KS cells have both endothelial and mural cell characteristics. (A) Expression of endothelial progenitor markers (CD133 and CD248) in KS cells was analyzed by RT-PCR. (B) LECs and LEC/KSHV cells were sorted for cell surface CD133 expression by flow cytometry. (C) Expression of mural cell markers (calponin, desmin, and α-SMA) in KS cells was analyzed by RT-PCR. Human UASMCs were used as positive control for mural cell markers. (D) Western blots analysis for α-SMA expression in KS cells. (E) Cells were labeled with green or orange CellTracker and cultured on Matrigel for 6 hours, alone or in various combinations. (Right panel) Enlarged boxed area in the middle panel. Arrows point to the tubes formed by integration of 2 types of endothelial cells. Arrowheads point to the endothelial cells lined with mural cells.