title: Effects of estriol on growth, gene expression and estrogen response element activation in human breast cancer cell lines.
abstract: OBJECTIVE
  Local application of estradiol (E2) to treat vulvovaginal atrophy in postmenopausal breast cancer patients receiving aromatase inhibitors is known to elevate serum estradiol levels and thereby might counteract breast cancer therapy. Thus, vaginal application of estriol (E3) has been recommended for these patients. However, it is unclear to what extent E3 stimulates breast cancer cell growth. In this study, we examined the effect of E3 on growth and gene expression of two human breast cancer cell lines.
  
  
  METHODS
  We used an established in vitro cell culture assay and compared the effect of E2 and E3 on growth of the estrogen receptor alpha-positive breast cancer cell lines MCF-7 and T-47D testing a wide range of hormone concentrations of 10(-12)-10(-7)M. E3 effects on gene expression were examined by means of reporter gene assays, RT-qPCR and Western blot analysis.
  
  
  RESULTS
  E3 acted as a potent estrogen and exerted a mitogenic effect on T-47D and MCF-7 cells at concentrations of 10(-9)M (288 pg/ml) and higher. With regard to activation of an estrogen response element (ERE) in breast cancer cells, effects of E3 were visible at 10(-10)M. The same concentrations of E3 activated expression of the estrogen-responsive gene PR and of the proliferation genes cyclin A2, cyclin B1, Ki-67, c-myc and b-myb, providing molecular mechanisms underlying the observed growth increase.
  
  
  CONCLUSIONS
  Like E2, low levels of E3 were able to trigger a robust estrogenic response in breast cancer cells. Thus, our data suggest caution regarding use of E3 by breast cancer survivors.
authors: Department of Obstetrics and Gynecology, University Medical Center Regensburg, Landshuter Str. 65, 93053 Regensburg, Germany.
authors: Magnus
authors: M
authors: Diller
authors: Department of Obstetrics and Gynecology, University Medical Center Regensburg, Landshuter Str. 65, 93053 Regensburg, Germany.
authors: Susanne
authors: S
authors: Schüler
authors: Department of Obstetrics and Gynecology, University Medical Center Regensburg, Landshuter Str. 65, 93053 Regensburg, Germany.
authors: Stefan
authors: S
authors: Buchholz
authors: Department of Obstetrics and Gynecology, University Medical Center Regensburg, Landshuter Str. 65, 93053 Regensburg, Germany.
authors: Claus
authors: C
authors: Lattrich
authors: Department of Obstetrics and Gynecology, University Medical Center Regensburg, Landshuter Str. 65, 93053 Regensburg, Germany. Electronic address: otreeck@caritasstjosef.de.
authors: Oliver
authors: O
authors: Treeck
authors: Department of Obstetrics and Gynecology, University Medical Center Regensburg, Landshuter Str. 65, 93053 Regensburg, Germany.
authors: Olaf
authors: O
authors: Ortmann
mesh_terms: D001943:Breast Neoplasms / Q000235:genetics* / Q000378:metabolism / Q000473:pathology*; D045744:Cell Line, Tumor; D049109:Cell Proliferation / Q000187:drug effects; D056751:Cyclin A2 / Q000235:genetics; D056744:Cyclin B1 / Q000235:genetics; D004964:Estriol / Q000008:administration & dosage / Q000494:pharmacology*; D047628:Estrogen Receptor alpha / Q000235:genetics* / Q000378:metabolism; D005260:Female; D015972:Gene Expression Regulation, Neoplastic / Q000187:drug effects*; D006801:Humans; D019394:Ki-67 Antigen / Q000235:genetics; D020598:Proto-Oncogene Proteins c-myb / Q000235:genetics; D016271:Proto-Oncogene Proteins c-myc / Q000235:genetics; D012313:RNA / Q000737:chemistry / Q000235:genetics; D060888:Real-Time Polymerase Chain Reaction; D011980:Receptors, Progesterone / Q000235:genetics; D020218:Response Elements / Q000187:drug effects
chemical_list: D056751:Cyclin A2; D056744:Cyclin B1; C506487:ESR1 protein, human; D047628:Estrogen Receptor alpha; D019394:Ki-67 Antigen; C489427:MYC protein, human; D020598:Proto-Oncogene Proteins c-myb; D016271:Proto-Oncogene Proteins c-myc; D011980:Receptors, Progesterone; D012313:RNA; D004964:Estriol
keywords: Breast cancer; Estradiol; Estriol; Growth