Functional Roles for Exosomal MicroRNAs in the Tumour Microenvironment

Abstract

Extracellular microRNAs are released from cells both passively and actively. The presence of these microRNAs in the tumour microenvironment (TME) can significantly impact on the plasticity of cancer cells leading to the promotion of metastatic and angiogenic processes. These extracellular microRNAs can act not only on other cancer cells, but also cells present in the TME, such as immune cells, endothelial cells, fibroblasts, and others acting to subvert the host immune system and drive tumour progression. In this review we highlight the current understanding of both the mechanisms by which microRNAs are released from tumour cells and the downstream functional effects that extracellular microRNAs have on recipient cells.

Keywords: Extracellular vesicles; MicroRNA; Tumour microenvironment.

Fig. 1

Cell-free microRNAs are taken up by cells in the tumour microenvironment. MicroRNAs are secreted by donor cells through active or passive release mechanisms. These cell-free microRNAs are then taken up by recipient tumour, immune, or stromal recipient cells present in the TME, where they elicit functional effects on gene expression in recipient cells leading to changes in cell proliferation, differentiation, migration, immune response, and angiogenesis that collectively influence tumour progression and metastasis.