Blocking Wnt signaling by SFRP-like molecules inhibits in vivo cell proliferation and tumor growth in cells carrying active ß-catenin.

Constitutive activation of Wnt/ß-catenin signaling in cancer results from mutations in pathway components, which frequently coexist with autocrine Wnt signaling or epigenetic silencing of extracellular Wnt antagonists. Among the extracellular Wnt inhibitors, the secreted frizzled-related proteins (SFRPs) are decoy receptors that contain soluble Wnt-binding frizzled domains. In addition to SFRPs, other endogenous molecules harboring frizzled motifs bind to and inhibit Wnt signaling. One of such molecules is V3Nter, a soluble SFRP-like frizzled polypeptide that binds to Wnt3a and inhibits Wnt signaling and expression of the ß-catenin target genes cyclin D1 and c-myc. V3Nter is derived from the cell surface extracellular matrix component collagen XVIII. Here, we used HCT116 human colon cancer cells carrying the ΔS45 activating mutation in one of the alleles of ß-catenin to show that V3Nter and SFRP-1 decrease baseline and Wnt3a-induced ß-catenin stabilization. Consequently, V3Nter reduces the growth of human colorectal cancer xenografts by specifically controlling cell proliferation and cell cycle progression, without affecting angiogenesis or apoptosis, as shown by decreased [(3)H]-thymidine (in vitro) or BrdU (in vivo) incorporation, clonogenesis assays, cell cycle analysis and magnetic resonance imaging in living mice. Additionally, V3Nter switches off the ß-catenin target gene expression signature in vivo. Moreover, experiments with ß-catenin allele-targeted cells showed that the ΔS45 ß-catenin allele hampers, but does not abrogate, inhibition of Wnt signaling by SFRP-1 or by the SFRP-like frizzled domain. Finally, neither SFRP-1 nor V3Nter affect ß-catenin signaling in SW480 cells carrying nonfunctional Adenomatous polyposis coli. Thus, SFRP-1 and the SFRP-like molecule V3Nter can inhibit tumor growth of ß-catenin-activated tumor cells in vivo.

Influence of different dietary fats on the incorporation of exogenous fatty acids into rat adipose glycerides.

Male Wistar rats were fed for 6 wk either a control low fat diet (1.5% sunflower seed oil) or a diet containing 10% fat: either saturated (coconut oil, cocoa butter) or unsaturated (olive oil, sunflower seed oil). In each dietary condition, in vitro incorporation of exogenously added fatty acids (ranging from capric to oleic acid) was studied in epididymal adipose glycerides. Analysis of variance of data revealed that there was a significant effect of the diet x substrate interaction. When results were expressed per cell lipid weight medium-chain fatty acids (capric and lauric) were esterified to a lesser extent than long-chain fatty acids regardless of the nature of dietary fat (saturated vs. unsaturated). The nature of dietary fat was found to have no effect on the incorporation of medium-chain fatty acids. Feeding saturated fats resulted in an increase of incorporation of long-chain fatty acids into adipose glycerides whereas feeding unsaturated fats did not modify fatty acid incorporation. Modifications of mean fat cell size by dietary fat could not account for all the observed variations.