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H Aberle

Publications and source records attributed to H Aberle.

11 recordsLinked to original sources
PubMed1999

E-cadherin binding prevents beta-catenin nuclear localization and beta-catenin/LEF-1-mediated transactivation.

Beta-catenin is a multifunctional protein found in three cell compartments: the plasma membrane, the cytoplasm and the nucleus. The cell has developed elaborate ways of regulating the level and localization of beta-catenin to assure its specific function in each compartment. One aspect of this regulation is inherent in the structural organization of beta-catenin itself; most of its protein-interacting motifs overlap so that interaction with one partner can block binding of another at the same time. Using recombinant proteins, we found that E-cadherin and lymphocyte-enhancer factor-1 (LEF-1) form mutually exclusive complexes with beta-catenin; the association of beta-catenin with LEF-1 was competed out by the E-cadherin cytoplasmic domain. Similarly, LEF-1 and adenomatous polyposis coli (APC) formed separate, mutually exclusive complexes with beta-catenin. In Wnt-1-transfected C57MG cells, free beta-catenin accumulated and was able to associate with LEF-1. The absence of E-cadherin in E-cadherin-/- embryonic stem (ES) cells also led to an accumulation of free beta-catenin and its association with LEF-1, thereby mimicking Wnt signaling. beta-catenin/LEF-1-mediated transactivation in these cells was antagonized by transient expression of wild-type E-cadherin, but not of E-cadherin lacking the beta-catenin binding site. The potent ability of E-cadherin to recruit beta-catenin to the cell membrane and prevent its nuclear localization and transactivation was also demonstrated using SW480 colon carcinoma cells.

Adenomatous Polyposis Coli Protein↗
PubMed1998

Signaling and adhesion activities of mammalian beta-catenin and plakoglobin in Drosophila.

The armadillo protein of Drosophila and its vertebrate homologues, beta-catenin and plakoglobin, are implicated in cell adhesion and wnt signaling. Here, we examine the conservation of these two functions by assaying the activities of mammalian beta-catenin and plakoglobin in Drosophila. We show that, in the female germ line, both mammalian beta-catenin and plakoglobin complement an armadillo mutation. We also show that shotgun mutant germ cells (which lack Drosophila E-cadherin) have a phenotype identical to that of armadillo mutant germ cells. It therefore appears that armadillo's role in the germ line is solely in a complex with Drosophila E-cadherin (possibly an adhesion complex), and both beta-catenin and plakoglobin can function in Drosophila cadherin complexes. In embryonic signaling assays, we find that plakoglobin has no detectable activity whereas beta-catenin's activity is weak. Surprisingly, when overexpressed, either in embryos or in wing imaginal disks, both beta-catenin and plakoglobin have dominant negative activity on signaling, an effect also obtained with COOH-terminally truncated armadillo. We suggest that the signaling complex, which has been shown by others to comprise armadillo and a member of the lymphocyte enhancer binding factor-1/T cell factor-family, may contain an additional factor that normally binds to the COOH-terminal region of armadillo.

Animals↗
PubMed1998

Expression of the Armadillo family member p120cas1B in Xenopus embryos affects head differentiation but not axis formation.

The Armadillo family is formed by proteins which possess an Arm domain comprising multiple copies of a 42-amino-acid motif, the Arm repeat, initially described for the Drosophila segment polarity gene product Armadillo. The Arm domain serves in protein-protein interactions which are required for the family members Armadillo, beta-catenin and plakoglobin to mediate cell-cell adhesion and Wnt/Wingless signalling. Similarily, p120cas, the Arm domain containing src substrate, also binds to cadherins and becomes tyrosine phosphorylated in response to a variety of stimuli. However, a putative function of p120cas in adhesion or signalling has not yet been demonstrated. It has also not been shown until now that an Arm domain is a common signal transduction motif. Using Xenopus embryos we show by expression of murine p120cas1B (mp120cas1B) in ventral blastomeres that this catenin cannot replace beta-catenin function in dorsal axis formation. Thus, the presence of an Arm domain per se is not sufficient to activate the Wnt/Wg pathway. Indeed, injection of mp120cas1B into dorsal blastomeres led instead to delayed blastopore closure and posteriorized phenotypes with malformed head structures indicative of disturbed gastrulation movements. Because neither convergent extension behaviour nor adhesion to fibronectin was altered in the injected embryos we assume that mp120cas1B influences motility or orientation of migrating mesodermal cells.

Animals↗
PubMed1997

beta-catenin is a target for the ubiquitin-proteasome pathway.

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.

3T3 Cells↗
PubMed1996

Cadherin-catenin complex: protein interactions and their implications for cadherin function.

Cadherins comprise a family of calcium-dependent glycoproteins that function in mediating cell-cell adhesion in virtually all solid tissues of multicellular organisms. In epithelial cells, E-cadherin represents a key molecule in the establishment and stabilization of cellular junctions. On the cellular level, E-cadherin is concentrated at the adherens junction and interacts homophilically with E-cadherin molecules of adjacent cells. Significant progress has been made in understanding the extra- and intracellular interactions of E-cadherin. Recent success in solving the three-dimensional structure of an extracellular cadherin domain provides a structural basis for understanding the homophilic interaction mechanism and the calcium requirement of cadherins. According to the crystal structure, individual cadherin molecules cooperate to form a linear cell adhesion zipper. The intracellular anchorage of cadherins is regulated by the dynamic association with cytoplasmic proteins, termed catenins. The cytoplasmic domain of E-cadherin is complexed with either beta-catenin or plakoglobin (gamma-catenin). Beta-catenin and plakoglobin bind directly to alpha-catenin, giving rise to two distinct cadherin-catenin complexes (CCC). Alpha-catenin is thought to link both CCC's to actin filaments. The anchorage of cadherins to the cytoskeleton appears to be regulated by tyrosine phosphorylation. Phosphorylation-induced junctional disassembly targets the catenins, indicating that catenins are components of signal transduction pathways. The unexpected association of catenins with the product of the tumor suppressor gene APC has led to the discovery of a second, cadherin-independent catenin complex. Two separate catenin complexes are therefore involved in the cross-talk between cell adhesion and signal transduction. In this review we focus on protein interactions regulating the molecular architecture and function of the CCC. In the light of a fundamental role of the CCC during mammalian development and tissue morphogenesis, we also discuss the phenotypes of embryos lacking E-cadherin or beta-catenin.

Animals↗
PubMed1996

Single amino acid substitutions in proteins of the armadillo gene family abolish their binding to alpha-catenin.

Analysis of the calcium-dependent cell adhesion molecule E-cadherin has led to the identification of catenins, which are necessary for cadherin function. Growing evidence that cadherins and catenins are subjected to genetic alterations in carcinogenesis makes it especially important to understand protein-protein interactions within the cadherin-catenin complex. Here we report the identification and analysis of the alpha-catenin binding site in plakoglobin (gamma-catenin). Using N- and C-terminal truncations of plakoglobin, we identified a domain of 29 amino acids necessary and sufficient for binding alpha-catenin. The alpha-catenin binding site is fully encoded within exon 3 of plakoglobin but only partially represented in Armadillo repeat 1. This suggests that exons rather than individual Arm repeats encode functional domains of plakoglobin. Site-directed mutagenesis identified residues in the alpha-catenin binding site indispensable for binding in vitro. Analogous mutations in beta-catenin and Armadillo had identical effects. Our results indicate that single amino acid mutations in the alpha-catenin binding site of homologs of Armadillo could prevent a stable association with alpha-catenin, thus affecting cadherin-mediated adhesion.

Amino Acid Sequence↗
PubMed1995

The human plakoglobin gene localizes on chromosome 17q21 and is subjected to loss of heterozygosity in breast and ovarian cancers.

The gene encoding human plakoglobin was mapped to chromosome 17q12-q22. An intragenic restriction fragment length polymorphism was used to localize the plakoglobin gene distal to locus KRT10 and proximal to the marker D17S858. The plakoglobin gene colocalizes with the polymorphic 17q21 marker UM8 on the same cosmid insert. This subregion of chromosome 17 is known to be particularly subjected to genetic alterations in sporadic breast and ovarian tumors. We show loss of heterozygosity of the plakoglobin gene in breast and ovarian tumors. We have identified a low-frequency polymorphism in the plakoglobin coding sequence which results in an arginine to histidine substitution at amino acid position 142 of the protein, as well as a silent mutation at nucleotide position 332 of the coding sequence. This polymorphism allowed us to demonstrate an allelic association of plakoglobin with predisposition to familial breast and ovarian cancers. Our results, together with the present knowledge about the biological function of plakoglobin, suggest that plakoglobin might represent a putative tumor suppressor gene for breast and ovarian cancers.

Amino Acid Sequence↗
PubMed1994

Beta-catenin mediates the interaction of the cadherin-catenin complex with epidermal growth factor receptor.

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.

Amino Acid Sequence↗
PubMed1994

Assembly of the cadherin-catenin complex in vitro with recombinant proteins.

The cytoplasmic domain of classical cadherins is tightly associated with three proteins termed alpha-, beta- and gamma-catenin. These accessory proteins are of central importance for the adhesive properties of this class of cell adhesion molecules. In order to examine the molecular architecture of the cadherin-catenin complex in more detail we have expressed the catenins and the cytoplasmic domain of E-cadherin as fusion proteins in Escherichia coli, and analyzed the interaction of purified recombinant cadherin and catenins in combinatorial protein-protein interaction experiments. The cytoplasmic domain of E-cadherin cannot directly associate with alpha-catenin but interacts with high affinity with beta-catenin, whereas the binding of gamma-catenin (plakoglobin) to E-cadherin is less efficient. alpha- and beta-catenin assemble into a 1:1 heterodimeric complex. The analysis of various truncated beta-catenins revealed that an alpha-catenin binding site in beta-catenin is localized between amino acid positions 120 and 151. The central role of beta-catenin for the assembly of the heterotrimeric E-cadherin/alpha-catenin/beta-catenin complex in mixing experiments with all components was demonstrated. The reconstitution in vitro of the cadherin-catenin complex should allow the study of the interaction with signalling molecules and with the actin-based cytoskeleton.

Base Sequence↗
PubMed1976

[Carcinoma metastases in neck lymph nodes in occult primary tumor: survival rate depending from localization, stadium, histology and therapeutic method (48 patients)].

In patients with metastatic cancer in cervical nodes without evidence of a primary cancer, radiation therapy eventually supplemented by surgery is indicated. The treated volume should include the regions of the possible primary (pharynx, base of tongue, tonsil) besides the cervical node regions. Five-year cure rates are: about 40% in cases with cervical nodes only, more than 50% in cases with cervical nodes in one region only and not fixed, less than 10% in cases with supraclavicular nodes. In about 30% a primary tumor is found later. About 50% of these primaries is located in the supraclavicular volume and about 50% is located in the infraclavicular volume. In cases with supraclavicular nodes the majority of the primary tumors are located in the infraclavicular colume.

Adult↗