Suppression of latent transforming growth factor (TGF)-beta1 restores growth inhibitory TGF-beta signaling through microRNAs

Pivotal Role of TGF-β/Smad Signaling in Cardiac Fibrosis: Non-coding RNAs as Effectual Players

Unintended cardiac fibroblast proliferation in many pathophysiological heart conditions, known as cardiac fibrosis, results in pooling of extracellular matrix (ECM) proteins in the heart muscle. Transforming growth factor β (TGF-β) as a pivotal cytokine/growth factor stimulates fibroblasts and hastens ECM production in injured tissues. The TGF-β receptor is a heterodimeric receptor complex on the plasma membrane, made up from TGF-β type I, as well as type II receptors, giving rise to Smad2 and Smad3 transcription factors phosphorylation upon canonical signaling. Phosphorylated Smad2, Smad3, and cytoplasmic Smad4 intercommunicate to transfer the signal to the nucleus, culminating in provoked gene transcription. Additionally, TGF-β receptor complex activation starts up non-canonical signaling that lead to the mitogen-stimulated protein kinase cascade activation, inducing p38, JNK1/2 (c-Jun NH2-terminal kinase 1/2), and ERK1/2 (extracellular signal–regulated kinase 1/2) signaling. TGF-β not only activates fibroblasts and stimulates them to differentiate into myofibroblasts, which produce ECM proteins, but also promotes fibroblast proliferation. Non-coding RNAs (ncRNAs) are important regulators of numerous pathways along with cellular procedures. MicroRNAs and circular long ncRNAs, combined with long ncRNAs, are capable of affecting TGF-β/Smad signaling, leading to cardiac fibrosis. More comprehensive knowledge based on these processes may bring about new diagnostic and therapeutic approaches for different cardiac disorders.

MicroRNA Control of TGF-β Signaling

Transcriptional and post-transcriptional regulation shapes the transcriptome and proteome changes induced by various cellular signaling cascades. MicroRNAs (miRNAs) are small regulatory RNAs that are approximately 22 nucleotides long, which direct the post-transcriptional regulation of diverse target genes and control cell states. Transforming growth factor (TGF)-β family is a multifunctional cytokine family, which plays many regulatory roles in the development and pathogenesis of diverse diseases, including fibrotic disease, cardiovascular disease and cancer. Previous studies have shown that the TGF-β pathway includes the miRNA pathway as an important component of its downstream signaling cascades. Multiple studies of epithelial–mesenchymal transition (EMT)-related miRNAs have highlighted that miRNAs constitute the intrinsic bistable molecular switches of cell states by forming double negative feedback loops with EMT-inducing transcription factors. This may be important for understanding the reversibility of EMT at the single-cell level, the presence of distinct EMT transition states and the intra- and inter-tumor heterogeneity of cancer cell phenotypes. In the present review, I summarize the connection between TGF-β signaling and the miRNA pathway, placing particular emphasis on the regulation of miRNA expression by TGF-β signaling, the modulation of TGF-β signaling by miRNAs, the miRNA-mediated modulation of EMT and endothelial–mesenchymal transition as well as the crosstalk between miRNA and TGF-β pathways in the tumor microenvironment.

Deregulation of Negative Controls on TGF-β1 Signaling in Tumor Progression

The multi-functional cytokine transforming growth factor-β1 (TGF-β1) has growth inhibitory and anti-inflammatory roles during homeostasis and the early stages of cancer. Aberrant TGF-β activation in the late-stages of tumorigenesis, however, promotes development of aggressive growth characteristics and metastatic spread. Given the critical importance of this growth factor in fibrotic and neoplastic disorders, the TGF-β1 network is subject to extensive, multi-level negative controls that impact receptor function, mothers against decapentaplegic homolog 2/3 (SMAD2/3) activation, intracellular signal bifurcation into canonical and non-canonical pathways and target gene promotor engagement. Such negative regulators include phosphatase and tensin homologue (PTEN), protein phosphatase magnesium 1A (PPM1A), Klotho, bone morphogenic protein 7 (BMP7), SMAD7, Sloan-Kettering Institute proto-oncogene/ Ski related novel gene (Ski/SnoN), and bone morphogenetic protein and activin membrane-bound Inhibitor (BAMBI). The progression of certain cancers is accompanied by loss of expression, overexpression, mislocalization, mutation or deletion of several endogenous repressors of the TGF-β1 cascade, further modulating signal duration/intensity and phenotypic reprogramming. This review addresses how their aberrant regulation contributes to cellular plasticity, tumor progression/metastasis and reversal of cell cycle arrest and discusses the unexplored therapeutic value of restoring the expression and/or function of these factors as a novel approach to cancer treatment.

Alternative mechanisms of miR-34a regulation in cancer

MicroRNA miR-34a is recognized as a master regulator of tumor suppression. The strategy of miR-34a replacement has been investigated in clinical trials as the first attempt of miRNA application in cancer treatment. However, emerging outcomes promote the re-evaluation of existing knowledge and urge the need for better understanding the complex biological role of miR-34a. The targets of miR-34a encompass numerous regulators of cancer cell proliferation, survival and resistance to therapy. MiR-34a expression is transcriptionally controlled by p53, a crucial tumor suppressor pathway, often disrupted in cancer. Moreover, miR-34a abundance is fine-tuned by context-dependent feedback loops. The function and effects of exogenously delivered or re-expressed miR-34a on the background of defective p53 therefore remain prominent issues in miR-34a based therapy. In this work, we review p53-independent mechanisms regulating the expression of miR-34a. Aside from molecules directly interacting with MIR34A promoter, processes affecting epigenetic regulation and miRNA maturation are discussed. Multiple mechanisms operate in the context of cancer-associated phenomena, such as aberrant oncogene signaling, EMT or inflammation. Since p53-dependent tumor-suppressive mechanisms are disturbed in a substantial proportion of malignancies, we summarize the effects of miR-34a modulation in cell and animal models in the clinically relevant context of disrupted or insufficient p53 function.

Treatment-Induced Viral Cure of Hepatitis C Virus-Infected Patients Involves a Dynamic Interplay among three Important Molecular Players in Lipid Homeostasis: Circulating microRNA (miR)-24, miR-223, and Proprotein Convertase Subtilisin/Kexin Type 9

In patients with chronic hepatitis C virus (HCV) infection, viral hijacking of the host-cell biosynthetic pathways is associated with altered lipid metabolism, which contributes to disease progression and may influence antiviral response. We investigated the molecular interplay among four key regulators of lipid homeostasis [microRNA (miR)-122, miR-24, miR-223, and proprotein convertase subtilisin/kexin type 9 (PCSK9)] in HCV-infected patients (n=72) who achieved a treatment-based viral cure after interferon-based therapy with first-generation direct-acting antivirals. Real-time PCR was used to quantify microRNA plasma levels, and ELISA assays were used to determine plasma concentrations of PCSK9. We report that levels of miR-24 and miR-223 significantly increased in patients achieving sustained virologic response (SVR), whereas the levels of miR-122, a liver-specific cofactor for HCV infection, decreased in these patients. PCSK9 concentrations were significantly increased in SVRs, suggesting that PCSK9 may help impede viral infection. The modulatory effect of PCSK9 on HCV infection was also demonstrated in the context of HCV-infected Huh-7.5.1 cells employing recombinant human PCSK9 mutants. Together, these results provide insights into a novel coordinated interplay among three important molecular players in lipid homeostasis - circulating miR-24, miR-223 and PCSK9 - whose regulation is affected by HCV infection and treatment-based viral cure.

Role of miR-24, Furin, and Transforming Growth Factor-β1 Signal Pathway in Fibrosis After Cardiac Infarction

BACKGROUND Cardiac fibrosis after primary infarction is a type of pathological phenomena as shown by increased collagen in myocardial cells. Transforming growth factor (TGF)-β1 is a critical factor participating in myocardial fibrosis. A previous study has shown the inhibitory role on TGF-β1 by microRNA-24 (miR-24) via targeting Furin. This study thus investigated the role of miR-24 and Furin/TGF-β1 in rat myocardial fibrosis. MATERIAL AND METHODS A total of 40 adult SD rats (both males and females) were prepared for myocardial infarction model by ligating the descending branch of left coronary artery after anesthesia. HE staining was performed to observe myocardial fibrosis after 1, 2, and 4 weeks. Tissue RNA was extracted to detect mRNA levels of Furin, TGF-β1, and miR-24 by real-time PCR. Western blotting was used to quantify protein expression of Furin and TGF-β1 in myocardial tissues. RESULTS Increased connective tissues were observed in myocardial tissues at 4 weeks after infarction by HE staining, which also revealed widening of the intra-myocardial cleft, along with more inflammatory cells and fibroblast hypertrophy. miR-24 expression was significantly depressed at 2 and 4 weeks after cardiac infarction (p<0.05). mRNA levels of Furin and TGF-β1 were elevated after infarction (p<0.05). With prolonged time periods of myocardial infarction, protein levels of Furin and TGF-β1 were further increased. The level of miR-24 was positively correlated with left ventricular end-diastolic diameter, left ventricular systolic diameter, and left ventricular ejection fraction. However, the level of Furin or TGF-β1 was negatively correlated with the above parameters. CONCLUSIONS This study demonstrated the important role of abnormal expression of miR-24 in myocardial fibrosis after infarction, and may provide drug targets for treating myocardial fibrosis.

MicroRNAs, TGF-β signaling, and the inflammatory microenvironment in cancer

Inflammatory cells and mediators form a major part of the tumor microenvironment and play important roles in the regulation of cancer initiation, tumor cell proliferation, and metastasis. MicroRNAs (miRNAs) play important roles in several physiological and pathological processes, including the regulation of the inflammatory microenvironment in cancer. Transforming growth factor-β (TGF-β) is an inflammation-related cytokine that functions in both tumor suppression and promotion; however, its underlying molecular mechanisms remain unclear. Recent evidence indicates an association between miRNAs and TGF-β signaling, providing new insight into the nature of the inflammatory microenvironment in cancer. The present review is an overview of the interaction between miRNAs and inflammatory cytokines, with emphasis on the cross talk between TGF-β signaling and miRNAs and their influence on cancer cell behavior. The emerging roles of miRNAs in cancer-related inflammation and the potential to target miRNA signaling pathways for cancer therapy are also discussed.

Expression of paired basic amino acid-cleaving enzyme 4 (PACE4) correlated with prognosis in non-small cell lung cancer (NSCLC) patients

BACKGROUND

Paired basic amino acid-cleaving enzyme 4 (PACE4) was shown to enhance tumor cells proliferation and invasive. This study provides the first investigation of PACE4 expression in non-small cell lung cancer (NSCLC) and the correlation with clinicopathologic features, prognostic indicators of 172 cases.

METHODS

Quantitative real-time PCR (RT-PCR) and immunofluorescence (IF) were applied to detect PACE4 expression in NSCLC and 16HBE cell lines, then 172 consecutive NSCLC and 15 normal lung tissues were studied through immunohistochemistry (IHC). The association between PACE4 expression and clinicopathological parameters was evaluated. Kaplan-Meier survival analysis and Cox proportional hazards models were used to estimate the effect of PACE4 expression on survival.

RESULTS

PACE4 expression in NSCLC were significantly higher than normal lung cell and tissues (P<0.05). PACE4 had cytoplasmic expression and was observed in 111 of the 172 (64.5%) NSCLC patients. Clinicopathologically, PACE4 expression was significantly associated with lymph node metastasis (N stage) (P=0.007), and clinical stage (P=0.024). Multivariable analysis confirmed that PACE4 expression increased the hazard of death after adjusting for other clinicopathological factors [hazards ratio (HR): 1.584; 95% confidence interval (CI): 1.167-2.151; P<0.001]. Overall survival (OS) was significantly prolonged in PACE4 negative group when compared with PACE4 positive group (5-year survival rates, 23.1% vs. 54.5%, log-rank test, χ(2)=17.717, P<0.001), as was disease-free survival (DFS) (5-year survival rates, 23.4% vs. 55.4%, log-rank test, χ(2)=20.486, P<0.001).

CONCLUSIONS

Our results suggest that positive expression of PACE4 is an independent factor for NSCLC patients and it might serve as a potential prognostic biomarker for patients with NSCLC.

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

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

Restoring TGFβ1 pathway-related microRNAs: possible impact in metastatic prostate cancer development

In developed countries, prostate cancer (PC) is the neoplasia more frequently diagnosed in men. The signaling pathway induced by the transforming growth factor β1 (TGFβ1) has an important role in cell growth, differentiation, and development, the downregulation of this pathway being associated with cancer development. In PC, the activation of this signaling pathway is lost, resulting in favoring of tumor growth, proliferation, and evasion of apoptosis. Several studies have shown that microRNAs (miRNAs), small non-coding RNA, are closely associated with the development, invasion, and metastasis, suggesting that they have a critical role in cancer development. Recently, Smad proteins, the signal transducers of the TGFβ1 signaling pathway, were found to regulate miRNA expression, through both transcriptional and posttranscriptional mechanisms. In this review, we summarize the mechanisms underlying Smad-mediated regulation of miRNA biogenesis and the effects on cancer development, particularly in PC. We identify that TGFβ1-related miR-143, miR-145, miR-146a, and miR-199a may have a key role in the development of prostate cancer metastasis and the restoration of their expression may be a promising therapeutic strategy for PC treatment.

MicroRNA-18a is elevated in prostate cancer and promotes tumorigenesis through suppressing STK4 in vitro and in vivo

MicroRNAs (miRNAs) comprise a class of short, non-coding RNAs that regulate protein synthesis through posttranscriptional modifications. In this study, we found significant upregulation of miR-18a in prostate cancer specimens and prostate cancer cell lines compared with the normal controls. MiRNAs can be separated into two groups based on whether they regulate tumor suppressors or oncogenes. In our previous study, we found that miR-18a, which belongs to the miR17-92 cluster, is upregulated in prostate cancer; the objective of this study was to investigate the associated regulatory mechanisms. We found that miR-18a is upregulated in clinical tumor specimens and cancer cell lines. Our bioinformatics analysis showed that the serine/threonine-protein kinase 4 (STK4) 3′ untranslated region contains a highly conserved binding site for the miR-18a seed region. Luciferase reporter assays were performed to indicate that STK4 is a direct target of miR-18a. Interestingly, miR-18a knockdown decreased cell growth in prostate cancer cells and significantly decreased prostate tumor growth in in vivo nude mice experiments through STK4-mediated dephosphorylation of AKT and thereby inducing apoptosis. Our results suggest that miR-18a acts as an oncomiR targeting STK4 in prostate cancer, and inhibition of miR-18a expression may offer therapeutically beneficial option for prostate cancer treatment.

Regulation of TGFβ and related signals by precursor processing

Secreted cytokines of the TGFβ family are found in all multicellular organisms and implicated in regulating fundamental cell behaviors such as proliferation, differentiation, migration and survival. Signal transduction involves complexes of specific type I and II receptor kinases that induce the nuclear translocation of Smad transcription factors to regulate target genes. Ligands of the BMP and Nodal subgroups act at a distance to specify distinct cell fates in a concentration-dependent manner. These signaling gradients are shaped by multiple factors, including proteases of the proprotein convertase (PC) family that hydrolyze one or several peptide bonds between an N-terminal prodomain and the C-terminal domain that forms the mature ligand. This review summarizes information on the proteolytic processing of TGFβ and related precursors, and its spatiotemporal regulation by PCs during development and various diseases, including cancer. Available evidence suggests that the unmasking of receptor binding epitopes of TGFβ is only one (and in some cases a non-essential) function of precursor processing. Future studies should consider the impact of proteolytic maturation on protein localization, trafficking and turnover in cells and in the extracellular space.

Multiple microRNAs derived from chemically synthesized precursors regulate thrombospondin 1 expression

Thrombospondin 1 (THBS1) is a secreted protein with a variety of biological functions, including a potent anti-angiogenic activity and activation of latent transforming growth factor beta (TGF-β). In many human cancers it is expressed at low levels, although mutations in the THBS1 gene have been rarely reported. Instead, the loss of THBS1 expression has been proposed to be due to transcriptional and post-transcriptional deregulations. In a systematic screen of predicted microRNA (miRNA) binding sites in the THBS1 3' untranslated region (UTR) we employed chemically synthesized pre-miRNAs-a new class of pre-miRNA mimics-to show that several miRNAs (let-7a, miR-18a, miR-29b, miR-194, and miR-221) can modulate THBS1 expression at the post-transcriptional level. Sequence-specific downregulation of THBS1 by let-7a, miR-18a or by a small interfering RNA induced TGF-β1 and SMAD4 transcript levels. Ectopic expression of latent TGF-β1 reduced THBS1 protein expression and was associated with increased expression of let-7a, let-7-b, and miR-18a in cells. These data suggest an inverse correlation of THBS1 and latent TGF-β1 expression levels possibly involving miRNAs.

Synthetic pre-microRNAs reveal dual-strand activity of miR-34a on TNF-α

Functional microRNAs (miRNAs) are produced from both arms of their precursors (pre-miRNAs). Their abundances vary in context-dependent fashion spatiotemporarily and there is mounting evidence of regulatory interplay between them. Here, we introduce chemically synthesized pre-miRNAs (syn-pre-miRNAs) as a general class of accessible, easily transfectable mimics of pre-miRNAs. These are RNA hairpins, identical in sequence to natural pre-miRNAs. They differ from commercially available miRNA mimics through their complete hairpin structure, including any regulatory elements in their terminal-loop regions and their potential to introduce both strands into RISC. They are distinguished from transcribed pre-miRNAs by their terminal 5' hydroxyl groups and their precisely defined terminal nucleotides. We demonstrate with several examples how they fully recapitulate the properties of pre-miRNAs, including their processing by Dicer into functionally active 5p; and 3p-derived mature miRNAs. We use syn-pre-miRNAs to show that miR-34a uses its 5p and 3p miRNAs in two pathways: apoptosis during TGF-β signaling, where SIRT1 and SP4 are suppressed by miR-34a-5p and miR-34a-3p, respectively; and the lipopolysaccharide (LPS)-activation of primary human monocyte-derived macrophages, where TNF (TNFα) is suppressed by miR-34a-5p indirectly and miR-34a-3p directly. Our results add to growing evidence that the use of both arms of a miRNA may be a widely used mechanism. We further suggest that syn-pre-miRNAs are ideal and affordable tools to investigate these mechanisms.

Sweating the small stuff: microRNAs and genetic changes define pancreatic cancer

MicroRNAs (miRNAs) are 18- to 22-nucleotide-long, single-stranded, noncoding RNAs that regulate important biological processes including differentiation, proliferation, and response to cellular stressors such as hypoxia, nutrient depletion, and traversion of the cell cycle by controlling protein expression within the cell. Many investigators have profiled cancer tissue and serum miRNAs to identify potential therapeutic targets, understand the pathways involved in tumorigenesis, and identify diagnostic tumor signatures. In the setting of pancreatic cancer, obtaining pancreatic tissue is invasive and impractical for early diagnosis. Several groups have profiled miRNAs that are present in the blood as a means to diagnose tumor progression and predict prognosis/survival or drug resistance. Several miRNA signatures found in pancreatic tissue and the peripheral blood, as well as the pathways that are associated with pancreatic cancer, are reviewed here in detail. Three miRNA biomarkers (miR-21, miR-155, and miR-200) have been repetitively identified in both pancreatic cancer tissue and patients' blood. Those miRNAs regulate and are regulated by the central genetic and epigenetic changes observed in pancreatic cancer including p53, transforming growth factor β, p16(INK4A), BRCA1/2, and Kras. These miRNAs are involved in DNA repair, cell cycle, and cell invasion and also play important roles in promoting metastases.

Role of proprotein convertases in prostate cancer progression

Better understanding of the distinct and redundant functions of the proprotein convertase (PC) enzyme family within pathophysiological states has a great importance for potential therapeutic strategies. In this study, we investigated the functional redundancy of PCs in prostate cancer in the commonly used androgen-sensitive LNCaP and the androgen-independent DU145 human cell lines. Using a lentiviral-based shRNA delivery system, we examined in vitro and in vivo cell proliferation characteristics of knockdown cell lines for the endogenous PCs furin, PACE4, and PC7 in both cell lines. Of the three PCs, only PACE4 was essential to maintain a high-proliferative status, as determined in vitro using XTT proliferation assays and in vivo using tumor xenografts in nude mice. Furin knockdowns in both cell lines had no effects on cell proliferation or tumor xenograft growth. Paradoxically, PC7 knockdowns reduced in vitro cellular proliferation but had no effect in vivo. Because PCs act within secretion pathways, we showed that conditioned media derived from PACE4 knockdown cells had very poor cell growth-stimulating effects in vitro. Immunohistochemistry of PACE4 knockdown tumors revealed reduced Ki67 and higher p27(KIP) levels (proliferation and cell cycle arrest markers, respectively). Interestingly, we determined that the epidermal growth factor receptor signaling pathway was activated in PC7 knockdown tumors only, providing some explanations of the paradoxical effects of PC7 silencing in prostate cancer cell lines. We conclude that PACE4 has a distinct role in maintaining proliferation and tumor progression in prostate cancer and this positions PACE4 as a relevant therapeutic target for this disease.

Simultaneous miRNA and mRNA transcriptome profiling of human myoblasts reveals a novel set of myogenic differentiation-associated miRNAs and their target genes

Background

miRNA profiling performed in myogenic cells and biopsies from skeletal muscles has previously identified miRNAs involved in myogenesis.

Results

Here, we have performed miRNA transcriptome profiling in human affinity-purified CD56+ myoblasts induced to differentiate in vitro. In total, we have identified 60 miRNAs differentially expressed during myogenic differentiation. Many were not known for being differentially expressed during myogenic differentiation. Of these, 14 (miR-23b, miR-28, miR-98, miR-103, miR-107, miR-193a, miR-210, miR-324-5p, miR-324-3p, miR-331, miR-374, miR-432, miR-502, and miR-660) were upregulated and 6 (miR-31, miR-451, miR-452, miR-565, miR-594 and miR-659) were downregulated. mRNA transcriptome profiling performed in parallel resulted in identification of 6,616 genes differentially expressed during myogenic differentiation.

Conclusions

This simultaneous miRNA/mRNA transcriptome profiling allowed us to predict with high accuracy target genes of myogenesis-related microRNAs and to deduce their functions.

Transforming growth factor-β gene silencing using adenovirus expressing TGF-β1 or TGF-β2 shRNA

Tumor cells secrete a variety of cytokines to outgrow and evade host immune surveillance. In this context, transforming growth factor-β1 (TGF-β1) is an extremely interesting cytokine because it has biphasic effects in cancer cells and normal cells. TGF-β1 acts as a growth inhibitor in normal cells, whereas it promotes tumor growth and progression in tumor cells. Overexpression of TGF-β1 in tumor cells also provides additional oncogenic activities by circumventing the host immune surveillance. Therefore, this study ultimately aimed to test the hypothesis that suppression of TGF-β1 in tumor cells by RNA interference can have antitumorigenic effects. However, we demonstrated here that the interrelation between TGF-β isotypes should be carefully considered for the antitumor effect in addition to the selection of target sequences with highest efficacy. The target sequences were proven to be highly specific and effective for suppressing both TGF-β1 mRNA and protein expression in cells after infection with an adenovirus expressing TGF-β1 short hairpin RNA (shRNA). A single base pair change in the shRNA sequence completely abrogated the suppressive effect on TGF-β1. Surprisingly, the suppression of TGF-β1 induced TGF-β3 upregulation, and the suppression of TGF-β2 induced another unexpected downregulation of both TGF-β1 and TGF-β3. Taken together, this information may prove useful when considering the design for a novel cancer immunogene therapy.

MicroRNA-24 regulates cardiac fibrosis after myocardial infarction

Cardiac fibrosis after myocardial infarction (MI) has been identified as a key factor in the development of heart failure. Although dysregulation of microRNA (miRNA) is involved in various pathophysiological processes in the heart, the role of miRNA in fibrosis regulation after MI is not clear. Previously we observed the correlation between fibrosis and the miR-24 expression in hypertrophic hearts, herein we assessed how miR-24 regulates fibrosis after MI. Using qRT-PCR, we showed that miR-24 was down-regulated in the MI heart; the change in miR-24 expression was closely related to extracellular matrix (ECM) remodelling. In vivo, miR-24 could improve heart function and attenuate fibrosis in the infarct border zone of the heart two weeks after MI through intramyocardial injection of Lentiviruses. Moreover, in vitro experiments suggested that up-regulation of miR-24 by synthetic miR-24 precursors could reduce fibrosis and also decrease the differentiation and migration of cardiac fibroblasts (CFs). TGF-β (a pathological mediator of fibrotic disease) increased miR-24 expression, overexpression of miR-24 reduced TGF-β secretion and Smad2/3 phosphorylation in CFs. By performing microarray analyses and bioinformatics analyses, we found furin to be a potential target for miR-24 in fibrosis (furin is a protease which controls latent TGF-β activation processing). Finally, we demonstrated that protein and mRNA levels of furin were regulated by miR-24 in CFs. These findings suggest that miR-24 has a critical role in CF function and cardiac fibrosis after MI through a furin–TGF-β pathway. Thus, miR-24 may be used as a target for treatment of MI and other fibrotic heart diseases.

Crosstalk between TGF-β signaling and the microRNA machinery

The activin/transforming growth factor-β (TGF-β) pathway plays an important role in tumorigenesis either by its tumor suppressor or tumor promoting effect. Loss of members of the TGF-β signaling by somatic mutations or epigenetic events, such as DNA methylation or regulation by microRNA (miRNA), may affect the signaling process. Most members of the TGF-β pathway are known to be targeted by one or more miRNAs. In addition, the biogenesis of miRNAs is also regulated by TGF-β both directly and through SMADs. Based on these interactions, it appears that autoregulatory feedback loops between TGF-β and miRNAs influence the fate of tumor cells. Our aim is to review the crosstalk between TGF-β signaling and the miRNA machinery to highlight potential novel therapeutic targets.

Properties of N(4)-methylated cytidines in miRNA mimics

Experiments conducted with micro RNA (miRNA) mimics often result in subtle phenotypic changes and hence require careful controls. A commonly used type of control reagent in the antisense/RNA interference fields is the mismatched sequence. However, it is difficult to use mismatch controls for miRNAs, mainly because base permutation in the seed region may generate a new miRNA seed with its own associated target transcripts. We incorporated N(4)-methylcytidine and N(4),N(4)-dimethylcytidine into a series of RNAs using the convertible nucleoside approach and measured their effects on hybridization affinity with complementary RNAs, and on miRNA-mediated and small interfering RNA (SiRNA)-mediated silencing. We report here that incorporation of a single N(4),N(4)-dimethylcytidine into the seed region of miRNAs can be used as a new class of negative miRNA control which (1) does not constitute a new seed sequence; (2) is accepted by the RNA-induced silencing complex (RISC); (3) causes a significant loss of binding affinity to target RNAs; and (4) is synthesized conveniently into oligoribonucleotides.

Down-regulation of microRNA-34a* in rheumatoid arthritis synovial fibroblasts promotes apoptosis resistance

OBJECTIVE

To investigate the expression and effect of the microRNA-34 (miR-34) family on apoptosis in rheumatoid arthritis synovial fibroblasts (RASFs).

METHODS

Expression of the miR-34 family in synovial fibroblasts with or without stimulation with Toll-like receptor (TLR) ligands, tumor necrosis factor α (TNFα), interleukin-1β (IL-1β), hypoxia, or 5-azacytidine was analyzed by real-time polymerase chain reaction (PCR). Promoter methylation was studied by combined bisulfite restriction analysis. The effects of overexpression and silencing of miR-34a and miR-34a* on apoptosis were analyzed by annexin V/propidium iodide staining. Production of X-linked inhibitor of apoptosis protein (XIAP) was assessed by real-time PCR and immunohistochemistry analysis. Reporter gene assay was used to study the signaling pathways of miR-34a*.

RESULTS

Basal expression levels of miR-34a* were found to be reduced in synovial fibroblasts from RA patients compared to osteoarthritis patients, whereas levels of miR-34a, miR-34b/b*, and miR-34c/c* did not differ. Neither TNFα, IL-1β, TLR ligands, nor hypoxia altered miR-34a* expression. However, we demonstrated that the promoter of miR-34a/34a* was methylated and showed that transcription of the miR-34a duplex was induced upon treatment with demethylating agents. Enforced expression of miR-34a* led to an increased rate of FasL- and TRAIL-mediated apoptosis in RASFs. Moreover, levels of miR-34a* were highly correlated with expression of XIAP, which was found to be up-regulated in RA synovial cells. Finally, we identified XIAP as a direct target of miR-34a*.

CONCLUSION

Our data provide evidence of a methylation-specific down-regulation of proapoptotic miR-34a* in RASFs. Decreased expression of miR- 34a* results in up-regulation of its direct target XIAP, thereby contributing to resistance of RASFs to apoptosis.