Background: Epidemiological data indicate that in females cigarette smoking
exerts antiestrogenic effects that manifest clinically in an increased inc
idence of osteoporosis, earlier menopause, increased spot bleeding, and dec
reased risk of endometrial cancer for female smokers. The molecular mechani
sm of this effect is unclear; however, decreased serum estrogen levels in f
emale smokers have been correlated with increased concentrations of the met
abolite 2-hydroxyestrogen in females who smoke. Induction of estrogen metab
olizing enzymes, CYP1A1 and 1A2, is one mechanism by which increased 2-hydr
oxyestrogen concentrations may occur. It has also been suggested that the e
strogen receptor (ER) may contribute to this anti-estrogenic effect by bind
ing to antagonist(s) in cigarette smoke. Methods: Gel retardation analysis
was employed to determine if diluted mainstream cigarette smoke condensates
(DMCSCs) could activate the aryl hydrocarbon receptor (AhR). AhR-regulated
ethoxyresorufin-O-deethylase (EROD) activity and dioxin response element (
DRE)-mediated luciferase induction were assessed in Hepa1c1c7 mouse hepatom
a cells. A competitive ligand binding assay was utilized to determine if DM
CSCs could bind to the ER. ER-dependent luciferase activity was assessed in
MCF-7 cells. Results: In gel retardation assays, DMCSCs induced a protein-
DNA complex when incubated with a radiolabeled wild-type DRE oligonucleotid
e. The complex was effectively competed by excess unlabeled DRE but not by
excess unlabeled mutant DRE. In Hepa1c1c7 mouse hepatoma cells transiently
transfected with a DRE-regulated luciferase reporter gene, pGudluc1.1, trea
tment with DMCSCs resulted in a 23- and 25-fold increase in luciferase acti
vity (P<0.01) and an 8.5- and 10.5-fold (P<0.01) induction in EROD activity
, respectively. DMCSCs completely displaced bound tritiated E2 from the ER
in a dose-dependent manner and induced ER-regulated luciferase activity sig
nificantly 6-fold (P<0.01),representing 86% of the maximal induction observ
ed with E2. Conclusions: DMCSCs can bind to and transcriptionally activate
the AhR and ER nuclear receptors and cause induction of DRE- and ER-regulat
ed genes. Further study is required to identify the specific compound(s) re
sponsible for these activities. (C) 1999 Academic Press.