Modulation of miR-155 and miR-125b levels following lipopolysaccharide/TNF-alpha stimulation and their possible roles in regulating the response to endotoxin shock

Bruton's tyrosine kinase is involved in miR-346-related regulation of IL-18 release by lipopolysaccharide-activated rheumatoid fibroblast-like synoviocytes

MicroRNAs (miRNAs) have emerged as key players in the regulation of expression of target mRNAs expression. They have been associated with diverse biological processes, and recent studies have demonstrated that miRNAs play a role in inflammatory responses. We reported previously that LPS-activated fibroblast-like synoviocytes (FLS) isolated from rheumatoid arthritis (RA) patients express IL-18 mRNA but they do not release IL-18. Based on the observation that this inhibition was due to a rapid degradation of IL-18 mRNA, our group has conducted a study to identify miRNAs that could play a role in the "antiinflammatory" response of LPS-activated RA FLS. LPS challenge modulated the expression of 63 miRNAs as assessed by microarray analysis. Fifteen miRNAs were up-regulated, including miR-346, for which overexpression upon LPS treatment was validated by quantitative RT-PCR. We then transfected FLS with an antisense oligonucleotide targeting miR-346 and found that, in these conditions, IL-18 release could be measured upon LPS activation of FLS. Moreover, we also demonstrated that miR-346 indirectly regulated IL-18 release by indirectly inhibiting LPS-induced Bruton's tyrosine kinase expression in LPS-activated RA FLS. These findings suggest that miRNAs function as regulators that help to fine-tune the inflammatory response in RA.

MicroRNA-155 modulates the pathogen binding ability of dendritic cells (DCs) by down-regulation of DC-specific intercellular adhesion molecule-3 grabbing non-integrin (DC-SIGN)

MicroRNA-155 (miR-155) has been involved in the response to inflammation in macrophages and lymphocytes. Here we show how miR-155 participates in the maturation of human dendritic cells (DC) and modulates pathogen binding by down-regulating DC-specific intercellular adhesion molecule-3 grabbing non-integrin (DC-SIGN), after directly targeting the transcription factor PU.1. During the maturation of DCs, miR-155 increases up to 130-fold, whereas PU.1 protein levels decrease accordingly. We establish that human PU.1 is a direct target for miR-155 and localize the target sequence for miR-155 in the 3'-untranslated region of PU.1. Also, overexpression of miR-155 in the THP1 monocytic cell line decreases PU.1 protein levels and DC-SIGN at both the mRNA and protein levels. We prove a link between the down-regulation of PU.1 and reduced transcriptional activity of the DC-SIGN promoter, which is likely to be the basis for its reduced mRNA expression, after miR-155 overexpression. Finally, we show that, by reducing DC-SIGN in the cellular membrane, miR-155 is involved in regulating pathogen binding as dendritic cells exhibited the lower binding capacity for fungi and HIV protein gp-120 when the levels of miR-155 were higher. Thus, our results suggest a mechanism by which miR-155 regulates proteins involved in the cellular immune response against pathogens that could have clinical implications in the way pathogens enter the human organism.

MicroRNAs: control and loss of control in human physiology and disease

Analysis of the human genome indicates that a large fraction of the genome sequences are RNAs that do not encode any proteins, also known as non-coding RNAs. MicroRNAs (miRNAs) are a group of small non-coding RNA molecules 20-22 nucleotides (nt) in length that are predicted to control the activity of approximately 30% of all protein-coding genes in mammals. miRNAs play important roles in many diseases, including cancer, cardiovascular disease, and immune disorders. The expression of miRNAs can be regulated by epigenetic modification, DNA copy number change, and genetic mutations. miRNAs can serve as a valuable therapeutic target for a large number of diseases. For miRNAs with oncogenic capabilities, potential therapies include miRNA silencing, antisense blocking, and miRNA modifications. For miRNAs with tumor suppression functions, overexpression of those miRNAs might be a useful strategy to inhibit tumor growth. In this review, we discuss the current progress of miRNA research, regulation of miRNA expression, prediction of miRNA targets, and regulatory role of miRNAs in human physiology and diseases, with a specific focus on miRNAs in pancreatic cancer, liver cancer, colorectal cancer, cardiovascular disease, the immune system, and infectious disease. This review provides valuable information for clinicians and researchers who want to recognize the newest advances in this new field and identify possible lines of investigation in miRNAs as important mediators in human physiology and diseases.

Rapid myeloid cell transcriptional and proteomic responses to periodontopathogenic Porphyromonas gingivalis

Long-lived monocytes, macrophages, and dendritic cells (DCs) are Toll-like receptor-expressing, antigen-presenting cells derived from a common myeloid lineage that play key roles in innate and adaptive immune responses. Based on immunohistochemical and molecular analyses of inflamed tissues from patients with chronic destructive periodontal disease, these cells, found in the inflammatory infiltrate, may drive the progressive periodontal pathogenesis. To investigate early transcriptional signatures and subsequent proteomic responses to the periodontal pathogen, Porphyromonas gingivalis, donor-matched human blood monocytes, differentiated DCs, and macrophages were exposed to P. gingivalis lipopolysaccharide (LPS) and gene expression levels were measured by oligonucleotide microarrays. In addition to striking differences in constitutive transcriptional profiles between these myeloid populations, we identify a P. gingivalis LPS-inducible convergent, transcriptional core response of more than 400 annotated genes/ESTs among these populations, reflected by a shared, but quantitatively distinct, proteomic response. Nonetheless, clear differences emerged between the monocytes, DCs, and macrophages. The finding that long-lived myeloid inflammatory cells, particularly DCs, rapidly and aggressively respond to P. gingivalis LPS by generating chemokines, proteases, and cytokines capable of driving T-helper cell lineage polarization without evidence of corresponding immunosuppressive pathways highlights their prominent role in host defense and progressive tissue pathogenesis. The shared, unique, and/or complementary transcriptional and proteomic profiles may frame the context of the host response to P. gingivalis, contributing to the destructive nature of periodontal inflammation.

Shhh! Silencing by microRNA-155

Small RNAs mediate a diverse pot-pourri of post-transcriptional silencing mechanisms, ranging from 'classical' RNA interference (RNAi), to gene repression by microRNAs (miRNAs), to maintenance of genomic stability by repeat-associated small RNAs. Here, we review recent findings on the function of miR-155, particularly its roles in mammalian innate and adaptive immunity, viral infection and oncogenesis.

MicroRNA and gene expression patterns in the differentiation of human embryonic stem cells

Background

The unique features of human embryonic stem (hES) cells make them the best candidate resource for both cell replacement therapy and development research. However, the molecular mechanisms responsible for the simultaneous maintenance of their self-renewal properties and undifferentiated state remain unclear. Non-coding microRNAs (miRNA) which regulate mRNA cleavage and inhibit encoded protein translation exhibit temporal or tissue-specific expression patterns and they play an important role in development timing.

Results

In this study, we analyzed miRNA and gene expression profiles among samples from 3 hES cell lines (H9, I6 and BG01v), differentiated embryoid bodies (EB) derived from H9 cells at different time points, and 5 adult cell types including Human Microvascular Endothelial Cells (HMVEC), Human Umbilical Vein Endothelial Cells (HUVEC), Umbilical Artery Smooth Muscle Cells (UASMC), Normal Human Astrocytes (NHA), and Lung Fibroblasts (LFB). This analysis rendered 104 miRNAs and 776 genes differentially expressed among the three cell types. Selected differentially expressed miRNAs and genes were further validated and confirmed by quantitative real-time-PCR (qRT-PCR). Especially, members of the miR-302 cluster on chromosome 4 and miR-520 cluster on chromosome 19 were highly expressed in undifferentiated hES cells. MiRNAs in these two clusters displayed similar expression levels. The members of these two clusters share a consensus 7-mer seed sequence and their targeted genes had overlapping functions. Among the targeted genes, genes with chromatin structure modification function are enriched suggesting a role in the maintenance of chromatin structure. We also found that the expression level of members of the two clusters, miR-520b and miR-302c, were negatively correlated with their targeted genes based on gene expression analysis

Conclusion

We identified the expression patterns of miRNAs and gene transcripts in the undifferentiation of human embryonic stem cells; among the miRNAs that are highly expressed in undifferentiated embryonic stem cells, the miR-520 cluster may be closely involved in hES cell function and its relevance to chromatin structure warrants further study.

MicroRNAs as a therapeutic target for cardiovascular diseases

MicroRNAs (miRNAs) are tiny, endogenous, conserved, non-coding RNAs that negatively modulate gene expression by either promoting the degradation of mRNA or down-regulating the protein production by translational repression. They maintain optimal dose of cellular proteins and thus play a crucial role in the regulation of biological functions. Recent discovery of miRNAs in the heart and their differential expressions in pathological conditions provide glimpses of undiscovered regulatory mechanisms underlying cardiovascular diseases. Nearly 50 miRNAs are overexpressed in mouse heart. The implication of several miRNAs in cardiovascular diseases has been well documented such as miRNA-1 in arrhythmia, miRNA-29 in cardiac fibrosis, miRNA-126 in angiogenesis and miRNA-133 in cardiac hypertrophy. Aberrant expression of Dicer (an enzyme required for maturation of all miRNAs) during heart failure indicates its direct involvement in the regulation of cardiac diseases. MiRNAs and Dicer provide a particular layer of network of precise gene regulation in heart and vascular tissues in a spatiotemporal manner suggesting their implications as a powerful intervention tool for therapy. The combined strategy of manipulating miRNAs in stem cells for their target directed differentiation and optimizing the mode of delivery of miRNAs to the desired cells would determine the future potential of miRNAs to treat a disease. This review embodies the recent progress made in microRNomics of cardiovascular diseases and the future of miRNAs as a potential therapeutic target - the putative challenges and the approaches to deal with it.

miR-155 gene: a typical multifunctional microRNA

In the last years small RNA molecules, i.e. microRNA (miRNA) encoded by miR genes, have been found to play a crucial role in regulating gene expression of a considerable part of plant's and animal's genome. Here, we report the essential information on biogenesis of miRNAs and recent evidence on their important role in human diseases. Emphasis has been given to miR-155, since this molecule represents a typical multifunctional miRNA. Recent data indicate that miR-155 has distinct expression profiles and plays a crucial role in various physiological and pathological processes such as haematopoietic lineage differentiation, immunity, inflammation, cancer, and cardiovascular diseases. Moreover, miR-155 has been found to be implicated in viral infections, particularly in those caused by DNA viruses. The available experimental evidence indicating that miR-155 is over expressed in a variety of malignant tumors allows us to include this miRNA in the list of genes of paramount importance in cancer diagnosis and prognosis. Exogenous molecular control in vivo of miR-155 expression could open up new ways to restrain malignant growth and viral infections, or to attenuate the progression of cardiovascular diseases.

MicroRNAs and their emerging roles in immunology

MicroRNAs (miRNAs) are evolutionarily conserved small noncoding RNAs that post-transcriptionally regulate gene expression by targeting specific messenger RNAs (mRNAs) for degradation or translational repression. Recent evidence indicates that miRNA-mediated gene regulation is critical for normal cellular functions, and as much as one-third of human mRNAs may be miRNA targets. Emerging evidence suggests that miRNAs play a key role in the regulation of immunological functions including innate and adaptive immune responses, development and differentiation of immune cells, and the prevention of autoimmunity. Here, we review the mechanisms of miRNA maturation and function, the roles of several miRNAs in immunological functions, and the involvement of miRNAs in disease pathogenesis.

MicroRNA-155 modulates the interleukin-1 signaling pathway in activated human monocyte-derived dendritic cells

In response to inflammatory stimulation, dendritic cells (DCs) have a remarkable pattern of differentiation (maturation) that exhibits specific mechanisms to control immunity. Here, we show that in response to Lipopolysaccharides (LPS), several microRNAs (miRNAs) are regulated in human monocyte-derived dendritic cells. Among these miRNAs, miR-155 is highly up-regulated during maturation. Using LNA silencing combined to microarray technology, we have identified the Toll-like receptor/interleukin-1 (TLR/IL-1) inflammatory pathway as a general target of miR-155. We further demonstrate that miR-155 directly controls the level of TAB2, an important signal transduction molecule. Our observations suggest, therefore, that in mature human DCs, miR-155 is part of a negative feedback loop, which down-modulates inflammatory cytokine production in response to microbial stimuli.

MicroRNA control in the immune system: basic principles

MicroRNA (miRNA) control has emerged as a critical regulatory principle in the mammalian immune system. Genetic ablation of the miRNA machinery, as well as loss or deregulation of certain individual miRNAs, severely compromises immune development and response and can lead to immune disorders like autoimmunity and cancer. Although individual miRNAs modulate protein output from hundreds of target genes, they may impact physiological processes by regulating the concentrations of just a few key cellular proteins that may be components of a single or of functionally interrelated pathways in a given cellular context.

MicroRNAs: novel regulators during the immune response

MicroRNAs (miRNAs), an abundant class of highly conversed, small noncoding RNAs, present an entirely new way of post-transcriptional gene regulation. miRNAs play a key role in diverse biological processes, such as embryogenesis, differentiation, inflammation, viral infections, and carcinogenesis. Recently, more studies showed the importance of these noncoding small RNAs on immune system development and response, and miRNAs are found to involve in the regulation of immunity, including the development and differentiation of immnue cells, antibody production and the inflammatory mediator release. Here, the latest findings were summarized to explore the function and mechanism of miRNAs in modulating innate and adaptive immune responses.

MicroRNAs in skeletogenesis

MicroRNAs (miRNAs) are a class of highly conserved small noncoding RNAs that negatively regulate gene expression by imperfectly base pairing to the 3'-untranslated region of their target mRNAs, leading to mRNA degradation or translational inhibition. The emerging field of miRNA biology has begun to unravel roles for these regulatory molecules in a variety of biological processes. This review concentrates on the roles of miRNAs in skeletogenesis as well as in skeleton-related disease processes. Before describing these data, we present a brief review of the biogenesis and action of miRNAs, the approaches to miRNAs study, and miRNAs as global regulators of development. We finish by emphasizing that the study of the biological functions of miRNAs in skeletogenesis and dysplasia represents an entirely new avenue in the exploration of bone and cartilage biology, and large gaps remain in our knowledge of miRNAs in skeletogenesis in vivo and in our knowledge of the molecular events underlying miRNA-mediated musculoskeletal disorders.

Advances in microRNAs: implications for immunity and inflammatory diseases

Since their discovery in 1993 and the introduction of the term microRNA in 2001, it has become evident that microRNAs (miRNAs) involved in many biological processes, including development, differentiation, proliferation and apoptosis. The function of miRNA the control of protein production in cells by sequence-specific targeting of mRNAs for translational repression or mRNA degradati Interestingly, immune genes are apparently preferentially targeted by miRNAs compared to the average of the human genome, indicat the significance of miRNA-mediated regulation for normal immune responses. Here, we review what is known about the role of miRN in the pathogenesis of immune-related diseases such as chronic inflammatory skin diseases, autoimmunity and viral infections.

Micromanagers of immune cell fate and function

MicroRNAs (miRNAs) regulate cell fate during development and in response to environmental cues. Here, we review the emerging story of how miRNAs regulate immune cell development and function.

MicroRNAs and the skin: tiny players in the body's largest organ

MicroRNAs (miRNAs) are very small endogenous RNA molecules about 22-25 nucleotides in length, capable of post-transcriptional gene regulation. miRNAs bind to their target messenger RNAs (mRNAs), leading to cleavage or suppression of target mRNA translation based on the degree of complementarity. miRNAs have recently been shown to play pivotal roles in diverse developmental and cellular processes and linked to a variety of skin diseases and cancers. Disruption of miRNA metabolism is also involved in wound healing and inflammatory skin conditions. Here, we review the role of miRNAs in cutaneous biology.

Role of miRNA-146a in the regulation of the innate immune response and cancer

In mammalian cells, miRNAs (microRNAs) are the most abundant family of small non-coding RNAs that regulate mRNA translation through the RNA interference pathway. In general, it appears that the major function of miRNAs is in development, differentiation and homoeostasis, which is indicated by studies showing aberrant miRNA expression during the development of cancer. Interestingly, changes in the expression of miR-146a have been implicated in both the development of multiple cancers and in the negative regulation of inflammation induced via the innate immune response. Furthermore, miR-146a expression is driven by the transcription factor NF-kappaB (nuclear factor kappaB), which has been implicated as an important causal link between inflammation and carcinogenesis. In the present article, we review the evidence for a role of miR-146a in innate immunity and cancer and assess whether changes in miR-146a might link these two biological responses.

Adding fuel to fire: microRNAs as a new class of mediators of inflammation

MicroRNAs (miRNAs) are recently discovered regulators of gene expression, and early studies have indicated that they have a role in the regulation of haematopoiesis, the immune response and inflammation. They bind the 3'UTR of target mRNAs and mainly prevent translation of the protein product. Dysregulation of these molecules has been shown to be a hallmark of cancer and now investigators are examining their role in the pathogenesis of inflammatory diseases. miR-146 and miR-155 have been a particular focus for investigators, and these two miRNAs have been shown to be induced by proinflammatory stimuli such as interleukin 1, tumour necrosis factor alpha (TNFalpha) and Toll-like receptors (TLRs). They have also been detected in synovial fibroblasts and rheumatoid synovial tissue. Both have multiple targets, with miR-146 inhibiting TLR signalling and miR-155 regulating Th1 cells and also, interestingly, positively regulating mRNA for TNFalpha. The potential of miRNAs for improving our understanding of the pathogenesis of diseases such as rheumatoid arthritis, and for developing potentially new treatments for these diseases, is substantial.

MicroRNAs: key players in the immune system, differentiation, tumorigenesis and cell death

Micro (mi)RNAs are small, highly conserved noncoding RNAs that control gene expression post-transcriptionally either via the degradation of target mRNAs or the inhibition of protein translation. Each miRNA is believed to regulate the expression of multiple mRNA targets, and many miRNAs have been linked to the initiation and progression of human cancer. miRNAs control various activities of the immune system and different stages of hematopoietic development, and their misexpression is the cause of various blood malignancies. Certain miRNAs have oncogenic activities, whereas others have the potential to act as tumor suppressors. Because they control fundamental processes such as differentiation, cell growth and cell death, the study of the role of miRNAs in human neoplasms holds great promise for novel forms of therapy. Here, we summarize the role of miRNAs and their targets in contributing to human cancers and their function as regulators of apoptotic pathways and the immune system.

MicroRNA signature and regulatory functions in the endometrium during normal and disease states

During the menstrual cycle, human endometrium undergoes extensive cyclic morphologic and biochemical modifications in preparation for embryo implantation. These processes are highly regulated by ovarian steroids and various locally expressed gene products and involve inflammatory reaction, apoptosis, cell proliferation, angiogenesis, differentiation (tissue formation), and tissue remodeling. MicroRNAs (miRNAs) have emerged as key regulators of gene expression, and their altered and/or aberrant expression has been associated with establishment and progression of various disorders, including tumorigenesis. This review highlights the endometrial expression of miRNAs and their potential regulatory functions under normal and pathologic conditions such as endometriosis, dysfunctional uterine bleeding, and endometrial cancer. Given the key regulatory function of miRNAs on gene expression stability, understanding the underlying mechanisms of how endometrial miRNAs are regulated and identifying their specific target genes and their functions might lead to the development of preventive and therapeutic strategies by regulating specific target genes associated with such reproductive disorders.

The expression and potential regulatory function of microRNAs in the pathogenesis of leiomyoma

Leiomyomas are benign uterine tumors considered to arise from transformation of myometrial cells. What initiates the conversion of myometrial cells into leiomyoma is unknown, however cytogenetic analysis often shows occurrence of nonrandom chromosomal abnormalities that may account for their establishment. It is clear that ovarian steroids are essential for leiomyoma growth, and local expression of many autocrine/paracrine mediators serving as key regulators of cell-cycle progression, cellular hypertrophy, extracellular matrix accumulation, and apoptosis appear to play central roles in this capacity. However, the stability of the expression of these genes represents the hallmarks of leiomyoma establishment, growth, and regression. With the emergence of microRNA (miRNA) as a key regulator of gene expression stability, in this review we present evidence for the expression and potential regulatory functions on miRNAs in leiomyoma with particular emphasis on the expression of their selective target genes whose products influence various cellular activities critical to pathogenesis of leiomyomas.

Vitamin E dependent microRNA regulation in rat liver

Dietary vitamin E (VE) is known to regulate gene expression by altering mRNA concentrations. Recently, microRNA (miRNA) have been discovered as a means of posttranscriptional gene regulation. Since the effect of VE on miRNA regulation is unknown, we fed rats for 6 months diets deficient or sufficient in VE and determined hepatic concentrations of miRNA involved in processes previously associated with VE (lipid metabolism, miRNA-122a; cancer and inflammation, miRNA-125b). VE-deficiency resulted in reduced concentrations of miRNA-122a and miRNA-125b. The findings of the present study demonstrate that differences in dietary VE may affect hepatic miRNA concentrations in vivo.

Suppression of LPS-induced Interferon-gamma and nitric oxide in splenic lymphocytes by select estrogen-regulated microRNAs: a novel mechanism of immune modulation

MicroRNAs (miRNAs), recently identified noncoding small RNAs, are emerging as key regulators in homeostasis of the immune system. Therefore, aberrant expression of miRNAs may be linked to immune dysfunction, such as in chronic inflammation and autoimmunity. In this study, we investigated the potential role of miRNAs in estrogen-mediated regulation of innate immune responses, as indicated by up-regulation of lipopolysaccharide (LPS)-induced interferon-gamma (IFNgamma), inducible nitric oxide synthase (iNOS), and nitric oxide in splenic lymphocytes from estrogen-treated mice. We found that miR-146a, a negative regulator of Toll-like receptor (TLR) signaling, was decreased in freshly isolated splenic lymphocytes from estrogen-treated mice compared with placebo controls. Increasing the activity of miR-146a significantly inhibited LPS-induced IFNgamma and iNOS expression in mouse splenic lymphocytes. Further, miRNA microarray and real-time reverse transcriptase-polymerase chain reaction (RT-PCR) analysis revealed that estrogen selectively up-regulates/down-regulates the expression of miRNAs in mouse splenic lymphocytes. miR-223, which is markedly enhanced by estrogen, regulates LPS-induced IFNgamma, but not iNOS or nitric oxide in splenic lymphocytes. Inhibition of miR-223 activity decreased LPS-induced IFNgamma in splenic lymphocytes from estrogen-treated mice. Our data are the first to demonstrate the selective regulation of miRNA expression in immune cells by estrogen and are indicative of an important role of miRNAs in estrogen-mediated immune regulation.

microRNAs and the immune response

microRNA (miRNA)-mediated RNA interference has been identified as a novel mechanism that regulates protein expression at the translational level. Recent publications have provided compelling evidence that a range of miRNAs are involved in the regulation of immunity, including the development and differentiation of B and T cells, proliferation of monocytes and neutrophils, antibody switching and the release of inflammatory mediators. In this review, we examine what is presently known of the function and mechanism of action of these miRNAs in the regulation of the innate and acquired immune response.

Diagnostic and prognostic implications of microRNAs in human hepatocellular carcinoma

MicroRNAs (miRNAs) are important gene regulators, which are often deregulated in cancers. In this study, the authors analyzed the microRNAs profiles of 78 matched cancer/noncanerous liver tissues from HCC patients and 10 normal liver tissues and found that 69 miRNAs were differentially expressed between hepatocellular carcinoma (HCC) and corresponding noncancerous liver tissues (N). Then the expressions of 8 differentially expressed miRNAs were validated by real time RT PCR. The set of differentially expressed miRNAs could distinctly classify HCC, N and normal liver tissues (NL). Moreover, some of these differentially expressed miRNAs were related to the clinical factors of HCC patients. Most importantly, Kaplan-Meier estimates and the log-rank test showed that high expression of hsa-miR-125b was correlated with good survival of HCC patients (hazard ratio, 1.787, 95% confidence interval, 1.020-3.133, p = 0.043). The transfection assay showed that overexpression of miR-125b in HCC cell line could obviously suppress the cell growth and phosporylation of Akt. In conclusion, the authors have demonstrated the diagnostic miRNA profile for HCC, and for the first time, identified the miR-125b with predictive significance for HCC prognosis.

Role of microRNAs in vascular diseases, inflammation, and angiogenesis

The integrity of the endothelial monolayer is fundamental for the homoeostasis of the vascular system. Functional endothelial cells are also required for the growth of new blood vessels during neovascularization. Although multiple growth factors have been shown to regulate angiogenesis and vascular development, little is known about the complex upstream regulation of gene expression and translation. MicroRNAs (miRNAs) are an emerging class of highly conserved, non-coding small RNAs that regulate gene expression on the post-transcriptional level by inhibiting the translation of protein from mRNA or by promoting the degradation of mRNA. More than 500 human miRNAs have been identified so far, and increasing evidence indicates that miRNAs have distinct expression profiles and play crucial roles in various physiological and pathological processes such as cardiogenesis, haematopoietic lineage differentiation, and oncogenesis. Meanwhile, a few specific miRNAs that regulate endothelial cell functions and angiogenesis have been described. Let7-f, miR-27b, and mir-130a were identified as pro-angiogenic miRNAs. In contrast, miR-221 and miR-222 inhibit endothelial cell migration, proliferation, and angiogenesis in vitro by targeting the stem cell factor receptor c-kit and indirectly regulating endothelial nitric oxide synthase expression. Moreover, some miRNAs are involved in tumour angiogenesis such as the miR-17-92 cluster and miR-378. Early studies also indicate the contribution of specific miRNAs (e.g. miR-155, miR-21, and miR-126) to vascular inflammation and diseases. Thus, the identification of miRNAs and their respective targets may offer new therapeutic strategies to treat vascular diseases such as atherosclerosis, to improve neovascularization after ischaemia, or to prevent tumour progression.

MicroRNAs in the immune response

MicroRNAs (miRs) were only discovered little more than a decade ago, yet it has become rapidly clear that they are crucial posttranscriptional regulators of gene expression by decreasing the abundance or translational efficiency of mRNAs [Maroney PA, Yu Y, Nilsen TW. MicroRNAs, mRNAs, and translation. Cold Spring Harb Symp Quant Biol 2006;71: 531-5; Nilsen TW. Mechanisms of microRNA-mediated gene regulation in animal cells. Trends Genet 2007;23: 243-9], [1,2]. While the role of miRs in cell fate decisions linked to proliferation, differentiation and apoptosis was recognized early on, the importance of these noncoding small RNAs on immune system development and response has only recently become evident. In addition to facilitating cell fate decisions of immune cells (e.g. miR-181a and miR-223), miRs also regulate central elements of the adaptive immune response such as antigen presentation (e.g. miR-155) and T cell receptor signaling (mir-181a). Furthermore, miRs are involved in innate immunity through regulation of Toll-like receptor signaling and cytokine responses (e.g. miR-146). Intriguingly, cellular miRs not only alter immune cell development and function, but are also able to directly affect viral replication. Conversely, virus-encoded miRs shape the host-virus interactions and regulate the viral life cycle. Here, we provide a brief overview on the role of cellular and viral miRs in the development and function of the immune system.

Epstein-Barr virus-induced miR-155 attenuates NF-kappaB signaling and stabilizes latent virus persistence

MicroRNAs have been implicated in the modulation of gene expression programs important for normal and cancer cell development. miR-155 is known to play a role in B-cell development and is upregulated in various B-cell lymphomas, including several that are latently infected with Epstein-Barr virus (EBV). We show here that EBV infection of primary human B lymphocytes leads to the sustained elevation of miR-155 and its precursor RNA, BIC. The EBV-encoded latency membrane protein 1 (LMP1) can partially reconstitute BIC activation in B lymphocytes but not in epithelial cell cultures. LMP1 is a potent activator of NF-kappaB signaling pathways and is essential for EBV immortalization of B lymphocytes. An inhibitor to miR-155 further stimulated NF-kappaB responsive gene transcription, and IKKepsilon was identified as a potential target of miR-155 translational repression. Remarkably, miR-155 inhibitor reduced EBNA1 mRNA and the EBV copy number in latently infected cells. This suggests that miR-155 contributes to EBV immortalization by modulation of NF-kappaB signaling and the suppression of host innate immunity to latent viral infection.

MicroRNAs: novel regulators in skin inflammation

Compelling evidence indicates that microRNAs (miRNAs), short, non-protein coding RNAs, are critical for the development and survival of multicellular organisms. Recently, miRNAs were implicated in the pathogenesis of psoriasis and atopic eczema (AE), the two most common chronic inflammatory disorders in skin. In particular, miR-203, the first skin-specific miRNA, showing an intriguing expression profile being confined to skin epithelium, is specifically overexpressed in psoriasis. MiR-146a, another miRNA showing specific upregulation in psoriasis, is involved in the regulation of innate immune responses and the tumour necrosis factor (TNF)-alpha pathway. Interestingly, miR-125b, another miRNA involved in the TNF-alpha pathway, is also deregulated in psoriasis and AE. As skin inflammation may serve as a model for chronic inflammatory disorders, it is likely that miRNAs involved in skin inflammation will eventually emerge in other inflammatory or autoimmune disorders, and some of these may become disease markers and therapeutic targets. In this review we present an overview of what is currently known about the roles of miRNAs in chronic inflammatory skin disorders.

MicroRNAs, the immune system and rheumatic disease

MicroRNAs (miRNAs) are short noncoding RNA molecules that modulate the expression of multiple target genes at the post-transcriptional level and are implicated in a wide array of cellular and developmental processes. In hematopoietic cells, miRNA levels are dynamically regulated during lineage differentiation and also during the course of the immune response. Mouse models have provided good evidence for miRNAs being key players in the establishment of hematopoietic lineages. Furthermore, miRNA-dependent alterations in gene expression in hematopoietic cells are critical for mounting an appropriate immune response to a wide range of pathogens, spontaneously emerging tumors, and autoimmune cells. Deregulation of hematopoietic-specific miRNA expression results in defects in both central and peripheral tolerance, hematopoietic malignancies, and sometimes both. Abnormal expression of miRNAs-which is implicated in inflammation-has also been found in patients with rheumatoid arthritis. These findings identify miRNAs as critical targets for immunomodulatory drug development.

MicroRNA prediction with a novel ranking algorithm based on random walks

MicroRNA (miRNAs) play essential roles in post-transcriptional gene regulation in animals and plants. Several existing computational approaches have been developed to complement experimental methods in discovery of miRNAs that express restrictively in specific environmental conditions or cell types. These computational methods require a sufficient number of characterized miRNAs as training samples, and rely on genome annotation to reduce the number of predicted putative miRNAs. However, most sequenced genomes have not been well annotated and many of them have a very few experimentally characterized miRNAs. As a result, the existing methods are not effective or even feasible for identifying miRNAs in these genomes.

Aiming at identifying miRNAs from genomes with a few known miRNA and/or little annotation, we propose and develop a novel miRNA prediction method, miRank, based on our new random walks- based ranking algorithm. We first tested our method on Homo sapiens genome; using a very few known human miRNAs as samples, our method achieved a prediction accuracy greater than 95%. We then applied our method to predict 200 miRNAs in Anopheles gambiae, which is the most important vector of malaria in Africa. Our further study showed that 78 out of the 200 putative miRNA precursors encode mature miRNAs that are conserved in at least one other animal species. These conserved putative miRNAs are good candidates for further experimental study to understand malaria infection.

Availability: MiRank is programmed in Matlab on Windows platform. The source code is available upon request.

Contact:zhang@cse.wustl.edu

MicroRNAs and noncoding RNAs in hematological malignancies: molecular, clinical and therapeutic implications

MicroRNAs (miRNAs) are a family of 19-24 nucleotide noncoding RNAs (ncRNAs) with posttranscriptional regulatory functions. Increasing evidences from the literature show that miRNAs play a pivotal role in human tumorigenesis. Many studies have addressed the role of miRNAs in normal hematopoiesis, giving an interpretative key to the aberrancies of expression observed in human hematological malignancies. Moreover, the recent demonstration that other ncRNAs, the ultraconserved genes (UCGs) or transcribed ultraconserved regions (T-UCRs), are involved in human cancerogenesis, suggests that the wider family of ncRNAs (including both miRNAs and UCGs) could contribute to the development of the malignant phenotype. Here we review the main studies investigating the role of miRNAs and UCRs in both normal hemopoiesis and hematological malignancies, and identify the molecular, clinical and therapeutic implications of these recent findings.

Cell-cycle control of microRNA-mediated translation regulation

MicroRNAs are small regulatory RNA molecules that exert post-transcriptional control overexpression of specific target mRNAs. AU-rich elements (AREs) are highly conserved 3'UTR sequences that alter the stability and translation of mRNAs of clinical importance as a rapid and transient response to external and internal changes. We recently demonstrated that a reporter mRNA containing the tumor necrosis factor alpha (TNFalpha) ARE activates translation in response to quiescence via microRNA target sites in the ARE. Further studies revealed that microRNAs in general have the potential to regulate translation in a cell cycle determined manner: in quiescent cells, microRNAs activate translation while in cycling/proliferating cells, microRNAs repress translation.

Altered expression of MicroRNA in synovial fibroblasts and synovial tissue in rheumatoid arthritis

OBJECTIVE

MicroRNAs (miRNA) have recently emerged as a new class of modulators of gene expression. In this study we investigated the expression, regulation, and function of miR-155 and miR-146a in rheumatoid arthritis (RA) synovial fibroblasts (RASFs) and RA synovial tissue.

METHODS

Locked nucleic acid microarray was used to screen for differentially expressed miRNA in RASFs treated with tumor necrosis factor alpha (TNFalpha). TaqMan-based real-time polymerase chain reaction was applied to measure the levels of miR-155 and miR-146a. Enforced overexpression of miR-155 was used to investigate the function of miR-155 in RASFs.

RESULTS

Microarray analysis of miRNA expressed in RASFs treated with TNFalpha revealed a prominent up-regulation of miR-155. Constitutive expression of both miR-155 and miR-146a was higher in RASFs than in those from patients with osteoarthritis (OA), and expression of miR-155 could be further induced by TNFalpha, interleukin-1beta, lipopolysaccharide, poly(I-C), and bacterial lipoprotein. The expression of miR-155 in RA synovial tissue was higher than in OA synovial tissue. Enforced expression of miR-155 in RASFs was found to repress the levels of matrix metalloproteinase 3 (MMP-3) and reduce the induction of MMPs 3 and 1 by Toll-like receptor ligands and cytokines. Moreover, compared with monocytes from RA peripheral blood, RA synovial fluid monocytes displayed higher levels of miR-155.

CONCLUSION

This study provides the first description of increased expression of miRNA miR-155 and miR-146a in RA. Based on these findings, we postulate that the inflammatory milieu may alter miRNA expression profiles in resident cells of the rheumatoid joints. Considering the repressive effect of miR-155 on the expression of MMPs 3 and 1 in RASFs, we hypothesize that miR-155 may be involved in modulation of the destructive properties of RASFs.

Expression and function of micro-RNAs in immune cells during normal or disease state

Micro-RNAs (miRNAs) are 19-24 nucleotide long non-coding RNAs that posttranscriptionally modulate gene expression. They are found in almost all species: viruses, plants, nematodes, fly, fish, mouse, human, and are implicated in a wide array of cellular and developmental processes. Microarray-based miRNA profiling brought to the discovery of miRNAs specific to different hematopoietic lineages. Furthermore, the functional assays performed in tissue cultures to discover miRNAs involved in immune responses in combination with the reports of miRNA-transgenic or miRNA -knockout mouse models has helped elucidating the miRNA roles in the development and function of immune system. Abnormal patterns of hematopoietic-specific miRNAs have been found in different types of cancer and miRNA based gene therapy is being considered as a potential technology of choice in immunological disorders and cancer. The purpose of this review is to discuss recent findings related with the expression and function of miRNAs in hematopoietic lineages.

MicroRNAs and immunity: novel players in the regulation of normal immune function and inflammation

The discovery of microRNAs (miRNAs) is one of the major scientific breakthroughs in recent years and has revolutionized the way we look at gene regulation. Although we are still at a very early stage in understanding their impact on immunity, miRNAs are changing the way we think about the development of the immune system and regulation of immune functions. MiRNAs are implicated in establishing and maintaining the cell fate of immune cells (e.g. miR-181a and miR-223), and they are involved in innate immunity by regulating Toll-like receptor signaling and ensuing cytokine response (e.g. miR-146). Moreover, miRNAs regulate central elements of the adaptive immune response such as antigen presentation (e.g. miR-155) and T cell receptor signaling (miR-181a). Recent evidence showing altered miRNA expression in chronic inflammatory diseases (e.g. miR-203 and miR-146) suggests their involvement in immune-mediated diseases. Furthermore, miRNAs have been implicated in viral immune escape and anti-viral defense (e.g. miR-196). In this review, we will summarize the latest findings about the role of miRNAs in the development of the immune system and regulation of immune functions and inflammation.

Epigenetic clues to rheumatoid arthritis

The innate immune response needs to be tightly regulated to balance elimination of microorganisms with the magnitude of inflammation. The rupture of this balance is crucial for the outcome of diseases such as rheumatoid arthritis (RA) in which an overflowed proinflammatory response is associated with self-damage. Epigenetics alludes to systems controlling gene expression and silencing independent of the germline, but stable enough to be inherited by daughter cells upon mitosis. We will show in this review how pathological processes in RA can be shaped by epigenetics, which may in turn explain differences in phenotypes between subgroups of patients and also between subsets of fibroblasts within the joint. On the whole, the concourse of epigenetic mechanisms can precipitate the aggressive behaviour of cells and the rupture of peripheral tolerance. Targeting these emerging regulatory pathways is a promising approach for RA therapeutics.