Tubercidin inhibits PRRSV replication via RIG-I/NF-κB pathways and interrupting viral nsp2 synthesis

Porcine reproductive and respiratory syndrome virus (PRRSV) is an RNA virus with constantly emerging recombinant and mutant strains. Because of the high genetic diversity of PRRSV, current vaccines only provide partial protection against the infection of heterologous strains, which makes it a challenge for PRRSV prevention and control. Tubercidin is a naturally extracted compound with potential antiviral properties. However, whether tubercidin has anti-PRRSV ability is unknown. Our study found that tubercidin showed effective antiviral effects on PRRSV replication. In terms of mechanism, tubercidin suppressed PRRSV at the entry, replication, and release steps of the viral life cycle. Additionally, we demonstrated that tubercidin treatment promoted the activation of retinoic acid-inducible gene I and nuclear factor kappa-light-chain-enhancer of activated B cell signaling pathway, thus increasing the type I interferon and inflammatory cytokine expression. Furthermore, tubercidin restrained the viral non-structural protein 2 expression and viral dsRNA synthesis and ultimately inhibited PRRSV replication. Hence, our data showed that tubercidin is promising and has potential antiviral ability against PRRSV replication in vitro.

IMPORTANCE

Porcine reproductive and respiratory syndrome (PRRS) is one of the most important swine diseases, which causes huge economic loss worldwide. However, there is no effective therapeutic method for PRRS prevention and control. Here, we found that tubercidin, a naturally extracted adenosine analog, exhibited strong anti-porcine reproductive and respiratory syndrome virus (PRRSV) activity. Mechanically, tubercidin inhibited viral binding, replication, and release. Tubercidin suppressed PRRSV non-structural protein 2 expression, which is important for the formation of replication and transcription complex, leading to the block of viral RNA synthesis and PRRSV replication. Moreover, tubercidin could activate retinoic acid-inducible gene I/nuclear factor kappa-light-chain-enhancer of activated B cell innate immune signaling pathway and increased the expression of interferons and proinflammatory cytokines, which was the other way to inhibit PRRSV replication. Our work evaluated the potential value of tubercidin as an antiviral agent on PRRSV replication and provided a new way to prevent PRRSV replication in vitro.

[3-Deazaadenosine (3-DAA) accelerates Japanese encephalitis virus replication and down-regulates levels of inflammatory factors in mouse and hamster cells]

Objective To investigate the effect of 3-deazaadenosine (3-DAA), an N6-methyladenosine (m6A) methylation modification inhibitor, on the replication of the Japanese encephalitis virus (JEV). Methods Neuro2a mouse neuroblastoma cells, N9 mouse microglial cells, and BHK baby hamster kidney cells were exposed to JEV and then treated with 3-DAA. JEV was also injected into the footpad of adult C57BL/6 mice, which were then administered 3-DAA intraperitoneally. Real-time quantitative PCR was utilized to measure mRNA expression levels of JEV, interleukin 1β (IL-1β), IL-6, tumor necrosis factor α (TNF-α), monocyte chemoattractant protein 1 (MCP-1), inducible nitric oxide synthase (iNOS), arginase 1 (Arg1), interferon (IFN)-α, IFN-β, IFN-γ, and C-X-C motif chemokine ligand 10 (CXCL10) in the cells and mouse brain tissues. Western blot analysis was used to detect JEV protein expression in the cells and mouse brain tissues. Furthermore, the survival of the mice was monitored and pathological changes in mouse brains were observed via hematoxylin and eosin (HE) staining. Results 3-DAA had a dose-dependent effect on the replication of RNA and protein expression of JEV in both BHK, N9, Neuro 2α cells and mouse brain tissues, which resulted in rapid progression of JEV infection in mice and a decrease in their survival rate. Furthermore, 3-DAA suppressed the expression of inflammatory factors such as IL-6, TNF-α, CXCL10, IL-1β and iNOS, thus weakening the immune response. Conclusion 3-DAA promotes JEV infection and hastens death of infected cells and mice, indicating that m6A modification may negatively regulate JEV replication.

In vitro activity of tubercidin against Mycobacterium tuberculosis and nontuberculosis Mycobacteria

Tubercidin is an adenosine analogue that has been shown to exhibit good activity against some tumours and parasites. In this study, the in vitro activity of tubercidin was evaluated against Mycobacterium tuberculosis (Mtb) and nontuberculosis Mycobacteria (NTM). For determining the MICs of tubercidin, 23 fully drug-sensitive (DS) Mtb strains, 33 multi-drug resistance tuberculosis (MDR-TB) strains, 29 pre-extensively drug-resistant tuberculosis (pre-XDR-TB) strains, 21 extensively drug-resistant tuberculosis (XDR-TB) strains, 17 rapidly growing mycobacteria (RGM) and nine slowly growing mycobacteria (SGM) references strains were tested by microplate-based Alamar Blue assay (MABA) method. The results indicate that tubercidin has high in vitro activity against some drug-resistance Mtb strains and NTM reference strains, which warrants further investigation on the actions of tubercidin and its derivatives as potential drugs for mycobacterial infections.

RNA m6A Modification Functions in Larval Development and Caste Differentiation in Honeybee (Apis mellifera)

Genetically identical female honeybee larvae with different diets develop into sterile workers or fertile queens. It remains unknown whether the reversible RNA N⁶-methyladenosine (m⁶A) mark functionally impact this "caste differentiation." Here, we profile the transcriptome-wide m⁶A methylome of honeybee queen and worker larvae at three instar stages and discover that m⁶A methylation dynamics are altered by differential feeding. Multiple methylome comparisons show an obvious increase in m⁶A marks during larval development and reveal a negative correlation between gene expression and m⁶A methylation. Notably, we find that worker larvae contain more hypermethylated m⁶A peaks than do queen larvae, and many caste-differentiation-related transcripts are differentially methylated. Chemical suppression of m⁶A methylation in worker larvae by 3-deazaadenosine (DAA) reduces overall m⁶A methylation levels and triggers worker larvae to develop queen caste features. Thus, our study demonstrates that m⁶A functionally impacts caste differentiation and larval development, yet it does not exclude potential contributions from other factors.

Extended storage of whole blood with 3-deazaadenosine for homocysteine assay

BACKGROUND

To assess the effectiveness of using 3-deazaadenosine (3DAA) to maintain plasma homocysteine concentrations (tHCy) in whole blood samples.

METHODS

Blood was obtained from five volunteers and samples were maintained at room temperature, in cold packs or in a fridge (0-4 degrees C) with and without 3DAA. At time points ranging from 6 to 168 h, samples were processed and analysed for tHCy using the Abbott IMx system.

RESULTS

There was a mean increase in tHCy of 29.4% at 6 h increasing to 242.6% after 168 h in whole blood kept at room temperature. There was no significant change in tHCy for 48 h when stored in cold packs, and for 72 h when stored in the fridge. The addition of 3DAA had a significant preservative effect (P<0.001), maintaining tHCy to 48 h in whole blood at room temperature, 120 h in the fridge and 96 h in cool packs. There was no statistical difference in results obtained from samples containing preservative and controls when using the Abbott IMx system.

CONCLUSION

3DAA is an effective preservative of tHCy in whole blood, particularly in samples maintained at 0-4 degrees C.

Effects of temperature on stability of blood homocysteine in collection tubes containing 3-deazaadenosine

BACKGROUND

The accuracy of homocysteine (Hcy) results is currently compromised by the requirement to separate the plasma within 1 h of sample collection. We studied the effect of temperature on the stability of plasma Hcy over a 72-h time course in blood collected into evacuated tubes containing either EDTA alone or both EDTA and 3-deazaadenosine (3DA).

METHODS

We recruited 100 volunteers, including both diseased and healthy individuals with a range of baseline plasma Hcy values, from two centers. Blood samples were collected into tubes containing EDTA, and EDTA plus 3DA and stored at ambient temperature (20-25 degrees C) or refrigerated (2-8 degrees C). Aliquots of blood were centrifuged at various times up to 72 h, the plasma was removed, and Hcy was measured by HPLC.

RESULTS

Plasma Hcy measurement covering the sample collection and storage conditions during the whole time course was possible on samples from 59 of those recruited. One-way ANOVA for repeated measures within subjects revealed that only samples that were collected into tubes containing EDTA plus 3DA and stored refrigerated were stable over 72 h (P = 0.2761).

CONCLUSIONS

A combination of 3DA and storage at 2-8 degrees C will allow collection of samples for plasma Hcy measurement outside of the hospital setting and wider population screening.

Stabilization of blood homocysteine in an epidemiological setting

The major problem in the determination of homocysteine (Hcy), which is thought to be a risk factor in colorectal cancer, is the rise in its concentration if blood is not centrifuged immediately after collection. We assess the interference of 3-deazaadenosine (which inhibits conversion of S-adenosylhomocysteine into Hcy within the erythrocyte), using the fluorescence polarization immunoassay (FPIA) assay, the stabilizing effect of 3-deazaadenosine and the impact of temperature on Hcy stabilization. To assess interference of 3-deazaadenosine, 12 blood samples were extracted; two aliquots were obtained from each and one of them was added 3-deazaadenosine (50 micromol/l). To assess the stabilizing value of 3-deazaadenosine, as well as the effect of temperature, two blood samples were extracted from 24 volunteers. One of the tubes was immediately placed on ice and centrifuged (reference concentration). To the second tube was immediately added 3-deazaadenosine (50 micromol/l), producing six aliquots, three of which were kept at room temperature (25 degrees C) for 1, 4 and 6 hours, the other three kept at 37 degrees C. The mean values (standard deviation) obtained for methodological interference were: 7.32 (3.58) micromol/l without stabilizer, and 7.11 (3.61) micromol/l with stabilizer. There were no statistically significant differences (P = 0.104) and intraclass correlation coefficient was 0.989, suggesting no methodological interference. We did not find any significant differences regarding our reference value in the samples kept at room temperature during the interval studied. A high Pearson correlation coefficient was obtained. Nevertheless, in those samples kept at 37 degrees C, a slight increase was observed in the 4-hour period (P = 0.009). The addition of 3-deazaadenosine may avoid problems in the critical pre-analytical phase in the Hcy measurement. There is no interference with the FPIA assay, nor any dilution effect, and new reference values are not necessary.

Use of anti-(tumour necrosis factor-alpha) antibody or 3-deaza-adenosine as additives to promote protection by University of Wisconsin solution in ischaemia/reperfusion injury

Experimental interventions that reduce ischaemia/reperfusion (I/R) lung injury can be used to improve the properties of preservation solutions. We attempted to increase the attenuation of I/R injury by University of Wisconsin solution (UW) by adding an antibody against tumour necrosis factor-alpha (TNF-alpha), to neutralize TNF-alpha, and/or by adding 3-deaza-adenosine (c3-Ado), to inhibit leucocyte adhesion and the biosynthesis of ICAM-1 (intercellular cell-adhesion molecule 1). We examined I/R injury using an isolated rat lung model. Six different solutions were perfused individually, followed by evaluation of I/R injury: (1) 0.9% NaCl (normal saline; NS), (2) NS+anti-TNF-alpha antibody, (3) UW alone, (4) UW+anti-TNF-alpha, (5) UW+c3-Ado and (6) UW+anti-TNF-alpha+c3-Ado. Haemodynamic changes, lung weight gain, capillary filtration coefficient, TNF-alpha levels and lung pathology were analysed in order to evaluate I/R injury. Compared with lungs perfused with NS, lungs treated with NS+anti-TNF-alpha showed less I/R injury. The addition of anti-TNF-alpha and/or c3-Ado to UW reduced I/R injury compared with unmodified UW. Among the six solutions tested, UW containing anti-TNF-alpha antibody reduced I/R injury to the greatest extent. We conclude that addition of anti-TNF-alpha antibody or c3-Ado protects against I/R lung injury when using UW. Further investigation of the improved properties of modified UWs would be beneficial with regard to lung transplantation research.

Chemical probes reveal no evidence of Hoogsteen base pairing in complexes formed between echinomycin and DNA in solution

Five different DNA fragments have been treated with a range of conformationally sensitive reagents in an effort to probe structural changes in DNA associated with binding of the bis-intercalating antibiotic echinomycin. For each probe, the intensity and pattern of its reactivity with DNA have been analyzed in order to elucidate the effect of antibiotic binding on the accessibility of a specific site or sites to chemical attack. It was found that in one of the DNA fragments, pTyr2 DNA, several purine residues exhibit enhanced reactivity to diethyl pyrocarbonate (DEPC) in the absence of bound antibiotic, and that this strongly sequence specific reaction is enhanced in the presence of quite low echinomycin concentrations. The echinomycin-dependent reactivities towards DEPC of three homologous DNA fragments, chosen for their subtly different antibiotic binding characteristics, were also investigated. It was found that small changes in base sequence generate striking changes in susceptibility to modification by DEPC. The abolition of one antibiotic binding site leads to the creation of a new, intense DEPC-reactive site. In the presence of moderate concentrations of echinomycin, specific thymidine residues exhibit enhanced reactivity towards osmium tetroxide. No differences in the reactivities of the DNA fragments towards bromoacetaldehyde, S1 nuclease, dimethyl sulphate or potassium tetrachloropalladinate were observed in the presence of the antibiotic. DEPC reactions were performed on tubercidin (7-deaza-adenosine) to determine the DEPC reactive positions in situation where N-7 is inaccessible. Tubercidin was found to be generally resistant to attack by DEPC followed by treatment with base. We conclude that the bulk of structural changes induced by the binding of echinomycin to DNA do not involve Hoogsteen base pairing, but rather are due to sequence-specific unwinding of the helix in a manner which is strongly dependent on the nature of surrounding nucleotide sequences.

Minor-groove-modified oligonucleotides: synthesis of decadeoxynucleotides containing hypoxanthine, N2-methylguanine and 3-deazaadenine, and their interactions with restriction endonucleases Bgl II, Sau, 3AI, and Mbo I (Nucleosides and Nucleotides Part 75)

Decadeoxynucleotides containing hypoxanthine, N2-methylguanine, 3-deazaadenine in the recognition sequences of restriction endonucleases Bgl II, Sau 3AI, and Mbo I were synthesized. These decanucleotides modified in the base moieties facing in to the minor groove were strongly resistant to hydrolysis by Bgl II and partially resistant to that of Sau 3AI and Mbo I. The decadeoxynucleotide containing 3-deazaadenine in place of adenine was bound to Bgl II strongly, whereas the nucleotides containing hypoxanthine and N2-methylguanine were bound less tightly.

Capping and adenosine metabolism. Genetic and pharmacologic studies

Capping of membrane Ig was studied in lymphocytes treated with agents that interfere with adenosine metabolism. Treatment of murine or human B cells with combinations of coformycin, an inhibitor of adenosine deaminase, homocysteine, and adenosine impaired Ig capping. Inhibition of capping was also produced by 3-deazaadenosine, a specific inhibitor of adenosylhomocysteine hydrolase. The inhibitors did not affect capping of the Thy-1 antigen or membrane sites reactive with antilymphocyte antibodies. Two patients with a hereditary deficiency in adenosine deaminase had impairment of Ig capping. Such an impairment was not found in lymphocytes of two other patients who had undergone successful bone marrow transplantation. It is known that the addition of a calcium ionophore results in activation of microfilament function and in disruption of Ig caps. The ionophore effect was not inhibited by the agents mentioned above. Our results suggest that the inhibition of Ig capping during aberrant adenosine metabolism may be caused by a methylation defect preceding the contracticle event that produces membrane reorganization.

Methionyl-tRNA synthetase from Escherichia coli. Absence of interaction between the metal ion and the purine ring of ATP in the L-methionine activation site

Enhancement of the nuclear relaxation rates by manganese has been used to derive manganese--purine-ring distances in the activation site of methionyl-tRNA synthetase. This is possible with the help of an abortive complex between the enzyme, methionine, adenosine, pyrophosphate and manganese which simulates an intermediate species of the activation reaction. It is found that the distances between the manganese ion and the purine ring are too high (greater than 0.8 nm) to allow interaction between them. Thus, metal-purine interaction is involved neither in the catalytic mechanism nor in the stabilization of abortive synergistic complexes [S. Blanquet, G. Fayat and J. P. Waller (1975) J. Mol. Biol. 94, 1-15].

Effects of cyclic nucleotides on the conformational states of the alpha core of the cyclic AMP receptor protein

The alpha core gragment produced by limited proteolysis contains the cyclic AMP binding domain and the two buried sulfhydryl groups of the cyclic AMP receptor protein. The buried sulfhydryl groups of the alpha core react with 5,5'-dithio-bis(2-nitrobenzoic acid) after denaturation by 3 M urea or digestion with subtilisin. The rate of sulfhydryl modification in the presence of 3 M urea or subtilisin is markedly decreased in the presence of cyclic nucleotides which are proposed to tighten the conformation of the alpha core. Incubation of the alpha core in 3 M urea or dithionitrobenzoic acid does not affect cyclic AMP binding while dithionitrobenzoic acid plus 3 M urea inhibits cyclic AMP binding suggesting a role for the buried sulfhydryls in cyclic AMP binding or their proximity to the cyclic AMP binding domain of the alpha core. The data are consistent with a ligand-induced conformational change in the alpha region of the native cyclic AMP receptor protein that is required for DNA binding.

Methionyl-tRNA synthetase from Escherichia coli: substituting magnesium by manganese in the L-methionine activating reaction

While Mg2+ can be efficiently replaced by Ni2+, Co2+ and Mn2+ in the ATP-PPi isotopic exchange reaction catalysed by methionyl-tRNA synthetase from Escherichia coli, the latter ion was selected for detailed analysis of the L-methionine activation reaction. In order to avoid artefactual results due to the slow aggregation of Mn2+ with pyrophosphate, this process was investigated by electron paramagnetic resonance and conditions were determined where it does not interfere with enzymic experiments. The thermodynamic parameters derived from steady-state (ATP-PPi isotopic exchange, fluorescence at equilibrium) or prestationary (fluorescence stopped-flow) experiments are compared to those obtained in the presence of Mg2+ [Hyafil et al. (1976) Biochemistry, 15, 3678-3685]. While the standard deltaG for the reaction (E-Met-ATP-Me2+equilibriumE-Met approximately AMP-PPi-Me2+) is close to zero in the case of Mg2+, Mn2+ slows down the rate of adenylate reversion and thus shifts the reaction towards the latter species. The deltaG for the formation of the E-Met approximately AMP complex does not depend on the metal used, suggesting that the divalent ion does not participate in the structuration of this complex. Substituting Mn2+ for Mg2+ decreases notably the dissociation constant of PPi-Me2+ from the E-Met approximately AMP-PPi-Me2+ species and from its abortive analog E-Met-Ado-PPi-Me2+. Similarly the dissociation constant of ATP-Me2+ from another dead-end analog E-methioninol-ATP-Me2+ is decreased by Mn2+. Involvement of the purine N7 atom in the binding of the metal ion to the active site of methionyl-tRNA synthetase is ruled out by the use of 7-deaza-adenosine. The role of the metal in the catalytic process of methionine activation and its relevance to the specificity of the reaction is then discussed in the light of the results obtained without metal and with Mg2+ and Mn2+.

Isolation of variants in phagocytosis of a macrophage-like continuous cell line

We have isolated cloned variants in phagocytosis from a cloned continuous murine macrophage-like cell line, J 774.2. A selection procedure against Fc receptor-mediated phagocytosis was devised using IgG-coated SRBC containing a toxic drug, tubercidin, as the lethal agent. A series of variant clones deficient in Fc receptor-mediated phagocytosis were isolated. Such variants occurred at low frequency (approximately 6 X 10(-5)), were stable, and appeared to possess Fc receptors. The degree to which they were defective in phagocytosis of IgG-coated SRBC varied from clone to clone, yet all clones, were able to phagocytize latex particles. The phagocytic defect in some variants could be corrected by the addition of 8 Br-cAMP, in others, the drug was without effect. It is likely, therefore, that different variants are defective in several distinct steps critical to Fc receptor-mediated phagocytosis.

Comparison of initial velocity and binding data for allosteric adenosine monophosphate nucleosidase

Adensine monophosphate nucleosidase (AMP nucleosidase) from Azotobacter vinelandii is composed of six subunits with similar or identical charge and size and has a molecular weight of approximately 320,000. Binding studies with tritiated tubercidin 5' -PO4 (4-amino-7-(beta-D-ribofuranosyl)pyrrolo[2,3-d]pyrimidine-5' -monophosphate), a competitive inhibitor with respect to the substrate, AMP, indicate the presence of three independent, identical binding sites for the substrate analog. The binding of tubercidin 5' -PO4 is not affected by either Mg2+ or MgATP2-; however, in initial velocity experiments MgATP2- caused from greater than100- to 4,000-fold activation of substrate hydrolysis depending on the concentration of AMP. Binding studies with [14C]ATP are consistent with six interdependent binding sites for MgAT2-. Initial velocity and binding curves for MgATP2- are similar in shape, but reveal a disproportionate increase in initial velocity at low saturation levels of MgAT2-. Binding of MgAT2- is inhibited by increasing concentrations of P1 which acts as a competitive inhibitor of MgATP2- activation in both initial velocity and binding experiments. In the absence of MgATP2-, 32Pi binds at six or more interdependent modifier sites. The simulataneous binding of Mg[14C]ATP2- and 32Pi was studied in experiments where MgATP2- and Pi were held in constant ratio. Extrapolation to infinite concentrations of both MgATP2- and Pi indicated that 3 molecules of each were bound to the enzyme. Thus the binding of the allosteric activator and inhibitor are mutually exclusive. These results are consistent with a single modifier site per subunit at which either MgATP2- or Pi may combine, or with separate activator and inhibitor sites which cannot be filled simultaneously. Comparative initial velocity and binding studies with Pi indicate that the initial rate of AMP hydrolysis depends primarily on the extent of modifier site saturation with MgATP2-. Thus when two sites are filled with MgATP2-, the initial rate is approximately the same as when two additional modifier sites are filled with Pi. Binding of Pi, therefore, does not appear to affect the catalytic effectiveness of the active site when MgATP2- is also present, except by the displacement of MgATP2-.

Polynucleotide duplexes based on poly(7-deazaadenylic acid)

In order to find a poly(A)-poly(U) analog which could not form a triple-stranded complex and which would have a sufficiently high thermal stability to survive under physiological conditions, the interaction of poly(7-deazaadenylic acid) (poly(c-7A)) with modified polyuridylic acids was examined. Mixing curves constructed by the method of continuous variation, isosbestic points and thermal melting profiles proved that poly(c-7A) formed only 1:1 complex with polyribothymidylic acid and poly(5-bromouridylic acid) (Tm values of 50 and 72 degrees C respectively, in 0.15 M NaCl, 0.01 M KH2 PO4, 0.001 M MgCl2, pH7). In addition poly(c-7A) formed a 1:1 complex with poly(I) (Tm equals 22 degrees C in 0.46 M salt, pH 7), and presumed duplexes were observed in the interaction of poly(c-7A) with poly(dT), poly(2'-azido-2'-deoxyuridylic acid) and poly(2'-O-methyluridylic acid) (Tm values of 35, 32 and 41 degrees C respectively, in 0.10 M NaCl, pH7).

Polynucleotides. XXII. Synthesis and properties of poly 7-deazainosinic acid

Poly 7-deazainosinic acid has been prepared by the deamination and phosphorylation of tubercidin and the nucleoside diphosphate was polymerised using polynucleotide phosphorylase. The polymer has similar physical properties to poly(I), but has a low thermal stability in the double-stranded complex with poly(C). Poly(7-deaza I), in contrast, forms a more stable triple-stranded complex with poly(A) than 2 poly(I). poly(A), presumably due to the higher pK value.