Epigenetic silencing of microRNA-34b/c plays an important role in the pathogenesis of malignant pleural mesothelioma

Hsp90 inhibitor NVP-AUY922 enhances the radiation sensitivity of lung cancer cell lines with acquired resistance to EGFR-tyrosine kinase inhibitors

Acquired resistance to epidermal growth factor receptor (EGFR)-tyrosine kinase inhibitors (TKIs) is a critical issue that needs to be overcome in the treatment of patients with non-small cell lung cancer (NSCLC) harboring EGFR activating mutations. EGFR and AKT are client proteins of the 90-kDa heat shock protein (Hsp90). Therefore, it was hypothesized that the use of Hsp90 inhibitors might allow the resistance to EGFR-TKIs to be overcome. Furthermore, Hsp90 inhibitors are known to function as radiosensitizers in various types of cancer. In the present study, we evaluated the radiosensitizing effect of the novel Hsp90 inhibitor, NVP-AUY922 (AUY), on NSCLC cell lines harboring EGFR activating mutations and showing acquired resistance to EGFR-TKIs via any of several mechanisms. We used HCC827 and PC-9, which are NSCLC cell lines harboring EGFR exon 19 deletions, and gefitinib-resistant sublines derived from the same cell lines with T790M mutation, MET amplification or stem-cell like properties. AUY was more effective against the gefitinib-resistant sublines with T790M mutation and MET amplification than against the parental cell lines, although the subline with stem cell-like properties showed more than a 10-fold higher resistance to AUY than the parental cell line. AUY exerted a significant radiosensitizing effect on the parental cell line and the MET-amplified subline through inducing G2/M arrest and inhibition of non-homologous end joining (NHEJ). In contrast, the radiosensitizing effect of AUY was limited on the subline with stem cell-like properties, in which it did not induce G2/M arrest or inhibition of NHEJ. In conclusion, combined inhibition of Hsp90 plus radiation was effective, and therefore a promising treatment alternative for overcoming major EGFR-TKI resistance, such as that induced by T790M mutation or MET amplification. However, other approaches are required to overcome minor resistance to EGFR-TKIs, such as that observed in cells with stem cell-like properties.

MicroRNA-126 suppresses mesothelioma malignancy by targeting IRS1 and interfering with the mitochondrial function

AIMS

MiR126 was found to be frequently lost in many types of cancer, including malignant mesothelioma (MM), which represents one of the most challenging neoplastic diseases. In this study, we investigated the potential tumor suppressor function of MiR126 in MM cells. The effect of MiR126 was examined in response to oxidative stress, aberrant mitochondrial function induced by inhibition of complex I, mitochondrial DNA (mtDNA) depletion, and hypoxia.

RESULTS

MiR126 was up-regulated by oxidative stress in nonmalignant mesothelial (Met5A) and MM (H28) cell lines. In Met5A cells, rotenone inhibited MiR126 expression, but mtDNA depletion and hypoxia up-regulated MiR126. However, these various stimuli suppressed the levels of MiR126 in H28 cells. MiR126 affected mitochondrial energy metabolism, reduced mitochondrial respiration, and promoted glycolysis in H28 cells. This metabolic shift, associated with insulin receptor substrate-1 (IRS1)-modulated ATP-citrate lyase deregulation, resulted in higher ATP and citrate production. These changes were linked to the down-regulation of IRS1 by ectopic MiR126, reducing Akt signaling and inhibiting cytosolic sequestration of Forkhead box O1 (FoxO1), which promoted the expression of genes involved in gluconeogenesis and oxidative stress defense. These metabolic changes induced hypoxia-inducible factor-1α (HIF1α) stabilization. Consequently, MiR126 suppressed the malignancy of MM cells in vitro, a notion corroborated by the failure of H28(MiR126) cells to form tumors in nude mice.

INNOVATION AND CONCLUSION

MiR126 affects mitochondrial energy metabolism, resulting in MM tumor suppression. Since MM is a fatal neoplastic disease with a few therapeutic options, this finding is of potential translational importance.

HGF/Met Signaling Is a Key Player in Malignant Mesothelioma Carcinogenesis

Malignant mesothelioma (MM) is a highly aggressive cancer related to asbestos or erionite exposure and resistant to current therapies. Hepatocyte Growth Factor (HGF) and its tyrosine kinase receptor Met regulate cell growth, survival, motility/migration, and invasion. HGF and Met are expressed in MM cells, suggesting that the HGF/Met signaling plays a role in development and progression of this tumor, by autocrine and/or paracrine mechanisms. Upregulation and ligand-independent activation of Met, which is under suppressive control of miR-34 family members, correlate with enhanced invasion, migration and metastatic potential in several cancers, including MM. Moreover, Simian Virus 40 (SV40) Tag expression also induces a HGF autocrine circuit in an Rb-dependent manner in human mesothelial cells (HM) and possibly other cell types, enhancing cell adhesion, invasion and angiogenesis. The resulting activation of Met causes HM transformation and cell cycle progression, and contributes to virus particle assembling and infection of adjacent cells. The constitutive activation of Met, frequently occurring in MM, has been successfully targeted in preclinical models of MM. In conclusion, Met expression, activation state, subcellular localization and also HGF co-receptors expression, such as CD44, have clinical relevance for novel targeted therapies in a cancer for which no effective treatment is currently available.

Additional stories of microRNAs

MicroRNAs (miRNAs) have been shown to be major regulators of eukaryotic gene expression. Traditionally, miRNAs were thought to control highly complex signal transduction and other biological pathways by targeting coding transcripts, accounting for their important role in cellular events. Traditional miRNA biogenesis and function focused on several key enzymes that functioned in miRNA maturation and miRNA inhibitory function upon binding to 3'-untranslated region of target transcripts. However, recent studies have revealed that miRNA biosynthesis and function is complicated, with many exceptions to conventional miRNA mechanisms. In addition to those noncanonical miRNA functions, this review introduces newly discovered biogenesis and regulatory mechanisms, as well as a new class of miRNA-sized small RNA and miRNA methylation. miRNA inhibition and intercellular miRNA signaling are also discussed. Taken together, these insights extend current understanding of miRNAs.

Role of microRNA-34 family in cancer with particular reference to cancer angiogenesis

MicroRNA-34 is involved in pathogenesis in cancer by targeting different tumor-related genes. It could be a biomarker for predicting the prognosis of patients with cancer. In addition, miR-34 is involved in the tumor angiogenesis. Understanding the mechanism of the miR-34 in cancer and tumor angiogenesis will open horizons for development of anti-cancer and anti-angiogenesis drugs.

Role of microRNAs in malignant mesothelioma

Malignant mesothelioma (MM) is an aggressive tumor, mainly derived from the pleura, which is predominantly associated with exposure to asbestos fibers. The prognosis of MM patients is particularly severe, with a median survival of approximately 9-12 months and latency between exposure and diagnosis ranging from 20-50 years (median 30 years). Emerging evidence has demonstrated that tumor aggressiveness is associated with genome and gene expression abnormalities; therefore, several studies have recently focused on the role of microRNAs (miRNAs) in MM tumorigenesis. miRNAs are small non-protein coding single-stranded RNAs (17-22 nucleotides) involved in numerous cellular processes that negatively regulate gene expression by modulating the expression of downstream target genes. miRNAs are often deregulated in cancer; in particular, the differential miRNA expression profiles of MM cells compared to unaffected mesothelial cells have suggested potential roles of miRNAs as either oncogenes or tumor suppressor genes in MM oncogenesis. In this review, the mechanism of MM carcinogenesis was evaluated through the analysis of the published miRNA expression data. The roles of miRNAs as diagnostic biomarkers and prognostic factors for potential therapeutic strategies will be presented and discussed.

Data integration of 104 studies related with microRNA epigenetics revealed that miR-34 gene family is silenced by DNA methylation in the highest number of cancer types

There is an increasing research interest regarding deregulation of microRNA (miRNA) expression by DNA methylation in cancer. The aim of this study was to integrate data from publications and identify miRNA genes shown to be silenced in the highest number of cancer types and thus facilitate biomarker and therapeutic development. We integrated relevant data from 104 published scientific articles. The following databases and bioinformatics tools were used for the analysis: miRBase, miRNA Genomic Viewer, MultAlin, miRNA SNiPer, TargetScan, Ensembl, MethPrimer, TarBase, miRecords, and ChIPBase. Among 2578 currently known human miRNAs and 158 known to be regulated by DNA methylation, miR-34 gene family (miR-34a, -34b, and -34c) was shown to be silenced by DNA methylation in the highest number of cancer types. Consequently, we developed the miR-34 gene family regulatory atlas, consisting of its upstream regulators and downstream targets including transcription factor binding sites (TFBSs), CpG islands, genetic variability and overlapping QTL. MicroRNA-34 gene family has a potential as a cancer biomarker and target for epigenetic drugs. This potential has already been recognized as MRX34 is well into phase I studies. The developed miR-34 gene family regulatory atlas presented in this study provides a starting point for further analyses and could thus facilitate development of therapeutics.

P53/microRNA-34-induced metabolic regulation: new opportunities in anticancer therapy

MicroRNA-34 (miR-34) is directly regulated by p53, and its potential tumor suppressive roles have been studied extensively. As a p53-induced microRNA, miR-34 functions as a tumor suppressor by playing a role in cell cycle arrest, apoptosis and metabolic regulation. Among these p53/miR-34 associated processes, apoptosis and cell cycle arrest are known as essential for p53/miR-34-mediated tumor suppression. P53-mediated metabolic processes have been shown to play pivotal roles in cancer cell biology. Recent studies have also identified several miR-34 targets involved in p53/miR-34-induced metabolic regulation. However, correlations among these metabolic targets remain to be fully elucidated. In this review, we summarize the current progress in the field of metabolic regulation by the p53/miR-34 axis and propose future directions for the development of metabolic approaches in anticancer therapy.

Methylation-associated silencing of microRNA-34b in hepatocellular carcinoma cancer

MicroRNAs (miRNAs) can act as oncogenes or tumor-suppressor genes in human cancers including HCC. Previous studies have identified miR-34 family as an important component of the tumor suppressor network during carcinogenesis. In this study, we investigated the methylation status of miR-34 family in HCC tumor and adjacent non-tumor tissues using methylation-specific PCR (MSP). The methylation frequencies of miR-34a and miR-34b/c were 72.1% (31/43) and 79.1% (34/43) in HCC tissues, which were significantly higher than that in the adjacent non-tumor tissues (P < 0.05), respectively. The results were validated by bisulfite sequencing PCR (BSP). Quantitative reverse transcription polymerase chain reaction (RT-PCR) analysis showed that the expression of miR-34a and miR-34b was significantly down-regulated in HCC tissues compared with adjacent non-tumor tissues (P < 0.05). Moreover, the expression of miR-34b was inversely correlated to CpG island methylation in tumor tissues, but not for miR-34a. In summary, our results suggest that DNA methylation may be involved in the inactivation of miR-34b in HCC.

Tumor suppressor alterations cooperate to drive aggressive mesotheliomas with enriched cancer stem cells via a p53-miR-34a-c-Met axis

Malignant mesothelioma is a highly aggressive, asbestos-related cancer frequently marked by mutations of both NF2 and CDKN2A. We demonstrate that germline knockout of one allele of each of these genes causes accelerated onset and progression of asbestos-induced malignant mesothelioma compared with asbestos-exposed Nf2(+/-) or wild-type mice. Ascites from some Nf2(+/-);Cdkn2a(+/-) mice exhibited large tumor spheroids, and tail vein injections of malignant mesothelioma cells established from these mice, but not from Nf2(+/-) or wild-type mice, produced numerous tumors in the lung, suggesting increased metastatic potential of tumor cells from Nf2(+/-);Cdkn2a(+/-) mice. Intraperitoneal injections of malignant mesothelioma cells derived from Nf2(+/-);Cdkn2a(+/-) mice into severe combined immunodeficient mice produced tumors that penetrated the diaphragm and pleural cavity and harbored increased cancer stem cells (CSC). Malignant mesothelioma cells from Nf2(+/-);Cdkn2a(+/-) mice stained positively for CSC markers and formed CSC spheroids in vitro more efficiently than counterparts from wild-type mice. Moreover, tumor cells from Nf2(+/-);Cdkn2a(+/-) mice showed elevated c-Met expression/activation, which was partly dependent on p53-mediated regulation of miR-34a and required for tumor migration/invasiveness and maintenance of the CSC population. Collectively, these studies demonstrate in vivo that inactivation of Nf2 and Cdkn2a cooperate to drive the development of highly aggressive malignant mesotheliomas characterized by enhanced tumor spreading capability and the presence of a CSC population associated with p53/miR-34a-dependent activation of c-Met. These findings suggest that cooperativity between losses of Nf2 and Cdkn2a plays a fundamental role in driving the highly aggressive tumorigenic phenotype considered to be a hallmark of malignant mesothelioma.

Epigenetic inactivation of microRNA-34b/c predicts poor disease-free survival in early-stage lung adenocarcinoma

PURPOSE

The microRNA-34b/c (miR-34b/c) is considered a tumor suppressor in different tumor types and a transcriptional target of TP53. The main objectives of this study were to investigate the clinical implications of miR-34b/c methylation in patients with early-stage lung adenocarcinoma and to determine the functional role of miR-34b/c re-expression in lung adenocarcinoma cell lines.

EXPERIMENTAL DESIGN

Aberrant methylation and expression of miR-34b/c were assessed in 15 lung adenocarcinoma cell lines and a cohort of 140 early-stage lung adenocarcinoma. Lung adenocarcinoma cell lines were transfected with miR-34b/c and the effects upon cell proliferation, migration, invasion, and apoptosis were investigated.

RESULTS

Aberrant methylation of miR-34b/c was detected in 6 (40%) of 15 lung adenocarcinoma cell lines and 64 of 140 (46%) primary lung adenocarcinoma. Expression of miR-34b/c was significantly reduced in all methylated cell lines and primary tumors, especially with TP53 mutations. Patients with increased miR-34b/c methylation had significantly shorter disease-free and overall survival as compared to patients with unmethylated or low level of miR-34b/c methylation. Ectopic expression of miR-34b/c in lung adenocarcinoma cell lines decreased cell proliferation, migration, and invasion.

CONCLUSIONS

Epigenetic inactivation of miR-34b/c by DNA methylation has independent prognostic value in patients with early-stage lung adenocarcinoma. Reexpression of miR-34b/c leads to a less aggressive phenotype in lung adenocarcinoma cell lines.

A competitive regulatory mechanism discriminates between juxtaposed splice sites and pri-miRNA structures

We have explored the functional relationships between spliceosome and Microprocessor complex activities in a novel class of microRNAs (miRNAs), named Splice site Overlapping (SO) miRNAs, whose pri-miRNA hairpins overlap splice sites. We focused on the evolutionarily conserved SO miR-34b, and we identified two indispensable elements for recognition of its 3′ splice site: a branch point located in the hairpin and a downstream purine-rich exonic splicing enhancer. In minigene systems, splicing inhibition owing to exonic splicing enhancer deletion or AG 3′ss mutation increases miR-34b levels. Moreover, small interfering-mediated silencing of Drosha and/or DGCR8 improves splicing efficiency and abolishes miR-34b production. Thus, the processing of this 3′ SO miRNA is regulated in an antagonistic manner by the Microprocessor and the spliceosome owing to competition between these two machineries for the nascent transcript. We propose that this novel mechanism is commonly used to regulate the relative amount of SO miRNA and messenger RNA produced from primary transcripts.

Associations of pri-miR-34b/c and pre-miR-196a2 polymorphisms and their multiplicative interactions with hepatitis B virus mutations with hepatocellular carcinoma risk

Background

Genetic polymorphisms of pri-miR-34b/c and pre-miR-196a2 have been reported to be associated with the susceptibility to cancers. However, the effect of these polymorphisms and their interactions with hepatitis B virus (HBV) mutations on the development of hepatocellular carcinoma (HCC) remains largely unknown. We hypothesized that these polymorphisms might interact with the HBV mutations and play a role in hepatocarcinogenesis.

Methods

Pri-miR-34b/c rs4938723 (T>C) and pre-miR-196a2 rs11614913 (T>C) were genotyped in 3,325 subjects including 1,021 HBV-HCC patients using quantitative PCR. HBV mutations were determined by direct sequencing. Contributions of the polymorphisms and their multiplicative interactions with gender or HCC-related HBV mutations to HCC risk were assessed using multivariate regression analyses.

Results

rs4938723 CC genotype was significantly associated with HCC risk compared to HBV natural clearance subjects, adjusted for age and gender (adjusted odds ratio [AOR] = 2.01, 95% confidence interval [CI] = 1.16–3.49). rs4938723 variant genotypes in dominant model significantly increased HCC risk in women, compared to female healthy controls (AOR = 1.85, 95% CI = 1.20–2.84) or female HCC-free subjects (AOR = 1.62, 95% CI = 1.14–2.31). rs4938723 CC genotype and rs11614913 TC genotype were significantly associated with increased frequencies of the HCC-related HBV mutations T1674C/G and G1896A, respectively. rs11614913 was not significantly associated with HCC risk, but its CC genotype significantly enhanced the effect of rs4938723 in women. In multivariate regression analyses, rs4938723 in dominant model increased HCC risk (AOR = 1.62, 95% CI = 1.05–2.49), whereas its multiplicative interaction with C1730G, a HBV mutation inversely associated with HCC risk, reduced HCC risk (AOR = 0.34, 95% CI = 0.15–0.81); rs11614913 strengthened the G1896A effect but attenuated the A3120G/T effect on HCC risk.

Conclusions

rs4938723 might be a genetic risk factor of HCC but its effect on HCC is significantly affected by the HBV mutations. rs11614913 might not be a HCC susceptible factor but it might affect the effects of the HBV mutations or rs4938723 on HCC risk.

Regulation of microtubule-associated protein tau (MAPT) by miR-34c-5p determines the chemosensitivity of gastric cancer to paclitaxel

BACKGROUND

Human miR-34c has been reported to be associated with various human malignancies; however, it remains unknown whether miR-34c is involved in chemoresistance in gastric cancer. The aim of this study was to investigate the role of miR-34c in gastric cancer.

MATERIALS AND METHODS

The adenosine triphosphate-based tumor chemosensitivity assay was used to measure drug sensitivity in gastric cancer samples. The expression levels of miRNA were determined by reverse transcriptase polymerase chain reaction (PCR) and those of protein were by Western blot analysis. Luciferase activity assay was used to verify the target genes of miRNAs. MTT assay was used to test the drug-resistant phenotype changes in cancer cells via overregulation of miRNAs. The methylation status of neighboring CpG islands of miR-34c-5p was analyzed by Bisulfite Sequencing PCR and methylation-specific PCR.

RESULTS

Quantitative real-time polymerase chain reaction demonstrated that expression of miR-34c-5p was downregulated in paclitaxel-resistant gastric cancer samples (p < 0.01). Cells derived from gastric cancer tissues with low miR-34c-5p expression and high microtubule-associated protein tau (MAPT) protein expression tended to have increased chemoresistance to paclitaxel in vitro. Luciferase activity assay confirmed that the 3'-UTR of MAPT mRNA contains a functional miR-34c-5p binding site. Overexpression of miR-34c-5p significantly downregulated MAPT protein expression and increased the chemosensitivity of paclitaxel-resistant gastric cancer cells. Further investigation demonstrated that differential methylation of CpG islands neighboring the miR-34c promoter regulated the expression of miR-34c-5p in gastric cancer cell lines.

CONCLUSIONS

DNA methylation, dysregulation of miR-34c-5p, and MAPT expression are critical factors in the chemoresistance of gastric cancer to paclitaxel.

Methylation-mediated silencing of the miR-124 genes facilitates pancreatic cancer progression and metastasis by targeting Rac1

Previous studies have demonstrated that microRNA (miRNA) expression is altered in human cancer. However, the molecular mechanism underlying these changes in miRNA expression remains unclear. In this study, we investigated the epigenetic modification of miR-124 genes and the potential function of miR-124 in pancreatic cancer. Using pyrosequencing analysis, we found that miR-124 genes (including miR-124-1, miR-124-2 and miR-124-3) are highly methylated in pancreatic cancer tissues compared with in non-cancerous tissues. Hypermethylation mediated the silencing of miR-124, which was a frequent event in pancreatic duct adenocarcinoma (PDAC). Furthermore, miR-124 downregulation was significantly associated with worse survival of PDAC patients. Functional studies showed that miR-124 inhibited cell proliferation, invasion and metastasis. Furthermore, we characterized Rac1 as a direct target of miR-124, and miR-124 interacted with the 3'-untranslated region of Rac1, which we showed to be a putative tumor promoter in pancreatic cancer. Thus, the miR-124-mediated downregulation of Rac1 led to the inactivation of the MKK4-JNK-c-Jun pathway. Therefore, our study demonstrates that miR-124 is a tumor suppressor miRNA that is epigenetically silenced in pancreatic cancer. Our findings suggest a previously unidentified molecular mechanism involved in the progression and metastasis of pancreatic cancer.

[Exploiting the therapeutic potential of microRNAs in human cancer]

大量研究表明microRNAs（miRNAs）的异常调节与癌症的发生和进展相关。新近研究发现了若干在各种人类癌症中具有可作为治疗靶标巨大潜能的miRNAs。这些肿瘤miRNAs的抑制或过表达可调节相关基因的表达，从而抑制各种癌症的增殖或转移。一些miRNAs可逆转上皮-间质转化的表型，有些则可用于增强细胞对抗癌药物的敏感性。它们大部分的抗癌作用均已在临床前动物模型中得到验证。miRNA治疗的一个优点是它可靶向作用于不同信号通路中的许多基因，但同时亦伴有许多未知的脱靶效应的缺点。此外，对于有效的miRNA治疗来说，成功转运也是一个主要的挑战。然而，新近研究的发现及药物转运系统的高速发展为该领域的飞跃展现了一个乐观的前景。

MicroRNAs in the p53 network: micromanagement of tumour suppression

In recent years, microRNAs (miRNAs) have been identified as mediators of tumour suppression and stress responses exerted by the p53 tumour suppressor. p53-regulated miRNAs contribute to tumour suppression by controlling the expression of central components of multiple processes, including cell cycle progression, epithelial-mesenchymal transition, stemness, metabolism, cell survival and angiogenesis. The expression and activity of p53 itself is also under the control of miRNAs. Finally, genetic and epigenetic alterations identified in the p53-miRNA network indicate that these pathways are important for the initiation and progression of tumours. In the future, knowledge about the p53-miRNA network may be able to be exploited for diagnostic and therapeutic approaches in cancer prevention and treatment.

DNA methylation and microRNA dysregulation in cancer

DNA methylation plays a key role in the silencing of numerous cancer-related genes, thereby affecting a number of vital cellular processes, including the cell cycle checkpoint, apoptosis, signal transduction, cell adhesion and angiogenesis. Also widely altered in human malignancies is the expression of microRNAs (miRNAs), a class of small noncoding RNAs that act as posttranscriptional regulators of gene expression. Furthermore, emerging evidence now supports the idea that DNA methylation is crucially involved in the dysregulation of miRNAs in cancer. This is in part the result of technological advances that enable more comprehensive analysis of miRNA expression profiles and the epigenome in cancer cells, which has led to the identification of a number of epigenetically regulated miRNAs. As with protein-coding genes, it appears that miRNA genes involved in regulating cancer-related pathways are silenced in association with CpG island hypermethylation. In addition, methylation in CpG island shore regions and DNA hypomethylation also appear to contribute to miRNA dysregulation in cancer. Aberrant DNA methylation of miRNA genes is a potentially useful biomarker for detecting cancer and predicting its outcome. Moreover, re-expression of miRNAs and the replacement of tumor suppressive miRNAs using miRNA mimics or expression vectors could be effective approaches to cancer therapy.

Characterization of DNA hypermethylation in two cases of peritoneal mesothelioma

Malignant mesothelioma (MM) is a rare disease with a poor prognosis. Pleural mesothelioma, which is the most common type of MM, is considered to be caused by asbestos exposure and is increasing in incidence, with about 15,000 new cases diagnosed worldwide annually. On the other hand, peritoneal mesothelioma is a very rare type of MM; thus, its pathogenesis is even less understood than pleural mesothelioma. Recent research on the pathogenesis of malignant pleural mesothelioma has indicated that both epigenetic and genetic alterations contribute to tumorigenesis. Here, we hypothesize that peritoneal mesothelioma also has an epigenetic alteration in the same genes (Kazal-type serine peptidase inhibitor domain 1 (KAZALD1), transmembrane protein 30B (TMEM30B), and mitogen-activated protein kinase 13 (MAPK13)). Our goal is to identify DNA methylation of these three candidate genes in two peritoneal mesothelioma cases. Laser capture microdissection was used to separate diseased sections of formalin-fixed paraffin-embedded samples from one surgically resected tissue (epithelial type) and one autopsy tissue (sarcomatous type). Genomic DNA was subsequently extracted by the standard phenol chloroform method. The DNA was then treated with sodium bisulphite, and pyrosequencing analysis was used to quantitatively analyze the methylation of candidate genes reported to be hypermethylated in malignant pleural mesothelioma (KAZALD1, TMEM30B, and MAPK13). TMEM30B and MAPK13 were not methylated in either case. However, KAZALD1 was highly methylated in sarcomatoid-type peritoneal mesothelioma. We first report that the KAZALD1 gene was hypermethylated in sarcomatoid-type malignant peritoneal mesothelioma.

Characterization of human gastric carcinoma-related methylation of 9 miR CpG islands and repression of their expressions in vitro and in vivo

Background

Many miR genes are located within or around CpG islands. It is unclear whether methylation of these CpG islands represses miR transcription regularly. The aims of this study are to characterize gastric carcinoma (GC)-related methylation of miR CpG islands and its relationship with miRNA expression.

Methods

Methylation status of 9 representative miR CpG islands in a panel of cell lines and human gastric samples (including 13 normal biopsies, 38 gastritis biopsies, 112 pairs of GCs and their surgical margin samples) was analyzed by bisulfite-DHPLC and sequencing. Mature miRNA levels were determined with quantitative RT-PCR. Relationships between miR methylation, transcription, GC development, and clinicopathological characteristics were statistically analyzed.

Results

Methylation frequency of 5 miR CpG islands (miR-9-1, miR-9-3, miR-137, miR-34b, and miR-210) gradually increased while the proportion of methylated miR-200b gradually decreased during gastric carcinogenesis (Ps < 0.01). More miR-9-1 methylation was detected in 62%-64% of the GC samples and 4% of the normal or gastritis samples (18/28 versus 2/48; Odds ratio, 41.4; P < 0.01). miR-210 methylation showed high correlation with H. pylori infection. miR-375, miR-203, and miR-193b methylation might be host adaptation to the development of GCs. Methylation of these miR CpG islands was consistently shown to significantly decrease the corresponding miRNA levels presented in human cell lines. The inverse relationship was also observed for miR-9-1, miR-9-3, miR-137, and miR-200b in gastric samples. Among 112 GC patients, miR-9-1 methylation was an independent favourable predictor of overall survival of GC patients in both univariate and multivariate analysis (P < 0.02).

Conclusions

In conclusion, alteration of methylation status of 6 of 9 tested miR CpG islands was characterized in gastric carcinogenesis. miR-210 methylation correlated with H. pylori infection. miR-9-1 methylation may be a GC-specific event. Methylation of miR CpG islands may significantly down-regulate their transcription regularly.

Knockdown of the epidermal growth factor receptor gene to investigate its therapeutic potential for the treatment of non-small-cell lung cancers

BACKGROUND

Epidermal growth factor receptor (EGFR) is often overexpressed in non-small-cell lung cancer (NSCLC). Anti-EGFR agents, including EGFR-tyrosine kinase inhibitors are considered to be effective when a drug-sensitive EGFR mutation is present. However, inherent and acquired resistances are major problems of EGFR-targeting therapies. In this study, we performed EGFR knockdown by using small interfering RNAs in NSCLC cell lines to examine the significance of targeting EGFR for NSCLC therapy.

METHODS

We treated 13 NSCLC cell lines, including 8 EGFR mutant and 5 EGFR wild type by using gefitinib or small interfering RNAs against EGFR (siEGFR). Three cell lines (PC-9-GR1, RPC-9, and HCC827-ER) were experimentally established with acquired resistance to EGFR-tyrosine kinase inhibitors. The antitumor effect was determined by using an 3-[4,5-dimethylthiazol-2-yl]-5-[3-carboxymethoxyphenyl]-2-[4-sulfophenyl]-2H-tetrazolium, inner salt (MTS) or colony formation assay. The protein expression was evaluated by using Western blotting.

RESULTS

All 13 cell lines expressed EGFR protein, and siEGFR downregulated EGFR protein expression in all. The cell viability was suppressed by siEGFR in 6 of 8 EGFR-mutant cell lines (suppressed 57%-92% of control cells), including PC-9-GR1 and RPC-9. The NCI-H1650 and HCC827-ER harbored EGFR mutations but were not suppressed. Of note, PTEN (phosphatase and tensin homolog) was deleted in NCI-H1650, and c-MET was amplified in HCC827-ER. It was not suppressed in any of the EGFR wild-type cells except in the NCI-H411, in which EGFR is phosphorylated, which indicates its activation.

CONCLUSIONS

Analysis of the results indicated that EGFR can be a therapeutic target in NSCLCs with EGFR activation. In contrast, targeting EGFR is not appropriate for tumors in which EGFR is not activated, even if EGFR is expressed.

Exploiting the therapeutic potential of microRNAs in human cancer

Dysregulation of microRNAs (miRNAs) has been widely shown to be associated with the development and progression of cancer. Recent studies discovered a handful of miRNAs with great potential to act as therapeutic targets in various human cancers. Inhibition or overexpression of these oncomirs may regulate the expressions of their associated genes, which in turn represses the proliferation or metastasis of different cancers. Some miRNAs can reverse the phenotype of epithelial-mesenchymal transition, while others can be utilized to sensitize cells to DNA-damaging drugs. Most of their anticancer abilities have been validated in preclinical animal models. A merit of miRNA-based therapy is that it can target plenty of genes in different signaling pathways, but this also comes with the drawback of many unknown off-target effects. In addition, successful delivery is also a major obstacle to effective miRNA-based therapeutics. Nevertheless, new findings from recent studies and the rapid advances in systemic drug delivery systems provide an optimistic perspective on the evolution of the field.

Epigenetic alteration of microRNAs in feces of colorectal cancer and its clinical significance

MicroRNAs regulate target gene expression through translation repression or mRNA decay, and they are emerging as important modulators in cellular pathways. Previous studies have shown the occurrence of epigenetically modified miRNAs in colorectal cancer (CRC), identifying these miRNA methylation signatures may provide candidate markers for the detection of malignant colonocytes. Fecal-based tests are widely adopted as noninvasive methods for CRC diagnosis, thus several studies have attempted to use miRNAs from feces as CRC markers. This article evaluates a recently published study investigating the usefulness of epigenetically silenced miRNAs in fecal specimens, including miR-34b/c and miR-148a, as potential markers for CRC screening and prognosis.

Emerging links between epigenetic alterations and dysregulation of noncoding RNAs in cancer

Epigenetic changes, including DNA methylation and histone modification, play key roles in the dysregulation of tumor-related genes, thereby affecting numerous cellular processes, including cell proliferation, cell adhesion, apoptosis, and metastasis. In recent years, numerous studies have shown that noncoding RNAs (ncRNAs) are key players in the initiation and progression of cancer and epigenetic mechanisms are deeply involved in their dysregulation. Indeed, the growing list of microRNA (miRNA) genes aberrantly methylated in cancer suggests that a large number of miRNAs exert tumor-suppressive or oncogenic effects. In addition, it now appears that long ncRNAs may be causally related to epigenetic dysregulation of critical genes in cancer. Dissection of the relationships between ncRNAs and epigenetic alterations may lead to the development of novel approaches to the diagnosis and treatment of cancer.

Frequent methylation and oncogenic role of microRNA-34b/c in small-cell lung cancer

Small-cell lung cancer (SCLC) is an aggressive tumor with a dismal prognosis among primary lung cancers. MicroRNAs (miRNAs) can act as oncogenes or tumor-suppressor genes in human malignancy. The miR-34 family is comprised of tumor-suppressive miRNAs, and its reduced expression by methylation has been reported in various cancers, including non-small cell lung cancer (NSCLC). In this study, we investigated the alteration and tumor-suppressive impact of miR-34s in SCLC. The methylation of miR-34a and miR-34b/c was observed in 4 (36%) and 7 (64%) of 11 SCLC cell lines, respectively. Among the 27 SCLC clinical specimens, miR-34a and miR-34b/c were methylated in 4 (15%) and 18 (67%), respectively. In contrast, 13 (28%) miR-34a methylated cases and 12 (26%) miR-34b/c methylated cases were found in 47 NSCLC primary tumors. The frequency of miR-34b/c methylation was significantly higher in SCLC than in NSCLC (p<0.001). The expressions of miR-34s were reduced in methylated cell lines and tumors and restored after 5-aza-2'-deoxycytidine treatment, indicating that methylation was responsible for the reduced expression of miR-34s. Because the frequency of methylation was higher in miR-34b/c, we focused on miR-34b/c for a functional analysis. We examined the effect of miR-34b/c introduction on cell proliferation, migration and invasion. The transfection of miR-34b/c to two SCLC cell lines (H1048 and SBC5) resulted in the significant inhibition of cell growth, migration, and invasion, compared with control transfectants. Our results indicate that the aberrant methylation of miR-34b/c plays an important role in the pathogenesis of SCLC, implying that miR-34b/c may be a useful therapeutic target for SCLC.

SASP mediates chemoresistance and tumor-initiating-activity of mesothelioma cells

Here we show that pemetrexed-treated mesothelioma cells undergo accelerated senescence. This is characterized by the secretion of proinflammatory and mitogenic cytokines, reminiscent of an SASP (senescence-associated secretory phenotype). Conditioned media from senescent MPM (malignant pleural mesothelioma) cells trigger the emergence of EMT (epithelial-to-mesenchymal)-like, clonogenic and chemoresistant cell subpopulations, expressing high levels of ALDH (aldehyde dehydrogenase) activity (ALDH(bright) cells). We show by fluorescence-activated cell sorting of purified ALDH(bright) and ALDH(low) cells, that both cell-autonomous and cell-non-autonomous mechanisms converge to maintain the SASP-induced, EMT-like cell subpopulations. Chemoresistant ALDH(bright) cells exist within primary MPM specimens and enrichment for ALDH(bright) cells correlates with an earlier tumor onset into NOD/SCID mice. We show that RAS(v12) expression induces SASP-like changes in untransformed human mesothelial cells, and that p53 ablation increases the effect of RAS(v12) expression. We identify STAT3 activation as a crucial event downstream to SASP signaling. In fact, small hairpin RNA-mediated ablation of STAT3 deeply attenuates the induction of EMT genes and the increase of ALDH(bright) cells induced by SASP-cytokines. This strongly affects the chemoresistance of MPM cells in vitro and leads to anticancer effects in vivo.