Herpes simplex virus-directed overreplication of chromosomal DNA physically linked to the simian virus 40 integration site of a transformed hamster cell line

Temperature-sensitive origin-binding protein as a tool for investigations of herpes simplex virus activities in vivo

While it is fairly clear that herpes simplex virus (HSV) DNA replication requires at least seven virus-encoded proteins in concert with various host cell factors, the mode of this process in infected cells is still poorly understood. Using HSV-1 mutants bearing temperature-sensitive (ts) lesions in the UL9 gene, we previously found that the origin-binding protein (OBP), a product of the UL9 gene, is only needed in the first 6 hours post-infection. As this finding was just a simple support for the hypothesis of a biphasic replication mode, we became convinced through these earlier studies that the mutants tsR and tsS might represent suitable tools for more accurate investigations in vivo. However, prior to engaging in highly sophisticated research projects, knowledge of the biochemical features of the mutated versions of OBP appeared to be essential. The results of our present study demonstrate that (i) tsR is most appropriate for cell biological studies, where only immediate early and early HSV gene products are being expressed without the concomital viral DNA replication, and (ii) tsS is a prime candidate for the analysis of HSV DNA replication processes because of its reversibly thermosensitive OBP-ATPase, which allows one to switch on the initiation of DNA synthesis precisely.

The Role of the Human Bocavirus (HBoV) in Respiratory Infections

The human bocavirus is one of the most common respiratory viruses and occurs in all age groups. Because Koch’s postulates have been fulfilled unintendedly, it is currently accepted that the virus is a real pathogen associated with upper and lower respiratory tract infections causing clinical symptoms ranging from a mild common cold to life-threatening respiratory diseases. In order to exclude a viremia, serological analysis should be included during laboratory diagnostics, as acute and chronic infections cannot be differentiated by detection of viral nucleic acids in respiratory specimen alone due to prolonged viral shedding. Besides its ability to persist, the virus appears to trigger chronic lung disease and increases clinical symptoms by causing fibrotic lung diseases. Due to the lack of an animal model, clinical trials remain the major method for studying the long-term effects of HBoV infections.

Respiratory infections of the human bocavirus

The human bocavirus is one of the most common respiratory viruses and occurs in all age groups. It is associated with upper and lower respiratory tract infections, and causes clinical symptoms from the mild common cold to life threatening respiratory diseases. Besides its ability to persist the virus appears to trigger chronic lung disease and increase the clinical symptoms, while being a putative trigger for fibrotic lung diseases.

Laboratory diagnostics should include serological diagnostics in order to rule out a viremia because due to prolonged viral shedding acute and chronic infections cannot be differentiated on the detection of viral nucleic acids in respiratory specimen alone.

Although Koch’s postulates cannot be formally fulfilled due to the lack of an animal model and the chance for clinical trials with volunteers are limited due to the long term effects of HBoV infections, there is no doubt that the virus is a serious pathogen and requires attention.

The aim of the chapter is to present an overview of our current knowledge on respiratory infections with the human bocavirus, and to provide basic and essential information on clinical features, molecular diagnostics, and epidemiologic challenges arising with this pathogen.

Does human bocavirus infection depend on helper viruses? A challenging case report

A case of severe diarrhoea associated with synergistic human bocavirus type 1 (HBoV) and human herpes virus type 6 (HHV6) is reported. The case supports the hypotheses that HBoV infection under clinical conditions may depend on helper viruses, or that HBoV replicates by a mechanism that is atypical for parvoviruses, or that HBoV infection can be specifically treated with cidofovir.

Durability of transgene expression and vector integration: recombinant SV40-derived gene therapy vectors

Many applications of gene delivery require long-term transgene expression. In dividing cells, this result necessitates vector genome persistence, usually by integrating into cellular DNA. Since recombinant gene delivery vectors derived from tag-deleted, replication-incompetent simian virus-40 (SV40) provide for long-term transgene expression in resting and dividing cells, we tested whether such enduring transgene expression reflected integration into cellular genomes. Several lines of evidence suggested this likelihood. After transduction in vitro, continuously dividing cell lines and continuously stimulated primary cells uniformly showed transgene expression for many months. Mice whose livers were transduced in vivo, partially resected, and allowed to regenerate showed comparable levels of transgene expression in regenerated and preoperative livers. Thus, replicationincompetent SV40 vectors (rSV40) persist in vitro and in vivo despite extensive cell division. We tested the possibility that this persistence reflected integration directly. Southern blot analyses of genomic DNA from transduced 293 cells showed that vector genome incorporation into cell DNA happened within days of transduction. Episomal vector DNA was barely detectable 96 hours post-transduction. Inverted PCR, used to characterize vector integration points, showed vector DNA integrated randomly into the cell genome. The circular rSV40 genome opened at different points in each integrand. A significant proportion of the integrands did not contain the entire vector sequence, but rather only portions thereof. Quantitative Southern blot analysis showed approximately 3.05 transgene copies per cell. Therefore, recombinant SV40 gene delivery vectors integrate into the cellular DNA of both resting and dividing cells, and do so randomly and within days of transduction. This integration may explain long-term transgene expression.

Selective Rep-Cap gene amplification as a mechanism for high-titer recombinant AAV production from stable cell lines

Gene transfer vectors based on adeno-associated virus mediate high-level, stable gene expression in a variety of postmitotic tissues; thus, there is interest in developing improved production systems. We previously described the generation of rAAV producer cell lines that, upon infection with adenovirus, yielded biologically active rAAV particles. In these studies we show that the adenovirus multiplicity of infection (m.o.i.) is a critical variable for efficient production of cell line-derived rAAV and can affect yields by over 200-fold. Moreover, a threshold level of adenovirus was found necessary for high-titer vector production. To define the possible factors responsible for adenovirus m.o.i. -dependent rAAV yields, we analyzed rep and cap expression as a function of adenovirus m.o.i. High-level AAV capsid protein synthesis was observed in rAAV producer cells at adenovirus m.o.i. > or =10. This prompted us to analyze the rep-cap copy number following adenovirus infection. We documented robust episomal DNA amplification (100-fold) of integrated rep-cap sequences. Interestingly, no amplification of rep-cap sequences was observed when the sequences (in plasmid form) were transfected into adenovirus-infected HeLa cells. These data suggest that adenovirus-dependent rep-cap gene amplification is a critical process responsible for efficient rAAV synthesis in stable cell lines.

Cervical cancer: is herpes simplex virus type II a cofactor?

In many ways, cervical cancer behaves as a sexually transmitted disease. The major risk factors are multiple sexual partners and early onset of sexual activity. Although high-risk types of human papillomaviruses (HPV) play an important role in the development of nearly all cases of cervical cancer, other sexually transmitted infectious agents may be cofactors. Herpes simplex virus type 2 (HSV-2) is transmitted primarily by sexual contact and therefore has been implicated as a risk factor. Several independent studies suggest that HSV-2 infections correlate with a higher than normal incidence of cervical cancer. In contrast, other epidemiological studies have concluded that infection with HSV-2 is not a major risk factor. Two separate transforming domains have been identified within the HSV-2 genome, but continued viral gene expression apparently is not necessary for neoplastic transformation. HSV infections lead to unscheduled cellular DNA synthesis, chromosomal amplifications, and mutations. These observations suggest that HSV-2 is not a typical DNA tumor virus. It is hypothesized that persistent or abortive infections induce permanent genetic alterations that interfere with differentiation of cervical epithelium and subsequently induce abnormal proliferation. Thus, HSV-2 may be a cofactor in some but not all cases of cervical cancer.

Herpes simplex virus induces unscheduled DNA synthesis in virus-infected cervical cancer cell lines

We evaluated herpes-simplex-virus-type-2(HSV2)-induced unscheduled DNA synthesis in virus-infected cervical cancer (HeLa, CaSki, C-33A, and SiHa) cells. HSV2 replication was approximately 100-fold more efficient in the HeLa cells than in less susceptible C-33A and SiHa cells. In dual parameter flow cytometric analysis of bromodeoxyuridine (BrdU) incorporation, HSV2-infected HeLa cells showed a rapid increase in the proportions of DNA-synthesizing G1- and S-phase cells, whereas in C-33A and SiHa cells, the proportions of DNA-synthesizing G1- and early S-phase cells were increased late in the infection. Blocking of HSV2 replication by phosphonoformate inhibited virus-induced changes in HeLa cells, but not in C-33A and SiHa cells. Anti-BrdU antibodies exhibited a coarse globular nuclear staining pattern in the C-33A cells, while the other cells showed speckled and/or fine globular nuclear fluorescence. Anti-ICP8 (HSV-specified major DNA-binding protein) antibodies revealed that, in C-33A cells, ICP8 remained in the cytoplasm, whereas in the other cells, speckled or globular nuclear fluorescence was found. Our results showed that HSV2 induced the unscheduled synthesis of cellular DNA, which was host-cell-dependent, and in virus infected C-33A cells, it may be attributable to both viral and cellular proteins.

Herpes simplex virus-induced "rolling circle" amplification of SV40 DNA sequences in a transformed hamster cell line correlates with tandem integration of the SV40 genome

Infection with herpes simplex virus leads to amplification of SV40 DNA in various SV40-transformed cells. In earlier studies with the SV40-transformed hamster cell line Elona two different types of DNA amplification could be identified: (i) Bidirectional overreplication of chromosomally integrated SV40 DNA expanding into the flanking cellular sequences ("onion skin" type) and (ii) highly efficient synthesis of extremely large head-to-tail concatemers containing exclusively SV40 DNA ("rolling circle" type). These investigations have indicated that the chromosomally integrated form of SV40 might be the substrate for both types of overreplication. There still had been uncertainties as to whether and how these events were connected. A hypothetical assumption of a recombinational event leading to the excision of SV40 DNA molecules is supported by the results presented here: In this study cloned Elona cell lines were investigated for their ability to amplify SV40 sequences and for the mechanism of amplification utilized. SV40 integration in a partial tandem manner correlates with a strong rolling circle amplification. In contrast, in one cell line harboring a truncated SV40 genome, amplification appears mainly restricted to intrachromosomal bidirectional overreplication. Possible implications for HSV functions involved in the amplification process will be discussed.