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1.  ARTD1/PARP1 negatively regulates glycolysis by inhibiting hexokinase 1 independent of NAD+ depletion 
Cell reports  2014;8(6):1819-1831.
Summary
ARTD1 (PARP1) is a key enzyme involved in DNA repair by synthesizing poly(ADP-ribose) (PAR) in response to strand breaks and plays an important role in cell death following excessive DNA damage. ARTD1-induced cell death is associated with NAD+ depletion and ATP loss, however the molecular mechanism of ARTD1-mediated energy collapse remains elusive. Using real-time metabolic measurements, we directly compared the effects of ARTD1 activation and direct NAD+ depletion. We found that ARTD1-mediated PAR synthesis, but not direct NAD+ depletion, resulted in a block to glycolysis and ATP loss. We then established a proteomics based PAR-interactome after DNA damage and identified hexokinase 1 (HK1) as a PAR binding protein. HK1 activity is suppressed following nuclear ARTD1 activation and binding by PAR. These findings help explain how prolonged activation of ARTD1 triggers energy collapse and cell death, revealing new insight on the importance of nucleus to mitochondria communication via ARTD1 activation.
doi:10.1016/j.celrep.2014.08.036
PMCID: PMC4177344  PMID: 25220464
PARP; DNA damage; metabolism; glycolysis; Hexokinase 1; NAD+; ATP; ARTD1
2.  Reprogramming cellular events by poly(ADP-ribose)-binding proteins 
Molecular aspects of medicine  2012;34(6):10.1016/j.mam.2012.12.005.
Poly(ADP-ribosyl)ation is a posttranslational modification catalyzed by the poly(ADP-ribose) polymerases (PARPs). These enzymes covalently modify glutamic, aspartic and lysine amino acid side chains of acceptor proteins by the sequential addition of ADP-ribose (ADPr) units. The poly(ADP-ribose) (pADPr) polymers formed alter the physico-chemical characteristics of the substrate with functional consequences on its biological activities. Recently, non-covalent binding to pADPr has emerged as a key mechanism to modulate and coordinate several intracellular pathways including the DNA damage response, protein stability and cell death. In this review, we describe the basis of non-covalent binding to pADPr that has led to the emerging concept of pADPr-responsive signaling pathways. This review emphasizes the structural elements and the modular strategies developed by pADPr-binding proteins to exert a fine-tuned control of a variety of pathways. Poly(ADP-ribosyl)ation reactions are highly regulated processes, both spatially and temporally, for which at least four specialized pADPr-binding modules accommodate different pADPr structures and reprogram protein functions. In this review, we highlight the role of well-characterized and newly discovered pADPr-binding modules in a diverse set of physiological functions.
doi:10.1016/j.mam.2012.12.005
PMCID: PMC3812366  PMID: 23268355
PARP; PARG; Poly(ADP-ribose); WWE; PBZ; Macro domain
3.  Ensconsin/Map7 promotes microtubule growth and centrosome separation in Drosophila neural stem cells 
The Journal of Cell Biology  2014;204(7):1111-1121.
Ensconsin cooperates with its binding partner, Kinesin-1, during interphase to trigger centrosome separation, but it promotes microtubule polymerization independently of Kinesin-1 to control spindle length during mitosis.
The mitotic spindle is crucial to achieve segregation of sister chromatids. To identify new mitotic spindle assembly regulators, we isolated 855 microtubule-associated proteins (MAPs) from Drosophila melanogaster mitotic or interphasic embryos. Using RNAi, we screened 96 poorly characterized genes in the Drosophila central nervous system to establish their possible role during spindle assembly. We found that Ensconsin/MAP7 mutant neuroblasts display shorter metaphase spindles, a defect caused by a reduced microtubule polymerization rate and enhanced by centrosome ablation. In agreement with a direct effect in regulating spindle length, Ensconsin overexpression triggered an increase in spindle length in S2 cells, whereas purified Ensconsin stimulated microtubule polymerization in vitro. Interestingly, ensc-null mutant flies also display defective centrosome separation and positioning during interphase, a phenotype also detected in kinesin-1 mutants. Collectively, our results suggest that Ensconsin cooperates with its binding partner Kinesin-1 during interphase to trigger centrosome separation. In addition, Ensconsin promotes microtubule polymerization during mitosis to control spindle length independent of Kinesin-1.
doi:10.1083/jcb.201311094
PMCID: PMC3971751  PMID: 24687279
4.  Polycomb repressive complex 2 contributes to DNA double-strand break repair 
Cell Cycle  2013;12(16):2675-2683.
Polycomb protein histone methyltransferase, enhancer of Zeste homolog 2 (EZH2), is frequently overexpressed in human malignancy and is implicated in cancer cell proliferation and invasion. However, it is largely unknown whether EZH2 has a role in modulating the DNA damage response. Here, we show that polycomb repressive complex 2 (PRC2) is recruited to sites of DNA damage. This recruitment is independent of histone 2A variant X (H2AX) and the PI-3-related kinases ATM and DNA-PKcs. We establish that PARP activity is required for retaining PRC2 at sites of DNA damage. Furthermore, depletion of EZH2 in cells decreases the efficiency of DSB repair and increases sensitivity of cells to gamma-irradiation. These data unravel a crucial role of PRC2 in determining cancer cellular sensitivity following DNA damage and suggest that therapeutic targeting of EZH2 activity might serve as a strategy for improving conventional chemotherapy in a given malignancy.
doi:10.4161/cc.25795
PMCID: PMC3865057  PMID: 23907130
PARP; DNA damage; polycomb group proteins; chromatin; epigenetics
5.  PARP activation regulates the RNA-binding protein NONO in the DNA damage response to DNA double-strand breaks 
Nucleic Acids Research  2012;40(20):10287-10301.
After the generation of DNA double-strand breaks (DSBs), poly(ADP-ribose) polymerase-1 (PARP-1) is one of the first proteins to be recruited and activated through its binding to the free DNA ends. Upon activation, PARP-1 uses NAD+ to generate large amounts of poly(ADP-ribose) (PAR), which facilitates the recruitment of DNA repair factors. Here, we identify the RNA-binding protein NONO, a partner protein of SFPQ, as a novel PAR-binding protein. The protein motif being primarily responsible for PAR-binding is the RNA recognition motif 1 (RRM1), which is also crucial for RNA-binding, highlighting a competition between RNA and PAR as they share the same binding site. Strikingly, the in vivo recruitment of NONO to DNA damage sites completely depends on PAR, generated by activated PARP-1. Furthermore, we show that upon PAR-dependent recruitment, NONO stimulates nonhomologous end joining (NHEJ) and represses homologous recombination (HR) in vivo. Our results therefore place NONO after PARP activation in the context of DNA DSB repair pathway decision. Understanding the mechanism of action of proteins that act in the same pathway as PARP-1 is crucial to shed more light onto the effect of interference on PAR-mediated pathways with PARP inhibitors, which have already reached phase III clinical trials but are until date poorly understood.
doi:10.1093/nar/gks798
PMCID: PMC3488241  PMID: 22941645
6.  Quantitative proteomic analysis of amphotericin B resistance in Leishmania infantum 
Graphical abstract
Highlights
•First large-scale quantitative proteomic study of amphotericin B resistance in Leishmania.•Identification of 97 differentially expressed proteins.•Upregulation of glycolysis and TCA cycle pathways.•Upregulation in reactive oxygen species scavenging and heat-shock proteins.
Amphotericin B (AmB) in its liposomal form is now considered as either first- or second-line treatment against Leishmania infections in different part of the world. Few cases of AmB resistance have been reported and resistance mechanisms toward AmB are still poorly understood. This paper reports a large-scale comparative proteomic study in the context of AmB resistance. Quantitative proteomics using stable isotope labeling of amino acids in cell culture (SILAC) was used to better characterize cytoplasmic and membrane-enriched (ME) proteomes of the in vitro generated Leishmania infantum AmB resistant mutant AmB1000.1. In total, 97 individual proteins were found as differentially expressed between the mutant and its parental sensitive strain (WT). More than half of these proteins were either metabolic enzymes or involved in transcription or translation processes. Key energetic pathways such as glycolysis and TCA cycle were up-regulated in the mutant. Interestingly, many proteins involved in reactive oxygen species (ROS) scavenging and heat-shock proteins were also up-regulated in the resistant mutant. This work provides a basis for further investigations to understand the roles of proteins differentially expressed in relation with AmB resistance.
doi:10.1016/j.ijpddr.2014.05.002
PMCID: PMC4095042  PMID: 25057462
Leishmania; Quantitative proteomics; Stable isotope labeling of amino acids in cell culture (SILAC); Amphotericin B; Drug resistance
7.  Crystallographic and Biochemical Analysis of the Mouse Poly(ADP-Ribose) Glycohydrolase 
PLoS ONE  2014;9(1):e86010.
Protein poly(ADP-ribosyl)ation (PARylation) regulates a number of important cellular processes. Poly(ADP-ribose) glycohydrolase (PARG) is the primary enzyme responsible for hydrolyzing the poly(ADP-ribose) (PAR) polymer in vivo. Here we report crystal structures of the mouse PARG (mPARG) catalytic domain, its complexes with ADP-ribose (ADPr) and a PARG inhibitor ADP-HPD, as well as four PARG catalytic residues mutants. With these structures and biochemical analysis of 20 mPARG mutants, we provide a structural basis for understanding how the PAR polymer is recognized and hydrolyzed by mPARG. The structures and activity complementation experiment also suggest how the N-terminal flexible peptide preceding the PARG catalytic domain may regulate the enzymatic activity of PARG. This study contributes to our understanding of PARG catalytic and regulatory mechanisms as well as the rational design of PARG inhibitors.
doi:10.1371/journal.pone.0086010
PMCID: PMC3897571  PMID: 24465839
8.  Proteomic and Genomic Analyses of Antimony Resistant Leishmania infantum Mutant 
PLoS ONE  2013;8(11):e81899.
Background
Antimonials remain the primary antileishmanial drugs in most developing countries. However, drug resistance to these compounds is increasing and our understanding of resistance mechanisms is partial.
Methods/Principal Findings
In the present study, quantitative proteomics using stable isotope labelling of amino acids in cell culture (SILAC) and genome next generation sequencing were used in order to better characterize in vitro generated Leishmania infantum antimony resistant mutant (Sb2000.1). Using the proteomic method, 58 proteins were found to be differentially regulated in Sb2000.1. The ABC transporter MRPA (ABCC3), a known marker of antimony resistance, was observed for the first time in a proteomic screen. Furthermore, transfection of its gene conferred antimony resistance in wild-type cells. Next generation sequencing revealed aneuploidy for 8 chromosomes in Sb2000.1. Moreover, specific amplified regions derived from chromosomes 17 and 23 were observed in Sb2000.1 and a single nucleotide polymorphism (SNP) was detected in a protein kinase (LinJ.33.1810-E629K).
Conclusion/Significance
Our results suggest that differentially expressed proteins, chromosome number variations (CNVs), specific gene amplification and SNPs are important features of antimony resistance in Leishmania.
doi:10.1371/journal.pone.0081899
PMCID: PMC3842243  PMID: 24312377
9.  Iduna Protects the Brain from Glutamate Excitotoxicity and Stroke by Interfering with Parthanatos 
Nature medicine  2011;17(6):692-699.
Glutamate acting on N-methyl-D-aspartate (NMDA) receptors plays an important role in neurodegenerative diseases and neuronal injury following stroke, through activation of poly(ADP-ribose) polymerase-1 and generation of the death molecule poly(ADP-ribose) (PAR) polymer. Here we identify Iduna, a novel NMDA receptor-induced survival gene that is neuroprotective against glutamate NMDA receptor mediated excitotoxicity both in vitro and in vivo and against stroke through interfering with PAR polymer induced cell death (parthanatos). Iduna’s protective effects are independent and downstream of PARP-1 activity. Iduna is a PAR polymer binding protein and mutations at the PAR polymer binding site abolishes the PAR binding activity of Iduna and attenuates its protective actions. Iduna is protective in vivo against NMDA-induced excitotoxicity and middle cerebral artery occlusion (MCAO)-induced stroke in mice. These results define Iduna as the first endogenous inhibitor of parthanatos. Interfering with PAR polymer signaling offers a new therapeutic strategy for the treatment of neurologic disorders.
doi:10.1038/nm.2387
PMCID: PMC3709257  PMID: 21602803
10.  Proteomic analysis of enriched lysosomes at early phase of camptothecin-induced apoptosis in human U-937 cells 
Journal of proteomics  2009;72(6):960-973.
A lysosomal pathway, characterized by partial rupture or labilization of lysosomal membranes and cathepsin activation, is evoked during camptothecin-induced apoptosis in human cancer cells, including human histiocytic lymphoma U-937 cells. These lysosomal events begin rapidly and simultaneously with mitochondrial permeabilization and caspase activation within 3 h after drug treatment. In this study, comparative and quantitative proteome analyses were performed to identify early changes in lysosomal protein expression/localization from U-937 cells undergoing apoptosis. In 2 independent experiments, among a total of more than 538 proteins putatively identified and quantitated by iTRAQ isobaric labeling and LC-ESI-MS/MS, 18 proteins were found to be upregulated and 9 downregulated in lysosomes purified from early apoptotic compared to control cells. Protein expression was validated by Western blotting on enriched lysosome fractions, and protein localization confirmed by fluorescence confocal microscopy of representative protein candidates, whose functions are associated with lysosomal membrane fluidity and dynamics. These include sterol-4-alpha-carboxylate 3-dehydrogenase (NSDHL), prosaposin (PSAP) and protein kinase C delta (PKC-δ). This comparative proteome analysis provides the basis for novel hypothesis and rationale functional experimentation, where the 3 validated candidate proteins are associated with lysosomal membrane fluidity and dynamics, particularly cholesterol, sphingolipid and glycosphingolipid metabolism.
doi:10.1016/j.jprot.2009.04.003
PMCID: PMC3708860  PMID: 19393779 CAMSID: cams3168
Apoptosis; Camptothecin; Lysosome; iTRAQ reagent; LC-ESI-MS/MS; Confocal Microscopy
11.  Failure of Iniparib to Inhibit Poly(ADP-ribose) Polymerase in Vitro 
Clinical Cancer Research  2012;18(6):1655-1662.
Purpose
Poly(ADP-ribose) polymerase (PARP) inhibitors are undergoing extensive clinical testing for their single-agent activity in homologous recombination- (HR-) deficient tumors and ability to enhance the action of certain DNA damaging agents. Compared to other PARP inhibitors in development, iniparib (4-iodo-3-nitrobenzamide) is notable for its simple structure and the reported ability of its intracellular metabolite 4-iodo-3-nitrosobenzamide to covalently inhibit PARP1 under cell-free conditions. The present preclinical studies were performed to compare the actions iniparib with the more extensively characterized PARP inhibitors olaparib and veliparib.
Experimental design
The abilities of iniparib, olaparib and veliparib to i) selectively induce apoptosis or inhibit colony formation in HR-deficient cell lines, ii) selectively sensitize HR-proficient cells to topoisomerase I poisons and iii) inhibit formation of poly(ADP-ribose) polymer in intact cells were compared.
Results
Consistent with earlier reports, olaparib and veliparib selectively induced apoptosis and inhibited colony formation in cells lacking BRCA2 or ATM. Moreover, like earlier-generation PARP inhibitors, olaparib and veliparib sensitized cells to the topoisomerase I poisons campto-thecin and topotecan. Finally, olaparib and veliparib inhibited formation of poly(ADP-ribose) polymer in intact cells. In contrast, iniparib exhibited little or no ability to selectively kill HR-deficient cells, sensitize cells to topoisomerase I poisons, or inhibit poly(ADP-ribose) polymer formation in situ. In further experiments, iniparib also failed to sensitize cells to cisplatin, gemcitabine or paclitaxel.
Conclusions
While iniparib kills normal and neoplastic cells at high (>40 µM) concentrations, its effects are unlikely to reflect PARP inhibition and should not be used to guide decisions about other PARP inhibitors.
doi:10.1158/1078-0432.CCR-11-2890
PMCID: PMC3306513  PMID: 22291137
Poly(ADP-ribose) polymerase; enzyme inhibitor; nicotinamide; topoisomerase; homologous recombination
12.  PARP-1 Modulation of mTOR Signaling in Response to a DNA Alkylating Agent 
PLoS ONE  2012;7(10):e47978.
Poly(ADP-ribose) polymerase-1 (PARP-1) is widely involved in cell death responses. Depending on the degree of injury and on cell type, PARP activation may lead to autophagy, apoptosis or necrosis. In HEK293 cells exposed to the alkylating agent N-methyl-N’-nitro-N’-nitrosoguanine (MNNG), we show that PARP-1 activation triggers a necrotic cell death response. The massive poly(ADP-ribose) (PAR) synthesis following PARP-1 activation leads to the modulation of mTORC1 pathway. Shortly after MNNG exposure, NAD+ and ATP levels decrease, while AMP levels drastically increase. We characterized at the molecular level the consequences of these altered nucleotide levels. First, AMP-activated protein kinase (AMPK) is activated and the mTORC1 pathway is inhibited by the phosphorylation of Raptor, in an attempt to preserve cellular energy. Phosphorylation of the mTORC1 target S6 is decreased as well as the phosphorylation of the mTORC2 component Rictor on Thr1135. Finally, Akt phosphorylation on Ser473 is lost and then, cell death by necrosis occurs. Inhibition of PARP-1 with the potent PARP inhibitor AG14361 prevents all of these events. Moreover, the antioxidant N-acetyl-L-cysteine (NAC) can also abrogate all the signaling events caused by MNNG exposure suggesting that reactive oxygen species (ROS) production is involved in PARP-1 activation and modulation of mTOR signaling. In this study, we show that PARP-1 activation and PAR synthesis affect the energetic status of cells, inhibit the mTORC1 signaling pathway and possibly modulate the mTORC2 complex affecting cell fate. These results provide new evidence that cell death by necrosis is orchestrated by the balance between several signaling pathways, and that PARP-1 and PAR take part in these events.
doi:10.1371/journal.pone.0047978
PMCID: PMC3480502  PMID: 23110147
13.  Quantitative proteomics profiling of the poly(ADP-ribose)-related response to genotoxic stress 
Nucleic Acids Research  2012;40(16):7788-7805.
Upon DNA damage induction, DNA-dependent poly(ADP-ribose) polymerases (PARPs) synthesize an anionic poly(ADP-ribose) (pADPr) scaffold to which several proteins bind with the subsequent formation of pADPr-associated multiprotein complexes. We have used a combination of affinity-purification methods and proteomics approaches to isolate these complexes and assess protein dynamics with respect to pADPr metabolism. As a first approach, we developed a substrate trapping strategy by which we demonstrate that a catalytically inactive Poly(ADP-ribose) glycohydrolase (PARG) mutant can act as a physiologically selective bait for the isolation of specific pADPr-binding proteins through its macrodomain-like domain. In addition to antibody-mediated affinity-purification methods, we used a pADPr macrodomain affinity resin to recover pADPr-binding proteins and their complexes. Second, we designed a time course experiment to explore the changes in the composition of pADPr-containing multiprotein complexes in response to alkylating DNA damage-mediated PARP activation. Spectral count clustering based on GeLC-MS/MS analysis was complemented with further analyses using high precision quantitative proteomics through isobaric tag for relative and absolute quantitation (iTRAQ)- and Stable isotope labeling by amino acids in cell culture (SILAC)-based proteomics. Here, we present a valuable resource in the interpretation of systems biology of the DNA damage response network in the context of poly(ADP-ribosyl)ation and provide a basis for subsequent investigations of pADPr-binding protein candidates.
doi:10.1093/nar/gks486
PMCID: PMC3439892  PMID: 22669911
14.  Poly (ADP-ribose) (PAR) Binding to Apoptosis-Inducing Factor Is Critical For PAR Polymerase-1-Dependent Cell Death (Parthanatos) 
Science signaling  2011;4(167):ra20.
The mitochondrial protein apoptosis-inducing factor (AIF) plays a pivotal role in poly(ADP-ribose) polymerase-1 (PARP-1)-mediated cell death (parthanatos), during which it is released from the mitochondria and translocates to the nucleus. Here, we show that AIF is a high affinity poly(ADP-ribose) (PAR)–binding protein and that PAR binding to AIF is required for parthanatos both in vitro and in vivo. AIF bound PAR at a site distinct from AIF’s DNA binding site and this interaction triggered AIF release from the cytosolic side of the mitochondrial outer membrane. Mutation of the PAR binding site in AIF did not affect its NADH oxidase activity, its ability to bind FAD or DNA, or its ability to induce nuclear condensation. However, this AIF mutant was not released from mitochondria and did not translocate to the nucleus or mediate cell death following PARP-1 activation. These results suggest a mechanism for PARP-1 to initiate AIF-mediated cell death and indicate that AIF’s bioenergetic cell survival-promoting functions are separate from its effects as a mitochondrially-derived death effector. Interference with the PAR-AIF interaction or PAR signaling may provide unique opportunities for preventing cell death following activation of PARP-1.
doi:10.1126/scisignal.2000902
PMCID: PMC3086524  PMID: 21467298
15.  CBX4-mediated SUMO modification regulates BMI1 recruitment at sites of DNA damage 
Nucleic Acids Research  2012;40(12):5497-5510.
Polycomb group (PcG) proteins are involved in epigenetic silencing where they function as major determinants of cell identity, stem cell pluripotency and the epigenetic gene silencing involved in cancer development. Recently numerous PcG proteins, including CBX4, have been shown to accumulate at sites of DNA damage. However, it remains unclear whether or not CBX4 or its E3 sumo ligase activity is directly involved in the DNA damage response (DDR). Here we define a novel role for CBX4 as an early DDR protein that mediates SUMO conjugation at sites of DNA lesions. DNA damage stimulates sumoylation of BMI1 by CBX4 at lysine 88, which is required for the accumulation of BMI1 at DNA damage sites. Moreover, we establish that CBX4 recruitment to the sites of laser micro-irradiation-induced DNA damage requires PARP activity but does not require H2AX, RNF8, BMI1 nor PI-3-related kinases. The importance of CBX4 in the DDR was confirmed by the depletion of CBX4, which resulted in decreased cellular resistance to ionizing radiation. Our results reveal a direct role for CBX4 in the DDR pathway.
doi:10.1093/nar/gks222
PMCID: PMC3384338  PMID: 22402492
16.  A Key Role for Poly(ADP-Ribose) Polymerase 3 in Ectodermal Specification and Neural Crest Development 
PLoS ONE  2011;6(1):e15834.
Background
The PARP family member poly(ADP-ribose) polymerase 3 (PARP3) is structurally related to the well characterized PARP1 that orchestrates cellular responses to DNA strand breaks and cell death by the synthesis of poly(ADP-ribose). In contrast to PARP1 and PARP2, the functions of PARP3 are undefined. Here, we reveal critical functions for PARP3 during vertebrate development.
Principal Findings
We have used several in vitro and in vivo approaches to examine the possible functions of PARP3 as a transcriptional regulator, a function suggested from its previously reported association with several Polycomb group (PcG) proteins. We demonstrate that PARP3 gene occupancy in the human neuroblastoma cell line SK-N-SH occurs preferentially with developmental genes regulating cell fate specification, tissue patterning, craniofacial development and neurogenesis. Addressing the significance of this association during zebrafish development, we show that morpholino oligonucleotide-directed inhibition of parp3 expression in zebrafish impairs the expression of the neural crest cell specifier sox9a and of dlx3b/dlx4b, the formation of cranial sensory placodes, inner ears and pectoral fins. It delays pigmentation and severely impedes the development of the median fin fold and tail bud.
Conclusion
Our findings demonstrate that Parp3 is crucial in the early stages of zebrafish development, possibly by exerting its transcriptional regulatory functions as early as during the specification of the neural plate border.
doi:10.1371/journal.pone.0015834
PMCID: PMC3022025  PMID: 21264220
17.  PARP inhibition: PARP1 and beyond 
Nature reviews. Cancer  2010;10(4):293-301.
Recent findings have thrust poly(ADP-ribose) polymerases (PARPs) into the limelight as potential chemotherapeutic targets. To provide a framework for understanding these recent observations, we review what is known about the structures and functions of the family of PARP enzymes, and then outline a series of questions that should be addressed to guide the rational development of PARP inhibitors as anticancer agents.
doi:10.1038/nrc2812
PMCID: PMC2910902  PMID: 20200537
18.  Investigation of PARP-1, PARP-2, and PARG interactomes by affinity-purification mass spectrometry 
Proteome Science  2010;8:22.
Background
Poly(ADP-ribose) polymerases (PARPs) catalyze the formation of poly(ADP-ribose) (pADPr), a post-translational modification involved in several important biological processes, namely surveillance of genome integrity, cell cycle progression, initiation of the DNA damage response, apoptosis, and regulation of transcription. Poly(ADP-ribose) glycohydrolase (PARG), on the other hand, catabolizes pADPr and thereby accounts for the transient nature of poly(ADP-ribosyl)ation. Our investigation of the interactomes of PARP-1, PARP-2, and PARG by affinity-purification mass spectrometry (AP-MS) aimed, on the one hand, to confirm current knowledge on these interactomes and, on the other hand, to discover new protein partners which could offer insights into PARPs and PARG functions.
Results
PARP-1, PARP-2, and PARG were immunoprecipitated from human cells, and pulled-down proteins were separated by gel electrophoresis prior to in-gel trypsin digestion. Peptides were identified by tandem mass spectrometry. Our AP-MS experiments resulted in the identifications of 179 interactions, 139 of which are novel interactions. Gene Ontology analysis of the identified protein interactors points to five biological processes in which PARP-1, PARP-2 and PARG may be involved: RNA metabolism for PARP-1, PARP-2 and PARG; DNA repair and apoptosis for PARP-1 and PARP-2; and glycolysis and cell cycle for PARP-1.
Conclusions
This study reveals several novel protein partners for PARP-1, PARP-2 and PARG. It provides a global view of the interactomes of these proteins as well as a roadmap to establish the systems biology of poly(ADP-ribose) metabolism.
doi:10.1186/1477-5956-8-22
PMCID: PMC2861645  PMID: 20388209
19.  A novel approach to denoising ion trap tandem mass spectra 
Proteome Science  2009;7:9.
Background
Mass spectrometers can produce a large number of tandem mass spectra. They are unfortunately noise-contaminated. Noises can affect the quality of tandem mass spectra and thus increase the false positives and false negatives in the peptide identification. Therefore, it is appealing to develop an approach to denoising tandem mass spectra.
Results
We propose a novel approach to denoising tandem mass spectra. The proposed approach consists of two modules: spectral peak intensity adjustment and intensity local maximum extraction. In the spectral peak intensity adjustment module, we introduce five features to describe the quality of each peak. Based on these features, a score is calculated for each peak and is used to adjust its intensity. As a result, the intensity will be adjusted to a local maximum if a peak is a signal peak, and it will be decreased if the peak is a noisy one. The second module uses a morphological reconstruction filter to remove the peaks whose intensities are not the local maxima of the spectrum. Experiments have been conducted on two ion trap tandem mass spectral datasets: ISB and TOV. Experimental results show that our algorithm can remove about 69% of the peaks of a spectrum. At the same time, the number of spectra that can be identified by Mascot algorithm increases by 31.23% and 14.12% for the two tandem mass spectra datasets, respectively.
Conclusion
The proposed denoising algorithm can be integrated into current popular peptide identification algorithms such as Mascot to improve the reliability of assigning peptides to spectra.
Availability of the software
The software created from this work is available upon request.
doi:10.1186/1477-5956-7-9
PMCID: PMC2670284  PMID: 19292921
20.  Quality assessment of tandem mass spectra using support vector machine (SVM) 
BMC Bioinformatics  2009;10(Suppl 1):S49.
Background
Tandem mass spectrometry has become particularly useful for the rapid identification and characterization of protein components of complex biological mixtures. Powerful database search methods have been developed for the peptide identification, such as SEQUEST and MASCOT, which are implemented by comparing the mass spectra obtained from unknown proteins or peptides with theoretically predicted spectra derived from protein databases. However, the majority of spectra generated from a mass spectrometry experiment are of too poor quality to be interpreted while some of spectra with high quality cannot be interpreted by one method but perhaps by others. Hence a filtering algorithm that removes those spectra with poor quality prior to the database search is appealing.
Results
This paper proposes a support vector machine (SVM) based approach to assess the quality of tandem mass spectra. Each mass spectrum is mapping into the 16 proposed features to describe its quality. Based the results from SEQUEST, four SVM classifiers with the input of the 16 features are trained and tested on ISB data and TOV data, respectively. The superior performance of the proposed SVM classifiers is illustrated both by the comparison with the existing classifiers and by the validation in terms of MASCOT search results.
Conclusion
The proposed method can be employed to effectively remove the poor quality spectra before the spectral searching, and also to find the more peptides or post-translational peptides from spectra with high quality using different search engines or de novo method.
doi:10.1186/1471-2105-10-S1-S49
PMCID: PMC2648784  PMID: 19208151
21.  Proteome-wide identification of poly(ADP-ribose) binding proteins and poly(ADP-ribose)-associated protein complexes 
Nucleic Acids Research  2008;36(22):6959-6976.
Poly(ADP-ribose) (pADPr) is a polymer assembled from the enzymatic polymerization of the ADP-ribosyl moiety of NAD by poly(ADP-ribose) polymerases (PARPs). The dynamic turnover of pADPr within the cell is essential for a number of cellular processes including progression through the cell cycle, DNA repair and the maintenance of genomic integrity, and apoptosis. In spite of the considerable advances in the knowledge of the physiological conditions modulated by poly(ADP-ribosyl)ation reactions, and notwithstanding the fact that pADPr can play a role of mediator in a wide spectrum of biological processes, few pADPr binding proteins have been identified so far. In this study, refined in silico prediction of pADPr binding proteins and large-scale mass spectrometry-based proteome analysis of pADPr binding proteins were used to establish a comprehensive repertoire of pADPr-associated proteins. Visualization and modeling of these pADPr-associated proteins in networks not only reflect the widespread involvement of poly(ADP-ribosyl)ation in several pathways but also identify protein targets that could shed new light on the regulatory functions of pADPr in normal physiological conditions as well as after exposure to genotoxic stimuli.
doi:10.1093/nar/gkn771
PMCID: PMC2602769  PMID: 18981049
22.  Human Papillomavirus E1 Helicase Interacts with the WD Repeat Protein p80 To Promote Maintenance of the Viral Genome in Keratinocytes▿  
Journal of Virology  2007;82(3):1271-1283.
Due to the limited coding capacity of their small genomes, human papillomaviruses (HPV) rely extensively on host factors for the completion of their life cycles. Accordingly, most HPV proteins, including the replicative helicase E1, engage in multiple protein interactions. The fact that conserved regions of E1 have not yet been ascribed a function prompted us to use tandem affinity protein purification (TAP) coupled to mass spectrometry to identify novel targets of this helicase. This method led to the discovery of a novel interaction between the N-terminal 40 amino acids of HPV type 11 (HPV11) E1 and the cellular WD repeat protein p80 (WDR48). We found that interaction with p80 is conserved among E1 proteins from anogenital HPV but not among cutaneous or animal types. Colocalization studies showed that E1 can redistribute p80 from the cytoplasm to the nucleus in a manner that is dependent on the E1 nuclear localization signal. Three amino acid substitutions in E1 proteins from HPV11 and -31 were identified that abrogate binding to p80 and its relocalization to the nucleus. In HPV31 E1, these substitutions reduced but did not completely abolish transient viral DNA replication. HPV31 genomes encoding two of the mutant E1 proteins were not maintained as episomes in immortalized primary keratinocytes, whereas one encoding the third mutant protein was maintained at a very low copy number. These findings suggest that the interaction of E1 with p80 is required for efficient maintenance of the viral episome in undifferentiated keratinocytes.
doi:10.1128/JVI.01405-07
PMCID: PMC2224424  PMID: 18032488
23.  Quality assessment of peptide tandem mass spectra 
BMC Bioinformatics  2008;9(Suppl 6):S13.
Background
Tandem mass spectrometry has emerged as a cornerstone of high throughput proteomic studies owing in part to various high throughput search engines which are used to interpret these tandem mass spectra. However, majority of experimental tandem mass spectra cannot be interpreted by any existing methods. There are many reasons why this happens. However, one of the most important reasons is that majority of experimental spectra are of too poor quality to be interpretable. It wastes time to interpret these "uninterpretable" spectra by any methods. On the other hand, some spectra of high quality are not able to get a score high enough to be interpreted by existing search engines because there are many similar peptides in the searched database. However, such spectra may be good enough to be interpreted by de novo methods or manually verifying methods. Therefore, it is worth in developing a method for assessing spectral quality, which can used for filtering the spectra of poor quality before any interpretation attempts or for finding the most potential candidates for de novo methods or manually verifying methods.
Results
This paper develops a novel method to assess the quality of tandem mass spectra, which can eliminate majority of poor quality spectra while losing very minority of high quality spectra. First, a number of features are proposed to describe the quality of tandem mass spectra. The proposed method maps each tandem spectrum into a feature vector. Then Fisher linear discriminant analysis (FLDA) is employed to construct the classifier (the filter) which discriminates the high quality spectra from the poor quality ones. The proposed method has been tested on two tandem mass spectra datasets acquired by ion trap mass spectrometers.
Conclusion
Computational experiments illustrate that the proposed method outperforms the existing ones. The proposed method is generic, and is expected to be applicable to assessing the quality of spectra acquired by instruments other than ion trap mass spectrometers.
doi:10.1186/1471-2105-9-S6-S13
PMCID: PMC2423436  PMID: 18541048
24.  Influence of Duration of Focal Cerebral Ischemia and Neuronal Nitric Oxide Synthase on Translocation of Apoptosis-Inducing Factor to the Nucleus 
Neuroscience  2006;144(1):56-65.
Translocation of apoptosis-inducing factor (AIF) from the mitochondria to the nucleus can play a major role in neuronal death elicited by oxidant stress. The time course of nuclear translocation of AIF after experimental stroke may vary with the severity of injury and may be accelerated by oxidant stress associated with reperfusion and nitric oxide (NO) production. Western immunoblots of AIF on nuclear fractions of ischemic hemisphere of male mice showed no significant increase with 1 hour of middle cerebral artery occlusion and no reperfusion, whereas increases were detectable after 6 and 24 hours of permanent ischemia. However, as little as 20 minutes of reperfusion after 1 hour of middle cerebral artery occlusion resulted in an increase in nuclear AIF coincident with an increase in poly(ADP-ribose) polymer (PAR) formation. Further nuclear AIF accumulation was seen at 6 and 24 hours of reperfusion. In contrast, 20 minutes of reperfusion after 2 hours of occlusion did not increase nuclear AIF. In this case, nuclear AIF became detectable at 6 and 24 hours of reperfusion. With brief occlusion of 30 minute duration, nuclear AIF remained undetectable at both 20 minutes and 6 hours and became evident only after 24 hours of reperfusion. Inhibition of neuronal NO synthase attenuated formation of PAR and nuclear AIF accumulation. Gene deletion of neuronal NO synthase also attenuated nuclear AIF accumulation. Therefore, reperfusion accelerates AIF translocation to the nucleus when focal ischemia is of moderate duration (1 hour), but is markedly delayed after brief ischemia (30 minutes). Nuclear translocation of AIF eventually occurs with prolonged focal ischemia with or without reperfusion. Neuronally-derived NO is a major factor contributing to nuclear AIF accumulation after stroke.
doi:10.1016/j.neuroscience.2006.08.065
PMCID: PMC1876769  PMID: 17049179
apoptosis; middle cerebral artery; mouse; poly(ADP-ribose); reperfusion; stroke
25.  PARPs database: A LIMS systems for protein-protein interaction data mining or laboratory information management system 
BMC Bioinformatics  2007;8:483.
Background
In the "post-genome" era, mass spectrometry (MS) has become an important method for the analysis of proteins and the rapid advancement of this technique, in combination with other proteomics methods, results in an increasing amount of proteome data. This data must be archived and analysed using specialized bioinformatics tools.
Description
We herein describe "PARPs database," a data analysis and management pipeline for liquid chromatography tandem mass spectrometry (LC-MS/MS) proteomics. PARPs database is a web-based tool whose features include experiment annotation, protein database searching, protein sequence management, as well as data-mining of the peptides and proteins identified.
Conclusion
Using this pipeline, we have successfully identified several interactions of biological significance between PARP-1 and other proteins, namely RFC-1, 2, 3, 4 and 5.
doi:10.1186/1471-2105-8-483
PMCID: PMC2266781  PMID: 18093328

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