**4.9 WNT**

The WNT signalling pathway mediates several vital processes such as cell proliferation, migration, differentiation, adhesion and death (Vincan et al., 2008). In addition, this pathway can promote migration and EMT in breast cancer cells through the stabilisation or increased expression of SNAIL1 and 2 and TWIST (Onder et al., 2008; Vogelstein et al., 2004). SNAIL has been implicated in regulatingWNT-1-induced EMT in MCF-7 cells. Furthermore, WNT signalling can also lead to the translocation of β-catenin to the nucleus where it can drive the expression of several EMT inducing transcription factors through the WNT induced inhibition of glycogen synthase kinase-3β (GSK3β)-mediated phosphorylation. However, β-catenin alone usually is not enough to induce EMT although in colorectal cancer WNT is indeed a silencer of its negative regulators SOX17 (Zhang et al., 2008), SFRPS18, 19 and DKK1 (Aguilera et al., 2006). Interestingly, both SFRP1 and DKK1 are frequently silenced by methylation in breast cancer.
