Poly(adenosine diphosphate ribose)

NSC-3852 synergistically enhances the cytotoxicity of olaparib in oral squamous cell carcinoma

The PARP inhibitor olaparib is an anti-cancer agent based on synthetic lethality that targets poly (ADP-ribose) polymerases. It is used as a therapeutic agent for breast, ovarian, pancreatic, and prostate cancers carrying BRCA1/2 mutations that cause deficiency in homologous recombination. In recent years, acquired resistance to PARP inhibitors has become a clinical problem in PARP inhibitor-treated patients. Meanwhile, the development of molecular targeted drugs for highly malignant oral cancers has not progressed, and effective treatment strategies are needed. In this study, we identified the histone deacetylase inhibitor NSC-3852 as a compound that synergistically enhances the effects of olaparib in oral squamous cell carcinoma cell lines. N-Acetyl-l-cysteine treatment partially recovered cell survival after co-treatment with olaparib and NSC-3852. Moreover, the combination of olaparib and NSC-3852 rapidly upregulated γH2AX at 2 h after treatment, and induced S-phase arrest and apoptosis at 24 h after treatment, suggesting that this combination induced apoptosis through accumulation of massive DNA damage. Taken together, these findings demonstrate that NSC-3852 is a sensitizer of olaparib and suggest that the combination of NSC-3852 and olaparib may be a useful therapeutic strategy for homologous recombination-proficient cancers, including cancers with acquired resistance to olaparib and high-grade oral squamous cell carcinoma.

Activated NAD+ biosynthesis pathway induces olaparib resistance in BRCA1 knockout pancreatic cancer cells

PARP inhibitors have been developed as anti-cancer agents based on synthetic lethality in homologous recombination deficient cancer cells. However, resistance to PARP inhibitors such as olaparib remains a problem in clinical use, and the mechanisms of resistance are not fully understood. To investigate mechanisms of PARP inhibitor resistance, we established a BRCA1 knockout clone derived from the pancreatic cancer MIA PaCa-2 cells, which we termed C1 cells, and subsequently isolated an olaparib-resistant C1/OLA cells. We then performed RNA-sequencing and pathway analysis on olaparib-treated C1 and C1/OLA cells. Our results revealed activation of cell signaling pathway related to NAD+ metabolism in the olaparib-resistant C1/OLA cells, with increased expression of genes encoding the NAD+ biosynthetic enzymes NAMPT and NMNAT2. Moreover, intracellular NAD+ levels were significantly higher in C1/OLA cells than in the non-olaparib-resistant C1 cells. Upregulation of intracellular NAD+ levels by the addition of nicotinamide also induced resistance to olaparib and talazoparib in C1 cells. Taken together, our findings suggest that upregulation of intracellular NAD+ is one of the factors underlying the acquisition of PARP inhibitor resistance.

Dysfunction of poly (ADP-ribose) glycohydrolase suppresses osteoclast differentiation in RANKL-stimulated RAW264 cells

Poly (ADP-ribose) glycohydrolase (PARG) is an enzyme that mainly degrades poly (ADP-ribose) (PAR) synthesized by poly (ADP-ribose) polymerase (PARP) family proteins. Although PARG is involved in many biological phenomena, including DNA repair, cell differentiation, and cell death, little is known about the relationship between osteoclast differentiation and PARG. It has also not been clarified whether PARG is a valuable target for therapeutic agents in the excessive activity of osteoclast-related bone diseases such as osteoporosis. In the present study, we examined the effects of PARG inhibitor PDD00017273 on osteoclast differentiation in RANKL-induced RAW264 cells. PDD00017273 induced the accumulation of intracellular PAR and suppressed the number of tartrate-resistant acid phosphatase (TRAP)-positive multinucleated cells. PDD00017273 also downregulated osteoclast differentiation marker genes such as Trap, cathepsin K (Ctsk), and dendrocyte expressed seven transmembrane protein (Dcstamp) and protein expression of nuclear factor of activated T cells 1 (NFATc1), a master regulator of osteoclast differentiation. Taken together, our findings suggest that dysfunction of PARG suppresses osteoclast differentiation via the PAR accumulation and partial inactivation of the NFATc1.

The dynamic process of covalent and non-covalent PARylation in the maintenance of genome integrity: a focus on PARP inhibitors

Poly(ADP-ribosylation) (PARylation) by poly(ADP-ribose) polymerases (PARPs) is a highly regulated process that consists of the covalent addition of polymers of ADP-ribose (PAR) through post-translational modifications of substrate proteins or non-covalent interactions with PAR via PAR binding domains and motifs, thereby reprogramming their functions. This modification is particularly known for its central role in the maintenance of genomic stability. However, how genomic integrity is controlled by an intricate interplay of covalent PARylation and non-covalent PAR binding remains largely unknown. Of importance, PARylation has caught recent attention for providing a mechanistic basis of synthetic lethality involving PARP inhibitors (PARPi), most notably in homologous recombination (HR)-deficient breast and ovarian tumors. The molecular mechanisms responsible for the anti-cancer effect of PARPi are thought to implicate both catalytic inhibition and trapping of PARP enzymes on DNA. However, the relative contribution of each on tumor-specific cytotoxicity is still unclear. It is paramount to understand these PAR-dependent mechanisms, given that resistance to PARPi is a challenge in the clinic. Deciphering the complex interplay between covalent PARylation and non-covalent PAR binding and defining how PARP trapping and non-trapping events contribute to PARPi anti-tumour activity is essential for developing improved therapeutic strategies. With this perspective, we review the current understanding of PARylation biology in the context of the DNA damage response (DDR) and the mechanisms underlying PARPi activity and resistance.

PARG inhibition limits HCC progression and potentiates the efficacy of immune checkpoint therapy

BACKGROUND & AIMS

Although the treatment of hepatocellular carcinoma (HCC) has been revolutionized by the advent of effective systemic therapies, the prognosis of patients with HCC remains dismal. Herein, we examined the pathophysiological role of PARG and assessed the utility of targeting dePARylation for HCC therapy.

METHODS

The oncogenic function of PARG was evaluated in 2 orthotopic xenograft models and a Parg^flox/flox mice model. The therapeutic efficacy of PARG inhibitors in combination with an anti-PD-1 antibody were assessed in murine orthotopic models. Microarray analysis was used to evaluate the pathological relevance of the PARG/DDB1/c-Myc/MMR axis.

RESULTS

High PARG expression was strongly associated with poor HCC prognosis. Hepatocyte-specific PARG deletion significantly impaired liver tumorigenesis. PARG promoted HCC growth and metastasis through DDB1-dependent modulation of c-Myc. Specifically, PARG dePARylated DDB1 and consequently promoted DDB1 autoubiquitination, thus stabilizing the c-Myc protein in HCC cells. PARG downregulation attenuated c-Myc-induced MMR expression and PARG deficiency was correlated with a favorable prognosis in patients with HCC treated with anti-PD-1-based immunotherapy. In addition, PARG inhibitors could act in synergy with anti-PD-1 antibodies in orthotopic mouse models.

CONCLUSIONS

PARG can act as an oncogene in HCC by modulating PARG/DDB1/c-Myc signaling and could be used as a biomarker to identify patients with HCC who may benefit from anti-PD-1 treatment. Our findings suggest that co-inhibition of PARG and PD-1 is an effective novel combination strategy for patients with HCC.

LAY SUMMARY

The increase in deaths due to hepatocellular carcinoma (HCC) is a growing concern, with the mechanisms responsible for HCC development still incompletely understood. Herein, we identify a novel mechanism by which the protein PARG contributes to HCC development. Inhibition of PARG increased the efficacy of anti-PD-1 therapy (a type of immunotherapy) in HCC. These findings support the future clinical development of PARG inhibitors, potentially in combination with anti-PD-1 inhibitors.

Inhibition of Poly (ADP-Ribose) Glycohydrolase Accelerates Osteoblast Differentiation in Preosteoblastic MC3T3-E1 Cells

Poly ADP-ribosylation (PARylation) is a post-translational modification catalyzed by poly (ADP-ribose) polymerase (PARP) family proteins such as PARP1. Although PARylation regulates important biological phenomena such as DNA repair, chromatin regulation, and cell death, little is known about the relationship between osteoblast differentiation and the PARylation cycle involving PARP1 and the poly (ADP-ribose)-degrading enzyme poly (ADP-ribose) glycohydrolase (PARG). Here, we examined the effects of PARP inhibitor olaparib, an approved anti-cancer agent, and PARG inhibitor PDD00017273 on osteoblast differentiation. Olaparib decreased alkaline phosphatase (ALP) activity and suppressed mineralized nodule formation evaluated by Alizarin Red S staining in preosteoblastic MC3T3-E1 cells, while PDD00017273 promoted ALP activity and mineralization. Furthermore, PDD00017273 up-regulated the mRNA expression levels of osteocalcin and bone sialoprotein, as osteoblast differentiation markers, and osterix as transcription inducers for osteoblast differentiation, whereas olaparib down-regulated the expression of these genes. These findings suggest that PARG inhibition by PDD00017273 accelerates osteoblast differentiation in MC3T3-E1 cells. Thus, PARG inhibitor administration could provide therapeutic benefits for metabolic bone diseases such as osteoporosis.

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.

Dysfunction of Poly (ADP-Ribose) Glycohydrolase Induces a Synthetic Lethal Effect in Dual Specificity Phosphatase 22-Deficient Lung Cancer Cells

Poly (ADP-ribose) glycohydrolase (PARG) is the main enzyme responsible for catabolism of poly (ADP-ribose) (PAR), synthesized by PARP. PARG dysfunction sensitizes certain cancer cells to alkylating agents and cisplatin by perturbing the DNA damage response. The gene mutations that sensitize cancer cells to PARG dysfunction-induced death remain to be identified. Here, we performed a comprehensive analysis of synthetic lethal genes using inducible PARG knockdown cells and identified dual specificity phosphatase 22 (DUSP22) as a novel synthetic lethal gene related to PARG dysfunction. DUSP22 is considered a tumor suppressor and its mutation has been frequently reported in lung, colon, and other tumors. In the absence of DNA damage, dual depletion of PARG and DUSP22 in HeLa and lung cancer A549 cells reduced survival compared with single-knockdown counterparts. Dual depletion of PARG and DUSP22 increased the apoptotic sub-G₁ fraction and upregulated PUMA in lung cancer A549, PC14, and SBC5 cells, and inhibited the PI3K/AKT/mTOR pathway in A549 cells, suggesting that dual depletion of PARG and DUSP22 induced apoptosis by upregulating PUMA and suppressing the PI3K/AKT/mTOR pathway. Consistently, the growth of tumors derived from double knockdown A549 cells was slower compared with those derived from control siRNA-transfected cells. Taken together, these results indicate that DUSP22 deficiency exerts a synthetic lethal effect when combined with PARG dysfunction, suggesting that DUSP22 dysfunction could be a useful biomarker for cancer therapy using PARG inhibitors. SIGNIFICANCE: This study identified DUSP22 as a novel synthetic lethal gene under the condition of PARG dysfunction and elucidated the mechanism of synthetic lethality in lung cancer cells.

Single-particle analysis of full-length human poly(ADP-ribose) polymerase 1

PolyADP-ribosylation (PARylation) is a posttranslational modification that is involved in the various cellular functions including DNA repair, genomic stability, and transcriptional regulation. PARylation is catalyzed by the poly(ADP-ribose) polymerase (PARP) family proteins, which mainly recognize damaged DNA and initiate repair processes. PARP inhibitors are expected to be novel anticancer drugs for breast and ovarian cancers having mutation in BRCA tumor suppressor genes. However the structure of intact (full-length) PARP is not yet known. We have produced and purified the full-length human PARP1 (h-PARP1), which is the major family member of PARPs, and analyzed it with single particle electron microscopy. The electron microscopic images and the reconstructed 3D density map revealed a dimeric configuration of the h-PARP1, in which two ring-shaped subunits are associated with two-fold symmetry. Although the PARP1 is hypothesized to form a dimer on damaged DNA, the quaternary structure of this protein is still controversial. The present result would provide the first structural evidence of the dimeric structure of PARP1.

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".

Rapid degradation of poly(ADP-ribose) after injection into the mouse bloodstream

Extensive DNA damage leads to the activation of poly(ADP-ribose) polymerase and subsequently to the formation of poly(ADP-ribose). When the damage is severe or leads to cell death, poly(ADP-ribose) may leak into the blood circulation. The metabolism of poly(ADP-ribose) in the bloodstream is not well understood. Thus, in the present study, the metabolism of P-labeled poly(ADP-ribose) was followed in mice after injection of this labeled compound into the tail vein. The results showed that 5 min after injection more than half of the radioactivity was concentrated in acid-soluble fractions, namely in low molecular weight compounds in the blood, liver, and kidneys. Most of this radioactivity was in the form of inorganic phosphate, detected 5 min post-injection in the blood, kidneys, and urine. By contrast, the metabolites ADP-ribose and phosphoribosyl-AMP were not detected in any of the tissues nor in blood or urine. Taken together, these findings suggest that once poly(ADP-ribose) enters the bloodstream it is rapidly degraded, thereby preventing its accumulation in the blood.

PARG dysfunction enhances DNA double strand break formation in S-phase after alkylation DNA damage and augments different cell death pathways

Poly(ADP-ribose) glycohydrolase (PARG) is the primary enzyme responsible for the degradation of poly(ADP-ribose). PARG dysfunction sensitizes cells to alkylating agents and induces cell death; however, the details of this effect have not been fully elucidated. Here, we investigated the mechanism by which PARG deficiency leads to cell death in different cell types using methylmethanesulfonate (MMS), an alkylating agent, and Parg^−/− mouse ES cells and human cancer cell lines. Parg^−/− mouse ES cells showed increased levels of γ-H2AX, a marker of DNA double strand breaks (DSBs), accumulation of poly(ADP-ribose), p53 network activation, and S-phase arrest. Early apoptosis was enhanced in Parg^−/− mouse ES cells. Parg^−/− ES cells predominantly underwent caspase-dependent apoptosis. PARG was then knocked down in a p53-defective cell line, MIAPaCa2 cells, a human pancreatic cancer cell line. MIAPaCa2 cells were sensitized to MMS by PARG knockdown. Enhanced necrotic cell death was induced in MIAPaCa2 cells after augmenting γ-H2AX levels and S-phase arrest. Taken together, these data suggest that DSB repair defect causing S-phase arrest, but p53 status was not important for sensitization to alkylation DNA damage by PARG dysfunction, whereas the cell death pathway is dependent on the cell type. This study demonstrates that functional inhibition of PARG may be useful for sensitizing at least particular cancer cells to alkylating agents.

The pioneering spirit of Takashi Sugimura: his studies of the biochemistry of poly(ADP-ribosylation) and of cancer

Takashi Sugimura has accomplished many scientific achievements in the field of biochemistry and in cancer research. Sugimura's group identified the novel polymer poly(ADP-ribose) in parallel to P. Mandel's and O. Hayaishi's groups and demonstrated the presence of the enzyme poly(ADP-ribose) polymerase (PARP). He also discovered the cognate catabolic enzyme, poly(ADP-ribose) glycohydrolase (PARG) and further elucidated the biology of poly(ADP-ribose). The astonishing discovery of pierisin, an apoptogenic peptide that ADP-ribosyaltes DNA, profoundly illuminates his scientific character and curiosity as well. Sugimura's work in cancer research shows an extraordinarily wide range, which includes the establishment of new methods in chemical carcinogenesis, the identification of various environmental mutagens/carcinogens and new tumour promoters. He also established the concept that cancer is a disease of DNA and contributed to the development of the concept of the multi-step model of carcinogenesis.

PolyADP-ribosylation and cancer

The polyADP-ribosylation reaction results in a unique post-translational modification involved in various cellular processes and conditions, including DNA repair, transcriptional control, genomic stability, cell death and transformation. The existence of 17 members of the poly(ADP-ribose) polymerase (PARP) family has so far been documented, with overlapping functional consequences. PARP-1 is known to be involved in DNA base excision repair and this explains the susceptibility spectrum of PARP-1 knockout animals to genotoxic carcinogens. The fact that centrosome amplification is induced by a non-genotoxic inhibitor of PARP and in PARP-1 knockout mouse cells, is in line with aneuploidy, which is frequent in cancers. Genetically engineered animal models have revealed that PARP-1 and VPARP impact carcinogenesis. Furthermore, accumulating experimental evidence supports the utility of PARP and PARG inhibitors in cancer therapy and several clinical trials are now ongoing. Increasing NAD(+) levels by pharmacological supplementation with niacin has also been found to exert preventive effects against cancer. In the present review, recent research progress on polyADP-ribosylation related to neoplasia is summarized and discussed.

The involvement of ATP produced via (ADP-Ribose)n in the maintenance of DNA replication apparatus during DNA repair

The formation of ATP produced from poly(ADP-ribose) [(ADP-R)n] has been suggested to be required to repair damaged DNA. Here we investigate whether this ATP is involved in DNA replication processes during DNA repair. Poly(ADP-ribosyl)ated mid-S phase cell nuclei, which were isolated from synchronized HeLa S3 cells followed by the treatment with a DNA damaging agent, N-methyl-N'-nitro-N-nitrosoguanidine (MNNG), were revealed to retain DNA replication synthesizing activity during preincubation for de-poly(ADP-ribosyl)ation only in the presence of pyrophosphate (PPi) before DNA synthesis was started by adding 3 mM ATP. This DNA replication activity was not maintained in the presence of a potent and specific inhibitor of poly(ADP-ribose) glycohydrolase (PARG), Oenothein B (Oen B) during the preincubation with PPi. In the preincubation with PPi, muM orders of ATP was produced from (ADP-R)n. These results point to an important function of ATP generated from (ADP-R)n in nuclei for the maintenance of replication apparatus during DNA repair.

Poly(etheno ADP-ribose) blocks poly(ADP-ribose) glycohydrolase activity

Poly(ADP-ribose) is a biopolymer synthesized by poly(ADP-ribose) polymerases. Recent findings suggest the possibility for modulation of cellular functions including cell death and mitosis by poly(ADP-ribose). Derivatization of poly(ADP-ribose) may be useful for investigating the effects of poly(ADP-ribose) on various cellular processes. We prepared poly(etheno ADP-ribose) (poly(epsilonADP-ribose)) by converting the adenine moiety of poly(ADP-ribose) to 1-N(6)-etheno adenine residues. Poly(epsilonADP-ribose) is shown to be highly resistant to digestion by poly(ADP-ribose) glycohydrolase (Parg). On the other hand, poly(epsilonADP-ribose) could be readily digested by phosphodiesterase. Furthermore, poly(epsilonADP-ribose) inhibited Parg activity to hydrolyse ribose-ribose bonds of poly(ADP-ribose). This study suggests the possibility that poly(epsilonADP-ribose) might be a useful tool for studying the poly(ADP-ribose) dynamics and function of Parg. This study also implies that modification of the adenine moiety of poly(ADP-ribose) abrogates the susceptibility to digestion by Parg.

Loss of Parp-1 affects gene expression profile in a genome-wide manner in ES cells and liver cells

BACKGROUND

Many lines of evidence suggest that poly(ADP-ribose) polymerase-1 (Parp-1) is involved in transcriptional regulation of various genes as a coactivator or a corepressor by modulating chromatin structure. However, the impact of Parp-1-deficiency on the regulation of genome-wide gene expression has not been fully studied yet.

RESULTS

We employed a microarray analysis covering 12,488 genes and ESTs using mouse Parp-1-deficient (Parp-1-/-) embryonic stem (ES) cell lines and the livers of Parp-1-/- mice and their wild-type (Parp-1+/+) counterparts. Here, we demonstrate that of the 9,907 genes analyzed, in Parp-1-/- ES cells, 9.6% showed altered gene expression. Of these, 6.3% and 3.3% of the genes were down- or up-regulated by 2-fold or greater, respectively, compared with Parp-1+/+ ES cells (p < 0.05). In the livers of Parp-1-/- mice, of the 12,353 genes that were analyzed, 2.0% or 1.3% were down- and up-regulated, respectively (p < 0.05). Notably, the number of down-regulated genes was higher in both ES cells and livers, than that of the up-regulated genes. The genes that showed altered expression in ES cells or in the livers are ascribed to various cellular processes, including metabolism, signal transduction, cell cycle control and transcription. We also observed expression of the genes involved in the pathway of extraembryonic tissue development is augmented in Parp-1-/- ES cells, including H19. After withdrawal of leukemia inhibitory factor, expression of H19 as well as other trophoblast marker genes were further up-regulated in Parp-1-/- ES cells compared to Parp-1+/+ ES cells.

CONCLUSION

These results suggest that Parp-1 is required to maintain transcriptional regulation of a wide variety of genes on a genome-wide scale. The gene expression profiles in Parp-1-deficient cells may be useful to delineate the functional role of Parp-1 in epigenetic regulation of the genomes involved in various biological phenomena.

Purification and molecular cloning of a DNA ADP-ribosylating protein, CARP-1, from the edible clam Meretrix lamarckii

The cabbage butterflies Pieris rapae and Pieris brassicae have unique enzymes, named pierisin-1 and -2, respectively, that catalyze the ADP-ribosylation of guanine residues of DNA, which has been linked with induction of apoptosis and mutation in mammalian cell lines. In the present study, we identified ADP-ribosylation activity targeting DNA in six kinds of edible clam. Similar to our observations with pierisin-1 and -2, crude extracts from the clams Meretrix lamarckii, Ruditapes philippinarum, and Corbicula japonica incubated with calf thymus DNA and beta-NAD resulted in production of N(2)-(ADP-ribos-1-yl)-2'-deoxyguanosine. The DNA ADP-ribosylating protein in the hard clam M. lamarckii, designated as CARP-1, was purified by column chromatography, and its cDNA was cloned. The cDNA encodes a 182-aa protein with a calculated molecular mass of 20,332. The protein synthesized in vitro from the cDNA in a reticulocyte lysate exhibited the same ADP-ribosylating activity as that of purified CARP-1. Neither the nucleotide nor the deduced amino acid sequence of CARP-1 showed homology with pierisin-1 or -2. However, a glutamic acid residue (E128) at the putative NAD-binding site, conserved in all ADP-ribosyltransferases, was found in CARP-1, and replacement of aspartic acid for this glutamic acid resulted in loss of almost all ADP-ribosylating activity. CARP-1 in the culture medium showed no cytotoxicity against HeLa and TMK-1 cells; however, introduction of this protein by electroporation induced apoptosis in these cells. The finding of clam ADP-ribosylating protein targeting guanine residues in DNA could offer new insights into the biological significance of ADP-ribosylation of DNA.

Involvement of quinolinate phosphoribosyl transferase in promotion of potato growth by a Burkholderia strain

Burkholderia sp. strain PsJN stimulates root growth of potato explants compared to uninoculated controls under gnotobiotic conditions. In order to determine the mechanism by which this growth stimulation occurs, we used Tn5 mutagenesis to produce a mutant, H41, which exhibited no growth-promoting activity but was able to colonize potato plants as well as the wild-type strain. The gene associated with the loss of growth promotion in H41 was shown to exhibit 65% identity at the amino acid level to the nadC gene encoding quinolinate phosphoribosyltransferase (QAPRTase) in Ralstonia solanacearum. Complementation of H41 with QAPRTase restored growth promotion of potato explants by this mutant. Expression of the gene identified in Escherichia coli yielded a protein with QAPRTase activities that catalyzed the de novo formation of nicotinic acid mononucleotide (NaMN). Two other genes involved in the same enzymatic pathway, nadA and nadB, were physically linked to nadC. The nadA gene was cotranscribed with nadC as an operon in wild-type strain PsJN, while the nadB gene was located downstream of the nadA-nadC operon. Growth promotion by H41 was fully restored by addition of NaMN to the tissue culture medium. These data suggested that QAPRTase may play a role in the signal pathway for promotion of plant growth by PsJN.

Detection and quantification of poly-ADP-ribosylated cellular proteins of spleen and liver tissues of mice in vivo by slot and Western blot immunoprobing using polyclonal antibody against mouse ADP-ribose polymer

Poly-ADP-ribosylation (PAR) of cellular proteins has been shown to have decisive roles in diverse cellular functions including carcinogenesis. There are indications that metabolic level of poly-ADP-ribosylated cellular proteins might indicate carcinogenesis and, therefore, could be potentially used in cancer screening program. Keeping in mind the limitations of currently available assays of cellular PAR, a new assay is being reported that measures the metabolic level of poly-ADP-ribosylated cellular proteins. The ELISA based slot and Western blot immunoassay used polyclonal antibody against natural, heterogeneous ADP-ribose polymers. It could be successfully employed to qualitatively and quantitatively assay metabolic levels of poly-ADP-ribosylated proteins of spleen and liver tissues of normal mice or mice exposed to dimethylnitrosamine for up to 8 weeks; potentially PAR of cellular proteins could be assayed in any tissue or biopsy. Implications of the results in cancer screening program have been discussed.

Parp-1 deficiency does not increase the frequency of tumors in the oral cavity and esophagus of ICR/129Sv mice by 4-nitroquinoline 1-oxide, a carcinogen producing bulky adducts

The impact of poly(ADP-ribose) polymerase-1 (Parp-1)-deficiency on 4-nitroquinoline 1-oxide (4NQO)-induced carcinogenesis was studied in mice with an ICR/129Sv mixed genetic background. Parp-1(+/+), Parp-1(+/-) and Parp-1(-/-) animals given 4NQO for thirty-two weeks at 0.001% in their drinking water developed papillomas and squamous cell carcinomas of the tongue, palate and esophagus, but with no statistically significant variation with the Parp-1 genotype. Thus Parp-1 deficiency does not elevate susceptibility to carcinogenesis induced by a carcinogen which gives rise to bulky DNA lesions. This study also indicated that the ICR/129Sv mixed genetic background is associated with high yield induction of esophageal tumors by 4NQO.

Changes in the activities and gene expressions of poly(ADP-ribose) glycohydrolases during the differentiation of human promyelocytic leukemia cell line HL-60

The metabolism of poly(ADP-ribose) is known to play important roles in the nuclear function of the mammalian cells. In this study, changes in the activities and gene expressions of poly(ADP-ribose) glycohydrolases (PARG) in HL-60 cells treated with 12-O-tetradecanoyl-phorbol-13-acetate (TPA) or a PARG inhibitor, tannic acid, were investigated. Nuclear PARG activities of HL-60 cells treated with TPA were reduced to 30-40% of the activity in untreated cells at 24 h, while PARG activities in the cytoplasm remained unchanged. The transient decrease in the nuclear PARG activity by TPA treatment was accompanied by differentiation as measured by the nitroblue tetrazolium (NBT) reducing activity and adhesion to the culture dishes. In the presence of H7, an inhibitor of protein kinase C (PKC), both the decrease in nuclear PARG activity and the induction of differentiation by TPA treatment were suppressed. On the other hand, treatment with tannic acid caused the nuclear PARG activity to decrease continuously while the NBT reducing activity increased, but no morphological differentiation to macrophage-like cells was apparent. In order to analyze PARG gene expression, we isolated the human PARG cDNA by the RT-PCR technique. RT-PCR analysis revealed that TPA treatment leads to a reduction in the PARG gene expression prior to the phenotypic expression of macrophage-like cell differentiation, which was diminished by the presence of H7. Also, PARG gene expression was reduced by tannic acid treatment. These results provide the first evidence that a transient decrease in nuclear PARG activity is important for the onset of differentiation of HL-60 cells to macrophage-like cells.

Poly(ADP-ribose) and carcinogenesis

Poly(ADP-ribose) and poly(ADP-ribose) polymerase (PARP) were discovered about 40 years ago, but their significance was not well elucidated until recently. In the early stage of the history of PARP, the presence of antibodies in the sera of human patients with lupus erythematosus indicated its natural occurrence. PARP, as well as the degrading enzyme, poly(ADP-ribose) glycohydrolase (PARG), are present in most eukaryotes except for yeasts. Studies that used inhibitors of PARP indicated the involvement of PARP and poly(ADP-ribose) in DNA damage repair, and eventually PARP was purified and the gene was cloned. Molecular analysis then revealed various functional domains, such as the one for binding to strand breaks of DNA. Parp-1-deficient and Parg-deficient cells showed, in general, enhanced sensitivity to the lethal effects of ionizing radiation and alkylating agents. Parp-1 knockout mouse embryonic stem cells developed into teratocarcinoma-like tumors when injected subcutaneously into nude mice, these tumors featuring giant cells similar to syncytiotrophoblastic giant cells with hyperploidy. Parp-1 was also found in centrosomes, suggesting that poly(ADP-ribose) and PARP-1 are functionally involved in the maintenance of chromatin structure and the equal distribution of chromosomes into daughter cells. Intriguing findings on the real biological significance continue to be generated, with new light shed on mechanisms of carcinogenesis and pointing to novel cancer treatments. Highlights during the last four decades of studies by laboratories focusing on poly(ADP-ribose)/PARP, including our own, are condensed and summarized in this review.

Role of (ADP-ribose)n catabolism in DNA repair

Poly(ADP-ribose) is a reversible covalent-modifier of chromosomal proteins in eukaryotic cells. The function of poly(ADP-ribose) is not clear, although it has been suggested to be involved in the regulation of DNA transactions such as replication, repair, and transcription. Here we describe a specific competitive inhibitor of poly(ADP-ribose) glycohydrolase, a macrocircular ellagitannin oenothein B, and a nuclear system prepared from synchronized HeLa S3 cells at mid-G1 phase that enable us to examine the role of poly(ADP-ribose) catabolism in DNA repair. The results suggest that poly(ADP-ribose) is capable of generating ATP by the concerted action of poly(ADP-ribose) glycohydrolase and ADP-ribose pyrophosphorylase and that this ATP enables repair DNA synthesis.

Identification of an endonuclease responsible for apoptosis in rat thymocytes

Analyses of cleavage ends of DNA fragments in apoptotic rat thymocytes induced by gamma-ray irradiation or by treatment with dexamethasone revealed that in both cases the fragments produced had 3'-hydroxyl (OH) and 5'-phosphoryl (P) ends of DNA chains. Rat thymocyte nuclei contained at least three endonuclease activities (deoxyribonucleases alpha, beta and gamma) that were able to cleave chromatin to mononucleosomal and oligonucleosomal fragments. The nuclei of apoptotic rat thymocytes induced by gamma-ray irradiation or dexamethasone retained considerable deoxyribonuclease gamma activity, but not alpha or beta deoxyribonuclease activity. During the induction of apoptosis, treatment with cycloheximide, which suppressed apoptosis, resulted in marked decreases of deoxyribonucleases alpha and beta activities. After release of cycloheximide inhibition, DNA fragmentation associated with apoptosis occurred in the cycloheximide-treated thymocyte nuclei, in which deoxyribonuclease gamma activity was only observed. The purified deoxyribonucleases alpha and beta were divalent cation-independent acidic endonucleases, which were separated on a CM5PW column by HPLC. The molecular masses of deoxyribonucleases alpha and beta were 28 kDa and 30 kDa, respectively, as determined by TSK G-2000SW gel-filtration HPLC, and both were 32 kDa in molecular mass as determined by SDS/PAGE. In contrast, deoxyribonuclease gamma, a neutral endonuclease, required both Ca2+ and Mg2+ for full activity and was inhibited by Zn2+. The molecular mass of deoxyribonuclease gamma was 31 kDa and 33 kDa when measured by gel filtration and SDS/PAGE, respectively. Under these optimal conditions, deoxyribonuclease gamma was shown to produce 3'-OH/5'-P ends of nucleosomal DNA fragments, while deoxyribonucleases alpha and beta both formed DNA fragments with 3'-P/5'-OH ends. The ends formed by cleavage with deoxyribonuclease gamma were the same as those produced in apoptotic rat thymocytes. On the basis of these results, it seems likely that deoxyribonuclease gamma is responsible for internucleosomal cleavage of chromatin during thymic apoptosis.

Poly(ADP-ribose): historical perspective

The early historical background of the discovery of poly(ADP-ribose) and the following development of science on poly(ADP-ribose) are reviewed. Fundamental knowledge on the natures of poly(ADP-ribose), poly(ADP-ribose) polymerase and enzymes degrading poly(ADP-ribose) are summarized with brief description on the methodology for their purification and characterization. Future prospect of research on biological significance of poly(ADP-ribose) has also been discussed briefly.

Effects of novobiocin on the induction of gamma-glutamyltranspeptidase positive foci in the liver of rats treated with diethylnitrosamine

Effects of novobiocin on the induction of gamma-glutamyltranspeptidase(GGT)-positive foci, an early lesion occurring during hepatocarcinogenesis, after diethylnitrosamine(DEN) initiation were investigated in Fischer 344 rats. Animals were given DEN at a dose of 20 mg/kg b. w. followed by novobiocin at doses of 50, 100 and 200 mg/kg b. w. The latter two doses, but not 50 mg/kg b. w., significantly inhibited the development of GGT-positive foci, providing evidence of the possible involvement of mono(ADP-ribosyl)ation in the initiation phase of hepatocarcinogenesis in rats.

Cloning and functional expression of poly(ADP-ribose) polymerase cDNA from Sarcophaga peregrina

A cDNA spanning the entire coding region for poly(ADP-ribose) polymerase (PARP) of Sarcophaga peregrina was isolated and the nucleotide sequence was determined. The longest open reading frame encodes a polypeptide of 996 amino acid residues with a molecular mass of 113,033 Da. The similarities to the human PARP in amino acid sequence were relatively low in the DNA-binding and auto-modification domains, but very high in the C-terminal catalytic domain: identity of amino acids is 34% in the N-terminal DNA-binding domain (residues 1-369), 27% in the auto-modification domain (residues 370-507), and 56% in the C-terminal NAD-binding domain (residues 508-996). Two zinc-fingers (C-X2-C-X28-H-X2-C and C-X2-C-X31-H-X2-C)2 and a basic region in the N-terminal DNA-binding domain recognized in other PARP are conserved. Downstream of the basic region, another cysteine-rich motif (C-X2-C-X13-C-X9-C), a putative zinc-finger, was found to be well conserved in the PARP of Sarcophaga, Drosophila and human. A leucine-zipper motif (L-X6-L-X6-L-X6-L) which was found in the auto-modification domain of Drosophila PARP, is disrupted in the Sarcophaga enzyme: the second leucine is replaced by proline, and the third leucine by valine. Full-length cDNA for Sarcophaga PARP was cloned into an expression plasmid and expressed in Escherichia coli. A lysate of E. coli cells containing expressed protein reacted with antibody against Sarcophaga PARP, and PARP activity was detected. Thus, we conclude that isolated cDNA encodes a functional Sarcophaga PARP cDNA.

Cell cycle-related expression of poly(ADP-ribosyl)transferase in proliferating rat thymocytes

The activity profile of poly(ADP-ribosyl)transferase was assayed during a complete cell cycle of rat thymocytes stimulated in the presence of interleukin-2 by concanavalin A or monoclonal antibodies against the T-cell antigen receptor (TCRmAB). Poly ADP-ribosylation was measured in permeabilized cells by the incorporation of [adenine-3H]NAD+ into protein bound poly ADP-ribose. The polymers of ADP-ribose were separated from the monomers using dihydroxyboronyl-Bio-Rex 70 columns. The rate of poly(ADP-ribosyl)ation increases during the G1 phase with a maximum 12 h after stimulation. This increase in activity is due to enhanced de novo synthesis of poly(ADP-ribosyl)transferase which can be abolished by the addition of cycloheximide. The half-life of this enzyme during the induction period was estimated to be 4 h. A second activity peak appears during the S-phase of the cell cycle 48 h after stimulation. The maxima of the poly(ADP-ribosyl)ation rate coincide with elevated immunoreactive enzyme levels at 12 and 48 h of culture assayed by Western blotting. The mRNA levels of pADPRT do not correlate with the first maximum of activity, whereas the second maximum was accompanied by a 5-fold increase of the specific mRNA. These results suggest a translational regulation of pADPRT in the G1 phase of the cell cycle, whereas the second activity peak in the S-phase is due to an increased transcription and translation. The induction of pADPRT activity in the G1 phase of TCRmAB-stimulated cells points to a function of poly(ADP-ribosyl)ation in the proliferation of thymocytes.

Role of poly(ADP-ribose) formation in DNA repair

The abundant nuclear enzyme poly(ADP-ribose) polymerase catalyses the synthesis of poly(ADP-ribose) from nicotinamide adenine dinucleotide (NAD+). This protein has an N-terminal DNA-binding domain containing two zinc-fingers, which is linked to the C-terminal NAD(+)-binding domain by a short region containing several glutamic acid residues that are sites of auto-poly(ADP-ribosyl)ation. The intracellular production of poly(ADP-ribose) is induced by agents that generate strand interruptions in DNA. The branched homopolymer chains may attain a size of 200-300 residues but are rapidly degraded after synthesis. The function of poly(ADP-ribose) synthesis is not clear, although it seems to be required for DNA repair. Here we describe a human cell-free system that enables the role of poly(ADP-ribose) synthesis in DNA repair to be characterized. The results indicate that unmodified polymerase molecules bind tightly to DNA strand breaks; auto-poly(ADP-ribosyl)ation of the protein then effects its release and allows access to lesions for DNA repair enzymes.

Effects of 3-aminobenzamide on the post-initiation phase of N-nitrosobis(2-oxopropyl)amine induced pancreatic carcinogenesis in Syrian hamsters

Effects of 3-aminobenzamide (ABA) on pancreatic carcinogenesis after initiation by N-nitrosobis(2-oxopropyl)amine (BOP) were investigated in Syrian hamsters. Animals were given BOP at a dose of 70 mg/kg body weight by subcutaneous injection and following a 2-week recovery period, were administered basal diet or basal diet containing 0.5, 0.75 and 1.5% ABA for 30 weeks. While the incidences of resultant pancreatic lesions, including hyperplasia, atypical hyperplasia and carcinoma, induced by BOP were not significantly influenced by ABA treatment, the mean numbers of those pancreatic lesions were significantly decreased in a dose-dependent way. The results therefore suggested the possible involvement of poly(ADP-ribosyl)ation in the post-initiation phase of pancreatic carcinogenesis in hamsters.

Effects of 3-aminobenzamide on induction of multiorgan carcinogenesis by N-nitrosobis(2-hydroxypropyl)amine in hamsters

The effects of an inhibitor of poly(ADP-ribose)polymerase, 3-aminobenzamide (ABA), on N-nitrosobis(2-hydroxypropyl)amine (BHP)-induced pancreas, liver, gallbladder and lung carcinogenesis in Syrian golden hamsters were investigated. Animals were given either BHP alone, by subcutaneous injection at a dose of 500 mg/kg body weight, or in combination with an intraperitoneal injection of ABA 30 min after the BHP at a dose of 300 or 600 mg/kg body weight once a week for 5 weeks, and then killed 35 weeks after the commencement of the experiment. ABA exerted inhibitory effects on pancreas and lung carcinogenesis induced by BHP, with mean numbers of lesions (including hyperplasias and carcinomas) being significantly decreased compared with the BHP-alone group values, while no significant effect was observed on liver or gallbladder carcinogenesis. These results suggest that the effects of ABA on carcinogenesis depend on the target organ as well as the chemical carcinogen examined.

Regulation of poly(ADP-ribose) polymerase mRNA levels during compensatory and mitogen-induced growth of rat liver

Poly(ADP-ribose) polymerase mRNA levels were studied in hepatic regeneration following partial hepatectomy, and in hyperplasia induced by the mitogen lead nitrate. A significant increase in the level of poly(ADP-ribose) polymerase mRNA was found 8 h after partial hepatectomy when no detectable increase of DNA synthesis could be observed; the level of poly(ADP-ribose) polymerase transcripts increased up to six-fold within 1-2 days. A similar increase of the level of poly(ADP-ribose) polymerase mRNA was found 24 h after treatment with lead nitrate. A twofold increase in poly(ADP-ribose) polymerase activity was observed 2 days after (a) partial hepatectomy and (b) lead nitrate treatment. From these results an important role of poly(ADP-ribose) polymerase in cell proliferation could be suggested.

Characterization of a putative promoter region of the human poly(ADP-ribose) polymerase gene: structural similarity to that of the DNA polymerase beta gene

The 5'-flanking region of the human poly(ADP-ribose) polymerase gene was isolated and characterized. The nucleotide sequence of a part of the poly(ADP-ribose) polymerase gene completely matched that of the cDNA. The transcriptional initiation sites (cap sites) of this gene, located about 166-bp upstream from the translational initiation site, were identified by S1 mapping analysis. Neither CAAT box nor TATA box was found within 500-bp upstream from the cap sites of poly(ADP-ribose) polymerase gene. The 200-bp immediately upstream of the cap site had a high G+C content (76.5%) and contained double repeats of the sequence CCGCCC, putative Sp1 binding sites, and a palindromic structure. The 5'-flanking region of poly(ADP-ribose) polymerase gene also showed promoter activity in chloramphenicol acetyltransferase assay and structural similarity to that of DNA polymerase beta gene.

Loss of the MYC gene amplified in human HL-60 cells after treatment with inhibitors of poly(ADP-ribose) polymerase or with dimethyl sulfoxide

In HL-60 cells, a human promyelocytic leukemia cell line, the human c-myc gene, designated MYC, is amplified about 16-fold. On differentiation of the HL-60 cells into granulocytes induced by several inhibitors of poly(ADP-ribose) polymerase [NAD+ poly(adenosine diphosphate D-ribose)ADP-D-ribosyltransferase, EC 2.4.2.30] including benzamide, nicotinamide, coumarin, and 4-hydroxyquinazoline or dimethyl sulfoxide, some MYC loss was observed. In contrast, benzoic acid, a noninhibitory analogue of benzamide, did not induce either granulocytic differentiation or loss of MYC. Loss of MYC seems to be associated with granulocytic differentiation because the time course of its loss was similar to that of appearance of nitroblue tetrazolium-positive cells, mature granulocytes, and its loss was not observed on differentiation of HL-60 cells into macrophages induced by phorbol 12-myristate 13-acetate or teleocidin. The loss of MYC is not the reason for the down regulation of MYC expression observed within 1 hr after addition of inducers, since the loss of MYC was not detected by 1-day treatment with inducers.

Expression of human poly(ADP-ribose) polymerase with DNA-dependent enzymatic activity in Escherichia coli

A cDNA for human poly(ADP-ribose) polymerase was inserted into a plasmid, transfected and expressed in E. coli. A lysate of the E. coli cells containing the expression plasmid reacted with antibody against human poly(ADP-ribose) polymerase and synthesized poly(ADP-ribose). The partially purified poly(ADP-ribose) polymerase expressed in E. coli had the same molecular weight and enzymological properties as human placental poly(ADP-ribose) polymerase, including affinity for NAD, turnover number and DNA-dependency for activity. This expression system should be useful for structure-function analysis of poly(ADP-ribose) polymerase.

High induction of poly(ADP-ribose) polymerase activity in bleomycin-resistant HeLa cells

Poly(ADP-ribose) polymerase activity was measured in bleomycin (BLM)-resistant HeLa (HeLa-BLMr) and the parental HeLa cells after BLM treatment. HeLa-BLMr cells, which had been subcultured in growth medium containing 1 micrograms/ml of BLM, showed a 3.75-fold higher enzyme activity than did HeLa cells, but this activity was decreased to the same level as that of HeLa cells after 48 h of BLM-free cultivation. When HeLa and HeLa-BLMr cells after a 48-h cultivation in BLM-free growth medium were treated with BLM, the enzyme activity was induced at a higher level (2.5-3.8 times) in HeLa-BLMr than in HeLa cells and was inhibited markedly in HeLa-BLMr and slightly in HeLa cells by nicotinamide, an inhibitor of this enzyme. The BLM-induced cell killing by nicotinamide was highly potentiated (about 18 times) in HeLa-BLMr as compared to HeLa cells.

Presence of phosphorylated O-ribosyl-adenosine in T-psi-stem of yeast methionine initiator tRNA

We report in this paper on isolation and characterization of two unknown nucleosides G* and [A*] located in the T-psi-stem of yeast methionine initiator tRNA, using the combined means of HPLC protocols, real time UV-absorption spectrum, and post-run mass spectrometry by electron impact or fast atom bombardment. The G* nucleoside in position 65 was identified as unmodified guanosine. The structure of the unknown [A*] in position 64 was characterized as an isomeric form of O-ribosyl-adenosine by comparison of its chromatographic, UV-spectral and mass spectrometric properties with those of authentic O-alpha-ribofuranosyl-(1"----2')-adenosine isolated from biosynthetic poly(adenosine diphosphate ribose). Our studies also brought evidence for the presence of a phosphorylmonoester group located on this new modified nucleoside [A*], when isolated by ion exchange chromatography from enzymic hydrolysis of yeast initiator tRNAMet without phosphatase treatment.

Deletion of transfected oncogenes from NIH 3T3 transformants by inhibitors of poly(ADP-ribose) polymerase

a1-1 cells, a transformant line obtained by transfection of NIH 3T3 cells with human c-Ha-rasT24 (hc-Ha-rasT24), were converted to morphologically normal flat cells following a 2-week culture in the presence of benzamide (BA), an inhibitor of poly(ADP-ribose) polymerase [ADP-ribosyltransferase (polymerizing); EC 2.4.2.30]. Concomitant with these morphological changes was the loss of the exogenous hc-Ha-rasT24 sequence. When cells were cultured without transfer, multiple clusters of flat revertant cells surrounded by transformed cells within single colonies of a1-1 cells were observed. This, together with the slow growth rate of flat cells in the presence of BA, indicated that flat revertants were induced rather than selected by BA. Flat cells isolated from mixed colonies completely lost the exogenous and amplified hc-Ha-rasT24 gene. In contrast, the endogenous mouse c-Ha-ras in flat revertant cells was not lost during culture with BA. Similarly, the endogenous hc-Ha-rasT24 in human bladder carcinoma T24 cells was not affected by BA. By using various chemicals, it was suggested that inhibition of poly(ADP-ribose) polymerase induces an efficient and specific loss of the exogenous transforming genes including Ki-ras, N-ras, c-raf, and ret-II.

Induction of poly(ADP-ribose) polymerase gene expression in lectin-stimulated human T lymphocytes is dependent on protein synthesis

The poly(ADP-ribose) polymerase mRNA level in quiescent T lymphocytes was low, but was significantly higher than that in B lymphocytes or monocytes. When T lymphocytes were stimulated with phytohemagglutinin, a prompt increase in the mRNA level was observed from 4 hours after stimulation. The level of poly(ADP-ribose) polymerase mRNA reached a maximum in the late G1 phase about 1-2 days after lectin stimulation, and then decreased gradually returning to the basal level 10 days after lectin stimulation. Cycloheximide abrogated increase in poly(ADP-ribose) polymerase gene expression suggesting that a newly synthesized protein(s) was involved in poly(ADP-ribose) polymerase gene induction in lectin-stimulated T lymphocytes.

Preventive effect of 3-aminobenzamide on the reduction of NAD levels in rat liver following administration of diethylnitrosamine

Nicotinamide adenine dinucleotide is utilized as the substrate of a chromatin-bound enzyme, poly(ADP-ribose) polymerase. The effects of diethylnitrosamine and/or 3-aminobenzamide, a potent inhibitor of poly(ADP-ribose) polymerase, on the cellular NAD levels in rat liver were investigated. 3-Aminobenzamide (600 mg/kg) administered intraperitoneally was not detectable in the liver within 12 hr after administration; the inhibitor had a calculated half life of 90 min. Diethylnitrosamine reduced the NAD levels in rat liver in a dose-dependent way. The NAD content reached a minimum level at 8 hr, returning to 78% of the control value after 48 hr. The reduction of the NAD levels caused by diethylnitrosamine was completely prevented when 3-aminobenzamide was administered either simultaneously with diethylnitrosamine or 4 hr after diethylnitrosamine treatment. Furthermore, an immunohistochemical study showed that nuclear poly(ADP-ribose) decreased 1 hr after the administration of 3-aminobenzamide. These results suggest that inhibition of poly(ADP-ribosyl)ation is involved in the initiation of liver carcinogenesis by diethylnitrosamine and 3-aminobenzamide.