The response of BHK21 cells to infection with type 12 adenovirus

Summary

Transformation of a clonal line of BHK21 cells by type 12 adenovirus (Ad 12) is described. A transformation rate of approximately 2 × 10⁻⁵ per initially infected cell was observed after high multiplicity infection. A study of the fate of the abortively infected cells revealed, however, that only a small fraction survived the infection and initiated growth of a colony. Of these rare surviving colonies, nearly half contained transformed cells. Of three BHK21 sublines tested, one yielded transformed cells only from colonies growing in soft agar suspension, a second yielded transformants only as foci in monolayers, while the third did not yield detectable transformants by either method.

The adenovirus-transformed cells were distinguished from the parental BHK21 cells by the following characteristics:

• 1) a marked morphological alteration;

• 2) the synthesis of adenovirus tumor antigen;

• 3) growth to high cell density in the presence of a low concentration of serum;

• 4) induction, in hamsters, of tumors identical to those induced by inoculation of type 12 virus;

• 5) restriction in the ability to support the multiplication of type 2 adenovirus (Ad2).

The latter property is most likely due to blockage of a step late in the adenovirus replicative cycle, since 88% of the cells, which synthesized Ad2-specific structural antigens did not yield infectious virus. A similar shift from a productive to a largely abortive response to Ad 2 was seen in BHK21 cells simultaneously infected with Ad 12 and Ad2. This finding supports the view that the restriction of Ad2 replication in Ad 12-transformed cells, like the other characteristics mentioned, is associated with continued activity of at least part of the Ad12 genome.