Cytological detection of poly (ADP-ribose) polymerase

An attempt was made to demonstrate poly (ADP-ribose) polymerase cytologically. In vitro incorporation from the nucleotide, [³H]NAD was detected in frozen sections of onion embryo and meristematic tissue by autoradiography. In meristematic tissue, there was a correlation between the number of cells displaying intensein vitro incorporation from [³H]NAD and cytological DNA polymerase activity. Performed enzymes effecting a distinct incorporation from [³H]NAd were localized in the nuclei of all tissues of the ungerminated seed except the endosperm. Evidence for poly (ADP-ribose) polymerase has been obtained for the first time from higher plant cells and localized cytologically.     

Cholera toxin affects nuclear ADP-ribosylation in GH1 cells

Incubation of GH1 cells with cholera toxin for 24 h inhibits [32P]ADP-ribose incorporation into histones and non-histone nuclear proteins by more than 50%. The toxin produces a generalized decrease of incorporation into all protein acceptors and into the poly(ADP-ribosyl)ated components excised from chromatin after micrococcal nuclease digestion. The cellular levels of NAD were also decreased (40 to 80%) after treatment with cholera toxin. The inhibition of poly(ADP-ribosyl)ation is preceded by an increase of [32P]ADP-ribose incorporation, since incubation with the toxin for 3 h caused an increase instead of a decrease of incorporation. Incubation with dibutyryl cyclic AMP for 24 h also inhibited nuclear poly(ADP-ribosyl)ation, thus showing that the effect of cholera toxin might be mediated by cyclic AMP.     

Regulation of poly(ADP-ribose) polymerase. Histone-specific adaptations of reaction products

The post-translational poly ADP-ribosylation of proteins by the nuclear enzyme poly(ADP-ribose) polymerase (EC 2.4.2.30) involves a complex pattern of ADP-ribose polymers. We have determined how this enzyme produces the various polymer size patterns responsible for altered protein function. The results show that histone H1 and core histones are potent regulators of both the numbers and sizes of ADP-ribose polymers. Each histone induced the polymerase to synthesize a specific polymer size pattern. Various other basic and/or DNA binding proteins as well as other known stimulators of poly(ADP-ribose) polymerase (spermine, MgCl2, nicked DNA) were ineffective as polymer size modulators. Testing specific proteolytic fragments of histone H1, the polymer number and polymer size modulating activity could be mapped to specific polypeptide domains. The results suggest that histones specifically regulate the polymer termination reaction of poly(ADP-ribose) polymerase.     

Increased synthesis of poly(ADP-ribose) in isolated liver nuclei from autoimmune NZB/NZW mice

The synthesis and degradation of poly(ADP-ribose) were investigated in isolated liver nuclei from autoimmune NZB/W mice and four strains of normal mice. Compared to normal mice the maximum levels of incorporation of [3H]NAD into poly(ADP-ribose) were increased about 2-fold in the autoimmune mice. The kinetics of incorporation suggested that this change was due to an increase in the activity of the polymerase rather than a decrease in the level of degradative enzymes. Thus there may be a connection between autoimmunity and poly(ADP-ribose) metabolism.     

Nuclear incorporation of [adenine 14C]NAD is altered by compounds which affect poly(ADP-ribose) formation.

The use of a DNA alkylating agent, which induces poly(ADP-ribose) formation, has been employed to study the incorporation of [adenine 14C]NAD into pea root meristem nuclei, which is a prerequisite for poly(ADP-ribose) synthesis. The incorporation of [adenine 14C]NAD is significantly reduced when the poly(ADP-ribose)polymerase inhibitors, 7-methylxanthine and 3-methoxybenzamide are present and this incorporation is augmented when the DNA alkylating agent methyl methanesulfonate is added. Such information supports the hypothesis that poly(ADP-ribose) may be involved in the cell cycle regulation of pea root meristem nuclei.     

Effect of polyamines on ADP-ribosylation by chick-embryo-liver nuclei

Effects of polyamines on poly(ADP-ribose) formation and DNA synthesis in the chick-embryo-liver nuclei were investigated. When 14-day chick-embryo-liver nuclei were incubated with [3H]NAD in the presence of 1 mM spermine, 2.5 mM spermidine, or 3.5 mM putrescine, a 9-fold increase in poly)ADP-ribose) formation was observed. Nuclei treated with nuclease showed high poly(ADP-ribose) synthetase activity as spermine-treated nuclei. However, no further increase in the polymer formation by polyamines was detected in the nuclease-treated nuclei. We found that an increase in the polymer formation by spermine was the result of an increase in both chain length and chain number of the polymer at 2.3- and 6-fold, respectively. The major ADP-ribosylated proteins were determined as two non-histone proteins of Mr 130 000 and 70 000. The experiment of DNA synthesis with nuclei ADP-ribosylated in the presence of spermine showed a 7-fold increase in [3H]dTMP incorporation into the acid-inaoluble fraction. A similar stimulation was also found with nuclei treated with other polysmines, spermidine and putrescine, in the presence of NAD. These results indicate that DNA synthesis in growing tissues containing polyamines at high levels, such as is the case with tumors and the fetus, is stimulated by polyamine-mediated ADP-ribosylation of the nuclear proteins.     

Disturbances in DNA precursor metabolism associated with exposure to an inhibitor of poly(ADP-ribose) synthetase

3-Aminobenzamide (3AB) is widely used as an inhibitor of poly(ADP-ribose) synthetase to study the effect of protein ribosylation on various cellular processes, but the specificity of its inhibition has not been demonstrated. We found that 3AB has a wide range of effects on DNA precursor metabolism, as determined by high-performance liquid chromatographic separation of deoxynucleosides derived from enzymatic digestion of cellular DNA. 3AB (10-20 mM) significantly reduced cell growth in human lymphoblastoid cells. Furthermore, the incorporation of [3H]deoxycytidine into DNA was significantly enhanced relative to incorporation of [3H]deoxythymidine, [3H]deoxyguanosine, and [3H]deoxyadenosine. Incorporation of fragments of [3H]glucose into the pyrimidine fraction of DNA was significantly inhibited relative to incorporation into the purine fraction. At only 1 mM, 3AB had a major inhibitory effect on the incorporation of the methyl group from [3H]methionine into deoxyguanosine, deoxyadenosine, and deoxycytidine, with 50% inhibition into deoxyguanosine and deoxyadenosine and 90% inhibition into deoxycytidine. The specificity of 3AB inhibition to poly(ADP-ribose) synthetase is therefore doubtful in view of this variety of metabolic effects, involving pyrimidine synthesis and de novo synthesis via the one-carbon pool.     

Disparity in the effects of two N-methyl nicotinamides on poly(ADP-ribose) synthetase and macromolecular synthesis in hepatomas

The inhibitory effects of nicotinamide analogs on the activity of poly(ADP-ribose)) synthetase were compared to effects on precursor incorporation into macromolecules in three lines of hepatoma cells (Morris hepatomas 5123C, 7777 and HTC). N'-methylnicotinamide was a less effective inhibitor of poly (ADP-ribose) synthetase than was 1-methylnicotinamide while both these compounds had smaller inhibitory effects on the enzyme than were seen with nicotinamide or 3-aminobenzamide. On the other hand, the incorporation of [3H]thymidine into DNA and of [3H]uridine into RNA were inhibited by N'-methylnicotinamide in the concentration range 2-20 mM but not by 1-methylnicotinamide. Under the conditions examined there were no significant effects on the incorporation of [14C]lysine and [3H]leucine in hepatoma cells. The data indicated that the inhibitory effect of N'-methylnicotinamide on nucleic acid synthesis may be unrelated to action on poly (ADP-ribose) synthetase.     

Poly(ADP-ribosylation) of nuclear proteins in rat thymocytes

Specific antibodies to poly(ADP-ribose) were obtained and characterized. Using these antibodies, the tissue specificity of poly(ADP-ribose) modified nuclear proteins from rat thymocytes and hepatocytes was studied. The differences in the levels of poly(ADP-ribosylation) of nuclear proteins from both tissues were found to be quantitative rather than qualitative. Analysis of intranuclear distribution of poly(ADP-ribose) acceptor proteins revealed that the bulk of them is localized in the nuclear sap and matrix. A comparison of spectral properties of poly(ADP-ribosylated) proteins, using specific antibodies and label incorporation from [14C]NAD showed the existence of two protein groups. Some of those were modified in a great degree but exchange poly(ADP-ribose) at a slow rate, whereas others (e.g., histones and HMG proteins) modified in a small degree exchanged poly(ADP-ribose) at a much higher rate. The results obtained by different methods are discussed.     

Poly(adenosine diphosphate-ribosylation) of nuclear matrix proteins in alkylating agent resistant and sensitive cell lines

Using Walker 256 breast carcinoma cell lines either with or without acquired resistance to alkylating agents, the structural framework proteins of the nucleus, the nuclear matrix proteins, were found to be effective acceptors for poly(ADP-ribose). Incubation of isolated nuclei with nicotinamide adenine [32P] dinucleotide ([32P] NAD), followed by the isolation of the nuclear matrix, demonstrated that two polypeptides of approximate molecular weight (Mr) 105 000 and 116 000 were extensively poly(ADP-ribosylated). By an in vitro [32P] NAD assay, the nuclear matrix fraction was found to maintain approx. 15% of the total nuclear matrix activity of poly(ADP-ribose) polymerase. Confirmation that the trichloroacetic acid (TCA) precipitable material represented ADP-ribose units was achieved by enzymatic digestion of the nuclear matrix preparation with snake venom phosphodiesterase (SVP). Within 15 min, greater than 85% of the 32P label was digested by SVP and the final digestion products were found to be phosphoribosyl-AMP (PR-AMP) and adenosine 5'-monophosphate (5'-AMP) by thin layer chromatographic analysis. The average polymer chain length was estimated to be 6-7 ADP-ribose units. Because poly(ADP-ribose) polymerase has a putative role in DNA repair, a comparison of the nuclear matrix fractions from Walker resistant and sensitive tumor cell lines was made. In both cell lines, the quantitative and qualitative patterns of the nuclear matrix associated poly(ADP-ribosylation) were similar.     

Synthesis of poly(ADP-ribose)-agarose beads: an affinity resin for studying (ADP-ribose)n-protein interactions.

Polymers of ADP-ribose bind chromatosomal histones in solution and may play a role in chromatin accessibility in vivo. We have enzymatically synthesized a poly(ADP-ribose) affinity resin to further characterize binding of nuclear proteins to ADP-ribose polymers. NAD+- and (ADP-ribose)-derivatized agarose beads were recognized as polymer acceptors by the nuclear enzyme poly(ADP-ribose) polymerase. This polymerase elongated the existing ligands by successive addition of exogenously available ADP-ribose residues to form polymers covalently linked to the agarose beads. Poly(ADP-ribose) formation on the beads was dependent on incubation time and the mode of ligand attachment to the agarose. The resulting poly(ADP-ribose)-derivatized agarose beads possessed polymers which closely resembled those modifying the ADP-ribose polymerase by the automodification reaction. Fractionation of rat liver nuclear lysate over the poly(ADP-ribose) resin revealed a strong affinity of H1 for ADP-ribose polymers, thereby supporting a role for poly(ADP-ribose) in chromatin functions. Poly(ADP-ribose)-agarose beads are extremely stable and will be useful not only for affinity studies, but also for mechanistic studies involving polymer elongation and catabolism.     

ADP-ribosylation of histones of the chicken liver nucleus at different rates of glycohydrolase hydrolysis of NAD

The rate of incorporation of nicotinamide-[adenosine-U-14C]adenine dinucleotide [( Ado-U-14C]NAD) into histones and the poly(ADPR) polymerase activity of chromatin suggest that the NAD-dependent ADP-ribosylation of histones depends on the rate of NAD hydrolysis by glycohydrolase in chicken liver nuclei. With a rise in the NAD-glycohydrolase activity after treatment of nuclei with Triton X-100 the synthesis of poly(ADP-ribose) via the poly(ADPR)polymerase reaction is augmented, as a result of which the rate of [Ado-U-14C]NAD incorporation into total histones is increased. On the contrary, the decrease of NAD-glycohydrolase hydrolysis after treatment of nuclei with SDS lowers the poly(ADPR)polymerase activity and [Ado-U-14C]NAD incorporation into histones. Under these conditions, i. e. different rates of glycohydrolase hydrolysis of NAD in the nuclei, some redistribution of [Ado U-14C]NAD incorporation into individual histones occurs.     

Cellular regulation of ADP-ribosylation of proteins. III. Selective augmentation of in vitro ADP-ribosylation of histone H3 in murine thymic cells after in vivo emetine treatment

Thymic cells were isolated at intervals of between 0 and 144 h from mice that received one intraperitoneal injection of emetine (33 mg/kg), and thymus weight, incorporation of [14C]leucine into proteins and [3H]thymidine into DNA in intact thymic cells, as well as initial rates of protein ADP-ribosylation in permeabilized cells [A. Sóoki-Tóth, F. Asghari, E. Kirsten, and E. Kun (1987) Exp. Cell Res. 170, 93] were simultaneously monitored. The effect of emetine as an inhibitor of protein synthesis [F. Antoni, N. G. Luat, I. Csuka, I. Oláh, A. Sóoki-Tóth, and G. Bánfalvi (1987) Int. J. Immunopharmacol. 9, 333] corresponds to the induction of sequential cellular events, such as cell exit and remigration, by other antimitotic agents [C. Penit and F. Vasseur (1988) J. Immunol. 140, 3315] and produces an activation of proliferation of cells reentering into this organ. Proliferation, as demonstrated by a large increase in DNA synthesis and entrance into S phase, was kinetically related to an apparent increase in poly(ADP-ribose) polymerase activity in thymic cells and a highly significant in vitro ADP-ribosylation of histone H3. Since no DNA fragmentation occurred in thymic cells, as tested by a fluorometric technique [C. Birnboim and J. J. Jevac (1981) Cancer Res. 41, 1889], it is probable that a selective activation of poly(ADP-ribose) polymerase may have been induced in cells that undergo differentiation and proliferation while repopulating the thymus.     

Decrease in ADP-ribosylation of HeLa non-histone proteins from interphase to metaphase

Variations for non-histones in the ADP-ribosylating activities of interphase and metaphase cells were investigated. 32P-Labeled nicotinamide adenine dinucleotide ([32P]NAD), the specific precursor for the modification, was used to radioactively label proteins. Permeabilized interphase and mitotic cells, as well as isolated nuclei and chromosomes, were incubated with the label. One-dimensional and two-dimensional gels of the proteins of total nuclei and chromatin labeled with [32P]NAD showed more than 100 modified species. Changing the labeling conditions resulted in generally similar patterns of modified proteins, though the overall levels of incorporation and the distributions of label among species were significantly affected. A less complex pattern was found for nuclear scaffolds. The major ADP-ribosylated proteins included the lamins and poly(ADP-ribose) polymerase. Inhibitors of ADP-ribosylation were effective in preventing the incorporation of label by most non-histones. Snake venom phosphodiesterase readily removed protein-bound 32P radioactivity. A fundamentally different distribution of label from that of interphase nuclei and chromatin was found for metaphase chromosome non-histones. Instead of 100 or more species, the only major acceptor of label was poly(ADP-ribose) polymerase. This profound change during mitosis may indicate a structural role for ADP-ribosylation of non-histone proteins.     

Measurement of poly(ADP-ribose) glycohydrolase activity by high resolution polyacrylamide gel electrophoresis: Specific inhibition by histones and nuclear matrix proteins

We have developed a novel enzyme assay that allows the simultaneous determination of noncovalent interactions of poly(ADP-ribose) with nuclear proteins as well as poly(ADP-ribose) glycohydrolase (PARG) activity by high resolution polyacrylamide gel electrophoresis. ADP-ribose chains between 2 and 70 residues in size were enzymatically synthesized with pure poly(ADP-ribose) polymerase (PARP) and were purified by affinity chromatography on a boronate resin following alkaline release from protein. This preparation of polymers of ADP-ribose was used as the enzyme substrate for purified PARG. We also obtained the nuclear matrix fraction from rat liver nuclei and measured the enzyme activity of purified PARG in the presence or absence of either histone proteins or nuclear matrix proteins. Both resulted in a marked inhibition of PARG activity as determined by the decrease in the formation of monomeric ADP-ribose. The inhibition of PARG was presumably due to the non-covalent interactions of these proteins with free ADP-ribose polymers. Thus, the presence of histone and nuclear matrix proteins should be taken into consideration when measuring PARG activity.     

Differentiation of 3T3-L1 pre-adipocytes induced by inhibitors of poly(ADP-ribose) polymerase and by related noninhibitory acids

To analyze a possible involvement of ADP-ribosylation reactions in 3T3-L1 pre-adipocyte differentiation. ADP-ribosyltransferase activities is permeabilized cells as well as endogenous amounts of protein-bound mono- and poly(ADP-ribose) residues were determined. Also, in vivo labeling with [3H]adenosine of ADP-ribose residues linked to high-mobility-group (HMG) proteins was performed. As an additional probe, the effects of ADP-ribosylation inhibitors and non-inhibitory analogs were studied. Basal and total poly(ADP-ribose) polymerase activities markedly increased prior to the appearance of the differentiation marker glycerol-3-phosphate dehydrogenase. Despite these apparent changes in activity, however, neither protein-bound poly(ADP-ribose) residue nor mono(ADP-ribosyl) groups in histones, nor the NAD content, changed significantly under these conditions. Furthermore, although HMG protein-associated [3H]ADP-ribose was reduced in differentiating [3H]adenosine-labeled cells, the data suggest altered precursor pool labeling rather than a specific decrease in ADP-ribosylated HMG proteins. Non-participation of ADP-ribosylation reactions in 3T3-L1 differentiation is further supported by experiments with inhibitors and non-inhibitory analogs. Benzamide at 0.3-3 mM per se without effect on differentiation, was able to induce specific gene expression when combined with insulin (10(-12)-10(-7) M). Similar effects were seen with benzoate as well as with nicotinamide, 3-aminobenzamide and their corresponding acids. The data indicate that benzamide and analogs have profound effects on chromatin functions that are not mediated by ADP-ribosylation reactions.     

Resistance of ADP-ribosylated histones and HMG proteins to proteases.

Calf thymus histones (individually isolated or mixtures) and high mobility group proteins were ADP-ribosylated in vitro using [32P]NAD+ and immobilized purified poly(ADP-ribose) polymerase. The modified histones were then subjected to V8 protease or alpha-chymotrypsin digestion and the resulting peptides were separated by electrophoresis on acetic acid-urea-Triton gels. It was found that in vitro ADP-ribosylated histones were much more resistant to proteases than unmodified histones. A similar approach was applied to histones modified by the endogenous poly(ADP-ribose) polymerase in permeabilized NS-1 mouse myeloma cells in culture. In this case, the proteases could not discriminate between modified and unmodified histones and putative mono(ADP-ribosyl)ated peptides appeared in a digestion frame corresponding to that of bulk peptides. These differences are most probably due to the specificity or number of ADP-ribose groups added to the histones by the endogenous or exogenous poly(ADP-ribose) polymerase. Thus, depending on the size of poly(ADP-ribose) attached to nuclear proteins, these modified proteins might display different degrees of resistance to proteolysis.     

Characterization of human poly(ADP-ribose) polymerase with autoantibodies

The addition of poly(ADP-ribose) chains to nuclear proteins has been reported to affect DNA repair and DNA synthesis in mammalian cells. The enzyme that mediates this reaction, poly(ADP-ribose) polymerase, requires DNA for catalytic activity and is activated by DNA with strand breaks. Because the catalytic activity of poly(ADP-ribose) polymerase does not necessarily reflect enzyme quantity, little is known about the total cellular poly(ADP-ribose) polymerase content and the rate of its synthesis and degradation. In the present experiments, specific human autoantibodies to poly(ADP-ribose) polymerase and a sensitive immunoblotting technique were used to determine the cellular content of poly(ADP-ribose) polymerase in human lymphocytes. Resting peripheral blood lymphocytes contained 0.5 X 10(6) enzyme copies per cell. After stimulation of the cells by phytohemagglutinin, the poly(ADP-ribose) polymerase content increased before DNA synthesis. During balanced growth, the T lymphoblastoid cell line CEM contained approximately 2 X 10(6) poly(ADP-ribose) polymerase molecules per cell. This value did not vary by more than 2-fold during the cell growth cycle. Similarly, mRNA encoding poly(ADP-ribose) polymerase was detectable throughout S phase. Poly(ADP-ribose) polymerase turned over at a rate equivalent to the average of total cellular proteins. Neither the cellular content nor the turnover rate of poly(ADP-ribose) polymerase changed after the introduction of DNA strand breaks by gamma irradiation. These results show that in lymphoblasts poly(ADP-ribose) polymerase is an abundant nuclear protein that turns over relatively slowly and suggest that most of the enzyme may exist in a catalytically inactive state.