An autocrine mechanism for constitutive Wnt pathway activation in human cancer cells

Abstract

Autocrine Wnt signaling in the mouse mammary tumor virus model was the first identified mechanism of canonical pathway activation in cancer. In search of this transformation mechanism in human cancer cells, we identified breast and ovarian tumor lines with upregulation of the uncomplexed transcriptionally active form of beta-catenin without mutations afflicting downstream components. Extracellular Wnt antagonists FRP1 and DKK1 caused a dramatic downregulation of beta-catenin levels in these tumor cells associated with alteration of biological properties and increased expression of epithelial differentiation markers. Colorectal carcinoma cells with knockout of the mutant beta-catenin allele retained upregulated beta-catenin levels, which also could be inhibited by these Wnt antagonists. Together, these findings establish the involvement of autocrine Wnt signaling in human cancer cells.

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

“…In HCT116 cells, transient expression of V3Nter, SFRP-1 or SFRP-5 induces cell death (Suzuki et al, 2004;Quelard et al, 2008). Consistently, attempts to obtain clones by limiting dilution were unsuccessful, suggesting a negative selection pressure, as shown for SFRP-1 in breast cancer cells (Bafico et al, 2004). However, after seeding three cells per well, several antibiotic-resistant cell populations expressing the relevant epitopes (Supplementary Figure 1a) were expanded.…”

“…Enhanced autocrine Wnt signaling (Bafico et al, 2004) and epigenetic silencing of genes encoding endogenous extracellular Wnt inhibitors (Suzuki et al, 2004) provide a positive selection advantage to cells carrying b-catenin pathway mutations (Barker and Clevers, 2006;Polakis, 2007;MacDonald et al, 2009). In this setting, frizzled receptor activation and enhanced Wnt expression drive positive cancer cell selection (Vider et al, 1996; Smith et al, An SFRP-like frizzled motif blocks tumor growth E Lavergne et al 1999; Dimitriadis et al, 2001;Holcombe et al, 2002;Ueno et al, 2008).…”

“…A previous report showed that SFRP-1 had no effect on growth of HCT116 cells in vivo (Bafico et al, 2004). In that work, the authors used allele-targeted HCT116 cells carrying only WT b-catenin that exhibited elevated basal-level CRT, as well as higher response to serum growth factors and tumor growth than parental cells (Sekine et al, 2002).…”

Dickkopf-1 activates cell death in MDA-MB435 melanoma cells

“…Previous studies showed that overexpression of DKK-1 leads to activation of apoptosis after treatment with chemotherapeutic agents or UV. Sensitization to apoptosis was demonstrated in glioma cells [13], Hela cells [2], breast carcinoma cells [11], mesothelioma cells [12]. Activation of apoptosis in DKK-1 expressing cells was suggested is due to increased JNK activity.…”

“…[8,10]. Overexpression of DKK-1 resulted in activation of apoptosis in vitro following treatment with different chemotherapeutic agents [11][12][13] and UV irradiation [2]. However it is not known if DKK-1 can activate apoptosis in tumor xenografts in vivo.…”