Opposing roles of angiomotin-like-1 and zona occludens-2 on pro-apoptotic function of YAP

Role of angiomotin family members in human diseases (Review)

Angiomotin (Amot) family members, including Amot, Amot-like protein 1 (Amotl1) and Amot-like protein 2 (Amotl2), have been found to interact with angiostatins. In addition, Amot family members are involved in various physiological and pathological functions such as embryonic development, angiogenesis and tumorigenesis. Some studies have also demonstrated its regulation in signaling pathways such as the Hippo signaling pathway, AMPK signaling pathway and mTOR signaling pathways. Amot family members play an important role in neural stem cell differentiation, dendritic formation and synaptic maturation. In addition, an increasing number of studies have focused on their function in promoting and/or suppressing cancer, but the underlying mechanisms remain to be elucidated. The present review integrated relevant studies on upstream regulation and downstream signals of Amot family members, as well as the latest progress in physiological and pathological functions and clinical applications, hoping to offer important ideas for further research.

YAP-mediated trophoblast dysfunction: the common pathway underlying pregnancy complications

Yes-associated protein (YAP) is a pivotal regulator in cellular proliferation, survival, differentiation, and migration, with significant roles in embryonic development, tissue repair, and tumorigenesis. At the maternal-fetal interface, emerging evidence underscores the importance of precisely regulated YAP activity in ensuring successful pregnancy initiation and progression. However, despite the established association between YAP dysregulation and adverse pregnancy outcomes, insights into the impact of aberrant YAP levels in fetal-derived, particularly trophoblast cells, and the ensuing dysfunction at the maternal-fetal interface remain limited. This review comprehensively examines YAP expression and its regulatory mechanisms in trophoblast cells throughout pregnancy. We emphasize its integral role in placental development and maternal-fetal interactions and delve into the correlations between YAP dysregulation and pregnancy complications. A nuanced understanding of YAP's functions during pregnancy could illuminate intricate molecular mechanisms and pave the way for innovative prevention and treatment strategies for pregnancy complications. Video Abstract.

SDCBP promotes pancreatic cancer progression by preventing YAP1 from β-TrCP-mediated proteasomal degradation

OBJECTIVE

Pancreatic ductal adenocarcinoma (PDAC) is a highly lethal tumour with limited treatment options. Here, we identified syndecan binding protein (SDCBP), also known as syntenin1, as a novel targetable factor in promoting PDAC tumour progression. We also explored a therapeutic strategy for suppressing SDCBP expression.

DESIGN

We used samples from patients with PDAC, human organoid models, LSL-KrasG12D/+mice, LSL-Trp53R172H/+ and Pdx1-Cre (KPC) mouse models, and PDX mouse models. Immunostaining, colony formation assay, ethynyl-2-deoxyuridine incorporation assay, real-time cell analysis, cell apoptosis assay, automated cell tracking, invadopodia detection and gelatin degradation assays, coimmunoprecipitation, and pull-down assays were performed in this study.

RESULTS

The median overall survival and recurrence-free survival rates in the high-SDCBP group were significantly shorter than those in the low-SDCBP group. In vitro and in vivo studies have demonstrated that SDCBP promotes PDAC proliferation and metastasis. Mechanically, SDCBP inhibits CK1δ/ε-mediated YAP-S384/S387 phosphorylation, which further suppresses β-TrCP-mediated YAP1 ubiquitination and proteasome degradation by directly interacting with YAP1. SDCBP interacts with the TAD domain of YAP1, mainly through its PDZ1 domain. Preclinical KPC mouse cohorts demonstrated that zinc pyrithione (ZnPT) suppresses PDAC tumour progression by suppressing SDCBP.

CONCLUSIONS

SDCBP promotes the proliferation and metastasis of PDAC by preventing YAP1 from β-TrCP-mediated proteasomal degradation. Therefore, ZnPT could be a promising therapeutic strategy to inhibit PDAC progression by suppressing SDCBP.

ZNF582 overexpression restrains the progression of clear cell renal cell carcinoma by enhancing the binding of TJP2 and ERK2 and inhibiting ERK2 phosphorylation

Recent evidences have suggested that Zinc finger protein 582 (ZNF582) plays different important roles in various tumors, but its clinical role, biological function and regulatory mechanism in clear cell renal cell carcinoma (ccRCC) are still vague. Through analyzing GEO and TCGA-KIRC data and validation with local samples, we identified the low expression pattern of ZNF582 in ccRCC. Decreased ZNF582 expression is correlated with higher tumor stage and grade, distant metastasis and poor prognosis. By analyzing the DNA methylation data of ccRCC in TCGA-KIRC and using Massarray DNA methylation and demethylation analysis, we confirmed the hypermethylation status of ZNF582 in ccRCC and its negative regulation on ZNF582 expression. Using cell phenotype experiments and orthotopic kidney tumor growth models, we determined the inhibitory effect of ZNF582 overexpression on ccRCC growth and metastasis in vivo and in vitro. Mechanistically, using TMT (Tandem mass tags) quantitative proteomics test, Co-IP (Co-immunoprecipitation) and Western Blot experiments, we clarified that ZNF582 binds to TJP2 and up-regulates TJP2 protein expression. Increased TJP2 protein combines with ERK2 to promote ERK2 protein expression and suppresses the phosphorylation of ERK2, thereby inhibiting the growth and metastasis of ccRCC. In general, our findings provide the first solid theoretical rationale for targeting ZNF582/TJP2/ERK2 axis to improve ccRCC treatment.

The Regulation of the Hippo Pathway by Intercellular Junction Proteins

The Hippo pathway is an evolutionarily conserved pathway that serves to promote cell death and differentiation while inhibiting cellular proliferation across species. The downstream effectors of this pathway, yes-associated protein (YAP) and transcriptional co-activator with PDZ-binding motif (TAZ), are considered vital in promoting the output of the Hippo pathway, with activation of upstream kinases negatively regulating YAP/TAZ activity. The upstream regulation of the Hippo pathway is not entirely understood on a molecular level. However, several studies have shown that numerous cellular and non-cellular mechanisms such as cell polarity, contact inhibition, soluble factors, mechanical forces, and metabolism can convey external stimuli to the intracellular kinase cascade, promoting the activation of key components of the Hippo pathway and therefore regulating the subcellular localisation and protein activity of YAP/TAZ. This review will summarise what we have learnt about the role of intercellular junction-associated proteins in the activation of this pathway, including adherens junctions and tight junctions, and in particular our latest findings about the desmosomal components, including desmoglein-3 (DSG3), in the regulation of YAP signalling, phosphorylation, and subcellular translocation.

ZO-2/Tjp2 suppresses Yap and Wwtr1/Taz-mediated hepatocyte to cholangiocyte transdifferentiation in the mouse liver

TJP2/ZO-2-inactivating mutations in humans cause progressive cholestatic liver disease. Liver-specific deletion of Tjp2 in the mouse (Tjp2 cKO mice) leads to mild progressive cholestasis without an overt degradation of the bile-blood barrier (BBB). These mice are more susceptible to cholic acid (CA) induced liver injury. Interestingly, while initially also more susceptible, Tjp2 cKO mice develop tolerance to a DDC-supplemented diet. The DDC diet induces an exacerbated ductular reaction in Tjp2 cKO mice, which arises from the transdifferentiation of hepatocytes to cholangiocytes. Consequently, this transdifferentiation is only observed if Tjp2 is inactivated in hepatocytes, but not if deleted in cholangiocytes. The DDC-diet-induced hepatocyte transdifferentiation in Tjp2 cKO mice requires Yap and Wwtr1/Taz, whose protein expression is upregulated in hepatocytes lacking Tjp2, but is independent of Notch2. Although inactivating Tjp2 is sufficient for the upregulation of Yap and Wwtr1/Taz protein, efficient transdifferentiation requires the DDC-diet insult. Thus, Tjp2 negatively regulates Yap/Taz-mediated transdifferentiation of hepatocytes to cholangiocytes in response to DDC-diet-induced liver injury. Furthermore, transdifferentiation is regulated at multiple levels and the type of injury inflicted on the Tjp2 deficient liver plays an important role in the resulting pathophysiology.

Molecular Alterations in Malignant Pleural Mesothelioma: A Hope for Effective Treatment by Targeting YAP

Malignant pleural mesothelioma is a rare and aggressive neoplasm, which has primarily been attributed to the exposure to asbestos fibers (83% of cases); yet, despite a ban of using asbestos in many countries, the incidence of malignant pleural mesothelioma failed to decline worldwide. While little progress has been made in malignant pleural mesothelioma diagnosis, bevacizumab at first, then followed by double immunotherapy (nivolumab plus ipilumumab), were all shown to improve survival in large phase III randomized trials. The morphological analysis of the histological subtyping remains the primary indicator for therapeutic decision making at an advanced disease stage, while a platinum-based chemotherapy regimen combined with pemetrexed, either with or without bevacizumab, is still the main treatment option. Consequently, malignant pleural mesothelioma still represents a significant health concern owing to poor median survival (12-18 months). Given this context, both diagnosis and therapy improvements require better knowledge of the molecular mechanisms underlying malignant pleural mesothelioma's carcinogenesis and progression. Hence, the Hippo pathway in malignant pleural mesothelioma initiation and progression has recently received increasing attention, as the aberrant expression of its core components may be closely related to patient prognosis. The purpose of this review was to provide a critical analysis of our current knowledge on these topics, the main focus being on the available evidence concerning the role of each Hippo pathway's member as a promising biomarker, enabling detection of the disease at earlier stages and thus improving prognosis.

Effect of TDP43-CTFs35 on Brain Endothelial Cell Functions in Cerebral Ischemic Injury

Pathological changes in the brain endothelium play an important role in the progression of ischemic stroke and the compromised BBB under ischemic stroke conditions cause neuronal damage. However, the pathophysiological mechanisms of the BBB under normal conditions and under ischemic stroke conditions have not been fully elucidated. The present study demonstrated that knockdown of TAR DNA-binding protein 43 (TDP-43) or overexpression of TDP43-CTFs35 inhibited tight junction protein expression, and mammalian sterile-20-like 1/2 (MST1/2) and YES-associated protein (YAP) phosphorylation in brain ECs and suppressed brain EC migration in vitro. The cytoplasmic TDP43-CTFs35 level was increased in brain ECs 24 h and 72 h after MCAO, but it disappeared 1 week after cerebral ischemia. The expression of tight junction proteins was also significantly deceased 24 h after MCAO and then gradually recovered at 72 h and 1 week after MCAO. The level of YAP phosphorylation was first significantly decreased 24 h after MCAO and then increased 72 h and 1 week after MCAO, accompanied by nuclear YAP translocation. The underlying mechanism is TDP43-CTFs35-mediated inhibition of Hippo signaling pathway activity through the dephosphorylation of MST1/2, which leads to the inhibition of YAP phosphorylation and the subsequent impairment of brain EC migration and tight junction protein expression. This study provides new insights into the mechanisms of brain vascular EC regulation, which may impact on BBB integrity after cerebral ischemic injury.

Multivalent Angiomotin-like 1 and Yes-associated protein form a dynamic complex

Multivalent complexes formed between the cancer-promoting transcriptional co-activator, Yes-associated protein (YAP), and proteins containing short linear motifs of type PPxY modulate cell proliferation and are attractive therapeutic targets. However, challenges producing PPxY polypeptides containing the full binding domain has limited understanding of the assembly process. Here, we successfully produced a polypeptide containing the complete set of three PPxY binding sites of Angiomotin-like 1 (AMOTL1), a scaffolding protein that regulates the nucleo-cytoplasmic shuttling of YAP via WW-PPxY interactions. Using an array of biophysical techniques including isothermal titration calorimetry, size-exclusion chromatography coupled to multi-angle light scattering, and solution nuclear magnetic resonance spectroscopy, we show that the AMOTL1 polypeptide is partially disordered, and binds the YAP WW domains to form an ensemble of complexes of varying stabilities. The binding process is initiated by the binding of one YAP WW domain to one AMOTL1 PPxY motif and is completed by transient interactions of the second YAP WW domain with a second AMOTL1 PPxY motif to form an equilibrating mixture composed of various species having two YAP sites bound to two conjugate AMOTL1 sites. We rationalize that the transient interactions fine-tune the stability of the complex for rapid assembly and disassembly in response to changes in the local cellular environment.

STAT3-YAP/TAZ signaling in endothelial cells promotes tumor angiogenesis

[Figure: see text].

Angiomotin-like 1 plays a tumor-promoting role in glioma by enhancing the activation of YAP1 signaling

Angiomotin-like 1 (AMOTL1) is reportedly a pivotal tumor-associated protein that is strongly associated with the tumorigenesis of multiple malignant tumors. However, the issue of whether AMOTL1 plays a role in the tumorigenesis of glioma remains unclear. The aim of this work was to explore the possible relationship between AMOTL1 and glioma progression. Results demonstrated that high levels of AMOTL1 in glioma tissues were associated with a reduced survival rate in patients with glioma. Cellular functional assays revealed that silencing of AMOTL1 in glioma cell lines substantially decreased cell proliferation and invasion and increased cell apoptosis. Further investigation revealed that silencing of AMOTL1 inhibited the activation of yes-associated protein 1 (YAP1) and decreased the expression of YAP1 target genes. Reactivation of YAP1 reversed AMOTL1-silencing-induced antitumor effects, whereas inhibition of YAP1 abolished AMOTL1-overexpression-induced tumor-promoting effects in glioma cells. Silencing of AMOTL1 also retarded the growth of glioma cell-derived xenograft tumors in vivo. In conclusion, these findings suggested that AMOTL1 may exert a tumor-promoting function in glioma by enhancing the activation of YAP1 signaling. This work suggested AMOTL1 as a potential target for the development of antiglioma therapy.

Identification, subcellular localization, and functional comparison of novel Yap splicing isoforms in mouse embryonic stem cells

Hippo signaling pathway is involved in many biological processes including the fate decision of embryonic stem cells (ESCs). Yes-associated protein (Yap) function as a key effector of Hippo pathway, but its role in ESCs is still controversial. So far, only two isoforms of Yap have been identified and they have both overlapping and distinct functions. Here, we identify six novel isoforms of mouse Yap, bringing the total number of isoforms to eight. According to the differences in the first exon, they are divided into two subtypes (a and b). Isoform-a and isoform-b exhibit different subcellular localizations. Moreover, isoform-a can fully reverse the impaired self-renewal phenotype induced by Yap knockout (KO). Upon overexpression, isoform-a moderately promotes mESCs self-renewal and markedly delays differentiation. On the contrary, no significant pro-self-renewal phenotype is observed when isoform-b overexpressed in wildtype (WT) mESCs or re-expressed in Yap KO cell lines. These finding not only help to clarify the role of Yap in mESCs, but also lay the foundation for advancing functional researches of Yap in other processes.

Strong as a Hippo's Heart: Biomechanical Hippo Signaling During Zebrafish Cardiac Development

The heart is comprised of multiple tissues that contribute to its physiological functions. During development, the growth of myocardium and endocardium is coupled and morphogenetic processes within these separate tissue layers are integrated. Here, we discuss the roles of mechanosensitive Hippo signaling in growth and morphogenesis of the zebrafish heart. Hippo signaling is involved in defining numbers of cardiac progenitor cells derived from the secondary heart field, in restricting the growth of the epicardium, and in guiding trabeculation and outflow tract formation. Recent work also shows that myocardial chamber dimensions serve as a blueprint for Hippo signaling-dependent growth of the endocardium. Evidently, Hippo pathway components act at the crossroads of various signaling pathways involved in embryonic zebrafish heart development. Elucidating how biomechanical Hippo signaling guides heart morphogenesis has direct implications for our understanding of cardiac physiology and pathophysiology.

From the Matrix to the Nucleus and Back: Mechanobiology in the Light of Health, Pathologies, and Regeneration of Oral Periodontal Tissues

Among oral tissues, the periodontium is permanently subjected to mechanical forces resulting from chewing, mastication, or orthodontic appliances. Molecularly, these movements induce a series of subsequent signaling processes, which are embedded in the biological concept of cellular mechanotransduction (MT). Cell and tissue structures, ranging from the extracellular matrix (ECM) to the plasma membrane, the cytosol and the nucleus, are involved in MT. Dysregulation of the diverse, fine-tuned interaction of molecular players responsible for transmitting biophysical environmental information into the cell's inner milieu can lead to and promote serious diseases, such as periodontitis or oral squamous cell carcinoma (OSCC). Therefore, periodontal integrity and regeneration is highly dependent on the proper integration and regulation of mechanobiological signals in the context of cell behavior. Recent experimental findings have increased the understanding of classical cellular mechanosensing mechanisms by both integrating exogenic factors such as bacterial gingipain proteases and newly discovered cell-inherent functions of mechanoresponsive co-transcriptional regulators such as the Yes-associated protein 1 (YAP1) or the nuclear cytoskeleton. Regarding periodontal MT research, this review offers insights into the current trends and open aspects. Concerning oral regenerative medicine or weakening of periodontal tissue diseases, perspectives on future applications of mechanobiological principles are discussed.

Modulation of Yorkie activity by alternative splicing is required for developmental stability

The Hippo signaling pathway is a major regulator of organ growth, which controls the activity of the transcription coactivator Yorkie (Yki) in Drosophila and its homolog YAP in mammals. Both Yki and YAP proteins exist as alternatively spliced isoforms containing either one or two WW domains. The biological importance of this conserved alternative splicing event is unknown. Here, we identify the splicing factor B52 as a regulator of yki alternative splicing in Drosophila and show that B52 modulates growth in part through modulation of yki alternative splicing. Yki isoforms differ by their transcriptional activity as well as their ability to bind and bridge PPxY motifs-containing partners, and can compete in vivo. Strikingly, flies in which yki alternative splicing has been abrogated, thus expressing only Yki2 isoform, exhibit fluctuating wing asymmetry, a signal of developmental instability. Our results identify yki alternative splicing as a new level of modulation of the Hippo pathway, that is required for growth equilibration during development. This study provides the first demonstration that the process of alternative splicing contributes to developmental robustness.

The zonula occludens protein family regulates the hepatic barrier system in the murine liver

The hepatic barrier is indispensable for the physiological functions of the liver and is impaired under various pathological conditions. Tight junctions reportedly play a central role in hepatic barrier regulation; however, there is limited direct evidence supporting this observation, with few in vivo models or confirmations of the implicated molecular mechanisms presented to date. We inactivated the tight junction component gene, Tjp2/ZO-2, and the related molecule, Tjp1/ZO-1, in mouse livers. In humans, TJP2/ZO-2 mutations have been implicated in the development of human progressive familial intrahepatic cholestasis 4 (PFIC4). The mice deficient in either ZO-1 or ZO-2 in the liver did not exhibit major abnormalities. However, the ablation of both molecules impaired the molecular architecture as well as the structure and function of hepatocyte tight junctions, which disrupted the hepatic barrier and was lethal to the mice by 6 weeks of age. In mutant mice, bile canaliculus formation and cellular polarity were compromised; also, transporter expression and localization were deregulated. Moreover, typical hepatic zonation and bile duct formation were inhibited, and sinusoidal vessels were disorganized. These findings clarify the role of tight junctions and polarity in the hepatic barrier as well as the effect that their disruption has on liver tissue. The observations also suggest that liver-specific ZO-1^-/- and ZO-2^-/- mice could be used as models for PFIC4, and this will provide new insights into liver pathophysiology and clinical applications.

Role of Clostridium perfringens Enterotoxin on YAP Activation in Colonic Sessile Serrated Adenoma/ Polyps with Dysplasia

Sessile serrated adenoma/polyp with dysplasia (SSA/P-D) is an SSA/P with cellular dysplasia and has a higher risk of progressing to colon carcinogenesis. Previously, we reported that tight junction impairment by Clostridiumperfringens enterotoxin (CPE) leads to activation of the transcriptional co-activator yes-associated protein (YAP) in oral squamous cell carcinoma. Here, we investigated whether CPE activates YAP to promote the malignant progression of SSA/P. E-cadherin expression was lower in the 12 cases with SSA/P-D examined than that in normal mucosa, SSA/P, or tubular adenoma (TA). Furthermore, intracellular translocation of claudin-4 (CLDN4) and nuclear translocation of YAP were observed. The CPE gene was detected in DNA extracted from SSA/P-D lesions, but not in SSA/P or TA. Treatment of the rat intestinal epithelial cell line IEC6 with low-dose CPE resulted in intracellular translocation of CLDN4 to the cytoplasmic membrane. Cytoplasmic CLDN4 showed co-precipitation with transcriptional co-activator with PDZ-binding motif, zonula occludens (ZO)-1, large tumor suppressor, and mammalian Ste20-like. Additionally, YAP co-precipitated with ZO-2 under CPE treatment led to decreased YAP phosphorylation and nuclear translocation. YAP activation promoted increase in nuclear TEA domain family member level, expression of cyclin D1, snail, vimentin, CD44, NS and decrease in E-cadherin levels, thereby inducing stemness and epithelial-mesenchymal-transition (EMT). The Hippo complex with the incorporation of CLDN4 increased stability. Upon low-dose CPE treatment, HT29 cells with BRAF^V600E gene mutation showed increased growth, enhanced invasive potential, stemness, and induced EMT phenotype, whereas HCT116 cells, which carry KRAS^G13D gene mutation, did not show such changes. In an examination of 10 colorectal cancers, an increase in EMT and stemness was observed in CPE (+) and BRAF mutation (+) cases. These findings suggest that C.perfringens might enhance the malignant transformation of SSA/P-D via YAP activation. Our findings further highlight the importance of controlling intestinal flora using probiotics or antibiotics.

The YAP/TAZ Pathway in Osteogenesis and Bone Sarcoma Pathogenesis

YAP and TAZ are intracellular messengers communicating multiple interacting extracellular biophysical and biochemical cues to the transcription apparatus in the nucleus and back to the cell/tissue microenvironment interface through the regulation of cytoskeletal and extracellular matrix components. Their activity is negatively and positively controlled by multiple phosphorylation events. Phenotypically, they serve an important role in cellular plasticity and lineage determination during development. As they regulate self-renewal, proliferation, migration, invasion and differentiation of stem cells, perturbed expression of YAP/TAZ signaling components play important roles in tumorigenesis and metastasis. Despite their high structural similarity, YAP and TAZ are functionally not identical and may play distinct cell type and differentiation stage-specific roles mediated by a diversity of downstream effectors and upstream regulatory molecules. However, YAP and TAZ are frequently looked at as functionally redundant and are not sufficiently discriminated in the scientific literature. As the extracellular matrix composition and mechanosignaling are of particular relevance in bone formation during embryogenesis, post-natal bone elongation and bone regeneration, YAP/TAZ are believed to have critical functions in these processes. Depending on the differentiation stage of mesenchymal stem cells during endochondral bone development, YAP and TAZ serve distinct roles, which are also reflected in bone tumors arising from the mesenchymal lineage at different developmental stages. Efforts to clinically translate the wealth of available knowledge of the pathway for cancer diagnostic and therapeutic purposes focus mainly on YAP and TAZ expression and their role as transcriptional co-activators of TEAD transcription factors but rarely consider the expression and activity of pathway modulatory components and other transcriptional partners of YAP and TAZ. As there is a growing body of evidence for YAP and TAZ as potential therapeutic targets in several cancers, we here interrogate the applicability of this concept to bone tumors. To this end, this review aims to summarize our current knowledge of YAP and TAZ in cell plasticity, normal bone development and bone cancer.

The WW domains dictate isoform-specific regulation of YAP1 stability and pancreatic cancer cell malignancy

YAP1 is a key mediator of the Hippo pathway capable of exerting a profound effect on organ size as well as tumorigenesis. Alternative mRNA splicing of human YAP1 results in at least 8 protein isoforms that differ within the 2nd WW motif and the transcriptional activation domain. Methods: To investigate the isoform-specific differences in their mRNA expression, transcriptional activity and tumor-promoting function, we cloned cDNA encoding all of the eight YAP1 protein isoforms. Then, we examined their mRNA expression, subcellular localization, transcriptional regulation properties, interactions with key regulatory partners, and protein stability in response to changes in cell density, as well as their effects on pancreatic cancer cell malignancy both in vitro and in vivo. Results: Multiple YAP1 mRNA isoforms are expressed in commonly used pancreatic cancer lines as well as human pancreatic cancer PDX lines. Based on the analysis of heterologous reporter and endogenous target genes, all YAP1 isoforms are capable of activating transcription, albeit to a different extent. Importantly, we unveiled a marked discrepancy between the mRNA and protein expression levels of the YAP1-1 and YAP1-2 isoforms. We further discovered that the YAP1-2 isoform, which contains two tandem WW motifs, is less stable at the protein level, particularly at high cell densities. Mechanistically, we found that the presence of the 2nd WW motif in YAP1-2 facilitates the de novo formation of the YAP1-2/AMOT/LATS1 complex and contributes to a stronger binding of YAP1-2 to LATS1 and subsequently increased YAP1-2 ubiquitination and degradation by β-TRCP. Conclusion: Our data reveals a potent effect of YAP1-1 on pancreatic cancer malignancy in vitro and in vivo and provides novel mechanistic insight into isoform-specific and cell density-dependent regulation of YAP1 stability, as well as its impact on cancer malignancy.

Clostridium perfringens enterotoxin induces claudin-4 to activate YAP in oral squamous cell carcinomas

Claudin (CLDN)-4 expression has been associated with malignancy in various cancers. When CLDN4 expression was examined in oral squamous cell carcinoma (OSCC), 22 out of 57 (39%) cases showed immunoreactivity in the nucleus. Nuclear CLDN4-positive cases showed a stronger correlation with cancer progression than the negative cases. Intratumoral anaerobic bacterial DNA examination revealed nuclear CLDN4 expression in 81% of Clostridium perfringens-positive cases. Treatment of human oral squamous cell carcinoma cell lines HSC3 and HSC4 with Clostridium perfringens enterotoxin (CPE), induced CLDN4 nuclear translocation to enhance epithelial-mesenchymal transition (EMT), stemness, cell proliferation and invasive ability. In addition, CPE treatment suppressed phosphorylation of yes-associated protein-1 (YAP1) and promoted YAP1 nuclear translocation, resulting in increased expression of YAP1 target genes; cyclin D1 and connective tissue growth factor. Moreover, it was revealed that the complex of YAP1, CLDN4 and zona occludens-2 (ZO-2) was formed by CPE treatment, further suppressing YAP1 phosphorylation by LATS1 and activating it. Thus YAP activation in OSCC was regarded important in promoting malignant phenotypes. Our research suggested that the control of oral anaerobic bacteria may suppress YAP activation and in turn tumor progression.

Modular mimicry and engagement of the Hippo pathway by Marburg virus VP40: Implications for filovirus biology and budding

Ebola (EBOV) and Marburg (MARV) are members of the Filoviridae family, which continue to emerge and cause sporadic outbreaks of hemorrhagic fever with high mortality rates. Filoviruses utilize their VP40 matrix protein to drive virion assembly and budding, in part, by recruitment of specific WW-domain-bearing host proteins via its conserved PPxY Late (L) domain motif. Here, we screened an array of 115 mammalian, bacterially expressed and purified WW-domains using a PPxY-containing peptide from MARV VP40 (mVP40) to identify novel host interactors. Using this unbiased approach, we identified Yes Associated Protein (YAP) and Transcriptional co-Activator with PDZ-binding motif (TAZ) as novel mVP40 PPxY interactors. YAP and TAZ function as downstream transcriptional effectors of the Hippo signaling pathway that regulates cell proliferation, migration and apoptosis. We demonstrate that ectopic expression of YAP or TAZ along with mVP40 leads to significant inhibition of budding of mVP40 VLPs in a WW-domain/PPxY dependent manner. Moreover, YAP colocalized with mVP40 in the cytoplasm, and inhibition of mVP40 VLP budding was more pronounced when YAP was localized predominantly in the cytoplasm rather than in the nucleus. A key regulator of YAP nuclear/cytoplasmic localization and function is angiomotin (Amot); a multi-PPxY containing protein that strongly interacts with YAP WW-domains. Interestingly, we found that expression of PPxY-containing Amot rescued mVP40 VLP egress from either YAP- or TAZ-mediated inhibition in a PPxY-dependent manner. Importantly, using a stable Amot-knockdown cell line, we found that expression of Amot was critical for efficient egress of mVP40 VLPs as well as egress and spread of authentic MARV in infected cell cultures. In sum, we identified novel negative (YAP/TAZ) and positive (Amot) regulators of MARV VP40-mediated egress, that likely function in part, via competition between host and viral PPxY motifs binding to modular host WW-domains. These findings not only impact our mechanistic understanding of virus budding and spread, but also may impact the development of new antiviral strategies.

By screening an array of 115 mammalian WW-domains with the PPxY motif from MARV VP40 (mVP40), we identified YAP1 and TAZ, transcriptional effectors of the Hippo pathway, as mVP40 interactors, and demonstrated that ectopically expressed YAP1 or TAZ inhibited budding of mVP40 virus-like particles (VLPs) in a WW-domain/PPxY dependent manner. Angiomotin (Amot), a multi-PPxY containing regulator of YAP1 nuclear/cytoplasmic localization and function, rescued mVP40 VLP egress from either YAP1- or TAZ-mediated inhibition in a PPxY-dependent manner. Indeed, endogenous Amot expression was critical for egress of mVP40 VLPs and authentic MARV. In sum, we have revealed a link between the Hippo pathway and filovirus egress by identifying negative (YAP/TAZ) and positive (Amot) regulators of MARV VP40-mediated egress.

Hippo signalling during development

The Hippo signalling pathway and its transcriptional co-activator targets Yorkie/YAP/TAZ first came to attention because of their role in tissue growth control. Over the past 15 years, it has become clear that, like other developmental pathways (e.g. the Wnt, Hedgehog and TGFβ pathways), Hippo signalling is a 'jack of all trades' that is reiteratively used to mediate a range of cellular decision-making processes from proliferation, death and morphogenesis to cell fate determination. Here, and in the accompanying poster, we briefly outline the core pathway and its regulation, and describe the breadth of its roles in animal development.

ZO-2 Is a Master Regulator of Gene Expression, Cell Proliferation, Cytoarchitecture, and Cell Size

ZO-2 is a cytoplasmic protein of tight junctions (TJs). Here, we describe ZO-2 involvement in the formation of the apical junctional complex during early development and in TJ biogenesis in epithelial cultured cells. ZO-2 acts as a scaffold for the polymerization of claudins at TJs and plays a unique role in the blood–testis barrier, as well as at TJs of the human liver and the inner ear. ZO-2 movement between the cytoplasm and nucleus is regulated by nuclear localization and exportation signals and post-translation modifications, while ZO-2 arrival at the cell border is triggered by activation of calcium sensing receptors and corresponding downstream signaling. Depending on its location, ZO-2 associates with junctional proteins and the actomyosin cytoskeleton or a variety of nuclear proteins, playing a role as a transcriptional repressor that leads to inhibition of cell proliferation and transformation. ZO-2 regulates cell architecture through modulation of Rho proteins and its absence induces hypertrophy due to inactivation of the Hippo pathway and activation of mTOR and S6K. The interaction of ZO-2 with viral oncoproteins and kinases and its silencing in diverse carcinomas reinforce the view of ZO-2 as a tumor regulator protein.

The Cross-Talk Between the TNF-α and RASSF-Hippo Signalling Pathways

The regulation of cell death through apoptosis is essential to a number of physiological processes. Defective apoptosis regulation is associated with many abnormalities including anomalies in organ development, altered immune response and the development of cancer. Several signalling pathways are known to regulate apoptosis including the Tumour Necrosis Factor-α (TNF-α) and Hippo signalling pathways. In this paper we review the cross-talk between the TNF-α pathway and the Hippo signalling pathway. Several molecules that tightly regulate the Hippo pathway, such as members of the Ras-association domain family member (RASSF) family proteins, interact and modulate some key proteins within the TNF-α pathway. Meanwhile, TNF-α stimulation also affects the expression and activation of core components of the Hippo pathway. This implies the crucial role of signal integration between these two major pathways in regulating apoptosis.

Identification of Prolyl isomerase Pin1 as a novel positive regulator of YAP/TAZ in breast cancer cells

The Hippo signalling pathway plays very important roles in tumorigenesis, metastasis, organ size control, and drug resistance. Although, it has been shown that the two major components of Hippo pathway, YAP and TAZ, play very crucial role in tumorigenesis and drug resistance, the exact molecular mechanisms are still unknown. Recently, we have shown that the prolyl isomerase Pin1 regulates the activity of Hippo pathway through interaction with Hippo component LATS kinase. Thus we asked if Pin1 is also able to interact with other Hippo pathway components. Therefore, in order to investigate whether Pin1 can interacts with other components of the Hippo pathway, we performed GST-pull down and co-immunoprecipitation (Co-IP) assays and have identified two Hippo components YAP and TAZ oncoproteins as novel binding partner of Pin1. We found that Pin1 interacts with YAP/TAZ in a phosphorylation-independent manner and WW domain of Pin1 is necessary for this interaction. Moreover, by using real time qRT-PCR, Cycloheximide chase, luciferase reporter, cell viability and soft agar assays, we have shown that Pin1 increases the tumorigenic and drug-resistant activity of YAP/TAZ through stabilization of YAP/TAZ at protein levels. Together, we have identified Pin1 as a novel positive regulator of YAP/TAZ in tumorigenesis and drug resistance of breast cancer cells. These findings will provide a significant contribution for targeting the Pin1-YAP/TAZ signaling for the successful treatment of tumorigenesis and drug resistance of breast and other cancers in the future.

Overlooked? Underestimated? Effects of Substrate Curvature on Cell Behavior

In biological systems, form and function are inherently correlated. Despite this strong interdependence, the biological effect of curvature has been largely overlooked or underestimated, and consequently it has rarely been considered in the design of new cell-material interfaces. This review summarizes current understanding of the interplay between the curvature of a cell substrate and the related morphological and functional cellular response. In this context, we also discuss what is currently known about how, in the process of such a response, cells recognize curvature and accordingly reshape their membrane. Beyond this, we highlight state-of-the-art microtechnologies for engineering curved biomaterials at cell-scale, and describe aspects that impair or improve readouts of the pure effect of curvature on cells.

YAPping about and not forgetting TAZ

The Hippo pathway has emerged as a major eukaryotic signalling pathway and is increasingly the subject of intense interest, as are the key effectors of canonical Hippo signalling, YES-associated protein (YAP) and TAZ. The Hippo pathway has key roles in diverse biological processes, including network signalling regulation, development, organ growth, tissue repair and regeneration, cancer, stem cell regulation and mechanotransduction. YAP and TAZ are multidomain proteins and function as transcriptional coactivators of key genes to evoke their biological effects. YAP and TAZ interact with numerous partners and their activities are controlled by a complex set of processes. This review provides an overview of Hippo signalling and its role in growth. In particular, the functional domains of YAP and TAZ and the complex mechanisms that regulate their protein stability and activity are discussed. Notably, the similarities and key differences are highlighted between the two paralogues including which partner proteins interact with which functional domains to regulate their activity.

YAP and TAZ, the conductors that orchestrate eye development, homeostasis, and disease

Yes-associated protein (YAP) and transcriptional coactivator with PDZ-binding motif (TAZ) are transcriptional coactivators established as a nexus in numerous signaling pathways, notably in Hippo signaling. Previous research revealed multifarious function of YAP and TAZ in oncology and cardiovasology. Recently, the focus has been laid on their pivotal role in eye morphogenesis and homeostasis. In this review, we synthesize advances of YAP and TAZ function during eye development in different model organisms, introduce their function in different ocular tissues and eye diseases, and highlight the potential for therapeutic interventions.

The physiological role of Motin family and its dysregulation in tumorigenesis

Members in Motin family, or Angiomotins (AMOTs), are adaptor proteins that localize in the membranous, cytoplasmic or nuclear fraction in a cell context-dependent manner. They control the bioprocesses such as migration, tight junction formation, cell polarity, and angiogenesis. Emerging evidences have demonstrated that AMOTs participate in cancer initiation and progression. Many of the previous studies have focused on the involvement of AMOTs in Hippo-YAP1 pathway. However, it has been controversial for years that AMOTs serve as either positive or negative growth regulators in different cancer types because of the various cellular origins. The molecular mechanisms of these opposite roles of AMOTs remain elusive. This review comprehensively summarized how AMOTs function physiologically and how their dysregulation promotes or inhibits tumorigenesis. Better understanding the functional roles of AMOTs in cancers may lead to an improvement of clinical interventions as well as development of novel therapeutic strategies for cancer patients.

WW and C2 domain-containing proteins regulate hepatic cell differentiation and tumorigenesis through the hippo signaling pathway

The Hippo pathway regulates cell differentiation, proliferation, and apoptosis. Upon activation, it inhibits the import of the transcriptional coactivator yes-associated protein (YAP) into the nucleus, thus suppressing transcription of pro-proliferative genes. Hence, dynamic and precise control of the Hippo pathway is crucial for organ size control and the prevention of tumor formation. Hippo signaling is controlled by a growing number of upstream regulators, including WW and C2 domain-containing (WWC) proteins, which trigger a serine/threonine kinase pathway. One component of this is the large tumor suppressor (LATS) kinase, which phosphorylates YAP, trapping it in the cytoplasm. WWC proteins have been shown to interact with LATS in vitro and stimulate its kinase activity, thus directly promoting cytoplasmic accumulation of phosphorylated YAP. However, the function of the WWC proteins in the regulation of cell proliferation, organ size control, and tumor prevention in vivo has not yet been determined. Here, we show that loss of hepatic WWC expression in mice leads to tissue overgrowth, inflammation, fibrosis, and formation of liver carcinoma. WWC-deficient mouse livers display reduced LATS activity, increased YAP-mediated gene transcription, and enhanced proliferation of hepatic progenitor cells. In addition, loss of WWC expression in the liver accelerates the turnover of angiomotin proteins, which act as negative regulators of YAP activity.

CONCLUSION

Our data define an essential in vivo function for WWC proteins as regulators of canonical and noncanonical Hippo signaling in hepatic cell growth and liver tumorigenesis. Thus, expression of WWC proteins may serve as novel prognostic factors in human liver carcinoma. (Hepatology 2018;67:1546-1559).

Upstairs, downstairs: spatial regulation of Hippo signalling

Cellular signalling lies at the heart of every decision involved in the development and homeostasis of multicellular organisms. The Hippo pathway was discovered nearly two decades ago through seminal work in Drosophila and rapidly emerged as a crucial signalling network implicated in developmental and oncogenic growth, tissue regeneration and stem cell biology. Here, we review recent advances in the field relating to the upstream regulation of Hippo signalling and the intracellular tug-of-war that tightly controls its main target, the transcriptional co-activator Yorkie/YAP.

Alternative Splicing in the Hippo Pathway-Implications for Disease and Potential Therapeutic Targets

Alternative splicing is a well-studied gene regulatory mechanism that produces biological diversity by allowing the production of multiple protein isoforms from a single gene. An involvement of alternative splicing in the key biological signalling Hippo pathway is emerging and offers new therapeutic avenues. This review discusses examples of alternative splicing in the Hippo pathway, how deregulation of these processes may contribute to disease and whether these processes offer new potential therapeutic targets.

Cysteine residues are essential for dimerization of Hippo pathway components YAP2L and TAZ

Hippo signalling pathway is an emerging signalling pathway that plays important roles in organ size control, tumorigenesis, metastasis, stress response, apoptosis, stem cell differentiation and renewal during development and tissue homeostasis. Recent studies reported that human serine/threonine protein kinase, Mst1, a core component of the Hippo pathway can be activated through formation of homodimer. However, it is still unclear whether or not other components of the Hippo pathway are also regulated through dimerization. Here we provide the first evidence that Hippo components and oncoprotein YAP2L and TAZ can form homodimer in vitro and in vivo by forming disulphide bond through cysteine residue(s). We have also shown that the homodimers of YAP2L/TAZ are more stable and showed more oncogenic behaviour than their corresponding monomers as revealed by colony formation and cell transformation assay. Since cysteine post-translational regulation plays important roles in redox signalling, tumorigenesis and drug resistance, further studies on the functional effect of this dimerization through post-translational modulation of cysteine residues in YAP2L/TAZ will provide a significant contribution to our understanding of the roles of YAP2L/TAZ in cancer development and therapy.

An evolutionarily conserved negative feedback mechanism in the Hippo pathway reflects functional difference between LATS1 and LATS2

The Hippo pathway represses YAP oncoprotein activity through phosphorylation by LATS kinases. Although variety of upstream components has been found to participate in the Hippo pathway, the existence and function of negative feedback has remained uncertain. We found that activated YAP, together with TEAD transcription factors, directly induces transcription of LATS2, but not LATS1, to form a negative feedback loop. We also observed increased mRNA levels of Hippo upstream components upon YAP activation. To reveal the physiological role of this negative feedback regulation, we deleted Lats2 or Lats1 in the liver-specific Sav1-knockout mouse model which develops a YAP-induced tumor. Additional deletion of Lats2 severely enhanced YAP-induced tumorigenic phenotypes in a liver specific Sav1 knock-out mouse model while additional deletion of Lats1 mildly affected the phenotype. Only Sav1 and Lats2 double knock-down cells formed larger colonies in soft agar assay, thereby recapitulating accelerated tumorigenesis seen in vivo. Importantly, this negative feedback is evolutionarily conserved, as Drosophila Yorkie (YAP ortholog) induces transcription of Warts (LATS2 ortholog) with Scalloped (TEAD ortholog). Collectively, we demonstrated the existence and function of an evolutionarily conserved negative feedback mechanism in the Hippo pathway, as well as the functional difference between LATS1 and LATS2 in regulation of YAP.

Angiomotin Family Members: Oncogenes or Tumor Suppressors?

Angiomotin (Amot) family contains three members: Amot (p80 and p130 isoforms), Amot-like protein 1 (Amotl1), and Amot-like protein 2 (Amotl2). Amot proteins play an important role in tube formation and migration of endothelial cells and the regulation of tight junctions, polarity, and epithelial-mesenchymal transition in epithelial cells. Moreover, these proteins regulate the proliferation and migration of cancer cells. In most cancers, Amot family members promote the proliferation and invasion of cancer cells, including breast cancer, osteosarcoma, colon cancer, prostate cancer, head and neck squamous cell carcinoma, cervical cancer, liver cancer, and renal cell cancer. However, in glioblastoma, ovarian cancer, and lung cancer, Amot inhibits the growth of cancer cells. In addition, there are controversies on the regulation of Yes-associated protein (YAP) by Amot. Amot promotes either the internalization of YAP into the nucleus or the retention of YAP in the cytoplasm of different cell types. Moreover, Amot regulates the AMPK, mTOR, Wnt, and MAPK signaling pathways. However, it is unclear whether Amot is an oncogene or a tumor suppressor gene in different cellular processes. This review focuses on the multifunctional roles of Amot in cancers.

Microbiota promotes systemic T-cell survival through suppression of an apoptotic factor

Symbiotic microbes impact the severity of a variety of diseases through regulation of T-cell development. However, little is known regarding the molecular mechanisms by which this is accomplished. Here we report that a secreted factor, Erdr1, is regulated by the microbiota to control T-cell apoptosis. Erdr1 expression was identified by transcriptome analysis to be elevated in splenic T cells from germfree and antibiotic-treated mice. Suppression of Erdr1 depends on detection of circulating microbial products by Toll-like receptors on T cells, and this regulation is conserved in human T cells. Erdr1 was found to function as an autocrine factor to induce apoptosis through caspase 3. Consistent with elevated levels of Erdr1, germfree mice have increased splenic T-cell apoptosis. RNA sequencing of Erdr1-overexpressing cells identified the up-regulation of genes involved in Fas-mediated cell death, and Erdr1 fails to induce apoptosis in Fas-deficient cells. Importantly, forced changes in Erdr1 expression levels dictate the survival of auto-reactive T cells and the clinical outcome of neuro-inflammatory autoimmune disease. Cellular survival is a fundamental feature regulating appropriate immune responses. We have identified a mechanism whereby the host integrates signals from the microbiota to control T-cell apoptosis, making regulation of Erdr1 a potential therapeutic target for autoimmune disease.

12-O-Tetradecanoylphorbol-13-acetate (TPA) is anti-tumorigenic in liver cancer cells via inhibiting YAP through AMOT

TPA stimulates carcinogenesis in various types of cancers. However, we found that TPA inhibits transformative phenotypes in liver cancer cells via the translocation of YAP from the nucleus, where it functions as a transcriptional co-factor, to the cytoplasm. Such effects led to a separation of YAP from its dependent transcription factors. The inhibitory effects of TPA on YAP were AMOT dependent. Without AMOT, TPA was unable to alter YAP activity. Importantly, the depletion of YAP and AMOT blocked the TPA-reduced transformative phenotypes. In sum, TPA has been established as an anti-tumorigenic drug in liver cancer cells via YAP and AMOT.

Novel transcriptome assembly and comparative toxicity pathway analysis in mahi-mahi (Coryphaena hippurus) embryos and larvae exposed to Deepwater Horizon oil

The impacts of Deepwater Horizon (DWH) oil on morphology and function during embryonic development have been documented for a number of fish species, including the economically and ecologically important pelagic species, mahi-mahi (Coryphaena hippurus). However, further investigations on molecular events and pathways responsible for developmental toxicity have been largely restricted due to the limited molecular data available for this species. We sought to establish the de novo transcriptomic database from the embryos and larvae of mahi-mahi exposed to water accommodated fractions (HEWAFs) of two DWH oil types (weathered and source oil), in an effort to advance our understanding of the molecular aspects involved during specific toxicity responses. By high throughput sequencing (HTS), we obtained the first de novo transcriptome of mahi-mahi, with 60,842 assembled transcripts and 30,518 BLAST hits. Among them, 2,345 genes were significantly regulated in 96hpf larvae after exposure to weathered oil. With comparative analysis to a reference-transcriptome-guided approach on gene ontology and tox-pathways, we confirmed the novel approach effective for exploring tox-pathways in non-model species, and also identified a list of co-expressed genes as potential biomarkers which will provide information for the construction of an Adverse Outcome Pathway which could be useful in Ecological Risk Assessments.

YAP and WWTR1: New targets for skin cancer treatment

The core components of the Hippo signaling pathway are a cascade of kinases that govern the phosphorylation of downstream transcriptional co-activators, namely, YES-associated protein (YAP) and WW domain-containing transcription regulator protein 1 (WWTR1, also known as TAZ). The Hippo signaling pathway is considered an important tumor-suppressor pathway, and its dysregulation has been noted in a variety of human cancers, in which YAP/WWTR1 enable cancerous cells to overcome contact inhibition, and to grow and spread uncontrollably. Interestingly, however, recent studies have told a somewhat different but perhaps more intriguing YAP/WWTR1 story, as these studies found that YAP/WWTR1 function as a central hub that integrates signals from multiple upstream signaling pathways, cell-cell interactions and mechanical forces and then bind to and activate different downstream transcriptional factors to direct cell social behavior and cell-cell interactions. In this review, we present the latest findings on the role of YAP/WWTR1 in skin physiology, pathology and tumorigenesis and discuss the statuses of newly developed therapeutic interventions that target YAP/WWTR1 in human cancers, as well as their prospects for use as skin cancer treatments.

Framework to function: mechanosensitive regulators of gene transcription

Mechanobiology has shifted our understanding of fundamental cellular and physiological functions. Changes to the stiffness of the extracellular matrix, cell rigidity, or shape of the cell environment were considered in the past to be a consequence of aging or pathological processes. We now understand that these factors can actually be causative biological mediators of cell growth to control organ size. Mechanical cues are known to trigger a relatively fast translocation of specific transcriptional co-factors such as MRTFs, YAP and TAZ from the cytoplasm to the cell nucleus to initiate discrete transcriptional programs. The focus of this review is the molecular mechanisms by which biophysical stimuli that induce changes in cytoplasmic actin dynamics are communicated within cells to elicit gene-specific transcription via nuclear localisation or activation of specialized transcription factors, namely MRTFs and the Hippo pathway effectors YAP and TAZ. We propose here that MRTFs, YAP and TAZ closely collaborate as mechano-effectors.

Conditional knockout of TFPI-1 in VSMCs of mice accelerates atherosclerosis by enhancing AMOT/YAP pathway

BACKGROUND

Tissue factor pathway inhibitor-1 (TFPI-1) has multiple functions and its precise role and molecular mechanism during the development of atherosclerosis are not clear.

OBJECTIVES

To determine the effect and molecular mechanism of TFPI-1 deficiency in vascular smooth muscle cells (VSMCs) in atherosclerosis in the apolipoprotein E knockout (ApoE^-/-) mouse.

METHODS AND RESULTS

A mouse model with a conditional knockout of TFPI-1 in VSMCs in an atherosclerosis-prone background (ApoE^-/-) was generated. Mice were fed a high fat diet for 18weeks and were then euthanized. Arterial trees and aortas were stained with Sudan IV and were labeled via immunohistochemistry. Cell proliferation and migration of VSMCs in atherosclerotic plaques were assessed. More atherosclerotic lesions and higher levels of proliferation and migration of VSMCs were observed in TFPI-1^fl/fl/Sma-Cre⁺ApoE^-/-mice. An interaction between TFPI-1 and angiomotin (AMOT) was identified in human VSMCs by mass spectrometry, immunoprecipitation and co-localization analyses. Signal pathway changes were detected by Western blot analysis, and the expression levels of target genes were determined by real-time PCR. Decreased phosphorylation of AMOT and Yes-associated protein 1 (YAP) in TFPI-1^fl/fl/Sma-Cre⁺ApoE^-/- mice resulted in increased expression levels of snail family zinc finger 2 (SLUG) and connective tissue growth factor (CTGF), which are target genes of the Hippo signaling pathway that have been verified as atherosclerosis candidate genes.

CONCLUSION

Deficiency in TFPI-1 in the VSMCs of ApoE^-/- mice accelerated the development of atherosclerosis by promoting the proliferation and migration of VSMCs which may be caused by the decreased phosphorylation of AMOT and YAP.

SIGNIFICANCE

TFPI-1 has been found to has an anticoagulant activity, induce cell apoptosis and prevent cell proliferation. For the first time, we constructed a line of conditional knockout mice in which the TPFI-1 gene is deleted in VSMCs. We found that TFPI-1 deficiency clearly promoted the development of atherosclerosis when these mice were crossed into an ApoE^-/-background. One notable feature of atherosclerosis is the proliferation and migration of smooth muscle cells. Previous reports involved TFPI-1 do not completely explain the proliferation and migration of VSMCs because heterozygous TF deficient (TF^±) mice bred in an ApoE^-/- background did not show diminished atherosclerosis compared to TF^+/+ mice bred in the same background. Our results first confirmed that TFPI-1 interacts with AMOT, which led to a decrease in the phosphorylation of YAP and further increased the genes expression of the proliferation and migration involved. Our results further confirmed that atherosclerosis was a localized disease.

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.

YAP Subcellular Localization and Hippo Pathway Transcriptome Analysis in Pediatric Hepatocellular Carcinoma

Pediatric hepatocellular carcinoma (HCC) is a rare tumor which is associated with an extremely high mortality rate due to lack of effective chemotherapy. Recently, the Hippo pathway and its transcriptional co-activator Yes-associated protein (YAP) have been shown to play a role in hepatocyte proliferation and development of HCC in animal models. Therefore, we sought to examine the activity of YAP and the expression of Hippo pathway components in tumor and non-neoplastic liver tissue from 7 pediatric patients with moderately differentiated HCC. None of the patients had underlying cirrhosis or viral hepatitis, which is commonly seen in adults with HCC. This highlights a major difference in the pathogenesis of HCC between children and adults. We found a statistically significant increase in YAP nuclear localization in 100% of tumors. YAP target gene (CCNE1, CTGF, Cyr61) mRNA expression was also increased in the tumors that had the most significant increase in YAP nuclear localization. Based on Ki67 co-localization studies YAP nuclear localization was not simply a marker of proliferation. Our results demonstrate a clear increase in YAP activity in moderately differentiated pediatric HCC, providing evidence that it may play an important role in tumor survival and propagation.

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.

Mechanoregulation of Wound Healing and Skin Homeostasis

Basic and clinical studies on mechanobiology of cells and tissues point to the importance of mechanical forces in the process of skin regeneration and wound healing. These studies result in the development of new therapies that use mechanical force which supports effective healing. A better understanding of mechanobiology will make it possible to develop biomaterials with appropriate physical and chemical properties used to treat poorly healing wounds. In addition, it will make it possible to design devices precisely controlling wound mechanics and to individualize a therapy depending on the type, size, and anatomical location of the wound in specific patients, which will increase the clinical efficiency of the therapy. Linking mechanobiology with the science of biomaterials and nanotechnology will enable in the near future precise interference in abnormal cell signaling responsible for the proliferation, differentiation, cell death, and restoration of the biological balance. The objective of this study is to point to the importance of mechanobiology in regeneration of skin damage and wound healing. The study describes the influence of rigidity of extracellular matrix and special restrictions on cell physiology. The study also defines how and what mechanical changes influence tissue regeneration and wound healing. The influence of mechanical signals in the process of proliferation, differentiation, and skin regeneration is tagged in the study.

A splicing isoform of TEAD4 attenuates the Hippo-YAP signalling to inhibit tumour proliferation

Aberrant splicing is frequently found in cancer, yet the biological consequences of such alterations are mostly undefined. Here we report that the Hippo–YAP signalling, a key pathway that regulates cell proliferation and organ size, is under control of a splicing switch. We show that TEAD4, the transcription factor that mediates Hippo–YAP signalling, undergoes alternative splicing facilitated by the tumour suppressor RBM4, producing a truncated isoform, TEAD4-S, which lacks an N-terminal DNA-binding domain, but maintains YAP interaction domain. TEAD4-S is located in both the nucleus and cytoplasm, acting as a dominant negative isoform to YAP activity. Consistently, TEAD4-S is reduced in cancer cells, and its re-expression suppresses cancer cell proliferation and migration, inhibiting tumour growth in xenograft mouse models. Furthermore, TEAD4-S is reduced in human cancers, and patients with elevated TEAD4-S levels have improved survival. Altogether, these data reveal a splicing switch that serves to fine tune the Hippo–YAP pathway.

The Hippo/Yap signalling pathway is found deregulated in several cancers. Here, the authors uncover an additional mechanism of YAP regulation that occurs via alternately spliced isoform of TEAD4, which acts as a dominant negative regulator of YAP-TEAD signalling.