Morphology of differentiating SCp2 cells exposed to TCDD. Photomicrographs of SCp2 cells, induced to differentiate and exposed to vehicle (0.1% DMSO) or TCDD (1 nM), were taken at 24h and 8d after plating. Reduced alveolar-like structure formation is observed after TCDD exposure. Images of the 8d cultures were obtained using both low (20X) and high (40X) magnification objective lenses. h, hours; d, days.

Levels of STAT5 phosphorylation in TCDD-exposed mammary glands during pregnancy. Expression of pSTAT5 is reduced in the mammary gland at day 17 of pregnancy, while expression of total STAT5 is unchanged, after exposure to TCDD (A). The bar graphs (B and C) depict results of densitometric analysis. Data represent mean ± SEM (n=3-4; *p<0.05 compared to vehicle control). Mammary gland: VEH (peanut oil), TCDD (5 μg/kg). Results are representative of two independent experiments.

E-cadherin levels following TCDD exposure both in vivo and in vitro. Expression of E-cadherin protein is reduced in the mammary gland at day 17 of pregnancy (A) and in differentiated SCp2 cells (C) after exposure to TCDD. The bar graphs (B and D) depict results of densitometric analysis. Data represent mean ± SEM (n=3-4); p-values indicate comparison to vehicle control. Mammary gland: VEH (peanut oil), TCDD (5 μg/kg). SCp2 Cells: VEH (0.1% DMSO), TCDD (1 nM). Results are representative of at least two independent experiments.

β-casein protein expression following TCDD exposure both in vivo and in vitro. Induction of β-casein is reduced in the mammary gland at day 17 of pregnancy (A) and in differentiated SCp2 cells (C) after exposure to TCDD. The bar graphs (B and D) depict results of densitometric analysis. Data represent mean ± SEM (n=3-4; *p<0.05 compared to vehicle control). Mammary gland: VEH (peanut oil), TCDD (5 μg/kg). SCp2 Cells: VEH (0.1% DMSO), TCDD (1 nM). Delayed addition of TCDD to SCp2 cell cultures reduced effects of TCDD on the suppression of β-casein induction (E and F). Data represent mean ± SEM (n=2; p<0.01, a vs b and a vs c; p<0.05, b vs c). h, hours; t_0h, t_24h, t_48hindicate the time of first exposure to TCDD. Results are representative of at least two independent experiments.

AhR and CYP1B1 expression in mammary tissue and SCp2 cells following TCDD exposure. AhR protein expression is evident in the day of pregnancy (DP) 17 mammary gland (A) and in differentiated SCp2 cells (B), with reduced expression following exposure to TCDD. SCp2 cells analyzed 24h after exposure to TCDD show increased expression CYP1B1 protein (C). Cyp1a1 and cyp1b1 gene expression is induced in mammary glands from both virgin and pregnant mice exposed to TCDD (D). Age-matched virgin mice (n=2/group) were treated with two doses of vehicle or TCDD administered 9 and 2 days prior to sacrifice. Impregnated mice were treated with vehicle or TCDD (n=3/group) on DP0 and DP7, and glands were collected for analysis on DP9. The graph depicts the average fold-change in gene expression in TCDD-exposed mammary glands relative to mammary glands from vehicle-treated control virgins or DP9 dams (expression in TCDD sample/expression in VEH sample). Statistical comparisons were made using original expression data, and mean gene expression was significantly different between vehicle-treated and TCDD-treated mammary glands in both virgin and DP9 groups (p<0.05). Mammary gland: VEH (peanut oil), TCDD (5 μg/kg). SCp2 Cells: VEH (0.1% DMSO), TCDD (1 nM).