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E Scharf

Publications and source records attributed to E Scharf.

7 recordsLinked to original sources
PubMed2000

Induction of anchorage-independent growth by transforming growth factor-beta linked to anchorage-independent expression of cyclin D1.

Transforming growth factor-beta (TGF-beta) was originally identified, characterized, and named on the basis of its ability to induce anchorage-independent growth (phenotypic transformation). This effect has received little attention in recent years, probably because the induction of anchorage-independent growth by TGF-beta has been observed only in a few cell lines, of which NRK fibroblasts are among the best studied. We have previously reported that normal rat kidney cells have lost their normal adhesion requirement for expression of cyclin D1, and we now show that this loss is causal for the induction of anchorage-independent growth by TGF-beta. First, we show that TGF-beta fails to induce anchorage-independent growth in NIH-3T3 cells and human fibroblasts that have retained their adhesion requirement for expression of cyclin D1. Second, we show that TGF-beta complements rather than affects cyclin D-cdk4/6 kinase activity in NRK cells. Third, we show that forced expression of cyclin D1 in suspended 3T3 cells renders them susceptible to transformation by TGF-beta. These results may explain why the induction of anchorage-independent growth by TGF-beta is a rare event and yet also describe a molecular scenario in which the mesenchymal response to TGF-beta could indeed involve the acquisition of an anchorage-independent phenotype.

3T3 Cells↗
PubMed1999

Transforming growth factor-beta overrides the adhesion requirement for surface expression of alpha(5)beta(1) integrin in normal rat kidney fibroblasts. A necessary effect for induction of anchorage-independent growth.

We have previously shown that the expression of alpha(5)beta(1) integrin on the cell surface is dependent upon cell adhesion to the extracellular matrix, and we report here that transforming growth factor-beta (TGF-beta) overcomes this requirement in normal rat kidney (NRK) fibroblasts. Thus, suspended NRK cells treated with TGF-beta show levels of surface alpha(5)beta(1) integrin that are equivalent to those seen in adherent cells. Moreover, several experiments showed that this effect is necessary for the induction of anchorage-independent growth by TGF-beta. First, a kinetic analysis showed that surface expression of alpha(5)beta(1) integrin was restored in TGF-beta-treated NRK cells prior to the induction of anchorage-independent growth. Second, NRK cell mutants that have lost their TGF-beta requirement for surface expression of alpha(5)beta(1) integrin were anchorage-independent in the absence of TGF-beta. Third, an antisense oligonucleotide to the beta(1) integrin subunit or, fourth, stable expression of an alpha(5)-antisense cDNA blocked the ability of TGF-beta to stimulate anchorage-independent growth. Thus, TGF-beta overrides the adhesion requirement for surface expression of alpha(5)beta(1) integrin in NRK cells, and this effect is necessary for the induction of anchorage-independent growth.

Animals↗
PubMed1996

Cytoskeletal integrity is required throughout the mitogen stimulation phase of the cell cycle and mediates the anchorage-dependent expression of cyclin D1.

The proliferation of many nontransformed cells depends on cell adhesion. We report here that disrupting the cytoskeleton in normal human fibroblasts causes the same cell cycle phenotype that is observed after blocking cell adhesion: suspended cells and cytochalasin D-treated monolayers fail to progress through G1 despite normal mitogen-induced expression of c-myc mRNA. Midway between G0 and the beginning of S-phase, cell cycle progression becomes independent of adhesion and the cytoskeleton. At this stage, the cells are also mitogen independent. Molecular analyses showed that Rb hyperphosphorylation and the induction of cyclin D1 occur slightly earlier than the transition to cytoskeleton independence. Moreover, these molecular events are blocked by cytochalasin D. Overall, our data indicate the following: 1) anchorage and cytoskeletal integrity are required throughout the mitogen-dependent part of G1; 2) mitogens and the cytoskeleton jointly regulate the phosphorylation of Rb; and 3) this interdependence is manifest in the regulation of cyclin D1.

Cell Adhesion↗
PubMed1995

Cell adhesion to extracellular matrix regulates the life cycle of integrins.

The expression of alpha 5 beta 1 integrin on the surface of fibroblasts requires adhesion to substratum. We have examined the basis for this adhesion-dependent surface expression by comparing the life cycle of integrins in parallel cultures of adherent and nonadherent cells. Results of biosynthetic labeling experiments in NRK fibroblasts showed that the synthesis and biosynthetic processing of the beta 1 integrin subunit proceed in the absence of cell attachment; however, when examining the behavior of preexisting cell surface integrins, we observed that the alpha beta 1 integrins are internalized and degraded when adhesion to substratum is blocked. A kinetic analysis of integrin internalization in cycloheximide-treated NRK cells showed that each of the fibroblast integrins we examined (in both the beta 1 and beta 3 families) are lost from the cell surface after detachment from substratum. Thus, the default integrin life cycle in fibroblasts involves continuous synthesis, processing, transport to the cell surface, and internalization/degradation. Interestingly, studies with NIH-3T3 cells expressing alpha 1 beta 1 integrin showed that the loss of cell-surface alpha 5 beta 1 integrin is blocked by adhesion of cells to dishes coated with type IV collagen (a ligand for alpha 1 beta 1 integrin) as well as fibronectin. Similarly, adhesion of these cells to dishes coated with type IV collagen stabilizes the surface expression of alpha 5 beta 1 as well as alpha 1 beta 1 integrin. We propose that the adhesion of fibroblasts to extracellular matrix protein alters the integrin life cycle and permits retention of these proteins at the cell surface where they can play important roles in transmitting adhesion-dependent signals.

3T3 Cells↗
PubMed1990

[Long-term course of conservatively and surgically treated patients with an intramural heart infarct].

Thirty patients with a first nontransmural myocardial infarction (MI) were examined retrospectively. The patients had been treated either surgically or conservatively on the basis of the clinical and morphological findings. Three years following infarction, 28 of the 30 patients were still alive (93.3%). 10 of the 13 patients with one vessel disease and 7 of the 17 patients with two or three vessel disease were gainfully employed. The unfavorable natural course of nontransmural myocardial infarction favors an aggressive diagnostic and therapeutic approach since the survival rate of these patients is only 60 to 70% after three years. The results of this study demonstrates convincingly the economic and social benefits of our diagnostic and therapeutical interventions.

Adult↗