Parp-1 deficiency implicated in colon and liver tumorigenesis induced by azoxymethane

DNA Alkylation Damage by Nitrosamines and Relevant DNA Repair Pathways

Nitrosamines occur widespread in food, drinking water, cosmetics, as well as tobacco smoke and can arise endogenously. More recently, nitrosamines have been detected as impurities in various drugs. This is of particular concern as nitrosamines are alkylating agents that are genotoxic and carcinogenic. We first summarize the current knowledge on the different sources and chemical nature of alkylating agents with a focus on relevant nitrosamines. Subsequently, we present the major DNA alkylation adducts induced by nitrosamines upon their metabolic activation by CYP450 monooxygenases. We then describe the DNA repair pathways engaged by the various DNA alkylation adducts, which include base excision repair, direct damage reversal by MGMT and ALKBH, as well as nucleotide excision repair. Their roles in the protection against the genotoxic and carcinogenic effects of nitrosamines are highlighted. Finally, we address DNA translesion synthesis as a DNA damage tolerance mechanism relevant to DNA alkylation adducts.

Cytidine deaminase deficiency in mice enhances genetic instability but limits the number of chemically induced colon tumors

Cytidine deaminase (CDA) catalyzes the deamination of cytidine (C) and deoxycytidine (dC) to uridine and deoxyuridine, respectively. We recently showed that CDA deficiency leads to genomic instability, a hallmark of cancers. We therefore investigated whether constitutive CDA inactivation conferred a predisposition to cancer development. We developed a novel mouse model of Cda deficiency by generating Cda-knockout mice. Cda^+/+ and Cda^-/- mice did not differ in lifetime phenotypic or behavioral characteristics, or in the frequency or type of spontaneous cancers. However, the frequency of chemically induced tumors in the colon was significantly lower in Cda^-/- mice. An analysis of primary kidney cells from Cda^-/- mice revealed an excess of C and dC associated with significantly higher frequencies of sister chromatid exchange and ultrafine anaphase bridges and lower Parp-1 activity than in Cda^+/+ cells. Our results suggest that, despite inducing genetic instability, an absence of Cda limits the number of chemically induced tumors. These results raise questions about whether a decrease in basal Parp-1 activity can protect against inflammation-driven tumorigenesis; we discuss our findings in light of published data for the Parp-1-deficient mouse model.

Intervention of 3-aminobenzamide against Dextran Sulphate Sodium induced colitis in mice: Investigations on molecular mechanisms

Various preclinical and clinical studies reported that Poly [ADP-ribose] polymerase 1 plays significant role in all acute and chronic inflammatory diseases with different etiopathogenesis. The present study aims to investigate the protective effect of 3-aminobenzamide in Dextran Sulphate Sodium induced ulcerative colitis and associated molecular mechanisms. Ulcerative colitis in male BALB/c mice was induced using Dextran sulphate sodium (3 %w/v) for 3 cycles with 7 days recovery period in-between. 3-aminobenzamide was administered at the doses of 5, 10 and 20 mg/kg starting from the I^st week of remission period and was continued till the termination of the experiment. The effect of 3-aminbenzamide was evaluated using biochemical parameters, histopathological evaluations, ELISA, immunohistochemistry, immunofluorescence and Western blot analysis. All the doses of 3-aminobenzamide (5 mg/kg; 10 mg/kg and 20 mg/kg) ameliorated the severity of ulcerative colitis by modulating various molecular targets such as poly[ADP-ribose] polymerase 1, nuclear factor kappa-light-chain-enhancer of activated B cells, NLR family pyrin domain containing 3, apoptosis-associated speck-like protein containing a caspase-recruitment domain, cysteine aspartases, interleukin-1β, proliferating cell nuclear antigen, sirtuin 1, adenosine monophosphate-activated protein kinase, tumour necrosis factor-α and catalase. However, the lower doses (5 and 10 mg/kg) exerted more prominent effects in comparison to the high dose (20 mg/kg). Further, 3-aminobenzamide treatment restored the intestinal integrity by increasing the expression of occludin and significantly ameliorated ulcerative colitis associated elevated lipopolysaccharides, oxidative and nitrosative stress, cellular damage and apoptosis. Lower doses of 3-aminobenzamide showed more prominent protective effects against ulcerative colitis associated damage as compared to higher dose.

Genomic Instability and Cancer Risk Associated with Erroneous DNA Repair

Many cancers develop as a consequence of genomic instability, which induces genomic rearrangements and nucleotide mutations. Failure to correct DNA damage in DNA repair defective cells, such as in BRCA1 and BRCA2 mutated backgrounds, is directly associated with increased cancer risk. Genomic rearrangement is generally a consequence of erroneous repair of DNA double-strand breaks (DSBs), though paradoxically, many cancers develop in the absence of DNA repair defects. DNA repair systems are essential for cell survival, and in cancers deficient in one repair pathway, other pathways can become upregulated. In this review, we examine the current literature on genomic alterations in cancer cells and the association between these alterations and DNA repair pathway inactivation and upregulation.

PARP1 Gene Polymorphisms and the Prognosis of Esophageal Cancer Patients from Cixian High-Incidence Region in Northern China

Objective:

Poly (ADP-ribose) polymerase 1 (PARP1), as a key enzyme in the base excision repair pathway, plays a crucial role in tumorigenesis and progression. This study aimed to assess whether polymorphisms of PARP1 gene could be used as predictive biomarkers for the survival of esophageal squamous cell carcinoma (ESCC) patients from Cixian high-incidence region in northern China.

Methods:

In 203 ESCC patients with survival information, PARP1 rs1136410 T/C and rs8679 T/C single nucleotide polymorphisms (SNPs) were genotyped by polymerase chain reaction ligase detection reaction (PCR-LDR) method. All statistical analyses were performed using the SPSS ver. 22.0 software package (SPSS, Chicago, IL, USA).

Results:

The mean age ± standard deviation of the ESCC patients was 60.4 ± 7.9 years. There was no significant relation of sex, age, smoking status and upper gastrointestinal cancer family history with the survival time of the ESCC patients. The mean survival time of rs1136410 T/T, T/C and C/C genotype carriers were 43.3, 42.3 and 46.6 months, respectively. The rs1136410 was not associated with the survival time of the ESCC patients. For rs8679, the mean survival time of T/T genotype carriers was 43.7 months, which was not significantly different from that of the patients with T/C genotype (42.1 months).

Conclusion:

In Cixian high-incidence region from northern China, rs1136410 and rs8679 SNPs might not be used to predict survival of ESCC patients. There is a need to explore whether other SNPs of PARP1 gene have an effect on prognosis of ESCC patients.

The role of ADP-ribose metabolism in metabolic regulation, adipose tissue differentiation, and metabolism

In this review, Szanto et al. summarize the metabolic regulatory roles of PARP enzymes and their associated pathologies.

Poly(ADP-ribose) polymerases (PARPs or ARTDs), originally described as DNA repair factors, have metabolic regulatory roles. PARP1, PARP2, PARP7, PARP10, and PARP14 regulate central and peripheral carbohydrate and lipid metabolism and often channel pathological disruptive metabolic signals. PARP1 and PARP2 are crucial for adipocyte differentiation, including the commitment toward white, brown, or beige adipose tissue lineages, as well as the regulation of lipid accumulation. Through regulating adipocyte function and organismal energy balance, PARPs play a role in obesity and the consequences of obesity. These findings can be translated into humans, as evidenced by studies on identical twins and SNPs affecting PARP activity.

Multifaceted Role of PARP-1 in DNA Repair and Inflammation: Pathological and Therapeutic Implications in Cancer and Non-Cancer Diseases

PARP-1 (poly(ADP-ribose)-polymerase 1), mainly known for its protective role in DNA repair, also regulates inflammatory processes. Notably, defects in DNA repair and chronic inflammation may both predispose to cancer development. On the other hand, inhibition of DNA repair and inflammatory responses can be beneficial in cancer therapy and PARP inhibitors are currently used for their lethal effects on tumor cells. Furthermore, excess of PARP-1 activity has been associated with many tumors and inflammation-related clinical conditions, including asthma, sepsis, arthritis, atherosclerosis, and neurodegenerative diseases, to name a few. Activation and inhibition of PARP represent, therefore, a double-edged sword that can be exploited for therapeutic purposes. In our review, we will discuss recent findings highlighting the composite multifaceted role of PARP-1 in cancer and inflammation-related diseases.

MACROD2 Haploinsufficiency Impairs Catalytic Activity of PARP1 and Promotes Chromosome Instability and Growth of Intestinal Tumors

ADP-ribosylation is an important posttranslational protein modification that regulates diverse biological processes, controlled by dedicated transferases and hydrolases. Here, we show that frequent deletions (∼30%) of the MACROD2 mono-ADP-ribosylhydrolase locus in human colorectal cancer cause impaired PARP1 transferase activity in a gene dosage-dependent manner. MACROD2 haploinsufficiency alters DNA repair and sensitivity to DNA damage and results in chromosome instability. Heterozygous and homozygous depletion of Macrod2 enhances intestinal tumorigenesis in ApcMin/+ mice and the growth of human colorectal cancer xenografts. MACROD2 deletion in sporadic colorectal cancer is associated with the extent of chromosome instability, independent of clinical parameters and other known genetic drivers. We conclude that MACROD2 acts as a haploinsufficient tumor suppressor, with loss of function promoting chromosome instability, thereby driving cancer evolution.Significance: Chromosome instability (CIN) is a hallmark of cancer. We identify MACROD2 deletion as a cause of CIN in human colorectal cancer. MACROD2 loss causes repression of PARP1 activity, impairing DNA repair. MACROD2 haploinsufficiency promotes CIN and intestinal tumor growth. Our results reveal MACROD2 as a major caretaker tumor suppressor gene. Cancer Discov; 8(8); 988-1005. ©2018 AACR.See related commentary by Jin and Burkard, p. 921This article is highlighted in the In This Issue feature, p. 899.

PARP-1 protects against colorectal tumor induction, but promotes inflammation-driven colorectal tumor progression

Colorectal cancer (CRC) is one of the most common tumor entities, which is causally linked to DNA repair defects and inflammatory bowel disease (IBD). Here, we studied the role of the DNA repair protein poly(ADP-ribose) polymerase-1 (PARP-1) in CRC. Tissue microarray analysis revealed PARP-1 overexpression in human CRC, correlating with disease progression. To elucidate its function in CRC, PARP-1 deficient (PARP-1^-/-) and wild-type animals (WT) were subjected to azoxymethane (AOM)/ dextran sodium sulfate (DSS)-induced colorectal carcinogenesis. Miniendoscopy showed significantly more tumors in WT than in PARP-1^-/- mice. Although the lack of PARP-1 moderately increased DNA damage, both genotypes exhibited comparable levels of AOM-induced autophagy and cell death. Interestingly, miniendoscopy revealed a higher AOM/DSS-triggered intestinal inflammation in WT animals, which was associated with increased levels of innate immune cells and proinflammatory cytokines. Tumors in WT animals were more aggressive, showing higher levels of STAT3 activation and cyclin D1 up-regulation. PARP-1^-/- animals were then crossed with O⁶-methylguanine-DNA methyltransferase (MGMT)-deficient animals hypersensitive to AOM. Intriguingly, PARP-1^-/-/MGMT^-/- double knockout (DKO) mice developed more, but much smaller tumors than MGMT^-/- animals. In contrast to MGMT-deficient mice, DKO animals showed strongly reduced AOM-dependent colonic cell death despite similar O⁶-methylguanine levels. Studies with PARP-1^-/- cells provided evidence for increased alkylation-induced DNA strand break formation when MGMT was inhibited, suggesting a role of PARP-1 in the response to O⁶-methylguanine adducts. Our findings reveal PARP-1 as a double-edged sword in colorectal carcinogenesis, which suppresses tumor initiation following DNA alkylation in a MGMT-dependent manner, but promotes inflammation-driven tumor progression.

NAD+ Deficits in Age-Related Diseases and Cancer

The phenomenon of aging has gained widespread attention in recent times. Although significant advances have been made to better understand aging and its related pathologies including cancer, there is not yet a clear mechanism explaining why diseases and cancer are inherent parts of the aging process. Finding a unifying equation that could bridge aging and its related diseases would allow therapeutic development and solve an immense human health problem to live longer and better. In this review, we discuss NAD⁺ reduction as the central mechanism that may connect aging to its related pathologies and cancer. NAD⁺ boosters would ensure and ameliorate health quality during aging.

Opportunities for the repurposing of PARP inhibitors for the therapy of non-oncological diseases

The recent clinical availability of the PARP inhibitor olaparib (Lynparza) opens the door for potential therapeutic repurposing for non-oncological indications. Considering (a) the preclinical efficacy data with PARP inhibitors in non-oncological diseases and (b) the risk-benefit ratio of treating patients with a compound that inhibits an enzyme that has physiological roles in the regulation of DNA repair, we have selected indications, where (a) the severity of the disease is high, (b) the available therapeutic options are limited, and (c) the duration of PARP inhibitor administration could be short, to provide first-line options for therapeutic repurposing. These indications are as follows: acute ischaemic stroke; traumatic brain injury; septic shock; acute pancreatitis; and severe asthma and severe acute lung injury. In addition, chronic, devastating diseases, where alternative therapeutic options cannot halt disease development (e.g. Parkinson's disease, progressive multiple sclerosis or severe fibrotic diseases), should also be considered. We present a preclinical and clinical action plan for the repurposing of PARP inhibitors.

LINKED ARTICLES

This article is part of a themed section on Inventing New Therapies Without Reinventing the Wheel: The Power of Drug Repurposing. To view the other articles in this section visit http://onlinelibrary.wiley.com/doi/10.1111/bph.v175.2/issuetoc.

Oncogenic Signaling Pathways Activated in DMBA-Induced Mouse Mammary Tumors

Only about 5% of human breast cancers can be attributed to inheritance of breast cancer susceptibility genes, while the balance are considered to be sporadic in origin. Breast cancer incidence varies with diet and other environmental influences, including carcinogen exposure. However, the effects of environmental carcinogens on cell growth control pathways are poorly understood. Here we have examined oncogenic signaling pathways that are activated in mammary tumors in mice treated with the prototypical polycyclic aromatic hydrocarbon (PAH) 7,12-dimethylbenz[ a]anthracene (DMBA). In female FVB mice given 6 doses of 1 mg of DMBA by weekly gavage beginning at 5 weeks of age, all of the mice developed tumors by 34 weeks of age (median 20 weeks after beginning DMBA); 75% of the mice had mammary tumors. DMBA-induced mammary tumors exhibited elevated expression of the aryl hydrocarbon receptor (AhR), c- myc, cyclin D1, and hyperphosphorylated retinoblastoma (Rb) protein. Because of this, the activation of upstream regulatory pathways was assessed, and elements of the Wnt signaling pathway, the NF-κB pathway, and the prolyl isomerase Pin-1 were found to be frequently up-regulated in the tumors when compared to normal mammary gland controls. These data suggest that environmental carcinogens can produce long-lasting alterations in growth and anti-apoptotic pathways, leading to mammary tumorigenesis.

Persistent phosphorylation at specific H3 serine residues involved in chemical carcinogen-induced cell transformation

Identification of aberrant histone H3 phosphorylation during chemical carcinogenesis will lead to a better understanding of the substantial roles of histone modifications in cancer development. To explore whether aberrant H3 phosphorylation contributes to chemical carcinogenesis, we examined the dynamic changes of H3 phosphorylation at various residues in chemical carcinogen-induced transformed human cells and human cancers. We found that histone H3 phosphorylation at Ser10 (p-H3S10) and Ser28 (p-H3S28) was upregulated by 1.5-4.8 folds and 2.1-4.3 folds, respectively in aflatoxin B₁ -transformed hepatocytes L02 cells (L02RT-AFB₁ ), benzo(a)pyrene-transformed HBE cells (HBERT-BaP), and coke oven emissions-transformed HBE cells (HBERT-COE). The ectopic expression of histone H3 mutant (H3S10A or H3S28A) in L02 cells led to the suppression of an anchorage-independent cell growth as well as tumor formation in immunodeficient mice. In addition, an enhanced p-H3S10 was found in 70.6% (24/34) of hepatocellular carcinoma (HCC), and 70.0% (21/30) of primary lung cancer, respectively. Notably, we found that expression of H3 carrying a mutant H3S10A or H3S28A conferred to cells the ability to maintain a denser chromatin and resistance to induction of DNA damage and carcinogen-induced cell transformation. Particularly, we showed that introduction of a mutant H3S10A abolished the bindings of p-H3S10 to the promoter of DNA repair genes, PARP1 and MLH1 upon AFB₁ treatment. Furthermore, we revealed that PP2A was responsible for dephosphorylation of p-H3S10. Taken together, these results reveal a key role of persistent H3S10 or H3S28 phosphorylation in chemical carcinogenesis through regulating gene transcription of DNA damage response (DDR) genes.

Trial watch - inhibiting PARP enzymes for anticancer therapy

Poly(ADP-ribose) polymerases (PARPs) are a members of family of enzymes that catalyze poly(ADP-ribosyl)ation (PARylation) and/or mono(ADP-ribosyl)ation (MARylation), two post-translational protein modifications involved in crucial cellular processes including (but not limited to) the DNA damage response (DDR). PARP1, the most abundant family member, is a nuclear protein that is activated upon sensing distinct types of DNA damage and contributes to their resolution by PARylating multiple DDR players. Recent evidence suggests that, along with DDR, activated PARP1 mediates a series of prosurvival and proapoptotic processes aimed at preserving genomic stability. Despite this potential oncosuppressive role, upregulation and/or overactivation of PARP1 or other PARP enzymes has been reported in a variety of human neoplasms. Over the last few decades, several pharmacologic inhibitors of PARP1 and PARP2 have been assessed in preclinical and clinical studies showing potent antineoplastic activity, particularly against homologous recombination (HR)-deficient ovarian and breast cancers. In this Trial Watch, we describe the impact of PARP enzymes and PARylation in cancer, discuss the mechanism of cancer cell killing by PARP1 inactivation, and summarize the results of recent clinical studies aimed at evaluating the safety and therapeutic profile of PARP inhibitors in cancer patients.

PARP-1 rs3219073 polymorphism may contribute to susceptibility to lung cancer

OBJECTIVE

To investigate the relationship between the PARP-1 rs3219073 C>G polymorphism and susceptibility to lung cancer in Chinese people.

METHODS

In accordance with the case-control study principle, 645 of the patients had histologically recognized primary lung cancer, among them 240 had squamous carcinoma, 217 had adenocarcinoma, and 188 had small-cell lung cancer. The control group consisted of 643 healthy subjects who had received a physical examination. Extracts of peripheral blood were taken from all subjects, and genomic DNA was extracted by the phenol-chloroform method.

RESULTS

After adjusting for age and smoking status, the results show significant association between genetic variations in the rs3219073 C/C genotype and an increased risk of lung cancer (p=0.045, odds ratio [OR]=0.625). After combining C/G, G/G is still statistically significant (p=0.042, OR=0.637). Hierarchical analysis found that the number of subjects with a G/G genotype in the adenocarcinoma group is lower than in the control group (p=0.015, OR=0.543). After combining C/G, G/G is still statistically significant (p=0.027, OR=0.595). After correcting for age and smoking status, the group with C/G genotype and the group with G/G genotype both appear to have a reduced risk for lung cancer compared with the control group (p=0.045, OR=0.566; p=0.013, OR=0.489). The combination of C/G and G/G displays a more statistically significant difference (p=0.018, OR=0.528).

CONCLUSIONS

The study found that PARP-1 rs3219073 C>G polymorphism is indeed associated with lung cancer susceptibility. The carriers of G alleles may have reduced risk of lung cancer, especially adenocarcinoma.

Hepatic repercussions of azoxymethane-induced colorectal carcinogenesis

OBJECTIVE

To evaluate the hepatic effects of colonic carcinogenesis induced by azoxymethane at different doses and times of exposure in rats.

METHODS

Forty-four Wistar rats were divided into four groups. The animals were eight weeks at the beginning of the experiment. group 1 received 1.0 ml of saline intraperitoneally once a week for two weeks. Group 2 received 15 mg/kg of azoxymethane intraperitoneally once a week for two weeks. These animals were killed at the 15th week of the experiment. The animals of group 3 received saline intraperitoneally once a week for two weeks. Group 4 animals received 20mg/kg of azoxymethane intraperitoneally once a week for two weeks. These animals were killed at the 26th week of the experiment. The fragments of liver tissue were stained with hematoxylin and eosin and evaluated microscopically.

RESULTS

Groups 1 and 2 differed significantly in relation to steatosis, no difference having been found between group 3 and group 4. However, in group 4 we observed pre-neoplastic lesions (foci of altered, clear, vacuolated, basophilic, amphophilic tigroid, oncocytic, small or acidophilus cells, spongiosis and peliosis) and neoplastic lesions (adenomas and colangiomas) containing atypical hepatocytes in between, not identified in group 3.

CONCLUSION

In the model of colorectal carcinogenesis, preneoplastic and neoplastic hepatic lesions appear and evolve in proportion to the time of exposure and dose of azoxymethane.

Update on hepatocellular carcinoma breakthroughs: poly(ADP-ribose) polymerase inhibitors as a promising therapeutic strategy

Hepatocellular carcinoma is the most common form of primary liver cancer which is the fifth most common cancer in men and the seventh in women and the third most common cause of cancer-related death worldwide. Only 10-20% of patients are eligible for curative treatments that result in a 5-year survival rate of 40% to 70%. Therefore, the development of novel treatment options is necessary for the majority of patients and remains a considerable challenge. Conformal radiotherapy is used in certain circumstances and preliminary data obtained from phase 1/2 trials are showing promising curative effects. There is thus an interest in identifying drugs that can be exploited to enhance radiation sensitivity that could be used in therapy and might improve clinical outcome. Small molecules inhibitors of poly(ADP-ribose) polymerases (PARP) are an example of a radio- and chemo-sensitizing drug, as well as being an efficient single agent treatment in certain genetic backgrounds. In this review, we discuss the role of PARP-1 in hepatocellular carcinoma and present the results of preclinical studies that have assessed the potential of PARP inhibition as a single treatment or combined with chemotherapy or radiotherapy for the treatment of hepatocellular carcinoma.

Involvement of PARP-1 Val762Ala polymorphism in the onset of cervical cancer in caucasian women

BACKGROUND AND OBJECTIVE

Data on the Val762Ala (rs1136410) polymorphism in the poly(adenosine diphosphate [ADP]-ribose) polymerase 1 (PARP-1) gene as a risk factor for various types of cancers in different ethnicities are inconsistent. We studied this association in a Caucasian population.

METHODS

Using high-resolution melting curve analysis (HRM), we studied the distribution of the PARP-1 Val762Ala polymorphism in patients with cervical cancer (n = 446) and in controls (n = 491).

RESULTS

Logistic regression analysis adjusting for age, pregnancy, oral contraceptive use, tobacco smoking, and menopausal status demonstrated that the PARP-1 Val762Ala polymorphism was associated with an increased risk of cervical cancer. The adjusted odds ratio (OR) for patients with the Ala/Val genotype versus the Val/Val genotype was 1.381 (95 % CI = 1.025-1.859, p = 0.033), and the adjusted OR for the Ala/Ala or Ala/Val genotype versus the Val/Val genotype was 1.403 (95 % CI = 1.057-1.863, p = 0.019). The p value from the chi-square test of the trend observed for the PARP-1 Val762Ala polymorphism was statistically significant (p trend = 0.0123). Stratified analyses of the PARP-1 Val762Ala genotype distribution and cervical cancer risk showed that the age-adjusted OR of Ala/Ala or Ala/Val vs Val/Val for pregnancy was 1.388 (95 % CI = 1.027-1.877, p = 0.0328), 1.773 (95 % CI = 1.145-2.745, p = 0.0100) for contraceptive use, and 1.604 (95 % CI = 1.132-2.272, p = 0.0077) for postmenopausal women. The age-adjusted OR of Ala/Val vs Val/Val for contraceptive use was 1.769 (95 % CI = 1.114-2.809, p = 0.0154) and for postmenopausal women was 1.577 (95 % CI = 1.094-2.272, p = 0.0143).

CONCLUSION

Our studies suggest that the PARP-1 Val762Ala polymorphism may be a genetic risk factor for cervical cancer.

Two DNA repair gene polymorphisms on the risk of gastrointestinal cancers: a meta-analysis

PARP-1 and MGMT play an important role in the DNA repair system and therefore have been implicated in human carcinogenesis. However, the association between the most studied PARP-1 rs1136410: T > C and MGMT rs12917: C > T polymorphism and risk of gastrointestinal (GI) cancers was reported with inconclusive results. Accordingly, a meta-analysis of 23 published case-control studies was conducted to assess the strength of association using crude odds ratios (ORs) with 95% confidence intervals (CIs). Overall, the C allele of PARP-1 rs1136410: T > C polymorphism was significantly associated with increased susceptibility of GI cancers (homozygote comparison: OR = 1.43, 95% CI 1.14-1.81; heterozygote comparison: OR = 1.18, 95% CI 1.07-1.29; dominant model: OR = 1.23, 95% CI 1.12-1.35; recessive model: OR = 1.30, 95% CI 1.04-1.62; allelic comparison: OR = 1.19, 95% CI 1.07-1.32). In the subgroup analysis, still obvious associations were found in the Asian population, gastric cancer, and high-quality studies. For MGMT rs12917: C > T polymorphism, no obvious associations were found for all genetic models overall. However, in the subgroup analysis, we found that the T allele was significantly associated with reduced colorectal cancer risk for heterozygote (OR = 0.83, 95% CI 0.70-0.97) and dominant model (OR = 0.84, 95% CI 0.72-0.98). In conclusion, this meta-analysis suggests that the PARP-1 rs1136410: T > C polymorphism is a susceptibility factor for GI cancers, but the variant allele of MGMT rs12917: C > T polymorphism appears to be a protective factor for colorectal cancer. Large-scale and well-designed case-control studies are necessary to validate the risk identified in the present meta-analysis.

Poly(ADP-ribosyl)ation in carcinogenesis

Cancer develops through diverse genetic, epigenetic and other changes, so-called 'multi-step carcinogenesis', and each cancer harbors different alterations and properties. Here in this article we review how poly(ADP-ribosyl)ation is involved in multi-step and diverse pathways of carcinogenesis. Involvement of poly- and mono-ADP-ribosylation in carcinogenesis has been studied at molecular and cellular levels, and further by animal models and human genetic approaches. PolyADP-ribosylation acts in DNA damage repair response and maintenance mechanisms of genomic stability. Several DNA repair pathways, including base-excision repair and double strand break repair pathways, involve PARP and PARG functions. These care-taker functions of poly(ADP-ribosyl)ation suggest that polyADP-ribosyation may mainly act in a tumor suppressive manner because genomic instability caused by defective DNA repair response could serve as a driving force for tumor progression, leading to invasion, metastasis and relapse of cancer. On the other hand, the new concept of 'synthetic lethality by PARP inhibition' suggests the significance of PARP activities for survival of cancer cells that harbor defects in DNA repair. Accumulating evidence has revealed that some PARP family molecules are involved in various signaling cascades other than DNA repair, including epigenetic and transcriptional regulations, inflammation/immune response and epithelial-mesenchymal transition, suggesting that poly(ADP-ribosyl)ation both promotes and suppresses carcinogenic processes depending on the conditions. Expanding understanding of poly(ADP-ribosyl)ation suggests that strategies to achieve cancer prevention targeting poly(ADP-ribosyl)ation for genome protection against life-long exposure to environmental carcinogens and endogenous carcinogenic stimuli.

Loss of PIDD limits NF-κB activation and cytokine production but not cell survival or transformation after DNA damage

Activation of NF-κB (nuclear factor of kappa light chain gene enhancer in B cells) in response to DNA damage is considered to contribute to repair of genetic lesions, increased cell survival and cytokine release. The molecular mechanisms orchestrating this cytoplasmic event involve core components of the nuclear DNA damage response machinery, including ATM-kinase (ataxia telangiectasia mutated kinase) and PARP-1 (poly (ADP-ribose) polymerase 1). The physiological consequences of defective NF-κB activation in this context, however, remain poorly investigated. Here we report on the role of the 'p53-induced protein with a death domain', PIDD, which appears rate limiting in this process, as is PARP-1. Despite impaired NF-κB activation, DNA damage did not increase cell death or reduce clonal survival of various cell types lacking PIDD, such as mouse embryonic fibroblasts or stem and progenitor cells of the hematopoietic system. Furthermore, lymphomagenesis induced by γ-irradiation (IR) was unaffected by deficiency for PIDD or PARP-1, indicating that loss of DNA damage-triggered NF-κB signalling does not affect IR-driven tumorigenesis. However, loss of either gene compromised cytokine release after acute IR injury. Hence, we propose that NF-κB's most notable function after DNA damage in primary cells is related to the release of cytokines, thereby contributing to sterile inflammation.

Pleiotropic cellular functions of PARP1 in longevity and aging: genome maintenance meets inflammation

Aging is a multifactorial process that depends on diverse molecular and cellular mechanisms, such as genome maintenance and inflammation. The nuclear enzyme poly(ADP-ribose) polymerase 1 (PARP1), which catalyzes the synthesis of the biopolymer poly(ADP-ribose), exhibits an essential role in both processes. On the one hand, PARP1 serves as a genomic caretaker as it participates in chromatin remodelling, DNA repair, telomere maintenance, resolution of replicative stress, and cell cycle control. On the other hand, PARP1 acts as a mediator of inflammation due to its function as a regulator of NF-κB and other transcription factors and its potential to induce cell death. Consequently, PARP1 represents an interesting player in several aging mechanisms and is discussed as a longevity assurance factor on the one hand and an aging-promoting factor on the other hand. Here, we review the molecular mechanisms underlying the various roles of PARP1 in longevity and aging with special emphasis on cellular studies and we briefly discuss the results in the context of in vivo studies in mice and humans.

An association between clock genes and clock-controlled cell cycle genes in murine colorectal tumors

Disruption of circadian machinery appears to be associated with the acceleration of tumor development. To evaluate the function of the circadian clock during neoplastic transformation, the daily profiles of the core clock genes Per1, Per2, Rev-Erbα and Bmal1, the clock-controlled gene Dbp and the clock-controlled cell cycle genes Wee1, c-Myc and p21 were detected by real-time RT-PCR in chemically induced primary colorectal tumors, the surrounding normal tissue and in the liver. The circadian rhythmicity of Per1, Per2, Rev-Erbα and Dbp was significantly reduced in tumor compared with healthy colon and the rhythmicity of Bmal1 was completely abolished. Interestingly, the circadian expression of Per1, Per2, Rev-Erbα and Dbp persisted in the colonic tissue surrounding the tumor but the rhythmic expression of Bmal1 was also abolished. Daily profiles of Wee1, c-Myc and p21 did not exhibit any rhythmicity either in tumors or in the colon of healthy animals. The absence of diurnal rhythmicity of cell cycle genes was partially associated with ageing, because young healthy mice showed rhythmicity in the core clock genes as well as in the Wee1 and p21. In the liver of tumor-bearing mice the clock gene rhythms were temporally shifted. The data suggest that the circadian regulation is distorted in colonic neoplastic tissue and that the gene-specific disruption may be also observed in the non-neoplastic tissues. These findings reinforce the role of peripheral circadian clockwork disruption for carcinogenesis and tumor progression.

Using mice to unveil the genetics of cancer resistance

In the UK, four in ten people will develop some form of cancer during their lifetime, with an individual's relative risk depending on many factors, including age, lifestyle and genetic make-up. Much research has gone into identifying the genes that are mutated in tumorigenesis with the overwhelming majority of genetically-modified (GM) mice in cancer research showing accelerated tumorigenesis or recapitulating key aspects of the tumorigenic process. Yet if six out of ten people will not develop some form of cancer during their lifetime, together with the fact that some cancer patients experience spontaneous regression/remission, it suggests there are ways of 'resisting' cancer. Indeed, there are wildtype, spontaneously-arising mutants and GM mice that show some form of 'resistance' to cancer. Identification of mice with increased resistance to cancer is a novel aspect of cancer research that is important in terms of providing both chemopreventative and therapeutic options. In this review we describe the different mouse lines that display a 'cancer resistance' phenotype and discuss the molecular basis of their resistance.

Association between PARP-1 V762A polymorphism and cancer susceptibility: a meta-analysis

Poly(ADP-ribose) polymerase-1 (PARP-1 catalyzes poly(ADP-ribosyl)ation to various proteins involved in many cellular processes, including DNA damage detection and repair and cell proliferation and death. PARP-1 has been implicated in human carcinogenesis, but the association between the most-studied PARP-1 V762A polymorphism (rs1136410) and risk of various cancers was reported with inconclusive results. The aim of this study was to assess the association between the PARP-1 V762A polymorphism and cancer risk. A meta-analysis of 21 studies with 12,027 cancer patients and 14,106 cancer-free controls was conducted to evaluate the strength of the association using odds ratio (OR) with 95% confidence interval (CI). Overall, no significant association was found between the PARP-1 V762A polymorphism and cancer risk. In the stratified analyses, however, it was found that the variant A allele of the PARP-1 V762A polymorphism was associated with an increased risk of cancer among Asian populations (VA + AA vs. VV: OR = 1.11, 95% CI: 1.01-1.23; P(heterogeneity) = 0.210), but a decreased risk of cancer (VA + AA vs. VV: OR = 0.89, 95% CI: 0.80-1.00; P(heterogeneity) = 0.004) among Caucasian populations, especially for glioma risk (OR = 0.79, 95% CI: 0.69-0.90; P(heterogeneity) = 0.800). This meta-analysis found evidence for an association of the PARP-1 V 762A polymorphism with increased risk of cancer among Asians, but decreased risk of cancer among Caucasians, particularly of glioma. Further well-designed studies with large sample sizes of different ethnic populations and different cancer types are warranted to confirm these findings.

Role of nicotinamide in DNA damage, mutagenesis, and DNA repair

Nicotinamide is a water-soluble amide form of niacin (nicotinic acid or vitamin B3). Both niacin and nicotinamide are widely available in plant and animal foods, and niacin can also be endogenously synthesized in the liver from dietary tryptophan. Nicotinamide is also commercially available in vitamin supplements and in a range of cosmetic, hair, and skin preparations. Nicotinamide is the primary precursor of nicotinamide adenine dinucleotide (NAD⁺), an essential coenzyme in ATP production and the sole substrate of the nuclear enzyme poly-ADP-ribose polymerase-1 (PARP-1). Numerous in vitro and in vivo studies have clearly shown that PARP-1 and NAD⁺ status influence cellular responses to genotoxicity which can lead to mutagenesis and cancer formation. This paper will examine the role of nicotinamide in the protection from carcinogenesis, DNA repair, and maintenance of genomic stability.

Poly (ADP-ribose) polymerase-1 deficiency does not affect ethylnitrosourea mutagenicity in liver and testis of lacZ transgenic mice

Poly (ADP-ribose) polymerase-1 (Parp1) has been implicated in DNA base excision repair, single- and double-strand break repair pathways, as well as in cell death by apoptosis or necrosis. We used Parp1(-/-) lacZ plasmid-based transgenic mice to investigate whether Parp1 deficiency influences the in vivo mutagenic and clastogenic response to the alkylating agent N-ethyl-N-Nitrosourea (ENU) in somatic and germ-cell tissues. The comparison of the lacZ mutant frequencies (MFs) between Parp1(+/+) and Parp1(-/-) mice showed that the ablation of Parp1 does not affect the spontaneous or ENU-induced MFs in liver and testis. In addition, the spectrum of the ENU-induced mutations was not dependent on the Parp1 status, given that similar spectra, consisting mostly of point mutations and a small fraction of deletions/insertions, wereobserved in organs of both Parp1(-/-) and Parp1(+/+) mice. Sequencing of point mutations revealed a consistent significant increase in A:T --> T:A base substitutions, typically induced by ENU. Overall, we observed that neither the frequency nor the spectrum of ENU-induced mutations demonstrated a specificity that could be attributed to the Parp1 impairment in mice organs. The analysis of micronucleus frequency in peripheral blood reticulocytes showed that ENU was clastogenic in both Parp1(-/-) and Parp1(+/+) mice and had a strong cytotoxic effect in Parp1(-/-) mice only. The present data suggest that, at a whole-organism level, Parp1-independent repair mechanisms may be operative in the removal of ENU-induced DNA lesions or that highly damaged cells may be preferentially committed to death when Parp1 is inactivated.

PARP-1 Val762Ala polymorphism is associated with reduced risk of non-Hodgkin lymphoma in Korean males

Background

Poly(ADP-ribose) polymerase-1 (PARP-1) is a nuclear enzyme that plays a role in DNA repair, differentiation, proliferation, and cell death. The polymorphisms of PARP-1 have been associated with the risk of various carcinomas, including breast, lung, and prostate. We investigated whether PARP-1 polymorphisms are associated with the risk of non-Hodgkin lymphoma (NHL).

Methods

Subjects from a Korean population consisting of 573 NHL patients and 721 controls were genotyped for 5 PARP-1 polymorphisms (Asp81Asp, Ala284Ala, Lys352Lys, IVS13+118A>G, and Val762Ala) using High Resolution Melting polymerase chain reaction (PCR) and an automatic sequencer.

Results

None of the 5 polymorphisms were associated with overall risk for NHL. However, the Val762Ala polymorphism was associated with reduced risk for NHL in males [odds ratio (OR), 0.62; 95% confidence interval (CI), 0.41-0.93 for CC genotype and OR, 0.84; 95% CI, 0.60-1.16 for TC genotype] with a trend toward a gene dose effect (p for trend, 0.02). The Asp81Asp (p for trend, 0.04) and Lys352Lys (p for trend, 0.03) polymorphisms revealed the same trend. In an association study of PARP-1 haplotypes, the haplotype-ACAAC was associated with decreased risk of NHL in males (OR, 0.75; 95% CI, 0.59-0.94).

Conclusion

The present data suggest that Val762Ala, Asp81Asp, and Lys352Lys polymorphisms and the haplotype-ACAAC in PARP-1 are associated with reduced risk of NHL in Korean males.

Analysis of poly(ADP-ribose) polymerase-1 (PARP1) gene alteration in human germ cell tumor cell lines

The poly(ADP-ribose) polymerase-1 protein (PARP-1) functions in DNA repair, maintenance of genomic stability, induction of cell death, and transcriptional regulation. We previously analyzed alterations of the PARP1 gene in 16 specimens of human germ cell tumors, and found a heterozygous sequence alteration that causes the amino acid substitution Met129Thr (M129T) in both tumor and normal tissues in a single patient. In this study, aberration of the PARP1 gene and protein was further analyzed in human germ cell tumor cell lines. We found a nonheterozygous sequence alteration that causes the amino acid substitution Glu251Lys (E251K) located at a conserved peptide stretch of PARP-1 in cell line NEC8. Sequencing of 95 samples from Japanese healthy volunteers revealed that all the samples were homozygous for the wild-type alleles at M129T and E251K. The M129T allele is thus suggested to be a rare single-nucleotide polymorphism (SNP). We observed a decrease in auto-poly(ADP-ribosyl)ation activity of PARP-1 proteins harboring M129T or E251K amino acid substitution, but the difference was not statistically significant. The levels of PARP-1 and poly(ADP-ribosyl)ation were heterogeneous among germ cell tumor cell lines. The SNPs of the PARP1 gene, as well as differences in the levels of PARP-1 and poly(ADP-ribosyl)ation of proteins, may influence germ cell tumor development and responses to chemotherapy and radiotherapy.

Inhibition of poly adenosine diphosphate-ribose polymerase decreases hepatocellular carcinoma growth by modulation of tumor-related gene expression

Hepatocellular carcinoma (HCC) is associated with a poor prognosis due to a lack of effective treatment options. In HCC a significant role is played by DNA damage and the inflammatory response. Poly (ADP-ribose) polymerase-1 (PARP-1) is an important protein that regulates both these mechanisms. The objective of this study was to examine the effect of pharmacology PARP-1 inhibition on the reduction of tumor volume of HCC xenograft and on the hepatocarcinogenesis induced by diethyl-nitrosamine (DEN). Pharmacologic PARP-1 inhibition with DPQ greatly reduces tumor xenograft volume with regard to a nontreated xenograft (394 mm(3) versus 2,942 mm(3), P < 0.05). This observation was paralleled by reductions in xenograft mitosis (P = 0.02) and tumor vasculogenesis (P = 0.007, confirmed by in vitro angiogenesis study), as well as by an increase in the number of apoptotic cells in DPQ-treated mice (P = 0.04). A substantial difference in key tumor-related gene expression (transformed 3T3 cell double minute 2 [MDM2], FLT1 [vascular endothelial growth factor receptor-1, VEGFR1], epidermal growth factor receptor [EPAS1]/hypoxia-inducible factor 2 [HIF2A], EGLN1 [PHD2], epidermal growth factor receptor [EGFR], MYC, JUND, SPP1 [OPN], hepatocyte growth factor [HGF]) was found between the control tumor xenografts and the PARP inhibitor-treated xenografts (data confirmed in HCC cell lines using PARP inhibitors and PARP-1 small interfering RNA [siRNA]). Furthermore, the results obtained in mice treated with DEN to induce hepatocarcinogenesis showed, after treatment with a PARP inhibitor (DPQ), a significant reduction both in preneoplastic foci and in the expression of preneoplastic markers and proinflammatory genes (Gstm3, Vegf, Spp1 [Opn], IL6, IL1b, and Tnf), bromodeoxyuridine incorporation, and NF-kappaB activation in the initial steps of carcinogenesis (P < 0.05).

CONCLUSION

This study shows that PARP inhibition is capable of controlling HCC growth and preventing tumor vasculogenesis by regulating the activation of different genes involved in tumor progression.

Role of Parp-1 in suppressing spontaneous deletion mutation in the liver and brain of mice at adolescence and advanced age

Poly(ADP-ribose) polymerase-1 knockout (Parp-1(-/-)) mice show increased frequency of spontaneous liver tumors compared to wild-type mice after aging. To understand the impact of Parp-1 deficiency on mutations during aging, in this study, we analyzed spontaneous mutations in Parp-1(-/-) aged mice. Parp-1(-/-) mice showed tendencies of higher mutation frequencies of the red/gam genes at 18 months of age, compared to Parp-1(+/+) mice, in the liver and brain. Complex-type deletions, accompanying small insertion were observed only in Parp-1(-/-) mice in the liver and brain. Further analysis in the liver showed that the frequency of single base deletion mutations at non-repeat or short repeat sequences was 5.8-fold higher in Parp-1(-/-) than in Parp-1(+/+) mice (p<0.05). A 3.2-fold higher tendency of the deletion frequency of two bases or more was observed in Parp-1(-/-) mice compared to Parp-1(+/+) mice (p=0.084). These results support the model that Parp-1 is involved in suppressing imprecise repair of endogenous DNA damage leading to deletion mutation during aging. The mutation frequencies of the gpt gene in the brain were found to be 3-fold lower in Parp-1(-/-) than in Parp-1(+/+) mice at 4 months of age (p<0.01), implying that Parp-1 may be positively involved in imprecise DNA repair in the brain. On the other hand, the frequencies of gpt mutation showed an increase at 18 months of age in the Parp-1(-/-) (p<0.05) but not in Parp-1(+/+) brains, suggesting that Parp-1 deficiency causes an increase of point mutations in the brain by aging.

Adiponectin deficiency enhances colorectal carcinogenesis and liver tumor formation induced by azoxymethane in mice

AIM: To investigate the causal relationship between hypoadiponectinemia and colorectal carcinogenesis in in vivo experimental model, and to determine the contribution of adiponectin deficiency to colorectal cancer development and proliferation.

METHODS: We examined the influence of adiponectin deficiency on colorectal carcinogenesis induced by the administration of azoxymethane (AOM) (7.5 mg/kg, intraperitoneal injection once a week for 8 wk), by using adiponectin-knockout (KO) mice.

RESULTS: At 53 wk after the first AOM treatment, KO mice developed larger and histologically more progressive colorectal tumors with greater frequency compared with wild-type (WT) mice, although the tumor incidence was not different between WT and KO mice. KO mice showed increased cell proliferation of colorectal tumor cells, which correlated with the expression levels of cyclooxygenase-2 (COX-2) in the colorectal tumors. In addition, KO mice showed higher incidence and frequency of liver tumors after AOM treatment. Thirteen percent of WT mice developed liver tumors, and these WT mice had only a single tumor. In contrast, 50% of KO mice developed liver tumors, and 58% of these KO mice had multiple tumors.

CONCLUSION: Adiponectin deficiency enhances colorectal carcinogenesis and liver tumor formation induced by AOM in mice. This study strongly suggests that hypoadiponectinemia could be involved in the pathogenesis for colorectal cancer and liver tumor in human subjects.

Increased susceptibility of Sf1(+/-) mice to azoxymethane-induced colon tumorigenesis

Aberrant transactivation of a certain set of target genes by the beta-catenin and T-cell factor-4 nuclear complex has been considered crucial for the initiation of colorectal carcinogenesis. We previously identified splicing factor-1 (SF1) as a novel component of the beta-catenin and T-cell factor-4 complex, and showed that the overexpression of SF1 inhibited the gene transactivational activity of the complex and markedly suppressed beta-catenin-evoked colony formation by human embryonic kidney 293 cells. However, the involvement of SF1 in the process of carcinogenesis in vivo remains unclear. In the present study, we established SF1-knockout mice using the gene trapping method. Homozygous mice (Sf1(-/-)) died during embryonic development before embryonic day (E)8.5, whereas heterozygous (Sf1(+/-)) mice were born alive and developed normally. Azoxymethane (AOM) was given at a dose of 10 mg/kg body weight once a week for 6 weeks to 7-week-old Sf1(+/-) and Sf1(+/+) mice. At 23 weeks after the start of AOM the average number (5.5 +/- 0.6 versus 2.2 +/- 0.2 in females [P = 0.003, Mann-Whitney U-test], 3.7 +/- 0.2 versus 1.7 +/- 0.7 in males [P = 0.014]) and volume of colon tumors per mouse (8.7 +/- 1.6 versus 2.2 +/- 0.5 mm(3) per female [P = 0.0008], 11.3 +/- 3.4 versus 0.6 +/- 0.2 mm(3) per male [P = 0.001]) were significantly higher in Sf1(+/-) than in Sf1(+/+) mice. The increased susceptibility of Sf1(+/-) mice to AOM-induced colon tumorigenesis indicates the crucial involvement of SF1 in the beta-catenin-mediated regulation of proliferation and differentiation of intestinal epithelial cells.

Analysis of genetic variants of the poly(ADP-ribose) polymerase-1 gene in breast cancer in French patients

Poly(ADP-ribose) polymerase-1 (PARP-1) is a nuclear enzyme that catalyzes the poly(ADP-ribosyl)ation of target proteins in response to DNA damage and has been proposed to play a role in DNA repair, recombination, transcription, cell death, cell proliferation, as well as in stabilization of the genome. We have recently shown that PARP-1 deficiency causes mammary tumorigenesis in mice. In the present study, we investigated whether genetic variants and single nucleotide polymorphisms (SNPs) of PARP-1 contribute to human breast cancer. To this end, we screened all PARP-1 exons, 7.1kb of intron-exon junction and 1.0-kb promoter sequences in 83 French patients with breast cancer and 100 controls by direct sequencing of genomic DNA. Twenty rare genetic variants of PARP-1, including c.1148C>A (Ser383Tyr), c.1354C>A (Arg452Arg), c.2819A>G (Lys940Arg) were detected in nine (10.8%) breast cancers of these patients. Among 31 polymorphic sites examined, five haplotype-tagging SNPs (htSNPs) of PARP-1 were identified. Interestingly, the genotype distribution of htSNP c.852T>C (Ala284Ala) was likely associated with loss of estrogen- and progesterone-receptor expression. The present study implies that genetic variants of PARP-1 may contribute to breast cancerogenesis and that PARP-1 htSNP c.852T>C (Ala284Ala) may influence hormonal therapy of breast cancer.

Genetic variation in base excision repair genes and the prevalence of advanced colorectal adenoma

Base excision repair (BER) corrects DNA damage caused by oxidative stress and low folate intake, which are putative risk factors for colorectal neoplasia. To examine the relationship between genetic variation in BER genes and colorectal adenoma risk, we conducted a case-control study of 767 cases of advanced colorectal adenoma and 773 controls from the baseline screening exam of the Prostate, Lung, Colorectal, and Ovarian Cancer Screening Trial. Cases included participants diagnosed with advanced left-sided adenoma, and controls were subjects without evidence of a left-sided polyp by sigmoidoscopy, frequency-matched to cases on race and gender. Twenty single nucleotide polymorphisms were genotyped in four BER genes (APEX1, PARP1, POLB, and XRCC1), and conditional logistic regression was used to estimate odds ratios (OR) and 95% confidence intervals (95% CI) for the association with colorectal adenoma. Two variants with possible functional significance were associated with risk. The APEX1 51H variant was associated with a borderline significant decreased risk of colorectal adenoma (OR, 0.66; 95% CI, 0.44-1.00), and the XRCC1 399Q variant was inversely associated with risk among Caucasians (OR, 0.80; 95% CI, 0.64-0.99). Homozygotes at two PARP1 loci (A284A and IVS13+118G>A) were also associated with a decreased risk of colorectal adenoma compared with wild-type carriers (OR, 0.70; 95% CI, 0.49-0.98 for both), which was restricted to advanced adenomas displaying histologically aggressive characteristics (OR, 0.51; 95% CI, 0.33-0.78, P = 0.002 for PARP1 A284A). This study suggests that polymorphisms in APEX1, XRCC1, and PARP1 may be associated with advanced colorectal adenoma.

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.

Poly(ADP-ribose) polymerase-1 plays a role in suppressing mammary tumourigenesis in mice

The DNA strand break-binding molecule, poly(ADP-ribose) polymerase-1 (PARP-1), plays a role in DNA repair, chromosomal stability, transcription and cell death. Accumulating evidence suggests that dysfunction of PARP-1 contributes to tumorigenesis. Here, we report that PARP-1 deficiency causes mammary carcinoma formation in female mice, and that the introduction of Trp53 mutations accelerates the onset and shortens the latency of mammary tumorigenesis. We show that PARP-1 deficiency results in chromosomal aneuploidy and centrosome amplification, which are substantiated by the inactivation of Trp53 in primary mammary epithelial (PME) cells. In addition, PARP-1 deficiency compromises p53 activation and impairs BRCA1 recruitment to the sites of DNA damage in PME cells. PARP-1 complementation partly rescues the defective DNA damage response mediated by p53 and BRCA1. The present study thus identifies a role of PARP-1 in suppressing mammary tumorigenesis in vivo and suggests that dysfunction of PARP-1 may be a risk factor for breast cancer in humans.

Relationship between expression of poly adenosine diphosphate-ribose polymerase-1 and its biological characteristics in human hepatocellular carcinoma

AIM: To investigate the expression of poly adenosine diphosphate-ribose polymerase-1 (PARP-1) in human hepatocellular carcinoma (HCC) and its adjacent liver tissues as well as the correlation between the expression of PARP-1 and the biological characteristics.

METHODS: Immunohistochemical staining and Western blotting were employed to examine the expression of PARP-1 in HCC and its adjacent liver tissues obtained from the surgical specimens of 40 HCC patients who underwent liver resections in our hospital, and the correlation between the expression level of PARP-1 and the differentiation, recurrence and metastasis of HCC were analyzed.

RESULTS: The expression of PARP-1 was mainly located in the nucleus, and the rate of PARP-1 expression in HCC was significantly higher than that in its adjacent liver tissues (t = 6.49, P < 0.01). The rates of PARP-1 expression in the poorly differentiated HCC were significantly greater than those in the well and moderately differentiated HCC (t = 4.57, P < 0.01). Furthermore, the expression rates in the HCC with recurrence and metastasis were significantly higher than those in the ones without recurrence and metastasis (t = 3.33, P < 0.01).

CONCLUSION: PARP-1 expression is up-regulated in HCC, and the up-regulation of PARP-1 is closely correlated with the differentiation and metastasis. This study indicates that the PARP-1 gene may be involved in the carcinogenesis and development of human HCC.

N/A

N/A

AMP-activated protein kinase is a positive regulator of poly(ADP-ribose) polymerase

AMPK acts as a cellular fuel gauge and responds to decreased cellular energy status by inhibiting ATP-consuming pathways and increasing ATP-synthesis. The aim of this study was to examine the role of AMPK in modulating poly(ADP-ribose) polymerase (PARP), a nuclear enzyme involved in maintaining chromatin structure and DNA repair. HT-29 cells infected with constitutively active AMPK demonstrated increased PARP automodification and an increase in bioNAD incorporation. AMPK and PARP co-immunoprecipitated under basal conditions and in response to H(2)O(2), suggesting a physical interaction under both resting and stress-induced conditions. Incubation of PARP with purified AMPK resulted in the phosphorylation of PARP; and the inclusion of AMP as an AMPK activator potentiated PARP phosphorylation. Using immobilized PARP, the incorporation of bioNAD by PARP was dramatically increased following the addition of AMPK. These data suggest a novel role for AMPK in regulating PARP activity through a direct interaction involving phosphorylation.

Increased susceptibility of vault poly(ADP-ribose) polymerase-deficient mice to carcinogen-induced tumorigenesis

Vault poly(ADP-ribose) polymerase (VPARP) and telomerase-associated protein 1 (TEP1) are components of the vault ribonucleoprotein complex. Vaults have been implicated in multidrug resistance of human tumors and are thought to be involved in macromolecular assembly and/or transport. Previous studies showed that VPARP-deficient mice were viable, fertile, and did not display any vault-related or telomerase-related phenotype, whereas disruption of telomerase-associated protein 1 in mice led to reduced stability of the vault RNA and affected its stable association with vaults, although there were no telomerase-related changes. In this study, we evaluated the susceptibility of Vparp-/- and Tep1-/- mice to dimethylhydrazine-induced colon tumorigenesis and urethane-induced lung tumorigenesis. Mice received i.p. injections of either 1 g/kg body weight of urethane twice a week for 2 weeks or 20 mg/kg body weight of dimethylhydrazine once a week for 10 weeks and were analyzed after 10 and 60 weeks, respectively. The colon tumor incidence and multiplicity were significantly higher and colon tumor latency was significantly shorter in Vparp-/- mice compared with wild-type mice. Increased colon tumor incidence, multiplicity, and reduced tumor latency were also seen in Tep1-/- mice, however, these results were statistically not significant. Lung tumor multiplicities were increased in both Vparp-/- and Tep1-/- mice but were not significant. The increase in carcinogen-induced tumors in VPARP-deficient mice is the only phenotype observed to date, and suggests a possible role for VPARP, directly or indirectly, in chemically induced neoplasia.

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.

Poly(ADP-ribosyl)ation by PARP-1: 'PAR-laying' NAD+ into a nuclear signal

Poly(ADP-ribose) (PAR) and the PAR polymerases (PARPs) that catalyze its synthesis from donor nicotinamide adenine dinucleotide (NAD+) molecules have received considerable attention in the recent literature. Poly(ADP-ribosyl)ation (PARylation) plays diverse roles in many molecular and cellular processes, including DNA damage detection and repair, chromatin modification, transcription, cell death pathways, insulator function, and mitotic apparatus function. These processes are critical for many physiological and pathophysiological outcomes, including genome maintenance, carcinogenesis, aging, inflammation, and neuronal function. This review highlights recent work on the biochemistry, molecular biology, physiology, and pathophysiology of PARylation, focusing on the activity of PARP-1, the most abundantly expressed member of a family of PARP proteins. In addition, connections between nuclear NAD+ metabolism and nuclear signaling through PARP-1 are discussed.

Clinical perspectives of PARP inhibitors

Poly(ADP-ribose) polymerase (PARP) activation plays a role in the pathogenesis of various cardiovascular and inflammatory diseases. At the same time, PARP activation is also relevant for the ability of cells to repair injured DNA. Thus, depending on the circumstances, pharmacological inhibitors of PARP may be able to attenuate ischemic and inflammatory cell and organ injury or may be able to enhance the cytotoxicity of antitumor agents. Both aspects of the "double-edged sword" role of PARP can be exploited for the experimental therapy of disease. As several classes of PARP inhibitors move towards clinical development, or have already entered the stage of clinical trials, we expect that in the upcoming few years, clinical proof of PARP inhibitors' therapeutic effect will be obtained in human disease. In the current short overview, we summarize the pros and cons and challenges with respect to the clinical use of PARP inhibitors, the expected clinical outcomes and potential risks. It appears that on the cytoprotective aspect of PARP, acute, life-threatening diseases (myocardial infarction, cardiopulmonary bypass in high-risk patients, and other, severe forms of ischemia-reperfusion to other organs including stroke and thoracoabdominal aneurysm repair) may represent some of the prime development indications. In the context of inhibition of DNA repair, combination of PARP inhibitors with certain antitumor agents (for example temozolomide) in patients with tumors with extremely poor prognosis are expected to provide the initial clinical results. Development of PARP inhibitors for additional indications (e.g. chronic use for the therapy of neurodegeneration and neuroinflammation, or diabetic complications) may be more challenging because of the unknown potential long-term side effects of PARP inhibitors.

Parp-1 deficiency does not enhance liver carcinogenesis induced by 2-amino-3-methylimidazo[4,5-f]quinoline in mice

The susceptibility of poly(ADP-ribose) polymerase-1 (Parp-1) knockout mice to 2-amino-3-methylimidazo[4,5-f]quinoline (IQ)-induced liver carcinogenesis was analyzed. Twelve-week-old male Parp-1(+/+), Parp-1(+/-) and Parp-1(-/-) mice of the C57BL/6 congenic strain were fed a diet containing IQ at a concentration of 300 ppm or a control diet for 60 weeks. Hepatocellular carcinomas were observed only in 1/19, 2/18 and 1/17 of the Parp-1(-/-), Parp-1(+/-) and Parp-1(+/+) mice, respectively. Parp-1 deficiency did not affect the susceptibility of mice to carcinogenicity of IQ, which produces bulky DNA adducts that are repaired mainly through the nucleotide excision repair pathway. This result is in sharp contrast to the increased susceptibility of Parp-1(-/-) mice to carcinogenesis induced by alkylating agents that produce DNA damage repaired mainly through base excision repair and DNA strand break repair pathways.