Quantitative assay for transformation of 3T3 cells by herpes simplex virus type 2

Alterations in the cellular phenotype induced by herpes simplex viruses

Numerous studies have shown that herpes simplex virus types 1 and 2 (HSV-1, HSV-2) are able to transform the morphological phenotype of rodent cells. Unlike other DNA tumor viruses the transformed cells did not consistently retain or express a given set of viral genes. In fact, transformation could be obtained using fragments of viral DNA that did not wholly encode viral proteins. Of interest within the transforming fragments were sequences which could assume a secondary structure like that of insertion elements. The failure to detect viral DNA in transformed cells led to the hit-and-run hypothesis of HSV transformation. The mechanism by which HSV induces transformation is not understood. Various lines of investigation have shown that HSV is able to cause mutations--both point mutations and gene rearrangements. HSV is also able to induce gene amplification, particularly of sequences harboring an origin of replication such as SV40 or papillomaviruses. Other experiments have shown that HSV can activate the expression of endogenous type C retroviruses. More broadly, HSV has been shown to activate cellular transcription or to switch on the synthesis of host cell proteins not normally expressed in untransformed cells. The failure to detect viral DNA in a high proportion of human anogenital tumors made it difficult to implicate HSV in the etiology of those neoplasias, but it is consistent, however, with the observations on the mode of HSV transformation in vitro, and suggests that HSV could be involved in a multistage process of oncogenic transformation.

Promoting effect of croton oil on the induction of cervical and vaginal cancers with herpes simplex virus types 1 and 2 in mice

Hybrid Swiss virgin mice (Kuan-min strain) were challenged intravaginally with uv-inactivated herpes simplex virus type 1 (HSV-1) or type 2 (HSV-2) twice a week for 16 times and subsequently with croton oil or control medium twice a week for 27 times. After a period of 180 days the exposure to HSV-2 plus control medium induced premalignant and malignant lesions of the cervix and vagina in 50.0% of the mice. The exposure to HSV-2 plus croton oil induced similar lesions in 78.2% of the mice. The exposure to HSV-1 combined with either control medium or croton oil induced lesions in 37.2 and 58.3% of the mice, respectively. No malignant lesions were found in the control mice. These results reveal that (1) HSV-1 and HSV-2 have a similar oncogenic potential, and (2) croton oil can promote the induction of cervical and vaginal cancers with HSV-1 and HSV-2. Additionally, these results suggest that the virus-induced carcinogenesis of cervix and vagina might be similar to the classical two-stage carcinogenesis model. This animal model seems to be more suitable for studying the prevention and treatment of cervical and vaginal cancers because the period of this experiment is significantly shorter than that of experiments reported by other investigators and the frequency of the malignant lesion is significantly higher than or similar to that of the same lesion reported in other experiments.

Current knowledge of mechanisms of viral carcinogenesis

Retroviruses are RNA-containing viruses using reverse transcriptase to produce DNA copies capable of insertion into host chromosomes. Appropriate genes are required to confer transforming ability to retroviruses. The src gene, a 60,000-dalton protein with protein kinase activity, is required by avian viruses to induce sarcomas. Normal cells have a gene (sarc) similar to the src gene. Retroviruses with oncogenic properties can arise by recombining with genes on the host chromosome. Herpesviruses, adenoviruses, and papovaviruses have transforming properties residing in only a portion of the genome. Probably, only one to two genes are required for transformation, regardless of the complexity of the virus.

The oncogenic potential of herpes simplex viruses: evidence for a 'hit-and-run' mechanism

Experiments to determine the mechanism of transformation of herpes simplex virus (HSV) have identified fragments of viral DNA which are able to initiate transformation. No set of viral genes seems to be consistently retained or expressed in the transformed cells or in human cervical tumours, suggesting that viral DNA is not needed to maintain the transformed phenotype. In fact there is no conclusive evidence that initiation of neoplasia is mediated by a viral protein. Here we revisit the 'hit-and-run' hypothesis and its implications for HSV-induced tumorigenicity.

Chemical interactions with herpes simplex type 2 virus: enhancement of transformation by hydrazine and 1,2-dimethylhydrazine

Quantitative assays for the morphological transformation of 3T3 Swiss mouse cells by herpes simplex type 2 virus (HSV-2) were employed to examine the effect on cell transformation of chemical carcinogens and suspected carcinogens. Exposure of the cells to the chemical compound, followed by virus infection, resulted in enhancement of transformation when compared to that observed with chemical or virus alone. Enhancement occurred in tests utilizing either UV light-inactivated HSV-2 (strain 333) or a temperature-sensitive (ts) mutant of HSV-2 (A8(293)]. A series of seven ts-mutants were tested and exhibited varying degrees of transformation. Enhancement of transformation occurred in cells treated with hydrazine (HZ) and 1,2-dimethylhydrazine (SDMH). No enhancement occurred when cells were treated with monomethylhydrazine, 1,1-dimethylhydrazine and the jet fuels JP-5, JP-10, RJ-4 and RJ-5. A strong time dependence after treatment was demonstrated with some enhancement seen at 6 h after chemical treatment but the greatest enhancement appeared when virus infection began after 24 h of chemical exposure.

Transformation of rodent cells by a cloned DNA fragment of herpes simplex virus type 2

Transformation of rodent cells with isolated restriction endonuclease fragments of herpes simplex virus type 2 DNA identified a region of the genome located between map positions 0.58 and 0.62. These sequences were cloned into pBR322, and the recombinant plasmid was used to transform primary rat embryo cells and NIH 3T3 cells. The transformants were selected for their ability to form dense foci on a monolayer or to form colonies in semisolid medium. In contrast to the parental rat or mouse cells, cell lines transformed with the cloned herpes simplex virus type 2 fragment grow to high saturation densities, replicate in medium containing 1% serum, form colonies in dilute methylcellulose, show reduced levels of fibronectin, and are tumorigenic in nude mice and in their syngeneic hosts. Southern blot hybridizations have detected sequences homologous to the viral fragment in high-molecular-weight DNA from the transformed cell lines that are not present in DNA from normal rodents. In all cases, the plasmid DNA was present in less than one copy per cell, and the patterns of viral sequences changed with passage of the cell line in vivo.

Herpes simplex virus DNA polymerase, thymidine kinase and deoxyribonuclease activities in cells infected with wild type, ultraviolet-irradiated and defective virus

The DNA polymerase, thymidine kinase and deoxyribonuclease activities were studied in cells infected with wild type (wt), ultraviolet (UV)-irradiated and defective herpes simplex virus type 1. All three enzymatic activities were expressed in cells infected with wt virus. In cells infected with UV-irradiated virus, the thymidine kinase and deoxyribonuclease activities were inhibited and the DNA polymerase activity was markedly suppressed. In cells producing defective virus, there was thymidine kinase activity, but the viral deoxyribonuclease activity was considerably reduced. The DNA polymerase activity was fully expressed in cells producing defective virus at passage level 5, but at passage level 6, the activity of the viral DNA polymerase declined.

Concanavalin A-mediated agglutination of 3T3 cells after exposure to UV-irradiated herpes simplex virus

Studies were made to determine the effect of UV-irradiation of herpes simplex virus (HSV) on Concanavalin A (Con-A)-mediated agglutination of 3T3 cells. There were three different phases of agglutination by Con-A of cells infected with HSV. The agglutinability began to increase from 3 or 4 hr, or 72 hr after exposure of cells to HSV. The early-appearing agglutinability was further divided into two phases, based on its sensitivity to metabolic inhibitors. These were tentatively called "Early 1 or inhibitor sensitive", "Early 2 or inhibitor insensitive" and "Late" agglutinability. "Early 1" agglutination, detected from 3 hr post infection (pi), was induced by treating cells with HSV, either active or UV-irradiated for less than 5 min and was inhibited when actinomycin D (1 microgram/ml) or cycloheximide (50 microgram/ml) was added to the cultures. "Early 2" agglutination began to increase from 4 hr pi when cells were inoculated with HSV irradiated for 7 to 20 min and was not affected by either inhibitor. HSV irradiated for 6 min failed to induce either agglutinability. "Late" agglutination, observed 72 hr pi, was detected in cultures which had been treated with HSV irradiated for 4 to 15 min. Among those, virus irradiated for 6 to 8 min was most efficient. HSV-transformed cells were also agglutinated without exception by low concentrations of Con-A.

Binding to chromosomes of herpes simplex-related antigens in biochemically transformed cells

Association of herpes simplex virus (HSV)-related antigens with chromosomes was demonstrated in human and mouse cells biochemically transformed by HSV that had been irradiated with ultraviolet light. This was accomplished by using peroxidase-anti-peroxidase immunological staining with rabbit antisera that had high neutralizing titers against both HSV-specific thymidine kinase activity and virus infectivity. Antisera-against HSV did not react with chromosomes of uninfected cells nor did normal sera react with any of the constitutents of biochemically transformed cells. Methanol/acetic acid treatment of biochemically transformed cells eliminated their nuclear staining for HSV-related antigens. In vitro binding of HSV-related antigens to chromosomes was demonstrated by incubating soluble antigens from high salt extracts of HSV-infected cells with methanol/acetic acid-fixed chromosomes of biochemically transformed or uninfected cells, followed by exposure to antiserum against HSV and peroxidase-anti-peroxidase staining. There was no staining when soluble extracts from uninfected cells were substituted for those from HSV-infected cells. The results show that cells biochemically transformed and lytically infected by HSV, respectively, contain antigens, which like the Epstein-Barr virus-associated nuclear antigen (EBNA), bind to chromosomes in vivo and in vitro.

RNA-tumour-virus genes and transforming genes: patterns of transmission

RNA tumour virus genes are contained in the chromosomal DNA of most vertebrates, and may be transmitted vertically from parent to progeny along with other cellular genes, as well as horizontally as infectious particles. Activation of these viral genes may be part of the means by which RNA tumour viruses produce cancer. Viral genes and their possible gene products have been characterized. The envelope glycoprotein, for example, interacts with specific membrane receptors on cell surfaces and the major phosphoprotein binds to specific viral RNA sequences. Type-C viral gene sequences have evolved as the species have evolved, and have been transferred between distantly related species under natural conditions. The presence of genetically transmitted viral genes in several vertebrate species, including primates, and the evidence that they may provide normal functions beneficial to the species carrying them, suggests that the potential to cause cancer is a pathological manifestation of a normal physiological process.

The interaction of Herpes Simplex Virus with murine lymphocytes. I. Mitogenic properties of herpes simplex virus

Herpes simplex virus (HSV) stimulates DNA synthesis in mouse spleen cultures prepared from normal, macrophage-depleted, and T-cell-depleted spleen cells, but not from thymocytes. In addition, a polyclonal antibody response is observed in HSV-infected spleen cultures. These findings indicate that the cells stimulated to undergo DNA synthesis after HSV infection appear to be the bone marrow-derived lymphocytes. The newly synthesized DNA is host cell and not of viral origin. Heat treatment and ultraviolet irradiation of HSV before addition to spleen cultures prevents the induction of DNA synthesis. We consider the use of this system as assay for the study of cell transformation by HSV and also for the study of host cell control of the expression of the viral genome.

Induction of murine p30 by superinfecting herpesviruses

The interaction of endogenous type C viruses with superinfecting herpes simplex virus type 2 (HSV-2) was investigated in two murine cell lines. Replication of HSV-2 was suboptimal in random-bred Swiss/3T3A cells and, in initial experiments, infection with a low virus-to-cell ratio resulted in carrier cultures with enhanced murine leukemia virus (MuLV) p30 expression. Immunofluorescence tests with Swiss/3T3A cells productively infected with HSV-2 also showed HSV-associated cytoplasmic antigens and enhanced MuLV p30 expression when compared with uninfected controls. Inactivation of HSV-2 with UV light did not abolish this reaction, although the number of cells expressing p30 was reduced. HSV-2 replicated more efficiently in a line of NIH Swiss cells (N c1 A c1 10). These cells are not readily inducible for type C expression by conventional methods; however, untreated and UV-inactivated HSV-2 induced both HSV-2-associated antigens and MuLV p30 in these cells. Although the Birch strain of human cytomegalovirus induced MuLV p30, neither mouse cytomegalovirus nor vesicular stomatitis virus induced MuLV p30 in either cell line.

Effect of passage in culture on a clone of BALB/c 3T3 cells transformed by simian virus 40

Most simian virus 40 (SV40)-transformed BALB/c 3T3 clones employed for biochemical studies have been used without regard to passage level. To determine whether virus-induced properties are stable as a function of passage, we have extensively characterized one transformed clone, FNE, which was isolated after SV40 infection BALB/c 3T3 cells in factor-free medium. From the initial testing at passage 5 and for at least 50 subsequent subcultures, the cells stably maintained many transformed growth properties, including high saturation density, morphology, colony formation on contact-inhibited monolayers, tumorigenicity, and synthesis of viral-specific RNA. However, other properties varied as a function of passage. There was a slight decrease in viral genome equivalents per cell from 1.1 copy/cell at passage 5 to 0.7 copies at passage 40. Initially, the cells were negative for all type C virus; however, cells carried at low density for 13 to 20 passages (65 to 100 generations) began to release an endogenous type C virus that then persisted in the culture. Spontaneous release of type C virus did not occur in control BALB/c 3T3 cells carried under identical culture conditions for 90 passages. When the cultures were releasing type C viruses they stained uniformly and brightly positive for SV40 tumor (T) antigen by immunofluorescence, whereas T antigen staining was variable at early passage. These experiments suggest that subtle but perhaps important differences in viral gene expression can occur as a function of passage; they also demonstrate the importance of evaluating the interactions between SV40 and endogenous type C viruses.

Clonal derivatives of a herpes type 2 transformed hamster cell line (333-8-9): cytogenetic analysis, tumorigenicity and virus sequence detection

The characteristics of the Syrian hamster cell line (333-8-9), putatively transformed by herpes virus type 2 (HSV-2), strain 333, have been examined. The line has been cloned and the clones characterized cytogenetically and morphologically. The original line and the clones have been assayed for tumorigenicity and for the presence of herpes-virus-specific nucleic acid sequences using in situ hybridization with 125I HSV-2 DNA. The line 333-8-9 is hyperdiploid with a mode of 49 chromosomes and contains a spectrum of cytogenetic marker chromosomes present in varying frequencies. The clones demonstrate a segregation of these marker chromosomes and other abnormal chromosomes. Cloned lines have distinct stem-cell types with the characteristic abnormal chromosomes present in a high percentage of cells. Some of the marker chromosomes have been identified by Giemsa banding techniques. All the clones have distinctive, persistent in vitro morphologies, ranging from purely epithelial to purely fibroblastic. They differ from the line 333-8-9 and between themselves in tumorigenicity, varying from highly tumorigenic to entirely non-tumorigenic. Herpes virus 2 specific sequences have been detected in the original cell line and in all but two of the clones. There does not appear to be any obvious correlation between the three parameters of: (1) detection of HSV-2 information; (2) marker chromosome occurrence; and (3) tumorigenicity.

Host range temperature-sensitive mutants of herpes simplex virus type 2

Two small-plaque mutants of herpes simplex virus type 2 (HSV-2) (strain 333), whose growth at 39 C was blocked in certain cell types (cell-dependent temperature sensitivity), were compared compared with parental virus in a number of biological assays. One mutant (no. 69) was found to produce a large number of morphologically normal, but noninfectious, particles; under nonpermissive conditions, these mutant particles were able to interfere with the replication of wild-type HSV-2. The other mutant (no. 74), which is known to belong to a different complementation group, appeared to direct little virus DNA synthesis, even at the permissive temperature. Progeny production and virus DNA synthesis in cells infected by mutant 74 were delayed in comparison with wild-type virus-infected cells. Both mutants were found to be more sensitive to UV irradiation than the parental virus; this was especially marked in the case of mutant 74. Moreover, this mutant was found to have a high transforming efficiency at much lower doses of irradiation than those needed to abolish the cytopathic effect of wildtype HSV-2.

Activation of an endogenous mouse type C virus by ultraviolet-irradiated herpes simplex virus types 1 and 2

Infection of BALB/c mouse cells with UV-irradiated herpes simplex virus (HSV) types 1 and 2 resulted in activation of a xenotropic type C virus detected by infectious center formation in permissive rat cells. The levels of type C virus activated by HSV were related to the UV dose and the multiplicity of infection used. The ability of HSV to activate type C virus was eliminated by heat-inactivation and by neutralization with specific antiserum against HSV, but was not affected by purification or treatment with DNase and RNase. Maximum levels of type C virus in the cells and medium were observed within 1 day after HSV infection, and the levels returned to control cell values within 3-4 days. The possible significance of these findings with respect to the putative oncogenic potential of HSV is discussed.