title: Estrogen response element-GFP (ERE-GFP) introduced MCF-7 cells demonstrated the coexistence of multiple estrogen-deprivation resistant mechanisms.
abstract: The acquisition of estrogen-deprivation resistance and estrogen receptor (ER) signal-independence in ER-positive breast cancer is one of the crucial steps in advancing the aggressiveness of breast cancer; however, this has not yet been elucidated in detail. To address this issue, we established several estrogen-deprivation-resistant (EDR) breast cancer cell lines from our unique MCF-7 cells, which had been stably transfected with an ERE-GFP reporter plasmid. Three cell lines with high ER activity and another 3 cell lines with no ER activity were established from cell cloning by monitoring GFP expression in living cells. The former three ERE-GFP-positive EDR cell lines showed the overexpression of ER and high expression of several ER-target genes. Further analysis of intracellular signaling factors revealed a marked change in the phosphorylation status of ERα on Ser167 and Akt on Thr308 by similar mechanisms reported previously; however, we could not find any changes in MAP-kinase factors. Comprehensive phospho-proteomic analysis also indicated the possible contribution of the Akt pathway to the phosphorylation of ERα. On the other hand, constitutive activation of c-Jun N-terminal kinase (JNK) was observed in ERE-GFP-negative EDR cells, and the growth of these cells was inhibited by a JNK inhibitor. An IGF1R-specific inhibitor diminished the phosphorylation of JNK, which suggested that a novel signaling pathway, IGF1R-JNK, may be important for the proliferation of ER-independent MCF-7 cells. These results indicate that ER-positive breast cancer cells can acquire resistance by more than two mechanisms at a time, which suggests that multiple mechanisms may occur simultaneously. This finding also implies that breast cancers with different resistance mechanisms can concomitantly occur and mingle in an individual patient, and may be a cause of the recurrence of cancer.
authors.affiliation: Department of Molecular and Functional Dynamics, Tohoku University Graduate School of Medicine, Aoba-ku, Sendai 980-8575, Japan.
authors.forename: Natsu
authors.initials: N
authors.lastname: Fujiki
authors.forename: Hiromi
authors.initials: H
authors.lastname: Konno
authors.forename: Yosuke
authors.initials: Y
authors.lastname: Kaneko
authors.forename: Tatsuyuki
authors.initials: T
authors.lastname: Gohno
authors.forename: Toru
authors.initials: T
authors.lastname: Hanamura
authors.forename: Koshi
authors.initials: K
authors.lastname: Imami
authors.forename: Yasushi
authors.initials: Y
authors.lastname: Ishihama
authors.forename: Kyoko
authors.initials: K
authors.lastname: Nakanishi
authors.forename: Toshifumi
authors.initials: T
authors.lastname: Niwa
authors.forename: Yuko
authors.initials: Y
authors.lastname: Seino
authors.forename: Yuri
authors.initials: Y
authors.lastname: Yamaguchi
authors.forename: Shin-ichi
authors.initials: S
authors.lastname: Hayashi
mesh_terms: D018931:Antineoplastic Agents, Hormonal / Q000494:pharmacology; D001943:Breast Neoplasms / Q000188:drug therapy; D049109:Cell Proliferation; D019008:Drug Resistance, Neoplasm; D020847:Estrogen Receptor Modulators / Q000494:pharmacology; D047628:Estrogen Receptor alpha / Q000235:genetics / Q000378:metabolism; D004967:Estrogens / Q000502:physiology; D005260:Female; D015870:Gene Expression; D015972:Gene Expression Regulation, Neoplastic; D017930:Genes, Reporter; D049452:Green Fluorescent Proteins / Q000096:biosynthesis / Q000235:genetics; D006801:Humans; D048031:JNK Mitogen-Activated Protein Kinases / Q000378:metabolism; D061986:MCF-7 Cells; D010766:Phosphorylation; D011499:Protein Processing, Post-Translational; D018719:Erb-b2 Receptor Tyrosine Kinases / Q000235:genetics / Q000378:metabolism; D017526:Receptor, IGF Type 1 / Q000378:metabolism; D020218:Response Elements; D015398:Signal Transduction; D018808:Transcription Factor AP-1 / Q000378:metabolism
chemical_list: D018931:Antineoplastic Agents, Hormonal; D020847:Estrogen Receptor Modulators; D047628:Estrogen Receptor alpha; D004967:Estrogens; D049452:Green Fluorescent Proteins; D048031:JNK Mitogen-Activated Protein Kinases; D018719:Erb-b2 Receptor Tyrosine Kinases; D017526:Receptor, IGF Type 1; D018808:Transcription Factor AP-1; C506487:ESR1 protein, human; C508053:ERBB2 protein, human
keywords: Breast cancer; EDR; Estrogen; Estrogen-deprivation resistance; Hormonal therapy; LTED; estrogen-deprivation-resistant; long-term estrogen-depleted