Characterization of cells transformed by Ad5/Ad12 hybrid early region I plasmids

Early region I (EI) of the human adenoviruses consists of two transcriptional units, EIa and EIb. We have constructed plasmids containing hybrid EI regions from the nononcogenic adenovirus type 5 (Ad5) and the highly oncogenic Ad12. Each plasmid essentially contains the EIa region of one serotype and the EIb region of the other serotype. These hybrid EI plasmids are capable of transforming baby rat kidney cells into cell lines with the typical adenovirus-transformed phenotype, indicating an extensive functional homology between the EI transcriptional units of the two serotypes at the level of transformation. The difference in transformation frequency between the two hybrid EI plasmids suggests that the efficiency of transformation is determined by the identity of the EIa region, i.e., the efficiency is high for clones containing the EIa region of Ad5 and low for clones containing the EIa region of Ad12. In nude mice the Ad5 EIa-Ad12 EIb hybrid-transformed cells show the same high oncogenic potential as Ad12 EI-transformed cells, whereas the Ad12 EIa-Ad5 EIb hybrid-transformed cells express an even lower potential than the Ad5 El-transformed cells, indicating that the difference in oncogenic potential between Ad5- and Ad12-transformed cells is specified by the EIb region.