SMAD4 and hepatocellular carcinoma: Moreover, miR-210 in exosomes produced by HCC inhibits the expression of SMAD4 and STAT6 in human umbilical vein endothelial cell (HUVECs) [143], and exosomes secreted by hypoxia-stimulated HCC cells enhance the expression of VEGF/VEGFR in endothelial cells, both of which can promote angiogenesis [144].