RNA toxicity and missplicing in the common eye disease fuchs endothelial corneal dystrophy

Fuchs endothelial corneal dystrophy (FECD) is an inherited degenerative disease that affects the internal endothelial cell monolayer of the cornea and can result in corneal edema and vision loss in severe cases. FECD affects ∼5% of middle-aged Caucasians in the United States and accounts for >14,000 corneal transplantations annually. Among the several genes and loci associated with FECD, the strongest association is with an intronic (CTG·CAG)_n trinucleotide repeat expansion in the TCF4 gene, which is found in the majority of affected patients. Corneal endothelial cells from FECD patients harbor a poly(CUG)_n RNA that can be visualized as RNA foci containing this condensed RNA and associated proteins. Similar to myotonic dystrophy type 1, the poly(CUG)_n RNA co-localizes with and sequesters the mRNA-splicing factor MBNL1, leading to missplicing of essential MBNL1-regulated mRNAs. Such foci and missplicing are not observed in similar cells from FECD patients who lack the repeat expansion. RNA-Seq splicing data from the corneal endothelia of FECD patients and controls reveal hundreds of differential alternative splicing events. These include events previously characterized in the context of myotonic dystrophy type 1 and epithelial-to-mesenchymal transition, as well as splicing changes in genes related to proposed mechanisms of FECD pathogenesis. We report the first instance of RNA toxicity and missplicing in a common non-neurological/neuromuscular disease associated with a repeat expansion. The FECD patient population with this (CTG·CAG)_n trinucleotide repeat expansion exceeds that of the combined number of patients in all other microsatellite expansion disorders.

Cyclin A2, a novel regulator of EMT

Our previous work showed that Cyclin A2 deficiency promotes cell invasion in fibroblasts. Given that the majority of cancers emerge from epithelia, we explored novel functions for Cyclin A2 by depleting it in normal mammary epithelial cells. This caused an epithelial to mesenchymal transition (EMT) associated with loss of cell-to-cell contacts, decreased E-Cadherin expression and increased invasive properties characterized by a reciprocal regulation of RhoA and RhoC activities, where RhoA-decreased activity drove cell invasiveness and E-Cadherin delocalization, and RhoC-increased activity only supported cell motility. Phenotypes induced by Cyclin A2 deficiency were exacerbated upon oncogenic activated-Ras expression, which led to an increased expression of EMT-related transcriptional factors. Moreover, Cyclin A2-depleted cells exhibited stem cell-like properties and increased invasion in an in vivo avian embryo model. Our work supports a model where Cyclin A2 downregulation facilitates cancer cell EMT and metastatic dissemination.

Association of common variants in TCF4 and PTPRG with Fuchs' corneal dystrophy: a systematic review and meta-analysis

TOPIC

A meta-analysis of TCF4 and PTPRG gene variants in Fuchs' corneal dystrophy (FCD).

CLINICAL RELEVANCE

To identify novel genetic markers in patients with FCD in different ethnic populations.

METHODS

MEDLINE and EMBASE were searched for eligible genetic studies on TCF4 and PTPRG in FCD. Odds ratios (OR) and 95% confidence intervals (CI) of each single-nucleotide polymorphism (SNP) in allelic, dominant and recessive models were estimated using fixed-effect model if I2<50% in the test for heterogeneity, otherwise the random effects model was used.

RESULTS

Thirty-three records were obtained, with 8 being suitable for meta-analysis, which included five SNPs in TCF4 and two in PTPRG. There were 1610 FCD patients and 1565 controls tested for TCF4 rs613872. This SNP was strongly associated with FCD in Caucasians (P = 5.0×10-106), with the risk allele G conferring an OR of 3.95 (95% CI: 3.49-4.46). A further 4 TCF4 SNPs (rs17595731, rs2286812, rs618869 and rs9954153) were also significantly associated with FCD in Caucasians (P<10-8). However, we found no SNP associated with FCD in Chinese. In addition, there was no significant association between FCD and PTPRG.

CONCLUSION

TCF4 rs613872 is strongly associated with FCD in Caucasians but not in Chinese, which may suggest ethnic diversity in FCD SNP associations. SNPs in PTPRG were not associated with FCD in Caucasians or Chinese populations. Results of this meta-analysis indicate the need for larger-scale and multi-ethnic genetic studies on FCD to further explore the associated gene variants and their roles on the mechanism and genetic basis of FCD.

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.

ITF2 prevents activation of the β-catenin-TCF4 complex in colon cancer cells and levels decrease with tumor progression

BACKGROUND & AIMS

Immunoglobulin transcription factor 2 (ITF2) was believed to promote neoplastic transformation via activation of β-catenin. However, ITF2 recently was reported to suppress colon carcinogenesis. We investigated the roles of ITF2 in colorectal cancer cell lines and tumor formation and growth in mice.

METHODS

Levels of ITF2, β-catenin, and c-Myc were measured in 12 human colorectal tumor samples and by immunohistochemistry. ITF2 regulation of β-catenin and T-cell factor (TCF) were analyzed using luciferase reporter, reverse-transcription quantitative polymerase chain reaction, flow cytometry, and immunoblot analyses. Mice were given subcutaneous injections of human colorectal cancer cell lines that stably express ITF2, small hairpin RNAs to reduce levels of ITF2, or control plasmids; xenograft tumor growth was assessed. Human colorectal carcinoma tissue arrays were used to associate levels of ITF2 expression and clinical outcomes.

RESULTS

Levels of β-catenin, cMyc, and ITF2 were increased in areas of human colon adenomas and carcinomas, compared with nontumor areas of the same tissues. ITF2 levels were reduced and cMyc levels were increased in areas of carcinoma, compared with adenoma. In human colorectal cancer cell lines, activation of the β-catenin-TCF4 complex and expression of its target genes were regulated negatively by ITF2. ITF2 inhibited formation of the β-catenin-TCF4 complex by competing with TCF4 for β-catenin binding. Stable transgenic expression of ITF2 in human colorectal cancer cell lines reduced their proliferation and tumorigenic potential in mice, whereas small hairpin RNA knockdown of ITF2 promoted growth of xenograft tumors in mice. In an analysis of colorectal tumor tissue arrays, loss of ITF2 from colorectal tumor tissues was associated with poor outcomes of patients. A gene set enrichment analysis supported the negative correlation between the level of ITF2 and activity of the β-catenin-TCF4 complex.

CONCLUSIONS

In human colorectal cancer cell lines and tissue samples, ITF2 appears to prevent activation of the β-catenin-TCF4 complex and transcription of its gene targets. Loss of ITF2 promotes the ability of colorectal cancer cells to form xenograft tumors, and is associated with tumor progression and shorter survival times of patients.

Role of microRNA in epithelial to mesenchymal transition and metastasis and clinical perspectives

The microRNAs (miRNAs) are a class of small, 20–22 nucleotides in length, endogenously expressed noncoding RNAs that regulate multiple targets posttranscriptionally. Interestingly, miRNAs have emerged as regulators of most physiological and pathological processes, including metastatic tumor progression, in part by controlling a reversible process called epithelial-to-mesenchymal transition (EMT). The activation of EMT increases the migratory and invasive properties fundamental for tumor cell spread while activation of the reverse mesenchymal-to-epithelial transition is required for metastasis outgrowth. The EMT triggering leads to the activation of a core of transcription factors (EMT-TFs) – SNAIL1/SNAIL2, bHLH (E47, E2-2, and TWIST1/TWIST2), and ZEB1/ZEB2 – that act as E-cadherin repressors and, ultimately, coordinate EMT. Recent evidence indicates that several miRNAs regulate the expression of EMT-TFs or EMT-activating signaling pathways. Interestingly, some miRNAs and EMT-TFs form tightly interconnected negative feedback loops that control epithelial cell plasticity, providing self-reinforcing signals and robustness to maintain the epithelial or mesenchymal cell status. Among the most significant feedback loops, we focus on the ZEB/miR-200 and the SNAIL1/miR-34 networks that hold a clear impact in the regulation of the epithelial-mesenchymal state. Recent insights into the p53 modulation of the EMT-TF/miRNA loops and epigenetic regulatory mechanisms in the context of metastasis dissemination will also be discussed. Understanding the regulation of EMT by miRNAs opens new avenues for the diagnosis and prognosis of tumors and identifies potential therapeutic targets that might help to negatively impact on metastasis dissemination and increasing patient survival.

Fuchs endothelial cornea dystrophy: a review of the genetics behind disease development

Fuchs dystrophy represents the most common form of endothelial dystrophy and is a significant cause of visual impairment. The cause of Fuchs dystrophy is a complicated combination of both genetic and environmental factors. Understanding the underlying causes of the disease can potentially lead to new medical treatments preventing loss of vision.

Genome-wide study of association and interaction with maternal cytomegalovirus infection suggests new schizophrenia loci

Genetic and environmental components as well as their interaction contribute to the risk of schizophrenia, making it highly relevant to include environmental factors in genetic studies of schizophrenia. This study comprises genome-wide association (GWA) and follow-up analyses of all individuals born in Denmark since 1981 and diagnosed with schizophrenia as well as controls from the same birth cohort. Furthermore, we present the first genome-wide interaction survey of single nucleotide polymorphisms (SNPs) and maternal cytomegalovirus (CMV) infection. The GWA analysis included 888 cases and 882 controls, and the follow-up investigation of the top GWA results was performed in independent Danish (1396 cases and 1803 controls) and German-Dutch (1169 cases, 3714 controls) samples. The SNPs most strongly associated in the single-marker analysis of the combined Danish samples were rs4757144 in ARNTL (P=3.78 × 10(-6)) and rs8057927 in CDH13 (P=1.39 × 10(-5)). Both genes have previously been linked to schizophrenia or other psychiatric disorders. The strongest associated SNP in the combined analysis, including Danish and German-Dutch samples, was rs12922317 in RUNDC2A (P=9.04 × 10(-7)). A region-based analysis summarizing independent signals in segments of 100 kb identified a new region-based genome-wide significant locus overlapping the gene ZEB1 (P=7.0 × 10(-7)). This signal was replicated in the follow-up analysis (P=2.3 × 10(-2)). Significant interaction with maternal CMV infection was found for rs7902091 (P(SNP × CMV)=7.3 × 10(-7)) in CTNNA3, a gene not previously implicated in schizophrenia, stressing the importance of including environmental factors in genetic studies.

The emerging roles of TCF4 in disease and development

Genome-wide association studies have identified common variants in transcription factor 4 (TCF4) as susceptibility loci for schizophrenia, Fuchs' endothelial corneal dystrophy, and primary sclerosing cholangitis. By contrast, rare TCF4 mutations cause Pitt-Hopkins syndrome, a disorder characterized by intellectual disability and developmental delay, and have also been described in patients with other neurodevelopmental disorders. TCF4 therefore sits at the nexus between common and rare disorders. TCF4 interacts with other basic helix-loop-helix proteins, forming transcriptional networks that regulate the differentiation of several distinct cell types. Here, we review the role of TCF4 in these seemingly diverse disorders and discuss recent data implicating TCF4 as an important regulator of neurodevelopment and epithelial-mesenchymal transition.

A core invasiveness gene signature reflects epithelial-to-mesenchymal transition but not metastatic potential in breast cancer cell lines and tissue samples

Introduction

Metastases remain the primary cause of cancer-related death. The acquisition of invasive tumour cell behaviour is thought to be a cornerstone of the metastatic cascade. Therefore, gene signatures related to invasiveness could aid in stratifying patients according to their prognostic profile. In the present study we aimed at identifying an invasiveness gene signature and investigated its biological relevance in breast cancer.

Methods & Results

We collected a set of published gene signatures related to cell motility and invasion. Using this collection, we identified 16 genes that were represented at a higher frequency than observed by coincidence, hereafter named the core invasiveness gene signature. Principal component analysis showed that these overrepresented genes were able to segregate invasive and non-invasive breast cancer cell lines, outperforming sets of 16 randomly selected genes (all P<0.001). When applied onto additional data sets, the expression of the core invasiveness gene signature was significantly elevated in cell lines forced to undergo epithelial-mesenchymal transition. The link between core invasiveness gene expression and epithelial-mesenchymal transition was also confirmed in a dataset consisting of 2420 human breast cancer samples. Univariate and multivariate Cox regression analysis demonstrated that CIG expression is not associated with a shorter distant metastasis free survival interval (HR = 0.956, 95%C.I. = 0.896–1.019, P = 0.186).

Discussion

These data demonstrate that we have identified a set of core invasiveness genes, the expression of which is associated with epithelial-mesenchymal transition in breast cancer cell lines and in human tissue samples. Despite the connection between epithelial-mesenchymal transition and invasive tumour cell behaviour, we were unable to demonstrate a link between the core invasiveness gene signature and enhanced metastatic potential.

LOXL2 catalytically inactive mutants mediate epithelial-to-mesenchymal transition

Lysyl-oxidase-like 2 (LOXL2) is a member of the lysyl oxidase family that catalyzes the cross-linking of collagens or elastins in the extracellular matrix, thus regulating the tensile strength of tissues. However, many reports have suggested different intracellular roles for LOXL2, including the ability to regulate gene transcription and tumor progression. We previously reported that LOXL2 mediates epithelial-to-mesenchymal transition (EMT) by Snail1-dependent and independent mechanisms, related to E-cadherin silencing and downregulation of epidermal differentiation and cell polarity components, respectively. Whether or not the catalytic activity of LOXL2 is required to induce/sustain EMT is actually unknown. Here we show that LOXL2 catalytic inactive mutants collaborate with Snail1 in E-cadherin gene repression to trigger EMT and, in addition, promote FAK/Src pathway activation to support EMT. These findings reveal a non-conventional role of LOXL2 on regulating epithelial cell plasticity.

The genetics of Fuchs' corneal dystrophy

Fuchs' corneal dystrophy (FCD) is a common late-onset genetic disorder of the corneal endothelium. It causes loss of endothelial cell density and excrescences in the Descemet membrane, eventually progressing to corneal edema, necessitating corneal transplantation. The genetic basis of FCD is complex and heterogeneous, demonstrating variable expressivity and incomplete penetrance. To date, three causal genes, ZEB1, SLC4A11 and LOXHD1, have been identified, representing a small proportion of the total genetic load of FCD. An additional four loci have been localized, including a region on chromosome 18 that is potentially responsible for a large proportion of all FCD cases. The elucidation of the causal genes underlying these loci will begin to clarify the pathogenesis of FCD and pave the way for the emergence of nonsurgical treatments.

Zac1 regulates cell cycle arrest in neuronal progenitors via Tcf4

Imprinted genes play a critical role in brain development and mental health, although the underlying molecular and cellular mechanisms remain incompletely understood. The family of basic helix-loop-helix (bHLH) proteins directs the proliferation, differentiation, and specification of distinct neuronal progenitor populations. Here, we identified the bHLH factor gene Tcf4 as a direct target gene of Zac1/Plagl1, a maternally imprinted transcriptional regulator, during early neurogenesis. Zac1 and Tcf4 expression levels concomitantly increased during neuronal progenitor differentiation; moreover, Zac1 interacts with two cis-regulatory elements in the Tcf4 gene locus, and these elements together confer synergistic activation of the Tcf4 gene. Tcf4 upregulation enhances the expression of the cyclin-dependent kinase inhibitor gene p57(Kip2), a paternally imprinted Tcf4 target gene, and increases the number of cells in G1 phase. Overall, we show that Zac1 controls cell cycle arrest function in neuronal progenitors through induction of p57(Kip2) via Tcf4 and provide evidence for cooperation between imprinted genes and a bHLH factor in early neurodevelopment.

Cadherins and epithelial-to-mesenchymal transition

Epithelial-mesenchymal transition (EMT) is a process whereby epithelial cells are transcriptionally reprogrammed, resulting in decreased adhesion and enhanced migration or invasion. EMT occurs during different stages of embryonic development, including gastrulation and neural crest cell delamination, and is induced by a panel of specific transcription factors. These factors comprise, among others, members of the Snail, ZEB, and Twist families, and are all known to modulate cadherin expression and, in particular, E-cadherin. By regulating expression of the cadherin family of proteins, EMT-inducing transcription factors dynamically modulate cell adhesion, allowing many developmental processes to take place. However, during cancer progression EMT can be utilized by cancer cells to contribute to malignancy. This is also reflected at the level of the cadherins, where the cadherin switch between E- and N-cadherins is a classical example seen in cancer-related EMT. In this chapter, we give a detailed overview of the entanglement between EMT-inducing transcription factors and cadherin modulation during embryonic development and cancer progression. We describe how classical cadherins such as E- and N-cadherins are regulated during EMT, as well as cadherin 7, -6B, and -11.

The roles of HLH transcription factors in epithelial mesenchymal transition and multiple molecular mechanisms

Epithelial-to-mesenchymal transition (EMT) is presently recognized as an important event and the initiating stage for tumor invasion and metastasis. Several EMT inducers have been identified, among which the big family of helix-loop-helix (HLH) transcription factors are rising as a novel and promising family of proteins in EMT mediation, such as Twist1, Twist2, E47, and HIFs, etc. Due to the variety and complexities of HLH members, the pathways and mechanisms they employ to promote EMT are also complex and characteristic. In this review, we will discuss the roles of various HLH proteins in the regulation and sustenance of the EMT and multiple cellular mechanisms, attempting to provide a novel and broadened view towards the link between HLH proteins and EMT.

Genetic and pharmacologic inhibition of mTORC1 promotes EMT by a TGF-β-independent mechanism

Epithelial-to-mesenchymal transition (EMT) is a transdifferentiation process that converts epithelial cells into highly motile mesenchymal cells. This physiologic process occurs largely during embryonic development but is aberrantly reactivated in different pathologic situations, including fibrosis and cancer. We conducted a siRNA screening targeted to the human kinome with the aim of discovering new EMT effectors. With this approach, we have identified mTOR complex 1 (mTORC1), a nutrient sensor that controls protein and lipid synthesis, as a key regulator of epithelial integrity. Using a combination of RNAi and pharmacologic approaches, we report here that inhibition of either mTOR or RPTOR triggers EMT in mammary epithelial cells. This EMT was characterized by the induction of the mesenchymal markers such as fibronectin, vimentin, and PAI-1, together with the repression of epithelial markers such as E-cadherin and ZO-3. In addition, mTORC1 blockade enhanced in vivo migratory properties of mammary cells and induced EMT independent of the TGF-β pathway. Finally, among the transcription factors known to activate EMT, both ZEB1 and ZEB2 were upregulated following mTOR repression. Their increased expression correlated with a marked reduction in miR-200b and miR-200c mRNA levels, two microRNAs known to downregulate ZEB1 and ZEB2 expression. Taken together, our findings unravel a novel function for mTORC1 in maintaining the epithelial phenotype and further indicate that this effect is mediated through the opposite regulation of ZEB1/ZEB2 and miR-200b and miR-200c. Furthermore, these results suggest a plausible etiologic explanation for the progressive pulmonary fibrosis, a frequent adverse condition associated with the therapeutic use of mTOR inhibitors.

MicroRNA-200c modulates epithelial-to-mesenchymal transition (EMT) in human colorectal cancer metastasis

OBJECTIVE

Distant metastasis is the major cause of cancer-related death in patients with colorectal cancer (CRC). Although the microRNA-200 (miR-200) family is a crucial inhibitor of epithelial-to-mesenchymal transition (EMT) in human cancer, the role of miR-200 members in the pathogenesis of metastatic CRC has not been investigated.

DESIGN

Fifty-four pairs of primary CRC and corresponding matched liver metastasis tissue specimens were analysed for expression and methylation status of the miR-200 family members. Functional analysis of miR-200c overexpression was investigated in CRC cell lines, and cells were analysed for proliferation, invasion and migration. Expression of several miR-200c target genes (ZEB1, ETS1 and FLT1) and EMT markers (E-cadherin and vimentin) in CRC cell lines and tissue specimens was validated.

RESULTS

Liver metastasis tissues showed higher expression of miR-200c (primary CRC = 1.31 vs. liver metastasis = 1.59; p = 0.0014) and miR-141 (primary CRC = 0.14 vs. liver metastasis = 0.17; p = 0.0234) than did primary CRCs, which was significantly associated with hypomethylation of the promoter region of these miRNAs (primary CRC = 61.2% vs. liver metastasis = 46.7%; p < 0.0001). The invasive front in primary CRC tissues revealed low miR-200c expression by in situ hybridization analysis. Transfection of miR-200c precursors resulted in enhanced cell proliferation but reduced invasion and migration behaviours in CRC cell lines. Overexpression of miR-200c in CRC cell lines caused reduced expression of putative gene targets, and resulted in increased E-cadherin and reduced vimentin expression. The associations between miR-200c, target genes and EMT markers were validated in primary CRCs and matching liver metastasis tissues.

CONCLUSIONS

miR-200c plays an important role in mediating EMT and metastatic behaviour in the colon. Its expression is epigenetically regulated, and miR-200c may serve as a potential diagnostic marker and therapeutic target for patients with CRC.

Knockdown of human TCF4 affects multiple signaling pathways involved in cell survival, epithelial to mesenchymal transition and neuronal differentiation

Haploinsufficiency of TCF4 causes Pitt-Hopkins syndrome (PTHS): a severe form of mental retardation with phenotypic similarities to Angelman, Mowat-Wilson and Rett syndromes. Genome-wide association studies have also found that common variants in TCF4 are associated with an increased risk of schizophrenia. Although TCF4 is transcription factor, little is known about TCF4-regulated processes in the brain. In this study we used genome-wide expression profiling to determine the effects of acute TCF4 knockdown on gene expression in SH-SY5Y neuroblastoma cells. We identified 1204 gene expression changes (494 upregulated, 710 downregulated) in TCF4 knockdown cells. Pathway and enrichment analysis on the differentially expressed genes in TCF4-knockdown cells identified an over-representation of genes involved in TGF-β signaling, epithelial to mesenchymal transition (EMT) and apoptosis. Among the most significantly differentially expressed genes were the EMT regulators, SNAI2 and DEC1 and the proneural genes, NEUROG2 and ASCL1. Altered expression of several mental retardation genes such as UBE3A (Angelman Syndrome), ZEB2 (Mowat-Wilson Syndrome) and MEF2C was also found in TCF4-depleted cells. These data suggest that TCF4 regulates a number of convergent signaling pathways involved in cell differentiation and survival in addition to a subset of clinically important mental retardation genes.

Epithelial to mesenchymal transition markers are associated with an increased metastatic risk in primary cutaneous squamous cell carcinomas but are attenuated in lymph node metastases

BACKGROUND

Cutaneous squamous cell carcinoma (cSCC) is the second most common malignancy in humans and approximately 5% metastasize, usually to regional lymph nodes. Epithelial to mesenchymal transition (EMT) is a process involving loss of intercellular adhesion, acquisition of a mesenchymal phenotype and enhanced migratory potential; epithelial markers, such as E-cadherin, are down-regulated and mesenchymal proteins (Vimentin), increased.

OBJECTIVE

To investigate the expression of EMT markers in metastatic SCC (MSCC) and their corresponding metastases, and to correlate them with clinico-pathological factors associated with an increased risk of metastasis.

METHODS

We performed a retrospective study that included 146 cSCC samples (51 primary non-metastatic, 56 primary metastatic, 39 lymphatic metastases). Immunohistochemistry for E-cadherin, Vimentin, Snail, beta-catenin, Twist, Zeb1 and Podoplanin was performed.

RESULTS

Loss of membranous E-cadherin was observed in 77% cSCCs, with no differences between MSCC and non-MSCC. Among the transcriptional factors controlling EMT, no significant Snail1 expression was detected. Twist, Zeb1, Vimentin, beta-catenin and Podoplanin were significantly overexpressed in MSCCs. Twist ectopic expression in SCC13 cells induced Zeb1, Vimentin and Podoplanin expression and E-cadherin delocalization. These changes resulted in a scattered migration pattern in vitro. Expression of EMT markers was decreased in the metastases when compared with the corresponding primary tumors.

CONCLUSION

These results suggest that a partial EMT, characterized by the expression of Twist but without a total E-cadherin depletion, is involved in the acquisition of invasive traits by cSCC, but the process is downregulated in lymph node metastases.

E47 and Id1 interplay in epithelial-mesenchymal transition

E12/E47 proteins (encoded by E2A gene) are members of the class I basic helix-loop-helix (bHLH) transcription factors (also known as E proteins). E47 has been described as repressor of E-cadherin and inducer of epithelial-mesenchymal transition (EMT). We reported previously that EMT mediated by E47 in MDCK cells occurs with a concomitant overexpression of Id1 and Id3 proteins. Id proteins belong to class V of HLH factors that lack the basic domain; they dimerise with E proteins and prevent their DNA interaction, thus, acting as dominant negative of E proteins. Here, we show that E47 interacts with Id1 in E47 overexpressing MDCK cells that underwent a full EMT as well as in mesenchymal breast carcinoma and melanoma cell lines. By conducting chromatin immunoprecipitation assays we demonstrate that E47 binds directly to the endogenous E-cadherin promoter of mesenchymal MDCK-E47 cells in a complex devoid of Id1. Importantly, our data suggest that both E47 and Id1 are required to maintain the mesenchymal phenotype of MDCK-E47 cells. These data support the collaboration between E47 and Id1 in the maintenance of EMT by mechanisms independent of the dominant negative action of Id1 on E47 binding to E-cadherin promoter. Finally, the analysis of several N0 breast tumour series indicates that the expression of E47 and ID1 is significantly associated with the basal-like phenotype supporting the biological significance of the present findings.

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.

TCF4 (e2-2; ITF2): a schizophrenia-associated gene with pleiotropic effects on human disease

Common SNPs in the transcription factor 4 (TCF4; ITF2, E2-2, SEF-2) gene, which encodes a basic Helix-Loop-Helix (bHLH) transcription factor, are associated with schizophrenia, conferring a small increase in risk. Other common SNPs in the gene are associated with the common eye disorder Fuch's corneal dystrophy, while rare, mostly de novo inactivating mutations cause Pitt-Hopkins syndrome. In this review, we present a systematic bioinformatics and literature review of the genomics, biological function and interactome of TCF4 in the context of schizophrenia. The TCF4 gene is present in all vertebrates, and although protein length varies, there is high conservation of primary sequence, including the DNA binding domain. Humans have a unique leucine-rich nuclear export signal. There are two main isoforms (A and B), as well as complex splicing generating many possible N-terminal amino acid sequences. TCF4 is highly expressed in the brain, where plays a role in neurodevelopment, interacting with class II bHLH transcription factors Math1, HASH1, and neuroD2. The Ca(2+) sensor protein calmodulin interacts with the DNA binding domain of TCF4, inhibiting transcriptional activation. It is also the target of microRNAs, including mir137, which is implicated in schizophrenia. The schizophrenia-associated SNPs are in linkage disequilibrium with common variants within putative DNA regulatory elements, suggesting that regulation of expression may underlie association with schizophrenia. Combined gene co-expression analyses and curated protein-protein interaction data provide a network involving TCF4 and other putative schizophrenia susceptibility genes. These findings suggest new opportunities for understanding the molecular basis of schizophrenia and other mental disorders.

PRSS23 is essential for the Snail-dependent endothelial-to-mesenchymal transition during valvulogenesis in zebrafish

AIMS

Cardiac valve disease is a common cause of congenital heart failure. Cardiac valve development requires a complex regulation of assorted protease activities. Nevertheless, the regulation of these proteases during atrioventricular (AV) valve formation is poorly understood. Previously, PRSS23, a novel vascular protease, is shown to be highly expressed at the AV canal during murine heart development; however, its function remains unknown. In this study, we sought to characterize the functional role of PRSS23 during cardiac valve formation.

METHODS AND RESULTS

We used a transgenic zebrafish line with fluorescently labelled vasculature as a tool to study the function of PRSS23. We first cloned the zebrafish prss23 and confirmed its sequence conservation with other vertebrate orthologues. Expression of prss23 was detected in the ventricle, atrium, and AV canal during zebrafish embryonic development. We found that morpholino knockdown of Prss23 inhibited the endothelial-to-mesenchymal transition (EndoMT) at the AV canal. Moreover, in human aortic endothelial cell-based assays, PRSS23 knockdown by short-hairpin RNA not only repressed the transforming growth factor-β-induced EndoMT, but also reduced Snail transcription, suggesting that Snail signalling is downstream of PRSS23 during EndoMT. We further demonstrated that human PRSS23 and SNAIL could rescue the prss23 morpholino-induced AV canal defect in zebrafish embryos, indicating that the function of PRSS23 in valvulogenesis is evolutionarily conserved.

CONCLUSION

We demonstrated for the first time that the initiation of EndoMT in valvulogenesis depends on PRSS23-Snail signalling and that the functional role of PRSS23 during AV valve formation is evolutionarily conserved.

Bhlhb5 and Prdm8 form a repressor complex involved in neuronal circuit assembly

Although transcription factors that repress gene expression play critical roles in nervous system development, their mechanism of action remains to be understood. Here, we report that the Olig-related transcription factor Bhlhb5 (also known as Bhlhe22) forms a repressor complex with the PR/SET domain protein, Prdm8. We find that Bhlhb5 binds to sequence-specific DNA elements and then recruits Prdm8, which mediates the repression of target genes. This interaction is critical for repressor function since mice lacking either Bhlhb5 or Prdm8 have strikingly similar cellular and behavioral phenotypes, including axonal mistargeting by neurons of the dorsal telencephalon and abnormal itch-like behavior. We provide evidence that Cadherin-11 functions as target of the Prdm8/Bhlhb5 repressor complex that must be repressed for proper neural circuit formation to occur. These findings suggest that Prdm8 is an obligate partner of Bhlhb5, forming a repressor complex that directs neural circuit assembly in part through the precise regulation of Cadherin-11.

Overexpression of ETV4 is oncogenic in prostate cells through promotion of both cell proliferation and epithelial to mesenchymal transition

The discovery of translocations that involve one of the genes of the ETS family (ERG, ETV1, ETV4 and ETV5) has been a major advance in understanding the molecular basis of prostate cancer (PC). Each one of these translocations results in deregulated expression of one of the ETS proteins. Here, we focus on the mechanism whereby overexpression of the ETV4 gene mediates oncogenesis in the prostate. By siRNA technology, we show that ETV4 inhibition in the PC3 cancer cell line reduces not only cell mobility and anchorage-independent growth, but also cell proliferation, cell cycle progression and tumor growth in a xenograft model. Conversely, ETV4 overexpression in the nonmalignant human prostate cell line (RWPE) increases anchorage-independent growth, cell mobility and cell proliferation, which is probably mediated by downregulation of p21, producing accelerated progression through the cell cycle. ETV4 overexpression is associated with changes in the pattern of E-cadherin and N-cadherin expression; the cells also become spindle-shaped, and these changes are characteristic of the so-called epithelial to mesenchymal transition (EMT). In RWPE cells overexpressing ETV4 EMT results from a marked increase in EMT-specific transcription factors such as TWIST1, SLUG1, ZEB1 and ZEB2. Thus, whereas ETV4 shares with the other ETS proteins (ERG, ETV5 and ETV1) a major role in invasiveness and cell migration, it emerges as unique in that it increases at the same time also the rate of proliferation of PC cells. Considering the wide spectrum in the clinical course of patients with PC, it may be highly relevant that ETV4 is capable of inducing most and perhaps all of the features that make a tumor aggressive.

EMT and oxidative stress: a bidirectional interplay affecting tumor malignancy

SIGNIFICANCE

Epithelial-mesenchymal transition (EMT) is emerging as a driving force in tumor progression, enabling cancer cells to evade their "homeland" and to colonize remote locations. In this review, we focus on the emerging views dealing with a redox control of EMT and with the importance of a pro-oxidant environment, both in cancer and stromal cells, to attain an improvement in tumor malignancy.

RECENT ADVANCES

The variety of signals able to promote EMT is large and continuously growing, ranging from soluble factors to components of the extracellular matrix. Compelling evidence highlights reactive oxygen species (ROS) as crucial conspirators in EMT engagement.

CRITICAL ISSUES

Tumor microenvironment exploits a fascinating role in ensuring EMT outcome within the primary tumor, granting for the achievement of an essential selective advantage for cancer cells. Cancer-associated fibroblasts, macrophages, and hypoxia are major players in this scenario, exerting a propelling role for EMT, as well as for invasiveness, stemness, and dissemination of metastatic cells.

FUTURE DIRECTIONS

Future research focused on EMT should address some key points that are still unclear. They include: i) the role of the reverse phenomenon (i.e., mesenchymal-epithelial transition) that is likely regulated in the final stages of tumor progression, or that of mesenchymal-amoeboid transition, a plasticity program of cancer cells, which often follows EMT and offers a further metastatic advantage, and ii) the molecular basis of the correlation between stemness, EMT and ROS content.

Association of TCF4 and CLU polymorphisms with Fuchs' endothelial dystrophy and implication of CLU and TGFBI proteins in the disease process

Fuchs' endothelial dystrophy (FED) is a disease affecting the corneal endothelium. Recent studies reported significant association of polymorphisms in the TCF4 (transcription factor 4) gene, and a borderline association of PTPRG (protein tyrosine phosphatase, receptor type, G) variants with late-onset FED in Caucasians from the United States. Association of TCF4 has also been reported in the Chinese population. We aimed to determine association of the reported polymorphisms in TCF4 and PTPRG, and association of polymorphisms in the candidate genes ZEB1 (zinc-finger E-box binding homoebox 1), COL8A2 (collagen, type VIII, alpha 2), TGFBI (transforming growth factor, β-induced) and CLU (clusterin) in Australian cases. We also compared the expression of TGFBI and CLU proteins between FED and normal whole corneas. In all, 30 single-nucleotide polymorphisms (SNPs) from the candidate genes were genotyped in 103 cases and 275 controls. Each SNP and haplotype was assessed for association with the disease. SNP analysis identified an association of TCF4 (rs613872 (P=5.25 × 10(-15), OR=4.05), rs9954153 (P=3.37 × 10(-7), OR=2.58), rs2286812 (P=4.23 × 10(-6), OR=2.55) and rs17595731 (P=3.57 × 10(-5), OR=3.79)), CLU (rs17466684; P=0.003, OR=1.85) and one haplotype of TGFBI SNPs (P=0.011, OR=2.29) with FED in Caucasian Australians. No evidence for genetic association of PTPRG, ZEB1 and COL8A2 was found. Immunohistochemistry showed differential expression of CLU and TGFBI proteins in FED-affected compared with normal corneas. In conclusion, variation in TCF4, CLU and TGFBI, but not PTPRG, ZEB1 and COL8A2 genes are associated with FED in Caucasian Australian cases. Differential expression of CLU and TGFBI proteins in FED-affected corneas provides novel insights into the disease mechanism.

Phenolic secoiridoids in extra virgin olive oil impede fibrogenic and oncogenic epithelial-to-mesenchymal transition: extra virgin olive oil as a source of novel antiaging phytochemicals

The epithelial-to-mesenchymal transition (EMT) genetic program is a molecular convergence point in the life-threatening progression of organ fibrosis and cancer toward organ failure and metastasis, respectively. Here, we employed the EMT process as a functional screen for testing crude natural extracts for accelerated drug development in fibrosis and cancer. Because extra virgin olive oil (EVOO) (i.e., the juice derived from the first cold pressing of the olives without any further refining process) naturally contains high levels of phenolic compounds associated with the health benefits derived from consuming an EVOO-rich Mediterranean diet, we have tested the ability of an EVOO-derived crude phenolic extract to regulate fibrogenic and oncogenic EMT in vitro. High-performance liquid chromatography (HPLC) coupled to time-of-flight (TOF) mass spectrometry assays revealed that the EVOO phenolic extract was mainly composed (∼70%) of two members of the secoiridoid family of complex polyphenols, namely oleuropein aglycone-the bitter principle of olives-and its derivative decarboxymethyl oleuropein aglycone. EVOO secoiridoids efficiently prevented loss of proteins associated with polarized epithelial phenotype (i.e., E-cadherin) as well as de novo synthesis of proteins associated with mesenchymal migratory morphology of transitioning cells (i.e., vimentin). The ability of EVOO to impede transforming growth factor-β (TGF-β)-induced disintegration of E-cadherin-mediated cell-cell contacts apparently occurred as a consequence of the ability of EVOO phenolics to prevent the upregulation of SMAD4-a critical mediator of TGF-β signaling-and of the SMAD transcriptional cofactor SNAIL2 (Slug)-a well-recognized epithelial repressor. Indeed, EVOO phenolics efficiently prevented crucial TGF-β-induced EMT transcriptional events, including upregulation of SNAI2, TCF4, VIM (Vimentin), FN (fibronectin), and SERPINE1 genes. While awaiting a better mechanistic understanding of how EVOO phenolics molecularly shut down the EMT differentiation process, it seems reasonable to suggest that nontoxic Oleaceae secoiridoids certainly merit to be considered for aging studies and, perhaps, for ulterior design of more pharmacologically active second-generation anti-EMT molecules.

Normal morphogenesis of epithelial tissues and progression of epithelial tumors

Epithelial cells organize into various tissue architectures that largely maintain their structure throughout the life of an organism. For decades, the morphogenesis of epithelial tissues has fascinated scientists at the interface of cell, developmental, and molecular biology. Systems biology offers ways to combine knowledge from these disciplines by building integrative models that are quantitative and predictive. Can such models be useful for gaining a deeper understanding of epithelial morphogenesis? Here, we take inventory of some recurring themes in epithelial morphogenesis that systems approaches could strive to capture. Predictive understanding of morphogenesis at the systems level would prove especially valuable for diseases such as cancer, where epithelial tissue architecture is profoundly disrupted.

Molecular bases of corneal endothelial dystrophies

The phrase "corneal endothelial dystrophies" embraces a group of bilateral corneal conditions that are characterized by a non-inflammatory and progressive degradation of corneal endothelium. Corneal endothelial cells exhibit a high pump site density and, along with barrier function, are responsible for maintaining the cornea in its natural state of relative dehydration. Gradual loss of endothelial cells leads to an insufficient water outflow, resulting in corneal edema and loss of vision. Since the pathologic mechanisms remain largely unknown, the only current treatment option is surgical transplantation when vision is severely impaired. In the past decade, important steps have been taken to understand how endothelial degeneration progresses on the molecular level. Studies of affected multigenerational families and sporadic cases identified genes and chromosomal loci, and revealed either Mendelian or complex disorder inheritance patterns. Mutations have been detected in genes that carry important structural, metabolic, cytoprotective, and regulatory functions in corneal endothelium. In addition to genetic predisposition, environmental factors like oxidative stress were found to be involved in the pathogenesis of endotheliopathies. This review summarizes and crosslinks the recent progress on deciphering the molecular bases of corneal endothelial dystrophies.

The transcription factor HLH-2/E/Daughterless regulates anchor cell invasion across basement membrane in C. elegans

Cell invasion through basement membrane is a specialized cellular behavior critical for many developmental processes and leukocyte trafficking. Invasive cellular behavior is also inappropriately co-opted during cancer progression. Acquisition of an invasive phenotype is accompanied by changes in gene expression that are thought to coordinate the steps of invasion. The transcription factors responsible for these changes in gene expression, however, are largely unknown. C. elegans anchor cell (AC) invasion is a genetically tractable in vivo model of invasion through basement membrane. AC invasion requires the conserved transcription factor FOS-1A, but other transcription factors are thought to act in parallel to FOS-1A to control invasion. Here we identify the transcription factor HLH-2, the C. elegans ortholog of Drosophila Daughterless and vertebrate E proteins, as a regulator of AC invasion. Reduction of HLH-2 function by RNAi or with a hypomorphic allele causes defects in AC invasion. Genetic analysis indicates that HLH-2 has functions outside of the FOS-1A pathway. Using expression analysis, we identify three genes that are transcriptionally regulated by HLH-2: the protocadherin cdh-3, and two genes encoding secreted extracellular matrix proteins, mig-6/papilin and him-4/hemicentin. Further, we show that reduction of HLH-2 function causes defects in polarization of F-actin to the invasive cell membrane, a process required for the AC to generate protrusions that breach the basement membrane. This work identifies HLH-2 as a regulator of the invasive phenotype in the AC, adding to our understanding of the transcriptional networks that control cell invasion.

Functional diversity of human basic helix-loop-helix transcription factor TCF4 isoforms generated by alternative 5' exon usage and splicing

BACKGROUND

Transcription factor 4 (TCF4 alias ITF2, E2-2, ME2 or SEF2) is a ubiquitous class A basic helix-loop-helix protein that binds to E-box DNA sequences (CANNTG). While involved in the development and functioning of many different cell types, recent studies point to important roles for TCF4 in the nervous system. Specifically, human TCF4 gene is implicated in susceptibility to schizophrenia and TCF4 haploinsufficiency is the cause of the Pitt-Hopkins mental retardation syndrome. However, the structure, expression and coding potential of the human TCF4 gene have not been described in detail.

PRINCIPAL FINDINGS

In the present study we used human tissue samples to characterize human TCF4 gene structure and TCF4 expression at mRNA and protein level. We report that although widely expressed, human TCF4 mRNA expression is particularly high in the brain. We demonstrate that usage of numerous 5' exons of the human TCF4 gene potentially yields in TCF4 protein isoforms with 18 different N-termini. In addition, the diversity of isoforms is increased by alternative splicing of several internal exons. For functional characterization of TCF4 isoforms, we overexpressed individual isoforms in cultured human cells. Our analysis revealed that subcellular distribution of TCF4 isoforms is differentially regulated: Some isoforms contain a bipartite nuclear localization signal and are exclusively nuclear, whereas distribution of other isoforms relies on heterodimerization partners. Furthermore, the ability of different TCF4 isoforms to regulate E-box controlled reporter gene transcription is varied depending on whether one or both of the two TCF4 transcription activation domains are present in the protein. Both TCF4 activation domains are able to activate transcription independently, but act synergistically in combination.

CONCLUSIONS

Altogether, in this study we have described the inter-tissue variability of TCF4 expression in human and provided evidence about the functional diversity of the alternative TCF4 protein isoforms.

A novel network profiling analysis reveals system changes in epithelial-mesenchymal transition

Patient-specific analysis of molecular networks is a promising strategy for making individual risk predictions and treatment decisions in cancer therapy. Although systems biology allows the gene network of a cell to be reconstructed from clinical gene expression data, traditional methods, such as Bayesian networks, only provide an averaged network for all samples. Therefore, these methods cannot reveal patient-specific differences in molecular networks during cancer progression. In this study, we developed a novel statistical method called NetworkProfiler, which infers patient-specific gene regulatory networks for a specific clinical characteristic, such as cancer progression, from gene expression data of cancer patients. We applied NetworkProfiler to microarray gene expression data from 762 cancer cell lines and extracted the system changes that were related to the epithelial-mesenchymal transition (EMT). Out of 1732 possible regulators of E-cadherin, a cell adhesion molecule that modulates the EMT, NetworkProfiler, identified 25 candidate regulators, of which about half have been experimentally verified in the literature. In addition, we used NetworkProfiler to predict EMT-dependent master regulators that enhanced cell adhesion, migration, invasion, and metastasis. In order to further evaluate the performance of NetworkProfiler, we selected Krueppel-like factor 5 (KLF5) from a list of the remaining candidate regulators of E-cadherin and conducted in vitro validation experiments. As a result, we found that knockdown of KLF5 by siRNA significantly decreased E-cadherin expression and induced morphological changes characteristic of EMT. In addition, in vitro experiments of a novel candidate EMT-related microRNA, miR-100, confirmed the involvement of miR-100 in several EMT-related aspects, which was consistent with the predictions obtained by NetworkProfiler.

Replication of the TCF4 intronic variant in late-onset Fuchs corneal dystrophy and evidence of independence from the FCD2 locus

PURPOSE

Fuchs corneal dystrophy (FCD) is an autosomal dominant disease of the corneal endothelium with variable penetrance and expressivity. Recently, rs613872, an intronic variation of TCF4 associated with late-onset FCD, was reported. The present study was undertaken to examine this association in our cohort of FCD patients, to assess the significance of this finding, and to investigate the candidacy of TCF4 in the context of the mapped FCD2 locus.

METHODS

The authors recruited 170 patients with late-onset FCD and 180 age-matched controls. Blood samples were collected, and genomic DNA was extracted. A panel of nine SNPs spanning the entire TCF4 locus was genotyped both on this cohort and on three previously reported FCD2-linked families. The association of an individual SNP with late-onset FCD was evaluated with the Fisher exact test, and the coding exons and exon-intron boundaries of TCF4 were sequenced in 96 affected persons.

RESULTS

The risk allele G of rs613872 is associated significantly with late-onset FCD (odds ratio, 4.2; P = 4.28 x 10⁻¹⁵) and was present in male and female affected persons without any sex bias, replicating recent findings, though the authors found no apparent correlation with the severity of the disease phenotype. Moreover, the risk allele did not cosegregate with the disease phenotype in any of the three FCD2-linked families. The authors did not identify any pathogenic variants in the coding region of TCF4.

CONCLUSIONS

The authors report the first independent replication of rs613872 conferring risk of late-onset FCD. Their data suggest that this risk factor is likely independent of the FCD2 locus, whose causality remains unknown.

Requirement of podocalyxin in TGF-beta induced epithelial mesenchymal transition

Epithelial mesenchymal transition (EMT) is characterized by the development of mesenchymal properties such as a fibroblast-like morphology with altered cytoskeletal organization and enhanced migratory potential. We report that the expression of podocalyxin (PODXL), a member of the CD34 family, is markedly increased during TGF-β induced EMT. PODXL is enriched on the leading edges of migrating A549 cells. Silencing of podocalyxin expression reduced cell ruffle formation, spreading, migration and affected the expression patterns of several proteins that normally change during EMT (e.g., vimentin, E-cadherin). Cytoskeleton assembly in EMT was also found to be dependent on the production of podocalyin. Compositional analysis of podocalyxin containing immunoprecipitates revealed that collagen type 1 was consistently associated with these isolates. Collagen type 1 was also found to co-localize with podocalyxin on the leading edges of migrating cells. The interactions with collagen may be a critical aspect of podocalyxin function. Podocalyxin is an important regulator of the EMT like process as it regulates the loss of epithelial features and the acquisition of a motile phenotype.

miR-155 promotes macroscopic tumor formation yet inhibits tumor dissemination from mammary fat pads to the lung by preventing EMT

miR-155, a micro-RNA, is over-expressed in many types of cancer cells, including breast cancer, and its role(s) in tumor metastasis has been studied on a very limited basis. Tumor metastasis is a multi-step process with the last step in the process being formation of macroscopic tumor in organs distant from the primary tumor site. This step is the least studied. Here, we report that stable expression of miR-155 in 4T1 breast tumor cells reduces significantly the aggressiveness of tumor cell dissemination as a result of preventing epithelial-to-mesenchymal transition (EMT) of tumor cells in vivo. Further, miR-155 directly suppresses the expression of the transcription factor TCF4, which is an important regulator of EMT. However, when tumor cells are injected directly into the bloodstream, miR-155 remarkably promotes macroscopic tumor formation in the lung. Analysis of gene expression profiling identified a group of genes that are associated with promoting macroscopic tumor formation in the lung. Importantly, most of these genes are over-expressed in epithelial cells. Our findings provide new insight into how miR-155 modulates the development of tumor metastasis. This study suggests that the location of tumor cells over-expressing miR-155 is a critical factor: in mammary fat pads miR-155 prevents tumor dissemination; whereas in the lung miR-155 apparently maintains the epithelial phenotype of tumor cells that is critical for macroscopic tumor formation.

Micro-RNA signature of the epithelial-mesenchymal transition in endometrial carcinosarcoma

Endometrial carcinosarcomas (ECSs) undergo a true epithelial-mesenchymal transition (EMT). The molecular determinants of the EMT in vivo are unclear, although a role for some miRNAs, mainly involving the miR-200 family, was recently suggested from in vitro cellular models. We analysed the microRNA (miRNA) signatures associated to EMT in human carcinosarcomas, and determined their relationships with EMT markers and repressors of E-cadherin transcription. The expression of E-, P- and N-cadherin, cadherin-11, p120, vimentin, SPARC, fascin and caveolin-1 was studied in a group of 76 ECS by immunohistochemistry. In addition, real-time PCR was used to measure the differences in the expression of 384 miRNAs, E-cadherin, cadherin-11, SPARC, SNAIL, ZEB1, ZEB2, TWIST-1, TCF4, TGFβ1 and TGFβ2 between the epithelial and mesenchymal components of 23 ECSs. A loss of epithelial characteristics, including cadherin switching and the acquisition of a mesenchymal phenotype, was accompanied by changes in the profile of miRNA expression and the up-regulation of all the E-cadherin repressors analysed. A greater than five-fold difference in the expression of 14 miRNAs between both neoplastic components was seen. Members of the miR-200 family were down-regulated in the mesenchymal part of the ECS. In addition, miR-23b and miR-29c, which are involved in the inhibition of mesenchymal markers, and miR-203, which is involved in the inhibition of cell stemness, were also down-regulated. Up-regulated miRNAs included miR-155, miR-369-5p, miR-370, miR-450a and miR-542-5p. These data suggest that in human ECS, the interplay between transcriptional repressors of E-cadherin and miRNAs provides a link between EMT-activation and the maintenance of stemness.

E2-2 protein and Fuchs's corneal dystrophy

BACKGROUND

Fuchs's corneal dystrophy (FCD) is a leading cause of corneal transplantation and affects 5% of persons in the United States who are over the age of 40 years. Clinically visible deposits called guttae develop under the corneal endothelium in patients with FCD. A loss of endothelial cells and deposition of an abnormal extracellular matrix are observed microscopically. In advanced disease, the cornea swells and becomes cloudy because the remaining endothelial cells are not sufficient to keep the cornea dehydrated and clear. Although rare genetic variation that contributes to both early-onset and typical late-onset forms of FCD has been identified, to our knowledge, no common variants have been reported.

METHODS

We performed a genomewide association study and replicated the most significant observations in a second, independent group of subjects.

RESULTS

Alleles in the transcription factor 4 gene (TCF4), encoding a member of the E-protein family (E2-2), were associated with typical FCD (P=2.3x10(-26)). The association increased the odds of having FCD by a factor of 30 for persons with two copies of the disease variants (homozygotes) and discriminated between case subjects and control subjects with about 76% accuracy. At least two regions of the TCF4 locus were associated independently with FCD. Alleles in the gene encoding protein tyrosine phosphatase receptor type G (PTPRG) were associated with FCD (P=4.0x10(-7)), but the association did not reach genomewide significance.

CONCLUSIONS

Genetic variation in TCF4 contributes to the development of FCD. (Funded by the National Eye Institute and others.)

ITF2 is a target of CXCR4 in MDA-MB-231 breast cancer cells and is associated with reduced survival in estrogen receptor-negative breast cancer

CXCR4, a chemokine receptor, plays an important role in breast cancer growth, invasion, and metastasis. The transcriptional targets of CXCR4 signaling are not known. Microarray analysis of CXCR4-enriched and CXCR4-low subpopulations of the MDA-MB-231 breast cancer cell line, which has a constitutively active CXCR4 signaling network, revealed differential expression of ∼ 200 genes in the CXCR4-enriched subpopulation. ITF2, upregulated in CXCR4-enriched cells, was investigated further. Expression array datasets of primary breast tumors revealed higher ITF2 expression in estrogen receptor negative tumors, which correlated with reduced progression free and overall survival and suggested its relevance in breast cancer progression. CXCL12, a CXCR4 ligand, increased ITF2 expression in MDA-MB-231 cells. ITF2 is a basic helix-loop-helix transcription factor that controls the epithelial-to-mesenchymal transition and the function of the ID family (inhibitor-of-differentiation) of transcription factors, such as ID2. ID2 promotes differentiation of breast epithelial cells and its reduced expression in breast cancer is associated with an unfavorable prognosis. Both CXCR4 and ITF2 repressed ID2 expression. In xenograft studies, CXCR4-enriched cells formed large tumors and exhibited significantly elevated lung metastasis. Short interfering RNA against ITF2 reduced invasion of the CXCR4-enriched MDA-MB-231 subpopulation, whereas ITF2 overexpression restored the invasive capacity of MDA-MB-231 cells expressing CXCR4shRNA. Furthermore, overexpression of ITF2 in these cells enhanced tumor growth. We propose that ITF2 is one of the CXCR4 targets, which is involved in CXCR4-dependent tumor growth and invasion of breast cancer cells.

Diversity in the molecular and cellular strategies of epithelium-to-mesenchyme transitions: Insights from the neural crest

Although epithelial to mesenchymal transitions (EMT) are often viewed as a unique event, they are characterized by a great diversity of cellular processes resulting in strikingly different outcomes. They may be complete or partial, massive or progressive, and lead to the complete disruption of the epithelium or leave it intact. Although the molecular and cellular mechanisms of EMT are being elucidated owing chiefly from studies on transformed epithelial cell lines cultured in vitro or from cancer cells, the basis of the diversity of EMT processes remains poorly understood. Clues can be collected from EMT occuring during embryonic development and which affect equally tissues of ectodermal, endodermal or mesodermal origins. Here, based on our current knowledge of the diversity of processes underlying EMT of neural crest cells in the vertebrate embryo, we propose that the time course and extent of EMT do not depend merely on the identity of the EMT transcriptional regulators and their cellular effectors but rather on the combination of molecular players recruited and on the possible coordination of EMT with other cellular processes.

Epithelial-mesenchymal transition: from molecular mechanisms, redox regulation to implications in human health and disease

Epithelial to mesenchymal transition (EMT) is a fundamental process, paradigmatic of the concept of cell plasticity, that leads epithelial cells to lose their polarization and specialized junctional structures, to undergo cytoskeleton reorganization, and to acquire morphological and functional features of mesenchymal-like cells. Although EMT has been originally described in embryonic development, where cell migration and tissue remodeling have a primary role in regulating morphogenesis in multicellular organisms, recent literature has provided evidence suggesting that the EMT process is a more general biological process that is also involved in several pathophysiological conditions, including cancer progression and organ fibrosis. This review offers first a comprehensive introduction to describe major relevant features of EMT, followed by sections dedicated on those signaling mechanisms that are known to regulate or affect the process, including the recently proposed role for oxidative stress and reactive oxygen species (ROS). Current literature data involving EMT in both physiological conditions (i.e., embryogenesis) and major human diseases are then critically analyzed, with a special final focus on the emerging role of hypoxia as a relevant independent condition able to trigger EMT.

Cell polarity in motion: redefining mammary tissue organization through EMT and cell polarity transitions

Epithelial to mesenchymal transition (EMT) and its reversion via mesenchymal to epithelial transition (MET), represent a stepwise cycle of epithelial plasticity that allows for normal tissue remodelling and diversification during development. In particular, epithelial-mesenchymal plasticity is central to many aspects of mammary development and has been proposed to be a key process in breast cancer progression. Such epithelial-mesenchymal plasticity requires complex cellular reprogramming to orchestrate a change in cell shape to an alternate morphology more conducive to migration. During this process, epithelial characteristics, including apical-basal polarity and specialised cell-cell junctions are lost and mesenchymal properties, such as a front-rear polarity associated with weak cell-cell contacts, increased motility, resistance to apoptosis and invasiveness are gained. The ability of epithelial cells to undergo transitions through cell polarity states is a central feature of epithelial-mesenchymal plasticity. These cell polarity states comprise a set of distinct asymmetric distributions of cellular constituents that are fashioned to allow specialized cellular functions, such as the regulated homeostasis of molecules across epithelial barriers, cell migration or cell diversification via asymmetric cell divisions. Each polarity state is engineered using a molecular toolbox that is highly conserved between organisms and cell types which can direct the initiation, establishment and continued maintenance of each asymmetry. Here we discuss how EMT pathways target cell polarity mediators, and how this EMT-dependent change in polarity states impact on the various stages of breast cancer. Emerging evidence places cell polarity at the interface of proliferation and morphology control and as such the changing dynamics within polarity networks play a critical role in normal mammary gland development and breast cancer progression.

An emerging role for class I bHLH E2-2 proteins in EMT regulation and tumor progression

EMT is a complex process whereby cells lose cell-cell interactions and other epithelial properties whilst acquiring a migratory and mesenchymal phenotype. EMT is presently recognized as an important even for tumor invasion and metastasis. Functional E-cadherin loss is a hallmark of EMT and required for tumor invasion in the majority of carcinomas. Transcriptional downregulation is one of the major mechanisms for E-cadherin suppression in carcinomas. In the last decade several E-cadherin repressors, belonging to different transcriptional families, have been identified that, importantly, also act as potent EMT inducers. One of the last additions to EMT regulators are the class I bHLH factors E2-2 (also known as TCF4). However, the hierarchical and functional interrelations between the different EMT inducers are still poorly understood. Here, we comment on the new and so far unrecognized function of E2-2 factors in EMT and discuss on the potential interactions among various EMT inducers. Emerging evidence supporting the participation of TCF4 in human malignancies is also discussed. Thus, increasing understanding of EMT and its regulators is providing meaningful insights into the present knowledge on tumor progression.

Epithelial-mesenchymal transitions in development and disease

The epithelial to mesenchymal transition (EMT) plays crucial roles in the formation of the body plan and in the differentiation of multiple tissues and organs. EMT also contributes to tissue repair, but it can adversely cause organ fibrosis and promote carcinoma progression through a variety of mechanisms. EMT endows cells with migratory and invasive properties, induces stem cell properties, prevents apoptosis and senescence, and contributes to immunosuppression. Thus, the mesenchymal state is associated with the capacity of cells to migrate to distant organs and maintain stemness, allowing their subsequent differentiation into multiple cell types during development and the initiation of metastasis.

The morphological and molecular features of the epithelial-to-mesenchymal transition

Here we describe several methods for the characterization of epithelial-mesenchymal transition (EMT) at the cellular, molecular and behavioral level. This protocol describes both in vitro and in vivo approaches designed to analyze different features that when taken together permit the characterization of cells undergoing transient or stable EMT. We define straightforward methods for phenotypical, cellular and transcriptional characterization of EMT in vitro in monolayer cultures. The procedure also presents technical details for the generation of in vitro three-dimensional (3D) cultures analyzing cell phenotype and behavior during the EMT process. In addition, we describe xenotransplantation techniques to graft 3D cell cultures into mice to study in vivo invasion in a physiological-like environment. Finally, the protocol describes the analysis of selected EMT markers from experimental and human tumor samples. This series of methods can be applied to the study of EMT under various experimental and biological situations. Once the methodology is established, the time required to complete the protocol may vary from 3 to 4 weeks (monolayer cultures) and up to 6-8 weeks if including 3D cultures.