Upregulation of estrogen receptor expression in the uterus of ovariectomized B6C3F1 mice and Ishikawa cells treated with bromoethane

Abstract

In a 2-year NTP bioassay, Bromoethane (BE) was found to induce endometrial neoplasms in the uterus of B6C3F1 mice [ National Toxicology Program, 1989. Toxicology and Carcinogenesis Studies of Bromoethane (Ethyl Bromide) in F344/N Rats and B6C3F1 Mice. TR No. 363, U.S. Department of Health and Human Services, Public Health Service, National Institutes of Health, ResearchTriangle Park, NC; Picut, C.A., Aoyama, H., Holder, J.W., Gold, L.S., Maronpot, R.R., Dixon, D., 2003. Bromoethane, chloroethane and ethylene oxide induced uterine neoplasms in B6C3F1 mice from 2-year NTP inhalation bioassays: pathology and incidence data revisited. Exp. Toxicol. Pathol. 55, 1–9]. In women, hormonal influences, such as “unopposed” estrogenic stimulus, have been implicated as important etiologic factors in uterine cancer. BE, however, does not affect the serum concentrations of sex hormones in female B6C3F1 mice [ Bucher, J.R., Morgan, D.L., Adkins Jr., B., Travlos, G.S., Davis, B.J., Morris, R., Elwell, M.R., 1995. Early changes in sex hormones are not evident in mice exposed to the uterine carcinogens chloroethane or bromoethane. Toxicol. Appl. Pharmacol. 130, 169–173] and the mechanism of BE-induced uterine carcinogenesis still remains unclear. In the present study, we examined the estrogenic effects of BE on the uterus of ovariectomized B6C3F1 mice and on Ishikawa cells. Groups of 6 mice were given daily s.c. injections of 0, 100, 500 or 1000 mg BE/kg for 3 consecutive days. Mice treated with 17β-estradiol served as positive controls. Mice were necropsied 24 h after the final injection, and uteri were weighed and examined histologically and immunohistochemically along with the vagina. Changes observed in the estrogen-treated mice included increased uterine weights, edema and inflammation of the endometrium, increased epithelial layers of the uterine and vaginal lumens and keratinization of the vaginal epithelium. In the BE-treated mice, no such changes occurred; however, immunohistochemical staining of the uterus revealed a significant increase in immunoexpression of the estrogen receptor alpha (ERα) in the two higher dose groups. Analysis of mRNA also showed slightly increased uterine ERα expression in these groups. Upregulated expression of ERα was confirmed in BE-treated Ishikawa cells, in which Western blotting analyses identified an intense signal at approximately 66 kDa, which is consistent with ERα. These data suggest that upregulated expression of ERα may be important in the induction of endometrial neoplasms in BE-treated mice.