Tumorigenicity and viral gene expression in rat cells transformed by Ad 12 virions or by the EcoRI c fragment of Ad 12 DNA

A comparative review of adenovirus A12 and C5 oncogenes

Oncogenic viruses contribute to 15% of global human cancers. To achieve that, virus-encoded oncoproteins deregulate cellular transcription, antagonize common cellular pathways, and thus drive cell transformation. Notably, adenoviruses were the first human viruses proven to induce cancers in diverse animal models. Over the past decades, human adenovirus (HAdV)-mediated oncogenic transformation has been pivotal in deciphering underlying molecular mechanisms. Key adenovirus oncoproteins, encoded in early regions 1 (E1) and 4 (E4), co-ordinate these processes. Among the different adenovirus species, the most extensively studied HAdV-C5 displays lower oncogenicity than HAdV-A12. A complete understanding of the different HAdV-A12 and HAdV-C5 oncoproteins in virus-mediated cell transformation, as summarized here, is relevant for adenovirus research and offers broader insights into viral transformation and oncogenesis.

Susceptibility to natural killer cells and down regulation of MHC class I expression in adenovirus 12 transformed cells are regulated by different E1A domains

All human adenoviruses transform rodent cells in vitro, but only cells transformed by serotypes belonging to subgroups A (Ad12) and B (Ad3) are tumorigenic for immunocompetent animals. In these cells, the expression of MHC-class I antigens is repressed and might allow them to escape from recognition by cytotoxic T lymphocytes (CTL) and to develop in tumor. Furthermore, these cell lines appear resistant to lysis by natural killer (NK) cells. To determine the E1A domain(s) responsible for these properties several cell lines were created by transforming baby rat kidney (BRK) cells with a set of plasmids expressing different Ad2/Ad12 hybrid E1A gene products. The MHC class 1 gene expression was inhibited in cells expressing the Ad12 13S mRNA product and in cells transformed with Ad2/Ad12 hybrid E1A gene product harboring the C-terminal part of the conserved region (CR) 3 of Ad12. Susceptibility of these transformed cell lines to NK cells was determined by cytolytic assays. The results obtained suggest that two Ad12 E1A domains are required to induce resistance of the cell lines to NK cells.

Heritable formation of neuroectodermal tumor in transgenic mice carrying the combined E1 region gene of adenovirus type 12 with the deregulated human renin promoter

Adenovirus early 1 (E1) region gene products, including E1A and E1B, are required for transcriptional regulation of viral and cellular promoters in infected and transfected culture cells and for transformation of primary rodent cells. Here, we established a line of transgenic mice carrying the E1 region gene of human adenovirus type 12 under the control of the human renin promoter, in which a neuroectodermal tumor derived from retroperitoneal, olfactory, and/or pelvic regions was heritably developed with varying degrees of incidence and the phenotype was successfully passed through six generations. The transgenes were located in the region E2-E3 bands of chromosome 7 with which no genetic linkage to neuroectodermal tumors was previously demonstrated, and expressed only in the tumors but not in another tissue examined. Notably, in addition to the expression of a neural marker gene N-CAM, the three nuclear oncogenes, c-, L-, and N-myc, were coexpressed in the tumors. These results suggest that E1A and E1B are cooperatively involved in the heritable formation of neuroectodermal tumors associated with co-expression of the three sets of myc family genes.

Separate regions of an adenovirus E1B protein critical for different biological functions

The E1B region of Ad12 encodes two major proteins, the 482R (55K) and 163R (19K). In this report we showed that the E1B 482R is multifunctional, in that its structure may somehow contribute to its own stability, in viral DNA and virus replication, in transformation of primary cells, and in tumorigenicity. Deletion of the first 24 amino acids and of aa residues 114-155 (dl42) results in an instability of the 55K protein. The N-terminal 24 aa residues (pm1852) or amino acids residues 80-96 (dl17) are not required for viral DNA or virus replication, whereas amino acid residues between 114 and 155 (dl42) are absolutely necessary for viral DNA synthesis. Deletion of amino acid residues 1-24, 80-96, and 114-155 (dl42) greatly reduces the transforming ability of both virus and plasmids containing any one of these deletions. One of the critical regions for tumorigenicity residues within amino acid residues 80-96, since cells transformed by this plasmid are nontumorigenic. On the other hand the region bounded by amino acid residues 114-155 (dl42) is not required for tumorigenicity in immunocompetent animals.

Experimental strategies for modification of histocompatibility antigens in tumor cells

Cancer may be thought of as an immunological disorder that arises because certain 'transformed' cells, endowed with the propensity to divide, have learned to evade detection by the immune system. The prospect of intervention by 'immunotherapy' depends very much on our ability to either [1] render cancer cells more recognizable to the immune system, or [2] potentiate the immune system towards a more effective recognition of cancer cells. There is now direct evidence that suppression of the major histocompatibility complex class I antigens, a family of cell-surface glycoproteins required for the presentation of cancer cells to the immune system, is directly responsible for the ability of tumor cells to escape immune surveillance. It has been shown that cancer cells can be made immunogenic either by the expression of an exogenous class I gene introduced by DNA-mediated gene transfer, or by the derepression of endogenous class I genes with interferon; these cells are efficiently rejected by the immune system. Even more interesting is the finding that the immune system can be potentiated to reject tumors by immunization with homologous tumor cells that have been manipulated to express normal levels of class I antigens. Since increasing numbers of human tumors have been found to have greatly reduced levels of class I antigens, these findings suggest a direct route to immunotherapy that involves debulking of the tumor mass, raising the level of class I antigens in a small number of explanted tumor cells, and re-immunizing the host.

tsJT60, a cell cycle G0-ts mutant, becomes lethal at non-permissive temperature by transformation with adenovirus 5 when the expression of E1B gene is lacking

tsJT60, a temperature-sensitive (ts) mutant cell line of Fischer rat, is viable at both permissive (34 degrees C) and non-permissive (39.5 degrees C) temperatures. The cells grow normally in exponential growth phase at both temperatures, but when stimulated with fetal bovine serum (FBS) from G0 phase they re-enter S phase at 34 degrees C but not at 39.5 degrees. When tsJT60 cells were transformed with adenovirus (Ad) 5 wild type, they grew well at both temperatures, expressed E1A and E1B genes, and formed colonies in soft agar. When tsJT60 cells were transformed with Ad5 dl313, that lacks E1B gene, the transformed cells grew well at 34 degrees C but failed to form colony in soft agar. They died very soon at 39.5 degrees C. 3Y1 cells (a parental line of tsJT60) transformed with dl313 grew well at both temperatures, although neither expressed E1B gene nor formed colonies in soft agar. The phenotype of being lethal at 39.5 degrees C of dl313-transformed tsJT60 cells was complemented by cell fusion with 3Y1BUr cells (5-BrdU-resistant 3Y1), but not with tsJT60TGr cells (6-thioguanine resistant tsJT60). These results indicate that the lethal phenotype is related to the ts mutation of tsJT60 cells and also to the deletion of E1B gene of Ad5.

Different activities of the adenovirus types 5 and 12 E1A regions in transformation with the EJ Ha-ras oncogene

We have compared the capacities of the E1A regions of nononcogenic adenovirus type 5 (Ad5) and highly oncogenic Ad12 to cooperate with the EJ bladder carcinoma Ha-ras-1 oncogene in the transformation of primary baby rat kidney cells. Both E1A regions, when cotransfected with the Ha-ras oncogene, transformed the primary cells with a low frequency. Ad5 E1A plus Ha-ras-transformed cells differed in phenotype from cells transformed by Ad12 E1A plus Ha-ras. The cells expressing Ad5 E1A appeared highly transformed and practically failed to adhere to plastic. This phenotype may be due to the virtually complete absence of fibronectin gene expression in these cells. In contrast, the cells expressing Ad12 E1A were flatter and adhered to plastic, whereas fibronectin gene expression was reduced but not absent. The oncogenic potential of the two types of E1A plus ras-transformed cells was tested by their injection into both athymic nude mice and weanling syngeneic rats. The Ad5 E1A plus ras-transformed cells were found to be highly oncogenic in both animal species, whereas the Ad12 E1A plus ras-transformed cells were only weakly oncogenic in both syngeneic rats and nude mice. The difference in oncogenic potential of the Ad5 E1A plus ras- and the Ad12 E1A plus ras-transformed cells is discussed in terms of the different capacities of the Ad5 and Ad12 E1A-encoded proteins to modulate cellular gene expression.

The sprue syndromes

The sprue syndromes, tropical and nontropical sprue, were both described as disease entities in the 1880s and share similar morphological features with varying degrees of villus atrophy of the small intestinal mucosa, and both present clinically with malabsorption. Recent cell kinetic studies of the turnover of the intestinal epithelium in sprue have convincingly demonstrated that the flat mucosa is caused by increased efflux (cell death) with compensatory crypt hyperplasia. The pathogenetic insult in tropical sprue appears to be a persistent overgrowth of the small intestine by enteric pathogens after a bout of turista. The pathogenesis of nontropical sprue is determined by both genetic factors, demonstrated with a strong association with certain HLA haplotypes (B8, DR3, DR7 and DC3) and presumably also environmental events (virus infection?), which render the mucosa susceptible to gluten. The cause of the malabsorption syndrome is multifactorial and results from both intraluminal and cellular events. The digestion of proteins, carbohydrates, and lipids is compromised due to decreased pancreatic and biliary secretion. The absorption of the digestive products is also severely affected due to decreased activity of microvillus enzymes (dipeptidases and disaccharidases) and a presumed reduction in the number of transport carriers. The clinical presentation is identical and the distinction between tropical and nontropical sprue is based on the history (ie, exposure to a tropical environment) and the response to treatment. Tropical sprue is cured by treatment with tetracycline and folic acid, whereas nontropical sprue responds to a gluten-free diet. Nontropical sprue is associated with dermatitis herpetiformis by common genetic and morphological features, and the skin lesions in dermatitis herpetiformis are also responsive to a gluten-free diet. Finally, there appears to be an increased incidence of intestinal malignancies (lymphoma, adenocarcinoma) in nontropical sprue.

Possible role for a human adenovirus in the pathogenesis of celiac disease

Celiac disease in humans is activated by the dietary ingestion of wheat, rye, triticale, barley, and possibly oats. Gliadins in wheat and similar proteins in the other grains are known to activate disease in susceptible individuals. There is a striking association between celiac disease and HLA-B8, -DR3 and/or -DR7, and -DC3. Nonetheless, less than 0.2% of individuals with those serologic HLA specificities develop celiac disease and disease is not always concordant among monozygotic twins. We propose that additional environmental factors may be important in the pathogenesis of celiac disease. To investigate that possibility, we examined a data bank of protein sequences for other proteins that might share amino acid sequence homologies with A-gliadin, an alpha-gliadin component known to activate celiac disease and whose complete primary amino acid sequence is known. These studies demonstrate that A-gliadin shares a region of amino acid sequence homology with the 54-kD E1b protein of human adenovirus type 12 (Ad12), an adenovirus usually isolated from the intestinal tract. The region spans 12 amino acid residues, includes 8 residue identities and an identical pentapeptide, and is hydrophilic in both proteins. Antibody reactive with the 54-kD Ad12 E1b protein cross-reacts with A-gliadin, a 119 amino acid cyanogen bromide peptide of A-gliadin that spans the region of homology and a synthetic heptapeptide of A-gliadin from within the region of homology. We suggest that an encounter of the immune system with antigenic determinants produced during intestinal viral infection may be important in the pathogenesis of celiac disease.

Adenovirus 12 nononcogenic mutants: oncogenicity of transformed cells and viral proteins synthesized in vivo and in vitro

Several nononcogenic cyt mutants of adenovirus type 12 induced the same E1A (55,000 [55K] and 25K) and E1B polypeptides (55K, 19K, and 17K) as did the wild-type virus, except that cyt 68 did not induce the E1B 19K protein. Tumorigenicity tests showed cells transformed by cyt 68 to be highly oncogenic in vivo. Therefore, it was concluded that the E1B 19K polypeptide is not necessary for tumor induction but may be involved in the efficiency of transformation.

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.

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)

Establishment and characterization of hamster cell lines transformed by restriction endonuclease fragments of adenovirus 5

We have established a library of hamster cells transformed by adenovirus 5 DNA fragments comprising all (XhoI-C, 0 to 16 map units) or only a part (HindIII-G, 0 to 7.8 map units) of early region 1 (E1: 0 to 11.2 map units). These lines have been analyzed in terms of content of viral DNA, expression of E1 antigens, and capacity to induce tumors in hamsters. All cells tested were found to express up to eight proteins encoded within E1A (0 to 4.5 map units) with apparent molecular weights between 52,000 (52K) and 25K. Both G and C fragment-transformed lines expressed a 19K antigen encoded within E1B (4.5 to 11.2 map units), whereas an E1B 58K protein was detected in C fragment-transformed, but not G-fragment-transformed, lines. No clear distinction could be drawn between cells transformed by HindIII-G and by XhoI-C in terms of morphology or tumorigenicity, suggesting that the E1B 58K antigen plays no major role in the maintenance of oncogenic transformation, although possible involvement of truncated forms of 58K cannot be ruled out. Sera were collected from tumor-bearing animals and examined for ability to immunoprecipitate proteins from infected cells. The relative avidity of sera for different proteins was characteristic of the cell line used for tumor induction, and the specificity generally reflected the array of viral proteins expressed by the corresponding transformed cells. However, one notable observation was that even though all transformed lines examined expressed antigens encoded by both the 1.1- and 0.9-kilobase mRNAs transcribed from E1A, tumor sera made against these lines only precipitated products of the 1.1-kilobase message. Thus, two families of E1A proteins, highly related in terms of primary amino acid sequence, appear to be immunologically quite distinct.

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.

Expression of class I major histocompatibility antigens switched off by highly oncogenic adenovirus 12 in transformed rat cells

Rat cells transformed by the highly oncogenic adenovirus 12 lack at least two cellular proteins which are present in cells transformed by the non-oncogenic adenovirus 5 and in untransformed cells. One protein has been identified as the heavy chain of the rat class I major histocompatibility complex. This finding may explain the difference in oncogenicity between adenoviral species.

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.

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.

Adenovirus-12 genes undetectable in human retinoblastoma

Retinoblastoma is a rare eye tumor found predominantly in young children. Intra-ocular injection of adenovirus-12 (Ad-12) into newborn recipients induces in rats and in baboons tumors morphologically similar to human retinoblastoma tumors. In addition, Ad-12 DNA can transform human embryonic retinal cells and the transformed cells form retinoblastoma-like tumors in nude mice. These observations have led to the suggestion that Ad-12 may also be involved in the induction of human retinoblastoma tumors. To test this possibility, DNA and RNA were isolated from six human tumors. Analysis of RNA and DNA by blotting with labelled Ad-12 failed to reveal viral sequences in human retinoblastoma.

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.

Complementation of adenovirus type 5 host range mutants by adenovirus type 12 in coinfected HeLa and BHK-21 cells

We have studied the ability of adenovirus type 12 (Ad12) to complement the Ad5 transformation-defective host rang (hr) mutants during infection of human cells (HeLa) or hamster cells (BHK-21). The group I mutant hr3 (mapped within 1.3 to 3.7 map units), which is incapable of synthesizing viral DNA, was complemented for both DNA synthesis and infectious virus production in nonpermissive HeLa cells during coinfection with Ad12. Similarly, the group II mutant hr6 (6.1 to 9.4 map units), which does synthesize DNA, was also shown to be complemented for virus production. When the host cells were BHK-21, an established hamster cell line that is permissive for Ad5 but nonpermissive for Ad12 DNA synthesis and virus production, coinfection with Ad5 and Ad12 did not overcome the block to Ad12 DNA synthesis. Coinfection of BHK-21 cells with Ad12 and either hr3 or hr6 leads to the complementation of only the group I mutant (hr3). The inability of Ad12 to complement hr6 in BHK-21 cells may be due to the failure of Ad12 to express an early gene product from the region corresponding to early region 1B (4.5 to 11 map units) Ad5 where hr6 and the other group II mutations are located.

Protein kinase activity immunoprecipitated from adenovirus infected cells by sera from tumor-bearing hamsters

Earlier, we reported (N. J. Lassam, S. T. Bayley, F. L. Graham, and P. E. Branton, Nature (London) 277:241-243, 1979) detecting protein kinase activity when cytoplasmic extracts of human adenovirus type 5 (Ad5)-infected KB cells immunoprecipitated with 14b antitumor serum directed against the transforming proteins of Ad5, were incubated with [gamma-32P]ATP. Here we show that in the in vitro assay this kinase phosphorylated both the heavy chain of immunoglobulin G and polypeptide than comigrated on sodium dodecyl sulfate gels with the 58,000-dalton Ad5 antigen. It also phosphorylated added histone H3. Evidence is presented that the protein kinase activity found with extracts from Ad5-infected cells is not due to nonspecific trapping of cellular enzymes in immune complexes, but to an enzyme which is distinct from kinases detected at background levels in controls. Serine and threonine were the major phosphorylated amino acids, and essentially no phosphotyrosine was detected. Protein kinase activity detected in Ad12-infected cells immunoprecipitated by an antiserum derived from hamsters bearing Ad12-induced tumors appeared to be immunologically distinct from that immunoprecipitated from Ad5-infected cells by 14b serum.