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Dioxin inhibition of estrogen-induced mouse uterine epithelial mitogenesis involves changes in cyclin and
David L Buchanan1, Seiichiro Ohsako, Chiharu Tohyama
1Center for Integrative Bioscience, Okazaki National Research Institutes, Okazaki, Aichi 444-8585, Japan. buchanal@nieyhs.nih.gov
Abstract:
A single dose of dioxin (2,3,7,8-tetrachlorodibenzo-p-dioxin or TCDD; 5 microg/kg, ip) inhibits 17beta-estradiol (E2)-induced uterine epithelial mitogenesis, apparently through disruption of stromal-epithelial interactions. To understand if TCDD alters early uterine (Ut) responses to E2, young adult C57BL/6J mice were ovariectomized and given (i.p.) either oil or 5 microg/kg TCDD. After 24 h, TCDD-treated mice received E2, and oil-treated mice were given E2 or oil. Body and Ut weights were collected 6 and 18 h later. Ut were flash-frozen at 6 h. E2 increased Ut weight (p < 0.0001) and Ut/body weight ratio (p < 0.0001), compared to mice given oil alone. Ut cyclin expression was assessed by an RNase protection assay. E2 increased mRNA expression for cyclin A2 and B1 (p < 0.05), in addition to D1, D2, and D3 (p < 0.001), while cyclin C was unchanged from oil controls and cyclins A1 and B2 were undetectable. In contrast, TCDD completely abolished E2-induced cyclin A2, which has been associated with S phase initiation, and reduced B1 and D2 (p < 0.05). Interestingly, TCDD did not alter E2-induced Ut weight increases at 6 h, but inhibited E2-induced Ut weight gain at 18 h. A 10-microg/kg TCDD dose was necessary for attenuation of the early E2-induced Ut weight increases (p < 0.01). Since TGF-beta regulates cyclins, Ut TGF-beta was also assessed in TCDD + E2-treated and control mice. TGF-beta mRNA levels were increased after TCDD compared to E2 alone (p < 0.01), suggesting a possible mechanism for TCDD inhibition of Ut cyclin A2. Thus, TCDD alters specific E2-regulated Ut G(1) phase activities and may inhibit E2-induced Ut epithelial mitogenesis by disrupting specific cell signaling mechanisms necessary for S phase initiation in vivo.
Insights
Dioxin (TCDD) exposure disrupts early uterine responses to estrogen (E2), inhibiting cell proliferation and altering gene expression. This suggests TCDD interferes with key signaling pathways essential for uterine growth.
Area of Science:
- Endocrinology
- Toxicology
- Molecular Biology
Background:
- 17beta-estradiol (E2) is crucial for uterine epithelial cell proliferation.
- Dioxins, such as 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD), are environmental pollutants with known endocrine-disrupting effects.
- Stromal-epithelial interactions are vital for E2-induced uterine responses.
Purpose of the Study:
- To investigate the impact of TCDD on early uterine responses to E2 in mice.
- To determine if TCDD alters E2-induced uterine weight gain and cyclin gene expression.
- To explore the potential role of TGF-beta in TCDD's effects on uterine cells.
Main Methods:
- Ovariectomized C57BL/6J mice were treated with TCDD or oil, followed by E2 administration.
- Uterine and body weights were measured at 6 and 18 hours post-E2 treatment.
- Uterine cyclin and TGF-beta mRNA expression were analyzed using RNase protection assays.
Main Results:
- E2 significantly increased uterine weight and uterine/body weight ratio.
- TCDD abolished E2-induced cyclin A2 expression and reduced cyclin B1 and D2 expression.
- TCDD inhibited E2-induced uterine weight gain at 18 hours, but not at 6 hours, requiring a higher TCDD dose for early effects.
- TCDD treatment increased uterine TGF-beta mRNA levels compared to E2 alone.
Conclusions:
- TCDD significantly alters E2-regulated uterine gene expression, particularly cyclins involved in cell cycle progression.
- TCDD may inhibit E2-induced uterine epithelial mitogenesis by disrupting cell signaling pathways necessary for S phase initiation.
- TGF-beta may play a role in TCDD's inhibitory effects on uterine cyclin A2 expression.