Prognostic value of the Hippo pathway transcriptional coactivators YAP/TAZ and β1-integrin in conventional osteosarcoma

Hierarchically Structured Hydroxyapatite Particles Facilitate the Enhanced Integration and Selective Anti-Tumor Effects of Amphiphilic Prodrug for Osteosarcoma Therapy

Efficient delivery of cargo into target cells is a formidable challenge in modern medicine. Despite the great promise of biomimetic hydroxyapatite (HA) particles in tissue engineering, their potential applications in bone tumor therapy, particularly their structure-function relationships in cargo delivery to target cells, have not yet been well explored. In this study, biomimetic multifunctional composite microparticles (Bm-cMPs) are developed by integrating an amphiphilic prodrug of curcumin with hierarchically structured HA microspheres (Hs-hMPs). Then, the effects of the hierarchical structure of vehicles on the integration and delivery of cargo as well as the anti-osteosarcoma (OS) effect of the composite are determined. Different hierarchical structures of the vehicles strongly influence the self-assembly behavior of the prodrug. The flake-like crystals of Hs-hMPs enable the highest loading capacity and enhance the stability of the cargo. Compared to the normal cells, OS cells exhibit 3.56-times better uptake of flake-like Hs-hMPs, facilitating the selective anti-tumor effect of the prodrug. Moreover, Bm-cMPs suppress tumor growth and metastasis by promoting apoptosis and inhibiting cell proliferation and tumor vascularization. The findings shed light on the potential application of Bm-cMPs and suggest a feasible strategy for developing an effective targeted therapy platform using hierarchically structured minerals for OS treatment.

Signal Pathways and microRNAs in Osteosarcoma Growth and the Dual Role of Mesenchymal Stem Cells in Oncogenesis

The major challenges in Osteosarcoma (OS) therapy are its heterogeneity and drug resistance. The development of new therapeutic approaches to overcome the major growth mechanisms of OS is urgently needed. The search for specific molecular targets and promising innovative approaches in OS therapy, including drug delivery methods, is an urgent problem. Modern regenerative medicine focuses on harnessing the potential of mesenchymal stem cells (MSCs) because they have low immunogenicity. MSCs are important cells that have received considerable attention in cancer research. Currently, new cell-based methods for using MSCs in medicine are being actively investigated and tested, especially as carriers for chemotherapeutics, nanoparticles, and photosensitizers. However, despite the inexhaustible regenerative potential and known anticancer properties of MSCs, they may trigger the development and progression of bone tumors. A better understanding of the complex cellular and molecular mechanisms of OS pathogenesis is essential to identify novel molecular effectors involved in oncogenesis. The current review focuses on signaling pathways and miRNAs involved in the development of OS and describes the role of MSCs in oncogenesis and their potential for antitumor cell-based therapy.

Mechanotransduction in tumor dynamics modeling

Mechanotherapy is a groundbreaking approach to impact carcinogenesis. Cells sense and respond to mechanical stimuli, translating them into biochemical signals in a process known as mechanotransduction. The impact of stress on tumor growth has been studied in the last three decades, and many papers highlight the role of mechanics as a critical self-inducer of tumor fate at the in vitro and in vivo biological levels. Meanwhile, mathematical models attempt to determine laws to reproduce tumor dynamics. This review discusses biological mechanotransduction mechanisms and mathematical-biomechanical models together. The aim is to provide a common framework for the different approaches that have emerged in the literature from the perspective of tumor avascularity and to provide insight into emerging mechanotherapies that have attracted interest in recent years.

Low p16 Cytoplasmic Staining Predicts Poor Treatment Outcome in Patients with p16-Negative Locally Advanced Head and Neck Squamous Cell Carcinoma Receiving TPF Induction Chemotherapy

Human papillomavirus (HPV) has been proven to be associated with head and neck squamous cell carcinoma (HNSCC), and diffuse p16 unclear staining is usually considered as HPV-positive. The aim of the current study was to investigate the role of p16 cytoplasmic staining in HNSCC prognosis. A total of 195 HNSCC patients who received docetaxel, cisplatin, and 5-fluouracil (TPF) induction chemotherapy followed by chemoradiotherapy were enrolled. The status of p16 cytoplasmic staining was determined using immunohistochemistry. The median follow-up was 26.0 months for the whole study population and 90.3 months for 51 living survivors. p16 cytoplasmic staining was low in 108 patients and high in 87 patients. Low expression of p16 cytoplasmic staining and primary tumor location in the oral cavity were both independent factors indicating a worse response rate to TPF induction chemotherapy in the univariate and multivariate analyses. The logistic regression model also showed that low expression of p16 cytoplasmic staining and clinical N2-3 status were independent prognostic factors for worse progression-free survival and overall survival. Our study showed that p16 cytoplasmic staining could predict the treatment response to TPF induction chemotherapy and is an independent prognostic factor of survival in HNSCC.

Genetic Alterations and Deregulation of Hippo Pathway as a Pathogenetic Mechanism in Bone and Soft Tissue Sarcoma

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

Single-Cell Transcriptome Analysis Reveals Paraspeckles Expression in Osteosarcoma Tissues

Nuclear paraspeckles are subnuclear bodies contracted by nuclear-enriched abundant transcript 1 (NEAT1) long non-coding RNA, localised in the interchromatin space of mammalian cell nuclei. Paraspeckles have been critically involved in tumour progression, metastasis and chemoresistance. To this date, there are limited findings to suggest that paraspeckles, NEAT1 and heterogeneous nuclear ribonucleoproteins (hnRNPs) directly or indirectly play roles in osteosarcoma progression. Herein, we analysed NEAT1, paraspeckle proteins (SFPQ, PSPC1 and NONO) and hnRNP members (HNRNPK, HNRNPM, HNRNPR and HNRNPD) gene expression in 6 osteosarcoma tumour tissues using the single-cell RNA-sequencing method. The normalised data highlighted that the paraspeckles transcripts were highly abundant in osteoblastic OS cells, except NEAT1, which was highly expressed in myeloid cell 1 and 2 subpopulations.

A calpain-6/YAP axis in sarcoma stem cells that drives the outgrowth of tumors and metastases

Sarcomas include cancer stem cells, but how these cells contribute to local and metastatic relapse is largely unknown. We previously showed the pro-tumor functions of calpain-6 in sarcoma stem cells. Here, we use an osteosarcoma cell model, osteosarcoma tissues and transcriptomic data from human tumors to study gene patterns associated with calpain-6 expression or suppression. Calpain-6 modulates the expression of Hippo pathway genes and stabilizes the hippo effector YAP. It also modulates the vesicular trafficking of β-catenin degradation complexes. Calpain-6 expression is associated with genes of the G2M phase of the cell cycle, supports G2M-related YAP activities and up-regulated genes controlling mitosis in sarcoma stem cells and tissues. In mouse models of bone sarcoma, most tumor cells expressed calpain-6 during the early steps of tumor out-growth. YAP inhibition prevented the neoformation of primary tumors and metastases but had no effect on already developed tumors. It could even accelerate lung metastasis associated with large bone tumors by affecting tumor-associated inflammation in the host tissues. Our results highlight a specific mechanism involving YAP transcriptional activity in cancer stem cells that is crucial during the early steps of tumor and metastasis outgrowth and that could be targeted to prevent sarcoma relapse.

Origin and Therapies of Osteosarcoma

Simple Summary

Osteosarcoma is the most common malignant bone tumor in children, with a 5-year survival rate ranging from 70% to 20% depending on the aggressiveness of the disease. The current treatments have not evolved over the past four decades due in part to the genetic complexity of the disease and its heterogeneity. This review will summarize the current knowledge of OS origin, diagnosis and therapies.

Abstract

Osteosarcoma (OS) is the most frequent primary bone tumor, mainly affecting children and young adults. Despite therapeutic advances, the 5-year survival rate is 70% but drastically decreases to 20–30% for poor responders to therapies or for patients with metastasis. No real evolution of the survival rates has been observed for four decades, explained by poor knowledge of the origin, difficulties related to diagnosis and the lack of targeted therapies for this pediatric tumor. This review will describe a non-exhaustive overview of osteosarcoma disease from a clinical and biological point of view, describing the origin, diagnosis and therapies.

Lung fibrosis is a novel therapeutic target to suppress lung metastasis of osteosarcoma

The prognosis of patients with metastatic and recurrent osteosarcoma has not improved over the last 30 years because no effective treatment strategy has been established for lung metastases. Although molecular-targeted drugs that modify the extracellular environment, such as anti-fibrotic agents, have been developed for cancer treatment, the suppressive effects of anti-fibrotic agents on osteosarcoma lung metastasis are unclear. Osteosarcomas need to adapt to considerable changes with respect to the stiffness of the environment and fibrosis during lung metastasis and may thus be vulnerable to fibrotic suppression as they originate at the site of a stiff bone with considerable fibrosis. In this study, we investigated whether fibrosis was a therapeutic target for suppressing osteosarcoma metastasis. Lung tissue samples from patients and a mouse model (LM8-Dunn model) showed that lung metastatic colonization of osteosarcoma cells proceeded with massive lung fibrosis. Metastatic osteosarcoma LM8 cells proliferated in a scaffold-dependent manner; the proliferation was less dependent on YAP-mediated mechanotransduction on soft polyacrylamide gels. The anti-fibrotic agents pirfenidone and nintedanib suppressed lung metastasis in the LM8-Dunn model. The osteosarcoma cells did not show increased proliferation, as reported in breast cancer, after continuous culture in a soft environment. We speculated that the anti-fibrotic agents were effective because the osteosarcoma cells remained scaffold-dependent in the soft tissue environment. Thus, anti-fibrotic strategies may be useful in suppressing lung metastasis of bone and soft tissue tumors with stiff primary sites such as those in osteosarcoma.

Correlation of nuclear pIGF-1R/IGF-1R and YAP/TAZ in a tissue microarray with outcomes in osteosarcoma patients

Osteosarcoma (OS) is a genetically diverse bone cancer that lacks a consistent targetable mutation. Recent studies suggest the IGF/PI3K/mTOR pathway and YAP/TAZ paralogs regulate cell fate and proliferation in response to biomechanical cues within the tumor microenvironment. How this occurs and their implication upon osteosarcoma survival, remains poorly understood. Here, we show that IGF-1R can translocate into the nucleus, where it may act as part of a transcription factor complex. To explore the relationship between YAP/TAZ and total and nuclear phosphorylated IGF-1R (pIGF-1R), we evaluated sequential tumor sections from a 37-patient tissue microarray by confocal microscopy. Next, we examined the relationship between stained markers, clinical disease characteristics, and patient outcomes. The nuclear to cytoplasmic ratios (N:C ratio) of YAP and TAZ strongly correlated with nuclear pIGF-1R (r = 0.522, p = 0.001 for each pair). Kaplan-Meier analyses indicated that nuclear pIGF-1R predicted poor overall survival, a finding confirmed in the Cox proportional hazards model. Though additional investigation in a larger prospective study will be required to validate the prognostic accuracy of these markers, our results may have broad implications for the new class of YAP, TAZ, AXL, or TEAD inhibitors that have reached early phase clinical trials this year.

The Hippo pathway in cancer: YAP/TAZ and TEAD as therapeutic targets in cancer

Tumorigenesis is a highly complex process, involving many interrelated and cross-acting signalling pathways. One such pathway that has garnered much attention in the field of cancer research over the last decade is the Hippo signalling pathway. Consisting of two antagonistic modules, the pathway plays an integral role in both tumour suppressive and oncogenic processes, generally via regulation of a diverse set of genes involved in a range of biological functions. This review discusses the history of the pathway within the context of cancer and explores some of the most recent discoveries as to how this critical transducer of cellular signalling can influence cancer progression. A special focus is on the various recent efforts to therapeutically target the key effectors of the pathway in both preclinical and clinical settings.

Targeting the IGF/PI3K/mTOR Pathway and AXL/YAP1/TAZ pathways in Primary Bone Cancer

Primary bone cancers (PBC) belong to the family of mesenchymal tumors classified based on their cellular origin, extracellular matrix, genetic regulation, and epigenetic modification. The three major PBC types, Ewing sarcoma, osteosarcoma, and chondrosarcoma, are frequently aggressive tumors, highly metastatic, and typically occur in children and young adults. Despite their distinct origins and pathogenesis, these sarcoma subtypes rely upon common signaling pathways to promote tumor progression, metastasis, and survival. The IGF/PI3K/mTOR and AXL/YAP/TAZ pathways, in particular, have gained significant attention recently given their ties to oncogenesis, cell fate and differentiation, metastasis, and drug resistance. Naturally, these pathways – and their protein constituents – have caught the eye of the pharmaceutical industry, and a wide array of small molecule inhibitors and antibody drug-conjugates have emerged. Here, we review how the IGF/PI3K/mTOR and AXL/YAP/TAZ pathways promote PBC and highlight the drug candidates under clinical trial investigation.

The Hippo signaling pathway in leukemia: function, interaction, and carcinogenesis

Cancer can be considered as a communication disease between and within cells; nevertheless, there is no effective therapy for the condition, and this disease is typically identified at its late stage. Chemotherapy, radiation, and molecular-targeted treatment are typically ineffective against cancer cells. A better grasp of the processes of carcinogenesis, aggressiveness, metastasis, treatment resistance, detection of the illness at an earlier stage, and obtaining a better therapeutic response will be made possible. Researchers have discovered that cancerous mutations mainly affect signaling pathways. The Hippo pathway, as one of the main signaling pathways of a cell, has a unique ability to cause cancer. In order to treat cancer, a complete understanding of the Hippo signaling system will be required. On the other hand, interaction with other pathways like Wnt, TGF-β, AMPK, Notch, JNK, mTOR, and Ras/MAP kinase pathways can contribute to carcinogenesis. Phosphorylation of oncogene YAP and TAZ could lead to leukemogenesis, which this process could be regulated via other signaling pathways. This review article aimed to shed light on how the Hippo pathway interacts with other cellular signaling networks and its functions in leukemia.

Involvement of the TGF-β Signaling Pathway in the Development of YAP-Driven Osteosarcoma Lung Metastasis

Background

The poor survival rate of patients with osteosarcoma (OS), specifically with metastases at diagnosis, undergoes the urgency to develop new therapeutic strategies. Although we recently demonstrated the key role of YAP/TEAD signaling in the growth of OS primary tumor, the molecular mechanisms by which YAP regulates metastases development remain poorly understood.

Methods

The molecular mechanisms by which YAP regulates metastases development were studied using an overexpression of mutated forms of YAP able or not able to interact with TEAD. Molecular signatures were identified using RNA-sequencing analysis and gene set enrichment. Interactions between YAP and Smad3 were studied using proximity ligation assay (PLA), immunoprecipitation, and promoter/specific gene assays. The involvement of the TGF-β pathway in the ability of YAP to stimulate metastatic development in vivo was studied using an inhibitor of the TGF-β cascade in a preclinical model of OS and in vitro on the ability of OS cells to migrate and invade.

Results

Our work shows that a high YAP expression is associated with the presence of lung metastases which predicts a poor prognosis. Molecular analysis indicates that TGF-β signaling is involved in YAP-driven osteosarcoma cell pro-migratory phenotype, epithelial mesenchymal transition, cell migration, and in vivo lung metastasis development. Regardless of its ability to bind to TEAD, YAP interacts with Smad3 and stimulates the transcriptional activity of TGF-β/Smad3, thereby enhancing the ability of TGF-β to stimulate lung metastasis development.

Conclusions

We demonstrated the crucial involvement of the TGF-β/Smad3 signaling pathway in YAP-driven lung metastasis development in OS.

Ribophorin II Overexpression Is Associated with Poor Response to Induction Chemotherapy with Docetaxel, Cisplatin, and Fluorouracil in P16-Negative Locally Advanced Head and Neck Squamous Cell Carcinoma

This study aims to evaluate the relationship between human ribophorin II (RPN2) and the effect of treatment using induction therapy with docetaxel, cisplatin, and fluorouracil (TPF) for p-16 negative locally advanced head and neck squamous cell carcinoma (HNSCC). A total of 203 patients with locally advanced p-16 negative HNSCC who received induction chemotherapy with TPF at the Kaohsiung Chang Gung Memorial Hospital between 2009 and 2014 were enrolled. Immunohistochemistry (IHC) for RPN2 was examined and correlated with treatment outcome. Our study showed that RPN2 overexpression was significantly correlated with a poor response to induction chemotherapy with TPF. Both RPN2 overexpression and clinical N1 to N3 stages represented adverse prognostic factors for progression-free survival (PFS) and overall survival (OS). RPN2 might be a predictive marker for treatment response to induction chemotherapy. Further clinical trials are needed to determine the therapeutic significance of RPN2 in patients with HNSCC.

12 Survival-related differentially expressed genes based on the TARGET-osteosarcoma database

The Therapeutically Applicable Research to Generate Effective Treatments (TARGET) project aims to determine molecular changes that drive childhood cancers, including osteosarcoma. The main purpose of the program is to use the open-source database to develop novel, effective, and less toxic therapies. We downloaded TARGET-OS RNA-Sequencing data through R studio and merged the mRNA expression of genes with clinical information (vital status, survival time and gender). Further, we analyzed differential gene expressions between dead and alive patients based on TARGET-OS project. By this study, we found 5758 differentially expressed genes between deceased and alive patients with a false discovery rate below 0.05; 4469 genes were upregulated in deceased patients compared to alive, whereas 1289 genes were downregulated. The survival-related genes were obtained using Kaplan-Meier survival analysis and Cox univariate regression (KM < 0.05 and Cox P-value < 0.05). Out of 5758 differentially expressed genes, only 217 have been associated with overall survival. Eight survival-related downregulated genes (ERCC4, CLUAP1, CTNNBIP1, GCA, RAB40C, SIRPA, USP11, and TCN2) and four survival-related upregulated genes (MUC1, COL13A1, JAG2 and KAZALD1) were selected for further analysis as potential independent prognostic candidate genes. This study may help to discover novel prognostic markers and potential therapeutic targets for osteosarcoma.

RGS12 is a novel tumor suppressor in osteosarcoma that inhibits YAP-TEAD1-Ezrin signaling

Osteosarcoma (OS) is the most common primary malignancy of the bone that predominantly affects children and adolescents. Hippo pathway is a crucial regulator of organ size and tumorigenesis. However, how Hippo pathway regulates the occurrence of osteosarcoma is largely unknown. Here, we reported the regulator of G protein signaling protein 12 (RGS12) is a novel Hippo pathway regulator and tumor suppressor of osteosarcoma. Depletion of Rgs12 promotes osteosarcoma progression and lung metastasis in an orthotopic xenograft mouse model. Our data showed that the knockdown of RGS12 upregulates Ezrin expression through promoting the GNA12/13-RhoA-YAP pathway. Moreover, RGS12 negatively regulates the transcriptional activity of YAP/TEAD1 complex through its PDZ domain function to inhibit the expression and function of the osteosarcoma marker Ezrin. PDZ domain peptides of RGS12 can inhibit the development of intratibial tumor and lung metastases. Collectively, this study identifies that the RGS12 is a novel tumor suppressor in osteosarcoma through inhibiting YAP-TEAD1-Ezrin signaling pathway and provides a proof of principle that targeting RGS12 may be a therapeutic strategy for osteosarcoma.

Allelic Expression Imbalance Analysis Identified YAP1 Amplification in p53- Dependent Osteosarcoma

Simple Summary

Osteosarcoma (OS) is a highly heterogenous cancer, making the identification of genetic driving factors difficult. Genetic factors, such as heritable mutations of Rb1 and TP53, are associated with an increased risk of OS. We previously generated pigs carrying a mutated TP53 gene, which develop OS at high frequency. RNA sequencing and allelic expression imbalance analysis identified an amplification of YAP1 involved in p53- dependent OS progression. The inactivation of YAP1 inhibits proliferation, migration, and invasion, and leads to the silencing of TP63 and reconstruction of p16 expression in p53-deficient porcine OS cells. This study confirms the importance of p53/YAP1 network in cancer.

Abstract

Osteosarcoma (OS) is a primary bone malignancy that mainly occurs during adolescent growth, suggesting that bone growth plays an important role in the aetiology of the disease. Genetic factors, such as heritable mutations of Rb1 and TP53, are associated with an increased risk of OS. Identifying driver mutations for OS has been challenging due to the complexity of bone growth-related pathways and the extensive intra-tumoral heterogeneity of this cancer. We previously generated pigs carrying a mutated TP53 gene, which develop OS at high frequency. RNA sequencing and allele expression imbalance (AEI) analysis of OS and matched healthy control samples revealed a highly significant AEI (p = 2.14 × 10⁻³⁹) for SNPs in the BIRC3-YAP1 locus on pig chromosome 9. Analysis of copy number variation showed that YAP1 amplification is associated with the AEI and the progression of OS. Accordingly, the inactivation of YAP1 inhibits proliferation, migration, and invasion, and leads to the silencing of TP63 and reconstruction of p16 expression in p53-deficient porcine OS cells. Increased p16 mRNA expression correlated with lower methylation of its promoter. Altogether, our study provides molecular evidence for the role of YAP1 amplification in the progression of p53-dependent OS.

Transcriptional activators YAP/TAZ and AXL orchestrate dedifferentiation, cell fate, and metastasis in human osteosarcoma

Osteosarcoma (OS) is a molecularly heterogeneous, aggressive, poorly differentiated pediatric bone cancer that frequently spreads to the lung. Relatively little is known about phenotypic and epigenetic changes that promote lung metastases. To identify key drivers of metastasis, we studied human CCH-OS-D OS cells within a previously described rat acellular lung (ACL) model that preserves the native lung architecture, extracellular matrix, and capillary network. This system identified a subset of cells—termed derived circulating tumor cells (dCTCs)—that can migrate, intravasate, and spread within a bioreactor-perfused capillary network. Remarkably, dCTCs highly expressed epithelial-to-mesenchymal transition (EMT)-associated transcription factors (EMT-TFs), such as ZEB1, TWIST, and SOX9, which suggests that they undergo cellular reprogramming toward a less differentiated state by coopting the same epigenetic machinery used by carcinomas. Since YAP/TAZ and AXL tightly regulate the fate and plasticity of normal mesenchymal cells in response to microenvironmental cues, we explored whether these proteins contributed to OS metastatic potential using an isogenic pair of human OS cell lines that differ in AXL expression. We show that AXL inhibition significantly reduced the number of MG63.2 pulmonary metastases in murine models. Collectively, we present a laboratory-based method to detect and characterize a pure population of dCTCs, which provides a unique opportunity to study how OS cell fate and differentiation contributes to metastatic potential. Though the important step of clinical validation remains, our identification of AXL, ZEB1, and TWIST upregulation raises the tantalizing prospect that EMT-TF-directed therapies might expand the arsenal of therapies used to combat advanced-stage OS.

The YAP/TEAD Axis as a New Therapeutic Target in Osteosarcoma: Effect of Verteporfin and CA3 on Primary Tumor Growth

Although some studies suggested that disruption of the Hippo signaling pathway is associated with osteosarcoma progression, the molecular mechanisms by which YAP regulates primary tumor growth is not fully clarified. In addition, the validation of YAP as a therapeutic target through the use of inhibitors in a preclinical model must be demonstrated. RNA-seq analysis and Kaplan-Meier assays identified a YAP signature in osteosarcoma patients and a correlation with patients' outcomes. Molecular and cellular analysis (RNAseq, PLA, immunoprecipitation, promoter/specific gene, proliferation, cell cycle assays) using overexpression of mutated forms of YAP able or unable to interact with TEAD, indicate that TEAD is crucial for YAP-driven cell proliferation and in vivo tumor growth. In addition, in vivo experiments using an orthotopic mice model of osteosarcoma show that two YAP/TEAD inhibitors, verteporfin and CA3, reduce primary tumor growth. In this context, in vitro experiments demonstrate that these inhibitors decrease YAP expression, YAP/TEAD transcriptional activity and cell viability mainly by their ability to induce cell apoptosis. We thus demonstrate that the YAP/TEAD signaling axis is a central actor in mediating primary tumor growth of osteosarcoma, and that the use of YAP inhibitors may be a promising therapeutic strategy against osteosarcoma tumor growth.

Targeting Mechanotransduction in Osteosarcoma: A Comparative Oncology Perspective

Mechanotransduction is the process in which cells can convert extracellular mechanical stimuli into biochemical changes within a cell. While this a normal process for physiological development and function in many organ systems, tumour cells can exploit this process to promote tumour progression. Here we summarise the current state of knowledge of mechanotransduction in osteosarcoma (OSA), the most common primary bone tumour, referencing both human and canine models and other similar mesenchymal malignancies (e.g., Ewing sarcoma). Specifically, we discuss the mechanical properties of OSA cells, the pathways that these cells utilise to respond to external mechanical cues, and mechanotransduction-targeting strategies tested in OSA so far. We point out gaps in the literature and propose avenues to address them. Understanding how the physical microenvironment influences cell signalling and behaviour will lead to the improved design of strategies to target the mechanical vulnerabilities of OSA cells.

The crosstalk between lncRNAs and the Hippo signalling pathway in cancer progression

LncRNAs play a pivotal role in the regulation of epigenetic modification, cell cycle, differentiation, proliferation, migration and other physiological activities. In particular, considerable studies have shown that the aberrant expression and dysregulation of lncRNAs are widely implicated in cancer initiation and progression by acting as tumour promoters or suppressors. Hippo signalling pathway has attracted researchers’ attention as one of the critical cancer‐related pathways in recent years. Increasing evidences have demonstrated that lncRNAs could interact with Hippo cascade and thereby contribute to acquisition of multiple malignant hallmarks, including proliferation, metastasis, relapse and resistance to anti‐cancer treatment. Specifically, Hippo signalling pathway is reported to modulate or be regulated by widespread lncRNAs. Intriguingly, certain lncRNAs could form a reciprocal feedback loop with Hippo signalling. More speculatively, lncRNAs related to Hippo pathway have been poised to become important putative biomarkers and therapeutic targets in human cancers. Herein, this review focuses on the crosstalk between lncRNAs and Hippo pathway in carcinogenesis, summarizes the comprehensive role of Hippo‐related lncRNAs in tumour progression and depicts their clinical diagnostic, prognostic or therapeutic potentials in tumours.

The Hippo in the room: Targeting the Hippo signalling pathway for osteosarcoma therapies

Osteosarcoma (OS) is a primary malignant bone tumour which usually occurs in children and adolescents. OS is primarily a result of chromosomal aberrations, a combination of acquired genetic changes and, hereditary, resulting in the dysregulation of cellular functions. The Hippo signalling pathway regulates cell and tissue growth by modulating cell proliferation, differentiation, and migration in developing organs. Mammalian STE20-like 1/2 (MST1/2) protein kinases are activated by neurofibromatosis type 2, Ras association domain family member 2, kidney and brain protein, or other factors. Interactions between MST1/2 and salvador family WW domain-containing protein 1 activate large tumour suppressor kinase 1/2 proteins, which in turn phosphorylate the downstream Yes-associated protein 1/transcriptional coactivator with PDZ-binding motif (YAP/TAZ). Moreover, dysregulation of this pathway can lead to aberrant cell growth, resulting in tumorigenesis. Interestingly, small molecules targeting the Hippo signalling pathways, through affecting YAP/TAZ cellular localisation and their interaction with members of the TEA/ATTS domain family of transcriptional enhancers are being developed and hold promise for the treatment of OS. This review discusses the existing knowledge about the involvement of the Hippo signalling cascade in OS and highlights several small molecule inhibitors as potential novel therapeutics.

Modeling the Tumor Microenvironment and Pathogenic Signaling in Bone Sarcoma

Investigations of cancer biology and screening of potential therapeutics for efficacy and safety begin in the preclinical laboratory setting. A staple of most basic research in cancer involves the use of tissue culture plates, on which immortalized cell lines are grown in monolayers. However, this practice has been in use for over six decades and does not account for vital elements of the tumor microenvironment that are thought to aid in initiation, propagation, and ultimately, metastasis of cancer. Furthermore, information gleaned from these techniques does not always translate to animal models or, more crucially, clinical trials in cancer patients. Osteosarcoma (OS) and Ewing sarcoma (ES) are the most common primary tumors of bone, but outcomes for patients with metastatic or recurrent disease have stagnated in recent decades. The unique elements of the bone tumor microenvironment have been shown to play critical roles in the pathogenesis of these tumors and thus should be incorporated in the preclinical models of these diseases. In recent years, the field of tissue engineering has leveraged techniques used in designing scaffolds for regenerative medicine to engineer preclinical tumor models that incorporate spatiotemporal control of physical and biological elements. We herein review the clinical aspects of OS and ES, critical elements present in the sarcoma microenvironment, and engineering approaches to model the bone tumor microenvironment. Impact statement The current paradigm of cancer biology investigation and therapeutic testing relies heavily on monolayer, monoculture methods developed over half a century ago. However, these methods often lack essential hallmarks of the cancer microenvironment that contribute to tumor pathogenesis. Tissue engineers incorporate scaffolds, mechanical forces, cells, and bioactive signals into biological environments to drive cell phenotype. Investigators of bone sarcomas, aggressive tumors that often rob patients of decades of life, have begun to use tissue engineering techniques to devise in vitro models for these diseases. Their efforts highlight how critical elements of the cancer microenvironment directly affect tumor signaling and pathogenesis.

The YAP/TAZ Pathway in Osteogenesis and Bone Sarcoma Pathogenesis

YAP and TAZ are intracellular messengers communicating multiple interacting extracellular biophysical and biochemical cues to the transcription apparatus in the nucleus and back to the cell/tissue microenvironment interface through the regulation of cytoskeletal and extracellular matrix components. Their activity is negatively and positively controlled by multiple phosphorylation events. Phenotypically, they serve an important role in cellular plasticity and lineage determination during development. As they regulate self-renewal, proliferation, migration, invasion and differentiation of stem cells, perturbed expression of YAP/TAZ signaling components play important roles in tumorigenesis and metastasis. Despite their high structural similarity, YAP and TAZ are functionally not identical and may play distinct cell type and differentiation stage-specific roles mediated by a diversity of downstream effectors and upstream regulatory molecules. However, YAP and TAZ are frequently looked at as functionally redundant and are not sufficiently discriminated in the scientific literature. As the extracellular matrix composition and mechanosignaling are of particular relevance in bone formation during embryogenesis, post-natal bone elongation and bone regeneration, YAP/TAZ are believed to have critical functions in these processes. Depending on the differentiation stage of mesenchymal stem cells during endochondral bone development, YAP and TAZ serve distinct roles, which are also reflected in bone tumors arising from the mesenchymal lineage at different developmental stages. Efforts to clinically translate the wealth of available knowledge of the pathway for cancer diagnostic and therapeutic purposes focus mainly on YAP and TAZ expression and their role as transcriptional co-activators of TEAD transcription factors but rarely consider the expression and activity of pathway modulatory components and other transcriptional partners of YAP and TAZ. As there is a growing body of evidence for YAP and TAZ as potential therapeutic targets in several cancers, we here interrogate the applicability of this concept to bone tumors. To this end, this review aims to summarize our current knowledge of YAP and TAZ in cell plasticity, normal bone development and bone cancer.

Hippo/YAP Signaling Pathway: A Promising Therapeutic Target in Bone Paediatric Cancers?

Osteosarcoma and Ewing sarcoma are the most prevalent bone pediatric tumors. Despite intensive basic and medical research studies to discover new therapeutics and to improve current treatments, almost 40% of osteosarcoma and Ewing sarcoma patients succumb to the disease. Patients with poor prognosis are related to either the presence of metastases at diagnosis or resistance to chemotherapy. Over the past ten years, considerable interest for the Hippo/YAP signaling pathway has taken place within the cancer research community. This signaling pathway operates at different steps of tumor progression: Primary tumor growth, angiogenesis, epithelial to mesenchymal transition, and metastatic dissemination. This review discusses the current knowledge about the involvement of the Hippo signaling pathway in cancer and specifically in paediatric bone sarcoma progression.

Hippo pathway effectors YAP1/TAZ induce an EWS-FLI1-opposing gene signature and associate with disease progression in Ewing sarcoma

YAP1 and TAZ (WWTR1) oncoproteins are the final transducers of the Hippo tumor suppressor pathway. Deregulation of the pathway leads to YAP1/TAZ activation fostering tumorigenesis in multiple malignant tumor types, including sarcoma. However, oncogenic mutations within the core components of the Hippo pathway are uncommon. Ewing sarcoma (EwS), a pediatric cancer with low mutation rate, is characterized by a canonical fusion involving the gene EWSR1 and FLI1 as the most common partner. The fusion protein is a potent driver of oncogenesis, but secondary alterations are scarce, and little is known about other biological factors that determine the risk of relapse or progression. We have observed YAP1/TAZ expression and transcriptional activity in EwS cell lines. Analyses of 55 primary human EwS samples revealed that high YAP1/TAZ expression was associated with progression of the disease and predicted poorer outcome. We did not observe recurrent SNV or copy number gains/losses in Hippo pathway-related loci. However, differential CpG methylation of the RASSF1 locus (a regulator of the Hippo pathway) was observed in EwS cell lines compared with mesenchymal stem cells, the putative cell of origin of EwS. Hypermethylation of RASSF1 correlated with the transcriptional silencing of the tumor suppressor isoform RASFF1A, and transcriptional activation of the pro-tumorigenic isoform RASSF1C, which promotes YAP1/TAZ activation. Knockdown of YAP1/TAZ decreased proliferation and invasion abilities of EwS cells and revealed that YAP1/TAZ transcription activity is inversely correlated with the EWS-FLI1 transcriptional signature. This transcriptional antagonism could be explained partly by EWS-FLI1-mediated transcriptional repression of TAZ. Thus, YAP1/TAZ may override the transcriptional program induced by the fusion protein, contributing to the phenotypic plasticity determined by dynamic fluctuation of the fusion protein, a recently proposed model for disease dissemination in EwS. © 2019 The Authors. The Journal of Pathology published by John Wiley & Sons Ltd on behalf of Pathological Society of Great Britain and Ireland.

Relation Between Immunohistochemical Expression of Hippo Pathway Effectors and Chronic Hepatitis Induced Fibrosis in Egyptian Patients

OBJECTIVE

Chronic hepatitis is a global health problem especially in Egypt. Hepatic fibrosis is a common end clinical manifestation of many chronic liver diseases. Although it is a wound-healing process, excessive accumulation of fibrillary collagen leads to architectural damage, cirrhosis and liver failure. Recently, a few studies have linked Hippo pathway effectors of yes-associated protein (YAP) and its paralog transcriptional coactivator with PDZ-binding motif (TAZ) to extracellular matrix deposition and ongoing fibrosis.

MATERIAL AND METHOD

Immunohistochemical expression of YAP and TAZ were analyzed in 121 liver needle core biopsies (91 core biopsies of chronic viral hepatitis, 20 biopsies of autoimmune hepatitis and 10 normal liver cores).

RESULTS

YAP and TAZ nuclear localization was absent in all normal liver cores. Autoimmune hepatitis cases showed higher nuclear expression of both YAP and TAZ in comparison to chronic viral cases. YAP and TAZ expression were correlated with severity of hepatocyte injury together with fibrosis in chronic viral cases but these correlations were absent in AIH cases despite the pronounced increase of YAP and TAZ nuclear localization.

CONCLUSION

The correlation between Hippo effectors activation and fibrosis in chronic viral hepatitis patients emphasize their role in the development and advancement of hepatic scarring and highlight the use of both YAP and TAZ as novel targets to ameliorate liver fibrosis.

Sarcoma Tumor Microenvironment

Components of the tumor microenvironment (TME) are known to play an essential role during malignant progression, but often in a context-dependent manner. In bone and soft tissue sarcomas, disease-regulatory activities in the TME remain largely uncharacterized. This chapter introduces the cellular, structural, and chemical composition of the sarcoma TME from a pathobiological and therapeutic perspective.Sarcomas are malignant tumors with diverse features when it comes to primary tumor appearance, metastatic potential, and response to treatment. Many of the classic subtypes are mainly composed of malignant cells and are therefore assumed to be committed to autocrine signaling. Some of the tumors are infiltrated by immune cells and contain necrotic areas or excessive amounts of extracellular matrix (ECM) that regulates tissue stiffness and interstitial fluid pressure. Vascular invasion and blood vessel characteristics can in some instances be considered in the prognostic setting.Further insights into the disease-regulatory activities of the sarcoma TME will provide essential knowledge on how to develop successful combination treatments targeting not only malignant cells, but also their routes of nutrition and ability to shield themselves toward existing therapy.

ROCK2 deprivation leads to the inhibition of tumor growth and metastatic potential in osteosarcoma cells through the modulation of YAP activity

Background

The treatment of metastatic osteosarcoma (OS) remains a challenge for oncologists, and novel therapeutic strategies are urgently needed. An understanding of the pathways that regulate OS dissemination is required for the design of novel treatment approaches. We recently identified Rho-associated coiled-coil containing protein kinase 2 (ROCK2) as a crucial driver of OS cell migration. In this study, we explored the impact of ROCK2 disruption on the metastatic capabilities of OS cells and analyzed its functional relationship with Yes-associated protein-1 (YAP), the main transcriptional mediator of mechanotransduction signaling.

Methods

The effects of ROCK2 depletion on metastasis were studied in NOD Scid gamma (NSG) mice injected with U-2OS cells in which ROCK2 expression had been stably silenced. Functional studies were performed in vitro in human U-2OS cells and in three novel cell lines derived from patient-derived xenografts (PDXs) by using standard methods to evaluate malignancy parameters and signaling transduction. The nuclear immunostaining of YAP and the evaluation of its downstream targets Cysteine Rich Angiogenic Inducer 6, Connective Tissue Growth Factor and Cyclin D1 by quantitative PCR were performed to analyze YAP activity. The effect of the expression and activity of ROCK2 and YAP on tumor progression was analyzed in 175 OS primary tumors.

Results

The silencing of ROCK2 markedly reduced tumor growth and completely abolished the metastatic ability of U-2OS cells. The depletion of ROCK2, either by pharmacological inhibition or silencing, induced a dose- and time-dependent reduction in the nuclear expression and transcriptional activity of YAP. The nuclear expression of YAP was observed in 80/175 (46%) tumor samples and was significantly correlated with worse patient prognosis and a higher likelihood of metastasis and death. The use of verteporfin, a molecule that specifically inhibits the TEAD–YAP association, remarkably impaired the growth and migration of OS cells in vitro. Moreover to inhibiting YAP activity, our findings indicate that verteporfin also affects the ROCK2 protein and its functions.

Conclusions

We describe the functional connection between ROCK2 and YAP in the regulation of OS cell migration and metastasis formation. These data provide support for the use of verteporfin as a possible therapeutic option to prevent OS cell dissemination.

Mechanically tunable coaxial electrospun models of YAP/TAZ mechanoresponse and IGF-1R activation in osteosarcoma

Current in vitro methods for assessing cancer biology and therapeutic response rely heavily on monolayer cell culture on hard, plastic surfaces that do not recapitulate essential elements of the tumor microenvironment. While a host of tumor models exist, most are not engineered to control the physical properties of the microenvironment and thus may not reflect the effects of mechanotransduction on tumor biology. Utilizing coaxial electrospinning, we developed three-dimensional (3D) tumor models with tunable mechanical properties in order to elucidate the effects of substrate stiffness and tissue architecture in osteosarcoma. Mechanical properties of coaxial electrospun meshes were characterized with a series of macroscale testing with uniaxial tensile testing and microscale testing utilizing atomic force microscopy on single fibers. Calculated moduli in our models ranged over three orders of magnitude in both macroscale and microscale testing. Osteosarcoma cells responded to decreasing substrate stiffness in 3D environments by increasing nuclear localization of Hippo pathway effectors, YAP and TAZ, while downregulating total YAP. Additionally, a downregulation of the IGF-1R/mTOR axis, the target of recent clinical trials in sarcoma, was observed in 3D models and heralded increased resistance to combination chemotherapy and IGF-1R/mTOR targeted agents compared to monolayer controls. In this study, we highlight the necessity of incorporating mechanical cues in cancer biology investigation and the complexity in mechanotransduction as a confluence of stiffness and culture architecture. Our models provide a versatile, mechanically variable substrate on which to study the effects of physical cues on the pathogenesis of tumors. STATEMENT OF SIGNIFICANCE: The tumor microenvironment plays a critical role in cancer pathogenesis. In this work, we engineered 3D, mechanically tunable, coaxial electrospun environments to determine the roles of the mechanical environment on osteosarcoma cell phenotype, morphology, and therapeutic response. We characterize the effects of varying macroscale and microscale stiffnesses in 3D environments on the localization and expression of the mechanoresponsive proteins, YAP and TAZ, and evaluate IGF-1R/mTOR pathway activation, a target of recent clinical trials in sarcoma. Increased nuclear YAP/TAZ was observed as stiffness in 3D was decreased. Downregulation of the IGF-1R/mTOR cascade in all 3D environments was observed. Our study highlights the complexity of mechanotransduction in 3D culture and represents a step towards controlling microenvironmental elements in in vitro cancer investigations.

Gankyrin promotes osteosarcoma tumorigenesis by forming a positive feedback loop with YAP

BACKGROUND

Although gankyrin has been identified as a vital regulator of tumorigenesis, its role and regulatory mechanism in osteosarcoma (OS) remain unclear.

METHODS

QRT-PCR, western blot and IHC staining were conducted to detect the expression of gankyrin in OS. Pearson's χ² test was adopted to examine the associations between gankyrin expression and clinicopathologic characteristics. Kaplan-Meier method was used to investigate the relationship between gankyrin expression and overall survival of patients with OS. Next, a series of in vitro and in vivo assays were performed to determine the positive feedback loop between gankyrin and YAP in OS.

RESULTS

We first reported that gankyrin is upregulated in human OS specimens and cell lines and predicts OS progression and poor prognosis. Furthermore, we demonstrated that gankyrin protects miR-200a-mediated yes-associated protein (YAP) downregulation through p53 and establishes a positive feedback loop to regulate YAP signaling in U2OS and MG63 cells. Intriguingly, gankyrin interacts with YAP to promote OS cell growth in vitro. In addition, our results showed that gankyrin promotes OS tumor growth and regulates YAP levels in vivo. Notably, we also observed a positive correlation between gankyrin and YAP expression in human OS tissues, and co-upregulation of gankyrin and YAP indicated a poor prognosis.

CONCLUSIONS

Our results identify that gankyrin acts as an oncogene in OS by forming a positive feedback loop with YAP, and disrupting the gankyrin-YAP regulation may be beneficial for controlling OS tumorigenesis.

Destined to Die: Apoptosis and Pediatric Cancers

Apoptosis (programmed cell death) is a systematic and coordinated cellular process that occurs in physiological and pathophysiological conditions. Sidestepping or resisting apoptosis is a distinct characteristic of human cancers including childhood malignancies. This review dissects the apoptosis pathways implicated in pediatric tumors. Understanding these pathways not only unraveled key molecules that may serve as potential targets for drug discovery, but also molecular nodes that integrate with other signaling networks involved in processes such as development. This review presents current knowledge of the complex regulatory system that governs apoptosis with respect to other processes in pediatric cancers, so that fresh insights may be derived regarding treatment resistance or for more effective treatment options.

Clinical and biological implications of Hippo pathway dysregulation in sarcomas

Sarcomas are mesenchymal malignant tumors with poor prognosis and limited treatment options. Hippo pathway is a recently discovered pathway normally involved in organ development and wound healing. Hippo signaling is often altered in solid tumors. The molecular elements of Hippo signaling include MST1/2 and LATS1/2 kinases which phosphorylate and regulate the activity of YAP and TAZ co-transcriptional activators. Hippo pathway cross-talks with several molecular pathways with known oncogenic function. In sarcomas Hippo signaling plays a pivotal role in tumorigenesis, evolution and resistance in chemotherapy regimens. Targeting Hippo pathway could potentially improve prognosis and outcome of sarcoma patients.

CYR61 triggers osteosarcoma metastatic spreading via an IGF1Rβ-dependent EMT-like process

BACKGROUND

Osteosarcoma is the most prevalent primary bone malignancy in children and young adults. These tumors are highly metastatic, leading to poor outcome. We previously demonstrated that Cysteine-rich protein 61 (CYR61/CCN1) expression level is correlated to osteosarcoma aggressiveness in preclinical model and in patient tumor samples. The aim of the present study was to investigate the CYR61-induced intracellular mechanisms leading to the acquisition of an invasive phenotype by osteosarcoma cells.

METHODS

Modified murine and human osteosarcoma cell lines were evaluated for cell adhesion, aggregation (spheroid), motility (wound healing assay), phenotypic markers expression (RT-qPCR, western blot). Cell-derived xenograft FFPE samples and patients samples (TMA) were assessed by IHC.

RESULTS

CYR61 levels controlled the expression of markers related to an Epithelial-mesenchymal transition (EMT)-like process, allowing tumor cells to migrate acquiring a competent morphology, and to be able to invade the surrounding stroma. This phenotypic shift indeed correlated with tumor grade and aggressiveness in patient samples and with the metastatic dissemination potential in cell-derived xenograft models. Unlike EGFR or PDGFR, IGF1Rβ levels correlated with CYR61 and N-cadherin levels, and with the aggressiveness of osteosarcoma and overall survival. The expression levels of IGF1Rβ/IGF1 axis were controlled by CYR61, and anti-IGF1 neutralizing antibody prevented the CYR61-induced phenotypic shift, aggregation, and motility abilities.

CONCLUSIONS

Taken together, our study provides new evidence that CYR61 acts as a key inducing factor in the metastatic progression of osteosarcoma by playing a critical role in primary tumor dissemination, with a process associated with IGF1/IGFR stimulation. This suggests that CYR61 may represent a potential pivotal target for therapeutic management of metastases spreading in osteosarcoma, in correlation with IGF1/IGFR pathway.

An actin-binding protein ESPN is an independent prognosticator and regulates cell growth for esophageal squamous cell carcinoma

Background

ESPN (Espin), an actin filament-binding protein, plays an important role in regulating the organization, dimensions, dynamics, and signaling capacities of the actin filament-rich, microvillus-type specializations that mediate sensory transduction in various mechanosensory and chemosensory cells. Recent few studies show that ESPN regulates metastasis and cell proliferation in melanoma. However, the significance of ESPN in other cancers such as esophageal squamous cell carcinoma (ESCC) remains largely unknown.

Methods

Immunohistochemistry was performed in 169 patients with ESCC and correlated with clinicopathological features and survival. The functional role of ESPN in ESCC cells was determined by ESPN-mediated siRNA.

Results

Univariate analyses showed that high ESPN expression was associated with inferior overall survival (P = 0.005) and disease-free survival (P = 0.035). High ESPN expression was an independent prognosticator in multivariate analysis for overall survival (P = 0.009, hazard ratio = 1.688) and disease-free survival (P = 0.049, hazard ratio = 1.451). The 5-year overall survival rates were 30% and 54% in patients with high and low expression of ESPN, respectively. Inhibition of endogenous ESPN in ESCC cells decreased ESCC growth by reducing cell proliferating rates.

Conclusions

High ESPN expression is independently associated with poor prognosis in patients with ESCC and downregulation of ESPN inhibits ESCC cell growth. Our results suggest that ESPN may be a novel therapeutic target for patients with ESCC.

An evaluation of TAZ and YAP crosstalk with TGFβ signalling in canine osteosarcoma suggests involvement of hippo signalling in disease progression

Background

Osteosarcoma (OSA) is the most common bone cancer in canines. Both transforming growth factor beta (TGFβ) and Hippo pathway mediators have important roles in bone development, stemness, and cancer progression. The role of Hippo signalling effectors TAZ and YAP has never been addressed in canine OSA. Further, the cooperative role of TGFβ and Hippo signalling has yet to be explored in osteosarcoma. To address these gaps, this study investigated the prognostic value of TAZ and YAP alone and in combination with pSmad2 (a marker of active TGFβ signalling), as well as the involvement of a TGFβ-Hippo signalling crosstalk in tumourigenic properties of OSA cells in vitro. An in-house trial tissue microarray (TMA) which contained 16 canine appendicular OSA cases undergoing standard care and accompanying follow-up was used to explore the prognostic role of TAZ, YAP and pSmad2. Published datasets were used to test associations between TAZ and YAP mRNA levels, metastasis, and disease recurrence. Small interfering RNAs specific to TAZ and YAP were utilized in vitro alone or in combination with TGFβ treatment to determine their role in OSA viability, proliferation and migration.

Results

Patients with low levels of both YAP and pSmad2 when evaluated in combination had a significantly longer time to metastasis (log-rank test, p = 0.0058) and a longer overall survival (log rank test, p = 0.0002). No similar associations were found for TAZ and YAP mRNA levels. In vitro, TAZ knockdown significantly decreased cell viability, proliferation, and migration in metastatic cell lines, while YAP knockdown significantly decreased viability in three cell lines, and migration in two cell lines, derived from either primary tumours or their metastases. The impact of TGFβ signaling activation on these effects was cell line-dependent.

Conclusions

YAP and pSmad2 have potential prognostic value in canine appendicular osteosarcoma. Inhibiting YAP and TAZ function could lead to a decrease in viability, proliferation, and migratory capacity of canine OSA cells. Assessment of YAP and pSmad2 in larger patient cohorts in future studies are needed to further elucidate the role of TGFβ-Hippo signalling crosstalk in canine OSA progression.

Electronic supplementary material

The online version of this article (10.1186/s12917-018-1651-5) contains supplementary material, which is available to authorized users.

Distinct Changes in the Expression TAZ are Associated with Normal Cervix and Human Cervical Cancer

The transcriptional coactivator with the PDZ-binding motif (TAZ) has been associated with different types of cancer. In this study, we examined the TAZ protein expression and cellular localization in 194 cases of human cervical squamous cell carcinoma (SCC). We observed that a normal cervix is characterized by higher expression levels of both nuclear and cytosolic TAZ compared to cervical SCC. Lower membranous and cytosolic TAZ expression levels are associated with lymph node involvement. We observed that TAZ expression levels are associated with β1 integrin and Src in SCC and cell lines derived from human cervical cancers. Of note, knock down of TAZ increased the expression of β1 integrin and Src in both normal and human cervical cancer cells. Our data indicate that the expression and cellular localization of TAZ are inversely associated with the development and progression of cervical SCC, and TAZ-mediated transcription may be involved in the activation of the integrin-Src signalling pathway.

Programmed death ligand 1 promotes lymph node metastasis and glucose metabolism in cervical cancer by activating integrin β4/SNAI1/SIRT3 signaling pathway

Although PD-L1 has been shown to play a well-characterized role in inhibiting antitumor immunity via engagement of its receptor PD-1 in T lymphocytes, little is known about the tumor cell-intrinsic function of PD-L1 and its association with prognosis. Here, we investigate this issue and dissect the molecular mechanisms underlying the role of PD-L1 in glucose metabolism, proliferation, migration, and invasion in human cervical cancer cells. As a result, we found that PD-L1 overexpression in cervical cancer cells increases glucose metabolism and metastasis-related behaviors. Mechanistically, PD-L1 bound directly to integrin β4 (ITGB4), activating the AKT/GSK3β signaling pathway and consequently inducing the expression of the transcriptional repressor SNAI1. SNAIL in turn influenced the expression of genes involved in the epithelial-to-mesenchymal transition and regulated glucose metabolism by inhibiting SIRT3 promoter activity. High expression of PD-L1 and ITGB4 in human cervical carcinomas was significantly associated with lymph node metastasis and poor prognosis. Finally, ¹⁸F-fluorodeoxyglucose microPET/CT and bioluminescence imaging analyses of cervical xenograft tumors in mice revealed that PD-L1 overexpression markedly increases tumor glucose uptake and promotes lymph node metastasis. Together, these results demonstrate that PD-L1 can promote the growth and metastasis of cervical cancer by activating the ITGB4/SNAI1/SIRT3 signaling pathway, and also suggest the possibility of targeting PD-L1 and its downstream effectors as a potential approach for interfering with cervical cancer growth and metastasis.

Knockdown of HuR represses osteosarcoma cells migration, invasion and stemness through inhibition of YAP activation and increases susceptibility to chemotherapeutic agents

This study aims to explore the roles and related mechanisms of HuR in osteosarcoma (OS) cells migration, invasion, stemness and chemotherapeutical sensitivity. Here, we found that HuR exhibited higher level in OS tissues compared with the adjacent normal tissues. Knockdown of HuR with lentivirus infection suppressed OS cells migration and invasion, and thus the epithelial-mesenchymal transition (EMT) process. Additionally, HuR knockdown inhibited OS cells stemness. Mechanistically, YAP was identified as a direct target of HuR in OS cells, and HuR knockdown decreased its expression. Moreover, YAP transcriptional activity was attenuated by HuR knockdown, and RNA immunization co-precipitation (RIP) assay showed that HuR directly bound with YAP. Importantly, YAP overexpression rescued the inhibition of HuR knockdown on OS cells migration, invasion and stemness. Furthermore, HuR knockdown enhanced adriamycin sensitivity in OS cells, this effect was attenuated by YAP overexpression too. Importantly, HuR and YAP expression was positively correlated in OS tissues. Therefore, HuR acts as a tumor promoter by enhancing YAP expression in OS cells.

Long non-coding RNA XIST promotes osteosarcoma progression by targeting YAP via miR-195-5p

The lncRNA XIST (X inactive-specific transcript) is an oncogenic lncRNA that is present in various malignant tumors; however, its role and molecular mechanisms in osteosarcoma (OS) progression remain unclear. In the current study, 40 pairs of OS tissues and matched adjacent non-tumor tissues were collected. qRT-PCR was conducted to investigate the differences in XIST expression in tissues and OS cell lines. The proliferation, invasion, and EMT status of OS cells after transfection were assessed with WST-1 assays, Transwell assays, and Western blot analysis, respectively. Whether miR-195-5p was a direct downstream target of XIST was verified by both bioinformatics target gene prediction and dual-luciferase report analysis. A mouse model was established to evaluate tumor proliferation in vivo. Our results demonstrated that XIST expression was significantly upregulated in OS tissues and cell lines and negatively correlated with clinical prognosis. XIST knockdown inhibited cancer cell proliferation and invasion in vitro, inhibited the EMT of OS cells in vitro, and suppressed subcutaneous tumor growth in vivo. Further analysis demonstrated that XIST regulated YAP expression by functioning as a competing endogenous RNA that sponged miR-195-5p in OS cells. XIST directly interacted with miR-195-5p and decreased the binding of miR-195-5p to the YAP 3'UTR, which suppressed the degradation of YAP mRNA by miR-195-5p. In conclusion, this work demonstrates that lncRNA XIST enhances OS cancer cell proliferation and invasion in part through the miR-195-5p/YAP pathway. Therefore, lncRNA XIST might be a promising therapeutic target for OS.

Effect of titanium ions on the Hippo/YAP signaling pathway in regulating biological behaviors of MC3T3-E1 osteoblasts

Titanium (Ti) and its corresponding alloys have been widely applied in dental and orthopedic implants. Owing to abrasion and corrosion of implants in the unfavorable electrolytic aqueous environment of the host body, Ti ions could be released from implants and accumulated in local tissues. Recent studies have found that excessive Ti ions were toxic to osteoblasts in adjacent bone tissues and subsequently influenced long-term effects on implant prostheses. However, the potential molecular mechanisms underlying the damage to osteoblasts induced by Ti ions remained unclear. Hippo signaling has been confirmed to be involved in organ size and tissue regeneration in many organs, while its roles in osteoblasts differentiation and bone repair remained elusive. Therefore, we hypothesize that YAP, a regulator of Hippo pathway, inhibited osteoblast growth, skeletal development and bone repair, as well as excessive Ti ions promoted the progression of YAP activation. This study aimed to explore the role of Hippo/YAP signaling pathway in the biotoxicity effect of Ti ions on osteoblast behaviors. Here, we confirmed that 10 ppm Ti ions, a minimum concentration gradient previously reported that was capable of suppressing osteoblasts growth, induced nuclear expression of YAP in osteoblasts in our study. Furthermore, 10 ppm Ti ion-induced YAP activation was found to downregulate osteogenic differentiation of MC3T3-E1 cells. Most importantly, the hypothesis we proposed that knockdown of YAP did reverse the inhibitory effect of 10 ppm Ti ions on osteogenesis has been verified. Taken together, our work provides insights into the mechanism of which YAP is involved in regulating osteoblast behaviors under the effect of Ti ions, which may help to develop therapeutic applications for Ti implant failures and peri-implantitis.

The Prognostic Significance of Histone Demethylase UTX in Esophageal Squamous Cell Carcinoma

The dysregulation of the ubiquitously transcribed TPR gene on the X chromosome (UTX) has been reported to be involved in the oncogenesis of several types of cancers. However, the expression and significance of UTX in esophageal squamous cell carcinoma (ESCC) remains largely undetermined. Immunohistochemistry was performed in 106 ESCC patients, and correlated with clinicopathological features and survival. The functional role of UTX in ESCC cells was determined by UTX-mediated siRNA. Univariate analyses showed that high UTX expression was associated with superior overall survival (OS, p = 0.011) and disease-free survival (DFS, p = 0.01). UTX overexpression was an independent prognosticator in multivariate analysis for OS (p = 0.013, hazard ratio = 1.996) and DFS (p = 0.009, hazard ratio = 1.972). The 5-year OS rates were 39% and 61% in patients with low expression and high expression of UTX, respectively. Inhibition of endogenous UTX in ESCC cells increased cell viability and BrdU incorporation, and decreased the expression of epithelial marker E-cadherin. Immunohistochemically, UTX expression was also positively correlated with E-cadherin expression. High UTX expression is independently associated with a better prognosis in patients with ESCC and downregulation of UTX increases ESCC cell growth and decreases E-cadherin expression. Our results suggest that UTX may be a novel therapeutic target for patients with ESCC.

Targeting YAP in malignant pleural mesothelioma

Malignant mesothelioma is an aggressive cancer that is resistant to current therapy. The poor prognosis of mesothelioma has been associated with elevated Yes-associated protein (YAP) activity. In this study, we evaluated the effect of targeting YAP in mesothelioma. First, we comprehensively studied YAP activity in five mesothelioma cell lines (211H, H2052, H290, MS-1 and H2452) and one normal mesothelial cell line (LP9). We found decreased phospho-YAP to YAP protein ratio and consistently increased GTIIC reporter activity in 211H, H2052 and H290 compared to LP9. The same three cell lines (IC50 s < 1 μM) were more sensitive than LP9 (IC50 = 3.5 μM) to the YAP/TEAD inhibitor verteporfin. We also found that verteporfin significantly reduced YAP protein level, mRNA levels of YAP downstream genes and GTIIC reporter activity in the same three cell lines, indicating inhibition of YAP signaling by verteporfin. Verteporfin also impaired invasion and tumoursphere formation ability of H2052 and H290. To validate the effect of specific targeting YAP in mesothelioma cells, we down-regulated YAP by siRNA. We found siYAP significantly decreased YAP transcriptional activity and impaired invasion and tumoursphere formation ability of H2052 and H290. Furthermore, forced overexpression of YAP rescued GTIIC reporter activity and cell viability after siYAP targeting 3'UTR of YAP. Finally, we found concurrent immunohistochemistry staining of ROCK2 and YAP (P < 0.05). Inhibition of ROCK2 decreased GTIIC reporter activity in H2052 and 211H suggesting that Rho/ROCK signaling also contributed to YAP activation in mesothelioma cells. Our results indicate that YAP may be a potential therapeutic target in mesothelioma.

β1 integrin-dependent Rac/group I PAK signaling mediates YAP activation of Yes-associated protein 1 (YAP1) via NF2/merlin

Cell adhesion to the extracellular matrix or to surrounding cells plays a key role in cell proliferation and differentiation and is critical for proper tissue homeostasis. An important pathway in adhesion-dependent cell proliferation is the Hippo signaling cascade, which is coregulated by the transcription factors Yes-associated protein 1 (YAP1) and transcriptional coactivator with PDZ-binding motif (TAZ). However, how cells integrate extracellular information at the molecular level to regulate YAP1's nuclear localization is still puzzling. Herein, we investigated the role of β1 integrins in regulating this process. We found that β1 integrin-dependent cell adhesion is critical for supporting cell proliferation in mesenchymal cells both in vivo and in vitro β1 integrin-dependent cell adhesion relied on the relocation of YAP1 to the nucleus after the down-regulation of its phosphorylated state mediated by large tumor suppressor gene 1 and 2 (LATS1/2). We also found that this phenotype relies on β1 integrin-dependent local activation of the small GTPase RAC1 at the plasma membrane to control the activity of P21 (RAC1)-activated kinase (PAK) of group 1. We further report that the regulatory protein merlin (neurofibromin 2, NF2) interacts with both YAP1 and LATS1/2 via its C-terminal moiety and FERM domain, respectively. PAK1-mediated merlin phosphorylation on Ser-518 reduced merlin's interactions with both LATS1/2 and YAP1, resulting in YAP1 dephosphorylation and nuclear shuttling. Our results highlight RAC/PAK1 as major players in YAP1 regulation triggered by cell adhesion.

TEAD1 mediates the oncogenic activities of Hippo-YAP1 signaling in osteosarcoma

Hippo signaling pathway is an evolutionarily conserved developmental network that governs the downstream transcriptional co-activators, YAP and TAZ, which bind to and activate the output of TEADs that responsible for cell proliferation, apoptosis, and stem cell self renewal. Emerging evidence has shown the tumor suppressor properties of Hippo signaling. However, limited knowledge is available concerning the downstream transcription factors of Hippo pathway in osteosarcoma (OS). In this study, we demonstrated that TEAD1 was the major transcription factor of Hippo signaling pathway in OS. Genetic silencing of TEAD1 suppressed multiple malignant phenotypes of OS cells including cell proliferation, apoptosis resistance, and invasive potential. Mechanistically, we showed that TEAD1 largely exerted its transcriptional control of its functional targets, PTGS2 and CYR61. Collectively, this work identifies the YAP1/TEAD1 complex as the representative dysregulated profile of Hippo signaling in OS and provides proof-of-principle that targeting TEAD1 may be a therapeutic strategy of osteosarcoma.

Knockdown of Long Non-Coding RNA KCNQ1OT1 Restrained Glioma Cells' Malignancy by Activating miR-370/CCNE2 Axis

Accumulating evidence has highlighted the potential role of long non-coding RNAs (lncRNAs) as biomarkers and therapeutic targets in solid tumors. Here, we elucidated the function and possible molecular mechanisms of lncRNA KCNQ1OT1 in human glioma U87 and U251 cells. Quantitative Real-Time polymerase chain reaction (qRT-PCR) demonstrated that KCNQ1OT1 expression was up-regulated in glioma tissues and cells. Knockdown of KCNQ1OT1 exerted tumor-suppressive function in glioma cells. Moreover, a binding region was confirmed between KCNQ1OT1 and miR-370 by dual-luciferase assays. qRT-PCR showed that miR-370 was down-regulated in human glioma tissue and cells. In addition, restoration of miR-370 exerted tumor-suppressive function via inhibiting cell proliferation, migration and invasion, while promoting the apoptosis of human glioma cells. Knockdown of KCNQ1OT1 decreased the expression level of Cyclin E2 (CCNE2) by binding to miR-370. Further, miR-370 bound to CCNE2 3′UTR region and decreased the expression of CCNE2. These results provided a comprehensive analysis of KCNQ1OT1-miR-370-CCNE2 axis in human glioma cells and might provide a novel strategy for glioma treatment.

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.