title: Dickkopf-Related Protein 2 is Epigenetically Inactivated and Suppresses Colorectal Cancer Growth and Tumor Metastasis by Antagonizing Wnt/β-Catenin Signaling.
abstract: OBJECTIVE
  Aberrant activation of the Wnt/β-catenin signaling pathway plays a key role in the pathogenesis of multiple tumors including digestive cancers. Recent studies have reported that Dickkopf-related protein 2 (DKK2) is epigenetically inactivated in numerous types of cancers and that its gene products exhibit tumor-suppressive properties. However, the biological functions and underlying molecular mechanisms of DKK2 in colon carcinoma remains obscure.
  
  
  METHODS
  We examined the expression of DKK2 in colon tumor cell lines by RT-PCR and its promoter methylation status in colon tumor cell lines and primary tumors by methylation-specific PCR (MSP). Ectopic expression of DKK2 was measured by RT-PCR prior to the other experiments. To investigate the function of DKK2, we assayed colony formation and cell proliferation, utilized flow cytometric analyses of the cell cycle and acridine orange/ethidium bromide (AO/EB) fluorescence staining for apoptosis, and examined wound healing, transwell migration and tumor growth in vivo. Western blots were used to explore the mechanisms of DKK2 in epithelial- mesenchymal transition and canonical Wnt/β-catenin signaling.
  
  
  RESULTS
  We show here that downregulation or silencing of DKK2 was closely associated with the hypermethylation status of its promoter and that DKK2 expression could be restored by demethylation treatment. Methylation of the DKK2 promoter was detected in nearly all tumors and tumor-adjacent tissues, but not in normal colon tissues. Ectopic expression of DKK2 in colon cell lines HCT116 and HT-29 inhibited colony formation and cell viability by inducing cell cycle G0/G1 arrest and apoptosis, and growth of stable DKK2-infected HCT116 cells in nude mice was decreased compared to controls. Furthermore, DKK2 restrained cell migration through partial reversal of epithelial-to- mesenchymal transition and also by downregulating several stem cell markers. Our data further showed that restoration of DKK2 expression resulted in downregulation of active β-catenin and its downstream target genes.
  
  
  CONCLUSIONS
  DKK2 appears to be a functional tumor suppressor regulating tumorigenesis of colorectal cancer by antagonizing Wnt/β-catenin signaling.
authors.forename: Can
authors.initials: C
authors.lastname: Wang
authors.forename: Yujuan
authors.initials: Y
authors.lastname: Yue
authors.forename: Bianfei
authors.initials: B
authors.lastname: Shao
authors.forename: Zhu
authors.initials: Z
authors.lastname: Qiu
authors.forename: Junhao
authors.initials: J
authors.lastname: Mu
authors.forename: Jun
authors.initials: J
authors.lastname: Tang
authors.forename: Xiaofan
authors.initials: X
authors.lastname: Han
authors.forename: Tingxiu
authors.initials: T
authors.lastname: Xiang
authors.forename: Guosheng
authors.initials: G
authors.lastname: Ren
mesh_terms: D000818:Animals; D015179:Colorectal Neoplasms / Q000235:genetics / Q000378:metabolism* / Q000473:pathology; D044127:Epigenesis, Genetic; D005260:Female; D015972:Gene Expression Regulation, Neoplastic; D006801:Humans; D036341:Intercellular Signaling Peptides and Proteins / Q000096:biosynthesis* / Q000235:genetics; D008297:Male; D051379:Mice; D008807:Mice, Inbred BALB C; D008819:Mice, Nude; D009362:Neoplasm Metastasis; D009363:Neoplasm Proteins / Q000235:genetics / Q000378:metabolism*; D060449:Wnt Signaling Pathway; D051176:beta Catenin / Q000235:genetics / Q000378:metabolism*
chemical_list: C498622:DKK2 protein, human; D036341:Intercellular Signaling Peptides and Proteins; D009363:Neoplasm Proteins; D051176:beta Catenin
keywords: Colon cancer; DKK2; Methylation; Tumor suppressor; Wnt/β-catenin