上皮-间质转化及其干性作用与肿瘤

上皮-间质转化（EMT）参与肿瘤转移过程,Twist作为关键调控因子在EMT中发挥重要作用,放疗、化疗和多种细胞因子均可诱导Twist介导的EMT。研究表明,肿瘤细胞可能通过EMT转变为肿瘤干细胞样细胞,并进一步导致放化疗抵抗、肿瘤血管形成及远处转移,对肿瘤的预后产生巨大影响,EMT有望成为肿瘤治疗的重要靶点。     

上皮细胞间质转化与miR-200及肿瘤细胞耐药机制的研究进展

目的:总结国内外上皮细胞间质转化与miR-200家族及肿瘤细胞耐药中的研究进展.方法:应用PubMed、CNKI及维普数据库以“EMT、miR-200和肿瘤耐药”为关键词,检索2000-2012年相关文献.共检索到英文文献5 789条,中文文献9条.纳入标准:1)上皮细胞间质转化的特性与功能;2)miR-200家族成员主要功能;3)EMT及miR-200与肿瘤耐药的关系;4)针对EMT及miR-200为靶点进行逆转肿瘤细胞耐药性的研究.根据纳入标准符合分析的文献共54篇.结果:EMT同诱导肿瘤细胞侵袭性改变以及获得性耐药的发生息息相关,miR-200家族在肿瘤细胞中的表达下调同样可以导致肿瘤耐药形成,且EMT与miR-200间可能存在一定联系,以EMT与miR-200为靶点逆转肿瘤细胞耐药性取得一定成效.结论:上皮细胞间质转化与miR-200在诱导肿瘤细胞耐药机制中有着重要作用,从两者入手是解决肿瘤细胞获得性耐药的可能途径.     

癌症相关成纤维细胞诱导的上皮间质转化增强肿瘤细胞干性的研究进展

在肿瘤细胞干性的获得和维持方面,肿瘤微环境扮演着十分重要的角色。作为其中数量最多的基质细胞,癌症相关成纤维细胞(cancer-associated fibroblasts,CAFs)可通过旁分泌信号和改变基质硬度的方式,诱导邻近的肿瘤细胞发生上皮-间质转化(epithelial-mesenchymal transition,EMT),使上皮来源细胞部分或完全地获得间充质表型。当细胞处于EMT进程中的某个过渡阶段时,即可被诱导表达干细胞表型,促进肿瘤的发生与进展。本文主要回顾了CAFs、EMT和肿瘤细胞干性相互之间的关系以及相关分子机制的研究,并尝试论述CAFs诱导肿瘤细胞的EMT增强其细胞干性。     

上皮间充质转化与肿瘤干细胞的研究进展

上皮细胞间充质转化(epithelial-mesenchymal transition, EMT) 在胚胎发育和肿瘤发生中具有重要作用, EMT可使上皮性肿瘤细胞获得间充质细胞表型, 在增强肿瘤细胞的侵袭和转移能力的同时, 也使得肿瘤细胞具有自我更新能力等干细胞样特性。多种转录因子、信号转导通路、microRNAs及细胞微环境等因素共同调控此过程。EMT与肿瘤干细胞之间有密不可分的联系, EMT可以促进肿瘤细胞获得干细胞特征, 具有干细胞特征的肿瘤细胞高表达EMT标记分子, microRNA可同时调控EMT和细胞干性。阐明EMT与肿瘤干细胞的相互关系及其调控机制, 有望为肿瘤转移与复发的靶向治疗开辟新思路。      

上皮间质转化与肿瘤干细胞的关系

目前越来越多的研究显示上皮间质转化(EMT)参与了肿瘤干细胞的形成以及肿瘤细胞的浸润、迁移和转移,不仅增强了癌细胞的侵袭和转移能力,还可使细胞获得自我更新等干细胞特性,促进肿瘤干细胞的产生.因此,研究EMT与常见干细胞之间的关系对于寻找控制肿瘤侵袭和转移的有效途径有非常重要的意义,亦可为肿瘤的治疗提供新的靶点.     

上皮间质转化和肿瘤干细胞

最近,两个新的概念出现在肿瘤生物学中：上皮间质转化（epitheilal-mesenchymal transition,EMT）和肿瘤干细胞（cancer stem cells,CSCs）。EMT不仅赋予细胞迁移和侵袭特征,还可使肿瘤细胞获得自我更新能力而具有干细胞的特性,从而促进CSCs的产生。本文讨论EMT和CSCs之间的联系、EMT获得干细胞特征促进CSCs产生、EMT是形成CSCs的重要环节及二者在干细胞巢中的转化,并分析影响EMT和CSCs的因素。研究EMT在肿瘤发生中的作用,与CSCs理论相融合,从而可能发现新的肿瘤靶向治疗。     

上皮间质转化和肿瘤干细胞

最近,两个新的概念出现在肿瘤生物学中:上皮间质转化(epitheilal-mesenchymal transition,EMT)和肿瘤干细胞(cancer stem cells,CSCs)。EMT不仅赋予细胞迁移和侵袭特征,还可使肿瘤细胞获得自我更新能力而具有干细胞的特性,从而促进CSCs的产生。本文讨论EMT和CSCs之间的联系、EMT获得干细胞特征促进CSCs产生、EMT是形成CSCs的重要环节及二者在干细胞巢中的转化,并分析影响EMT和CSCs的因素。研究EMT在肿瘤发生中的作用,与CSCs理论相融合,从而可能发现新的肿瘤靶向治疗。     

肿瘤细胞上皮间质转化表观遗传调控机制的研究进展

上皮间质转化(epithelial to mesenchymal transition,EMT)指上皮细胞向间质细胞转变的现象,其在组织损伤修复等生命过程中是必需的.研究发现,EMT在肿瘤细胞侵袭和转移中发挥至关重要的作用,EMT不仅使肿瘤细胞获得迁移、侵袭、转移能力,同时还与肿瘤细胞抑制衰老和凋亡、抵抗放化疗和形成肿瘤干细胞(cancer stem cells,CSCs)密切相关,因此抑制EMT成为抑制肿瘤转移的新策略.肿瘤细胞EMT受到表观遗传的复杂调控,DNA甲基化、组蛋白修饰、非编码RNA在EMT发生中扮演十分重要的角色,因此肿瘤细胞EMT的表观遗传调控已经成为国内外的研究热点.本文就肿瘤细胞EMT表观遗传调控机制的研究进展予以综述.     

Numb与上皮间质转化关系的研究进展

目的:总结Numb与上皮间质转化(epithelial mesenchymal transitions,EMT)的研究进展,并讨论Numb在EMT中的可能作用机制。方法:应用PubMed及CNKI期刊全文数据库检索系统以"Numb、肿瘤和EMT"等为关键词,检索1990-01-2012-10的相关文献。共检索到英文文献815篇,中文文献285篇。纳入标准:1)以肿瘤中的Numb与EMT的关系;2)Numb在上皮间质转化中的作用机制研究。根据纳入标准分析文献38篇。结果:Numb是参与肿瘤信号转导途径的重要成分,新的研究表明,Numb表达下调或缺失,EMT的发生加剧。作用机制可能是其通过影响肿瘤细胞E-钙黏蛋白的定位、调控Notch等信号通路在肿瘤EMT过程中起关键作用,研究发现,10%的癌组织中伴有Notch1基因变异。通过参与EMT而诱导肿瘤形成和发展可能为Numb影响肿瘤发生、发展的又一重要机制。结论:肿瘤中Numb的表达水平及其相关信号通路在EMT中可能起重要作用,但具体作用方式和机制仍未阐明。     

肿瘤相关巨噬细胞与肿瘤细胞上皮间质转化关系的研究进展

上皮间质转化(epithelial-mesenchymal transition,EMT)是上皮细胞在形态学上发生向间质细胞表型的转变,在肿瘤的侵袭和转移过程中发挥重要作用,肿瘤相关巨噬细胞(tumor-associatedmacrophage,TAM)是肿瘤的基本成分之一,通过分泌TNF-α、IL-6、EGF、VEGF、MMP-9、uPA等因子诱导肿瘤细胞发生EMT,协同其刺激新生血管形成、降解基质、促进肿瘤细胞发生局部侵袭及远处转移.     

Cancer stem cells in squamous cell carcinoma switch between two distinct phenotypes that are preferentially migratory or proliferative

Epithelial-to-mesenchymal transition (EMT) is an important driver of tumor invasion and metastasis, which causes many cancer deaths. Cancer stem cells (CSC) that maintain and initiate tumors have also been implicated in invasion and metastasis, but whether EMT is an important contributor to CSC function is unclear. In this study, we investigated whether a population of CSCs that have undergone EMT (EMT CSCs) exists in squamous cell carcinoma (SCC). We also determined whether a separate population of CSCs that retain epithelial characteristics (non-EMT CSCs) is also present. Our studies revealed that self-renewing CSCs in SCC include two biologically-distinct phenotypes. One phenotype, termed CD44(high)ESA(high), was proliferative and retained epithelial characteristics (non-EMT CSCs), whereas the other phenotype, termed CD44(high)ESA(low), was migratory and had mesenchymal traits characteristic of EMT CSCs. We found that non-EMT and EMT CSCs could switch their epithelial or mesenchymal traits to reconstitute the cellular heterogeneity which was characteristic of CSCs. However, the ability of EMT CSCs to switch to non-EMT character was restricted to cells that were also ALDH1(+), implying that only ALDH1(+) EMT cells had the ability to seed a new epithelial tumor. Taken together, our findings highlight the identification of two distinct CSC phenotypes and suggest a need to define therapeutic targets that can eradicate both of these variants to achieve effective SCC treatment.     

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.     

Targeting cancer stem cells by curcumin and clinical applications

Curcumin is a well-known dietary polyphenol derived from the rhizomes of turmeric, an Indian spice. The anticancer effect of curcumin has been demonstrated in many cell and animal studies, and recent research has shown that curcumin can target cancer stem cells (CSCs). CSCs are proposed to be responsible for initiating and maintaining cancer, and contribute to recurrence and drug resistance. A number of studies have suggested that curcumin has the potential to target CSCs through regulation of CSC self-renewal pathways (Wnt/β-catenin, Notch, sonic hedgehog) and specific microRNAs involved in acquisition of epithelial–mesenchymal transition (EMT). The potential impact of curcumin, alone or in combination with other anticancer agents, on CSCs was evaluated as well. Furthermore, the safety and tolerability of curcumin have been well-established by numerous clinical studies. Importantly, the low bioavailability of curcumin has been dramatically improved through the use of structural analogues or special formulations. More clinical trials are underway to investigate the efficacy of this promising agent in cancer chemoprevention and therapy. In this article, we review the effects of curcumin on CSC self-renewal pathways and specific microRNAs, as well as its safety and efficacy in recent human studies. In conclusion, curcumin could be a very promising adjunct to traditional cancer treatments.     

SOX8 regulates cancer stem‐like properties and cisplatin‐induced EMT in tongue squamous cell carcinoma by acting on the Wnt/β‐catenin pathway

A sub‐population of chemoresistant cells exhibits biological properties similar to cancer stem cells (CSCs), and these cells are believed to be a main cause for tumor relapse and metastasis. In our study, we explored the role of SOX8 and its molecular mechanism in the regulation of the stemness properties and the epithelial mesenchymal transition (EMT) of cisplatin‐resistant tongue squamous cell carcinoma (TSCC) cells. We found that SOX8 was upregulated in cisplatin‐resistant TSCC cells, which displayed CSC‐like properties and exhibited EMT. SOX8 was also overexpressed in chemoresistant patients with TSCC and was associated with higher lymph node metastasis, advanced tumor stage and shorter overall survival. Stable knockdown of SOX8 in cisplatin‐resistant TSCC cells inhibited chemoresistance, tumorsphere formation, and EMT. The Wnt/β‐catenin pathway mediated the cancer stem‐like properties in cisplatin‐resistant TSCC cells. Further studies showed that the transfection of active β‐catenin in SOX8 stable‐knockdown cells partly rescued the SOX8 silencing‐induced repression of stem‐like features and chemoresistance. Through chromatin immunoprecipitation and luciferase assays, we observed that SOX8 bound to the promoter region of Frizzled‐7 (FZD7) and induced the FZD7‐mediated activation of the Wnt/β‐catenin pathway. In summary, SOX8 confers chemoresistance and stemness properties and mediates EMT processes in chemoresistant TSCC via the FZD7‐mediated Wnt/β‐catenin pathway.     

Programmed death ligand 1 regulates epithelial–mesenchymal transition and cancer stem cell phenotypes in hepatocellular carcinoma through the serum and glucocorticoid kinase 2/β-catenin signaling pathway

Programmed death ligand 1 (PD-L1) plays an important role in the occurrence of hepatocellular carcinoma (HCC). The present study indicated that epithelial–mesenchymal transition (EMT) and induction of cancer stem cell (CSC)-like properties contribute to metastasis of cancers. However, the molecular mechanisms underlying PD-L1 and EMT and CSC phenotypes in HCC remain to be elucidated. Here, we report that PD-L1 regulates not only EMT but also the stem-like transition in liver cancer cells. We observed high PD-L1 expression in CD133⁺ liver CSCs and CSC-enriched tumor spheres. Altering PD-L1 expression promoted liver CSC phenotypes by increasing the expression of stemness genes, the CD133⁺ cell population sizes, and the ability to form tumor spheres. Programmed death ligand 1 enhanced HCC cell tumorigenicity and invasion in nude mice. Additionally, PD-L1 overexpression in cells significantly increased cell motility and invasion, as well as the EMT process. Conversely, suppression of PD-L1 in cells had an opposite effect. Prolonged treatment of HCC cells with Akt inhibitor prefosine leads to activation of serum and glucocorticoid kinase 2 (SGK2) and rescued downregulation of PD-L1. Mechanistically, PD-L1 directly interacted with SGK2. Programmed death ligand 1 upregulated SGK2 and activated the SGK2/β-catenin signaling pathway, and promoted EMT and CSC expansion in liver cancer cells, highlighting the role of SGK2 in PD-L1-mediated EMT and CSC phenotypes in liver cancer cells. In conclusion, our findings suggest that PD-L1 activated the SGK2/β-catenin signaling pathway, to induce EMT and acquisition of a stem cell phenotype.     

Epithelial-to-mesenchymal transition and cancer stem(-like) cells in head and neck squamous cell carcinoma

Head and neck squamous cell carcinoma (HNSCC) is the 6th commonest cancer worldwide. Relapse, thought to involve cancer stem(-like) cells (CSCs), and the development of metastases are common and survival rates remain low. Epithelial-to-mesenchymal transition (EMT) is a key event in metastasis and increasing evidence suggests a link between EMT and CSCs. MicroRNAs regulate multiple cellular processes including EMT and have been implicated in a CSC phenotype. This review aims to highlight key events that are involved in EMT, discusses their relevance in HNSCC progression and metastasis and explores the possibility of targeting EMT as a novel therapy in HNSCC.     

Disclosure of a stem cell phenotype in an oral squamous cell carcinoma cell line induced by BMP-4 via an epithelial-mesenchymal transition

A small subset of cells within a malignant neoplasm, named cancer stem cells (CSCs) or tumour initiating cells, are thought to be capable of initiating the neoplasm itself, and of driving its growth and recurrence after treatment. It is unclear whether CSCs can be identified and experimentally induced within oral squamous cell carcinoma (OSCC), although this has been reported for a number of other tumour types. In this study, we aimed to determine whether BMP-4 (bone morphogenetic protein-4) could induce epithelial-mesenchymal transition (EMT) with acquisition of stem cell-like phenotypes in a cell-culture model. Furthermore, the differential expression of ABCG2, a putative CSC marker, was determined in human normal oral mucosa and OSCC tissues at mRNA and protein level. The results showed that after treatment with BMP-4, most Tca8113 cells (a human tongue OSCC cell line) changed their morphology from slabstone to spindle-shaped, and demonstrated enhanced expression of ABCG2 compared with non-treated cells. Expression of Oct-4 was induced in cell nuclei with up-regulation of EMT markers (Snail, Slug and vimentin), and down-regulation of E-cadherin. Interestingly, the expression of hTERT, CD44 and Bmi-1 (generally accepted as markers of CSCs) were up-regulated, but this was not synchronous with the expression of EMT markers. Tumour spheres were formed after stimulation with BMP-4, with high expression of CD44 and ABCG2. In human tissues, ABCG2 was strongly expressed in OSCC, but not in normal mucosa. This study suggests that BMP-4-mediated EMT constitutes one possible pathway for the development of CSCs in oral cancer, implying a transient therapeutic opportunity if EMT can be interrupted early in the evolution of such a neoplasm.     

First among equals: the cancer cell hierarchy

Primary cancer cells exhibit heterogeneity in their proliferative ability. The cancer stem cell (CSC) model accounts for this heterogeneity by proposing that each cancer consists of a small population of CSCs that are capable of unlimited growth and self-renewal and a much larger population of cells, descendants of the CSCs, that have lost self-renewal capacity. The CSC model has important implications for cancer therapy. Eradication of CSCs, the cells responsible for maintenance of the neoplasm, would be necessary and sufficient to achieve cure. By extension, both the frequency of stem cells in a tumor and their propensity to undergo self-renewal (P_sr) would have a direct impact on the curability of that tumor. The P_sr is a critical biological characteristic of CSCs—small differences in P_sr have enormous impact on the probability of success in cancer therapy. Differentiation therapy, defined as treatment that reduces the P_sr of CSCs, is one approach to targeting CSCs.     

In vitro models of cancer stem cells and clinical applications

Cancer cells, stem cells and cancer stem cells have for a long time played a significant role in the biomedical sciences. Though cancer therapy is more effective than it was a few years ago, the truth is that still none of the current non-surgical treatments can cure cancer effectively. The reason could be due to the subpopulation called “cancer stem cells” (CSCs), being defined as those cells within a tumour that have properties of stem cells: self-renewal and the ability for differentiation into multiple cell types that occur in tumours.The phenomenon of CSCs is based on their resistance to many of the current cancer therapies, which results in tumour relapse. Although further investigation regarding CSCs is still needed, there is already evidence that these cells may play an important role in the prognosis of cancer, progression and therapeutic strategy. Therefore, long-term patient survival may depend on the elimination of CSCs. Consequently, isolation of pure CSC populations or reprogramming of cancer cells into CSCs, from cancer cell lines or primary tumours, would be a useful tool to gain an in-depth knowledge about heterogeneity and plasticity of CSC phenotypes and therefore carcinogenesis. Herein, we will discuss current CSC models, methods used to characterize CSCs, candidate markers, characteristic signalling pathways and clinical applications of CSCs. Some examples of CSC-specific treatments that are currently in early clinical phases will also be presented in this review.