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Hoffmann, R. A wiki for the life sciences where authorship matters. Nature Genetics (2008)

PDX-1 protein is internalized by lipid raft-dependent macropinocytosis.

PDX-1 plays a central role in regulating insulin gene transcription and differentiation of insulin-producing cells. It was previously reported that, due to its own Antennapedia-like protein transduction domain (PTD), exogenous PDX-1 protein can permeate cells and induces insulin gene expression in pancreatic ducts, thought to be islet progenitor cells. These data suggest that PDX-1 protein transduction could be a safe and valuable strategy for facilitating differentiation of progenitor cells into insulin-producing cells without requiring gene transfer technology. Here it is shown that after an initial ionic cell-surface interaction, PDX-1 proteins are rapidly internalized by lipid raft-dependent macropinocytosis. HeLa cells were treated with both FITC-conjugated PDX-1 PTD and FM 4-64, a general fluorescent marker of endocytosis. A punctate cytoplasmic distribution of PDX-1 PTD, which colocalized with FM 4-64, was observed in treated cells. Because expression of dominant-negative dynamin-1 did not block PDX-1 PTD uptake, PDX-1 protein transduction is independent on phagocytosis and clathrin- or caveolar-mediated endocytosis. Cells were pretreated with amiloride, a specific inhibitor of the Na+/H+ exchange required for macropinocytosis, or cytochalasin D, an F-actin elongation inhibitor. Treatment of cells with both macropinosome inhibitors resulted in the reduction in PDX-1 PTD transduction into vesicles, suggesting that PDX-1 PTD-mediated cellular entry occurs by lipid raft-mediated macropinocytosis. Taken together, these observations provide the mechanism of PDX-1 protein transduction and suggest that the protein transduction system could work for experimental and therapeutic strategies.[1]


  1. PDX-1 protein is internalized by lipid raft-dependent macropinocytosis. Noguchi, H., Matsumoto, S., Okitsu, T., Iwanaga, Y., Yonekawa, Y., Nagata, H., Matsushita, M., Wei, F.Y., Matsui, H., Minami, K., Seino, S., Masui, Y., Futaki, S., Tanaka, K. Cell transplantation. (2005) [Pubmed]
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