Circ-0000284 arouses malignant phenotype of cholangiocarcinoma cells and regulates the biological functions of peripheral cells through cellular communication

Circular RNAs (circRNAs) play a vital role in cancers. Accumulated evidences showed that the physiological condition of cells can be reflected by the circRNAs in the exosomes they secrete, and these exosomal circRNAs can be captured by the receptor cells, thereby inducing a series of cellular responses. We performed qRT-PCR to detect the expression level of circ-0000284 in cholangiocarcinoma cell lines, tissues and plasma exosomes. Then the direct interaction between circ-0000284 and miR-637 was investigated through dual-luciferase reporter assay, RNA binding protein immunoprecipitation (RIP) assay and Fluorescent in situ hybridization (FISH) assay. Subsequently, EdU (5-ethynyl-2'-deoxyuridine), migration, invasion assay, flow cytometry and nude mouse tumorigenicity assay were adopted to evaluate the effect of circ-0000284 on migration, invasion, proliferation and apoptosis of cholangiocarcinoma cells. Additionally, TEM was conducted to investigate the shape and size of exosomes from cholangiocarcioma and 293T cell lines. Circ-0000284 was evidently elevated in cholangiocarcinoma cell lines, tumor tissues and plasma exosomes. Meanwhile, the high expression of circ-0000284 enhanced the migration, invasion and proliferation abilities of cholangiocarcinoma cells in vivo and in vitro Besides, the levels of circ-0000284 were increased in cholangiocarcinoma cells and exosomes from them. Moreover, exosomes from cholangiocarcinoma cells enhanced circ-0000284 expression and stimulated migration and proliferation of the surrounding normal cells. Our findings suggest that on the one hand circ-0000284 functions as a competitive endogenous RNA to promote cholangiocarcinoma progression, and on the other hand, circ-0000284 can be directly transferred from cholangiocarcinoma cells to surrounding normal cells via exosomes and in this way regulate the biological functions of surrounding normal cells.