Figure 1.

Illustrated interaction between the cadherin–catenin complex and the APC protein. (A) In the absence of Wnt-1 and the presence of glycogen synthase kinase (GSK), β-catenin (β-cat) is stabilized and bound to cadherin or APC protein. Cadherin acts as a negative regulator of β-catenin by regulating the amount of free β-catenin. The free cytoplasmic β-catenin is degraded. (B) In the presence of Wnt-1, GSK is antagonized and mutant APC or tyrosine phosphorylated β-catenin cannot bind to each other, cytosolic free β-catenin concentrations rise, which leads to down-stream cell signalling and may be involved in carcinogenesis.