Cancer Exosomes as miRNA Factories

miRNAs modulate gene expression while exosomes are extracellular cargo vessels that transport miRNAs and other materials to surrounding cells. When exosomes are taken up by recipient cells, the released miRNAs can modulate immune responses, inhibit apoptosis, and promote angiogenesis to maintain tumor growth. Central to this regulation is the processing of the primary transcripts into active miRNAs, which occurs exclusively within mammalian cells. Challenging this dogma is the discovery that Dicer and Ago2, key components of miRNA processing, are also present inside exosomes. While the exact nature of this processing requires extensive proof, it is an exciting notion that exogenous miRNA factories could exist outside the canonical boundaries of mammalian cells.