Xisheng Yang

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.

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.

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.

Fbxw7 regulates hepatocellular carcinoma migration and invasion via Notch1 signaling pathway

Hepatocellular carcinoma (HCC) is one of the most common human malignancies and also the leading cause of cancer-related death in the world. The mechanisms underlying the progression and metastasis of HCC remain unclear. The E3 ubiquitin ligase F-box and WD repeat domain-containing 7 (Fbxw7) is broadly considered as a tumor suppressor gene. However, the role of Fbxw7 in HCC is not clear. To investigate the expression and biological functions of Fbxw7 in HCC, we examined Fbxw7 expression level using HCC tissue microarray and immunohistochemistry. Our data showed that Fbxw7 expression is significantly reduced in HCC compared with non-cancerous tissues (P<0.05). Fbxw7 levels were significantly associated with tumor differentiation (P=0.013), the incidence of portal or hepatic venous invasion (P=0.031), metastasis (P=0.027) and AJCC cancer stage (P=0.047). Then, we observed a strong correlation between low Fbxw7 expression and a worse 5-year survival of HCC patients (P<0.001). Furthermore, multivariate Cox regression analyses demonstrated that the Fbxw7 expression (P<0.001) was an independent factor for the prediction of the overall survival of HCC patients. We also found that both Fbxw7 mRNA and protein levels were significantly reduced in HCC cell lines compared with human liver non-tumor cell line. Moreover, our in vitro experiments showed a remarkable increase of cell migration and invasion in Fbxw7-knockdown cells and a decrease in Fbxw7-overexpress cells. In addition, the present study demonstrated that Fbxw7 is involved in the migration and invasion of HCC cells via regulating Notch1 and the downstream molecules of Notch1. Taken together, our findings indicate that Fbxw7 can be used as a prognostic marker; it has an important role in HCC progression and inhibits HCC cell migration and invasion through the Notch1 signaling pathway.

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.

MicroRNA-200a Suppresses Cell Invasion and Migration by Directly Targeting GAB1 in Hepatocellular Carcinoma.

MicroRNA-200a (miR-200a) is frequently downregulated in most cancer types and plays an important role in carcinogenesis and cancer progression. In this study, we determined that miR-200a was downregulated in hepatocellular carcinoma (HCC) tissues and cell lines, consistent with the results of our previous study. Because a previous study suggested that downregulation of miR-200a is correlated with HCC metastasis, we aimed to elucidate the mechanism underlying the role of miR-200a in metastasis in HCC. Here we observed that overexpression of miR-200a resulted in suppression of HCC metastatic ability, including HCC cell migration, invasion, and metastasis, in vitro and in vivo. Furthermore, bioinformatics and luciferase reporter assays indicated that GAB1 is a direct target of miR-200a. Inhibition of GAB1 resulted in substantially decreased cell invasion and migration similar to that observed with overexpression of miR-200a in HCC cell lines, whereas restoration of GAB1 partially rescued the inhibitory effects of miR-200a. Taken together, these data provide novel information for comprehending the tumor-suppressive role of miR-200a in HCC pathogenesis through inhibition of GAB1 translation.

Combining Exosomes Derived from Immature DCs with Donor Antigen-Specific Treg Cells Induces Tolerance in a Rat Liver Allograft Model.

Allograft tolerance is the ultimate goal in the field of transplantation immunology. Immature dendritic cells (imDCs) play an important role in establishing tolerance but have limitations, including potential for maturation, short lifespan in vivo and short storage times in vitro. However, exosomes (generally 30–100 nm) from imDCs (imDex) retain many source cell properties and may overcome these limitations. In previous reports, imDex prolonged the survival time of heart or intestine allografts. However, tolerance or long-term survival was not achieved unless immune suppressants were used. Regulatory T cells (Tregs) can protect allografts from immune rejection, and our previous study showed that the effects of imDex were significantly associated with Tregs. Therefore, we incorporated Tregs into the treatment protocol to further reduce or avoid suppressant use. We defined the optimal exosome dose as approximately 20 μg (per treatment before, during and after transplantation) in rat liver transplantation and the antigen-specific role of Tregs in protecting liver allografts. In the co-treatment group, recipients achieved long-term survival, and tolerance was induced. Moreover, imDex amplified Tregs, which required recipient DCs and were enhanced by IL-2. Fortunately, the expanded Tregs retained their regulatory ability and donor-specificity. Thus, imDex and donor-specific Tregs can collaboratively induce graft tolerance.

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.

Silencing of CDCA5 inhibits cancer progression and serves as a prognostic biomarker for hepatocellular carcinoma

Cell division cycle associated 5 (CDCA5) has been associated with the progression of several types of cancers. However, its possible role and mechanism in hepatocellular carcinoma (HCC) remain unknown. In the present study, immunohistochemical staining and real-time PCR were used to assess CDCA5 protein and mRNA levels in clinical samples. Statistical analysis was performed to explore the clinical correlation between CDCA5 protein expression and clinicopathological features and overall survival in HCC patients. Cell counting and colony formation assays were employed to analyse the effect of CDCA5 on cell proliferation, and flow cytometry was used to study the role of CDCA5 in cell cycle progression and apoptosis. Moreover, subcutaneous xenograft tumour models were implemented to predict the efficacy of targeting CDCA5 in HCC in vivo. We found that CDCA5 expression was significantly higher in HCC tumour tissues, was associated with clinicopathological characteristics, and predicted poor overall survival in HCC patients. Silencing of CDCA5 with small interfering RNA (siRNA) inhibited cell proliferation and induced G2/M cell cycle arrest in vitro. The xenograft growth assay revealed that CDCA5 downregulation impeded HCC growth in vivo. Further study indicated that CDCA5 depletion decreased the levels of ERK1/2 and AKT phosphorylation in vitro and in vivo. Taken together, these results indicate that CDCA5 may act as a novel prognostic biomarker and therapeutic target for HCC.

PTBP3 splicing factor promotes hepatocellular carcinoma by destroying the splicing balance of NEAT1 and pre-miR-612

Nuclear-enriched RNA-binding proteins (RBPs) are mainly involved in transcriptional regulation, which is a critical checkpoint to tune gene diversity and expression levels. We analyzed nuclear RBPs in human HCC tissues and matched normal control tissues. Based on the gene expression levels, PTBP3 was identified as top-ranked in the nuclei of HCC cells. HCC cell lines then were transfected with siRNAs or lentiviral vectors. PTBP3 promoted HCC cell proliferation and metastasis both in vitro and in vivo. RNA immunoprecipitation (RIP), fluorescence in situ hybridization (FISH) and qRT-PCR assays verified that PTBP3 protein recruited abundant lnc-NEAT1 splicing variants (NEAT1_1 and NEAT1_2) and pre-miR-612 (precursor of miR-612) in the nucleus. NEAT1_1, NEAT1_2 and miR-612 expression levels were determined by PTBP3. Correlational analyses revealed that PTBP3 was positively correlated with NEAT1, but it was inversely correlated with miR-612 in HCC. The P53/CCND1 and AKT2/EMT pathways were determined by NEAT1 and miR-612 respectively in HCC. The PTBP3high and NEAT1high/miR-612low patients had a shorter overall survival. Therefore, nuclear-enriched RBP, PTBP3, promotes HCC cell malignant growth and metastasis by regulating the balance of splicing variants (NEAT1_1, NEAT1_2 and miR-612) in HCC.