No abstract

Cell-penetrating peptides (CPPs) are a growing family of peptides that have opened a new avenue in drug delivery, allowing various hydrophilic macromolecules to enter cells. In accordance with most other cationic delivery vectors, CPPs seem to rely mostly on endocytosis for internalization. However, due to conflicting results the exact endocytic pathways for CPP uptake have not yet been resolved. Here, we evaluated the ability of seven CPPs, with different chemical properties, to convey peptide nucleic acids (PNAs) inside cells. Assays based on both splice correction, generating biologically active read-out, and on traditional fluorescence measurements were utilized. The same assays were employed to assess different endocytic pathways and the dependence on extracellular heparan sulfates for internalization. Both highly cationic CPPs (M918, penetratin, and Tat) and amphipathic peptides (transportan, TP10, MAP, and pVEC) were investigated in this study. Conjugate uptake relied on endocytosis for all seven peptides but splice-correcting activity varied greatly for the investigated CPPs. The exact endocytic internalization routes were evaluated through the use of well-known endocytosis inhibitors and tracers. In summary, the different chemical properties of CPPs have little correlation with their ability to efficiently deliver splice-correcting PNA. However, conjugates of polycationic and amphipathic peptides appear to utilize different internalization routes.

No abstract

Attempts to unravel the cell translocation mechanism of a growing number of cell-penetrating peptides (CPP) have revealed molecular determinants essential for internalization ability. The peptide sequence and the charge have been proposed to be the major factors in determining the membrane interaction mode and subsequent internalization pathway. Recent research in this field has shifted to search and design of novel CPPs with predefined vectorial properties and elucidation of the mechanism of cell entry of CPPs with high cargo delivery efficiency. Here we present a map of interaction modes with cell surface and intracellular traffic of transportan and its analogue TP10 complexed with fluorescently labeled avidin or streptavidin-gold conjugates. The protein cargo complexed with either peptide is transduced into HeLa and Bowes cells mostly in the endocytic vesicles with heterogeneous morphology and size as demonstrated by transmission electron microscopy (TEM) and confocal laser scanning fluorescence microscopy. Most of the induced vesicles are large, with 0.5-2 mum diameter, probably macropinosomes, but the complexes are present also in smaller vesicles, suggesting involvement of different pathways. Later the majority of complexes are translocated from the cell periphery into vesicles of perinuclear region and partly to lysosomes. A fraction of transportan-streptavidin complexes is present also freely in cytoplasm, both in the close vicinity of plasma membrane and more centrally, suggesting the escape from endosomal vesicles, since vesicles with discontinuous membrane were also detected by TEM. The cell-translocation process of transportan-protein complexes is temperature dependent and strongly inhibited at 8-10 degrees C and blocked at 4 degrees C when only interaction with the plasma membrane takes place.