title: The two SAMP repeats and their phosphorylation state in Drosophila Adenomatous polyposis coli-2 play mechanistically distinct roles in negatively regulating Wnt signaling.
abstract: The tumor suppressor Adenomatous polyposis coli (APC) plays a key role in regulating the canonical Wnt signaling pathway as an essential component of the β-catenin destruction complex. C-terminal truncations of APC are strongly implicated in both sporadic and familial forms of colorectal cancer. However, many questions remain as to how these mutations interfere with APC's tumor suppressor activity. One set of motifs frequently lost in these cancer-associated truncations is the SAMP repeats that mediate interactions between APC and Axin. APC proteins in both vertebrates and Drosophila contain multiple SAMP repeats that lack high sequence conservation outside of the Axin-binding motif. In this study, we tested the functional redundancy between different SAMPs and how these domains are regulated, using Drosophila APC2 and its two SAMP repeats as our model. Consistent with sequence conservation-based predictions, we show that SAMP2 has stronger binding activity to Axin in vitro, but SAMP1 also plays an essential role in the Wnt destruction complex in vivo. In addition, we demonstrate that the phosphorylation of SAMP repeats is a potential mechanism to regulate their activity. Overall our findings support a model in which each SAMP repeat plays a mechanistically distinct role but they cooperate for maximal destruction complex function.
authors.affiliation: Department of Biological Sciences, Carnegie Mellon University, Pittsburgh, PA 15213.
authors.forename: Ezgi
authors.initials: E
authors.lastname: Kunttas-Tatli
authors.affiliation: Department of Biology, Franklin and Marshall College, Lancaster, PA 17604.
authors.forename: Ryan A
authors.initials: RA
authors.lastname: Von Kleeck
authors.affiliation: Department of Biology, Franklin and Marshall College, Lancaster, PA 17604.
authors.forename: Bradford D
authors.initials: BD
authors.lastname: Greaves
authors.affiliation: Department of Biological Sciences, Carnegie Mellon University, Pittsburgh, PA 15213.
authors.forename: David
authors.initials: D
authors.lastname: Vinson
authors.affiliation: Department of Biology, Franklin and Marshall College, Lancaster, PA 17604 bmccartney@cmu.edu david.roberts@fandm.edu.
authors.forename: David M
authors.initials: DM
authors.lastname: Roberts
authors.affiliation: Department of Biological Sciences, Carnegie Mellon University, Pittsburgh, PA 15213 bmccartney@cmu.edu david.roberts@fandm.edu.
authors.forename: Brooke M
authors.initials: BM
authors.lastname: McCartney
mesh_terms: D020816:Amino Acid Motifs; D000595:Amino Acid Sequence; D000818:Animals; D030801:Animals, Genetically Modified; D060466:Axin Protein / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D045744:Cell Line, Tumor; D015179:Colorectal Neoplasms / Q000737:chemistry / Q000235:genetics; D004330:Drosophila; D029721:Drosophila Proteins / Q000737:chemistry / Q000235:genetics* / Q000378:metabolism*; D006801:Humans; D008969:Molecular Sequence Data; D009154:Mutation; D010766:Phosphorylation; D011485:Protein Binding; D017434:Protein Structure, Tertiary; D020449:Repetitive Sequences, Amino Acid; D013329:Structure-Activity Relationship; D025521:Tumor Suppressor Proteins / Q000737:chemistry / Q000235:genetics* / Q000378:metabolism*; D060449:Wnt Signaling Pathway; D051176:beta Catenin / Q000378:metabolism
chemical_list: C467323:APC2 protein, Drosophila; D060466:Axin Protein; D029721:Drosophila Proteins; D025521:Tumor Suppressor Proteins; D051176:beta Catenin