The miR-34 family in cancer and apoptosis

Differential profiles of microRNAs in retinoblastoma cell lines of different proliferation and adherence patterns

Retinoblastoma (RB) is the most common intraocular malignant tumor in childhood. To investigate differential expression of microRNAs (miRNAs) in RB cell lines of different growth patterns: SNUOT-Rb1 with adherent and more rapid growth and Y79 with nonadherent and slower growth, miRNA microarray was performed. Common mRNA targets of each miRNA were extracted from 4 web-based databases: TargetScan, miRanda, RNAhybrid, and PicTar. Biological functions of target genes were predicted with the PANTHER Classification System. We identified 39 differentially expressed miRNAs between 2 cell lines: 22 were upregulated in SNUOT-Rb1 cells, and the other 17 were overexpressed in Y79 cells. More than half of top 10 mRNA targets of hsa-miR-10b, hsa-miR-29a, hsa-miR-29b, hsa-miR-29c, and hsa-let-7c in SNUOT-Rb1 cells and hsa-miR-34a, hsa-miR-34c-5p, hsa-miR-124, hsa-miR-135b, hsa-miR-142-5p, and hsa-let-7i in Y79 cells were related with biological processes, which could affect the growth patterns of cells: cell adhesion, cell cycle, cell death, and cell division. On the basis of the data from the target analysis of each miRNA, we found out several miRNAs, which were differentially expressed and had targets of possible impact on progression of RB. From these analyses, we suggest that some differential miRNAs could have roles in miRNA-targeted treatments on RB.

Regulation of microRNA expression and function by nuclear receptor signaling

MicroRNAs (miRNAs) are small non-coding RNA transcripts that affect various cellular pathways by serving as regulators of gene expression at the translational and transcriptional level. Nuclear receptors (NRs) are ligand-activated transcription factors that regulate gene transcription by binding to the promoter region or by interacting with other transcription factors. NRs can regulate miRNA expression either at the transcriptional level, or through posttranscriptional maturation by interacting with miRNA processing factors. This review will summarize recent advances in knowledge of the modulation of miRNA expression by NRs. Increased understanding of the molecular basis of miRNA expression may enable new therapeutic interventions that modulate miRNA activities through NR-mediated signaling.

MicroRNA-34a modulates genes involved in cellular motility and oxidative phosphorylation in neural precursors derived from human umbilical cord mesenchymal stem cells

Background

Mesenchymal stem cell (MSC) found in bone marrow (BM-MSCs) and the Wharton's jelly matrix of human umbilical cord (WJ-MSCs) are able to transdifferentiate into neuronal lineage cells both in vitro and in vivo and therefore hold the potential to treat neural disorders such as stroke or Parkinson's disease. In bone marrow MSCs, miR-130a and miR-206 have been show to regulate the synthesis of neurotransmitter substance P in human mesenchymal stem cell-derived neuronal cells. However, how neuronal differentiation is controlled in WJ-MSC remains unclear.

Methods

WJ-MSCs were isolated from human umbilical cords. We subjected WJ-MSCs into neurogenesis by a published protocol, and the miRNome patterns of WJ-MSCs and their neuronal progenitors (day 9 after differentiation) were analyzed by the Agilent microRNA microarray.

Results

Five miRNAs were enriched in WJ-MSCs, including miR-345, miR-106a, miR-17-5p, miR-20a and miR-20b. Another 11 miRNAs (miR-206, miR-34a, miR-374, miR-424, miR-100, miR-101, miR-323, miR-368, miR-137, miR-138 and miR-377) were abundantly expressed in transdifferentiated neuronal progenitors. Among these miRNAs, miR-34a and miR-206 were the only 2 miRNAs been linked to BM-MSC neurogenesis. Overexpressing miR-34a in cells suppressed the expression of 136 neuronal progenitor genes, which all possess putative miR-34a binding sites. Gene enrichment analysis according to the Gene Ontology database showed that those 136 genes were associated with cell motility, energy production (including those with oxidative phosphorylation, electron transport and ATP synthesis) and actin cytoskeleton organization, indicating that miR-34a plays a critical role in precursor cell migration. Knocking down endogenous miR-34a expression in WJ-MSCs resulted in the augment of WJ-MSC motility.

Conclusions

Our data suggest a critical role of miRNAs in MSC neuronal differentiation, and miR-34a contributes in neuronal precursor motility, which may be crucial for stem cells to home to the target sites they should be.

Dissection of human MiRNA regulatory influence to subpathway

The global insight into the relationships between miRNAs and their regulatory influences remains poorly understood. And most of complex diseases may be attributed to certain local areas of pathway (subpathway) instead of the entire pathway. Here, we reviewed the studies on miRNA regulations to pathways and constructed a bipartite miRNAs and subpathways network for systematic analyzing the miRNA regulatory influences to subpathways. We found that a small fraction of miRNAs were global regulators, environmental information processing pathways were preferentially regulated by miRNAs, and miRNAs had synergistic effect on regulating group of subpathways with similar function. Integrating the disease states of miRNAs, we also found that disease miRNAs regulated more subpathways than nondisease miRNAs, and for all miRNAs, the number of regulated subpathways was not in proportion to the number of the related diseases. Therefore, the study not only provided a global view on the relationships among disease, miRNA and subpathway, but also uncovered the function aspects of miRNA regulations and potential pathogenesis of complex diseases. A web server to query, visualize and download for all the data can be freely accessed at http://bioinfo.hrbmu.edu.cn/miR2Subpath.

MicroRNA-99a inhibits hepatocellular carcinoma growth and correlates with prognosis of patients with hepatocellular carcinoma

In our in-depth analysis carried out by the Illumina Solexa massive parallel signature sequencing, microRNA-99a (miR-99a) was found to be the sixth abundant microRNA in the miRNome of normal human liver but was markedly down-regulated in hepatocellular carcinoma (HCC). Compelling evidence has suggested the important roles of microRNAs in HCC development. However, the biological function of miR-99a deregulation in HCC remains unknown. In this study, we found that miR-99a was remarkably decreased in HCC tissues and cell lines. Importantly, lower miR-99a expression in HCC tissues significantly correlated with shorter survival of HCC patients, and miR-99a was identified to be an independent predictor for the prognosis of HCC patients. Furthermore, restoration of miR-99a dramatically suppressed HCC cell growth in vitro by inducing the G(1) phase cell cycle arrest. Intratumoral injection of cholesterol-conjugated miR-99a mimics significantly inhibited tumor growth and reduced the α-fetoprotein level in HCC-bearing nude mice. Insulin-like growth factor 1 receptor (IGF-1R) and mammalian target of rapamycin (mTOR) were further characterized as the direct targets of miR-99a. Furthermore, protein levels of IGF-1R and mTOR were found to be inversely correlated with miR-99a expression in HCC tissues. miR-99a mimics inhibited IGF-1R and mTOR pathways and subsequently suppressed expression of cell cycle-related proteins, including cyclin D1 in HCC cells. Conclusively, miR-99a expression was frequently down-regulated in HCC tissues and correlates with the prognosis of HCC patients, thus proposing miR-99a as a prospective prognosis predictor of HCC. miR-99a suppresses HCC growth by inducing cell cycle arrest, suggesting miR-99a as potential tumor suppressor for HCC therapeutics.

MIRTFnet: analysis of miRNA regulated transcription factors

Background

Several expression datasets of miRNA transfection experiments are available to analyze the regulatory mechanisms downstream of miRNA effects. The miRNA induced regulatory effects can be propagated via transcription factors (TFs). We propose the method MIRTFnet to identify miRNA controlled TFs as active regulators if their downstream target genes are differentially expressed.

Methodology/Principal Findings

MIRTFnet enables the determination of active transcription factors (TFs) and is sensitive enough to exploit the small expression changes induced by the activity of miRNAs. For this purpose, different statistical tests were evaluated and compared. Based on the identified TFs, databases, computational predictions and the literature we construct regulatory models downstream of miRNA actions. Transfecting miRNAs are connected to active regulators via a network of miRNA-TF, miRNA-kinase-TF as well as TF-TF relationships. Based on 43 transfection experiments involving 17 cancer relevant miRNAs we show that MIRTFnet detects active regulators reliably.

Conclusions/Significance

The consensus of the individual regulatory models shows that the examined miRNAs induce activity changes in a common core of transcription factors involved in cancer related processes such as proliferation or apoptosis.

Plasma miRNA as biomarkers for assessment of total-body radiation exposure dosimetry

The risk of radiation exposure, due to accidental or malicious release of ionizing radiation, is a major public health concern. Biomarkers that can rapidly identify severely-irradiated individuals requiring prompt medical treatment in mass-casualty incidents are urgently needed. Stable blood or plasma-based biomarkers are attractive because of the ease for sample collection. We tested the hypothesis that plasma miRNA expression profiles can accurately reflect prior radiation exposure. We demonstrated using a murine model that plasma miRNA expression signatures could distinguish mice that received total body irradiation doses of 0.5 Gy, 2 Gy, and 10 Gy (at 6 h or 24 h post radiation) with accuracy, sensitivity, and specificity of above 90%. Taken together, these data demonstrate that plasma miRNA profiles can be highly predictive of different levels of radiation exposure. Thus, plasma-based biomarkers can be used to assess radiation exposure after mass-casualty incidents, and it may provide a valuable tool in developing and implementing effective countermeasures.

Identification of the receptor tyrosine kinase AXL in breast cancer as a target for the human miR-34a microRNA

The identification of molecular features that contribute to the progression of breast cancer can provide valuable insight into the pathogenesis of this disease. Deregulated microRNA expression represents one type of molecular event that has been associated with many different human cancers. In order to identify a miRNA/mRNA regulatory interaction that is biologically relevant to the triple-negative breast cancer genotype/phenotype, we initially conducted a miRNA profiling experiment to detect differentially expressed miRNAs in cell line models representing triple-negative (MDA-MB-231), ER(+) (MCF7), and HER-2 overexpressed (SK-BR-3) histotypes. We identified human miR-34a expression as being >3-fold down (from its median expression value across all cell lines) in MDA-MB-231 cells, and identified AXL as a putative mRNA target using multiple miRNA/target prediction algorithms. The miR-34a/AXL interaction was functionally characterized through ectopic overexpression experiments with a miR-34a mimic in two independent triple-negative breast cancer cell lines. In reporter assays, miR-34a binds to its putative target site within the AXL 3'UTR to inhibit luciferase expression. We also observed degradation of AXL mRNA and decreased AXL protein levels, as well as cell signaling effects on AKT phosphorylation and phenotypic effects on cell migration. Finally, we present an inverse correlative trend in miR-34a and AXL expression for both cell line and patient tumor samples.

miR-34a regulates mouse neural stem cell differentiation

Background

MicroRNAs (miRNAs or miRs) participate in the regulation of several biological processes, including cell differentiation. Recently, miR-34a has been implicated in the differentiation of monocyte-derived dendritic cells, human erythroleukemia cells, and mouse embryonic stem cells. In addition, members of the miR-34 family have been identified as direct p53 targets. However, the function of miR-34a in the control of the differentiation program of specific neural cell types remains largely unknown. Here, we investigated the role of miR-34a in regulating mouse neural stem (NS) cell differentiation.

Methodology/Principal Findings

miR-34a overexpression increased postmitotic neurons and neurite elongation of mouse NS cells, whereas anti-miR-34a had the opposite effect. SIRT1 was identified as a target of miR-34a, which may mediate the effect of miR-34a on neurite elongation. In addition, acetylation of p53 (Lys 379) and p53-DNA binding activity were increased and cell death unchanged after miR-34a overexpression, thus reinforcing the role of p53 during neural differentiation. Interestingly, in conditions where SIRT1 was activated by pharmacologic treatment with resveratrol, miR-34a promoted astrocytic differentiation, through a SIRT1-independent mechanism.

Conclusions

Our results provide new insight into the molecular mechanisms by which miR-34a modulates neural differentiation, suggesting that miR-34a is required for proper neuronal differentiation, in part, by targeting SIRT1 and modulating p53 activity.

Restitution of tumor suppressor microRNAs using a systemic nanovector inhibits pancreatic cancer growth in mice

Mis-expression of microRNAs (miRNA) is widespread in human cancers, including in pancreatic cancer. Aberrations of miRNA include overexpression of oncogenic miRs (Onco-miRs) or downregulation of so-called tumor suppressor TSG-miRs. Restitution of TSG-miRs in cancer cells through systemic delivery is a promising avenue for pancreatic cancer therapy. We have synthesized a lipid-based nanoparticle for systemic delivery of miRNA expression vectors to cancer cells (nanovector). The plasmid DNA-complexed nanovector is approximately 100 nm in diameter and shows no apparent histopathologic or biochemical evidence of toxicity upon intravenous injection. Two miRNA candidates known to be downregulated in the majority of pancreatic cancers were selected for nanovector delivery: miR-34a, which is a component of the p53 transcriptional network and regulates cancer stem cell survival, and the miR-143/145 cluster, which together repress the expression of KRAS2 and its downstream effector Ras-responsive element binding protein-1 (RREB1). Systemic intravenous delivery with either miR-34a or miR-143/145 nanovectors inhibited the growth of MiaPaCa-2 subcutaneous xenografts (P < 0.01 for miR-34a; P < 0.05 for miR-143/145); the effects were even more pronounced in the orthotopic (intrapancreatic) setting (P < 0.0005 for either nanovector) when compared with vehicle or mock nanovector delivering an empty plasmid. Tumor growth inhibition was accompanied by increased apoptosis and decreased proliferation. The miRNA restitution was confirmed in treated xenografts by significant upregulation of the corresponding miRNA and significant decreases in specific miRNA targets (SIRT1, CD44 and aldehyde dehydrogenase for miR34a, and KRAS2 and RREB1 for miR-143/145). The nanovector is a platform with potential broad applicability in systemic miRNA delivery to cancer cells.

Effects of simulated microgravity on expression profile of microRNA in human lymphoblastoid cells

This study explores the changes in expression of microRNA (miRNA) and related genes under simulated microgravity conditions. In comparison with static 1 × g, microgravity has been shown to alter global gene expression patterns and protein levels in cultured cells or animals. miRNA has recently emerged as an important regulator of gene expression, possibly regulating as many as one-third of all human genes. However, very little is known about the effect of altered gravity on miRNA expression. To test the hypothesis that the miRNA expression profile would be altered in zero gravity resulting in altered regulation of gene expression leading to metabolic or functional changes in cells, we cultured TK6 human lymphoblastoid cells in a high aspect ratio vessel (bioreactor) for 72 h either in the rotating condition to model microgravity in space or in the static condition as a control. Expression of several miRNAs was changed significantly in the simulated microgravity condition including miR-150, miR-34a, miR-423-5p, miR-22, miR-141, miR-618, and miR-222. To confirm whether this altered miRNA expression correlates with gene expression and functional changes of the cells, we performed DNA microarray and validated the related genes using quantitative RT-PCR. Expression of several transcription factors including EGR2, ETS1, and c-REL was altered in simulated microgravity conditions. Taken together, the results reported here indicate that simulated microgravity alters the expression of miRNAs and genes in TK6 cells. To our knowledge, this study is the first to report the effects of simulated microgravity on the expression of miRNA and related genes.

Prognostic, therapeutic and diagnostic potential of microRNAs in non-small cell lung cancer

Non-small cell lung carcinomas (NSCLC) account for about 80% of lung cancers and their remarkable heterogeneity manifests in histology, pathogenesis, prognosis, and response to treatments. Recent advances in molecular characterization help stratifying NSCLC patients for their potential benefit from targeting therapies. However, the fundamental mechanisms underlying the tumoral heterogeneity remain poorly understood. Expression profiling of many microRNAs (miRNAs) in various normal and disease tissues demonstrated unique spatial and temporal expression patterns and some miRNAs have been functionally characterized as oncogenes or tumor suppressor genes. Genome-wide screening identified specific miRNA expression signatures associated with clinical outcome of NSCLC patients. A group of miRNAs that has enriched expression in normal lung was found down regulated in NSCLC and may function as tumor suppressor genes. In this review we: a) summarize the current understanding of the critical role that miRNAs play in normal cell functions and in disease biology especially in lung cancer tumorigenesis, b) highlight their potential as biomarkers for lung cancer risk stratification, outcome prediction and classification of histologic subtypes, c) critically assess current knowledge on lung-enriched miRNAs and expression of their predicted target genes in NSCLC and d) evaluate their potential as circulating biomarkers and therapeutic targets in lung cancer.

Immortalization of MEF is characterized by the deregulation of specific miRNAs with potential tumor suppressor activity

The life span (Hayflick limit) of primary mouse embryo fibroblasts (MEF) in culture is variable but it is still unclear if the escape of the Hayflick limit is also variable. To address this point MEF were expanded every fifteen days (6T15) instead of every three days (6T3) until they became immortal. With this protocol MEF lifespan was extended and immortalization accordingly delayed. By testing a panel of genes (p19ARF, p16, p21) and miRNAs (miR-20a, miR-21, miR-28, miR-290) related to primary MEF senescence, a switch of p21 from up to down regulation, the down regulation of specific miRNAs as well as a massive shift from diploidy to hyperdiploidy were observed in coincidence with the resumption of cell proliferation. Collectively, these data indicate that the inactivation of genes and miRNAs, important in controlling cell proliferation, might be determinant for the escape from the Hayflick limit. In support of this hypothesis was the finding that some of the down regulated miRNAs transfected in immortalized MEF inhibited cell proliferation thus displaying a tumor suppressor-like activity.

MicroRNAs in colorectal cancer metastasis

Metastatic disease is the major cause of death in colorectal cancer (CRC) patients. The metastatic process is highly inefficient and comprises multiple sequential steps. While many genetic factors relevant in this process have already been identified, the epigenetic factors underlying each step still remain obscure. MicroRNAs (miRNAs) are key regulators in tumourigenesis, but their role in the development of cancer metastasis is poorly investigated. The majority of miRNAs involved in the metastatic process have been identified in breast cancer cell lines, and in CRC less data are available. We review the role of miRNAs in the metastatic pathway of CRC, including escape of apoptosis, epithelial-mesenchymal transition (EMT), angiogenesis, and invasion. Better understanding of the complex role of miRNAs in the development of CRC metastases may provide new insights that could be of therapeutic consequence.

MicroRNA expression and clinical outcome of small cell lung cancer

The role of microRNAs in small-cell lung carcinoma (SCLC) is largely unknown. miR-34a is known as a p53 regulated tumor suppressor microRNA in many cancer types. However, its therapeutic implication has never been studied in SCLC, a cancer type with frequent dysfunction of p53. We investigated the expression of a panel of 7 microRNAs (miR-21, miR-29b, miR-34a/b/c, miR-155, and let-7a) in 31 SCLC tumors, 14 SCLC cell lines, and 26 NSCLC cell lines. We observed significantly lower miR-21, miR-29b, and miR-34a expression in SCLC cell lines than in NSCLC cell lines. The expression of the 7 microRNAs was unrelated to SCLC patients' clinical characteristics and was neither prognostic in term of overall survival or progression-free survival nor predictive of treatment response. Overexpression or downregulation of miR-34a did not influence SCLC cell viability. The expression of these 7 microRNAs also did not predict in vitro sensitivity to cisplatin or etoposide in SCLC cell lines. Overexpression or downregulation of miR-34a did not influence sensitivity to cisplatin or etoposide in SCLC cell lines. In contrast to downregulation of the miR-34a target genes cMET and Axl by overexpression of miR-34a in NSCLC cell lines, the intrinsic expression of cMET and Axl was low in SCLC cell lines and was not influenced by overexpression of miR-34a. Our results suggest that the expression of the 7 selected microRNAs are not prognostic in SCLC patients, and miR-34a is unrelated to the malignant behavior of SCLC cells and is unlikely to be a therapeutic target.

miR-20a and miR-290, multi-faceted players with a role in tumourigenesis and senescence

Expression of microRNAs changes markedly in tumours and evidence indicates that they are causatively related to tumourigenesis, behaving as tumour suppressor microRNAs or onco microRNAs; in some cases they can behave as both depending on the type of cancer. Some tumour suppressor microRNAs appear to be an integral part of the p53 and Retinoblastoma (RB) network, the main regulatory pathways controlling senescence, a major tumour suppressor mechanism. The INK4a/ARF locus which codifies for two proteins, p19ARF and p16INK4a, plays a central role in senescence by controlling both p53 and RB. Recent evidence shows that the proto-oncogene leukaemia/lymphoma related factor, a p19ARF specific repressor, is controlled by miRNAs and that miRNAs, in particular miR-20a and miR-290, are causatively involved in mouse embryo fibroblasts (MEF) senescence in culture. Intriguingly, both miR-20a, member of the oncogenic miR-17–92 cluster, and miR-290, belonging to the miR-290–295 cluster, are highly expressed in embryonic stem (ES) cells. The pro-senescence role of miR-20a and miR-290 in MEF is apparently in contrast with their proliferative role in tumour and ES cells. We propose that miRNAs may exert opposing functions depending on the miRNAs repertoire as well as target/s level/s present in different cellular contexts, suggesting the importance of evaluating miRNAs activity in diverse genetic settings before their therapeutic use as tumour suppressors.

Estrogen-regulated genes in rat testes and their relationship to recovery of spermatogenesis after irradiation

Despite numerous observations of the effects of estrogens on spermatogenesis, identification of estrogen-regulated genes in the testis is limited. Using rats in which irradiation had completely blocked spermatogonial differentiation, we previously showed that testosterone suppression with gonadotropin-releasing hormone-antagonist acyline and the antiandrogen flutamide stimulated spermatogenic recovery and that addition of estradiol (E2) to this regimen accelerated this recovery. We report here the global changes in testicular cell gene expression induced by the E2 treatment. By minimizing the changes in other hormones and using concurrent data on regulation of the genes by these hormones, we were able to dissect the effects of estrogen on gene expression, independent of gonadotropin or testosterone changes. Expression of 20 genes, largely in somatic cells, was up- or downregulated between 2- and 5-fold by E2. The unexpected and striking enrichment of transcripts not corresponding to known genes among the E2-downregulated probes suggested that these might represent noncoding mRNAs; indeed, we have identified several as miRNAs and their potential target genes in this system. We propose that genes for which expression levels are altered in one direction by irradiation and in the opposite direction by both testosterone suppression and E2 treatment are candidates for controlling the block in differentiation. Several genes, including insulin-like 3 (Insl3), satisfied those criteria. If they are indeed involved in the inhibition of spermatogonial differentiation, they may be candidate targets for treatments to enhance recovery of spermatogenesis following gonadotoxic exposures, such as those resulting from cancer therapy.

miRNA expression profiles in myelodysplastic syndromes reveal Epstein-Barr virus miR-BART13 dysregulation

Recently, the microRNA (miRNA) signature has been used for better characterization and understanding of the pathogenesis of different malignancies, including myelodysplastic syndromes (MDS). MDS are a heterogeneous group of stem cell disorders in which the genetic and molecular defects are not well defined. In the present study, we applied array based miRNA profiling to study 19 bone marrow cell samples of de novo MDS compared with eight healthy individuals. In addition, integration of the miRNA profiling data with our previous array comparative genomic hybridization data, from the same cohort of patients, was performed. We observed up-regulation of hsa-miR-720 and hsa-miR-21, and down-regulation of hsa-miR-671-5p and one human virus miRNA (Epstein-Barr virus miR-BART13) in MDS samples compared with normal samples. In our study, the copy number alteration harboring miRNA was not affecting miRNA expression, but a distinct microRNA expression pattern was observed, not only in MDS compared with controls, but also between MDS entities.

Tumour-suppressor microRNAs let-7 and mir-101 target the proto-oncogene MYCN and inhibit cell proliferation in MYCN-amplified neuroblastoma

Background:

MicroRNAs (miRNAs) regulate expression of many cancer-related genes through posttranscriptional repression of their mRNAs. In this study we investigate the proto-oncogene MYCN as a target for miRNA regulation.

Methods:

A luciferase reporter assay was used to investigate software-predicted miRNA target sites in the 3′-untranslated region (3′UTR) of MYCN. The miRNAs were overexpressed in cell lines by transfection of miRNA mimics or miRNA-expressing plasmids. Mutation of the target sites was used to validate MYCN 3′UTR as a direct target of several miRNAs. To measure miRNA-mediated suppression of endogenous N-myc protein, inhibition of proliferation and inhibition of clonogenic growth, miRNAs were overexpressed in a MYCN-amplified neuroblastoma cell line.

Results:

The results from this study show that MYCN is targeted by several miRNAs. In addition to the previously shown mir-34a/c, we experimentally validate mir-449, mir-19a/b, mir-29a/b/c, mir-101 and let-7e/mir-202 as direct MYCN-targeting miRNAs. These miRNAs were able to suppress endogenous N-myc protein in a MYCN-amplified neuroblastoma cell line. The let-7e and mir-202 were strong negative regulators of MYCN expression. The mir-101 and the let-7 family miRNAs let-7e and mir-202 inhibited proliferation and clonogenic growth when overexpressed in Kelly cells.

Conclusion:

The tumour-suppressor miRNAs let-7 and mir-101 target MYCN and inhibit proliferation and clonogenic growth of MYCN-amplified neuroblastoma cells.

MicroRegulators come of age in senescence

Cellular senescence was first reported five decades ago as a state of long-term growth inhibition in viable, metabolically active cells cultured in vitro. However, evidence that senescence occurs in vivo and underlies pathophysiologic processes has only emerged over the past few years. Coincident with this increased knowledge, understanding of the mechanisms that control senescent-cell gene expression programs has also recently escalated. Such mechanisms include a prominent group of regulatory factors (miRNA), a family of small, noncoding RNAs that interact with select target mRNAs and typically repress their expression. Here, we review recent reports that miRNAs are key modulators of cellular senescence, and we examine their influence upon specific senescence-regulatory proteins. We discuss evidence that dysregulation of miRNA-governed senescence programs underlies age-associated diseases, including cancer.

Transcriptional and post-transcriptional mechanisms for oncogenic overexpression of ether à go-go K+ channel

The human ether-à-go-go-1 (h-eag1) K(+) channel is expressed in a variety of cell lines derived from human malignant tumors and in clinical samples of several different cancers, but is otherwise absent in normal tissues. It was found to be necessary for cell cycle progression and tumorigenesis. Specific inhibition of h-eag1 expression leads to inhibition of tumor cell proliferation. We report here that h-eag1 expression is controlled by the p53-miR-34-E2F1 pathway through a negative feed-forward mechanism. We first established E2F1 as a transactivator of h-eag1 gene through characterizing its promoter region. We then revealed that miR-34, a known transcriptional target of p53, is an important negative regulator of h-eag1 through dual mechanisms by directly repressing h-eag1 at the post-transcriptional level and indirectly silencing h-eag1 at the transcriptional level via repressing E2F1. There is a strong inverse relationship between the expression levels of miR-34 and h-eag1 protein. H-eag1antisense antagonized the growth-stimulating effects and the upregulation of h-eag1 expression in SHSY5Y cells, induced by knockdown of miR-34, E2F1 overexpression, or inhibition of p53 activity. Therefore, p53 negatively regulates h-eag1 expression by a negative feed-forward mechanism through the p53-miR-34-E2F1 pathway. Inactivation of p53 activity, as is the case in many cancers, can thus cause oncogenic overexpression of h-eag1 by relieving the negative feed-forward regulation. These findings not only help us understand the molecular mechanisms for oncogenic overexpression of h-eag1 in tumorigenesis but also uncover the cell-cycle regulation through the p53-miR-34-E2F1-h-eag1 pathway. Moreover, these findings place h-eag1 in the p53-miR-34-E2F1-h-eag1 pathway with h-eag as a terminal effecter component and with miR-34 (and E2F1) as a linker between p53 and h-eag1. Our study therefore fills the gap between p53 pathway and its cellular function mediated by h-eag1.

Epigenetically silenced miR-34b/c as a novel faecal-based screening marker for colorectal cancer

BACKGROUND

MicroRNAs are tiny non-coding small endogenous RNAs that regulate gene expression by translational repression, mRNA cleavage and mRNA inhibition. The aim of this study was to investigate the hypermethylation of miR-34b/c and miR-148a in colorectal cancer, and correlate this data to clinicopathological features. We also aimed to evaluate the hypermethylation of miR-34b/c in faeces specimens as a novel non-invasive faecal-DNA-based screening marker.

METHODS

The 5-aza-2'-deoxycytidine treatment and methylation-specific PCR were carried out to detect the hypermethylation of miR-34b/c and miR-148a.

RESULTS

The miR-34b/c hypermethylation was found in 97.5% (79 out of 82) of primary colorectal tumours, P=0.0110. In 75% (21 out of 28) of faecal specimens we found a hypermethylation of miR-34b/c while only in 16% (2 out of 12) of high-grade dysplasia. In addition, miR-148a was found to be hypermethylated in 65% (51 out of 78) of colorectal tumour tissues with no significant correlation to clinicopathological features. However, a trend with female gender and advanced age was found, P=0.083. We also observed a trend to lower survival rate in patients with miR-148a hypermethylation with 10-year survival probability: 48 vs 65%, P=0.561.

CONCLUSIONS

These findings show that aberrant hypermethylation of miR-34b/c could be an ideal class of early screening marker, whereas miR-148a could serve as a disease progression follow-up marker.

miR-34a and miR-15a/16 are co-regulated in non-small cell lung cancer and control cell cycle progression in a synergistic and Rb-dependent manner

Background

microRNAs (miRNAs) are small non-coding RNAs that are frequently involved in carcinogenesis. Although many miRNAs form part of integrated networks, little information is available how they interact with each other to control cellular processes. miR-34a and miR-15a/16 are functionally related; they share common targets and control similar processes including G₁-S cell cycle progression and apoptosis. The aim of this study was to investigate the combined action of miR-34a and miR-15a/16 in non-small cell lung cancer (NSCLC) cells.

Methods

NSCLC cells were transfected with miR-34a and miR-15a/16 mimics and analysed for cell cycle arrest and apoptosis by flow cytometry. Expression of retinoblastoma and cyclin E1 was manipulated to investigate the role of these proteins in miRNA-induced cell cycle arrest. Expression of miRNA targets was assessed by real-time PCR. To investigate if both miRNAs are co-regulated in NSCLC cells, tumour tissue and matched normal lung tissue from 23 patients were collected by laser capture microdissection and compared for the expression of these miRNAs by real-time PCR.

Results

In the present study, we demonstrate that miR-34a and miR-15a/16 act synergistically to induce cell cycle arrest in a Rb-dependent manner. In contrast, no synergistic effect of these miRNAs was observed for apoptosis. The synergistic action on cell cycle arrest was not due to a more efficient down-regulation of targets common to both miRNAs. However, the synergistic effect was abrogated in cells in which cyclin E1, a target unique to miR-15a/16, was silenced by RNA interference. Thus, the synergistic effect was due to the fact that in concerted action both miRNAs are able to down-regulate more targets involved in cell cycle control than each miRNA alone. Both miRNAs were significantly co-regulated in adenocarcinomas of the lung suggesting a functional link between these miRNAs.

Conclusions

In concerted action miRNAs are able to potentiate their impact on G₁-S progression. Thus the combination of miRNAs of the same network rather than individual miRNAs should be considered for assessing a biological response. Since miR-34a and miR-15a/16 are frequently down-regulated in the same tumour tissue, administrating a combination of both miRNAs may also potentiate their therapeutic impact.

Genome-wide characterization of miR-34a induced changes in protein and mRNA expression by a combined pulsed SILAC and microarray analysis

The gene encoding the miR-34a microRNA is a transcriptional target of the p53 tumor suppressor protein and subject to epigenetic inactivation in colorectal cancer and numerous other tumor types. Here, we combined pulsed SILAC (pSILAC) and microarray analyses to identify miR-34a-induced changes in protein and mRNA expression. pSILAC allowed to quantify the de novo protein synthesis of 1206 proteins after activation of a conditional miR-34a allele in a colorectal cancer cell line. ∼19% of the detected proteins were differentially regulated, with 113 proteins being down- and 115 up-regulated. The proteins with a miR-34a seed-matching-sequence in the 3'-untranslated region (UTR) of the corresponding mRNA showed a clear bias toward translational repression. Proteins involved in DNA replication, e.g. the MCM proteins, and cell proliferation, were over-represented among indirectly down-regulated proteins lacking a miR-34a seed-match. The decrease in de novo protein synthesis of direct miR-34a targets correlated with reduced levels of the corresponding mRNA in most cases, indicating an interdependence of both types of regulation. In addition, 43 mRNAs encoding proteins not detected by pSILAC were down-regulated after miR-34a expression and contained miR-34a seed-matches. The direct regulation of selected miR-34a target-mRNAs was confirmed using reporter assays. Via down-regulation of the proteins encoded by these mRNAs miR-34a presumably inhibits glycolysis (LDHA), WNT-signaling (LEF1), invasion/migration (AXL) and lipid metabolism (ACSL1, ACSL4). Furthermore, miR-34a may activate p53 by inhibiting its acetylation (MTA2, HDAC1) and degradation (YY1). In summary, miR-34a presumably participates in multiple tumor suppressive pathways by directly and indirectly suppressing the expression of numerous, critical proteins.

MicroRNAs as potential target gene in cancer gene therapy of gastrointestinal tumors

INTRODUCTION

MicroRNA (miRNA) is a small non-coding RNA, which negatively regulates the expression of many target genes, thereby contributing to the modulation of diverse cell fates. Recent advances in molecular biology have revealed the potential role of miRNAs in tumor initiation, progression and metastasis. Aberrant regulation of miRNAs has been frequently reported in a variety of cancers, including gastrointestinal tumors, suggesting that cancer-related miRNAs are promising as novel biomarkers for tumor diagnosis and are potential target genes for cancer gene therapy against gastrointestinal tumors.

AREAS COVERED

The review focuses on the role of specific miRNAs (miR-192/194/215 and miR-7) in the differentiation of gastrointestinal epithelium and on the role of tumor-suppressive (miR-34, miR-143, miR-145) and oncogenic miRNAs (miR-21, miR-17-92 cluster) in gastrointestinal tumors. Furthermore, the potential role of miRNAs as novel biomarkers and target genes for cancer gene therapy against gastrointestinal tumors are discussed. We will also outline the potential clinical application of miRNAs for tumor diagnosis and cancer gene therapy against gastrointestinal tumors.

EXPERT OPINION

Exploration of tumor-related miRNAs would provide important opportunities for the development of novel cancer gene therapies aimed at normalizing the critical miRNAs that are deregulated in gastrointestinal tumors.

Regulation of cancer aggressive features in melanoma cells by microRNAs

MicroRNAs (miRNAs) are small non-coding RNAs with regulatory roles, which are involved in a broad spectrum of physiological and pathological processes, including cancer. A common strategy for identification of miRNAs involved in cell transformation is to compare malignant cells to normal cells. Here we focus on identification of miRNAs that regulate the aggressive phenotype of melanoma cells. To avoid differences due to genetic background, a comparative high-throughput miRNA profiling was performed on two isogenic human melanoma cell lines that display major differences in their net proliferation, invasion and tube formation activities. This screening revealed two major cohorts of differentially expressed miRNAs. We speculated that miRNAs up-regulated in the more-aggressive cell line contribute oncogenic features, while the down-regulated miRNAs are tumor suppressive. This assumption was further tested experimentally on five candidate tumor suppressive miRNAs (miR-31, -34a, -184, -185 and -204) and on one candidate oncogenic miRNA (miR-17-5p), all of which have never been reported before in cutaneous melanoma. Remarkably, all candidate Suppressive-miRNAs inhibited net proliferation, invasion or tube formation, while miR-17-5p enhanced cell proliferation. miR-34a and miR-185 were further shown to inhibit the growth of melanoma xenografts when implanted in SCID-NOD mice. Finally, all six candidate miRNAs were detected in 15 different metastatic melanoma specimens, attesting for the physiological relevance of our findings. Collectively, these findings may prove instrumental for understanding mechanisms of disease and for development of novel therapeutic and staging technologies for melanoma.

Shielding the messenger (RNA): microRNA-based anticancer therapies

It has been a decade since scientists realized that microRNAs (miRNAs) are not an oddity invented by worms to regulate gene expression at post-transcriptional levels. Rather, many of these 21-22-nucleotide-short RNAs exist in invertebrates and vertebrates alike and some of them are in fact highly conserved. miRNAs are now recognized as an important class of non-coding small RNAs that inhibit gene expression by targeting mRNA stability and translation. In the last ten years, our knowledge of the miRNAs world was expanding at vertiginous speed, propelled by the development of computational engines for miRNA identification and target prediction, biochemical tools and techniques to modulate miRNA activity, and last but not least, the emergence of miRNA-centric animal models. One important conclusion that has emerged from this effort is that many microRNAs and their cognate targets are strongly implicated in cancer, either as oncogenes or tumor and metastasis suppressors. In this review we will discuss the diverse role that miRNAs play in cancer initiation and progression and also the tools with which miRNA expression could be corrected in vivo. While the idea of targeting microRNAs towards therapeutic ends is getting considerable traction, basic, translational, and clinical research done in the next few years will tell whether this promise is well-founded.

Hsa-miR-34b is a plasma-stable microRNA that is elevated in pre-manifest Huntington's disease

Huntington's disease (HD) is a devastating, neurodegenerative condition, which lacks effective treatment. Normal Huntingtin (HTT) and mutant Huntingtin (mHTT) are expressed in multiple tissues and can alter transcription of microRNAs (miRs). Importantly, miRs are present in a bio-stable form in human peripheral blood plasma and have recently been shown to be useful biomarkers in other diseases. We therefore sought to identify potential miR biomarkers of HD that are present in, and have functional consequences for, neuronal and non-neuronal tissues. In a cell line over-expressing mHTT-Exon-1, miR microarray analysis was used to identify candidate miRs. We then examined their presence and bio-stability in control and HD plasma. We found that miR-34b is significantly elevated in response to mHTT-Exon-1, and its blockade alters the toxicity of mHTT-Exon-1 in vitro. We also show that miR-34b is detectable in plasma from small input volumes and is insensitive to freeze-thaw-induced RNA degradation. Interestingly, miR-34b is significantly elevated in plasma from HD gene carriers prior to symptom onset. This is the first study suggesting that plasma miRs might be used as biomarkers for HD.

Apoptosis and aging: increased resistance to apoptosis enhances the aging process

Apoptosis is a vital component in the evolutionarily conserved host defense system. Apoptosis is the guardian of tissue integrity by removing unfit and injured cells without evoking inflammation. However, apoptosis seems to be a double-edged sword since during low-level chronic stress, such as in aging, increased resistance to apoptosis can lead to the survival of functionally deficient, post-mitotic cells with damaged housekeeping functions. Senescent cells are remarkably resistant to apoptosis, and several studies indicate that host defense mechanisms can enhance anti-apoptotic signaling, which subsequently induces a senescent, pro-inflammatory phenotype during the aging process. At the molecular level, age-related resistance to apoptosis involves (1) functional deficiency in p53 network, (2) increased activity in the NF-κB-IAP/JNK axis, and (3) changes in molecular chaperones, microRNAs, and epigenetic regulation. We will discuss the molecular basis of age-related resistance to apoptosis and emphasize that increased resistance could enhance the aging process.

Apoptotic cell signaling in cancer progression and therapy

Apoptosis is a tightly regulated cell suicide program that plays an essential role in the development and maintenance of tissue homeostasis by eliminating unnecessary or harmful cells. Impairment of this native defense mechanism promotes aberrant cellular proliferation and the accumulation of genetic defects, ultimately resulting in tumorigenesis, and frequently confers drug resistance to cancer cells. The regulation of apoptosis at several levels is essential to maintain the delicate balance between cellular survival and death signaling that is required to prevent disease. Complex networks of signaling pathways act to promote or inhibit apoptosis in response to various cues. Apoptosis can be triggered by signals from within the cell, such as genotoxic stress, or by extrinsic signals, such as the binding of ligands to cell surface death receptors. Various upstream signaling pathways can modulate apoptosis by converging on, and thereby altering the activity of, common central control points within the apoptotic signaling pathways, which involve the BCL-2 family proteins, inhibitor of apoptosis (IAP) proteins, and FLICE-inhibitory protein (c-FLIP). This review highlights the role of these fundamental regulators of apoptosis in the context of both normal apoptotic signaling mechanisms and dysregulated apoptotic pathways that can render cancer cells resistant to cell death. In addition, therapeutic strategies aimed at modulating the activity of BCL-2 family proteins, IAPs, and c-FLIP for the targeted induction of apoptosis are briefly discussed.

Systematic analysis of microRNAs targeting the androgen receptor in prostate cancer cells

Androgen receptor (AR) is expressed in all stages of prostate cancer progression, including in castration-resistant tumors. Eliminating AR function continues to represent a focus of therapeutic investigation, but AR regulatory mechanisms remain poorly understood. To systematically characterize mechanisms involving microRNAs (miRNAs), we conducted a gain-of function screen of 1129 miRNA molecules in a panel of human prostate cancer cell lines and quantified changes in AR protein content using protein lysate microarrays. In this way, we defined 71 unique miRNAs that influenced the level of AR in human prostate cancer cells. RNA sequencing data revealed that the 3'UTR of AR (and other genes) is much longer than currently used in miRNA target prediction programs. Our own analyses predicted that most of the miRNA regulation of AR would target an extended 6 kb 3'UTR. 3'UTR-binding assays validated 13 miRNAs that are able to regulate this long AR 3'UTR (miR-135b, miR-185, miR-297, miR-299-3p, miR-34a, miR-34c, miR-371-3p, miR-421, miR-449a, miR-449b, miR-634, miR-654-5p, and miR-9). Fifteen AR downregulating miRNAs decreased androgen-induced proliferation of prostate cancer cells. In particular, analysis of clinical prostate cancers confirmed a negative correlation of miR-34a and miR-34c expression with AR levels. Our findings establish that miRNAs interacting with the long 3'UTR of the AR gene are important regulators of AR protein levels, with implications for developing new therapeutic strategies to inhibit AR function and androgen-dependent cell growth.

microRNAs in cancer: from bench to bedside

microRNAs (miRNAs) are master regulators of gene expression. By degrading or blocking translation of messenger RNA targets, these noncoding RNAs can regulate the expression of more than half of all protein-coding genes in mammalian genomes. Aberrant miRNA expression is well characterized in cancer progression and has prognostic implications for cancer in general. Over the past several years, accumulating evidence has demonstrated that genomic alterations in miRNA genes are correlated with all aspects of cancer biology. In this review, we describe the effects of miRNA deregulation in the cellular pathways that lead to the progressive conversion of normal cells into cancer cells as well as in cancer diagnosis and therapy in humans.

p53 Gene deficiency promotes hypoxia-induced pulmonary hypertension and vascular remodeling in mice

Chronic hypoxia induces pulmonary arterial remodeling, resulting in pulmonary hypertension and right ventricular hypertrophy. Hypoxia has been implicated as a physiological stimulus for p53 induction and hypoxia-inducible factor-1α (HIF-1α). However, the subcellular interactions between hypoxic exposure and expression of p53 and HIF-1α remain unclear. To examine the role of p53 and HIF-1α expression on hypoxia-induced pulmonary arterial remodeling, wild-type (WT) and p53 knockout (p53KO) mice were exposed to either normoxia or hypoxia for 8 wk. Following chronic hypoxia, both genotypes demonstrated elevated right ventricular pressures, right ventricular hypertrophy as measured by the ratio of the right ventricle to the left ventricle plus septum weights, and vascular remodeling. However, the right ventricular systolic pressures, the ratio of the right ventricle to the left ventricle plus septum weights, and the medial wall thickness of small vessels were significantly greater in the p53KO mice than in the WT mice. The p53KO mice had lower levels of p21 and miR34a expression, and higher levels of HIF-1α, VEGF, and PDGF expression than WT mice following chronic hypoxic exposure. This was associated with a higher proliferating cell nuclear antigen expression of pulmonary artery in p53KO mice. We conclude that p53 plays a critical role in the mitigation of hypoxia-induced small pulmonary arterial remodeling. By interacting with p21 and HIF-1α, p53 may suppress hypoxic pulmonary arterial remodeling and pulmonary arterial smooth muscle cell proliferation under hypoxia.

miR-605 joins p53 network to form a p53:miR-605:Mdm2 positive feedback loop in response to stress

In cancers with wild-type (WT) p53 status, the function of p53 is inhibited through direct interaction with Mdm2 oncoprotein, a negative feedback loop to limit the function of p53. In response to cellular stress, p53 escapes the p53:Mdm2 negative feedback to accumulate rapidly to induce cell cycle arrest and apoptosis. We demonstrate herein that an microRNA miR-605 is a new component in the p53 gene network, being transcriptionally activated by p53 and post-transcriptionally repressing Mdm2. Activation of p53 upregulated miR-605 via interacting with the promoter region of the gene. Overexpression of miR-605 directly decreased Mdm2 expression at the post-transcriptional level but indirectly increased the transcriptional activity of p53 on miR-34a via downregulating Mdm2; knockdown of miR-605 did the opposite. Mdm2 inhibitor upregulated expression of both miR-34a and miR-605, which was mitigated by p53 inhibitor. miR-605 preferentially induced apoptosis in WT p53-expressing cells, an effect abolished by p53 inhibition. These results indicate that miR-605 acts to interrupt p53:Mdm2 interaction to create a positive feedback loop aiding rapid accumulation of p53 to facilitate its function in response to stress.

The microRNA miR-34a inhibits prostate cancer stem cells and metastasis by directly repressing CD44

Cancer stem cells (CSCs) or tumor progenitor cells are involved in tumor progression and metastasis1. MicroRNAs (miRNAs) regulate both normal stem cells and CSCs2–5 and miRNA dysregulation has been implicated in tumorigenesis6. CSCs in many tumors, including cancers of the breast7, pancreas8, head and neck9, colon10,11, small intestine12, liver13, stomach14, bladder15, and ovary16 have been identified using adhesion molecule CD44, either individually or in combination with other marker(s). Prostate cancer (PCa) stem/progenitor cells with enhanced clonogenic17 and tumor-initiating and metastatic18,19 capacities are also enriched in the CD44⁺ cell population, but whether miRNAs regulate the CD44⁺ PCa cells and PCa metastasis remains unclear. Here we show, through expression analysis, that miR-34a, a p53 target20–24, was under-expressed in CD44⁺ PCa cells purified from xenograft and primary tumors. Enforced expression of miR-34a in bulk PCa cells inhibited clonogenic expansion and tumor development. miR-34a re-expression in CD44⁺ PCa cells blocked whereas miR-34a antagomirs in CD44⁻ PCa cells promoted tumor regeneration and metastasis. Systemically delivered miR-34a inhibited PCa metastasis and extended animal survival. Of significance, CD44 was identified and validated as a direct and functional target of miR-34a and CD44 knockdown phenocopied miR-34a over-expression in inhibiting PCa regeneration and metastasis. Our study reveals miR-34a as a critical negative regulator of CD44⁺ PCa cells and establishes a strong rationale for developing miR-34a as a novel therapeutic against prostate CSCs.

microRNAs in kidneys: biogenesis, regulation, and pathophysiological roles

MicroRNAs (miRNA) are endogenously produced, short RNAs that repress and thus regulate the expression of almost half of known protein-coding genes. miRNA-mediated gene repression is an important regulatory mechanism to modulate fundamental cellular processes such as the cell cycle, growth, proliferation, phenotype, and death, which in turn have major influences on pathophysiological outcomes. In kidneys, miRNAs are indispensable for renal development and homeostasis. Emerging evidence has further pinpointed the pathogenic roles played by miRNAs in major renal diseases, including diabetic nephropathy, acute kidney injury, renal carcinoma, polycystic kidney disease, and others. Although the field of renal miRNA research is still in its infancy and important questions remain, future investigation on miRNA regulation in kidneys has the potential to revolutionize both the diagnosis and treatment of major renal diseases.

Frequent concomitant inactivation of miR-34a and miR-34b/c by CpG methylation in colorectal, pancreatic, mammary, ovarian, urothelial, and renal cell carcinomas and soft tissue sarcomas

The microRNA encoding genes miR-34a and miR-34b/c represent direct p53 target genes and possess tumor suppressive properties as they mediate apoptosis, cell cycle arrest, and senescence. We previously reported that the miR-34a gene is subject to epigenetic inactivation by CpG methylation of its promoter region in primary prostate cancer and melanomas, and in 110 different cancer cell lines of diverse origin. Here we analyzed the methylation status of miR-34a and miR-34b/c in additional primary tumors of divergent sites. We found methylation of miR-34a or miR-34b/c in formalin-fixed, paraffin-embedded (FFPE) tumor samples from 178 patients with the following frequencies: colorectal cancer (74% miR-34a, 99% miR-34b/c; n = 114), pancreatic cancer (64%, 100%; n = 11), mammary cancer (60%, 90%; n = 10), ovarian cancer (62%, 69%; n = 13), urothelial cancer (71%, 57%; n = 7), and renal cell cancer (58%, 100%; n = 12). Furthermore, soft tissue sarcomas showed methylation of miR-34 gene promoters in FFPE samples (64%, 45%; n = 11), in explanted, cultured cells (53%, 40%; n = 40), and in frozen tissue samples (75%, 75%, n = 8). In the colorectal cancer samples a statistically significant correlation of miR-34a methylation and the absence of p53 mutation was detected. With the exception of sarcoma cell lines, the inactivation of miR-34a and miR-34b/c was concomitant in most cases. These results show that miR-34 inactivation is a common event in tumor formation, and suggest that CpG methylation of miR-34a and miR-34-b/c may have diagnostic value. The mutual exclusiveness of miR-34a methylation and p53 mutation indicates that miR-34a inactivation may substitute for loss of p53 function in cancer.

miR-34a confers chemosensitivity through modulation of MAGE-A and p53 in medulloblastoma

Recent studies have established miR-34a as a key effector of the p53 signaling pathway and have implicated its role in multiple cancer types. Here, we establish that miR-34a induces apoptosis, G2 arrest, and senescence in medulloblastoma and renders these cells more sensitive to chemotherapeutic agents. These effects are mediated in part by the direct post-transcriptional repression of the oncogenic MAGE-A gene family. We demonstrate that miR-34a directly targets the 3' untranslated regions of MAGE-A genes and decreases MAGE-A protein levels. This decrease in MAGE-A results in a concomitant increase in p53 and its associated transcriptional targets, p21/WAF1/CIP1 and, importantly, miR-34a. This establishes a positive feedback mechanism where miR-34a is not only induced by p53 but increases p53 mRNA and protein levels through the modulation of MAGE-A genes. Additionally, the forced expression of miR-34a or the knockdown of MAGE-A genes by small interfering RNA similarly sensitizes medulloblastoma cells to several classes of chemotherapeutic agents, including mitomycin C and cisplatin. Finally, the analysis of mRNA and micro-RNA transcriptional profiles of a series of primary medulloblastomas identifies a subset of tumors with low miR-34a expression and correspondingly high MAGE-A expression, suggesting the coordinate regulation of these genes. Our work establishes a role for miR-34a in modulating responsiveness to chemotherapy in medulloblastoma and presents a novel positive feedback mechanism involving miR-34a and p53, via direct targeting of MAGE-A.

Downregulation of miR-205 and miR-31 confers resistance to chemotherapy-induced apoptosis in prostate cancer cells

Advanced prostate cancers are known to acquire not only invasive capabilities but also significant resistance to chemotherapy-induced apoptosis. To understand how microRNAs (miRNAs) may contribute to prostate cancer resistance to apoptosis, we compared microRNA expression profiles of a benign prostate cancer cell line WPE1-NA22 and a highly malignant WPE1-NB26 cell line (derived from a common lineage). We found that miR-205 and miR-31 are significantly downregulated in WPE1-NB26 cells, as well as in other cell lines representing advanced-stage prostate cancers. Antiapoptotic genes BCL2L2 (encoding Bcl-w) and E2F6 are identified as the targets of miR-205 and miR-31, respectively. By downregulating Bcl-w and E2F6, miR-205 and miR-31 promote chemotherapeutic agents-induced apoptosis in prostate cancer cells. The promoter region of the miR-205 gene was cloned and was found to be hypermethylated in cell lines derived from advanced prostate cancers, contributing to the downregulation of the gene. Treatment with DNA methylation inhibitor 5-aza-2'-deoxycytidine induced miR-205 expression, downregulated Bcl-w, and sensitized prostate cancer cells to chemotherapy-induced apoptosis. Thus, downregulation of miR-205 and miR-31 has an important role in apoptosis resistance in advanced prostate cancer.

MicroRNA regulation of core apoptosis pathways in cancer

Recent research has demonstrated that microRNAs (miRNAs) are key regulators of many cell processes often deregulated in cancer, including apoptosis. Indeed, it is becoming clear that many miRNAs are anti-apoptotic and mediate this effect by targeting pro-apoptotic mRNAs or positive regulators of pro-apoptotic mRNAs. Conversely, many pro-apoptotic miRNAs target anti-apoptotic mRNAs or their positive regulators. We have reviewed the current knowledge in this area including evidence of miRNA involvement in cancer drug resistance.

Involvement of microRNAs in physiological and pathological processes in the lung

To date, at least 900 different microRNA (miRNA) genes have been discovered in the human genome. These short, single-stranded RNA molecules originate from larger precursor molecules that fold to produce hairpin structures, which are subsequently processed by ribonucleases Drosha/Pasha and Dicer to form mature miRNAs. MiRNAs play role in the posttranscriptional regulation of about one third of human genes, mainly via degradation of target mRNAs. Whereas the target mRNAs are often involved in the regulation of diverse physiological processes ranging from developmental timing to apoptosis, miRNAs have a strong potential to regulate fundamental biological processes also in the lung compartment. However, the knowledge of the role of miRNAs in physiological and pathological conditions in the lung is still limited. This review, therefore, summarizes current knowledge of the mechanism, function of miRNAs and their contribution to lung development and homeostasis. Besides the involvement of miRNAs in pulmonary physiological conditions, there is evidence that abnormal miRNA expression may lead to pathological processes and development of various pulmonary diseases. Next, the review describes current state-of-art on the miRNA expression profiles in smoking-related diseases including lung cancerogenesis, in immune system mediated pulmonary diseases and fibrotic processes in the lung. From the current research it is evident that miRNAs may play role in the posttranscriptional regulation of key genes in human pulmonary diseases. Further studies are, therefore, necessary to explore miRNA expression profiles and their association with target mRNAs in human pulmonary diseases.

RETRACTED: Downregulation of p53-inducible microRNAs 192, 194, and 215 impairs the p53/MDM2 autoregulatory loop in multiple myeloma development

This article has been retracted: please see Elsevier Policy on Article Withdrawal (http://www.elsevier.com/locate/withdrawalpolicy). This article has been retracted at the request of the editors. This article was published on October 19, 2010, and Figures 4A and 7A were later corrected on August 8, 2016. In January 2021, The Ohio State University notified the Cancer Cell editors that an internal investigation concluded that Figures 1E, 4A, 4D, 5A, and 7A were falsified and that part of Figure 1E of the article is the same as part of Figure 1F in the correction of another article (Pichiorri et al., 2017, J. Exp. Med., 214, 1557, https://doi.org/10.1084/jem.2012095001172017c) and recommended retraction of the article. The editors no longer have confidence in the validity of the data and are retracting the article. S.-S. S. agrees with the retraction, and F.P., C.H., A.P., and C.M.C. disagree with the retraction; all other authors couldn't be reached or didn't respond.

C/EBPα regulated microRNA-34a targets E2F3 during granulopoiesis and is down-regulated in AML with CEBPA mutations

The transcription factor, CCAAT enhancer binding protein alpha (C/EBPα), is crucial for granulopoiesis and is deregulated by various mechanisms in acute myeloid leukemia (AML). Mutations in the CEBPA gene are reported in 10% of human patients with AML. Even though the C/EBPα mutants are known to display distinct biologic function during leukemogenesis, the molecular basis for this subtype of AML remains elusive. We have recently showed the significance of deregulation of C/EBPα-regulated microRNA (miR) in AML. In this study, we report that miR-34a is a novel target of C/EBPα in granulopoiesis. During granulopoiesis, miR-34a targets E2F3 and blocks myeloid cell proliferation. Analysis of AML samples with CEBPA mutations revealed a lower expression of miR-34a and elevated levels of E2F3 as well as E2F1, a transcriptional target of E2F3. Manipulation of miR-34a reprograms granulocytic differentiation of AML blast cells with CEBPA mutations. These results define miR-34a as a novel therapeutic target in AML with CEBPA mutations.

MicroRNAs: tiny targets for engineering CHO cell phenotypes?

The ability of microRNAs to influence gene expression is now recognized as a fundamental layer of regulation within the cell. MicroRNAs have a major impact on most biological processes and have generated considerable interest as potential biomarkers as well as therapeutic or engineering targets. In this review we provide a brief overview of their biogenesis, genomic organization and mode of action, followed by a description of the methods and approaches to studying their expression. We go on to consider some of the approaches to utilizing them as tools and their potential application in the bioprocessing area, with particular emphasis on Chinese hamster ovary cell engineering.

Apoptosis-associated microRNAs are modulated in mouse, rat and human neural differentiation

Background

MicroRNAs (miRs or miRNAs) regulate several biological processes in the cell. However, evidence for miRNAs that control the differentiation program of specific neural cell types has been elusive. Recently, we have shown that apoptosis-associated factors, such as p53 and caspases participate in the differentiation process of mouse neural stem (NS) cells. To identify apoptosis-associated miRNAs that might play a role in neuronal development, we performed global miRNA expression profiling experiments in NS cells. Next, we characterized the expression of proapoptotic miRNAs, including miR-16, let-7a and miR-34a in distinct models of neural differentiation, including mouse embryonic stem cells, PC12 and NT2N cells. In addition, the expression of antiapoptotic miR-19a and 20a was also evaluated.

Results

The expression of miR-16, let-7a and miR-34a was consistently upregulated in neural differentiation models. In contrast, expression of miR-19a and miR-20a was downregulated in mouse NS cell differentiation. Importantly, differential expression of specific apoptosis-related miRNAs was not associated with increased cell death. Overexpression of miR-34a increased the proportion of postmitotic neurons of mouse NS cells.

Conclusions

In conclusion, the identification of miR-16, let-7a and miR-34a, whose expression patterns are conserved in mouse, rat and human neural differentiation, implicates these specific miRNAs in mammalian neuronal development. The results provide new insights into the regulation of neuronal differentiation by apoptosis-associated miRNAs.