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The two SAMP repeats and their phosphorylation state in Drosophila Adenomatous polyposis coli-2 play mechanistically distinct roles in negatively regulating Wnt signaling.

Kunttas-Tatli E, Von Kleeck RA, Greaves BD, Vinson D, Roberts DM, McCartney BM - Mol. Biol. Cell (2015)

Bottom Line: One set of motifs frequently lost in these cancer-associated truncations is the SAMP repeats that mediate interactions between APC and Axin.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.

View Article: PubMed Central - PubMed

Affiliation: Department of Biological Sciences, Carnegie Mellon University, Pittsburgh, PA 15213.

No MeSH data available.


Related in: MedlinePlus

Both SAMP1 and SAMP2 are necessary for destructosome activity in the Drosophila embryo. (A, B) Hatch rate and cuticle analysis of APC2 APC1 double- (APC2g10APC1Q8) embryos with transgenes expressing APC2-FL and SAMP deletion mutants. (B, C) The cuticle phenotypes of embryos that failed to hatch were assessed, and the phenotypic average (PA) was calculated for mutant embryos. Cuticles were classified as either MZ+ (maternally mutant but zygotically rescued) or MZ (maternally and zygotically mutant). Higher numbers indicate more severe defects (scoring criteria as in McCartney et al., 2006). N, number of embryos scored. (D) Representative embryos showing the striped Arm accumulation and En expression. In all images, anterior is to the left and dorsal is up. Differential Arm accumulation is lost and the En expression domain is expanded in APC2- (APC2g10) embryos (2) compared with wild type (1). APC2-FL (3) and either single SAMP deletion (APC2-S1–/S2+ [4] and APC2-S1–/S2+ [5]) are sufficient to restore the normal Arm and En patterns in APC2- embryos. In contrast, deletion of both SAMPs (APC2-S1–/S2–) (6) fails to rescue the wild-type pattern of Arm and En. Scale bar, 25 μm.
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Figure 4: Both SAMP1 and SAMP2 are necessary for destructosome activity in the Drosophila embryo. (A, B) Hatch rate and cuticle analysis of APC2 APC1 double- (APC2g10APC1Q8) embryos with transgenes expressing APC2-FL and SAMP deletion mutants. (B, C) The cuticle phenotypes of embryos that failed to hatch were assessed, and the phenotypic average (PA) was calculated for mutant embryos. Cuticles were classified as either MZ+ (maternally mutant but zygotically rescued) or MZ (maternally and zygotically mutant). Higher numbers indicate more severe defects (scoring criteria as in McCartney et al., 2006). N, number of embryos scored. (D) Representative embryos showing the striped Arm accumulation and En expression. In all images, anterior is to the left and dorsal is up. Differential Arm accumulation is lost and the En expression domain is expanded in APC2- (APC2g10) embryos (2) compared with wild type (1). APC2-FL (3) and either single SAMP deletion (APC2-S1–/S2+ [4] and APC2-S1–/S2+ [5]) are sufficient to restore the normal Arm and En patterns in APC2- embryos. In contrast, deletion of both SAMPs (APC2-S1–/S2–) (6) fails to rescue the wild-type pattern of Arm and En. Scale bar, 25 μm.

Mentions: Between 4 and 6 h after egg laying, Wnt signaling plays a key role in the patterning of embryonic segments in Drosophila. Whereas ventral epidermal cells receiving Wnt secrete a smooth cuticle, ventral cells not receiving the signal generate cuticular projections called denticles (arrows in Figure 4C). The same pattern can be visualized as an accumulation of Armadillo (Arm; fly ß-catenin) in stripes of cells receiving Wnt signal and in the patterned expression of the Wnt target gene engrailed (Figure 4D1). This pattern is disrupted in embryos with aberrant Wnt signaling such as in APC mutants. In Drosophila, APC1 and APC2 play redundant roles in Wnt signaling throughout development. APC1- (APC1Q8) mutant flies are adult viable, with phenotypes restricted to apoptosis of photoreceptors in the compound eye (Ahmed et al., 2002). In contrast, APC2- (APC2g10) embryos are embryonic lethal, displaying a modest accumulation of Arm, an expanded engrailed expression domain, and a significant loss of denticles (McCartney et al., 1999, 2006; Kunttas-Tatli et al., 2012); Supplemental Figure S4, A and D2). Although APC2 is the primary Wnt regulator during embryogenesis, APC1 does contribute destructosome function; loss of APC1 in the embryo enhances the APC2- phenotype with a more robust accumulation of Arm and complete loss of denticles (Ahmed et al., 2002; Akong et al., 2002). Previous studies suggested that testing APC2 mutants in both the APC2 single- and APC2 APC1 double- backgrounds is informative: the APC2 APC1 double- background provides the most stringent test of destruction function, requiring substantial transgene function for rescue, whereas the APC2 single- background can reveal more subtle differences (Roberts et al., 2011; Kunttas-Tatli et al., 2012).


The two SAMP repeats and their phosphorylation state in Drosophila Adenomatous polyposis coli-2 play mechanistically distinct roles in negatively regulating Wnt signaling.

Kunttas-Tatli E, Von Kleeck RA, Greaves BD, Vinson D, Roberts DM, McCartney BM - Mol. Biol. Cell (2015)

Both SAMP1 and SAMP2 are necessary for destructosome activity in the Drosophila embryo. (A, B) Hatch rate and cuticle analysis of APC2 APC1 double- (APC2g10APC1Q8) embryos with transgenes expressing APC2-FL and SAMP deletion mutants. (B, C) The cuticle phenotypes of embryos that failed to hatch were assessed, and the phenotypic average (PA) was calculated for mutant embryos. Cuticles were classified as either MZ+ (maternally mutant but zygotically rescued) or MZ (maternally and zygotically mutant). Higher numbers indicate more severe defects (scoring criteria as in McCartney et al., 2006). N, number of embryos scored. (D) Representative embryos showing the striped Arm accumulation and En expression. In all images, anterior is to the left and dorsal is up. Differential Arm accumulation is lost and the En expression domain is expanded in APC2- (APC2g10) embryos (2) compared with wild type (1). APC2-FL (3) and either single SAMP deletion (APC2-S1–/S2+ [4] and APC2-S1–/S2+ [5]) are sufficient to restore the normal Arm and En patterns in APC2- embryos. In contrast, deletion of both SAMPs (APC2-S1–/S2–) (6) fails to rescue the wild-type pattern of Arm and En. Scale bar, 25 μm.
© Copyright Policy - creative-commons
Related In: Results  -  Collection

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Figure 4: Both SAMP1 and SAMP2 are necessary for destructosome activity in the Drosophila embryo. (A, B) Hatch rate and cuticle analysis of APC2 APC1 double- (APC2g10APC1Q8) embryos with transgenes expressing APC2-FL and SAMP deletion mutants. (B, C) The cuticle phenotypes of embryos that failed to hatch were assessed, and the phenotypic average (PA) was calculated for mutant embryos. Cuticles were classified as either MZ+ (maternally mutant but zygotically rescued) or MZ (maternally and zygotically mutant). Higher numbers indicate more severe defects (scoring criteria as in McCartney et al., 2006). N, number of embryos scored. (D) Representative embryos showing the striped Arm accumulation and En expression. In all images, anterior is to the left and dorsal is up. Differential Arm accumulation is lost and the En expression domain is expanded in APC2- (APC2g10) embryos (2) compared with wild type (1). APC2-FL (3) and either single SAMP deletion (APC2-S1–/S2+ [4] and APC2-S1–/S2+ [5]) are sufficient to restore the normal Arm and En patterns in APC2- embryos. In contrast, deletion of both SAMPs (APC2-S1–/S2–) (6) fails to rescue the wild-type pattern of Arm and En. Scale bar, 25 μm.
Mentions: Between 4 and 6 h after egg laying, Wnt signaling plays a key role in the patterning of embryonic segments in Drosophila. Whereas ventral epidermal cells receiving Wnt secrete a smooth cuticle, ventral cells not receiving the signal generate cuticular projections called denticles (arrows in Figure 4C). The same pattern can be visualized as an accumulation of Armadillo (Arm; fly ß-catenin) in stripes of cells receiving Wnt signal and in the patterned expression of the Wnt target gene engrailed (Figure 4D1). This pattern is disrupted in embryos with aberrant Wnt signaling such as in APC mutants. In Drosophila, APC1 and APC2 play redundant roles in Wnt signaling throughout development. APC1- (APC1Q8) mutant flies are adult viable, with phenotypes restricted to apoptosis of photoreceptors in the compound eye (Ahmed et al., 2002). In contrast, APC2- (APC2g10) embryos are embryonic lethal, displaying a modest accumulation of Arm, an expanded engrailed expression domain, and a significant loss of denticles (McCartney et al., 1999, 2006; Kunttas-Tatli et al., 2012); Supplemental Figure S4, A and D2). Although APC2 is the primary Wnt regulator during embryogenesis, APC1 does contribute destructosome function; loss of APC1 in the embryo enhances the APC2- phenotype with a more robust accumulation of Arm and complete loss of denticles (Ahmed et al., 2002; Akong et al., 2002). Previous studies suggested that testing APC2 mutants in both the APC2 single- and APC2 APC1 double- backgrounds is informative: the APC2 APC1 double- background provides the most stringent test of destruction function, requiring substantial transgene function for rescue, whereas the APC2 single- background can reveal more subtle differences (Roberts et al., 2011; Kunttas-Tatli et al., 2012).

Bottom Line: One set of motifs frequently lost in these cancer-associated truncations is the SAMP repeats that mediate interactions between APC and Axin.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.

View Article: PubMed Central - PubMed

Affiliation: Department of Biological Sciences, Carnegie Mellon University, Pittsburgh, PA 15213.

No MeSH data available.


Related in: MedlinePlus