Poliovirus and vesicular stomatitis virus replication in the presence of 6-diazo-5-oxo-L-norleucine or 2-deoxy-D-glucose

Metabolomics captures the differential metabolites in the replication pathway of snakehead vesiculovirus regulated by glutamine

Snakehead vesiculovirus (SHVV) is a negative-sense single-stranded RNA virus that infects snakehead fish. This virus leads to illness and mortality, causing significant economic losses in the snakehead aquaculture industry. The replication and spread of SHVV in cells, which requires glutamine as a nitrogen source, is accompanied by alterations in intracellular metabolites. However, the metabolic mechanisms underlying the inhibition of viral replication by glutamine deficiency are poorly understood. This study utilized liquid chromatography-mass spectrometry to measure the differential metabolites between the channel catfish Parasilurus asotus ovary cell line infected with SHVV under glutamine-containing and glutamine-deprived conditions. Results showed that the absence of glutamine regulated 4 distinct metabolic pathways and influenced 9 differential metabolites. The differential metabolites PS(16:0/16:0), 5,10-methylene-THF, and PS(18:0/18:1(9Z)) were involved in amino acid metabolism. In the nuclear metabolism functional pathway, differential metabolites of guanosine were observed. In the carbohydrate metabolism pathway, differential metabolites of UDP-d-galacturonate were detected. In the signal transduction pathway, differential metabolites of SM(d18:1/20:0), SM(d18:1/22:1(13Z)), SM(d18:1/24:1(15 Z)), and sphinganine were found. Among them, PS(18:0/18:1(9Z)), PS(16:0/16:0), and UDP-d-galacturonate were involved in the synthesis of phosphatidylserine and glycoprotein. The compound 5,10-methylene-THF provided raw materials for virus replication, and guanosine and sphingosine are related to virus virulence. The differential metabolites may collectively participate in the replication, packaging, and proliferation of SHVV under glutamine deficiency. This study provides new insights and potential metabolic targets for combating SHVV infection in aquaculture through metabolomics approaches.

Protective Effects of Glutamine Antagonist 6-Diazo-5-Oxo-l-Norleucine in Mice with Alphavirus Encephalomyelitis

Inflammation is a necessary part of the response to infection but can also cause neuronal injury in both infectious and autoimmune diseases of the central nervous system (CNS). A neurovirulent strain of Sindbis virus (NSV) causes fatal paralysis in adult C57BL/6 mice during clearance of infectious virus from the CNS, and the virus-specific immune response is implicated as a mediator of neuronal damage. Previous studies have shown that survival is improved in T-cell-deficient mice and in mice with pharmacological inhibition of the inflammatory response and glutamate excitotoxicity. Because glutamine metabolism is important in the CNS for the generation of glutamate and in the immune system for lymphocyte proliferation, we tested the effect of the glutamine antagonist DON (6-diazo-5-oxo-l-norleucine) on the outcome of NSV infection in mice. DON treatment for 7 days from the time of infection delayed the onset of paralysis and death. Protection was associated with reduced lymphocyte proliferation in the draining cervical lymph nodes, decreased leukocyte infiltration into the CNS, lower levels of inflammatory cytokines, and delayed viral clearance. In vitro studies showed that DON inhibited stimulus-induced proliferation of lymphocytes. When in vivo treatment with DON was stopped, paralytic disease developed along with the inflammatory response and viral clearance. These studies show that fatal NSV-induced encephalomyelitis is immune mediated and that antagonists of glutamine metabolism can modulate the immune response and protect against virus-induced neuroinflammatory disease.

IMPORTANCE

Encephalomyelitis due to infection with mosquito-borne alphaviruses is an important cause of death and of long-term neurological disability in those who survive infection. This study demonstrates the role of the virus-induced immune response in the generation of neurological disease. DON, a glutamine antagonist, inhibited the proliferation of lymphocytes in response to infection, prevented the development of brain inflammation, and protected mice from paralysis and death during treatment. However, because DON inhibited the immune response to infection, clearance of the virus from the brain was also prevented. When treatment was stopped, the immune response was generated, brain inflammation occurred, virus was cleared, and mice developed paralysis and died. Therefore, more definitive treatment for alphaviral encephalomyelitis should inhibit virus replication as well as neuroinflammatory damage.

Inhibition of endoplasmic reticulum-to-Golgi traffic by poliovirus protein 3A: genetic and ultrastructural analysis

Poliovirus protein 3A, only 87 amino acids in length, is a potent inhibitor of protein secretion in mammalian cells, blocking anterograde protein traffic from the endoplasmic reticulum (ER) to the Golgi complex. The function of viral protein 3A in blocking protein secretion is extremely sensitive to mutations near the N terminus of the protein. Deletion of the first 10 amino acids or insertion of a single amino acid between amino acids 15 and 16, a mutation that causes a cold-sensitive defect in poliovirus RNA replication, abrogates the inhibition of protein secretion although wild-type amounts of the mutant proteins are expressed. Immunofluorescence light microscopy and immunoelectron microscopy demonstrate that 3A protein, expressed in the absence of other viral proteins, colocalizes with membranes derived from the ER. The precise topology of 3A with respect to ER membranes is not known, but it is likely to be associated with the cytosolic surface of the ER. Although the glycosylation of 3A in translation extracts has been reported, we show that tunicamycin, under conditions in which glycosylation of cellular proteins is inhibited, has no effect on poliovirus growth. Therefore, glycosylation of 3A plays no functional role in the viral replicative cycle. Electron microscopy reveals that the ER dilates dramatically in the presence of 3A protein. The absence of accumulated vesicles and the swelling of the ER-derived membranes argues that ER-to-Golgi traffic is inhibited at the step of vesicle formation or budding from the ER.

Antiviral effects of 6-diazo-5-oxo-L-norleucin on replication of herpes simplex virus type 1

An L-glutamine antagonist, 6-diazo-5-oxo-L-norleucin (L-DON), inhibits replication of vesicular stomatitis virus, poliovirus and paramyxoviruses in cultured cells. We tested the antiviral activity of L-DON against different strains of herpes simplex virus type 1 (HSV-1) in Vero cells. In the presence of a physiological plasma concentration of L-glutamine (0.5mM) L-Don inhibited 50% production of virus plaques at concentrations ranging from 7.9 to 16 microM. At concentrations of 40 microM L-Don inhibited infectious virus yield by 99%. The antiviral activity of L-DON decreased with increasing L-glutamine concentrations. A concentration of 5000 microM of L-Don had no significant effects on the viability of Vero cells. Transmission electron microscopical investigations showed that L-DON prevented mainly envelopment of viral nucleocapsids in the cytoplasm. The immunoprecipitation experiments demonstrated selective inhibition of synthesis of HSV-1 glycoproteins in L-DON treated cells. The results showed that L-DON inhibits HSV-1 replication at a late stage in the virus replication cycle, probably the cytoplasmic maturation of virions and subsequent virion egress from the cells.

Inhibition of replication of human respiratory syncytial virus by 6-diazo-5-oxo-L-norleucine

The effect of 6-diazo-5-oxo-L-norleucine (L-DON), a glutamine analog, on RSV replication was studied. At a concentration of 0.01 mM L-DON, 99% of RSV replication in treated CV-1 cells was inhibited. At this concentration of L-DON, the level of cellular protein synthesis was identical to untreated control cells. Trypan blue staining revealed that all the cells remained viable even at concentrations of L-DON as high as 10 mM. In addition, L-DON added as late as 24 h post infection can effectively suppress viral replication. Analysis of viral mRNA levels by Northern blot revealed that secondary transcription and subsequent steps in the virus life cycle were inhibited. Immunoprecipitation of viral proteins from drug treated or untreated cultures showed that synthesis of all viral proteins was drastically reduced by L-DON, with a slightly greater inhibition of viral glycoproteins. Furthermore, immunofluorescent staining showed that drug treated cells expressed both F and N proteins and that F was inserted into the membrane as the native F protein.

Expression and subcellular localization of poliovirus VPg-precursor protein 3AB in eukaryotic cells: evidence for glycosylation in vitro

The poliovirus-encoded, membrane-associated VPg-precursor polypeptide 3AB has been implicated in the initiation of viral RNA synthesis. We have expressed 3AB and 3A polypeptides in eukaryotic cells and examined their localization using indirect immunofluorescence and a direct in vitro membrane-binding assay. Results presented here demonstrate that both 3AB and 3A are capable of localizing in the endoplasmic reticulum and the Golgi apparatus in transfected HeLa cells in the absence of any other poliovirus protein. We have also shown that the carboxy-terminal 18 amino acids of 3A that constitute an amphipathic domain are important in membrane binding of 3A and 3AB. Additionally, we demonstrate that a significant fraction of both 3A and 3AB can be glycosylated in a membrane-dependent fashion during in vitro translation in reticulocyte lysate. We demonstrate that 6-diazo-5-oxo-L-norleucine, an inhibitor of glycoprotein synthesis, significantly inhibits poliovirus RNA synthesis in vivo. The implications of glycosylation of 3AB (and 3A) in viral replication are discussed.

Inhibition in vitro of the replication of murine cytomegalovirus or reovirus type 3 by the glutamine analogue acivicin

The replication of synchronised cultures of Balb/c L-3T3 fibroblasts was shown to require glutamine at a concentration of at least 0.12 mM, but the replication of murine cytomegalovirus (MCMV) or reovirus type 3 in the cells required at least 0.25 mM glutamine. In the presence of 2 mM glutamine, the glutamine analogue acivicin inhibited DNA synthesis at a minimum concentration of 2 microM in uninfected cells but partially inhibited the replication of MCMV at 0.12 microM and reovirus at 0.03 microM, and totally inhibited MCMV production at 1.0 microM and reovirus at 0.5 microM. Although the therapeutic index in this instance is not great, it does offer encouragement to explore other amino acid analogues as possible broad-spectrum antiviral agents.