Transformation of a rat cell line by an adenovirus 7 DNA fragment

Nucleotide sequence of E1 region of canine adenovirus type 2

The nucleotide sequence of the leftmost EcoRI-C fragment (0 to 11.3%) of canine adenovirus type 2 (CAd2) which could transform rodent cells morphologically but required additional sequences from 10 to 32 map units (m.u.) for full expression of its oncogenic potential was determined. The EcoRI-C fragment contains 3609 nucleotide base pairs (bp) encoding E1A, E1B, and pIX genes. Although the nucleotide sequence of CAd2 E1 shows little homology to those of human Ads, the amino acid sequences of the E1 proteins predicted from nucleotide sequence of CAd2 E1 and those for human and simian Ads are partially conserved.

E1a regions of the human adenoviruses and of the highly oncogenic simian adenovirus 7 are closely related

Simian adenovirus 7 (SA7) is a highly oncogenic virus, capable of causing tumors in hamsters upon the direct injection of viral DNA. We determined the transcriptional organization of the transforming region and compared it with that of the human adenoviruses. This analysis demonstrated that there are two independently promoted transcription units similar to the E1a and E1b regions of the human adenoviruses. The nucleotide sequence of the SA7 E1a region demonstrated considerable homology with the human adenoviruses, both in the sequences that regulate E1a expression and in the encoded polypeptides. The amino acid homology was reflected in the ability of SA7 to complement the growth of human adenoviruses mutant in the E1a region. Furthermore, we found two regions of amino acid homology unique to SA7 and the highly oncogenic human adenovirus 12.

Expression of the E4 gene is required for establishment of soft-agar colony-forming rat cell lines transformed by the adenovirus 12 E1 gene

Rat 3Y1 cells were transfected with recombinant gARC ( pSV2gpt carrying the adenovirus 12 early region 1 [E1] gene), and focus formation was observed in monolayer cultures after culture of cells in gpt-selective medium (Eagle medium containing 10% fetal calf serum, xanthine, thymidine, aminopterin, and mycophenolic acid) for 10 days, followed by focus formation. Transformed E1Y cell lines were then established from these foci. The E1Y cells were transformed morphologically similarly to cells transformed with intact adenovirus 12 DNA but formed no colonies in soft-agar culture and induced tumors in transplanted rats only after a long incubation period. For the establishment of completely transformed cells, 3Y1 cells were transformed with combinations of gARC , pE3 (pBR322 carrying the adenovirus 12 E3 gene), and gE4 ( pSV2gpt carrying the adenovirus 12 E4 gene) DNA. E1- 3Y cells (3Y1 cells transformed with gARC and pE3 DNA), E1- 4Y cells (3Y1 cells transformed with gARC and gE4 DNA), and E1-3- 4Y cells (3Y1 cells transformed with gARC , pE3 , and gE4 DNA) were established. These transformed cell lines were compared for growth in Eagle medium with 2 or 10% fetal calf serum, colony formation in soft-agar culture, and tumor growth in rats transplanted with the transformed cells. Several transformed cell lines of E1- 4Y and E1-3- 4Y cells showed colony formation in soft-agar culture and abundant expression of the E1B gene. T antigen f was seen by immunofluorescence as flecks in these cells, in which the E4 gene was transcribed, but was not seen in E1Y cells, suggesting that T antigen f was encoded by the E4 gene. The suggestion was confirmed by the observation that T antigen f was detected in COS-1 cells transfected singly with gE4 DNA by immunofluorescence with polyclonal and monoclonal antibodies. Transcription of the E4 gene was confirmed in gE4 -transfected COS-1 cells. T antigen f, one of the E4 gene products, was identified as a polypeptide of molecular weight 11,000 (E4- 11K ) by immunoprecipitation with monoclonal antibodies. The above results also suggest that expression of the E4 gene gives cells the advantage of forming colonies in soft-agar culture. A tendency was noticed for E1B gene expression to be enhanced by E4 gene expression. The relationship between enhancement of colony formation in soft-agar culture and enhancement of E1B gene expression is discussed.

Transformation by human adenoviruses

When, approximately 10 years ago, it was shown that the functions essential for cell transformation were localized in a small region of the adenovirus genome, a DNA segment which at that time was thought to be capable of encoding two or three average-sized proteins at most, it seemed reasonable to hope that an understanding of the mechanisms by which adenoviruses transform cells might be quickly achieved. While such optimism might be forgiven, it was quite clearly naive in the extreme. As a consequence of mRNA splicing and the use of overlapping reading frames the number of proteins encoded within E1 is 2-3-times greater than would have been predicted a decade ago, and post-translational modifications may add another dimension of complexity. In fact it has taken nearly all of the past decade just to identify the proteins encoded in E1 and to characterize them in the most rudimentary way. However, we have now entered a period in which new information is accumulating at an extremely rapid rate as a result of several major technical and fundamental advances. Chief among these are the use of recombinant DNA techniques, particularly site-directed mutagenesis, which combined with methods for introducing mutations made in cloned sequences back into infectious virus, clearly represents a powerful approach to studying the functions of transforming proteins. In addition, the ability to express transforming proteins in bacteria and to produce large amounts of highly purified proteins which previously were only just detectable in infected and transformed cells is a major breakthrough. Advances in immunological techniques, particularly the development of monoclonal antibodies and antisera against synthetic peptides, have enormously simplified the task of detecting and characterizing E1 proteins. Finally, recent results suggesting that adenovirus transforming proteins may be functionally and structurally similar to other oncogenes brings a new perspective to the study of oncogenic transformation. Have all the proteins involved in transformation by adenoviruses been identified? It seems probable that all those virally coded proteins which play a major role are now known but of course minor players in the cast could still be waiting in the wings. We have pointed out that viral functions encoded outside region E1 may have some importance at least in initiation of transformation by virions and have speculated on the possibility that one or more of these may be involved in the integration of viral DNA into the host cell chromosome.(ABSTRACT TRUNCATED AT 400 WORDS)

Genetic analysis of control of proliferation in fibroblastic cells in culture. I. Isolation and characterization of mutants temperature-sensitive for proliferation or survival of untransformed diploid rat cell line 3Y1

Mutants temperature sensitive for proliferation or survival were isolated from an untransformed diploid clone of fibroblastic rat cells (3Y1), according to an isolation protocol that selected for mutants defective at 38.5 degrees C (selection temperature) in undergoing the transition from quiescent to proliferating state while maintaining viability at 38.5 degrees C. Of the 108 temperature-sensitive clones isolated, 32 were examined for survival in sparse cultures at 39.8 degrees C (nonpermissive temperature) and classified into four classes. Results of temperature shift-up experiments suggest that functions defective in 11 of the 32 mutants are necessary not only for changing from the quiescent to proliferating state but also for maintenance of the proliferating state. Of the 32 mutants, 17 were assigned to eight complementation groups. Results of the physiological characterization of the representative mutants of each of the eight complementation groups are presented.

Analysis of retinoblastoma for human adenovirus type 12 genome

Adenovirus type 12 has high oncogenic potential in newborn rodents. Moreover, adenovirus 12 induces retinoblastoma-like tumours in baboons and transforms in vitro human embryo retinoblasts. Since adenovirus-transformed cells contain adenovirus transforming gene sequences, the detection of adenovirus 12 transforming gene in tumour cell DNA can provide evidence for or against a possible aetiological role of adenovirus 12 in retinoblastoma. In this experiment, cell DNAs from six retinoblastomas were assayed for adenovirus 12 transforming gene sequences by spot hybridization and Southern blot hybridization, using the labelled EcoRI-C fragment of adenovirus 12 DNA as a probe (the far left 16.5% of the viral genome). No adenovirus 12 transforming gene sequences were detected at the level of 0.1 or 0.5 copy of the probe per diploid cell DNA in all of six retinoblastomas.

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.

Integration of foreign genome fragments into cells transformed or cotransformed with fragmented adenoviral DNA

The integration of DNA of highly oncogenic simian adenovirus type 7 (SA7) and non-oncogenic human adenovirus type 6 (Ad6) into the genome of newborn rat kidney cells transformed by fragmented DNA preparations was studied using reassociation kinetics and spot hybridization. Transforming DNA was fragmented with the specific endonuclease SalI (SA7) and BglII (Ad6). In contrast to the cell transformation by intact viral DNA, transformation by fragmented DNA resulted in integration into the cellular genome of not only the lefthand fragment with the oncogene but also of other regions of the viral genome. Additionally integrated fragments were stable and preserved during numerous passages of cells lines, although they were no expressed, at least in the case of the Ad6-transformed cell line. The integration of the fragments of SA7 DNA was accompanied by loss of 25-50% of the mass of each fragment. Adding the linear form of the pBR322 plasmid to the preparation of transforming Ad6 DNA also contributed to its cointegration into the genome of the transformed cell. This technique of cell cotransformation with any foreign DNAs together with the viral oncogens may be used as an equivalent of an integration vector for eukaryotic cells.

Transforming genes among three different oncogenic subgroups of human adenoviruses have similar replicative functions

We have examined the functional similarity of the transforming genes for replicative functions among three different subgroups of human adenoviruses (A, B, and C), using mutant complementation as an assay. A host range deletion mutant (dl201.2) of Ad2 (nononcogenic subgroup C) lacking about 5% of the viral DNA covering two early gene blocks (E1a and E1b) involved in cellular transformation was isolated and tested for its ability to replicate in nonpermissive KB cells in the presence of Ad7 (weakly oncogenic group B) or ad12 (highly oncogenic group A). The complementation of the mutant defect was demonstrated by cleaving the viral DNA extracted from mixed infected cells or the DNA extracted from purified virions from mixed infected cells with restriction endonuclease BamHI, which produces a different cleavage pattern with the DNA of each serotype. It was found that the defects in E1a plus E1b of dl201.2 could be complemented by Ad7 and Ad12, indicating that these genes in Ad2, Ad7, and Ad12 have similar functions during productive infection.

Incomplete transformation of rat cells by a deletion mutant of adenovirus type 5

Rat 3Y1 cells were infected with adenovirus type 5 (Ad5) wild type, dl312 (deletion of 902 base pairs between 1.5-4.5 map units), and dl313 (deletion of 2,350 base pairs between 3.5-10.5 map units). After cultivation for 4 weeks, transformed foci appeared in wild type- and dl313-infected cells. No focus was observed in dl312- and mock-infected cells. Foci induced by dl313 were less dense than those induced by wild type. Cell lines (313Y cells) established from dl313-induced foci contained the E1 gene of the dl313 genome (E1a only). Cell lines (5WY cells) established from Ad5 wild type-induced foci contained the E1 gene of wild type (E1a and b). The difference between the transcriptional patterns of the E1 gene in 313Y cells and that in 5WY cells was the same as the difference in dl313- and wild type-infected cells. Colonies were formed in soft agar culture inoculated with 5WY cells, but no colony was formed after inoculation of 313Y cells. The transformed phenotype of 313Y cells was incomplete compared with that in 5WY cells. In nongrowing 3Y1 cells, dl313 and Ad5 wild type induced cellular DNA synthesis but dl312 did not. The above results suggest that the E1a gene is functioning in dl313-infected but not in dl312-infected cells and that such functions as induction of cellular DNA synthesis and transformation of cells are dependent on expression of the Ad5 E1a gene.

Mapping of adenovirus 12 mRNA's transcribed from the transforming region

Adenovirus 12 mRNA's transcribed from the transforming region were analyzed and mapped on viral DNA by the nuclease S1 gel and diazobenzyloxymethyl paper blot techniques in cells transformed of adenovirus 12 DNA and in cells early and late after lytic infection with adenovirus 12. Two initiation sites of mRNA transcription and two kinds of splicing were found in each of early regions 1A and 1B. For early region 1A mRNA's, four species were found in lytically infected cells. Three of them were commonly found in cells transformed by either HindIII-G or EcoRI-C. Cells transformed by HindIII-G contained two additional 1A transcripts, which could be the 3' portions of chimeric mRNA's of cellular-viral or viral-viral sequences. Transcription in the 1B region diverged among the above cell lines. Early after lytic infection, no appreciable amount of 1B mRNA was detected, whereas two species of mRNA's, one corresponding to protein IX mRNA and another having splicing, were found at the late stage. In cells transformed by EcoRI-C, a distinct mRNA species with splicing was observed. Cells transformed by HindIII-G contained a transcript from the leftmost part of the 1B sequence at the 5' portion of chimeric mRNA species, suggesting the presence of tandem integration of viral DNA in the cells. Other mRNA species in the 1A and 1B regions were also detected in both transformed cell lines. The results are discussed in relation to the nucleotide sequence of the HindIII-G fragment of adenovirus 12 DNA.

Structure of two adenovirus type 12 transforming polypeptides and their evolutionary implications

The human adenoviruses are classified according to their nucleotide sequence homology and their oncogenic potential in rodents. The left-hand end of the genome of the adenovirus types 5 (ad5), 7 (ad7) and 12 (ad12), which are respectively, non-oncogenic (subgroup C), weakly oncogenic (subgroup B) and highly oncogenic (subgroup A), contains all the genetic information needed to induce and maintain the transformed phenotype. This part of the genome contains the early transcription unit designated E1 which is subdivided in two transcription units E1A and E1B. Two spliced mRNAs are transcribed from the E1A region which codes for several phosphorylated polypeptides. These polypeptides play a key role by controlling the expression of the other early transcription units. The major role of region E1A in adenovirus cell transformation might not be activate the true transforming genes of the region E1B. An additional role probably consists of the activation of some cellular genes as a restriction fragment containing this region can immortalize rodent cells in vitro. An important question is why some adenoviruses are oncogenic and others are not. We report here differences in the structures of the E1A polypeptides from ad7 and ad12, compared to ad5, which may partially account for their differing oncogenicity.

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.

Chromosomal alterations of rat cell lines transformed by human adenovirus type-12 virion, whole DNA and left-end DNA fragments

A normal rat cell line, 3Y1-B clone 1-6 (3Y1) and its adenovirus (Ad) type-12-transformed derivatives, W4 (transformed by Ad12 Virion), WY3 (transformed by Ad12 whole DNA), CY1-1 (transformed by the Ad12 EcoRI-C fragment, left 16.5%), GY1-1 (transformed by the Ad12 HindIII-G fragment, left 6.8%) and HY1 (transformed by the Ad12 Acd-H fragment, left 4.7%) were studied cytogenetically. 3Y1 and some of the transformed cell lines (W4, WY3 and GY1-1) were diploid or pseudodiploid, while others (CY1-1 and HY1) were hypotetraploid. A metacentric marker M1 was detected in GY1-1 cells and another marker M2 in W4 and CY1-1 cells at a high frequency. By the Giemsa banding technique, the metacentric markers M1 and M2 from these fully transformed cell lines were identified as isochromosomes derived from 1q (M1) and 3q (M2), respectively. On the other hand, the markers were detected only at a low frequency in incompletely transformed HY1 cells. However, hypersomy in chromosome No. 1 was observed at a high frequency in this cell line. It can be concluded that hypersomy of chromosomes No. 1 or 3 found in transformants and metacentric markers found in complete transformants are characteristic features in rat cells transformed by Ad12.

Integration sites of adenovirus type 12 DNA in transformed hamster cells and hamster tumor cells

The patterns and sites of integration of adenovirus type 12 (Ad12) DNA were determined in three lines of Ad12-transformed hamster cells and in two lines of Ad12-induced hamster tumor cells. The results of a detailed analysis can be summarized as follows. (i) All cell lines investigated contained multiple copies (3 to 22 genome equivalents per cell in different lines) of the entire Ad12 genome. In addition, fragments of Ad12 DNA also persisted separately in non-stoichiometric amounts. (ii) All Ad12 DNA copies were integrated into cellular DNA. Free viral DNA molecules did not occur. The terminal regions of Ad12 DNA were linked to cellular DNA. The internal parts of the integrated viral genomes, and perhaps the entire viral genome, remained colinear with virion DNA. (iii) Except for line HA12/7, there were fewer sites of integration than Ad12 DNA molecules persisting. This finding suggested either that viral DNA was integrated at identical sites in repetitive DNA or, more likely, that one or a few viral DNA molecules were amplified upon integration together with the adjacent cellular DNA sequences, leading to a serial arrangement of viral DNA molecules separated by cellular DNA sequences. Likewise, in the Ad12-induced hamster tumor lines (CLAC1 and CLAC3), viral DNA was linked to repetitive cellular sequences. Serial arrangement of Ad12 DNA molecules in these lines was not likely. (iv) In general, true tandem integration with integrated viral DNA molecules directly abutting each other was not found. Instead, the data suggested that the integrated viral DNA molecules were separated by cellular or rearranged viral DNA sequences. (v) The results of hybridization experiments, in which a highly specific probe (143-base pair DNA fragment) derived from the termini of Ad12 DNA was used, were not consistent with models of integration involving true tandem integration of Ad12 DNA or covalent circularization of Ad12 DNA before insertion into the cellular genome. (vi) Evidence was presented that a small segment at the termini of the integrated Ad12 DNA in cell lines HA12/7, T637, and A2497-3 was repeated several times. The exact structures of these repeat units remained to be determined. The occurrence of these units might reflect the mechanism of amplification of viral and cellular sequences in transformed cell lines.

Structure and gene organization in the transformed Hind III-G fragment of Ad12

The nucleotide sequence of the transforming Hind III-G fragment of Ad12 DNA which encompasses the left 6.8% of the genome has been determined. The fragment was 2320 nucleotides long, and contained a GC cluster at positions 126-155 and a region extremely rich in AT at positions 1098-1142 (number from the leftmost end). Possible coding regions for the two transforming gene products were assigned. The predicted coding region for T antigen g is positions 502-1069 and positions 1144-1373, which are joined by splicing (266 amino acid residues, 30 kd), and that for T antigen f is positions 1845-2126 (94 amino acid residues, 10 kd). The sequence of the Hind III-G fragment was compared with that of the transforming DNA fragment of Ad5 which encompasses the left 8.0% of the genome (2809 nucleotides). There are several discrete regions with significant sequence homology. The comparison suggests that the regions in the left two thirds of the Ad5 and Ad12 transforming DNA fragments (map units 0-4.7% in Ad5 and 0-4.4% in Ad12) bear some resemblance in their gene organizations, and code for proteins containing structurally homologous regions.

The nucleotide sequence of the transforming BglII-H fragment of adenovirus type 7 DNA

The nucleotide sequence of the leftmost BglII-H fragment (0--4.5%) of weakly oncogenic human adenovirus serotype 7 (Ad7) has been determined (1568 base pairs). This is the shortest Ad7 DNA fragment reported to transform primary rat cells into an immortal cell line (Dijkema et al., 1979). The l-strand of BhlII-H was found to contain the complete information for a polypeptide of at most 28 051 daltons, followed by the putative promoter site of the next gene. Comparison of the determined Ad7 sequence with that of the corresponding region of non-oncogenic Ad5 (Van Ormondt et al., 1978; Maat and Van Ormondt, 1979) showed that the over-all organization of the two DNAs is quite similar, but that the sequences, except in regions of suspected strategic importance, diverge considerably.

Two tumor antigens and their polypeptides in adenovirus type 12-infected and transformed cells

A tumor (T) antigen, designated T antigen g, was visualized as fine fluorescent granules in nuclei of adenovirus type 12 (Ad12)-infected cells by immunofluorescence with sera from rats bearing HY cell tumors (H sera). HY cells are rat cells incompletely transformed by the Acc I-H endonuclease fragment (0-4.7 map units) of Ad12 DNA. The antigen is different from the usually described T antigen, designated T antigen f, which is visualized as fluorescent flecks or filaments in both nucleus and cytoplasm of Ad12-infected cells when tested with narrowly reacting T sera. Extracts of [(35)S]methioninelabeled infected cells were immunoprecipitated with H sera, and the resultant precipitate was analyzed by the two-dimensional gel electrophoresis technique of O'Farrell. The autoradiogram showed the presence of a cluster of several polypeptides (M(r) 35,000-40,000, pI 5.0-5.5) that was absent in extracts of mock-infected cells. A similar autoradiogram of infected cells analyzed with narrowly reacting T sera showed the presence of a small polypeptide (M(r) 10,000, pI 6.4), that was absent in extracts of mock-infected cells. The results show that M(r) 35,000-40,000 polypeptides are components of T antigen g and a M(r) 10,000 polypeptide is a component of T antigen f. Ad12-transformed cells showed a similar result. T antigen g was present and T antigen f was absent in HY cells. Both T antigen g and T antigen f were present in CY cells, which are rat cells completely transformed by the EcoRI-C endonuclease fragment (0-16 map units) of Ad12 DNA. The possible functions of these proteins are discussed.

Mappings of adenovirus type 7 cytoplasmic RNA species synthesized early in lytically infected cells and synthesized in transformed cells

Early virus-specific RNA synthesized in KB cells infected with adenovirus type 7 and virus-specific RNA synthesized in rat embryo cells (71JY1-2) transformed by the adenovirus type 7 HindIII-I.J fragment (left-hand 8.1% of the viral genome) have been mapped on the viral genome. About 25% of the viral genome, four discrete regions, two on each strand of the viral genome, are expressed as "early" mRNA. Almost similar regions in the left-hand 8.1% of the viral genome are transcribed both in KB cells at early times after infection and in 71JY1-2 cells.