Background: It has been previously demonstrated that plasmid DNA transport into the nucleus could be increased by transcription factor binding. We chose the glucocorticoid responsive element (GRE) which binds to the glucocorticoid receptor (GR), a transcription factor which is shuttled into the nucleus upon ligand binding such as dexamethasone.
Methods: We cloned two, four, and eight repetitive sequences of the GRE into the reporter plasmid pEGFPLuc. Binding of the pEGFPLuc-GRE to the GR was examined by electrophoretic mobility shift assay (EMSA) experiments. GR expression in bronchiolar and alveolar epithelial cells was confirmed by Western blotting. Intracellular trafficking of GR was examined using a fusion protein of cyano-fluorescent protein (CFP) and GR. Transfection efficiencies of pEGFPLuc compared to pEGFPLucGRE(2-8) were examined in vitro and in vivo upon tail vein injection of cationic liposome gene vectors containing dexamethasone (safeplexes) and aerosol application of polyethylenimine (PEI)-pDNA particles.
Results: Binding of GRE containing plasmids to the GR was shown in EMSA experiments and intranuclear shuttling of CFP-GR after ligand stimulation was confirmed. Enhanced gene transfer efficiency of pEGFPLucGRE(2) in vitro was only observed on confluent cells. A 2.5-fold increase in gene expression in the lungs of mice after tail vein injection of pEGFPLucGRE(2) complexed with safeplexes compared with pEGFPLuc was observed. PEI-mediated aerosol gene delivery of pEGFPLucGRE(2) was 4.7-fold higher than pEGFPLuc only after intraperitoneal dexamethasone.
Conclusion: The results suggest that inclusion of GRE sequences into plasmid DNA vectors combined with dexamethasone application could improve transgene expression in the lungs in vivo.