title: Membrane-associated binding sites for estrogen contribute to growth regulation of human breast cancer cells.
abstract: Membrane-associated binding sites for estrogen may mediate rapid effects of estradiol-17beta that contribute to proliferation of human breast cancers. After controlled homogenization and fractionation of MCF-7 breast cancer cells, the bulk of specific estradiol binding is found in nuclear fractions. However, a significant portion of specific, high-affinity estradiol-17beta binding-sites are also enriched in plasma membranes. These estradiol binding-sites co-purify with 5'-nucleotidase, a plasma membrane-marker enzyme, and are free from major contamination by cytosol or nuclei. Electrophoresis of membrane fractions allowed detection of a primary 67-kDa protein and a secondary 46-kDa protein recognized by estradiol-17beta and by a monoclonal antibody directed to the ligand-binding domain of the nuclear form of estrogen receptor. Estrogen-induced growth of MCF-7 breast cancer cells in vitro was blocked by treatment with the antibody to estrogen receptor and correlated closely with acute hormonal activation of mitogen-activated protein kinase and Akt kinase signaling. Estrogen-promoted growth of human breast cancer xenografts in nude mice was also significantly reduced by treatment in vivo with the estrogen receptor antibody. Thus, membrane-associated forms of estrogen receptor may play a role in promoting intracellular signaling for hormone-mediated proliferation and survival of breast cancers and offer a new target for antitumor therapy.
authors.affiliation: Department of Medicine, Division of Hematology-Oncology, UCLA School of Medicine, Los Angeles, California, 90095-1678, USA.
authors.forename: D C
authors.initials: DC
authors.lastname: Márquez
authors.forename: R J
authors.initials: RJ
authors.lastname: Pietras
mesh_terms: D000818:Animals; D000906:Antibodies / Q000494:pharmacology; D001665:Binding Sites; D001943:Breast Neoplasms / Q000201:enzymology / Q000473:pathology*; D002455:Cell Division / Q000187:drug effects; D002462:Cell Membrane / Q000378:metabolism; D004958:Estradiol / Q000378:metabolism* / Q000494:pharmacology*; D047628:Estrogen Receptor alpha; D005260:Female; D006801:Humans; D007700:Kinetics; D051379:Mice; D008819:Mice, Nude; D019950:Mitogen-Activated Protein Kinase 1 / Q000378:metabolism; D048052:Mitogen-Activated Protein Kinase 3; D020928:Mitogen-Activated Protein Kinases / Q000378:metabolism; D017346:Protein Serine-Threonine Kinases; D011518:Proto-Oncogene Proteins / Q000378:metabolism; D051057:Proto-Oncogene Proteins c-akt; D011956:Receptors, Cell Surface / Q000502:physiology; D011960:Receptors, Estrogen / Q000037:antagonists & inhibitors / Q000737:chemistry / Q000502:physiology*; D012710:Serum Albumin, Bovine / Q000494:pharmacology; D014407:Tumor Cells, Cultured; D023041:Xenograft Model Antitumor Assays
chemical_list: D000906:Antibodies; D047628:Estrogen Receptor alpha; D011518:Proto-Oncogene Proteins; D011956:Receptors, Cell Surface; D011960:Receptors, Estrogen; C043090:estradiol-bovine serum albumin; D012710:Serum Albumin, Bovine; D004958:Estradiol; C494918:AKT1 protein, human; D017346:Protein Serine-Threonine Kinases; D051057:Proto-Oncogene Proteins c-akt; D019950:Mitogen-Activated Protein Kinase 1; D048052:Mitogen-Activated Protein Kinase 3; D020928:Mitogen-Activated Protein Kinases