Penetration without cells: membrane translocation of cell-penetrating peptides in the model giant plasma membrane vesicles.

The cellular internalization of cell-penetrating peptides (CPPs) is proposed to take place by both endocytic processes and by a direct translocation across the plasma membrane. So far only scarce data is available about what determines the choice between the two uptake routes, or the proportion of used pathways when both are active simultaneously. Furthermore, the mechanism(s) of membrane penetration by peptides is itself still a matter of debate. We have introduced the giant plasma membrane vesicles (GPMVs) to study the interaction of six well-described CPPs (fluorescently labeled nona-arginine, Tat peptide, Penetratin, MAP, Transportan and TP10) in a model system of native plasma membrane without the interference of endocytic processes. The membranes of GPMVs are shown to segregate into liquid-ordered and liquid-disordered phases at low temperatures and we demonstrate here by confocal microscopy that amphipathic CPPs preferentially associate with liquid-disordered membrane areas. Moreover, all tested CPPs accumulate into the lumen of GPMVs both at ambient and low temperature. The uncharged control peptide and dextran, in contrary, do not translocate from the medium into the lumen of vesicles. The absence of energy-dependent cellular processes and the impermeability to hydrophilic macromolecules makes the GPMVs a useful model to study the translocation of CPPs across the plasma membrane in conditions lacking endocytosis.