(beta)-Catenin is a key downstream effector in the Wnt signaling pathway. It is implicated in two major biological processes in vertebrates: early embryonic development and tumorigenesis. CK1 phosphorylates (beta)-catenin at Ser45. This phosphorylation event primes (beta)-catenin for subsequent phosphorylation by GSK-3(beta). GSK-3(beta) destabilizes (beta)-catenin by phosphorylating it at Ser33, Ser37, and Thr41. Mutations at these sites result in the stabilization of (beta)-catenin protein levels and have been found in many tumor cell lines.