呼吸系统中上皮-间质转化的研究进展及细胞黏附连接调控机制

近年来的研究证实,上皮-间质转化(epithelial-mesenchymal transition, EMT)对呼吸系统发育和疾病有重要作用。细胞间的连接缺失是EMT的关键环节。各类黏附分子的平衡表达对于维持上皮细胞正常结构和功能稳态有重要意义。本文综述了EMT在肺发育、肺损伤修复以及肺部慢性疾病中的研究进展,并结合EMT分子事件的详细过程,就细胞连接结构和细胞黏附分子对EMT的影响作一概述。     

EMT在癌症转移中的作用：内环境依赖的调控过程

上皮-间质转化(epithelial-mesenchymal transition, EMT)发生在胚胎发生和肿瘤进展过程中,是一个动态的、受到高度调控的过程。EMT和其反过程间质-上皮转化(mesenchymal-epithelial transition,MET)不仅参与了机体的正常发育过程,在肿瘤的侵袭和转移等方面也起着重要的作用。越来越多的证据表明,在不同的肿瘤类型或同一肿瘤的不同发展阶段中,EMT发生的驱动因素不同,导致它在肿瘤转移中的作用也不尽相同,即呈现出内环境依赖特性。另外,部分EMT是EMT在肿瘤中的一种常见的表现形式,可以赋予细胞更高的可塑性,从而获得更强的侵袭能力。本综述将总结EMT在肿瘤细胞中的生物学特性以及多层级的调节机制,对不同的癌症内环境条件下,EMT与癌症转移的关系以及EMT作为潜在治疗靶点的临床意义进行探讨。     

上皮间质转化和细胞衰老在肿瘤发生中的共同调节分子

上皮间质转化(epithelial-mesenchymal transition,EMT)和细胞衰老是与肿瘤发生密切相关的两个重要事件。在肿瘤发展过程中,上皮间质转化是促进迁移和侵袭的重要机制。细胞衰老作为一个重要的细胞自主的肿瘤预防机制,可以抑制细胞转化和肿瘤发生。虽然EMT和细胞衰老发生在肿瘤发展过程中的不同时间段,但众多研究发现,多种介导EMT发生的关键信号通路和转录因子能调节细胞衰老过程;同时,参与细胞衰老的经典信号通路也影响着EMT进程。就联系这两种细胞生物学事件的调控因素作一综述。     

间质-上皮转化在肿瘤转移中的作用

肿瘤转移是一个多步骤、多因素参与的复杂过程,是目前临床上绝大多数肿瘤患者的致死因素.上皮-间质转化(epithelial-mesenchymal transition, EMT)过程已被证实可促使肿瘤细胞发生转移.近年来许多研究表明,间质-上皮转化(mesenchymal-epithelial transition, MET)即EMT的逆过程,与肿瘤也密切相关,特别是肿瘤转移即形成继发性的肿瘤转移灶.深入研究肿瘤MET有望为肿瘤转移的预防和诊治提供新思路.     

上皮-间质转化在肿瘤转移中的作用

肿瘤转移是一个多步骤、多因素参与的复杂过程,是目前临床上绝大多数肿瘤患者的致死因素.上皮-间质转化(epithelial-mesenchymal transition,EMT)过程已被证实可促使肿瘤细胞发生转移.近年来许多研究表明,间质-上皮转化(mesenchymal-epithelial transition,MET)即EMT的逆过程,与肿瘤也密切相关,特别是肿瘤转移即形成继发性的肿瘤转移灶.深入研究肿瘤MET有望为肿瘤转移的预防和诊治提供新思路.     

MicroRNA对EMT的调节作用及其与肿瘤侵袭的关系

上皮间质转化（epithelial mesenchymal transition,EMT）是指上皮细胞表型由上皮向间质转换的生物学过程,可发生在生理过程中促进发育、组织愈合和修复。近年对肿瘤的研究发现,EMT与肿瘤的发生发展密切相关。肿瘤细胞发生EMT时,伴随着迁移、侵袭能力的增强,进而促进肿瘤的转移。EMT发生的程度以及相关标志分子的检测还可以用于判断肿瘤转移的危险和评估预后。MicroRNA(miRNA)作为非编码小RNA,通过与特定mRNA的3′UTR结合,在蛋白翻译水平抑制基因表达。本文主要综述目前发现的作用于EMT相关转录因子,如ZEB、SNAIL、TWIST的miRNA,以及在各种肿瘤中的表达情况和作用。其中,有些转录因子和miRNA之间,还存在相互抑制的复杂调节网络,因此,了解miRNA在肿瘤中对EMT的作用可能为肿瘤的治疗提供新的方法和策略。     

环状RNA在不同类型上皮间质转化中的作用

近年来发现环状RNA(circular RNA, circRNA)在各种类型的上皮间质转化(epithelial-mesenchymal transition,EMT)中发挥了重要的作用。本文就EMT的概念和分类、circRNA的分类和生成,以及circRNA分别在EMT过程中作用的国内外研究进展作一综述,以期为发生EMT的器官纤维化、肿瘤等疾病的靶向治疗和预防寻找新的研究方向。     

上皮—间质转化在肾间质纤维化中的作用

上皮－间质转化在发育和纤维化过程中具有重要作用。本文综述了上皮－间质转化发生的过程及其机制的研究进展,尤其是细胞外基质、生长因子、粘附分子及基因对上皮－间质转化的影响。并就在肾间质纤维化过程中因上皮－间质转化致成纤维细胞增多,从而导致肾纤维化的可能作用及其影响因素作一述。     

TGF-β在肿瘤细胞上皮-间质转化发生中的作用

上皮-间质转化(epithelial-mesenchymal transition,EMT)指具有粘着性的上皮细胞转化成可迁移的间充质细胞的过程,该过程有助于肿瘤细胞的迁移。而转化生长因子-β(transforming growthfactor-β,TGF-β)超家族可激活Smad和Non-Smad两条信号通路而诱导细胞进行EMT,从而促进肿瘤细胞的迁移。深入研究EMT中TGF-β诱导的信号通路有望为肿瘤的治疗提供新方向。     

L1-mediated colon cancer cell metastasis does not require changes in EMT and cancer stem cell markers

Aberrant activation of Wnt/β-catenin signaling is common in most sporadic and inherited colorectal cancer (CRC) cells leading to elevated β-catenin/TCF transactivation. We previously identified the neural cell adhesion molecule L1 as a target gene of β-catenin/TCF in CRC cells. Forced expression of L1 confers increased cell motility, invasion, and tumorigenesis, and the induction of human CRC cell metastasis to the liver. In human CRC tissue, L1 is exclusively localized at the invasive front of such tumors in a subpopulation of cells displaying nuclear β-catenin. We determined whether L1 expression confers metastatic capacities by inducing an epithelial to mesenchymal transition (EMT) and whether L1 cosegregates with cancer stem cell (CSC) markers. We found that changes in L1 levels do not affect the organization or expression of E-cadherin in cell lines, or in invading CRC tissue cells, and no changes in other epithelial or mesenchymal markers were detected after L1 transfection. The introduction of major EMT regulators (Slug and Twist) into CRC cell lines reduced the levels of E-cadherin and induced fibronectin and vimentin, but unlike L1, Slug and Twist expression was insufficient for conferring metastasis. In CRC cells L1 did not specifically cosegregate with CSC markers including CD133, CD44, and EpCAM. L1-mediated metastasis required NF-κB signaling in cells harboring either high or low levels of endogenous E-cadherin. The results suggest that L1-mediated metastasis of CRC cells does not require changes in EMT and CSC markers and operates by activating NF-κβ signaling.     

A novel role of ribonuclease inhibitor in regulation of epithelial-to-mesenchymal transition and ILK signaling pathway in bladder cancer cells

Human ribonuclease inhibitor (RI) is a cytoplasmic acidic protein possibly involved in biological functions other than the inhibition of RNase A and angiogenin activities. We have previously shown that RI can inhibit growth and metastasis in some cancer cells. Epithelial-mesenchymal transition (EMT) is regarded as the beginning of invasion and metastasis and has been implicated in the metastasis of bladder cancer. We therefore postulate that RI regulates EMT of bladder cancer cells. We find that the over-expression of RI induces the up-regulation of E-cadherin, accompanied with the decreased expression of proteins associated with EMT, such as N-cadherin, Snail, Slug, vimentin and Twist and of matrix metalloprotein-2 (MMP-2), MMP-9 and Cyclin-D1, both in vitro and in vivo. The up-regulation of RI inhibits cell proliferation, migration and invasion, alters cell morphology and adhesion and leads to the rearrangement of the cytoskeleton in vitro. We also demonstrate that the up-regulation of RI can decrease the expression of integrin-linked kinase (ILK), a central component of signaling cascades controlling an array of biological processes. The over-expression of RI reduces the phosphorylation of the ILK downstream signaling targets p-Akt and p-GSK3β in T24 cells. We further find that bladder cancer with a high-metastasis capability shows higher vimentin, Snail, Slug and Twist and lower E-cadherin and RI expression in human clinical specimens. Finally, we provide evidence that the up-regulation of RI inhibits tumorigenesis and metastasis of bladder cancer in vivo. Thus, RI might play a novel role in the development of bladder cancer through regulating EMT and the ILK signaling pathway.     

Secreted Frizzled-Related Protein 4 Inhibits Glioma Stem-Like Cells by Reversing Epithelial to Mesenchymal Transition,Inducing Apoptosis and Decreasing Cancer Stem Cell Properties

The Wnt pathway is integrally involved in regulating self-renewal, proliferation, and maintenance of cancer stem cells (CSCs). We explored the effect of the Wnt antagonist, secreted frizzled-related protein 4 (sFRP4), in modulating epithelial to mesenchymal transition (EMT) in CSCs from human glioblastoma cells lines, U87 and U373. sFRP4 chemo-sensitized CSC-enriched cells to the most commonly used anti-glioblastoma drug, temozolomide (TMZ), by the reversal of EMT. Cell movement, colony formation, and invasion in vitro were suppressed by sFRP4+TMZ treatment, which correlated with the switch of expression of markers from mesenchymal (Twist, Snail, N-cadherin) to epithelial (E-cadherin). sFRP4 treatment elicited activation of the Wnt-Ca₂ ⁺ pathway, which antagonizes the Wnt/ß-catenin pathway. Significantly, the chemo-sensitization effect of sFRP4 was correlated with the reduction in the expression of drug resistance markers ABCG2, ABCC2, and ABCC4. The efficacy of sFRP4+TMZ treatment was demonstrated in vivo using nude mice, which showed minimum tumor engraftment using CSCs pretreated with sFRP4+TMZ. These studies indicate that sFRP4 treatment would help to improve response to commonly used chemotherapeutics in gliomas by modulating EMT via the Wnt/ß-catenin pathway. These findings could be exploited for designing better targeted strategies to improve chemo-response and eventually eliminate glioblastoma CSCs.     

Expression of the E-cadherin repressors Snail, Slug and Zeb1 in urothelial carcinoma of the urinary bladder: relation to stromal fibroblast activation and invasive behaviour of carcinoma cells

Epithelial–mesenchymal transition (EMT) is regulated by interaction of carcinoma and stromal cells and crucial for progression of urinary bladder carcinoma (UBC). Therefore, the influence of activated fibroblasts on the expression of E-cadherin repressors as well as EMT and invasion in UBC was investigated. A correlative analysis of the immunohistochemical expression of fibroblast (ASMA, S100A4, FAP, SDF1, PDGFRβ) and EMT (Snail, Slug, Zeb1, E-cadherin) markers was performed on 49 UBC cases of different stages. The impact of distinguishable growth factor stimulated fibroblasts on invasion, EMT, and E-cadherin repressor expression was investigated in an invasion model. In situ, invasiveness was significantly correlated to the loss of membranous E-cadherin (E-cad_m) and increased Snail, Slug, Zeb1 in tumour cells, as well as to increased ASMA, S100A4, and PDGFRβ in stromal cells. A significant correlation to nodal metastasis could be evidenced for the loss of E-Cad_m, and for an increase in S100A4 and PDGFRβ. Comparison of stromal and EMT markers revealed significant correlations of ASMA to Snail and Slug; of S100A4 to the loss of E-cad_m and Zeb1; and of PDGFRβ to the loss of E-Cad_m, Slug and Zeb1. In vitro, TGFβ1 induced myofibroblasts were the strongest attractants, while aFGF or TGFβ1/aFGF stimulated fibroblasts were the most potent EMT inductors. As shown here for the first time, distinct sub-populations of fibroblasts are to various extents associated with EMT and tumour progression in UBC. These relevant findings might be the basis for the identification of new diagnostic markers and therapeutic targets selectively affecting tumour supporting CAF effects.