title: ERBB2 influences the subcellular localization of the estrogen receptor in tamoxifen-resistant MCF-7 cells leading to the activation of AKT and RPS6KA2.
abstract: Acquired resistance to endocrine therapies remains a major clinical obstacle in hormone-sensitive breast tumors. We used an MCF-7 breast tumor cell line (Tam(R)-1) resistant to tamoxifen to investigate this mechanism. We demonstrate that Tam(R)-1 express elevated levels of phosphorylated AKT and MAPK3/1-activated RPS6KA2 compared with the parental MCF-7 cell line (MCF-7). There was no change in the level of total ESR between the two cell lines; however, the Tam(R)-1 cells had increased phosphorylation of ESR1 ser(167). SiRNA blockade of AKT or MAPK3/1 had little effect on ESR1 ser(167) phosphorylation, but a combination of the two siRNAs abrogated this. Co-localization studies revealed an association between ERBB2 and ESR1 in the Tam(R)-1 but not MCF-7 cells. ESR1 was redistributed to extranuclear sites in Tam(R)-1 and was less transcriptionally competent compared with MCF-7 suggesting that nuclear ESR1 activity was suppressed in Tam(R)-1. Tamoxifen resistance in the Tam(R)-1 cells could be partially overcome by the ERBB2 inhibitor AG825 in combination with tamoxifen, and this was associated with re-localization of ESR1 to the nucleus. These data demonstrate that tamoxifen-resistant cells have the ability to switch between ERBB2 or ESR1 pathways promoting cell growth and that pharmacological inhibition of ERBB2 may be a therapeutic strategy for overcoming tamoxifen resistance.
authors.affiliation: Institute of Cancer Research, The Breakthrough Breast Cancer Research Centre, 237 Fulham Road, London SW3 6JB, UK.
authors.forename: Sunil
authors.initials: S
authors.lastname: Pancholi
authors.forename: Anne E
authors.initials: AE
authors.lastname: Lykkesfeldt
authors.forename: Caroline
authors.initials: C
authors.lastname: Hilmi
authors.forename: Susana
authors.initials: S
authors.lastname: Banerjee
authors.forename: Alexandra
authors.initials: A
authors.lastname: Leary
authors.forename: Suzanne
authors.initials: S
authors.lastname: Drury
authors.forename: Stephen
authors.initials: S
authors.lastname: Johnston
authors.forename: Mitch
authors.initials: M
authors.lastname: Dowsett
authors.forename: Lesley-Ann
authors.initials: LA
authors.lastname: Martin
mesh_terms: D018931:Antineoplastic Agents, Hormonal / Q000494:pharmacology*; D017209:Apoptosis / Q000187:drug effects; D015153:Blotting, Western; D049109:Cell Proliferation / Q000187:drug effects; D047369:Chromatin Immunoprecipitation; D019008:Drug Resistance, Neoplasm; D004958:Estradiol / Q000031:analogs & derivatives / Q000494:pharmacology; D004965:Estrogen Antagonists / Q000494:pharmacology; D020847:Estrogen Receptor Modulators / Q000494:pharmacology; D047628:Estrogen Receptor alpha / Q000235:genetics / Q000378:metabolism; D005260:Female; D000077267:Fulvestrant; D006801:Humans; D019950:Mitogen-Activated Protein Kinase 1 / Q000378:metabolism; D048052:Mitogen-Activated Protein Kinase 3 / Q000378:metabolism; D010641:Phenotype; D051057:Proto-Oncogene Proteins c-akt / Q000037:antagonists & inhibitors / Q000235:genetics / Q000378:metabolism*; D012333:RNA, Messenger / Q000235:genetics / Q000378:metabolism; D034741:RNA, Small Interfering / Q000494:pharmacology; D018719:Erb-b2 Receptor Tyrosine Kinases / Q000235:genetics / Q000378:metabolism*; D020133:Reverse Transcriptase Polymerase Chain Reaction; D038744:Ribosomal Protein S6 Kinases, 90-kDa / Q000235:genetics / Q000378:metabolism*; D015398:Signal Transduction; D013629:Tamoxifen / Q000494:pharmacology*; D014158:Transcription, Genetic / Q000187:drug effects; D014407:Tumor Cells, Cultured / Q000187:drug effects; D051025:bcl-Associated Death Protein / Q000378:metabolism
chemical_list: D018931:Antineoplastic Agents, Hormonal; D004958:Estradiol; D004965:Estrogen Antagonists; D020847:Estrogen Receptor Modulators; D047628:Estrogen Receptor alpha; D000077267:Fulvestrant; D019950:Mitogen-Activated Protein Kinase 1; D048052:Mitogen-Activated Protein Kinase 3; D051057:Proto-Oncogene Proteins c-akt; D012333:RNA, Messenger; D034741:RNA, Small Interfering; D018719:Erb-b2 Receptor Tyrosine Kinases; D038744:Ribosomal Protein S6 Kinases, 90-kDa; D013629:Tamoxifen; D051025:bcl-Associated Death Protein; C494819:BAD protein, human; C506487:ESR1 protein, human; C069330:ribosomal protein S6 kinase, 90kDa, polypeptide 3