CD44 variant isoforms associate with tetraspanins and EpCAM

Regulation of the Function and Expression of EpCAM

The epithelial cell adhesion molecule (EpCAM) is a single transmembrane protein on the cell surface. Given its strong expression on epithelial cells and epithelial cell-derived tumors, EpCAM has been identified as a biomarker for circulating tumor cells (CTCs) and exosomes and a target for cancer therapy. As a cell adhesion molecule, EpCAM has a crystal structure that indicates that it forms a cis-dimer first and then probably a trans-tetramer to mediate intercellular adhesion. Through regulated intramembrane proteolysis (RIP), EpCAM and its proteolytic fragments are also able to regulate multiple signaling pathways, Wnt signaling in particular. Although great progress has been made, increasingly more findings have revealed the context-specific expression and function patterns of EpCAM and their regulation processes, which necessitates further studies to determine the structure, function, and expression of EpCAM under both physiological and pathological conditions, broadening its application in basic and translational cancer research.

Fibrolamellar carcinomas-growth arrested by paracrine signals complexed with synthesized 3-O sulfated heparan sulfate oligosaccharides

Fibrolamellar carcinomas (FLCs), lethal tumors occurring in children to young adults, have genetic signatures implicating derivation from biliary tree stem cell (BTSC) subpopulations, co-hepato/pancreatic stem cells, involved in hepatic and pancreatic regeneration. FLCs and BTSCs express pluripotency genes, endodermal transcription factors, and stem cell surface, cytoplasmic and proliferation biomarkers. The FLC-PDX model, FLC-TD-2010, is driven ex vivo to express pancreatic acinar traits, hypothesized responsible for this model's propensity for enzymatic degradation of cultures. A stable ex vivo model of FLC-TD-2010 was achieved using organoids in serum-free Kubota's Medium (KM) supplemented with 0.1% hyaluronans (KM/HA). Heparins (10 ng/ml) caused slow expansion of organoids with doubling times of ∼7-9 days. Spheroids, organoids depleted of mesenchymal cells, survived indefinitely in KM/HA in a state of growth arrest for more than 2 months. Expansion was restored with FLCs co-cultured with mesenchymal cell precursors in a ratio of 3:7, implicating paracrine signaling. Signals identified included FGFs, VEGFs, EGFs, Wnts, and others, produced by associated stellate and endothelial cell precursors. Fifty-three, unique heparan sulfate (HS) oligosaccharides were synthesized, assessed for formation of high affinity complexes with paracrine signals, and each complex screened for biological activity(ies) on organoids. Ten distinct HS-oligosaccharides, all 10-12 mers or larger, and in specific paracrine signal complexes elicited particular biological responses. Of note, complexes of paracrine signals and 3-O sulfated HS-oligosaccharides elicited slowed growth, and with Wnt3a, elicited growth arrest of organoids for months. If future efforts are used to prepare HS-oligosaccharides resistant to breakdown in vivo, then [paracrine signal-HS-oligosaccharide] complexes are potential therapeutic agents for clinical treatments of FLCs, an exciting prospect for a deadly disease.

Patch grafting of organoids of stem/progenitors into solid organs can correct genetic-based disease states

Patch grafting, a novel strategy for transplantation of stem/progenitor organoids into porcine livers, has been found successful also for organoid transplantation into other normal or diseased solid organs in pigs and mice. Each organoid contained ∼100 cells comprised of biliary tree stem cells (BTSCs), co-hepato/pancreatic stem/progenitors, and partnered with early lineage stage mesenchymal cells (ELSMCs), angioblasts and precursors to endothelia and stellate cells. Patch grafting enabled transplantation into livers or pancreases of ≥108th (pigs) or ≥106th-7th (mice) organoids/patch. Graft conditions fostered expression of multiple matrix-metalloproteinases (MMPs), especially secretory isoforms, resulting in transient loss of the organ's matrix-dictated histological features, including organ capsules, and correlated with rapid integration within a week of organoids throughout the organs and without emboli or ectopic cell distribution. Secondarily, within another week, there was clearance of graft biomaterials, followed by muted expression of MMPs, restoration of matrix-dictated histology, and maturation of donor cells to functional adult fates. The ability of patch grafts of organoids to rescue hosts from genetic-based disease states was demonstrated with grafts of BTSC/ELSMC organoids on livers, able to rescue NRG/FAH-KO mice from type I tyrosinemia, a disease caused by absence of fumaryl acetoacetate hydrolase. With the same grafts, if on pancreas, they were able to rescue NRG/Akita mice from type I diabetes, caused by a mutation in the insulin 2 gene. The potential of patch grafting for cell therapies for solid organs now requires translational studies to enable its adaptation and uses for clinical programs.

Proteomic alteration of endometrial tissues during secretion in polycystic ovary syndrome may affect endometrial receptivity

Embryo implantation is a complex developmental process that requires coordinated interactions among the embryo, endometrium, and the microenvironment of endometrium factors. Even though the impaired endometrial receptivity of patients with polycystic ovary syndrome (PCOS) is known, understanding of endometrial receptivity is limited. A proteomics study in three patients with PCOS and 3 fertile women was performed to understand the impaired endometrial receptivity in patients with PCOS during luteal phases. Through isobaric tags for relative and absolute quantitation (iTRAQ) analyses, we identified 232 unique proteins involved in the metabolism, inflammation, and cell adhesion molecules. Finally, our results suggested that energy metabolism can affect embryo implantation, whereas inflammation and cell adhesion molecules can affect both endometrial conversion and receptivity. Our results showed that endometrial receptive damage in patients with PCOS is not a single factor. It is caused by many proteins, pathways, systems, and abnormalities, which interact with each other and make endometrial receptive research more difficult.

EpCAM-claudin-tetraspanin-modulated ovarian cancer progression and drug resistance

Alterations of cell adhesion are involved in cancer progression, but the mechanisms underlying the progression and cell adhesion have remained poorly understood. Focusing on the complex between EpCAM, claudins and tetraspanins, we described a sequence of events by which of the molecules associate each other in ovarian cancer. The interactions between molecules were evaluated by immunoprecipitations and then immunoblotting. To identify the effects of complex formation on the ovarian cancer progression, the different types of ovarian cancer cell lines were compared. In this study, we report the identification of the EpCAM-claudin-4 or -7-CD82 complex in the ovarian cancer progression and metastasis in vitro. Additionally, we demonstrated palmitoylation and intra- or extra-cellular regions are critically required for the complex formation. These results represent the first direct evidence for the link between the dynamism of cell adhesion molecules and ovarian cancer progression.

Molecular pathology underlying the robustness of cancer stem cells

Intratumoral heterogeneity is tightly associated with the failure of anticancer treatment modalities including conventional chemotherapy, radiation therapy, and molecularly targeted therapy. Such heterogeneity is generated in an evolutionary manner not only as a result of genetic alterations but also by the presence of cancer stem cells (CSCs). CSCs are proposed to exist at the top of a tumor cell hierarchy and are undifferentiated tumor cells that manifest enhanced tumorigenic and metastatic potential, self-renewal capacity, and therapeutic resistance. Properties that contribute to the robustness of CSCs include the abilities to withstand redox stress, to rapidly repair damaged DNA, to adapt to a hyperinflammatory or hyponutritious tumor microenvironment, and to expel anticancer drugs by the action of ATP-binding cassette transporters as well as plasticity with regard to the transition between dormant CSC and transit-amplifying progenitor cell phenotypes. In addition, CSCs manifest the phenomenon of metabolic reprogramming, which is essential for maintenance of their self-renewal potential and their ability to adapt to changes in the tumor microenvironment. Elucidation of the molecular underpinnings of these biological features of CSCs is key to the development of novel anticancer therapies. In this review, we highlight the pathological relevance of CSCs in terms of their hallmarks and identification, the properties of their niche—both in primary tumors and at potential sites of metastasis—and their resistance to oxidative stress dependent on system xc (−).

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Intratumoral heterogeneity driven by CSCs is responsible for therapeutic resistance.

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CTCs survive in the distant organs and achieve colonization, causing metastasis.

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E/M hybrid cancer cells due to partial EMT exhibit the highest metastatic potential.

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The CSC niche regulates stemness in metastatic disease as well as in primary tumor.

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Activation of system xc(-) by CD44 variant in CSCs is a promising therapeutic target.

EpCAM cellular functions in adhesion and migration, and potential impact on invasion: A critical review

EpCAM has long been known as a cell surface protein highly expressed in carcinomas. It has since become one of the key cancer biomarkers. Despite its high fame, its actual role in cancer development is still controversial. Beyond a flurry of correlative studies, which point either to a positive or a negative link with tumour progression, there has been surprisingly few studies on the actual cellular mechanisms of EpCAM and on their functional consequences. Clearly, EpCAM plays multiple important roles, in cell proliferation as well as in cell adhesion and migration. The two latter functions, directly relevant for metastasis, are the focus of this review. We attempt here to bring together the available experimental data to build a global coherent view of EpCAM functions. We also include in this overview EpCAM2/Trop2, the close relative of EpCAM. At the core of EpCAM (and EpCAM2/Trop2) function stands the ability to repress contractility of the actomyosin cell cortex. This activity appears to involve direct inhibition by EpCAM of members of the novel PKC family and of a specific downstream PKD-Erk cascade. We will discuss how this activity can result in a variety of adhesive and migratory phenotypes, thus potentially explaining at least part of the apparent inconsistencies between different studies. The picture remains fragmented, and we will highlight some of the conflicting evidence and the many unsolved issues, starting with the controversy around its original description as a cell-cell adhesion molecule.

EpCAM as Modulator of Tissue Plasticity

The Epithelial Cell Adhesion Molecule or EpCAM is a well-known marker highly expressed in carcinomas and showing a strong correlation with poor cancer prognosis. While its name relates to its proposed function as a cell adhesion molecule, EpCAM has been shown to have various signalling functions. In particular, it has been identified as an important positive regulator of cell adhesion and migration, playing an essential role in embryonic morphogenesis as well as intestinal homeostasis. This activity is not due to its putative adhesive function, but rather to its ability to repress myosin contractility by impinging on a PKC signalling cascade. This mechanism confers EpCAM the unique property of favouring tissue plasticity. I review here the currently available data, comment on possible connections with other properties of EpCAM, and discuss the potential significance in the context of cancer invasion.

Tetraspanin CD9: A Key Regulator of Cell Adhesion in the Immune System

The tetraspanin CD9 is expressed by all the major subsets of leukocytes (B cells, CD4⁺ T cells, CD8⁺ T cells, natural killer cells, granulocytes, monocytes and macrophages, and immature and mature dendritic cells) and also at a high level by endothelial cells. As a typical member of the tetraspanin superfamily, a prominent feature of CD9 is its propensity to engage in a multitude of interactions with other tetraspanins as well as with different transmembrane and intracellular proteins within the context of defined membranal domains termed tetraspanin-enriched microdomains (TEMs). Through these associations, CD9 influences many cellular activities in the different subtypes of leukocytes and in endothelial cells, including intracellular signaling, proliferation, activation, survival, migration, invasion, adhesion, and diapedesis. Several excellent reviews have already covered the topic of how tetraspanins, including CD9, regulate these cellular processes in the different cells of the immune system. In this mini-review, however, we will focus particularly on describing and discussing the regulatory effects exerted by CD9 on different adhesion molecules that play pivotal roles in the physiology of leukocytes and endothelial cells, with a particular emphasis in the regulation of adhesion molecules of the integrin and immunoglobulin superfamilies.

Long intergenic non-protein-coding RNA 1567 (LINC01567) acts as a "sponge" against microRNA-93 in regulating the proliferation and tumorigenesis of human colon cancer stem cells

Background

Cancer stem cells (CSCs) are considered to be the major factor in tumor initiation, progression, metastasis, recurrence and chemoresistance. Maintaining the stemness and promoting differentiation of these cells involve various factors. Recently, long non-coding RNAs (lncRNAs) have been identified as new regulatory factors in human cancer cells. However, the function of lncRNAs in colon CSCs is still unknown.

Methods

Primary colon cancer cells were maintained in serum-free medium to form spheres and CD133⁺/CD166⁺/CD44⁺ spheroid cells were selected using FACS technique. Then we detected growth curve, colony formation, invasion and migration ability, and tumorigenicity of CD133⁺/CD166⁺/CD44⁺ cells. LOCCS-siRNA and pcDNA-LOCCS plasmid vectors were constructed and transfected to evaluate impact of the lncRNA. We also performed dual luciferase reporter assay to verify the interaction of LOCCS and miR-93.

Results

The research explored lncRNA expression and the regulatory role of novel lncRNAs in colon CSCs. Using the stem cell markers CD133, CD166 and CD44, we found a subpopulation of highly tumorigenic human colon cancer cells. They displayed some characteristics of stem cells, including the ability to proliferate and form colonies, to resist chemotherapeutic drugs, and to produce xenografts in nude mice. We also found an lncRNA, LOCCS, with obviously upregulated expression in colon CSCs. Knockdown of LOCCS reduced cell proliferation, invasion, migration, and generation of tumor xenografts. Furthermore, microRNA-93 (miR-93) and Musashi-1 mediated the tumor suppression of LOCCS knockdown.

Conclusions

There was reciprocal repression between LOCCS and miR-93. Research on mechanisms suggested direct binding, as a predicted miR-93 binding site was identified in LOCCS. This comprehensive analysis of LOCCS in colon CSCs provides insight for elucidating important roles of the lncRNA–microRNA functional network in human colon cancer.

Electronic supplementary material

The online version of this article (10.1186/s12885-017-3731-5) contains supplementary material, which is available to authorized users.

Cholangiocytes: Cell transplantation

BACKGROUND

Due to significant limitations to the access to orthotropic liver transplantation, cell therapies for liver diseases have gained large interest worldwide.

SCOPE OF REVIEW

To revise current literature dealing with cell therapy for liver diseases. We discussed the advantages and pitfalls of the different cell sources tested so far in clinical trials and the rationale underlying the potential benefits of transplantation of human biliary tree stem cells (hBTSCs).

MAJOR CONCLUSIONS

Transplantation of adult hepatocytes showed transient benefits but requires immune-suppression that is a major pitfall in patients with advanced liver diseases. Mesenchymal stem cells and hematopoietic stem cells transplanted into patients with liver diseases are not able to replace resident hepatocytes but rather they target autoimmune or inflammatory processes into the liver. Stem cells isolated from fetal or adult liver have been recently proposed as alternative cell sources for advanced liver cirrhosis and metabolic liver disease. We demonstrated the presence of multipotent cells expressing a variety of endodermal stem cell markers in (peri)-biliary glands of bile ducts in fetal or adult human tissues, and in crypts of gallbladder epithelium. In the first cirrhotic patients treated in our center with biliary tree stem cell therapy, we registered no adverse event but significant benefits.

GENERAL SIGNIFICANCE

The biliary tree stem cell could represent the ideal cell source for the cell therapy of liver diseases. This article is part of a Special Issue entitled: Cholangiocytes in Health and Diseaseedited by Jesus Banales, Marco Marzioni, Nicholas LaRusso and Peter Jansen.

Molecular Mechanisms of Human Papillomavirus Induced Skin Carcinogenesis

Infection of the cutaneous skin with human papillomaviruses (HPV) of genus betapapillomavirus (βHPV) is associated with the development of premalignant actinic keratoses and squamous cell carcinoma. Due to the higher viral loads of βHPVs in actinic keratoses than in cancerous lesions, it is currently discussed that these viruses play a carcinogenic role in cancer initiation. In vitro assays performed to characterize the cell transforming activities of high-risk HPV types of genus alphapapillomavirus have markedly contributed to the present knowledge on their oncogenic functions. However, these assays failed to detect oncogenic functions of βHPV early proteins. They were not suitable for investigations aiming to study the interactive role of βHPV positive epidermis with mesenchymal cells and the extracellular matrix. This review focuses on βHPV gene functions with special focus on oncogenic mechanisms that may be relevant for skin cancer development.

Hyaluronan coating improves liver engraftment of transplanted human biliary tree stem/progenitor cells

BACKGROUND

Cell therapy of liver diseases with human biliary tree stem cells (hBTSCs) is biased by low engraftment efficiency. Coating the hBTSCs with hyaluronans (HAs), the primary constituents of all stem cell niches, could facilitate cell survival, proliferation, and, specifically, liver engraftment given that HAs are cleared selectively by the liver.

METHODS

We developed a fast and easy method to coat hBTSCs with HA and assessed the effects of HA-coating on cell properties in vitro and in vivo.

RESULTS

The HA coating markedly improved the viability, colony formation, and population doubling of hBTSCs in primary cultures, and resulted in a higher expression of integrins that mediate cell attachment to matrix components. When HA-coated hBTSCs were transplanted via the spleen into the liver of immunocompromised mice, the engraftment efficiency increased to 11% with respect to 3% of uncoated cells. Notably, HA-coated hBTSC transplantation in mice resulted in a 10-fold increase of human albumin gene expression in the liver and in a 2-fold increase of human albumin serum levels with respect to uncoated cells. Studies in distant organs showed minimal ectopic cell distribution without differences between HA-coated and uncoated hBTSCs and, specifically, cell seeding in the kidney was excluded.

CONCLUSIONS

A ready and economical procedure of HA cell coating greatly enhanced the liver engraftment of transplanted hBTSCs and improved their differentiation toward mature hepatocytes. HA coating could improve outcomes of stem cell therapies of liver diseases and could be immediately translated into the clinic given that GMP-grade HAs are already available for clinical use.

Proteomic insights into extracellular vesicle biology - defining exosomes and shed microvesicles

INTRODUCTION

Extracellular vesicles (EVs) are critical mediators of intercellular communication, capable of regulating the transcriptional landscape of target cells through horizontal transmission of biological information, such as proteins, lipids, and RNA species. This capability highlights their potential as novel targets for disease intervention. Areas covered: This review focuses on the emerging importance of discovery proteomics (high-throughput, unbiased quantitative protein identification) and targeted proteomics (hypothesis-driven quantitative protein subset analysis) mass spectrometry (MS)-based strategies in EV biology, especially exosomes and shed microvesicles. Expert commentary: Recent advances in MS hardware, workflows, and informatics provide comprehensive, quantitative protein profiling of EVs and EV-treated target cells. This information is seminal to understanding the role of EV subtypes in cellular crosstalk, especially when integrated with other 'omics disciplines, such as RNA analysis (e.g., mRNA, ncRNA). Moreover, high-throughput MS-based proteomics promises to provide new avenues in identifying novel markers for detection, monitoring, and therapeutic intervention of disease.

The fibronectin/α3β1 integrin axis serves as molecular basis for keratinocyte invasion induced by βHPV

Organ-transplant-recipients exhibit cancerization of the skin from which multiple human papillomavirus (HPV)-positive squamous cell carcinomas (SCCs) arise. However, the molecular basis for HPV-induced invasion of skin keratinocytes is not known. We generated a transgenic mouse model expressing the E7 oncoprotein of HPV8 in the murine epidermis under the control of the keratin-14 promoter and showed that E7 is carcinogenic in mice. We further showed that both, the E7-expressing keratinocyte and mesenchymal components of the extracellular matrix as critical in eliciting the invasive behavior. E7 expression in basal keratinocytes, grown on fibronectin, led to epithelial-mesenchymal transition mediated by a cadherin switch. E7-positive keratinocytes displayed enhanced EDA-fibronectin expression and secretion and stimulated dermal fibroblasts to express EDA-fibronectin. Deposition of fibronectin was also detected in the peritumoral stroma of HPV8-positive skin SCC. When grown on fibronectin, E7-positive keratinocytes, in particular stem cell-like cells, exhibited increased cell surface levels of the α3-integrin chain. Functional blocking confirmed α3 as a critical molecule sufficient to induce E7-mediated invasion. This mechanistic link is further supported by expression of an E7-mutant, impaired in targeting α3 to the cell surface. These findings highlight the importance of epithelial-extracellular matrix interaction required for keratinocyte invasion and provide further mechanistic evidence for a role of HPV in skin carcinogenesis.

Circulating tumor cells isolation: the "post-EpCAM era"

Circulating tumor cells (CTCs) represent a submicroscopic fraction detached from a primary tumor and in transit to a secondary site. The prognostic significance of CTCs in metastatic cancer patients was demonstrated for the first time more than ten years ago. To date, it seems clear enough that CTCs are highly heterogeneous and dynamically change their shape. Thus, the inadequacy of epithelial cell adhesion molecule (EpCAM) as universal marker for CTCs detection seems unquestionable and alternative methods able to recognize a broader spectrum of phenotypes are definitely needed. In this review the pleiotropic functions of EpCAM are discussed in detail and the role of the molecule in the biology of CTCs is critically dissected.

Generation of Multicellular Tumor Spheroids with Microwell-Based Agarose Scaffolds for Drug Testing

Three dimensional multicellular aggregate, also referred to as cell spheroid or microtissue, is an indispensable tool for in vitro evaluating antitumor activity and drug efficacy. Compared with classical cellular monolayer, multicellular tumor spheroid (MCTS) offers a more rational platform to predict in vivo drug efficacy and toxicity. Nevertheless, traditional processing methods such as plastic dish culture with nonadhesive surfaces are regularly time-consuming, laborious and difficult to provide uniform-sized spheroids, thus causing poor reproducibility of experimental data and impeding high-throughput drug screening. In order to provide a robust and effective platform for in vitro drug evaluation, we present an agarose scaffold prepared with the template containing uniform-sized micro-wells in commercially available cell culture plates. The agarose scaffold allows for good adjustment of MCTS size and large-scale production of MCTS. Transparent agarose scaffold also allows for monitoring of spheroid formation under an optical microscopy. The formation of MCTS from MCF-7 cells was prepared using different-size-well templates and systematically investigated in terms of spheroid growth curve, circularity, and cell viability. The doxorubicin cytotoxicity against MCF-7 spheroid and MCF-7 monolayer cells was compared. The drug penetration behavior, cell cycle distribution, cell apoptosis, and gene expression were also evaluated in MCF-7 spheroid. The findings of this study indicate that, compared with cellular monolayer, MCTS provides a valuable platform for the assessment of therapeutic candidates in an in vivo-mimic microenvironment, and thus has great potential for use in drug discovery and tumor biology research.

The cytosolic tail of the tumor marker protein Trop2--a structural switch triggered by phosphorylation

Trop2 is a transmembrane signaling glycoprotein upregulated in stem and carcinoma cells. Proliferation-enhancing signaling involves regulated intramembrane proteolytic release of a short cytoplasmic fragment, which is later engaged in a cytosolic signaling complex. We propose that Trop2 function is modulated by phosphorylation of a specific serine residue within this cytosolic region (Ser303), and by proximity effects exerted on the cytosolic tail by Trop2 dimerization. Structural characterization of both the transmembrane (Trop2TM) and cytosolic regions (Trop2IC) support this hypothesis, and shows that the central region of Trop2IC forms an α-helix. Comparison of NMR structures of non-phosphorylated and phosphorylated forms suggest that phosphorylation of Trop2IC triggers salt bridge reshuffling, resulting in significant conformational changes including ordering of the C-terminal tail. In addition, we demonstrate that the cytosolic regions of two Trop2 subunits can be brought into close proximity via transmembrane part dimerization. Finally, we show that Ser303-phosphorylation significantly affects the structure and accessibility of functionally important regions of the cytosolic tail. These observed structural features of Trop2 at the membrane-cytosol interface could be important for regulation of Trop2 signaling activity.

EpCAM and the biology of hepatic stem/progenitor cells

Epithelial cell adhesion molecule (EpCAM) is a transmembrane glycoprotein, which is frequently and highly expressed on carcinomas, tumor-initiating cells, selected tissue progenitors, and embryonic and adult stem cells. During liver development, EpCAM demonstrates a dynamic expression, since it can be detected in fetal liver, including cells of the parenchyma, whereas mature hepatocytes are devoid of EpCAM. Liver regeneration is associated with a population of EpCAM-positive cells within ductular reactions, which gradually lose the expression of EpCAM along with maturation into hepatocytes. EpCAM can be switched on and off through a wide panel of strategies to fine-tune EpCAM-dependent functional and differentiative traits. EpCAM-associated functions relate to cell-cell adhesion, proliferation, maintenance of a pluripotent state, regulation of differentiation, migration, and invasion. These functions can be conferred by the full-length protein and/or EpCAM-derived fragments, which are generated upon regulated intramembrane proteolysis. Control by EpCAM therefore not only depends on the presence of full-length EpCAM at cellular membranes but also on varying rates of the formation of EpCAM-derived fragments that have their own regulatory properties and on changes in the association of EpCAM with interaction partners. Thus spatiotemporal localization of EpCAM in immature liver progenitors, transit-amplifying cells, and mature liver cells will decisively impact the regulation of EpCAM functions and might be one of the triggers that contributes to the adaptive processes in stem/progenitor cell lineages. This review will summarize EpCAM-related molecular events and how they relate to hepatobiliary differentiation and regeneration.

Lineage-dependent effects of aryl hydrocarbon receptor agonists contribute to liver tumorigenesis

Rodent cancer bioassays indicate that the aryl hydrocarbon receptor (AHR) agonist, 2,3,7,8-tetracholorodibenzo-p-dioxin (TCDD), causes increases in both hepatocytic and cholangiocytic tumors. Effects of AHR activation have been evaluated on rodent hepatic stem cells (rHpSCs) versus their descendants, hepatoblasts (rHBs), two lineage stages of multipotent, hepatic precursors with overlapping but also distinct phenotypic traits. This was made possible by defining the first successful culture conditions for ex vivo maintenance of rHpScs consisting of a substratum of hyaluronans and Kubota's medium (KM), a serum-free medium designed for endodermal stem/progenitor cells. Supplementation of KM with leukemia inhibitory factor elicited lineage restriction to rHBs. Cultures were treated with various AHR agonists including TCDD, 6-formylindolo-[3,2-b]carbazole (FICZ), and 3-3'-diindolylmethane (DIM) and then analyzed with a combination of immunocytochemistry, gene expression, and high-content image analysis. The AHR agonists increased proliferation of rHpSCs at concentrations producing a persistent AHR activation as indicated by induction of Cyp1a1. By contrast, treatment with TCDD resulted in a rapid loss of viability of rHBs, even though the culture conditions, in the absence of the agonists, were permissive for survival and expansion of rHBs. The effects were not observed with FICZ and at lower concentrations of DIM.

CONCLUSION

Our findings are consistent with a lineage-dependent mode of action for AHR agonists in rodent liver tumorigenesis through selective expansion of rHpSCs in combination with a toxicity-induced loss of viability of rHBs. These lineage-dependent effects correlate with increased frequency of liver tumors.

EpCAM is decreased but is still present in uterine epithelial cells during early pregnancy in the rat: potential mechanism for maintenance of mucosal integrity during implantation

The non-receptive uterine luminal epithelium forms a polarised epithelial barrier, protective against potential pathogenic assault from the external environment and invasion by the blastocyst. However, during the window of implantation, the uterine luminal epithelial cells (UECs) transition to a receptive state by dismantling many of their intercellular and cell-matrix adhesions in preparation for epithelial detachment and subsequent blastocyst implantation. The present study investigated the presence and regulation of the intercellular adhesion protein, Epithelial Cell Adhesion Molecule (EpCAM) during early pregnancy in the rat to understand its role in the transition to receptivity. Immunofluorescence and western blotting analysis were used to study EpCAM expression in normal pregnancy, hormone replacement studies and pseudopregnancy. EpCAM was abundantly expressed and localised to the uterine luminal and glandular epithelium during the non-receptive state but decreased to lower but still observable levels around the time of implantation. This decrease was not dependent on ovarian hormones or the blastocyst. Further, EpCAM colocalised with but did not associate with its frequent binding partner, Tumour necrosis factor α (TNFα)-converting enzyme, also known as A Disintegrin And Metalloprotease 17 (TACE/ADAM17), at the time of fertilisation. These results suggest that, prior to implantation, EpCAM mediates intercellular adhesion in the uterine epithelium, but that, during implantation when UECs lose the majority of their intercellular and cell-matrix adhesions, EpCAM levels are decreased but still present for the maintenance of mucosal integrity.

Coexpression of EpCAM, CD44 variant isoforms and claudin-7 in anaplastic thyroid carcinoma

Background

Anaplastic thyroid cancer is considered to be one of the most aggressive human malignancies, and the mean survival time after diagnosis is approximately six months, regardless of treatments. This study aimed to examine how EpCAM and its related molecules are involved in the characteristics of anaplastic thyroid carcinoma.

Methodology/Principal Findings

Two differentiated thyroid cancer cell lines (TPC-1 and FTC-133), and two anaplastic thyroid cancer cell lines (FRO, ACT-1) were analyzed for expression of CD44 standard isoform (CD44s), CD44 variant isoforms, and EpCAM, and human aldehyde dehydrogenase-1 (ALDH1) enzymatic activity using flow cytometry. CD44s expression was higher in TPC-1 and FTC-133 than in the FRO and ACT-1, whereas ALDH1 activities were higher in FRO and ACT-1 than in TPC-1 and FTC-133. An inverse correlation between CD44s expression and ALDH1 activity was observed in all thyroid cancer cell lines. As for the expressions of CD44 variant isoforms, ACT-1 showed higher and FRO showed moderate CD44v6 expressions, whereas either TPC-1 or FTC-133 showed negative CD44v6 expression. EpCAM expressions in FRO and ACT-1 were higher than those in TPC-1 and FTC-133, and EpCAM expressions inversely correlated with those of CD44s. A positive correlation was observed between EpCAM expression and ALDH1 activity in thyroid cancer cell lines. In the RT-PCR analysis, the expression levels of EpCAM, caludin-7 and ALDH1 in FRO and ATC-1 cells were significantly higher than those in TPC-1 and FTC-133 cells. In clinical specimens of thyroid cancers, nuclear expression of EpCAM and high expression of CD44v6 were detected significantly more frequently in anaplastic carcinomas.

Conclusions/Significance

Our study suggests the possibility that EpCAM, together with CD44v6 and claudin-7 as well as ALDH1, may be involved in the development of the aggressive phenotype of anaplastic thyroid carcinoma. Our findings may suggest a novel therapeutic strategy for treatment of anaplastic thyroid carcinoma.

EpCAM: structure and function in health and disease

Injection of tumor cells in mice more than 30 years ago resulted in the discovery of an epithelial antigen, later defined as a cell adhesion molecule (EpCAM). Although EpCAM has since evoked significant interest as a target in cancer therapy, mechanistic insights on the functions of this glycoprotein have been emerging only very recently. This may have been caused by the multitude of functions attributed to the glycoprotein, its localization at different subcellular sites and complex posttranslational modifications. Here, we review how EpCAM modifies cell-cell contact adhesion strength and tissue plasticity, and how it regulates cell proliferation and differentiation. Major knowledge derived from human diseases will be highlighted: Mutant EpCAM that is absent from the cell surface leads to fatal intestinal abnormalities (congenital tufting enteropathy). EpCAM-mediated cell proliferation in cancer may result from signaling (i) via regulated intramembrane proteolysis and/or (ii) the localization and association with binding partners in specialized membrane microdomains. New insight in EpCAM signaling will help to develop optimized cancer therapies and open new avenues in the field of regenerative medicine.

EpCAM-associated claudin-7 supports lymphatic spread and drug resistance in rat pancreatic cancer

Pancreatic cancer has a dismal prognosis because of early metastatic spread, a suggested feature of cancer-initiating cells (CIC). To control for a functional contribution of the pancreatic CIC-marker EpCAM, we explored metastasis formation by a stable EpCAM-knockdown (ASML-EpC(kd)) of the rat pancreatic adenocarcinoma line BSp73ASML (ASML(wt)). As EpCAM associates with claudin-7, an ASML-claudin-7-knockdown (ASML-cld7(kd)) was included to differentiate between EpC- and EpC-cld7-mediated effects. The metastatic capacity of ASML-EpC(kd) and more pronounced ASML-cld7(kd) cells is strikingly reduced. EpC-associated cld7 interferes with EpC-mediated cell-cell adhesion and supports migration. This requires cld7 phosphorylation and formation of an EpC-cld7-tetraspanin-alpha6beta4 complex in glycolipid-enriched membrane domains (GEM), where cld7 associates via the tetraspanin-alpha6beta4 complex with phosphorylated ezrin. The association of cld7 with alpha6beta4 and cytoskeleton strongly stimulates tumor cell migration. However, EpC does not actively contribute. Instead, GEM-located cld7 associates with presenilin-2, which facilitates EpC cleavage and thereby tumor cell proliferation. Finally, the EpC-cld7 complex promotes drug resistance. Both EpC and cld7 support MAPK and JNK activation, such that in ASML-EpC(kd) and ASML-cld7(kd) cells an undue expansion of proapoptotic molecules is observed. Only cld7 promotes activation of the PI3K/Akt pathway by a strong downregulation of Pten. Accordingly, cisplatin treatment prolongs the survival time of ASML-cld7(kd)-bearing rats. Taken together, cld7 supports tumorigenic features of EpC by provoking EpC cleavage and thereby its cotranscription factor activity. On the other hand, only cld7 is directly engaged in motility and apoptosis resistance. Thus, at least in concern of migrating CIC, it is cld7 that acts as a CIC biomarker.

Expression and role of epithelial cell adhesion molecule in dysplastic nodule and hepatocellular carcinoma

Epithelial cell adhesion molecule (EpCAM) has been proposed as a marker for cancer stem cells in human hepatocellular carcinoma (HCC). However, the function and clinical significance of EpCAM in HCC is largely unknown. We examined EpCAM expression and localization in 28 dysplastic nodules (DNs) and their corresponding cirrhotic nodules, 79 HCC tissue sections and 132 HCC tissue microarray cores by immunohistochemistry and determined the relationship to clinicopathologic findings. We also examined the role of EpCAM in HCC using synthetic small interfering RNA to silence EpCAM gene expression in Huh-7 cells. EpCAM expression was very rare in DNs but dominantly appeared in a distinctly nodular type of small HCC. Expression of EpCAM was observed in 39% (31/79) of HCC tissue sections and in 34.1% (45/132) of tissue microarray sections. EpCAM expression in HCC was significantly associated with high tumor grade and serum α-fetoprotein level. Silencing EpCAM gene expression significantly decreased the proliferative activity and invasiveness of HCC cells. EpCAM expression was an independent prognostic factor for survival in patients with T1 HCC. The data indicate that EpCAM expression occurs at distinct nodular stage of HCC and could play an important role in HCC progression.

Cultivation and identification of colon cancer stem cell-derived spheres from the Colo205 cell line

Our group established a method to culture spheres under serum-free culture condition. However, the biological characteristics and the tumorigenicity of spheres are unknown. Here, we demonstrate that sphere cells expressed high levels of the putative colorectal cancer stem cell markers CD133 and CD44. The CD133-positive rates were 13.27 ± 5.62, 52.71 ± 16.97 and 16.47 ± 2.45% in sphere cells, regular Colo205 cells and differentiated sphere cells, respectively, while the CD44-positive rates were 62.92 ± 8.38, 79.06 ± 12.10 and 47.80 ± 2.5%, respectively, and the CD133/CD44-double-positive rates were 10.77 ± 4.96, 46.89 ± 19.17 and 12.41 ± 2.27%, respectively (P < 0.05). Cancer sphere cells formed crypt-like structures in 3-D culture. Moreover, cells from cancer spheres exhibited more tumorigenicity than regular Colo205 cells in a xenograft assay. The cancer sphere cells displayed much higher oncogenicity than regular Colo205 cells to initiate neoplasms, as assayed by H&E staining, Musashi-1 staining and electron microscopy. Our findings indicated that the sphere cells were enriched with cancer stem cells (CSCs), and exhibited more proliferation capacity, more differentiation potential and especially more tumorigenicity than regular Colo205 cells in vitro and in vivo. Further isolation and characterization of these CSCs may provide new insights for novel therapeutic targets and prognostic markers.

Cancer spheres from gastric cancer patients provide an ideal model system for cancer stem cell research

Cancer stem cells have been hypothesized to drive the growth and metastasis of tumors. Because they need to be targeted for cancer treatment, they have been isolated from many solid cancers. However, cancer stem cells from primary human gastric cancer tissues have not been isolated as yet. For the isolation, we used two cell surface markers: the epithelial cell adhesion molecule (EpCAM) and CD44. When analyzed by flow cytometry, the EpCAM(+)/CD44(+) population accounts for 4.5% of tumor cells. EpCAM(+)/CD44(+) gastric cancer cells formed tumors in immunocompromised mice; however, EpCAM(-)/CD44(-), EpCAM(+)/CD44(-) and EpCAM(-)/CD44(+) cells failed to do so. Xenografts of EpCAM(+)/CD44(+) gastric cancer cells maintained a differentiated phenotype and reproduced the morphological and phenotypical heterogeneity of the original gastric tumor tissues. The tumorigenic subpopulation was serially passaged for several generations without significant phenotypic alterations. Moreover, EpCAM(+)/CD44(+), but not EpCAM(-)/CD44(-), EpCAM(+)/CD44(-) or EpCAM(-)/CD44(+) cells grew exponentially in vitro as cancer spheres in serum-free medium, maintaining the tumorigenicity. Interestingly, a single cancer stem cell generated a cancer sphere that contained various differentiated cells, supporting multi-potency and self-renewal of a cancer stem cell. EpCAM(+)/CD44(+) cells had greater resistance to anti-cancer drugs than other subpopulation cells. The above in vivo and in vitro results suggest that cancer stem cells, which are enriched in the EpCAM(+)/CD44(+) subpopulation of gastric cancer cells, provide an ideal model system for cancer stem cell research.

Epithelial cell adhesion molecule (EpCAM) complex proteins promote transcription factor-mediated pluripotency reprogramming

Epithelial cell adhesion molecule (EpCAM) is a transmembrane glycoprotein that is highly expressed in embryonic stem cells (ESCs) and its role in maintenance of pluripotency has been suggested previously. In epithelial cancer cells, activation of the EpCAM surface-to-nucleus signaling transduction pathway involves a number of membrane proteins. However, their role in somatic cell reprogramming is still unknown. Here we demonstrate that EpCAM and its associated protein, Cldn7, play a critical role in reprogramming. Quantitative RT-PCR analysis of Oct4, Sox2, Klf4, and c-Myc (OSKM) infected mouse embryonic fibroblasts (MEFs) indicated that EpCAM and Cldn7 were up-regulated during reprogramming. Analysis of numbers of alkaline phosphatase- and Nanog-positive clones, and the expression level of pluripotency-related genes demonstrated that inhibition of either EpCAM or Cldn7 expression resulted in impairment in reprogramming efficiency, whereas overexpression of EpCAM, EpCAM plus Cldn7, or EpCAM intercellular domain (EpICD) significantly enhanced reprogramming efficiency in MEFs. Furthermore, overexpression of EpCAM or EpICD significantly repressed the expression of p53 and p21 in the reprogramming MEFs, and both EpCAM and EpICD activated the promoter activity of Oct4. These observations suggest that EpCAM signaling may enhance reprogramming through up-regulation of Oct4 and possible suppression of the p53-p21 pathway. In vitro and in vivo characterization indicated that the EpCAM-reprogrammed iPSCs exhibited similar molecular and functional features to the mouse ESCs. In summary, our studies provide additional insight into the molecular mechanisms of reprogramming and suggest a more effective means of induced pluripotent stem cell generation.

Functional polymorphisms in CD166/ALCAM gene associated with increased risk for breast cancer in a Chinese population

Activated Leukocyte Cell Adhesion Molecules (ALCAM, also called CD166, MEMD) are cell surface immunoglobulins that are considered to be prognostic markers for breast cancer. CD166/ALCAM has gained increasing attention because of its significant association with tumor progression and the metastatic spread of breast cancer. Two polymorphisms have been identified in the CD166/ALCAM gene: 5'UTR C/T (rs6437585) and 3'UTR A/G (rs11559013). We analyzed the genotypes of 1033 individuals with breast cancer, and 1116 controls; odds ratios (ORs) and 95% confidence intervals (CIs) were estimated using logistic regression. The effects and functions of polymorphisms were examined using luciferase gene expression assays and real-time PCR analyses. Our data demonstrated that individuals with the rs6437585 CT + TT genotype had an OR of 1.38 (95% CI, 1.11-1.72) for developing breast cancer, compared to those with the CC genotype. The T allele increased the risk of breast cancer in a dose-dependent manner (P (trend) < 0.001). However, there were no significant differences found between cases and controls at the rs11559013 A/G site. Additional experiments that we performed, which focused on reporter gene expression driven by CD166/ALCAM promoters, demonstrated that the presence of an rs6437585 T allele led to greater transcriptional activity than the rs6437585 C allele. This was consistent with the increased cancer risk that we observed in our case-control analysis.

The tumor-associated EpCAM regulates morphogenetic movements through intracellular signaling

Epithelial cell adhesion molecule (EpCAM) is best known as a tumor-associated protein highly expressed in carcinomas. The function of this cell surface protein during embryonic development and its potential role in cancer are still poorly understood. We identified EpCAM in a gain-of-function screen for inducers of abnormal tissue mixing during gastrulation. Elevated EpCAM levels in either the ectoderm or the mesoderm confer "invasive" properties to cells in both populations. We found that this phenotype represents an "overstimulation" of an essential activity of EpCAM in controlling cell movements during embryonic development. Surprisingly, this property is independent of the putative adhesive function of EpCAM, and rather relies on a novel signaling function that operates through down-regulation of PKC activity. We show that inhibition of novel PKCs accounts entirely for the invasive phenotype induced by abnormally high levels of EpCAM as well as for its normal function in regulating cell rearrangement during early development.

Selection and analysis of anti-cancer antibodies for cancer therapy obtained from antibody phage library

The search for effective antibodies (Ab) for curable cancer immunotherapy has been a quest of many research groups in order to find an effective target that exists on the cancer cell surface. So far there have been no conclusive answers to shed light on the search. This study therefore aimed to bridge the gap of cancer therapy. Screening against 49 kinds of cell lines belonging to 11 kinds of solids cancers was performed. Isolation and characterization for approximately 4200 monoclonal antibodies (mAb) was also performed thereafter. Of those mAb 488 clones that turned out to bind to 29 tumor-associated antigens (TAA) were subjected to immunohistochemical (IHC) analyses. Selection of target antigens (Ag) and a potential antibody for cancer therapy was conducted prior to clinical examinations. In order to find predictably effective targets for therapeutic Ab against solid cancers, expression of the Ag on the surface of cancer and normal cells was extensively examined by IHC analyses using fresh cancer specimens resected from patients. In this study, the tendencies of all staining patterns and distribution of the Ab are reported. While all of the TAA appeared to be involved in tumorigenesis, their expression was not restricted to some specific tumor types but rather randomly distributed among various cancers. Some kinds of Ab including anti-epidermal growth factor receptor (EGFR) and anti-human epidermal growth factor receptor 2 (HER2) indicated the frequency of expression in normal cells was generally low. We concluded that identification of 488 mAb and the accumulated results of IHC analyses in this study could be the key for further therapeutic Ab against cancers. The targets that showed cancer-specific expression are expected to be better for therapeutic Ab than the other Ab. Moreover, further investigation into the growth of cancer cell lines using full human IgG form of Ab shows available efficacy in specific cases.

EpCAM: a potential antimetastatic target for gastric cancer

PURPOSE

Epithelial cellular adhesion molecule (EpCAM) is an attractive immunotherapeutic target to overcome metastasis of a variety of epithelium-oriented cancers. Edrecolomab, one kind of EpCAM monoclonal antibody (Panorex), has been approved for clinical application as postoperative adjuvant therapy in breast and colorectal cancer. However, the role of EpCAM in gastric cancer metastasis remains unclear.

RESULTS

EpCAM was found to be more highly overexpressed in metastatic gastric cancer than in nonmetastatic samples by immunohistochemistry staining. The expression level of EpCAM in gastric cancer cell lines was determined by reverse-transcription polymerase chain reaction (RT-PCR) and Western blotting, respectively. Downregulation of EpCAM by small interfering RNA (siRNA) significantly suppressed in vitro adhesive, invasive, and migratory and in vivo metastatic abilities of gastric cancer cells.

CONCLUSION

We provide first evidence that EpCAM contributes to the migration of gastric cancer, suggesting that EpCAM-targeted therapy might be a promising strategy in metastatic gastric cancer.

The stem cell code in oral epithelial tumorigenesis: 'the cancer stem cell shift hypothesis'

Tumors of the oral cavity provide an ideal model to study various stages of epithelial tumor progression. A group of cancer cells termed cancer stem cells (CSCs) eludes therapy, persists and initiates recurrence augmenting malignant spread of the disease. Hitherto, accurate identification and separation of such minimal residual cells have proven futile due to lack of identifiable traits to single out these cells from the heterogeneous tumor bulk. In this review we have compiled comprehensive evidence from comparative phenotypic and genotypic studies on normal oral mucosa as well as tumors of different grades to elucidate that differential expression patterns of putative stem cells markers may identify 'minimal residual disease' in oral squamous cell carcinoma. We propose the "cancer stem cell shift hypothesis" to explain the exact identity and switch-over, tumor-promoting mechanisms adapted by putative CSCs with correlation to tumor staging.

Ep-CAM RNA expression predicts metastasis-free survival in three cohorts of untreated node-negative breast cancer

Epithelial cell adhesion molecule (Ep-CAM) recently received increased attention as a prognostic factor in breast cancer. We aimed to validate the influence of Ep-CAM RNA expression in untreated node-negative breast cancer. Ep-CAM RNA expression was evaluated utilizing microarray-based gene-expression profiling in 194 consecutive node-negative breast cancer patients with long-term follow-up not treated in the adjuvant setting. The prognostic significance of Ep-CAM RNA expression for disease-free survival (DFS), metastasis-free survival (MFS), and breast cancer-specific overall survival (OS) was evaluated in univariate and multivariate analysis adjusted for age, grading, pTstage, ER as well as PR receptor and HER-2 status. Additionally, Ep-CAM RNA expression was compared with immunohistochemistry (IHC) for Ep-CAM in 194 patients. The prognostic impact of Ep-CAM gene expression was validated in further 588 node-negative breast cancer patients. Levels of Ep-CAM RNA expression showed a significant correlation with IHC (P = 0.001) and predicted in univariate analysis DFS (P = 0.001, HR = 2.4), MFS (P = 0.003, HR = 2.5), and OS (P = 0.002, HR = 3.1) accurately. The prognostic influence of Ep-CAM RNA was significant also in multivariate analysis for DFS (P = 0.017, HR = 2.0), MFS (P = 0.049, HR = 1.9), and OS (P = 0.042, HR = 2.3), respectively. The association with MFS was confirmed in an independent validation cohort in univariate (P = 0.006, HR = 1.9) and multivariate (P = 0.035, HR = 1.7) analysis. Ep-CAM RNA correlated with the proliferation metagene (P < 0.001, R=0.425) Nevertheless, in multivariate analysis, Ep-CAM was associated with MFS independent from the proliferation metagene (P = 0.030, HR = 1.8). In conclusion, Ep-CAM RNA expression is associated with poor MFS in three cohorts of untreated node-negative breast cancer.

Characterization of epithelial cell adhesion molecule as a surface marker on undifferentiated human embryonic stem cells

Human embryonic stem cells (hESCs) have the capacity to remain pluripotent and self-renew indefinitely. To discover novel players in the maintenance of hESCs, we have previously reported the generation of monoclonal antibodies that bind to cell surface markers on hESCs, and not to mouse embryonic stem cells or differentiated embryoid bodies. In this study, we have identified the antigen target of one such monoclonal antibody as the epithelial cell adhesion molecule (EpCAM). In undifferentiated hESCs, EpCAM is localized to Octamer 4 (OCT4)-positive pluripotent cells, and its expression is down-regulated upon differentiation. To further understand its biological function in hESCs, endogenous EpCAM expression was silenced using small interfering RNA. EpCAM knockdown had marginal negative effects on OCT4 and TRA-1-60 expression, however cell proliferation was decreased by >40%. Examination of lineage marker expression showed marked upregulation of endoderm and mesoderm genes in EpCAM-silenced cells, under both pluripotent and differentiating conditions. These results were validated using a hESC line whose EpCAM expression has been stably knocked down. Data from the stable line confirmed that downregulation of EpCAM decreases cell growth and increases gene expression in the endoderm and mesoderm lineages. In vivo, hESCs lacking EpCAM were able to form teratomas containing tissues representing the three germ layers, and gene expression analysis yielded marked increase in the endoderm marker alpha fetoprotein compared with control. Together these data demonstrate that EpCAM is a surface marker on undifferentiated hESCs and plays functional roles in proliferation and differentiation.

CD44v6 dependence of premetastatic niche preparation by exosomes

The metastasizing capacity of the rat pancreatic adenocarcinoma BSp73ASML (ASML(wt)) is strikingly reduced by a knockdown of CD44v4-v7 (ASML(kd)). We used this model to analyze the role of the CD44 variant isoform (CD44v) in (pre)metastatic niche formation. Intrafootpad injections of ASML(wt)-, but not ASML(kd)-conditioned medium (CM), strongly promote settlement of ASML(kd) cells in lymph nodes and lung. Fractionation of CM revealed a contribution by a soluble matrix and exosomes, where the CD44v6-containing ASML(wt)-soluble fraction can complement ASML(kd)-exosomes, but not vice versa. This implies that exosomes are the final actors, are CD44v-independent, but require a soluble matrix, which depends on CD44v. Analyzing the composition revealed that only the ASML(wt)-matrix contains c-Met and urokinase-type plasminogen activator receptor. In vitro, mostly ASML(wt)-exosomes promote proliferation and induce gene expression in metastatic organ cells. However, in vivo corresponding changes in the (pre) metastatic organ are only observed when both, exosomes plus the soluble matrix, are provided. Thus, neither CD44v nor exosomes alone suffice for (pre)metastatic niche formation. Instead, CD44v suffices for assembling a soluble matrix, which allows exosomes, independent of their origin from poorly or highly metastatic cells, to modulate (pre) metastatic organ cells for tumor cell embedding and growth.

Abnormal placental development and early embryonic lethality in EpCAM-null mice

BACKGROUND

EpCAM (CD326) is encoded by the tacstd1 gene and expressed by a variety of normal and malignant epithelial cells and some leukocytes. Results of previous in vitro experiments suggested that EpCAM is an intercellular adhesion molecule. EpCAM has been extensively studied as a potential tumor marker and immunotherapy target, and more recent studies suggest that EpCAM expression may be characteristic of cancer stem cells.

METHODOLOGY/PRINCIPAL FINDINGS

To gain insights into EpCAM function in vivo, we generated EpCAM -/- mice utilizing an embryonic stem cell line with a tacstd1 allele that had been disrupted. Gene trapping resulted in a protein comprised of the N-terminus of EpCAM encoded by 2 exons of the tacstd1 gene fused in frame to betageo. EpCAM +/- mice were viable and fertile and exhibited no obvious abnormalities. Examination of EpCAM +/- embryos revealed that betageo was expressed in several epithelial structures including developing ears (otocysts), eyes, branchial arches, gut, apical ectodermal ridges, lungs, pancreas, hair follicles and others. All EpCAM -/- mice died in utero by E12.5, and were small, developmentally delayed, and displayed prominent placental abnormalities. In developing placentas, EpCAM was expressed throughout the labyrinthine layer and by spongiotrophoblasts as well. Placentas of EpCAM -/- embryos were compact, with thin labyrinthine layers lacking prominent vascularity. Parietal trophoblast giant cells were also dramatically reduced in EpCAM -/- placentas.

CONCLUSION

EpCAM was required for differentiation or survival of parietal trophoblast giant cells, normal development of the placental labyrinth and establishment of a competent maternal-fetal circulation. The findings in EpCAM-reporter mice suggest involvement of this molecule in development of vital organs including the gut, kidneys, pancreas, lungs, eyes, and limbs.

Epithelial cell adhesion molecule (EpCAM) is overexpressed in breast cancer metastases

EpCAM (CD326) has diverse roles in cell adhesion and proliferation, and is known to be overexpressed in primary breast carcinomas (PBCs). While clinical and preclinical data suggest a role for EpCAM in metastases, the only prior study of EpCAM expression in breast cancer metastases suggested that EpCAM expression is decreased after first-line chemotherapy. This study evaluates EpCAM expression in metastatic breast carcinoma (MBC) versus matched PBC . Rapid autopsies were performed on 17 patients with widely metastatic breast cancer. Single patient tissue microarrays (TMAs) were constructed from archived PBC and post-mortem MBCs. In total, 169 spots from 17 PBCs and 895 spots from 195 MBCs were labeled for EpCAM by immunohistochemistry (IHC). Expression was scored as intensity (1-3) multiplied by percent membrane labeling (0-100%) and was subclassified as low (0-100), moderate (101-200), or high (201-300) labeling. PBCs exhibited exclusively low-moderate EpCAM labeling. EpCAM labeling was present in all metastases and was significantly increased in MBCs of 14 of 17 patients (P value range <0.05 to <0.0001, t test). In the remaining three patients, EpCAM labeling was nonsignificantly increased in 1 and unchanged in 2. High EpCAM labeling was verified using a different antibody for IHC, as well as in a separate series of surgically resected metastases compared to unmatched surgically resected primary breast cancers. In conclusion, EpCAM is highly expressed in MBCs compared to matched PBCs, verifying that it is a promising therapeutic target.

Trop2: a possible therapeutic target for late stage epithelial carcinomas

Trop2 is a cell-surface glycoprotein overexpressed in a variety of late stage epithelial carcinomas with low to no expression in normal tissues. Some of the important roles that Trop2 plays in epithelial cancers have recently been revealed. Trop2 overexpression is associated with decreased patient survival as well as increased tumor aggressiveness and metastasis. Its overexpression in metastatic tissue makes it a very attractive and potential therapeutic target for late stage disease. This protein can transduce an intracellular calcium signal and contains a conserved phosphatidylinositol 4,5-bisphosphate (PIP(2)) binding motif as well as a serine phosphorylation site which interacts with protein kinase C. This protein has recently being found to be expressed in cells with stem-like properties which allude to a potential role in progenitor cell biology. Further understanding of the signaling pathways involved with this molecule and its important role in metastasis will shed new light on the mechanism of Trop2 overexpression in late stage disease and could result in the development of new therapies targeting this widely overexpressed oncogene.

The epithelial cell adhesion molecule EpCAM is required for epithelial morphogenesis and integrity during zebrafish epiboly and skin development

The aberrant expression of the transmembrane protein EpCAM is associated with tumor progression, affecting different cellular processes such as cell–cell adhesion, migration, proliferation, differentiation, signaling, and invasion. However, the in vivo function of EpCAM still remains elusive due to the lack of genetic loss-of-function studies. Here, we describe epcam (tacstd) null mutants in zebrafish. Maternal-zygotic mutants display compromised basal protrusive activity and epithelial morphogenesis in cells of the enveloping layer (EVL) during epiboly. In partial redundancy with E-cadherin (Ecad), EpCAM made by EVL cells is further required for cell–cell adhesion within the EVL and, possibly, for proper attachment of underlying deep cells to the inner surface of the EVL, thereby also affecting deep cell epiboly movements. During later development, EpCAM per se becomes indispensable for epithelial integrity within the periderm of the skin, secondarily leading to disrupted morphology of the underlying basal epidermis and moderate hyper-proliferation of skin cells. On the molecular level, EVL cells of epcam mutant embryos display reduced levels of membranous Ecad, accompanied by an enrichment of tight junction proteins and a basal extension of apical junction complexes (AJCs). Our data suggest that EpCAM acts as a partner of E-cadherin to control adhesiveness and integrity as well as plasticity and morphogenesis within simple epithelia. In addition, EpCAM is required for the interaction of the epithelia with underlying cell layers.

EpCAM is a well-established marker for carcinomas of epithelial origin and a potential target for immunotherapy. In vitro analyses have implicated EpCAM in a plethora of different cellular processes, such as adhesion, motility, proliferation, differentiation, and signaling. Strikingly, depending on the context, EpCAM displayed rather opposite effects, either promoting or attenuating cell–cell adhesion versus cell migration and tissue invasion, a phenomenon described as the “double-face” of EpCAM. However, the in vivo relevance of its different effects remained largely unclear. Here, we present the first genetic analysis of EpCAM function in vivo, based on loss-of-function mutants in the zebrafish. As it is in mammals, zebrafish EpCAM is expressed in simple epithelia. Mutant embryos display defects both in epithelial morphogenesis and in epithelial integrity. Reduced epithelial morphogenesis is accompanied, and possibly caused, by an extension of apical junctional complexes and compromised basal protrusive activity. Furthermore, mutant epithelia display alterations in the relative abundance of adherence junction versus tight junction components. In addition, EpCAM tightly cooperates with E-cadherin and has a previously unrecognized trans effect on the morphogenesis and integrity of underlying cell layers. Cell differentiation and proliferation in EpCAM mutants are not, or only secondarily, affected. During later development and adulthood, EpCAM is largely dispensable, reinforcing its suitability as a target for anti-carcinoma immunotherapy with minimal side effects.

Atypical E-cadherin expression in cell clusters overlying focally disrupted mammary myoepithelial cell layers: implications for tumor cell motility and invasion

Our recent studies showed that cell clusters overlying focal myoepithelial cell layer disruptions (FMCLD) had a significantly higher rate of ER negativity, genetic instabilities, and expression of invasion-related genes than adjacent cells within the same duct. This study attempted to determine if these cells would show aberrant E-cadherin expression, which imparts greater propensity for cell motility and invasion. Consecutive sections from breast tumors with a high frequency of FMCLD were double-immunostained for E-cadherin and a panel of related markers. The E-cadherin mRNA levels in cells overlying FMCLD and adjacent cells within the same duct were compared using real-time PCR. Nearly all the cell clusters overlying FMCLD were strongly immunoreactive for E-cadherin, whereas their adjacent counterparts within the same duct were largely negative. Cell clusters overlying FMCLD were generally arranged as tongue-like projections, "puncturing" deep into the stroma or tube-like structures that often contained red blood cells. The sub-cellular localization of E-cadherin in the above structures, however, was primarily cytoplasmic. The mRNA level of E-cadherin in cell clusters overlying FMCLD was significantly higher than that in adjacent cells within the same duct. These findings suggest that aberrant expression of E-cadherin may contribute to cell motility and invasion.

Claudin-7 regulates EpCAM-mediated functions in tumor progression

EpCAM has been described as a therapeutically relevant tumor marker. We noted an interaction between EpCAM and the tight junction protein claudin-7 and here explored the nature of this interaction and its effect on EpCAM-mediated functions. The interaction between EpCAM and claudin-7 was defined in HEK293 cells transfected with rat claudin-7 and EpCAM cDNA. Deletions of the epidermal growth factor-like and the thyroglobin repeat domains of EpCAM or the cytoplasmic domain of EpCAM or claudin-7 did not prevent the EpCAM-claudin-7 association. A chimeric EpCAM molecule with an exchange of the cytoplasmic and transmembrane domains and an EpCAM molecule with point mutations in an AxxxG motif in the transmembrane region do not associate with claudin-7. HEK cells and the rat pancreatic tumor line BSp73AS, transfected with (mutated) EpCAM and claudin-7 cDNA, revealed that the association of both molecules severely alters the functional activity of EpCAM. Claudin-7-associated EpCAM is recruited into tetraspanin-enriched membrane microdomains (TEM). The TEM-located claudin-7-EpCAM complex supports proliferation accompanied by sustained extracellular signal-regulated kinase-1/2 phosphorylation, up-regulation of antiapoptotic proteins, and drug resistance, but not EpCAM-mediated cell-cell adhesion. Enhanced motility may be supported by colocalization of claudin-7 with actin bundles, which is only seen in EpCAM-claudin-7-expressing cells. The EpCAM-claudin-7 complex strongly promotes tumorigenicity, accelerates tumor growth, and supports ascites production and thymic metastasis formation. High expression of the tumor marker EpCAM is frequently associated with poor prognosis, which could well rely on the EpCAM-claudin-7 association that prohibits EpCAM-mediated cell-cell adhesion but promotes migration, proliferation, apoptosis resistance, and tumorigenicity.