Background: The weak efficiency of plasmid transfer into the cytosol remains one of the major limiting factors to achieve an efficient transfection with DNA/cationic polymer complexes. We found that divalent metal Zn2+ can improve the polyfection efficiency, especially with DNA/histidylated polylysine (His-pLK) complexes.
Methods and results: The supplementation of the transfection medium with 250 micro M ZnCl2 increased the polyfection of human hepatocarcinoma (HepG2) cells with a plasmid encoding EGFP complexed with pLK, polyethyleneimine and His-pLK. Zn2+ is more efficient on DNA/His-pLK complexes: the number of EGFP-positive cells increased from 1% to more than 40%. This phenomenon is selective to Zn2+ because no effect was obtained with other divalent cations. The effect of zinc varies from cell to cell. The binding of Zn2+ to histidyl residues might increase zinc endosomal concentration favoring membrane fusion. Flow cytometry and confocal microscopy studies clearly indicate that with His-pLK, the plasmid is better delivered in the cytosol as well as in the cell nucleus in zinc-treated cells. An investigation conducted with the histidine-rich peptide H5WYG showed that zinc inhibits membrane permeabilization but promotes membrane fusion as evidenced by resonance energy transfer.
Conclusions: Data reported here imply that the addition of zinc ions in the transfection medium can trigger an increase of the fusion of endosomes containing polyplexes which is more effective in the presence of histidine-rich molecules. Consequently, the amount of plasmid in the cytosol available to reach the nucleus is increased leading to an improvement of polyfection.
Copyright 2002 John Wiley & Sons, Ltd.