Role Of PARP-1 Research Articles

“PARG Inhibitors’ Success: A Long Way to Go!”

Poly(ADP-ribosyl)ation is one of the most pertinent post translational modifications involved in regulation of chromatin structure, cell cycle progression, tissue development and differentiation and other vital biological phenomena. The enzymes that catalyze the synthesis and degradation of poly(ADP) ribose polymers are PARP and PARG, respectively. The role of PARP has been implicated in development of various diseases since a long time and hence it has evolved as an important pharmacological target but a plethora of drawbacks associated with PARP inhibitors compelled the shift of focus towards PARG. Recently PARG has evolved as an alternative target to overcome the hurdles being faced in the treatment of various conditions like multiple organ failure, ischemic organ damage, diabetic nephropathy, neurodegenerative diseases and cancer. The review provides a compendium on PARG, its mode of action, inhibitors, and its therapeutic applications and also discusses the reasons due to which PARG inhibitors have not been able to reach the clinical trials. PARG inhibitors, though far from success, definitely appear as alluring topics for further research as PARG emerges out as an eminent pharmacological target in making which can shape the future of medicines to provide better therapy with reduced side effects and more efficiency. Keywords: Cancer, inflammatory diseases, ischemic diseases, PARG, PARG inhibitors, PARP.

Neuroprotective Role of Vitamin B 3 in Experimentally Induced Oxidative Stress

Paraquat is a widely used herbicide. The main mechanism underlying PQ toxicity is oxidative stress. Niacin (nicotinic acid) a precursor for NAD+ It has also been reported to possess oxygen radical scavenging activity. The enzyme PARP-1 is activated by DNA strand breaks, using NAD+ as a substrate. Thus, the present study aimed to assess the magnitude of oxidative DNA damage and the role of PARP and the advantages of modulating its activity by niacin supplementation in experimentally induced oxidative stress by PQ. 50 male albino rats were equally divided into five groups; the first and second groups were the control and PQ treated groups respectively while the 3rd group was nicotinic acid treated group; the 4th and 5th groups were co- and post treated PQ treated rats with nicotinic acid respectively. Serum 8-hydroxy-2'-deoxyguanosine and brain MDA levels in PQ treated group showed a significant increase when compared with control group, while levels of PARP activity and TAC in PQ treated group showed a significant decrease when compared with control group. A significant increase of PARP activity & TAC and a significant decrease in serum 8-hydroxy-2'-deoxyguanosine&MDA after nicotinic acid injection when compared with control group was observed. Post-treatment with nicotinic acid improved the biochemical and histopathological alterations in brain treated with nicotinic acid, while co-treatment with nicotinic acid protected against ROS production.

Role of PARP2 in DNA repair

The genome stability of higher eukaryotes depends largely on the functioning of the DNA repair systems. In turn, the precise regulation of each step of repair processes is necessary for the efficient DNA repair. Although most pathways of DNA repair have already been established, their regulation mechanisms require further investigation. Poly(ADP-ribose) polymerases (PARPs) are widely considered to be potential regulators of DNA repair. The role of the most prominent member of this protein family, i.e., PARP1, in DNA repair has been being intensively studied, while the literature data on participation in the repair processes of PARP2, the closest PARP1 homolog, are poorly summarized, although a great body of information concerning its participation in DNA repair has been accumulated. Using the PARP2-deficient model organisms and cell lines, their increased sensitivity to several DNA damaging agents was elucidated. The accumulation of PARP2 at the DNA damage sites in cells was shown. There are data that demonstrate the proteinprotein interaction of PARP2 with several proteins of the base excision repair/single-strand break repair and nonhomologous end joining. Most of the data on the PARP2 role were obtained in experiments with model organisms and cell lines; thus, it is difficult to elucidate the influence of PARP2 on specific processes in vivo. In this review, we tried to summarize data on the participation of PARP2 in the DNA repair processes, including our recent results.

Involvement of poly(ADP-ribose) polymerase in paraptotic cell death of D. discoideum

Paraptosis is mediated by several proteins, poly(ADP-ribose) polymerase being one of them. D. discoideum lacks caspases thus providing a better system to dissect out the role of PARP in paraptosis. The cell death phenotype in unicellular eukaryote, D. discoideum is similar to the programmed cell death phenotype of multicellular animals. However, the events downstream to the death signal of PCD in D. discoideum are yet to be understood. Our results emphasize that oxidative stress in D. discoideum lacking caspases leads to PARP activation, mitochondrial membrane potential changes, followed by the release of apoptosis inducing factor from mitochondria. AIF causes large scale DNA fragmentation, a hallmark feature of paraptosis. The role of PARP in paraptosis is reiterated via PARP inhibition by benzamide, PARG inhibition by gallotannin and PARP down-regulation, which delays paraptosis. PARP, PARG and AIF interplay is quintessential in paraptosis of D. discoideum. This is the first report to establish the involvement of PARP in the absence of caspase activity in D. discoideum which could be of evolutionary significance and gives a lead to understand the caspase independent paraptotic mechanism in higher organisms.

Modeling pharmacodynamic response to the poly(ADP-Ribose) polymerase inhibitor ABT-888 in human peripheral blood mononuclear cells.

BackgroundPoly(ADP-ribose) polymerase (PARP)facilitates DNA repair and PARP inhibitors may potentiate the effect of DNA-damaging chemotherapeutic agents in patients with cancer. Collection of peripheral blood mononuclear cells (PBMCs)as a surrogate tissue to monitor PARP inhibitor pharmacodynamic effects has several advantages over tumor biopsy collection, including minimally invasive sample collection and the ability to collect multiple samples for longitudinal assessment of drug effect.Methodology/Principal FindingsUsing our previously validated immunoassay for measuring poly(ADP-ribose) (PAR), a product of PARP, in tumor biopsies, we validated a method to quantify PAR levels in PBMCs to monitor the pharmacodynamic effects of the PARP inhibitor ABT-888 in clinical trials. The inter-individual variation in PAR levels was large. No significant difference (P = 0.67) was measured between median baseline PAR levels in 144 healthy volunteers (131.7 pg/1×107 PBMCs [interquartile range, 79.5–241.6]) and 49 patients with cancer (149.2 pg/1×107 PBMCs [interquartile range, 83.2–249.3]). In addition, PAR levels monitored in healthy volunteers over 3 weeks had considerable intra- and inter-individual variation (range, 44–1073 pg PAR/1×107 PBMCs). As a pharmacodynamic model, we quantified changes in PAR levels in human PBMCs treated ex vivo with clinically relevant concentrations of ABT-888. Of 40 healthy volunteer PBMC samples treated with ABT-888, 47.5% had greater than 50% PAR reduction compared to vehicle-treated controls. Considerable inter-sample heterogeneity in PAR levels was measured, and several ABT-888–insensitive samples were identified.Conclusions/SignificanceOur results emphasize the importance of using a validated method to measure PAR levels, and support further investigation into the role of PARP in PBMCs. To this end, the PAR immunoassay has been validated for use with PBMCs and incorporated into clinical trials to assess PBMCs as a potential pharmacodynamic surrogate for tumor biopsies in clinical trials of PARP inhibitors.

The role of PARP in DNA repair and its therapeutic exploitation

Historically, PARP inhibitors (PARPi) were developed to potentiate the cytotoxic effect of certain chemotherapeutic agents and are currently being investigated in combination with chemotherapy in diverse cancer types. These agents are also radiosensitisers and clinical trials of PARPi with concurrent radiation are required. It has long been recognised that defective DNA repair pathways lead to tumour susceptibility. Recent studies indicate that tumour cells with defective homologous recombination (HR) repair pathways, the classic example being BRCA mutations, are exquisitely sensitive to PARPi. Defects in HR are not restricted to BRCA-associated tumours and other cancer types may be enriched for HR defects and hence susceptible to PARP inhibition. The identification of predictive markers for sensitivity to PARP inhibition is a priority area for research.

Poly(ADP-Ribose) Polymerase Inhibition Reverses Nitrergic Neurovascular Dysfunctions in Penile Erectile Tissue from Streptozotocin-Diabetic Mice

Activation of the DNA repair enzyme, poly(adenosine diphosphate [ADP]-ribose) polymerase (PARP), in response to hyperglycemia-driven oxidative/nitrosative stress, may be an important mechanism in the development of vascular and neural complications in diabetes mellitus. However, a role for PARP in diabetic erectile dysfunction (ED) has not been demonstrated. To assess whether treatment with a novel PARP-1 inhibitor, GPI 15427, could improve neurovascular dysfunction in corpus cavernosum (CC) from diabetic mice. Diabetes was induced by streptozotocin in male MF1 mice; duration was 6 weeks. Intervention GPI 15427 treatment (20mg/kg/day intraperitoneal [i.p.]) was given for 2 weeks following 4 weeks of untreated diabetes. CC strips were mounted in aerated organ baths for measurement of pharmacological or electrical stimulation-evoked changes in smooth muscle tension. Contractile responses to noradrenergic stimulation and to pharmacological agents stimulating endothelium-dependent and -independent relaxation, and nerve-mediated relaxations against a background precontraction. Contractions in response to phenylephrine or activation of noradrenergic nerves were not significantly altered by diabetes. In contrast, maximum nitrergic nerve-mediated relaxation of phenylephrine-precontracted CC was approximately 28% reduced by diabetes: GPI 15427 treatment completely corrected this diabetic deficit. Similarly, maximal nitric oxide (NO)-mediated endothelium-dependent and -independent relaxations to acetylcholine and sodium nitroprusside, against phenylephrine precontraction, were attenuated approximately 37% and 23% by diabetes, respectively. These deficits were completely reversed by PARP-1 inhibition. Furthermore, GPI 15427 corrected a modest diabetic deficit in sensitivity to nitroprusside (EC(50) reduced by 0.14 log units); a similar trend was observed for acetylcholine-induced relaxation. GPI 15427 treatment provides marked benefits for NO-dependent neurovascular function in diabetic mouse CC. Therefore, PARP-1 inhibition may be worthy of further investigation for diabetes-associated ED.

Abstract 803: Expression of poly(adenosine diphosphate-ribose) polymerase (PARP) and p53 in epithelial ovarian cancer

Abstract Objectives: PARP, poly(adenosine diphosphate-ribose) polymerase, is a damage sensing protein that is essential to the repair of DNA single-strand breaks. P53 acts as a “genome guardian” molecule that in response to DNA damage mediates cell cycle arrest or induces apoptosis. PARP and p53 function synergistically in repairing DNA damage and suppressing chromosomal rearrangements. The aim of this study was to determine the expression of PARP and p53 in epithelial ovarian cancer (EOC) and correlate with clinico-pathologic characteristics. Methods: PARP and p53 was examined using immuno-histochemistry applied on a tissue microarray of 189 EOC. PARP and p53 expression were examined in relation to clinco-pathologic variables, including age of diagnosis, stage, grade, histologic type, optimal debulking, progression free survival and overall survival. Progression free survival and overall survival were estimated by Kaplan-Meier method, and statistical significance was calculated by the log-rank test. Results: PARP expression was demonstrated in 61% (115/189) of specimens and 99/185 (54%) samples exhibited p53 staining. PARP positive tumors tended to have higher grade (P = 0.03) and complete response to initial treatment (P = 0.009). Patients with positive p53 staining tended to have higher stage of disease (P = 0.004) and there was a trend of patients with positive p53 and weak PARP expression to increase the likelihood of disease progression (OR 2.25 (CI 0.389-13)). The median follow-up was 40 months. However, there were no significant associations between PARP and p53 expression. There was no significant difference in disease free or overall survival for PARP or p53. Conclusion: This study indicates that PARP and p53 are upregulated in EOC with higher grade tumors and more advanced stages, respectively, and may serve as a marker of aggressive disease behavior. Additional studies are warranted to evaluate the role of PARP and p53 expression as a predictor of response to initial treatment, and to identify patients that may benefit from alternative treatments in the adjuvant setting. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 101st Annual Meeting of the American Association for Cancer Research; 2010 Apr 17-21; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2010;70(8 Suppl):Abstract nr 803.

Loss of poly(ADP-ribose) polymerase-2 leads to rapid development of spontaneous T-cell lymphomas in p53-deficient mice

Poly(ADP-ribose) polymerase-2 (Parp-2) belongs to a family of enzymes that catalyse poly(ADP-ribosyl)ation of proteins. Parp-2 deficiency in mice (Parp-2(-/-)) results in reduced thymic cellularity associated with increased apoptosis in thymocytes, defining Parp-2 as an important mediator of T-cell survival during thymopoiesis. To determine whether there is a link between Parp-2 and the p53 DNA-damage-dependent apoptotic response, we have generated Parp-2/p53-double-null mutant mice. We found that p53(-/-) backgrounds completely restored the survival and development of Parp-2(-/-) thymocytes. However, Parp-2-deficient thymocytes accumulated high levels of DNA double-strand breaks (DSB), independently of the p53 status, in line with a function of Parp-2 as a caretaker promoting genomic stability during thymocytes development. Although Parp-2(-/-) mice do not have spontaneous tumours, Parp-2 deficiency accelerated spontaneous tumour development in p53-null mice, mainly T-cell lymphomas. These data suggest a synergistic interaction between Parp-2 and p53 in tumour suppression through the role of Parp-2 in DNA-damage response and genome integrity surveillance, and point to the potential importance of examining human tumours for the status of both genes.

Emergence of truly “Individualized” therapy: The poly (adenosine diphosphate-ribose) polymerase inhibitors

Introduction: The process of DNA surveillance for, and repair of, intrinsic and extrinsic injury is complex, redundant, and necessary for cell viability. An enzyme family involved in this oversight is the poly (adenosine diphosphate [ADP]-ribose) polymerases (PARPs), which primarily function to repair single strand injury [1]. PARP enacts this function through a process known as nucleotide base excision and repair. It was recently discovered that the inhibition of PARP promotes the probability for double strand DNA breaks at replication forks. Under normal conditions, these injuries are managed through successful error-free homologous recombination [2]. However, if this function is further thwarted, DNA damage ensues, leading to catastrophic genetic aberrations and mortality. Such is the case in cells that harbor mutations in BRCA1 or BRCA2. These tumor suppressor genes, known for their association with familial breast, ovarian, and prostate cancer, among others, play an active role in homologous recombination under normal conditions. BRCA1 appears to function predominately in the signaling of DNA double strand breaks, whereas BRCA2 appears mechanistically important to the homologous repair process itself [3]. Nevertheless, when tumors develop in patients who are heterozygous for a mutant allele, the otherwise compensating normal BRCA allele becomes compromised or inactivated, enabling cumulative DNA injury. The apparent signifi cant role of PARP in DNA repair under these circumstances led to the hypothesis that PARP inhibition in cells lacking BRCA-directed homologous recombination would be lethal. Further, because PARP inhibition in cells heterozygous for BRCA is no more toxic than in cells with normal BRCA, the hypothetical therapeutic window would appear to be large [4,5].

Poly(ADP-ribose) Polymerase as a Drug Target for Cardiovascular Disease and Cancer: An Update

Poly(ADP-ribose) polymerase-1 (PARP-1) is a member of the PARP enzyme family consisting of PARP-1 and four additional, recently identified poly(ADP-ribosylating) enzymes. PARP-1 is one of the most abundant nuclear proteins and functions as a DNA nick sensor enzyme. Upon binding to DNA breaks, activated PARP cleaves NAD+ into nicotinamide and ADP-ribose and polymerizes the latter onto nuclear acceptor proteins including histones, transcription factors and PARP itself. On one hand, PARP is viewed as a guardian angel of genomic integrity, and inhibition of PARP has been used to facilitate the death of tumor cells alone, or in combination with antitumor agents. On the other hand, overactivation of PARP in response to oxidant- and free radical-mediated excessive DNA single strand breaks promotes cell dysfunction and necrotic type cell death in a variety of pathophysiological conditions. Pharmacological inhibition of PARP, consequently, exerts cytoprotective effects in a variety of diseases including stroke, myocardial infarction, heart failure and diabetes mellitus. The research into the role of PARP in diabetic cardiovascular injury is now supported by novel tools such as new classes of potent inhibitors of PARP as well as genetically engineered animals lacking the gene for PARP. In addition, potent PARP inhibitors have entered the stage of clinical testing. The current review provides an update on the most recent developments in the area of PARP.

PARP as a drug target for the therapy of diabetic cardiovascular dysfunction

Poly(ADP-ribose) polymerase-1 (PARP-1) is a member of the PARP enzyme family consisting of PARP-1 and a growing family of additional, novel poly(ADP-ribosylating) enzymes. PARP-1 is one of the most abundant nuclear proteins, and it functions as a DNA nick sensor enzyme. Upon binding to DNA breaks, activated PARP cleaves NAD(+) into nicotinamide and ADP-ribose and polymerizes the latter onto nuclear acceptor proteins including histones, transcription factors and PARP itself. Overactivation of PARP in response to oxidant- and free radical-mediated excessive DNA single strand breaks promotes cell dysfunction and necrotic-type cell death in a variety of pathophysiological conditions. Emerging data indicate that high circulating glucose in diabetes mellitus is able to induce free radical and oxidant generation in the cardiovascular system with the concomitant activation of PARP. This process results in acute loss of the ability of the endothelium to release nitric oxide (endothelial dysfunction) and leads to a severe functional impairment of the heart (diabetic cardiomyopathy). Accordingly, pharmacological inhibition of PARP protects against diabetic cardiovascular dysfunction. Surprisingly, PARP inhibition not only prevents the development of diabetic endothelial dysfunction, but also restores normal vascular function in established diabetes. In addition to the direct cytotoxic pathway regulated by DNA injury and PARP activation, PARP also modulates the course of cardiovascular inflammation and injury by regulating the activation of NF-kappaB, and the expression of a number of proinflammatory genes. The research into the role of PARP in diabetic cardiovascular injury is now supported by novel tools, such as new classes of potent inhibitors of PARP, as well as genetically engineered animals lacking the gene for PARP. Inhibitors of PARP may become useful in the experimental therapy of diabetic vascular complications. (c) 2002 Prous Science. All rights reserved.

PARP co-activates B-MYB through enhanced phosphorylation at cyclin/cdk2 sites.

PARP is a multifunctional protein that can affect genome stability, transcription control, telomere length and cell death. Recently we have reported that PARP binds to and enhances B-MYB transactivating potential. B-MYB is a potentially oncogenic transcription factor involved in mammalian cell proliferation, survival and differentiation. B-MYB gene expression is growth regulated and B-MYB protein is phosphorylated during S phase by cyclin A or E/cdk2 kinase, resulting in augmented transactivating potential. Here we show that PARP induces phosphorylation of B-MYB protein at cdk2 phosphorylation sites, since a B-MYB protein with mutated cdk2 phosphorylation sites is refractory to PARP-induced phosphorylation and co-activation in mammalian cells. We propose that PARP functions as a B-MYB co-factor by promoting cyclin/cdk2-dependent B-MYB phosphorylation. These results highlight a novel role for PARP as a factor that integrates cyclin-dependent kinases signaling with gene transcription.

Involvement of poly(ADP-ribose) polymerase in trophoblastic cell differentiation during tumorigenesis

Poly(ADP-ribose) polymerase (Parp) monitors DNA strand breaks and poly(ADP-ribosyl)ates nuclear proteins using NAD as a substrate. The participation of Parp in DNA damage responses has been demonstrated by recent studies using Parp knockout mice. On the other hand, accumulated evidence has shown that Parp is involved in the regulation of gene expression and cell differentiation. In this study, the role of Parp in tumorigenesis and differentiation was studied with Parp −/− embryonic stem (ES) cells. When Parp +/+, Parp +/−, and Parp −/− ES cells were injected subcutaneously into nude mice, teratocarcinoma-like tumors developed from ES cells. However, only tumors derived from Parp −/− ES cells showed trophoblast giant cells (TGCs) containing single or multiple megalo-nuclei. These TGCs are located in a large blood-lake like hemorrhage. This example suggests that Parp is not essential for tumor formation, however, it is involved in trophoblastic cell differentiation and could consequently affect tumor phenotype.

Binding of topo I to PARP I - antibody immunocomplex.

It is frequently quoted in the literature that the cellular role of PARP I is its participation in the recognition of single strand breaks of genomic DNA (l.c.1). Although there is little doubt that PARP I can be made to respond powerfully as an factor in the recognition of DNA damage, it seems unlikely that this auxilliary, or telelogically defined, role of this highly abundant nuclear protein exhausts its physiologic cellular function. We have reported that Topo I is greatly activated by its association with PARP I (J Mol Med 5: 533-540, 2000). Translation of this in vitro model experiments to physiologic conditions was accomplished by the demonstration of the quantitative binding of Topo I to a PARP I - antibody complex, as reported here. This experiment demonstrates for the first time that the colligative action of PARP I can regulate a highly significant cellular process, the control of readability of genomic DNA, i.e., gene expression, without the artificiality of induced DNA damage.

Genomic Organization of Drosophila Poly(ADP-ribose) Polymerase and Distribution of Its mRNA during Development

Poly(ADP-ribosyl)ation of proteins catalyzed by poly(ADP-ribose) polymerase (PARP; EC 2.4.2.30) modulates several biological activities. However, little is known about the role of PARP in developmental process. Here we report the organization of the Drosophila PARP gene and the expression patterns during Drosophila development. The Drosophila PARP gene was a single copy gene mapped at 81F and composed of six exons. Organization of exons corresponds to the functional domains of PARP. The DNA-binding domain was encoded by exons 1, 2, 3, and 4. The auto-modification domain was encoded by exon 5, and the catalytic domain was in exon 6. The promoter region of the PARP gene contained putative TATA box and CCAAT box unlike human PARP. Expression of the PARP gene was at high levels in embryos at 0-6 h after egg laying and gradually decreased until 8 h. PARP mRNA increased again at 8-12 h and was observed in pupae and adult flies but not in larvae. In situ mRNA hybridization of embryos revealed large amount of PARP mRNA observed homogeneously except the pole cells at the early stage of embryos, possibly due to presence of the maternal mRNA for PARP, and decreased gradually until the stage 12 in which stage PARP mRNA localized in anal plates. At late stage of embryogenesis PARP mRNA was localized in cells along the central nervous system.