27122

DKK3

REIC|RIG;dickkopf 3 homolog (Xenopus laevis);DKK3;dickkopf 3 homolog (Xenopus laevis)

RIG-like 5-6|RIG-like 7-1|dickkopf homolog 3|dickkopf-3|dickkopf-related protein 3|dkk-3|hDkk-3|regulated in glioma

11p15.2

protein-coding

Neuroblastoma is the most common extra-cranial solid childhood cancer; it arisesfrom neural crest-derived cells of the sympathetic nervous system. The anomalousregulation of embryonic developmental pathways like Delta-Notch and Wnt has beenimplicated in aberrant cell growth and differentiation in many (childhood) tumours. We have previously found regulation of Delta-Notch pathway genes by theMSX1 neural crest development gene in a neuroblastoma cell line, and significantcorrelations between these genes in neuroblastic tumours. However, a clear role for the Wnt pathway in neuroblastic tumours has not yet been determined. We now analyze the complete spectrum of genes regulated by inducible expression of MSX1in the SJNB8 neuroblastoma cell line using Affymetrix expression profiling. We show that MSX1 induces the expression of four different Wnt pathway inhibitor genes: Dickkopf 1-3 (DKK1-3) and secreted frizzled-related protein 1 (SFRP1), and provide evidence that high expression of two of these genes correlates with goodprognosis. We were able to demonstrate that both the canonical Wnt3 and the alternative Wnt5A ligands are highly expressed in neuroblastic tumours and cell lines, and specifically activate the DVL3 Wnt co-receptor protein in SJNB8 neuroblastoma cells. These results suggest involvement of MSX1 in Wnt signallingand demonstrate activity of the more upstream Wnt pathway in neuroblastic cells.#CI- Copyright 2009 Elsevier Ireland Ltd. ALL rights reserved.

Medulloblastoma (MB) is a malignant pediatric brain tumor arising in the cerebellum consisting of four distinct subgroups: WNT, SHH, Group 3 and Group 4,which exhibit different molecular phenotypes. We studied the expression of Dickkopf (DKK) 1-4 family genes, inhibitors of the Wnt signaling cascade, in MB by screening 355 expression profiles derived from four independent datasets. Upregulation of DKK1, DKK2 and DKK4 mRNA was observed in the WNT subgroup, whereas DKK3 was downregulated in 80% MBs across subgroups with respect to the normal cerebellum (p < 0.001). Since copy number aberrations targeting the DKK3 locus (11p15.3) are rare events, we hypothesized that epigenetic factors could play a role in DKK3 regulation. Accordingly, we studied 77 miRNAs predicting to repress DKK3; however, no significant inverse correlation between miRNA/mRNA expression was observed. Moreover, the low methylation levels in the DKK3 promoters (median: 3%, 5% and 5% for promoter 1, 2 and 3, respectively) excludedthe downregulation of gene expression by methylation. On the other hand, the treatment of MB cells with Trichostatin A (TSA), a potent inhibitor of histone deacetylases (HDAC), was able to restore both DKK3 mRNA and protein. In conclusion, DKK3 downregulation across ALL MB subgroups may be due to epigeneticmechanisms, in particular, through chromatin condensation.