Oligomycin A molecular weight (A) Effect of FZD7_siRNA on cell viability. HCT-116 and HT-29 cells were transiently transfected with FZD7_siRNA or scramble siRNA control. At 6 days after transfection, HCT-116 and HT-29 cells were stained … To observe the effect of FZD7_siRNA on cell cycle, we transfected HCT-116 cells with scramble siRNA or FZD7_siRNA, and the cells were analysed by flow cytometry 48h after transfection. The percentage of cells at G2/M phase was reduced from 40 to 30% with FZD7_siRNA transfection (Figure 2B). To evaluate the effect of FZD7_siRNA on the expression and activation of MAP kinases, we subjected HCT-116 cells transfected with scramble siRNA or FZD7_siRNA to immunoblotting. As shown in Figure 2C, the band intensities of c-Jun, p-JNK and p-c-Jun were decreased by FZD7_siRNA.
JNK/c-Jun is involved in the non-canonical Wnt pathway and is regulated by the small GTPase RhoA (Cohen et al, 2008). We therefore examined whether FZD7_siRNA affects RhoA activation. HCT-116 cells were transfected with scramble siRNA or FZD7_siRNA and were subjected to the RhoA activation assay. As shown in Figure 2D, FZD7_siRNA decreased RhoA activation. Because RhoA has been shown to be involved in migration and dissemination of colon cancer cells (Croft et al, 2004), we assessed, using the Matrigel invasion assay, whether FZD7_siRNA affected the in vitro invasion activity of HCT-116 (Figure 2E). The number of invading cells was significantly decreased (P<0.0005) with FZD7_siRNA transfection.
To assess whether FZD7_siRNA indeed altered Wnt target genes including invasion/metastasis-related ones, we transfected FZD7_siRNA into HCT-116 cells and measured the expression levels of mRNAs with real-time PCR. The transcriptional levels of Wnt target genes including CD44v8-9 and MT1-MMP were decreased with FZD7_siRNA (Figure 2F). FZD7_siRNA inhibits in vivo metastasis HCT-116 cells were transfected with pcDNA3.1-U6EGFP_siRNA or pcDNA3.1-U6 FZD7_siRNA, and the expression level of FZD7 and two target genes (MT1-MMP and Jun) in stable transfectants was measured with real-time PCR. We used two stable transfectants (FZD7_siRNA clone 1 and clone 2) that show the decreased expression of these genes compared with control cells harbouring EGFP_siRNA for the following experiments (Figure 3A). To test canonical Wnt signal-transducing activity, we transfected TOPflash reporter plasmid into the transfectants, and measured the Tcf transcriptional activity (Figure 3B).
We found that Tcf activity was decreased to ~20% in both FZD7_siRNA clones compared to control cells. Cell viability and invasion activity were also significantly decreased in FZD7_siRNA transfectants (P<0.005 and <0.05, Cilengitide respectively; Figures 3C and D). Figure 3 FZD7_siRNA inhibits in vivo metastasis. (A) The level of mRNA expression of FZD7, MT1-MMP and Jun in stable transfectants expressing FZD7_siRNA.