Modulation of Glucose-6-phosphate Dehydrogenase Activity and
Expression Is Associated with Aryl Hydrocarbon Resistance in
Vitro*
Grace Chao
Yeh
,
Phillip J.
Daschner,
Joanna
Lopaczynska,
Christopher J.
MacDonald, and
Henry P.
Ciolino
From the Cellular Defense and Carcinogenesis Section, Basic
Research Laboratory, NCI at Frederick, National Institutes of Health,
Frederick, Maryland 21702
The mutagenic effect of environmental
carcinogens has been well documented in animal models and in human
studies but the mechanisms involved in preventing carcinogen insult
have not been fully elucidated. In this study we examined the molecular
and biochemical changes associated with carcinogen resistance in a
series of aryl hydrocarbon-resistant MCF-7 cell lines developed by
exposure to benzo[a]pyrene (BP). The cell lines were
designated as AHR40, AHR100, and
AHR200 to denote their increasing fold resistance to BP
compared with wild type cells. These cell lines were also resistant to
another aryl hydrocarbon (AH), dimethylbenz[a]anthracene,
but not to pleiotropic drugs (doxorubicin, vinblastine, and taxol). The
resistant cell lines showed an increase in the level of the primary
intracellular antioxidant, reduced glutathione, corresponding to
increasing AH resistance. However, there was no change in glutathione
reductase activity. The generation of reduced glutathione requires
NADPH, and we therefore examined the activity and expression of the
rate-limiting enzyme in NADPH production, glucose-6-phosphate
dehydrogenase (G6PD). An increase in G6PD specific activity was
associated with increasing aryl hydrocarbon resistance. This was due to
an increased expression of G6PD in resistant cells, which was
demonstrated by increases in both protein and mRNA levels. However,
there was no increase in the transcription rate of G6PD in the
resistant cell lines, indicating that the increase G6PD expression is
due to a post-transcriptional modulation, which was confirmed by
actinomycin D chase experiments. These results demonstrate that
modulation of G6PD expression and activity is an important mechanism in
AH resistance.
*
This work was supported in part with Federal funds from the
NCI, National Institutes of Health, under contract number NO1-CO-56000.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.
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