The Journal of Cell Biology, Vol 101, 2245-2252, Copyright © 1985 by The Rockefeller University Press
Mechanism of benzo(a)pyrene induction of alpha-human chorionic gonadotropin gene expression in human lung tumor cells
DT Wong and DK Biswas
Human lung cells (ChaGo) derived from a bronchogenic carcinoma synthesize
and secrete in the culture medium the alpha subunit of the glycoprotein
hormone, human chorionic gonadotropin (alpha-hCG). The synthesis of
alpha-hCG by ChaGo cells could be further stimulated by treatment with
sublethal concentrations of the polycyclic aromatic hydrocarbons (PAHs),
benzo(a)pyrene (BaP), or dimethylbenzanthracene. The production of
alpha-hCG could be correlated to the levels of alpha- hCG-specific mRNA
sequences in control and PAH-treated cells. Further analysis of the RNA
species (Northern blot) revealed that the level of the mature
(approximately 1.0 kb) and the high molecular weight alpha- hCG specific
nuclear RNA sequences (approximately 2.2 and 5 kb) were all greater in
PAH-treated cells. Addition of [3H]BaP (0.25 microgram/ml) in the culture
medium of ChaGo cells led to immediate uptake of the radioactive compound
apparently by simple diffusion. SDS PAGE and subsequent fluorography
revealed that the radioactive compound interacted and formed covalent
complexes with cytoplasmic and nuclear proteins. This covalent interaction
of the [3H]BaP molecule with cellular proteins could be significantly
inhibited by either inhibiting the activity of the enzyme aryl hydrocarbon
hydroxylase with 7,8- benzoflavone or by reducing the cellular
concentration of the enzyme by simultaneous incubation with cycloheximide.
These results suggested that in ChaGo cells, the observed covalent
complexes were formed by the interaction of the BaP metabolites with
cellular proteins. The concentrations at which 7,8-benzoflavone or
cycloheximide inhibited formation of metabolites from [3H]BaP and their
covalent interaction with cell protein did not affect the BaP-induced
stimulation of alpha- hCG gene expression. However, the cytotoxic effects
of BaP in ChaGo cells seemed to be exerted by the metabolism of the
compounds. Results presented in this report suggest that BaP metabolism and
the interaction of the metabolites with cell proteins were not essential
for the BaP-induced modulation of alpha-hCG gene expression.
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