Imaging and Tracking of Tat Peptide-Conjugated Quantum Dots in Living Cells: New Insights into Nanoparticle Uptake, Intracellular Transport, and Vesicle Shedding

Department of Chemistry, Emory University, Atlanta, Georgia, United States
Journal of the American Chemical Society (Impact Factor: 12.11). 12/2007; 129(47):14759-66. DOI: 10.1021/ja074936k
Source: PubMed


We report the use of Tat peptide-conjugated quantum dots (Tat-QDs) to examine the complex behavior of nanoparticle probes in live cells, a topic that is of considerable current interest in developing advanced nanoparticle agents for molecular and cellular imaging. Dynamic confocal imaging studies indicate that the peptide-conjugated QDs are internalized by macropinocytosis, a fluid-phase endocytosis process triggered by Tat-QD binding to negatively charged cell membranes. The internalized Tat-QDs are tethered to the inner vesicle surfaces and are trapped in cytoplasmic organelles. The QD loaded vesicles are found to be actively transported by molecular machines (such as dyneins) along microtubule tracks. The destination of this active transport is an asymmetric perinuclear region (outside the cell nucleus) known as the microtubule organizing center (MTOC). We also find that Tat-QDs strongly bind to cellular membrane structures such as filopodia and that large QD-containing vesicles are released from the tips of filopodia by vesicle shedding. These results provide new insights into the mechanisms of Tat peptide-mediated delivery as well as toward the design of functionalized nanoparticles for molecular imaging and targeted therapy.

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    • "These dynamic events were not clearly synchronized in time and could be observed over a wide duration of time (t = 3–12 min) following pulsed QD-BDNF treatment (1 min). Unlike the linearly-directed trafficking found in neuronal processes or the nuclear-directed trafficking of other intracellular complexes [73], [74], QD-BDNF complexes did not show a net directional gain toward any particular subcellular target destination. Instead BDNF complexes could be found meandering over surprisingly long durations (several minutes) and over long distances (up to tens of microns) throughout the neuronal soma. "
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    • "Different types of peptides have been used as the promising candidates for intracellular delivery of QDs9101112131415. Recent advances include the enhancement of intracellular delivery of streptavidin-conjugated QDs into mouse fibroblast cells using biotinylated L-arginine peptides10, TAT-functionalized QDs for selective intracellular transport, vesicle shedding and delivery91314. Arginine–glycine–aspartic acid (RGD) peptides have been conjugated to target QDs specifically to tumor angiogenesis for theranostics1216. "
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    • "Thus, this study supported previous description of exosomes attaching to cell surface receptors (Miyanishi et al., 2007; Nolte-'t Hoen et al., 2009). Besides, the latter two intracellular modes indicated confined diffusion in local microenvironments of cytoplasm and active transport along cytoskeleton, highly correlated to the endocytic-derived transport reported for vesicles containing polyplexes (de Bruin et al., 2007), influenza virus (Lakadamyali et al., 2003), or golden nanoparticles (Ruan et al., 2007). The three-stage intracellular transport process of exosomes described before by us (Tian et al., 2010), similar to influenza transport (Lakadamyali et al., 2003), was also supported by this work. "
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