Exosomal B7-H3 facilitates colorectal cancer angiogenesis and metastasis through AKT1/mTOR/VEGFA pathway.

B7-H3 (CD276), an immune checkpoint molecule, is aberrantly overexpressed in many types of cancer, and plays important roles in tumor immune evasion, carcinogenesis and metastasis, as well as angiogenesis. However, the mechanisms underlying B7-H3-promoted angiogenesis are still largely unknown. In this study, based on the observation of overexpression of B7-H3 on the tumor cells and vascular endothelial cells (VECs) in colorectal cancer (CRC) tissues, we investigated the roles of cancer cell-drived exosomal B7-H3 in tumor angiogenesis and metastasis through crosstalk between cancer cells and VECs. We found that CRC cell-drived exosomal B7-H3 was uptaken by human umbilical vein endothelial cells (HUVECs) and consequently activated the AKT serine/threonine kinase 1 (AKT1) / mechanistic target of rapamycin kinase (mTOR) / vascular endothelial growth factor A (VEGFA) signaling pathway, thus augmenting the abilities of migration, invasion and tube formation of HUVECs. Furthermore, administration of CRC cell-drived exosomes with reinforced B7-H3 promoted the pulmonary angiogenesis and metastasis of CRC cells in mice. In addition, high expression of B7-H3 was observed in urinary exosomes isolated from CRC patients. Our findings reveal that CRC-derived exosomal B7-H3 promotes tumor angiogenesis and metastasis by activating the AKT1/mTOR/VEGFA signaling pathway. It provides novel insights into the roles of CRC-drived exosomes in CRC progression.