Oncolytic E1B 55KDa-deleted adenovirus replication is independent of p53 levels in cancer cells.

Oncolytic adenoviruses represent a new approach for cancer therapy due to its tumor specificity. E1B 55kDa-deleted adenovirus type 5 (Ad5dlE1B 55kDa) is a promising therapeutic agent that can selectively replicate in and lyse p53 defective cancer cells. However, the overall efficacy has shown varying degrees of success with raised doubts about the correlation between p53 status and E1B-deleted adenovirus replication ability. In this study, we investigated the relationship between the efficiency of Ad5dlE1B 55kDa replication and p53 levels in cancer cells. Five transient p53 expression vectors were engineered to expresses different p53 levels in transfected cells. Then, the effect of the variable p53 levels and cellular backgrounds on the replication efficiency of oncolytic Ad5dlE1B 55kDa was evaluated in H1299 and HeLa cell lines. We found that the replication efficiency of these oncolytic viruses is dependent on the status, but not the expression levels, of p53. Ad5dlE1B 55kDa was shown to have selective replication activity in H1299 cells (p53-null) and decreased viral replication in HeLa cells (p53-positive), relative to the wild-type adenovirus in both cell lines. Our findings suggest that there is a relation between the E1B-deleted adenovirus replication and the presence as well as the activity of p53, independent of its quantity.

Role of Endonuclease G in Exogenous DNA Stability in HeLa Cells.

Endonuclease G (EndoG) is a well-conserved mitochondrial-nuclear nuclease with dual lethal and vital roles in the cell. The aim of our study was to examine whether EndoG exerts its nuclease activity on exogenous DNA substrates such as plasmid DNA (pDNA), considering their importance in gene therapy applications. The effects of EndoG knockdown on pDNA stability and levels of encoded reporter gene expression were evaluated in the cervical carcinoma HeLa cells. Transfection of pDNA vectors encoding short-hairpin RNAs (shRNAs) reduced levels of EndoG mRNA in HeLa cells. In physiological circumstances, EndoG knockdown did not have an effect on the stability of pDNA or the levels of encoded transgene expression as measured over a four-day time course. However, when endogenous expression of EndoG was induced by an extrinsic stimulus, targeting of EndoG by shRNA improved the perceived stability and transgene expression of pDNA vectors. Therefore, EndoG is not a mediator of exogenous DNA clearance, but in non-physiological circumstances, it may nonspecifically cleave intracellular DNA regardless of its origin. These findings make it unlikely that targeting of EndoG is a viable strategy for improving the duration and level of transgene expression from nonviral DNA vectors in gene therapy efforts.

[Effect of endonuclease G depletion on plasmid DNA uptake and levels of homologous recombination in hela cells].

Endonuclease G (EndoG) is a mitochondrial apoptosis regulator that also has roles outside of programmed cell death. It has been implicated as a defence DNase involved in the degradation of exogenous DNA after transfection of mammalian cells and in homologous recombination of viral and endogenous DNA. In this study, we looked at the effect of EndoG depletion on plasmid DNA uptake and the levels of homologous recombination in HeLa cells. We show that the proposed defence role of EndoG against uptake of non-viral DNA vectors does not extend to the cervical carcinoma HeLa cells, as targeting of EndoG expression by RNA interference failed to increase intracellular plasmid DNA levels. However, reducing EndoG levels in HeLa cells resulted in a statistically significant reduction of homologous recombination between two plasmid DNA substrates. These findings suggest that non-viral DNA vectors are also substrates for EndoG in its role in homologous recombination.

Endonuclease G depletion may improve efficiency of first generation adenovirus vector DNA replication in HeLa cells.

First generation adenovirus (Ad5 ΔE1,E3) vectors are able to replicate their DNA in many tumour cells and can be used for oncotherapy. Highest rates of viral DNA replication occur in the G2/M transition of the cell cycle. In this study, we tried to increase the efficiency of Ad5 ΔE1,E3 DNA replication in the cervical carcinoma HeLa cells by using RNA interference (RNAi) to target endonuclease G (EndoG) whose depletion leads to an accumulation of cells in the G2/M transition. Targeting of EndoG by an shRNA encoded on an Ad5 ΔE1,E3 vector resulted in an early proliferation defect of cervical carcinoma HeLa cells. This effect coincided with enhanced DNA replication and encoded transgene expression of an Ad5 ΔE1,E3 vector. Applied in high concentrations, the EndoG-targeting Ad5 ΔE1,E3 vector showed enhanced HeLa cell killing ability relative to control Ad5 ΔE1,E3 vectors. These effects are most likely the result of EndoG depletion, which causes cells to accumulate in the G2/M transition of the cell cycle and extends favourable cellular conditions for Ad5 ΔE1,E3 DNA replication. Targeting of EndoG by RNAi may be a viable strategy for improving both the levels of transgene expression and the oncolytic properties of first generation adenovirus vectors.

Sequencing analysis of the region encoding the DNA polymerase of bovine adenovirus serotypes 2 and 3.

Bovine adenoviruses (BAVs) are important pathogens causing significant economic losses to the cattle industry. We have been interested in the differences among serotypes of these viruses, particularly in their pathogenicity and host range. As part of our efforts to better understand these viruses, we have determined the nucleotide sequences for serotype 3 (BAV3) at map coordinates beween 11.7 and 23.7% and for serotype 2 (BAV2) between 13.1 and 24.0%. Analyses of these sequences revealed large open reading frames (ORFs) encoded within the leftward-reading strand of the viral DNA. The coding capacity of the ORF in BAV3 is 1,167 amino acid residues and 1,138 in BAV2. A search in the GenEMBL protein sequence databank for homology to the predicted polypeptide products of these ORFs established their identity as that for the adenovirus (Ad) DNA polymerase (DNA pol). The deduced polypeptide sequences were aligned with each other and with other known Ad DNA pols to reveal regions of homology and similarity. The comparison at the amino acid sequence level not only showed that the bovine Ad DNA pols from the two serotypes are quite distinct from each other, but also revealed that Ad DNA pols contain multiple domains that are highly conserved among human, canine and bovine Ads. These conserved domains are likely important for the multiple functions attributed to Ad DNA pol, which include catalysis of its own initiation complex, elongation of nascent DNA strand, as well as correction of DNA replication errors.

Cloning and sequencing of the bovine adenovirus type 2 early region 4.

Bovine adenovirus type 2 (BAV2) is a medium size double-stranded DNA virus which infects both bovine and ovine species, resulting in mild respiratory and gastrointestinal disorders. To better understand the virus and its growth characteristics in Madin-Darby bovine kidney (MDBK) cells, we have cloned and sequenced the extreme right-end segment of the BAV2 genome (90.5-100 map units). Analysis of the nucleotide sequence revealed 40 potential open reading frames (ORFs) with coding capacity for polypeptides that are 25 or more amino acid (aa) residues long. Six of these ORFs encode polypeptides that show homology to well-characterized early region 4 (E4) proteins of human adenovirus type 2 (Ad2) and Ad12. ORF1 has the potential to encode a 114 aa long polypeptide that is 54% homologous to the E4 14kDa protein of Ad2. ORF2 encodes a 78 aa long polypeptide that exhibits 40% homology to the E4 13 kDa protein of Ad2. ORFs 3-6 encode polypeptides that have homology to the E4 34 kDa protein encoded by ORF6 of Ad2 and Ad12. ORFs 3, 4 and 5 encode 128, 96 and 31 aa long polypeptides, respectively. The 128-aa polypeptide exhibits 59% homology, while the 96 and 31 aa long polypeptides exhibit 61% and 70% homology to the E4 34 kDa protein, respectively. ORF6 has the potential to encode a 57 aa long polypeptide that has 67% homology to the E4 34 kDa protein of Ad2 and 50% homology to the E4 34 kDa protein of Ad12.

Sequence analysis of the terminal protein precursor coding regions from bovine adenovirus serotypes 2 and 3.

As part of our efforts to develop bovine adenoviruses into a vector system, we sequenced the region predicted to encode the terminal protein precursor of either bovine adenoviruses type 2 and bovine adenoviruses type 3. We examined the regions containing the terminal protein precursors and showed that the bovine adenovirus early region 2B had an identical organization to all adenoviruses so far examined. The bovine adenovirus terminal protein precursors and those of other adenoviruses were also compared in a sequence alignment analysis and several highly conserved structural domains were identified. Finally, we showed how the various terminal protein precursors were related in a sequence pair similarity analysis and concluded that the terminal protein precursors of bovine adenoviruses types 2 and 3 are significantly different from each other at the protein sequence level.

Sequence analysis of the putative E3 region of bovine adenovirus type 2.

Adenoviruses are nonenveloped icosahedral-shaped particles. The double-stranded viral DNA genome contains four major early transcription units, designated E1 (a and b), E2 (a and b), E3 and E4, which are expressed in a regulated manner soon after infection. The gene products of the region E3, shown to be nonessential for viral replication in vitro, are believed to be involved in counteracting host immunosurveillance. Human adenovirus type 5 DNA sequences of transcription units L4 and L5 adjacent to E3 were used to localize E3 within the bovine adenovirus type 2. The DNA sequences between 74.8 and 84.4 mu containing E3 and the fiber gene were determined. The E3 region was found to consist of about 2.3 kb pairs and to encode four proteins longer than 60 amino acids. However, these four open reading frames did not show significant homology to any other known adenovirus DNA or protein sequence.

Sequence analysis of bovine adenovirus type 2 early region 1 and pIX gene.

Bovine adenoviruses (BAVs) cause both respiratory and/or enteral diseases in cattle and are widespread throughout the world. We have sequenced the extreme left end (0 to 12.2 mu) of the BAV2 genome. Partial analysis of the nucleotide sequence revealed 12 potential open reading frames (ORFs) which could encode for polypeptides of 50 or more amino acids. These ORFs were compared to those of the early region 1 (E1) proteins and hexon-associated protein IX (pIX) from other adenoviruses (Ads). The 4 major ORFs show homology to known Ad polypeptides. The 4 BAV2 ORFs are located in approximately the same area as that of the human Ad type 5 (HAd5) E1A, E1B and pIX ORFs. ORF1 has the potential to encode a 119-amino-acid-long polypeptide that is 85.7% homologous (over 42 amino acids) to the E1A conserved region III of both HAd2 and HAd5. ORF2 and ORF3 have the potential to code for 160- and 408-amino-acid-long polypeptides, respectively. The 160-amino-acid-long polypeptide exhibits 71.3% homology to the small T antigen of HAd40, and the 408-amino-acid polypeptide exhibits 67.0% homology with the large T antigen of HAd2. Both the small T antigen of HAd40 and the large T antigen of HAd2 are translated from the E1B mRNAs. ORF4 has the potential to code for a 117-amino-acid-long polypeptide that has 77.9% homology with the Tupaia adenovirus pIX.

Sequence and sequence analysis of E1 and pIX regions of the BAV3 genome.

Bovine adenovirus type 3 (BAV3) is a DNA virus that causes respiratory and gastrointestinal disorders in cattle. We have sequenced the extreme left end of BAV3 genome (0-11.7 map units). Partial analysis of the nucleotide sequence revealed 19 potential open reading frames (ORFs) that could encode for polypeptides of 50 or more amino acids. Four of these ORFs show homology to known adenovirus polypeptides. The four BAV3 ORFs are located in approximately the same area as the Ad5 E1a, E1b, and pIX ORFs. ORF 1 has the potential to code for a 208 amino acid long polypeptide that is 75.5% homologous to the E1a conserved region III of Ad5. ORFs 2 and 3 encode 157 and 420 amino acid long polypeptide, respectively. The 157 amino acid polypeptides exhibits 69.3% homology to the Ad5 small T antigen, and the 420 amino acid polypeptide exhibits 73% homology to the large T antigen of Ad5. ORF4 has the potential to code for a 125 amino acid long polypeptide that has 73% homology to the hexon-associated pIX of Ad7.

Subcloning and restriction enzyme mapping of bovine adenovirus type 2.

Bovine adenoviruses (BAVs), causing both respiratory and/or enteral diseases in cattle, have been isolated in many countries all over the world. In this study we report on the molecular cloning of the internal EcoRI fragments spanning 20.6-90.5%, and the internal SalI fragments spanning 3.1-65.2% of the BAV type 2 (BAV2; strain No. 19) genome into the plasmid vector pUC19. Moreover, the subcloning of the BAV2 genome facilitated the construction of a detailed physical restriction endonuclease map for BamHI, ClaI, EcoRI, HindIII, KpnI, NotI, NspV, PstI, PvuI, SalI, XbaI and XhoI.

Thiamine secretion in yeast.

To isolate thiamine excretors and (or) overproducers, 188 cultures belonging to nine yeast and three fungal genera were screened. Nine excreted thiamine as determined by both the presence of cross-feeding zones on a thiamine-free agar medium seeded with a thiamine-requiring yeast strain and by the direct detection of excreted thiamine on agar plates. Several of these cultures produced several-fold more intracellular thiamine than the general culture population. Thiamine-requiring strains of Saccharomyces cerevisiae and S. uvarum (carlsbergensis) were identified and were tentatively assigned to 10 complementation groups.

Molecular cloning and restriction enzyme analysis of bovine adenovirus type 3.

Bovine adenovirus type 3 (BAV3) is a DNA virus that causes respiratory and gastrointestinal disorders in cattle. The viral genome consists of a linear double-stranded DNA molecule (35,000 base pairs) with inverted terminal repeats at each of its 5' molecular ends. We have subcloned 10 HindIII fragments spanning 4.9-96.0%, 5 EcoRI fragments spanning 3.4-89.5% and 2 XbaI fragments spanning 35.7-82.9% of the BAV3 (strain WBR-1) genome into the bacterial cloning vector pUC19. The subcloning of the viral genome facilitated the construction of linear restriction enzyme maps for BamHI, ClaI, EcoRI, HindIII, KpnI, NotI, NspV, PstI, PvuI, SalI, XbaI and XhoI. In this study we report on the molecular cloning and restriction endonuclease mapping of the BAV3 genome.

Construction of a recombinant adenovirus containing the denV gene from bacteriophage T4 which can partially restore the DNA repair deficiency in xeroderma pigmentosum fibroblasts.

The denV gene from bacteriophage T4 encodes a pyrimidine dimer-specific endonuclease that has the capacity to initiate excision repair of DNA. Cells from excision repair-deficient xeroderma pigmentosum (XP) patients are able to carry out excision repair initiated by the denV gene product and introduction of the denV gene into XP cells results in the partial restoration of colony-forming ability after irradiation with UV light. In this work we have constructed a helper-independent recombinant human adenovirus, Ad5denV, which contains the denV gene. A 1.9 kb cartridge consisting of the denV gene flanked by the long terminal repeat (LTR) promoter from Rous sarcoma virus (RSV) and the simian virus 40 (SV40) polyadenylation (poly A) splice signals, was inserted into the E3 region of an E3 deletion mutant (Ad5d1E3) of adenovirus type 5. Infection of human fibroblasts and other permissive human cells with Ad5denV resulted in lytic infection and expression of the denV gene was confirmed by primer extension of infected cell RNA. The ability of the denV gene to restore the DNA repair deficiency in XP fibroblasts was examined using host cell reactivation of viral structural antigen formation for UV-irradiated adenovirus. The control virus, Ad5VSV, was also a recombinant which contained the gene for vesicular stomatitis virus glycoprotein G inserted into the E3 region of Ad5d1E3. UV survival of Ad5denV was similar to that of Ad5VSV following infection of two normal fibroblast strains and a Cockayne syndrome fibroblast strain, CS7SE, from complementation group B. In contrast, UV survival of Ad5denV was significantly greater than that for Ad5VSV after infection of three unrelated XP fibroblast strains from complementation groups A, C and E. However, UV survival of Ad5denV in the XP fibroblasts did not reach levels obtained in normal fibroblasts, indicating that restoration of the XP defect was partial.

Expression of the HSV-2 ribonucleotide reductase subunits in adenovirus vectors or stably transformed cells: restoration of enzymatic activity by reassociation of enzyme subunits in the absence of other HSV proteins.

We have cloned the large subunit (RR1) of the HSV-2 ribonucleotide reductase into a helper-independent adenovirus 5 vector under control of the viral major late promoter. Infection of 293 cells with the AdRed-1 recombinant virus resulted in the expression of the HSV-2 RR1 protein. We have also produced cells which constitutively express the small (RR2) subunit of the HSV-2 enzyme by transfecting 293 cells with a plasmid encoding this protein and the neo resistance marker (pSV2neo-RR2). Infection of the A439-14 producer cells with AdRed-1 resulted in the expression of enzymatically active HSV-2 ribonucleotide reductase. HSV-2 reductase activity could also be detected upon mixing of extracts from cells expressing either subunit. Our results indicate that the HSV-2 holoenzyme can be reconstituted in vivo and in vitro and that no HSV-2 proteins, beyond the enzyme subunits, are required for the formation and activity of the viral reductase.

Protein IX, a minor component of the human adenovirus capsid, is essential for the packaging of full length genomes.

Human adenovirus type 5 (Ad5) contains a 36-kb double-stranded DNA molecule in an icosahedral capsid. Attempts to construct Ad5 insertion mutants containing DNA of more than about 105% of the genome size resulted in viral progeny in which deletions had occurred suggesting the existence of severe constraints on the size of packageable DNA molecules. To partially circumvent these constraints we used an adenovirus vector, Ad5dlE1,3, with deletions in early regions 1 (E1) and 3 for a total net reduction in genome size of 5349 bp and an expected capacity for inserts of greater than 7 kb. To use this vector efficiently we generated a circular form of dlE1,3 DNA which could be propagated as an infectious bacterial plasmid. When this plasmid was used as a recipient for inserts of various sizes it was found that its capacity was much less than expected and that dlE1,3 virion capsids could not even package DNA as large as the wt genome. Because the E1 deletion of dlE1,3 extends into the coding sequences for protein IX, a minor capsid component known to affect the heat stability of adenovirions, the possibility that absence of this polypeptide might also affect the DNA capacity of the virion was investigated. It was found that when the coding sequences for protein IX were restored the packaging capacity of the vector was also restored to that of wt virions. Thus protein IX is an essential constituent of virion capsids dispensable only for virions containing DNA of less than genomic size.

Characterization of an adenovirus type 5 mutant carrying embedded inverted terminal repeats.

During construction of an adenovirus type 5 (Ad5) deletion mutant, dlE1,3, lacking E1 and E3 sequences, we isolated a variant, dlE1,3-1, which had a direct repeat of viral DNA terminal sequences attached to the left end of the genome. Analysis of this variant with restriction enzymes and by hybridization of Southern blots with specific probes indicated that the extra terminal segment contained the left 2.6% (920 bp) of Ad5 joined to 352 bp of pBR322 which in turn was linked to the left end (minus 21 bp) of dlE1,3. During replication of dlE1,3-1 the extra terminal segment was found to transfer to the right end of the genome resulting in a second variant, dlE1,3-2, with duplicated terminal sequences at both ends of the viral genome. DlE1,3-2 in turn was shown to revert back to dlE1,3-1 at high frequency. Although evidence was obtained indicating that the extra segment could be lost from the left end, spontaneous mutants which had lost direct repeats from both ends were never isolated. It was, however, possible to remove the extra terminal repeat of dlE1,3-1 by cleavage with a restriction enzyme and to isolate dlE1,3 containing wt termini. The rearrangements occurring during replication of dlE1,3-1 and dlE1,3-2 may be consequences of the mode of replication of Ad5 DNA and bear some resemblance to segment inversion in herpesviruses.

Human adenovirus cloning vectors based on infectious bacterial plasmids.

By making use of the fact that human adenovirus DNA circularizes in infected cells, and that circular forms of the viral genome are infectious, we have developed an improved adenovirus-based cloning system. A deletion mutant of adenovirus type 5 (Ad5) with deletions in early regions 1 (E1) and 3 (E3) was converted to a bacterial plasmid which can regenerate infectious virus following transfection into human 293 cells. A single XbaI recognition site in the deleted E3 region serves as a site for the insertion of foreign DNA. We have used this system to clone a number of genes into the Ad5 genome and describe the insertion of the neomycin/G418 resistance marker into Ad5 as an example.

Development of a helper-independent human adenovirus vector and its use in the transfer of the herpes simplex virus thymidine kinase gene.

Approximately 2 kilobases (kb) of additional DNA can be packaged into wild-type virions of human adenovirus type 5 (Ad5). To extend this limit, a helper independent Ad5 cloning vector was constructed by deleting most of early region 3 (E3) from map coordinates 78.5 to 84.7 and essentially all of early region 1 (E1) from coordinates 1.0 to 10.6. E3 is nonessential for adenovirus replication in cultured cells, and E1 is nonessential when the virus is propagated in 293 cells which constitutively express the E1 gene products. The resulting new virus, dlE1,3 is about 5.5 kb shorter than wild-type Ad5 and therefore should be able to accept up to 7.5 kb in foreign DNA. To test the usefulness of this vector, the herpes simplex virus type 1 (HSV-1) thymidine kinase gene (tk) along with its regulatory sequences was inserted into the unique XbaI site of dlE1,3 (at map position 78.5/84.7). The resulting recombinant virus, Adtk, expressed the HSV tk at a low level (as compared with HSV-1) in infected cells; however, tk expression was markedly enhanced when Adtk-infected cells were superinfected with a tk- mutant of HSV. Furthermore, the Adtk virus efficiently transformed tk- mouse cells (line LTA) to the tk+ phenotype. At a low efficiency, it was also possible to transform tk- human cells (line 143), and tk+ transformants of both mouse and human origin have been established as permanent lines.