PDGFRB Promotes Liver Metastasis Formation of Mesenchymal-Like Colorectal Tumor Cells

In epithelial tumors, the platelet-derived growth factor receptor B (PDGFRB) is mainly expressed by stromal cells of mesenchymal origin. Tumor cells may also acquire PDGFRB expression following epithelial-to-mesenchymal transition (EMT), which occurs during metastasis formation. Little is known about PDGFRB signaling in colorectal tumor cells. We studied the relationship between PDGFRB expression, EMT, and metastasis in human colorectal cancer (CRC) cohorts by analysis of gene expression profiles. PDGFRB expression in primary CRC was correlated with short disease-free and overall survival. PDGFRB was co-expressed with genes involved in platelet activation, transforming growth factor beta (TGFB) signaling, and EMT in three CRC cohorts. PDGFRB was expressed in mesenchymal-like tumor cell lines in vitro and stimulated invasion and liver metastasis formation in mice. Platelets, a major source of PDGF, preferentially bound to tumor cells in a non-activated state. Platelet activation caused robust PDGFRB tyrosine phosphorylation on tumor cells in vitro and in liver sinusoids in vivo. Platelets also release TGFB, which is a potent inducer of EMT. Inhibition of TGFB signaling in tumor cells caused partial reversion of the mesenchymal phenotype and strongly reduced PDGFRB expression and PDGF-stimulated tumor cell invasion. These results suggest that PDGFRB may contribute to the aggressive phenotype of colorectal tumors with mesenchymal properties, most likely downstream of platelet activation and TGFB signaling.     

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.     

SNAIL1 combines competitive displacement of ASCL2 and?epigenetic mechanisms to rapidly silence the EPHB3 tumor suppressor in colorectal cancer

EPHB3 is a critical cellular guidance factor in the intestinal epithelium and an important tumor suppressor in colorectal cancer (CRC) whose expression is frequently lost at the adenoma‐carcinoma transition when tumor cells become invasive. The molecular mechanisms underlying EPHB3 silencing are incompletely understood. Here we show that EPHB3 expression is anti‐correlated with inducers of epithelial‐mesenchymal transition (EMT) in primary tumors and CRC cells. In vitro, SNAIL1 and SNAIL2, but not ZEB1, repress EPHB3 reporter constructs and compete with the stem cell factor ASCL2 for binding to an E‐box motif. At the endogenous EPHB3 locus, SNAIL1 triggers the displacement of ASCL2, p300 and the Wnt pathway effector TCF7L2 and engages corepressor complexes containing HDACs and the histone demethylase LSD1 to collapse active chromatin structure, resulting in rapid downregulation of EPHB3. Beyond its impact on EPHB3, SNAIL1 deregulates markers of intestinal identity and stemness and in vitro forces CRC cells to undergo EMT with altered morphology, increased motility and invasiveness. In xenotransplants, SNAIL1 expression abrogated tumor cell palisading and led to focal loss of tumor encapsulation and the appearance of areas with tumor cells displaying a migratory phenotype. These changes were accompanied by loss of EPHB3 and CDH1 expression. Intriguingly, SNAIL1‐induced phenotypic changes of CRC cells are significantly impaired by sustained EPHB3 expression both in vitro and in vivo. Altogether, our results identify EPHB3 as a novel target of SNAIL1 and suggest that disabling EPHB3 signaling is an important aspect to eliminate a roadblock at the onset of EMT processes.     

Epigenetics of epithelial‐to‐mesenchymal transition in pancreatic carcinoma

Pancreatic ductal adenocarcinoma (PDAC) is one of the most lethal malignant diseases with late diagnosis, rapid progression, high invasiveness, and early metastasis. Epithelial‐to‐mesenchymal transition (EMT) is a crucial step in metastasis that enables polarized immotile epithelial cells to gain fibroblast‐like mesenchymal abilities such as enhanced motility. The dynamic process of EMT in PDAC with its powerful influence on disease progression and especially metastasis is of vigorous interest in biomedical research to elucidate its signaling pathways and regulation mechanisms. It is evident that epigenetics such as histone and DNA modification or noncoding RNAs such as microRNAs and long noncoding RNAs are of high importance in initiation and progress of EMT in PDAC. This review analyzes the latest research dealing with EMT and its epigenetic regulation in PDAC and summarizes its potentials in diagnostic, prognostic, and therapeutic management.     

Blebbing as a physical force in cancer EMT - Parallels with mitosis

Epithelial to mesenchymal transition (EMT) during metastasis is initially a two-step process beginning with delamination of cells from the solid tumor followed by acquisition of a migratory phenotype. Several reports indicate that plasma membrane blebbing, associated with cell division, coincides with cell delamination during developmental EMT. This raises a speculative question if blebbing drives EMT in cancer cells in a similar way. Here, we review available data on factors and processes that may support such a connection.     

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.     

microRNA-214 promotes epithelial-mesenchymal transition and metastasis in lung adenocarcinoma by targeting the suppressor-of-fused protein (Sufu)

Distant metastasis is the major cause of cancer-related deaths in patients with lung adenocarcinoma (LAD). Emerging evidence reveals that miRNA is critical for tumor metastasis. miR-214 expression has been associated with LAD progression. However, whether and how miR-214 is involved in the development and metastasis of LAD remain unaddressed. Here, we found that the expression of miR-214 was elevated in LAD and correlated positively with LAD metastasis and epithelial-mesenchymal transition (EMT). In addition, we found that miR-214 enhanced the molecular program controlling the EMT of LAD cells and promoted LAD cell metastasis both in vitro and in vivo. This study thus provides the first evidence to show that the miR-214 expression by LAD cells contributes to the EMT and metastasis of LAD. Mechanistically, Sufu was identified as an important miR-214 functional target for the EMT and metastasis of LAD, ectopic expression of Sufu alleviated miR-214 promoted EMT and metastasis. Importantly, the expression of Sufu inversely correlated with the expression of miR-214 and vimentin and positively associated with the expression of E-cadherin in the tumor cells from human LAD patients. Collectively, this study uncovers a previously unappreciated miR-214-Sufu pathway in controlling EMT and metastasis of LAD and suggests that interfering with miR-214 and Sufu could be a viable approach to treat late stage metastatic LAD patients.     

Epithelial-to-mesenchymal transition promotes tubulin detyrosination and microtentacles that enhance endothelial engagement

Epithelial-to-mesenchymal transition (EMT) is associated with increased breast tumor metastasis; however, the specific mechanisms by which EMT promotes metastasis remain somewhat unclear. Despite the importance of cytoskeletal dynamics during both EMT and metastasis, very few current studies examine the cytoskeleton of detached and circulating tumor cells. Specific posttranslational α-tubulin modifications are critical for adherent cell motility and implicated in numerous pathologies, but also remain understudied in detached cells. We report here that EMT induced through ectopic expression of Twist or Snail promotes α-tubulin detyrosination and the formation of tubulin-based microtentacles in detached HMLEs. Mechanistically, EMT downregulates the tubulin tyrosine ligase enzyme, resulting in an accumulation of detyrosinated α-tubulin (Glu-tubulin), and increases microtentacles that penetrate endothelial layers to facilitate tumor cell reattachment. Confocal microscopy shows that microtentacles are capable of penetrating the junctions between endothelial cells. Suppression of endogenous Twist in metastatic human breast tumor cells is capable of reducing both tubulin detyrosination and microtentacles. Clinical breast tumor samples display high concordance between Glu-tubulin and Twist expression levels, emphasizing the coupling between EMT and tubulin detyrosination in vivo. Coordinated elevation of Twist and Glu-tubulin at invasive tumor fronts, particularly within ductal carcinoma in situ samples, establishes that EMT-induced tubulin detyrosination occurs at the earliest stages of tumor invasion. These data support a novel model where the EMT that occurs during tumor invasion downregulates tubulin tyrosine ligase, increasing α-tubulin detyrosination and promoting microtentacles that could enhance the reattachment of circulating tumor cells to the vascular endothelium during metastasis.     

Sixteenth Annual Pezcoller Symposium: stem cells and epigenesis in cancer

In the postgenomic era of cancer biology, it is becoming increasingly evident that epigenetic controls of gene expression play an important role in determining the phenotype of cancer cells, also indicating the possibility of restoring epigenetically a normal phenotype in cancer cells. Related to these mechanisms of control and their dynamic changes during carcinogenesis and tumor progression are the phenomena determining the relationships between stem cells and cancer cells. This symposium focused on epigenetic mechanisms affecting cancer development and possibly providing a basis for intervention. The basic biology of stem cells and the relationships between stem cells and cancer were discussed. Epigenetic control mechanisms affecting gene expression with emphasis on DNA methylation and histone function were considered. Therapeutic strategies stemming from the knowledge acquired in the basic topics discussed also were outlined.     

上皮向间质转化在消化道肿瘤中的研究进展

 近年研究发现,肿瘤细胞发生上皮向间质转化（EMT）摆脱细胞与细胞间连接而发生转移侵袭,已成为上皮细胞癌转移侵袭以及化疗耐药的一个重要途径。Snail家族成员,尤其是Snail被认为是肿瘤EMT发生的重要调节因子,它可以通过竞争性抑制E 钙黏蛋白基因的表达,引起上皮细胞向间质细胞表型的转变,最终引起EMT。多项研究显示,在消化系统肿瘤中普遍存在EMT现象,并与这些肿瘤的侵袭转移及化疗耐药密切相关。     

Role of histone deacetylase 1 in distant metastasis of pancreatic ductal cancer

Current therapies for pancreatic ductal cancer (PDAC) do not sufficiently control distant metastasis. Thus, new therapeutic targets are urgently needed. Numerous studies have suggested that the epithelial‐mesenchymal transition (EMT) is pivotal for metastasis of carcinomas. The fact that the EMT is reversible suggests the possibility that it is induced by an epigenetic mechanism. In this study, we aimed to investigate the role of histone deacetylase 1 (HDAC1), which is an epigenetic mechanism on distant metastasis of PDAC. We investigated the HDAC1 expression in 103 resected PDAC specimens obtained from patients who were treated with/without preoperative therapy using immunohistochemistry. To validate the findings in the clinical samples, we evaluated the HDAC1 activity, the EMT‐associated genes and the migration/invasion ability in vitro, and performed an HDAC1 inhibitor assay. The high expression of HDAC1 in clinical samples was significantly associated with poor progression‐free survival, especially distant metastasis‐free survival. In vitro, HDAC1 inhibitors decreased the invasion ability and reversed the EMT change; the only factor to show a concomitant decrease was the expression of SNAIL. We confirmed that the HDAC1 expression was associated with the SNAIL expression in clinical samples. Moreover, the resistant cells and parental cells did not show any significant differences in the expression of HDAC1; this was consistent with the finding that preoperative therapy did not alter the HDAC1 expression in clinical samples. The targeting of HDAC1, which could suppress metastasis by inhibiting the EMT, is a promising treatment option for PDAC.