MicroRNA expression signature in gastric cancer

Epigenetic silencing of miRNA-9 is correlated with promoter-proximal CpG island hypermethylation in gastric cancer in vitro and in vivo

Silencing of protein-coding tumor suppressor genes (TSGs) by CpG island hypermethylation is a common occurrence in gastric cancer (GC). Here, we examine if tumor suppressor microRNAs (miRNAs) are silenced in a similar manner. Real-time quantitative PCR (RTQ-PCR) was employed to investigate the expression level of four candidate miRNAs in GC tissues (n=30) and cell lines. Basing on RTQ-PCR results and bioinformatics approach, miR-9 was chosen for further study on epigenetic regulation. Bisulfite genomic sequencing PCR (BSP) was performed to assess the methylation status of miR-9 in GC tissues. In both GC cell lines and animal models, demethylation was performed either by treatment with 5-aza-2'-deoxycytidine (5-AZA-CdR) or by siRNA targeting DNMT1. We also analyzed the relationship between miRNAs and several clinicopathological features. Candidate miRNAs (miR-9, miR-433, miR-19b, and miR-370) were found strongly downregulated in GC tissues and cell lines. Their expression was increased following 5-AZA-CdR treatment. CpG island methylation of miR-9 was significantly higher in GC tissues compared to normal controls. After two demethylation treatments, miR-9 methylation degree was significantly decreased and miR-9 expression was ob-viously restored in GC cells and animal models. Deregulation of miR-9 was positively correlated with tumor lesion size. Three other miRNAs, miR-19b, miR-433, and miR-370 were assοciated with lymph node metastasis, decreased curvature, and poorly differentiated carcinoma. miR-19b and miR-433 were positively correlated with male gender. Of four candidate miRNAs downregulated in GC, miR-9 is epigenetically regulated by DNA methylation both in vitro and in vivo.

MicroRNA-338 inhibits growth, invasion and metastasis of gastric cancer by targeting NRP1 expression

NRP1 as multifunctional non-tyrosine-kinase receptors play critical roles in tumor progression. MicroRNAs (miRNAs) are an important class of pervasive genes that are involved in a variety of biological functions, particularly cancer. It remains unclear whether miRNAs can regulate the expression of NRP1. The goal of this study was to identify miRNAs that could inhibit the growth, invasion and metastasis of gastric cancer by targeting NRP1 expression. We found that miR-338 expression was reduced in gastric cancer cell lines and in gastric cancer tissues. Moreover, we found that miR-338 inhibited gastric cancer cell migration, invasion, proliferation and promoted apoptosis by targeting NRP1 expression. As an upstream regulator of NRP1, miR-338 directly targets NRP1. The forced expression of miR-338 inhibited the phosphorylation of Erk1/2, P38 MAPK and Akt; however, the expression of phosphorylated Erk1/2, P38 MAPK and Akt was restored by the overexpression of NRP1. In AGS cells infected with miR-338 or transfected with SiNRP1, the protein levels of fibronectin, vimentin, N-cadherin and SNAIL were decreased, but the expression of E-cadherin was increased. The expression of mesenchymal markers in miR-338-expressing cells was restored to normal levels by the restoration of NRP1 expression. In vivo, miR-338 also decreased tumor growth and suppressed D-MVA by targeting NRP1. Therefore, we conclude that miR-338 acts as a novel tumor suppressor gene in gastric cancer. miR-338 can decrease migratory, invasive, proliferative and apoptotic behaviors, as well as gastric cancer EMT, by attenuating the expression of NRP1.

microRNA-503 inhibits gastric cancer cell growth and epithelial-to-mesenchymal transition

Epithelial-to-mesenchymal transition (EMT) is believed to be associated with cancer cell malignancy, and also to cause cancer invasion and metastasis. Recent evidence indicates that small non-protein coding RNA [microRNAs (miRNAs/miRs)] may act as powerful regulators of EMT. The present study aimed to systematically delineate miR-503 expression in gastric cancer and analyse the function of miR-503 in gastric cancer EMT. In the present study, miR-503 expression was detected in gastric cancer cell lines and gastric cancer tissues by quantitative polymerase chain reaction. Gastric cancer cell migration, invasion and proliferation capabilities were analysed by Transwell, MTT and clonability assays. The expression of mesenchymal markers, including fibronectin, vimentin, N-cadherin, SNAIL and the epithelial marker, E-cadherin, was examined by immunoblot analysis following miR-503 transfection. miR-503 expression was found to be reduced in gastric cancer cell lines compared with normal gastric mucosa cell lines, and the expression of miR-503 was upregulated in non-metastatic-derived gastric cancer cell lines compared with metastatic-derived lines. miR-503 expression levels were significantly reduced in tumour tissues in comparison with adjacent normal mucosa tissues, and the miR-503 expression levels in patients with metastases were significantly lower than those in patients without. miR-503 inhibited gastric cancer cell migration, invasion and proliferation. Fibronectin, vimentin, N-cadherin and SNAIL protein levels were decreased, but E-cadherin expression was increased in an AGS cell line transfected with miR-503. Taken together, the present findings indicate that miR-503 acts as a novel tumour suppressor gene in gastric cancer and can inhibit EMT in gastric cancer cells.

Circulating microRNAs, possible indicators of progress of rat hepatocarcinogenesis from early stages

MicroRNAs (miRNAs), a class of small noncoding RNAs that regulate gene expression at the posttranscriptional level, are believed promising biomarkers for several diseases as well as a novel target of drugs, including cancer. In particular, miRNAs might allow detection of early stages of carcinogenesis. The present study was conducted to provide concrete evidence using chemical-induced hepatocarcinogenesis in rat as a model. We thereby observed aberrant fluctuation of circulating miRNAs in the serum of rats not only with neoplastic lesions such as hepatocellular adenoma (HCA) and hepatocellular carcinoma (HCC), but also with preneoplastic lesions, such as foci of hepatocellular alteration (FHA). Additional qRT-PCR analysis revealed gradual elevation of some circulating miRNAs (i.e., let-7a, let-7f, miR-34a, miR-98, miR-331, miR-338 and miR-652) with progress of hepatocarcinogenesis. Interestingly, increased levels of let-7a, let-7f and miR-98 were statistically significant even in the serum of rats at very early stages. These findings provide the first evidences that circulating miRNAs have the potential to predict carcinogenesis at earlier stages, preneoplastic lesions than with previous biomarkers and that they might be utilized to monitor the progress of tumor development.