Effects of the Ad5 upstream E1 region and gene products on heterologous promoters

Background All recombinant adenovirus vectors contain the upstream region of the E1A gene comprising the viral origin of replication, encapsidation signal, and cis-acting regulatory elements for transcription of the E1A and other early genes. Using different reporter genes, some previous studies demonstrated the maintenance of heterologous promoter specificity in the adenoviral context, while others reported that adenoviral sequences interfere with promoter activity. Methods Plasmid DNA-based luciferase reporter gene assays and adenovirus type 5 (Ads) infection were combined to examine the effect of the Ads (nt 1-353) element and/or adenoviral gene products on tissue-specific (Midkine (MK) and COX-2), cell cycle associated (Ki-67 and E2F1) and viral promoters (Ads El, Ads E4 and SV40). As a proof of concept, data were verified in the setting of recombinant replication-defective and replication-competent adenoviral vectors. Results Viral and E2F1 promoter activities were enhanced by the Ads (nt 1-353) segment by similar to 100% and 145%, respectively, regardless of its position. A polyadenylation sequence (polyA) upstream of the promoter had no effect, confirming an enhancer element within the Ads (nt 1-353) segment. Ads (nt 1-353) increased COX-2 promoter activity by 146% but was blocked by an upstream polyA, indicating a cryptic transcription start site. When placing the reporter gene cassette in a replication-defective adenovirus, similar data were obtained. In the plasmid vector-based system, adenoviral gene products transactivated the E2F1 and viral promoters by 194%, 19%, 67%, and 16%, respectively. Tissue-specific promoter activities were not significantly affected by the Ads (nt 1-353) segment, nor adenoviral gene products. In concert with these data, we were able to target replication-competent adenoviral vectors with the COX-2 promoter, but not with the cell cycle associated promotor. Conclusions The adenovirus E1A upstream regulatory region and gene products interact with some but not all heterologous promoters. Often, the basal promoter activity can be reduced with an upstream polyA. Since the data obtained in our plasmid vector-based assay with internal control and infection with adenovirus could be confirmed in the adenoviral setting, our system might be suitable to speed up the identification of promoters which maintain their specificity in the adenoviral context and circumvent the problems associated with determining infectious adenovirus titers. Copyright (c) 2005 John Wiley & Sons, Ltd.