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Biomedical subjects

G Vidali

Publications and source records attributed to G Vidali.

At least 37 records · Page 2Linked to original sources
PubMed1992

Regulation of plasma retinol binding protein secretion in human HepG2 cells.

Retinol binding protein (RBP) is the plasma transport protein of retinol. Mobilization of RBP from the liver stores is stimulated by retinol. During vitamin A deficiency, RBP secretion is specifically inhibited while its rate of biosynthesis is unaffected. As a consequence, RBP, as apoprotein, accumulates inside the endoplasmic reticulum (ER) of the hepatocyte, and a new elevated steady-state concentration is reached. We have studied the role of degradation on the regulation of RBP metabolism in retinol deficient HepG2 cells and determined the intracellular site where RBP degradation takes place. Pulse-chase experiments show that RBP half-life is ca.9 h in retinol-depleted cells. RBP degradation is slow and is insensitive to the treatment with NH4Cl, which inactivates lysosomal proteases and to the drug brefeldin A, which prevents protein export from the ER. The data obtained suggest that RBP degradation occurs, at least in part, in a pre-Golgi compartment. 2-Mercaptoethanol, at millimolar concentration, induces RBP secretion, suggesting a possible role for sulfhydryl-mediated apo-RBP retention by resident ER proteins.

Carcinoma, Hepatocellular↗
PubMed1992

Chromatin structure, DNA methylation, and gene expression at sites of viral integration in human fibroblasts. Implications for chromosomal fragility.

We analyzed the structural and functional properties of a chromosomal region in which a recombinant hybrid virus adenovirus 5/SV40 preferentially integrates. Our results demonstrated that the structure of the cellular targets for DNA and RNA viruses is very similar and that the cellular sequence flanking the integrated virus possesses, simultaneously, all the features postulated to be the molecular basis for chromosomal fragility.

Adenoviridae↗
PubMed1992

Post-transcriptional control of H3 histone variants synthesis.

In cultured HeLa cells the rates of H3.1 and H3.2 synthesis measured by pulse labeling experiments reflect the steady state content of the two histone variants. This pattern, however, is largely modified when histone translation is carried out in vitro on RNA isolated from the same cell line. In vivo, H3.1 and H3.2 are synthesized approximately at the same rates while the product of H3 mRNA translation in vitro is mostly represented by H3.1 histones. Factors which have so far been invoked for the control of histone messenger RNA stability and translation efficiency are not sufficient to explain our data which in addition indicate that histone H3.1 and H3.2 have different roles in the organization of the genetic material.

Autoradiography↗
PubMed1991

Cell cycle dependent alterations of chromatin structure in situ as revealed by the accessibility of the nuclear protein AF-2 to monoclonal antibodies.

We have recently described a novel nuclear antigen, AF-2, which is related to cell cycle dependent alterations of chromatin structure. We show by two parameter flow cytometry on a cell by cell basis that the antigen is accessible to specific monoclonal antibodies only in mitotic and postmitotic early G1-phase cells. The evaluation of nuclease susceptibility and AF-2 antigen accessibility reveals different subcompartments of the G1-phase of the cell cycle with distinct chromatin conformations. Digestion with DNase I seems to alter the chromatin structure according to concentration and this is reflected by an increase of the antigen accessibility. Chromatin in the more condensed early G1-phase is specifically digested by lower concentrations of the enzyme than chromatin in later stages of interphase. Chromatin from cells in the late-G1, S-, and G2-phases shows a higher relative resistance to DNase I and a reduced accessibility of the AF-2 antigen to monoclonal antibodies. Nuclease S1 has a similar effect on chromatin topology, as revealed by the reaction with anti-AF-2 antibodies, without digestion of detectable amounts of DNA. The antigen becomes available to the antibodies in almost all cells by digestion with high concentrations of DNase I or Nuclease S1.

Antibodies, Monoclonal↗
PubMed1991

A novel protein related to cell cycle-dependent alterations of chromatin structure.

We have detected a novel nuclear antigen, AF-2, which appears to be involved in cell cycle-dependent alterations of chromatin structure. Specific monoclonal antibodies detect the antigen spread over the whole cell during mitosis and in islet-like structures in the nuclei of a subpopulation of cells in interphase. Upon nucleolytic digestion of fixed cells, the antigen becomes available to the antibodies in all cells, indicating that AF-2 antigen is present during the whole cell cycle but differentially accessible. Digestion with the single strand specific S1 nuclease reveals that the alteration of chromatin structure induced by the introduction of nicks into the DNA rather than the digestion of DNA bound to the immunogenic epitope accounts for the change in accessibility of AF-2 antigen in interphase nuclei. The epitope recognized by the antibody in human cells is present in two polypeptides of 65 and 36 kDa, respectively, which are tightly bound to chromatin and cross-linkable to the nuclear matrix. The proteins also occur in the midbody during cytokinesis. The immunogenic epitope is conserved between man and fission yeast.

Antibodies, Monoclonal↗
PubMed1989

Core histone acetylation during lymphocyte activation.

Histone acetylation has been followed in cultures of human lymphocytes, in PHA-stimulated lymphocytes and in mixed lymphocytes obtained from identical twins and from unrelated donors. A computer assisted analysis of two-dimensional gels and autoradiograms revealed that in cultured lymphocytes only H3 and H4 core histones incorporate labeled acetate and that two H3 variants greatly differ in their rate of acetate uptake.

Acetylation↗
PubMed1989

Interaction retinol-chromatin: an analysis of DNA from vitamin A-treated V79 Chinese hamster cells.

When V79 cells are incubated in the presence of radiolabeled retinol, a small but consistent amount of radioactivity remains associated with nuclear DNA. Chromatographic analysis of enzymatic hydrolysates of DNA shows that no irreversible changes, such as adducts, have taken place on DNA. We present evidence that this radioactive incorporation may occur via a metabolic conversion of retinol, leading mainly to the formation of radiolabeled thymidine, which is then incorporated into newly made DNA. Mutagenic effects by retinol, given at concentrations well above physiological levels, have been also excluded.

Animals↗
PubMed1989

Histone acetylation in conjugating Tetrahymena thermophila.

We have monitored histone acetylation during conjugation of the ciliated protozoan Tetrahymena thermophila using antibodies against the tetraacetylated form of H4 histone (Pfeffer, U., N. Ferrari, and G. Vidali. 1986. J. Biol. Chem. 261:2496-2498). During meiosis, the three prezygotic divisions, fertilization, and the first postzygotic division, micronuclei, do not contain highly acetylated forms of H4 histone. However, after the second postzygotic division, when anteriorly located micronuclei begin to develop into new macronuclei, they are strongly stained by the anti-tetraacetylated H4 histone antibody. In the old macronucleus, histones are actively deacetylated when it has ceased to transcribe but before it is eliminated. Histone acetylation processes analyzed here appear to be correlated to the commitment to transcription rather than to the transcription process itself. This is in good correlation with evidence we have obtained in chick erythrocyte nuclei during reactivation upon fusion with mammalian cells (Pfeffer, U., N. Ferrari, F. Tosetti, and G. Vidali. 1988. Exp. Cell Res. 178:25-30). Furthermore, it becomes clear from our data that histone acetylation occurs in close correlation to the position of nuclei within the cytoplasm of T. thermophila. Mechanisms that control differential histone acetylation and deacetylation are discussed.

Acetylation↗
PubMed1988

In vivo binding of retinol to chromatin. The binding is mediated by a lipoprotein.

We have previously shown that exposure of responding cells to vitamin A leads to profound modifications of chromatin structure as revealed by an increased susceptibility to DNase I digestion, modified patterns of histone acetylation, and impaired synthesis of a nonhistone chromosomal protein (Ferrari, N., and Vidali, G. (1985) Eur. J. Biochem. 151, 305-310). The present results show that these effects are most probably due to the direct interaction between retinol and chromatin, and analysis of mononucleosomes and higher oligomers obtained from retinol-treated cells shows that retinol is indeed tightly bound to chromatin. Enzymatic digestions of vitamin A containing nucleosomes with proteinase K, phospholipase C, and phospholipase A2 support a model where the final binding of retinol to chromatin is mediated by a lipoprotein: the recognition of the binding sites on DNA being dictated by the proteic component while the hydrophobic retinol is solubilized in the fatty acid moiety.

Cell Nucleus↗
PubMed1988

Histone acetylation: a step in gene activation.

Cellular ageing appears to consist mainly in a loss of adaptability and a progressive decrease in the capacity of the cell to maintain homeostasis. Such age related phenomenon can be the result of stochastic or of programmed events, and may occur through changes in the base pairs or coding of the DNA, through increasing levels of error in transcription and finally through alterations at the translation step of proteins synthesis. The purpose of this chapter is to present histone acetylation as a key event in the control of chromatin structure and transcription.

Acetylation↗