title: Caveolae-mediated internalization of extracellular HIV-1 tat fusion proteins visualized in real time.
abstract: The Tat protein from HIV-1, when fused with heterologous proteins or peptides, can traverse cell membranes. This ability has generated great interest due to potential therapeutic applications. However, the relevant cellular pathway and its dynamics have not been elucidated yet. Here we unravel the intracellular fate of exogenously added Tat fused with green fluorescent protein (GFP) in live HeLa and CHO cells, from the early interaction with the plasma membrane up to the long-term accumulation in the perinuclear region. We demonstrate that the internalization process of full-length Tat and of heterologous proteins fused to the transduction domain of Tat exploits a caveolar-mediated pathway and is inhibited at 4 degrees C. Remarkably, a slow linear movement toward the nucleus of individual GFP-tagged Tat-filled caveolae with an average velocity of 3 micro m/h was observed. No fluorescence was observed in the nucleus, possibly suggesting that Tat fusion protein unfolding is required for nuclear translocation. In addition, early sensitivity to cytochalasin-D treatment indicates the essential role of the actin cytoskeleton in the displacement of Tat vesicles toward the nucleus. Our results imply that HIV-1 Tat mediates the internalization of protein cargos in a slow and temperature-dependent manner by exploiting the caveolar pathway.
authors.affiliation: NEST-INFM and Scuola Normale Superiore, Piazza dei Cavalieri 7, I-56126, Pisa, Italy. a.ferrari@sns.it
authors.forename: Aldo
authors.initials: A
authors.lastname: Ferrari
authors.forename: Vittorio
authors.initials: V
authors.lastname: Pellegrini
authors.forename: Caterina
authors.initials: C
authors.lastname: Arcangeli
authors.forename: Antonio
authors.initials: A
authors.lastname: Fittipaldi
authors.forename: Mauro
authors.initials: M
authors.lastname: Giacca
authors.forename: Fabio
authors.initials: F
authors.lastname: Beltram
mesh_terms: D000818:Animals; D001692:Biological Transport / Q000187:drug effects; D021941:Caveolae / Q000737:chemistry / Q000187:drug effects / Q000378:metabolism*; D006224:Cricetinae; D015638:Cytochalasin D / Q000494:pharmacology; D004705:Endocytosis / Q000187:drug effects; D015696:Gene Products, tat / Q000378:metabolism*; D015497:HIV-1; D006367:HeLa Cells; D006801:Humans; D018613:Microscopy, Confocal; D015739:Nocodazole / Q000494:pharmacology; D011993:Recombinant Fusion Proteins / Q000378:metabolism; D013997:Time Factors; D014617:Vacuoles / Q000737:chemistry / Q000187:drug effects / Q000378:metabolism; D054322:tat Gene Products, Human Immunodeficiency Virus
chemical_list: D015696:Gene Products, tat; D011993:Recombinant Fusion Proteins; D054322:tat Gene Products, Human Immunodeficiency Virus; D015638:Cytochalasin D; D015739:Nocodazole