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A I Scovassi

Publications and source records attributed to A I Scovassi.

At least 55 records · Page 3Linked to original sources
PubMed1990

Changes in activity and mRNA levels of poly(ADP-ribose) polymerase during rat liver regeneration.

ADP-ribosylation of nuclear proteins, catalysed by the enzyme poly(ADP-ribose) polymerase, is involved in the regulation of different cellular processes of DNA metabolism. To further clarify the role of the enzyme during proliferating activity of mammalian cells, we have studied the control of gene expression in regenerating rat liver. The changes in activity and mRNA levels were analysed during the early and late phases of the compensatory model. When enzyme activity was measured in isolated liver nuclei obtained at different times after hepatectomy, two different phases were observed: an early wave occurring before the onset of DNA synthesis, and a second one, starting several hours after the onset of DNA synthesis and returning to control values at later times. The evaluation of the enzymatic level in nuclear extracts and by activity gel analysis showed a more gradual increase starting 1 day after hepatectomy, in concomitance with the peak of DNA synthesis. By using a specific murine cDNA probe, a significant enhancement of mRNA levels for poly(ADP-ribose) polymerase was observed during liver regeneration, slightly preceding the onset of DNA synthesis. The results obtained show that changes in poly(ADP-ribose) polymerase activity, during liver regeneration, are associated both to early events preceding the increase in DNA synthesis and to later phases of the cell proliferation process.

Animals↗
PubMed1990

Autoantibodies to poly(ADP-ribose)polymerase in autoimmune diseases.

Antibodies to various nuclear proteins are frequently found in sera of patients affected by connective tissue diseases and other autoimmune diseases. We investigated the specificity of circulating autoantibodies to poly(ADP-ribose)polymerase (pADPRP) in different autoimmune and connective tissue diseases: Systemic Lupus Erythematosus (SLE), Rheumatoid Arthritis (RA), Progressive Systemic Sclerosis (PSS), Sjogren's Syndrome (SS), Undifferentiated Connective Tissue Disease (UCTD), Cryptogenic Fibrosing Alveolitis (CFA) and Sarcoidosis. pADPRP was purified from calf thymus. Antibody specificity was detected by ELISA, western blot and enzyme activity precipitation. Positive values (mean O.D. values + 3 S.D. of 36 normal controls) were obtained in 7/15 SLE patients, 1/18 RA patients, 1/30 PSS, 3/14 SS, 0/5 UCTD, 5/21 CFA and 4/25 Sarcoidosis. The positive sera also recognized the pADPRP protein when tested by western blot. Furthermore the enzyme activity was inhibited after immunoprecipitation by some highly positive sera.

Adolescent↗
PubMed1988

Depletion of adenosine diphosphate-ribosyl transferase activity in rat liver during exposure to N-2-acetylaminofluorene: effect of thiols.

The exposure of rats to a feeding regimen containing N-2-acetylaminofluorene (2AAF) causes an accumulation of lesions on liver DNA and a progressive impairment in DNA repair capacity. We used the in vivo experimental model of Teebor and Becker (Cancer Res., 31:1-3, 1971) with the carcinogen given to rats during four consecutive cycles, each one composed of 3 weeks of treatment and 1 week of recovery. The extent of DNA damage and repair was determined during each cycle by the alkaline elution technique. The results obtained showed that the number of alkalilabile sites in DNA is significantly enhanced after the first cycle and remains increased during following cycles. Since ADP-ribosyl transferase (ADPRT) is known to play a central role in the response to DNA damage, we investigated the effect of 2AAF on this enzyme during the carcinogenic process. The activity and the structure of ADPRT were analyzed using the activity gel and Western blot techniques. The catalytic band with a molecular weight of 116,000, clearly evident in liver extracts of control rats, was no longer detectable after one cycle of exposure to 2AAF returning progressively to an almost normal level within the last two cycles. When the aminothiol N-acetyl-L-cysteine (NAC) was added to the 2AAF diet, the extent of DNA damage was drastically reduced, and DNA repair activity preserved for a longer period. In addition, the loss of ADPRT was not observed after the first cycle, but delayed to the end of the second, indicating that NAC exerts a protective effect on DNA and on ADPRT. Such effect was not evident when NAC was substituted by glutathione. The analysis of liver extracts on Western blot showed that the ADPRT immunoreactive band was almost undetectable after the first cycle suggesting that the loss in enzyme activity could be due to a block in de novo synthesis of the enzyme and not to an inhibition of its activity.

2-Acetylaminofluorene↗
PubMed1988

Different distribution of DNA polymerases alpha and beta in bone marrow and peripheral blood from human leukemia.

An activity gel method was used to analyze the catalytic polypeptides of polymerases alpha and beta in human acute myeloblastic and lymphoblastic leukemia. A 175 kDa alpha-polymerase was found in 85% of bone marrow and in 57% of peripheral blood samples. At variance, a 40 kDa beta-polymerase was found in 94% of peripheral blood and only in 12% of bone marrow samples. No difference in the pattern of polymerase expression was found according to the type of leukemia and the disease status. The role of these enzymes in leukemia and their implications in drug sensitivity are discussed.

Adolescent↗
PubMed1988

Enzymatically active forms of reverse transcriptase of the human immunodeficiency virus.

The reverse transcriptase of HIV-1 (AIDS virus) is characterized by the presence of two highly immunogenic proteins of 66 and 51 kD known to be enzymatically active as a complex p66/51. Using an activity gel procedure that allows identification of catalytic polypeptides in situ after PAGE in denaturing conditions, we visualized two major active bands of 66 and 51 kD of reverse transcriptase from highly purified preparations of HIV-1. We show that both p66 and p51 are enzymatically active. An additional active band was also associated with a 165 kD polypeptide, representing about 2-4% of total activity and possibly corresponding to the putative gag-pol precursor. In H9-infected cells the 66 kD active band became visible 70 hours after infection. These studies show that the two major forms of reverse transcriptase (66 and 51 kD) of HIV-1 are independently active and that a higher Mr form of 165 kD is also enzymatically active.

Cell Line↗
PubMed1987

Response of mammalian ADP-ribosyl transferase to lymphocyte stimulation, mutagen treatment and cell cycling.

The inhibitors of the nuclear enzyme ADP-ribosyl transferase (ADPRT) had been shown to block the stimulation of quiescent lymphocytes with mitogens suggesting the involvement of the enzyme in the control of gene expression and cell differentiation. By means of the activity-gel assay we have analysed the intensity and the molecular mass of the catalytic bands of the enzyme at early and late times after stimulation of human lymphocytes by phytohemagglutinin. We observed that the increase in the activity of ADPRT is concurrent with the onset of DNA synthesis and is maintained for up to 10 days after lymphocyte stimulation, when DNA replication is over but the capacity to perform repair synthesis is still elevated. The analysis of ADPRT in stimulated lymphocytes by Western blots indicated that the increase in enzyme activity is due to the de novo synthesis of enzyme protein. The response of ADPRT to the treatment of human lymphocytes with DNA-damaging agents was studied at various dose-ranges, using the activity-gel technique. The results obtained indicate that dimethyl sulfate is 10 times as active as methyl methane sulfonate in stimulating ADPRT activity and that, at very high doses, the activity band of the enzyme tends to disappear. Very similar observations were obtained when Chinese hamster ovary cells were treated with the same agents, although the concentrations of the mutagens eliciting maximal ADPRT activation were 10 times higher than in human lymphocytes. When analysed by Western blots, no significant difference of the protein band of the enzyme was observed in comparing control and treated cells. This suggests that the activity-gel system can detect two different phenomena: the increase in enzyme protein, as in the case of stimulated lymphocytes, and the enzyme-activating effect of DNA-damaging agents, which occurs without changing the number of enzyme molecules. Of particular interest is the observation that mitomycin C is capable of activating ADPRT in human lymphocytes, thus suggesting that cross-linking agents are involved in promoting ADP-ribosylation reactions. We have also analysed the variations of the enzyme throughout the cell cycle in HeLa cells synchronized in S phase or in mitosis. No significant changes in the levels of the enzyme activity were revealed by the activity-gel assay during the progression of the cycle, although an overall increase of active polypeptides of larger size in concomitance with the S period was observed.

Cell Cycle↗
PubMed1986

Structural analysis of poly(ADP-ribose)polymerase in higher and lower eukaryotes.

A phylogenetic survey for the poly(ADP-ribose)polymerase has been conducted by analyzing enzyme activity in various organisms and determining the structure of the catalytic peptides by renaturation of functional activities of the enzyme in situ after electrophoresis in denaturing conditions (activity gel). The enzyme is widely distributed in cells from all different classes of vertebrates, from arthropods, mollusks and plant cells but could not be detected in echinoderms, nematodes, platyhelminths, thallophytes (including yeast) and bacteria. The presence on activity gels of a catalytic peptide with Mr = 115,000-120,000 was demonstrated in vertebrates, arthropods and mollusks but no activity bands were recovered in many lower eukaryotes, in plant cells and bacteria. By using an immunological procedure that used an antiserum against homogeneous calf thymus poly(ADP-ribose) polymerase, common immunoreactive peptides were visualized in mammals, avians, reptiles, amphibians and fishes, while lacking in non-vertebrate organisms. Our results indicate that the structure of poly(ADP-ribose) polymerase is conserved down to the mollusks suggesting its important role for DNA metabolism of multicellular organisms.

Animals↗
PubMed1985

Terminal deoxynucleotidyl transferase-positive acute leukemias evolving from a myelodysplastic syndrome.

We have analyzed the distribution of terminal deoxynucleotidyl transferase (TdT) in 30 patients with myelodysplastic syndromes (MDS), in connection with morphology, cytochemistry, and cytogenetics. All cases in preleukemic phase were strictly TdT-negative. At variance, 4 (19%) of 21 cases with subsequent leukemia were TdT-positive and showed a pure lymphoid (one case) or a mixed lymphoid-myelomonocytic (three cases) morphology. The TdT enzymatic activity ranged from 2 to 21 U/10(8) cells and the percent of positive cells in the immunofluorescence test ranged from 10 to 80% of total. All cases were Philadelphia chromosome-negative. The clonal origin of MDS from the pluripotent stem cell, capable of originating both a lymphoid and myeloid progeny, is further corroborated.

Acute Disease↗
PubMed1984

Catalytic activities of human poly(ADP-ribose) polymerase from normal and mutagenized cells detected after sodium dodecyl sulfate-polyacrylamide gel electrophoresis.

An activity gel procedure is described to identify functional polypeptides of human poly(ADP-ribose) polymerase. Purified or crude enzyme preparations from HeLa cells were electrophoresed in sodium dodecyl sulfate-polyacrylamide gels containing gapped DNA. After renaturation of the peptides in situ, the intact gel was incubated in a poly(ADP-ribose) polymerase reaction mixture containing [32P]NAD. Autoradiograms of the gels consistently exhibited a major activity band at Mr = 116,000-120,000; in many runs, three minor distinct bands at Mr = 125,000, 135,000, and 145,000 were also seen. [32P]NAD appeared to be incorporated into poly(ADP-ribose) since: (i) the activity bands were not detectable when the enzyme-inhibitor 3-aminobenzamide was added to the gel incubation mixture; and (ii) the radioactive polymer, electroeluted from the bands, was completely digested by phosphodiesterase I. Preliminary activity gel analysis of extracts of HeLa cells treated with different DNA-damaging agents revealed that the apparent activity of the Mr = 116,000 form increased by about 10-fold in cells treated with 1 mM dimethyl sulfate and 10-20-fold in cells treated with 10 microM mitomycin C. Only a small increase was obtained in cells treated with 1 mM methyl methanesulfonate, and no change in the activity band pattern was observed after 50 and 100 J/m-2 of UV irradiation.

Electrophoresis, Polyacrylamide Gel↗
PubMed1983

A DNA polymerase alpha partially resistant to aphidicolin in cells and embryos of Med-fly (Ceratitis capitata Wied.).

We have studied the DNA polymerase activities in cultured cells and embryos of Med-fly (Ceratitis capitata Wied.) and we observed that only DNA polymerases alpha and gamma were detectable in crude extracts. The level of DNA polymerase alpha, measured during the life cycle of the insect embryos, increased in parallel with the rate of embryonic cell proliferation, whereas DNA polymerase gamma increased at much later fertilization time, when cell differentiation is already taking place. DNA polymerase alpha, purified 100 folds from Med-fly embryos, was 10 times more resistant to aphidicolin, its specific inhibitor, than the mammalian DNA polymerase alpha. In situ visualization of the active peptides after NaDodSO4/PAGE, confirmed that only high Mr DNA polymerase fragments were present in embryo extracts and in purified preparations of DNA polymerase alpha. It appears that C. capitata cells represent a rather peculiar system in the phylogeny of DNA polymerases since they are devoid of DNA polymerase beta and present a DNA polymerase alpha partially resistant to aphidicolin.

Animals↗
PubMed1982

Active polypeptide fragments common to prokaryotic, eukaryotic, and mitochondrial DNA polymerases.

With a procedure that allows the renaturation of the DNA polymerase catalytic activity in situ after SDS-polyacrylamide gel electrophoresis, we have compared the active polypeptides present in extracts from organisms covering a wide evolutionary range from prokaryotes to eukaryotes, namely: Escherichia coli, Oryza sativa, Daucus carota , Neurospora crassa, Dictyostelium discoideum, Saccharomyces cerevisiae, Ceratitis capitata, Leucophaea maderae , Xenopus laevis, rat tissues and human lymphoblastoid cells. Two main clusters of active peptides are visible in mammalian and adult insect tissues, characterized by a mol. wt. greater than 70000 and less than 50000, respectively. High mol. wt. peptides are heterogeneous in size and correspond to active fragments of DNA polymerase alpha, whereas low mol. wt. peptides show the same migration rate as purified DNA polymerase beta and are not generated by proteolysis of the high mol. wt. cluster, In the three species of fungi studied, only high mol. wt. peptides are found. The same is true in plant cells, where no DNA polymerase beta activity is detectable and the pattern of the high mol. wt. cluster is similar to that observed in E. coli extracts (which also lack low mol. wt. peptides). Also in mitochondria from higher and lower eukaryotes only high mol. wt. species are observed, and the active band(s) range from 70000 to 145000 daltons. Our results indicate that the structure of DNA polymerase has been highly conserved during evolution so that an active fragment of mol. wt. greater than or equal to 70 000 is always found in prokaryotic enzymes and in the replicative species of eukaryotic and mitochondrial DNA polymerases; at a certain stage in evolution, another species of low mol. wt. DNA polymerase (beta or beta-like) appears.

Animals↗
PubMed1982

Clinical relevance of terminal transferase and adenosine deaminase in leukemia.

Terminal Transferase (TdT), Adenosine Deaminase (ADA), immunological membrane markers, cytochemical reactivity and cytogenetics were analyzed in 226 patients with ALL, AUL and AML, in 70 patients with CML and in 3 cases of Ph' positive acute leukemia presenting as ALL. TdT was tested in peripheral blood and bone marrow with both the biochemical and immunofluorescence (IF) methods, and ADA was determined biochemically only in peripheral blood cells. By using conventional cytochemistry, cell surface markers determinations, TdT and ADA analysis, three distinct groups are recognized in ALL at presentation: T-ALL with TdT+ and very high ADA values; non-T, non-B ALL with TdT+ and intermediate levels of ADA; B-ALL with TdT absence and low levels of ADA. Clinical presentation and responses to therapy in adult and children ALL were correlated to TdT determinations. The median survivals in adults, calculated for TdT+ and TdT- groups, were 14.2 and 5.6 months, respectively. TdT and ADA were determined in ALL during remission. The wide fluctuation observed for TdT IF and ADA values prevented a reliable monitoring of remissions. At relapse, TdT and ADA values were similar to those found for ALL at presentation; TdT IF determinations were diagnostic in cases showing CNS involvement as the only localization. Forty per cent of AUL and 11% of AML cases were positive for TdT; the medians of ADA values of the TdT+ cases in both AML and AUL were several times higher than those obtained in the TdT- group. While TdT positivity and high ADA had a favorable prognostic value in AUL, similar conclusions can not be drawn at the moment for AML. In chronic phase of CML, TdT was strictly negative and ADA values were increased over the control line only in cases showing initial signs of transformation. In acute phase, the cases positive for TdT (32%) presented a significantly higher ADA activity than the TdT negative ones. The actuarial survival curves for the TdT+ and TdT- groups differ significantly, presenting median survivals from onset of phase of 11 and 4.8 months respectively. The three cases of Ph' positive ALL were all TdT+, presented high ADA values and entered chronic phase of CML after therapy.

Acute Disease↗
PubMed1982

Prognostic significance of terminal transferase and adenosine deaminase in acute and chronic myeloid leukemia.

We have analyzed the distribution and prognostic significance of terminal deoxynucleotidyl transferase (TdT) and adenosine deaminase (ADA) in connection with conventional cytology, cytogenetics, response to therapy, and survival. The study population consisted of 78 patients with AML, 44 patients with Ph1 + CML in chronic phase, and 35 adult patients with Ph1 + CML in blastic phase, among which 5 cases presented as Ph1 + acute leukemia. Nine percent of the AML cases were positive for TdT and were characterized by a high percentage of blast cells in bone marrow, myeloid features by cytochemistry and absence of the Philadelphia chromosome. The median ADA values of the TdT+ AML cases were several times higher than those obtained for the TdT- cases. The survival calculated for the two groups of AML cases subdivided according to ADA levels was significantly longer (p less than 0.025) for the patients with low levels of ADA (less than 250 U/10(8) cells). In chronic phase of CML, TdT was absent and ADA values were increased over normal controls only in cases with early signs of transformation. In blastic phase, 31% of the 35 cases were positive for TdT, and ADA values were significantly higher (p less than 0.001) in TdT+ than TdT- cases. The survival calculated from the onset of transformation was significantly longer for the TdT+ acute phase (10.4 mo) compared to the TdT- patients (4.8 mo; p less than 0.025). Four cases presenting as Ph1 + acute leukemia were TdT+ and had elevated levels of ADA; 3 of them responded to ALL therapy, reverting to a stable phase of CML.

Adenosine Deaminase↗
PubMed1979

A phylogenetic study on vertebrate mitochondrial DNA polymerase.

We have started a phylogenetic survey for the mitochondrial DNA polymerase and present in this study the results obtained for all the different classes for the vertebrates. The operating conditions include the purification of mitochondria, the analysis of the DNA polymerase activity in the extract and the determination of the sedimentation coefficient on sucrose gradients. The utilization of digitonin for removing the external membrane of the organelle and contaminating proteins has been generalized since this detergent shows no effect on the activities of either DNA polymerases alpha or gamma. The results obtained for the mitochondria of different classes of vertebrates show that the activity responding to the specific assay of DNA polymerase gamma tended invariably to increase during purification while that of DNA polymerase alpha tended to decrease. Furthermore in almost all the cases the gamma-polymerase represented the only DNA polymerase activity found in the mitochondria after digitonin treatment. The analysis of the sedimentation patterns of the mitochondrial DNA polymerase strongly suggests the presence of a single type of DNA polymerase showing the typical properties of the gamma-polymerase. It is concluded that the vertebrate mitochondria contain a well-defined and unique form of DNA polymerase which corresponds to the DNA polymerase gamma.

Animals↗
PubMed1979

DNA polymerase alpha, beta and gamma activities in ultraviolet irradiated CV-1 monkey cells.

To determine the possible role of DNA polymerase alpha, beta and gamma during the repair period following ultraviolet (lambda max : 254 nm) irradiation of monkey CV-1 cells, we measured the three enzymatic activities by using specific tests, either in crude extracts or after fractionation by sucrose gradient (5--20%) centrifugation at high salt concentration. When compared to the unirradiated control, we could not detect any significant variation in the levels of activity of DNA polymerases alpha, beta and gamma at any time (0, 12 to 48 h) after ultraviolet irradiation of the cells with doses ranging from 9 to 52.5 J.m-2.

Animals↗