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744 Exosome-mediated miR-4655-3p contributes to UV-radiation induced bystander effects by targeting E2F2

      Radiation induced bystander effects(RIBE) refer to the reactions appearing in nonirradiated cells which triggered by the intercellular communication between directly irradiated cells and non-radiated cells. Ultraviolet radiation induced bystander effects(UV-RIBE) are a part of RIBE short of researches. miRNAs are a kind of non-coding RNAs which participate in biological activity by act on target mRNAs. Recent researches imply that exosome-mediated miRNAs play a role in RIBE. HSFs were exposed to 20J/cm2 single UVA radiation or 60mJ/cm2 single UVB radiation. The exosomes were isolated from the culture medium of human skin fibroblasts(HSFs) by differential centrifugation. Three biology targets relevant to photo damage were used to measure the UV-RIBE, including cell proliferation, oxidative damage and apoptosis rate. The miR-4655-3p binding sites of E2F2 mRNA 3’UTR were forecasted by TargetScan and verified by dual luciferase reporter assay. After UV radiation, the expression of miR-4655-3p were significantly higher in irradiated cells and exosomes secreted from irradiated cells, comparing with control group (p<0.05). Exosomes from UV-irradiated HSFs induced UV-RIBE, including decreased cell proliferation, increased oxidative damage and increased apoptosis rate of bystander cells. Up- or down-regulating the expression of miR-4655-3p in exosomes respectively enhanced or weakened UV-RIBE to some extent. All the differences were statistically significant (p<0.05). miR-4655-3p down-regulated E2F2 mRNA expression by directly targeting its 3’UTR. Our outcomes prove that UV radiation could increase the miR-4655-3p expression in irradiated HSFs and their exosomes. Meanwhile, exosomal miR-4655-3p plays a main role in UV-RIBE by directly inhibiting the expression of E2F2 mRNA.