Fig. 1

Identification of circPDK1 as an exosomal biomarker for PC and characteristic of circPDK1. A Heatmap showing the differentially exosomal circRNA expression between normoxic exosomes and hypoxic exosomes in PC cells. B Volcano plot displaying exosomal circRNAs that differentially notably between normoxic exosomes and hypoxic exosomes in PC cells. C Relative expression of top 5 most upregulated and downregulated circRNAs in 10 PC tumor and matched normal tissues. D The circPDK1 expression level in PC tumor tissues and matched normal tissues verified by ISH. Scale bar = 1000 μm. E The circPDK1 expression was detected in different TNM stage by ISH. Scale bar = 200 μm. F The expression of circPDK1 in 110 cases of PC tumor tissues and matched normal tissues. G The expression of circPDK1 in PC patients with lymph node metastasis. H circPDK1 expression in PC patients was divided by stage. I Prognostic analysis of circPDK1 in 110 cases of PC patients from our center. J circPDK1 in serum exosomes of PC patients (n = 20) and normal people (n = 10). K Correlation of circPDK1 expression between PC tumors and serum exosomes. L The back-splice junction site of circPDK1 was verified by Sanger sequencing. M The divergent primers for circPDK1 could be amplified by using PCR analysis, from cDNA but not gDNA, meanwhile, the divergent primers for GAPDH could not be amplified. N circPDK1 and PDK1 mRNAs expression after treatment with RNase R. O RNA abundance of circPDK1 and PDK1 after treatment with Actinomycin D. P Relative circPDK1 expression levels in subcellular fractions. Q Representative FISH images displaying the expression of circPDK1 in MIA PaCa-2 (RED). Scale bar = 20 μm. *P < 0.05; **P < 0.01; ***P < 0.001; ns, no significance