Tumor-derived or non-tumor-derived exosomal noncodingRNAs and signaling pathways in tumor microenvironment.

The tumor microenvironment (TME) involved in multiple pathological processes of tumors is highly complex. Exosomes, as organelles, can be produced by some cells in the TME and have been verified as a special carriers and a key factor for communication between tumor and TME-associated cells. Noncoding RNAs (ncRNAs) involved in tumorigenesis and development have been demonstrated to be released into the TME by exosomes. However, the detailed regulatory functions of exosomal ncRNAs through signaling pathways in the TME are still unclear. In this review, we systematically summarized the detailed molecular mechanisms by which exosomal ncRNAs mediate the modulation of both tumor cells and nontumor cells. Exosomal ncRNAs in the TME exhibited the potential ability to influence cancer development through signaling pathways, including PTEN signaling, NF-κB signaling, Wnt/β-catenin signaling, PI3K/AKT signaling, etc. Expressly, considering that research on circRNAs has gained much momentum in recent years, we more thoroughly described the implication of exosomal circRNAs in the regulation of signaling. Our review might hopefully inspire a deeper understanding of exosomal ncRNA function in terms of signaling pathways. We speculated that exosomal ncRNAs, as useful biomarkers and therapeutic targets, play an important role in the diagnosis and prognosis of cancer.