Human Mena+11a isoform serves as a marker of epithelial phenotype and sensitivity to epidermal growth factor receptor inhibition in human pancreatic cancer cell lines

The discovery, function, and regulation of epithelial splicing regulatory proteins (ESRP) 1 and 2

Alternative splicing is a broad and evolutionarily conserved mechanism to diversify gene expression and functionality. The process relies on RNA binding proteins (RBPs) to recognize and bind target sequences in pre-mRNAs, which allows for the inclusion or skipping of various alternative exons. One recently discovered family of RBPs is the epithelial splicing regulatory proteins (ESRP) 1 and 2. Here, we discuss the structure and physiological function of the ESRPs in a variety of contexts. We emphasize the current understanding of their splicing activities, using the classic example of fibroblast growth factor receptor 2 mutually exclusive splicing. We also describe the mechanistic roles of ESRPs in coordinating the splicing and functional output of key signaling pathways that support the maintenance of, or shift between, epithelial and mesenchymal cell states. In particular, we highlight their functions in the development of mammalian limbs, the inner ear, and craniofacial structure while discussing the genetic and biochemical evidence that showcases their conserved roles in tissue regeneration, disease, and cancer pathogenesis.

Cooperative NF-κB and Notch1 signaling promotes macrophage-mediated MenaINV expression in breast cancer

Metastasis is a multistep process that leads to the formation of clinically detectable tumor foci at distant organs and frequently to patient demise. Only a subpopulation of breast cancer cells within the primary tumor can disseminate systemically and cause metastasis. To disseminate, cancer cells must express MenaINV, an isoform of the actin regulatory protein Mena, encoded by the ENAH gene, that endows tumor cells with transendothelial migration activity, allowing them to enter and exit the blood circulation. We have previously demonstrated that MenaINV mRNA and protein expression is induced in cancer cells by macrophage contact. In this study, we discovered the precise mechanism by which macrophages induce MenaINV expression in tumor cells. We examined the promoter of the human and mouse ENAH gene and discovered a conserved NF-κB transcription factor binding site. Using live imaging of an NF-κB activity reporter and staining of fixed tissues from mouse and human breast cancer, we further determined that for maximal induction of MenaINV in cancer cells, NF-κB needs to cooperate with the Notch1 signaling pathway. Mechanistically, Notch1 signaling does not directly increase MenaINV expression, but it enhances and sustains NF-κB signaling through retention of p65, an NF-κB transcription factor, in the nucleus of tumor cells, leading to increased MenaINV expression. In mice, these signals are augmented following chemotherapy treatment and abrogated upon macrophage depletion. Targeting Notch1 signaling in vivo decreased NF-κB signaling activation and MenaINV expression in the primary tumor and decreased metastasis. Altogether, these data uncover mechanistic targets for blocking MenaINV induction that should be explored clinically to decrease cancer cell dissemination and improve survival of patients with metastatic disease.

Clinical and Morphological Study of Cervical Squamous Intraepithelial Lesions

Squamous intraepithelial lesions (SILs) are cancer precursors targeted by secondary prevention of cervical cancer programs that are sometimes difficult to grade accurately. Mena is an actin regulatory protein involved in membrane protrusion, cell motility, in tumor invasion and metastasis. We studied retrospectively 68 cases of patients diagnosed with squamous intraepithelial lesions that received expedited treatment (treatment without colposcopic biopsy). We analyzed demographic, behavioral data, obstetrical and medical history, from the patients' medical charts and we studied the cervical fragments or cones harvested after the excisional procedure. Our study failed to identify a correlation between SILs and risk factors such as low socioeconomic status, combined oral contraceptive use, intrauterine device use, parity, gravity, except for the tobacco smoking habit that proved to be related to the cervical lesions' development. Mena was expressed in most of the analyzed SILs and its expression was correlated with lesions' grade in terms of both area and intensity, suggesting that Mena stains especially abnormal cells and that its expression intensity correlates with the risk of malignant transformation. Further studies are needed to validate Mena as an early stage of cervical carcinogenesis marker.

LncRNA ZFAS1 promotes laryngeal cancer progression through RBFOX2-mediated MENA alternative splicing

Laryngeal cancer (LC) is the most common aggressive malignancy of the head and neck. LncRNA ZNFX1 antisense RNA 1 (ZFAS1) displays oncogenic properties in head and neck squamous cell carcinoma, but its regulatory role in laryngeal cancer progression remains obscure. Here, we found that ZFAS1 expression in laryngeal cancer tissues and cells was higher than that in adjacent normal tissues and normal nasopharyngeal epithelial cells. Highly expressed ZFAS1 was associated with advanced lymph node metastasis stages and clinical stages. ZFAS1 overexpression promoted LC cell proliferation, invasion, and N-cadherin and Vimentin expression, and suppressed E-cadherin expression. While ZFAS1 knockdown played an opposite role. Mechanistically, ZFAS1 stabilized RNA binding fox-1 homolog 2 (RBFOX2) protein expression by binding to RBFOX2, and RBFOX2 overexpression reversed the effect of ZFAS1 silence on cell functions. Moreover, highly expressed RBFOX2 led to skipping of MENA exon 11a and generating a pro-invasive isoform (MENA^INV ). MENA^INV overexpression effectively abolished the inhibitory effect of RBFOX2 knockdown on cell malignant progression. Furthermore, Hep2 cells infected with lentivirus-mediated ZFAS1 shRNA or negative control shRNA were subcutaneously injected into mice to assess the role of ZFAS1 in tumor growth. And the data showed that silencing ZFAS1 in vivo hindered xenograft tumor growth. In conclusion, silencing ZFAS1 alleviated malignant progression of laryngeal cancer cells and mouse xenograft tumor growth by regulating RBFOX2-mediated alternative splicing of MENA.

A Hybrid Machine Learning Approach to Screen Optimal Predictors for the Classification of Primary Breast Tumors from Gene Expression Microarray Data

The high dimensionality and sparsity of the microarray gene expression data make it challenging to analyze and screen the optimal subset of genes as predictors of breast cancer (BC). The authors in the present study propose a novel hybrid Feature Selection (FS) sequential framework involving minimum Redundancy-Maximum Relevance (mRMR), a two-tailed unpaired t-test, and meta-heuristics to screen the most optimal set of gene biomarkers as predictors for BC. The proposed framework identified a set of three most optimal gene biomarkers, namely, MAPK 1, APOBEC3B, and ENAH. In addition, the state-of-the-art supervised Machine Learning (ML) algorithms, namely Support Vector Machine (SVM), K-Nearest Neighbors (KNN), Neural Net (NN), Naïve Bayes (NB), Decision Tree (DT), eXtreme Gradient Boosting (XGBoost), and Logistic Regression (LR) were used to test the predictive capability of the selected gene biomarkers and select the most effective breast cancer diagnostic model with higher values of performance matrices. Our study found that the XGBoost-based model was the superior performer with an accuracy of 0.976 ± 0.027, an F1-Score of 0.974 ± 0.030, and an AUC value of 0.961 ± 0.035 when tested on an independent test dataset. The screened gene biomarkers-based classification system efficiently detects primary breast tumors from normal breast samples.

Cooperative NF-κB and Notch1 signaling promotes macrophage-mediated MenaINV expression in breast cancer

Metastasis is a multistep process that leads to the formation of clinically detectable tumor foci at distant organs and frequently patient demise. Only a subpopulation of breast cancer cells within the primary tumor can disseminate systemically and cause metastasis. To disseminate, cancer cells must express MenaINV, an isoform of the actin-regulatory protein Mena encoded by the ENAH gene that endows tumor cells with transendothelial migration activity allowing them to enter and exit the blood circulation. We have previously demonstrated that MenaINV mRNA and protein expression is induced in cancer cells by macrophage contact. In this study, we discovered the precise mechanism by which macrophages induce MenaINV expression in tumor cells. We examined the promoter of the human and mouse ENAH gene and discovered a conserved NF-κB transcription factor binding site. Using live imaging of an NF-κB activity reporter and staining of fixed tissues from mouse and human breast cancer we further determined that for maximal induction of MenaINV in cancer cell NF-κB needs to cooperate with the Notch1 signaling pathway. Mechanistically, Notch1 signaling does not directly increase MenaINV expression, but it enhances and sustains NF-κB signaling through retention of p65, an NF-κB transcription factor, in the nucleus of tumor cells, leading to increased MenaINV expression. In mice, these signals are augmented following chemotherapy treatment and abrogated upon macrophage depletion. Targeting Notch1 signaling in vivo decreased NF-κB signaling and MenaINV expression in the primary tumor and decreased metastasis. Altogether, these data uncover mechanistic targets for blocking MenaINV induction that should be explored clinically to decrease cancer cell dissemination and improve survival of patients with metastatic disease.

Overexpression of Mena is associated with tumor progression and poor prognosis in oral squamous cell carcinoma via EMT

Background

Mena, a cytoskeletal regulatory protein, is involved in actin-based regulation of cell motility and adhesion, and contributes to tumor invasion and metastasis. However, the role of Mena in oral squamous cell carcinoma remains unclear. This is the first research focusing on the prognostic value of Mena in OSCC. In this study, we aimed to investigate the correlation between Mena expression and clinicopathological significance, as well as prognostic value in OSCC.

Methods

Mena gene expression profiles of OSCC and normal tissues were collected from Oncomine, TCGA, and GEO databases. Biological function was analyzed through GO, KEGG and GSEA enrichment. Further, the expression level of Mena and tumor-related markers in 151 OSCC specimens was examined by IHC staining based on tissue microarray. Kaplan-Meier analysis was used to assess the prognostic performance of Mena in OSCC.

Result

Mena was generally upregulation in various malignancies, especially OSCC. The functional analyses indicated that Mena was involved in the assembly and regulation of actin, cell movement, and EMT. IHC staining revealed that high expression of Mena in OSCC was correlated with Lymphatic metastasis, TNM stage, E-cadherin, Vimentin, and MMP-2, but insignificantly Ki67. Kaplan-Meier analysis demonstrated that elevated expression of Mena was significantly associated with poor overall survival and disease-free survival of OSCC patients.

Conclusion

Mena could be a novel biomarker for predicting the prognosis of OSCC patients, which supports a theoretical basis for developing molecular target therapy.

Arginine methylation in the epithelial-to-mesenchymal transition

Epithelial cells acquire mesenchymal characteristics during embryonic development, wound healing, fibrosis, and in cancer in a processed termed epithelial-to-mesenchymal transition (EMT). Regulatory networks of EMT are controlled by post-transcriptional, translational, and post-translational mechanisms, in which arginine methylation is critically involved. Here, we review arginine methylation-dependent mechanisms that regulate EMT in the aspects of signaling, transcriptional, and splicing regulation.

Actin Cytoskeleton and Regulation of TGFβ Signaling: Exploring Their Links

Human tissues, to maintain their architecture and function, respond to injuries by activating intricate biochemical and physical mechanisms that regulates intercellular communication crucial in maintaining tissue homeostasis. Coordination of the communication occurs through the activity of different actin cytoskeletal regulators, physically connected to extracellular matrix through integrins, generating a platform of biochemical and biomechanical signaling that is deregulated in cancer. Among the major pathways, a controller of cellular functions is the cytokine transforming growth factor β (TGFβ), which remains a complex and central signaling network still to be interpreted and explained in cancer progression. Here, we discuss the link between actin dynamics and TGFβ signaling with the aim of exploring their aberrant interaction in cancer.

Phenotypic Plasticity of Cancer Cells Based on Remodeling of the Actin Cytoskeleton and Adhesive Structures

There is ample evidence that, instead of a binary switch, epithelial-mesenchymal transition (EMT) in cancer results in a flexible array of phenotypes, each one uniquely suited to a stage in the invasion-metastasis cascade. The phenotypic plasticity of epithelium-derived cancer cells gives them an edge in surviving and thriving in alien environments. This review describes in detail the actin cytoskeleton and E-cadherin-based adherens junction rearrangements that cancer cells need to implement in order to achieve the advantageous epithelial/mesenchymal phenotype and plasticity of migratory phenotypes that can arise from partial EMT.

Splicing factor SF3B1 promotes endometrial cancer progression via regulating KSR2 RNA maturation

Although endometrial cancer is the most common cancer of the female reproductive tract, we have little understanding of what controls endometrial cancer beyond the transcriptional effects of steroid hormones such as estrogen. As a result, we have limited therapeutic options for the ~62,000 women diagnosed with endometrial cancer each year in the United States. Here, in an attempt to identify new prognostic and therapeutic targets, we focused on a new area for this cancer—alternative mRNA splicing—and investigated whether splicing factor, SF3B1, plays an important role in endometrial cancer pathogenesis. Using a tissue microarray, we found that human endometrial tumors expressed more SF3B1 protein than non-cancerous tissues. Furthermore, SF3B1 knockdown reduced in vitro proliferation, migration, and invasion of the endometrial cancer cell lines Ishikawa and AN3CA. Similarly, the SF3B1 inhibitor, Pladienolide-B (PLAD-B), reduced the Ishikawa and AN3CA cell proliferation and invasion in vitro. Moreover, PLAD-B reduced tumor growth in an orthotopic endometrial cancer mouse model. Using RNA-Seq approach, we identified ~2000 differentially expressed genes (DEGs) with SF3B1 knockdown in endometrial cancer cells. Additionally, alternative splicing (AS) events analysis revealed that SF3B1 depletion led to alteration in multiple categories of AS events including alternative exon skipping (ES), transcript start site usage (TSS), and transcript termination site (TTS) usage. Subsequently, bioinformatics analysis showed KSR2 as a potential candidate for SF3B1-mediated functions in endometrial cancer. Specifically, loss of SF3B1 led to decrease in KSR2 expression, owing to reduced maturation of KSR2 pre-mRNA to a mature RNA. Importantly, we found rescuing the KSR2 expression with SF3B1 knockdown partially restored the cell growth of endometrial cancer cells. Taken together, our data suggest that SF3B1 plays a crucial oncogenic role in the tumorigenesis of endometrial cancer and hence may support the development of SF3B1 inhibitors to treat this disease.

The role of the tumor microenvironment in tumor cell intravasation and dissemination

Metastasis, a process that requires tumor cell dissemination followed by tumor growth, is the primary cause of death in cancer patients. An essential step of tumor cell dissemination is intravasation, a process by which tumor cells cross the blood vessel endothelium and disseminate to distant sites. Studying this process is of utmost importance given that intravasation in the primary tumor, as well as the secondary and tertiary metastases, is the key step in the systemic spread of tumor cells, and that this process continues even after removal of the primary tumor. High-resolution intravital imaging of the tumor microenvironment of breast carcinoma has revealed that tumor cell intravasation exclusively occurs at doorways, termed "Tumor MicroEnvironment of Metastasis" (TMEM), composed of three different cell types: a Tie2^high/VEGF^high perivascular macrophage, a Mena overexpressing tumor cell, and an endothelial cell, all in direct contact. In this review article, we discuss the interactions between these cell types, the subsequent signaling events which lead to tumor cell intravasation, and the role of invadopodia in supporting tumor cell invasion and dissemination. We end our review by discussing how the knowledge acquired from the use of intravital imaging is now leading to new clinical trials targeting tumor cell dissemination and preventing metastatic progression.

PTBP1 enhances exon11a skipping in Mena pre-mRNA to promote migration and invasion in lung carcinoma cells

Alternative splicing (AS) events occur in the majority of human genes. AS in a single gene can give rise to different functions among multiple isoforms. Human ortholog of mammalian enabled (Mena) is a conserved regulator of actin dynamics that plays an important role in metastasis. Mena has been shown to have multiple splice variants in human tumor cells due to AS. However, the mechanism mediated Mena AS has not been elucidated. Here we showed that polypyrimidine tract-binding protein 1 (PTBP1) could modulate Mena AS. First, PTBP1 levels were elevated in metastatic lung cancer cells as well as during epithelial-mesenchymal transition (EMT) process. Then, knockdown of PTBP1 using shRNA inhibited migration and invasion of lung carcinoma cells and decreased the Mena exon11a skipping, whereas overexpression of PTBP1 had the opposite effects. The results of RNA pull-down assays and mutation analyses demonstrated that PTBP1 functionally targeted and physically interacted with polypyrimidine sequences on both upstream intron11 (TTTTCCCCTT) and downstream intron11a (TTTTTTTTTCTTT). In addition, the results of migration and invasion assays as well as detection of filopodia revealed that the effect of PTBP1 was reversed by knockdown of Mena but not Mena11a+. Overexpressed MenaΔ11a also rescued the PTBP1-induced migration and invasion. Taken together, our study provides a novel mechanism that PTBP1 modulates Mena exon11a skipping, and indicates that PTBP1 depends on the level of Mena11a- to promote lung cancer cells migration and invasion. The regulation of Mena AS may be a potential prognostic marker and a promising target for treatment of lung carcinoma.

Enah overexpression is correlated with poor survival and aggressive phenotype in gastric cancer

Enabled homolog (Enah), which is a member of the Ena/VASP family that also includes VASP (vasodilator-stimulated phosphoprotein) and Ena/VASP like, is a mammalian ortholog of Drosophila Enabled (Ena). An increasing number of studies demonstrated Enah overexpression is involved in human colorectal carcinomas, breast cancers and hepatocellular carcinoma. However, the significance of Enah expression in gastric cancer (GC) is poorly elucidated. Here, we demonstrate that Enah is upregulated in GC and associated with AJCC stage, depth of invasion and poor overall survival (OS). Knockdown of Enah inhibited GC cell proliferation and metastasis and vice versa. Further experiments suggested that p-Erk1/2, p-AKT, p-p65, Vimentin and Fibronectin were downregulated and E-cadherin was upregulated after Enah silencing, implicating altered functions in GC proliferation and metastasis. Thus, our study suggests that Enah is a harmful factor for GC and a novel target for GC treatment.

Expression status of cytoskeleton regulatory protein Mena as a prognostic marker for human thyroid carcinoma

OBJECTIVE

In recent years, Mena (Mammalian Enabled) has been reported to be highly expressed in malignant tumors. However, data on the expression pattern and clinical relevance of Mena in thyroid carcinoma are unclear. The purpose of this study was to investigate the expression of Mena and its prognostic significance in human thyroid carcinoma.

MATERIALS AND METHODS

Mena expression at the mRNA level was examined by real-time quantitative polymerase chain reaction (RT-PCR) in 8 paired thyroid carcinoma and adjacent normal tissues. Mena protein expression in clinical samples was analyzed in paraffin-embedded papillary thyroid carcinoma samples and normal thyroid tissues by immunohistochemistry (IHC). Statistical analyses were also performed to evaluate the clinicopathological significance of Mena expression.

RESULTS

The results show that expression of Mena mRNA is higher in thyroid carcinoma than in adjacent normal tissues in 8 paired samples. In paraffin-embedded tissue samples, the expression of Mena was higher in papillary thyroid carcinoma than normal thyroid tissues. Compared with normal thyroid tissues, overexpression of Mena was detected in 47.11% (57/121) of papillary thyroid carcinoma patients. Overexpression of Mena was significantly associated with T Stage (P = 0.007), capsular invasion (P = 0.015), lymph node metastasis (P = 0.000), and clinical stage (P = 0.029).

CONCLUSION

Mena is up-regulated in thyroid carcinoma and is associated with expression of T Stage, lymph node metastasis, clinical stage and disease-free survival. Mena may serve as a prognostic indicator for patients with thyroid carcinoma.

GLMEEMSAL epitope common in different isoforms of hMena elicits in vitro activation of cytotoxic T cells and stimulates specific antitumor immunity in BALB/c mice

BACKGROUND

Alternative expression of human ortholog of murine Mena (hMena) hMena/hMena^11a and hMena/hMenaΔv6 isoforms regulate the invasiveness and metastatic potential of tumor cells. It is then important to identify epitopes of these proteins that can elicit antitumor immune response to contribute to the elimination of cells with metastatic potential.

METHODS

We assayed the capacity of the peptide GLMEEMSAL, common in hMena/hMena^11a and hMena/hMenaΔv6 isoforms, to generate an antitumor immune response through an in vitro vaccination system with mature dendritic cells (MDC) loaded with this peptide and in vivo immunization using a tumor model with the mammary adenocarcinoma JC cell line to induce tumors in BALBc mice.

RESULTS

MDC loaded with the peptide GLMEEMSAL elicited strong proliferation and activation of CD8⁺ T lymphocytes. The CTLs generated with this system were capable to lyse specifically BrCa and CeCa cell lines expressing either hMena/hMena^11a or hMena/hMenaΔv6. Immunization with GLMEEMSAL provided protective and therapeutic antitumor activity as well as increased survival in BALB/c mice.

CONCLUSION

These results are highly relevant for the use of common peptides among the different isoforms of hMena to develop immunotherapy protocols to counteract the growth and metastatic potential of tumors with over-expression of hMena.

Expression of the cytoskeleton regulatory protein Mena in human gastric carcinoma and its prognostic significance

The cytoskeleton regulatory protein Mena is reportedly overexpressed in breast cancer; however, data regarding its expression level and clinical significance in gastric carcinoma (GC) is limited. The aim of the present study was to investigate Mena expression levels and prognostic significance in GC. Mena mRNA expression level was determined by reverse transcription-quantitative polymerase chain reaction in 10 paired GC and adjacent normal tissues. The Mena protein expression level was analyzed in paraffin-embedded GC samples and adjacent normal tissues by immunohistochemistry. Statistical analyses were also performed to evaluate the clinicopathological significance of Mena. The results revealed that the mRNA expression level of Mena was significantly higher in G Ct issues compared with in adjacent normal tissues from10 paired samples. In the paraffin-embedded tissue samples, the protein expression level of Mena was higher in G Ct issues compared with in adjacent normal tissues. Compared with adjacent normal tissues, Mena overexpression was observed in 52.83% (56/106) of patients. The overexpression of Mena was significantly associated with the T stage (P=0.033), tumor-node-metastasis (TNM) stage (P<0.001) and decreased overall survival (P<0.001). Based on a multivariate analysis, Mena expression level was an independent prognostic factor for overall survival time. In conclusion, Mena wasoverexpressed in G C tissues and significantly associated with the T stage, TNM stage and overall survival time. Mena may therefore be suitable as a prognostic indicator for patients with GC.

EMT and stemness: flexible processes tuned by alternative splicing in development and cancer progression

Epithelial-to-mesenchymal transition (EMT) is associated with metastasis formation as well as with generation and maintenance of cancer stem cells. In this way, EMT contributes to tumor invasion, heterogeneity and chemoresistance. Morphological and functional changes involved in these processes require robust reprogramming of gene expression, which is only partially accomplished at the transcriptional level. Alternative splicing is another essential layer of gene expression regulation that expands the cell proteome. This step in post-transcriptional regulation of gene expression tightly controls cell identity between epithelial and mesenchymal states and during stem cell differentiation. Importantly, dysregulation of splicing factor function and cancer-specific splicing isoform expression frequently occurs in human tumors, suggesting the importance of alternative splicing regulation for cancer biology.

In this review, we briefly discuss the role of EMT programs in development, stem cell differentiation and cancer progression. Next, we focus on selected examples of key factors involved in EMT and stem cell differentiation that are regulated post-transcriptionally through alternative splicing mechanisms. Lastly, we describe relevant oncogenic splice-variants that directly orchestrate cancer stem cell biology and tumor EMT, which may be envisioned as novel targets for therapeutic intervention.

MenaINV dysregulates cortactin phosphorylation to promote invadopodium maturation

Invadopodia, actin-based protrusions of invasive carcinoma cells that focally activate extracellular matrix-degrading proteases, are essential for the migration and intravasation of tumor cells during dissemination from the primary tumor. We have previously shown that cortactin phosphorylation at tyrosine residues, in particular tyrosine 421, promotes actin polymerization at newly-forming invadopodia, promoting their maturation to matrix-degrading structures. However, the mechanism by which cells regulate the cortactin tyrosine phosphorylation-dephosphorylation cycle at invadopodia is unknown. Mena, an actin barbed-end capping protein antagonist, is expressed as various splice-isoforms. The Mena^INV isoform is upregulated in migratory and invasive sub-populations of breast carcinoma cells, and is involved in tumor cell intravasation. Here we show that forced Mena^INV expression increases invadopodium maturation to a far greater extent than equivalent expression of other Mena isoforms. Mena^INV is recruited to invadopodium precursors just after their initial assembly at the plasma membrane, and promotes the phosphorylation of cortactin tyrosine 421 at invadopodia. In addition, we show that cortactin phosphorylation at tyrosine 421 is suppressed by the phosphatase PTP1B, and that PTP1B localization to the invadopodium is reduced by Mena^INV expression. We conclude that Mena^INV promotes invadopodium maturation by inhibiting normal dephosphorylation of cortactin at tyrosine 421 by the phosphatase PTP1B.

The alternatively-included 11a sequence modifies the effects of Mena on actin cytoskeletal organization and cell behavior

During tumor progression, alternative splicing gives rise to different Mena protein isoforms. We analyzed how Mena11a, an isoform enriched in epithelia and epithelial-like cells, affects Mena-dependent regulation of actin dynamics and cell behavior. While other Mena isoforms promote actin polymerization and drive membrane protrusion, we find that Mena11a decreases actin polymerization and growth factor-stimulated membrane protrusion at lamellipodia. Ectopic Mena11a expression slows mesenchymal-like cell motility, while isoform-specific depletion of endogenous Mena11a in epithelial-like tumor cells perturbs cell:cell junctions and increases membrane protrusion and overall cell motility. Mena11a can dampen membrane protrusion and reduce actin polymerization in the absence of other Mena isoforms, indicating that it is not simply an inactive Mena isoform. We identify a phosphorylation site within 11a that is required for some Mena11a-specific functions. RNA-seq data analysis from patient cohorts demonstrates that the difference between mRNAs encoding constitutive Mena sequences and those containing the 11a exon correlates with metastasis in colorectal cancer, suggesting that 11a exon exclusion contributes to invasive phenotypes and leads to poor clinical outcomes.

The prognostic potential of alternative transcript isoforms across human tumors

BACKGROUND

Phenotypic changes during cancer progression are associated with alterations in gene expression, which can be exploited to build molecular signatures for tumor stage identification and prognosis. However, it is not yet known whether the relative abundance of transcript isoforms may be informative for clinical stage and survival.

METHODS

Using information theory and machine learning methods, we integrated RNA sequencing and clinical data from The Cancer Genome Atlas project to perform the first systematic analysis of the prognostic potential of transcript isoforms in 12 solid tumors to build new signatures for stage and prognosis. This study was also performed in breast tumors according to estrogen receptor (ER) status and melanoma tumors with proliferative and invasive phenotypes.

RESULTS

Transcript isoform signatures accurately separate early from late-stage groups and metastatic from non-metastatic tumors, and are predictive of the survival of patients with undetermined lymph node invasion or metastatic status. These signatures show similar, and sometimes better, accuracies compared with known gene expression signatures in retrospective data and are largely independent of gene expression changes. Furthermore, we show frequent transcript isoform changes in breast tumors according to ER status, and in melanoma tumors according to the invasive or proliferative phenotype, and derive accurate predictive models of stage and survival within each patient subgroup.

CONCLUSIONS

Our analyses reveal new signatures based on transcript isoform abundances that characterize tumor phenotypes and their progression independently of gene expression. Transcript isoform signatures appear especially relevant to determine lymph node invasion and metastasis and may potentially contribute towards current strategies of precision cancer medicine.

The pattern of hMENA isoforms is regulated by TGF-β1 in pancreatic cancer and may predict patient outcome

Pancreatic ductal adenocarcinoma (PDAC) is an aggressive disease in need of prognostic markers to address therapeutic choices. We have previously shown that alternative splicing of the actin regulator, hMENA, generates hMENA^11a, and hMENAΔv6 isoforms with opposite roles in cell invasion. We examined the expression pattern of hMENA isoforms by immunohistochemistry, using anti-pan hMENA and specific anti-hMENA^11a antibodies, in 285 PDACs, 15 PanINs, 10 pancreatitis, and normal pancreas. Pan hMENA immunostaining, absent in normal pancreas and low-grade PanINs, was weak in PanIN-3 and had higher levels in virtually all PDACs with 64% of cases showing strong staining. Conversely, the anti-invasive hMENA^11a isoform only showed strong staining in 26% of PDAC. The absence of hMENA^11a in a subset (34%) of pan-hMENA-positive tumors significantly correlated with poor outcome. The functional effects of hMENA isoforms were analyzed by loss and gain of function experiments in TGF-β1-treated PDAC cell lines. hMENA^11a knock-down in PDAC cell lines affected cell-cell adhesion but not invasion. TGF-β1 cooperated with β-catenin signaling to upregulate hMENA and hMENAΔv6 expression but not hMENA^11a In the absence of hMENA^11a, the hMENA/hMENAΔv6 up-regulation is crucial for SMAD2-mediated TGF-β1 signaling and TGF-β1-induced EMT. Since the hMENA isoform expression pattern correlates with patient outcome, the data suggest that hMENA splicing and related pathways are novel key players in pancreatic tumor microenvironment and may represent promising targets for the development of new prognostic and therapeutic tools in PDAC.

Roles and Regulation of Epithelial Splicing Regulatory Proteins 1 and 2 in Epithelial-Mesenchymal Transition

The transformation of polarized epithelial cells into cells with mesenchymal characteristics by the morphogenetic process of epithelial-mesenchymal transition (EMT) is a well-characterized process essential for embryonic development and associated with cancer progression. EMT is a program driven by changes in gene expression induced by several EMT-specific transcription factors, which inhibit the expression of cell-cell adhesion proteins and other epithelial markers, causing a characteristic loss of cell-cell adhesion, a switch to mesenchymal cell morphology, and increased migratory capabilities. Recently, it has become apparent that in addition to these transcriptionally regulated changes, EMT may also be regulated posttranscriptionally, that is, by alternative splicing. Specifically, the epithelial splicing regulatory proteins 1 and 2 (ESRP1 and ESRP2) have been described as epithelial-specific splicing master regulators specifically involved in EMT-associated alternative splicing. Here, we discuss the regulation of ESRP activity, as well as the evidence supporting a causal role of ESRPs in EMT.

Amyloid precursor-like protein 2 (APLP2) affects the actin cytoskeleton and increases pancreatic cancer growth and metastasis

Amyloid precursor-like protein 2 (APLP2) is aberrantly expressed in pancreatic cancer. Here we showed that APLP2 is increased in pancreatic cancer metastases, particularly in metastatic lesions found in the diaphragm and intestine. Examination of matched human primary tumor-liver metastasis pairs showed that 38.1% of the patients had positive APLP2 expression in both the primary tumor and the corresponding liver metastasis. Stable knock-down of APLP2 expression (with inducible shRNA) in pancreatic cancer cells reduced the ability of these cells to migrate and invade. Loss of APLP2 decreased cortical actin and increased intracellular actin filaments in pancreatic cancer cells. Down-regulation of APLP2 decreased the weight and metastasis of orthotopically transplanted pancreatic tumors in nude mice.

A novel splice variant of XIAP-associated factor 1 (XAF1) is expressed in peripheral blood containing gastric cancer-derived circulating tumor cells

BACKGROUND

XIAP-associated factor 1 (XAF1) is ubiquitously expressed in normal tissues, but its suppression in cancer cells is strongly associated with tumor progression. Although downregulation of XAF1 is observed in tumors, its expression profile in the peripheral blood of cancer patients has not yet been investigated. Here, we identified a novel XAF1 splice variant in cancer cells and then investigated the expression level of this variant in peripheral blood containing gastric cancer-derived circulating tumor cells (CTCs).

METHODS

To identify splice variants, RT-PCR and DNA sequencing were performed in mRNAs extracted from many cancer cells. We then carried out quantitative RT-PCR to investigate expression in peripheral blood from all 96 gastric cancer patients and 22 healthy volunteers.

RESULTS

The XAF1 variant harbored a premature termination codon (PTC) and was differentially expressed in highly metastatic cancer cells versus the parental cells, and that nonsense-mediated mRNA decay (NMD) was suppressed in the variant-expressing cells. Furthermore, splice variants of XAF1 were upregulated in peripheral blood containing CTCs. In XAF1 variant-expressing patients, the expression levels of other NMD-targeted genes also increased, suggesting that the NMD pathway was suppressed in CTCs.

CONCLUSIONS

Our study identified a novel splice variant of XAF1 in cancer cells. This variant was regulated through the NMD pathway and accumulated in NMD-suppressed metastatic cancer cells and peripheral blood containing CTCs. The presence of XAF1 transcripts harboring the PTC in the peripheral blood may be useful as an indicator of NMD inhibition in CTCs.

Prognostic impact of alternative splicing-derived hMENA isoforms in resected, node-negative, non-small-cell lung cancer

Risk assessment and treatment choice remain a challenge in early non-small-cell lung cancer (NSCLC). Alternative splicing is an emerging source for diagnostic, prognostic and therapeutic tools. Here, we investigated the prognostic value of the actin cytoskeleton regulator hMENA and its isoforms, hMENA^11a and hMENAΔv6, in early NSCLC.

The epithelial hMENA^11a isoform was expressed in NSCLC lines expressing E-CADHERIN and was alternatively expressed with hMENAΔv6. Enforced expression of hMENAΔv6 or hMENA^11a increased or decreased the invasive ability of A549 cells, respectively. hMENA isoform expression was evaluated in 248 node-negative NSCLC. High pan-hMENA and low hMENA^11a were the only independent predictors of shorter disease-free and cancer-specific survival, and low hMENA^11a was an independent predictor of shorter overall survival, at multivariate analysis. Patients with low pan-hMENA/high hMENA^11a expression fared significantly better (P≤0.0015) than any other subgroup. Such hybrid variable was incorporated with T-size and number of resected lymph nodes into a 3-class-risk stratification model, which strikingly discriminated between different risks of relapse, cancer-related death, and death. The model was externally validated in an independent dataset of 133 patients.

Relative expression of hMENA splice isoforms is a powerful prognostic factor in early NSCLC, complementing clinical parameters to accurately predict individual patient risk.

Selectivity in subunit composition of Ena/VASP tetramers

Ena/VASP tetramer composition was analysed and mixed oligomerization of Mena with EVL was found to be unfavourable, while other paralogue combinations formed without apparent bias. The tetramerization domain of Ena/VASP proteins is responsible for their selective tetramer formation.

The members of the actin regulatory family of Ena/VASP proteins form stable tetramers. The vertebrate members of the Ena/VASP family, VASP, Mena and EVL, have many overlapping properties and expression patterns, but functional and regulatory differences between paralogues have been observed. The formation of mixed oligomers may serve a regulatory role to refine Ena/VASP activity. While it has been assumed that family members can form mixed oligomers, this possibility has not been investigated systematically. Using cells expressing controlled combinations of VASP, Mena and EVL, we evaluated the composition of Ena/VASP oligomers and found that VASP forms oligomers without apparent bias with itself, Mena or EVL. However, Mena and EVL showed only weak hetero-oligomerization, suggesting specificity in the association of Ena/VASP family members. Co-expression of VASP increased the ability of Mena and EVL to form mixed oligomers. Additionally, we found that the tetramerization domain (TD) at the C-termini of Ena/VASP proteins conferred the observed selectivity. Finally, we demonstrate that replacement of the TD with a synthetic tetramerizing coiled coil sequence supports homo-oligomerization and normal VASP subcellular localization.

The role of splicing factors in deregulation of alternative splicing during oncogenesis and tumor progression

In past decades, cancer research has focused on genetic alterations that are detected in malignant tissues and contribute to the initiation and progression of cancer. These changes include mutations, copy number variations, and translocations. However, it is becoming increasingly clear that epigenetic changes, including alternative splicing, play a major role in cancer development and progression. There are relatively few studies on the contribution of alternative splicing and the splicing factors that regulate this process to cancer development and progression. Recently, multiple studies have revealed altered splicing patterns in cancers and several splicing factors were found to contribute to tumor development. Studies using high-throughput genomic analysis have identified mutations in components of the core splicing machinery and in splicing factors in several cancers. In this review, we will highlight new findings on the role of alternative splicing and its regulators in cancer initiation and progression, in addition to novel approaches to correct oncogenic splicing.

Circulating tumor cells and epithelial, mesenchymal and stemness markers: characterization of cell subpopulations

Until now detection and numeration of circulating tumor cells (CTCs) were essentially used as a prognostic factor in cancer progression. To extend the role of these kinds of analysis, it seems necessary to improve analytical methods related to isolation and characterization of CTCs. Discrepancies between published results corroborates this requirement. In this review we suggest a combination of markers able to reach the goal. Moreover to improve the clinical utility of CTC analysis, particularly in the therapeutic follow up of the disease, epithelial mesenchymal transition (EMT) level of a global CTC population should be studied.

Invasive breast carcinoma cells from patients exhibit MenaINV- and macrophage-dependent transendothelial migration

Metastasis is a complex, multistep process of cancer progression that has few treatment options. A critical event is the invasion of cancer cells into blood vessels (intravasation), through which cancer cells disseminate to distant organs. Breast cancer cells with increased abundance of Mena [an epidermal growth factor (EGF)-responsive cell migration protein] are present with macrophages at sites of intravasation, called TMEM sites (for tumor microenvironment of metastasis), in patient tumor samples. Furthermore, the density of these intravasation sites correlates with metastatic risk in patients. We found that intravasation of breast cancer cells may be prevented by blocking the signaling between cancer cells and macrophages. We obtained invasive breast ductal carcinoma cells of various subtypes by fine-needle aspiration (FNA) biopsies from patients and found that, in an in vitro transendothelial migration assay, cells that migrated through a layer of human endothelial cells were enriched for the transcript encoding Mena(INV), an invasive isoform of Mena. This enhanced transendothelial migration required macrophages and occurred with all of the breast cancer subtypes. Using mouse macrophages and the human cancer cells from the FNAs, we identified paracrine and autocrine activation of colony-stimulating factor-1 receptor (CSF-1R). The paracrine or autocrine nature of the signal depended on the breast cancer cell subtype. Knocking down Mena(INV) or adding an antibody that blocks CSF-1R function prevented transendothelial migration. Our findings indicate that Mena(INV) and TMEM frequency are correlated prognostic markers and CSF-1 and Mena(INV) may be therapeutic targets to prevent metastasis of multiple breast cancer subtypes.

Synthetic lethality screen identifies RPS6KA2 as modifier of epidermal growth factor receptor activity in pancreatic cancer

Pancreatic cancer is characterized by a high degree of resistance to chemotherapy. Epidermal growth factor receptor (EGFR) inhibition using the small-molecule inhibitor erlotinib was shown to provide a small survival benefit in a subgroup of patients. To identify kinases whose inhibition acts synergistically with erlotinib, we employed a kinome-wide small-interfering RNA (siRNA)-based loss-of-function screen in the presence of erlotinib. Of 779 tested kinases, we identified several targets whose inhibition acted synergistically lethal with EGFR inhibition by erlotinib, among them the S6 kinase ribosomal protein S6 kinase 2 (RPS6KA2)/ribosomal S6 kinase 3. Activated RPS6KA2 was expressed in approximately 40% of 123 human pancreatic cancer tissues. RPS6KA2 was shown to act downstream of EGFR/RAS/mitogen-activated protein kinase kinase (MEK)/extracellular-signal regulated kinase (ERK) signaling and was activated by EGF independently of the presence of KRAS mutations. Knockdown of RPS6KA2 by siRNA led to increased apoptosis only in the presence of erlotinib, whereas RPS6KA2 activation or overexpression rescued from erlotinib- and gemcitabine-induced apoptosis. This effect was at least in part mediated by downstream activation of ribosomal protein S6. Genetic as well as pharmacological inhibition of RPS6KA2 by the inhibitor BI-D1870 acted synergistically with erlotinib. By applying this synergistic lethality screen using a kinome-wide RNA interference-library approach, we identified RPS6KA2 as potential drug target whose inhibition synergistically enhanced the effect of erlotinib on tumor cell survival. This kinase therefore represents a promising drug candidate suitable for the development of novel inhibitors for pancreatic cancer therapy.

Expression of cytoskeleton regulatory protein Mena in human hepatocellular carcinoma and its prognostic significance

The molecular mechanisms of the development and progression of hepatocellular carcinoma (HCC) are poorly understood. The main objective of this study was to analyze the expression of Enabled [mammalian Ena (Mena)] protein and its clinical significance in human HCC. The Mena expression was examined at mRNA and protein levels by real-time quantitative polymerase chain reaction and Western blotting analysis in ten paired HCC tissues and the adjacent normal tissues. The expression of Mena protein in 81 specimens of HCC tissues was determined by immunohistochemistry. Associations of Mena expression with the clinicopathological features were analyzed, and prognosis of HCC patients was evaluated. The result shows the expression of Mena mRNA and protein was higher in HCC than in the adjacent normal tissues in ten paired samples. Mena was mainly accumulated in the cytoplasm of tumor cells and over-expressed in 40.74% (33/81) patients by immunohistochemical staining. Over-expression of Mena was significantly associated with poor cellular differentiation (P = 0.025), advanced tumor stage (P = 0.003) and worse disease-free survival (DFS, P < 0.001). In addition, Mena is an independent prognostic factor for DFS in multivariate analysis (HR 2.309, 95% CI 1.104-4.828; P = 0.026). Mena is up-regulated in HCC and associated with tumor differentiation and clinical stage. Mena may be an independent prognostic marker for DFS of HCC patients.

hMena: altered expression in psoriatic skin

Psoriasis is a chronic inflammatory skin disease, characterized by an enhanced proliferation and a deregulated differentiation of keratinocytes. hMena is an actin regulatory protein involved in the control of cell motility and adhesion. hMena results up-modulated in several human tumors with respect to normal tissues and its expression has been positively correlated to proliferation rate, tumor size and aggressiveness in response to mitogenic stimuli, such as epidermal growth factor. The hyperproliferation of keratinocytes observed in psoriasis prompted us to evaluate hMena expression on biopsies collected from involved and uninvolved skin of 12 patients with active plaque-type psoriasis with respect to healthy skin. We analyzed the expression of hMena at transcript and protein levels by quantitative RT-PCR and immunohistochemistry. We correlated the expression of hMena to Ki67 proliferation index and to keratin 10 (K10) and keratin 16 (K16) used as markers of keratinocyte differentiation and activation. We demonstrated the expression of hMena in a hyperproliferative skin condition not related to neoplastic transformation. Interestingly, we observed that hMena is not expressed in healthy skin, but it becomes detectable in non-lesional areas and it is even more expressed in lesional psoriatic skin. In addition, we found that hMena expression is correlated to the rate of keratinocyte proliferation and activation. Hence, our observations indicate hMena as a new possible player, involved in the development and/or maintenance of the hyperproliferative state of psoriatic keratinocytes.

Expression and Distribution Characteristics of Human Ortholog of Mammalian Enabled (hMena) in Glioma

OBJECTIVE

To investigate the utility of hMena, a family of enabled/vasodilator-stimulated phosphoprotein (Ena/VASP), we sought to characterize the expression profile and distribution characteristics of hMena in a large panel of glioma samples and determine whether hMena expression levels might correlate with the pathological grade of glioma.

METHODS

Sixty-five specimens of glioma with different pathological grades and five control brain tissues were collected. In 6 of the 21 glioblastoma patients, multi-specimens were obtained respectively from the main tumor mass, the junction zone between the tumor and the normal tissue, and adjacent brain tissue 1.5 cm away from the tumor boundary under assistance of neuronavigation system during the operation. Immunohistochemistry was used to detect the expression and distribution characteristics of hMena. hMena expression was analyzed by Western blot in 20 specimens.

RESULTS

The hMena expression was negative in control brain tissue but positive in different grades of glioma. The expression rate of hMena was positively correlated with the increasing grade of the World Health Orgnization (WHO) classification (r(s)=0.682, P=0.000). hMena was located in cytoplasm. Positive cells only distributed around the vessels within the tumor mass in low grade glioma, while in high grade glioma, these cells were able to be detected not only in the tumor but also in the boundary zone and adjacent brain parenchyma. In the tumor mass, hMena expressed highly and diffusedly. In the junction zone, hMena positive cells formed radiolitic pattern around the vessels. In adjacent brain parenchyma, single positive cell was scattered. hMena expression was markedly elevated in Grade III and IV glioma compared with Grade II and I.

CONCLUSION

Our data suggested that the expression of hMena is closely related to malignant grade of glioma. hMena can label the migrating cells, and indicate the migrating path of glioma cells from the tumor to adjacent tissue along with the vascular basement membranes and tracts of white matter.

The possible role of Mena protein and its splicing-derived variants in embryogenesis, carcinogenesis, and tumor invasion: a systematic review of the literature

The Ena/VASP (enabled/vasodilator stimulated phosphoprotein) family includes the binding actin proteins such as mammalian Ena (Mena), VASP, and Ena-VASP-like. It is known that the perturbation of actin cycle could determine alteration in the mobility of cells and in consequence of organogenesis. Few recent studies have revealed that Mena protein could play a role in breast or pancreatic carcinogenesis. Based on our researches, we observed that the intensity of Mena expression increased from premalignant to malignant lesions in some organs such as large bowel, stomach, cervix, and salivary glands. These findings prove that Mena could be a marker of premalignant epithelial lesions. In premalignant lesions, it could be helpful to define more accurately the risk for malignant transformation. In malignant tumors, correlation of expression of its splice variants could indicate metastatic behavior. In conclusion, we consider that it is necessary to analyze the expression of Mena splice variants in a higher number of cases, in different epithelial lesions, and also in experimental studies to define its exact role in carcinogenesis and also its possible prognostic and predictive values.

RBFOX2 is an important regulator of mesenchymal tissue-specific splicing in both normal and cancer tissues

Alternative splicing provides a critical and flexible layer of regulation intervening in many biological processes to regulate the diversity of proteins and impact cell phenotype. To identify alternative splicing differences that distinguish epithelial from mesenchymal tissues, we have investigated hundreds of cassette exons using a high-throughput reverse transcription-PCR (RT-PCR) platform. Extensive changes in splicing were noted between epithelial and mesenchymal tissues in both human colon and ovarian tissues, with many changes from mostly one splice variant to predominantly the other. Remarkably, many of the splicing differences that distinguish normal mesenchymal from normal epithelial tissues matched those that differentiate normal ovarian tissues from ovarian cancer. Furthermore, because splicing profiling could classify cancer cell lines according to their epithelial/mesenchymal characteristics, we used these cancer cell lines to identify regulators for these specific splicing signatures. By knocking down 78 potential splicing factors in five cell lines, we provide an extensive view of the complex regulatory landscape associated with the epithelial and mesenchymal states, thus revealing that RBFOX2 is an important driver of mesenchymal tissue-specific splicing.

Splicing program of human MENA produces a previously undescribed isoform associated with invasive, mesenchymal-like breast tumors

Human mena (hMENA), a member of the actin cytoskeleton regulators Ena/VASP, is overexpressed in high-risk preneoplastic lesions and in primary breast tumors and has been identified as playing a role in invasiveness and poor prognosis in breast cancers that express HER2. Here we identify a unique isoform, hMENAΔv6, derived from the hMENA alternative splicing program. In an isogenic model of human breast cancer progression, we show that hMENA(11a) is expressed in premalignant cells, whereas hMENAΔv6 expression is restricted to invasive cancer cells. "Reversion" of the malignant phenotype leads to concurrent down-regulation of all hMENA isoforms. In breast cancer cell lines, isoform-specific hMENA overexpression or knockdown revealed that in the absence of hMENA(11a), overexpression of hMENAΔv6 increased cell invasion, whereas overexpression of hMENA(11a) reduced the migratory and invasive ability of these cells. hMENA(11a) splicing was shown to be dependent on the epithelial regulator of splicing 1 (ESRP1), and forced expression of ESRP1 in invasive mesenchymal breast cancer cells caused a phenotypic switch reminiscent of a mesenchymal-to-epithelial transition (MET) characterized by changes in the cytoskeletal architecture, reexpression of hMENA(11a), and a reduction in cell invasion. hMENA-positive primary breast tumors, which are hMENA(11a)-negative, are more frequently E-cadherin low in comparison with tumors expressing hMENA(11a). These data suggest that polarized and growth-arrested cellular architecture correlates with absence of alternative hMENA isoform expression, and that the hMENA splicing program is relevant to malignant progression in invasive disease.

Quantitative assessment of invasive mena isoforms (Menacalc) as an independent prognostic marker in breast cancer

INTRODUCTION

Mena, an Ena/VASP protein family member, is a key actin regulatory protein. Mena is up-regulated in breast cancers and promotes invasion and motility of tumor cells. Mena has multiple splice variants, including Mena invasive (MenaINV) and Mena11a, which are expressed in invasive or non-invasive tumor cells, respectively. We developed a multiplex quantitative immunofluorescence (MQIF) approach to assess the fraction of Mena lacking 11a sequence as a method to infer the presence of invasive tumor cells represented as total Mena minus Mena11a (called Menacalc) and determined its association with metastasis in breast cancer.

METHODS

The MQIF method was applied to two independent primary breast cancer cohorts (Cohort 1 with 501 and Cohort 2 with 296 patients) using antibodies against Mena and its isoform, Mena11a. Menacalc was determined for each patient and assessed for association with risk of disease-specific death.

RESULTS

Total Mena or Mena11a isoform expression failed to show any statistically significant association with outcome in either cohort. However, assessment of Menacalc showed that relatively high levels of this biomarker is associated with poor outcome in two independent breast cancer cohorts (log rank P = 0.0004 for Cohort 1 and 0.0321 for Cohort 2). Multivariate analysis on combined cohorts revealed that high Menacalc is associated with poor outcome, independent of age, node status, receptor status and tumor size.

CONCLUSIONS

High Menacalc levels identify a subgroup of breast cancer patients with poor disease-specific survival, suggesting that Menacalc may serve as a biomarker for metastasis.

MENA is a transcriptional target of the Wnt/beta-catenin pathway

Wnt/β-catenin signalling pathway plays important roles in embryonic development and carcinogenesis. Overactivation of the pathway is one of the most common driving forces in major cancers such as colorectal and breast cancers. The downstream effectors of the pathway and its regulation of carcinogenesis and metastasis are still not very well understood. In this study, which was based on two genome-wide transcriptomics screens, we identify MENA (ENAH, Mammalian enabled homologue) as a novel transcriptional target of the Wnt/β-catenin signalling pathway. We show that the expression of MENA is upregulated upon overexpression of degradation-resistant β-catenin. Promoters of all mammalian MENA homologues contain putative binding sites for Tcf4 transcription factor – the primary effector of the Wnt/β-catenin pathway and we demonstrate functionality of these Tcf4-binding sites using luciferase reporter assays and overexpression of β-catenin, Tcf4 and dominant-negative Tcf4. In addition, lithium chloride-mediated inhibition of GSK3β also resulted in increase in MENA mRNA levels. Chromatin immunoprecipitation showed direct interaction between β-catenin and MENA promoter in Huh7 and HEK293 cells and also in mouse brain and liver tissues. Moreover, overexpression of Wnt1 and Wnt3a ligands increased MENA mRNA levels. Additionally, knock-down of MENA ortholog in D. melanogaster eyeful and sensitized eye cancer fly models resulted in increased tumor and metastasis formations. In summary, our study identifies MENA as novel nexus for the Wnt/β-catenin and the Notch signalling cascades.

Complex changes in alternative pre-mRNA splicing play a central role in the epithelial-to-mesenchymal transition (EMT)

The epithelial-to-mesenchymal transition (EMT) is an important developmental process that is also implicated in disease pathophysiology, such as cancer progression and metastasis. A wealth of literature in recent years has identified important transcriptional regulators and large-scale changes in gene expression programs that drive the phenotypic changes that occur during the EMT. However, in the past couple of years it has become apparent that extensive changes in alternative splicing also play a profound role in shaping the changes in cell behavior that characterize the EMT. While long known splicing switches in FGFR2 and p120-catenin provided hints of a larger program of EMT-associated alternative splicing, the recent identification of the epithelial splicing regulatory proteins 1 and 2 (ESRP1 and ESRP2) began to reveal this genome-wide post-transcriptional network. Several studies have now demonstrated the truly vast extent of this alternative splicing program. The global switches in splicing associated with the EMT add an important additional layer of post-transcriptional control that works in harmony with transcriptional and epigenetic regulation to effect complex changes in cell shape, polarity, and behavior that mediate transitions between epithelial and mesenchymal cell states. Future challenges include the need to investigate the functional consequences of these splicing switches at both the individual gene as well as systems level.

Mena, a new available marker in tumors of salivary glands?

Mena (mammalian Ena) is an actin regulatory protein involved in cell motility and adhesion. Based on its potential role in malignant transformation revealed in other organs, we analyzed the Mena expression in normal salivary glands (SG) and salivary tumors. Mena expression was determined in normal SG (n=10) and also benign (n=20) and malignant (n=35) lesions of SG. For the immunohistochemical staining we used the anti-Mena antibody. All normal SG and the benign lesions (10 pleomorphic adenomas, 10 Warthin's tumors) were Mena negative. Salivary duct carcinomas (n=5), carcinomas in pleomorphic adenoma (n=5), acinic cell carcinomas (n=5), squamous cell carcinomas (n=10) and high-grade mucoepidermoid carcinomas (n=2) were positive. The lymphomas (n=5) and low-grade mucoepidermoid carcinomas (n=1) were Mena negative. In one case the lymphoblastic cells stained positive for Mena. Some of the endothelial cells, in the peritumoral vessels, were Mena positive. To the best of our knowledge, this is the first study in the literature about Mena expression in salivary tumors. Our study suggests that Mena protein seems to play a role in malignant transformation and its intensity is correlated with the type and grade of tumor and also with vascular invasion. Its positivity in endothelial cells may suggest its potential role in tumor angiogenesis.

Epithelial-mesenchymal transition: general principles and pathological relevance with special emphasis on the role of matrix metalloproteinases

Epithelial-mesenchymal transition (EMT) is a physiological process in which epithelial cells acquire the motile and invasive characteristics of mesenchymal cells. Although EMT in embryonic development is a coordinated, organized process involving interaction between many different cells and tissue types, aspects of the EMT program can be inappropriately activated in response to microenvironmental alterations and aberrant stimuli, and this can contribute to disease conditions including tissue fibrosis and cancer progression. Here we will outline how EMT functions in normal development, how it could be activated in pathologic conditions-especially by matrix metalloproteinases-and how it may be targeted for therapeutic benefit.

An EMT-driven alternative splicing program occurs in human breast cancer and modulates cellular phenotype

Epithelial-mesenchymal transition (EMT), a mechanism important for embryonic development, plays a critical role during malignant transformation. While much is known about transcriptional regulation of EMT, alternative splicing of several genes has also been correlated with EMT progression, but the extent of splicing changes and their contributions to the morphological conversion accompanying EMT have not been investigated comprehensively. Using an established cell culture model and RNA–Seq analyses, we determined an alternative splicing signature for EMT. Genes encoding key drivers of EMT–dependent changes in cell phenotype, such as actin cytoskeleton remodeling, regulation of cell–cell junction formation, and regulation of cell migration, were enriched among EMT–associated alternatively splicing events. Our analysis suggested that most EMT–associated alternative splicing events are regulated by one or more members of the RBFOX, MBNL, CELF, hnRNP, or ESRP classes of splicing factors. The EMT alternative splicing signature was confirmed in human breast cancer cell lines, which could be classified into basal and luminal subtypes based exclusively on their EMT–associated splicing pattern. Expression of EMT–associated alternative mRNA transcripts was also observed in primary breast cancer samples, indicating that EMT–dependent splicing changes occur commonly in human tumors. The functional significance of EMT–associated alternative splicing was tested by expression of the epithelial-specific splicing factor ESRP1 or by depletion of RBFOX2 in mesenchymal cells, both of which elicited significant changes in cell morphology and motility towards an epithelial phenotype, suggesting that splicing regulation alone can drive critical aspects of EMT–associated phenotypic changes. The molecular description obtained here may aid in the development of new diagnostic and prognostic markers for analysis of breast cancer progression.

Epithelial-to-mesenchymal transition (EMT) is the process by which cancer cells lose their epithelial characteristics and obtain a mesenchymal phenotype that is thought to allow them to migrate away from the primary tumor. A better understanding of how EMT is controlled would be valuable in predicting the likelihood of metastasis and in designing targeted therapies to block metastatic progression. While there have been many studies on the contribution of changes in gene expression to EMT, much less is known regarding the role of alternative splicing of mRNA during EMT. Alternative splicing can produce different protein isoforms from the same gene that often have distinct activities and functions. Here, we used a recently developed method to characterize changes in alternative splicing during EMT and found that thousands of multi-exon genes underwent alternative splicing. Alternative isoform expression was confirmed in human breast cancer cell lines and in primary human breast cancer samples, indicating that EMT–dependent splicing changes occur commonly in human tumors. Since EMT is considered an early step in metastatic progression, novel markers of EMT that we identified in human breast cancer samples might become valuable prognostic and diagnostic tools if confirmed in a larger cohort of patients.

Mena invasive (Mena(INV)) and Mena11a isoforms play distinct roles in breast cancer cell cohesion and association with TMEM

Mena, an actin regulatory protein, functions at the convergence of motility pathways that drive breast cancer cell invasion and migration in vivo. The tumor microenvironment spontaneously induces both increased expression of the Mena invasive (Mena(INV)) and decreased expression of Mena11a isoforms in invasive and migratory tumor cells. Tumor cells with this Mena expression pattern participate with macrophages in migration and intravasation in mouse mammary tumors in vivo. Consistent with these findings, anatomical sites containing tumor cells with high levels of Mena expression associated with perivascular macrophages were identified in human invasive ductal breast carcinomas and called TMEM. The number of TMEM sites positively correlated with the development of distant metastasis in humans. Here we demonstrate that mouse mammary tumors generated from EGFP-Mena(INV) expressing tumor cells are significantly less cohesive and have discontinuous cell-cell contacts compared to Mena11a xenografts. Using the mouse PyMT model we show that metastatic mammary tumors express 8.7 fold more total Mena and 7.5 fold more Mena(INV) mRNA than early non-metastatic ones. Furthermore, Mena(INV) expression in fine needle aspiration biopsy (FNA) samples of human invasive ductal carcinomas correlate with TMEM score while Mena11a does not. These results suggest that Mena(INV) is the isoform associated with breast cancer cell discohesion, invasion and intravasation in mice and in humans. They also imply that Mena(INV) expression and TMEM score measure related aspects of a common tumor cell dissemination mechanism and provide new insight into metastatic risk.

Mena invasive (MenaINV) promotes multicellular streaming motility and transendothelial migration in a mouse model of breast cancer

We have shown previously that distinct Mena isoforms are expressed in invasive and migratory tumor cells in vivo and that the invasion isoform (Mena(INV)) potentiates carcinoma cell metastasis in murine models of breast cancer. However, the specific step of metastatic progression affected by this isoform and the effects on metastasis of the Mena11a isoform, expressed in primary tumor cells, are largely unknown. Here, we provide evidence that elevated Mena(INV) increases coordinated streaming motility, and enhances transendothelial migration and intravasation of tumor cells. We demonstrate that promotion of these early stages of metastasis by Mena(INV) is dependent on a macrophage-tumor cell paracrine loop. Our studies also show that increased Mena11a expression correlates with decreased expression of colony-stimulating factor 1 and a dramatically decreased ability to participate in paracrine-mediated invasion and intravasation. Our results illustrate the importance of paracrine-mediated cell streaming and intravasation on tumor cell dissemination, and demonstrate that the relative abundance of Mena(INV) and Mena11a helps to regulate these key stages of metastatic progression in breast cancer cells.

The cooperation between hMena overexpression and HER2 signalling in breast cancer

hMena and the epithelial specific isoform hMena^11a are actin cytoskeleton regulatory proteins belonging to the Ena/VASP family. EGF treatment of breast cancer cell lines upregulates hMena/hMena^11a expression and phosphorylates hMena^11a, suggesting cross-talk between the ErbB receptor family and hMena/hMena^11a in breast cancer. The aim of this study was to determine whether the hMena/hMena^11a overexpression cooperates with HER-2 signalling, thereby affecting the HER2 mitogenic activity in breast cancer. In a cohort of breast cancer tissue samples a significant correlation among hMena, HER2 overexpression, the proliferation index (high Ki67), and phosphorylated MAPK and AKT was found and among the molecular subtypes the highest frequency of hMena overexpressing tumors was found in the HER2 subtype. From a clinical viewpoint, concomitant overexpression of HER2 and hMena identifies a subgroup of breast cancer patients showing the worst prognosis, indicating that hMena overexpression adds prognostic information to HER2 overexpressing tumors. To identify a functional link between HER2 and hMena, we show here that HER2 transfection in MCF7 cells increased hMena/hMena^11a expression and hMena^11a phosphorylation. On the other hand, hMena/hMena^11a knock-down reduced HER3, AKT and p44/42 MAPK phosphorylation and inhibited the EGF and NRG1-dependent HER2 phosphorylation and cell proliferation. Of functional significance, hMena/hMena^11a knock-down reduced the mitogenic activity of EGF and NRG1. Collectively these data provide new insights into the relevance of hMena and hMena^11a as downstream effectors of the ErbB receptor family which may represent a novel prognostic indicator in breast cancer progression, helping to stratify patients.