Frizzled-7 as a Potential Therapeutic Target in Colorectal Cancer

Abstract

We investigated whether one of the Wnt receptors, frizzled-7 (FZD7), functions in the canonical Wnt signaling pathway of colorectal cancer (CRC) cells harboring an APC or CTNNB1 mutation and may be a potential therapeutic target for sporadic CRCs. The expression level of FZD gene family members in colon cancer cells and primary CRC tissues were determined by real-time PCR. Activation of the Wnt signaling pathway was evaluated by TOPflash assay. The expression level of Wnt target genes was determined by real-time polymerase chain reaction and/or Western blot analysis. Cell growth and cell invasion were assessed by MTS and matrigel assays, respectively. Among 10 FZD gene family members, FZD7 mRNA was predominantly expressed in six colon cancer cell lines with APC or CTNNB1 mutation. These six cell lines were transfected with FZD7 cDNA together with a TOPflash reporter plasmid, resulting in a 1.5- to 24.3-fold increase of Tcf transcriptional activity. The mRNA expression levels of seven known Wnt target genes were also increased by 1.5- to 3.4-fold after transfection of FZD7 cDNA into HCT-116 cells. The six cell lines were then cotransfected with FZD7-siRNA and a TOPflash reporter plasmid, which reduced Tcf transcriptional activity to 20% to 80%. FZD7-siRNA was shown to significantly decrease cell viability and in vitro invasion activity after transfection into HCT-116 cells. Our present data demonstrated that FZD7 activates the canonical Wnt pathway in colon cancer cells despite the presence of APC or CTNNB1 mutation and that FZD7-siRNA may be used as a therapeutic reagent for CRCs.

Down-regulation of frizzled-7 expression decreases survival, invasion and metastatic capabilities of colon cancer cells

“…Transient transfection of FZD7_siRNA prepared for this study into colon cancer HCT-116 or HT-29 cells gave rise to a significant suppression of cell viability (Figure 2A), confirming our previous finding (Ueno et al, 2008). This also seems to be consistent with a previous finding that siRNA inhibition of FZD7 decreased the viability of mesenchymal stem cells (hMSCs; Song et al, 2006).…”

“…Moreover, the down-regulation of FZD7 with Small-interfering RNA (siRNA) in colon cancer cells resulted in decreased in vitro invasion activity (Ueno et al, 2008), which is consistent with previous findings that inhibition of FZD7 expression with dominant-negative mutant construct or siRNA reduced the motility of hepatocellular carcinoma cells (Merle et al, 2004) or colon cancer cells (Vincan et al, 2007), respectively. These data suggest that FZD7 may be important in the invasion and metastasis of CRC.…”

“…We have recently reported that frizzled-7 (FZD7), 1 of 10 members of the FZD gene family, is predominantly expressed in colon cancer cells and is implicated in canonical Wnt signalling in colon cancer cells with APC or CTNNB1 mutations (Ueno et al, 2008). Moreover, the down-regulation of FZD7 with Small-interfering RNA (siRNA) in colon cancer cells resulted in decreased in vitro invasion activity (Ueno et al, 2008), which is consistent with previous findings that inhibition of FZD7 expression with dominant-negative mutant construct or siRNA reduced the motility of hepatocellular carcinoma cells (Merle et al, 2004) or colon cancer cells (Vincan et al, 2007), respectively.…”

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

“…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). Consequently, extracellular Wnt inhibitors such as SFRPs (Taketo, 2004), Wnt inhibitory factor-1 (Hu et al, 2009) or anti-Wnt1 antibodies (He et al, 2005) block tumor cell growth in cells carrying mutant b-catenin.…”

The Wnt receptor FZD1 mediates chemoresistance in neuroblastoma through activation of the Wnt/β-catenin pathway

“…In a majority of tumours, aberrant activation of the Wnt/b-catenin is the consequence of APC, Axin or b-catenin gene mutations (Lustig and Behrens, 2003). Moreover, it has been shown that overactivation of the Wnt signalling pathway is due to the overexpression of different FZD receptors in a variety of cancers (Milovanovic et al, 2004;Merle et al, 2005;Ueno et al, 2008). In NB, b-catenin has been shown to be strongly expressed and aberrantly localized in the nucleus in highly aggressive NB cells without MYCN amplification, whereas no b-catenin-specific mutations were identified (Liu et al, 2008).…”