Integrin-mediated uptake of TSP2 by MKs in vitro.

rTSP2 was added to MKs in panels B-F. MKs were grown in the absence (A-D) or presence (E-F) of plasma. The uptake of TSP2 was inhibited by an RGD-containing peptide (C) but not by a control peptide (D). The inset in panel A shows results of RT-PCR with TSP2-specific primers (top bands) and with ribosomal protein SP6-specific primers as control (bottom bands) from dermal fibroblasts (Fb) and MKs. Representative images, obtained by confocal microscopy, of rTSP2-treated MKs grown in the absence of plasma are shown (G-H). Uptake of TSP2 was detected by FITC-conjugated IgG. Nuclei in panels E-H were visualized with DAPI, and the cytoskeleton in panel F was visualized with phalloidin. Bars represent 25 μm (A-F) and 10 μm (G-H).