title: The Wnt antagonist DICKKOPF-1 gene is a downstream target of beta-catenin/TCF and is downregulated in human colon cancer.
abstract: Wnt glycoproteins regulate homeostasis and development by binding to membrane Frizzled-LRP5/6 receptor complexes. Wnt signaling includes a canonical pathway involving cytosolic beta-catenin stabilization, nuclear translocation and gene regulation, acting as a co-activator of T-cell factor (TCF) proteins, and noncanonical pathways that activate Rho, Rac, JNK and PKC, or modulate Ca(2+) levels. DICKKOPF-1 (DKK-1) encodes a secreted Wnt antagonist that binds to LRP5/6 and induces its endocytosis, leading to inhibition of the canonical pathway. We show that activation of canonical signaling by Wnt1 or ectopic expression of active beta-catenin, TCF4 or LRP6 mutants induces transcription of the human DKK-1 gene. Multiple beta-catenin/TCF4 sites in the DKK-1 gene promoter contribute to this activation. In contrast, Wnt5a, which signals through noncanonical pathways, does not activate DKK-1. Northern and Western blot studies show that activation of the Wnt/beta-catenin pathway by treatment with lithium or Wnt3a-conditioned medium, or by stable expression of either Wnt1 or beta-catenin, increases DKK-1 RNA and protein, thus initiating a negative feedback loop. However, we found that DKK-1 expression decreases in human colon tumors, which suggests that DKK-1 acts as a tumor suppressor gene in this neoplasia. Our data indicate that the Wnt/beta-catenin pathway is downregulated by the induction of DKK-1 expression, a mechanism that is lost in colon cancer.
authors.affiliation: Instituto de Investigaciones Biomédicas Alberto Sols, Consejo Superior de Investigaciones Científicas-Universidad Autónoma de Madrid, Arturo Duperier 4, E-28029 Madrid, Spain.
authors.forename: José Manuel
authors.initials: JM
authors.lastname: González-Sancho
authors.forename: Oscar
authors.initials: O
authors.lastname: Aguilera
authors.forename: José Miguel
authors.initials: JM
authors.lastname: García
authors.forename: Natalia
authors.initials: N
authors.lastname: Pendás-Franco
authors.forename: Cristina
authors.initials: C
authors.lastname: Peña
authors.forename: Santiago
authors.initials: S
authors.lastname: Cal
authors.forename: Antonio
authors.initials: A
authors.lastname: García de Herreros
authors.forename: Félix
authors.initials: F
authors.lastname: Bonilla
authors.forename: Alberto
authors.initials: A
authors.lastname: Muñoz
mesh_terms: D003110:Colonic Neoplasms / Q000235:genetics* / Q000473:pathology*; D003598:Cytoskeletal Proteins / Q000494:pharmacology*; D004268:DNA-Binding Proteins / Q000494:pharmacology*; D015536:Down-Regulation; D020869:Gene Expression Profiling; D015972:Gene Expression Regulation, Neoplastic; D016147:Genes, Tumor Suppressor; D018257:Helix-Loop-Helix Motifs; D006706:Homeostasis; D006801:Humans; D036341:Intercellular Signaling Peptides and Proteins / Q000494:pharmacology; D011506:Proteins / Q000235:genetics*; D015398:Signal Transduction; D051820:TCF Transcription Factors; D015534:Trans-Activators / Q000494:pharmacology*; D058118:Transcription Factor 7-Like 2 Protein; D014157:Transcription Factors / Q000494:pharmacology*; D051153:Wnt Proteins; D051155:Wnt1 Protein; D051176:beta Catenin
chemical_list: C495270:CTNNB1 protein, human; D003598:Cytoskeletal Proteins; C501126:DKK1 protein, human; D004268:DNA-Binding Proteins; D036341:Intercellular Signaling Peptides and Proteins; D011506:Proteins; D051820:TCF Transcription Factors; C544894:TCF7L2 protein, human; D015534:Trans-Activators; D058118:Transcription Factor 7-Like 2 Protein; D014157:Transcription Factors; C495247:WNT1 protein, human; D051153:Wnt Proteins; D051155:Wnt1 Protein; D051176:beta Catenin