Exosomal miRNAs from highly metastatic cells can induce metastasis in non-metastatic cells

Breast cancer is a high prevalence cancer among women worldwide. 15-20% of breast cancer cases are triple-negative with a poor prognosis. miRNA aberrant expression is one of the reasons of cancer development and metastasis. Exosomes are vesicles that carry cargos such as miRNAs to other cells. Therefore, we hypothesized that miRNAs transported by exosomes to other cells can induce malignant transformation.

We extracted exosomes from highly metastatic MDA-MB-231 cells and characterized them using Dynamic light scattering, scanning and transmitting electron microscopy as well as western blot. Then, we treated non-metastatic MCF-7 cells with the exosomes. Afterwards, we evaluated exosome uptake by MCF-7 cells using PHK67 staining. Finally, we used soft agar colony formation, migration, and invasion assays to explore any increase in/induction of metastatic behavior of exosome-treated MCF-7 cells.

Our result indicated that the particles extracted from MDA-MB-231 cells' supernatant were actually exosomes. PKH67 staining and confocal microscopy showed that the exosomes were actively taken up by MCF-7 cells. Treatment of MCF-7 cells with the exosomes resulted in increased ability of MCF-7 cells to grow independent of anchorage. In addition, migration and invasion capacity of exosome-treated MCF-7 cells increased in a dose-dependent manner.

Along with our previous study, we here indicate that highly metastatic MDA-MB-231 cells' exosomes and exosomal miRNAs may induce malignant transformation in non-metastatic MCF-7 cells, thus introducing a novel route of cancer development and metastasis.