title: MicroRNA-9 promotes the proliferation, migration, and invasion of breast cancer cells via down-regulating FOXO1.
abstract: OBJECTIVE
  The objective of the study was to investigate the role of microRNA-9 (miR-9) targeting forkhead box O1 (FOXO1) in the proliferation, migration, and invasion of breast cancer cells.
  
  
  METHODS
  Quantitative real-time polymerase chain reaction (qRT-PCR) was employed to determine the expressions of miR-9 and FOXO1 mRNA in breast cancer tissues, normal breast tissues, breast cancer cell lines, and normal breast epithelial cells. After the up-regulation of miR-9 expression, qRT-PCR and Western blotting were used to determine the expression of FOXO1. The luciferase reporter gene assay was used to validate the target gene. The CCK-8 assay, scratch-wound healing assay, and Transwell invasion assay were used to investigate the changes in the proliferation, migration, and invasion of breast cancer cells, respectively.
  
  
  RESULTS
  MicroRNA-9 expression was significantly up-regulated in breast cancer tissues and breast cancer cell lines when compared with normal breast tissues and normal breast epithelial cells (both P < 0.05). FOXO1 mRNA and protein expressions were substantially down-regulated in breast cancer tissues and breast cancer cell lines when compared with normal breast tissues and normal breast epithelial cells (both P < 0.05). There can be a negative correlation between miR-9 and FOXO1 mRNA in breast cancer. Luciferase reporter gene assay indicated that miR-9 can down-regulate FOXO1 expression at a post-transcriptional level through binding specifically to FOXO1 3'UTR. The results of CCK-8 assay, scratch-wound healing assay, and Transwell invasion assay revealed that the inhibition of miR-9 can suppress MCF7 cell proliferation, migration, and invasion. Additionally, the expression of miR-9 increased significantly whilst that of FOXO1 decreased substantially as the disease progressed (P < 0.05).
  
  
  CONCLUSIONS
  Our study provides evidence that miR-9 can promote the proliferation, migration, and invasion of breast cancer cells via down-regulating FOXO1.
authors.affiliation: Department of Emmengey, The First Affiliated Hospital of Shantou University Medical College, Shantou, 515041, People's Republic of China.
authors.forename: D-Z
authors.initials: DZ
authors.lastname: Liu
authors.affiliation: Department of Emmengey, The First Affiliated Hospital of Shantou University Medical College, Shantou, 515041, People's Republic of China.
authors.forename: B
authors.initials: B
authors.lastname: Chang
authors.affiliation: Department of Orthopedics, The First Affiliated Hospital of Shantou University Medical College, Shantou, 515041, People's Republic of China.
authors.forename: X-D
authors.initials: XD
authors.lastname: Li
authors.affiliation: Department of Orthopedics, The First Affiliated Hospital of Shantou University Medical College, Shantou, 515041, People's Republic of China.
authors.forename: Q-H
authors.initials: QH
authors.lastname: Zhang
authors.affiliation: Department of Hepatobiliary Surgery, the First Affiliated Hospital of Shantou University Medical College, No. 57, Changping Road, Shantou, 515041, Guangdong, People's Republic of China. yuanhang929@163.com.
authors.forename: Y-H
authors.initials: YH
authors.lastname: Zou
mesh_terms: D000328:Adult; D001943:Breast Neoplasms / Q000235:genetics* / Q000378:metabolism / Q000473:pathology; D002465:Cell Movement / Q000235:genetics; D049109:Cell Proliferation / Q000235:genetics; D015536:Down-Regulation; D005260:Female; D000071161:Forkhead Box Protein O1 / Q000096:biosynthesis*; D015972:Gene Expression Regulation, Neoplastic / Q000235:genetics*; D006801:Humans; D061986:MCF-7 Cells; D035683:MicroRNAs / Q000096:biosynthesis*; D008875:Middle Aged; D009361:Neoplasm Invasiveness / Q000235:genetics*
chemical_list: C085126:FOXO1 protein, human; D000071161:Forkhead Box Protein O1; C541874:MIRN92 microRNA, human; D035683:MicroRNAs
keywords: Breast cancer; FOXO1; Invasion; MicroRNA-9; Migration; Proliferation