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Biomedical subjects

G Handschuh

Publications and source records attributed to G Handschuh.

8 recordsLinked to original sources
PubMed2001

Single amino acid substitutions in conserved extracellular domains of E-cadherin differ in their functional consequences.

The calcium-dependent homophilic cell adhesion molecule E-cadherin typically connects epithelial cells. The extracellular portion of the mature transmembrane protein consists of five homologous domains. The four sequences linking these domains contain the structural amino acid motif DXXD that is thought to be involved in direct calcium binding. In gastric cancer patients mutations affecting this motif between the second and third domain are frequently seen. In order to determine the functional significance of similar sequence alterations with regard to their location, we analyzed single amino acid substitutions changing the DXXD motif to DXXA in each linker region according to a mutation found in gastric cancer (D370A). The cDNA sequences coding for DQND, DVLD and DVND were changed (D257A, D479A, D590A, respectively) and stably expressed in E-cadherin negative MDA-MB-435S mammary carcinoma cells. We found that the D257A and D370A mutations result in abnormal protein localization, changes in the actin cytoskeleton, markedly reduced homophilic cell adhesion, and altered cell morphology. Unexpectedly, the tumor-associated D370A mutation but not the D257A mutation induced increased cell motility. The D479A mutation only had slight functional consequences whereas cells expressing the D590A mutant did not differ from cells expressing the wild-type molecule. Although the putative calcium binding motif DXXD is located at repetitive positions in the extracellular portion of E-cadherin, our results indicate that it has different functions depending on the location. Remarkably, tumor cells select for mutations in the most critical domains resulting both in loss of function (decreased cell adhesion) and in gain of function (increased cell motility). Since multiple DXXD motifs are typically seen in other cadherins, our structure-function study is relevant for this gene family in general.

Actins↗
PubMed2000

Tumor-derived mutated E-cadherin influences beta-catenin localization and increases susceptibility to actin cytoskeletal changes induced by pervanadate.

E-cadherin participates in homophilic cell-to-cell adhesion and is localized to intercellular junctions of the adherens type. In the present study, we investigated the localization of adherens junction components in cells expressing mutant E-cadherin derivatives which had been previously cloned from diffuse-type gastric carcinoma. The mutations are in frame deletions of exons 8 or 9 and a point mutation in exon 8 and affect the extracellular domain of E-cadherin. Our findings indicate that E-cadherin mutated in exon 8 causes beta-catenin staining at lateral cell-to-cell contact sites and, in addition, abnormally located beta-catenin in the perinuclear region. Moreover, the various mutant E-cadherin derivatives increased the steady-state levels of alpha- and beta-catenin and were found in association with these catenins even after induction of tyrosine phosphorylation by pervanadate. Sustained pervanadate treatment led, however, to rounding-up of cells and induction of filopodia, changes which were first detectable in cells expressing E-cadherin mutated in exon 8. The deterioration of the cell contact was not accompanied with disassembly of the E-cadherin-catenin complex. Based on these observations, we propose a model whereby in the presence of mutant E-cadherin tyrosine phoshorylation of components of the cell adhesion complex triggers loss of cell-to-cell contact and actin cytoskeletal changes which are not caused by the disruption of the E-cadherin-catenin complex per se, but instead might be due to phosphorylation of other signaling molecules or activation of proteins involved in the regulation of the actin cytoskeleton.

Actin Cytoskeleton↗
PubMed1999

Tumour-associated E-cadherin mutations alter cellular morphology, decrease cellular adhesion and increase cellular motility.

A major function of the cell-to-cell adhesion molecule E-cadherin is the maintenance of cell adhesion and tissue integrity. E-cadherin deficiency in tumours leads to changes in cell morphology and motility, so that E-cadherin is considered to be a suppressor of invasion. In this study we investigated the functional consequences of three tumour-associated gene mutations that affect the extracellular portion of E-cadherin: in-frame deletions of exons 8 or 9 and a point mutation in exon 8, as they were found in human gastric carcinomas. Human MDA-MB-435S breast carcinoma cells and mouse L fibroblasts were stably transfected with the wild-type and mutant cDNAs, and the resulting changes in localization of E-cadherin, cell morphology, strength of calcium-dependent aggregation as well as cell motility and actin cytoskeleton organization were studied. We found that cells transfected with wild-type E-cadherin showed an epitheloid morphology, while all cell lines expressing mutant E-cadherin exhibited more irregular cell shapes. Cells expressing E-cadherin mutated in exon 8 showed the most scattered appearance, whereas cells with deletion of exon 9 had an intermediate state. Mutant E-cadherins were localized to the lateral regions of cell-to-cell contact sites. Additionally, both exon 8-mutated E-cadherins showed apical and perinuclear localization, and actin filaments were drastically reduced. MDA-MB-435S cells with initial calcium-dependent cell aggregation exhibited decreased aggregation and, remarkably, increased cell motility, when mutant E-cadherin was expressed. Therefore, we conclude that these E-cadherin mutations may not simply affect cell adhesion but may act in a trans-dominant-active manner, i.e. lead to increased cell motility. Our study suggests that E-cadherin mutations affecting exons 8 or 9 are the cause of multiple morphological and functional disorders and could induce the scattered morphology and the invasive behaviour of diffuse type-gastric carcinomas.

Actins↗
PubMed1999

Analysis of E-cadherin in diffuse-type gastric cancer using a mutation-specific monoclonal antibody.

In-frame deletions from the E-cadherin mRNA, coding for a homophilic cell adhesion molecule, are characteristic for diffuse-type gastric carcinomas. Using immunohistochemical analysis the mutant form cannot be distinguished from normal E-cadherin, making results difficult to interpret. In this study, a rat monoclonal antibody, designated E-cad delta 9-1, was generated against a peptide spanning the fusion junction region between exons 8 and 10. This new epitope is present in an E-cadherin variant that lacks exon 9 from the mRNA due to different splice-site gene mutations. Using Western blotting and immunohistochemistry of E-cadherin-transfected cells, we demonstrate that E-cad delta 9-1 specifically reacts with E-cadherin lacking exon 9 but not with the wild-type protein. No immunoreactivity was observed in 31 nontumorous and embryonal tissues analyzed. In gastric carcinoma specimens known to express mutant E-cadherin mRNA lacking exon 9, E-cad delta 9-1 targets exclusively tumor cells in routine formalin-fixed and paraffin-embedded material from biopsies, primary tumors, and lymph node metastases. In a retrospective series of 172 diffuse-type gastric carcinomas expressing E-cadherin, E-cad delta 9-1 reacted with 22 tumors (13%). This new tumor marker-monoclonal antibody system could open novel avenues for selective diagnosis and specific therapy of a subgroup of diffuse-type gastric cancer patients.

Animals↗
PubMed1999

[Novel mutation-specific monoclonal E-cadherin antibodies make possible allele differentiation at the protein level in tumors].

Somatic deletion mutations in the cell adhesion molecule E-cadherin are present in almost 50% of diffuse type gastric cancer. We recently generated monoclonal antibodies against an in-frame deletion of exon 9. The aim of this study was to generate and characterize monoclonal antibodies against the second mutational hot spot, in-frame deletions of exon 8. Lou/C rats were immunized using a KLH-coupled peptide that represents a unique sequence generated by fusion of exon 7 and exon 9 from an E-cadherin deletion mutation lacking exon 8. Hybridoma supernatants were tested in a solid-phase immunoassay using BSA-coupled peptide. Positive reacting hybridomas were confirmed by Western Blots, FACS analysis, and immunohistochemistry of E-cadherin negative carcinoma cells that had been transfected with mutant and wild-type E-cadherin cDNA, respectively. In addition, routine formalin fixed and paraffin embedded tissues from gastric cancer patients were analyzed using both mutation-specific and commercial monoclonal antibodies against E-cadherin, including HECD-1 and AEC. Two hybridoma supernatants, termed E-cad delta 8-1, were selected that reacted with the mutant peptide used for immunization and gave strong signals in Western Blot and FACS analysis with cells expressing mutant E-cadherin lacking exon 8. Wild-type protein expressing cells only reacted with the commercial antibodies but not with the two selected hybridoma supernatants. In contrast to AEC, monoclonal antibody HECD-1 did not react with exon 8 deleted E-cadherin, suggesting that the previously unknown epitope for this often used monoclonal antibody is located at least in part within exon 8. Four gastric cancer specimens known to express mutated E-cadherin mRNA strongly reacted with both mutation-specific supernatants and with AEC monoclonal antibody but not with HECD-1. Taken together, we succeeded in generating monoclonal antibodies reacting with mutant E-cadherin protein lacking exon 8. Furthermore, using both HECD-1 and the new mutation-specific antibodies E-cadherin immunoreactivity can for the first time be evaluated in an allele-specific manner in archival tissues.

Animals↗
PubMed1995

Bacterial expression and purification of hepatitis C virus capsid proteins of different size.

Two capsid sequences of the hepatitis C virus were cloned and expressed in an E. coli system. One sequence (c190) comprised the complete capsid region with 573 nucleotides. The other sequence (c125) spanned 375 5'-nucleotides lacking the hydrophobic 3'-part of the hepatitis C virus capsid gene. A full-length and a truncated construct were chosen, since it is not known whether there is 3'-truncation of the hepatitis C virus capsid during protein maturation similar to the situation in some flaviviridae. The corresponding expression clones 190/4 and 125/4 were constructed by polymerase chain reaction cloning into pQE-vectors. The protein expressed, pc125, which is lacking the hydrophobic carboxyterminus of the full-length capsid protein pc190, showed a stronger signal in western blots using anti-hepatitis C virus/EIAII-positive patient's serum. This could be due to better expression and/or better solubilization of pc125. The truncated protein pc125 displayed the predicted molecular weight of 19 kD, whereas the full-length protein pc190 migrated faster than expected. This could be due to intracellular proteolytic processing, giving rise to a truncated protein or to an atypical mobility in SDS-PAGE gels caused by the hydrophobic nature of the full-length protein. Both proteins were synthesized with an aminoterminal tag of six histidines that could be used for purification by Nickel chelate affinity chromatography. The elution fractions of the two proteins showed additional bands in western blots. Most of these proteins had a mass between 2 and 16 kD and are likely to be degradation products. Protein pc125 could be purified in larger quantities than pc190.(ABSTRACT TRUNCATED AT 250 WORDS)

Amino Acid Sequence↗
PubMed1977

Creatine kinase isoenzyme MB in myocardial infarction: methods compared.

Several methods are available for specifically identifying and assessing the activity of MB isoenzyme of creatine kinase in serum. We compared two electrophoretic techniques with three column-chromatographic ones for efficacy in the diagnosis of myocardial infarction. No technique was considered absolute, but we found surprisingly large errors of diagnosis in the column-chromatographic techniques, attributable to incomplete elution.

Chromatography↗