MicroRNAs in Exosomes in Cancer

MicroRNAs (miRNAs) are small, noncoding RNAs that epigenetically regulate gene expression by modulating stability and/or expression of target mRNAs. miRNAs are found in cells, freely in circulation, and also ensconced in exosomes. Exosomes are small, membrane-bound extracellular vesicles that originate as intraluminal vesicles within multivesicular bodies/endosomes of the endocytic pathway. The endocytic pathway plays an important role in sorting and packaging the cargo of exosomes, which includes a variety of proteins, lipids, DNAs, and RNAs, including miRNAs. Deregulation of exosomal miRNAs have been implicated in many diseases, especially cancer. In cancer, exosomal miRNAs play important roles in regulating invasion and metastasis, angiogenesis, cross talk with the immune system, metabolic changes, and chemosensitivity or chemoresistance. Exosomal miRNAs may also be promising biomarkers for the early detection of cancer and prediction of treatment response. In this chapter, we discuss the many ways exosomal miRNAs have an impact on cancer.