title: Ligand-independent canonical Wnt activity in canine mammary tumor cell lines associated with aberrant LEF1 expression.
abstract: Pet dogs very frequently develop spontaneous mammary tumors and have been suggested as a good model organism for breast cancer research. In order to obtain an insight into underlying signaling mechanisms during canine mammary tumorigenesis, in this study we assessed the incidence and the mechanism of canonical Wnt activation in a panel of 12 canine mammary tumor cell lines. We show that a subset of canine mammary cell lines exhibit a moderate canonical Wnt activity that is dependent on Wnt ligands, similar to what has been described in human breast cancer cell lines. In addition, three of the tested canine mammary cell lines have a high canonical Wnt activity that is not responsive to inhibitors of Wnt ligand secretion. Tumor cell lines with highly active canonical Wnt signaling often carry mutations in key members of the Wnt signaling cascade. These cell lines, however, carry no mutations in the coding regions of intracellular Wnt pathway components (APC, β-catenin, GSK3β, CK1α and Axin1) and have a functional β-catenin destruction complex. Interestingly, however, the cell lines with high canonical Wnt activity specifically overexpress LEF1 mRNA and the knock-down of LEF1 significantly inhibits TCF-reporter activity. In addition, LEF1 is overexpressed in a subset of canine mammary carcinomas, implicating LEF1 in ligand-independent activation of canonical Wnt signaling in canine mammary tumors. We conclude that canonical Wnt activation may be a frequent event in canine mammary tumors both through Wnt ligand-dependent and novel ligand-independent mechanisms.
authors.affiliation: Department of Clinical Sciences of Companion Animals, Utrecht University, Utrecht, The Netherlands.
authors.forename: Ana
authors.initials: A
authors.lastname: Gracanin
authors.affiliation: Department of Clinical Sciences of Companion Animals, Utrecht University, Utrecht, The Netherlands.
authors.forename: Elpetra P M
authors.initials: EP
authors.lastname: Timmermans-Sprang
authors.affiliation: Department of Clinical Sciences of Companion Animals, Utrecht University, Utrecht, The Netherlands.
authors.forename: Monique E
authors.initials: ME
authors.lastname: van Wolferen
authors.affiliation: Department of Molecular Biology, Radboud University, Nijmegen, The Netherlands.
authors.forename: Nagesha A S
authors.initials: NA
authors.lastname: Rao
authors.affiliation: Clinic for Obestrics and Reproduction, Faculty of Veterinary Medicine, Zagreb, Croatia.
authors.forename: Juraj
authors.initials: J
authors.lastname: Grizelj
authors.affiliation: Clinic for Obestrics and Reproduction, Faculty of Veterinary Medicine, Zagreb, Croatia.
authors.forename: Silvijo
authors.initials: S
authors.lastname: Vince
authors.affiliation: Department of Anatomy, Physiology and Biochemistry, Swedish University of Agricultural Sciences, Uppsala, Sweden.
authors.forename: Eva
authors.initials: E
authors.lastname: Hellmen
authors.affiliation: Department of Clinical Sciences of Companion Animals, Utrecht University, Utrecht, The Netherlands.
authors.forename: Jan A
authors.initials: JA
authors.lastname: Mol
mesh_terms: D000818:Animals; D001483:Base Sequence; D015153:Blotting, Western; D015820:Cadherins / Q000378:metabolism; D045744:Cell Line, Tumor; D017931:DNA Primers; D004283:Dog Diseases / Q000378:metabolism*; D004285:Dogs; D006801:Humans; D008024:Ligands; D051821:Lymphoid Enhancer-Binding Factor 1 / Q000235:genetics / Q000378:metabolism*; D015674:Mammary Neoplasms, Animal / Q000378:metabolism*; D016133:Polymerase Chain Reaction; D051153:Wnt Proteins / Q000378:metabolism*
chemical_list: D015820:Cadherins; D017931:DNA Primers; D008024:Ligands; D051821:Lymphoid Enhancer-Binding Factor 1; D051153:Wnt Proteins