Enhanced proliferation, growth factor induction and immortalization by adenovirus E1A 12S in the absence of E1B

Immortalization and transformation of primary epithelial cells requires expression of the adenovirus E1A and E1B genes, respectively. The E1A gene is involved in growth stimulatory processes. Little is known about the mechanism utilized by E1B, however, roles in growth stimulatory processes have also been implied. To determine whether there are any functional interactions between E1A 12S and the E1B 55K and 19K polypeptides, primary epithelial cells were infected with 12S viruses with different E1B regions. In the absence of both E1B proteins, there was an increase in 12S expression. This resulted in increased levels of DNA synthesis, entry into S-phase of the cell cycle and increased levels of proliferation, in the presence or absence of serum. There was also a higher induction of growth factor activity. In the presence of the 55K and absence of the 19K protein, there was a decrease in 12S expression. However, the highest induction of proliferative responses was observed. This suggests that expression of the 19K polypeptide inhibits 12S function directly. The lack of 19K expression also enabled the epithelial cells to have a much higher plating efficiency, achieve a greater cell density and reach the immortalized state faster. Although some modest differences in p53 expression were observed when compared to mock, they could not be correlated with any phenotype.