Extracellular Vesicles As miRNA Nano-Shuttles: Dual Role in Tumor Progression

Tumor-derived extracellular vesicles (EVs) have a pleiotropic role in cancer, interacting with target cells of the tumor microenvironment, such as fibroblasts, immune and endothelial cells. EVs can modulate tumor progression, angiogenic switch, metastasis, and immune escape. These vesicles are nano-shuttles containing a wide spectrum of miRNAs that contribute to tumor progression. MiRNAs contained in extracellular vesicles (EV-miRNAs) are disseminated in the extracellular space and are able to influence the expression of target genes with either tumor suppressor or oncogenic functions, depending on both parental and target cells. Metastatic cancer cells can balance their oncogenic potential by expressing miRNAs with oncogenic function, whilst exporting miRNAs with tumor suppressor roles out of the cells. Importantly, treatment of cancer cells with specific natural and chemical compounds could induce the elimination of miRNAs with oncogenic function, thereby reducing their aggressiveness. In this review, we discuss the mechanisms by which EV-miRNAs, acting as miRNAs with oncogenic or tumor suppressor functions, could contribute to cancer progression.     

Simultaneous inhibition of multiple oncogenic miRNAs by a multi-potent microRNA sponge

The roles of oncogenic miRNAs are widely recognized in many cancers. Inhibition of single miRNA using antagomiR can efficiently knock-down a specific miRNA. However, the effect is transient and often results in subtle phenotype, as there are other miRNAs contribute to tumorigenesis. Here we report a multi-potent miRNA sponge inhibiting multiple miRNAs simultaneously. As a model system, we targeted miR-21, miR-155 and miR-221/222, known as oncogenic miRNAs in multiple tumors including breast and pancreatic cancers. To achieve efficient knockdown, we generated perfect and bulged-matched miRNA binding sites (MBS) and introduced multiple copies of MBS, ranging from one to five, in the multi-potent miRNA sponge. Luciferase reporter assay showed the multi-potent miRNA sponge efficiently inhibited 4 miRNAs in breast and pancreatic cancer cells. Furthermore, a stable and inducible version of the multi-potent miRNA sponge cell line showed the miRNA sponge efficiently reduces the level of 4 target miRNAs and increase target protein level of these oncogenic miRNAs. Finally, we showed the miRNA sponge sensitize cells to cancer drug and attenuate cell migratory activity. Altogether, our study demonstrates the multi-potent miRNA sponge is a useful tool to examine the functional impact of simultaneous inhibition of multiple miRNAs and proposes a therapeutic potential.     

miRNA在骨肉瘤中的研究进展

骨肉瘤是一种恶性程度很高的原发性骨肿瘤,其发生率约为0．04～0．05／万,多数起源于骨间叶细胞,好发部位为长骨,一般为股骨远端或胫骨近端,其次为肱骨近端。好发于10～20岁的青少年,占骨恶性肿瘤的20％左右,肺转移是其主要死亡原因,随着新辅助化疗、保肢手术等的开展,5年生存率提高到近60％～70％。但由于化疗耐药性等问题的存在,患者仍面临着复发及肺转移的困扰。基因治疗、免疫治疗和分子靶向治疗等生物治疗技术的发展也为骨肉瘤的治疗开辟了新的道路,为骨肉瘤患者带来希望。     

MicroRNA与肿瘤信号通路交互作用的研究进展

miRNAs是一类非编码单链小分子RNA,主要通过特异性的基因沉默引起靶mRNA的降解或翻译抑制,调控转录后基因表达,影响细胞增殖、分化和凋亡等。某些oncomiRs充当着＂癌基因＂或者＂抑癌基因＂的角色,与众多信号通路存在交互作用,参与肿瘤的发生发展,而其表达水平的改变具有抗肿瘤作用,预示着其将为新药的开发及肿瘤的治疗提供一个新的作用靶点,现综述如下。     

MicroRNAs在乳腺癌干细胞中的作用研究进展

乳腺癌干细胞（breast cancer stem cells,BCSCs）是导致乳腺癌发生、转移、耐药、复发等的重要原因。MicroRNAs（miRNAs）是近年来发现的一种非编码小分子RNA,可通过与靶标基因的3 '-非翻译区（3'-UTR）的完全或不完全配对,抑制靶标基因的翻译或降解靶标基因,从而发挥多种生物学功能。miRNAs在BCSCs中的异常表达可调控BCSCs的自我更新、抗凋亡、上皮间质转化（epithelial-mesenchymal transition,EMT）等生物学行为,从而促进乳腺癌的复发、转移。以miRNAs为研究靶点,为乳腺癌的诊断、预后及治疗提供了全新的思路。本文就近年来该方面的研究进展简要综述。     

Molecular and anatomic considerations in the pathogenesis of breast cancer

In spite of the recent recognition of specific genes associated with an elevated lifetime incidence risk of breast cancer, the molecular mechanisms of breast tumor formation remain largely unknown. Tumorigenesis is thought to be highly complex, likely involving the accumulation of 5-10 genetic and epigenetic events. Recent investigations have begun to identify some of these events, and in vitro model systems for breast tumorigenesis, including radiation-induced breast cancer, are expected to provide further insight. Normal human breast epithelial cells exhibit a finite life span, both in vivo and in vitro. A critical event in oncogenic transformation is the ability of cells to multiply indefinitely, a phenomenon referred to as "immortalization." Using human papillomavirus (HPV) oncogenes, multiple normal breast epithelial subtypes have been shown to have distinct susceptibilities to immortalization by the HPV E6 and E7 oncogenes. Because HPV E6 and E7 inactivate two well-known tumor suppressor proteins, p53 and Rb, respectively, this suggests that a cell-type-specific predominance exists with respect to these tumor suppressor pathways. Additional evidence for variability to oncogenic stimuli among normal breast epithelial cells is provided by findings of locally confined loss of heterozygosity. An in vitro model of radiation-induced breast cancer is associated with early abrogation of p53 function. The resultant pair of normal and radiation-transformed breast epithelial cells serves as a useful system to identify other genes critically relevant to breast tumorigenesis. These and other models should help further define the molecular mechanisms underlying the early steps of breast cancer formation.     

Epigenetics and genetics. MicroRNAs en route to the clinic: progress in validating and targeting microRNAs for cancer therapy

In normal cells multiple microRNAs (miRNAs) converge to maintain a proper balance of various processes, including proliferation, differentiation and cell death. miRNA dysregulation can have profound cellular consequences, especially because individual miRNAs can bind to and regulate multiple mRNAs. In cancer, the loss of tumour-suppressive miRNAs enhances the expression of target oncogenes, whereas increased expression of oncogenic miRNAs (known as oncomirs) can repress target tumour suppressor genes. This realization has resulted in a quest to understand the pathways that are regulated by these miRNAs using in vivo model systems, and to comprehend the feasibility of targeting oncogenic miRNAs and restoring tumour-suppressive miRNAs for cancer therapy. Here we discuss progress in using mouse models to understand the roles of miRNAs in cancer and the potential for manipulating miRNAs for cancer therapy as these molecules make their way towards clinical trials.     

miRNA signature of schwannomas: possible role(s) of "tumor suppressor" miRNAs in benign tumors

miRNAs have been recently implicated as drivers in several carcinogenic processes, where they can act either as oncogenes or as tumor suppressors. Schwannomas arise from Schwann cells, the myelinating cells of the peripheral nervous system. These benign tumors typically result from loss of the neurofibromatosis type 2 (NF2) tumor suppressor gene. We have recently carried out high-throughput miRNA expression profiling of human vestibular schwannomas using an array representing 407 known miRNAs in order to explore the role of miRNAs in the tumorigenesis of schwannomas. We found that miR-7 functions as a "tumor suppressor" by targeting proteins in three major oncogenic pathways - EGFR, Pak1, and Ack1. Interestingly, in this study, we also observed that several previously described potential tumor suppressor miRNAs that are down-regulated in malignant tumors were up-regulated in schwannomas. Here we discuss the possibility that "tumor suppressor" miRNAs may play a role in the transition stage(s) of cancer from benign to malignant forms.     

MicroRNA gene expression deregulation in human breast cancer

MicroRNAs (miRNAs) are a class of small noncoding RNAs that control gene expression by targeting mRNAs and triggering either translation repression or RNA degradation. Their aberrant expression may be involved in human diseases, including cancer. Indeed, miRNA aberrant expression has been previously found in human chronic lymphocytic leukemias, where miRNA signatures were associated with specific clinicobiological features. Here, we show that, compared with normal breast tissue, miRNAs are also aberrantly expressed in human breast cancer. The overall miRNA expression could clearly separate normal versus cancer tissues, with the most significantly deregulated miRNAs being mir-125b, mir-145, mir-21, and mir-155. Results were confirmed by microarray and Northern blot analyses. We could identify miRNAs whose expression was correlated with specific breast cancer biopathologic features, such as estrogen and progesterone receptor expression, tumor stage, vascular invasion, or proliferation index.     

The roles of oncogenic miRNAs and their therapeutic importance in breast cancer

Since the discovery of tumour suppressive miRNA in 2002, the dysregulation of miRNAs was implicated in many cancers, exhibiting both tumour suppressive and oncogenic roles. Dysregulation of miRNAs was found to be involved in the initiation of oncogenesis, as well as the progression, invasion and metastasis of cancers. While normal miRNA inhibitory functions help regulate gene expression in the cell, oncogenic miRNA, when dysregulated can lead to suppression of critical pathways that control apoptosis, cell cycle progression, growth and proliferation. This suppression allows for the upregulation of pro-oncogenic factors that drive cell survival, growth and proliferation. Due to emerging discoveries, oncogenic miRNAs are proving to be a critical component in cancers, such as breast cancer, and may provide novel avenues for cancer treatment. In this article, we discuss the roles of the most studied oncogenic miRNAs in breast cancer including clusters and families involved as well as the less studied and recently discovered oncogenic miRNAs. These miRNAs provide valuable information into the complexity of regulatory elements affected by their overexpression and the overall impact in the progression of breast cancer. Also, identifying miRNAs causing or leading to resistance or sensitivity to current anti-cancer drugs prior to treatment may lead to an improvement in treatment selection and overall patient response. This review summarizes known and recently discovered miRNAs in literature found to have oncogenic roles in breast cancer initiation and the progression, invasion and metastasis of the disease.     

MicroRNA function in cancer: oncogene or a tumor suppressor?

MicroRNAs (miRNAs) are small noncoding, double-stranded RNA molecules that can mediate the expression of target genes with complementary sequences. About 5,300 human genes have been implicated as targets for miRNAs, making them one of the most abundant classes of regulatory genes in humans. MiRNAs recognize their target mRNAs based on sequence complementarity and act on them to cause the inhibition of protein translation by degradation of mRNA. Besides contributing to development and normal function, microRNAs have functions in various human diseases. Given the importance of miRNAs in regulating cellular differentiation and proliferation, it is not surprising that their misregulation is linked to cancer. In cancer, miRNAs function as regulatory molecules, acting as oncogenes or tumor suppressors. Amplification or overexpression of miRNAs can down-regulate tumor suppressors or other genes involved in cell differentiation, thereby contributing to tumor formation by stimulating proliferation, angiogenesis, and invasion; i.e., they act as oncogenes. Similarly, miRNAs can down-regulate different proteins with oncogenic activity; i.e., they act as tumor suppressors. This review will highlight the recent discoveries regarding miRNAs and their importance in cancer.     

Decreased microRNA-214 levels in breast cancer cells coincides with increased cell proliferation, invasion and accumulation of the Polycomb Ezh2 methyltransferase

MicroRNAs (miRNAs) are small non-coding RNAs, which regulate gene expression by inhibiting translation or promoting degradation of specific target messenger RNAs (mRNAs). Alteration of the levels of a number of miRNAs is common in solid and hematological tumors. We have shown previously that miR-214 regulates Ezh2 in skeletal muscle and embryonic stem cells. The current study was aimed at examining the role of miR-214 in breast cancer where miR-214 levels are reduced but whether this phenomenon bears a functional relevance is unknown. MiR-214 expression was inversely correlated with Ezh2 mRNA and protein levels in breast cancer cell lines and at least one copy of the miR-214 alleles was found to be deleted in 24% (6/25) of primary breast tumors. Experimental increase of miR-214 in breast cancer cell lines correlated with reduction of Ezh2 protein levels, a known marker of invasion and aggressive breast cancer behavior. Supporting a direct targeting mechanism, miR-214 decreased luciferase activity from a construct containing the Ezh2 3' untranslated region. Expression of miR-214 specifically reduced cell proliferation of breast cancer cells and inhibited the invasive potential of a highly metastatic breast cancer cell line. These findings indicate that reduced miR-214 levels may contribute to breast tumorigenesis by allowing abnormally elevated Ezh2 accumulation and subsequent unchecked cell proliferation and invasion.     

MicroRNAs in Colorectal Cancer: from Diagnosis to Targeted Therapy

Colorectal cancer (CRC) is one of the major healthcare problems worldwide and its processes of genesis include a sequence of molecular pathways from adenoma to carcinoma. The discovery of microRNAs, a subset of regulatory non-coding RNAs, has added new insights into CRC diagnosis and management. Together with several causes of colorectal neoplasia, aberrant expression of oncomiRs (oncogenic and tumor suppressor miRNAs) in cancer cells was found to be indirectly result in up- or down-regulation of targeted mRNAs specific to tumor promoter or inhibitor genes. The study of miRNAs as CRC biomarkers utilizes expression profiling methods from traditional tissue samples along with newly introduced non-invasive samples of faeces and body fluids. In addition, miRNAs could be employed to predict chemo- and radio-therapy responses and be manipulated in order to alleviate CRC characteristics. The scope of this article is to provide a comprehensive review of scientific literature describing aberrantly expressed miRNAs, and consequently dysregulation of targeted mRNAs alongwith the potential role of miRNAs in CRC diagnosis and prognosis, as well as to summarize the recent findings on miRNA-based manipulation methods with the aim of advancing in anti-CRC therapies.     

The guardian's little helper: microRNAs in the p53 tumor suppressor network

Several microRNAs (miRNAs) have been implicated in tumor development based on both changes in their expression patterns and gene structural alterations in human tumors. However, we are only now beginning to see how miRNAs interact with classic oncogene and tumor suppressor mechanisms. Several recent studies have implicated the miR-34 family of miRNAs in the p53 tumor suppressor network. The expression of miR-34a, miR-34b, and miR-34c is robustly induced by DNA damage and oncogenic stress in a p53-dependent manner. When overexpressed, miR-34 leads to apoptosis or cellular senescence, whereas reduction of miR-34 function attenuates p53-mediated cell death. These findings, together with the fact that miR-34 is down-regulated in several types of human cancer, show that miRNAs can affect tumorigenesis by working within the confines of well-known tumor suppressor pathways.     

Genetic variants within miR-126 and miR-335 are not associated with breast cancer risk

MicroRNAs (miRNAs) are 20-22 nt non-coding RNAs which promote the degradation of target mRNAs or repression of the translation of mRNAs by sequence specific targeting. Many miRNAs are considered as oncogenes or tumor suppressors. MiR-126 and miR-335 play roles in the suppression of breast cancer metastasis by inhibiting tumor growth, proliferation, and cell invasion. The effects of SNPs within the two miRNAs are still unknown. In our study, we analyzed two SNPs, rs4636297 within miR-126 and rs41272366 within miR-335, in three study populations for a putative association with breast cancer risk. We compared the genotype and allele frequencies of rs4636297 and rs41272366 in 2854 cases versus 3188 controls of the three study populations independently and combined. None of the performed analyses showed statistically significant results. In conclusion, our data suggest that the two genetic variants within miR-126 and miR-335 are not associated with breast cancer risk.