Visualizing intercellular transfer of hypoxia-induced exosomal miR-210 between breast cancer cells

Abstract

Purpose: Cancer cells actively release exosomes containing many functional proteins, mRNA, and miRNA to communicate with tumor microenvironment, providing a novel mechanism of paracrine signaling between the tumors and surrounding tissues. In this study, we visualized exosome-mediated transfer of miR-210 between breast cancer cells. Methods: Mouse breast cancer cell lines, 4T1, were transfected with pCMV-luc2/miR-210 reporter vector which was designed to be turned off its luciferase signal by binding of miR-210. Hypoxia was induced by Deferoxamine Mesylate (DFO). Exosomes were characterized by western blot (Alix, CD63, and CD9) and TEM. Exosomes from hypoxic conditions were isolated and treated to normoxic breast cancer cells. Real-time PCR was performed to compare levels of miR-210. Luciferase activity was measured by luciferase activity assay and bioluminescence imaging. Immunohistochemistry was performed with antibodies of HIF-1a, luciferase, and Ephrin-A3. Results: Amount of isolated exosome from hypoxic condition was 1.4 fold more than that of normoxic condition. Expression of miR-210 was increased in 15.70 and 12.73 fold in hypoxic cells and exosomes, respectively. Luciferase activity and bioluminescence imaging signal intensity of the cells treated with hypoxic exosome were significantly decreased at 0.50 and 0.67 fold compare to that of untreated cells. In xenograft models, luciferase signals of tumor treated hypoxic exosomes were also decreased in 0.56 fold. Luciferase was decreased in the tumor tissues treated with hypoxic exosomes, and the expression of Ephrin-A3, a target of miR-210, was also decreased in tumor tissues treated hypoxic exosome. Conclusions: Reporter gene imaging system for monitoring hypoxia-induced miR-210 successsfully demonstrated the exosome-mediated intercellular transfer of miR-210 in vitro and in vivo.