Circular RNAs (circRNAs) are a new class of non-coding RNAs formed by covalently closed loops through backsplicing. Recent methodologies have enabled in-depth characterization of circRNAs for identification and potential functions. CircRNAs play important roles in various biological functions as microRNA sponges, transcriptional regulators and combining with RNA binding proteins. Recent studies indicated that some cytoplasmic circRNAs can be effectively translated into detectable peptides, which enlightened us on the importance of circRNAs in cellular physiology function. Internal Ribosome Entry site (IRES)- and N6-methyladenosines (m6A)-mediated cap-independent translation initiation have been suggested to be potential mechanism for circRNA translation. To date, several translated circRNAs have been uncovered to play pivotal roles in human cancers. In this review, we introduced the properties and functions of circRNAs, and characterized the possible mechanism of translation initiation and complexity of the translation ability of circRNAs. We summarized the emerging functions of circRNA-encoded proteins in human cancer. The works on circRNA translation will open a hidden human proteome, and enhance us to understand the importance of circRNAs in human cancer, which has been poorly explored so far.

中文翻译：

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环状RNA在人类癌症中的翻译和功能作用。

环状RNA（circRNA）是一类新的非编码RNA，是通过反向剪接通过共价闭合环形成的。最近的方法已经能够对circRNA进行深入表征，以用于鉴定和潜在功能。CircRNA在各种生物学功能中起着重要作用，例如microRNA海绵，转录调节剂以及与RNA结合蛋白的结合。最近的研究表明，一些胞质circRNA可以有效地翻译成可检测的肽，这使我们对circRNA在细胞生理功能中的重要性有了启发。内部核糖体进入位点（IRES）-和N6-甲基腺苷（m6A）介导的不依赖帽的翻译起始被认为是circRNA翻译的潜在机制。至今，已发现几种翻译的circRNA在人类癌症中起关键作用。在这篇综述中，我们介绍了circRNA的特性和功能，并描述了翻译起始的可能机制和circRNAs翻译能力的复杂性。我们总结了circRNA编码的蛋白质在人类癌症中的新兴功能。circRNA翻译的工作将打开一个隐藏的人类蛋白质组，并增强我们对circRNA在人类癌症中的重要性的了解，到目前为止，该研究还很少进行探讨。