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[
Dev Biol,
2011]
The Wnt and Src pathways are widely used signal transduction pathways in development. -catenin is utilized in both pathways, as a signal transducer and a component of the cadherin cell adhesion complex, respectively. A C. elegans -catenin HMP-2 is involved in cell adhesion, but its signaling role has been unknown. Here, we report that in early embryogenesis HMP-2 acts as a signaling molecule in the Src signal. During early embryogenesis in C. elegans, the Wnt and Src pathways are redundantly involved in endoderm induction at the four-cell stage and spindle orientation in an ABar blastomere. RNAi experiments demonstrated that HMP-2 functions in the Src pathway, but in parallel with the Wnt pathway in these processes. HMP-2 localized at the cell boundaries and nuclei, and its localization at cell boundaries was negatively regulated by SRC-1. In addition, HMP-2 was Tyr-phosphorylated in a SRC-1-dependent manner in vivo. Taken together, we propose that HMP-2 functions downstream of the Src signaling pathway and contribute to endoderm induction and ABar spindle orientation, in parallel with the Wnt signaling pathway.
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[
J Biol Chem,
2017]
Stable tissue integrity during embryonic development relies on the function of the cadherin-catenin complex (CCC). The C. elegans CCC is a useful paradigm for analyzing in vivo requirements for specific interactions among the core components of the CCC, and provides a unique opportunity to examine evolutionarily conserved mechanisms that govern the interaction between - and -catenin. HMP-1, unlike its mammalian homolog -catenin, is constitutively monomeric and its binding affinity for HMP-2/catenin is higher than that of -catenin for -catenin. A crystal structure shows that the HMP-1-HMP-2 complex forms a five-helical bundle structure distinct from the structure of the mammalian -catenin--catenin complex. Deletion analysis based on the crystal structure shows that the first helix of HMP-1 is necessary for binding HMP-2 avidly in vitro and for efficient recruitment of HMP-1 to adherens junctions in embryos. HMP-2 S47 and Y69 flank its binding interface with HMP-1, and we show that phosphomimetic mutations at these two sites decrease binding affinity of HMP-1 to HMP-2 by 40-100 fold in vitro. In vivo rescue experiments using HMP-2 S47E and Y69E mutants showed that they are unable to rescue
hmp-2(
zu364) mutants, suggesting that phosphorylation of HMP-2 on S47 and Y69 could be important for regulating CCC formation in C. elegans. Our data provide novel insights into how cadherin-dependent cell-cell adhesion is modulated in metazoans by conserved elements as well as features unique to specific organisms.
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[
Acta Crystallogr F Struct Biol Commun,
2015]
-Catenin is a multifunctional protein involved in both cell adhesion and Wnt signaling in metazoans. The nematode Caenorhabditis elegans is unusual in that it expresses four -catenin paralogs with separate functions. C. elegans HMP-2 participates in cell adhesion but not in Wnt signaling, so structural and biochemical studies of this protein will help in understanding its unusual specialization and the evolution of -catenin. HMP-2 was expressed, purified and crystallized in two different salt conditions. Crystals grown from a sodium formate condition diffracted to a resolution of 2A and belonged to space group C2, with unit-cell parameters a = 165.2, b = 39.0, c = 101.1A, = 116.7. Crystals obtained from a lithium sulfate condition diffracted to 3A resolution and belonged to space group P43, with unit-cell parameters a = b = 85.3, c = 138.7A. Diffraction data were collected and processed from both crystal forms and the structure was solved by molecular replacement. Model refinement is in progress.
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[
Genetics,
2001]
beta -Catenins function both in cell adhesion as part of the cadherin/catenin complex and in Writ signal transduction as transcription factors. Vertebrates express two related proteins, beta -catenin and plakoglobin, while Drosophila has a single family member, Armadillo. Caenorhabditis elegans expresses three beta -catenin-related proteins, BAR-1, HMP-2, and WRM-1, which are quite diverged sequence from each other and other beta -catenins. While BAR-1 and WRM-1 are known to act in Wnt-mediated processes, and HMP-2 acts in a complex with cadherin/alpha -catenin homologs, it is unclear whether all three proteins retain the other functions of beta -catenin. Here we show that BAR-1, like vertebrate beta -catenin, has redundant transcription activation domains in its amino- and carboxyl-terminal regions but that HMP-2 and WRM-1 also possess the ability to activate transcription. We show via yeast two-hybrid analysis that these three proteins display distinct patterns of protein interactions. Surprisingly, we find that both WRM-1 and HMP-2 can substitute for BAR-1 in C. elegans when expressed from the
bar-1 promoter. Therefore, although their mutant phenotypes and protein interaction patterns strongly suggest that the functions of beta -catenin in other species have been segregated among three diverged proteins in C. elegans, these proteins still retain sufficient similarity to display functional redundancy in vivo.
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[
J Environ Sci (China),
2020]
Exposure to engineered nanomaterials (ENMs), such as graphene oxide (GO), can potentially induce the response of various molecular signaling pathways, which can mediate the protective function or the toxicity induction. Wnt signaling pathway is conserved evolutionarily in organisms. Using Caenorhabditis elegans as an in vivo assay model, we investigated the effect of GO exposure on intestinal Wnt signaling. In the intestine, GO exposure dysregulated Frizzled receptor MOM-5, Disheveled protein DSH-2, GSK-3 (a component of APC complex), and two -catenin proteins (BAR-1 and HMP-2), which mediated the induction of GO toxicity. In GO exposed nematodes, a Hox protein EGL-5 acted as a downstream target of BAR-1, and fatty acid transport ACS-22 acted as a downstream target of HMP-2. Functional analysis on HMP-2 and ACS-22 suggested that the dysregulation of these two proteins provides an important basis for the observed deficit in functional state of intestinal barrier. Our results imply the association of dysregulation in physiological and functional states of intestinal barrier with toxicity induction of GO in organisms.
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[
Proc Natl Acad Sci U S A,
2010]
The ternary complex of cadherin, beta-catenin, and alpha-catenin regulates actin-dependent cell-cell adhesion. alpha-Catenin can bind beta-catenin and F-actin, but in mammals alpha-catenin either binds beta-catenin as a monomer or F-actin as a homodimer. It is not known if this conformational regulation of alpha-catenin is evolutionarily conserved. The Caenorhabditis elegans alpha-catenin homolog HMP-1 is essential for actin-dependent epidermal enclosure and embryo elongation. Here we show that HMP-1 is a monomer with a functional C-terminal F-actin binding domain. However, neither full-length HMP-1 nor a ternary complex of HMP-1-HMP-2(beta-catenin)-HMR-1(cadherin) bind F-actin in vitro, suggesting that HMP-1 is auto-inhibited. Truncation of either the F-actin or HMP-2 binding domain of HMP-1 disrupts C. elegans development, indicating that HMP-1 must be able to bind F-actin and HMP-2 to function in vivo. Our study defines evolutionarily conserved properties of alpha-catenin and suggests that multiple mechanisms regulate alpha-catenin binding to F-actin.
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Weis WI, Nelson WJ, Kwiatkowski AV, Hardin J, Kang H, Jin KS, Heier JA, Choi HJ, Bang I, Shao X, Lee B, Lee J
[
J Biol Chem,
2017]
Intercellular epithelial junctions formed by classical cadherins, -catenin and the actin-binding protein -catenin link the actin cytoskeletons of adjacent cells into a structural continuum. These assemblies transmit forces through the tissue and respond to intracellular and extracellular signals. However, the mechanisms of junctional assembly and regulation are poorly understood. Studies of cadherin-catenin assembly in a number of metazoans have revealed both similarities and unexpected differences in the biochemical properties of the cadherin/catenin complex that likely reflect the developmental and environmental requirements of different tissues and organisms. Here, we report the structural and biochemical characterization of HMP-1, the Caenorhabditis elegans -catenin homolog, and compare it with mammalian -catenin. HMP-1 shares overall similarity in structure and actin-binding properties, but displayed differences in conformational flexibility and allosteric regulation from mammalian -catenin. HMP-1 bound filamentous actin with an affinity in the single micromolar range, even when complexed with the -catenin homolog HMP-2 or when present in a complex of HMP-2 and the cadherin homolog HMR-1, indicating that HMP-1 binding to F-actin is not allosterically regulated by the HMP-2-HMR-1 complex. The middle (i.e., M) domain of HMP-1 appears to be less conformationally flexible than mammalian -catenin, which may underlie the dampened effect of HMP-2 binding on HMP-1 actin-binding activity compared with that of the mammalian homolog. In conclusion, our data indicate that HMP-1 constitutively binds -catenin and F-actin, and although the overall structure and function of HMP-1 and related -catenins are similar the vertebrate proteins appear to be under more complex conformational regulation.
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[
Proc Natl Acad Sci U S A,
2010]
The Wnt signaling pathway must be properly modulated to ensure an appropriate output: pathological conditions result from either insufficient or excessive levels of Wnt signal. For example, hyperactivation of the Wnt pathway is associated with various cancers and subnormal Wnt signaling can lead to increased invasiveness of tumor cells. We found that the Caenorhabditis elegans ortholog of the Fer nonreceptor tyrosine kinase, FRK-1, limits Wnt signaling by preventing the adhesion complex-associated -catenin, HMP-2, from participating in Wnt-dependent specification of the endoderm during embryogenesis. Removal of FRK-1 function results in relocalization of HMP-2 to the nucleus of epidermal cells, and allows it to substitute for WRM-1, the nuclear -catenin that normally transduces the Wnt signal during endoderm development. APR-1, the C. elegans APC ortholog, is similarly required to prevent HMP-2 relocalization and keeps it from participating in Wnt signal transduction; this finding partially explains the paradoxical observation that APR-1 acts either negatively or positively in Wnt signaling, depending on context. The apparent hyperactivation of the Wnt response in the absence of FRK-1 leads to hyperproliferation in the endoderm, as is also seen when WRM-1 is overexpressed in wild-type embryos. The specification and proliferation activities of Wnt signaling are separable: although the Tcf/Lef factor POP-1 acts in Wnt-dependent endoderm specification, it is not apparently required for hyperproliferation resulting from excessive Wnt signaling. These findings highlight a role for a Fer-type kinase in setting the proper levels of Wnt signaling and demonstrate the importance of this modulation in ensuring appropriate cell division.
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[
Biochem J,
2015]
Adherens junctions play key roles in mediating cell-cell contacts during tissue development. In Caenorhabditis elegans embryos, the cadherin-catenin complex (CCC), composed of the classical cadherin HMR-1 and members of three catenin families, HMP-1, HMP-2 and JAC-1, is necessary for normal blastomere adhesion, gastrulation, ventral enclosure of the epidermis and embryo elongation. Disruption of CCC assembly or function results in embryonic lethality. Previous work suggests that components of the CCC are subject to phosphorylation. However, the identity of phosphorylated residues in CCC components and their contributions to CCC stability and function in a living organism remain speculative. Using mass spectrometry, we systematically identify phosphorylated residues in the essential CCC subunits HMR-1, HMP-1 and HMP-2 in vivo. We demonstrate that HMR-1/cadherin phosphorylation occurs on three sites within its beta-catenin binding domain that each contributes to CCC assembly on lipid bilayers. In contrast, phosphorylation of HMP-2/beta-catenin inhibits its association with HMR-1/cadherin in vitro, suggesting a role in CCC disassembly. Although HMP-1/alpha-catenin is also phosphorylated in vivo, phosphomimetic mutations do not affect its ability to associate with other CCC components or interact with actin in vitro. Collectively, our findings support a model in which distinct phosphorylation events contribute to rapid CCC assembly and disassembly, both of which are essential for morphogenetic rearrangements during development.
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[
Dev Cell,
2015]
In metazoan adherens junctions, -catenin links the cytoplasmic tail of classical cadherins to the F-actin-binding protein -catenin. Phosphorylation of a Ser/Thr-rich region in the cadherin tail dramatically enhances affinity for -catenin and promotes cell-cell adhesion in cell culture systems, but its importance has not been demonstrated in vivo. Here, we identify a critical phosphorylated serine in the C. elegans cadherin HMR-1 required for strong binding to the -catenin homolog HMP-2. Ablation of this phosphoserine interaction produces developmental defects that resemble full loss-of-function (Hammerhead and Humpback) phenotypes. Most metazoans possess a single gene for -catenin, which is also a transcriptional coactivator in Wnt signaling. Nematodes and planaria, however, have a set of paralogous -catenins; for example, C. elegans HMP-2 functions only in cell-cell adhesion, whereas SYS-1 mediates transcriptional activation through interactions with POP-1/Tcf. Our structural data define critical sequence differences responsible for the unique ligand specificities of these two proteins.