The Research Progress of Exosomal CircRNAs in Urinary System Tumors

Exosomes are membranous vesicles containing complex RNA and proteins, which are mainly derived from polyvesicles formed by intracellular lysosomal microparticles invagination, and released into the extracellular matrix after fusion of polyvesicles extracorporeal membrane and cell membrane. Exosomes mediate cell-to-cell communication in the tumor microenvironment and their function depends on the cell type of origin. CircRNAs are a class of non-coding RNAs generated by reverse splicing of pre-mRNA, which are enriched and expressed stably in exosomes. Exosomal circRNAs play an important role in regulation in urinary system tumors, and have biological functions such as affecting the proliferation, metastasis and apoptosis of urinary system tumor cells and regulating chemotherapy resistance, which are mainly realized through competing endogenous RNAs network mechanism and protein binding mechanism. Compared with the biological functions and mechanisms of circRNAs, there are still fewer relevant studies on exosomal circRNAs. For example, the function of regulating tumor angiogenesis and the mechanism of m6A modification affecting tumor progression have not been reported. In terms of gene regulation, circRNAs have more regulation on genes in the nucleus, while exosomal circRNAs have more regulation on target genes outside the nucleus. Because exosomes are widely found in various body fluids, such as urine, and the expression of circRNAs is abundant in exosomes, exosomal circRNAs can be used as biomarkers for urinary system tumors. In addition, exosomes themselves have the advantages of nanoscale size, long life span and strong carrying capacity, while circRNAs have the characteristics of good stability. Therefore, exosomal circRNAs can be used as targets for anti-urinary tumor therapy. Exosomal circRNAs are also associated with TNM stages of urinary tumors and can be used to monitor tumor progression and patients' prognosis. Compared with exosomes from other body fluids, urinary exosomes have more sensitivity and specificity in the diagnosis and prognosis of urinary tumors, which is a new research focus in the field at present. However, exosomes extraction and purification technologies are limited, and exosomes of specific donor cells cannot be mass-produced for targeting drug carriers. Therefore, the clinical application prospects of exosomes and exosomal circRNAs in urinary system tumors are still worth studying.