The Hippo pathway transcriptional co-activator, YAP, is an ovarian cancer oncogene

YAP/TAZ at the Roots of Cancer

YAP and TAZ are highly related transcriptional regulators pervasively activated in human malignancies. Recent work indicates that, remarkably, YAP/TAZ are essential for cancer initiation or growth of most solid tumors. Their activation induces cancer stem cell attributes, proliferation, chemoresistance, and metastasis. YAP/TAZ are sensors of the structural and mechanical features of the cell microenvironment. A number of cancer-associated extrinsic and intrinsic cues conspire to overrule the YAP-inhibiting microenvironment of normal tissues, including changes in mechanotransduction, inflammation, oncogenic signaling, and regulation of the Hippo pathway. Addiction to YAP/TAZ thus potentially represents a central cancer vulnerability that may be exploited therapeutically.

Effect of YAP1 silencing on esophageal cancer

Background

YAP1, the nuclear effector of the Hippo pathway, has become an attractive target for treatment of malignancies and is a candidate oncogene in esophageal cancer (EC). We hypothesized that knockdown of YAP1 could suppress EC and could be used for targeted therapy. However, there are few reports of the effect of YAP1 knockdown in EC.

Materials and methods

Quantitative real-time polymerase chain reaction and Western blot assays were performed to determine the expression levels of YAP1 mRNA and protein in primary EC tissue samples, EC cell lines, and controls. Immunohistochemistry was also performed to detect YAP1 protein expression in primary EC tumor and matched nontumor control tissues. YAP1-knockdown cell lines were constructed using short-hairpin RNA, and MTT, flow cytometry, and transwell chamber assays were used to analyze the effect of YAP1 knockdown on EC cell proliferation, apoptosis, and invasion. In vivo tumor formation assays were used to investigate the antitumor effect of YAP1 knockdown.

Results

We found that YAP1 mRNA and protein were upregulated in EC and that YAP1 expression correlated significantly with metastasis and tumor stage. We also found that YAP1 knockdown repressed cell proliferation and invasion and promoted apoptosis of EC cell lines. In addition, animal experiments revealed that YAP1 knockdown suppressed the growth of esophageal tumors in vivo.

Conclusion

Collectively, these data confirm our hypothesis that YAP1 knockdown suppresses EC and suggest that YAP1 knockdown could be exploited in the targeted gene therapy of EC in the future.

YAP induces cisplatin resistance through activation of autophagy in human ovarian carcinoma cells

Objective

To identify the role of YAP in cisplatin resistance in human ovarian cancer cells and in the regulation of autophagy in these cancer cells.

Materials and methods

The cisplatin-sensitive OV2008 parental cell line and its cisplatin-resistant variant C13K were cultured. RNA interference was used to knock down the YAP gene. Accumulation of GFP-LC3 puncta was performed by fluorescence microscopy. The formation of autophagosomes was observed by transmission electron microscopy. Drug sensitivity was examined using CCK-8 assay, while apoptosis, the level of intracellular rhodamine 123 and lysosomal acidification were analyzed by fluorescence-activated cell sorting. Acid phosphatase activity was measured using an acid phosphatase-assay kit. Real-time polymerase chain reaction, Western blotting, and immunofluorescence detection were used to detect the protein and messenger RNA expression of YAP, YAP target genes, CCND1, cleaved PARP, and caspase 3, Atg-3 and -5, and the LC3B protein.

Results

YAP signaling may regulate cisplatin resistance in ovarian cancer cells by augmenting cellular autophagic flux. After knockdown of YAP-sensitized C13K cells to cisplatin by inducing a decrease in autophagy, YAP led to an increase in autophagy via enhancement of autolysosome degradation.

Conclusion

YAP-mediated autophagy may play a protective role in cisplatin-resistant human ovarian cancer cells. Therefore, YAP-mediated autophagy should be explored as a new target for enhancing the efficacy of cisplatin against ovarian cancer and other types of malignancies.

Nuclear accumulation of Yes-Associated Protein (YAP) maintains the survival of doxorubicin-induced senescent cells by promoting survivin expression

Although chemotherapeutic drugs can induce senescence to prohibit further division of tumor cells, senescence could also promote tumorigenesis mainly through a senescence-associated secretory phenotype. Therefore, senescent tumor cells should be eliminated immediately to prevent drug resistance and recurrence. Here, we used a doxorubicin-induced senescence model to explore the mechanism underlying the survival of therapy-induced senescent cells. After low-dose doxorubicin treatment, tumor cells turned on a senescence program and became large and flattened, increasing their contact area with the extracellular matrix (ECM). Furthermore, Yes-associated protein (YAP) accumulated in the nucleus and YAP activity was increased in doxorubicin-induced senescent cells. Knockdown of YAP increased the sensitivity of cells to low-dose doxorubicin treatment, causing apoptosis rather than senescence. Moreover, the anti-apoptotic gene survivin, a YAP target gene, was overexpressed in senescent cells. Inhibition of survivin could lead to selective elimination of senescent cells through apoptosis. Our study indicates that nuclear accumulation of YAP could promote the survival of senescent cells by increasing survivin expression. Therefore, targeting YAP or survivin might be a new strategy for clearing senescent cancer cells during drug treatment.

A novel role for microRNA-129-5p in inhibiting ovarian cancer cell proliferation and survival via direct suppression of transcriptional co-activators YAP and TAZ

Transcriptional co-activator Yes-associated protein (YAP) and transcriptional co-activator with PDZ-binding motif (TAZ) are key oncogenes in mammalian cells. Activities of YAP and TAZ are largely restricted by the Hippo tumor suppressor pathway through phosphorylation-ubiquitination mechanisms. The involvement of microRNA in cancer progression has recently been reported, though whether they have a role in activating YAP and TAZ in human cancer cells remains unclear. Here, we report a microRNA, miR-129-5p, directly represses YAP and TAZ expression, leading to the inactivation of TEA domain (TEAD) transcription, and the downregulation of Hippo downstream genes, connective tissue growth factor (CTGF) and Cyclin A. Furthermore, we reveal miR-129-5p inhibits ovarian cancer cell proliferation, survival and tumorigenicity, and that downregulation of miR-129-5p in ovarian cancer cells highly correlates with malignant progression and poor survival. Hence, we demonstrate a novel mechanism for YAP and TAZ activation in cancers, indicating not only a potentially pivotal role for miR-129-5p in the progression of ovarian cancer, but also offering new therapeutic strategies to circumvent the disease.

Emerging role of Hippo pathway in gastric and other gastrointestinal cancers

More evidence has underscored the importance of Hippo signaling pathway in gastrointestinal tissue homeostasis, whereas its deregulation induces tumorigenesis. Yes-associated protein 1 (YAP1) and its close paralog TAZ, transcriptional co-activator with a PDZ-binding motif, function as key effectors negatively controlled by the Hippo pathway. YAP1/TAZ exerts oncogenic activities by transcriptional regulation via physical interaction with TEAD transcription factors. In various cancers, Hippo pathway cross-talks with pro- or anti-tumorigenic pathways such as GPCR, Wnt/β-catenin, Notch and TGF-β signaling and is deregulated by multiple factors including cell density/junction and microRNAs. As YAP1 expression is significantly associated with poor prognosis of gastric and other gastrointestinal cancers, detailed delineation of Hippo regulation in tumorigenesis provides novel insight for therapeutic intervention. In current review, we summarized the recent research progresses on the deregulation of Hippo pathway in the gastrointestinal tract including stomach and discuss the molecular consequences leading to tumorigenesis.

Emerging evidence on the role of the Hippo/YAP pathway in liver physiology and cancer

The Hippo pathway and its regulatory target, YAP, has recently emerged as an important biochemical signaling pathway that tightly governs epithelial tissue growth. Initially defined in Drosophilia, this pathway has shown remarkable conservation in vertebrate systems with many components of the Hippo/YAP pathway showing biochemical and functional conservation. The liver is particularly sensitive to changes in Hippo/YAP signaling with rapid increases in liver size becoming manifest on the order of days to weeks after perturbation. The first identified direct targets of Hippo/YAP signaling were pro-proliferative and anti-apoptotic gene programs, but recent work has now implicated this pathway in cell fate choice, stem cell maintenance/renewal, epithelial to mesenchymal transition, and oncogenesis. The mechanisms by which Hippo/YAP signaling is changed endogenously are beginning to come to light as well as how this pathway interacts with other signaling pathways, and important details for designing new therapeutic interventions. This review focuses on the known roles for Hippo/YAP signaling in the liver and promising avenues for future study.

YAP induces high-grade serous carcinoma in fallopian tube secretory epithelial cells

Accumulating evidence indicates that ovarian high-grade serous carcinoma (HGSC) originates from fallopian tube secretory epithelial cells (FTSECs). However, the molecular mechanisms underlying the initiation and progression of HGSC derived from FTSECs remains unclear. In this study, we found that the Hippo/Yes-associated protein (YAP) signaling pathway has a critical role in the initiation and progression of fallopian tube and ovarian HGSC. Importantly, YAP was overexpressed in inflammatory and cancerous fallopian tube tissues. Further, overexpression of wild-type YAP, or constitutively active YAP in immortalized FTSECs, induced cell proliferation, migration, colony formation and tumorigenesis. Moreover, the Hippo/YAP and the fibroblast growth factor (FGF) signaling pathways formed an autocrine/paracrine-positive feedback loop to drive the progression of the FTSEC-derived HGSC. Evidence in this study strongly suggests that combined therapy with inhibitors of YAP (such as verteporfin) and FGF receptors (such as BGJ398) can provide a novel therapeutic strategy to treat fallopian tube and ovarian HGSC.

The ubiquitin E3 ligase ITCH enhances breast tumor progression by inhibiting the Hippo tumor suppressor pathway

The Hippo kinase pathway is emerging as a conserved signaling pathway that is essential for organ growth and tumorigenesis. Recently, we reported that the ubiquitin E3 ligase ITCH negatively regulates LATS1, thereby increasing YAP activity, which leads to increased cell proliferation and decreased apoptosis. Here, we investigated the role of ITCH in breast tumorigenesis. In particular, we show that ITCH enhances epithelial-to-mesenchymal transition (EMT) through boosting YAP oncogenic function. By contrast, a point mutation in the catalytic domain or WW1 domain of ITCH abolished its EMT-mediated effects. Furthermore, while overexpression of ITCH expression in breast cells is associated with increased incidence of mammary tumor formation and progression, its knockdown inhibited breast cancer cell tumorigenicity and metastasis. Importantly, YAP knockdown was able to attenuate ITCH pro-tumorigenic functions. Lastly, we found that ITCH expression is significantly upregulated in invasive and metastatic breast cancer cases and is associated with worse survival. Together, our results reveal that ITCH pro-tumorigenic functions in breast cancer are mediated, at least in part, through inactivation of the Hippo tumor suppressor pathway.

Growth Inhibition Accompanied by MOB1 Upregulation in Human Acute Lymphoid Leukemia Cells by 3-Deazaneplanocin A

Our purpose was to investigate the effect of 3-deazaneplanocin A (DZNep) on human T-cell acute lymphoid leukemia (T-ALL) cells, and to explore the underlying molecular mechanisms. The human T-ALL cell line Molt4 was treated with DZNep, and cell proliferation was examined. The expression of Mps one binder kinase activator 1 gene (MOB1) mRNA and protein was determined by RT-PCR and Western blotting, respectively. The histone modification effect of DZNep on the lysine 9 of histone 3 associated with MOB1 promoters was examined with chromatin immunoprecipitation and quantitative PCR, and CpG methylation in MOB1 promoters was detected by bisulfite sequencing PCR. DZNep treatment inhibited the growth of Molt4 cells. The expressions of MOB1 genes were upregulated by DZNep treatment, and histone methylations in their promoters were significantly reduced. The results indicate that DZNep is a promising therapeutic compound for the treatment of human T-ALL.

Ligand-independent requirements of steroid receptors EcR and USP for cell survival

The active form of the Drosophila steroid hormone ecdysone, 20-hydroxyecdysone (20E), binds the heterodimer EcR/USP nuclear receptor to regulate target genes that elicit proliferation, cell death and differentiation during insect development. Although the 20E effects are relatively well known, the physiological relevance of its receptors remains poorly understood. We show here that the prothoracic gland (PG), the major steroid-producing organ of insect larvae, requires EcR and USP to survive in a critical period previous to metamorphosis, and that this requirement is 20E-independent. The cell death induced by the downregulation of these receptors involves the activation of the JNK-encoding basket gene and it can be rescued by upregulating EcR isoforms which are unable to respond to 20E. Also, while PG cell death prevents ecdysone production, blocking hormone synthesis or secretion in normal PG does not lead to cell death, demonstrating further the ecdysone-independent nature of the receptor-deprivation cell death. In contrast to PG cells, wing disc or salivary glands cells do not require these receptors for survival, revealing their cell and developmental time specificity. Exploring the potential use of this feature of steroid receptors in cancer, we assayed tumor overgrowth induced by altered yorkie signaling. This overgrowth is suppressed by EcR downregulation in PG, but not in wing disc, cells. The mechanism of all these cell death features is based on the transcriptional regulation of reaper. These novel and context-dependent functional properties for EcR and USP receptors may help to understand the heterogeneous responses to steroid-based therapies in human pathologies.

YAP activation protects urothelial cell carcinoma from treatment-induced DNA damage

Current standard of care for muscle-invasive urothelial cell carcinoma (UCC) is surgery along with perioperative platinum-based chemotherapy. UCC is sensitive to cisplatin-based regimens, but acquired resistance eventually occurs, and a subset of tumors is intrinsically resistant. Thus, there is an unmet need for new therapeutic approaches to target chemotherapy-resistant UCC. Yes-associated protein (YAP) is a transcriptional co-activator that has been associated with bladder cancer progression and cisplatin resistance in ovarian cancer. In contrast, YAP has been shown to induce DNA damage associated apoptosis in non-small cell lung carcinoma. However, no data have been reported on the YAP role in UCC chemo-resistance. Thus, we have investigated the potential dichotomous role of YAP in UCC response to chemotherapy utilizing two patient-derived xenograft models recently established. Constitutive expression and activation of YAP inversely correlated with in vitro and in vivo cisplatin sensitivity. YAP overexpression protected while YAP knock-down sensitized UCC cells to chemotherapy and radiation effects via increased accumulation of DNA damage and apoptosis. Furthermore, pharmacological YAP inhibition with verteporfin inhibited tumor cell proliferation and restored sensitivity to cisplatin. In addition, nuclear YAP expression was associated with poor outcome in UCC patients who received perioperative chemotherapy. In conclusion, these results suggest that YAP activation exerts a protective role and represents a pharmacological target to enhance the anti-tumor effects of DNA damaging modalities in the treatment of UCC.

Lats1 Deletion Causes Increased Germ Cell Apoptosis and Follicular Cysts in Mouse Ovaries

The Hippo signaling pathway is essential for regulating proliferation and apoptosis in mammalian cells. The LATS1 kinase is a core member of the Hippo signaling pathway that phosphorylates and inactivates the transcriptional co-activators YAP1 and WWTR1. Deletion of Lats1 results in low neonate survival and ovarian stromal tumors in surviving adults, but the effects of Lats1 on early follicular development are not understood. Here, the expression of Hippo pathway components including Wwtr1, Stk4, Stk3, Lats2, and Yap1 transcripts were decreased by 50% in mouse ovaries between 2 and 8 days of age while expression was maintained from 8 days to 21 days and after priming with eCG. LATS1, LATS2, and MOB1B were localized to both germ and somatic cells of primordial to antral follicles. Interestingly, YAP1 was predominantly cytoplasmic, whereas WWTR1 was nuclear in oocytes and somatic cells. Deletion of Lats1 caused an increase in germ cell apoptosis from 1.7% in control ovaries to 3.6% in Lats1 mutant ovaries and a 58% and 32% decrease in primordial and activated follicle numbers in cultured mutant ovaries. Surprisingly, there was an increase in Bmp15 but not Gdf9, Figla, Nobox transcripts or the somatic-specific transcripts Amh and Wnt4 in cultured Lats1 mutant ovaries. Last, Lats1 mutant ovaries developed ovarian cysts at a higher frequency (43%) than heterozygous (24%) and control ovaries (8%). Results showed that the Hippo pathway is active in ovarian follicles and that LATS1 is required to maintain the pool of germ cells and primordial follicles.

Knockdown of yes-associated protein inhibits proliferation and downregulates large tumor suppressor 1 expression in MHCC97H human hepatocellular carcinoma cells

The pathogenesis of hepatocellular carcinoma (HCC) is thought to involve the interaction of numerous genes. Identification of these genes and proteins which regulate liver carcinogenesis is critical for the exploration of novel targeted therapies. Yes‑associated protein (YAP) and large tumor suppressor 1 (LATS1) are associated with HCC cells. LATS1 is an upstream inhibitory factor of YAP in the Hippo pathway. The aim of the present study was to measure the expression of LATS1 in Yap‑downregulated cancer cells. Immunohistochemistry was used to determine YAP and LATS1 levels in HCC tissue samples. High YAP‑expressing cell lines were selected from two human hepatocellular carcinoma cells with different metastatic potential. In addition, changes in cell growth rates and LATS1 expression in human HCC 97H cells, in which YAP had been knocked down using RNA interference (RNAi). The proliferation of cells was evaluated using an MTS assay and changes in the progression of cell division were assessed through cell cycle analysis. Western blot analysis was then used to determine YAP and LATS1 expression levels in 97H cells. The results of the present study demonstrated that overexpression of YAP was negatively correlated with LATS1 expression in HCC cells (P=0.016). Knockdown of YAP using lentivirus‑small hairpin (sh)RNA significantly inhibited 97H cell growth; in addition, the downregulation of YAP protein levels (33.4%) was accompanied by downregulation of LATS1 protein levels (68.5%). In conclusion, these results demonstrated that as an inhibitor of YAP, LATS1 was decreased via downregulation of YAP using RNAi. This therefore indicated that the change in YAP levels in HCC cells may regulate LATS1 in a feedback manner.

Hippo/YAP pathway for targeted therapy

Malignant pleural mesothelioma (MPM) is molecularly characterized by loss of function or mutations in the neurofibromin 2 (NF2) and the cyclin-dependent kinase inhibitor 2 genes. NF2 activates a cascade of kinases, called Hippo pathway, which downregulates Yes associated protein (YAP) function as transcription co-activator for TEA domain transcription factors (TEAD). In the absence of functional NF2, the expression of genes essential for cell cycling such as survivin is increased. New therapeutic strategies aimed at interfering with YAP activity include inhibition of hedgehog pathway, which downregulates the YAP protein, verteporfin, which inhibits the assembly of a functional YAP-TEAD transcription factor, and interference with thrombin and lysophosphatidic acid (LPA) receptors downstream signalling, since upon agonist binding they activate YAP.

YAP forms autocrine loops with the ERBB pathway to regulate ovarian cancer initiation and progression

Mechanisms underlying ovarian cancer initiation and progression are unclear. Herein, we report that the Yes-associated protein (YAP), a major effector of the Hippo tumor suppressor pathway, interacts with ERBB signaling pathways to regulate the initiation and progression of ovarian cancer. Immunohistochemistry studies indicate that YAP expression is associated with poor clinical outcomes in patients. Overexpression or constitutive activation of YAP leads to transformation and tumorigenesis in human ovarian surface epithelial cells, and promotes growth of cancer cells in vivo and in vitro. YAP induces the expression of epidermal growth factor (EGF) receptors (EGFR, ERBB3) and production of EGF-like ligands (HBEGF, NRG1 and NRG2). HBEGF or NRG1, in turn, activates YAP and stimulates cancer cell growth. Knockdown of ERBB3 or HBEGF eliminates YAP effects on cell growth and transformation, whereas knockdown of YAP abrogates NRG1- and HBEGF-stimulated cell proliferation. Collectively, our study demonstrates the existence of HBEGF & NRGs/ERBBs/YAP/HBEGF & NRGs autocrine loop that controls ovarian cell tumorigenesis and cancer progression.

YAP regulates the expression of Hoxa1 and Hoxc13 in mouse and human oral and skin epithelial tissues

Yes-associated protein (YAP) is a Hippo signaling transcriptional coactivator that plays pivotal roles in stem cell proliferation, organ size control, and tumor development. The downstream targets of YAP have been shown to be highly context dependent. In this study, we used the embryonic mouse tooth germ as a tool to search for the downstream targets of YAP in ectoderm-derived tissues. Yap deficiency in the dental epithelium resulted in a small tooth germ with reduced epithelial cell proliferation. We compared the gene expression profiles of embryonic day 14.5 (E14.5) Yap conditional knockout and YAP transgenic mouse tooth germs using transcriptome sequencing (RNA-Seq) and further confirmed the differentially expressed genes using real-time PCR and in situ hybridization. We found that YAP regulates the expression of Hoxa1 and Hoxc13 in oral and dental epithelial tissues as well as in the epidermis of skin during embryonic and adult stages. Sphere formation assay suggested that Hoxa1 and Hoxc13 are functionally involved in YAP-regulated epithelial progenitor cell proliferation, and chromatin immunoprecipitation (ChIP) assay implies that YAP may regulate Hoxa1 and Hoxc13 expression through TEAD transcription factors. These results provide mechanistic insights into abnormal YAP activities in mice and humans.

The hippo pathway effector YAP regulates motility, invasion, and castration-resistant growth of prostate cancer cells

Yes-associated protein (YAP) is an effector of the Hippo tumor suppressor pathway. The functional significance of YAP in prostate cancer has remained elusive. In this study, we first show that enhanced expression of YAP is able to transform immortalized prostate epithelial cells and promote migration and invasion in both immortalized and cancerous prostate cells. We found that YAP mRNA was upregulated in androgen-insensitive prostate cancer cells (LNCaP-C81 and LNCaP-C4-2 cells) compared to the level in androgen-sensitive LNCaP cells. Importantly, ectopic expression of YAP activated androgen receptor signaling and was sufficient to promote LNCaP cells from an androgen-sensitive state to an androgen-insensitive state in vitro, and YAP conferred castration resistance in vivo. Accordingly, YAP knockdown greatly reduced the rates of migration and invasion of LNCaP-C4-2 cells and under androgen deprivation conditions largely blocked cell division in LNCaP-C4-2 cells. Mechanistically, we found that extracellular signal-regulated kinase-ribosomal s6 kinase signaling was downstream of YAP for cell survival, migration, and invasion in androgen-insensitive cells. Finally, immunohistochemistry showed significant upregulation and hyperactivation of YAP in castration-resistant prostate tumors compared to their levels in hormone-responsive prostate tumors. Together, our results identify YAP to be a novel regulator in prostate cancer cell motility, invasion, and castration-resistant growth and as a potential therapeutic target for metastatic castration-resistant prostate cancer (CRPC).

The Hippo pathway regulates homeostatic growth of stem cell niche precursors in the Drosophila ovary

The Hippo pathway regulates organ size, stem cell proliferation and tumorigenesis in adult organs. Whether the Hippo pathway influences establishment of stem cell niche size to accommodate changes in organ size, however, has received little attention. Here, we ask whether Hippo signaling influences the number of stem cell niches that are established during development of the Drosophila larval ovary, and whether it interacts with the same or different effector signaling pathways in different cell types. We demonstrate that canonical Hippo signaling regulates autonomous proliferation of the soma, while a novel hippo-independent activity of Yorkie regulates autonomous proliferation of the germ line. Moreover, we demonstrate that Hippo signaling mediates non-autonomous proliferation signals between germ cells and somatic cells, and contributes to maintaining the correct proportion of these niche precursors. Finally, we show that the Hippo pathway interacts with different growth pathways in distinct somatic cell types, and interacts with EGFR and JAK/STAT pathways to regulate non-autonomous proliferation of germ cells. We thus provide evidence for novel roles of the Hippo pathway in establishing the precise balance of soma and germ line, the appropriate number of stem cell niches, and ultimately regulating adult female reproductive capacity.

During development, organ growth must be carefully regulated to make sure that organs achieve the correct final size needed for organ function. In organs that are made of many different types of cells, this growth regulation is likely to be particularly complex, because it is important for organs to have appropriate proportions, or relative numbers, of the different kinds of cells that make up the organ, as well as the correct number of total cells. One method that cells use to regulate organ growth is a signaling pathway called the Hippo pathway. However, Hippo signaling has been studied, to date, primarily in organ systems that are made up of one cell type. In this study, we examine how Hippo signaling can work to regulate the proportions of different types of cells, as well as the total number of cells in an organ. To do this, we used the developing ovary of the fruit fly as a study system. We found that (1) Hippo signaling regulates the proliferation of many different cell types of the ovary; and (2) Hippo signaling activity in one cell type influences proliferation of other cell types, thus ensuring appropriate proportions of different ovarian cell types.

Oncoprotein YAP regulates the spindle checkpoint activation in a mitotic phosphorylation-dependent manner through up-regulation of BubR1

The transcriptional co-activator YAP (Yes-associated protein) functions as an oncogene; however, it is largely unclear how YAP exerts its oncogenic role. In this study, we further explored the functional significance of YAP and its mitotic phosphorylation in the spindle checkpoint. We found that the dynamic mitotic phosphorylation of YAP was CDC14-dependent. We also showed that YAP was required for the spindle checkpoint activation induced by spindle poisons. Mitotic phosphorylation of YAP was required for activation of the spindle checkpoint. Furthermore, enhanced expression of active YAP hyperactivated the spindle checkpoint and induced mitotic defects in a mitotic phosphorylation-dependent manner. Mechanistically, we documented that mitotic phosphorylation of YAP controlled transcription of genes associated with the spindle checkpoint. YAP constitutively associated with BubR1 (BUB1-related protein kinase), and knockdown of BubR1 relieved YAP-driven hyperactivation of the spindle checkpoint. Finally, we demonstrated that YAP promoted epithelial cell invasion via both mitotic phosphorylation and BubR1-dependent mechanisms. Together, our results reveal a novel link between YAP and the spindle checkpoint and indicate a potential mechanism underlying the oncogenic function of YAP through dysregulation of the spindle checkpoint.

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

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

The biology of YAP/TAZ: hippo signaling and beyond

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

The hippo signaling pathway: implications for heart regeneration and disease

Control of cell number and organ size is critical for appropriate development and tissue homeostasis. Studies in both Drosophila and mammals have established the Hippo signaling pathway as an important modulator of organ size and tumorigenesis. Upon activation, this kinase cascade modulates gene expression through the phosphorylation and inhibition of transcription co-activators that are involved in cell proliferation, differentiation, growth and apoptosis. Hippo signaling serves to limit organ size and suppress malignancies, and has been implicated in tissue regeneration following injury. These outcomes highlight the important role that Hippo signaling plays in regulating both physiologic and pathologic processes. In this review, an overview of the signaling pathway will be discussed as well as recent work that has investigated its role in cardiac development, regeneration and disease.

Significant association of oncogene YAP1 with poor prognosis and cetuximab resistance in colorectal cancer patients

PURPOSE

Activation of YAP1, a novel oncogene in the Hippo pathway, has been observed in many cancers, including colorectal cancer. We investigated whether activation of YAP1 is significantly associated with prognosis or treatment outcomes in colorectal cancer.

EXPERIMENTAL DESIGN

A gene expression signature reflecting YAP1 activation was identified in colorectal cancer cells, and patients with colorectal cancer were stratified into two groups according to this signature: activated YAP1 colorectal cancer (AYCC) or inactivated YAP1 colorectal cancer (IYCC). Stratified patients in five test cohorts were evaluated to determine the effect of the signature on colorectal cancer prognosis and response to cetuximab treatment.

RESULTS

The activated YAP1 signature was associated with poor prognosis for colorectal cancer in four independent patient cohorts with stage I-III disease (total n = 1,028). In a multivariate analysis, the impact of the YAP1 signature on disease-free survival was independent of other clinical variables [hazard ratio (HR), 1.63; 95% confidence interval (CI), 1.25-2.13; P < 0.001]. In patients with stage IV colorectal cancer and wild-type KRAS, IYCC patients had a better disease control rate and progression-free survival (PFS) after cetuximab monotherapy than did AYCC patients; however, in patients with KRAS mutations, PFS duration after cetuximab monotherapy was not different between IYCC and AYCC patients. In multivariate analysis, the effect of YAP1 activation on PFS was independent of KRAS mutation status and other clinical variables (HR, 1.82; 95% CI, 1.05-3.16; P = 0.03).

CONCLUSIONS

Activation of YAP1 is highly associated with poor prognosis for colorectal cancer and may be useful in identifying patients with metastatic colorectal cancer resistant to cetuximab.

The Hippo pathway controls border cell migration through distinct mechanisms in outer border cells and polar cells of the Drosophila ovary

The Hippo pathway is a key signaling cascade in controlling organ size. The core components of this pathway are two kinases, Hippo (Hpo) and Warts (Wts), and a transcriptional coactivator, Yorkie (Yki). Yes-associated protein (YAP, a Yki homolog in mammals) promotes epithelial-mesenchymal transition and cell migration in vitro. Here, we use border cells in the Drosophila ovary as a model to study Hippo pathway functions in cell migration in vivo. During oogenesis, polar cells secrete Unpaired (Upd), which activates JAK/STAT signaling of neighboring cells and specifies them into outer border cells. The outer border cells form a cluster with polar cells and undergo migration. We find that hpo and wts are required for migration of the border cell cluster. In outer border cells, overexpression of hpo disrupts polarization of the actin cytoskeleton and attenuates migration. In polar cells, knockdown of hpo and wts or overexpression of yki impairs border cell induction and disrupts migration. These manipulations in polar cells reduce JAK/STAT activity in outer border cells. Expression of upd-lacZ is increased and decreased in yki and hpo mutant polar cells, respectively. Furthermore, forced expression of upd in polar cells rescues defects of border cell induction and migration caused by wts knockdown. These results suggest that Yki negatively regulates border cell induction by inhibiting JAK/STAT signaling. Together, our data elucidate two distinct mechanisms of the Hippo pathway in controlling border cell migration: (1) in outer border cells, it regulates polarized distribution of the actin cytoskeleton; (2) in polar cells, it regulates upd expression to control border cell induction and migration.

Phosphoproteomic analysis of gossypol-induced apoptosis in ovarian cancer cell line, HOC1a

Ovarian cancer is a major cause for death of gynecological cancer patients. The efficacy of traditional surgery and chemotherapy is rather compromised and platinum-resistant cancer recurs. Finding new therapeutic targets is urgently needed to increase the survival rate and to improve life quality of patients with ovarian cancer. In the present work, phosphoproteomic analysis was carried out on untreated and gossypol-treated ovarian cancer cell line, HOC1a. We identified approximately 9750 phosphopeptides from 3030 phosphoproteins, which are involved in diverse cellular processes including cytoskeletal organization, RNA and nucleotide binding, and cell cycle regulation. Upon gossypol treatment, changes in phosphorylation of twenty-nine proteins including YAP1 and AKAP12 were characterized. Western blotting and qPCR analysis were used to determine expression levels of proteins in YAP1-related Hippo pathway showing that gossypol induced upregulation of LATS1, which phosphorylates YAP1 at Ser 61. Furthermore, our data showed that gossypol targets the actin cytoskeletal organization through mediating phosphorylation states of actin-binding proteins. Taken together, our data provide valuable information to understand effects of gossypol on protein phosphorylation and apoptosis of ovarian cancer cells.

Geranylgeranylation signals to the Hippo pathway for breast cancer cell proliferation and migration

Protein geranylgeranylation (GGylation) is an important biochemical process for many cellular signaling molecules. Previous studies have shown that GGylation is essential for cell survival in many types of cancer. However, the molecular mechanism mediating the cell survival effect remains elusive. In this report, we show that the Hippo pathway mediates GGylation-dependent cell proliferation and migration in breast cancer cells. Blockade of GGylation enhanced phosphorylation of Mst1/2 and Lats1, and inhibited YAP and TAZ activity and the Hippo-YAP/TAZ pathway-dependent transcription. The effect of GGylation blockade on inhibition of breast cancer cell proliferation and migration is dependent on the Hippo-YAP/TAZ signaling, in which YAP appears to regulate cell proliferation and TAZ to regulate cell migration. Furthermore, GGylation-dependent cell proliferation is correlated with the activity of YAP/TAZ in breast cancer cells. Finally, Gγ and RhoA are the GGylated proteins that may transduce GGylation signals to the Hippo-YAP/TAZ pathway. Taken together, our studies have demonstrated that the Hippo-YAP/TAZ pathway is essential for GGylation-dependent cancer cell proliferation and migration.

The Yes-associated protein controls the cell density regulation of Hedgehog signaling

The evolutionarily conserved Hedgehog (Hh) signaling pathway is essential for correct embryogenesis and is misregulated in several malignancies. In cell culture, Hh-sensitive cells display a striking dependence on cell density with active Hh signaling requiring cell-to-cell contact. As the Hippo/YAP system is tightly linked to cell density control and contact inhibition, we investigated the cross-talk between the two pathways. Our data reveal that the suppression of Hh signaling in the absence of cellular contacts is independent of primary cilia and is mediated by the YAP oncogene. Overexpression of YAP blocks Hh signaling whereas RNA interference-mediated knockdown of YAP enhances Hh/GLI activity. Despite this negative regulation, Hh signaling promotes YAP activity through post-transcriptional mechanisms, resulting in a negative feedback loop. In vivo, we found strong nuclear YAP immunoreactivity restricted to compartments with low Hh pathway activity in human and mouse pancreatic cancer. Finally, we identified protease-activated receptors (PARs) as molecules being able to override the inverse Hippo/Hh regulation, potentially giving tumors a mechanism to utilize both oncogenic pathways in parallel.

Hypoxic conditions differentially regulate TAZ and YAP in cancer cells

The Hippo-YAP pathway is altered and implicated as an oncogenic signaling pathway in many human cancers. Hypoxia is an important microenvironmental factor that promotes tumorigenesis. However, the effects of hypoxia on the two most important Hippo-YAP effectors, YAP (Yes-associated protein) and TAZ (transcriptional co-activator with PDZ-binding motif), have not been reported. In this work, we demonstrated that TAZ was functionally involved in cell proliferation and/or migration in epithelial ovarian cancer (EOC) or human ovarian surface epithelial (HOSE) cells. Hypoxic conditions (1% O2 or hypoxia mimics) induced a reduction of YAP phosphorylation (S127) and total YAP expression in EOC cell lines OVCAR5 and SKOV3. However, these conditions up-regulated levels of S69 phosphorylated TAZ in EOC cells. The known TAZ kinases, Lats1 and Akt, were unlikely to be involved in up-regulated pTAZ by hypoxic conditions. Together, our data revealed new and differential regulating mechanisms of TAZ and YAP in cancer cells by hypoxia conditions.

The role of the Hippo pathway in human disease and tumorigenesis

Understanding the molecular nature of human cancer is essential to the development of effective and personalized therapies. Several different molecular signal transduction pathways drive tumorigenesis when deregulated and respond to different types of therapeutic interventions. The Hippo signaling pathway has been demonstrated to play a central role in the regulation of tissue and organ size during development. The deregulation of Hippo signaling leads to a concurrent combination of uncontrolled cellular proliferation and inhibition of apoptosis, two key hallmarks in cancer development. The molecular nature of this pathway was first uncovered in Drosophila melanogaster through genetic screens to identify regulators of cell growth and cell division. The pathway is strongly conserved in humans, rendering Drosophila a suitable and efficient model system to better understand the molecular nature of this pathway. In the present study, we review the current understanding of the molecular mechanism and clinical impact of the Hippo pathway. Current studies have demonstrated that a variety of deregulated molecules can alter Hippo signaling, leading to the constitutive activation of the transcriptional activator YAP or its paralog TAZ. Additionally, the Hippo pathway integrates inputs from a number of growth signaling pathways, positioning the Hippo pathway in a central role in the regulation of tissue size. Importantly, deregulated Hippo signaling is frequently observed in human cancers. YAP is commonly activated in a number of in vitro and in vivo models of tumorigenesis, as well as a number of human cancers. The common activation of YAP in many different tumor types provides an attractive target for potential therapeutic intervention.

Yes-associated protein (YAP) modulates oncogenic features and radiation sensitivity in endometrial cancer

BACKGROUND

Yes-associated protein (YAP) is a transcriptional co-activator and regulates cell proliferation and apoptosis. We investigated the clinical and biological significance of YAP in endometrial cancer (EMCA).

METHODS

YAP expression in 150 primary tumor tissues from patients with EMCA was evaluated by immunohistochemistry and its association with clinicopathological data was assessed. The biological functions of YAP were determined in EMCA cell lines through knockdown/overexpression of YAP. The role of YAP in modulating radiation sensitivity was also investigated in EMCA cells.

RESULTS

Increased nuclear YAP expression was significantly associated with higher grade, stage, lympho-vascular space invasion, postoperative recurrence/metastasis and overall survival in estrogen mediated EMCA, called type 1 cancer (p = 0.019,  = 0.028,  = 0.0008,  = 0.046 and  = 0.015, respectively). In multivariate analysis, nuclear YAP expression was confirmed as an independent prognostic factor for overall survival in type 1 EMCA. YAP knockdown by siRNA resulted in a significant decrease in cell proliferation (p<0.05), anchorage-dependent growth (p = 0.015) and migration/invasion (p<0.05), and a significant increase in the number of cells in G0/G1 phase (p = 0.002). Conversely, YAP overexpression promoted cell proliferation. Clonogenic assay demonstrated enhanced radiosensitivity by approximately 36% in YAP inhibited cells.

CONCLUSIONS

Since YAP functions as a transcriptional co-activator, its differential localization in the nucleus of cancer cells and subsequent impact on cell proliferation could have important consequences with respect to its role as an oncogene in EMCA. Nuclear YAP expression could be useful as a prognostic indicator or therapeutic target and predict radiation sensitivity in patients with EMCA.

Downstream of mutant KRAS, the transcription regulator YAP is essential for neoplastic progression to pancreatic ductal adenocarcinoma

Pancreatic ductal adenocarcinoma (PDAC) is an aggressive cancer with poor survival rates and frequently carries oncogenic KRAS mutation. However, KRAS has thus far not been a viable therapeutic target. We found that the abundance of YAP mRNA, which encodes Yes-associated protein (YAP), a protein regulated by the Hippo pathway during tissue development and homeostasis, was increased in human PDAC tissue compared with that in normal pancreatic epithelia. In genetically engineered Kras(G12D) and Kras(G12D):Trp53(R172H) mouse models, pancreas-specific deletion of Yap halted the progression of early neoplastic lesions to PDAC without affecting normal pancreatic development and endocrine function. Although Yap was dispensable for acinar to ductal metaplasia (ADM), an initial step in the progression to PDAC, Yap was critically required for the proliferation of mutant Kras or Kras:Trp53 neoplastic pancreatic ductal cells in culture and for their growth and progression to invasive PDAC in mice. Yap functioned as a critical transcriptional switch downstream of the oncogenic KRAS-mitogen-activated protein kinase (MAPK) pathway, promoting the expression of genes encoding secretory factors that cumulatively sustained neoplastic proliferation, a tumorigenic stromal response in the tumor microenvironment, and PDAC progression in Kras and Kras:Trp53 mutant pancreas tissue. Together, our findings identified Yap as a critical oncogenic KRAS effector and a promising therapeutic target for PDAC and possibly other types of KRAS-mutant cancers.

Genetics and mechanisms of ovarian cancer: parallels between Drosophila and humans

Considering the degree of detail available at the genetic and cellular levels, the Drosophila ovary stands out as a powerful system to identify new players in the regulation of key aspects of cancer progression. In this review, we will comment on how the use of the Drosophila ovary has helped to elucidate some of the molecular bases of ovarian malignancies and to identify and characterize critical tumour suppressor genes and oncogenes with an impact in human pathologies.

YAP regulates cell proliferation, migration, and steroidogenesis in adult granulosa cell tumors

The Hippo signaling pathway has been implicated as a conserved regulator of organ size in both Drosophila and mammals. Yes-associated protein (YAP), the central component of the Hippo signaling cascade, functions as an oncogene in several malignancies. Ovarian granulosa cell tumors (GCT) are characterized by enlargement of the ovary, excess production of estrogen, a high frequency of recurrence, and the potential for malignancy and metastasis. Whether the Hippo pathway plays a role in the pathogenesis of GCT is unknown. This study was conducted to examine the expression of YAP in human adult GCTs and to determine the role of YAP in the proliferation and steroidogenesis of GCT cells. Compared with age-matched normal human ovaries, GCT tissues exhibited higher levels of YAP expression. YAP protein was predominantly expressed in the nucleus of tumor cells, whereas the non-tumor ovarian stromal cells expressed very low levels of YAP. YAP was also expressed in cultured primary human granulosa cells and in KGN and COV434 GCT cell lines. siRNA-mediated knockdown of YAP in KGN cells resulted in a significant reduction in cell proliferation (P<0.001). Conversely, overexpression of wild type YAP or a constitutively active YAP (YAP1) mutant resulted in a significant increase in KGN cell proliferation and migration. Moreover, YAP knockdown reduced FSH-induced aromatase (CYP19A1) protein expression and estrogen production in KGN cells. These results demonstrate that YAP plays an important role in the regulation of GCT cell proliferation, migration, and steroidogenesis. Targeting the Hippo/YAP pathway may provide a novel therapeutic approach for GCT.

Overexpression of YAP1 is correlated with progression, metastasis and poor prognosis in patients with gastric carcinoma

YAP1 is overexpressed in numerous cancers, but its molecular mechanism in the carcinogenesis and clinic significance in tumor diagnosis and prognosis remains to be determined. We attempted to analyze the clinicopathologic significance of YAP1 expression and the correlation of the YAP1 levels with the progression, metastasis and prognosis of patients with gastric carcinoma. By immunohistochemistry, we determined YAP1 expression in 214 of primary gastric carcinoma (GC), 167 of matched normal gastric mucosa, 40 of chronic atrophic gastritis, 11 of dysplasia and 73 of intestinal metaplasia. The positive rate of YAP1 in gastric carcinoma was significantly higher than that in normal gastric mucosa, chronic atrophic gastritis and intestinal metaplasia. In the gastric cancers with lymph node metastasis, the positive rate of YAP1 was much higher than that in the group without lymph node metastasis. Moreover, gastric cancer patients with YAP1 overexpression demonstrated poorer prognosis than those with YAP1 negative staining. Finally, multivariate analysis of 191 patients with gastric carcinoma indicated that YAP1 overexpression, the invasion depth and lymph node metastasis were high hazard factors for gastric carcinoma. Our results demonstrated that YAP1 overexpression is correlated to the progression, lymph node metastasis and poor prognosis of gastric carcinoma, suggesting that overexpression of YAP1 might be an adjuvant factor for predicting lymph node metastasis, and a useful biomarker for the diagnosis and prediction of prognosis in patients with gastric cancers.

YAP promotes ovarian cancer cell tumorigenesis and is indicative of a poor prognosis for ovarian cancer patients

YAP is a key component of the Hippo signaling pathway and plays a critical role in the development and progression of multiple cancer types, including ovarian cancer. However, the effects of YAP on ovarian cancer development in vivo and its downstream effectors remain uncertain. In this study we found that strong YAP expression was associated with poor ovarian cancer patient survival. Specifically, we showed for the first time that high YAP expression levels were positively correlated with TEAD4 gene expression, and their co-expression was a prognostic marker for poor ovarian cancer survival. Hyperactivation of YAP by mutating its five inhibitory phosphorylation sites (YAP-5SA) increased ovarian cancer cell proliferation, resistance to chemotherapeutic drugs, cell migration, and anchorage-independent growth. In contrast, expression of a dominant negative YAP mutant reversed these phenotypes in ovarian cancer cells both in vitro and in vivo. Our results suggested that YAP caused these effects by promoting an epithelial-to-mesenchymal transition. Thus, YAP promotes ovarian cancer cell growth and tumorigenesis both in vitro and in vivo. Further, high YAP and TEAD4 expression is a prognostic marker for ovarian cancer progression and a potential target for ovarian cancer treatment.

Decreased expression of Yes-associated protein is associated with outcome in the luminal A breast cancer subgroup and with an impaired tamoxifen response

BACKGROUND

Yes-associated protein (YAP1) is frequently reported to function as an oncogene in many types of cancer, but in breast cancer results remain controversial. We set out to clarify the role of YAP1 in breast cancer by examining gene and protein expression in subgroups of patient material and by downregulating YAP1 in vitro and studying its role in response to the widely used anti-estrogen tamoxifen.

METHODS

YAP1 protein intensity was scored as absent, weak, intermediate or strong in two primary breast cancer cohorts (n = 144 and n = 564) and mRNA expression of YAP1 was evaluated in a gene expression dataset (n = 1107). Recurrence-free survival was analysed using the log-rank test and Cox multivariate analysis was used to test for independence. WST-1 assay was employed to measure cell viability and a luciferase ERE (estrogen responsive element) construct was used to study the effect of tamoxifen, following downregulation of YAP1 using siRNAs.

RESULTS

In the ER+ (Estrogen Receptor α positive) subgroup of the randomised cohort, YAP1 expression was inversely correlated to histological grade and proliferation (p = 0.001 and p = 0.016, respectively) whereas in the ER- (Estrogen Receptor α negative) subgroup YAP1 expression correlated positively to proliferation (p = 0.005). Notably, low YAP1 mRNA was independently associated with decreased recurrence-free survival in the gene expression dataset, specifically for the luminal A subgroup (p < 0.001) which includes low proliferating tumours of lower grade, usually associated with a good prognosis. This subgroup specificity led us to hypothesize that YAP1 may be important for response to endocrine therapies, such as tamoxifen, extensively used for luminal A breast cancers. In a tamoxifen randomised patient material, absent YAP1 protein expression was associated with impaired tamoxifen response which was significant upon interaction analysis (p = 0.042). YAP1 downregulation resulted in increased progesterone receptor (PgR) expression and a delayed and weaker tamoxifen in support of the clinical data.

CONCLUSIONS

Decreased YAP1 expression is an independent prognostic factor for recurrence in the less aggressive luminal A breast cancer subgroup, likely due to the decreased tamoxifen sensitivity conferred by YAP1 downregulation.

A peptide mimicking VGLL4 function acts as a YAP antagonist therapy against gastric cancer

The Hippo pathway has been implicated in suppressing tissue overgrowth and tumor formation by restricting the oncogenic activity of YAP. However, transcriptional regulators that inhibit YAP activity have not been well studied. Here, we uncover clinical importance for VGLL4 in gastric cancer suppression and find that VGLL4 directly competes with YAP for binding TEADs. Importantly, VGLL4's tandem Tondu domains are not only essential but also sufficient for its inhibitory activity toward YAP. A peptide mimicking this function of VGLL4 potently suppressed tumor growth in vitro and in vivo. These findings suggest that disruption of YAP-TEADs interaction by a VGLL4-mimicking peptide may be a promising therapeutic strategy against YAP-driven human cancers.

Clinical significance of yes-associated protein overexpression in cervical carcinoma: the differential effects based on histotypes

OBJECTIVES

The objective of this study was to explore the prognostic values of Yes-associated protein (YAP) expression in cervical carcinoma.

METHODS

We compared the YAP expression of 120 samples from squamous cell carcinomas (SCCs) and 42 samples from adenocarcinomas with 22 normal cervical specimens by immunohistochemistry. The expressions of cytoplasmic and nuclear YAP were analyzed separately.

RESULT

Yes-associated protein expression in tumors is significantly higher than the level in normal tissues. In SCCs, cytoplasmic YAP expression is associated with histologic grading, lymph node metastasis, and recurrence. Nuclear expression of YAP is absent in SCC. In adenocarcinomas, cytoplasmic YAP overexpression is associated with histologic grading, and nuclear overexpression is associated with shorter overall survival and disease-free survival.

CONCLUSIONS

Our results indicate the oncogenic potential of YAP in cervical cancer and its distinct functions in SCC and adenocarcinoma.

VGLL4 functions as a new tumor suppressor in lung cancer by negatively regulating the YAP-TEAD transcriptional complex

Lung cancer is one of the most devastating diseases worldwide with high incidence and mortality. Hippo (Hpo) pathway is a conserved regulator of organ size in both Drosophila and mammals. Emerging evidence has suggested the significance of Hpo pathway in cancer development. In this study, we identify VGLL4 as a novel tumor suppressor in lung carcinogenesis through negatively regulating the formation of YAP-TEAD complex, the core component of Hpo pathway. Our data show that VGLL4 is frequently observed to be lowly expressed in both mouse and human lung cancer specimens. Ectopic expression of VGLL4 significantly suppresses the growth of lung cancer cells in vitro. More importantly, VGLL4 significantly inhibits lung cancer progression in de novo mouse model. We further find that VGLL4 inhibits the activity of the YAP-TEAD transcriptional complex. Our data show that VGLL4 directly competes with YAP in binding to TEADs and executes its growth-inhibitory function through two TDU domains. Collectively, our study demonstrates that VGLL4 is a novel tumor suppressor for lung cancer through negatively regulating the YAP-TEAD complex formation and thus the Hpo pathway.

A genetic screen identifies an LKB1-MARK signalling axis controlling the Hippo-YAP pathway

The Hippo-YAP pathway is an emerging signalling cascade involved in the regulation of stem cell activity and organ size. To identify components of this pathway, we performed an RNAi-based kinome screen in human cells. Our screen identified several kinases not previously associated with Hippo signalling that control multiple cellular processes. One of the hits, LKB1, is a common tumour suppressor whose mechanism of action is only partially understood. We demonstrate that LKB1 acts through its substrates of the microtubule affinity-regulating kinase family to regulate the localization of the polarity determinant Scribble and the activity of the core Hippo kinases. Our data also indicate that YAP is functionally important for the tumour suppressive effects of LKB1. Our results identify a signalling axis that links YAP activation with LKB1 mutations, and have implications for the treatment of LKB1-mutant human malignancies. In addition, our findings provide insight into upstream signals of the Hippo-YAP signalling cascade.

Hedgehog signaling induces osteosarcoma development through Yap1 and H19 overexpression

Osteosarcoma is one of the most common bone tumors. However, the genetic basis for its pathogenesis remains elusive. Here, we investigated the roles of Hedgehog (Hh) signaling in osteosarcoma development. Genetically-engineered mice with ubiquitous upregulated Hh signaling specifically in mature osteoblasts develop focal bone overgrowth, which greatly resembles the early stage of osteosarcoma. However, these mice die within three months, which prohibits further analysis of tumor progression. We therefore generated a mouse model with partial upregulated Hh signaling in mature osteoblasts and crossed it into a p53 heterozygous background to potentiate tumor development. We found that these mutant mice developed malignant osteosarcoma with high penetrance. Isolated primary tumor cells were mainly osteoblastic and highly proliferative with many characteristics of human osteosarcomas. Allograft transplantation into immunocompromised mice displayed high tumorigenic potential. More importantly, both human and mouse tumor tissues express high level of yes-associated protein 1 (Yap1), a potent oncogene that is amplified in various cancers. We show that inhibition of Hh signaling reduces Yap1 expression and knockdown of Yap1 significantly inhibits tumor progression. Moreover, long non-coding RNA H19 is aberrantly expressed and induced by upregulated Hh signaling and Yap1 overexpression. Our results demonstrate that aberrant Hh signaling in mature osteoblasts is responsible for the pathogenesis of osteoblastic osteosarcoma through Yap1 and H19 overexpression.

Regulation of the Hippo pathway and implications for anticancer drug development

Research in the past decade has revealed key components of the Hippo tumor suppressor pathway and its critical role in organ size regulation and tumorigenesis. Recent progress has identified a wide range of upstream factors that control the Hippo pathway, which include cell-cell contact, various diffusible signals, and cognate receptors. Dysregulation of the Hippo pathway, caused by gene mutation or aberrant expression, promotes cell proliferation and tumorigenesis. Here, we discuss the current state of Hippo pathway research, primarily focusing on upstream regulators and protein-protein interactions as potential therapeutic targets. Consideration of pharmacological intervention of the Hippo pathway may provide novel avenues for future therapeutic treatment of human diseases, particularly in cancer.