EFFECT OF ADENOVIRUS-2 EARLY REGION-4 PRODUCTS ON E1-TRANSFORMATION

We show that transformation of rat CREF fibroblasts by adenovirus-2 ea rly regions 1A and 1B (E1) is stimulated by expression of the viral ea rly region 4 (E4) products. Cotransfection of CREF cells with E1 and E 4 did not affect the number of E1-transformed foci, but resulted in th e formation of larger and more dense foci compared to E1 transfection alone. Cells obtained from these foci were capable of anchorage-indepe ndent growth. The adenovirus-2 E4 region encodes for a minimum of seve n proteins, several of which have been shown to have distinct biologic al activities. To assay for the activity of these individual proteins on E1 transformation, we used expression vectors designed to encode si ngle E4 proteins in the CREF cell transformation assay. By this strate gy, we could show that two E4 proteins had a significant capacity to s timulate E1 transformation. Cotransfection of E1 and vectors encoding the E4-ORF1 or E4-ORF6 proteins resulted in the formation of large den se foci typical of E4-cotransformed cells. However, no single E4-ORF-e xpressing plasmid was sufficient to reproduce the stimulative effect o n CREF cell transformation observed using the entire E4 region.