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

Skeletal cell YAP and TAZ combinatorially promote bone development

The functions of the paralogous transcriptional coactivators Yes-associated protein (YAP) and transcriptional coactivator with PDZ-binding motif (TAZ) in bone are controversial. Each has been observed to promote or inhibit osteogenesis in vitro, with reports of both equivalent and divergent functions. Their combinatorial roles in bone physiology are unknown. We report that combinatorial YAP/TAZ deletion from skeletal lineage cells, using Osterix-Cre, caused an osteogenesis imperfecta-like phenotype with severity dependent on allele dose and greater phenotypic expressivity with homozygous TAZ vs. YAP ablation. YAP/TAZ deletion decreased bone accrual and reduced intrinsic bone material properties through impaired collagen content and organization. These structural and material defects produced spontaneous fractures, particularly in mice with homozygous TAZ deletion and caused neonatal lethality in dual homozygous knockouts. At the cellular level in vivo, YAP/TAZ ablation reduced osteoblast activity and increased osteoclast activity, in an allele dose-dependent manner, impairing bone accrual and remodeling. Transcriptionally, YAP/TAZ deletion and small-molecule inhibition of YAP/TAZ interaction with the transcriptional coeffector TEAD reduced osteogenic and collagen-related gene expression, both in vivo and in vitro. These data demonstrate that YAP and TAZ combinatorially promote bone development through regulation of osteoblast activity, matrix quality, and osteoclastic remodeling.-Kegelman, C. D., Mason, D. E., Dawahare, J. H., Horan, D. J., Vigil, G. D., Howard, S. S., Robling, A. G., Bellido, T. M., Boerckel, J. D. Skeletal cell YAP and TAZ combinatorially promote bone development.

The polarity protein Angiomotin p130 controls dendritic spine maturation

Wigerius et al. identify the polarity protein AMOT-130 as vital for dendritic spine morphogenesis. They show that reduced Lats1 kinase activity in the neonatal brain is required for the recruitment of AMOT-130 to postsynaptic compartments to stabilize dendritic spines.

The actin cytoskeleton is essential for the structural changes in dendritic spines that lead to the formation of new synapses. Although the molecular mechanisms underlying spine formation are well characterized, the events that drive spine maturation during development are largely unknown. In this study, we demonstrate that Angiomotin (AMOT-130) is necessary for spine stabilization. AMOT-130 is enriched in mature dendritic spines and functions to stabilize the actin cytoskeleton by coupling F-actin to postsynaptic protein scaffolds. These functions of AMOT are transiently restricted during postnatal development by phosphorylation imposed by the kinase Lats1. Our study proposes that AMOT-130 is essential for normal spine morphogenesis and identifies Lats1 as an upstream regulator in this process. Moreover, our findings may link AMOT-130 loss and the related spine defects to neurological disorders.

FAK controls the mechanical activation of YAP, a transcriptional regulator required for durotaxis

Focal adhesion kinase (FAK) is a key molecule in focal adhesions and regulates fundamental processes in cells such as growth, survival, and migration. FAK is one of the first molecules recruited to focal adhesions in response to external mechanical stimuli and therefore is a pivotal mediator of cell mechanosignaling, and relays these stimuli to other mechanotransducers within the cytoplasm. Yes-associated protein (YAP) has been identified recently as one of these core mechanotransducers. YAP translocates to the nucleus following changes in cell mechanics to promote the expression of genes implicated in motility, apoptosis, proliferation, and organ growth. Here, we show that FAK controls the nuclear translocation and activation of YAP in response to mechanical activation and submit that the YAP-dependent process of durotaxis requires a cell with an asymmetric distribution of active and inactive FAK molecules.-Lachowski, D., Cortes, E., Robinson, B., Rice, A., Rombouts, K., Del Río Hernández, A. E. FAK controls the mechanical activation of YAP, a transcriptional regulator required for durotaxis.

3D microniches reveal the importance of cell size and shape

Geometrical cues have been shown to alter gene expression and differentiation on 2D substrates. However, little is known about how geometrical cues affect cell function in 3D. One major reason for this lack of understanding is rooted in the difficulties of controlling cell geometry in a complex 3D setting and for long periods of culture. Here, we present a robust method to control cell volume and shape of individual human mesenchymal stem cells (hMSCs) inside 3D microniches with a range of different geometries (e.g., cylinder, triangular prism, cubic, and cuboid). We find that the actin filaments, focal adhesions, nuclear shape, YAP/TAZ localization, cell contractility, nuclear accumulation of histone deacetylase 3, and lineage selection are all sensitive to cell volume. Our 3D microniches enable fundamental studies on the impact of biophysical cues on cell fate, and have potential applications in investigating how multicellular architectures organize within geometrically well-defined 3D spaces.

Polycystin-1 interacts with TAZ to stimulate osteoblastogenesis and inhibit adipogenesis

The molecular mechanisms that transduce the osteoblast response to physical forces in the bone microenvironment are poorly understood. Here, we used genetic and pharmacological experiments to determine whether the polycystins PC1 and PC2 (encoded by Pkd1 and Pkd2) and the transcriptional coactivator TAZ form a mechanosensing complex in osteoblasts. Compound-heterozygous mice lacking 1 copy of Pkd1 and Taz exhibited additive decrements in bone mass, impaired osteoblast-mediated bone formation, and enhanced bone marrow fat accumulation. Bone marrow stromal cells and osteoblasts derived from these mice showed impaired osteoblastogenesis and enhanced adipogenesis. Increased extracellular matrix stiffness and application of mechanical stretch to multipotent mesenchymal cells stimulated the nuclear translocation of the PC1 C-terminal tail/TAZ (PC1-CTT/TAZ) complex, leading to increased runt-related transcription factor 2-mediated (Runx2-mediated) osteogenic and decreased PPARγ-dependent adipogenic gene expression. Using structure-based virtual screening, we identified a compound predicted to bind to PC2 in the PC1:PC2 C-terminal tail region with helix:helix interaction. This molecule stimulated polycystin- and TAZ-dependent osteoblastogenesis and inhibited adipogenesis. Thus, we show that polycystins and TAZ integrate at the molecular level to reciprocally regulate osteoblast and adipocyte differentiation, indicating that the polycystins/TAZ complex may be a potential therapeutic target to increase bone mass.

Cell contact and pressure control of YAP localization and clustering revealed by super-resolution imaging

Yes-associated protein (YAP) is well known for being an effecter of the Hippo signaling cascade that plays a critical role in organ size control, tumorigenesis, and regeneration. As YAP is a transcriptional coactivator, nuclear accumulation is a crucial determinant of its function. Numerous investigations have provided insights into the regulation of YAP, such as upstream molecules of the Hippo pathway, cell contact inhibition, and mechanical forces. However, detailed information regarding YAP spatial localization and organization in cells remains uncertain, and how mechanical signals control YAP distribution and function is not fully known. Therefore, we used one of the super-resolution imaging techniques, direct stochastic optical reconstruction microscopy (dSTORM), combined with confocal microscopy, to solve these problems. We found that YAP is mainly distributed in clusters in the cells, and that both cell contact and pressure on cell surfaces promote the nuclear-to-cytoplasm translocation of YAP and its phosphorylation, but weaken the clustering of nuclear YAP and its transcriptional activity. Moreover, we found that pressure regulation may be more effective on YAP from cancer cells as compared to normal cells, which could help open a door to target YAP for anticancer drug design.

MicroRNA-185 suppresses pancreatic cell proliferation by targeting transcriptional coactivator with PDZ-binding motif in pancreatic cancer

The aim of the present study was to compare the expression of transcriptional coactivator with the PDZ-binding motif (TAZ) in pancreatic cancer (PC) patients, and to investigate the regulation mechanisms of TAZ in the proliferation of PC. PC tissues and matched peritumoral tissues, pancreatic juice and serum were collected from PC patients who underwent pancreatectomy between June 2012 and December 2015 at the Affiliated Hospital of Qingdao University (Qingdao, China). Pancreatic juice and serum were collected from patients with chronic pancreatitis as a control. The levels of taz mRNA expression in the samples were examined by reverse-transcription quantitative polymerase chain reaction, and the protein expression of TAZ was assessed by western blot analysis and ELISA. MicroRNAs (miRNAs) that regulate TAZ expression were also predicted by bioinformatics analysis and validated by dual luciferase reporter and rescue assays. In addition, the proliferation of PC cells was evaluated after transfection with TAZ small interfering RNA (siRNA) or its upstream miRNA agomir. Expression of TAZ was significantly increased in the PC tissues, pancreatic juice and serum of PC patients at the mRNA and protein levels compared with controls (P<0.05). Furthermore, TAZ was predicted and verified to be a target of miRNA (miR)-185, and miR-185 and TAZ were inversely expressed in samples from PC patients (P<0.05). In addition, TAZ siRNA or agomiR-185 transfection significantly inhibited human pancreatic adenocarcinoma cell proliferation (P<0.05). However, overexpression of TAZ in the agomiR-185 group rescued the inhibition (P<0.05). Finally, the expression of TAZ effector proteins, namely ankyrin repeat domain-containing protein and cysteine-rich 61, were upregulated in PC tissues (P<0.05), but repressed following transfection of PC cells with agomiR-185 (P<0.05). Thus, miR-185 may regulate the proliferation of PC by targeting TAZ, making it a promising diagnostic marker for PC.

Periostin in cardiovascular disease and development: a tale of two distinct roles

Tissue development and homeostasis are dependent upon the concerted synthesis, maintenance, and degradation of extracellular matrix (ECM) molecules. Cardiac fibrosis is now recognized as a primary contributor to incidence of heart failure, particularly heart failure with preserved ejection fraction, wherein cardiac filling in diastole is compromised. Periostin is a cell-associated protein involved in cell fate determination, proliferation, tumorigenesis, and inflammatory responses. As a non-structural component of the ECM, secreted 90 kDa periostin is emerging as an important matricellular factor in cardiac mesenchymal tissue development. In addition, periostin's role as a mediator in cell-matrix crosstalk has also garnered attention for its association with fibroproliferative diseases in the myocardium, and for its association with TGF-β/BMP signaling. This review summarizes the phylogenetic history of periostin, its role in cardiac development, and the major signaling pathways influencing its expression in cardiovascular pathology. Further, we provide a synthesis of the current literature to distinguish the multiple roles of periostin in cardiac health, development and disease. As periostin may be targeted for therapeutic treatment of cardiac fibrosis, these insights may shed light on the putative timing for application of periostin-specific therapies.

Targeted Disruption of YAP and TAZ Impairs the Maintenance of the Adrenal Cortex

Yes-associated protein (YAP) and transcriptional coactivator with PDZ-binding motif (TAZ) are functionally redundant transcriptional regulators that are downstream effectors of the Hippo signaling pathway. They act as major regulators of stem cell maintenance, cell growth, and differentiation. To characterize their roles in the adrenal cortex, we generated a mouse model in which Yap and Taz were conditionally deleted in steroidogenic cells (Yapflox/flox;Tazflox/flox;Nr5a1cre/+). Male Yapflox/flox;Tazflox/flox;Nr5a1cre/+ mice were characterized by an age-dependent degeneration of the adrenal cortex associated with an increase in apoptosis and a progressive reduction in the expression levels of steroidogenic genes. Evaluation of the expression levels of stem and progenitor cell population markers in the adrenal glands of Yapflox/flox;Tazflox/flox;Nr5a1cre/+ mice also showed the downregulation of sonic hedgehog (Shh), a marker of the subcapsular progenitor cell population. Gross degenerative changes were not observed in the adrenal glands of Yapflox/flox;Tazflox/flox;Nr5a1cre/+ females, although steroidogenic capacity and Shh expression were reduced, suggesting that mechanisms of adrenocortical maintenance are sex specific. These results define a crucial role for YAP and TAZ in the maintenance of the postnatal adrenal cortex.

Tendon injury and repair - A perspective on the basic mechanisms of tendon disease and future clinical therapy

Tendon is an intricately organized connective tissue that efficiently transfers muscle force to the bony skeleton. Its structure, function, and physiology reflect the extreme, repetitive mechanical stresses that tendon tissues bear. These mechanical demands also lie beneath high clinical rates of tendon disorders, and present daunting challenges for clinical treatment of these ailments. This article aims to provide perspective on the most urgent frontiers of tendon research and therapeutic development. We start by broadly introducing essential elements of current understanding about tendon structure, function, physiology, damage, and repair. We then introduce and describe a novel paradigm explaining tendon disease progression from initial accumulation of damage in the tendon core to eventual vascular recruitment from the surrounding synovial tissues. We conclude with a perspective on the important role that biomaterials will play in translating research discoveries to the patient.

STATEMENT OF SIGNIFICANCE

Tendon and ligament problems represent the most frequent musculoskeletal complaints for which patients seek medical attention. Current therapeutic options for addressing tendon disorders are often ineffective, and the need for improved understanding of tendon physiology is urgent. This perspective article summarizes essential elements of our current knowledge on tendon structure, function, physiology, damage, and repair. It also describes a novel framework to understand tendon physiology and pathophysiology that may be useful in pushing the field forward.

Dual roles of yes-associated protein (YAP) in colorectal cancer

Yes-associated protein (YAP) is a downstream effector molecule of a newly emerging tumour suppressor pathway called the Hippo pathway. YAP is a transcriptional co-activator and mis-expressed in various cancers, including colorectal cancer (CRC). Accumulating studies show that the high expression of nuclear YAP is linked with tumour progression and decreased survival. Nuclear YAP can interact with other transcription factors to promote cancer cell proliferation, apoptosis, metastasis and maintenance of stemness. Therefore, YAP has the potential to be a tumour biomarker or therapeutic target for CRC. However, recently, a number of studies have supported a contradictory role for YAP as a tumour suppressor, demonstrating inhibition of the tumorigenesis of CRC, involvement in promoting cell apoptosis, and inhibiting the maintenance of intestinal stem cells and inflammatory activity. In these studies, high expression of YAP was highly correlated with worse survival in CRC. In this review, we will comprehensively summarize and analyse these paradoxical reports, and discuss both the oncogenic and tumour suppressor functions of YAP in the differential status of CRC progression. Further investigation into the mechanisms responsible for the dual function of YAP will be of great value in the prevention, early diagnosis, and therapy of CRC.

YAP/TAZ and Hedgehog Coordinate Growth and Patterning in Gastrointestinal Mesenchyme

YAP/TAZ are the major mediators of mammalian Hippo signaling; however, their precise function in the gastrointestinal tract remains poorly understood. Here we dissect the distinct roles of YAP/TAZ in endodermal epithelium and mesenchyme and find that, although dispensable for gastrointestinal epithelial development and homeostasis, YAP/TAZ function as the critical molecular switch to coordinate growth and patterning in gut mesenchyme. Our genetic analyses reveal that Lats1/2 kinases suppress expansion of the primitive mesenchymal progenitors, where YAP activation also prevents induction of the smooth muscle lineage through transcriptional repression of Myocardin. During later development, zone-restricted downregulation of YAP/TAZ provides the positional cue and allows smooth muscle cell differentiation induced by Hedgehog signaling. Taken together, our studies identify the mesenchymal requirement of YAP/TAZ in the gastrointestinal tract and highlight the functional interplays between Hippo and Hedgehog signaling underlying temporal and spatial control of tissue growth and specification in developing gut.

Integrin-FAK-CDC42-PP1A signaling gnaws at YAP/TAZ activity to control incisor stem cells

How epithelial tissues are able to self-renew to maintain homeostasis and regenerate in response to injury remains a persistent question. The transcriptional effectors YAP and TAZ are increasingly being recognized as central mediators of epithelial stem cell biology, and a wealth of recent studies have been directed at understanding the control and activity of these factors. Recent work by Hu et al. has added to this knowledge, as they identify an Integrin-FAK-CDC42-PP1A signaling cascade that directs nuclear YAP/TAZ activity in stem cell populations of the mouse incisor, and define convergence on mTORC1 signaling as an important mediator of the proliferation of these cells. Here, we review recent studies on YAP/TAZ function and regulation in epithelial tissue-specific stem cells, merging the Hu et al. study together with our current knowledge of YAP/TAZ.

YAP stabilizes SMAD1 and promotes BMP2-induced neocortical astrocytic differentiation

‪YAP (yes-associated protein), a key transcriptional co-factor that is negatively regulated by the Hippo pathway, is crucial for the development and size control of multiple organs, including the liver. However, its role in the brain remains unclear. Here, we provide evidence for YAP regulation of mouse neocortical astrocytic differentiation and proliferation. YAP was undetectable in neurons, but selectively expressed in neural stem cells (NSCs) and astrocytes. YAP in NSCs was required for neocortical astrocytic differentiation, with no apparent role in self-renewal or neural differentiation. However, YAP in astrocytes was necessary for astrocytic proliferation. Yap (Yap1) knockout, Yap(nestin) conditional knockout and Yap(GFAP) conditional knockout mice displayed fewer neocortical astrocytes and impaired astrocytic proliferation and, consequently, death of neocortical neurons. Mechanistically, YAP was activated by BMP2, and the active/nuclear YAP was crucial for BMP2 induction and stabilization of SMAD1 and astrocytic differentiation. Expression of SMAD1 in YAP-deficient NSCs partially rescued the astrocytic differentiation deficit in response to BMP2. Taken together, these results identify a novel function of YAP in neocortical astrocytic differentiation and proliferation, and reveal a BMP2-YAP-SMAD1 pathway underlying astrocytic differentiation in the developing mouse neocortex.

Therapeutic Targeting of TAZ and YAP by Dimethyl Fumarate in Systemic Sclerosis Fibrosis

Systemic sclerosis (scleroderma, SSc) is a devastating fibrotic disease with few treatment options. Fumaric acid esters, including dimethyl fumarate (DMF, Tecfidera; Biogen, Cambridge, MA), have shown therapeutic effects in several disease models, prompting us to determine whether DMF is effective as a treatment for SSc dermal fibrosis. We found that DMF blocks the profibrotic effects of transforming growth factor-β (TGFβ) in SSc skin fibroblasts. Mechanistically, we found that DMF treatment reduced nuclear localization of transcriptional coactivator with PDZ binding motif (TAZ) and Yes-associated protein (YAP) proteins via inhibition of the phosphatidylinositol 3 kinase/protein kinase B (Akt) pathway. In addition, DMF abrogated TGFβ/Akt1 mediated inhibitory phosphorylation of glycogen kinase 3β (GSK3β) and a subsequent β-transducin repeat-containing proteins (βTRCP) mediated proteasomal degradation of TAZ, as well as a corresponding decrease of TAZ/YAP transcriptional targets. Depletion of TAZ/YAP recapitulated the antifibrotic effects of DMF. We also confirmed the increase of TAZ/YAP in skin biopsies from patients with diffuse SSc. We further showed that DMF significantly diminished nuclear TAZ/YAP localization in fibroblasts cultured on a stiff surface. Importantly, DMF prevented bleomycin-induced skin fibrosis in mice. Together, our work demonstrates a mechanism of the antifibrotic effect of DMF via inhibition of Akt1/GSK3β/TAZ/YAP signaling and confirms a critical role of TAZ/YAP in mediating the profibrotic responses in dermal fibroblasts. This study supports the use of DMF as a treatment for SSc dermal fibrosis.

Amlexanox, a selective inhibitor of IKBKE, generates anti-tumoral effects by disrupting the Hippo pathway in human glioblastoma cell lines

Glioblastoma multiforme (GBM) is the most prevalent form of malignant brain tumor. Amlexanox, a novel compound, has been shown to have anti-cancer potential. In this study, the anti-tumoral effects and the underlying mechanisms of amlexanox were investigated. Amlexanox significantly suppressed proliferation and invasion and induced apoptosis in glioblastoma cells. Furthermore, we found that amlexanox altered the protein expression of the Hippo pathway by downregulating IKBKE. Our data indicates that IKBKE directly targets LATS1/2 and induces degradation of LATS1/2, thereby inhibiting the activity of the Hippo pathway. In vivo results further confirmed the tumor inhibitory effect of amlexanox via the downregulation of IKBKE, and amlexanox induced no apparent toxicity. Collectively, our studies suggest that amlexanox is a promising therapeutic agent for the treatment of GBM.

Cytoplasmic and Nuclear TAZ Exert Distinct Functions in Regulating Primed Pluripotency

Mouse epiblast stem cells (mEpiSCs) and human embryonic stem cells (hESCs) are primed pluripotent stem cells whose self-renewal can be maintained through cytoplasmic stabilization and retention of β-catenin. The underlying mechanism, however, remains largely unknown. Here, we show that cytoplasmic β-catenin interacts with and retains TAZ, a Hippo pathway effector, in the cytoplasm. Cytoplasmic retention of TAZ promotes mEpiSC self-renewal in the absence of nuclear β-catenin, whereas nuclear translocation of TAZ induces mEpiSC differentiation. TAZ is dispensable for naive mouse embryonic stem cell (mESC) self-renewal but required for the proper conversion of mESCs to mEpiSCs. The self-renewal of hESCs, like that of mEpiSCs, can also be maintained through the cytoplasmic retention of β-catenin and TAZ. Our study indicates that how TAZ regulates cell fate depends on not only the cell type but also its subcellular localization.

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TAZ is a binding partner of cytoplasmic β-catenin

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TAZ is essential for the conversion of mESCs to mEpiSCs

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Cytoplasmic retention of TAZ promotes mEpiSC and hESC self-renewal

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Nuclear translocation of TAZ induces mEpiSC and hESC differentiation

YAP, TAZ and AREG expression in eighth cranial nerve schwannoma

BACKGROUND

Although the diagnosis and treatment of eighth cranial nerve (VIII CN) schwannoma (acoustic neuroma) has improved over the years, no factors capable of predicting tumor growth have been identified as yet. This study is a preliminary investigation of the expression in sporadic VIII CN schwannomas of Yes-associated protein (YAP), transcriptional coactivator with PDZ-binding motif (TAZ), and amphiregulin (AREG), a direct target gene of YAP and TAZ. The expression of YAP, TAZ and AREG was correlated with the volumetric dimensions of tumors on contrast-enhanced magnetic resonance imaging (ceMRI).

METHODS

YAP, TAZ and AREG expression was assessed immunohistochemically in surgical specimens of 36 consecutive sporadic VIII CN schwannomas. 3D reconstructions of the tumors and their corresponding volumes in cm3 were obtained from measurements on ceMRI images using the OsiriX® software.

RESULTS

We found a significant direct correlation between TAZ expression and VIII CN schwannoma volumes on latest preoperative ceMRI (p<0.0003). Mean TAZ expression was also significantly higher in VIII CN schwannomas with a volume ≥2.1 cm3 than in those with a volume <2.1 cm3(p<0.0018). No significant correlations emerged for YAP or AREG expression and VIII CN schwannoma volume.

CONCLUSIONS

The immunohistochemical expression of TAZ (but not YAP or AREG) correlated significantly with schwannoma volume measured on ceMRI. Further investigations are needed to identify the biological factors influencing tumor proliferation (ideally secreted proteins like AREG) that might be detected using non-invasive approaches (i.e., blood samples).

Pathogenesis of systemic sclerosis: recent insights of molecular and cellular mechanisms and therapeutic opportunities

Systemic sclerosis (SSc) is a complex disease characterized by early microvascular abnormalities, immune dysregulation and chronic inflammation, and subsequent fibrosis of the skin and internal organs. Excessive fibrosis, distinguishing hallmark of SSc, is the end result of a complex series of interlinked vascular injury and immune activation, and represents a maladaptive repair process. Activated vascular, epithelial, and immune cells generate pro-fibrotic cytokines, chemokines, growth factors, lipid mediators, autoantibodies, and reactive oxygen species. These paracrine and autocrine cues in turn induce activation, differentiation, and survival of mesenchymal cells, ensuing tissue fibrosis through increased collagen synthesis, matrix deposition, tissue rigidity and remodeling, and vascular rarefaction. This review features recent insights of the pathogenic process of SSc, highlighting three major characteristics of SSc, microvasculopathy, excessive fibrosis, and immune dysregulation, and sheds new light on the understanding of molecular and cellular mechanisms contributing to the pathogenesis of SSc and providing novel avenues for targeted therapies.

Hippo Pathway: An Emerging Regulator of Craniofacial and Dental Development

The evolutionarily conserved Hippo signaling pathway is a vital regulator of organ size that fine-tunes cell proliferation, apoptosis, and differentiation. A number of important studies have revealed critical roles of Hippo signaling and its effectors Yap (Yes-associated protein) and Taz (transcriptional coactivator with PDZ binding motif) in tissue development, homeostasis, and regeneration, as well as in tumorigenesis. In addition, recent studies have shown evidence of crosstalk between the Hippo pathway and other key signaling pathways, such as Wnt signaling, that not only regulates developmental processes but also contributes to disease pathogenesis. In this review, we summarize the major discoveries in the field of Hippo signaling and what has been learned about its regulation and crosstalk with other signaling pathways, with a particular focus on recent findings involving the Hippo-Yap pathway in craniofacial and tooth development. New and exciting studies of the Hippo pathway are anticipated that will significantly improve our understanding of the molecular mechanisms of human craniofacial and tooth development and disease and will ultimately lead to the development of new therapies.

Palmitic acid dysregulates the Hippo-YAP pathway and inhibits angiogenesis by inducing mitochondrial damage and activating the cytosolic DNA sensor cGAS-STING-IRF3 signaling mechanism

Impaired angiogenesis and wound healing carry significant morbidity and mortality in diabetic patients. Metabolic stress from hyperglycemia and elevated free fatty acids have been shown to inhibit endothelial angiogenesis. However, the underlying mechanisms remain poorly understood. In this study, we show that dysregulation of the Hippo-Yes-associated protein (YAP) pathway, an important signaling mechanism in regulating tissue repair and regeneration, underlies palmitic acid (PA)-induced inhibition of endothelial angiogenesis. PA inhibited endothelial cell proliferation, migration, and tube formation, which were associated with increased expression of mammalian Ste20-like kinases 1 (MST1), YAP phosphorylation/inactivation, and nuclear exclusion. Overexpression of YAP or knockdown of MST1 prevented PA-induced inhibition of angiogenesis. When searching upstream signaling mechanisms, we found that PA dysregulated the Hippo-YAP pathway by inducing mitochondrial damage. PA treatment induced mitochondrial DNA (mtDNA) release to cytosol, and activated cytosolic DNA sensor cGAS-STING-IRF3 signaling. Activated IRF3 bound to the MST1 gene promoter and induced MST1 expression, leading to MST1 up-regulation, YAP inactivation, and angiogenesis inhibition. Thus, mitochondrial damage and cytosolic DNA sensor cGAS-STING-IRF3 signaling are critically involved in PA-induced Hippo-YAP dysregulation and angiogenesis suppression. This mechanism may have implication in impairment of angiogenesis and wound healing in diabetes.

Role of TAZ in Lysophosphatidic Acid-Induced Migration and Proliferation of Human Adipose-Derived Mesenchymal Stem Cells

Transcriptional co-activator with a PDZ-binding motif (TAZ) is an important factor in lysophosphatidic acid (LPA)-induced promotion of migration and proliferation of human mesenchymal stem cells (MSCs). The expression of TAZ significantly increased at 6 h after LPA treatment, and TAZ knockdown inhibited the LPA-induced migration and proliferation of MSCs. In addition, embryonic fibroblasts from TAZ knockout mice exhibited the reduction in LPA-induced migration and proliferation. The LPA1 receptor inhibitor Ki16425 blocked LPA responses in MSCs. Although TAZ knockdown or knockout did not reduce LPA-induced phosphorylation of ERK and AKT, the MEK inhibitor U0126 or the ROCK inhibitor Y27632 blocked LPA-induced TAZ expression along with the reduction in the proliferation and migration of MSCs. Our data suggest that TAZ is an important mediator of LPA signaling in MSCs in the downstream of MEK and ROCK signaling.

Retinal Degeneration Triggers the Activation of YAP/TEAD in Reactive Müller Cells

Purpose

During retinal degeneration, Müller glia cells respond to photoreceptor loss by undergoing reactive gliosis, with both detrimental and beneficial effects. Increasing our knowledge of the complex molecular response of Müller cells to retinal degeneration is thus essential for the development of new therapeutic strategies. The purpose of this work was to identify new factors involved in Müller cell response to photoreceptor cell death.

Methods

Whole transcriptome sequencing was performed from wild-type and degenerating rd10 mouse retinas at P30. The changes in mRNA abundance for several differentially expressed genes were assessed by quantitative RT-PCR (RT-qPCR). Protein expression level and retinal cellular localization were determined by western blot and immunohistochemistry, respectively.

Results

Pathway-level analysis from whole transcriptomic data revealed the Hippo/YAP pathway as one of the main signaling pathways altered in response to photoreceptor degeneration in rd10 retinas. We found that downstream effectors of this pathway, YAP and TEAD1, are specifically expressed in Müller cells and that their expression, at both the mRNA and protein levels, is increased in rd10 reactive Müller glia after the onset of photoreceptor degeneration. The expression of Ctgf and Cyr61, two target genes of the transcriptional YAP/TEAD complex, is also upregulated following photoreceptor loss.

Conclusions

This work reveals for the first time that YAP and TEAD1, key downstream effectors of the Hippo pathway, are specifically expressed in Müller cells. We also uncovered a deregulation of the expression and activity of Hippo/YAP pathway components in reactive Müller cells under pathologic conditions.

Cross talk between the Crumbs complex and Hippo signaling in renal epithelial cells

Cell polarity has a crucial role in organizing cells into tissues and in mediating transport processes and cell-cell communication. Especially the cells of the nephron require apicobasal polarity to establish and maintain their barrier function. The Crumbs complex including the integral membrane protein Crumbs, as well as Pals1 and Patj, is essential for the establishment of apicobasal polarity. The interactions of the core proteins and the interplay with other processes have been characterized in various epithelial cell lines in detail. Notably, Crb2 and Crb3 are expressed within the kidney and play an important role in the proper function of podocytes and tubules, respectively. The interaction of polarity proteins and components of the Hippo pathway-an evolutionarily highly conserved kinase cascade regulating cell proliferation, organ size, and tissue regeneration-has been discovered recently. Here, we discuss potential molecular and physiological links between the Crumbs complex and the Hippo pathway in renal cells.

NAFLD as a Sexual Dimorphic Disease: Role of Gender and Reproductive Status in the Development and Progression of Nonalcoholic Fatty Liver Disease and Inherent Cardiovascular Risk

Nonalcoholic fatty liver disease (NAFLD) spans steatosis through nonalcoholic steatohepatis, cirrhosis, and hepatocellular carcinoma (HCC) associated with striking systemic features and excess cardiovascular and liver-related mortality. The pathogenesis of NAFLD is complex and multifactorial. Endocrine derangements are closely linked with dysmetabolic traits. For example, in animal and human studies, female sex is protected from dysmetabolism thanks to young individuals' ability to partition fatty acids towards ketone body production rather than very low density lipoprotein (VLDL)-triacylglycerol, and to sex-specific browning of white adipose tissue. Ovarian senescence facilitates both the development of massive hepatic steatosis and the fibrotic progression of liver disease in an experimental overfed zebrafish model. Consistently, estrogen deficiency, by potentiating hepatic inflammatory changes, hastens the progression of disease in a dietary model of nonalcoholic steatohepatitis (NASH) developing in ovariectomized mice fed a high-fat diet. In humans, NAFLD more often affects men; and premenopausal women are equally protected from developing NAFLD as they are from cardiovascular disease. It would be expected that early menarche, definitely associated with estrogen activation, would produce protection against the risk of NAFLD. Nevertheless, it has been suggested that early menarche may confer an increased risk of NAFLD in adulthood, excess adiposity being the primary culprit of this association. Fertile age may be associated with more severe hepatocyte injury and inflammation, but also with a decreased risk of liver fibrosis compared to men and postmenopausal status. Later in life, ovarian senescence is strongly associated with severe steatosis and fibrosing NASH, which may occur in postmenopausal women. Estrogen deficiency is deemed to be responsible for these findings via the development of postmenopausal metabolic syndrome. Estrogen supplementation may at least theoretically protect from NAFLD development and progression, as suggested by some studies exploring the effect of hormonal replacement therapy on postmenopausal women, but the variable impact of different sex hormones in NAFLD (i.e., the pro-inflammatory effect of progesterone) should be carefully considered.

Comparative analysis of osteoblast gene expression profiles and Runx2 genomic occupancy of mouse and human osteoblasts in vitro

Fast progress of the next generation sequencing (NGS) technology has allowed global transcriptional profiling and genome-wide mapping of transcription factor binding sites in various cellular contexts. However, limited number of replicates and high amount of data processing may weaken the significance of the findings. Comparative analyses of independent data sets acquired in the different laboratories would greatly increase the validity of the data. Runx2 is the key transcription factor regulating osteoblast differentiation and bone formation. We performed a comparative analysis of three published Runx2 data sets of chromatin immunoprecipitation followed by deep sequencing (ChIP-seq) analysis in osteoblasts from mouse and human origin. Moreover, we assessed the similarity of the corresponding transcription data of these studies available online. The ChIP-seq data analysis confirmed general features of Runx2 binding, including location at genic vs intergenic regions and abundant Runx2 binding on promoters of the highly expressed genes. We also found high frequency of Runx2 DNA binding without a consensus Runx2 motif at the binding site. Importantly, mouse and human Runx2 showed moderately similar binding patterns in terms of peak-associated closest genes and their associated genomic ontology (GO) pathways. Accordingly, the gene expression profiles were highly similar and osteoblastic phenotype was prominent in the differentiated stage in both species. In conclusion, ChIP-seq method shows good reproducibility in the context of mature osteoblasts, and mouse and human osteoblast models resemble each other closely in Runx2 binding and in gene expression profiles, supporting the use of these models as adequate tools in studying osteoblast differentiation.

The Hippo pathway effector YAP is an essential regulator of ductal progenitor patterning in the mouse submandibular gland

Salivary glands, such as submandibular glands (SMGs), are composed of branched epithelial ductal networks that terminate in acini that together produce, transport and secrete saliva. Here, we show that the transcriptional regulator Yap, a key effector of the Hippo pathway, is required for the proper patterning and morphogenesis of SMG epithelium. Epithelial deletion of Yap in developing SMGs results in the loss of ductal structures, arising from reduced expression of the EGF family member Epiregulin, which we show is required for the expansion of Krt5/Krt14-positive ductal progenitors. We further show that epithelial deletion of the Lats1 and Lats2 genes, which encode kinases that restrict nuclear Yap localization, results in morphogenesis defects accompanied by an expansion of Krt5/Krt14-positive cells. Collectively, our data indicate that Yap-induced Epiregulin signaling promotes the identity of SMG ductal progenitors and that removal of nuclear Yap by Lats1/2-mediated signaling is critical for proper ductal maturation.

DOI:http://dx.doi.org/10.7554/eLife.23499.001

Our mouths are continually bathed by saliva – a thick, clear liquid that helps us to swallow and digest our food and protects us against infections. Saliva is produced by and released from salivary glands, which are organs that contain a branched network of tubes. Salivary glands can only properly develop if immature cells known as stem cells, which give rise to the mature cells in the organ, are controlled. Despite their importance for development of salivary glands, little has been known about the signals that control these stem cells.

Szymaniak et al. have now discovered new regulators of the salivary gland stem cells in mice, including essential roles in the regulation of these cells by a protein known as Yap. The Yap protein is controlled by a set of proteins that together are known as the Hippo pathway. Szymaniak et al. found that when the gene for Yap was deleted in mice very few stem cells were made, and the transport tubes of the salivary tubes failed to develop. Conversely, when the Hippo pathway was disrupted in mice there were too many stem cells because they could not properly develop into the mature cells, leading to incorrect transport tube development..

These results indicate that Yap is essential for controlling the stem cells of the salivary glands, and offer important insight into the signals that control how the salivary glands develop. The next step will be to investigate whether the Hippo pathway or Yap are affected in diseases of the salivary gland, which often show incorrect numbers of stem cells.

DOI:http://dx.doi.org/10.7554/eLife.23499.002

Mutant p53 Protein and the Hippo Transducers YAP and TAZ: A Critical Oncogenic Node in Human Cancers

p53 protein is a well-known tumor suppressor factor that regulates cellular homeostasis. As it has several and key functions exerted, p53 is known as “the guardian of the genome” and either loss of function or gain of function mutations in the TP53 coding protein sequence are involved in cancer onset and progression. The Hippo pathway is a key regulator of developmental and regenerative physiological processes but if deregulated can induce cell transformation and cancer progression. The p53 and Hippo pathways exert a plethora of fine-tuned functions that can apparently be in contrast with each other. In this review, we propose that the p53 status can affect the Hippo pathway function by switching its outputs from tumor suppressor to oncogenic activities. In detail, we discuss: (a) the oncogenic role of the protein complex mutant p53/YAP; (b) TAZ oncogenic activation mediated by mutant p53; (c) the therapeutic potential of targeting mutant p53 to impair YAP and TAZ oncogenic functions in human cancers.

Multiple-response regression analysis links magnetic resonance imaging features to de-regulated protein expression and pathway activity in lower grade glioma

BACKGROUND AND PURPOSE

Lower grade gliomas (LGGs), lesions of WHO grades II and III, comprise 10-15% of primary brain tumors. In this first-of-a-kind study, we aim to carry out a radioproteomic characterization of LGGs using proteomics data from the TCGA and imaging data from the TCIA cohorts, to obtain an association between tumor MRI characteristics and protein measurements. The availability of linked imaging and molecular data permits the assessment of relationships between tumor genomic/proteomic measurements with phenotypic features.

MATERIALS AND METHODS

Multiple-response regression of the image-derived, radiologist scored features with reverse-phase protein array (RPPA) expression levels generated correlation coefficients for each combination of image-feature and protein or phospho-protein in the RPPA dataset. Significantly-associated proteins for VASARI features were analyzed with Ingenuity Pathway Analysis software. Hierarchical clustering of the results of the pathway analysis was used to determine which feature groups were most strongly correlated with pathway activity and cellular functions.

RESULTS

The multiple-response regression approach identified multiple proteins associated with each VASARI imaging feature. VASARI features were found to be correlated with expression of IL8, PTEN, PI3K/Akt, Neuregulin, ERK/MAPK, p70S6K and EGF signaling pathways.

CONCLUSION

Radioproteomics analysis might enable an insight into the phenotypic consequences of molecular aberrations in LGGs.

A New View of Pathway-Driven Drug Resistance in Tumor Proliferation

Defeating drug resistance in tumor cell proliferation is challenging. We propose that signaling in cell proliferation takes place via two core pathways, each embodying multiple alternative pathways. We consider drug resistance through an alternative proliferation pathway - within the same or within the other core pathway. Most drug combinations target only one core pathway; blocking both can restrain proliferation. We define core pathways as independent and acting similarly in cell-cycle control, which can explain why their products (e.g., ERK and YAP1) can substitute for each other in resistance. Core pathways can forecast possible resistance because acquired resistance frequently occurs through alternative proliferation pathways. This concept may help to predict the efficacy of drug combinations. The selection of distinct combinations for specific mutated pathways would be guided by clinical diagnosis.

A reciprocal regulatory loop between TAZ/YAP and G-protein Gαs regulates Schwann cell proliferation and myelination

Schwann cell (SC) myelination in the peripheral nervous system is essential for motor function, and uncontrolled SC proliferation occurs in cancer. Here, we show that a dual role for Hippo effectors TAZ and YAP in SC proliferation and myelination through modulating G-protein expression and interacting with SOX10, respectively. Developmentally regulated mutagenesis indicates that TAZ/YAP are critical for SC proliferation and differentiation in a stage-dependent manner. Genome-wide occupancy mapping and transcriptome profiling reveal that nuclear TAZ/YAP promote SC proliferation by activating cell cycle regulators, while targeting critical differentiation regulators in cooperation with SOX10 for myelination. We further identify that TAZ targets and represses Gnas, encoding Gαs-protein, which opposes TAZ/YAP activities to decelerate proliferation. Gnas deletion expands SC precursor pools and blocks peripheral myelination. Thus, the Hippo/TAZ/YAP and Gαs-protein feedback circuit functions as a fulcrum balancing SC proliferation and differentiation, providing insights into molecular programming of SC lineage progression and homeostasis.

The Hippo pathway has recently been implicated in Schwann cell (SC) development and myelination. Here the authors reveal mechanistic insights into how TAZ and YAP regulate and interact with target genes; they further identify a negative feedback loop between TAZ/YAP and G protein Gαs that balances SC proliferation and differentiation.

YAP is essential for mechanical force production and epithelial cell proliferation during lung branching morphogenesis

Branching morphogenesis is a fundamental program for tissue patterning. We show that active YAP, a key mediator of Hippo signaling, is distributed throughout the murine lung epithelium and loss of epithelial YAP severely disrupts branching. Failure to branch is restricted to regions where YAP activity is removed. This suggests that YAP controls local epithelial cell properties. In support of this model, mechanical force production is compromised and cell proliferation is reduced in Yap mutant lungs. We propose that defective force generation and insufficient epithelial cell number underlie the branching defects. Through genomic analysis, we also uncovered a feedback control of pMLC levels, which is critical for mechanical force production, likely through the direct induction of multiple regulators by YAP. Our work provides a molecular pathway that could control epithelial cell properties required for proper morphogenetic movement and pattern formation.

Systematic morphological profiling of human gene and allele function via Cell Painting

We hypothesized that human genes and disease-associated alleles might be systematically functionally annotated using morphological profiling of cDNA constructs, via a microscopy-based Cell Painting assay. Indeed, 50% of the 220 tested genes yielded detectable morphological profiles, which grouped into biologically meaningful gene clusters consistent with known functional annotation (e.g., the RAS-RAF-MEK-ERK cascade). We used novel subpopulation-based visualization methods to interpret the morphological changes for specific clusters. This unbiased morphologic map of gene function revealed TRAF2/c-REL negative regulation of YAP1/WWTR1-responsive pathways. We confirmed this discovery of functional connectivity between the NF-κB pathway and Hippo pathway effectors at the transcriptional level, thereby expanding knowledge of these two signaling pathways that critically regulate tumor initiation and progression. We make the images and raw data publicly available, providing an initial morphological map of major biological pathways for future study.

DOI:http://dx.doi.org/10.7554/eLife.24060.001

Many human diseases are caused by particular changes, called mutations, in patients’ DNA. A genome is the complete DNA set of an organism, which contains all the information to build the body and keep it working. This information is stored as a code made up of four chemicals called bases. Humans have about 30,000 genes built from DNA, which contain specific sequences of bases. Genome sequencing can determine the exact order of these bases, and has revealed a long list of mutations in genes that could cause particular diseases. However, over 30% of genes in the human body do not have a known role. Genes can serve multiple roles, some of which are not yet discovered, and even when a gene’s purpose is known, the impact of each particular mutation in a given gene is largely uncatalogued. Therefore, new methods need to be developed to identify the biological roles of both normal and abnormal gene sequences.

For hundreds of years, biologists have used microscopy to study how living cells work. Rohban et al. have now asked whether modern software that extracts data from microscopy images could create a fingerprint-like profile of a cell that would reflect how its genes affect its role and appearance. While some genes do not necessarily carry a code with instructions of what a cell should look like, they can indirectly modify the structure of the cell. The resulting changes in the shape of the cell can then be captured in images. The idea was that two cells with matching profiles would indicate that their combinations of genes had matching biological roles too.

Rohban et al. tested their approach with human cells grown in the laboratory. In each sample of cells, they ‘turned on’ one of a few hundred relatively well-known human genes, some of which were known to have similar roles. The cells were then stained via a technique called ‘Cell Painting’ to reveal eight specific components of each cell, including its DNA and its surface membrane. The stained cells were imaged under a microscope and the resulting microscopy images analyzed to create a profile of each type of cell. Rohban et al. confirmed that turning on genes known to perform similar biological roles lead to similar-looking cells. The analysis also revealed a previously unknown interaction between two major pathways in the cell that control how cancer starts and develops.

In the future, this approach could predict the biological roles of less-understood genes by looking for profiles that match those of well-known genes. Applying this strategy to every human gene, and mutations in genes that are linked to diseases, could help to answer many mysteries about how genes build the human body and keep it working.

DOI:http://dx.doi.org/10.7554/eLife.24060.002

Discovering sparse transcription factor codes for cell states and state transitions during development

Computational analysis of gene expression to determine both the sequence of lineage choices made by multipotent cells and to identify the genes influencing these decisions is challenging. Here we discover a pattern in the expression levels of a sparse subset of genes among cell types in B- and T-cell developmental lineages that correlates with developmental topologies. We develop a statistical framework using this pattern to simultaneously infer lineage transitions and the genes that determine these relationships. We use this technique to reconstruct the early hematopoietic and intestinal developmental trees. We extend this framework to analyze single-cell RNA-seq data from early human cortical development, inferring a neocortical-hindbrain split in early progenitor cells and the key genes that could control this lineage decision. Our work allows us to simultaneously infer both the identity and lineage of cell types as well as a small set of key genes whose expression patterns reflect these relationships.

miR-285-Yki/Mask double-negative feedback loop mediates blood-brain barrier integrity in Drosophila

The Hippo signaling pathway is highly conserved from Drosophila to mammals and plays a central role in maintaining organ size and tissue homeostasis. The blood-brain barrier (BBB) physiologically isolates the brain from circulating blood or the hemolymph system, and its integrity is strictly maintained to perform sophisticated neuronal functions. Until now, the underlying mechanisms of subperineurial glia (SPG) growth and BBB maintenance during development are not clear. Here, we report an miR-285-Yorkie (Yki)/Multiple Ankyrin repeats Single KH domain (Mask) double-negative feedback loop that regulates SPG growth and BBB integrity. Flies with a loss of miR-285 have a defective BBB with increased SPG ploidy and disruptive septate junctions. Mechanistically, miR-285 directly targets the Yki cofactor Mask to suppress Yki activity and down-regulates the expression of its downstream target cyclin E, a key regulator of cell cycle. Disturbance of cyclin E expression in SPG causes abnormal endoreplication, which leads to aberrant DNA ploidy and defective septate junctions. Moreover, the expression of miR-285 is increased by knockdown of yki or mask and is decreased with yki overexpression, thus forming a double-negative feedback loop. This regulatory loop is crucial for sustaining an appropriate Yki/Mask activity and cyclin E level to maintain SPG ploidy and BBB integrity. Perturbation of this signaling loop, either by dysregulated miR-285 expression or Yki activity, causes irregular SPG ploidy and BBB disruption. Furthermore, ectopic expression of miR-285 promotes canonical Hippo pathway-mediated apoptosis independent of the p53 or JNK pathway. Collectively, these results reveal an exquisite regulatory mechanism for BBB maintenance through an miR-285-Yki/Mask regulatory circuit.

MicroRNA-21 preserves the fibrotic mechanical memory of mesenchymal stem cells

Expansion on stiff culture substrates activates pro-fibrotic cell programs that are retained by mechanical memory. Here, we show that priming on physiologically soft silicone substrates suppresses fibrogenesis and desensitizes mesenchymal stem cells (MSCs) against subsequent mechanical activation in vitro and in vivo, and identify the microRNA miR-21 as a long-term memory keeper of the fibrogenic program in MSCs. During stiff priming, miR-21 levels were gradually increased by continued regulation through the acutely mechanosensitive myocardin-related transcription factor-A (MRTF-A/MLK-1) and remained high over 2 weeks after removal of the mechanical stimulus. Knocking down miR-21 once by the end of the stiff-priming period was sufficient to erase the mechanical memory and sensitize MSCs to subsequent exposure to soft substrates. Soft priming and erasing mechanical memory following cell culture expansion protects MSCs from fibrogenesis in the host wound environment and increases the chances for success of MSC therapy in tissue-repair applications.

YAP and the Hippo pathway in pediatric cancer

The Hippo pathway is an important signaling pathway that controls cell proliferation and apoptosis. It is evolutionarily conserved in mammals and is stimulated by cell-cell contact, inhibiting cell proliferation in response to increased cell density. During early embryonic development, the Hippo signaling pathway regulates organ development and size, and its functions result in the coordinated balance between proliferation, apoptosis, and differentiation. Its principal effectors, YAP and TAZ, regulate signaling by the embryonic stem cells and determine cell fate and histogenesis. Dysfunction of this pathway contributes to cancer development in adults and children. Emerging studies have shed light on the upregulation of Hippo pathway members in several pediatric cancers and may offer prognostic information on rhabdomyosarcoma, osteosarcoma, Wilms tumor, neuroblastoma, medulloblastoma, and other brain gliomas. We review the results of such published studies and highlight the potential clinical application of this pathway in pediatric oncologic and pathologic studies. These studies support targeting this pathway as a novel treatment strategy.

MARK4 inhibits Hippo signaling to promote proliferation and migration of breast cancer cells

The Hippo pathway is a critical regulator of tissue size, and aberrations in pathway regulation lead to cancer. MST1/2 and LATS1/2 kinases comprise the core of the pathway that, in association with adaptor proteins SAV and MOB, functions in a sequential manner to phosphorylate and inhibit the transcription factors YAP and TAZ. Here we identify mammalian MARK family members as activators of YAP/TAZ. We show that depletion of MARK4 in MDA-MB-231 breast cancer cells results in the loss of nuclear YAP/TAZ and decreases the expression of YAP/TAZ targets. We demonstrate that MARK4 can bind to MST and SAV, leading to their phosphorylation, and that MARK4 expression attenuates the formation of a complex between MST/SAV and LATS, which depends on the kinase activity of MARK4. Abrogation of MARK4 expression using siRNAs and CRISPR/Cas9 gene editing attenuates the proliferation and migration of MDA-MB-231 cells. Our results show that MARK4 acts as a negative regulator of the Hippo kinase cassette to promote YAP/TAZ activity and that loss of MARK4 restrains the tumorigenic properties of breast cancer cells.

Dimethyl Fumarate ameliorates pulmonary arterial hypertension and lung fibrosis by targeting multiple pathways

Pulmonary arterial hypertension (PAH) is a fatal condition for which there is no cure. Dimethyl Fumarate (DMF) is an FDA approved anti-oxidative and anti-inflammatory agent with a favorable safety record. The goal of this study was to assess the effectiveness of DMF as a therapy for PAH using patient-derived cells and murine models. We show that DMF treatment is effective in reversing hemodynamic changes, reducing inflammation, oxidative damage, and fibrosis in the experimental models of PAH and lung fibrosis. Our findings indicate that effects of DMF are facilitated by inhibiting pro-inflammatory NFκB, STAT3 and cJUN signaling, as well as βTRCP-dependent degradation of the pro-fibrogenic mediators Sp1, TAZ and β-catenin. These results provide a novel insight into the mechanism of its action. Collectively, preclinical results demonstrate beneficial effects of DMF on key molecular pathways contributing to PAH, and support its testing in PAH treatment in patients.

Advances in myelinating glial cell development

In the vertebrate nervous system, the fast conduction of action potentials is potentiated by the myelin sheath, a multi-lamellar, lipid-rich structure that also provides vital trophic and metabolic support to axons. Myelin is elaborated by the plasma membrane of specialized glial cells, oligodendrocytes in the central nervous system (CNS) and Schwann cells (SCs) in the peripheral nervous system (PNS). The diseases that result from damage to myelin or glia, including multiple sclerosis and Charcot-Marie-Tooth disease, underscore the importance of these cells for human health. Therefore, an understanding of glial development and myelination is crucial in addressing the etiology of demyelinating diseases and developing patient therapies. In this review, we discuss new insights into the roles of mechanotransduction and cytoskeletal rearrangements as well as activity dependent myelination and axonal maintenance by glia. Together, these discoveries advance our knowledge of myelin and glia in nervous system health and plasticity throughout life.

YAP/TAZ initiate and maintain Schwann cell myelination

Nuclear exclusion of the transcriptional regulators and potent oncoproteins, YAP/TAZ, is considered necessary for adult tissue homeostasis. Here we show that nuclear YAP/TAZ are essential regulators of peripheral nerve development and myelin maintenance. To proliferate, developing Schwann cells (SCs) require YAP/TAZ to enter S-phase and, without them, fail to generate sufficient SCs for timely axon sorting. To differentiate, SCs require YAP/TAZ to upregulate Krox20 and, without them, completely fail to myelinate, resulting in severe peripheral neuropathy. Remarkably, in adulthood, nuclear YAP/TAZ are selectively expressed by myelinating SCs, and conditional ablation results in severe peripheral demyelination and mouse death. YAP/TAZ regulate both developmental and adult myelination by driving TEAD1 to activate Krox20. Therefore, YAP/TAZ are crucial for SCs to myelinate developing nerve and to maintain myelinated nerve in adulthood. Our study also provides a new insight into the role of nuclear YAP/TAZ in homeostatic maintenance of an adult tissue.

Snail/Slug-YAP/TAZ complexes cooperatively regulate mesenchymal stem cell function and bone formation

Snail and Slug are zinc-finger transcription factors that play key roles in directing the epithelial-mesenchymal transition (EMT) programs associated with normal development as well as disease progression. More recent work suggests that these EMT-associated transcription factors also modulate the function of both embryonic and adult stem cells. Interestingly, YAP and TAZ, the co-transcriptional effectors of the Hippo pathway, likewise play an important role in stem cell self-renewal and lineage commitment. While direct intersections between the Snail/Slug and Hippo pathways have not been described previously, we recently described an unexpected cooperative interaction between Snail/Slug and YAP/TAZ that controls the self-renewal and differentiation properties of bone marrow-derived mesenchymal stem cells (MSCs), a cell population critical to bone development. Additional studies revealed that both Snail and Slug are able to form binary complexes with either YAP or TAZ that, together, control YAP/TAZ transcriptional activity and function throughout mouse development. Given the more recent observations that MSC-like cell populations are found in association throughout the vasculature where they participate in tissue regeneration, fibrosis and cancer, the Snail/Slug-YAP/TAZ axis is well-positioned to regulate global stem cell function in health and disease.