Small but mighty: microRNAs as novel signalling molecules in cancer

Abstract

MicroRNAs (miRNAs) are short, noncoding RNAs that silence target messenger RNAs by blocking translation or promoting transcript degradation. While the roles of miRNAs within cells have been extensively characterized, emerging evidence suggests that miRNAs are also transported between cells, providing a novel form of intercellular communication. Circulating miRNAs have been identified, packaged in extracellular vesicles or associated with high-density lipoproteins and Argonaute proteins. Specific extracellular miRNAs have been associated with human cancers. They not only serve as measurable disease biomarkers, but recent findings suggest secreted miRNAs may also mediate crosstalk between cancer cells and other cell types, including those that comprise the prometastatic tumor niche. Previous studies, reviewed here, demonstrate that miRNAs released by cancer cells can be internalized by nearby or distant cells, to modify gene expression and alter the tumor microenvironment. As critical drivers of both oncogenesis and metastasis, miRNAs may be attractive therapeutic targets in a wide range of cancers.