Altered expression of adenovirus 12 DNA-binding protein but not DNA polymerase during abortive infection of hamster cells

Transcriptional blocks limit adenoviral replication in primary ovarian tumor

PURPOSE

Despite the success of conditionally replicating adenoviruses in tumor models, clinical success has been limited when they are used as a single modality agent. Overcoming the disparity in efficacy between in vivo animal models and human use is a key hurdle for better conditionally replicating adenovirus therapy in humans. We endeavored to identify biological blocks to adenoviral infection and replication in tumor cells.

EXPERIMENTAL DESIGN

We hypothesized that the differences in adenoviral replication between ovarian cancer cell lines and patient tumor samples are the result of a block in viral RNA transcription. To test this hypothesis, established ovarian cancer cell lines and purified patient ovarian cancer cells were infected with wild-type adenovirus. RNA for early adenoviral genes E1A and E1B as well as the late transcripts for fiber and hexon were measured using real-time PCR.

RESULTS

Established ovarian cancer cell lines treated with wild-type virus had a lower E1A:E1B ratio than the patient samples. Additionally, the levels of fiber and hexon relative to E1A were also decreased in the patient samples compared with the established cell lines. These findings were consistent with an early- to late-phase block in the adenovirus replication cycle.

CONCLUSIONS

These data suggest that the biology of abortive infection in the patient samples may be linked to a defect in the production of early and late viral transcripts. Identification of factors leading to abortive infection will be crucial to understanding the low viral replication in patient samples.

Biology of ovine adenovirus infection of nonpermissive cells

Nonhuman adenoviruses, including those of the genus Atadenovirus, have the potential to serve as vectors for vaccine and gene therapy applications in humans, since they are resistant to preexisting immunity induced by human adenoviruses in the majority of the population. In this study, we elucidate the outcome of infection by ovine adenovirus type 7 isolate 287 (OAdV) of several nonovine cell types. We show here that OAdV infects a wide range of nonovine cells but is unable to complete its replication cycle in any of them. In nonovine, nonfibroblast cells, viral replication is blocked at an early stage before the onset of, or early in, DNA replication. Some fibroblasts, on the other hand, allow viral DNA replication but block virus production at a later stage during or after the translation of late viral proteins. Late viral proteins are expressed in cells where viral DNA replication takes place, albeit at a reduced level. Significantly, late proteins are not properly processed, and their cellular distribution differs from that observed in infected ovine cells. Thus, our results clearly show that OAdV infection of all nonovine cells tested is abortive even if significant viral DNA replication occurs. These findings have significant positive implications with respect to the safety of the vector system and its future use in humans.

Insufficient levels of NFIII and its low affinity for the origin of adenovirus type 12 (Ad12) DNA replication contribute to the abortive infection of BHK21 hamster cells by Ad12

Human adenovirus type 12 (Ad12) induces undifferentiated sarcomas in neonate Syrian hamsters and hence presents a suitable model for studies of the molecular mechanism of viral oncogenesis. Since we submit that an understanding of the early steps in the interaction between Ad12 and hamster cells might shed light on the initiation of malignant transformation, the abortive infection of BHK21 hamster cells with Ad12 has been investigated in detail. Ad12 replication in these cells is blocked in early stages, while Ad2 can replicate to moderate titers. Early Ad12 genes are expressed in BHK21 hamster cells, but there is a total block in Ad12 DNA replication and late gene transcription. The Ad5-transformed hamster cell line BHK297-C131, with the left terminus of Ad5 DNA chromosomally integrated and constitutively expressed, allows limited levels of Ad12 DNA replication and late transcription, probably through Ad5 E1 functions, but not the translation of late Ad12 gene products. We have now investigated the capacities of binding of nuclear proteins NFI and NFIII from permissive human KB cells, nonpermissive hamster BHK21 cells, and complementing BHK297-C131 cells to the origin of replication (ori) of Ad2 or Ad12 DNA. The electrophoretic mobility shift assay has been used to assess these binding reactions. The data support the notions that NFIII of BHK21 cells has a lower affinity for the ori of Ad12 DNA than for the ori of Ad2 DNA and that the levels of NFIII in BHK21 cells are markedly reduced compared with the levels in the permissive human KB cells or the complementing BHK297-C131 hamster cells. These deficiencies are contributing factors for the abortive infection of BHK21 hamster cells with Ad12. The lack of sufficient levels of NFIII in BHK21 cells is also consistent with the decreased replication capacity of Ad2 in hamster compared with human cell lines.

Tyrosine kinase-dependent release of an adenovirus preterminal protein complex from the nuclear matrix

Adenovirus (Ad) replicative complexes form at discrete sites on the nuclear matrix (NM) through the interaction of Ad preterminal protein (pTP). The NM is a highly salt-resistant fibrillar network which is known to anchor transcription, mRNA splicing, and DNA replication complexes. Incubation of rATP with NM to which pTP was bound caused the release of pTP as a pTP-NM complex with a size of 220 to 230 kDa; incubation with 5' adenylylimidodiphosphate (rAMP-PNP) showed no significant release, indicating that rATP hydrolysis was required. With NM extracts, it was shown that a pTP-NM complex which was capable of binding Ad origin DNA could be reconstituted in vitro. A number of high-molecular-weight NM proteins ranging in size from 120 to 200 kDa were identified on Far Western blots for their ability to bind pTP. rATP-dependent release of pTP from the NM was inhibited in a dose-dependent fashion by the addition of tyrosine kinase inhibitors, such as quercetin, methyl-2,5-dihydroxycinnamate, or genistein. NM-mediated phosphorylation of a poly(Glu, Tyr) substrate was also significantly abrogated by the addition of these compounds. rATP-dependent release of Ad DNA termini bound to the NM via pTP was also blocked by the addition of these inhibitors. These results indicate that a tyrosine kinase mechanism controls the release of pTP from its binding sites on the NM. These data support the concept that phosphorylation may play a key role in the modulation of pTP binding sites on the NM.