Pre-EMTing metastasis? Recapitulation of morphogenetic processes in cancer

Epithelial-mesenchymal transition in mouse mammary tumorigenesis

Epithelial-mesenchymal transition tumorigenesis in the mouse has been described for over 100 years using various terms and with little comprehension of the underlying mechanisms. Recently, epithelial-mesenchymal transition tumors have been recognized in mammary glands of genetically engineered mice. This review provides a historical perspective and the current observations in the context of some of the key molecular biology. The biology of mouse mammary epithelial-mesenchymal transition tumorigenesis is discussed with comparisons to human breast cancer.

NF-kappaB-dependent plasticity of the epithelial to mesenchymal transition induced by Von Hippel-Lindau inactivation in renal cell carcinomas

The critical downstream signaling consequences contributing to renal cancer as a result of loss of the tumor suppressor gene von Hippel-Lindau (VHL) have yet to be fully elucidated. Here, we report that VHL loss results in an epithelial to mesenchymal transition (EMT). In studies of paired isogenic cell lines, VHL silencing increased the levels of N-cadherin and vimentin and reduced the levels of E-cadherin relative to the parental VHL(+) cell line, which displayed the opposite profile. VHL(+) cells grew as clusters of cuboidal and rhomboid cells, whereas VHL-silenced cells took on an elongated, fibroblastoid morphology associated with a more highly invasive character in Matrigel chamber assays. Based on earlier evidence that VHL loss can activate NF-kappaB, a known mediator of EMT, we tested whether NF-kappaB contributed to VHL-mediated effects on EMT. On pharmacologic or molecular inhibition of NF-kappaB, VHL-silenced cells regained expression of E-cadherin, lost expression of N-cadherin, and reversed their highly invasive phenotype. Introducing a pVHL-resistant hypoxia-inducible factor 1alpha (HIF1alpha) mutant (HIFalpha(M)) into VHL(+) cells heightened NF-kappaB activity, phenocopying EMT effects produced by VHL silencing. Conversely, inhibiting the heightened NF-kappaB activity in this setting reversed the EMT phenotype. Taken together, these results suggest that VHL loss induces an EMT that is largely dependent on HIFalpha-induced NF-kappaB. Our findings rationalize targeting the NF-kappaB pathway as a therapeutic strategy to treat renal tumors characterized by biallelic VHL inactivation.

E-/P-selectins and colon carcinoma metastasis: first in vivo evidence for their crucial role in a clinically relevant model of spontaneous metastasis formation in the lung

Background:

Interactions of endothelial selectins with tumour cell glycoconjugates have been shown to have a major role in tumour cell dissemination in previous experiments. However, experiments validating this observation were limited in value, as ‘metastases’ in these experiments were artificially induced by i.v. injection rather than developed spontaneously as in true metastases.

Methods:

Endothelial (E) and platelet (P)-selectin-deficient severe combined immunodeficient (scid) mice were generated and human HT 29 colon cancer cells were subcutaneously inoculated in these mice and in wild-type scid mice. Tumour growth, spontaneous metastasis formation in the lung and adherence of HT29 cells to E- and P-selectin under flow were determined.

Results:

The number of metastases decreased by 84% in E- and P-selectin-deficient scid mice, compared with wild-type scid mice. The remaining 16% metastases in the E- and P-selectin-deficient scid mice grew within the pulmonary artery and not in the alveolar septae as they did in wild-type scid mice. Flow experiments indicate that tumour cells roll and tether on an E- and P-selectin matrix similar to leukocytes; however, firm adhesion is mainly mediated in E-selectin.

Conclusion:

Our results indicate that E- and P-selectins have a crucial role in spontaneous metastasis formation. As the human HT 29 colon cancer cells are positive for the lectin Helix pomatia agglutinin (HPA), which identified the metastatic phenotype in earlier clinical studies, these results are of particular clinical relevance.

Confocal images of circulating tumor cells obtained using a methodology and technology that removes normal cells

A completely negative enrichment technology was used to detect circulating tumor cells, CTCs, in the peripheral blood of head and neck cancer patients. Of 32 blood samples, 63% contained CTCs and the number of CTCs identified per mL of blood collected ranged from 0 to 214. The final purity ranged from 1 CTC in 9 total cells to 1 CTC in 20,000 total cells, the final purity being both a function of the number of CTCs and the performance of the specific enrichment. Consistent with previous reports, CTC were positively identified if: (1) they contained a nucleus based on DAPI stain, (2) stained positive for cytokeratins, and (3) have a high nuclei to cytoplasmic ratio. In addition, for a blood sample to be considered positive for CTCs, the enriched sample must be positive for epithelial growth factor receptor, EGFR, as measured by RT-PCR. While most of the blood samples were obtained during surgery, a number were taken prior to and during surgery. In all of the pre- and postsurgery paired samples, significant numbers of CTCs were detected. A number of these enriched samples were observed under confocal microscope in addition to the microscopic observations under traditional wide-field fluorescent microscope. As expected, the FITC stained cytokeratins appeared in the cytoplasm and the average size of these positively stained cells, on the cytospin, was in the range of 8-12 mum. Future studies will involve the investigation if cancer stem cell and mesenchymal markers are present on these CTCs and correlations of patient outcome to the number and type of CTC present.

Involvement of members of the cadherin superfamily in cancer

We review the role of cadherins and cadherin-related proteins in human cancer. Cellular and animal models for human cancer are also dealt with whenever appropriate. E-cadherin is the prototype of the large cadherin superfamily and is renowned for its potent malignancy suppressing activity. Different mechanisms for inactivating E-cadherin/CDH1 have been identified in human cancers: inherited and somatic mutations, aberrant protein processing, increased promoter methylation, and induction of transcriptional repressors such as Snail and ZEB family members. The latter induce epithelial mesenchymal transition, which is also associated with induction of "mesenchymal" cadherins, a hallmark of tumor progression. VE-cadherin/CDH5 plays a role in tumor-associated angiogenesis. The atypical T-cadherin/CDH13 is often silenced in cancer cells but up-regulated in tumor vasculature. The review also covers the status of protocadherins and several other cadherin-related molecules in human cancer. Perspectives for emerging cadherin-related anticancer therapies are given.

The EMT-activator ZEB1 promotes tumorigenicity by repressing stemness-inhibiting microRNAs

Invasion and metastasis of carcinomas is promoted by the activation of the embryonic 'epithelial to mesenchymal transition' (EMT) program, which triggers cellular mobility and subsequent dissemination of tumour cells. We recently showed that the EMT-activator ZEB1 (zinc finger E-box binding homeobox 1) is a crucial promoter of metastasis and demonstrated that ZEB1 inhibits expression of the microRNA-200 (miR-200) family, whose members are strong inducers of epithelial differentiation. Here, we report that ZEB1 not only promotes tumour cell dissemination, but is also necessary for the tumour-initiating capacity of pancreatic and colorectal cancer cells. We show that ZEB1 represses expression of stemness-inhibiting miR-203 and that candidate targets of miR-200 family members are also stem cell factors, such as Sox2 and Klf4. Moreover, miR-200c, miR-203 and miR-183 cooperate to suppress expression of stem cell factors in cancer cells and mouse embryonic stem (ES) cells, as demonstrated for the polycomb repressor Bmi1. We propose that ZEB1 links EMT-activation and stemness-maintenance by suppressing stemness-inhibiting microRNAs (miRNAs) and thereby is a promoter of mobile, migrating cancer stem cells. Thus, targeting the ZEB1-miR-200 feedback loop might form the basis of a promising treatment for fatal tumours, such as pancreatic cancer.

Direct cancer-stromal interaction increases fibroblast proliferation and enhances invasive properties of scirrhous-type gastric carcinoma cells

BACKGROUND

Scirrhous-type gastric carcinoma (SGC) exhibits an extensive submucosal fibrosis and extremely poor patient prognosis. We investigated the importance of the cancer-stromal interaction in the histogenesis of SGC.

METHODS

Gastric fibroblasts NF-25 and intestinal fibroblasts NF-j2 were co-cultured with SGC-derived (HSC-39) or non-SGC-derived (HSC-57 and HSC-64) cells. To identify genes that are up- or downregulated in NF-25, complementary DNA (cDNA) microarray analysis was performed. The antibody against vascular-cell adhesion molecule-1 (VCAM-1) was used for cell growth test and immunohistochemistry. Moreover, the impact of interaction with NF-25 fibroblasts on HSC-39 cells was investigated using western blot and reverse transcription-polymerase chain reaction.

RESULTS

HSC-39 cells stimulated growth of NF-25 but not NF-j2 when co-cultured. Induction of VCAM-1 in NF-25 fibroblasts was identified, which was specific when co-cultured with HSC-39 but not with non-SGC-derived HSC-57 and HSC-64 cells. Neutralising antibody to VCAM-1 suppressed NF-25 growth in dose-dependent manners. In tissue samples, positive immunoreactivity of VCAM-1 in SGC-derived fibroblasts was significantly higher than that in non-SGC-derived fibroblasts. Furthermore, interaction with NF-25 fibroblasts not only induced the epithelial-mesenchymal transition-like change, but also expressions of matrix metalloproteinase- related genes in HSC-39 cells.

CONCLUSION

Direct interaction between SGC cells and gastric fibroblasts establishes the tumour microenvironment and reinforces the aggressiveness of SGC.

The miR200 family of microRNAs regulates WAVE3-dependent cancer cell invasion

MicroRNAs are small non-coding RNAs that are directly involved in the regulation of gene expression by either translational repression or degradation of target mRNAs. Because of the high level of conservation of the target motifs, known as seed sequences, within the 3'-untranslated regions, a single microRNA can regulate numerous target genes simultaneously, making this class of RNAs a powerful regulator of gene expression. The miR200 family of microRNAs has recently been shown to regulate the process of epithelial to mesenchymal transition during tumor progression and metastasis. Here, we report that the expression of WAVE3, an actin cytoskeleton remodeling and metastasis promoter protein, is regulated by miR200 microRNAs. We show a clear inverse correlation between expression levels of WAVE3 and miR200 microRNAs in invasive versus non-invasive cancer cells. miR200 directly targets the 3'-untranslated regions of the WAVE3 mRNA and inhibits its expression. The miR200-mediated down-regulation of WAVE3 results in a significant reduction in the invasive phenotype of cancer cells, which is specific to the loss of WAVE3 expression. Re-expression of a miR200-resistant WAVE3 reverses miR200-mediated inhibition of cancer cell invasion. Loss of WAVE3 expression downstream of miR200 also results in a dramatic change in cell morphology resembling that of a mesenchymal to epithelial transition. In conclusion, a novel mechanism for the regulation of WAVE3 expression in cancer cells has been identified, which controls the invasive properties and morphology of cancer cells associated with their metastatic potential.

miR-200 enhances mouse breast cancer cell colonization to form distant metastases

BACKGROUND

The development of metastases involves the dissociation of cells from the primary tumor to penetrate the basement membrane, invade and then exit the vasculature to seed, and colonize distant tissues. The last step, establishment of macroscopic tumors at distant sites, is the least well understood. Four isogenic mouse breast cancer cell lines (67NR, 168FARN, 4TO7, and 4T1) that differ in their ability to metastasize when implanted into the mammary fat pad are used to model the steps of metastasis. Only 4T1 forms macroscopic lung and liver metastases. Because some miRNAs are dysregulated in cancer and affect cellular transformation, tumor formation, and metastasis, we examined whether changes in miRNA expression might explain the differences in metastasis of these cells.

METHODOLOGY/PRINCIPAL FINDINGS

miRNA expression was analyzed by miRNA microarray and quantitative RT-PCR in isogenic mouse breast cancer cells with distinct metastatic capabilities. 4T1 cells that form macroscopic metastases had elevated expression of miR-200 family miRNAs compared to related cells that invade distant tissues, but are unable to colonize. Moreover, over-expressing miR-200 in 4TO7 cells enabled them to metastasize to lung and liver. These findings are surprising since the miR-200 family was previously shown to promote epithelial characteristics by inhibiting the transcriptional repressor Zeb2 and thereby enhancing E-cadherin expression. We confirmed these findings in these cells. The most metastatic 4T1 cells acquired epithelial properties (high expression of E-cadherin and cytokeratin-18) compared to the less metastatic cells.

CONCLUSIONS/SIGNIFICANCE

Expression of miR-200, which promotes a mesenchymal to epithelial cell transition (MET) by inhibiting Zeb2 expression, unexpectedly enhances macroscopic metastases in mouse breast cancer cell lines. These results suggest that for some tumors, tumor colonization at metastatic sites might be enhanced by MET. Therefore the epithelial nature of a tumor does not predict metastatic outcome.

Comparative analysis of metastasis variants derived from human prostate carcinoma cells: roles in intravasation of VEGF-mediated angiogenesis and uPA-mediated invasion

To analyze the process of tumor cell intravasation, we used the human tumor-chick embryo spontaneous metastasis model to select in vivo high (PC-hi/diss) and low (PC-lo/diss) disseminating variants from the human PC-3 prostate carcinoma cell line. These variants dramatically differed in their intravasation and dissemination capacities in both chick embryo and mouse spontaneous metastasis models. Concomitant with enhanced intravasation, PC-hi/diss exhibited increased angiogenic potential in avian and murine models. PC-hi/diss angiogenesis and intravasation were dependent on increased secretion of vascular endothelial growth factor (VEGF), since treating developing tumors with a function-blocking anti-VEGF antibody simultaneously inhibited both processes without affecting primary tumor growth. PC-hi/diss cells were also more migratory and invasive, suggestive of heightened ability to escape from primary tumors due to matrix-degrading activity. Consistent with this suggestion, PC-hi/diss cells produced more of the serine protease urokinase-type plasminogen activator (uPA) as compared with PC-lo/diss. The functional role of uPA in PC-hi/diss dissemination was confirmed by inhibition of invasion, angiogenesis, and intravasation with specific function-blocking antibodies that prevented uPA activation and blocked uPA activity. These processes were similarly sensitive to aprotinin, a potent inhibitor of serine proteases, including uPA-generated plasmin. Thus, our comparison of the PC-3 intravasation variants points to key roles for the uPA-plasmin system in PC-hi/diss intravasation, possibly via (1) promoting tumor cell matrix invasion and (2) facilitating development of VEGF-dependent angiogenic blood vessels.

Constitutively active MEK1 is sufficient to induce epithelial-to-mesenchymal transition in intestinal epithelial cells and to promote tumor invasion and metastasis

Constitutive activation of the MAP kinase kinase MEK1 induces oncogenic transformation in intestinal epithelial cells. Loss of cell-cell adhesion followed by the dissociation of epithelial structures is a prerequisite for increased cell motility and tumor invasion. This phenotypic switch is designated epithelial-to-mesenchymal transition (EMT). EMT also plays an important role in determining the dissemination of tumors. However, the role of MEK1 in intestinal EMT, tumor invasion and metastasis has not been elucidated. To determine the functions of activated MEK1 in intestinal tumorigenesis, we established intestinal epithelial cell lines that overexpress wild-type MEK1 (wtMEK) or activated MEK1 (caMEK). Our results indicate that expression of caMEK is sufficient to induce EMT as confirmed with the induction of N-cadherin, vimentin, Snail1 and Snail2, whereas a reduction in E-cadherin, occludin, ZO-1 and cortical F-actin was noted. The Snail1 and Snail2 promoter analyses revealed that Egr-1 and Fra-1, an AP-1 protein, are responsible for MEK1-induced Snail1 and Snail2 expression, respectively. Cells expressing activated MEK1 clearly acquired an invasive capacity when compared to wtMEK-expressing cells. Zymography studies confirmed elevated levels of MMP2 and MMP9 activities in media of caMEK-expressing cells. Importantly, cells expressing activated MEK1 induced tumors with short latency in correlation with their ability to induce experimental metastasis in vivo and to express factors known to promote colorectal cancer cell metastasis. In conclusion, our results demonstrate, for the first time, that constitutive activation of MEK1 in intestinal epithelial cells is sufficient to induce an EMT associated with tumor invasion and metastasis.

Cancer stem cells, hypoxia and metastasis

The successful growth of a metastasis, by definition, requires the presence of at least 1 cancer stem cell. Metastasis is a complex process, and an important contributor to this process is the influence of the tissue microenvironment, both cell-cell and cell-matrix interactions and the pathophysiologic conditions in tumors, such as hypoxia. A number of studies have suggested that normal stem cells may reside in "niches," where cell-cell and cell-matrix interactions can provide critical signals to support and maintain the undifferentiated phenotype of the stem cells. In this article, the evidence that these niches may be hypoxic is described, and the potential role that hypoxia may play in maintaining the stem cell phenotype in cancers is discussed. Recent work has suggested that there may be a linkage between the stem cell phenotype and that induced by the process of epithelial-mesenchymal transition (EMT). EMT plays an important role in cell movement and organ formation during embryogenesis, and it is currently hypothesized to be a major mechanism by which epithelial cancers may generate cells that can form metastases. Recent evidence suggests that the expression of certain genes involved in EMT is influenced by low oxygen levels, again suggesting a linkage between stem cells and hypoxia. Whether this supposition is correct remains an open question that will only be answered by further experimentation, but the potential role of hypoxia is critical because of its widespread existence in tumors and its known role in resistance to both radiation and drug treatment.

PKCepsilon regulation of an alpha5 integrin-ZO-1 complex controls lamellae formation in migrating cancer cells

Disruption of intercellular adhesions, increased abundance of alpha(5)beta(1) integrin, and activation of protein kinase Cepsilon (PKCepsilon) correlate with invasion and unfavorable prognosis in lung cancer. However, it remains elusive how these distinct factors contribute to the invasive behavior of cancer cells. Persistent cell motility requires the formation of stable lamellae at the leading edge of a migrating cell. Here, we report that the tight junction protein zonula occludens-1 (ZO-1) preferentially interacts with alpha(5)beta(1) integrin at the lamellae of migrating cells. Disruption of ZO-1 binding to an internal PDZ-binding motif in the alpha(5) cytoplasmic tail prevented the polarized localization of ZO-1 and alpha(5) at the leading edge. Furthermore, silencing of alpha(5) integrin inhibited migration and invasion of lung cancer cells, and silencing of ZO-1 resulted in increased Rac activity and reduced directional cell motility. The formation of the alpha(5)-ZO-1 complex was dependent on PKCepsilon: Phosphorylation of ZO-1 at serine-168 regulated the subcellular localization of ZO-1 and thus controlled its association with alpha(5) integrin. In conclusion, PKCepsilon activation drives the formation of a spatially restricted, promigratory alpha(5)-ZO-1 complex at the leading edge of lung cancer cells.

A Twist-Snail axis critical for TrkB-induced epithelial-mesenchymal transition-like transformation, anoikis resistance, and metastasis

In a genomewide anoikis suppression screen for metastasis genes, we previously identified the neurotrophic receptor tyrosine kinase TrkB. In mouse xenografts, activated TrkB caused highly invasive and metastatic tumors. Here, we describe that TrkB also induces a strong morphological transformation, resembling epithelial-mesenchymal transition (EMT). This required TrkB kinase activity, a functional mitogen-activated protein kinase pathway, suppression of E-cadherin, and induction of Twist, a transcription factor contributing to EMT and metastasis. RNA interference (RNAi)-mediated Twist depletion blocked TrkB-induced EMT-like transformation, anoikis suppression, and growth of tumor xenografts. By searching for essential effectors of TrkB-Twist signaling, we found that Twist induces Snail, another EMT regulator associated with poor cancer prognosis. Snail depletion impaired EMT-like transformation and anoikis suppression induced by TrkB, but in contrast to Twist depletion, it failed to inhibit tumor growth. Instead, Snail RNAi specifically impaired the formation of lung metastases. Epistasis experiments suggested that Twist acts upstream from Snail. Our results demonstrate that TrkB signaling activates a Twist-Snail axis that is critically involved in EMT-like transformation, tumorigenesis, and metastasis. Moreover, our data shed more light on the epistatic relationship between Twist and Snail, two key transcriptional regulators of EMT and metastasis.

Epithelial-mesenchymal transition: a cancer researcher's conceptual friend and foe

Epithelial-mesenchymal transition (EMT) describes a series of rapid changes in cellular phenotype. During EMT, epithelial cells down-modulate cell-cell adhesion structures, alter their polarity, reorganize their cytoskeleton, and become isolated, motile, and resistant to anoikis. The term EMT is often applied to distinct biological events as if it were a single conserved process, but in fact EMT-related processes can vary in intensity from a transient loss of cell polarity to the total cellular reprogramming, as found by transcriptional analysis. Based on clinical observations, it is more appropriate in most cases to describe the emergence of an EMT-like phenotype during tumor progression. Although EMT implies complete trans-differentiation, EMT-like emphasizes the intermediary phenotype associated with tumor cell renewal and adaptation to specific microenvironments. Here, we categorize the various EMT-like phenotypes found in human carcinomas that, depending on the tumor type, may or not represent analogous stages in tumor progression. We based these categories on the global tumor phenotype. The tumor microenvironment, which is associated with stromal reactions, hypoxia, paucity of nutrients, impaired differentiation, and activation of various EMT-associated pathways, modulates overall tumor phenotype and leads to tumor heterogeneity.

Epithelial-mesenchymal transition: a cancer researcher's conceptual friend and foe

Epithelial-mesenchymal transition (EMT) describes a series of rapid changes in cellular phenotype. During EMT, epithelial cells down-modulate cell-cell adhesion structures, alter their polarity, reorganize their cytoskeleton, and become isolated, motile, and resistant to anoikis. The term EMT is often applied to distinct biological events as if it were a single conserved process, but in fact EMT-related processes can vary in intensity from a transient loss of cell polarity to the total cellular reprogramming, as found by transcriptional analysis. Based on clinical observations, it is more appropriate in most cases to describe the emergence of an EMT-like phenotype during tumor progression. Although EMT implies complete trans-differentiation, EMT-like emphasizes the intermediary phenotype associated with tumor cell renewal and adaptation to specific microenvironments. Here, we categorize the various EMT-like phenotypes found in human carcinomas that, depending on the tumor type, may or not represent analogous stages in tumor progression. We based these categories on the global tumor phenotype. The tumor microenvironment, which is associated with stromal reactions, hypoxia, paucity of nutrients, impaired differentiation, and activation of various EMT-associated pathways, modulates overall tumor phenotype and leads to tumor heterogeneity.

ZEB1 enhances transendothelial migration and represses the epithelial phenotype of prostate cancer cells

Metastatic colonization involves cancer cell lodgment or adherence in the microvasculature and subsequent migration of those cells across the endothelium into a secondary organ site. To study this process further, we analyzed transendothelial migration of human PC-3 prostate cancer cells in vitro. We isolated a subpopulation of cells, TEM4-18, that crossed an endothelial barrier more efficiently, but surprisingly, were less invasive than parental PC-3 cells in other contexts in vitro. Importantly, TEM4-18 cells were more aggressive than PC-3 cells in a murine metastatic colonization model. Microarray and FACS analysis of these cells showed that the expression of many genes previously associated with leukocyte trafficking and cancer cell extravasation were either unchanged or down-regulated. Instead, TEM4-18 cells exhibited characteristic molecular markers of an epithelial-to-mesenchymal transition (EMT), including frank loss of E-cadherin expression and up-regulation of the E-cadherin repressor ZEB1. Silencing ZEB1 in TEM4-18 cells resulted in increased E-cadherin and reduced transendothelial migration. TEM4-18 cells also express N-cadherin, which was found to be necessary, but not sufficient for increased transendothelial migration. Our results extend the role of EMT in metastasis to transendothelial migration and implicate ZEB1 and N-cadherin in this process in prostate cancer cells.

Optimization of an enrichment process for circulating tumor cells from the blood of head and neck cancer patients through depletion of normal cells

The optimization of a purely negative depletion, enrichment process for circulating tumor cells (CTCs) in the peripheral blood of head and neck cancer patients is presented. The enrichment process uses a red cell lysis step followed by immunomagnetic labeling, and subsequent depletion, of CD45 positive cells. A number of relevant variables are quantified, or attempted to be quantified, which control the performance of the enrichment process. Six different immunomagnetic labeling combinations were evaluated as well as the significant difference in performance with respect to the blood source: buffy coats purchased from the Red Cross, fresh, peripheral blood from normal donors, and fresh peripheral blood from human cancer patients. After optimization, the process is able to reduce the number of normal blood cells in a cancer patient's blood from 4.05 x 10(9) to 8.04 x 10(3) cells/mL and still recover, on average, 2.32 CTC per mL of blood. For all of the cancer patient blood samples tested in which CTC were detected (20 out of 26 patients) the average recovery of CTCs was 21.7 per mL of blood, with a range of 282 to 0.53 CTC. Since the initial number of CTC in a patient's blood is unknown, and most probably varies from patient to patient, the recovery of the CTC is unknown. However, spiking studies of a cancer cell line into normal blood, and subsequent enrichment using the optimized protocol indicated an average recovery of approximately 83%. Unlike a majority of other published studies, this study focused on quantifying as many factors as possible to facilitate both the optimization of the process as well as provide information for current and future performance comparisons. The authors are not aware any other reported study which has achieved the performance reported here (a 5.66 log(10)) in a purely negative enrichment mode of operation. Such a mode of operation of an enrichment process provides significant flexibility in that it has no bias with respect to what attributes define a CTC; thereby allowing the researcher or clinician to use any maker they choose to define whether the final, enrich product contains CTCs or other cell type relevant to the specific question (i.e., does the CTC have predominantly epithelial or mesenchymal characteristics?).

Epithelial-mesenchymal transition induced by growth suppressor p12CDK2-AP1 promotes tumor cell local invasion but suppresses distant colony growth

Epithelial-mesenchymal transition (EMT) has been considered essential for metastasis, a multistep process including local invasion, intravasation, extravasation, and proliferation at distant sites. However, controversy remains as to whether EMT truly happens and how important it is to metastasis. We studied the involvement of EMT in individual steps of metastasis and found that p12(CDK2-AP1), a down-stream effector of transforming growth factor beta, induced EMT of hamster cheek pouch carcinoma-1 cells by promoting the expression of Twist2. EMT cells have an increased invasive but decreased metastatic phenotype. When s.c. inoculated, both EMT and non-EMT cells established primary tumors, but only EMT cells invaded into the adjacent tissues and blood vessels; however, neither cells formed lung metastases. When i.v. inoculated, only non-EMT cells established lung metastases. Moreover, s.c. inoculation of a mixture of the two cell types resulted in intravasation of both cell types and formation of lung metastasis from non-EMT cells. Our results allowed us to propose a novel model for the role of EMT in cancer metastasis. We showed that EMT and non-EMT cells cooperate to complete the spontaneous metastasis process. We thus hypothesize that EMT cells are responsible for degrading the surrounding matrix to lead the way of invasion and intravasation. Non-EMT cells then enter the blood stream and reestablish colonies in the secondary sites.

Plasticity of cloned canine mammary spindle cell tumor, osteosarcoma and carcinoma cells

Female dogs are frequently affected by mammary tumors, both carcinomas and sarcomas. The mechanisms behind mammary-tumor formation and the high degree of heterogeneity are not understood. To provide insight into this issue, it is important to determine the properties of the cells forming the different types of tumors. One question is if individual neoplastic cells can give rise to phenotypically distinct tumor types, i.e., show plasticity. We studied 3 different tumors (a spindle-cell tumor, an osteosarcoma, and a carcinoma) and followed the change of lineage marker expression between the primary canine mammary tumors, the clones derived from the corresponding tumors and in tumors generated after inoculation of tumor clones into nude mice (n = 75). Inoculation of clones derived from the spindle-cell tumor gave rise to spindle-cell tumors in nude mice. Several of these contained bone tissue, a sign of plasticity. Clones derived from the osteosarcoma were negative for a panel of lineage markers but, when inoculated into nude mice, they were able to form bone, again a sign of plasticity. In contrast to the primary carcinoma, most of the clones derived thereof lacked keratin expression, but keratin expression was recovered in most of the tumors formed after inoculation of clones into nude mice. Moreover, tumors generated from the carcinoma clones, in contrast to the primary tumor, were positive for smooth-muscle-cell markers. Our results point to plasticity in canine mammary tumors, as shown both by morphologic criteria and by expression patterns for lineage specific markers.

Epithelial to mesenchymal transition of a primary prostate cell line with switches of cell adhesion modules but without malignant transformation

BACKGROUND

Epithelial to mesenchymal transition (EMT) has been connected with cancer progression in vivo and the generation of more aggressive cancer cell lines in vitro. EMT has been induced in prostate cancer cell lines, but has previously not been shown in primary prostate cells. The role of EMT in malignant transformation has not been clarified.

METHODOLOGY/PRINCIPAL FINDINGS

In a transformation experiment when selecting for cells with loss of contact inhibition, the immortalized prostate primary epithelial cell line, EP156T, was observed to undergo EMT accompanied by loss of contact inhibition after about 12 weeks in continuous culture. The changed new cells were named EPT1. EMT of EPT1 was characterized by striking morphological changes and increased invasion and migration compared with the original EP156T cells. Gene expression profiling showed extensively decreased epithelial markers and increased mesenchymal markers in EPT1 cells, as well as pronounced switches of gene expression modules involved in cell adhesion and attachment. Transformation assays showed that EPT1 cells were sensitive to serum or growth factor withdrawal. Most importantly, EPT1 cells were not able to grow in an anchorage-independent way in soft agar, which is considered a critical feature of malignant transformation.

CONCLUSIONS/SIGNIFICANCE

This work for the first time established an EMT model from primary prostate cells. The results show that EMT can be activated as a coordinated gene expression program in association with early steps of transformation. The model allows a clearer identification of the molecular mechanisms of EMT and its potential role in malignant transformation.

Molecular and pathological signatures of epithelial-mesenchymal transitions at the cancer invasion front

Reduction of epithelial cell-cell adhesion via the transcriptional repression of cadherins in combination with the acquisition of mesenchymal properties are key determinants of epithelial-mesenchymal transition (EMT). EMT is associated with early stages of carcinogenesis, cancer invasion and recurrence. Furthermore, the tumor stroma dictates EMT through intensive bidirectional communication. The pathological analysis of EMT signatures is critically, especially to determine the presence of cancer cells at the resection margins of a tumor. When diffusion barriers disappear, EMT markers may be detected in sera from cancer patients. The detection of EMT signatures is not only important for diagnosis but can also be exploited to enhance classical chemotherapy treatments. In conclusion, further detailed understanding of the contextual cues and molecular mediators that control EMT will be required in order to develop diagnostic tools and small molecule inhibitors with potential clinical implications.

A reciprocal repression between ZEB1 and members of the miR-200 family promotes EMT and invasion in cancer cells

The embryonic programme ‘epithelial–mesenchymal transition' (EMT) is thought to promote malignant tumour progression. The transcriptional repressor zinc-finger E-box binding homeobox 1 (ZEB1) is a crucial inducer of EMT in various human tumours, and was recently shown to promote invasion and metastasis of tumour cells. Here, we report that ZEB1 directly suppresses transcription of microRNA-200 family members miR-141 and miR-200c, which strongly activate epithelial differentiation in pancreatic, colorectal and breast cancer cells. Notably, the EMT activators transforming growth factor β2 and ZEB1 are the predominant targets downregulated by these microRNAs. These results indicate that ZEB1 triggers an microRNA-mediated feedforward loop that stabilizes EMT and promotes invasion of cancer cells. Alternatively, depending on the environmental trigger, this loop might switch and induce epithelial differentiation, and thus explain the strong intratumorous heterogeneity observed in many human cancers.

A reciprocal repression between ZEB1 and members of the miR-200 family promotes EMT and invasion in cancer cells

The embryonic programme 'epithelial-mesenchymal transition' (EMT) is thought to promote malignant tumour progression. The transcriptional repressor zinc-finger E-box binding homeobox 1 (ZEB1) is a crucial inducer of EMT in various human tumours, and was recently shown to promote invasion and metastasis of tumour cells. Here, we report that ZEB1 directly suppresses transcription of microRNA-200 family members miR-141 and miR-200c, which strongly activate epithelial differentiation in pancreatic, colorectal and breast cancer cells. Notably, the EMT activators transforming growth factor beta2 and ZEB1 are the predominant targets downregulated by these microRNAs. These results indicate that ZEB1 triggers an microRNA-mediated feedforward loop that stabilizes EMT and promotes invasion of cancer cells. Alternatively, depending on the environmental trigger, this loop might switch and induce epithelial differentiation, and thus explain the strong intratumorous heterogeneity observed in many human cancers.

Role of cancer microenvironment in metastasis: focus on colon cancer

One person on three will receive a diagnostic of cancer during his life. About one third of them will die of the disease. In most cases, death will result from the formation of distal secondary sites called metastases. Several events that lead to cancer are under genetic control. In particular, cancer initiation is tightly associated with specific mutations that affect proto-oncogenes and tumour suppressor genes. These mutations lead to unrestrained growth of the primary neoplasm and a propensity to detach and to progress through the subsequent steps of metastatic dissemination. This process depends tightly on the surrounding microenvironment. In fact, several studies support the point that tumour development relies on a continuous cross-talk between cancer cells and their cellular and extracellular microenvironments. This signaling cross-talk is mediated by transmembrane receptors expressed on cancer cells and stromal cells. The aim of this manuscript is to review how the cancer microenvironment influences the journey of a metastatic cell taking liver invasion by colorectal cancer cells as a model.