MicroRNA-21 targets the tumor suppressor gene tropomyosin 1 (TPM1)

Interactions between the estrogen receptor, its cofactors and microRNAs in breast cancer

The activity of selective estrogen receptor modulators (SERMs) is not fully explained by an estrogen receptor (ER) switch model that simply turns estrogen activity on or off. A better understanding of the mechanisms involved in estrogen signaling and the development of drug resistance could help stratify patients into more coherent treatment groups and identify novel therapeutic candidates. This review describes how interactions between two novel factors known to influence estrogenic activity: nuclear receptor cofactors--protein partners which modulate estrogen action, and microRNAs--a class of recently discovered regulatory elements, may impact hormone-sensitive breast cancer. The role of nuclear receptor cofactors in estrogen signaling and the associations between ER cofactors and breast cancer are described. We outline the activity of microRNAs (miRNAs) and their associations with breast cancer and detail recent evidence of interactions between the ER and its cofactors and miRNA and provide an overview of the emerging field of miRNA-based therapeutics. We propose that previously unrecognised interactions between these two species of regulatory molecules may underlie at least some of the heterogeneity of breast cancer in terms of its clinical course and response to treatment. The exploitation of such associations will have important implications for drug development.

Locked nucleic acid in situ hybridization analysis of miR-21 expression during colorectal cancer development

PURPOSE

To better understand microRNA miR-21 function in carcinogenesis, we analyzed miR-21 expression patterns in different stages of colorectal cancer development using in situ hybridization (ISH).

EXPERIMENTAL DESIGN

Locked nucleic acid (LNA)/DNA probes and a biotin-free tyramide signal amplification system were used in ISH analyses of miRNA expression. Conditions for specific detection of miR-21 were determined using human cell lines and miR-21-expressing lentiviral vectors. Expression was determined in 39 surgically excised colorectal tumors and 34 endoscopically resected colorectal polyps.

RESULTS

In the surgical samples, miR-21 expression was much higher in colorectal cancers than in normal mucosa. Strong miR-21 expression was also observed in cancer-associated stromal fibroblasts, suggesting miR-21 induction by cancer-secreted cytokines. Protein expression of PDCD4, a miR-21 target, was inversely correlated with miR-21 expression, confirming that miR-21 is indeed a negative regulator of PDCD4 in vivo. In the endoscopic samples, miR-21 expression was very high in malignant adenocarcinomas but was not elevated in nontumorigenic polyps. Precancerous adenomas also frequently showed miR-21 up-regulation.

CONCLUSION

Using the LNA-ISH system for miRNA detection, miR-21 was detectable in precancerous adenomas. The frequency and extent of miR-21 expression increased during the transition from precancerous colorectal adenoma to advanced carcinoma. Expression patterns of miR-21 RNA and its target, tumor suppressor protein PDCD4, were mutually exclusive. This pattern may have clinical application as a biomarker for colorectal cancer development and might be emphasized by self-reinforcing regulatory systems integrated with the miR-21 gene, which has been previously shown in cell culture.

MicroRNA-based therapeutics for cancer

MicroRNAs (miRNAs) are non-protein-coding small RNA molecules that negatively regulate target messenger RNA through degradation or suppression of protein translation. MiRNAs play important roles in the control of many biologic processes, such as development, differentiation, proliferation, and apoptosis. Increasing evidence shows that aberrant miRNA expression profiles and unique miRNA signaling pathways are present in a variety of cancers. MiRNAs function as oncogenes or tumor suppressors during tumor development and progression. Experimental evidence demonstrates that correction of specific miRNA alterations using miRNA mimics or antagomirs can normalize the gene regulatory network and signaling pathways, and reverse the phenotype in cancerous cells. MiRNA-based gene therapy provides an attractive anti-tumor approach for integrated cancer therapy. In this review, we focus on miRNA-based treatment for cancers, summarize the delivery systems used in experimental and preclinical research, such as liposomes, viral vectors, and nanoparticles, and consider the safety and toxicity of miRNA therapy.

The PTEN-regulating microRNA miR-26a is amplified in high-grade glioma and facilitates gliomagenesis in vivo

Activated oncogenic signaling is central to the development of nearly all forms of cancer, including the most common class of primary brain tumor, glioma. Research over the last two decades has revealed the particular importance of the Akt pathway, and its molecular antagonist PTEN (phosphatase and tensin homolog), in the process of gliomagenesis. Recent studies have also demonstrated that microRNAs (miRNAs) may be responsible for the modulation of cancer-implicated genes in tumors. Here we report the identification miR-26a as a direct regulator of PTEN expression. We also show that miR-26a is frequently amplified at the DNA level in human glioma, most often in association with monoallelic PTEN loss. Finally, we demonstrate that miR-26a-mediated PTEN repression in a murine glioma model both enhances de novo tumor formation and precludes loss of heterozygosity and the PTEN locus. Our results document a new epigenetic mechanism for PTEN regulation in glioma and further highlight dysregulation of Akt signaling as crucial to the development of these tumors.

Suppression of cell growth and invasion by miR-205 in breast cancer

MicroRNAs (miRNAs) are endogenous, small, non-coding RNAs, which are capable of silencing gene expression at the post-transcriptional level. In this study, we report that miR-205 is significantly underexpressed in breast tumor compared to the matched normal breast tissue. Similarly, breast cancer cell lines, including MCF-7 and MDA-MB-231, express a lower level miR-205 than the non-malignant MCF-10A cells. Of interest, ectopic expression of miR-205 significantly inhibits cell proliferation and anchorage independent growth, as well as cell invasion. Furthermore, miR-205 was shown to suppress lung metastasis in an animal model. Finally, western blot combined with the luciferase reporter assays demonstrate that ErbB3 and vascular endothelial growth factor A (VEGF-A) are direct targets for miR-205, and this miR-205-mediated suppression is likely through the direct interaction with the putative miR-205 binding site in the 3'-untranslated region (3'-UTR) of ErbB3 and VEGF-A. Together, these results suggest that miR-205 is a tumor suppressor in breast cancer.

BMP-6 inhibits microRNA-21 expression in breast cancer through repressing deltaEF1 and AP-1

MicroRNAs (miRNAs), which are small noncoding RNA molecules, play important roles in the post-transcriptional regulation process. The microRNA-21 gene (miR-21) has been reported to be highly expressed in various solid tumors, including breast cancer. Bone morphogenetic protein-6 (BMP-6) has been identified as an inhibitor of breast cancer epithelial-mesenchymal transition (EMT) through rescuing E-cadherin expression. We initiated experiments to identify the relationships between miR-21 and BMP-6 in breast cancer progression. Real-time PCR analysis showed that miR-21 expression was very high in MDA-MB-231 cells that expressed little BMP-6. A reverse correlation between BMP-6 and miR-21 was also determined in breast cancer tissue samples. Moreover, BMP-6 inhibited miR-21 transcription in MDA-MB-231 cells. In order to investigate how BMP-6 inhibited the miR-21 promoter (miPPR-21), we constructed a series of miPPR-21 reporters. Luciferase assay results indicated that BMP-6 inhibited miPPR-21 activity through the E2-box and AP-1-binding sites. We also demonstrated that both deltaEF1 and TPA induced miR-21 expression. Using site-directed mutation and CHIP assay, we found that deltaEF1 induced miPPR-21 activity by binding to the E2-box on miPPR-21. Moreover, TPA triggered miPPR-21 activity through the AP-1 binding sites. BMP-6 treatment significantly reduced the binding of these factors to miPPR-21 by decreasing the expression of deltaEF1 and c-Fos/c-Jun. We also demonstrated that BMP-6-induced downregulation of miR-21 modified the activity of PDCD4 3'UTR and inhibited MDA-MB-231 cell invasion. deltaEF1 overexpression and TPA induction blocked this inhibitory effect of BMP-6. In conclusion, BMP-6-induced inhibition of miR-21 suggests that BMP-6 may function as an anti-metastasis factor by a mechanism involving transcriptional repression of miR-21 in breast cancer.

Identification of miR-21 targets in breast cancer cells using a quantitative proteomic approach

MicroRNA (miRNA) play essential roles in biological processes ranging from cellular proliferation to apoptosis. Recently, miRNA have also been implicated in a number of diseases including cancers. However, the targets of most miRNA remain unknown. The majority of reports describing identification of miRNA targets are based on computational approaches or detection of altered mRNA levels despite the fact that most miRNA are thought to regulate their targets primarily at the level of translational inhibition in animals. miR-21 is a miRNA with oncogenic activity that is involved in various cancer-related processes such as invasion and migration. Given the importance of miR-21 in tumorigenesis, we employed a quantitative proteomic strategy to systematically identify potential targets of miR-21. By knocking down the expression of endogenous miR-21 in MCF-7 breast cancer cells, we observed an increase in the abundance of 58 proteins, implying that they could be potential targets of miR-21. Validation of 12 of these candidate targets in luciferase assays showed that 6 of them were likely direct targets of miR-21. Importantly, the mRNA of the majority of the candidate targets tested did not show a concomitant increase in abundance. Overall, our results demonstrate that miR-21 affects the expression of many of its targets through translational inhibition and highlights the utility of proteomic approaches for identifying miRNA targets.

Genomic profiling of microRNAs in bladder cancer: miR-129 is associated with poor outcome and promotes cell death in vitro

microRNAs (miRNA) are involved in cancer development and progression, acting as tumor suppressors or oncogenes. Here, we profiled the expression of 290 unique human miRNAs in 11 normal and 106 bladder tumor samples using spotted locked nucleic acid-based oligonucleotide microarrays. We identified several differentially expressed miRNAs between normal urothelium and cancer and between the different disease stages. miR-145 was found to be the most down-regulated in cancer compared with normal, and miR-21 was the most up-regulated in cancer. Furthermore, we identified miRNAs that significantly correlated to the presence of concomitant carcinoma in situ. We identified several miRNAs with prognostic potential for predicting disease progression (e.g., miR-129, miR-133b, and miR-518c*). We localized the expression of miR-145, miR-21, and miR-129 to urothelium by in situ hybridization. We then focused on miR-129 that exerted significant growth inhibition and induced cell death upon transfection with a miR-129 precursor in bladder carcinoma cell lines T24 and SW780 cells. Microarray analysis of T24 cells after transfection showed significant miR-129 target down-regulation (P = 0.0002) and pathway analysis indicated that targets were involved in cell death processes. By analyzing gene expression data from clinical tumor samples, we identified significant expression changes of target mRNA molecules related to the miRNA expression. Using luciferase assays, we documented a direct link between miR-129 and the two putative targets GALNT1 and SOX4. The findings reported here indicate that several miRNAs are differentially regulated in bladder cancer and may form a basis for clinical development of new biomarkers for bladder cancer.

Transcriptome-wide prediction of miRNA targets in human and mouse using FASTH

Transcriptional regulation by microRNAs (miRNAs) involves complementary base-pairing at target sites on mRNAs, yielding complex secondary structures. Here we introduce an efficient computational approach and software (FASTH) for genome-scale prediction of miRNA target sites based on minimizing the free energy of duplex structure. We apply our approach to identify miRNA target sites in the human and mouse transcriptomes. Our results show that short sequence motifs in the 5′ end of miRNAs frequently match mRNAs perfectly, not only at validated target sites but additionally at many other, energetically favourable sites. High-quality matching regions are abundant and occur at similar frequencies in all mRNA regions, not only the 3′UTR. About one-third of potential miRNA target sites are reassigned to different mRNA regions, or gained or lost altogether, among different transcript isoforms from the same gene. Many potential miRNA target sites predicted in human are not found in mouse, and vice-versa, but among those that do occur in orthologous human and mouse mRNAs most are situated in corresponding mRNA regions, i.e. these sites are themselves orthologous. Using a luciferase assay in HEK293 cells, we validate four of six predicted miRNA-mRNA interactions, with the mRNA level reduced by an average of 73%. We demonstrate that a thermodynamically based computational approach to prediction of miRNA binding sites on mRNAs can be scaled to analyse complete mammalian transcriptome datasets. These results confirm and extend the scope of miRNA-mediated species- and transcript-specific regulation in different cell types, tissues and developmental conditions.

Expression of miR-21 and its targets (PTEN, PDCD4, TM1) in flat epithelial atypia of the breast in relation to ductal carcinoma in situ and invasive carcinoma

BACKGROUND

Flat epithelial atypia (FEA) of the breast is characterised by a few layers of mildly atypical luminal epithelial cells. Genetic changes found in ductal carcinoma in situ (DCIS) and invasive ductal breast cancer (IDC) are also found in FEA, albeit at a lower concentration. So far, miRNA expression changes associated with invasive breast cancer, like miR-21, have not been studied in FEA.

METHODS

We performed miRNA in-situ hybridization (ISH) on 15 cases with simultaneous presence of normal breast tissue, FEA and/or DCIS and 17 additional cases with IDC. Expression of the miR-21 targets PDCD4, TM1 and PTEN was investigated by immunohistochemistry.

RESULTS

Two out of fifteen cases showed positive staining for miR-21 in normal breast ductal epithelium, seven out of fifteen cases were positive in the FEA component and nine out of twelve cases were positive in the DCIS component. A positive staining of miR-21 was observed in 15 of 17 IDC cases. In 12 cases all three components were present in one tissue block and an increase of miR-21 from normal breast to FEA and to DCIS was observed in five cases. In three cases the FEA component was negative, whereas the DCIS component was positive for miR-21. In three other cases, normal, FEA and DCIS components were negative for miR-21 and in the last case all three components were positive. Overall we observed a gradual increase in percentage of miR-21 positive cases from normal, to FEA, DCIS and IDC. Immunohistochemical staining for PTEN revealed no obvious changes in staining intensities in normal, FEA, DCIS and IDC. Cytoplasmic staining of PDCD4 increased from normal to IDC, whereas, the nuclear staining decreased. TM1 staining decreased from positive in normal breast to negative in most DCIS and IDC cases. In FEA, the staining pattern for TM1 was similar to normal breast tissue.

CONCLUSION

Upregulation of miR-21 from normal ductal epithelial cells of the breast to FEA, DCIS and IDC parallels morphologically defined carcinogenesis. No clear relation was observed between the staining pattern of miR-21 and its previously reported target genes.

Up-regulation of microRNA in bladder tumor tissue is not common

MicroRNAs (miRNAs) have recently been shown to down-regulate gene expression by targeting mRNA translation and to play a critical role in tumorigenesis; how they regulate bladder tumor development, particularly in patients, is, however, poorly understood. The difference in miRNA expression in a bladder tumor compared with healthy tissue from the same patients was examined using microRNA arrays in seven patients. Here, we showed that up-regulation of miRNA was not commonly found in this limited number of patients, and four miRNAs (miR-26a, miR-29c, miR-30c, miR-30e-5p) were down-regulated as a common marker in patients with a 1-3 grade of disease. Our data suggest that instead of up-regulation of carcinogenic miRNAs, loss of regulation of these miRNA may be critical for bladder tumor development in patients.

MicroRNAs: novel regulators in the hallmarks of human cancer

MicroRNAs (miRNAs) are small non-coding RNAs of 18-25 nucleotides in length that function as negative regulators. miRNAs post-transcriptionally regulate gene expression by either inhibiting mRNA translation or inducing mRNA degradation, and participate in a wide variety of physiological and pathological cellular processes. Recent reports have revealed that the deregulation of miRNAs correlates with various human cancers and is involved in the initiation and progression of human cancers. miRNAs can act as oncogenes or tumor suppressors to inhibit the expression of cancer-related target genes and to promote or suppress tumorigenesis in various tissues. Therefore, abnormal miRNA expression can be regarded as a common feature of human cancers, and the identification of miRNAs and their respective targets may provide potential diagnostic and prognostic tumor biomarkers and new therapeutic strategies to treat cancers. In the present review, we discuss the emerging roles of miRNAs in the hallmarks of human cancers.

Altered miRNA expression in sputum for diagnosis of non-small cell lung cancer

Analysis of molecular genetic markers in biological fluids has been proposed as a useful tool for cancer diagnosis. MicroRNAs (miRNAs) are small regulatory RNAs that are frequently dysregulated in lung cancer and have shown promise as tissue-based markers for its prognostication. The aim of this study was to determine whether aberrant miRNA expression can be used as a marker in sputum specimen for the diagnosis of non-small cell lung cancer (NSCLC).

EXPERIMENTAL DESIGN

expressions of mature miRNAs, mir-21 and mir-155, were examined by real-time reverse transcription polymerase chain reaction (RT-PCR) and normalized to that of control miRNA, U6B, in sputum of 23 patients with NSCLC and 17 cancer-free subjects. The data was compared with conventional sputum cytology for the diagnosis of lung cancer. All endogenous miRNAs were present in sputum in a remarkably stable form and sensitively and specifically detected by real-time RT-PCR. Mir-21 expression in the sputum specimens was significantly higher in cancer patients (76.32+/-9.79) than cancer-free individuals (62.24+/-3.82) (P<0.0001). Furthermore, overexpression of mir-21 showed highly discriminative receiver-operator characteristic (ROC) curve profile, clearly distinguishing cancer patients from cancer-free subjects with areas under the ROC curve at 0.902+/-0.054. Detection of mir-21 expression produced 69.66% sensitivity and 100.00% specificity in diagnosis of lung cancer, as compared with 47.82% sensitivity and 100.00% specificity by sputum cytology. The measurement of altered miRNA expression in sputum could be a useful noninvasive approach for the diagnosis of lung cancer.

Genetic alterations and oncogenic pathways associated with breast cancer subtypes

Breast cancers can be divided into subtypes with important implications for prognosis and treatment. We set out to characterize the genetic alterations observed in different breast cancer subtypes and to identify specific candidate genes and pathways associated with subtype biology. mRNA expression levels of estrogen receptor, progesterone receptor, and HER2 were shown to predict marker status determined by immunohistochemistry and to be effective at assigning samples to subtypes. HER2(+) cancers were shown to have the greatest frequency of high-level amplification (independent of the ERBB2 amplicon itself), but triple-negative cancers had the highest overall frequencies of copy gain. Triple-negative cancers also were shown to have more frequent loss of phosphatase and tensin homologue and mutation of RB1, which may contribute to genomic instability. We identified and validated seven regions of copy number alteration associated with different subtypes, and used integrative bioinformatics analysis to identify candidate oncogenes and tumor suppressors, including ERBB2, GRB7, MYST2, PPM1D, CCND1, HDAC2, FOXA1, and RASA1. We tested the candidate oncogene MYST2 and showed that it enhances the anchorage-independent growth of breast cancer cells. The genome-wide and region-specific differences between subtypes suggest the differential activation of oncogenic pathways.

MicroRNA-21 modulates biological functions of pancreatic cancer cells including their proliferation, invasion, and chemoresistance

Due to the poor prognosis of pancreatic cancer, novel diagnostic modalities for early diagnosis and new therapeutic strategy are urgently needed. Recently, microRNA-21 (miR-21) was reported to be strongly overexpressed in pancreatic cancer as well as in other solid cancers. We investigated the functional roles of miR-21, which have not been fully elucidated in pancreatic cancer. miR-21 expression was assessed in pancreatic cancer cell lines (14 cancer cell lines, primary cultures of normal pancreatic epithelial cells and fibroblasts, and a human normal pancreatic ductal epithelial cell line) and pancreatic tissue samples (25 cancer tissues and 25 normal tissues) by quantitative real-time reverse transcription-PCR amplification. Moreover, we investigated the proliferation, invasion, and chemoresistance of pancreatic cancer cells transfected with miR-21 precursor or inhibitor. miR-21 was markedly overexpressed in pancreatic cancer cells compared with nonmalignant cells, and miR-21 in cancer tissues was much higher than in nonmalignant tissues. The cancer cells transfected with the miR-21 precursor showed significantly increased proliferation, Matrigel invasion, and chemoresistance for gemcitabine compared with the control cells. In contrast, inhibition of miR-21 decreased proliferation, Matrigel invasion, and chemoresistance for gemcitabine. Moreover, miR-21 positively correlated with the mRNA expression of invasion-related genes, matrix metalloproteinase-2 and -9, and vascular endothelial growth factor. These data suggest that miR-21 expression is increased in pancreatic cancer cells and that miR-21 contributes to the cell proliferation, invasion, and chemoresistance of pancreatic cancer.

Up-regulation of miR-21 by HER2/neu signaling promotes cell invasion

The cell surface receptor tyrosine kinase HER2/neu enhances tumor metastasis. Recent studies suggest that deregulated microRNA (miRNA) expression promotes invasion and metastasis of cancer cells; we therefore explored the possibility that HER2/neu signaling induces the expression of specific miRNAs involved in this process. We identified a putative oncogenic miRNA, miR-21, whose expression is correlated with HER2/neu up-regulation and is functionally involved in HER2/neu-induced cell invasion. We show that miR-21 is up-regulated via the MAPK (ERK1/2) pathway upon stimulation of HER2/neu signaling in breast cancer cells, and overexpression of other ERK1/2 activators such as RASV12 or ID-1 is sufficient to induce miR-21 up-regulation in HER2/neu-negative breast cancer cells. Furthermore, the metastasis suppressor protein PDCD4 (programmed cell death 4) is down-regulated by miR-21 in breast cancer cells expressing HER2/neu. Our data reveal a mechanism for HER2/neu-induced cancer cell invasion via miRNA deregulation. In addition, our results identify miR-21 as a potential therapeutic target for the prevention of breast cancer invasion and metastasis.

MicroRNAs and cancer--new paradigms in molecular oncology

The 'classic' view of molecular oncology indicates that cancer is a genetic disease involving tumor suppressor and oncogenic proteins. However, in the recent years, it has been demonstrated that small regulatory non-coding RNAs (ncRNAs) named microRNAs (miRNAs) are involved in human tumorigenesis, thus revealing a new layer in the molecular architecture of human cancer. Gene expression studies revealed that hundreds of miRNAs are deregulated in cancer cells and functional studies clarified that miRNAs are involved in all the molecular and biological processes that drive tumorigenesis. Here, we summarize the recent advances in miRNA involvement in human cancer and illustrate the benefits of using these knowledge for medical practice. New diagnostic classifiers based on miRNAs will soon be available for medical practitioners and, even more importantly, miRNAs may become novel anti-cancer tools.

MicroRNA-21 is up-regulated in allergic airway inflammation and regulates IL-12p35 expression

Allergic airway inflammation is characterized by marked in situ changes in gene and protein expression, yet the role of microRNAs (miRNAs), a new family of key mRNA regulatory molecules, in this process has not yet been reported. Using a highly sensitive microarray-based approach, we identified 21 miRNAs with differential expression between doxycycline-induced lung-specific IL-13 transgenic mice (with allergic airway inflammation) and control mice. In particular, we observed overexpression of miR-21 and underexpression of miR-1 in the induced IL-13 transgenic mice compared with control mice. These findings were validated in two independent models of allergen-induced allergic airway inflammation and in IL-4 lung transgenic mice. Although IL-13-induced miR-21 expression was IL-13Ralpha1 dependent, allergen-induced miR-21 expression was mediated mainly independent of IL-13Ralpha1 and STAT6. Notably, predictive algorithms identified potential direct miR-21 targets among IL-13-regulated lung transcripts, such as IL-12p35 mRNA, which was decreased in IL-13 transgenic mice. Introduction of pre-miR-21 dose dependently inhibited cellular expression of a reporter vector harboring the 3'-untranslated region of IL-12p35. Moreover, mutating miR-21 binding sites in IL-12p35 3'-untranslated region abrogated miR-21-mediated repression. In summary, we have identified a miRNA signature in allergic airway inflammation, which includes miR-21 that modulates IL-12, a molecule germane to Th cell polarization.

Emerging functions of microRNAs in glioblastoma

Distinct patterns of microRNA expression have been observed in glioblastomas. The functional significance of some of these microRNAs is beginning to emerge. This data indicates that microRNAs play roles in multiple hallmark biological characteristics of glioblastoma, including cell proliferation, invasion, glioma stem cell behavior, and angiogenesis. Research in this area is quickly gathering pace and is illuminating important aspects of the disease that may ultimately lead to novel therapeutic interventions, as well as diagnostic and prognostic tools for brain tumors.

MicroRNA expression ratio is predictive of head and neck squamous cell carcinoma

PURPOSE

The involvement of microRNAs in cancer and their potential as biomarkers of diagnosis and prognosis are becoming increasingly appreciated. We sought to identify microRNAs altered in head and neck squamous cell carcinoma (HNSCC) and to determine whether microRNA expression is predictive of disease.

EXPERIMENTAL DESIGN

RNA isolated from fresh-frozen primary tumors, fresh-frozen nondiseased head and neck epithelial tissues, and HNSCC cell lines was profiled for the expression of 662 microRNAs by microarray. The microRNAs that were both differentially expressed on the array and by quantitative reverse transcription-PCR were subsequently validated by quantitative reverse transcription-PCR using a total of 99 HNSCC samples and 14 normal epithelia.

RESULTS

A marked difference in microRNA expression pattern was observed between tumors and cell lines. Eighteen microRNAs were significantly altered in their expression between normal tissues and tumors. Four of these microRNAs were validated in the larger sample series, and each showed significant differential expression (P < 0.0001). Furthermore, an expression ratio of miR-221:miR-375 showed a high sensitivity (0.92) and specificity (0.93) for disease prediction.

CONCLUSIONS

These data suggest that cultured tumor cell lines are inappropriate for microRNA biomarker identification and that the pattern of microRNA expression in primary head and neck tissues is reflective of disease status, with certain microRNAs exhibiting strong predictive potential. These results indicate that miR-221 and miR-375 should be evaluated further as diagnostic biomarkers because they may hold utility in defining broadly responsive prevention and treatment strategies for HNSCC.

MicroRNA involvement in hepatocellular carcinoma

Hepatocellular carcinoma (HCC) is the third cause of cancer-related death worldwide. Curative options for HCC are limited and exclusively available for patients carrying an early stage HCC. In advanced stages, traditional chemotherapy proved to be only marginally effective or even toxic. Thus, the identification of new treatment options is needed. New targets for non-conventional treatment will necessarily take advantage of progresses on the molecular pathogenesis of HCC. MicroRNAs (miRNAs) are a group of tiny RNAs with a fundamental role in the regulation of gene expression. Aberrant expression of several miRNAs was found to be involved in human hepatocarcinogenesis. miRNA expression signatures were correlated with bio-pathological and clinical features of HCC. In some cases, aberrantly expressed miRNAs could be linked to cancer-associated pathways, indicating a direct role in liver tumourigenesis. For example, up-regulation of mir-221 and mir-21 could promote cell cycle progression, reduce cell death and favour angiogenesis and invasion. These findings suggest that miRNAs could become novel molecular targets for HCC treatment. The demonstration of in vivo efficacy and safety of anti-miRNA compounds has opened the way to their use in clinical trials.

MicroRNAs: control and loss of control in human physiology and disease

Analysis of the human genome indicates that a large fraction of the genome sequences are RNAs that do not encode any proteins, also known as non-coding RNAs. MicroRNAs (miRNAs) are a group of small non-coding RNA molecules 20-22 nucleotides (nt) in length that are predicted to control the activity of approximately 30% of all protein-coding genes in mammals. miRNAs play important roles in many diseases, including cancer, cardiovascular disease, and immune disorders. The expression of miRNAs can be regulated by epigenetic modification, DNA copy number change, and genetic mutations. miRNAs can serve as a valuable therapeutic target for a large number of diseases. For miRNAs with oncogenic capabilities, potential therapies include miRNA silencing, antisense blocking, and miRNA modifications. For miRNAs with tumor suppression functions, overexpression of those miRNAs might be a useful strategy to inhibit tumor growth. In this review, we discuss the current progress of miRNA research, regulation of miRNA expression, prediction of miRNA targets, and regulatory role of miRNAs in human physiology and diseases, with a specific focus on miRNAs in pancreatic cancer, liver cancer, colorectal cancer, cardiovascular disease, the immune system, and infectious disease. This review provides valuable information for clinicians and researchers who want to recognize the newest advances in this new field and identify possible lines of investigation in miRNAs as important mediators in human physiology and diseases.

MicroRNAs--the micro steering wheel of tumour metastases

Recently, microRNAs (miRNAs) have been discovered to have a role in metastasis. Here we describe how miRNAs are involved in advanced stages of tumour progression, stressing their roles as metastasis activators or suppressors, and discuss their possible use in the clinic as predictive markers and as therapeutic strategies for patients with metastases. Furthermore, we develop the concept that the same miRNAs could be involved both in the cancer stem cell phenotype and in the ability of specific cancer cells to produce metastases, thus representing a mechanistic link between the initial and the final steps of tumorigenesis.

microRNA-205 regulates HER3 in human breast cancer

An increasing amount of experimental evidence shows that microRNAs can have a causal role in breast cancer tumorigenesis as a novel class of oncogenes or tumor suppressor genes, depending on the targets they regulate. HER2 overexpression is a hallmark of a particularly aggressive subset of breast tumors, and its activation is strictly dependent on the trans-interaction with other members of HER family; in particular, the activation of the PI3K/Akt survival pathway, so critically important in tumorigenesis, is predominantly driven through phosphorylation of the kinase-inactive member HER3. Here, we show that miR-205, down-modulated in breast tumors compared with normal breast tissue, directly targets HER3 receptor, and inhibits the activation of the downstream mediator Akt. The reintroduction of miR-205 in SKBr3 cells inhibits their clonogenic potential and increases the responsiveness to tyrosine-kinase inhibitors Gefitinib and Lapatinib, abrogating the HER3-mediated resistance and restoring a potent proapoptotic activity. Our data describe miR-205 as a new oncosuppressor gene in breast cancer, able to interfere with the proliferative pathway mediated by HER receptor family. Our study also provides experimental evidence suggesting that miR-205 can improve the responsiveness to specific anticancer therapies.

MicroRNA-21 regulates the proliferation and invasion in esophageal squamous cell carcinoma

PURPOSE

MicroRNAs are approximately 22 nucleotide noncoding RNA molecules that posttranscriptionally regulate gene expression. The aim of this study was (a) to determine a role of microRNA-21 in esophageal squamous cell carcinoma and (b) to elucidate the regulation of the programmed cell death 4 (PDCD4) gene by microRNA-21.

EXPERIMENTAL DESIGN

MicroRNA-21 expression was investigated in 20 matched normal esophageal epitheliums and esophageal squamous cell carcinomas and seven esophageal squamous cell carcinoma cell lines (TE6, TE8, TE10, TE11, TE12, TE14, KYSE30) by TaqMan quantitative real-time PCR and in situ hybridization. To evaluate the role of microRNA-21, cell proliferation and invasion were analyzed with anti-microRNA-21-transfected cells. In addition, the regulation of PDCD4 by microRNA-21 was elucidated to identify the mechanisms of this regulation.

RESULTS

Of 20 paired samples, 18 cancer tissues overexpressed microRNA-21 in comparison with matched normal epitheliums. Specifically, patients with lymph node metastasis or venous invasion showed significantly high expression of microRNA-21. In situ hybridization for microRNA-21 showed strong positive staining in paraffin-embedded esophageal squamous cell carcinoma tissues. All seven esophageal squamous cell carcinoma cell lines also overexpressed microRNA-21, and anti-microRNA-21-transfected cells showed significant reduction in cellular proliferation and invasion. The PDCD4 protein levels in esophageal squamous cell carcinoma cells have an inverse correlation with microRNA-21 expression. Anti-microRNA-21-transfected cells increased PDCD4 protein expression without changing the PDCD4 mRNA level and increased a luciferase-reporter activity containing the PDCD4-3' untranslated region construct.

CONCLUSIONS

MicroRNA-21 targets PDCD4 at the posttranscriptional level and regulates cell proliferation and invasion in esophageal squamous cell carcinoma. It may serve as a novel therapeutic target in esophageal squamous cell carcinoma.

Gfi1 regulates miR-21 and miR-196b to control myelopoiesis

The zinc finger protein growth factor independent-1 (Gfi1) is a transcriptional repressor that is critically required for normal granulocytic differentiation. GFI1 loss-of-function mutations are found in some patients with severe congenital neutropenia (SCN). The SCN-associated GFI1-mutant proteins act as dominant negatives to block granulopoiesis through selective deregulation of a subset of GFI1 target genes. Here we show that Gfi1 is a master regulator of microRNAs, and that deregulated expression of these microRNAs recapitulates a Gfi1 loss-of-function block to granulocyte colony-stimulating factor (G-CSF)-stimulated granulopoiesis. Specifically, bone marrow cells from a GFI1-mutant SCN patient and Gfi1(-/-) mice display deregulated expression of miR-21 and miR-196B expression. Flow cytometric analysis and colony assays reveal that the overexpression or depletion of either miR induces changes in myeloid development. However, coexpression of miR-21 and miR-196b (as seen in Gfi1(-/-) mice and a GFI1N382S SCN patient) completely blocks G-CSF-induced granulopoiesis. Thus, our results not only identify microRNAs whose regulation is required during myelopoiesis, but also provide an example of synergy in microRNA biologic activity and illustrate potential mechanisms underlying SCN disease pathogenesis.

Diagnostic assay based on hsa-miR-205 expression distinguishes squamous from nonsquamous non-small-cell lung carcinoma

PURPOSE

Recent advances in treatment of lung cancer require greater accuracy in the subclassification of non-small-cell lung cancer (NSCLC). Targeted therapies which inhibit tumor angiogenesis pose higher risk for adverse response in cases of squamous cell carcinoma. Interobserver variability and the lack of specific, standardized assays limit the current abilities to adequately stratify patients for such treatments. In this study, we set out to identify specific microRNA biomarkers for the identification of squamous cell carcinoma, and to use such markers for the development of a standardized assay.

PATIENTS AND METHODS

High-throughput microarray was used to measure microRNA expression levels in 122 adenocarcinoma and squamous NSCLC samples. A quantitative real-time polymerase chain reaction (qRT-PCR) platform was used to verify findings in an independent set of 20 NSCLC formalin-fixed, paraffin-embedded (FFPE) samples, and to develop a diagnostic assay using an additional set of 27 NSCLC FFPE samples. The assay was validated using an independent blinded cohort consisting of 79 NSCLC FFPE samples.

RESULTS

We identified hsa-miR-205 as a highly specific marker for squamous cell lung carcinoma. A microRNA-based qRT-PCR assay that measures expression of hsa-miR-205 reached sensitivity of 96% and specificity of 90% in the identification of squamous cell lung carcinomas in an independent blinded validation set.

CONCLUSION

Hsa-miR-205 is a highly accurate marker for lung cancer of squamous histology. The standardized diagnostic assay presented here can provide highly accurate subclassification of NSCLC patients.

Molecular assays for the detection of microRNAs in prostate cancer

Background

MicroRNAs (miRNAs) are small non-coding RNAs (about 21 to 24 nucleotides in length) that effectively reduce the translation of their target mRNAs. Several studies have shown miRNAs to be differentially expressed in prostate cancer, many of which are found in fragile regions of chromosomes. Expression profiles of miRNAs can provide information to separate malignancies based upon stage, progression and prognosis. Here we describe research prototype assays that detect a number of miRNA sequences with high analytical sensitivity and specificity, including miR-21, miR-182, miR-221 and miR-222, which were identified through expression profiling experiments with prostate cancer specimens. The miRNAs were isolated, amplified and quantified using magnetic bead-based target capture and a modified form of Transcription-Mediated Amplification (TMA).

Results

Analytical sensitivity and specificity were demonstrated in model system experiments using synthetic mature microRNAs or in vitro miRNA hairpin precursor transcripts. Research prototype assays for miR-21, miR-182, miR-221 and miR-222 provided analytical sensitivities ranging from 50 to 500 copies of target per reaction in sample transport medium. Specific capture and detection of mature miR-221 from complex samples was demonstrated in total RNA isolated from human prostate cancer cell lines and xenografts.

Conclusion

Research prototype real-time TMA assays for microRNAs provide accurate and reproducible quantitation using 10 nanograms of input total RNA. These assays can also be used directly with tissue specimens, without the need for a preanalytic RNA isolation step, and thus provide a high-throughput method of microRNA profiling in clinical specimens.

Tropomyosin as a regulator of cancer cell transformation

Tropomyosins (Tms) are among the most studied structural proteins of the actin cytoskeleton that are implicated in neoplastic-specific alterations in actin filament organization. Decreased expression of specific nonmuscle Tm isoforms is commonly associated with the transformed phenotype. These changes in Tm expression appear to contribute to the rearrangement of microfilament bundles and morphological alterations, increased cell motility and oncogenic signaling properties of transformed cells. Below we review aspects of Tm biology as it specifically relates to transformation and cancer including its expression in culture models of transformed cells and human tumors, mechanisms that regulate Tm expression and the role of Tm in oncogenic signaling.

MicroRNAs: novel biomarkers for human cancer

BACKGROUND

MicroRNAs (miRNAs), small RNA molecules of approximately 22 nucleotides, have been shown to be up- or downregulated in specific cell types and disease states. These molecules have become recognized as one of the major regulatory gatekeepers of coding genes in the human genome.

CONTENT

We review the structure, nomenclature, mechanism of action, technologies used for miRNA detection, and associations of miRNAs with human cancer. miRNAs are produced in a tissue-specific manner, and changes in miRNA within a tissue type can be correlated with disease status. miRNAs appear to regulate mRNA translation and degradation via mechanisms that are dependent on the degree of complementarity between the miRNA and mRNA molecules. miRNAs can be detected via several methods, such as microarrays, bead-based arrays, and quantitative real-time PCR. The tissue concentrations of specific miRNAs have been associated with tumor invasiveness, metastatic potential, and other clinical characteristics for several types of cancers, including chronic lymphocytic leukemia, and breast, colorectal, hepatic, lung, pancreatic, and prostate cancers.

SUMMARY

By targeting and controlling the expression of mRNA, miRNAs can control highly complex signal-transduction pathways and other biological pathways. The biologic roles of miRNAs in cancer suggest a correlation with prognosis and therapeutic outcome. Further investigation of these roles may lead to new approaches for the categorization, diagnosis, and treatment of human cancers.

A study of microRNAs in silico and in vivo: diagnostic and therapeutic applications in cancer

There is emerging evidence of the production in human tumors of abnormal levels of microRNAs (miRNAs), which have been assigned oncogenic and/or tumor-suppressor functions. While some miRNAs commonly exhibit altered amounts across tumors, more often, different tumor types produce unique patterns of miRNAs, related to their tissue of origin. The role of miRNAs in tumorigenesis underscores their value as mechanism-based therapeutic targets in cancer. Similarly, unique patterns of altered levels of miRNA production provide fingerprints that may serve as molecular biomarkers for tumor diagnosis, classification, prognosis of disease-specific outcomes and prediction of therapeutic responses.

MicroRNA profiling of clear cell renal cell cancer identifies a robust signature to define renal malignancy

MicroRNAs are short single-stranded RNAs that are associated with gene regulation at the transcriptional and translational level. Changes in their expression were found in a variety of human cancers. Only few data are available on microRNAs in clear cell renal cell carcinoma (ccRCC). We performed genome-wide expression profiling of microRNAs using microarray analysis and quantification of specific microRNAs by TaqMan real-time RT-PCR. Matched malignant and non-malignant tissue samples from two independent sets of 12 and 72 ccRCC were profiled. The microarray-based experiments identified 13 over-expressed and 20 down-regulated microRNAs in malignant samples. Expression in ccRCC tissue samples compared with matched non-malignant samples measured by RT-PCR was increased on average by 2.7- to 23-fold for the hsa-miR-16, -452*, -224, -155 and -210, but decreased by 4.8- to 138-fold for hsa-miR-200b, -363, -429, -200c, -514 and -141. No significant associations between these differentially expressed microRNAs and the clinico-pathological factors tumour stage, tumour grade and survival rate were found. Nevertheless, malignant and non-malignant tissue could clearly be differentiated by their microRNA profile. A combination of miR-141 and miR-155 resulted in a 97% overall correct classification of samples. The presented differential microRNA pattern provides a solid basis for further validation, including functional studies.

MicroRNA-mediated regulation of Ubc9 expression in cancer cells

PURPOSE

As an E2-conjugating enzyme for sumoylation, Ubc9 plays a critical role in sumoylation-mediated cellular pathways, ultimately impacting cell growth and cancer development. The aim of this study was to investigate the regulation of Ubc9 in cancer cells.

EXPERIMENTAL DESIGN

Immunohistochemistry and Western blot were used to determine Ubc9 expression in paraffin-embedded tumor tissue and frozen specimens of the matched tumors from the same patient, respectively. To establish the causal relationship between miR-30e and Ubc9 expression, we overexpressed miR-30e and then determined the resultant effects on Ubc9 expression. To determine whether miR-30e directly targets Ubc9, we did luciferase assays using luciferase reporters carrying the 3'-untranslated region (3'-UTR) of the Ubc9 gene.

RESULTS

We found that Ubc9 is up-regulated in breast, head and neck, and lung cancer specimens. In addition, an examination of eight pairs of matched breast tumor specimens by Western blot analysis revealed that, on average, the level of Ubc9 is 5.7-fold higher in tumor than in the matched normal breast tissue. Of interest, we present evidence that Ubc9 is subjected to posttranscriptional regulation by microRNA, and the miR-30 family, such as miR-30e, negatively regulates Ubc9 expression. In contrast to Ubc9, miR-30e is underexpressed in tumors. Moreover, ectopic expression of miR-30e suppresses cell growth, which can be partially reversed by Ubc9. Finally, using luciferase-Ubc9-3'-UTR reporters, we show that Ubc9 is a direct target for miR-30e by interactions with the putative miR-30e binding sites.

CONCLUSION

These results provide new insight into regulation of Ubc9 in cancer cells.

An investigation of microRNAs mapping to breast cancer related genomic gain and loss regions

Various regions of amplification or loss are observed in breast tumors as a manifestation of genomic instability. To date, numerous oncogenes or tumor suppressors on some of these regions have been characterized. An increasing body of evidence suggests that such regions also harbor microRNA genes with crucial regulatory roles in cellular processes and disease mechanisms, including cancer. Here, we investigated 35 microRNAs localized to common genomic gain and/or loss regions in breast cancers. To examine amplification or loss of these microRNAs as a result of genomic instability, we performed semiquantitative duplex polymerase chain reaction in 20 breast cancer cell lines, 2 immortalized mammary cell lines, and 2 normal DNA controls. A comprehensive DNA fold number change data for 35 microRNA genes on chromosomal gain/loss regions are presented in breast cancer cells. A 23% (8/35) of the investigated microRNAs showed significant fold number increases (greater than fourfold) compared to GAPDH in one or more of the breast cell lines. Although no homozygous deletions were detected, fold number decreases indicating potential loss regions were observed for 26% (9/35) of the investigated microRNAs. Such fold number changes may point out some of these microRNAs as potential targets of the genomic instability regions as oncogene and tumor suppressor candidates.

miR-21 and 221 upregulation and miR-181b downregulation in human grade II-IV astrocytic tumors

MicroRNAs (miRNAs) are small noncoding regulatory RNAs that reduce stability and/or translation of fully or partially sequence-complementary target mRNAs. Recent evidence indicates that miRNAs can function both as tumor suppressors and as oncogenes. It has been demonstrated that in glioblastoma multiforme miR-21 and 221 are upregulated whereas miR-128 and 181 are downregulated. Expression of miR-21, 221, 128a, 128b, 128c, 181a, 181b, 181c was studied using real-time quantitative reverse transcriptase polymerase chain reaction and northern blotting for human astrocytic tumors with different grade of malignancy. miR-21 and 221 were overexpressed in glioma samples, whereas miRNA 181b was downregulated compared with normal brain tissue. miRNA-21 was hyperexpressed in all tumor samples whereas higher levels of miRNA-221 were found in high-grade gliomas. This study is the first analysis of miRNAs in astrocytic tumor at different stages of malignancy. The different expression pattern observed in tumors at different stages of malignancy is probably dependent on the cell-specific repertoire of target genes of tumors sharing different molecular pathways activity and suggests miRNAs may have also a place in diagnosis and staging of brain tumors.

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.

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.

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.

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.

The emerging role of microRNAs in cardiac remodeling and heart failure

Recent studies have suggested a potentially important role for a family of tiny regulatory RNAs, known as microRNAs (miRNAs or miRs), in the control of diverse aspects of cardiac function in health and disease. Although the field of miRNA biology is relatively new, there is emerging evidence that miRNAs may play an important role in the pathogenesis of heart failure through their ability to regulate the expression levels of genes that govern the process of adaptive and maladaptive cardiac remodeling. Here, we review the biology of miRNAs in relation to their role in modulating various aspects of the process of cardiac remodeling, as well as discuss the potential application of miRNA biology to the field of heart failure.

The roles of microRNA in cancer and apoptosis

microRNAs (miRNAs) are highly conserved, non-protein-coding RNAs that function to regulate gene expression. In mammals this regulation is primarily carried out by repression of translation. miRNAs play important roles in homeostatic processes such as development, cell proliferation and cell death. Recently the dysregulation of miRNAs has been linked to cancer initiation and progression, indicating that miRNAs may play roles as tumour suppressor genes or oncogenes. The role of miRNAs in apoptosis is not fully understood, however, evidence is mounting that miRNAs are important in this process. The dysregulation of miRNAs involved in apoptosis may provide a mechanism for cancer development and resistance to cancer therapy. This review examines the biosynthesis of miRNA, the mechanisms of miRNA target regulation and the involvement of miRNAs in the initiation and progression of human cancer. It will include miRNAs involved in apoptosis, specifically those miRNAs involved in the regulation of apoptotic pathways and tumour suppressor/oncogene networks. It will also consider emerging evidence supporting a role for miRNAs in modulating sensitivity to anti-cancer therapy.

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.