A tight junction-associated Merlin-angiomotin complex mediates Merlin's regulation of mitogenic signaling and tumor suppressive functions

Genome-wide gene expression array identifies novel genes related to disease severity and excessive daytime sleepiness in patients with obstructive sleep apnea

We aimed to identify novel molecular associations between chronic intermittent hypoxia with re-oxygenation and adverse consequences in obstructive sleep apnea (OSA). We analyzed gene expression profiles of peripheral blood mononuclear cells from 48 patients with sleep-disordered breathing stratified into four groups: primary snoring (PS), moderate to severe OSA (MSO), very severe OSA (VSO), and very severe OSA patients on long-term continuous positive airway pressure treatment (VSOC). Comparisons of the microarray gene expression data identified eight genes up-regulated with OSA and down-regulated with CPAP treatment, and five genes down-regulated with OSA and up-regulated with CPAP treatment. Protein expression levels of two genes related to endothelial tight junction (AMOT P130, and PLEKHH3), and three genes related to anti-or pro-apoptosis (BIRC3, ADAR1 P150, and LGALS3) were all increased in the VSO group, while AMOT P130 was further increased, and PLEKHH3, BIRC3, and ADAR1 P150 were all decreased in the VSOC group. Subgroup analyses revealed that AMOT P130 protein expression was increased in OSA patients with excessive daytime sleepiness, BIRC3 protein expression was decreased in OSA patients with hypertension, and LGALS3 protein expression was increased in OSA patients with chronic kidney disease. In vitro short-term intermittent hypoxia with re-oxygenation experiment showed immediate over-expression of ADAR1 P150. In conclusion, we identified a novel association between AMOT/PLEKHH3/BIRC3/ADAR1/LGALS3 over-expressions and high severity index in OSA patients. AMOT and GALIG may constitute an important determinant for the development of hypersomnia and kidney injury, respectively, while BIRC3 may play a protective role in the development of hypertension.

Regulation of localization and function of the transcriptional co-activator YAP by angiomotin

The Hippo-YAP pathway is a central regulator of cell contact inhibition, proliferation and death. There are conflicting reports regarding the role of Angiomotin (Amot) in regulating this pathway. While some studies suggest a YAP-inhibitory function other studies indicate Amot is required for YAP activity. Here, we describe an Amot-dependent complex comprised of Amot, YAP and Merlin. The phosphorylation of Amot at Serine 176 shifts localization of this complex to the plasma membrane, where it associates with the tight-junction proteins Pals1/PATJ and E-cadherin. Conversely, hypophosphorylated Amot shifts localization of the complex to the nucleus, where it facilitates the association of YAP and TEAD, induces transcriptional activation of YAP target genes and promotes YAP-dependent cell proliferation. We propose that phosphorylation of Amot^S176 is a critical post-translational modification that suppresses YAP’s ability to promote cell proliferation and tumorigenesis by altering the subcellular localization of an essential YAP co-factor.

DOI:http://dx.doi.org/10.7554/eLife.23966.001

Cells in animals and other multi-cellular organisms need to know when and where they should grow and divide. Individual cells communicate with their surrounding environment and each other via signaling pathways such as the Hippo-YAP pathway, which stimulates cells to grow and therefore influences the size of organs. When the Hippo part of the pathway is active it causes a protein known as YAP to move out of a compartment in the cell called the nucleus. Inside the nucleus, YAP helps to activate genes that promote cell growth. If the Hippo pathway can no longer respond to cues from the environment, YAP becomes over-active and can contribute to the development of various cancers. Therefore researchers are trying to better understand how it is regulated.

Many signals both from inside and outside the cell influence YAP activity. For example, some signals block YAP from entering the nucleus, whereas others cause YAP to be broken down entirely. Several studies have recently identified a signal protein called angiomotin as a regulator of YAP. However, the studies provide conflicting reports as to whether angiomotin promotes or inhibits cell growth.

Like many other proteins, angiomotin can be tagged with a small molecule called a phosphate group that can alter its activity. Moleirinho, Hoxha et al. studied human cells containing versions of angiomotin that mimic different forms of the protein with or without the phosphate. The experiments indicate that when a phosphate is attached at a particular position (known as serine 176), angiomotin predominantly interacts with YAP and another protein called Merlin at the cell surface. On the other hand, when angiomotin does not have a phosphate attached to it, all three proteins can move into the nucleus, where YAP is able to activate genes and promote cell growth.

Overall, these findings indicate that adding a phosphate group to angiomotin can act as a switch to regulate where in the cell it and YAP are found and thus, whether YAP is active. Future experiments will investigate which enzymes add the phosphate group to serine 176, and when they are able to do so.

DOI:http://dx.doi.org/10.7554/eLife.23966.002

Clinical Benefit in Response to Palbociclib Treatment in Refractory Uterine Leiomyosarcomas with a Common CDKN2A Alteration

BACKGROUND

Uterine leiomyosarcoma (uLMS) responds poorly to conventional chemotherapeutic agents, and personalized therapies have yet to be systematically explored. Comprehensive genomic profiling (CGP) can identify therapeutic targets and provide insight into the biology of this highly aggressive tumor. We report a case of uLMS treated with the CGP-matched therapy palbociclib, a CDK4/6 inhibitor, with sustained clinical benefit in this rare and deadly malignancy.

MATERIALS AND METHODS

This study analyzed 279 clinically advanced/recurrent uLMS samples. Median patient age was 54 years (range, 23-83 years). DNA was extracted from 40 µm of formalin-fixed, paraffin-embedded sections, and CGP was performed on hybridization-captured, adaptor ligation-based libraries for up to 405 cancer-related genes plus introns from up to 31 genes frequently rearranged in cancer. Sequencing data were analyzed for base pair substitutions, insertions/deletions, copy number alterations, and rearrangements.

RESULTS

CGP shows that 97.1% of uLMS harbor at least one alteration, and approximately 57% harbor alterations in one or more therapeutically targetable pathways. CDKN2A mutations that inactivate p16INK4a were identified in 11% of uLMS. We report the first demonstration of clinical benefit in response to palbociclib treatment for a uLMS patient with a CDKN2A mutation, resulting in disease stabilization and significant symptom reduction.

CONCLUSION

A patient with uLMS harboring a CDKN2A mutation experienced clinical benefit from treatment with palbociclib, and genomic analysis of 279 uLMS samples revealed that 19% of patients had mutations affecting the cyclin-dependent kinase (CDK) pathway. These observations provide a rationale for a clinical trial investigating treatment with CDK pathway inhibitors for uLMS harboring relevant genomic alterations. The Oncologist 2017;22:416-421Implications for Practice: Comprehensive genomic profiling (CGP) of individuals with uterine leiomyosarcoma (uLMS) indicates that nearly 20% of patients may harbor a mutation affecting the cyclin-dependent kinase (CDK) pathway. The case presented demonstrates that a CDK inhibitory drug may provide clinical benefit to such individuals. Given the lack of curative therapies for uLMS, CGP could be performed on all cases of advanced uLMS and a CDK inhibitor could be recommended (preferably as part of a clinical trial) for individuals harboring a mutation in the CDK pathway.

Hippo Signaling in the Liver Regulates Organ Size, Cell Fate, and Carcinogenesis

The Hippo signaling pathway, also known as the Salvador-Warts-Hippo pathway, is a regulator of organ size. The pathway takes its name from the Drosophila protein kinase, Hippo (STK4/MST1 and STK3/MST2 in mammals), which, when inactivated, leads to considerable tissue overgrowth. In mammals, MST1 and MST2 negatively regulate the transcriptional co-activators yes-associated protein 1 and WW domain containing transcription regulator 1 (WWTR1/TAZ), which together regulate expression of genes that control proliferation, survival, and differentiation. Yes-associated protein 1 and TAZ activation have been associated with liver development, regeneration, and tumorigenesis. How their activity is dynamically regulated in these contexts is just beginning to be elucidated. We review the mechanisms of Hippo signaling in the liver and explore outstanding questions for future research.

Molecular targets of developmental exposure to bisphenol A in diabesity: a focus on endoderm-derived organs

Several studies associate foetal human exposure to bisphenol A (BPA) to metabolic/endocrine diseases, mainly diabesity. They describe the role of BPA in the disruption of pancreatic beta cell, adipocyte and hepatocyte functions. Indeed, the complexity of the diabesity phenotype is due to the involvement of different endoderm-derived organs, all targets of BPA. Here, we analyse this point delineating a picture of different mechanisms of BPA toxicity in endoderm-derived organs leading to diabesity. Moving from epidemiological data, we summarize the in vivo experimental data of the BPA effects on endoderm-derived organs (thyroid, pancreas, liver, gut, prostate and lung) after prenatal exposure. Mainly, we gather molecular data evidencing harmful effects at low-dose exposure, pointing to the risk to human health. Although the fragmentation of molecular data does not allow a clear conclusion to be drawn, the present work indicates that the developmental exposure to BPA represents a risk for endoderm-derived organs development as it deregulates the gene expression from the earliest developmental stages. A more systematic analysis of BPA impact on the transcriptomes of endoderm-derived organs is still missing. Here, we suggest in vitro toxicogenomics approaches as a tool for the identification of common mechanisms of BPA toxicity leading to the diabesity in organs having the same developmental origin.

Rac1-Mediated DNA Damage and Inflammation Promote Nf2 Tumorigenesis but Also Limit Cell-Cycle Progression

Merlin encoded by the Nf2 gene is a bona fide tumor suppressor that has been implicated in regulation of both the Hippo-Yap and Rac1-Pak1 pathways. Using genetically engineered murine liver models, we show that co-deletion of Rac1 with Nf2 blocks tumor initiation but paradoxically exacerbates hepatomegaly induced by Nf2 loss, which can be suppressed either by treatment with pro-oxidants or by co-deletion of Yap. Our results suggest that while Yap acts as the central driver of proliferation during Nf2 tumorigenesis, Rac1 primarily functions as an inflammation switch by inducing reactive oxygen species that, on one hand, induce nuclear factor κB signaling and expression of inflammatory cytokines, and on the other activate p53 checkpoint and senescence programs dampening the cyclin D1-pRb-E2F1 pathway. Interestingly, senescence markers are associated with benign NF2 tumors but not with malignant NF2 mutant mesotheliomas, suggesting that senescence may underlie the benign nature of most NF2 tumors.

AMOTL1 Promotes Breast Cancer Progression and Is Antagonized by Merlin

The Hippo signaling network is a key regulator of cell fate. In the recent years, it was shown that its implication in cancer goes well beyond the sole role of YAP transcriptional activity and its regulation by the canonical MST/LATS kinase cascade. Here we show that the motin family member AMOTL1 is an important effector of Hippo signaling in breast cancer. AMOTL1 connects Hippo signaling to tumor cell aggressiveness. We show that both canonical and noncanonical Hippo signaling modulates AMOTL1 levels. The tumor suppressor Merlin triggers AMOTL1 proteasomal degradation mediated by the NEDD family of ubiquitin ligases through direct interaction. In parallel, YAP stimulates AMOTL1 expression. The loss of Merlin expression and the induction of Yap activity that are frequently observed in breast cancers thus result in elevated AMOTL1 levels. AMOTL1 expression is sufficient to trigger tumor cell migration and stimulates proliferation by activating c-Src. In a large cohort of human breast tumors, we show that AMOTL1 protein levels are upregulated during cancer progression and that, importantly, the expression of AMOTL1 in lymph node metastasis appears predictive of the risk of relapse. Hence we uncover an important mechanism by which Hippo signaling promotes breast cancer progression by modulating the expression of AMOTL1.

Targeting the Hippo Signaling Pathway for Tissue Regeneration and Cancer Therapy

The Hippo signaling pathway is a highly-conserved developmental pathway that plays an essential role in organ size control, tumor suppression, tissue regeneration and stem cell self-renewal. The YES-associated protein (YAP) and the transcriptional co-activator with PDZ-binding motif (TAZ) are two important transcriptional co-activators that are negatively regulated by the Hippo signaling pathway. By binding to transcription factors, especially the TEA domain transcription factors (TEADs), YAP and TAZ induce the expression of growth-promoting genes, which can promote organ regeneration after injury. Therefore, controlled activation of YAP and TAZ can be useful for regenerative medicine. However, aberrant activation of YAP and TAZ due to deregulation of the Hippo pathway or overexpression of YAP/TAZ and TEADs can promote cancer development. Hence, pharmacological inhibition of YAP and TAZ may be a useful approach to treat tumors with high YAP and/or TAZ activity. In this review, we present the mechanisms regulating the Hippo pathway, the role of the Hippo pathway in tissue repair and cancer, as well as a detailed analysis of the different strategies to target the Hippo signaling pathway and the genes regulated by YAP and TAZ for regenerative medicine and cancer therapy.

The RNF146 and tankyrase pathway maintains the junctional Crumbs complex through regulation of angiomotin

The Crumbs complex is an important determinant of epithelial apical-basal polarity that functions in regulation of tight junctions, resistance to epithelial-to-mesenchymal transitions and as a tumour suppressor. Although the functional role of the Crumbs complex is being elucidated, its regulation is poorly understood. Here, we show that suppression of RNF146, an E3 ubiquitin ligase that recognizes ADP-ribosylated substrates, and tankyrase, a poly(ADP-ribose) polymerase, disrupts the junctional Crumbs complex and disturbs the function of tight junctions. We show that RNF146 binds a number of polarity-associated proteins, in particular members of the angiomotin (AMOT) family. Accordingly, AMOT proteins are ADP-ribosylated by TNKS2, which drives ubiquitylation by RNF146 and subsequent degradation. Ablation of RNF146 or tankyrase, as well as overexpression of AMOT, led to the relocation of PALS1 (a Crumbs complex component) from the apical membrane to internal puncta, a phenotype that is rescued by AMOTL2 knockdown. We thus reveal a new function of RNF146 and tankyrase in stabilizing the Crumbs complex through downregulation of AMOT proteins at the apical membrane.

The endothelial E3 ligase HECW2 promotes endothelial cell junctions by increasing AMOTL1 protein stability via K63-linked ubiquitination

Cell-to-cell junctions are critical for the formation of endothelial barriers, and its disorganization is required for sprouting angiogenesis. Members of the angiomotin (AMOT) family have emerged as key regulators in the control of endothelial cell (EC) junction stability and permeability. However, the underlying mechanism by which the AMOT family is regulated in ECs remains unclear. Here we report that HECW2, a novel EC ubiquitin E3 ligase, plays a critical role in stabilizing endothelial cell-to-cell junctions by regulating AMOT-like 1 (AMOTL1) stability. HECW2 physically interacts with AMOTL1 and enhances its stability via lysine 63-linked ubiquitination. HECW2 depletion in human ECs decreases AMOTL1 stability, loosening the cell-to-cell junctions and altering subcellular localization of yes-associated protein (YAP) from cytoplasm into the nucleus. Knockdown of HECW2 also results in increased angiogenic sprouting, and this effect is blocked by depletion of ANG-2, a potential target of YAP. These results demonstrate that HECW2 is a novel regulator of angiogenesis and provide new insights into the mechanisms coordinating junction stability and angiogenic activation in ECs.

Angiomotin like-1 is a novel component of the N-cadherin complex affecting endothelial/pericyte interaction in normal and tumor angiogenesis

Transmission of mechanical force via cell junctions is an important component that molds cells into shapes consistent with proper organ function. Of particular interest are the cadherin transmembrane proteins, which play an essential role in connecting cell junctions to the intra-cellular cytoskeleton. Understanding how these biomechanical complexes orchestrate intrinsic and extrinsic forces is important for our understanding of the underlying mechanisms driving morphogenesis. We have previously identified the Amot protein family, which are scaffold proteins that integrate polarity, junctional, and cytoskeletal cues to modulate cellular shape in endothelial as well as epithelial cells. In this report, we show that AmotL1 is a novel partner of the N-cadherin protein complex. We studied the role of AmotL1 in normal retinal as well as tumor angiogenesis using inducible endothelial-specific knock-out mice. We show that AmotL1 is essential for normal establishment of vascular networks in the post-natal mouse retina as well as in a transgenic breast cancer model. The observed phenotypes were consistent with a non-autonomous pericyte defect. We show that AmotL1 forms a complex with N-cadherin present on both endothelial cells and pericytes. We propose that AmotL1 is an essential effector of the N-cadherin mediated endothelial/pericyte junctional complex.

NF2 Activates Hippo Signaling and Promotes Ischemia/Reperfusion Injury in the Heart

RATIONALE

NF2 (neurofibromin 2) is an established tumor suppressor that promotes apoptosis and inhibits growth in a variety of cell types, yet its function in cardiomyocytes remains largely unknown.

OBJECTIVE

We sought to determine the role of NF2 in cardiomyocyte apoptosis and ischemia/reperfusion (I/R) injury in the heart.

METHODS AND RESULTS

We investigated the function of NF2 in isolated cardiomyocytes and mouse myocardium at baseline and in response to oxidative stress. NF2 was activated in cardiomyocytes subjected to H2O2 and in murine hearts subjected to I/R. Increased NF2 expression promoted the activation of Mst1 (mammalian sterile 20-like kinase 1) and the inhibition of Yap (Yes-associated protein), whereas knockdown of NF2 attenuated these responses after oxidative stress. NF2 increased the apoptosis of cardiomyocytes that appeared dependent on Mst1 activity. Mice deficient for NF2 in cardiomyocytes, NF2 cardiomyocyte-specific knockout (CKO), were protected against global I/R ex vivo and showed improved cardiac functional recovery. Moreover, NF2 cardiomyocyte-specific knockout mice were protected against I/R injury in vivo and showed the upregulation of Yap target gene expression. Mechanistically, we observed nuclear association between NF2 and its activator MYPT-1 (myosin phosphatase target subunit 1) in cardiomyocytes, and a subpopulation of stress-induced nuclear Mst1 was diminished in NF2 CKO hearts. Finally, mice deficient for both NF2 and Yap failed to show protection against I/R indicating that Yap is an important target of NF2 in the adult heart.

CONCLUSIONS

NF2 is activated by oxidative stress in cardiomyocytes and mouse myocardium and facilitates apoptosis. NF2 promotes I/R injury through the activation of Mst1 and inhibition of Yap, thereby regulating Hippo signaling in the adult heart.

Tight junctions: from simple barriers to multifunctional molecular gates

Epithelia and endothelia separate different tissue compartments and protect multicellular organisms from the outside world. This requires the formation of tight junctions, selective gates that control paracellular diffusion of ions and solutes. Tight junctions also form the border between the apical and basolateral plasma-membrane domains and are linked to the machinery that controls apicobasal polarization. Additionally, signalling networks that guide diverse cell behaviours and functions are connected to tight junctions, transmitting information to and from the cytoskeleton, nucleus and different cell adhesion complexes. Recent advances have broadened our understanding of the molecular architecture and cellular functions of tight junctions.

Cellular Organization and Cytoskeletal Regulation of the Hippo Signaling Network

The Hippo signaling network integrates diverse upstream signals to control cell fate decisions and regulate organ growth. Recent studies have provided new insights into the cellular organization of Hippo signaling, its relationship to cell-cell junctions, and how the cytoskeleton modulates Hippo signaling. Cell-cell junctions serve as platforms for Hippo signaling by localizing scaffolding proteins that interact with core components of the pathway. Interactions of Hippo pathway components with cell-cell junctions and the cytoskeleton also suggest potential mechanisms for the regulation of the pathway by cell contact and cell polarity. As our understanding of the complexity of Hippo signaling increases, a future challenge will be to understand how the diverse inputs into the pathway are integrated and to define their respective contributions in vivo.

Arhgap17, a RhoGTPase activating protein, regulates mucosal and epithelial barrier function in the mouse colon

Coordinated regulation of the actin cytoskeleton by the Rho GTPase family is required for the maintenance of polarity in epithelial cells as well as for their proliferation and migration. A RhoGTPase-activating protein 17 (Arhgap17) is known to be involved in multiple cellular processes in vitro, including the maintenance of tight junctions and vesicle trafficking. However, the function of Arhgap17 has not been studied in the physiological context. Here, we generated Arhgap17-deficient mice and examined the effect in the epithelial and mucosal barriers of the intestine. Reporter staining revealed that Arhgap17 expression is limited to the luminal epithelium of intestine. Arhgap17-deficient mice show an increased paracellular permeability and aberrant localization of the apical junction complex in the luminal epithelium, but do not develop spontaneous colitis. The inner mucus layer is impervious to the enteric bacteria irrespective of Tff3 downregulation in the Arhgap17-deficient mice. Interestingly however, treatment with dextran sulfate sodium (DSS) causes an increased accumulation of DSS and TNF production in intraluminal cells and rapid destruction of the inner mucus layer, resulting in increased severity of colitis in mutant mice. Overall, these data reveal that Arhgap17 has a novel function in regulating transcellular transport and maintaining integrity of intestinal barriers.

YAP Mediates Tumorigenesis in Neurofibromatosis Type 2 by Promoting Cell Survival and Proliferation through a COX-2-EGFR Signaling Axis

The Hippo-YAP pathway has emerged as a major driver of tumorigenesis in many human cancers. YAP is a transcriptional coactivator and while details of YAP regulation are quickly emerging, it remains unknown what downstream targets are critical for the oncogenic functions of YAP. To determine the mechanisms involved and to identify disease-relevant targets, we examined the role of YAP in neurofibromatosis type 2 (NF2) using cell and animal models. We found that YAP function is required for NF2-null Schwann cell survival, proliferation, and tumor growth in vivo Moreover, YAP promotes transcription of several targets including PTGS2, which codes for COX-2, a key enzyme in prostaglandin biosynthesis, and AREG, which codes for the EGFR ligand, amphiregulin. Both AREG and prostaglandin E2 converge to activate signaling through EGFR. Importantly, treatment with the COX-2 inhibitor celecoxib significantly inhibited the growth of NF2-null Schwann cells and tumor growth in a mouse model of NF2. Cancer Res; 76(12); 3507-19. ©2016 AACR.

Ezrin: a regulator of actin microfilaments in cell junctions of the rat testis

Ezrin, radixin, moesin and merlin (ERM) proteins are highly homologous actin-binding proteins that share extensive sequence similarity with each other. These proteins tether integral membrane proteins and their cytoplasmic peripheral proteins (e.g., adaptors, nonreceptor protein kinases and phosphatases) to the microfilaments of actin-based cytoskeleton. Thus, these proteins are crucial to confer integrity of the apical membrane domain and its associated junctional complex, namely the tight junction and the adherens junction. Since ectoplasmic specialization (ES) is an F-actin-rich testis-specific anchoring junction-a highly dynamic ultrastructure in the seminiferous epithelium due to continuous transport of germ cells, in particular spermatids, across the epithelium during the epithelial cycle-it is conceivable that ERM proteins are playing an active role in these events. Although these proteins were first reported almost 25 years and have since been extensively studied in multiple epithelia/endothelia, few reports are found in the literature to examine their role in the actin filament bundles at the ES. Studies have shown that ezrin is also a constituent protein of the actin-based tunneling nanotubes (TNT) also known as intercellular bridges, which are transient cytoplasmic tubular ultrastructures that transport signals, molecules and even organelles between adjacent and distant cells in an epithelium to coordinate cell events that occur across an epithelium. Herein, we critically evaluate recent data on ERM in light of recent findings in the field in particular ezrin regarding its role in actin dynamics at the ES in the testis, illustrating additional studies are warranted to examine its physiological significance in spermatogenesis.

Merlin/NF2-Lin28B-let-7 Is a Tumor-Suppressive Pathway that Is Cell-Density Dependent and Hippo Independent

Contact inhibition of proliferation is critical for tissue organization, and its dysregulation contributes to tumorigenesis. Merlin/NF2 is a tumor suppressor that governs contact inhibition. Although Merlin/NF2 inhibits YAP1 and TAZ, which are paralogous Hippo pathway transcriptional co-activators and oncoproteins, it is not fully understood how Merlin/NF2-mediated signal transduction triggered by cell-cell contact exerts tumor suppression. Here, we identify Lin28B, an inhibitor of let-7 microRNAs (miRNAs), as an important downstream target of Merlin/NF2. Functional studies revealed that, at low cell density, Merlin/NF2 is phosphorylated and does not bind to Lin28B, allowing Lin28B to enter the nucleus, bind to pri-let-7 miRNAs, and inhibit their maturation in a YAP1/TAZ-independent manner. This inhibition of pri-let-7 maturation then promotes cell growth. However, cell-cell contact triggers Merlin/NF2 dephosphorylation, which sequesters Lin28B in the cytoplasm and permits pri-let-7 maturation. Our results reveal that Merlin/NF2-mediated signaling drives a tumor-suppressive pathway that is cell-density dependent and Hippo independent.

Neurofibromatosis as a gateway to better treatment for a variety of malignancies

The neurofibromatoses (NF) are a group of rare genetic disorders that can affect all races equally at an incidence from 1:3000 (NF1) to a log unit lower for NF2 and schwannomatosis. Since the research community is reporting an increasing number of malignant cancers that carry mutations in the NF genes, the general interest of both the research and pharma community is increasing and the authors saw an opportunity to present a novel, fresh approach to drug discovery in NF. The aim of the paper is to challenge the current drug discovery approach to NF, whereby existing targeted therapies that are either in the clinic or on the market for other disease indications are repurposed for NF. We offer a suggestion for an alternative drug discovery approach. In the new approach, selective and tolerable targeted therapies would be developed for NF and later expanded to patients with more complex diseases such as malignant cancer in which the NF downstream pathways are deregulated. The Children's Tumor Foundation, together with some other major NF funders, is playing a key role in funding critical initiatives that will accelerate the development of better targeted therapies for NF patients, while these novel, innovative treatments could potentially be beneficial to molecularly characterized cancer patients in which NF mutations have been identified.

Role of Merlin/NF2 inactivation in tumor biology

Merlin (Moesin-ezrin-radixin-like protein, also known as schwannomin) is a tumor suppressor protein encoded by the neurofibromatosis type 2 gene NF2. Loss of function mutations or deletions in NF2 cause neurofibromatosis type 2 (NF2), a multiple tumor forming disease of the nervous system. NF2 is characterized by the development of bilateral vestibular schwannomas. Patients with NF2 can also develop schwannomas on other cranial and peripheral nerves, as well as meningiomas and ependymomas. The only potential treatment is surgery/radiosurgery, which often results in loss of function of the involved nerve. There is an urgent need for chemotherapies that slow or eliminate tumors and prevent their formation in NF2 patients. Interestingly NF2 mutations and merlin inactivation also occur in spontaneous schwannomas and meningiomas, as well as other types of cancer including mesothelioma, glioma multiforme, breast, colorectal, skin, clear cell renal cell carcinoma, hepatic and prostate cancer. Except for malignant mesotheliomas, the role of NF2 mutation or inactivation has not received much attention in cancer, and NF2 might be relevant for prognosis and future chemotherapeutic approaches. This review discusses the influence of merlin loss of function in NF2-related tumors and common human cancers. We also discuss the NF2 gene status and merlin signaling pathways affected in the different tumor types and the molecular mechanisms that lead to tumorigenesis, progression and pharmacological resistance.

MicroRNA-497 inhibits cell proliferation, migration, and invasion by targeting AMOT in human osteosarcoma cells

MicroRNAs (miRNAs) have a role in the development and progression of human malignancy. The expression of miR-497 is decreased in malignant tumors, which suggests a role for miR-497 as a tumor suppressor. Angiomotin is encoded by the AMOT gene, which is a target for miR-497. Angiomotin has a role in angiogenesis, cell proliferation, and invasion in human malignancies, including osteosarcoma. However, the role of miR-497 in human osteosarcoma is unknown. This preliminary study included human osteosarcoma tissues and normal tissues from 20 patients, the osteosarcoma cell lines, MG-63, SAOS-2, U-2 OS, and the human osteoblast cell line hFOB (OB3). Western blots for angiomotin and quantitative real-time polymerase chain reaction for the expression of miR-497 and AMOT were performed. Knockdown studies were performed using RNA interference and transfection studies used miR-497 mimics. Quantitative cell migration assays were performed, and cell apoptosis was studied by flow cytometry. Osteosarcoma cells and cell lines showed reduced expression of miR-497 and increased expression of angiomotin. Transfection of osteosarcoma cells with miR-497 mimics suppressed the expression of angiomotin. Results from a dual-luciferase reporter system supported AMOT as a direct target gene of miR-497. Knockdown of AMOT using RNA interference resulted in inhibition of osteosarcoma cell proliferation, migration, and invasion. These preliminary studies support a role for miR-497 as a suppressor of AMOT gene expression in human osteosarcoma cells, resulting in suppression of tumor cell proliferation and invasion. Further studies are recommended to investigate the role of miR-497 in osteosarcoma and other malignant mesenchymal tumors.

Polarity and cell division orientation in the cleavage embryo: from worm to human

Cleavage is a period after fertilization, when a 1-cell embryo starts developing into a multicellular organism. Due to a series of mitotic divisions, the large volume of a fertilized egg is divided into numerous smaller, nucleated cells—blastomeres. Embryos of different phyla divide according to different patterns, but molecular mechanism of these early divisions remains surprisingly conserved. In the present paper, we describe how polarity cues, cytoskeleton and cell-to-cell communication interact with each other to regulate orientation of the early embryonic division planes in model animals such as Caenorhabditis elegans, Drosophila and mouse. We focus particularly on the Par pathway and the actin-driven cytoplasmic flows that accompany it. We also describe a unique interplay between Par proteins and the Hippo pathway in cleavage mammalian embryos. Moreover, we discuss the potential meaning of polarity, cytoplasmic dynamics and cell-to-cell communication as quality biomarkers of human embryos.

Role of Angiomotin-like 2 mono-ubiquitination on YAP inhibition

LATS1/2 (large tumor suppressor) kinases and the Angiomotin family proteins are potent inhibitors of the YAP (yes-associated protein) oncoprotein, but the underlying molecular mechanism is not fully understood. Here, we report for the first time that USP9X is a deubiquitinase of Angiomotin-like 2 (AMOTL2) and that AMOTL2 mono-ubiquitination is required for YAP inhibition. USP9X knockdown increased the LATS-mediated phosphorylation of YAP and decreased the transcriptional output of YAP. Conversely, over-expression of USP9X reactivated YAP in densely cultured cells. Both genetic and biochemical approaches identified AMOTL2 as a target of USP9X. AMOTL2 was found to be ubiquitinated at K347 and K408, which both reside in the protein's coiled-coil domain. The AMOTL2 K347/408R mutant, which cannot be ubiquitinated, was impaired in its ability to inhibit YAP. Furthermore, ubiquitinated AMOTL2 can bind to the UBA domain of LATS kinase, and this domain is required for the function of LATS. Our results provide novel insights into the activation mechanisms of core Hippo pathway components.

NF2 Loss Promotes Oncogenic RAS-Induced Thyroid Cancers via YAP-Dependent Transactivation of RAS Proteins and Sensitizes Them to MEK Inhibition

Ch22q LOH is preferentially associated with RAS mutations in papillary and in poorly differentiated thyroid cancer (PDTC). The 22q tumor suppressor NF2, encoding merlin, is implicated in this interaction because of its frequent loss of function in human thyroid cancer cell lines. Nf2 deletion or Hras mutation is insufficient for transformation, whereas their combined disruption leads to murine PDTC with increased MAPK signaling. Merlin loss induces RAS signaling in part through inactivation of Hippo, which activates a YAP-TEAD transcriptional program. We find that the three RAS genes are themselves YAP-TEAD1 transcriptional targets, providing a novel mechanism of promotion of RAS-induced tumorigenesis. Moreover, pharmacologic disruption of YAP-TEAD with verteporfin blocks RAS transcription and signaling and inhibits cell growth. The increased MAPK output generated by NF2 loss in RAS-mutant cancers may inform therapeutic strategies, as it generates greater dependency on the MAPK pathway for viability.

SIGNIFICANCE

Intensification of mutant RAS signaling through copy-number imbalances is commonly associated with transformation. We show that NF2/merlin inactivation augments mutant RAS signaling by promoting YAP/TEAD-driven transcription of oncogenic and wild-type RAS, resulting in greater MAPK output and increased sensitivity to MEK inhibitors.

Long non-coding RNA small nucleolar RNA host gene 12 (SNHG12) promotes cell proliferation and migration by upregulating angiomotin gene expression in human osteosarcoma cells

The long non-coding RNA (lncRNA) small nucleolar RNA host gene 12 (SNHG12) has a role in cell proliferation and migration. Angiomotin, encoded by the AMOT gene, is a protein that regulates the migration and organization of endothelial cells. SNHG12 and AMOT have been shown to play a role in a variety of human cancers but have yet to be studied in detail in human osteosarcoma. Tissue samples from primary osteosarcoma (n = 20) and adjacent normal tissues (n = 20), the osteosarcoma cell lines, SAOS-2, MG-63, U-2 OS, and the human osteoblast cell line hFOB (OB3) were studied using Western blot for angiomotin, and quantitative real-time polymerase chain reaction for the expression of SNHG12 and AMOT. The expression of SNHG12 was knocked down using RNA interference. Cell migration assays were performed. Cell apoptosis was studied using flow cytometry. SNHG12 and AMOT messenger RNA (mRNA) expression was upregulated in osteosarcoma tissues and cell lines when compared with normal tissues and cells. Upregulation of AMOT mRNA was associated with upregulation of SNHG12. Knockdown of SNHG12 reduced the expression of angiomotin in osteosarcoma cells and suppressed cell proliferation and migration but did not affect cell apoptosis. This preliminary study has shown that the lncRNA SNHG12 promotes cell proliferation and migration by upregulating AMOT gene expression in osteosarcoma cells in vivo and in vitro. Further studies are recommended to investigate the role of SNHG12 and AMOT expression in tumor cell proliferation and migration and angiogenesis in osteosarcoma and a range of malignant mesenchymal tumors.

Tankyrase Inhibitors Target YAP by Stabilizing Angiomotin Family Proteins

As the key effector in the Hippo pathway, YAP was identified as an oncoprotein whose expression is elevated in various human cancers. However, the development of potentially therapeutic compounds targeting YAP has been slow and limited. Here, we find that tankyrase inhibitors suppress YAP activity. This effect is mediated by anigomotin (AMOT) family proteins. Tankyrases associate with AMOT family proteins and promote their degradation through E3 ligase RNF146. By antagonizing tankyrase activity, tankyrase inhibitors stabilize AMOT family proteins, thereby suppressing YAP oncogenic functions. Together, our studies not only demonstrate the tankyrase-RNF146-AMOT axis as an upstream pathway regulating YAP but also reveal a therapeutic opportunity in targeting YAP for cancer treatment.

Epithelial junctions and Rho family GTPases: the zonular signalosome

The establishment and maintenance of epithelial cell-cell junctions is crucially important to regulate adhesion, apico-basal polarity and motility of epithelial cells, and ultimately controls the architecture and physiology of epithelial organs. Junctions are supported, shaped and regulated by cytoskeletal filaments, whose dynamic organization and contractility are finely tuned by GTPases of the Rho family, primarily RhoA, Rac1 and Cdc42. Recent research has identified new molecular mechanisms underlying the cross-talk between these GTPases and epithelial junctions. Here we briefly summarize the current knowledge about the organization, molecular evolution and cytoskeletal anchoring of cell-cell junctions, and we comment on the most recent advances in the characterization of the interactions between Rho GTPases and junctional proteins, and their consequences with regards to junction assembly and regulation of cell behavior in vertebrate model systems. The concept of “zonular signalosome” is proposed, which highlights the close functional relationship between proteins of zonular junctions (zonulae occludentes and adhaerentes) and the control of cytoskeletal organization and signaling through Rho GTPases, transcription factors, and their effectors.

Merlin Isoforms 1 and 2 Both Act as Tumour Suppressors and Are Required for Optimal Sperm Maturation

The tumour suppressor Merlin, encoded by the gene NF2, is frequently mutated in the autosomal dominant disorder neurofibromatosis type II, characterised primarily by the development of schwannoma and other glial cell tumours. However, NF2 is expressed in virtually all analysed human and rodent organs, and its deletion in mice causes early embryonic lethality. Additionally, NF2 encodes for two major isoforms of Merlin of unknown functionality. Specifically, the tumour suppressor potential of isoform 2 remains controversial. In this study, we used Nf2 isoform-specific knockout mouse models to analyse the function of each isoform during development and organ homeostasis. We found that both isoforms carry full tumour suppressor functionality and can completely compensate the loss of the other isoform during development and in most adult organs. Surprisingly, we discovered that spermatogenesis is strictly dependent on the presence of both isoforms. While the testis primarily expresses isoform 1, we noticed an enrichment of isoform 2 in spermatogonial stem cells. Deletion of either isoform was found to cause decreased sperm quality as observed by maturation defects and head/midpiece abnormalities. These defects led to impaired sperm functionality as assessed by decreased sperm capacitation. Thus, we describe spermatogenesis as a new Nf2-dependent process. Additionally, we provide for the first time in vivo evidence for equal tumour suppressor potentials of Merlin isoform 1 and isoform 2.

MicroRNA-205 inhibits the proliferation and invasion of breast cancer by regulating AMOT expression

It has been reported that the expression of angiomotin (AMOT) is upregulated in breast cancer. However, the regulatory mechanism remains unknown. In the present study, we aimed to ascertain whether the expression of AMOT is regulated by microRNAs (miRNAs) in breast cancer. In the present study, miR-205 was significantly downregulated in breast cancer samples and it was identified to directly target the 3'-untranslated region (3'-UTR) of AMOT in breast cancer MCF-7 cells by luciferase assay. miR-205 and small interfering RNA (siRNA)-mediated AMOT-knockdown experiments revealed that miR-205 significantly inhibited the proliferation and the invasion of MCF-7 cells through a decrease in the expression of AMOT, yet had no effect on apoptosis. Furthermore, we observed that the overexpression of AMOT partially reversed the inhibitory effect of miR-205 on the growth and the invasion of MCF-7 cells. The data indicated that miR-205 regulated the proliferation and the invasion of breast cancer cells through suppression of AMOT expression, at least partly. Therefore, the disordered decreased expression of miR-205 and the resulting AMOT upregulation contributes to breast carcinogenesis, and miR-205-AMOT represents a new potential therapeutic target for the treatment of breast carcinoma.

Developmental plasticity, cell fate specification and morphogenesis in the early mouse embryo

A critical point in mammalian development is when the early embryo implants into its mother's uterus. This event has historically been difficult to study due to the fact that it occurs within the maternal tissue and therefore is hidden from view. In this review, we discuss how the mouse embryo is prepared for implantation and the molecular mechanisms involved in directing and coordinating this crucial event. Prior to implantation, the cells of the embryo are specified as precursors of future embryonic and extra-embryonic lineages. These preimplantation cell fate decisions rely on a combination of factors including cell polarity, position and cell–cell signalling and are influenced by the heterogeneity between early embryo cells. At the point of implantation, signalling events between the embryo and mother, and between the embryonic and extraembryonic compartments of the embryo itself, orchestrate a total reorganization of the embryo, coupled with a burst of cell proliferation. New developments in embryo culture and imaging techniques have recently revealed the growth and morphogenesis of the embryo at the time of implantation, leading to a new model for the blastocyst to egg cylinder transition. In this model, pluripotent cells that will give rise to the fetus self-organize into a polarized three-dimensional rosette-like structure that initiates egg cylinder formation.

Angiomotin binding-induced activation of Merlin/NF2 in the Hippo pathway

The tumor suppressor Merlin/NF2 functions upstream of the core Hippo pathway kinases Lats1/2 and Mst1/2, as well as the nuclear E3 ubiquitin ligase CRL4(DCAF1). Numerous mutations of Merlin have been identified in Neurofibromatosis type 2 and other cancer patients. Despite more than two decades of research, the upstream regulator of Merlin in the Hippo pathway remains unknown. Here we show by high-resolution crystal structures that the Lats1/2-binding site on the Merlin FERM domain is physically blocked by Merlin's auto-inhibitory tail. Angiomotin binding releases the auto-inhibition and promotes Merlin's binding to Lats1/2. Phosphorylation of Ser518 outside the Merlin's auto-inhibitory tail does not obviously alter Merlin's conformation, but instead prevents angiomotin from binding and thus inhibits Hippo pathway kinase activation. Cancer-causing mutations clustered in the angiomotin-binding domain impair angiomotin-mediated Merlin activation. Our findings reveal that angiomotin and Merlin respectively interface cortical actin filaments and core kinases in Hippo signaling, and allow construction of a complete Hippo signaling pathway.

Rho GAPs and GEFs: controling switches in endothelial cell adhesion

Within blood vessels, endothelial cell–cell and cell–matrix adhesions are crucial to preserve barrier function, and these adhesions are tightly controlled during vascular development, angiogenesis, and transendothelial migration of inflammatory cells. Endothelial cellular signaling that occurs via the family of Rho GTPases coordinates these cell adhesion structures through cytoskeletal remodelling. In turn, Rho GTPases are regulated by GTPase-activating proteins (GAPs) and guanine nucleotide exchange factors (GEFs). To understand how endothelial cells initiate changes in the activity of Rho GTPases, and thereby regulate cell adhesion, we will discuss the role of Rho GAPs and GEFs in vascular biology. Many potentially important Rho regulators have not been studied in detail in endothelial cells. We therefore will first overview which GAPs and GEFs are highly expressed in endothelium, based on comparative gene expression analysis of human endothelial cells compared with other tissue cell types. Subsequently, we discuss the relevance of Rho GAPs and GEFs for endothelial cell adhesion in vascular homeostasis and disease.

Rich1 negatively regulates the epithelial cell cycle, proliferation and adhesion by CDC42/RAC1-PAK1-Erk1/2 pathway

Rich1, a previously identified Rho GTPase-activating protein (RhoGAP), was found to have close relationship with Rho GTPase family members in multiple cellular processes in nervous cells and platelets. But the exact role of Rich1 in epithelial cells remains obscure. The present investigation demonstrated that up-regulation of Rich1 could cause S-phase arrest, proliferation inhibition and adhesion decline with F-actin amount decrease in epithelial cells. Further exploration in hepatocyte HL7702 revealed that overexpression of Rich1 could greatly elevate the intrinsic GTPase activities on both of CDC42 and RAC1 by stimulating GTP hydrolysis, which consequently attenuated the activities of the Rho proteins and the phosphorylation level of those in PAK1-ERK1/2 signaling cascade. While the GAP domain deleted Rich1 variant or silence of endogenous Rich1 expression could not result in any of the biological effects. It is indicated that Rich1, completely different from in other types of cells, might act as a crucial upstream negative regulator via its GAP domain in control of epithelial cell cycle, proliferation and focal adhesion through CDC42/RAC1-PAK1-ERK1/2 signaling pathway and F-actin dynamics.

Position- and polarity-dependent Hippo signaling regulates cell fates in preimplantation mouse embryos

During the preimplantation stage, mouse embryos establish two cell lineages by the time of early blastocyst formation: the trophectoderm (TE) and the inner cell mass (ICM). Historical models have proposed that the establishment of these two lineages depends on the cell position within the embryo (e.g., the positional model) or cell polarization along the apicobasal axis (e.g., the polarity model). Recent findings have revealed that the Hippo signaling pathway plays a central role in the cell fate-specification process: active and inactive Hippo signaling in the inner and outer cells promote ICM and TE fates, respectively. Intercellular adhesion activates, while apicobasal polarization suppresses Hippo signaling, and a combination of these processes determines the spatially regulated activation of the Hippo pathway in 32-cell-stage embryos. Therefore, there is experimental evidence in favor of both positional and polarity models. At the molecular level, phosphorylation of the Hippo-pathway component angiomotin at adherens junctions (AJs) in the inner (apolar) cells activates the Lats protein kinase and triggers Hippo signaling. In the outer cells, however, cell polarization sequesters Amot from basolateral AJs and suppresses activation of the Hippo pathway. Other mechanisms, including asymmetric cell division and Notch signaling, also play important roles in the regulation of embryonic development. In this review, I discuss how these mechanisms cooperate with the Hippo signaling pathway during cell fate-specification processes.

Signalling at tight junctions during epithelial differentiation and microbial pathogenesis

Tight junctions are a component of the epithelial junctional complex, and they form the paracellular diffusion barrier that enables epithelial cells to create cellular sheets that separate compartments with different compositions. The assembly and function of tight junctions are intimately linked to the actomyosin cytoskeleton and, hence, are under the control of signalling mechanisms that regulate cytoskeletal dynamics. Tight junctions not only receive signals that guide their assembly and function, but transmit information to the cell interior to regulate cell proliferation, migration and survival. As a crucial component of the epithelial barrier, they are often targeted by pathogenic viruses and bacteria, aiding infection and the development of disease. In this Commentary, we review recent progress in the understanding of the molecular signalling mechanisms that drive junction assembly and function, and the signalling processes by which tight junctions regulate cell behaviour and survival. We also discuss the way in which junctional components are exploited by pathogenic viruses and bacteria, and how this might affect junctional signalling mechanisms.

Merlin's wizardry guides cohesive migration

Cells often migrate in tightly connected groups with coordinated movement and polarity. The collective migration of epithelial cell sheets is now shown to be mediated by a signalling axis that involves the merlin tumour-suppressor protein, the tight-junction-associated angiomotin-Rich1 complex and the Rac1 small GTPase.

Aerobic glycolysis tunes YAP/TAZ transcriptional activity

Increased glucose metabolism and reprogramming toward aerobic glycolysis are a hallmark of cancer cells, meeting their metabolic needs for sustained cell proliferation. Metabolic reprogramming is usually considered as a downstream consequence of tumor development and oncogene activation; growing evidence indicates, however, that metabolism on its turn can support oncogenic signaling to foster tumor malignancy. Here, we explored how glucose metabolism regulates gene transcription and found an unexpected link with YAP/TAZ, key transcription factors regulating organ growth, tumor cell proliferation and aggressiveness. When cells actively incorporate glucose and route it through glycolysis, YAP/TAZ are fully active; when glucose metabolism is blocked, or glycolysis is reduced, YAP/TAZ transcriptional activity is decreased. Accordingly, glycolysis is required to sustain YAP/TAZ pro-tumorigenic functions, and YAP/TAZ are required for the full deployment of glucose growth-promoting activity. Mechanistically we found that phosphofructokinase (PFK1), the enzyme regulating the first committed step of glycolysis, binds the YAP/TAZ transcriptional cofactors TEADs and promotes their functional and biochemical cooperation with YAP/TAZ. Strikingly, this regulation is conserved in Drosophila, where phosphofructokinase is required for tissue overgrowth promoted by Yki, the fly homologue of YAP. Moreover, gene expression regulated by glucose metabolism in breast cancer cells is strongly associated in a large dataset of primary human mammary tumors with YAP/TAZ activation and with the progression toward more advanced and malignant stages. These findings suggest that aerobic glycolysis endows cancer cells with particular metabolic properties and at the same time sustains transcription factors with potent pro-tumorigenic activities such as YAP/TAZ.

G protein-coupled receptors: bridging the gap from the extracellular signals to the Hippo pathway

The Hippo pathway is crucial in organ size control, whereas its dysregulation contributes to organ degeneration or tumorigenesis. The kinase cascade of MST1/2 and LATS1/2 and the coupling transcription co-activators YAP/TAZ represent the core components of the Hippo pathway. Extensive studies have identified a number of upstream regulators of the Hippo pathway, including contact inhibition, mechanic stress, extracellular matrix stiffness, cytoskeletal rearrangement, and some molecules of cell polarity and cell junction. However, how the diffuse extracellular signals regulate the Hippo pathway puzzles the researchers for a long time. Unexpectedly, recent elegant studies demonstrated that stimulation of some G protein-coupled receptors (GPCRs), such as lysophosphatidic acid receptor, sphingosine-1-phosphate receptor, and the protease activated receptor PAR1, causes potent YAP/TAZ dephosphorylation and activation by promoting actin cytoskeleton assemble. In this review, we briefly describe the components of the Hippo pathway and focus on the recent progress with respect to the regulation of the Hippo pathway by GPCRs and G proteins in cancer cells. In addition, we also discuss the potential therapeutic roles targeting the Hippo pathway in human cancers.

The mammalian Hippo pathway: regulation and function of YAP1 and TAZ

The Hippo pathway was originally identified as the signaling that controls organ size in Drosophila, with the core architecture conserved in mammals. In the mammalian Hippo pathway, mammalian Ste20-like kinases (MST1/2) and large tumor suppressor kinases (LATS1/2) regulate transcriptional co-activators, Yes-associated protein (YAP1) and Transcriptional co-activator with a PDZ-binding motif (TAZ). The Hippo pathway was initially thought to be quite straightforward; however, the identification of additional components has revealed its inherent complexity. Regulation of YAP1 and TAZ is not always dependent on MST1/2 and LATS1/2. MST1/2 and LATS1/2 play various YAP1/TAZ-independent roles, while YAP1 and TAZ cross-talk with other signaling pathways. In this review we focus on YAP1 and TAZ and discuss their regulation, function, and the consequences of their dysregulation.

Genome-wide methylation analysis in vestibular schwannomas shows putative mechanisms of gene expression modulation and global hypomethylation at the HOX gene cluster

Schwannomas are tumors that develop from Schwann cells in the peripheral nerves and commonly arise from the vestibular nerve. Vestibular schwannomas can present unilaterally and sporadically or bilaterally when the tumor is associated with neurofibromatosis Type 2 (NF2) syndrome. The molecular hallmark of the disease is biallelic inactivation of the NF2 gene. The epigenetic signature of schwannomas remains poorly understood and is mostly limited to DNA methylation of the NF2 gene, whose altered expression due to epigenetic factors in this tumor is controversial. In this study, we tested the genomewide DNA methylation pattern of schwannomas to shed light on this epigenetic alteration in these particular tumors. The methodology used includes Infinium Human Methylation 450K BeadChip microarrays in a series of 36 vestibular schwannomas, 4 nonvestibular schwannomas, and 5 healthy nerves. Our results show a trend toward hypomethylation in schwannomas. Furthermore, homeobox (HOX) genes, located at four clusters in the genome, displayed hypomethylation in several CpG sites in the vestibular schwannomas but not in the nonvestibular schwannomas. Several microRNA (miRNA) and protein-coding genes were also found to be hypomethylated at promoter regions and were confirmed as upregulated by expression analysis; including miRNA-21, Met Proto-Oncogene (MET), and PMEPA1. We also detected methylation patterns that might be involved in alternative transcripts of several genes such as NRXN1 or MBP, which would increase the complexity of the methylation and expression patterns. Overall, our results show specific epigenetic signatures in several coding genes and miRNAs that could potentially be used as therapeutic targets.

The biology of YAP/TAZ: hippo signaling and beyond

The transcriptional regulators YAP and TAZ are the focus of intense interest given their remarkable biological properties in development, tissue homeostasis and cancer. YAP and TAZ activity is key for the growth of whole organs, for amplification of tissue-specific progenitor cells during tissue renewal and regeneration, and for cell proliferation. In tumors, YAP/TAZ can reprogram cancer cells into cancer stem cells and incite tumor initiation, progression and metastasis. As such, YAP/TAZ are appealing therapeutic targets in cancer and regenerative medicine. Just like the function of YAP/TAZ offers a molecular entry point into the mysteries of tissue biology, their regulation by upstream cues is equally captivating. YAP/TAZ are well known for being the effectors of the Hippo signaling cascade, and mouse mutants in Hippo pathway components display remarkable phenotypes of organ overgrowth, enhanced stem cell content and reduced cellular differentiation. YAP/TAZ are primary sensors of the cell's physical nature, as defined by cell structure, shape and polarity. YAP/TAZ activation also reflects the cell "social" behavior, including cell adhesion and the mechanical signals that the cell receives from tissue architecture and surrounding extracellular matrix (ECM). At the same time, YAP/TAZ entertain relationships with morphogenetic signals, such as Wnt growth factors, and are also regulated by Rho, GPCRs and mevalonate metabolism. YAP/TAZ thus appear at the centerpiece of a signaling nexus by which cells take control of their behavior according to their own shape, spatial location and growth factor context.

Angiomotin is a novel component of cadherin-11/β-catenin/p120 complex and is critical for cadherin-11-mediated cell migration

Loss of E-cadherin and up-regulation of mesenchymal cadherins, a hallmark of the epithelial-mesenchymal transition, contributes to migration and dissemination of cancer cells. Expression of human cadherin-11 (Cad11), also known as osteoblast cadherin, in prostate cancer increases the migration of prostate cancer cells. How Cad11 mediates cell migration is unknown. Using the human Cad11 cytoplasmic domain in pulldown assays, we identified human angiomotin (Amot), known to be involved in cell polarity, migration, and Hippo pathway, as a component of the Cad11 protein complex. Deletion analysis showed that the last C-terminal 10 amino acids in Cad11 cytoplasmic domain are required for Amot binding. Further, Cad11 preferentially interacts with Amot-p80 than Amot-p130 isoform and binds directly to the middle domain of Amot-p80. Cad11-Amot interaction affects Cad11-mediated cell migration, but not homophilic adhesion, as deletion of Amot binding motif of Cad11 (Cad11-ΔAmot) did not abolish Cad11-mediated cell-cell adhesion of mouse L cells, but significantly reduced Cad11-mediated cell migration of human C4-2B4 and PC3-mm2 prostate cancer cells and human HEK293T cells. Together, our studies identified Amot-p80 as a novel component of the Cad11 complex and demonstrated that Amot-p80 is critical for Cad11-mediated cell migration.

Sensing the local environment: actin architecture and Hippo signalling

The Hippo network is a major conserved growth suppressor pathway that participates in organ size control during development and prevents tumour formation during adult homeostasis. Recent evidence has implicated the actin cytoskeleton as a link between tissue architecture and Hippo signalling. In this review, we will consider the evidence and models proposed for the regulation of Hippo signalling by actin dynamics and structure. We cover aspects of signalling regulation by mechanotransduction, cytoskeletal tethering and the spatial reorganization of signalling components. We also examine the physiological and pathological contexts in which these mechanisms are relevant.

Angiomotin decreases lung cancer progression by sequestering oncogenic YAP/TAZ and decreasing Cyr61 expression

Lung cancer is the leading cause of cancer death worldwide, with metastasis underlying majority of related deaths. Angiomotin (AMOT), a scaffold protein, has been shown to interact with oncogenic Yes-associated protein/transcriptional co-activator with a PDZ-binding motif (YAP/TAZ) proteins, suggesting a potential role in tumor progression. However, the functional role of AMOT in lung cancer remains unknown. This study aimed to identify the patho-physiological characteristics of AMOT in lung cancer progression. Results revealed that AMOT expression was significantly decreased in clinical lung cancer specimens. Knockdown of AMOT in a low metastatic CL1-0 lung cancer cell line initiated cancer proliferation, migration, invasion and epithelial-mesenchymal transition. The trigger of cancer progression caused by AMOT loss was transduced by decreased cytoplasmic sequestration and increased nuclear translocation of oncogenic co-activators YAP/TAZ, leading to increased expression of the growth factor, Cyr61. Tumor promotion by AMOT knockdown was reversed when YAP/TAZ or Cyr61 was absent. Further, AMOT knockdown increased the growth and spread of Lewis lung carcinoma in vivo. These findings suggest that AMOT is a crucial suppressor of lung cancer metastasis and highlight its critical role as a tumor suppressor and its potential as a prognostic biomarker and therapeutic target for lung cancer.

Energy stress regulates hippo-YAP signaling involving AMPK-mediated regulation of angiomotin-like 1 protein

Hippo signaling is a tumor-suppressor pathway involved in organ size control and tumorigenesis through the inhibition of YAP and TAZ. Here, we show that energy stress induces YAP cytoplasmic retention and S127 phosphorylation and inhibits YAP transcriptional activity and YAP-dependent transformation. These effects require the central metabolic sensor AMP-activated protein kinase (AMPK) and the upstream Hippo pathway components Lats1/Lats2 and angiomotin-like 1 (AMOTL1). Furthermore, we show that AMPK directly phosphorylates S793 of AMOTL1. AMPK activation stabilizes and increases AMOTL1 steady-state protein levels, contributing to YAP inhibition. The phosphorylation-deficient S793Ala mutant of AMOTL1 showed a shorter half-life and conferred resistance to energy-stress-induced YAP inhibition. Our findings link energy sensing to the Hippo-YAP pathway and suggest that YAP may integrate spatial (contact inhibition), mechanical, and metabolic signals to control cellular proliferation and survival.