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BACKGROUND Extracellular vesicles (EVs) contain a rich cargo of different RNA species with specialized functions and clinical applications. However, the landscape and characteristics of extracellular vesicle long RNA (exLR) in human blood remain largely unknown. METHODS We presented an optimized strategy for exLR sequencing (exLR-seq) of human plasma. The sample cohort included 159 healthy individuals, 150 patients with cancer (5 cancer types), and 43 patients with other diseases. Bioinformatics approaches were used to analyze the distribution and features of exLRs. Support vector machine algorithm was performed to construct the diagnosis classifier, and diagnostic efficiency was evaluated by ROC analysis. RESULTS More than 10000 exLRs, including mRNA, circRNA, and lncRNA, were reliably detected in each exLR-seq sample from 1–2 mL of plasma. We observed that blood EVs contain a substantial fraction of intact mRNAs and a large number of assembling spliced junctions; circRNA was also enriched in blood EVs. Interestingly, blood exLRs reflected their tissue origins and the relative fractions of different immune cell types. Additionally, the exLR profile could distinguish patients with cancer from healthy individuals. We further showed that 8 exLRs can serve as biomarkers for hepatocellular carcinoma (HCC) diagnosis with high diagnostic efficiency in training [area under the curve (AUC) = 0.9527; 95% CI, 0.9170–0.9883], validation cohort (AUC = 0.9825; 95% CI, 0.9606–1), and testing cohort (AUC = 0.9627; 95% CI, 0.9263–0.9991). CONCLUSIONS In summary, this study revealed abundant exLRs in human plasma and identified diverse specific markers potentially useful for cancer diagnosis.

Summary: The diversity and complexity of the cancer transcriptome may contain transcripts unique to the tumor environment. Here, we report a LIN28B variant, LIN28B-TST, which is specifically expressed in hepatocellular carcinoma (HCC) and many other cancer types. Expression of LIN28B-TST is associated with significantly poor prognosis in HCC patients. LIN28B-TST initiates from a de novo alternative transcription initiation site that harbors a strong promoter regulated by NFYA but not c-Myc. Demethylation of the LIN28B-TST promoter might be a prerequisite for its transcription and transcriptional regulation. LIN28B-TST encodes a protein isoform with additional N-terminal amino acids and is critical for cancer cell proliferation and tumorigenesis. Our findings reveal a mechanism of LIN28B activation in cancer and the potential utility of LIN28B-TST for clinical purposes.

Exosomes, which are nanosized endocytic vesicles that are secreted by most cells, contain an abundant cargo of different RNA species that can modulate the behavior of recipient cells and may be used as circulating biomarkers for diseases. Here, we develop a web-accessible database (http://www.exoRBase.org), exoRBase, which is a repository of circular RNA (circRNA), long non-coding RNA (lncRNA) and messenger RNA (mRNA) derived from RNA-seq data analyses of human blood exosomes. Experimental validations from the published literature are also included. exoRBase features the integration and visualization of RNA expression profiles based on normalized RNA-seq data spanning both normal individuals and patients with different diseases. exoRBase aims to collect and characterize all long RNA species in human blood exosomes. The first release of exoRBase contains 58 330 circRNAs, 15 501 lncRNAs and 18 333 mRNAs. The annotation, expression level and possible original tissues are provided. exoRBase will aid researchers in identifying molecular signatures in blood exosomes and will trigger new exosomal biomarker discovery and functional implication for human diseases.

Hepatocellular carcinoma (HCC) is a highly lethal cancer and its underlying etiology remains understudied. The immense diversity and complexity of the cancer transcriptome hold the potential to yield tumor-specific transcripts (TSTs). Here, we showed that hundreds of TSTs are frequently expressed in HCC by an assembling spliced junction analysis of RNA sequencing raw data from approximately 1,000 normal and HCC tissues. Many of the TSTs were found to be unannotated and noncoding RNAs. We observed that intergenic TSTs are generated from transcription initiation sites frequently harboring long terminal repeat (LTR) elements. The strong presence of TSTs indicates significantly poor prognoses in HCC. Functional screening revealed a noncoding TST (termed TST1), which acted as a regulator of HCC cell proliferation and tumorigenesis. TST1 is generated from an LTR12C promoter regulated by DNA methylation and retinoic-acid-related drugs. Additionally, we observed that TSTs may be detected in the blood extracellular vesicles of patients with HCC. Conclusion: Our findings suggest an abundance of TSTs in HCC and their potential in clinical settings. The identification and characterization of TSTs may help toward the development of strategies for cancer diagnosis and treatment.

Circular RNAs (circRNAs) represent a class of widespread and diverse endogenous RNAs that may regulate gene expression in eukaryotes. However, the regulation and function of human circRNAs remain largely unknown. Here we generate ribosomal-depleted RNA sequencing data from six normal tissues and seven cancers, and detect at least 27,000 circRNA candidates. Many of these circRNAs are differently expressed between the normal and cancerous tissues. We further characterize one abundant circRNA derived from Exon2 of the HIPK3 gene, termed circHIPK3. The silencing of circHIPK3 but not HIPK3 mRNA significantly inhibits human cell growth. Via a luciferase screening assay, circHIPK3 is observed to sponge to 9 miRNAs with 18 potential binding sites. Specifically, we show that circHIPK3 directly binds to miR-124 and inhibits miR-124 activity. Our results provide evidence that circular RNA produced from precursor mRNA may have a regulatory role in human cells., Circular RNAs are formed from exon back-splicing, the significance of these endogenous RNAs is beginning to be unraveled. Here, the authors identify thousands of circular RNAs differentially expressed between normal and cancer tissues and show that an abundant circular RNA generated from HIPK3 regulates cell growth.

Circular RNAs (circRNAs) are a specific form of non-coding RNAs, that serve a pivotal role in the development of human diseases, including Alzheimer's disease and cancer; however, only a few are known with respect to cancer. The present study identified a novel circRNA, circ lysophosphatidic acid receptor 1 (LPAR1) (hsa_circ_0087960), derived from two exons 226 base pairs in length, in muscle-invasive bladder cancer (MIBC) tissues. circLPAR1 was identified to be lowly expressed in MIBC tissues in a cohort of 125 cases, and predicted a poor disease-specific survival time, compared with patients with high circLPAR1 expression (52.4 vs. 56.0 months; P=0.001) by univariate and multivariate Cox regression analyses. Matrigel and wound healing assays also demonstrated that the invasion of 5637 and T24 bladder cancer cells were significantly enhanced following the knockdown of circLPAR1 by small interfering RNA (si-circLPAR1-1 in T24 cell line, P=0.01; si-circLPAR1-2 in 5637 cell line, P=0.003; si-circLPAR1-2 in T24 cell line, P=0.002; si-circLPAR1-2 in 5637 cell line, P=0.006). The bioinformatics analysis indicated that circLPAR1 may harbor specific microRNAs (miRNAs) according to the miRNAs seed sequence matching. A luciferase reporter assay revealed that miR-762 can inhibit the activity of the transfected luciferase gene when inserted in a circLPAR1 wild-type fragment, and this inhibition could be alleviated when the luciferase gene was inserted in a circLPAR1 fragment with the mutated miR-762 target site. In conclusion, the circLPAR1 may function as a potential novel and stable biomarker for the prognosis of MIBC and may be associated with the invasion and metastasis by miR-762.

Circular RNAs (circRNAs) comprise a novel class of widespread non-coding RNAs that may regulate gene expression in eukaryotes. However, the characterization and function of circRNAs in human cancer remain elusive. Here we identified at least 5500 distinct circRNA candidates and a series of circRNAs that are differentially expressed in gastric cancer (GC) tissues compared with matched normal tissues. We further characterized one circRNA derived from the PVT1 gene and termed it as circPVT1. The expression of circPVT1 is often upregulated in GC tissues due to the amplification of its genomic locus. circPVT1 may promote cell proliferation by acting as a sponge for members of the miR-125 family. The level of circPVT1 was observed as an independent prognostic marker for overall survival and disease-free survival of patients with GC. Our findings suggest that circPVT1 is a novel proliferative factor and prognostic marker in GC.