The epithelial cell default-phenotype hypothesis and its implications for cancer

Almost famous: Human adenoviruses (and what they have taught us about cancer)

Papillomaviruses, polyomaviruses and adenoviruses are collectively categorized as the small DNA tumour viruses. Notably, human adenoviruses were the first human viruses demonstrated to be able to cause cancer, albeit in non-human animal models. Despite their long history, no human adenovirus is a known causative agent of human cancers, unlike a subset of their more famous cousins, including human papillomaviruses and human Merkel cell polyomavirus. Nevertheless, seminal research using human adenoviruses has been highly informative in understanding the basics of cell cycle control, gene expression, apoptosis and cell differentiation. This review highlights the contributions of human adenovirus research in advancing our knowledge of the molecular basis of cancer.

Mesenchymal-to-Epithelial Transitions in Development and Cancer

The evolutionary emergence of the mesenchymal phenotype greatly increased the complexity of tissue architecture and composition in early Metazoan species. At the molecular level, an epithelial-to-mesenchymal transition (EMT) was permitted by the innovation of specific transcription factors whose expression is sufficient to repress the epithelial transcriptional program. The reverse process, mesenchymal-to-epithelial transition (MET), involves direct inhibition of EMT transcription factors by numerous mechanisms including tissue-specific MET-inducing transcription factors (MET-TFs), micro-RNAs, and changes to cell and tissue architecture, thus providing an elegant solution to the need for tight temporal and spatial control over EMT and MET events during development and adult tissue homeostasis.

Grainyhead-like-2 confers NK-sensitivity through interactions with epigenetic modifiers

Natural Killer (NK) cells suppress tumor initiation and metastasis. Most carcinomas are heterogeneous mixtures of epithelial, mesenchymal and hybrid tumor cells, but the relationships of these phenotypes to NK susceptibility are understood incompletely. Grainyhead-like-2 (GRHL2) is a master programmer of the epithelial phenotype, that is obligatorily down-regulated during experimentally induced Epithelial-Mesenchymal Transition (EMT). Here, we utilize GRHL2 re-expression to discover unifying molecular mechanisms that link the epithelial phenotype with NK-sensitivity. GRHL2 enhanced the expression of ICAM-1, augmenting NK-target cell synaptogenesis and NK killing of target cells. The expression of multiple interferon response genes, including ICAM1, anti-correlated with EMT. We identified two novel GRHL2-interacting proteins, the histone methyltransferases KMT2C and KMT2D. Mesenchymal-epithelial transition, NK-sensitization and ICAM-1 expression were promoted by GRHL2-KMT2C/D interactions and by GRHL2 inhibition of p300, revealing novel and potentially targetable epigenetic mechanisms connecting the epithelial phenotype with target cell susceptibility to NK killing.

Sciellin mediates mesenchymal-to-epithelial transition in colorectal cancer hepatic metastasis

Hepatic metastasis is the major cause of mortality in colorectal cancer (CRC) patients. Using proteomic analysis, we found sciellin (SCEL) to be specifically expressed in hepatic metastatic CRC cell lines. SCEL knockdown increased CRC cell migration and invasion, while overexpression had the opposite effect. SCEL knockdown also caused cancer cells to form more invasive structures within 3D cultures, increased the mesenchymal marker vimentin, and attenuated the epithelial marker E-cadherin. SCEL increased WNT signaling by activating β-catenin and its downstream target c-myc, and activated mesenchymal-to-epithelial transition (MET) through a SCEL-β-catenin-E-cadherin axis. SCEL showed higher expression in late stage primary CRC than in its hepatic metastatic counterpart. SCEL expression is dynamically modulated by TGF-β1 and hypoxia, revealing a plastic MET mechanism for tumor colonization. Intrahepatic injection in immunodeficient mice revealed that SCEL is necessary for metastatic CRC tumor growth in the liver. These results demonstrate that SCEL is a MET inducer dynamically regulated through the metastasis process. They suggest SCEL may be a useful therapeutic target for preventing or eliminating CRC hepatic metastasis.

Epithelial-to-Mesenchymal Transition and MicroRNAs in Lung Cancer

Despite major advances, non-small cell lung cancer (NSCLC) remains the major cause of cancer-related death in developed countries. Metastasis and drug resistance are the main factors contributing to relapse and death. Epithelial-to-mesenchymal transition (EMT) is a complex molecular and cellular process involved in tissue remodelling that was extensively studied as an actor of tumour progression, metastasis and drug resistance in many cancer types and in lung cancers. Here we described with an emphasis on NSCLC how the changes in signalling pathways, transcription factors expression or microRNAs that occur in cancer promote EMT. Understanding the biology of EMT will help to define reversing process and treatment strategies. We will see that this complex mechanism is related to inflammation, cell mobility and stem cell features and that it is a dynamic process. The existence of intermediate phenotypes and tumour heterogeneity may be debated in the literature concerning EMT markers, EMT signatures and clinical consequences in NSCLC. However, given the role of EMT in metastasis and in drug resistance the development of EMT inhibitors is an interesting approach to counteract tumour progression and drug resistance. This review describes EMT involvement in cancer with an emphasis on NSCLC and microRNA regulation.

Roles of Grainyhead-like transcription factors in cancer

The mammalian homologs of the D. melanogaster Grainyhead gene, Grainyhead-like 1-3 (GRHL1, GRHL2 and GRHL3), are transcription factors implicated in wound healing, tubulogenesis and cancer. Their induced target genes encode diverse epithelial cell adhesion molecules, while mesenchymal genes involved in cell migration and invasion are repressed. Moreover, GRHL2 suppresses the oncogenic epithelial-mesencyhmal transition, thereby acting as a tumor suppressor. Mechanisms, some involving established cancer-related signaling/transcription factor pathways (for example, Wnt, TGF-β, mir200, ZEB1, OVOL2, p63 and p300) and translational implications of the Grainyhead proteins in cancer are discussed in this review article.

ZNF143 enhances metastasis of gastric cancer by promoting the process of EMT through PI3K/AKT signaling pathway

The zinc finger protein 143 (ZNF143) is a transcription factor, which regulates many cell cycle-associated genes. ZNF143 expressed strongly in multiple solid tumors. However, the influence of ZNF143 on gastric cancer (GC) remains largely unknown. In this study, we investigated the ZNF143 mRNA level in GC tissues and cells by quantitative real-time PCR (qRT-PCR). The protein expression of ZNF143 in GC cells, and the signaling pathway proteins were detected by Western blotting. Transwell assay and wound healing assay were performed to explore the effects of ZNF143 for the migration ability of GC cells in vitro. We also performed the tail vein injection in nude mice with GC cells to explore the impact of ZNF143 on GC metastasis in vivo. ZNF143 was overexpressed in specimens of GC compared with adjacent normal tissues and increased more significantly in GC tissues of patients who had lymph node metastasis. Ectopic overexpression of ZNF143 enhanced GC migration, whereas ZNF143 knockdown suppressed this effect in vitro. In vivo, ZNF143 knockdown reduced distant metastasis of GC cells in nude mice. In addition, overexpression of ZNF143 reduced the expression of epithelial cell marker (E-cadherin) and induced the expression of mesenchymal cell marker (N-cadherin,Vimentin), Snail and Slug. We also found that ZNF143 enhanced GC cell migration by promoting the process of EMT through PI3K/AKT signaling pathway. In general, our findings show that ZNF143 expressed strongly in GC and enhanced migration of GC cells in vitro and in vivo. It is conceivable that ZNF143 could be a therapeutic genetic target for GC treatment.

Grainyhead-like 2 inhibits the coactivator p300, suppressing tubulogenesis and the epithelial-mesenchymal transition

GRHL2 suppresses EMT to give a default epithelial phenotype. GRHL2 inhibits this process through the histone acetyltransferase coactivator p300, repressing the partial EMT and preventing induction of MMPs. The results demonstrate novel roles for p300 and GRHL2 in promoting or suppressing EMT in morphogenesis and tumor progression.

Developmental morphogenesis and tumor progression require a transient or stable breakdown of epithelial junctional complexes to permit programmed migration, invasion, and anoikis resistance, characteristics endowed by the epithelial–mesenchymal transition (EMT). The epithelial master-regulatory transcription factor Grainyhead-like 2 (GRHL2) suppresses and reverses EMT, causing a mesenchymal–epithelial transition to the default epithelial phenotype. Here we investigated the role of GRHL2 in tubulogenesis of Madin–Darby canine kidney cells, a process requiring transient, partial EMT. GRHL2 was required for cystogenesis, but it suppressed tubulogenesis in response to hepatocyte growth factor. Surprisingly, GRHL2 suppressed this process by inhibiting the histone acetyltransferase coactivator p300, preventing the induction of matrix metalloproteases and other p300-dependent genes required for tubulogenesis. A 13–amino acid region of GRHL2 was necessary for inhibition of p300, suppression of tubulogenesis, and interference with EMT. The results demonstrate that p300 is required for partial or complete EMT occurring in tubulogenesis or tumor progression and that GRHL2 suppresses EMT in both contexts through inhibition of p300.

FRA-1 as a driver of tumour heterogeneity: a nexus between oncogenes and embryonic signalling pathways in cancer

Tumour heterogeneity is a major factor undermining the success of therapies targeting metastatic cancer. Two major theories are thought to explain the phenomenon of heterogeneity in cancer--clonal evolution and cell plasticity. In this review, we examine a growing body of work implicating the transcription factor FOS-related antigen 1 (FRA-1) as a central node in tumour cell plasticity networks, and discuss mechanisms regulating its activity in cancer cells. We also discuss evidence from the FRA-1 perspective supporting the notion that clonal selection and cell plasticity represent two sides of the same coin. We propose that FRA-1-overexpressing clones featuring high plasticity undergo positive selection during consecutive stages of multistep tumour progression. This model underscores a potential mechanism through which tumour cells retaining elevated levels of plasticity acquire a selective advantage over other clonal populations within a tumour.

Toward decoding the principles of cancer metastasis circuits

Understanding epithelial-mesenchymal transitions (EMT) during cancer metastasis remains a major challenge in modern biology. Recent observations of cell behavior together with progress in mapping the underlying regulatory genetic networks led to new understandings of carcinoma metastasis. It is now established that the genetic network that regulates the EMT also enables an epithelial-mesenchymal hybrid phenotype. These hybrid cells possess mixed carcinoma epithelial and mesenchymal characteristics that enable specialized capabilities such as collective cell migration. On the gene network perspective, a four-component decision unit composed of two highly interconnected chimeric modules--the miR34/SNAIL and the miR200/ZEB mutual-inhibition feedback circuits--regulates the coexistence of and transitions between the different phenotypes. Here, we present a new tractable theoretical framework to model and decode the underlying principles governing the operation of the regulatory unit. Our approach connects the knowledge about intracellular pathways with observations of cellular behavior and advances toward understanding the logic of cancer decision-making. We found that the miR34/SNAIL module acts as an integrator while the miR200/ZEB module acts as a three-way switch. Consequently, the combined unit can give rise to three phenotypes (stable states): (i) a high miR200 and low ZEB, or (1, 0) state; (ii) a low miR200 and high ZEB, or (0, 1) state; and (iii) a medium miR200 and medium ZEB, or (½, ½) state. We associate these states with the epithelial, mesenchymal, and hybrid phenotypes, respectively. We reflect on the consistency between our theoretical predictions and recent observations in several types of carcinomas and suggest new testable predictions. See all articles in this Cancer Research section,

Epithelial-mesenchymal transitions: from cell plasticity to concept elasticity

Epithelial-mesenchymal transition (EMT) is a developmental cellular process occurring during early embryo development, including gastrulation and neural crest cell migration. It can be broken down in distinct functional steps: (1) loss of baso-apical polarization characterized by cytoskeleton, tight junctions, and hemidesmosomes remodeling; (2) individualization of cells, including a decrease in cell-cell adhesion forces, (3) emergence of motility, and (4) invasive properties, including passing through the subepithelial basement membrane. These phases occur in an uninterrupted process, without requiring mitosis, in an order and with a degree of completion dictated by the microenvironment. The whole process reflects the activation of specific transcription factor families, called EMT transcription factors. Several mechanisms can combine to induce EMT. Some are reversible, involving growth factors and cytokines and/or environmental signals including extracellular matrix and local physical conditions. Others are irreversible, such as genomic alterations during carcinoma progression, along a selective and irreversible clonal drift. In carcinomas, these signals can converge to initiate a metastable phenotype. In this state, similarly to activated keratinocytes during re-epithelialization, cells can initiate a cohort migration and engage into a transient and reversible EMT controlled by the local environment prior to efficient intravasation and metastasis. EMT transcription factors also participate in cancer progression by inducing apoptosis resistance and maintaining stem-like properties exposed in tumor recurrences. These properties, very important on a clinical point of view, are not intrinsically linked to EMT, but can share common pathways.

PI3K signalling is required for a TGFβ-induced epithelial-mesenchymal-like transition (EMT-like) in human melanoma cells

Epithelial to mesenchymal transition (EMT) is a programme defined in epithelial cells and recognized as playing a critical role in cancer progression. Although melanoma is not a cancer of epithelial cells, hallmarks of EMT have been described to play a critical role in melanoma progression. Here, we demonstrate that long-term TGFβ exposure can induce a dedifferentiated EMT-like state resembling a previously described invasive phenotype (EMT-like). TGFβ-induced EMT-like is marked by the downregulation of melanocyte differentiation markers, such as MITF, and the upregulation of mesenchymal markers, such as N-cadherin, and an increase in melanoma cell migration and cell invasion. Pharmacological interference shows the dependency of TGFβ-induced EMT-like on the activation of the PDGF signalling pathway and the subsequent activation of PI3K in human melanoma cells. Together, the data provide novel insights into the transcriptional plasticity of melanoma cells that might contribute to tumor progression in patients and propose avenues to therapeutic interventions.

Emerging role of mucins in epithelial to mesenchymal transition

Epithelial to mesenchymal transition (EMT) is an important and complex phenomenon that determines the aggressiveness of cancer cells. The morphological transformation of cancerous cells is accompanied by various cellular processes such as alterations in cell-cell adhesion, cell matrix degradation, down regulation of epithelial marker Ecadherin and upregulation of mesenchymal markers N-cadherin and Vimentin. Besides these markers several other important tumor antigens/mucins are also involved in the EMT process. Mainly high molecular weight glycoproteins such as mucin molecules (MUC1, MUC4 and MUC16) play a major role in the cellular transformation and signaling alteration in EMT process. In addition to these factors, EMT may be an essential process triggering the emergence or expansion of the CSC population, which slowly results in the initiation of tumor at metastatic sites. Furthermore, mucins have been demonstrated to be involved in the EMT process and also in the enrichment of cancer stem cell population. Mucin mediated EMT is very complex since the key components of tumor microenvironment are also regulating mucin molecules. In this review, we have discussed all the aforementioned factors and their mechanistic involvement for EMT process.

Specificity protein 1 (Sp1) maintains basal epithelial expression of the miR-200 family: implications for epithelial-mesenchymal transition

Epithelial-mesenchymal transition (EMT) is required for the specification of tissues during embryonic development and is recapitulated during the metastatic progression of tumors. The miR-200 family plays a critical role in enforcing the epithelial state with their expression lost in cells undergoing EMT. EMT can be mediated by activation of the ZEB1 and ZEB2 (ZEB) transcription factors, which repress miR-200 expression via a self-reinforcing double negative feedback loop to promote the mesenchymal state. However, it remains unclear what factors drive and maintain epithelial-specific expression of miR-200 in the absence of EMT-inducing factors. Here, we show that the transcription factor Specificity Protein 1 (Sp1) binds to the miR-200b∼200a∼429 proximal promoter and activates miR-200 expression in epithelial cells. In mesenchymal cells, Sp1 expression is maintained, but its ability to activate the miR-200 promoter is perturbed by ZEB-mediated repression. Reduction of Sp1 expression caused changes in EMT-associated markers in epithelial cells. Furthermore, we observed co-expression of Sp1 and miR-200 during mouse embryonic development wherein miR-200 expression was only lost in regions with high ZEB expression. Together, these findings indicate that miR-200 family members require Sp1 to drive basal expression and to maintain an epithelial state.

Tumor metastasis: moving new biological insights into the clinic

As the culprit behind most cancer-related deaths, metastasis is the ultimate challenge in our effort to fight cancer as a life-threatening disease. The explosive growth of metastasis research in the past decade has yielded an unprecedented wealth of information about the tumor-intrinsic and tumor-extrinsic mechanisms that dictate metastatic behaviors, the molecular and cellular basis underlying the distinct courses of metastatic progression in different cancers and what renders metastatic cancer refractory to available therapies. However, integration of such new knowledge into an improved, metastasis-oriented oncological drug development strategy is needed to thwart the development of metastatic disease at every stage of progression.

The epigenetics of epithelial-mesenchymal plasticity in cancer

During the course of malignant cancer progression, neoplastic cells undergo dynamic and reversible transitions between multiple phenotypic states, the extremes of which are defined by the expression of epithelial and mesenchymal phenotypes. This plasticity is enabled by underlying shifts in epigenetic regulation. A small cohort of pleiotropically acting transcription factors is widely recognized to effect these shifts by controlling the expression of a constituency of key target genes. These master regulators depend on complex epigenetic regulatory mechanisms, notably the induction of changes in the modifications of chromatin-associated histones, in order to achieve the widespread changes in gene expression observed during epithelial-mesenchymal transitions (EMTs). These associations indicate that an understanding of the functional interactions between such EMT-inducing transcription factors and the modulators of chromatin configuration will provide crucial insights into the fundamental mechanisms underlying cancer progression and may, in the longer term, generate new diagnostic and therapeutic modalities for treating high-grade malignancies.

Crosstalk between breast cancer stem cells and metastatic niche: emerging molecular metastasis pathway?

Metastatic colonization represents the final step of metastasis, and is the major cause of cancer mortality. Metastasis as an "inefficient" process requires the right population of tumor cells in a suitable microenvironment to form secondary tumors. Cancer stem cells are the only capable population of tumor cells to progress to overt metastasis. On the other hand, the occurrence of appropriate microenvironmental conditions within the target tissue would be critical for metastasis formation. Metastatic niche seems to be the specialized microenvironment to support tumor initiating cells at the distant organ. Master regulators not only determine cancer stem cell state, but also may have regulatory roles in metastatic niche elements. Meanwhile, both cancer stem cell and metastatic niche may function like two sides of the metastatic coin. Hypoxia inducible factors have multiple roles in regulation of both sides of this coin. TGF-β superfamily, also, have been considered as master regulators of epithelial to mesenchymal transition and metastasis and may play crucial roles in regulation of metastatic niche as well. In this regard, we hypothesize the presence of a possible emerging molecular pathway in the biological process of breast cancer metastasis. In this process, non-Smad TGF-β-induced metastasis connects cancer stem cell and metastatic niche formation through a central path, "Metastasis Pathway".

Regulatory networks defining EMT during cancer initiation and progression

Epithelial to mesenchymal transition (EMT) is essential for driving plasticity during development, but is an unintentional behaviour of cells during cancer progression. The EMT-associated reprogramming of cells not only suggests that fundamental changes may occur to several regulatory networks but also that an intimate interplay exists between them. Disturbance of a controlled epithelial balance is triggered by altering several layers of regulation, including the transcriptional and translational machinery, expression of non-coding RNAs, alternative splicing and protein stability.

ZEB/miR-200 feedback loop: at the crossroads of signal transduction in cancer

Embryonic differentiation programs of epithelial-mesenchymal and mesenchymal-epithelial transition (EMT and MET) represent a mechanistic basis for epithelial cell plasticity implicated in cancer. Transcription factors of the ZEB protein family (ZEB1 and ZEB2) and several microRNA species (predominantly miR-200 family members) form a double negative feedback loop, which controls EMT and MET programs in both development and tumorigenesis. In this article, we review crosstalk between the ZEB/miR-200 axis and several signal transduction pathways activated at different stages of tumor development. The close association of ZEB proteins with these pathways is indirect evidence for the involvement of a ZEB/miR-200 loop in tumor initiation, progression and spread. Additionally, the configuration of signaling pathways involving ZEB/miR-200 loop suggests that ZEB1 and ZEB2 may have different, possibly even opposing, roles in some forms of human cancer.

To differentiate or not--routes towards metastasis

Why are many metastases differentiated? Invading and disseminating carcinoma cells can undergo an epithelial-mesenchymal transition (EMT), which is associated with a gain of stem cell-like behaviour. Therefore, EMT has been linked to the cancer stem cell concept. However, it is a matter of debate how subsequent mesenchymal-epithelial transition (MET) fits into the metastatic process and whether a MET is essential. In this Opinion article, I propose two principle types of metastatic progression: phenotypic plasticity involving transient EMT-MET processes and intrinsic genetic alterations keeping cells in an EMT and stemness state. This simplified classification integrates clinically relevant aspects of dormancy, metastatic tropism and therapy resistance, and implies perspectives on treatment strategies against metastasis.

Mechanism of the mesenchymal-epithelial transition and its relationship with metastatic tumor formation

Cancer metastasis consists of a sequential series of events, and the epithelial-mesenchymal transition (EMT) and mesenchymal-epithelial transition (MET) are recognized as critical events for metastasis of carcinomas. A current area of focus is the histopathological similarity between primary and metastatic tumors, and MET at sites of metastases has been postulated to be part of the process of metastatic tumor formation. Here, we summarize accumulating evidence from experimental studies that directly supports the role of MET in cancer metastasis, and we analyze the main mechanisms that regulate MET or reverse EMT in carcinomas. Given the critical role of MET in metastatic tumor formation, the potential to effectively target the MET process at sites of metastasis offers new hope for inhibiting metastatic tumor formation.

An autocrine TGF-beta/ZEB/miR-200 signaling network regulates establishment and maintenance of epithelial-mesenchymal transition

Epithelial-mesenchymal transition (EMT) is a form of cellular plasticity that is critical for embryonic development and tumor metastasis. A double-negative feedback loop involving the miR-200 family and ZEB (zinc finger E-box-binding homeobox) transcription factors has been postulated to control the balance between epithelial and mesenchymal states. Here we demonstrate using the epithelial Madin Darby canine kidney cell line model that, although manipulation of the ZEB/miR-200 balance is able to repeatedly switch cells between epithelial and mesenchymal states, the induction and maintenance of a stable mesenchymal phenotype requires the establishment of autocrine transforming growth factor-β (TGF-β) signaling to drive sustained ZEB expression. Furthermore, we show that prolonged autocrine TGF-β signaling induced reversible DNA methylation of the miR-200 loci with corresponding changes in miR-200 levels. Collectively, these findings demonstrate the existence of an autocrine TGF-β/ZEB/miR-200 signaling network that regulates plasticity between epithelial and mesenchymal states. We find a strong correlation between ZEBs and TGF-β and negative correlations between miR-200 and TGF-β and between miR-200 and ZEBs, in invasive ductal carcinomas, consistent with an autocrine TGF-β/ZEB/miR-200 signaling network being active in breast cancers.

Transitions between epithelial and mesenchymal states: acquisition of malignant and stem cell traits

Transitions between epithelial and mesenchymal states have crucial roles in embryonic development. Emerging data suggest a role for these processes in regulating cellular plasticity in normal adult tissues and in tumours, where they can generate multiple, distinct cellular subpopulations contributing to intratumoural heterogeneity. Some of these subpopulations may exhibit more differentiated features, whereas others have characteristics of stem cells. Owing to the importance of these tumour-associated phenotypes in metastasis and cancer-related mortality, targeting the products of such cellular plasticity is an attractive but challenging approach that is likely to lead to improved clinical management of cancer patients.

BAR the door: cancer suppression by amphiphysin-like genes

The evolutionarily conserved amphiphysin-like genes Bin1 and Bin3 function in membrane and actin dynamics, cell polarity, and stress signaling. Recent genetic studies in mice discriminate non-essential roles in endocytic processes commonly ascribed to amphiphysins from essential roles in cancer suppression. Bin1 acts in default pathways of apoptosis and senescence that are triggered by the Myc and Raf oncogenes in primary cells, and Bin1 gene products display a 'moonlighting function' in the nucleus where a variety of other 'endocytic' proteins are also found. Together, genetic investigations in yeast, flies, and mice suggest that amphiphysin-like adapter proteins may suppress cancer by helping integrate cell polarity signals generated by actin and vesicle dynamics with central regulators of cell cycle arrest, apoptosis, and immune surveillance.

Phosphoinositides Signaling and Epithelial-to-Mesenchymal Transition: Putative Topic for Basic Toxicological Research

Ptdlns(4,5)P₂ is a key cellular phosphoinositide that localizes in separate and distinctive pools in subcellular membrane and vesicular compartments. In membranes, Ptdlns(4,5)P₂ acts as a precursor to second messengers and is itself a main signaling and targeting molecule. Specific subcellular localization of type I PIP kinases directed by interacting with specific targeting module differentiates Ptdlns(4,5)P₂ production in a spatial and temporal manner. Several lines of evidences support the idea that Ptdlns(4,5)P₂ is generated in very specific pools in a spatial and temporal manner or by feeding Ptdlns(4,5)P₂ directly to effectors. In this concept, the interaction of PIPKI isoforms with a specific targeting module to allow precise subcellular targeting modulates highly specific Ptdlns(4,5)P₂ synthesis and channeling overall effectors. For instance, localization of PIPKIγ661 to focal adhesions by an interaction with talin results in spatial and temporal production of Ptdlns(4,5)P₂, which regulates EGF-stimulated directional cell migration. In addition, Type lγ PIPK is targeted to E-cadherin in cell adherence junction and plays a role in controlling dynamics of cell adherence junction and endocytosis of E-cadherin. Characterizing how PIP kinase isoforms are regulated by interactions with their targeting modules, as well as the mechanisms by which their product, Ptdlns(4,5)P₂, exerts its effects on cellular signaling processes, is crucial to understand the harmonized control of numerous cellular signaling pathways. Thus, in this review the roles of the Ptdlns(4)P(5) kinases and Ptdlns(4,5)P₂ were described and critically reviewed in terms of regulation of the E-cadherin trafficking, cell migration, and formation of cell adherence junction which is indispensable and is tightly controlled in epithelial-to-mesenchymal transition process.

Frizzled-7 dictates three-dimensional organization of colorectal cancer cell carcinoids

Progression of colorectal cancer (CRC) involves spatial and temporal occurrences of epithelial-mesenchymal transition (EMT), whereby tumour cells acquire a more invasive and metastatic phenotype. Subsequently, the disseminated mesenchymal tumour cells must undergo a reverse transition (mesenchymal-epithelial transition, MET) at the site of metastases, as most metastases recapitulate the pathology of their corresponding primary tumours. Importantly, initiation of tumour growth at the secondary site is the rate-limiting step in metastasis. However, investigation of this dynamic reversible EMT and MET that underpins CRC morphogenesis has been hindered by a lack of suitable in vitro models. To this end, we have established a unique in vitro model of CRC morphogenesis, which we term LIM1863-Mph (morphogenetic). LIM1863-Mph cells spontaneously undergo cyclic transitions between two-dimensional monolayer (migratory, mesenchymal) and three-dimensional sphere (carcinoid, epithelial) states. Using RNAi, we demonstrate that FZD7 is necessary for MET of the monolayer cells as loss of FZD7 results in the persistence of a mesenchymal state (increased SNAI2/decreased E-cadherin). Moreover, FZD7 is also required for migration of the LIM1863-Mph monolayer cells. During development, FZD7 orchestrates either migratory or epithelialization events depending on the context. Our findings strongly implicate similar functional diversity for FZD7 during CRC morphogenesis.

HEF1-aurora A interactions: points of dialog between the cell cycle and cell attachment signaling networks

Regulated timing of cell division cycles, and geometrical precision in the planar orientation of cell division, are critical during organismal development and remain important for the maintenance of polarized structures in adults. Mounting evidence suggests that these processes are coordinated at the centrosome through the action of proteins that mediate both cell cycle and cell attachment. Our recent work identifying HEF1 as an activator of the Aurora A kinase suggests a novel hub for such integrated signaling. We suggest that defects in components of the machinery specifying the temporal and spatial integration of cell division may induce cancer and other diseases through pleiotropic effects on cell migration, proliferation, apoptosis, and genomic stability.

Transcriptional Control of the Mouse Col7a1 Gene in Keratinocytes: Basal and Transforming Growth Factor-β Regulated Expression

Anchoring fibrils at the cutaneous basement membrane zone of the stratified squamous epithelia are essential to maintaining skin integrity, as absence of these structures leads to the chronic blistering disease, dystrophic epidermolysis bullosa. Type VII collagen, the major component of anchoring fibrils, is synthesized primarily by basal keratinocytes and to a lesser degree by dermal fibroblasts. To elucidate the transcriptional control elements of the type VII collagen gene (Col7a1), 3 kb of 5' flanking sequence of the mouse gene was cloned, sequenced, and fused to the chloramphenicol acetyltransferase reporter gene. Promoter deletion analyses revealed that 560 bp of Col7a1 5' flanking sequence was sufficient and necessary for basal level of transcription in cultured murine keratinocytes. Mutagenesis of DNA sequences with similarity to consensus binding sites for transcription factors, including Sp1/Sp3, AP2, AP1, and Smads, within the p-560Col7a1 promoter/chloramphenicol acetyltransferase construct, coupled with DNA binding assays, revealed the importance of these sites for basal Col7a1 expression. The effect of transforming growth factor beta, an activator of Col7a1 expression in keratinocytes and dermal fibroblasts, was examined using the same Col7a1 promoter/chloramphenicol acetyltransferase constructs. These analyses demonstrated that transforming growth factor beta1 stimulation of Col7a1 transcription is dependent on a putative interaction between Smads and AP1. Interestingly, the Smad-like binding site was essential for both basal and transforming growth factor beta1 stimulated Col7a1 transcription. Collectively, these findings attest to the complex regulation of Col7a1 transcription in epidermal keratinocytes.

C-terminal-binding protein corepresses epithelial and proapoptotic gene expression programs

The genesis of carcinoma cells often involves epithelial-to-mesenchymal transitions and the acquisition of apoptosis resistance, but it is unclear whether these alterations are controlled coordinately or independently. Our previously reported effects of adenovirus E1a in human tumor cells raised the possibility that the E1a-interacting corepressor protein C-terminal-binding protein (CtBP) might selectively repress epithelial cell adhesion and proapoptotic genes. Here, we report that CtBP-knockout cells were hypersensitive to apoptosis. Correspondingly, microarray analysis of CtBP-knockout vs. CtBP-rescued mouse embryo fibroblasts revealed that many epithelial-specific and proapoptotic genes were indeed regulated by CtBP. Neither the apoptosis nor the repression activities of CtBP required histidine-315, suggesting that the proposed dehydrogenase activity is not essential for CtBP function. The results presented herein establish two functional roles of CtBP: to corepress epithelial genes, thus permitting epithelial-to-mesenchymal transitions, and to modulate the cellular threshold for apoptotic responses.

Adenovirus-5 E1A: paradox and paradigm

The adenovirus early region 1A (E1A) proteins were described originally as immortalizing oncoproteins that altered transcription in rodent cells. Surprisingly, the 243-amino-acid form of adenovirus-5 E1A was found subsequently to reverse-transform many human tumour cells. Tumour suppression apparently results from the ability of E1A to re-programme transcription in tumour cells, and the molecular basis of this intriguing effect is now beginning to emerge. These discoveries have provided a tool with which to study the regulation of fundamental cellular processes.

Cell adhesion-mediated transformation of a human SCLC cell line is associated with the development of a normal phenotype

Small cell lung carcinoma (SCLC) is a highly metastatic disease with a poor prognosis due to its resistance to current modes of therapy. SCLC cells appear to arise by oncogenic transformation of self-renewing pulmonary neuroendocrine cells, which have the potential to differentiate into a variety of lung epithelial cell lineages. Epithelial-mesenchymal conversion involved in such cell type transitions leads to the acquisition of an invasive and metastatic phenotype and may be critical for neoplastic progression and its eventual resistance to therapy. In order to investigate mechanisms involved in such transitions, a SCLC cell line was exposed to 5-bromodeoxyuridine. This treatment induced a dramatic conversion from non-substrate-adherent aggregates to monolayers of cells exhibiting an epithelioid phenotype. The phenotypic transition was concomitant with downregulation of vimentin, upregulation of cytokeratins, and cell-cell and cell-matrix adhesion molecules as well as redistribution of the actin cytoskeleton. The changes in the levels and organization of cell-cell and cell-matrix adhesion molecules were correlated with an in vivo loss of tumorigenicity.

Epithelial-type and neural-type cadherin expression in malignant noncarcinomatous neoplasms with epithelioid features that involve the soft tissues

CONTEXT

Transmembrane adhesion molecules, epithelial-type cadherin (ECAD) and neural-type cadherin (NCAD), help in regulating transformations between epithelial and mesenchymal cells in the developing embryo and in maintaining the epithelioid phenotype. Consequently, the presence of epithelioid cells in certain malignant noncarcinomatous neoplasms raises speculation that the expression of ECAD and NCAD in these neoplasms may have diagnostic significance.

OBJECTIVE

To investigate the utility of ECAD and NCAD immunoexpression in distinguishing malignant (noncarcinomatous) neoplasms with epithelioid features that involve the soft tissues.

DESIGN

Membranous immunoreactivity of anti-ECAD and anti-NCAD was evaluated on archived cases selected from the files of the Armed Forces Institute of Pathology.

RESULTS

Epithelial-type cadherin was found in biphasic synovial sarcoma (35 of 35 cases), malignant melanoma (13/21), monophasic fibrous synovial sarcoma (13/26), clear cell sarcoma (4/9), poorly differentiated synovial sarcoma (3/13), diffuse mesothelioma (4/20), malignant epithelioid peripheral nerve sheath tumor (1/6), and epithelioid sarcoma (5/62). Neural-type cadherin was observed in chordoma (11/11), biphasic synovial sarcoma (30/35), diffuse mesothelioma (14/20), malignant melanoma (14/25), epithelioid sarcoma (24/63), epithelioid angiosarcoma (1/4), poorly differentiated synovial sarcoma (2/13), clear cell sarcoma (1/10), and monophasic fibrous synovial sarcoma (1/26). Eighteen cases of primary cutaneous squamous cell carcinomas all tested positive for ECAD, whereas NCAD was focally observed in 5 cases. No expression of either molecule was observed in cases of epithelioid hemangioendothelioma (n = 9), alveolar soft part sarcoma (n = 8), and extraskeletal myxoid chondrosarcoma (n = 7).

CONCLUSIONS

Epithelial-type and neural-type cadherins are found in a variety of noncarcinomatous neoplasms with epithelioid features that involve the soft tissues and can be utilized, in association with other immunomarkers, in distinguishing chordoma (100% NCAD) from extraskeletal myxoid chondrosarcoma and conventional chondrosarcoma of bone (0% NCAD), squamous cell carcinoma (100% ECAD) from epithelioid sarcoma (8% ECAD), and biphasic synovial sarcoma (100% ECAD) from diffuse mesothelioma (20% ECAD).

Leaving the neighborhood: molecular mechanisms involved during epithelial-mesenchymal transition

Several molecular mechanisms contribute directly and mechanically to the loss of epithelial phenotype. During epithelial-mesenchymal transition (EMT), adherens junctions and desmosomes are at least partially dissociated. At the same time, a massive cytoskeleton reorganization takes place, involving the rho family and the remodeling of the actin microfilament mesh. Numerous pathways have been described in vitro that control phenotype transition in specific cell models. In vivo developmental studies suggest that transcriptional control, activated by a specific pathway involving Ras, Src and potentially the Wnt pathway, is an essential step. Recent functional and localization experiments indicate that the slug/snail family of transcription factors functions overall as an epithelial phenotype repressor and could represent a key EMT contributor.

Fusions of the SYT and SSX genes in synovial sarcoma

Synovial sarcomas are high grade spindle cell tumors that are divided into two major histologic subtypes, biphasic and monophasic, according to the respective presence or absence of a well-developed glandular epithelial component. They contain in essentially all cases a t(X;18) representing the fusion of SYT (at 18q11) with either SSX1 or SSX2 (both at Xp11). Neither SYT, nor the SSX proteins contain DNA-binding domains. Instead, they appear to be transcriptional regulators whose actions are mediated primarily through protein-protein interactions, with BRM in the case of SYT, and with Polycomb group repressors in the case of SSX. Ongoing work on the SYT-SSX fusion and synovial sarcoma should yield a variety of data of broader biological interest, in areas such as BRM and Polycomb group function and dysfunction, transcriptional targets of SYT-SSX proteins and their native counterparts, differential gene regulation by SYT-SSX1 and SYT-SSX2, control of glandular morphogenesis, among others.

CRHSP-28 regulates Ca(2+)-stimulated secretion in permeabilized acinar cells

CRHSP-28 is a Ca(2+)-regulated heat-stable phosphoprotein, abundant in the apical cytoplasm of epithelial cells that are specialized in exocrine protein secretion. To define a functional role for the protein in pancreatic secretion, recombinant CRHSP-28 (rCRHSP-28) was introduced into streptolysin-O-permeabilized acinar cells, and amylase secretion in response to elevated Ca(2+) was determined. Secretion was enhanced markedly by rCRHSP-28 over a time course that closely corresponded with the loss of the native protein from the intracellular compartment. No effects of rCRHSP-28 were detected until approximately 50% of the native protein was lost from the cytosol. Secretion was enhanced by rCRHSP-28 over a physiological range of Ca(2+) concentrations with 2-3-fold increases in amylase release occurring in response to low micromolar levels of free Ca(2+). Further, rCRHSP-28 augmented secretion in a concentration-dependent manner with minimal and maximal effects occurring at 1 and 25 microg/ml, respectively. Covalent cross-linking experiments demonstrated that native CRHSP-28 was present in a 60-kDa complex in cytosolic fractions and in a high molecular mass complex in particulate fractions, consistent with the slow leak rate of the protein from streptolysin-O-permeabilized cells. Probing acinar lysates with rCRHSP-28 in a gel-overlay assay identified two CRHSP-28-binding proteins of 35 (pp35) and 70 kDa (pp70). Interestingly, preparation of lysates in the presence of 1 mm Ca(2+) resulted in a marked redistribution of both proteins from a cytosolic to a Triton X-100-insoluble fraction, suggesting a Ca(2+)-sensitive interaction of these proteins with the acinar cell cytoskeleton. In agreement with our previous study immunohistochemically localizing CRHSP-28 around secretory granules in acinar cells, gel-overlay analysis revealed pp70 copurified with acinar cell secretory granule membranes. These findings demonstrate an important cell physiological function for CRHSP-28 in the Ca(2+)-regulated secretory pathway of acinar cells.

The Caenorhabditis elegans gene lin-26 can trigger epithelial differentiation without conferring tissue specificity

How epithelial cell fates become specified is poorly understood. We have previously shown that the putative C2H2 zinc-finger transcription factor LIN-26 is required for the differentiation of ectodermal and mesodermal epithelial cells in Caenorhabditis elegans. Here, we report that ectopic LIN-26 expression during early gastrulation transforms most blastomeres into epithelial-like cells. Specifically, LIN-26 induced the expression of three epithelial markers: the adherens junction protein JAM-1; DLG-1, which is essential for the assembly of JAM-1 at junctions; and CHE-14, which is involved in apical trafficking. Furthermore, ultrastructural studies revealed that ectopic LIN-26 expression induced the formation of adherens-like junctions. However, ectopic lin-26 expression did not confer any tissue-specific cell fate, such as the epidermal cell fate, as evidenced from the observation that several epidermal-specific genes were not induced. Conversely, we show that epidermal cells displayed some polarity defects in lin-26 mutants. We conclude that lin-26 can induce epithelial differentiation and that epitheliogenesis is not a default pathway in C. elegans.

Change in gene expression subsequent to induction of Pnn/DRS/memA: increase in p21(cip1/waf1)

Pnn (PNN) is a nuclear and cell adhesion-related protein. Previous work has suggested that Pnn/DRS/memA is a potential tumor suppressor involved in the regulation of cell adhesion and cell migration. Using the ecdysone-inducible mammalian expression system, a stable inducible GFP-tagged human Pnn gene (PNNGFP) expressing 293 cell line was created (EcR293-PNNGFP). Cells induced to express PNNGFP not only exhibited increased cell-cell adhesion but also exhibited changes in cell growth and cell cycle progression. cDNA array analyses, together with real time PCR, revealed that the effects of exogenously expressed Pnn on cellular behavior may be linked to the regulation of the expression of specific subset genes. This subset includes cell cycle-related genes such as p21(cip1/waf1), CDK4, CPR2; cell migration and invasion regulatory genes such as RhoA, CDK5, TIMP-1, MMP-7, and EMMPRIN; and MIC-1. Concordant with previous observations of Pnn-induced phenotype changes, genes coding for epithelial associated processes and cell division controls were elevated, while those coding for increased cell motility and cellular reorganizations were downregulated. We utilized p21 promoter-luciferase reporter constructs and demonstrated that a marked stimulation of p21 promoter activity in 293 cells correlated with increased Pnn expression. Taken together, these data indicate that Pnn may participate in the regulation of gene expression, thereby, positively promoting cell-cell adhesion, and negatively affecting cell migration and cell proliferation.

Tumor suppression activity of adenovirus E1a protein: anoikis and the epithelial phenotype

Adenovirus E1a proteins reverse-transform diverse human tumor cells in culture. This has stimulated interest in the arenas of clinical and basic cancer research. Clinically, cancer gene therapy trials on E1a are in progress, and drug discovery strategies based on E1a are being considered. Biologically, the effect of E1a is unique in that it overrides most or all oncogenic signaling pathways to yield nontumorigenic cells. Apparently, this is a consequence of the ability of E1a to reprogram transcription in tumor cells so as to produce an epithelial phenotype that is refractory to oncogenic growth stimulation. The molecular basis for this effect is emerging.

Evidence for a function of CtBP in epithelial gene regulation and anoikis

Previously, we reported that adenovirus E1a protein behaves as a tumor suppressor in human cells. It apparently functions by transcriptionally inducing an array of epithelial cell adhesion genes, while repressing other cell-type specific genes, thus producing an epithelial phenotype. Concomitantly, the cells become sensitive to anoikis (apoptosis of epithelial cells detached from extracellular matrix), potentially causing tumor suppression. E1a protein interacts with the nuclear acetylases p300, CBP and P/CAF, and also with the co-repressor protein CtBP. In this study, we have determined the role of these interactions in E1a's phenotypic effects on human tumor cells. The results indicate that E1a's interaction with CtBP activates at least three epithelial cell adhesion gene promoters. The E-cadherin repressor appeared to be the CtBP-interacting protein delta EF1/ZEB, which bound the ras-repressible E-boxes of the E-cadherin promoter. The E1a-CtBP interaction also contributed to anoikis-sensitization. E1a's interactions with the nuclear acetylases conferred epithelial morphologies but did not activate epithelial genes. These latter interactions did not sensitize tumor cells to anoikis but nevertheless conferred tumor suppression. These results implicate CtBP as an antagonist of the epithelial phenotype and anoikis. They also indicate a new but undefined role for nuclear acetylases in maintaining the transformed phenotype.

RhoB alteration is necessary for apoptotic and antineoplastic responses to farnesyltransferase inhibitors

Farnesyltransferase inhibitors (FTIs) are in clinical trials, but how they selectively inhibit malignant cell growth remains uncertain. One important player in this process appears to be RhoB, an endosomal Rho protein that regulates receptor trafficking. FTI treatment elicits a gain of the geranylgeranylated RhoB isoform (RhoB-GG) that occurs due to modification of RhoB by geranylgeranyltransferase I in drug-treated cells. Notably, this event is sufficient to mediate antineoplastic effects in murine models and human carcinoma cells. To further assess this gain-of-function mechanism and determine whether RhoB-GG has a necessary role in drug action, we examined the FTI response of murine fibroblasts that cannot express RhoB-GG due to homozygous deletion of the rhoB gene. Nullizygous (-/-) cells were susceptible to cotransformation by adenovirus E1A plus activated H-Ras but defective in their FTI response, despite complete inhibition of H-Ras prenylation. Actin cytoskeletal and phenotypic events were disrupted in -/- cells, implicating RhoB-GG in these effects. Interestingly, -/- cells were resistant to FTI-induced growth inhibition under anchorage-dependent but not anchorage-independent conditions, indicating that, while RhoB-GG is sufficient, it is not necessary for growth inhibition under all conditions. In contrast, -/- cells were resistant to FTI-induced apoptosis in vitro and in vivo. Significantly, the apoptotic defect of -/- cells compromised the antitumor efficacy of FTI in xenograft assays. This study offers genetic proof of the hypothesis that RhoB-GG is a crucial mediator of the antineoplastic effects of FTIs.

Strong association of SYT-SSX fusion type and morphologic epithelial differentiation in synovial sarcoma

Synovial sarcoma is characterized by a specific recurrent translocation t(X; 18), resulting in either the SYT-SSX1 or SYT-SSX2 gene fusion. Because this is the primary genetic alteration in these tumors, we sought to identify the impact of molecular heterogeneity of the t(X;18) on cell proliferation, apoptosis, and epithelial differentiation in synovial sarcoma. Seventy-three patients with synovial sarcoma (18 biphasic, 55 monophasic) were selected on the basis of availability of tumor material for molecular and immunohistochemical analysis. Tumors were classified as biphasic on the basis of morphologic glandular differentiation. SYT-SSX fusion transcripts were examined by reverse transcriptase polymerase chain reaction using tumor RNA extracted from frozen or paraffin-embedded tissue. Cell proliferation was assessed immunohistochemically by the Ki-67 labeling index. Apoptosis was analyzed immunohistochemically with BAX and BCL2 antibodies and by the TUNEL method. Immunohistochemical evidence of epithelial differentiation was assessed using antibodies to cytokeratins and epithelial membrane antigen. Approximately two thirds of the tumors had an SYT-SSX1 and one third had an SYT-SSX2 fusion transcript. There was a strong association between SYT-SSX fusion type and histologic subtype. All biphasic synovial sarcomas had the SYT-SSX1 fusion, whereas all tumors with SYT-SSX2 were of monophasic morphology. There was, however, no association between SYT-SSX fusion type and expression of cytokeratins and epithelial membrane antigen among monophasic tumors. Tumors with SYT-SSX2 had a significantly higher mean and median Ki-67 labeling index than those with SYT-SSX1, but a comparison of Ki-67 according to fusion type, histologic type, and sample source suggested that the main determinants of proliferation rate were the latter two factors. Specifically, monophasic tumors and metastatic tumors showed significantly higher Ki-67 scores. Apoptosis (by TUNEL) was rarely observed, consistent with prominent expression of the anti-apoptotic protein BCL2 in almost all cases. TUNEL, BCL2, and BAX results did not correlate with SYT-SSX fusion type. These data confirm the strong association of SYT-SSX fusion transcript type with morphologic but not immunophenotypic epithelial differentiation in synovial sarcoma.

Pathological relevance of epithelial and mesenchymal phenotype plasticity

Epithelium and mesenchyme, two tissue types virtually found in every organ, are endowed with fundamentally different functional properties. Active motility, a capability that is limited to the mesenchymal repertoire, is the principal characteristic that distinguishes them. During embryonic development, conversions from epithelium to mesenchyme and from mesenchyme to epithelium normally occur, allowing morphogenetic processes and tissue remodelling to take place. However, there is now increasing evidence that the modulation between the epithelial and the mesenchymal phenotypes is not limited to embryonic life. Indeed, the pathogenesis of some adult diseases seems to implicate an inappropriate activation of this change. On the other hand, failure of normally occurring embryonic epithelial-mesenchymal interconversions could result in the development of some pathologies. It is now possible to study some molecular events underlying these phenotype transitions, since several biological agents implicated in the epithelial-mesenchymal interconversion, such as growth factors, extracellular matrix components and their receptors, transcription factors and oncogenes have been identified. The malignant potential of some oncogenes seems to express itself through the disruption of the mechanisms involved in the maintenance of the epithelial phenotype while, on the other hand, some observations suggest the existence of regulatory genes able to counteract the action of oncogenes by restoring epithelial characteristics. Therefore, the manipulation of the tissue phenotype could represent a novel strategy for the prevention and treatment of diseases in the future.

New Myc-interacting proteins: a second Myc network emerges

Despite its intensive investigation for almost two decades, c-Myc remains a fascinating and enigmatic subject. A large and compelling body of evidence indicates that c-Myc is a transcription factor with central roles in the regulation of cell proliferation, differentiation, and apoptosis, but its exact function has remained elusive. In this review we survey recent advances in the identification and analysis of c-Myc-binding proteins, which suggest insights into the transcriptional roles of c-Myc but which also extend the existing functional paradigms. The C-terminal domain (CTD) of c-Myc mediates interaction with Max and physiological recognition of DNA target sequences, events needed for all biological actions. Recently described interactions between the CTD and other cellular proteins, including YY-1, AP-2, BRCA-1, TFII-I, and Miz-1, suggest levels of regulatory complexity beyond Max in controlling DNA recognition by c-Myc. The N-terminal domain (NTD), which includes the evolutionarily conserved and functionally crucial Myc Box sequences (MB1 and MB2), contains the transcription activation domain (TAD) of c-Myc as well as regions required for transcriptional repression, cell cycle regulation, transformation, and apoptosis. In addition to interaction with the retinoblastoma family protein p107, the NTD has been shown to interact with alpha-tubulin and the novel adaptor proteins Binl, MM-1, Pam, TRRAP, and AMY-1. The structure of these proteins and their effects on c-Myc actions suggest links to the transcriptional regulatory machinery as well as to cell cycle regulation, chromatin modeling, and apoptosis. Investigations of this emerging NTD-based network may reveal how c-Myc is regulated and how it affects cell fate, as well as providing tools to distinguish the physiological roles of various Myc target genes.

Regulation of E-cadherin gene expression during tumor progression: the role of a new Ets-binding site and the E-pal element

A new regulatory region (-108 to -86), named CE, containing potential CRE- and Ets-binding sites has been identified in the murine E-cadherin promoter. The Ets-binding site (at -97 position) negatively modulates the activity of the E-cadherin promoter in expressing keratinocyte cell lines and was responsible for the specific retarded complexes obtained with the CE region. Analysis of the methylation status of the endogenous E-cadherin promoter indicated that silencing of E-cadherin expression in malignant keratinocytes cannot be explained by hypermethylation mechanisms. Furthermore, treatment with 5'-aza-2'-deoxycytidine was unable to induce the expression of E-cadherin in deficient keratinocytes. However, in vivo footprinting analysis of the endogenous E-cadherin promoter showed a very distinct pattern in expressing and nonexpressing keratinocytes. Extensive interactions in the previously postulated proximal regulatory elements and in the CE region were detected in expressing cells, while only some nucleotides of the E-pal element and of the CE region were protected in nonexpressing keratinocytes. These results indicate a complex regulation of the mouse E-cadherin promoter and support a model where the combination of positive (CCAAT-box and GC-rich region) and negative (E-pal element and CE region) cis-acting elements contribute to the final level of E-cadherin gene expression. In addition, our results show that downregulation of E-cadherin expression in transformed epidermal keratinocytes is mainly exerted through the interaction of repressor factor(s) with the E-pal element and to the lack of interaction of positive acting factors with the proximal regions.

Transforming growth factor beta 1 induces squamous carcinoma cell variants with increased metastatic abilities and a disorganized cytoskeleton

Previous studies indicated that mouse transformed keratinocytes undergo an epithelial-fibroblastic conversion when cultured in the presence of TGF-beta1. This conversion is associated in vivo with a squamous-spindle carcinoma transition. We derived epithelioid (A6, FPA6) and spindle (B5) clonal cell variants from a squamous carcinoma cell line (PDV) after treatment with TGF-beta1. FPA6 cells were isolated from the ascites fluid of an A6-tumor-bearing mouse. FPA6 and A6 cell lines produced in nude mice mixed carcinomas with a squamous and poorly differentiated component. Both cell lines coexpressed keratins and vimentin and synthesized E-cadherin protein, although FPA6 cells cultured at early passages (FPA6-ep) had reduced levels of E-cadherin mRNA and increased synthesis of keratin K8, a marker of malignant progression. Immunofluorescence analysis revealed that FPA6-ep cells exhibited a disorganized cytoskeleton with keratins forming focal juxtanuclear aggregates and loss of F-actin stress fibers and cortical bundles, and E-cadherin was localized in the cytoplasm out of cell-cell contact areas. Sporadic cells in A6 and PDV cultures also presented those anomalous keratin structures, suggesting that FPA6 cells originated from a subpopulation of A6 tumor cells that metastasized into the peritoneal cavity. The analysis of the spontaneous and experimental metastatic potentials of the cell lines showed that epithelioid and fibroblastic cell variants had acquired metastatic abilities compared to PDV which was nonmetastatic. The FPA6-ep cell line exhibited a highly aggressive behavior, killing the animals at about 17 days after intravenous injection of the cells into athymic mice. The phenotype of FPA6-ep cells was unstable and reverted at later passages in which the normal organization of keratin and F-actin in filaments and the localization of E-cadherin at cell-cell contacts were restored. This phenotypic reversion occurred concomitantly with a reduction of the experimental metastatic potential of FPA6 cells.