Researchers from Fudan University show for the first time the presence of abundant circRNAs in exosomes. RNA-seq analyses revealed that circRNAs were enriched in exosomes compared to the producer cells.
circRNAs are enriched and stable in exosomes and may serve as a potential biomarker for cancer detection. (A) Circos plots showing all circRNAs from cell and cell-derived exosome. (B) Correlation between cellular circRNA and exo-circRNA levels (SRPBM > 1). (C) Representative RNA-seq results for the HIPK3 gene and circ-HIPK3 (exon2) locus in various RNA-seq libraries. The read density of circ-HIPK3 was marked with red. (D) Comparison of the ratio of back-spliced to forward-spliced product reads between cell and cell-derived exosome. (E) qRT-PCR analysis of cellular CDR1as and exo-CDR1as circular RNA levels in cells and cell-derived exosomes after transfection with control or miR-7 mimics in HEK-293T cells. Data are presented as mean ± SD. **P < 0.01 by Student’s t-test. (F) Cell proliferation assay of SMCC-7721 cells after transfection with control or miR-7 mimics followed by treatment with control or CDR1as exosomes. CDR1as exosomes and control exosomes were collected from cell culture medium after transfection of CDR1as expression vector or control vector into HEK-293T cells. miR-7 mimics or negative control were transfected into SMCC-7721 cancer cells in 96-well plate. After 4 h transfection, CDR1as exosomes or control exosomes were added to the transfected cells. The cells were subsequently incubated for 48 h, and cell proliferation was measured using the Cell Counting Kit-8 (CCK-8). Data are presented as mean ± SD. **P < 0.01 by Student’s t-test. (G) Genomic origin of human blood exo-circRNAs. (H) Distribution of serum exo-circRNA lengths (n = 1 107, only exo-circRNAs with known spliced length were considered). (I) qRT-PCR analysis of serum exo-circRNA levels after treatment with or without RNase R. The level without RNase R treatment was set as 1. Data are presented as mean ± SD. (J) qRT-PCR analysis of serum exo-circRNA levels after incubation at room temperature for the indicated time. Ct values were shown. (K) Serum levels of exo-circCDYL were measured in all control and xenografted mice (n = 6, respectively). (L) Correlation between the level of tumor-derived exo-circCDYL in serum of xenografted mice and tumor mass. (M) Comparison of the exo-circRNA profile of normal serum and that of CRC serum. (N) qRT-PCR analysis of circ-KLDHC10 levels in normal serum and CRC serum (n = 11, respectively).