Modulation of the specificity and activity of a cellular promoter in an adenoviral vector

Most gene therapy studies with recombinant adenoviruses employ viral promoters and lack tissue specificity. To determine whether a tissue-specific cellular promoter inserted into the adenoviral genome can direct the expression of a reporter gene in a tissue-specific manner, recombinant adenoviruses containing a nuclear lacZ gene driven by a human ventricular/slow muscle myosin light chain 1 promoter with and without a muscle creatine kinase enhancer were constructed. The ability of these viruses to express the reporter genes in infected myogenic and nonmyogenic cell lines was studied. Intramuscular injection of these viruses into mice showed that little or no reporter gene expression occurred in muscle fibers, although a relatively high level of lacZ gene expression was observed in surrounding connective tissue. Insertion of adenovirus sequences from the 5' inverted terminal repeat (ITR) region and/or the protein IX region into plasmids resulted in decreased reporter gene expression from myosin light chain 1 promoter in transfected C2C12 myotubes and 293 cells, as well as in injected muscles. These results suggested that negative elements are present in the adenoviral genome. This negative effect seems neither tissue nor species specific. Adenovirus cis-elements that may affect the specificity and activity of a cellular promoter are discussed.