Loss of mir-146a function in hormone-refractory prostate cancer

Genetic variations in microRNA-related genes are associated with survival and recurrence in patients with renal cell carcinoma

We took a polygenic approach to evaluate the effects of 41 potentially functional single-nucleotide polymorphisms (SNPs) in microRNAs (miRNAs)-related genes on survival and recurrence among renal cell carcinoma (RCC) patients. During a median follow-up of 21.8 months, among 316 RCC patients, 64 died and 56 developed recurrence. In single-SNP analysis, we identified seven SNPs significantly associated with RCC survival and five SNPs with recurrence. The most significant associations were SNPs in GEMIN4 with the variant alleles of both rs7813 and rs910925 associated with 1.74-fold [95% confidence interval (CI) = 1.15-2.62] increased risk of death, whereas the variant allele of rs3744741 conferred a decreased risk of death [hazard ratio (HR) = 0.39; 95% CI = 0.19-0.77]. Several SNPs belonging to the pre-miRNA and were identified to be significantly associated with RCC recurrence. Haplotypes of DICER and DROSHA were also associated with altered patient survival and recurrence. More importantly, we observed cumulative effects of multiple SNPs on RCC survival. Compared with subjects carrying zero to two unfavorable genotypes, those carrying three to five and six and more unfavorable genotypes had an increased risk of death with a HR of 2.49 (95% CI = 1.24-5.00) and 6.66 (95% CI = 2.49-17.86), respectively, with significant dose-response trend (P for trend<0.001). As the first study of miRNA-related genetic polymorphisms on RCC clinical outcome, our results strongly suggested that miRNA-related SNPs may impact the recurrence and survival in RCC patients. Future investigation in larger populations and functional characterizations are necessary to validate these results.

Loss of inducible nitric oxide synthase expression in the mouse renal cell carcinoma cell line RENCA is mediated by microRNA miR-146a

Tumor-associated macrophages can potentially kill tumor cells via the high concentrations of nitric oxide (NO) produced by inducible nitric oxide synthase (iNOS); however, tumor-associated macrophages actually support tumor growth, as they are skewed toward M2 activation, which is characterized by low amounts of NO production and is proangiogenic. We show that the mouse renal cell carcinoma cell line, RENCA, which, on stimulation, expresses high levels of iNOS mRNA, loses its ability to express the iNOS protein. This effect is mediated by the microRNA miR-146a, as inhibition of RENCA cells with anti-miR- 146a restores iNOS expression and NO production (4.8 ± 0.4 versus 0.3 ± 0.1 μmol/L in uninhibited cells, P < 0.001). In vivo, RENCA tumor cells do not stain for iNOS, while infiltrating tumor-associated macrophages showed intense staining, and both cell types expressed iNOS mRNA. Restoring iNOS protein expression in RENCA cells using anti-miR-146a increases macrophage-induced death of RENCA cells by 73% (P < 0.01) in vitro and prevents tumor growth in vivo. These results suggest that, in addition to NO production by macrophages, tumor cells must produce NO to induce their own deaths, and some tumor cells may use miR-146a to reduce or abolish endogenous NO production to escape macrophage-mediated cell death. Thus, inhibiting miR-146a may render these tumor cells susceptible to therapeutic strategies, such as adoptive transfer of M1-activated macrophages.

Correlation between pre-miR-146a C/G polymorphism and gastric cancer risk in Chinese population

AIM: To investigate the association between pre-miR-146a C/G polymorphism and gastric cancer risk.

METHODS: We performed a hospital-based, case-control study using polymerase chain reaction-restriction fragment length polymorphism method in 608 individuals (304 gastric cancer patients and 304 age and sex matched cancer-free controls).

RESULTS: The frequencies of pre-miR-146a C/G genotypes in the case group were significantly different from those in the control groups (P = 0.037). Compared with CC genotype carriers, subjects with the variant genotypes (GC + GG) had a 58% increased risk of gastric cancer (adjusted OR = 1.58, 95% CI: 1.11-2.20, P = 0.009). Moreover, a higher gastric cancer risk was especially evident in younger individuals aged ≤ 58 years, nonsmokers, and males (adjusted OR = 1.76, 95% CI: 1.08-2.87, P = 0.024; adjusted OR = 1.55, 95% CI: 1.06-2.28, P = 0.025; adjusted OR = 1.53, 95% CI: 1.04-2.27, P = 0.033; respectively).

CONCLUSION: Pre-miR-146a C/G polymorphism might be associated with an elevated risk of gastric cancer in Chinese population.

The association between two polymorphisms in pre-miRNAs and breast cancer risk: a meta-analysis

Emerging evidence has shown that miRNAs participate in human carcinogenesis as tumor suppressors or oncogenes. Single nucleotide polymorphism (SNP) which located in the pre-miRNA may affect the processing and then influence the expression of mature miRNA. Previous studies yielded conflicting results as to the association of two common polymorphisms in pre-miRNAs (i.e. hsa-miR-146 rs2910164 and hsa-miR-196a2 rs11614913) with breast cancer. To derive a more precise effect on the association between these polymorphisms and breast cancer risk, we conducted a meta-analysis. Through retrieving PubMed for the period up to May 2010, a total of four studies were identified with 3,007 cases and 3,718 controls for has-miR-146a rs2910164 polymorphism and with 3,287 cases and 4,298 controls for hsa-miR-196a2 rs11614913 polymorphism. We found that individuals carrying CC genotype of has-miR-196a2 rs11614913 polymorphism was associated with an increased breast cancer risk in homozygote comparison (OR = 1.30; 95% CI, 1.01-1.68), and dominant model (OR = 1.11; 95% CI, 1.01-1.23). However, no significant association between has-miR-146a rs2910164 polymorphism and breast cancer risk was observed in all comparison models tested. These findings suggest that has-miR-196a2 rs11614913 polymorphism may play crucial roles in breast cancer development.

hsa-miR-520h downregulates ABCG2 in pancreatic cancer cells to inhibit migration, invasion, and side populations

Background:

Expression of ABCG2 is normally absent or low in the pancreas, but high in human pancreatic cancer cells. The mechanism by which ABCG2 is altered in human cancers remains unknown.

Methods:

We investigated ABCG2 expression in four pancreatic cancer cell lines, and used three microRNA (miRNA) target prediction programmes, and information from the existing literature to predict and identify hsa-miR-520h as an miRNA that targets ABCG2. The function of this miRNA was investigated by transient transfection of the pancreatic cancer cell line PANC-1 with oligonucleotides that mimic hsa-miR-520h.

Results:

Results showed that both mRNA and protein levels of ABCG2 were reduced, indicating that it was a target of hsa-miR-520h. Introduction of hsa-miR-520h mimics into PANC-1 cells also resulted in inhibition of cell migration and invasion, and reduction of side population cells. Cell proliferation, cell cycle progression and apoptosis were not affected.

Conclusions:

We propose that the effects of hsa-miR-520h may be, at least in part, caused by its regulation of ABCG2. Thus, our findings provide a new insight into the function of miRNA in the regulation of ABCG2 expression in pancreatic cancer. Gene therapy using miRNA mimics may therefore be useful as a pancreatic cancer therapy.

Expression phenotype changes of EBV-transformed lymphoblastoid cell lines during long-term subculture and its clinical significance

OBJECTIVES

The EBV-transformed lymphoblastoid cell line (LCL) is a useful resource for population-based human genetic and pharmacogenetic studies. The principal objective here was to assess expression phenotype changes during long-term subculture of LCLs, and its clinical significance.

MATERIALS AND METHODS

We searched for genes that were differentially expressed in 17 LCLs at late (p161) passage compared to early passage (p4) using microarray assay, then validated them by real-time RT-PCR analysis. In addition, we estimated correlations between expression phenotypes of 20 LCL strains at early passage and 23 quantitative clinical traits from blood donors of particular LCL strains.

RESULTS

Transcript sequences of 16 genes including nuclear factor-kappaB (NF-kappaB) pathway-related genes (such as PTPN13, HERC5 and miR-146a) and carcinogenesis-related genes (such as XAF1, TCL1A, PTPN13, CD38 and miR-146a) were differentially expressed (>2-fold change) in at least 15 of the 17 LCL strains. In particular, TC2N, FCRL5, CD180, CD38 and miR-146a were downregulated in all 17 of the evaluated LCL strains. In addition, we identified clinical trait-associated expression phenotypes in LCLs.

CONCLUSION

Our results showed that LCLs acquired expression phenotype changes involving expression of NF-kappaB pathway- and carcinogenesis-related genes during long-term subculture. These differentially expressed genes can be considered to be a gene signature of LCL immortalization or EBV-induced carcinogenesis. Clinical trait-associated expression phenotypes should prove useful in the discovery of new candidate genes for particular traits.

Resveratrol decreases the levels of miR-155 by upregulating miR-663, a microRNA targeting JunB and JunD

An inflammatory component is present in the microenvironment of most neoplastic tissues, including those not causally related to an obvious inflammatory process. Several microRNAs, and especially miR-155, play an essential role in both the innate and adaptative immune response. Resveratrol (trans-3,4',5-trihydroxystilbene) is a natural antioxidant with anti-inflammatory properties that is currently at the stage of preclinical studies for human cancer prevention. Here, we establish that, in human THP-1 monocytic cells as well as in human blood monocytes, resveratrol upregulates miR-663, a microRNA potentially targeting multiple genes implicated in the immune response. In THP-1 cells, miR-663 decreases endogenous activator protein-1 (AP-1) activity and impairs its upregulation by lipopolysaccharides (LPS), at least in part by directly targeting JunB and JunD transcripts. We further establish that the downregulation of AP-1 activity by resveratrol is miR-663 dependent and that the effects of resveratrol on both AP-1 activity and JunB levels are dose dependent. Finally, we show that resveratrol impairs the upregulation of miR-155 by LPS in a miR-663-dependent manner. Given the role of miR-155 in the innate immune response and the fact that it is upregulated in many cancers, our results suggest that manipulating miR-663 levels may help to optimize the use of resveratrol as both an anti-inflammatory and anticancer agent against malignancies associated with high levels of miR-155.

MicroRNAs: synthesis, mechanism, function, and recent clinical trials

MicroRNAs (miRNAs) are a class of small, endogenous RNAs of 21-25 nucleotides (nts) in length. They play an important regulatory role in animals and plants by targeting specific mRNAs for degradation or translation repression. Recent scientific advances have revealed the synthesis pathways and the regulatory mechanisms of miRNAs in animals and plants. miRNA-based regulation is implicated in disease etiology and has been studied for treatment. Furthermore, several preclinical and clinical trials have been initiated for miRNA-based therapeutics. In this review, the existing knowledge about miRNAs synthesis, mechanisms for regulation of the genome, and their widespread functions in animals and plants is summarized. The current status of preclinical and clinical trials regarding miRNA therapeutics is also reviewed. The recent findings in miRNA studies, summarized in this review, may add new dimensions to small RNA biology and miRNA therapeutics.

The function of microRNAs, small but potent molecules, in human prostate cancer

Prostate cancer is one of the most significant cancers of men all over the world. The microRNAs (miRNAs) possess crucial functions in pathogenesis of the disease and its gain of androgen independency. The miRNAs are small, approximately 18-24 nucleotides, non-coding, endogenously synthesized RNAs that regulate gene expression post-transcriptionally. They are found in viruses, plants, and animal cells. The miRNAs have critical functions in gene expression and their dysregulation may cause tumor formation and progression of several diseases. Here, we have reviewed the most current literature to elucidate the function of miRNAs in human prostate cancer. We believe that this will help investigators not only working in prostate cancer, but also studying the miRNAs in other diseases to delineate the functions of miRNAs implicated in human prostate cancer development and progression.

MicroRNAs and prostate cancer

MicroRNAs (miRNAs) are a class of small, non-coding, single-stranded RNAs that negatively regulate gene expression by mainly binding to 30 untranslated region (UTR) of target mRNAs at the post-transcriptional level. Recent studies have demonstrated that aberrant expressions of miRNAs are closely associated with the development, invasion, metastasis and prognosis of various cancers including prostate cancer (PCa). The proposed molecular mechanisms that underlie the aberrant expression of miRNAs result from gene changes, epigenetic modification and alteration of Dicer abundance. Although up to 50 miRNAs have been reported to be significantly expressed in human PCa, only a small number of them were experimentally shown to make contribution to the pathogenesis of PCa. The aim of this review is to describe the mechanisms of several known miRNAs, summarize recent studies on the relevance of altered expression of oncogenic miRNAs (e.g. miR-221/-222, miR-21, and miR-125b) and tumor suppressor miRNAs (e.g. miR-101, miR-126*, miR-146a, miR-330, miR-34 cluster, and miR-200 family) for PCa. Additionally, their potential clinical applications and prospects in PCa, such as biomarkers and clinical therapies, are also briefly discussed.

Up-regulated microRNA-146a negatively modulate Helicobacter pylori-induced inflammatory response in human gastric epithelial cells

Helicobacter pylori (H. pylori) is a major human pathogenic bacterium in gastric mucosa. However, the regulatory mechanism of H. pylori-induced immune response is not clear. MicroRNAs (miRNAs) have recently emerged as key post-transcriptional regulators of gene expression, and their role in H. pylori infection is just beginning to be explored. Here, we first reported that H. pylori infection up-regulated the expression of miR-146a in gastric epithelial cells as well as in gastric mucosal tissues in NF-κB-dependent manner. In turn, miR-146a may downregulate the expression of target genes, interleukin-1 receptor-associated kinase 1 (IRAK1) and TNF receptor-associated factor 6 (TRAF6). Furthermore, miR-146a negatively regulated H. pylori-triggered interleukin (IL)-8, growth-related oncogene (GRO)-α, and macrophage inflammatory protein (MIP) -3α through diminishing NF-κB activity. In conclusion, H. pylori-induced miR-146a plays a potential role in a negative feedback loop to modulate the inflammation by targeting IRAK1 and TRAF6.

Pharmacological studies of the mechanism and function of interleukin-1beta-induced miRNA-146a expression in primary human airway smooth muscle

BACKGROUND

Despite the widespread induction of miR-146a during the innate immune response little is known regarding its biogenesis, function and mechanism. We have therefore examined the role of miR-146a during the interleukin (IL)-1beta-stimulated IL-6 and IL-8 release and proliferation in primary human airway smooth muscle (HASM) cells.

METHODS

HASM cells were isolated from human lung re-section, cultured to a maximum of 3 - 6 passages and then exposed to IL-1beta. miR-146a expression were determined by qRT-PCR, IL-6 and IL-8 release by ELISA and proliferation using bromodeoxyuridine incorporation. The role of NF-kappaB and the MAP kinase pathways was assessed using pharmacological inhibitors of IKK2 (TPCA-1), JNK (SP600125), p38 MAP kinase (SB203580) and MEK-1/2 (PD98059). miR-146a function was determined following transfection of HASM with inhibitors and mimics using Amaxa electroporation.

RESULTS

IL-1beta induced a time-dependent and prolonged 100-fold induction in miR-146a expression, which correlated with release of IL-6 and IL-8. Exposure to IL-1beta had no effect upon HASM proliferation. Pharmacological studies showed that expression of primary miR-146a was regulated at the transcriptional levels by NF-kappaB whilst post-transcriptional processing to mature miR-146a was regulated by MEK-1/2 and JNK-1/2. Functional studies indicated that IL-1beta-induced miR-146a expression does not negatively regulate IL-6 and IL-8 release or basal proliferation. However, inhibition of IL-1beta-induced IL-6 and IL-8 release was observed at the super-maximal intracellular miR-146a levels obtained by transfection with miR-146a mimics and indicates that studies using miRNA mimics can produce false positive results. Mechanistic studies showed that in the presence of super-maximal levels, the action of miR-146a mimics was mediated at a step following IL-6 and IL-8 mRNA transcription and not through down-regulation of IL-1 receptor associated kinase 1 (IRAK-1) and TNF receptor-associated factor 6 (TRAF6) protein expression, two predicted miR-146a targets involved in IL-1beta signalling.

CONCLUSIONS

We have shown that IL-1beta-induced miR-146a expression in HASM and that this was regulated at the transcriptional level by NF-kappaB and at the post-transcriptional level by the MEK-1/2 and JNK-1/2. Unlike previous reports, studies using miRNA inhibitors showed that miR-146a expression did not regulate IL-6 and IL-8 release or proliferation and suggest miR-146a function and mechanism is cell-type dependent.

Diet, microRNAs and prostate cancer

MicroRNAs (miRNAs) constitute an evolutionarily conserved class of small non-coding RNAs that are endogenously expressed with crucial functions in fundamental cellular processes such as cell cycle, apoptosis and differentiation. Disturbance of miRNA expression and function leads to deregulation of basic cellular processes leading to tumorigenesis. A growing body of experimental evidence suggests that human tumors have deregulated expression of microRNAs, which have been proposed as novel oncogenes or tumor suppressors. Recent studies have shown that microRNA expression patterns serve as phenotypic signatures of different cancers and could be used as diagnostic, prognostic and therapeutic tools. A few studies have analyzed global microRNA expression profiles or the functional role of microRNAs in prostate cancer. Here we have reviewed the role of microRNAs in prostate carcinogenesis by summarizing the findings from such studies. In addition, recent evidence indicates that dietary factors play an important role in the process of carcinogenesis through modulation of miRNA expression, though such studies are lacking in regards to prostate cancer. It has been proposed that dietary modulation of miRNA expression may contribute to the cancer-protective effects of dietary components. In this review, we have summarized findings from studies on the effect of dietary agents on miRNA expression and function.

Small molecules with big effects: the role of the microRNAome in cancer and carcinogenesis

Small non-coding RNAs-microRNAs, are potent negative regulators of gene expression. MicroRNAs are involved in multiple biological processes, metabolic regulation, including cell proliferation, differentiation, and programmed cell death. Since the dysregulation of these processes is a hallmark of cancer, microRNAs can be viewed as major contributors to the pathogenesis of cancer, including initiation and progression of cancer. This review focuses on microRNA biogenesis and function, and their role in cancer, metastasis, drug resistance, and tumorigenesis.

Bisphenol A exposure leads to specific microRNA alterations in placental cells

Exposure to bisphenol A (BPA) has been observed to alter developmental pathways and cell processes, at least in part, through epigenetic mechanisms. This study sought to investigate the effect of BPA on microRNAs (miRNAs) in human placental cells. miRNA microarray was performed following BPA treatment in three immortalized cytotrophoblast cell lines and the results validated using quantitative real-time PCR. For functional analysis, overexpression constructs were stably transfected into cells that were then assayed for changes in proliferation and response to toxicants. Microarray analysis revealed several miRNAs to be significantly altered in response to BPA treatment in two cell lines. Real-time PCR results confirmed that miR-146a was particularly strongly induced and its overexpression in cells led to slower proliferation as well as higher sensitivity to the DNA damaging agent, bleomycin. Overall, these results suggest that BPA can alter miRNA expression in placental cells, a potentially novel mode of BPA toxicity.

Diagnostic, prognostic and therapeutic implications of microRNAs in urologic tumors

MicroRNAs (miRNAs) are small, non-coding RNAs that have an important role in the regulation of carcinogenic pathways. The observations that miRNAs are differentially expressed in tumor versus corresponding normal tissue, and that they regulate important breakpoints during carcinogenesis, are of interest for urologic oncologists. As biomarkers, they might be helpful tools for diagnostic, prognostic and monitoring purposes. Furthermore, miRNAs might be potential targets for novel therapeutic strategies, especially in patients with tumor subtypes that do not respond to currently available therapies. In this Review, we will focus on the current proceedings of miRNA research in urologic tumors. In the past decade, the number of published articles related to miRNAs in urologic oncology has increased, highlighting the ongoing importance of miRNAs in this field. Current studies support the hypothesis that miRNA will gain influence in clinical practice. Here, therefore, we illustrate the current knowledge of miRNA function in urologic tumors and draw the attention of urologists to the future opportunities and challenges of this research field.

Secretory mechanisms and intercellular transfer of microRNAs in living cells

The existence of circulating microRNAs (miRNAs) in the blood of cancer patients has raised the possibility that miRNAs may serve as a novel diagnostic marker. However, the secretory mechanism and biological function of extracellular miRNAs remain unclear. Here, we show that miRNAs are released through a ceramide-dependent secretory machinery and that the secretory miRNAs are transferable and functional in the recipient cells. Ceramide, whose biosynthesis is regulated by neutral sphingomyelinase 2 (nSMase2), triggers secretion of small membrane vesicles called exosomes. The decreased activity of nSMase2 with a chemical inhibitor, GW4869, and a specific small interfering RNA resulted in the reduced secretion of miRNAs. Complementarily, overexpression of nSMase2 increased extracellular amounts of miRNAs. We also revealed that the endosomal sorting complex required for transport system is unnecessary for the release of miRNAs. Furthermore, a tumor-suppressive miRNA secreted via this pathway was transported between cells and exerted gene silencing in the recipient cells, thereby leading to cell growth inhibition. Our findings shed a ray of light on the physiological relevance of secretory miRNAs.

Discovery of prostate cancer biomarkers by microarray gene expression profiling

Prostate cancer is the most commonly diagnosed malignancy in males in the Western world. This review focuses on advances in biomarker discovery for prostate cancer by microarray profiling of mRNA and microRNA expression. Novel biomarkers are strongly needed to enable more accurate detection of prostate cancer, improve prediction of tumor aggressiveness and facilitate discovery of new therapeutic targets for tailored medicine. Promising molecular markers identified from gene expression profiling studies include AMACR, EZH2, TMPRSS2-ERG, miR-221 and miR-141, which are described in more detail. In addition, a compilation of prognostic gene expression signatures for prediction of prostate cancer patient outcome is provided, and their possible clinical utility is discussed. Furthermore, limitations in the application of microarray-based expression profiling for identification of prostate cancer biomarkers are addressed.

The Roles of MicroRNAs in the Cancer Invasion-Metastasis Cascade

Cancer metastasis results from a multi-step cascading process that includes: 1) vascularization of the primary tumor; 2) detachment and invasion of cancer cells; 3) intravasation into lymphatic and blood vessels; 4) survival and arrest in the circulation; 5) extravasation into distant organs; and 6) colonization and growth of metastatic tumors. microRNAs (miRNAs) play critical roles in this multi-step process, both promoting and suppressing metastasis. This review updates the progress made in understanding the roles of miRNAs for invasion and metastasis during cancer progression. A specific miRNA signature of cancer metastasis is also reviewed.

miR-146a suppresses invasion of pancreatic cancer cells

The aggressive course of pancreatic cancer is believed to reflect its unusually invasive and metastatic nature, which is associated with epidermal growth factor receptor (EGFR) overexpression and NF-kappaB activation. MicroRNAs (miRNA) have been implicated in the regulation of various pathobiological processes in cancer, including metastasis in pancreatic cancer and in other human malignancies. In this study, we report lower expression of miR-146a in pancreatic cancer cells compared with normal human pancreatic duct epithelial cells. Reexpression of miR-146a inhibited the invasive capacity of pancreatic cancer cells with concomitant downregulation of EGFR and the NF-kappaB regulatory kinase interleukin 1 receptor-associated kinase 1 (IRAK-1). Cellular mechanism studies revealed crosstalk between EGFR, IRAK-1, IkappaBalpha, NF-kappaB, and MTA-2, a transcription factor that regulates metastasis. Treatment of pancreatic cancer cells with the natural products 3,3'-diinodolylmethane (DIM) or isoflavone, which increased miR-146a expression, caused a downregulation of EGFR, MTA-2, IRAK-1, and NF-kappaB, resulting in an inhibition of pancreatic cancer cell invasion. Our findings reveal DIM and isoflavone as nontoxic activators of a miRNA that can block pancreatic cancer cell invasion and metastasis, offering starting points to design novel anticancer agents.

Diagnostic and prognostic implications of microRNA profiling in prostate carcinoma

This study aimed to investigate the microRNA (miRNA) profile in prostate carcinoma tissue by microarray analysis and RT-qPCR, to clarify associations of miRNA expression with clinicopathologic data and to evaluate the potential of miRNAs as diagnostic and prognostic markers. Matched tumor and adjacent normal tissues were obtained from 76 radical prostatectomy specimens. Twenty-four tissue pairs were analyzed using human miRNA microarrays for 470 human miRNAs. Differentially expressed miRNAs were validated by TaqMan RT-qPCR using all 76 tissue pairs. The diagnostic potential of miRNAs was calculated by receiver operating characteristics analyses. The prognostic value was assessed in terms of biochemical recurrence using Kaplan-Meier and Cox regression analyses. Fifteen differentially expressed miRNAs were identified with concordant fold-changes by microarray and RT-qPCR analyses. Ten microRNAs (hsa-miR-16, hsa-miR-31, hsa-miR-125b, hsa-miR-145, hsa-miR-149, hsa-miR-181b, hsa-miR-184, hsa-miR-205, hsa-miR-221, hsa-miR-222) were downregulated and 5 miRNAs (hsa-miR-96, hsa-miR-182, hsa-miR-182, hsa-miR-183, hsa-375) were upregulated. Expression of 5 miRNAs correlated with Gleason score or pathological tumor stage. Already 2 microRNAs classified up to 84% of malignant and nonmalignant samples correctly. Expression of hsa-miR-96 was associated with cancer recurrence after radical prostatectomy and that prognostic information was confirmed by an independent tumor sample set from 79 patients. That was shown with hsa-miR-96 and the Gleason score as final variables in the Cox models build in the 2 patient sets investigated. Thus, differential miRNAs in prostate cancer are useful diagnostic and prognostic indicators. This study provides a solid basis for further functional analyses of miRNAs in prostate cancer.

Impact of probe annotation on the integration of miRNA-mRNA expression profiles for miRNA target detection

MicroRNAs (miRNAs) are small non-coding RNAs that mediate gene expression at the post-transcriptional and translational levels by an imperfect binding to target mRNA 3′UTR regions. While the ab-initio computational prediction of miRNA–mRNA interactions still poses significant challenges, it is possible to overcome some of its limitations by carefully integrating into the analysis the paired expression profiles of miRNAs and mRNAs. In this work, we show how the choice of a proper probe annotation for microarray platforms is an essential requirement to achieve good sensitivity in the identification of miRNA–mRNA interactions. We compare the results obtained from the analysis of the same expression profiles using both gene and transcript based custom CDFs that we have developed for a number of different annotations (ENSEMBL, RefSeq, AceView). In all cases, transcript-based annotations clearly improve the effectiveness of data integration and thus provide a more reliable confirmation of computationally predicted miRNA–mRNA interactions.

MicroRNA miR-146a is induced by HTLV-1 tax and increases the growth of HTLV-1-infected T-cells

Human T-cell leukemia virus type 1 (HTLV-1) is the causative agent of adult T-cell leukemia (ATL), which is an aggressive and fatal CD4(+) T cell malignancy. MicroRNA (miRNA), a novel class of RNA that regulates gene expression, is involved in many cellular processes such as growth, development and apoptosis. It has recently been linked to several cancer phenotypes. However, aberrant miRNA expression and its pathologic significance in ATL are not well documented. Here, we investigated the role of miRNAs in HTLV-1-related leukemogenesis. The results showed that miR-146a was upregulated in HTLV-1-infected T-cell lines compared to uninfected T-cell lines. Tax-induced miR-146a expression in a NF-κB-dependent manner and inhibited the expression of gene harboring the target sequence of miR-146a on its 3'UTR. Inhibition of miR-146a function by anti-miRNA inhibitor reduced the proliferation of HTLV-1-infected T-cell lines but not that of uninfected T-cell lines. Moreover, overexpression of miR-146a enhanced the growth of an HTLV-1-infected T-cell line. Our findings suggest that miR-146a is a potentially suitable therapeutic target of ATL.

Identification of the potential target genes of microRNA-146a induced by PMA treatment in human microvascular endothelial cells

Phorbol 12-myristate 13-acetate (PMA) is known to activate protein kinase C (PKC) and increase angiogenesis in cultured endothelial cells. Using a microRNA (miRNA) array, we found that PMA induced miR-146a expression in human microvascular endothelial cells. The miR-146a expression was dependent on dose and time and independent of PKC activation. Using a combined approach involving predictions using miRanda algorithm and whole genome microarray experiments with or without inhibition of miR-146a expression by LNA-antimir-146a or LNA-control, 29 potential target genes of miR-146a were identified. Because endothelial cell S phase progression is an early event in the induction of angiogenesis, we evaluated 5 cell cycle-related genes from the 29 target genes and found that the transcripts of 3 genes (CCNA2, PA2G4, and BRCA1) were downregulated after PMA treatment, but their expression was rescued upon miR-146a inhibition. However, inhibition of miR-146a expression failed to alter the cell cycle distribution or angiogenesis induced by PMA treatment. By using a combined approach involving computational prediction and a whole genome microarray experiment in the presence or absence of antimir, the observations in this presented article raise the possibility that antimir strategies might be used to identify the potential miRNA targets.

Divergent intracellular pathways regulate interleukin-1beta-induced miR-146a and miR-146b expression and chemokine release in human alveolar epithelial cells

We have previously reported that IL-beta-induced miR-146a and miR-146b expression negatively regulates IL-8 and RANTES release in human alveolar A549 epithelial cells. To determine the intracellular pathways that regulate this response, we demonstrate IL-1beta-induced activation of the nuclear factor (NF)-kappaB, extracellular regulated kinase (ERK)-1/2, c-jun N-terminal kinase (JNK)-1/2 and p38 mitogen activated kinase (MAP) kinase pathways. Subsequent pharmacological studies show that IL-1beta-induced miR-146a, IL-8 and RANTES production was regulated via NF-kappaB and JNK-1/2 whilst miR-146b expression was mediated via MEK-1/2 and JNK-1/2. These divergent intracellular pathways likely explain the differential expression and biological action of the miR-146 isoforms.

Metastamir: the field of metastasis-regulatory microRNA is spreading

Despite advancements in knowledge from more than a century of metastasis research, the genetic programs and molecular mechanisms required for cancer metastasis are still incompletely understood. Genes that specifically regulate the process of metastasis are useful tools to elucidate molecular mechanisms and may become markers and/or targets for antimetastatic therapy. Recently, several noncoding regulatory RNA genes, microRNA (miRNA), were identified, which play roles in various steps of metastasis, some without obvious roles in tumorigenesis. Understanding how these metastasis-associated miRNA, which we term metastamir, are involved in metastasis will help identify possible biomarkers or targets for the most lethal attribute of cancer: metastasis.

miR-21: an androgen receptor-regulated microRNA that promotes hormone-dependent and hormone-independent prostate cancer growth

Androgen receptor (AR)-mediated oncogenic pathways have not been fully elucidated. In this study, we used high-throughput microarray analysis on two AR-positive prostate cancer (CaP) cell lines to identify 16 AR-responsive microRNAs (miRNA). We focused on miR-21 because of its previously reported oncogenic activity in other cancers. We show androgen-induced AR binding to the defined miR-21 promoter, miPPR-21, suggesting direct transcriptional regulation. Inhibition of miR-21 diminished androgen-induced CaP cell proliferation, providing new evidence that miRNAs can contribute to androgen-driven cell growth. Elevated expression of miR-21 enhanced CaP tumor growth in vivo and, surprisingly, was sufficient for androgen-dependent tumors to overcome castration-mediated growth arrest. Thus, elevated miR-21 expression alone is sufficient to impart castration resistance. Moreover, quantitative reverse transcription-PCR analysis revealed elevated miR-21 expression in CaP when compared with adjacent normal tissue. These results suggest that miR-21 may contribute to CaP pathogenesis.

Linking metastasis suppression with metastamiR regulation

Cancer metastasis requires the coordinate expression of multiple genes during every step of the metastatic cascade. Molecules that regulate these genetic programs have the potential to impact metastasis at multiple levels. Breast cancer metastasis suppressor 1 (BRMS1) suppresses metastasis by inhibiting multiple steps in the cascade through regulation of many protein-encoding, metastasis-associated genes as well as metastasis-regulatory microRNA, termed metastamiR. In this Feature , we will highlight connections between BRMS1 biology and regulation of metastamiR.

Epigenetic alterations in human prostate cancers

Human prostate cancer cells carry a myriad of genome defects, including both genetic and epigenetic alterations. These changes, which can be maintained through mitosis, generate malignant phenotypes capable of selective growth, survival, invasion, and metastasis. During prostatic carcinogenesis, epigenetic changes arise earlier than genetic defects, linking the appearance of epigenetic alterations in some way to disease etiology. The most common genetic defect thus far described, leading to fusion transcripts between the androgen-regulated gene TMPRSS2 and genes from the ETS family of transcription factors, likely endows prostate cancer cells with the ability to co-opt androgen signaling, the major prostate differentiation pathway, to support the malignant phenotype. Whether epigenetic changes promote the appearance of TMPRSS2-ETS family fusion transcripts or collaborate with fusion transcript expression in the pathogenesis of prostate cancer has not been established. However, a growing list of epigenetic alterations has provided new opportunities for clinical tests that might aid in prostate cancer screening, detection, diagnosis, staging, and risk stratification. The epigenetic changes appear to be more attractive than genetic changes as prostate cancer biomarkers because epigenetic alterations are present in a greater fraction of prostate cancer cases than any of the known genetic defects. In addition, an emerging generation of assay strategies for detection of specific DNA sequences carrying (5-me)C, the major epigenetic genome mark, has pushed somatic epigenetic alterations to the forefront of molecular biomarker assay development for cancer. Finally, a growing portfolio of epigenetic drugs, capable of reversing the phenotypic consequences of somatic epigenetic defects, has entered clinical trials for prostate cancer in the search for a new rational therapy for the disease.

Intrinsic expression of host genes and intronic miRNAs in prostate carcinoma cells

Background

Recent data show aberrant and altered expression of regulatory noncoding micro (mi) RNAs in prostate cancer (PCa). A large number of miRNAs are encoded in organized intronic clusters within many protein coding genes. While expression profiling studies of miRNAs are common place, little is known about the host gene and their resident miRNAs coordinated expression in PCa cells. Furthermore, whether expression of a subset of miRNAs is distinct in androgen-responsive and androgen-independent cells is not clear. Here we have examined the expression of mature miRNAs of miR 17–92, miR 106b-25 and miR 23b-24 clusters along with their host genes C13orf25, MCM7 and AMPO respectively in PCa cell lines.

Results

The expression profiling of miRNAs and host genes was performed in androgen-sensitive MDA PCa 2b and LNCaP as well as in androgen-refractory PC-3 and DU 145 cell culture models of PCa. No significant correlation between the miRNA expression and the intrinsic hormone-responsive property of PCa cells was observed. Androgen-sensitive MDA PCa 2b cells exhibited the highest level of expression of most miRNAs studied in this report. We found significant expression variations between host genes and their resident miRNAs. The expressions of C13orf25 and miR 17–92 cluster as well as MCM7 and miR 106b-25 cluster did not reveal statistically significant correlation, thus suggesting that host genes and resident miRNAs may be expressed independent of each other.

Conclusion

Our results suggest that miRNA expression profiles may not predict intrinsic hormone-sensitive environment of PCa cells. More importantly, our data indicate the possibility of additional novel mechanisms for intronic miRNA processing in PCa cells.

Differential expression profile of microRNAs in the different stages of hepatitis B virus infection-related hepatocarcinogenesis

AIM: To investigate the differential expression profile of microRNAs in the different stages of hepatitis B virus (HBV) infection-related hepatocarcinogenesis.

METHODS: MicroRNA microarray was used to detect the differential expression profile of microRNAs in the liver tissue taken from healthy controls as well as patients with HBV-induced cirrhosis or HBV-related hepatocellular carcinoma. Real-time quantitative PCR was performed to verify the differential expression of candidate microRNAs obtained from microarray experiment.

RESULTS: Compared with normal liver tissue, six microRNAs (hsa-miR-602, hsa-miR-129-5p, has-miR-210, hsa-miR-671-5p, hsa-miR-30b*, and hsa-miR-572) were upregulated more than two-fold, and eight microRNAs (hsa-miR-143, hsa-miR-199a-5p, has-miR-195, hsa-miR-27a, hsa-miR-99a, hsa-miR-519e, has-miR -130a and hsa-miR-597) were downregulated in the liver tissue taken from patients with HBV-induced cirrhosis or HBV-related hepatocellular carcinoma. Though these identified microRNAs showed significant differential expression between normal liver tissue and HBV-related hepatocellular carcinoma tissue and cirrhotic tissue, they exhibited no significant differential expression between HBV-related hepatocellular carcinoma tissue and cirrhotic tissue.

CONCLUSION: HBV-related hepatocarcinogenesis is associated with the change in the expression profile of microRNAs.

miR-331-3p regulates ERBB-2 expression and androgen receptor signaling in prostate cancer

MicroRNAs (miRNAs) are short, non-coding RNAs that regulate gene expression and are aberrantly expressed in human cancer. The ERBB-2 tyrosine kinase receptor is frequently overexpressed in prostate cancer and is associated with disease progression and poor survival. We have identified two specific miR-331-3p target sites within the ERBB-2 mRNA 3'-untranslated region and show that miR-331-3p expression is decreased in prostate cancer tissue relative to normal adjacent prostate tissue. Transfection of multiple prostate cancer cell lines with miR-331-3p reduced ERBB-2 mRNA and protein expression and blocked downstream phosphatidylinositol 3-kinase/AKT signaling. Furthermore, miR-331-3p transfection blocked the androgen receptor signaling pathway in prostate cancer cells, reducing activity of an androgen-stimulated prostate-specific antigen promoter and blocking prostate-specific antigen expression. Our findings provide insight into the regulation of ERBB-2 expression in cancer and suggest that miR-331-3p has the capacity to regulate signaling pathways critical to the development and progression of prostate cancer cells.

MicroRNAs: novel regulators in the hallmarks of human cancer

MicroRNAs (miRNAs) are small non-coding RNAs of 18-25 nucleotides in length that function as negative regulators. miRNAs post-transcriptionally regulate gene expression by either inhibiting mRNA translation or inducing mRNA degradation, and participate in a wide variety of physiological and pathological cellular processes. Recent reports have revealed that the deregulation of miRNAs correlates with various human cancers and is involved in the initiation and progression of human cancers. miRNAs can act as oncogenes or tumor suppressors to inhibit the expression of cancer-related target genes and to promote or suppress tumorigenesis in various tissues. Therefore, abnormal miRNA expression can be regarded as a common feature of human cancers, and the identification of miRNAs and their respective targets may provide potential diagnostic and prognostic tumor biomarkers and new therapeutic strategies to treat cancers. In the present review, we discuss the emerging roles of miRNAs in the hallmarks of human cancers.

The role of microRNA-221 and microRNA-222 in androgen-independent prostate cancer cell lines

Androgen-dependent prostate cancer typically progresses to castration-resistant prostate cancer (CRPC) after the androgen deprivation therapy. MicroRNAs (miR) are noncoding small RNAs (19-25nt) that play an important role in the regulation of gene expression. Recent studies have shown that miR expression patterns are significantly different in normal and neoplastic prostate epithelial cells. However, the importance of miRs in the development of CRPC has not yet been explored. By performing genome-wide expression profiling of miRs, we found that expression levels of several miRs, in particular miR-221 and miR-222, were significantly increased in CRPC cells (the LNCaP-derived cell line LNCaP-Abl), compared with those in the androgen-dependent prostate cancer cell line (LNCaP). Overexpression of miR-221 or miR-222 in LNCaP or another androgen-dependent cell line, LAPC-4, significantly reduced the level of the dihydrotestosterone (DHT) induced up-regulation of prostate-specific antigen (PSA) expression and increased androgen-independent growth of LNCaP cells. Knocking down the expression level of miR-221 and miR-222 with antagonist miRs in the LNCaP-Abl cell line restored the response to the DHT induction of PSA transcription and also increased the growth response of the LNCaP-Abl cells to the androgen treatment. Changing the expression level of p27/kip1, a known target of miR-221 and miR-222, alone in LNCaP cells affected the DHT-independent cell growth but did not significantly influence the response of PSA transcription to the DHT treatment. In conclusion, our data suggest the involvement of miR-221 and miR-222 in the development or maintenance of the CRPC phenotype.

MicroRNAs--the micro steering wheel of tumour metastases

Recently, microRNAs (miRNAs) have been discovered to have a role in metastasis. Here we describe how miRNAs are involved in advanced stages of tumour progression, stressing their roles as metastasis activators or suppressors, and discuss their possible use in the clinic as predictive markers and as therapeutic strategies for patients with metastases. Furthermore, we develop the concept that the same miRNAs could be involved both in the cancer stem cell phenotype and in the ability of specific cancer cells to produce metastases, thus representing a mechanistic link between the initial and the final steps of tumorigenesis.

Expression of MicroRNA-146a in osteoarthritis cartilage

OBJECTIVE

A role of microRNA, which are approximately 22-nucleotide noncoding RNAs, has recently been recognized in human diseases. The objective of this study was to identify the expression pattern of microRNA-146a (miR-146a) in cartilage from patients with osteoarthritis (OA).

METHODS

The expression of miR-146a in cartilage from 15 patients with OA was analyzed by quantitative reverse transcription-polymerase chain reaction (RT-PCR) and by in situ hybridization. Induction of the expression of miR-146a by cultures of normal human articular chondrocytes following stimulation with interleukin-1beta (IL-1beta) was examined by quantitative RT-PCR.

RESULTS

All cartilage samples were divided into 3 groups according to a modification of the Mankin score (grade I = mild OA scored 0-5, grade II = moderate OA scored 6-10, and grade III = severe OA scored 11-14). In grade I OA cartilage samples, the expression of miR-146a and COL2A1 was significantly higher than that in the other groups (P < 0.05). In grades II and III OA cartilage, the expression of miR-146a and COL2A1 was decreased, whereas the expression of matrix metalloproteinase 13 (MMP-13) was elevated in grade II OA cartilage. These data showed that miR-146a is expressed intensely in cartilage with a low Mankin grade and that miR-146a expression decreases in parallel with the level of MMP-13 expression. Tissue section in situ hybridization of primary miR-146a (pri-miR-146a) revealed that pri-miR-146a was expressed in chondrocytes residing in all tissue layers, especially in the superficial layer, where it was intensely expressed. The expression of miR-146 was markedly elevated by IL-1beta stimulation in human chondrocytes in vitro.

CONCLUSION

This study shows that miR-146 is intensely expressed in low-grade OA cartilage and that its expression is induced by stimulation of IL-1beta. Thus, miR-146 might play a role in OA cartilage pathogenesis.

miR-34a inhibits migration and invasion by down-regulation of c-Met expression in human hepatocellular carcinoma cells

Several studies have shown that miR-34a represses the expression of many genes and induces G1 arrest, apoptosis, and senescence. In the present study, we identified the role of miR-34a in the regulation of tumor cell scattering, migration, and invasion. Down-regulation of miR-34a expression was highly significant in 19 of 25 (76%) human hepatocellular carcinoma (HCC) tissues compared with adjacent normal tissues and associated with the metastasis and invasion of tumors. Furthermore, resected normal/tumor tissues of 25 HCC patients demonstrated an inverse correlation between miR-34a and c-Met-protein. In HepG2 cells, ectopic expression of miR-34a potently inhibited tumor cell migration and invasion in a c-Met-dependent manner. miR-34a directly targeted c-Met and reduced both mRNA and protein levels of c-Met; thus, decreased c-Met-induced phosphorylation of extracellular signal-regulated kinases 1 and 2 (ERK1/2). Taken together, these results provide evidence to show the suppression role of miR-34a in tumor migration and invasion through modulation of the c-Met signaling pathway.

microRNA-146b inhibits glioma cell migration and invasion by targeting MMPs

MicroRNAs (miRNAs) are a class of endogenous, small non-protein coding single-stranded RNA molecules, which are crucial post-transcriptional regulators of gene expression. Previous studies have shown that miRNAs participate in a wide range of biological functions and play important roles in various human diseases including glioma. However, the role of miRNAs in mediating glioblastoma cell migration and invasion has not been elucidated. Using miRNA microarray, we identified miR-146b as one of the miRNAs that is significantly dysregulated in human glioblastoma tissue. We showed that miR-146b overexpression by transfection with the precursor miR-146b, or knock-down by Locked Nucleic Acid (LNA)-modified anti-miR-146b, has no effect on the growth of human glioblastoma U373 cells. However, precursor miR-146b transfection significantly reduced the migration and invasion of U373 cells, while LNA-anti-miR-146b transfection generated the opposite result. Furthermore, we discovered that a matrix metalloproteinase gene, MMP16, is one of the downstream targets of miR-146b. Taken together, our findings suggest that miR-146b is involved in glioma cell migration and invasion by targeting MMPs, and implicate miR-146b as a metastasis-inhibiting miRNA in glioma.

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.

MicroRNAs and cancer: current state and future perspectives in urologic oncology

MicroRNAs (miRNAs) are small non-protein coding RNAs that regulate basic cellular processes and are associated with cancer characteristics. It is the aim of this review to describe the basics of the biogenesis and function of miRNAs, provide their role in tumorigenesis, and demonstrate their clinical potential in general and especially in urologic oncology. For that purpose, a PubMed search up to August 2008 was conducted using the Medical Subject Heading (MeSH) terms for miRNAs alone and the urological carcinomas of kidney, prostate, bladder, testis, and penis combined with the Boolean operator "AND". Until August 2008, about 3,500 miRNA publications were included in the PubMed database. It has been estimated that about 1,500 would be published in 2008 alone. Several miRNA expression studies and corresponding functional experiments in various cancers showed the important role of miRNAs in cancer initiation and progression and proved their potential as diagnostic, prognostic, and predictive biomarkers and as basis for novel therapeutic strategies. However, in uro-oncology, only a few miRNA related articles (22 for prostate, 4 for kidney, 3 for bladder, and 6 for testis) were published. Cancer-specific expressions of miRNA patterns were shown, but the limited and partly inconsistent data underscore that we are at an early stage regarding this topic in urology. In spite of the obvious significance of miRNAs in malignant tumors, the relatively sparse data on miRNAs in uro-oncology clearly advocate that this area should be more intensively studied. Detailed understanding of the characteristic miRNA abnormalities could contribute to novel approaches in diagnosis and treatment of urological tumors.

Beyond HPV: oncomirs as new players in cervical cancer

MicroRNAs (miRNAs) are a recently discovered family of 18-24 nucleotide non-coding RNAs that can negatively regulate target mRNAs. All studied multicellular eukaryotes utilize miRNAs to regulate basic cellular functions including proliferation, differentiation, and death. It is now apparent that abnormal miRNA expression is a common feature of human malignancies. This review discusses the various cancer-relevant miRNAs (oncomirs) especially in cervical tumorigenesis and the potential role of oncomirs as therapeutic agents and targets for the treatment of cervical cancer.

MicroRNA profile analysis of human prostate cancers

We examined the microRNA (miRNA) expression profile of 40 prostatectomy specimens from stage T2a/b, early relapse and non-relapse cancer patients, to better understand the relationship between miRNA dysregulation and prostate oncogenesis. Paired analysis was carried out with microdissected, malignant and non-involved areas of each specimen, using high-throughput liquid-phase hybridization (mirMASA) reactions and 114 miRNA probes. Five miRNAs (miR-23b, -100, -145, -221 and -222) were significantly downregulated in malignant tissues, according to significance analysis of microarrays and paired t-test with Bonferroni correction. Lowered expression of miR-23b, -145, -221 and -222 in malignant tissues was validated by quantitative reverse transcription (qRT)-PCR analyses. Ectopic expression of these miRNAs significantly reduced LNCaP cancer cell growth, suggesting growth modulatory roles for these miRNAs. Patient subset analysis showed that those with post-surgery elevation of prostate-specific antigen (chemical relapse) displayed a distinct expression profile of 16 miRNAs, as compared with patients with non-relapse disease. A trend of increased expression (>40%) of miR-135b and miR-194 was observed by qRT-PCR confirmatory analysis of 11 patients from each clinical subset. These findings indicate that an altered miRNA expression signature accompanied the prostate oncogenic process. Additional, aberrant miRNA expression features may reflect a tendency for early disease relapse. Growth inhibition through the reconstitution of miRNAs is potentially applicable for experimental therapy of prostate cancer, pending molecular validation of targeted genes.

MicroRNAs: new regulators of immune cell development and function

Decades of research went into understanding immune cell development and function without awareness that consideration of a key element, microRNA (miRNA), was lacking. The discovery of miRNAs as regulators of developmental events in model organisms suggested to many investigators that miRNA might be involved in the immune system. In the past few years, widespread examination of this possibility has produced notable results. Results have shown that miRNAs affect mammalian immune cell differentiation, the outcome of immune responses to infection and the development of diseases of immunological origin. Some miRNAs repress expression of target proteins with well established functions in hematopoiesis. Here we bring together much of this work, which has so far only scratched the surface of this very fertile field of investigation, and show how the results illuminate many historic questions about hematopoiesis and immune function.

Alterations in microRNA expression contribute to fatty acid-induced pancreatic beta-cell dysfunction

OBJECTIVE

Visceral obesity and elevated plasma free fatty acids are predisposing factors for type 2 diabetes. Chronic exposure to these lipids is detrimental for pancreatic beta-cells, resulting in reduced insulin content, defective insulin secretion, and apoptosis. We investigated the involvement in this phenomenon of microRNAs (miRNAs), a class of noncoding RNAs regulating gene expression by sequence-specific inhibition of mRNA translation.

RESEARCH DESIGN AND METHODS

We analyzed miRNA expression in insulin-secreting cell lines or pancreatic islets exposed to palmitate for 3 days and in islets from diabetic db/db mice. We studied the signaling pathways triggering the changes in miRNA expression and determined the impact of the miRNAs affected by palmitate on insulin secretion and apoptosis.

RESULTS

Prolonged exposure of the beta-cell line MIN6B1 and pancreatic islets to palmitate causes a time- and dose-dependent increase of miR34a and miR146. Elevated levels of these miRNAs are also observed in islets of diabetic db/db mice. miR34a rise is linked to activation of p53 and results in sensitization to apoptosis and impaired nutrient-induced secretion. The latter effect is associated with inhibition of the expression of vesicle-associated membrane protein 2, a key player in beta-cell exocytosis. Higher miR146 levels do not affect the capacity to release insulin but contribute to increased apoptosis. Treatment with oligonucleotides that block miR34a or miR146 activity partially protects palmitate-treated cells from apoptosis but is insufficient to restore normal secretion.

CONCLUSIONS

Our findings suggest that at least part of the detrimental effects of palmitate on beta-cells is caused by alterations in the level of specific miRNAs.

MicroRNAs in development and disease

Since the discovery of microRNAs (miRNAs) in Caenorhabditis elegans, mounting evidence illustrates the important regulatory roles for miRNAs in various developmental, differentiation, cell proliferation, and apoptosis pathways of diverse organisms. We are just beginning to elucidate novel aspects of RNA mediated gene regulation and to understand how heavily various molecular pathways rely on miRNAs for their normal function. miRNAs are small non-protein-coding transcripts that regulate gene expression post-transcriptionally by targeting messenger RNAs (mRNAs). While individual miRNAs have been specifically linked to critical developmental pathways, the deregulated expression of many miRNAs also has been shown to have functional significance for multiple human diseases, such as cancer. We continue to discover novel functional roles for miRNAs at a rapid pace. Here, we summarize some of the key recent findings on miRNAs, their mode of action, and their roles in both normal development and in human pathology. A better understanding of how miRNAs operate during the normal life of a cell as well as in the pathogenesis of disease when deregulated will provide new avenues for diagnostic, prognostic, and therapeutic applications.