miR-21-mediated tumor growth

MicroRNA alterations in head and neck squamous cell carcinoma

MicroRNAs (mirs) are small noncoding RNA molecules (~22 nucleotides) that regulate posttranscriptional gene expression. Currently, there has not been a comprehensive study of their role in primary head and neck squamous cell carcinoma (HNSCC). To determine the role of mirs in HNSCC, we screened for altered microRNA expression in HNSCC primary tissue and cell lines. We then further tested the functional impact of alterations of specific mirs. An initial screening of 4 primary HNSCC, 4 normal mucosal controls and 4 HNSCC cell lines was analyzed for mature microRNA expression by microarray. Significance was determined using significance analysis of microarrays (SAM). Nine microRNAs were found by SAM to be upregulated or downregulated in tumor tissue including mir-21, let-7, 18, 29c, 142-3p, 155, 146b (overexpressed) and 494 (underexpressed). Mir-21 was validated by qRT-PCR. Functional validation by growth assays was performed, further validating mir-21. Transfection of mir-21 into JHU-011 and JHU-012 cell lines showed a 39% increase in cell growth at 72 hr relative to controls (p < 0.05). Transfection of the inhibitor into JHU-O12 cell lines showed a 92% decrease in cell growth relative to controls at 72 hr (p < 0.05). In addition, flow cytometry analysis of JHU-012 cells 48 hr after mir-21 inhibitor transfection showed a statistically significant increase in cytochrome c release and increased apoptosis. These differentially expressed microRNAs may be of interest as potential novel oncogenes and tumor suppressor genes in HNSCC. Mir-21 is a putative oncogenic microRNA in head and neck cancer.

MicroRNA expression in response to murine myocardial infarction: miR-21 regulates fibroblast metalloprotease-2 via phosphatase and tensin homologue

AIMS

MicroRNAs (miRNAs) are small non-coding RNAs that regulate gene expression at the post-transcriptional level by either degradation or translational repression of a target mRNA. Encoded in the genome of most eukaryotes, miRNAs have been proposed to regulate specifically up to 90% of human genes through a process known as miRNA-guided RNA silencing. For the first time, we sought to test how myocardial ischaemia-reperfusion (IR) changes miR expression.

METHODS AND RESULTS

Following 2 and 7 h of IR or sham operation, myocardial tissue was collected and subjected to miRNA expression profiling and quantification using a Bioarray system that screens for human-, mice-, rat-, and Ambi-miR. Data mining and differential analyses resulted in 13 miRs that were up-regulated on day 2, 9 miRs that were up-regulated on day 7, and 6 miRs that were down-regulated on day 7 post-IR. Results randomly selected from expression profiling were validated using real-time PCR. Tissue elements laser-captured from the infarct site showed marked induction of miR-21. In situ hybridization studies using locked nucleic acid miR-21-specific probe identified that IR-inducible miR-21 was specifically localized in the infarct region of the IR heart. Immunohistochemistry data show that cardiac fibroblasts (CFs) are the major cell type in the infarct zone. Studies with isolated CFs demonstrated that phosphatase and tensin homologue (PTEN) is a direct target of miR-21. Modulation of miR-21 regulated expression of matrix metalloprotease-2 (MMP-2) via a PTEN pathway. Finally, we noted a marked decrease in PTEN expression in the infarct zone. This decrease was associated with increased MMP-2 expression in the infarct area.

CONCLUSION

This work constitutes the first report describing changes in miR expression in response to IR in the mouse heart, showing that miR-21 regulates MMP-2 expression in CFs of the infarct zone via a PTEN pathway.

An autoregulatory loop mediated by miR-21 and PDCD4 controls the AP-1 activity in RAS transformation

The transcription factor AP-1 plays key roles in tumorigenesis, by regulating a variety of protein-coding genes, implicated in multiple hallmarks of cancer. Among non-coding genes, no AP-1 target has been described yet in tumorigenesis. MicroRNAs (miRNAs) are negative post-transcriptional regulators of protein-coding genes. miRNA expression signatures are highly relevant in cancer and several tumor-associated miRNAs (oncomirs) play critical roles in oncogenesis. Here, we show that the miRNA miR-21, which represents the most frequently upregulated oncomir in solid tumors, is induced by AP-1 in response to RAS. By analyzing validated miR-21 targets, we have found that the tumor suppressors PTEN and PDCD4 are downregulated by RAS in an AP-1- and miR-21-dependent fashion. We further show that, given the role of PDCD4 as negative regulator of AP-1, the miR-21-mediated downregulation of PDCD4 is essential for the maximal induction of AP-1 activity in response to RAS. Our data reveal a novel mechanism of positive autoregulation of the AP-1 complex in RAS transformation and disclose the function of oncomirs as critical targets and regulators of AP-1 in tumorigenesis.

Multiple approach to analyzing the role of microRNAs in apoptosis

MicroRNAs (miRNAs) are noncoding RNAs whose hallmarks are the very short sequences and the ability to repress the translation and/or transcription of target genes. miRNAs can have diverse functions, including regulation of cellular differentiation, proliferation, and embryogenesis. Over the past 5 years, an increasing number of studies have linked different miRNAs with programmed cell death or apoptosis. The principal aim of this chapter is to describe a method that (1) identifies miRNAs involved in apoptosis, using a validated array profiling approach, (2) assesses the direct involvement of candidate miRNAs in apoptosis, and (3) identifies the molecular mechanisms possibly involved in apoptotic response. To disclose the possible molecular targets of miRNAs, we propose the generation of a database created using a list of presumptive miRNA targets and the changes in the transcriptome after ectopic expression of the miRNAs. Our proposed method for doing this is suitable for both discovery of apoptotic pathways that regulate miRNAs and finding new miRNAs able to induce apoptosis.

MicroRNAs in cancer

Within the past few years, studies on microRNA (miRNA) and cancer have burst onto the scene. Profiling of the miRNome (global miRNA expression levels) has become prevalent, and abundant miRNome data are currently available for various cancers. The pattern of miRNA expression can be correlated with cancer type, stage, and other clinical variables, so miRNA profiling can be used as a tool for cancer diagnosis and prognosis. miRNA expression analyses also suggest oncogenic (or tumor-suppressive) roles of miRNAs. miRNAs play roles in almost all aspects of cancer biology, such as proliferation, apoptosis, invasion/metastasis, and angiogenesis. Given that many miRNAs are deregulated in cancers but have not yet been further studied, it is expected that more miRNAs will emerge as players in the etiology and progression of cancer. Here we also discuss miRNAs as a tool for cancer therapy.

Expression profile of microRNA in epithelial cancer: diagnosis, classification and prediction

BACKGROUND

MicroRNAs (miRNAs), the small non-coding RNAs, regulate gene expression in a sequence-specific manner. Up to one-third of human messenger RNAs (mRNAs) appear to be miRNA targets. Each miRNA can target hundreds of mRNA transcripts and production of proteins directly or indirectly, while more than one miRNA can converge on a single transcript target. Therefore, potential regulatory circuitries afforded by miRNAs are enormous. Recent studies indicate that miRNAs act as key regulators of various fundamental biological processes, in which common pathways are shared with cancer.

OBJECTIVE/METHODS

To provide an overview of the potential application of miRNA profile in human epithelial cancer diagnosis, more than 180 miRNA-related publications have been reviewed.

CONCLUSION

Increasing evidence shows that the expression of miRNAs is remarkably deregulated in human cancer owing to multiple epigenetic and genomic alterations, and several miRNAs have been demonstrated to serve as tumor suppressor genes or oncogenes in cancer. The deregulated miRNA expression profile in human cancer may prove a powerful tool for cancer detection, diagnosis, classification and prognosis.

Expression of microRNAs in diffuse large B cell lymphoma is associated with immunophenotype, survival and transformation from follicular lymphoma

MicroRNAs are naturally occurring small RNA species that regulate gene expression and are frequently abnormally expressed in cancers. However, the role of microRNAs in lymphoma is poorly understood. Therefore, we undertook a comprehensive study of microRNA expression in two of the most common lymphomas: diffuse large B-cell lymphoma (DLBCL) (n= 80) and follicular lymphoma (FCL) (n= 18) using microarrays containing probes for 464 human microRNAs. Unsupervised cluster analysis revealed distinct expression patterns between these two lymphomas and specific microRNA signatures (including members of the miR-17–92 cluster) were derived that correctly predicted lymphoma type in >95% of cases. Furthermore, we identified microRNAs in de novo DLBCL (n= 64) associated with germinal centre-like and non-germinal centre-like immunophenotypes, international prognostic index status and event-free survival in CHOP and rituximab (R)-CHOP treated patients. Despite the indolent nature of FCL a significant proportion of cases undergo high-grade transformation to more aggressive DLBCL. In order to see if transformation is associated with changes in microRNA expression we compared transformed DLBCL cases (n= 16) with de novo DLBCL, as well as FCL cases that underwent subsequent transformation (n= 7) with FCL cases that had not transformed at a median follow-up of 60 months (n= 11). Differential expression of 12 microRNAs correctly predicted >85% of transformed versus de novo DLBCL cases; six microRNAs (miR-223, 217, 222, 221 and let-7i and 7b) were found which could similarly predict or transformation in FCL (P< 0.05). These data suggest that microRNAs have potential as diagnostic and prognostic markers in these lymphomas and may be used to identify FCL patients at risk of high-grade transformation.

Endogenous microRNAs induced by heat-shock reduce myocardial infarction following ischemia-reperfusion in mice

We investigated the role of microRNAs (miRNA) in protection against ischemia/reperfusion (I/R) injury in heart. Mice subjected to cytoprotective heat-shock (HS) showed a significant increase of miRNA-1, miRNA-21 and miRNA-24 in the heart. miRNAs isolated from HS mice and injected into non-HS mice significantly reduced infarct size after I/R injury, which was associated with the inhibition of pro-apoptotic genes and increase in anti-apoptotic genes. Chemically synthesized miRNA-21 also reduced infarct size, whereas a miRNA-21 inhibitor abolished this effect. Overall, these studies for the first time provide evidence for the potential role of endogenously synthesized miRNA's in cardioprotection following I/R injury.

Epstein-Barr virus growth/latency III program alters cellular microRNA expression

The Epstein-Barr virus (EBV) is associated with lymphoid and epithelial cancers. Initial EBV infection alters lymphocyte gene expression, inducing cellular proliferation and differentiation as the virus transitions through consecutive latency transcription programs. Cellular microRNAs (miRNAs) are important regulators of signaling pathways and are implicated in carcinogenesis. The extent to which EBV exploits cellular miRNAs is unknown. Using micro-array analysis and quantitative PCR, we demonstrate differential expression of cellular miRNAs in type III versus type I EBV latency including elevated expression of miR-21, miR-23a, miR-24, miR-27a, miR-34a, miR-146a and b, and miR-155. In contrast, miR-28 expression was found to be lower in type III latency. The EBV-mediated regulation of cellular miRNAs may contribute to EBV signaling and associated cancers.

Let-7a microRNA suppresses therapeutics-induced cancer cell death by targeting caspase-3

MicroRNAs (miRNA) are endogenously expressed non-coding RNAs that regulate gene expression post-transcriptionally. Let-7a miRNA is a founding member in the let-7 family and its down-regulation in association with over-expression of RAS and HMGA2 oncogenes has previously been reported. In the present study, caspase-3, the executioner caspase, was confirmed to be the target of let-7a as ectopic expression of let-7a decreased the luciferase activity of a reporter construct containing the 3' untranslated region of caspase-3 and at the same time repressed the enzyme expression in human squamous carcinoma A431 cells and hepatocellular carcinoma HepG2 cells. Moreover, let-7a was over-expressed while caspase-3 was down-regulated in A10A cells, a doxorubicin-resistant A431 subline. Enforced let-7a expression increased the resistance in A431 cells and HepG2 cells to apoptosis induced by therapeutic drugs such as interferon-gamma, doxorubicin and paclitaxel. On the other hand, down-regulation of let-7a by the anti-let-7a inhibitor increased the doxorubicin-induced apoptosis in A431 parent cells, A10A cells and HepG2 cells while the increase was suppressed by caspase-3 inhibitor. Both anti-let-7a inhibitor and caspase-3 inhibitor however failed to affect the drug-induced apoptosis in human breast cancer MCF7 cells, the cells that do not express caspase-3. Therefore, let-7a by targeting caspase-3 may play a functional role in modulating drug-induced cell death in human cancer cells.

Regulation of epidermal growth factor receptor signaling in human cancer cells by microRNA-7

The epidermal growth factor receptor (EGFR) is frequently overexpressed in cancer and is an important therapeutic target. Aberrant expression and function of microRNAs have been associated with tumorigenesis. Bioinformatic predictions suggest that the human EGFR mRNA 3'-untranslated region contains three microRNA-7 (miR-7) target sites, which are not conserved across mammals. We found that miR-7 down-regulates EGFR mRNA and protein expression in cancer cell lines (lung, breast, and glioblastoma) via two of the three sites, inducing cell cycle arrest and cell death. Because miR-7 was shown to decrease EGFR mRNA expression, we used microarray analysis to identify additional mRNA targets of miR-7. These included Raf1 and multiple other genes involved in EGFR signaling and tumorigenesis. Furthermore, miR-7 attenuated activation of protein kinase B (Akt) and extracellular signal-regulated kinase 1/2, two critical effectors of EGFR signaling, in different cancer cell lines. These data establish an important role for miR-7 in controlling mRNA expression and indicate that miR-7 has the ability to coordinately regulate EGFR signaling in multiple human cancer cell types.

miR-21 plays a pivotal role in gastric cancer pathogenesis and progression

Gastric cancer causes nearly one million deaths worldwide per year. Although Helicobacter pylori infection is the main risk factor, in about 80% or more of gastric cancers, the molecular pathway underlying H. pylori infection leading to the development of gastric cancers remains unclear. Recently accumulating evidence suggests that microRNAs (miRNAs) may regulate diverse biological processes and may be important in tumorigenesis. miR-21 has been frequently observed to be aberrantly overexpressed in various tumors. Using TaqMan quantitative real-time PCR, we confirmed that miR-21 was significantly overexpressed in human gastric cancer tissues and cell lines. Remarkably, miR-21 was also significantly overexpressed in H. pylori-infected gastric mucosa, implying that overexpression of miR-21 in gastric cancer may be due in part to H. pylori infection. More importantly, we showed that forced expression of miR-21 significantly enhanced cell proliferation and invasion in AGS cells, a human gastric cancer cell line, whereas knockdown of miR-21 by inhibitor caused a significant reduction in cell proliferation and a significant increase in apoptosis. Furthermore, we demonstrated that knockdown of miR-21 significantly decreased cell invasion and migration of AGS cells. Finally, we showed that RECK, a known tumor suppressor in gastric cancer, is a bona fide target of miR-21. Taken together, miR-21 may be important in the initiation and progression of gastric cancers as an oncomiR, likely through regulating RECK. Our findings suggest a potential regulatory pathway in which H. pylori infection upregulates expression of miR-21, which in turn downregulates RECK, and then leads to the development of gastric cancer.

MicroRNAs as potential cancer therapeutics

MicroRNAs (miRNAs) have been shown to have an important role in various cellular processes, such as apoptosis, differentiation and development. Recent studies have shown that miRNAs are mis-expressed in human cancers where they can exert their effect as oncogenes or tumor suppressors. Here, we review the potential for using miRNAs as biomarkers for diagnosis, prognosis and cancer therapies.

Reliable microRNA profiling in routinely processed formalin-fixed paraffin-embedded breast cancer specimens using fluorescence labelled bead technology

BACKGROUND

During the last years the analysis of microRNA expression patterns has led to completely new insights into cancer biology. Furthermore, these patterns are a very promising tool for the development of new diagnostic and prognostic markers. However, most human tumour samples for which long term clinical records are available exist only as formalin-fixed paraffin-embedded specimens. Therefore, the aim of this study was to examine the feasibility of microRNA profiling studies in routinely processed formalin-fixed paraffin-embedded human breast cancer specimens using fluorescence labelled bead technology.

RESULTS

A statistically highly significant correlation (Spearman r: 0.78 - 0.90, p < 0.0001) was observed for the expression of 319 microRNAs in routinely processed FFPE breast cancer specimens and paired fresh frozen tissue samples (n = 5). Results were confirmed in a larger series analyzing a selection of 10 microRNAs reported to be deregulated in breast cancer (n = 12). The expression pattern of 3 microRNAs was independently validated in this cohort using real-time RT-PCR technology.

CONCLUSION

Comprehensive microRNA expression patterns can be reliably derived from routinely processed FFPE breast cancer specimens using fluorescence labelled bead technology.

MicroRNA-21 targets a network of key tumor-suppressive pathways in glioblastoma cells

MicroRNA dysregulation is observed in different types of cancer. MiR-21 up-regulation has been reported for the majority of cancers profiled to date; however, knowledge is limited on the mechanism of action of miR-21, including identification of functionally important targets that contribute to its proproliferative and antiapoptotic actions. In this study, we show for the first time that miR-21 targets multiple important components of the p53, transforming growth factor-beta (TGF-beta), and mitochondrial apoptosis tumor-suppressive pathways. Down-regulation of miR-21 in glioblastoma cells leads to derepression of these pathways, causing repression of growth, increased apoptosis, and cell cycle arrest. These phenotypes are dependent on two of the miR-21 targets validated in this study, HNRPK and TAp63. These findings establish miR-21 as an important oncogene that targets a network of p53, TGF-beta, and mitochondrial apoptosis tumor suppressor genes in glioblastoma cells.

MicroRNA profiling as a tool to understand prognosis, therapy response and resistance in breast cancer

Despite advances in detection and therapies, breast cancer is still the leading cause of cancer death in women worldwide. The etiology of this neoplasm is complex, and both genetic and environmental factors contribute to the complicated scenario. Gene profiling studies have been extensively used over the past decades as a powerful tool in defining the signature of different cancers and in predicting outcome and response to therapies. More recently, a new class of small non-coding RNAs, microRNAs (miRNAs), able to regulate gene expression binding seed sequences on the 3'UTR of mRNA targets, has been linked to several human diseases, including cancer. An increasing amount of experimental evidence shows that miRNAs are aberrantly expressed in different tumour types, and that they can have a causal role in tumourigenesis. Here, we describe and discuss the evidence supporting the association between miRNAs and breast cancer, underlining their role in the development of this neoplasia, and the impact on putative innovative therapeutical approaches.

MicroRNA-21 down-regulates the expression of tumor suppressor PDCD4 in human glioblastoma cell T98G

MicroRNAs have been linked to different cancer-related processes. The microRNA miR-21 appears to function as an anti-apoptosis factor in glioblastomas. However, the functional target genes of miR-21 are largely unknown in glioblastomas. In this study, bioinformatics analysis was used to identify miR-21 target sites in various genes. Luciferase activity assay showed that a number of genes involved in apoptosis, PDCD4, MTAP, and SOX5, carry putative miR-21 binding sites. Expression of PDCD4 protein correlates inversely with expression of miR-21 in a number of human glioblastoma cell lines such as T98G, A172, U87, and U251. Inhibition of miR-21 increases endogenous levels of PDCD4 in cell line T98G and over-expression miR-21 inhibits PDCD4-dependent apoptosis. Together, these results indicate that miR-21 expression plays a key role in regulating cellular processes in glioblastomas and may serve as a target for effective therapies.

MicroRNAs: key players in the immune system, differentiation, tumorigenesis and cell death

Micro (mi)RNAs are small, highly conserved noncoding RNAs that control gene expression post-transcriptionally either via the degradation of target mRNAs or the inhibition of protein translation. Each miRNA is believed to regulate the expression of multiple mRNA targets, and many miRNAs have been linked to the initiation and progression of human cancer. miRNAs control various activities of the immune system and different stages of hematopoietic development, and their misexpression is the cause of various blood malignancies. Certain miRNAs have oncogenic activities, whereas others have the potential to act as tumor suppressors. Because they control fundamental processes such as differentiation, cell growth and cell death, the study of the role of miRNAs in human neoplasms holds great promise for novel forms of therapy. Here, we summarize the role of miRNAs and their targets in contributing to human cancers and their function as regulators of apoptotic pathways and the immune system.

MicroRNA miR-21 overexpression in human breast cancer is associated with advanced clinical stage, lymph node metastasis and patient poor prognosis

To investigate the global expression profile of miRNAs in primary breast cancer (BC) and normal adjacent tumor tissues (NATs) and its potential relevance to clinicopathological characteristics and patient survival, the genome-wide expression profiling of miRNAs in BC was investigated using a microarray containing 435 mature human miRNA oligonucleotide probes. Nine miRNAs of hsa-miR-21, hsa-miR-365, hsa-miR-181b, hsa-let-7f, hsa-miR-155, hsa-miR-29b, hsa-miR-181d, hsa-miR-98, and hsa-miR-29c were observed to be up-regulated greater than twofold in BC compared with NAT, whereas seven miRNAs of hsa-miR-497, hsa-miR-31, hsa-miR-355, hsa-miR-320, rno-mir-140, hsa-miR-127 and hsa-miR-30a-3p were observed to be down-regulated greater than twofold. The most significantly up-regulated miRNAs, hsa-mir-21 (miR-21), was quantitatively analyzed by TaqMan real-time PCR in 113 BC tumors. Interestingly, among the 113 BC cases, high level expression of miR-21 was significantly correlated with advanced clinical stage (P = 0.006, Fisher's exact text), lymph node metastasis (P = 0.007, Fisher's exact text), and shortened survival of the patients (hazard ratio [HR]=5.476, P < 0.001). Multivariate Cox regression analysis revealed this prognostic impact (HR=4.133, P = 0.001) to be independent of disease stage (HR=2.226, P = 0.013) and histological grade (HR=3.681, P = 0.033). This study could identify the differentiated miRNAs expression profile in BC and reveal that miR-21 overexpression was correlated with specific breast cancer biopathologic features, such as advanced tumor stage, lymph node metastasis, and poor survival of the patients, indicating that miR-21 may serve as a molecular prognostic marker for BC and disease progression.

MicroRNA signature and regulatory functions in the endometrium during normal and disease states

During the menstrual cycle, human endometrium undergoes extensive cyclic morphologic and biochemical modifications in preparation for embryo implantation. These processes are highly regulated by ovarian steroids and various locally expressed gene products and involve inflammatory reaction, apoptosis, cell proliferation, angiogenesis, differentiation (tissue formation), and tissue remodeling. MicroRNAs (miRNAs) have emerged as key regulators of gene expression, and their altered and/or aberrant expression has been associated with establishment and progression of various disorders, including tumorigenesis. This review highlights the endometrial expression of miRNAs and their potential regulatory functions under normal and pathologic conditions such as endometriosis, dysfunctional uterine bleeding, and endometrial cancer. Given the key regulatory function of miRNAs on gene expression stability, understanding the underlying mechanisms of how endometrial miRNAs are regulated and identifying their specific target genes and their functions might lead to the development of preventive and therapeutic strategies by regulating specific target genes associated with such reproductive disorders.

The expression and potential regulatory function of microRNAs in the pathogenesis of leiomyoma

Leiomyomas are benign uterine tumors considered to arise from transformation of myometrial cells. What initiates the conversion of myometrial cells into leiomyoma is unknown, however cytogenetic analysis often shows occurrence of nonrandom chromosomal abnormalities that may account for their establishment. It is clear that ovarian steroids are essential for leiomyoma growth, and local expression of many autocrine/paracrine mediators serving as key regulators of cell-cycle progression, cellular hypertrophy, extracellular matrix accumulation, and apoptosis appear to play central roles in this capacity. However, the stability of the expression of these genes represents the hallmarks of leiomyoma establishment, growth, and regression. With the emergence of microRNA (miRNA) as a key regulator of gene expression stability, in this review we present evidence for the expression and potential regulatory functions on miRNAs in leiomyoma with particular emphasis on the expression of their selective target genes whose products influence various cellular activities critical to pathogenesis of leiomyomas.

Toward microRNA-based therapeutics for heart disease: the sense in antisense

MicroRNAs act as negative regulators of gene expression by inhibiting the translation or promoting the degradation of target mRNAs. Because individual microRNAs often regulate the expression of multiple target genes with related functions, modulating the expression of a single microRNA can, in principle, influence an entire gene network and thereby modify complex disease phenotypes. Recent studies have identified signature expression patterns of microRNAs associated with pathological cardiac hypertrophy, heart failure, and myocardial infarction in humans and mouse models of heart disease. Gain- and loss-of-function studies in mice have revealed profound and unexpected functions for these microRNAs in numerous facets of cardiac biology, including the control of myocyte growth, contractility, fibrosis, and angiogenesis, providing glimpses of new regulatory mechanisms and potential therapeutic targets for heart disease. Especially intriguing is the discovery of a network of muscle-specific microRNAs embedded within myosin heavy chain genes, which control myosin expression and the response of the heart to stress and thyroid hormone signaling. Disease-inducing cardiac microRNAs can be persistently silenced in vivo through systemic delivery of antimiRs, allowing for the direct therapeutic modulation of disease mechanisms. Here, we summarize current knowledge of the roles of miRNAs in heart disease and consider the advantages and potential challenges of microRNA-based approaches compared to conventional drug-based therapies.

High miR-21 expression in breast cancer associated with poor disease-free survival in early stage disease and high TGF-beta1

MicroRNA-21 (miR-21) is considered an onco-microRNA given its abilities to suppress the actions of several tumor suppressor genes and to promote tumor cell growth, invasion and metastasis. Recently, transforming growth factor-beta (TGF-beta) is found to up-regulate the expression of miR-21, and elevated miR-21 expression is seen frequently in breast cancer. To evaluate the effect of miR-21 on disease progression and its association with TGF-beta, we analyzed miR-21 expression in breast cancer. Fresh tumor samples were collected during surgery from 344 patients diagnosed with primary breast cancer. The expression of miR-21 in tumor samples was measured with a TaqMan microRNA assay using U6 as reference. Levels of miR-21 expression by disease stage, tumor grade, histology, hormone receptor status and lymph node involvement were compared. Cox proportional hazards regression analysis was performed to assess the association of miR-21 expression with disease-free and overall survival. The study results showed that the expression of miR-21 was detected in all tumor samples with substantial variation. High miR-21 expression was associated with features of aggressive disease, including high tumor grade, negative hormone receptor status, and ductal carcinoma. High miR-21 was also positively correlated with TGF-beta1. No associations were found between patient survival and miR-21 expression among all patients, but high miR-21 was associated with poor disease-free survival in early stage patients (HR = 2.08, 95% CI: 1.08-4.00) despite no value for prognosis. The study supports the notion that miR-21 is an onco-microRNA for breast cancer. Elevated miR-21 expression may facilitate tumor progression, and TGF-beta may up-regulate its expression.

Regulation of microRNA processing in development, differentiation and cancer

microRNA (miRNA) is a class of small, noncoding, regulatory RNAs. The approximately 21 nt mature miRNA is processed from larger precursor molecules following a coordinated series of events. In theory, miRNA processing may be regulated at any of these steps. A growing body of evidence has demonstrated various steps in the miRNA biogenesis process for which regulation occurs. RNA editing of miRNA precursors, SNPs or mutations in the miRNA precursors, regulation by RNA binding proteins, alterations in the levels of key processing proteins, as well as a number of unknown mechanisms contribute to the regulation of miRNA processing. This article reviews the available literature on the regulation of miRNA processing that occurs within normal cells, during development or in diseases such as cancer.

Altered MicroRNA expression in cervical carcinomas

PURPOSE

MicroRNAs (miRNA) are small noncoding RNAs that are 18 to 25 nucleotides in length; they regulate the stability or translational efficiency of target mRNAs. Emerging evidence suggests that miRNAs might be involved in the pathogenesis of a variety of human cancers.

EXPERIMENTAL DESIGN

In this study, we profiled miRNA expression in 10 early stage invasive squamous cell carcinomas (ISCC) and 10 normal cervical squamous epithelial specimens using TaqMan real-time quantitative PCR array methods. In order to evaluate the role of miR-199a, one of the most significantly overexpressed in ISCCs, we transfected cervical cancer cells (SiHa and ME-180) with anti-miR-199a oligonucleotides and assessed the cell viability.

RESULTS

We found 70 genes (68 up-regulated, 2 down-regulated) with significantly different expression in the ISCCs compared with normal samples (P < 0.05). When we analyzed the expression of the 10 most significant miRNAs in 31 ISCCs, increased miR-127 expression was significantly associated with lymph node metastasis (P = 0.006). Transfection of anti-miR-199a oligonucleotides to cervical cancer cells suppressed cell growth in vitro, which was potentiated with the anticancer agent cisplatin.

CONCLUSIONS

Our results show that miRNA deregulation may play an important role in the malignant transformation of cervical squamous cells. In addition, they may offer new candidate targets to be exploited for both prognostic and therapeutic strategies in patients with cervical cancer.

Mature miR-184 as Potential Oncogenic microRNA of Squamous Cell Carcinoma of Tongue

PURPOSE

The aim of this study was to evaluate the microRNA expression patterns in squamous cell carcinoma (SCC) of the tongue.

EXPERIMENTAL DESIGN

Expression levels of 156 human mature microRNAs were examined using real-time quantitative PCR (Taq Man MicroRNA Assays; Human Panel) on laser microdissected cells of 4 tongue carcinomas and paired normal tissues. Expression of mature miR-184 was further validated in 20 paired tongue SCC and the normal tissues. Potential oncogenic functions of miR-184 were evaluated in tongue SCC cell lines (Cal27, HN21B, and HN96) with miR-184 inhibitor. Plasma miR-184 levels were evaluated using real-time quantitative PCR.

RESULTS

Using 3-fold expression difference as a cutoff level, we identified 24 up-regulated mature miRNAs including miR-184, miR-34c, miR-137, miR-372, miR-124a, miR-21, miR-124b, miR-31, miR-128a, miR-34b, miR-154, miR-197, miR-132, miR-147, miR-325, miR-181c, miR-198, miR-155, miR-30a-3p, miR-338, miR-17-5p, miR-104, miR-134, and miR-213; and 13 down-regulated mature miRNAs including miR-133a, miR-99a, miR-194, miR-133b, miR-219, miR-100, miR-125b, miR-26b, miR-138, miR-149, miR-195, miR-107, and miR-139. Overexpression of miR-184 was further validated in 20 paired tongue SCC and normal tissues (P = 0.002). Inhibition of miR-184 in tongue SCC cell lines could reduce cell proliferation rate. Down-regulation of c-Myc was observed in two cell lines in response to miR-184 inhibitor. Suppressing miR-184 could induce apoptosis in all three cell lines. Plasma miR-184 levels were significantly higher in tongue SCC patients in comparison with normal individuals, and the levels were significantly reduced after surgical removal of the primary tumors.

CONCLUSIONS

Overexpression of miR-184 might play an oncogenic role in the antiapoptotic and proliferative processes of tongue SCC. In addition, plasma miR-184 levels were associated with the presence of primary tumor. Further studies on the aberrantly expressed miRNAs in tongue SCC as well as using plasma miRNAs as novel tumor markers are warranted.

A microRNA expression ratio defining the invasive phenotype in bladder tumors

OBJECTIVE

The goal of this study was to identify a microRNA (miRNA) signature in bladder cancer capable of differentiating superficial from invasive disease.

METHODS

Expression profiling of 343 miRNAs was performed in a microarray format using noninvasive and invasive bladder carcinoma cell lines with differential expression confirmed using a single molecule detection platform assay. miR-21 and miR-205 expression levels were determined in 53 bladder tumors (28 superficial and 25 invasive). Sensitivity, specificity, and a ROC curve were calculated to determine the discriminatory power of the miRNA ratio to predict invasion. Knockdown and forced expression of miRNAs was performed to evaluate their role in invasion.

RESULTS

Expression profiling of 343 miRNAs, using noninvasive and invasive bladder cell lines, revealed significant differential expression of 9 miRNAs. Cell lines characterized as invasive showed a miR-21:miR-205 ratio at least 10-fold higher than the quantitative ratio obtained from non-invasive cell lines. The same expression ratio was determined in 53 bladder tumors. From these results, we recorded a sensitivity and specificity of 100% and 78%, respectively, using a cutoff of 1.79 to predict an invasive lesion. The area under the receiver operator characteristic curve was 0.89. Using in vitro invasion assays, we have demonstrated a role for miR-21 in establishing the invasive phenotype of bladder carcinoma cells.

CONCLUSION

In this study, we identified a miR-21:miR-205 expression ratio that has the ability to distinguish between invasive and noninvasive bladder tumors with high sensitivity and specificity, with the potential to identify superficial lesions at high risk to progress.

Transcription factor and microRNA regulation in androgen-dependent and -independent prostate cancer cells

Background

Prostate cancer is one of the leading causes of cancer death in men. Androgen ablation, the most commonly-used therapy for progressive prostate cancer, is ineffective once the cancer cells become androgen-independent. The regulatory mechanisms that cause this transition (from androgen-dependent to androgen-independent) remain unknown. In this study, based on the microarray data comparing global gene expression patterns in the prostate tissue between androgen-dependent and -independent prostate cancer patients, we indentify a set of transcription factors and microRNAs that potentially cause such difference, using a model-based computational approach.

Results

From 335 position weight matrices in the TRANSFAC database and 564 microRNAs in the microRNA registry, our model identify 5 transcription factors and 7 microRNAs to be potentially responsible for the level of androgen dependency. Of these transcription factors and microRNAs, the estimated function of all the 5 transcription factors are predicted to be inhibiting transcription in androgen-independent samples comparing with the dependent ones. Six out of 7 microRNAs, however, demonstrated stimulatory effects. We also find that the expression levels of three predicted transcription factors, including AP-1, STAT3 (signal transducers and activators of transcription 3), and DBP (albumin D-box) are significantly different between androgen-dependent and -independent patients. In addition, microRNA microarray data from other studies confirm that several predicted microRNAs, including miR-21, miR-135a, and miR-135b, demonstrate differential expression in prostate cancer cells, comparing with normal tissues.

Conclusion

We present a model-based computational approach to identify transcription factors and microRNAs influencing the progression of androgen-dependent prostate cancer to androgen-independent prostate cancer. This result suggests that the capability of transcription factors to initiate transcription and microRNAs to facilitate mRNA degradation are both decreased in androgen-independent prostate cancer. The proposed model-based approach indicates that considering combinatorial effects of transcription factors and microRNAs in a unified model provides additional transcriptional and post-transcriptional regulatory mechanisms on global gene expression in the prostate cancer with different hormone-dependency.

MicroRNA 21 promotes glioma invasion by targeting matrix metalloproteinase regulators

Substantial data indicate that microRNA 21 (miR-21) is significantly elevated in glioblastoma (GBM) and in many other tumors of various origins. This microRNA has been implicated in various aspects of carcinogenesis, including cellular proliferation, apoptosis, and migration. We demonstrate that miR-21 regulates multiple genes associated with glioma cell apoptosis, migration, and invasiveness, including the RECK and TIMP3 genes, which are suppressors of malignancy and inhibitors of matrix metalloproteinases (MMPs). Specific inhibition of miR-21 with antisense oligonucleotides leads to elevated levels of RECK and TIMP3 and therefore reduces MMP activities in vitro and in a human model of gliomas in nude mice. Moreover, downregulation of miR-21 in glioma cells leads to decreases of their migratory and invasion abilities. Our data suggest that miR-21 contributes to glioma malignancy by downregulation of MMP inhibitors, which leads to activation of MMPs, thus promoting invasiveness of cancer cells. Our results also indicate that inhibition of a single oncomir, like miR-21, with specific antisense molecules can provide a novel therapeutic approach for "physiological" modulation of multiple proteins whose expression is deregulated in cancer.

Role of MicroRNA miR-27a and miR-451 in the regulation of MDR1/P-glycoprotein expression in human cancer cells

MicroRNAs are short non-coding RNA molecules able to affect stability and/or translation of mRNA, thereby regulating the expression of genes involved in many biological processes. We report here that microRNAs miR-27a and miR-451 are involved in activating the expression of P-glycoprotein, the MDR1 gene product that confers cancer cell resistance to a broad range of chemotherapeutics. We showed that expressions of miR-27a and miR-451 were up-regulated in multidrug resistant (MDR) cancer cell lines A2780DX5 and KB-V1, as compared with their parental lines A2780 and KB-3-1. Treatment of A2780DX5 cells with the antagomirs of miR-27a or miR-451 decreased the expression of P-glycoprotein and MDR1 mRNA. In contrast, the mimics of miR-27a and miR-451 increased MDR1 expression in the parental cells A2780. The sensitivity to and intracellular accumulation of cytotoxic drugs that are transported by P-glycoprotein were enhanced by the treatment with the antagomirs of miR-27a or miR-451. Our results demonstrate for the first time the roles of microRNAs in the regulation of drug resistance mediated by MDR1/P-glycoprotein, and suggest the potential for targeting miR-27a and miR-451 as a therapeutic strategy for modulating MDR in cancer cells.

Prognostic value of mature microRNA-21 and microRNA-205 overexpression in non-small cell lung cancer by quantitative real-time RT-PCR

BACKGROUND

microRNA (miRNA) expression profiles are being intensively investigated for their involvement in carcinogenesis. We evaluated the prognostic value of mature microRNA-21 (miR-21) and mature microRNA-205 (miR-205) overexpression in non-small cell lung cancer (NSCLC).

PATIENTS AND METHODS

We studied 48 pairs of NSCLC fresh frozen tissue specimens collected at time of surgery and before chemotherapy. Highly specific amplification and quantification of mature miR-21 and mature miR-205 was achieved using looped real time RT-PCR.

RESULTS

miRNA expression, determined by real time RT-PCR, was defined by DeltaDeltaCt measurements. We detected overexpression of mature miR-21 in 25 (52.0%) of the 48 NSCLC paired specimens and overexpression of miR-205 in 31 (64.6%). Overexpression was assessed after comparison of miRNA expression in NSCLC tissues and in their corresponding noncancerous tissues with respect to U6 expression. During the follow-up period, 29 of 48 (60.4%) patients relapsed, and 23 of 48 died (47.9%). Mature miR-21 was upregulated in 16 of 29 (55.2%) patients who relapsed and 15 of 23 (65.2%) patients who died. Mature miR-205 was overexpressed in 19 of 29 patients who relapsed (65.5%) and 15 of 23 patients who died (65.2%). Mature miR-21 overexpression correlated with overall survival (OS) of the patients (P = 0.027), whereas overexpression of mature miR-205 did not.

CONCLUSIONS

Our results suggest that overexpression of mature miR-21 is an independent negative prognostic factor for OS in NSCLC patients.

Elevated expression of the miR-17-92 polycistron and miR-21 in hepadnavirus-associated hepatocellular carcinoma contributes to the malignant phenotype

Alterations in microRNA (miRNA) expression in both human and animal models have been linked to many forms of cancer. Such miRNAs, which act directly as repressors of gene expression, have been found to frequently reside in fragile sites and genomic regions associated with cancer. This study describes a miRNA signature for human primary hepatitis B virus-positive human hepatocellular carcinoma. Moreover, two known oncomiRs--miRNAs with known roles in cancer--the miR-17-92 polycistron and miR-21, exhibited increased expression in 100% of primary human and woodchuck hepatocellular carcinomas surveyed. To determine the importance of these miRNAs in tumorigenesis, an in vitro antisense oligonucleotide knockdown model was evaluated for its ability to reverse the malignant phenotype. Both in human and woodchuck HCC cell lines, separate treatments with antisense oligonucleotides specific for either the miR-17-92 polycistron (all six members) or miR-21 caused a 50% reduction in both hepatocyte proliferation and anchorage-independent growth. The combination of assays presented here supports a role for these miRNAs in the maintenance of the malignant transformation of hepatocytes.

miR-206 Expression is down-regulated in estrogen receptor alpha-positive human breast cancer

Expression levels of estrogen receptor (ER) alpha govern estrogen-dependent growth, response to endocrine therapy, and prognosis in ERalpha-positive breast cancer. Multiple mechanisms involved in altering ERalpha gene expression in breast cancer have been identified, including ERalpha gene amplification as well as transcriptional silencing by DNA methylation of CpG islands within the ERalpha promoter and mutations within the open reading frame of ERalpha. However, expression levels of ERalpha in breast cancer tissues differ widely among patients, and frequently change during disease progression and in response to systemic therapies. Recent evidence has shown that microRNA mutations or misexpression correlate with various human cancers, and miR-206 is reported to decrease endogenous ERalpha mRNA and protein levels in human MCF-7 breast cancer cells via two specific target sites within the 3'-untranslated region of the human ERalpha transcript. In this study, we show for the first time that miR-206 expression is markedly decreased in ERalpha-positive human breast cancer tissues assayed by quantitative reverse transcription-PCR analysis. Moreover, we observe that miR-206 expression is inversely correlated with ERalpha but not ERbeta mRNA expression in breast cancer tissues. Transfection experiments revealed that introduction of miR-206 into estrogen-dependent MCF-7 breast cancer cells inhibits cell growth in a dose- and time-dependent manner. Our results suggest that miR-206 could be a novel candidate for endocrine therapy that targets only ERalpha in breast cancer.

Expression of microRNAs and protein-coding genes associated with perineural invasion in prostate cancer

BACKGROUND

Perineural invasion (PNI) is the dominant pathway for local invasion in prostate cancer. To date, only few studies have investigated the molecular differences between prostate tumors with PNI and those without it.

METHODS

To evaluate the involvement of both microRNAs and protein-coding genes in PNI, we determined their genome-wide expression with a custom microRNA microarray and Affymetrix GeneChips in 50 prostate adenocarcinomas with PNI and 7 without it. In situ hybridization (ISH) and immunohistochemistry was used to validate candidate genes.

RESULTS

Unsupervised classification of the 57 adenocarcinomas revealed two clusters of tumors with distinct global microRNA expression. One cluster contained all non-PNI tumors and a subgroup of PNI tumors. Significance analysis of microarray data yielded a list of microRNAs associated with PNI. At a false discovery rate (FDR)<10%, 19 microRNAs were higher expressed in PNI tumors than in non-PNI tumors. The most differently expressed microRNA was miR-224. ISH showed that this microRNA is expressed by perineural cancer cells. The analysis of protein-coding genes identified 34 transcripts that were differently expressed by PNI status (FDR<10%). These transcripts were down-regulated in PNI tumors. Many of those encoded metallothioneins and proteins with mitochondrial localization and involvement in cell metabolism. Consistent with the microarray data, perineural cancer cells tended to have lower metallothionein expression by immunohistochemistry than nonperineural cancer cells.

CONCLUSIONS

Although preliminary, our findings suggest that alterations in microRNA expression, mitochondrial function, and cell metabolism occur at the transition from a noninvasive prostate tumor to a tumor with PNI.

MicroRNA-21 targets Sprouty2 and promotes cellular outgrowths

The posttranscriptional regulator, microRNA-21 (miR-21), is up-regulated in many forms of cancer, as well as during cardiac hypertrophic growth. To understand its role, we overexpressed it in cardiocytes where it revealed a unique type of cell-to-cell "linker" in the form of long slender outgrowths and branches. We subsequently confirmed that miR-21 directly targets and down-regulates the expression of Sprouty2 (SPRY2), an inhibitor of branching morphogenesis and neurite outgrowths. We found that beta-adrenergic receptor (betaAR) stimulation induces up-regulation of miR-21 and down-regulation of SPRY2 and is, likewise, associated with connecting cell branches. Knockdown of SPRY2 reproduced the branching morphology in cardiocytes, and vice versa, knockdown of miR-21 using a specific 'miRNA eraser' or overexpression of SPRY2 inhibited betaAR-induced cellular outgrowths. These structures enclose sarcomeres and connect adjacent cardiocytes through functional gap junctions. To determine how this aspect of miR-21 function translates in cancer cells, we knocked it down in colon cancer SW480 cells. This resulted in disappearance of their microvillus-like protrusions accompanied by SPRY2-dependent inhibition of cell migration. Thus, we propose that an increase in miR-21 enhances the formation of various types of cellular protrusions through directly targeting and down-regulating SPRY2.

MicroRNA expression in canine mammary cancer

MicroRNAs (miRNAs) are 18-22-nt noncoding RNAs that are involved in post-transcriptional regulation of genes. Oncomirs, a subclass of miRNAs, include genes whose expression, or lack thereof, are associated with cancers. Until the last decade, the domestic dog was an underused model for the study of various human diseases that have genetic components. The dog exhibits marked genetic and physiologic similarity to the human, thereby making it an excellent model for study and treatment of various hereditary diseases. Furthermore, because the dog presents with distinct, spontaneously occurring mammary tumors, it may serve as a model for genetic analysis and treatments of humans with malignant breast tumors. Because miRNAs have been found to act as both tumor suppressors and oncogenes in several different cancers, expression patterns of ten miRNAs (miR-15a, miR-16, miR-17-5p, miR-21, miR-29b, miR-125b, miR-145, miR-155, miR-181b, let-7f) known to be associated with human breast cancers were compared to malignant canine mammary tumors (n = 6) and normal canine mammary tissue (n = 10). Resulting data revealed miR-29b and miR-21 to have a statistically significant (p < 0.05 by MANOVA analysis) upregulation in cancerous samples. The ten canine miRNAs follow the same pattern of expression as in the human, except for miR-145 which does not show a difference in expression between the normal and cancerous canine samples. In addition, when analyzed according to specific cancer phenotypes, miR-15a and miR-16 show a significant downregulation in canine ductal carcinomas while miRsR-181b, -21, -29b, and let-7f show a significant upregulation in canine tubular papillary carcinomas.

Differentiation of two types of mobilized peripheral blood stem cells by microRNA and cDNA expression analysis

Background

Mobilized-peripheral blood hematopoietic stem cells (HSCs) have been used for transplantation, immunotherapy, and cardiovascular regenerative medicine. Agents used for HSC mobilization include G-CSF and the CXCR4 inhibitor AMD3100 (plerixafor). The HSCs cells mobilized by each agent may contain different subtypes and have different functions. To characterize mobilized HSCs used for clinical applications, microRNA (miRNA) profiling and gene expression profiling were used to compare AMD3100-mobilized CD133+ cells from 4 subjects, AMD3100 plus G-CSF-mobilized CD133+ cells from 4 subjects and G-CSF-mobilized CD34+ cells from 5 subjects. The HSCs were compared to peripheral blood leukocytes (PBLs) from 7 subjects.

Results

Hierarchical clustering of miRNAs separated HSCs from PBLs. miRNAs up-regulated in all HSCs included hematopoiesis-associated miRNA; miR-126, miR-10a, miR-221 and miR-17-92 cluster. miRNAs up-regulated in PBLs included miR-142-3p, -218, -21, and -379. Hierarchical clustering analysis of miRNA expression separated the AMD3100-mobilized CD133+ cells from G-CSF-mobilized CD34+ cells. Gene expression analysis of the HSCs naturally segregated samples according to mobilization and isolation protocol and cell differentiation status.

Conclusion

HSCs and PBLs have unique miRNA and gene expression profiles. miRNA and gene expression microarrays maybe useful for assessing differences in HSCs.

MicroRNAs: key players in carcinogenesis and novel therapeutic targets

MicroRNAs (miRNAs) represent a recently uncovered class of small and endogenous non-coding RNAs. MiRNA function is critical to normal cellular processes such as differentiation and apoptosis, and recent studies have demonstrated that deregulated miRNA expression contributes to the malignant phenotype. The purpose of this review is to summarise these findings in relation to the most common human malignancies, and to analyse the clinical and therapeutic opportunities they provide.

MicroRNA-21 promotes cell transformation by targeting the programmed cell death 4 gene

MicroRNAs (miRNAs) are small noncoding RNA molecules that negatively control expression of target genes in animals and plants. The microRNA-21 gene (mir-21) has been identified as the only miRNA commonly overexpressed in solid tumors of the lung, breast, stomach, prostate, colon, brain, head and neck, esophagus and pancreas. We initiated a screen to identify miR-21 target genes using a reporter assay and identified a potential miR-21 target in the 3'-UTR of the programmed cell death 4 (PDCD4) gene. We cloned the full-length 3'-UTR of human PDCD4 downstream of a reporter and found that mir-21 downregulated, whereas a modified antisense RNA to miR-21 upregulated reporter activity. Moreover, deletion of the putative miR-21-binding site (miRNA regulatory element, MRE) from the 3'-UTR of PDCD4, or mutations in the MRE abolished the ability of miR-21 to inhibit reporter activity, indicating that this MRE is a critical regulatory region. Western blotting showed that Pdcd4 protein levels were reduced by miR-21 in human and mouse cells, whereas quantitative real-time PCR revealed little difference at the mRNA level, suggesting translational regulation. Finally, overexpression of mir-21 in MCF-7 human breast cancer cells and mouse epidermal JB6 cells promoted soft agar colony formation by downregulating Pdcd4 protein levels. The demonstration that miR-21 promotes cell transformation supports the concept that mir-21 functions as an oncogene by a mechanism that involves translational repression of the tumor suppressor Pdcd4.

MicroRNA-21 targets tumor suppressor genes in invasion and metastasis

MicroRNAs (miRNAs) are a class of naturally occurring small non-coding RNAs that target protein-coding mRNAs at the post-transcriptional level. Our previous studies suggest that mir-21 functions as an oncogene and has a role in tumorigenesis, in part through regulation of the tumor suppressor gene tropomyosin 1 (TPM1). Given that TPM1 has been implicated in cell migration, in this study we further investigated the role of mir-21 in cell invasion and tumor metastasis. We found that suppression of mir-21 in metastatic breast cancer MDA-MB-231 cells significantly reduced invasion and lung metastasis. Consistent with this, ectopic expression of TPM1 remarkably reduced cell invasion. Furthermore, we identified two additional direct mir-21 targets, programmed cell death 4 (PDCD4) and maspin, both of which have been implicated in invasion and metastasis. Like TPM1, PDCD4 and maspin also reduced invasiveness of MDA-MB-231 cells. Finally, the expression of PDCD4 and maspin inversely correlated with mir-21 expression in human breast tumor specimens, indicating the potential regulation of PDCD4 and maspin by mir-21 in these tumors. Taken together, the results suggest that, as an oncogenic miRNA, mir-21 has a role not only in tumor growth but also in invasion and tumor metastasis by targeting multiple tumor/metastasis suppressor genes. Therefore, suppression of mir-21 may provide a novel approach for the treatment of advanced cancers.

MicroRNAs and prostate cancer

Prostate cancer (CaP) is the most frequently diagnosed malignant tumour and the second leading cause of cancer deaths in American men. One of the most troubling aspects of this disease is that, after androgen ablation therapy, androgen-dependent cancer cells inevitably progress to an androgen-independent status, for which no effective treatment has yet been developed. To date, the mechanisms that underlie the occurrence and progression of CaP remain largely unknown. Recent studies suggest that microRNAs (miRNAs) are involved in human tumourigenesis. Some aberrantly expressed miRNAs have been discovered in CaP cell lines, xenografts and clinical tissues and these CaP-related miRNAs may play critical roles in the pathogenesis of CaP. This review provides an overview of current findings about aberrantly expressed miRNAs in CaP. Although a number of CaP-related miRNAs were discovered, to date, only five are characterized for their functionalities: three as oncogenes and two as tumour suppressors. To understand the mechanisms of miRNA action as oncogenes or tumour suppressors, mRNA targets of miRNAs were characterized. Oncogenic miRNAs down-regulate the expression of apoptosis-related genes, and tumour suppressor miRNAs target the proliferation-related genes. Importantly, there is evidence that CaP-related miRNAs are regulated through androgen signalling and that this regulation may contribute to the development of androgen independence. Due to the oncogenic or tumour-suppressive properties of CaP-related miRNAs, they are highly likely to be of clinical use first as biomarkers but more importantly as therapeutic targets for prostate cancer treatment in the near future.

SMAD proteins control DROSHA-mediated microRNA maturation

MicroRNAs (miRNAs) are small non-coding RNAs that participate in the spatiotemporal regulation of messenger RNA and protein synthesis. Aberrant miRNA expression leads to developmental abnormalities and diseases, such as cardiovascular disorders and cancer; however, the stimuli and processes regulating miRNA biogenesis are largely unknown. The transforming growth factor beta (TGF-beta) and bone morphogenetic protein (BMP) family of growth factors orchestrates fundamental biological processes in development and in the homeostasis of adult tissues, including the vasculature. Here we show that induction of a contractile phenotype in human vascular smooth muscle cells by TGF-beta and BMPs is mediated by miR-21. miR-21 downregulates PDCD4 (programmed cell death 4), which in turn acts as a negative regulator of smooth muscle contractile genes. Surprisingly, TGF-beta and BMP signalling promotes a rapid increase in expression of mature miR-21 through a post-transcriptional step, promoting the processing of primary transcripts of miR-21 (pri-miR-21) into precursor miR-21 (pre-miR-21) by the DROSHA (also known as RNASEN) complex. TGF-beta- and BMP-specific SMAD signal transducers are recruited to pri-miR-21 in a complex with the RNA helicase p68 (also known as DDX5), a component of the DROSHA microprocessor complex. The shared cofactor SMAD4 is not required for this process. Thus, regulation of miRNA biogenesis by ligand-specific SMAD proteins is critical for control of the vascular smooth muscle cell phenotype and potentially for SMAD4-independent responses mediated by the TGF-beta and BMP signalling pathways.

Small is beautiful: microRNAs and breast cancer-where are we now?

MicroRNAs are a recently discovered class of small regulatory RNAs that influence the stability and translational efficiency of target mRNAs. They have been implicated in an increasing number of biological processes, including neoplasia. Recent studies have shown an involvement for these regulatory molecules in breast cancer. For example, miRNA profiling studies have identified microRNAs that are deregulated in breast cancer. Furthermore, functional studies have uncovered their roles in breast cancer as both tumour suppressor genes (eg miR-335) and oncogenes (eg miR-21). miRNAs deregulated in breast cancer influence the translational regulation of well-established regulatory molecules, such as oestrogen receptor-alpha, which is regulated by miR-206, and novel cancer-related molecules whose functions are not yet fully understood.. Here we present an overview of our current understanding of miRNA in breast cancer.

MicroRNA expression and identification of putative miRNA targets in ovarian cancer

Background

MicroRNAs (miRNAs) represent a class of small non-coding RNAs that control gene expression by targeting mRNAs and triggering either translation repression or RNA degradation. Emerging evidence suggests the potential involvement of altered regulation of miRNA in the pathogenesis of cancers, and these genes are thought to function as both tumor suppressors and oncogenes.

Methodology/Principal Findings

Using microRNA microarrays, we identify several miRNAs aberrantly expressed in human ovarian cancer tissues and cell lines. miR-221 stands out as a highly elevated miRNA in ovarian cancer, while miR-21 and several members of the let-7 family are found downregulated. Public databases were used to reveal potential targets for the highly differentially expressed miRNAs. In order to experimentally identify transcripts whose stability may be affected by the differentially expressed miRNAs, we transfected precursor miRNAs into human cancer cell lines and used oligonucleotide microarrays to examine changes in the mRNA levels. Interestingly, there was little overlap between the predicted and the experimental targets or pathways, or between experimental targets/pathways obtained using different cell lines, highlighting the complexity of miRNA target selection.

Conclusion/Significance

Our results identify several differentially expressed miRNAs in ovarian cancer and identify potential target transcripts that may be regulated by these miRNAs. These miRNAs and their targets may have important roles in the initiation and development of ovarian cancer.

miR-15b and miR-16 modulate multidrug resistance by targeting BCL2 in human gastric cancer cells

microRNAs are endogenous small noncoding RNAs that regulate gene expression negatively at posttranscriptional level. This latest addition to the complex gene regulatory circuitry revolutionizes our way to understanding physiological and pathological processes in the human body. Here we investigated the possible role of microRNAs in the development of multidrug resistance (MDR) in gastric cancer cells. microRNA expression profiling revealed a limited set of microRNAs with altered expression in multidrug- resistant gastric cancer cell line SGC7901/VCR compared to its parental SGC7901 cell line. Among the downregulated microRNAs are miR-15b and miR-16, members of miR-15/16 family, whose expression was further validated by qRT-PCR. In vitro drug sensitivity assay demonstrated that overexpression of miR-15b or miR-16 sensitized SGC7901/VCR cells to anticancer drugs whereas inhibition of them using antisense oligonucleotides conferred SGC7901 cells MDR. The downregulation of miR-15b and miR-16 in SGC7901/VCR cells was concurrent with the upregulation of Bcl-2 protein. Enforced mir-15b or miR-16 expression reduced Bcl-2 protein level and the luciferase activity of a BCL2 3' untranslated region-based reporter construct in SGC7901/VCR cells, suggesting that BCL2 is a direct target of miR-15b and miR-16. Moreover, overexpression of miR-15b or miR-16 could sensitize SGC7901/VCR cells to VCR-induced apoptosis. Taken together, our findings suggest that miR-15b and miR-16 could play a role in the development of MDR in gastric cancer cells at least in part by modulation of apoptosis via targeting BCL2.