Immunofluorescent staining of poly(ADP-ribose) in situ in HeLa cell chromosomes in the M phase

Poly ADP-ribose signaling is dysregulated in Huntington disease

Huntington disease (HD) is a genetic neurodegenerative disease caused by cytosine, adenine, guanine (CAG) expansion in the Huntingtin (HTT) gene, translating to an expanded polyglutamine tract in the HTT protein. Age at disease onset correlates to CAG repeat length but varies by decades between individuals with identical repeat lengths. Genome-wide association studies link HD modification to DNA repair and mitochondrial health pathways. Clinical studies show elevated DNA damage in HD, even at the premanifest stage. A major DNA repair node influencing neurodegenerative disease is the PARP pathway. Accumulation of poly adenosine diphosphate (ADP)-ribose (PAR) has been implicated in Alzheimer and Parkinson diseases, as well as cerebellar ataxia. We report that HD mutation carriers have lower cerebrospinal fluid PAR levels than healthy controls, starting at the premanifest stage. Human HD induced pluripotent stem cell-derived neurons and patient-derived fibroblasts have diminished PAR response in the context of elevated DNA damage. We have defined a PAR-binding motif in HTT, detected HTT complexed with PARylated proteins in human cells during stress, and localized HTT to mitotic chromosomes upon inhibition of PAR degradation. Direct HTT PAR binding was measured by fluorescence polarization and visualized by atomic force microscopy at the single molecule level. While wild-type and mutant HTT did not differ in their PAR binding ability, purified wild-type HTT protein increased in vitro PARP1 activity while mutant HTT did not. These results provide insight into an early molecular mechanism of HD, suggesting possible targets for the design of early preventive therapies.

Mitotic functions of poly(ADP-ribose) polymerases

Mitosis ensures accurate segregation of duplicated DNA through tight regulation of chromosome condensation, bipolar spindle assembly, chromosome alignment in the metaphase plate, chromosome segregation and cytokinesis. Poly(ADP-ribose) polymerases (PARPs), in particular PARP1, PARP2, PARP3, PARP5a (TNKS1), as well as poly(ADP-ribose) glycohydrolase (PARG), regulate different mitotic functions, including centrosome function, mitotic spindle assembly, mitotic checkpoints, telomere length and telomere cohesion. PARP depletion or inhibition give rise to various mitotic defects such as centrosome amplification, multipolar spindles, chromosome misalignment, premature loss of cohesion, metaphase arrest, anaphase DNA bridges, lagging chromosomes, and micronuclei. As the mechanisms of PARP1/2 inhibitor-mediated cell death are being progressively elucidated, it is becoming clear that mitotic defects caused by PARP1/2 inhibition arise due to replication stress and DNA damage in S phase. As it stands, entrapment of inactive PARP1/2 on DNA phenocopies replication stress through accumulation of unresolved replication intermediates, double-stranded DNA breaks (DSBs) and incorrectly repaired DSBs, which can be transmitted from S phase to mitosis and instigate various mitotic defects, giving rise to both numerical and structural chromosomal aberrations. Cancer cells have increased levels of replication stress, which makes them particularly susceptible to a combination of agents that compromise replication fork stability. Indeed, combining PARP1/2 inhibitors with genetic deficiencies in DNA repair pathways, DNA-damaging agents, ATR and other cell cycle checkpoint inhibitors has yielded synergistic effects in killing cancer cells. Here I provide a comprehensive overview of the mitotic functions of PARPs and PARG, mitotic phenotypes induced by their depletion or inhibition, as well as the therapeutic relevance of targeting mitotic cells by directly interfering with mitotic functions or indirectly through replication stress.

Targeting poly(ADP-ribose) glycohydrolase to draw apoptosis codes in cancer

Poly(ADP-ribosyl)ation is a unique post-translational modification of proteins. The metabolism of poly(ADP-ribose) (PAR) is tightly regulated mainly by poly(ADP-ribose) polymerases (PARP) and poly(ADP-ribose) glycohydrolase (PARG). Accumulating evidence has suggested the biological functions of PAR metabolism in control of many cellular processes, such as cell proliferation, differentiation and death by remodeling chromatin structure and regulation of DNA transaction, including DNA repair, replication, recombination and transcription. However, the physiological roles of the catabolism of PAR catalyzed by PARG remain less understood than those of PAR synthesis by PARP. Noteworthy biochemical studies have revealed the importance of PAR catabolic pathway generating nuclear ATP via the coordinated actions of PARG and ADP-ribose pyrophosphorylase (ADPRPPL) for the driving of DNA repair and the maintenance of DNA replication apparatus while repairing DNA damage. Furthermore, genetic studies have shown the value of PARG as a therapeutic molecular target for PAR-mediated diseases, such as cancer, inflammation and many pathological conditions. In this review, we present the current knowledge of de-poly(ADP-ribosyl)ation catalyzed by PARG focusing on its role in DNA repair, replication and apoptosis. Furthermore, the induction of apoptosis code of DNA replication catastrophe by synthetic lethality of PARG inhibition and the recent progresses regarding the development of small molecule PARG inhibitors and their therapeutic potentials in cancer chemotherapy are highlighted in this review.

Overview on poly(ADP-ribose) immuno-biomedicine and future prospects

Poly(ADP-ribose), identified in 1966 independently by three groups Strassbourg, Kyoto and Tokyo, is synthesized by poly(ADP-ribose) polymerases (PARP) from NAD(+) as a substrate in the presence of Mg(2+). The structure was unique in that it has ribose-ribose linkage. In the early-1970s, however, its function in vivo/in vitro was still controversial and the antibody against it was desired to help clear its significance. Thereupon, the author tried to produce antibody against poly(ADP-ribose) in rabbits and succeeded in it for the first time in the world. Eventually, this success has led to the following two groundbreaking papers in Nature: "Naturally-occurring antibody against poly(ADP-ribose) in patients with autoimmune disease SLE", and "Induction of anti-poly(ADP-ribose) antibody by immunization with synthetic double-stranded RNA, poly(A)·poly(U)".On the way to the publication of the first paper, a reviewer gave me a friendly comment that there is "heteroclitic" fashion as a mechanism of the production of natural antibody. This comment was really a God-send for me, and became a train of power for publication of another paper, as described above. Accordingly, I thought this, I would say, episode is worth describing herein. Because of its importance in biomedical phenomena, a certain number of articles related to "heteroclitic" have become to be introduced in this review, although they were not always directly related to immuno-biological works on poly(ADP-ribose). Also, I tried to speculate on the future prospects of poly(ADP-ribose), product of PARP, as an immuno-regulatory molecule, including either induced or naturally-occurring antibodies, in view of "heteroclitic".

Natural and glucosyl flavonoids inhibit poly(ADP-ribose) polymerase activity and induce synthetic lethality in BRCA mutant cells

Poly(ADP-ribose) polymerase (PARP) inhibitors have been proven to represent superior clinical agents targeting DNA repair mechanisms in cancer therapy. We investigated PARP inhibitory effects of the natural and synthetic flavonoids (quercetin, rutin, monoglucosyl rutin and maltooligosyl rutin) and tested the synthetic lethality in BRCA2 mutated cells. In vitro ELISA assay suggested that the flavonoids have inhibitory effects on PARP activity, but glucosyl modifications reduced the inhibitory effect. Cytotoxicity tests of Chinese hamster cells defective in BRCA2 gene (V-C8) and its parental V79 cells showed BRCA2-dependent synthetic lethality when treated with the flavonoids. BRCA2 mutated cells were three times more sensitive to the flavonoids than the wild-type and gene complemented cells. Reduced toxicity was observed in a glucosyl modification-dependent manner. The present study provides support for the clinical use of new treatment drugs, and is the beginning of the potential application of flavonoids in cancer prevention and the periodic consumption of appropriate flavonoids to reduce cancer risk in individuals carrying a mutant allele of the BRCA2 gene.

Poly(ADP-ribosyl)ation reactions in the regulation of nuclear functions

Poly(ADP-ribosyl)ation is a post-translational modification of proteins. During this process, molecules of ADP-ribose are added successively on to acceptor proteins to form branched polymers. This modification is transient but very extensive in vivo, as polymer chains can reach more than 200 units on protein acceptors. The existence of the poly(ADP-ribose) polymer was first reported nearly 40 years ago. Since then, the importance of poly(ADP-ribose) synthesis has been established in many cellular processes. However, a clear and unified picture of the physiological role of poly(ADP-ribosyl)ation still remains to be established. The total dependence of poly(ADP-ribose) synthesis on DNA strand breaks strongly suggests that this post-translational modification is involved in the metabolism of nucleic acids. This view is also supported by the identification of direct protein-protein interactions involving poly(ADP-ribose) polymerase (113 kDa PARP), an enzyme catalysing the formation of poly(ADP-ribose), and key effectors of DNA repair, replication and transcription reactions. The presence of PARP in these multiprotein complexes, in addition to the actual poly(ADP-ribosyl)ation of some components of these complexes, clearly supports an important role for poly(ADP-ribosyl)ation reactions in DNA transactions. Accordingly, inhibition of poly(ADP-ribose) synthesis by any of several approaches and the analysis of PARP-deficient cells has revealed that the absence of poly(ADP-ribosyl)ation strongly affects DNA metabolism, most notably DNA repair. The recent identification of new poly(ADP-ribosyl)ating enzymes with distinct (non-standard) structures in eukaryotes and archaea has revealed a novel level of complexity in the regulation of poly(ADP-ribose) metabolism.

Poly(ADP-ribosyl)ation reactions in the regulation of nuclear functions

Poly(ADP-ribosyl)ation is a post-translational modification of proteins. During this process, molecules of ADP-ribose are added successively on to acceptor proteins to form branched polymers. This modification is transient but very extensive in vivo, as polymer chains can reach more than 200 units on protein acceptors. The existence of the poly(ADP-ribose) polymer was first reported nearly 40 years ago. Since then, the importance of poly(ADP-ribose) synthesis has been established in many cellular processes. However, a clear and unified picture of the physiological role of poly(ADP-ribosyl)ation still remains to be established. The total dependence of poly(ADP-ribose) synthesis on DNA strand breaks strongly suggests that this post-translational modification is involved in the metabolism of nucleic acids. This view is also supported by the identification of direct protein-protein interactions involving poly(ADP-ribose) polymerase (113 kDa PARP), an enzyme catalysing the formation of poly(ADP-ribose), and key effectors of DNA repair, replication and transcription reactions. The presence of PARP in these multiprotein complexes, in addition to the actual poly(ADP-ribosyl)ation of some components of these complexes, clearly supports an important role for poly(ADP-ribosyl)ation reactions in DNA transactions. Accordingly, inhibition of poly(ADP-ribose) synthesis by any of several approaches and the analysis of PARP-deficient cells has revealed that the absence of poly(ADP-ribosyl)ation strongly affects DNA metabolism, most notably DNA repair. The recent identification of new poly(ADP-ribosyl)ating enzymes with distinct (non-standard) structures in eukaryotes and archaea has revealed a novel level of complexity in the regulation of poly(ADP-ribose) metabolism.

Poly(ADP-ribose) polymerase: early involvement in glutamate-induced neurotoxicity in cultured cerebellar granule cells

Glutamate neurotoxicity is correlated with an increase of cytosolic free Ca2+. In some cell systems, activation of Ca2+ dependent endonucleases or formation of free radicals can damage DNA and activate the chromatin bound enzyme poly(ADP-ribose) polymerase (pADPRP). We have investigated whether pADPRP may be involved in glutamate neurotoxicity in vitro. Cerebellar granule cells at 12 days in culture when treated with a toxic dose of glutamate (100 microM) showed a rapid and transient increase of polyADP-ribose immunoreactivity. Cellular immunostaining was heterogeneous and returned to control levels after washout of glutamate. In the same cell preparations glutamate elicited a marked increase in enzyme protein immunoreactivity which persisted at later times. Non-toxic doses of glutamate did not affect immunostaining. In another set of experiments, pADPRP mRNA was increased 30 min after glutamate. In order to investigate the role of pADPRP in glutamate-mediated neurotoxicity, structurally different inhibitors of pADPRP (3-aminobenzamide, benzamide,3-aminophthalhydrazide) and their inactive analogues (benzoic acid and phthalimide) were tested in this model. Addition of the inhibitors to cultures 60 min before and during the 30 min of glutamate treatment prevented neuronal death by 60-100%, assessed 24 hr later. Glutamate-induced Ca2+ influx was not affected. Inactive analogues failed to afford neuroprotection. These data indicate that not only is pADPRP activated by the early, possibly Ca(2+)-mediated mechanisms initiated by glutamate, but that it might also actively contribute to the subsequent neuronal death.

In vitro inhibition of HeLa cell nuclear ribonucleases by ADP-ribosylation

Ribonuclease activity in HeLa cell nuclei is markedly inhibited by ADP-ribosylation following incubation of intact isolated nuclei with [14C]NAD. Time course experiments demonstrate that [14C] incorporation into proteins is accompanied by a 50% inhibition of ribonuclease activity on single-strand and double-strand polynucleotides. Inhibition does not occur when 3-aminobenzamide, a potent (ADP-ribose) polymerase inhibitor, is present. Two enzymatic activities that degrade double-strand polynucleotides have been purified and partially characterized. A relevant level of radioactivity resulting from [14C]NAD incubation of nuclei was associated to the purified enzyme. The RNase F1 component, which shows maximal activity on polyU-polyA is demonstrated to be the major ADP-ribose acceptor protein.

A major 62-kD intranuclear matrix polypeptide is a component of metaphase chromosomes

We have isolated and partially characterized a major intranuclear matrix polypeptide from rat liver. This polypeptide, which is reversibly stabilized into the intranuclear matrix under conditions which promote intermolecular disulfide bond formation, has a Mr of 62,000 and pI of 6.8-7.2 as determined by two-dimensional IEF/SDS-PAGE. A chicken polyclonal antiserum was raised against the polypeptide purified from two-dimensional polyacrylamide gels. Affinity-purified anti-62-kD IgG was prepared and used to immunolocalize this polypeptide in rat liver tissue hepatocytes. In interphase hepatocytes the 62-kD antigen is localized in small, discrete patches within the nucleus consistent with the distribution of chromatin. The staining is most prominent at the nuclear periphery and somewhat less dense in the nuclear interior. Nucleoli and cytoplasm are devoid of staining. During mitosis the 62-kD antigen localizes to the condensed chromosomes with no apparent staining of cytoplasmic areas. The chromosomal staining during mitosis is uniform with no suggestion of the patching seen in interphase nuclei. Fractionation and immunoblotting studies using rat hepatoma tissue culture cells blocked in metaphase with colcemid confirm the chromosomal localization of this 62-kD intranuclear protein during mitosis. The 62-kD polypeptide fractionates completely with metaphase chromosome scaffolds generated by sequential treatment of isolated chromosomes with DNAse I and 1.6 M NaCl, suggesting that this major 62-kD intranuclear protein may be involved in maintaining metaphase chromosomal architecture.

Antibodies to the five histones and poly(adenosine diphosphate-ribose) in drug induced lupus: implications for pathogenesis

Certain drugs are a frequent source of antinuclear antibody (ANA) induction, and ANA is invariably present in the few patients who progress to the drug induced lupus syndrome. This report concerns the fine specificity of the ANA response to hydralazine, penicillamine, and sulphasalazine therapy. Using highly purified individual histones in fluorimetric assays, antihistone antibodies are always detectable, often in large amounts, but the pattern of response to individual histones is variable and not drug specific. In addition to the response to the three histones H1, H2B, and H3 reminiscent of idiopathic systemic lupus erythematosus, antibody to histone H2A predominates in some drug induced cases. Contrary to previous thought, histones are not the sole target of the antinuclear response: we also demonstrate a significant correlation between ANA titre and antibody to poly(adenosine diphosphate-ribose). Like the histones, this is a macromolecule that can bind to deoxyribonucleic acid (DNA). It is proposed that drug induced damage to chromatin leads to ANA production, while drug induced impairment of complement activity may then enable these autoantibodies to mediate the lupus syndrome.

A monoclonal antibody to triplex DNA binds to eucaryotic chromosomes

A monoclonal antibody (Jel 318) was produced by immunizing mice with poly[d(TmC)].poly[d(GA)].poly[d(mCT) which forms a stable triplex at neutral pH. Jel 318 did not bind to calf thymus DNA or other non pyrimidine.purine DNAs such as poly[d(TG)].poly[d(CA)]. In addition the antibody did not recognize pyrimidine.purine DNAs containing mA (e.g. poly[d(TC)].poly[d(GmA)]) which cannot form a triplex since the methyl group blocks Hoogsteen base-pairing. The binding of Jel 318 to chromosomes was assessed by immunofluorescent microscopy of mouse myeloma cells which had been fixed in methanol/acetic acid. An antibody specific for duplex DNA (Jel 239) served as a control. The fluorescence due to Jel 318 was much weaker than that of Jel 239 but binding to metaphase chromosomes and interphase nuclei was observed. The staining by Jel 318 was unaffected by addition of E. coli DNA but it was obliterated in the presence of triplex. Since an acid pH favours triplex formation, nuclei were also prepared from mouse melanoma cells by fixation in cold acetone. Again Jel 318 showed weak but consistent staining of the nuclei. Therefore it seems likely that triplexes are an inherent feature of the structure of eucaryotic DNA.

ADP-ribosylation of metaphase and interphase nonhistones using [3H]adenosine as a radioactive label

ADP-ribosylation of HeLa nonhistone proteins was investigated by using [3H]adenosine as an in vivo radioactive label. The aim was to determine basic differences in the patterns of modification of interphase and metaphase nonhistones. Fluorography revealed a relatively small number of modified proteins for isolated metaphase chromosomes. In addition to the core histones, a protein of 116 kDa, which is identified as poly-(ADP-ribose) polymerase, was a primary acceptor of [3H]adenosine. Two-dimensional gels revealed a profound difference in the modification of metaphase and interphase nonhistones. For interphase nuclei, 3H label was distributed among a large number of nonhistone acceptors.

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.

Naturally occurring antibodies to poly(ADP-ribose) in autoimmune MRL/Mp-lpr/lpr mice

The presence of antibodies to poly(ADP-ribose) was demonstrated in the sera of MRL/Mp-lpr/lpr (MRL/l) mice by an enzyme linked immunosorbent assay (ELISA). Antibody to poly(ADP-ribose) was strongly inhibited by single stranded DNA (ssDNA) and poly(ADP-ribose), and less by double stranded DNA (dsDNA). Affinity purified anti-poly(ADP-ribose) antibodies bound more with immobilized ssDNA than with poly(ADP-ribose), and were significantly inhibited by soluble ssDNA, although poly(ADP-ribose) was the best soluble inhibitor. On the contrary, affinity purified anti-ssDNA antibodies bound best with ssDNA and significantly but less with poly(ADP-ribose); however, they were scarcely inhibited by poly(ADP-ribose). These results suggest that similar antigenic determinants exist in poly(ADP-ribose) and ssDNA. It is conceivable, however, at the present moment that 'naturally occurring antibodies to poly(ADP-ribose)' in MRL/l mice are subpopulations of anti-ssDNA antibodies that react equally well with poly(ADP-ribose) and ssDNA.

Relationship between histone H1 poly(adenosine diphosphate ribosylation) and histone H1 phosphorylation using anti-poly(adenosine diphosphate ribose) antibody

The chromatin-associated enzyme poly(ADP-Rib) polymerase catalyzes the posttranslational modification of histones. Antibody to poly(ADP-Rib) has been coupled to Sepharose, and the resultant immunoadsorbent was used to fractionate, specifically, histone H1 subpopulations undergoing this nuclear protein modification. When this method of separation was used, it was additionally observed that poly-(ADP-ribosylated) H1 species were highly accessible to in vitro phosphorylation by nuclear protein kinase. Phosphorylated H1 molecules were retained by the anti-poly(ADP-Rib)-Sepharose column due to the presence of endogenous poly-(ADP-Rib) components. Degradation of the latter moieties on phosphorylated H1 reversed their adsorption to the column.

ADP-ribosylation in permeable HeLa S3 cells

ADP-ribosylation in permeabilized metaphase and interphase cells using [32P]NAD at pH 8.0 have been compared. Incorporation into trichloroacetic acid insoluble material was 4-5-times greater in metaphase cells. 17-22% was in the soluble fraction which contained material released from the cells, 16-22% in the 0.2 M HCl extract (histones) of the cell ghosts and the remaining activity in the residual fraction. Fractions were analyzed using dodecylsulphate/polyacrylamide gel electrophoresis at pH 6.0. The soluble fractions from metaphase and interphase cells exhibited three common unidentified ADP-ribosylated proteins corresponding to 78 000, 54 000 and 36 000 Da. In addition metaphase cells contained several other ADP-ribosylated proteins not present in interphase cells. The 0.2 M HCl extracts gave from metaphase cells radioactivity in the 32 000-39 000-Da region suggesting ADP-ribosylation of histone H1 with up to 10 residues of ADP-ribose and in the 17 000-20 000-Da region indicating ADP-ribosylation of core histones. The pattern of ADP-ribosylation of core histone in metaphase and interphase cells was qualitatively similar whereas the number of ADP-ribose residues per H1 molecule was higher in metaphase cells. The residual fraction contained free poly(ADP-ribose) and oligo(ADP-ribose). The results do not lend support to a special function of ADP-ribosylated histones in the mitotic event while certain ADP-ribosylated non-histone proteins may be specific for metaphase cells.