Adenovirus-mediated regulable target gene expression in vivo

To regulate expression of a transferred gene in response to an exogenous co mpound, we have combined a high capacity adenoviral vector devoid of all vi ral coding sequences with a regulatory system that can be used to express a target gene in vivo in a selected site and at a desired time. This system uses a chimeric transactivator, GLp65, which consists of a mutated progeste rone receptor-ligand binding domain fused to the GAL4 DNA binding domain an d part of the activation domain of the human p65 protein, a component of th e NF-KB complex. In the presence of the antiprogestin mifepristone, this ch imeric regulator binds to a target gene containing the 17-mer GAL4 binding site, resulting in an efficient ligand-inducible transactivation of the tar get gene, We inserted the regulator GLp65 and a regulable human growth horm one target gene containing the 17-mer GAL4 binding site into the same adeno viral vector. To obtain tissue-specific expression of the target gene, we c oupled the regulator to a liver-specific promoter. Infection of HepG2 cells and experimental mice with the adenovirus resulted in consistently high in duction levels of human growth hormone in the presence of mifepristone wher eas the transgene expression was undetectable in the absence of the ligand, Taken together, our regulable adenoviral vector represents an important to ol for transgene regulation that can be used for potentially diverse applic ations, ranging from tissue-specific gene expression in transgenic animals to human gene therapy.