Benzo(a)pyrene, but not 2,3,7,8-tetrachlorodibenzo-p-dioxin, alters cell proliferation and c-myc and growth factor expression in human placental choriocarcinoma JEG-3 cells.

This study compared the effects of benzo(a)pyrene (BaP) and 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD), two aryl hydrocarbon receptor (AhR) agonists, on proliferation and gene expression in the human placental choriocarcinoma JEG-3 cell line. BaP significantly inhibited [3H]thymidine incorporation, whereas no effect of TCDD was observed over a 7 day period. TCDD and BaP both showed induction of cytochrome P450 1A1 (CYP1A1), whereas only BaP caused a significant loss of EGFRs. Exposure to 10 microM BaP significantly increased the steady state mRNA level of transforming growth factor (TGF)-beta 1, while the c-myc mRNA levels were decreased by 61%. In contrast, TCDD showed no changes in mRNA levels for TGF-beta 1 and c-myc. Thus, although both compounds induce CYP1A1, only BaP inhibits cell proliferation which is correlated with disruption of expression of significant regulators of trophoblast growth.