title: APC and oncogenic KRAS are synergistic in enhancing Wnt signaling in intestinal tumor formation and progression.
abstract: OBJECTIVE
  Synchronous activation of the Wnt signaling pathway, mostly because of loss of function of the APC tumor suppressor, and of the oncogenic KRAS-signaling pathway is very frequent in colorectal cancer and is associated with poor prognosis.
  
  
  METHODS
  We have generated a compound transgenic mouse model, KRAS(V12G)/Apc(+/1638N), to recapitulate the human disease and compared it with single transgenic littermates.
  
  
  RESULTS
  Compound mutant mice are characterized by a 10-fold increase in tumor multiplicity and by accelerated tumor progression, resulting in strongly enhanced morbidity and mortality. Tumors from compound mutant mice proliferate faster and show decreased levels of apoptosis. Several lines of evidence indicate that the observed increase in tumor multiplicity and malignant transformation is caused by the synergistic activation of Wnt signaling in cells with oncogenic KRAS and loss-of-function Apc mutations. Activated KRAS is known to induce tyrosine phosphorylation of beta-catenin, leading to its release from E-cadherin at the adherens junction. This results in an increased beta-catenin pool in the cytoplasma, its subsequent translocation to the nucleus, and the transcriptional activation of Wnt downstream target genes. Accordingly, intestinal tumors from KRAS(V12G)/Apc(+/1638N) mice show a significant increase in cells with nuclear accumulation of beta-catenin when compared with Apc(+/1638N) animals. Moreover, Apc/KRAS-mutant embryonic stem cells show a significantly enhanced beta-catenin/T-cell factor-mediated transcriptional activation, accompanied by increased beta-catenin nuclear localization.
  
  
  CONCLUSIONS
  This KRAS-induced increase in Wnt/beta-catenin signaling may enhance the plasticity and self-renewal capacity of the tumor, thus resulting in the drastically augmented tumor multiplicity and malignant behavior in compound mutant animals.
authors.affiliation: UMR144/Institut Curie, 26 rue d'Ulm, 75248 Paris Cedex 05, France.
authors.forename: Klaus-Peter
authors.initials: KP
authors.lastname: Janssen
authors.forename: Paola
authors.initials: P
authors.lastname: Alberici
authors.forename: Hafida
authors.initials: H
authors.lastname: Fsihi
authors.forename: Claudia
authors.initials: C
authors.lastname: Gaspar
authors.forename: Cor
authors.initials: C
authors.lastname: Breukel
authors.forename: Patrick
authors.initials: P
authors.lastname: Franken
authors.forename: Christophe
authors.initials: C
authors.lastname: Rosty
authors.forename: Miguel
authors.initials: M
authors.lastname: Abal
authors.forename: Fatima
authors.initials: F
authors.lastname: El Marjou
authors.forename: Ron
authors.initials: R
authors.lastname: Smits
authors.forename: Daniel
authors.initials: D
authors.lastname: Louvard
authors.forename: Riccardo
authors.initials: R
authors.lastname: Fodde
authors.forename: Sylvie
authors.initials: S
authors.lastname: Robine
mesh_terms: D025601:Adenomatous Polyposis Coli Protein / Q000235:genetics / Q000378:metabolism*; D000818:Animals; D017209:Apoptosis / Q000502:physiology; D002455:Cell Division / Q000502:physiology; D045744:Cell Line, Tumor; D015179:Colorectal Neoplasms / Q000378:metabolism* / Q000473:pathology / Q000503:physiopathology; D015972:Gene Expression Regulation, Neoplastic; D019656:Loss of Heterozygosity; D051379:Mice; D008810:Mice, Inbred C57BL; D008811:Mice, Inbred DBA; D008822:Mice, Transgenic; D015689:Oncogene Protein p21(ras) / Q000235:genetics / Q000378:metabolism*; D015398:Signal Transduction / Q000502:physiology*; D051153:Wnt Proteins / Q000378:metabolism*; D051176:beta Catenin / Q000378:metabolism
chemical_list: D025601:Adenomatous Polyposis Coli Protein; C495267:CTNNB1 protein, mouse; D051153:Wnt Proteins; D051176:beta Catenin; D015689:Oncogene Protein p21(ras)