Elliott G, Mouzakitis G, O'Hare P (1995) VP16 interacts via its activation domain with VP22, a tegument protein of herpes simplex virus, and is relocated to a novel macromolecular assembly in coexpressing cells., J Virol 69 (12) pp. 7932-7941
In addition to its function as a powerful transactivator of viral immediate-early transcription, VP16 is an essential component of the herpes simplex virus (HSV) virion. As such, VP16 is introduced into cells, to effect its function in transactivation, as part of the virus tegument. Here we examine the potential for VP16 protein-protein interactions specific to virus-infected cells and show that VP16 copurifies in a highly enriched fraction with a single major polypeptide which we identify as the virus-encoded structural protein VP22. We further show that in vitro-translated VP22 binds specifically to purified VP16. The activation domain of VP16 was required and largely sufficient for this binding. Mutations within this domain, which disrupt its transactivation function, also affected VP22 binding. Furthermore, we show that while VP16 and VP22 showed distinct patterns of compartmentalization in vivo, coexpression of both proteins resulted in a profound reorganization from their normal locations to a novel macromolecular assembly. The colocalization was also dependent on the activation domain of VP16 but required additional determinants within the N terminus. These results are discussed in the context of VP16 regulation of transcription both early in infection during delivery of tegument proteins and at late times during virus assembly.
Elliott G, O'Hare P (1998) Herpes simplex virus type 1 tegument protein VP22 induces the stabilization and hyperacetylation of microtubules., J Virol 72 (8) pp. 6448-6455
The role of the herpes simplex virus type 1 tegument protein VP22 during infection is as yet undefined. We have previously shown that VP22 has the unusual property of efficient intercellular transport, such that the protein spreads from single expressing cells into large numbers of surrounding cells. We also noted that in cells expressing VP22 by transient transfection, the protein localizes in a distinctive cytoplasmic filamentous pattern. Here we show that this pattern represents a colocalization between VP22 and cellular microtubules. Moreover, we show that VP22 reorganizes microtubules into thick bundles which are easily distinguishable from nonbundled microtubules. These bundles are highly resistant to microtubule-depolymerizing agents such as nocodazole and incubation at 4 degreesC, suggesting that VP22 has the capacity to stabilize the microtubule network. In addition, we show that the microtubules contained in these bundles are modified by acetylation, a marker for microtubule stability. Analysis of infected cells by both immunofluorescence and measurement of microtubule acetylation further showed that colocalization between VP22 and microtubules, and induction of microtubule acetylation, also occurs during infection. Taken together, these results suggest that VP22 exhibits the properties of a classical microtubule-associated protein (MAP) during both transfection and infection. This is the first demonstration of a MAP encoded by an animal virus.
Donnelly M, Elliott G (2001) Nuclear localization and shuttling of herpes simplex virus tegument protein VP13/14., J Virol 75 (6) pp. 2566-2574
The herpes simplex virus type 1 gene UL47 encodes the tegument proteins referred to collectively as VP13/14, which are believed to be differentially modified forms of the same protein. Here we show that the major product of the UL47 gene during transient expression is VP14, suggesting that some feature of virus infection is required to produce VP13. We have tagged VP13/14 with green fluorescent protein and have demonstrated that the protein is targeted efficiently to the nucleus, where it often localizes in numerous punctate domains. Furthermore, we show that removal of the N-terminal 127 residues of the protein abrogates nuclear accumulation, and we have identified a 14-amino-acid peptide from this region that is sufficient to function as a nuclear targeting signal and transport a heterologous protein to the nucleus. This short peptide contains two runs of four arginine residues, suggesting that the VP13/14 nuclear localization signal may behave in a manner similar to that of the arginine-rich nuclear localization signals of the retrovirus transactivator proteins Tat, Rev, and Rex. In addition, by using heterokaryon assays, we show that VP13/14 is capable of shuttling between the nucleus and cytoplasm of the cell, a property that may be attributed to three leucine-rich stretches in the C-terminal half of the protein that again bear similarity to the nuclear export signals of Rev and Rex. This is the first demonstration of a tegument protein that is specifically targeted to the nucleus, a feature which may be relevant both during virus entry, when VP13/14 enters the cell as a component of the tegument, and at later times, when large amounts of newly synthesized VP13/14 are present within the cell.
Donnelly M, Verhagen J, Elliott G (2007) RNA binding by the herpes simplex virus type 1 nucleocytoplasmic shuttling protein UL47 is mediated by an N-terminal arginine-rich domain that also functions as its nuclear localization signal., J Virol 81 (5) pp. 2283-2296
The function of the alphaherpesvirus UL47 tegument protein has not yet been defined. Nonetheless, previous studies with transfected cells have shown that both the herpes simplex virus type 1 homologue (hUL47, or VP13/14) and the bovine herpesvirus type 1 (BHV-1) homologue (bUL47, or VP8) have the capacity to shuttle between the nucleus and the cytoplasm. Furthermore, hUL47 packaged into the virion has also been shown to bind several individual virus-specific RNA transcripts. Here, we extend these observations and show that hUL47 binds a wide range of RNA species in vitro. It has a high affinity for polyadenylated transcripts but has no apparent selectivity for virus-encoded RNA over cellular RNA. We also show that the virion population of bUL47 binds RNA in vitro. However, while purified recombinant hUL47 retains its RNA binding activity, recombinant bUL47 does not, suggesting that the BHV-1 homologue may require virus-induced modification for its activity. We identify the minimal RNA binding domain in hUL47 as a 26-residue N-terminal peptide containing an arginine-rich motif that is essential but not sufficient for optimal RNA binding, and we demonstrate that this RNA binding domain incorporates the hUL47 minimal nuclear localization signal. In addition, we show that soon after hUL47 is expressed during infection, it colocalizes in the infected cell nucleus with ICP4, the major virus transcriptional activator. Using RNA immunoprecipitations, we demonstrate that hUL47 is also bound in vivo to at least one viral transcript, the ICP0 mRNA. Taken together, these results suggest that hUL47 may play a role in RNA biogenesis in the infected cell.
Martin A, O'Hare P, McLauchlan J, Elliott G (2002) Herpes simplex virus tegument protein VP22 contains overlapping domains for cytoplasmic localization, microtubule interaction, and chromatin binding., J Virol 76 (10) pp. 4961-4970
We have previously shown that the 301-amino-acid herpes simplex virus tegument protein VP22 exhibits a range of subcellular localization patterns when expressed in isolation from other virus proteins. By using live-cell analysis of cells expressing green fluorescent protein (GFP)-tagged VP22 we have shown that when VP22 is first expressed in the cell it localizes to the cytoplasm, where, when present at high enough concentrations, it can assemble onto microtubules, causing them to bundle and become highly stabilized. In addition we have shown that when a cell expressing VP22 enters mitosis, the cytoplasmic population of VP22 translocates to the nucleus, where it efficiently binds mitotic chromatin. Here we have investigated the specific regions of the VP22 open reading frame required for these properties. Using GFP-VP22 as our starting molecule, we have constructed a range of N- and C-terminal truncations and analyzed their localization patterns in live cells. We show that the C-terminal 242 residues of VP22 are sufficient to induce microtubule bundling. Within this subregion, the C-terminal 89 residues contain a signal for cytoplasmic localization of the protein, while a larger region comprising the C-terminal 128 residues of the VP22 protein is required for mitotic chromatin binding. Furthermore, a central 100-residue domain of VP22 maintains the ability to bind microtubules without inducing bundling, suggesting that additional regions flanking this microtubule binding domain may be required to alter the microtubule network. Hence, the signals involved in dictating the complex localization patterns of VP22 are present in overlapping regions of the protein.
Potel C, Elliott G (2005) Phosphorylation of the herpes simplex virus tegument protein VP22 has no effect on incorporation of VP22 into the virus but is involved in optimal expression and virion packaging of ICP0., J Virol 79 (22) pp. 14057-14068
Herpes simplex virus VP22 is a major tegument protein of unknown function. Very recently, we reported that the predominant effect of deleting the VP22 gene was on the expression, localization, and virion incorporation of ICP0. In addition, the Delta22 virus replicated poorly in epithelial MDBK cells. We have also previously shown that VP22 interacts with the tegument protein VP16 and the cellular microtubule network. While the majority of VP22 in infected cells is highly phosphorylated, the nonphosphorylated form of VP22 is the predominant species in the virion, suggesting a differential requirement for phosphorylation through virus replication. Hence, to study the significance of VP22 phosphorylation, we have now constructed two recombinant viruses expressing green fluorescent protein-VP22 (G22) in which the previously identified serine phosphorylation sites have been mutated either to alanine to abolish the phosphorylation status of VP22 (G22P-) or to glutamic acid to mimic permanent phosphorylation (G22P+). Localization studies indicated that the G22P- protein associated tightly with microtubules in some infected cells, suggesting that VP22 phosphorylation may control its interaction with the microtubule network. By contrast, VP22 phosphorylation had no effect on its ability to interact with VP16 and, importantly, had no effect on the relative packaging of VP22. Intriguingly, virion packaging of ICP0 was reduced in the G22P+ virus while ICP0 expression was reduced in the G22P- virus, suggesting that these two ICP0 defects, previously observed in the Delta22 virus, were attributable to different forms of VP22. Furthermore, the Delta22 virus replication defect in MDBK cells correlated with the expression of constitutively charged VP22 in the G22P+ virus. Taken together, these results suggest an important role for VP22 phosphorylation in its relationship with ICP0.
Hutchinson I, Whiteley A, Browne H, Elliott G (2002) Sequential localization of two herpes simplex virus tegument proteins to punctate nuclear dots adjacent to ICP0 domains., J Virol 76 (20) pp. 10365-10373
The subcellular localization of herpes simplex virus tegument proteins during infection is varied and complex. By using viruses expressing tegument proteins tagged with fluorescent proteins, we previously demonstrated that the major tegument protein VP22 exhibits a cytoplasmic localization, whereas the major tegument protein VP13/14 localizes to nuclear replication compartments and punctate domains. Here, we demonstrate the presence of a second minor population of VP22 in nuclear dots similar in appearance to those formed by VP13/14. We have constructed the first-described doubly fluorescence-tagged virus expressing VP22 and VP13/14 as fusion proteins with cyan fluorescent protein and yellow fluorescent protein, respectively. Visualization of both proteins within the same live infected cells has indicated that these two tegument proteins localize to the same nuclear dots but that VP22 appears there earlier than VP13/14. Further studies have shown that these tegument-specific dots are detectable as phase-dense bodies as early as 2 h after infection and that they are different from the previously described nuclear domains that contain capsid proteins. They are also different from the ICP0 domains formed at cellular nuclear domain 10 sites early in infection but, in almost all cases, are located in juxtaposition to these ICP0 domains. Hence, these tegument proteins join a growing number of proteins that are targeted to discrete nuclear domains in the herpesvirus-infected cell nucleus.
Dilber MS, Phelan A, Aints A, Mohamed AJ, Elliott G, Smith CIE, O'Hare P (1999) Intercellular delivery of thymidine kinase prodrug activating enzyme by the herpes simplex virus protein, VP22, GENE THERAPY 6 (1) pp. 12-21 STOCKTON PRESS
Elliott G, O'Hare P (1997) Intercellular trafficking and protein delivery by a herpesvirus structural protein., Cell 88 (2) pp. 223-233
We show that the HSV-1 structural protein VP22 has the remarkable property of intercellular transport, which is so efficient that following expression in a subpopulation the protein spreads to every cell in a monolayer, where it concentrates in the nucleus and binds chromatin. VP22 movement was observed both after delivery of DNA by transfection or microinjection and during virus infection. Moreover, we demonstrate that VP22 trafficking occurs via a nonclassical Golgi-independent mechanism. Sensitivity to cytochalasin D treatment suggests that VP22 utilizes a novel trafficking pathway that involves the actin cytoskeleton. In addition, we demonstrate intercellular transport of a VP22 fusion protein after endogenous synthesis or exogenous application, indicating that VP22 may have potential in the field of protein delivery.
Herpes simplex virus 1 (HSV1) infects humans through stratified epithelia that are composed primarily of keratinocytes. The route of HSV1 entry into keratinocytes has been the subject of limited investigation, but is proposed to involve pH-dependent endocytosis, requiring the gD-binding receptor, nectin-1. Here, we have utilized the nTERT human keratinocyte cell line as a new model for dissecting the mechanism of HSV1 entry in to the host. Although immortalised, these cells nonetheless retain normal growth and differentiation properties of primary cells. Using siRNA depletion studies, we confirm that, despite nTERT cells expressing high levels of the alternative gD receptor HVEM, HSV1 requires nectin-1, not HVEM, to enter these cells. Strikingly, virus entry into nTERT cells occured with unusual rapidity, such that maximum penetration was achieved within 5 minutes. Moreover, HSV1 was able to enter keratinocytes but not other cell types at temperatures as low as 7°C, conditions where endocytosis was shown to be completely inhibited. Transmission electron microscopy of early entry events at both 37°C and 7°C identified numerous examples of naked virus capsids located immediately beneath the plasma membrane, with no evidence of virions in cytoplasmic vesicles. Taken together, these results imply that HSV1 uses the nectin-1 receptor to enter human keratinocyte cells via a previously uncharacterised rapid plasma membrane fusion pathway that functions at low temperature. These studies have important implications for current understanding of the relationship between HSV1 and its relevant in vivo target cell.
Elliott G, O'Hare P (2000) Cytoplasm-to-nucleus translocation of a herpesvirus tegument protein during cell division., J Virol 74 (5) pp. 2131-2141
We have previously shown that the herpes simplex virus tegument protein VP22 localizes predominantly to the cytoplasm of expressing cells. We have also shown that VP22 has the unusual property of intercellular spread, which involves the movement of VP22 from the cytoplasm of these expressing cells into the nuclei of nonexpressing cells. Thus, VP22 can localize in two distinct subcellular patterns. By utilizing time-lapse confocal microscopy of live cells expressing a green fluorescent protein-tagged protein, we now report in detail the intracellular trafficking properties of VP22 in expressing cells, as opposed to the intercellular trafficking of VP22 between expressing and nonexpressing cells. Our results show that during interphase VP22 appears to be targeted exclusively to the cytoplasm of the expressing cell. However, at the early stages of mitosis VP22 translocates from the cytoplasm to the nucleus, where it immediately binds to the condensing cellular chromatin and remains bound there through all stages of mitosis and chromatin decondensation into the G(1) stage of the next cycle. Hence, in VP22-expressing cells the subcellular localization of the protein is regulated by the cell cycle such that initially cytoplasmic protein becomes nuclear during cell division, resulting in a gradual increase over time in the number of nuclear VP22-expressing cells. Importantly, we demonstrate that this process is a feature not only of VP22 expressed in isolation but also of VP22 expressed during virus infection. Thus, VP22 utilizes an unusual pathway for nuclear targeting in cells expressing the protein which differs from the nuclear targeting pathway used during intercellular trafficking.
O'Rourke D, Elliott G, Papworth M, Everett R, O'Hare P (1998) Examination of determinants for intranuclear localization and transactivation within the RING finger of herpes simplex virus type 1 IE110k protein., J Gen Virol 79 ( Pt 3) pp. 537-548
The herpesvirus regulatory protein IE110k possesses a cysteine-rich, RING finger motif required for its role in transactivation and virus replication. IE110k also localizes to subnuclear compartments termed PODs (PML oncogenic domains). Localization to PODs induces redistribution of the proteins associated with this nuclear compartment, including the cellular RING finger protein, PML. Here we construct a series of deletions, RING domain swaps and point mutations to analyse specific requirements within the IE110k RING finger for subnuclear localization, redistribution of PML and transactivation and we examine the relationship between these activities. We find that IE110k localizes to distinct nuclear subdomains that are more numerous than the cellular PODs and that mutation of two residues within a predicted loop of the RING finger, or replacing the IE110k RING finger with a RING finger from a cellular gene abrogates the ability of IE110k to localize to these extra compartments and traps IE110k in the original PODs. We further demonstrate that RING fingers from the cellular genes mdm-2 and Bmi I, when placed within IE110k, alter the nuclear distribution of IE110k, do not transactivate, and do not redistribute PML. We also demonstrate that the majority of wild-type IE110k, like PML, is associated with the nuclear matrix. Although substitutions and deletions within the RING finger abolish transactivation, these mutant proteins remain tightly associated with the matrix. These results further dissect the determinants involved in different aspects of nuclear compartmentalization of IE110k and are discussed in relation to PML, PODs and the IE110k RING finger.
Brewis N, Phelan A, Webb J, Drew J, Elliott G, O'Hare P (2000) Evaluation of VP22 spread in tissue culture., J Virol 74 (2) pp. 1051-1056
We compare methods of detection of intercellular transport of the herpes simplex virus protein VP22 and of a green fluorescent protein (GFP)-VP22 fusion protein. Spread of both proteins was observed by immunofluorescence (IF) using organic fixatives. Spread of both proteins was also detected by IF after paraformaldehyde (PFA) fixation and detergent permeabilization, albeit at reduced levels. However, while spread of GFP-VP22 was observed by examining intrinsic GFP fluorescence after methanol fixation, little spread was observed after PFA fixation, suggesting that the levels of the fusion protein in recipient cells were below the detection limits of intrinsic-fluorescence or that PFA fixation quenches the fluorescence of GFP-VP22. We further considered whether elution of VP22 from methanol-fixed cells and postfixation binding to surrounding cells contributed to the increased detection of spread observed after methanol fixation. The results show that while this could occur, it appeared to be a minor effect not accounting for the observed VP22 cell-to-cell spread in culture.
Assembly of the herpesvirus tegument is poorly understood but is believed to involve interactions between outer tegument proteins and the cytoplasmic domains of envelope glycoproteins. Here, we present the detailed characterization of a multicomponent glycoprotein-tegument complex found in herpes simplex virus 1 (HSV-1)-infected cells. We demonstrate that the tegument protein VP22 bridges a complex between glycoprotein E (gE) and glycoproteinM(gM). Glycoprotein I (gI), the known binding partner of gE, is also recruited into this gE-VP22-gM complex but is not required for its formation. Exclusion of the glycoproteins gB and gD and VP22's major binding partner VP16 demonstrates that recruitment of virion components into this complex is highly selective. The immediate-early protein ICP0, which requires VP22 for packaging into the virion, is also assembled into this gE-VP22-gM-gI complex in a VP22-dependent fashion. Although subcomplexes containing VP22 and ICP0 can be formed when either gE or gM are absent, optimal complex formation requires both glycoproteins. Furthermore, and in line with complex formation, neither of these glycoproteins is individually required for VP22 or ICP0 packaging into the virion, but deletion of gE and gM greatly reduces assembly of both VP22 and ICP0. Double deletion of gE and gM also results in small plaque size, reduced virus yield, and defective secondary envelopment, similar to the phenotype previously shown for pseudorabies virus. Hence, we suggest that optimal gE-VP22-gM-gI-ICP0 complex formation correlates with efficient virus morphogenesis and spread. These data give novel insights into the poorly understood process of tegument acquisition. © 2012, American Society for Microbiology.
Elliott G, O'Reilly D, O'Hare P (1996) Phosphorylation of the herpes simplex virus type 1 tegument protein VP22., Virology 226 (1) pp. 140-145
The herpes simplex virus type 1 tegument protein VP22 is known to be highly phosphorylated during infection. Here we show that two electrophoretic forms of VP22 can be identified in infected cell extracts and that this heterogeneity is accounted for by phosphorylation. Furthermore, the nonphosphorylated form of VP22 appears to be specifically incorporated into virions. We also show that the phosphorylated form of VP22 is the only form detected during transient transfection and as such that VP22 can act as a substrate for a cellular kinase. Phospho-amino acid and phospho-peptide analyses of in vivo labeled VP22 were utilized to demonstrate that the phosphorylation profiles of VP22 synthesized during transfection and infection are the same. In both cases VP22 was modified solely on serine residues located in the N-terminal 120 residues of the protein. Moreover, in vitro phosphorylation was utilized to show that the constitutive cellular kinase, casein kinase II, which has four serine consensus recognition sites at the N-terminus of VP22, phosphorylates VP22 in the same manner as observed in vivo. This kinase also phosphorylates VP22 at the N-terminus in intact capsid-tegument structures. Casein kinase II is therefore likely to be the major kinase of VP22 during infection.
Ebert K, Depledge DP, Breuer J, Harman L, Elliott G (2013) Mode of Virus Rescue Determines the Acquisition of VHS Mutations in VP22 Negative Viruses of Herpes Simplex Virus Type 1., J Virol
Herpes simplex virus 1 deleted for VP22 is proposed to require secondary mutation of VHS for viability. Here we show that a replication-competent 22 virus constructed by homologous recombination maintains a Wt VHS gene and has no other gross mutations. By contrast, 22 viruses recovered from a bacterial artificial chromosome contain multiple codon changes within a conserved region of VHS. Hence, the mode of virus rescue influences the acquisition of secondary mutations.
Johns HL, Gonzalez-Lopez C, Sayers CL, Hollinshead M, Elliott G (2013) Rab6 Dependent Post-Golgi Trafficking of HSV1 Envelope Proteins to Sites of Virus Envelopment, Traffic
Herpes simplex virus 1 (HSV1) is an enveloped virus that uses undefined transport carriers for trafficking of its glycoproteins to envelopment sites. Screening of an siRNA library against 60 Rab GTPases revealed Rab6 as the principal Rab involved in HSV1 infection, with its depletion preventing Golgi-to-plasma membrane transport of HSV1 glycoproteins in a pathway used by several integral membrane proteins but not the luminal secreted protein Gaussia luciferase. Knockdown of Rab6 reduced virus yield to 1% and inhibited capsid envelopment, revealing glycoprotein exocytosis as a prerequisite for morphogenesis. Rab6-dependent virus production did not require the effectors myosin-II, bicaudal-D, dynactin-1 or rabkinesin-6, but was facilitated by ERC1, a factor involved in linking microtubules to the cell cortex. Tubulation and exocytosis of Rab6-positive, glycoprotein-containing membranes from the Golgi was substantially augmented by infection, resulting in enhanced and targeted delivery to cell tips. This reveals HSV1 morphogenesis as one of the first biological processes shown to be dependent on the exocytic activity of Rab6. © 2013 The Authors.
Phelan A, Elliott G, O'Hare P (1998) Intercellular delivery of functional p53 by the herpesvirus protein VP22., Nat Biotechnol 16 (5) pp. 440-443
The herpes simplex virus type 1 (HSV-1) virion protein VP22 exhibits the remarkable property of intercellular trafficking whereby the protein spreads from the cell in which it is synthesized to many surrounding cells. In addition to having implications for protein trafficking mechanisms, this function of VP22 might be exploited to overcome a major hurdle in gene therapy, i.e., efficient delivery of genes and gene products. We show that chimeric polypeptides, consisting of VP22 linked to the entire p53 protein, retain their ability to spread between cells and accumulate in recipient cell nuclei. Furthermore the p53-VP22 chimeric protein efficiently induces apoptosis in p53 negative human osteosarcoma cells resulting in a widespread cytotoxic effect. The intercellular delivery of functional p53-VP22 fusion protein is likely to prove beneficial in therapeutic strategies based on restoration of p53 function. These results, demonstrating intracellular transport of large functional proteins, indicate that VP22 delivery may have applications in gene therapy.
Elliott G, Hafezi W, Whiteley A, Bernard E (2005) Deletion of the herpes simplex virus VP22-encoding gene (UL49) alters the expression, localization, and virion incorporation of ICP0., J Virol 79 (15) pp. 9735-9745
The role of the herpes simplex virus tegument protein VP22 is not yet known. Here we describe the characterization of a virus in which the entire VP22 open reading frame has been deleted. We show that VP22 is not essential for virus growth but that virus lacking VP22 (Delta22) displays a cell-specific replication defect in epithelial MDBK cells. Virus particles assembled in the absence of VP22 show few obvious differences to wild-type (WT) particles, except for a moderate reduction in glycoproteins gD and gB. In addition, the Delta22 virus exhibits a general delay in the initiation of virus protein synthesis, but this is not due to a glycoprotein-related defect in virus entry. Intriguingly, however, the absence of VP22 has an obvious effect on the intracellular level of the immediate-early (IE) protein ICP0. Moreover, following translocation from the nucleus to the cytoplasm, ICP0 is unable to localize to the characteristic cytoplasmic sites observed in a WT infection. We demonstrate that, in WT-infected cells, VP22 and ICP0 are concentrated in the same cytoplasmic sites. Furthermore, we show that, while ICP0 and ICP4 are components of WT extracellular virions, the altered localization of ICP0 in the cytoplasm of Delta22-infected cells correlates with an absence of both ICP0 and ICP4 from Delta22 virions. Hence, while a role has not yet been defined for virion IE proteins in virus infection, our results suggest that their incorporation is a specific event requiring the tegument protein VP22. This report provides the first direct evidence that VP22 influences virus assembly.
Elliott G, O'Hare P (1999) Intercellular trafficking of VP22-GFP fusion proteins., Gene Ther 6 (1) pp. 149-151
The herpes simplex virus protein VP22 exhibits the unusual property of intercellular transport whereby after being synthesised in a subpopulation of cells, in which it is largely cytoplasmic, the protein is transported to adjacent cells where it accumulates mainly in the nucleus. Here we examine the transport of a fusion protein consisting of VP22 linked to the green fluorescent protein (GFP). Intercellular transport, nuclear accumulation and chromatin binding of VP22-GFP could be detected by intrinsic GFP fluorescence in fixed cells. However, while the cytoplasmic localisation of VP22-GFP could be detected in live cells actively synthesising the protein, we were unable to detect intercellular transport by intrinsic GFP fluorescence in livecells, indicating that the levels of transported protein may be below those required for live detection, or that GFP fluorescence was quenched. The use of antibody to GFP was more sensitive than intrinsic GFP fluorescence and allowed ready detection of transport and nuclear accumulation of VP22-GFP. Intercellular transport was also confirmed in coplating experiments. Consistent with previous results showing a requirement for the C-terminus of VP22 in transport of the native protein, a fusion protein consisting of GFP linked to the N-terminal 1-192 residues of VP22 failed to transport between cells. The results support the proposal that VP22 has the ability to transport cargo proteins between cells and that it has significant potential in the field of gene therapy.
Hafezi W, Bernard E, Cook R, Elliott G (2005) Herpes simplex virus tegument protein VP22 contains an internal VP16 interaction domain and a C-terminal domain that are both required for VP22 assembly into the virus particle., J Virol 79 (20) pp. 13082-13093
Many steps along the herpesvirus assembly and maturation pathway remain unclear. In particular, the acquisition of the virus tegument is a poorly understood process, and the molecular interactions involved in tegument assembly have not yet been defined. Previously we have shown that the two major herpes simplex virus tegument proteins VP22 and VP16 are able to interact, although the relevance of this to virus assembly is not clear. Here we have constructed a number of recombinant viruses expressing N- and C-terminal truncations of VP22 and have used them to identify regions of the protein involved in its assembly into the virus structure. Analysis of the packaging of these VP22 variants into extracellular virions revealed that the C terminus of VP22 is absolutely required for this process, with removal of the C-terminal 89 residues abrogating its incorporation. However, while these 89 residues alone were sufficient for specific incorporation of small amounts of VP22 into the tegument, efficient packaging of VP22 to the levels of full-length protein required an additional 52 residues of the protein. Coimmunoprecipitation assays indicated that these 52 residues also contained the interaction domain for VP16. Furthermore, analysis of the subcellular localization of the mutant forms of VP22 revealed that only those truncations that were efficiently assembled formed characteristic cytoplasmic trafficking complexes, suggesting that these complexes may represent the cellular location for VP22 assembly into the virus. Taken together, these results suggest that there are two determinants involved in the packaging of VP22-a C-terminal domain and an internal VP16 interaction domain, both of which are required for the efficient recruitment of VP22 to sites of virus assembly.
The mechanism by which herpesviruses acquire their tegument is not yet clear. One model is that outer tegument proteins are recruited by the cytoplasmic tails of viral glycoproteins. In the case of herpes simplex virus tegument protein VP22, interactions with the glycoproteins gE and gD have been shown. We have previously shown that the C-terminal half of VP22 contains the necessary signal for assembly into the virus. Here, we show that during infection VP22 interacts with gE and gM, as well as its tegument partner VP16. However, by using a range of techniques we were unable to demonstrate VP22 binding to gD. By using pulldown assays, we show that while the cytoplasmic tails of both gE and gM interact with VP22, only gE interacts efficiently with the C-terminal packaging domain of VP22. Furthermore, gE but not gM can recruit VP22 to the Golgi/trans-Golgi network region of the cell in the absence of other virus proteins. To examine the role of the gE-VP22 interaction in infection, we constructed a recombinant virus expressing a mutant VP22 protein with a 14-residue deletion that is unable to bind gE (gEbind). Coimmunoprecipitation assays confirmed that this variant of VP22 was unable to complex with gE. Moreover, VP22 was no longer recruited to its characteristic cytoplasmic trafficking complexes but exhibited a diffuse localization. Importantly, packaging of this variant into virions was abrogated. The mutant virus exhibited poor growth in epithelial cells, similar to the defect we have observed for a VP22 knockout virus. These results suggest that deletion of just 14 residues from the VP22 protein is sufficient to inhibit binding to gE and hence recruitment to the viral envelope and assembly into the virus, resulting in a growth phenotype equivalent to that produced by deleting the entire reading frame. Copyright © 2009, American Society for Microbiology. All Rights Reserved.
Williams P, Verhagen J, Elliott G (2008) Characterization of a CRM1-dependent nuclear export signal in the C terminus of herpes simplex virus type 1 tegument protein UL47, Journal of Virology 82 (21) pp. 10946-10952
The herpes simplex virus type 1 tegument protein known as VP13/14, or hUL47, localizes to the nucleus and binds RNA. Using fluorescence loss in photobleaching analysis, we show that hUL47 undergoes nucleocytoplasmic shuttling during infection. We identify the hUL47 nuclear export signal (NES) as a C-terminal 10-residue hydrophobic peptide and measure its efficiency relative to that of the classical human immunodeficiency virus type 1 Rev NES. Finally, we show that the hUL47 NES is sensitive to the inhibitor of CRM1-mediated nuclear export leptomycin B. Hence, hUL47 joins a growing list of virus-encoded RNA-binding proteins that use CRM1 to exit the nucleus. Copyright © 2008, American Society for Microbiology. All Rights Reserved.
Hollinshead M, Johns HL, Sayers CL, Gonzalez-Lopez C, Smith GL, Elliott G (2012) Endocytic tubules regulated by Rab GTPases 5 and 11 are used for envelopment of herpes simplex virus., EMBO J 31 (21) pp. 4204-4220
Enveloped viruses employ diverse and complex strategies for wrapping at cellular membranes, many of which are poorly understood. Here, an ultrastructural study of herpes simplex virus 1 (HSV1)-infected cells revealed envelopment in tubular membranes. These tubules were labelled by the fluid phase marker horseradish peroxidase (HRP), and were observed to wrap capsids as early as 2 min after HRP addition, indicating that the envelope had recently cycled from the cell surface. Consistent with this, capsids did not colocalise with either the trans-Golgi network marker TGN46 or late endosomal markers, but showed coincidence with the transferrin receptor. Virus glycoproteins were retrieved from the plasma membrane (PM) to label wrapping capsids, a process that was dependent on both dynamin and Rab5. Combined depletion of Rab5 and Rab11 reduced virus yield to
Maringer K, Elliott G (2010) Recruitment of herpes simplex virus type 1 immediate-early protein ICP0 to the virus particle, Journal of Virology 84 (9) pp. 4682-4696
Although the herpes simplex virus type 1 (HSV-1) tegument is comprised of a large number of viral and cellular proteins, how and where in the cell these proteins are recruited into the virus structure is poorly understood. We have shown previously that the immediate-early gene product ICP0 is packaged by a mechanism dependent on the major tegument protein VP22, while others have shown a requirement for ICP27. We now extend our studies to show that ICP0 packaging correlates directly with the ability of ICP0 to complex with VP22 in infected cells. ICP27 is not, however, present in this VP22-ICP0 complex but is packaged into the virion in a VP22- and ICP0-independent manner. Biochemical fractionation of virions indicated that ICP0 associates tightly with the virus capsid, but intranuclear capsids contained no detectable ICP0. The RING finger domain of ICP0 and the N terminus of VP22 were both shown to be essential but not sufficient for ICP0 packaging and complex formation. Strikingly, however, the N-terminal region of VP22, while unable to form a complex with ICP0, inhibited its translocation from the nucleus to the cytoplasm. PML degradation by ICP0 was efficient in cells infected with this VP22 mutant virus, confirming that ICP0 retains activity. Hence, we would suggest that VP22 is an important molecular partner of ICP0 that controls at least one of its activities: its assembly into the virion. Moreover, we propose that the pathway by which VP22 recruits ICP0 to the virion may begin in the nucleus prior to ICP0 translocation to its final site of assembly in the cytoplasm. Copyright © 2010, American Society for Microbiology.
Donnelly M, Elliott G (2001) Fluorescent tagging of herpes simplex virus tegument protein VP13/14 in virus infection., J Virol 75 (6) pp. 2575-2583
The cellular site of herpesvirus tegument assembly has yet to be defined. We have previously used a recombinant herpes simplex virus type 1 expressing a green fluorescent protein (GFP)-tagged tegument protein, namely VP22, to show that VP22 is localized exclusively to the cytoplasm during infection. Here we have constructed a similar virus expressing another fluorescent tegument protein, YFP-VP13/14, and have visualized the intracellular localization of this second tegument protein in live infected cells. In contrast to VP22, VP13/14 is targeted predominantly to the nuclei of infected cells at both early and late times in infection. More specifically, YFP-13/14 localizes initially to the nuclear replication compartments and then progresses into intense punctate domains that appear at around 12 h postinfection. At even later times this intranuclear punctate fluorescence is gradually replaced by perinuclear micropunctate and membranous fluorescence. While the vast majority of YFP-13/14 seems to be targeted to the nucleus, a minor subpopulation also appears in a vesicular pattern in the cytoplasm that closely resembles the pattern previously observed for GFP-22. Moreover, at late times weak fluorescence appears at the cell periphery and in extracellular virus particles, confirming that YFP-13/14 is assembled into virions. This predominantly nuclear targeting of YFP-13/14 together with the cytoplasmic targeting of VP22 may imply that there are multiple sites of tegument protein incorporation along the virus maturation pathway. Thus, our YFP-13/14-expressing virus has revealed the complexity of the intracellular targeting of VP13/14 and provides a novel insight into the mechanism of tegument, and hence virus, assembly.
Elliott G, O'Hare P (1995) Equine herpesvirus 1 gene 12, the functional homologue of herpes simplex virus VP16, transactivates via octamer sequences in the equine herpesvirus IE gene promoter., Virology 213 (1) pp. 258-262
The HSV-1 transactivator of immediate-early (IE) gene expression, VP16, has several functional homologues among the alphaherpesviruses which have not yet been extensively studied in relation to their modes of action. To date, nothing is known of the exact sites or mechanism of interaction of the equine herpesvirus type 1 (EHV-1) homologue, the gene 12 protein, with the EHV-1 IE promoter. We show that the gene 12 protein utilises the promoter proximal region of the IE gene to induce activation and identify four potential octamer DNA binding sites within that region. Although there was divergence from its consensus, Oct-1 bound to each of these sites in an in vitro complex formation assay, and in the presence of the gene 12 product a second complex of slower migration, which was also dependent on Oct-1, was detected. When each site was inserted into a basal promoter, two conferred activation by gene 12 with a resulting increase in expression of up to 50-fold compared to basal levels. These results show that, despite the differences between the two proteins, the mechanism of interaction of the gene 12 protein with its target is analogous to that of VP16.
van Leeuwen H, Elliott G, O'Hare P (2002) Evidence of a role for nonmuscle myosin II in herpes simplex virus type 1 egress., J Virol 76 (7) pp. 3471-3481
After cell entry, herpes simplex virus (HSV) particles are transported through the host cell cytoplasm to nuclear pores. Following replication, newly synthesized virus particles are transported back to the cell periphery via a complex pathway including a cytoplasmic phase involving some form of unenveloped particle. These various transport processes are likely to make use of one or more components of the cellular cytoskeletal systems and associated motor proteins. Here we report that the HSV type 1 (HSV-1) major tegument protein, VP22, interacts with the actin-associated motor protein nonmuscle myosin IIA (NMIIA). HSV-1 infection resulted in reorganization of NMIIA, inducing retraction of NMIIA from the cell periphery and condensation into a spoke-like distribution around the nucleus along with a second effect of accumulation in a perinuclear cluster. VP22 did not appear to colocalize with the reorganized cagelike distribution of NMIIA. However, VP22 has been previously reported to localize in a perinuclear vesicular pattern, and significant overlap was observed between this pattern and the perinuclear clusters of NMIIA. Inhibition of the ATPase activity of NMIIA with the myosin-specific inhibitor butanedione monoxime impaired the formation of the perinuclear vesicular VP22 accumulations and also the release of virus into the extracellular medium while having much less effect on the yield of cell-associated virus. Virus infection frequently results in the induction of highly extended processes emanating from the infected cell, and we observed that VP22-containing particles line up along NMIIA-containing filaments which run through these protrusions.
Elliott G, O'Hare P (1999) Live-cell analysis of a green fluorescent protein-tagged herpes simplex virus infection., J Virol 73 (5) pp. 4110-4119
Many stages of the herpes simplex virus maturation pathway have not yet been defined. In particular, little is known about the assembly of the virion tegument compartment and its subsequent incorporation into maturing virus particles. Here we describe the construction of a herpes simplex virus type 1 (HSV-1) recombinant in which we have replaced the gene encoding a major tegument protein, VP22, with a gene expressing a green fluorescent protein (GFP)-VP22 fusion protein (GFP-22). We show that this virus has growth properties identical to those of the parental virus and that newly synthesized GFP-22 is detectable in live cells as early as 3 h postinfection. Moreover, we show that GFP-22 is incorporated into the HSV-1 virion as efficiently as VP22, resulting in particles which are visible by fluorescence microscopy. Consequently, we have used time lapse confocal microscopy to monitor GFP-22 in live-cell infection, and we present time lapse animations of GFP-22 localization throughout the virus life cycle. These animations demonstrate that GFP-22 is present in a diffuse cytoplasmic location when it is initially expressed but evolves into particulate material which travels through an exclusively cytoplasmic pathway to the cell periphery. In this way, we have for the first time visualized the trafficking of a herpesvirus structural component within live, infected cells.
Boyer-Guittaut M, Birsoy K, Potel C, Elliott G, Jaffray E, Desterro JM, Hay RT, Oelgeschläger T (2005) SUMO-1 modification of human transcription factor (TF) IID complex subunits: inhibition of TFIID promoter-binding activity through SUMO-1 modification of hsTAF5., J Biol Chem 280 (11) pp. 9937-9945
The TFIID complex is composed of the TATA-binding protein (TBP) and TBP-associated factors (TAFs) and is the only component of the general RNA polymerase II (RNAP II) transcription machinery with intrinsic sequence-specific DNA-binding activity. Binding of transcription factor (TF) IID to the core promoter region of protein-coding genes is a key event in RNAP II transcription activation and is the first and rate-limiting step of transcription initiation complex assembly. Intense research efforts in the past have established that TFIID promoter-binding activity as well as the function of TFIID-promoter complexes is tightly regulated through dynamic TFIID interactions with positive- and negative-acting transcription regulatory proteins. However, very little is known about the role of post-translational modifications in the regulation of TFIID. Here we show that the human TFIID subunits hsTAF5 and hsTAF12 are modified by the small ubiquitin-related modifier SUMO-1 in vitro and in human cells. We identify Lys-14 in hsTAF5 and Lys-19 in hsTAF12 as the primary SUMO-1 acceptor sites and show that SUMO conjugation has no detectable effect on nuclear import or intranuclear distribution of hsTAF5 and hsTAF12. Finally, we demonstrate that purified human TFIID complex can be SUMO-1-modified in vitro at both hsTAF5 and hsTAF12. We find that SUMO-1 conjugation at hsTAF5 interferes with binding of TFIID to promoter DNA, whereas modification of hsTAF12 has no detectable effect on TFIID promoter-binding activity. Our observations suggest that reversible SUMO modification at hsTAF5 contributes to the dynamic regulation of TFIID promoter-binding activity in human cells.
Elliott G, O'Reilly D, O'Hare P (1999) Identification of phosphorylation sites within the herpes simplex virus tegument protein VP22., J Virol 73 (7) pp. 6203-6206
The herpes simplex virus protein VP22 is a major phosphoprotein of infected cells. In this study, we identify two serine phosphorylation sites within VP22 and show that the N-terminal site is a substrate for casein kinase II, while the extreme C-terminal site is a substrate for another, as yet unidentified, cellular kinase. Furthermore, we show that a mutant of VP22 which has both sites altered is unable to incorporate phosphate in vivo, confirming that there are no other phosphorylation sites within VP22.
Verhagen J, Hutchinson I, Elliott G (2006) Nucleocytoplasmic shuttling of bovine herpesvirus 1 UL47 protein in infected cells., J Virol 80 (2) pp. 1059-1063
Previous studies with transfected cells have shown that the herpes simplex virus type 1 (HSV-1) and bovine herpesvirus 1 (BHV-1) UL47 proteins shuttle between the nucleus and the cytoplasm. HSV-1 UL47 has also been shown to bind RNA. Here we examine the BHV-1 UL47 protein in infected cells using a green fluorescent protein-UL47-expressing virus. We show that UL47 is detected in the nucleus early in infection. We use fluorescence loss in photobleaching to show that nuclear UL47 undergoes rapid nucleocytoplasmic shuttling. Furthermore, we demonstrate that actinomycin D inhibits the reaccumulation of UL47 in the nuclei of infected cells. These results suggest that UL47 exhibits behavior similar to that of previously characterized RNA-transporting proteins.
Johns HL, Gonzalez-Lopez C, Sayers CL, Hollinshead M, Elliott G, Elliott G (2014) Rab6 Dependent Post-Golgi Trafficking of HSV1 Envelope Proteins to Sites of Virus Envelopment, Traffic 15 (2) pp. 157-178
Herpes simplex virus 1 (HSV1) is an enveloped virus that uses undefined transport carriers for trafficking of its glycoproteins to envelopment sites. Screening of an siRNA library against 60 Rab GTPases revealed Rab6 as the principal Rab involved in HSV1 infection, with its depletion preventing Golgi-to-plasma membrane transport of HSV1 glycoproteins in a pathway used by several integral membrane proteins but not the luminal secreted protein Gaussia luciferase. Knockdown of Rab6 reduced virus yield to 1% and inhibited capsid envelopment, revealing glycoprotein exocytosis as a prerequisite for morphogenesis. Rab6-dependent virus production did not require the effectors myosin-II, bicaudal-D, dynactin-1 or rabkinesin-6, but was facilitated by ERC1, a factor involved in linking microtubules to the cell cortex. Tubulation and exocytosis of Rab6-positive, glycoprotein-containing membranes from the Golgi was substantially augmented by infection, resulting in enhanced and targeted delivery to cell tips. This reveals HSV1 morphogenesis as one of the first biological processes shown to be dependent on the exocytic activity of Rab6. © 2013 The Authors. Traffic published by John Wiley & Sons Ltd.
The HSV1 virion host shutoff (vhs) protein is an endoribonuclease that binds to the cellular
translation initiation machinery and degrades associated mRNAs, resulting in shut-off of host
protein synthesis. Hence its unrestrained activity is considered to be lethal, and it has been
proposed that vhs is regulated by two other virus proteins, VP22 and VP16. We have found
that during infection, translation of vhs requires VP22 but not the VP22-VP16 complex.
Moreover, in the absence of VP22, vhs is not overactive against cellular or viral transcripts. In
transfected cells, vhs was also poorly translated, correlating with aberrant localization of its
mRNA. Counterintuitively, vhs mRNA was predominantly nuclear in cells where vhs protein
was detected. Likewise, transcripts from co-transfected plasmids were also retained in the
same nuclei where vhs mRNA was located, while polyA binding protein (PABP) was
relocalised to the nucleus in a vhs-dependent manner, implying a general block to mRNA
export. Co-expression of VP16 and VP22 rescued cytoplasmic localization of vhs mRNA but
failed to rescue vhs translation. We identified a 230-nucleotide sequence in the 5? region of
vhs that blocked its translation and, when transferred to a heterologous GFP transcript,
reduced translation without altering mRNA levels or localization. We propose that expression
of vhs is tightly regulated by a combination of inherent untranslatability and auto-induced
nuclear retention of its mRNA that results in a negative feedback loop, with nuclear retention
but not translation of vhs mRNA being the target of rescue by the vhs-VP16-VP22 complex.
Despite differences in the pathogenesis and host range of alphaherpesviruses, many
stages of their morphogenesis are thought to be conserved. Here, an ultrastructural
study of bovine herpesvirus 1 (BoHV-1) envelopment revealed similar profiles to
those previously found for HSV-1, with BoHV-1 capsids associating with endocytic
tubules. Consistent with the similarity of their genomes and envelopment strategies,
the proteomic composition of BoHV-1 and HSV-1 virions was also comparable.
However, BoHV-1 morphogenesis exhibited a diversity in envelopment events. First,
heterogeneous primary envelopment profiles were readily detectable at the inner
nuclear membrane of BoHV-1 infected cells. Second, the BoHV-1 progeny
comprised not just full virions, but also an abundance of capsidless, non-infectious
light (L)-particles that were released from the infected cell in similar numbers to
virions, and in the absence of DNA replication. Proteomic analysis of BoHV-1 L-
particles and the much less abundant HSV-1 L-particles revealed that they contained
the same complement of envelope proteins as virions but showed variations in
tegument content. In the case of HSV-1, the UL46 tegument protein was reproducibly
found to be more than 6-fold enriched in HSV-1 L-particles. More strikingly, the
tegument proteins UL36, UL37, UL21 and UL16 were depleted in BoHV-1 but not
HSV-1 L-particles. We propose that these combined differences reflect the presence
of a truly segregated ?inner? and ?outer? tegument in BoHV-1, making it a critical
system for studying the structure and process of tegumentation and envelopment.
HSV1 encodes an endoribonuclease termed virion host shutoff (vhs) that is produced late in infection and packaged into virions. Paradoxically, vhs is active against not only host but also virus transcripts, and is involved in host shutoff and the temporal expression of the virus transcriptome. Two other virus proteins?VP22 and VP16 ?are proposed to regulate vhs to prevent uncontrolled and lethal mRNA degradation but their mechanism of action is unknown. We have performed dual transcriptomic analysis and single-cell mRNA FISH of human fibroblasts, a cell type where in the absence of VP22, HSV1 infection results in extreme translational shutoff. In Wt infection, host mRNAs exhibited a wide range of susceptibility to vhs ranging from resistance to 1000-fold reduction, a variation that was independent of their relative abundance or transcription rate. However, vhs endoribonuclease activity was not found to be overactive against any of the cell transcriptome in 22-infected cells but rather was delayed, while its activity against the virus transcriptome and in particular late mRNA was minimally enhanced. Intriguingly, immediate-early and early transcripts exhibited vhs-dependent nuclear retention later in Wt infection but late transcripts were cytoplasmic. However, in the absence of VP22, not only early but also late transcripts were retained in the nucleus by a vhs-dependent mechanism, a characteristic that extended to cellular transcripts that were not efficiently degraded by vhs. Moreover, the ability of VP22 to bind VP16 enhanced but was not fundamental to the rescue of vhs-induced nuclear retention of late transcripts. Hence, translational shutoff in HSV1 infection is primarily a result of vhs-induced nuclear retention and not degradation of infected cell mRNA. We have therefore revealed a new mechanism whereby vhs and its co-factors including VP22 elicit a temporal and spatial regulation of the infected cell transcriptome, thus co-ordinating efficient late protein production.