YAP activation is an early event and a potential therapeutic target in liver cancer development

WW domain binding protein 5 induces multidrug resistance of small cell lung cancer under the regulation of miR-335 through the Hippo pathway

BACKGROUND

Our previous study indicated that WW domain binding protein 5 (WBP5) expression was elevated significantly in a drug-resistant cell compared with its parental cell. Nevertheless, its functional role and underlying mechanisms remain unknown.

METHODS

In this study, WBP5 was examined in 62 small cell lung cancer (SCLC) patient samples by immunohistochemical technique. Stable WBP5-overexpressed and WBP5-underexpressed cells were further established to assess the role of WBP5 in drug resistance, apoptosis and tumour growth. We also conducted western blot to detect the expression of MST2 and YAP1 and their phosphorylated protein.

RESULTS

The results revealed that WBP5 expression was significantly associated with the shorter survival time in SCLC patients. Upregulation of WBP5 induced multidrug resistance (MDR) and decreased apoptosis, whereas downregulation of WBP5 enhanced drug sensitivity and increased apoptosis. We also found that miR-335 negatively regulated the MDR of WBP5 by targeting its 3'UTR. Furthermore, WBP5 can lower YAP1 phosphorylation at Serine 127 and induce nuclear accumulation of YAP1. Inhibition of YAP1 by Verteporfin could blunt the MDR phenotype of WBP5.

CONCLUSIONS

WW domain binding protein 5 can modulate MDR through the Hippo pathway under the regulation of miR-335. WW domain binding protein 5 may be a prognostic predictor and a potential target for interfering with MDR in SCLC.

Furan-induced transcriptomic and gene-specific DNA methylation changes in the livers of Fischer 344 rats in a 2-year carcinogenicity study

Furan is a significant food contaminant and a potent hepatotoxicant and rodent liver carcinogen. The carcinogenic effect of furan has been attributed to genotoxic and non-genotoxic, including epigenetic, changes in the liver; however, the mechanisms of the furan-induced liver tumorigenicity are still unclear. The goal of the present study was to investigate the role of transcriptomic and epigenetic events in the development of hepatic lesions in Fischer (F344) rats induced by furan treatment in a classic 2-year rodent tumorigenicity bioassay. High-throughput whole-genome transcriptomic analysis demonstrated distinct alterations in gene expression in liver lesions induced in male F344 rats treated with 0.92 or 2.0 mg furan/kg body weight (bw)/day for 104 weeks. Compared to normal liver tissue, 1336 and 1541 genes were found to be differentially expressed in liver lesions in rats treated with 0.92 and 2.0 mg furan/kg bw/day, respectively, among which 1001 transcripts were differentially expressed at both doses. Pairing transcriptomic and next-generation bisulfite sequencing analyses of the common differentially expressed genes identified 42 CpG island-containing genes in which the methylation level was correlated inversely with gene expression. Forty-eight percent of these genes (20 genes, including Areg, Jag1, and Foxe1) that exhibited the most significant methylation and gene expression changes were involved in key pathways associated with different aspects of liver pathology. Our findings illustrate that gene-specific DNA methylation changes have functional consequences and may be an important component of furan hepatotoxicity and hepatocarcinogenicity.

α2A adrenergic receptors highly expressed in mesoprefrontal dopamine neurons

α2 adrenoreceptors (α2-ARs) play a key role in the control of noradrenaline and dopamine release in the medial prefrontal cortex (mPFC). Here, using UV-laser microdissection-based quantitative mRNA expression in individual neurons we show that in hTH-GFP rats, a transgenic line exhibiting intense and specific fluorescence in dopaminergic (DA) neurons, α2A adrenoreceptor (α2A-AR) mRNA is expressed at high and low levels in DA cells in the ventral tegmental area (VTA) and substantia nigra compacta (SNc), respectively. Confocal microscopy fluorescence immunohistochemistry revealed that α2A-AR immunoreactivity colocalized with tyrosine hydroxylase (TH) in nearly all DA cells in the VTA and SNc, both in hTH-GFP rats and their wild-type Sprague-Dawley (SD) counterparts. α2A-AR immunoreactivity was also found in DA axonal projections to the mPFC and dorsal caudate in the hTH-GFP and in the anterogradely labeled DA axonal projections from VTA to mPFC in SD rats. Importantly, the α2A-AR immunoreactivity localized in the DA cells of VTA and in their fibers in the mPFC was much higher than that in DA cells of SNc and their fibers in dorsal caudate, respectively. The finding that α2A-ARs are highly expressed in the cell bodies and axons of mesoprefrontal dopaminergic neurons provides a morphological basis to the vast functional evidence that somatodendritic and nerve-terminal α2A-AR receptors control dopaminergic activity and dopamine release in the prefrontal cortex. This finding raises the question whether α2A-ARs might function as autoreceptors in the mesoprefrontal dopaminergic neurons, replacing the lack of D2 autoreceptors.

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.

YAP is a critical oncogene in human cholangiocarcinoma

Yes-associated protein (YAP), a transcriptional co-activator, has important regulatory roles in cell signaling and is dysregulated in a number of cancers. However, the role of YAP in cholangiocarcinoma (CCA) progression remains unclear. Here, we demonstrated that YAP was overexpressed in CCA cells and human specimens. High levels of nuclear YAP (nYAP) correlated with histological differentiation, TNM stage, metastasis and poor prognosis in CCA. Silencing YAP increased tumor sensitivity to chemotherapy and inhibited CCA tumorigenesis and metastasis both in vivo and in vitro. YAP overexpression in vivo and in vitro promoted CCA tumorigenesis and metastasis. Additionally, we found that YAP induced epithelial-mesenchymal transition (EMT) and formed a regulatory circuit with miR-29c, IGF1, AKT and gankyrin to promote the progression of CCA. Results of CCA tissue microarray showed positive correlations between nYAP and gankyrin or p-AKT expression. Combination of nYAP and gankyrin or p-AKT exhibited improved prognostic accuracy for CCA patients. In conclusion, YAP promotes carcinogenesis and metastasis by up-regulating gankyrin through activation of the AKT pathway.

A Hippo and Fibroblast Growth Factor Receptor Autocrine Pathway in Cholangiocarcinoma

Herein, we have identified cross-talk between the Hippo and fibroblast growth factor receptor (FGFR) oncogenic signaling pathways in cholangiocarcinoma (CCA). Yes-associated protein (YAP) nuclear localization and up-regulation of canonical target genes was observed in CCA cell lines and a patient-derived xenograft (PDX). Expression of FGFR1, -2, and -4 was identified in human CCA cell lines, driven, in part, by YAP coactivation of TBX5. In turn, FGFR signaling in a cell line with minimal basal YAP expression induced its cellular protein expression and nuclear localization. Treatment of YAP-positive CCA cell lines with BGJ398, a pan-FGFR inhibitor, resulted in a decrease in YAP activation. FGFR activation of YAP appears to be driven largely by FGF5 activation of FGFR2, as siRNA silencing of this ligand or receptor, respectively, inhibited YAP nuclear localization. BGJ398 treatment of YAP-expressing cells induced cell death due to Mcl-1 depletion. In a YAP-associated mouse model of CCA, expression of FGFR 1, 2, and 4 was also significantly increased. Accordingly, BGJ398 treatment was tumor-suppressive in this model and in a YAP-positive PDX model. These preclinical data suggest not only that the YAP and Hippo signaling pathways culminate in an Mcl-1-regulated tumor survival pathway but also that nuclear YAP expression may be a biomarker to employ in FGFR-directed therapy.

MicroRNA-212 suppresses tumor growth of human hepatocellular carcinoma by targeting FOXA1

MicroRNA-212 (miR-212) has been reported to play oncogenic or tumor suppressive role in different human malignancies. Here, we demonstrated that the mean level of miR-212 in hepatocellular carcinoma (HCC) tissues was significantly lower than that in matched tumor-adjacent tissues. Similarly, the expression of miR-212 was obviously reduced in HCC cell lines as compared with a nontransformed hepatic cell line. Ectopic expression of miR-212 inhibited cell viability and proliferation, and induced apoptosis in HepG2 cells. In contrast, down-regulation of miR-212 increased cell viability and proliferation, and suppressed apoptosis in Bel-7402 cells. In vivo studies showed that miR-212 inhibited tumor growth of HCC via suppressing proliferation and inducing apoptosis. Furthermore, we confirmed that Forkhead box protein A1 (FOXA1) was a direct target of miR-212, and it abrogated the function of miR-212 in HCC. Finally, we disclosed that the aberrant expression of miR-212 and FOXA1 was evidently correlated with poor prognostic features of HCC. MiR-212, FOXA1 and their combination were valuable prognostic markers for predicting survival of HCC patients. In conclusion, miR-212 may serve as a prognostic indicator for HCC patients and exerts tumor suppressive role, at least in part, by inhibiting FOXA1.

A genetic variant in large tumor suppressor kinase 2 of Hippo signaling pathway contributes to prognosis of hepatocellular carcinoma

The Hippo pathway plays an important role in the development of hepatocellular carcinoma (HCC). The present study aimed at exploring the genetic variants of Hippo pathway-related genes and their association with HCC prognosis. A total of 331 HCC patients who tested positive for hepatitis B surface antigen were recruited in this study. None of the patients had prior surgical treatment. Twelve potentially functional single-nucleotide polymorphisms (rs7317471 and rs9509492 in LATS2; rs4810446, rs2267853, rs8000, and rs6073627 in MST1; rs10955176 in MST2; and rs16861979, rs2043550, rs16861985, rs1055153, and rs7630434 in TAZ) in the Hippo pathway were genotyped from patients’ peripheral leukocytes using the Sequenom MassARRAY iPLEX platform. Cox proportional hazard models and log-rank test were used for the survival analyses. LATS2 rs7317471 C>T polymorphism was significantly associated with decreased risk of death in HCC using the dominant model (adjusted hazard ratio [HR] =0.63, 95% confidence interval [CI] =0.46–0.87, P=0.004). Furthermore, using stratified analysis, LATS2 rs7317471 CT/TT genotypes were found to be significantly associated with decreased risk of death in patients who were below 53 years of age (adjusted HR =0.50), females (adjusted HR =0.60), smokers (adjusted HR =0.56), drinkers (adjusted HR =0.58), have Barcelona clinic liver cancer stage B (adjusted HR =0.62), and received no prior chemotherapy or transcatheter hepatic arterial chemoembolization (adjusted HR =0.48). Our results suggested that LATS2 rs7317471 could be used as a potential biomarker for the prediction of HCC prognosis.

The metabolic gene HAO2 is downregulated in hepatocellular carcinoma and predicts metastasis and poor survival

BACKGROUND & AIMS

l-2-Hydroxy acid oxidases are flavin mononucleotide-dependent peroxisomal enzymes, responsible for the oxidation of l-2-hydroxy acids to ketoacids, resulting in the formation of hydrogen peroxide. We investigated the role of HAO2, a member of this family, in rat, mouse and human hepatocarcinogenesis.

METHODS

We evaluated Hao2 expression by qRT-PCR in the following rodent models of hepatocarcinogenesis: the Resistant-Hepatocyte, the CMD and the chronic DENA rat models, and the TCPOBOP/DENA and TCPOBOP only mouse models. Microarray and qRT-PCR analyses were performed on two cohorts of human hepatocellular carcinoma (HCC) patients. Rat HCC cells were transduced by a Hao2 encoding lentiviral vector and grafted in mice.

RESULTS

Downregulation of Hao2 was observed in all investigated rodent models of hepatocarcinogenesis. Interestingly, Hao2 mRNA levels were also profoundly downregulated in early preneoplastic lesions. Moreover, HAO2 mRNA levels were strongly downregulated in two distinct series of human HCCs, when compared to both normal and cirrhotic peri-tumoral liver. HAO2 levels were inversely correlated with grading, overall survival and metastatic ability. Finally, exogenous expression of Hao2 in rat cells impaired their tumorigenic ability.

CONCLUSION

Our work identifies for the first time the oncosuppressive role of the metabolic gene Hao2. Indeed, its expression is severely decreased in HCC of different species and etiology, and its reintroduction in HCC cells profoundly impairs tumorigenesis. We also demonstrate that dysregulation of HAO2 is a very early event in the development of HCC and it may represent a useful diagnostic and prognostic marker for human HCC.

Activated Hippo/Yes-Associated Protein Pathway Promotes Cell Proliferation and Anti-apoptosis in Endometrial Stromal Cells of Endometriosis

CONTEXT

The imbalance in cell proliferation and apoptosis is considered an important role in the pathogenesis of endometriosis, but the exact mechanisms remains unclear. A newly established signaling pathway–Hippo/Yes-associated protein (YAP) pathway plays a critical role in the proliferation and apoptosis processes. However, studies focusing on Hippo/YAP pathway and endometriosis are lacking.

OBJECTIVE

The objective was to explore the function of the Hippo/YAP pathway in endometriosis.

SETTING AND DESIGN

The expression of YAP was first investigated in endometrium of women with or without endometriosis. The role of YAP in cell proliferation and apoptosis is identified by transfection of endometrial stromal cells (ESCs) in vitro, subsequent Verteporfin treatments in eutopic ESCs in vitro, and endometriosis animal model of nude mice in vivo.

RESULTS

Our results revealed that increased expression of YAP and decreased expression of p-YAP in ectopic and eutopic endometrium compared with normal endometrium. YAP knockdown in eutopic ESCs decreased cell proliferation and enhanced cell apoptosis companied with decreased expression of TEAD1, CTGF, and B-cell lymphoma/leukemia (BCL)-2; whereas overexpression of YAP resulted in increased proliferation and decreased apoptosis of normal ESCs with increased expression of TEAD1, CTGF, and BCL-2. By chromatin immunoprecipitation qPCR CTGF and BCL-2 were identified as directly downstream target genes of YAP-TEAD1 active complex. Eutopic ESCs treated with Verteporfin revealed decreased proliferation and enhanced apoptosis whereas in endometriosis animal models of nude mice treated with Verteporfin, the size of endometriotic lesions was significantly reduced.

CONCLUSIONS

Our study suggests that the Hippo/YAP-signaling pathway plays a critical role in the pathogenesis of endometriosis and should present a novel therapeutic method against endometriosis.

MicroRNA-186 targets Yes-associated protein 1 to inhibit Hippo signaling and tumorigenesis in hepatocellular carcinoma

Liver cancer, particularly hepatocellular carcinoma (HCC), is one of leading causes of cancer-related mortality worldwide. Upregulation of the evolutionary conserved Hippo signaling pathway has been observed in HCC patients, and Yes-associated protein 1 (YAP1) has been reported to play a key role in HCC tumorigenesis. microRNAs (miRNAs) are a family of small non-coding RNAs, usually 21-25 nucleotides in length, and are essential in the regulation of gene expression. Abnormal miRNA expression has been implicated in the initiation and progression of numerous forms of cancers, including liver cancer. Here, we report the identification of a novel miRNA, miR-186, and its functions as an HCC tumor suppressor. We observed that miR-186 was downregulated in several HCC cell lines, and that it directly targets YAP1 mRNA. Overexpression of miR-186 in HCC cells significantly downregulates YAP1 mRNA and protein levels, leading to downregulation of the Hippo signaling pathway, which in turn severely inhibits HCC cell migration, invasion and proliferation. Our study is the first to report the direct involvement of miR-186 in downregulating YAP1 and, more significantly, inhibiting HCC tumorigenesis, and supports the role miR-186 as a potential therapeutic target in treating liver cancer.

CIZ1 interacts with YAP and activates its transcriptional activity in hepatocellular carcinoma cells

Dysregulation of Hippo-Yes-associate protein (YAP) signaling has important roles in the tumorigenesis of hepatocellular carcinoma (HCC). Our previous studies have shown that Cip1 interacting zinc finger protein 1 (CIZ1) activated YAP signaling in the HCC cells and promoted the growth and migration of cancer cells. However, the mechanisms for the activation of YAP signaling by CIZ1 are unknown. In this study, it was found that CIZ1 interacted with the transcriptional factor YAP in HCC cells. The nuclear matrix anchor domain of CIZ1 is responsible for its interaction with YAP. Moreover, CIZ1 enhanced the interaction between YAP and TEAD. Knocking down the expression of CIZ1 impaired the transcriptional activity as well as the biological functions of YAP. Taken together, our study demonstrated that CIZ1 is a positive regulator of YAP signaling, and CIZ1 might be a therapeutic target for HCC.

Nuclear translocation and activation of YAP by hypoxia contributes to the chemoresistance of SN38 in hepatocellular carcinoma cells

Although hypoxia is a prominent feature contributing to the therapeutic resistance of hepatocellular carcinoma cells (HCC) against chemotherapeutic agents, including the Topoisomerase I inhibitor SN38, the underlying mechanism is not fully understood and its understanding remains a major clinical challenge. In the present study, we found that hypoxia-induced nuclear translocation and accumulation of YAP acted as a survival input to promote resistance to SN38 in HCC. The induction of YAP by hypoxia was not mediated by HIF-1α because manipulating the abundance of HIF-1α with CoCl2, exogenous expression, and RNA interference had no effect on the phosphorylation or total levels of YAP. The mevalonate-HMG-CoA reductase (HMGCR) pathway may modulate the YAP activation under hypoxia. Combined YAP inhibition using either siRNA or the HMGCR inhibitor statins together with SN38 treatment produced improved anti-cancer effects in HCC cells. The increased anti-cancer effect of the combined treatment with statins and irinotecan (the prodrug of SN-38) was further validated in a human HepG2 xenograft model of HCC in nude mice. Taken together, our findings identify YAP as a novel mediator of hypoxic-resistance to SN38. These results suggest that the administration of SN28 together with the suppression of YAP using statins is a promising strategy for enhancing the treatment response in HCC patients, particularly in advanced stage HCC cases presenting hypoxic resistance.

microRNA-497 inhibits cell proliferation and induces apoptosis by targeting YAP1 in human hepatocellular carcinoma

microRNAs (miRNAs) function as oncogenes or tumor suppressors in human cancers by targeting mRNAs for degradation and/or translational repression. miR‐497 has been proposed as a tumor suppressive miRNA and its deregulation is observed in human cancers. However, the prognostic value of miR‐497 and its underlying molecular pathways involved in the initiation and development of hepatocellular carcinoma (HCC) are poorly investigated. In the present study, we found that the mean level of miR‐497 in HCC tissues was lower than that in adjacent nontumor tissues. Clinical data indicated that low expression of miR‐497 was prominently associated with adverse prognostic features of HCC including high serum alpha‐fetoprotein (AFP) level, large tumor size, high Edmondson–Steiner grading and advanced tumor–node–metastasis (TNM) stage. Furthermore, miR‐497 was an independent prognostic factor for indicating both 5‐year overall survival and disease‐free survival of HCC patients. Gain‐ and loss‐of‐function studies showed that miR‐497 reduced cell proliferation and induced apoptosis in HCC cells. Yes‐associated protein 1 (YAP1) was identified as a direct target of miR‐497 in HCC. An inverse correlation between YAP1 and miR‐497 expression was observed in HCC tissues. Notably, YAP1 knockdown abrogated the effects of miR‐497 deletion on HCC cells with decreased cell proliferation and increased apoptosis. In conclusion, we report that miR‐497 is a potent prognostic indicator and may suppress tumor growth of HCC by targeting YAP1.

The TEAD Family and Its Oncogenic Role in Promoting Tumorigenesis

The TEAD family of transcription factors is necessary for developmental processes. The family members contain a TEA domain for the binding with DNA elements and a transactivation domain for the interaction with transcription coactivators. TEAD proteins are required for the participation of coactivators to transmit the signal of pathways for the downstream signaling processes. TEADs also play an important role in tumor initiation and facilitate cancer progression via activating a series of progression-inducing genes, such as CTGF, Cyr61, Myc and Gli2. Recent studies have highlighted that TEADs, together with their coactivators, promote or even act as the crucial parts in the development of various malignancies, such as liver, ovarian, breast and prostate cancers. Furthermore, TEADs are proposed to be useful prognostic biomarkers due to the ideal correlation between high expression and clinicopathological parameters in gastric, breast, ovarian and prostate cancers. In this review, we summarize the functional role of TEAD proteins in tumorigenesis and discuss the key role of TEAD transcription factors in the linking of signal cascade transductions. Improved knowledge of the TEAD proteins will be helpful for deep understanding of the molecular mechanisms of tumorigenesis and identifying ideal predictive or prognostic biomarkers, even providing clinical translation for anticancer therapy in human cancers.

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.

Clinicopathological indices to predict hepatocellular carcinoma molecular classification

BACKGROUND & AIMS

Hepatocellular carcinoma (HCC) is the second most lethal cancer caused by lack of effective therapies. Although promising, HCC molecular classification, which enriches potential responders to specific therapies, has not yet been assessed in clinical trials of anti-HCC drugs. We aimed to overcome these challenges by developing clinicopathological surrogate indices of HCC molecular classification.

METHODS

Hepatocellular carcinoma classification defined in our previous transcriptome meta-analysis (S1, S2 and S3 subclasses) was implemented in an FDA-approved diagnostic platform (Elements assay, NanoString). Ninety-six HCC tumours (training set) were assayed to develop molecular subclass-predictive indices based on clinicopathological features, which were independently validated in 99 HCC tumours (validation set). Molecular deregulations associated with the histopathological features were determined by pathway analysis. Sample sizes for HCC clinical trials enriched with specific molecular subclasses were determined.

RESULTS

Hepatocellular carcinoma subclass-predictive indices were steatohepatitic (SH)-HCC variant and immune cell infiltrate for S1 subclass, macrotrabecular/compact pattern, lack of pseudoglandular pattern, and high serum alpha-foetoprotein (>400 ng/ml) for S2 subclass, and microtrabecular pattern, lack of SH-HCC and clear cell variants, and lower histological grade for S3 subclass. Macrotrabecular/compact pattern, a predictor of S2 subclass, was associated with the activation of therapeutically targetable oncogene YAP and stemness markers EPCAM/KRT19. BMP4 was associated with pseudoglandular pattern. Subclass-predictive indices-based patient enrichment reduced clinical trial sample sizes from 121, 184 and 53 to 30, 43 and 22 for S1, S2 and S3 subclass-targeting therapies respectively.

CONCLUSIONS

Hepatocellular carcinoma molecular subclasses can be enriched by clinicopathological indices tightly associated with deregulation of therapeutically targetable molecular pathways.

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 promotes proliferation, chemoresistance, and angiogenesis in human cholangiocarcinoma through TEAD transcription factors

The Yes-associated protein (YAP)/Hippo pathway has been implicated in tissue development, regeneration, and tumorigenesis. However, its role in cholangiocarcinoma (CC) is not established. We show that YAP activation is a common feature in CC patient biopsies and human CC cell lines. Using microarray expression profiling of CC cells with overexpressed or down-regulated YAP, we show that YAP regulates genes involved in proliferation, apoptosis, and angiogenesis. YAP activity promotes CC growth in vitro and in vivo by functionally interacting with TEAD transcription factors (TEADs). YAP activity together with TEADs prevents apoptosis induced by cytotoxic drugs, whereas YAP knockdown sensitizes CC cells to drug-induced apoptosis. We further show that the proangiogenic microfibrillar-associated protein 5 (MFAP5) is a direct transcriptional target of YAP/TEAD in CC cells and that secreted MFAP5 promotes tube formation of human microvascular endothelial cells. High YAP activity in human CC xenografts and clinical samples correlates with increased MFAP5 expression and CD31(+) vasculature.

CONCLUSIONS

These findings establish YAP as a key regulator of proliferation and antiapoptotic mechanisms in CC and provide first evidence that YAP promotes angiogenesis by regulating the expression of secreted proangiogenic proteins.

Tumor-selective proteotoxicity of verteporfin inhibits colon cancer progression independently of YAP1

Yes-associated protein 1 (YAP1) is a transcriptional coactivator in the Hippo signaling pathway. Increased YAP1 activity promotes the growth of tumors, including that of colorectal cancer (CRC). Verteporfin, a drug that enhances phototherapy to treat neovascular macular degeneration, is an inhibitor of YAP1. We found that verteporfin inhibited tumor growth independently of its effects on YAP1 or the related protein TAZ in genetically or chemically induced mouse models of CRC, in patient-derived xenografts, and in enteroid models of CRC. Instead, verteporfin exhibited in vivo selectivity for killing tumor cells in part by impairing the global clearance of high-molecular weight oligomerized proteins, particularly p62 (a sequestrome involved in autophagy) and STAT3 (signal transducer and activator of transcription 3; a transcription factor). Verteporfin inhibited cytokine-induced STAT3 activity and cell proliferation and reduced the viability of cultured CRC cells. Although verteporfin accumulated to a greater extent in normal cells than in tumor cells in vivo, experiments with cultured cells indicated that the normal cells efficiently cleared verteporfin-induced protein oligomers through autophagic and proteasomal pathways. Culturing CRC cells under hypoxic or nutrient-deprived conditions (modeling a typical CRC microenvironment) impaired the clearance of protein oligomers and resulted in cell death, whereas culturing cells under normoxic or glucose-replete conditions protected cell viability and proliferation in the presence of verteporfin. Furthermore, verteporfin suppressed the proliferation of other cancer cell lines even in the absence of YAP1, suggesting that verteporfin may be effective against multiple types of solid cancers.

Regulation of hepatocyte identity and quiescence

The liver is a highly differentiated organ with a central role in metabolism, detoxification and systemic homeostasis. To perform its multiple tasks, liver parenchymal cells, the hepatocytes, express a large complement of enabling genes defining their complex phenotype. This phenotype is progressively acquired during fetal development and needs to be maintained in adulthood to guarantee the individual's survival. Upon injury or loss of functional mass, the liver displays an extraordinary regenerative response, mainly based on the proliferation of hepatocytes which otherwise are long-lived quiescent cells. Increasing observations suggest that loss of hepatocellular differentiation and quiescence underlie liver malfunction in chronic liver disease and pave the way for hepatocellular carcinoma development. Here, we briefly review the essential mechanisms leading to the acquisition of liver maturity. We also identify the key molecular factors involved in the preservation of hepatocellular homeostasis and finally discuss potential strategies to preserve liver identity and function.

Yes-associated protein in the liver: Regulation of hepatic development, repair, cell fate determination and tumorigenesis

The liver is a vital organ that plays a major role in many bodily functions from protein production and blood clotting to cholesterol, glucose and iron metabolism and nutrition storage. Maintenance of liver homeostasis is critical for these essential bodily functions and disruption of liver homeostasis causes various kinds of liver diseases, some of which have high mortality rate. Recent research advances of the Hippo signalling pathway have revealed its nuclear effector, Yes-associated protein, as an important regulator of liver development, repair, cell fate determination and tumorigenesis. Therefore, a precise control of Yes-associated protein activity is critical for the maintenance of liver homeostasis. This review is going to summarize the discoveries on how the manipulation of Yes-associated protein activity affects liver homeostasis and induces liver diseases and the regulatory mechanisms that determine the Yes-associated protein activity in the liver. Finally, we will discuss the potential of targeting Yes-associated protein as therapeutic strategies in liver diseases.

Hsa-miR-132 inhibits proliferation of hepatic carcinoma cells by targeting YAP

MicroRNAs and Yes-associated protein (YAP) play an important role in the occurrence and development of hepatic carcinomas. However, the interaction between microRNAs and YAP was seldom elucidated. In this study, we showed that miR-132 could target YAP gene by using dual-luciferase reporter system. Further quantitative polymerase chain reaction analysis and western blotting showed that miR-132 could significantly reduce the expression of YAP at mRNA and protein levels. Results of annexin V-fluorescein isothiocyanate, 5-ethynyl-2'-deoxyuridine staining and transwell assays showed that miR-132 significantly promoted the cell apoptosis and effectively inhibited the proliferation and invasion of hepatoma cells. These results indicated that miR-132 could inhibit the growth of hepatoma cells by targeting YAP gene and reducing its expression level. Taken together, results from this study would help us to understand the mechanisms for occurrence and development of hepatic carcinoma and provide new targets for diagnosis and treatment of liver cancer.

CD166 positively regulates MCAM via inhibition to ubiquitin E3 ligases Smurf1 and βTrCP through PI3K/AKT and c-Raf/MEK/ERK signaling in Bel-7402 hepatocellular carcinoma cells

Both Cluster of Differentiation 166 (CD166) and Melanoma Cell Adhesion Molecule (MCAM) play critical roles in maintaining transformative phenotype of Hepatocellular Carcinoma (HCC) cells. However, the relationship between these two membrane proteins remains unknown. Here, we found that CD166 has a positive impact on the expression of MCAM, while MCAM has no feedback on CD166. Tissue microarray analysis (TMA) also showed a positive correlation between CD166 and MCAM. Depletion of CD166-induced anti-carcinogenic phenotype could be reversed by overexpression of MCAM, suggesting MCAM is functional important in the CD166-induced liver tumorigenesis. Furthermore, we found CD166 regulates MCAM mainly through protecting MCAM from ubiquitin-mediated protein degradation. Mechanically, CD166 down-regulated two ubiquitin E3 ligases, βTrCP and Smurf1, which play critical roles in the destability of MCAM protein. In addition, overexpression of βTrCP and Smurf1-reduced transformative phenotype could be partially reversed by MCAM, providing evidence that MCAM is a target of βTrCP and Smurf1. Moreover, we identified c-Raf/MEK/ERK signaling acts as a downstream effecter of CD166/PI3K/AKT axis to stimulate ubiquitination and destability of βTrCP and Smurf1. Taken together, we establish a model that CD166 regulates MCAM through a signaling flow from activation of PI3K/AKT and c-Raf/MEK/ERK signaling to the inhibition of potential MCAM ubiquitin E3 ligases, βTrCP and Smurf1, blockage of this signaling cascade may be useful in the treatment of CD166 and MCAM-dependent HCC.

Co-activation of PIK3CA and Yap promotes development of hepatocellular and cholangiocellular tumors in mouse and human liver

Activation of the PI3K and Yes-associated protein (Yap) signaling pathways has been independently reported in human hepatocellular carcinoma (HCC). However, the oncogenic interactions between these two cascades in hepatocarcinogenesis remain undetermined. To assess the consequences of the crosstalk between the PI3K and Yap pathways along liver carcinogenesis, we generated a mouse model characterized by combined overexpression of activated mutant forms of PIK3CA (PIK3CAH1047R) and Yap (YapS127A) in the mouse liver using hydrodynamic transfection (PIK3CA/Yap). In addition, suppression of PI3K and Yap pathways was conducted in human HCC and cholangiocarcinoma (CCA) cell lines. We found that concomitant activation of PI3K and Yap pathways triggered rapid liver tumor development in mice. Histologically, tumors were pure HCC, CCA, or mixed HCC/CCA. At the molecular level, PIK3CA/Yap tumors were characterized by activation of the mTORC1/2, ERK/MAPK, and Notch pathways. Simultaneous activation of PI3K and Yap pathways frequently occurred in human liver tumor specimens and their combined suppression was highly detrimental for the growth of HCC and CCA cell lines. In conclusion, our study demonstrates the oncogenic cooperation between PI3K and Yap pathways along liver carcinogenesis. The PIK3CA/Yap mouse represents an important preclinical liver tumor model for the development of novel therapeutics against this malignancy.