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Yes-associated protein (YAP) and its homologue TAZ are transducers of several biochemical and biomechanical signals, integrating multiplexed inputs from the microenvironment into higher level cellular functions such as proliferation, differentiation and migration. Emerging evidence suggests that Ca2+ is a key second messenger that connects microenvironmental input signals and YAP/TAZ regulation. However, studies that directly modulate Ca2+ have reported contradictory YAP/TAZ responses: in some studies, a reduction in Ca2+ influx increases the activity of YAP/TAZ, while in others, an increase in Ca2+ influx activates YAP/TAZ. Importantly, Ca2+ and YAP/TAZ exhibit distinct spatiotemporal dynamics, making it difficult to unravel their connections from a purely experimental approach. In this study, we developed a network model of Ca2+ -mediated YAP/TAZ signalling to investigate how temporal dynamics and crosstalk of signalling pathways interacting with Ca2+ can alter the YAP/TAZ response, as observed in experiments. By including six signalling modules (e.g. GPCR, IP3-Ca2+ , kinases, RhoA, F-actin and Hippo-YAP/TAZ) that interact with Ca2+ , we investigated both transient and steady-state cell response to angiotensin II and thapsigargin stimuli. The model predicts that stimuli, Ca2+ transients and frequency-dependent relationships between Ca2+ and YAP/TAZ are primarily mediated by cPKC, DAG, CaMKII and F-actin. Simulation results illustrate the role of Ca2+ dynamics and CaMKII bistable response in switching the direction of changes in Ca2+ -induced YAP/TAZ activity. A frequency-dependent YAP/TAZ response revealed the competition between upstream regulators of LATS1/2, leading to the YAP/TAZ non-monotonic response to periodic GPCR stimulation. This study provides new insights into underlying mechanisms responsible for the controversial Ca2+ -YAP/TAZ relationship observed in experiments. KEY POINTS: YAP/TAZ integrates biochemical and biomechanical inputs to regulate cellul

Regulation of hepatocyte proliferation and liver morphology is of critical importance to tissue and whole-body homeostasis. However, the molecular mechanisms that underlie this complex process are incompletely understood. Here, we describe a role for the ubiquitin ligase BRCA1-associated protein (BRAP) in regulation of hepatocyte morphology and turnover via regulation of MST2, a protein kinase in the Hippo pathway. The Hippo pathway has been implicated in the control of liver morphology, inflammation, and fibrosis. We demonstrate here that liver-specific ablation of Brap in mice results in gross and cellular morphological alterations of the liver. Brap-deficient livers exhibit increased hepatocyte proliferation, cell death, and inflammation. We show that loss of BRAP protein alters Hippo pathway signaling, causing a reduction in phosphorylation of YAP and increased expression of YAP target genes, including those regulating cell growth and interactions with the extracellular environment. Finally, increased Hippo signaling in Brap knockout mice alters the pattern of liver lipid accumulation in dietary models of obesity. These studies identify a role for BRAP as a modulator of the hepatic Hippo pathway with relevance to human liver disease.

Enterovirus 71 (EV71) is the major pathogens of human hand, foot, and mouth disease (HFMD). EV71 efficiently escapes innate immunity responses of the host to cause infection. At present, no effective antiviral drugs for EV71 are available. Anemoside B4 (B4) is a natural saponin isolated from the roots of Pulsatilla chinensis (Bunge) Regel. P. chinensis extracts that shows a wide variety of biological activities. In this study, we investigated the antiviral activities of B4 against EV71 both in cell culture and in suckling mice. We showed that B4 (12.5-200 mu M) dose dependently increased the viability of EV71-infected RD cells with an IC50 value of 24.95 +/- 0.05 mu M against EV71. The antiviral activity of B4 was associated with enhanced interferon (IFN)-beta response, since knockdown of IFN-beta abolished its antiviral activity. We also confirmed that the enhanced IFN response was mediated via activation of retinoic acid-inducible gene I (RIG-I) like receptors (RLRs) pathway, and it was executed by upregulation of 14-3-3 protein, which disrupted the interaction between yes-associated protein (YAP) and interferon regulatory factor 3 (IRF3). By using amino acids in cell culture (SILAC)-based proteomics profiling, we identified the Hippo pathway as the top-ranking functional cluster in B4-treated EV71-infected cells. In vivo experiments were conducted in suckling mice (2-day-old) infected with EV71 and subsequently B4 (200 mg center dot kg(-1) center dot d(-1), i.p.) was administered for 16 days. We showed that B4 administration effectively suppressed EV71 replication and improved muscle inflammation and limb activity. Meanwhile, B4 administration regulated the expressions of HFMD biomarkers IL-10 and IFN-gamma, attenuating complications of EV71 infection. Collectively, our results suggest that B4 could enhance the antiviral effect of IFN-beta by orchestrating Hippo and RLRs pathway, and B4 would be a potential lead compound for developing an anti-EV71 drug.

The Hippo pathway is an evolutionarily conserved modulator of developmental biology with a key role in tissue and organ size regulation under homeostatic conditions. Like other signaling pathways with a significant role in embryonic development, the deregulation of Hippo signaling contributes to oncogenesis. Central to the Hippo pathway is a conserved cascade of adaptor proteins and inhibitory kinases that converge and regulate the activity of the oncoproteins YAP and TAZ, the final transducers of the pathway. Elevated levels and aberrant activation of YAP and TAZ have been described in many cancers. Though most of the studies describe their pervasive activation in epithelial neoplasms, there is increasing evidence pointing out its relevance in mesenchymal malignancies as well. Interestingly, somatic or germline mutations in genes of the Hippo pathway are scarce compared to other signaling pathways that are frequently disrupted in cancer. However, in the case of sarcomas, several examples of genetic alteration of Hippo members, including gene fusions, have been described during the last few years. Here, we review the current knowledge of Hippo pathway implication in sarcoma, describing mechanistic hints recently reported in specific histological entities and how these alterations represent an opportunity for targeted therapy in this heterogeneous group of neoplasm.

The Hippo pathway is an evolutionarily conserved modulator of developmental biology with a key role in tissue and organ size regulation under homeostatic conditions. Like other signaling pathways with a significant role in embryonic development, the deregulation of Hippo signaling contributes to oncogenesis. Central to the Hippo pathway is a conserved cascade of adaptor proteins and inhibitory kinases that converge and regulate the activity of the oncoproteins YAP and TAZ, the final transducers of the pathway. Elevated levels and aberrant activation of YAP and TAZ have been described in many cancers. Though most of the studies describe their pervasive activation in epithelial neoplasms, there is increasing evidence pointing out its relevance in mesenchymal malignancies as well. Interestingly, somatic or germline mutations in genes of the Hippo pathway are scarce compared to other signaling pathways that are frequently disrupted in cancer. However, in the case of sarcomas, several examples of genetic alteration of Hippo members, including gene fusions, have been described during the last few years. Here, we review the current knowledge of Hippo pathway implication in sarcoma, describing mechanistic hints recently reported in specific histological entities and how these alterations represent an opportunity for targeted therapy in this heterogeneous group of neoplasm.

Recent reports suggest a link between positive regulation of the Hippo pathway with bipolar disorder (BD), and the Hippo pathway is known to interact with multiple other signaling pathways previously associated with BD and other psychiatric disorders. In this study, neuronal-like NT2 cells were treated with amisulpride (10 µM), aripiprazole (0.1 µM), clozapine (10 µM), lamotrigine (50 µM), lithium (2.5 mM), quetiapine (50 µM), risperidone (0.1 µM), valproate (0.5 mM), or vehicle control for 24 h. Genome-wide mRNA expression was quantified and analyzed using gene set enrichment analysis (GSEA), with genes belonging to Hippo, Wnt, Notch, TGF- β, and Hedgehog retrieved from the KEGG database. Five of the eight drugs downregulated the genes of the Hippo pathway and modulated several genes involved in the interacting pathways. We speculate that the regulation of these genes, especially by aripiprazole, clozapine, and quetiapine, results in a reduction of MAPK and NFκB pro-inflammatory signaling through modulation of Hippo, Wnt, and TGF-β pathways. We also employed connectivity map analysis to identify compounds that act on these pathways in a similar manner to the known psychiatric drugs. Thirty-six compounds were identified. The presence of antidepressants and antipsychotics validates our approach and reveals possible new targets for drug repurposing.

Malignant mesothelioma is an aggressive cancer of the mesothelium for which asbestos-exposure is the predominant etiological factor. The standard treatment regime for mesothelioma is systemic chemotherapy, which exhibits poor efficacy with a median post-diagnosis survival of 12 months. This highlights the need for alternate therapies, such as targeted therapies, to improve patient outcomes. Genomic and cell biological analyses of mesotheliomas indicate that deficiency of key tumour suppressor genes including BAP1 or members of the Hippo tumour suppressor pathway such as NF2, are frequent genetic aberrations in this cancer. Inhibition of cancer-promoting events that occur downstream of these genetic aberrations represents a potential mechanism by which mesothelioma patient outcomes can be improved. Originally identified in Drosophila, the Hippo pathway is highly conserved in mammals and regulates the activity of the oncoproteins and transcriptional coactivators YAP and TAZ and their nuclear interaction partners, the TEAD family of transcription factors. YAP/TAZ-TEAD hyperactivation is an oncogenic driver in Hippo pathway deregulated mesotheliomas, indicating that inhibition of these proteins could represent a new treatment strategy for this disease. An emerging class of small molecule inhibitors of YAP/TAZ-TEAD target the recently identified post-translational modification of TEAD palmitoylation. One such compound, VT107, has shown promising pre-clinical activity in in vitro and in vivo models of Hippo pathway deregulated mesothelioma. Whilst VT107 is a promising therapeutic, the current understanding of its molecular impact is incomplete. Moreover, further identification of therapeutic targets in BAP1 or NF2 deficient mesothelioma cells might enable development of additional targeted therapies to treat candidate tumours. To address these considerations, I aimed to answer three key questions: 1) Which genes are potential therapeutic targets for treatment of NF2 or BA

WW domain-containing transcription regulator 1 (WWTR1) is one of the primary effectors in the Hippo pathway, which plays essential roles in cell differentiation into trophectoderm (TE) and inner cell mass cell lineages at the blastocyst stage. However, little is known about the roles of WWTR1 in preimplantation development. The present study aimed to explore the significance of WWTR1 expression in preimplantation development using an mRNA knockdown (KD) system in bovine embryos. We first quantitated WWTR1 expression at protein and mRNA levels from fertilization to blastocyst stage. WWTR1 proteins gradually shifted from extranuclear localization during the 16-cell stage to nuclear localization by morula stage. WWTR1 mRNA expression was also transiently upregulated at the 16-cell stage. WWTR1 KD efficiently repressed WWTR1 expression at protein and mRNA levels. The WWTR1 KD embryos developed to the blastocyst stage at rates equivalent to those of controls, but TE cell numbers were significantly decreased. Representative TE-expressed genes, including CDX2 and IFNT were also significantly decreased in WWTR1 KD blastocysts. These results provide the first demonstration that WWTR1 expression is responsible for normal TE cell development in preimplantation embryos. (c) 2021 Elsevier Inc. All rights reserved.

The exocyst is an evolutionarily conserved protein complex that regulates vesicular trafficking and scaffolds signal transduction. Key upstream components of the exocyst include monomeric RAL GTPases, which help mount cell-autonomous responses to trophic and immunogenic signals. Here, we present a quantitative proteomics-based characterization of dynamic and signal-dependent exocyst protein interactomes. Under viral infection, an Exo84 exocyst subcomplex assembles the immune kinase Protein Kinase R (PKR) together with the Hippo kinase Macrophage Stimulating 1 (MST1). PKR phosphorylates MST1 to activate Hippo signaling and inactivate Yes Associated Protein 1 (YAP1). By contrast, a Sec5 exocyst subcomplex recruits another immune kinase, TANK binding kinase 1 (TBK1), which interacted with and activated mammalian target of rapamycin (mTOR). RALB was necessary and sufficient for induction of Hippo and mTOR signaling through parallel exocyst subcomplex engagement, supporting the cellular response to virus infection and oncogenic signaling. This study highlights RALB-exocyst signaling subcomplexes as mechanisms for the integrated engagement of Hippo and mTOR signaling in cells challenged by viral pathogens or oncogenic signaling.

YAP (Yes-associated protein) and TAZ (transcriptional coactivator with PDZ-binding motif) are transcription co-regulators that make up the terminal components of the Hippo signaling pathway, which plays a role in organ size control and derived tissue homeostasis through regulation of the proliferation, differentiation and apoptosis of a wide variety of differentiated and stem cells. Hippo/YAP signaling contributes to normal development of the nervous system, as it participates in self-renewal of neural stem cells, proliferation of neural progenitor cells and differentiation, activation and myelination of glial cells. Not surprisingly, alterations in this pathway underlie the development of severe neurological diseases. In glioblastomas, YAP and TAZ levels directly correlate with the amount of the actin-binding molecule WIP (WASP interacting protein), which regulates stemness and invasiveness. In neurons, WIP modulates cytoskeleton dynamics through actin polymerization/depolymerization and acts as a negative regulator of neuritogenesis, dendrite branching and dendritic spine formation. Our working hypothesis is that WIP regulates the YAP/TAZ pools using a Hippo-independent pathway. Thus, in this review we will present some of the data that links WIP, YAP and TAZ, with a focus on their function in cells from the central and peripheral nervous systems. It is hoped that a better understanding of the mechanisms involved in brain and nervous development and the pathologies that arise due to their alteration will reveal novel therapeutic targets for neurologic diseases.

How cells sense and respond to mechanical stimuli remains an open question. Recent advances have identified the translocation of Yes-associated protein (YAP) between nucleus and cytoplasm as a central mechanism for sensing mechanical forces and regulating mechanotransduction. We formulate a spatiotemporal model of the mechanotransduction signalling pathway that includes coupling of YAP with the cell force-generation machinery through the Rho family of GTPases. Considering the active and inactive forms of a single Rho protein (GTP/GDP-bound) and of YAP (non-phosphorylated/phosphorylated), we study the cross-talk between cell polarization due to active Rho and YAP activation through its nuclear localization. For fixed mechanical stimuli, our model predicts stationary nuclear-to-cytoplasmic YAP ratios consistent with experimental data at varying adhesive cell area. We further predict damped and even sustained oscillations in the YAP nuclear-to-cytoplasmic ratio by accounting for recently reported positive and negative YAP-Rho feedback. Extending the framework to time-varying mechanical stimuli that simulate cyclic stretching and compression, we show that the YAP nuclear-to-cytoplasmic ratio's time dependence follows that of the cyclic mechanical stimulus. The model presents one of the first frameworks for understanding spatiotemporal YAP mechanotransduction, providing several predictions of possible YAP localization dynamics, and suggesting new directions for experimental and theoretical studies.

Background: Activation of the oncogene yes-associated protein (YAP) is frequently detected in intrahepatic cholangiocarcinoma (iCCA); however, the expression pattern and the functional impact of its paralogue WW domain-containing transcription regulator 1 (WWTR1; synonym: TAZ) are not well described in different CCA subtypes. Methods: Immunohistochemical analysis of YAP and TAZ in iCCA and extrahepatic CCA (eCCA) cohorts was performed. YAP/TAZ shuttling and their functional impact on CCA cell lines were investigated. Target genes expression after combined YAP/TAZ inhibition was analyzed. Results: Immunohistochemical analysis of iCCA and eCCA revealed YAP or TAZ positivity in up to 49.2%; however, oncogene co-expression was less frequent (up to 23%). In contrast, both proteins were jointly detectable in most CCA cell lines and showed nuclear/cytoplasmic shuttling in a cell density-dependent manner. Next to the pro-proliferative function of YAP/TAZ, both transcriptional co-activators cooperated in the regulation of a gene signature that indicated the presence of chromosomal instability (CIN). A correlation between YAP and the CIN marker phospho-H2A histone family member X (pH2AX) was particularly observed in tissues from iCCA and distal CCA (dCCA). The presence of the CIN genes in about 25% of iCCA was statistically associated with worse prognosis. Conclusions: YAP and TAZ activation is not uncoupled from cell density in CCA cells and both factors cooperatively contribute to proliferation and expression of CIN-associated genes. The corresponding group of CCA patients is characterized by CIN and may benefit from YAP/TAZ-directed therapies.

Epithelia grow and shape into functional structures during organogenesis. Although most of the focus on organogenesis has been drawn to the building of biological structures, the disassembly of pre-existing structures is also an important event to reach a functional adult organ. Examples of disassembly processes include the regression of the Müllerian or Wolffian ducts during gonad development and mammary gland involution during the post-lactational period in adult females. To date, it is unclear how organ disassembly is controlled at the cellular level. Here, we follow the Drosophila larval trachea through metamorphosis and show that its disassembly is a hormone-driven and precisely orchestrated process. It occurs in two phases: first, remodeling of the apical extracellular matrix (aECM), mediated by matrix metalloproteases and independent of the actomyosin cytoskeleton, results in a progressive shortening of the entire trachea and a nuclear-to-cytoplasmic relocalization of the Hippo effector Yorkie (Yki). Second, a decreased transcription of the Yki target, Diap1, in the posterior metameres and the activation of caspases result in the apoptotic loss of the posterior half of the trachea while the anterior half escapes cell death. Thus, our work unravels a mechanism by which hormone-driven ECM remodeling controls sequential tissue shortening and apoptotic cell removal through the transcriptional activity of Yki, leading to organ disassembly during animal development.

Les cellules souches primordiales, qui sont situées à la base de la crypte dans l'intestin des mammifères, fournissent toutes les cellules épithéliales situées dans les cryptes et les villosités, comme les cellules absorbantes, les cellules caliciformes, les cellules de Paneth et les cellules entéroendocrines. La survie des cellules souches est associée à la niche qui est composée de divers signaux et facteurs provenant des cellules épithéliales et du mésenchyme environnant. Un signal important dont le rôle dans le maintien et la prolifération des cellules souches a été démontré est la voie de signalisation Hippo. Les signaux en amont, la cascade kinases et les gènes cibles en aval composent les trois parties de la voie de signalisation d'Hippo. Cette voie limite la croissance des cellules et la taille des organes par la régulation de YAP1 et TAZ qui sont les composants du coeur de la kinase. La voie active d'Hippo contribue à la phosphorylation et à l'inactivation des YAP1/TAZ, ce qui conduit à leur dégradation ou leur séquestration cytoplasmique. En l'absence de la voie Hippo, YAP1/TAZ actifs passent dans le noyau et induisent la transcription des gènes impliqués dans la croissance cellulaire. La présente étude vise à évaluer l'effet de YAP1 sur la différenciation des cellules épithéliales intestinales. Ainsi, l'expression de YAP1 a été neutralisée dans la cellule HT29 à l'aide de l'ARN interférant. Ensuite, l'immunoblot, l'immunofluorescence indirecte et l'analyse RT-qPCR ont été utilisées pour caractériser les cellules absorbantes et sécrétoires. Les résultats ont montré que l'expression des marqueurs de cellules absorbantes SI et DPPIV et des marqueurs de cellules caliciformes MUC2 et TFF3 a été augmentée de manière significative au niveau transcriptionnel et protéique par l'ablation de YAP1. La formation des cellules de type absorbante et de type caliciforme a été confirmée par immunofluorescence indirecte et microscopie électronique à transmission. De plus, l, LGR5+ crypt base columnar (CBC) stem cells that are located at the base of the crypt in the mammalian intestine, provide all the epithelial cells located in the crypts and villi including absorptive, goblet, Paneth and enteroendocrine cells. The maintenance of LGR5+ stem cells is associated with the niche that is composed of various signals and factors originating from the epithelial cells and surrounding mesenchyme. One important signal which has been reported to have a role in stem cell maintenance and proliferation is the Hippo signaling pathway. Upstream signals, a kinase core and downstream target genes compose the three parts of the Hippo pathway. This pathway restricts cell growth and organ size through regulation of YAP1 and TAZ, which are kinase core components. An active Hippo pathway contributes to the phosphorylation and inactivation of the YAP1/TAZ which leads to its degradation or cytoplasmic sequestration. In the absence of the Hippo pathway, active YAP1/TAZ passes into the nucleus and induces the transcription of genes involved in cell growth. The present study is aimed at the investigation of the effect of YAP1 on intestinal epithelial cell differentiation. Thus, YAP1 expression was knocked down in HT29 cells using shRNA. Then Western blot, immunofluorescence and RT-qPCR analysis were used for the characterization of absorptive and secretory cells. The results showed that the expression of the absorptive cell markers SI and DPPIV, and goblet cell markers MUC2 and TFF3 was increased significantly at both transcriptional and protein levels by YAP1 ablation. The formation of absorptive-like and goblet-like cells was confirmed using indirect immunofluorescence and transmission electron microscopy. Furthermore, the expression of the two stem cell markers LGR5 and PROM1 was decreased significantly in YAP1 knockdown HT29 cells compared with the control. Then the mechanism by which YAP1 controls the differentiation of the intestinal epithelial ce

In these recent years nanotechnology has gained interest as a powerful tool for drug delivery. It allows to overcome important drawbacks such as drug poor physico-chemical proprieties, toxicity and bioavailability challenges thereby ensuring better therapeutic efficacy with low side-effects and, sometimes, it permits to discover new drug applications. This review aims to analyse the impact of nanotechnology in the pharmaceutical development of VERTEPORFIN (VP), a benzoporphyrin derivative, which was conceived as second generation photosensitizer (PS) in photodynamic therapy (PDT), and later became a milestone in ophthalmology for treating age-related macular degeneration (AMD) disease. VP photoinduced and non-photoinduced biological features will be surveyed and nanotechnology implication in improving VP performances outlined. Currently, VP loaded nanostructured delivery systems (VP-nanoSs), administered alone or in combination with other drugs, are widely studied for the treatment of many widespread diseases including several tumoral forms and severe fibrotic conditions.

The canonical mammalian Hippo pathway contains a core kinase signaling cascade requiring upstream MST to form a stable complex with SAV1 in order to phosphorylate the downstream LATS/MOB complex. Though SAV1 dimerization is essential for the trans-activation of MST, the molecular mechanism underlying SAV1 dimerization is unclear. Here, we discover that the SAV1 WW tandem containing a short Pro-rich extension immediately following the WW tandem (termed as "WW12ex") forms a highly stable homodimer. The crystal structure of SAV1 WW12ex reveals that the Pro-rich extension of one subunit binds to both WW domains from the other subunit. Thus, SAV1 WW12ex forms a domain-swapped dimer instead of a WW2 homodimerization-mediated dimer. The WW12ex-mediated dimerization of SAV1 is required for the MST/SAV1 complex assembly and MST kinase activation. Finally, we show that several cancer-related SAV1 variants disrupt SAV1 dimer formation, and thus, these mutations may impair the tumor-suppression activity of SAV1.

The advancement of new therapies, including targeted therapies and immunotherapies, has improved the survival of non-small-cell lung cancer (NSCLC) patients in the last decade. Some NSCLC patients still do not benefit from therapies or encounter progressive disease during the course of treatment because they have intrinsic resistance, acquired resistance, or lack a targetable driver mutation. More investigations on the molecular biology of NSCLC are needed to find useful biomarkers for current therapies and to develop novel therapeutic strategies. Src is a non-receptor tyrosine kinase protein that interacts with cell surface growth factor receptors and the intracellular signaling pathway to maintain cell survival tumorigenesis in NSCLC. The Yes-associated protein (YAP) is one of the main effectors of the Hippo pathway and has been identified as a promoter of drug resistance, cancer progression, and metastasis in NSCLC. Here, we review studies that have investigated the activation of YAP as mediated by Src kinases and demonstrate that Src regulates YAP through three main mechanisms: (1) direct phosphorylation; (2) the activation of pathways repressing Hippo kinases; and (3) Hippo-independent mechanisms. Further work should focus on the efficacy of Src inhibitors in inhibiting YAP activity in NSCLC. In addition, future efforts toward developing potentially reasonable combinations of therapy targeting the Src-YAP axis using other therapies, including targeted therapies and/or immunotherapies, are warranted.

Cyclin-dependent kinase 7 (CDK7) is a protein kinase that plays a major role in transcription initiation. Yes-associated protein (YAP) is a main effector of the Hippo/YAP signalling pathway. Here, we investigated the role of CDK7 on YAP regulation in human malignant pleural mesothelioma (MPM). We found that in microarray samples of human MPM tissue, immunohistochemistry staining showed correlation between the expression level of CDK7 and YAP (n = 70, r = .513). In MPM cells, CDK7 expression level was significantly correlated with GTIIC reporter activity (r = .886, P = .019). Inhibition of CDK7 by siRNA decreased the YAP protein level and the GTIIC reporter activity in the MPM cell lines 211H, H290 and H2052. Degradation of the YAP protein was accelerated after CDK7 knockdown in 211H, H290 and H2052 cells. Inhibition of CDK7 reduced tumour cell migration and invasion, as well as tumorsphere formation ability. Restoration of the CDK7 gene rescued the YAP protein level and GTIIC reporter activity after siRNA knockdown in 211H and H2052 cells. Finally, we performed a co-immunoprecipitation analysis using an anti-YAP antibody and captured the CDK7 protein in 211H cells. Our results suggest that CDK7 inhibition reduces the YAP protein level by promoting its degradation and suppresses the migration and invasion of MPM cells. Cyclin-dependent kinase 7 may be a promising therapeutic target for MPM.

Lin et al. report the crystal structure of the SAV1 WW12 tandem dimer, showing that the proline-rich tail following the WW tandem governs domain-swapped SAV1 dimer formation. WW tandem-mediated SAV1 dimer formation is important for the interaction between SAV1 and MST during Hippo signaling. © 2020 The Author(s)The canonical mammalian Hippo pathway contains a core kinase signaling cascade requiring upstream MST to form a stable complex with SAV1 in order to phosphorylate the downstream LATS/MOB complex. Though SAV1 dimerization is essential for the trans-activation of MST, the molecular mechanism underlying SAV1 dimerization is unclear. Here, we discover that the SAV1 WW tandem containing a short Pro-rich extension immediately following the WW tandem (termed as “WW12ex”) forms a highly stable homodimer. The crystal structure of SAV1 WW12ex reveals that the Pro-rich extension of one subunit binds to both WW domains from the other subunit. Thus, SAV1 WW12ex forms a domain-swapped dimer instead of a WW2 homodimerization-mediated dimer. The WW12ex-mediated dimerization of SAV1 is required for the MST/SAV1 complex assembly and MST kinase activation. Finally, we show that several cancer-related SAV1 variants disrupt SAV1 dimer formation, and thus, these mutations may impair the tumor-suppression activity of SAV1. © 2020 The Author(s)

The Hippo pathway is a master regulator of tissue homeostasis and organ size. NF2 is a well-established tumor suppressor, and loss of NF2 severely compromises Hippo pathway activity. However, the precise mechanism of how NF2 mediates upstream signals to regulate the Hippo pathway is not clear. Here we report that, in mammalian cells, NF2's lipid-binding ability is critical for its function in activating the Hippo pathway in response to osmotic stress. Mechanistically, osmotic stress induces PI(4,5)P2 plasma membrane enrichment by activating the PIP5K family, allowing for NF2 plasma membrane recruitment and subsequent downstream Hippo pathway activation. An NF2 mutant deficient in lipid binding is unable to activate the Hippo pathway in response to osmotic stress, as measured by LATS and YAP phosphorylation. Our findings identify the PIP5K family as novel regulators upstream of Hippo signaling, and uncover the importance of phosphoinositide dynamics, specifically PI(4,5)P2, in Hippo pathway regulation. © 2020 Hong et al.; Published by Cold Spring Harbor Laboratory Press.

The Hippo pathway, first discovered in the fruit fly Drosophila melanogaster, is an evolutionarily conserved regulator of organ growth. The Hippo pathway controls organ growth by regulating the nuclear activity of the transcriptional coactivator Yorkie (Yki). Yki binds to sequence-specific transcription factors to regulate target gene expression, including the TEAD/TEF family transcription factor Scalloped (Sd). It was recently discovered that the Hippo pathway controls the growth of organs in Drosophila by balancing transcriptional activation mediated by Yki and Sd, and transcriptional repression mediated by Tondu-domain- containing Growth Inhibitor (Tgi) and Sd. If this fine balance is disrupted and Yki is hyperactivated, organs can grow beyond their normal size. Importantly, deregulation of Hippo signalling drives tumorigenesis in a variety of human cancers. The high degree of conservation of the Hippo pathway throughout the animal kingdom makes the fruit fly a powerful model organism to understand how this pathway regulates tissue growth during development and cancer. The Hippo pathway regulates the expression of genes involved in cell proliferation, survival, stemness, differentiation, and migration. However, we lack a clear understanding of the full transcriptional program that the Hippo pathway regulates in growing tissues beyond a small number of well-studied target genes. In this thesis, I aimed to deepen our understanding of the transcriptional program that the Hippo pathway controls in the growing Drosophila eye. To do this, I addressed three key questions: 1) What are the target genes of Yki, Sd and Tgi? 2) What gene expression changes occur as a result of hyperactive Yki? 3) What additional transcriptional regulators control Hippo pathway target gene expression and eye growth? 1) Using targeted DamID-seq, I identified target genes of Yki, Sd and Tgi in growing Drosophila eye discs. I found a very high degree of overlapping target genes between Yki, Sd

Promoter proximal pausing (PPP) of RNA polymerase II has emerged as a crucial rate-limiting step in the regulation of gene expression. Regulation of PPP is brought about by complexes 7SK snRNP, P-TEFb (Cdk9/cycT), and the negative elongation factor (NELF), which are highly conserved from Drosophila to humans. Here, we show that RNAi-mediated depletion of bin3 or Hexim of the 7SK snRNP complex or depletion of individual components of the NELF complex enhances Yki-driven growth, leading to neoplastic transformation of Drosophila wing imaginal discs. We also show that increased CDK9 expression cooperates with Yki in driving neoplastic growth. Interestingly, overexpression of CDK9 on its own or in the background of depletion of one of the components of 7SK snRNP or the NELF complex necessarily, and specifically, needed Yki overexpression to cause tumorous growth. Genome-wide gene expression analyses suggested that deregulation of protein homeostasis is associated with tumorous growth of wing imaginal discs. As both Fat/Hippo/Yki pathway and PPP are highly conserved, our observations may provide insights into mechanisms of oncogenic function of YAP-the ortholog of Yki in humans.

YAP1 and TAZ (WWTR1) oncoproteins are thefinal transducers of the Hippo tumor suppressor pathway. Deregula-tion of the pathway leads to YAP1/TAZ activation fostering tumorigenesis in multiple malignant tumor types, includ-ing sarcoma. However, oncogenic mutations within the core components of the Hippo pathway are uncommon.Ewing sarcoma (EwS), a pediatric cancer with low mutation rate, is characterized by a canonical fusion involvingthe geneEWSR1andFLI1as the most common partner. The fusion protein is a potent driver of oncogenesis, but sec-ondary alterations are scarce, and little is known about other biological factors that determine the risk of relapse orprogression. We have observed YAP1/TAZ expression and transcriptional activity in EwS cell lines. Analyses of 55 pri-mary human EwS samples revealed that high YAP1/TAZ expression was associated with progression of the diseaseand predicted poorer outcome. We did not observe recurrent SNV or copy number gains/losses in Hippo pathway-related loci. However, differential CpG methylation of theRASSF1locus (a regulator of the Hippo pathway) wasobserved in EwS cell lines compared with mesenchymal stem cells, the putative cell of origin of EwS. Hypermethyla-tion ofRASSF1correlated with the transcriptional silencing of the tumor suppressor isoformRASFF1A, and tran-scriptional activation of the pro-tumorigenic isoformRASSF1C, which promotes YAP1/TAZ activation. Knockdownof YAP1/TAZ decreased proliferation and invasion abilities of EwS cells and revealed that YAP1/TAZ transcriptionactivity is inversely correlated with the EWS–FLI1 transcriptional signature. This transcriptional antagonism couldbe explained partly by EWS–FLI1-mediated transcriptional repression of TAZ. Thus, YAP1/TAZ may override the tran-scriptional program induced by the fusion protein, contributing to the phenotypic plasticity determined by dynamicfluctuation of the fusion protein, a recently proposed model for disease dissemination in EwS

Mitogen-activated protein kinase kinase kinase kinases (MAP4Ks) constitute a mammalian STE20-like serine/threonine kinase subfamily. Recent studies provide substantial evidence for MAP4K family kinases in the Hippo pathway regulation, suggesting a broad role of MAP4Ks in human physiology and diseases. However, a comprehensive analysis of the regulators and effectors for this key kinase family has not been fully achieved. Using a proteomic approach, we define the protein-protein interaction network for human MAP4K family kinases and reveal diverse cellular signaling events involving this important kinase family. Through it, we identify a STRIPAK complex component, STRN4, as a generic binding partner for MAP4Ks and a key regulator of the Hippo pathway in endometrial cancer development. Taken together, the results of our study not only generate a rich resource for further characterizing human MAP4K family kinases in numerous biological processes but also dissect the STRIPAK-mediated regulation of MAP4Ks in the Hippo pathway.

In vitro activation of resting ovarian follicles, with the use of mechanical stress and/or pharmacological compounds, is an emerging and novel approach for infertility treatment. The aim of this study was to assess the sphingolipid, sphingosine-1-phosphate (S1P), as a potential in vitro activation agent in murine and human ovarian tissues and isolated follicles. Juvenile murine ovaries and donated human ovarian tissues, from 10 women undergoing ovarian tissue cryopreservation for fertility preservation, were incubated with or without 12 µM S1P for 3 h for quantitative PCR analysis, and 12 h for xenotransplantation or culture studies. Gene expression analyses were performed for genes downstream of the Hippo signaling pathway. Murine ovaries and isolated murine and human preantral follicles showed significantly increased mRNA expression levels of Ccn2/CCN2 following S1P treatment compared to controls. This increase was shown to be specific for the Hippo signaling pathway and for the S1P2 receptor, as co-treatment with Hippo-inhibitor, verteporfin and S1PR2 antagonist, JTE-013, reduced the S1P-induced Ccn2 gene expression in murine ovaries. Histological evaluation of human cortical tissues (5 × 5 × 1 mm; n = 30; three pieces per patient) xenografted for 6 weeks and juvenile murine ovaries cultured for 4 days (n = 9) or allografted for 2 weeks (n = 48) showed no differences in the distribution of resting or growing follicles in S1P-treated ovarian tissues compared to controls. Collectively, S1P increased Ccn2/CCN2 gene expression in isolated preantral follicles and ovarian tissue from mice and human, but it did not promote follicle activation or growth in vivo. Thus, S1P does not appear to be a potent in vitro activation agent under these experimental conditions.

The Hippo pathway has been associated with regulation of early follicle growth. Studies of murine ovaries suggest that changes in the actin cytoskeleton, caused by fragmentation, result in inhibition of the Hippo pathway, and in turn, may activate follicle growth. In humans, the connections between fragmentation, the actin cytoskeleton, and follicle activation are yet to be confirmed. In this study, we investigated the impact in vitro fragmentation of a human ovarian cortex on (a) actin polymerization, (b) components of the Hippo pathway, and (c) follicle growth in vivo. The results showed that the ratio between globular and filamentous actin remained unchanged at all timepoints (0, 10, 30, 60, 120, and 240 min) following tissue fragmentation. Neither was the Hippo pathway effector protein YES-associated protein upregulated nor was gene expression of the downstream growth factors CCN2, CCN3, or CCN5 increased at any timepoint in the fragmented cortex. Furthermore, the number of growing follicles was similar in fragmented and intact cortex pieces after 6 weeks' xenotransplantation. However, the total number of surviving follicles was considerably lower in the fragmented cortex compared with intact tissue, suggesting detrimental effects of fragmentation on tissue grafting. These results indicate that fragmentation is likely to be ineffective to activate follicle growth in the human ovarian cortex.

Genetic approaches in Drosophila have successfully identified many genes involved in regulation of growth control as well as genetic interactions relevant to the initiation and progression of cancer in vivo. Here, we report on large-scale RNAi-based screens to identify potential tumor suppressor genes that interact with known cancer-drivers: the Epidermal Growth Factor Receptor and the Hippo pathway transcriptional cofactor Yorkie. These screens were designed to identify genes whose depletion drove tissue expressing EGFR or Yki from a state of benign overgrowth into neoplastic transformation in vivo. We also report on an independent screen aimed to identify genes whose depletion suppressed formation of neoplastic tumors in an existing EGFR-dependent neoplasia model. Many of the positives identified here are known to be functional in growth control pathways. We also find a number of novel connections to Yki and EGFR driven tissue growth, mostly unique to one of the two. Thus, resources provided here would be useful to all researchers who study negative regulators of growth during development and cancer in the context of activated EGFR and/or Yki and positive regulators of growth in the context of activated EGFR. Resources reported here are available freely for anyone to use.

The Hippo pathway regulates growth and apoptosis. We identify RhoBTB proteins as novel regulators of Hippo signaling. RhoBTB depletion in the Drosophila wing disc epithelium cooperated with Yki to drive hyperplasia into neoplasia. Depletion of RhoBTB2 caused elevated YAP activity in human cells. RhoBTB2 deficiency resulted in increased colony formation in assays for anchorage-independent growth. We provide evidence that RhoBTBs acts on Hippo signaling through regulation of the kinase LKB1. LKB1 protein levels were reduced upon RhoBTB2 depletion, which correlated with increased LKB1 ubiquitination. Restoring LKB1 levels rescued loss of RhoBTB in Drosophila Our results suggest that RhoBTB-dependent LKB1 regulation may contribute to its tumor-suppressive function.

YAP1 and TAZ (WWTR1) oncoproteins are the final transducers of the Hippo tumor suppressor pathway. Deregulation of the pathway leads to YAP1/TAZ activation fostering tumorigenesis in multiple malignant tumor types, including sarcoma. However, oncogenic mutations within the core components of the Hippo pathway are uncommon. Ewing sarcoma (EwS), a pediatric cancer with low mutation rate, is characterized by a canonical fusion involving the gene EWSR1 and FLI1 as the most common partner. The fusion protein is a potent driver of oncogenesis, but secondary alterations are scarce, and little is known about other biological factors that determine the risk of relapse or progression. We have observed YAP1/TAZ expression and transcriptional activity in EwS cell lines. Analyses of 55 primary human EwS samples revealed that high YAP1/TAZ expression was associated with progression of the disease and predicted poorer outcome. We did not observe recurrent SNV or copy number gains/losses in Hippo pathway-related loci. However, differential CpG methylation of the RASSF1 locus (a regulator of the Hippo pathway) was observed in EwS cell lines compared with mesenchymal stem cells, the putative cell of origin of EwS. Hypermethylation of RASSF1 correlated with the transcriptional silencing of the tumor suppressor isoform RASFF1A, and transcriptional activation of the pro-tumorigenic isoform RASSF1C, which promotes YAP1/TAZ activation. Knockdown of YAP1/TAZ decreased proliferation and invasion abilities of EwS cells and revealed that YAP1/TAZ transcription activity is inversely correlated with the EWS–FLI1 transcriptional signature. This transcriptional antagonism could be explained partly by EWS–FLI1-mediated transcriptional repression of TAZ. Thus, YAP1/TAZ may override the transcriptional program induced by the fusion protein, contributing to the phenotypic plasticity determined by dynamic fluctuation of the fusion protein, a recently proposed model for disease dissemination in EwS. ©

[Background] Ovarian cancer is one of the most common and malignant cancers, partly due to its late diagnosis and high recurrence. Chemotherapy resistance has been linked to poor prognosis and is believed to be linked to the cancer stem cell (CSC) pool. Therefore, elucidating the molecular mechanisms mediating therapy resistance is essential to finding new targets for therapy-resistant tumors., [Methods] shRNA depletion of MYPT1 in ovarian cancer cell lines, miRNA overexpression, RT-qPCR analysis, patient tumor samples, cell line- and tumorsphere-derived xenografts, in vitro and in vivo treatments, analysis of data from ovarian tumors in public transcriptomic patient databases and in-house patient cohorts., [Results] We show that MYPT1 (PPP1R12A), encoding myosin phosphatase target subunit 1, is downregulated in ovarian tumors, leading to reduced survival and increased tumorigenesis, as well as resistance to platinum-based therapy. Similarly, overexpression of miR-30b targeting MYPT1 results in enhanced CSC-like properties in ovarian tumor cells and is connected to the activation of the Hippo pathway. Inhibition of the Hippo pathway transcriptional co-activator YAP suppresses the resistance to platinum-based therapy induced by either low MYPT1 expression or miR-30b overexpression, both in vitro and in vivo., [Conclusions] Our work provides a functional link between the resistance to chemotherapy in ovarian tumors and the increase in the CSC pool that results from the activation of the Hippo pathway target genes upon MYPT1 downregulation. Combination therapy with cisplatin and YAP inhibitors suppresses MYPT1-induced resistance, demonstrating the possibility of using this treatment in patients with low MYPT1 expression, who are likely to be resistant to platinum-based therapy.

The Hippo pathway is important for tissue homeostasis, regulation of organ size and growth in most tissues. The co‐transcription factor yes‐associated protein 1 (YAP1) serves as a main downstream effector of the Hippo pathway and its dysregulation increases cancer development and blocks colonic tissue repair. Nevertheless, little is known about the transcriptional regulation of YAP1 in intestinal cells. The aim of this study to identify gene control regions in the YAP1 gene and transcription factors important for intestinal expression. Bioinformatic analysis of caudal type homeobox 2 (CDX2) and hepatocyte nuclear factor 4 alpha (HNF4α) chromatin immunoprecipitated DNA from differentiated Caco‐2 cells revealed potential intragenic enhancers in the YAP1 gene. Transfection of luciferase‐expressing YAP1 promoter‐reporter constructs containing the potential enhancer regions validated one potent enhancer of the YAP1 promoter activity in Caco‐2 and T84 cells. Two potential CDX2 and one HNF4α binding sites were identified in the enhancer by in silico transcription factor binding site analysis and protein‐DNA binding was confirmed in vitro using electrophoretic mobility shift assay. It was found by chromatin immunoprecipitation experiments that CDX2 and HNF4α bind to the YAP1 enhancer in Caco‐2 cells. These results reveal a previously unknown enhancer of the YAP1 promoter activity in the YAP1 gene, with importance for high expression levels in intestinal epithelial cells. Additionally, CDX2 and HNF4α binding are important for the YAP1 enhancer activity in intestinal epithelial cells.

Hypoxia is the state of lowered O2 tension condition that influence skeletal muscle mass when associated to resistance exercise whether after acute or chronic exposure. The effects of hypoxia on muscle mass are largely investigated but the regulatory mechanisms remain blurring. Aiming to investigate these mechanisms and the possible contribution of Hippo pathway in both protein turnover and satellite cells regulation, we exposed young healthy subjects to acute hypoxia coupled to resistance exercise. Skeletal muscle protein synthesis was blunted by hypoxia and differentiation genes were upregulated while Hippo pathway remained unaffected. Moreover, skeletal muscle machinery genes were regulated by hypoxia suggesting structural adaptations. Surprisingly, a four-week training in hypoxic condition failed to induce those adaptations. This topic requires further investigation to highlight the precise mechanisms and adaptations induced by hypoxia in sport., (MOTR - Sciences de la motricité) -- UCL, 2019

The Hippo pathway is an important regulator of organ growth during development where it ensures correct scaling of tissues and organs. It is well-conserved in animals and deregulation of the pathway has been found to drive development of a range of cancers. The Hippo pathway was first identified in the fruit fly, Drosophila melanogaster, and has been extensively studied in a number of different tissues. As well as controlling organ growth in Drosophila, the Hippo pathway has been repurposed to control the binary cell fate choice of the R8 photoreceptor cell in the Drosophila eye. The R8 photoreceptor cell is one of eight photoreceptor cell types in the Drosophila eye and is responsible for much of colour vision in Drosophila. There are two main subtypes of R8 cells – around 30% are the 'pale' (p) subtype and express Rhodopsin 5 (Rh5; responsive to blue light); the remaining 70% are the 'yellow' (y) subtype and express Rh6 (responsive to green light). The Hippo pathway acts in a bistable feedback loop to both specify and maintain R8 subtype specification. This bistable feedback loop is composed of the Hippo pathway kinase, Warts, the downstream transcriptional coactivator, Yorkie, and the Pleckstrin-homology domain containing protein, Melted. Yorkie and Melted both promote pR8 cell fate, while Warts represses pR8 cell fate and promotes yR8 cell fate. Although we have begun to study the role of the Hippo pathway in R8 cell fate choices, we still lack a clear understanding how the Hippo pathway functions in these cells. I sought to further our understanding of the Hippo pathway in R8 cells by answering three key questions: (1) Which Hippo pathway proteins control R8 cell fate? (2) What is the subcellular localisation of Hippo pathway components in R8 cells? (3) What are the target genes of the Hippo pathway in each R8 subtype? (1) I used genetic experiments to modulate the expression of Hippo pathway genes and found that Crumbs and Cka promote pR8 cell fate, while the

Which comes first: tissue structure or cell differentiation? While different cell types establish distinct structures delineating the in- and outside of an embryo, they progressively become specified by the blastocyst stage, when two types of cell lineages are formed: inner cell mass (ICM) and trophectoderm (TE). This inside-outside aspect can be experimentally converted by the isolation of the ICM from a blastocyst, leading to a posteriori externalization of the blastomeres composing the outermost layer of the ICM. Here, we investigated the totipotency of isolated mouse and bovine ICMs to determine whether they are competent for TE regeneration. Surprisingly, a calf was generated from the bovine isolated ICM with re-formed blastocoel (re-iICM), but no mouse re-iICMs developed to term. To further explore the cause of difference in developmental competency between the mouse and bovine re-iICMs, we investigated the SOX17 protein expression that is a representative molecular marker of primitive endoderm. The localization pattern of SOX17 was totally different between mouse and bovine embryos. Particularly, the ectopic SOX17 localization in the TE might be associated with lethality of mouse re-iICMs. Meanwhile, transcriptome sequencing revealed that some of the bovine re-iICMs showed transcriptional patterns of TE-specific genes similar to those of whole blastocysts. Our findings suggest that TE regeneration competency is maintained longer in bovine ICMs than in mouse ICMs and provide evidence that the ICM/TE cell fate decision is influenced by structural determinants, including positional information of each blastomere in mammalian embryos.

Despite recent advances, the poor outcomes in renal cell carcinoma (RCC) suggest novel therapeutics are needed. Ferroptosis is a form of regulated cell death, which may have therapeutic potential toward RCC; however, much remains unknown about the determinants of ferroptosis susceptibility. We found that ferroptosis susceptibility is highly influenced by cell density and confluency. Because cell density regulates the Hippo-YAP/TAZ pathway, we investigated the roles of the Hippo pathway effectors in ferroptosis. TAZ is abundantly expressed in RCC and undergoes density-dependent nuclear or cytosolic translocation. TAZ removal confers ferroptosis resistance, whereas overexpression of TAZS89A sensitizes cells to ferroptosis. Furthermore, TAZ regulates the expression of Epithelial Membrane Protein 1 (EMP1), which, in turn, induces the expression of nicotinamide adenine dinucleotide phosphate (NADPH) Oxidase 4 (NOX4), a renal-enriched reactive oxygen species (ROS)-generating enzyme essential for ferroptosis. These findings reveal that cell density-regulated ferroptosis is mediated by TAZ through the regulation of EMP1-NOX4, suggesting its therapeutic potential for RCC and other TAZ-activated tumors.

The Hippo pathway, a signaling pathway highly conserved across species, plays a crucial role in organ size control and cancer suppression. Our recent study shows that phosphatidic acid can regulate the Hippo pathway through a physical lipid-protein interaction, providing additional insights into the Hippo-related tissue homeostasis and cancer development.

Human beings are facing emerging degenerative and cancer diseases, in large part, as a consequence of increased life expectancy. In the near future, researchers will have to put even more effort into fighting these new challenges, one of which will be prevention of cancer while continuing to improve the aging process through this increased life expectancy. In the last few decades, relevance of the Hippo pathway on cancer has become an important study since it is a major regulator of organ size control and proliferation. However, its deregulation can induce tumors throughout the body by regulating cell proliferation, disrupting cell polarity, releasing YAP and TAZ from the Scribble complexes and facilitating survival gene expression via activation of TEAD transcription factors. This pathway is also involved in some of the most important mechanisms that control the aging processes, such as the AMP-activated protein kinase and sirtuin pathways, along with autophagy and oxidative stress response/antioxidant defense. This could be the link between two tightly connected processes that could open a broader range of targeted molecular therapies to fight aging and cancer. Therefore, available knowledge of the processes involved in the Hippo pathway during aging and cancer must necessarily be well understood.

The Hippo pathway and its downstream effectors, transcriptional coactivators YAP and TAZ, are important for regulating tissue homeostasis and their dysregulation has been implicated in many human diseases and cancer. However, it is not clear how the Hippo pathway becomes dysregulated because few mutations have been identified in Hippo pathway components. Therefore, recent work in the Hippo field has focused on identifying upstream regulators of the Hippo pathway. Nevertheless, it is not always clear which components are most physiologically relevant in regulating YAP/TAZ. To provide an overview of which components are most physiologically relevant in regulating YAP/TAZ, we used CRISPR/Cas9 to create knockout cell lines for many of these components and tested their responses to a variety of physiological signals to determine which components are most critical in regulating YAP/TAZ. By this approach, we demonstrate that NF2 and RHOA are important regulators of YAP/TAZ, and TAOK1/3 are direct kinases for LATS1/2.Additionally, YAP and TAZ are traditionally viewed as being largely redundant, although there are evolutionary, structural, and physiological differences that suggest there may be differences in how they are regulated and in their downstream functions. To delineate any differences between YAP and TAZ, we compared LATS1/2 KO cells, in which YAP/TAZ are constitutively-active, YAP KO, TAZ KO, and YAP/TAZ KO cells, in which YAP/TAZ are constitutively-inactive. We found that inactivation of YAP had a much greater negative effect on many measures of cell physiology, including cell spreading, cell volume, glucose uptake and metabolism, cell proliferation, and migration, while YAP activation in the LATS1/2 KO cells had the opposite effect. Differences between YAP and TAZ may be explained by differences in protein stability and expression, as YAP protein expression is much higher than that of TAZ. We also identified some differences in the transcriptional profiles induc

A remarkable feat of animal development is the precision with which organs grow to aconsistent and characteristic size. The lengths of the right and left arm of a human, forinstance, match with an accuracy of about 0.2%, and the size of adult mouse brains variesby only about 5%. How a developing organ|and the individual cells within|can knowwhen it is time to stop growing has long-fascinated biologists.Reciprocal organ transplantation experiments from the 1920s were among the rst todemonstrate that, for an individual organ, growth is subject to both extrinsic and intrinsicprograms. Working with two closely related but dierent-sized species of salamanders, thefaster-growing yet smaller-sized Ambystoma punctatum and the slower-growing yet largersizedAmbystoma tigrinum, Harrison found that the growth rate of a limb transplanted fromone species to the other matched that of the host, but the overall size of the transplantedlimb matched that of the donor. He concluded, therefore, that while some circulating factor,perhaps a hormone, dictated the rate of limb growth, the organ's size overall was determinedby some intrinsic "growth potential."Now, close to a century later, we know the identities of many evolutionarily-conservedfactors that are critical to achieving a properly-sized organ, but our understanding of whatultimately determines an organ's size remains far from complete. Much of what we do knowabout the mechanisms regulating tissue growth comes from studies using the model organismDrosophila melanogaster, whose genetic tractability and high reproducibility of organ sizeallow us to easily evaluate the eects of genetic perturbations on tissue growth.In Chapter 1, I provide an overview of some of these growth-regulatory mechanismsand describe how genetic studies using a well-characterized tissue model of growth|theDrosophila wing imaginal disc|have helped to provide some clues into how these mechanismsmight operate. I will highlight two signaling pathways|the Hippo p