Biomedical subjects

S Levenberg

Publications and source records attributed to S Levenberg.

4 recordsLinked to original sources

PubMed1999

p27 is involved in N-cadherin-mediated contact inhibition of cell growth and S-phase entry.

In this study the direct involvement of cadherins in adhesion-mediated growth inhibition was investigated. It is shown here that overexpression of N-cadherin in CHO cells significantly suppresses their growth rate. Interaction of these cells and two additional fibroblastic lines with synthetic beads coated with N-cadherin ligands (recombinant N-cadherin ectodomain or specific antibodies) leads to growth arrest at the G1 phase of the cell cycle. The cadherin-reactive beads inhibit the entry into S phase and the reduction in the levels of cyclin-dependent kinase (cdk) inhibitors p21 and p27, following serum-stimulation of starved cells. In exponentially growing cells these beads induce G1 arrest accompanied by elevation in p27 only. We propose that cadherin-mediated signaling is involved in contact inhibition of growth by inducing cell cycle arrest at the G1 phase and elevation of p27 levels.

Animals↗

PubMed1998

Modulation of cell-cell adherens junctions by surface clustering of the N-cadherin cytoplasmic tail.

Cadherins mediate the formation of cell-cell adherens junctions (AJ) by homophilic interactions through their extracellular domains as well as by interacting with the actin cytoskeleton via their cytoplasmic portions. Cadherin clustering initiates cytoplasmic signaling that results in the assembly of structural components into cell-cell AJ. To elucidate the function of the cytoplasmic tail of cadherins in initiating the assembly signal, we generated and characterized a chimeric cadherin tail fused to an inert transmembrane anchor. The chimera enabled us to cluster the cadherin cytoplasmic tail in the absence of extracellular portions of the molecule. The transfected cadherin tail chimera localized to cell-cell AJ of epithelial cells, indicating that the submembrane junctional plaque has the capacity to recruit additional cadherins, with no involvement of their extracellular domains. Expression of the chimera in cells of mesenchymal origin resulted in dominant negative effects on the formation of cell-cell AJ. Surface clustering of cadherin cytoplasmic tails induced the recruitment of components and structural assembly of cell-cell AJ, thereby reversing the initial dominant-negative effects. We conclude that the cadherin cytoplasmic tail contains information required to direct the molecule to cell-cell AJ. Its function as modulator of cell-cell AJ depends on cell type and on whether the tail is clustered.

3T3 Cells↗

PubMed1998

Long-range and selective autoregulation of cell-cell or cell-matrix adhesions by cadherin or integrin ligands.

In this study we demonstrate that local stimulation of cell surface cadherins or integrins induces a selective enhancement of adherens junction or focal contact assembly, respectively, throughout the cell. N-cadherin transfected CHO cells (CHO-Ncad) were incubated with different ligands including N-cadherin extracellular domain (NEC), anti-N-cadherin antibodies, fibronectin and concanavalin A (ConA), conjugated to synthetic beads. Electron microscopic examination indicated that both cadherin- and integrin-reactive beads bound tightly to the cell surface and were apparently endocytosed after several hours of incubation. The ConA-beads remained largely at the cell surface. Immunofluorescence labeling of the cells with antibodies to different adhesion-associated molecules indicated that both NEC- and anti-N-cadherin-conjugated beads induced a major increase in the level of junction-associated cadherin and beta-catenin labeling and a modest increase in junctional vinculin labeling, compared to untreated cells or cells bound to ConA-beads. FN-conjugated beads, on the other hand, significantly enhanced vinculin labeling at focal contacts and suppressed cadherin and beta-catenin staining in cell-cell junctions. The cadherin-reactive beads specifically stimulated tyrosine phosphorylation at cell-cell junctions, while the FN-beads increased the levels of focal contact-associated phosphotyrosine, as shown by immunofluorescence labeling of the cells for phosphotyrosine. Inhibition of this phosphorylation by genistein resulted in a complete suppression of the effects of both types of beads. These findings indicate that specific cadherin- and integrin-mediated surface interactions can trigger positively cooperative long-range signaling events which lead to the selective assembly of cell-cell or cell-matrix adhesions, and that these signals involve tyrosine phosphorylation.

Animals↗

PubMed1998

Cadherin-mediated transmembrane interactions.

We show in this study that cadherin ligands, either soluble or immobilized on different surfaces, can bind to cells carrying a compatible cadherin and induce long-range signals which affect cell adhesion and dynamics. Addition of recombinant N-cadherin extracellular domain (NEC) to CHO cells expressing N-cadherin (FL4) greatly enhanced the calcium-dependent aggregation of the cells and blocked their migration into an "in vitro wound". Monoclonal antibody which blocks cadherin interactions inhibited the aggregation of suspended FL4 cells and facilitated the "wound closure". As previously shown (Levenberg et al., 1998) synthetic beads coupled to NEC interacted specifically with the surface of FL4 cells and significantly enhanced the formation of adherens junctions. This effect was obtained also with the parental CHO cells, which contain low levels of N-cadherin, and in additional N-cadherin expressing cells such as cultured myoblasts. We further show here that stimulation of adhesion is not affected by the geometry of the NEC-bound surface and that cells plated on flat NEC-coated substratum also develop enhanced adherens junctions. Interaction of cells expressing low levels of endogenous N-cadherin, such as CHO cells with surface-immobilized N-cadherin ligands had a prominent effect also on the total level of N-cadherin and beta-catenin in the cells, probably due to stabilization of the cadherin-catenin complex by the interaction with the external surface.

Actinin↗