title: Destruction complex function in the Wnt signaling pathway of Drosophila requires multiple interactions between Adenomatous polyposis coli 2 and Armadillo.
abstract: The tumor suppressor Adenomatous polyposis coli (APC) negatively regulates Wnt signaling through its activity in the destruction complex. APC binds directly to the main effector of the pathway, β-catenin (βcat, Drosophila Armadillo), and helps to target it for degradation. In vitro studies demonstrated that a nonphosphorylated 20-amino-acid repeat (20R) of APC binds to βcat through the N-terminal extended region of a 20R. When phosphorylated, the phospho-region of an APC 20R also binds βcat and the affinity is significantly increased. These distinct APC-βcat interactions suggest different models for the sequential steps of destruction complex activity. However, the in vivo role of 20R phosphorylation and extended region interactions has not been rigorously tested. Here we investigated the functional role of these molecular interactions by making targeted mutations in Drosophila melanogaster APC2 that disrupt phosphorylation and extended region interactions and deletion mutants missing the Armadillo binding repeats. We tested the ability of these mutants to regulate Wnt signaling in APC2 null and in APC2 APC1 double-null embryos. Overall, our in vivo data support the role of phosphorylation and extended region interactions in APC2's destruction complex function, but suggest that the extended region plays a more significant functional role. Furthermore, we show that the Drosophila 20Rs with homology to the vertebrate APC repeats that have the highest affinity for βcat are functionally dispensable, contrary to biochemical predictions. Finally, for some mutants, destruction complex function was dependent on APC1, suggesting that APC2 and APC1 may act cooperatively in the destruction complex.
authors.affiliation: Department of Biological Sciences, Carnegie Mellon University, Pittsburgh, Pennsylvania 15213, USA.
authors.forename: Ezgi
authors.initials: E
authors.lastname: Kunttas-Tatli
authors.forename: Meng-Ning
authors.initials: MN
authors.lastname: Zhou
authors.forename: Sandra
authors.initials: S
authors.lastname: Zimmerman
authors.forename: Olivia
authors.initials: O
authors.lastname: Molinar
authors.forename: Fangyuan
authors.initials: F
authors.lastname: Zhouzheng
authors.forename: Krista
authors.initials: K
authors.lastname: Carter
authors.forename: Megha
authors.initials: M
authors.lastname: Kapur
authors.forename: Alys
authors.initials: A
authors.lastname: Cheatle
authors.forename: Richard
authors.initials: R
authors.lastname: Decal
authors.forename: Brooke M
authors.initials: BM
authors.lastname: McCartney
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D051186:Armadillo Domain Proteins / Q000378:metabolism*; D060465:Axin Signaling Complex / Q000378:metabolism*; D004330:Drosophila / Q000378:metabolism*; D029721:Drosophila Proteins / Q000378:metabolism*; D023061:Gene Order; D008969:Molecular Sequence Data; D046912:Multiprotein Complexes; D009154:Mutation; D010766:Phosphorylation; D011485:Protein Binding; D021381:Protein Transport; D016415:Sequence Alignment; D014157:Transcription Factors / Q000378:metabolism*; D025521:Tumor Suppressor Proteins / Q000378:metabolism*; D060449:Wnt Signaling Pathway
chemical_list: C467323:APC2 protein, Drosophila; C495305:ARM protein, Drosophila; D051186:Armadillo Domain Proteins; D060465:Axin Signaling Complex; D029721:Drosophila Proteins; D046912:Multiprotein Complexes; D014157:Transcription Factors; D025521:Tumor Suppressor Proteins