Effect of E1A and E1B viral proteins on the expression of a calcium ionophore-inducible gene and its promoter.

The adenovirus E1A products have been shown to confer both positive and negative regulations on viral as well as cellular genes. To investigate further the effect of the E1A products on cellular genes and their promoters, we measured the endogenous transcript levels of two calcium ionophore-regulated genes (p3C5 and p4A3) in 293 cells which expressed the E1A and E1B products as a result of adenovirus transformation. In addition, we compared the activities of the p3C5 promoter and the simian virus (SV40) early promoter under both induced and noninduced conditions in 293 and other cell lines. Our results indicate that the presence of the E1A and E1B products in 293 cells do not have any significant effect on the endogenous level of expression of both p3C5 and p4A3 genes, nor does it negatively affect the p3C5 promoter activity. We conclude that the activity of the viral products on cellular gene expression is selective; genes that are constitutively expressed and are readily inducible are not necessarily general targets for the E1A functions and while the p3C5 promoter contains an enhancer-like element which shares sequence homology with the SV40 promoter and other viral enhancer core sequences, its activity is not repressed by the E1A products.