Transformation of rat embryo cells by adenovirus type 1

An ovine adenovirus vector lacks transforming ability in cells that are transformed by AD5 E1A/B sequences

Adenoviruses of the Mastadenovirus and Aviadenovirus genera are able to transform certain cell types and induce tumor formation in susceptible animals. For the mastadenoviruses the E1A/B sequences are largely responsible for these properties but E4 sequences may also be involved. The transforming sequences of the aviadenoviruses, which lack E1A/B and E4 homologues, have not yet been fully identified. The recent proposal for a third genus of adenoviruses, which apparently lack an E1A homologue and have weak E1B homology, prompted an examination of the transforming properties of ovine adenovirus OAV287 (OAV), the prototype member of the new group. When OAV and human adenovirus type 5 (Ad5) were used to infect primary rat embryo cells, transformed foci developed in Ad5- but not in OAV-infected cultures. Similarly, after plasmid transfection, baby rat kidney cells were transformed by Ad5 E1A/B but not by OAV sequences. When CSL503 cells, an ovine cell line that is permissive for OAV, were transfected with Ad5 E1A/B sequences, transformed foci again appeared. However, plasmids or fragments containing complete or partial OAV genome sequences did not detectably transform CSL503 cells under the same conditions. When Ad5 E1A/B sequences were incorporated into the complete OAV genome and transfected, transformed clones were again obtained, showing that the gene dosage and transfection conditions were not limiting for transformation. The provision of Ad5 E1A and OAV sequences in combination marginally increased the number of morphologically altered foci in baby rat kidney cells but failed to induce multilayered focus formation. The data suggest that OAV lacks transforming functions in the cell types examined. Additional information suggesting that OAV may have a fundamentally distinct strategy for replication compared with other Ads is discussed.

Identification of functional domains of adenovirus tumor-specific transplantation antigen in types 5 and 12 by viable viruses carrying chimeric E1A genes

The adenovirus (Ad) E1A gene induces in immunized animals a strong tumor transplantation (TSTA) immunity against Ad tumors. Such immunity with group-A and group-C viruses is highly group-specific and no cross-protection is detected between serotypes 5 and 12. This fact was used to map the domains of the Ad5 and Ad12 E1A gene products, respectively, which control the TSTA. We constructed a library of 8 recombinant viruses (H5sub1101 through H5sub1108) which carry chimeric Ad5/Ad12 E1A genes in the background of Ad5. The chimeric genes are functional and these viruses are viable. Some of these constructs induce strong and highly specific tumor syngraft immunity in immunized rats. The viruses carrying the 5' terminus of the first E1A exon derived from Ad12 (viruses H5sub1101, H5sub1102 and H5sub1103) induce strong protection against Ad12 tumors irrespective of the rest of their E1A sequence. The viruses which carry the second exon of the Ad5 E1A gene (viruses H5sub1101, H5sub1102 and H5sub1106) protect against group-C tumors, regardless of the origin of the rest of their E1A gene. The 2 viruses that carry the 5' E1A terminus of the first exon of Ad12 and the second exon of Ad5 (H5sub1101 and H5sub1102) are thus effective in inducing immunity against Ad12 tumors as well as against Ad2 tumors. The viruses which carry the 5' terminus of the first exon derived from Ad5 and the second exon of Ad12 (H5sub1107 and H5sub 1108) fail to induce immunity against either tumor. Expression of only the truncated 5' terminus of the Ad12 E1A gene (viruses H5sub1104 and H5sub1105) is sufficient for induction of Ad12 TSTA. Our results provide direct and unequivocal in vivo evidence that TSTA activities of adenovirus groups A and C are controlled by different domains of their respective E1A genes. The Ad12 TSTA is a function of the 5' terminus of the first E1A exon, while the Ad5 TSTA is coded for by the 3' exon of its E1A gene.

Dissection of functional domains in the adenovirus 2 early 1B 55K polypeptide by suppressor-linker insertional mutagenesis

To determine whether the viral replication functions of the adenovirus E1B 55K protein play a role in its ability to transform cloned rat embryo fibroblast cells in culture, we constructed an extensive series of insertion mutations throughout the 55K gene. The mutations were recombined into infectious virus and characterized for their abilities to produce stable 55K protein in HeLa cells, replicate virus in HeLa cells, express late viral proteins efficiently, and transform CREF cells following infection. Mutant 55K transforming activity in primary baby rat kidney cells was also assayed following DNA transfection. The functions required for viral replication are encoded in several patches of the 55K linear sequence, while the CREF transforming functions are sensitive to all of the insertions. An insertion at amino acid 380 created a mutant virus which was reduced in transforming activity, but was not reduced for viral replication. Therefore, a function required for efficient transformation of CREF cells can be separated from functions required for late gene expression and viral replication. Transformation of BRK cells following DNA transfection was reduced by complete disruption of the 55K protein gene, but was not significantly affected by any of the insertions.

Cellular protein differences between nontumorigenic Ad5 and tumorigenic Ad12 transformed mouse cells

Murine fibroblasts transformed by adenovirus 12 (Ad12) show reduced class I major histocompatibility complex (MHC) antigen synthesis and form tumors in syngeneic mice whereas those transformed by adenovirus 5 (Ad5) show no alteration in class I antigen synthesis and do not form tumors (K. B. Eager, J. Williams, D. Breiding, S. Pan, B. Knowles, E. Appella, and R. P. Ricciardi (1985) Proc. Natl. Acad. Sci. USA 82, 5525-5529). Nearly 1500 metabolically labeled polypeptides from the Ad5 and Ad12 transformed cell lines as well as polypeptides from a nontransformed murine line of the same haplotype were compared by two-dimensional gel electrophoresis. In addition to the reduction of the class I H-2 transplantation antigens seen in the Ad12-transformed lines, we detect few but reproducible polypeptide differences between the tumorigenic and nontumorigenic cell lines.

Adenovirus tumor-specific transplantation antigen is a function of the E1A early region

Viable recombinant adenoviruses that carry a portion of the type 12 E1A and E1B transcription units in a type 5 background were used to identify genes controlling expression of the adenovirus tumor-specific transplantation antigen (TSTA). The TSTA immunity is not crossreacting between the group A and group C adenovirus serotypes. Viruses carrying the E1A region (sub370-12E1A), or both E1A and E1B (sub370-12E1AB) regions of Ad12, induce a strong transplantation immunity against tumors induced by syngeneic cells transformed with adenovirus 12, but fail to induce any protection against syngeneic cells transformed with adenovirus 2. Immunization with the virus carrying only the E1B region (sub370-12E1B) of adenovirus 12 induces no immunity to adenovirus 12 transformed cell line, but confers a strong protection against cells transformed with adenovirus 2. These results provide strong evidence that the adenovirus tumor-specific transplantation antigen is a function of the E1A early region.

Expression of histocompatibility antigens H-2K, -D, and -L is reduced in adenovirus-12-transformed mouse cells and is restored by interferon gamma

Primary mouse cells transformed by adenovirus type 12 (Ad12) expressed negligible amounts of class I antigens H-2K, -D, and -L on the cell surface and were capable of forming tumors in syngeneic animals, whereas cells transformed by Ad5 continued to express class I antigens and were nontumorigenic. Cells from a tumor, generated by injection of Ad12-transformed mouse cells into a syngeneic mouse, also expressed low levels of H-2 antigens, indicating that this phenotype is maintained in vivo. In all Ad12-transformed cells, synthesis of the H-2 heavy chain was not detected whereas the beta 2-microglobulin light chain was synthesized. Furthermore, the level of cytoplasmic H-2 mRNA in the Ad12 lines was greatly reduced. Reduction of H-2 expression is instructed solely by the transforming region of the viral genome, since this repression occurred in cells transformed by a DNA fragment containing only Ad12 E1A and E1B genes. Addition of recombinant murine interferon gamma strongly stimulated expression of class I antigens in the Ad12 transformants as well as in cells from the Ad12 tumor. This result indicates that Ad12 does not preferentially transform cells that are deficient for class I genes and that Ad12 does not mutate the class I genes in cells it transforms. The correlation between tumorigenicity and loss of H-2 expression in Ad12-transformed cells is discussed.

Oncogenicity by adenovirus is not determined by the transforming region only

We have constructed a nondefective recombinant virus between the nononcogenic adenovirus 5 (Ad5) and the highly oncogenic Ad12. The recombinant genome consists essentially of Ad5 sequences, with the exception of the transforming early region 1 (E1) which is derived from Ad12. HeLa cells infected with the recombinant virus were shown to contain the Ad12-specific E1 proteins of 41 kilodaltons (E1a) and 19 and 54 kilodaltons (both encoded by E1b). The recombinant virus replicated efficiently in human embryonic kidney cells and HeLa cells, showing that the transforming regions of Ad5 and Ad12 had similar functions in productive infection. After the recombinant virus was injected into newborn hamsters, no tumors were produced during an observation period of 200 days. Thus, despite the fact that all products required for oncogenic transformation in vitro were derived from the highly oncogenic Ad12, the recombinant virus did not produce tumors in vivo. These data show that tumor induction by adenovirus virions is not determined only by the gene products of the transforming region.

Construction and characterization of an adenovirus type 5/adenovirus type 12 recombinant virus

We have constructed an adenovirus type 5 (Ad5) recombinant virus in which the early region 1b (E1b) of the nononcogenic Ad5 is replaced by the E1b region of the highly oncogenic Ad12. Analysis of cells lytically infected with the recombinant virus showed that both the Ad5 E1a genes and the Ad12 E1b genes are faithfully expressed. The recombinant virus replicates efficiently in human embryonic kidney cells and in HeLa cells, indicating that the Ad12 E1b region can fully replace the Ad5 E1b region in lytic infection. Inoculation of the Ad5/Ad12 hybrid virus into newborn hamsters did not result in development of tumors. This shows that the E1b region of Ad12, previously shown to be responsible for the high oncogenic potential of Ad12-transformed cells in nude mice is not capable of converting the nononcogenic Ad5 into an oncogenic virus.

Tumorigenicity of cells transformed by adenovirus type 12 by evasion of T-cell immunity

Evidence is presented that cells transformed by adenovirus type 12 are oncogenic because they escape from T-cell immunity. This effect is brought about by reducing the expression of class I transplantation antigens and is a function of the protein translated from the 13S mRNA, transcribed from early region 1a. These findings establish a novel mechanism by which transformed cells can acquire an oncogenic phenotype.

Role of adenovirus types 5 and 12 early region 1b tumor antigens in oncogenic transformation

Recently we have reported that the difference in oncogenic potential between adenovirus type 5 (Ad5)-and Ad12-transformed cells in athymic nude mice is specified by early region 1b. In order to determine which of the two early region 1b (E1b) tumor antigens is responsible for the observed difference in oncogenicity we have constructed two Ad5/Ad12 hybrid plasmids: one allowing expression of the Ad5 19kD and Ad12 54kD E1b proteins, the other of the Ad5 58kD plus Ad12 19kD E1b polypeptides. Both hybrid plasmids contain the intact E1a regions of both serotypes. The chimeric plasmids were used to transform primary cultures of baby rat kidney cells and the resulting transformed cells were tested for oncogenicity in athymic nude mice. It was found that the degree of oncogenicity is determined by the identity of the large E1b tumor antigen. Studies with cells transformed by an Ad12 region E1 plasmid in which the gene coding for the 19kD tumor antigen was mutated showed that expression of this protein is nevertheless required for manifestations of the oncogenic phenotype of the transformed cell.

Analysis of type 5 adenovirus transformation with a cloned rat embryo cell line (CREF)

A recently isolated cloned cell line of Fischer rat embryo fibroblasts (CREF) can be transformed at high frequency by adenovirus serotype 5 (Ad5). The CREF cells display a near diploid karyotype, do not crisscross at confluency, can be maintained at confluency for greater than 7 wk at 36 degrees C, and do not form macroscopic colonies when seeded in agar. Transformed cells are identified by their altered morphology and the presence of adenovirus DNA sequences in the transformants, which can be demonstrated by lysing cells directly on nitrocellulose filters and hybridizing with 32P-labeled Ad5 DNA (spot hybridization). The frequency of transformation at 36 degrees C is approximately equal to 2 x 10(-4) with wild-type Ad5 and approximately equal to 2 x 10(-3) with the temperature-sensitive mutant H5ts125. Southern blot hybridization analysis indicates that five out of six wild-type Ad5- and six out of six H5ts125-transformed CREF clones isolated at 36 degrees C contain the complete integrated Ad5 genome. Preliminary characterization of four transformed clones (two wild-type and two H5ts125) indicates that, even though transformation was done in CREF cells (a clonal cell line), they differ in their biological properties, such as saturation density and anchorage dependence.

Dependence of tumor-forming capacities of cells transformed by recombinants between adenovirus types 5 and 12 on expression of early region 1

Recombinants between an adenovirus type 5 (Ad5) deletion mutant and the Ad12 DNA fragment containing early region 1 (E1) were isolated from cells cotransfected with the EcoRI-C fragment of Ad12 DNA and Ad5 dl312 (deletion in E1A) DNA (rcA) and from cells cotransfected with the SalI-C fragment of Ad12 DNA and Ad5 dl312 DNA (rcB). No recombinant was isolated from cells cotransfected with Ad5 dl313 (deletion in E1B) DNA and restriction fragments of Ad12 DNA. Both rcA and rcB are defective and able to replicate in human embryo kidney (HEK) and KB cells with complementation by dl312. Both rcA and rcB formed Ad12 T antigen g, but not T antigen f, in infected HEK and KB cells. In rcA- and rcB-infected cells, Ad5 E1B and Ad12 E1A genes are transcribed. Heteroduplex and size analyses of rcA-1 or rcB-1 DNA fragments hybridized with Ad12 DNA revealed that rcA-1 DNA has a deletion between 5 and 15 map units with an insertion of a portion of Ad12 DNA (10%) and that rcB-1 DNA has a deletion between 70 and 80 map units with an insertion of a portion of Ad12 DNA (10%). The transformed cell lines, RCAY and RCBY, were established after infection of rat 3Y1 cells with rcA and rcB, respectively. Both Ad5 and Ad12 DNA sequences are contained in these cells. In RCAY cells, Ad12 T antigen g is detected, but Ad12 T antigen f is not. In RCBY cells, both Ad12 T antigen g and f are detected. Only the Ad12 E1A gene is transcribed in RCAY cells, whereas Ad5 E1B, Ad12 E1A, and Ad12 E1B genes are transcribed in RCBY cells. In soft-agar cultures, RCBY cells form large colonies, whereas RCAY cells form only tiny colonies. RCBY cells form tumors as efficiently as 12WY cells in transplanted rats. RCAY cells formed tumors inefficiently. Ad5-transformed 5WY cells do not form tumors. These observations indicate that the efficient tumor formation by RCBY cells is dependent on the expression of the Ad12 E1A and E1B genes, whereas the inefficient tumor formation by RCAY cells is due to the expression of only the Ad12 E1A gene.

Tumorigenicity and in vitro characteristics of rat liver epithelial cells and their adenovirus-transformed derivatives

Cloned and uncloned epithelial cultures were established from the liver of a 3-week-old AS rat. These epithelial cultures were neither tumorigenic nor did they display anchorage-independent growth. One of the clones was cytogenetically normal after 53 in vitro passages (approximately 200 population doublings after cloning). Eight transformed lines were isolated from the liver epithelial cells after infection with adenovirus type 12 (Ad-12). Five of these produced typical Ad12 T-antigen, whereas three appeared to be T-antigen-negative. All were tumorigenic in newborn syngeneic rats. The T-antigen-positive transformed lines produced anaplastic-epithelial tumors, whereas the T-antigen-negative transformed lines produced adenocarcinomas. Although all the transformed lines were tumorigenic, some were fibronectin-positive while others produced no detectable fibronectin. The normal (untransformed) epithelial cells produced fibronectin. These results are interesting for two reasons: (1) there are relatively few reports of fibronectin on epithelial cells and (2) they emphasize the view that there is no absolute correlation between reduced fibronectin and tumorigenicity in transformed cells. The transformed lines displayed in vitro characteristics similar to those of transformants derived from embryonic and fibroblastic cell strains, notably, increased saturation density and changes in cellular morphology. Some of the transformed cell lines, but not all, displayed anchorage-independent growth. All the transformed cell lines were picked from multi-layered foci so that morphological criteria (i.e. piling-up focus) for isolating transformants from the epithelial cultures were similar as in embryonic and fibroblastic transforming cell systems. With the new cell system we have developed we can, using the same epithelial cell line (clone C3), study both virus transformation and virus mutagenesis.

A study of the oncogenicity of adenovirus type 2 transformed rat embryo cells

Rat embryo cells were transformed by adenovirus type 2 at different multiplicities of infection. The oncogenic potential of the resulting transformed lines varied considerably but a relationship was found to exist between transforming virus dose and oncogenicity of the resulting transformed lines. Possible reasons for the considerable variation in oncogenicity of the transformed lines are discussed, giving particular consideration to cellular antigenicity and recent molecular biology studies of adenovirus type 2 transformed cell lines.

Studies of nondefective adenovirus 2-simian virus 40 hybrid viruses. Transformation of hamster kidney cells by adenovirus 2 and the nondefective hybrid viruses

Nonhybrid adenovirus 2 (Ad2) and five nondefective Ad2-simian virus 40 (SV40) hybrids (Ad2(+)ND(1)-Ad2(+)ND(5)) failed to produce tumors when injected into newborn hamsters. However, each of these agents transformed hamster kidney cells in vitro, and the transformed cell lines produced tumors when injected into suckling hamsters. Foci of cells transformed by the hybrids could not be distinguished from foci of cells transformed by nonhybrid Ad2. Histopathologically, tumors induced by the nondefective hybrid-transformed lines were of the adenovirus type with no areas of SV40-type fibrosarcoma. All of the cell lines studied contained Ad2 T antigen and Ad2 RNA. Only the B55HK(1) line contained the three early SV40 antigens, U, TSTA, and T. The ND(4)HK(1) line contained SV40 T and TSTA antigens (the latter antigen being detected only after 48 to 49 tissue culture passages) and SV40 RNA. The ND(2)HK(2) line contained SV40 RNA but no detectable SV40 antigens; the other hybrid-transformed lines contained no SV40 RNA. The transformation of hamster cells by the nondefective Ad2-SV40 hybrids seemed to be caused by the Ad2 genome and could not be attributed to the regions of the SV40 genome contained within the hybrids. Additionally, these results indicate that interactions between the genomes of the nondefective hybrid viruses and the hamster cells they transform are complex and could involve the site of integration, the size of the incorporated viral genome, the transcription or translation of the viral genome, or various combinations of these processes.

The mechanism of viral carcinogenesis by DNA mammalian viruses. VI. A new class of virus-specific RNA molecules in cells transformed by group C human adenoviruses

A new class of virus-specific RNA molecules was found in cells transformed by group C human adenovirus types 2, 5, and 6. RNA isolated from virus-free rat embryo cells transformed by adenovirus 2, 5, and 6 hybridized with all group C adenovirus DNA's (adenovirus 1, 2, 5, and 6) equally well, but not appreciably with group A and B adenovirus DNA's. Most likely no viral genes common to group A, B, and C adenoviruses are transcribed in adenovirus-transformed cells. Group C adenoviruses are closely related since they share 83 to 93 per cent of their base sequences as shown by DNA-DNA homology measurements. Group C DNA's share only 10 to 26 per cent of their base sequences with group A and B DNA's. Moreover, the shared sequences are not transcribed detectably in adenovirus transformed cells.Virus-specific RNA isolated from group C transformed cells contains 49 to 51 per cent G + C, but viral DNA's possess a 7 to 9 per cent higher G + C content. These differences suggest that only a portion of the viral genome with an average G + C content of 49 to 51 per cent is transcribed in group C adenovirus transformed cells.

Ultraviolet inactivation of the cytocidal and transforming activities of human adenovirus type 1

The transforming activity of adenovirus type 1 was more resistant to ultraviolet irradiation than was the cytocidal activity.