Liposome-mediated DNA transfer in eukaryotic cells. Dependence of the transfer efficiency upon the type of liposomes used and the host cell cycle stage.

The pBR322 plasmid containing the sequence encoding beta-lactamase, the enzyme conferring resistance to ampicillin, was encapsulated in liposomes of different phospholipid composition and incubated with synchronized cells. In mitotic cells as compared to cells synchronized in G1, twice as many exogeneous DNA molecules were found associated with the cell nuclear DNA, when fluid, neutral liposomes were used. These liposomes are taken up by the cells mainly via endocytosis. When fluid, negatively charged liposomes were used as carriers about the same number of exogenous DNA molecules were found associated with the nuclear DNA both in mitotic and in G1-synchronized cells. The efficiency for gene transfer of liposomes entering the cells by different mechanisms was further studied and expressed both by the fraction of the radioactive plasmid associated with the nuclear DNA and by the level of the beta-lactamase activity detected in the transfected cells. It appears that liposomes entering the cells mainly via an energy-dependent mechanisms are more efficient for this type of DNA transfer.