Characteristics of Transcription-regulatory Elements for Gene Expression from Plasmid Vectors in Human Trophoblast Cell Lines

Nonviral gene delivery systems are useful for basic research in trophoblasts. In these systems, gene expression is regulated by a cassette of regulatory elements within the plasmid, and the transcriptional activity differs among cell lines. In the present study, we used BeWo and JAR human trophoblast cell lines to systematically compare the transcriptional activities of several expression cassettes and those of a control plasmid made up of a simian virus 40 (SV40) promoter, a polyadenylation (PA) signal, and an enhancer. We also found that insertion of intron elements enhanced transcriptional activities in the following order: intron A > hybrid β-globin-immunoglobin intron > no intron. Of several PA signals tested including those from SV40, bovine growth hormone, and the minimal rabbit β-globin, the latter had the highest transcriptional activities (3.9- and 26-fold over control plasmid in BeWo and JAR cells, respectively). Addition of a second enhancer increased the transcriptional activity in these cells. We also found that gene expression level can be controlled by selecting the expression cassette. These results should be useful for further transgene experiments in BeWo and JAR cells.