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Montreal Center for Experimental Therapeutics in Cancer, Lady Davis Institute for Medical Research, the Sir Mortimer B. Davis-Jewish General Hospital, and McGill University, Montreal, Quebec, Canada
Received December 3, 2002; accepted April 24, 2003
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Abstract |
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 Top Abstract Materials and MethodsResultsDiscussionReferences |
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;
Kensler et al., 1999).
Numerous data have demonstrated that oltipraz provides significant protection
from tumorigenesis in hepatocellular, mammary, colon, and lung tumor models,
and that it induces resistance to many types of carcinogens including
aflatoxin B1 (AFB1), a well known hepatocellular carcinogen
(Clapper, 1998).
It has been shown that oltipraz's chemopreventive effect is caused by the
selective induction of phase II drug-metabolizing enzymes and/or the
inhibition of some phase I cytochrome P450 enzyme activities
(Kensler et al., 1999). As a
major molecular mechanism, the induction of the phase II drug metabolism
enzymes helps to detoxify various types of carcinogens. It was previously
demonstrated that up-regulation of phase II enzymes by oltipraz is caused by
the direct activation of the antioxidant-responsive element (ARE), a
cis-acting regulatory element that is widely present in the
5'-flanking regions of many detoxifying genes
(Kensler et al., 1999). The
ARE was first identified in rat glutathione S-transferase Ya
(Rushmore et al., 1990,
1991), and a mouse counterpart
was found in the murine glutathione S-transferase Ya gene and has
been named the electrophile responsive element (EpRE) because of its
responsiveness to electrophilic compounds (Friling et al.,
1990,
1992). It has since been found
that ARE/EpRE is composed of two copies of adjacent activator
protein-1–like motifs (TGACNNNGC) and is required for maximum basal
expression and induction by some xenobiotic compounds
(Friling et al., 1992;
Favreau and Pickett, 1995).
Recent studies implicated a critical involvement of a basic leucine zipper
transcriptional factor, Nrf2 (NF-E2 p45-related factor 2), in the regulatory
activation of the ARE (Hayes and McMahon,
2001).
As a derivative of dithiolethione, oltipraz is thought to be a
monofunctional inducer, selectively activating phase II genes
(Prochaska and Talalay, 1988;
Kensler et al., 1999;
Hayes and McMahon, 2001),
however it was also found to affect P450 activity. There are several reports
of inhibition of enzyme activities of CYP1A1, CYP3A4 (Langouet et al.,
1995,
2000) and CYP1A2
(Sofowora et al., 2001),
suggesting that inhibition of activation of procarcinogens by P450s could be a
mechanism contributing to oltipraz's antitumor effects. Another study found
that oltipraz's inhibition of phase I enzymes is only transient and is
completely reversed after 24 h (Langouet
et al., 1997). Several reports demonstrated potent induction of
CYP genes by oltipraz at the transcriptional level
(Buetler et al., 1995;
Maheo et al., 1998).
CYP1A1 gene regulation has been extensively studied; inducers such as
2,3,7,8-tetrachlorodibenzo-p-dioxin or 
-naphthoflavone
(-NF) bind to the aryl hydrocarbon receptor (AhR), which translocates to
the nucleus, dimerizes with the AhR nuclear translocator, and interacts with
the cis-acting regulatory element XRE
(Rushmore and Kong, 2002).
More recently, Le Ferrec et al.
(2002) reported a significant
transcriptional induction of CYP1A1 by oltipraz in human Caoco-2
cells that is AhR-dependent.
In this work, we studied the transcriptional modulation of rat
GSTA5 by oltipraz. GSTs are among the most important members of phase
II detoxifying enzymes. Rat GSTA5 stands out from other drug-metabolizing
enzymes in that it consistently shows a high level of inducibility by
chemopreventive agents such as oltipraz, and is highly efficient at
metabolizing AFB1 (Hayes et al.,
1991). Both ARE and XRE homologous sequences are present in the
promoter area of rGSTA5 (Pulford
and Hayes, 1996). We found that the ARE of rGSTA5 is not
fully functional and has lost responsiveness to oltipraz activation, whereas
the XRE, located downstream of the transcription initiation site, functions as
the cis-acting regulatory element responsible for oltipraz-induced
expression of rGSTA5.
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Materials and Methods |
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TopAbstractMaterials and MethodsResultsDiscussionReferences |
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Reporter Gene Constructs. A series of fragments containing the rat
GSTA5 promoter described in a previous report from this lab
(Jaitovitch-Groisman et al.,
2000) were amplified by polymerase chain reaction (PCR) from rat
genomic DNA using primers specific for the rat GSTA5
5'-flanking region. The PCR product was digested with XhoI and
HindIII and ligated into pGL3-basic vector (Promega, Madison, WI)
containing a firefly luciferase reporter gene.
The sense and antisense oligonucleotides (oligos) containing XRE or ARE sequences were synthesized by Invitrogen. For annealing, the complementary single strand oligos were heated at 75°C for 10 min and then gradually cooled to room temperature (RT). The annealed oligos were ligated to the KpnI and MluI sites of pGL3-promoter vector (Promega) containing a heterologous SV40 promoter and a firefly luciferase reporter gene. All constructs were sequenced to confirm the accuracy of cloning.
Cell Culture, Transient Transfection and Luciferase Assay. The human
hepatoma cell line HepG2 was obtained from the American Type Culture
Collection (ATCC; Manassas, VA). Cells were grown in 
-minimal essential
media supplemented with nonessential amino acids, sodium pyruvate, 90% Earle's
balanced salt solution, and 10% fetal bovine serum. The murine hepatoma cell
line Hepa 1c1c7 and its derivative cell lines tao-bprcl and C37 were also
obtained from ATCC.
For transfection experiments, cells were seeded at 9 x 104 per well, using 24-well plates, and grown overnight in normal media. The following day, cells were transiently transfected using LipofectAMINE (Invitrogen, Carlsbad, CA) with pGL3 luciferase reporter constructs. The plasmid pRL, containing a Renilla reniformis luciferase reporter gene, was cotransfected as internal control. Briefly, cells were incubated with DNA-LipofectAMINE complexes for 5 h, after which they were washed gently and cultured in fresh serum-supplemented media. When drug treatment was performed, oltipraz at designated concentrations was added. After 24 h, the cells were washed twice with phosphate-buffered saline and harvested in 100 µl of 1x passive lysis buffer (Promega). The luciferase activities were analyzed in 20-µl cell extracts with the Dual Luciferase assay kit (Promega) on a Lumat LB 9507 luminometer (Berthold Technologies, Bad Wildbad, Germany). The relative luciferase activities reported are expressed as a ratio of the pGL3 reporter activity to that of the control plasmid pRL. For all luciferase assays, data represent measurements from three independent transfections and are presented as the mean ± S.E.M. All experiments were repeated at least three times, and one representative experiment was shown in each figure. For statistics, Student's t tests were carried out with GraphPad Prism, and significance (*) was reached at P < 0.05.
Electrophoretic Mobility Shift Assay. The sense and antisense
synthetic oligos containing XRE sequences from rat GSTA5 were
synthesized by Invitrogen. For annealing, the complementary single oligos were
heated at 75°C for 10 min and allowed to cool gradually to RT. Then the
double-stranded oligos containing XRE were purified by acrylamide gel
electrophoresis and used as probes in gel shift experiments. The sequence is
as follows: The rGSTA5-XRE:
5'-CACGCGTGTGCGTGCGTGTGCGTGCGTGTGCACG-3'/3'-GTGCGCACACGCACGCACACGCACGCACACGTGC-5'.
The rGSTA5-XRE probe was end-labeled with [
-32P]ATP
using T4 polynucleotide kinase, and unincorporated nucleotides were removed
using Sephadex G-50 mini-columns (Amersham Biosciences, Piscataway, NJ).
Electrophoretic mobility shift assays were performed as described
previously (Denison et al.,
1988). Briefly, cells were treated with designated concentrations
of oltipraz for 2 h before preparation of nuclear extracts. For DNA-protein
binding reactions, 5 µg of nuclear extract was mixed with 1 µg of
poly(dI-dC) in a 24-µl buffer containing 30 mM HEPES-KOH, pH 7.9, 60 mM
KCl, 1 mM EDTA, 1 mM dithiothreitol, and 14% glycerol. The reaction mixture
was preincubated for 10 min at RT, after which the probe DNA was added.
Incubation was continued for another 20 min at RT. Competition reactions were
carried out under the same conditions plus the addition of 200-fold unlabeled
oligos or 1 µg of AhR antibody. Protein-DNA complexes were resolved through
a 5% polyacrylamide gel using 0.25x Tris-borate/EDTA buffer. The gel was
then dried and subjected to autoradiography with an intensifying screen at
-80°C overnight.
RNA Preparation and Semiquantitative Detection of Gene Expression by Reverse Transcriptase-Polymerase Chain Reaction. The rat hepatoma cell line H4IIE was obtained from ATCC and maintained in Dulbecco's modified Eagle's medium with 10% fetal bovine serum. The cells were treated with 20 µM oltipraz and then were harvested at designated time points. Total RNA was isolated from cells using TRIzol reagent (Invitrogen). To perform RT-PCR, we used the OneStep RT-PCR kit (QIAGEN) according to the manufacturer's instructions. Each RT-PCR reaction was performed with 1 µg of RNA, 250 µM deoxynucleotide triphosphate, 50 pmol of each primer (synthesized by Invitrogen), and 10 units of enzyme mixture containing an optimized combination of OmniScript reverse transcriptase, Sensiscript reverse transcriptase, and Hot-StarTaq DNA polymerase (for details, see QIAGEN OneStep RT-PCR kit handbook), in a final volume of 25 µl. The RT-PCR profile was 50°C for 30 min, 95°C for 15 min, followed by 32 cycles of 94°C for 40 s, 55°C for 30 s, and 72°C for 1 min, then an additional extension at 72°C for 10 min. Half of the PCR product was analyzed by electrophoresis through 1.0% agarose gels. The primer sequences for rGSTA5, rGSTA2, rQR, CYP1A1, and GADPH are shown in Table 1.
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Results |
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TopAbstractMaterials and MethodsResultsDiscussionReferences |
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) are
shown in the promoter map (Fig.
1A). HepG2 cells were transfected with these pGL3 constructs and
then treated with oltipraz or ethoxyquin. Twenty-four hours after drug
treatment, cells were harvested and luciferase activities of the cell lysates
were measured. Our experiments showed that the -928 to +192 pGL3-basic
construct containing an ARE homologous sequence failed to respond to oltipraz
treatment but can be activated as high as 4.6-fold by 10 µM ethoxyquin
(Fig. 1B), whereas the -460 to
+485 pGL3-basic construct containing both ARE and XRE can be induced 3.3-fold
by 50 µM oltipraz and 3.8-fold by 10 µM ethoxyquin
(Fig. 1C).
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To further explore whether the XRE is the cis-acting element in rGSTA5 responsible for oltipraz induction, four rGSTA5 promoter fragments in which the ARE/XRE was present/or absent were cloned into pGL3-basic vectors (Fig. 2A). The luciferase assay showed that the -416 to +430 pGL3-basic plasmid, containing neither ARE nor XRE doesn't respond to oltipraz or ethoxyquin; the -453 to +462 pGL3-basic construct, containing both ARE and XRE, can be activated 2.9-fold by 20 µM oltipraz and 4.8-fold by 10 µM ethoxyquin; the construct -416 to +462 containing only XRE can be activated 3.2-fold by oltipraz but does not respond to ethoxyquin treatment, and the construct -453 to +430 pGL3-basic, containing only ARE, doesn't respond to oltipraz treatment but can be induced 4.2-fold by ethoxyquin (Fig. 2B). These preliminary data suggest that in rGSTA5, the XRE is likely to be responsible for induction by oltipraz.
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To confirm our hypothesis, oligos containing rGSTA5 ARE and XRE sequences were synthesized and cloned into the KpnI and MluI sites of the luciferase reporter vector pGL3-promoter. The construct contains a heterologous SV40 promoter, and a rGSTA5-ARE or -XRE sequence as enhancer. The luciferase assay demonstrated that the A5-ARE pGL3-promoter construct does not respond to oltipraz but is induced 3.9-fold by ethoxyquin. In contrast, the A5-XRE pGL3-promoter construct is induced 3.2-fold by oltipraz but is unresponsive to ethoxyquin exposure (Fig. 3). These data are entirely consistent with our earlier results.
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The ARE/EpRE is composed of two activator protein-1–like motifs
(TGACNNNGC), designated the distal-half site and the proximal-half site,
because deletion or mutation of either site cripples its effect on basal
expression enhancement and inducibility by -NF
(Friling et al., 1992;
Favreau and Pickett, 1995). By
comparing the ARE homologous sequence from the rGSTA5 with those from
other members of the GST enzymes, we noticed that rGSTA5-ARE
possesses only the proximal-half site, and its distal-half site (the distal
copy of core sequence motif) is extensively mutated
(Fig. 4A). Because the A5-ARE
contains only one half site, it is necessary to examine its function. Hence,
we cloned the typical ARE enhancer-rGSTA2-ARE
(Rushmore et al., 1991), and
its murine counterpart EpRE (Friling et
al., 1992), into the pGL3-promoter
(Fig. 4A), and the effect of
oltipraz on luciferase activity driven by these promoter constructs was
compared. The data indicated a dramatic 6-fold attenuation in the basal
expression level of the rGSTA5-ARE (A5-ARE) compared with those of
rGSTA2-ARE (A2-ARE) and EpRE (Fig.
4B). For oltipraz induction, A5-ARE had completely lost any
responsiveness, whereas A2-ARE and EpRE can be induced 1.9- and 2.1-fold,
respectively. In the case of ethoxyquin, A5-ARE can be induced 4.0-fold,
whereas A2-ARE and EpRE can be induced 2.4- and 2.2-fold, respectively
(Fig. 4B). The data suggest
that A5-ARE has lost functions of basal expression enhancement and
responsiveness to oltipraz exposure; surprisingly, it retains the inducibility
by ethoxyquin. To further assess the significance of ARE in GSTA5
gene expression, the effect of another antioxidant, BHQ, was tested. Cells
were treated with three doses of BHQ (2, 5, and 10 µM) together with a
vehicle ETOH control, and the effects on activation of A5-ARE and A2-ARE were
measured (Fig. 4C). The results
again showed that the basal expression level (ETOH group) driven by A5-ARE
decreased drastically (12.9-fold) compared with that driven by A2-ARE. At the
dose of 2 µM BHQ, A5-ARE showed no induction (0.9-fold); however, A2-ARE
was induced 1.9-fold. At the dose of 5 µM BHQ, A5-ARE was also induced, but
the magnitude of induction for A5-ARE (1.7-fold) is less than that of A2-ARE
(2.2-fold); at the dose of 10 µM BHQ, the induction of A5-ARE (1.8-fold) is
also less than that of A2-ARE (2.4-fold). The results suggest that, in
addition to a substantial loss of basal expression enhancement function,
A5-ARE also retains partial inducibility by BHQ; however, the magnitude of
induction is attenuated compared with that of A2-ARE.
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To determine whether it is true in other contexts as well that XRE is an
alternative cis-acting element responding to oltipraz, XREs from
other phase II genes such as rGSTA2
(Rushmore et a., 1990), rat
NAD(P)H: Quinone Reductase (QR)
(Favreau and Pickett, 1991),
and the phase I gene CYP 1A1
(Denison et al., 1988) were
cloned into the pGL3-promoter vector (Fig.
5A), and the response to oltipraz was measured. The results
indicate that oltipraz can induce all of these XREs, and the effect is
dose-dependent (Fig. 5B). The
fold induction for rGSTA5-XRE (A5-XRE), rGSTA2-XRE (A2-XRE),
rQR-XRE (QR-XRE) is in a similar range of 3- to 5-fold, while
hCYP1A1-DRE3 (DRE3) seems to be two times more efficient in induction
than the other XREs (Fig. 5B). This suggests that induction of oltipraz is specific to the XRE structure and
that A5-XRE is no more efficient than other XREs in response to oltipraz's
induction, even though it contains two adjacent core sequence (TGCGTG) repeats
(Fig. 5A).
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To confirm the effect of oltipraz on the XRE-AhR pathway in HepG2 cells, nuclear extracts from cells treated with oltipraz were prepared. Electrophoretic mobility shift assay clearly showed that a XRE-AhR retarded band was formed when cells were treated with oltipraz, and XRE-AhR binding can be blocked by excess unlabeled XRE oligos or AhR antibody but not by excess ARE oligos (Fig. 6).
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The HepG2 cells were also transfected with
rGSTA5-XRE-pGL3-promoter (Fig.
7A) or -453 to 460-pGL3-basic construct
(Fig. 7B) and then were treated
with the AhR antagonist resveratrol (Casper
et al., 1999) and oltipraz; the results showed that
oltipraz-induced expression, driven by the XRE enhancer, can be totally
abrogated by resveratrol at 20–30 µM
(Fig. 7). To further assess the
role of AhR in the mediation of A5-XRE activation, we tested oltipraz
inducibility in the AhR-deficient mouse hepatoma cell line tao-bprcl. The
results showed that in the wild-type mouse hepatoma cell line Hepa1c1c7, the
A5-XRE can be induced by oltipraz, and effects are generally dose-dependent.
However in tao-bprcl, oltipraz-induced A5-XRE activation was largely
abolished, demonstrating that AhR is critically important in the activation of
A5-XRE (Fig. 8). In another
mouse hepatoma cell line C37, which has a nonfunctional CYP1A1, oltipraz is
still effective in activating A5-XRE, demonstrating that metabolism of
oltipraz by CYP1A1 is not necessary for its activation of XRE
(Fig. 8).
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XRE is present in many phase II detoxifying genes, such as rGSTA2
(Rushmore et al., 1990),
rGSTA5 (Pulford and Hayes,
1996), and rQR
(Favreau and Pickett, 1991),
and it is also present in some phase I genes, such as CYP1A1
(Corchero et al., 2001).
Therefore, we hypothesize that oltipraz exposure can affect both phase I and
II drug-metabolizing enzymes. To test this, a rat hepatoma cell line H4IIE was
treated with 20 µM oltipraz, and cells were harvested at 2, 6, 16, and 24
h, and gene expression was detected by semiquantitative RT-PCR. Our data
showed that the phase II genes rGSTA5, rGSTA2, and rQR, as
well as the phase I gene CYP1A1, were significantly activated,
although the time and magnitude patterns of induction differ among the genes
(Fig. 9). These data
demonstrate that oltipraz is a bifunctional inducer, modulating both phase I
and II drug-metabolizing enzymes.
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Discussion |
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TopAbstractMaterials and MethodsResultsDiscussionReferences |
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). The normal human drug-metabolizing system is generally
divided into two groups of enzymes. The phase I enzymes include the P450
supergene family, and the phase II enzymes include a number of enzymes, such
as GST, QR, and UDP-glucuronosyltransferase. It is well recognized that
induction of phase II enzymes, especially the GSTs, plays a central role in
detoxifying environmental carcinogens.
In this work, rGSTA5 was chosen as our study model because this GST subunit
is highly inducible by several chemoproventive agents, including ethoxyquin,
butylated hydroxyanisole, and oltipraz. Moreover, rGSTA5 is of critical
importance in detoxifying the hepatocellular carcinogen AFB1, because it
exhibits approximately 180-fold greater activity toward AFB1–8,9-epoxide
than rGSTA3 and 1000-fold greater activity than rGSTA1 and rGSTA2
(Hayes et al., 1991;
Pulford and Hayes, 1996).
Oltipraz, a derivative of dithiolethione, has demonstrated excellent
chemopreventive effects in many target organs challenged with various
carcinogens. A number of studies indicate that oltipraz is a potent inducer of
phase II enzymes, and the molecular mechanism is thought to involve
transcriptional up-regulation of phase II genes through activation of the
ARE-Nrf2 pathway (Clapper,
1998). It was reported that the presence of two adjacent copies of
the ARE core sequence motif (GATCNNNGC) is necessary for maximum basal
expression and induction by -NF in murine GstA1
(Friling et al., 1992) and rat
QR (Favreau and Pickett,
1995). Therefore, it is not surprising that rGSTA5 ARE
has lost the basal expression enhancement function as well as oltipraz
inducibility, because extensive mutations are present in its distal-half site
(the distal copy of core sequence motif;
Fig. 4A). Interestingly, our
experiment showed that rGSTA5 ARE still retains inducibility by the
antioxidant ethoxyquin and BHQ, suggesting differences in the molecular
mechanisms for ethoxyquin and BHQ compared with oltipraz and
-NF–induced ARE activations. It is possible that there are
different proteins or protein complexes binding to the regulatory
sequences.
In a series of studies, Talalay's lab showed that eight different classes
of chemopreventive agents can transactivate ARE, suggesting that the ARE
mediates most, if not all, of the induction of phase II enzymes by these
compounds (Prestera et al.,
1993). Kensler's lab demonstrated activation of ARE by a score of
dithiolethione family members, including oltipraz
(Egner et al., 1994). Moreover,
studies with Nrf2-null mice demonstrate a dramatic decrease in phase II enzyme
basal levels as well as the level of enzyme induction by oltipraz, suggesting
that the ARE-Nrf2 pathway is critical in both constitutive and inductive
expression of phase II enzymes (McMahon et
al., 2001; Ramos-Gomez et al.,
2001). Because the ARE exists only in phase II detoxication genes
and is absent in P450s, many ARE inducers are referred to as
monofunctional inducers (Prochaska and
Talalay, 1988; Hayes and
McMahon, 2001).
Oltipraz is traditionally considered such a monofunctional inducer working
directly and exclusively through the ARE cis-acting element. However,
there have been several reports of induction of P450s by oltipraz, suggesting
that an ARE-independent mechanism of oltipraz action exists. Although the
effects on the P450 genes have been variable in different systems, a recent
study demonstrated a significant induction of CYP1A1 by oltipraz in
Caco cells that is AhR- and calcium-dependent
(Le Ferrec et al., 2002). A
more recent article first confirmed that oltipraz activates a phase II gene
UGT1A6 by means of XRE activation
(Auyeung et al., 2003). In this
report, we have further demonstrated that oltipraz induction of phase II
rGSTA5 gene is via XRE instead of ARE activation. XRE represents one
of the major cis-regulatory elements in the CYP1A subfamily
(Rushmore and Kong, 2002),
whereas it is also widely present in the promoters of many phase II
detoxifying genes. For example, in phase II genes such as rGSTA2
(Rushmore et al., 1990) and
rQR (Favreau and Pickett,
1991), XRE and ARE coexist in the gene promoter region, suggesting
that XRE may work independently or synergistically with ARE in the modulation
of these genes. Moreover, in some phase II detoxifying genes, such as
UDP-glucuronosyltransferase (UGT)
(Emi et al., 1996;
Metz and Ritter, 1998;
Auyeung et al., 2003), and
Cu/Zn superoxide dismutase (SOD1)
(Cho et al., 2001), only the
XRE is present in the promoter regulatory region and plays major role in
up-regulation of these genes. Another interesting point is the location of the
XRE element in the rGSTA5 gene. In most previous reported genes, the
XRE is present in the 5'-upstream sequences of the promoters, although
the distance from the transcriptional initiation site varies. In this article,
however, we have shown evidence that a functional XRE element is located in
the first intron of the rGSTA5 gene, which is several hundred
nucleotides downstream of the transcriptional start site. This finding
highlights the importance of downstream cis-acting regulatory
elements. Taken together, the presence of XRE in both phase I and II genes
explains why and how oltipraz should be considered a bifunctional
chemopreventive agent.
CYP1A1 is one of the most studied phase I genes, and it contains
multiple copies of XRE but no ARE in its 5'-flanking region. The
activation of P450s by oltipraz may, on the one hand, help to transform some
types of carcinogens into nontoxic metabolites; on the other hand, however, it
could also generate more electrophilic metabolites, which consequently trigger
a secondary more broad activation of phase II detoxifying enzymes. It is also
possible that the activation of P450s results in metabolism of some
procarcinogens into active carcinogens and that this compromises oltipraz's
tumor prevention effect. This effect could ultimately be important if the
oltipraz clinical trials prove to be unsuccessful in chemoprevention. In any
event, it is evident that, given the common regulatory XRE pathway in both
phase I and II enzyme systems, more work is required to understand how the
effective balance between the two is maintained. Furthermore, our data suggest
that a simple distinction between phase I and II enzymes, and their definition
as antagonistic functions, may be an incomplete classification. Potent
chemopreventive agents, such as oltipraz, are clearly capable of activating
both systems, so that the search for selective phase II inducers should be
evaluated critically. Recently, it was reported that garlic extracts, which
have significant antitumorigenesis effects, activate P450s as well as GSTs
(Guyonnet et al., 2002),
suggesting another example of modulating both phase I and II enzymes to
enhance carcinogen detoxifications.
In conclusion, our work demonstrates that, in addition to ARE, XRE is another cis-acting element mediating oltipraz's transcriptional induction of rGSTA5 and other drug metabolizing enzymes. Oltipraz is a bifunctional inducer, which may exert its antitumorigenic effect by modulating both phase I and II detoxifying enzymes.
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Acknowledgements |
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Footnotes |
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ABBREVIATIONS: AFB1, aflatoxin B1; ARE, antioxidant responsive
element; EpRE, electrophile responsive element; QR, NAD(P)H:quinone reductase
(EC 1.6.5.5
[EC]
); -NF, -naphthoflavone; P450, cytochrome P450; AhR,
aryl hydrocarbon receptor; BHQ, tert-butyl hydroquinone; oligos,
oligonucleotides; XRE, xenobiotic responsive element; RT, room temperature;
ATCC, American Type Culture Collection; RT-PCR, reverse
transcriptase-polymerase chain reaction; GST, glutathione
S-transferase; Nrf2, NF-E2p45-related factor 2; OPZ, oltipraz; Eth,
ethoxyquin.
Address correspondence to: Dr. Gerald Batist, Montreal Center for Experimental Therapeutics in Cancer, Lady Davis Institute for Medical Research, The Sir Mortimer B Davis-Jewish General Hospital, 3755 Cote Sainte Catherine Road, Montreal, Quebec, Canada H3T 1E2. E-mail: gbatist{at}onc.jgh.mcgill.ca
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