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Some long noncoding RNAs (lncRNAs) play important roles in the regulation of gene expression by acting as competing endogenous RNAs (ceRNAs). However, the roles of lncRNA associated-ceRNAs in oncogenesis are not fully understood. Here, based on lncRNA microarray data of gastric cancer, bioinformatic algorithm miRcode and microRNA (miRNA) targets database TarBase, we first constructed an lncRNA-miRNA-mRNA network. Then, we confirmed it by data of six types of other cancer including head and neck squamous cell carcinoma, prostate cancer, papillary thyroid carcinoma, pituitary gonadotrope tumors, ovarian cancer, and chronic lymphocytic leukemia. The results showed a clear cancer-associated ceRNA network. Eight lncRNAs (AC009499.1, GACAT1, GACAT3, H19, LINC00152, AP000288.2, FER1L4, and RP4-620F22.3) and nine miRNAs (miR-18a-5p, miR-18b-5p, miR-19a-3p, miR-20b-5p, miR-106a-5p, miR-106b-5p, miR-31-5p, miR-139-5p, and miR-195-5p) were involved. For instance, through its miRNA response elements (MREs) to compete for miR-106a-5p, lncRNA-FER1L4 regulates the expression of PTEN, RB1, RUNX1, VEGFA, CDKN1A, E2F1, HIPK3, IL-10, and PAK7. Furthermore, cellular experimental results indicated that FER1L4-small interfering RNA (siRNA) simultaneously suppressed FER1L4 and RB1 mRNA level. These results suggest that lncRNAs harbor MREs and play important roles in post-transcriptional regulation in cancer.

Background and Aim: MicroRNAs (miRNAs) play important roles in carcinogenesis. The global miRNA expression profile of gastric cancer has not been reported. The purpose of the present study was to determine the miRNA expression profile of gastric cancer. Methods: Total RNA were first extracted from primary gastric cancer tissues and adjacent non-tumorous tissues and then small isolated RNAs (< 300 nt) were 3′-extended with a poly(A) tail. Hybridization was carried out on a mParaflo™ microfluidic chip (LC Sciences, Houston, TX, USA). After hybridization detection by fluorescence labeling using tagspecific Cy3 and Cy5 dyes, hybridization images were collected using a laser scanner and digitized using Array-Pro image analysis software (Media Cybernetics, Silver Spring, MD, USA). To validate the results and investigate the biological meaning of differential expressed miRNAs, immunohistochemistry was used to detect the differential expression of target genes. Results: The most highly expressed miRNAs in non-tumorous tissues were miR-768-3p, miR-139-5p, miR-378, miR-31, miR-195, miR-497 and miR-133b. Three of them, miR-139-5p, miR-497 and miR-768-3p, were first found in non-tumorous tissues. The most highly expressed miRNAs in gastric cancer tissues were miR-20b, miR-20a, miR-17, miR-106a, miR-18a, miR-21, miR-106b, miR-18b, miR-421, miR-340*, miR-19a and miR-658. Among them, miR-340*, miR-421 and miR-658 were first found highly expressed in cancer cells. The expression of some target genes (such as Rb and PTEN) in cancer tissues was found to be decreased. Conclusion: To our knowledge, this is the first report about these miRNAs associated with gastric cancer. This new information may suggest the potential roles of these miRNAs in the diagnosis of gastric cancer.

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Long intergenic non-protein-coding RNA 152 (LINC00152) is one of the long noncoding RNAs (lncRNAs) abnormally expressed in gastric cancer tissues. However, its value in the diagnosis of gastric cancer is unclear. The aim of this study is to evaluate the clinical significance of plasma LINC00152 as a biomarker in the screening of gastric cancer and to explore the possible mechanism underling its stable existence in blood. We analyzed the levels of plasma LINC00152 in patients with gastric cancer and gastric epithelial dysplasia and healthy controls using quantitative reverse transcription polymerase chain reaction and then confirmed by sequencing. We also compared its levels in paired preoperative and postoperative plasma samples. In addition, we compared the levels of LINC00152 in plasma and in exosomes, which were extracted from the same plasma and confirmed by transmission electron microscopy. The levels of plasma LINC00152 were significantly elevated in gastric cancer patients compared with healthy controls. The sensitivity and specificity of plasma LINC00152 in the diagnosis of gastric cancer were 48.1 and 85.2%, respectively. There were no significant differences of LINC00152 levels between gastric epithelial dysplasia patients and healthy controls. LINC00152 levels in preoperative plasma samples were lower than those in postoperative ones. There were also no differences between LINC00152 levels in plasma and in exosomes. All these results suggested that LINC00152 can be detected in plasma, and one of the possible mechanisms of its stable existence in blood was protected by exosomes. It has the possibility to be applied in gastric cancer diagnosis as a novel blood-based biomarker.

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Long noncoding RNAs (lncRNAs) are non-protein coding transcripts longer than 200 nucleotides. Aberrant expression of lncRNAs has been found associated with gastric cancer, one of the most malignant tumors. By complementary base pairing with mRNAs or forming complexes with RNA binding proteins (RBPs), some lncRNAs including GHET1, MALAT1, and TINCR may mediate mRNA stability and splicing. Other lncRNAs, such as BC032469, GAPLINC, and HOTAIR, participate in the competing endogenous RNA (ceRNA) network. Under certain circumstances, ANRIL, GACAT3, H19, MEG3, and TUSC7 exhibit their biological roles by associating with microRNAs (miRNAs). By recruiting histone-modifying complexes, ANRIL, FENDRR, H19, HOTAIR, MALAT1, and PVT1 may inhibit the transcription of target genes in cis or trans. Through these mechanisms, lncRNAs form RNA-dsDNA triplex. CCAT1, GAPLINC, GAS5, H19, MEG3, and TUSC7 play oncogenic or tumor suppressor roles by correlated with tumor suppressor P53 or onco-protein c-Myc, respectively. In conclusion, interaction with DNA, RNA and proteins is involved in lncRNAs’ participation in gastric tumorigenesis and development.