Drosophila Apc2 Is a Cytoskeletally-Associated Protein That Regulates Wingless Signaling in the Embryonic Epidermis

Department of Biology, University of North Carolina at Chapel Hill, Chapel Hill, North Carolina 27599-3280, USA.
The Journal of Cell Biology (Impact Factor: 9.83). 10/1999; 146(6):1303-18. DOI: 10.1083/jcb.146.6.1303
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ABSTRACT The tumor suppressor adenomatous polyposis coli (APC) negatively regulates Wingless (Wg)/Wnt signal transduction by helping target the Wnt effector beta-catenin or its Drosophila homologue Armadillo (Arm) for destruction. In cultured mammalian cells, APC localizes to the cell cortex near the ends of microtubules. Drosophila APC (dAPC) negatively regulates Arm signaling, but only in a limited set of tissues. We describe a second fly APC, dAPC2, which binds Arm and is expressed in a broad spectrum of tissues. dAPC2's subcellular localization revealed colocalization with actin in many but not all cellular contexts, and also suggested a possible interaction with astral microtubules. For example, dAPC2 has a striking asymmetric distribution in neuroblasts, and dAPC2 colocalizes with assembling actin filaments at the base of developing larval denticles. We identified a dAPC2 mutation, revealing that dAPC2 is a negative regulator of Wg signaling in the embryonic epidermis. This allele acts genetically downstream of wg, and upstream of arm, dTCF, and, surprisingly, dishevelled. We discuss the implications of our results for Wg signaling, and suggest a role for dAPC2 as a mediator of Wg effects on the cytoskeleton. We also speculate on more general roles that APCs may play in cytoskeletal dynamics.

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Available from: Catherine A Kirkpatrick, May 31, 2014
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    • "The middle third of APC carries a series of short binding sites for proteins involved in Wnt regulation, including 15- and 20-amino acid repeats (15R and 20R), which bind ß-catenin and SAMP repeats, which bind Axin. It also contains the short conserved sequence B [31], also known as the Catenin inhibitory domain (CID) [32]. Proposed models also consider the fact that both APC and Axin have ß-catenin binding sites, but unlike APC, Axin has a single ß-catenin binding site. "
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    ABSTRACT: The tumor suppressor Adenomatous Polyposis coli (APC) gene is mutated or lost in most colon cancers. Alterations in Protein kinase C (PKC) isozyme expression and aberrant regulation also comprise early events in intestinal carcinomas. Here we show that PKCδ expression levels are decreased in colon tumor cell lines with respect to non-malignant cells. Reciprocal co-immunoprecipitation and immunofluorescence studies revealed that PKCδ interacts specifically with both full-length (from non-malignant cells) and truncated APC protein (from cancerous cells) at the cytoplasm and at the cell nucleus. Selective inhibition of PKCδ in cancer SW480 cells, which do not possess a functional β-catenin destruction complex, did not affect β-catenin-mediated transcriptional activity. However, in human colon carcinoma RKO cells, which have a normal β-catenin destruction complex, negatively affected β-catenin-mediated transcriptional activity, cell proliferation, and the expression of Wnt target genes C-MYC and CYCLIN D1. These negative effects were confirmed by siRNA-mediated knockdown of PKCδ and by the expression of a dominant negative form of PKCδ in RKO cells. Remarkably, the PKCδ stably depleted cells exhibited augmented tumorigenic activity in grafted mice. We show that PKCδ functions in a mechanism that involves regulation of β-catenin degradation, because PKCδ inhibition induces β-catenin stabilization at the cytoplasm and its nuclear presence at the C-MYC enhancer even without Wnt3a stimulation. In addition, expression of a dominant form of PKCδ diminished APC phosphorylation in intact cells, suggesting that PKCδ may modulate canonical Wnt activation negatively through APC phosphorylation.
    PLoS ONE 03/2013; 8(3):e58540. DOI:10.1371/journal.pone.0058540 · 3.23 Impact Factor
    • ") Cell extract interaction, Localization (Oda et al., 1994; Pai et al., 1996; Peifer, 1993; Peifer and Wieschaus, 1990) DE-cadherin p120-catenin Yeast two-hybrid (Myster et al., 2003) Cell extract interaction, Localization (Myster et al., 2003) Armadillo a-Catenin Yeast two-hybrid In vitro binding (Pai et al., 1996) Cell extract interaction, Localization (Oda et al., 1993; Pai et al., 1996; Peifer, 1993) Cytoskeletal associations Armadillo APC2/E-APC Yeast two-hybrid (McCartney et al., 1999) Cell extract interaction, Localization (McCartney et al., 1999) p120-catenin a-Catenin Rho1 In vitro binding (Magie et al., 2002) Cell extract interaction, Localization (Magie et al., 2002) DE-cadherin Sisyphus Yeast two-hybrid In vitro binding (Liu et al., 2008) Cell extract interaction, Localization (Liu et al., 2008) Bitesize – Localization (Pilot et al., 2006) Moesin – Localization (Pilot et al., 2006) Abelson – Localization (Fox and Peifer, 2007) Enabled – Localization (Grevengoed et al., 2001) bHeavy-spectrin – Localization (Thomas et al., 1998) Cortactin – Localization (Katsube et al., 1998) Actin – Localization (Eaton et al., 1995) "
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    ABSTRACT: Adherens junctions are essential for the development and physiology of epithelial tissues. The Drosophila embryo is an excellent model for understanding adherens junction assembly, maintenance, and regulation during tissue development. Here, I review our current state of knowledge in this model system. The review begins by outlining the structure of the cadherin-catenin complex in Drosophila including core (DE-cadherin, Armadillo, α-catenin, and p120-catenin) and peripheral proteins. Then, it summarizes adherens junction assembly at cellularization and maturation at gastrulation. Finally, the regulation of adherens junctions during tissue morphogenesis is discussed. This discussion compares major morphogenetic events in the embryo (invagination of the ventral furrow, convergent extension of the germband, flattening of the amnioserosa, maintenance of tissue borders, epithelial branching, lumen formation, cell delamination, cell division, apoptosis, and dorsal closure) and common mechanisms involved (myosin activity, endocytosis, and mesenchymal-to-epithelial transitions).
    International review of cell and molecular biology 12/2012; 293:45-83. DOI:10.1016/B978-0-12-394304-0.00007-5 · 3.42 Impact Factor
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    • "Drosophila contains two APC genes, one expressed ubiquitously (called E-APC/Apc2 [31,32]), for which a null allele became available recently (e-apcf90 [30]), and another one predominantly expressed in neurons, for which a null allele was isolated and characterized many years ago (dApcQ8 [33]). To re-assess the role of APC in promoting Armadillo destabilization, we monitored the expression and function of Axin tagged with green fluorescent protein (Axin–GFP) in embryos completely lacking the function of both APC genes (apc null mutants; dApcQ8e-apcf90) using the GAL4 system as previously described [18]. "
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    ABSTRACT: Most cases of colorectal cancer are linked to mutational inactivation of the Adenomatous polyposis coli (APC) tumour suppressor. APC downregulates Wnt signalling by enabling Axin to promote the degradation of the Wnt signalling effector β-catenin (Armadillo in flies). This depends on Axin's DIX domain whose polymerization allows it to form dynamic protein assemblies ('degradasomes'). Axin is inactivated upon Wnt signalling, by heteropolymerization with the DIX domain of Dishevelled, which recruits it into membrane-associated 'signalosomes'. How APC promotes Axin's function is unclear, especially as it has been reported that APC's function can be bypassed by overexpression of Axin. Examining apc null mutant Drosophila tissues, we discovered that APC is required for Axin degradasome assembly, itself essential for Armadillo downregulation. Degradasome assembly is also attenuated in APC mutant cancer cells. Notably, Axin becomes prone to Dishevelled-dependent plasma membrane recruitment in the absence of APC, indicating a crucial role of APC in opposing the interaction of Axin with Dishevelled. Indeed, co-expression experiments reveal that APC displaces Dishevelled from Axin assemblies, promoting degradasome over signalosome formation in the absence of Wnts. APC thus empowers Axin to function in two ways-by enabling its DIX-dependent self-assembly, and by opposing its DIX-dependent copolymerization with Dishevelled and consequent inactivation.
    Open Biology 11/2011; 1(3):110013. DOI:10.1098/rsob.110013 · 5.78 Impact Factor
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