title: Reciprocal regulation of microRNA-99a and insulin-like growth factor I receptor signaling in oral squamous cell carcinoma cells.
abstract: BACKGROUND
  MicroRNAs (miRNAs), small noncoding RNA molecules can function as oncogenes or tumor suppressors in tumorigenesis. Oral squamous cell carcinoma (OSCC) is one of the most prevalent cancers worldwide with a 5-year survival rate of approximately 50%.
  
  
  METHODS
  The expression of microRNA-99a (miR-99a) in OSCC tissues and cell lines was investigated using quantitative reverse transcription-polymerase chain reaction (qRT-PCR) analysis. The functions of miR-99a in migration/invasion and lung colonization were determined by transwell and tail vein injection assays, respectively. Specific targets of miR-99a were determined by software prediction, correlation with target protein expression, and luciferase reporter assay. The signaling pathways involved in regulation of miR-99a were investigated using the kinase inhibitors.
  
  
  RESULTS
  We observed reduced levels of miR-99a, identified as one of the most downregulated miRNA in OSCC and all tested OSCC cell lines compared to normal oral keratinocytes. Ectopic miR-99a expression in OSCC cells markedly reduced migration and invasion in vitro as well as lung colonization in vivo. When evaluating the specific targets of miR-99a, we found that ectopic miR-99a expression downregulates insulin-like growth factor 1 receptor (IGF1R) protein and that the expression of miR-99a correlates negatively with IGF1R protein in OSCC cells. Insertion of the 3'UTR of IGF1R mRNA into the 3'UTR of a reporter gene markedly reduced luciferase activity in OSCC cells expressing miR-99a, suggesting that miR-99a reduces luciferase activity by targeting the 3'UTR of IGF1R mRNA. When evaluating the mechanisms of miR-99a downregulation, we observed the upregulation of miR-99a expression in serum-starved conditions and its suppression in response to insulin-like growth factor (IGF1) stimulation. Inhibitors of phosphatidylinositol 3-kinase (PI3K) and mitogen-activated protein kinase (MAPK) kinase inhibited IGF1-induced suppression of miR-99a, suggesting the negative regulation of miR-99a expression by IGF1R signaling.
  
  
  CONCLUSIONS
  Overall, results indicate that miR-99a functions as a tumor metastasis suppressor in OSCC cells and mutually regulates IGF1R expression in a reciprocal regulation.
authors.forename: Yi-Chen
authors.initials: YC
authors.lastname: Yen
authors.forename: Shine-Gwo
authors.initials: SG
authors.lastname: Shiah
authors.forename: Hsiao-Chien
authors.initials: HC
authors.lastname: Chu
authors.forename: Yuan-Ming
authors.initials: YM
authors.lastname: Hsu
authors.forename: Jenn-Ren
authors.initials: JR
authors.lastname: Hsiao
authors.forename: Jang-Yang
authors.initials: JY
authors.lastname: Chang
authors.forename: Wen-Chun
authors.initials: WC
authors.lastname: Hung
authors.forename: Chun-Ta
authors.initials: CT
authors.lastname: Liao
authors.forename: Ann-Joy
authors.initials: AJ
authors.lastname: Cheng
authors.forename: Ya-Ching
authors.initials: YC
authors.lastname: Lu
authors.affiliation: National Institute of Cancer Research, National Health Research Institutes, Miaoli, Taiwan. ywc@nhri.org.tw.
authors.forename: Ya-Wen
authors.initials: YW
authors.lastname: Chen
mesh_terms: D000818:Animals; D002294:Carcinoma, Squamous Cell / Q000235:genetics* / Q000378:metabolism / Q000473:pathology; D002465:Cell Movement / Q000235:genetics; D005455:Fluorescent Antibody Technique; D015972:Gene Expression Regulation, Neoplastic / Q000235:genetics*; D064593:Heterografts; D006801:Humans; D015151:Immunoblotting; D051379:Mice; D008819:Mice, Nude; D035683:MicroRNAs / Q000235:genetics*; D009062:Mouth Neoplasms / Q000235:genetics* / Q000378:metabolism / Q000473:pathology; D009361:Neoplasm Invasiveness / Q000235:genetics; D017526:Receptor, IGF Type 1 / Q000235:genetics* / Q000378:metabolism; D020133:Reverse Transcriptase Polymerase Chain Reaction; D015398:Signal Transduction / Q000502:physiology
chemical_list: C561679:MIRN99 microRNA, human; D035683:MicroRNAs; D017526:Receptor, IGF Type 1