The let-7 microRNA represses cell proliferation pathways in human cells

MicroRNA expression after ionizing radiation in human endothelial cells

Background

Endothelial cells (EC) in tumor and normal tissue constitute critical radiotherapy targets. MicroRNAs have emerged as master switchers of the cellular transcriptome. Here, we seek to investigate the role of miRNAs in primary human dermal microvascular endothelial cells (HDMEC) after ionizing radiation.

Methods

The microRNA status in HDMEC after 2 Gy radiation treatment was measured using oligo-microarrays covering 361 miRNAs. To functionally analyze the role of radiation-induced differentially regulated miRNAs, cells were transfected with miRNA precursor or inhibitor constructs. Clonogenic survival and proliferation assays were performed.

Results

Radiation up-regulated miRNA expression levels included let-7g, miR-16, miR-20a, miR-21 and miR-29c, while miR-18a, miR-125a, miR-127, miR-148b, miR-189 and miR-503 were down-regulated. We found that overexpression or inhibition of let-7g, miR-189, and miR-20a markedly influenced clonogenic survival and cell proliferation per se. Notably, the radiosensitivity of HDMEC was significantly influenced by differential expression of miR-125a, -127, -189, and let-7g. While miR-125a and miR-189 had a radioprotective effect, miR-127 and let-7g enhanced radiosensitivity in human endothelial cells.

Conclusion

Our data show that ionizing radiation changes microRNA levels in human endothelial cells and, moreover, exerts biological effects on cell growth and clonogenicity as validated in functional assays. The data also suggest that the miRNAs which are differentially expressed after radiation modulate the intrinsic radiosensitivity of endothelial cells in subsequent irradiations. This indicates that miRNAs are part of the innate response mechanism of the endothelium to radiation.

MicroRNA function in cancer: oncogene or a tumor suppressor?

MicroRNAs (miRNAs) are small noncoding, double-stranded RNA molecules that can mediate the expression of target genes with complementary sequences. About 5,300 human genes have been implicated as targets for miRNAs, making them one of the most abundant classes of regulatory genes in humans. MiRNAs recognize their target mRNAs based on sequence complementarity and act on them to cause the inhibition of protein translation by degradation of mRNA. Besides contributing to development and normal function, microRNAs have functions in various human diseases. Given the importance of miRNAs in regulating cellular differentiation and proliferation, it is not surprising that their misregulation is linked to cancer. In cancer, miRNAs function as regulatory molecules, acting as oncogenes or tumor suppressors. Amplification or overexpression of miRNAs can down-regulate tumor suppressors or other genes involved in cell differentiation, thereby contributing to tumor formation by stimulating proliferation, angiogenesis, and invasion; i.e., they act as oncogenes. Similarly, miRNAs can down-regulate different proteins with oncogenic activity; i.e., they act as tumor suppressors. This review will highlight the recent discoveries regarding miRNAs and their importance in cancer.

Hsa-let-7g inhibits proliferation of hepatocellular carcinoma cells by downregulation of c-Myc and upregulation of p16(INK4A)

zMicroRNAs (miRNAs) are endogenously expressed small noncoding RNAs that regulate approximately one-third of human genes at post-transcription level. Previous studies have shown that miRNAs were implicated in many cellular processes and participated in the progress of various tumors including hepatocellular carcinoma (HCC). Among all miRNAs, the let-7 family is well recognized to play pivotal roles in tumorigenesis by functioning as potential growth suppressor. In the present study, we aimed to investigate the role of let-7 family, particularly the hsa-let-7g, in the molecular pathogenesis of HCC. By use of MTT, qPCR, Western blotting and 2-dimensional electrophoresis (2-DE), over-expression of hsa-let-7g was found to inhibit the proliferation of HCC cell line via negative and positive regulations of c-Myc and p16(INK4A) , respectively. The expression of hsa-let-7g was noted to be markedly lowered in the HepG2, Hep3B and Huh7 cells, yet higher in the Bel-7404 HCC cell line. Proliferation of HCC cell line was significantly inhibited after the transfection of hsa-let-7g mimics, while hsa-let-7g inhibitor transfection exerted an opposite effect. Concurrently, the mRNA and protein levels of c-Myc were found significantly decreased in HepG2 cells after transfection of hsa-let-7g mimics, but obviously increased in Bel-7404 cells after transfection of hsa-let-7g inhibitor. As revealed by 2-DE, a significant upregulation of p16(INK4A) was revealed after the gain-of-function study using hsa-let-7g. Therefore, we suggest that hsa-let-7g may act as a tumor suppressor gene that inhibits HCC cell proliferation by downregulating the oncogene, c-Myc, and upregulating the tumor suppressor gene, p16(INK4A) .

Regulation of microRNAs by natural agents: an emerging field in chemoprevention and chemotherapy research

In recent years, microRNAs have received greater attention in cancer research. These small, non-coding RNAs could inhibit target gene expression by binding to the 3' untranslated region of target mRNA, resulting in either mRNA degradation or inhibition of translation. miRNAs play important roles in many normal biological processes; however, studies have also shown that aberrant miRNA expression is correlated with the development and progression of cancers. The miRNAs could have oncogenic or tumor suppressor activities. Moreover, some miRNAs could regulate formation of cancer stem cells and epithelial-mesenchymal transition phenotype of cancer cells which are typically drug resistant. Furthermore, miRNAs could be used as biomarkers for diagnosis and prognosis, and thus miRNAs are becoming emerging targets for cancer therapy. Recent studies have shown that natural agents including curcumin, isoflavone, indole-3-carbinol, 3,3'-diindolylmethane, (-)-epigallocatechin-3-gallate, resveratrol, etc. could alter miRNA expression profiles, leading to the inhibition of cancer cell growth, induction of apoptosis, reversal of epithelial-mesenchymal transition, or enhancement of efficacy of conventional cancer therapeutics. These emerging results clearly suggest that specific targeting of miRNAs by natural agents could open newer avenues for complete eradication of tumors by killing the drug-resistant cells to improve survival outcome in patients diagnosed with malignancies.

Implication of microRNAs in drug resistance for designing novel cancer therapy

Recently, microRNAs (miRNAs) have received increasing attention in the field of cancer research. miRNAs play important roles in many normal biological processes; however, the aberrant miRNA expression and its correlation with the development and progression of cancers is an emerging field. Therefore, miRNAs could be used as biomarkers for diagnosis of cancer and prediction of prognosis. Importantly, some miRNAs could regulate the formation of cancer stem cells and the acquisition of epithelial-mesenchymal transition, which are critically associated with drug resistance. Moreover, some miRNAs could target genes related to drug sensitivity, resulting in the altered sensitivity of cancer cells to anti-cancer drugs. Emerging evidences have also shown that knock-down or re-expression of specific miRNAs by synthetic anti-sense oligonucleotides or pre-miRNAs could induce drug sensitivity, leading to increased inhibition of cancer cell growth, invasion, and metastasis. More importantly, recent studies have shown that natural agents including isoflavone, 3,3'-diindolylmethane, and (-)-epigallocatechin-3-gallate altered miRNA expression profiles, leading to an increased sensitivity of cancer cells to conventional therapeutics. These emerging results suggest that specific targeting of miRNAs by different approaches could open new avenues for cancer treatment through overcoming drug resistance and thereby improve the outcome of cancer therapy.

Characterization of the Melanoma miRNAome by Deep Sequencing

Background

MicroRNAs (miRNAs) are 18–23 nucleotide non-coding RNAs that regulate gene expression in a sequence specific manner. Little is known about the repertoire and function of miRNAs in melanoma or the melanocytic lineage. We therefore undertook a comprehensive analysis of the miRNAome in a diverse range of pigment cells including: melanoblasts, melanocytes, congenital nevocytes, acral, mucosal, cutaneous and uveal melanoma cells.

Methodology/Principal Findings

We sequenced 12 small RNA libraries using Illumina's Genome Analyzer II platform. This massively parallel sequencing approach of a diverse set of melanoma and pigment cell libraries revealed a total of 539 known mature and mature-star sequences, along with the prediction of 279 novel miRNA candidates, of which 109 were common to 2 or more libraries and 3 were present in all libraries.

Conclusions/Significance

Some of the novel candidate miRNAs may be specific to the melanocytic lineage and as such could be used as biomarkers to assist in the early detection of distant metastases by measuring the circulating levels in blood. Follow up studies of the functional roles of these pigment cell miRNAs and the identification of the targets should shed further light on the development and progression of melanoma.

Whole mount in situ hybridization detection of mRNAs using short LNA containing DNA oligonucleotide probes

In situ hybridization is widely used to visualize transcribed sequences in embryos, tissues, and cells. For whole mount detection of mRNAs in embryos, hybridization with an antisense RNA probe is followed by visual or fluorescence detection of target mRNAs. A limitation of this approach is that a cDNA template of the target RNA must be obtained in order to generate the antisense RNA probe. Here we investigate the use of short (12-24 nucleotides) locked nucleic acid (LNA) containing DNA probes for whole mount in situ hybridization detection of mRNAs. Following extensive protocol optimization, we show that LNA probes can be used to localize several mRNAs of varying abundances in chicken embryos. LNA probes also detected alternatively spliced exons that are processed in a tissue specific manner. The use of LNA probes for whole mount in situ detection of mRNAs will enable in silico design and chemical synthesis and will expand the general use of in situ hybridization for studies of transcriptional regulation and alternative splicing.

Computational discovery of miR-TF regulatory modules in human genome

MicroRNAs (miRNAs) are small non-coding RNAs that regulate gene expression at the post-transcriptional level. They play an important role in several biological processes such as cell development and differentiation. Similar to transcription factors (TFs), miRNAs regulate gene expression in a combinatorial fashion, i.e., an individual miRNA can regulate multiple genes, and an individual gene can be regulated by multiple miRNAs. The functions of TFs in biological regulatory networks have been well explored. And, recently, a few studies have explored miRNA functions in the context of gene regulation networks. However, how TFs and miRNAs function together in the gene regulatory network has not yet been examined. In this paper, we propose a new computational method to discover the gene regulatory modules that consist of miRNAs, TFs, and genes regulated by them. We analyzed the regulatory associations among the sets of predicted miRNAs and sets of TFs on the sets of genes regulated by them in the human genome. We found 182 gene regulatory modules of combinatorial regulation by miRNAs and TFs (miR-TF modules). By validating these modules with the Gene Ontology (GO) and the literature, it was found that our method allows us to detect functionally-correlated gene regulatory modules involved in specific biological processes. Moreover, our miR-TF modules provide a global view of coordinated regulation of target genes by miRNAs and TFs.

Advances in understanding the relationship between microRNAs and cholangiocarcinoma

MicroRNAs (miRNAs) are a class of short non-coding RNAs widely distributed in plants and animals. They can inhibit the expression of protein-coding genes by binding to the 3' UTR of mRNAs and inducing either translational repression or mRNA degradation. It has been demonstrated that miRNAs play important roles in regulating cell proliferation, apoptosis and differentiation. In addition, miRNAs can function as oncogenes or tumor suppressor genes and are therefore closely associated with oncogenesis. This review will focus on the biogenesis, silencing mechanism, and biological function of miRNAs, and their roles in the development and progression of cholangiocarcinoma.

Deregulated expression of miR-21, miR-143 and miR-181a in non small cell lung cancer is related to clinicopathologic characteristics or patient prognosis

CONTEXT

MicroRNAs (miRNAs) represent a class of small non-coding RNAs that regulate the gene expressions at the posttranscriptional level, subsequently control crucial physiological processes. Recent evidence demonstrates that some miRNAs have the functions similar to oncogene or tumor suppressors, it may play important roles in tumorigenesis. MiRNA expression profiles may become useful biomarkers for cancer diagnostics, prognosis and prediction of response to treatment, and it could be a powerful tool for cancer prevention and therapeutics.

OBJECTIVE

To explore the global expression profile of miRNAs in non small cell lung cancer (NSCLC) and its potential relevance to clinicopathological characteristics and prognosis.

METHODS

LNA microRNA microarrays were utilized to detect miRNA expression levels in eight surgically removed lung carcinoma tissues (LCT) and their corresponding normal lung tissues (NT). After initial microarray validation by quantitative real-time reverse transcription polymerase chain reaction assays (qRT-PCR), miR-21, miR-143 and miR-181a were selected for further study in another 47 paired LCTs and matched NTs by qRT-PCR using Taqman microRNA assay.

RESULTS

Twenty-seven microRNAs were observed to be deregulated greater than two-fold in LCT compared with NT by microarray. Consistenting with the microarray, the expression level of miR-21 by qRT-PCR was significantly higher in tumor tissues than in adjacent normal tissues (P=0.026); while miR-143 (P=0.000) and miR-181a (P=0.000) were downregulated in LCT. Interestingly, among the 47 NSCLC cases, low level expression of miR-143 was significantly correlated with smoking status (P=0.026), high miR-21 expression (hazard ratio, 5.993; 95% confidence interval, 2.518-14.264; P=0.000) and low miR-181a expression (hazard ratio, 0.328; 95% confidence interval 0.142-0.756; P=0.009) were associated with poor survival, independent of clinical covariates, including TNM staging, lymph note status.

CONCLUSION

Our data thus indicating the potential of miR-21, miR-143 and miR-181a as a novel diagnostic or prognostic biomarker for NSCLC. Besides, these data will guide further studies of specific microRNAs might become potential targets for therapeutic intervention.

miRNA control of tumor cell invasion and metastasis

MicroRNAs have emerged as a novel class of noncoding RNAs that regulate gene expression at the post-translational level in almost every biological event. A large body of evidence indicates that microRNAs regulate the expression of different genes that play an important role in cancer cell invasion, migration and metastasis. In this review, we briefly describe the role of various miRNAs in invasion, migration and metastasis which are essential steps during cancer progression.

Genetic modulation of the Let-7 microRNA binding to KRAS 3'-untranslated region and survival of metastatic colorectal cancer patients treated with salvage cetuximab-irinotecan

There is increasing evidence that the Let-7 microRNA (miRNA) exerts an effect as a tumor suppressor by targeting the KRAS mRNA. The Let-7 complementary site (LCS6) T>G variant in the KRAS 3'-untranslated region weakens Let-7 binding. We analyzed whether the LCS6 variant may be clinically relevant to patients with metastatic colorectal cancer (MCRC) treated with anti-epidermal growth factor receptor (EGFR) therapy. LCS6 genotypes and KRAS/BRAF mutations were determined in the tumor DNA of 134 patients with MCRC who underwent salvage cetuximab-irinotecan therapy. There were 34 G-allele (T/G+G/G) carriers (25%) and 100 T/T genotype carriers (75%). G-allele carriers were significantly more frequent in the KRAS mutation group than in patients with KRAS wild type (P=0.004). In the 121 patients without BRAF V600E mutation, overall survival (OS) and progression-free survival (PFS) times were compared between carriers of the LCS6 G-allele genotypes and carriers of the wild-type T/T genotype. LCS6 G-allele carriers showed worse OS (P=0.001) and PFS (P=0.004) than T/T genotype carriers (confirmed in the multivariate model including the KRAS status). In the exploratory analysis of the 55 unresponsive patients with KRAS mutation, LCS6 G-allele carriers showed adverse OS and PFS times. These findings deserve additional investigations as they may open novel perspectives for the treatment of patients with MCRC.

Non-coding RNAs: regulators of disease

For 50 years the term 'gene' has been synonymous with regions of the genome encoding mRNAs that are translated into protein. However, recent genome-wide studies have shown that the human genome is pervasively transcribed and produces many thousands of regulatory non-protein-coding RNAs (ncRNAs), including microRNAs, small interfering RNAs, PIWI-interacting RNAs and various classes of long ncRNAs. It is now clear that these RNAs fulfil critical roles as transcriptional and post-transcriptional regulators and as guides of chromatin-modifying complexes. Here we review the biology of ncRNAs, focusing on the fundamental mechanisms by which ncRNAs facilitate normal development and physiology and, when dysfunctional, underpin disease. We also discuss evidence that intergenic regions associated with complex diseases express ncRNAs, as well as the potential use of ncRNAs as diagnostic markers and therapeutic targets. Taken together, these observations emphasize the need to move beyond the confines of protein-coding genes and highlight the fact that continued investigation of ncRNA biogenesis and function will be necessary for a comprehensive understanding of human disease.

An estrogen receptor alpha suppressor, microRNA-22, is downregulated in estrogen receptor alpha-positive human breast cancer cell lines and clinical samples

Previous studies have suggested that microRNAs (miRNAs) may play important roles in tumorigenesis, but little is known about the functions of most miRNAs in cancer development. In the present study, we set up a cell-based screen using a luciferase reporter plasmid carrying the whole approximately 4.7 kb 3'-UTR of estrogen receptor alpha (ERalpha) mRNA cotransfected with a synthetic miRNA expression library to identify potential ERalpha-targeting miRNAs. Among all the miRNAs, miR-22 was found to repress robustly the luciferase signal in both HEK-293T and ERalpha-positive MCF-7 cells. Mutation of the target site was found to abrogate this repression effect of miR-22, whereas antagonism of endogenous miR-22 in MDA-MB-231 cells resulted in elevated reporter signals. We assessed the miR-22 expression patterns in five breast cancer cell lines and 23 clinical biopsies and revealed that there is a significant inverse association between the miR-22 levels and ERalpha protein expression. To evaluate the potential of miR-22 as a potential therapeutic intervention, we found that reduction of endogenous ERalpha protein levels and suppression of cancer cell growth could be achieved in MCF-7 cells by miR-22 overexpression in a way that can be recapitulated by the introduction of specific small interfering RNA against ERalpha. The phenomena can be rescued by the reintroduction of ERalpha. Taken together, our data indicate that miR-22 was frequently downregulated in ERalpha-positive human breast cancer cell lines and clinical samples. Direct involvement in the regulation of ERalpha may be one of the mechanisms through which miR-22 could play a pivotal role in the pathogenesis of breast cancer.

Revealing global regulatory perturbations across human cancers

The discovery of pathways and regulatory networks whose perturbation contributes to neoplastic transformation remains a fundamental challenge for cancer biology. We show that such pathway perturbations, and the cis-regulatory elements through which they operate, can be efficiently extracted from global gene expression profiles. Our approach utilizes information-theoretic analysis of expression levels, pathways, and genomic sequences. Analysis across a diverse set of human cancers reveals the majority of previously known cancer pathways. Through de novo motif discovery we associate these pathways with transcription-factor binding sites and miRNA targets, including those of E2F, NF-Y, p53, and let-7. Follow-up experiments confirmed that these predictions correspond to functional in vivo regulatory interactions. Strikingly, the majority of the perturbations, associated with putative cis-regulatory elements, fall outside of known cancer pathways. Our study provides a systems-level dissection of regulatory perturbations in cancer-an essential component of a rational strategy for therapeutic intervention and drug-target discovery.

Analysis of deep sequencing microRNA expression profile from human embryonic stem cells derived mesenchymal stem cells reveals possible role of let-7 microRNA family in downstream targeting of hepatic nuclear factor 4 alpha

Background

Recent literature has revealed that genetic exchange of microRNA between cells can be essential for cell-cell communication, tissue-specificity and developmental processes. In stem cells, as in other cells, this can be accomplished through microvesicles or exosome mediated transfer. However, molecular profiles and functions of microRNAs within the cells and in their exosomes are poorly studied. Next generation sequencing technologies could provide a broad-spectrum of microRNAs and their expression and identify possible microRNA targets. In this work, we performed deep sequencing of microRNAs to understand the profile and expression of the microRNAs in microvesicles and intracellular environment of human embryonic stem cells derived mesenchymal stem cells (hES-MSC).

We outline a workflow pertaining to visualizing, statistical analysis and interpreting deep sequencing data of known intracellular and extracellular microRNAs from hES-MSC). We utilized these results of which directed our attention towards establishing hepatic nuclear factor 4 alpha (HNF4A) as a downstream target of let-7 family of microRNAs.

Results

In our study, significant differences in expression profile of microRNAs were found in the intracellular and extracellular environment of hES-MSC. However, a high level of let-7 family of microRNAs is predominant in both intra- and extra- cellular samples of hES-MSC. Further results derived from visualization of our alignment data and network analysis showed that let-7 family microRNAs could affect the downstream target HNF4A, which is a known endodermal differentiation marker. The elevated presence of let-7 microRNA in both intracellular and extra cellular environment further suggests a possible intercellular signalling mechanism through microvesicles transfer. We suggest that let-7 family microRNAs might play a signalling role via such a mechanism amongst populations of stem cells in maintaining self renewal property by suppressing HNF4A expression. This is in line with recent paradigm where microRNAs regulate self-renewal and differentiation pathways of embryonic stem cells by forming an integral biological network with transcription factors.

Conclusion

In summary, our study using a combination of alignment, statistical and network analysis tools to examine deep sequencing data of microRNAs in hES-MSC has led to a result that (i) identifies intracellular and exosome microRNA expression profiles of hES-MSCwith a possible mechanism of miRNA mediated intercellular regulation by these cells and (ii) placed HNF4A within the cross roads of regulation by the let-7 family of microRNAs.

Computational prediction and experimental validation of evolutionarily conserved microRNA target genes in bilaterian animals

BACKGROUND

In many eukaryotes, microRNAs (miRNAs) bind to complementary sites in the 3'-untranslated regions (3'-UTRs) of target messenger RNAs (mRNAs) and regulate their expression at the stage of translation. Recent studies have revealed that many miRNAs are evolutionarily conserved; however, the evolution of their target genes has yet to be systematically characterized. We sought to elucidate a set of conserved miRNA/target-gene pairs and to analyse the mechanism underlying miRNA-mediated gene regulation in the early stage of bilaterian evolution.

RESULTS

Initially, we extracted five evolutionarily conserved miRNAs (let-7, miR-1, miR-124, miR-125/lin-4, and miR-34) among five diverse bilaterian animals. Subsequently, we designed a procedure to predict evolutionarily conserved miRNA/target-gene pairs by introducing orthologous gene information. As a result, we extracted 31 orthologous miRNA/target-gene pairs that were conserved among at least four diverse bilaterian animals; the prediction set showed prominent enrichment of orthologous miRNA/target-gene pairs that were verified experimentally. Approximately 84% of the target genes were regulated by three miRNAs (let-7, miR-1, and miR-124) and their function was classified mainly into the following categories: development, muscle formation, cell adhesion, and gene regulation. We used a reporter gene assay to experimentally verify the downregulation of six candidate pairs (out of six tested pairs) in HeLa cells.

CONCLUSIONS

The application of our new method enables the identification of 31 miRNA/target-gene pairs that were expected to have been regulated from the era of the common bilaterian ancestor. The downregulation of all six candidate pairs suggests that orthologous information contributed to the elucidation of the primordial set of genes that has been regulated by miRNAs; it was also an efficient tool for the elimination of false positives from the predicted candidates. In conclusion, our study identified potentially important miRNA-target pairs that were evolutionarily conserved throughout diverse bilaterian animals and that may provide new insights into early-stage miRNA functions.

A microRNA expression signature for cervical cancer prognosis

Invasive cervical cancer is a leading cause of cancer death in women worldwide, resulting in about 300,000 deaths each year. The clinical outcomes of cervical cancer vary significantly and are difficult to predict. Thus, a method to reliably predict disease outcome would be important for individualized therapy by identifying patients with high risk of treatment failures before therapy. In this study, we have identified a microRNA (miRNA)-based signature for the prediction of cervical cancer survival. miRNAs are a newly identified family of small noncoding RNAs that are extensively involved in human cancers. Using an established PCR-based miRNA assay to analyze 102 cervical cancer samples, we identified miR-200a and miR-9 as two miRNAs that could predict patient survival. A logistic regression model was developed based on these two miRNAs and the prognostic value of the model was subsequently validated with independent cervical cancers. Furthermore, functional studies were done to characterize the effect of miRNAs in cervical cancer cells. Our results suggest that both miR-200a and miR-9 could play important regulatory roles in cervical cancer control. In particular, miR-200a is likely to affect the metastatic potential of cervical cancer cells by coordinate suppression of multiple genes controlling cell motility.

MicroRNAs reduce tumor growth and contribute to enhance cytotoxicity induced by gefitinib in non-small cell lung cancer

MicroRNAs (miRNAs) have emerged as key post-transcriptional regulators of gene expression, involved in diverse physiological and pathological processes. An oncogenic or tumor-suppressive miRNA may have potential as a therapeutic target to control cancers. Gefitinib is a tyrosine kinase inhibitor that targets epidermal growth factor receptor (EGFR). H460 and A549 cells with EGFR receptor-independent over-activation of protein kinase B (Akt) or extracellular signal-regulated kinases (ERK) are significantly resistant to gefitinib. The first aim of this study was to confirm a role for three miRNAs (let-7a, hsa-miR-126, and hsa-miR-145) in the inhibition of proliferation in non-small cell lung cancer (NSCLC) cells. A second aim was to evaluate three miRNAs for their abilities to overcome cellular resistance and enhance the gefitinib cytotoxicity. The expression of miRNAs was estimated by real-time quantitative reverse transcription polymerase chain reaction (qRT-PCR). Cell proliferation was examined by sulforhodamine B assay and tumor xenografts were measured in SCID/beige mice. The activation of Akt and ERK was observed by Western blotting. Forced expression of individual miRNA suppressed the growth of two cell lines and xenografts. The effect varied among different miRNAs and cells. Restoration of hsa-miR-126 more obviously inhibited cell growth than did restoration of hsa-miR-145 in both cells, and the suppressive effect was more significant in H460 xenografts than in A549 xenografts. Western blotting revealed that the inhibition of cell proliferation resulted from the inhibition of the activation of Akt and ERK. Moreover, forced expression of miRNAs contributed to enhanced cytotoxicity induced by gefitinib in lung cancer cells; especially in hsa-miR-126, the highest value of half max inhibitory (IC50) was increased sixfold. These findings confirm that tumor-suppressive miRNAs can inhibit the growth of NSCLC cells and enhance the targeted agents cytotoxicity, suggesting novel potential approaches to an improvement in chemotherapy.

MicroRNA let-7b regulates neural stem cell proliferation and differentiation by targeting nuclear receptor TLX signaling

Neural stem cell self-renewal and differentiation is orchestrated by precise control of gene expression involving nuclear receptor TLX. Let-7b, a member of the let-7 microRNA family, is expressed in mammalian brains and exhibits increased expression during neural differentiation. However, the role of let-7b in neural stem cell proliferation and differentiation remains unknown. Here we show that let-7b regulates neural stem cell proliferation and differentiation by targeting the stem cell regulator TLX and the cell cycle regulator cyclin D1. Overexpression of let-7b led to reduced neural stem cell proliferation and increased neural differentiation, whereas antisense knockdown of let-7b resulted in enhanced proliferation of neural stem cells. Moreover, in utero electroporation of let-7b to embryonic mouse brains led to reduced cell cycle progression in neural stem cells. Introducing an expression vector of Tlx or cyclin D1 that lacks the let-7b recognition site rescued let-7b-induced proliferation deficiency, suggesting that both TLX and cyclin D1 are important targets for let-7b-mediated regulation of neural stem cell proliferation. Let-7b, by targeting TLX and cyclin D1, establishes an efficient strategy to control neural stem cell proliferation and differentiation.

Novel modulators of senescence, aging, and longevity: Small non-coding RNAs enter the stage

During the last decade evidence has accumulated that the aging process is driven by limited allocation of energy to somatic maintenance resulting in accumulation of stochastic damage. This damage, affecting molecules, cells, and tissues, is counteracted by genetically programmed repair, the efficiency of which thus importantly determines the life and 'health span' of organisms. Therefore, understanding the regulation of gene expression during cellular and organismal aging as well as upon exposure to various damaging events is important to understand the biology of aging and to positively influence the health span. The recent identification of small non-coding RNAs (ncRNAs), has added an additional layer of complexity to the regulation of gene expression with the classes of endogenous small inhibitory RNAs (siRNAs), PIWI-interacting RNAs (piRNAs), QDE1-interacting RNAs (qiRNAs) and microRNAs (miRNAs). Some of these ncRNAs have not yet been identified in mammalian cells and are dependent on RNA-dependent RNA polymerases. The first mammalian enzyme with such activity has only now emerged and surprisingly consists of the catalytic subunit of telomerase (hTERT) together with RMPR, an alternative RNA component. The so far most studied small non-coding RNAs, miRNAs, however, are now increasingly found to operate in the complex network of cellular aging. Recent findings show that (i) miRNAs are regulated during cellular senescence in vitro, (ii) they contribute to tissue regeneration by regulation of stem cell function, and (iii) at least one miRNA modulates the life span of the model organism C. elegans. Additionally, (iv) they act as inhibitors of proteins mediating the insulin/IGF1 and target of rapamycin (TOR) signalling, both of which are conserved modulators of organism life span. Here we will give an overview on the current status of these topics. Since little is so far known on the functions of small ncRNAs in the context of aging and longevity, the entry of the RNA world into the field of biogerontology certainly holds additional surprises and promises. Even more so, as miRNAs are implicated in many age-associated pathologies, and as RNAi and miRNA based therapeutics are on their way to clinics.

microRNA, cell cycle, and human breast cancer

The discovery of microRNAs as a novel class of gene expression regulators has led to a new strategy for disease diagnostics and therapeutics. Cell cycle, cell proliferation, and tumorigenesis are all regulated by microRNAs. Several general principles linking microRNAs and cancer have been recently reviewed; therefore, the current review focuses specifically on the perspective of microRNAs in control of cell cycle, stem cells, and heterotypic signaling, as well as the role of these processes in breast cancer. Altered abundance of cell cycle regulation proteins and aberrant expression of microRNAs frequently coexist in human breast cancers. Altered microRNA expression in breast cancer cell lines is associated with altered cell cycle progression and cell proliferation. Indeed, recent studies have demonstrated a causal role for microRNA in governing breast tumor suppression or collaborative oncogenesis. This review summarizes the current understanding of the role for microRNA in regulating the cell cycle and summarizes the evidence for aberrant microRNA expression in breast cancer. The new evidence for microRNA regulation by annotated genes and the involvement of microRNA in breast cancer metastasis are discussed, as is the potential for microRNA to improve breast cancer diagnosis and therapy.

Lung cancer: a modified epigenome

Epigenetic is the study of heritable changes in gene expression that occur without changes in DNA sequence. This process is important for gene expression and genome stability and its disruption is now thought to play a key role in the onset and progression of numerous tumor types. The most studied epigenetic phenomena includes post-translational modifications in DNA and histone proteins as well as microRN As expression. As epigenetic aberrations are potentially reversible, their correction has emerged as a potential strategy for the treatment of cancer. This review highlights the roles of chromatin epigenetic modifications and of microRN As expression in lung tumorigenesis and discusses the emerging epigenetic therapies which are being developed for the treatment of lung cancer.

MicroRNA Regulation of Embryonic Stem Cell Self-Renewal and Differentiation

Stem cell differentiation requires a complex coordination of events to transition from a self-renewing to a differentiated cell fate. Stem cells can be pluripotent (capable of giving rise to all embryonic lineages), multipotent (possessing the potential to give rise to multiple lineages) and unipotent (capable of given rise to a single cell lineage). Regardless of their potency all stem cells must silence their self-renewal program during differentiation. The self-renewal program can be defined as the integration of external and internal stimuli that enables a cell to proliferate while maintaining its potency. Two hallmarks of the self-renewal program are a self-reinforcing transcriptional network and a specialized cell-cycle profile. In this chapter we discuss the impact of various microRNAs (miRNAs) to either reinforce or inhibit the self-renewal program of stem cells and how this added regulatory layer provides robustness to cell-fate decisions. We will focus on embryonic stem cells (ESCs) describing miRNA function in self-renewal, differentiation and de-differentiation. We will compare and contrast miRNA functions in ESCs with miRNA function in lineage specific somatic stem cells and in cancer.

Solution structure of miRNA:mRNA complex

The use of contemporary nuclear magnetic resonance (NMR) methods in the studies of model systems between microRNA (miRNA) and messenger RNA (mRNA) is reviewed. We describe our studies on structural features of 33-nt RNA model construct between let-7 miRNA and lin-41 mRNA at the second binding site. let-7 miRNA inhibits translation of lin-41 gene through formation of two complexes with the target sequence within 3' untranslated region of lin-41 mRNA in Caenorhabditis elegans. The base pairing, asymmetric internal loops, and adenine bulge in both the complementary sites are important for regulation of gene expression. NMR study on the uniformly (13)C- and (15)N-labeled RNA construct has shown that RNA molecule folds into a stable structure consisting of two stem regions separated by a well-defined asymmetric internal loop. Solution-state NMR can make important contribution toward deeper understanding of assembly, folding, and structural features of miRNA:mRNA complexes.

Regulation of pre-miRNA Processing

microRNAs are endogenously expressed ∼21 nucleotide noncoding RNAs. microRNA-mediated regulation of the translation of specific mRNA is implicated in a range of developmental processes and pathologies. As such, miRNA expression is tightly controlled in normal development by both transcriptional and post-transcriptional mechanisms. This chapter is concerned with the control of pre-miRNA processing of individual miRNAs by specific factors. It is focussed on the regulation of a subset of miRNAs by the RNA-binding protein Lin28/LIN-28. We discuss how Lin28/LIN-28 can sequester pre-let-7 miRNA precursor to prevent Dicer-mediated processing. We describe how interaction of pre-let-7 with Lin28/ LIN-28 leads to pre-let-7 uridylation and subsequent degradation. Finally, we analyze how let-7 and Lin28/LIN-28 together act as a highly conserved developmental switch that controls stem cell differentiation in C. elegans and mammals.

Stem cells in normal development and cancer

In this chapter we provide an overview of stem cells in normal tissues as well as in many different types of cancers. All tissues in the body are derived from organ-specific stem cells that retain the ability to self-renew and differentiate into specific cell types. The cancer stem cell hypothesis suggests that tumors arise from cell populations with dysregulated self-renewal. This may be tissue stem cells or more differentiated cells that acquire self-renewal capabilities. In addition, we outline some useful assays for purification and isolation of cancer stem cells including the dye exclusion side population assay, flow cytometry sorting techniques for identification of putative cancer stem cell markers, tumorspheres assay, aldehyde dehydrogenase activity assay, PKH, and other membrane staining used to label the cancer stem cells, as well as in vivo xenograft transplantation assays. We also examine some of the cell signaling pathways that regulate stem cell self-renewal including the Notch, Hedgehog, HER2/PI3K/Akt/PTEN, and p53 pathways. We also review information demonstrating the involvement of the microenvironment or stem cell niche and its effects on the growth and maintenance of cancer stem cells. Finally, we highlight the therapeutic implications of targeting stem cells by inhibiting these pathways for the treatment and prevention of cancer.

Cross-talk between miRNA and Notch signaling pathways in tumor development and progression

Notch signaling pathways are known to regulate many cellular processes, including cell proliferation, apoptosis, migration, invasion, and angiogenesis, and is one of the most important signaling pathway during normal development. Recently, emerging evidences suggest that microRNAs (miRNAs) can function as key regulators of various biological and pathologic processes during tumor development and progression. Notch signaling has also been reported to be regulated through cross-talk with many pathways and factors where miRNAs appears to play a major role. This article will provide a brief overview of the published evidences for the cross-talks between Notch and miRNAs. Further, we summarize how targeting miRNAs by natural agents could become a novel and safer approach for the prevention of tumor progression and treatment.

RNA degradation compromises the reliability of microRNA expression profiling

Background

MicroRNAs are small non-coding RNAs that post-transcriptionally regulate gene expression and their expression is frequently altered in human diseases, including cancer. To correlate clinically relevant parameters with microRNA expression, total RNA is frequently prepared from samples that were archived for various time periods in frozen tissue banks but, unfortunately, RNA integrity is not always preserved in these frozen tissues. Here, we investigate whether experimentally induced RNA degradation affects microRNA expression profiles.

Results

Tissue samples were maintained on ice for defined time periods prior to total RNA extraction, which resulted in different degrees of RNA degradation. MicroRNA expression was then analyzed by microarray analysis (miCHIP) or microRNA-specific real-time quantitative PCR (miQPCR). Our results demonstrate that the loss of RNA integrity leads to in unpredictability of microRNA expression profiles for both, array-based and miQPCR assays.

Conclusion

MicroRNA expression cannot be reliably profiled in degraded total RNA. For the profiling of microRNAs we recommend use of RNA samples with a RNA integrity number equal to or above seven.

Correlation of overexpression of HMGA1 and HMGA2 with poor tumor differentiation, invasion, and proliferation associated with let-7 down-regulation in retinoblastomas

In addition to RB1, the causative genes involved in the tumorigenesis and progression of retinoblastomas remain to be elucidated. High-mobility group A1 and high-mobility group A2 proteins are expressed at high levels in various benign and malignant tumors and are associated with expressions of malignant phenotypes and poor prognoses. Reduction in let-7 expression levels was detected in cancers; it may be related to high-mobility group A1 and high-mobility group A2 overexpressions. Little is known about the correlations among high-mobility group A1, high-mobility group A2, and let-7 expression and clinicopathologic features of retinoblastoma. In our study, the expressions of high-mobility group A1 and high-mobility group A2 were studied in 44 retinoblastomas by immunohistochemical analysis. Semiquantitative reverse transcription-polymerase chain reaction was used to assay the let-7 expression levels in 28 nontumor retina and 44 tumor samples. Nuclear immunostaining of high-mobility group A1 and high-mobility group A2 was frequently observed in retinoblastomas (68% and 75%, respectively). Expression levels of both high-mobility group A1 and high-mobility group A2 were significantly higher in poorly differentiated retinoblastomas than in well-differentiated retinoblastomas (P < .05 and P < .0001, respectively). In addition, overexpressions of high-mobility group A1 and high-mobility group A2 were more frequently detected in poorly differentiated tumors than in well-differentiated tumors (P < .01 and P = .0001, respectively). High-mobility group A2 expression levels were significantly higher in invasive tumors than in noninvasive tumors (P < .05). In addition, the MIB-1 labeling index was higher in poorly differentiated tumors than in well-differentiated tumors (P < .0001). Our study revealed that high-mobility group A1 and high-mobility group A2 expressions correlated with the MIB-1 labeling index (R = 0.327, P = .029; R = 0.602, P < .0001; respectively). The let-7 was expressed in high levels in all 28 nontumor retina samples. However, reduced expression levels of let-7 were observed in 17 (39%) tumors. A potentially inverse correlation exists between the expression levels of let-7 and high-mobility group A1 (r = -0.247, P = .105). In addition, a significantly inverse association was detected between let-7 and high-mobility group A2 and MIB-1 labeling index (r = -0.31, P = .04; r = -0.392, P = .007, respectively). Our findings imply that the overexpressions of high-mobility group A1, high-mobility group A2, and down-regulation of let-7 may be associated with tumorigenesis and progression of retinoblastomas.

Regression of murine lung tumors by the let-7 microRNA

MicroRNAs (miRNAs) have recently emerged as an important new class of cellular regulators that control various cellular processes and are implicated in human diseases, including cancer. Here, we show that loss of let-7 function enhances lung tumor formation in vivo, strongly supporting the hypothesis that let-7 is a tumor suppressor. Moreover, we report that exogenous delivery of let-7 to established tumors in mouse models of non-small-cell lung cancer (NSCLC) significantly reduces the tumor burden. These results demonstrate the therapeutic potential of let-7 in NSCLC and point to miRNA replacement therapy as a promising approach in cancer treatment.

Regression of murine lung tumors by the let-7 microRNA

MicroRNAs (miRNAs) have recently emerged as an important new class of cellular regulators that control various cellular processes and are implicated in human diseases, including cancer. Here, we show that loss of let-7 function enhances lung tumor formation in vivo, strongly supporting the hypothesis that let-7 is a tumor suppressor. Moreover, we report that exogenous delivery of let-7 to established tumors in mouse models of non-small-cell lung cancer (NSCLC) significantly reduces the tumor burden. These results demonstrate the therapeutic potential of let-7 in NSCLC and point to miRNA replacement therapy as a promising approach in cancer treatment.

MiR-125b is critical for the suppression of human U251 glioma stem cell proliferation

Stem cells are unique in their ability to self-renew and maintain tissue homoeostasis by differentiating into different cell types to replace aged or damaged cells. The key characteristic of the stem cell is its capacity to divide for long periods of time. MicroRNAs (miRNAs) are small noncoding RNA molecules that regulate protein expression by cleaving or repressing the translation of target mRNAs. miR-125b, one of neuronal miRNAs, recently was found to be necessary for stem cell fission to bypass the normal G1/S checkpoint and make stem cells insensitive to chemotherapy signals, which normally stop the cell cycle at the G1/S transition. Given the insensitivity of gliomas to chemotherapy and the hypothesis that glioma stem cells cause resistance to drug therapy, exploring the functions and mechanisms of miR-125b in glioma stem cells would be valuable. In this study, we found that miR-125b was downregulated in human U251 glioma stem cells, therefore suggesting that its upregulation can lead to the growth inhibition of U251 glioma stem cells in vitro. Further research on the mechanism demonstrated that inhibition of miR-125b-induced U251 glioma stem cell proliferation was due to cell cycle arrest at the G1/S transition and involved the cell cycle regulated proteins CDK6 and CDC25A; miR-125b overexpression decreased CDK6 and CDC25A expression. These findings underscore the potential of miR-125b to regulate the proliferation of U251 glioma stem cells through the cell cycle regulated proteins CDK6 and CDC25A.

A MicroRNA expression profile defining the invasive bladder tumor phenotype

OBJECTIVE

The purpose of this study was to identify microRNA (miRNA) involved in the transition between the noninvasive and invasive urothelial carcinoma of the bladder (UCB) phenotype.

METHODS

Differential expression of miRNA was identified in a microarray format between noninvasive and invasive UCB cell lines and confirmed using quantitative reverse transcriptase-polymerase chain reaction (qRT-PCR) within this cell panel. Normalization of qRT-PCR with miR-222 was established from the microarray data and validated within a panel of 57 UCB tumors (26 noninvasive lesions (Ta/G1) and 31 invasive lesions (T2-T4). Pre-miR constructs were transfected into appropriate UCB cell lines to establish a change in invasive potential.

RESULTS

Differential expression of miRNAs was identified from microarray analysis and included reduced expression associated with miR-30b, miR-31, miR-141, miR-200a, miR-200b, miR-200c, miR-205, miR-21 in invasive lesions and elevated miR-99a in noninvasive UCB lesions. Reduced invasion potential was recorded in UM-UC-3, following pre-miR transfection, in all UCB cell lines with the exception of UM-UC-3/miR-30b transfectants. Our results identify a panel of miRNA modulated and expressed in invasive UCB tumors and demonstrates a role for them in the invasive phenotype.

CONCLUSIONS

The diagnostic test, based on the three most discriminatory miRNAs in our panel (miR-200c, miR-141, and miR-30b), showed a sensitivity of 100% and a specificity of 96.2%. Such a panel of miRNAs has the potential to identify invasive bladder tumors misclassified in pathologic assessment of bladder biopsy specimens.

Analysis of microRNA expression profiles during the cell cycle in synchronized HeLa cells

Cell cycle progression is regulated by both transcriptional and post-transcriptional mechanisms. MicroRNAs (miRNAs) emerge as a new class of small non-coding RNA regulators of cell cycle as recent evidence suggests. It is hypothesized that expression of specific miRNAs oscillates orderly along with cell cycle progression. However, the oscillated expression patterns of many candidate miRNAs have yet to be determined. Here, we describe miRNA expression profiling in double-thymidine synchronized HeLa cells as cell cycle progresses. Twenty-five differentially expressed miRNAs were classified into five groups based on their cell cycle-dependent expression patterns. The cyclic expression of six miRNAs (miR-221, let-7a, miR-21, miR-34a, miR-24, miR-376b) was validated by real-time quantitative RT-PCR (qRT-PCR). These results suggest that specific miRNAs, along with other key factors are required for maintaining and regulating proper cell cycle progression. The study deepens our understanding on cell cycle regulation. [BMB reports 2009; 42(9): 593-598].

The let-7 target gene mouse lin-41 is a stem cell specific E3 ubiquitin ligase for the miRNA pathway protein Ago2

The let-7 miRNA and its target gene Lin-28 interact in a regulatory circuit controlling pluripotency. We investigated an additional let-7 target, mLin41 (mouse homologue of lin-41), as a potential contributor to this circuit. We demonstrate the presence of mLin41 protein in several stem cell niches, including the embryonic ectoderm, epidermis and male germ line. mLin41 colocalized to cytoplasmic foci with P-body markers and the miRNA pathway proteins Ago2, Mov10 and Tnrc6b. In co-precipitation assays, mLin41 interacted with Dicer and the Argonaute proteins Ago1, Ago2 and Ago4. Moreover, we show that mLin41 acts as an E3 ubiquitin ligase in an auto-ubiquitylation assay and that mLin41 mediates ubiquitylation of Ago2 in vitro and in vivo. Overexpression and depletion of mLin41 led to inverse changes in the level of Ago2 protein, implicating mLin41 in the regulation of Ago2 turnover. mLin41 interfered with silencing of target mRNAs for let-7 and miR-124, at least in part by antagonizing Ago2. Furthermore, mLin41 cooperated with the pluripotency factor Lin-28 in suppressing let-7 activity, revealing a dual control mechanism regulating let-7 in stem cells.

Molecular biomarkers for predicting chemotherapy response in lung cancer

BACKGROUND

Chemotherapy in non-small-cell lung cancer (NSCLC) has reached a plateau, with no evidence of substantial improvement in survival. However, recent advances in the management of lung cancer have paved the way for the optimization of treatment. Several lines of evidence indicate that multiple genetic disturbances found in human cancer cell lines and in the tumors of NSCLC patients have a role as predictive markers for response and survival with chemotherapy regimens now in use.

OBJECTIVE

This review highlights relevant translational research findings on potential predictive markers in lung cancer with therapeutic impact in both the near and distant future.

CONCLUSION

The next step is to develop clinical trials that will prospectively validate the benefits of customizing chemotherapy, which should translate into an improvement in outcome in NSCLC patients.

MicroRNA 92b controls the G1/S checkpoint gene p57 in human embryonic stem cells

Human embryonic stem (ES) cells exhibit a shorter G(1) cell cycle phase than most somatic cells. Here, we examine the role of an abundant, human ES cell-enriched microRNA, miR-92b, in cell cycle distribution. Inhibition of miR-92b in human ES cells results in a greater number of cells in the G(1) phase and a lower number in the S phase. Conversely, overexpression of miR-92b in differentiated cells results in a decreased number of cells in G1 phase and an increased number in S-phase. p57, a gene whose product inhibits G(1) to S-phase progression, is one of the predicted targets of miR-92b. Inhibition of miR-92b in human ES cells increases p57 protein levels, and miR-92b overexpression in differentiated cells decreases p57 protein levels. Furthermore, miR-92b inhibits a luciferase reporter construct that includes part of the 3' untranslated region of the p57 gene containing the predicted target of the miR-92b seed sequence. Thus, we show that the miRNA miR-92b directly downregulates protein levels of the G(1)/S checkpoint gene p57. STEM CELLS 2009;27:1524-1528.

Therapeutic microRNA strategies in human cancer

MicroRNAs (miRNAs) are approximately 22 nucleotide long, noncoding, endogenous RNA molecules which exert their functions by base pairing with messenger RNAs (mRNAs), thereby regulate protein-coding gene expression. In eukaryotic cells, miRNAs play important roles in regulating biological processes such as proliferation, differentiation, apoptosis, and stem cell self-renewal. The human genome may contain as many as 1,000 miRNAs, and more than 700 of them have been identified. miRNAs are predicted to target up to one third of mRNAs. Each miRNA can target hundreds of transcripts directly or indirectly, while more than one miRNA can converge on a single transcript target. Therefore, the potential regulatory circuitry afforded by miRNA is enormous. Recently, mounting evidence implicates miRNAs as a new class of modulator for human tumor initiation and progression. Therefore, it has been proposed that manipulating miRNA activity and miRNA biogenesis may be a novel avenue for developing efficient therapies against cancer.

Phosphorylation of the human microRNA-generating complex mediates MAPK/Erk signaling

MicroRNAs (miRNAs) govern an expanding number of biological and disease processes. Understanding the mechanisms by which the miRNA pathway is regulated, therefore, represents an important area of investigation. We determined that the human miRNA-generating complex is comprised of Dicer and phospho-TRBP isoforms. Phosphorylation of TRBP is mediated by the mitogen-activated protein kinase (MAPK) Erk. Expression of phospho-mimic TRBP and TRBP phosphorylation enhanced miRNA production by increasing stability of the miRNA-generating complex. Mitogenic signaling in response to serum and the tumor promoter PMA was dependent on TRBP phosphorylation. These effects were accompanied by a coordinated increase in levels of growth-promoting miRNA and reduced expression of let-7 tumor suppressor miRNA. Conversely, pharmacological inhibition of MAPK/Erk resulted in an anti-growth miRNA profile. Taken together, these studies indicate that the MAPK/Erk pathway regulates the miRNA machinery and suggest a general principle, wherein signaling systems target the miRNA pathway to achieve biological responses.

MicroRNA regulation of cancer stem cells and therapeutic implications

MicroRNAs (miRNAs) are a class of endogenous non-protein-coding RNAs that function as important regulatory molecules by negatively regulating gene and protein expression via the RNA interference (RNAi) machinery. MiRNAs have been implicated to control a variety of cellular, physiological, and developmental processes. Aberrant expressions of miRNAs are connected to human diseases such as cancer. Cancer stem cells are a small subpopulation of cells identified in a variety of tumors that are capable of self-renewal and differentiation. Dysregulation of stem cell self-renewal is a likely requirement for the initiation and formation of cancer. Furthermore, cancer stem cells are a very likely cause of resistance to current cancer treatments, as well as relapse in cancer patients. Understanding the biology and pathways involved with cancer stem cells offers great promise for developing better cancer therapies, and might one day even provide a cure for cancer. Emerging evidence demonstrates that miRNAs are involved in cancer stem cell dysregulation. Recent studies also suggest that miRNAs play a critical role in carcinogenesis and oncogenesis by regulating cell proliferation and apoptosis as oncogenes or tumor suppressors, respectively. Therefore, molecularly targeted miRNA therapy could be a powerful tool to correct the cancer stem cell dysregulation.

Induction of apoptosis in the synovium of mice with autoantibody-mediated arthritis by the intraarticular injection of double-stranded MicroRNA-15a

OBJECTIVE

MicroRNA is a family of noncoding RNAs that exhibit tissue-specific or developmental stage-specific expression patterns and are associated with human diseases. MicroRNA-15a (miR-15a) is reported to induce cell apoptosis by negatively regulating the expression of Bcl-2, which suppresses the apoptotic processes. The purpose of this study was to investigate whether double-stranded miR-15a administered by intraarticular injection could be taken up by cells and could induce Bcl-2 dysfunction and cell apoptosis in the synovium of arthritic mice in vivo.

METHODS

Autoantibody-mediated arthritis was induced in male DBA/1J mice. In the experimental group, double-stranded miR-15a labeled with FAM-atelocollagen complex was injected into the knee joint. In the control group, control small interfering RNA-atelocollagen complex was injected into the knee joint. Synovial expression of miR-15a was analyzed by quantitative polymerase chain reaction, FAM by fluorescence microscopy, Bcl-2 by Western blotting, and Bcl-2 and caspase 3 by immunohistochemistry.

RESULTS

The expression of miR-15a in the synovium of the experimental group was significantly higher than that in the control group. Green fluorescence emission of FAM was observed in the synovium of the experimental group. Bcl-2 protein was down-regulated and the expression of caspase 3 was increased as compared with that in the control group.

CONCLUSION

These results indicate that the induction of cell apoptosis after intraarticular injection of double-stranded miR-15a occurs through inhibition of the translation of Bcl-2 protein in arthritic synovium.

Decreased expression of miR-125b and miR-100 in oral cancer cells contributes to malignancy

Altered microRNA (miRNA) expression profiles have been observed in numerous malignancies, including oral squamous cell carcinoma (OSCC). However, their role in disease is not entirely clear. Several genetic aberrations are characteristic of OSCC, with amplification of chromosomal band 11q13 and loss of distal 11q being among the most prevalent. It is not known if the expression levels of miRNAs in these regions are altered or whether they play a role in disease. We hypothesize that the expression of miRNAs mapping to 11q are altered in OSCC because of loss or amplification of chromosomal material, and that this contributes to the development and progression of OSCC. We found that miR-125b and miR-100 are down-regulated in OSCC tumor and cell lines, and that transfecting cells with exogenous miR-125b and miR-100 significantly reduced cell proliferation and modified the expression of target and nontarget genes, including some that are overexpressed in radioresistant OSCC cells. In conclusion, the down-regulation of miR-125b and miR-100 in OSCC appears to play an important role in the development and/or progression of disease and may contribute to the loss of sensitivity to ionizing radiation.

Let-7a elevates p21(WAF1) levels by targeting of NIRF and suppresses the growth of A549 lung cancer cells

Down-regulation of let-7 microRNA (miRNA) is a key event in lung cancer. Despite recent advances in survival signaling, the roles of let-7 in the context of lung cancer are not fully clear. In this study, we showed that let-7a, a member of let-7 family, negatively regulated the expression of NIRF through NIRF 3' UTR. We also showed that NIRF was required for the let-7a-mediated elevation of p21(WAF1). These findings suggest that growth-inhibitory effect of let-7a on the A549 cells in vitro and in vivo may be explained in part by le-7a-induced suppression of NIRF and elevation of p21(WAF1). This work reveals a novel regulatory mechanism for let-7a in the control of cellular proliferation and lung carcinogenesis.

MicroRNAs in the pathogenesis of Lung Cancer

Lung cancer is the leading cause of cancer related deaths in the United States. It is estimated that in 2008 there were 215,000 new diagnoses of lung cancer and 163,000 deaths. Despite emerging technologies for potential early diagnosis and discovery of novel targeted therapies, the overall 5-year survival remains a disappointing 15%. Explanations for the poor survival include late presentation of disease, a lack of markers for early detection, and both phenotypic and genotypic heterogeneity within patients of similar histologic classification. To further understand this heterogeneity and thus complexity of lung cancer, investigators have applied various technologies including high throughput analysis of both the genome and proteome. Such approaches have been successful in identifying signatures that may clarify molecular differences in tumors, identify new targets, and improve prognostication. In the last decade, investigators have identified a new mode of gene regulation in the form of noncoding RNAs termed microRNAs (miRNAs or miRs). First determined to be of importance in larval development, microRNAs are approximately 19-22 nucleotide single stranded RNAs that regulate genes by either inducing mRNA degradation or inhibiting translation. MiRNAs have been implicated in several cellular processes including apoptosis, development, proliferation, and differentiation. By regulating hundreds of genes simultaneously, miRNAs have the capacity for regulation of biologic networks. Global alterations in miRNA expression in both solid organ and hematological malignancies suggest their importance in the pathogenesis of disease. To date, both in vivo and in vitro studies in lung cancer demonstrate a dysregulation of miRNA expression. Furthermore, investigators are beginning to identify individual targets and pathways of miRNAs relevant to lung tumorigenesis. Thus, miRNAs may identify critical targets and be important in the pathogenesis of lung cancer.

Global signatures of protein and mRNA expression levels

Cellular states are determined by differential expression of the cell's proteins. The relationship between protein and mRNA expression levels informs about the combined outcomes of translation and protein degradation which are, in addition to transcription and mRNA stability, essential contributors to gene expression regulation. This review summarizes the state of knowledge about large-scale measurements of absolute protein and mRNA expression levels, and the degree of correlation between the two parameters. We summarize the information that can be derived from comparison of protein and mRNA expression levels and discuss how corresponding sequence characteristics suggest modes of regulation.

The miR200 family of microRNAs regulates WAVE3-dependent cancer cell invasion

MicroRNAs are small non-coding RNAs that are directly involved in the regulation of gene expression by either translational repression or degradation of target mRNAs. Because of the high level of conservation of the target motifs, known as seed sequences, within the 3'-untranslated regions, a single microRNA can regulate numerous target genes simultaneously, making this class of RNAs a powerful regulator of gene expression. The miR200 family of microRNAs has recently been shown to regulate the process of epithelial to mesenchymal transition during tumor progression and metastasis. Here, we report that the expression of WAVE3, an actin cytoskeleton remodeling and metastasis promoter protein, is regulated by miR200 microRNAs. We show a clear inverse correlation between expression levels of WAVE3 and miR200 microRNAs in invasive versus non-invasive cancer cells. miR200 directly targets the 3'-untranslated regions of the WAVE3 mRNA and inhibits its expression. The miR200-mediated down-regulation of WAVE3 results in a significant reduction in the invasive phenotype of cancer cells, which is specific to the loss of WAVE3 expression. Re-expression of a miR200-resistant WAVE3 reverses miR200-mediated inhibition of cancer cell invasion. Loss of WAVE3 expression downstream of miR200 also results in a dramatic change in cell morphology resembling that of a mesenchymal to epithelial transition. In conclusion, a novel mechanism for the regulation of WAVE3 expression in cancer cells has been identified, which controls the invasive properties and morphology of cancer cells associated with their metastatic potential.