Restriction of human adenovirus replication in Chinese hamster cell lines and their hybrids with human cells

A mouse mammary epithelial cell line permissive for highly efficient human adenovirus growth

Although a few immunocompetent animal models to study the immune response against human adenoviruses (HAdV) are available, such as Syrian hamsters and cotton rats, HAdV replication is several logs lower compared to human control cells. We have identified a non-transformed mouse epithelial cell line (NMuMG) where HAdV-2 gene expression and progeny formation was as efficient as in the highly permissive human A549 cells. HAdV from species, D and E (HAdV-37 and HAdV-4, respectively) also caused a rapid cytopathic effect in NMuMG cells, while HAdV from species A, B1, B2 and F (HAdV-12, HAdV-3, HAdV-11 and HAdV-41, respectively) failed to do so. NMuMG cells might therefore be useful in virotherapy research and the analysis of antiviral defense mechanisms and the determination of toxicity, biodistribution and specific antitumour activity of oncolytic HAdV vectors.

Transient overexpression of κ and μ opioid receptors using recombinant adenovirus vectors

In order to study the trafficking and signal transduction mechanisms of the multiple opioid receptors, these receptors are expressed either transiently or stably in cell lines. Often, it is difficult to express receptors at a sufficiently high density to obtain reproducible results. To achieve a high density of receptors, replication-defective adenovirus (rAd5) vectors encoding the mu (MOR) and kappa (KOR) opioid receptors, both in their native form and as fusion proteins bearing the green fluorescent protein (GFP) at their C-terminus, were constructed. These vectors efficiently and reproducibly infected Chinese hamster ovary (CHO) cells that stably express the human coxsackie-adenovirus receptor (hCAR), with up to 90% of cells becoming infected at a low multiplicity of infection (MOI). Saturation receptor binding studies using mu- and kappa-selective agonists, [3H][D-Ala2, N-Me-Phe4, Gly5-ol]enkephalin (DAMGO) and [3H](5alpha7alpha,8beta)-(-)-N-methyl-N-(7-(1-pyrrolidinyl)-1-oxaspiro(4,5)dec-8-yl)benzeneacetamide (U69,593), respectively, and a nonselective antagonist, [3H]diprenorphine, revealed that rAd5-transduced cells expressed MOR and KOR for at least 3 days, at levels which exceeded those present on widely-used CHO sublines that stably express MOR or KOR. Expression levels were highest for the vectors encoding native MOR or KOR, and slightly reduced for the GFP fusion proteins. These findings demonstrate the feasibility of using rAd5 vectors to express opioid receptors at high densities, which may facilitate opioid receptor studies.

An activity associated with human chromosome 21 permits nuclear colocalization of the adenovirus E1B-55K and E4orf6 proteins and promotes viral late gene expression

The adenovirus E1B-55K and E4orf6 proteins cooperate during virus infection while performing several tasks that contribute to a productive infection, including the selective nucleocytoplasmic transport of late viral mRNA. Previous studies have shown that the E4orf6 protein retains the E1B-55K protein in the nucleus of human and monkey cells, but not in those of rodents, suggesting that primate-specific cellular factors contribute to the E4orf6-mediated retention of the E1B-55K protein in the nucleus. In an effort to identify these proposed primate-specific cellular factors, the interaction of the E1B-55K and E4orf6 proteins was studied in a panel of stable human-rodent monochromosomal somatic cell hybrids. Analysis of this panel of cell lines has demonstrated the existence of an activity associated with human chromosome 21 that permits the E1B-55K and E4orf6 proteins to colocalize in the nucleus of a rodent cell. Additional hybrid cells bearing portions of human chromosome 21 were used to map this activity to a 10-megabase-pair segment of the chromosome, extending from 21q22.12 to a region near the q terminus. Strikingly, this region also facilitates the expression of adenovirus late genes in a rodent cell background while having little impact on the expression of early viral genes.

Two closely related adenovirus genome types with kidney or respiratory tract tropism differ in their binding to epithelial cells of various origins

The host cell interactions of the genome types Ad11p and Ad11a of human adenovirus serotype 11, displaying kidney or respiratory tropism, were compared using FACS analysis. Kinetic experiments indicated that the virus binding stated immediately and reached a plateau after 30 min. The binding of biotinylated virions to seven continuous cell lines. A549, A498, J82, HeLa, CHO, MDCK, and human diploid fibroblasts (HEDF), was quantitated by FACS analysis. The binding capacities of the two viruses to all human cell lines but A549 cells appeared to differ. Ad11p virions manifested high affinities, whereas Ad11a virions presented low affinities. Neither of the two viruses bound to CHO or MDCK cells. Reciprocal competition experiments showed that the Ad11a virions could be weakly blocked by the Ad11p virions, whereas the Ad11p virions could not be competed at all by the Ad11a virions. The binding of the Ad11p virions to cells could be blocked by the rfiber antiserum of Ad11p, but not by the corresponding antiserum against Ad11a or Ad35p. A comparison of the cytopathogenicity of the seven cell lines infected by Ad11p and Ad11a demonstrated that the efficiency of the initial event of an adenovirus infection directly affects the outcome of the viral infection. The Ad11a in the A498, J82, HeLa, or HEDF cells that presented lower affinity and receptor concentration showed 100 times less infectivity than that in A549 cells displaying high affinity and receptor concentration. These results indicate that the cell susceptibility to Ad11p and Ad11a infection strongly depends on both the number of fiber receptors on the host cells and the receptor affinity for ligands on the fiber knob. Our findings also suggest that the receptors for Ad11p and Ad11a on the surface of different cell types may be different or on different sites.

Isolation of a common receptor for Coxsackie B viruses and adenoviruses 2 and 5

A complementary DNA clone has been isolated that encodes a coxsackievirus and adenovirus receptor (CAR). When transfected with CAR complementary DNA, nonpermissive hamster cells became susceptible to coxsackie B virus attachment and infection. Furthermore, consistent with previous studies demonstrating that adenovirus infection depends on attachment of a viral fiber to the target cell, CAR-transfected hamster cells bound adenovirus in a fiber-dependent fashion and showed a 100-fold increase in susceptibility to virus-mediated gene transfer. Identification of CAR as a receptor for these two unrelated and structurally distinct viral pathogens is important for understanding viral pathogenesis and has implications for therapeutic gene delivery with adenovirus vectors.

Adenovirus early region 4 34-kilodalton protein directs the nuclear localization of the early region 1B 55-kilodalton protein in primate cells

The localization of the adenovirus type 5 34-kDa E4 and 55-kDa E1B proteins was determined in the absence of other adenovirus proteins. When expressed by transfection in human, monkey, hamster, rat, and mouse cell lines, the E1B protein was predominantly cytoplasmic and typically was excluded from the nucleus. When expressed by transfection, the E4 protein accumulated in the nucleus. Strikingly, when coexpressed by transfection in human, monkey, or baby hamster kidney cells, the E1B protein colocalized in the nucleus with the E4 protein. A complex of the E4 and E1B proteins was identified by coimmunoprecipitation in transfected HeLa cells. By contrast to the interaction observed in primate and baby hamster kidney cells, the E4 protein failed to direct the E1B protein to the nucleus in rat and mouse cell lines as well as CHO and V79 hamster cell lines. This failure of the E4 protein to direct the nuclear localization of the E1B protein in REF-52 rat cells was overcome by fusion with HeLa cells. Within 4 h of heterokaryon formation and with protein synthesis inhibited, a portion of the E4 protein present in the REF-52 nuclei migrated to the HeLa nuclei. Simultaneously, the previously cytoplasmic E1B protein colocalized with the E4 protein in both human and rat cell nuclei. These results suggest that a primate cell-specific factor mediates the functional interaction of the E1B and E4 proteins of adenovirus.

Integrin alpha v beta 5 selectively promotes adenovirus mediated cell membrane permeabilization

Human adenovirus type 2 (Ad2) enters host cells by receptor-mediated endocytosis, an event mediated by the virus penton base binding to cell surface integrins alpha v beta 3 and alpha v beta 5. While both alpha v integrins promote virus internalization, alpha v beta 5 is involved in the subsequent event of membrane permeabilization. Cells transfected with the beta 5 or beta 3 subunit, expressing either alpha v beta 5 and alpha v beta 3, respectively, were capable of supporting Ad2 infection to varying degrees. In this case, cells expressing alpha v beta 5 were significantly more susceptible to Ad2-induced membrane permeabilization, as well as to Ad2 infection, than cells expressing alpha v beta 3. Adenovirus-mediated gene delivery was also more efficient in cells expressing alpha v beta 5. These results suggest that the interaction of alpha v beta 5 with Ad2 penton base facilitates the subsequent step of virus penetration into the cell. These studies provide evidence for the involvement of a cellular receptor in virus-mediated membrane permeabilization and suggest a novel biological role for integrin alpha v beta 5 in the infectious pathway of a human adenovirus.

Accumulation of p53 in a mutant cell line defective in the ubiquitin pathway

The wild-type p53 gene product plays an important role in the control of cell proliferation, differentiation, and survival. Altered function is frequently associated with changes in p53 stability. We have studied the role of the ubiquitination pathway in the degradation of p53, utilizing a temperature-sensitive mutant, ts20, derived from the mouse cell line BALB/c 3T3. We found that wild-type p53 accumulates markedly because of decreased breakdown when cells are shifted to the restrictive temperature. Introduction of sequences encoding the human ubiquitin-activating enzyme E1 corrects the temperature sensitivity defect in ts20 and prevents accumulation of p53. The data therefore strongly indicate that wild-type p53 is degraded intracellularly by the ubiquitin-mediated proteolytic pathway.

Accumulation of p53 in a mutant cell line defective in the ubiquitin pathway

The wild-type p53 gene product plays an important role in the control of cell proliferation, differentiation, and survival. Altered function is frequently associated with changes in p53 stability. We have studied the role of the ubiquitination pathway in the degradation of p53, utilizing a temperature-sensitive mutant, ts20, derived from the mouse cell line BALB/c 3T3. We found that wild-type p53 accumulates markedly because of decreased breakdown when cells are shifted to the restrictive temperature. Introduction of sequences encoding the human ubiquitin-activating enzyme E1 corrects the temperature sensitivity defect in ts20 and prevents accumulation of p53. The data therefore strongly indicate that wild-type p53 is degraded intracellularly by the ubiquitin-mediated proteolytic pathway.

Retinoblastoma protein and simian virus 40-dependent immortalization of human fibroblasts

Transformation and immortalization of human diploid fibroblasts by simian virus 40 (SV40) is at least a two-stage process, since transformants have a limited lifespan in culture. We have isolated immortalized derivatives (AR5 and HAL) from transformants generated with an origin-defective SV40 genome encoding a heat-labile large T protein (T antigen) and reported that both preimmortal and immortal transformants are continuously dependent on T antigen function for growth as determined by temperature shift experiments. In this study, we demonstrate complex formation between T antigen and the retinoblastoma susceptibility gene product (Rb) at 35 degrees C and observed a reduction in complexes under conditions of loss of T antigen function and growth inhibition at 39 degrees C. Viral oncogenes (polyomavirus large T protein and adenovirus E1A 12S protein) known to bind Rb were introduced into AR5 and HAL cells, both stably by gene transfer and transiently by virus vectors. Such double transformants are still unable to proliferate at 39 degrees C, although complex formation with the newly introduced oncogenes was demonstrated. We suggest that T antigen interacts with other cellular processes in addition to Rb to transform and immortalize human cells in culture. Our finding that p53-T antigen complexes are also temperature dependent in AR5 and HAL cells could provide such an additional mechanism.

Temperature-sensitive DNA mutant of Chinese hamster ovary cells with a thermolabile ribonucleotide reductase activity

JB3-B is a Chinese hamster ovary cell mutant previously shown to be temperature sensitive for DNA replication (J. J. Dermody, B. E. Wojcik, H. Du, and H. L. Ozer, Mol. Cell. Biol. 6:4594-4601, 1986). It was chosen for detailed study because of its novel property of inhibiting both polyomavirus and adenovirus DNA synthesis in a temperature-dependent manner. Pulse-labeling studies demonstrated a defect in the rate of adenovirus DNA synthesis. Measurement of deoxyribonucleoside triphosphate (dNTP) pools as a function of time after shift of uninfected cultures from 33 to 39 degrees C revealed that all four dNTP pools declined at similar rates in extracts prepared either from whole cells or from rapidly isolated nuclei. Ribonucleoside triphosphate pools were unaffected by a temperature shift, ruling out the possibility that the mutation affects nucleoside diphosphokinase. However, ribonucleotide reductase activity, as measured in extracts, declined after cell cultures underwent a temperature shift, in parallel with the decline in dNTP pool sizes. Moreover, the activity of cell extracts was thermolabile in vitro, consistent with the model that the JB3-B mutation affects the structural gene for one of the ribonucleotide reductase subunits. The kinetics of dNTP pool size changes after temperature shift are quite distinct from those reported after inhibition of ribonucleotide reductase with hydroxyurea. An indirect effect on ribonucleotide reductase activity in JB3-B has not been excluded since human sequences other than those encoding the enzyme subunits can correct the temperature-sensitive growth defect in the mutant.

Temperature-sensitive DNA mutant of Chinese hamster ovary cells with a thermolabile ribonucleotide reductase activity

JB3-B is a Chinese hamster ovary cell mutant previously shown to be temperature sensitive for DNA replication (J. J. Dermody, B. E. Wojcik, H. Du, and H. L. Ozer, Mol. Cell. Biol. 6:4594-4601, 1986). It was chosen for detailed study because of its novel property of inhibiting both polyomavirus and adenovirus DNA synthesis in a temperature-dependent manner. Pulse-labeling studies demonstrated a defect in the rate of adenovirus DNA synthesis. Measurement of deoxyribonucleoside triphosphate (dNTP) pools as a function of time after shift of uninfected cultures from 33 to 39 degrees C revealed that all four dNTP pools declined at similar rates in extracts prepared either from whole cells or from rapidly isolated nuclei. Ribonucleoside triphosphate pools were unaffected by a temperature shift, ruling out the possibility that the mutation affects nucleoside diphosphokinase. However, ribonucleotide reductase activity, as measured in extracts, declined after cell cultures underwent a temperature shift, in parallel with the decline in dNTP pool sizes. Moreover, the activity of cell extracts was thermolabile in vitro, consistent with the model that the JB3-B mutation affects the structural gene for one of the ribonucleotide reductase subunits. The kinetics of dNTP pool size changes after temperature shift are quite distinct from those reported after inhibition of ribonucleotide reductase with hydroxyurea. An indirect effect on ribonucleotide reductase activity in JB3-B has not been excluded since human sequences other than those encoding the enzyme subunits can correct the temperature-sensitive growth defect in the mutant.

Growth of immortal simian virus 40 tsA-transformed human fibroblasts is temperature dependent

Simian virus 40 (SV40)-mediated transformation of human fibroblasts offers an experimental system for studying both carcinogenesis and cellular aging, since such transformants show the typical features of altered cellular growth but still have a limited life span in culture and undergo senescence. We have previously demonstrated (D. S. Neufeld, S. Ripley, A. Henderson, and H. L. Ozer, Mol. Cell. Biol. 7:2794-2802, 1987) that transformants generated with origin-defective mutants of SV40 show an increased frequency of overcoming senescence and becoming immortal. To clarify further the role of large T antigen, we have generated immortalized transformants by using origin-defective mutants of SV40 encoding a heat-labile large T antigen (tsA58 transformants). At a temperature permissive for large-T-antigen function (35 degrees C), the cell line AR5 had properties resembling those of cell lines transformed with wild-type SV40. However, the AR5 cells were unable to proliferate or form colonies at temperatures restrictive for large-T-antigen function (39 degrees C), demonstrating a continuous need for large T antigen even in immortalized human fibroblasts. Such immortal temperature-dependent transformants should be useful cell lines for the identification of other cellular or viral gene products that induce cell proliferation in human cells.

Growth of immortal simian virus 40 tsA-transformed human fibroblasts is temperature dependent

Simian virus 40 (SV40)-mediated transformation of human fibroblasts offers an experimental system for studying both carcinogenesis and cellular aging, since such transformants show the typical features of altered cellular growth but still have a limited life span in culture and undergo senescence. We have previously demonstrated (D. S. Neufeld, S. Ripley, A. Henderson, and H. L. Ozer, Mol. Cell. Biol. 7:2794-2802, 1987) that transformants generated with origin-defective mutants of SV40 show an increased frequency of overcoming senescence and becoming immortal. To clarify further the role of large T antigen, we have generated immortalized transformants by using origin-defective mutants of SV40 encoding a heat-labile large T antigen (tsA58 transformants). At a temperature permissive for large-T-antigen function (35 degrees C), the cell line AR5 had properties resembling those of cell lines transformed with wild-type SV40. However, the AR5 cells were unable to proliferate or form colonies at temperatures restrictive for large-T-antigen function (39 degrees C), demonstrating a continuous need for large T antigen even in immortalized human fibroblasts. Such immortal temperature-dependent transformants should be useful cell lines for the identification of other cellular or viral gene products that induce cell proliferation in human cells.