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Rolf Kemler - One of the best experts on this subject based on the ideXlab platform.
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inactivation of the β catenin gene by wnt1 cre mediated deletion results in dramatic brain malformation and failure of craniofacial development
Development, 2001Co-Authors: Veronique Brault, Robert Moore, Stefanie Kutsch, Makoto Ishibashi, David H Rowitch, Andrew P Mcmahon, Lukas Sommer, Oreda Boussadia, Rolf KemlerAbstract:Beta-Catenin is a central component of both the cadherin-catenin cell adhesion complex and the Wnt signaling pathway. We have investigated the role of Beta-Catenin during brain morphogenesis, by specifically inactivating the Beta-Catenin gene in the region of Wnt1 expression. To achieve this, mice with a conditional ('floxed') allele of Beta-Catenin with required exons flanked by loxP recombination sequences were intercrossed with transgenic mice that expressed Cre recombinase under control of Wnt1 regulatory sequences. Beta-Catenin gene deletion resulted in dramatic brain malformation and failure of craniofacial development. Absence of part of the midbrain and all of the cerebellum is reminiscent of the conventional Wnt1 knockout (Wnt1(-/-)), suggesting that Wnt1 acts through Beta-Catenin in controlling midbrain-hindbrain development. The craniofacial phenotype, not observed in embryos that lack Wnt1, indicates a role for Beta-Catenin in the fate of neural crest cells. Analysis of neural tube explants shows that (Beta-Catenin is efficiently deleted in migrating neural crest cell precursors. This, together with an increased apoptosis in cells migrating to the cranial ganglia and in areas of prechondrogenic condensations, suggests that removal of Beta-Catenin affects neural crest cell survival and/or differentiation. Our results demonstrate the pivotal role of Beta-Catenin in morphogenetic processes during brain and craniofacial development.
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inactivation of the beta catenin gene by wnt1 cre mediated deletion results in dramatic brain malformation and failure of craniofacial development
Development, 2001Co-Authors: Veronique Brault, Robert Moore, Stefanie Kutsch, Makoto Ishibashi, David H Rowitch, Andrew P Mcmahon, Lukas Sommer, Oreda Boussadia, Rolf KemlerAbstract:Beta-Catenin is a central component of both the cadherin-catenin cell adhesion complex and the Wnt signaling pathway. We have investigated the role of Beta-Catenin during brain morphogenesis, by specifically inactivating the Beta-Catenin gene in the region of Wnt1 expression. To achieve this, mice with a conditional ('floxed') allele of Beta-Catenin with required exons flanked by loxP recombination sequences were intercrossed with transgenic mice that expressed Cre recombinase under control of Wnt1 regulatory sequences. Beta-Catenin gene deletion resulted in dramatic brain malformation and failure of craniofacial development. Absence of part of the midbrain and all of the cerebellum is reminiscent of the conventional Wnt1 knockout (Wnt1(-/-)), suggesting that Wnt1 acts through Beta-Catenin in controlling midbrain-hindbrain development. The craniofacial phenotype, not observed in embryos that lack Wnt1, indicates a role for Beta-Catenin in the fate of neural crest cells. Analysis of neural tube explants shows that (Beta-Catenin is efficiently deleted in migrating neural crest cell precursors. This, together with an increased apoptosis in cells migrating to the cranial ganglia and in areas of prechondrogenic condensations, suggests that removal of Beta-Catenin affects neural crest cell survival and/or differentiation. Our results demonstrate the pivotal role of Beta-Catenin in morphogenetic processes during brain and craniofacial development.
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β catenin is a target for the ubiquitin proteasome pathway
The EMBO Journal, 1997Co-Authors: Hermann Aberle, J. Stappert, Andreas Bauer, Andreas Kispert, Rolf KemlerAbstract:Beta-Catenin is a central component of the cadherin cell adhesion complex and plays an essential role in the Wingless/Wnt signaling pathway. In the current model of this pathway, the amount of Beta-Catenin (or its invertebrate homolog Armadillo) is tightly regulated and its steady-state level outside the cadherin-catenin complex is low in the absence of Wingless/Wnt signal. Here we show that the ubiquitin-dependent proteolysis system is involved in the regulation of Beta-Catenin turnover. Beta-Catenin, but not E-cadherin, p120(cas) or alpha-catenin, becomes stabilized when proteasome-mediated proteolysis is inhibited and this leads to the accumulation of multi-ubiquitinated forms of Beta-Catenin. Mutagenesis experiments demonstrate that substitution of the serine residues in the glycogen synthase kinase 3beta (GSK3beta) phosphorylation consensus motif of Beta-Catenin inhibits ubiquitination and results in stabilization of the protein. This motif in Beta-Catenin resembles a motif in IkappaB (inhibitor of NFkappaB) which is required for the phosphorylation-dependent degradation of IkappaB via the ubiquitin-proteasome pathway. We show that ubiquitination of Beta-Catenin is greatly reduced in Wnt-expressing cells, providing the first evidence that the ubiquitin-proteasome degradation pathway may act downstream of GSK3beta in the regulation of Beta-Catenin.
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n cadherin in adult rat cardiomyocytes in culture ii spatio temporal appearance of proteins involved in cell cell contact and communication formation of two distinct n cadherin catenin complexes
Journal of Cell Science, 1996Co-Authors: Cecilia M Hertig, Rolf Kemler, Stefan Butz, Sabine Koch, Monika Eppenbergereberhardt, Hans M EppenbergerAbstract:The spatio-temporal appearance and distribution of proteins forming the intercalated disc were investigated in adult rat cardiomyocytes (ARC). The 'redifferentiation model' of ARC involves extensive remodelling of the plasma membrane and of the myofibrillar apparatus. It represents a valuable system to elucidate the formation of cell-cell contact between cardiomyocytes and to assess the mechanisms by which different proteins involved in the cell-cell adhesion process are sorted in a precise manner to the sites of function. Appearance of N-cadherin, the catenins and connexin43 within newly formed adherens and gap junctions was studied. Here first evidence is provided for a formation of two distinct and separable N-cadherin/catenin complexes in cardiomyocytes. Both complexes are composed of N-cadherin and alpha-catenin which bind to either Beta-Catenin or plakoglobin in a mutually exclusive manner. The two N-cadherin/catenin complexes are assumed to be functionally involved in the formation of cell-cell contacts in ARC; however, the differential appearance and localization of the two types of complexes may also point to a specific role during ARC differentiation. The newly synthesized Beta-Catenin containing complex is more abundant during the first stages in culture after ARC isolation, while the newly synthesized plakoglobin containing complex progressively accumulates during the morphological changes of ARC. ARC formed a tissue-like pattern in culture whereby the new cell-cell contacts could be dissolved through Ca2+ depletion. Presence of cAMP and replenishment of Ca2+ content in the culture medium not only allowed reformation of cell-cell contacts but also affected the relative protein ratio between the two N-cadherin/catenin complexes, increasing the relative amount of newly synthesized Beta-Catenin over plakoglobin at a particular stage of ARC differentiation. The clustered N-cadherin/catenin complexes at the plasma membrane appear to be a prerequisite for the following gap junction formation; a temporal sequence of the appearance of adherens junction proteins and of gap junctions forming connexin-43 is suggested.
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beta catenin mediates the interaction of the cadherin catenin complex with epidermal growth factor receptor
Journal of Cell Biology, 1994Co-Authors: Heinz Hoschuetzky, Hermann Aberle, Rolf KemlerAbstract:Catenins mediate the linkage of classical cadherins with actin microfilaments and are part of a higher order protein structure by which cadherins are connected to other cytoplasmic and transmembrane proteins. The ratio of actin-bound to free cadherin-catenin complex, which varies depending on the type and growth rate of cells, is thought to be altered by cellular signals, such as those associated with mitosis, polarization of cells and growth factors during development. EGF induces an immediate tyrosine phosphorylation of Beta-Catenin and gamma-catenin (plakoglobin). We show here an association of the EGF-receptor with the cadherin-catenin complex. Using recombinant proteins we demonstrate the interaction of EGF-receptor and Beta-Catenin in in vitro kinase assays. This interaction is mediated by the evolutionarily conserved central "core" region of Beta-Catenin. These results suggest that catenins represent an important link between EGF-induced signal transduction and cadherin function.
Akira Kikuchi - One of the best experts on this subject based on the ideXlab platform.
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Roles of Axin in the Wnt signalling pathway.
Cellular Signalling, 1999Co-Authors: Akira KikuchiAbstract:The Wnt signalling pathway is conserved in various species from worms to mammals, and plays important roles in development, cellular proliferation, and differentiation. The molecular mechanisms by which the Wnt signal regulates cellular functions are becoming increasingly well understood. Wnt stabilizes cytoplasmic Beta-Catenin, which stimulates the expression of genes including c-myc, c-jun, fra-1, and cyclin D1. Axin, newly recognized as a component of the Wnt signalling pathway, negatively regulates this pathway. Other components of the Wnt signalling pathway, including Dvl, glycogen synthase kinase-3beta, Beta-Catenin, and adenomatous polyposis coli, interact with Axin, and the phosphorylation and stability of Beta-Catenin are regulated in the Axin complex. Thus, Axin acts as a scaffold protein in the Wnt signalling pathway, thereby regulating cellular functions.
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dix domains of dvl and axin are necessary for protein interactions and their ability to regulate β catenin stability
Molecular and Cellular Biology, 1999Co-Authors: Satoshi Ikeda, Shosei Kishida, Hideki Yamamoto, Shinichiro Hino, Michiko Kishida, Akira KikuchiAbstract:The N-terminal region of Dvl-1 (a mammalian Dishevelled homolog) shares 37% identity with the C-terminal region of Axin, and this related region is named the DIX domain. The functions of the DIX domains of Dvl-1 and Axin were investigated. By yeast two-hybrid screening, the DIX domain of Dvl-1 was found to interact with Dvl-3, a second mammalian Dishevelled relative. The DIX domains of Dvl-1 and Dvl-3 directly bound one another. Furthermore, Dvl-1 formed a homo-oligomer. Axin also formed a homo-oligomer, and its DIX domain was necessary. The N-terminal region of Dvl-1, including its DIX domain, bound to Axin directly. Dvl-1 inhibited Axin-promoted glycogen synthase kinase 3beta-dependent phosphorylation of Beta-Catenin, and the DIX domain of Dvl-1 was required for this inhibitory activity. Expression of Dvl-1 in L cells induced the nuclear accumulation of Beta-Catenin, and deletion of the DIX domain abolished this activity. Although expression of Axin in SW480 cells caused the degradation of Beta-Catenin and reduced the cell growth rate, expression of an Axin mutant that lacks the DIX domain did not affect the level of Beta-Catenin or the growth rate. These results indicate that the DIX domains of Dvl-1 and Axin are important for protein-protein interactions and that they are necessary for the ability of Dvl-1 and Axin to regulate the stability of Beta-Catenin.
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an f box protein fwd1 mediates ubiquitin dependent proteolysis of β catenin
The EMBO Journal, 1999Co-Authors: Masatoshi Kitagawa, Shigetsugu Hatakeyama, Michiko Shirane, Masaki Matsumoto, Noriko Ishida, Kimihiko Hattori, Ikuo Nakamichi, Akira Kikuchi, Keiichi I Nakayama, Keiko NakayamaAbstract:Beta-Catenin plays an essential role in the Wingless/Wnt signaling cascade and is a component of the cadherin cell adhesion complex. Deregulation of Beta-Catenin accumulation as a result of mutations in adenomatous polyposis coli (APC) tumor suppressor protein is believed to initiate colorectal neoplasia. Beta-Catenin levels are regulated by the ubiquitin-dependent proteolysis system and Beta-Catenin ubiquitination is preceded by phosphorylation of its N-terminal region by the glycogen synthase kinase-3beta (GSK-3beta)/Axin kinase complex. Here we show that FWD1 (the mouse homologue of Slimb/betaTrCP), an F-box/WD40-repeat protein, specifically formed a multi-molecular complex with Beta-Catenin, Axin, GSK-3beta and APC. Mutations at the signal-induced phosphorylation site of Beta-Catenin inhibited its association with FWD1. FWD1 facilitated ubiquitination and promoted degradation of Beta-Catenin, resulting in reduced cytoplasmic Beta-Catenin levels. In contrast, a dominant-negative mutant form of FWD1 inhibited the ubiquitination process and stabilized Beta-Catenin. These results suggest that the Skp1/Cullin/F-box protein FWD1 (SCFFWD1)-ubiquitin ligase complex is involved in Beta-Catenin ubiquitination and that FWD1 serves as an intracellular receptor for phosphorylated Beta-Catenin. FWD1 also links the phosphorylation machinery to the ubiquitin-proteasome pathway to ensure prompt and efficient proteolysis of Beta-Catenin in response to external signals. SCFFWD1 may be critical for tumor development and suppression through regulation of Beta-Catenin protein stability.
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axin a negative regulator of the wnt signaling pathway forms a complex with gsk 3β and β catenin and promotes gsk 3β dependent phosphorylation of β catenin
The EMBO Journal, 1998Co-Authors: Satoshi Ikeda, Shosei Kishida, Hideki Yamamoto, Hiroshi Murai, Shinya Koyama, Akira KikuchiAbstract:Glycogen synthase kinase-3 (GSK-3) mediates epidermal growth factor, insulin and Wnt signals to various downstream events such as glycogen metabolism, gene expression, proliferation and differentiation. We have isolated here a GSK-3beta-interacting protein from a rat brain cDNA library using a yeast two-hybrid method. This protein consists of 832 amino acids and possesses Regulators of G protein Signaling (RGS) and dishevelled (Dsh) homologous domains in its N- and C-terminal regions, respectively. The predicted amino acid sequence of this GSK-3beta-interacting protein shows 94% identity with mouse Axin, which recently has been identified as a negative regulator of the Wnt signaling pathway; therefore, we termed this protein rAxin (rat Axin). rAxin interacted directly with, and was phosphorylated by, GSK-3beta. rAxin also interacted directly with the armadillo repeats of Beta-Catenin. The binding site of rAxin for GSK-3beta was distinct from the Beta-Catenin-binding site, and these three proteins formed a ternary complex. Furthermore, rAxin promoted GSK-3beta-dependent phosphorylation of Beta-Catenin. These results suggest that rAxin negatively regulates the Wnt signaling pathway by interacting with GSK-3beta and Beta-Catenin and mediating the signal from GSK-3beta to Beta-Catenin.
Paul Polakis - One of the best experts on this subject based on the ideXlab platform.
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deletion of an amino terminal sequence beta catenin in vivo and promotes hyperphosporylation of the adenomatous polyposis coli tumor suppressor protein
Molecular and Cellular Biology, 1996Co-Authors: Susan Munemitsu, Bonnee Rubinfeld, Iris Albert, Paul PolakisAbstract:Regulation of cell adhesion and cell signaling by Beta-Catenin occurs through a mechanism likely involving the targeted degradation of the protein. Deletional analysis was used to generate a Beta-Catenin refractory to rapid turnover and to examine its effects on complexes containing either cadherin or the adenomatous polyposis coli (APC) protein. The results show that amino-terminal deletion of Beta-Catenin results in a protein with increased stability that acts in a dominant fashion with respect to wild-type Beta-Catenin. Constitutive expression in AtT20 cells of a Beta-Catenin lacking 89 N-terminal amino acids (deltaN89Beta-Catenin) resulted in severely reduced levels of the more labile wild-type Beta-Catenin. The mutant Beta-Catenin was expressed at endogenous levels but displaced the vast majority of wild-type Beta-Catenin associated with N-cadherin. The deltaN89Beta-Catenin accumulated on the APC protein to a level 10-fold over that of wild-type Beta-Catenin and recruited a kinase into the APC complex. The kinase was highly active toward APC in vitro and promoted a sodium dodecyl sulfate gel band shift that was also evident for endogenous APC from cells expressing the mutant Beta-Catenin. Unlike wild-type Beta-Catenin, which partitions solely as part of a high-molecular-weight complex, the deltaN89 mutant protein also fractionated as a stable monomer, indicating that it had escaped the requirement to associate with other proteins. That similar N-terminal mutants of Beta-Catenin have been implicated in cellular transformation suggests that their abnormal association with APC may, in part, be responsible for this phenotype.
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Wnt-1 regulates free pools of catenins and stabilizes APC-catenin complexes.
Molecular and Cellular Biology, 1996Co-Authors: Jackie Papkoff, Bonnee Rubinfeld, B Schryver, Paul PolakisAbstract:The Wnt-1 proto-oncogene induces the accumulation of Beta-Catenin and plakoglobin, two related proteins that associate with and functionally modulate the cadherin cell adhesion proteins. Here we have investigated the effects of Wnt-1 expression on the tumor suppressor protein APC, which also associates with catenins. Expression of Wnt-1 in two different cell lines greatly increased the stability of APC-catenin complexes. The steady-state levels of both catenins and APC were elevated by Wnt-1, and the half-lives of both Beta-Catenin and plakoglobin associated with APC were also markedly increased. The stabilization of catenins by Wnt-1 was primarily the result of a selective increase in the amount of uncomplexed, monomeric Beta-Catenin and plakoglobin, detected both by affinity precipitation and size-exclusion chromatography of cell extracts. Exogenous expression of Beta-Catenin was possible in cells already responding to Wnt-1 but not in the parental cells, suggesting that Wnt-1 inhibits an essential regulatory mechanism for Beta-Catenin turnover. APC has the capacity to oppose this Wnt-1 effect in experiments in which overexpression of the central region of APC significantly reduced the size of the monomeric pool of Beta-Catenin induced by Wnt-1. Thus, the Wnt-1 signal transduction pathway leads to the accumulation of monomeric catenins and stabilization of catenin complex formation with both APC and cadherins.
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the apc protein and e cadherin form similar but independent complexes with alpha catenin beta catenin and plakoglobin
Journal of Biological Chemistry, 1995Co-Authors: Bonnee Rubinfeld, Brian Souza, Iris Albert, Susan Munemitsu, Paul PolakisAbstract:The tumor suppressor APC protein associates with the cadherin-binding proteins alpha- and Beta-Catenin. To examine the relationship between cadherin, catenins, and APC, we have tested combinatorial protein-protein interactions in vivo, using a yeast two-hybrid system, and in vitro, using purified proteins. Beta-Catenin directly binds to APC at high and low affinity sites. alpha-Catenin cannot directly bind APC but associates with it by binding to Beta-Catenin. Plakoglobin, also known as gamma-catenin, directly binds to both APC and alpha-catenin and also to the APC-Beta-Catenin complex, but not directly to Beta-Catenin. Beta-Catenin binds to multiple independent regions of APC, some of which include a previously identified consensus motif and others which contain the centrally located 20 amino acid repeat sequences. The APC binding site on Beta-Catenin may be discontinuous since neither the carboxyl- nor amino-terminal halves of Beta-Catenin will independently associate with APC, although the amino-terminal half independently binds alpha-catenin. The catenins bind to APC and E-cadherin in a similar fashion, but APC and E-cadherin do not associate with each other either in the presence or absence of catenins. Thus, APC forms distinct heteromeric complexes containing combinations of alpha-catenin, Beta-Catenin, and plakoglobin which are independent from the cadherin-catenin complexes.
Margaret J. Wheelock - One of the best experts on this subject based on the ideXlab platform.
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characterization of the interactions of alpha catenin with alpha actinin and beta catenin plakoglobin
Journal of Cell Science, 1997Co-Authors: J E Nieset, Amy Redfield L Redfield, K A Knudsen, K R Johnson, Fang Jin, Margaret J. WheelockAbstract:Cadherins are calcium-dependent, cell surface glycoproteins involved in cell-cell adhesion. To function in cell-cell adhesion, the transmembrane cadherin molecule must be associated with the cytoskeleton via cytoplasmic proteins known as catenins. Three catenins, alpha-catenin, Beta-Catenin and gamma-catenin (also known as plakoglobin), have been identified. Beta-Catenin or plakoglobin is associated directly with the cadherin; alpha-catenin binds to Beta-Catenin/plakoglobin and serves to link the cadherin/catenin complex to the actin cytoskeleton. The domains on the cadherin and betacatenin/plakoglobin that are responsible for protein-protein interactions have been mapped. However, little is known about the molecular interactions between alpha-catenin and Beta-Catenin/plakoglobin or about the interactions between alpha-catenin and the cytoskeleton. In this study we have used the yeast two-hybrid system to map the domains on alpha-catenin that allow it to associate with Beta-Catenin/plakoglobin and with alpha-actinin. We also identify a region on alpha-actinin that is responsible for its interaction with alpha-catenin. The yeast two-hybrid data were confirmed with biochemical studies.
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the catenin cadherin adhesion system is localized in synaptic junctions bordering transmitter release zones
Journal of Cell Biology, 1996Co-Authors: Naoshige Uchida, Margaret J. Wheelock, Yasuko Honjo, Masatoshi TakeichiAbstract:Molecular mechanisms linking pre- and postsynaptic membranes at the interneuronal synapses are little known. We tested the cadherin adhesion system for its localization in synapses of mouse and chick brains. We found that two classes of cadherin-associated proteins, alpha N- and Beta-Catenin, are broadly distributed in adult brains, colocalizing with a synaptic marker, synaptophysin. At the ultrastructural level, these proteins were localized in synaptic junctions of various types, forming a symmetrical adhesion structure. These structures sharply bordered the transmitter release sites associated with synaptic vesicles, although their segregation was less clear in certain types of synapses. N-cadherin was also localized at a similar site of synaptic junctions but in restricted brain nuclei. In developing synapses, the catenin-bearing contacts dominated their junctional structures. These findings demonstrate that interneuronal synaptic junctions comprise two subdomains, transmitter release zone and catenin-based adherens junction. The catenins localized in these junctions are likely associated with certain cadherin molecules including N-cadherin, and the cadherin/ catenin complex may play a critical role in the formation or maintenance of synaptic junctions.
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interaction of alpha actinin with the cadherin catenin cell cell adhesion complex via alpha catenin
Journal of Cell Biology, 1995Co-Authors: K A Knudsen, Alejandro Peralta Soler, K R Johnson, Margaret J. WheelockAbstract:Cadherins are Ca(2+)-dependent, cell surface glycoproteins involved in cell-cell adhesion. Extracellularly, transmembrane cadherins such as E-, P-, and N-cadherin self-associate, while intracellularly they interact indirectly with the actin-based cytoskeleton. Several intracellular proteins termed catenins, including alpha-catenin, Beta-Catenin, and plakoglobin, are tightly associated with these cadherins and serve to link them to the cytoskeleton. Here, we present evidence that in fibroblasts alpha-actinin, but not vinculin, colocalizes extensively with the N-cadherin/catenin complex. This is in contrast to epithelial cells where both cytoskeletal proteins colocalize extensively with E-cadherin and catenins. We further show that alpha-actinin, but not vinculin, coimmunoprecipitates specifically with alpha- and Beta-Catenin from N- and E-cadherin-expressing cells, but only if alpha-catenin is present. Moreover, we show that alpha-actinin coimmunoprecipitates with the N-cadherin/catenin complex in an actin-independent manner. We therefore propose that cadherin/catenin complexes are linked to the actin cytoskeleton via a direct association between alpha-actinin and alpha-catenin.
Bonnee Rubinfeld - One of the best experts on this subject based on the ideXlab platform.
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deletion of an amino terminal sequence beta catenin in vivo and promotes hyperphosporylation of the adenomatous polyposis coli tumor suppressor protein
Molecular and Cellular Biology, 1996Co-Authors: Susan Munemitsu, Bonnee Rubinfeld, Iris Albert, Paul PolakisAbstract:Regulation of cell adhesion and cell signaling by Beta-Catenin occurs through a mechanism likely involving the targeted degradation of the protein. Deletional analysis was used to generate a Beta-Catenin refractory to rapid turnover and to examine its effects on complexes containing either cadherin or the adenomatous polyposis coli (APC) protein. The results show that amino-terminal deletion of Beta-Catenin results in a protein with increased stability that acts in a dominant fashion with respect to wild-type Beta-Catenin. Constitutive expression in AtT20 cells of a Beta-Catenin lacking 89 N-terminal amino acids (deltaN89Beta-Catenin) resulted in severely reduced levels of the more labile wild-type Beta-Catenin. The mutant Beta-Catenin was expressed at endogenous levels but displaced the vast majority of wild-type Beta-Catenin associated with N-cadherin. The deltaN89Beta-Catenin accumulated on the APC protein to a level 10-fold over that of wild-type Beta-Catenin and recruited a kinase into the APC complex. The kinase was highly active toward APC in vitro and promoted a sodium dodecyl sulfate gel band shift that was also evident for endogenous APC from cells expressing the mutant Beta-Catenin. Unlike wild-type Beta-Catenin, which partitions solely as part of a high-molecular-weight complex, the deltaN89 mutant protein also fractionated as a stable monomer, indicating that it had escaped the requirement to associate with other proteins. That similar N-terminal mutants of Beta-Catenin have been implicated in cellular transformation suggests that their abnormal association with APC may, in part, be responsible for this phenotype.
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Wnt-1 regulates free pools of catenins and stabilizes APC-catenin complexes.
Molecular and Cellular Biology, 1996Co-Authors: Jackie Papkoff, Bonnee Rubinfeld, B Schryver, Paul PolakisAbstract:The Wnt-1 proto-oncogene induces the accumulation of Beta-Catenin and plakoglobin, two related proteins that associate with and functionally modulate the cadherin cell adhesion proteins. Here we have investigated the effects of Wnt-1 expression on the tumor suppressor protein APC, which also associates with catenins. Expression of Wnt-1 in two different cell lines greatly increased the stability of APC-catenin complexes. The steady-state levels of both catenins and APC were elevated by Wnt-1, and the half-lives of both Beta-Catenin and plakoglobin associated with APC were also markedly increased. The stabilization of catenins by Wnt-1 was primarily the result of a selective increase in the amount of uncomplexed, monomeric Beta-Catenin and plakoglobin, detected both by affinity precipitation and size-exclusion chromatography of cell extracts. Exogenous expression of Beta-Catenin was possible in cells already responding to Wnt-1 but not in the parental cells, suggesting that Wnt-1 inhibits an essential regulatory mechanism for Beta-Catenin turnover. APC has the capacity to oppose this Wnt-1 effect in experiments in which overexpression of the central region of APC significantly reduced the size of the monomeric pool of Beta-Catenin induced by Wnt-1. Thus, the Wnt-1 signal transduction pathway leads to the accumulation of monomeric catenins and stabilization of catenin complex formation with both APC and cadherins.
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the apc protein and e cadherin form similar but independent complexes with alpha catenin beta catenin and plakoglobin
Journal of Biological Chemistry, 1995Co-Authors: Bonnee Rubinfeld, Brian Souza, Iris Albert, Susan Munemitsu, Paul PolakisAbstract:The tumor suppressor APC protein associates with the cadherin-binding proteins alpha- and Beta-Catenin. To examine the relationship between cadherin, catenins, and APC, we have tested combinatorial protein-protein interactions in vivo, using a yeast two-hybrid system, and in vitro, using purified proteins. Beta-Catenin directly binds to APC at high and low affinity sites. alpha-Catenin cannot directly bind APC but associates with it by binding to Beta-Catenin. Plakoglobin, also known as gamma-catenin, directly binds to both APC and alpha-catenin and also to the APC-Beta-Catenin complex, but not directly to Beta-Catenin. Beta-Catenin binds to multiple independent regions of APC, some of which include a previously identified consensus motif and others which contain the centrally located 20 amino acid repeat sequences. The APC binding site on Beta-Catenin may be discontinuous since neither the carboxyl- nor amino-terminal halves of Beta-Catenin will independently associate with APC, although the amino-terminal half independently binds alpha-catenin. The catenins bind to APC and E-cadherin in a similar fashion, but APC and E-cadherin do not associate with each other either in the presence or absence of catenins. Thus, APC forms distinct heteromeric complexes containing combinations of alpha-catenin, Beta-Catenin, and plakoglobin which are independent from the cadherin-catenin complexes.
