MicroRNA-34a inhibits cell proliferation by repressing mitogen-activated protein kinase kinase 1 during megakaryocytic differentiation of K562 cells

Roles of non-coding RNA in megakaryocytopoiesis and thrombopoiesis: new target therapies in ITP

Noncoding RNAs (ncRNAs) are a group of RNA molecules that cannot encode proteins, and a better understanding of the complex interaction networks coordinated by ncRNAs will provide a theoretical basis for the development of therapeutics targeting the regulatory effects of ncRNAs. Platelets are produced upon the differentiation of hematopoietic stem cells into megakaryocytes, 10¹¹ per day, and are renewed every 8-9 days. The process of thrombopoiesis is affected by multiple factors, in which ncRNAs also exert a significant regulatory role. This article reviewed the regulatory roles of ncRNAs, mainly microRNAs (miRNAs), circRNAs (circular RNAs), and long non-coding RNAs (lncRNAs), in thrombopoiesis in recent years as well as their roles in primary immune thrombocytopenia (ITP).

Meta-analysis of miR-34 target mRNAs using an integrative online application

Members of the microRNA-34/miR-34 family are induced by the p53 tumor suppressor and themselves possess tumor suppressive properties, as they inhibit the translation of mRNAs that encode proteins involved in processes, such as proliferation, migration, invasion, and metastasis. Here we performed a comprehensive integrative meta-analysis of multiple computational and experimental miR-34 related datasets and developed tools to identify and characterize novel miR-34 targets. A miR-34 target probability score was generated for every mRNA to estimate the likelihood of representing a miR-34 target. Experimentally validated miR-34 targets were strongly enriched among mRNAs with the highest scores providing a proof of principle for our analysis. We integrated the results from the meta-analysis in a user-friendly METAmiR34TARGET website (www.metamir34target.com/) that allows to graphically represent the meta-analysis results for every mRNA. Moreover, the website harbors a screen function, which allows to select multiple miR-34-related criteria/analyses and cut-off values to facilitate the stringent and comprehensive prediction of relevant miR-34 targets in expression data obtained from cell lines and tumors/tissues. Furthermore, information on more than 200 miR-34 target mRNAs, that have been experimentally validated so far, has been integrated in the web-tool. The website and datasets provided here should facilitate further investigation into the mechanisms of tumor suppression by the p53/miR-34 connection and identification of potential cancer drug targets.

Combination therapy with miR34a and doxorubicin synergistically inhibits Dox-resistant breast cancer progression via down-regulation of Snail through suppressing Notch/NF-κB and RAS/RAF/MEK/ERK signaling pathway

Resistance to breast cancer (BCa) chemotherapy severely hampers the patient's prognosis. MicroRNAs provide a potential therapeutic prospect for BCa. In this study, the reversal function of microRNA34a (miR34a) on doxorubicin (Dox) resistance of BCa and the possible mechanism was investigated. We found that the relative level of miR34a was significantly decreased in Dox-resistant breast cancer cell MCF-7 (MCF-7/A) compared with Dox-sensitive MCF-7 cells. Transfection with miR34a significantly suppressed the invasion, migration, adhesion of MCF-7/A cells without inhibiting their growth obviously. The combination of miR34a and Dox could significantly inhibit the proliferation, migration, invasion and induce the apoptosis of MCF-7/A cells. The synergistic effect of this combination on resistant MCF-7/A cells has no obvious relation with the expressions of classical drug-resistant proteins P-GP, MRP and GST-π, while closely related with the down-regulation on TOP2A and BCRP. Moreover, we found both protein and mRNA expression of Snail were significantly up-regulated in MCF-7/A cells in comparison with MCF-7 cells. Transfection with small interfering RNA (siRNA) of Snail could inhibit the invasion, migration and adhesion of drug-resistant MCF-7/A cells, while high-expression of Snail could remarkably promote the invasion, migration and adhesion of MCF-7 cells, which might be related with regulation of N-cadherin and E-cadherin. Transfection with miR34a in MCF-7/A cells induced a decrease of Snail expression. The potential binding sites of miR34a with 3' UTR of Snail were predicted by miRDB target prediction software, which was confirmed by luciferase reporter gene method. Results showed that the relative activity of luciferase was reduced in MCF-7/A cells after co-transfection of miR34a and wild type (wt)-Snail, while did not change by co-transfection with miR34a and 3' UTR mutant type (mut) Snail. Combination of miR34a and Dox induced a stronger decrease of Snail in MCF-7/A cells in comparison to miR34a or Dox treatment alone. What' more, for the first time, we also found miR34a combined with Dox could obviously inhibit the expression of Snail through suppressing Notch/NF-κB and RAS/RAF/MEK/ERK pathway in MCF-7/A cells. In vivo study indicated that combination of miR34a and Dox significantly slowed down tumor growth in MCF-7/A nude mouse xenograft model compared with Dox alone, which was manifested by the down-regulation of Snail and pro-apoptosis effect in tumor xenografts. These results together underline the relevance of miR34a-driven regulation of Snail in drug resistance and co-administration of miR34a and Dox may produce an effective therapy outcome in the future in clinic.

The Role of miRNA in the Pathophysiology of Neuroendocrine Tumors

Neuroendocrine tumors (NETs) represent a tumor group that is both rare and heterogeneous. Prognosis is largely determined by the tumor grading and the site of the primary tumor and metastases. Despite intensive research efforts, only modest advances in diagnostic and therapeutic approaches have been achieved in recent years. For patients with non-respectable tumor stages, prognosis is poor. In this context, the development of novel diagnostic tools for early detection of NETs and prediction of tumor response to therapy as well as estimation of the overall prognosis would greatly improve the clinical management of NETs. However, identification of novel diagnostic molecules is hampered by an inadequate understanding of the pathophysiology of neuroendocrine malignancies. It has recently been demonstrated that microRNA (miRNA), a family of small RNA molecules with an established role in the pathophysiology of quite different cancer entities, may also play a role as a biomarker. Here, we summarize the available knowledge on the role of miRNAs in the development of NET and highlight their potential use as serum-based biomarkers in the context of this disease. We discuss important challenges currently preventing their use in clinical routine and give an outlook on future directions of miRNA research in NET.

MicroRNA-34a: the bad guy in age-related vascular diseases

The age-related vasculature alteration is the prominent risk factor for vascular diseases (VD), namely, atherosclerosis, abdominal aortic aneurysm, vascular calcification (VC) and pulmonary arterial hypertension (PAH). The chronic sterile low-grade inflammation state, alias inflammaging, characterizes elderly people and participates in VD development. MicroRNA34-a (miR-34a) is emerging as an important mediator of inflammaging and VD. miR-34a increases with aging in vessels and induces senescence and the acquisition of the senescence-associated secretory phenotype (SASP) in vascular smooth muscle (VSMCs) and endothelial (ECs) cells. Similarly, other VD risk factors, including dyslipidemia, hyperglycemia and hypertension, modify miR-34a expression to promote vascular senescence and inflammation. miR-34a upregulation causes endothelial dysfunction by affecting ECs nitric oxide bioavailability, adhesion molecules expression and inflammatory cells recruitment. miR-34a-induced senescence facilitates VSMCs osteoblastic switch and VC development in hyperphosphatemia conditions. Conversely, atherogenic and hypoxic stimuli downregulate miR-34a levels and promote VSMCs proliferation and migration during atherosclerosis and PAH. MiR34a genetic ablation or miR-34a inhibition by anti-miR-34a molecules in different experimental models of VD reduce vascular inflammation, senescence and apoptosis through sirtuin 1 Notch1, and B-cell lymphoma 2 modulation. Notably, pleiotropic drugs, like statins, liraglutide and metformin, affect miR-34a expression. Finally, human studies report that miR-34a levels associate to atherosclerosis and diabetes and correlate with inflammatory factors during aging. Herein, we comprehensively review the current knowledge about miR-34a-dependent molecular and cellular mechanisms activated by VD risk factors and highlight the diagnostic and therapeutic potential of modulating its expression in order to reduce inflammaging and VD burn and extend healthy lifespan.

The Role of Epigenetics in the Regulation of Hemostatic Balance

Epigenetics, a term conventionally used to explain the intricate interplay between genes and the environment, is now regarded as the fundament of developmental biology. Several lines of evidence garnered over the past decades suggest that epigenetic alterations, mostly encompassing DNA methylation, histone tail modifications, and generation of microRNAs, play an important, though still incompletely explored, role in both primary and secondary hemostasis. Epigenetic variations may interplay with platelet functions and their responsiveness to antiplatelet drugs, and they may also exert a substantial contribution in modulating the production and release into the bloodstream of proteins involved in blood coagulation and fibrinolysis. This emerging evidence may have substantial biological and clinical implications. An enhanced understanding of posttranscriptional mechanisms would help to clarify some remaining enigmatic issues in primary and secondary hemostasis, which cannot be thoughtfully explained by genetics or biochemistry alone. Increased understanding would also pave the way to developing innovative tests for better assessment of individual risk of bleeding or thrombosis. The accurate recognition of key epigenetic mechanisms in hemostasis would then contribute to identify new putative therapeutic targets, and develop innovative agents that could be helpful for preventing or managing a vast array of hemostasis disturbances.

miR-34a induces spine damages via inhibiting synaptotagmin-1 in depression

MicroRNAs (miRNAs) are noncoding RNAs that participate in the pathophysiology of depression by targeting many functional genes. As shown in our previous study, chronic stress up-regulates miR-34a in the hippocampus. However, little is known about the mechanism by which miR-34a regulates the process of depression or its functions as an antidepressant by regulating its targets. In the present study, the dynamic alterations in miR-34a expression and the mechanism underlying miR-34a regulation were assessed after the administration of the antidepressant fluoxetine to mice exposed to chronic stress. In addition, the effects of miR-34a inhibition on mice were directly evaluated. Both lipopolysaccharide (LPS) and corticosterone treatment caused depression-like symptoms and increased miR-34a expression. Additionally, the expression of miR-34a, which was regulated by tropomyosin receptor kinase B (TrkB)/MEK1/ERK signaling, was consistent with the onset of action of fluoxetine. A luciferase reporter assay identified synaptotagmin-1 and Bcl-2 as the targets of miR-34a. Moreover, a miR-34a antagomir exerted antidepressant-like effects, activated TrkB/MEK1/ERK signaling and improved spine morphology in the hippocampus. In conclusion, hippocampal miR-34a overexpression was a typical feature in depression-like animals, and miR-34a downregulation exerts antidepressant-like effects by restoring the spine morphology through its target synaptotagmin-1.

How microRNAs affect the PD-L1 and its synthetic pathway in cancer

Programmed cell death-ligand 1 (PD-L1) is a glycoprotein that is expressed on the cell surface of both hematopoietic and nonhematopoietic cells. PD-L1 play a role in the immune tolerance and protect self-tissues from immune system attack. Dysfunction of this molecule has been highlighted in the pathogenesis of tumors, autoimmunity, and infectious disorders. MicroRNAs (miRNAs) are endogenous molecules that are classified as small non-coding RNA with approximately 20-22 nucleotides (nt) length. The function of miRNAs is based on complementary interactions with target mRNA via matching completely or incompletely. The result of this function is decay of the target mRNA or preventing mRNA translation. In the past decades, several miRNAs have been discovered which play an important role in the regulation of PD-L1 in various malignancies. In this review, we discuss the effect of miRNAs on PD-L1 expression and consider the effect of miRNAs on the synthetic pathway of PD-L1, especially during cancers.

miRNAs in NK Cell-Based Immune Responses and Cancer Immunotherapy

The incidence of certain forms of tumors has increased progressively in recent years and is expected to continue growing as life expectancy continues to increase. Tumor-infiltrating NK cells may contribute to develop an anti-tumor response. Optimized combinations of different cancer therapies, including NK cell-based approaches for targeting tumor cells, have the potential to open new avenues in cancer immunotherapy. Functional inhibitory receptors on NK cells are needed to prevent their attack on healthy cells. Nevertheless, disruption of inhibitory receptors function on NK cells increases the cytotoxic capacity of NK cells against cancer cells. MicroRNAs (miRNAs) are small non-coding RNA molecules that target mRNA and thus regulate the expression of genes involved in the development, maturation, and effector functions of NK cells. Therapeutic strategies that target the regulatory effects of miRNAs have the potential to improve the efficiency of cancer immunotherapy. Interestingly, emerging evidence points out that some miRNAs can, directly and indirectly, control the surface expression of immune checkpoints on NK cells or that of their ligands on tumor cells. This suggests a possible use of miRNAs in the context of anti-tumor therapy. This review provides the current overview of the connections between miRNAs and regulation of NK cell functions and discusses the potential of these miRNAs as innovative biomarkers/targets for cancer immunotherapy.

microRNA-22 promotes megakaryocyte differentiation through repression of its target, GFI1

Precise control of microRNA expression contributes to development and the establishment of tissue identity, including in proper hematopoietic commitment and differentiation, whereas aberrant expression of various microRNAs has been implicated in malignant transformation. A small number of microRNAs are upregulated in megakaryocytes, among them is microRNA-22 (miR-22). Dysregulation of miR-22 leads to various hematologic malignancies and disorders, but its role in hematopoiesis is not yet well established. Here we show that upregulation of miR-22 is a critical step in megakaryocyte differentiation. Megakaryocytic differentiation in cell lines is promoted upon overexpression of miR-22, whereas differentiation is disrupted in CRISPR/Cas9-generated miR-22 knockout cell lines, confirming that miR-22 is an essential mediator of this process. RNA-sequencing reveals that miR-22 loss results in downregulation of megakaryocyte-associated genes. Mechanistically, we identify the repressive transcription factor, GFI1, as the direct target of miR-22, and upregulation of GFI1 in the absence of miR-22 inhibits megakaryocyte differentiation. Knocking down aberrant GFI1 expression restores megakaryocytic differentiation in miR-22 knockout cells. Furthermore, we have characterized hematopoiesis in miR-22 knockout animals and confirmed that megakaryocyte differentiation is similarly impaired in vivo and upon ex vivo megakaryocyte differentiation. Consistently, repression of Gfi1 is incomplete in the megakaryocyte lineage in miR-22 knockout mice and Gfi1 is aberrantly expressed upon forced megakaryocyte differentiation in explanted bone marrow from miR-22 knockout animals. This study identifies a positive role for miR-22 in hematopoiesis, specifically in promoting megakaryocyte differentiation through repression of GFI1, a target antagonistic to this process.

Mechanisms shaping the role of ERK1/2 in cellular senescence (Review)

Senescence is a result of cellular stress and is a potential mechanism for regulating cancer. As a member of the mitogen-activated protein kinase family, ERK1/2 (extracellular signal-regulated protein kinase) has an important role in delivering extracellular signals to the nucleus, and these signals regulate the cell cycle, cell proliferation and cell development. Previous studies demonstrated that ERK1/2 is closely associated with cell aging; however other previous studies suggested that ERK1/2 exerts an opposite effect on aging models and target proteins, even within the same cell model. Recent studies demonstrated that the effect of ERK1/2 on aging is likely associated with its target proteins and regulators, negative feedback loops, phosphorylated ERK1/2 factors and ERK1/2 translocation from the cytoplasm to the nucleus. The present review aims to examine the mechanism of ERK1/2 and discuss its role in cellular outcomes and novel drug development.

MicroRNA-34a inhibits metastasis in liver cancer cells

MicroRNAs (miRNA/miRs) have the ability to target specific mRNAs, resulting in degradation of mRNA or inhibition of translation. Notably, miR-34a is able to regulate cell cycle and tumorigenicity. The level of miR-34a expression is usually low in tumors, and previous studies have indicated miR-34a to be an important tumor suppressor. In order to elucidate the association between miR-34a and metastasis, stable cell lines were established and transfected with miR-34a. Cell invasion assay was subsequently performed. The present study demonstrated that cell invasion was inhibited in cells that were transfected with miR-34a compared with the control group (P<0.05). Therefore, miR-34a was able to inhibit metastasis in liver cancer cells.

Stochasticity and robustness analysis of microRNA-mediated ERK signaling network

MicroRNAs (miRNAs) play a critical role in regulating the signaling network such as the extracellular signal regulated kinase (ERK) pathway. However, the mechanisms of miRNA-mediated posttranscriptional regulations with regard to their impacts on signaling require further investigation from a systematic level. Therefore, we develop a mathematical model by analyzing the precise dynamic mechanisms with a bevy of miRNAs involved in the Ras/Raf/MEK/ERK pathway. A systems-based analysis approach is introduced into this model and the dynamics have been implemented deterministically and stochastically. Our analysis reveals that miRNAs are key participants regulating the gene expression of ERK network, and the cooperative actions of miRNAs are important in keeping the normal biological characteristics and amplification effects of the system. Meanwhile, the appearance of system disorder in the absence of miRNAs suggests that miRNAs may play a role in the pathological processes, such as tumor and inflammation. The sensitivity analysis and the kinetic parameter perturbation show that the binding of receptor (EGFR) and adaptor protein (Shc, Grb2 and Sos) under normal physiological conditions is crucial for the robustness of the whole pathway. In addition, the stochastic dynamic patterns are in a good agreement with the deterministic results, further demonstrating that the variability of the system due to the presence of some stochastic noise is low. All these will be helpful for a deeper understanding of the dynamic mechanism of miRNA-mediated ERK signal network, which might present a rich area of future research with the relevant regulatory roles of miRNAs in cell signaling pathway.

Targeting IGF1R pathway in cancer with microRNAs: How close are we?

Cancer of the head and neck are the most common cancers in India and account for 30% of all cancers. At molecular level, it could be attributed to the overexpression of growth factors like IGF1-R, EGFR, VEGF-R and deregulation of cell cycle regulators and tumor suppressors. IGF1-R is an emerging target in head and neck cancer treatment, because of its reported role in tumor development, progression and metastasis. IGF1R targeted agents are in advanced stages of clinical development. Nevertheless, these agents suffer from several disadvantages including acquired resistance and toxic side effects. Hence there is a need for developing newer agents targeting not only the receptor but also its downstream signaling. miRNAs are considered as master regulators of gene expression of multiple genes and has been widely reported to be a promising therapeutic strategy. This review discusses the present status of research in both these arenas and emphasizes the role of miRNA as a promising agent for biologic therapy.

AS1041, a Novel Synthesized Derivative of Marine Natural Compound Aspergiolide A, Arrests Cell Cycle, Induces Apoptosis, and Inhibits ERK Activation in K562 Cells

AS1041 is a novel synthesized anthraquinone lactone derivative of marine natural compound aspergiolide A (ASP-A) with new structure skeleton and marked cytotoxicity in cancer cells. To study its cytotoxicity in detail, we evaluated its activity on human K562 chronic myelogenous leukemia cells and investigated the related molecule mechanisms. AS1041 significantly inhibited the proliferation and colony formation of K562 cells. Moreover, AS1041 arrested cell cycle progression at G2/M phase in a concentration-dependent manner, and also caused concentration- and time-dependent induction of apoptosis. In addition, the molecular mechanisms investigation showed that AS1041 did not localize in the cellular nucleus and did not affect topoisomerases I or II. However, AS1041 could inactivate extracellular signal-regulated kinase (ERK) and contribute to AS1041-induced apoptosis. We concluded that AS1041 was cytotoxic to K562 leukemia cells and the cytotoxicity related to the cell cycle arrest, apoptosis induction, and ERK inhibition. These results implied that AS1041 was a novel derivative of ASP-A with significant cytotoxicity to chronic myelogenous leukemia cells and may have therapeutic potential for the treatment of cancer and leukemia.

Beyond mRNA: The role of non-coding RNAs in normal and aberrant hematopoiesis

The role of non-coding Ribonucleic Acids (ncRNAs) in biology is currently an area of intense focus. Hematopoiesis requires rapidly changing regulatory molecules to guide appropriate differentiation and ncRNA are well suited for this. It is not surprising that virtually all aspects of hematopoiesis have roles for ncRNAs assigned to them and doubtlessly much more await characterization. Stem cell maintenance, lymphoid, myeloid and erythroid differentiation are all regulated by various ncRNAs, including microRNAs (miRNAs), long non-coding RNAs (lncRNAs) and various transposable elements within the genome. As our understanding of the many and complex ncRNA roles continues to grow, new discoveries are challenging the existing classification schemes. In this review we briefly overview the broad categories of ncRNAs and discuss a few examples regulating normal and aberrant hematopoiesis.

Cancer Hallmarks and MicroRNAs: The Therapeutic Connection

Human cancers are characterized by a number of hallmarks, including sustained proliferative signaling, evasion of growth suppressors, activated invasion and metastasis, replicative immortality, angiogenesis, resistance to cell death, and evasion of immune destruction. As microRNAs (miRNAs) are deregulated in virtually all human cancers, they show involvement in each of the cancer hallmarks as well. In this chapter, we describe the involvement of miRNAs in cancer from a cancer hallmarks and targeted therapeutics point of view. As no miRNA-based cancer therapeutics are available to date, and the only clinical trial on miRNA-based cancer therapeutics (MRX34) was terminated prematurely due to serious adverse events, we are focusing on protein-coding miRNA targets for which targeted therapeutics in oncology are already approved by the FDA. For each of the cancer hallmarks, we selected major protein-coding players and describe the miRNAs that target them.

MicroRNA-34 dysregulation in gastric cancer and gastric cancer stem cell

Gastric cancer is a major cause of cancer mortality worldwide, with a low survival rate for patients with advanced forms of the disease. Over the recent decades, the investigation of the pathophysiological mechanisms of tumourigenesis has opened promising avenues to understand some of the complexities of cancer treatment. However, tumour regeneration and metastasis impose great difficulty for gastric cancer cure. In recent years, cancer stem cells - a small subset of tumour cells in many cancers - have become a major focus of cancer research. Cancer stem cells are capable of self-renewal and are known to be responsible for tumour initiation, metastasis, therapy resistance and cancer recurrence. Recent studies have revealed the key role of microRNAs - small noncoding RNAs regulating gene expression - in these processes. MicroRNAs play crucial roles in the regulation of a wide range of biological processes in a post-transcriptional manner, though their expression is dysregulated in most malignancies, including gastric cancer. In this article, we review the consequences of aberrant expression of microRNA-34 in cancer and cancer stem cells, with a specific focus on the miR-34 dysregulation in gastric cancer and gastric cancer stem cells. We address the critical effects of the aberrant expression of miR-34 and its target genes in maintaining cancer stem cell properties. Information collection and discussion about the advancements in gastric cancer stem cells and microRNAs can be useful for providing novel insights into patient treatment.

MiR-34a contributes to diabetes-related cochlear hair cell apoptosis via SIRT1/HIF-1α signaling

Type 2 diabetes (T2DM) has been considered to be associated with a higher likelihood of hearing impairment (HI). However, the molecular mechanisms underlying the association between diabetes and HI are poorly understood. MicroRNAs have recently been demonstrated to be closely associated with hearing loss and considered as promising therapeutic targets. Herein, we investigated whether miR-34a contributes to diabetes-related cochlear hair cell apoptosis and sought to identify the underlying mechanism. The results showed that miR-34a was up-regulated in the cochleas of db/db mice, accompanied by significant hearing threshold elevation and hair cell loss. However, the expression of SIRT1 was significantly down-regulated, while hypoxia-inducible factor-1alpha (HIF-1α) levels were dramatically increased in the cochleas of db/db mice. In addition, in the high-glucose cultured House Ear Institute-Organ of Corti 1 (HEI-OC1) cell line, miR-34a overexpression inhibited sirtuin1 (SIRT1) expression, increased HIF-1α levels and promoted apoptosis. MiR-34a knockdown exerted effects that were diametrically opposed to those observed with overexpression. Interestingly, HIF-1α knockdown almost eliminated the cell apoptosis induced by high glucose levels. We also examined the modulation of HIF-1α expression by SIRT1. The results showed that SIRT1 knockdown further promoted high-glucose-induced HIF-1α expression, while SIRT1 overexpression significantly inhibited HIF-1α level induced by high glucose. These findings point to a new mechanism by which miR-34a exerts its detrimental effects by negatively regulating SIRT1/HIF-1α signaling and provide new therapeutic targets for treating hearing impairment during diabetes.

Exosomal miR-34s panel as potential novel diagnostic and prognostic biomarker in patients with hepatoblastoma

PURPOSE

The aim of this study is to identify the diagnostic values of serum exosomal miRNA-34s of patients with HB in a large Asian group and explore the prognostic value of the exosomal miRNA-34s panel compared with other risk factors.

METHODS

We retrospectively reviewed 89 children with HB. Among these patients, 63 patients were included as training group to build the diagnostic model for HB. 26 patients were defined as the validation group. The expressions of miRNA-34s were detected by real-time PCR. The comparison of diagnostic and prognostic performance of serum exosomal miRNA-34s was measured using the area under ROC curve (AUC).

RESULTS

For patients in the training group, expression of miRNA-34a, miRNA-34b and miRNA-34c was significantly lower in patients with HB compared with control group in serum exosomes. Between HB training group and the control group, exosomal miRNA-34a, miRNA-34b and miRNA-34c had no significant differences compared with the AFP level in diagnosing HB. The performance of the exosomal miRNA-34s panel in differentiating the HB training group from the control group was superior to the AFP level. The value of the exosomal miRNA-34s panel in predicting prognosis of patients with HB was superior to other risk factors in both training group and validation group.

CONCLUSIONS

In this study, we found that the expression of exosomal miRNA-34a, miRNA-34b and miRNA-34c was significantly lower in patients with HB compared with the control group, and we confirmed the exosomal miRNA-34s panel could be defined as a diagnostic and prognostic biomarker for patients with HB.

LEVEL OF EVIDENCE

Level II.

TYPE OF STUDY

Retrospective Study.

Mechanisms of Impaired Neutrophil Migration by MicroRNAs in Myelodysplastic Syndromes

In myelodysplastic syndromes (MDS), functional defects of neutrophils result in high mortality because of infections; however, the molecular basis remains unclear. We recently found that miR-34a and miR-155 were significantly increased in MDS neutrophils. To clarify the effects of the aberrant microRNA expression on neutrophil functions, we introduced miR-34a, miR-155, or control microRNA into neutrophil-like differentiated HL60 cells. Ectopically introduced miR-34a and miR-155 significantly attenuated migration toward chemoattractants fMLF and IL-8, but enhanced degranulation. To clarify the mechanisms for inhibition of migration, we studied the effects of miR-34a and miR-155 on the migration-regulating Rho family members, Cdc42 and Rac1. The introduced miR-34a and miR-155 decreased the fMLF-induced active form of Cdc42 to 29.0 ± 15.9 and 39.7 ± 4.8% of that in the control cells, respectively, although Cdc42 protein levels were not altered. miR-34a decreased a Cdc42-specific guanine nucleotide exchange factor (GEF), dedicator of cytokinesis (DOCK) 8, whereas miR-155 reduced another Cdc42-specific GEF, FYVE, RhoGEF, and PH domain-containing (FGD) 4. The knockdown of DOCK8 and FGD4 by small interfering RNA suppressed Cdc42 activation and fMLF/IL-8-induced migration. miR-155, but not miR-34a, decreased Rac1 protein, and introduction of Rac1 small interfering RNA attenuated Rac1 activation and migration. Neutrophils from patients showed significant attenuation in migration compared with healthy cells, and protein levels of DOCK8, FGD4, and Rac1 were well correlated with migration toward fMLF (r = 0.642, 0.686, and 0.436, respectively) and IL-8 (r = 0.778, 0.659, and 0.606, respectively). Our results indicated that reduction of DOCK8, FGD4, and Rac1 contributes to impaired neutrophil migration in MDS.

The epigenetically-regulated miR-34a targeting c-SRC suppresses RAF/MEK/ERK signaling pathway in K-562 cells

Previous reports show that miR-34a suppressed K-562 cell proliferation and contributed to megakaryocytic differentiation of K-562 cells. Here, we reported that miR-34a, a tumor suppressor gene, is down-regulated in the K-562 cells and chronic myeloid leukemia (CML) patients due to aberrant DNA hypermethylation. c-SRC is a target of miR-34a. Restoring miR-34a expression resulted in down-regulation of c-SRC and phosphorylated (Tyr416) c-SRC protein in K-562 cells, which consequently triggered suppression of the RAF/MEK/ERK signaling pathway to decrease cell proliferation.

Role of miR-34a-5p in Hematopoietic Progenitor Cells Proliferation and Fate Decision: Novel Insights into the Pathogenesis of Primary Myelofibrosis

Primary Myelofibrosis (PMF) is a chronic Philadelphia-negative myeloproliferative neoplasm characterized by a skewed megakaryopoiesis and an overproduction of proinflammatory and profibrotic mediators that lead to the development of bone marrow (BM) fibrosis. Since we recently uncovered the upregulation of miR-34a-5p in PMF CD34+ hematopoietic progenitor cells (HPCs), in order to elucidate its role in PMF pathogenesis here we unravelled the effects of miR-34a-5p overexpression in HPCs. We showed that enforced expression of miR-34a-5p partially constrains proliferation and favours the megakaryocyte and monocyte/macrophage commitment of HPCs. Interestingly, we identified lymphoid enhancer-binding factor 1 (LEF1) and nuclear receptor subfamily 4, group A, member 2 (NR4A2) transcripts as miR-34a-5p-targets downregulated after miR-34a-5p overexpression in HPCs as well as in PMF CD34+ cells. Remarkably, the knockdown of NR4A2 in HPCs mimicked the antiproliferative effects of miR-34a-5p overexpression, while the silencing of LEF1 phenocopied the effects of miR-34a-5p overexpression on HPCs lineage choice, by favouring the megakaryocyte and monocyte/macrophage commitment. Collectively our data unravel the role of miR-34a-5p in HPCs fate decision and suggest that the increased expression of miR-34a-5p in PMF HPCs could be important for the skewing of megakaryopoiesis and the production of monocytes, that are key players in BM fibrosis in PMF patients.

Gene and miRNA expression signature of Lewis lung carcinoma LLC1 cells in extracellular matrix enriched microenvironment

Background

The extracellular matrix (ECM), one of the key components of tumor microenvironment, has a tremendous impact on cancer development and highly influences tumor cell features. ECM affects vital cellular functions such as cell differentiation, migration, survival and proliferation. Gene and protein expression levels are regulated in cell-ECM interaction dependent manner as well. The rate of unsuccessful clinical trials, based on cell culture research models lacking the ECM microenvironment, indicates the need for alternative models and determines the shift to three-dimensional (3D) laminin rich ECM models, better simulating tissue organization. Recognized advantages of 3D models suggest the development of new anticancer treatment strategies. This is among the most promising directions of 3D cell cultures application. However, detailed analysis at the molecular level of 2D/3D cell cultures and tumors in vivo is still needed to elucidate cellular pathways most promising for the development of targeted therapies. In order to elucidate which biological pathways are altered during microenvironmental shift we have analyzed whole genome mRNA and miRNA expression differences in LLC1 cells cultured in 2D or 3D culture conditions.

Methods

In our study we used DNA microarrays for whole genome analysis of mRNA and miRNA expression differences in LLC1 cells cultivated in 2D or 3D culture conditions. Next, we indicated the most common enriched functional categories using KEGG pathway enrichment analysis. Finally, we validated the microarray data by quantitative PCR in LLC1 cells cultured under 2D or 3D conditions or LLC1 tumors implanted in experimental animals.

Results

Microarray gene expression analysis revealed that 1884 genes and 77 miRNAs were significantly altered in LLC1 cells after 48 h cell growth under 2D and ECM based 3D cell growth conditions. Pathway enrichment results indicated metabolic pathway, MAP kinase, cell adhesion and immune response as the most significantly altered functional categories in LLC1 cells due to the microenvironmental shift from 2D to 3D. Comparison of the expression levels of selected genes and miRNA between LLC1 cells grown in 3D cell culture and LLC1 tumors implanted in the mouse model indicated correspondence between both model systems.

Conclusions

Global gene and miRNA expression analysis in LLC1 cells under ECM microenvironment indicated altered immune response, adhesion and MAP kinase pathways. All these processes are related to tumor development, progression and treatment response, suggesting the most promising directions for the development of targeted therapies using the 3D cell culture models.

Electronic supplementary material

The online version of this article (doi:10.1186/s12885-016-2825-9) contains supplementary material, which is available to authorized users.

Roles of TP53 in determining therapeutic sensitivity, growth, cellular senescence, invasion and metastasis

TP53 is a critical tumor suppressor gene that regulates cell cycle progression, apoptosis, cellular senescence and many other properties critical for control of normal cellular growth and death. Due to the pleiotropic effects that TP53 has on gene expression and cellular physiology, mutations at this tumor suppressor gene result in diverse physiological effects. T53 mutations are frequently detected in numerous cancers. The expression of TP53 can be induced by various agents used to treat cancer patients such as chemotherapeutic drugs and ionizing radiation. Radiation will induce Ataxia telangiectasia mutated (ATM) and other kinases that results in the phosphorylation and activation of TP53. TP53 is also negatively regulated by other mechanisms, such as ubiquitination by ligases such as MDM2. While TP53 has been documented to control the expression of many "classical" genes (e.g., p21^Cip-1, PUMA, Bax) by transcriptional mechanisms for quite some time, more recently TP53 has been shown to regulate microRNA (miR) gene expression. Different miRs can promote oncogenesis (oncomiR) whereas others act to inhibit tumor progression (tumor suppressor miRs). Targeted therapies to stabilize TP53 have been developed by various approaches, MDM2/MDM4 inhibitors have been developed to stabilize TP53 in TP53-wild type (WT) tumors. In addition, small molecules have been isolated that will reactivate certain mutant TP53s. Both of these types of inhibitors are in clinical trials. Understanding the actions of TP53 may yield novel approaches to suppress cancer, aging and other health problems.

Original Research: Stable expression of miR-34a mediates fetal hemoglobin induction in K562 cells

Sickle cell anemia is a common genetic disorder caused by a point mutation in the sixth codon of the β-globin gene affecting people of African descent worldwide. A wide variety of clinical phenotypes ranging from mild to severe symptoms and complications occur due to hemoglobin S polymerization, red blood cell sickling, and vaso-occlusion. Research efforts are ongoing to develop strategies of fetal hemoglobin (HbF; α2γ2) induction to inhibit sickle hemoglobin polymerization and improve clinical outcomes. Insights have been gained from investigating mutations in the β-globin locus or transcription factors involved in the mechanisms of hemoglobin switching. Recent efforts to expand molecular targets that modulate γ-globin expression involve microRNAs that work through posttranscriptional gene regulation. Therefore, the goal of our study was to identify novel microRNA genes involved in fetal hemoglobin expression. Using in silico analysis, we identified a miR-34a binding site in the γ-globin mRNA which was tested for functional relevance. Stable expression of the shMIMIC miR-34a lentivirus vector increased fetal hemoglobin levels in single cell K562 clones consistent with silencing of a γ-globin gene repressor. Furthermore, miR-34a promoted cell differentiation supported by increased expression of KLF1, glycophorin A, and the erythropoietin receptor. Western blot analysis of known negative regulators of γ-globin including YY1, histone deacetylase 1, and STAT3, which are regulated by miR-34a showed no change in YY1 and histone deacetylase 1 levels; however, total- and phosphorylated-STAT3 levels were decreased in single cell miR-34a K562 clones. These data support a mechanism of fetal hemoglobin activation by miR-34a involving STAT3 gene silencing.

The Role of miR-34a in Tritiated Water Toxicity in Human Umbilical Vein Endothelial Cells

In this work, we investigated the toxic effects of tritiated water (HTO) on the cardiovascular system. We examined the role of microRNA-34a (miR-34a) in DNA damage and repair in human umbilical vein endothelial cells (HUVECs) exposed to HTO. Cell proliferation capacity was evaluated by cell counting, and miR-34a expression was detected using quantitative PCR (QT-PCR). The Comet assay and γ-H2AX immunostaining were used to measure DNA double-strand breaks (DSBs). Reverse transcription polymerase chain reaction was used to measure the expression level of c-myc messenger RNA (mRNA). The cells exposed to HTO showed significantly lower proliferation than the control cells over 3 days. The DNA damage in the HTO group was more severe than that in the control group, at each time point examined. The expression of miR-34a mimics caused increased DNA DSBs whereas that of the miR-34a inhibitor caused decreased DNA DSBs. The proliferation viability was the opposite for the miR-34a mimics and inhibitor groups. The expression levels of c-myc mRNA in cells transfected with miR-34a mimics were lower than that in cells transfected with the miR-34a-5p inhibitor, at 0.5 hours and 2 hours after transfection. In summary, miR-34a mediates HTO toxicity in HUVECs by downregulating the expression of c-myc.

MiR144/451 Expression Is Repressed by RUNX1 During Megakaryopoiesis and Disturbed by RUNX1/ETO

A network of lineage-specific transcription factors and microRNAs tightly regulates differentiation of hematopoietic stem cells along the distinct lineages. Deregulation of this regulatory network contributes to impaired lineage fidelity and leukemogenesis. We found that the hematopoietic master regulator RUNX1 controls the expression of certain microRNAs, of importance during erythroid/megakaryocytic differentiation. In particular, we show that the erythorid miR144/451 cluster is epigenetically repressed by RUNX1 during megakaryopoiesis. Furthermore, the leukemogenic RUNX1/ETO fusion protein transcriptionally represses the miR144/451 pre-microRNA. Thus RUNX1/ETO contributes to increased expression of miR451 target genes and interferes with normal gene expression during differentiation. Furthermore, we observed that inhibition of RUNX1/ETO in Kasumi1 cells and in RUNX1/ETO positive primary acute myeloid leukemia patient samples leads to up-regulation of miR144/451. RUNX1 thus emerges as a key regulator of a microRNA network, driving differentiation at the megakaryocytic/erythroid branching point. The network is disturbed by the leukemogenic RUNX1/ETO fusion product.

MicroRNAs in apoptosis, autophagy and necroptosis

MicroRNAs (miRNAs) are endogenous 22 nt non-coding RNAs that target mRNAs for cleavage or translational repression. Numerous miRNAs regulate programmed cell death including apoptosis, autophagy and necroptosis. We summarize how miRNAs regulate apoptotic, autophagic and necroptotic pathways and cancer progression. We also discuss how miRNAs link different types of cell death.

HPV-p53-miR-34a axis in HPV-associated cancers

Human papillomaviruses (HPVs) are known to cause many cancers by altering multiple signalling pathways through their oncogene integration into host genome and expression. Studies have shown that many microRNAs (miRs) may function as oncogenes (called as oncomiRs) to promote an oncogenic effect. MiR-34a among the reported oncomiRs is a key player in the carcinogenesis caused by infection with HPVs. In this mini-review, we summarise the roles of miR-34a in HPV-caused cancers. MiR-34a is transcriptionally regulated by tumour suppressor p53. HPV oncogene E6 inhibits expression of p53 to decrease the levels of miR-34a, leading to the increased expression of multiple genes which are targeted by miR-34a. The upregulation of these genes increases cancer cell proliferation, survival and migration in HPV-associated cancers.

The tumor-suppressive and potential therapeutic functions of miR-34a in epithelial carcinomas

INTRODUCTION

Many RNA species have been identified as important players in the development of chronic diseases including cancer. Certain classes of regulatory RNAs such as microRNAs (miRNAs) have been investigated in such detail that bona fide tumor suppressive and oncogenic miRNAs have been identified. Because of this, there has been a major effort to therapeutically target these small RNAs. One in particular, a liposomal formulation of miR-34a (MRX34), has entered Phase I trials.

AREAS COVERED

This review aims to summarize miRNA biology, its regulation within normal versus disease states and how it can be targeted therapeutically, with a particular emphasis on miR-34a. Understanding the complexity of a single miRNA will aid in the development of future RNA-based therapeutics for a broader range of chronic diseases.

EXPERT OPINION

The potential of miRNAs to be developed into anti-cancer therapeutics has become an increasingly important area of research. miR-34a is a tumor suppressive miRNA across many tumor types through its ability to inhibit cellular proliferation, invasion and tumor sphere formation. miR-34a also shows promise within certain in vivo solid tumor models. Finally, as miR-34a moves into clinical trials it will be important to determine if it can further sensitize tumors to certain chemotherapeutic agents.

A human 3'UTR clone collection to study post-transcriptional gene regulation

Background

3′untranslated regions (3′UTRs) are poorly understood portions of eukaryotic mRNAs essential for post-transcriptional gene regulation. Sequence elements in 3′UTRs can be target sites for regulatory molecules such as RNA binding proteins and microRNAs (miRNAs), and these interactions can exert significant control on gene networks. However, many such interactions remain uncharacterized due to a lack of high-throughput (HT) tools to study 3′UTR biology. HT cloning efforts such as the human ORFeome exemplify the potential benefits of genomic repositories for studying human disease, especially in relation to the discovery of biomarkers and targets for therapeutic agents. Currently there are no publicly available human 3′UTR libraries. To address this we have prepared the first version of the human 3′UTRome (h3′UTRome v1) library. The h3′UTRome is produced to a single high quality standard using the same recombinational cloning technology used for the human ORFeome, enabling universal operating methods and high throughput experimentation. The library is thoroughly sequenced and annotated with simple online access to information, and made publically available through gene repositories at low cost to all scientists with minimal restriction.

Results

The first release of the h3′UTRome library comprises 1,461 human 3′UTRs cloned into Gateway® entry vectors, ready for downstream analyses. It contains 3′UTRs for 985 transcription factors, 156 kinases, 171 RNA binding proteins, and 186 other genes involved in gene regulation and in disease. We demonstrate the feasibility of the h3′UTRome library by screening a panel of 87 3′UTRs for targeting by two miRNAs: let-7c, which is implicated in tumorigenesis, and miR-221, which is implicated in atherosclerosis and heart disease. The panel is enriched with genes involved in the RAS signaling pathway, putative novel targets for the two miRNAs, as well as genes implicated in tumorigenesis and heart disease.

Conclusions

The h3′UTRome v1 library is a modular resource that can be utilized for high-throughput screens to identify regulatory interactions between trans-acting factors and 3′UTRs, Importantly, the library can be customized based on the specifications of the researcher, allowing the systematic study of human 3′UTR biology.

Electronic supplementary material

The online version of this article (doi:10.1186/s12864-015-2238-1) contains supplementary material, which is available to authorized users.

The predictive effect of overexpressed miR-34a on good survival of cancer patients: a systematic review and meta-analysis

Background

MicroRNA-34a (miR-34a) is a potential prognostic factor for survival in patients with several types of cancer according to previous clinical researches. We conducted a systematic review and meta-analysis to summarize the significance of increased miR-34a expression in the prognosis of patients’ overall survival.

Materials and methods

The present systematic review and meta-analysis of 15 researches included 2,597 patients. Overexpression of miR-34a may predict good overall survival ([OS], HR =0.76, 95% confidence interval: 0.55–1.06, P=0.105), but the effect was not significant enough. Subgroup analysis results showed miR-34a was an ideal predictor for digestive system cancer (OS, HR =0.50, 95% confidence interval: 0.25–0.99, P=0.048). The predictive effects of elevated expression of miR-34a on the OS of untreated and treated patients were not of obvious differences.

Conclusion

This systematic review and meta-analysis showed that miR-34a has a predictive effect on overall survival of patients with digestive system cancer.

The role of microRNAs in the control of innate immune response in cancer

Ligands for receptors of natural killer (NK) cells and CD8(+) cytotoxic T lymphocytes (CTL), such as the inhibitory nonclassical HLA-G, the activating stress-induced major histocompatibility complex class I-related antigens MICA and MICB, and/or the UL16-binding proteins (ULBPs), are often aberrantly expressed upon viral infection and neoplastic transformation, thereby preventing virus-infected or malignant-transformed cells from elimination by immune effector cells. Recently, it has been shown that ligands of both NK and CD8(+) T cells are regulated by a number of cellular and/or viral microRNAs (miRs). These miRs are involved in shaping the antiviral and/or antitumoral immune responses as well as neoplastic growth properties. This review summarizes the expression pattern and function of miRs directed against selected NK and T cell receptor ligands, their putative role in shaping immune surveillance and tumorigenicity, and their clinical relevance. In addition, the potential role of RNA-binding proteins in the post-transcriptional gene regulation of these ligands will be discussed.

MicroRNA-34a targets Forkhead box j2 to modulate differentiation of endothelial progenitor cells in response to shear stress

Flow shear stress plays important roles in modulating differentiation of endothelial progenitor cells (EPCs). MicroRNAs are crucial for diverse cellular processes, but the expressions and functions of microRNAs in EPCs responding to mechanical stimuli remain unclear. We sought to determine the effects of microRNA-34a (miR-34a) and a novel target Forkhead box j2 (Foxj2) on shear stress-induced EPC differentiation. Human umbilical cord blood-derived EPCs were exposed to laminar shear stress of 15dyn/cm(2) with parallel plate flow chamber system. Real time RT-PCR showed that shear stress significantly increased miR-34a expression, which was accompanied by the endothelial differentiation of EPCs. Whereas Foxj2, a putative target of miR-34a predicted by multiple algorithms, was suppressed in this process. Dual luciferase reporter assays, as well as miR-34a mimics and inhibitor treatment were used to confirm the interplay between miR-34a and Foxj2. Our results revealed an inverse correlation of miR-34a and Foxj2 expressions implicated in the endothelial differentiation of EPCs. MiR-34a contributed to this process by up-regulating the expressions of endothelial cell markers, and down-regulating smooth muscular cell markers. In addition, Foxj2 overexpression attenuated endothelial differentiation of EPCs, while Foxj2 siRNA had the opposite effect. These data suggested a unique mechanism that shear stress induces the expression of miR-34a, which targets to Foxj2 and promotes endothelial differentiation of EPCs. The results provide new insights into miR-34a/Foxj2 on shear stress-induced EPC differentiation.

MicroRNA-34a: a potential therapeutic target in human cancer

MicroRNAs (miRs) are small noncoding RNAs that negatively regulate gene expression by binding to the three untranslated regions of their target mRNAs. Deregulations of miRs were shown to play pivotal roles in tumorigenesis and progression. Recent research efforts have been devoted to translating these basic discoveries into applications that could improve the therapeutic outcome of patients with cancer. MiR-34a is a highly conserved miR throughout many different species. In humans, there are three homologs (hsa-miR34a, hsa-miR-34b and hsa-miR-34c). Early studies have shown that miR-34a acts as a tumor-suppressor gene by targeting many oncogenes related to proliferation, apoptosis and invasion. In this review, we provide a complex overview of miR-34a, including regulating its expression, its known functions in cancer and future challenges as a potential therapeutic target in human cancers.

microRNAs in cancer cell response to ionizing radiation

SIGNIFICANCE

microRNAs (miRNA) have been characterized as master regulators of the genome. As such, miRNAs are responsible for regulating almost every cellular pathway, including the DNA damage response (DDR) after ionizing radiation (IR). IR is a therapeutic tool that is used for the treatment of several types of cancer, yet the mechanism behind radiation response is not fully understood.

RECENT ADVANCES

It has been demonstrated that IR can alter miRNA expression profiles, varying greatly from one cell type to the next. It is possible that this variation contributes to the range of tumor cell responsiveness that is observed after radiotherapy, especially considering the extensive role for miRNAs in regulating the DDR. In addition, individual miRNAs or miRNA families have been shown to play a multifaceted role in the DDR, regulating multiple members in a single pathway.

CRITICAL ISSUES

In this review, we will discuss the effects of radiation on miRNA expression as well as explore the function of miRNAs in regulating the cellular response to radiation-induced damage. We will discuss the importance of miRNA regulation at each stage of the DDR, including signal transduction, DNA damage sensing, cell cycle checkpoint activation, DNA double-strand break repair, and apoptosis. We will focus on emphasizing the importance of a single miRNA targeting several mediators within a pathway.

FUTURE DIRECTIONS

miRNAs will continue to emerge as critical regulators of the DDR. Understanding the role of miRNAs in the response to IR will provide insights for improving the current standard therapy.

MicroRNA-34a overcomes HGF-mediated gefitinib resistance in EGFR mutant lung cancer cells partly by targeting MET

In non-small-cell lung cancer (NSCLC) that harbours an activating epidermal growth factor receptor (EGFR) mutation, over-expression of hepatocyte growth factor (HGF) is an important mechanism involved in the acquired resistance to EGFR-tyrosine kinase inhibitors (TKIs) by restoring activity of the PI3K/Akt pathway via phosphorylation of MET. In our study, we found that the forced expression of miR-34a inhibited cell growth and induced apoptosis partly by targeting MET in HGF-induced gefitinib-resistant HCC827 and PC-9 cells. Furthermore, dramatic tumour regression was observed in the miR-34a plus gefitinib group in HGF-induced gefitinib resistant mouse xenograft models. This study demonstrates for the first time that miR-34a rescues HGF-induced gefitinib resistance in EGFR mutant NSCLC cells.

miR-34a regulates mesangial cell proliferation via the PDGFR-β/Ras-MAPK signaling pathway

The main pathological characteristic of glomerulonephritis is diffuse mesangial cell proliferation. MiR-34a is associated with the proliferation of various organs and cancer cells. However, the role of miR-34a in renal proliferation diseases is not clear. Therefore, this study aimed to elucidate the mechanism of miR-34a in the regulation of renal mesangial cell proliferation. The miR-34a expression level at different time points in an anti-Thy1 mesangial proliferative nephritis rat model was determined by qRT-PCR. The cell proliferation rate and cell cycle changes were measured in the in vitro cultured rat mesangial cells (RMCs). Our results suggested that miR-34a expression was negatively correlated with the degree of cell proliferation in the anti-Thy1 nephritis model. MiR-34a could extend the G0/G1 phase and block cell proliferation in RMCs. Dual-luciferase assay results showed that there were binding sites of miR-34a at 3′-UTR of platelet-derived growth factor receptor-β (PDGFR-β). MiR-34a can inhibit PDGFR-β protein expression at a post-transcriptional level, suppress Ras/MAPK signaling pathways, and down-regulate expression of cell cycle proteins at the G0/G1 phase, such as cyclin D1, CDK4/CDK6. In addition, miR-34a may also inhibit RMC proliferation by directly targeting cyclin E and CDK2. MiR-34a inhibits exogenous stimuli-induced proliferation of mesangial cells. Expression levels of phospho-PDGFR-β and phospho-MEK1 (an important downstream molecule in PDGFR-β-induced signaling pathway) were significantly increased in the anti-Thy-1 nephritis rat model. These results suggest that miR-34a may regulate RMC proliferation by directly inhibiting expressions of PDGFR-β, MEK1, and cell cycle proteins, cyclin E and CDK2.

c-Jun N-terminal kinase 1/c-Jun activation of the p53/microRNA 34a/sirtuin 1 pathway contributes to apoptosis induced by deoxycholic acid in rat liver

MicroRNAs (miRs) are increasingly associated with metabolic liver diseases. We have shown that ursodeoxycholic acid, a hydrophilic bile acid, counteracts the miR-34a/sirtuin 1 (SIRT1)/p53 pathway, activated in the liver of nonalcoholic steatohepatitis (NASH) patients. In contrast, hydrophobic bile acids, particularly deoxycholic acid (DCA), activate apoptosis and are increased in NASH. We evaluated whether DCA-induced apoptosis of rat hepatocytes occurs via miR-34a-dependent pathways and whether they connect with c-Jun N-terminal kinase (JNK) induction. DCA enhanced miR-34a/SIRT1/p53 proapoptotic signaling in a dose- and time-dependent manner. In turn, miR-34a inhibition and SIRT1 overexpression significantly rescued targeting of the miR-34a pathway and apoptosis by DCA. In addition, p53 overexpression activated the miR-34a/SIRT1/p53 pathway, further induced by DCA. DCA increased p53 expression as well as p53 transcriptional activation of PUMA and miR-34a itself, providing a functional mechanism for miR-34a activation. JNK1 and c-Jun were shown to be major targets of DCA, upstream of p53, in engaging the miR-34a pathway and apoptosis. Finally, activation of this JNK1/miR-34a proapoptotic circuit was also shown to occur in vivo in the rat liver. These results suggest that the JNK1/p53/miR-34a/SIRT1 pathway may represent an attractive pharmacological target for the development of new drugs to arrest metabolism- and apoptosis-related liver pathologies.

MiR-34a regulates apoptosis in liver cells by targeting the KLF4 gene

MicroRNAs (miRNAs) regulate gene expression by inhibiting translation or targeting messenger RNA (mRNA) for degradation in a posttranscriptional fashion. In this study, we show that ectopic expression of miR-34a-5p reduces the mRNA and protein levels of Krüppel-like factor 4 (KLF4). We also demonstrate that miR-34a targets the 3′-untranslated mRNA region of KLF4 and show that overexpression of miR-34a induces a significant level of apoptosis in BNL CL.2 cells exposed to doxorubicin or 10 Gy X-ray. Our data suggest that the effects of miR-34a on apoptosis occur due to the downregulation of KLF4.

MicroRNAs as Haematopoiesis Regulators

The production of different types of blood cells including their formation, development, and differentiation is collectively known as haematopoiesis. Blood cells are divided into three lineages erythriod (erythrocytes), lymphoid (B and T cells), and myeloid (granulocytes, megakaryocytes, and macrophages). Haematopoiesis is a complex process regulated by several mechanisms including microRNAs (miRNAs). miRNAs are small RNAs which regulate the expression of a number of genes involved in commitment and differentiation of hematopoietic stem cells. Evidence shows that miRNAs play an important role in haematopoiesis; for example, myeloid and erythroid differentiation is blocked by the overexpression of miR-15a. miR-221, miR-222, and miR-24 inhibit the erythropoiesis, whereas miR-150 plays a role in B and T cell differentiation. miR-146 and miR-10a are downregulated in megakaryopoiesis. Aberrant expression of miRNAs was observed in hematological malignancies including chronic myelogenous leukemia, chronic lymphocytic leukemia, multiple myelomas, and B cell lymphomas. In this review we have focused on discussing the role of miRNA in haematopoiesis.