Frizzled/WNT signalling: the insidious promoter of tumour growth and progression.

The recognition that the processes involved in tumour formation are strikingly similar to developmental morphogenetic processes, such as gastrulation, has refashioned our approach to cancer research. Wnt and its receptor Frizzled govern the morphogenetic processes of gastrulation. Directed cell movements during gastrulation require the cells to undergo transient epithelial to mesenchymal transitions, enabling the cells to dissociate and migrate. To do this, Frizzleds activate different intracellular signalling cascades that affect cellular processes such as differentiation, proliferation, cell motility and cell polarity. Cell dissociation and migration are also essential for tumour cell invasion and metastases and the frequent deregulation of Wnt and Frizzled in human cancers implicates them in this process. Indeed recent evidence links both canonical (Wnt/beta-catenin) and non-canonical (Wnt/Ca2+) pathways to tumour invasion and metastases, emphasizing the importance of Frizzled in tumour growth and progression.