Herpes simplex virus type 2 mutagenesis: characterization of mutants induced at the hprt locus of nonpermissive XC cells

Modulation of apoptosis by caprine herpesvirus 1 infection in a neuronal cell line

Caprine herpesvirus type 1 (CpHV-1), like other members of the alpha subfamily of herpesviruses, establishes latent infections in trigeminal ganglion neurons. Our groups previously demonstrated that CpHV-1 induces apoptosis in goat peripheral blood mononuclear cells and in an epithelial bovine cell line, but the ability of CpHV-1 to induce apoptosis in neuronal cells remains unexplored. In this report, the susceptibility of Neuro 2A cells to infection by CpHV-1 was examined. Following infection of cultured cells with CpHV-1, expression of cell death genes was evaluated using real-time PCR and Western blot assays. Analysis of virus-infected cells revealed activation of caspase-8, a marker for the extrinsic pathway of apoptosis, and caspase-9, a marker for the intrinsic pathway of apoptosis at 12 and 24 h post-infection. Significant increase in the levels of cleaved caspase-3 was also observed at the acme of cytopathic effect at 24 h post-infection. In particular, at 3 and 6 h post-infection, several proapototic genes were under-expressed. At 12 h post-infection several proapototic genes such as caspases, TNF, Cd70, and Traf1 were over expressed while Bcl2a1a, Fadd, and TNF genes were underexpressed. In conclusion, the simultaneous activation of caspase-8 and caspase-9 suggests that CpHV-1 can trigger the death-receptor pathway and the mitochondrial pathway separately and in parallel. Our findings are significant because this is the first published study showing the effect of CpHV-1 infection in neuronal cells in terms of gene expression and apoptosis modulation.

Bovine Herpes Virus 1 (BHV-1) and Herpes Simplex Virus Type 1 (HSV-1) Promote Survival of Latently Infected Sensory Neurons, in Part by Inhibiting Apoptosis

α-Herpesvirinae subfamily members, including herpes simplex virus type 1 (HSV-1) and bovine herpes virus 1 (BHV-1), initiate infection in mucosal surfaces. BHV-1 and HSV-1 enter sensory neurons by cell-cell spread where a burst of viral gene expression occurs. When compared to non-neuronal cells, viral gene expression is quickly extinguished in sensory neurons resulting in neuronal survival and latency. The HSV-1 latency associated transcript (LAT), which is abundantly expressed in latently infected neurons, inhibits apoptosis, viral transcription, and productive infection, and directly or indirectly enhances reactivation from latency in small animal models. Three anti-apoptosis genes can be substituted for LAT, which will restore wild type levels of reactivation from latency to a LAT null mutant virus. Two small non-coding RNAs encoded by LAT possess anti-apoptosis functions in transfected cells. The BHV-1 latency related RNA (LR-RNA), like LAT, is abundantly expressed during latency. The LR-RNA encodes a protein (ORF2) and two microRNAs that are expressed in certain latently infected neurons. Wild-type expression of LR gene products is required for stress-induced reactivation from latency in cattle. ORF2 has anti-apoptosis functions and interacts with certain cellular transcription factors that stimulate viral transcription and productive infection. ORF2 is predicted to promote survival of infected neurons by inhibiting apoptosis and sequestering cellular transcription factors which stimulate productive infection. In addition, the LR encoded microRNAs inhibit viral transcription and apoptosis. In summary, the ability of BHV-1 and HSV-1 to interfere with apoptosis and productive infection in sensory neurons is crucial for the life-long latency-reactivation cycle in their respective hosts.

Towards an understanding of the herpes simplex virus type 1 latency-reactivation cycle

Infection by herpes simplex virus type 1 (HSV-1) can cause clinical symptoms in the peripheral and central nervous system. Recurrent ocular shedding can lead to corneal scarring and vision loss making HSV-1 a leading cause of corneal blindness due to an infectious agent. The primary site of HSV-1 latency is sensory neurons within trigeminal ganglia. Periodically, reactivation from latency occurs resulting in virus transmission and recurrent disease. During latency, the latency-associated transcript (LAT) is abundantly expressed. LAT expression is important for the latency-reactivation cycle in animal models, in part, because it inhibits apoptosis, viral gene expression, and productive infection. A novel transcript within LAT coding sequences (AL3) and small nonprotein coding RNAs are also expressed in trigeminal ganglia of latently infected mice. In this review, an update of viral factors that are expressed during latency and their potential roles in regulating the latency-reactivation cycle is discussed.

Replication and interaction of herpes simplex virus and human papillomavirus in differentiating host epithelial tissue

We have investigated the interactions and consequences of superinfecting and coreplication of human papillomavirus (HPV) and herpes simplex virus (HSV) in human epithelial organotypic (raft) culture tissues. In HPV-positive tissues, HSV infection and replication induced significant cytopathic effects (CPE), but the tissues were able to recover and maintain a certain degree of tissue integrity and architecture. HPV31b not only maintained the episomal state of its genomic DNA but also maintained its genomic copy number even during times of extensive HSV-induced CPE. E2 transcripts encoded by HPV31b were undetectable even though HPV31b replication was maintained in HSV- infected raft tissues. Expression of HPV31b oncogenes (E6 and E7) was also repressed but to a lesser degree than was E2 expression. The extent of CPE induced by HSV is dependent on the magnitude of HPV replication and gene expression at the time of HSV infection. During active HSV infection, HPV maintains its genomic copy number even though genes required for its replication were repressed. These studies provide new insight into the complex interaction between two common human sexually transmitted viruses in an in vitro system, modeling their natural host tissue in vivo.

Chromosomal aberrations induced by BK virus T antigen in human fibroblasts

Human fibroblasts, transfected with a recombinant DNA containing the neo gene and BK virus (BKV) early region, which expresses BPV large T antigen (TAg), show cytogenetic alterations characterized by dicentric chromosomes and other structural aberrations such as deletions, duplications, translocations, and ring chromosomes. Such alterations were absent or significantly less frequent in human fibroblasts transfected with a plasmid expressing only the neo gene. The chromosome damage in BKV-transfected cells was evident before the appearance of the morphologically transformed phenotype and therefore seems to be a primary effect of TAg expression in human cells. The specific pattern of chromosome aberrations suggests the prevalence of an indirect clastogenic effect, determined by the inhibition of p53 regulatory functions on genome stability by BKV TAg. Due to the widespread distribution of BKV in the human population and to the latent state of BKV DNA in many human organs, the clastogenic activity of BKV TAg may potentially participate in an oncogenic process involving BKV latently infected cells.

Increased frequency of specific locus mutation following human cytomegalovirus infection

The effect of human cytomegalovirus (HCMV) infection on the frequency of mutations at the hypoxanthine-guanine phosphoribosyl transferase (hprt) locus was studied in Chinese hamster lung V79 cells. When V79 cells were infected with HCMV (strain AD169) at multiplicities of 0.1 to 50 plaque forming units (PFU) per cell the presumptive mutation frequency, as determined by the number of 6-thioguanine-resistant (TGr) colonies, was increased up to 16.8-fold (P < 0.005), depending on the multiplicity of infection. Increases in the mutation frequency at the hprt locus were also observed for other laboratory-adapted HCMV strains (C-87, Davis) and for low passage clinical isolates (82-1, 84-2). The expression time required for the maximum increase in TGr colonies was 3 days and was consistent among the HCMV strains evaluated in this study. UV-irradiation of HCMV stock up to a dose of 9.6 x 10(4) ergs/mm2 increased the mutation frequency, but further exposure to UV light or to heat (56 degrees for 30 min) significantly decreased the frequency of TGr-resistant colonies, suggesting that expression of HCMV genes was involved in the mutation process. HCMV-induced TGr cells demonstrated substantially reduced (> 96%) incorporation of [3H]hypoxanthine. PCR analysis of the hprt locus demonstrated deletions in 9 of 19 HCMV-induced TGr colonies randomly selected for further study, while 2 of 17 spontaneously developed TGr colonies demonstrated deletions. Although insertions were not detected in spontaneously developed clones, 3 of 19 HCMV-induced TGr clones had insertions in the hprt gene. Neither HCMV-specific DNA sequences nor HCMV-specific proteins were detected in the TGr clones obtained after HCMV infection. Infection of V79 cells with HCMV also increased their sensitivity to mutation with N-methyl-N'-nitro-N-nitrosoguanidine, giving a synergistic enhancement of the mutation frequency. These results indicate that HCMV infection has the capacity to induce mutations in the cellular genome and increase the sensitivity of infected cells to mutation by genotoxic chemicals. Although inactivated HCMV particles are responsible for a modest increase in the mutation frequency, expression of HCMV genes is associated with a substantial enhancement of the mutation frequency.

Mutagenesis occurring following infection with herpes simplex virus does not require virus replication

Infection of eukaryotic cells in culture with herpes simplex virus type-1 (HSV-1) or HSV-2 increased the mutation frequency of the supF gene carried on the shuttle vector pZ189 by around sixfold. The increase was apparent 2 hr postinfection and reached a peak after 8 hr. To investigate this mutagenesis, plasmids pCKRR1 and pCKRR2 were constructed to express the large and small subunits, respectively, of HSV-2 ribonucleotide reductase (RR) under the control of the inducible mouse metallothionein promoter. Expression from these plasmids, either singly or together, had no effect on the mutation frequency of pZ189 under conditions when virus RR activity was detected. The HSV-1 temperature sensitive (ts) mutant viruses ts 1207 and ts 1222, which have ts lesions in the genes encoding R1 and R2, respectively, were as mutagenic as wild-type HSV-1 at both the permissive and nonpermissive temperatures. These results indicate that expression of HSV RR is not mutagenic in this system. Experiments using other HSV-1 mutants and ultraviolet-inactivated virus localized the cause of the increased mutagenic frequency either to a component of the incoming virion or to an effect exerted by the virus DNA itself. The present study confirms previous reports that infection with HSV exerts a mutagenic effect. Further, virus replication and gene expression were not required for the mutagenic effect studied here. This may have implications for a role of HSV in cellular transformation, as a nonproductive infection could mutagenize cellular genes.

Herpes simplex virus type 1 mutants for the origin-binding protein induce DNA amplification in the absence of viral replication

Herpes simplex virus (HSV) induces DNA amplification within the host cell genome, which is mediated by a set of six of seven HSV replication genes. The origin-binding protein (UL9) is dispensible. By the use of HSV mutants for the UL9 gene we show here that HSV can induce DNA amplification in the absence of lytic viral growth in contrast to replication-negative mutants for either the UL8 or UL52 gene used as control. The amplification-inducing potential of HSV may be relevant for the pathogenicity of the virus.

Mutagenic activity of BKV and JCV in human and other mammalian cells

We present data suggesting that human polyomaviruses BKV and JCV, widely distributed throughout human populations, are able to induce gene mutations in cultured cells. In this study, using different infecting agents, cell lines to be infected, mutation expression periods, and selection systems, we observed mutagenic effects of varying extent with values of spontaneous mutant frequencies being increased after BKV infection up to 100-fold in BHK cells (6-thioguanine resistance) and nearly 35-fold in virus-transformed human Lesch-Nyhan cells (ouabain resistance). In experiments with BKV the viral mutagenic potential was found to be raised both in moderately uv-irradiated cells, or when wild-type virus was replaced by the variant BKV-IR isolated from a human tumor. Since BKV-IR is defective in the expression of small-t antigen, the viral mutagenicity does not require this protein to be active. BKV was shown to mutate, besides different established cell lines, human peripheral blood lymphocytes. Moreover, as demonstrated by comparing mutagenicities of DNAs from BKV, JCV, and the related polyomavirus SV40, the mutagenic effects of the three viruses do not appear to be essentially different. Implications of these findings are discussed.

Differential regulation of keratin 8 and 18 messenger RNAs in differentiating F9 cells

F9 embryonal carcinoma cells (F9EC) can be induced to differentiate in vitro into epithelial cells expressing keratin 8 (K8) and keratin 18 (K18). cDNAs corresponding to K8 and K18 mRNAs were cloned and used to study the change in the abundance of these mRNAs during differentiation of F9 cells into parietal endoderm-like cells by treatment with retinoic acid (RA) or with RA and dibutyryl cAMP (Bt2cAMP). Using an RNase protection assay, it was determined that K8 mRNA was induced slightly before K18 mRNA and that it accumulated to a greater extent than K18 mRNA. Furthermore, differentiation in presence of Bt2cAMP plus RA resulted in an earlier induction of the two mRNAs and a higher level of expression of K8 mRNA. These results indicate that K8 and K18 mRNAs are regulated differently in F9 cells.

Mouse keratin 19: complete amino acid sequence and gene expression during development

The complete amino acid sequence of the mouse keratin 19 (K19) was determined from a partial sequence of cDNA isolated from a mouse (day 10.5) embryo library and an amplified genomic fragment. Analysis of the sequence reveals strong evolutionary conservation with other K19s. Examination of the expression of the gene encoding K19 (K19) during development using an RNase protection assay reveals it is expressed in extra-embryonic tissues by day 8.5 and in the embryo proper by at least day 9.5. Furthermore, the K19 gene is induced in differentiating F9 embryonal carcinoma cells. These results indicate that K19 is another keratin, in addition to the K8-K18 pair, which is synthesized early during mouse development. Finally, Southern analysis of the K19 gene reveals that it is found as a unique copy in the mouse genome, in contrast to what is found in humans, which have at least one processed pseudogene.

Transformation of NIH 3T3 cells by herpes simplex type 2 BglII n fragment and sub-fragments is independent from induction of mutation at the HPRT locus

The effect of transfection of the herpes simplex virus type 2 transforming fragment BglII n and of its three Xhol subfragments on mutagenesis and morphological transformation was assayed in NIH 3T3 cells. While BglII n and the right hand portion of this fragment increased the number of transformed foci, no significant effects on the mutation frequency at the hprt locus were observed. Our results indicate that transformation by BglII n is independent from the induction of somatic mutations and suggest that other mechanisms must be considered to explain transformation by this sequence.

Sexually transmitted cancers and viruses

Both cervical cancer and its precancerous state cervical intraepithelial neoplasia (CIN) have the characteristics of being sexually transmitted. Formerly herpes simplex virus (HSV) but more recently human papillomavirus (HPV) which both infect the cervix have been implicated in causation. The role of these viruses as possible initiators of cancer or as potential cofactors of cocarcinogens is discussed at the molecular level within the context of the disease process.

Identification of a proliferation-related transcript with an elevated expression in the mid-gestation mouse embryo

Polyadenylated RNA enriched in transformation specific sequences from hamster embryo fibroblast cells transformed by HSV-2 was used to construct a cDNA library. A cDNA clone (pKG4) contained a sequence which was upregulated in HSV-2 transformed cells and also in fibroblastic cell lines transformed by SV40 and 3-methylcholanthrene. The expression of the KG4 sequences in HSV-2-transformed cells was found to be modulated by the growth state of the cells. In confluent cells its level was reduced 5-times compared to the homologous RNAs from exponentially growing cells. Expression of the KG4 sequence was also examined in mouse embryos from day 8 onwards and in adult tissues. During development, KG4 is expressed at all times examined. However, there is a dramatic increase in expression on day 11. In adult tissues, a low and variable level of expression was observed. These findings suggest that the KG4 sequence is related to cellular proliferation.

DNA methylation and genetic inactivation at thymidine kinase locus: two different mechanisms for silencing autosomal genes

Patterns of methylation of CpG dinucleotides in the promoter region of the thymidine kinase (TK) gene in wild-type and TK-deficient Chinese hamster cell lines were studied. Whereas wild-type cells were unmethylated, three conventionally derived TK-deficient cell lines were all almost completely methylated in the promoter region. Demethylation at a number of different CpG sites was observed upon selection for reexpression of the TK gene. Of thirteen HhaI (GCGC) or HpaII (CCGG) sites studied, the highest correlation between absence of methylation and at least partial TK activity was obtained at one HhaI site within 20 bp of the putative cap site. Silencing in the three conventionally derived mutants is therefore accompanied by hypermethylation of the promoter-associated CpG-rich island. We contrast this situation with another type of silencing event, in which TK was coordinately inactivated at a high frequency with at least one other linked allele. Methylation of the promoter region of TK was not associated with this event, but two lines of evidence suggested a role for methylation at sites other than in the promoter region of TK.