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

Yes-associated protein (YAP) binds to HIF-1α and sustains HIF-1α protein stability to promote hepatocellular carcinoma cell glycolysis under hypoxic stress

BACKGROUND

Hypoxia-inducible factor 1α (HIF-1α) is essential in hepatocellular carcinoma (HCC) glycolysis and progression. Yes-associated protein (YAP) is a powerful regulator and is overexpressed in many cancers, including HCC. The regulatory mechanism of YAP and HIF-1α in HCC glycolysis is unknown.

METHODS

We detected YAP expression in 54 matched HCC tissues and the adjacent noncancerous tissues. The relationship between YAP mRNA expression and that of HIF-1α was analyzed using The Cancer Genome Atlas HCC tissue data. We cultured HepG2 and Huh7 HCC cells under normoxic (20% O2) and hypoxic (1% O2) conditions, and measured the lactate and glucose levels, migration and invasive capability, and the molecular mechanism of HCC cell glycolysis and progression.

RESULTS

In this study, we detected YAP expression in 54 matched HCC tissues and the adjacent noncancerous tissues. We observed that hypoxia-induced YAP activation is crucial for accelerating HCC cell glycolysis. Hypoxia inhibited the Hippo signaling pathway and promoted YAP nuclear localization, and decreased phosphorylated YAP expression in HCC cells. YAP knockdown inhibited HCC cell glycolysis under hypoxic. Mechanistically, hypoxic stress in the HCC cells promoted YAP binding to HIF-1α in the nucleus and sustained HIF-1α protein stability to bind to PKM2 gene and directly activates PKM2 transcription to accelerate glycolysis.

CONCLUSIONS

Our findings describe a new regulatory mechanism of hypoxia-mediated HCC metabolism, and YAP might be a promising therapeutic target in HCC.

The role of YAP/TAZ activity in cancer metabolic reprogramming

In contrast to normal cells, which use the aerobic oxidation of glucose as their main energy production method, cancer cells prefer to use anaerobic glycolysis to maintain their growth and survival, even under normoxic conditions. Such tumor cell metabolic reprogramming is regulated by factors such as hypoxia and the tumor microenvironment. In addition, dysregulation of certain signaling pathways also contributes to cancer metabolic reprogramming. Among them, the Hippo signaling pathway is a highly conserved tumor suppressor pathway. The core oncosuppressive kinase cascade of Hippo pathway inhibits the nuclear transcriptional co-activators YAP and TAZ, which are the downstream effectors of Hippo pathway and oncogenic factors in many solid cancers. YAP/TAZ function as key nodes of multiple signaling pathways and play multiple regulatory roles in cancer cells. However, their roles in cancer metabolic reprograming are less clear. In the present review, we examine progress in research into the regulatory mechanisms of YAP/TAZ on glucose metabolism, fatty acid metabolism, mevalonate metabolism, and glutamine metabolism in cancer cells. Determining the roles of YAP/TAZ in tumor energy metabolism, particularly in relation to the tumor microenvironment, will provide new strategies and targets for the selective therapy of metabolism-related cancers.

A time for YAP1: Tumorigenesis, immunosuppression and targeted therapy

YAP1 is one of the most important effectors of the Hippo pathway and has crosstalk with other cancer promoting pathways. YAP1 contributes to cancer development in various ways that include promoting malignant phenotypes, expansion of cancer stem cells and drug resistance of cancer cells. Because pharmacologic or genetic inhibition of YAP1 suppresses tumor progression and increases the drug sensitivity, targeting YAP1 may open a fertile avenue for a novel therapeutic approach in relevant cancers. Recent enormous studies have established the efficacy of immunotherapy, and several immune checkpoint blockades are in clinical use or in the phase of development to treat various cancer types. Immunosuppression in the tumor microenvironment (TME) induced by cancer cells, immune cells and associated stromal cells promotes tumor progression and causes drug resistance. Accumulated evidences of scientific efforts from the last few years suggest that YAP1 influences macrophages, myeloid-derived suppressor cells and regulatory T-cells to facilitate immunosuppressive TME. Although the underlying mechanisms is not clearly discerned, it is evident that YAP1 activating pathways in different cellular components induce immunosuppressive TME. In this review, we summarize the evidences involved in the dual roles of YAP1 in cancer development and immunosuppression in the TME. We also discuss the possibility of YAP1 as a novel therapeutic target.

TEAD4 exerts pro-metastatic effects and is negatively regulated by miR6839-3p in lung adenocarcinoma progression

Several studies have shown the tumorigenesis role of transcriptional enhancer associate domain (TEAD) proteins; here, we initially explored expression, function and signalling mechanisms of TEAD4 in lung adenocarcinoma (LAD). Both the mRNA and protein levels of TEAD4 were increased in LAD tissues than those in adjacent nontumourous tissues. Besides, database search indicated a poorer clinical outcome in LAD patients with higher TEAD4 expression, revealing its potential tumour-promoting role. Therefore, we conducted cellular experiments to further investigate its effect on tumour phenotypes. Accordingly, TEAD4 showed little impact on LAD cell cycle, proliferation, or apoptosis. However, silencing TEAD4 remarkably attenuated cell migration and invasion capacities. Consistently, several important epithelial-mesenchymal transition (EMT) markers such as E-cadherin and Slug were consequently altered by silencing TEAD4. Furthermore, we identified a novel TEAD4-targeted microRNA, namely miR6839-3p, and confirmed its function in suppressing TEAD4 expression. Finally, the impact of overexpressing miR6839-3p mimics on LAD progression was validated, which showed a similar pattern with TEAD4 knockdown cells. Taken together, our data not only revealed the significant role of TEAD4 in promoting LAD progression and predicting clinical outcome but also distinguished miR6839-3p mimics as a promising therapeutic direction.

Hippo Signaling: Key Emerging Pathway in Cellular and Whole-Body Metabolism

The evolutionarily conserved Hippo pathway is a key regulator of organ size and tissue homeostasis. Its dysregulation is linked to multiple pathological disorders. In addition to regulating development and growth, recent studies show that Hippo pathway components such as MST1/2 and LATS1/2 kinases, as well as YAP/TAZ transcriptional coactivators, are regulated by metabolic pathways and that the Hippo pathway controls metabolic processes at the cellular and organismal levels in physiological and metabolic disease states such as obesity, type 2 diabetes (T2D), nonalcoholic fatty liver disease (NAFLD), cardiovascular disorders, and cancer. In this review we summarize the connection between key Hippo components and metabolism, and how this interplay regulates cellular metabolism and metabolic pathways. The emerging function of Hippo in the regulation of metabolic homeostasis under physiological and pathological conditions is highlighted.

Neuropilin 1 (NRP1) is a novel tumor marker in hepatocellular carcinoma

BACKGROUND

TEA domain transcription factor (TEAD) has an oncogenic role in hepatocellular carcinoma (HCC). However, whether a membrane protein can serve not only as a tumor marker that reflects TEAD function but also as a therapeutic target that stimulates tumorigenesis in HCC remains unknown.

METHODS

Tissue NRP1 was measured using immunohistochemistry. Cell viability, colony formation and caspase3/7 activity were assessed using MTT, soft agar and caspase 3/7 Glo assays, respectively. Serum NRP1 was examined using ELISA and Western blotting.

RESULTS

NRP1 expression was up-regulated by TEAD. We also identified a conserved TEAD-binding motif in the NRP1 promoters, which was essential for the TEAD-NRP1 interaction. NRP1 was upregulated in HCC tissues and cell lines, and knockdown of NRP1 inhibited the transformative phenotypes of HCC cells. Notably, the concentrations of serum NRP1 in the HCC patients were much higher than those of hepatitis B, hepatitis C, cirrhosis, breast cancer, colon cancer, gastric cancer and lung cancer patients. Moreover, serum NRP1 was significantly associated with AFP, γ-GT, Alb, bile acid, ALT, AST, ALP and pre-Alb. The area under the receiver operating characteristic curve (AUC-ROC) for serum NRP1 was 0.971, presenting better diagnostic performance compared to AFP.

CONCLUSIONS

NRP1 is a novel tumor marker in HCC.

Serotonin and YAP/VGLL4 Balance Correlated with Progression and Poor Prognosis of Hepatocellular Carcinoma

YAP-TEAD complex plays an important role in tumorigenesis. 5-HT is proved to upregulate YAP expression by our previous study and VGLL4 is found to compete with YAP for binding to TEAD in several of cancers. Here, we investigated whether 5-HT could affect progression and prognosis of hepatocellular carcinoma (HCC) patients and regulate YAP/VGLL4 balance. We found that 5-HT and YAP/VGLL4 ratio were higher in HCC patients and closely related with progression and poor prognosis. Furthermore, 5-HT level, YAP/VGLL4 ratio and tumor size were proved as independent risk factors of HCC patients in our study. Based on the independent risk factors, nomogram was established to exactly predict prognosis of HCC patients. Additionally, the study revealed that a higher total point of the nomogram was closely correlated with poorer prognosis. As a result, 5-HT might contribute to the progression and poor prognosis of hepatocellular carcinoma via regulating YAP/VGLL4 balance. Therefore, the established nomogram based on the independent risk factors may become an important part of HCC prediction system and YAP/VGLL4 balance may be a potential therapeutic target in future.

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.

High mobility group protein B1 controls liver cancer initiation through yes-associated protein -dependent aerobic glycolysis

Emerging studies have suggested that the Hippo pathway is involved in the tumorigenesis of hepatocellular carcinoma (HCC). However, the key regulator of the Hippo pathway in liver tumor metabolic reprogramming remains elusive. Here, we provide evidence that high mobility group box 1 (HMGB1), a chromosomal protein, plays a role in the regulation of the Hippo pathway during liver tumorigenesis. Cre/loxP recombination-mediated HMGB1 depletion in hepatocytes blocks diethylnitrosamine-induced liver cancer initiation in mice, whereas short hairpin RNA-mediated gene silencing of HMGB1 inhibits HCC cell proliferation. Mechanistically, the binding of HMGB1 to GA-binding protein alpha promotes the expression of yes-associated protein (YAP), a major downstream effector of the Hippo pathway that contributes to liver tumorigenesis by inducing hypoxia-inducible factor 1α (HIF1α)-dependent aerobic glycolysis. Like wild-type YAP-complementary DNA, YAP-5SA-S94A can restore HIF1α DNA binding activity, glycolysis-associated gene expression, and HIF1α-YAP complex formation in YAP-knockdown HCC cell lines. In contrast, verteporfin, a reagent targeting the interface between YAP and TEA domain transcription factor, has the ability to block YAP-HIF1α complex formation. Notably, genetic or pharmacologic inhibition of the HMGB1-YAP-HIF1α pathway confers protection against excessive glycolysis and tumor growth in mice.

CONCLUSION

These findings demonstrate that HMGB1 plays a novel role in modulating the YAP-dependent HIF1α pathway and shed light on the development of metabolism-targeting therapeutics for HCC chemoprevention. (Hepatology 2018;67:1823-1841).

Standard CD44 modulates YAP1 through a positive feedback loop in hepatocellular carcinoma

High expression levels of CD44 and YAP have been identified as poor prognostic factors in hepatocellular carcinoma (HCC). However, the mechanistic relationship between CD44 and YAP during HCC tumorigenesis remains largely unknown. To investigate the mutual regulation between standard CD44 (CD44S) and YAP1 in HCC cell lines and tissue samples, CD44S and YAP1 expression in 40 pairs of tumor samples and matched distal normal tissues from HCC patients was examined by immunohistochemical staining. High expression of either CD44S or YAP1 was associated with a younger age and worse pathology grade. In addition, high levels of CD44S and YAP1 were associated with increased vascular invasion and more severe liver cirrhosis, respectively. CD44S expression was positively correlated with YAP1 expression in these HCC tissues. In vitro experiments suggested that CD44S could positively regulate the expression of YAP1 and its target genes via the PI3K/Akt pathway in HCC cells. Moreover, CD44S is regulated by the YAP1/TEAD axis. These results reveal a novel positive feedback loop involving CD44S and YAP1, in which CD44S functions as both an upstream regulator and a downstream effector of YAP1 in HCC. This feedback loop might constitute a broadly conserved module for regulating cell proliferation and invasion during HCC tumorigenesis. Blocking this positive feedback loop that involves CD44S and YAP1 might represent a new approach for HCC treatment.

Effects and related mechanisms of serotonin on malignant biological behavior of hepatocellular carcinoma via regulation of Yap

5-hydroxytryptamine (5-HT, serotonin) and Yes-associated protein (Yap), which act as a mitogen and an oncogene, respectively, play an important role in tumors. Here, we investigated whether 5-HT could affect the hepatocarcinogenic process via promoting the activation and expression of Yap, as well as the possible underlying molecular mechanisms. We found that 5-HT promoted hepatoma cell proliferation, invasion and metastasis via regulating Yap expression in vitro and in vivo, and Yap knockdown had opposite effects. Furthermore, 5-HT activated 5-HT_2BR to promote Yap expression via upregulating the pERK level. Inhibitors of 5-HT_2BR and ERK attenuated the overexpression of Yap and promotional effects of 5-HT in vitro and in vivo. As a result, 5-HT affected the malignant biological behavior of hepatoma cells via the 5-HT-5-HT_2BR-pERK-Yap axis. Therefore, 5-HT and Yap may be prognostic predictors and potential therapeutic targets for HCC patients in the future.

Yes-associated protein (YAP) in pancreatic cancer: at the epicenter of a targetable signaling network associated with patient survival

Pancreatic ductal adenocarcinoma (PDAC) is generally a fatal disease with no efficacious treatment modalities. Elucidation of signaling mechanisms that will lead to the identification of novel targets for therapy and chemoprevention is urgently needed. Here, we review the role of Yes-associated protein (YAP) and WW-domain-containing Transcriptional co-Activator with a PDZ-binding motif (TAZ) in the development of PDAC. These oncogenic proteins are at the center of a signaling network that involves multiple upstream signals and downstream YAP-regulated genes. We also discuss the clinical significance of the YAP signaling network in PDAC using a recently published interactive open-access database (www.proteinatlas.org/pathology) that allows genome-wide exploration of the impact of individual proteins on survival outcomes. Multiple YAP/TEAD-regulated genes, including AJUBA, ANLN, AREG, ARHGAP29, AURKA, BUB1, CCND1, CDK6, CXCL5, EDN2, DKK1, FOSL1,FOXM1, HBEGF, IGFBP2, JAG1, NOTCH2, RHAMM, RRM2, SERP1, and ZWILCH, are associated with unfavorable survival of PDAC patients. Similarly, components of AP-1 that synergize with YAP (FOSL1), growth factors (TGFα, EPEG, and HBEGF), a specific integrin (ITGA2), heptahelical receptors (P2Y₂R, GPR87) and an inhibitor of the Hippo pathway (MUC1), all of which stimulate YAP activity, are associated with unfavorable survival of PDAC patients. By contrast, YAP inhibitory pathways (STRAD/LKB-1/AMPK, PKA/LATS, and TSC/mTORC1) indicate a favorable prognosis. These associations emphasize that the YAP signaling network correlates with poor survival of pancreatic cancer patients. We conclude that the YAP pathway is a major determinant of clinical aggressiveness in PDAC patients and a target for therapeutic and preventive strategies in this disease.

Yes-associated protein (YAP) signaling contributes to pancreatic cancer progression and is associated with poor patient survival. Previous studies have shown that YAP activates genes involved in cell proliferation to incite tumor growth and metastasis. Enrique Rozengurt and colleagues at University of California Los Angeles review the latest knowledge on YAP signaling and used the open access database The Human Protein Atlas to analyze the gene expression profile and prognosis of 176 patients with pancreatic ductal adenocarcinoma. Activation of upstream or downstream elements of the YAP signaling pathway correlated with shorter survival in patients. Conversely, the activation of signaling pathways that oppose YAP signaling were associated with a more favorable prognosis. These findings highlight YAP signaling pathway components as both prognostic markers and potential targets for developing much needed therapeutic and preventative strategies.

Inhibition of yes-associated protein suppresses brain metastasis of human lung adenocarcinoma in a murine model

Yes‐associated protein (YAP) is a main mediator of the Hippo pathway and promotes cancer development and progression in human lung cancer. We sought to determine whether inhibition of YAP suppresses metastasis of human lung adenocarcinoma in a murine model. We found that metastatic NSCLC cell lines H2030‐BrM3(K‐ras^G12C mutation) and PC9‐BrM3 (EGFR^Δexon19 mutation) had a significantly decreased p‐YAP(S127)/YAP ratio compared to parental H2030 (K‐ras^G12C mutation) and PC9 (EGFR^Δexon19 mutation) cells (P < .05). H2030‐BrM3 cells had significantly increased YAP mRNA and expression of Hippo downstream genes CTGF and CYR61 compared to parental H2030 cells (P < .05). Inhibition of YAP by short hairpin RNA (shRNA) and small interfering RNA (siRNA) significantly decreased mRNA expression in downstream genes CTGF and CYR61 in H2030‐BrM3 cells (P < .05). In addition, inhibiting YAP by YAP shRNA significantly decreased migration and invasion abilities of H2030‐BrM3 cells (P < .05). We are first to show that mice inoculated with YAP shRNA‐transfected H2030‐BrM3 cells had significantly decreased metastatic tumour burden and survived longer than control mice (P < .05). Collectively, our results suggest that YAP plays an important role in promoting lung adenocarcinoma brain metastasis and that direct inhibition of YAP by shRNA suppresses H2030‐BrM3 cell brain metastasis in a murine model.

Model Prediction and Validation of an Order Mechanism Controlling the Spatiotemporal Phenotype of Early Hepatocellular Carcinoma

Recently, hepatocyte-sinusoid alignment (HSA) has been identified as a mechanism that supports the coordination of hepatocytes during liver regeneration to reestablish a functional micro-architecture (Hoehme et al. in Proc Natl Acad Sci 107(23):10371-10376, 2010). HSA means that hepatocytes preferentially align along the closest micro-vessels. Here, we studied whether this mechanism is still active in early hepatocellular tumors. The same agent-based spatiotemporal model that previously correctly predicted HSA in liver regeneration was further developed to simulate scenarios in early tumor development, when individual initiated hepatocytes gain increased proliferation capacity. The model simulations were performed under conditions of realistic liver micro-architectures obtained from 3D reconstructions of confocal laser scanning micrographs. Interestingly, the established model predicted that initiated hepatocytes at first arrange in elongated patterns. Only when the tumor progresses to cell numbers of approximately 4000, does it adopt spherical structures. This prediction may have relevant consequences, since elongated tumors may reach critical structures faster, such as larger vessels, compared to a spherical tumor of similar cell number. Interestingly, this model prediction was confirmed by analysis of the spatial organization of initiated hepatocytes in a rat liver tumor initiation study using single doses of 250 mg/kg of the genotoxic carcinogen N-nitrosomorpholine (NNM). Indeed, small clusters of GST-P positive cells induced by NNM were elongated, almost columnar, while larger GDT-P positive foci of approximately the size of liver lobuli adopted spherical shapes. From simulations testing numerous possible mechanisms, only HSA could explain the experimentally observed initial deviation from spherical shape. The present study demonstrates that the architecture of small cell clusters of hepatocytes early after initiation is still controlled by physiological mechanisms. However, this coordinating influence is lost when the tumor grows to approximately 4000 cells, leading to further growth in spherical shape. Our findings stress the potential importance of organ micro-architecture in understanding tumor phenotypes.

Hepatitis C Virus Mimics Effects of Glypican-3 on CD81 and Promotes Development of Hepatocellular Carcinomas via Activation of Hippo Pathway in Hepatocytes

Glypican (GPC)-3 is overexpressed in hepatocellular carcinomas (HCCs). GPC3 binds to CD81. Forced expression of CD81 in a GPC3-expressing HCC cell line caused activation of Hippo, a decrease in ezrin phosphorylation, and a decrease in yes-associated protein (YAP). CD81 is also associated with hepatitis C virus (HCV) entry into hepatocytes. Activation of CD81 by agonistic antibody causes activation of tyrosine-protein kinase SYK (SYK) and phosphorylation of ezrin, a regulator of the Hippo pathway. In cultures of normal hepatocytes, CD81 agonistic antibody led to enhanced phosphorylation of ezrin and an increase in nuclear YAP. HCV E2 protein mimicked GPC3 and led to enhanced Hippo activity and decreased YAP in cultured normal human hepatocytes. HCC tissue microarray revealed a lack of expression of CD81 in most HCCs, rendering them insusceptible to HCV infection. Activation of CD81 by agonistic antibody suppressed the Hippo pathway and increased nuclear YAP. HCV mimicked GPC3, causing Hippo activation and a decrease in YAP. HCV is thus likely to enhance hepatic neoplasia by acting as a promoter of growth of early CD81-negative neoplastic hepatocytes, which are resistant to HCV infection, and thus have a proliferative advantage to clonally expand as they participate in compensatory regeneration for the required maintenance of 100% of liver weight (hepatostat).

Epigenetic restriction of Hippo signaling by MORC2 underlies stemness of hepatocellular carcinoma cells

The evolutionarily conserved Hippo signaling pathway is a key regulator of stem cell self-renewal, differentiation, and organ size. While alterations in Hippo signaling are causally linked to uncontrolled cell growth and a broad range of malignancies, genetic mutations in the Hippo pathway are uncommon and it is unclear how the tumor suppressor function of the Hippo pathway is disrupted in human cancers. Here, we report a novel epigenetic mechanism of Hippo inactivation in the context of hepatocellular carcinoma (HCC). We identify a member of the microrchidia (MORC) protein family, MORC2, as an inhibitor of the Hippo pathway by controlling upstream Hippo regulators, neurofibromatosis 2 (NF2) and kidney and brain protein (KIBRA). Mechanistically, MORC2 forms a complex with DNA methyltransferase 3A (DNMT3A) at the promoters of NF2 and KIBRA, leading to their DNA hyper-methylation and transcriptional repression. As a result, NF2 and KIBRA are crucial targets of MORC2 to regulate confluence-induced activation of Hippo signaling and contact inhibition of cell growth under both physiological and pathological conditions. The MORC2-NF2/KIBRA axis is critical for maintaining self-renewal, sorafenib resistance, and oncogenicity of HCC cells in vitro and in nude mice. Furthermore, MORC2 expression is elevated in HCC tissues, associated with stem-like properties of cancer cells, and disease progression in patients. Collectively, MORC2 promotes cancer stemness and tumorigenesis by facilitating DNA methylation-dependent silencing of Hippo signaling and could be a potential molecular target for cancer therapeutics.

Verteporfin exhibits YAP-independent anti-proliferative and cytotoxic effects in endometrial cancer cells

Endometrial Carcinoma (EMCA) is the most common gynecologic malignancy and the fourth most common malignancy in women in the United States. Yes-associated protein (YAP) is a potent transcription coactivator acting via binding to the TEAD transcription factor, and plays a critical role in organ size regulation. Verteporfin (VP), a benzoporphyrin derivative, was identified as an inhibitor of YAP-TEAD interaction. We investigated the therapeutic efficacy and mechanism of VP in EMCA. The efficacy of VP on cell viability, cytotoxicity and invasion was assayed in EMCA cell lines. An organoid model system was also developed to test the effect of VP on apoptotic markers in an in vitro model system. Treatment with VP resulted in a decrease in cell viability, invasion and an increase in cytotoxicity of EMCA cells. These effects occurred as early as 15 minutes following treatment. Similarly, VP treatment versus vehicle control increased apoptosis in human organoid model systems. Quantitative RT-PCR, cDNA based RTPCR array analysis and western blotting were performed to investigate the mechanism of VP action. The cytotoxic and anti-proliferative effects appeared to be independent of its effect on YAP. Our results suggest that VP is a promising chemotherapeutic agent for the treatment of endometrial cancer.

Proteomic analysis of laser capture microdissected focal lesions in a rat model of progenitor marker-positive hepatocellular carcinoma

We have shown previously that rapamycin, the canonical inhibitor of the mechanistic target of rapamycin (mTOR) complex 1, markedly inhibits the growth of focal lesions in the resistant hepatocyte (Solt-Farber) model of hepatocellular carcinoma (HCC) in the rat. In the present study, we characterized the proteome of persistent, pre-neoplastic focal lesions in this model. One group was administered rapamycin by subcutaneous pellet for 3 weeks following partial hepatectomy and euthanized 4 weeks after the cessation of rapamycin. A second group received placebo pellets. Results were compared to unmanipulated control animals and to animals that underwent an incomplete Solt-Farber protocol to activate hepatic progenitor cells. Regions of formalin-fixed, paraffin-embedded tissue were obtained by laser capture microdissection (LCM). Proteomic analysis yielded 11,070 unique peptides representing 2,227 proteins. Quantitation of the peptides showed increased abundance of known HCC markers (e.g., glutathione S-transferase-P, epoxide hydrolase, 6 others) and potential markers (e.g., aflatoxin aldehyde reductase, glucose 6-phosphate dehydrogenase, 10 others) in foci from placebo-treated and rapamycin-treated rats. Peptides derived from cytochrome P450 enzymes were generally reduced. Comparisons of the rapamycin samples to normal liver and to the progenitor cell model indicated that rapamycin attenuated a loss of differentiation relative to placebo. We conclude that early administration of rapamycin in the Solt-Farber model not only inhibits the growth of pre-neoplastic foci but also attenuates the loss of differentiated function. In addition, we have demonstrated that the combination of LCM and mass spectrometry-based proteomics is an effective approach to characterize focal liver lesions.

EGFR-PI3K-PDK1 pathway regulates YAP signaling in hepatocellular carcinoma: the mechanism and its implications in targeted therapy

The epidermal growth factor receptor (EGFR) pathway and Hippo signaling play an important role in the carcinogenesis of hepatocellular carcinoma (HCC). However, the crosstalk between these two pathways and its implications in targeted therapy remains unclear. We found that the activated EGFR signaling could bypass RhoA to promote the expression of YAP(Yes-associated protein), the core effector of the Hippo signaling, and its downstream target Cyr61. Further studies indicated that EGFR signaling mainly acted through the PI3K-PDK1 (Phosphoinositide 3-kinase-Phosphoinositide-dependent kinase-1) pathway to activate YAP, but not the AKT and MAPK pathways. While YAP knockdown hardly affected the EGFR signaling. In addition, EGF could promote the proliferation of HCC cells in a YAP-independent manner. Combined targeting of YAP and EGFR signaling by simvastatin and the EGFR signaling inhibitors, including the EGFR tyrosine kinase inhibitor (TKI) gefitinib, the RAF inhibitor sorafenib and the MEK inhibitor trametinib, presented strong synergistic cytotoxicities in HCC cells. Therefore, the EGFR-PI3K-PDK1 pathway could activate the YAP signaling, and the activated EGFR signaling could promote the HCC cell growth in a YAP-independent manner. Combined use of FDA-approved inhibitors to simultaneously target YAP and EGFR signaling presented several promising therapeutic approaches for HCC treatment.

Hippo Cascade Controls Lineage Commitment of Liver Tumors in Mice and Humans

Primary liver cancer consists mainly of hepatocellular carcinoma (HCC) and intrahepatic cholangiocarcinoma (ICC). A subset of human HCCs expresses a ICC-like gene signature and is classified as ICC-like HCC. The Hippo pathway is a critical regulator of normal and malignant liver development. However, the precise function(s) of the Hippo cascade along liver carcinogenesis remain to be fully delineated. The role of the Hippo pathway in a murine mixed HCC/ICC model induced by activated forms of AKT and Ras oncogenes (AKT/Ras) was investigated. The authors demonstrated the inactivation of Hippo in AKT/Ras liver tumors leading to nuclear localization of Yap and TAZ. Coexpression of AKT/Ras with Lats2, which activates Hippo, or the dominant negative form of TEAD2 (dnTEAD2), which blocks Yap/TAZ activity, resulted in delayed hepatocarcinogenesis and elimination of ICC-like lesions in the liver. Mechanistically, Notch2 expression was found to be down-regulated by the Hippo pathway in liver tumors. Overexpression of Lats2 or dnTEAD2 in human HCC cell lines inhibited their growth and led to the decreased expression of ICC-like markers, as well as Notch2 expression. Altogether, this study supports the key role of the Hippo cascade in regulating the differentiation status of liver tumors.

The Hippo pathway as a drug target in gastric cancer

The Hippo tumor suppressor pathway is critical for balancing cellular differentiation and proliferation in response to cell-cell contact, mechanical signals and diffusible signals such as lysophosphatidic acid. Hippo pathway signaling is frequently dysregulated in gastric cancer (GC), as well as many other kinds of solid tumors, contributing to multiple aspects of malignant progression including unchecked cell division and metastasis. Considering the importance of this Hippo pathway in cancer, its pharmacological disruption may be of huge benefit in the fight against this disease. In this review, we summarize the components of the Hippo pathway, its crosstalk with other major oncogenic signaling pathways, common mechanisms of its dysregulation, as well as potential therapeutic approaches of targeting this pathway for cancer treatment, specifically in a GC context.

YAP promotes erlotinib resistance in human non-small cell lung cancer cells

Yes-associated protein (YAP) is a main mediator of the Hippo pathway, which promotes cancer development. Here we show that YAP promotes resistance to erlotinib in human non-small cell lung cancer (NSCLC) cells. We found that forced YAP overexpression through YAP plasmid transfection promotes erlotinib resistance in HCC827 (exon 19 deletion) cells. In YAP plasmid-transfected HCC827 cells, GTIIC reporter activity and Hippo downstream gene expression of AREG and CTGF increased significantly (P<0.05), as did ERBB3 mRNA expression (P<0.05). GTIIC reporter activity, ERBB3 protein and mRNA expression all increased in HCC827 erlotinib-resistance (ER) cells compared to parental HCC827 cells. Inhibition of YAP by small interfering RNA (siRNA) increased the cytotoxicity of erlotinib to H1975 (L858R+T790M) cells. In YAP siRNA-transfected H1975 cells, GTIIC reporter activity and downstream gene expression of AREG and CTGF decreased significantly (P<0.05). Verteporfin, YAP inhibitor had an effect similar to that of YAP siRNA; it increased sensitivity of H1975 cells to erlotinib and in combination with erlotinib, synergistically reduced migration, invasion and tumor sphere formation abilities in H1975 cells. Our results indicate that YAP promotes erlotinib resistance in the erlotinib-sensitive NSCLC cell line HCC827. Inhibition of YAP by siRNA increases sensitivity of erlotinib-resistant NSCLC cell line H1975 to erlotinib.

Netrin-1 promotes metastasis of gastric cancer by regulating YAP activity

Yes-associated protein (YAP) is a major downstream molecular of the Hippo pathway, which plays important role in cancer development. Netrin-1 conveys oncogenic activity in many types of malignant tumors. However, the downstream signaling of netrin-1 mediating its oncogenic effects in gastric cancer (GC) is not well defined. Here, we aim to investigate the role of netrin-1 in metastasis potential of GC by regulating YAP. In this study, we showed that netrin-1 inhibition significantly decreased migration and invasion abilities of GC cells, while netrin-1 overexpression effectively reversed this effect. We also demonstrated that netrin-1 upregulated YAP expression via its transmembrane receptor neogenin. Furthermore, our in vitro and in vivo results showed that the effect of netrin-1 on GC cells migration and invasion abilities was regulated by YAP. Collectively, our results defined netrin-1 as a positive regulator of malignant tumor metastasis in GC by activating the YAP signaling, with potential implications for new approaches to GC therapy.

Soft-shelled turtle peptide modulates microRNA profile in human gastric cancer AGS cells

Cancer prevention using natural micronutrition on epigenetic mechanisms primarily revolves around plant extracts. However, the role of macronutrition, including animal peptides, on epigenetic modification in cancer has been elusive. In traditional Chinese medicine, the soft-shelled turtle has a long-history of being a functional food that strengthens immunity through unknown mechanisms. The present study aimed to investigate the impact of soft-shelled turtle peptide on microRNA (miRNA) expression in gastric cancer (GC) cells and to analyze the potential anticancer mechanisms for GC. Affymetrix GeneChip miRNA 3.0 Array and quantitative polymerase chain reaction were used to detect the miRNA expression profile in human GC AGS cells treated with the soft-shelled turtle peptide. The results demonstrated that 101 miRNAs (49 upregulated miRNAs and 52 downregulated miRNAs) were significantly differentially expressed in the AGS cells following soft-shelled turtle peptide treatment. Several tumor suppressor miRNAs were upregulated markedly, including miRNA-375, let-7d, miRNA-429, miRNA-148a/148b and miRNA-34a. Pathway analysis indicated that soft-shelled turtle peptide may function with anticancer properties through the Hippo signaling pathway and the forkhead box O signaling pathway. Therefore, these results demonstrated that soft-shelled turtle peptide has the capacity to influence cancer-related pathways through the regulation of miRNA expression in GC cells.

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.

A Large Set of miRNAs Is Dysregulated from the Earliest Steps of Human Hepatocellular Carcinoma Development

Hepatocellular carcinoma (HCC) typically results from a stepwise process characterized by the development of premalignant lesions, such as low- or high-grade dysplastic nodules (LGDNs and HGDNs, respectively), in a cirrhotic setting. MicroRNAs (miRNAs) are small noncoding RNAs involved in post-transcriptional regulation of gene expression that can act as oncogenes or tumor suppressors. Whether and which miRNAs are involved in the early stages of HCC development remains elusive. Here, small-RNA sequencing was applied to profile miRNA expression in 55 samples (cirrhotic nodules; CNs), LGDNs, HGDNs, early HCCs, and small progressed HCCs, obtained from 17 patients bearing HCCs of different etiologies. An miRNA expression signature of 62 miRNAs distinguishing small progressed HCCs from matched CNs was identified. Interestingly, 52 of these miRNAs discriminated CNs from LGDNs/HGDNs, regardless of etiology, and remained modified along the tumorigenic process. Functional analysis of the predicted mRNA targets of deregulated miRNAs identified common modifications between the early and late stages of HCC development likely involved in the stepwise process of HCC development. Our results demonstrate that miRNA deregulation happens very early in HCC in humans, implying their crucial role in the tumorigenic process. The identification of miRNAs discriminating CNs from neoplastic nodules may have relevant translational implications in early diagnosis.

Nuclear localization of TEF3-1 promotes cell cycle progression and angiogenesis in cancer

TEF3-1 (transcriptional enhancer factor 3 isoform 1), also known as TEAD4 (TEA domain family member 4), was recently revealed as an oncogenic character in cancer development. However, the underlying molecular pathogenic mechanisms remain undefined. In this paper, we investigated nuclear TEF3-1 could promote G1/S transition in HUVECs, and the expression levels of cyclins and CDKs were upregulated. Additionally, if TEF3-1 was knocked down, the expression of cyclins and CDKs was downregulated while the expression of P21, a negative regulator of the cell cycle, was upregulated. A microarray analysis also confirmed that TEF3-1 overexpression upregulates genes that are related to cell cycle progression and the promotion of angiogenesis. Moreover, we observed that nuclear TEF3-1 was highly expressed during the formation of vascular structures in gastric cancer (GC). Finally, tumor xenograft experiments indicated that, when TEF3-1 was knocked down, tumor growth and angiogenesis were also suppressed. Taken together, these results demonstrate for the first time that TEF3-1 localization to the nucleus stimulates the cell cycle progression in HUVECs and specifically contributes to tumor angiogenesis. Nuclear TEF3-1 in HUVECs may serve as an oncogenic biomarker, and the suppression of TEF3-1 may be a potential target in anti-tumor therapy.

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.

Recent Advances in Understanding Cholangiocarcinoma

Cholangiocarcinoma (CCA) is an aggressive malignancy that arises from damaged epithelial cells, cholangiocytes, and possibly de-differentiated hepatocytes. CCA has a poor overall survival rate and limited therapeutic options. Based on this data, it is imperative that new diagnostic and therapeutic interventions be developed. Recent work has attempted to understand the pathological mechanisms driving CCA progression. Specifically, recent publications have delved into the role of cancer stem cells (CSCs), mesenchymal stem cells (MSCs), and microRNAs (miRNAs) during CCA pathology. CSCs are a specific subset of cells within the tumor environment that are derived from a cell with stem-like properties and have been shown to influence recurrence and chemoresistance during CCA. MSCs are known for their anti-inflammatory activity and have been postulated to influence malignancy during CCA, but little is known about their exact functions. miRNAs exert various functions via gene regulation at both the transcriptional and the translational levels, giving miRNAs diverse roles in CCA progression. Additionally, current miRNA-based therapeutic approaches are in clinical trials for various liver diseases, giving hope for similar approaches for CCA. However, the interactions among these three factors in the context of CCA are unknown. In this review, we focus on recently published data (within the last 3 years) that discuss the role of CSCs, MSCs, and miRNAs and their possible interactions during CCA pathogenesis.

MiR-3910 Promotes the Growth and Migration of Cancer Cells in the Progression of Hepatocellular Carcinoma

INTRODUCTION

Previous studies have reported that specific depletion of mammalian sterile-like kinase (MST1) in the mouse liver driven Hepatocellular carcinoma (HCC). However, how the expression of MST1 was regulated in the progression of HCC remains largely unknown.

MATERIALS AND METHODS

The expression of miR-3910 in the HCC tissues and cell lines were examined using q-PCR. The functions of miR-3910 in HCC were examined using MTT assay, Boyden chamber assay and soft agar assay. The effects of miR-3910 on the metastasis of HCC cells were evaluated using the mouse model.

RESULTS

Here, we have shown that miR-3910 regulated the expression of MST1. MiR-3910 was up-regulated in HCC samples and cell lines, and the expression of miR-3910 was induced by the oncogenic RasV12. In the functional study, miR-3910 was found to promote the growth and migration of HCC cells, and knocking down miR-3910 inhibited the metastasis of HCC cells. Mechanically, it was found that miR-3910 activated YAP signaling by targeting MST1.

CONCLUSION

Taken together, this study demonstrated that miR-3910 exerted oncogenic effects on the progression of HCC and suggested that miR-3910 might be a therapeutic target for cancer therapy.

The prognostic impacts of TEA domain (TEAD) transcription factor polymorphisms in Chinese hepatocellular carcinoma patients

TEA domain (TEAD) transcription factors play an important role in hepatocellular carcinoma (HCC) development and progression by regulating the expression of a number of genes. However, the association of their genetic variations with HCC prognosis remains elusive. Seven potentially functional single nucleotide polymorphisms in TEAD1-4 (rs2304733, rs10831923, rs12104362, rs3745305, rs11756089, rs2076173, rs7135838) were genotyped from 331 hepatitis B virus positive HCC patients using the Sequenom MassARRAY iPLEX platform. The TEAD3 rs2076173 C allele and rs11756089 T allele were identified as protective alleles as they were significantly associated with longer median overall survival time (MST). The T allele of rs2076173 was significantly associated with HCC survival independent of age, gender, smoking and drinking status, BCLC stage, and chemotherapy or TACE status (HR = 0.73, 95% CI = 0.56-0.93, P = 0.012). This protective effect was more prominent for patients who were non-drinkers (P for multiplicative interaction = 0.002). Patients had more than one of these protective alleles had significant longer MST of 19.25 months than those had none (MST=12.85 months, adjusted HR = 0.56, 95% CI = 0.33-0.95, P=0.030), especially for those non-drinkers (adjusted HR = 0.48, 95% CI = 0.32-0.74, P = 0.001). These findings suggested that rs2076173 and rs11756089 in TEAD3 gene could serve as genetic markers for favorable survival in the Chinese HCC patients.

Tankyrase inhibitors suppress hepatocellular carcinoma cell growth via modulating the Hippo cascade

Previous data indicate that Tankyrase inhibitors exert anti-growth functions in many cancer cell lines due to their ability to inactivate the YAP protooncogene. In the present manuscript, we investigated the effect of Tankyrase inhibitors on the growth of hepatocellular carcinoma (HCC) cell lines and the molecular mechanisms involved. For this purpose, we performed cell proliferation assay by colony-forming ability in seven human HCC cells subjected to XAV-939 and G007-LK Tankyrase inhibitors. Noticeably, the two Tankyrase inhibitors suppressed the HCC cell growth in a dose-dependent manner. Furthermore, we found that Tankyrase inhibitors synergized with MEK and AKT inhibitors to suppress HCC cell proliferation. At the molecular level, Tankyrase inhibitors significantly decreased YAP protein levels, reduced the expression of YAP target genes, and inhibited YAP/TEAD luciferase reporter activity. In addition, Tankyrase inhibitors administration was accompanied by upregulation of Angiomotin-like 1 (AMOTL1) and Angiomotin-like 2 (AMOTL2) proteins, two major negative regulators of YAP. Altogether, the present data indicate that XAV-939 and G007-LK Tankyrase inhibitors could suppress proliferation of hepatocellular carcinoma cells and downregulate YAP/TAZ by stabilizing AMOTL1 and AMOTL2 proteins, thus representing new potential anticancer drugs against hepatocellular carcinoma.

TNFAIP8 interacts with LATS1 and promotes aggressiveness through regulation of Hippo pathway in hepatocellular carcinoma

Although TNFAIP8 overexpression has been implicated in several human cancers, its clinical significance and biological function in hepatocellular carcinoma (HCC) remains unknown. Our study demonstrated that TNFAIP8 overexpression in primary HCC samples correlated with TNM stage, recurrence, poor prognosis and served as an independent favorable prognostic factor. We further showed that TNFAIP8 upregulated cell proliferation, migration, invasion and xenograft tumor growth of HCC cells. In addition, TNFAIP8 overexpression inhibited YAP phosphorylation, increased its nuclear localization and stabilization, leading to upregulation of cyclin proteins, CTGF and cell proliferation. We also found that TNFAIP8 could interact with LATS1 and decreased its phosphorylation. Depletion of LATS1 and YAP by siRNA blocked the biological effects of TNFAIP8. Collectively, the present study provides a novel finding that TNFAIP8 promotes HCC progression through LATS1-YAP signaling pathway. TNFAIP8 may serve as a candidate biomarker for poor prognosis and a target for new therapies.

TEAD1/4 exerts oncogenic role and is negatively regulated by miR-4269 in gastric tumorigenesis

TEA domain (TEAD) transcription factors are key components of the Hippo–YAP1 signaling pathway, but their functional role and regulatory mechanisms remain unclear. This study aims to comprehensively explore the expression pattern and functional role of TEAD family in gastric carcinogenesis and investigate its regulation by microRNAs (miRNAs). The mRNA and protein expression of TEAD family were examined by quantitative reverse transcription–PCR (qRT–PCR) and western blot. Their functional roles were determined by in vitro and in vivo studies. The clinicopathological association of TEAD4 in gastric cancer (GC) was studied using immunohistochemistry on tissue microarray. The prediction of miRNAs, which potentially target TEAD1/4, was performed by TargetScan and miRDB. The regulation of TEAD1/4 by miRNAs was confirmed by qRT–PCR, western blot and luciferase assays. TEAD1/4 were overexpressed in GC cell lines and primary GC tissues. Knockdown of TEAD1/4 induced a significant anticancer effect in vitro and in vivo. TEAD1 was confirmed to be a direct target of miR-377-3p and miR-4269, while TEAD4 was negatively regulated by miR-1343-3p and miR-4269. Among them, miR-4269 was the most effective inhibitor of TEAD1/4. Ectopic expression of these miRNAs substantiated their tumor-suppressive effects. In primary GC tumors, downregulation of miR-4269 was associated with poor disease-specific survival and showed a negative correlation with TEAD4. TEAD1 and TEAD4 are oncogenic factors, whose aberrant activation are, in part, mediated by the silence of miR-377-3p, miR-1343-3p and miR-4269. For the first time, the nuclear accumulated TEAD4 and downregulated miR-4269 are proposed to serve as novel prognostic biomarkers in GC.

Yes-associated protein: A novel molecular target for the diagnosis, treatment and prognosis of hepatocellular carcinoma

Hepatocellular carcinoma (HCC) is a common type of malignant tumor. The early-diagnosis and treatment options for HCC are limited, which is primarily due to an incomplete understanding of the underlying molecular mechanisms of the disease. Yes-associated protein (YAP) overexpression promotes proliferation and phenotypic transformation of HCC cells. Recently, elucidating the molecular mechanisms of the Hippo/YAP signaling pathway and investigating the interactions between the signaling molecules, as a potential strategy for the treatment of HCC, has become an area of interest. The present review will discuss the role of YAP in HCC pathogenesis, and the significance of YAP in diagnosis, treatment and determining the prognosis.

The correlation between poor prognosis and increased yes-associated protein 1 expression in keratin 19 expressing hepatocellular carcinomas and cholangiocarcinomas

Background

The Hippo pathway plays a vital role in liver regeneration and development by determining cellular lineage and regulating cell proliferation and apoptosis. In this study, we aimed to assess the role of the Hippo pathway in hepatic carcinogenesis and morphogenesis by examining Yes-associated protein 1 (YAP1) expression in the spectrum of hepatic carcinomas based on cellular lineage.

Methods

We examined 913 primary hepatic carcinomas, including hepatocellular carcinomas (HCCs), combined hepatocellular and cholangiocarcinomas (cHC-CCAs), intrahepatic cholangiocarcinomas (IHCCAs) and perihilar extrahepatic bile duct carcinomas (EHBCAs). Our study group was categorized into 8 disease groups, based on histological diagnosis and cytokeratin 19 (CK19) expression, and immunohistochemistry was used to detect and compare YAP1 expression levels between the groups. The eight disease groups we identified were: 1) CK19(−) HCC, 2) CK19(−) scirrhous HCC, 3) CK19(+) HCC, 4) stem cell feature of cHC-CCA, 5) classical cHC-CCA, 6) cholangiolocellular IHCCA, 7) non-cholangiolocellular IHCCA, and 8) EHBCA.

Results

Positive rates of YAP1 were the highest in the EHBCA group (21%). CK19(+) HCC and non-cholangiolocellular IHCCA groups also showed high expression levels (10% -11%), while the CK19 (−) HCC, CK19 (−) scirrhous HCC, cHC-CCA, and cholangiolocellular IHCCA groups showed low expression levels, ranging between 0% and 5%. Survival analysis, restricted to pT1 stage HCCs and IHCCAs, showed poor overall survival for YAP1(+) IHCCA patients (39 ± 17 vs. 109 ± 10 months, mean ± SD, log rank p-value 0.005). For HCCs, a trend of poor progression-free survival for YAP1(+) HCCs was observed (39 ± 18 vs. 81 ± 5 months, mean ± SD, log rank p-value 0.205)

Conclusions

YAP1 activation was more commonly found in CCAs than in pure HCCs. However, a differing pattern of YAP1 expression between cHC-CCAs and CK19(+) HCCs and the poor prognosis of YAP1 positive hepatic carcinomas suggests that YAP1 may have a preferential role in aggressive tumor behavior, rather than in the determination of cellular lineage in hepatic carcinomas.

Electronic supplementary material

The online version of this article (doi:10.1186/s12885-017-3431-1) contains supplementary material, which is available to authorized users.

Suppression of miR-16 promotes tumor growth and metastasis through reversely regulating YAP1 in human cholangiocarcinoma

Background & Aims

Aberrant expression of microRNAs is associated with many cancers progression. Many studies have shown that miR-16 is down-regulated in many cancers. However, its role in cholangiocarcinoma (CCA) is unknown.

Methods

Quantitative real-time PCR (qRT-PCR) was developed to measure miR-16 expression in CCA tissues and cell lines. CCK-8, colony formation and transwell assays were used to reveal the role of miR-16 in CCA cell proliferation and malignant transformation in vitro. The loss-and-gain function was further validated by subcutaneous xenotransplantation and tail vein injection xenotransplantation model in vivo. Dual-luciferase reporter assay was performed to validate the relationship of miR-16 with YAP1.

Results

MiR-16 was notably downregulated in CCA tissues, which was associated with tumor size, metastasis, and TNM stage. Both in vitro and in vivo studies demonstrated that miR-16 could suppress proliferation, invasion and metastasis throughout the progression of CCA. We further identified YAP1 as a direct target gene of miR-16 and found that miR-16 could regulate CCA cell growth and invasion in a YAP1-dependent manner. In addition, YAP1 was markedly upregulated in CCA tissues, which was reversely correlated with miR-16 level in tissue samples. Besides, Down-regulation of miR-16 was remarkably associated with tumor progression and poor survival in CCA patients through a Kaplan–Meier survival analysis.

Conclusions

miR-16, as a novel tumor suppressor in CCA through directly targeting YAP1, might be a promising therapeutic target or prognosis biomarker for CCA.

The essential role of YAP O-GlcNAcylation in high-glucose-stimulated liver tumorigenesis

O-GlcNAcylation has been implicated in the tumorigenesis of various tissue origins, but its function in liver tumorigenesis is not clear. Here, we demonstrate that O-GlcNAcylation can enhance the expression, stability and function of Yes-associated protein (YAP), the downstream transcriptional regulator of the Hippo pathway and a potent oncogenic factor in liver cancer. O-GlcNAcylation induces transformative phenotypes of liver cancer cells in a YAP-dependent manner. An O-GlcNAc site of YAP was identified at Thr241, and mutating this site decreased the O-GlcNAcylation, stability, and pro-tumorigenic capacities of YAP, while increasing YAP phosphorylation. Importantly, we found via in vitro cell-based and in vivo mouse model experiments that O-GlcNAcylation of YAP was required for high-glucose-induced liver tumorigenesis. Interestingly, a positive feedback between YAP and global cellular O-GlcNAcylation is also uncovered. We conclude that YAP O-GlcNAcylation is a potential therapeutic intervention point for treating liver cancer associated with high blood glucose levels and possibly diabetes.

Yap is a transcriptional factor involved in tumorigenesis. Here the authors show that a previously unknown post-translational modification of Yap, O-GlcNAcylation, increases its transcriptional activity and is required for high glucose-induced liver cancer development.

Verteporfin suppresses cell survival, angiogenesis and vasculogenic mimicry of pancreatic ductal adenocarcinoma via disrupting the YAP-TEAD complex

Pancreatic ductal adenocarcinoma (PDAC) is one of the most aggressive human malignancies. The Yes-associated protein-1 (YAP) plays a critical role in cell proliferation, apoptosis and angiogenesis. Verteporfin is a photosensitizer used in photodynamic therapy and also a small molecular inhibitor of the Hippo-YAP pathway. However, little is known about whether verteporfin could inhibit YAP activity in PDAC cells. Our present results showed that verteporfin suppressed the proliferation of human PDAC PANC-1 and SW1990 cells by arresting cells at the G1 phase, and inducing apoptosis in dose- and time-dependent manners. Verteporfin also inhibited the tumor growth on the PDAC xenograft model. Treatment with verteporfin led to downregulation of cyclinD1 and cyclinE1, modulation of Bcl-2 family proteins and activation of PARP. In addition, verteporfin exhibited an inhibitory effect on angiogenesis and vasculogenic mimicry via suppressing Ang2, MMP2, VE-cadherin, and α-SMA expression in vitro and in vivo. Mechanism studies demonstrated that verteporfin impaired YAP and TEAD interaction to suppress the expression of targeted genes. Our results provide a foundation for repurposing verteporfin as a promising anti-tumor drug in the treatment of pancreatic cancer by targeting the Hippo pathway.

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.

VGLL4 targets a TCF4-TEAD4 complex to coregulate Wnt and Hippo signalling in colorectal cancer

Concerted co-regulation of multiple signalling pathways is crucial for tissue homoeostasis and tumorigenesis. Here we report that VGLL4, a previously identified YAP antagonist, also functions as a regulator of Wnt/β-catenin signalling. The expression of VGLL4 is significantly downregulated in clinical colorectal carcinoma (CRC) specimens, positively associated with patient survival rate, and inversely correlated with the expression of Wnt target genes in CRCs. Knockdown of VGLL4 enhances proliferation and tumour formation of CRC cells. A designed peptide mimicking the function of VGLL4 effectively inhibits CRC progression in a de novo mouse model. Mechanistically, TEAD4 associates with TCF4 to form a complex and cobind target genes. VGLL4 targets this TEAD4–TCF4 complex to interfere the functional interplay between TEAD4 and TCF4, suppressing the transactivation of TCF4. Collectively, our study indicates that Wnt/β-catenin and Hippo-YAP signalling are directly linked at transcription factor-level, and VGLL4 can target a TEAD4–TCF4 complex to co-regulate both pathways.

The Wnt/β-catenin and YAP signaling pathways have fundamental roles in cancer. Here, the authors show that VGLL4, a known YAP antagonist, also negatively regulates Wnt/β-catenin signaling by targeting TEAD-DNA-TCF4 complex, thereby inhibiting colorectal cancer growth.

Verteporfin Inhibits Cell Proliferation and Induces Apoptosis in Human Leukemia NB4 Cells without Light Activation

Background and Aims: Verteporfin (VP), clinically used in photodynamic therapy for neovascular macular degeneration, has recently been proven a suppressor of yes-associated protein (YAP) and has shown potential in anticancer treatment. However, its anti-human leukemia effects in NB4 cells remain unclear. In this study, we investigated the effects of VP on proliferation and apoptosis in human leukemia NB4 cells. Methods: NB4 cells were treated with VP for 24 h. The effects of VP on cell proliferation were determined using a Cell-Counting Kit-8 assay (CCK-8) assay and colony forming assay. Apoptosis and cell cycle were evaluated by flow cytometry (FCM). The protein levels were detected by western blot. Results: We found that VP inhibited the proliferation of NB4 cells in a concentration and time-dependent manner. FCM analysis showed that VP induced apoptosis in a concentration dependent manner and that VP treatment led to cell cycle arrest at G0/G1 phase. Moreover, VP significantly decreased the protein expression of YAP, p-YAP, Survivin, c-Myc, cyclinD1, p-ERK, and p-AKT. In addition, VP increased the protein expression of cleaved caspase3, cleaved PARP, Bax, and p-p38 MAPK. Conclusions: VP inhibited the proliferation and induced apoptosis in NB4 cells.

Cytokeratin-19 positivity is acquired along cancer progression and does not predict cell origin in rat hepatocarcinogenesis

Although the expression of the stem/progenitor cell marker cytokeratin-19 (CK-19) has been associated with the worst clinical prognosis among all HCC subclasses, it is yet unknown whether its presence in HCC is the result of clonal expansion of hepatic progenitor cells (HPCs) or of de-differentiation of mature hepatocytes towards a progenitor-like cell phenotype. We addressed this question by using two rat models of hepatocarcinogenesis: the Resistant-Hepatocyte (R-H) and the Choline-methionine deficient (CMD) models. Our data indicate that the expression of CK-19 is not the result of a clonal expansion of HPCs (oval cells in rodents), but rather of a further step of preneoplastic hepatocytes towards a less differentiated phenotype and a more aggressive behavior. Indeed, although HCCs were positive for CK-19, very early preneoplastic foci (EPFs) were completely negative for this marker. While a few weeks later the vast majority of preneoplastic nodules remained CK-19 negative, a minority became positive, suggesting that CK-19 expression is the result of de-differentiation of a subset of EPFs, rather than a marker of stem/progenitor cells. Moreover, the gene expression profile of CK-19-negative EPFs clustered together with CK-19-positive nodules, but was clearly distinct from CK-19 negative nodules and oval cells.

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.

Post-translational deregulation of YAP1 is genetically controlled in rat liver cancer and determines the fate and stem-like behavior of the human disease

Previous studies showed that YAP1 is over-expressed in hepatocellular carcinoma (HCC). Here we observed higher expression of Yap1/Ctgf axis in dysplastic nodules and HCC chemically-induced in F344 rats, genetically susceptible to hepatocarcinogenesis, than in lesions induced in resistant BN rats. In BN rats, highest increase in Yap1-tyr357, p73 phosphorylation and Caspase 3 cleavage occurred. In human HCCs with poorer prognosis (< 3 years survival after partial liver resection, HCCP), levels of YAP1, CTGF, 14-3-3, and TEAD proteins, and YAP1-14-3-3 and YAP1-TEAD complexes were higher than in HCCs with better outcome (> 3 years survival; HCCB). In the latter, higher levels of phosphorylated YAP1-ser127, YAP1-tyr357 and p73, YAP1 ubiquitination, and Caspase 3 cleavage occurred. Expression of stemness markers NANOG, OCT-3/4, and CD133 were highest in HCCP and correlated with YAP1 and YAP1-TEAD levels. In HepG2, Huh7, and Hep3B cells, forced YAP1 over-expression led to stem cell markers expression and increased cell viability, whereas inhibition of YAP1 expression by specific siRNA, or transfection of mutant YAP1 which does not bind to TEAD, induced opposite alterations. These changes were associated, in Huh7 cells transfected with YAP1 or YAP1 siRNA, with stimulation or inhibition of cell migration and invasivity, respectively. Furthermore, transcriptome analysis showed that YAP1 transfection in Huh7 cells induces over-expression of genes involved in tumor stemness. In conclusion, Yap1 post-translational modifications favoring its ubiquitination and apoptosis characterize HCC with better prognosis, whereas conditions favoring the formation of YAP1-TEAD complexes are associated with aggressiveness and acquisition of stemness features by HCC cells.

Inactivation of hypoxia-induced YAP by statins overcomes hypoxic resistance tosorafenib in hepatocellular carcinoma cells

Sorafenib is a multikinase inhibitor used as a first-line treatment for advanced hepatocellular carcinoma (HCC), but it has shown modest to low response rates. The characteristic tumour hypoxia of advanced HCC maybe a major factor underlying hypoxia-mediated treatment failure. Thus, it is urgent to elucidate the mechanisms of hypoxia-mediated sorafenib resistance in HCC. In this study, we found that hypoxia induced the nuclear translocation of Yes associate-Protein (YAP) and the subsequent transactivation of target genes that promote cell survival and escape apoptosis, thereby leading to sorafenib resistance. Statins, the inhibitors of hydroxymethylglutaryl-CoA reductase, could ameliorate hypoxia-induced nuclear translocation of YAP and suppress mRNA levels of YAP target genes both in vivo and in vitro. Combined treatment of statins with sorafenib greatly rescued the loss of anti-proliferative effects of sorafenib under hypoxia and improved the inhibitory effects on HepG2 xenograft tumour growth, accompanied by enhanced apoptosis as evidenced by the increased sub-G1 population and PARP cleavage. The expression levels of YAP and its target genes were highly correlated with poor prognosis and predicted a high risk of HCC patients. These findings collectively suggest that statins utilization maybe a promising new strategy to counteract hypoxia-mediated resistance to sorafenib in HCC patients.

Transformation by Polyomavirus Middle T Antigen Involves a Unique Bimodal Interaction with the Hippo Effector YAP

Murine polyomavirus has repeatedly provided insights into tumorigenesis, revealing key control mechanisms such as tyrosine phosphorylation and phosphoinositide 3-kinase (PI3K) signaling. We recently demonstrated that polyomavirus small T antigen (ST) binds YAP, a major effector of Hippo signaling, to regulate differentiation. Here we characterize YAP as a target of middle T antigen (MT) important for transformation. Through a surface including residues R103 and D182, wild-type MT binds to the YAP WW domains. Mutation of either R103 or D182 of MT abrogates YAP binding without affecting binding to other signaling molecules or the strength of PI3K or Ras signaling. Either genetic abrogation of YAP binding to MT or silencing of YAP via short hairpin RNA (shRNA) reduced MT transformation, suggesting that YAP makes a positive contribution to the transformed phenotype. MT targets YAP both by activating signaling pathways that affect it and by binding to it. MT signaling, whether from wild-type MT or the YAP-binding MT mutant, promoted YAP phosphorylation at S127 and S381/397 (YAP2/YAP1). Consistent with the known functions of these phosphorylated serines, MT signaling leads to the loss of YAP from the nucleus and degradation. Binding of YAP to MT brings it together with protein phosphatase 2A (PP2A), leading to the dephosphorylation of YAP in the MT complex. It also leads to the enrichment of YAP in membranes. Taken together, these results indicate that YAP promotes MT transformation via mechanisms that may depart from YAP's canonical oncogenic transcriptional activation functions.

IMPORTANCE

The highly conserved Hippo/YAP pathway is important for tissue development and homeostasis. Increasingly, changes in this pathway are being associated with cancer. Middle T antigen (MT) is the primary polyomavirus oncogene responsible for tumor formation. In this study, we show that MT signaling promotes YAP phosphorylation, loss from the nucleus, and increased turnover. Notably, MT genetics demonstrate that YAP binding to MT is important for transformation. Because MT also binds PP2A, YAP bound to MT is dephosphorylated, stabilized, and localized to membranes. Taken together, these results indicate that YAP promotes MT transformation via mechanisms that depart from YAP's canonical oncogenic transcriptional activation functions.

ω-3 PUFAs ameliorate liver fibrosis and inhibit hepatic stellate cells proliferation and activation by promoting YAP/TAZ degradation

Elevated levels of the transcriptional regulators Yes-associated protein (YAP) and transcriptional coactivators with PDZ-binding motif (TAZ), key effectors of the Hippo pathway, have been shown to play essential roles in controlling liver cell fate and the activation of hepatic stellate cells (HSCs). The dietary intake of omega-3 polyunsaturated fatty acids (ω-3 PUFAs) has been positively associated with a number of health benefits including prevention and reduction of cardiovascular diseases, inflammation and cancers. However, little is known about the impact of ω-3 PUFAs on liver fibrosis. In this study, we used CCl₄-induced liver fibrosis mouse model and found that YAP/TAZ is over-expressed in the fibrotic liver and activated HSCs. Fish oil administration to the model mouse attenuates CCl₄-induced liver fibrosis. Further study revealed that ω-3 PUFAs down-regulate the expression of pro-fibrogenic genes in activated HSCs and fibrotic liver, and the down-regulation is mediated via YAP, thus identifying YAP as a target of ω-3 PUFAs. Moreover, ω-3 PUFAs promote YAP/TAZ degradation in a proteasome-dependent manner. Our data have identified a mechanism of ω-3 PUFAs in ameliorating liver fibrosis.

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.