Production of recombinant rat viruses as a method of oncogene isolation in coculture medium.

A simple oncogene isolation was proved using the SD1-T rat embryonic cell line. The SD1-T cell line, which releases endogenous rat leukemia virus, was cocultured with (a) normal rat kidney cells transformed by cloned v-mos DNA, (b) the rat mammary tumor cell line (63SP), or (c) normal rat kidney cells transformed by 63SP DNA. Within 1 mo, oncogenic viruses were recovered from all three coculture supernatants. During this period, increase of oncogenic transcripts was observed in the cocultured cells. The oncogenic viruses appeared to contain the mos gene in cocultures (a) and ras-related sequences in cocultures (b) and (c). The emergence of virus containing mos from mos DNA-mediated normal rat kidney transformants demonstrated "rescue" of the active cellular oncogene by the rat leukemia virus. This coculture system seems to facilitate "rescue" of oncogenes functioning in the tumor and transformed cells.