Recently, the role of tumor microenvironment (niche) in regulating cancer progression has been indicated. Tumor microenvironments consists of tumor vasculature, bone marrow mesenchymal stem cells, immune cells and the components of the extracellular matrix. It is believed that the phenotypic advantages acquired by tumor cells are partly the outcome of their interaction with their niche. Endothelial cells are the building blocks of tumor vasculature and have lately been shown to have additional benefits than merely a conduit for supplying oxygen and nutrients. Here, we intend to demonstrate the critical role of the Akt-activated endothelial (E4ORF1) cells on breast cancer development, survival and spreading. The effect of E4ORF1 cells on breast cancer (BC) and breast cancer stem cells (BCSC) self-renewal was assessed by co-cultivating E4ORF1 with MDA-MB231 and MCF-7 BC cells under adherent and suspension conditions. BCSC enrichment by E4ORF1 cells was measured by analyzing the CD44+/CD24Low/- population of BC cells by flow cytometry as well as by evaluating the expression of pluripotency markers by RT-PCR. BCSCs resistance to treatment was investigated by addition of metformin and determining BCSC proliferation with/out E4ORF1. The role of E4ORF1 on BC cell metastasis was shown by migration and adhesion potential of BC cells with/out E4ORF1 cells. Our results demonstrated a 5-fold increase in the self-renewal capacity of BC cells and BCSCs in the presence of E4ORF1. Also, E4ORF1 was able to promote stemness in BC cells as was shown by significant increase in CD44+/CD24Low/- BCSC population and the up-regulation of pluripotency markers. Moreover, BCSCs survived drug treatment by 2.5 folds in the presence of E4ORF1. Besides, BC cells showed enhanced invasion/adhesion property when exposed to E4ORF1 cells. Our data suggest a major role for E4ORFl cells in BC progression, stemness, resistance and metastasis. This characteristic of E4ORF1 cells in maintaining BC cells can be exploited in developing novel anti-cancer therapy to combat BC in a more effective way.


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