title: β-catenin represses expression of the tumour suppressor 15-prostaglandin dehydrogenase in the normal intestinal epithelium and colorectal tumour cells.
abstract: BACKGROUND
  Cyclooxygenase-2 (COX-2) overexpression in colorectal cancer increases levels of its pro-tumorigenic product prostaglandin E2 (PGE(2)). The recently identified colorectal tumour suppressor 15-prostaglandin dehydrogenase (15-PGDH) catalyses prostaglandin turnover and is downregulated at a very early stage in colorectal tumorigenesis; however, the mechanism responsible remains unclear. As Wnt/β-catenin signalling is also deregulated early in colorectal neoplasia, a study was undertaken to determine whether β-catenin represses 15-PGDH expression.
  
  
  METHODS
  The effect of modulating Wnt/β-catenin signalling (using β-catenin siRNA, mutant TCF4, Wnt3A or GSK3 inhibition) on 15-PGDH mRNA, protein expression and promoter activity was determined in colorectal cell lines by immunoblotting, qRT-PCR and reporter assays. The effect of β-catenin deletion in vivo was addressed by 15-PGDH immunostaining of β-catenin(-/lox)-villin-creERT2 mouse tissue. 15-PGDH promoter occupancy was determined using chromatin immunoprecipitation and PGE(2) levels by ELISA.
  
  
  RESULTS
  The study shows for the first time that β-catenin knockdown upregulates 15-PGDH in colorectal adenoma and carcinoma cells without affecting COX-2 protein levels. A dominant negative mutant form of TCF4 (dnTCF4), unable to bind β-catenin, also upregulated 15-PGDH; conversely, increasing β-catenin activity using Wnt3A or GSK3 inhibition downregulated 15-PGDH. Importantly, inducible β-catenin deletion in vivo also upregulated intestinal epithelial 15-PGDH. 15-PGDH regulation occurred at the protein, mRNA and promoter activity levels and chromatin immunoprecipitation indicated β-catenin/TCF4 binding to the 15-PGDH promoter. β-catenin knockdown decreased PGE(2) levels, and this was significantly rescued by 15-PGDH siRNA.
  
  
  CONCLUSIONS
  These data suggest a novel role for β-catenin in promoting colorectal tumorigenesis through very early 15-PGDH suppression leading to increased PGE(2) levels, possibly even before COX-2 upregulation.
authors.affiliation: Cancer Research UK Colorectal Tumour Biology Research Group, School of Cellular and Molecular Medicine, University Walk, University of Bristol, Bristol, UK.
authors.forename: Helena J M
authors.initials: HJ
authors.lastname: Smartt
authors.forename: Alexander
authors.initials: A
authors.lastname: Greenhough
authors.forename: Paloma
authors.initials: P
authors.lastname: Ordóñez-Morán
authors.forename: Elena
authors.initials: E
authors.lastname: Talero
authors.forename: Catherine A
authors.initials: CA
authors.lastname: Cherry
authors.forename: Catherine A
authors.initials: CA
authors.lastname: Wallam
authors.forename: Lee
authors.initials: L
authors.lastname: Parry
authors.forename: Manal
authors.initials: M
authors.lastname: Al Kharusi
authors.forename: Heather R
authors.initials: HR
authors.lastname: Roberts
authors.forename: John M
authors.initials: JM
authors.lastname: Mariadason
authors.forename: Alan R
authors.initials: AR
authors.lastname: Clarke
authors.forename: Joerg
authors.initials: J
authors.lastname: Huelsken
authors.forename: Ann C
authors.initials: AC
authors.lastname: Williams
authors.forename: Chris
authors.initials: C
authors.lastname: Paraskeva
mesh_terms: D000236:Adenoma / Q000201:enzymology*; D000818:Animals; D045744:Cell Line, Tumor; D015179:Colorectal Neoplasms / Q000201:enzymology*; D051546:Cyclooxygenase 2 / Q000378:metabolism; D015232:Dinoprostone / Q000378:metabolism; D015536:Down-Regulation; D004794:Enzyme Repression; D015972:Gene Expression Regulation, Neoplastic; D055785:Gene Knockdown Techniques; D006801:Humans; D006911:Hydroxyprostaglandin Dehydrogenases / Q000096:biosynthesis / Q000235:genetics / Q000378:metabolism*; D015151:Immunoblotting; D007150:Immunohistochemistry; D007413:Intestinal Mucosa / Q000201:enzymology*; D051379:Mice; D012333:RNA, Messenger / Q000378:metabolism; D020133:Reverse Transcriptase Polymerase Chain Reaction; D015533:Transcriptional Activation; D015854:Up-Regulation; D051176:beta Catenin / Q000235:genetics / Q000502:physiology*
chemical_list: D012333:RNA, Messenger; D051176:beta Catenin; D006911:Hydroxyprostaglandin Dehydrogenases; C035859:15-hydroxyprostaglandin dehydrogenase; D051546:Cyclooxygenase 2; C496540:PTGS2 protein, human; D015232:Dinoprostone