The Hippo pathway effectors TAZ and YAP in development, homeostasis and disease

Dynamic Click Hydrogels for Xeno-Free Culture of Induced Pluripotent Stem Cells

Xeno-free, chemically defined poly(ethylene glycol) (PEG)-based hydrogels are being increasingly used for in vitro culture and differentiation of human induced pluripotent stem cells (hiPSCs). These synthetic matrices provide tunable gelation and adaptable material properties crucial for guiding stem cell fate. Here, sequential norbornene-click chemistries are integrated to form synthetic, dynamically tunable PEG-peptide hydrogels for hiPSCs culture and differentiation. Specifically, hiPSCs are photoencapsulated in thiol-norbornene hydrogels crosslinked by multiarm PEG-norbornene (PEG-NB) and proteaselabile crosslinkers. These matrices are used to evaluate hiPSC growth under the influence of extracellular matrix properties. Tetrazine-norbornene (Tz-NB) click reaction is then employed to dynamically stiffen the cell-laden hydrogels. Fast reactive Tz and its stable derivative methyltetrazine (mTz) are tethered to multiarm PEG, yielding mono-functionalized PEG-Tz, PEG-mTz, and dualfunctionalized PEG-Tz/mTz that react with PEG-NB to form additional crosslinks in the cell-laden hydrogels. The versatility of Tz-NB stiffening is demonstrated with different Tz-modified macromers or by intermittent incubation of PEG-Tz for temporal stiffening. Finally, the Tz-NB-mediated dynamic stiffening is explored for 4D culture and definitive endoderm differentiation of hiPSCs. Overall, this dynamic hydrogel platform affords exquisite controls of hydrogel crosslinking for serving as a xeno-free and dynamic stem cell niche.

TAZ/Wnt-β-catenin/c-MYC axis regulates cystogenesis in polycystic kidney disease

Autosomal-dominant polycystic kidney disease (ADPKD) is the most common genetic renal disease, primarily caused by germline mutation of PKD1 or PKD2, leading to end-stage renal disease. There are few cures for ADPKD, although many researchers are trying to find a cure. The Hippo signaling pathway regulates organ growth and cell proliferation. Transcriptional coactivator with PDZ-binding motif (TAZ) is a Hippo signaling effector. In this study, we demonstrated that the PKD1–TAZ–Wnt–β-catenin–c-MYC signaling axis plays a critical role in cystogenesis. Endo IWR1 treatment, which inhibited β-catenin activity via AXIN stabilization, reduced cyst growth in an ADPKD model. Our findings provide a potential therapeutic target against ADPKD and would be important for clinical translation.

Autosomal-dominant polycystic kidney disease (ADPKD) is the most common genetic renal disease, primarily caused by germline mutation of PKD1 or PKD2, leading to end-stage renal disease. The Hippo signaling pathway regulates organ growth and cell proliferation. Herein, we demonstrate the regulatory mechanism of cystogenesis in ADPKD by transcriptional coactivator with PDZ-binding motif (TAZ), a Hippo signaling effector. TAZ was highly expressed around the renal cyst-lining epithelial cells of Pkd1-deficient mice. Loss of Taz in Pkd1-deficient mice reduced cyst formation. In wild type, TAZ interacted with PKD1, which inactivated β-catenin. In contrast, in PKD1-deficient cells, TAZ interacted with AXIN1, thus increasing β-catenin activity. Interaction of TAZ with AXIN1 in PKD1-deficient cells resulted in nuclear accumulation of TAZ together with β-catenin, which up-regulated c-MYC expression. Our findings suggest that the PKD1–TAZ–Wnt–β-catenin–c-MYC signaling axis plays a critical role in cystogenesis and might be a potential therapeutic target against ADPKD.

YAP/TAZ Signalling in Colorectal Cancer: Lessons from Consensus Molecular Subtypes

Simple Summary

Colorectal cancer (CRC) is a heterogeneous disease that can be divided into 4 consensus molecular subtypes (CMS) according to molecular profiling. The CMS classification is now considered as a reference framework for understanding the heterogeneity of CRC and for the implementation of precision medicine. Although the contribution of YAP/TAZ signalling to CRC has been intensively studied, there is little information on its role within each CMS subtype. This article aims to provide an overview of our knowledge of YAP/TAZ in CRC through the lens of the CMS classification.

Abstract

Recent advance in the characterization of the heterogeneity of colorectal cancer has led to the definition of a consensus molecular classification within four CMS subgroups, each associated with specific molecular and clinical features. Investigating the signalling pathways that drive colorectal cancer progression in relation to the CMS classification may help design therapeutic strategies tailored for each CMS subtype. The two main effectors of the Hippo pathway YAP and its paralogue TAZ have been intensively scrutinized for their contribution to colon carcinogenesis. Here, we review the knowledge of YAP/TAZ implication in colorectal cancer from the perspective of the CMS framework. We identify gaps in our current understanding and delineate research avenues for future work.

Targeting Mechanotransduction in Osteosarcoma: A Comparative Oncology Perspective

Mechanotransduction is the process in which cells can convert extracellular mechanical stimuli into biochemical changes within a cell. While this a normal process for physiological development and function in many organ systems, tumour cells can exploit this process to promote tumour progression. Here we summarise the current state of knowledge of mechanotransduction in osteosarcoma (OSA), the most common primary bone tumour, referencing both human and canine models and other similar mesenchymal malignancies (e.g., Ewing sarcoma). Specifically, we discuss the mechanical properties of OSA cells, the pathways that these cells utilise to respond to external mechanical cues, and mechanotransduction-targeting strategies tested in OSA so far. We point out gaps in the literature and propose avenues to address them. Understanding how the physical microenvironment influences cell signalling and behaviour will lead to the improved design of strategies to target the mechanical vulnerabilities of OSA cells.

It takes two to tango: coupling of Hippo pathway and redox signaling in biological process

Hippo pathway is a chain of kinases consists of a series of protein kinases and transcription factors. Meanwhile, oxidative stress is a condition of elevated concentrations of reactive oxygen species (ROS) that cause molecular damage to vital structures and functions. Both of them are key regulators in cell proliferation, survival, and development. These processes are strictly regulated by highly coordinated mechanisms, including c-Jun n-terminal kinase (JNK) pathway, mTOR pathway and a number of extrinsic and intrinsic factors. Recently, emerging evidence suggests that Hippo pathway is involved in the responses to cellular stresses, including mechanic stress, DNA damage, and oxidative stress, to mediate biological process, such as apoptosis, pyroptosis, and metastasis. But the exact mechanism remains to be further explored. Therefore, the purpose of this review is to summarize recent findings and discuss how Hippo pathway, oxidative stress, and the crosstalk between them regulate some biological process which determines cell fate.

Fibroblast mechanosensing, SKI and Hippo signaling and the cardiac fibroblast phenotype: Looking beyond TGF-β

Cardiac fibroblast activation to hyper-synthetic myofibroblasts following a pathological stimulus or in response to a substrate with increased stiffness may be a key tipping point for the evolution of cardiac fibrosis. Cardiac fibrosis per se is associated with progressive loss of heart pump function and is a primary contributor to heart failure. While TGF-β is a common cytokine stimulus associated with fibroblast activation, a druggable target to quell this driver of fibrosis has remained an elusive therapeutic goal due to its ubiquitous use by different cell types and also in the signaling complexity associated with SMADs and other effector pathways. More recently, mechanical stimulus of fibroblastic cells has been revealed as a major point of activation; this includes cardiac fibroblasts. Further, the complexity of TGF-β signaling has been offset by the discovery of members of the SKI family of proteins and their inherent anti-fibrotic properties. In this respect, SKI is a protein that may bind a number of TGF-β associated proteins including SMADs, as well as signaling proteins from other pathways, including Hippo. As SKI is also known to directly deactivate cardiac myofibroblasts to fibroblasts, this mode of action is a putative candidate for further study into the amelioration of cardiac fibrosis. Herein we provide a synthesis of this topic and highlight novel candidate pathways to explore in the treatment of cardiac fibrosis.

RNA binding proteins: Linking mechanotransduction and tumor metastasis

Mechanotransduction is the leading cellular process that mammalian cells adopted to receive and respond to various mechanical cues from their local microenvironment. Increasing evidence suggests that mechano-transduction is involved in many physiological and disease conditions, ranging from early embryonic development, organogenesis, to a variety of human diseases including cancer. Mechanotransduction is mediated through several classes of senor proteins on the cell surface, intracellular signaling mediators, and core transcriptional regulation networks. Dissecting the molecular mechanisms regulating mechanotransduction and their association with cancer metastasis has received much attention in recent years. RNA binding proteins (RBPs) are a special group of nucleic acid interacting factors that participate in many important cellular processes. In this review, we would like to summarize recent research progresses in understanding the role of RBPs-mediated regulation in mechanotransduction and cancer metastasis. Those intriguing findings will provide novel insights for the disease and guide the potential development of new therapeutic approaches.

YAP and TAZ Are Not Identical Twins

Yes-associated protein (YAP) and TAZ (WW domain containing transcription regulator 1, or WWTR1) are paralog transcriptional regulators, able to integrate mechanical, metabolic, and signaling inputs to regulate cell growth and differentiation during development and neoplastic progression. YAP and TAZ hold common and distinctive structural features, reflecting only partially overlapping regulatory mechanisms. The two paralogs interact with both shared and specific transcriptional partners and control nonidentical transcriptional programs. Although most of the available literature considers YAP and TAZ as functionally redundant, they play distinctive or even contrasting roles in different contexts. The issue of their divergent roles is currently underexplored but holds fundamental implications for mechanistic and translational studies. Here, we aim to review the available literature on the biological functions of YAP and TAZ, highlighting differential roles that distinguish these two paralogues.

A TAZ-AXL-ABL2 Feed-Forward Signaling Axis Promotes Lung Adenocarcinoma Brain Metastasis

Brain metastases are a common consequence of advanced lung cancer, resulting in cranial neuropathies and increased mortality. Currently, there are no effective therapies to treat brain metastases due to a lack of actionable targets and a failure of systemic therapies to penetrate the blood-brain barrier (BBB). Here we identify an autocrine signaling axis required for lung adenocarcinoma brain metastasis, whereby nuclear accumulation of the TAZ transcriptional co-activator drives expression of a panel of transcripts enriched in brain metastases, including ABL2 and AXL, encoding for protein tyrosine kinases that engage in bidirectional signaling. Activation of ABL2 in turn promotes TAZ tyrosine phosphorylation and nuclear localization, establishing an autocrine AXL-ABL2-TAZ feed-forward signaling loop required for brain metastasis colonization. Notably, treatment with a BBB-penetrant ABL allosteric inhibitor or knockdown of ABL2, AXL, or TAZ markedly decreases brain metastases. These findings suggest that ABL and AXL inhibitors might be effective against brain metastases.

An Insight into Reprogramming Barriers to iPSC Generation

Derivation of induced Pluripotent Stem Cells (iPSCs) by reprogramming somatic cells to a pluripotent state has revolutionized stem cell research. Ensuing this, various groups have used genetic and non-genetic approaches to generate iPSCs from numerous cell types. However, achieving a pluripotent state in most of the reprogramming studies is marred by serious limitations such as low reprogramming efficiency and slow kinetics. These limitations are mainly due to the presence of potent barriers that exist during reprogramming when a mature cell is coaxed to achieve a pluripotent state. Several studies have revealed that intrinsic factors such as non-optimal stoichiometry of reprogramming factors, specific signaling pathways, cellular senescence, pluripotency-inhibiting transcription factors and microRNAs act as a roadblock. In addition, the epigenetic state of somatic cells and specific epigenetic modifications that occur during reprogramming also remarkably impede the generation of iPSCs. In this review, we present a comprehensive overview of the barriers that inhibit reprogramming and the understanding of which will pave the way to develop safe strategies for efficient reprogramming.

YAP-Mediated Repression of HRK Regulates Tumor Growth, Therapy Response, and Survival Under Tumor Environmental Stress in Neuroblastoma

Following chemotherapy and relapse, high-risk neuroblastoma tumors harbor more genomic alterations than at diagnosis, including increased transcriptional activity of the Yes-associated protein (YAP), a key downstream component of the Hippo signaling network. Although YAP has been implicated in many cancer types, its functional role in the aggressive pediatric cancer neuroblastoma is not well-characterized. In this study, we performed genetic manipulation of YAP in human-derived neuroblastoma cell lines to investigate YAP function in key aspects of the malignant phenotype, including mesenchymal properties, tumor growth, chemotherapy response, and MEK inhibitor response. Standard cytotoxic therapy induced YAP expression and transcriptional activity in patient-derived xenografts treated in vivo, which may contribute to neuroblastoma recurrence. Moreover, YAP promoted a mesenchymal phenotype in high-risk neuroblastoma that modulated tumor growth and therapy resistance in vivo. Finally, the BH3-only protein, Harakiri (HRK), was identified as a novel target inhibited by YAP, which, when suppressed, prevented apoptosis in response to nutrient deprivation in vitro and promoted tumor aggression, chemotherapy resistance, and MEK inhibitor resistance in vivo. Collectively, these findings suggest that YAP inhibition may improve chemotherapy response in patients with neuroblastoma via its regulation of HRK, thus providing a critical strategic complement to MEK inhibitor therapy. SIGNIFICANCE: This study identifies HRK as a novel tumor suppressor in neuroblastoma and suggests dual MEK and YAP inhibition as a potential therapeutic strategy in RAS-hyperactivated neuroblastomas.

Selective YAP/TAZ inhibition in fibroblasts via dopamine receptor D1 agonism reverses fibrosis

Tissue fibrosis is characterized by uncontrolled deposition and diminished clearance of fibrous connective tissue proteins, ultimately leading to organ scarring. Yes-associated protein (YAP) and transcriptional coactivator with PDZ-binding motif (TAZ) have recently emerged as pivotal drivers of mesenchymal cell activation in human fibrosis. Therapeutic strategies inhibiting YAP and TAZ have been hindered by the critical role that these proteins play in regeneration and homeostasis in different cell types. Here, we find that the Gα_s-coupled dopamine receptor D1 (DRD1) is preferentially expressed in lung and liver mesenchymal cells relative to other resident cells of these organs. Agonism of DRD1 selectively inhibits YAP/TAZ function in mesenchymal cells and shifts their phenotype from profibrotic to fibrosis resolving, reversing in vitro extracellular matrix stiffening and in vivo tissue fibrosis in mouse models. Aromatic l-amino acid decarboxylase [DOPA decarboxylase (DDC)], the enzyme responsible for the final step in biosynthesis of dopamine, is decreased in the lungs of subjects with idiopathic pulmonary fibrosis, and its expression inversely correlates with disease severity, consistent with an endogenous protective role for dopamine signaling that is lost in pulmonary fibrosis. Together, these findings establish a pharmacologically tractable and cell-selective approach to targeting YAP/TAZ via DRD1 that reverses fibrosis in mice.

Microenvironment stiffness requires decellularized cardiac extracellular matrix to promote heart regeneration in the neonatal mouse heart

The transient period of regeneration potential in the postnatal heart suggests molecular changes with maturation influence the cardiac response to damage. We have previously demonstrated that injury and exercise can stimulate cardiomyocyte proliferation in the adult heart suggesting a sensitivity to exogenous signals. Here, we consider whether exogenous fetal ECM and mechanically unloading interstitial matrix can drive regeneration after myocardial infarction (MI) surgery in low-regenerative hearts of day5 mice. Compared to controls, exogenous fetal ECM increases cardiac function and lowers fibrosis at 3 weeks post-injury and this effect can be augmented by softening heart tissue. In vitro experiments support a mechano-sensitivity to exogenous ECM signaling. We tested potential mechanisms and observed that fetal ECM increases nuclear YAP localization which could be enhanced by pharmacological stabilization of the cytoskeleton. Blocking YAP expression lowered fetal ECM effects though not completely. Lastly we observed mechanically unloading heart interstitial matrix increased agrin expression, an extracellular node in the YAP signaling pathway. Collectively, these data support a combined effect of exogenous factors and mechanical activity in altering agrin expression, cytoskeletal remodeling, and YAP signaling in driving cardiomyocyte cell cycle activity and regeneration in postnatal non-regenerative mice. STATEMENT OF SIGNIFICANCE: With the purpose of developing regenerative strategies, we investigate the influence of the local niche on the cardiac injury response. We conclude tissue stiffness, as anticipated in aging or disease, impairs regenerative therapeutics. Most novel, mechanical unloading facilitates enhanced cardiac regeneration only after cells are pushed into a permissive state by fetal biomolecules. Specifically, mechanical unloading appears to increase extracellular agrin expression that amplifies fetal-stimulation of nuclear YAP signaling which correlates with observed increases of cell cycle activity in cardiomyocytes. The results further suggest the cytoskeleton is critical to this interaction between mechanical unloading and independently actived YAP signaling. Using animal models, tissue explants, and cells, this work indicates that local mechanical stimuli can augment proliferating-permissive cardiomyocytes in the natural cardiac niche.

Effect of Maternal Age on Hippo Pathway Related Gene Expressions and Protein Localization Pattern in Human Embryos

Objective

The Hippo pathway plays an important role in embryo development, and separation of trophectoderm (TE) and inner cell mass (ICM) cell lines. Therefore, this study investigated effect of maternal age on activity of Hippo pathway in human embryos.

Materials and Methods

In this experimental study, the developed up embryos to the blastocyst stage and the embryos whose growth stopped at the morula stage were collected from women aged 20-30 years old (young group, 94 embryos) and >37 years (old group, 89 embryos). Expression of OCT4, SOX2, CDX2, GATA3, YAP genes and the relevant proteins, in the both groups were evaluated using respectively quantitative reverse transcription-polymerase chain reaction (qRT-PCR) and immunofluorescence methods.

Results

There was no significant difference in the expression level of OCT4, SOX2, CDX2, GATA3 and YAP genes in blastocyst and morula stages, between the two groups. However, SOX2 and CDX2 gene expressions in morula stage embryos of the old group was statistically lower than that of the young group (P=0.007 and P=0.008, respectively). Additionally, in the embryos collected from women with >37 years of age, at the blastocyst stage, phospho-YAP (p-YAP) protein was found to be accumulated in the TE, but it was almost disappeared from the ICM. Additionally, in the old group, contrary to the expectation, YAP protein was expressed in the ICM, rather than TE.

Conclusion

The results of this study showed that YAP and P-YAP among the Hippo signalling pathway may be altered by increasing age.

New insights into the core Hippo signaling and biological macromolecules interactions in the biology of solid tumors

As an evolutionarily conserved pathway, Hippo signaling pathway impacts different pathology and physiology processes such as wound healing, tissue repair/size and regeneration. When some components of Hippo signaling dysregulated, it affects cancer cells proliferation. Moreover, the relation Hippo pathway with other signaling including Wnt, TGFβ, Notch, and EGFR signaling leaves effect on the proliferation of cancer cells. Utilizing a number of therapeutic approaches, such as siRNAs and long noncoding RNA (lncRNA) to prevent cancer cells through the targeting of Hippo pathways, can provide new insights into cancer target therapy. The purpose of present review, first of all, is to demonstrate the importance of Hippo signaling and its relation with other signaling pathways in cancer. It also tries to demonstrate targeting Hippo signaling progress in cancer therapy.

Isoprenylcysteine carboxylmethyltransferase is required for the impact of mutant KRAS on TAZ protein level and cancer cell self-renewal

Cancer stem cells possess the capacity for self-renewal and resistance to chemotherapy. It is therefore crucial to understand the molecular regulators of stemness in the quest to develop effective cancer therapies. TAZ is a transcription activator that promotes stem cell functions in post-development mammalian cells; suppression of TAZ activity reduces or eliminates cancer stemness in select cancers. Isoprenylcysteine carboxylmethyltransferase (ICMT) is the unique enzyme of the last step of posttranslational prenylation processing pathway that modifies several oncogenic proteins, including RAS. We found that suppression of ICMT results in reduced self-renewal/stemness in KRAS-driven pancreatic and breast cancer cells. Silencing of ICMT led to significant reduction of TAZ protein levels and loss of self-renewal ability, which could be reversed by overexpressing mutant KRAS, demonstrating the functional impact of ICMT modification on the ability of KRAS to control TAZ stability and function. Contrary to expectation, YAP protein levels appear to be much less susceptible than TAZ to the regulation by ICMT and KRAS, and YAP is less consequential in regulating stemness characteristics in these cells. Further, we found that the ICMT-dependent KRAS regulation of TAZ was mediated through RAF, but not PI3K, signaling. Functionally, we demonstrate that a signaling cascade from ICMT modification of KRAS to TAZ protein stability supports cancer cell self-renewal abilities in both in vitro and in vivo settings. In addition, studies using the proof-of-concept small molecule inhibitors of ICMT confirmed its role in regulating TAZ and self-renewal, demonstrating the potential utility of targeting ICMT to control aggressive KRAS-driven cancers.

YAP Aggravates Inflammatory Bowel Disease by Regulating M1/M2 Macrophage Polarization and Gut Microbial Homeostasis

Inflammation, epithelial cell regeneration, macrophage polarization, and gut microbial homeostasis are critical for the pathological processes associated with inflammatory bowel disease (IBD). YAP (Yes-associated protein) is a key component of the Hippo pathway and was recently suggested to promote epithelial cell regeneration for IBD recovery. However, it is unclear how YAP regulates macrophage polarization, inflammation, and gut microbial homeostasis. Although YAP has been shown to promote epithelial regeneration and alleviate IBD, here we show that YAP in macrophages aggravates IBD, accompanied by the production of antimicrobial peptides and changes in gut microbiota. YAP impairs interleukin-4 (IL-4)/IL-13-induced M2 macrophage polarization while promoting lipopolysaccharide (LPS)/interferon γ (IFN-γ)-triggered M1 macrophage activation for IL-6 production. In addition, YAP expression is differently regulated during the induction of M2 versus M1 macrophages. This study suggests that fully understanding the multiple functions of YAP in different cell types is crucial for IBD therapy.

Pivotal role of the transcriptional co-activator YAP in trophoblast stemness of the developing human placenta

Various pregnancy complications, such as severe forms of preeclampsia or intrauterine growth restriction, are thought to arise from failures in the differentiation of human placental trophoblasts. Progenitors of the latter either develop into invasive extravillous trophoblasts, remodeling the uterine vasculature, or fuse into multinuclear syncytiotrophoblasts transporting oxygen and nutrients to the growing fetus. However, key regulatory factors controlling trophoblast self-renewal and differentiation have been poorly elucidated. Using primary cells, three-dimensional organoids, and CRISPR-Cas9 genome-edited JEG-3 clones, we herein show that YAP, the transcriptional coactivator of the Hippo signaling pathway, promotes maintenance of cytotrophoblast progenitors by different genomic mechanisms. Genetic or chemical manipulation of YAP in these cellular models revealed that it stimulates proliferation and expression of cell cycle regulators and stemness-associated genes, but inhibits cell fusion and production of syncytiotrophoblast (STB)-specific proteins, such as hCG and GDF15. Genome-wide comparisons of primary villous cytotrophoblasts overexpressing constitutively active YAP-5SA with YAP KO cells and syncytializing trophoblasts revealed common target genes involved in trophoblast stemness and differentiation. ChIP-qPCR unraveled that YAP-5SA overexpression increased binding of YAP-TEAD4 complexes to promoters of proliferation-associated genes such as CCNA and CDK6 Moreover, repressive YAP-TEAD4 complexes containing the histone methyltransferase EZH2 were detected in the genomic regions of the STB-specific CGB5 and CGB7 genes. In summary, YAP plays a pivotal role in the maintenance of the human placental trophoblast epithelium. Besides activating stemness factors, it also directly represses genes promoting trophoblast cell fusion.

Yes-associated protein (YAP) and transcriptional coactivator with a PDZ-binding motif (TAZ): a nexus between hypoxia and cancer

Hypoxia is a common feature of solid tumors. As transcription factors, hypoxia-inducible factors (HIFs) are the master regulators of the hypoxic microenvironment; their target genes function in tumorigenesis and tumor development. Intriguingly, both yes-associated protein (YAP) and its paralog transcriptional coactivator with a PDZ-binding motif (TAZ) play fundamental roles in the malignant progression of hypoxic tumors. As downstream effectors of the mammalian Hippo pathway, YAP and/or TAZ (YAP/TAZ) are phosphorylated and sequestered in the cytoplasm by the large tumor suppressor kinase 1/2 (LATS1/2)-MOB kinase activator 1 (MOB1) complex, which restricts the transcriptional activity of YAP/TAZ. However, dephosphorylated YAP/TAZ have the ability to translocate to the nucleus where they induce transcription of target genes, most of which are closely related to cancer. Herein we review the tumor-related signaling crosstalk between YAP/TAZ and hypoxia, describe current agents and therapeutic strategies targeting the hypoxia–YAP/TAZ axis, and highlight questions that might have a potential impact in the future.

Axon-dependent expression of YAP/TAZ mediates Schwann cell remyelination but not proliferation after nerve injury

Previously we showed that YAP/TAZ promote not only proliferation but also differentiation of immature Schwann cells (SCs), thereby forming and maintaining the myelin sheath around peripheral axons (Grove et al., 2017). Here we show that YAP/TAZ are required for mature SCs to restore peripheral myelination, but not to proliferate, after nerve injury. We find that YAP/TAZ dramatically disappear from SCs of adult mice concurrent with axon degeneration after nerve injury. They reappear in SCs only if axons regenerate. YAP/TAZ ablation does not impair SC proliferation or transdifferentiation into growth promoting repair SCs. SCs lacking YAP/TAZ, however, fail to upregulate myelin-associated genes and completely fail to remyelinate regenerated axons. We also show that both YAP and TAZ are redundantly required for optimal remyelination. These findings suggest that axons regulate transcriptional activity of YAP/TAZ in adult SCs and that YAP/TAZ are essential for functional regeneration of peripheral nerve.

Targeting Hippo signaling pathway by phytochemicals in cancer therapy

The current era of cancer research has been continuously advancing upon identifying novel aspects of tumorigenesis and the principal mechanisms behind the unleashed proliferation, invasion, drug resistance and immortality of cancer cells in hopes of exploiting these findings to achieve a more effective treatment for cancer. In pursuit of this goal, the identification of the first components of an extremely important regulatory pathway in Drosophila melanogaster that largely determines cell fate during the developmental stages, ended up in the discovery of the highly sophisticated Hippo signaling cascade. Soon after, it was revealed that deregulation of the components of this pathway either via mutations or through epigenetic alterations can be observed in a vast variety of tumors and these alterations greatly contribute to the neoplastic transformation of cells, their survival, growth and resistance to therapy. As more hidden aspects of this pathway such as its widespread entanglement with other major cellular signaling pathways are continuously being uncovered, many researchers have sought over the past decade to find ways of therapeutic interventions targeting the major components of the Hippo cascade. To date, various approaches such as the use of exogenous targeting miRNAs and different molecular inhibitors have been recruited herein, among which naturally occurring compounds have shown a great promise. On such a basis, in the present work we review the current understanding of Hippo pathway and the most recent evidence on targeting its components using natural plant-derived phytochemicals.

Morphogenetic mechanisms forming the notochord rod: The turgor pressure-sheath strength model

The notochord is a defining feature of chordates. During notochord formation in vertebrates and tunicates, notochord cells display dynamic morphogenetic movement, called convergent extension, in which cells intercalate and align at the dorsal midline. However, in cephalochordates, the most basal group of chordates, the notochord is formed without convergent extension. It is simply developed from mesodermal cells at the dorsal midline. This suggests that convergent extension movement of notochord cells is a secondarily acquired developmental attribute in the common ancestor of olfactores (vertebrates + tunicates), and that the chordate ancestor innovated the notochord upon a foundation of morphogenetic mechanisms independent of cell movement. Therefore, this review focuses on biological features specific to notochord cells, which have been well studied using clawed frogs, zebrafish, and tunicates. Attributes of notochord cells, such as vacuolation, membrane trafficking, extracellular matrix formation, and apoptosis, can be understood in terms of two properties: turgor pressure of vacuoles and strength of the notochord sheath. To maintain the straight rod-like structure of the notochord, these parameters must be counterbalanced. In the future, the turgor pressure-sheath strength model, proposed in this review, will be examined in light of quantitative molecular data and mathematical simulations, illuminating the evolutionary origin of the notochord.

The Role of the Hippo Pathway in Breast Cancer Carcinogenesis, Prognosis, and Treatment: A Systematic Review

Background

The Hippo pathway is a developmental pathway recently discovered in Drosophila melanogaster; in mammals it normally controls organ development and wound healing. Hippo signaling is deregulated in breast cancer (BC). MST1/2 and LATS1/2 kinases are the upstream molecular elements of Hippo signaling which phosphorylate and regulate the two effectors of Hippo signaling, YAP1 and TAZ cotranscriptional activators. The two molecular effectors of the Hippo pathway facilitate their activity through TEAD transcription factors. Several molecular pathways with known oncogenic functions cross-talk with the Hippo pathway.

Methods

A systematic review studying the correlation of the Hippo pathway with BC tumorigenesis, prognosis, and treatment was performed.

Results

Recent literature highlights the critical role of Hippo signaling in a wide spectrum of biological mechanisms in BC.

Discussion

The Hippo pathway has a crucial position in BC molecular biology, cellular behavior, and response to treatment. Targeting the Hippo pathway could potentially improve the prognosis and outcome of BC patients.

Expression and prognostic significance of YAP, TAZ, TEAD4 and p73 in human laryngeal cancer

OBJECTIVES

The Hippo signaling pathway plays a critical role in organ size control and tissue homeostasis and its perturbation is associated with tumorigenesis. YAP (Yes associated protein) and TAZ (transcriptional co-activator with PDZ- binding motif) are the major nuclear effectors of the Hippo pathway interacting with TEADs (TEA domain) and p73 transcriptional factors to regulate gene expression. Altered expression of the above proteins promotes tumor initiation, progression and metastasis in a variety of cancer types. This study addresses their expression and prognostic significance in human laryngeal carcinoma.

METHODS

Protein expression of YAP, TAZ, TEAD4 and p73 was examined by immunohistochemistry in 121 human laryngeal squamous cell carcinomas. Correlations with clinicopathological data and survival were evaluated.

RESULTS

All proteins were overexpressed in human laryngeal carcinomas compared to non-neoplastic adjacent epithelium. High expression of YAP, TAZ, TEAD4 and p73 correlated significantly with high grade, advanced stage, supraglottic location of tumor, nodal metastases and recurrence. Furthermore, high expression of all proteins was significantly associated with poor overall and disease- free survival. p73 expression proved to be an independent predictive factor of survival and YAP expression proved to be an independent predictive factor of disease recurrence.

CONCLUSIONS

Deregulation of the expression of the Hippo pathway proteins is implicated in human laryngeal carcinogenesis and YAP and p73 have prognostic significance in the outcome of the disease.

Targeted Disruption of Lats1 and Lats2 in Mice Impairs Adrenal Cortex Development and Alters Adrenocortical Cell Fate

It has recently been shown that the loss of the Hippo signaling effectors Yes-associated protein (YAP) and transcriptional coactivator with PDZ-binding motif (TAZ) in adrenocortical steroidogenic cells impairs the postnatal maintenance of the adrenal gland. To further explore the role of Hippo signaling in mouse adrenocortical cells, we conditionally deleted the key Hippo kinases large tumor suppressor homolog kinases 1 and -2 (Lats1 and Lats2, two kinases that antagonize YAP and TAZ transcriptional co-regulatory activity) in steroidogenic cells using an Nr5a1-cre strain (Lats1flox/flox;Lats2flox/flox;Nr5a1-cre). We report here that developing adrenocortical cells adopt characteristics of myofibroblasts in both male and female Lats1flox/flox;Lats2flox/flox;Nr5a1-cre mice, resulting in a loss of steroidogenic gene expression, adrenal failure and death by 2 to 3 weeks of age. A marked accumulation of YAP and TAZ in the nuclei of the myofibroblast-like cell population with an accompanying increase in the expression of their transcriptional target genes in the adrenal glands of Lats1flox/flox;Lats2flox/flox;Nr5a1-cre animals suggested that the myofibroblastic differentiation could be attributed in part to YAP and TAZ. Taken together, our results suggest that Hippo signaling is required to maintain proper adrenocortical cell differentiation and suppresses their differentiation into myofibroblast-like cells.

Changes in Protein Phosphorylation during Salivary Gland Degeneration in Haemaphysalis longicornis

The ticks feed large amount of blood from their hosts and transmit pathogens to the victims. The salivary gland plays an important role in the blood feeding. When the female ticks are near engorgement, the salivary gland gradually loses its functions and begins to rapidly degenerate. In this study, data-independent acquisition quantitative proteomics was used to study changes in the phosphorylation modification of proteins during salivary gland degeneration in Haemaphysalis longicornis. In this quantitative study, 400 phosphorylated proteins and 850 phosphorylation modification sites were identified. Trough RNA interference experiments, we found that among the proteins with changes in phosphorylation, apoptosis-promoting Hippo protein played a role in salivary gland degeneration.

Combining Nanomaterials and Developmental Pathways to Design New Treatments for Cardiac Regeneration: The Pulsing Heart of Advanced Therapies

The research for heart therapies is challenged by the limited intrinsic regenerative capacity of the adult heart. Moreover, it has been hampered by the poor results obtained by tissue engineering and regenerative medicine attempts at generating functional beating constructs able to integrate with the host tissue. For this reason, organ transplantation remains the elective treatment for end-stage heart failure, while novel strategies aiming to promote cardiac regeneration or repair lag behind. The recent discovery that adult cardiomyocytes can be ectopically induced to enter the cell cycle and proliferate by a combination of microRNAs and cardioprotective drugs, like anti-oxidant, anti-inflammatory, anti-coagulants and anti-platelets agents, fueled the quest for new strategies suited to foster cardiac repair. While proposing a revolutionary approach for heart regeneration, these studies raised serious issues regarding the efficient controlled delivery of the therapeutic cargo, as well as its timely removal or metabolic inactivation from the site of action. Especially, there is need for innovative treatment because of evidence of severe side effects caused by pleiotropic drugs. Biocompatible nanoparticles possess unique physico-chemical properties that have been extensively exploited for overcoming the limitations of standard medical therapies. Researchers have put great efforts into the optimization of the nanoparticles synthesis and functionalization, to control their interactions with the biological milieu and use as a viable alternative to traditional approaches. Nanoparticles can be used for diagnosis and deliver therapies in a personalized and targeted fashion. Regarding the treatment of cardiovascular diseases, nanoparticles-based strategies have provided very promising outcomes, in preclinical studies, during the last years. Efficient encapsulation of a large variety of cargos, specific release at the desired site and improvement of cardiac function are some of the main achievements reached so far by nanoparticle-based treatments in animal models. This work offers an overview on the recent nanomedical applications for cardiac regeneration and highlights how the versatility of nanomaterials can be combined with the newest molecular biology discoveries to advance cardiac regeneration therapies.

From gut to glutes: The critical role of niche signals in the maintenance and renewal of adult stem cells

Stem cell behavior is tightly regulated by spatiotemporal signaling from the niche, which is a four-dimensional microenvironment that can instruct stem cells to remain quiescent, self-renew, proliferate, or differentiate. In this review, we discuss recent advances in understanding the signaling cues provided by the stem cell niche in two contrasting adult tissues, the rapidly cycling intestinal epithelium and the slowly renewing skeletal muscle. Drawing comparisons between these two systems, we discuss the effects of niche-derived growth factors and signaling molecules, metabolic cues, the extracellular matrix and biomechanical cues, and immune signals on stem cells. We also discuss the influence of the niche in defining stem cell identity and function in both normal and pathophysiologic states.

Yap1 is required for maintenance of adult RPE differentiation

Nuclear YAP1 plays a critical role in regulation of stem cell proliferation, tissue regeneration, and organ size in many types of epithelia. Due to rapid turnover of most epithelial cell types, the cytoplasmic function of YAP1 in epithelial cells has not been well studied. The retinal pigment epithelium (RPE) is a highly polarized epithelial cell type maintained at a senescence state, and offers an ideal cell model to study the active role of YAP1 in maintenance of the adult epithelial phenotype. Here, we show that the cytoplasmic function of YAP1 is essential to maintain adult RPE differentiation. Knockout of Yap1 in the adult mouse RPE caused cell depolarization and tight junction breakdown, and led to inhibition of RPE65 expression, diminishment of RPE pigments, and retraction of microvilli and basal infoldings. These changes in RPE further prompted the loss of adjacent photoreceptor outer segments and photoreceptor death, which eventually led to decline of visual function in older mice between 6 and 12 months of age. Furthermore, nuclear β-catenin and its activity were significantly increased in mutant RPE. These results suggest that YAP1 plays an important role in active inhibition of Wnt/β-catenin signaling, and is essential for downregulation of β-catenin nuclear activity and prevention of dedifferentiation of adult RPE.

Naringin protects endothelial cells from apoptosis and inflammation by regulating the Hippo-YAP Pathway

Atherosclerosis is the primary cause of several cardiovascular diseases. Oxidized low-density lipoprotein (ox-LDL)-induced apoptosis, endothelial-mesenchymal transition (EndMT), and inflammation are crucial for the progression of cardiovascular diseases, including atherosclerosis. Naringin, a major compound from tomatoes, grapefruits, and related citrus, reportedly exhibits potential protective effects during atherosclerosis development; however, its effect on ox-LDL-induced human umbilical vein endothelial cell (HUVEC) damage remains unknown. In the present study, we investigated the anti-apoptotic and anti-inflammatory activities of naringin against ox-LDL-induced endothelial cells, and the underlying mechanism. Naringin pretreatment significantly and concentration-dependently inhibited ox-LDL-induced cell injury and apoptosis. Additionally, naringin restored endothelial barrier integrity by preventing VE-cadherin disassembly and F-actin remodeling, and down-regulated pro-inflammatory factors like IL-1β, IL-6, and IL-18, in the HUVECs. We also demonstrated that naringin treatment restored ox-LDL-induced YAP (yes-associated protein) down-regulation, given the YAP-shRNA attenuated cytoprotective effect of naringin on ox-LDL-induced endothelial cell injury and apoptosis. Collectively, our data indicate that naringin reversed ox-LDL-triggered HUVEC apoptosis, EndMT, and inflammation by inhibiting the YAP pathway. Therefore, naringin may have a therapeutic effect on endothelial injury-related disorders.

Yes-Associated Protein and PDZ Binding Motif: A Critical Signaling Pathway in the Control of Human Pluripotent Stem Cells Self-Renewal and Differentiation

Human pluripotent stem cells (hPSCs) can self-renew indefinitely to generate cells like themselves with a normal karyotype and differentiate into other types of cells when stimulated with a proper set of internal and external signals. hPSCs including human embryonic stem cells (hESCs) and induced pluripotent stem cells (iPSCs) are an alternative approach toward stem cell biology, drug discovery, disease modeling, and regenerative medicine. hESCs are commonly derived from the inner cell mass of preimplantation embryos and can maintain their pluripotency in appropriate culture media. The Hippo pathway is a major integrator of cell surface-mediated signals and plays an essential role in regulating hESCs function. Yes-associated protein (YAP) and TAZ (PDZ binding motif) are critical downstream transcriptional coactivators in the Hippo pathway. The culture conditions have effects on the cytoplasmic or nuclear YAP/TAZ localization. Also, the activity of Hippo pathway is influenced by cell density, mechanical tension, and biochemical signals. In this review article, we summarize the function of YAP/TAZ and focus on the regulation of YAP/TAZ in self-renewal and differentiation of hESCs.

Metastatic Hepatic Epithelioid Hemangioendothelioma Treated with Olaratumab: A Falling Star Rising?

Epithelioid hemangioendothelioma (EHE) is a rare vascular malignant tumor with indolent course. Liver transplantation for local disease is the treatment of choice. In the metastatic setting there is no consensus regarding the appropriate systemic treatment. We present two cases of metastatic hepatic epithelioid hemangioendothelioma (hEHE) treated with the combination of Doxorubicin and Olaratumab. Both patients showed Stable Disease (SD) as a response, after the completion of six cycles of this combination therapy.

Curcumin Inhibits the Tumorigenesis of Breast Cancer by Blocking Tafazzin/Yes-Associated Protein Axis

Purpose

This study was aimed to explore the anti-tumor effect of curcumin on breast cancer (BC) and the underlying mechanism involving Tafazzin (TAZ)/Yes-associated protein (YAP) axis.

Methods

Different concentrations of curcumin (0, 10, 20 and 30 μM) were used to treat BC cells (MCF-7 and MDA-MB-231 cells). The viability, colony formation, apoptosis, migration, and invasion of BC cells were detected by MTT, colony formation, flow cytometry, wound-healing and transwell assay, respectively. The protein expression of TAZ and YAP (effectors of Hippo signaling pathway) was detected by Western blot. MDA-MB-231 cells were injected into mice to verify the anti-tumor effect of curcumin in vivo.

Results

Curcumin (20 and 30 μM) inhibited the proliferation, migration and invasion, and promoted the apoptosis of MCF-7 and MDA-MB-231 cells. Curcumin decreased the protein expression of TAZ and YAP in MCF-7 and MDA-MB-231 cells. Overexpression of YAP reversed the anti-tumor effect of curcumin on MDA-MB-231 cells. In addition, curcumin (100, 200 and 300 mg/kg/d) inhibited the growth of tumor xenografts in mice, and down-regulated the protein expression of TAZ and YAP in tumor xenografts. However, curcumin at a concentration of 300 mg/kg/d slowed the increasing of body weight in mice.

Conclusion

Curcumin inhibited the tumorigenesis of BC by blocking TAZ/YAP axis.

Rho Signaling-Directed YAP/TAZ Regulation Encourages 3D Spheroid Colony Formation and Boosts Plasticity of Parthenogenetic Stem Cells

Cell proliferation, apoptosis and differentiation are essential processes from the early phases of embryogenesis to adult tissue formation and maintenance. These mechanisms also play a key role in embryonic stem cells (ESCs) that are able to proliferate maintaining pluripotency and, at the same time, to give rise to all populations belonging to the three germ layers, in response to specific stimuli. ESCs are, therefore, considered a well-established in vitro model to study the complexity of these processes. In this perspective, we previously generated parthenogenetic embryonic stem cells (ParthESC), that showed many features and regulatory pathways common to bi-parental ESCs. However, we observed that mono-parental cells demonstrate a high ability to form outgrowths and generate 3D spheroid colonies, which are distinctive signs of high-plasticity. Furthermore, preliminary evidence obtained by WTA, revealed the presence of several differentially expressed genes belonging to the Rho and Hippo signaling pathways. In the present study, we compare bi-parental ESCs and ParthESC and analyze by Real-Time PCR the differentially expressed genes. We demonstrate up-regulation of the Rho signaling pathway and an increased expression of YAP and TAZ in ParthESC. We also show that YAP remains in a dephosphorylated form. This allows its nuclear translocation and its direct binding to TEADs and SMADs, that are up-regulated in ParthESC. Altogether, these complex regulatory interactions result in overexpression of pluripotency related genes, in a global DNA hypomethylation and a histone-dependent chromatin high permissive state that may account for ParthESC high potency, possibly related to their exclusive maternal origin.

Expression and regulation of FRMD6 in mouse DRG neurons and spinal cord after nerve injury

FRMD6, a member of the group of FERM-domain proteins, is involved both in communication between cells, interactions with extracellular matrix, cellular apoptotic and regenerative mechanisms. FRMD6 was first discovered in the rodent sciatic nerve, and in the present immunohistochemical study we investigated the distribution of FRMD6 in the dorsal root ganglia (DRGs), sciatic nerve and spinal cord following sciatic nerve injury. FRMD6-immunoreactivity was found in the cytoplasm, nucleus or both, and in a majority of DRG neurons. FRMD6-immunoreactivity co-existed with several well-known neuronal markers, including calcitonin gene-related peptide, isolectin B4 and neurofilament 200 in mouse DRGs. After peripheral nerve injury, the FRMD6 mRNA levels and the overall percentage of FRMD6-positive neuron profiles (NPs) were decreased in ipsilateral lumbar DRGs, the latter mainly affecting small size neurons with cytoplasmic localization. Conversely, the proportion of NPs with nuclear FRMD6-immunoreactivity was significantly increased. In the sciatic nerve, FRMD6-immunoreactivity was observed in non-neuronal cells and in axons, and accumulated proximally to a ligation of the nerve. In the spinal cord FRMD6-immunoreactivity was detected in neurons in both dorsal and ventral horns, and was upregulated in ipsilateral dorsal horn after peripheral nerve axotomy. Our results demonstrate that FRMD6 is strictly regulated by peripheral nerve injury at the spinal level.

Integrative pathway enrichment analysis of multivariate omics data

Multi-omics datasets represent distinct aspects of the central dogma of molecular biology. Such high-dimensional molecular profiles pose challenges to data interpretation and hypothesis generation. ActivePathways is an integrative method that discovers significantly enriched pathways across multiple datasets using statistical data fusion, rationalizes contributing evidence and highlights associated genes. As part of the ICGC/TCGA Pan-Cancer Analysis of Whole Genomes (PCAWG) Consortium, which aggregated whole genome sequencing data from 2658 cancers across 38 tumor types, we integrated genes with coding and non-coding mutations and revealed frequently mutated pathways and additional cancer genes with infrequent mutations. We also analyzed prognostic molecular pathways by integrating genomic and transcriptomic features of 1780 breast cancers and highlighted associations with immune response and anti-apoptotic signaling. Integration of ChIP-seq and RNA-seq data for master regulators of the Hippo pathway across normal human tissues identified processes of tissue regeneration and stem cell regulation. ActivePathways is a versatile method that improves systems-level understanding of cellular organization in health and disease through integration of multiple molecular datasets and pathway annotations.

YAP/TAZ direct commitment and maturation of lymph node fibroblastic reticular cells

Fibroblastic reticular cells (FRCs) are immunologically specialized myofibroblasts of lymphoid organ, and FRC maturation is essential for structural and functional properties of lymph nodes (LNs). Here we show that YAP and TAZ (YAP/TAZ), the final effectors of Hippo signaling, regulate FRC commitment and maturation. Selective depletion of YAP/TAZ in FRCs impairs FRC growth and differentiation and compromises the structural organization of LNs, whereas hyperactivation of YAP/TAZ enhances myofibroblastic characteristics of FRCs and aggravates LN fibrosis. Mechanistically, the interaction between YAP/TAZ and p52 promotes chemokine expression that is required for commitment of FRC lineage prior to lymphotoxin-β receptor (LTβR) engagement, whereas LTβR activation suppresses YAP/TAZ activity for FRC maturation. Our findings thus present YAP/TAZ as critical regulators of commitment and maturation of FRCs, and hold promise for better understanding of FRC-mediated pathophysiologic processes.

Fibroblastic reticular cells (FRC) are important for lymph node (LN) structure and function. Here the authors show that the YAP/TAZ complex downstream of Hippo signalling regulates FRC commitment and maturation, with YAP/TAZ deficiency impairing FRC differentiation, while hyperactivation of YAZ/TAZ inducing myofibroblastic FRCs and LN fibrosis.

The Hippo Pathway and Viral Infections

The Hippo signaling pathway is a novel tumor suppressor pathway, initially found in Drosophila. Recent studies have discovered that the Hippo signaling pathway plays a critical role in a wide range of biological processes, including organ size control, cell proliferation, cancer development, and virus-induced diseases. In this review, we summarize the current understanding of the biological feature and pathological role of the Hippo pathway, focusing particularly on current findings in the function of the Hippo pathway in virus infection and pathogenesis.

A 3D approach to reproduction

For over a century, 2D cell culture has been extensively used for all the different research fields. However, this in vitro system does not allow to reproduce the natural structures of the original tissue, causing several changes and, in most cases, the loss of cell-to-cell communications and cell-to-extracellular matrix interactions. Based on this, during the last years, novel 3D platforms, able to mimic the in vivo milieu, are being developed. The advantages of the use of 3D models are: the reduction of the gap between cell culture and physiological environment; imitation of the specific architecture; partially maintenance of the mechanical and biochemical cues of the original tissue. Currently, 3D systems are used in a broad range of studies, including the field of reproduction, where they have been applied to promote maturation of follicles and oocytes and embryo culture. Here, we review 2D and 3D cell culture methods, discussing advantages and limitations of these techniques. We report the fundamental mechanisms involved in cell ability to perceive and respond to mechanical cues and their role in transmitting signals to and between cells and in regulating intracellular signaling pathways. In particular, we focus on the main effectors of the Hippo pathway, Yes-associated protein (YAP) and WW domain-containing transcription regulator protein 1 (TAZ), describing their behavior and function in oocytes and embryos. Lastly, we provide an overall perspective of the most recent 3D technologies developed in the field of reproduction, describing how their use may revolutionize the understanding of cellular behavior and provide novel tools, useful in reproductive technologies and livestock production.

Dysfunctional Mechanotransduction through the YAP/TAZ/Hippo Pathway as a Feature of Chronic Disease

In order to ascertain their external environment, cells and tissues have the capability to sense and process a variety of stresses, including stretching and compression forces. These mechanical forces, as experienced by cells and tissues, are then converted into biochemical signals within the cell, leading to a number of cellular mechanisms being activated, including proliferation, differentiation and migration. If the conversion of mechanical cues into biochemical signals is perturbed in any way, then this can be potentially implicated in chronic disease development and processes such as neurological disorders, cancer and obesity. This review will focus on how the interplay between mechanotransduction, cellular structure, metabolism and signalling cascades led by the Hippo-YAP/TAZ axis can lead to a number of chronic diseases and suggest how we can target various pathways in order to design therapeutic targets for these debilitating diseases and conditions.

Yap suppresses T-cell function and infiltration in the tumor microenvironment

A major challenge for cancer immunotherapy is sustaining T-cell activation and recruitment in immunosuppressive solid tumors. Here, we report that the levels of the Hippo pathway effector Yes-associated protein (Yap) are sharply induced upon the activation of cluster of differentiation 4 (CD4)-positive and cluster of differentiation 8 (CD8)-positive T cells and that Yap functions as an immunosuppressive factor and inhibitor of effector differentiation. Loss of Yap in T cells results in enhanced T-cell activation, differentiation, and function, which translates in vivo to an improved ability for T cells to infiltrate and repress tumors. Gene expression analyses of tumor-infiltrating T cells following Yap deletion implicates Yap as a mediator of global T-cell responses in the tumor microenvironment and as a negative regulator of T-cell tumor infiltration and patient survival in diverse human cancers. Collectively, our results indicate that Yap plays critical roles in T-cell biology and suggest that Yap inhibition improves T-cell responses in cancer.

Relation Between Immunohistochemical Expression of Hippo Pathway Effectors and Chronic Hepatitis Induced Fibrosis in Egyptian Patients

OBJECTIVE

Chronic hepatitis is a global health problem especially in Egypt. Hepatic fibrosis is a common end clinical manifestation of many chronic liver diseases. Although it is a wound-healing process, excessive accumulation of fibrillary collagen leads to architectural damage, cirrhosis and liver failure. Recently, a few studies have linked Hippo pathway effectors of yes-associated protein (YAP) and its paralog transcriptional coactivator with PDZ-binding motif (TAZ) to extracellular matrix deposition and ongoing fibrosis.

MATERIAL AND METHOD

Immunohistochemical expression of YAP and TAZ were analyzed in 121 liver needle core biopsies (91 core biopsies of chronic viral hepatitis, 20 biopsies of autoimmune hepatitis and 10 normal liver cores).

RESULTS

YAP and TAZ nuclear localization was absent in all normal liver cores. Autoimmune hepatitis cases showed higher nuclear expression of both YAP and TAZ in comparison to chronic viral cases. YAP and TAZ expression were correlated with severity of hepatocyte injury together with fibrosis in chronic viral cases but these correlations were absent in AIH cases despite the pronounced increase of YAP and TAZ nuclear localization.

CONCLUSION

The correlation between Hippo effectors activation and fibrosis in chronic viral hepatitis patients emphasize their role in the development and advancement of hepatic scarring and highlight the use of both YAP and TAZ as novel targets to ameliorate liver fibrosis.

PMEPA1 isoform a drives progression of glioblastoma by promoting protein degradation of the Hippo pathway kinase LATS1

The Hippo signaling pathway controls organ development and is also known, in cancer, to have a tumor suppressing role. Within the Hippo pathway, we here demonstrate, in human gliomas, a functional interaction of a transmembrane protein, prostate transmembrane protein, androgen induced 1 (PMEPA1) with large tumor suppressor kinase 1 (LATS1). We show that PMEPA1 is upregulated in primary human gliomas. The PMEPA1 isoform PMEPA1a was predominantly expressed in glioma specimens and cell lines, and ectopic expression of the protein promoted glioma growth and invasion in vitro and in an orthotopic xenograft model in nude mice. In co-immunoprecipitation experiments, PMEPA1a associated with the Hippo tumor suppressor kinase LATS1. This interaction led to a proteasomal degradation of LATS1 through recruitment of the ubiquitin ligase, neural precursor cell expressed, developmentally downregulated 4 (NEDD4), which led to silencing of Hippo signaling. Alanine substitution in PMEPA1a at PY motifs resulted in failed LATS1 degradation. Targeting of a downstream component in the Hippo signaling pathway, YAP, with shRNA, interfered with the growth promoting activities of PMEPA1a in vitro and in vivo. In conclusion, the presented work shows that PMEPA1a contributes to glioma progression by a dysregulation of the Hippo signaling pathway and thus represents a promising target for the treatment of gliomas.

Self-Assembling Scaffolds Supported Long-Term Growth of Human Primed Embryonic Stem Cells and Upregulated Core and Naïve Pluripotent Markers

The maintenance and expansion of human embryonic stem cells (ESCs) in two-dimensional (2-D) culture is technically challenging, requiring routine manipulation and passaging. We developed three-dimensional (3-D) scaffolds to mimic the in vivo microenvironment for stem cell proliferation. The scaffolds were made of two 8-arm polyethylene glycol (PEG) polymers functionalized with thiol (PEG-8-SH) and acrylate (PEG-8-Acr) end groups, which self-assembled via a Michael addition reaction. When primed ESCs (H9 cells) were mixed with PEG polymers, they were encapsulated and grew for an extended period, while maintaining their viability, self-renewal, and differentiation potential both in vitro and in vivo. Three-dimensional (3-D) self-assembling scaffold-grown cells displayed an upregulation of core pluripotency genes, OCT4, NANOG, and SOX2. In addition, the expression of primed markers decreased, while the expression of naïve markers substantially increased. Interestingly, the expression of mechanosensitive genes, YAP and TAZ, was also upregulated. YAP inhibition by Verteporfin abrogated the increased expression of YAP/TAZ as well as core and naïve pluripotent markers. Evidently, the 3-D culture conditions induced the upregulation of makers associated with a naïve state of pluripotency in the primed cells. Overall, our 3-D culture system supported the expansion of a homogenous population of ESCs and should be helpful in advancing their use for cell therapy and regenerative medicine.

Hippo-Yap/Taz signaling: Complex network interactions and impact in epithelial cell behavior

The Hippo pathway has emerged as a crucial integrator of signals in biological events from development to adulthood and in diseases. Although extensively studied in Drosophila and in cell cultures, major gaps of knowledge still remain on how this pathway functions in mammalian systems. The pathway consists of a growing number of components, including core kinases and adaptor proteins, which control the subcellular localization of the transcriptional co-activators Yap and Taz through phosphorylation of serines at key sites. When localized to the nucleus, Yap/Taz interact with TEAD transcription factors to induce transcriptional programs of proliferation, stemness, and growth. In the cytoplasm, Yap/Taz interact with multiple pathways to regulate a variety of cellular functions or are targeted for degradation. The Hippo pathway receives cues from diverse intracellular and extracellular inputs, including growth factor and integrin signaling, polarity complexes, and cell-cell junctions. This review highlights the mechanisms of regulation of Yap/Taz nucleocytoplasmic shuttling and their implications for epithelial cell behavior using the lung as an intriguing example of this paradigm. This article is categorized under: Gene Expression and Transcriptional Hierarchies > Regulatory Mechanisms Signaling Pathways > Cell Fate Signaling Establishment of Spatial and Temporal Patterns > Cytoplasmic Localization.