title: MicroRNAs targeting oncogenes are down-regulated in pancreatic malignant transformation from benign tumors.
abstract: BACKGROUND
  MicroRNA (miRNA) expression profiles have been described in pancreatic ductal adenocarcinoma (PDAC), but these have not been compared with pre-malignant pancreatic tumors. We wished to compare the miRNA expression signatures in pancreatic benign cystic tumors (BCT) of low and high malignant potential with PDAC, in order to identify miRNAs deregulated during PDAC development. The mechanistic consequences of miRNA dysregulation were further evaluated.
  
  
  METHODS
  Tissue samples were obtained at a tertiary pancreatic unit from individuals with BCT and PDAC. MiRNA profiling was performed using a custom microarray and results were validated using RT-qPCR prior to evaluation of miRNA targets.
  
  
  RESULTS
  Widespread miRNA down-regulation was observed in PDAC compared to low malignant potential BCT. We show that amongst those miRNAs down-regulated, miR-16, miR-126 and let-7d regulate known PDAC oncogenes (targeting BCL2, CRK and KRAS respectively). Notably, miR-126 also directly targets the KRAS transcript at a "seedless" binding site within its 3'UTR. In clinical specimens, miR-126 was strongly down-regulated in PDAC tissues, with an associated elevation in KRAS and CRK proteins. Furthermore, miR-21, a known oncogenic miRNA in pancreatic and other cancers, was not elevated in PDAC compared to serous microcystic adenoma (SMCA), but in both groups it was up-regulated compared to normal pancreas, implicating early up-regulation during malignant change.
  
  
  CONCLUSIONS
  Expression profiling revealed 21 miRNAs down-regulated in PDAC compared to SMCA, the most benign lesion that rarely progresses to invasive carcinoma. It appears that miR-21 up-regulation is an early event in the transformation from normal pancreatic tissue. MiRNA expression has the potential to distinguish PDAC from normal pancreas and BCT. Mechanistically the down-regulation of miR-16, miR-126 and let-7d promotes PDAC transformation by post-transcriptional up-regulation of crucial PDAC oncogenes. We show that miR-126 is able to directly target KRAS; re-expression has the potential as a therapeutic strategy against PDAC and other KRAS-driven cancers.
authors.affiliation: Hepato-Pancreato-Biliary Surgical Unit, Department of Surgery and Cancer, Imperial College, Hammersmith Hospital, London, UK.
authors.forename: Long R
authors.initials: LR
authors.lastname: Jiao
authors.forename: Adam E
authors.initials: AE
authors.lastname: Frampton
authors.forename: Jimmy
authors.initials: J
authors.lastname: Jacob
authors.forename: Loredana
authors.initials: L
authors.lastname: Pellegrino
authors.forename: Jonathan
authors.initials: J
authors.lastname: Krell
authors.forename: Georgios
authors.initials: G
authors.lastname: Giamas
authors.forename: Nicole
authors.initials: N
authors.lastname: Tsim
authors.forename: Panagiotis
authors.initials: P
authors.lastname: Vlavianos
authors.forename: Patrizia
authors.initials: P
authors.lastname: Cohen
authors.forename: Raida
authors.initials: R
authors.lastname: Ahmad
authors.forename: Andreas
authors.initials: A
authors.lastname: Keller
authors.forename: Nagy A
authors.initials: NA
authors.lastname: Habib
authors.forename: Justin
authors.initials: J
authors.lastname: Stebbing
authors.forename: Leandro
authors.initials: L
authors.lastname: Castellano
mesh_terms: D020413:3' Untranslated Regions; D017209:Apoptosis; D045744:Cell Line, Tumor; D002471:Cell Transformation, Neoplastic / Q000378:metabolism*; D018899:CpG Islands; D015536:Down-Regulation; D020869:Gene Expression Profiling; D006801:Humans; D007150:Immunohistochemistry / Q000379:methods; D008156:Luciferases / Q000378:metabolism; D035683:MicroRNAs / Q000378:metabolism*; D015233:Models, Statistical; D009369:Neoplasms / Q000378:metabolism / Q000473:pathology*; D020411:Oligonucleotide Array Sequence Analysis; D009857:Oncogenes; D010190:Pancreatic Neoplasms / Q000175:diagnosis / Q000378:metabolism / Q000473:pathology*; D060888:Real-Time Polymerase Chain Reaction / Q000379:methods; D014162:Transfection; D015854:Up-Regulation; D018631:ras Proteins / Q000378:metabolism
chemical_list: D020413:3' Untranslated Regions; D035683:MicroRNAs; D008156:Luciferases; D018631:ras Proteins