Co-ordinate regulation of herpes simplex virus gene expression is mediated by the functional interaction of two immediate early gene products

Impaired STING Pathway in Human Osteosarcoma U2OS Cells Contributes to the Growth of ICP0-Null Mutant Herpes Simplex Virus

Human herpes simplex virus 1 (HSV-1) is a widespread pathogen, with 80% of the population being latently infected. To successfully evade the host, the virus has evolved strategies to counteract antiviral responses, including the gene-silencing and innate immunity machineries. The immediately early protein of the virus, infected cell protein 0 (ICP0), plays a central role in these processes. ICP0 blocks innate immunity, and one mechanism is by degrading hostile factors with its intrinsic E3 ligase activity. ICP0 also functions as a promiscuous transactivator, and it blocks repressor complexes to enable viral gene transcription. For these reasons, the growth of a ΔICP0 virus is impaired in most cells, except cells of the human osteosarcoma cell line U2OS, and it is only partially impaired in cells of the human osteosarcoma cell line Saos-2. We found that the two human osteosarcoma cell lines that supported the growth of the ΔICP0 virus failed to activate innate immune responses upon treatment with 2'3'-cyclic GAMP (2'3'-cGAMP), the natural agonist of STING (i.e., stimulator of interferon genes) or after infection with the ΔICP0 mutant virus. Innate immune responses were restored in these cells by transient expression of the STING protein but not after overexpression of interferon-inducible protein 16 (IFI16). Restoration of STING expression resulted in suppression of ΔICP0 virus gene expression and a decrease in viral yields. Overexpression of IFI16 also suppressed ΔICP0 virus gene expression, albeit to a lesser extent than STING. These data suggest that the susceptibility of U2OS and Saos-2 cells to the ΔICP0 HSV-1 is in part due to an impaired STING pathway.IMPORTANCE The DNA sensor STING plays pivotal role in controlling HSV-1 infection both in cell culture and in mice. The HSV-1 genome encodes numerous proteins that are dedicated to combat host antiviral responses. The immediate early protein of the virus ICP0 plays major role in this process as it targets hostile host proteins for degradation with its E3 ligase activity, and it disrupts repressor complexes via protein-protein interaction to enable viral gene transcription. Therefore, the ΔICP0 HSV-1 virus is defective for growth in most cells, except the human osteosarcoma cell lines U2OS and Saos-2. We found that both cell lines that support ΔICP0 virus infection have defects in the STING DNA-sensing pathway, which partially accounts for the rescue of the ΔICP0 virus growth. Restoration of STING expression in these cells rescued innate immunity and suppressed ΔICP0 virus infection. This study underscores the importance of STING in the control of HSV-1.

HSV1 latent transcription and non-coding RNA: A critical retrospective

Virologists have invested great effort into understanding how the herpes simplex viruses and their relatives are maintained dormant over the lifespan of their host while maintaining the poise to remobilize on sporadic occasions. Piece by piece, our field has defined the tissues in play (the sensory ganglia), the transcriptional units (the latency-associated transcripts), and the responsive genomic region (the long repeats of the viral genomes). With time, the observed complexity of these features has compounded, and the totality of viral factors regulating latency are less obvious. In this review, we compose a comprehensive picture of the viral genetic elements suspected to be relevant to herpes simplex virus 1 (HSV1) latent transcription by conducting a critical analysis of about three decades of research. We describe these studies, which largely involved mutational analysis of the notable latency-associated transcripts (LATs), and more recently a series of viral miRNAs. We also intend to draw attention to the many other less characterized non-coding RNAs, and perhaps coding RNAs, that may be important for consideration when trying to disentangle the multitude of phenotypes of the many genetic modifications introduced into recombinant HSV1 strains.

ICP0 dismantles microtubule networks in herpes simplex virus-infected cells

Infected-cell protein 0 (ICP0) is a RING finger E3 ligase that regulates herpes simplex virus (HSV) mRNA synthesis, and strongly influences the balance between latency and replication of HSV. For 25 years, the nuclear functions of ICP0 have been the subject of intense scrutiny. To obtain new clues about ICP0's mechanism of action, we constructed HSV-1 viruses that expressed GFP-tagged ICP0. To our surprise, both GFP-tagged and wild-type ICP0 were predominantly observed in the cytoplasm of HSV-infected cells. Although ICP0 is exclusively nuclear during the immediate-early phase of HSV infection, further analysis revealed that ICP0 translocated to the cytoplasm during the early phase where it triggered a previously unrecognized process; ICP0 dismantled the microtubule network of the host cell. A RING finger mutant of ICP0 efficiently bundled microtubules, but failed to disperse microtubule bundles. Synthesis of ICP0 proved to be necessary and sufficient to disrupt microtubule networks in HSV-infected and transfected cells. Plant and animal viruses encode many proteins that reorganize microtubules. However, this is the first report of a viral E3 ligase that regulates microtubule stability. Intriguingly, several cellular E3 ligases orchestrate microtubule disassembly and reassembly during mitosis. Our results suggest that ICP0 serves a dual role in the HSV life cycle, acting first as a nuclear regulator of viral mRNA synthesis and acting later, in the cytoplasm, to dismantle the host cell's microtubule network in preparation for virion synthesis and/or egress.

Role of the IE62 consensus binding site in transactivation by the varicella-zoster virus IE62 protein

The varicella-zoster virus (VZV) IE62 protein is the major transcriptional activator. IE62 is capable of associating with DNA both nonspecifically and in a sequence-specific manner via a consensus binding site (5'-ATCGT-3'). However, the function of the consensus site is poorly understood, since IE62 efficiently transactivates promoter elements lacking this sequence. In the work presented here, sequence analysis of the VZV genome revealed the presence of 245 IE62 consensus sites throughout the genome. Some 54 sites were found to be present within putative VZV promoters. Electrophoretic mobility shift assay (EMSA) experiments using an IE62 fragment containing the IE62 DNA-binding domain and duplex oligonucleotides that did or did not contain the IE62 consensus binding sequence yielded K(D) (equilibrium dissociation constant) values in the nanomolar range. Further, the IE62 DNA binding domain was shown to have a 5-fold-increased affinity for its consensus site compared to nonconsensus sequences. The effect of consensus site presence and position on IE62-mediated activation of native VZV and model promoters was examined using site-specific mutagenesis and transfection and superinfection reporter assays. In all promoters examined, the consensus sequence functioned as a distance-dependent repressive element. Protein recruitment assays utilizing the VZV gI promoter indicated that the presence of the consensus site increased the recruitment of IE62 but not Sp1. These data suggest a model where the IE62 consensus site functions to down-modulate IE62 activation, and interaction of IE62 with this sequence may result in loss or decrease of the ability of IE62 to recruit cellular factors needed for full promoter activation.

ICP0 antagonizes ICP4-dependent silencing of the herpes simplex virus ICP0 gene

ICP0 is a regulatory protein that plays a critical role in the replication-latency balance of herpes simplex virus (HSV). Absence of ICP0 renders HSV prone to establish quiescent infections, and thus cellular repressor(s) are believed to silence HSV mRNA synthesis when ICP0 fails to accumulate. To date, an ICP0-antagonized repressor has not been identified that restricts HSV mRNA synthesis by more than 2-fold. We report the unexpected discovery that HSV's major transcriptional regulator, ICP4, meets the criteria of a bona fide ICP0-antagonized repressor of viral mRNA synthesis. Our study began when we noted a repressive activity that restricted ICP0 mRNA synthesis by up to 30-fold in the absence of ICP0. When ICP0 accumulated, the repressor only restricted ICP0 mRNA synthesis by 3-fold. ICP4 proved to be necessary and sufficient to repress ICP0 mRNA synthesis, and did so in an ICP4-binding-site-dependent manner. ICP4 co-immunoprecipitated with FLAG-tagged ICP0; thus, a physical interaction likely explains how ICP0 antagonizes ICP4's capacity to silence the ICP0 gene. These findings suggest that ICP0 mRNA synthesis is differentially regulated in HSV-infected cells by the virus-encoded repressor activity embedded in ICP4, and a virus-encoded antirepressor, ICP0. Bacteriophage λ relies on a similar repression-antirepression regulatory scheme to “decide” whether a given infection will be productive or silent. Therefore, our findings appear to add to the growing list of inexplicable similarities that point to a common evolutionary ancestry between the herpesviruses and tailed bacteriophage.

Herpes simplex virus tegument ICP0 is capsid associated, and its E3 ubiquitin ligase domain is important for incorporation into virions

Herpes simplex virus (HSV) immediate-early (IE) protein ICP0 is a multifunctional regulator of HSV infection. ICP0 that is present in the tegument layer has not been well characterized. Protein compositions of wild-type and ICP0 null virions were similar, suggesting that the absence of ICP0 does not grossly impair virion assembly. ICP0 has a RING finger domain with E3 ubiquitin ligase activity that is necessary for IE functions. Virions with mutations in this domain contained greatly reduced levels of tegument ICP0, suggesting that the domain influences the incorporation of ICP0. Virion ICP0 was resistant to removal by detergent and salt and was associated with capsids, features common to inner tegument proteins.

Negative autoregulation of Epstein-Barr virus (EBV) replicative gene expression by EBV SM protein

The Epstein-Barr virus (EBV) SM protein is essential for lytic EBV DNA replication and virion production. When EBV replication is induced in cells infected with an SM-deleted recombinant EBV, approximately 50% of EBV genes are expressed inefficiently. When EBV replication is rescued by transfection of SM, SM enhances expression of these genes by direct and indirect mechanisms. While expression of most EBV genes is either unaffected or enhanced by SM, expression of several genes is decreased in the presence of SM. Expression of BHRF1, a homolog of cellular bcl-2, is particularly decreased in the presence of SM. Investigation of the mechanism of BHRF1 downregulation revealed that SM downregulates expression of the immediate-early EBV transactivator R. In EBV-infected cells, R-responsive promoters, including the BHRF1 and SM promoters, were less active in the presence of SM, consistent with SM inhibition of R expression. SM decreased spliced R mRNA levels, supporting a posttranscriptional mechanism of R inhibition. R and BHRF1 expression were also found to decrease during later stages of EBV lytic replication in EBV-infected lymphoma cells. These data indicate that feedback regulation of immediate-early and early genes occurs during the lytic cycle of EBV regulation.

ICP0 is not required for efficient stress-induced reactivation of herpes simplex virus type 1 from cultured quiescently infected neuronal cells

Viral genes sufficient and required for herpes simplex virus type 1 (HSV-1) reactivation were identified using neuronally differentiated PC12 cells (ND-PC12 cells) in which quiescent infections with wild-type and recombinant strains were established. In this model, the expression of ICP0, VP16, and ICP4 from adenovirus vectors was sufficient to reactivate strains 17+ and KOS. The transactivators induced similar levels of reactivation with KOS; however, 17+ responded more efficiently to ICP0. To identify viral transactivators required for reactivation, we examined quiescently infected PC12 cell cultures (QIF-PC12 cell cultures) established with HSV-1 deletion mutants R7910 (deltaICP0), KD6 (deltaICP4), and in1814, a virus containing an insertion mutation in VP16. Although growth of these mutant viruses was impaired in ND-PC12 cells, R7910 and in1814 reactivated at levels equivalent to or better than their respective parental controls following stress (i.e., heat or forskolin) treatment. After treatment with trichostatin A, in1814 and 17+ reactivated efficiently, whereas the F strain and R7910 reactivated inefficiently. In contrast, KD6 failed to reactivate. In experiments with the recombinant KM100, which contains the in1814 mutation in VP16 and the n212 mutation in ICP0, spontaneous and stress-induced reactivation was observed. However, two strains, V422 and KM110, which lack the acidic activation domain of VP16, did not reactivate above low spontaneous levels after stress. These results demonstrate that in QIF-PC12 cells ICP0 is not required for efficient reactivation of HSV-1, the acidic activation domain of VP16 is essential for stress-induced HSV-1 reactivation, and HSV-1 reactivation is modulated uniquely by different treatment constraints and phenotypes.

The cellular localization pattern of Varicella-Zoster virus ORF29p is influenced by proteasome-mediated degradation

Varicella-zoster virus (VZV) open reading frame 29 (ORF29) encodes a single-stranded DNA binding protein. During lytic infection, ORF29p is localized primarily to infected-cell nuclei, whereas during latency it appears in the cytoplasm of infected neurons. Following reactivation, ORF29p accumulates in the nucleus. In this report, we analyze the cellular localization patterns of ORF29p during VZV infection and during autonomous expression. Our results demonstrate that ORF29p is excluded from the nucleus in a cell-type-specific manner and that its cellular localization pattern may be altered by subsequent expression of VZV ORF61p or herpes simplex virus type 1 ICP0. In these cases, ORF61p and ICP0 induce nuclear accumulation of ORF29p in cell lines where it normally remains cytoplasmic. One cellular system utilized by ICP0 to influence protein abundance is the proteasome degradation pathway. Inhibition of the 26S proteasome, but not heat shock treatment, resulted in accumulation of ORF29p in the nucleus, similar to the effect of ICP0 expression. Immunofluorescence microscopy and pulse-chase experiments reveal that stabilization of ORF29p correlates with its nuclear accumulation and is dependent on a functional nuclear localization signal. ORF29p nuclear translocation in cultured enteric neurons and cells derived from an astrocytoma is reversible, as the protein's distribution and stability revert to the previous states when the proteasomal activity is restored. Thus, stabilization of ORF29p leads to its nuclear accumulation. Although proteasome inhibition induces ORF29p nuclear accumulation, this is not sufficient to reactivate latent VZV or target the immediate-early protein ORF62p to the nucleus in cultured guinea pig enteric neurons.

UL54-null pseudorabies virus is attenuated in mice but productively infects cells in culture

The pseudorabies virus (PRV) UL54 homologs are important multifunctional proteins with roles in shutoff of host protein synthesis, transactivation of virus and cellular genes, and regulation of splicing and translation. Here we describe the first genetic characterization of UL54. We constructed UL54 null mutations in a PRV bacterial artificial chromosome using sugar suicide and lambdaRed allele exchange systems. Surprisingly, UL54 is dispensable for growth in tissue culture but exhibits a small-plaque phenotype that can be complemented in trans by both the herpes simplex virus type 1 ICP27 and varicella-zoster virus open reading frame 4 proteins. Deletion of UL54 in the virus vJSdelta54 had no effect on the ability of the virus to shut off host cell protein synthesis but did affect virus gene expression. The glycoprotein gC accumulated to lower levels in cells infected with vJSdelta54 compared to those infected with wild-type virus, while gK levels were undetectable. Other late gene products, gB, gE, and Us9, accumulated to higher levels than those seen in cells infected with wild-type virus in a multiplicity-dependent manner. DNA replication is also reduced in cells infected with vJSdelta54. UL54 appears to regulate UL53 and UL52 at the transcriptional level as their respective RNAs are decreased in cells infected with vJSdelta54. Interestingly, vJSdelta54 is highly attenuated in a mouse model of PRV infection. Animals infected with vJSdelta54 survive twice as long as animals infected with wild-type virus, and this results in delayed accumulation of virus-specific antigens in skin, dorsal root ganglia, and spinal cord tissues.

Regulation of the vhs gene promoter of pseudorabies virus by IE180 and EP0, and the requirement of a Sp1 Site for the promoter function

The virion host shutoff (vhs) protein is a virion component of Alphaherpesviruses, including pseudorabies virus. In this work, the upstream sequences of vhs gene of pseudorabies virus (TNL strain) was cloned and sequenced. We linked the upstream sequences of vhs gene to the CAT reporter gene and examined the promoter function of this region. The immediate-early protein IE180 of Pseudorabies Virus (PRV) is expressed immediately after infection and plays a vital role in the regulation of other viral genes. Our results demonstrated that the vhs promoter was regulated by the IE180 in a dosage-dependent manner; the vhs promoter was stimulated by low concentration of IE180 but suppressed by high concentration of IE180. Mutational analysis indicated that the only IE180 binding site at the vhs promoter was not essential for its function; however, a Sp1 binding site (15 bp downstream to TATA box) was critical to its function. In addition, the result of cotransfection demonstrated that early protein 0 (EP0) of PRV, another protein with transcriptional function, inhibited the activity of the vhs promoter.

Herpes simplex virus type 1 immediate-early gene expression is required for the induction of apoptosis in human epithelial HEp-2 cells

Wild-type herpes simplex virus type 1 (HSV-1) induces apoptosis in human epithelial HEp-2 cells, but infected cell proteins produced later in infection block the process from killing the cells. Thus, HSV-1 infection in the presence of the translational inhibitor cycloheximide (CHX) results in apoptosis. Our specific goal was to gain insight as to the viral feature(s) responsible for triggering apoptosis during HSV-1 infection. We now report the following. (i) No viral protein synthesis or death factor processing was detected after infection with HSV-1(HFEMtsB7) at 39.5 degrees C; this mutant virus does not inject its virion DNA into the nucleus at this nonpermissive temperature. (ii) No death factor processing or apoptotic morphological changes were detected following infection with UV-irradiated, replication-defective viruses possessing transcriptionally active incoming VP16. (iii) Addition of the transcriptional inhibitor actinomycin D prevented death factor processing upon infection with the apoptotic, ICP27-deletion virus HSV-1(vBSDelta27). (iv) Apoptotic morphologies and death factor processing were not observed following infection with HSV-1(d109), a green fluorescent protein-expressing recombinant virus possessing deletions of all five immediate-early (IE) (or alpha) genes. (v) Finally, complete death factor processing was observed upon infection with the VP16 transactivation domain-mutant HSV-1(V422) in the presence of CHX. Based on these findings, we conclude that (vi) the expression of HSV-1 alpha/IE genes is required for the viral induction of apoptosis and (vii) the transactivation activity of VP16 is not necessary for this induction.

Analysis of herpes simplex virus ICP0 promoter function in sensory neurons during acute infection, establishment of latency, and reactivation in vivo

We have begun an analysis of the functional architecture of the ICP0 promoter in neurons in vivo with the ultimate goal of determining how this gene is regulated during reactivation in vivo. Promoter/reporter mutants in which the Escherichia coli beta-galactosidase (beta-Gal) gene was driven by various permutations of the ICP0 promoter were employed to permit the analysis of promoter function without the added complications that would arise due to inappropriate regulation of ICP0 protein levels. A whole-ganglion immunohistochemical staining procedure (N. M. Sawtell, J. Virol. 77:4127-4138, 2003) was used for direct comparisons of the expression of the promoter/reporter gene to expression of the native protein in the same cell. In this way, the expression of the putative wild-type promoter could be validated and results for mutant promoters could be compared to expression of the native gene. We found that a DNA fragment from bp -562 through the methionine start codon of the ICP0 gene contained all sequences required for properly regulated ICP0 expression in diverse cell types (including sensory neurons of the trigeminal ganglia [TG]) in vitro and in vivo, as indicated by colocalization of ICP0 and beta-Gal. Truncation of the ICP0 promoter to bp -145 or -129 resulted in the loss of immediate-early (alpha) kinetics. The truncated promoters expressed high levels of the reporter gene with leaky late (gamma1) kinetics in vitro and in some cell types in vivo. Unexpectedly, the truncated promoters did not express in TG neurons. Thus, TAATGARAT or other sequences upstream of bp -145 in the ICP0 promoter are required for basal expression of ICP0 in neurons but are not required for basal expression in other cells in vivo. There was a >95% concordance between reporter and native protein expression detected with the 562-bp promoter in neurons during the acute stage. However, this was not the case during reactivation from latency in vivo, as nearly twice as many neurons contained detectable beta-Gal as contained detectable ICP0. This same 562-bp promoter/reporter cassette, when placed in the context of a latency-associated transcript (LAT) null mutant, resulted in >95% concordance of expression of beta-Gal and ICP0 during reactivation in vivo. These last results strongly suggest that there is a posttranscriptional constraint on the expression of ICP0 protein during reactivation from latency and that this constraint is mediated by LAT.

The Epstein-Barr virus SM protein is functionally similar to ICP27 from herpes simplex virus in viral infections

The herpes simplex virus type 1 (HSV-1) ICP27 protein is an essential RNA-binding protein that shuttles between the nucleus and cytoplasm to increase the cytoplasmic accumulation of viral late mRNAs. ICP27 homologs have been identified in each of the herpesvirus subfamilies, and accumulating evidence indicates that homologs from the gammaherpesvirus subfamily function similarly to ICP27. In particular, the Epstein-Barr virus (EBV) SM protein posttranscriptionally regulates gene expression, binds RNA in vitro and in vivo, and shuttles between the nucleus and cytoplasm. To determine if these two proteins function through a common mechanism, the ability of EBV SM to complement the growth defect of an HSV-1 ICP27-null virus was examined in a transient-expression assay. ICP27 stimulated the growth of the null mutant more efficiently than did SM, but the ability of SM to compensate for the ICP27 defects suggests conservation of common functions. To assay for complementation in the context of a viral infection, the growth properties of an HSV recombinant expressing SM in an ICP27-null background were analyzed. SM stimulated growth of the recombinant, although this growth was reduced by comparison to that of an ICP27-expressing virus. By contrast, an HSV recombinant expressing an SM mutant allele defective for transactivation activity and nucleocytoplasmic shuttling did not grow at all. These results suggest that SM and ICP27 may regulate gene expression through a common pathway that is evolutionarily conserved in herpesviruses.

Neurons differentially activate the herpes simplex virus type 1 immediate-early gene ICP0 and ICP27 promoters in transgenic mice

Herpes simplex virus type 1 (HSV-1) immediate-early (IE) proteins are required for the expression of viral early and late proteins. It has been hypothesized that host neuronal proteins regulate expression of HSV-1 IE genes that in turn control viral latency and reactivation. We investigated the ability of neuronal proteins in vivo to activate HSV-1 IE gene promoters (ICP0 and ICP27) and a late gene promoter (gC). Transgenic mice containing IE (ICP0 and ICP27) and late (gC) gene promoters of HSV-1 fused to the Escherichia coli beta-galactosidase coding sequence were generated. Expression of the ICP0 and ICP27 reporter transgenes was present in anatomically distinct subsets of neurons in the absence of viral proteins. The anatomic locations of beta-galactosidase-positive neurons in the brains of ICP0 and ICP27 reporter transgenic mice were similar and included cerebral cortex, lateral septal nucleus, cingulum, hippocampus, thalamus, amygdala, and vestibular nucleus. Trigeminal ganglion neurons were positive for beta-galactosidase in adult ICP0 and ICP27 reporter transgenic mice. The ICP0 reporter transgene was differentially regulated in trigeminal ganglion neurons depending upon age. beta-galactosidase-labeled cells in trigeminal ganglia and cerebral cortex of ICP0 and ICP27 reporter transgenic mice were confirmed as neurons by double labeling with antineurofilament antibody. Nearly all nonneuronal cells in ICP0 and ICP27 reporter transgenic mice and all neuronal and nonneuronal cells in gC reporter transgenic mice were negative for beta-galactosidase labeling in the absence of HSV-1. We conclude that factors in neurons are able to differentially regulate the HSV-1 IE gene promoters (ICP0 and ICP27) in transgenic mice in the absence of viral proteins. These findings are important for understanding the regulation of the latent and reactivated stages of HSV-1 infection in neurons.

Identification of an export control sequence and a requirement for the KH domains in ICP27 from herpes simplex virus type 1

The herpes simplex virus type 1 (HSV-1) immediate-early protein ICP27 is an RNA-binding protein that performs multiple functions required for the expression of HSV-1 genes during a productive infection. One essential function involves shuttling between the nucleus and the cytoplasm. Some of the domains identified in ICP27 include a leucine-rich nuclear export sequence (NES), a nuclear localization signal, three KH-like RNA-binding domains, and an RGG-box type RNA-binding motif. To study the contribution of two of the essential domains in ICP27 to HSV gene expression, we generated recombinant herpesviruses carrying deleterious mutations in the NES and KH domains of ICP27. To accomplish this, we fused the green fluorescent protein (GFP) to ICP27 and utilized fluorescence as a marker to isolate recombinant herpesviruses. Fusion of GFP to wild-type ICP27 did not disturb its localization or function or significantly reduce virus yield. Analysis of HSV gene expression in cells infected with a recombinant virus carrying a point mutation in the first KH-like RNA-binding domain revealed that nuclear export of ICP27 was not blocked, and the expression of only a subset of ICP27-dependent late genes was affected. These findings suggest that individual KH-like RNA-binding motifs in ICP27 may be involved in binding distinct RNAs. Analysis of recombinant viruses carrying a lethal mutation in the NES of ICP27 was not accomplished because this mutation results in a strong dominant-negative phenotype. Finally, we demonstrate that shuttling by ICP27 is regulated by an export control sequence adjacent to its NES that functions like the inhibitory sequence element found adjacent to the NES of NS1 from influenza virus.

Control of cytoskeletal architecture by the src-suppressed C kinase substrate, SSeCKS

Activation of protein kinase C (PKC) in many cell types results in cytoskeletal reorganization associated with cell proliferation. We previously described a new cell cycle-regulated myristylated PKC substrate, SSeCKS (pronounced essex), that interacts with the actin cytoskeleton [Lin et al., 1995, 1996]. SSeCKS shares significant homology with Gravin, which encodes kinase scaffolding functions for PKC and PKA [Nauert et al., 1997]. This article describes the cellular effects of ectopically expressing SSeCKS in untransformed NIH3T3 fibroblasts. Because the constitutive overexpression of SSeCKS is toxic [Lin et al., 1995], we developed cell lines with tetracycline (tet)-regulated SSeCKS expression. The induction of SSeCKS (removal of tet) caused significant cell flattening and the elaboration of an SSeCKS-associated cortical cytoskeletal matrix resistant to Triton X-100 extraction. Flattened cells were growth-arrested and marked by the formation of cellular projections and the temporary loss of actin stress fibers and vinculin-associated adhesion plaques. SSeCKS overexpression did not affect steady-state levels of actin, vinculin, or focal adhesion kinase (FAK) but did increase integrin-independent FAK tyrosine phosphorylation. Stress fiber loss was coincident with induced SSeCKS expression, strongly suggesting a direct effect. Cytochalasin, and to a lesser extent nocodazole, inhibited SSeCKS-induced cell flattening, however, only cytochalasin affected the shape of pre-flattened cells, suggesting a greater dependence on microfilaments, rather than microtubules. By contrast, only nocodazole caused retraction of the filopodia-like processes. These data indicate a role for SSeCKS in modulating both cytoskeletal and signaling pathways. Thus, we propose to expand SSeCKS scaffolding functions to include the ability to control actin-based cytoskeletal architecture, as well as mitogenic signal pathways.

Herpesvirus mRNAs are sorted for export via Crm1-dependent and -independent pathways

Cellular pre-mRNA splicing is inhibited by ICP27, a herpes simplex virus regulatory protein, resulting in the shutoff of host protein synthesis. Here we reveal that ICP27 also mediates the export of some virus RNAs via a Crm1-dependent pathway and present evidence that independent domains are required for these functions. Sorting of some viral mRNAs for nuclear export requires Crm1, while other virus mRNAs are exported via another pathway.

A single amino acid substitution in the cyclin D binding domain of the infected cell protein no. 0 abrogates the neuroinvasiveness of herpes simplex virus without affecting its ability to replicate

The infected cell protein no. 0 (ICP0) of herpes simplex virus 1 is a promiscuous transactivator shown to enhance the expression of genes introduced into cells by infection or transfection. The protein interacts with several viral and cellular proteins. Earlier studies have shown that ICP0 binds and stabilizes cyclin D3 but does interfere with the phosphorylation of retinoblastoma protein, its major function. Cyclin D3 plays a key role in the transition from G1 to S phase. To define the role of cyclin D3 in productive infection, the ICP0 binding site for cyclin D3 was mapped and mutagenized by substitution of aspartic acid codon 199 with the alanine codon. We report that the substitution precluded the interaction of this protein with cyclin D3 in the yeast two-hybrid system and the stabilization of cyclin D3 in infected cells. A recombinant virus carrying this mutation could not be differentiated from wild-type parent with respect to replication in dividing cells but yielded 10-fold less progeny from infected resting cells and serum-deprived or contact-inhibited human fibroblasts. In mice, the mutant was only slightly less pathogenic than the wild-type parent by intracerebral route but was significantly less neuroinvasive after peripheral inoculation. Replacement of the mutated amino acid with aspartic acid restored wild-type phenotype. Stabilization of cyclin D3 therefore is linked to higher virus yields in nondividing cells and potentially higher virulence in experimental and natural hosts. One function of ICP0 is to scavenge the cell for proteins that could bolster viral replication.

ND10 protein PML is recruited to herpes simplex virus type 1 prereplicative sites and replication compartments in the presence of viral DNA polymerase

Herpes simplex virus type 1 (HSV-1) infection results in the disruption of ND10 (also called nuclear bodies, PODs, or PML-associated bodies), which are nuclear matrix domains of unknown function present in mammalian cells. After ND10 disruption, viral transcription and DNA replication occur in globular nuclear domains called replication compartments. In this report we define four stages of infection by using antibodies to ICP8 (also called SSB and UL29) and the ND10 antigen PML. Immediately after infection, cells contain intact ND10 as detected by staining for PMLs (stage I); within 1 hour, however, ND10 are disrupted and cells begin to exhibit diffuse staining for the major viral DNA binding protein, ICP8 (stage II). After all ND10 have been disrupted, foci which resemble but are not equivalent to ND10 appear, containing both PML and ICP8 (stage III). Cells infected with mutants defective in the helicase-primase or origin binding protein are unable to form stage III foci. Cells infected with a mutant that is null for the polymerase catalytic subunit, however, form stage III-like ICP8 foci which do not contain PML. Thus, stage III foci recruit the cellular PML protein in the presence but not the absence of HSV polymerase. PML was recruited to stage III foci in some but not all cells infected with a mutant defective in the polymerase accessory protein, UL42. Thus, UL42 is not required for the recruitment of PML to viral foci. In wild-type infection, stage III cells are quickly replaced by cells containing replication compartments (stage IV). PML and ICP8 staining are both observed within replication compartments, indicating a potential role for PML in HSV-1 replication. Models for the role of ND10 proteins in the formation of replication compartments are discussed.

The NH2 terminus of the herpes simplex virus type 1 regulatory protein ICP0 contains a promoter-specific transcription activation domain

The transcriptional program of herpes simplex virus is regulated by the concerted action of three immediate-early (alpha) proteins, ICP4, ICP27, and ICP0. The experiments described in this study examine the role of the acidic amino terminus (amino acids 1 to 103) of ICP0 in gene activation. When tethered to a DNA binding domain, this sequence activates transcription in the yeast Saccharomyces cerevisiae. Deletion of these amino acids affects the ability of ICP0 to activate alpha-gene promoter reporters in transient expression assays, while it has little or no effect on a beta- and a gamma-gene reporter in the same assay. Viruses that express the deleted form of ICP0 (ICP0-NX) have a small-plaque phenotype on both Vero cells and the complementing cell line L7. Transient expression and immunofluorescence analyses demonstrate that ICP0-NX is a dominant negative form of ICP0. Immunoprecipitation of ICP0 from cells coinfected with viruses expressing ICP0-NX and ICP0 revealed that ICP0 oligomerizes in infected cells. These data, in conjunction with the finding that ICP0-N/X is dominant negative, provide both biochemical and genetic evidence that ICP0 functions as a multimer in infected cells.

Shuttling of the herpes simplex virus type 1 regulatory protein ICP27 between the nucleus and cytoplasm mediates the expression of late proteins

The herpes simplex virus type 1 (HSV-1) immediate-early protein ICP27 is required posttranscriptionally for the expression of HSV-1 late genes during a productive infection. ICP27 also inhibits host cell pre-mRNA splicing, effectively shutting off host cell protein synthesis. Here we describe intragenic suppressors of LG4, a virus with a conditional lethal mutation in the gene encoding ICP27. At the restrictive temperature, tsICP27 from LG4 fails to inhibit host cell pre-mRNA splicing and to activate the expression of HSV-1 late-gene products. Although the suppressors of LG4 restore virus growth, they still fail to inhibit host cell pre-mRNA splicing. Thus, the role of ICP27 in the synthesis of late proteins is independent of host shutoff. In HSV-1-infected cells, ICP27 shuttles between the nucleus and the cytoplasm. Shuttling of ICP27 occurs only at late times during infection. In transfected cells, ICP27 shuttling was dependent on coexpression of RNA from a late HSV-1 gene. While shuttling does not occur in cells infected with LG4 at 39.5 degrees C, the suppressors of LG4 restore shuttling. Temperature shift experiments correlate the defect in shuttling with the temperature-sensitive phenotype of LG4. These data provide a correlation between shuttling of ICP27 and the expression of HSV-1 late-gene products. We propose that ICP27 regulates late-gene protein synthesis by facilitating the export of late RNAs.

Mutational analysis of the herpes simplex virus type 1 ICP0 C3HC4 zinc ring finger reveals a requirement for ICP0 in the expression of the essential alpha27 gene

The herpes simplex virus type 1 (HSV-1) immediate-early (IE) protein ICP0 has been implicated in the regulation of viral gene expression and the reactivation of latent HSV-1. Evidence demonstrates that ICP0 is an activator of viral gene expression yet does not distinguish between a direct or indirect role in this process. To further our understanding of the function of ICP0 in the context of the virus life cycle, site-directed mutagenesis of the consensus C3HC4 zinc finger domain was performed, and the effects of these mutations on the growth and replication of HSV-1 were assessed. We demonstrate that alteration of any of the consensus C3HC4 cysteine or histidine residues within this domain abolishes ICP0-mediated transactivation, alters the intranuclear localization of ICP0, and significantly increases its stability. These mutations result in severe defects in the growth and DNA replication of recombinant herpesviruses and in their ability to initiate lytic infections at low multiplicities of infection. These viruses, at low multiplicities of infection, synthesize wild-type levels of the IE proteins ICP0 and ICP4 at early times postinfection yet exhibit significant decreases in the synthesis of the essential IE protein ICP27. These findings reveal a role for ICP0 in the expression of ICP27 and suggest that the multiplicity-dependent growth of alpha0 mutant viruses results partially from reduced levels of ICP27.

Transcriptional targeting of herpes simplex virus for cell-specific replication

Tissue- or cell-specific targeting of vectors is critical to the success of gene therapy. We describe a novel approach to virus-mediated gene therapy, where viral replication and associated cytotoxicity are limited to a specific cell type by the regulated expression of an essential immediate-early viral gene product. This is illustrated with a herpes simplex virus type 1 (HSV-1) vector (G92A) whose growth is restricted to albumin-expressing cells. G92A was constructed by inserting an albumin enhancer/promoter-ICP4 transgene into the thymidine kinase gene of mutant HSV-1 d120, deleted for both copies of the ICP4 gene. This vector also contains the Escherichia coli lacZ gene under control of the thymidine kinase promoter, a viral early promoter, to permit easy detection of infected cells containing replicating vector. In the adult, albumin is expressed uniquely in the liver and in hepatocellular carcinoma and is transcriptionally regulated. The plaquing efficiency of G92A is > 10(3) times higher on human hepatoma cells than on non-albumin-expressing human cells. The growth kinetics of G92A in albumin-expressing cells is delayed compared with that of wild-type HSV-1, likely due to aberrant expression of ICP4 protein. Cells undergoing a productive infection expressed detectable levels of ICP4 protein, as well as the reporter gene product beta-galactosidase. Confining a productive, cytotoxic viral infection to a specific cell type should be useful for tumor therapy and the ablation of specific cell types for the generation of animal models of disease.

The herpes simplex virus immediate-early protein ICP0 affects transcription from the viral genome and infected-cell survival in the absence of ICP4 and ICP27

ICP4, ICP0, and ICP27 are the immediate-early (IE) regulatory proteins of herpes simplex virus that have the greatest effect on viral gene expression and growth. Comparative analysis of viral mutants defective in various subsets of these IE genes should help elucidate how these proteins affect cellular and viral processes. This study focuses on the mutant d97, which is defective for the genes encoding ICP4, ICP0, and ICP27 and expresses the bacterial beta-galactosidase (beta-gal) gene from the ICP0 promoter. Together with the d92 virus (ICP4- ICP27-) and the ICP0-complementing cell line L7, d97 provided a unique opportunity to evaluate ICP0 function in the absence of the regulatory activities specified by ICP4 and ICP27. The pattern of protein synthesis in d97-infected cells was unique relative to other IE gene mutants in that it was similar to that seen in the absence of prior viral protein synthesis, possibly approximating the effect of cellular factors and virion components alone. Inactivation of ICP0 in the absence of ICP4 produced a significant decrease in the levels of the early mRNAs ICP6 and thymidine kinase (tk). There was also a marginal reduction in the levels of the IE ICP22 mRNA, and this was most notable at low multiplicity of infection (MOI). In d97-infected L7 cells, the levels of the viral mRNAs were mostly restored to those observed in infections with d92. Nuclear runoff transcription analysis demonstrated that the presence of ICP0 resulted in an increase in the transcription rates of the analyzed genes. The transcription rates of the early genes were dramatically reduced in the absence of ICP0. At low MOI, the transcription rates of ICP6 and tk were comparable to the rate of transcription of a cellular gene. Relevant to the potential use of d97 as a transfer vector, it was also determined that the absence of ICP0 reduced the cellular toxicity of the virus compared to that of d92. The beta-gal transgene expressed from an IE promoter was detected for up to 14 days postinfection; however, the level of beta-gal expression declined dramatically after 1 day postinfection. In the presence of ICP0, the level of expression of beta-gal was increased; however the infected monolayer was destroyed by 3 days postinfection. Therefore, deletion of ICP0 in the absence of ICP4 and ICP27 reduces toxicity and lowers the level of expression of genes from the viral genome.

Interaction of herpes simplex virus 1 alpha regulatory protein ICP0 with elongation factor 1delta: ICP0 affects translational machinery

The herpes simplex virus 1 (HSV-1)-infected cell protein 0 (ICP0) is a promiscuous transactivator, and by necessity, its functions must be mediated through cellular gene products. In an attempt to identify cellular factors interacting with ICP0, we used the carboxyl-terminal domain of ICP0 as "bait" in the yeast (Saccharomyces cerevisiae) two-hybrid system. Our results were as follows: (i) All 43 cDNAs in positive yeast colonies were found to encode the same translation factor, elongation factor delta-1 (EF-1delta). (ii) Purified chimeric protein consisting of glutathione S-transferase (GST) fused to EF-1delta specifically formed complexes with ICP0 contained in HSV-1-infected cell lysate. (iii) Fractionation of infected HEp-2 cells and immunofluorescence studies revealed that ICP0 was localized both in the nucleus and in the cytoplasm. In primary human foreskin fibroblasts, ICP0 was localized predominantly in the cytoplasm throughout HSV-1 infection even early in infection. (iv) Addition of the chimeric protein GST-carboxyl-terminal domain of ICP0 to the rabbit reticulocyte lysate in vitro translation system resulted in a dose-dependent decrease in protein synthesis. In contrast, GST alone or GST fused to the amino-terminal domain of ICP0 had no effect on the in vitro translation system. (v) The predominant forms of EF-1delta on electrophoresis in denaturing gels have apparent Mrs of 38,000 and 40,000. The higher-Mr form is a minor species in mock-infected cells, whereas in human fibroblasts and Vero cells infected with HSV-1, this isoform becomes dominant. These results indicate that ICP0 is present and may have a significant role in the cytoplasm of infected cells, possibly by altering the efficiency of translation of viral mRNAs.

Physical and functional interactions between herpes simplex virus immediate-early proteins ICP4 and ICP27

The ordered expression of herpes simplex virus type 1 (HSV-1) genes, during the course of a productive infection, requires the action of the virus immediate-early regulatory proteins. Using a protein interaction assay, we demonstrate specific in vitro protein-protein interactions between ICP4 and ICP27, two immediate-early proteins of HSV-1 that are essential for virus replication. We map multiple points of contact between these proteins. Furthermore, by coimmunoprecipitation experiments, we demonstrate the following. (i) ICP4-ICP27 complexes are present in extracts from HSV-1 infected cells. (ii) ICP27 binds preferentially to less modified forms of ICP4, a protein that is extensively modified posttranslationally. We also demonstrate, by performing electrophoretic mobility shift assays and supershifts with monoclonal antibodies to ICP4 or ICP27, that both proteins are present in a DNA-protein complex with a noncanonical ICP4 binding site present in the HSV thymidine kinase (TK) gene. ICP4, in extracts from cells infected with ICP27-deficient viruses, is impaired in its ability to form complexes with the TK site but not with the canonical site from the alpha4 gene. However, ICP4 is able to form complexes with the TK probe, in the absence of ICP27, when overproduced in mammalian cells or expressed in bacteria. These data suggest that the inability of ICP4 from infected cell extracts to bind the TK probe in the absence of ICP27 does not reflect a requirement for the physical presence of ICP27 in the complex. Rather, they imply that ICP27 is likely to modulate the DNA binding activity of ICP4 by affecting its posttranslational modification status. Therefore, we propose that ICP27, in addition to its established role as a posttranscriptional regulator of virus gene expression, may also modulate transcription either through direct or indirect interactions with HSV regulatory regions, or through its ability to modulate the DNA binding activity of ICP4.

Overexpression of the herpes simplex virus type 1 immediate-early regulatory protein, ICP27, is responsible for the aberrant localization of ICP0 and mutant forms of ICP4 in ICP4 mutant virus-infected cells

ICP0 and ICP4 are immediate-early regulatory proteins of herpes simplex virus type 1. Previous studies by Knipe and Smith demonstrated that these two proteins are characteristically observed in the nuclei of wild-type virus-infected cells but predominantly in the cytoplasms of cells infected with several ICP4 temperature-sensitive (ts) mutant viruses at the nonpermissive temperature (NPT) (D. M. Knipe and J. L. Smith, Mol. Cell. Biol. 6:2371-2381, 1986). Consistent with this observation, it has been shown previously that ICP0 is present predominantly in the cytoplasms of cells infected with an ICP4 null mutant virus (n12) at high multiplicities of infection and that the level of ICP27, a third viral regulatory protein, plays an important role in determining the intracellular localization of ICP0 (Z. Zhu, W. Cai, and P. A. Schaffer, J. Virol. 68:3027-3040, 1994). To address whether the cytoplasmic localization of ICP0 is a common feature of cells infected with all ICP4 mutant viruses or whether mutant ICP4 polypeptides, together with ICP27, determine the intracellular localization of ICP0, we used double-staining immunofluorescence tests to examine the intracellular staining patterns of ICP0 and ICP4 in cells infected with an extensive series of ICP4 mutant viruses. In these tests, compared with the localization pattern of ICP0 in wild-type virus-infected cells, more ICP0 was detected in the cytoplasms of cells infected with all ICP4 mutants tested at high multiplicities of infection. Each of the mutant forms of ICP4 exhibiting predominantly cytoplasmic staining contains both the nuclear localization signal and the previously mapped ICP27-responsive region (Z. Zhu and P. A. Schaffer, J. Virol. 69:49-59, 1995). No correlation between the intracellular staining patterns of ICP0 and mutant forms of ICP4 was demonstrated, suggesting that mutant ICP4 polypeptides per se are not responsible for retention of ICP0 in the cytoplasm. This observation was confirmed in studies of cells cotransfected with plasmids expressing ICP0 and mutant forms of ICP4, in which the staining pattern of ICP0 was not changed in the presence of mutant ICP4 proteins. Studies of cells infected at low multiplicities with a variety of ICP4 ts mutant viruses at the NPT showed that both ICP0 and ts forms of ICP4 were localized predominantly within the nucleus. These observations are a further indication that the aberrant localization of the ts forms of ICP4 at the NPT is not a direct result of specific mutations in the ICP4 gene. In the final series of tests, the localization of ICP0 in cells infected with a double-mutant virus unable to express either ICP4 or ICP27 was examined. In these tests, ICP0 was detected exclusively in the nuclei of Vero cells but in both the nuclei and the cytoplasms of ICP27-expressing cells infected with the double mutant. These results demonstrate that ICP27, rather than the absence of functional ICP4, is responsible for the cytoplasmic localization of ICP0 in ICP4 mutant virus-infected cells. Taken together, these findings demonstrate that the aberrant localization of ICP0 and certain mutant forms of ICP4 in cells infected with ICP4 mutant viruses is mediated by high levels of ICP27 resulting from the inability of mutant forms of ICP4 to repress the expression of ICP27.

Repression of the alpha0 gene by ICP4 during a productive herpes simplex virus infection

During a productive infection by herpes simplex virus type 1 (HSV-1), ICP4, the major regulatory protein encoded by the alpha4 gene, binds to its transcription initiation site and represses the accumulation of alpha4 RNA. Evidence suggests that the degree of repression by ICP4 is a function of the absolute distance of an ICP4 binding site 3' from a TATA box. However, repression of HSV-1 gene expression by ICP4 through binding sites located 5' of TATA boxes, as in the case of the alpha0 gene, has not been adequately addressed. To this end, recombinant alpha0 promoters with various arrays of ICP4 binding sites flanking the alpha0 TATA box were constructed and recombined into the HSV-1 genome. Our results demonstrate the following. (i) Destruction of the endogenous alphaO ICP4 binding site, located 5' of the TATA box, results in derepression of alpha0 protein and RNA accumulation in infected Vero cells. (ii) The degree of alpha0 derepression is equivalent to that reported for the alpha4 gene following destruction of the ICP4 binding site at the alpha4 mRNA cap site in HSV-1. (iii) Introduction of an ICP4 binding site at the alpha0 mRNA cap site represses the accumulation of alpha0 RNA greater than threefold relative to the wild type. (iv) Changes in the abundance of alpha0 protein and RNA in infected cells do not affect replication or growth of HSV-1 in tissue culture. Our findings are consistent with the conclusion that alpha0 transcription is repressed by ICP4. These results demonstrate that repression by ICP4 can occur through binding sites located 5' of virus gene TATA boxes in HSV-1. Thus, models addressing repression of HSV-1 gene expression by ICP4 should incorporate the role of binding sites located 5', as well as 3', of virus gene TATA boxes.

An activity specified by the osteosarcoma line U2OS can substitute functionally for ICP0, a major regulatory protein of herpes simplex virus type 1

Among the five immediate-early regulatory proteins of herpes simplex virus (HSV) type 1, only ICP0 is capable of activating all kinetic classes of viral genes. Consistent with its broad transactivating activity, ICP0 plays a major role in enhancing the reactivation of HSV from latency both in vivo and in vitro. Although not essential for viral replication, ICP0 confers a significant growth advantage on the virus, especially at low multiplicities of infection. In this report we describe the expression of a novel activity by the osteosarcoma cell line U2OS that can substitute functionally for ICP0. Compared with Vero cells, both U2OS cells and cells of the ICP0-expressing line 0-28 significantly enhanced the plating efficiency of an ICP0 null mutant, 7134. In contrast, the plating efficiencies of the wild-type virus in all three cell types were similar. Single-step growth experiments demonstrated that the yield of 7134 in U2OS cells was severalfold higher than that in 0-28 cells and about 100-fold higher than that in Vero cells. In order to identify the viral genes whose expression is enhanced by the activity in U2OS cells, levels of expression of selected viral proteins in extracts of Vero and U2OS cells were compared by Western blot (immunoblot) analysis following low-multiplicity infection. At a multiplicity of 0.1 PFU per cell, the levels of expression of the immediate-early protein ICP4 and the early protein gD in 7134-infected U2OS cells were significantly higher than those in 7134-infected Vero cells. When infections were carried out at a multiplicity of 1 PFU per cell, however, no major differences in the levels of expression of these proteins in U2OS and Vero cells were observed. Cycloheximide reversal experiments demonstrated that the cellular activity expressed in U2OS cells that promotes high-level expression of ICP4 is not synthesized de novo but appears to exist as a preformed protein(s). To confirm this observation and to determine whether, like immediate-early genes, early, delayed-early, and late viral genes are also responsive to the cellular activity, transient-expression assays were performed. The results of these tests demonstrated that basal levels of expression from immediate-early, early, and delayed-early promoters, but not that from a late promoter, were significantly higher in U2OS cells than in Vero cells and that this enhancement occurred in the absence of viral proteins.(ABSTRACT TRUNCATED AT 400 WORDS)

Isolation and characterization of a novel mitogenic regulatory gene, 322, which is transcriptionally suppressed in cells transformed by src and ras

In an attempt to isolate novel regulatory and/or tumor suppressor genes, we identified cDNAs whose abundance is low in NIH 3T3 cells and further decreased following the expression of the activated oncogene, v-src. The transcription of one such gene, 322, is suppressed at least 15-fold in src-, ras-, and fos-transformed cells and 3-fold in myc-transformed cells but is unaffected in raf-, mos-, or neu-transformed cells. Activation of a ts-v-src allele in confluent 3Y1 fibroblasts resulted in an initial increase in 322 mRNA levels after 1 to 2 h followed by a rapid decrease to suppressed levels after 4 to 8 h. Morphological transformation was not detected until 12 h later, indicating that the accumulation of 322 transcripts is regulated by v-src and not as a consequence of transformation. Addition of fetal calf serum to starved subconfluent NIH 3T3 or 3Y1 fibroblasts resulted in a similar biphasic regulation of 322, indicating that 322 transcription is responsive to mitogenic factors. Sequence analysis of a putative full-length 322 cDNA clone (5.4 kb) identified a large open reading frame (ORF) encoding a 148.1-kDa product. In vitro transcription and translation of the 322 cDNA from a T7 promoter resulted in a 207-kDa product whose electrophoretic mobility on a sodium dodecyl sulfate-polyacrylamide gel electrophoresis gel was unaffected by digestion with endoglycosidase F. The discrepancy in predicted versus measured molecular weights may result from the high percentage of acidic residues (roughly 20% Glu or Asp) in the 322 ORF product. Comparison of the 322 cDNA ORF with sequences in data banks indicates that this gene is novel. The 322 ORF product contains a potential Cys-1-His-3 Zn finger, at least five nuclear localization signals of the adenovirus E1a motif K(R/K)X(R/K), and alternating acidic and basic domains. Overexpression of the 322 cells resulted in the selection of rapidly growing cells which had lost the transduced 322 cDNA. Thus, 322 represent a novel src- and ras-regulated gene which encodes a potential regulator of mitogenesis and/or tumor suppressor.

Two overlapping transcription units which extend across the L-S junction of herpes simplex virus type 1

A region of the herpes simplex virus type 1 genome located upstream of the alpha 0 promoter contains a promoter which regulates transcription in the opposite orientation to that driven by alpha 0. Analyses of mutants from which this promoter, alpha X, was deleted and a mutant in which a fragment that serves as a transcription terminator and polyadenylation signal was inserted upstream of this promoter demonstrate that two distinct transcription units overlap this region of the genome and are transcribed in a direction antisense to the neurovirulence gene gamma (1)34.5. One unit, dependent on the alpha X promoter, is active when cells are infected in the presence of the protein synthesis inhibitor cycloheximide. The second unit, independent of alpha X, is active during the course of productive infection. This transcription unit originates from a promoter upstream of alpha X which is distinct from the latency-associated promoter (LAP). Two polyadenylated transcripts of 0.9 and 4.9 kb accumulate from this region of the genome during productive infection, but no mature transcripts accumulate in infected cells maintained in the presence of cycloheximide. Kinetic analyses demonstrate that the transcripts that accumulate during productive infection fall into the beta class of herpes simplex virus type 1 genes.

Evaluation of colocalization interactions between the IE110, IE175, and IE63 transactivator proteins of herpes simplex virus within subcellular punctate structures

A number of previous studies have implied that three herpes simplex virus-encoded nuclear transactivator proteins, IE175 (ICP4), IE110 (ICP0), and IE63 (ICP27), may cooperate in transcriptional and posttranscriptional stimulation of viral gene expression. Using double-label immunofluorescence assays (IFA) in transient expression assays, we have examined the intracellular localization of these three proteins in DNA-transfected cells. The IE110 protein on its own forms spherical punctate domains within the nucleus, whereas the IE175 and IE63 proteins alone give uniform and speckled diffuse patterns, respectively. In infected cells, the IE110 punctate granules have been shown to correspond to novel preexisting subnuclear structures referred to as ND10 domains or PODs that contain a variety of cellular proteins, including SP100 and the PML proto-oncogene product. Cotransfection experiments with wild-type nuclear forms of both IE175 and IE110 provided direct evidence for partial redistribution of IE175 into the same punctate granules that contained IE110. Surprisingly, nuclear forms of IE110 were found to move a cytoplasmic form of IE175 into nuclear punctate structures, and a cytoplasmic form of IE110 was able to retain nuclear forms of IE175 in cytoplasmic punctate structures. Therefore, the punctate characteristic of IE110 appeared to both dominate the interactions and override the normal nuclear localization signals. The domains responsible for the interaction mapped to between codons 518 and 768 in 1E110 and to between codons 835 and 1029 in IE175. Importantly, a truncated nuclear form of the 1,298-amino-acid IE175 protein, which lacked the C-terminal domain beyond codon 834, was found to be excluded from the IE110 punctate granules. Cotransfection of nuclear or cytoplasmic IE110 with a truncated nuclear form of IE63 also led to partial redistribution of IE63 into either nuclear or cytoplasmic punctate granules containing IE110. Both the IE63-IE110 and IE175-IE110 colocalization interactions were demonstrated in Vero cells but not in 293 cells. Consequently, they differ from IE110 self-interactions, which correlate with in vitro dimerization and occur efficiently in both cell types. These interactions may help to explain the altered promoter target specificity and synergism observed when IE175 is cotransfected with IE110 in transactivation studies.

Intracellular localization of the herpes simplex virus type 1 major transcriptional regulatory protein, ICP4, is affected by ICP27

Infected-cell protein 4 (ICP4) is the major transcriptional activator of herpes simplex virus (HSV) gene expression during productive infection. ICP0 has broad transactivating activity for all classes of HSV genes as well as cellular genes and genes of heterologous viruses. Together, the transactivating activities of ICP4 and ICP0 are synergistic. ICP27, which alone does not exhibit major transregulatory activity, is able to differentially activate and repress viral gene expression induced by ICP4 and ICP0. Thus, ICP27 plays a modulatory role in viral gene expression. In order to explore the functional relationships among ICP4, ICP0, and ICP27 in the regulation of viral gene expression, we have used indirect immunofluorescence to examine the intracellular localization of ICP4 in cells infected with wild-type virus or with mutant viruses that did not express functional forms of ICP0 or ICP27. Although ICP4 localized to both the nuclei and cytoplasm of cells infected with either the wild-type virus or an ICP0 null mutant virus, this protein was present exclusively in the nuclei of cells infected with an ICP27 null mutant virus, suggesting that ICP27 is able to inhibit the nuclear localization of ICP4 during virus infection. Transient expression assays with pairs of plasmids that express wild-type forms of ICP4 and ICP0 or of ICP4 and ICP27 demonstrated that ICP27 has a significant inhibitory effect on the nuclear localization of ICP4, confirming the observations made with the mutant-virus-infected cells. By using a plasmid expressing wild-type ICP4 and a series of ICP27 mutant plasmids in transient expression assays, the C-terminal half of ICP27 was shown to be required for its inhibitory effect on the nuclear localization of ICP4. In similar studies using a series of ICP4 mutant plasmids, the region of ICP4 responsive to wild-type ICP27 was mapped to the C-terminal portion of the molecule between amino acid residues 820 and 1029. The level of expression of ICP27 was shown to have a significant effect on the intracellular localization of ICP4 in transient assays. These findings are consistent with previous studies in which ICP27 was shown to have an inhibitory effect on the nuclear localization of ICP0 (Z. Zhu, W. Cai, and P. A. Schaffer J. Virol. 68:3027-3040, 1994). Thus, ICP27 has a significant inhibitory effect on the ability of the two major HSV type 1 (HSV-1) regulatory proteins to localize to the nucleus. Collectively, these findings indicate that cooperative regulation of HSV-1 gene expression may well involve intracellular compartmental constraints.

Physical interaction between the herpes simplex virus type 1 immediate-early regulatory proteins ICP0 and ICP4

The herpes simplex virus type 1 immediate-early protein ICP0 enhances expression of a spectrum of viral genes alone and synergistically with ICP4. To test whether ICP0 and ICP4 interact physically, we performed far-Western blotting analysis of proteins from mock-, wild-type-, and ICP4 mutant virus-infected cells with in vitro-synthesized [35S]Met-labeled ICP0 and ICP4 as probes. The ICP4 and ICP0 polypeptides synthesized in vitro exhibited molecular weights similar to those of their counterparts in herpes simplex virus type 1-infected cells, and the in vitro-synthesized ICP4 was able to bind to a probe containing the ICP4 consensus binding site. Far-Western blotting experiments demonstrated that ICP0 interacts directly and specifically with ICP4 and with itself. To further define the interaction between ICP0 and ICP4, we generated a set of glutathione S-transferase (GST)-ICP0 fusion proteins that contain GST and either ICP0 N-terminal amino acids 1 to 244 or 1 to 394 or C-terminal amino acids 395 to 616 or 395 to 775. Using GST-ICP0 fusion protein affinity chromatography and in vitro-synthesized [35S]Met-labeled ICP0 and ICP4, ICP4 was shown to interact preferentially with the fusion protein containing ICP0 C-terminal amino acids 395 to 775, whereas ICP0 interacted efficiently with both the N-terminal GST-ICP0 fusion proteins and the C-terminal GST-ICP0 fusion proteins containing amino acids 395 to 775. Fusion protein affinity chromatography also demonstrated that the C-terminal 235 amino acid residues of ICP4 are important for efficient interaction with ICP0. Collectively, these results reveal a direct and specific physical interaction between ICP0 and ICP4.

Identification and characterization of the ICP22 protein of equine herpesvirus 1

The equine herpesvirus 1 (EHV-1) homolog of herpes simplex virus type 1 ICP22 is differently expressed from the fourth open reading frame of the inverted repeat (IR4) as a 1.4-kb early mRNA and a 1.7-kb late mRNA which are 3' coterminal (V. R. Holden, R. R. Yalamanchili, R. N. Harty, and D. J. O'Callaghan, J. Virol. 66:664-673, 1992). To extend the characterization of IR4 at the protein level, the synthesis and intracellular localization of the IR4 protein were investigated. Antiserum raised against either a synthetic peptide corresponding to amino acids 270 to 286 or against a TrpE-IR4 fusion protein (IR4 residues 13 to 150) was used to identify the IR4 protein. Western immunoblot analysis revealed that IR4 is expressed abundantly from an open reading frame composed of 293 codons as a family of proteins that migrate between 42 to 47 kDa. The intracellular localization of IR4 was examined by cell fractionation, indirect immunofluorescence, and laser-scanning confocal microscopy. These studies revealed that IR4 is localized predominantly in the nucleus and is dispersed uniformly throughout the nucleus. Interestingly, when IR4 is expressed transiently in COS-1 or LTK- cells, a punctate staining pattern within the nucleus is observed by indirect immunofluorescence. Cells transfected with an IR4 mutant construct that encodes a C-terminal truncated (19 amino acids) IR4 protein exhibited greatly reduced intranuclear accumulation of the IR4 protein, indicating that this domain possesses an important intranuclear localization signal. Western blot analysis of EHV-1 virion proteins revealed that IR4 proteins are structural components of the virions. Surprisingly, the 42-kDa species, which is the least abundant and the least modified form of the IR4 protein family in infected cell extracts, was the most abundant IR4 protein present in purified virions.

Cooperativity among herpes simplex virus type 1 immediate-early regulatory proteins: ICP4 and ICP27 affect the intracellular localization of ICP0

The results of transient expression assays and studies of viral mutants have shown that three of the five immediate-early proteins of herpes simplex virus type 1 (HSV-1) perform regulatory functions, individually and cooperatively. As part of efforts designed to explore the molecular basis for the functional cooperativity among ICP0, ICP4, and ICP27 in the regulation of HSV gene expression, we have examined the intracellular localization of ICP0 in cells infected with ICP4 and ICP27 null mutant viruses by indirect immunofluorescence. Although ICP0 was localized predominantly to the nuclei of wild-type virus-infected cells, it was found exclusively in the nuclei of ICP27 mutant-infected cells and in both the cytoplasm and nuclei of ICP4 mutant-infected cells, the cytoplasmic component being especially strong. These observations indicate that both ICP4 and ICP27 can affect the intracellular localization of ICP0. Transient expression assays with plasmids that express wild-type and mutant forms of ICP0, ICP4, and ICP27 confirmed that ICP4 promotes and that ICP27 inhibits the nuclear localization of ICP0. These results confirm the observations made for mutant virus-infected cells and indicate that the localization pattern seen in infected cells can be established by these three immediate-early proteins exclusive of other viral proteins. The C-terminal half of ICP27 was shown to be required to achieve its inhibitory effect on the nuclear localization of ICP0. The region of ICP0 responsive to ICP27 was mapped to the C terminus of the molecule between amino acid residues 720 and 769. In addition, the concentration of ICP27 was shown to have a significant effect on the intracellular localization of ICP0. Because the major regulatory activities of ICP0, ICP4, and ICP27 are expressed in the nucleus, the ability of these three proteins collectively to determine their own localization patterns within cells adds a new dimension to the complex process of viral gene regulation in HSV.

Identification of a dimerization domain in the C-terminal segment of the IE110 transactivator protein from herpes simplex virus

The 775-amino-acid IE110 (or ICP0) phosphoprotein of herpes simplex virus (HSV) functions as an accessory transcription factor during the lytic cycle and plays a critical role in reactivation from latent infection. By immunofluorescence analysis, IE110 localizes in a novel pattern consisting of several dozen spherical punctate granules in the nuclei of DNA-transfected cells. We constructed a hybrid version of IE110 that contained an epitope-tagged domain from the N terminus of the HSV IE175 protein and lacked the IE110 N-terminal domain that confers punctate characteristics. This hybrid IE175(N)/IE110(C) protein gave an irregular nuclear diffuse pattern on its own but was redistributed very efficiently into spherical punctate granules after cotransfection with the wild-type HSV-1 IE110 protein. Similar colocalization interactions occurred with internally deleted forms of IE110 that lacked the zinc finger region or large segments from the center of the protein, including both cytoplasmic and elongated punctate forms, but C-terminal truncated versions of IE110 did not interact. In all such interactions, the punctate phenotype was dominant. Evidence that C-terminal segments of IE110 could also form stable mixed-subunit oligomers in vitro was obtained by coimmunoprecipitation of in vitro-translated IE110 polypeptides with different-size hemagglutinin epitope-tagged forms of the protein. This occurred only when the two forms were cotranslated, not when they were simply mixed together. An in vitro-synthesized IE110 C-terminal polypeptide also gave immunoprecipitable homodimers and heterodimers when two different-size forms were cross-linked with glutaraldehyde and reacted specifically with a bacterial glutathione S-transferase/IE110 C-terminal protein in far-Western blotting experiments. The use of various N-terminal and C-terminal truncated forms of IE110 in the in vivo assays revealed that the outer boundaries of the interaction domain mapped between codons 617 and 711, although inclusion of adjacent codons on either side increased the efficiency severalfold in some assays. We conclude that the C-terminal region of IE110 contains a high-affinity self-interaction domain that leads to stable dimer and higher-order complex formation both in DNA-transfected cells and in in vitro assays. This segment of IE110 is highly conserved between HSV-1 and HSV-2 and appears to have the potential to play an important role in the interaction with the IE175 protein, as well as in correct intracellular localization, but it is not present in the equivalent proteins from varicella-zoster virus, pseudorabies virus, or equine abortion virus.

Mapping of intracellular localization domains and evidence for colocalization interactions between the IE110 and IE175 nuclear transactivator proteins of herpes simplex virus

Transcriptional regulation by the IE175 (ICP4) and IE110 (ICP0) phosphorylated nuclear proteins encoded by herpes simplex virus (HSV) appears to be a key determinant for the establishment of successful lytic cycle infection. By indirect immunofluorescence in transient DNA transfection assays, we have examined the intracellular distribution of deletion and truncation mutants of both IE175 and IE110 from HSV-1. Insertion of short oligonucleotides encoding the basic amino acid motifs 726-GRKRKSP-732 from IE175 and 500-VRPRKRR-506 from IE110 into deleted cytoplasmic forms of the two proteins restored the karyophilic phenotype and confirmed that these motifs are both necessary and sufficient for proper nuclear localization. Analysis of IE110 deletion mutants and a panel of IE110/IE175 hybrid proteins was also used to evaluate the characteristic IE110 distribution within nuclear punctate granules as seen by immunofluorescence and phase-contrast microscopy. The phase-dense punctate pattern persisted with both large C-terminal truncations and deletions of the Cys-rich zinc finger region and even with a form of IE110 that localized in the cytoplasm, implying that the punctate characteristic is an intrinsic property of the N-terminal segment of the IE110 protein. Transfer of the full IE110-like punctate phenotype to the normally uniform diffuse nuclear pattern of the IE175 protein by exchange of the N-terminal domains of the two proteins demonstrated that the first 105 to 244 amino acids of IE110 represent the most important region for conferring punctate characteristics. Surprisingly, cotransfection of a wild-type nuclear IE175 gene together with the IE110 gene revealed that much of the IE175 protein produced was redistributed into a punctate pattern that colocalized with the IE110-associated punctate granules seen in the same cells. This colocalization did not occur after cotransfection of IE110 with the IE72 (IE1) nuclear protein of human cytomegalovirus and therefore cannot represent simple nonspecific trapping. Evidently, the punctate phenotype of IE110 represents a dominant characteristic that reveals the potential of IE110 and IE175 to physically interact with each other either directly or indirectly within the intracellular environment.

The herpes simplex virus type 1 regulatory protein ICP0 enhances virus replication during acute infection and reactivation from latency

ICP0 is a potent activator of herpes simplex virus type 1 gene expression in transient assays and in productive infection. A role for ICP0 in reactivation from latency in vivo has also been suggested on the basis of the observation that viruses with mutations in both copies of the diploid gene for ICP0 reactivate less efficiently than wild-type virus. Because the ICP0 gene is contained entirely within the coding sequences for the latency-associated transcripts (LATs), ICP0 mutants also contain mutations in LAT coding sequences. This overlap raises the question of whether mutations in ICP0 or the LATs, which have also been implicated in reactivation, are responsible for the reduced reactivation frequencies characteristic of ICP0 mutants. Two approaches were taken to examine more definitively the role of ICP0 in the establishment and reactivation of latency. First, a series of ICP0 nonsense, insertion, and deletion mutant viruses that exhibit graded levels of ICP0-specific transactivating activity were tested for parameters of the establishment and reactivation of latency in a mouse ocular model. Although these mutants are ICP0 LAT double mutants, all nonsense mutants induced the synthesis of near-wild-type levels of the 2-kb LAT, demonstrating that the nonsense linker did not disrupt the synthesis of this LAT species. All mutants replicated less efficiently than the wild-type virus in mouse eyes and ganglia during the acute phase of infection. The replication efficiencies of the mutants at these sites corresponded well with the ICP0 transactivating activities of individual mutant peptides in transient expression assays. All mutants exhibited reduced reactivation frequencies relative to those of wild-type virus, and reactivation frequencies, like replication efficiencies in eyes and ganglia, correlated well with the level of ICP0 transactivating activity exhibited by individual mutant peptides. The amount of DNA of the different mutants varied in latently infected ganglia, as demonstrated by polymerase chain reaction analysis. No correlation was evident between reactivation frequencies and the levels of viral DNA in latently infected ganglia. Thus, replication and reactivation efficiencies of ICP0 mutant viruses correlated well with the transactivating efficiency of the corresponding mutant peptides. In a second approach to examining the role of ICP0 in latency, a single copy of the wild-type gene for ICP0 was inserted into the genome of an ICP0- LAT- double mutant, 7134, which exhibits a marked impairment in its ability to replicate in the mouse eye and reactivate from latency.(ABSTRACT TRUNCATED AT 400 WORDS)

The RR1 gene of herpes simplex virus type 1 is uniquely trans activated by ICP0 during infection

As has been demonstrated for herpes simplex virus type 2, we show in this report that the herpes simplex virus type 1 ribonucleotide reductase large subunit (RR1) gene is trans activated in transient transfection assays by VP16 and ICP0 but not by ICP4. Deletion analysis demonstrated that responsiveness to induction to VP16 resides in an octamer/TAATGARAT sequence of the RR1 promoter and that the TATA box alone is sufficient to provide induction by ICP0. The induction of the RR1 gene by ICP0 but not by ICP4 suggested that it might be possible to identify the cis-acting element(s) responsive to ICP4 in an ICP4-inducible promoter. To this end, a series of chimeric promoters containing various portions of the regulatory sequences of the RR1 promoter and thymidine kinase (TK) promoter were constructed. The TK promoter is trans activated by both ICP0 and ICP4 in transient transfection assays and by ICP4 in infection. The data show that replacing the RR1 TATA region with the TK TATA region permits ICP4 inducibility even if the rest of the RR1 promoter elements remain intact. To test whether the RR1 gene is induced by ICP0 during infection, four mutant viruses were constructed. (i) TAATGARAT+ has the wild-type RR1 promoter driving chloramphenicol acetyltransferase (CAT) and the RR2 promoter driving the lacZ gene. The RR2 gene codes for the small subunit of the ribonucleotide reductase and is expressed as a beta gene. (ii) TAATGARAT- has a triple-base change in the octamer/TAATGARAT element which renders it unresponsive to VP16 trans activation, eliminating that portion of the activation of the RR1 gene. (iii) TAATGARAT- delta alpha 0 has a deletion of the alpha 0 gene. (iv) TAATGARAT- delta alpha 4 has a deletion of the alpha 4 gene. Infections were carried out in Vero cells at a multiplicity of infection of 10 per cell; cells were assayed for CAT and beta-galactosidase (beta-Gal) activities and for virus yields. The first two infections gave strong CAT and beta-Gal activities and high yields of progeny virus. Infection with the third virus showed no CAT activity but did produce high levels of beta-Gal activity and virus progeny. The fourth infection resulted in strong CAT activity but no beta-Gal activity or progeny virus. The data demonstrated that the RR1 promoter was activated in the absence of ICP4 but not in the absence of ICP0 in these infections.(ABSTRACT TRUNCATED AT 400 WORDS)

Guanylylation and adenylylation of the alpha regulatory proteins of herpes simplex virus require a viral beta or gamma function

Herpes simplex virus genes form several groups whose expression is coordinately regulated and sequentially ordered in a cascade fashion. Most of the products of the first group, the alpha genes, appear to have regulatory functions. We report that the alpha proteins, infected cell proteins 4, 0, 22, and 27 of herpes simplex virus 1 and 4, 0, and 27 of herpes simplex virus 2, were labeled in the isolated nuclei of infected HeLa cells with [alpha-32P]GTP or [alpha-32P]ATP late in infection and that these proteins represent the largest group of virus-specific proteins labeled in this fashion. Studies with [2-3H]ATP, in which the label is in the purine ring, showed that a portion of the label in alpha proteins and in at least one other infected cell protein is due to nucleotidylylation. Analyses of the labeling reactions in nuclei of (i) cells infected with temperature-sensitive mutants at nonpermissive temperatures, (ii) cells infected with wild-type virus and harvested at different times postinfection, and (iii) cells treated with inhibitors of protein synthesis or of synthesis of viral DNA led to the conclusion that viral gene functions expressed after the synthesis of alpha proteins are required for the labeling of the alpha proteins with [alpha-32P]GTP. We conclude that several of the alpha proteins are extensively posttranslationally modified and that these modifications include nucleotidylylation.

Varicella-zoster virus open reading frame 10 protein, the herpes simplex virus VP16 homolog, transactivates herpesvirus immediate-early gene promoters

The varicella-zoster virus (VZV) open reading frame 10 (ORF10) protein is the homolog of the herpes simplex virus type 1 (HSV-1) protein VP16. These are two virion tegument proteins that have extensive amino acid sequence identity in their amino-terminal and middle domains. ORF10, however, lacks the acidic carboxy terminus which is critical for transactivation by VP16. Earlier studies showed that VZV ORF10 does not form a tertiary complex with the TAATGARAT regulatory element (where R is a purine) with which HSV-1 VP16 interacts, suggesting that ORF10 may not have transactivating ability. Using transient-expression assays, we show that VZV ORF10 is able to transactivate VZV immediate-early (IE) gene (ORF62) and HSV-1 IE gene (ICP4 and ICP0) promoters. Furthermore, cell lines stably expressing ORF10 complement the HSV-1 mutant in1814, which lacks the transactivating function of VP16, and enhance the de novo synthesis of infectious virus following transfection of HSV-1 virion DNA. These results indicate that ORF10, like its HSV-1 homolog VP16, is a transactivating protein despite the absence of sequences similar to the VP16 carboxy-terminal domain. The transactivating function of the VZV ORF10 tegument protein may be critical for efficient initiation of viral infection.

Identification of a promoter mapping within the reiterated sequences that flank the herpes simplex virus type 1 UL region

Analysis of the promoter for the herpes simplex virus (HSV) immediate-early (alpha) gene alpha 0 in a short-term transient expression assay revealed that a SacI-to-NcoI fragment from -786 to +148 relative to the cap site directed the synthesis of chloramphenicol acetyltransferase when the fragment was present in either orientation. Although the constitutive levels of promoter activity were similar with either orientation, the reverse-orientation promoter was not induced in response to infection with HSV. Analysis of sequences composing the putative promoter in the opposite orientation revealed the presence of important regulatory elements associated with alpha promoters. These include an alpha-trans-inducing factor (alpha-TIF)-like response element, a high-affinity ICP4-binding site, numerous Sp1-binding sites, and a TATA box. Sequences contained within this region formed specific DNA-protein complexes in extracts from mock-infected and HSV-infected HeLa cells. Transient expression assays revealed that this sequence was positively regulated by the alpha 0 and alpha-TIF genes but negatively regulated by alpha 4. Finally, nuclear run-on transcription assays revealed that this promoter is active in its correct genomic context during the course of virus infection. We suggest that the promoter is a hybrid between an alpha and beta promoter because it exhibits maximal expression at 8 h postinfection and is expressed in the presence of cycloheximide.

The varicella-zoster virus immediate early protein, IE62, can positively regulate its cognate promoter

Varicella-Zoster virus (VZV) is a neurotropic alphaherpes virus closely related to herpes simplex virus (HSV). However, unlike its close relative HSV, VZV lacks a functional alpha-TIF (alpha-gene transinducing factor) that activates the transcription of immediate early genes during the initial events of the virus life cycle. Hence, in the absence of a functional alpha-TIF, the mechanism triggering the expression of immediate early genes in VZV at present remains unclear. Accumulating evidence indicates that the gene product of the putative immediate early gene ORF62 (IE62) plays a pivotal role in activating VZV genes of all three putative kinetic classes, namely immediate early (alpha), early (beta), and late (gamma) classes of VZV genes. In the present study, we show that IE62 can positively autoregulate its cognate promoter using a transient transfection assay, both in lymphocytes and in neural cells. In the same system, we can also demonstrate activation of the VZV IE62 promoter by HSV ICP4. By deletion analysis and oligonucleotide-directed site-specific mutagenesis we have localized specific regions in the IE62 promoter/upstream sequences that mediate inducibility by IE62 and HSV ICP4, and provide evidence that this promoter activation by these two proteins may be through different mechanisms. These data, taken together with the recent demonstration of the presence of IE62 in the VZ virion tegument (Kinchington, P.R., Hoagland, J.K., Arvin, A.M., Ruyechan, W.T., and Hay, J. 1992. J. Virol. 66, 359-366) provides a possible mechanism by which the triggering of VZV gene expression occurs in the absence of a functional alpha-TIF protein.

Differences in the poly(ADP-ribosyl)ation patterns of ICP4, the herpes simplex virus major regulatory protein, in infected cells and in isolated nuclei

Infected-cell protein 4 (ICP4), the major regulatory protein in herpes simplex viruses 1 and 2, was previously reported to accept 32P from [32P]NAD in isolated nuclei. This modification was attributed to poly(ADP-ribosyl)ation (C. M. Preston and E. L. Notarianni, Virology 131:492-501, 1983). We determined that an antibody specific for poly(ADP-ribose) reacts with ICP4 extracted from infected cells, electrophoretically separated in denaturing gels, and electrically transferred to nitrocellulose. Our results indicate that all forms of ICP4 observed in one-dimensional gel electrophoresis are poly(ADP-ribosyl)ated. Poly(ADP-ribose) on ICP4 extracted from infected cells was resistant to cleavage by purified poly(ADP-ribose) glycohydrolase unless ICP4 was in a denatured state. Poly(ADP-ribose) added to ICP4 in isolated nuclei was sensitive to this enzyme. This result indicates that the two processes are distinct and may involve different sites on the ICP4 molecule.

Multimerization of ICP0, a herpes simplex virus immediate-early protein

ICP0, a herpes simplex virus immediate-early gene product, is a highly phosphorylated nuclear protein that is a potent activator of virus and host genes. Using biochemical and genetic assays employing plasmids encoding mutant forms of ICP0 and a recombinant adenovirus that expresses ICP0, we mutant forms of ICP0 and a recombinant adenovirus that expresses ICP0, we provide evidence that the protein multimerizes. Some mutant forms of ICP0 were transdominant and interfered with activation of a target reporter gene or with complementation of an ICP0-minus virus.

HSV-1-inducible proteins bind to NF-kappa B-like sites in the HSV-1 genome

Several putative NF-kappa B-binding sites in the ICP0 and Vmw65 herpes simplex virus type-1 (HSV-1) genes have been identified. Oligonucleotides encoding some of these sites bind specifically to purified NF-kappa B protein and an NF-kappa B-like protein in nuclear extracts of phorbol ester- or cycloheximide-induced human embryonic lung (HEL) cells. HSV-1 infection of HEL cells induced a nuclear factor that binds specifically to kappa B sites in the ICP0 and Vmw65 gene regions and comigrates with complexes formed by purified NF-kappa B. The HSV-1-inducible nuclear factor bound to the authentic immunoglobulin (Ig) kappa B site. Transient expression of chloramphenicol acetyltransferase (CAT) plasmids containing two copies of the Ig kappa B site upstream of the c-fos promoter (kappa B2-CAT) showed activity in HEL cells. HSV-1 infection of kappa B2-CAT-transfected HEL cells, however, induced a dramatic increase in CAT activity; mutation in the NF-kappa B-binding site of kappa B2-CAT abolished the inducibility of CAT gene expression. Our results demonstrate that the HSV-1 ICP0 and Vmw65 gene regions contain binding sites for NF-kappa B, and that HSV-1-inducible proteins bind to NF-kappa B-like sites in the HSV-1 genome.