Effect of glycosylation inhibitors on the release of enveloped vaccinia virus

Multi-omics characterization of the monkeypox virus infection

Multiple omics analyzes of Vaccinia virus (VACV) infection have defined molecular characteristics of poxvirus biology. However, little is known about the monkeypox (mpox) virus (MPXV) in humans, which has a different disease manifestation despite its high sequence similarity to VACV. Here, we perform an in-depth multi-omics analysis of the transcriptome, proteome, and phosphoproteome signatures of MPXV-infected primary human fibroblasts to gain insights into the virus-host interplay. In addition to expected perturbations of immune-related pathways, we uncover regulation of the HIPPO and TGF-β pathways. We identify dynamic phosphorylation of both host and viral proteins, which suggests that MAPKs are key regulators of differential phosphorylation in MPXV-infected cells. Among the viral proteins, we find dynamic phosphorylation of H5 that influenced the binding of H5 to dsDNA. Our extensive dataset highlights signaling events and hotspots perturbed by MPXV, extending the current knowledge on poxviruses. We use integrated pathway analysis and drug-target prediction approaches to identify potential drug targets that affect virus growth. Functionally, we exemplify the utility of this approach by identifying inhibitors of MTOR, CHUK/IKBKB, and splicing factor kinases with potent antiviral efficacy against MPXV and VACV.

Investigating Ketone Bodies as Immunometabolic Countermeasures against Respiratory Viral Infections

Respiratory viral infections remain a scourge, with seasonal influenza infecting millions and killing many thousands annually and viral pandemics, such as COVID-19, recurring every decade. Age, cardiovascular disease, and diabetes mellitus are risk factors for severe disease and death from viral infection. Immunometabolic therapies for these populations hold promise to reduce the risks of death and disability. Such interventions have pleiotropic effects that might not only target the virus itself but also enhance supportive care to reduce cardiopulmonary complications, improve cognitive resilience, and facilitate functional recovery. Ketone bodies are endogenous metabolites that maintain cellular energy but also feature drug-like signaling activities that affect immune activity, metabolism, and epigenetics. Here, we provide an overview of ketone body biology relevant to respiratory viral infection, focusing on influenza A and severe acute respiratory syndrome (SARS)-CoV-2, and discuss the opportunities, risks, and research gaps in the study of exogenous ketone bodies as novel immunometabolic interventions in these diseases.

New method for the assessment of molluscum contagiosum virus infectivity

Molluscum contagiosum virus (MCV), a poxvirus pathogenic for humans, replicates well in human skin in vivo, but not in vitro in standard monolayer cell cultures. In order to determine the nature of the replication deficiency in vitro, the MCV infection process in standard culture has to be studied step by step. The method described in this chapter uses luciferase and GFP reporter constructs to measure poxviral mRNA transcription activity in cells in standard culture infected with known quantities of MCV or vaccinia virus. Briefly, MCV isolated from human tissue specimen is quantitated by PCR and used to infect human HEK293 cells, selected for ease of transfection. The cells are subsequently transfected with a reporter plasmid encoding firefly luciferase gene under the control of a synthetic early/late poxviral promoter and a control plasmid encoding a renilla luciferase reporter under the control of a eukaryotic promoter. After 16 h, cells are harvested and tested for expression of luciferase. MCV genome units are quantitated by PCR targeting a genome area conserved between MCV and vaccinia virus. Using a GFP reporter plasmid, this method can be further used to infect a series of epithelial and fibroblast-type cell lines of human and animal origin to microscopically visualize MCV-infected cells, to assess late promoter activation, and, using these parameters, to optimize MCV infectivity and gene expression in more complex eukaryotic cell culture models.

A study of the glycoproteins of Autographa californica nuclear polyhedrosis virus (AcNPV)

Pulse labeling with tritiated mannose was used to follow the time course of Autographa californica nuclear polyhedrosis virus (AcNPV) glycoprotein synthesis in Spodoptera frugiperda IPLB-21 cells. Nine viral-induced intracellular glycoproteins were first detected from as early as 2 hr postinoculation (67K, early phase) to as late as 14 hr (36K and 19K glycoproteins, intermediate phase). Glycosylation of these proteins was observed to continue to the end of the experiment (28 hr postinoculation). Seven of these intracellular glycoproteins could also be detected in infected Trichoplusia ni TN-368 cells 24 hr postinoculation. When the glycosylation inhibitor tunicamycin was present (from 0 hr postinoculation) there was no detectable glycosylation of any of these viral-induced glycoproteins. Metabolic labeling of the nonoccluded virus budded from IPLB-21 and TN-368 with tritiated mannose or N-acetylglucosamine identified 11 structural glycoproteins, 8 of which were identical in both virus preparations. All of these structural glycoproteins were sensitive to the inhibitory action of tunicamycin. A single 42K structural glycoprotein was detected (with acetylglucosamine only) in the occluded form of AcNPV. Glycosylation of this structural protein appeared to be insensitive to tunicamycin. Lactoperoxidase-catalyzed radioiodination was used to determine which of the virus structural glycoproteins are exposed on the virion surface.

Morphogenesis and release of fowlpox virus

Release of fowlpox virus (FWPV) as extracellular enveloped virus (EEV) appears to proceed both by the budding of intracellular mature virus (IMV) through the plasma membrane and by the fusion of intracellular enveloped virus (IEV) with the plasma membrane. Based on the frequency of budding events compared to wrapping events observed by electron microscopy, FWPV FP9 strain seems to exit chick embryo fibroblast cells predominantly by budding. In contrast to vaccinia virus (VV), the production of FWPV extracellular virus particles is not affected by N(1)-isonicotinoyl-N(2)-3-methyl-4-chlorobenzoylhydrazine (IMCBH). Comparison of the sequence of the VV F13L gene product with its FWPV orthologue showed a mutation, in the fowlpox protein, at the residue involved in IMCBH resistance in a mutant VV. Glucosamine, monensin or brefeldin A did not have any specific effect on FWPV extracellular virus production. Cytochalasin D, which inhibits the formation of actin filaments, reduces the production of extracellular virus particles by inhibiting the release of cell-associated enveloped virus (CEV) particles from the plasma membrane. Involvement of actin filaments in this mechanism is further supported by the co-localization of actin with viral particles close to the plasma membrane in the absence of cytochalasin D. Actin is also co-localized with virus factories.

Attenuation of B5R mutants of rabbitpox virus in vivo is related to impaired growth and not an enhanced host inflammatory response

The rabbitpox virus (RPV) B5R protein, synthesized late in infection, is found as a 45-kDa membrane-associated protein of the envelope of infectious extracellular enveloped virus (EEV) and as a 38-kDa protein secreted from the cell by a process independent of morphogenesis. The protein is not found associated with intracellular mature virus (IMV). Deletion of the gene attenuates the virus (RPV delta B5R) in animals (mice and rabbits), has relatively little effect on formation of IMV, prevents EEV formation in some but not all cells, and leads to a reduced host range. Analysis of the sequence of the protein suggests relatedness to factor H of the complement cascade. Collectively, these observations suggest that attenuation of the virus in vivo could be linked to an inhibition of the inflammatory response, a deficiency in growth, or both. In this report we have analyzed the behavior of RPV delta B5R in infected mice and rabbits and conclude that attenuation of the mutant virus likely results from simple failure to grow within the infected animal and that the inflammatory response probably contributes little to the observed attenuation.

Identification and characterization of an extracellular envelope glycoprotein affecting vaccinia virus egress

Sequence analysis of the vaccinia virus strain Western Reserve genome revealed the presence of an open reading frame (ORF), SalL4R, which has the potential to encode a transmembrane glycoprotein with homology to C-type animal lectins (G. L. Smith, Y. S. Chan, and S. T. Howard, J. Gen. Virol. 72:1349-1376, 1991). Here we show that the SalL4R gene is transcribed late during infection from a TAAATG motif at the beginning of the ORF. Antisera raised against a TrpE-SalL4R fusion protein identified three glycoprotein species of Mr 22,000 to 24,000 in infected cells. Immunogold electron microscopy demonstrated that SalL4R protein is present in purified extracellular enveloped virus particles but not in intracellular naked virus (INV). A mutant virus was constructed by placing a copy of the SalL4R ORF downstream of an isopropyl-beta-D-thiogalactopyranoside (IPTG)-inducible vaccinia virus promoter within the thymidine kinase locus and subsequently deleting the endogenous SalL4R gene. The growth kinetics of this virus demonstrated that SalL4R was nonessential for the production of infectious INV but was required for virus dissemination. Consistent with this finding, the formation of wild-type-size plaques by this mutant was dependent on the presence of IPTG. Electron microscopy showed that without SalL4R expression, the inability of the virus to spread is due to a lack of envelopment of INV virions by Golgi-derived membrane, a morphogenic event required for virus egress.

A mutation in the gene encoding the vaccinia virus 37,000-M(r) protein confers resistance to an inhibitor of virus envelopment and release

Plaque formation in vaccinia virus is inhibited by the compound N1-isonicotinoyl-N2-3-methyl-4-chlorobenzoylhydrazine (IMCBH). We have isolated a mutant virus that forms wild-type plaques in the presence of the drug. Comparison of wild-type and mutant virus showed that both viruses produced similar amounts of infectious intracellular naked virus in the presence of the drug. In contrast to the mutant, no extracellular enveloped virus was obtained from IMCBH-treated cells infected with wild-type virus. Marker rescue experiments were used to map the mutation conferring IMCBH resistance to the mutant virus. The map position coincided with that of the gene encoding the viral envelope antigen of M(r) 37,000. Sequence analysis of both wild-type and mutant genes showed a single nucleotide change (G to T) in the mutant gene. In the deduced amino acid sequence, the mutation changes the codon for an acidic Asp residue in the wild-type gene to one for a polar noncharged Tyr residue in the mutant.

The polypeptide composition of vaccinia-infected cell membranes and rifampicin bodies

The protein and glycoprotein composition of a sucrose gradient fraction from vaccinia infected cells treated with rifampicin was studied. This particulate fraction contained cytoplasmic membranes and pleomorphic membranous structures. The glycoproteins (89, 42 and 20-23 kDa, respectively) were identified as the same glycoproteins that are found in plasma membranes of infected cells and the envelope of extracellular enveloped vaccinia (EEV). These glycoproteins could be solubilized by 0.1% NP-40. The Golgi membrane associated 41K acylated vaccinia protein was also NP-40 soluble. In contrast, most particulate fraction proteins (125, 100, 86, 65, 41, 39, 31, 27, 25, 14 and 12.5 kDa) with the exception of the 33 and 29 kDa proteins remained essentially insoluble after NP-40 treatment. The 86 and 65 kDa proteins are the rifampicin inhibited precursors to INV core proteins while the 33 and 29 kDa proteins are INV surface proteins. Twelve proteins behaved like their respective comigrating INV proteins when extracted with NP-40 and 2ME. Electron microscopy showed that a centrifuged sediment from NP-40 treated cells contained pleomorphic protein containing membranous structures that we have called rifampicin bodies. We conclude that (1) the major glycoproteins found in the particulate fraction from sucrose gradients are vaccinia glycoproteins residing in cytoplasmic membranes while (2) the major non-glycosylated proteins are components of the rifampicin bodies and that (3) the rifampicin bodies represent an intermediate in the morphogenetic process leading to mature INV.

Golgi-derived membranes that contain an acylated viral polypeptide are used for vaccinia virus envelopment

A 37,000-dalton polypeptide (p37K) present on purified extracellular vaccinia virus but absent from intracellular virus particles of classical morphology (G. Hiller et al., J. Virol. 39:903-913, 1981; L. G. Payne, J. Virol. 27:28-37, 1978) was further characterized. The polypeptide was only expressed in infected cells after onset of viral DNA replication. Phase partition experiments showed that it is relatively hydrophobic. Although p37K apparently is not a glycoprotein, in vivo radioisotope labeling detected tightly associated palmitic acid. Antibodies to p37K were used to monitor its distribution within infected cells at the light and electron microscopic levels. After synthesis p37K first accumulated in the Golgi region due to a tight membrane association. During progressing infection p37K-carrying membranes were used to form double-walled envelopes around brick-shaped vaccinia particles. Within these specialized vesicles vaccinia particles were moved through the cytoplasm toward the cell's surface, presumably along cellular routes for certain secretory products. Finally, single enveloped viruses were released into the extracellular space by an exocytotic process.

Effect of tunicamycin and monensin on biosynthesis, transport, and maturation of bovine herpesvirus type-1 glycoproteins

The effect of tunicamycin and monensin on the biosynthesis, intracellular transport, and maturation of bovine herpesvirus type-1 (BHV-1) glycoproteins was examined. Tunicamycin completely inhibited the production of infectious virus particles and significantly reduced the incorporation of [3H]glucosamine into viral glycoproteins. In the presence of monensin, reduced amounts of infectious virus particles were produced, which was mainly due to inhibition of virus release, rather than virus production. Monensin only slightly inhibited viral glycoprotein synthesis. The effects of these compounds on infectivity indicated that glycosylation is required for the production of infectious virus, though complete processing of the glycoproteins is not essential. In addition, egress of the virions from infected cells probably requires a functional Golgi complex. In the presence of tunicamycin or monensin various degrees of glycosylation of the major glycoproteins occurred, consequently their rates of migration differed from that of the normal glycoproteins. Tunicamycin completely blocked glycosylation of GVP 6/11a/16 and GVP 7. In contrast, GVP 3/9 and GVP 11b were partially glycosylated in the presence of tunicamycin. These results indicated that GVP 6/11a/16 and GVP 7 are N-linked glycoproteins, but GVP 3/9 and GVP 11b contain both N- and O-linked oligosaccharide side chains. Tunicamycin blocked the transport of all viral glycoproteins to the cell surface, suggesting that glycosylation is required for this process. In the presence of monensin, the viral glycoproteins were transported and expressed on the cell surface indicating that transport does not require complete processing of the glycoproteins and may occur via a Golgi-independent pathway. In addition, monensin-treated BHV-1 infected cells could act as target cells in an antibody-dependent cell cytotoxicity assay. Thus, complete glycosylation may not be essential for maintenance of antigenicity and participation in immune destruction.

Expression of vaccinia virus early mRNA in Ehrlich ascites tumor cells. 2. Part of the polysomes at an early stage of virus infection are not bound to the cytoskeleton

A method for preparing detergent cytoskeletons from uninfected or vaccinia-virus-infected cells is described. This method resulted in the fractionation of the cytoplasmic compartment into soluble and cytoskeletal fractions. More than 85% of small molecules and tRNA were released from the cytoskeleton and recovered into the soluble fraction. The cytoskeletal fraction contained about 40% of the cytoplasmic proteins and 67% of total cytoplasmic RNA. Similar values were obtained for vaccinia-virus-infected cells. In contrast, whereas 85% of the cellular polysomes and poly(A)-rich RNA remained associated with the cytoskeleton in uninfected cells, more than 40% of vaccinia early mRNA engaged into polysomes was found to be not associated with the cytoskeleton. A similar partition was found when the viral RNA was labeled for 15 min at 5 min and 20 min after the infection or when varying the duration of the pulse. Soluble and cytoskeletal viral polysomes were found to synthesize a similar set of proteins after translation in vitro of the corresponding mRNA. The fate of rapidly labeled cellular poly(A)-rich RNA upon vaccinia virus infection was followed by a glucosamine/uridine chase procedure, and also that of relatively stable poly(A)-rich RNA after long-term labeling and chase. In both cases no release of poly(A)-rich RNA from the cytoskeleton occurred after vaccinia virus infection. These experiments reveal that cellular mRNA remains associated to the cytoskeleton in EAT cells infected with vaccinia virus (early period) whereas at least 40% of the vaccinia early polysomes are not associated with the cytoskeleton. A model for vaccinia early mRNA metabolism is presented, which may account for the rapid shut-off of host protein synthesis.

The effect of cytochalasin D and monensin on enveloped vaccinia virus release

Both monensin and cytochalasin D reduced the production of infectious cell associated virus and infectious extracellular virus with the latter clearly being the more sensitive. The difference in yields were even more clearly seen if the yield of virus particles was monitored instead of yield of infectious virus. Addition of 1 microgram/ml cytochalasin D or 1 microM monensin to the growth medium of vaccinia virus-infected cells inhibited the appearance of extracellular enveloped vaccinia virus (EEV) in the growth medium without affecting the production of intracellular naked vaccinia virus (INV) particles. Although EEV was not released into the medium of cytochalasin D treated cells, EEV was, nevertheless, detectable in CsCl gradients of cell associated virus. Monensin treatment did not affect the synthesis of vaccinia glycoproteins but did significantly reduce the transport of these glycoproteins to the cell surface and also reduced the secretion of proteins. Monensin had the additional effect of causing the appearance of numerous large vacuoles in the cytoplasm. Vaccinia is normally wrapped by cytoplasmic membranes in preparation for release. The monensin induced conversion of cytoplasmic membranes to large vacuoles is presumably the basis for the block in virus wrapping and subsequent release. Cytochalasin D did not alter any of the steps in protein synthesis, transport or secretion. Electronmicroscopic studies confirmed the existence of EEV on the surface of infected cells treated with cytochalasin D. This drug which specifically affects cellular microfilament organisation thus imposes a block on the final release of EEV from the cell surface.