One cellular pathway involved in cancer progression that has received much recent attention is epithelial-mesenchymal transition (EMT)(Thiery, 2002, Hugo et al., 2007). EMT is a cellular program important during normal development (Nieto, 2002). However, recent studies have shown its importance in cancer progression and metastases (Turley et al., 2008, Thiery and Sleeman, 2006, Hugo et al., 2007). During EMT, epithelial cells lose tight junctions and acquire a more migratory and invasive (mesenchymal) phenotype. These changes include downregulation of junctional proteins including E-cadherin and expression of mesenchymal proteins like vimentin. In addition cells express matrix metalloprotease (MMP) enzymes that dissolve the extracellular matrix and promote cell migration and cancer cell invasion and metastases (Thiery and Sleeman, 2006, Egeblad and Werb, 2002). One key transcription factor regulating EMT is Snail (Nieto, 2002). Others include Snail2, ZEB1/2, and Twist with WNT/β-catenin signaling also being a critical component of EMT (Thiery and Sleeman, 2006, Peinado et al., 2007). Signaling through several growth factor receptors including the epidermal growth factor receptor (EGFR) can induce EMT and Snail expression (Ackland et al., 2003, Peinado et al., 2007).
