MicroRNA regulation of epithelial plasticity in cancer

Effects of miRNA-199a-5p on cell proliferation and apoptosis of uterine leiomyoma by targeting MED12

Background/aims

Uterine leiomyoma (ULM) is a kind of gene-involved benign tumor, which is located in the front of female reproductive tract. It is one of the most common reproductive tract tumors in women, which leads to abnormal menstruation, repeated pregnancy loss, and other serious gynecological diseases. Recently, microRNAs (miRNAs) have attracted much more attention in the process of exploring the molecular mechanisms of tumorigenesis. Furthermore, the deregulated miRNAs had been reported to play important roles in ULM pathology.

Methods

In this study, we assessed the expression level of microRNA-199a-5p (miR-199a-5p) in human ULM by quantitative polymerase chain reaction. After that cell counting kit 8, colony formation, 5-ethynyl-20-deoxyuridine, flow cytometry, and Western blot analyses were performed to investigate the effects of miR-199a-5p on ULM cell proliferation and apoptosis.

Results

We confirmed that miR-199a-5p was significantly downregulated in human ULM. The results of function analyses showed that miR-199a-5p inhibited cell proliferation and induced cell apoptosis in vitro. Bioinformatics tool showed oncogene MED12 was one of the target genes of miR-199a-5p, which mediated the effect of miR-199a-5p on the ULM.

Conclusion

Our results showed that miR-199a-5p functioned as an antitumor factor in human ULM cells. These findings broaden the current findings on the function of miR-199a-5p into the ULM pathogenesis, and miR-199a-5p may serve as a prognosis and therapeutic target for the ULM and its related diseases.

MicroRNAs in Epithelial-Mesenchymal Transition Process of Cancer: Potential Targets for Chemotherapy

In the last decades, a kind of small non-coding RNA molecules, called as microRNAs, has been applied as negative regulators in various types of cancer treatment through down-regulation of their targets. More recent studies exert that microRNAs play a critical role in the EMT process of cancer, promoting or inhibiting EMT progression. Interestingly, accumulating evidence suggests that pure compounds from natural plants could modulate deregulated microRNAs to inhibit EMT, resulting in the inhibition of cancer development. This small essay is on the purpose of demonstrating the significance and function of microRNAs in the EMT process as oncogenes and tumor suppressor genes according to studies mainly conducted in the last four years, providing evidence of efficient target therapy. The review also summarizes the drug candidates with the ability to restrain EMT in cancer through microRNA regulation.

Cancer Plasticity: The Role of mRNA Translation

Tumor progression is associated with dedifferentiated histopathologies concomitant with cancer cell survival within a changing, and often hostile, tumor microenvironment. These processes are enabled by cellular plasticity, whereby intracellular cues and extracellular signals are integrated to enable rapid shifts in cancer cell phenotypes. Cancer cell plasticity, at least in part, fuels tumor heterogeneity and facilitates metastasis and drug resistance. Protein synthesis is frequently dysregulated in cancer, and emerging data suggest that translational reprograming collaborates with epigenetic and metabolic programs to effectuate phenotypic plasticity of neoplasia. Herein, we discuss the potential role of mRNA translation in cancer cell plasticity, highlight emerging histopathological correlates, and deliberate on how this is related to efforts to improve understanding of the complex tumor ecology.

MicroRNA Ratios Distinguish Melanomas from Nevi

The use of microRNAs as biomarkers has been proposed for many diseases, including the diagnosis of melanoma. Although hundreds of microRNAs have been identified as differentially expressed in melanomas as compared to benign melanocytic lesions, a limited consensus has been achieved across studies, constraining the effective use of these potentially useful markers. In this study, we applied a machine learning-based pipeline to a dataset consisting of genetic features, clinical features, and next-generation microRNA sequencing from micro-dissected formalin-fixed paraffin embedded melanomas and their adjacent benign precursor nevi. We identified patient age and tumor cellularity as variables that frequently confound the measured expression of potentially diagnostic microRNAs. By employing the ratios of microRNAs that were either enriched or depleted in melanoma compared to the nevi as a normalization strategy, we developed a model that classified all the available published cohorts with an area under the receiver operating characteristic curve of 0.98. External validation on an independent cohort classified lesions with 81% sensitivity and 88% specificity and was uninfluenced by the tumor content of the sample or patient age.

MiR-199a-5p Inhibits the Growth and Metastasis of Colorectal Cancer Cells by Targeting ROCK1

Mounting evidence indicates that microRNAs play important roles in the development of various cancers. Aberrant expression of microRNA-199a-5p has been frequently reported in cancer studies; however, the mechanistic details of the role of microRNA-199a-5p in colorectal cancer still remain unclear. Our study aimed to explore the role of microRNA-199a-5p in colorectal cancer cells by targeting Rho-associated coiled coil-containing protein kinase 1. Here, we showed that microRNA-199a-5p was significantly downregulated in colorectal cancer cell lines and tissue samples and was associated with a poor prognostic phenotype. MicroRNA-199a-5p suppressed colorectal cancer cell proliferation, migration, and invasion and induced cell apoptosis. Moreover, we identified Rho-associated coiled coil-containing protein kinase 1 as the direct target of microRNA-199a-5p using luciferase and Western blot assays. Importantly, Rho-associated coiled coil-containing protein kinase 1 overexpression rescued the microRNA-199a-5p-induced suppression of proliferation, migration, and invasion of colorectal cancer cells. Furthermore, the overexpression of microRNA-199a-5p inhibited tumor growth and metastasis by inactivating the phosphoinositide 3-kinase/AKT and Janus kinase 1/signal transducing activator of transcription signaling pathways through downregulation of Rho-associated coiled coil-containing protein kinase 1. Altogether, microRNA-199a-5p/Rho-associated coiled coil-containing protein kinase 1 may be a potential therapeutic target for colorectal cancer therapy.

Microarray analysis of miRNA expression profiles following whole body irradiation in a mouse model

CONTEXT

Accidental exposure to life-threatening radiation in a nuclear event is a major concern; there is an enormous need for identifying biomarkers for radiation biodosimetry to triage populations and treat critically exposed individuals.

OBJECTIVE

To identify dose-differentiating miRNA signatures from whole blood samples of whole body irradiated mice.

METHODS

Mice were whole body irradiated with X-rays (2 Gy-15 Gy); blood was collected at various time-points post-exposure; total RNA was isolated; miRNA microarrays were performed; miRNAs differentially expressed in irradiated vs. unirradiated controls were identified; feature extraction and classification models were applied to predict dose-differentiating miRNA signature.

RESULTS

We observed a time and dose responsive alteration in the expression levels of miRNAs. Maximum number of miRNAs were altered at 24-h and 48-h time-points post-irradiation. A 23-miRNA signature was identified using feature selection algorithms and classifier models. An inverse correlation in the expression level changes of miR-17 members, and their targets were observed in whole body irradiated mice and non-human primates.

CONCLUSION

Whole blood-based miRNA expression signatures might be used for predicting radiation exposures in a mass casualty nuclear incident.

Downregulation of MiR-31 stimulates expression of LATS2 via the hippo pathway and promotes epithelial-mesenchymal transition in esophageal squamous cell carcinoma

Background

Dysregulation of miRNAs is associated with cancer development by coordinately suppressing abundant target genes. Emerging evidence indicates that miR-31 plays a dual role in tumorigenicity. However, whether miR-31 plays as an oncogene in esophageal squamous cell carcinoma (ESCC) and the potential target molecules are still unclear. MiR-31 role in ESCC was investigated and an association of the target molecules with EMT was identified in the progression of ESCC.

Methods

Western blot assays and qRT-PCR was performed to detect the protein and mRNA levels. We investigated the role of miR-31 in the regulation of LATS2 expression in ESCC cell lines via functional assays both in vivo and in vitro. The luciferase reporter assays was conducted to confirm LATS2 is a potential target of miR-31. Immunohistochemistry was used to measure LATS2 and TAZ expression in normal and ESCC tissue.

Results

LATS2 is a component of the Hippo tumor-suppressive signaling pathway. Frequent loss of heterozygosity of LATS2 has been reported in esophageal cancer. We analyzed the reciprocal expression regulation of miR-31 and LATS2 and demonstrated that LATS2 expression was elevated by down-regulation of miR-31 at the post-transcriptional level in ESCC. Moreover, miR-31 significantly suppressed the luciferase activity of mRNA combined with the LATS2 3′-UTR, a key molecule in the Hippo pathway. Then, LATS2 consequently promoted the translocation of TAZ, which was examined using immunohistochemistry. Silencing of miR-31 significantly inhibited the cell proliferation, induced apoptosis and decreased the ability of migration/invasion in vitro. LATS2 impedes ESCC cell proliferation and invasion by suppressing miR-31, as well as mice xenograft model in vivo. Meanwhile, the nuclear localization of LATS2 constrained the phosphorylation of TAZ. Then, the expression level of TAZ was notably heightened with a high risk of recurrence compared to that observed in the low-risk patients, as well as, the higher expression associated with a poor survival.

Conclusions

Our study demonstrated that overexpression of miR-31 undertook an oncogenic role in ESCC by repressing expression of LATS2 via the Hippo Pathway and activating epithelial-mesenchymal transition. LATS2 and TAZ could be potential novel molecular markers for predicting the risk of recurrence and prognosis of ESCC.

Electronic supplementary material

The online version of this article (10.1186/s13046-017-0622-1) contains supplementary material, which is available to authorized users.

Identification of common oncogenic and early developmental pathways in the ovarian carcinomas controlling by distinct prognostically significant microRNA subsets

Background

High-grade serous ovarian carcinoma (HG-SOC) is the dominant tumor histologic type in epithelial ovarian cancers, exhibiting highly aberrant microRNA expression profiles and diverse pathways that collectively determine the disease aggressiveness and clinical outcomes. However, the functional relationships between microRNAs, the common pathways controlled by the microRNAs and their prognostic and therapeutic significance remain poorly understood.

Methods

We investigated the gene expression patterns of microRNAs in the tumors of 582 HG-SOC patients to identify prognosis signatures and pathways controlled by tumor miRNAs. We developed a variable selection and prognostic method, which performs a robust selection of small-sized subsets of the predictive features (e.g., expressed microRNAs) that collectively serves as the biomarkers of cancer risk and progression stratification system, interconnecting these features with common cancer-related pathways.

Results

Across different cohorts, our meta-analysis revealed two robust and unbiased miRNA-based prognostic classifiers. Each classifier reproducibly discriminates HG-SOC patients into high-confidence low-, intermediate- or high-prognostic risk subgroups with essentially different 5-year overall survival rates of 51.6-85%, 20-38.1%, and 0-10%, respectively. Significant correlations of the risk subgroup’s stratification with chemotherapy treatment response were observed. We predicted specific target genes involved in nine cancer-related and two oocyte maturation pathways (neurotrophin and progesterone-mediated oocyte maturation), where each gene can be controlled by more than one miRNA species of the distinct miRNA HG-SOC prognostic classifiers.

Conclusions

We identified robust and reproducible miRNA-based prognostic subsets of the of HG-SOC classifiers. The miRNAs of these classifiers could control nine oncogenic and two developmental pathways, highlighting common underlying pathologic mechanisms and perspective targets for the further development of a personalized prognosis assay(s) and the development of miRNA-interconnected pathway-centric and multi-agent therapeutic intervention.

Electronic supplementary material

The online version of this article (doi:10.1186/s12864-017-4027-5) contains supplementary material, which is available to authorized users.

Tumor microenvironment and noncoding RNAs as co-drivers of epithelial-mesenchymal transition and cancer metastasis

Reciprocal interactions between cancer cells and tumor microenvironment (TME) are crucial events in tumor progression and metastasis. Pervasive stromal reprogramming of TME modifies numerous cellular functions, including extracellular matrix (ECM) stiffness, inflammation, and immunity. These environmental factors allow selection of more aggressive cells that develop adaptive strategies associating plasticity and epithelial-mesenchymal transition (EMT), stem-like phenotype, invasion, immunosuppression, and resistance to therapies. EMT is a morphomolecular process that endows epithelial tumor cells with mesenchymal properties, including reduced adhesion and increased motility. Numerous studies have demonstrated involvement of noncoding RNAs (ncRNAs), such as miRNAs and lncRNAs, in tumor initiation, progression, and metastasis. NcRNAs regulate every hallmark of cancer and have now emerged as new players in induction and regulation of EMT. The reciprocal regulatory interactions between ncRNAs, TME components, and cancer cells increase the complexity of gene expression and protein translation in cancer. Thus, deeper understanding of molecular mechanisms controlling EMT will not only shed light on metastatic processes of cancer cells, but enhance development of new therapies targeting metastasis. In this review, we will provide recent findings on the role of known ncRNAs relevant to EMT and cancer metastasis and discuss the role of the interaction between ncRNAs and TME as co-drivers of EMT. Developmental Dynamics 247:405-431, 2018. © 2017 Wiley Periodicals, Inc.

The crosstalk between lncRNA and microRNA in cancer metastasis: orchestrating the epithelial-mesenchymal plasticity

Noncoding RNAs (ncRNAs) have been demonstrated to closely associate with gene regulation and encompass the well-known microRNAs (miRNAs), as well as the most recently acknowledged long noncoding RNAs (lncRNAs). Current evidence indicates that lncRNAs can interact with miRNAs and these interactions play crucial roles in cancer metastasis, through regulating critical events especially the epithelial-mesenchymal transition (EMT). This review summarizes the types of lncRNA-miRNA crosstalk identified to-date and discusses their influence on the epithelial-mesenchymal plasticity and clinical metastatic implication.

In Vitro Dose Studies on Chitosan Nanoplexes for microRNA Delivery in Breast Cancer Cells

Changes in microRNA (miRNA) expression levels that play important roles in regulation lead to many pathological events such as cancer. The miR-200 family is an important target in cancer therapy. The aim of this study is to equilibrate endogenous levels between cancer and noncancerous cells to prevent serious side effects of miR-200c- and miR-141-like metastatic colonization. For the first time, the characterization of miR-200c and miR-141 cluster containing chitosan nanoplexes was shown, and the optimization of miRNA expression levels by conducting dose studies in breast cancer cell lines was made. The mean diameter of chitosan/miR-141 and chitosan/miR-200c nanoplexes ranged from 296 to 355 nm and from 294 to 380 nm depending on the N/P ratio, respectively. The surface charge of nanoplexes was positive with zeta potential of +12 to +26 mV. While naked miRNA was degraded after 0 min in a 10% serum-containing medium, chitosan/miRNA nanoplexes were protected for 72 h. During the in vitro cellular uptake study, nanoplexes were observed to be accumulating in the cytoplasm or nucleus. After using different doses for miR-200c, the determined doses are 750, 100, and 750 ng in the MCF-7, MDA-MB-231, and MDA-MB-435 cell lines, respectively. Doses were determined as 100 ng for MDA-MB-231 and 150 ng for MDA-MB-435 to reach endogenous miR-141 levels of MCF-10A. Our results suggest that chitosan nanoplexes for miR-200c and miR-141 are an efficient delivery system in terms of formulation and transfection. As a conclusion, dose studies are important to provide effective treatment with miRNAs.

Down-regulation of miR-129-5p via the Twist1-Snail feedback loop stimulates the epithelial-mesenchymal transition and is associated with poor prognosis in breast cancer

The epithelial to mesenchymal transition (EMT) plays a pivotal role in breast cancer progression. We found that overexpression of miR-129-5p reversed EMT, whereas depletion of miR-129-5p induced EMT in breast cancer cells. We demonstrated that Twist1 is a direct target of miR-129-5p. Both Twist1 and Snail transcriptionally suppressed miR-129-5p expression. Levels of miR-129-5p were low in breast cancer tissues. miR-129-5p down-regulation correlated with advanced clinical stage and poor prognosis in patients with breast cancer. miR-129-5p expression negatively correlated with Twist1 and Snail expression. Thus, miR-129-5p down-regulation fosters EMT in breast cancer by increasing Twist1-Snail and activating a negative feedback loop.

ADAM12-L is a direct target of the miR-29 and miR-200 families in breast cancer

Background

ADAM12-L and ADAM12-S represent two major splice variants of human metalloproteinase-disintegrin 12 mRNA, which differ in their 3′-untranslated regions (3′UTRs). ADAM12-L, but not ADAM12-S, has prognostic and chemopredictive values in breast cancer. Expression levels of the two ADAM12 splice variants in clinical samples are highly discordant, suggesting post-transcriptional regulation of the ADAM12 gene. The miR-29, miR-30, and miR-200 families have potential target sites in the ADAM12-L 3′UTR and they may negatively regulate ADAM12-L expression.

Methods

miR-29b/c, miR-30b/d, miR-200b/c, or control miRNA mimics were transfected into SUM159PT, BT549, SUM1315MO2, or Hs578T breast cancer cells. ADAM12-L and ADAM12-S mRNA levels were measured by qRT-PCR, and ADAM12-L protein was detected by Western blotting. Direct targeting of the ADAM12-L 3′UTR by miRNAs was tested using an ADAM12-L 3′UTR luciferase reporter. The rate of ADAM12-L translation was evaluated by metabolic labeling of cells with ³⁵S cysteine/methionine. The roles of endogenous miR-29b and miR-200c were tested by transfecting cells with miRNA hairpin inhibitors.

Results

Transfection of miR-29b/c mimics strongly decreased ADAM12-L mRNA levels in SUM159PT and BT549 cells, whereas ADAM12-S levels were not changed. ADAM12-L, but not ADAM12-S, levels were also significantly diminished by miR-200b/c in SUM1315MO2 cells. In Hs578T cells, miR-200b/c mimics impeded translation of ADAM12-L mRNA. Importantly, both miR-29b/c and miR-200b/c strongly decreased steady state levels of ADAM12-L protein in all breast cancer cell lines tested. miR-29b/c and miR-200b/c also significantly decreased the activity of an ADAM12-L 3′UTR reporter, and this effect was abolished when miR-29b/c and miR-200b/c target sequences were mutated. In contrast, miR-30b/d did not elicit consistent and significant effects on ADAM12-L expression. Analysis of a publicly available gene expression dataset for 100 breast tumors revealed a statistically significant negative correlation between ADAM12-L and both miR-29b and miR-200c. Inhibition of endogenous miR-29b and miR-200c in SUM149PT and SUM102PT cells led to increased ADAM12-L expression.

Conclusions

The ADAM12-L 3′UTR is a direct target of miR-29 and miR-200 family members. Since the miR-29 and miR-200 families play important roles in breast cancer progression, these results may help explain the different prognostic and chemopredictive values of ADAM12-L and ADAM12-S in breast cancer.

Posttranscriptional deregulation of signaling pathways in meningioma subtypes by differential expression of miRNAs

BACKGROUND

Micro (mi)RNAs are key regulators of gene expression and offer themselves as biomarkers for cancer development and progression. Meningioma is one of the most frequent primary intracranial tumors. As of yet, there are limited data on the role of miRNAs in meningioma of different histological subtypes and the affected signaling pathways.

METHODS

In this study, we compared expression of 1205 miRNAs in different meningioma grades and histological subtypes using microarrays and independently validated deregulation of selected miRNAs with quantitative real-time PCR. Clinical utility of a subset of miRNAs as biomarkers for World Health Organization (WHO) grade II meningioma based on quantitative real-time data was tested. Potential targets of deregulated miRNAs were discovered with an in silico analysis.

RESULTS

We identified 13 miRNAs deregulated between different subtypes of benign meningiomas, and 52 miRNAs deregulated in anaplastic meningioma compared with benign meningiomas. Known and putative target genes of deregulated miRNAs include genes involved in epithelial-to-mesenchymal transition for benign meningiomas, and Wnt, transforming growth factor-β, and vascular endothelial growth factor signaling for higher-grade meningiomas. Furthermore, a 4-miRNA signature (miR-222, -34a*, -136, and -497) shows promise as a biomarker differentiating WHO grade II from grade I meningiomas with an area under the curve of 0.75.

CONCLUSIONS

Our data provide novel insights into the contribution of miRNAs to the phenotypic spectrum in benign meningiomas. By deregulating translation of genes belonging to signaling pathways known to be important for meningioma genesis and progression, miRNAs provide a second in line amplification of growth promoting cellular signals. MiRNAs as biomarkers for diagnosis of aggressive meningiomas might prove useful and should be explored further in a prospective manner.

Pivotal role of pervasive neoplastic and stromal cells reprogramming in circulating tumor cells dissemination and metastatic colonization

Reciprocal interactions between neoplastic cells and their microenvironment are crucial events in carcinogenesis and tumor progression. Pervasive stromal reprogramming and remodeling that transform a normal to a tumorigenic microenvironment modify numerous stromal cells functions, status redox, oxidative stress, pH, ECM stiffness and energy metabolism. These environmental factors allow selection of more aggressive cancer cells that develop important adaptive strategies. Subpopulations of cancer cells acquire new properties associating plasticity, stem-like phenotype, unfolded protein response, metabolic reprogramming and autophagy, production of exosomes, survival to anoikis, invasion, immunosuppression and therapeutic resistance. Moreover, by inducing vascular transdifferentiation of cancer cells and recruiting endothelial cells and pericytes, the tumorigenic microenvironment induces development of tumor-associated vessels that allow invasive cells to gain access to the tumor vessels and to intravasate. Circulating cancer cells can survive in the blood stream by interacting with the intravascular microenvironment, extravasate through the microvasculature and interact with the metastatic microenvironment of target organs. In this review, we will focus on many recent paradigms involved in the field of tumor progression.

Fra-1/AP-1 induces EMT in mammary epithelial cells by modulating Zeb1/2 and TGFβ expression

Epithelial-to-mesenchymal transition (EMT) is essential for embryonic morphogenesis and wound healing and critical for tumour cell invasion and dissemination. The AP-1 transcription factor Fra-1 has been implicated in tumorigenesis and in tumour-associated EMT in human breast cancer. We observed a significant inverse correlation between Fra-1 mRNA expression and distant-metastasis-free survival in a large cohort of breast cancer patients derived from multiple array data sets. This unique correlation among Fos genes prompted us to assess the evolutionary conservation between Fra-1 functions in EMT of human and mouse cells. Ectopic expression of Fra-1 in fully polarized, non-tumourigenic, mouse mammary epithelial EpH4 cells induced a mesenchymal phenotype, characterized by a loss of epithelial and gain of mesenchymal markers. Proliferation, motility and invasiveness were also increased in the resulting EpFra1 cells, and the cells were tumourigenic and efficiently colonized the lung upon transplantation. Molecular analyses revealed increased expression of Tgfβ1 and the EMT-inducing transcription factors Zeb1, Zeb2 and Slug. Mechanistically, Fra-1 binds to the tgfb1 and zeb2 promoters and to an evolutionarily conserved region in the first intron of zeb1. Furthermore, increased activity of a zeb2 promoter reporter was detected in EpFra1 cells and shown to depend on AP-1-binding sites. Inhibiting TGFβ signalling in EpFra1 cells moderately increased the expression of epithelial markers, whereas silencing of zeb1 or zeb2 restored the epithelial phenotype and decreased migration in vitro and tumorigenesis in vivo. Thus Fra-1 induces changes in the expression of genes encoding EMT-related transcription factors leading to the acquisition of mesenchymal, invasive and tumorigenic capacities by epithelial cells. This study defines a novel function of Fra-1/AP-1 in modulating tgfb1, zeb1 and zeb2 expression through direct binding to genomic regulatory regions, which establishes a basis for future in vivo genetic manipulations and preclinical studies using mouse models.

OncomiR-196 promotes an invasive phenotype in oral cancer through the NME4-JNK-TIMP1-MMP signaling pathway

Background

MicroRNA-196 (miR-196), which is highly up-regulated in oral cancer cells, has been reported to be aberrantly expressed in several cancers; however, the significance of miR-196 in oral cancer has not yet been addressed.

Methods

Cellular functions in response to miR-196 modulation were examined, including cell growth, migration, invasion and radio/chemosensitivity. Algorithm-based studies were used to identify the regulatory target of miR-196. The miR-196 target gene and downstream molecular mechanisms were confirmed by RT-qPCR, western blot, luciferase reporter and confocal microscopy analyses. miR-196 expression was determined in paired cancer and adjacent normal tissues from oral cancer patients.

Results

Both miR-196a and miR-196b were highly over-expressed in the cancer tissue and correlated with lymph node metastasis (P = 0.001 and P = 0.006, respectively). Functionally, miR-196 actively promoted cell migration and invasion without affecting cell growth. Mechanistically, miR-196 performed it's their function by inhibiting NME4 expression and further activating p-JNK, suppressing TIMP1, and augmenting MMP1/9.

Conclusion

miR-196 contributes to oral cancer by promoting cell migration and invasion. Clinically, miR-196a/b was significantly over-expressed in the cancer tissues and correlated with lymph node metastasis. Thus, our findings provide new knowledge of the underlying mechanism of cancer metastasis. miR-196 may serve as a promising marker for better oral cancer management.

Electronic supplementary material

The online version of this article (doi:10.1186/1476-4598-13-218) contains supplementary material, which is available to authorized users.

Towards a molecular basis of oligometastatic disease: potential role of micro-RNAs

Oligometastasis is a cancer disease state characterized by a limited number of metastatic tumors involving single or few organs and with biological properties that make them potentially amenable to locoregional antitumor therapy. Current clinical data show that they are potentially curable with surgical resection or/and radiotherapy. Yet, mechanisms of progression from primary tumor to oligometastasis, rather than to polymetastases, is lacking in detail. In the current review we focus on the role of micro-RNAs in the regulation of metastases development and the role they may play in the differentiation of oligometastatic from polymetastatic progression. We also discuss the analyses of metastatic samples from oligo-and polymetastatic patients, which suggest that oligometastasis is a distinct biologic entity regulated in part by micro-RNAs. In addition, a review of the known functions of oligometastatic-specific micro-RNAs suggest that they regulate multiple steps in the metastatic cascade, including epithelial–mesenchymal transition, tumor invasion, intravasation, distant vascular extravasation and proliferation in a distant organ. Understanding the role of micro-RNAs and their target genes in oligometastatic disease may allow for the development of targeted therapies to effectively conrol the spread of metastases.

MicroRNA-200b targets protein kinase Cα and suppresses triple-negative breast cancer metastasis

Triple-negative breast cancer (TNBC) is an aggressive subtype of breast cancer with poor prognosis and lacks effective targeted therapies. The microRNA-200 (miR-200) family is found to inhibit or promote breast cancer metastasis; however, the underlying mechanism is not well understood. This study was performed to investigate the effect and mechanism of miR-200b on TNBC metastasis and identify targets for developing more efficient treatment for TNBC. We found that miR-200 family expression levels are significantly lower in highly migratory TNBC cells and metastatic TNBC tumors than other types of breast cancer cells and tumors. Ectopically expressing a single member (miR-200b) of the miR-200 family drastically reduces TNBC cell migration and inhibits tumor metastasis in an orthotopic mouse mammary xenograft tumor model. We identified protein kinase Cα (PKCα) as a new direct target of miR-200b and found that PKCα protein levels are inversely correlated with miR-200b levels in 12 kinds of breast cancer cells. Inhibiting PKCα activity or knocking down PKCα levels significantly reduces TNBC cell migration. In contrast, forced expression of PKCα impairs the inhibitory effect of miR-200b on cell migration and tumor metastasis. Further mechanistic studies revealed that PKCα downregulation by miR-200b results in a significant decrease of Rac1 activation in TNBC cells. These results show that loss of miR-200b expression plays a crucial role in TNBC aggressiveness and that miR-200b suppresses TNBC cell migration and tumor metastasis by targeting PKCα. Our findings suggest that miR-200b and PKCα may serve as promising therapeutic targets for metastatic TNBC.

miR-300 inhibits epithelial to mesenchymal transition and metastasis by targeting Twist in human epithelial cancer

BACKGROUND

Epithelial-to-mesenchymal transition (EMT) is a key step of the progression of tumor cell metastasis. Recent work has demonstrated some miRNAs play critical roles in EMT. In this study, we focused on the roles of miR-300 in regulating EMT.

METHODS

The expression levels of miR-300 were examined in epithelial carcinoma cells that underwent an EMT using quantitative reverse transcription-PCR. The role of miR-300 in EMT was investigated by transfection of the miR-300 mimic or inhibitor in natural epithelial-mesenchymal phenotype cell line pairs and in transforming growth factor (TGF) beta-induced EMT cell models. A luciferase reporter assay and a rescue experiment were conducted to confirm the target gene of miR-300. The efficacy of miR-300 against tumor invasion and metastasis was evaluated both in vitro and in vivo. Correlation analysis between miR-300 expression and the expression levels of its target gene, as well as tumor metastasis was performed in specimens from patients with head and neck squamous cell carcinoma (HNSCC).

RESULTS

MiR-300 was found down-regulated in the HNSCC cells and breast cancer cells that underwent EMT. Ectopic expression of miR-300 effectively blocked TGF-beta-induced EMT and reversed the phenotype of EMT in HN-12 and MDA-MB-231 cells, but inhibition of miR-300 in the epithelial phenotype cells, HN-4 and MCF-7 cells, could induce EMT. The luciferase reporter assay and the rescue assay results showed that miR-300 directly targets the 3'UTR of Twist. Enforced miR-300 expression suppressed cell invasion in vitro and experimental metastasis in vivo. Clinically, miR-300 expression was found inversely correlated with Twist expression and reduced miR-300 was associated with metastasis in patient specimens.

CONCLUSIONS

Down-regulation of miR-300 is required for EMT initiation and maintenance. MiR-300 may negatively regulate EMT by direct targeting Twist and therefore inhibit cancer cell invasion and metastasis, which implicates miR-300 as an attractive candidate for cancer therapy.

HGF induces epithelial-to-mesenchymal transition by modulating the mammalian hippo/MST2 and ISG15 pathways

Epithelial to mesenchymal transition (EMT) is a fundamental cell differentiation/dedifferentiation process which is associated with dramatic morphological changes. Formerly polarized and immobile epithelial cells which form cell junctions and cobblestone-like cell sheets undergo a transition into highly motile, elongated, mesenchymal cells lacking cell-to-cell adhesions. To explore how the proteome is affected during EMT we profiled protein expression and tracked cell biological markers in Madin-Darby kidney epithelial cells undergoing hepatocyte growth factor (HGF) induced EMT. We were able to identify and quantify over 4000 proteins by mass spectrometry. Enrichment analysis of this revealed that expression of proteins associated with the ubiquitination machinery was induced, whereas expression of proteins regulating apoptotic pathways was suppressed. We show that both the mammalian Hippo/MST2 and the ISG15 pathways are regulated at the protein level by ubiquitin ligases. Inhibition of the Hippo pathway by overexpression of either ITCH or A-Raf promotes HGF-induced EMT. Conversely, ISG15 overexpression is sufficient to induce cell scattering and an elongated morphology without external stimuli. Thus, we demonstrate for the first time that the Hippo/MST2 and ISG15 pathways are regulated during growth-factor induced EMT.

A core microRNA signature associated with inducers of the epithelial-to-mesenchymal transition

Although it is becoming clear that certain miRNAs fulfil a fundamental role in the regulation of the epithelial-to-mesenchymal transition (EMT), a comprehensive study of the miRNAs associated with this process has yet to be performed. Here, we profiled the signature of miRNA expression in an in vitro model of EMT, ectopically expressing in MDCK cells one of seven EMT transcription factors (SNAI1, SNAI2, ZEB1, ZEB2, TWIST1, TWIST2 or E47) or the EMT inducer LOXL2. In this way, we identified a core subset of deregulated miRNAs that were further validated in vivo, studying endometrial carcinosarcoma (ECS), a tumour entity that represents an extreme example of phenotypic plasticity. Moreover, epigenetic silencing through DNA methylation of miRNA genes of the miR-200 family and miR-205 that are down-regulated during EMT was evident in both the in vitro (MDCK transfectants) and in vivo (ECS) models of EMT. The strong correlation between expression and DNA methylation suggests a major role for this epigenetic mark in the regulation of the miR-141-200c locus.

MicroRNAs: master regulators of drug resistance, stemness, and metastasis

MicroRNAs (miRNAs) are 20-22 nucleotides long small non-coding RNAs that regulate gene expression post-transcriptionally. Last decade has witnessed emerging evidences of active roles of miRNAs in tumor development, progression, metastasis, and drug resistance. Many factors contribute to their dysregulation in cancer, such as chromosomal aberrations, differential methylation of their own or host genes' promoters and alterations in miRNA biogenesis pathways. miRNAs have been shown to act as tumor suppressors or oncogenes depending on the targets they regulate and the tissue where they are expressed. Because miRNAs can regulate dozens of genes simultaneously and they can function as tumor suppressors or oncogenes, they have been proposed as promising targets for cancer therapy. In this review, we focus on the role of miRNAs in driving drug resistance and metastasis which are associated with stem cell properties of cancer cells. Furthermore, we discuss systems biology approaches to combine experimental and computational methods to study effects of miRNAs on gene or protein networks regulating these processes. Finally, we describe methods to target oncogenic or replace tumor suppressor miRNAs and current delivery strategies to sensitize refractory cells and to prevent metastasis. A holistic understanding of miRNAs' functions in drug resistance and metastasis, which are major causes of cancer-related deaths, and the development of novel strategies to target them efficiently will pave the way towards better translation of miRNAs into clinics and management of cancer therapy.