title: Global increase of p16INK4a in APC-deficient mouse liver drives clonal growth of p16INK4a-negative tumors.
abstract: Reduction of β-catenin (CTNNB1) destroying complex components, for example, adenomatous polyposis coli (APC), induces β-catenin signaling and subsequently triggers activation of genes involved in proliferation and tumorigenesis. Though diminished expression of APC has organ-specific and threshold-dependent influence on the development of liver tumors in mice, the molecular basis is poorly understood. Therefore, a detailed investigation was conducted to determine the underlying mechanism in the development of liver tumors under reduced APC levels. Mouse liver at different developmental stages was analyzed in terms of β-catenin target genes including Cyp2e1, Glul, and Ihh using real-time RT-PCR, reporter gene assays, and immunohistologic methods with consideration of liver zonation. Data from human livers with mutations in APC derived from patients with familial adenomatous polyposis (FAP) were also included. Hepatocyte senescence was investigated by determining p16(INK4a) expression level, presence of senescence-associated β-galactosidase activity, and assessing ploidy. A β-catenin activation of hepatocytes does not always result in β-catenin positive but unexpectedly also in mixed and β-catenin-negative tumors. In summary, a senescence-inducing program was found in hepatocytes with increased β-catenin levels and a positive selection of hepatocytes lacking p16(INK4a), by epigenetic silencing, drives the development of liver tumors in mice with reduced APC expression (Apc(580S) mice). The lack of p16(INK4a) was also detected in liver tumors of mice with triggers other than APC reduction.
  
  
  CONCLUSIONS
  Epigenetic silencing of p16(Ink4a) in selected liver cells bypassing senescence is a general principle for development of liver tumors with β-catenin involvement in mice independent of the initial stimulus.
authors.affiliation: Faculty of Medicine, Institute of Biochemistry, University of Leipzig, Leipzig, Germany. Department of Cell Engineering/GLP, Fraunhofer Institute for Cell Therapy and Immunology, Leipzig, Germany.
authors.forename: Elke
authors.initials: E
authors.lastname: Ueberham
authors.affiliation: Department for Molecular and Cellular Mechanisms of Neurodegeneration, University of Leipzig, Paul Flechsig Institute of Brain Research, Leipzig, Germany.
authors.forename: Pia
authors.initials: P
authors.lastname: Glöckner
authors.affiliation: Faculty of Medicine, Institute of Biochemistry, University of Leipzig, Leipzig, Germany.
authors.forename: Claudia
authors.initials: C
authors.lastname: Göhler
authors.affiliation: Institute of Pathology, University Clinic, University Heidelberg, Heidelberg, Germany.
authors.forename: Beate K
authors.initials: BK
authors.lastname: Straub
authors.affiliation: Institute of Laboratory Medicine, Clinical Chemistry and Molecular Diagnostics, University of Leipzig, Leipzig, Germany. Institute of Laboratory Medicine, Ludwig-Maximilians-University Munich, Munich, Germany.
authors.forename: Daniel
authors.initials: D
authors.lastname: Teupser
authors.affiliation: Central Institute of Mental Health, Department of Molecular Biology, University of Heidelberg, Mannheim, Germany.
authors.forename: Kai
authors.initials: K
authors.lastname: Schönig
authors.affiliation: Department of Toxicology, Institute of Experimental and Clinical Pharmacology and Toxicology, Tübingen, Germany.
authors.forename: Albert
authors.initials: A
authors.lastname: Braeuning
authors.affiliation: Institute of Pathology, University of Leipzig, Leipzig, Germany.
authors.forename: Anne Kathrin
authors.initials: AK
authors.lastname: Höhn
authors.affiliation: Max-Delbrueck-Center for Molecular Medicine, Berlin-Buch, Germany.
authors.forename: Boris
authors.initials: B
authors.lastname: Jerchow
authors.affiliation: Max-Delbrueck-Center for Molecular Medicine, Berlin-Buch, Germany.
authors.forename: Walter
authors.initials: W
authors.lastname: Birchmeier
authors.affiliation: Department of Neurosurgery, University of Leipzig, Leipzig, Germany.
authors.forename: Frank
authors.initials: F
authors.lastname: Gaunitz
authors.affiliation: Department for Molecular and Cellular Mechanisms of Neurodegeneration, University of Leipzig, Paul Flechsig Institute of Brain Research, Leipzig, Germany.
authors.forename: Thomas
authors.initials: T
authors.lastname: Arendt
authors.affiliation: The Beatson Institute for Cancer Research, Glasgow, United Kingdom.
authors.forename: Owen
authors.initials: O
authors.lastname: Sansom
authors.affiliation: Faculty of Medicine, Institute of Biochemistry, University of Leipzig, Leipzig, Germany.
authors.forename: Rolf
authors.initials: R
authors.lastname: Gebhardt
authors.affiliation: Department for Molecular and Cellular Mechanisms of Neurodegeneration, University of Leipzig, Paul Flechsig Institute of Brain Research, Leipzig, Germany. Uwe.Ueberham@medizin.uni-leipzig.de.
authors.forename: Uwe
authors.initials: U
authors.lastname: Ueberham
mesh_terms: D011125:Adenomatous Polyposis Coli / Q000235:genetics* / Q000378:metabolism; D025601:Adenomatous Polyposis Coli Protein / Q000235:genetics* / Q000378:metabolism; D000818:Animals; D002478:Cells, Cultured; D019941:Cyclin-Dependent Kinase Inhibitor p16 / Q000235:genetics* / Q000378:metabolism*; D044127:Epigenesis, Genetic; D015972:Gene Expression Regulation, Neoplastic; D006801:Humans; D008099:Liver / Q000378:metabolism / Q000473:pathology*; D008113:Liver Neoplasms / Q000235:genetics* / Q000378:metabolism / Q000473:pathology; D051379:Mice; D008822:Mice, Transgenic; D015398:Signal Transduction; D051176:beta Catenin / Q000378:metabolism
chemical_list: D025601:Adenomatous Polyposis Coli Protein; C495267:CTNNB1 protein, mouse; C417743:Cdkn2a protein, mouse; D019941:Cyclin-Dependent Kinase Inhibitor p16; D051176:beta Catenin