Promoters and Influence Expression

Although retroviral vectors show promise for gene therapy, their expression in animals has been low. An im-proved understanding of h o w promoters function from a retroviral vector should facilitate the design of im-proved vectors. In this study, Uver-specific promoters were cloned into a retroviral vector and expression from the retroviral long terminal repeat (LTR) and the internal promoter was analyzed. In addition, oligomerized liver-specific transcription factor binding sites were placed upstream of each promoter in an attempt to in-crease expression further. Additional oligomerized binding sites only increased expression slightly or inhib-ited expression in hepatoma ceUs, suggesting that this is not an effective way to increase expression from a retroviral vector. Unexpectedly, the liver-specific albumin promoter was expressed at high levels from a retro-viral vector in fibroblasts, suggesting that retroviral elements functioned as an enhancer. Furthermore, the addition of H N F- 4 binding sites adjacent to the albumin promoter inhibited both the L T R and albumin pro-moter in fibroblasts, an effect that was probably mediated by inhibitory proteins present in nonhepatic cells that can bind to H N r- 4 sites. These results suggest that both positive and negative influences can be trans-mitted between the L T R and the albumin promoter. In contrast, the liver-specific h u m a n ai-antitrypsin pro-moter did not appear to interact with the L T R by either of these criteria. Retroviral vectors have sequence