Deregulation of Hippo kinase signalling in human hepatic malignancies

β-Catenin and Yes-Associated Protein 1 Cooperate in Hepatoblastoma Pathogenesis

Hepatoblastoma (HB), the most common pediatric primary liver neoplasm, shows nuclear localization of β-catenin and yes-associated protein 1 (YAP1) in almost 80% of the cases. Co-expression of constitutively active S127A-YAP1 and ΔN90 deletion-mutant β-catenin (YAP1-ΔN90-β-catenin) causes HB in mice. Because heterogeneity in downstream signaling is being identified owing to mutational differences even in the β-catenin gene alone, we investigated if co-expression of point mutants of β-catenin (S33Y or S45Y) with S127A-YAP1 led to similar tumors as YAP1-ΔN90-β-catenin. Co-expression of S33Y/S45Y-β-catenin and S127A-YAP1 led to activation of Yap and Wnt signaling and development of HB, with 100% mortality by 13 to 14 weeks. Co-expression with YAP1-S45Y/S33Y-β-catenin of the dominant-negative T-cell factor 4 or dominant-negative transcriptional enhanced associate domain 2, the respective surrogate transcription factors, prevented HB development. Although histologically similar, HB in YAP1-S45Y/S33Y-β-catenin, unlike YAP1-ΔN90-β-catenin HB, was glutamine synthetase (GS) positive. However, both ΔN90-β-catenin and point-mutant β-catenin comparably induced GS-luciferase reporter in vitro. Finally, using a previously reported 16-gene signature, it was shown that YAP1-ΔN90-β-catenin HB tumors exhibited genetic similarities with more proliferative, less differentiated, GS-negative HB patient tumors, whereas YAP1-S33Y/S45Y-β-catenin HB exhibited heterogeneity and clustered with both well-differentiated GS-positive and proliferative GS-negative patient tumors. Thus, we demonstrate that β-catenin point mutants can also collaborate with YAP1 in HB development, albeit with a distinct molecular profile from the deletion mutant, which may have implications in both biology and therapy.

TEA Domain Transcription Factor 4 Is the Major Mediator of Yes-Associated Protein Oncogenic Activity in Mouse and Human Hepatoblastoma

Hepatoblastoma (HB) is the most common type of pediatric liver cancer. Activation of yes-associated protein (YAP) has been implicated in HB molecular pathogenesis. The transcriptional co-activator Yap regulates downstream gene expression through interaction with the TEA domain (TEAD) proteins. Nonetheless, YAP also displays functions that are independent of its transcriptional activity. The underlying molecular mechanisms by which Yap promotes HB development remain elusive. In the current study, we demonstrated that blocking TEAD function via the dominant-negative form of TEAD2 abolishes Yap-driven HB formation in mice and restrains human HB growth in vitro. When TEAD2 DNA-binding domain was fused with virus protein 16 transcriptional activation domain, it synergized with activated β-catenin to promote HB formation in vivo. Among TEAD genes, silencing of TEAD4 consistently inhibited tumor growth and Yap target gene expression in HB cell lines. Furthermore, TEAD4 mRNA expression was significantly higher in human HB lesions when compared with corresponding nontumorous liver tissues. Human HB specimens also exhibited strong nuclear immunoreactivity for TEAD4. Altogether, data demonstrate that TEAD-mediated transcriptional activity is both sufficient and necessary for Yap-driven HB development. TEAD4 is the major TEAD isoform and Yap partner in human HB. Targeting TEAD4 may represent an effective treatment option for human HB.

YAP/TAZ Signaling as a Molecular Link between Fibrosis and Cancer

Tissue fibrosis is a pathological condition that is associated with impaired epithelial repair and excessive deposition of extracellular matrix (ECM). Fibrotic lesions increase the risk of cancer in various tissues, but the mechanism linking fibrosis and cancer is unclear. Yes-associated protein (YAP) and the transcriptional coactivator with PDZ-binding motif (TAZ) are core components of the Hippo pathway, which have multiple biological functions in the development, homeostasis, and regeneration of tissues and organs. YAP/TAZ act as sensors of the structural and mechanical features of the cell microenvironment. Recent studies have shown aberrant YAP/TAZ activation in both fibrosis and cancer in animal models and human tissues. In fibroblasts, ECM stiffness mechanoactivates YAP/TAZ, which promote the production of profibrotic mediators and ECM proteins. This results in tissue stiffness, thus establishing a feed-forward loop of fibroblast activation and tissue fibrosis. In contrast, in epithelial cells, YAP/TAZ are activated by the disruption of cell polarity and increased ECM stiffness in fibrotic tissues, which promotes the proliferation and survival of epithelial cells. YAP/TAZ are also involved in the epithelial–mesenchymal transition (EMT), which contributes to tumor progression and cancer stemness. Importantly, the crosstalk with transforming growth factor (TGF)-β signaling and Wnt signaling is essential for the profibrotic and tumorigenic roles of YAP/TAZ. In this article, we review the latest advances in the pathobiological roles of YAP/TAZ signaling and their function as a molecular link between fibrosis and cancer.

Hepatocyte-Derived Lipocalin 2 Is a Potential Serum Biomarker Reflecting Tumor Burden in Hepatoblastoma

Hepatoblastoma (HB) is the most common pediatric liver malignant tumor. Previously, we reported co-activation of β-catenin and Yes-associated protein-1 (YAP1) in 80% of HB. Hepatic co-expression of active β-catenin and YAP1 via sleeping beauty transposon/transposase and hydrodynamic tail vein injection led to HB development in mice. Here, we identify lipocalin 2 (Lcn2) as a target of β-catenin and YAP1 in HB and show that serum Lcn2 values positively correlated with tumor burden. Lcn2 was strongly expressed in HB tumor cells in our mouse model. A tissue array of 62 HB cases showed highest LCN2 expression in embryonal and lowest in fetal, blastemal, and small cell undifferentiated forms of HB. Knockdown of LCN2 in HB cells had no effect on cell proliferation but reduced NF-κB reporter activity. Next, liver-specific Lcn2 knockout (KO) mice were generated. No difference in tumor burden was observed between Lcn2 KO mice and wild-type littermate controls after sleeping beauty transposon/transposase and hydrodynamic tail vein injection delivery of active YAP1 and β-catenin, although Lcn2 KO mice with HB lacked any serum Lcn2 elevation, demonstrating that transformed hepatocytes are the source of serum Lcn2. More blastemal areas and inflammation were observed within HB in Lcn2 KO compared with wild-type tumors. In conclusion, Lcn2 expressed in hepatocytes appears to be dispensable for the pathogenesis of HB. However, transformed hepatocytes secrete serum Lcn2, making Lcn2 a valuable biomarker for HB.

YAP Tyrosine Phosphorylation and Nuclear Localization in Cholangiocarcinoma Cells Are Regulated by LCK and Independent of LATS Activity

The Hippo pathway effector, Yes-associated protein (YAP), is a transcriptional coactivator implicated in cholangiocarcinoma (CCA) pathogenesis. YAP is known to be regulated by a serine/threonine kinase relay module (MST1/2-LATS1/2) culminating in phosphorylation of YAP at Serine 127 and cytoplasmic sequestration. However, YAP also undergoes tyrosine phosphorylation, and the role of tyrosine phosphorylation in YAP regulation remains unclear. Herein, YAP regulation by tyrosine phosphorylation was examined in human and mouse CCA cells, as well as patient-derived xenograft (PDX) models. YAP was phosphorylated on tyrosine 357 (Y357) in CCA cell lines and PDX models. SRC family kinase (SFK) inhibition with dasatinib resulted in loss of YAPY357 phosphorylation, promoted its translocation from the nucleus to the cytoplasm, and reduced YAP target gene expression, including cell lines expressing a LATS1/2-resistant YAP mutant in which all serine residues were mutated to alanine. Consistent with these observations, precluding YAPY357 phosphorylation by site-directed mutagenesis (YAPY357F) excluded YAP from the nucleus. Targeted siRNA experiments identified LCK as the SFK that most potently mediated YAPY357 phosphorylation. Likewise, inducible CRISPR/Cas9-targeted LCK deletion decreased YAPY357 phosphorylation and its nuclear localization. The importance of LCK in CCA biology was demonstrated by clinical observations suggesting LCK expression levels were associated with early tumor recurrence following resection of CCA. Finally, dasatinib displayed therapeutic efficacy in PDX models. Mol Cancer Res; 16(10); 1556-67. ©2018 AACR.

Microenvironment and tumor cells: two targets for new molecular therapies of hepatocellular carcinoma

Hepatocellular carcinoma (HCC), is one of the most frequent human cancer and is characterized by a high mortality rate. The aggressiveness appears strictly related to the liver pathological background on which cancer develops. Inflammation and the consequent fibro/cirrhosis, derived from chronic injuries of several origins (viral, toxic and metabolic) and observable in almost all oncological patients, represents the most powerful risk factor for HCC and, at the same time, an important obstacle to the efficacy of systemic therapy. Multiple microenvironmental cues, indeed, play a pivotal role in the pathogenesis, evolution and recurrence of HCC as well as in the resistance to standard therapies observed in most of patients. The identification of altered pathways in cancer cells and of microenvironmental changes, strictly connected in pathogenic feedback loop, may permit to plan new therapeutic approaches targeting tumor cells and their permissive microenvironment, simultaneously.

Molecular Mechanisms Driving Cholangiocarcinoma Invasiveness: An Overview

The acquisition of invasive functions by tumor cells is a first and crucial step toward the development of metastasis, which nowadays represents the main cause of cancer-related death. Cholangiocarcinoma (CCA), a primary liver cancer originating from the biliary epithelium, typically develops intrahepatic or lymph node metastases at early stages, thus preventing the majority of patients from undergoing curative treatments, consistent with their very poor prognosis. As in most carcinomas, CCA cells gradually adopt a motile, mesenchymal-like phenotype, enabling them to cross the basement membrane, detach from the primary tumor, and invade the surrounding stroma. Unfortunately, little is known about the molecular mechanisms that synergistically orchestrate this proinvasive phenotypic switch. Autocrine and paracrine signals (cyto/chemokines, growth factors, and morphogens) permeating the tumor microenvironment undoubtedly play a prominent role in this context. Moreover, a number of recently identified signaling systems are currently drawing attention as putative mechanistic determinants of CCA cell invasion. They encompass transcription factors, protein kinases and phosphatases, ubiquitin ligases, adaptor proteins, and miRNAs, whose aberrant expression may result from either stochastic mutations or the abnormal activation of upstream pro-oncogenic pathways. Herein we sought to summarize the most relevant molecules in this field and to discuss their mechanism of action and potential prognostic relevance in CCA. Hopefully, a deeper knowledge of the molecular determinants of CCA invasiveness will help to identify clinically useful biomarkers and novel druggable targets, with the ultimate goal to develop innovative approaches to the management of this devastating malignancy.

YAP-associated chromosomal instability and cholangiocarcinoma in mice

Deregulated Hippo pathway signaling is associated with aberrant activation of the downstream effector yes-associated protein (YAP), an emerging key oncogenic mediator in cholangiocarcinoma (CCA). In our prior work, we have demonstrated that biliary transduction of YAP along with Akt as a permissive factor induces CCA in mice. To further delineate the mechanisms associated with YAP-associated biliary oncogenesis, we have established seven malignant murine cell lines from our YAP-driven murine CCA model. These cells express the CCA markers SRY (Sex Determining Region Y)-Box 9 (SOX9), cytokeratin (CK)-7 and 19 but lack hepatocyte nuclear factor 4 alpha and alpha-smooth muscle actin, markers of hepatocellular carcinoma and cancer-associated fibroblasts, respectively. Notably, the murine CCA cells can be readily implanted into mouse livers with resultant orthotopic tumor formation. In this unique syngeneic orthotopic murine model, tumors exhibit histopathologic features resembling human CCA. We analyzed transcriptome data from YAP-associated parent CCA tumor nodules and identified a gene expression pattern associated with chromosomal instability, known as CIN25. Similarly, mate-pair sequencing of the murine CCA cells revealed chromosomal missegregation with gains and losses of several whole chromosomes demonstrating aneuploidy. Of the CIN25 genes, forkhead box M1 (Foxm1), a key cell cycle regulator, was the most significantly upregulated CIN25 gene product. Accordingly, small interfering RNA (siRNA)-mediated silencing of YAP as well as FOXM1 inhibition with thiostrepton induced CCA cell death. These preclinical data imply a role for YAP-mediated chromosomal instability in cholangiocarcinoma, and suggest FOXM1 inhibition as a therapeutic target for CCA.

Two faces of Hippo: activate or suppress the Hippo pathway in cancer

The Hippo pathway has generated considerable interest in recent years because of its involvement in several key hallmarks of cancer progression and metastasis. Research on the Hippo signaling pathway in cancer has been used to determine the activity of yes-associated protein (YAP) in tumorigenesis and disease progression. Previous studies have shown that the Hippo pathway can be used as a target to inhibit YAP activity and is a viable treatment for cancer. However, more studies are required to further advance our understanding of the Hippo signaling pathway in cancer. It has been shown that knockout of serine/threonine-kinases LATS1/2 in the Hippo pathway suppresses cancer immunity in mice. In addition, suppression of the oncogene YAP could contribute toward cancer immune therapy. Therefore, regulation of Hippo signaling can be an attractive alternative strategy for cancer treatment. This review will provide a summary of currently known compounds that activate or suppress the Hippo pathway.

Clinicopathological Significance of Large Tumor Suppressor (LATS) Expression in Gastric Cancer

Purpose

The aims of this study were to evaluate the expression of the large tumor suppressor (LATS) genes LATS1 and LATS2 by immunohistochemical staining of gastric cancer, and to evaluate the clinicopathological significance of LATS expression and its correlation with overall survival (OS).

Materials and Methods

LATS1 and LATS2 expression in a tissue microarray was detected by immunohistochemistry, using 264 gastric cancer specimens surgically resected between July 2006 and December 2009.

Results

Low expression of LATS1 was significantly associated with more advanced American Joint Committee on Cancer (AJCC) stage (P=0.001) and T stage (P=0.032), lymph node (LN) metastasis (P=0.040), perineural invasion (P=0.042), poor histologic grade (P=0.007), and diffuse-type histology by the Lauren classification (P=0.033). Low expression of LATS2 was significantly correlated with older age (≥65, P=0.027), more advanced AJCC stage (P=0.001) and T stage (P=0.001), LN metastasis (P=0.004), perineural invasion (P=0.004), poor histologic grade (P<0.001), and diffuse-type histology by the Lauren classification (P<0.001). Kaplan-Meier survival analysis revealed significantly poor OS rates in the groups with low LATS1 (P=0.037) and LATS2 (P=0.037) expression.

Conclusions

Expression of LATS1 or LATS2 is a significant marker for a good prognosis in patients with gastric cancer.

Loss of large tumor suppressor 1 promotes growth and metastasis of gastric cancer cells through upregulation of the YAP signaling

Accumulating evidence shows that large tumor suppressor 1 (LATS1) as a novel resident governor of cellular homeostasis is implicated in multiple tumorigenic properties including cell growth, apoptosis and metastasis. However, the contribution of LATS1 to gastric carcinoma (GC) remains unclear. The correlation of LATS1 expression with clinicopathologic characteristics, GC prognosis and recurrence was analyzed by immunohistochemistry, Univariate and Kaplan-Meier analysis. Functional experiments were performed to investigate biological behaviors of GC cells and underlying molecular mechanisms. Tumor growth and metastasis was assessed in vivo using orthotopic implantation GC models in severe combined immune deficiency (SCID) mice. Consequently, decreased LATS1 expression was significantly associated with the lymph node metastasis, poor prognosis and recurrence. Ectopic expression of LATS1 decreased GC cell proliferation and invasion in vitro and inhibited tumor growth and liver metastasis in vivo, but depletion of LATS1 expression restored the invasive phenotype. Further observation indicated that YAP pathway was required for LATS1-induced inhibition of cell growth and invasion, and LATS1 restrained nuclear transfer of YAP, downregulated YAP, PCNA, CTGF, MMP-2, MMP-9, Bcl-2 and CyclinD1 expression and upregulated p-YAP and Bax expression. Our findings suggest that LATS1 is a potential candidate tumor suppressor and inhibits the growth and metastasis of GC cells via downregulation of the YAP signaling.

Increased YAP Activation Is Associated With Hepatic Cyst Epithelial Cell Proliferation in ARPKD/CHF

Autosomal recessive polycystic kidney disease/congenital hepatic fibrosis (ARPKD/CHF) is a rare but fatal genetic disease characterized by progressive cyst development in the kidneys and liver. Liver cysts arise from aberrantly proliferative cholangiocytes accompanied by pericystic fibrosis and inflammation. Yes-associated protein (YAP), the downstream effector of the Hippo signaling pathway, is implicated in human hepatic malignancies such as hepatocellular carcinoma, cholangiocarcinoma, and hepatoblastoma, but its role in hepatic cystogenesis in ARPKD/CHF is unknown. We studied the role of the YAP in hepatic cyst development using polycystic kidney (PCK) rats, an orthologous model of ARPKD, and in human ARPKD/CHF patients. The liver cyst wall epithelial cells (CWECs) in PCK rats were highly proliferative and exhibited expression of YAP. There was increased expression of YAP target genes, Ccnd1 (cyclin D1) and Ctgf (connective tissue growth factor), in PCK rat livers. Extensive expression of YAP and its target genes was also detected in human ARPKD/CHF liver samples. Finally, pharmacological inhibition of YAP activity with verteporfin and short hairpin (sh) RNA-mediated knockdown of YAP expression in isolated liver CWECs significantly reduced their proliferation. These data indicate that increased YAP activity, possibly through dysregulation of the Hippo signaling pathway, is associated with hepatic cyst growth in ARPKD/CHF.

WWC2 is an independent prognostic factor and prevents invasion via Hippo signalling in hepatocellular carcinoma

WWC family proteins negatively regulate HEK293 cell proliferation and organ growth by suppressing the transcriptional activity of Yes‐associated protein (YAP), a major effector of the Hippo pathway. The function of the scaffolding protein WWC1 (also called KIBRA) has been intensively studied in cells and animal models. However, the expression and clinicopathologic significance of WWC2 in cancer are poorly characterized. This study aimed to clarify the biological function and mechanism of action of WWC2 in hepatocellular carcinoma (HCC). Retrospective analysis revealed WWC2 was significantly down‐regulated in 95 clinical HCC tissues compared to the paired adjacent non‐cancerous tissues. Moreover, loss of WWC2 expression was significantly associated with advanced clinicopathological features, including venous infiltration, larger tumour size and advanced TNM stage. Positive WWC2 expression was associated with significantly better 5‐year overall survival, and WWC2 was an independent prognostic factor for overall survival in HCC. Moreover, we confirmed WWC2 inhibits HCC cell invasive ability in vitro. Elevated YAP expression was also observed in the same cohort of HCC tissues. Pearson's correlation coefficient analysis indicated WWC2 expression correlated inversely with nuclear YAP protein expression in HCC. Mechanistically, we confirmed overexpression of WWC2 suppresses the invasive and metastatic potential of HCC cells by activating large tumour suppressor 1 and 2 kinases (LATS1/2), which in turn phosphorylates the transcriptional co‐activator YAP. Overall, this study indicates WWC2 functions as a tumour suppressor by negatively regulating the Hippo signalling pathway and may serve as a prognostic marker in HCC.

Platelet-derived growth factor regulates YAP transcriptional activity via Src family kinase dependent tyrosine phosphorylation

The Hippo pathway effector YAP is implicated in the pathogenesis of cholangiocarcinoma (CCA). The Hippo pathway relies on signaling cross talk for its regulation. Given the importance of platelet derived growth factor receptor (PDGFR) signaling in CCA biology, our aim was to examine potential YAP regulation by PDGFR. We employed human and mouse CCA specimens and cell lines for these studies. Initially, we confirmed upregulation of PDGFRβ and PDGFR ligands in human and mouse CCA specimens and cell lines. YAP, a transcriptional co-activator, was localized to the nucleus in human CCA specimens and a cell line, as well as patient derived xenografts (PDX). PDGFR pharmacologic inhibition led to a redistribution of YAP from the nucleus to cytosol and downregulation of YAP target genes in a human CCA cell line. siRNA silencing of PDGFR-β similarly downregulated YAP target genes. YAP activation (nuclear localization and target gene expression) was regulated by Src family kinases (SFKs) downstream of PDGFR. SFK activity resulted in phosphorylation of YAP on tyrosine³⁵⁷ (YAP^Y357 ). The importance of YAP^Y357 phosphorylation in regulating YAP activation was confirmed utilizing the SB-1 cell line, a mouse cell line expressing YAP S127A precluding canonical serine phosphorylation. PDGFR inhibition decreased cellular abundance of the survival protein Mcl-1, a known YAP target gene, and accordingly increased cell death in CCA cells in vitro and in vivo. These preclinical data demonstrate that a PDGFR-SFK cascade regulates YAP activation via tyrosine phosphorylation in CCA. Inhibiting this cascade may provide a viable therapeutic strategy for this human malignancy.

Glypican-3: A promising biomarker for hepatocellular carcinoma diagnosis and treatment

Liver cancer is the second leading cause of cancer-related deaths, and hepatocellular carcinoma (HCC) is the most common type. Therefore, molecular targets are urgently required for the early detection of HCC and the development of novel therapeutic approaches. Glypican-3 (GPC3), an oncofetal proteoglycan anchored to the cell membrane, is normally detected in the fetal liver but not in the healthy adult liver. However, in HCC patients, GPC3 is overexpressed at both the gene and protein levels, and its expression predicts a poor prognosis. Mechanistic studies have revealed that GPC3 functions in HCC progression by binding to molecules such as Wnt signaling proteins and growth factors. Moreover, GPC3 has been used as a target for molecular imaging and therapeutic intervention in HCC. To date, GPC3-targeted magnetic resonance imaging, positron emission tomography, and near-infrared imaging have been investigated for early HCC detection, and various immunotherapeutic protocols targeting GPC3 have been developed, including the use of humanized anti-GPC3 cytotoxic antibodies, treatment with peptide/DNA vaccines, immunotoxin therapies, and genetic therapies. In this review, we summarize the current knowledge regarding the structure, function, and biology of GPC3 with a focus on its clinical potential as a diagnostic molecule and a therapeutic target in HCC immunotherapy.

YAP and the Hippo pathway in pediatric cancer

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

Novel Advances in Understanding of Molecular Pathogenesis of Hepatoblastoma: A Wnt/β-Catenin Perspective

Hepatoblastoma is the most common pediatric liver malignancy, typically striking children within the first 3 years of their young lives. While advances in chemotherapy and newer surgical techniques have improved survival in patients with localized disease, unfortunately, for the 25% of patients with metastasis, the overall survival remains poor. These tumors, which are thought to arise from hepatic progenitors or hepatoblasts, hence the name hepatoblastoma, can be categorized by histological subtyping based on their level of cell differentiation. Genomic and histological analysis of human tumor samples has shown exon-3 deletions or missense mutations in gene coding for β-catenin, a downstream effector of the Wnt signaling pathway, in up to 90% of hepatoblastoma cases. The current article will review key aberrations in molecular pathways that are implicated in various subtypes of hepatoblastoma with an emphasis on Wnt signaling. It will also discuss cooperation among components of pathways such as β-catenin and Yes-associated protein in cancer development. Understanding the complex network of molecular signaling in oncogenesis will undoubtedly aid in the discovery of new therapeutics to help combat hepatoblastoma.

Hippo Signaling in the Liver Regulates Organ Size, Cell Fate, and Carcinogenesis

The Hippo signaling pathway, also known as the Salvador-Warts-Hippo pathway, is a regulator of organ size. The pathway takes its name from the Drosophila protein kinase, Hippo (STK4/MST1 and STK3/MST2 in mammals), which, when inactivated, leads to considerable tissue overgrowth. In mammals, MST1 and MST2 negatively regulate the transcriptional co-activators yes-associated protein 1 and WW domain containing transcription regulator 1 (WWTR1/TAZ), which together regulate expression of genes that control proliferation, survival, and differentiation. Yes-associated protein 1 and TAZ activation have been associated with liver development, regeneration, and tumorigenesis. How their activity is dynamically regulated in these contexts is just beginning to be elucidated. We review the mechanisms of Hippo signaling in the liver and explore outstanding questions for future research.

Loss of EGFR-ASAP1 signaling in metastatic and unresectable hepatoblastoma

Hepatoblastoma (HBL), the most common childhood liver cancer is cured with surgical resection after chemotherapy or with liver transplantation if local invasion and multifocality preclude resection. However, variable survival rates of 60-80% and debilitating chemotherapy sequelae argue for more informed treatment selection, which is not possible by grading the Wnt-β-catenin over activity present in most HBL tumors. A hypothesis-generating whole transcriptome analysis shows that HBL tumors removed at transplantation are enriched most for cancer signaling pathways which depend predominantly on epidermal growth factor (EGF) signaling, and to a lesser extent, on aberrant Wnt-β-catenin signaling. We therefore evaluated whether EGFR, ASAP1, ERBB2 and ERBB4, which signal downstream after ligation of EGF, and which show aberrant expression in several other invasive cancers, would also predict HBL tumor invasiveness. Immunohistochemistry of HBL tumors (n = 60), which are histologically heterogeneous, shows that compared with well-differentiated fetal cells, less differentiated embryonal and undifferentiated small cells (SCU) progressively lose EGFR and ASAP1 expression. This trend is exaggerated in unresectable, locally invasive or metastatic tumors, in which embryonal tumor cells are EGFR-negative, while SCU cells are EGFR-negative and ASAP1-negative. Loss of EGFR-ASAP1 signaling characterizes undifferentiated and invasive HBL. EGFR-expressing HBL tumors present novel therapeutic targeting opportunities.

Expression and significance of Hippo/YAP signaling in glioma progression

Dysregulation of Hippo/YAP signaling leads to aberrant cell growth and neoplasia. Although the roles and regulation of Hippo/YAP signaling were extensively studied in cancer biology recently, study systematically checking the expression pattern of core components of this pathway at the tumor tissue level remains lacking. In this study, we thoroughly examined the profile of core components of Hippo/YAP signaling in patient specimens both at the mRNA and at protein levels. We found that the mRNA level of YAP1/TAZ and their target genes, CRY61, CTGF, and BIRC5, was remarkably amplified in glioma tissues. Consistently, the protein level of YAP1/TAZ increased and meanwhile those of p-YAP1/p-TAZ and LATS1/2 decreased in gliomas. Unexpectedly, both the mRNA and protein levels of MST1/2 increased in the glioma tissues, inconsistent with its presumed tumor suppressor identity. In addition, over-expression of LATS2 decreased, while over-expression of YPA1 increased the cell proliferation ability. Furthermore, based on the data from the free public database, YAP1/TAZ and BIRC5 were positively associated with the prognosis of glioma patients, while LATS1/2 exhibited negative correlation with the glioma patient prognosis. Collectively, we deduce that, in glioma tissue context, MST1/2 may not be the essential component of the hippo/YAP pathway. Moreover, our findings uncover a new evidence supporting that YAP1/TAZ-BIRC5 might be abnormally activated due to LATS1/2 down-regulation, which in turn promote the occurrence and development of gliomas, paving the way to identify the potential therapeutic molecular target for gliomas.

YAP Subcellular Localization and Hippo Pathway Transcriptome Analysis in Pediatric Hepatocellular Carcinoma

Pediatric hepatocellular carcinoma (HCC) is a rare tumor which is associated with an extremely high mortality rate due to lack of effective chemotherapy. Recently, the Hippo pathway and its transcriptional co-activator Yes-associated protein (YAP) have been shown to play a role in hepatocyte proliferation and development of HCC in animal models. Therefore, we sought to examine the activity of YAP and the expression of Hippo pathway components in tumor and non-neoplastic liver tissue from 7 pediatric patients with moderately differentiated HCC. None of the patients had underlying cirrhosis or viral hepatitis, which is commonly seen in adults with HCC. This highlights a major difference in the pathogenesis of HCC between children and adults. We found a statistically significant increase in YAP nuclear localization in 100% of tumors. YAP target gene (CCNE1, CTGF, Cyr61) mRNA expression was also increased in the tumors that had the most significant increase in YAP nuclear localization. Based on Ki67 co-localization studies YAP nuclear localization was not simply a marker of proliferation. Our results demonstrate a clear increase in YAP activity in moderately differentiated pediatric HCC, providing evidence that it may play an important role in tumor survival and propagation.

Yap reprograms glutamine metabolism to increase nucleotide biosynthesis and enable liver growth

The Hippo pathway is an important regulator of organ size and tumorigenesis. It is unclear, however, how Hippo signalling provides the cellular building blocks required for rapid growth. Here, we demonstrate that transgenic zebrafish expressing an activated form of the Hippo pathway effector Yap1 (also known as YAP) develop enlarged livers and are prone to liver tumour formation. Transcriptomic and metabolomic profiling identify that Yap1 reprograms glutamine metabolism. Yap1 directly enhances glutamine synthetase (glul) expression and activity, elevating steady-state levels of glutamine and enhancing the relative isotopic enrichment of nitrogen during de novo purine and pyrimidine biosynthesis. Genetic or pharmacological inhibition of GLUL diminishes the isotopic enrichment of nitrogen into nucleotides, suppressing hepatomegaly and the growth of liver cancer cells. Consequently, Yap-driven liver growth is susceptible to nucleotide inhibition. Together, our findings demonstrate that Yap1 integrates the anabolic demands of tissue growth during development and tumorigenesis by reprogramming nitrogen metabolism to stimulate nucleotide biosynthesis.

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.

Markers of Hippo-Pathway Activity in Tumor Forming Liver Lesions

Hepatocellular Carcinoma (HCC) is a lethal cancer worldwide. Recently, the hippo signaling pathway has been implicated in tumorigenesis of HCC and other malignant tumors. Aim of the study was therefore to evaluate the hippo signaling pathway activity and its clinico-pathological associations and crosstalk in different tumor forming hepatocellular lesions (HCC, hepatocellular adenoma (HCA), focal nodular hyperplasia (FNH) and cirrhosis). A tissue micro array (TMA) from paired human tumorous and non-tumorous (NT) tissue samples of HCC (n = 92), HCA (n = 25), FNH (n = 28) and cirrhosis (n = 28; no NT) was constructed. The hippo-pathway related proteins of MST1/2, (nuclear(n)/cytoplasmic(c)) YAP and (phospho(p)) TAZ and interactors as Glypican3, RASSF1a, pAKT, pERK and pP70S6K were evaluated by immunohistochemistry (IHC). Proliferation was assessed by Ki67-IHC and apoptosis by TUNEL-technique. MST1/2- and nYAP-immunoreactivity was associated with lymph node status (p = 0.048, p = 0.001), higher grading (p = 0.012, p = 0.24) and unfavorable relapse-free survival (p = 0.004, p = 0.003). MST1/2, c/nYAP and pTAZ were significantly different between HCC/NT (p < 0.001, p = 0.029, p < 0.001, p < 0.001) and mono-/polyclonal hepatocellular lesions (HCC/HCA vs. FNH/cirrhosis; all p ≤ 0.001). Phospho-TAZ-negativity and nYAP-positivity were almost exclusively and MST1/2 exclusively detected in HCC. MST1/2 correlated with pP70S6K (p = 0.002), pERK (p = 0.042), RASSF1a-IRS (p = 0.002) and GPC3 (p < 0.001) and nYAP with GPC3 (p = 0.025), higher Ki67-indices (p = 0.016) and lower apoptosis rate (p = 0.078). MST1/2 and nYAP are unfavorable prognostic markers associated with an aggressive tumor-phenotype in HCC. Positive nYAP- and negative pTAZ-immunostaining were strong indicators of a monoclonal hepatocellular lesion. The unexpected findings for MST1/2 remain to be elucidated.

The Hippo pathway in intestinal regeneration and disease

The Hippo pathway is a signalling cascade conserved from Drosophila melanogaster to mammals. The mammalian core kinase components comprise MST1 and MST2, SAV1, LATS1 and LATS2 and MOB1A and MOB1B. The transcriptional co-activators YAP1 and TAZ are the downstream effectors of the Hippo pathway and regulate target gene expression. Hippo signalling has crucial roles in the control of organ size, tissue homeostasis and regeneration, and dysregulation of the Hippo pathway can lead to uncontrolled cell growth and malignant transformation. Mammalian intestine consists of a stem cell compartment as well as differentiated cells, and its ability to regenerate rapidly after injury makes it an excellent model system to study tissue homeostasis, regeneration and tumorigenesis. Several studies have established the important role of the Hippo pathway in these processes. In addition, crosstalk between Hippo and other signalling pathways provides tight, yet versatile, regulation of tissue homeostasis. In this Review, we summarize studies on the role of the Hippo pathway in the intestine on these physiological processes and the underlying mechanisms responsible, and discuss future research directions and potential therapeutic strategies targeting Hippo signalling in intestinal disease.

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.

Environmental Ligands of the Aryl Hydrocarbon Receptor and Their Effects in Models of Adult Liver Progenitor Cells

The toxicity of environmental and dietary ligands of the aryl hydrocarbon receptor (AhR) in mature liver parenchymal cells is well appreciated, while considerably less attention has been paid to their impact on cell populations exhibiting phenotypic features of liver progenitor cells. Here, we discuss the results suggesting that the consequences of the AhR activation in the cellular models derived from bipotent liver progenitors could markedly differ from those in hepatocytes. In contact-inhibited liver progenitor cells, the AhR agonists induce a range of effects potentially linked with tumor promotion. They can stimulate cell cycle progression/proliferation and deregulate cell-to-cell communication, which is associated with downregulation of proteins forming gap junctions, adherens junctions, and desmosomes (such as connexin 43, E-cadherin, β-catenin, and plakoglobin), as well as with reduced cell adhesion and inhibition of intercellular communication. At the same time, toxic AhR ligands may affect the activity of the signaling pathways contributing to regulation of liver progenitor cell activation and/or differentiation, such as downregulation of Wnt/β-catenin and TGF-β signaling, or upregulation of transcriptional targets of YAP/TAZ, the effectors of Hippo signaling pathway. These data illustrate the need to better understand the potential role of liver progenitors in the AhR-mediated liver carcinogenesis and tumor promotion.

Melanoma cell adhesion molecule stimulates yes-associated protein transcription by enhancing CREB activity via c-Jun/c-Fos in hepatocellular carcinoma cells

Dysfunction of the yes-associated protein (YAP) signaling pathway has previously been associated with liver tumorigenesis. Recently, the membrane protein melanoma cell adhesion molecule (MCAM) was identified as a novel, hepatocellular carcinoma (HCC)-specific YAP target protein that promotes carcinogenesis in HCC. However, whether MCAM conversely regulates YAP remains unknown. The aim of the current study was to demonstrate whether and how MCAM regulates YAP in HCC cells. The present study demonstrated that MCAM has a positive effect on the regulation of YAP activity and expression. Mechanistically, MCAM stimulated YAP transcription through its downstream effector c-Jun/c-Fos heterodimer. Gain and loss of function analysis by the present study indicated that c-Jun/c-Fos is capable of inducing cAMP response element-binding protein activation, which is a transcription factor that directly binds to the YAP promoter. Finally, it was identified that an impaired transformative phenotype in MCAM- or c-Jun/c-Fos-depleted HCC cells could be partially rescued by simultaneous overexpression of YAP, suggesting that YAP may function as a downstream effector of the MCAM-c-Jun/c-Fos signaling pathway. Collectively, a complete, positive, auto-regulatory loop was established by the present study, in which YAP is not only an upstream regulator, but also a downstream target of MCAM in HCC cells.

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.

Adult cell plasticity in vivo: de-differentiation and transdifferentiation are back in style

Biologists have long been intrigued by the possibility that cells can change their identity, a phenomenon known as cellular plasticity. The discovery that terminally differentiated cells can be experimentally coaxed to become pluripotent has invigorated the field, and recent studies have demonstrated that changes in cell identity are not limited to the laboratory. Specifically, certain adult cells retain the capacity to de-differentiate or transdifferentiate under physiological conditions, as part of an organ's normal injury response. Recent studies have highlighted the extent to which cell plasticity contributes to tissue homeostasis, findings that have implications for cell-based therapy.

Deacetylation of tumor-suppressor MST1 in Hippo pathway induces its degradation through HBXIP-elevated HDAC6 in promotion of breast cancer growth

Reduction or loss of tumor-suppressor mammalian STE20-like kinase 1 (MST1) in Hippo pathway contributes to the tumorigenesis. However, the mechanism leading to reduction of MST1 in cancers remains poorly understood. In this study, we explored the hypothesis that the oncoprotein hepatitis B X-interacting protein (HBXIP) is involved in the reduction of MST1 in breast cancer. Immunohistochemical analysis of tissue microarrays revealed that the expression of HBXIP was negatively associated with that of MST1 in 98 clinical breast tissue samples. Then we found that HBXIP could posttranslationally downregulate MST1 in breast cancer cells. Mechanistically, we identified that MST1 could be acetylated on its lysine 35 residue in the cells. Strikingly, the treatment with trichostatin A, an inhibitor of histone deacetylases (HDACs), markedly increased the levels of MST1 acetylation and protein in the cells. Interestingly, the oncoprotein HBXIP could significantly inhibit acetylation of MST1, resulting in the reduction of MST1 protein. Notably, we revealed that the HDAC6 could reduce the protein levels of MST1 through deacetylation modification of MST1 in the cells. Moreover, our data revealed that HBXIP upregulated HDAC6 at the levels of mRNA and protein by activating transcription factor nuclear factor-κB. Deacetylation of MST1 promoted the interaction of MST1 with HSC70 in the cells, resulting in a lysosome-dependent degradation of MST1 via chaperone-mediated autophagy (CMA). Functionally, the reduction of tumor-suppressor MST1 mediated by HBXIP promoted the growth of breast cancer cells in vitro and in vivo. Thus we conclude that the deacetylation of MST1 mediated by HBXIP-enhanced HDAC6 results in MST1 degradation in a CMA manner in promotion of breast cancer growth. Our finding provides new insights into the mechanism of tumor-suppressor MST1 reduction in breast cancer.

SerpinB3 and Yap Interplay Increases Myc Oncogenic Activity

SerpinB3 has been recently described as an early marker of liver carcinogenesis, but the potential mechanistic role of this serpin in tumor development is still poorly understood. Overexpression of Myc often correlates with more aggressive tumour forms, supporting its involvement in carcinogenesis. Yes-associated protein (Yap), the main effector of the Hippo pathway, is a central regulator of proliferation and it has been found up-regulated in hepatocellular carcinomas. The study has been designed to investigate and characterize the interplay and functional modulation of Myc by SerpinB3 in liver cancer. Results from this study indicate that Myc was up-regulated by SerpinB3 through calpain and Hippo-dependent molecular mechanisms in transgenic mice and hepatoma cells overexpressing human SerpinB3, and also in human hepatocellular carcinomas. Human recombinant SerpinB3 was capable to inhibit the activity of Calpain in vitro, likely reducing its ability to cleave Myc in its non oncogenic Myc-nick cytoplasmic form. SerpinB3 indirectly increased the transcription of Myc through the induction of Yap pathway. These findings provide for the first time evidence that SerpinB3 can improve the production of Myc through direct and indirect mechanisms that include the inhibition of generation of its cytoplasmic form and the activation of Yap pathway.

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.

Protein-protein interactions among signaling pathways may become new therapeutic targets in liver cancer (Review)

Numerous signaling pathways have been shown to be dysregulated in liver cancer. In addition, some protein-protein interactions are prerequisite for the uncontrolled activation or inhibition of these signaling pathways. For instance, in the PI3K/AKT signaling pathway, protein AKT binds with a number of proteins such as mTOR, FOXO1 and MDM2 to play an oncogenic role in liver cancer. The aim of the present review was to focus on a series of important protein-protein interactions that can serve as potential therapeutic targets in liver cancer among certain important pro-carcinogenic signaling pathways. The strategies of how to investigate and analyze the protein-protein interactions are also included in this review. A survey of these protein interactions may provide alternative therapeutic targets in liver cancer.

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.

Emerging role of Hpo signaling and YAP in hepatocellular carcinoma

Hepatocellular carcinoma (HCC) is the sixth most common cancer and the third most common cause of cancer-related mortality worldwide. Due to the poor prognosis and limited therapeutic options, there is great interest in further understanding better the molecular underpinnings and potential molecular targets associated with HCC. The Hippo (Hpo) signaling pathway and YAP, its principal downstream effector, represent an innovative area of research in HCC. Pioneered in Drosophila melanogaster, the Hpo cascade controls tissue homeostasis including organ size, cell proliferation, apoptosis, as well as cell-cycle regulation and differentiation. This conserved kinase cascade in mammals depends on central control by the tumor suppressor mammalian sterile 20-like kinase 1/2 (Mst1/2). The Mst1/2 commences the downstream kinase cascade, ultimately activating the oncoprotein YAP and allowing its physical association with downstream targets to enhance the gene expression signatures that are involved in proliferation and survival. Alterations in YAP expression and defective regulation of other key Hpo pathway members, such as Mst1/2, Salvador, neurofibromatosis and Mer (Nf2/mer), large tumor suppressor homolog 1/2 (Lats1/2), and Mps one binder kinase activator-like 1A and 1B (Mob1) drive carcinogenesis in animal models. The dysregulation of the Hpo pathway – resulting in an unchecked activation of YAP – culminates in the development of a broad range of human tumor types, including HCC. The abrogation of Mst1/2-mediated YAP phosphorylation permits YAP entry into the nucleus in murine models and functions similarly in human HCCs. Chemoresistance mechanisms displayed by HCC tumors occur in a YAP-dependent manner. The HCC specimens exhibit YAP overexpression, and YAP serves as an independent prognostic marker for disease-free survival and overall survival in patients with HCC. Recently, the small molecule inhibitor, verteporfin has been shown to attenuate YAP activity in murine models, perhaps offering a novel therapeutic approach for patients with advanced HCC.

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.

Signalling at tight junctions during epithelial differentiation and microbial pathogenesis

Tight junctions are a component of the epithelial junctional complex, and they form the paracellular diffusion barrier that enables epithelial cells to create cellular sheets that separate compartments with different compositions. The assembly and function of tight junctions are intimately linked to the actomyosin cytoskeleton and, hence, are under the control of signalling mechanisms that regulate cytoskeletal dynamics. Tight junctions not only receive signals that guide their assembly and function, but transmit information to the cell interior to regulate cell proliferation, migration and survival. As a crucial component of the epithelial barrier, they are often targeted by pathogenic viruses and bacteria, aiding infection and the development of disease. In this Commentary, we review recent progress in the understanding of the molecular signalling mechanisms that drive junction assembly and function, and the signalling processes by which tight junctions regulate cell behaviour and survival. We also discuss the way in which junctional components are exploited by pathogenic viruses and bacteria, and how this might affect junctional signalling mechanisms.

IL-33 facilitates oncogene-induced cholangiocarcinoma in mice by an interleukin-6-sensitive mechanism

Cholangiocarcinoma (CCA) is a lethal hepatobiliary neoplasm originating from the biliary apparatus. In humans, CCA risk factors include hepatobiliary inflammation and fibrosis. The recently identified interleukin (IL)-1 family member, IL-33, has been shown to be a biliary mitogen which also promotes liver inflammation and fibrosis. Our aim was to generate a mouse model of CCA mimicking the human disease. Ectopic oncogene expression in the biliary tract was accomplished by the Sleeping Beauty transposon transfection system with transduction of constitutively active AKT (myr-AKT) and Yes-associated protein. Intrabiliary instillation of the transposon-transposase complex was coupled with lobar bile duct ligation in C57BL/6 mice, followed by administration of IL-33 for 3 consecutive days. Tumors developed in 72% of the male mice receiving both oncogenes plus IL-33 by 10 weeks but in only 20% of the male mice transduced with the oncogenes alone. Tumors expressed SOX9 and pancytokeratin (features of CCA) but were negative for HepPar1 (a marker of hepatocellular carcinoma). Substantive overlap with human CCA specimens was revealed by RNA profiling. Not only did IL-33 induce IL-6 expression by human cholangiocytes but it likely facilitated tumor development in vivo by an IL-6-sensitive process as tumor development was significantly attenuated in Il-6(-/-) male animals. Furthermore, tumor formation occurred at a similar rate when IL-6 was substituted for IL-33 in this model.

CONCLUSION

The transposase-mediated transduction of constitutively active AKT and Yes-associated protein in the biliary epithelium coupled with lobar obstruction and IL-33 administration results in the development of CCA with morphological and biochemical features of the human disease; this model highlights the role of inflammatory cytokines in CCA oncogenesis.

Mannose-mediated inhibitory effects of PA-MSHA on invasion and metastasis of hepatocellular carcinoma via EGFR/Akt/IκBβ/NF-κB pathway

BACKGROUND & AIMS

Elevation of high-mannose glycans is a common feature of malignant cells and has been suggested to be the basis for alternative cancer therapy for several years. Here we want to investigate the antitumour effect of pseudomonas aeruginosa-mannosesensitive haemagglutinin (PA-MSHA), a genetically engineered heat-inactivated PA strain with mannose-sensitive binding activity, on hepatocellular carcinoma (HCC).

METHODS

Tumourigenicity and metastatic potentials of HCC were studied after PA-MSHA treatment by utilizing the in vitro/in vivo model of HCC. Expression of apoptosis-associated proteins and epithelial-mesenchymal transition (EMT) related genes were evaluated, and possible signalling pathways involved were investigated.

RESULTS

PA-MSHA induced significant cell proliferation inhibition and cell cycle arrest of HCC through decreasing the levels of cyclins D1, cyclins E, CDK2, CDK4, proliferating cell nuclear antigen (PCNA), and increasing the level of p21 and p27. Moreover, PA-MSHA suppressed the invasion, migration and adhesion of HCC through inhibiting epithelial-mesenchymal transition (EMT). PA-MSHA also inhibited EGFR/Akt/IκBβ/NF-κB pathway and overexpression of NF-κB significantly abrogated PA-MSHA induced EMT inhibition. In addition, competitive inhibition of the mannose binding activity of PA-MSHA by D-mannose significantly blocked its effect on cell cycle arrest and EMT. PA-MSHA also abrogated lung metastasis of HCC and significantly inhibited tumour growth in the in vivo study.

CONCLUSIONS

Our study demonstrated the essential role of EGFR/Akt/IκBβ/NF-κB pathway in the inhibitory effect of PA-MSHA on invasion and metastasis of HCC through suppressing EMT, and revealed an attractive prospect of PA-MSHA as a novel candidate agent in the treatment of HCC.

The membrane protein melanoma cell adhesion molecule (MCAM) is a novel tumor marker that stimulates tumorigenesis in hepatocellular carcinoma

Yes-associated protein (YAP) is overexpressed and has an oncogenic role in hepatocellular carcinoma (HCC). However, whether membrane protein can serve not only as a tumor marker that reflects YAP function but also as a therapeutic target that stimulates tumorigenesis in HCC remains unknown. Here we report that the membrane protein melanoma cell adhesion molecule (MCAM) was under positive regulation by YAP and was highly elevated in HCC cells. Within the MCAM promoter, we found the presence of a cAMP Response Element (CRE; -32 to -25 nt), which is conserved among species and is essential for YAP- and CREB-dependent regulation. Moreover, the interaction between CREB and YAP at the CRE site was dependent on PTPIY-WW domain interactions. However, MCAM expression was low and could not be regulated by YAP in breast and colon cancer cells because of the low levels of the acetyltransferase p300. In HCC cells, high levels of p300 facilitated the binding of YAP to the MCAM promoter, which in turn enhanced histone acetylation and polymerase II recruitment through the dissociation of the deacetylase Sirt1. These results suggest that MCAM is an HCC-specific target of YAP. In clinical serum samples, we found that the serum levels of MCAM were highly elevated in patients with HCC compared with healthy controls and with patients with cirrhosis, hepatitis, colon cancer and breast cancer. MCAM levels were shown to be a slightly better indicator than serum alpha-fetoprotein for predicting HCC. We further demonstrated that MCAM is essential for the survival and transformation of HCC. Mechanistically, MCAM induced translation initiation and the transcriptional activities of c-Jun/c-Fos. In addition, AKT activation had an essential role in the MCAM-promoted binding of eukaryotic initiation factor 4E to c-Jun/c-Fos mRNA. In conclusion, we demonstrated that MCAM may be a potential tumor marker and therapeutic target for the diagnosis and treatment of HCC.

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).

LATS2-mediated YAP1 phosphorylation is involved in HCC tumorigenesis

YAP (yes-associated protein) is a transcriptional co-activator that acts downstream of the Hippo signaling pathway and regulates multiple cellular processes, including proliferation and apoptosis. Although YAP plays an important role in various tumors, the underlying mechanism in hepatocellular carcinoma (HCC) tumorigenesis remains unclear. In this study, we observed that the LATS2 was highly expressed in Bel-7402 and HepG2 cell lines, and LATS2 protein level was negatively correlated with YAP1 in HCC cells. And then, we inhibited LATS2 expression by transfecting with siRNA. Western blot and Immunofluorescent staining analysis demonstrated that LATS2 inhibition decreased the dephosphorylation of YAP1 protein and promoted YAP1 nuclear accumulation in HCC cells. Moreover, Immunoprecipitation assay results also indicated that Yap binds directly to TEAD2 and LATS2 inhibition-mediated dephosphorylation increased the YAP1/TEAD2 association, leading to YAP1/TEAD2 transcriptional activation, which in turn upregulated cell invasion in HCC cells. Taken together, our current data indicated a new regulatory mechanism of YAP1 by the LATS2-mediated phosphorylation that was involved in HCC tumorigenesis.

Yes-associated protein expression is a predictive marker for recurrence of hepatocellular carcinoma after liver transplantation

PURPOSE

To explore the expression of Yes-associated protein (YAP) in hepatocellular carcinoma (HCC) patients, and assess its prognostic value to recurrence of HCC after liver transplantation (LT).

METHODS

Collected data of 105 consecutive patients undergoing LT for HCC were analyzed retrospectively. The immunohistochemistry was used to detect the expression of YAP, Mst1, Lats1/2, pYAP, pLats1/2 and pMst1/2 in tumor tissues. Contingency table and χ(2)-test were used to investigate the correlation between expression of YAP, Mst1, Lats1/2 and clinical characteristics. Univariate survival analysis and Multivariate Cox regression analysis were also performed to analyze the correlation of clinical and pathological factors with tumor recurrence after LT. The Kaplan-Meier method and log-rank test were used to analyze HCC-specific disease-free survival (DFS) rate.

RESULTS

Forty patients fulfilled Milan criteria with 1-, 2-, 3- and 5-years DFS of 86.7, 84.6, 84, 84%, respectively. The positive rates of YAP, Lats1/2, Mst1 in HCC were 51.4, 45.7, 64.8%, respectively. YAP expression in HCC tumors was significantly associated with tumor size (p = 0.041), venous infiltration (p = 0.002), AJCC tumor stage (p = 0.027). Lats1/2 expression was significantly associated with tumor size (p = 0.001) and AJCC tumor stage (p = 0.019). Mst1 expression was also significantly associated with tumor size (p = 0.042). HCC-specific DFS was significantly longer for patients with YAP negative expression compared with patients with YAP positive expression (1-, 2-, 3- and 5-years DFS of 71.7, 65.3, 65.3, 65.3 vs. 42.5, 36.6, 32.5, 30.4%, respectively, log-rank = 12.89, p < 0.001). Multivariate Cox regression analysis indicated that YAP expression (HR = 2.011, p = 0.020) in HCC was an independent prognostic factor for HCC-specific DFS after liver transplantation.

CONCLUSIONS

YAP is an independent prognostic marker for tumor recurrence for HCC patients after liver transplantation.

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

BACKGROUND & AIMS

Although the growth suppressing Hippo pathway has been implicated in hepatocellular carcinoma (HCC) pathogenesis, it is unknown at which stage of hepatocarcinogenesis its dysregulation occurs. We investigated in rat and human preneoplastic lesions whether overexpression of the transcriptional co-activator Yes-associated protein (YAP) is an early event.

METHODS

The experimental model used is the resistant-hepatocyte (R-H) rat model. Gene expression was determined by qRT-PCR or immunohistochemistry. Forward genetic experiments were performed in human HCC cells and in murine oval cells.

RESULTS

All foci of preneoplastic hepatocytes, generated in rats 4weeks after diethylnitrosamine (DENA) treatment, displayed YAP accumulation. This was associated with down-regulation of the β-TRCP ligase, known to mediate YAP degradation, and of microRNA-375, targeting YAP. YAP accumulation was paralleled by the up-regulation of its target genes. Increased YAP expression was also observed in human early dysplastic nodules and adenomas. Animal treatment with verteporfin (VP), which disrupts the formation of the YAP-TEAD complex, significantly reduced preneoplastic foci and oval cell proliferation. In vitro experiments confirmed that VP-mediated YAP inhibition impaired cell growth in HCC and oval cells; notably, oval cell transduction with wild type or active YAP conferred tumorigenic properties in vitro and in vivo.

CONCLUSIONS

These results suggest that (i) YAP overexpression is an early event in rat and human liver tumourigenesis; (ii) it is critical for the clonal expansion of carcinogen-initiated hepatocytes and oval cells, and (iii) VP-induced disruption of the YAP-TEAD interaction may provide an important approach for the treatment of YAP-overexpressing cancers.

Adhesion molecule-mediated hippo pathway modulates hemangioendothelioma cell behavior

Hemangioendotheliomas are categorized as intermediate-grade vascular tumors that are commonly localized in the lungs and livers. The regulation of this tumor cell's proliferative and apoptotic mechanisms is ill defined. We recently documented an important role for Hippo pathway signaling via endothelial cell adhesion molecules in brain microvascular endothelial cell proliferation and apoptosis. We found that endothelial cells lacking cell adhesion molecules escaped from contact inhibition and exhibited abnormal proliferation and apoptosis. Here we report on the roles of adherens junction molecule modulation of survivin and the Hippo pathway in the proliferation and apoptosis of a murine hemangioendothelioma (EOMA) cell. We demonstrated reduced adherens junction molecule (CD31 and VE-cadherin) expression, increased survivin and Ajuba expression, and a reduction in Hippo pathway signaling resulting in increased proliferation and decreased activation of effector caspase 3 in postconfluent EOMA cell cultures. Furthermore, we confirmed that YM155, an antisurvivin drug that interferes with Sp1-survivin promoter interactions, and survivin small interference RNA (siRNA) transfection elicited induction of VE-cadherin, decreased Ajuba expression, increased Hippo pathway and caspase activation and apoptosis, and decreased cell proliferation. These findings support the importance of the Hippo pathway in hemangioendothelioma cell proliferation and survival and YM155 as a potential therapeutic agent in this category of vascular tumors.