Abstract
Angiogenesis not only play a critical role in embryonic development and tissue repair, but also is an important process for tumor growth and metastasis. Recent studies have shown that tumor cells could induce the mobilization of endothelial progenitor cell (EPC) and outgrowth endothelial cell (OEC) from bone marrow via many cytokines, such as GM-CSF、SDF-1 and VEGF. Furthermore, those EPC could migrate and invade to tumor micro-metastatic niche, and gradually differentiate into endothelial like-cell incorporate the growing vasculature. Using ex vitro culture-expanded EPC or OEC transplanted in to the tumor bearing mice, many researches suggest that EPC control the angiogenic switch and OEC facilitate the neoangiogenesis in the tumor progression. However, the underlying interaction mechanism of EPC/OEC and carcinoma cells in the progression of tumor cell remains unclear. Thus, the aim of the present study to elucidate the effect of tumor cell on differentiation, migration, invasion, and tubular structure formation of EPC and OEC, using in vitro co-cultured system. Firstly, we need to identified EPC and OEC derived from peripheral blood mononuclear cells. We found both of EPC and OEC displayed several commonly accepted EPC phenotypes, including spindle/cobblestone morphology, ac-LDL incorporation, UEA-1 binding, and CD31/KDR/Flt-1 reactivity. The previous clinical reports have indicated that hepatocellular carcinoma (HCC) is one of malignant tumor with rich neovascularization, which can be clearly observed in hepatic angiography. On the basis of co-culture transwell model and time-lapse video microscopy system, we show that migration and invasion capability of EPC was augmented by HCC, and also can induce EPC express higher intensity of endothelial markers to promote the differentiation of EPC. On the other hand, the migration, invasion and tubular structure formation of OEC was inhibited by HCC. In addition, HCC did not alter cell cycle of EPC, whereas they prevented OEC from entering S and G2/M phases and induce OEC cell cycle G0/G1 arrest. The present study suggests that the different effect of HCC on EPC and OEC may mediate their different contribution to tumor angiogenesis. Our findings may provide new insights into the interaction mechanism of EPC/OEC and HCC involve in the progression of angiogenesis.