miR-152 is a tumor suppressor microRNA that is silenced by DNA hypermethylation in endometrial cancer

The etiology and development of human cancers that remain little understood might be enlightened by defining tumor suppressor microRNAs (TS-miRNA). In this study, we identified TS-miRNAs silenced by aberrant DNA hypermethylation in endometrial cancer. Functional screening of 327 synthetic miRNAs in an endometrial cancer cell proliferation assay identified 103 miRNAs that inhibited cell growth. We then determined the sequence, DNA methylation status, and expression levels of these miRNAs in endometrial cancer cell lines and primary tumors. These determinations led to the identification of miR-152 as a candidate TS-miRNA gene in endometrial cancer. Epigenetic silencing documented in miR-152 was consistent with its location at 17q21.32 in intron 1 of the COPZ2 gene, which is also silenced often in endometrial cancer by DNA hypermethylation, and also with evidence that miR-152 targets the DNA methyltransferase DNMT1. Notably, restoration of miR-152 expression in endometrial cancer cell lines was sufficient to inhibit tumor cell growth in vitro and in vivo. We identified E2F3, MET, and Rictor as novel candidate targets of miR-152, suggesting how its epigenetic silencing can drive endometrial carcinogenesis. Our findings define a central role for miR-152 in endometrial cancer, and they also suggest its use in new therapeutic strategies to treat this cancer.     

Genome-wide pharmacologic unmasking identifies tumor suppressive microRNAs in multiple myeloma

Epigenetic alterations have emerged as an important cause of microRNA (miRNA) deregulation. In Multiple Myeloma (MM), a few tumor suppressive miRNAs silenced by DNA hypermethylation have been reported, but so far there are few systemic investigations on epigenetically silenced miRNAs. We conducted genome-wide screening for tumor suppressive miRNAs epigenetically silenced in MM. Four Human MM Cell lines were treated with demethylating agent 5′azacytidine (5′aza). Consistently upregulated miRNAs include miR-155, miR-198, miR-135a*, miR-200c, miR-125a-3p, miR-188-5p, miR-483-5p, miR-663, and miR-630. Methylation array analysis revealed increased methylation at or near miRNA-associated CpG islands in MM patients. Ectopic restoration of miR-155, miR-198, miR-135a*, miR-200c, miR-663 and miR-483-5p significantly repressed MM cell proliferation, migration and colony formation. Furthermore, we derived a 33-gene signature from predicted miRNA target genes that were also upregulated in MM patients and associated with patient survival in three independent myeloma datasets. In summary, we have revealed important, epigenetically silenced tumor suppressive miRNAs by pharmacologic reversal of epigenetic silencing.     

Stabilization of phenotypic plasticity through mesenchymal-specific DNA hypermethylation in cancer cells

The epithelial-mesenchymal transition (EMT) has a crucial role in normal and disease processes including tumor progression. In this study, we first classified epithelial-like and mesenchymal-like oral squamous cell carcinoma (OSCC) cell lines based on expression profiles of typical EMT-related genes using a panel of 18 OSCC cell lines. Then, we performed methylation-based and expression-based analyses of components of the Wnt signaling pathway, and identified WNT7A and WNT10A as genes silenced by mesenchymal-specific DNA hypermethylation in OSCCs. A significant association was revealed between some clinicopathological findings and the DNA methylation status of WNT7A (normal vs tumor, P=0.007; T1-2 vs T3-4, P=0.040; I-III vs IV, P=0.016) and WNT10A (N0-N1 vs N2-N3, P=0.046) in the advanced stages of OSCC. Moreover, we found that E-cadherin expression in cancer cells may be positively regulated by WNT7A, whose expression is negatively regulated by mesenchymal-specific DNA hypermethylation or ZEB1 in mesenchymal-like OSCC cells. Our findings indicate that epithelial-specific gene silencing through mesenchymal-specific DNA hypermethylation may stabilize the phenotypic plasticity of cancer cells during EMT/MET.     

miR-218 on the genomic loss region of chromosome 4p15.31 functions as a tumor suppressor in bladder cancer

Growing evidence suggests that microRNAs (miRNAs) are aberrantly expressed in many human cancers, and that they play significant roles in carcinogenesis and cancer progression. The identification of tumor suppressive miRNAs and their target genes could provide new insights into the mechanism of carcinogenesis. However, the genetic or epigenetic regulations of these miRNAs have not yet been fully elucidated in bladder cancer (BC). Chromosomal alterations of cancer cells give us important information for the identification of tumor suppressor genes. Our miRNA array-comparative genomic hybridization (CGH) analysis showed several miRNAs to be candidate tumor suppressors of BC. Our array-CGH analysis revealed that chromosome 4 was lost in all BC cell lines. We selected 19 miRNAs located on chromosome 4 and evaluated their expression levels in cancer cell lines as well as clinical samples. Gain-of-function analysis revealed that miR-218 inhibited BC cell proliferation, migration and invasion. Furthermore, flow cytometry analysis showed that it induced BC cell apoptosis. Genome-wide gene expression analysis showed that it targeted multiple oncogenes in BC. Our study is the first to demonstrate that miR-218 located on chrosomosme 4p15.31 is a tumor suppressive miRNA in BC. The identification of tumor suppressive miRNAs and their target genes on the basis of array-CGH analysis could provide new insights into the mechanisms of BC carcinogenesis.     

Methylation-associated silencing of microRNA-34b/c in gastric cancer and its involvement in an epigenetic field defect

Altered expression of microRNA (miRNA) is strongly implicated in cancer, and recent studies have shown that the silencing of some miRNAs is associated with CpG island hypermethylation. To identify epigenetically silenced miRNAs in gastric cancer (GC), we screened for miRNAs induced by treatment with 5-aza-2'-deoxycytidine and 4-phenylbutyrate. We found that miR-34b and miR-34c are epigenetically silenced in GC and that their downregulation is associated with hypermethylation of the neighboring CpG island. Methylation of the miR-34b/c CpG island was frequently observed in GC cell lines (13/13, 100%) but not in normal gastric mucosa from Helicobacter pylori-negative healthy individuals. Transfection of a precursor of miR-34b and miR-34c into GC cells induced growth suppression and dramatically changed the gene expression profile. Methylation of miR-34b/c was found in a majority of primary GC specimens (83/118, 70%). Notably, analysis of non-cancerous gastric mucosae from GC patients (n = 109) and healthy individuals (n = 85) revealed that methylation levels are higher in gastric mucosae from patients with multiple GC than in mucosae from patients with single GC (27.3 versus 20.8%; P < 0.001) or mucosae from H. pylori-positive healthy individuals (27.3 versus 20.7%; P < 0.001). These results suggest that miR-34b and miR-34c are novel tumor suppressors frequently silenced by DNA methylation in GC, that methylation of miR-34b/c is involved in an epigenetic field defect and that the methylation might be a predictive marker of GC risk.     

Methylation-associated silencing of MicroRNA-335 contributes tumor cell invasion and migration by interacting with RASA1 in gastric cancer

MicroRNAs (miRNAs) are small non-coding RNAs that function as endogenous silencers of target genes, previous studies have shown that miR-335 play an important role in suppressing metastasis and migration in human cancer including gastric cancer (GC). However, the mechanisms which result in aberrant expression of miR-335 in GC are still unknown. Recent studies have shown that the silencing of some miRNAs is associated with DNA hypermethylation. In this study, we find the promoter of miR-335 we embedded in CpG island by accessing to bioinformatics data and the low expression of miR-335 in 5 gastric cell lines can be restored by 5-aza-2’-deoxycytidine (5-Aza-dC) treatment. So we postulated that the miR-335 genes undergo epigenetic inactivation in GC. Subsequently, in GC cells and tissues, we performed quantitative real-time PCR (RTQ-PCR) to assess the expression of miR-335, and methylation-specific PCR (MSP) and bisulfite sequence-PCR (BSP) to evaluate the DNA methylation status in the CpG islands upstream of MiR-335. The result showed that the expression of miR-335 was significantly reduce in gastric cancer cell lines and tumor tissues compared to matched normal gastric tissues, and cell lines, and which is inverse correlation with DNA hypermethylation of miR-335 both in GC cells lines and tissues, but not in normal tissues. In addition, we found that the lower miR-335 expression induced by abnormal methylation may be mainly involved in gastric cell invasion and metastasis in GC tissues. No statistical significance was found about miR-335 expression and methylation level between healthy individuals with and without H. pylori (HP) infection. Finally, we carry out miRNA transfection, RTQ-PCR and western blot assay to find the RAS p21 protein activator (GTPase activating protein) 1 (RASA1) may be the possible target genes which lead to the gastric cell invasion and metastasis, furthermore, the re-expression of endogenous miR-335 by 5-Aza-dC treatment can exert effects similar to exogenous miRNAs transfection. Taken together, our results suggest that miR-335 may be silenced by promoter hypermethylation and play important roles in gastric cell invasion and metastasis through its target genes, such as RASA1. Its methylation level might be a predictive epigenetic marker of GC and remodeling on the expression by demethylation can provided a potential therapeutic strategy.     

miRNA-335基因启动子区甲基化与胃癌细胞不良生物学行为的关系

目的:探讨miR-335基因启动子区异常甲基化状态对胃癌细胞系中miR-335表达水平的影响,以及miR-335基因启动子区甲基化状态对胃癌细胞侵袭,迁移,以及增殖能力的影响。方法:1株永生化胃黏膜上皮细胞系(GES-1)和4株胃癌细胞系(SGC-7901,MKN-45,BGC-823和AGS)。实时荧光定量PCR(qRT-PCR)检测胃癌细胞株miR-335及CRKL的表达水平。甲基化特异性PCR(MSP)方法检测胃癌细胞株miR-335的基因启动子区甲基化状态。应用MTT方法检测恢复miR-335表达对胃癌细胞增殖能力的影响,Transwell侵袭迁移实验及划痕愈合实验分析恢复miR-335表达对胃癌细胞系侵袭及迁移能力的影响。结果:MSP实验结果表明,MKN-45、SGC-7901和BGC-823细胞系均存在基因启动子区异常的高甲基化状态,AGS细胞系基因启动子区亦呈部分高甲基化状态。去甲基药物5-aza-2′-deoxycytidine处理后胃癌细胞miR-335的表达水平可升高2~3倍。Transwell侵袭迁移实验及划痕愈合实验表明miR-335表达水平恢复后SGC-7901细胞的侵袭和迁移能力明显降低。MTT实验结果表明5-aza-2′-deoxycytidine处理后的SGC-7901细胞系与对照组相比,增殖能力显著降低。结论:miR-335启动子区的异常高甲基化状态抑制了miR-335在胃癌细胞系中的表达,恢复miR-335的表达水平可以抑制胃癌细胞的增殖,迁移和侵袭能力。miR-335为胃癌的肿瘤抑制因子。     

Human papillomavirus type 16 reduces the expression of microRNA-218 in cervical carcinoma cells

Human papillomaviruses (HPVs) are involved in the pathogenesis of cancer of the cervix (CaCx). MicroRNA (miRNA) expression analysis using Ambion (Austin, TX, USA) arrays showed that three miRNAs were overexpressed and 24 underexpressed in cervical cell lines containing integrated HPV-16 DNA compared to the normal cervix. Furthermore, nine miRNAs were overexpressed and one underexpressed in integrated HPV-16 cell lines compared to the HPV-negative CaCx cell line C-33A. Based on microarray and/or quantitative real-time PCR and northern blot analyses, microRNA-218 (miR-218) was specifically underexpressed in HPV-positive cell lines, cervical lesions and cancer tissues containing HPV-16 DNA compared to both C-33A and the normal cervix. Expression of the E6 oncogene of high-risk HPV-16, but not that of low-risk HPV-6, reduced miR-218 expression, and conversely, RNA interference of E6/E7 oncogenes in an HPV-16-positive cell line increased miR-218 expression. We also demonstrate that the epithelial cell-specific marker LAMB3 is a target of miR-218. We also show that LAMB3 expression is increased in the presence of the HPV-16 E6 oncogene and this effect is mediated through miR-218. These findings may contribute to a better understanding of the molecular mechanisms involved in cervical carcinogenesis.     

miR-218与宫颈癌关系的研究进展(英文)

MicroRNAs (miRNAs) are small endogenous non-coding RNAs which can specifically silence gene expression, and thereby alter cell and organism phenotype. Deregulation of miRNA expression has been discovered in a variety of tumors and it is now clear that they contribute to cancer development and progression. Previous studies have indicated that miRNAs are involved in developmental timing, cell proliferation, apoptosis, morphogenesis [1] , antiviral defense [2] , and tumorigenesis [3] . In cancer pathways, altered expression of tumor suppressive or oncogenic miRNAs can disrupt regulatory mechanisms normal. Altered miRNAs expression patterns have been observed in a variety of diseased tissues. Cervical cancer is the most common malignant tumor in female reproductive tract. Recently more and more study showed a large number of miRNAs were down-regulated or up-regulated in cervical cancer. Recent data revealed that miRNA-218 (miR-218) played important roles in tumor initiation and development. This review focuses on analysis of miR-218 and will provide some insight into the progress of cervical cancer.     

Tumor suppressive microRNA-218 inhibits cancer cell migration and invasion through targeting laminin-332 in head and neck squamous cell carcinoma

Recent our microRNA (miRNA) expression signature revealed that expression of microRNA-218 (miR-218) was reduced in cancer tissues, suggesting a candidate of tumor suppressor in head and neck squamous cell carcinoma (HNSCC). The aim of this study was to investigate the functional significance of miR-218 and its mediated moleculer pathways in HNSCC. Restoration of miR-218 in cancer cells led to significant inhibition of cell migration and invasion activities in HNSCC cell lines (FaDu and SAS). Genome-wide gene expression analysis of miR-218 transfectants and in silico database analysis showed that focal adhesion pathway was a promising candidate of miR-218 target pathways. The laminins are an important and biologically active part of the basal lamina, the function of that are various such as influencing cell differentiation, migration and adhesion as well as proliferation and cell survival. Interestingly, all components of laminin-332 (LAMA3, LAMB3 and LAMC2) are listed on the candidate genes in focal adhesion pathway. Furthermore, we focused on LAMB3 which has a miR-218 target site and gene expression studies and luciferase reporter assays showed that LAMB3 was directly regulated by miR-218. Silencing study of LAMB3 demonstrated significant inhibition of cell migration and invasion. In clinical specimens with HNSCC, the expression levels of laminin-332 were significantly upregulated in cancer tissues compared to adjacent non-cancerous tissues. Our analysis data showed that tumor suppressive miR-218 contributes to cancer cell migration and invasion through regulating focal adhesion pathway, especially laminin-332. Tumor suppressive miRNA-mediated novel cancer pathways provide new insights into the potential mechanisms of HNSCC oncogenesis.     

MicroRNA-212 functions as an epigenetic-silenced tumor suppressor involving in tumor metastasis and invasion of gastric cancer through down-regulating PXN expression

Altered expression of paxillin (PXN) is closely linked to the pathogenesis progression, metastasis and prognosis of different malignancies including gastric cancer (GC). Epigenetic silencing of tumor-suppressive microRNAs (miRNAs) is a crucial component of the mechanism underlying activation of oncogenes in tumor. To screen for epigenetically silenced miRNAs which target PXN in GC, we performed bioinformatics algorithms and real-time PCR analysis, and identified miR-212 as the optimum candidate gene. A luciferase reporter gene assay validated that miR-212 directly targets the 3’UTR region of PXN. Importantly, miR-212 levels were inversely correlated with PXN expression in GC cell lines and clinical tumor tissues. The use of miR-212 minics decrease PXN mRNA and protein level in GC cell lines. Moreover, low expression of miR-212 and its promoter hypermethylation were causally related and were associated with aggressive tumor phenotype and adverse prognosis in GC. Restoring mir-212 expression by exogenous mirprecursor molecules transfection or reexpression of endogenous miR-212 treated by 5-aza-2’-deoxycytidine (5-aza) can exert similar effect that reduce GC cells invasion and metastasis abilities in vitro by interacting PXN gene. In addition, 5-aza-induced PXN reduction could be partically blocked by miR-212 inhibitor, resulting in a reversal of weankening cell migration and invasion ability of 5-aza. A rescue experiment and a loss-of-function experiment in vitro and vivo showed that PXN restoration rescues migration and invasion phenotype in miR-212 overexpressed GC cell lines and PXN knockdown blocks GC cells migration and invasion in the presence miR-212 inhibitors. Taken together, our results clearly show that overexpression of PXN induced by methylationsuppressed miR-212 promotes tumor metastasis and invasion, and regulation of miR-212 expression may be a novel therapeutic strategy for gastric cancer.     

miR-101靶向调控SPOP影响口腔鳞癌转移机制的研究

目的:探讨miR-101对口腔鳞状细胞癌（oral squamous cell carcinoma,OSCC）细胞SPOP基因的靶向关系及其对细胞迁移的影响。方法:使用Real time-PCR技术检测miR-101在OSCC细胞中的表达;利用生物信息分析预测SPOP可能是miR-101靶基因,将miR-101转染至Tca-8113细胞株,通过增强或者抑制miR-101的表达,利用蛋白质印迹实验检测SPOP表达,从而判断两者靶向关系;利用细胞迁移试验,通过miR-101表达强弱改变,判断Tca-8113细胞株迁移能力的变化情况。结果:miR-101在三个OSCC细胞株中表达均降低;在Tca-8113细胞株中增强miR-101表达,则SPOP表达下降,细胞迁移能力减弱;抑制miR-101表达,则SPOP表达升高,细胞迁移能力增强。结论:miR-101对OSCC细胞SPOP有靶向抑制作用,并且可以抑制OSCC细胞转移。     

胃癌转移相关miRNA的差异表达谱及miR-218的生物学分析

目的 探讨胃癌转移相关微小RNA（miRNA）的差异表达情况并进行miR-218的生物学分析。方法 采用实时荧光定量PCR（qPCR）及miRNA芯片法检测低转移潜能的胃癌细胞亚系（SGC7901-NM、MKN28-NM）与高转移潜能的胃癌细胞亚系（SGC7901-M、MKN28-M）间miRNA的差异表达。提取不同转移潜能胃癌细胞系和10例胃癌冰冻组织及相应的转移淋巴结中的总RNA,利用qPCR检测miR-218在不同细胞及组织中的表达情况。结果 对不同转移潜能的胃癌细胞亚系进行芯片检测发现,与SGC7901-NM细胞比较,SGC7901-M 细胞有47个分子表达下调,15个分子表达上调。与MKN28-NM细胞比较,MKN28-M细胞有41个分子表达下调,83个分子表达上调。在SGC7901-M及MKN28-M细胞中,34个分子表达均出现下降,11个分子表达均出现上升。对不同转移潜能的胃癌细胞亚系以及人永生化正常胃黏膜细胞系GES进行检测可以发现,4种不同转移潜能的胃癌细胞亚系中miR-218的表达均低于正常胃黏膜细胞系GES,差异有统计学意义（P＜0.05）,且在高转移潜能胃癌细胞亚系中miR-218的表达均低于低转移潜能胃癌细胞系,差异有统计学意义（P＜0.05）。胃癌转移淋巴结中miR-218的表达水平为0.23±0.02,低于胃癌原发灶的1.09±0.05,差异有统计学意义（P＜0.05）。结论 胃癌转移相关miRNA会出现差异表达情况,高转移潜能胃癌细胞中的miR-218表达水平上调可能与胃癌转移存在一定关系。