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

Epigenetic dimension of oxygen radical injury in spermatogonial epithelial cells

The present work reports a direct role of mitochondrial oxidative stress induced aberrant chromatin regulation, as a central phenomenon, to perturbed genomic integrity in the testicular milieu. Oxygen-radical injury following N-succinimidyl N-methylcarbamate treatment in mouse spermatogonial epithelial (GC-1 spg) cells induced functional derailment of mitochondrial machinery. Mitophagy resulted in marked inhibition of mitochondrial respiration and reduced mtDNA copy number. Impaired cell cycle progression along with altered H3K9me1, H4K20me3, H3, AcH3 and uH2A histone modifications were observed in the treated cells. Dense heterochromatin foci and aberrant expression of HP1α in nuclei of treated cells implied onset of senescence associated secretory phenotype mediated through nuclear accumulation of NF-κB. Neoplastic nature of daughter clones, emerged from senescent mother phenotypes was confirmed by cytogenetic instability, aberrant let-7a and let-7b miRNA expression and anchorage independent growth. Together, our results provide the first insights of redox-dependent epigenomic imbalance in spermatogonia, a previously unknown molecular paradigm.

MUC4 regulates cellular senescence in head and neck squamous cell carcinoma through p16/Rb pathway

The limited effectiveness of therapy for patients with advanced stage head and neck squamous cell carcinoma (HNSCC) or recurrent disease is a reflection of an incomplete understanding of the molecular basis of HNSCC pathogenesis. MUC4, a high molecular weight glycoprotein, is differentially overexpressed in many human cancers and implicated in cancer progression and resistance to several chemotherapies. However, its clinical relevance and the molecular mechanisms through which it mediates HNSCC progression are not well understood. This study revealed a significant upregulation of MUC4 in 78% (68/87) of HNSCC tissues compared with 10% positivity (1/10) in benign samples (P=0.006, odds ratio (95% confidence interval)=10.74 (2.0-57.56). MUC4 knockdown (KD) in SCC1 and SCC10B HNSCC cell lines resulted in significant inhibition of growth in vitro and in vivo, increased senescence as indicated by an increase in the number of flat, enlarged and senescence-associated β-galactosidase (SA-β-Gal)-positive cells. Decreased cellular proliferation was associated with G0/G1 cell cycle arrest and decrease expression of cell cycle regulatory proteins like cyclin E, cyclin D1 and decrease in BrdU incorporation. Mechanistic studies revealed upregulation of p16, pRb dephosphorylation and its interaction with histone deacetylase 1/2. This resulted in decreased histone acetylation (H3K9) at cyclin E promoter leading to its downregulation. Orthotopic implantation of MUC4 KD SCC1 cells into the floor of the mouth in nude mice resulted in the formation of significantly smaller tumors (170±18.30 mg) compared to those (375±17.29 mg) formed by control cells (P=0.00007). In conclusion, our findings showed that MUC4 overexpression has a critical role by regulating proliferation and cellular senescence of HNSCC cells. Downregulation of MUC4 may be a promising therapeutic approach for treating HNSCC patients.

Size control: the developmental physiology of body and organ size regulation

The developmental regulation of final body and organ size is fundamental to generating a functional and correctly proportioned adult. Research over the last two decades has identified a long list of genes and signaling pathways that, when perturbed, influence final body size. However, body and organ size are ultimately a characteristic of the whole organism, and how these myriad genes and pathways function within a physiological context to control size remains largely unknown. In this review, we first describe the major size-regulatory signaling pathways: the Insulin/IGF-, RAS/RAF/MAPK-, TOR-, Hippo-, and JNK-signaling pathways. We then explore what is known of how these pathways regulate five major aspects of size regulation: growth rate, growth duration, target size, negative growth and growth coordination. While this review is by no means exhaustive, our goal is to provide a conceptual framework for integrating the mechanisms of size control at a molecular-genetic level with the mechanisms of size control at a physiological level.

Down-regulation of microRNA-9 leads to activation of IL-6/Jak/STAT3 pathway through directly targeting IL-6 in HeLa cell

MicroRNA‐9 (miR‐9) presents to exert distinct and even opposite functions in different kinds of tumors through targeting different cellular genes. However, its role in cervical adenocarcinoma remains uncertain. Here, we report that miR‐9 is down‐regulated in cervical adenocarcinoma due to its frequent promoter‐hypermethylation and exerts its tumor suppressor role through inhibiting several novel target genes, including interleukin‐6 (IL‐6). The promoters of miR‐9 precursors (mir‐9‐1, ‐2, and ‐3) were hypermethylated in cervical adenocarcinoma tissues. Demethylation treatment of HeLa dramatically increased the expression of mature miR‐9. Both in vitro and in vivo functional experiments confirmed that miR‐9 can inhibit the proliferation, migration, and malignant transformation abilities of HeLa cells. Bioinformatics methods and array‐based RNA expression profiles were used to screen the downstream target genes of miR‐9. Dual‐luciferase reporting assay, real‐time qPCR, and ELISA or Western blot confirmed four genes (CKAP2, HSPC159, IL‐6, and TC10) to be novel direct target genes of miR‐9. Pathway annotation analysis of the differently expressed genes (DEGs) induced by ectopic miR‐9 expression revealed the enrichment in Jak/STAT3 pathway, which is one of the downstream pathways of IL‐6. Ectopic expression of miR‐9 in HeLa inhibited Jak/STAT3 signaling activity. Moreover, such effect could be partially reversed by the addition of exogenous IL‐6. In conclusion, our results here present a tumor suppressor potential of miR‐9 in cervical adenocarcinoma for the first time and suggest that miR‐9 could repress tumorigenesis through inhibiting the activity of IL‐6/Jak/STAT3 pathway. © 2015 The Authors. Molecular Carcinogenesis, published by Wiley Periodicals, Inc.

miRNA expression profile and involvement of Let-7d-APP in aged rats with isoflurane-induced learning and memory impairment

MicroRNAs (miRNAs) play a key role in different nervous system diseases. We sought to determine the role of miRNAs in isoflurane-induced learning and memory impairment in aged rats. Male Sprague-Dawley (SD) rats of 18 month were randomly assigned to control group (exposed to mock anesthesia), 2-hour group and 6-hour group (exposed to 2% isoflurane for 2 and 6 hours respectively). By Morris Water Maze, 6-hour group showed impaired learning and memory ability while 2-hour group not. As shown by miRNA array, control group and 2-hour group showed a similar miRNA expression profile. And 38 miRNAs are differently expressed in 6-hour group compared to the other 2 groups, including 21 up-regulated miRNAs and 17 down-regulated miRNAs. And 4 of the differentially expressed miRNAs were validated independently by qRT-PCR. Let-7d was downregulated in 6-hour group. Additionally, we demonstrated that amyloid precursor protein (APP) was a direct target of let-7d by Fluorescent report assay. Increased expression of APP and amyloid-β (Aβ) were found in the hippocampi of 6-hour group. Downregulation of let-7d might contribute to isoflurane-induced learning and memory impairment through upregulating its target APP, and increasing the production of Aβ subsequently.

The different expression profiles of microRNAs in elderly and young human dental pulp and the role of miR-433 in human dental pulp cells

As a kind of endogenous noncoding small RNA, MicroRNA (miRNA) plays important roles of regulation to various physiological functions, while its affections on senescence of human dental pulp cell (HDPCs) are still unknown. Thus, we identified the senescence-associated miRNAs in HDPCs by microarray analysis, predicted their targets and regulatory signaling pathway by gene ontology and Kyoto encyclopedia of genes and genomes pathway database analysis. After validated, the senescence-associated miRNAs' expression level was up- and down-regulated using lentivirus package and cell transfection to find its role in HDPCs' morphology, proliferation, apoptosis, and mineralization. The results showed 27 miRNAs differentially expressed at least 1.5-fold, of which 16 were up-regulated and 11 down-regulated, the function of their targets was mainly focused on signal transduction, cell proliferation, apoptosis, and transcription regulation. According to the change fold, we speculated that miR-433 could be one of the vital senescence-associated miRNAs of HDPCs and found its target (GRB2), validated that miR-433 could negatively regulate GRB2 and the RAS-MAPK signaling pathway, leading to the decline of proliferation and mineralization ability of HDPCs and the acceleration of cell apoptosis, suggesting the regulation of miR-433 might be the potential target to promote repair and regeneration of HDPCs in the elderly.

Development of small RNA delivery systems for lung cancer therapy

RNA interference (RNAi) has emerged as a powerful tool for studying target identification and holds promise for the development of therapeutic gene silencing. Recent advances in RNAi delivery and target selection provide remarkable opportunities for translational medical research. The induction of RNAi relies on small silencing RNAs, which affect specific messenger RNA (mRNA) degradation. Two types of small RNA molecules, small interfering RNAs (siRNAs) and microRNAs (miRNAs), have a central function in RNAi technology. The success of RNAi-based therapeutic delivery may be dependent upon uncovering a delivery route, sophisticated delivery carriers, and nucleic acid modifications. Lung cancer is still the leading cause of cancer death worldwide, for which novel therapeutic strategies are critically needed. Recently, we have reported a novel platform (PnkRNA™ and nkRNA^®) to promote naked RNAi approaches through inhalation without delivery vehicles in lung cancer xenograft models. We suggest that a new class of RNAi therapeutic agent and local drug delivery system could also offer a promising RNAi-based strategy for clinical applications in cancer therapy. In this article, we show recent strategies for an RNAi delivery system and suggest the possible clinical usefulness of RNAi-based therapeutics for lung cancer treatment.

Proteasome inhibitor-resistant cells cause EMT-induction via suppression of E-cadherin by miR-200 and ZEB1

Downregulation of E-cadherin (gene: CDH1) plays an important role in epithelial-mesenchymal transition (EMT), which is critical for normal development and disease states. As a result of long-term treatment of endometrial carcinoma Ishikawa cells with epoxomicin (EXM), the cells exhibited the phenotype for EXM-resistance (Ish/EXM cells). Moreover, CDH1 mRNA and its protein were suppressed and EMT was induced in Ish/EXM cells. Ish/EXM cells exhibited drug-resistance to other proteasome inhibitors, MG-132, PSI and PS-341 (Bortezomib). The proteasome inhibitor-resistant cells acquired invasiveness as a result of the chemotherapy. In Ish/EXM cells, E-cadherin was suppressed by upregulation of its transcriptional repressor ZEB1. Furthermore, expression of the miR-200 family (miR-200a, miR-200b, miR-200c and miR-141) found in Ishikawa cells was suppressed in Ish/EXM cells. Overexpression of the miR-200 family in Ish/EXM cells caused by transfection with the pre-miR-200 family induced downregulation of ZEB1 and enhanced expression of E-cadherin. Conversely, suppression of miR-200 expression in the Ishikawa cells by transfection with anti-miR-200 elevated the expression of ZEB1 and suppressed the expression of E-cadherin. These results suggest that acquirement of EXM-resistance in Ish/EXM cells induces up regulation of ZEB1 via suppression of the miR-200 family following suppression of E-cadherin. Since suppression of ZEB1 in Ish/EXM cells by treatment with its siRNA did not restore the miR-200 family expression, miR-200 family was placed upstream of ZEB1 to regulate the expression.

Differential microRNA expression profile comparison between epidermal stem cells and differentiated keratinocytes

The aim of the current study was to analyze the differential microRNA (miRNA) expression profiles of human epidermal stem cells (ESCs) and differentiated keratinocytes. Enzyme digestion was used in combination with rapid adhesion to collagen IV to isolate primary human ESCs and differentiated keratinocytes, from which total RNA was extracted. Fluorescence labeling, microarray hybridization and differential expression analyses were performed. Reverse transcription quantitative polymerase chain reaction (RT‑qPCR) was performed to validate the reliability of the microarray results and predict the target genes of the differentially expressed miRNAs. A total of 25 miRNAs, including hsa‑miR‑197‑5p, hsa‑miR‑125b‑5p and hsa‑miR‑376a‑3p, were upregulated, whereas 166 miRNAs, including hsa‑miR‑29b‑3p, hsa‑miR‑203 and hsa‑miR‑34a‑3p, were downregulated in the human ESCs compared with the expression in differentiated keratinocytes. RT‑qPCR results confirmed the upregulation of hsa‑miR‑197‑5p and the downregulation of hsa‑miR‑29b‑3p, which were consistent with the microarray results. miRNA target prediction indicated that the miRNA expression levels correlated with cell proliferation, differentiation, apoptosis and senescence. Expression levels of miRNAs significantly differed between human ESCs and differentiated keratinocytes. This finding may be attributed to their biological characteristics, such as proliferative behavior and differentiation abilities.

A genetic interactome of the let-7 microRNA in C. elegans

The heterochronic pathway controls temporal patterning during Caenorhabditis elegans larval development. The highly conserved let-7 microRNA (miRNA) plays a key role in this pathway, directing the larval-to-adult (L/A) transition. Hence, knowledge of the genetic interactome of let-7 has the potential to provide insight into both control of temporal cell fates and mechanisms of regulation and function of miRNAs. Here, we report the results of a genome-wide, RNAi-based screen for suppressors of let-7 mutant vulval bursting. The 201 genetic interaction partners of let-7 thus identified include genes that promote target silencing activity of let-7, seam cell differentiation, or both. We illustrate the suitability of our approach by uncovering the mitotic cyclin-dependent kinase CDK-1 as a downstream effector of let-7 that affects both seam cell proliferation and differentiation, and by identifying a core set of candidate modulators of let-7 activity, which includes all subunits of the condensin II complex. We propose that the genes identified in our screen thus constitute a valuable resource for studies of the heterochronic pathway and miRNAs.

Non-small-cell lung cancer and miRNAs: novel biomarkers and promising tools for treatment

Lung cancer is the leading cause of cancer-related death worldwide, with approximately 80–85% of cases being non-small-cell lung cancer (NSCLC). The miRNAs are small non-coding RNAs that regulate gene expression at a post-transcriptional level by either degradation or inhibition of the translation of target genes. Evidence is mounting that miRNAs exert pivotal effects in the development and progression of human malignancies, including NSCLC. A better understanding of the role that miRNAs play in the disease will contribute to the development of new diagnostic biomarkers and individualized therapeutic tools. In the present review, we briefly describe the role of miRNAs in NSCLC as well as the possible future of these discoveries in clinical applications.

DICER1 regulated let-7 expression levels in p53-induced cancer repression requires cyclin D1

Let-7 miRNAs act as tumour suppressors by directly binding to the 3′UTRs of downstream gene products. The regulatory role of let-7 in downstream gene expression has gained much interest in the cancer research community, as it controls multiple biological functions and determines cell fates. For example, one target of the let-7 family is cyclin D1, which promotes G0/S cell cycle progression and oncogenesis, was correlated with endoribonuclease DICER1, another target of let-7. Down-regulated let-7 has been identified in many types of tumours, suggesting a feedback loop may exist between let-7 and cyclin D1. A potential player in the proposed feedback relationship is Dicer, a central regulator of miRNA expression through sequence-specific silencing. We first identified that DICER1 is the key downstream gene for cyclin D1-induced let-7 expression. In addition, we found that let-7 miRNAs expression decreased because of the p53-induced cell death response, with deregulated cyclin D1. Our results also showed that cyclin D1 is required for Nutlin-3 and TAX-induced let-7 expression in cancer repression and the cell death response. For the first time, we provide evidence that let-7 and cyclin D1 form a feedback loop in regulating therapy response of cancer cells and cancer stem cells, and importantly, that alteration of let-7 expression, mainly caused by cyclin D1, is a sensitive indicator for better chemotherapies response.

LIN28A marks the spermatogonial progenitor population and regulates its cyclic expansion

One of the hallmarks of highly proliferative adult tissues is the presence of a stem cell population that produces progenitor cells bound for differentiation. Progenitor cells undergo multiple transit amplifying (TA) divisions before initiating terminal differentiation. In the adult male germline, daughter cells arising from the spermatogonial stem cells undergo multiple rounds of TA divisions to produce undifferentiated clones of interconnected 2, 4, 8, and 16 cells, collectively termed A(undifferentiated) (A(undiff)) spermatogonia, before entering a stereotypic differentiation cascade. Although the number of TA divisions markedly affects the tissue output both at steady state and during regeneration, mechanisms regulating the expansion of the TA cell population are poorly understood in mammals. Here, we show that mice with a conditional deletion of Lin28a in the adult male germline, display impaired clonal expansion of the progenitor TA A(undiff) spermatogonia. The in vivo proliferative activity of Au(ndiff) spermatogonial cells as indicated by BrdU incorporation during S-phase was reduced in the absence of LIN28A. Thus, contrary to the role of LIN28A as a key determinant of cell fate signals in multiple stem cell lineages, in the adult male germline it functions as an intrinsic regulator of proliferation in the population of A(undiff) TA spermatogonia. In addition, neither precocious differentiation nor diminished capacity for self-renewal potential as assessed by transplantation was observed, suggesting that neither LIN28A itself nor the pool of Aal progenitor cells substantially contribute to the functional stem cell compartment.

MicroRNA let-7a modifies the effect of self-renewal gene HIWI on patient survival of epithelial ovarian cancer

Aberrant expressions of self-renewal gene HIWI and microRNA (miRNA) let-7a are observed in epithelial ovarian cancer (EOC). A U-shape association between HIWI expression and overall survival is seen in several human cancers but unknown in EOC. HIWI directly and/or indirectly interacts with let-7a, but the clinical relevance of this interaction is yet to be addressed. Here, we analyzed HIWI and let-7a expressions in 211 primary EOC tissues using quantitative reverse-transcription PCR to investigate HIWI and its interaction with let-7a in the prognostic significance of EOC. Associations of HIWI and its interaction with miRNA let-7a with patient survival were analyzed using the Kaplan-Meier survival curves and Cox proportional hazard regression models. Kaplan-Meier survival curves showed that patients with medium HIWI had poorer overall survival than those with low or high HIWI. An 89% increased death risk (HR = 1.89, 95% CI: 1.29-2.98) was observed in the medium HIWI group in multivariate Cox proportional hazard regression analyses. Among patients with high let-7a expression, those with medium HIWI had an increased risk of death compared to those with low HIWI (HR = 2.62, 95% CI: 1.30-5.30), whereas among those with low let-7a, no significant association between HIWI expression and overall survival was observed (HR = 1.63, 95% CI: 0.86-3.08). Moreover, HIWI expression also affected chemotherapy response. The results suggested that miRNA let-7a could modify the effect of HIWI expression on patient survival of EOC, expanding our understanding of the clinical relevance of HIWI and let-7a interaction in EOC prognosis. © 2015 Wiley Periodicals, Inc.

MicroRNA let-7b regulates genomic balance by targeting Aurora B kinase

The let-7 microRNA (miRNA) family has been implicated in the regulation of diverse cellular processes and disease pathogenesis. In cancer, loss-of-function of let-7 miRNAs has been linked to tumorigenesis via increased expression of target oncogenes. Excessive proliferation rate of tumor cells is often associated with deregulation of mitotic proteins. Here, we show that let-7b contributes to the maintenance of genomic balance via targeting Aurora B kinase, a key regulator of the spindle assembly checkpoint (SAC). Our results indicate that let-7b binds to Aurora B kinase 3'UTR reducing mRNA and protein expression of the kinase. In cells, excess let-7b induced mitotic defects characteristic to Aurora B perturbation including increased rate of polyploidy and multipolarity, and premature SAC inactivation that leads to forced exit from chemically induced mitotic arrest. Moreover, the frequency of aneuploid HCT-116 cells was significantly increased upon let-7b overexpression compared to controls. Interestingly, together with a chemical Aurora B inhibitor, let-7b had an additive effect on polyploidy induction in HeLa cells. In breast cancer patients, reduced let-7b expression was found to be associated with increased Aurora B expression in grade 3 tumors. Furthermore, let-7b was found downregulated in the most aggressive forms of breast cancer determined by clinicopathological parameters. Together, our findings suggest that let-7b contributes to the fidelity of cell division via regulation of Aurora B. Moreover, the loss of let-7b in aggressive tumors may drive tumorigenesis by up-regulation of Aurora B and other targets of the miRNA, which further supports the role of let-7b in tumor suppression.

Loss of estrogen-regulated microRNA expression increases HER2 signaling and is prognostic of poor outcome in luminal breast cancer

Among the genes regulated by estrogen receptor (ER) are miRNAs that play a role in breast cancer signaling pathways. To determine whether miRNAs are involved in ER-positive breast cancer progression to hormone independence, we profiled the expression of 800 miRNAs in the estrogen-dependent human breast cancer cell line MCF7 and its estrogen-independent derivative MCF7:2A (MCF7:2A) using NanoString. We found 78 miRNAs differentially expressed between the two cell lines, including a cluster comprising let-7c, miR99a, and miR125b, which is encoded in an intron of the long noncoding RNA LINC00478. These miRNAs are ER targets in MCF7 cells, and nearby ER binding and their expression are significantly decreased in MCF7:2A cells. The expression of these miRNAs was interrogated in patient samples profiled in The Cancer Genome Atlas (TCGA). Among luminal tumors, these miRNAs are expressed at higher levels in luminal A versus B tumors. Although their expression is uniformly low in luminal B tumors, they are lost only in a subset of luminal A patients. Interestingly, this subset with low expression of these miRNAs had worse overall survival compared with luminal A patients with high expression. We confirmed that miR125b directly targets HER2 and that let-7c also regulates HER2 protein expression. In addition, HER2 protein expression and activity are negatively correlated with let-7c expression in TCGA. In summary, we identified an ER-regulated miRNA cluster that regulates HER2, is lost with progression to estrogen independence, and may serve as a biomarker of poor outcome in ER(+) luminal A breast cancer patients.

Over-expression of cofilin-1 suppressed growth and invasion of cancer cells is associated with up-regulation of let-7 microRNA

Cofilin-1, a non-muscle isoform of actin regulatory protein that belongs to the actin-depolymerizing factor (ADF)/cofilin family is known to affect cancer development. Previously, we found that over-expression of cofilin-1 suppressed the growth and invasion of human non-small cell lung cancer (NSCLC) cells in vitro. In this study, we further investigated whether over-expression of cofilin-1 can suppress tumor growth in vivo, and performed a microRNA array analysis to better understand whether specific microRNA would be involved in this event. The results showed that over-expression of cofilin-1 suppressed NSCLC tumor growth using the xenograft tumor model with the non-invasive reporter gene imaging modalities. Additionally, cell motility and invasion were significantly suppressed by over-expressed cofilin-1, and down-regulation of matrix metalloproteinase (MMPs) -1 and -3 was concomitantly detected. According to the microRNA array analysis, the let-7 family, particularly let-7b and let-7e, were apparently up-regulated among 248 microRNAs that were affected after over-expression of cofilin-1 up to 7 days. Knockdown of let-7b or let-7e using chemical locked nucleic acid (LNA) could recover the growth rate and the invasion of cofilin-1 over-expressing cells. Next, the expression of c-myc, LIN28 and Twist-1 proteins known to regulate let-7 were analyzed in cofilin-1 over-expressing cells, and Twist-1 was significantly suppressed under this condition. Up-regulation of let-7 microRNA by over-expressed cofilin-1 could be eliminated by co-transfected Twist-1 cDNA. Taken together, current data suggest that let-7 microRNA would be involved in over-expression of cofilin-1 mediated tumor suppression in vitro and in vivo.

HPV16 early gene E5 specifically reduces miRNA-196a in cervical cancer cells

High-risk human papillomavirus (HPV) type 16, which is responsible for greater than 50% of cervical cancer cases, is the most prevalent and lethal HPV type. However, the molecular mechanisms of cervical carcinogenesis remain elusive, particularly the early steps of HPV infection that may transform normal cervical epithelium into a pre-neoplastic state. Here, we report that a group of microRNAs (microRNAs) were aberrantly decreased in HPV16-positive normal cervical tissues, and these groups of microRNAs are further reduced in cervical carcinoma. Among these miRNAs, miR196a expression is the most reduced in HPV16-infected tissues. Interestingly, miR196a expression is low in HPV16-positive cervical cancer cell lines but high in HPV16-negative cervical cancer cell lines. Furthermore, we found that only HPV16 early gene E5 specifically down-regulated miRNA196a in the cervical cancer cell lines. In addition, HoxB8, a known miR196a target gene, is up-regulated in the HPV16 cervical carcinoma cell line but not in HPV18 cervical cancer cell lines. Various doses of miR196a affected cervical cancer cell proliferation and apoptosis. Altogether, these results suggested that HPV16 E5 specifically down-regulates miR196a upon infection of the human cervix and initiates the transformation of normal cervix cells to cervical carcinoma.

The Tumor Cytosol miRNAs, Fluid miRNAs, and Exosome miRNAs in Lung Cancer

The focus of this review is to provide an update on the progress of microRNAs (miRNAs) as potential biomarkers for lung cancer. miRNAs are single-stranded, small non-coding RNAs that regulate gene expression and show tissue-specific signatures. Accumulating evidence indicates that miRNA expression patterns represent the in vivo status in physiology and disease. Moreover, miRNAs are stable in serum and other clinically convenient and available tissue sources, so they are being developed as biomarkers for cancer and other diseases. Cancer is currently the primary driver of the field, but miRNA biomarkers are being developed for many other diseases such as cardiovascular and central nervous system diseases. Here, we examine the framework and scope of the miRNA landscape as it specifically relates to the translation of miRNA expression patterns/signatures into biomarkers for developing diagnostics for lung cancer. We focus on examining tumor cytosol miRNAs, fluid miRNAs, and exosome miRNAs in lung cancer, the connections among these miRNAs, and the potential of miRNA biomarkers for the development of diagnostics. In lung cancer, miRNAs have been studied in both cell populations and in the circulation. However, a major challenge is to develop biomarkers to monitor cancer development and to identify circulating miRNAs that are linked to cancer stage. Importantly, the fact that miRNAs can be successfully harvested from biological fluids allows for the development of biofluid biopsies, in which miRNAs as circulating biomarkers can be captured and analyzed ex vivo. Our hope is that these minimally invasive entities provide a window to the in vivo milieu of the patients without the need for costly, complex invasive procedures, rapidly moving miRNAs from research to the clinic.

MicroRNA regulatory networks in idiopathic pulmonary fibrosis

Idiopathic pulmonary fibrosis (IPF) is a chronic, progressive, and fatal scarring lung disease of unknown etiology, characterized by changes in microRNA expression. Activation of transforming growth factor (TGF-β) is a key event in the development of IPF. Recent reports have also identified epigenetic modification as an important player in the pathogenesis of IPF. In this review, we summarize the main results of studies that address the role of microRNAs in IPF and highlight the synergistic actions of these microRNAs in regulating TGF-β, the primary fibrogenic mediator. We outline epigenetic regulation of microRNAs by methylation. Functional studies identify microRNAs that alter proliferative and migratory properties of fibroblasts, and induce phenotypic changes in epithelial cells consistent with epithelial-mesenchymal transition. Though these studies were performed in isolation, we identify multiple co-operative actions after assembling the results into a network. Construction of such networks will help identify disease-propelling hubs that can be targeted for therapeutic purposes.

Therapeutic potential of microRNA let-7: tumor suppression or impeding normal stemness

The first microRNA, let-7, and its family were discovered in Caenorhabditis elegans and are functionally conserved from worms to humans in the regulation of embryonic development and stemness. The let-7 family has been shown to have an essential role in stem cell differentiation and tumor-suppressive activity. Deregulating expression of let-7 is commonly reported in many human cancers. Emerging evidence has accumulated and suggests that reestablishment of let-7 in tumor cells is a valuable therapeutic strategy. However, findings reach beyond tumor therapeutics and may impinge on stemness and differentiation of stem cells. In this review, we discuss the role of let-7 in development and differentiation of normal adult stem/progenitor cells and offer a viewpoint of the association between deregulated let-7 expression and tumorigenesis. The regulation of let-7 expression, cancer-relevant let-7 targets, and the application of let-7 are highlighted.

Fluorescence probing of metal-ion-mediated hybridization of oligonucleotides

The structure-dependent fluorescence of pyrrolocytosine has been harnessed to quantify the affinity of metal-ion-chelating oligonucleotides for their native counterparts.

Lin28 and let-7 in cell metabolism and cancer

Malignant cells exhibit major metabolic alterations. The regulatory gene networks that regulate metabolism and the impact of these alterations on overall cellular fitness deserve further exploration. The let-7 microRNAs and their antagonists, the Lin28 RNA-binding proteins, are well-known for controlling the timing of embryonic development. This pathway has recently been shown to regulate glucose metabolism in adult mice and to reprogram metabolism during tissue injury and repair. In addition, many lines of evidence have established that Lin28 is an oncogene that drives tumorigenesis in part by suppressing let-7. The metabolic underpinnings of this oncogenic program are just beginning to be uncovered. Here, we will review the current understanding of how Lin28 exerts regenerative and oncogenic effects through metabolic mechanisms.

A biochemical approach to identify direct microRNA targets

We have recently developed a biochemical approach to isolate miRNA-bound mRNAs and have used this method to identify the genome-wide mRNAs regulated by the tumor suppressor miRNA miR-34a. This method involves transfection of cells with biotinylated miRNA mimics, streptavidin pulldown, RNA isolation, and qRT-PCR. The protocol in this chapter describes these steps and the issues that should be considered while designing such pulldown experiments.

DNA hybridization on silicon nanowire platform prepared by glancing angle deposition and metal assisted chemical etching process

Porous nanowire surface provides high capacity for oligonucleotide hybridization.

Combination of microRNA therapeutics with small-molecule anticancer drugs: mechanism of action and co-delivery nanocarriers

MicroRNAs (miRNAs) regulate multiple molecular pathways vital for the hallmarks of cancer with a high degree of biochemical specificity and potency. By restoring tumor suppressive miRNAs or ablating oncomiRs, miRNA-based therapies can sensitize cancer cells to conventional cytotoxins and the molecularly targeted drugs by promoting apoptosis and autophagy, reverting epithelial-to-mesenchymal transition, suppressing tumor angiogenesis, and downregulating efflux transporters. The development of miRNA-based therapeutics in combination with small-molecule anticancer drugs provides an unprecedented opportunity to counteract chemoresistance and improve treatment outcome in a broad range of human cancers. This review summarizes the mechanisms and advantages for the combination therapies involving miRNAs and small-molecule drugs, as well as the recent advances in the co-delivery nanocarriers for these agents.

The emerging role of microRNAs in resistance to lung cancer treatments

One of the major challenges in the treatment of lung cancer is the development of drug resistance. This represents a major obstacle in the treatment of patients, limiting the efficacy of both conventional chemotherapy and biological therapies. Deciphering the mechanisms of resistance is critical to further understanding the multifactorial pathways involved, and in developing more specific targeted treatments. To date, numerous studies have reported the potential role of microRNAs (miRNAs) in resistance to various cancer treatments. MicroRNAs are a family of small non-coding RNAs that regulate gene expression by sequence-specific targeting of mRNAs causing translational repression or mRNA degradation. More than 1200 validated human miRNAs have been identified to date. While as little as one miRNA can regulate hundreds of targets, a single target can also be affected by multiple miRNAs. Evidence suggests that dysregulation of specific miRNAs may be involved in the acquisition of resistance to a number of cancer treatments, thereby modulating the sensitivity of cancer cells to such therapies. Therefore, targeting miRNAs may be an attractive strategy for developing novel and more effective individualized therapies, improving drug efficiency, and for predicting patient response to different treatments. In this review, we provide an overview on the role of miRNAs in resistance to current lung cancer therapies and novel biological agents.

A summary for molecular regulations of miRNAs in breast cancer

BACKGROUND

Breast cancer is the most frequently diagnosed cancer and the leading cause of cancer-related death among women worldwide. MicroRNAs (miRNAs) are naturally-occurring, non-coding small RNA molecules that can modulate protein coding-genes, which makes it contributing to nearly all the physiological and pathological processes. Progression of breast cancer and resistance to endocrine therapies have been attributed to the possibility of hormone-responsive miRNAs involved in the regulation of certain signaling pathways.

METHODOLOGY

This review introduces better understanding of miRNAs to provide promising advances for treatment. miRNAs have multiple targets, and they were found to regulate different signaling pathways; consequently it is important to characterize their mechanisms of action and their cellular targets in order to introduce miRNAs as novel and promising therapies.

RESULTS

This review summarizes the molecular mechanisms of miRNAs in TGF-beta signaling, apoptosis, metastasis, cell cycle, ER-signaling, and drug resistance.

CONCLUSION

Finally, miRNAs will be introduced as promising molecules to be used in the fight against breast cancer and its developed drug resistance.

Serum miR-152, miR-148a, miR-148b, and miR-21 as novel biomarkers in non-small cell lung cancer screening

Lung cancer, predominantly by non-small cell lung cancer (NSCLC), is the leading cause of cancer-related deaths over the world. Late diagnosis is one of important reasons for high mortality rate in lung cancer. Current diagnostic approaches have disadvantages such as low accuracy, high cost, invasive procedure, etc. MicroRNAs were previously proposed as promising novel biomarkers in cancer screening. In this study, we evaluated the predictive power of four candidate miRNAs in NSCLC detection. Our study involved 152 NSCLC patients and 300 healthy controls. Blood samples were obtained from the total 452 subjects. After miRNA extraction from serum, the expression of miRNAs in cases and controls were quantified by qRT-PCR and normalized to the level of U6 small RNA. Statistical analyses were performed to compare miRNA levels between cases and controls. Stratified analyses were employed to compare miRNA levels in NSCLC patients with different clinical characteristics. Serum miR-148a, miR-148b, and miR-152 were significantly downregulated in NSCLC patients. However, overexpression of serum miR-21 was observed in NSCLC patients. The combination of four candidate miRNAs exhibited the highest predictive accuracy in NSCLC screening compared with individual miRNAs (AUC = 0.97). Low level of miRNA-148/152 members may associate with advanced stage, large tumor size, malignant cell differentiation, and metastasis. High expression of miR-21 was possibly correlated with large size tumor and advanced cancer stage. Our results showed the dysregulation of miR-148/152 family and miR-21 in NSCLC patients. Hence, the four candidate miRNAs have great potential to serve as promising novel biomarkers in NSCLC screening. Further large-scale studies are needed to validate our results.

EBV-encoded miR-BART20-5p and miR-BART8 inhibit the IFN-γ-STAT1 pathway associated with disease progression in nasal NK-cell lymphoma

Nasal NK-cell lymphoma (NNL) is an Epstein-Barr virus (EBV)-associated lymphoma of cytotoxic natural killer (NK) cell origin. Because normal NK cells secrete the principal cytotoxic cytokine IFN-γ to suppress both tumor growth and viral replication, we investigated how EBV may have used miRNAs of viral origin to inhibit the IFN-γ-STAT1 pathway to facilitate viral replication and tumor growth. In EBV(-) Jurkat cells, transfection of miR-BART20-5p and miR-BART8 inhibited translation of luciferase-IFN-γ-3'-UTR and luciferase-STAT1-3'-UTR, respectively. In EBV(+) IFN-γ(weak)/STAT1(strong) YT leukemic cells and IFN-γ(strong)/STAT1(weak) NK92 cells, relative endogenous levels between miR-BART20-5p and IFN-γ mRNAs or between miR-BART8 and STAT1 mRNAs determined expression of the targets. Chromatin immunoprecipitation studies showed that STAT1 regulates the transcription of the tumor suppressor TP53 (encoding p53) and miR-let7a. Consistent with these findings, overexpression of miR-BART8 in YT cells or of miR-BART20-5p in NK92 cells inhibited p53 and increased resistance to doxorubicin. In 36 NNLs, the levels of miR-BART20-5p or miR-BART8 correlated inversely with the expression of STAT1. Additionally, in 46 NNLs, expression of both miR-BART20-5p and miR-BART8 identified a group of NNLs with decreased p53 mRNAs and evidence of disease progression. We conclude that miR-BART20-5p and miR-BART8 cause progression of nasal NK-cell lymphomas through inhibition of the IFN-γ-STAT1 pathway.

MicroRNAome of porcine conceptuses and trophoblasts: expression profile of micrornas and their potential to regulate genes crucial for establishment of pregnancy

Tightly coordinated, reciprocal embryo-maternal interactions affect gene expression during early pregnancy. Recently, microRNAs (miRNAs) have emerged as new players in the fine tuning of embryo development and implantation in mammals via posttranscriptional gene regulation mechanisms. Here, we integrated transcriptomic and computational approaches to profile miRNAs and miRNA synthesis and transport-related genes at different developmental stages of porcine conceptuses and trophoblast during early pregnancy in the pig. Using semiquantitative RT-PCR, we examined mRNA levels of 10 genes encoding proteins involved in miRNA synthesis and transport: DROSHA, DGCR8, XPO5, DICER1, TARBP2, TNRC6A, AGO1, AGO2, AGO3, and AGO4. Custom, multispecies microarrays were used to profile miRNAs. Prediction algorithms of miRNA-mRNA interactions allowed identification of target transcripts for the analyzed miRNAs. These included VEGF, LIF, PTGS2, and IL-6R, known to be crucial components of embryo-maternal interactions in the pig. Two selected miRNAs, miR-26a and miR-125b, were tested for the presence in the extracellular vesicles isolated from uterine luminal flushings during pregnancy. Results of in vitro study demonstrated that miRNAs, such as miR-125b, can regulate expression of genes crucial for embryo development and implantation in porcine endometrial luminal epithelial cells. For the first time, expression profiles of miRNAs and related genes in porcine conceptuses and trophoblast during maternal recognition of pregnancy and embryo implantation in the pig were described. Altogether, our results indicate potential roles of these small, noncoding RNAs in the early development of embryos and embryo-maternal cross-talk during early pregnancy in the pig.

Identification of microRNAs linked to regulators of muscle protein synthesis and regeneration in young and old skeletal muscle

Background

Over the course of ageing there is a natural and progressive loss of skeletal muscle mass. The onset and progression of age-related muscle wasting is associated with an attenuated activation of Akt-mTOR signalling and muscle protein synthesis in response to anabolic stimuli such as resistance exercise. MicroRNAs (miRNAs) are novel and important post-transcriptional regulators of numerous cellular processes. The role of miRNAs in the regulation of muscle protein synthesis following resistance exercise is poorly understood. This study investigated the changes in skeletal muscle miRNA expression following an acute bout of resistance exercise in young and old subjects with a focus on the miRNA species predicted to target Akt-mTOR signalling.

Results

Ten young (24.2±0.9 years) and 10 old (66.6±1.1 years) males completed an acute resistance exercise bout known to maximise muscle protein synthesis, with muscle biopsies collected before and 2 hours after exercise. We screened the expression of 754 miRNAs in the muscle biopsies and found 26 miRNAs to be regulated with age, exercise or a combination of both factors. Nine of these miRNAs are highly predicted to regulate targets within the Akt-mTOR signalling pathway and 5 miRNAs have validated binding sites within the 3′ UTRs of several members of the Akt-mTOR signalling pathway. The miR-99/100 family of miRNAs notably emerged as potentially important regulators of skeletal muscle mass in young and old subjects.

Conclusion

This study has identified several miRNAs that were regulated with age or with a single bout of resistance exercise. Some of these miRNAs were predicted to influence Akt-mTOR signalling, and therefore potentially skeletal muscle mass. These miRNAs should be considered as candidate targets for in vivo modulation.

Dosage and temporal thresholds in microRNA proteomics

MicroRNAs (miRNAs) modulate protein and mRNA expression through translational repression and/or mRNA decay. In this study, we combined SILAC-based proteomics and RNAseq to identify primary targets based on measurements of protein and mRNA repression and analysis of transcript 3'UTR sequences. The primary target set was used to compare different prediction algorithms, revealing higher stringency of selection by Targetscan and PITA compared with miRanda, at the expense of higher false negatives. A key finding was that significant and unexpected variations occurred in the kinetics of repression as well as the sensitivity to exogeneous miRNA concentration. Bimodal thresholds were observed, which distinguished responses to low (10 nm) versus high (50-100 nm) miRNA, as well as the onset of repression at early (12-18 h) versus late (36-48 h) times. Similar behavior was seen at the transcript level with respect to kinetics of repression. The differential thresholds were most strongly correlated with ΔΔG, the net free energy of miRNA-target interactions, which mainly reflected inverse correlations with ΔGopen, the free energy of forming 3'UTR secondary structures, at or nearby the miRNA seed matching sites. Thus, our working model is that protein binding or other competitive mechanisms variably interfere with the accessibility of miRISC to the transcript binding site. In addition, biphasic responses were observed in a subset of proteins that were partially down-regulated at early times, and further down-regulated at later times. Taken together, our findings provide evidence for varying modes of miRNA target repression, which lead to different thresholds of target responses with respect to kinetics and concentration, and predict that certain transcripts will show graded responses in sensitivity and fold-change under cellular conditions that lead to varying steady state miRNA levels.

The tumor suppressor miR-124 inhibits cell proliferation by targeting STAT3 and functions as a prognostic marker for postoperative NSCLC patients

The aim of the present study was to investigate the role of miR-124 in lung cancer and identify the potential predictive value of miR-124 in postoperative non-small cell lung cancer (NSCLC) patients. We detected miR-124 expression in A549, NCL-H460 and normal lung epithelial BEAS-2E cells and showed a significantly lower expression level of miR-124 in NSCLC cells than in BEAS-2E cells. Upregulation of miR-124 expression levels in both A549 and NCL-H460 cells by transfection with miR-124 mimics suppressed cell proliferation and induced apoptosis. Further investigation revealed that miR-124 bound directly to the 3' UTR region of STAT3, thereby inhibiting STAT3 expression. In addition, miR-124 levels detected in NSCLC tissues were lower than those in adjacent normal lung tissues, while the opposite was observed for STAT3. In NSCLC, the expression levels of miR-124 and STAT3 correlated significantly with the tumor node metastases (TNM) stage, differentiation grade and lymph node metastasis, while the levels of these molecules did not differ significantly by gender, age, location, smoking index, pleural invasion or pathological type. The expression level of miR-124 was significantly associated with disease-free survival (DFS) in both positive and negative lymph node groups. Furthermore, patients with low miR-124 or high STAT3 expression generally received a worse prognosis in terms of both overall survival (OS) and DFS. In conclusion, our findings suggest that miR-124 functions as a tumor suppressor by targeting STAT3, and that miR-124 may potentially serve as a useful biomarker for the prognosis of NSCLC patients.

BRCA mutations cause reduction in miR-200c expression in triple negative breast cancer

Triple negative breast cancer (TNBC) is the most aggressive and poorly understood subclass of breast cancer (BC). Over the recent years, miRNA expression studies have been providing certain detailed overview that aberrant expression of miRNAs is associated with TNBC. Although TNBC tumors are strongly connected with loss of function of BRCA genes, there is no knowledge about the effect of BRCA mutation status on miRNA expressions in TNBC cases. The aims of this study were to evaluate the expression profile of miRNAs that plays role in TNBC progression and the role of BRCA mutations in their regulation. The expression level of BC associated 13 miRNAs was analyzed in 7 BRCA mutations positive, 6 BRCA mutations negative TNBC cases and 20 non-tumoral tissues using RT-PCR. According to RT2 Profiler PCR Array Data Analysis, let-7a expression was 4.67 fold reduced in TNBCs as compared to normal tissues (P=0.031). In addition, miR-200c expression was 5.75 fold reduced in BRCA mutation positive TNBC tumors (P=0.005). Analysis revealed a negative correlation between miR-200c and VEGFA expressions (r=-468). Thus, miR-200c may be involved in invasion and metastasis in TNBC cases with BRCA mutation. In this study we provide the knowledge on the first report of association between microRNA-200c and BRCA mutations in TNBC. Further studies and evaluations are required, but this miRNA may provide novel therapeutic molecular targets for TNBC treatment and new directions for the development of anticancer drugs.

Non-coding RNAs in lung cancer

The discovery that protein-coding genes represent less than 2% of all human genome, and the evidence that more than 90% of it is actively transcribed, changed the classical point of view of the central dogma of molecular biology, which was always based on the assumption that RNA functions mainly as an intermediate bridge between DNA sequences and protein synthesis machinery. Accumulating data indicates that non-coding RNAs are involved in different physiological processes, providing for the maintenance of cellular homeostasis. They are important regulators of gene expression, cellular differentiation, proliferation, migration, apoptosis, and stem cell maintenance. Alterations and disruptions of their expression or activity have increasingly been associated with pathological changes of cancer cells, this evidence and the prospect of using these molecules as diagnostic markers and therapeutic targets, make currently non-coding RNAs among the most relevant molecules in cancer research. In this paper we will provide an overview of non-coding RNA function and disruption in lung cancer biology, also focusing on their potential as diagnostic, prognostic and predictive biomarkers.

The effects of telomere shortening on cancer cells: a network model of proteomic and microRNA analysis

Previously, we have shown that shortening of telomeres by telomerase inhibition sensitized cancer cells to cisplatinum, slowed their migration, increased DNA damage and impaired DNA repair. The mechanism behind these effects is not fully characterized. Its clarification could facilitate novel therapeutics development and may obviate the time consuming process of telomere shortening achieved by telomerase inhibition. Here we aimed to decipher the microRNA and proteomic profiling of cancer cells with shortened telomeres and identify the key mediators in telomere shortening-induced damage to those cells. Of 870 identified proteins, 98 were differentially expressed in shortened-telomere cells. 47 microRNAs were differentially expressed in these cells; some are implicated in growth arrest or act as oncogene repressors. The obtained data was used for a network construction, which provided us with nodal candidates that may mediate the shortened-telomere dependent features. These proteins' expression was experimentally validated, supporting their potential central role in this system.

MicroRNA let-7g and let-7i inhibit hepatoma cell growth concurrently via downregulation of the anti-apoptotic protein B-cell lymphoma-extra large

Let-7 family members have been identified as tumor-suppressing microRNAs, which are important in human hepatocellular carcinoma (HCC). These family members may function differently as a result of different base sequences at the 3′end. The aim of this study was to determine the antitumor effects of miR-let-7g/i (let-7g/i) on HCC cells and to investigate whether let-7g and let-7i have a combinatorial effect on HCC. The expression levels of let-7g/i in hepatoma cells were determined by quantitative reverse transcription polymerase chain reaction. In addition, a 5-ethynyl-2′-deoxyuridine retention assay and flow cytometry analysis were used to detect the effect of let-7g/i on the proliferation and apoptosis of BEL-7402 cells, respectively. The expression of anti-apoptotic protein B-cell lymphoma-extra large (Bcl-xL) was analyzed using western blot analysis. The results revealed that the expression levels of let-7g/i were significantly decreased in HCC cell lines when compared with L-02 cells. Furthermore, the overexpression of let-7g/i significantly suppressed DNA replication, inhibited cell proliferation and promoted apoptosis of BEL-7402 hepatoma cells. The expression of the anti-apoptotic protein, Bcl-xL, was inhibited by the combined role of let-7g and let-7i. We hypothesize that let-7g and let-7i exhibit a concurrent effect to regulate cell proliferation and the apoptosis of hepatoma cells, and this function is mediated by the Bcl-xL protein.

Distinct microRNA expression profiles in mouse renal cortical tissue after 177Lu-octreotate administration

Aim

The aim of this study was to investigate the variation of the miRNA expression levels in normal renal cortical tissue after ¹⁷⁷Lu-octreotate administration, a radiopharmaceutical used for treatment of neuroendocrine cancers.

Methods

Female BALB/c nude mice were i.v. injected with 1.3, 3.6, 14, 45, or 140 MBq ¹⁷⁷Lu-octreotate, while control animals received saline. The animals were killed at 24 h after injection and total RNA, including miRNA, was extracted from the renal cortical tissue and hybridized to the Mouse miRNA Oligo chip 4plex to identify differentially regulated miRNAs between exposed and control samples.

Results

In total, 57 specific miRNAs were differentially regulated in the exposed renal cortical tissues with 1, 29, 21, 27, and 31 miRNAs identified per dose-level (0.13, 0.34, 1.3, 4.3, and 13 Gy, respectively). No miRNAs were commonly regulated at all dose levels. miR-194, miR-107, miR-3090, and miR-3077 were commonly regulated at 0.34, 1.3, 4.3, and 13 Gy. Strong effects on cellular mechanisms ranging from immune response to p53 signaling and cancer-related pathways were observed at the highest absorbed dose. Thirty-nine of the 57 differentially regulated miRNAs identified in the present study have previously been associated with response to ionizing radiation, indicating common radiation responsive pathways.

Conclusion

In conclusion, the ¹⁷⁷Lu-octreotate associated miRNA signatures were generally dose-specific, thereby illustrating transcriptional regulation of radiation responsive miRNAs. Taken together, these results imply the importance of miRNAs in early immunological responses in the kidneys following ¹⁷⁷Lu-octreotate administration.

New insights into lung development and diseases: the role of microRNAs

MicroRNAs (miRNAs) are short endogenous noncoding RNA molecules (∼ 22 nucleotides) that can regulate gene expression at the post-transcription level. Research interest in the role of miRNAs in lung biology is emerging. MiRNAs have been implicated in a range of processes such as development, homeostasis, and inflammatory diseases in lung tissues and are capable of inducing differentiation, morphogenesis, and apoptosis. In recent years, several studies have reported that miRNAs are differentially regulated in lung development and lung diseases in response to epigenetic changes, providing new insights for their versatile role in various physiological and pathological processes in the lung. In this review, we discuss the contribution of miRNAs to lung development and diseases and possible future implications in the field of lung biology.

The mystery of let-7d - a small RNA with great power

miRNAs belong to a class of small non-coding RNAs which can modulate gene expression. Disturbances in their expression and function may cause cancer formation, progression and cell response to various types of stress. The let-7 family is one of the most studied groups of miRNAs. The family contains 13 members with similar sequences and a wide spectrum of target genes. In this paper, we mostly focus on one member of the family – let-7d. This miRNA is dysregulated in many types of cancers. It can be over- or down-expressed, and it acts as a tumor suppressor or oncogene. It regulates various genes such as LIN28, C-MYC, K-RAS, HMGA2 and IMP-1. Moreover, let-7d has a significant impact on epithelial-to-mesenchymal transition (EMT) and formation of cancer initiating cells which are resistant to irradiation and chemical exposure and responsible for cancer metastasis. Let-7d can serve as a prognostic and predictive marker for personalization of the treatment. Let-7d is a small RNA with great power, but in different cell genetic backgrounds it acts in different ways, which makes this molecule still mysterious.

miR-125b inhibitor may enhance the invasion-prevention activity of temozolomide in glioblastoma stem cells by targeting PIAS3

BACKGROUND

Temozolomide, an alkylating agent, is a promising chemotherapeutic agent for treating glioblastoma. Although chemotherapy with temozolomide may restrain tumor growth for some months, invariable tumor recurrence suggests that cancer stem cells maintaining these tumors persist. Previous research has shown that temozolomide can inhibit the proliferation of human glioblastoma stem cells (GSCs); however, no research has focused on the invasion of GSCs, which is an important factor for glioblastoma recurrence. Accumulating evidence indicates that microRNA (miR)-125b over-expression in GSCs may increase their invasiveness.

OBJECTIVE

Our objective was to identify the effects and mechanism of action of an miR-125b inhibitor combined with temozolomide in the invasive pathogenesis of GSCs.

METHODS

We modified the levels of miR-125b expression in primary GSCs in order to observe the effect on sensitivity to temozolomide on invasion, and we further analyzed the differences in mechanism between miR-125b treatment alone and treatment with miR-125b plus temozolomide using the Cancer PathwayFinder PCR Array.

RESULTS

Our results demonstrated that either an miR-125b inhibitor or temozolomide could modestly inhibit the invasiveness of GSCs. Furthermore, GSCs that were pre-transfected with an miR-125b inhibitor, then treated with temozolomide, showed significantly decreased invasiveness when compared with GSCs treated with an miR-125b inhibitor or temozolomide alone. Further research into the underlying mechanism demonstrated that the miR-125b inhibitor enhanced the invasion-prevention activity of temozolomide in GSCs through targeting PIAS3 (protein inhibitor of activated STAT [signal transducer and activator of transcription]), which contributed to reduced STAT3 transcriptional activity and subsequent decreased expression of matrix metalloproteinase (MMP)-2 and -9.

CONCLUSIONS

miR-125b could play a role in the development of temozolomide resistance in GSCs. Inhibition of miR-125b expression may enhance sensitivity of GSCs to temozolomide by targeting PIAS3 on cell invasion.

Let-7b binding site polymorphism in the B-cell lymphoma-extra large 3'UTR is associated with fluorouracil resistance of hepatocellular carcinoma

B-cell lymphoma-extra large (Bcl-xl) is an anti-apoptotic member of the B-cell lymphoma 2 (Bcl-2) family that is often found to be overexpressed in human hepatocellular carcinoma (HCC), therefore conferring a survival advantage to tumor cells. microRNA (miRNA) let-7b is downregulated in HCC and its expression correlates with multidrug resistance. Using computational programs, it was predicted that the 3' untranslated region (UTR) of the Bcl-xl gene contains a potential miRNA binding site for let-7b, and that a single nucleotide polymorphism (SNP) site rs3208684 (A or C allele) resides within this binding site. Luciferase assays and western blot analysis demonstrated that let‑7b targeted Bcl-xl gene expression and negatively regulated the amount of Bcl-xl protein. SNP rs3208684 (A>C) variation enhanced the expression of Bcl-xl by disrupting the binding of let-7b to the 3'UTR of Bcl-xl. The effects of the two polymorphic variants on chemotherapeutic drug sensitivity were determined by cell counting kit 8 assays. Overexpression of the Bcl-xl mutated (C) allele in BEL-7402 HCC cells significantly decreased fluorouracil (5-FU) sensitivity, as compared with mock transfection and overexpression of the wild-type allele. From this, it was concluded that let-7b increased 5-FU sensitivity by repressing Bcl-xl expression in HCC cells. These results suggest that SNP (rs3208684) may be a potential marker for personalized treatment.

Biology of childhood germ cell tumours, focussing on the significance of microRNAs

Genomic and protein-coding transcriptomic data have suggested that germ cell tumours (GCTs) of childhood are biologically distinct from those of adulthood. Global messenger RNA profiles segregate malignant GCTs primarily by histology, but then also by age, with numerous transcripts showing age-related differential expression. Such differences are likely to account for the heterogeneous clinico-pathological behaviour of paediatric and adult malignant GCTs. In contrast, as global microRNA signatures of human tumours reflect their developmental lineage, we hypothesized that microRNA profiles would identify common biological abnormalities in all malignant GCTs owing to their presumed shared origin from primordial germ cells. MicroRNAs are short, non-protein-coding RNAs that regulate gene expression via translational repression and/or mRNA degradation. We showed that all malignant GCTs over-express the miR-371-373 and miR-302/367 clusters, regardless of patient age, histological subtype or anatomical tumour site. Furthermore, bioinformatic approaches and subsequent Gene Ontology analysis revealed that these two over-expressed microRNAs clusters co-ordinately down-regulated genes involved in biologically significant pathways in malignant GCTs. The translational potential of this finding has been demonstrated with the detection of elevated serum levels of miR-371-373 and miR-302/367 microRNAs at the time of malignant GCT diagnosis, with levels falling after treatment. The tumour-suppressor let-7 microRNA family has also been shown to be universally down-regulated in malignant GCTs, because of abundant expression of the regulatory gene LIN28. Low let-7 levels resulted in up-regulation of oncogenes including MYCN, AURKB and LIN28 itself, the latter through a direct feedback mechanism. Targeting LIN28, or restoring let-7 levels, both led to effective inhibition of this pathway. In summary, paediatric malignant GCTs show biological differences from their adult counterparts at a genomic and protein-coding transcriptome level, whereas they both display very similar microRNA expression profiles. These similarities and differences may be exploited for diagnostic and/or therapeutic purposes.

MicroRNAs participate in the murine oligodendroglial response to perinatal hypoxia-ischemia

BACKGROUND

Hypoxic-ischemic injury (HI) to preterm brain results in white matter loss. The endogenous oligodendroglial response to perinatal HI is characterized by increased oligodendroglial progenitor cells (OPCs). MicroRNAs (miRs) are important post-transcriptional regulators of gene expression, and a few miRs have been shown to regulate differentiation of OPCs into mature oligodendroglia. We tested the hypothesis that miRs play a role in the increase in OPCs in response to perinatal HI.

METHODS

We inducibly deleted the miR-processing enzyme Dicer in OPCs using a tamoxifen-inducible NG2CreER(T2) transgene in Dicer(fl/fl) mice. After HI, mice were analyzed for OPC differentiation using immunofluorescence and for white matter formation by Luxol fast blue (LFB) staining. Functional recovery from injury was investigated using digital gait analysis. We also tested whether HI changed miRs known to regulate OPC differentiation using quantitative RT-PCR.

RESULTS

Perinatal HI induced significant increases in miR-138 and miR-338, two miRs known to regulate OPC differentiation. Knockdown of Dicer increased myelin basic protein and LFB staining within the corpus callosum after HI. In addition, there was significant improvement in motor function 14 and 24 d post lesion.

CONCLUSION

Changes in specific mature miRs expressed in OPCs following HI may contribute to white matter injury.

A genome-wide survey of sexually dimorphic expression of Drosophila miRNAs identifies the steroid hormone-induced miRNA let-7 as a regulator of sexual identity

MiRNAs bear an increasing number of functions throughout development and in the aging adult. Here we address their role in establishing sexually dimorphic traits and sexual identity in male and female Drosophila. Our survey of miRNA populations in each sex identifies sets of miRNAs differentially expressed in male and female tissues across various stages of development. The pervasive sex-biased expression of miRNAs generally increases with the complexity and sexual dimorphism of tissues, gonads revealing the most striking biases. We find that the male-specific regulation of the X chromosome is relevant to miRNA expression on two levels. First, in the male gonad, testis-biased miRNAs tend to reside on the X chromosome. Second, in the soma, X-linked miRNAs do not systematically rely on dosage compensation. We set out to address the importance of a sex-biased expression of miRNAs in establishing sexually dimorphic traits. Our study of the conserved let-7-C miRNA cluster controlled by the sex-biased hormone ecdysone places let-7 as a primary modulator of the sex-determination hierarchy. Flies with modified let-7 levels present doublesex-related phenotypes and express sex-determination genes normally restricted to the opposite sex. In testes and ovaries, alterations of the ecdysone-induced let-7 result in aberrant gonadal somatic cell behavior and non-cell-autonomous defects in early germline differentiation. Gonadal defects as well as aberrant expression of sex-determination genes persist in aging adults under hormonal control. Together, our findings place ecdysone and let-7 as modulators of a somatic systemic signal that helps establish and sustain sexual identity in males and females and differentiation in gonads. This work establishes the foundation for a role of miRNAs in sexual dimorphism and demonstrates that similar to vertebrate hormonal control of cellular sexual identity exists in Drosophila.

MicroRNA Sensor Based on Magnetic Beads and Enzymatic Probes

MicroRNAs are associated with multiple cellular processes and diseases. Here, we designed a highly sensitive, magnetically retrievable biosensor using magnetic beads (MBs) as a model RNA sensor. The assay utilized two biotinylated probes, which were hybridized to the complementary target miRNA in a sandwich assay format. One of the biotinylated ends of the hybridization complex was immobilized onto the surface of a NeutrAvidin (NAV) coated MB and the other biotinylated end was conjugated to HRP via NAV-biotin interaction. The results were presented by colorimetric absorbance of the resorufin product from amplex red oxidation. We show that by combining the use of MBs as well as bio-specific immobilization, the sensitivity of miRNA detection is down to 100 pM. This model HRP-MBs system can be used for simple, rapid colorimetric quantification of low level DNA/RNA or other small molecules.