Binding of GSK3β to the APC-β-Catenin Complex and Regulation of Complex Assembly

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Abstract
The adenomatous polyposis coli gene ( APC ) is mutated in most colon cancers. The APC protein binds to the cellular adhesion molecule β-catenin, which is a mammalian homolog of ARMADILLO, a component of the WINGLESS signaling pathway in Drosophila development. Here it is shown that when β-catenin is present in excess, APC binds to another component of the WINGLESS pathway, glycogen synthase kinase 3β (GSK3β), a mammalian homolog of Drosophila ZESTE WHITE 3. APC was a good substrate for GSK3β in vitro, and the phosphorylation sites were mapped to the central region of APC. Binding of β-catenin to this region was dependent on phosphorylation by GSK3β.