Actin-GFP mRNA from PLPs is transferred to and translated by HepG2 cells. (A) Representative fluorescence microscopy image from actin-GFP–transfected MEG-01 cells 48 hours after transfection. Shown is a bright-field image combined with actin-GFP signal. Original magnification ×100. Scale bar, 25 µm. (B) Representative flow cytometry analysis of isolated PLPs from actin-GFP–transfected MEG-01 cells. Histogram plot of actin-GFP-expressing MEG-01 cells (green line) compared with control MEG-01 cells (black line) (left). Histogram plot of PLPs derived from actin-GFP–expressing MEG-01 cells (green line) compared with control PLPs (black line) (right). (C) PLPs from actin-GFP–transfected MEG-01 cells (green, indicated by arrowheads) were cocultured with HepG2 cells for 4 hours. Internalization was assessed by confocal microscopy. (i) Total actin inside the HepG2 cell is stained in red. (ii) Actin-GFP from PLPs (green) was localized throughout the cytoplasm of the HepG2 cell. (iii) Total actin in HepG2 cells that were not treated with PLPs is shown for comparison. Original magnification ×400. Scale bar, 5 µm. (D) Actin-GFP–expressing PLPs were cultured alone or in combination with HepG2 cells for up to 48 hours. PLPs that were cocultured with HepG2 cells were pretreated with 100 U/ml RNaseA or vehicle prior to addition to the HepG2 cells. Actin-GFP expression was quantified at the indicated time points. *P < .05. Data represent the mean of 3 independent triplicate experiments. Error bars indicate SD. (E) Activated platelets treated with vehicle or different concentrations of RNaseA were added to HepG2 cells and incubated under serum-free conditions. After 48 hours, the cell proliferation rate was estimated by quantifying BrdU incorporation. Control groups represent HepG2 cells cultured in the presence or absence of FCS. *P < .05. Data represent the mean of 3 independent triplicate experiments. Error bars indicate SD.