microRNAs in cancer: from bench to bedside

The association of miR-204 and mir-483 5p expression with clinicopathological features of Wilms tumor: Could this provide foresight?

BACKGROUND

Wilms tumor is the most common cancer of the kidney that occurs during childhood, and histologically, it mimics renal embryogenesis. With the development and improvement of up-to-date treatment protocols, the survival rates of Wilms tumor have increased. However, metastases or local relapses are still observed in 15% of patients. The search for reliable biomarkers to identify at-risk patients is ongoing to predict the variability in treatment success. Currently, the evaluation of clinical, histopathological and genetic features are common diagnostic methods; however, epigenetic features can be examined with microRNA expression analyses and might allow us to comment on the behavior of the tumor and treatment response.

METHODS

In this study, we aimed to evaluate the relationship between microRNA-204 and microRNA-483-5p expression with clinicopathological data and the effect on Wilms tumor survival. For this purpose, the expression levels of RNU6B, microRNA-204 and microRNA-483-5p were evaluated in tumor and normal tissue by qreal time-polymerase chain reaction. We also investigated the relationship between microRNA expression levels with the clinicopathological and histological features of Wilms tumor.

RESULTS AND CONCLUSION

The results of our study indicate that the relative expression levels of microRNA-204 in Wilms tumor tissues were significantly lower than that in adjacent normal tissues. By contrast, tumor tissue had a higher microRNA-483-5p expression than the corresponding normal tissues. A statistically significant difference between microRNA-204 expression level with age and the presence of anaplasia was observed. The upregulation of microRNA-483-5p was found to have a significant correlation with patients after preoperative chemotherapy and complete tumor necrosis. Taken together, our data suggest that microRNA-204 could play a critical role as a tumor suppressor, whereas microRNA-483-5p acts as an oncogene in Wilms tumor progression. More importantly, microRNA-204 might be a novel predictive biomarker for anaplastic histology and could be useful for developing therapeutic interventions targeting this marker.

Exosomal miR-21-5p derived from bone marrow mesenchymal stem cells promote osteosarcoma cell proliferation and invasion by targeting PIK3R1

Mesenchymal stem cells (MSCs) are a class of pluripotent cells that can release a large number of exosomes which act as paracrine mediators in tumour-associated microenvironment. However, the role of MSC-derived exosomes in pathogenesis and progression of cancer cells especially osteosarcoma has not been thoroughly clarified until now. In this study, we established a co-culture model for human bone marrow-derived MSCs with osteosarcoma cells, then extraction of exosomes from induced MSCs and study the role of MSC-derived exosomes in the progression of osteosarcoma cell. The aim of this study was to address potential cell biological effects between MSCs and osteosarcoma cells. The results showed that MSC-derived exosomes can significantly promote osteosarcoma cells' proliferation and invasion. We also found that miR-21-5p was significantly over-expressed in MSCs and MSC-derived exosomes by quantitative real-time polymerase chain reaction (qRT-PCR), compared with human foetal osteoblastic cells hFOB1.19. MSC-derived exosomes transfected with miR-21-5p could significantly enhance the proliferation and invasion of osteosarcoma cells in vitro and in vivo. Bioinformatics analysis and dual-luciferase reporter gene assays validated the targeted relationship between exosomal miR-21-5p and PIK3R1; we further demonstrated that miR-21-5p-abundant exosomes derived human bone marrow MSCs could activate PI3K/Akt/mTOR pathway by suppressing PIK3R1 expression in osteosarcoma cells. In summary, our study provides new insights into the interaction between human bone marrow MSCs and osteosarcoma cells in tumour-associated microenvironment.

The miR-361-3p increases enzalutamide (Enz) sensitivity via targeting the ARv7 and MKNK2 to better suppress the Enz-resistant prostate cancer

The androgen receptor splicing variant 7 (ARv7) that lacks the ligand-binding domain is increasingly considered as a key player leading to enzalutamide (Enz) resistance in patients with prostate cancer (PCa). However, the detailed mechanisms of how ARv7 expression is regulated and whether it also needs other factors to induce maximal Enz resistance remain unclear. Here, we identified a microRNA, miR-361-3p, whose expression is lower in patients with recurrent PCa, could function via binding to the 3'UTR of ARv7, but not the wild type of AR, to suppress its expression to increase the Enz sensitivity. Importantly, we found that miR-361-3p could also bind to the 3'UTR of MAP kinase-interacting serine/threonine kinase 2 (MKNK2) to suppress its expression to further increase the Enz sensitivity. In turn, the increased Enz can then function via a feedback mechanism through altering the HIF-2α/VEGFA signaling to suppress the expression of miR-361-3p under hypoxia conditions. Preclinical studies using an in vivo mouse model with orthotopically xenografted CWR22Rv1 cells demonstrated that combining the Enz with the small molecule miR-361-3p would result in better suppression of the Enz-resistant PCa tumor progression. Together, these preclinical studies demonstrate that miR-361-3p can function via suppressing the expression of ARv7 and MKNK2 to maximally increase the Enz sensitivity, and targeting these newly identified Enz/miR-361-3p/ARv7 and/or Enz/miR-361-3p/MKNK2 signals with small molecules may help in the development of novel therapies to better suppress the CRPC in patients that already have developed the Enz resistance.

Salivary microRNAs identified by small RNA sequencing as potential predictors of response to intensity-modulated radiotherapy in head and neck cancer patients

PURPOSE

Progress in radiation therapy of head and neck squamous cell carcinomas (HNSCCs) is logically linked to the development of molecular predictors that would help to enhance individually tailored treatment. MicroRNA (miRNA) expression profiles in tumors have repeatedly been tested to optimize the molecular diagnostics of HNSCC. In addition to tumor tissues, miRNAs are stably present in body fluids, including saliva, and can thus be collected non-invasively. The aim of our current study was to evaluate whether salivary miRNAs have potential as response predictors in HNSCC patients treated with intensity modulated radiation therapy (IMRT).

METHODS

In total 48 HNSCC patients treated by definitive IMRT were enrolled in our prospective study. To identify predictive salivary miRNAs, we used small RNA sequencing in 14 saliva samples of HNSCC patients and qRT-PCR validation of selected miRNA candidates in an independent set of 34 patients.

RESULTS

We found that salivary miR-15a-5p and miR-15b-5p exhibited differential levels between patients with and without complete remission (p = 0.025 and p = 0.028, respectively). Subsequent Kaplan-Meier analysis confirmed that patients with higher levels of miR-15a-5p reached a significantly longer locoregional progression-free survival (LPFS) than those with low levels (p = 0.024). Finally, multivariate Cox regression analysis revealed that miR-15a-5p may serve as an independent predictive biomarker of LPFS in HNSCC patients treated with IMRT (HR 0.104; 95% CI 0.004-0.911; p = 0.04).

CONCLUSIONS

We conclude that salivary miR-15a-5p may represent a potential biomarker for individualized treatment decision-making in HNSCC patients.

microRNAs in the haemostatic system: More than witnesses of thromboembolic diseases?

MicroRNAs (miRNAs) are small endogenous RNAs that post-transcriptionally regulate gene expression. In the last few years, these molecules have been implicated in the regulation of haemostasis, and an increasing number of studies have investigated their relationship with the development of thrombosis. In this review, we discuss the latest developments regarding the role of miRNAs in the regulation of platelet function and secondary haemostasis. We also discuss the genetic and environmental factors that regulate miRNAs. Finally, we address the potential use of miRNAs as prognostic and diagnostic tools in thrombosis.

Detection of Plasma MicroRNA Signature in Osteosarcoma Patients

Circulating microRNAs are increasingly being used as noninvasive prognostic and predictive biomarkers for various types of cancer. We describe a method that uses real-time quantitative PCR (qPCR) for establishing a signature plasma microRNA profile that can distinguish patients with osteosarcoma from healthy control samples.

The role of MicroRNA molecules and MicroRNA-regulating machinery in the pathogenesis and progression of epithelial ovarian cancer

MicroRNA molecules are small, single-stranded RNA molecules that function to regulate networks of genes. They play important roles in normal female reproductive tract biology, as well as in the pathogenesis and progression of epithelial ovarian cancer. DROSHA, DICER, and Argonaute proteins are components of the microRNA-regulatory machinery and mediate microRNA production and function. This review discusses aberrant expression of microRNA molecules and microRNA-regulating machinery associated with clinical features of epithelial ovarian cancer. Understanding the regulation of microRNA molecule production and function may facilitate the development of novel diagnostic and therapeutic strategies to improve the prognosis of women with epithelial ovarian cancer. Additionally, understanding microRNA molecules and microRNA-regulatory machinery associations with clinical features may influence prevention and early detection efforts.

Decreased expression of let-7c is associated with non-response of muscle-invasive bladder cancer patients to neoadjuvant chemotherapy

The identification and development of biomarkers which predict response of muscle invasive bladder cancer (MIBC) patients to neoadjuvant chemotherapy would likely increase usage of this treatment option and thereby improve patient survival rates. MiRNA array and qRT-PCR validation was used to identify miRNA which are associated with response to neoadjuvant chemotherapy. RNA was extracted from a total of 41 archival, fully annotated, MIBC patient diagnostic biopsies (20 chemo-responders and 21 non-responders (response is defined as > 5 year survival rate and being pT0 post-chemotherapy)). Microarray and qPCR identified let-7c as being differentially expressed in chemo-responder versus non-responder patients. Patients with higher let-7c expression levels had significantly higher odds of responding to chemotherapy (p = 0.023, OR 2.493, 95% CI 1.121, 5.546), and assessment of let-7c levels allowed for prediction of patient response (AUC 0.72, positive predictive value 59%). Decreased let-7c was associated with MIBC incidence (p < 0.001), and significantly correlated with other related miRNA including those that were not differentially expressed between responders and non-responders. The combined data indicate let-7c plays a role in mediating chemoresistance to neoadjuvant chemotherapy in MIBC patients, and is a modest, yet clinically meaningful, predictor of patient response.

Combining miRNA and mRNA Expression Profiles in Wilms Tumor Subtypes

Wilms tumor (WT) is the most common childhood renal cancer. Recent findings of mutations in microRNA (miRNA) processing proteins suggest a pivotal role of miRNAs in WT genesis. We performed miRNA expression profiling of 36 WTs of different subtypes and four normal kidney tissues using microarrays. Additionally, we determined the gene expression profile of 28 of these tumors to identify potentially correlated target genes and affected pathways. We identified 85 miRNAs and 2107 messenger RNAs (mRNA) differentially expressed in blastemal WT, and 266 miRNAs and 1267 mRNAs differentially expressed in regressive subtype. The hierarchical clustering of the samples, using either the miRNA or mRNA profile, showed the clear separation of WT from normal kidney samples, but the miRNA pattern yielded better separation of WT subtypes. A correlation analysis of the deregulated miRNA and mRNAs identified 13,026 miRNA/mRNA pairs with inversely correlated expression, of which 2844 are potential interactions of miRNA and their predicted mRNA targets. We found significant upregulation of miRNAs-183, -301a/b and -335 for the blastemal subtype, and miRNAs-181b, -223 and -630 for the regressive subtype. We found marked deregulation of miRNAs regulating epithelial to mesenchymal transition, especially in the blastemal subtype, and miRNAs influencing chemosensitivity, especially in regressive subtypes. Further research is needed to assess the influence of preoperative chemotherapy and tumor infiltrating lymphocytes on the miRNA and mRNA patterns in WT.

miR-124 and Androgen Receptor Signaling Inhibitors Repress Prostate Cancer Growth by Downregulating Androgen Receptor Splice Variants, EZH2, and Src

miR-124 targets the androgen receptor (AR) transcript, acting as a tumor suppressor to broadly limit the growth of prostate cancer. In this study, we unraveled the mechanisms through which miR-124 acts in this setting. miR-124 inhibited proliferation of prostate cancer cells in vitro and sensitized them to inhibitors of androgen receptor signaling. Notably, miR-124 could restore the apoptotic response of cells resistant to enzalutamide, a drug approved for the treatment of castration-resistant prostate cancer. We used xenograft models to examine the effects of miR-124 in vivo when complexed with polyethylenimine-derived nanoparticles. Intravenous delivery of miR-124 was sufficient to inhibit tumor growth and to increase tumor cell apoptosis in combination with enzalutamide. Mechanistic investigations revealed that miR-124 directly downregulated AR splice variants AR-V4 and V7 along with EZH2 and Src, oncogenic targets that have been reported to contribute to prostate cancer progression and treatment resistance. Taken together, our results offer a preclinical rationale to evaluate miR-124 for cancer treatment.

Cross-species identification of a plasma microRNA signature for detection, therapeutic monitoring, and prognosis in osteosarcoma

Osteosarcoma (OS) is the primary bone tumor in children and young adults. Currently, there are no reliable, noninvasive biologic markers to detect the presence or progression of disease, assess therapy response, or provide upfront prognostic insights. MicroRNAs (miRNAs) are evolutionarily conserved, stable, small noncoding RNA molecules that are key posttranscriptional regulators and are ideal candidates for circulating biomarker development due to their stability in plasma, ease of isolation, and the unique expressions associated with specific disease states. Using a qPCR-based platform that analyzes more than 750 miRNAs, we analyzed control and diseased-associated plasma from a genetically engineered mouse model of OS to identify a profile of four plasma miRNAs. Subsequent analysis of 40 human patient samples corroborated these results. We also identified disease-specific endogenous reference plasma miRNAs for mouse and human studies. Specifically, we observed plasma miR-205-5p was decreased 2.68-fold in mice with OS compared to control mice, whereas, miR-214, and miR-335-5p were increased 2.37- and 2.69-fold, respectively. In human samples, the same profile was seen with miR-205-5p decreased 1.75-fold in patients with OS, whereas miR-574-3p, miR-214, and miR-335-5p were increased 3.16-, 8.31- and 2.52-fold, respectively, compared to healthy controls. Furthermore, low plasma levels of miR-214 in metastatic patients at time of diagnosis conveyed a significantly better overall survival. This is the first study to identify plasma miRNAs that could be used to prospectively identify disease, potentially monitor therapeutic efficacy and have prognostic implications for OS patients.

MicroRNAs in hemostasis

Epidemiologic studies have revealed that modification of the levels of individual components of the hemostatic system may have effects on the development of thrombosis or hemorrhage. To maintain the necessary equilibrium, the hemostatic system is finely regulated. It is known that acquired factors and/or alterations in genes (single-nucleotide polymorphisms or mutations) may be the cause of interindividual differences or exacerbated levels of hemostatic proteins in plasma, but there are still many non-characterized factors that provoke such variations. The search for new elements, such as microRNAs (miRNAs), a family of small non-coding RNAs that are novel regulators of protein expression, may reveal an additional layer at which to investigate the causes of hemostatic diseases. In this review, we discuss the latest developments in research into the role of miRNAs in the regulation of several hemostatic factors, and the potential use of miRNAs as prognostic or diagnostic tools in hemostasis and thrombosis.

Quantitative assessment of miR34a as an independent prognostic marker in breast cancer

Background:

Aberrant expression of microRNAs (miRNAs) is associated with cancer progression, initiation and metastasis. MiR34a is a miRNA that has been previously described as a tumour suppressor. Herein, we assess the expression of miR34a in three independent breast cancer cohorts using a quantitative in situ hybridisation assay (qISH) and determined its association with disease-specific death in breast cancer.

Methods:

The qISH method was applied to three independent primary breast cancer cohorts (Cohort 1 with 461, Cohort 2 with 279 and Cohort 3 with 795 patients) using 5′ and 3′ double DIG-labelled LNA-modified probe against miR34a using the protocol described previously. Level of expression measured as automated quantitative analysis (AQUA) score for miR34a was determined for each patient and assessed for association with risk of disease-specific death. An optimal cutpoint was determined using the X-tile software for disease-specific survival in Cohort 1 and this cutpoint was then applied to the other two cohorts after median normalisation of AQUA scores.

Results:

Loss of miR34a is associated with poor outcome in three independent breast cancer cohorts (uncorrected log-rank P=0.0188 for Cohort 1, log-rank P=0.0024 for Cohort 2 and log-rank P=0.0455 for Cohort 3). In all three cohorts, loss of miR34a is able to stratify patients with poor disease-specific survival among node-negative patients, but not in node-positive population. Multivariate Cox proportional hazards analysis in Cohort 1 (P=0.0381) and Cohort 2 (P=0.0468) revealed that loss of miR34a is associated with poor outcome, independent of age, node status, receptor status and tumour size.

Conclusion:

Loss of the tumour suppressor, miR34a, identifies a subgroup of breast cancer patients with poor disease-specific survival. This study is consistent with the well-established preclinical observations for miR34a as a tumour suppressor and suggests that miR34a may have future value as a biomarker in breast cancer.

miR-200c inhibits invasion, migration and proliferation of bladder cancer cells through down-regulation of BMI-1 and E2F3

Background

MicroRNA-200c (miR-200c) is one of the short noncoding RNAs that play crucial roles in tumorigenesis and tumor progression. It also acts as considerable modulator in the process of epithelial-to-mesenchymal transition (EMT), a cell development regulating process that affects tumor development and metastasis. However, the role of miR-200c in bladder cancer cells and its mechanism has not been well studied. The purpose of this study was to determine the potential role of miR-200c in regulating EMT and how it contributed to bladder cancer cells in invasion, migration and proliferation.

Methods

Real-time reverse transcription-PCR was used to identify and validate the differential expression of MiR-200c involved in EMT in 4 bladder cancer cell lines and clinical specimens. A list of potential miR-200 direct targets was identified through the TargetScan database. The precursor of miR-200c was over-expressed in UMUC-3 and T24 cells using a lentivirus construct, respectively. Protein expression and signaling pathway modulation were validated through Western blot analysis and confocal microscopy, whereas BMI-1 and E2F3, direct target of miR-200c, were validated by using the wild-type and mutant 3′-untranslated region BMI-1/E2F3 luciferase reporters.

Results

We demonstrate that MiR-200c is down-regulated in bladder cancer specimens compared with adjacent ones in the same patient. Luciferase assays showed that the direct down-regulation of BMI-1 and E2F3 were miR-200c-dependent because mutations in the two putative miR-200c-binding sites have rescued the inhibitory effect. Over-expression of miR-200c in bladder cancer cells resulted in significantly decreased the capacities of cell invasion, migration and proliferation. miR-200c over-expression resulted in conspicuous down-regulation of BMI-1and E2F3 expression and in a concomitant increase in E-cadherin levels.

Conclusions

miR-200c appears to control the EMT process through BMI-1 in bladder cancer cells, and it inhibits their proliferation through down-regulating E2F3. The targets of miR-200c include BMI-1 and E2F3, which are a novel regulator of EMT and a regulator of proliferation, respectively.

Electronic supplementary material

The online version of this article (doi:10.1186/s12967-014-0305-z) contains supplementary material, which is available to authorized users.

Differentially expressed miRNAs in cancer-stem-like cells: markers for tumor cell aggressiveness of pancreatic cancer

Pancreatic cancer (PC) is one of the most deadly cancers. The higher mortality is in part due to treatment resistance and early onset of metastasis. The existence of cancer-stem-like cells (CSLCs) has been widely accepted to be responsible for tumor aggressiveness in PC. Emerging evidence suggests that CSLCs have the capacity for increased cell growth, cell migration/invasion, metastasis, and treatment resistance, which leads to poor clinical outcome. However, the molecular role of CSLCs in tumor development and progression is poorly understood. Therefore, mechanistic understanding, and targeted killing of CSLCs may provide a newer therapeutic strategy for the treatment of PC. It has been well accepted that microRNAs (miRNAs) play critical roles during tumor development and progression through deregulation of multiple genes. Moreover, deregulated expression of miRNAs may also play a key role in the regulation of CSLC characteristics and functions. Here we show that isolated CD44(+)/CD133(+)/EpCAM(+) cells (triple-marker-positive cells) from human PC cell lines, MiaPaCa-2 and L3.6pl cells, display aggressive characteristics, such as increased cell growth, clonogenicity, cell migration, and self-renewal capacity, which is consistent with overexpression of CSLC signatures/markers. We also found deregulated expression of over 400 miRNAs, including let-7, miR-30, miR-125b, and miR-335, in CSLCs. As a proof-of-concept, knockdown of miR-125b resulted in the inhibition of tumor cell aggressiveness of CSLCs (triple-marker-positive cells), consistent with the downregulation of CD44, EpCAM, EZH2, and snail. These results clearly suggest the importance of miRNAs in the regulation of CSLC characteristics, and may serve as novel targets for therapy.

Epigenetic control of autophagy by microRNAs in ovarian cancer

Autophagy is a lysosomal-driven catabolic process that contributes to the preservation of cell homeostasis through the regular elimination of cellular damaged, aged, and redundant molecules and organelles. Autophagy plays dual opposite roles in cancer: on one hand it prevents carcinogenesis; on the other hand it confers an advantage to cancer cells to survive under prohibitive conditions. Autophagy has been implicated in ovarian cancer aggressiveness and in ovarian cancer cell chemoresistance and dormancy. Small noncoding microRNAs (miRNAs) regulate gene expression at posttranscriptional level, thus playing an important role in many aspects of cell pathophysiology, including cancerogenesis and cancer progression. Certain miRNAs have recently emerged as important epigenetic modulators of autophagy in cancer cells. The mRNA of several autophagy-related genes contains, in fact, the target sequence for miRNAs belonging to different families, with either oncosuppressive or oncogenic activities. MiRNA profiling studies have identified some miRNAs aberrantly expressed in ovarian cancer tissues that can impact autophagy. In addition, plasma and stroma cell-derived miRNAs in tumour-bearing patients can regulate the expression of relevant autophagy genes in cancer cells. The present review focuses on the potential implications of miRNAs regulating autophagy in ovarian cancer pathogenesis and progression.

The role of microRNAs in melanoma

Melanoma is the most dangerous form of skin cancer, being largely resistant to conventional therapies at advanced stages. Understanding the molecular mechanisms behind this disease might be the key for the development of novel therapeutic strategies. MicroRNAs (miRNAs) are small non-coding RNAs that post-transcriptionally control gene expression, thereby regulating various cellular signaling pathways involved in the initiation and progression of different cancer types, including melanoma. In this review, we summarize approaches for the identification of candidate miRNAs and their target genes and review the functions of miRNAs in melanoma. Finally, we highlight the recent progress in pre-clinical use of miRNAs as prognostic markers and therapeutic targets.

The rejuvenated scenario of epithelial-mesenchymal transition (EMT) and cancer metastasis

The molecular mechanisms underlying cancer progression and metastasis are still poorly understood. In recent years, the epithelial-to-mesenchymal transition (EMT), a traditional phenomenon revealed in embryonic development, has been gradually accepted as a potential mechanism underlying cancer progression and metastasis. Many cell signaling pathways involved in development have been shown to contribute to EMT. An increasing number of genetic and epigenetic elements have been discovered, and their cross-talk relationship in EMT remains to be explored. In addition, accumulating experimental evidence suggests that EMT plays a critical role in different aspects of cancer progression, such as metastasis, stem cell traits, and chemoresistance. However, there are some disagreements and debate about these studies, which raise critical questions worthy of further investigation. Solving these questions will lead to a more complete understanding of cancer metastasis. Due to the close relationship of EMT to cancer metastasis and chemoresistance, targeting EMT or reversing EMT is likely to lead to novel therapeutic approaches for the treatment of human cancers.

Gastric adenocarcinoma has a unique microRNA signature not present in esophageal adenocarcinoma

BACKGROUND

MicroRNAs (miRNAs) play critical roles in tumor development and progression. The finding that a single miRNA can regulate hundreds of genes places miRNAs at critical hubs of signaling pathways. For the current study, the authors investigated the miRNA expression profile of gastric adenocarcinomas and compared it with esophageal adenocarcinomas to better identify a unique miRNA signature of gastric adenocarcinoma.

METHODS

miRNA expression profiles were obtained using 2 different proprietary microarray platforms on primary gastric adenocarcinoma tissue samples. The cross comparison of results identified 17 up-regulated miRNAs and 12 down-regulated miRNAs that overlapped in both platforms. Quantitative real-time polymerase chain reaction was performed for independent validation of a representative set of 8 miRNAs in gastric and esophageal adenocarcinomas compared with normal gastric mucosa or esophageal mucosa, respectively.

RESULTS

The deregulation of miR-146b-5p, miR-375, miR-148a, miR-31, and miR-451 was associated significantly with gastric adenocarcinomas. Conversely, deregulation of miR-21 (up-regulation) and miR-133b (down-regulation) was detectable in both gastric and esophageal adenocarcinomas. It was noteworthy that miR-200a was significantly down-regulated in gastric adenocarcinoma samples (P = .04) but was up-regulated in esophageal adenocarcinoma samples (P = .001). In addition, the expression level of miR-146b-5p displayed a strong correlation with the tumor stage of gastric cancer.

CONCLUSIONS

Gastric adenocarcinoma displayed a unique miRNA signature that distinguished it from esophageal adenocarcinoma. This specific signature may reflect differences in the etiology and/or molecular signaling in these 2 closely related cancers. The current findings suggest important miRNA candidates that can be investigated for their biological functions and for their possible diagnostic, prognostic, and therapeutic role in gastric adenocarcinoma.

Induction of p53-inducible microRNA miR-34 by gamma radiation and bleomycin are different

microRNAs (miRNAs) are small molecules in their mature form and master regulators of gene expression. Recent work has shown that miRNAs are involved in the p53 network. Of the various miRNAs, miR-34 is regulated by the p53 protein. miR-34 can be induced by ionizing radiation (IR) in vitro and in vivo. However, there is no data in the literature for induction of miR-34 by a chemical agent inducing DNA damage. Here we studied the expression of miR-34 in HeLa and MCF-7 cells exposed to genotoxic stress-induced by bleomycin (BLM) or γ-radiation. We first analyzed p53 accumulation upon DNA damage induction. The basal level of p53 in MCF-7 cells was higher (approx. 6-fold) than in HeLa cells, and its accumulation was similar for both DNA-damaging agents in both cell lines. We have shown that miR-34 is significantly induced by γ-radiation in HeLa cells, but not in MCF-7 cells. BLM did not significantly affect miR-34 expression in both cell types. In conclusion, our findings reveal that miR-34 induction by genotoxic stress may be cell-type specific.

miR-200c inhibits melanoma progression and drug resistance through down-regulation of BMI-1

MicroRNAs (miRNAs) are short noncoding RNAs that play crucial roles in tumorigenesis and tumor progression. Melanoma is the most aggressive skin cancer that is resistant or rapidly develops resistance to a variety of chemotherapeutic agents. The role of miRNAs in melanoma progression and drug resistance has not been well studied. Herein, we demonstrate that miR-200c is down-regulated in melanomas (primary and metastatic) compared with melanocytic nevi. Overexpression of miR-200c in melanoma cells resulted in significantly decreased cell proliferation and migratory capacity as well as drug resistance. miR-200c overexpression resulted in significant down-regulation of BMI-1, ABCG2, ABCG5, and MDR1 expression and in a concomitant increase in E-cadherin levels. Knockdown of BMI-1 showed similar effects as miR-200c overexpression in melanoma cells. In addition, miR-200c overexpression significantly inhibited melanoma xenograft growth and metastasis in vivo, and this correlated with diminished expression of BMI-1 and reduced levels of E-cadherin in these tumors. The effects of miR-200c on melanoma cell proliferation and migratory capacity and on self-renewal were rescued by overexpression of Bmi-1, and the reversal of these phenotypes correlated with a reduction in E-cadherin expression and increased levels of ABCG2, ABCG5, and MDR1. Taken together, these findings demonstrate a key role for miR-200c in melanoma progression and drug resistance. These results suggest that miR-200c may represent a critical target for increasing melanoma sensitivity to clinical therapies.

[Pathobiology of the microRNA system]

MicroRNAs are approximately 22 nucleotides short, non-protein-coding RNA molecules, which bind semi-complementary to mRNA and have an inhibitory effect on protein expression. Aberrant microRNA expression is part of the molecular pathological damage in several degenerative, inflammatory and neoplastic diseases and deregulation can also be virus-associated. Apart from intracellular regulatory functions, microRNA in platelets and exosomes or bound to extracellular protein complexes can also circulate in the blood. Artificial microRNA analogues (small interference RNA/siRNA) and anti-microRNA (antagomir) are used in molecular pathological research of microRNA/mRNA interaction and it is thought that they will also be used as therapeutic agents in the future.

Loss of microRNA-205 expression is associated with melanoma progression

In this study, we used formalin-fixed paraffin-embedded melanocytic tumors to demonstrate reproducible alterations in microRNA expression in nevi compared with melanomas using a microarray platform. We validated those results in an independent set of nevi and melanomas by quantitative RT-PCR. miR-205 demonstrated a statistically significant, progressive diminution in expression from nevi to primary melanomas to metastatic melanomas. Enforced miR-205 expression in melanoma cells profoundly impairs cell motility and migration along with significantly decreased F-actin polymerization with only a modest reduction in cell proliferation. Using a xenograft model, melanoma cells overexpressing miR-205 exhibit a reduced migratory capacity compared with control tumor cells. Mechanistically, miR-205 overexpression results in decreased expression of the zinc-finger E-box binding homeobox 2 (ZEB2) mRNA and protein. This coincides with increased expression of E-cadherin mRNA and protein. Furthermore, re-introduction of ZEB2 into melanoma cells overexpressing miR-205 rescues these phenotypic effects and results in a restoration of cell migration and F-actin polymerization with a concomitant reduction in E-cadherin expression. Together, these results provide in vitro and in vivo evidence for miR-205 as a critical suppressor of melanoma cell migration.

microRNA-based cancer cell reprogramming technology

Epigenetic modifications play crucial roles in cancer initiation and development. Complete reprogramming can be achieved through the introduction of defined biological factors such as Oct4, Sox2, Klf4, and cMyc into mouse and human fibroblasts. Introduction of these transcription factors resulted in the modification of malignant phenotype behavior. Recent studies have shown that human and mouse somatic cells can be reprogrammed to become induced pluripotent stem cells using forced expression of microRNAs, which completely eliminates the need for ectopic protein expression. Considering the usefulness of RNA molecules, microRNA-based reprogramming technology may have future applications in regenerative and cancer medicine.

Evaluation of SNPs in miR-196-a2, miR-27a and miR-146a as risk factors of colorectal cancer

AIM: To investigate whether selected single nucleotide polymorphisms (SNPs) in miR-196a2, miR-27a and miR-146a genes are associated with sporadic colorectal cancer (CRC).

METHODS: In order to investigate the effect of these SNPs in CRC, we performed a case-control study of 197 cases of sporadic CRC and 212 cancer-free controls originating from the Central-European Caucasian population using TaqMan Real-Time polymerase chain reaction and allelic discrimination analysis.

RESULTS: The genotype and allele frequencies of SNPs were compared between the cases and the controls. None of the performed analysis showed any statistically significant results.

CONCLUSION: Our data suggest a lack of association between rs11614913, rs895819 and rs2910164 and colorectal cancer risk in the Central-European Caucasian population, a population with an extremely high incidence of sporadic colorectal cancer.

MicroRNAs as therapeutic targets and their potential applications in cancer therapy

INTRODUCTION

The results of cancer-associated miRNA research have yielded surprising insights into the pathogenesis of a range of different cancers. Many of the dysregulated miRNAs are involved in the regulation of genes that are essential for carcinogenesis.

AREAS COVERED

This review discusses the latest discovery of miRNAs acting as oncogenes and tumor suppressor genes, as well as the potential applications of miRNA regulations in cancer therapy. Several translational studies have demonstrated the feasibility of targeting oncogenic miRNAs and restoring tumor-suppressive miRNAs for cancer therapy using in vivo model systems.

EXPERT OPINION

miRNAs are extensive regulators of cancer progression. With increasing understanding of the miRNA target genes and the cellular behaviors influenced by them, modulating the miRNA activities may provide exciting opportunities for cancer therapy. Despite the hurdles incurred in acquiring effective systemic drug delivery systems, in vivo delivery of miRNAs for therapeutic purposes in preclinical animal models is rapidly developing. Accumulating evidences indicate that using miRNA expression alterations to influence molecular pathways has the potential of being translated into clinical applications.

miR-93/106b and their host gene, MCM7, are differentially expressed in leiomyomas and functionally target F3 and IL-8

miR-93/106b and their host gene minichromosome maintenance complex component 7 (MCM7) reside at chr7q22, a region frequently rearranged in leiomyomas. We explored the expression of miR-93/106b in leiomyoma and paired myometrium (n = 63) from untreated and patients exposed to hormonal therapies (GnRH agonist, Depo-Provera, and oral contraceptives) from African-Americans and Caucasians and their regulatory functions in isolated paired (n = 15) leiomyoma and myometrial smooth muscle cells and the leiomyosarcoma cell line. At tissue level leiomyomas expressed significantly lower levels of miR-93 and elevated MCM7 as compared with myometrium with limited racial influence or hormonal exposure on their expression. Assessing the regulatory function of miR-93/106b through doxycycline-inducible lentiviral transduction in a microarray analysis, tissue factor (F3) and IL8 were identified as their possible targets. At the tissue level, leiomyomas expressed a significantly lower level of F3 and an elevated IL-8 level, which exhibited an inverse relationship with miR-93 but with limited racial or hormonal influences. The gain of function of miR-93/106b in leiomyoma smooth muscle cells, myometrial smooth muscle cells, and the leiomyosarcoma cell line dose dependently repressed F3 and IL8 through direct interactions with their respective 3'-untranslated region and indirectly through F3 repression inhibited IL8, CTGF, and PAI-1 expression, confirmed by using small interfering RNA silencing or factor Vlla (FVIIa) activation of F3, as well as reducing the rate of proliferation, while increasing caspase-3/7 activity. We concluded that differential expression of miR-93/106b and their direct and/or indirect regulatory functions on F3, IL8, CTGF, and PAI-1 expression, with key roles in inflammation and tissue turnover may be of significance in the outcome of leiomyoma growth and associated symptoms.

Epigenomics of leukemia: from mechanisms to therapeutic applications

Leukemogenesis is a multistep process in which successive transformational events enhance the ability of a clonal population arising from hematopoietic progenitor cells to proliferate, differentiate and survive. Clinically and pathologically, leukemia is subdivided into four main categories: chronic lymphocytic leukemia, chronic myeloid leukemia, acute lymphocytic leukemia and acute myeloid leukemia. Leukemia has been previously considered only as a genetic disease. However, in recent years, significant advances have been made in the elucidation of the leukemogenesis-associated processes. Thus, we have come to understand that epigenetic alterations including DNA methylation, histone modifications and miRNA are involved in the permanent changes of gene expression controlling the leukemia phenotype. In this article, we will focus on the epigenetic defects associated with leukemia and their implications as biomarkers for diagnostic, prognostic and therapeutic applications.

MicroRNAs and lymph node metastatic disease in lung cancer

Lymphatic and distant metastases are primary factors in determining survival in patients with lung cancer. The identification of novel molecular biomarkers that can predict the presence of micrometastasis in lymph nodes and their incorporation in traditional histologic staging is needed. MicroRNAs are emerging as powerful biomarkers for several neoplastic disorders. This article reports the experimental results that have recently led to the identification of several microRNAs deregulated in lung cancer that are strongly associated with lymph node metastasis and advanced clinical stage. This evidence indicates that microRNAs are a promising tool for the clinical management of lung cancer.

A novel mean-centering method for normalizing microRNA expression from high-throughput RT-qPCR data

Background

Normalization is critical for accurate gene expression analysis. A significant challenge in the quantitation of gene expression from biofluids samples is the inability to quantify RNA concentration prior to analysis, underscoring the need for robust normalization tools for this sample type. In this investigation, we evaluated various methods of normalization to determine the optimal approach for quantifying microRNA (miRNA) expression from biofluids and tissue samples when using the TaqMan^® Megaplex™ high-throughput RT-qPCR platform with low RNA inputs.

Findings

We compared seven normalization methods in the analysis of variation of miRNA expression from biofluid and tissue samples. We developed a novel variant of the common mean-centering normalization strategy, herein referred to as mean-centering restricted (MCR) normalization, which is adapted to the TaqMan Megaplex RT-qPCR platform, but is likely applicable to other high-throughput RT-qPCR-based platforms. Our results indicate that MCR normalization performs comparable to or better than both standard mean-centering and other normalization methods. We also propose an extension of this method to be used when migrating biomarker signatures from Megaplex to singleplex RT-qPCR platforms, based on the identification of a small number of normalizer miRNAs that closely track the mean of expressed miRNAs.

Conclusions

We developed the MCR method for normalizing miRNA expression from biofluids samples when using the TaqMan Megaplex RT-qPCR platform. Our results suggest that normalization based on the mean of all fully observed (fully detected) miRNAs minimizes technical variance in normalized expression values, and that a small number of normalizer miRNAs can be selected when migrating from Megaplex to singleplex assays. In our study, we find that normalization methods that focus on a restricted set of miRNAs tend to perform better than methods that focus on all miRNAs, including those with non-determined (missing) values. This methodology will likely be most relevant for studies in which a significant number of miRNAs are not detected.

Suffocating cancer: hypoxia-associated epimutations as targets for cancer therapy

Lower than normal levels of oxygen (hypoxia) is a hallmark of all solid tumours rendering them frequently resistant to both radiotherapy and chemotherapy regimes. Furthermore, tumour hypoxia and activation of the hypoxia inducible factor (HIF) transcriptional pathway is associated with poorer prognosis. Driven by both genetic and epigenetic changes, cancer cells do not only survive but thrive in hypoxic conditions. Detailed knowledge of these changes and their functional consequences is of great clinical utility and is already helping to determine phenotypic plasticity, histological tumour grading and overall prognosis and survival stratification in several cancer types. As epigenetic changes - contrary to genetic changes - are potentially reversible, they may prove to be potent therapeutic targets to add to the cancer physicians' armorarium in the future.Here, we review the therapeutic potential of epigenetic modifications (including DNA methylation, histone modifications and miRNAs) occurring in hypoxia with particular reference to cancer and tumourigenesis.

Human papillomavirus and cervical cancer: biomarkers for improved prevention efforts

While organized screening programs in industrialized countries have significantly reduced cervical cancer incidence, cytology-based screening has several limitations. Equivocal or mildly abnormal Pap tests require costly retesting or diagnostic work-up by colposcopy and biopsy. In low-resource countries, it has been difficult to establish and sustain cytology-based programs. Advances in understanding human papillomavirus biology and the natural history of human papillomavirus-related precancers and cancers have led to the discovery of a range of novel biomarkers in the past decade. In this article, we will discuss the potential role of new biomarkers for primary screening, triage and diagnosis in high-resource countries and their promise for prevention efforts in resource constrained settings.