min
in both vehicle and PCN-treated experimental groups following
zoxazolamine administration. The vehicle treated PXR-KO mice exhibited
a significant decrease in zoxazolamine-induced paralysis time when
compared with their vehicle treated wild-type littermates. These
results are similar to those previously published by Xie et al.
(2000a), although the line of PXR-null mice that exhibited a decrease
in zoxazolamine-induced paralysis time expressed the constitutively
active SXR/PXR transgene under the control of the albumin promoter.
PXR Regulates the Expression and Activity of Oatp2.
Because PCN treatment is known to increase hepatic uptake of cardiac
glycosides in rodents and hepatocytes (Klaassen, 1972, 1973; Eaton and
Klaassen, 1979), Oatp2 expression was measured following PCN
administration in the wild-type mice and PXR-KO mice. Oatp2
expression was induced in a dose-dependent manner following PCN
administration in the wild-type mice but was not induced in the PXR-KO
mice (Fig. 5A), as was previously
demonstrated (Staudinger et al., 2001).
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; Reichel et al., 1999), hepatic uptake of
[3H]digoxin was measured in the wild-type mice
and PXR-KO mice following PCN treatment. The wild-type mice treated
with PCN exhibited a 2-fold increase in hepatic
[3H]digoxin content following PCN treatment
(Fig. 5B). Although the basal level of
[3H]digoxin content was higher in the PXR-KO
mice when compared with the wild-type mice, PCN treatment did not
increase the hepatic [3H]digoxin in the PXR-KO mice.
PXR Regulates the Expression of Cyp7a1 and the Activity of
Cholesterol 7-Hydroxylase.
The rodent Cyp7a1 gene encodes cholesterol 7-hydroxylase,
the first and rate-limiting enzyme in the biochemical pathway that converts cholesterol into bile acids. Because PCN treatment is known to
down-regulate Cyp7a1 expression in rodents (Li et al., 1990), it was of interest to determine whether PCN treatment also led
to down-regulation of Cyp7a1 expression in the PXR-KO mice. The wild-type mice exhibited a reduction in hepatic Cyp7a1
expression following PCN treatment, whereas the PXR-KO mice were
refractory to Cyp7a1 down-regulation by PCN treatment (Fig.
6A), as was previously shown (Staudinger
et al., 2001).
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-hydroxylase and excretion of bile acids
into bile (Mason and Boyd, 1978; Turley and Dietschy, 1984; Li et al.,
1990), it was of interest to determine whether PCN treatment had any
effect upon bile acid excretion into bile in the PXR-KO mice. Treatment
with PCN led to a significant decrease in bile acid excretion in
wild-type mice but had no effect in PXR-KO mice (Fig. 6B).
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Discussion |
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Top
Abstract
Introduction
Experimental Procedures
Results
Discussion
References
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The response elements that mediate CYP3A induction in
different species are known to bind and activate transcription through PXR (Jones et al., 2000). Species-specific CYP3A induction
can be accounted for by PXR evolution because the replacement of mouse PXR with human PXR yields a "humanized" mouse that responds to human PXR activators by up-regulating mouse Cyp3a11
transcription (Xie et al., 2000a). This is significant because
transcriptional regulation of CYP3A family members in liver
is at the center of many clinically important drug interactions
(Guzelian, 1988; Maurel, 1996). PXR is a master regulator of hepatic
CYP3A transcription that is activated by a number of
structurally unrelated lipophilic compounds. Although much is known
about the role of PXR in regulating induction of CYP3A
transcription in transfected cell lines, little is known about the role
of PXR in regulating drug-induced liver cell hyperplasia and
hypertrophy in vivo. In addition, little data exists regarding the
physiological consequence of PXR activation in regulating CYP3A, Oatp2,
and cholesterol 7-hydroxylase activities in vivo. Thus, the work
presented here seeks to elucidate the role of PXR in regulating
PCN-induced hepatomegaly and the activities of CYP3A, Oatp2, and
cholesterol 7-hydroxylase in vivo in mice.
In this study, it was demonstrated that PXR-KO mice do not exhibit
liver cell hypertrophy or hyperplasia following PCN treatment. These
data indicate that PXR activation is required for PCN-induced hepatomegaly and suggest an important role for PXR in regulating liver
cell hypertrophy and proliferation following xenobiotic and drug
treatment. Activation of PXR by PCN leads to induction of the rodent
hepatic Cyp3a11 gene in a PXR-dependent manner. PXR
activation by PCN also increased testosterone 6-hydroxylation and
decreased the duration of zoxazolamine-induced paralysis time in a
PXR-dependent manner, indicating a central role for PXR in regulating
hepatic CYP3A activity in vivo. These results are similar to those
reported by Xie et al. (2000a) in the PXR-null mice expressing the
constitutively active human SXR/PXR transgene under the control of the
albumin promoter. Ablation of PXR function in vivo surprisingly increased basal Cyp3a11 transcription and CYP3A activity,
indicating a previously unrecognized role for PXR in repression and
activation of CYP3A gene expression. Additionally, PCN
treatment resulted in increased expression of Oatp2 and increased
hepatic uptake of the Oatp2 substrate
[3H]digoxin, suggesting that Oatp2 probably
represents a direct PXR-target gene. By contrast, the PCN-dependent
induction of CYP3A and Oatp2 expression and activity was not observed
in the PXR-KO mice, further supporting an important role for PXR in the
regulation of uptake and metabolism of xenobiotics in vivo. PXR
activation by PCN reduced Cyp7a1 transcription and decreased
bile acid excretion in a PXR-dependent manner, indicating a previously
unrecognized role for PXR in cholesterol and bile acid homeostasis in
vivo. The molecular mechanisms by which PXR suppresses
Cyp7a1 expression are yet to be elucidated. Notably,
expression of the small heterodimeric partner gene, an orphan nuclear
receptor implicated in the farnesoid X receptor-mediated suppression of
Cyp7a1 (Goodwin et al., 2000; Lu et al., 2000), was not
regulated in a PXR-dependent manner (data not shown). Thus, multiple
mechanisms exist to suppress Cyp7a1 expression and thereby
prevent accumulation of potentially hepatotoxic bile acids. Taken
together, these data conclusively demonstrate a central role for PXR in
regulating PCN-induced hepatomegaly, Cyp3a11,
Oatp2, and Cyp7a1 gene expression levels and
their respective activities in vivo. These studies also suggest an
important role for PXR in the modulation of hepatic uptake, metabolism,
and biosynthesis of xenobiotics, steroids, and bile acids.
In the present study, ablation of PXR function in vivo led to a slight
but statistically significant increase in the levels of
Cyp3a11 gene expression, testosterone 6-hydroxylase
activity, and zoxazolamine resistance. This contradicts earlier reports by Xie et al. (2000a,b) in which they suggested that ablation of PXR
function has no effect on the basal level of Cyp3a11 gene transcription and CYP3A activity. Because PXR is thought to interact with a corepressor, the silencing mediator of repression and thyroid receptors protein, it is possible that the significant increase in
Cyp3a11 transcription and activity in the PXR-KO mice is due to the removal of corepressor activity. Alternatively, the increased level of Cyp3a11 expression and CYP3A activity could be due
to the action of the constitutive androstane receptor (NR1I3) in the
absence of functional PXR because the constitutive androstane receptor
also appears to regulate CYP3A gene expression by competing for ligands (Moore et al., 2000) and response elements (Xie et al.,
2000c). Another explanation for this disparity could include strain or
allelic differences between the two lines of PXR-null mice.
In summary, these studies indicate a pivotal role for PXR activation in PCN-induced hepatomegaly. These studies also further our understanding regarding the regulation of biochemically linked genes involved in xenobiotic, steroid, and bile acid homeostasis in vivo. PXR activation in vivo regulates key steps involved in the hepatic uptake, metabolism, and biosynthesis of steroids and bile acids in a coordinate manner. In conclusion, the PXR-KO animals used in this study will be a valuable tool for the discovery of additional PXR target genes and ligands, as well as in elucidating mechanisms of drug interactions and cell proliferation following xenobiotic treatment.
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Footnotes |
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Received June 28, 2001; accepted August 3, 2001.
Research supported by National Institutes of Health Grant NIEHS ES-09649. J. S. supported by National Institutes of Health Training Grant NIEHS ES-07079.
Dr. Curtis D. Klaassen, Department of Pharmacology and Toxicology, University of Kansas Medical Center, Breidenthal Building, Kansas City KS, 66160-7417. E-mail: cklaasse{at}kumc.edu
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Abbreviations |
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Abbreviations used are:
PXR, pregnane X
receptor;
Oatp2, organic anion transporting polypeptide;
PCN, pregnenolone-16-carbonitrile;
PXR-KO, PXR-knockout mouse;
PCNA, proliferating cell nuclear antigen;
SXR, steroid and xenobiotic
receptor.
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References |
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Top
Abstract
Introduction
Experimental Procedures
Results
Discussion
References
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J. P. Hernandez, W. Huang, L. M. Chapman, S. Chua, D. D. Moore, and W. S. Baldwin The Environmental Estrogen, Nonylphenol, Activates the Constitutive Androstane Receptor Toxicol. Sci., August 1, 2007; 98(2): 416 - 426. [Abstract] [Full Text] [PDF]
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 M.-L. Ricketts, M. V. Boekschoten, A. J. Kreeft, G. J. E. J. Hooiveld, C. J. A. Moen, M. Muller, R. R. Frants, S. Kasanmoentalib, S. M. Post, H. M. G. Princen, et al. The Cholesterol-Raising Factor from Coffee Beans, Cafestol, as an Agonist Ligand for the Farnesoid and Pregnane X Receptors Mol. Endocrinol., July 1, 2007; 21(7): 1603 - 1616. [Abstract] [Full Text] [PDF]
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Y. Xue, L. B. Moore, J. Orans, L. Peng, S. Bencharit, S. A. Kliewer, and M. R. Redinbo Crystal Structure of the Pregnane X Receptor-Estradiol Complex Provides Insights into Endobiotic Recognition Mol. Endocrinol., May 1, 2007; 21(5): 1028 - 1038. [Abstract] [Full Text] [PDF]
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 S. D. Hester, D. C. Wolf, S. Nesnow, and S.-F. Thai Transcriptional Profiles in Liver from Rats Treated with Tumorigenic and Non-tumorigenic Triazole Conazole Fungicides: Propiconazole, Triadimefon, and Myclobutanil Toxicol Pathol, December 1, 2006; 34(7): 879 - 894. [Abstract] [Full Text] [PDF]
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J. P. Jackson, S. S. Ferguson, M. Negishi, and J. A. Goldstein Phenytoin Induction of the Cyp2c37 Gene Is Mediated by the Constitutive Androstane Receptor Drug Metab. Dispos., December 1, 2006; 34(12): 2003 - 2010. [Abstract] [Full Text] [PDF]
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J. Guzelian, J. L. Barwick, L. Hunter, T. L. Phang, L. C. Quattrochi, and P. S. Guzelian Identification of Genes Controlled by the Pregnane X Receptor by Microarray Analysis of mRNAs from Pregnenolone 16{alpha}-Carbonitrile-Treated Rats Toxicol. Sci., December 1, 2006; 94(2): 379 - 387. [Abstract] [Full Text] [PDF]
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X. Cheng and C. D. Klaassen Regulation of mRNA Expression of Xenobiotic Transporters by the Pregnane X Receptor in Mouse Liver, Kidney, and Intestine Drug Metab. Dispos., November 1, 2006; 34(11): 1863 - 1867. [Abstract] [Full Text] [PDF]
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 X. Ding, K. Lichti, I. Kim, F. J. Gonzalez, and J. L. Staudinger Regulation of Constitutive Androstane Receptor and Its Target Genes by Fasting, cAMP, Hepatocyte Nuclear Factor {alpha}, and the Coactivator Peroxisome Proliferator-activated Receptor {gamma} Coactivator-1{alpha} J. Biol. Chem., September 8, 2006; 281(36): 26540 - 26551. [Abstract] [Full Text] [PDF]
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D. Jung, D. J. Mangelsdorf, and U. A. Meyer Pregnane X Receptor Is a Target of Farnesoid X Receptor J. Biol. Chem., July 14, 2006; 281(28): 19081 - 19091. [Abstract] [Full Text] [PDF]
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K. Wang, A. J. Mendy, G. Dai, H.-R. Luo, L. He, and Y.-J. Y. Wan Retinoids Activate the RXR/SXR-Mediated Pathway and Induce the Endogenous CYP3A4 Activity in Huh7 Human Hepatoma Cells Toxicol. Sci., July 1, 2006; 92(1): 51 - 60. [Abstract] [Full Text] [PDF]
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S. J. Baldwin, J. L. Bramhall, C. A. Ashby, L. Yue, P. R. Murdock, S. R. Hood, A. D. Ayrton, and S. E. Clarke CYTOCHROME P450 GENE INDUCTION IN RATS EX VIVO ASSESSED BY QUANTITATIVE REAL-TIME REVERSE TRANSCRIPTASE-POLYMERASE CHAIN REACTION (TAQMAN) Drug Metab. Dispos., June 1, 2006; 34(6): 1063 - 1069. [Abstract] [Full Text] [PDF]
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G. Zollner, M. Wagner, T. Moustafa, P. Fickert, D. Silbert, J. Gumhold, A. Fuchsbichler, E. Halilbasic, H. Denk, H.-U. Marschall, et al. Coordinated induction of bile acid detoxification and alternative elimination in mice: role of FXR-regulated organic solute transporter-{alpha}/beta in the adaptive response to bile acids Am J Physiol Gastrointest Liver Physiol, May 1, 2006; 290(5): G923 - G932. [Abstract] [Full Text] [PDF]
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A. L. Slitt, N. J. Cherrington, M. Z. Dieter, L. M. Aleksunes, G. L. Scheffer, W. Huang, D. D. Moore, and C. D. Klaassen trans-Stilbene Oxide Induces Expression of Genes Involved in Metabolism and Transport in Mouse Liver via CAR and Nrf2 Transcription Factors Mol. Pharmacol., May 1, 2006; 69(5): 1554 - 1563. [Abstract] [Full Text] [PDF]
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 W. Huang, K. Ma, J. Zhang, M. Qatanani, J. Cuvillier, J. Liu, B. Dong, X. Huang, and D. D. Moore Nuclear receptor-dependent bile acid signaling is required for normal liver regeneration. Science, April 14, 2006; 312(5771): 233 - 236. [Abstract] [Full Text] [PDF]
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 O. Briz, R. I. R. Macias, M. J. Perez, M. A. Serrano, and J. J. G. Marin Excretion of fetal biliverdin by the rat placenta-maternal liver tandem Am J Physiol Regulatory Integrative Comp Physiol, March 1, 2006; 290(3): R749 - R756. [Abstract] [Full Text] [PDF]
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J. Orans, D. G. Teotico, and M. R. Redinbo The Nuclear Xenobiotic Receptor Pregnane X Receptor: Recent Insights and New Challenges Mol. Endocrinol., December 1, 2005; 19(12): 2891 - 2900. [Abstract] [Full Text] [PDF]
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X. Cheng, J. Maher, M. Z. Dieter, and C. D. Klaassen REGULATION OF MOUSE ORGANIC ANION-TRANSPORTING POLYPEPTIDES (OATPS) IN LIVER BY PROTOTYPICAL MICROSOMAL ENZYME INDUCERS THAT ACTIVATE DISTINCT TRANSCRIPTION FACTOR PATHWAYS Drug Metab. Dispos., September 1, 2005; 33(9): 1276 - 1282. [Abstract] [Full Text] [PDF]
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 C. Gnerre, G. U. Schuster, A. Roth, C. Handschin, L. Johansson, R. Looser, P. Parini, M. Podvinec, K. Robertsson, J.-A. Gustafsson, et al. LXR deficiency and cholesterol feeding affect the expression and phenobarbital-mediated induction of cytochromes P450 in mouse liver J. Lipid Res., August 1, 2005; 46(8): 1633 - 1642. [Abstract] [Full Text] [PDF]
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J. M. Maher, X. Cheng, A. L. Slitt, M. Z. Dieter, and C. D. Klaassen INDUCTION OF THE MULTIDRUG RESISTANCE-ASSOCIATED PROTEIN FAMILY OF TRANSPORTERS BY CHEMICAL ACTIVATORS OF RECEPTOR-MEDIATED PATHWAYS IN MOUSE LIVER Drug Metab. Dispos., July 1, 2005; 33(7): 956 - 962. [Abstract] [Full Text] [PDF]
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M. D. Krasowski, K. Yasuda, L. R. Hagey, and E. G. Schuetz Evolution of the Pregnane X Receptor: Adaptation to Cross-Species Differences in Biliary Bile Salts Mol. Endocrinol., July 1, 2005; 19(7): 1720 - 1739. [Abstract] [Full Text] [PDF]
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J. E. Chrencik, J. Orans, L. B. Moore, Y. Xue, L. Peng, J. L. Collins, G. B. Wisely, M. H. Lambert, S. A. Kliewer, and M. R. Redinbo Structural Disorder in the Complex of Human Pregnane X Receptor and the Macrolide Antibiotic Rifampicin Mol. Endocrinol., May 1, 2005; 19(5): 1125 - 1134. [Abstract] [Full Text] [PDF]
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S. Ekins, E. Kirillov, E. A. Rakhmatulin, and T. Nikolskaya A NOVEL METHOD FOR VISUALIZING NUCLEAR HORMONE RECEPTOR NETWORKS RELEVANT TO DRUG METABOLISM Drug Metab. Dispos., March 1, 2005; 33(3): 474 - 481. [Abstract] [Full Text] [PDF]
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 X. Ding and J. L. Staudinger Induction of Drug Metabolism by Forskolin: The Role of the Pregnane X Receptor and the Protein Kinase A Signal Transduction Pathway J. Pharmacol. Exp. Ther., February 1, 2005; 312(2): 849 - 856. [Abstract] [Full Text] [PDF]
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M. V. St-Pierre, T. Stallmach, A. Freimoser Grundschober, J.-F. Dufour, M. A. Serrano, J. J. G. Marin, Y. Sugiyama, and P. J. Meier Temporal expression profiles of organic anion transport proteins in placenta and fetal liver of the rat Am J Physiol Regulatory Integrative Comp Physiol, December 1, 2004; 287(6): R1505 - R1516. [Abstract] [Full Text] [PDF]
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J. Zhang, W. Huang, M. Qatanani, R. M. Evans, and D. D. Moore The Constitutive Androstane Receptor and Pregnane X Receptor Function Coordinately to Prevent Bile Acid-induced Hepatotoxicity J. Biol. Chem., November 19, 2004; 279(47): 49517 - 49522. [Abstract] [Full Text] [PDF]
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S. Bhalla, C. Ozalp, S. Fang, L. Xiang, and J. K. Kemper Ligand-activated Pregnane X Receptor Interferes with HNF-4 Signaling by Targeting a Common Coactivator PGC-1{alpha}: FUNCTIONAL IMPLICATIONS IN HEPATIC CHOLESTEROL AND GLUCOSE METABOLISM J. Biol. Chem., October 22, 2004; 279(43): 45139 - 45147. [Abstract] [Full Text] [PDF]
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W. Huang, J. Zhang, P. Wei, W. T. Schrader, and D. D. Moore Meclizine Is an Agonist Ligand for Mouse Constitutive Androstane Receptor (CAR) and an Inverse Agonist for Human CAR Mol. Endocrinol., October 1, 2004; 18(10): 2402 - 2408. [Abstract] [Full Text] [PDF]
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C. J. Matheny, R. Y. Ali, X. Yang, and G. M. Pollack EFFECT OF PROTOTYPICAL INDUCING AGENTS ON P-GLYCOPROTEIN AND CYP3A EXPRESSION IN MOUSE TISSUES Drug Metab. Dispos., September 1, 2004; 32(9): 1008 - 1014. [Abstract] [Full Text] [PDF]
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D. E. Brobst, X. Ding, K. L. Creech, B. Goodwin, B. Kelley, and J. L. Staudinger Guggulsterone Activates Multiple Nuclear Receptors and Induces CYP3A Gene Expression through the Pregnane X Receptor J. Pharmacol. Exp. Ther., August 1, 2004; 310(2): 528 - 535. [Abstract] [Full Text] [PDF]
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 C. Handschin and U. A. Meyer Induction of Drug Metabolism: The Role of Nuclear Receptors Pharmacol. Rev., December 1, 2003; 55(4): 649 - 673. [Abstract] [Full Text] [PDF]
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L. Wang, Y. Han, C.-S. Kim, Y.-K. Lee, and D. D. Moore Resistance of SHP-null Mice to Bile Acid-induced Liver Damage J. Biol. Chem., November 7, 2003; 278(45): 44475 - 44481. [Abstract] [Full Text] [PDF]
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A. L. Slitt, N. J. Cherrington, J. M. Maher, and C. D. Klaassen INDUCTION OF MULTIDRUG RESISTANCE PROTEIN 3 IN RAT LIVER IS ASSOCIATED WITH ALTERED VECTORIAL EXCRETION OF ACETAMINOPHEN METABOLITES Drug Metab. Dispos., September 1, 2003; 31(9): 1176 - 1186. [Abstract] [Full Text] [PDF]
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J. C. Ourlin, F. Lasserre, T. Pineau, J. M. Fabre, A. Sa-Cunha, P. Maurel, M.-J. Vilarem, and J. M. Pascussi The Small Heterodimer Partner Interacts with the Pregnane X Receptor and Represses Its Transcriptional Activity Mol. Endocrinol., September 1, 2003; 17(9): 1693 - 1703. [Abstract] [Full Text] [PDF]
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N. Mizuno, T. Niwa, Y. Yotsumoto, and Y. Sugiyama Impact of Drug Transporter Studies on Drug Discovery and Development Pharmacol. Rev., September 1, 2003; 55(3): 425 - 461. [Abstract] [Full Text] [PDF]
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C. Chen, J. L. Staudinger, and C. D. Klaassen NUCLEAR RECEPTOR, PREGNANE X RECEPTOR, IS REQUIRED FOR INDUCTION OF UDP-GLUCURONOSYLTRANSFERASES IN MOUSE LIVER BY PREGNENOLONE-16{alpha}-CARBONITRILE Drug Metab. Dispos., July 1, 2003; 31(7): 908 - 915. [Abstract] [Full Text] [PDF]
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J. L. Staudinger, A. Madan, K. M. Carol, and A. Parkinson Regulation of Drug Transporter Gene Expression by Nuclear Receptors Drug Metab. Dispos., May 1, 2003; 31(5): 523 - 527. [Abstract] [Full Text] [PDF]
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S. C. Nallani, B. Goodwin, J. M. Maglich, D. J. Buckley, A. R. Buckley, and P. B. Desai Induction of Cytochrome P450 3A by Paclitaxel in Mice: Pivotal Role of the Nuclear Xenobiotic Receptor, Pregnane X Receptor Drug Metab. Dispos., May 1, 2003; 31(5): 681 - 684. [Abstract] [Full Text] [PDF]
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 M. Trauner and J. L. Boyer Bile Salt Transporters: Molecular Characterization, Function, and Regulation Physiol Rev, April 1, 2003; 83(2): 633 - 671. [Abstract] [Full Text] [PDF]
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T. A. Kocarek, M. S. Dahn, H. Cai, S. C. Strom, and N. A. Mercer-Haines Regulation of CYP2B6 and CYP3A Expression by Hydroxymethylglutaryl Coenzyme A Inhibitors in Primary Cultured Human Hepatocytes Drug Metab. Dispos., December 1, 2002; 30(12): 1400 - 1405. [Abstract] [Full Text] [PDF]
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 J. Sonoda, W. Xie, J. M. Rosenfeld, J. L. Barwick, P. S. Guzelian, and R. M. Evans Regulation of a xenobiotic sulfonation cascade by nuclear pregnane X receptor (PXR) PNAS, October 15, 2002; 99(21): 13801 - 13806. [Abstract] [Full Text] [PDF]
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 S. A. Kliewer, B. Goodwin, and T. M. Willson The Nuclear Pregnane X Receptor: A Key Regulator of Xenobiotic Metabolism Endocr. Rev., October 1, 2002; 23(5): 687 - 702. [Abstract] [Full Text] [PDF]
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J. Y. L. Chiang Bile Acid Regulation of Gene Expression: Roles of Nuclear Hormone Receptors Endocr. Rev., August 1, 2002; 23(4): 443 - 463. [Abstract] [Full Text] [PDF]
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Y. S. Lin, A. L. S. Dowling, S. D. Quigley, F. M. Farin, J. Zhang, J. Lamba, E. G. Schuetz, and K. E. Thummel Co-Regulation of CYP3A4 and CYP3A5 and Contribution to Hepatic and Intestinal Midazolam Metabolism Mol. Pharmacol., July 1, 2002; 62(1): 162 - 172. [Abstract] [Full Text] [PDF]
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N. L. Urizar, A. B. Liverman, D'N. T. Dodds, F. V. Silva, P. Ordentlich, Y. Yan, F. J. Gonzalez, R. A. Heyman, D. J. Mangelsdorf, and D. D. Moore A Natural Product That Lowers Cholesterol As an Antagonist Ligand for FXR Science, May 31, 2002; 296(5573): 1703 - 1706. [Abstract] [Full Text] [PDF]
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S. A. Kliewer and T. M. Willson Regulation of xenobiotic and bile acid metabolism by the nuclear pregnane X receptor J. Lipid Res., March 1, 2002; 43(3): 359 - 364. [Abstract] [Full Text] [PDF]
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