title: Phenotypic changes in MCF-7 cells during prolonged exposure to tamoxifen.
abstract: MCF-7 breast tumor cells form multicellular nodules (foci) over a confluent monolayer in an estradiol (E2)-dependent, antiestrogen-sensitive reaction. A cell line cloned from MCF-7 that displays these phenotypes was probed to determine the effects of long term exposure to tamoxifen on the growth of foci, estrogen receptor alpha (ERalpha) status, and gene responsiveness to E2. In one of two experiments, a heterogeneous cell population emerged (TMX2) that over-expressed estrogen receptor alpha wild type mRNA (ERalpha mRNA) (approximately 20-fold) missing exon 3 (ERDelta3 mRNA) and its corresponding protein (ERDelta3P). On a per mRNA to protein basis, ERDelta3P and wild-type ERalpha were equivalently expressed. Return of the TMX2 population to medium without tamoxifen eventually selected for a population that expressed predominately wild-type ERalpha, whereas TMX2 clones over expressing ERDelta3 mRNA and ERDelta3P retained this phenotype in tamoxifen-free media. In both experiments, expression of all ERalpha mRNAs and proteins declined to barely detectable levels during 6-12 months exposure, concomitant with a progressive increase in the ability of the cells to form foci independently of E2 or tamoxifen. Selection for these various populations suggests that tamoxifen can induce and/or support certain cellular changes that lead to altered ERalpha expression, E2-independent cell growth and resistance to antiestrogens.
authors.affiliation: Laboratory of Human Toxicology and Molecular Epidemiology, Department of Environmental Disease Prevention, Wadsworth Center, New York State Department of Health, Albany, NY 12201, USA. fasco@wadsworth.org
authors.forename: Michael J
authors.initials: MJ
authors.lastname: Fasco
authors.forename: Agita
authors.initials: A
authors.lastname: Amin
authors.forename: Brian T
authors.initials: BT
authors.lastname: Pentecost
authors.forename: Yi
authors.initials: Y
authors.lastname: Yang
authors.forename: John F
authors.initials: JF
authors.lastname: Gierthy
mesh_terms: D017398:Alternative Splicing / Q000187:drug effects; D001943:Breast Neoplasms / Q000235:genetics / Q000473:pathology*; D018929:Cell Culture Techniques; D002455:Cell Division; D045744:Cell Line, Tumor; D004958:Estradiol / Q000494:pharmacology; D047628:Estrogen Receptor alpha; D005260:Female; D015972:Gene Expression Regulation, Neoplastic / Q000187:drug effects*; D006801:Humans; D010641:Phenotype; D012333:RNA, Messenger / Q000187:drug effects; D011960:Receptors, Estrogen / Q000032:analysis / Q000235:genetics*; D013629:Tamoxifen / Q000494:pharmacology*; D013997:Time Factors; D014158:Transcription, Genetic
chemical_list: D047628:Estrogen Receptor alpha; D012333:RNA, Messenger; D011960:Receptors, Estrogen; D013629:Tamoxifen; D004958:Estradiol