Isolation of a nondefective recombinant between adenovirus type 5 and early region 1A of adenovirus type 12

Activation of the human beta interferon gene by the adenovirus type 12 E1B gene

The transcription of endogenous beta interferon mRNA was activated in human embryo kidney (HEK) cells infected with adenovirus type 12 (Ad12) but was activated only inefficiently or not at all in HEK cells infected with Ad5 and rc-1 (Ad5 dl312 containing the Ad12 E1A region). The analysis with Ad12 mutants showed that Ad12 E1B products, especially the 19K protein, were important for the expression of the endogenous beta interferon gene and Ad12 E1A products were not involved in the expression. The expression of exogenously transfected pIFN-CAT (a hybrid plasmid having the human beta interferon promoter fused with the CAT gene) was activated in HEK and chicken embryo fibroblast (CEF) cells infected with either Ad12 or Ad5. The analysis of cotransfection of CEF cells with pIFN-CAT and plasmids containing fragments of Ad12 or Ad5 DNA showed that Ad12 or Ad5 E1B (possibly the 19K protein) was and E1A was not involved in the expression of the exogenous pIFN-CAT.

Adenovirus E1A gene induction of susceptibility to lysis by natural killer cells and activated macrophages in infected rodent cells

Rodent cells immortalized by the E1A gene of nononcogenic adenoviruses are susceptible to lysis by natural killer (NK) cells and activated macrophages. This cytolysis-susceptible phenotype may contribute to the rejection of adenovirus-transformed cells by immunocompetent animals. Such increased cytolytic susceptibility has also been observed with infected rodent cells. This infection model provided a means to study the role of E1A gene products in induction of cytolytic susceptibility without cell selection during transformation. Deletion mutations outside of the E1A gene had no effect on adenovirus type 2 (Ad2) or Ad5 induction of cytolytic susceptibility in infected hamster cells, while E1A-minus mutant viruses could not induce this phenotype. E1A mutant viruses that induced expression of either E1A 12S or 13S mRNA in infected cells were competent to induce cytolytic susceptibility. Furthermore, there was a correlation between the accumulation of E1A gene products in Ad5-infected cells and the level of susceptibility of such target cells to lysis by NK cells. The results of coinfection studies indicated that the E1A gene products of highly oncogenic Ad12 could not complement the lack of induction of cytolytic susceptibility by E1A-minus Ad5 virus in infected cells and also could not block induction of this infected-cell phenotype by Ad5. These data suggest that expression of the E1A gene of nononcogenic adenoviruses may cause the elimination of infected cells by the immunologically nonspecific host inflammatory cell response prior to cellular transformation. The lack of induction of this cytolysis-susceptible phenotype by Ad12 E1A may result in an increased persistence of Ad12-infected cells in vivo and may lead to an increased Ad12-transformed cell burden for the host.

Interferon induction by adenovirus type 12: stimulatory function of early region 1A

Adenoviruses are generally weak interferon inducers, triggering chicken embryo fibroblast cells by a UV-resistant viral component, probably the capsid or capsid elements, to produce 50 to 100 IU of interferon per ml. Adenovirus types 12, 18, and 31, however, can induce by a UV-sensitive mechanism 10 to 20 times more interferon than other types do. By using mutant and recombinant adenoviruses, we demonstrated that early region 1A was responsible for the enhanced interferon production of chicken cells infected with adenovirus type 12.

Adenovirus types 2 and 5 functions elicit replication and late expression of adenovirus type 12 DNA in hamster cells

Human adenovirus type 12 (Ad12) cannot replicate in hamster cells. There is a complete block of viral DNA replication and of the expression of late viral genes. Early viral functions are expressed. In contrast, hamster cells are permissive for human adenovirus type 2 (Ad2). Some of the Ad12-specific functions are insufficient to support viral replication in hamster cells, or else cellular functions are missing or inhibitory for Ad12 replication. It was shown that the block in the replication and late expression of the Ad12 genome in hamster cells could, at least in part, be complemented by Ad2 and adenovirus type 5 (Ad5) functions. When hamster cells were coinfected with Ad2 (or Ad5) and Ad12, both Ad2 (Ad5) and Ad12 DNA replicated. Ad2 (Ad5) virions were produced in double-infected hamster cells. The assembly of intact Ad12 virions was not detectable by the techniques used here. The analysis was further refined by Ad12 superinfecting Ad2- or Ad5-transformed cells which carried in an integrated form defined fragments of the Ad2 or Ad5 genome. Persistence and continued expression of the left terminus of the Ad2 or Ad5 DNA in these cells has been documented and helped to support replication and late expression of Ad12 DNA. It remains to be determined which of the E1 functions of Ad2 or Ad5 were responsible for the helper effect. Investigations on the biochemical mechanism of this complementation will entail studies on very complex viral and possibly cellular functions involved in the control of viral gene expression.

Construction of nondefective adenovirus type 5 bearing a 2.8-kilobase hepatitis B virus DNA near the right end of its genome

A novel helper-free adenovirus type 5 (Ad5) vector system, which utilizes a cloning site 0.2 kilobase (kb) from the right end of the genome, has been developed. To construct a nondefective Ad5 bearing the 2.8-kb DNA fragment of hepatitis B virus (HBV) at this site, we deleted the 2.1-kb nonessential E3 fragment from cloned DNA covering the right one-fourth of the Ad5 genome (76 to 100 map units), inserted the HBV DNA into this site, ligated the recombinant DNA to the rest of the Ad5 genome, and transfected the ligated DNA into human embryo kidney cells. Most of the recovered virus clones had only the E3 deletion and no HBV insertion, suggesting that a homologous recombination occurs between transfected DNAs in these cells. The isolated Ad5 virus bearing the HBV DNA (Ad5-HBL) grew without helper virus in HeLa cells as efficiently as wild-type Ad5, although the 1.9-kb major E4 transcript was detected only poorly in the early phase in the Ad5-HBL-infected cells, suggesting that the HBV DNA inserted upstream of the E4 promoter reduces the E4 transcript. HBV mRNAs transcribed from the inserted DNA were at least as abundant as Ad5 early mRNAs in the late phase of Ad5-HBL infection, but the HBV surface antigen was barely detectable in the infected-cell lysate and culture medium. This result suggests that HBV mRNAs can be transcribed from the inserted genes but no protein can be translated from the HBV mRNAs, presumably because of the translational suppression of cellular mRNAs caused by adenovirus in its late phase.