title: Boosting Wnt activity during colorectal cancer progression through selective hypermethylation of Wnt signaling antagonists.
abstract: BACKGROUND
  There is emerging evidence that Wnt pathway activity may increase during the progression from colorectal adenoma to carcinoma and that this increase is potentially an important step towards the invasive stage. Here, we investigated whether epigenetic silencing of Wnt antagonists is the biological driver for this increased Wnt activity in human tissues and how these methylation changes correlate with MSI (Microsatelite Instability) and CIMP (CpG Island Methylator Phenotype) statuses as well as known mutations in genes driving colorectal neoplasia.
  
  
  METHODS
  We conducted a systematic analysis by pyrosequencing, to determine the promoter methylation of CpG islands associated with 17 Wnt signaling component genes. Methylation levels were correlated with MSI and CIMP statuses and known mutations within the APC, BRAF and KRAS genes in 264 matched samples representing the progression from normal to pre-invasive adenoma to colorectal carcinoma.
  
  
  RESULTS
  We discovered widespread hypermethylation of the Wnt antagonists SFRP1, SFRP2, SFRP5, DKK2, WIF1 and SOX17 in the transition from normal to adenoma with only the Wnt antagonists SFRP1, SFRP2, DKK2 and WIF1 showing further significant increase in methylation from adenoma to carcinoma. We show this to be accompanied by loss of expression of these Wnt antagonists, and by an increase in nuclear Wnt pathway activity. Mixed effects models revealed that mutations in APC, BRAF and KRAS occur at the transition from normal to adenoma stages whilst the hypermethylation of the Wnt antagonists continued to accumulate during the transitions from adenoma to carcinoma stages.
  
  
  CONCLUSIONS
  Our study provides strong evidence for a correlation between progressive hypermethylation and silencing of several Wnt antagonists with stepping-up in Wnt pathway activity beyond the APC loss associated tumour-initiating Wnt signalling levels.
authors.forename: Ana-Luisa
authors.initials: AL
authors.lastname: Silva
authors.forename: Sarah N
authors.initials: SN
authors.lastname: Dawson
authors.forename: Mark J
authors.initials: MJ
authors.lastname: Arends
authors.forename: Kiran
authors.initials: K
authors.lastname: Guttula
authors.forename: Nigel
authors.initials: N
authors.lastname: Hall
authors.forename: Ewen A
authors.initials: EA
authors.lastname: Cameron
authors.forename: Tim H-M
authors.initials: TH
authors.lastname: Huang
authors.forename: James D
authors.initials: JD
authors.lastname: Brenton
authors.forename: Simon
authors.initials: S
authors.lastname: Tavaré
authors.forename: Mariann
authors.initials: M
authors.lastname: Bienz
authors.affiliation: Department of Pathology, Division of Molecular Histopathology, University of Cambridge, Addenbrooke's Hospital, Hills Road, Cambridge CB2 2QQ, UK. aeki2@cam.ac.uk.
authors.forename: Ashraf E K
authors.initials: AE
authors.lastname: Ibrahim
mesh_terms: D016022:Case-Control Studies; D015179:Colorectal Neoplasms / Q000737:chemistry / Q000235:genetics* / Q000378:metabolism*; D019175:DNA Methylation; D044127:Epigenesis, Genetic; D006801:Humans; D036341:Intercellular Signaling Peptides and Proteins / Q000737:chemistry / Q000235:genetics* / Q000378:metabolism; D051153:Wnt Proteins / Q000037:antagonists & inhibitors*; D060449:Wnt Signaling Pathway / Q000235:genetics*
chemical_list: D036341:Intercellular Signaling Peptides and Proteins; D051153:Wnt Proteins