title: Tamoxifen through GPER upregulates aromatase expression: a novel mechanism sustaining tamoxifen-resistant breast cancer cell growth.
abstract: Tamoxifen resistance is a major clinical challenge in breast cancer treatment. Aromatase inhibitors are effective in women who progressed or recurred on tamoxifen, suggesting a role of local estrogen production by aromatase in driving tamoxifen-resistant phenotype. However, the link between aromatase activity and tamoxifen resistance has not yet been reported. We investigated whether long-term tamoxifen exposure may affect aromatase activity and/or expression, which may then sustain tamoxifen-resistant breast cancer cell growth. We employed MCF-7 breast cancer cells, tamoxifen-resistant MCF-7 cells (MCF-7 TR1 and TR2), SKBR-3 breast cancer cells, cancer-associated fibroblasts (CAFs1 and CAFs2). We used tritiated-water release assay, realtime-RT-PCR, and immunoblotting analysis for evaluating aromatase activity and expression; anchorage-independent assays for growth; reporter-gene, electrophoretic-mobility-shift, and chromatin-immunoprecipitation assays for promoter activity studies. We demonstrated an increased aromatase activity and expression, which supports proliferation in tamoxifen-resistant breast cancer cells. This is mediated by the G-protein-coupled receptor GPR30/GPER, since knocking-down GPER expression or treatment with a GPER antagonist reversed the enhanced aromatase levels induced by long-term tamoxifen exposure. The molecular mechanism was investigated in ER-negative, GPER/aromatase-positive SKBR3 cells, in which tamoxifen acts as a GPER agonist. Tamoxifen treatment increased aromatase promoter activity through an enhanced recruitment of c-fos/c-jun complex to AP-1 responsive elements located within the promoter region. As tamoxifen via GPER induced aromatase expression also in CAFs, this pathway may be involved in promoting aggressive behavior of breast tumors in response to tamoxifen treatment. Blocking estrogen production and/or GPER signaling activation may represent a valid option to overcome tamoxifen-resistance in breast cancers.
authors.affiliation: Department of Pharmacy, Health and Nutritional Sciences, University of Calabria, 87036, Arcavacata di Rende, CS, Italy.
authors.forename: Stefania
authors.initials: S
authors.lastname: Catalano
authors.forename: Cinzia
authors.initials: C
authors.lastname: Giordano
authors.forename: Salvatore
authors.initials: S
authors.lastname: Panza
authors.forename: Francesca
authors.initials: F
authors.lastname: Chemi
authors.forename: Daniela
authors.initials: D
authors.lastname: Bonofiglio
authors.forename: Marilena
authors.initials: M
authors.lastname: Lanzino
authors.forename: Pietro
authors.initials: P
authors.lastname: Rizza
authors.forename: Francesco
authors.initials: F
authors.lastname: Romeo
authors.forename: Suzanne A W
authors.initials: SA
authors.lastname: Fuqua
authors.forename: Marcello
authors.initials: M
authors.lastname: Maggiolini
authors.forename: Sebastiano
authors.initials: S
authors.lastname: Andò
authors.forename: Ines
authors.initials: I
authors.lastname: Barone
mesh_terms: D018931:Antineoplastic Agents, Hormonal / Q000494:pharmacology*; D001141:Aromatase / Q000235:genetics* / Q000378:metabolism; D001943:Breast Neoplasms / Q000235:genetics* / Q000378:metabolism* / Q000473:pathology; D045744:Cell Line, Tumor; D019008:Drug Resistance, Neoplasm; D004789:Enzyme Activation / Q000187:drug effects; D005260:Female; D015870:Gene Expression; D015972:Gene Expression Regulation, Neoplastic / Q000187:drug effects*; D006801:Humans; D061986:MCF-7 Cells; D011401:Promoter Regions, Genetic; D011485:Protein Binding; D016760:Proto-Oncogene Proteins c-fos / Q000378:metabolism; D016755:Proto-Oncogene Proteins c-jun / Q000378:metabolism; D011960:Receptors, Estrogen / Q000378:metabolism*; D043562:Receptors, G-Protein-Coupled / Q000378:metabolism*; D013629:Tamoxifen / Q000494:pharmacology*; D018808:Transcription Factor AP-1 / Q000378:metabolism; D015533:Transcriptional Activation
chemical_list: D018931:Antineoplastic Agents, Hormonal; C109584:GPER1 protein, human; D016760:Proto-Oncogene Proteins c-fos; D016755:Proto-Oncogene Proteins c-jun; D011960:Receptors, Estrogen; D043562:Receptors, G-Protein-Coupled; D018808:Transcription Factor AP-1; D013629:Tamoxifen; D001141:Aromatase