MiR-181 mediates cell differentiation by interrupting the Lin28 and let-7 feedback circuit

MicroRNAs (miRNAs) have attracted attention because of their key regulatory functions in many biological events, including differentiation and tumorigenesis. Recent studies have reported the existence of a reciprocal regulatory loop between the family of let-7 miRNAs and an RNA-binding protein, Lin28, both of which have been documented for their important roles during cell differentiation. Hence, using bipotent K562 human leukemia cells and human CD34+ hematopoietic progenitor cells as research models, we demonstrate that let-7 and Lin28 have contrary roles in megakaryocytic (MK) differentiation with a dynamic balance; expression of miR-181 is capable of effectively repressing Lin28 expression, disrupting the Lin28-let-7 reciprocal regulatory loop, upregulating let-7, and eventually promoting MK differentiation. However, miR-181 lacks a significant effect on hemin-induced erythrocyte differentiation. These results demonstrate that miR-181 can function as a 'molecular switch' during hematopoietic lineage progression specific to MK differentiation, thus providing insight into future development of miRNA-oriented therapeutics.     

Short loop-targeting oligoribonucleotides antagonize Lin28 and enable pre-let-7 processing and suppression of cell growth in let-7-deficient cancer cells

MicroRNAs (miRNAs) originate from stem-loop-containing precursors (pre-miRNAs, pri-miRNAs) and mature by means of the Drosha and Dicer endonucleases and their associated factors. The let-7 miRNAs have prominent roles in developmental differentiation and in regulating cell proliferation. In cancer, the tumor suppressor function of let-7 is abrogated by overexpression of Lin28, one of several RNA-binding proteins that regulate let-7 biogenesis by interacting with conserved motifs in let-7 precursors close to the Dicer cleavage site. Using in vitro assays, we have identified a binding site for short modified oligoribonucleotides (‘looptomirs’) overlapping that of Lin28 in pre-let-7a-2. These looptomirs selectively antagonize the docking of Lin28, but still permit processing of pre-let-7a-2 by Dicer. Looptomirs restored synthesis of mature let-7 and inhibited growth and clonogenic potential in Lin28 overexpressing hepatocarcinoma cells, thereby demonstrating a promising new means to rescue defective miRNA biogenesis in Lin28-dependent cancers.     

Post-transcriptional fine-tuning of COP9 signalosome subunit biosynthesis is regulated by the c-Myc/Lin28B/let-7 pathway

The COP9 signalosome (CSN) complex controls protein degradation via the ubiquitin (Ub) proteasome system (UPS) in eukaryotes. In mammalian cells, the multimeric CSN is composed of eight subunits (CSN1 - CSN8). It regulates cullin-RING Ub ligases (CRLs), which target essential regulatory proteins for ubiquitination and subsequent degradation. Thereby, the CSN cooperates with the UPS in a variety of essential cellular functions, including DNA repair, cell cycle and differentiation. Although functions of the CSN have been elucidated, mechanisms and regulatory principles of its de novo formation are completely unknown. Here, we show that there is a fundamental mechanism that allows a coordinated expression of all CSN subunits, a prerequisite for CSN assembly. CSN subunit mRNAs are targets of miRNAs of the let-7 family suppressing CSN subunit expression in human cells. Factors that reduce or block let-7 miRNAs induce the coordinated expression of CSN subunits. For instance, over-expression of CSN1 specifically traps let-7a-1 miRNA and elevates CSN subunit levels by two- to fourfold in a coordinated manner. CSN subunit expression is also increased by specific miRNA inhibitors or by interferon (IFN)-mediated induction of STAT1 and c-Myc reducing levels of let-7 miRNAs. Activation of STAT1 by IFNα or IFNγ induces c-Myc, which increases CSN subunit expression via the Lin28B/let-7 regulatory pathway. By contrast, a let-7a-1 mimic reduces CSN subunit expression. Our data show that let-7 miRNAs control the fine-tuning and coordinated expression of subunits for CSN de novo formation, presumably a general regulatory principle for other Zomes complexes as well.     

Marked change in microRNA expression during neuronal differentiation of human teratocarcinoma NTera2D1 and mouse embryonal carcinoma P19 cells

MicroRNAs (miRNAs) are small noncoding RNAs, with a length of 19-23 nucleotides, which appear to be involved in the regulation of gene expression by inhibiting the translation of messenger RNAs carrying partially or nearly complementary sequences to the miRNAs in their 3' untranslated regions. Expression analysis of miRNAs is necessary to understand their complex role in the regulation of gene expression during the development, differentiation and proliferation of cells. Here we report on the expression profile analysis of miRNAs in human teratocarcinoma NTere2D1, mouse embryonic carcinoma P19, mouse neuroblastoma Neuro2a and rat pheochromocytoma PC12D cells, which can be induced into differentiated cells with long neuritic processes, i.e., after cell differentiation, such that the resultant cells look similar to neuronal cells. The data presented here indicate marked changes in the expression of miRNAs, as well as genes related to neuronal development, occurred in the differentiation of NTera2D1 and P19 cells. Significant changes in miRNA expression were not observed in Neuro2a and PC12D cells, although they showed apparent morphologic change between undifferentiated and differentiated cells. Of the miRNAs investigated, the expression of miRNAs belonging to the miR-302 cluster, which is known to be specifically expressed in embryonic stem cells, and of miR-124a specific to the brain, appeared to be markedly changed. The miR-302 cluster was potently expressed in undifferentiated NTera2D1 and P19 cells, but hardly in differentiated cells, such that miR-124a showed an opposite expression pattern to the miR-302 cluster. Based on these observations, it is suggested that the miR-302 cluster and miR-124a may be useful molecular indicators in the assessment of degree of undifferentiation and/or differentiation in the course of neuronal differentiation.     

Licochalcone A reverses NNK-induced ectopic miRNA expression to elicit in vitro and in vivo chemopreventive effects

BackgroundChemoprevention is the best cost-effective way regarding cancers. MicroRNAs (miRNAs) have been reported to be differentially expressed during the development of lung cancer. However, if lung cancer prevention can be achieved through modulating miRNAs expression so far remains unknown.PurposeTo discover ectopically expressed miRNAs in NNK-induced lung cancer and clarify whether Licochalcone A (lico A) can prevent NNK-induced lung cancer by modulating miRNA expression.Study design and methodsA/J mice were used to construct a lung cancer model by intraperitoneal injection with physiological saline NNK (100 mg/kg). Chemopreventive effects of lico A against lung cancer at 2 mg/kg and 20 mg/kg doses were evaluated in vivo. MicroRNA array and RT-qPCR were used to assess the expression levels of miRNAs. MLE-12 cells were treated with 0.1 mg/ml NNK, stimulating the ectopic expression pattern of miR-144-3p, miR-20a-5p, miR-29c-3p, let-7d-3p, and miR-328-3p. miR-144-3p mimics and inhibitors were used to manipulate miR-144-3p levels. The effects of lico A (10 μM) on cell cycle distribution, apoptosis, and the expression of CK19, RASA1, miR-144-3p, miR-20a-5p, miR-29c-3p, let-7d-3p, and miR-328-3p in NNK-treated MLE-12 cells were studied.ResultsThe expression levels of miR-144-3p, miR-20a-5p, and miR-29c-3p increased, while those of let-7d-3p and miR-328-3p decreased in both NNK-induced A/J mice and MLE-12 cells. Lico A could reverse the NNK-induced ectopic miRNA (miR-144-3p, miR-20a-5p, miR-29c-3p, let-7d-3p, and miR-328-3p) expression both in vivo and in vitro and elicit in vivo lung cancer chemopreventive effect against NNK. In MLE-12 cells, the overexpression of miR-144-3p elicited the same effect as NNK regarding the expression of lung cancer biomarker CK19; the silencing of miR-144-3p reversed the effect of NNK on cell cycle distribution and apoptosis. Lico A could reverse the effect of NNK on the expression of miR-144-3p, CK19, and RASA1 (predicted target of miR-144-3p).ConclusionThe present study suggests that miR-144-3p, miR-20a-5p, miR-29c-3p, let-7d-3p, and miR-328-3p were involved in the in vivo pathogenesis of NNK-induced lung cancer, and lico A could reverse the effect of NNK both in vivo and in vitro to elicit lung cancer chemopreventive effects through, at least partially, these five ectopically expressed miRNAs, especially miR-144-3p.     

miR-124 promotes neural differentiation in mouse bulge stem cells by repressing Ptbp1 and Sox9

Hair follicle stem cells (HFSCs) are able to differentiate into neurons and glial cells. Distinct microRNAs (miRNAs) regulate the proliferation and differentiation of HFSCs. However, the exact role of miR-124 in the neural differentiation of HFSCs has not been elucidated. HFSCs were isolated from mouse whisker follicles. miR-9, let-7b, and miR-124, Ptbp1 , and Sox9 expression levels were detected by real-time polymerase chain reaction (RT-PCR). The influence of miR-124 transfection was evaluated using immunostaining. We demonstrated that miR-124 and let-7b expression levels were significantly increased after the neural differentiation. Sox9 and Ptbp1 were identified as the target of miR-124 in the HFSCs. During neural differentiation and miR-124 mimicking, Ptbp1 and Sox9 levels were decreased. Moreover, the miR-124 overexpression increased MAP2 (58.43 ± 11.26) and NeuN (48.34 ± 11.15) proteins expression. The results demonstrated that miR-124 may promote the differentiation of HFSCs into neuronal cells by targeting Sox9 and Ptbp1.     

Transcriptional changes in response to X chromosome dosage in the mouse: implications for X inactivation and the molecular basis of Turner Syndrome

Background

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

Results

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

Conclusions

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

Exposure to Endocrine Disruptor Induces Transgenerational Epigenetic Deregulation of MicroRNAs in Primordial Germ Cells

In mammals, germ cell differentiation is initiated in the Primordial Germ Cells (PGCs) during fetal development. Prenatal exposure to environmental toxicants such as endocrine disruptors may alter PGC differentiation, development of the male germline and induce transgenerational epigenetic disorders. The anti-androgenic compound vinclozolin represents a paradigmatic example of molecule causing transgenerational effects on germ cells. We performed prenatal exposure to vinclozolin in mice and analyzed the phenotypic and molecular changes in three successive generations. A reduction in the number of embryonic PGCs and increased rate of apoptotic cells along with decrease of fertility rate in adult males were observed in F1 to F3 generations. Blimp1 is a crucial regulator of PGC differentiation. We show that prenatal exposure to vinclozolin deregulates specific microRNAs in PGCs, such as miR-23b and miR-21, inducing disequilibrium in the Lin28/let-7/Blimp1 pathway in three successive generations of males. As determined by global maps of cytosine methylation, we found no evidence for prominent changes in DNA methylation in PGCs or mature sperm. Our data suggest that embryonic exposure to environmental endocrine disruptors induces transgenerational epigenetic deregulation of expression of microRNAs affecting key regulatory pathways of germ cells differentiation.     

Decrease of Let-7f in Low-Dose Metronomic Paclitaxel Chemotherapy Contributed to Upregulation of Thrombospondin-1 in Breast Cancer

Low-dose metronomic (LDM) paclitaxel therapy displayed a stronger anti-angiogenic activity on breast tumors with fewer side effects. Upregulation of anti-angiogenic factor Thrombospondin-1 (TSP-1) accords for therapeutic potency of LDM paclitaxel, but its molecular mechanism has not been elucidated yet. microRNAs (miRNAs) have emerged as new important regulators of tumor growth and metastasis. Here, we hypothesize that miRNAs are involved in TSP-1 overexpression in paclitaxel LDM therapy of breast tumors. The miRNA profile of tumor tissues from control, LDM and MTD groups in 4T1 mouse breast cancer model was detected by microarray, and then verified by quantitative real-time PCR (qRT-PCR). Luciferase assay and western blot were employed to explore the mechanisms of miRNAs involved in this process. We found that let-7f, let-7a, miR-19b and miR-340-5p were reduced by >2 fold, and miR-543* and miR-684 were upregulated by at least 50% in paclitaxel LDM therapy. qRT-PCR verification revealed that let-7f level was reduced most significantly in LDM therapy. Computational prediction using TargetScan and miRanda suggested THBS1 which encodes TSP-1 as a potential target for let-7f. Luciferase activity assay further confirmed that let-7f may bind to 3''UTR of THBS1 gene and inhibit its activity. Moreover, forced expression of let-7f led to a decrease of TSP-1 at both mRNA and protein levels in MCF-7 cells. Contrastly, let-7f inhibition induced an increased expression of THBS1 mRNA and TSP-1 protein, but did not affect the proliferation and apoptosis of MCF-7 cells. Paclitaxel LDM therapy led to a decrease of let-7f and the elevation of TSP-1 protein expression in MCF-7 cells, while overexpression of let-7f may abolish LDM-induced the upregulation of TSP-1 in MCF-7 cells. In summary, let-7f inhibition contributed to the upregulation of TSP-1 in paclitaxel LDM therapy, independently of proliferation, cell cycle arrest and apoptosis of breast cancer. This study indicates let-7f as a potential therapeutic target for breast tumor.     

Expression profiling of mammalian microRNAs uncovers a subset of brain-expressed microRNAs with possible roles in murine and human neuronal differentiation

Background  

The microRNAs (miRNAs) are an extensive class of small noncoding RNAs (18 to 25 nucleotides) with probable roles in the regulation of gene expression. In Caenorhabditis elegans, lin-4 and let-7 miRNAs control the timing of fate specification of neuronal and hypodermal cells during larval development. lin-4, let-7 and other miRNA genes are conserved in mammals, and their potential functions in mammalian development are under active study.     

Regulatory roles of miR-155 and let-7b on the expression of inflammation-related genes in THP-1 cells: effects of fatty acids

The main aim of this investigation was to study the regulatory roles of let-7b and miR-155-3p on the expression of inflammation-associated genes in monocytes, macrophages, and lipopolysaccharide (LPS)-activated macrophages (AcM). A second goal was to analyze the potential modulatory roles of different fatty acids, including oleic, palmitic, eicosapentaenoic (EPA), and docosahexaenoic (DHA), on the expression of these miRNAs in the three cell types. This hypothesis was tested in human acute monocytic leukemia cells (THP-1), which were differentiated into macrophages with 2-O-tetradecanoylphorbol-13-acetate (TPA) and further activated with LPS for 24 h. Monocytes, macrophages, and AcM were transfected with a negative control, or mimics for miR-155-3p and miR-let-7b-5p. The expression of both miRNAs and some proinflammatory genes was analyzed by qRT-PCR. Interestingly, let-7b mimic reduced the expression of IL6 and TNF in monocytes, and SERPINE1 expression in LPS-activated macrophages. However, IL6, TNF, and SERPINE1 were upregulated in macrophages by let-7b mimic. IL6 expression was higher in the three types of cells after transfecting with miR-155-3p mimic. Similarly, expression of SERPINE1 was increased by miR-155-3p mimic in monocytes and macrophages. However, TLR4 was downregulated by miR-155-3p in monocytes and macrophages. Regarding the effects of the different fatty acids, oleic acid increased the expression of let-7b in macrophages and AcM and also increased the expression of miR-155 in monocytes when compared with DHA but not when compared with non-treated cells. Overall, these results suggest anti- and proinflammatory roles of let-7b and miR-155-3p in THP-1 cells, respectively, although these outcomes are strongly dependent on the cell type. Noteworthy, oleic acid might exert beneficial anti-inflammatory effects in immune cells (i.e., non-activated and LPS-activated macrophages) by upregulating the expression of let-7b.