An intracellular kinase signal-responsive gene carrier for disordered cell-specific gene therapy

We have previously reported artificial gene-regulation systems responding to cyclic AMP-dependent protein kinase (PKA) using cationic polymer. This cationic polymer (PAK) was a graft-type polymer with an oligopeptide that is a substrate for PKA and could regulate gene-expression in a cell-free system. In the present study, we carried out a detailed characterization of the PAK-DNA complex (AFM observation and DLS measurement) and tried to apply this polymer to living cells. In the unstimulated NIH 3T3 cells, transfection of the PAK-DNA complex showed no expression of the delivered gene. This means that PAK formed a stable complex with DNA in the normal cells to totally suppress gene expression. In contrast, significant expression was seen when the PAK-DNA complex was delivered to forskolin-treated cells. Thus, activated PKA disintegrates the complexes even in living cells, resulting in gene expression. Our results indicate that this type of intracellular signal-responsive polymer will be useful for the cell-specific release of genes.