Epithelial plasticity and cancer stem cells: Major mechanisms of cancer pathogenesis and therapy resistance

Epithelial-mesenchymal transition(EMT) has been linked with aggressive tumor biology and therapy resistance. It plays central role not only in the generation of cancer stem cells(CSCs) but also direct them across the multiple organ systems to promote tumor recurrence and metastasis. CSCs are reported to express stem cell genes as well as specific cell surfacemarkers and allow aberrant differentiation of progenies.It facilitates cancer cells to leave primary tumor, acquire migratory characteristics, grow into new environment and develop radio-chemo-resistance. Based on the current information, present review discusses and summarizes the recent advancements on the molecular mechanisms that derive epithelial plasticity and its major role in generating a subset of tumor cells with stemness properties and pathophysiological spread of tumor. This paper further highlights the critical need to examine the regulation of EMT and CSC pathways in identifying the novel probable therapeutic targets.These improved therapeutic strategies based on the co-administration of inhibitors of EMT, CSCs as well as differentiated tumor cells may provide improved antineoplastic response with no tumor relapse.     

DLX4 Upregulates TWIST and Enhances Tumor Migration,Invasion and Metastasis

The distal-less homeobox gene 4 (DLX4) is a member of the DLX family of homeobox genes. Although absent from most normal adult tissues, DLX4 is widely expressed in leukemia, lung, breast, ovarian and prostate cancers. However the molecular targets, mechanisms and pathways that mediate the role of DLX4 in tumor metastasis are poorly understood. In this study, we found that DLX4 induces cancer cells to undergo epithelial to mesenchymal transition (EMT) through TWIST. Overexpression of DLX4 increased expression of TWIST expression in cancer cell lines, resulting in increased migratory and invasive capacity. Likewise, knocking down expression of DLX4 decreased TWIST expression and the migration ability of cancer cell lines. DLX4 bound to regulatory regions of the TWIST gene. Both western blotting and immunohistochemistry staining showed that the expression of DLX4 and TWIST are correlated in most of breast tumors. Taken together, these data from both cell models and tumor tissues demonstrate that DLX4 not only upregulates TWIST expression but also induces EMT and tumor metastasis. Altogether, we propose a new pathway in which DLX4 drives expression of TWIST to promote EMT, cancer migration, invasion and metastasis.     

A novel epithelial-mesenchymal transition molecular signature predicts the oncological outcomes in colorectal cancer

Epithelial-mesenchymal transition (EMT), a biological process involving the transformation of epithelial cells into mesenchymal cells, promotes tumour initiation and metastasis. The aim of this study was to construct an EMT molecular signature for predicting colorectal cancer (CRC) prognosis and evaluate the efficacy of the model. The risk scoring system, constructed by log-rank test and multivariate Cox regression analysis according to EMT-related gene expression in CRC patients from TCGA database, demonstrated the highest correlation with prognosis compared with other parameters in CRC patients. The risk scores were significantly correlated with more lymph node metastasis, distal metastasis and advanced clinical stage of CRC. The model was further successfully validated in two independent external cohorts from GEO database. Furthermore, we developed a nomogram to integrate the EMT signature with the pathological stage of CRC, which was found to perform well in predicting the overall survival. Additionally, this risk scoring model was found to be associated with immune cell infiltration, implying a potential role of EMT involved in immunity regulation in tumour microenvironment. Taken together, our novel EMT molecular model may be useful in identifying high-risk patients who need an intensive follow-up and more aggressive therapy, finally contributing to more precise individualized therapeutic strategies.     

EGFR Signal-Network Reconstruction Demonstrates Metabolic Crosstalk in EMT

Epithelial to mesenchymal transition (EMT) is an important event during development and cancer metastasis. There is limited understanding of the metabolic alterations that give rise to and take place during EMT. Dysregulation of signalling pathways that impact metabolism, including epidermal growth factor receptor (EGFR), are however a hallmark of EMT and metastasis. In this study, we report the investigation into EGFR signalling and metabolic crosstalk of EMT through constraint-based modelling and analysis of the breast epithelial EMT cell model D492 and its mesenchymal counterpart D492M. We built an EGFR signalling network for EMT based on stoichiometric coefficients and constrained the network with gene expression data to build epithelial (EGFR_E) and mesenchymal (EGFR_M) networks. Metabolic alterations arising from differential expression of EGFR genes was derived from a literature review of AKT regulated metabolic genes. Signaling flux differences between EGFR_E and EGFR_M models subsequently allowed metabolism in D492 and D492M cells to be assessed. Higher flux within AKT pathway in the D492 cells compared to D492M suggested higher glycolytic activity in D492 that we confirmed experimentally through measurements of glucose uptake and lactate secretion rates. The signaling genes from the AKT, RAS/MAPK and CaM pathways were predicted to revert D492M to D492 phenotype. Follow-up analysis of EGFR signaling metabolic crosstalk in three additional breast epithelial cell lines highlighted variability in in vitro cell models of EMT. This study shows that the metabolic phenotype may be predicted by in silico analyses of gene expression data of EGFR signaling genes, but this phenomenon is cell-specific and does not follow a simple trend.     

A data-assimilation approach to predict population dynamics during epithelial-mesenchymal transition

Epithelial-mesenchymal transition (EMT) is a biological process that plays a central role in embryonic development, tissue regeneration, and cancer metastasis. Transforming growth factor-β (TGFβ) is a potent inducer of this cellular transition, comprising transitions from an epithelial state to partial or hybrid EMT state(s), to a mesenchymal state. Recent experimental studies have shown that, within a population of epithelial cells, heterogeneous phenotypical profiles arise in response to different time- and TGFβ dose-dependent stimuli. This offers a challenge for computational models, as most model parameters are generally obtained to represent typical cell responses, not necessarily specific responses nor to capture population variability. In this study, we applied a data-assimilation approach that combines limited noisy observations with predictions from a computational model, paired with parameter estimation. Synthetic experiments mimic the biological heterogeneity in cell states that is observed in epithelial cell populations by generating a large population of model parameter sets. Analysis of the parameters for virtual epithelial cells with biologically significant characteristics (e.g., EMT prone or resistant) illustrates that these sub-populations have identifiable critical model parameters. We perform a series of in silico experiments in which a forecasting system reconstructs the EMT dynamics of each virtual cell within a heterogeneous population exposed to time-dependent exogenous TGFβ dose and either an EMT-suppressing or EMT-promoting perturbation. We find that estimating population-specific critical parameters significantly improved the prediction accuracy of cell responses. Thus, with appropriate protocol design, we demonstrate that a data-assimilation approach successfully reconstructs and predicts the dynamics of a heterogeneous virtual epithelial cell population in the presence of physiological model error and parameter uncertainty.     

In vivo gene manipulations of epithelial cell sheets: a novel model to study epithelial-to-mesenchymal transition

Embryonic cells are classified into two types of cells by their morphology, epithelial and mesenchymal cells. During dynamic morphogenesis in development, epithelial cells often switch to mesenchymal by the process known as epithelial-to-mesenchymal transition (EMT). EMT is a central issue in cancer metastasis where epithelial-derived tumor cells are converted to mesenchymal with high mobility. Although many molecules have been identified to be involved in the EMT mostly by in vitro studies, in vivo model systems have been limited. We here established a novel model with which EMT can be analyzed directly in the living body. By an electroporation technique, we targeted a portion of the lateral plate mesoderm that forms epithelial cell sheets delineating the kidney region, called nephric coelomic epithelium (Neph-CE). Enhanced green fluorescent protein-electroporated Neph-CE retained the epithelial integrity without invading into the underling stroma (mesonephros). The Neph-CE transgenesis further allowed us to explore EMT inducers in vivo, and to find that Ras-Raf and RhoA signals were potent inducers. Live-imaging confocal microscopy revealed that during EMT processes cells started extending cellular protrusions toward the stroma, followed by translocation of their cell bodies. Furthermore, we established a long-term tracing of EMT-induced cells, which were dynamically relocated within the kidney stroma. The Neph-CE-transgenesis will open a way to study cellular and molecular mechanisms underlying EMT directly in actual body.     

CD44S-hyaluronan interactions protect cells resulting from EMT against anoikis

The detachment of normal epithelial cells from matrix triggers an apoptotic response known as anoikis, during homeostatic turnover. Metastatic tumor cells evade anoikis, by mechanisms that are only partly characterized. In particular, the epithelial–mesenchymal transition (EMT) in a subset of invasive tumor cells confers anoikis-resistance. In some cases, EMT up-regulates the cancer stem cell marker CD44S and the enzyme hyaluronic acid synthase-2 (HAS2). CD44S is the major receptor for hyaluronan in the extracellular matrix. Herein, we demonstrate that CD44S, unlike the CD44E isoform expressed in normal epithelial cells, contributes to the protection against anoikis. This protection requires the interaction of CD44S with hyaluronan (HA). CD44S–HA interaction is proposed to play an important role in tumor metastasis through enhanced cell survival under detached conditions.     

上皮间质转化在肿瘤侵袭转移中的研究进展

上皮-间质转化（epithelial-mesenchymal transitions,EMT）是上皮细胞向间质细胞转化的现象,不仅参与胚胎发育和正常生理,还参与许多病理过程。同样EMT也参与肿瘤的发生与发展,尤其在促进肿瘤侵袭转移中发挥着重要作用。研究表明,肿瘤细胞借助EMT方式增强肿瘤细胞迁移和运动能力,促进肿瘤的侵袭与转移。在肿瘤侵袭转移历程中,关于EMT发生的分子调控机制研究已取得了良好的进展,但其详细机制仍然不是十分清楚。本文主要介绍生长因子、转录因子、miRNAs、甲基化及其他调控因子在肿瘤EMT中的调控功能,进一步综述EMT在肿瘤侵袭转移中的作用。     

Epithelial-mesenchymal transition and the invasive potential of tumors

The development of metastasis requires the movement and invasion of cancer cells from the primary tumor into the surrounding tissue. To acquire such invasive abilities, epithelial cancer cells must undergo several phenotypic changes. Some of these, including alterations in cell adhesion and migration, are reminiscent of those observed during the developmental process termed epithelial-mesenchymal transition (EMT). Several master gene regulatory programs known to promote EMT during development have recently been discovered to play key roles in cancer progression. In particular, the regulation of cell adhesion molecules and the signaling pathways linking them to mechanisms of gene regulation has emerged as an important determinant of tumor cell invasion and metastasis. A deeper understanding of these mechanisms should allow both better diagnosis and the development of specific treatments for invasive cancer.     

上皮间质转化与干细胞自我更新和分化

上皮间质转化(epithelial-mesenchymal transition,EMT)是指上皮细胞失去连接和极性转变为间质细胞的过程,这一现象普遍存在于胚胎发育、创伤愈合、器官纤维化以及肿瘤转移.在胚胎早期发育和晚期发育过程,例如着床、原肠运动、心血管发育等事件中有EMT和间质上皮转化(mesenchymal-ep...