GSK-3beta-dependent phosphorylation of adenomatous polyposis coli gene product can be modulated by beta-catenin and protein phosphatase 2A complexed with Axin.
Axin forms a complex with adenomatous polyposis coli gene product (APC), glycogen synthase kinase-3beta (GSK-3beta), and beta-catenin through different binding sites and downregulates beta-catenin. GSK-3beta-dependent phosphorylation of APC-(1211-2075) which has the Axin-binding site was facilitated by Axin, but that of APC-(959-1338) which lacks the Axin-binding site was not. Axin-(298-506) or Axin-(298-832), which has the GSK-3beta- and beta-catenin- but not APC-binding sites, did not enhance GSK-3beta-dependent phosphorylation of either APC-(1211-2075) or APC-(959-1338). Furthermore, beta-catenin stimulated the phosphorylation of APC-(959-1338) and APC-(1211-2075) by GSK-3beta in the presence of Axin. Consistent with these in vitro observations, expression of beta-catenin or Axin in COS cells promoted an SDS gel band shift of APC. These results indicate that APC complexed with Axin is effectively phosphorylated by GSK-3beta and that beta-catenin may modulate this phosphorylation. In addition, the heterodimeric form of protein phosphatase 2A (PP2A) directly bound to Axin, and PP2A complexed with Axin dephosphorylated APC phosphorylated by GSK-3beta. Taken together, these results suggest that GSK-3beta-dependent phosphorylation of APC can be modulated by beta-catenin and PP2A complexed with Axin.
Ikeda
S
S
Department of Biochemistry, Hiroshima University School of Medicine, Japan.
Kishida
M
M
Matsuura
Y
Y
Usui
H
H
Kikuchi
A
A
D025601:Adenomatous Polyposis Coli Protein; D000818:Animals; D060466:Axin Protein; D001665:Binding Sites; D019556:COS Cells; D017871:Calcium-Calmodulin-Dependent Protein Kinases / Q000378:metabolism*; D002522:Chlorocebus aethiops; D003598:Cytoskeletal Proteins / Q000235:genetics / Q000378:metabolism*; D005786:Gene Expression Regulation; D017491:Genes, APC; D038362:Glycogen Synthase Kinase 3; D038341:Glycogen Synthase Kinases; D007739:L Cells; D046911:Macromolecular Substances; D051379:Mice; D010446:Peptide Fragments / Q000378:metabolism; D010749:Phosphoprotein Phosphatases / Q000378:metabolism*; D010766:Phosphorylation; D054648:Protein Phosphatase 2; D011499:Protein Processing, Post-Translational; D011506:Proteins / Q000378:metabolism*; D011993:Recombinant Fusion Proteins / Q000096:biosynthesis; D012097:Repressor Proteins; D015534:Trans-Activators; D051176:beta Catenin
D025601:Adenomatous Polyposis Coli Protein; D060466:Axin Protein; C495267:CTNNB1 protein, mouse; D003598:Cytoskeletal Proteins; D046911:Macromolecular Substances; D010446:Peptide Fragments; D011506:Proteins; D011993:Recombinant Fusion Proteins; D012097:Repressor Proteins; D015534:Trans-Activators; D051176:beta Catenin; D038341:Glycogen Synthase Kinases; D017871:Calcium-Calmodulin-Dependent Protein Kinases; D038362:Glycogen Synthase Kinase 3; D010749:Phosphoprotein Phosphatases; D054648:Protein Phosphatase 2