Histones, protamine, and polylysine but not poly(E:K) enhance transfection efficiency

Liposomal gene delivery has a great potential for the treatment of cancer and other human diseases. In this work we have investigated the optimal conditions for liposome-mediated transfer of the luciferase gene to human erythroleukemia K562 cells. DDAB:DOPE liposomes were more efficient than lysyl-DOPE:DOPE (1:2) and DDAB:cholesterol for transfection. Total histones from bovine thymus, salmon sperm protamine, and polylysine at an optimal ratio of 0.5 mg protein/mg DNA enhanced up to 7-fold the transfection efficiency of luciferase plasmids; on the contrary, the synthetic polymer poly(E:K), containing glutamic acid and lysine residues in a random order at a ratio 1:4, diminished luciferase expression. Transfection was nearly zero at high histone:DNA ratio by reversal of the charge of the particle from negative to positive leading:to its inability to interact with cationic liposomes. The increase in luciferase gene expression by DNA-binding proteins might arise from an increased transfer across the cell membrane of the liposome-DNA-protein complex but also by an increase in nuclear import of the DNA-protein complex because of the presence of nuclear localization signals on the protein molecule used for DNA condensation.