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Early-life estrogen exposure and uterine pathogenesis: ?A model for gene-environment interactions
Citation:
Suen, A. AND C. Wood. Early-life estrogen exposure and uterine pathogenesis: ?A model for gene-environment interactions. NIEHS Reproductive and Developmental Biology Laboratory Seminar, Durham, NC, February 16, 2018.
Impact/Purpose:
Early-life exposure to estrogenic chemicals in the environment has been associated with increased susceptibility to cancer and other adverse reproductive health outcomes later in life. Biological pathways driving these effects are still largely unknown. This case study investigated the role of a developmental protein called SIX1 as a molecular driver and biomarker of latent estrogenic effects in a mouse model of early-life estrogen exposure. The ultimate goal of this work is to enable more rapid identification of AOPs for cancer incorporating life stage susceptibility.
Description:
Aberrant cellular differentiation early in life can contribute to increased cancer risk later in life. In a classic model of this effect, female mice exposed on postnatal day (PND) 1-5 to the synthetic estrogen diethylstilbestrol (DES) have a high incidence of uterine carcinoma. These cancers are associated with an abnormal population of uterine basal cells that represent the earliest and most prominent precursor lesion. Sine oculis homeobox 1 (SIX1) is an oncoprotein that is persistently upregulated in the uteri of mice following neonatal DES exposure and localizes to uterine basal cells within all neoplastic lesions. We hypothesize that SIX1 is necessary for uterine basal cell differentiation and carcinogenesis following neonatal DES exposure. To test this hypothesis, a conditional knockout mouse model was generated in which floxed Six1 was excised in the uterus using the PgR-cre transgene. Ablation of uterine SIX1 was confirmed by real time RT-PCR and immunoblotting on PND5 and in adults. Uterine morphology and glandular development was normal following SIX1 deletion. At 12 months of age, uterine carcinoma was observed in 9/11 (81%) DES-exposed wildtype (DES-Six1+/+) mice and 9/12 (75%) DES-exposed SIX1 knockout (DES-Six1d/d) mice but not in controls, indicating that SIX1 is not required for DES-induced uterine carcinogenesis. However, DES-Six1d/d mice exhibited distinct differences in cellular differentiation. Abnormal basal cells expressing Keratin 14 (K14) were present throughout the uterine body and horns of DES-Six1+/+ mice but were absent in the uterine horns of the DES-Six1d/d mice. Quantitative image analysis indicated a >10-fold decrease in K14 labeling in the uterine horns of DES-Six1d/d mice compared to DES-Six1+/+ mice, but was similar to controls. Microarray analysis revealed 470 differentially expressed genes (P<0.05, 1.5-fold, Intensity Cutoff ≤ 100) between uteri from DES-Six1+/+ and DESSix1d/d mice, suggesting that DES-induced SIX1 expression contributes to altered gene expression. Furthermore, several basal cell-related genes, including P63, Krt5, Krt14, and Krt15, were downregulated in DES-Six1d/d mice, consistent with morphologic changes. These data indicate that SIX1 acts as a key cellular differentiation factor following early-life estrogen exposure. This abstract does not reflect U.S. EPA policy.