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Vol. 280, Issue 1, 506-511, 1997
Department of Alcohol Research, National Public Health Institute,
Helsinki, Finland and
Department of Medical Biochemistry and
Biophysics, Karolinska Institutet, Stockholm, Sweden (I.J., M.I.-S.)
The aryl hydrocarbon receptor (AHR) is a transcriptional activator of
genes encoding a group of drug-metabolizing enzymes, including
cytochrome P450 1A1 (CYP1A1), glutathione
S-transferase, tumor-associated aldehyde dehydrogenase
and quinone reductase. Both the constitutive and inducible expression
of these genes in the liver is zonated, i.e., dominant
in hepatocytes of the centrilobular region, a poorly understood
position-dependent phenomenon. By comparing cell lysates obtained from
opposite acinar regions we observed that immunoreactive AHR protein was
almost exclusively confined to centrilobular cells. The AHR mRNA, as
analyzed from cell lysates by reverse transcriptase polymerase chain
reaction, exhibited a similar, although somewhat less pronounced
zonation. By contrast, only slight zonation of the AHR nuclear
translocator mRNA was observed. Treatment of rats with omeprazole, an
atypical nonligand activator of the AHR, caused a zone-specific
induction of CYP1A1 in the centrilobular region similar to that seen
after pretreatment with the AHR ligand 3-methylcholanthrene. Our
results suggest that the zone-restricted expression of AHR protein will allow the constitutive and inducible expression of AHR-regulated genes
in the centrilobular region, but will limit their expression in the
periportal region.
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