Circular RNAs: Biogenesis, Function, and a Role as Possible Cancer Biomarkers

Research progress of circular RNAs in lung cancer

Lung cancer is one of the most common cancers and the leading cause of cancer-related death worldwide. Despite encouraging results achieved with targeted therapy in recent years, the early diagnosis and treatment of lung cancer remains a major problem. Circular RNA (circRNA), a type of RNA with covalently closed continuous loop structures, has structural stability and certain tissue specificity. Recent studies have found that circRNAs have an important role in tumor development and are expected to be revealed as new targets for tumor prediction and treatment. Research on the biological functions and regulation mechanisms of circRNAs in lung cancer is in its infancy but is gathering momentum. In this review, we discuss the properties, biogenesis, biological function, and research progress of circRNAs in lung cancer to provide a theoretical foundation and new directions for studies on circRNAs in lung cancer.

Circ_0027599/PHDLA1 suppresses gastric cancer progression by sponging miR-101-3p.1

Background

Pleckstrin homology-like domain family A member 1 (PHLDA1) is a tumor suppressor gene in gastric cancer, but its role regulated by circular RNAs (circRNAs) is not known. CircRNAs are important regulators in cancer growth and progression, however, the molecular roles of circRNAs in gastric cancer are rarely known. The study was aimed to investigate the role of circRNAs in regulating PHLDA1 expression in gastric cancer.

Results

The circRNA expression profile in the gastric cancer tissues by circRNA microarray showed that hsa_circ_0027599 (circ_0027599) was significantly down-regulated in gastric cancer patients and cells when comparing with the controls. Circ_0027599 overexpression suppressed gastric cancer cell proliferation and metastasis. By using bioinformatics tools and luciferase reporter assays, circ_0027599 was verified as a sponge of miR-101-3p.1 (miR-101) and suppressed cancer cell survival and metastasis. It was also verified that PHLDA1 was regulated by circ_0027599 in gastric cancer cells.

Conclusions

The study uncovered that PHLDA1 was regulated by circ_0027599/miR-101, which suppressed gastric cancer survival and metastasis in gastric cancer.

A novel circulating hsa_circ_0081001 act as a potential biomarker for diagnosis and prognosis of osteosarcoma

Chemo-resistance and lung metastasis have been the two obstacles in the osteosarcoma (OS) treatment, which is still lack of effective biomarkers for prediction, diagnosis and treatment. Circular RNA (circRNA) is a new type of endogenous noncoding RNA that could serve as ideal biomarkers in cancer because of its stable loop structure. However, little is known about the diagnostic value of circRNAs in OS as well as their associations with clinicopathologic characteristics of OS patients. In the current study, we identified a novel circRNA, hsa_circ_0081001, screened by the RNA sequencing in the three paired chemo-resistant and chemo-sensitive OS cell lines (MG63/DXR vs MG63, KHOS/DXR vs KHOS, U2OS/DXR vs U2OS), and found that hsa_circ_0081001 was significantly up-regulated in the OS cell lines, tissues and serums, associated with poor overall survival and cox multivariate analysis showed that hsa_circ_0081001 was a novel independent prognostic factor for OS patients. Then, receiver operating characteristic (ROC) curve analysis revealed that hsa_circ_0081001 could act as a biomarker for the OS diagnosis and prognosis prediction, better than alkaline phosphatase (ALP) and lactate dehydrogenase (LDH). In addition, we preliminarily found that hsa_circ_0081001 expression level may dynamically monitor and reflect the condition changes of OS patients in a small-scale prospective clinical pretest. In conclusion, our study suggested that circulating hsa_circ_0081001 could serve as a potential biomarker and therapeutic target for OS patients.

Circ_0056618 and CXCR4 act as competing endogenous in gastric cancer by regulating miR-206

Circular RNAs (circRNAs) have proved to play an important role in gastric cancer. In this study, we found that circ_0056618 took part in gastric cancer cell proliferation and survival. The real-time polymerase chain reaction result showed that circ_0056618 was overexpressed in tumor tissues or cells compared with adjacent normal tissues or normal cells and had a negative relationship to gastric cancer patients' survival time. Meanwhile, the inhibition of circ_0056618 suppressed the proliferation and metastasis of gastric cancer cells. Further bioinformatical analysis indicated that circ_0056618 sponged miR-206 to regulate CXCR4 according to the prediction of TargetScan and miRanda. Dual-luciferase reporter assay and Western blot analysis revealed the underlying relationship of circ_0056618, miR-206, and CXCR4. Hence, circ_0056618 negatively regulated miR-206 expression promoting CXCR4 expression. Altogether, circ_0056618 is a potential gastric cancer prognostic marker, as well as a potential therapeutic target to inhibit gastric cancer metastasis.

Visualizing Genetic Variants, Short Targets, and Point Mutations in the Morphological Tissue Context with an RNA In Situ Hybridization Assay

Because precision medicine is highly dependent on the accurate detection of biomarkers, there is an increasing need for standardized and robust technologies that measure RNA biomarkers in situ in clinical specimens. While grind-and-bind assays like RNAseq and quantitative RT-PCR enable highly sensitive gene expression measurements, they also require RNA extraction and thus prevent valuable expression analysis within the morphological tissue context. The in situ hybridization (ISH) assay described here can detect RNA target sequences as short as 50 nucleotides at single-nucleotide resolution and at the single-cell level. This assay is complementary to the previously developed commercial assay and enables sensitive and specific in situ detection of splice variants, short targets, and point mutations within the tissue. In this protocol, probes were designed to target unique exon junctions for two clinically important splice variants, EGFRvIII and METΔ14. The detection of short target sequences was demonstrated by the specific detection of CDR3 sequences of T-cell receptors α and β in the Jurkat T-cell line. Also shown is the utility of this ISH assay for the distinction of RNA target sequences at single-nucleotide resolution (point mutations) through the visualization of EGFR L858R and KRAS G12A single-nucleotide variations in cell lines using automated staining platforms. In summary, the protocol shows a specialized RNA ISH assay that enables the detection of splice variants, short sequences, and mutations in situ for manual performance and on automated stainers.

Role of non-coding RNAs in cardiotoxicity of chemotherapy

The long-time paradoxical situation of non-coding RNAs (ncRNAs) has been terminated for they emerge as executive at full spectrum of gene expression and translation. More recently, it has been demonstrated that some ncRNAs apparently are associated with chemotherapy, causing cardiotoxicity, which taint long-term recovery of patients in growing body of evidence. The current review focused on up-to-date knowledge on regulation change and molecular signaling of ncRNAs, at mean time evaluate their potentials as diagnostic biomarkers or therapeutic targets to monitor and protect cardio function.

Circular RNAs in Cancer - Lessons Learned From microRNAs

Circular RNAs (circRNA) are RNA molecules built from fragments of linear pre-messenger RNAs and other linear RNA species through a process termed "back-splicing" in which the 3' and 5' ends are joined together giving rise to a covalently uninterrupted loop. circRNAs are not new members of the RNA world; they were first discovered in the early 1990s. The novelty is their abundance in the mammalian cells, as recently thousands of circRNAs were discovered and annotated. The biogenesis of circRNAs is a partially characterized process, regulated by three different mechanisms: exon skipping, intron pairing, and RNA-binding proteins. On the other hand, the function of circRNAs remains largely unknown and only a handful of singular reports describe in detail the biological roles of some circular transcripts. In a very short period of time, numerous circRNAs were associated with various cancer types and were also identified in bodily fluids with the potential of being disease-specific biomarkers. In this review, we briefly describe the biogenesis and function of circRNAs and present the circular transcripts that were more than once reported in literature to be associated with cancer. Finally, we point out some of the difficulties encountered in the study of circRNAs in cancer, as we consider that taking these into account could accelerate and improve our understanding of the biologic and translational use of circRNAs in human diseases.

Functional Role of Circular RNA in Regenerative Medicine

Every year, millions of people around the world suffer from different forms of tissue trauma. Regenerative medicine refers to therapy that replaces the injured organ or cells. Stem cells are the frontiers and hotspots of current regenerative medicine research. Circular RNAs (circRNAs) are essential for the early development of many species. It was found that they could guide stem cell differentiation through interacting with certain microRNAs (miRNAs). Based on this concept, it is meaningful to look into how circRNAs influence stem cells and its role in regenerative medicine. In this chapter we will discuss the functional roles of circRNAs in the prevention, repair, or progression of chronic diseases, through the communication between stem cells.