Intratumoral bidirectional transitions between epithelial and mesenchymal cells in triple‐negative breast cancer

Epithelial–mesenchymal transition (EMT) and its reverse process, mesenchymal–epithelial transition MET, are crucial in several stages of cancer metastasis. Epithelial–mesenchymal transition allows cancer cells to move to proximal blood vessels for intravasation. However, because EMT and MET processes are dynamic, mesenchymal cancer cells are likely to undergo MET transiently and subsequently re‐undergo EMT to restart the metastatic process. Therefore, spatiotemporally coordinated mutual regulation between EMT and MET could occur during metastasis. To elucidate such regulation, we chose HCC38, a human triple‐negative breast cancer cell line, because HCC38 is composed of epithelial and mesenchymal populations at a fixed ratio even though mesenchymal cells proliferate significantly more slowly than epithelial cells. We purified epithelial and mesenchymal cells from Venus‐labeled and unlabeled HCC38 cells and mixed them at various ratios to follow EMT and MET. Using this system, we found that the efficiency of EMT is approximately an order of magnitude higher than that of MET and that the two populations significantly enhance the transition of cells from the other population to their own. In addition, knockdown of Zinc finger E‐box‐binding homeobox 1 (ZEB1) or Zinc finger protein SNAI2 (SLUG) significantly suppressed EMT but promoted partial MET, indicating that ZEB1 and SLUG are crucial to EMT and MET. We also show that primary breast cancer cells underwent EMT that correlated with changes in expression profiles of genes determining EMT status and breast cancer subtype. These changes were very similar to those observed in EMT in HCC38 cells. Consequently, we propose HCC38 as a suitable model to analyze EMT–MET dynamics that could affect the development of triple‐negative breast cancer.     

Vimentin regulates EMT induction by Slug and oncogenic H-Ras and migration by governing Axl expression in breast cancer

Epithelial-to-mesenchymal transition (EMT) is a critical event in the progression toward cancer metastasis. The intermediate filament protein vimentin is an important marker of EMT and a requisite regulator of mesenchymal cell migration. However, it is not known how vimentin functionally contributes to cancer cell invasion. Here, we report that ectopic expression of oncogenic H-Ras-V12G and Slug induces vimentin expression and migration in pre-malignant breast epithelial cells. Conversely, vimentin expression is necessary for Slug- or H-Ras-V12G-induced EMT-associated migration. Furthermore, silencing of vimentin in breast epithelial cells results in specific changes in invasiveness-related gene expression including upregulation of RAB25 (small GTPase Rab25) and downregulation of AXL (receptor tyrosine kinase Axl), PLAU (plasminogen activator, urokinase) and ITGB4 (integrin β4-subunit). Importantly, gene expression profiling analyses reveal that vimentin expression correlates positively/negatively with these genes also in multiple breast cancer cell lines and breast cancer patient samples. Focusing on the tyrosine kinase Axl, we show that induction of vimentin by EMT is associated with upregulation of Axl expression and that Axl enhances the migratory activity of pre-malignant breast epithelial cells. Using null and knock-down cells and overexpression models, we also show that regulation of breast cancer cell migration in two- and three-dimensional matrices by vimentin is Axl- dependent and that Axl functionally contributes to lung extravasation of breast cancer cells in mice. In conclusion, our data show that vimentin functionally contributes to EMT and is required for induction of Axl expression. Moreover, these results provide a molecular explanation for vimentin-dependent cancer cell migration during EMT by identifying Axl as a key proximal component in this process.     

循环肿瘤细胞的异质性在转移性乳腺癌中的作用研究进展

循环肿瘤细胞（CTC）的计数可以预测转移性乳腺癌的预后,但其改善患者预后的能力在临床试验中尚未得到证实。目前研究专注于CTC的分子表征,作为肿瘤组织的“替代物”以非侵入性地方式评估癌症基因组表达及其在治疗过程中的演变。CTC中存在上皮-间质转化过程（EMT）,其特点为上皮标志物的缺失。EMT过程可以存在于侵袭性及耐药性较强的细胞,其计数和表征,能够引起肿瘤的复发和进展,具有较高的临床价值。本文深入探讨循环肿瘤细胞的异质性及在转移性乳腺癌上皮-间质转化过程中的作用。使其成为乳腺癌患者监测转移和预后的常规的检测指标,并有助于明确转移的机制,更有望发现乳腺癌转移治疗的新靶点。     

PD-1/PD-L1信号通路在结直肠癌免疫逃逸及其治疗中作用的研究进展

结直肠癌是常见的消化系统肿瘤。近年来,免疫治疗是继放化疗及靶向治疗之后,结直肠癌治疗领域的新方向。而作为T细胞免疫反应的协同刺激信号通路,程序性死亡分子1（programmed death-1,PD-1）/PD-1配体（PD-1 ligand,PD-L1)信号通路在肿瘤的免疫治疗中起着至关重要的作用。PD-1/PD-L1信号通路被激活后,可参与肿瘤的免疫逃逸,与肿瘤的发生、发展密切相关。体内外实验证实,阻断该通路可增强机体内源性抗肿瘤免疫效应。本文就PD-1/PD-L1信号通路及其阻滞剂在结直肠癌领域中的研究进展作一综述。     

Epithelial-mesenchymal transition and breast cancer: role, molecular mechanisms and clinical impact

Epithelial-mesenchymal transition (EMT) is defined by the loss of epithelial characteristics and the acquisition of a mesenchymal phenotype. In this process, cells acquire molecular alterations that facilitate dysfunctional cell-cell adhesive interactions and junctions. These processes may promote cancer cell progression and invasion into the surrounding microenvironment. Such transformation has implications in progression of breast carcinoma to metastasis, and increasing evidences support most tumors contain a subpopulation of cells with stem-like and mesenchymal features that is resistant to chemotherapy. This review focuses on the physiological and pathological role of EMT process, its molecular related network, its putative role in the metastatic process and its implications in response/resistance to the current and/or new approaching drugs in the clinical management of breast cancer.     

Mesenchymal stem cells play a potential role in regulating the establishment and maintenance of epithelial-mesenchymal transition in MCF7 human breast cancer cells by paracrine and induced autocrine TGF-β

Although the epithelial-mesenchymal transition (EMT) is a normal process that occurs during development, it is thought to be associated with cancer progression and metastasis. Emerging evidence links mesenchymal stem cells (MSCs) in the tumor microenvironment with the occurrence of EMT in cancer progression. In this study, the human breast cancer cell line MCF7 was co-cultured with human adipose-derived MSCs (hAD-MSCs) in a transwell system. Co-cultured cells were analyzed for changes in cellular morphology, EMT markers, protein expression and tumor characteristics. We found that co-cultured MCF7 cells underwent EMT and established a stable mesenchymal phenotype after prolonged co-culturing. Here, we demonstrate that paracrine transforming growth factor-β1 (TGF-β1) secreted by hAD-MSCs regulated the establishment of EMT in MCF7 cells by targeting the ZEB/miR-200 regulatory loop. The downregulation of paracrine TGF-β1 levels can inhibit and reverse the EMT progress by downregulating ZEB1/2 and upregulating miR-200b and miR-200c. The maintenance of a stable mesenchymal state by MCF7 cells required the establishment of autocrine TGF-β signaling to drive and sustain ZEB expression, which had been initiated by the prolonged co-culturing with hAD-MSCs. These results suggest that MSCs may promote breast cancer metastasis by stimulating and facilitating the EMT process.     

MicroRNAs:regulators of cancer metastasis and epithelial-mesenchymal transition (EMT)

Tumor metastasis is the main cause of death in patients with solid tumors. The epithelial-mesenchymal transition(EMT) process, in which epithelial cells are converted into mesenchymal cells, is frequently activated during cancer invasion and metastasis. MicroRNAs(miRNAs) are small, non-coding RNAs that provide widespread expressional control by repressing mRNA translation and inducing mRNA degradation. The fundamental roles of miRNAs in tumor growth and metastasis have been increasingly well recognized. A growing number of miRNAs are reported to regulate tumor invasion/metastasis through EMT-related and/or non-EMT–related mechanisms. In this review, we discuss the functional role and molecular mechanism of miRNAs in regulating cancer metastasis and EMT.     

上皮间质转化与乳腺癌的研究进展

在肿瘤演进中,原发性肿瘤中的一些细胞再次激活调控胚胎发育被称之为上皮间质转化(epithelial-mesenchymal transition,EMT)的潜在途径,使得上皮细胞获得间质细胞特征,更易发生侵袭和转移。EMT的异常激活与高侵袭基底型乳腺癌相关,提高了细胞生存能力、获得干细胞潜能及增强其侵袭转移能力,EMT化的癌干细胞对常规治疗更具有抵抗性。本文总结了与EMT相关的调控因子及癌干细胞在乳腺癌进展中的作用。     

EMT: a new vision of hypoxia promoting cancer progression

A hypoxic microenvironment plays a critical role in the development and progression of tumors. The epithelial to mesenchymal transition (EMT) is a process by which epithelial cells lose their polarity and are converted to a mesenchymal phenotype, which is regarded as a critical event in morphogenetic changes during embryonic development, wound healing, and cancer metastasis. Recent advances in our understanding of the molecular pathways that govern the association of hypoxia with malignant tumors point to the epithelial to mesenchymal transition (EMT). The hypoxic microenvironment common to cancer cells emerges as an important factor in the induction of a pathological EMT, which is a key link in cancer progression. This review presents the potential molecular mechanisms underlying the hypoxia/HIF-dependent regulation of the EMT in cancer.     

Retinoblastoma protein determines aggressiveness in triple-negative breast cancer

Retinoblastoma protein (RB) is one of the most important tumor suppressors and functions in multiple biological pathways that are deregulated during tumor initiation and progression. Epithelial-to-mesenchymal transition (EMT) is a reversible embryonic process by which epithelial cells lose cell-cell contact and polarity, and its aberrant activation can trigger tumor progression and metastasis. Previously, it has been shown that depletion of RB initiates EMT by downregulating the adhesion molecule E-cadherin. The evaluated article suggests that RB inactivation contributes to loss of cell cycle control and also leads to downregulation of the miR-200 family, thereby causing upregulation of ZEB expression and consequently EMT by downregulation of E-cadherin. RB inactivation could be a key event underlying the mesenchymal and aggressive phenotype of triple-negative breast cancer. Furthermore, exploring links between RB inactivation and EMT might reveal new therapeutic targets for triple-negative breast cancer.     

The roles of TGF-β signaling in carcinogenesis and breast cancer metastasis

Transforming growth factor-β (TGF-β) ligand is a multifunctional growth factor that regulates various cell behavior, such as cell proliferation, differentiation, migration, and apoptosis. Because TGF-β is a potent growth inhibitor, abnormalities in TGF-β signaling result in carcinogenesis. In addition to tumor suppressor function, TGF-β acts as an oncogenic factor. In particular, TGF-β signaling plays an important role during metastasis of breast cancer. Recently, epithelial-mesenchymal transition (EMT) has been shown to confer malignant properties such as cell motility and invasiveness to cancer cells and plays crucial roles during cancer metastasis. Moreover, breast stem-like cells exhibit EMT properties. Because TGF-β is a potent regulator of EMT as well as cell stemness, TGF-β signaling might play a crucial role in the regulation of breast cancer stem cells.     

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。      

Bmi-1 promotes invasion and metastasis,and its elevated expression is correlated with an advanced stage of breast cancer

Background  

B-lymphoma Moloney murine leukemia virus insertion region-1 (Bmi-1) acts as an oncogene in various tumors, and its overexpression correlates with a poor outcome in several human cancers. Ectopic expression of Bmi-1 can induce epithelial-mesenchymal transition (EMT) and enhance the motility and invasiveness of human nasopharyngeal epithelial cells (NPECs), whereas silencing endogenous Bmi-1 expression can reverse EMT and reduce the metastatic potential of nasopharyngeal cancer cells (NPCs). Mouse xenograft studies indicate that coexpression of Bmi-1 and H-Ras in breast cancer cells can induce an aggressive and metastatic phenotype with an unusual occurrence of brain metastasis; although, Bmi-1 overexpression did not result in oncogenic transformation of MCF-10A cells. However, the underlying molecular mechanism of Bmi-1-mediated progression and the metastasis of breast cancer are not fully elucidated at this time.