title: Cell-penetrating peptides. A reevaluation of the mechanism of cellular uptake.
abstract: Cellular uptake of a family of cationic cell-penetrating peptides (examples include Tat peptides and penetratin) have been ascribed in the literature to a mechanism that does not involve endocytosis. In this work we reevaluate the mechanisms of cellular uptake of Tat 48-60 and (Arg)(9). We demonstrate here that cell fixation, even in mild conditions, leads to the artifactual uptake of these peptides. Moreover, we show that flow cytometry analysis cannot be used validly to evaluate cellular uptake unless a step of trypsin digestion of the cell membrane-adsorbed peptide is included in the protocol. Fluorescence microscopy on live unfixed cells shows characteristic endosomal distribution of peptides. Flow cytometry analysis indicates that the kinetics of uptake are similar to the kinetics of endocytosis. Peptide uptake is inhibited by incubation at low temperature and cellular ATP pool depletion. Similar data were obtained for Tat-conjugated peptide nucleic acids. These data are consistent with the involvement of endocytosis in the cellular internalization of cell-penetrating peptides and their conjugates to peptide nucleic acids.
authors.affiliation: Unité Mixte de Recherches 5124 CNRS, Université Montpellier 2, Montpellier, France.
authors.forename: Jean Philippe
authors.initials: JP
authors.lastname: Richard
authors.forename: Kamran
authors.initials: K
authors.lastname: Melikov
authors.forename: Eric
authors.initials: E
authors.lastname: Vives
authors.forename: Corinne
authors.initials: C
authors.lastname: Ramos
authors.forename: Birgit
authors.initials: B
authors.lastname: Verbeure
authors.forename: Mike J
authors.initials: MJ
authors.lastname: Gait
authors.forename: Leonid V
authors.initials: LV
authors.lastname: Chernomordik
authors.forename: Bernard
authors.initials: B
authors.lastname: Lebleu
mesh_terms: D000255:Adenosine Triphosphate / Q000378:metabolism; D000818:Animals; D002460:Cell Line; D004705:Endocytosis / Q000502:physiology*; D005404:Fixatives / Q000378:metabolism; D005434:Flow Cytometry; D005456:Fluorescent Dyes / Q000378:metabolism; D015696:Gene Products, tat / Q000235:genetics / Q000378:metabolism*; D006801:Humans; D008856:Microscopy, Fluorescence; D010455:Peptides / Q000235:genetics / Q000378:metabolism*; D016707:Tissue Fixation; D014357:Trypsin / Q000378:metabolism
chemical_list: D005404:Fixatives; D005456:Fluorescent Dyes; D015696:Gene Products, tat; D010455:Peptides; D000255:Adenosine Triphosphate; D014357:Trypsin