In this study, we did not elucidate the molecular mechanisms by which CXCR7 regulated the invasion of HCC cells. Another recent study suggests that signaling pathways mediated by CXCR7 are independent of those triggered through CXCR4 . Therefore, it is reasonable to speculate that CXCR7 may exert effects on other
signaling. Also, the different biological effects elicited by CXCR7 may depend on cell type. Thus, further studies elucidating roles of CXCR7 in invasion and signaling cascades activated by CXCL12/CXCR7 axis are required. Tumor cells interact with ECM components and basement membranes, an essential initial event during the process of invasion. It also has been reported that expression of CXCR7 can regulate PP2 adhesion of tumor cells to endothelial cells [19, 24]. Our IACS-10759 concentration results demonstrated that CXCL12 could induce adhesion of SMMC-7721 cells to FN and LN. The enhanced cell-matrix adhesion may contribute to metastasis of tumor cells. In addition, we also found that RNAi-mediated
down-regulation of CXCR7 significantly inhibited CXCL12 induced adhesion of SMMC-7721 cells to LN or FN. Therefore, these findings clearly indicate that CXCR7 participate in CXCL12 induced cell-matrix adhesion. Tumor metastasis is a multistep process that involves the coordinated events of invasion, adhesion, proteolysis and migration. The decreased adhesive ability of HCC cells could lead to inhibition of the invasion of SMMC-7721. Cancer cells check details depend on angiogenesis to survive and proliferate . We observed that HCC cells could induce in vitro Paclitaxel tube formation, which could promote tumor growth. Although CXCL12 induced VEGF secretion has been reported in various cells, such as lymphohematopoietic cells and prostate cancer cells [32, 33], CXCL12 induced VEGF production in HCC cells has not been
previously studied. In the current study, we found that CXCL12/CXCR7 interaction promoted secretion of VEGF, a potent survival factor for endothelial cells, and one of the most prominent angiogenic factors produced by various tumor cells. Furthermore, our data demonstrate that knockdown of CXCR7 inhibits secretion of VEGF and tube formation, suggesting that CXCR7 may be involved in the regulation of angiogenesis in HCC. Initial evidence has indicated that expression levels of CXCR7 are frequently high in tumor-associated endothelial cells and activated endothelial cells, but not in normal endothelial cells [4, 19]. Our results also confirm that CXCR7 expresses in HUVECs with low levels. To date, very little is known in regard to the regulation of CXCR7 expression in cancer cells and normal cells. In this study, we demonstrated that VEGF stimulation enhanced CXCR7 mRNA and protein levels not only in HCC cell lines but also in HUVECs. A large quantity of VEGF is produced from tumor microenvironment, which could result in enhanced expression of CXCR7 in tumor-associated blood vessels.