Expression of the chloramphenicol acetyl transferase gene in human cells under the control of early adenovirus subgroup C promoters: effect of E1 A gene products from other subgroups on gene expression

Abstract

A hierarchy of dominance has been observed in HeLa cells co-infected with two serotypes of adenovirus belonging to different subgroups. DNA replication and late protein synthesis of one serotype are inhibited by those of the other. The degree of inhibitory effect has the following decreasing order: adenovirus type 3 (Ad3) and Ad7 (subgroup B), Ad9 (D), Ad4 (E), Ad12 (A), Ad2 and Ad5 (C) [Delsert and D'Halluin, Virus Res. 1 (1984) 365–380]. HeLa cells were first transfected with recombinant plasmids carrying Ad5 E2A or E3 promoters fused to the chloramphenicol acetyl transferase gene ( cat), and then infected with human Ad belonging to different subgroups. All the serotypes tested were found to be able to stimulate both E2A and E3 promoters. When HeLa cells were co-transfected with either of the previous plasmids, plus a second plasmid carrying the Ad3 E1 A region, the same stimulatory effect was observed. However, an inhibitory effect on Ad5 E2A and E3 promoters seemed to occur when both Ad2 E1A (subgroup C) and Ad3 E1A (subgroup B) genes were present together. To determine which one of the early products was responsible for the observed repression effect, and to assign the target on the genome of subgroup C Ad, a plasmid was constructed in which the sequences at the 5' end of the Ad2 E1A region were fused to the structural sequences of the cat gene. In HeLa cells transfected with this plasmid, CAT activity was significantly increased after co-transfection with a plasmid carrying the Ad2 E1A region, but decreased with a plasmid carrying the Ad3 E1A region. This suggests that some product of the Ad3 E1A genes represses the Ad2 E1A promoter region, but is capable of stimulating the Ad5 E2A and E3 promoters in the absence of Ad2 E1A gene products.