Efficient cellular uptake of recombinant murine Hoxc8 homeoprotein in COS-7 cells

The third helix of the Hoxc8 homeodomain peptide enhances the efficiency of gene transfer in combination with lipofectamine

Protein transduction domains (PTDs) have been shown to cross the biological cell membranes efficiently through a receptor and energy independent mechanism. Because of its ease in membrane transducing ability, PTDs could be used as a gene delivery vector. Since we already have shown that purified Hoxc8 homeoprotein has the ability to cross the cellular membrane, we analyzed the possibility of the third helix of the Hoxc8 homeodomain as a useful gene delivery vector. For that purpose, a 16-aa long synthetic oligopeptide Hoxc8 Protein Transduction Domain (HPTD) was chemically synthesized and then tested to see whether the HPTD could form a complex with DNA or not. Gel retardation analysis revealed that the HPTD interacts with plasmid DNA efficiently but failed to transfer the DNA into the cells. However, HPTD can enhance the efficiency of gene transfer in combination with Lipofectamine which doubled the gene transfer rate into COS-7 cells compared with the DNA/Lipofectamine control. An MTT assay indicated that the amount of HPTD used in the complex for the transfection did not show any cytotoxicty in COS-7 cells. The TEM studies showed compact particle formation in the presence of HPTD. These results indicate that the HPTD could be a good candidate adjuvant molecule to enhance the gene transfer efficiency of Lipofectamine in eukaryotic cells.

Membrane transducing activity of recombinant Hoxc8 protein and its possible application as a gene delivery vector

In order to examine whether the Hoxc8 protein can deliver nucleic acid into mammalian cells, we designed several Hoxc8-derived recombinant proteins to be synthesized as glutathione S-transferase (GST) fused forms in E. coli (GST-Hoxc8(1-242), containing a full length of Hoxc8; GST-Hoxc8(152-242), possessing a deletion of the acidic N-terminus of Hoxc8; GST-Hoxc8(149-208), which contained the homeodomain only). After labeling these proteins with Oregon 488, we examined their membrane transduction ability under the fluorescence microscope and verified that all three proteins showed similar transduction efficiency. The ability of the proteins to form in vitro protein-DNA complexes was analyzed on agarose gel; both GST-Hoxc8(1-242) and GST-Hoxc8(149-208) formed complexes. In contrast, the GST-Hoxc8(152-242) protein did not form a complex. The GST-Hoxc8(149-208) protein formed a complex with DNA at a mass ratio of 1ú1 (DNAúprotein), and GST-Hoxc8(1-242) formed a complex at a mass ratio of 1ú5. When the DNA (pDsRed1-C1) and protein complexes were added to culture media containing mammalian cells, the cells uptook the complexes, which was indicated by red fluorescence expression under the fluorescent microscope. These results indicate that recombinant Hoxc8 derivatives that harbor a homeodomain are able to traverse the mammalian cellular membrane. DNA that is bound to the recombinant derivatives can be carried across the membrane as well. This process could be applied in the development of a useful delivery vector for gene therapy in the future.