Molecular biology of adenovirus type 2 semipermissive infections. I. Viral growth and expression of viral replicative functions during restricted adenovirus infection.

As an initial step toward understanding the mechanisms underlying host cell restriction of adenovirus 2 (Ad2) replication, we have studied various cell lines derived from hamster (CHO-K1), rat (CREF, NRK-49F, C-3, C-9), and mouse (3T3-Swiss) tissues to determine their degree of permissivity to Ad2 replication. For each cell line tested, the time course of Ad2 growth was determined; the yield of infectious virus, as measured by titration on HeLa cell monolayers, was reduced 3 to 5 logs. This result is independent of the multiplicity of infection at multiplicities between 4 and 100 plaque-forming units (PFU) per cell. The Western immunoblotting technique was used to quantitate the amounts of early proteins (E1A 45-54K proteins, E1B 21 and 58K proteins, E2A 72K DNA binding protein) and late structural proteins (hexon, fiber) produced during restricted infections. All cell lines expressed 72K DNA binding protein and variable levels of other early proteins. C-3, C-9, and NRK-49F cells expressed hexon as well as low, but detectable levels of fiber protein. Mouse 3T3-Swiss cells failed to synthesize any detectable levels of late structural proteins. DNA synthesis analysis indicated all rodent cell lines were capable of replicating viral DNA. A decreased rate of viral DNA synthesis was observed in CREF cells. Evidence is presented which suggests newly synthesized viral DNA is unstable in 3T3-Swiss cells.