Shibin Qu

Circular RNA: A new star of noncoding RNAs

Circular RNAs (circRNAs) are a novel type of RNA that, unlike linear RNAs, form a covalently closed continuous loop and are highly represented in the eukaryotic transcriptome. Recent studies have discovered thousands of endogenous circRNAs in mammalian cells. CircRNAs are largely generated from exonic or intronic sequences, and reverse complementary sequences or RNA-binding proteins (RBPs) are necessary for circRNA biogenesis. The majority of circRNAs are conserved across species, are stable and resistant to RNase R, and often exhibit tissue/developmental-stage-specific expression. Recent research has revealed that circRNAs can function as microRNA (miRNA) sponges, regulators of splicing and transcription, and modifiers of parental gene expression. Emerging evidence indicates that circRNAs might play important roles in atherosclerotic vascular disease risk, neurological disorders, prion diseases and cancer; exhibit aberrant expression in colorectal cancer (CRC) and pancreatic ductal adenocarcinoma (PDAC); and serve as diagnostic or predictive biomarkers of some diseases. Similar to miRNAs and long noncoding RNAs (lncRNAs), circRNAs are becoming a new research hotspot in the field of RNA and could be widely involved in the processes of life. Herein, we review the formation and properties of circRNAs, their functions, and their potential significance in disease.

The emerging landscape of circular RNA in life processes

abstract Circular RNAs (circRNAs) are a novel class of non-coding RNA that assumes a covalently closed continuous conformation. CircRNAs were previously thought to be the byproducts of splicing errors caused by low abundance and the technological limitations. With the recent development of high-throughput sequencing technology, numerous circRNAs have been discovered in many species. Recent studies have revealed that circRNAs are stable and widely expressed, and often exhibit cell type-specific or tissue-specific expression. Most circRNAs can be generated from exons, introns, or both. Remarkably, emerging evidence indicates that some circRNAs can serve as microRNA (miRNA) sponges, regulate transcription or splicing, and can interact with RNA binding proteins (RBPs). Moreover, circRNAs have been reported to play essential roles in myriad life processes, such as aging, insulin secretion, tissue development, atherosclerotic vascular disease risk, cardiac hypertrophy and cancer. Although circRNAs are ancient molecules, they represent a newly appreciated form of noncoding RNA and as such have great potential implications in clinical and research fields. Here, we review the current understanding of circRNA classification, function and significance in physiological and pathological processes. We believe that future research will increase our understanding of the regulation and function of these novel molecules.

Microarray expression profile of circular RNAs in human pancreatic ductal adenocarcinoma

Pancreatic ductal adenocarcinoma (PDAC) remains a common and deadly cancer. Despite numerous efforts, no reliable biomarker is available for daily clinical practice. Circular RNAs (circRNAs) are an abundant, stable and conserved class of RNA molecules that exhibit tissue/developmental-stage-specific expression (Salzman et al., 2012; Jeck et al., 2013; Memczak et al., 2013). CircRNAs play a crucial role in disease, especially in cancer, and provide new potential diagnostic and therapeutic targets for disease (Hansen et al., 2013; Qu et al., 2015).This research was designed to explore the expression profile of circRNAs in PDAC to serve as new diagnosis and treatment strategies for PDAC. Microarray and sample annotation data were deposited in Gene Expression Omnibus (GEO) under accession number GSE69362.

Circular RNA Expression Profile of Pancreatic Ductal Adenocarcinoma Revealed by Microarray.

Background/Aims: Circular RNAs (circRNAs) are a special novel type of a stable, diverse and conserved noncoding RNA in mammalian cells. Particularly in cancer, circRNAs have been reported to be widely involved in the physiological/pathological process of life. However, it is unclear whether circRNAs are specifically involved in pancreatic ductal adenocarcinoma (PDAC). Methods: We investigated the expression profile of circRNAs in six PDAC cancer samples and paired adjacent normal tissues using microarray. A high-throughput circRNA microarray was used to identify dysregulated circular RNAs in six PDAC patients. Bioinformatic analyses were applied to study these differentially expressed circRNAs. Furthermore, quantitative reverse transcription polymerase chain reaction (qRT-PCR) was performed to confirm these results. Results: We revealed and confirmed that a number of circRNAs were dysregulated, which suggests a potential role in pancreatic cancer. Conclusions: this study demonstrates that clusters of circRNAs are aberrantly expressed in PDAC compared with normal samples and provides new potential targets for the future treatment of PDAC and novel insights into PDAC biology.

Downregulation of lncRNA-ATB correlates with clinical progression and unfavorable prognosis in pancreatic cancer.

Long noncoding RNAs (lncRNAs) have been shown to play critical roles in the development and progression of diseases. lncRNA activated by transforming growth factor beta (TGF-β) (lncRNA-ATB) was discovered as a prognostic factor in hepatocellular carcinoma, gastric cancer, and colorectal cancer. However, little is known about the role of lncRNA-ATB in pancreatic cancer. This study aimed to assess lncRNA-ATB expression in pancreatic cancer and explore its role in pancreatic cancer pathogenesis. Quantitative real-time polymerase chain reaction was performed to detect lncRNA-ATB expression in 150 pancreatic cancer tissues and five pancreatic cancer cell lines compared to paired adjacent normal tissues and normal human pancreatic ductal epithelial cell line HPDE6c-7. The correlations between lncRNA-ATB expression and clinicopathological characteristics and prognosis were also analyzed. We found that lncRNA-ATB expression was decreased in pancreatic cancer tissues and pancreatic cancer cell lines. Low lncRNA-ATB expression levels were significantly correlated with lymph node metastases (yes vs. no, P = 0.009), neural invasion (positive vs. negative, P = 0.049), and clinical stage (early stage vs. advanced stage, P = 0.014). Moreover, patients with low lncRNA-ATB expression levels exhibited markedly worse overall survival prognoses (P < 0.001). Multivariate analysis indicated that decreased lncRNA-ATB expression was an independent predictor of poor prognosis in pancreatic cancer patients (P = 0.005). In conclusion, lncRNA-ATB may play a critical role in pancreatic cancer progression and prognosis and may serve as a potential prognostic biomarker in pancreatic cancer patients.

Reprogramming of glucose metabolism in hepatocellular carcinoma: Progress and prospects

Hepatocellular carcinoma (HCC) is one of the most lethal cancers, and its rate of incidence is rising annually. Despite the progress in diagnosis and treatment, the overall prognoses of HCC patients remain dismal due to the difficulties in early diagnosis and the high level of tumor invasion, metastasis and recurrence. It is urgent to explore the underlying mechanism of HCC carcinogenesis and progression to find out the specific biomarkers for HCC early diagnosis and the promising target for HCC chemotherapy. Recently, the reprogramming of cancer metabolism has been identified as a hallmark of cancer. The shift from the oxidative phosphorylation metabolic pathway to the glycolysis pathway in HCC meets the demands of rapid cell proliferation and offers a favorable microenvironment for tumor progression. Such metabolic reprogramming could be considered as a critical link between the different HCC genotypes and phenotypes. The regulation of metabolic reprogramming in cancer is complex and may occur via genetic mutations and epigenetic modulations including oncogenes, tumor suppressor genes, signaling pathways, noncoding RNAs, and glycolytic enzymes etc. Understanding the regulatory mechanisms of glycolysis in HCC may enrich our knowledge of hepatocellular carcinogenesis and provide important foundations in the search for novel diagnostic biomarkers and promising therapeutic targets for HCC.

MicroRNA-150 suppresses cell proliferation and metastasis in hepatocellular carcinoma by inhibiting the GAB1-ERK axis

MicroRNA-150 (miR-150) is frequently dysregulated in cancer and is involved in carcinogenesis and cancer progression. In this study, we found that miR-150 was significantly downregulated in hepatocellular carcinoma (HCC) tissues compared to adjacent noncancerous tissues. Low levels of miR-150 were significantly associated with worse clinicopathological characteristics and a poor prognosis for patients with HCC. miR-150 overexpression inhibited cell proliferation, migration and invasion in vitro and tumor growth and metastasis in vivo. Further experiments indicated that Grb2-associated binding protein 1 (GAB1) was a direct target of miR-150 in HCC cells. In addition, GAB1 expression was increased in HCC tissues and inversely correlated with miR-150 levels. Knockdown of GAB1 mimicked the tumor-suppressive effects of miR-150 overexpression on HCC cells, whereas restoration of GAB1 expression partially abolished the inhibitory effects. Moreover, miR-150 overexpression decreased GAB1 expression, subsequently downregulated phospho-ERK1/2 and suppressed epithelial-mesenchymal-transition (EMT). These effects caused by miR-150 overexpression were alleviated by exogenous GAB1 expression. Taken together, this study demonstrates that miR-150 may be useful as a prognostic marker and that the identified miR-150-GAB1-ERK axis is a potential therapeutic target for HCC.

The mTOR inhibition in concurrence with ERK1/2 activation is involved in excessive autophagy induced by glycyrrhizin in hepatocellular carcinoma

Autophagy is a life phenomenon in which autophagosomes remove damaged or aging organelles and long‐lived circulating proteins to maintain the cells stability. However, disorders of excessive autophagy are a response of cancer cells to a variety of anticancer treatments which lead to cancer cell death. The Akt/mammalian target of rapamycin (mTOR) and the extracellular signal‐regulated kinase 1/2 (ERK1/2) pathways are both involved in nutrient‐induced autophagic phenomenon and exhibit vital relevance to oncogenesis in various cancer cell types, including hepatocellular carcinoma (HCC). However, the influence of autophagy for cancer cell death remains controversial and few scientists have investigated the variation of these two signaling pathways in cancer cell autophagic phenomenon induced by anticancer treatment simultaneously. Here, we explored the anticancer efficacy and mechanisms of glycyrrhizin (GL), a bioactive compound of licorice with little toxicity in normal cells. It is interesting that inhibition of Akt/mTOR signaling in concurrence with enhanced ERK1/2 activity exists in GL‐induced autophagy and cytotoxicity in HepG2 and MHCC97‐H hepatocellular carcinoma cells. These results imply that the GL‐related anticancer ability might correlate with the induction of autophagy. The influence of induced autophagic phenomenon on cell viability might depend on the severity of autophagy and be pathway specific. In the subsequent subcutaneous xenograft experiment in vivo with MHCC97‐H cells, GL obviously exhibited its inhibitory efficacy in tumor growth via inducing excess autophagy in MHCC97‐H cells (P < 0.05). Our data prompt that GL possesses a property of excess autophagic phenomenon induction in HCC and exerts high anticancer efficacy in vitro and in vivo. This warrants further investigation toward possible clinical applications in patients with HCC.

RRAD inhibits aerobic glycolysis, invasion, and migration and is associated with poor prognosis in hepatocellular carcinoma.

Hepatocellular carcinoma (HCC) is one of the most prevalent and lethal cancer worldwide. However, the mechanism underlying the HCC development remains unclear. Ras-related associated with diabetes (RRAD) is a small Ras-related GTPase which has been implicated in metabolic disease and several types of cancer, yet its functions in HCC remain unknown. A tissue microarray constructed by 90 paired HCC tissues and adjacent non-cancerous liver tissues was used to examine the protein levels of RRAD, and the messenger RNA (mRNA) expression of RRAD was also detected in a subset of this cohort. The prognostic significance of RRAD was estimated by the Kaplan-Meier analysis and Cox regression. The glucose utilization assay and lactate production assay were performed to measure the role of RRAD in HCC glycolysis. The effect of RRAD in HCC invasion and metastasis was analyzed by transwell assays. Our results suggested that the expression of RRAD was downregulated in HCC tissues compared to the adjacent non-tumorous liver tissues both in mRNA and protein levels and lower RRAD expression served as an independent prognostic indicator for the survival of HCC patients. Moreover, RRAD inhibited hepatoma cell aerobic glycolysis by negatively regulating the expression of glucose transporter 1 (GLUT1) and hexokinase II (HK-II). In addition, RRAD inhibition dramatically increased hepatoma cell invasion and metastasis. In conclusion, our study revealed that RRAD expression was decreased in HCC tumor tissues and predicted poor clinical outcome for HCC patients and played an important role in regulating aerobic glycolysis and cell invasion and metastasis and may represent potential targets for improving the treatment of HCC.

Overexpression of miR-200a suppresses epithelial-mesenchymal transition of liver cancer stem cells

Due to high incidence of invasion and intrahepatic metastasis, hepatocellular carcinoma (HCC) is one of the most aggressive tumors in the world, which is also associated with the acquisition of epithelial-mesenchymal transition (EMT). Increasing evidence suggests that cancer cells with EMT traits share many biological characteristics with cancer stem cells. And miR-200a has been known as a powerful regulator of EMT. Here, we sought to investigate the role of miR-200a in regulation of EMT phenotype of liver cancer stem cells (LCSCs). We used side population (SP) sorting to obtain cancer stem-like cells from HCC cell lines and identified that the SP fraction could be enriched with LCSCs. Then, we detected the expression of miR-200a and EMT makers in SP and non-SP cells. Our results suggested that miR-200a was down-regulated in SP cells, along with relatively low epithelial marker and high mesenchymal marker. In order to find the role of miR-200a in the manipulation of EMT, we transfected miR-200a mimic into LCSCs and found that overexpression of miR-200a resulted in down-regulation of N-cadherin, ZEB2, and vimentin, but up-regulation of E-cadherin. Moreover, overexpression of miR-200a resulted in decreased migration and invasion ability in LCSCs. In conclusion, our study revealed that miR-200a played an important role in linking the characteristics of cancer stem cells with EMT phenotype in HCC, and targeting miR-200a might be an effective strategy to weaken the invasive behavior of LCSCs.