title: Mechanisms governing the accumulation of estrogen receptor alpha in MCF-7 breast cancer cells treated with hydroxytamoxifen and related antiestrogens.
abstract: This study aimed at a better understanding of estrogen receptor alpha (ER) up regulation induced by partial estrogen antagonists. Effect of treatment with hydroxytamoxifen (OH-Tam) on ER level in MCF-7 cells was investigated by an approach combining ER measurement (enzyme immunoassay) and morphological demonstration (immunofluorescence). Furthermore, the influence of drug exposure on the rates of ER synthesis and degradation was assessed by determining [35S]methionine incorporated into the receptor in different experimental conditions (measurement of synthesis or pulse-chase experiments). ER up regulation was already induced by a 1-h pulse treatment with OH-Tam, thus a continuous exposure was not required. This process appeared reversible (i.e. ER accumulation due to OH-Tam rapidly vanished upon subsequent exposure to 17beta-estradiol (E2) or the pure antiestrogen RU 58668). While OH-Tam did not affect the rate of [35S]methionine incorporation into ER, it clearly caused an impairment of ER degradation (pulse-chase experiments) indicating that up regulation results from a stabilization of the receptor associated with the maintenance of its synthesis. Various tamoxifen derivatives, as well as a few related partial antiestrogens, were compared on the basis of binding ability and propensity to induce ER up regulation. A close relationship was found between both properties. Structure-activity analysis revealed that the capacity of these compounds to induce ER up regulation is associated with characteristics of their aminoalkyle side-chain, similar to those required for antiestrogenicity.
authors.affiliation: Laboratoire J.-C. Heuson de Cancérologie Mammaire, Service de Médecine Interne, Institut Jules Bordet, Université Libre de Bruxelles, 1 rue Héger-Bordet, B-1000 Brussels, Belgium.
authors.forename: Ioanna
authors.initials: I
authors.lastname: Laïos
authors.forename: Fabrice
authors.initials: F
authors.lastname: Journe
authors.forename: Guy
authors.initials: G
authors.lastname: Laurent
authors.forename: Denis
authors.initials: D
authors.lastname: Nonclercq
authors.forename: Robert-Alain
authors.initials: RA
authors.lastname: Toillon
authors.forename: Hye-Sook
authors.initials: HS
authors.lastname: Seo
authors.forename: Guy
authors.initials: G
authors.lastname: Leclercq
mesh_terms: D001943:Breast Neoplasms / Q000188:drug therapy / Q000378:metabolism*; D045744:Cell Line, Tumor; D002467:Cell Nucleus / Q000378:metabolism; D003600:Cytosol / Q000378:metabolism; D015536:Down-Regulation; D004797:Enzyme-Linked Immunosorbent Assay; D004958:Estradiol / Q000031:analogs & derivatives / Q000494:pharmacology; D020847:Estrogen Receptor Modulators / Q000494:pharmacology*; D047628:Estrogen Receptor alpha; D005455:Fluorescent Antibody Technique; D015972:Gene Expression Regulation, Neoplastic; D006801:Humans; D010636:Phenols / Q000494:pharmacology; D011869:Radioligand Assay; D011960:Receptors, Estrogen / Q000096:biosynthesis* / Q000378:metabolism; D013329:Structure-Activity Relationship; D013629:Tamoxifen / Q000031:analogs & derivatives* / Q000737:chemistry / Q000494:pharmacology*; D015854:Up-Regulation; D005466:Fluorocarbons
chemical_list: D004958:Estradiol; D020847:Estrogen Receptor Modulators; D047628:Estrogen Receptor alpha; D010636:Phenols; D011960:Receptors, Estrogen; D013629:Tamoxifen; C086511:RU 58668; D005466:Fluorocarbons; C016601:afimoxifene