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C Blat

Publications and source records attributed to C Blat.

At least 37 records · Page 2Linked to original sources
PubMed1986

Inhibitory diffusible factor IDF45, a G1 phase inhibitor.

An inhibitory diffusible factor of 45 kDa (IDF45) was isolated from medium conditioned by dense cultures of 3T3 cells. The procedure involved Bio-Gel P150 chromatography and 2 reverse-phase FPLC. After the final step of purification, 60 ng/ml of IDF45 inhibited 50% of alpha-globulin-stimulated DNA synthesis. It was shown that IDF45 acted in the G1 phase of the cell cycle. When added for 8 h in the G1 phase of the cell cycle, it was able to inhibit DNA synthesis in the S phase which followed this G1 phase. Furthermore, IDF45 inhibited the early stimulation of RNA synthesis induced by alpha-globulin.

Alpha-Globulins↗
PubMed1986

Growth inhibitory factor diffusing from chick embryo fibroblasts.

Density-dependent inhibition (DDI) of growth is assumed to be the result of diffusion in the medium of growth inhibitory molecules. In this work, we demonstrate the presence of inhibitory molecules (IDFc: chicken inhibitory diffusible factor) in the medium of chick embryo fibroblasts (CEF) cultures. IDFc partially purified by Bio-Gel P150 chromatography followed by reverse phase FPLC. The dose-response curve showed that 250 ng/ml IDFc inhibited 50% DNA synthesis. IDFc was also able to inhibit the growth of sparse cultures of CEF; this inhibition was reversible. IDFc was unable to prevent the DNA synthesis in cells transformed by v-src gene expression. These results suggest that IDFc is involved in the DDI of CEF growth.

Animals↗
PubMed1985

Regulation of cell proliferation inhibitory and stimulatory factors diffused by 3T3 cultured cells.

The growth rate of normal cells multiplied in vitro decreases as the cell density of the culture increases. Previous results suggested that this density-dependent inhibition of growth in nontransformed cells was due to the diffusion of growth inhibitory substances in the medium of dense cultures. In this paper, we demonstrate that dense cultures of 3T3 cells secrete inhibitory and stimulatory factors. Macromolecules of conditioned medium were fractionated on Biogel P150 and the different fractions were tested on quiescent cultures of 3T3 cells stimulated or not to proliferate by addition of alpha globulin. When target cells were not stimulated to proliferate by addition of exocrine growth factors, we observed the inhibitory activity of a large molecular weight inhibitor (IDF45) and the stimulatory activity of autocrine growth factors (fraction about 35 and 10 K molecular weight), on the incorporation of 14C inosine into nucleotide pool and RNA. However, DNA synthesis was significantly stimulated with fraction 10 K only. This discrepancy between the stimulation of RNA and DNA synthesis may be explained by the presence, simultaneously, of inhibitory and stimulatory factors in fraction 35 and 10 K molecular weight. The presence of inhibitory factor was demonstrated when the fractions were tested on target cells stimulated to proliferate by alpha globulin addition and labeled with 14C thymidine. In these conditions, the stimulatory activity of autocrine growth factors was not observable, and only the inhibitory activity on DNA synthesis of fractions 35 and 10 K appeared. It is tempting to assume that the regulation of in vitro cell proliferation is determined by the balance between these antagonist stimulatory and inhibitory autocrine growth factors.

Alpha-Globulins↗
PubMed1985

[Changes induced by expression of the v-src gene in the regulation of cell proliferation. Hypothesis and preliminary results].

Similarities between the mode of action of growth factors and the oncogene product (pp 60 src protein) of Rous Sarcoma virus have been described. However, a major difference is that addition of growth factors does not induce a malignant transformation of cells. The present work proposes a hypothesis concerning this difference. Various data suggest that density-dependent inhibition (DDI) of growth in non-transformed cells is due to the diffusion of growth inhibitory molecules. Inhibitory factors of 45 K (IDF 45) and 12 K have been fractionated. We assume that the stimulation of DNA synthesis induced by growth factor addition to dense quiescent cultures of non-transformed cells leads to an increase in the activity of autocrine inhibitory molecules in such a manner that the growth factor stimulatory effect is only transient, and cells re-enter the Go phase. On the contrary, the stimulation of DNA synthesis by v-src transformation would not be counterbalanced by inhibitory diffusing factors and cells would not enter Go phase. We present preliminary results which support this assumption. Dense quiescent cultures of chick embryo fibroblasts infected by Ny 68 virus (ts mutant for transformation of Rous Sarcoma virus) were stimulated to proliferate either by addition of growth factors in cultures maintained at 41 degrees C or by expression of transformation (by the cell transfer from 41 to 37 degrees C, the permissive temperature for expression of transformation). Stimulation of DNA synthesis by growth factors was totally inhibited by the inhibitory diffusing factors of 45 K (IDF45) whereas the stimulation of DNA synthesis produced by transformation was reproducibly not decreased by IDF45.

Alpha-Globulins↗
PubMed1983

Rous sarcoma virus-induced changes in the pattern of phosphorylation of non-histone nuclear proteins.

We here studied the protein kinase activity and in vitro phosphorylable sites of non-histone nuclear proteins, 0.4 M NaCl extracts (mostly chromosomal proteins) from chick embryo fibroblasts (CEF), infected or not with a Schmidt Ruppin strain subgroup A of Rous sarcoma virus (RSV). The infection and transformation of chick fibroblasts by RSV induced an increase in kinase activity and endogenous phosphorylation of non-histone chromosomal (NHC) proteins. The stimulation, by a change of medium, of the proliferation of dense cultures of normal chick fibroblasts also induced an increase in the kinase activity and endogenous phosphorylation of NHC proteins. However, two-dimensional gel electrophoresis of the 32P-phosphorylated proteins showed that stimulation due to a change of medium and that due to the expression of transformation were very different. The stimulation by a change of medium increased to a greater or lesser extent the phosphorylation of the different NHC proteins, with no fundamental variations in the pattern of protein phosphorylation. In contrast, RSV infection induced significant changes in the pattern of protein phosphorylation. One of the most striking feature was the large increase of amount and phosphorylation of high molecular weight (HMW) proteins in particular of phosphoproteins having an evaluated molecular weight (MW) of 78 K and 82 K and pI greater than 8.2. The percent of phosphotyrosine residues in NHC proteins was clearly increased when the proteins were extracted from transformed cells instead of normal cells. But the alkaline treatment of two-dimensional gel electrophoresis indicated that the 80 K phosphoproteins did not contain phosphotyrosine residues, and thus cannot be considered as substrates for pp60src kinase.

Animals↗
PubMed1983

Density-dependent inhibition of growth: fractionation of inhibitory diffusible factor(s) released by dense cultures of 3T3 cells.

Different data have suggested that the density-dependent inhibition of growth in normal 3T3 cells is due to the release of inhibitory factor(s) into the medium. The present results provide more evidence supporting this hypothesis. From conditioned medium of dense cultures of 3T3 cells, we fractionated a thermolabile inhibitory diffusible factor (I.D.F.) with a molecular weight of about 40.000 This factor decreased the [11C]-inosine incorporation into purine nucleotides and into nucleic acids of stimulated 3T3 cells. DNA synthesis, determined by [11C]-thymidine incorporation into nucleic acids, and protein synthesis (determined by the protein content of the cultures maintained in the presence or absence of I.D.F.), were also decreased. The possibility that I.D.F. is involved in density-dependent inhibition of growth is discussed.

Animals↗
PubMed1981

Altered RNA/protein ratio associated with the induction of differentiation of Friend erythroleukemia cells.

The synthesis and accumulation of RNA in Friend erythroleukemia (FL) cells induced to differentiate by treatment with the aminonucleoside of puromycin (AMS) or inhibited from differentiating by the addition of inosine to the medium were studied. When FL cells were grown in the presence of AMS, RNA synthesis was substantially inhibited. This effect could not be attributed solely to the inhibition of de novo purine synthesis because the biosynthesis of purine nucleotides from labeled inosine was much less depressed. The ratios of ATP to protein and of GTP to protein were slightly modified as compared to the untreated controls. However, the RNA/protein ratio was decreased. Thus, the RNA content of the cells was reduced 30-40%, but the protein content was not significantly affected. When the cells were treated with AMS together with inosine at a concentration that inhibits AMS-induced differentiation, the RNA/protein ratio was increased as compared with that found in cells treated with AMS alone and approached the level of the ratio in untreated control cells. Adenosine had a similar effect in overcoming the inhibition of RNA synthesis by AMS. Because the RNA/protein ratio of FL cells treated with dimethyl sulfoxide or sodium butyrate, two other potent inducers, was decreased by 44%, our results suggest that a correlation exists between the RNA content of the cells and the triggering of differentiation by inducers.

Adenosine↗