title: Aromatase inhibitor treatment of breast cancer cells increases the expression of let-7f, a microRNA targeting CYP19A1.
abstract: Aromatase inhibitors (AIs) are considered the gold standard of endocrine therapy for oestrogen receptor-positive postmenopausal breast cancer patients. AI treatment was reported to result in marked alterations of genetic profiles in cancer tissues but its detailed molecular mechanisms have not been elucidated. Therefore, we profiled miRNA expression before and after treatment with letrozole in MCF-7 co-cultured with primary breast cancer stromal cells. Letrozole significantly altered the expression profiles of cancer miRNAs in vitro. Among the elevated miRNAs following letrozole treatment, computational analysis identified let-7f, a tumour-suppressor miRNA which targeted the aromatase gene (CYP19A1) expression. Quantitative real-time PCR assay using MCF-7 and SK-BR-3 cells as well as clinical specimens of a neoadjuvant study demonstrated a significant inverse correlation between aromatase mRNA and let-7f expression. In addition, high let-7f expression was significantly correlated with low aromatase protein levels evaluated by both immunohistochemistry and the western blotting method in breast cancer cases. Results of 3'UTR luciferase assay also demonstrated the actual let-7f binding sites in CYP19A1, indicating that let-7f directly targets the aromatase gene. Subsequent WST-8 and migration assays performed in let-7f-transfected MCF-7 and SK-BR-3 cells revealed a significant decrement of their proliferation and migration. These findings all demonstrated that let-7f, a tumour suppressor miRNA in breast cancer, directly targeted the aromatase gene and was restored by AI treatment. Therefore, AIs may exert tumour-suppressing effects upon breast cancer cells by suppressing aromatase gene expression via restoration of let-7f.
authors.affiliation: Department of Pathology, Tohoku University Graduate School of Medicine, 2-1 Seiryo-machi, Aoba-ku, Sendai, Miyagi 980-8575, Japan.
authors.forename: Yukiko
authors.initials: Y
authors.lastname: Shibahara
authors.forename: Yasuhiro
authors.initials: Y
authors.lastname: Miki
authors.forename: Yoshiaki
authors.initials: Y
authors.lastname: Onodera
authors.forename: Shuko
authors.initials: S
authors.lastname: Hata
authors.forename: Monica Sm
authors.initials: MS
authors.lastname: Chan
authors.forename: Christopher Cp
authors.initials: CC
authors.lastname: Yiu
authors.forename: Tjing Y
authors.initials: TY
authors.lastname: Loo
authors.forename: Yasuhiro
authors.initials: Y
authors.lastname: Nakamura
authors.forename: Jun-Ichi
authors.initials: J
authors.lastname: Akahira
authors.forename: Takanori
authors.initials: T
authors.lastname: Ishida
authors.forename: Keiko
authors.initials: K
authors.lastname: Abe
authors.forename: Hisashi
authors.initials: H
authors.lastname: Hirakawa
authors.forename: Louis Wc
authors.initials: LW
authors.lastname: Chow
authors.forename: Takashi
authors.initials: T
authors.lastname: Suzuki
authors.forename: Noriaki
authors.initials: N
authors.lastname: Ouchi
authors.forename: Hironobu
authors.initials: H
authors.lastname: Sasano
mesh_terms: D020413:3' Untranslated Regions; D018931:Antineoplastic Agents, Hormonal / Q000627:therapeutic use*; D001141:Aromatase / Q000235:genetics / Q000378:metabolism*; D047072:Aromatase Inhibitors / Q000627:therapeutic use*; D001665:Binding Sites; D015153:Blotting, Western; D001943:Breast Neoplasms / Q000188:drug therapy* / Q000201:enzymology / Q000235:genetics / Q000473:pathology; D045744:Cell Line, Tumor; D049109:Cell Proliferation / Q000187:drug effects; D017024:Chemotherapy, Adjuvant; D018920:Coculture Techniques; D005260:Female; D020869:Gene Expression Profiling / Q000379:methods; D015971:Gene Expression Regulation, Enzymologic / Q000187:drug effects; D015972:Gene Expression Regulation, Neoplastic / Q000187:drug effects; D006801:Humans; D007150:Immunohistochemistry; D035683:MicroRNAs / Q000378:metabolism*; D020360:Neoadjuvant Therapy; D020411:Oligonucleotide Array Sequence Analysis; D060888:Real-Time Polymerase Chain Reaction; D020133:Reverse Transcriptase Polymerase Chain Reaction; D017154:Stromal Cells / Q000187:drug effects / Q000378:metabolism; D013997:Time Factors; D014162:Transfection; D015854:Up-Regulation
chemical_list: D020413:3' Untranslated Regions; D018931:Antineoplastic Agents, Hormonal; D047072:Aromatase Inhibitors; D035683:MicroRNAs; C487931:mirnlet7 microRNA, human; D001141:Aromatase; C561410:CYP19A1 protein, human