Cancer exosomes harbor diverse hypoxia-targeted mRNAs and contribute toward tumor angiogenesis

Exosomes are extracellular vesicles of endosome origin secreted by various cells. The exosomal cargo, especially proteins and microRNAs, have been extensively investigated for their roles in intercellular communication and as biomarkers for clinical applications. However, the understanding of types and functions of exosomal mRNAs remains limited. Here, we evaluated the mRNAs of 61 hypoxia-targeted genes in exosomes by quantitative reverse transcription PCR (RT-qPCR). Among these 61 mRNAs, 14.8% of them were detected in the MCF10A-derived exosomes, 42.6% in the MCF7-derived exosomes, and 49.2% in the MDA-MB-231-derived exosomes, many of which are differentially regulated in response to hypoxic stress in a cell-line dependent manner. Consequently, 30 exosomal mRNAs are identified as cancer related biomarkers as they are present in cancer cell-derived exosomes and absent in MCF10A-derived exosomes. Co-culture of MDA-MB-231 cells with HUVECs shows uptake of MDA-MB-231 secreted exosomes by the Human umbilical vein endothelial cells (HUVECs). Subsequently, the cancer exosomal VEGFA mRNAs were translated within the HUVECs into proteins that promoted VEGFR-dependent angiogenesis. This finding provides novel insights into how cancer cells can directly contribute towards angiogenesis. RNA-seq also shows that cancer exosomes can upregulate epithelial-mesenchymal transition-related and metabolism-related genes. The transcripts of these genes are found present in the cancer exosomes, suggesting that the uptake of exosomal mRNAs at least partially contributed to the upregulation of the corresponding mRNAs. This study shows that cancer exosomes harbor diverse mRNAs, some of which can act as promising biomarkers as well as contribute towards reprogramming of recipient cells.