Effect of CXCR7 silencing on tube formation induced by SMMC-7721 cells. HUVECs were cocultured with SMMC-7721 cells, as described in Materials and Methods. Inhibition of CXCR7 expression in SMMC-7721 cells impaired tube formation induced by SMMC-7721 cells. Each bar represents mean ± SD from three independent experiments. *p < 0.05 (as compared with control cells).