1. ¹Instituto de Investigaciones Biomédicas 'Alberto Sols', Consejo Superior de Investigaciones Científicas–Universidad Autónoma de Madrid, Madrid, Spain
2. ²Hospital Universitario Puerta de Hierro, Madrid, Spain
3. ³Cambridge Research Institute, Cambridge, UK
4. ⁴Life Science Research Unit, University of Luxembourg, Luxembourg
5. ⁵Departamento de Bioquímica, Facultad de Medicina–Universidad Autónoma de Madrid, Madrid, Spain

Correspondence: Professor A Muñoz, Department of Cancer Biology, Instituto de Investigaciones Biomédicas 'Alberto Sols', Arturo Duperier 4, E-28029 Madrid, Spain. E-mail: amunoz@iib.uam.es

Received 29 August 2007; Revised 23 January 2008; Accepted 29 February 2008; Published online 14 April 2008.

Abstract

Aberrant activation of the Wnt/-catenin signaling pathway is a hallmark of colon cancer. We show that the Wnt antagonist DICKKOPF-4 (DKK-4) gene is repressed by 1,25-dihydroxyvitamin D₃ (1,25(OH)₂D₃) in human colon cancer cells. This effect correlated with the inhibition of the DKK-4 promoter. Chromatin immunoprecipitation assays revealed that 1,25(OH)₂D₃ induces early and transient binding of the vitamin D receptor (VDR) and the SMRT corepressor to the region adjacent to the transcription start site of DKK-4. Additionally, we demonstrate that the DKK-4 gene is a new downstream target of TCF/-catenin. Remarkably, expression of DKK-4 messenger RNA (mRNA) was not detected in a series of 29 human normal (N) colon biopsies but expression was upregulated in all the matched tumour (T) tissues. An inverse correlation existed between the expression of DKK-4 and VDR RNA in the Ts. Ectopic DKK-4 expression increased the migration and invasion properties of colon cancer cells and conditioned media (CM) from DKK-4-expressing cells enhanced the capacity to migrate and form capillary-like tubules of human primary microvascular endothelial cells. In conclusion, DKK-4 is upregulated in colon cancer and is associated with the acquisition of malignant properties by neoplastic cells. DKK-4 downregulation is a novel effect of 1,25(OH)₂D₃ that may contribute to its anticancer action.