Promotion of tumor cell binding to vascular endothelium by osteopontin. A and B, KRIB osteosarcoma cells were treated with DMEM, GST-osteopontin, GST-osteopontin-RGE, or phosphatase inhibitors prior to GST-osteopontin and were subsequently incubated with the endothelium of the dorsal aorta. Relative to the GST-osteopontin-RGE and phosphatase inhibition groups, GST-osteopontin significantly increased cell binding (arrows) to the aortas (p<0.05; asterisk). Bars indicate mean ± SD. Scale bar, 20 μm. C, The number of tumor foci was increased in nude mice receiving human sarcoma cells previously incubated with GST-osteopontin relative to DMEM-treated cells.