Effects of beta-Estradiol and Bisphenol A on Heat Shock Protein Levels and Localization in the Mouse Uterus Are Antagonized by the Antiestrogen ICI 182,780

Abstract

Bisphenol A (BPA) exhibits many estrogen-like effects in the rodent uterus, but not all of these can be attenuated by antiestrogens. This suggests the involvement of alternate pathways of BPA action that do not involve the estrogen receptor (ER). An examination of the in vivo effects of BPA on uterine gene expression and protein levels should contribute to an understanding of its mechanism of action. In this study we examined the dose-related effects of BPA on levels of a suite of heat shock proteins (hsps) and on the localization of hsp90alpha, a chaperone of the ER, in uteri of ovariectomized B6C3F1 mice and compared these effects with those of beta-estradiol (E2). The antiestrogen ICI 182,780 (ICI) was co-administered with BPA or E2 in order to examine the potential role of the ER. BPA, although less potent than E2, increased hsp90alpha and grp94 to similar levels, but was much less effective than E2 in increasing levels of hsp72. Treatment with 100 mg BPA/kg/day or 2 microg E2/kg/day increased hsp90alpha to 300% of control levels and altered its tissue expression pattern. In uteri of corn oil (control)-treated mice, hsp90alpha predominantly localized in the cytoplasm and nuclei of epithelial cells. Upon treatment with BPA or E2 there was increased intensity of staining in the stroma and myometrium, and in the epithelium hsp90alpha was localized almost exclusively in the cytoplasm. The effects of BPA or E2 on hsp levels and hsp90alpha localization were attenuated by ICI. These results suggest an involvement of the ER in BPA- and E2-induced increases in uterine levels of hsp90alpha, grp94, and hsp72, and localization of hsp90alpha.

Increases in mouse uterine heat shock protein levels are a sensitive and specific response to uterotrophic agents.

“…MED induced a nonsignificant increase in hsp90α levels, decreased hsp72 levels, and had no effect on uterine weight. As in our previous study (Papaconstantinou et al 2001), the results of this study suggest a correlation between increases in hsp levels and uterine proliferation. This is not surprising, because several studies have shown that hsps can activate protein kinases and other cell-signaling proteins that stimulate cell proliferation and inhibit apoptosis (Kaur et al 2000;Mizuno et al 2001;Neckers et al 1999;Zhang et al 2001).…”

“…This argues for a role of the ER in the regulation of these genes in the uterus and is supported by our previous observations that E 2 and BPAinduced increases in hsp levels are antagonized by the ER antagonist ICI 182,780 (Papaconstantinou et al 2001). Whether ER agonists directly affect the transcriptional activity of theses hsp genes is uncertain.…”

“…The increase in grp94 levels induced by MXC 100 mg/kg/day, CM 10 mg/kg/day, or BPA 100 mg/kg/day was the same as that induced by E 2 2 µg/kg/day. The ability of BPA to be as efficacious as E 2 in increasing uterine grp94 levels has been shown previously (Papaconstantinou et al 2001).…”

“…Doses for E 2 and BPA were based on our previous observation of increases in uterine weight (Papaconstantinou et al 2000) and hsp levels (Papaconstantinou et al 2001). The doses for TAM (Carthew et al 1999b), DES (Farmakalides and Murphy 1984), DEX (Bigsby and Young 1993), MXC (Laws et al 2000), and CM (Tinwell et al 2000) were based on previous studies of uterotrophic effects.…”

“…We have previously shown that BPA resembles E 2 in its ability to induce increases in uterine heat shock protein (hsp) levels, mainly hsp90α and glucose-regulated protein (grp) 94 and, to a lesser extent, hsp72 (Papaconstantinou et al 2001). We also demonstrated that both E 2 and BPA increased levels of hsp90α and grp94 (Papaconstantinou et al 2001) at doses lower than those necessary for a significant increase in uterine weight (Papaconstantinou et al 2000). The use of hsps as biomarkers of environmental pertubation shows promise despite some criticisms (Bierkens 2000).…”