The disaggregation of host polyribosomes in productive and abortive infection with herpes simplex virus

Tristetraprolin Recruits the Herpes Simplex Virion Host Shutoff RNase to AU-Rich Elements in Stress Response mRNAs To Enable Their Cleavage

Herpes simplex viruses (HSV) package and bring into cells an RNase designated virion host shutoff (VHS) RNase. In infected cells, the VHS RNase targets primarily stress response mRNAs characterized by the presence of AU-rich elements in their 3' untranslated regions (UTRs). In uninfected cells, these RNAs are sequestered in exosomes or P bodies by host proteins that bind to the AU-rich elements. In infected cells, the AU-rich RNAs are deadenylated and cleaved close to the AU-rich elements, leading to long-term persistence of nontranslatable RNAs consisting of the 5' portions of the cleavage products. The host proteins that bind to the AU-rich elements are either resident in cells (e.g., TIA-1) or induced (e.g., tristetraprolin). Earlier, this laboratory reported that tristetraprolin binds VHS RNase. To test the hypothesis that tristetraprolin directs VHS RNase to the AU-rich elements, we mapped the domains of VHS and tristetraprolin required for their interactions. We report that VHS binds to the domain of tristetraprolin that enables its interaction with RNA. A single amino acid substitution in that domain abolished the interaction with RNA but did not block the binding to VHS RNase. In transfected cells, the mutant but not the wild-type tristetraprolin precluded the degradation of the AU-rich RNAs by VHS RNase. We conclude that TTP mediates the cleavage of the 3' UTRs of stress response mRNAs by recruiting the VHS RNase to the AU-rich elements.

IMPORTANCE

The primary host response to HSV infection is the synthesis of stress response mRNAs characterized by the presence of AU-rich elements in their 3' UTRs. These mRNAs are the targets of the virion host shutoff (VHS) RNase. The VHS RNase binds both to mRNA cap structure and to tristetraprolin, an inducible host protein that sequesters AU-rich mRNAs in exosomes or P bodies. Here we show that tristetraprolin recruits VHS RNase to the AU-rich elements and enables the degradation of the stress response mRNAs.

HSV-1 Cgal+ infection promotes quaking RNA binding protein production and induces nuclear-cytoplasmic shuttling of quaking I-5 isoform in human hepatoma cells

Herpesvirus type 1 (HSV-1) based oncolytic vectors arise as a promising therapeutic alternative for neoplastic diseases including hepatocellular carcinoma. However, the mechanisms mediating the host cell response to such treatments are not completely known. It is well established that HSV-1 infection induces functional and structural alterations in the nucleus of the host cell. In the present work, we have used gel-based and shotgun proteomic strategies to elucidate the signaling pathways impaired in the nucleus of human hepatoma cells (Huh7) upon HSV-1 Cgal(+) infection. Both approaches allowed the identification of differential proteins suggesting impairment of cell functions involved in many aspects of host-virus interaction such as transcription regulation, mRNA processing, and mRNA splicing. Based on our proteomic data and additional functional studies, cellular protein quaking content (QKI) increases 4 hours postinfection (hpi), when viral immediate-early genes such as ICP4 and ICP27 could be also detected. Depletion of QKI expression by small interfering RNA results in reduction of viral immediate-early protein levels, subsequent decrease in early and late viral protein content, and a reduction in the viral yield indicating that QKI directly interferes with viral replication. In particular, HSV-1 Cgal(+) induces a transient increase in quaking I-5 isoform (QKI-5) levels, in parallel with an enhancement of p27(Kip1) protein content. Moreover, immunofluorescence microscopy showed an early nuclear redistribution of QKI-5, shuttling from the nucleus to the cytosol and colocalizing with nectin-1 in cell to cell contact regions at 16-24 hpi. This evidence sheds new light on mechanisms mediating hepatoma cell response to HSV-1 vectors highlighting QKI as a central molecular mediator.

The virion-packaged endoribonuclease of herpes simplex virus 1 cleaves mRNA in polyribosomes

The virion host shutoff protein product of the U(L)41 gene of herpes simplex virus 1 is an endoribonuclease that selectively degrades mRNAs during the first hours after infection. Specifically, in contrast to the events in uninfected cells or cells infected with a mutant lacking the RNase, in wild-type virus-infected cells mRNA of housekeeping genes exemplified by GAPDH is degraded rapidly, whereas mRNAs containing AU elements are cleaved and the 5' cleavage product of these RNAs persists for many hours. We report that in wild-type virus-infected cells there was a rapid increase in the number and size of processing bodies (P-bodies). These P-bodies were also preset in cycloheximide (CHX)-treated cells but not in either treated or untreated uninfected cells or cells infected with the RNase minus mutant. Additional studies revealed that polyribosomes extracted from cytoplasm of wild-type virus-infected cells treated with CHX and displayed in sucrose gradients contained ribosome-loaded, truncated AU-rich mRNAs lacking the 3' UTR and poly(A) tails. The results suggest that the virion RNase is bound to polyribosomes by virtue of the reported association with translation machinery and cleaves the RNAs 5' to the AU elements. In contrast to the slow degradation of the of the residual 5' domain, the 3' UTR of the AU-rich mRNA and the GAPDH mRNA are rapidly degraded in wild-type virus-infected cells.

Messenger RNA turnover and its regulation in herpesviral infection

The ability to regulate cellular gene expression is a key aspect of the lifecycles of a diverse array of viruses. In fact, viral infection often results in a global shutoff of host cellular gene expression; such inhibition serves not only to ensure maximal viral gene expression without competition from the host for essential machinery and substrates but also aids in evasion of immune responses detrimental to successful viral replication and dissemination. Within the herpesvirus family, host shutoff is a prominent feature of both the alpha- and gamma-herpesviruses. Intriguingly, while both classes of herpesviruses block cellular gene expression by inducing decay of messenger RNAs, the viral factors responsible for this phenotype as well as the mechanisms by which it is achieved are quite distinct. However, data suggest that the host shutoff functions of alpha- and gamma-herpesviruses are likely achieved both through the activity of virally encoded nucleases as well as via modulation of cellular RNA degradation pathways. This review highlights the processes governing normal cellular messenger RNA decay and then details the mechanisms by which herpesviruses promote accelerated RNA turnover. Parallels between the viral and cellular degradation systems as well as the known interactions between viral host shutoff factors and the cellular RNA turnover machinery are highlighted.

Picornavirus internal ribosome entry site elements target RNA cleavage events induced by the herpes simplex virus virion host shutoff protein

The herpes simplex virus (HSV) virion host shutoff (vhs) protein (UL41 gene product) is a component of the HSV virion tegument that triggers shutoff of host protein synthesis and accelerated mRNA degradation during the early stages of HSV infection. vhs displays weak amino acid sequence similarity to the fen-1 family of nucleases and suffices to induce accelerated RNA turnover through endoribonucleolytic cleavage events when it is expressed as the only HSV protein in a rabbit reticulocyte in vitro translation system. Although vhs selectively targets mRNAs in vivo, the basis for this selectivity remains obscure, since in vitro activity is not influenced by the presence of a 5' cap or 3' poly(A) tail. Here we show that vhs activity is greatly altered by placing an internal ribosome entry site (IRES) from encephalomyocarditis virus or poliovirus in the RNA substrate. Transcripts bearing the IRES were preferentially cleaved by the vhs-dependent endoribonuclease at multiple sites clustered in a narrow zone located immediately downstream of the element in a reaction that did not require ribosomes. Targeting was observed when the IRES was located at the 5' end or placed at internal sites in the substrate, indicating that it is independent of position or sequence context. These data indicate that the vhs-dependent nuclease can be selectively targeted by specific cis-acting elements in the RNA substrate, possibly through secondary structure or a component of the translational machinery.

The herpes simplex virus vhs protein induces endoribonucleolytic cleavage of target RNAs in cell extracts

The herpes simplex virus virion host shutoff (vhs) protein (UL41 gene product) is a component of the HSV virion tegument that triggers shutoff of host protein synthesis and accelerated mRNA degradation during the early stages of HSV infection. Previous studies have demonstrated that extracts from HSV-infected cells and partially purified HSV virions display vhs-dependent RNase activity and that vhs is sufficient to trigger accelerated RNA degradation when expressed as the only HSV protein in an in vitro translation system derived from rabbit reticulocytes. We have used the rabbit reticulocyte translation system to characterize the mode of vhs-induced RNA decay in more detail. We report here that vhs-dependent RNA decay proceeds through endoribonucleolytic cleavage, is not affected by the presence of a 5' cap or a 3' poly(A) tail in the RNA substrate, requires Mg(2+), and occurs in the absence of ribosomes. Intriguingly, sites of preferential initial cleavage were clustered over the 5' quadrant of one RNA substrate that was characterized in detail. The vhs homologue of pseudorabies virus also induced accelerated RNA decay in this in vitro system.

Herpes simplex virus gD and virions accumulate in endosomes by mannose 6-phosphate-dependent and -independent mechanisms

Herpes simplex virus (HSV) glycoprotein D (gD) is modified with mannose 6-phosphate (M6P) and binds to M6P receptors (MPRs). MPRs are involved in the well-characterized pathway by which lysosomal enzymes are directed to lysosomes via a network of endosomal membranes. Based on the impaired ability of HSV to form plaques under conditions in which glycoproteins could not interact with MPRs, we proposed that MPRs may function during HSV egress or cell-to-cell spread (C. R. Brunetti, R. L. Burke, B. Hoflack, T. Ludwig, K. S. Dingwell, and D. C. Johnson, J. Virol. 69:3517-3528, 1995). To further analyze M6P modification and intracellular trafficking of gD in the absence of other HSV proteins, adenovirus (Ad) vectors were used to express soluble and membrane-anchored forms of gD. Both membrane-bound and soluble gD were modified with M6P residues and were localized to endosomes that contained the 275-kDa MPR or the transferrin receptor. Similar results were observed in HSV-infected cells. Cell fractionation experiments showed that gD was not present in lysosomes. However, a mutant form of gD and another HSV glycoprotein, gI, that were not modified with M6P were also found in endosomes in HSV-infected cells. Moreover, a substantial fraction of the HSV nucleocapsid protein VP6 was found in endosomes, consistent with accumulation of virions in an endosomal compartment. Therefore, it appears that HSV glycoproteins and virions are directed to endosomes, by M6P-dependent as well as by M6P-independent mechanisms, either as part of the virus egress pathway or by endocytosis from the cell surface.

Functional Domains within the Nucleus of a Cell Infected with HSV-1

HSV-1 is a nuclear replicating DNA virus capable of establishing both lytic and latent infections in mammalian cells. Expression of the more than 80 HSV genes (the majority of which do not contain introns) requires complex coordination of viral and cellular factors both temporally, at appropriate points during the infectious cycle, and spatially as the virus transcription, replication and DNA packaging factories develop in the cell nucleus. Whilst the HSV genome encodes sufficient proteins to sustain viral DNA replication, it is reliant upon its host cell for RNA polymerase II and RNA processing machinery, in addition to an increasing number of cellular cofactors, for gene expression. As HSV establishes a lytic infection, cellular gene expression and splicing are inhibited as cellular chromatin is displaced and a dramatic reorganisation of the host cell nucleus occurs. The formation of large protein-rich factories synthesising viral RNA and replicating and packaging the viral genomes is the most striking alteration. In addition to the synthetic factories, large clumps of cellular and viral intron-containing RNAs accumulate in the nucleus as a result of the inhibition of splicing, at locations which colocalise with splicing factors, but are separate from transcription sites. An essential HSV protein IE63, discussed here, has been identified with a role in the organisation of the nucleus at many levels including replication and transcription site formation, splicing factor organisation and the transport of RNA. This review is a summary of our present understanding of the organisation of the HSV infected cell nucleus, relating viral genomes, RNA, DNA and proteins in the context of the nucleus. However this is a rapidly evolving field and new factors (both viral and cellular) involved in the regulation of these functional domains are constantly being identified. Copyright 1997 by John Wiley & Sons, Ltd.

Differentiation of the shutoff of protein synthesis by virion host shutoff and mutant gamma (1)34.5 genes of herpes simplex virus 1

vhs protein is the product of the UL41 open reading frame of herpes simplex virus 1. The protein, made late in infection, is packaged into virions and, in newly infected cells, shuts off host protein synthesis by degrading mRNA. gamma (1)34.5 gene encodes a protein which precludes total shutoff of protein synthesis after the onset of viral DNA synthesis in infected cells of human derivation. The experiments reported here were designed to test the hypothesis that in cells infected with gamma (1)34.5- mutant the total shutoff of protein synthesis reflects the failure to alter the function of vhs made late in infection. Hence, double mutants, vhs- and gamma (1)34.5 should not cause total shutoff of protein synthesis. The mutants constructed to test the hypothesis were (i) viruses lacking 1 kbp from the coding domain of gamma (1)34.5 and carrying lacZ inserted into the coding domain of UI41, (ii) viruses with deletions in gamma (1)34.5 genes, (iii) viruses with lacZ inserted into UL41, and (iv) viruses in which the sequences of the deleted or interrupted genes were restored. We report that viruses with wild-type UL41 gene shut off the synthesis of actin, whereas viruses with interrupted genes made amounts of actin comparable to those of mock-infected cells. However, late in infection, protein synthesis in human neuroblastoma cells infected with the gamma (1)34.5- mutants was shut off irrespective of the status of the UL41 gene. Conversely, the phenotype of UI41 viruses with wild-type gamma (1)34.5 gene could not be differentiated from those of wild-type virus in the same assays. These studies indicate that the functions of the UL41 and gamma (1)34.5 genes and their products are independent of each other.

Herpes simplex virus type 1 (HSV-1) HSZP interferes also after antibody neutralization with early shutoff of host protein synthesis induced by HSV-1 KOS

The HSZP strain of herpes simplex virus type 1 (HSV-1) is defective with respect to the early shutoff of host protein synthesis. However, in superinfection experiments using Vero cells, the HSZP strain was effective, even after neutralization by antibody, at interfering with the early shutoff function of the HSV-1 KOS strain. Evidence was given that the observed interference was not due to exclusion of the KOS by HSZP at the level of adsorption or penetration. The neutralized KOS strain failed to induce early shutoff of host protein synthesis.

Differential suppression of host cell protein synthesis and mRNA levels in herpes simplex virus-infected endothelial cells

Earlier studies from this laboratory have shown that infection of vascular cells with herpes simplex virus 1 or 2 (HSV-1, HSV-2) results in the differential suppression of extracellular matrix proteins including fibronectin (FN), type IV collagen, thrombospondin (TSP) and Factor VIII von Willebrand protein. The present study was designed to determine whether a correlation exists between suppression of synthesis of specific proteins and their mRNA levels. We have measured the steady-state levels of mRNAs for several extracellular matrix proteins (type IV collagen, FN and TSP) and two intracellular proteins (actin and tubulin) in human endothelial cells (EC) following HSV-1 infection. The results show that during the first 5 h post-infection, when there is a rapid decrease in the synthesis of extracellular matrix proteins, the steady-state levels of the corresponding mRNAs remain relatively high, but progressively decline to levels of less than 20% by 13 h post-infection. These findings suggest that in the early hours post-infection there is an alteration in the translatability of the hybridizable message followed by degradation in the later hours.

Herpes simplex virus type-1 immediate-early gene expression and shut off of host protein synthesis are inhibited in neomycin-treated human epidermoid carcinoma 2 cells

Infection of human epidermoid carcinoma-2 (HEp-2) cells by Herpes simplex virus type 1 (HSV-1) leads to significant activation of inositol phospholipid turnover after 15 min. The effect of neomycin, an inhibitor of inositol phospholipid turnover, has been investigated for its effect on HSV-1 multiplication in HEp-2 cells. HSV-1 multiplication is inhibited by neomycin. This inhibition is not due to a block of virus adsorption or penetration. Neomycin inhibits the expression of virus immediate-early genes, as well as expression of early genes and viral DNA synthesis. In neomycin-treated cells, the usual virion-associated shut off of host protein synthesis does not occur. These results indicate that the inositol phospholipid pathway is involved in immediate-early gene expression and shut off of host protein synthesis in HEp-2 cells.

Herpes simplex virus activates expression of a cellular gene by specific binding to the cell surface

The herpes simplex virus (HSV) type 1 mutant ts1204 attaches to the cell surface at 38.5 degrees but fails to penetrate the plasma membrane. A striking feature of human fetal lung cells infected with ts1204 at 38.5 degrees was the presence of enhanced amounts of a 56,000 molecular weight host protein, p56. Studies with protein and RNA synthesis inhibitors suggested that binding of the mutant virus to cells activated expression of the cellular gene encoding p56 and not an intermediary protein. Evidence presented in this paper supports the idea that p56 is induced by a specific interaction between ts1204 virions and the cell surface.

Inhibition of proteoglycan synthesis in human endothelial cells after infection with herpes simplex virus type 1 in vitro

The effects of herpes simplex virus type 1 (HSV-1) infection on proteoglycan synthesis by human endothelial cells were studied as a model of endothelial cell injury. Confluent cultures of early passage endothelial cells from human umbilical vein were infected with HSV-1 at multiplicities of infection from 0.001 to 1.0. HSV-1 infection produced a dose-dependent inhibition of total proteoglycan synthesis of up to 85%. Although there was a 2- to 3-fold increase in the quantity of virus necessary to cause 50% inhibition of heparan sulfate compared to chondroitin/dermatan sulfate proteoglycan, the inhibition was relatively parallel, even up to high virus doses. There was no inhibition of an undersulfated heparan sulfate proteoglycan that contained glycosaminoglycan chains shorter than the predominant species. The results indicate that HSV-1 infection of human endothelial cells produces complex effects on host-cell metabolism. The viral-induced changes in proteoglycan metabolism may influence cell-matrix interactions and lead to altered vessel wall function.

Ribosome and protein synthesis modifications after infection of human epidermoid carcinoma cells with herpes simplex virus type 1

Modifications of ribosomes have been investigated in human epidermoid carcinoma-2 cells at different stages of herpes simplex virus type 1 infection. Very early in infection, there is an increase in ribosomal protein S6 phosphorylation even in the absence of serum. The same result is obtained in the presence of actinomycin D. At early infection time, ribosomal proteins S2, S3a and Sa are newly phosphorylated. At early and early-late times, three phosphorylated non-ribosomal proteins (v1, v2 and v3) are differently associated temporally to ribosomes. Analyses of proteins extracted from 40S subunits, 80S ribosomes and polysomes show that v1 and v2 are distributed differently among the different ribosomal populations. S6 phosphopeptides were found to be identical after serum stimulation and after viral infection. In every case phosphoserine and phosphothreonine were identified in S6. Only phosphoserine was found in other phosphorylated proteins. Our results indicate that herpes simplex virus type 1 is able to modify pre-existing ribosomes: (i) by stimulating a pre-existing kinase for S6 phosphorylation even in the absence of serum and of viral genome expression; (ii) by inducing new specific kinase activity(ies); and (iii) by association of new, phosphorylated proteins to ribosomes. These ribosomal modifications are correlated with changes in protein synthesis, as shown by two-dimensional electrophoretic analyses of newly synthesized 35S-labelled proteins.

Induction and repression of cellular gene transcription during herpes simplex virus infection are mediated by different viral immediate-early gene products

Nuclear run-off and pulse-labelling techniques have been used to study the changes in transcription rates of a number of cellular genes during infection with Herpes simplex virus. The majority of these genes show a decrease in transcription rate to about 60% of that observed prior to infection. In contrast, a small number of genes are transcriptionally activated during infection. These effects, which occur at a point in infection after the synthesis of viral proteins but prior to the onset of viral DNA synthesis, are mediated by different immediate-early proteins of the virus. Thus we show that, whilst transcriptional activation requires a functional ICP4 protein, repression is dependent upon the presence of another immediate early protein--ICP22.

Synthesis and metabolism of cellular transcripts in HSV-1 infected cells

The effects of productive herpes simplex virus infection on host gene expression were examined by measuring the rates of synthesis and subsequent fates of several Vero cell mRNAs. The rates of transcription of actin, beta-tubulin, and histone-3 and -4 RNAs were measured by pulse-labeling of intact cells as well as by run-on transcription in isolated nuclei. At both early (2 hr) and late (6 hr) times, the relative rates of transcription of these RNAs were greater than in uninfected cells. Kinetic labeling experiments performed at late times also revealed increased turnover rates of nuclear RNAs. That the rate of appearance of these RNAs in the cytoplasm was also reduced suggests that these cellular RNAs are being specifically retained and degraded in the nucleus. Levels of pre-existing cytoplasmic RNAs as measured by Northern blot analysis declined rapidly after infection though the nuclear steady-state levels of these RNAs increased up to 3 hr postinfection and then declined between 3 and 10 hr postinfection. At no time was the accumulation of processing intermediates detectable. Finally, we also determined that, consistent with the decline in levels of histone mRNA, rates of histone protein synthesis declined rapidly after infection.

Nuclear accumulation of a heat-shock 70-like protein during herpes simplex virus replication

A monoclonal antibody defines an antigen, p68, related to hsp70, which is located in nuclei of uninfected exponential cells. Nuclear p68 is released by DNase but not RNase treatment suggesting an association with DNA. Lytic productive infection of confluent quiescent BHK 21 cells with herpes simplex virus type-2 causes p68 to accumulate in nuclei. The effect is specific for HSV-2, and does not occur in HSV-1 infected cells. Maximum nuclear accumulation of p68 requires virus DNA synthesis although a significant accumulation occurs in the absence of such synthesis. It is suggested that the nuclear accumulation of p68 is an aspect of a cellular stress response to lytic infection with HSV-2.

A mutant of herpes simplex virus type 1 exhibits increased stability of immediate-early (alpha) mRNAs

vhs1 is a herpes simplex virus type 1 mutant defective in the shutoff of both host and alpha polypeptide synthesis. In cycloheximide reversal experiments, alpha mRNAs were significantly more stable in vhs1-infected cells than in cells infected with wild-type virus, whether assayed by in vitro translation or Northern blotting.

Suppression of matrix protein synthesis by herpes simplex virus type 1 in human endothelial cells

The synthesis of matrix proteins was investigated in cultures of human umbilical vein endothelial cells (EC) infected with herpes simplex virus type 1 (HSV-1). EC cultures were either mock-infected or infected for 1 hour at a multiplicity of infection (MOI) of 5 or 20 infectious particles per cell. Synthesis was followed by determining [14C]-proline or [35S]-methionine incorporation into non-dialyzable proteins. Using SDS-PAGE we observed that synthesis of fibronectin (FN), type IV procollagen and thrombospondin (TSP) was inhibited in infected cultures as early as 2 hours becoming almost complete by 15 hours post-infection. The degree of inhibition of matrix protein synthesis was dependent on the dose of the virus inoculum (MOI 20 greater than MOI 5) and varied with the particular matrix protein, i.e. shut-off of type IV collagen occurred first followed by that of FN and then TSP. Pulse-chase experiments suggest that the absence of labeled matrix protein in the medium of infected cultures is not due to accumulation of protein within the infected cells since there was an equal and parallel reduction in the cell layer. Suppression of matrix proteins in infected cultures was confirmed by measuring the level of FN and TSP in uninfected and infected cultures in an enzyme-linked immunosorbent assay (ELISA). The three proteins were identified by ELISA, electroimmunoblot, immunoprecipitation and ion-exchange chromatography. The data suggest that HSV-1 infection of human EC suppresses matrix protein synthesis; the degree and time of complete shut-off varies with the protein and the virus dose.

Virion component of herpes simplex virus type 1 KOS interferes with early shutoff of host protein synthesis induced by herpes simplex virus type 2 186

Herpes simplex virus (HSV) strains HSV type 1 (HSV-1) KOS and HSV-2 186 are representative of delayed and early shutoff strains, respectively, with regard to their ability to inhibit protein synthesis in Friend erythroleukemia cells. When these cells were simultaneously infected with HSV-1 KOS and HSV-2 186, HSV-1 KOS interfered with the rapid suppression of globin synthesis induced by HSV-2 186. The observed interference was competitive and not due to exclusion of HSV-2 by HSV-1 at the level of adsorption. Furthermore, UV-irradiated HSV-1 KOS was also effective at interfering with the early shutoff function of HSV-2 186, indicating that a virion component is responsible for the observed interference.

Differential stability of host mRNAs in Friend erythroleukemia cells infected with herpes simplex virus type 1

The consequences of herpes simplex virus type 1 infection on cellular macromolecules were investigated in Friend erythroleukemia cells. The patterns of protein synthesis, examined by polyacrylamide gel electrophoresis, demonstrated that by 4 h postinfection the synthesis of many host proteins, with the exception of histones, was inhibited. Examination of the steady-state level of histone H3 mRNA by molecular hybridization of total RNA to a cloned mouse histone H3 complementary DNA probe demonstrated that the ratio of histone H3 mRNA to total RNA remained unchanged for the first 4 h postinfection. In contrast, the steady-state levels of globin and actin mRNAs decreased progressively at early intervals postinfection. Studies on RNA synthesis in isolated nuclei demonstrated that the transcription of the histone H3 gene was inhibited to approximately the same extent as that of actin gene. We concluded that the stabilization of preexisting histone H3 mRNA was responsible for the persistence of H3 mRNA and histone protein synthesis in herpes simplex virus type 1-infected Friend erythroleukemia cells. The possible mechanisms influencing the differential stability of host mRNAs during the course of productive infection with herpes simplex virus type 1 are discussed.

Transduction of the Chinese hamster ovary aprt gene by herpes simplex virus

The Chinese hamster ovary adenine phosphoribosyl transferase gene (aprt) was reengineered to be flanked by sequences from the thymidine kinase (tk) gene of herpes simplex virus. This construct was cotransfected with DNA from herpes simplex virus type 1, and after 3 days, virus was harvested and Tk- plaques were selected after the virus was plated on Tk- cells in the presence of bromodeoxycytosine. Recombinant viruses were identified by dot-blot hybridization, and the arrangement of aprt and tk sequences were determined by Southern blot hybridization. Analysis of the recombinants revealed that acquisition of aprt sequences resulted from insertional inactivation of the tk locus as a consequence of homology-based recombination. Recombination was precise, as evidenced by the failure to detect plasmid sequences or the synthetic restriction endonuclease sites that bounded the mutant tk gene in the aprt-tk construct. Infection of Aprt- mouse or Chinese hamster ovary cells with UV-irradiated virus and selection in medium containing azaserine and adenine resulted in the survival of numerous colonies that stably express the aprt gene. Transformed cells synthesized an aprt mRNA that is identical to wild-type mRNA as determined by Northern blot and S1 nuclease analyses. Cells lytically infected with the recombinant virus do not appear to transcribe the aprt gene. Thus, infected cells differentiate between virus and foreign promoters even when a cellular gene is cis to the virus chromosome.

Nuclear localization of herpesvirus proteins: potential role for the cellular framework

Two herpes simplex virus proteins, the major capsid protein and the major DNA binding protein, are specifically localized to the nucleus of infected cells. We have found that the major proportion of these proteins is associated with the detergent-insoluble matrix or cytoskeletal framework of the infected cell from the time of their synthesis until they have matured to their final binding site in the cell nucleus. These results suggest that these two proteins may interact with or bind to the cellular cytoskeleton during or soon after their synthesis and throughout transport into the cell nucleus. In addition, the DNA binding protein remains associated with the nuclear skeleton at times when it is bound to viral DNA. Thus, viral DNA may also be attached to the nuclear framework. We have demonstrated that the DNA binding protein and the capsid protein exchange from the cytoplasmic framework to the nuclear framework, suggesting the direct movement of the proteins from one structure to the other. Inhibition of viral DNA replication enhanced the binding of the DNA binding protein to the cytoskeleton and increased the rate of exchange from the cytoplasmic framework to the nuclear framework, suggesting a functional relationship between these events. Inhibition of viral DNA replication resulted in decreased synthesis and transport of the capsid protein. We have been unable to detect any artificial binding of these proteins to the cytoskeleton when solubilized viral proteins were mixed with a cytoskeletal fraction or a cell monolayer. This suggested that the attachment of these proteins to the cytoskeleton represents the actual state of these proteins within the cell.

Nuclear localization of herpesvirus proteins: potential role for the cellular framework

Two herpes simplex virus proteins, the major capsid protein and the major DNA binding protein, are specifically localized to the nucleus of infected cells. We have found that the major proportion of these proteins is associated with the detergent-insoluble matrix or cytoskeletal framework of the infected cell from the time of their synthesis until they have matured to their final binding site in the cell nucleus. These results suggest that these two proteins may interact with or bind to the cellular cytoskeleton during or soon after their synthesis and throughout transport into the cell nucleus. In addition, the DNA binding protein remains associated with the nuclear skeleton at times when it is bound to viral DNA. Thus, viral DNA may also be attached to the nuclear framework. We have demonstrated that the DNA binding protein and the capsid protein exchange from the cytoplasmic framework to the nuclear framework, suggesting the direct movement of the proteins from one structure to the other. Inhibition of viral DNA replication enhanced the binding of the DNA binding protein to the cytoskeleton and increased the rate of exchange from the cytoplasmic framework to the nuclear framework, suggesting a functional relationship between these events. Inhibition of viral DNA replication resulted in decreased synthesis and transport of the capsid protein. We have been unable to detect any artificial binding of these proteins to the cytoskeleton when solubilized viral proteins were mixed with a cytoskeletal fraction or a cell monolayer. This suggested that the attachment of these proteins to the cytoskeleton represents the actual state of these proteins within the cell.

Inhibition by vesicular stomatitis virus of herpes simplex virus-directed protein synthesis

Infection of mammalian cells with either herpes simplex virus (HSV) or vesicular stomatitis virus (VSV) results in a marked inhibition of host protein synthesis. These viruses employ different mechanisms to turn off the host. In previous studies we showed that following infection with HSV, cellular mRNA was degraded and host polyribosomes were dissociated (Nishioka and Silverstein, Proc. Nat. Acad. Sci. USA 74, 2370-2374, 1977; Nishioka and Silverstein, J. Virol. 25, 422-426, 1978a). Degradation required synthesis of an HSV-specified polypeptide whereas dissociation appeared to be mediated by a heat-labile virion associated function (Nishioka and Silverstein, J. Virol. 27, 619-627, 1978b). In contrast, when cells are infected with VSV, host mRNAs are not degraded and polyribosome profiles are not drastically altered (Nishioka and Silverstein, 1978a). We have exploited the properties of these two viruses by infecting cells either simultaneously or sequentially in an effort to test our previous hypotheses. Analyses of the distribution of polyribosomes, stability of mRNA, synthesis of mRNA, and patterns of protein synthesis in coinfected cells permit us to conclude that dissociation of polyribosomes in cells infected with HSV results from expression of a virion associated function, degradation of cellular mRNA requires expression of the HSV genome, and VSV is dominant in doubly infected cells because it inhibits de novo transcription of the HSV genome.

Viruses and gynecologic cancers: herpesvirus protein (ICP 10/AG-4), a cervical tumor antigen that fulfills the criteria for a marker of carcinogenicity

The studies associating infections by herpes simplex virus type 2 (HSV-2) with carcinoma of the human uterine cervix are reviewed within the context of three possible interpretations. Extensive seroepidemiologic evidence indicates that the virus does not grow preferentially in neoplastic tissue, nor is the association of HSV-2 with cervical carcinoma a reflection of their independent relationship to promiscuity. While a number of infectious agents, including other viruses, are associated with cervical atypia, only HSV-2 is a significant risk factor for CIS. In vitro transformation data supporting the oncogenic potential of the virus are summarized, and evidence is presented that an antigen designated ICP 10/AG-4 is a valid candidate for the role of a virus-encoded protein involved in the maintenance of a transformed phenotype. Antibody to AG-4 is IgM, and it is detected by microquantitative complement fixation. With this assay, it is demonstrated that conversion to anti-AG-4 occurs during primary infection with HSV-2; however, it is transient. In testing 1325 patients, a correlation was observed between antibody to AG-4 and cervical carcinoma. Thus, whereas only 11.7% of controls and 7.7% of patients with cancer at other sites are AG-4 seropositive, as many as 49.6% of patients with dysplasia, 63% of those with CIS, and 72.7% of those with invasive cancer are positive for the antibody. Antibody to AG-4 is related to tumor growth. This is evidence by 1) retrospective analyses demonstrating that the proportion of AG-4 seropositive individuals is directly correlated to the state of the disease and 2) prospective study of 209 patients demonstrating loss of antibody in patients with a successfully removed tumor mass and reappearance of AG-4 antibody in cancer recurrence. The possible use of AG-4 (or its antibody) in the diagnosis and monitoring of cervical carcinoma and its treatment is discussed.

[Structure and function of virus-induced antigens in cultured cells infected with Merek's disease and turkey herpes viruses. II. Isolation of intracellular antigens from infected cells (author's transl)]

Virus-induced antigens were isolated from MDV and HVT-infected cells by salt extraction with 3M KCl and purified by Con.A chromatography and isoelectric focusing. Electrophoretic analysis of 35S-methionine, 3H-fucose and 32P-orthophosphate labeled antigens revealed 7 different polypeptides, two of them containing labeled carbohydrates, and one phospholipid component. The isolated virus-induced antigens from infected cells were identified as serologically active membrane complexes carrying common antigenic determinants of MDV and HVT. They were able to bind to virus-neutralizing immunglobulins as shown by antibody binding tests. Summarizing the presented analytic and serologic findings it was proposed to classify MDV and HVT as different serotypes of a common Marek's disease virus group.