Influence of chimeric human-bovine fibers on adenoviral uptake by liver cells and the antiviral immune response

Human adenoviruses (HAdV) are widely used for in vitro and in vivo gene transfer. Viral hepatotropism, inflammatory responses and neutralization by pre-existing antibodies (NAbs) are obstacles for clinical applications of HAdV vectors. Although the multifactorial events leading to innate HAdV toxicity are far from being elucidated, there is a consensus that the majority of intravenously injected-HAdV vectors is sequestered by Kuppfer cells, probably independently of coagulation factors. In this study, we show that the adenoviral-associated humoral and innate cytokine immune responses are significantly reduced when HAdV-5 vector carrying human bovine chimeric fibers (HAdV-5-F2/BAdV-4) is intravenously injected into mice. Fiber pseudotyping modified its interaction with blood coagulation factors, as FIX and FX no longer mediate the infection of liver cells by HAdV-5-F2/BAdV-4. As a consequence, at early time points post-infection, several cytokines and chemokines (IFN-gamma, IL-6, IP-10, MCP-1, RANTES and MP1beta) were found to be present at lower levels in the plasma of mice that had been intravenously injected with HAdV-5-F2/BAdV-4 compared with mice injected with the parental vector HAdV-5. Moreover, genetic modification of the fiber allowed HAdV-5-F2/BAdV-4 to partially escape neutralization by NAbs.

Characterization of new mutations in the coding sequence and 5'-untranslated region of the human prostacylcin synthase gene (CYP8A1)

Inheritable interindividual differences in prostacyclin production may be implicated in the pathogenesis of several human vascular diseases. Using a polymerase chain reaction/single-strand conformation polymorphism strategy, we screened for mutations in the gene encoding cytochrome P450 prostacyclin synthase (CYP8A1). DNA samples from healthy French volunteers (n = 130) of Caucasian origin were examined. Five mutations, comprising two previously reported silent mutations and three novel rare missense mutations (P38L, S118R, and R379S), were identified in the coding sequence of the gene. In the 5'-proximal region, we also found a variable number of tandem repeats (VNTR) polymorphism that consisted of four different alleles with 4-6 tandem repeats of a 9-bp unit containing a putative Spl transcriptional factor binding site. One of these (R6), a frequent allele (23.6% of alleles tested) harboring six repeats, is novel, whereas the other three are known. In vitro analysis of the effect of each VNTR allele on promoter activity of a reporter gene was performed by a transient transfection assay. Data confirmed the modulator effect of the VNTR polymorphism on reporter gene transcription. Furthermore, the data demonstrate that allele R6 has the most potent inducing effects in the A549 cell line and, after IL-6 stimulation, in human pulmonary artery endothelial cells. Overall, the data demonstrate that CYP8A1 is polymorphic in Caucasians, and that a polymorphism affecting the 5'-proximal region may result in interindividual differences in CYP8A1 transcriptional regulation in vivo. Additional factors, such as the presence of inflammatory mediators, may be required to modulate transcription of the CYP8A1 gene.

c-Myb protein binds to the EP element of the HBV enhancer and regulates transcription in synergy with NF-M

The hepatitis B virus (HBV) enhancer contains multiple active elements, one of which is the EP element, a 15 bp site important for its regulation by acting on other functional elements like the E site. The EP element, in the HBV enhancer context, contains two putative binding sites for c-myb family gene products. Electrophoretic mobility shift assays showed that the minimal c-Myb DNA-binding domain binds to the EP sequence. DNase I footprinting experiments revealed that only one consensus binding site was effectively protected. We found that c-Myb down-regulates transcription driving by the HBV enhancer in CAT assays performed in a haematopoietic (K562) and in a hepatic (HepG2) cell line. Interestingly, co-expression of both c-Myb and NF-M, a C/EBPbeta homologue which recognises the E element of the HBV enhancer, showed a synergistic transactivation of the HBV enhancer while, separately, each of them had an inhibitory effect on transcription in HepG2 and K562 cell lines, two cell types potentially infected by the hepatitis B virus.

The DNA-binding domain of human c-Abl tyrosine kinase promotes the interaction of a HMG chromosomal protein with DNA

The biological activity of the c-Abl protein is linked to its tyrosine kinase and DNA-binding activities. The protein, which plays a major role in the cell cycle response to DNA damage, interacts preferentially with sequences containing an AAC motif and exhibits a higher affinity for bent or bendable DNA, as is the case with high mobility group (HMG) proteins. We have compared the DNA-binding characteristics of the DNA-binding domain of human c-Abl and the HMG-D protein from Drosophila melanogaster. c-Abl binds tightly to circular DNA molecules and potentiates the interaction of DNA with HMG-D. In addition, we used a series of DNA molecules containing modified bases to determine how the exocyclic groups of DNA influence the binding of the two proteins. Interfering with the 2-amino group of purines affects the binding of the two proteins similarly. Adding a 2-amino group to adenines restricts the access of the proteins to the minor groove, whereas deleting this bulky substituent from guanines facilitates the protein-DNA interaction. In contrast, c-Abl and HMG-D respond very differently to deletion or addition of the 5-methyl group of pyrimidine bases in the major groove. Adding a methyl group to cytosines favours the binding of c-Abl to DNA but inhibits the binding of HMG-D. Conversely, deleting the methyl group from thymines promotes the interaction of the DNA with HMG-D but diminishes its interaction with c-Abl. The enhanced binding of c-Abl to DNA containing 5-methylcytosine residues may result from an increased propensity of the double helix to denature locally coupled with a protein-induced reduction in the base stacking interaction. The results show that c-Abl has unique DNA-binding properties, quite different from those of HMG-D, and suggest an additional role for the protein kinase.

The DNA binding domain of the human c-Abl tyrosine kinase preferentially binds to DNA sequences containing an AAC motif and to distorted DNA structures

The c-Abl tyrosine kinase protein is implicated in the signaling pathway as well as in transcription, DNA repair, apoptosis, and several other vital biological processes essential for cell proliferation or differentiation. The interaction of c-Abl with DNA is important for some of these functions, but the exact nature of this interaction is still a matter of controversy. The present study addresses the DNA-binding properties of the human c-Abl protein. Using CASTing experiments, the consensus binding site 5'-AA/CAACAAA/C was determined. The central highly conserved AAC triplet appears to constitute the crucial core element in the binding sequences of the c-Abl protein. The c-Abl DNA-binding domain recognizes specific sequences and interacts with deformed DNA structures such as four-way junctions and bubble DNA containing a large single-stranded loop, as determined by electromobility shift assay, melting temperature studies, and binding to specific oligonucleotides covalently linked to beads. Additional competition experiments suggest that the interaction mainly involves contacts within the minor groove of the double helix. The DNA-binding properties of c-Abl are reminiscent of those of high-mobility group (HMG)-like proteins such as LEF-1 and SRY. However, the circular permutation and ring closure assays and DNA unwinding experiments reveal that, unlike HMGs, c-Abl does not bend its target sequence. In addition, it is shown that the protein potentiates the DNA relaxation activity of topoisomerase I. These findings indicate that the interaction of c-Abl with DNA is both sequence-selective and structure-dependent.

Determination of the human c-Abl consensus DNA binding site

c-Abl tyrosine kinase, an essential protein of the cell cycle signalling pathways, is implicated in the regulation of RNA polymerase II activity, apoptosis and DNA repair. Its DNA binding activity is important for its biological functions. However, the molecular basis of c-Abl interaction with DNA remains largely unclear. We delimited the human c-Abl DNA binding domain and identified its preferred binding site, 5'-A(A/C)AACAA(A/C). The central AAC motif is highly conserved and constitutes the major core element in the binding sites. EMSAs and footprinting experiments were performed to explore how the c-Abl fusion protein recognizes specific sequences in DNA.

Activation of p65 NF-kappaB protein by p210BCR-ABL in a myeloid cell line (P210BCR-ABL activates p65 NF-kappaB)

The chimeric tyrosine kinase p210BCR-ABL is involved in the pathogenesis of chronic myelogenous leukemia. It transforms immature hematopoietic cells in vitro and abrogates IL-3-dependent growth. The mechanisms by which p210BCR-ABL mediates its oncogenicity are not well elucidated. Identifying transcription factors targeted by the chimeric protein may help to clarify these mechanisms. We have analysed the effect of p210BCR-ABL expression on NF-kappaB activity in DA1 cells (an IL-3-dependent murine myeloid progenitor cell line). A specific stimulation of NF-kappaB activity by kinase-active wild-type p210BCR-ABL has been evidenced by transcriptional activation assays. Electrophoretic mobility supershift assays revealed the presence of p65 protein (RelA) DNA binding activity in p210BCR-ABL transformed DA1 cells but not in parental DA1 cells. Activation of RelA in transformed DA1 cells may occur by protein stabilization. Experiments using oligonucleotides antisense to RelA showed that p210BCR-ABL transfected cells failed to survive after IL-3 removal. Moreover, inhibition of cellular growth was shown following treatment of p210BCR-ABL transformed DA1 cells by p65 antisense oligonucleotides. This study suggests that p65 NF-kappaB may be an effector for p210BCR-ABL and probably contributes to its induced transformation process.

Downregulation of major histocompatibility complex class I expression and susceptibility to natural killer cells in cells transformed with the oncogenic adenovirus 12 are regulated by different E1A domains

All adenoviruses transform rodent cells in vitro, but only cells transformed by serotypes belonging to subgroups A (Ad12) and B (Ad3) are tumorigenic for immunocompetent animals. In these cells, the expression of major histocompatibility complex (MHC) class I antigens is repressed and might allow them to escape from recognition by cytotoxic T lymphocytes and to develop in tumor. Furthermore, these cell lines appear resistant to lysis by natural killer (NK) cells. To determine the E1A domain(s) responsible for these properties several cell lines were created by transforming baby rat kidney cells with a set of plasmids expressing different Ad2/Ad12 hybrid E1A gene products. The class I gene expression was inhibited in cells expressing the Ad12 13S mRNA product and in cells transformed with Ad2/Ad12 hybrid E1A gene product harboring the C-terminal part of the conserved region (CR) 3 of Ad12. Susceptibility of these transformed cell lines to NK cells was determined by cytolytic assays. The results obtained suggest that two of Ad12 E1A domains are required to induce resistance of the cell lines to NK cells.

Susceptibility to natural killer cells and down regulation of MHC class I expression in adenovirus 12 transformed cells are regulated by different E1A domains

All human adenoviruses transform rodent cells in vitro, but only cells transformed by serotypes belonging to subgroups A (Ad12) and B (Ad3) are tumorigenic for immunocompetent animals. In these cells, the expression of MHC-class I antigens is repressed and might allow them to escape from recognition by cytotoxic T lymphocytes (CTL) and to develop in tumor. Furthermore, these cell lines appear resistant to lysis by natural killer (NK) cells. To determine the E1A domain(s) responsible for these properties several cell lines were created by transforming baby rat kidney (BRK) cells with a set of plasmids expressing different Ad2/Ad12 hybrid E1A gene products. The MHC class 1 gene expression was inhibited in cells expressing the Ad12 13S mRNA product and in cells transformed with Ad2/Ad12 hybrid E1A gene product harboring the C-terminal part of the conserved region (CR) 3 of Ad12. Susceptibility of these transformed cell lines to NK cells was determined by cytolytic assays. The results obtained suggest that two Ad12 E1A domains are required to induce resistance of the cell lines to NK cells.

Comparison between E1A gene from oncogenic and non-oncogenic adenoviruses in cellular transformation (Ad E1A conserved region)

All adenoviruses transform primary BRK cells in vitro, but only cells transformed by oncogenic adenoviruses are tumorigenic for immunocompetent animals. The transforming E1 regions of human Ad 2 and Ad 12 also differ from each other in the frequency in which they can transform BRK cells. We have investigated these properties which can be assigned to the specific domain of the E1A region. For this purpose, chimeric E1A regions between Ad 2 and Ad 12 have been constructed. The efficiency of cell transformation appeared to be determined by the encoding region. The promoter sequences were not important for an efficient cellular transformation although the E1B region cis activated in E1A transcription in both cell transformation and transient expression. We show that sequences located in the E1B promoter were responsible for this effect. In the encoding region the CR 1 domain was essential for the cell transformation frequency.

Adenovirus capsid proteins interact with HSP70 proteins after penetration in human or rodent cells

Soon after penetration of adenovirus serotype 2 in BHK-21 and HeLa cells, HSP70 and HSC70 proteins become associated with the viral capsid. By analysis with a polyclonal antibody derived from a fusion protein containing the C-terminal domain, 290 amino acids of HSP70, and using both immunological methods and infected cells fractionation we observed that a significant amount of HSP70 proteins moved to the nucleus and colocalized with the adenovirus particles. HSP70 proteins of infected cells were isolated as a complex cross-linked with intracytoplasmic adenovirus type 2. By coprecipitation, using a polyclonal-specific antiserum derived from the fusion protein, or two different monoclonal-specific antisera, we showed that HSP70 and HSC70 proteins were associated with hexon, the major adenovirus capsid protein.

Growth of fastidious adenovirus serotype 40 in HRT 18 cells: interactions with E1A and E1B deletion mutants of subgenus C adenoviruses

Growth of fastidious adenovirus serotype 40 (Ad40) in several cell lines was investigated. Ad40 was able to readily propagate in human intestinal cell line, HRT 18. Coinfection assays were made in non-permissive and permissive cells between Ad40 and Ad5dl312 or dl1520, mutants deleted in E1A and E1B regions, respectively, to test the ability of Ad40 to complement these mutants and vice versa. Ad40 could enhance Ad5dl312 DNA synthesis in HRT18 and HeLa cells, although its own DNA disappeared in the presence of this mutant in HRT18 cells. In coinfection with dl1520, Ad40 DNA synthesis was inhibited by dl1520 in HRT18 cells and dl1520 DNA synthesis was inhibited by Ad40 in 293 cells. This might reflect the presence of unusual products encoded by Ad40 E1B region.

Regulation of the biosynthesis of subgroup C adenovirus protein IVa2

The IVa2 gene is located between 16 and 11.3 map units on the left strand of the adenovirus type 5 (Ad5) genome. The coded RNA contains an intron of 277 nucleotides. To determine whether protein IVa2 is synthetized during productive infection and to obtain an immunological reagent to study its function, we prepared antibodies directed to 414 amino acids of protein IVa2 fused to the N-terminal domain of Staphylococcus aureus protein A. Western immunoblot analysis of viral proteins demonstrates that protein IVa2 is a minor component of mature viral particles and that it is also present in assembly intermediates and young virions. Thus, contrary to a previous report (H. Persson, B. Mathisen, L. Philipson, and U. Pettersson, Virology 93:198-208, 1979), protein IVa2 is not related to the 50-kDa polypeptide, a scaffolding protein present in assembly intermediates. The biosynthesis of protein IVa2 during productive infection was examined. Time course studies using immunofluorescence analysis with polyclonal antibodies targeted to protein IVa2 revealed that this protein is first synthesized at 12 h in a few cells exhibiting very striking fluorescence. Synthesis continues until at least 24 h postinfection. When hydroxyurea is added, protein IVa2 is not detected. In cells infected with mutant H5 ts125, blocked at the nonpermissive temperature (40 degrees C) in viral DNA replication, protein IVa2 is overexpressed. These results suggest that protein IVa2 synthesis requires cellular rather than viral DNA replication. RNase protection assay results indicate that hydroxyurea inhibits protein IVa2 synthesis at the transcriptional level. Thus, overexpression of protein IVa2 in H5 ts125-infected cells may be regulated at the translational level.

Nucleotide sequence and regulation of the adenovirus type 3 E2A early promoter

The nucleotide sequence of the adenovirus serotype 3 E2A early promoter has been determined. In contrast to Ad2, the Ad3 E2A early promoter possessed only one TATA-like box and one nuclear transcription factor E2F binding site and lacked the silencer sequences; however, as in Ad2, the ATF binding site was present. Moreover, the Ad3 E2A promoter harbored a protein binding sequence recognized by the SP1 factor. By transient expression analysis in HeLa cells, we demonstrated that the E1A gene products of Ad3 and Ad2 stimulated Ad3 E2A transcription. In competition experiments, the Ad3 E2A promoter was used in preference to the Ad2 E2A promoter.

Cellular transformation by E1 genes of enteric adenoviruses

The ability of Ad40 and Ad41 E1A plus E1B genes to transform BRK cells was considerably lower than that of Ad5 and Ad12 corresponding genes. However, as for Ad5, the E1A genes of enteric adenoviruses could cooperate with an activated ras oncogene for full cell transformation and the Ad41 E1B could be complemented by E1A gene of Ad5 or Ad12 for cell transformation. Complementation studies suggested that the conserved region 1 of Ad41 E1A was responsible for this inefficient transformation. The Ad40- and Ad41-transformed cell lines exhibited a low level of major histocompatibility complex (MHC) class I antigens correlated to the low level of Ad12-transformed cells. Class I MHC antigen amounts expressed at the surface of the cells transformed by the weakly oncogenic Ad3 were between the high level of Ad5- and the low level of Ad12-transformed cells.

Adenovirus transformed monkey cell lines permissive to enteric adenovirus type 40

Plasmids containing the E1 regions of adenovirus serotypes 3 and 5 were transfected into primary Rhesus monkey kidney cells. The presence of viral DNA sequences was detected in transformed cell lines. All these cell lines expressed the E1A proteins. In addition, Ad5 transformed cells, have the E1B 21 kDa protein located in the nuclear membrane. These cell lines were permissive to the enteric adenovirus serotype 40 but not to serotype 41.

Molecular cloning and physical mapping of the DNA of bovine adenovirus serotype 4; study of the DNA homology among bovine, human and porcine adenoviruses

The DNA of bovine adenovirus (BAV) serotype 4, a member of the subgroup 2 BAVs, has been cloned and mapped with 11 restriction enzymes. Southern blot hybridizations probed by a clone containing about 50% of the BAV-4 genome revealed a very strong and extended DNA sequence homology amongst the members of subgroup 2, but no homology was detectable to the subgroup 1 bovine, or any of those human (HAV) and porcine adenovirus serotypes examined. These findings were strengthened by reciprocal hybridizations. When using the cloned hexon gene region of BAV-3 (subgroup 1) or the total genome of HAV-2 as probes, again no homology could be shown to the bovine subgroup 2 serotypes. The extent of DNA homology detectable between the members of bovine subgroup 1, the porcine and the human serotypes was variable, but in general less expressed than that observed within the bovine subgroup 2.

Negative effect of a cis-acting pBR322 element on adenovirus E1a gene expression

A sequence element within plasmid pBR322 has a cis-acting negative effect on the expression of a cloned Ad gene in transient expression assays. The negative element is located between the PvuII and Tth111I restriction sites on pBR322 (nt 2068-2223). This element was also shown to be responsible for the decrease in focus number, when plasmids carrying Ad2 E1 genes were used to transform baby rat kidney cells. In a similar manner, this element diminished the number of G418-resistant cell foci, when plasmids containing the neo marker gene under the control of E1a promoter were used. Plasmid stability in transfected cells was not modified by deletion of this cis-acting negative element.

The role of the two E1a mRNA products of subgroup B adenoviruses in the regulation of early promoters of subgroup C adenoviruses

HeLa cells were co-transfected with recombinant plasmids carrying adenovirus (Ad)2 or Ad3 E1a promoters fused to the chloramphenicol acetyl transferase gene (cat), and a plasmid encoding the Ad3 E1a promoter. Whereas no stimulating effect was observed on the Ad3 E1a promoter, the Ad2 promoter was inhibited. To determine which of the E1a gene products of Ad3 was responsible for the repressive effect, plasmids were constructed in which only the 13S or 12S mRNA product of Ad3 was expressed. Both the 12S and 13S mRNA products of Ad3 E1a were found to depress the transcription from the Ad2 E1a promoter. Each Ad3 E1a gene product was able to stimulate transcription from the Ad5 E2a early promoter in a manner similar to that of the Ad2 E1a gene products. In the case of the Ad5 E3 promoter, neither of the Ad3 E1a gene products stimulated transcription, but an inhibition was observed. These results suggest that both mRNA products of the Ad3 E1a region inhibit transcription at the TATA box transcription complex.

Differences in the organization of adenovirus E1A promoters are not important for their full activity

The 5'-E1A control regions of adenovirus (Ad) types 2, 3 and 12 were cloned upstream from the cat gene. Each serotype was characterized by unique organization of the 5'-E1A non-coding region. All three 5'-non-coding E1A regions were able to stimulate the cat gene transcription in HeLa cells. Hybrid plasmids between Ad2/Ad3 and Ad2/Ad12 revealed the same level of CAT activity as the native plasmids but the optimum activity of promoter was achieved only when its organization was not modified. These observations suggest that various nuclear factors take part in the activation process of each promoter.

Expression of protein IIIa of human adenovirus type 2 in Escherichia coli

We have constructed a plasmid encoding the protein IIIa gene of human adenovirus type 2. The gene was expressed under the control of the hybrid tac (trp-lac) promoter; the protein was synthesized at levels up to 5% of newly synthesized protein after IPTG induction. The protein IIIa produced in Escherichia coli has an apparent Mr on sodium dodecyl sulfate-polyacrylamide gels of 67 kDa, and was revealed with anti-adenovirus serum in Western blotting. The protein IIIa produced in bacteria was phosphorylated in the presence of [gamma-32P]ATP.

Human adenovirus 2 temperature-sensitive mutant 112 contains three mutations in the protein IIIa gene

The temperature-sensitive (ts) mutant 112 of human adenovirus 2 is defective in the late stage of virus maturation. The region of functional mutation has been localised by marker rescue. It was observed that the ts mutation can be rescued by the left-hand part of the wild-type gene (nucleotides 12,301-12,891). By nucleotide sequencing, two mutations, both C to T (at position 12,386 and 12,741), were found in this region. The first one, in the glycine 20 codon, is silent, whereas the second changes alanine 145 to valine. A third mutation, which changed C to A (nucleotide 13,613), was identified in the right-hand part of the gene, resulting in the replacement of alanine-436 by threonine.

Expression of the chloramphenicol acetyl transferase gene in human cells under the control of early adenovirus subgroup C promoters: effect of E1A gene products from other subgroups on gene expression

A hierarchy of dominance has been observed in HeLa cells co-infected with two serotypes of adenovirus belonging to different subgroups. DNA replication and late protein synthesis of one serotype are inhibited by those of the other. The degree of inhibitory effect has the following decreasing order: adenovirus type 3 (Ad3) and Ad7 (subgroup B), Ad9 (D), Ad4 (E), Ad12 (A), Ad2 and Ad5 (C) [Delsert and D'Halluin, Virus Res. 1 (1984) 365-380]. HeLa cells were first transfected with recombinant plasmids carrying Ad5 E2A or E3 promoters fused to the chloramphenicol acetyl transferase gene (cat), and then infected with human Ad belonging to different subgroups. All the serotypes tested were found to be able to stimulate both E2A and E3 promoters. When HeLa cells were co-transfected with either of the previous plasmids, plus a second plasmid carrying the Ad3 E1A region, the same stimulatory effect was observed. However, an inhibitory effect on Ad5 E2A and E3 promoters seemed to occur when both Ad2 E1A (subgroup C) and Ad3 E1A (subgroup B) genes were present together. To determine which one of the early products was responsible for the observed repression effect, and to assign the target on the genome of subgroup C Ad, a plasmid was constructed in which the sequences at the 5' end of the Ad2 E1A region were fused to the structural sequences of the cat gene. In HeLa cells transfected with this plasmid, CAT activity was significantly increased after co-transfection with a plasmid carrying the Ad2 E1A region, but decreased with a plasmid carrying the Ad3 E1A region.(ABSTRACT TRUNCATED AT 250 WORDS)

An adenovirus cytocidal function related to the control of a cellular pH 4 endonuclease activity

An adenovirus (Ad) interserotypic recombinant (H2cyt141) between temperature-sensitive mutant H2ts111 of Ad2 and deletion mutant H5dl313 of Ad5 was isolated and characterized. It was phenotypically ts+, dl+, hr+ and formed large plaques (or cytocidal: cyt). It contained the right 89% of Ad5 DNA and the leftmost 11% of Ad2 DNA. Genetic recombination data suggested the cytocidal mutation lay in the transforming region E1B, confirming sequence analysis. The cytocidal effect resulted in part from the breakdown of cellular DNA. Host cell and virus DNA breakdown induced by H2cyt141 appeared cell-dependent: it occurred in HeLa, KB or BHK-21 cells, but not in CV1 or 293 cells. In human cells the cyt effect was recessive and adenovirus DNA degradation was prevented by co-infection with adenovirus wild-type (H2WT), other adenovirus serotypes or simian virus 40 (SV40). In simian cells, H2cyt141 did not inhibit SV40 DNA replication, unlike H2WT. The amount of H2cyt141 DNA integrated in human cell DNA at early stages of the lytic cycle was found to be significantly lower than for H2WT. Novobiocin inhibited viral DNA breakdown in human cells. Cellular DNA extracted from H2cyt141-infected cells exhibited a repeat band pattern in gel electrophoresis reminiscent of the nuclease digestion pattern of chromatin, with monosome-size fragments as the digestion limit. The H2cyt141-induced nucleolytic effect would therefore occur in the linker regions of cell DNA and might result from the observed stimulation (by a factor of greater than 100) of an acidic (optimum pH 4.0) endonuclease activity. The nucleolytic effect also appeared to be recessive in vitro and absent in mixed samples containing extracts from H2cyt141-infected cells plus extracts from H2WT- or mock-infected cells. The virus gene product responsible for the enhancement of the acidic endonuclease was found to function stoichiometrically and not catalytically. The cytocidal and nucleolytic effects of the viral E1B region 19K protein may be mediated by a cellular inhibitor of acidic endonuclease.

Restriction maps of human adenovirus types 2, 5, and 3 for BstEII, MluI, NdeI, NruI and SfiI endonucleases

The positions of cleavage sites for BstEII, MluI, NdeI, NruI and SfiI restriction endonucleases in the DNA from human adenovirus (Ad) serotypes 2, 5 and 3 were determined. In addition, the sites of cleavage for BglII in Ad3 DNA were located. All these enzymes possess a narrow specificity and generated a small number of discrete DNA fragments. Ad3 DNA was not cleaved by MluI and SfiI. It was the first observation of the absence of cleavage of an adenovirus DNA by a restriction endonuclease.

Characterization of an Early Temperature-sensitive and Cytocidal Double Mutant of Adenovirus Type 2

Human adenovirus type 2 mutant, H2 ts 111, presented a double phenotype: temperature-sensitive (ts) for initiation and elongation of DNA synthesis, and cytocidal (cyt) by its large-plaque formation and the nucleolytic cleavage of both viral and cellular DNAs. Both characters were recessive since they were efficiently complemented by wild-type or other DNA-negative ts mutants. H2 ts 111 DNA--terminal protein complex formed at 33 degrees C and chased at 39.5 degrees C showed a decreased affinity for glass fibre filters, concurrently with the loss of protein-linked DNA ends. H2 ts 111 DNA breakdown occurring upon shift-up to 39.5 degrees C therefore appeared to start in close proximity to the genome extremities. Marker rescue experiments showed that the ts character was abolished by co-infection with plasmid recombinants containing whole or part of the E2A region, encoding for the 72K DNA-binding protein. The N-terminal domain of this 72K protein has been assigned between 0 and 200 amino acids, and is supposed to have a function in late transcription control. Since H2 ts 111 mapped between 0 and 300 residues (63.6 to 65.9 map units), its mutation was most likely located between 200 and 300 amino acids, namely in the C-terminal domain of the protein, which is involved in DNA replication. Recombination between H2 ts 111 and H5 dl 313 mutant revealed that the cyt function was localized in the E1B zone, between 3.8 and 11.3 map units. The nucleolytic and cytocidal effects were complemented by HEK 293 cells, an H5-transformed cell line expressing the left-most 12.5% of the viral genome. H2 ts 111 appeared, therefore, as a double ts-cyt mutant. The gene product rendered temperature-sensitive by the H2 ts 111 mutation was found to act stoichiometrically, and not catalytically, a result compatible with a lesion in the 72K protein. Although inactive at the non-permissive temperature, the early 72K protein was normally synthesized and stable in H2 ts 111-infected cells at 39.5 degrees C. Assymetric complementation obtained with the DNA-defective H5 ts 36 implied a certain degree of type specificity in the DNA-binding protein function.

Initiation rate of adenovirus DNA synthesis in infected cell

A method was developed to determine the rate of viral DNA synthesis initiation in adenovirus 2-infected cells. The initiation of DNA synthesis appeared as the rate-limiting step for accumulation of viral DNA. The multiplicity of infection slightly influenced the rate of synthesis of viral DNA, and only during the linear phase of viral DNA production. The initiation of DNA-synthesis was found to occur preferentially on newly synthesized DNA molecules. These kinetics data and the effect of novobiocin suggested that binding of viral DNA with some enzymatic complexes favored the replication of a minor, active class of adenovirus DNA molecules.

Genetic expression of human adenoviruses in simian cells. Evidence for interserotypic inhibition of viral DNA synthesis

Most simian cells are permissive for SV40 and adenovirus-SV40 hybrids but nonpermissive for human adenoviruses, and the defect has been shown to take place at the level of processing of late viral mRNAs (Klessig and Grodzicker, 1979). Viral DNA synthesis and virus progeny production were studied in simian cells infected with different adenovirus serotypes. Adenoviruses belonging to oncogenic subgroups A and B (Ad31 and Ad3) failed to replicate their DNA in CV1 cells, whereas DNA replication occurred for all the other serotypes. Co-infection of CV1 cells with SV40 and Ad3 (or Ad31) resulted in the inhibition of SV40 DNA synthesis, as well as cellular DNA synthesis. The inhibition was not related to adenovirus DNA replication, since SV40 did not complement the Ad3/Ad31 replication defective function. Similar results were obtained in coinfected BSC and MK2 simian cell lines. Inhibition of Ad2ND1 DNA synthesis and gene expression also occurred in co-infection of simian cells with nondefective Ad2ND1 hybrid and defective Ad3/Ad31. In permissive human cell lines (HeLa or KB) co-infected with Ad2 and Ad3 (or Ad31), a dominant, inhibitory effect of Ad3 (or Ad31) over Ad2 was also observed. The inhibition appeared to function stoichiometrically and not catalytically, and to involve early adenovirus gene products. In both simian and human cells a hierarchy of dominance appeared between serotypes belonging to different subgroups. The degree of inhibitory effect occurred in the following decreasing order: Ad3 and Ad7 (subgroup B), Ad9 (D), Ad4 (E), Ad31 (A), Ad2 and Ad5 (C).

Restriction maps of human adenovirus types 2, 5 and 3 for BclI, ClaI, pvul and SphI endonucleases

The sites of cleavage by BclI, ClaI, PvuI and SphI in the DNA from adenovirus (Ad) serotypes 2, 5 and 3 have been located. Certain site coordinates were in accord with nucleotide sequences already published. A small difference in size between the PvuI-E fragments from Ad2 and Ad5 confirmed the existence of a deletion in the N-terminal moiety of Ad5 hexon gene, as previously implied by interserotypic recombinants (Boursnell and Mautner, Virology 112 (1981) 198-209) and more recently by amino acid sequencing (Von Bahr-Lindström et al., Virology 118 (1982) 352-362).

Physical mapping of adenovirus type 2 temperature-sensitive mutations by restriction endonuclease analysis of interserotypic recombinants

The genome structures of about 100 interserotypic ts recombinants produced in crosses between human adenovirus type 2 (H2) and 5 (H5) temperature-sensitive mutants were analyzed by cleavage with restriction endonucleases to determine the map coordinates of the following temperature-sensitive mutants: penton base plus fiber-defective H2 ts103, -104, and -136, assembly-defective H2 ts112, fiber-defective H2 ts125, hexon-defective H2 ts118 and -121, and DNA-negative H2 ts111. H5 ts1 (100 K defective), H5 ts36 (DNA negative), H5 ts125 (mutated in the early 72,000-dalton protein), H5 ts22 (fiber defective), H5 ts58 (IIIa defective), and H5 ts18 and -19 were used as one of the parents. The physical locations of the H2 temperature-sensitive mutations thus defined are discussed in relation to the genetic map, the biological function altered, and the positions of the structural genes on the genome.

Effects of novobiocin on adenovirus DNA synthesis and encapsidation

Novobiocin, an inhibitor of DNA gyrase implicated in bacterial and likely mammalian, chromosome replication, inhibited the initiation, but not the elongation of human adenovirus DNA replicative synthesis. The inhibition was partially reversible, even in the presence of protein synthesis inhibitor. Novobiocin inhibited also the encapsidation of viral DNA, and this effect was independent of the block in DNA replication. It was suggested that novobiocin acted on two different functions, one involved in viral DNA replication initiation, the other in DNA encapsidation.

Morphogenesis of human adenovirus type 2 studied with fiber- and fiber and penton base-defective temperature-sensitive mutants

The nature, polypeptide composition, and antigenic composition of the particles formed by six human adenovirus type 2 temperature-sensitive (ts) mutants were studied. ts115, ts116, and ts125 were phenotypically fiber-defective mutants, and ts103, ts104, and ts136 failed to synthesize detectable amounts of fiber plus penton base at 39.5 degrees C. The mutants belonged to five complementation groups, one group including ts116 and ts125. Except for ts103 and ts136, the other mutants were capable of producing particles at 39.5 degrees C. ts116 and ts125 accumulated light assembly intermediate particles (or top components) at nonpermissive temperatures, with few virus particles. The sodium dodecyl sulfate polypeptide pattern of ts116- or ts125-infected cells, intermediate particles, and virus particles showed that polypeptide IV (fiber) was smaller by a molecular weight of 2,000 than that in the wild-type virion and was glycosylated. In fiber plus penton base-defective ts104-infected cells, equivalent quantities of top components and viruses with a buoyant density (rho) of 1.345 g/ml (rho = 1.345 particles) were produced at 39.5 degrees C. These rho = 1.345 particles corresponded to young virions, as evidenced by the presence of uncleaved precursors to proteins VI, VIII, and VII. These young virions matured upon a shift down. Virus capsid vertex antigenic components underwent a phase of eclipse during their incorporation into mature virus particles. No antigenic penton base or IIa was detected in intermediate particles of all the ts mutants tested. Only hexon and traces of fiber antigens were found in ts104 young virions. Penton base and IIIa appeared as fully antigenically expressed capsid subunits in mature wild-type virions or ts104 virions after a shift down. The ts104 lesion is postulated to affect a regulatory function related in some way to penton base and fiber overproduction and the maturation processing of precursors PVI, PVII, and PVII.

Adenovirus early function required for protection of viral and cellular DNA

Studies were done to characterize a DNA-negative temperature-sensitive (ts) mutant of human adenovirus type 2, H2 ts111. The temperature-sensitive defect, which was reversible on shift-down in the absence of protein synthesis, was expressed as early as 2 h postinfection, and the results of density-labeling experiments are in agreement with at least a DNA replication initiation block. On shift-up, after allowing viral DNA synthesis at permissive temperatures, the newly synthesized viral DNA and the mature viral DNA were cleaved into fragments which sedimented as a broad peak with a mean coefficient of 10-12S. This cleavage was more marked in the presence of hydroxyurea as the DNA synthesis inhibitor. Parental DNA in infected cells was degraded to a much lesser extent regardless of the incubation temperature. In contrast, the parental DNA was strongly degraded when early gene expression was permitted at 33 degrees C before shift-up to 39.5 degrees C. Furthermore, cellular DNA was also degraded at 39.5 degrees C in ts111-infected cells, the rate of cleavage being related to the multiplicity of infection. This cleavage effect, which did not seem to be related to penton base-associated endonuclease activity, was also enhanced when early gene expression was allowed at 33 degrees C before shift-up. The ts111 defect, which was related to an initiation block and endonucleolytic cleavage of viral and cellular DNA, seemed to correspond to a single mutation. The implication of the ts111 gene product in protection of viral and cellular DNA by way of a DNase-inhibitory function is discussed.

Isolation and phenotypic characterization of human adenovirus type 2 temperature-sensitive mutants

Thirty-nine temperature-sensitive (ts) mutants that fail to grow at 39.5 degrees C but develop normally at 33 degrees C have been isolated from a nitrous-acid-treated stock of a wild-type strain of type 2 human adenovirus. The frequency of ts mutants among the surviving viruses was about 10%. Complementation tests in doubly infected cell cultures at restrictive temperature permitted the assignment of 19 of these mutants to 11 complementation groups. They are characterized phenotypically according to their soluble capsid antigen production quantified by two-dimensional immunoelectrophoresis, virus DNA synthesis, as measured by alkaline sucrose gradient sedimentation of 34S DNA, and virion morphogenesis, as analysed by electron microscopy os cell sections. Two complementation groups were defective for DNA synthesis, four for soluble hexon production and two groups for total penton (penton base + fibre), while one group revealed no fibre production. Two complementation groups presented a normal antigen pattern, but the particles exhibited altered morphology as observed in cell sections.

Adenovirus type 2 assembly analyzed by reversible cross-linking of labile intermediates

Dimethyl-4,4'-dithiobisbutyrimidate dihydrochloride was used as a cleavable cross-linking reagent to maintain the structure of labile intermediates in adenovirus type 2 assembly. Analysis on sucrose gradients of nuclear adenovirus particles revealed two size classes, with sedimentation rates of 750 and 600S. After reversible fixation with diimido ester, the different classes were further separated on CsCl gradients and characterized with regard to their buoyant density, DNA content, and polypeptide composition. The 750S particles banded at 1.345 g/cm3 in CsCl, contained a DNA with a sedimentation coefficient of 34S in alkaline sucrose gradients, and had a polypeptide composition similar to that of young virions. The 600S population consisted of two types of particles with buoyant densities of 1.315 and 1.37 g/cm3. The 1.315-g/cm3 particles contained a DNA fragment of 7--11S and lacked the core proteins V and VII. In their place were found precursors P VI and P VIII and two nonvirion proteins with molecular weights of 50,000 (50K) and 39,000 (39K). 34S DNA was present in the 1.37-g/cm3 particles, which also lacked core proteins V and VII, as well as the 50K and 39K. Pulse-chase labeling kinetics suggested that the 1.315-g/cm3 particles were anterior to the 1.37-g/cm3 particles, themselves preceding the 1.345-g/cm3 young virions, and that the release of both 50K and 39K, possible scaffolding proteins, was required for entry of viral DNA.

Temperature-sensitive mutant of adenovirus type 2 blocked in virion assembly: accumulation of light intermediate particles

A temperature-sensitive mutant of human adenovirus type 2, ts112, was isolated and characterized, ts112 was blocked in a late function required for virus maturation. At restrictive temperature, it accumulated light precursor particles that were able to mature into infectious virions upon temperature shift-down. Use of a mild extraction procedure and a reversible fixation by a cleavable diimido ester permitted the isolation and analysis of these labile intermediates in the adenovirus assembly. These accumulated particles had a sedimentation coefficient of about 600S and a buoyant density of 1.315 g/cm3 in CsCl. They contained a DNA fragment of 7--11S and two nonvirion proteins having molecular weights of 50,000 (50K) and 39.000 (39K), respectively. They resembled in composition and morphology the light intermediate particles found in wild-type adenovirus 2, which were identified as precursors of heavy intermediates, preceding the young virions. The ts112 lesion was apparently located at the exit of either the 50K and/or 39K proteins and at the entry of viral DNA.