The miR-106b-25 cluster targets Smad7, activates TGF-β signaling, and induces EMT and tumor initiating cell characteristics downstream of Six1 in human breast cancer

TGFβR2 is a major target of miR-93 in nasopharyngeal carcinoma aggressiveness

Background

MiR-17-92 cluster and its paralogues have emerged as crucial regulators of many oncogenes and tumor suppressors. Transforming growth factor-β receptor II (TGFβR2), as an important tumor suppressor, is involved in various cancer types. However, it is in cancer that only two miRNAs of this cluster and its paralogues have been reported so far to regulate TGFβR2. MiR-93 is oncogenic, but its targetome in cancer has not been fully defined. The role of miR-93 in nasopharyngeal carcinoma (NPC) still remains largely unknown.

Methods

We firstly evaluated the clinical signature of TGFβR2 down-regulation in clinical samples, and next used a miRNA expression profiling analysis followed by multi-validations, including Luciferase reporter assay, to identify miRNAs targeting TGFβR2 in NPC. In vitro and in vivo studies were performed to further investigate the effects of miRNA-mediated TGFβR2 down-regulation on NPC aggressiveness. Finally, mechanism studies were conducted to explore the associated pathway and genes influenced by this miRNA-mediated TGFβR2 down-regulation.

Results

TGFβR2 was down-regulated in more than 50% of NPC patients. It is an unfavorable prognosis factor contributing to clinical NPC aggressiveness. A cluster set of 4 TGFβR2-associated miRNAs was identified; they are all from miR-17-92 cluster and its paralogues, of which miR-93 was one of the most significant miRNAs, directly targeting TGFβR2, promoting cell proliferation, invasion and metastasis in vitro and in vivo. Moreover, miR-93 resulted in the attenuation of Smad-dependent TGF-β signaling and the activation of PI3K/Akt pathway by suppressing TGFβR2, further promoting NPC cell uncontrolled growth, invasion, metastasis and EMT-like process. Impressively, the knockdown of TGFβR2 by siRNA displayed a consentaneous phenocopy with the effect of miR-93 in NPC cells, supporting TGFβR2 is a major target of miR-93. Our findings were also substantiated by investigation of the clinical signatures of miR-93 and TGFβR2 in NPC.

Conclusion

The present study reports an involvement of miR-93-mediated TGFβR2 down-regulation in NPC aggressiveness, thus giving extended insights into molecular mechanisms underlying cancer aggressiveness. Approaches aimed at blocking miR-93 may serve as a promising therapeutic strategy for treating NPC patients.

Differentially expressed microRNAs in TGFβ2-induced epithelial-mesenchymal transition in retinal pigment epithelium cells

The epithelial-mesenchymal transition (EMT) of retinal pigment epithelium (RPE) cells plays a key role in proliferative vitreoretinopathy (PVR) and proliferative diabetic retinopathy (PDR), both of which lead to severe loss of vision. Recently, microRNAs (miRNAs) have been found to be involved in the regulation of various physiological and pathological processes, such as embryogenesis, organ development, oncogenesis and angiogenesis. However, the expression profile and function of miRNAs in the EMT of RPE cells remain to be clarified. In this study, human miRNA expression profiles were identified using microarrays and 304 miRNAs were found to be differentially expressed in TGFβ2-induced EMT in human RPE cells. Of these differentially expressed miRNAs, 185 miRNAs were downregulated and 119 miRNAs were upregulated at least 2-fold in TGFβ2 treatment samples. Similar alterations of miRNA expression were validated for 35 representative miRNAs by quantitative polymerase chain reaction analysis. Therefore, these results suggested that differentially expressed miRNAs play potential roles in TGFβ2-induced EMT in RPE cells. This is an essential step in the identification of miRNAs associated with PVR and PDR progression, and in the identification of potential therapeutic targets for these diseases.

Post-transcriptional regulatory network of epithelial-to-mesenchymal and mesenchymal-to-epithelial transitions

Epithelial-to-mesenchymal transition (EMT) and its reverse process, mesenchymal-to-epithelial transition (MET), play important roles in embryogenesis, stem cell biology, and cancer progression. EMT can be regulated by many signaling pathways and regulatory transcriptional networks. Furthermore, post-transcriptional regulatory networks regulate EMT; these networks include the long non-coding RNA (lncRNA) and microRNA (miRNA) families. Specifically, the miR-200 family, miR-101, miR-506, and several lncRNAs have been found to regulate EMT. Recent studies have illustrated that several lncRNAs are overexpressed in various cancers and that they can promote tumor metastasis by inducing EMT. MiRNA controls EMT by regulating EMT transcription factors or other EMT regulators, suggesting that lncRNAs and miRNA are novel therapeutic targets for the treatment of cancer. Further efforts have shown that non-coding-mediated EMT regulation is closely associated with epigenetic regulation through promoter methylation (e.g., miR-200 or miR-506) and protein regulation (e.g., SET8 via miR-502). The formation of gene fusions has also been found to promote EMT in prostate cancer. In this review, we discuss the post-transcriptional regulatory network that is involved in EMT and MET and how targeting EMT and MET may provide effective therapeutics for human disease.

MicroRNA control of epithelial-mesenchymal transition in cancer stem cells

Cancer stem cells (CSCs) represent a small subset of cancer cell populations that possess characteristics associated with normal stem cells. They have the ability to self-renew, and are able to generate diverse tumor cells and account for metastases. Therefore, CSCs are widely accepted as potential mediators of therapeutic resistance and novel targets for anti-cancer treatments. Recent progress has highlighted the significance of epithelial-mesenchymal transition (EMT) process in CSC formation, as well as the crucial role of microRNAs in controlling EMT and cancer metastasis. MicroRNAs are also reported to take part in the control of CSC functions and the regulation of cancer progression by affecting EMT process. Thus, it is highly crucial to develop deeper understanding of the mechanisms that how microRNAs control EMT processes and regulate CSC functions for better therapeutics of cancer disease. Herein we make this review to summarize the current understanding of the regulatory mechanisms of EMT in CSC initiation, with a special focus on the role of microRNAs in EMT control, and discuss the implications of targeting CSCs for cancer therapeutics.

Molecular characterization of exosome-like vesicles from breast cancer cells

Background

Membrane vesicles released by neoplastic cells into extracellular medium contain potential of carrying arrays of oncogenic molecules including proteins and microRNAs (miRNA). Extracellular (exosome-like) vesicles play a major role in cell-to-cell communication. Thus, the characterization of proteins and miRNAs of exosome-like vesicles is imperative in clarifying intercellular signaling as well as identifying disease markers.

Methods

Exosome-like vesicles were isolated using gradient centrifugation from MCF-7 and MDA-MB 231 cultures. Proteomic profiling of vesicles using liquid chromatography-mass spectrometry (LC-MS/MS) revealed different protein profiles of exosome-like vesicles derived from MCF-7 cells (MCF-Exo) than those from MDA-MB 231 cells (MDA-Exo).

Results

The protein database search has identified 88 proteins in MDA-Exo and 59 proteins from MCF-Exo. Analysis showed that among all, 27 proteins were common between the two exosome-like vesicle types. Additionally, MDA-Exo contains a higher amount of matrix-metalloproteinases, which might be linked to the enhanced metastatic property of MDA-MB 231 cells. In addition, microarray analysis identified several oncogenic miRNA between the two types vesicles.

Conclusions

Identification of the oncogenic factors in exosome-like vesicles is important since such vesicles could convey signals to non-malignant cells and could have an implication in tumor progression and metastasis.

miR-92a family and their target genes in tumorigenesis and metastasis

The miR-92a family, including miR-25, miR-92a-1, miR-92a-2 and miR-363, arises from three different paralog clusters miR-17-92, miR-106a-363, and miR-106b-25 that are highly conservative in the process of evolution, and it was thought as a group of microRNAs (miRNAs) correlated with endothelial cells. Aberrant expression of miR-92a family was detected in multiple cancers, and the disturbance of miR-92a family was related with tumorigenesis and tumor development. In this review, the progress on the relationship between miR-92a family and their target genes and malignant tumors will be summarized.

Therapeutic Opportunities for Targeting microRNAs in Cancer

MicroRNAs (miRNAs) are small noncoding RNAs that can function as either powerful tumor promoters or suppressors in numerous types of cancer. The ability of miRs to target multiple genes and biological signaling pathways has created intense interest in their potential clinical utility as predictive and diagnostic biomarkers, and as innovative therapeutic agents. Recently, accumulating preclinical studies have illustrated the feasibility of slowing tumor progression by either overexpressing tumor suppressive miRNAs, or by neutralizing the activities of oncogenic miRNAs in cell- and animal-based models of cancer. Here we highlight prominent miRNAs that may represent potential therapeutic targets in human malignancies, as well as review current technologies available for inactivating or restoring miRNA activity in clinical settings.

The microRNA networks of TGFβ signaling in cancer

In metazoans, the transforming growth factor β (TGFβ) signaling regulates a host of activities ranging from embryonic development to tissue homeostasis. The normal as well as tumor cells respond to this cytokine signaling pathway in a highly context-dependent manner. It acts as a potent tumor suppressor initially by inducing cell cycle arrest and apoptosis. But advanced tumors often misuse TGFβ signaling for tumor progression by selectively disabling the tumor suppressor arm and using other properties of TGFβ signaling such as induction of angiogenesis, epithelial to mesenchymal transition, and metastases. This dual role of TGFβ in cancer remained a mystery until recently. But recent advances in the field of microRNA provided a deeper understanding about this dual nature of TGFβ signaling in cancers. In the present review, we present an account of the role of microRNAs in deregulating TGFβ signaling and modulating cancer cell behavior during tumor initiation and cancer progression. This review also includes a discussion on the recent advances in the deregulation of TGFβ signaling in carcinogenesis.

The dual role of Smad7 in the control of cancer growth and metastasis

Smad7 was initially identified as an inhibitor of Transforming growth factor (TGF)-β due mainly to its ability to bind TGF-β receptor type I and prevent TGF-β-associated Smad signaling. More recently, it has been demonstrated that Smad7 can interact with other intracellular proteins and regulate also TGF-β-independent signaling pathways thus making a valid contribution to the neoplastic processes in various organs. In particular, data emerging from experimental studies indicate that Smad7 may differently modulate the course of various tumors depending on the context analyzed. These observations, together with the demonstration that Smad7 expression is deregulated in many cancers, suggest that therapeutic interventions around Smad7 can help interfere with the development/progression of human cancers. In this article we review and discuss the available data supporting the role of Smad7 in the modulation of cancer growth and progression.

The Role of microRNAs in Stemness of Cancer Stem Cells

Cancer is one of the most important diseases of humans, for which no cure has been found so far. Understanding the causes of cancer can pave the way for its treatment. Alteration in genetic elements such as oncogenes and tumor suppressor genes results in cancer. The most recent theory for the origin of cancer has been provided by cancer stem cells (CSCs). Tumor-initiating cells (T-ICs) or CSCs are a small population isolated from tumors and hematologic malignancies. Since CSCs are similar to embryonic stem cells (ESCs) in many aspects (such as pluripotency and self-renewal), recognizing the signaling pathways through which ESCs maintain their stemness can also help identify CSC signaling. One component of these signaling pathways is non-coding RNAs (ncRNAs). ncRNAs are classified in two groups: microRNAs (miRNAs) and long non-coding RNAs (lncRNAs). miRNAs undergo altered expression in cancer. In this regard, they are classified as Onco-miRNAs or tumor suppressor miRNAs. Some miRNAs play similar roles in ESCs and CSCs, such as let-7 and miR-302. This review focuses on the miRNAs involved in stemness of ESCs and CSCs by presenting a summary of the role of miRNAs in other tumor cells.

MiR-106b expression determines the proliferation paradox of TGF-β in breast cancer cells

TGF-β has paradoxical effects on cancer cell proliferation, as it suppresses proliferation of normal epithelial and low-invasive cancer cells, but enhances that of high-invasive cancer cells. However, how cancer cells acquire the ability to evade the tumor-suppressing effects of TGF-β, yet still take advantage of its tumor-promoting effects, remains elusive. Here, we identified miR-106b as a molecular switch to determine TGF-β effects on cell proliferation. TGF-β1 enhances the transcription of miR-106b via a promoter independent of its host gene MCM7 by activating c-jun. In high-invasive breast cancer cells, miR-106b is upregulated by TGF-β1 at a much higher level than that in normal or low-invasive cancer cells. Accumulation of miR-106b counterbalances TGF-β growth-inhibiting effects by eliminating activated retinoblastoma (RB) and results in enhanced proliferation. Furthermore, miR-106b mediates TGF-β effects on tumor growth and metastasis in breast cancer xenografts. In addition, miR-106b expression is elevated in higher stage tumors and correlated with tumor progression in breast cancer patients. These findings suggest that high level of miR-106b induced by TGF-β determines the tumor-promoting effects of TGF-β in breast cancer.

An integrative meta-analysis of microRNAs in hepatocellular carcinoma

We aimed to shed new light on the roles of microRNAs (miRNAs) in liver cancer using an integrative in silico bioinformatics analysis. A new protocol for target prediction and functional analysis is presented and applied to the 26 highly differentially deregulated miRNAs in hepatocellular carcinoma. This framework comprises: (1) the overlap of prediction results by four out of five target prediction tools, including TargetScan, PicTar, miRanda, DIANA-microT and miRDB (combining machine-learning, alignment, interaction energy and statistical tests in order to minimize false positives), (2) evidence from previous microarray analysis on the expression of these targets, (3) gene ontology (GO) and pathway enrichment analysis of the miRNA targets and their pathways and (4) linking these results to oncogenesis and cancer hallmarks. This yielded new insights into the roles of miRNAs in cancer hallmarks. Here we presented several key targets and hundreds of new targets that are significantly enriched in many new cancer-related hallmarks. In addition, we also revealed some known and new oncogenic pathways for liver cancer. These included the famous MAPK, TGFβ and cell cycle pathways. New insights were also provided into Wnt signaling, prostate cancer, axon guidance and oocyte meiosis pathways. These signaling and developmental pathways crosstalk to regulate stem cell transformation and implicate a role of miRNAs in hepatic stem cell deregulation and cancer development. By analyzing their complete interactome, we proposed new categorization for some of these miRNAs as either tumor-suppressors or oncomiRs with dual roles. Therefore some of these miRNAs may be addressed as therapeutic targets or used as therapeutic agents. Such dual roles thus expand the view of miRNAs as active maintainers of cellular homeostasis.

The miR-106b~25 cluster promotes bypass of doxorubicin-induced senescence and increase in motility and invasion by targeting the E-cadherin transcriptional activator EP300

Resistance to chemotherapeutic treatment, which is indirectly responsible for many cancer deaths, is normally associated with an aggressive phenotype including increased cell motility and acquisition of invasive properties. Here we describe how breast cancer cells overcome doxorubicin-induced senescence and become drug resistant by overexpression of the microRNA (miR)-106b~25 cluster. Although all three miRs in the cluster contribute to the generation of doxorubicin resistance, miR-25 is the major contributor to this phenotype. All three miRs in this cluster target EP300, a transcriptional activator of E-cadherin, resulting in cells acquiring a phenotype characteristic of cells undergoing epithelial-to-mesenchymal transition (EMT), including an increase in both cell motility and invasion, as well as the ability to proliferate after treatment with doxorubicin. These findings provide a novel drug resistance/EMT regulatory pathway controlled by the miR-106b~25 cluster by targeting a transcriptional activator of E-cadherin.

Exploring and exploiting the fundamental role of microRNAs in tumor pathogenesis

miRNAs (miRs) are short RNA molecules that are involved in the posttranscriptional regulation of mRNA. The roles of miRs in tumor pathogenesis have only recently become a focus of research. It is becoming increasingly clear that miRs are important regulators of apoptosis, proliferation, invasion, and metastasis in cancer cells during cancer genesis and progression, furthering our understanding of cancer. In the present review, we summarize and evaluate the recent advances in our understanding of the characteristics of miRs as well as their regulated functions in cancer stem cells (CSCs), the epithelial-mesenchymal transition (EMT), and the tumor microenvironment (TM), describing their roles in tumor pathogenesis and their possible use as new therapeutic targets and biomarkers.

MicroRNA-106b-5p boosts glioma tumorigensis by targeting multiple tumor suppressor genes

Aberrant expression of microRNAs (miRNAs) has been implicated in cancer initiation and progression. However, little is known about the potential role of miRNAs in glioma tumorigenesis. In this study, we found that miRNA-106b-5p was significantly upregulated in glioma tumor samples and cell lines compared with normal brain tissues, and its expression level correlated with the pathological grading. Overexpression of miR-106b-5p in glioma tumor cells significantly promoted cell proliferation, although inhibited cell apoptosis in vitro and in vivo. In contrast, knockdown of miR-106b-5p significantly inhibited cell proliferation, although enhanced cell apoptosis. Mechanistic study revealed that two target genes, retinoblastoma-like 1 (RBL1) and RBL2, were involved in miR-106b-5p's regulation of cell proliferation and one target gene, caspase-8 (CASP8), mediated miR-106b-5p's regulation of apoptosis. We also investigated the function of the three targets in glioma tumorigenesis by RNA interference manipulation and demonstrated that knockdown of these target genes led to cell proliferation enhancement or cell apoptosis inhibition in vitro. More interestingly, the expression levels of these targets were significantly downregulated in glioma samples and knockdown of these targets in glioma cells inhibited the xenograft tumor formation in vivo. Moreover, we verified the regulation function of miR-106b-5p and its targets on cell proliferation and apoptosis of the primary cultured astrocytes isolated from glioma tumor samples and healthy controls. Collectively, our findings show the critical roles of miR-106b-5p and its targets, RBL1, RBL2 and CASP8, in glioma tumorigenesis and provide potential candidates for malignant glioma therapy.

Renin-sensitive microRNAs correlate with atherosclerosis plaque progression

Recent trials with inhibition of the renin-angiotensin-aldosterone system (RAAS) in patients with established atherosclerosis have been equivocal. MicroRNAs (miRs) are known to affect multiple pathways relevant to atherosclerosis, including RAAS. We postulated that the use of a direct renin antagonist would result in differential regulation of miRs. We examined monocyte miR expression before and after treatment with renin antagonist, Aliskiren, in patients with established cardiovascular disease as part of a prospective, single-center, randomized, double-blind and placebo-controlled clinical trial (NCT01417104). After screening, patients (mean age 62±3 years) were randomized to placebo or Aliskiren. Three-dimensional dark-blood magnetic resonance imaging assessment of atherosclerosis in the thoracic and abdominal aorta was conducted at baseline and at study completion (19-36 weeks). MiR expression arrays were performed on RNA from peripheral blood mononuclear cells collected at baseline and 12 weeks following randomization to placebo or Aliskiren and showed that hsa-miR-106b-5p, 27a-3p and 18b-5p were significantly downregulated with Aliskiren. Baseline expression of these miRs positively correlated with normalized total wall volume in subjects taking Aliskiren (miR-106b, R=0.62; miR-27a, R=0.63; miR-18b, R=0.77; P<0.05). Hsa-miR-106b-5p, 27a-3p and 18b-5p may represent pathway-specific adaptations to renin inhibition relevant to atherosclerosis.

Non-coding RNAs regulate tumor cell plasticity

Tumor metastasis is one of the most serious challenges for human cancers as the majority of deaths caused by cancer are associated with metastasis, rather than the primary tumor. Recent studies have demonstrated that tumor cell plasticity plays a critical role in tumor metastasis by giving rise to various cell types which is necessary for tumor to invade adjacent tissues and form distant metastasis. These include differentiation of cancer stem cells (CSCs), or epithelial-mesenchymal transition (EMT) and its reverse process, mesenchymal-epithelial transition (MET). A growing body of evidence has demonstrated that the biology of tumor cell plasticity is tightly linked to functions of non-coding RNAs (ncRNAs), especially microRNAs (miRNAs) and long non-coding RNAs (lncRNAs). Therefore, understanding the mechanisms how non-coding RNAs regulate tumor cell plasticity is essential for discovery of new diagnostic markers and therapeutic targets to overcome metastasis.

A proteomic approach of pediatric astrocytomas: MiRNAs and network insight

Pediatric astrocytomas, a leading cause of death associated with cancer, are the most common primary central nervous system tumors found in children. Most studies of these tumors focus on adults, not on children. We examined the global protein and microRNA expression pattern by 2D SDS-PAGE, mass spectrometry (MALDI-TOF), and RT(2) miRNA PCR Array System. Proteomic studies revealed 49 proteins with changes on the expression. Interactome showed that vimentin, calreticulin, and 14-3-3 epsilon protein are hub proteins in these neoplasms. MicroRNA analyses demonstrated for the first time novel microRNAs involved in the astrocytoma biology. In conclusion, our results show that novel proteins and microRNAs with expression changes on pediatric astrocytoma could serve as biomarkers of tumor progression.

BIOLOGICAL SIGNIFICANCE

Astrocytomas are tumors that progress rapidly and that invade surrounding tissues. Although some drugs have been developed to treat these neoplasms, the mortality of patients is still very high. In this study, we describe for the first time, to our knowledge, some proteins and miRNAs associated with the biology of astrocytic tumors that could be postulated as possible diagnostic or prognostic biomarkers. Altogether, our results indicate that large-scale analyses allow making a fairly accurate prediction of different cellular processes altered in astrocytic tumors.

miR-93-directed downregulation of DAB2 defines a novel oncogenic pathway in lung cancer

The disabled homolog 2 (DAB2) gene was recently identified as a tumor suppressor gene with its expression down-regulated in multiple cancer types. The role of DAB2 in lung tumorigenesis, however, is not fully characterized, and the mechanisms of DAB2 dysregulation in lung cancer are not defined. Here we show that low DAB2 levels in lung tumor specimens are significantly correlated with poor patient survival, and that DAB2 over-expression significantly inhibits cell growth in cultured lung cancer cells, indicating its potent tumor suppressor function. We next identify that microRNA miR-93 functions as a potent repressor of DAB2 expression by directly targeting the 3′UTR of the DAB2 mRNA. Using in vitro and in vivo approaches, we demonstrate that miR-93 over-expression plays an important role in promoting lung cancer cell growth, and that its oncogenic function is primarily mediated by down-regulating DAB2 expression. Our clinical investigations further indicate that high tumor levels of miR-93 are correlated with poor survival of lung cancer patients. The correlations of both low DAB2 and high miR-93 expression with poor patient survival strongly support the critical role of the miR-93/DAB2 pathway in determining lung cancer progression.

Candidate microRNA biomarkers in human gastric cancer: a systematic review and validation study

Gastric cancer (GC) remains a major cause of morbidity and mortality worldwide and there is therefore a clear need to search for more sensitive early diagnostic biomarkers. We performed a systematic review of eight published miRNA profiling studies that compared GC tissues with adjacent noncancerous tissues. A miRNA ranking system was used that took the frequency of comparisons, direction of differential expression and total sample size into consideration. We identified five miRNAs that were most consistently reported to be upregulated (miR-21, miR-106b, miR-17, miR-18a and miR-20a) and two miRNAs that were downregulated (miR-378 and miR-638). Six of these were further validated in 32 paired sets of GC and adjacent noncancerous tissue samples using real-time PCR. MiR-21, miR-106b, miR-17, miR-18a and miR-20a were confirmed to be upregulatedin GC tissues, while the expression of miR-378 was decreased. Moreover, we found a significant association between expression levels of miR-21, miR-106b, miR-17, miR-18a and miR-20a and clinicopathological features of GC. These miRNAs may be used for diagnostic and/or prognostic biomarkers for GC and therefore warrant further investigation.

MicroRNA-106b modulates epithelial-mesenchymal transition by targeting TWIST1 in invasive endometrial cancer cell lines

Type II endometrial carcinoma is an aggressive subtype of endometrial cancer (EC). TWIST1, a helix-loop-helix transcription regulator, is known to induce epithelial-mesenchymal transition (EMT) and promote tumor metastasis. MicroRNAs (miRNAs) also serve as important regulators of EMT and metastasis by regulating EMT-related genes. In this study, we sought to explore the role of TWIST1 in inducing EMT in representative type II EC cell lines, and to determine the miRNAs involved in regulating TWIST1 gene expression. Functional analysis suggested that TWIST1 contributes to the EMT phenotypes of EC cells, as evidenced by the acquisition of fibroblast-like properties, enhanced invasiveness, and induction of an EN-switch (downregulation of epithelial marker E-cadherin and upregulation of mesenchymal marker N-cadherin). Conversely, silencing of TWIST1 by siRNA inhibited cell invasion and the mesenchymal phenotype, which was accompanied by a reversion of the EN-switch. We also observed a novel post-transcriptional regulatory mechanism of TWIST1 expression mediated by miR-106b via its direct interaction with TWIST1 mRNAs at the 3'-untranslated region. Our data suggest that TWIST1 is a critical inducer of EMT in invasive EC cells and that miR-106b could suppress EC cell invasion by downregulating TWIST1 expression.

MicroRNA-216a/217-induced epithelial-mesenchymal transition targets PTEN and SMAD7 to promote drug resistance and recurrence of liver cancer

Tumor recurrence and metastases are the major obstacles to improving the prognosis of patients with hepatocellular carcinoma (HCC). To identify novel risk factors associated with HCC recurrence and metastases, we have established a panel of recurrence-associated microRNAs (miRNAs) by comparing miRNA expression in recurrent and nonrecurrent human HCC tissue samples using microarrays (recurrence is defined as recurrent disease occurring within a 2-year time point of the original treatment). Among the panel, expression of the miR-216a/217 cluster was consistently and significantly up-regulated in HCC tissue samples and cell lines associated with early tumor recurrence, poor disease-free survival, and an epithelial-mesenchymal transition (EMT) phenotype. Stable overexpression of miR-216a/217-induced EMT increased the stem-like cell population, migration, and metastatic ability of epithelial HCC cells. Phosphatase and tensin homolog (PTEN) and mothers against decapentaplegic homolog 7 (SMAD7) were subsequently identified as two functional targets of miR-216a/217, and both PTEN and SMAD7 were down-regulated in HCC. Ectopic expression of PTEN or SMAD7 partially rescued miR-216a/217-mediated EMT, cell migration, and stem-like properties of HCC cells. Previously, SMAD7 was shown to be a transforming growth factor beta (TGF-β) type 1 receptor antagonist. Here, we further demonstrated that overexpression of miR-216a/217 acted as a positive feedback regulator for the TGF-β pathway and the canonical pathway involved in the activation of phosphoinositide 3-kinase/protein kinase K (PI3K/Akt) signaling in HCC cells. Additionally, activation of the TGF-β- and PI3K/Akt-signaling pathways in HCC cells resulted in an acquired resistance to sorafenib, whereas blocking activation of the TGF-β pathway overcame miR-216a/217-induced sorafenib resistance and prevented tumor metastases in HCC.

CONCLUSION

Overexpression of miR-216a/217 activates the PI3K/Akt and TGF-β pathways by targeting PTEN and SMAD7, contributing to hepatocarcinogenesis and tumor recurrence in HCC.

Systemically circulating viral and tumor-derived microRNAs in KSHV-associated malignancies

MicroRNAs (miRNAs) are stable, small non-coding RNAs that modulate many downstream target genes. Recently, circulating miRNAs have been detected in various body fluids and within exosomes, prompting their evaluation as candidate biomarkers of diseases, especially cancer. Kaposi's sarcoma (KS) is the most common AIDS-associated cancer and remains prevalent despite Highly Active Anti-Retroviral Therapy (HAART). KS is caused by KS-associated herpesvirus (KSHV), a gamma herpesvirus also associated with Primary Effusion Lymphoma (PEL). We sought to determine the host and viral circulating miRNAs in plasma, pleural fluid or serum from patients with the KSHV-associated malignancies KS and PEL and from two mouse models of KS. Both KSHV-encoded miRNAs and host miRNAs, including members of the miR-17–92 cluster, were detectable within patient exosomes and circulating miRNA profiles from KSHV mouse models. Further characterization revealed a subset of miRNAs that seemed to be preferentially incorporated into exosomes. Gene ontology analysis of signature exosomal miRNA targets revealed several signaling pathways that are known to be important in KSHV pathogenesis. Functional analysis of endothelial cells exposed to patient-derived exosomes demonstrated enhanced cell migration and IL-6 secretion. This suggests that exosomes derived from KSHV-associated malignancies are functional and contain a distinct subset of miRNAs. These could represent candidate biomarkers of disease and may contribute to the paracrine phenotypes that are a characteristic of KS.

Circulating microRNAs (miRNAs), such as those found in exosomes, have emerged as diagnostic tools and hold promise as minimally invasive, stable biomarkers. Transfer of tumor-derived exosomal miRNAs to surrounding cells may be an important form of cellular communication. Kaposi's sarcoma-associated herpesvirus (KSHV) is the etiological agent of Kaposi's sarcoma (KS), the most common AIDS-defining cancer worldwide. Here, we survey systemically circulating miRNAs and reveal potential biomarkers for KS and Primary Effusion Lymphoma (PEL). This expands previous tissue culture studies by profiling clinical samples and by using two new mouse models of KSHV tumorigenesis. Profiling of circulating miRNAs revealed that oncogenic and viral miRNAs were present in exosomes from KS patient plasma, pleural effusions and mouse models of KS. Analysis of human oncogenic miRNAs, including the well-known miR-17-92 cluster, revealed that several miRNAs were preferentially incorporated into exosomes in our KS mouse model. Gene ontology analysis of upregulated miRNAs showed that the majority of pathways affected were known targets of KSHV signaling pathways. Transfer of these oncogenic exosomes to immortalized hTERT-HUVEC cells enhanced cell migration and IL-6 secretion. These circulating miRNAs and KS derived exosomes may therefore be part of the paracrine signaling mechanism that mediates KSHV pathogenesis.

Loss of N-Myc interactor promotes epithelial-mesenchymal transition by activation of TGF-β/SMAD signaling

Epithelial-mesenchymal transition is one of the critical cellular programs that facilitate the progression of breast cancer to an invasive disease. We have observed that the expression of N-myc interactor (NMI) decreases significantly during progression of breast cancer, specifically in invasive and metastatic stages. Recapitulation of this loss in breast cell lines with epithelial morphology (MCF10A (non-tumorigenic) and T47D (tumorigenic)) by silencing NMI expression causes mesenchymal-like morphological changes in 3D growth, accompanied by upregulation of SLUG and ZEB2 and increased invasive properties. Conversely, we found that restoring NMI expression attenuated the mesenchymal attributes of metastatic breast cancer cells, accompanied by distinctly circumscribed 3D growth with basement membrane deposition and decreased invasion. Further investigations into the downstream signaling modulated by NMI revealed that NMI expression negatively regulates SMAD signaling, which is a key regulator of cellular plasticity. We demonstrate that NMI blocks TGF-β/SMAD signaling via upregulation of SMAD7, a negative feedback regulator of the pathway. We also provide evidence that NMI activates STAT signaling, which negatively modulates TGF-β/SMAD signaling. Taken together, our findings suggest that loss of NMI during breast cancer progression could be one of the driving factors that enhance the invasive ability of breast cancer by aberrant activation of TGF-β/SMAD signaling.

A poor prognosis subtype of HNSCC is consistently observed across methylome, transcriptome, and miRNome analysis

PURPOSE

Distant metastasis after treatment is observed in about 20% of squamous cell carcinoma of the head and neck (HNSCC). In the absence of any validated robust biomarker, patients at higher risk for metastasis cannot be provided with tailored therapy. To identify prognostic HNSCC molecular subgroups and potential biomarkers, we have conducted genome-wide integrated analysis of four omic sets of data.

EXPERIMENTAL DESIGN

Using state-of-the-art technologies, a core set of 45 metastasizing and 55 nonmetastasizing human papillomavirus (HPV)-unrelated HNSCC patient samples were analyzed at four different levels: gene expression (transcriptome), DNA methylation (methylome), DNA copy number (genome), and microRNA (miRNA) expression (miRNome). Molecular subgroups were identified by a model-based clustering analysis. Their clinical relevance was evaluated by survival analysis, and functional significance by pathway enrichment analysis.

RESULTS

Patient subgroups selected by transcriptome, methylome, or miRNome integrated analysis are associated with shorter metastasis-free survival (MFS). A common subgroup, R1, selected by all three omic approaches, is statistically more significantly associated with MFS than any of the single omic-selected subgroups. R1 and non-R1 samples display similar DNA copy number landscapes, but more frequent chromosomal aberrations are observed in the R1 cluster (especially loss at 13q14.2-3). R1 tumors are characterized by alterations of pathways involved in cell-cell adhesion, extracellular matrix (ECM), epithelial-to-mesenchymal transition (EMT), immune response, and apoptosis.

CONCLUSIONS

Integration of data across several omic profiles leads to better selection of patients at higher risk, identification of relevant molecular pathways of metastasis, and potential to discover biomarkers and drug targets.

Global profiling in vestibular schwannomas shows critical deregulation of microRNAs and upregulation in those included in chromosomal region 14q32

Background

Vestibular schwannomas are benign tumors that arise from Schwann cells in the VIII cranial pair and usually present NF2 gene mutations and/or loss of heterozygosity on chromosome 22q. Deregulation has also been found in several genes, such as ERBB2 and NRG1. MicroRNAs are non-coding RNAs approximately 21 to 23 nucleotides in length that regulate mRNAs, usually by degradation at the post-transcriptional level.

Methods

We used microarray technology to test the deregulation of miRNAs and other non-coding RNAs present in GeneChip miRNA 1.0 (Affymetrix) over 16 vestibular schwannomas and 3 control-nerves, validating 10 of them by qRT-PCR.

Findings

Our results showed the deregulation of 174 miRNAs, including miR-10b, miR-206, miR-183 and miR-204, and the upregulation of miR-431, miR-221, miR-21 and miR-720, among others. The results also showed an aberrant expression of other non-coding RNAs. We also found a general upregulation of the miRNA cluster located at chromosome 14q32.

Conclusion

Our results suggest that several miRNAs are involved in tumor formation and/or maintenance and that global upregulation of the 14q32 chromosomal site contains miRNAs that may represent a therapeutic target for this neoplasm.

MicroRNA-106b-25 cluster targets β-TRCP2, increases the expression of Snail and enhances cell migration and invasion in H1299 (non small cell lung cancer) cells

Lung cancer causes high mortality without a declining trend and non small cell lung cancer represents 85% of all pulmonary carcinomas. MicroRNAs (miRNAs) serve as fine regulators of proliferation, migration, invasion/metastasis and angiogenesis of normal and cancer cells. Using TargetScan6.2, we predicted that the ubiquitin ligase, β-TRCP2, could be a target for two of the constituent miRNAs of the miR-106b-25 cluster (miR-106b and miR-93). We generated a stable clone of miR-106b-25 cluster (CL) or the empty vector (EV) in H1299 (non small cell lung cancer) cells. The expression of β-TRCP2 mRNA was significantly lower in CL than that in EV cells. Transient expression of miR-93 but not antimiR-93 decreased the expression of β-TRCP2 mRNA in H1299 cells. β-TRCP2-3'UTR reporter assay revealed that its activity in CL cells was only 60% of that in EV cells. Snail protein expression was higher in CL than that in EV cells and H1299 cells exhibited an increase in the expression of Snail upon transient transfection with miR-93. miR-106b-25 cluster-induced migration of CL measured by scratch assay was more than that in EV cells and no significant difference in migration was observed between antimiR-93-transfected H1299 cells and the corresponding control-oligo-transfected cells. miR-106b-25 cluster-induced migration of CL cells was again confirmed in a Boyden chamber assay without the matrigel. CL cells were more invasive than EV cells when assessed using Boyden chambers with matrigel but there were no significant changes in the cell viabilities between EV and CL cells. Colony formation assay revealed that the CL cells formed more number of colonies than EV cells but they were smaller in size than those formed by EV cells. The supernatant from CL cells was more effective than that from EV cells in inducing tube formation in endothelial cells. Taken together, our data indicate that miR-106b-25 cluster may play an important role in the metastasis of human non-small cell lung cancer cells by directly suppressing the β-TRCP2 gene expression with a consequent increase in the expression of Snail.

MicroRNA and signal transduction pathways in tumor radiation response

Tumor radiation response is an essential issue in radiotherapy and a core determining factor of tumor radioresistance or radiosensitivity. Multiple factors can influence tumor radiation response, and among them tumor genetic and epigenetic background, tumor microenvironment and tumor blood flow status may take a leading role. During the whole process of tumor radiation response, tumor radiosensitivity can be regulated in an orderly manner through some classical signal transduction pathways. Although these pathways have already owned multiple biological functions and involved in the process of carcinogenesis, their regulatory roles in tumor radiation response can not be ignored. MicroRNA (miRNA) is a class of non-coding RNA of about 22 nucleotides in length, which binds to the 3'-untranslated region (3'-UTR) of target gene and controls the expression of it at the post-transcriptional level. MiRNA participates in numerous physiology and pathology processes and acts as oncogene or tumor suppressor to affect cancer progression. Through interplaying with the key components in radiation related signal transduction pathways, miRNA could effectively activate the expression of DNA damage response genes and cell cycle related genes in the nucleus, and play a critical role in the modulation of radiation response and radiosensitivity in tumor cells. In this review, we mainly elucidate the regulatory mechanisms and functions of miRNA in these radiation related signal transduction pathways from three different aspects which include the upstream receptors, midstream transducer pathways, and downstream effector genes.

De-regulated microRNAs in pediatric cancer stem cells target pathways involved in cell proliferation, cell cycle and development

Background

microRNAs (miRNAs) have been implicated in the control of many biological processes and their deregulation has been associated with many cancers. In recent years, the cancer stem cell (CSC) concept has been applied to many cancers including pediatric. We hypothesized that a common signature of deregulated miRNAs in the CSCs fraction may explain the disrupted signaling pathways in CSCs.

Methodology/Results

Using a high throughput qPCR approach we identified 26 CSC associated differentially expressed miRNAs (DEmiRs). Using BCmicrO algorithm 865 potential CSC associated DEmiR targets were obtained. These potential targets were subjected to KEGG, Biocarta and Gene Ontology pathway and biological processes analysis. Four annotated pathways were enriched: cell cycle, cell proliferation, p53 and TGF-beta/BMP. Knocking down hsa-miR-21-5p, hsa-miR-181c-5p and hsa-miR-135b-5p using antisense oligonucleotides and small interfering RNA in cell lines led to the depletion of the CSC fraction and impairment of sphere formation (CSC surrogate assays).

Conclusion

Our findings indicated that CSC associated DEmiRs and the putative pathways they regulate may have potential therapeutic applications in pediatric cancers.

MicorRNA 106b ∼ 25 cluster and gastric cancer

Conventional strategies for the early diagnosis and treatment of gastric cancer are not yet satisfactory, and it calls for better diagnosis and treatments based on a deeper understanding of the molecular mechanisms. It has been revealed that the number of verified human microRNA (miRNA) expression contribute to the initiation and progression of cancer. Among them, miR-106b ∼ 25 cluster is of particular interest. The miRNA-106b ∼ 25 cluster is composed of the highly conserved miRNA-106b, miRNA-93 and miRNA-25. The miRNA-106b ∼ 25 polycistron exerted potential proliferative, anti-apoptotic and cell cycle-promoting effects on cancer cells. Over-expression of the miRNA-106b ∼ 25 cluster is known to overcome TGF-beta mediated growth suppression via targeting p21 and Bim. This cluster can additionally target the inhibitory Smad7 protein and increase TGF-beta RI which is sufficient to induce epithelial-to-mesenchymal transition (EMT). MiRNA-93 can promote angiogenesis. The tumor suppressor genes RB and PTEN are the direct targets of miRNA-106b ∼ 25. Especially, miRNA-106b ∼ 25 clusters play an important role in oncogenesis of gastric cancer. Focus on the essential role in tumorgenisis and extremely low expression of miRNA-106b ∼ 25 in normal tissues, it maybe an appropriate target of gastric cancer treatment and a novel biomarkers for detecting gastric cancer.

MicroRNA-93 regulates NRF2 expression and is associated with breast carcinogenesis

MicroRNAs (miRNA) are small non-coding RNAs that regulate the expression of approximately 60% of all human genes and play important roles in disease processes. Recent studies have demonstrated a link between dysregulated expression of miRNAs and breast carcinogenesis. Long-term estrogen exposure is implicated in development of human breast cancers, yet underlying mechanisms remain elusive. We have recently demonstrated that antioxidant vitamin C (vit C) prevents estrogen-induced breast tumor development. In this study, we investigated the role of vit C in the regulation of microRNA-93 (miR-93) and its target gene(s) in a rat model of mammary carcinogenesis. Female August Copenhagen Irish (ACI) rats were treated with vit C in the presence or absence of 17β-estradiol (E2) for 8 months. We demonstrate an increased expression of the miR-93 in E2-treated mammary tissues and in human breast cell lines and vit C treatment reverted E2-mediated increase in miR-93 levels. MiRNA target prediction programs suggest one of the target genes of miR-93 to be nuclear factor erythroid 2-related factor 2 (NRF2). In contrast with miR-93 expression, NRF2 protein expression was significantly decreased in E2-treated mammary tissues, mammary tumors, and in breast cancer cell lines, and its expression was significantly increased after vit C treatment. Ectopic expression of miR-93 decreased protein expression of NRF2 and NRF2-regulated genes. Furthermore, miR-93 decreased apoptosis, increased colony formation, mammosphere formation, cell migration and DNA damage in breast epithelial cells, whereas silencing of miR-93 in these cells inhibited these carcinogenic processes. Taken together, our findings suggest an oncogenic potential of miR-93 during E2-induced breast carcinogenesis.

The relevance of the TGF-β Paradox to EMT-MET programs

The role of transforming growth factor-β (TGF-β) during tumorigenesis is complex and paradoxical, reflecting its ability to function as a tumor suppressor in normal and early-stage cancers, and as a tumor promoter in their late-stage counterparts. The switch in TGF-β function is known as the "TGF-β Paradox," whose manifestations are intimately linked to the initiation of epithelial-mesenchymal transition (EMT) programs in developing and progressing carcinomas. Indeed, as carcinoma cells emerge from EMT programs stimulated by TGF-β, they readily display a variety of acquired phenotypes that provide a selective advantage to growing carcinomas, including (i) enhanced cell migration and invasion; (ii) heightened resistance to cytotoxic agents, targeted chemotherapeutic, and radiation treatments; and (iv) boosted expansion of cancer-initiating and stem-like cell populations that underlie tumor metastasis and disease recurrence. At present, the molecular, cellular, and microenvironmental mechanisms that enable post-EMT and metastatic carcinoma cells to hijack the oncogenic activities of TGF-β remain incompletely understood. Additionally, the molecular mechanisms that counter EMT programs and limit the aggressiveness of late-stage carcinomas, events that transpire via mesenchymal-epithelial transition (MET) reactions, also need to be further elucidated. Here we review recent advances that provide new insights into how TGF-β promotes EMT programs in late-stage carcinoma cells, as well as how these events are balanced by MET programs during the development and metastatic progression of human carcinomas.

MicroRNAs regulate both epithelial-to-mesenchymal transition and cancer stem cells

Concepts and experimental models derived from basic research have been successfully applied to the field of molecular oncology, tremendously increasing our knowledge of the nature and the progression of tumors. The process of epithelial-to-mesenchymal transition, the cancer stem cell hypothesis, and their functional association and interdependence represent some of the most significant examples. The molecular determinants underlying the plasticity of cancers are currently the object of extensive research efforts, and a substantial body of evidence suggests that these models can be connected by the regulatory role of microRNAs, small noncoding RNA molecules with a fundamental role in many cellular functions. This review will highlight and discuss this link and its possible implications for the fight against cancer.

Regulation of epithelial-mesenchymal and mesenchymal-epithelial transitions by microRNAs

Epithelial-mesenchymal transition (EMT) and the reverse process, mesenchymal-epithelial transition (MET), are essential during development and in the regulation of stem cell pluripotency, yet these processes are also activated in pathological contexts, such as in fibrosis and cancer progression. In EMT and MET, diverse signaling pathways cooperate in the initiation and progression of the EMT and MET programs, through regulation at transcriptional, post-transcriptional, translational, and post-translational levels. MicroRNAs recently emerged as potent regulators of EMT and MET, with their abilities to target multiple components involved in epithelial integrity or mesenchymal traits. By affecting EMT and MET processes, microRNAs are involved in the regulation of stem cell pluripotency and the control of tumor progression.

MicroRNA-25 functions as a potential tumor suppressor in colon cancer by targeting Smad7

Because it is a member of the miR-106b~25 cluster, microRNA-25 (miR-25) is known to be dysregulated in human cancers. However, the expression and role of miR-25 in colon cancer remain unclear. In this study, miR-25 was found to be down-regulated in human colon cancer tissues when compared to those in matched, non-neoplastic mucosa tissues. Functional studies revealed that restoration of miR-25 expression inhibited cell proliferation and migration. In contrast, miR-25 inhibition could promote the proliferation and migratory ability of cells. Stable over-expression of miR-25 also suppressed the growth of colon cancer-cell xenografts in vivo. Furthermore, bioinformatic predictions and experimental validation were used to identify Smad7 as a direct target of miR-25. Functional reverse experiments indicated that the antitumor effects of miR-25 were probably mediated by its repression of Smad7. These results suggest that miR-25 may function as a tumor suppressor by targeting Smad7 in colon cancer. Thus, miR-25 may serve as a potential therapeutic agent or target for cancer therapy.

MicroRNA-92a negatively regulates Toll-like receptor (TLR)-triggered inflammatory response in macrophages by targeting MKK4 kinase

Toll-like receptors (TLRs) play a critical role in the initiation of immune responses against invading pathogens. MicroRNAs have been shown to be important regulators of TLR signaling. In this study, we have found that the stimulation of multiple TLRs rapidly reduced the levels of microRNA-92a (miRNA-92a) and some other members of the miRNA-92a family in macrophages. miR-92a mimics significantly decreased, whereas miR-92a knockdown increased, the activation of the JNK/c-Jun pathway and the production of inflammatory cytokines in macrophages when stimulated with ligands for TLR4. Furthermore, mitogen-activated protein kinase kinase 4 (MKK4), a kinase that activates JNK/stress-activated protein kinase, was found to be directly targeted by miR-92a. Similar to the effects of the miR-92a mimics, knockdown of MKK4 inhibited the activation of JNK/c-Jun signaling and the production of TNF-α and IL-6. In conclusion, we have demonstrated that TLR-mediated miR-92a reduction feedback enhances TLR-triggered production of inflammatory cytokines in macrophages, thus outlining new mechanisms for fine-tuning the TLR-triggered inflammatory response.

Regulation of miR106b cluster through the RB pathway: mechanism and functional targets

The RB pathway plays a critical role in proliferation control that is commonly subverted in tumor development. However, restoration of RB pathway function can be elicited in many tumor cells by the inhibition of CDK4/6 activity that leads to dephosphorylation of RB and subsequent repression of E2F-mediated transcription. In this context, active RB/E2F complexes inhibit the expression of a critical program of coding genes that promote cell cycle progression. However, the non-coding RNA target genes downstream from RB that could be relevant for tumor biology remain obscure. Here, miRNA gene expression profiling identified the miR106b cluster as being efficiently repressed with CDK4/6 inhibition in an E2F and RB-dependent manner. Importantly, the miR106B-cluster is intragenic of MCM7, and through a series of functional studies, the basis of MCM7 regulation and concordant expression of the miRNA species within the 106b cluster was determined. Importantly, RB-mediated repression of the 106b cluster enhances the transcript levels of p21Cip1 and PTEN. These data provide a mechanistic basis for cross-talk between the RB pathway and p21 and PTEN through the regulation of the MCM7/miR106b locus.

Folliculin, the product of the Birt-Hogg-Dube tumor suppressor gene, interacts with the adherens junction protein p0071 to regulate cell-cell adhesion

Birt-Hogg-Dube (BHD) is a tumor suppressor gene syndrome associated with fibrofolliculomas, cystic lung disease, and chromophobe renal cell carcinoma. In seeking to elucidate the pathogenesis of BHD, we discovered a physical interaction between folliculin (FLCN), the protein product of the BHD gene, and p0071, an armadillo repeat containing protein that localizes to the cytoplasm and to adherens junctions. Adherens junctions are one of the three cell-cell junctions that are essential to the establishment and maintenance of the cellular architecture of all epithelial tissues. Surprisingly, we found that downregulation of FLCN leads to increased cell-cell adhesion in functional cell-based assays and disruption of cell polarity in a three-dimensional lumen-forming assay, both of which are phenocopied by downregulation of p0071. These data indicate that the FLCN-p0071 protein complex is a negative regulator of cell-cell adhesion. We also found that FLCN positively regulates RhoA activity and Rho-associated kinase activity, consistent with the only known function of p0071. Finally, to examine the role of Flcn loss on cell-cell adhesion in vivo, we utilized keratin-14 cre-recombinase (K14-cre) to inactivate Flcn in the mouse epidermis. The K14-Cre-Bhd(flox/flox) mice have striking delays in eyelid opening, wavy fur, hair loss, and epidermal hyperplasia with increased levels of mammalian target of rapamycin complex 1 (mTORC1) activity. These data support a model in which dysregulation of the FLCN-p0071 interaction leads to alterations in cell adhesion, cell polarity, and RhoA signaling, with broad implications for the role of cell-cell adhesion molecules in the pathogenesis of human disease, including emphysema and renal cell carcinoma.

MicroRNA-106b-25 cluster expression is associated with early disease recurrence and targets caspase-7 and focal adhesion in human prostate cancer

The miR-106b-25 microRNA (miRNA) cluster is a candidate oncogene in human prostate cancer. Here, we report that miRNAs encoded by miR-106b-25 are upregulated in both primary tumors and distant metastasis. Moreover, increased tumor miR-106b expression was associated with disease recurrence and the combination of high miR-106b and low CASP7 (caspase-7) expressions in primary tumors was an independent predictor of early disease recurrence (adjusted hazard ratio=4.1; 95% confidence interval: 1.6-12.3). To identify yet unknown oncogenic functions of miR-106b, we overexpressed it in LNCaP human prostate cancer cells to examine miR-106b-induced global expression changes among protein-coding genes. The approach revealed that CASP7 is a direct target of miR-106b, which was confirmed by western blot analysis and a 3'-untranslated region reporter assay. Moreover, selected phenotypes induced by miR-106b knockdown in DU145 human prostate cancer cells did not develop when both miR-106b and CASP7 expression were inhibited. Further analyses showed that CASP7 is downregulated in primary prostate tumors and metastatic lesions across multiple data sets and is by itself associated with disease recurrence and disease-specific survival. Using bioinformatics, we also observed that miR-106b-25 may specifically influence focal adhesion-related pathways. This observation was experimentally examined using miR-106b-25-transduced 22Rv1 human prostate cancer cells. After infection with a miR-106b-25 lentiviral expression construct, 22Rv1 cells showed increased adhesion to basement membrane- and bone matrix-related filaments and enhanced soft agar growth. In summary, miR-106b-25 was found to be associated with prostate cancer progression and disease outcome and may do so by altering apoptosis- and focal adhesion-related pathways.

MicroRNAs involved in regulating epithelial-mesenchymal transition and cancer stem cells as molecular targets for cancer therapeutics

One of the major challenges in cancer gene therapy is the identification of functionally relevant tumor-specific genes as the therapeutic targets. MicroRNAs (miRNAs) are a class of small, 22-25 nucleotides, endogenously expressed noncoding RNA. miRNAs are important genetic regulators: one miRNA can possibly target multiple genes and they can function as tumor promoters (oncogenic miRNAs, oncomirs) or tumor suppressors (anti-oncomirs). Therefore, the identification of misregulated miRNAs in cellular signaling pathways related to oncogenesis can have profound implications for cancer therapy. The epithelial-mesenchymal transition (EMT) converts epithelial cells into mesenchymal cells, a normal embryological process that frequently get activated during cancer invasion and metastasis. Recent evidence also supports the presence of a small subset of self-renewing, stem-like cells within the tumor mass that possess the capacity to seed new tumors and they have been termed 'cancer stem cells (CSC)'. Conceivably, these CSCs could provide a resource for cells that cause therapy resistance. Although the cell origin of CSCs remains to be fully elucidated, a growing body of evidence has demonstrated that the biology of EMT and CSCs is tightly linked with the sequences and compositions of miRNA molecules. Therefore, targeting miRNAs involved in EMT and CSCs regulation can provide novel miRNA-based therapeutic strategies in oncology.

Molecular pathways: targeting the TGF-β pathway for cancer therapy

TGF-β is a ubiquitous cytokine that plays an active role in many cellular processes. Nearly every cell type has the ability to secrete TGF-β, as well as the ability to respond to TGF-β via the presence of TGF-β receptors on the cell surface. Consequently, gain or loss of function of the TGF-β pathway and its components are known to lead to a variety of diseases, including cancer. In epithelial cells, TGF-β functions as a tumor suppressor, where it inhibits proliferation, induces apoptosis, and mediates differentiation. Conversely, in other contexts, TGF-β promotes tumor progression through increasing tumor cell invasion and metastasis. Thus, TGF-β can have opposing roles, likely dependent, in part, on whether the cancer is early or late stage. The effects of TGF-β on tumor suppression and promotion are not limited to the tumor cell itself; rather, these effects can also be mediated through the stroma and the immune system. The dichotomous role of TGF-β in cancer highlights our need to understand the contextual effects of this cytokine to better guide patient selection for the use of anti-TGF-β therapies currently in clinical trials.

Post-translational regulation of TGF-β receptor and Smad signaling

TGF-β family signaling through Smads is conceptually a simple and linear signaling pathway, driven by sequential phosphorylation, with type II receptors activating type I receptors, which in turn activate R-Smads. Nevertheless, TGF-β family proteins induce highly complex programs of gene expression responses that are extensively regulated, and depend on the physiological context of the cells. Regulation of TGF-β signaling occurs at multiple levels, including TGF-β activation, formation, activation and destruction of functional TGF-β receptor complexes, activation and degradation of Smads, and formation of Smad transcription complexes at regulatory gene sequences that cooperate with a diverse set of DNA binding transcription factors and coregulators. Here we discuss recent insights into the roles of post-translational modifications and molecular interaction networks in the functions of receptors and Smads in TGF-β signal responses. These layers of regulation demonstrate how a simple signaling system can be coopted to exert exquisitely regulated, complex responses.