Identification of adenovirus-type 12 gene products involved in transformation and oncogenesis

Abstract

Primary baby rat kidney cells were transfected with Ad12 DNA fragments EcoRI C (left-terminal 16%) and HindIII G (left-terminal 7.2%), and the resulting transformed cells were established as cell lines. Injection of newborn hamsters with purified Ad12 DNA resulted in the induction of tumors in 2 out of 59 animals. A number of the in vitro transformed cells and a cell line derived from a tumor were found to contain DNA sequences homologous to the fragments used for transfection or tumor induction, and to express virus-specific RNA and T antigens. The cell lines were also studied with respect to their tumorigenicity in nude mice or hamsters. It was found that cells transformed by Ad12 EcoRI C, or by intact DNA or virus, were tumorigenic whereas cells transformed by fragment HindIII G were unable to induce tumors. To correlate this result with the presence or absence of viral gene products, virus-specific T antigens were identified by immunoprecipitation. From lytically infected cells major proteins of 60, 41, 19, 14.5, and 13.5 kD were precipitated. Cells transformed by fragment EcoRI C or intact viral DNA contained proteins of 60, 41, and 19 kD and of 50 and 36 kD. HindIII G-transformed cells contained proteins of 41 and 19 kD. Studies of the T antigens in two-dimensional gels and by tryptic peptide analysis have indicated that two virus-specific 60-kD proteins are expressed in Ad12-infected cells. The major protein probably represents the single-stranded DNA-binding protein encoded by region Ell (Ell-60 kD), while the minor protein represents a region EI-specific T antigen (EI-60 kD) encoded by region EIb. The 41-kD protein is encoded by region EIa and 19 kD by EIb. Our results suggest that expression of the EI-60-kD protein is required for oncogenicity in nude mice, but not for morphological transformation.