Strength evaluation of transcriptional regulatory elements for transgene expression by adenovirus vector

In studies of both gene function and gene therapy, transgene expression may be assisted considerably through the use of transcriptional regulatory elements with high activity. In this study, we evaluated the strength of various transcriptional regulatory elements both in vitro (six types of cell line) and in vivo (mouse heart, lung, kidney, spleen, and liver) by adenovirus-mediated gene transfer. In the case of the promoter/enhancer (P/E), the activity of CMV P/E (from the human cytomegalovirus immediate-early 1 gene) and hybrid CA P/E (composed of the CMV enhancer and chicken beta-actin promoter) were investigated, both of which are known to be strong and widely used. While hybrid CA P/E showed a higher transgene expression activity than CMV P/E, the addition of the intron A sequence (the largest intron of CMV) to CMV P/E increased the activity of CMV P/E to the same or higher level than that of hybrid CA P/E. Concerning the polyadenylation signal (P(A)) sequence, one from the bovine growth hormone (BGH) gene was about two times more efficient than that from the Simian virus 40 (SV40) late gene, both in vitro and in vivo. In the context of the CMV P/E containing the intron A sequence, a further increase in transgene expression was obtained by the addition of a SV40 enhancer downstream from the P(A) sequence. The combination of the SV40 P(A) and a SV40 enhancer showed almost comparable activity to BGH P(A). This information would be helpful for the construction of adenovirus vectors for studies regarding both gene function and gene therapy.