Biomedical subjects

S Finnemann

Publications and source records attributed to S Finnemann.

6 recordsLinked to original sources

PubMed1997

Uncoupling of XB/U-cadherin-catenin complex formation from its function in cell-cell adhesion.

Xenopus XB/U-cadherin forms functional complexes with mouse alpha- and beta-catenins and p120(cas) when expressed in murine L-TK- fibroblasts. These cells were stably transfected with cDNAs encoding different cytoplasmic XB/U-cadherin mutants, each partially deleted in the different parts of the 38 most carboxyl-terminal amino acids. The binding of p120(cas) was not affected by carboxyl-terminal deletions, confirming its binding to a region more amino-terminal and distinct from the catenins. alpha- and beta-catenins associate with truncated XB/U-cadherins if either 19 amino acid half of the cadherin 38 amino acid tail is present, indicating that the site of catenin interaction is upstream of the deletions. However, for adhesive function of XB/U-cadherin constructs, the most carboxyl-terminal 19 amino acids are essential; if these amino acids are deleted, cadherin-catenin complexes unable to mediate cell-cell adhesion are formed. Nonadhesive complexes are solubilized by mild detergent, whereas functional complexes are stable. Provided that detergent stability of cadherin-catenin complexes is taken as a measure of their cytoskeletal association, our results give first evidence that cytoskeletal stabilization occurs independent of cadherin-catenin complex formation and requires the 19-amino acid cadherin carboxyl terminus.

Amino Acid Sequence↗

PubMed1997

LI-cadherin-mediated cell-cell adhesion does not require cytoplasmic interactions.

The adhesive function of classical cadherins depends on the association with cytoplasmic proteins, termed catenins, which serve as a link between cadherins and the actin cytoskeleton. LI-cadherin, a structurally different member of the cadherin family, mediates Ca2+-dependent cell-cell adhesion, although its markedly short cytoplasmic domain exhibits no homology to this highly conserved region of classical cadherins. We now examined whether the adhesive function of LI-cadherin depends on the interaction with catenins, the actin cytoskeleton or other cytoplasmic components. In contrast to classical cadherins, LI-cadherin, when expressed in mouse L cells, was neither associated with catenins nor did it induce an upregulation of beta-catenin. Consistent with these findings, LI-cadherin was not resistant to detergent extraction and did not induce a reorganization of the actin cytoskeleton. However, LI-cadherin was still able to mediate Ca2+-dependent cell-cell adhesion. To analyze whether this function requires any interaction with proteins other than catenins, a glycosyl phosphatidylinositol-anchored form of LI-cadherin (LI-cadherin(GPI)) was constructed and expressed in Drosophila S2 cells. The mutant protein was able to induce Ca2+-dependent, homophilic cell-cell adhesion, and its adhesive properties were indistinguishable from those of wild type LI-cadherin. These findings indicate that the adhesive function of LI-cadherin is independent of any interaction with cytoplasmic components, and consequently should not be sensitive to regulatory mechanisms affecting the binding of classical cadherins to catenins and to the cytoskeleton. Thus, we postulate that the adhesive function of LI-cadherin is complementary to that of coexpressed classical cadherins ensuring cell-cell contacts even under conditions that downregulate the function of classical cadherins.

Actins↗

PubMed1996

Dominant negative expression of a cytoplasmically deleted mutant of XB/U-cadherin disturbs mesoderm migration during gastrulation in Xenopus laevis.

XB/U-cadherin is a maternal Xenopus cadherin which mediates interblastomere adhesion in early embryogenesis. In order to explore its role in gastrulation, we expressed a cytoplasmic deletion mutant of XB/U-cadherin (XB delta c38) under the control of the CMV promoter in Xenopus embryos. This truncated XB-cadherin fails to form complexes with catenins and does not mediate cell-cell aggregation as shown by transfection of mouse Ltk- cells. Injections of the deletion for XB/U-cadherin into the dorsal-marginal region of four cell stage embryos resulted in a dominant negative expression of the cadherin mutant after MBT. Two different phenotypes were observed in a dose dependent manner: high doses (125-250 pg DNA) led to severe distortions of the gastrulation movement. Involution of the mesoderm was impaired, posterior mesoderm migrated laterally around the blastopore and formed two bands of axial tissue. Low doses (up to 50 pg DNA) resulted in embryos of a posteriorized phenotype with disorganized neural structures. Both phenotypes could be rescued by coinjection of cDNA constructs containing wild-type XB/U-cadherin. Injections of constructs encoding a XB/U-cadherin protein truncated both in its extracellular and cytoplasmic domains yielded normal phenotypes. These results suggest that a proper function of XB/U-cadherin is essential for mesoderm movements during gastrulation.

Animals↗

PubMed1995

Cadherin transfection of Xenopus XTC cells downregulates expression of substrate adhesion molecules.

Cadherins are discussed not in terms of their adhesive function but rather as morphoregulatory proteins. Changes in gene expression following cadherin transfection of cells in culture or by overexpression in embryos have, until now, not been reported. We established a protocol for stable transfection of Xenopus XTC cells and generated cells bearing high levels of membrane-integrated mouse uvomorulin (E-cadherin) or Xenopus XB-cadherin. These cell lines showed drastically impaired substrate adhesion on fibronectin and laminin. In immunoblot and radioimmunoprecipitation experiments, we found that fibronectin and alpha 3/beta 1 integrin are downregulated. The reduced amounts of proteins result from a decrease of the respective mRNAs as proven by RNase protection assays. Coprecipitations revealed that transfected cadherin molecules are complexed with alpha-catenin and beta-catenin at plasma membranes. However, the alpha-catenin present in the XB-cadherin complex differs immunologically from that found in the uvomorulin complex. When a truncated form of XB-cadherin lacking 38 of the most C-terminal amino acids was expressed in XTC cells, complex formation with endogenous catenins was abolished. In these transfectants, substrate adhesion was not affected. These results prove that complex formation of transfected cadherins in XTC cells with endogenous beta-catenin correlates with altered synthesis of certain substrate adhesion molecules.

Animals↗

PubMed1994

Xenopus cadherins: the maternal pool comprises distinguishable members of the family.

Three maternal cadherins have been reported to occur in the pregastrula Xenopus embryo. EP- and XB-cadherin are distinguished by their distinct cDNA sequences. U-cadherin has been characterized by its reaction with a specific monoclonal antibody (mAb 6D5). Thus far, lack of specific probes that discriminate between these molecules has prevented their identification as distinct cadherins. We now demonstrate by means of RNase protection assays that both EP- and XB-cadherin mRNAs are present in oocytes and mature eggs. By use of the Xenopus cadherin proteins expressed in mammalian cell lines, we find that mAb 6D5 crossreacts with XB-cadherin, but not with EP-cadherin. The major fraction of the maternal cadherins does not contain the 6D5 epitope and probably represents EP-cadherin. A minor fraction carries the 6D5 epitope indicative for the XB- and U-type of cadherins. We have termed this fraction XB/U-cadherin. The function of maternal cadherins was examined by in vitro cell adhesion assays. A newly developed antiserum with a broad specificity for various Xenopus cadherins efficiently blocks all calcium dependent cell adhesion in the early embryo. We conclude that the maternal cadherins play a central role in interblastomere adhesion in the early embryo and comprise at least two discrete cadherin forms, EP- and XB/U-cadherin.

Amino Acid Sequence↗

PubMed1992

Antibody response in Plasmodium vinckei malaria after treatment with chloroquine and adjuvant interferon-gamma.

The antibody response of mice infected with Plasmodium vinckei after treatment with chloroquine either alone or in combination with interferon-gamma (IFN-gamma) was determined. Sequential serum samples were drawn from BALB/c mice receiving either 240 micrograms chloroquine on the day of infection or 120 micrograms chloroquine plus 10(4) units IFN-gamma daily for 11 days beginning on day 3 prior to infection. Mice treated with additional IFN-gamma showed an early induction of IgG2a response and a reduction in IgG1 antibodies as detected by the immunofluorescence technique at between 10 and 16 days after infection as compared with mice treated with chloroquine alone. Thus, IFN-gamma may partly exert its antimalarial activity via the induction of IgG2a antibody formation. At 4-6 weeks after infection, when mice from both groups resisted homologous re-infection, the predominant antibody isotypes found in both groups were IgG1 and IgG2a. Serum samples obtained from mice in both treatment groups at 6 weeks after infection were used for serum transfer experiments. When parasitised erythrocytes were preincubated with such immune serum, a retardation of the course of parasitaemia by 2 days was observed.

Animals↗