Muscle-specific enhancement of gene expression by incorporation of SV/40 enhancer in the expression plasmid

Skeletal muscle is established as an ideal tissue for gene delivery to trea t systemic diseases. However, the relatively low levels of gene expression obtained from using naturally occurring promoters, including the strong cyt omegalovirus (CMV) enhancer/promoter (E/P), have limited the use of muscle as a target tissue. The relatively weak simian virus 40 (SV40) enhancer is known to have dual functions promoting localization of DNA to the nucleus a nd activating transcription. An SV40 enhancer incorporated either at the 5' end of CMV E/P or the 3' end of the polyadenylation site gave as much as a 20-fold increase in the level of exogenous gene expression in muscle in vi vo, compared with expression observed with CMV E/P alone. The minimum requi rement for this enhancement is a single copy of a 72-bp element of the SV40 enhancer, in combination with either the CMV E/P or skeletal actin (SkA) p romoter. Enhancement of gene expression in muscle by this SV40 enhancer was also observed by using the powerful electroporation delivery. However, the SV40 enhancer does not increase the level of CMV E/P driven reporter gene expression in dividing tumor cells in vivo and in the dividing myoblast cel l C2C12 in vitro. The data suggest that including this enhancer in the plas mid will enhance the level of gene production for muscle-based gene therapy .