Adenosine Diphosphate Ribosyl Transferase Research Articles

Extracellular Vesicle Inhibitors Enhance Cholix-Induced Cell Death via Regulation of the JNK-Dependent Pathway.

Vibrio cholerae is an important foodborne pathogen. Cholix cytotoxin (Cholix), produced by V. cholerae, is a novel eukaryotic elongation factor 2 (eEF2) adenosine diphosphate ribosyltransferase that causes host cell death by inhibiting protein synthesis. However, the role of Cholix in the infectious diseases caused by V. cholerae remains unclear. Some bacterial cytotoxins are carried by host extracellular vesicles (EVs) and transferred to other cells. In this study, we investigated the effects of EV inhibitors and EV-regulating proteins on Cholix-induced hepatocyte death. We observed that Cholix-induced cell death was significantly enhanced in the presence of EV inhibitors (e.g., dimethyl amiloride, and desipramine) and Rab27a-knockdown cells, but it did not involve a sphingomyelin-dependent pathway. RNA sequencing analysis revealed that desipramine, imipramine, and EV inhibitors promoted the Cholix-activated c-Jun NH2-terminal kinase (JNK) pathway. Furthermore, JNK inhibition decreased desipramine-enhanced Cholix-induced poly (ADP-ribose) polymerase (PARP) cleavage. In addition, suppression of Apaf-1 by small interfering RNA further enhanced Cholix-induced PARP cleavage by desipramine. We identified a novel function of desipramine in which the stimulated JNK pathway promoted a mitochondria-independent cell death pathway by Cholix.

A viral ADP-ribosyltransferase attaches RNA chains to host proteins

The mechanisms by which viruses hijack the genetic machinery of the cells they infect are of current interest. When bacteriophage T4 infects Escherichia coli, it uses three different adenosine diphosphate (ADP)-ribosyltransferases (ARTs) to reprogram the transcriptional and translational apparatus of the host by ADP-ribosylation using nicotinamide adenine dinucleotide (NAD) as a substrate1,2. NAD has previously been identified as a 5′ modification of cellular RNAs3–5. Here we report that the T4 ART ModB accepts not only NAD but also NAD-capped RNA (NAD–RNA) as a substrate and attaches entire RNA chains to acceptor proteins in an ‘RNAylation’ reaction. ModB specifically RNAylates the ribosomal proteins rS1 and rL2 at defined Arg residues, and selected E. coli and T4 phage RNAs are linked to rS1 in vivo. T4 phages that express an inactive mutant of ModB have a decreased burst size and slowed lysis of E. coli. Our findings reveal a distinct biological role for NAD–RNA, namely the activation of the RNA for enzymatic transfer to proteins. The attachment of specific RNAs to ribosomal proteins might provide a strategy for the phage to modulate the host’s translation machinery. This work reveals a direct connection between RNA modification and post-translational protein modification. ARTs have important roles far beyond viral infections6, so RNAylation may have far-reaching implications.

Reversible modification of mitochondrial ADP/ATP translocases by paired Legionella effector proteins

Adenosine diphosphate (ADP) ribosylation is a reversible posttranslational modification involved in the regulation of numerous cellular processes. Prototype ADP ribosyltransferases (ARTs) from many pathogenic bacteria are known to function as toxins, while other bacterial ARTs have just recently emerged. Recent studies have shown that bacteria also possess enzymes that function as poly-ADP ribose (ADPr) glycohydrolases (PARGs), which reverse poly-ADP ribosylation. However, how bacteria manipulate host target proteins by coordinated reactions of ARTs and ADPr hydrolases (ARHs) remains elusive. The intracellular bacterial pathogen Legionella pneumophila, the causative agent of Legionnaires’ disease, transports a large array of effector proteins via the Dot/Icm type IV secretion system to host cells. The effector proteins, which mostly function as enzymes, modulate host cellular processes for the bacteria’s benefit. In this study, we identified a pair of L. pneumophila effector proteins, Lpg0080 and Lpg0081, which function as an ART and an ARH, respectively. The two proteins were shown to coordinately modulate mitochondrial ADP/adenosine triphosphate (ATP) translocases (ANTs) by their enzymatic activities to conjugate ADPr to, and remove it from, a key arginine residue. The crystal structures of Lpg0081 and the Lpg0081:ADPr complex indicated that Lpg0081 is a macroD-type ARH with a noncanonical macrodomain, whose folding topology is strikingly distinct from that of the canonical macrodomain that is ubiquitously found in eukaryotic PARGs and ARHs. Our results illustrate that L. pneumophila has acquired an effector pair that coordinately manipulate mitochondrial activity via reversible chemical modification of ANTs.

Ribosylation of the CD8αβ heterodimer permits binding of the nonclassical major histocompatibility molecule, H2-Q10

The CD8αβ heterodimer plays a crucial role in the stabilization between major histocompatibility complex class I molecules (MHC-I) and the T cell receptor (TCR). The interaction between CD8 and MHC-I can be regulated by posttranslational modifications, which are proposed to play an important role in the development of CD8 T cells. One modification that has been proposed to control CD8 coreceptor function is ribosylation. Utilizing NAD+, the ecto-enzyme adenosine diphosphate (ADP) ribosyl transferase 2.2 (ART2.2) catalyzes the addition of ADP-ribosyl groups onto arginine residues of CD8α or β chains and alters the interaction between the MHC and TCR complexes. To date, only interactions between modified CD8 and classical MHC-I (MHC-Ia), have been investigated and the interaction with non-classical MHC (MHC-Ib) has not been explored. Here, we show that ADP-ribosylation of CD8 facilitates the binding of the liver-restricted nonclassical MHC, H2-Q10, independent of the associated TCR or presented peptide, and propose that this highly regulated binding imposes an additional inhibitory leash on the activation of CD8-expressing cells in the presence of NAD+. These findings highlight additional important roles for nonclassical MHC-I in the regulation of immune responses.

Synthesis of Stable NAD+ Mimics as Inhibitors for the Legionella pneumophila Phosphoribosyl Ubiquitylating Enzyme SdeC.

Stable NAD+ analogues carrying single atom substitutions in either the furanose ring or the nicotinamide part have proven their value as inhibitors for NAD+‐consuming enzymes. To investigate the potential of such compounds to inhibit the adenosine diphosphate ribosyl (ADPr) transferase activity of the Legionella SdeC enzyme, we prepared three NAD+ analogues, namely carbanicotinamide adenosine dinucleotide (c‐NAD+), thionicotinamide adenosine dinucleotide (S‐NAD+) and benzamide adenosine dinucleotide (BAD). We optimized the chemical synthesis of thionicotinamide riboside and for the first time used an enzymatic approach to convert all three ribosides into the corresponding NAD+ mimics. We thus expanded the known scope of substrates for the NRK1/NMNAT1 enzyme combination by turning all three modified ribosides into NAD+ analogues in a scalable manner. We then compared the three NAD+ mimics side‐by‐side in a single assay for enzyme inhibition on Legionella effector enzyme SdeC. The class of SidE enzymes to which SdeC belongs was recently identified to be important in bacterial virulence, and we found SdeC to be inhibited by S‐NAD+ and BAD with IC50 values of 28 and 39 μM, respectively.

Outbreak of an Uncommon Rifampin-resistant blaNDM-1Citrobacter amalonaticus Strain in a Digestive Rehabilitation Center: The Putative Role of Rifaximin.

We describe a sudden 2-week outbreak due to a blaNDM-1Citrobacter amalonaticus strain in a 22-bed digestive rehabilitation center. Three of the 5 colonized patients received long-term rifaximin treatment to prevent hepatic encephalopathy. The strains were genotypically identical, phenotypically resistant to rifampin, and harbored arr-3, a rifampin adenosine diphosphate-ribosyl transferase.

SIRT1 gene polymorphisms and its protein level in colorectal cancer

Colorectal cancer (CRC) is a major cause of mortality and morbidity, and accounts for over 9% of cancer incidence worldwide. Nuclear localized silent information regulator 2 homolog 1 (SIRT1) gene exerts its effects via modulation of histone and non-histone targets. SIRT1 gene functions in the cell via histone deacetylase (HDAC) and/or adenosine diphosphate ribosyl transferase (ADPRT) enzymatic activity. The aim of this work is to study the relationship between SIRT1 polymorphism and its protein level in colorectal cancer patients in comparison to control cases. This study includes two group, thirty healthy subjects (control group) and one hundred CRC patients. SIRT-1 serum level was measured in both the groups by ELISA and gene polymorphisms of rs12778366, rs375891 and rs3740051were detected by real time PCR. For CRC patients clinical data was collected including tumor size, tumor grade, tumor site, obesity. CRC patients showed a significant increase in the mean level of serum SIRT-1 compared to control group (P<0.001). Mean serum level of SIRT-1 showed a significant increase in patients with tumor size ≥5cm compared to the size <5cm (P<0.05). In CRC patients, the percentage of T allele of rs12778366 was significantly lower than controls, CC genotype and C allele C of rs375891 were significantly higher than control group. In CRC patients, the CC genotype of rs12778366, was 75% in the rectosigmoid colon and 25% in cecum & ascending colon. According to tumor size, the percentage of CC genotype was 87.5% in tumor size ≥5cm. ConclusionSerum level of SIRT-1 and T allele, C allele of rs12778366 and rs375891 respectively can be used as diagnostic markers for CRC patients.

Sirtuins in glucose and lipid metabolism.

Sirtuins are evolutionarily conserved protein, serving as nicotinamide adenine dinucleotide-dependent deacetylases or adenosine diphosphate-ribosyltransferases. The mammalian sirtuins family, including SIRT1~7, is involved in many biological processes such as cell survival, proliferation, senescence, stress response, genome stability and metabolism. Evidence accumulated over the past two decades has indicated that sirtuins not only serve as important energy status sensors but also protect cells against metabolic stresses. In this review, we summarize the background of glucose and lipid metabolism concerning sirtuins and discuss the functions of sirtuins in glucose and lipid metabolism. We also seek to highlight the biological roles of certain sirtuins members in cancer metabolism.

Chemoselective Dimerization of Phosphates.

A methodology for the synthesis of oligophosphate conjugates using phosphordiamidites is described. This strategy facilitates the straightforward preparation of C2-symmetric dinucleoside tri-, penta-, and heptaphosphates. Moreover, unsymmetric compounds such as thiamine adenosine triphosphate and thiamine cytidine triphosphate can be prepared. The material is used to study the inhibitory activity of thiaminylated nucleotides against adenosine diphosphate ribosyltransferases.

Analysis of oxidative DNA damage and its repair in Polish patients with diabetes mellitus type 2: Role in pathogenesis of diabetic neuropathy

PurposeDistal symmetric polyneuropathy (DSPN) is common complication of type 2 diabetes (T2DM). In this work we investigated the role of oxidative damage in connection with particular polymorphisms of DNA repair genes and their repair capacity. Material/methodsMaterials constitute the peripheral blood of patients with T2DM with and without DSPN and control subjects without disturbance of the carbohydrate fraction. The study of gene polymorphisms which products take part in base excision repair (BER) pathway: 726 Val/Ala adenosine diphosphate ribosyl transferase (ADPRT), 324 His/Glu MutYhomolog (MUTYH) and 148 Asp/Glu human apurinic/apyrimidinic endonuclease (APE) was carried out using restriction fragment length polymorphism polymerase chain reaction (PCR-RFLP) method. The study of DNA damage induced by hydrogen peroxide and the efficiency of their repair was carried out using comet assay. ResultsNone of the 3 polymorphisms were associated with the risk of DSPN. However, in group of patients together with T2DM and T2DM/DSPN 726 Ala ADPRT allele was significantly susceptible to increased risk of T2DM (OR=1.59; 95% CI: 1.08–2.36). Investigation of DNA damage and repair revealed that T2DM patients have decreased ability to DNA repair. This capacity even drops down in the group of T2DM/DSPN patients compared to subjects with diabetes alone. ADPRT and APE polymorphisms were significantly associated with higher DNA damages (P<0.05) in heterozygous and mutant homozygous in correlation to homozygous wild type, but for MUTYH polymorphism relation was not confirmed. ConclusionsPathogenesis of T2DM and development of DSPN may be related to oxidative stress connected with BER gene polymorphisms.

The Escherichia coli effector EspJ blocks Src kinase activity via amidation and ADP ribosylation.

The hallmark of enteropathogenic Escherichia coli (EPEC) infection is the formation of actin-rich pedestal-like structures, which are generated following phosphorylation of the bacterial effector Tir by cellular Src and Abl family tyrosine kinases. This leads to recruitment of the Nck–WIP–N-WASP complex that triggers Arp2/3-dependent actin polymerization in the host cell. The same phosphorylation-mediated signalling network is also assembled downstream of the Vaccinia virus protein A36 and the phagocytic Fc-gamma receptor FcγRIIa. Here we report that the EPEC type-III secretion system effector EspJ inhibits autophosphorylation of Src and phosphorylation of the Src substrates Tir and FcγRIIa. Consistent with this, EspJ inhibits actin polymerization downstream of EPEC, Vaccinia virus and opsonized red blood cells. We identify EspJ as a unique adenosine diphosphate (ADP) ribosyltransferase that directly inhibits Src kinase by simultaneous amidation and ADP ribosylation of the conserved kinase-domain residue, Src E310, resulting in glutamine-ADP ribose.

The effects of MIBG on the invasive properties of HepG2 hepatocellular carcinoma cells.

The aim of the present study was to investigate the effects of meta-iodobenzylguanidine (MIBG) on the invasive properties of hepatocellular carcinoma (HCC) cells and examine whether these effects are due to the ability of MIBG to inhibit arginine-specific mono-ADP-ribosylation. Samples from patients with HCC were divided into 2groups, a metastatic group and a non-metastatic group. Immunohistochemistry and RT-PCR were used to detect the protein and mRNA expression of arginine-specific adenosine diphosphate-ribosyltransferase1 (ART1) and integrinα7 in the HCC tissues. In addition, the expression of ART1 was measured in HepG2 HCC cells by immunofluorescence. The inhibition of the metastasis of HepG2 cells by MIBG at various concentrations was measured by MTT assay. In addition, the effects of MIBG on HepG2 cell metastasis were measured using a scratch wound assay and a transwell invasion assay. Western blot analysis was used to detect the protein expression of ART1, integrinα7, focal adhesion kinase (FAK), phosphatidylinositol 3-kinase (PI3K) and urokinase-type plasminogen activator (uPA) in the HepG2 cells. The mRNA and protein levels of ART1 and integrinα7 were higher in the metastatic HCC samples than in the non-metastatic HCC samples. ART1 expression was detected in the HepG2 cells. The half maximal inhibition concentration (IC50) of MIBG in the HepG2 cells was 200µmol/l (P<0.05). Within a certain dose range, MIBG exerted inhibitory effects on HepG2 cell migration in a dose-dependent manner. Treatment with MIBG significantly inhibited the migration and invasion of the HepG2 cells relative to the control cells (P<0.05) and reduced the protein expression of ART1, integrinα7, FAK, PI3K and uPA (P<0.05). Our data demonstrate that ART1 and integrinα7 may be involved in the invasive and metastatic properties of HCC cells. MIBG inhibited the migration and invasion of HepG2 cells, possibly through the inhibition of arginine-specific single-adenosine diphosphate ribosylation and the suppression of the protein expression of integrinα7β1, FAK and PI3K and the secretion of uPA, leading to reduced invasion by HepG2 cells.

Engineering the Substrate Specificity of ADP-Ribosyltransferases for Identifying Direct Protein Targets

Adenosine diphosphate ribosyltransferases (ARTDs; ARTD1-17 in humans) are emerging as critical regulators of cell function in both normal physiology and disease. These enzymes transfer the ADP-ribose moiety from its substrate, nicotinamide adenine dinucleotide (NAD(+)), to amino acids of target proteins. The functional redundancy and overlapping target specificities among the 17 ARTDs in humans make the identification of direct targets of individual ARTD family members in a cellular context a formidable challenge. Here we describe the rational design of orthogonal NAD(+) analogue-engineered ARTD pairs for the identification of direct protein targets of individual ARTDs. Guided by initial inhibitor studies with nicotinamide analogues containing substituents at the C-5 position, we synthesized an orthogonal NAD(+) variant and found that it is used as a substrate for several engineered ARTDs (ARTD1, -2, and -6) but not their wild-type counterparts. Comparing the target profiles of ARTD1 (PARP1) and ARTD2 (PARP2) in nuclear extracts highlighted the semi-complementary, yet distinct, protein targeting. Using affinity purification followed by tandem mass spectrometry, we identified 42 direct ARTD1 targets and 301 direct ARTD2 targets. This represents a powerful new technique for identifying direct protein targets of individual ARTD family members, which will facilitate studies delineating the pathway from ARTD activation to a given cellular response.

The emerging and diverse roles of sirtuins in cancer: a clinical perspective

Sirtuins are a highly conserved family of nicotinamide adenine dinucleotide (NAD+)-dependent protein lysine modifying enzymes with deacetylase, adenosine diphosphateribosyltransferase and other deacylase activities. Mammals have seven sirtuins, namely SIRT1-7. They are key regulators for a wide variety of cellular and physiological processes such as cell proliferation, differentiation, DNA damage and stress response, genome stability, cell survival, metabolism, energy homeostasis, organ development, aging, and cancer. Here we present an extensive literature review of the roles of mammalian sirtuins, particularly SIRT1 as that is the most studied sirtuin, in human epithelial, neuronal, hematopoietic, and mesenchymal malignancies, covering breast, prostate, lung, thyroid, liver, colon, gastric, pancreatic, ovarian, and cervical cancers, tumors of the central nervous system, leukemia and lymphoma, and soft tissue sarcomas. Collective evidence suggests sirtuins are involved in both promoting and suppressing tumorigenesis depending on cellular and molecular contexts. We discuss the potential use of sirtuin modulators, especially sirtuin inhibitors, in cancer treatment.

The Joint Effect of hOGG1, APE1, and ADPRT Polymorphisms and Cooking Oil Fumes on the Risk of Lung Adenocarcinoma in Chinese Non-Smoking Females

BackgroundThe human 8-oxoguanine DNA glycosylase 1 (hOGG1), apurinic/apyrimidinic endonuclease 1 (APE1), and adenosine diphosphate ribosyl transferase (ADPRT) genes play an important role in the DNA base excision repair pathway. Single nucleotide polymorphisms (SNPs) in critical genes are suspected to be associated with the risk of lung cancer. This study aimed to identify the association between the polymorphisms of hOGG1 Ser326Cys, APE1 Asp148Glu, and ADPRT Val762Ala, and the risk of lung adenocarcinoma in the non-smoking female population, and investigated the interaction between genetic polymorphisms and environmental exposure in lung adenocarcinoma.MethodsWe performed a hospital-based case-control study, including 410 lung adenocarcinoma patients and 410 cancer-free hospital control subjects who were matched for age. Each case and control was interviewed to collect information by well-trained interviewers. A total of 10 ml of venous blood was collected for genotype testing. Three polymorphisms were analyzed by the polymerase chain reaction-restriction fragment length polymorphism technique.ResultsWe found that individuals who were homozygous for the variant hOGG1 326Cys/Cys showed a significantly increased risk of lung adenocarcinoma (OR = 1.54; 95% CI: 1.01–2.36; P = 0.045). When the combined effect of variant alleles was analyzed, we found an increased OR of 1.89 (95% CI: 1.24–2.88, P = 0.003) for lung adenocarcinoma individuals with more than one homozygous variant allele. In stratified analyses, we found that the OR for the gene-environment interaction between Ser/Cys and Cys/Cys genotypes of hOGG1 codon 326 and cooking oil fumes for the risk of lung adenocarcinoma was 1.37 (95% CI: 0.77–2.44; P = 0.279) and 2.79 (95% CI: 1.50–5.18; P = 0.001), respectively.ConclusionsThe hOGG1 Ser326Cys polymorphism might be associated with the risk of lung adenocarcinoma in Chinese non-smoking females. Furthermore, there is a significant gene-environment association between cooking oil fumes and hOGG1 326 Cys/Cys genotype in lung adenocarcinoma among female non-smokers.

CD8‐β ADP‐ribosylation affects CD8+T‐cell function

The CD8αβ coreceptor is crucial for effective peptide: MHC-I recognition by the TCR of CD8(+) T cells. Adenosine diphosphate ribosyl transferase 2.2 (ART2.2) utilizes extracellular NAD(+) to transfer ADP-ribose to arginine residues of extracellular domains of surface proteins. Here, we show that in the presence of extracellular NAD(+) , ART2.2 caused ADP-ribosylation of CD8-β on murine CD8(+) T cells in vitro and in vivo. Treatment with NAD(+) prevented binding of anti-CD8-β mAb YTS156.7.7 but not of mAb H35-17.2, indicating that NAD(+) caused modification of certain epitopes and not a general loss of CD8-β. Loss of antibody binding was strictly dependent on ART2.2, because it was not observed on ART2-deficient T cells or in the presence of inhibitory anti-ART2.2 single-domain antibodies. ADP-ribosylation of CD8-β occurred during cell isolation, particularly when cells were isolated from CD38-deficient mice. Incubation of ART2-expressing, but not of ART2-deficient, OVA-specific CD8(+) T cells with NAD(+) interfered with binding of OVA257-264 :MHC-I tetramers. In line with this result, treatment of WT mice with NAD(+) resulted in reduced CD8(+) T-cell mediated cytotoxicity in vivo. We propose that ADP-ribosylation of CD8-β can regulate the coreceptor function of CD8 in the presence of elevated levels of extracellular NAD(+) .

Sirtuins in dermatology: applications for future research and therapeutics

Sirtuins are a family of seven proteins in humans (SIRT1-SIRT7) that are involved in multiple cellular processes relevant to dermatology. The role of sirtuins in other organ systems is established. However, the importance of these proteins in dermatology is less defined. Recently, sirtuins gained international attention because of their role as "longevity proteins" that may extend and enhance human life. Sirtuins function in the cell via histone deacetylase and/or adenosine diphosphate ribosyltransferase enzymatic activity that target histone and non-histone substrates, including transcription regulators, tumor suppressors, structural proteins, DNA repair proteins, cell signaling proteins, transport proteins, and enzymes. Sirtuins are involved in cellular pathways related to skin structure and function, including aging, ultraviolet-induced photoaging, inflammation, epigenetics, cancer, and a variety of cellular functions including cell cycle, DNA repair and proliferation. This review highlights sirtuin-related cellular pathways, therapeutics and pharmacological targets in atopic dermatitis, bullous dermatoses, collagen vascular disorders, psoriasis, systemic lupus erythematosus, hypertrophic and keloid scars, cutaneous infections, and non-melanoma and melanoma skin cancer. Also discussed is the role of sirtuins in the following genodermatoses: ataxia telangiectasia, Cowden's syndrome, dyskeratosis congenita, Rubenstein-Taybi, Werner syndrome, and xeroderma pigmentosum. The pathophysiology of these inherited diseases is not well understood, and sirtuin-related processes represent potential therapeutic targets for diseases lacking suitable alternative treatments. The goal of this review is to bring attention to the dermatology community, physicians, and scientists, the importance of sirtuins in dermatology and provide a foundation and impetus for future discussion, research and pharmacologic discovery.

Racial and tissue-specific cancer risk associated with PARP1 (ADPRT) Val762Ala polymorphism: a meta-analysis

The Val762Ala polymorphism poly [ADP-ribose] polymerase 1 (PARP1) gene [ADPRT (adenosine diphosphate ribosyltransferase) gene] affects enzymatic activity, which modulates cancer susceptibility among human populations. Individual data on 13,745 cases and 16,947 controls from 28 published case-control studies were re-evaluated. Odds ratios (OR) were estimated for ethnic group, cancer type, smoking joint effects and studies confined to the Hardy-Weinberg equilibrium. We applied subgroup, sensitivity and outlier analyses as well as the Bonferroni correction for multiple testing. The results show strong evidence that the variant (C) allele confers significant increased risk in the Chinese (OR 1.20-1.44, P < 0.0001-0.002), exacerbated by smoking (OR 1.66-2.53, P < 0.0001) and joint interaction with XRCC1 Arg399Gln (OR 1.39, P < 0.0001) as well as adjustment for tumor type (gastric carcinoma ORs 1.39-2.01, P < 0.0001). These significant effects were unaltered following conservative correction for multiple tests. By contrast, this procedure erased the protective significance in Caucasians, but not in two American subgroups, (i) those in the brain tumor category (0.77-0.79, P < 0.0001) and (ii) smokers in the dominant model (OR 0.86, P < 0.0001). These differential findings between the two ethnicities maybe correlated with significantly (P < 0.0001) greater allele frequency of the variant allele (C) among the Chinese compared to Caucasians. Our racial and tissue-specific summary estimates imply consideration of the Val762Ala polymorphism as candidate gene marker for screening cancer patients' best suited for PARP inhibitor therapy.

Poly(ADP-Ribose) Regulates Stress Responses and MicroRNA Activity in the Cytoplasm

Poly(ADP-ribose) is a major regulatory macromolecule in the nucleus, where it regulates transcription, chromosome structure, and DNA damage repair. Functions in the interphase cytoplasm are less understood. Here, we identify a requirement for poly(ADP-ribose) in the assembly of cytoplasmic stress granules, which accumulate RNA-binding proteins that regulate the translation and stability of mRNAs upon stress. We show that poly(ADP-ribose), six specific poly(ADP-ribose) polymerases, and two poly(ADP-ribose) glycohydrolase isoforms are stress granule components. A subset of stress granule proteins, including microRNA-binding Argonaute family members Ago1-4, are modified by poly(ADP-ribose), and such modification increases upon stress, a condition when both microRNA-mediated translational repression and microRNA-directed mRNA cleavage are relieved. Similar relief of repression is also observed upon overexpression of specific poly(ADP-ribose) polymerases or, conversely, upon knockdown of glycohydrolase. We conclude that poly(ADP-ribose) is a key regulator of posttranscriptional gene expression in the cytoplasm.

No associations of polymorphisms in ADPRT with hepatitis B virus clearance and hepatocellular carcinoma occurrence in a Korean population

The human adenosine diphosphate ribosyl transferase (ADPRT) gene might significantly affect cancer by encoding poly(ADP-ribose) polymerase 1 enzyme (PARP-1) and promoting an important role in cellular responses to DNA damage, genomic stabilization and regulation of tumor suppressor genes. We explored whether polymorphisms of ADPRT affect clearance of hepatitis B virus (HBV) infection or risk of hepatocellular carcinoma (HCC) occurrence in a Korean HBV cohort. Genotyping was performed in a total of 1066 subjects composed of 434 spontaneously recovered (SR) subjects as normal controls and 632 chronic carriers (CC) of HBV who were further classified into 325 patients with liver cirrhosis (LC)/chronic hepatitis (CH) and 307 patients with HCC. Logistic analyses of six common single nucleotide polymorphisms (SNP) and their haplotypes revealed that none of the polymorphisms were significantly associated with clearance of HBV infection and HCC occurrence, except for nominal evidence of association between haplotype 2 (ht2) with HBV clearance (P = 0.05). In the analysis of age of HCC occurrence which is an important factor in disease progression to HCC, results from Cox proportional hazards showed that none of the variants were significantly associated with onset age of HCC occurrence, although a nominal signal in ht4 (P = 0.03, but P(corr) > 0.05) was initially detected. Although ADPRT is an important gene for cellular responses and tumor regulations, our study provides evidence that ADPRT variations do not affect HBV clearance and HCC occurrence.