Functional Passenger-Strand miRNAs in Exosomes Derived from Human Colon Cancer Cells and Their Heterogeneous Paracrine Effects

Exosome-mediated microRNAs (miRNAs) are closely related to the occurrence, development, invasion, metastasis, therapeutic resistance, diagnosis and treatment of malignant tumors. Guide-strand miRNA and passenger-strand miRNA (miRNA*) exist in miRNA processing, but the function of passenger-strand miRNA is often overlooked. In this study, we attempted to identify functional miRNA*s in exosomes derived from human colon cancer SW620 cells. miRNA expression profiles of human normal colonic epithelial cells NCM460 and colon cancer cells SW620 were compared by high-throughput sequencing. According to the sequencing results, we defined two sets of differentially expressed miRNAs: "high in exosome and high in cell" (HEHC) and "high in exosome but low in cell" (HELC). As passenger-strand miRNAs, miR-2277-3p and miR-26b-3p, which belong to different sets, have diametrically opposite functions. MiR-2277-3p promotes proliferation, migration, and invasion of SW620 cells by targeting NUPR1L, while miR-26b-3p exerts an inhibitory effect by targeting PFDN1. Using exosomes as transport vectors, the effect of exosomes rich in miR-2277-3p on cells is consistent with the effect of liposome-transfected overexpressed miR-2277-3p, resulting in a cancer-promoting effect. However, exosomes rich in miR-26b-3p did not have a tumor suppressor effect. Further analysis revealed that exosomes rich in miR-2277-3p also had a high abundance of integrin beta4. Altering the abundance of integrin beta4 in exosomes changes the ability of exosomes to be taken up by cells, thereby altering the paracrine effects of exosomes. In summary, we revealed the fact that a large number of passenger-strand miRNAs exist in exosomes of colon cancer cells, these miRNAs are preliminarily categorized into two sets, and miR-2277-3p and miR-26b-3p, as representatives of each set, showed opposite functions. In addition, we revealed that integrin beta4 is a marker of exosome heterogeneity in colon cancer cells, which directly correlates with the ability of exosomes to be uptaken by cells of the same kind, thus regulating the paracrine effect of exosomes.