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Analysis of the effects of oestrogen receptor alpha (ERalpha)- and ERbeta-selective ligands given in combination to ovariectomized rats.

ABSTRACT: BACKGROUND AND PURPOSE: Studies with oestrogen receptoralpha (ERalpha)- and ERbeta-selective compounds have already shown that the effects of 17beta-estradiol (E2) on body weight, movement drive and bone-protection are mediated via ERalpha. This study was based on the hypothesis that activation of ERbeta may antagonize ERalpha-mediated effects and designed to investigate potential effects of ERalpha/ERbeta heterodimers. EXPERIMENTAL APPROACH: Ovariectomized (OVX) female Wistar rats were treated with combinations of the ERalpha-specific agonist 16alpha-LE2 (ALPHA; 1 and 10 microg kg(-1) d(-1)), the ERbeta-specific agonist 8beta-VE2 (BETA; 100 microg kg(-1) d(-1)), the phytoestrogen, genistein (10 mg kg(-1) d(-1)) and with the anti-oestrogen compound, ICI 182,780 (3 mg kg(-1) d(-1)) for three weeks. The combined effects of the substances on body weight increase, tibial bone mineral density (BMD) and the influence on running wheel activity (RWA) were investigated. KEY RESULTS: OVX-induced body weight increase was reduced by co-administration of genistein and BETA. Co-application of BETA or genistein with ALPHA had no effect on ALPHA-mediated bone-protection. The RWA of OVX animals was significantly reduced by treatment with genistein but stimulated by application of ALPHA. The stimulatory effect of ALPHA on RWA could be antagonized by co-treatment with the pure antioestrogen ICI 182,780 but also by co-administration of genistein or BETA. CONCLUSIONS AND IMPLICATIONS: Our results indicate that activation of ERbeta may modulate ERalpha-mediated physiological effects in vivo. The observation that substances with selective affinity for ERbeta are able to antagonize distinct physiological functions, like RWA, may be of great relevance to the pharmaceutical use of such drugs.

SUBMITTER: Hertrampf T

PROVIDER: S-EPMC2437917 | biostudies-other | 2008 Apr

REPOSITORIES: biostudies-other

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Project description:BackgroundEndometrial cancer is the most common gynaecological malignancy; risk factors include exposure to oestrogens and high body mass index. Expression of enzymes involved in biosynthesis of oestrogens and prostaglandins (PG) is often higher in endometrial cancers when compared with levels detected in normal endometrium. Oestrogens bind one of two receptors (ERalpha and ERbeta) encoded by separate genes. The full-length receptors function as ligand-activated transcription factors; splice variant isoforms of ERbeta lacking a ligand-binding domain have also been described. PGs act in an autocrine or paracrine manner by binding to specific G-protein coupled receptors.MethodsWe compared expression of ERs, progesterone receptor (PR) and cyclooxygenase-2 (COX-2) in stage 1 endometrial adenocarcinomas graded as well (G1), moderately (G2) or poorly (G3) differentiated (n >or= 10 each group) using qRTPCR, single and double immunohistochemistry. We used endometrial adenocarcinoma cell lines to investigate the impact of PGF2alpha on expression of ERs and PR.ResultsFull length ERbeta (ERbeta1) and two ERbeta variants (ERbeta2, ERbeta5) were expressed in endometrial cancers regardless of grade and the proteins were immunolocalised to the nuclei of cells in both epithelial and stromal compartments. Immunoexpression of COX-2 was most intense in cells that were ERalphaneg/low. Expression of PR in endometrial adenocarcinoma (Ishikawa) cell lines and tissues broadly paralleled that of ERalpha. Treatment of adenocarcinoma cells with PGF2alpha reduced expression of ERalpha but had no impact on ERbeta1. Cells incubated with PGF2alpha were unable to increase expression of PR mRNA when they were incubated with E2.ConclusionWe have demonstrated that ERbeta5 protein is expressed in stage 1 endometrial adenocarcinomas. Expression of three ERbeta variants, including the full-length protein is not grade-dependent and most cells in poorly differentiated cancers are ERbetapos/ERalphaneg. We found evidence of a link between COX-2, its product PGF2alpha, and expression of ERalpha and PR that sheds new light on the cross talk between steroid and PG signalling pathways in this disease.

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Analysis of the effects of oestrogen receptor alpha (ERalpha)- and ERbeta-selective ligands given in combination to ovariectomized rats.

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