Effect of adenovirus-2 early region-4 products on e1-transformation

We show that transformation of rat CREF fibroblasts by adenovirus-2 early regions 1A and 1B (E1) is stimulated by expression of the viral early region 4 (E4) products. Cotransfection of CREF cells with E1 and E4 did not affect the number of E1-transformed foci, but resulted in the formation of larger and more dense foci compared to E1 transfection alone. Cells obtained from these foci were capable of anchorage-independent growth. The adenovirus-2 E4 region encodes for a minimum of seven proteins, several of which have been shown to have distinct biological activities. To assay for the activity of these individual proteins on E1 transformation, we used expression vectors designed to encode single E4 proteins in the CREF cell transformation assay. By this strategy, we could show that two E4 proteins had a significant capacity to stimulate E1 transformation. Cotransfection of E1 and vectors encoding the E4-ORF1 or E4-ORF6 proteins resulted in the formation of large dense foci typical of E4-cotransformed cells. However, no single E4-ORF-expressing plasmid was sufficient to reproduce the stimulative effect on CREF cell transformation observed using the entire E4 region.