Am. J. Respir. Cell Mol. Biol., Vol 11, No. 4, Oct 1994, 386-396.
Cell localization and regulation of expression of cytochrome P450 1A1 and 2B1 in rat lung after induction with 3-methylcholanthrene using mRNA hybridization and immunohistochemistry
JC Pairon, N Trabelsi, A Buard, J Fleury-Feith, CM Bachelet, F Poron, P Beaune, P Brochard and P Laurent
INSERM Unite 139, Hopital Henri Mondor, Creteil, France.
In order to characterize the response of various pulmonary cell types to
polycyclic aromatic hydrocarbons, the expression of cytochrome P450 (CYP)
1A1 and 2B1 mRNA in the lung of rats, with or without induction by
3-methylcholanthrene (3MC), was analyzed by in situ hybridization using
appropriate 35S-labeled riboprobes. The expression of the corresponding
proteins was investigated immunohistochemically. Following induction with
3MC, the kinetics of mRNA expression differed considerably between Clara
cells and type II pneumocytes and venous endothelial cells. In Clara cells,
mRNA expression was detected as early as 1 h after induction, peaked
between 2 and 4 h, and was completely undetectable at 14 h. In contrast,
venous endothelial cells and type II pneumocytes exhibited permanent mRNA
expression of CYP 1A1 in 3MC-pretreated rats. These kinetic results explain
the striking absence of correlation between mRNA and protein expression
observed in Clara cells 24 h after the end of the induction protocol, as
these cells exhibited intense protein expression with no mRNA. In contrast,
a good correlation was observed for mRNA and protein expression of CYP 2B1,
with similar expressions for Clara cells and type II pneumocytes, but no
expression in endothelial cells. This study clearly distinguished the
regulation of CYP 1A1 expression in the rat lung from that described in the
liver. The differences observed in the various lung cell types, whatever
the post-transcriptional mechanisms involved, emphasize that studies must
be performed at the cellular level in order to understand the specific
response to xenobiotics, not only of this organ as a whole but also of its
various anatomic structures.