MicroRNA-494 is required for the accumulation and functions of tumor-expanded myeloid-derived suppressor cells via targeting of PTEN

Phenotype, development, and biological function of myeloid-derived suppressor cells

CD11b⁺Gr-1⁺ myeloid-derived suppressor cells (MDSCs) are an important population of innate regulatory cells mainly comprising monocytic MDSCs (M-MDSCs) with a phenotype of CD11b⁺Ly6G^-Ly6C^high and granulocytic MDSCs (G-MDSCs) with a phenotype of CD11b⁺Ly6G⁺Ly6C^low in mice. They play crucial roles in the pathogenesis of cancers, chronic infections, autoimmune diseases, and transplantation. Various extracellular factors such as lipopolysaccharide (LPS), macrophage colony-stimulating factor (M-CSF), granulocyte macrophage colony-stimulating factor (GM-CSF), stem cell factor (SCF), interleukin (IL)-6, interferon gamma (IFNγ), IL-1β, vascular endothelial growth factor (VEGF), Hsp72, IL-13, C5a, and prostaglandin E2 (PGE2) can induce MDSC differentiation, whereas IL-4 and all-trans-retinoic acid can inhibit this process. For the intracellular signals, signal transducer and activator of transcription (STAT) family members, C/EBPβ and cyclooxigenase-2 (COX-2) promote MDSC function, whereas interferon regulatory factor-8 (IRF-8) and Smad3 downregulate MDSC activity. The immunosuppressive function of MDSCs is mediated through various effector molecules, primarily cellular metabolism-related molecules such as nitric oxide (NO), arginase, reactive oxygen species (ROS), transforming growth factor β (TGFβ), IL-10, indoleamine 2,3-dioxygenase (IDO), heme oxygenase-1 (HO-1), carbon monoxide (CO), and PGE2. In this article, we will summarize the molecules involved in the induction and function of MDSCs as well as the regulatory pathways of MDSCs.

Tolerance and immune suppression in the tumor microenvironment

The concept of immunological tolerance has guided and permeated much of modern immunology. Ray Owen's ground-breaking observations in twin cattle provided the first mechanistic explanation for tolerance to self-molecules and established tolerance as a beneficial process that protects the host against autoreactivity. However, his studies also opened the door to understanding that tolerance may be detrimental, such as occurs when cancer cells induce tolerance/immune suppression resulting in inhibition of anti-tumor immunity. This article briefly traces the early history of the field of tumor immunology with respect to tolerance, and then focuses on a relatively recently identified population of cells called myeloid-derived suppressor cells (MDSCs). MDSC are instrumental in causing tolerance/immune suppression in individuals with cancer. They are present in most individuals with cancer and because of their potent immune suppressive activity are a major deterrent to natural anti-tumor immunity and a significant obstacle to immunotherapy.

MicroRNA-200c Promotes Suppressive Potential of Myeloid-Derived Suppressor Cells by Modulating PTEN and FOG2 Expression

Myeloid-derived suppressor cells (MDSCs) constitute one of the major populations that potently suppress anti-tumor immune responses and favor tumor growth in tumor microenvironment. However, the mechanism(s) regulating the differentiation and suppressive function of tumor-associated MDSCs remain(s) unclear. Here, we identified a microRNA-200c (miR-200c), whose expression was dramatically induced by tumor-derived factors. Meanwhile, we also demonstrated that GM-CSF was a main inducer of miR-200c in tumor environment, and miR-200c in turn promoted the expansion and immune suppressive activity of MDSCs via targeting phosphatase and tensin homolog (PTEN) and friend of Gata 2 (FOG2), which can lead to STAT3 and PI3K/Akt activation. Finally, we examined in vivo suppressive function of miR-200c transfected MDSCs and found that miR-200c could remarkably promote tumor growth via modifying MDSCs. Thus, GM-CSF induced miR-200c in tumor environment plays a critical role in governing the expansion and functions of tumor-associated MDSCs and serves as a potential target in immunotherapy against tumor.

NFI-A disrupts myeloid cell differentiation and maturation in septic mice

Mounting evidence supports that sepsis-associated immunosuppression increases mortality. As potential contributors to poor sepsis outcomes, myeloid-derived suppressor cells, which are Gr1(+) CD11b(+) innate-immune cell progenitors unable to differentiate and possess suppressive activities, expand dramatically in septic mice by a process requiring increased microRNA-21 and microRNA-181b expression. The inhibition of these microRNAs in vivo in septic mice restores Gr1(+) CD11b(+) cell differentiation and maturation and improves survival. Here, we show that during sepsis-induced generation of myeloid-derived suppressor cells, transcription factor nuclear factor 1 A type represses cyclin-dependent kinase inhibitor p21 to arrest differentiation of Gr1(+) CD11b(+) cells. Our findings include the following: 1) Gr1(+) CD11b(+) myeloid cells from late septic mice genetically lacking nuclear factor 1 A type cannot suppress CD4(+) T cell proliferation and activation; 2) the reconstitution of nuclear factor 1 A type in microRNA-21 and microRNA-181b-depleted Gr1(+) CD11b(+) myeloid-derived suppressor cells inhibits cyclin-dependent kinase inhibitor p21 and restores the immune-suppressor phenotype; 3) ex vivo nuclear factor 1 A type knockdown in Gr1(+) CD11b(+) myeloid-derived suppressor cells from late septic mice restores cyclin-dependent kinase inhibitor p21 expression and promotes monocyte and dendritic cell differentiation; and 4) ectopic nuclear factor 1 A type expression in normal Gr1(+) CD11b(+) cells generates an immunosuppressive phenotype. We suggest that therapeutically targeting nuclear factor 1 A type during late sepsis might improve survival.

Overexpression of secretagogin inhibits cell apoptosis and induces chemoresistance in small cell lung cancer under the regulation of miR-494

Secretagogin (SCGN) has recently been identified to play a crucial role in cell apoptosis, receptor signaling and differentiation. However, its clinical significance and functional roles in SCLC chemoresistance remain unknown. Here we examined the expression of SCGN in clinical samples from SCLC patients and evaluated its relation with clinical prognosis. Then up and down-regulation of SCGN were carried out in SCLC cell lines to assess its influence on chemoresistance. Furthermore, luciferase reporter assay was used to evaluate whether SCGN is a novel direct target of miR-494. Our results revealed that elevated expression of SCGN was correlated with the poorer prognosis of SCLC patients and the more significant correlation with chemosensitivity. We also found that knockdown of SCGN expression in H69AR and H446AR cells increased chemosensitivity via increasing cell apoptosis and cell cycle arrest of G0/G1 phase, while over-expression of SCGN reduced chemosensitivity in sensitive H69 and H446 cells. SCGN as a novel target of miR-494 by luciferase reporter assay, up-regulation of miR-494 can sensitize H69AR cells to chemotherapeutic drugs. These results suggest SCGN is involved in the chemoresistance of SCLC under the regulation of miR-494 and may be a potential biomarker for predicting therapeutic response in treatment SCLC.

Exploring MicroRNA Expression Profiles Related to the mTOR Signaling Pathway in Mouse Embryonic Fibroblast Cells Treated with Polyethylenimine

Although the toxicology of poly(ethylenimine) (PEI) in gene expression levels has been previously investigated, little is known about the effects of PEI on the expression of microRNAs (miRNAs) that regulate gene expression at the post-transcriptional level. In this study, we explored miRNA expression profiles related to cell death mechanisms in mouse embryonic fibroblast (MEF) cells treated with PEI by applying microarray analysis. Based on the analysis of the mTOR signaling pathway, three upregulated miRNAs (mmu-miR-3090-5p, mmu-miR-346-3p, and mmu-miR-494-3p) were verified in MEF cells treated with PEI at 24 h using real-time quantitative reverse transcriptase-polymerase chain reaction. We further demonstrated that these three upregulated miRNAs resulted in the decrease of gene and protein expressions of the target gene growth factor Igf1 in MEF cells treated with PEI or transfected with three upregulated miRNA mimics. However, these three upregulated miRNAs are not all cell-specific. Finally, we demonstrated that the mTOR signaling pathway is inhibited by autophagy induction and that the cell viability decreases in MEF cells treated with PEI or transfected with these three miRNA mimics. Collectively, our data suggested that PEI may affect the regulation of miRNAs in target cells.

Interleukin 33 in tumor microenvironment is crucial for the accumulation and function of myeloid-derived suppressor cells

Tumor-induced, myeloid-derived suppressor cells (MDSCs)-mediated immune dysfunction is an important mechanism that leads to tumor immune escape and the inefficacy of cancer immunotherapy. Importantly, tumor-infiltrating MDSCs have much stronger ability compared to MDSCs in the periphery. However, the mechanisms that tumor microenvironment induces the accumulation and function of MDSCs are poorly understood. Here, we report that Interleukin-33 (IL-33) - a cytokine which can be abundantly released in tumor tissues both in 4T1-bearing mice and breast cancer patients, is crucial for facilitating the expansion of MDSCs. IL-33 in tumor microenvironment reduces the apoptosis and sustains the survival of MDSCs through induction of autocrine secretion of GM-CSF, which forms a positive amplifying loop for MDSC accumulation. This is in conjunction with IL-33-driven induction of arginase-1 expression and activation of NF-κB and MAPK signaling in MDSCs which augments their immunosuppressive ability, and histone modifications were involved in IL-33 signaling in MDSCs. In ST2^-/- mice, the defect of IL-33 signaling in MDSCs attenuates the immunosuppressive and pro-tumoral capacity of MDSCs. Our results identify IL-33 as a critical mediator that contributes to the abnormal expansion and enhanced immunosuppressive function of MDSCs within tumor microenvironment, which can be potentially targeted to reverse MDSC-mediated tumor immune evasion.

The roles of microRNAs in the regulation of tumor metastasis

MicroRNAs (miRNAs) are small noncoding regulatory RNAs that regulate gene expression post-transcriptionally by either inhibiting protein translation or degrading target mRNAs. The differential expression profiles of miRNAs in different types of cancers and in the multi-step process of tumor progression indicate that miRNAs are involved in tumor onset, growth and progression. Metastasis is the most common cause of cancer-related mortality. Current evidence demonstrates that aberrant miRNA expression promotes or inhibits tumor metastasis by modulating the expression of numerous target genes. Therefore, the identification of metastasis-related miRNAs and a better understanding of the complex functions of miRNAs in tumor metastasis will provide potential diagnostic and prognostic biomarkers, as well as therapeutic targets for clinical application. Here, we review the functions of miRNAs in the control of multiple steps of tumor metastasis.

MicroRNA-9 Regulates the Differentiation and Function of Myeloid-Derived Suppressor Cells via Targeting Runx1

Myeloid-derived suppressor cells (MDSCs) play a critical role in tumor-associated immunosuppression, thus affecting effective immunotherapies for cancers. However, the molecular mechanisms involved in regulating the differentiation and function of MDSCs remain largely unclear. In this study, we found that inhibition of microRNA (miR)-9 promoted the differentiation of MDSCs with significantly reduced immunosuppressive function whereas overexpression of miR-9 markedly enhanced the function of MDSCs. Notably, knockdown of miR-9 significantly impaired the activity of MDSCs and inhibited the tumor growth of Lewis lung carcinoma in mice. Moreover, miR-9 regulated MDSCs differentiation by targeting the runt-related transcription factor 1, an essential transcription factor in regulating MDSC differentiation and function. Furthermore, the CREB was found to regulate miR-9 expression in MDSCs. Taken together, our findings have identified a critical role of miR-9 in regulating the differentiation and function of MDSCs.

MicroRNA regulons in tumor microenvironment

Cancer initiation and progression are defined by the behavior of cancer cells per se and the development of tumor tissues, both of which are modulated by crosstalk between cancer cells and the surrounding microenvironment. Advances in cancer research have highlighted the significance of constant evolution of the tumor microenvironment, leading to tumor formation, metastasis and refractoriness to therapy. MicroRNAs (miRNAs) are small non-coding RNAs that function as major players of posttranscriptional gene regulation in diverse biological processes. They function as both tumor suppressors and promoters in many aspects of the autonomous behavior of cancer cells. Theoretically, dysfunction in the gene regulatory networks of cancer cells is one of the major driving forces for alterations of ostensibly normal surrounding cells. In this context, the core targets of miRNAs, termed miRNA regulons, are currently being expanded to include various modulators of the tumor microenvironment. Recent advances have highlighted two important roles played by miRNAs in the evolution of tumor microenvironments: miRNAs in tumor cells transform the microenvironment via non-cell-autonomous mechanisms, and miRNAs in neighboring cells stabilize cancer hallmark traits. These observations epitomize the distal and proximal functions of miRNAs in tumor microenvironments, respectively. Such regulation by miRNAs affects tumor angiogenesis, immune invasion and tumor-stromal interactions. This review summarizes recent findings on the mechanisms of miRNA-mediated regulation of tumor microenvironments, with a perspective on the design of therapeutic interventions.

MicroRNA-29b attenuates non-small cell lung cancer metastasis by targeting matrix metalloproteinase 2 and PTEN

BACKGROUND

Our pilot study using miRNA PCR array found that miRNA-29b (miR-29b) is differentially expressed in primary cultured CD133-positive A549 cells compared with CD133-negative A549 cells.

METHODS

Ten human non-small cell lung cancer (NSCLC) cell lines and samples from thirty patients with NSCLC were analyzed for the expression of miR-29b by quantitative RT-PCR. Bioinformatics analysis combined with tumor metastasis PCR array showed the potential target genes for miR-29b. miR-29b lentivirus and inhibitors were transfected into NSCLC cells to investigate its role on regulating cell proliferation which was measured by CCK-8 assay in vitro and nude mice xenograft tumor assay in vivo. Cell motility ability was evaluated by transwell assay. The target genes of miR-29b were determined by luciferase assay, quantitative RT-PCR and western blot.

RESULTS

Bioinformatics analysis combined with tumor metastasis PCR array showed that matrix metalloproteinase 2 (MMP2) and PTEN could be important target genes of miR-29b. The expression of miR-29b was down regulated in NSCLC tissues compared to the normal tissues. Clinicopathological analysis demonstrated that miR-29b had significant negative correlation with lymphatic metastasis. The gain-of-function studies revealed that ectopic expression of miR-29b decreased cell proliferation, migration and invasion abilities of NSCLC cells. In contrasts, loss-of-function studies showed that inhibition of miR-29b promoted cell proliferation, migration and invasion of NSCLC cells in vitro. Nude mice xenograft tumor assay confirmed that miR-29b inhibited lung cancer growth in vivo. High-invasion (A549-H) and low-invasion (A549-L) NSCLC cell sublines from A549 cells were created by using the repeated transwell assay aimed to confirm the effect of miR-29b on migration and invasion of NSCLC. Furthermore, the dual-luciferase reporter assay demonstrated that miR-29b inhibited the expression of the luciferase gene containing the 3'-UTRs of MMP2 and PTEN mRNA. Western blotting and quantitative RT-PCR indicated that miR-29b down-regulated the expression of MMP2 at the protein and mRNA levels.

CONCLUSION

Taken together, our results demonstrate that miR-29b serves as a tumor metastasis suppressor, which suppresses NSCLC cell metastasis by directly inhibiting MMP2 expression. The results show that miR-29b may be a novel therapeutic candidate target to slow NSCLC metastasis.

Tumor-derived microRNA-494 promotes angiogenesis in non-small cell lung cancer

Angiogenesis, a crucial step in tumor growth and metastasis, is regulated by various pro- or anti-angiogenic factors. Recently, microRNAs have been shown to modulate angiogenic processes by modulating the expression of critical angiogenic factors. However, roles of tumor-derived microRNAs in regulating tumor vascularization remain to be elucidated. In this study, we found that delivery of miR-494 into human vascular endothelial cells (ECs) enhanced the EC migration and promoted angiogenesis. The angiogenic effect of miR-494 was mediated by the targeting of PTEN and the subsequent activation of Akt/eNOS pathway. Importantly, co-culture experiments demonstrated that a lung cancer cell line, A549, secreted and delivered miR-494 into ECs via a microvesicle-mediated route. In addition, we found that the expression of miR-494 was induced in the tumor cells in response to hypoxia, likely via a HIF-1α-mediated mechanism. Furthermore, a specific miR-494 antagomiR effectively inhibited angiogenesis and attenuated the growth of tumor xenografts in nude mice. Taken together, these results demonstrated that miR-494 is a novel tumor-derived paracrine signal to promote angiogenesis and tumor growth under hypoxic condition.

Regulating Tumor Myeloid-Derived Suppressor Cells by MicroRNAs

Myeloid-derived suppressor cells (MDSCs) are one of the major cell components responsible for cancer immune evasion. Studying mechanisms associated with the regulation of MDSCs is becoming appreciated as another way to manipulate immune responses. MicroRNAs (miRNAs) have been recognized as substances which may interact with MDSCs, and eight miRNAs including miR-17-5p, miR-20a, miR-223, miR-21, miR-155, miR-494, miR-690 and miR-101 are of particular interest regarding MDSC accumulation and function. We have reviewed the data supporting this activity of these entities.

Myeloid-Derived Suppressor Cells and Therapeutic Strategies in Cancer

Development of solid cancer depends on escape from host immunosurveillance. Various types of immune cells contribute to tumor-induced immune suppression, including tumor associated macrophages, regulatory T cells, type 2 NKT cells, and myeloid-derived suppressor cells (MDSCs). Growing body of evidences shows that MDSCs play pivotal roles among these immunosuppressive cells in multiple steps of cancer progression. MDSCs are immature myeloid cells that arise from myeloid progenitor cells and comprise a heterogeneous immune cell population. MDSCs are characterized by the ability to suppress both adaptive and innate immunities mainly through direct inhibition of the cytotoxic functions of T cells and NK cells. In clinical settings, the number of circulating MDSCs is associated with clinical stages and response to treatment in several cancers. Moreover, MDSCs are reported to contribute to chemoresistant phenotype. Collectively, targeting MDSCs could potentially provide a rationale for novel treatment strategies in cancer. This review summarizes recent understandings of MDSCs in cancer and discusses promissing clinical approaches in cancer patients.

Myeloid-Derived Suppressor Cells: Critical Cells Driving Immune Suppression in the Tumor Microenvironment

Myeloid-derived suppressor cells (MDSCs) are a heterogeneous population of immature myeloid cells that suppress innate and adaptive immunity. MDSCs are present in many disease settings; however, in cancer, they are a major obstacle for both natural antitumor immunity and immunotherapy. Tumor and host cells in the tumor microenvironment (TME) produce a myriad of pro-inflammatory mediators that activate MDSCs and drive their accumulation and suppressive activity. MDSCs utilize a variety of mechanisms to suppress T cell activation, induce other immune-suppressive cell populations, regulate inflammation in the TME, and promote the switching of the immune system to one that tolerates and enhances tumor growth. Because MDSCs are present in most cancer patients and are potent immune-suppressive cells, MDSCs have been the focus of intense research in recent years. This review describes the history and identification of MDSCs, the role of inflammation and intracellular signaling events governing MDSC accumulation and suppressive activity, immune-suppressive mechanisms utilized by MDSCs, and recent therapeutics that target MDSCs to enhance antitumor immunity.

MicroRNAs as mediators and communicators between cancer cells and the tumor microenvironment

Cancer cells grow in an environment comprised of multiple components that support tumor growth and contribute to therapy resistance. Major cell types in the tumor microenvironment are fibroblasts, endothelial cells and infiltrating immune cells all of which communicate with cancer cells. One way that these cell types promote cancer progression is by altering the expression of microRNAs (miRNAs), small noncoding RNAs that negatively regulate protein expression, either in the cancer cells or in the associated normal cells. Changes in miRNA expression can be brought about by direct interaction between the stromal cells and cancer cells, by paracrine factors secreted by any of the cell types or even through direct communication between cells through secreted miRNAs. Understanding the role of miRNAs in the complex interactions between the tumor and cells in its microenvironment is necessary if we are to understand tumor progression and devise new treatments.

Differential expression of miRNAs in enterovirus 71-infected cells

Background

Enterovirus 71 (EV71) is one of the major etiological pathogens of hand, foot and mouth disease (HFMD) and can cause severe cerebral and pulmonary complications and even fatality. MicroRNAs (miRNAs), a class of small non-coding RNA molecules, play an important role in post-transcriptional regulation of gene expression and thereby influencing various physiological and pathological processes. Increasing evidence suggests that miRNAs act as key effector molecules in the complicated pathogen-host interactions. However, the roles of miRNAs in EV71 infection and pathogenesis are not well understood.

Methods

To identify special miRNAs involved in EV71 infection, a microarray assay was performed to study the expression pattern of miRNAs in EV71-infected human rhabdomyosarcoma cells (RD cells) and uninfected RD cells. We further predicted the putative target genes for the dysregulated miRNAs using the online bioinformatic algorithms (TargetScan, miRanda and PicTar) and carried out functional annotation including GO enrichment and KEGG pathway analysis for miRNA predicted targets. Then, the results of microarray were further confirmed by quantitative RT-PCR.

Results

Totally, 45 differentially expressed miRNAs ware identified by microarray, among which 36 miRNAs were up-regulated and 9 were down-regulated. 7166 predicted target genes for the dysregulated miRNAs were revealed by using TargetScan in conjunction with miRanda and PicTar. The GO annotation suggested that predicted targets of miRNAs were enriched into the category of signal transduction, regulation of transcription, metabolic process, protein phosphorylation, apoptotic process and immune response. KEGG pathway analysis suggested that these predicted target genes were involved in many important pathways, mainly including endocytosis and focal adhesion, MAPK signaling pathway, hypertrophic cardiomyopathy, melanogenesis and ErbB signaling pathway. The expression levels of 8 most differentially up-regulated miRNAs and 3 most differentially down-regulated miRNAs were confirmed by qRT-PCR. The expressions of hsa-miR-4530, hsa-miR-4492, hsa-miR-6125, hsa-miR-494-3p, hsa-miR-638, hsa-miR-6743-5p, hsa-miR-4459 and hsa-miR-4443 detected by qRT-PCR were consistent with the microarray data.

Conclusion

These results might extend our understanding to the regulatory mechanism of miRNAs underlying the pathogenesis of EV71 infection, thus strengthening the preventative and therapeutic strategies of HFMD caused by EV71.

Expression and clinical evidence of miR-494 and PTEN in non-small cell lung cancer

The aim of this study was to explore the expression and clinical significance of miR-494 and PTEN (phosphatase and tensin homologue deleted on chromosome ten) in non-small cell lung cancer (NSCLC). Immunohistochemistry for PTEN and in situ hybridization (ISH) for miR-494 were performed in 92 NSCLC tissues and 10 normal lung tissues to detect their expression, and correlation between their expression with clinical characteristics and prognosis was analyzed. The expression of miR-494 was significantly higher in NSCLC than in normal lung tissues (P = 0.004). The positive expression of PTEN protein in the lung carcinoma tissues was significantly lower than that in the normal lung tissues (P = 0.013), while the level of miR-494 expression was negatively correlated with PTEN expression (r = -0.577, P < 0.01). The high positive rate of miR-494 was positively correlated with pathological TNM (p-TNM) staging and lymph node metastasis. The expression of miR-494 was negatively correlated with grade of differentiation. However, the expression of PTEN was positively correlated with grade of differentiation. Patients with over-expression of miR-494 had a shorter overall survival (OS), while the negative group of PTEN was correlated with poor OS. MiR-494 over-expression and low PTEN expression are closely related to tumor p-TNM staging and lymph node metastasis, differentiation, and OS. Combined detection of PTEN and miR-494 can aid in determining malignancy degree and the prognosis of patients with NSCLC. MiR-494 may be served as a novel prognostic factor and may lead to new treatment strategies for NSCLC.

A new method for discovering disease-specific MiRNA-target regulatory networks

Genes and their expression regulation are among the key factors in the comprehension of the genesis and development of complex diseases. In this context, microRNAs (miRNAs) are post-transcriptional regulators that play an important role in gene expression since they are frequently deregulated in pathologies like cardiovascular disease and cancer. In vitro validation of miRNA - targets regulation is often too expensive and time consuming to be carried out for every possible alternative. As a result, a tool able to provide some criteria to prioritize trials is becoming a pressing need. Moreover, before planning in vitro experiments, the scientist needs to evaluate the miRNA-target genes interaction network. In this paper we describe the miRable method whose purpose is to identify new potentially relevant genes and their interaction networks associate to a specific pathology. To achieve this goal miRable follows a system biology approach integrating together general-purpose medical knowledge (literature, Protein-Protein Interaction networks, prediction tools) and pathology specific data (gene expression data). A case study on Prostate Cancer has shown that miRable is able to: 1) find new potential miRNA-targets pairs, 2) highlight novel genes potentially involved in a disease but never or little studied before, 3) reconstruct all possible regulatory subnetworks starting from the literature to expand the knowledge on the regulation of miRNA regulatory mechanisms.

MiR-494-3p induced by compressive force inhibits cell proliferation in MC3T3-E1 cells

Mechanical stimuli regulate fundamental cell processes such as proliferation, differentiation, and morphogenesis. We attempted to identify microRNA (miRNA) whose expression is changed during compressive treatment in MC3T3-E1, a pre-osteoblastic cell line. Microarray analysis followed by reverse transcription-quantitative polymerase chain reaction revealed that compressive force at 294 Pa for 24 h in MC3T3-E1 cells increased levels of miR-494-3p, miR-146a-5p, miR-210-3p, and miR-1247-3p. Among these miRNAs, miR-494-3p was found to inhibit cell proliferation in MC3T3-E1 cells. Furthermore, cells subjected to compressive force showed slower cell growth compared with control cells. Levels of mRNA for fibroblast growth factor receptor 2 (FGFR2) and Rho-associated coiled-coil kinase 1 (ROCK1), which were predicted to be targets of miR-494-3p, were decreased by compressive force or overexpression of miR-494-3p mimics in MC3T3-E1 cells. Furthermore, binding sites of miR-494-3p within 3'-untranslated regions of Fgfr2 and Rock1 were determined using luciferase reporter assay. In conclusion, compressive force affected expressions of several miRNAs including miR-494-3p in MC3T3-E1 cells. Compressive force might inhibit cell proliferation in osteoblasts by up-regulating miR-494-3p followed by FGFR2 and ROCK1 gene repressions.

MicroRNA-494 promotes cervical cancer proliferation through the regulation of PTEN

The phosphoinositide 3-kinase (PI3K)/Akt signaling pathway appears to be a key regulator in cervical carcinogenesis. The phosphatase and tensin homolog deleted on chromosome 10 (PTEN) protein is principally involved in the homeostatic maintenance of PI3K/Akt signaling and PTEN has been identified to play an important role in the occurrence and development of cervical cancer. MicroRNA (miRNA)-494 has been proven to be involved in the carcinogenesis and development of various types of cancer by directly targeting PTEN. However the role, mechanism and clinical significance of miR-494 in cervical cancer have not been further reported. In the present study, we analyzed the expression of miR-494 in -with PTEN expression and clinicopathological data of cervical cancer patients. The results showed that miR-494 expression was significantly upregulated in human cervical cancer cell lines and tissues. miR-494 upregulation was significantly associated with PTEN downregulation, adverse clinicopathological characteristics, poor overall and progression-free survival and poor prognosis. In vitro experiments showed that inhibition of miR-494 suppressed cell proliferation and growth by directly targeting the 3'-untranslated region (3'-UTR) of PTEN mRNA. These findings identified a novel molecular mechanism involved in the regulation of PTEN expression and cervical cancer progression. Results of the present study indicated that miR-494 may have an essential role in the carcinogenesis and progression of cervical cancer and targeting miR-494 may be a promising therapeutic strategy for the treatment of cervical cancer.

miR-494-3p Regulates Cellular Proliferation, Invasion, Migration, and Apoptosis by PTEN/AKT Signaling in Human Glioblastoma Cells

Malignant gliomas are the most common primary brain tumors, and the molecular mechanisms involving their progression and recurrence are still largely unclear. Substantial data indicate that the oncogene miR-494-3p is significantly elevated in gliomas, but the molecular functions of miR-494-3p in gliomagenesis are largely unknown. The present study aimed to explore the role of miR-494-3p and its molecular mechanism in human brain gliomas, malignant glioma cell lines, and cancer stem-like cells. The expression level of miR-494-3p in 48 human glioma issues and 8 normal brain tissues was determined using stem-loop real-time polymerase chain reaction (PCR). To study the function of miR-494-3p inhibitor in glioma cells, the miR-494-3p inhibitor lentivirus was used to transfect glioma cells. Transwell invasion system was used to estimate the effects of miR-494-3p inhibitor on the invasiveness of glioma cells. A mouse model was used to test the effect of miR-494-3p inhibitor on glioma proliferation and invasion in vivo. Results showed that the expression of miR-494-3p in human brain glioma tissues was higher than in normal brain tissues. Downregulated expression of miR-494-3p can inhibit the invasion and proliferation and promote apoptosis in glioma cells. Quantitative reverse transcription PCR and Western blotting analysis revealed that the expression of PTEN was increased after downexpression of miR-494-3p in glioma cells (U87 and U251). miR-494-3p inhibitor could prevent migration, invasion, proliferation, and promote apotosis in gliomas through PTEN/AKT pathway. Therefore, the study results have shown that miR-494-3p may act as a therapeutic target in gliomas.

MicroRNA-125b upregulation confers aromatase inhibitor resistance and is a novel marker of poor prognosis in breast cancer

Introduction

Increasing evidence indicates that microRNAs (miRNAs) are important players in oncogenesis. Considering the widespread use of aromatase inhibitors (AIs) in endocrine therapy as a first-line treatment for postmenopausal estrogen receptor α–positive breast cancer patients, identifying deregulated expression levels of miRNAs in association with AI resistance is of utmost importance.

Methods

To gain further insight into the molecular mechanisms underlying the AI resistance, we performed miRNA microarray experiments using a new model of acquired resistance to letrozole (Res-Let cells), obtained by long-term exposure of aromatase-overexpressing MCF-7 cells (MCF-7aro cells) to letrozole, and a model of acquired anastrozole resistance (Res-Ana cells). Three miRNAs (miR-125b, miR-205 and miR-424) similarly deregulated in both AI-resistant cell lines were then investigated in terms of their functional role in AI resistance development and breast cancer cell aggressiveness and their clinical relevance using a cohort of 65 primary breast tumor samples.

Results

We identified the deregulated expression of 33 miRNAs in Res-Let cells and of 18 miRNAs in Res-Ana cells compared with the sensitive MCF-7aro cell line. The top-ranked Kyoto Encyclopedia of Genes and Genomes pathways delineated by both miRNA signatures converged on the AKT/mTOR pathway, which was found to be constitutively activated in both AI-resistant cell lines. We report for the first time, to our knowledge, that ectopic overexpression of either miR-125b or miR-205, or the silencing of miR-424 expression, in the sensitive MCF-7aro cell line was sufficient to confer resistance to letrozole and anastrozole, to target and activate the AKT/mTOR pathway and to increase the formation capacity of stem-like and tumor-initiating cells possessing self-renewing properties. Increasing miR-125b expression levels was also sufficient to confer estrogen-independent growth properties to the sensitive MCF-7aro cell line. We also found that elevated miR-125b expression levels were a novel marker for poor prognosis in breast cancer and that targeting miR-125b in Res-Let cells overcame letrozole resistance.

Conclusion

This study highlights that acquisition of specific deregulated miRNAs is a newly discovered alternative mechanism developed by AI-resistant breast cancer cells to achieve constitutive activation of the AKT/mTOR pathway and to develop AI resistance. It also highlights that miR-125b is a new biomarker of poor prognosis and a candidate therapeutic target in AI-resistant breast cancers.

Electronic supplementary material

The online version of this article (doi:10.1186/s13058-015-0515-1) contains supplementary material, which is available to authorized users.

In vivo delivery of miRNAs for cancer therapy: challenges and strategies

MicroRNAs (miRNAs), small non-coding RNAs, can regulate post-transcriptional gene expressions and silence a broad set of target genes. miRNAs, aberrantly expressed in cancer cells, play an important role in modulating gene expressions, thereby regulating downstream signaling pathways and affecting cancer formation and progression. Oncogenes or tumor suppressor genes regulated by miRNAs mediate cell cycle progression, metabolism, cell death, angiogenesis, metastasis and immunosuppression in cancer. Recently, miRNAs have emerged as therapeutic targets or tools and biomarkers for diagnosis and therapy monitoring in cancer. Since miRNAs can regulate multiple cancer-related genes simultaneously, using miRNAs as a therapeutic approach plays an important role in cancer therapy. However, one of the major challenges of miRNA-based cancer therapy is to achieve specific, efficient and safe systemic delivery of therapeutic miRNAs in vivo. This review discusses the key challenges to the development of the carriers for miRNA-based therapy and explores current strategies to systemically deliver miRNAs to cancer without induction of toxicity.

Myeloid-derived suppressor cells in multiple myeloma: pre-clinical research and translational opportunities

Immunosuppressive cells have been reported to play an important role in tumor-progression mainly because of their capability to promote immune-escape, angiogenesis, and metastasis. Among them, myeloid-derived suppressor cells (MDSCs) have been recently identified as immature myeloid cells, induced by tumor-associated inflammation, able to impair both innate and adaptive immunity. While murine MDSCs are usually identified by the expression of CD11b and Gr1, human MDSCs represent a more heterogeneous population characterized by the expression of CD33 and CD11b, low or no HLA-DR, and variable CD14 and CD15. In particular, the last two may alternatively identify monocyte-like or granulocyte-like MDSC subsets with different immunosuppressive properties. Recently, a substantial increase of MDSCs has been found in peripheral blood and bone marrow (BM) of multiple myeloma (MM) patients with a role in disease progression and/or drug resistance. Pre-clinical models recapitulating the complexity of the MM-related BM microenvironment (BMM) are major tools for the study of the interactions between MM cells and cells of the BMM (including MDSCs) and for the development of new agents targeting MM-associated immune-suppressive cells. This review will focus on current strategies for human MDSCs generation and investigation of their immunosuppressive function in vitro and in vivo, taking into account the relevant relationship occurring within the MM–BMM. We will then provide trends in MDSC-associated research and suggest potential application for the treatment of MM.

Cinobufacin suppresses cell proliferation via miR-494 in BGC- 823 gastric cancer cells

Cinobufacin is used clinically to treat patients with many solid malignant tumors. However, the mechanisms underlying action remain to be detailed. Our study focused on miRNAs involved in cinobufacin inhibition of GC cell proliferation. miRNA microarray analysis and real time PCR identified miR-494 as a significant cinobufacin- associated miRNA. In vivo, ectopic expression of miR-494 inhibited the proliferation and induced apoptosis of BGC-823 cells on CCK-8 and flow cytometry analysis. Further study verified BAG-1 (anti-apoptosis gene) to bea target of miR-494 by luciferase reporter assay and Western blotting. In summary, our study demonstrated that cinobufacin may inhibit the proliferation and promote the apoptosis of BGC-823 cells. Cinobufacin-associated miR-494 may indirectly be involved in cell proliferation and apoptosis by targeting BAG-1, pointing to use as a potential molecular target of cinobufacin in gastric cancer therapy.

Modeling glands with PTEN deficient cells and microscopic methods for assessing PTEN loss: endometrial cancer as a model

PTEN is an important tumor suppressor gene. Interpreting PTEN deficiency in the appropriate microscopic context of cancer may be important to understand its role in tumor development and progression. This may be particularly relevant in heterogeneous tumors. Here, we discuss the usefulness of 3D cultures in understanding the consequences of PTEN inactivation in tissue architecture. Afterwards, we discuss the role of immunohistochemistry and fluorescent in situ hybridization in assessing PTEN loss in tumors. In this review, endometrial carcinoma is used as a model.

MicroRNA expression as risk biomarker of breast cancer metastasis: a pilot retrospective case-cohort study

BACKGROUND

MicroRNAs (miRNAs) are small, non-coding RNA molecules involved in post-transcriptional gene regulation and have recently been shown to play a role in cancer metastasis. In solid tumors, especially breast cancer, alterations in miRNA expression contribute to cancer pathogenesis, including metastasis. Considering the emerging role of miRNAs in metastasis, the identification of predictive markers is necessary to further the understanding of stage-specific breast cancer development. This is a retrospective analysis that aimed to identify molecular biomarkers related to distant breast cancer metastasis development.

METHODS

A retrospective case cohort study was performed in 64 breast cancer patients treated during the period from 1998-2001. The case group (n = 29) consisted of patients with a poor prognosis who presented with breast cancer recurrence or metastasis during follow up. The control group (n = 35) consisted of patients with a good prognosis who did not develop breast cancer recurrence or metastasis. These patient groups were stratified according to TNM clinical stage (CS) I, II and III, and the main clinical features of the patients were homogeneous. MicroRNA profiling was performed and biomarkers related to metastatic were identified independent of clinical stage. Finally, a hazard risk analysis of these biomarkers was performed to evaluate their relation to metastatic potential.

RESULTS

MiRNA expression profiling identified several miRNAs that were both specific and shared across all clinical stages (p ≤ 0.05). Among these, we identified miRNAs previously associated with cell motility (let-7 family) and distant metastasis (hsa-miR-21). In addition, hsa-miR-494 and hsa-miR-21 were deregulated in metastatic cases of CSI and CSII. Furthermore, metastatic miRNAs shared across all clinical stages did not present high sensitivity and specificity when compared to specific-CS miRNAs. Between them, hsa-miR-183 was the most significative of CSII, which miRNAs combination for CSII (hsa-miR-494, hsa-miR-183 and hsa-miR-21) was significant and were a more effective risk marker compared to the single miRNAs.

CONCLUSIONS

Women with metastatic breast cancer, especially CSII, presented up-regulated levels of miR-183, miR-494 and miR-21, which were associated with a poor prognosis. These miRNAs therefore represent new risk biomarkers of breast cancer metastasis and may be useful for future targeted therapies.

Gr-1⁺CD11b⁺ immature myeloid cells (IMC) promote resistance of pro-inflammatory T cells to suppression by regulatory T cells in atherosclerotic Apo E- deficient mice

Accumulating evidence indicates that both defects in Treg numbers and/or function as well as resistance of effector T cells to suppression may contribute to the development of human chronic inflammatory diseases. However, which mechanism involved in the progression of atherosclerosis remains unclear. In this study, we evaluated the production and function of CD4⁺ inflammatory and regulatory T cells in atherosclerosis-prone mice. We found that the hyperactivity and unresponsiveness to Treg-mediated suppression of inflammatory CD4⁺ T cells occurred in the progression of atherosclerosis, though Treg cells were present in very large numbers and fully functional. We further found that Gr-1⁺CD11b⁺ immature myeloid cells were significantly accumulated in atherosclerotic Apo E^−/− mice, and they promoted resistance of inflammatory CD4⁺ T cells to Treg-mediated suppression in vitro and in vivo. we further confirmed that Gr-1⁺CD11b⁺ immature myeloid cells produced high level of interleukin 6 which was at least partially responsible for inducing unresponsiveness of inflammatory CD4⁺ T cells to suppression via activation of Jak/Stat signaling pathway. Taken together, these findings might provide new insights to explore potential targets for immune therapeutic intervention in atherosclerosis.

miR‑494 is an independent prognostic factor and promotes cell migration and invasion in colorectal cancer by directly targeting PTEN

Accumulating evidence has shown that micro-RNAs (miRNAs) are involved in multiple processes in cancer development and progression. Upregulation of miRNA-494 (miR-494) has been identified as an oncogenic miRNA and is associated with poor prognosis in several types of human cancer. However, the specific function of miR-494 in colorectal cancer remains unclear. In this study we found that the expression of miR-494 in colorectal cancer tissues and cell lines was much higher than in normal control tissues and cells, respectively. In addition, upregulation of miR-494 more frequently occurred in tissue specimens with adverse clinical stage and the presence of distant metastasis. Moreover, multivariate survival analyses demonstrated that overexpression of miR-494 is an independent prognostic factor for both progression-free and overall survival. In addition miR-494 promoted invasion and migration in colorectal cancer cells, and miR-494 directly inhibited the phosphatase and tensin homolog deleted on chromosome 10 (PTEN) expression by targeting its 3'-untranslated region (3'-UTR). Moreover, PTEN is down regulated and inversely correlated with miR-494 expression in tissues. Thus, for the first time, we provided convincing evidence that upregulation of miR-494 was associated with tumor aggressiveness and tumor metastasis and promoted cell migration and invasion by targeting PTEN gene in colorectal cancer, and miR-494 is an independent prognostic marker for colorectal cancer patients.

MicroRNA-492 expression promotes the progression of hepatic cancer by targeting PTEN

BACKGROUND

Aberrant microRNA (miRNA) expression plays an essential role in the pathogenesis of Hepatocellular Carcinoma (HCC). However, specific involvement of miRNAs in HCC remains incompletely understood. The aim of this study was to explore the relevant microRNAs involved in the development of HCC.

METHODS

MicroRNA microarray was used to screen for the differentially expressed miRNAs in cancerous tissue and adjacent non-cancerous control tissue from patients with HCC (n = 3). Quantitative PCR was subsequently used to verify the results of microarray. Based on the findings, we investigated the role of miR-492 in the pathogenesis of HCC in vitro and in vivo using three tumor cells lines. Furthermore, we analyzed the clinical correlation of miR-492 expression with patient survival (n = 28).

RESULTS

We showed that microRNA-492 (miR-492) was elevated in HCC samples from patients with hepatic cancer. Knockdown of miR-492 attenuated the proliferation of cancer cell lines in vitro and inhibited primary tumor growth in vivo in SCID mice. We identified PTEN as a functional target for miR-492. Overexpression of miR-492 resulted in decreased PTEN expression and was associated with increased AKT activation in cancer cell lines. Moreover, miR-492-mediated increase of the proliferation of cancer cells was able to be suppressed by a PI3K inhibitor and an AKT inhibitor. The HCC patients with high miR-492/low PTEN had poorer survival.

CONCLUSIONS

miR-492 is implicated in the regulation of HCC progression through PTEN and AKT pathway. The data suggest that miR-492 is a biomarker of HCC and a potential therapeutic target for hepatocellular carcinoma.

Low serum miR-19a expression as a novel poor prognostic indicator in multiple myeloma

Multiple myeloma (MM) is the second most common hematologic malignancy characterized by the clonal expansion of plasma cells. Despite continuing advances, novel biomarkers are needed for diagnosis and prognosis of MM. In our study, we characterized the diagnostic and prognostic potential of circulating microRNAs (miRNAs) in MM. Serum miRNA levels were analyzed in 108 newly diagnosed symptomatic MM patients and 56 healthy donors (HDs). Our analysis identified 95 dysregulated miRNAs in newly diagnosed MM patients. Of the 95 dysregulated miRNAs, dysregulation of miR-19a, miR-92a, miR-214-3p, miR-135b-5p, miR-4254, miR-3658 and miR-33b was confirmed by quantitative reverse transcription PCR (RT-qPCR). Receiver operating characteristic analysis revealed that a combination of miR-19a and miR-4254 can distinguish MM from HD with a sensitivity of 91.7% and specificity of 90.5%. Decreased expression of miR-19a was positively correlated with international staging system advancement, del(13q14) and 1q21 amplification. Furthermore, downregulation of miR-19a resulted in significantly decreased progression-free survival (PFS) and overall survival (OS). Our analysis indicated that the poor prognostic correlation of miR-19a expression was independent of genetic abnormalities in MM. Multivariate analysis revealed that miR-19a was a significant predictor of shortened PFS and OS. Interestingly, although miR-19a levels portend a poor prognosis, patients with low miR-19a levels had an improved response to bortezomib compared to those with high miR-19a profile. Patients with downregulated miR-19a experienced a significantly extended survival upon bortezomib-based therapy. These data demonstrate that the expression patterns of serum microRNAs are altered in MM, and miR-19a levels are a valuable prognostic marker to identify high-risk MM.

Harnessing the immune system for the treatment of breast cancer

Standard treatment options for breast cancer include surgery, chemotherapy, radiation, and targeted therapies, such as adjuvant hormonal therapy and monoclonal antibodies. Recently, the recognition that chronic inflammation in the tumor microenvironment promotes tumor growth and survival during different stages of breast cancer development has led to the development of novel immunotherapies. Several immunotherapeutic strategies have been studied both preclinically and clinically and already have been shown to enhance the efficacy of conventional treatment modalities. Therefore, therapies targeting the immune system may represent a promising next-generation approach for the treatment of breast cancers. This review will discuss recent findings that elucidate the roles of suppressive immune cells and proinflammatory cytokines and chemokines in the tumor-promoting microenvironment, and the most current immunotherapeutic strategies in breast cancer.

MicroRNA 21 (miR-21) and miR-181b couple with NFI-A to generate myeloid-derived suppressor cells and promote immunosuppression in late sepsis

The sepsis initial hyperinflammatory reaction, if not treated early, shifts to a protracted state of immunosuppression that alters both innate and adaptive immunity and is associated with elevated mortality. Myeloid-derived suppressor cells (MDSCs) are myeloid progenitors and precursors that fail to differentiate into mature innate-immunity cells and are known for their potent immunosuppressive activities. We previously reported that murine MDSCs expand dramatically in the bone marrow during late sepsis, induced by cecal ligation and puncture, and demonstrated that they contribute to late-sepsis immunosuppression. However, the molecular mechanism responsible for generating these immature Gr1(+) CD11b(+) myeloid cells during sepsis remains unknown. We show here that sepsis generates a microRNA (miRNA) signature that expands MDSCs. We found that miRNA 21 (miR-21) and miR-181b expression is upregulated in early sepsis and sustained in late sepsis. Importantly, we found that simultaneous in vivo blockade of both miRNAs via antagomiR (a chemically modified miRNA inhibitor) injection after sepsis initiation decreased the bone marrow Gr1(+) CD11b(+) myeloid progenitors, improved bacterial clearance, and reduced late-sepsis mortality by 74%. Gr1(+) CD11b(+) cells isolated from mice injected with antagomiRs were able to differentiate ex vivo into macrophages and dendritic cells and produced smaller amounts of the immunosuppressive interleukin 10 (IL-10) and transforming growth factor β (TGF-β) after stimulation with bacterial lipopolysaccharide, suggesting that immature myeloid cells regained their maturation potential and have lost their immunosuppressive activity. In addition, we found that the protein level of transcription factor NFI-A, which plays a role in myeloid cell differentiation, was increased during sepsis and that antagomiR injection reduced its expression. Moreover, knockdown of NFI-A in the Gr1(+) CD11b(+) cells isolated from late-septic mice increased their maturation potential and reduced their production of the immunosuppressive mediators, similar to antagomiR injection. These data support the hypothesis that sepsis reprograms myeloid cells and thus alters the innate immunity cell repertoire to promote immunosuppression, and they demonstrate that this process can be reversed by targeting miR-21 and miR-181b to improve late-sepsis survival.

microRNA expression in peripheral blood cells following acute ischemic stroke and their predicted gene targets

Background

microRNA (miRNA) are important regulators of gene expression. In patients with ischemic stroke we have previously shown that differences in immune cell gene expression are present. In this study we sought to determine the miRNA that are differentially expressed in peripheral blood cells of patients with acute ischemic stroke and thus may regulate immune cell gene expression.

Methods

miRNA from peripheral blood cells of forty-eight patients with ischemic stroke and vascular risk factor controls were compared. Differentially expressed miRNA in patients with ischemic stroke were determined by microarray with qRT-PCR confirmation. The gene targets and pathways associated with ischemic stroke that may be regulated by the identified miRNA were characterized.

Results

In patients with acute ischemic stroke, miR-122, miR-148a, let-7i, miR-19a, miR-320d, miR-4429 were decreased and miR-363, miR-487b were increased compared to vascular risk factor controls. These miRNA are predicted to regulate several genes in pathways previously identified by gene expression analyses, including toll-like receptor signaling, NF-κβ signaling, leukocyte extravasation signaling, and the prothrombin activation pathway.

Conclusions

Several miRNA are differentially expressed in blood cells of patients with acute ischemic stroke. These miRNA may regulate leukocyte gene expression in ischemic stroke including pathways involved in immune activation, leukocyte extravasation and thrombosis.

Ionizing radiation-inducible miR-494 promotes glioma cell invasion through EGFR stabilization by targeting p190B rhoGAP

MicroRNAs (miRNAs) play an important role in various stages of tumor progression. miR-494, which we had previously identified as a miRNA induced by ionizing radiation (IR) in the glioma cell line U-251, was observed to enhance invasion of U-251 cells by activating MMP-2. The miR-494-induced invasive potential was accompanied by, and dependent on, epidermal growth factor receptor (EGFR) upregulation and the activation of its downstream signaling constituents, Akt and ERK. The upregulation of EGFR by miR-494 involved the suppression of lysosomal protein turnover. Among the putative target proteins tested, p190B RhoGAP (p190B) was downregulated by miR-494, and its reduced expression was responsible for the increase in EGFR expression. A reporter assay using a luciferase construct containing p190B 3'-untranslated region (3'UTR) confirmed that p190B is a direct target of miR-494. Downregulation of p190B by small interfering RNA (siRNA) transfection closely mimicked the outcomes of miR-494 transfection, and showed increased EGFR expression, MMP-2 secretion, and invasion. Ectopic expression of p190B suppressed the miR-494-induced EGFR upregulation and invasion promotion, thereby suggesting that p190B depletion is critical for the invasion-promoting action of miR-494. Collectively, our results suggest a novel function for miR-494 and its potential application as a target to control invasiveness in cancer therapy.

Roles of miRNAs in regulating the differentiation and maturation of myeloid-derived suppressor cells

Myeloid-derived suppressor cells (MDSCs) accumulate in tumor-bearing hosts and play an essential role in tumor-associated immunosuppression, which hampers effective immunotherapeutic approaches. MicroRNAs (miRNAs) are short noncoding RNAs that negatively regulate target gene expression at the posttranscriptional level. miRNAs are involved in regulating cell proliferation, differentiation and maturation, and abnormal expression and function of miRNAs are recognized in various human diseases. Accumulating evidence shows that various miRNAs modulate the development and differentiation of myeloid cells, which implies their possible role in the differentiation of MDSCs into mature myeloid cells. Our recent studies have found that the classical myeloid differentiation related gene runt-related transcription factor 1 (Runx1) and target nuclear factor 1/A (NFI-A) are modulated during the differentiation and maturation of MDSCs while six miRNAs are found to possibly regulate these two targets by miRNA array analysis. Thus, we hypothesize that the predicted miRNAs may modulate the target genes to regulate the differentiation and maturation of MDSCs. Further studies will provide a novel potential approach for tumor immunotherapy.

Identification of miR-494 direct targets involved in senescence of human diploid fibroblasts

Cellular senescence is a permanent cell cycle arrest triggered by different stimuli. We recently identified up-regulation of microRNA (miR)-494 as a component of the genetic program leading to senescence of human diploid IMR90 fibroblasts. Here, we used 2-dimensional differential gel electrophoresis (2D-DIGE) coupled to mass spectrometry to profile protein expression changes induced by adoptive overexpression of miR-494 in IMR90 cells. miR-494 induced robust perturbation of the IMR90 proteome by significantly (P≤0.05) down-regulating a number of proteins. Combination of mass spectrometry-based identification of down-regulated proteins and bioinformatic prediction of the miR-494 binding sites on the relevant mRNAs identified 26 potential targets of miR-494. Among them, computational analysis identified 7 potential evolution-conserved miR-494 targets. Functional miR-494 binding sites were confirmed in 3'-untranslated regions (UTRs) of 4 of them [heterogeneous nuclear ribonucleoprotein A3 (hnRNPA3), protein disulfide isomerase A3 (PDIA3), UV excision repair protein RAD23 homolog B (RAD23B), and synaptotagmin-binding cytoplasmic RNA-interacting protein (SYNCRIP)/heterogeneous nuclear ribonucleoprotein Q (hnRNPQ)]. Their reduced expression correlated with miR-494 up-regulation in senescent cells. RNA interference-mediated knockdown of hnRNPA3 and, to a lesser extent, RAD23B mirrored the senescent phenotype induced by miR-494 overexpression, blunting cell proliferation and causing up-regulation of SA-β-galactosidase and DNA damage. Ectopic expression of hnRNPA3 or RAD23B slowed the appearance of the senescent phenotype induced by miR-494. Overall, these findings identify novel miR-494 direct targets that are involved in cellular senescence.

Myeloid-derived cells are key targets of tumor immunotherapy

Tumors are composed of heterogeneous cell populations recruited by cancer cells to promote growth and metastasis. Among cells comprising the tumor stroma, myeloid-derived cells play pleiotropic roles in supporting tumorigenesis at distinct stages of tumor development. The tumor-infiltrating myeloid cell contingent is composed of mast cells, neutrophils, dendritic cells, macrophages, and myeloid-derived suppressor cells. Such cells are capable of evading the hostile tumor environment typically prone to immune cell destruction and can even promote angiogenesis, chronic inflammation, and invasion. This paper briefly summarizes the different myeloid-derived subsets that promote tumor development and the strategies that have been used to counteract the protumorigenic activity of these cells. These strategies include myeloid cell depletion, reduction of recruitment, and inactivation or remodeling of cell phenotype. Combining drugs designed to target tumor myeloid cells with immunotherapies that effectively trigger antitumor adaptive immune responses holds great promise in the development of novel cancer treatments.

Signaling pathways involved in MDSC regulation

The immune system has evolved mechanisms to protect the host from the deleterious effects of inflammation. The generation of immune suppressive cells like myeloid derived suppressor cells (MDSCs) that can counteract T cell responses represents one such strategy. There is an accumulation of immature myeloid cells or MDSCs in bone marrow (BM) and lymphoid organs under pathological conditions such as cancer. MDSCs represent a population of heterogeneous myeloid cells comprising of macrophages, granulocytes and dendritic cells that are at early stages of development. Although, the precise signaling pathways and molecular mechanisms that lead to MDSC generation and expansion in cancer remains to be elucidated. It is widely believed that perturbation of signaling pathways involved during normal hematopoietic and myeloid development under pathological conditions such as tumorogenesis contributes to the development of suppressive myeloid cells. In this review we discuss the role played by key signaling pathways such as PI3K, Ras, Jak/Stat and TGFb during myeloid development and how their deregulation under pathological conditions can lead to the generation of suppressive myeloid cells or MDSCs. Targeting these pathways should help in elucidating mechanisms that lead to the expansion of MDSCs in cancer and point to methods for eliminating these cells from the tumor microenvironment.

Myeloid-derived suppressor cells: the dark knight or the joker in viral infections?

Myeloid derived suppressor cells (MDSCs) are immature cells of myeloid origin, frequently found in tumor microenvironments and in the blood of cancer patients. In recent years, MDSCs have also been found in non-cancer settings, including a number of viral infections. The evasion of host immunity employed by viruses to establish viral persistence strikingly parallels mechanisms of tumor escape, prompting investigations into the generation and function of MDSCs in chronic viral infections. Importantly, analogous to the tumor microenvironment, MDSCs effectively suppress antiviral host immunity by limiting the function of several immune cells including T cells, natural killer cells, and antigen-presenting cells. In this article, we review studies on the mechanisms of MDSC generation, accumulation, and survival in an effort to understand their emergent importance in viral infections. We include a growing list of viral infections in which MDSCs have been reported. Finally, we discuss how MDSCs might play a role in establishing chronic viral infections and identify potential therapeutics that target MDSCs.

MicroRNA-155 and MicroRNA-21 promote the expansion of functional myeloid-derived suppressor cells

Myeloid-derived suppressor cells (MDSC) are one of the main cell populations that negatively regulate immune responses. However, the mechanism underlying the expansion of MDSC remains unclear. Using miRNA microarray and TaqMan probe-based quantitative RT-PCR assay, we identified microRNA (miR)-155 and miR-21 as the two most upregulated miRNAs during the induction of MDSC from the bone marrow cells by GM-CSF and IL-6. High levels of miR-155 and miR-21 also were detected in bone marrow and spleen MDSC isolated from tumor-bearing mice. Our results also showed that TGF-β promoted the induction of MDSC through upregulating miR-155 and miR-21 expression. Overexpression of miR-155 and miR-21 enhanced whereas depletion of miR-155 and miR-21 reduced the frequencies of cytokine-induced MDSC. Subpopulation analysis indicated that miR-21 and miR-155 induced the expansion of both monocytic and granulocytic MDSC. Furthermore, miR-155 and miR-21 showed a synergistic effect on MDSC induction via targeting SHIP-1 and phosphatase and tensin homolog, respectively, leading to STAT3 activation. Finally, dexamethasone treatment strongly enhanced MDSC expansion through upregulating miR-155 and miR-21 expression, and the effect of dexamethasone on MDSC induction was abolished by depleting cellular miR-155 and miR-21. These results demonstrate a novel miR-155/miR-21-based regulatory mechanism that modulates functional MDSC induction.

MicroRNA-494 within an oncogenic microRNA megacluster regulates G1/S transition in liver tumorigenesis through suppression of mutated in colorectal cancer

Hepatocellular carcinoma (HCC) is associated with poor survival for patients and few effective treatment options, raising the need for novel therapeutic strategies. MicroRNAs (miRNAs) play important roles in tumor development and show deregulated patterns of expression in HCC. Because of the liver's unique affinity for small nucleic acids, miRNA-based therapy has been proposed in the treatment of liver disease. Thus, there is an urgent need to identify and characterize aberrantly expressed miRNAs in HCC. In our study, we profiled miRNA expression changes in de novo liver tumors driven by MYC and/or RAS, two canonical oncogenes activated in a majority of human HCCs. We identified an up-regulated miRNA megacluster comprised of 53 miRNAs on mouse chromosome 12qF1 (human homolog 14q32). This miRNA megacluster is up-regulated in all three transgenic liver models and in a subset of human HCCs. An unbiased functional analysis of all miRNAs within this cluster was performed. We found that miR-494 is overexpressed in human HCC and aids in transformation by regulating the G1 /S cell cycle transition through targeting of the Mutated in Colorectal Cancer tumor suppressor. miR-494 inhibition in human HCC cell lines decreases cellular transformation, and anti-miR-494 treatment of primary MYC-driven liver tumor formation significantly diminishes tumor size.

CONCLUSION

Our findings identify a new therapeutic target (miR-494) for the treatment of HCC.

Over-expression of microRNA-494 up-regulates hypoxia-inducible factor-1 alpha expression via PI3K/Akt pathway and protects against hypoxia-induced apoptosis

BACKGROUND

Hypoxia-inducible factor-1 alpha (HIF-1α) is one of the key regulators of hypoxia/ischemia. MicroRNA-494 (miR-494) had cardioprotective effects against ischemia/reperfusion (I/R)-induced injury, but its functional relationship with HIF-1α was unknown. This study was undertaken to determine if miR-494 was involved in the induction of HIF-1α.

RESULTS

Quantitative RT-PCR showed that miR-494 was up-regulated to peak after 4 hours of hypoxia in human liver cell line L02. To investigate the role of miR-494, cells were transfected with miR-494 mimic or miR-negative control, followed by incubation under normoxia or hypoxia. Our results indicated that overexpression of miR-494 significantly induced the expression of p-Akt, HIF-1α and HO-1 determined by qRT-PCR and western blot under normoxia and hypoxia, compared to negative control (p < 0.05). While LY294002 treatment markedly abolished miR-494-inducing Akt activation, HIF-1α and HO-1 increase under both normoxic and hypoxic conditions (p < 0.05). Moreover, apoptosis detection using Annexin V indicated that overexpression of miR-494 significantly decreased hypoxia-induced apoptosis in L02 cells, compared to control (p < 0.05). MiR-494 overexpression also decreased caspase-3/7 activity by 1.27-fold under hypoxia in L02 cells.

CONCLUSIONS

Overexpression of miR-494 upregulated HIF-1α expression through activating PI3K/Akt pathway under both normoxia and hypoxia, and had protective effects against hypoxia-induced apoptosis in L02 cells. Thus, these findings suggested that miR-494 might be a target of therapy for hepatic hypoxia/ischemia injury.

MicroRNA expression signatures of stage, grade, and progression in clear cell RCC

Clear cell RCC is the most common, and more likely to metastasize, of the three main histological types of RCC. Pathologic stage is the most important prognostic indicator and nuclear grade can predict outcome within stages of localized RCC. Epithelial tumors are thought to accumulate a series of genetic and epigenetic changes as they progress through well-defined clinical and histopathological changes. MicroRNAs (miRNAs) are involved in the regulation of mRNA expression from many human genes and miRNA expression is dysregulated in cancer. To better understand the contribution of dysregulated miRNA expression to the progression and biology of ccRCC, we examined the differences in expression levels of 723 human miRNAs through a series of analyses by stage, grade, and disease progression status in a large series of 94 ccRCC. We found a consistent signature that included significant upregulation of miR-21-5p, 142-3p, let-7g-5p, let-7i-5p and 424-5p, as well as downregulation of miR-204-5p, to be associated with ccRCC of high stage, or high grade, or progression. Discrete signatures associated with each of stage, grade, or progression were also identified. The let-7 family was significantly downregulated in ccRCC compared with normal renal parenchyma. Expression of the 6 most significantly differentially expressed miRNAs between ccRCC was verified by stem-loop qRT-PCR. Pathways predicted as targets of the most significantly dysregulated miRNAs included signaling, epithelial cancers, metabolism, and epithelial to mesenchymal transition. Our studies help to further elucidate the biology underlying the progression of ccRCC and identify miRNAs for potential translational application.

MicroRNA-494, upregulated by tumor necrosis factor-α, desensitizes insulin effect in C2C12 muscle cells

Chronic inflammation is fundamental for the induction of insulin resistance in the muscle tissue of vertebrates. Although several miRNAs are thought to be involved in the development of insulin resistance, the role of miRNAs in the association between inflammation and insulin resistance in muscle tissue is poorly understood. Herein, we investigated the aberrant expression of miRNAs by conducting miRNA microarray analysis of TNF-α-treated mouse C₂C₁₂ myotubes. We identified two miRNAs that were upregulated and six that were downregulated by a >1.5-fold change compared to normal cells. Among the findings, qRT-PCR analysis confirmed that miR-494 is consistently upregulated by TNF-α-induced inflammation. Overexpression of miR-494 in CHO_IR/IRS1 and C₂C₁₂ myoblasts suppressed insulin action by down-regulating phosphorylations of GSK-3α/β, AS160 and p70S6K, downstream of Akt. Moreover, overexpression of miR-494 did not regulate TNF-α-mediated inflammation . Among genes bearing the seed site for miR-494, RT-PCR analysis showed that the expression of Stxbp5, an inhibitor of glucose transport, was downregulated following miR-494 inhibition. In contrast, the expression of PTEN decreased in the cells analyzed, thus showing that both positive and negative regulators of insulin action may be simultaneously controlled by miR-494. To investigate the overall effect of miR-494 on insulin signaling, we performed a PCR array analysis containing 84 genes related to the insulin signaling pathway, and we observed that 25% of genes were downregulated (P<0.05) and 11% were upregulated (P<0.05). These results confirm that miR-494 might contribute to insulin sensitivity by positive and negative regulation of the expression of diverse genes. Of note, PCR array data showed downregulation of Slc2A4, a coding gene for Glut4. Altogether, the present study concludes that the upregulation of miR-494 expression by TNF-α-mediated inflammation exacerbates insulin resistance. Therefore, we suggest that miR-494 could prove an important target for the diagnosis and therapy of inflammation-mediated insulin resistance in muscle.