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R Baserga

Publications and source records attributed to R Baserga.

375 records · Page 21Linked to original sources
PubMedDate not supplied

Conformational changes in chromatin from density inhibited WI-38 fibroblasts stimulated to proliferate.

Quiescent confluent monolayers of WI-38 human diploid fibroblasts can be stimulated to proliferate by replacing the old medium with fresh medium plus 10% serum. Circular dichroism spectra of chromatin from stimulated cells between 2 and 10 hrs after stimulation show an increase in positive ellipticity maxima and a blue shift in the 250-300 nm region. These changes are reversed when the stimulated cells enter DNA synthesis (which, in the present conditions, begins to increase at 12-15 hrs and reaches a peak at 20 hrs). The circular dichroism changes occurring 3 hrs after stimulation have been studied in greater detail. They consist in a 35% (average) increase in positive ellipticity and a blue shift in the 250-300 nm region. Changes in the gamma less than 244 nm region are less consistent. The differences between chromatins of stimulated and unstimulated cells are abolished when both chromatins are washed with 0.25 M NaC1. This procedure removes 10-12% of chromosomal proteins, which chromatograph with non-histone proteins. DNA, RNA and histones could not be detected in the 0.25 M NaC1 extract. In gel electrophoretic profiles of radioactively labelled chromosomal proteins from stimulated and unstimulated WI-38 cells there were no detectable differences between histones. The non-histone proteins of stimulated cells showed one radioactive peak which was increased above the level of non-histone proteins from control cells. These results show that structural changes occur in the chromatin of WI-38 cells stimulated to proliferate several hrs before the onset of DNA synthesis. The fact that differences in the chromatins can be abolished by washing with 0.25 M NaC1 could give a clue as to the mechanisms responsible for these structural changes.

Animals↗
PubMedDate not supplied

Epidermal growth factor and platelet-derived growth factor regulate the activity of the insulin-like growth factor I gene promoter.

The expression of insulin-like growth factor I (IGF-I) is regulated by hormones, oncogenes, and other growth factors, and is markedly decreased or even absent in senescent human diploid fibroblasts. In previous articles, we have reported that the SV40 large T antigen increases the production of IGF-I and that the expression of the IGF-I gene is negatively regulated by an E2F binding site in the IGF-I promoter. We have now investigated the activity of the IGF-I promoter, in response to stimulation of cells by either PDGF or EGF. Both growth factors stimulate the activity of the IGF-I promoter, indicating that they regulate the levels of expression of IGF-I. When the E2F binding sequence in the IGF-I promoter is mutated, the IGF-I promoter is constitutively active and no longer responds to the action of growth factors.

3T3 Cells↗
PubMedDate not supplied

Subcellular localization of IRS-1 in cell proliferation and differentiation.

The type 1 insulin-like growth factor receptor (IGF-IR) and its docking protein, insulin receptor substrate-1 (IRS-1), play important roles in cell transformation, cell differentiation and aging. IRS-1 and other IRS proteins can, under certain conditions, localize to the nuclei of cells, where they undergo interactions with nuclear and nucleolar proteins. In this study, we confirm and extend these observations, demonstrating that IRS-1 is preferentially nuclear in growing cells. Differentiation and inhibition of ribosomal RNA synthesis cause subcellular redistribution of IRS-1 and other nuclear proteins to the cytoplasm.

Animals↗
PubMedDate not supplied

Insulin and IGF-I receptors signaling in protection from apoptosis.

R-cells are mouse embryo fibroblasts with a targeted disruption of the insulin-like growth factor I receptor (IGF-IR) genes. Because R-cells do not express the IGF-IR, they are ideal for studying the biological effects of the insulin receptor (IR), independently from any contribution by the IGF-IR. By stably transfecting R-cells with constructs expressing the IR, we show here the IR can protect cells from apoptosis induced by anoikis or by okadaic acid. The IR, however, is not as efficient as the IGF-IR in protecting mouse embryo fibroblasts from apoptosis, even when IRS-1, one of its major substrates, is over-expressed. In addition, the protection by the IGF-IR is resistant to inhibitors of phosphatidylinositol 3-kinase (PI 3-ki), while the anti-apoptotic effect of the IR is sensitive. These experiments suggest that the IGF-IR uses an alternative anti-apoptotic pathway, not shared with the IR, which is PI3-ki-independent.

3T3 Cells↗
PubMedDate not supplied

Regulatory mechanisms in the expression of cell cycle dependent genes.

There are several prominent features of cell cycle dependent gene regulation which are apparent from the data reviewed here. First, almost all of the genes studied are regulated by a combination of transcriptional and post transcriptional mechanisms. Thus, the regulation of mRNA levels through the cell cycle is a complex process, with control at many different levels. This is not surprising, if we keep in mind that the modulation of these mRNAs at the proper times may be critical to cell division. Secondly, there does not appear to be a common theme in the regulation of the genes discussed here. It appears as if each gene will be regulated by its own specific mechanism. Table 3 shows the serum responsive sequences which have been identified so far, and they are all different; there does not appear to be a consensus sequence yet for a serum response element. The identification of more such sequences should be forthcoming, and should give us a better idea of the general and specific nature of growth factor regulation of gene expression. We know less about the regulation of genes at the posttranscriptional level than about their transcription. We still have very little information about the specific sequences in mRNA which render it susceptible to degradation. Elucidation of such sequences, such as the AU rich region in GM-CSF mRNA should help us to understand serum and growth-factor gene regulation, since this means of control is as widespread, and probably as important as transcriptional control. We have only just begun to understand the mechanisms controlling the expression of CCD genes. The next few years should bring a great increase in our knowledge of these processes.

Animals↗
PubMedDate not supplied

A novel growth stimulating activity from BRL-3A cell conditioned medium.

The R- cell line is a 3T3-like cell line originating from mouse embryos with a homozygous disruption of the type 1 insulin-like growth factor receptor (IGF-IR) genes. Although R- cells cannot grow at all in serum-free medium (SFM) supplemented by several known growth factors, either singly or in combination, they are able to grow in 10% serum, albeit at a reduced rate. These findings suggested that serum contains an unknown, or unidentified, growth factor that can promote cell growth even in cells devoid of IGF-IRs. In an effort to identify such growth factor, we searched, using R- cells, for a growth and DNA synthesis stimulating activity in SFM conditioned by different cell lines. We found that the BRL-3A cell line secreted an activity capable of stimulating DNA synthesis and cell proliferation in R- cells. This activity (which is concentration-dependent) can be collected and concentrated by ultrafiltration, it is heat-labile, proteinase K-sensitive and has a size larger than 10 kDa. Because of the resistance of R1 cells to stimulation by known growth factors, we believe that this activity is due to a novel polypeptide secreted by BRL-3A cells. Further characterization of the active component(s) is in progress.

3T3 Cells↗