The agonist activity of tamoxifen is inhibited by the short heterodimer partner orphan nuclear receptor in human endometrial cancer cells.

Short heterodimer partner (SHP) is an orphan nuclear receptor that interacts with ER(alpha) and ERbeta and inhibits E2-induced transcription. We examined how SHP affects tamoxifen's estrogen agonist activity in endometrial cells. We report that SHP interacts with 4-hydroxytamoxifen (4-OHT) or E2-occupied ER(alpha) in a temperature-dependent manner in vitro. In transient transfection assays, SHP inhibited 4-OHT-stimulated reporter gene activity from an estrogen response element (ERE) in ER-positive RL95-2 but not in HEC-1A human endometrial carcinoma cells transfected with ER(alpha) or ERbeta. SHP inhibited E2-induced transcriptional activity in ER(alpha)- or ERbeta-transfected HEC-1A or Chinese hamster ovary-K1 cells. SHP inhibition of E2 activity was greater for ER(alpha) than ERbeta from the nonpalindromic ERE in the pS2 gene promoter in Chinese hamster ovary-K1 but not HEC-1A cells. Thus, ER subtype, cell type, and ERE sequence influence SHP repressor activity. An ER(alpha) mutant lacking activator function-1 showed reduced inhibition by SHP. In glutathione S-transferase pull-down experiments, SHP inhibited ER(alpha) dimerization, providing a possible mechanism to account for the inhibitory effect of SHP on ER activity. These results identify SHP as novel target for blocking 4-OHT agonist activity in endometrial cells.

Estrogen receptor beta isoforms exhibit differences in ligand-activated transcriptional activity in an estrogen response element sequence-dependent manner.

Estrogen receptor beta (ERbeta) has been reported to have lower estradiol (E2)-induced transcriptional activity than human (h)ERalpha from estrogen response element (ERE)-driven reporters in transiently transfected cells. Conflicting data for activities of full-length and short hERbeta [hERbeta1, 530 amino acids (aa); and hERbeta1s, 477aa] have been reported. To test the hypothesis that hERbeta1 has higher transcriptional activity than hERbeta1s, we compared E2, 2,3-bis(4-hydroxyphenyl)propionitrile (a selective ERbeta agonist), and resveratrol-induced transcription by hERbeta1, hERbeta1s, and rat (r) ERbeta with hERalpha on different EREs in transiently transfected CHO-K1 and HEC-1A cells. Our results demonstrate for the first time that hERbeta1 has similar E2-induced activity to hERalpha and greater activity than rERbeta or hERbeta1s on a consensus palindromic ERE, either as a single or double copy; a minimal ERE; and the nonpalindromic pS2 ERE. 2,3-Bis(4-hydroxyphenyl)propionitrile showed greater efficacy with hERbeta1 and hERbeta1s than for rERbeta or hERalpha. We found that transcriptional differences between the ERbeta isoforms and ERalpha depend on the ERE sequence, confirming that the DNA sequence bound by ER is an allosteric effector of ER action. For the minimal 13-bp ERE and the pS2 ERE, the increase in transcriptional activity with hERbeta1 correlated with increased binding affinity. Coactivators steroid receptor coactivator-1 and cAMP response element binding protein-binding protein synergistically activated hERalpha and ERbeta transcription and showed reduced efficacy with rERbeta and hERbeta1s, suggesting a role for the N terminus of ERbeta1 in coactivator interaction. Collectively, these data indicate that the cellular expression of ERbeta isoforms may differentially impact ERE-regulated target gene expression in a ligand-dependent manner.

Identification of estrogen receptor beta expression in Chinese hamster ovary (CHO) cells and comparison of estrogen-responsive gene transcription in cells adapted to serum-free media.

Most cultured cell lines require addition of serum to the medium to maintain their proliferative capacity. For studies examining the cellular effects of estrogens serum is charcoal-stripped to remove steroids. Nonetheless, addition of the selective estrogen receptor modulator (SERM) 4-hydroxytamoxifen (4-OHT) inhibits the basal transcriptional activity of estrogen receptors alpha or beta (ERalpha or ERbeta) in transfected cells. We tested the hypothesis that elimination of serum from the culture medium will block 4-OHT's repression of basal activity. Chinese hamster ovary (CHO-K1) cells adapted to serum-free medium exhibited estrogen responsiveness that was identical with that of the cells grown in serum-containing media. 4-OHT-suppressed basal transcription of an estrogen response element (ERE)-reporter in ERalpha-transfected cells even in the absence of serum, indicating that the 4-OHT suppressive activity is not mediated by blocking ER interaction with serum estrogens. We speculate that 4-OHT-ER recruits co-repressors to suppress basal transcription. We discovered that CHO-K1 cells express ERalpha and ERbeta mRNA. However only ERbeta protein was expressed and use of ERbeta-selective 2,3-bis(4-hydroxy-phenyl)propionitrile (DPN) and ERalpha-selective 4-propyl-1,3,5-tris(4-hydroxy-phenyl)pyrazole) (PPT) revealed that only ERbeta was transcriptionally active. In conclusion, growing CHO-K1 in serum-free medium does not impact the estrogen responsiveness and this cell line expresses functional ERbeta.

Estrogenic activity in white and red wine extracts.

Red wine is enriched in resveratrol, trans-3,5,4'-trihydroxystilbene, a compound in grape skin that inhibits the development of pre-neoplastic lesions in mouse mammary tumor cells in culture and inhibits cancer cell proliferation in vitro. Grapes also contain other bioactive compounds including flavonoids, flavans, and anthocyanins. The estrogenic activities of extracts prepared from one white (Freie Weingärtner Wachau, Grüner Veltliner, Austria) and two red wines (Woodbridge, Cabernet Sauvignon, California; and Lenz Moser Prestige, Blaufränkisch Barrique, Austria) were examined and compared with those induced by estradiol (E(2)) and trans-resveratrol. First, the estrogenic activity of the wine extracts was evaluated in a yeast estrogen screen (YES) assay, in which yeast express copper-inducible estrogen receptor alpha (ERalpha) and an estrogen-response-element (ERE)-driven beta-galactosidase reporter. In YES, the white wine extract showed no estrogenic activity. In contrast, both of the red wine extracts showed estrogenic activity equivalent to that of 0.2 nM E(2). Similarly, the white wine extract showed no transcriptional activity with either ERalpha and ERbeta in transiently transfected CHO-K1 cells. In contrast, both red wine extracts stimulated ERE-reporter activity in a concentration-dependent manner that was inhibited by 4-hydroxytamoxifen (4-OHT), indicating that the observed transcriptional activity was ER-mediated. The red wine extracts showed significantly higher ERbeta versus ERalpha agonist activity. Resveratrol showed no agonist activity in YES but activated ERalpha and ERbeta in CHO-K1 cells in a concentration-dependent manner that was inhibited by 4-OHT. This indicates that resveratrol requires mammalian cell components that are absent in yeast for estrogen agonist activity, whereas the estrogenic activity of wine extracts is directly through ERalpha and does not require mammalian cell factors such as coactivators. The estrogenic activity in red wine found by using YES indicates that estrogenic compounds other than resveratrol are present. Chemical analysis clearly showed that the trans-resveratrol content of the red wine extracts was 1 order of magnitude below the detection limit for YES assay.

Resveratrol and estradiol rapidly activate MAPK signaling through estrogen receptors alpha and beta in endothelial cells.

Vascular endothelial cells (EC) are an important target of estrogen action through both the classical genomic (i.e. nuclear-initiated) activities of estrogen receptors alpha and beta (ERalpha and ERbeta) and the rapid "non-genomic" (i.e. membrane-initiated) activation of ER that stimulates intracellular phosphorylation pathways. We tested the hypothesis that the red wine polyphenol trans-resveratrol activates MAPK signaling via rapid ER activation in bovine aortic EC, human umbilical vein EC, and human microvascular EC. We report that bovine aortic EC, human umbilical vein EC, and human microvascular EC express ERalpha and ERbeta. We demonstrate that resveratrol and estradiol (E(2)) rapidly activated MAPK in a MEK-1, Src, matrix metalloproteinase, and epidermal growth factor receptor-dependent manner. Importantly, resveratrol activated MAPK and endothelial nitric-oxide synthase (eNOS) at nm concentrations (i.e. an order of magnitude less than that required for ER genomic activity) and concentrations possibly achieved transiently in serum following oral red wine consumption. Co-treatment with ER antagonists ICI 182,780 or 4-hydroxytamoxifen blocked resveratrol- or E(2)-induced MAPK and eNOS activation, indicating ER dependence. We demonstrate for the first time that ERalpha-and ERbeta-selective agonists propylpyrazole triol and diarylpropionitrile, respectively, stimulate MAPK and eNOS activity. A red but not a white wine extract also activated MAPK, and activity was directly correlated with the resveratrol concentration. These data suggest that ER may play a role in the rapid effects of resveratrol in EC and that some of the atheroprotective effects of resveratrol may be mediated through rapid activation of ER signaling in EC.