Circular RNAs (circRNAs) are single-stranded, covalently closed RNA molecules that are produced from pre-mRNAs through a process known as back-splicing. Although circRNAs are expressed under specific conditions, current understanding of their comprehensive expression status is still limited. Here, we performed a large-scale circRNA profiling analysis in human pancreatic ductal adenocarcinoma (PDAC) tissues, using circular RNA-specific RNA sequencing. We identified more than 40,000 previously unknown circRNAs, some of which were upregulated in PDAC tissues, compared with normal pancreatic tissues. We determined the full-length sequence of a circRNA upregulated in PDAC, which was derived from two noncoding RNA loci on chromosome 12. The novel circRNA, named circPDAC RNA, was not expressed in normal human cells, but was expressed in PDAC and other carcinoma cells. While postulated biological functions, such as peptide production from the circPDAC RNA, were not detected, its aberrant expression was confirmed in other PDAC tissues and in serum from a PDAC patient. These results demonstrate that comprehensive studies are necessary to reveal the expression status of circRNAs and that the circPDAC RNA identified here might serve as a novel biomarker for cancers, including PDAC.

环状RNA（circRNA）是单链，共价封闭的RNA分子，它们是通过称为反向剪接的过程从前mRNA产生的。尽管circRNA在特定条件下表达，但目前对其全面表达状态的了解仍然有限。在这里，我们使用环状RNA特异性RNA测序技术在人胰导管腺癌（PDAC）组织中进行了大规模circRNA分析。我们鉴定了40,000多个以前未知的circRNA，与正常的胰腺组织相比，其中的一些在PDAC组织中被上调。我们确定了PDAC中上调的circRNA的全长序列，该序列源自12号染色体上的两个非编码RNA位点。名为circPDAC RNA的新型circRNA在正常人细胞中未表达，但在PDAC和其他癌细胞中表达。虽然未检测到假定的生物学功能，例如从circPDAC RNA产生肽，但在其他PDAC组织和PDAC患者的血清中证实了其异常表达。这些结果表明，全面的研究对于揭示circRNA的表达状态是必要的，并且此处鉴定的circPDAC RNA可以作为包括PDAC在内的癌症的新型生物标记。