Inhibitor Of ADP-ribosyltransferase Research Articles

NAD Precursors, Mitochondria Targeting Compounds and ADP-Ribosylation Inhibitors in Treatment of Inflammatory Diseases and Cancer.

Mitochondrial dysfunction and oxidative stress are prominent features of a plethora of human disorders. Dysregulation of mitochondrial functions represents a common pathogenic mechanism of diseases such as neurodegenerative disorders and cancer. The maintenance of the Nicotinamide adenine dinucleotide (NAD+) pool, and a positive NAD+/NADH ratio, are essential for mitochondrial and cell functions. The synthesis and degradation of NAD+ and transport of its key intermediates among cell compartments play an important role in maintaining optimal NAD levels, for the regulation of NAD+-utilizing enzymes, such as sirtuins (Sirt), poly-ADP-ribose polymerases, and CD38/157 enzymes, either intracellularly as well as extracellularly. In this review, we present and discuss the links between NAD+, NAD+-consuming enzymes, mitochondria functions, and diseases. Attempts to treat various diseases with supplementation of NAD+ cycling intermediates and inhibitors of sirtuins and ADP-ribosyl transferases may highlight a possible therapeutic approach for therapy of cancer and neurodegenerative diseases.

ADP-ribosyltransferases, an update on function and nomenclature.

ADP-ribosylation, a modification of proteins, nucleic acids, and metabolites, confers broad functions, including roles in stress responses elicited, for example, by DNA damage and viral infection and is involved in intra- and extracellular signaling, chromatin and transcriptional regulation, protein biosynthesis, and cell death. ADP-ribosylation is catalyzed by ADP-ribosyltransferases (ARTs), which transfer ADP-ribose from NAD+ onto substrates. The modification, which occurs as mono- or poly-ADP-ribosylation, is reversible due to the action of different ADP-ribosylhydrolases. Importantly, inhibitors of ARTs are approved or are being developed for clinical use. Moreover, ADP-ribosylhydrolases are being assessed as therapeutic targets, foremost as antiviral drugs and for oncological indications. Due to the development of novel reagents and major technological advances that allow the study of ADP-ribosylation in unprecedented detail, an increasing number of cellular processes and pathways are being identified that are regulated by ADP-ribosylation. In addition, characterization of biochemical and structural aspects of the ARTs and their catalytic activities have expanded our understanding of this protein family. This increased knowledge requires that a common nomenclature be used to describe the relevant enzymes. Therefore, in this viewpoint, we propose an updated and broadly supported nomenclature for mammalian ARTs that will facilitate future discussions when addressing the biochemistry and biology of ADP-ribosylation. This is combined with a brief description of the main functions of mammalian ARTs to illustrate the increasing diversity of mono- and poly-ADP-ribose mediated cellular processes.

Single-Peptide TR-FRET Detection Platform for Cysteine-Specific Post-Translational Modifications.

Post-translational modifications (PTMs) are one of the most important regulatory mechanisms in cells, and they play key roles in cell signaling both in health and disease. PTM catalyzing enzymes have become significant drug targets, and therefore, tremendous interest has been focused on the development of broad-scale assays to monitor several different PTMs with a single detection platform. Most of the current methodologies suffer from low throughput or rely on antibody recognition, increasing the assay costs, and decreasing the multifunctionality of the assay. Thus, we have developed a sensitive time-resolved Förster resonance energy transfer (TR-FRET) detection method for PTMs of cysteine residues using a single-peptide approach performed in a 384-well format. In the developed assay, the enzyme-specific biotinylated substrate peptide is post-translationally modified at the cysteine residue, preventing the subsequent thiol coupling with a reactive AlexaFluor 680 acceptor dye. In the absence of enzymatic activity, increase in the TR-FRET signal between the biotin-bound Eu(III)-labeled streptavidin donor and the cysteine-coupled AlexaFluor 680 acceptor dye is observed. We demonstrate the detection concept with cysteine modifying S-nitrosylation and ADP-ribosylation reactions using a chemical nitric oxide donor S-nitrosoglutathione and enzymatic ADP-ribosyltransferase PtxS1-subunit of pertussis toxin, respectively. As a proof of concept, three peptide substrates derived from the small GTPase K-Ras and the inhibitory α-subunit of the heterotrimeric G-protein Gαi showed expected functionality in both chemical and enzymatic assays. Measurements yielded signal-to-background ratios of 28.7, 33.0, and 8.7 between the modified and the nonmodified substrates for the three peptides in the S-nitrosylation assay, 5.8 in the NAD+ hydrolysis assay, and 6.8 in the enzymatic ADP-ribosyltransferase inhibitor dose–response assay. The developed antibody-free assay for cysteine-modifying enzymes provides a detection platform with low nanomolar peptide substrate consumption, and the assay is potentially applicable to investigate various cysteine-modifying enzymes in a high throughput compatible format.

Structure–activity relationships for inhibitors of Pseudomonas aeruginosa exoenzyme S ADP-ribosyltransferase activity

During infection, the Gram-negative opportunistic pathogen Pseudomonas aeruginosa employs its type III secretion system to translocate the toxin exoenzyme S (ExoS) into the eukaryotic host cell cytoplasm. ExoS is an essential in vivo virulence factor that enables P. aeruginosa to avoid phagocytosis and eventually kill the host cell. ExoS elicits its pathogenicity mainly via ADP-ribosyltransferase (ADPRT) activity. We recently identified a new class of ExoS ADPRT inhibitors with in vitro IC50 of around 20 μM in an enzymatic assay using a recombinant ExoS ADPRT domain. Herein, we report structure–activity relationships of this compound class by comparing a total of 51 compounds based on a thieno [2,3-d]pyrimidin-4(3H)-one and 4-oxo-3,4-dihydroquinazoline scaffolds. Improved inhibitors with in vitro IC50 values of 6 μM were identified. Importantly, we demonstrated that the most potent inhibitors block ADPRT activity of native full-length ExoS secreted by viable P. aeruginosa with an IC50 value of 1.3 μM in an enzymatic assay. This compound class holds promise as starting point for development of novel antibacterial agents.

Chemical proteomics reveals ADP-ribosylation of small GTPases during oxidative stress.

ADP-ribosylation is a post-translational modification that is known to be involved in cellular homeostasis and stress but has been challenging to analyze biochemically. To facilitate the detection of ADP-ribosylated proteins, we show that an alkyne-adenosine analog, N6-propargyl adenosine (N6pA), is metabolically incorporated in mammalian cells and enables fluorescence detection and proteomic analysis of ADP-ribosylated proteins. Notably, our analysis of N6pA-labeled proteins that are upregulated by oxidative stress revealed differential ADP-ribosylation of small GTPases. We discovered that oxidative stress induced ADP-ribosylation of Hras on Cys181 and Cys184 in the C-terminal hypervariable region, which are normally S-fatty-acylated. Downstream Hras signaling is impaired by ADP-ribosylation during oxidative stress, but is rescued by ADP-ribosyltransferase inhibitors. Our study demonstrates that ADP-ribosylation of small GTPases not only is mediated by bacterial toxins but is endogenously regulated in mammalian cells. N6pA provides a useful tool to characterize ADP-ribosylated proteins and their regulatory mechanisms in cells.

Auto ADP‐ribosylation of NarE, aNeisseria meningitidisADP‐ribosyltransferase, regulates its catalytic activities

NarE is an arginine-specific mono-ADP-ribosyltransferase identified in Neisseria meningitidis that requires the presence of iron in a structured cluster for its enzymatic activities. In this study, we show that NarE can perform auto-ADP-ribosylation. This automodification occurred in a time- and NAD-concentration-dependent manner; was inhibited by novobiocin, an ADP-ribosyltransferase inhibitor; and did not occur when NarE was heat inactivated. No reduction in incorporation was evidenced in the presence of high concentrations of ATP, GTP, ADP-ribose, or nicotinamide, which inhibits NAD-glycohydrolase, impeding the formation of free ADP-ribose. Based on the electrophoretic profile of NarE on auto-ADP-ribosylation and on the results of mutagenesis and mass spectrometry analysis, the auto-ADP-ribosylation appeared to be restricted to the addition of a single ADP-ribose. Chemical stability experiments showed that the ADP-ribosyl linkage was sensitive to hydroxylamine, which breaks ADP-ribose-arginine bonds. Site-directed mutagenesis suggested that the auto-ADP-ribosylation site occurred preferentially on the R(7) residue, which is located in the region I of the ADP-ribosyltransferase family. After auto-ADP-ribosylation, NarE showed a reduction in ADP-ribosyltransferase activity, while NAD-glycohydrolase activity was increased. Overall, our findings provide evidence for a novel intramolecular mechanism used by NarE to regulate its enzymatic activities.

Tankyrases as drug targets

Tankyrase 1 and tankyrase 2 are poly(ADP-ribosyl)ases that are distinguishable from other members of the enzyme family by the structural features of the catalytic domain, and the presence of a sterile α-motif multimerization domain and an ankyrin repeat protein-interaction domain. Tankyrases are implicated in a multitude of cellular functions, including telomere homeostasis, mitotic spindle formation, vesicle transport linked to glucose metabolism, Wnt-β-catenin signaling, and viral replication. In these processes, tankyrases interact with target proteins, catalyze poly(ADP-ribosyl)ation, and regulate protein interactions and stability. The proposed roles of tankyrases in disease-relevant cellular processes have made them attractive drug targets. Recently, several inhibitors have been identified. The selectivity and potency of these small molecules can be rationalized by how they fit within the NAD(+)-binding groove of the catalytic domain. Some molecules bind to the nicotinamide subsite, such as generic diphtheria toxin-like ADP-ribosyltransferase inhibitors, whereas others bind to a distinct adenosine subsite that diverges from other diphtheria toxin-like ADP-ribosyltransferases and confers specificity. A highly potent dual-site inhibitor is also available. Within the last few years, tankyrase inhibitors have proved to be useful chemical probes and potential lead compounds, especially for specific cancers.

From cosubstrate similarity to inhibitor diversity—inhibitors of ADP-ribosyltransferases from kinase inhibitor screening

ADP-ribosyltransferases (ADP-RTs) use NAD(+) to transfer an ADP-ribosyl group to target proteins. Although some ADP-RTs are bacterial toxins only few inhibitors are known. Here we present the development of fluorescence-based assays and a focussed library screening using kinase inhibitors as a new approach towards inhibitors of ADP-RTs. Different screening setups were established using surrogate small molecule substrates or the quantitation of the cofactor NAD(+). Proof-of-principle screening experiments were performed using a kinase inhibitor library in order to target the NAD(+) binding pockets. This led to the discovery of structurally different lead inhibitors for the mono-ADP-ribosyltransferases Mosquitocidal toxin (MTX) from Bacillus sphaericus SSII-1, C3bot toxin from Clostridium botulinum and CDTa from Clostridium difficile. The interaction of the inhibitors with the toxin proteins was analyzed by means of docking and binding free energy calculations. Binding at the nicotinamide subpocket, which shows a significant difference in the three enzymes, is used to explain the selectivity of the identified inhibitors and offers an opportunity for further development of potent and selective inhibitors.

Crystal Structure of the Catalytic Domain of Human PARP2 in Complex with PARP Inhibitor ABT-888

Poly-ADP-ribose polymerases (PARPs) catalyze transfer of ADP-ribose from NAD(+) to specific residues in their substrate proteins or to growing ADP-ribose chains. PARP activity is involved in processes such as chromatin remodeling, transcription control, and DNA repair. Inhibitors of PARP activity may be useful in cancer therapy. PARP2 is the family member that is most similar to PARP1, and the two can act together as heterodimers. We used X-ray crystallography to determine two structures of the catalytic domain of human PARP2: the complexes with PARP inhibitors 3-aminobenzamide and ABT-888. These results contribute to our understanding of structural features and compound properties that can be employed to develop selective inhibitors of human ADP-ribosyltransferases.

Mechanism of rat mesenteric arterial KATP channel activation by 14,15-epoxyeicosatrienoic acid

Recently, we reported that 11,12-epoxyeicosatrienoic acid (11,12-EET) potently activates rat mesenteric arterial ATP-sensitive K(+) (K(ATP)) channels and produces significant vasodilation through protein kinase A-dependent mechanisms. In this study, we tried to further delineate the signaling steps involved in the activation of vascular K(ATP) channels by EETs. Whole cell patch-clamp recordings [0.1 mM ATP in the pipette, holding potential (HP) = 0 mV and testing potential (TP) = -100 mV] in freshly isolated rat mesenteric smooth muscle cells showed small glibenclamide-sensitive K(ATP) currents (19.0 +/- 7.9 pA, n = 5) that increased 6.9-fold on exposure to 5 microM 14,15-EET (132.0 +/- 29.0 pA, n = 7, P < 0.05 vs. control). With 1 mM ATP in the pipette solution, K(ATP) currents (HP = 0 mV and TP = -100 mV) were increased 3.5-fold on exposure to 1 microM 14,15-EET (57.5 +/- 14.3 pA, n = 9, P < 0.05 vs. baseline). In the presence of 100 nM iberiotoxin, 1 microM 14,15-EET hyperpolarized the membrane potential from -20.5 +/- 0.9 mV at baseline to -27.1 +/- 3.0 mV (n = 6 for both, P < 0.05 vs. baseline), and the EET effects were significantly reversed by 10 microM glibenclamide (-21.8 +/- 1.4 mV, n = 6, P < 0.05 vs. EET). Incubation with 5 microM 14,15-epoxyeicosa-5(Z)-enoic acid (14,15-EEZE), a 14,15-EET antagonist, abolished the 14,15-EET effects (31.0 +/- 11.8 pA, n = 5, P < 0.05 vs. 14,15-EET, P = not significant vs. control). The 14,15-EET effects were inhibited by inclusion of anti-G(s)alpha antibody (1:500 dilution) but not by control IgG in the pipette solution. The effects of 14,15-EET were mimicked by cholera toxin (100 ng/ml), an exogenous ADP-ribosyltransferase. Treatment with the ADP-ribosyltransferase inhibitors 3-aminobenzamide (1 mM) or m-iodobenzylguanidine (100 microM) abrogated the effects of 14,15-EET on K(ATP) currents. These results were corroborated by vasodilation studies. 14,15-EET dose-dependently dilated isolated small mesenteric arteries, and this was significantly attenuated by treatment with 14,15-EEZE or 3-aminobenzamide. These results suggest that 14,15-EET activates vascular K(ATP) channels through ADP-ribosylation of G(s)alpha.

Regulation of BK(Ca) channels expressed in human embryonic kidney 293 cells by epoxyeicosatrienoic acid.

Epoxyeicosatrienoic acids (EETs) are arachidonic acid metabolites of cytochrome P450 monooxygenase, which are released from endothelial cells and dilate arteries. Dilation seems to be caused by activation of large-conductance Ca2+ activated K+ channels (BK(Ca)) leading to membrane hyperpolarization. Previous studies suggest that EETs activate BK(Ca) channels via ADP-ribosylation of the G protein Galphas with a subsequent membrane-delimited action on the channel [Circ Res 78:415-423, 1996; 80:877-884, 1997; 85:349-356, 1999]. The present study examined whether this pathway is present in human embryonic kidney (HEK) 293 cells when the BK(Ca) alpha-subunit (cslo-alpha) is expressed without the beta-subunit. 11,12-EET increased outward K+ current in whole-cell recordings of HEK293 cells. In cell-attached patches, 11,12-EET also increased the activity of cslo-alpha channels without affecting unitary conductance. This action was mimicked by cholera toxin. The ADP-ribosyltransferase inhibitors 3-aminobenzamide and m-iodobenxylguanidine blocked the stimulatory effect of 11,12-EET. In inside-out patches 11,12-EET was without effect on channel activity unless GTP was included in the bathing solution. GTP and GTPgammaS alone also activated cslo-alpha channels. Dialysis of cells with anti-Galphas antibody completely blocked the activation of cslo-alpha channels by 11,12-EET, whereas anti-Galphai/o and anti-Gbetagamma antibodies were without effect. The protein kinase A inhibitor KT5720 and the adenylate cyclase inhibitor SQ22536 did not reduce the stimulatory effect of 11,12-EET on cslo-alpha channels in cell-attached patches. These data suggest that EET leads to Galphas-dependent activation of the cslo-alpha subunits expressed in HEK293 cells and that the cslo-beta subunit is not required.

Effects of nitric oxide release in an area of the chick forebrain which is essential for early learning

Extracellular recording techniques were used to study the effects of the nitric oxide releasing agents diethylamine-NO (DEA-NO) and S-nitroso- N-acetyl-penicillamine (SNAP) on synaptic transmission in the intermediate and medial part of the hyperstriatum ventrale (IMHV), a part of the domestic chick forebrain that is essential for some forms of early learning. The field response evoked by local electrical stimulation was recorded in the IMHV in an in vitro slice preparation. DEA-NO (100–200 μM) significantly depressed the field response in a concentration dependent and reversible manner. However, the depression produced by perfusion with 400 μM DEA-NO, was not reversed following washout of the drug. With 400 μM DEA-NO, NO reaches a maximum concentration of 10 μM at 2 min of perfusion, and then declines slowly. SNAP (400 μM) produced an effect similar to 400 μM DEA-NO. Neither the immediate nor the longer-term depressive effect of NO is mediated by activation of guanylyl cyclase because in the presence of both low and high doses of ODQ, a potent and selective inhibitor of NO-stimulated guanylyl cyclase, NO produced the same depression of the field response. There is evidence however that the IMHV possesses c-GMP responsive elements since direct perfusion of 8-Br-cGMP (1 mM) produced a long-term but not an immediate depression. The long-term depression produced by 400 μM DEA-NO was eliminated in the presence of either a selective adenosine A 1 receptor antagonist or an ADP-ribosyltransferase inhibitor. It was also possible to prevent the long-term effect in the presence of tetraethyl ammonium a K +-channel blocker. These results suggest that the NO may be acting presynaptically in a synergistic fashion with the adenosine A 1 receptor to depress transmitter release.

Suppression of GTP/T alpha-dependent activation of cGMP phosphodiesterase by ADP-ribosylation by its gamma subunit in amphibian rod photoreceptor membranes.

Our previous study has shown that P gamma, the regulatory subunit of cGMP phosphodiesterase (PDE), is ADP-ribosylated by endogenous ADP-ribosyltransferase when P gamma is free or complexed with the catalytic subunits of PDE in amphibian rod photoreceptor membranes. The P gamma domain containing ADP-ribosylated arginines was shown to be involved in its interaction with T alpha, a key interaction for PDE activation. In this study, we describe a possible function of the P gamma ADP-ribosylation in the GTP/T alpha-dependent PDE activation. When rod membranes were preincubated with or without NAD and washed with a buffer containing GTP, the PDE activity of NAD-preincubated membranes was increased by the GTP-washing only to approximately 50% of that of membranes preincubated without NAD. The P gamma release by the GTP-washing from these NAD-preincubated membranes was also suppressed to approximately 50% of that preincubated without NAD. Taking into consideration that approximately 50% of P gamma is ADP-ribosylated under these conditions, these observations suggest that the ADP-ribosylated P gamma cannot interact with GTP/T alpha. We have also shown that a soluble fraction of ROS contains an enzyme(s) to release the radioactivity of [32P]ADP-ribosylated P gamma in concentration- and time-dependent manners, suggesting that the P gamma ADP-ribosylation is reversible. Rod ADP-ribosyltransferase solubilized from membranes by phosphatidylinositol-specific phospholipase C was separated into two fractions by ion-exchange columns. Biochemical characterization of these two fractions, including measurement of the Km for NAD and P gamma, estimation of their molecular masses, ADP-ribosylation of P gamma arginine mutants, effects of ADP-ribosyltransferase inhibitors on the P gamma ADP-ribosylation, and effects of salts and pH on the P gamma ADP-ribosylation, indicates that rod ADP-ribosyltransferase contains two isozymes, and that these two isozymes have similar properties for the P gamma ADP-ribosylation. Our observations strongly suggest that the negative regulation of PDE through the reversible P gamma ADP-ribosylation may function in the phototransduction mechanism.

The lethal effect of a benzamide derivative, 3-methoxybenzamide, can be suppressed by mutations within a cell division gene, ftsZ, in Bacillus subtilis.

3-Methoxybenzamide (3-MBA), which is known to be an inhibitor of ADP-ribosyltransferase, inhibits cell division in Bacillus subtilis, leading to filamentation and eventually lysis of cells. Our genetic analysis of 3-MBA-resistant mutants indicated that the primary target of the drug is the cell division system involving FtsZ function during both vegetative growth and sporulation.

ADP-ribosyltransferase inhibitors and pseudo-substrates inhibit rat smooth muscle cell migration in vitro.

ADP-ribosyltransferase inhibitors and pseudo-substrates inhibit rat smooth muscle cell migration in vitro.

Nitric-oxide-guanylyl-cyclase-dependent and -independent components of multiple forms of long-term synaptic depression.

Long-term depression (LTD) of synaptic strength is induced by glutamate-triggered increases in postsynaptic [Ca2+], through either influx or release from intracellular stores. Induction of LTD has also been reported to require release of Ca2+ from presynaptic stores and activation of presynaptic Ca2+/calmodulin-dependent protein kinase II. This finding leads to the hypothesis that the intercellular messenger nitric oxide (NO) may be a means by which postsynaptic Ca2+ triggers changes expressing LTD in presynaptic terminals. We report that bath application of the oxadiazoloquinoxalone derivative ODQ (4 microM), a selective inhibitor of NO-sensitive guanylyl cyclase (NOGC), markedly attenuated (90%) the magnitude of LTD induced by low-frequency stimulation (LFS; 1 Hz/15 min) of Schaffer collateral-CA1 synapses in hippocampal slices in vitro. Both the NO donor S-nitroso-N-acetylpenicillamine (100 microM) and the membrane-permeant cyclic guanine 3',5'-monophosphate (cGMP) analogue 8-(-4-chlorophenylthio) guanosine (8-pCPT)-cGMP (50 microM) enhanced the magnitude of LTD, which is consistent with he hypothesis that activation of NOGC plays a role in the induction of LTD. Nicotinamide (20 mM), an inhibitor of NO-activated ADP ribosyltransferase, did not impair the induction of LTD. In contrast to de novo LTD, the reversal of long-term potentiation by LFS (depotentiation) was only partially blocked (55%) by ODQ, and heterosynaptic LTD was not impaired at all, suggesting that there are both NOGC-dependent and -independent forms of LTD. Because postsynaptic intracellular infusion of ODQ (500 microM) failed to block the induction of LTD, we conclude that activation of presynaptic NOGC is a necessary step in the induction of an NOGC-dependent component of LTD.

ADP-ribosylation of proteins in Bacillus subtilis and its possible importance in sporulation.

Endogenous ADP-ribosylation was detected in Bacillus subtilis, as determined in vitro with crude cellular extracts. The ADP-ribosylated protein profile changed during growth in sporulation medium, displaying a temporary appearance of two ADP-ribosylated proteins (36 and 58 kDa) shortly after the end of exponential growth. Mutants resistant to 3-methoxybenzamide, a known inhibitor of ADP-ribosyltransferase, were obtained, and a significant proportion (15%) were found to be defective in both sporulation and antibiotic production. These mutants failed to ADP-ribosylate the 36- and 58-kDa proteins. The parent strain also lost the ability to ADP-ribosylate these proteins when grown in the presence of 3-methoxybenzamide at a concentration at which sporulation but not cell growth was severely inhibited. Results from genetic transformations showed that the mutation conferring resistance to 3-methoxybenzamide, named brgA, was cotransformed with the altered phenotypes, i.e., defects in ADP-ribosylation and sporulation. spoOA and spoOF mutants displayed an ADP-ribosylation profile similar to that of the parent strain, but a spoOH mutant failed to ADP-ribosylate any proteins, including the 36- and 58-kDa proteins. The significance of protein ADP-ribosylation in sporulation was further indicated by the observation that ADP-ribosylation of the 36-kDa protein could be induced by treatment with decoyinine, an inhibitor of GMP-synthetase, and by amino acid limitation, both of which resulted in an immediate decrease in GTP pool size eventually leading to massive sporulation. We propose that a new sporulation gene, which presumably controls sporulation via ADP-ribosylation of certain functional proteins, exists.

Changes in patterns of ADP-ribosylated proteins during differentiation of Streptomyces coelicolor A3(2) and its development mutants.

Mutants resistant to 3-aminobenzamide, a known inhibitor of ADP-ribosyltransferase, were obtained from Streptomyces coelicolor A3(2). One (strain 27) was analyzed in detail. Mutant 27 had a reduced ADP-ribosyl-transferase activity, exhibited substantial changes from the wild type in ADP-ribosylated protein profile during cell aging, and was defective in producing aerial mycelium and antibiotics. A 92-kDa ADP-ribosylated protein disappeared at the onset of differentiation in the parent strain but was present in mutant 27. Four ADP-ribosylated proteins (39, 41, 43, and 46 kDa) appeared at the onset of differentiation in the parent strain but were missing in mutant 27. Failure to ADP-ribosylate these four proteins was detected when the parent strain was grown in the presence of subinhibitory amounts of 3-aminobenzamide. Genetic analysis showed that the mutation, named brgA, conferring resistance to 3-aminobenzamide, cosegregated with the altered phenotypes (i.e., defects in ADP-ribosylation and aerial mycelium formation) and was mapped to a new locus near uraA. The brgA mutants were nonconditionally deficient in producing aerial mycelium and antibiotics, as determined by using various media, and had a morphological and physiological phenotype quite different from that of a bldG mutant carrying a mutation which was previously mapped near uraA. Among the known bld mutants, bldA, bldD, and bldG mutants exhibited a ADP-ribosylated protein profile similar to that of the wild type, while like mutant 27, bldB, bldC, and bldH mutants failed to ADP-ribosylate certain proteins.

Target Proteins for Arginine-Specific Mono(ADP-Ribosyl) Transferase in Membrane Fractions from Chick Skeletal Muscle Cells

In a previous study, we found that a specific inhibitor of cellular arginine-specific mono(ADP-ribosyl) transferase, meta-iodobenzylguanidine (MIBG), reversibly inhibited both proliferation and differentiation of cultured embryonic chick primary muscle myoblasts. In addition, we observed that arginine-specific ADP-ribosyltransferase activity increased with muscle-cell differentiation in cultures. Therefore, muscle-cell cultures, especially the 96-h myotube cultures that contain the highest levels of ADP-ribosyltransferase, were used as a working system to determine the cellular protein substrates for arginine-specific ADP-ribosyltransferase. When membrane fractions extracted from 96-h chick myotubes were incubated with [32P]NAD at 30°C for 30 min, only a few proteins were labeled. The labeling of two proteins of 36 and 56 kDa was inhibited by the presence of an arginine-specific mono(ADP-ribosyl) transferase inhibitor, MIBG, and by novobiocin. To prove that these proteins are indeed the targets for arginine-specific mono(ADP-ribosyl)ation, active recombinant muscle ADP-ribosyltransferase was incubated with membrane proteins under the same conditions. ADP-ribosylation of these two membrane proteins, as seen in the endogenous reactions, was also catalyzed by the added muscle transferase and was also inhibited by MIBG and novobiocin. By using antibody specific for desmin for immunoprecipitation and immunoblot analysis, we found that a 56-kDa protein associated with the membrane of myotubes is desmin. Our results showed that incorporation of isotope into this protein band from [32P]NAD is due to ADP-ribosylation of desmin.

Inhibition of NAD+ Glycohydrolase and ADP-ribosyl Cyclase Activities of Leukocyte Cell Surface Antigen CD38 by Gangliosides

We have recently reported that gangliosides act as inhibitors of ADP-ribosyltransferases and NAD+ glycohydrolases (NADase) of pertussis toxin and the C3 exoenzyme from Clostridium botulinum (Hara-Yokoyama, M., Hirabayashi, Y., Irie, F., Syuto, B., Moriishi, K., Sugiya, H., and Furuyama, S. (1995) J. Biol. Chem. 270, 8115-8121). Here, we investigated the effect of gangliosides on the enzymatic activity of leukocyte cell surface antigen CD38, which is identified as an ecto-NADase (Kontani, K., Nishina, H., Ohoka, Y., Takahashi, K., and Katada, T. (1993) J. Biol. Chem. 268, 16895-16898). Gangliosides GM1a and GQ1balpha inhibited the NADase activity in the immunoprecipitate of anti-CD38 antibody from the membrane extract of retinoic acid-treated human leukemic HL-60 cells. Gangliosides also inhibited the NADase activity of the extracellular domain of CD38 antigen that was deprived of the transmembrane domain and was expressed in Escherichia coli as a fusion protein with maltose-binding protein (MBP-CD38). The order of the inhibitory effect of purified ganglioside species on the NADase activity on MBP-CD38 was as follows: GQ1balpha > GT1b, GQ1b > GD1a, GD1b, GM1a, GM1b, GD3, GM3. GQ1balpha inhibited the NADase of MBP-CD38 in a noncompetitive manner versus NAD+ with a Ki value of about 0.3 microM. Neither ceramide nor the oligosaccharide moiety of GQ1balpha had an effect on the NADase activity. GQ1balpha, GT1b, and GQ1b also efficiently inhibited the ADP-ribosyl cyclase activity of MBP-CD38. At present, gangliosides are the only endogenous species that can block the enzymatic activity of CD38 antigen. The present results suggest a potential role of gangliosides as inhibitors of the ecto-NADases.