A MDM2‐dependent positive‐feedback loop is involved in inhibition of miR‐375 and miR‐106b induced by Helicobacter pylori lipopolysaccharide

Dysregulation of microRNAs (miRNAs) has been linked to virulence factors of Helicobacter pylori and shown to contribute to the progression of gastric cancer. However, the mechanisms of these processes remain poorly understood. The aim of this study was to investigate the mechanisms by which lipopolysaccharide (LPS), a virulence factor of H. pylori, regulates miR‐375 and miR‐106b expression in gastric epithelial cells. The results show that LPS from H. pylori 26695 downregulated the expression of miR‐375 and miR‐106b in gastric epithelial cells, and low levels of Dicer were also observed. Downregulation of miR‐375 was found to increase expression of MDM2 with SP1 activation. Overexpression of MDM2 inhibited Dicer by repressing p63 to create a positive‐feedback loop involving SP1/MDM2/p63/Dicer that leads to inhibition of miR‐375 and miR‐106b expression. In addition, we demonstrated that JAK1 and STAT3 were downstream target genes of miR‐106b. H. pylori LPS also enhanced the tyrosine phosphorylation of JAK1, JAK2 and STAT3. Together, these results provide insight into the regulatory mechanisms of MDM2 on H. pylori LPS‐induced specific miRNAs, and furthermore, suggest that gastric epithelial cells treated with H. pylori LPS may be susceptible to JAK/STAT3 signal pathway activation via inhibition of miR‐375 and miR‐106b.     

miR‐212 is downregulated and suppresses methyl‐CpG‐binding protein MeCP2 in human gastric cancer

To clarify the role of micro (mi) RNAs in gastric carcinogenesis, we studied the expression and function of miRNAs in gastric carcinoma (GC) cells. Initially, we performed microarray analysis using total RNA from 3 human GC cell lines and noncancerous gastric tissue. Among the downregulated miRNAs in GC cells, miR‐212 expression was decreased in all 8 GC cell lines examined and a significant decrease of miR‐212 expression in human primary GC tissues was also observed in 6 of 11 cases. Transfection of the precursor miR‐212 molecule induced decreased growth of 3 GC cell lines. Using 3 different databases, methyl‐CpG‐binding protein MeCP2 was postulated to be a target of miR‐212. As seen on reporter assaying, miR‐212 repressed the construct with the MECP2 3′‐UTR. Ectopic expression of miR‐212 repressed expression of the MeCP2 protein but not the MECP2 mRNA level. These data suggest that downregulation of miR‐212 may be related to gastric carcinogenesis through its target genes, such as MECP2.     

Increased T‐helper 17 cell differentiation mediated by exosome‐mediated microRNA‐451 redistribution in gastric cancer infiltrated T cells

MicroRNA (miR)‐451 is a cell metabolism‐related miRNA that can mediate cell energy‐consuming models by several targets. As miR‐451 can promote mechanistic target of rapamycin (mTOR) activity, and increased mTOR activity is related to increased differentiation of T‐helper 17 (Th17) cells, we sought to investigate whether miR‐451 can redistribute from cancer cells to infiltrated T cells and enhance the distribution of Th17 cells through mTOR. Real‐time PCR was used for detecting expression of miR‐451 in gastric cancer, tumor infiltrated T cells and exosomes, and distribution of Th17 was evaluated by both flow cytometry and immunohistochemistry (IHC). Immunofluorescence staining was used in monitoring the exosome‐enveloped miR‐451 from cancer cells to T cells with different treatments, and signaling pathway change was analyzed by western blot. miR‐451 decreased significantly in gastric cancer (GC) tissues but increased in infiltrated T cells and exosomes; tumor miR‐451 was negatively related to infiltrated T cells and exosome miR‐451. Exosome miR‐451 can not only serve as an indicator for poor prognosis of post‐operation GC patients but is also related to increased Th17 distribution in gastric cancer. miR‐451 can redistribute from cancer cells to T cells with low glucose treatment. Decreased 5′ AMP‐activated protein kinase (AMPK) and increased mTOR activity was investigated in miR‐451 redistributed T cells and the Th17 polarized differentiation of these T cells were also increased. Exosome miR‐451 derived from tumor tissues can serve as an indicator for poor prognosis and redistribution of miR‐451 from cancer cells to infiltrated T cells in low glucose treatment can enhance Th17 differentiation by enhancing mTOR activity.     

Genetic polymorphism of miR‐146a is associated with gastric cancer risk: a meta‐analysis

Several studies have investigated the associations between miR‐146a rs2910164 and gastric cancer (GC) risk, but results have been inconclusive. To derive a more precise estimation of the relationship, a meta‐analysis was performed. PubMed and China National Knowledge Infrastructure searches were carried out for relevant studies published before July 2014. Meta‐analysis was performed with the stata , version 11.0. A total of seven case–control studies, including 3283 cases and 4535 controls, were selected. A significant association was found between rs2910164 and GC risk under all genetic models (CC vs. GG, OR = 0.76, 95% CI = 0.66–0.87; CC vs. GC+GG, OR = 0.84, 95% CI = 0.71–0.99; CC+GC vs. GG, OR = 0.82, 95% CI = 0.73–0.91) for the total data. In the subgroup analysis by ethnicity, statistically significant association was found in Asian. This meta‐analysis suggested that the miR‐146a rs2910164 was a risk factor for developing GC.     

Differential expression of miR‐21, miR‐125b and miR‐191 in breast cancer tissue

Aims: To develop new biomarkers for early detection and to inform effective clinical management of breast cancer. Methods: Real‐time polymerase chain reaction was used to profile microRNA (miRNA) in tumor tissue from 50 breast cancer patients using non‐tumor breast tissue from each patient as a control. We have focussed on three miRNA; miR‐21, miR‐125b and miR‐191, all of which have been implicated in breast cancer with either proven or predicted target genes involved in critical cancer‐associated cellular pathways. Results: Upregulation of miR‐21 and miR‐191 and downregulation of miR‐125b, was found in breast cancer tissue. Combined expression analysis of miR‐125b/miR‐191 increased sensitivity to 100% and specificity to 94% while miR‐21/miR‐191 increased to 92% and 100%, respectively. Therefore, combination of two miRNA gives a better prediction than individual miRNA. Conclusions: We could differentiate between breast cancer and adjacent non‐tumor breast tissue as a control with a high degree of sensitivity and specificity in the Mexican population using a combined expression analysis of only two miRNA. These observations, although a proof of principle finding at this time, show that a combined expression profile of two miRNA (miR‐125b/miR‐191 and miR‐21/miR‐191) can discriminate between breast cancer and non‐tumor tissue with high specificity and sensitivity.     

miR‐106a is frequently upregulated in gastric cancer and inhibits the extrinsic apoptotic pathway by targeting FAS

Emerging evidence has shown the association of aberrantly expressed miR‐106a with cancer development, however, little is known about its potential role in gastric carcinogenesis. In our present study, obviously overexpressed miR‐106a was found in gastric cancer tissues compared with their nontumor counterparts. Suppression of miR‐106a significantly inhibited gastric cancer cell proliferation and triggered apoptosis. Bioinformatic analysis combining with validation experiments identified FAS as a direct target of miR‐106a. Rescue experiments and examination of caspase‐8, PARP and caspase‐3 further approved that miR‐106a could inhibit gastric cancer cell apoptosis through interfering with FAS‐mediated apoptotic pathway. Moreover, a significant inverse correlation was found between miR‐106a and FAS expression not only in gastric cancer cell lines but also in gastric cancer specimens. Taken together, these findings suggest that ectopicly overexpressed miR‐106a may play an oncogenic role in gastric carcinogenesis and impair extrinsic apoptotic pathway through targeting FAS. © 2012 Wiley Periodicals, Inc.     

Downregulation of miR‐491‐5p promotes gastric cancer metastasis by regulating SNAIL and FGFR4

Gastric cancer (GC) is among the most fatal cancers in China. MicroRNAs (miRNAs) are versatile regulators during GC development and progression. miR‐491‐5p has been demonstrated to act as a tumor suppressor in several types of cancer. However, the role of miR‐491‐5p in GC metastasis remains unknown. Here, we found that miR‐491‐5p was significantly decreased in GC tissues compared with adjacent non‐cancerous tissues, and low miR‐491‐5p level was associated with large tumor size. Overexpression of miR‐491‐5p significantly suppressed GC cell epithelial‐to‐mesenchymal transition (EMT) and tumor metastasis in vitro and in vivo. Mechanistically, SNAIL was identified as a direct target of miR‐491‐5p. The silencing of SNAIL phenocopied the tumor suppressive function of miR‐491‐5p, whereas re‐expression of SNAIL in GC cells rescued the EMT markers and cell migratory ability that were inhibited by miR‐491‐5p. In addition, miR‐491‐5p inhibited FGFR4 indirectly. Inhibition of FGFR4 also decreased the SNAIL level and impaired EMT and cell migration. Taken together, these findings indicate that downregulation of miR‐491‐5p promoted GC metastasis by inducing EMT via regulation of SNAIL and FGFR4.     

miR‐135b‐ and miR‐146b‐dependent silencing of calcium‐sensing receptor expression in colorectal tumors

Studies have shown that the calcium‐sensing receptor (CaSR) mediates the antitumorigenic effects of calcium against colorectal cancer (CRC). Expression of the CaSR in colorectal tumors is often reduced. We have reported previously that silencing of CaSR in CRC is caused in part by methylation of CaSR promoter 2 and loss of histone acetylation. We investigated the impact of aberrant microRNA expression on loss of CaSR expression. A microarray study in two Caco‐2 subclones (Caco2/AQ and Caco2/15) that have similar genetic background, but different CaSR expression levels (Caco2/AQ expressing more CaSR than Caco2/15), identified 22 differentially expressed microRNAs that potentially target the CaSR. We validated these results by performing gain‐ and loss‐of‐function studies with the top candidates: miR‐9, miR‐27a, miR‐135b, and miR‐146b. Modulation of miR‐135b or miR‐146b expression by mimicking or inhibiting their expression regulated CaSR protein levels in two different colon cancer cell lines: Caco2/AQ (moderate endogenous CaSR expression) and HT29 (low endogenous CaSR levels). Inhibition of miR‐135b and miR‐146b expression led to high CaSR levels and significantly reduced proliferation. In samples of colorectal tumors we observed overexpression of miR‐135b and miR‐146b, and this correlated inversely with CaSR expression (miR‐135b: r = ?0.684, p < 0.001 and miR‐146b: r = ?0.448, p < 0.001), supporting our in vitro findings. We demonstrate that miR‐135b and miR‐146b target the CaSR and reduce its expression in colorectal tumors, reducing the antiproliferative and prodifferentiating actions of calcium. This provides a new approach for finding means to prevent CaSR loss, developing better treatment strategies for CRC.     

The tumor suppressor microRNA‐29c is downregulated and restored by celecoxib in human gastric cancer cells

MicroRNAs (miRNAs) are small noncoding RNAs that function as endogenous silencers of target genes and play critical roles during carcinogenesis. The selective cyclooxygenase‐2 (COX‐2) inhibitor celecoxib has been highlighted as a potential drug for treatment of gastrointestinal tumors. The aim of this study was to investigate the role of miRNAs in gastric carcinogenesis and the feasibility of a new therapeutic approach for gastric cancer. miRNA expression profiles were examined in 53 gastric tumors including gastric adenomas (atypical epithelia), early gastric cancers and advanced gastric cancers and in gastric cancer cells treated with celecoxib. miRNA microarray analysis revealed that miR‐29c was significantly downregulated in gastric cancer tissues relative to nontumor gastric mucosae. miR‐29c was significantly activated by celecoxib in gastric cancer cells. Downregulation of miR‐29c was associated with progression of gastric cancer and was more prominent in advanced gastric cancers than in gastric adenomas and early gastric cancer. In addition, expression of the oncogene Mcl‐1, a target of miR‐29c, was significantly increased in gastric cancer tissues relative to nontumor gastric mucosae. Activation of miR‐29c by celecoxib induced suppression of Mcl‐1 and apoptosis in gastric cancer cells. These results suggest that downregulation of the tumor suppressor miR‐29c plays critical roles in the progression of gastric cancer. Selective COX‐2 inhibitors may have clinical promise for the treatment of gastric cancer via restoration of miR‐29c.     

Oncogenic microRNA‐27a is a target for anticancer agent methyl 2‐cyano‐3,11‐dioxo‐18β‐olean‐1,12‐dien‐30‐oate in colon cancer cells

Methyl 2‐cyano‐3,11‐dioxo‐18β‐olean‐1,12‐dien‐30‐oate (CDODA‐Me) is a synthetic derivative of glycyrrhetinic acid, a triterpenoid phytochemical found in licorice extracts. CDODA‐Me inhibited growth of RKO and SW480 colon cancer cells and this was accompanied by decreased expression of Sp1, Sp3 and Sp4 protein and mRNA and several Sp‐dependent genes including survivin, vascular endothelial growth factor (VEGF), and VEGF receptor 1 (VEGFR1 or Flt‐1). CDODA‐Me also induced apoptosis, arrested RKO and SW480 cells at G₂/M, and inhibited tumor growth in athymic nude mice bearing RKO cells as xenografts. CDODA‐Me decreased expression of microRNA‐27a (miR‐27a), and this was accompanied by increased expression of 2 miR‐27a‐regulated mRNAs, namely ZBTB10 (an Sp repressor) and Myt‐1 which catalyzes phosphorylation of cdc2 to inhibit progression of cells through G₂/M. Both CDODA‐Me and antisense miR‐27a induced comparable responses in RKO and SW480 cells, suggesting that the potent anticarcinogenic activity of CDODA‐Me is due to repression of oncogenic miR‐27a. © 2009 UICC     

Suppression of AKT expression by miR‐153 produced anti‐tumor activity in lung cancer

Lung cancer is one of the leading causes of cancer death worldwide. microRNAs have been shown to be a novel class of regulators in lung cancer. Here, we explored the role of miR‐153 in the pathogenesis of lung cancer and its therapeutic potential. miR‐153 was significantly decreased in lung cancer tissues than the adjacent tissues. The protein and mRNA levels of protein kinase B (AKT), which were shown to promote tumor growth, were both increased in lung cancer tissues than adjacent tissues. Overexpression of miR‐153 significantly inhibited AKT protein expression, which were abrogated by co‐transfection of AMO‐153, the specific inhibitor of miR‐153. Luciferase assay showed that transfection of miR‐153 markedly suppressed the fluorescent intensity of chimeric vectors carrying the 3'UTR of AKT1, while produced no effect on the mutant construct, indicating that AKT is regulated by miR‐153. Overexpression of miR‐153 significantly inhibited the proliferation and migration, and promoted apoptosis of cultured lung cancer cells in vitro, and suppressed the growth of xenograft tumors in vivo. Interestingly, lung cancer cells with lower endogenous miR‐153 expression are more sensitive to ectopic overexpressed miR‐153. The IC₅₀ of miR‐153 on lung cancer cells is positive correlated with the endogenous miR‐153 level, while negative correlated with AKT level. Knockdown of AKT expression suppressed lung cancer cell proliferation. In summary, miR‐153 exerted anti‐tumor activity in lung cancer by targeting on AKT. The sensitivity of lung cancer cells to miR‐153 is determined by its endogenous miR‐153 level.     

Downregulation of leucine‐rich repeats and immunoglobulin‐like domains 1 by microRNA‐20a modulates gastric cancer multidrug resistance

Multidrug resistance (MDR) significantly restricts the clinical efficacy of gastric cancer (GC) chemotherapy, and it is critical to search novel targets to predict and overcome MDR. Leucine‐rich repeats and immunoglobulin‐like domains 1 (LRIG1) has been proved to be correlated with drug resistance in several cancers. The present study revealed that LRIG1 was overexpressed in chemosensitive GC tissues and decreased expression of LRIG1 predicted poor survival in GC patients. We observed that upregulation of LRIG1 enhanced chemosensitivity in GC cells. Interestingly, miR‐20a, which was overexpressed in GC MDR cell lines and tissues, was identified to regulate LRIG1 expression by directly targeting its 3′ untranslated region. We also found that inhibition of miR‐20a suppressed GC MDR, and upregulation showed opposite effects. Moreover, we demonstrated that the miR‐20a/LRIG1 axis regulated GC cell MDR through epidermal growth factor receptor (EGFR)‐mediated PI3K/AKT and MAPK/ERK signaling pathways. Finally, LRIG1 expression in human GC tissues is inversely correlated with miR‐20a and EGFR. Taken together, the newly identified miR‐20a/LRIG1/EGFR link provides insight into the MDR process of GC, and targeting this axis represents a novel potential therapeutic strategy to block GC chemoresistance.