Effect of adenovirus on host cell DNA synthesis in synchronized cells

Human Adenovirus Gene Expression and Replication Is Regulated through Dynamic Changes in Nucleoprotein Structure throughout Infection

Human adenovirus (HAdV) is extremely common and can rapidly spread in confined populations such as daycare centers, hospitals, and retirement homes. Although HAdV usually causes only minor illness in otherwise healthy patients, HAdV can cause significant morbidity and mortality in certain populations, such as the very young, very old, or immunocompromised individuals. During infection, the viral DNA undergoes dramatic changes in nucleoprotein structure that promote the rapid expression of viral genes, replication of the DNA, and generation of thousands of new infectious virions-each process requiring a distinct complement of virus and host-encoded proteins. In this review, we summarize our current understanding of the nucleoprotein structure of HAdV DNA during the various phases of infection, the cellular proteins implicated in mediating these changes, and the role of epigenetics in HAdV gene expression and replication.

E1B-55K is a phosphorylation-dependent transcriptional and post-transcriptional regulator of viral gene expression in HAdV-C5 infection

The multifunctional adenoviral E1B-55K phosphoprotein is a major regulator of viral replication and plays key roles in virus-mediated cell transformation. While much is known about its function in oncogenic cell transformation, underlying features and exact mechanisms that implicate E1B-55K in regulation of viral gene expression are less well understood. Therefore, this work aimed at unravelling basic intranuclear principles of E1B-55K-regulated viral mRNA biogenesis using wild type HAdV-C5 E1B-55K, a virus mutant with abrogated E1B-55K expression and a mutant that expresses a phosphomimetic E1B-55K. By subnuclear fractionation, mRNA, DNA and protein analyses as well as luciferase reporter assays, we show that (i) E1B-55K promotes efficient release of viral late mRNAs from their site of synthesis in viral replication compartments (RCs) to the surrounding nucleoplasm, that (ii) E1B-55K modulates the rate of viral gene transcription and splicing in RCs, that (iii) E1B-55K participates in the temporal regulation of viral gene expression, that (iv) E1B-55K can enhance or repress the expression of viral early and late promoters and that (v) the phosphorylation of E1B-55K regulates the temporal effect of the protein on each of these activities. Together, these data demonstrate that E1B-55K is a phosphorylation-dependent transcriptional and post-transcriptional regulator of viral genes during HAdV-C5 infection. Importance Human adenoviruses are useful models to study basic aspects of gene expression and splicing. Moreover, they are one of the most commonly used viral vectors for clinical applications. However, key aspects of the activities of essential viral proteins that are commonly modified in adenoviral vectors have not been fully described. A prominent example is the multifunctional adenoviral oncoprotein E1B-55K that is known to promote efficient viral genome replication and expression while simultaneously repressing host gene expression and antiviral host responses. Our study combined different quantitative methods to study how E1B-55K promotes viral mRNA biogenesis. The data presented here propose a novel role for E1B-55K as a phosphorylation-dependent transcriptional and post-transcriptional regulator of viral genes.

Evidence That the Adenovirus Single-Stranded DNA Binding Protein Mediates the Assembly of Biomolecular Condensates to Form Viral Replication Compartments

A common viral replication strategy is characterized by the assembly of intracellular compartments that concentrate factors needed for viral replication and simultaneously conceal the viral genome from host-defense mechanisms. Recently, various membrane-less virus-induced compartments and cellular organelles have been shown to represent biomolecular condensates (BMCs) that assemble through liquid-liquid phase separation (LLPS). In the present work, we analyze biophysical properties of intranuclear replication compartments (RCs) induced during human adenovirus (HAdV) infection. The viral ssDNA-binding protein (DBP) is a major component of RCs that contains intrinsically disordered and low complexity proline-rich regions, features shared with proteins that drive phase transitions. Using fluorescence recovery after photobleaching (FRAP) and time-lapse studies in living HAdV-infected cells, we show that DBP-positive RCs display properties of liquid BMCs, which can fuse and divide, and eventually form an intranuclear mesh with less fluid-like features. Moreover, the transient expression of DBP recapitulates the assembly and liquid-like properties of RCs in HAdV-infected cells. These results are of relevance as they indicate that DBP may be a scaffold protein for the assembly of HAdV-RCs and should contribute to future studies on the role of BMCs in virus-host cell interactions.

Bovine Adenovirus-3 pVIII Suppresses Cap-Dependent mRNA Translation Possibly by Interfering with the Recruitment of DDX3 and Translation Initiation Factors to the mRNA Cap

Earlier, targeting of DDX3 by few viral proteins has defined its role in mRNA transport and induction of interferon production. This study was conducted to investigate the function of bovine adenovirus (BAdV)-3 pVIII during virus infection. Here, we provided evidence regarding involvement of DDX3 in cap dependent cellular mRNA translation and demonstrated that targeting of DDX3 by adenovirus protein VIII interfered with cap-dependent mRNA translation function of DDX3 in virus infected cells. Adenovirus late protein pVIII interacted with DDX3 in transfected and BAdV-3 infected cells. pVIII inhibited capped mRNA translation in vitro and in vivo by limiting the amount of DDX3 and eIF3. Diminished amount of DDX3 and eIFs including eIF3, eIF4E, eIF4G, and PABP were present in cap binding complex in BAdV-3 infected or pVIII transfected cells with no trace of pVIII in cap binding complex. The total amount of eIFs appeared similar in uninfected or infected cells as BAdV-3 did not appear to degrade eIFs. The co-immunoprecipitation experiments indicated the absence of direct interaction between pVIII and eIF3, eIF4E, or PABP. These data indicate that interaction of pVIII with DDX3 interferes with the binding of eIF3, eIF4E and PABP to the 5′ Cap. We conclude that DDX3 promotes cap-dependent cellular mRNA translation and BAdV-3 pVIII inhibits translation of capped cellular mRNA possibly by interfering with the recruitment of eIFs to the capped cellular mRNA.

Chromatin structure of adenovirus DNA throughout infection

For more than half a century, researchers have studied the basic biology of Adenovirus (Ad), unraveling the subtle, yet profound, interactions between the virus and the host. These studies have uncovered previously unknown proteins and pathways crucial for normal cell function that the virus manipulates to achieve optimal virus replication and gene expression. In the infecting virion, the viral DNA is tightly condensed in a virally encoded protamine-like protein which must be remodeled within the first few hours of infection to allow for efficient expression of virus-encoded genes and subsequent viral DNA replication. This review discusses our current knowledge of Ad DNA–protein complex within the infected cell nucleus, the cellular proteins the virus utilizes to achieve chromatinization, and how this event contributes to efficient gene expression and progression of the virus life cycle.

Optimization of HEK-293S cell cultures for the production of adenoviral vectors in bioreactors using on-line OUR measurements

The culture of HEK-293S cells in a stirred tank bioreactor for adenoviral vectors production for gene therapy is studied. Process monitoring using oxygen uptake rate (OUR) was performed. The OUR was determined on-line by the dynamic method, providing good information of the process evolution. OUR enabled cell activity monitoring, facilitating as well the determination of the feeding rate in perfusion cultures and when to infect the culture. Batch cultures were used to validate the monitoring methodology. A cell density of 10×10(5)cell/mL was infected, producing 1.3×10(9) infectious viral particles/mL (IVP/mL). To increase cell density values maintaining cell specific productivity, perfusion cultures, based on tangential flow filtration, were studied. In this case, OUR measurements were used to optimize the dynamic culture medium feeding strategy, addressed to avoid any potential nutrient limitation. Furthermore, the infection protocol was defined in order to optimize the use of the viral inoculum, minimizing the uncontrolled release of particles through the filter unit mesh. All these developments enabled an infection at 78×10(5)cell/mL with the consequent production of 44×10(9)IVP/mL, representing a cell specific productivity 4.3 times higher than for the batch culture.

Tumor associated stromal cells play a critical role on the outcome of the oncolytic efficacy of conditionally replicative adenoviruses

The clinical efficacy of conditionally replicative oncolytic adenoviruses (CRAd) is still limited by the inefficient infection of the tumor mass. Since tumor growth is essentially the result of a continuous cross-talk between malignant and tumor-associated stromal cells, targeting both cell compartments may profoundly influence viral efficacy. Therefore, we developed SPARC promoter-based CRAds since the SPARC gene is expressed both in malignant cells and in tumor-associated stromal cells. These CRAds, expressing or not the Herpes Simplex thymidine kinase gene (Ad-F512 and Ad(I)-F512-TK, respectively) exerted a lytic effect on a panel of human melanoma cells expressing SPARC; but they were completely attenuated in normal cells of different origins, including fresh melanocytes, regardless of whether cells expressed or not SPARC. Interestingly, both CRAds displayed cytotoxic activity on SPARC positive-transformed human microendothelial HMEC-1 cells and WI-38 fetal fibroblasts. Both CRAds were therapeutically effective on SPARC positive-human melanoma tumors growing in nude mice but exhibited restricted efficacy in the presence of co-administered HMEC-1 or WI-38 cells. Conversely, co-administration of HMEC-1 cells enhanced the oncolytic efficacy of Ad(I)-F512-TK on SPARC-negative MIA PaCa-2 pancreatic cancer cells in vivo. Moreover, conditioned media produced by stromal cells pre-infected with the CRAds enhanced the in vitro viral oncolytic activity on pancreatic cancer cells, but not on melanoma cells. The whole data indicate that stromal cells might play an important role on the outcome of the oncolytic efficacy of conditionally replicative adenoviruses.

Modulation of host cell gene expression during onset of the late phase of an adenovirus infection is focused on growth inhibition and cell architecture

Microarray analysis of host cell gene expression during an adenovirus type 2 infection showed that the number of regulated genes, as well as the magnitude of change, was increased as the infection proceeded into the late phase. In contrast to the early phase of infection when the majority of differentially expressed genes were upregulated, expression of most of the regulated genes (82 out of 112) declined during the late phase. In particular, numerous TGF-beta inducible genes and several TGF-beta-independent growth-arrest-inducing genes were targeted. Of the 30 genes upregulated more than 2-fold at 20 h post-infection, nearly two-thirds of encoded proteins are involved in cell metabolism. The data indicate that adenovirus primarily targets cellular genes involved in antiviral defense, cell growth arrest and apoptosis, as well as cell metabolism, to ensure sufficient production of viral progeny.

5-fluorouracil and hydroxyurea enhance adenovirus-mediated transgene expression in colon and hepatocellular carcinoma cells

PURPOSE

To investigate the efficient transduction of tumor cells which remains a major limitation of cancer gene therapy.

METHODS

In this study, we tested whether treatment with antimetabolic drugs 5-FU and hydroxyurea (HU) could improve adenovirus-mediated gene expression in tumor cells.

RESULTS

We found that 5-FU and HU treatment significantly increased beta-gal activity in adenovirus (Ad.CMVBG)-infected human colon carcinoma (LoVo) and hepatocellular carcinoma (SMMC7721) cells in a dose- and time-dependent manner. These increases were maximized at 5.01+/-0.42-fold and 3.32+/-0.32-fold for 5-FU (50 microM), and at 6.60+/-0.50-fold and 4.82+/-0.43-fold for HU (5 mM) treatment, respectively, after 48 h infection. Transient increases in viral uptake, determined by real-time PCR for viral DNA content and by confocal microscopy for viral particles, were observed in 5-FU or HU-treated cells that partially contribute to the overall increases of beta-gal expression. Moreover, mRNA levels for the beta-gal gene in infected cells were significantly increased in both LoVo and SMMC7721 cells by 5-FU and HU treatment in contrast to the inhibition of viral DNA replication and the unchanged mRNA levels for alpha-actin gene. The induction appeared to be the result of enhanced transcription since beta-gal mRNA half-life was not affected by drug treatment. However, similar induction was not detected in CMV-beta-gal-expressing stable cells, suggesting that an adenovirus-associated mechanism might be involved in this induction.

CONCLUSIONS

Our findings suggest that it may be possible to improve tumor cell transduction by adenovirus using chemotherapy.

Production of adenovirus vector for gene therapy

The field of gene therapy is rapidly expanding with a major focus on the treatment of cancer. Replication-defective adenoviruses are vectors of choice for delivering corrective genes into human cells. Major efforts are directed to design new generations of adenoviral vectors that feature reduced immunogenicity and improved targeting ability. However, the production of adenoviral vectors for gene therapy applications faces a number of challenges that limit the availability of high quality material at the early stages of research and development in the gene therapy field. Moreover, very few papers have been published on the subject and information on large-scale production methods are only available through specialized conference proceedings. This review outlines the problems associated with mass production of adenovirus vectors and describes research efforts by a number of groups who have contributed to optimize production methods. Better understanding of the adenovirus infection and replication kinetics as well as better understanding of complementing cell line physiology and metabolism greatly contributed to improving vector titers and volumetric productivity at higher cell densities. Also, the critical aspect of viral vector quantitation is discussed.

DNA replication of first-generation adenovirus vectors in tumor cells

A major role of the early gene 1A and 1B products (E1A and E1B) in adenovirus infection is to create a cellular environment appropriate for viral DNA replication. This is, in part, achieved by inactivation of tumor suppressor gene products such as pRb or p53. The functions of these same cellular proteins are also frequently lost in tumor cells. Therefore, we hypothesized that tumor cell lines with deregulated p53 and/or pRb pathways might support replication of E1A/E1B-deleted, first-generation adenovirus vectors (AdE1(-)). Here, we analyzed the impact of virus uptake, cell cycling, and the status of cell cycle regulators on AdE1(-) DNA synthesis. Cellular internalization of AdE1(-) vectors varied significantly among different tumor cell lines, whereas nuclear import of incoming viral DNA appeared to be less variable. Replication assays performed under equalized infection conditions demonstrated that all analyzed tumor cell lines supported AdE1(-) synthesis to varying degrees. There was no obvious correlation between the efficiency of viral DNA replication and the status of p53, pRb, and p16. However, the amount of virus attached and internalized changed with the cell cycle, affecting the intracellular concentration of viral DNA and thereby the replication efficacy. Furthermore, infection with AdE1 - vectors caused a partial G(2)/M arrest or delay in cell cycle progression, which became more pronounced in consecutive cell cycles. Correspondingly, vector DNA replication was found to be enhanced in cells artificially arrested in G(2)/M. Our findings suggest that cell cycling and thus passing through G(2)/M supports AdE1(-) DNA replication in the absence of E1A/E1B. This has potential implications for the use of first-generation adenovirus vectors in tumor gene therapy.

Roles for the E4 orf6, orf3, and E1B 55-kilodalton proteins in cell cycle-independent adenovirus replication

Adenoviruses bearing lesions in the E1B 55-kDa protein (E1B 55-kDa) gene are restricted by the cell cycle such that mutant virus growth is most impaired in cells infected during G(1) and least restricted in cells infected during S phase (F. D. Goodrum and D. A. Ornelles, J. Virol. 71:548-561, 1997). A similar defect is reported here for E4 orf6-mutant viruses. An E4 orf3-mutant virus was not restricted for growth by the cell cycle. However, orf3 was required for enhanced growth of an E4 orf6-mutant virus in cells infected during S phase. The cell cycle restriction may be linked to virus-mediated mRNA transport because both E1B 55-kDa- and E4 orf6-mutant viruses are defective at regulating mRNA transport at late times of infection. Accordingly, the cytoplasmic-to-nuclear ratio of late viral mRNA was reduced in G(1) cells infected with the mutant viruses compared to that in G(1) cells infected with the wild-type virus. By contrast, this ratio was equivalent among cells infected during S phase with the wild-type or mutant viruses. Furthermore, cells infected during S phase with the E1B 55-kDa- or E4 orf6-mutant viruses synthesized more late viral protein than did cells infected during G(1). However, the total amount of cytoplasmic late viral mRNA was greater in cells infected during G(1) than in cells infected during S phase with either the wild-type or mutant viruses, indicating that enhanced transport of viral mRNA in cells infected during S phase cannot account for the difference in yields in cells infected during S phase and in cells infected during G(1). Thus, additional factors affect the cell cycle restriction. These results indicate that the E4 orf6 and orf3 proteins, in addition to the E1B 55-kDa protein, may cooperate to promote cell cycle-independent adenovirus growth.

The early region 1B 55-kilodalton oncoprotein of adenovirus relieves growth restrictions imposed on viral replication by the cell cycle

The E1B 55-kDa oncoprotein of adenovirus enables the virus to overcome restrictions imposed on viral replication by the cell cycle. Approximately 20% of HeLa cells infected with an E1B 55-kDa mutant adenovirus produced virus when evaluated by electron microscopy or by assays for infectious centers. By contrast, all HeLa cells infected with a wild-type adenovirus produced virus. The yield of E1B mutant virus from randomly cycling HeLa cells correlated with the fraction of cells in S phase at the time of infection. In synchronously growing HeLa cells, approximately 75% of the cells infected during S phase with the E1B mutant virus produced virus, whereas only 10% of the cells infected during G1 produced virus. The yield of E1B mutant virus from HeLa cells infected during S phase was sevenfold greater than that of cells infected during G1 and threefold greater than that of cells infected during asynchronous growth. Cells infected during S phase with the E1B mutant virus exhibited severe cytopathic effects, whereas cells infected with the E1B mutant virus during G1 exhibited a mild cytopathic effect. Viral DNA synthesis appeared independent of the cell cycle because equivalent amounts of viral DNA were synthesized in cells infected with either wild-type or E1B mutant virus. The inability of the E1B mutant virus to replicate was not mediated by the status of p53. These results define a novel property of the large tumor antigen of adenovirus in relieving growth restrictions imposed on viral replication by the cell cycle.

Nuclear organization of splicing small nuclear ribonucleoproteins in adenovirus-infected cells

We have studied the effect of adenovirus infection on the nuclear organization of splicing small nuclear ribonucleoproteins (snRNPs) in HeLa cells. In uninfected HeLa cells, snRNPs are widespread throughout the nucleoplasm but also are concentrated in specific nuclear structures, including coiled bodies, interchromatin granules, and perichromatin fibrils. We have used immunofluorescence microscopy to study the localization of splicing snRNPs relative to centers of viral DNA synthesis and accumulation identified with antiserum against the viral 72,000-molecular-weight single-stranded DNA-binding protein (72K protein). Splicing snRNPs were independently detected with both monoclonal and polyclonal antibodies specific for common snRNP antigens, snRNP-specific proteins, and the snRNA-specific 2,2,7-trimethylguanosine 5' cap structure. We have examined infected cells 2 to 24 h after infection, and, in the majority of these cells, we observed no colocalization of the snRNP and 72K-protein staining patterns. In the late phase, snRNPs were found to markedly concentrate in discrete clusters that were distinct from the centers of viral DNA synthesis and accumulation identified with anti-72K protein. We have treated cells with hydroxyurea at various times after infection to inhibit aspects of the virus infectious program. We have found that the accumulation of snRNP clusters is correlated with late gene expression rather than with DNA synthesis or early gene expression. Finally, we show that the late-phase snRNP clusters colocalize with a monoclonal antibody that primarily stains interchromatin granules. These results suggest that the centers of snRNP concentration in late-phase infected cells are likely to correspond to interchromatin granule clusters.

Identification of temperature-sensitive DNA- mutants of Chinese hamster cells affected in cellular and viral DNA synthesis

We described a strategy which facilitates the identification of cell mutants which are restricted in DNA synthesis in a temperature-dependent manner. A collection of over 200 cell mutants temperature-sensitive for growth was isolated in established Chinese hamster cell lines (CHO and V79) by a variety of selective and nonselective techniques. Approximately 10% of these mutants were identified as ts DNA- based on differential inhibition of macromolecular synthesis at the restrictive temperature (39 degrees C) as assessed by incorporation of [3H]thymidine and [35S]methionine. Nine such mutants, selected for further study, demonstrated rapid shutoff of DNA replication at 39 degrees C. Infections with two classes of DNA viruses extensively dependent on host-cell functions for their replication were used to distinguish defects in DNA synthesis itself from those predominantly affecting other aspects of DNA replication. All cell mutants supported human adenovirus type 2 (Ad2) and mouse polyomavirus DNA synthesis at the permissive temperature. Five of the nine mutants (JB3-B, JB3-O, JB7-K, JB8-D, and JB11-J) restricted polyomavirus DNA replication upon transfection with viral sequences at 33 degrees C and subsequent shift to 39 degrees C either before or after the onset of viral DNA synthesis. Only one of these mutants (JB3-B) also restricted Ad2 DNA synthesis after virion infection under comparable conditions. No mutant was both restrictive for Ad2 and permissive for polyomavirus DNA synthesis at 39 degrees C. The differential effect of these cell mutants on viral DNA synthesis is expected to assist subsequent definition of the biochemical defect responsible.

Identification of temperature-sensitive DNA- mutants of Chinese hamster cells affected in cellular and viral DNA synthesis

We described a strategy which facilitates the identification of cell mutants which are restricted in DNA synthesis in a temperature-dependent manner. A collection of over 200 cell mutants temperature-sensitive for growth was isolated in established Chinese hamster cell lines (CHO and V79) by a variety of selective and nonselective techniques. Approximately 10% of these mutants were identified as ts DNA- based on differential inhibition of macromolecular synthesis at the restrictive temperature (39 degrees C) as assessed by incorporation of [3H]thymidine and [35S]methionine. Nine such mutants, selected for further study, demonstrated rapid shutoff of DNA replication at 39 degrees C. Infections with two classes of DNA viruses extensively dependent on host-cell functions for their replication were used to distinguish defects in DNA synthesis itself from those predominantly affecting other aspects of DNA replication. All cell mutants supported human adenovirus type 2 (Ad2) and mouse polyomavirus DNA synthesis at the permissive temperature. Five of the nine mutants (JB3-B, JB3-O, JB7-K, JB8-D, and JB11-J) restricted polyomavirus DNA replication upon transfection with viral sequences at 33 degrees C and subsequent shift to 39 degrees C either before or after the onset of viral DNA synthesis. Only one of these mutants (JB3-B) also restricted Ad2 DNA synthesis after virion infection under comparable conditions. No mutant was both restrictive for Ad2 and permissive for polyomavirus DNA synthesis at 39 degrees C. The differential effect of these cell mutants on viral DNA synthesis is expected to assist subsequent definition of the biochemical defect responsible.

Effect of adenovirus infection on expression of human histone genes

The influence of adenovirus type 2 infection of HeLa cells upon expression of human histone genes was examined as a function of the period of infection. Histone RNA synthesis was assayed after run-off transcription in nuclei isolated from mock-infected cells and after various periods of adenovirus infection. Histone protein synthesis was measured by [3H]leucine labeling of intact cells and fluorography of electrophoretically fractionated nuclear and cytoplasmic proteins. The cellular representation of RNA species complementary to more than 13 different human histone genes was determined by RNA blot analysis of total cellular, nuclear or cytoplasmic RNA by using a series of 32P-labeled cloned human histone genes as hybridization probes and also by analysis of 3H-labeled histone mRNA species synthesized in intact cells. By 18 h after infection, HeLa cell DNA synthesis and all parameters of histone gene expression, including transcription and the nuclear and cytoplasmic concentrations of core and H1 mRNA species, were reduced to less than 5 to 10% of the control values. By contrast, transcription and processing of other cellular mRNA sequences have been shown to continue throughout this period of infection. The early period of adenovirus infection was marked by an inhibition of transcription of histone genes that accompanied the reduction in rate of HeLa cell DNA synthesis. These results suggest that the adenovirus-induced inhibition of histone gene expression is mediated in part at the transcriptional level. However, the persistence of histone mRNA species at concentrations comparable to those of mock-infected control cells during the early phase of the infection, despite a reduction in histone gene transcription and histone protein synthesis, implies that histone gene expression is also regulated post-transcriptionally in adenovirus-infected cells. These results suggest that the tight coupling between histone mRNA concentrations and the rate of cellular DNA synthesis, observed when DNA replication is inhibited by a variety of drugs, is not maintained after adenovirus infection.

Effect of adenovirus infection on expression of human histone genes

The influence of adenovirus type 2 infection of HeLa cells upon expression of human histone genes was examined as a function of the period of infection. Histone RNA synthesis was assayed after run-off transcription in nuclei isolated from mock-infected cells and after various periods of adenovirus infection. Histone protein synthesis was measured by [3H]leucine labeling of intact cells and fluorography of electrophoretically fractionated nuclear and cytoplasmic proteins. The cellular representation of RNA species complementary to more than 13 different human histone genes was determined by RNA blot analysis of total cellular, nuclear or cytoplasmic RNA by using a series of 32P-labeled cloned human histone genes as hybridization probes and also by analysis of 3H-labeled histone mRNA species synthesized in intact cells. By 18 h after infection, HeLa cell DNA synthesis and all parameters of histone gene expression, including transcription and the nuclear and cytoplasmic concentrations of core and H1 mRNA species, were reduced to less than 5 to 10% of the control values. By contrast, transcription and processing of other cellular mRNA sequences have been shown to continue throughout this period of infection. The early period of adenovirus infection was marked by an inhibition of transcription of histone genes that accompanied the reduction in rate of HeLa cell DNA synthesis. These results suggest that the adenovirus-induced inhibition of histone gene expression is mediated in part at the transcriptional level. However, the persistence of histone mRNA species at concentrations comparable to those of mock-infected control cells during the early phase of the infection, despite a reduction in histone gene transcription and histone protein synthesis, implies that histone gene expression is also regulated post-transcriptionally in adenovirus-infected cells. These results suggest that the tight coupling between histone mRNA concentrations and the rate of cellular DNA synthesis, observed when DNA replication is inhibited by a variety of drugs, is not maintained after adenovirus infection.

Ionic and nonionic interactions in adenoviral nucleoprotein complexes

Ionic and nonionic interactions between the adenoviral histone-like proteins and DNA were examined by determining effects of ionic strength and urea concentration on disruption of viral nucleoprotein. The viral proteins were as susceptible to dissociation by salt in the presence of urea as histones. Nonionic interactions between viral proteins appeared more extensive than those between histones.

Analysis of expression of adenovirus DNA (fragments) by microinjection in Xenopus oocytes. Independent synthesis of minor early region 2 proteins

Injection of whole adenovirus DNA into Xenopus oocytes results in the synthesis of large amounts of the early region 2A DNA-binding protein (E2A-DBP) and smaller amounts of polypeptide IX. The lack of synthesis of any functional messenger RNAs transcribed from the major late promotor at 16.3 map units is remarkable. Cleavage of the adenovirus DNA outside the E2A gene proper by restriction enzymes decreases synthesis of the DBP to about 10% of the amount produced after injection of intact DNA. On the other hand, presence of the terminal (Bellett) protein on the injected template enhances DBP synthesis considerably. Experiments with injected DNA restriction fragments, as well as reconstructed genes cloned into pBR322, indicate that efficient synthesis of DBP in oocytes requires the presence of either or both of the two main promoters from which the E2A gene is transcribed plus an intact 3' end of the gene. In the absence of any known promotor, 100-fold lower amounts of otherwise normal DBP are produced. Unlike in a regular infection, synthesis of DBP in oocytes does not require the product of the E1A gene. The same series of experiments also demonstrates that the DBP, a phosphoprotein, is the substrate of a cellular rather than a virus-encoded protein kinase. Two minor E2A proteins, although colinear with the major DBP, are synthesized independently. Synthesis of a 44,000 Mr protein, probably corresponding to the carboxy-terminal 360 amino acid residues of the DBP, is not decreased after injection of "promotorless" E2A genes. Unlike the 44,000 Mr protein, production of a 67,000 Mr protein (carboxy-terminal 483 amino acid residues) by one DNA-construct is probably directed by a T-A-T-A-A-A-T-A sequence in the vector DNA.

Adenovirus core protein synthesis in the absence of viral DNA synthesis late in infection

The acid extraction of the adenovirus type 5 core proteins V, VII, and pVII (the precursor to VII) from infected cells and the subsequent electrophoresis on a 15% acrylamide-2.5 M urea-0.9 N acetic acid (pH 2.7) gel, revealed that peptide VII has a similar electrophoretic mobility to that of histone H1. The core proteins, which are coded by late adenovirus mRNA, continued to be synthesized late in infection when viral DNA synthesis was inhibited either by cytosine arabinoside in wild-type infections or by shifting adenovirus H5 ts 125-infected cells to the nonpermissive temperature (40 degree C). Only the initiation, not the continuation, of viral DNA replication was essential for core protein synthesis. The synthesis of viral core proteins continued for over 8 h after the cassation of DNA synthesis. This was in contrast to the rapid shutdown of cellular histone synthesis in the absence of cellular DNA synthesis.

Uptake and early fate of metaphase chromosomes ingested by the Wi-L2 human lymphoid cell line

Aspects of the ingestion and early intracellular fate of homologous. [3H]-thymidine-labeled chromosomes (donor) were studied in recipient Wi-L2 cells in the absence of reutilized radioactivity. As much as 67% of the cell-associated radioactivity was resistant to hydrolysis by DNase I after 4 h of incubation. Cell fractionation and electron microscope autoradiography indicated that chromosome uptake was rapid, into both cytoplasmic and nuclear fractions and was facilitator and dose dependent. Sedimentation analysis demonstrated that at 4 h donor DNA of approximate single-strand mol wt of 1--6 X 10(6), as compared to 6--12 X 10(6) for chromosomal DNA, was recoverable in cell fractions. By 6 h, a significant portion of the nucleus-associated donor DNA was converted into material of higher mol wt, although no evidence was found for integration into recipient DNA. Cytoplasmic donor DNA continued to be degraded. An average number of chromosome equivalents of nucleus-associated donor DNA to recipient cell nuclei of 1--4 was obtained and its relationship to the lower frequency of chromosome-mediated gene transfer is discussed.

Mitochondrial DNA synthesis in adenovirus type 2-infected HeLa cells

Mitochondrial DNA synthesis in adenovirus type 2-infected HeLa cells was measured at various times from 0 to 24 h postinfection. Although viral infection effectively turned off host chromosomal DNA synthesis, mitochondrial DNA synthesis was not inhibited. These findings indicate a dissociation between the regulation of host and mitochondrial DNA synthesis after infection with adenovirus type 2.

Nuclear matrix of HeLa S3 cells. Polypeptide composition during adenovirus infection and in phases of the cell cycle

A subnuclear fraction has been isolated from HeLa S3 nuclei after treatment with high salt buffer, deoxyribonuclease, and dithiothreitol. This fraction retains the approximate size and shape of nuclei and resembles the nuclear matrix recently isolated from rat liver nuclei. Ultrastructural and biochemical analyses indicate that this structure consists of nonmembranous elements as well as some membranous elements. Its chemical composition is 87% protein, 12% phospholipid, 1% DNA, and 0.1% RNA by weight. The protein constituents are resolved in SDS-polyacrylamide slab gels into 30-35 distinguishable bands in the apparent molecular weight range of 14,000 - 200,000 with major peptides at 14,000 - 18,000 and 45,000 - 75,000. Analysis of newly synthesized polypeptides by cylindrical gel electrophoresis reveals another cluster in the 90,000-130,000 molecular weight range. Infection with adenovirus results in an altered polypeptide profile. Additional polypeptides with apparent molecular weights of 21,000, 23,000, and 92,000 become major components by 22 h after infection. Concomitantly, some peptides in the 45,000-75,000 mol wt range become less prominent. In synchronized cells the relative staining capacity of the six bands in the 45,000-75,000 mol wt range changes during the cell cycle. Synthesis of at least some matrix polypeptides occures in all phases of the cell cycle, although there is decreased synthesis in late S/G2. In the absence of protein synthesis after cell division, at least some polypeptides in the 45,000-75,000 mol wt range survive nuclear dispersal and subsequent reformation during mitosis. The possible significance of this subnuclear structure with regard to structure-function relationships within the nucleus during virus replication and during the life cycle of the cell is discussed.

Characterization of adenovirus type 2 transcriptional complexes isolated from infected HeLa cell nuclei

HeLa cell nuclei, isolated 17 h after infection with human adenovirus type 2 (Ad2), were treated with 200 mM ammonium sulfate. The extract (S200 fraction) contained 50 to 70% of the nonintegrated Ad2 DNA, which was in the form of nucleoprotein complexes. These complexes contained native, intact Ad2 DNA (with the exception of replicative intermediates) and could be partially purified and resolved by velocity gradient centrifugation. Using high-salt (200 mM ammonium sulfate) incubation conditions, more than 95% of the nuclear RNA polymerase activity belonged to class B. About 45% of the class B enzyme molecules bound to DNA in the nuclei (those "engaged" in RNA synthesis) were released from the nuclei in the form of Ad2 transcriptional complexes by treatment with 200 mM ammonium sulfate. At least 90% of the RNA synthesized in high salt in the nuclei or in the S200 fraction was Ad2 specific, and essentially all of this RNA was complementary to the l strand of Ad2 DNA. These findings are compatible with what is known about Ad2-specific RNA synthesis in vivo. The analysis of the RNA synthesized from partially purified transcriptional complexes supports the contention that its transcription is almost entirely asymmetric, and that the asymmetry observed in vivo is not a consequence of the rapid degradation of h-strand transcripts. The RNA synthesized in vitro in the absence of detectable RNase activity sedimented with a maximum size of 35 to 40S. Less than 5% of the nuclear or the S200 fraction RNA polymerase activity was class C when assayed under non-reinitiating conditions. Although much of the RNA synthesized by the class C enzyme was Ad2 specific, 5.5S virus-associated RNA was not the predominant product. The isolation of Ad2 DNA transcriptional complexes provides an attractive system for further characterizing the Ad2 DNA template used for transcription and for studying the regulation of the expression of the Ad2 genome during the productive infection cycle.

Temperature-sensitive cell mutations that inhibit adenovirus 2 replication

Five temperature-sensitive growth mutants of the hamster cell line BHK-21 were tested for the ability to support adenovirus 2 multiplication at 39 degrees and 33 degrees. Wild-type BHK-21 and mutants ts 422E and ts BCH yielded comparable amounts of virus at 33 degrees and 39 degrees, whereas in three other mutants, ts T22, ts T23, and ts AF8, virus production at 39 degrees was reduced to about 1% of that at 33 degrees. Virus yield in the three mutants was not reduced because of a delay in virus production; for all cells tested maximal virus yield at 39 degrees was obtained by 40-50 hr after infection. Normal yields of infectious virus were not obtained from ts AF8 even with a very high multiplicity of infection. In contrast, the virus yield from ts T22 and ts T23 was multiplicity-dependent. Shiftup experiments demonstrated that in ts AF8, a cell cycle mutant which at 39 degrees becomes arrested in G1, virus multiplication was thermosensitive for the first 40 hr of infection. In ts T22 and ts T23, the thermosensitivity was only for the first 3-4 hr of the infection. In all three mutants viral DNA synthesis was reduced by at least 95% at the higher temperature. The cell function specified by the ts AF8 mutation seems to be required for the early period of adenovirus 2 replication, after virus entry into the cell but before the onset of viral DNA replication.

Adenovirus messenger RNA in mammalian cells: failure of polyribosome association in the absence of nuclear cleavage

The nuclear synthesis of adenovirus-specific RNA late in the infectious cycle in the presence of toyocamycin (an adenosine analogue) has been investigated. There is reduced synthesis of viral RNA with an accumulation of virus-specific RNA in the molecular weight range of at least 4 to 8 x 10(6). No new viral RNA associates with cytoplasmic polyribosomes. In addition, hybridization competition experiments indicate a 70% competition between these large nuclear transcripts and polyribosome-associated viral RNA that was synthesized in the absence of inhibitor. These data are consistent with the following interpretations: complete nuclear processing of viral RNA is necessary for polyribosome association, and precursor viral message(s) contain sequences that are lost normally during post-transcriptional processing.