MicroRNAs (miRNAs) are thought to regulate tumor progression and metastasis via direct interaction with target
genes within cells. Emerging evidence has demonstrated the secretion of miRNAs into environment via cancer cell
exosomes, called “exosomal shuttle small RNA”. Microenvironmental miRNAs are important mediators of cell-to-cell
communication, and they play important roles in regulating cancer metastasis. RNA analysis indicates enrichment of the
miRNA population in cell-culturing medium. miRNA-conditioned medium is able to mediate the function of miRNAs in
regulating cancer cell migration and invasion. Here we combine our recent work with literature discussing multiple
mechanisms through which exosomal miRNAs regulate cancer cell migration, invasion and metastasis. We summarize a
heterotypic signaling pathway by which miRNA regulates the cellular secretion and tumor microenvironment in control of
breast cancer cell migration and invasion. In conclusion, exosomal miRNAs are able to regulate cancer metastasis via heterotypic
signals in the microenvironment.
Keywords: Cancer, exosome, metastasis, microenvironment, miRNA.
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