Characterization of host-range and temperature-sensitive mutants of adenovirus type 5 with particular regard to transformation of a hamster embryo cell line (Nil)

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.

Altered cell cycle progression and aberrant mitosis in adenovirus-infected rodent cells

Actively growing mouse or rat embryo cells suffered structural chromosome damage, mitotic anomalies, and polyploidy after infection by human adenovirus type 5. Chromosome damage required expression of one or more early viral genes and showed regular periodicity in its frequency. The growth cycle time of some of the infected cells was reduced by about 5 hours due to a decrease in G1, and the interval between successive waves of chromosome damage corresponded to this reduced cycle time. After infection there was a decrease in cells with G1 DNA content and an increase in cells with G2 diploid, aneuploid, and polyploid DNA contents. We suggest these effects are due to the expression in semipermissive cells fo early viral gene(s), whose function in productive infection in vivo is to alter cell cycle controls in order to maximize the number of cells able to replicate viral DNA and the time such cells spend in DNA replication.