Dy. Ryu et al., REGULATION OF HEPATIC CYP1A ISOZYMES BY PIPERONYL BUTOXIDE AND ACENAPHTHYLENE IN THE MOUSE, Chemico-biological interactions, 105(1), 1997, pp. 53-63
The regulation of CYP1A1 and CYP1A2 isozymes by piperonyl butoxide (PB
O) and acenaphthylene (ACN) was studied in the liver of male C57BL/6 a
nd DBA/2 mice. These two cytochrome P450 genes are known to be regulat
ed by the aromatic hydrocarbon-responsive receptor (AHR), however, it
has been suggested that CYP1A2 is also induced by an AHR-independent m
echanism. In this study, PBO induced hepatic CYP1A1 considerably more
in C57BL/6 (Ahr(b-1)) than in DBA/2 (Ahr(d)) mice. In addition, the su
perinduction of CYP1A1 in wildtype hepa1c1c7 cells, which is AHR-depen
dent, resulted from PBO and cycloheximide treatment of the cells, In o
ther studies in this laboratory using AHR knock-out (AHR(-/-)) mice, a
hybrid of 129/SV and C57BL/6 strains, no induction of CYP1A1 occurred
with PBO or ACN. [D.-Y. Ryu, P.E. Levi, P. Fernandez-Salguero, F.J. G
onzalez, E. Hodgson, Mol. Pharmacol., 50 (1996) 443-346.] ACN, however
, did not induce CYP1A1 tinder the experimental conditions used. These
results suggest that PBO, but not ACN, induces CYP1A1 through a weak
activation of AHR. On the other hand: hepatic CYP1A2 mRNA and hnRNA we
re induced by PBO in both C57BL/6 and DBA/2 strains, but were not indu
ced by ACN, a strong inducer of CYP1A2 in the B6C3F1 strain. However,
both PBO and ACN induced CYP1A2 in AHF(-/-) mice. It is assumed, there
fore, that the transcriptional induction of CYP1A2 by PBO and ACN is A
HR-independent. In addition,the induction of CYP1A2 by ACN depends upo
n the strain of mice. Immunohistochemical studies for CYP1A1/CYP1A2 ap
oproteins showed that PBO induced CYP1A1/CYP1A2 around the central vei
ns as did 3-methylcholanthrene (3-MC). The induction of CYP1A1/CYP1A2
by ACN, however, was not observed. consistent with the northern blot r
esults. (C) 1997 Elsevier Science Ireland Ltd.