Production and characteristics of seven rat embryo cell lines transformed by adenovirus type 5 and its DNA

Seven cell lines transformed by adenovirus type 5 and its DNA were obtained. It was shown that different cell lines contain the fragments of viral DNA which differ in length and number of copies per DNA of diploid cells. They contain from the left end 6% of the viral DNA to complete or almost complete viral genome. All studied cell lines were sensitive to reinfection with adenovirus type 5. They produced no virus being cocultivated with cell sensitive to the virus. No cell line was able to induce tumors even in immunosuppressed newborn rats. All cell lines formed colonies in soft agar. The level of virus-specific antigens was higher in cells that contained a large part of the viral genome. The methods used did not allow to correlate the biological properties of the transformed cells with the length and the number of copies of the integrated part of the viral genome.     

Transformation of rat cells by cyt mutants of adenovirus type 12 and mutants of adenovirus type 5.

Several mutants with much reduced oncogenicity (spontaneous mutants H12 cyt 52 and H12 cyt 70 and UV-induced mutants H12 cyt 61, H12 cyt 62, and H12 cyt 68) of the highly oncogenic adenovirus type 12 (Ad12) were studied for their ability to transform primary baby rat kidney cells. Four of the mutants showed much reduced capacity to transform cells in vitro, while H12 cyt 61 transformed cells as efficiently as the wild-type virus. Viral gene expression in several cell lines established from cultures infected by cyt mutants was studied, and it was found that viral sequences belonging to the left 16% of Ad12 were always transcribed. These results suggest that the function of the transformed state is not defective in the cyt mutants studied. Heterotypic complementation studies showed that the defect(s) in a cyt mutant can be corrected by an Ad7 function. Ad5 dl 313, with a deletion between 3.5 and 10.5 map units, transformed rat cells only at high multiplicity. These results suggest that the region E1B of adenoviruses may be required for efficient transformation of rat cells.     

Isolation of adenovirus type 5 host range deletion mutants defective for transformation of rat embryo cells.

A series of adenovirus type 5 (Ad5) deletion, insertion and substitution mutants, some of which are defective for transformation of rat cells, have been isolated. The mutants were selected as variants which lack the Xba I endonuclease cleavage site at 4 map units on the viral chromosome. The deletions range in size from 150-2300 bp and are located between 1.5 and 10.5 map units. The mutants can be propagated in 293 cells (Ad5-transformed human embryonic kidney cells), but are defective for growth in HeLa or human embryonic kidney cells. No viral DNA synthesis was observed in mutant virus-infected HeLa cells. All but one of the deletion mutants tested were defective for transformation of rat embryo and rat embryo brain cells.     

In vitro synthesis of adenovirus type 5 T antigens. II. Translation of virus-specific RNA from cells transformed by fragments of adenovirus type 5 DNA.

Virus-specific cytoplasmic RNA was isolated from rat cell lines transformed by fragments of adenovirus type 5 DNA, and the RNAs were translated in cell-free systems derived from wheat germ or rabbit reticulocytes. RNA was isolated from cell lines transformed by the following fragments: XhoI-C (leftmost 15.5%), HindIII-G (leftmost 8%), and HpaI-E (leftmost 4.5%). In addition, the adenovirus type 5-transformed human embryonic kidney line 293.C31 was investigated. The products were immunoprecipitated with serum from tumor-bearing hamsters and analyzed by electrophoresis in sodium dodecyl sulfate-polyacrylamide gels. The results show that all transformed cells investigated contain early region 1a-specific RNAs which can be translated into proteins with molecular weights of 34,000 (34K), 36K, 40K, and 42K. Transformed cells that also contain an intact early region 1b synthesized RNA which can be translated into proteins with molecular weights of 19K and 65K. Minor proteins of 15K, 16K, 17.5K, 18K, 25K, and 29K were also observed, but these proteins could not be mapped unambiguously. Cells transformed by the 8% HindIII-G apparently lack RNA encoding the 65K protein, but they do contain RNA coding for the 19K protein.     

Integration and expression of viral DNA in cells transformed by host range mutants of adenovirus type 5.

Group I host range (hr) mutants of adenovirus type 5 are unable to transform rat embryo or rat embryo brain cells but induce an abnormal transformation of baby rat kidney cells. We established several transformed rat kidney cell lines and characterized them with respect to the transformed phenotype and the structure of the integrated viral DNA. The hr mutant-transformed cells, unlike wild-type virus transformants, were fibroblastic rather than epithelial, failed to grow in soft agar, and were also less tumorigenic in nude mice. Studies on the structure of the integrated viral DNA sequences showed that hr-transformed cells always contained the left end of the adenovirus DNA, but the size of the integrated DNA fragment varied among different lines, and a high percentage of the lines contained the entire viral genome colinearly integrated. The patterns of integration were maintained after prolonged growth in culture and after subcloning. Attempts to rescue infectious virus from lines which contained the entire genome were unsuccessful. Using immunoprecipitation and sodium dodecyl sulfate-polyacrylamide gel electrophoresis, we analyzed the viral proteins expressed in hr-transformed cells. Results of these studies indicated that, like wild type-transformed cells, hr transformants expressed E1B proteins of molecular weight 58,000 and 19,000.     

Transforming DNA sequences in rat cells transformed by DNA fragments of highly oncogenic human adenovirus type 12.

Rat cell lines tranformed by viral DNA fragments, EcoRI-C and HindIII-G, of adenovirus type 12 DNA were analyzed for the viral transforming DNA sequences present in cell DNAs. Cell lines transformed by the EcoRI-C fragment of adenovirus type 12 DNA (leftmost 16.5% of the viral genome) contain most of the HindIII-G sequences of the HindIII-G fragment, but at a different frequency depending on the portions of the fragment. The sequence of the AccI-H fragment of adenovirus type 12 DNA (the left part of the HindIII-G; leftmost 4.5% of the viral genome) was detected dominantly in cells transformed by the HindIII-G fragment Southern blot analysis showed that viral DNA sequences are present at multiple integration sites in high-molecular-weight cell DNA from cells transformed by the EcoRI-C or HindIII-G fragment of adenovirus type 12 DNA. These results suggest that most of the HindIII-G sequences in cells transformed by the HindIII-G fragment are present as fragmented forms.     

Cells transformed by adenovirus type 12 but not by type 5 are dependent on insulin or insulin-like growth factor I for their proliferation

We have investigated the responsiveness to growth factors (GFs) of primary baby rat kidney (BRK) cells transformed by the E1 region of adenovirus 5 or 12. The in vitro growth of non-oncogenic adenovirus 5-transformed BRK cells is largely independent of serum GFs, whereas growth of highly oncogenic adenovirus 12-transformed cells is strictly dependent on GFs present in serum. For the growth of adenovirus 12 E1-transformed BRK cells serum can be replaced by insulin or insulin-like growth factor-I but not by epidermal growth factor. To maintain the in vitro growth of adenovirus 12-transformed cells physiological levels of insulin-like growth factor-I, but not of insulin, are sufficient. Similar results have been found with adenovirus-transformed primary murine cells and with transformants of an established rat cell line, NRK 49F. This indicates that the observed GF responsiveness is not dependent of the cell type used but is determined by the serotype of the adenovirus-transforming region. Using hybrid E1 regions consisting of E1A of one serotype and E1B of the other, we show that the pattern of GF-responsiveness correlates with the origin of the E1A region. The differences in the GF-responsiveness of the adenovirus 5-transformed and adenovirus 12-transformed cells will be discussed in terms of the oncogenicity of these cells.     

Mutations in the E1a gene of type 5 adenovirus result in oncogenic transformation of Fischer rat embryo cells

Transformation of a specific clone of Fischer rat embryo (CREF) cells with wild-type 5 adenovirus (Ad5) or the E1a plus E1b transforming gene regions of Ad5 results in epithelioid transformants that grow efficiently in agar but that do not induce tumors when inoculated into nude mice or syngeneic Fischer rats. In contrast, CREF cells transformed by a host-range Ad5 mutant, H5hrl, which contains a single base-pair deletion of nucleotide 1055 in E1a resulting in a 28-kd protein (calculated) in place of the wild-type 51-kd acidic protein, display a cold-sensitive transformation phenotype and an incomplete fibroblastic morphology but surprisingly do induce tumors in nude mice and syngeneic rats. Tumors develop in both types of animals following injection of CREF cells transformed by other cold-sensitive Ad5 E1a mutants (H5dl101 and H5in106), which contain alterations in their 13S mRNA and consequently truncated 289AA proteins. CREF cells transformed with only the E1a gene (0-4.5 m.u.) from H5hrl or H5dl101 also produce tumors in these animals. To directly determine the role of the 13S E1a encoded 289AA protein and the 12S E1a encoded 243AA protein in initiating an oncogenic phenotype in adenovirus-transformed CREF cells, we generated transformed cell lines following infection with the Ad2 mutant pm975, which synthesizes the 289AA E1a protein but not the 243AA protein, and the Ad5 mutant H5dl520 and the Ad2 mutant H2dl1500, which do not produce the 289AA E1a protein but synthesize the normal 243AA E1a protein. All three types of mutant adenovirus-transformed CREF cells induced tumors in nude mice and syngeneic rats. Tumor formation by these mutant adenovirus-transformed CREF cells was not associated with changes in the arrangement of integrated adenovirus DNA or in the expression of adenovirus early genes. These results indicate, therefore, that oncogenic transformation of CREF cells can occur in the presence of a wild-type 13S E1a protein or a wild-type 12S E1a protein when either protein is present alone, but does not occur when both wild-type E1a proteins are present.     

Reduced microfilament organization in adenovirus type 5-infected rat embryo cells: a function of early region 1a.

The actin microfilament organization in rat embryo cells was examined by fluorescence microscopy with 7-nitrobenz-2-oxa-1,3-diazole-phallacidin and by electron microscopy, after mock infection or infection with adenovirus type 5 (Ad5). Infected cells showed severely reduced numbers of actin microfilaments and stress fibers, detectable early after infection. Mutants defective in Ad5 early genes were used to show that reduced microfilament organization was a function of the Ad5 transformation early gene 1a (E1a) and did not require expression of any other viral gene. The product of the E1a 13s mRNA was essential for the effect, although the 12s mRNA product appeared to contribute. Ad5 infection of the cells had no observable effect on total cell actin levels or on the ratio of monomeric to polymeric actin. E1a, therefore, affected only the higher-order organization of actin.     

Amount of viral DNA in the genome of cells transformed by adenovirus type 2

The number of copies of viral DNA in DNA of cells transformed by adenovirus type 2 has been determined by following the kinetics of reassociation of ³²P-labeled viral DNA in the presence of unlabeled DNA extracted from transformed and control cells. There is close to one copy of adenovirus 2 DNA for every diploid quantity of cell DNA.     

Unique species of mRNA from adenovirus type 7 early region 1 in cells transformed by adenovirus type 7 DNA fragment.

Adenovirus type 7 (Ad7) early region 1 mRNA species transcribed in rat cell lines transformed by the HindIII-I . J fragment (the left 7.8% of the viral genome) and in human KB cells infected with Ad7 were mapped on the viral genome, using S1 nuclease gel and diazobenzyloxymethyl paper hybridization techniques. At the early stage of productive infection, two mRNA's (950 and 840 nucleotides long) with the common 5' and 3' ends but different internal splicings were mapped from region 1A (map units 1.4 to 4.3), and one mRNA (2,310 nucleotides long, with the internal splicing between map units 9.9 to 10.1) was mapped from region 1B (map units 4.6 to 11.4). At the late stage, these early spliced mRNA's were also found and at least three additional Ad7 mRNA's were identified: 700-nucleotide-long mRNA in region 1A; and 1,100- and nucleotide-long mRNA's in region 1B. In transformed rat cell lines, two early region 1A mRNA's (950 and 840 nucleotides long) were also transcribed. Surprisingly, in addition, several unique Ad7 mRNA's, not found in productivity infected cells, were identified in all of the transformed cell lines. Their molecular sizes and coding sequences varied in individual cell lines. However, these mRNA's had the 5' end-proximal portion in region 1B and the 3' end-proximal portion in region 1A, these portions being transcribed by extending from region 1B to 1A on viral DNA fragments joined in a tandem array in transformed cells.     

Gangliosides of chemically and virally transformed rat embryo cells.

The gangliosides of control rat embryo cells, 3-methylcholanthrene, Rauscher leukemia virus, and combined 3-methylcholanthrene-Rauscher leukemia virus transformants were examined using [14 C]glucosamine as a tracer. All four cell lines exhibited a complex pattern of gangliosides. While N-acetylgalactosaminyl-(N-acetylneuraminyl)-galactosyl-glucosyl-ceramide was the major ganglioside in the control cell line, N-acetylneuraminyl-galactosyl-glucosyl-ceramide was the major ganglioside in the three transformants. The 3-methylcholanthrene transformant possessed a ganglioside pattern different from that of the Rauscher leukemia virus transformant. Hydrolysis of the gangliosides indicated that galactosamine, N-acetyl-and N-glycolylneuraminic acid were the labeled components in all cell lines.     

Viral DNA sequences and gene products in hamster cells transformed by adenovirus type 2.

Complementary strand-specific adenovirus DNA of full length or from endonuclease BamHI fragments was used as a probe to estimate the fractional representation and abundance of viral sequences in five hamster cell lines (Ad2HE1-5) transformed with UV-inactivated adenovirus type 2. The fraction of the viral genome present in the five transformed cell lines varied from 44% in the Ad2HE5 cell line to 84% in the Ad2HE3 cell line. The number of viral DNA copies per diploid cell equivalent ranged from 1.8 in the Ad2HE1 line to 7.1 in the Ad2HE4 line. In vivo labeling with [35S]methionine followed by immunoprecipitation with an antiserum against adenovirus type 2 early proteins revealed virus-specific polypeptides with molecular weights of 42,000 to 58,000 in extracts from all five hamster cell lines. Several other early viral polypeptides were detected in some of the adenovirus type 2-transformed hamster cell lines.     

Acceleration of transformation of rat embryo cells by rat type C virus.

Sprague-Dawley and Fischer rat embryo cells became spontaneously transformed about 20 passages after release of endogenous ecotropic type C virus (SD-RaLV and F-RaLV). The virus-producing transformed cells showed loss of contact inhibition, increased growth rate, and tumorigenicity in vivo. Exogenous infection of other Fischer rat embryo cultures in early passage with SD-RaLV and F-RaLV markedly accelerated their rates of transformation.     

Inactivation of adenovirus type 5 by caustics

Adenovirus shows significant promise as a vehicle for transfer of therapeutic genes into humans. Based on the importance of this viral vector, it is critical that adequate decontamination procedures are implemented during its large-scale production in multiproduct manufacturing facilities to prevent cross-product contamination and to reduce the risk of personnel exposure. Liquid decontamination procedures based on caustics are easily implemented in a manufacturing setting and are not corrosive to stainless steel surfaces at the concentrations found to inactivate viral proteins and nucleic acids. In this study, we have conducted small-scale experiments to determine the effectiveness of caustic inactivation procedures on adenovirus type 5 and have evaluated the robustness of the process to different sample matrices and adenovirus constructs. We find that the pH of a sample post-addition of caustic solution is a more accurate indicator of the effectiveness of the caustic than its concentration. We have demonstrated that a greater than 6 log reduction in the potency of adenovirus type 5 may be obtained upon exposure of the sample to sodium hydroxide and CIP-100 at concentrations greater than 0.09 M and 0.9%, respectively, at times greater than 10 min.