YAP and the Hippo pathway in pediatric cancer

Induced expression of AMOT reverses adriamycin resistance in breast cancer cells

Adriamycin (ADR) is widely used against breast cancer, but subsequent resistance always occurs. YAP, a downstream protein of angiomotin (AMOT), importantly contributes to ADR resistance, whereas the mechanism is largely unknown. MCF-7 cells and MDA-MB-231 cells were used to establish ADR-resistant cell. Then, mRNA and protein expressions of AMOT and YAP expressions were determined. After AMOT transfection alone or in combination with YAP, the sensitivity of the cells to ADR were evaluated in vitro by examining cell proliferation, apoptosis, and cell cycle, as well as in vivo by examining tumor growth. Additionally, the expressions of proteins in YAP pathway were determined in AMOT-overexpressing cells. In the ADR-resistant cells, the expression of AMOT was decreased while YAP was increased, respectively, and the nucleus localization of YAP was increased at the same time. After AMOT overexpression, these were inhibited, whereas the cell sensitivity to ADR was enhanced. However, the AMOT-induced changes were significantly suppressed by YAP knockdown. The consistent results in vivo showed that AMOT enhanced the inhibition of ADR on tumor growth, and inhibited YAP signaling, evidenced by decreased levels of YAP, CycD1, and p-ERK. Our data revealed that decreased AMOT contributed to ADR resistance in breast cancer cells, which was importantly negatively mediated YAP. These observations provide a potential therapy against breast cancer with ADR resistance.

The yes-associated protein (YAP) is associated with resistance to anti-GD2 immunotherapy in neuroblastoma through downregulation of ST8SIA1

Pediatric patients with high-risk neuroblastoma often relapse with chemotherapy-resistant, incurable disease. Relapsed neuroblastomas harbor chemo-resistant mesenchymal tumor cells and increased expression/activity of the transcriptional co-regulator, the Yes-Associated Protein (YAP). Patients with relapsed neuroblastoma are often treated with immunotherapy such as the anti-GD2 antibody, dinutuximab, in combination with chemotherapy. We have previously shown that YAP mediates both chemotherapy and MEK inhibitor resistance in relapsed RAS mutated neuroblastoma and so posited that YAP might also be involved in anti-GD2 antibody resistance. We now show that YAP genetic inhibition significantly enhances sensitivity of mesenchymal neuroblastomas to dinutuximab and gamma delta (γδ) T cells both in vitro and in vivo. Mechanistically, YAP inhibition induces increased GD2 cell surface expression through upregulation of ST8SIA1, the gene encoding GD3 synthase and the rate-limiting enzyme in GD2 biosynthesis. The mechanism of ST8SIA1 suppression by YAP is independent of PRRX1 expression, a mesenchymal master transcription factor, suggesting YAP may be the downstream effector of mesenchymal GD2 resistance. These results therefore identify YAP as a therapeutic target to augment GD2 immunotherapy responses in patients with neuroblastoma.

The Hippo Pathway Effectors YAP/TAZ-TEAD Oncoproteins as Emerging Therapeutic Targets in the Tumor Microenvironment

Various cancer cell-associated intrinsic and extrinsic inputs act on YAP/TAZ proteins to mediate the hyperactivation of the TEAD transcription factor-based transcriptome. This YAP/TAZ-TEAD activity can override the growth-limiting Hippo tumor-suppressor pathway that maintains normal tissue homeostasis. Herein, we provide an integrated summary of the contrasting roles of YAP/TAZ during normal tissue homeostasis versus tumor initiation and progression. In addition to upstream factors that regulate YAP/TAZ in the TME, critical insights on the emerging functions of YAP/TAZ in immune suppression and abnormal vasculature development during tumorigenesis are illustrated. Lastly, we discuss the current methods that intervene with the YAP/TAZ-TEAD oncogenic signaling pathway and the emerging applications of combination therapies, gut microbiota, and epigenetic plasticity that could potentiate the efficacy of chemo/immunotherapy as improved cancer therapeutic strategies.

White Spot Syndrome Virus (WSSV) Inhibits Hippo Signaling and Activates Yki To Promote Its Infection in Penaeus vannamei

White spot syndrome virus (WSSV) is a serious threat to shrimp aquaculture, especially Pacific white shrimp, Penaeus vannamei, the most farmed shrimp in the world. Activation of the Hippo-Yki signaling pathway, characterized by the intracellular Hippo-Wts kinase cascade reactions and the phosphorylation and cytoplasmic retention of Yki, is widely involved in various life activities. The current work established the fundamental structure and signal transduction profile of the Hippo-Yki pathway in P. vannamei and further investigated its role in viral infection. We demonstrated that WSSV promoted the dephosphorylation and nuclear translocation of Yki, suggesting that Hippo signaling is impaired and Yki is activated after WSSV infection in shrimp. In vivo, Yki gene silencing suppressed WSSV infection, while Hippo and Wts silencing promoted it, indicating a positive role of Hippo signaling in antiviral response. Further analyses showed that Yki suppressed Dorsal pathway activation and inhibited hemocyte apoptosis in WSSV-infected shrimp, while Hippo and Wts showed opposite effects, which contributed to the role of Hippo signaling in WSSV infection. Therefore, the current study suggests that WSSV annexes Yki to favor its infection in shrimp by inhibiting Hippo signaling. IMPORTANCE White spot syndrome virus (WSSV) is one of the most harmful viral pathogens to shrimp. The pathological mechanism of WSSV infection remains unclear to date. The Hippo-Yki signaling pathway is important for various biological processes and is extensively involved in mammalian immunity, but little is known about its role in infectious diseases in invertebrates. Based on revealing the fundamental structure of the shrimp Hippo pathway, this study investigated its implication in the pathogenesis of WSSV disease. We demonstrated that WSSV enhanced Yki activation by inhibiting Hippo signaling in shrimp. The activated Yki promoted WSSV infection by inhibiting hemocyte apoptosis and suppressing the activation of Dorsal, an NF-κB family member in shrimp that is critical for regulating antiviral response. Therefore, this study suggests that WSSV can hijack the Hippo-Yki signaling pathway to favor its infection in shrimp.

Deciphering Potential Role of Hippo Signaling Pathway in Breast Cancer: A Comprehensive Review

Breast cancer is a heterogeneous disease and a leading malignancy around the world. It is a vital cause of untimely mortality among women. Drug resistance is the major challenge for effective cancer therapeutics. In contrast, cancer stem cells (CSCs) are one of the reasons for drug resistance, tumor progression, and metastasis. The small population of CSCs present in each tumor has the ability of self-renewal, differentiation, and tumorigenicity. CSCs are often identified and enriched using a variety of cell surface markers (CD44, CD24, CD133, ABCG2, CD49f, LGR5, SSEA-3, CD70) that exert their functions by different regulatory networks, i.e., Notch, Wnt/β-catenin, hedgehog (Hh), and Hippo signaling pathways. Particularly the Hippo signaling pathway is the emerging and very less explored cancer stem cell pathway. Here, in this review, the Hippo signaling molecules are elaborated with respect to their ability of stemness as epigenetic modulators and how these molecules can be targeted for better cancer treatment and to overcome drug resistance.

Sex differences in methylation profiles are apparent in medulloblastoma, particularly among SHH tumors

Background

Medulloblastoma, the most common malignant pediatric brain tumor, displays marked sex differences in prevalence of the four main molecular subgroups: SHH, WNT, Group 3 and Group 4. Males are more frequently diagnosed with SHH, Group 3 and 4 tumors, which have worse prognoses than WNT tumors. Little is known about sex differences in methylation profiles within subgroups.

Methods

Using publicly available methylation data (Illumina HumanMethylation450K array), we compared beta values for males versus females. Differentially methylated positions (DMP) by sex within medulloblastoma subgroups were identified on the autosomes. DMPs were mapped to genes and Reactome pathway analysis was run by subgroup. Kaplan-Meier survival curves (Log-Rank p-values) were assessed for each sex within subgroup. MethylCIBERSORT was used to investigate the tumor microenvironment using deconvolution to estimate the abundances of immune cell types using DNA methylation data.

Results

There were statistically significant differences in sex by medulloblastoma subgroups (chi-squared p-value=0.00004): Group 3 (n=144; 65% male), Group 4 (n=326; 67% male), SHH (n=223; 57% male) and WNT (n=70; 41% male). Females had worse survival than males for SHH (p-value=0.02). DMPs by sex were identified within subgroups: SHH (n=131), Group 4 (n=29), Group 3 (n=19), and WNT (n=16) and validated in an independent dataset. Unsupervised hierarchical clustering showed that sex-DMPs in SHH did not correlate with other tumor attributes. Ten genes with sex DMPs (RFTN1, C1orf103, FKBP1B, COL25A1, NPDC1, B3GNT1, FOXN3, RNASEH2C, TLE1, and PHF17) were shared across subgroups. Significant pathways (p<0.05) associated with DMPs were identified for SHH (n=22) and Group 4 (n=4) and included signaling pathways for RET proto-oncogene, advanced glycosylation end product receptor, regulation of KIT, neurotrophic receptors, NOTCH, and TGF-β. In SHH, we identified DMPs in four genes (CDK6, COL25A1, MMP16, PRIM2) that encode proteins which are the target of therapies in clinical trials for other cancers. There were few sex differences in immune cell composition within tumor subgroups.

Conclusion

There are sexually dimorphic methylation profiles for SHH medulloblastoma where survival differences were observed. Sex-specific therapies in medulloblastoma may impact outcomes.

The crosstalk between LINC01089 and hippo pathway inhibits osteosarcoma progression

INTRODUCTION

Osteosarcoma is the most common malignancy in children, with high morbidity worldwide. Researches indicated that long non-coding RNAs (lncRNAs) played crucial roles in various cancers. Nevertheless, study investigating lncRNA long intergenic non-protein coding RNA 1089 (LINC01089) in osteosarcoma is extremely rare. Thus, the research of LINC01089 is of great significance.

MATERIALS AND METHODS

qRT-PCR and western blot were done to test the expression of RNAs and proteins in osteosarcoma cells. Functional assays were carried out to evaluate biological behaviors of hFOB1.19 and osteosarcoma cells with or without LINC01089 knockdown and overexpression. In vitro and in vivo experiments in a rescue manner were performed to reveal the influences of LINC01089 and Hippo pathway on osteosarcoma cell phenotype and tumor growth.

RESULTS

LINC01089 was down-regulated in osteosarcoma cells and overexpressing LINC01089 was validated to restrain cell growth in vitro and tumor growth in vivo. Additionally, silencing LINC01089 could exacerbate cell malignant behaviors. Correlation of LINC01089 and Hippo pathway was proved. Overexpressing LINC01089 could activate Hippo pathway to exert antitumor effects.

CONCLUSION

LINC01089 could restrain the progression of osteosarcoma through activating Hippo pathway.

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.

Genotype-cancer association in patients with Fanconi anemia due to pathogenic variants in FANCD1 (BRCA2) or FANCN (PALB2)

Fanconi anemia (FA) is the most common inherited bone marrow failure syndrome and a cancer predisposition disorder. Cancers in FA include acute leukemia and solid tumors; the most frequent solid tumor is head and neck squamous cell carcinoma. FA is a primarily autosomal recessive disorder. Several of the genes in which biallelic pathogenic variants cause FA are also autosomal monoallelic cancer predisposition genes e.g. FANCD1 (BRCA2) and FANCN (PALB2). We observed that patients with FA due to biallelic or homozygous pathogenic variants in FANCD1 and FANCN have a unique cancer association. We curated published cases plus our NCI cohort cases, including 71 patients in the FANCD1 group (94 cancers and 69 variants) and 16 patients in the FANCN group (23 cancers and 20 variants). Only patients in FANCD1 and FANCN groups had one or more of these tumors: brain tumors (primarily medulloblastoma), Wilms tumor and neuroblastoma; this is a genotype-specific cancer combination of tumors of embryonal origin. Acute leukemias, seen in all FA genotypes, also occurred in FANCD1 and FANCN group patients at young ages. In silico predictions of pathogenicity for FANCD1 variants were compared with results from a mouse embryonic stem cell-based functional assay. Patients with two null FANCD1 variants did not have an increased frequency of cancer nor earlier onset of cancer compared with those with hypomorphic variants. Patients with FA and these specific cancers should consider genetic testing focused on FANCD1 and FANCN, and patients with these genotypes may consider ongoing surveillance for these specific cancers.

Alisol A Inhibited the Proliferation, Migration, and Invasion of Nasopharyngeal Carcinoma Cells by Inhibiting the Hippo Signaling Pathway

PURPOSE

Alisol A is a bioactive triterpenoid isolated from the Rhizoma Alismatis. Previous studies have shown that alisol A has anticancer potential. In this study, we explored the effect of alisol A on the growth of nasopharyngeal carcinoma (NPC) cells.

MATERIALS AND METHODS

MTT assay, colony formation assay, flow cytometry, transwell assay, wound healing assay, and western blotting were used to assess cell viability, proliferation, cell cycle, migration, invasion, and protein expression, respectively, in vitro. AutoDock Vina and Discovery Studio software were used for molecular docking.

RESULTS

Alisol A inhibited the viability, proliferation, migration, and invasion of NPC cells. The molecular docking simulation assay confirmed that alisol A bound to YAP protein. In addition, alisol A promoted the phosphorylation of YAP and suppressed the expression of YAP in NPC cells.

CONCLUSION

Alisol A inhibited the proliferation, migration, and invasion of NPC cells by inhibiting the Hippo signaling pathway. Alisol A may be a candidate drug for NPC.

A New Player in Neuroblastoma: YAP and Its Role in the Neuroblastoma Microenvironment

Neuroblastoma is the most common extra-cranial pediatric solid tumor that accounts for more than 15% of childhood cancer-related deaths. High risk neuroblastomas that recur during or after intense multimodal therapy have a <5% chance at a second sustained remission or cure. The solid tumor microenvironment (TME) has been increasingly recognized to play a critical role in cancer progression and resistance to therapy, including in neuroblastoma. The Yes-Associated Protein (YAP) in the Hippo pathway can regulate cancer proliferation, tumor initiation, and therapy response in many cancer types and as such, its role in the TME has gained interest. In this review, we focus on YAP and its role in neuroblastoma and further describe its demonstrated and potential effects on the neuroblastoma TME. We also discuss the therapeutic strategies for inhibiting YAP in neuroblastoma.

Emerging roles for the YAP/TAZ transcriptional regulators in brain tumour pathology and targeting options

The transcriptional co-activators Yes-associated protein 1/transcriptional co-activator with PDZ-binding motif (YAP/TAZ) have emerged as significant regulators of a wide variety of cellular and organ functions with impact in early embryonic development, especially during the expansion of the neural progenitor cell pool. YAP/TAZ signalling regulates organ size development, tissue homeostasis, wound healing and angiogenesis by participating in a complex network of various pathways. However, recent evidence suggests an association of these physiologic regulatory effects of YAP/TAZ with pro-oncogenic activities. Herein, we discuss the physiological functions of YAP/TAZ as well as the extensive network of signalling pathways that control their expression and activity, leading to brain tumour development and progression. Furthermore, we describe current targeting approaches and drug options including direct YAP/TAZ and YAP-TEA domain transcription factor (TEAD) interaction inhibitors, G-protein coupled receptors (GPCR) signalling modulators and kinase inhibitors, which may be used to successfully attack YAP/TAZ-dependent tumours.

Signaling pathway deregulation and molecular alterations across pediatric medulloblastomas

Medulloblastomas (MBs) account for 15% of brain tumors in children under the age of 15. To date, the overall 5-year survival rate for all children is only around 60%. Recent advances in cancer genomics have led to a fundamental change in medulloblastoma classification and is evolving along with the genomic discoveries, allowing to regularly reclassify this disease. The previous molecular classification defined 4 groups (WNT-activated MB, SHH-activated MB and the groups 3 and 4 characterized partially by NMYC and MYC driven MBs). This stratification moved forward recently to better define these groups and their correlation to outcome. This new stratification into 7 novel subgroups was helpful to lay foundations and complementary data on the understanding regarding molecular pathways and gene mutations underlying medulloblastoma biology. This review was aimed at answering the recent key questions on MB genomics and go further in the relevance of those genes in MB development as well as in their targeted therapies.

Development of LM98, a Small-Molecule TEAD Inhibitor Derived from Flufenamic Acid

The YAP-TEAD transcriptional complex is responsible for the expression of genes that regulate cancer cell growth and proliferation. Dysregulation of the Hippo pathway due to overexpression of TEAD has been reported in a wide range of cancers. Inhibition of TEAD represses the expression of associated genes, demonstrating the value of this transcription factor for the development of novel anti-cancer therapies. We report herein the design, synthesis and biological evaluation of LM98, a flufenamic acid analogue. LM98 shows strong affinity to TEAD, inhibits its autopalmitoylation and reduces the YAP-TEAD transcriptional activity. Binding of LM98 to TEAD was supported by ¹⁹ F-NMR studies while co-crystallization experiments confirmed that LM98 is anchored within the palmitic acid pocket of TEAD. LM98 reduces the expression of CTGF and Cyr61, inhibits MDA-MB-231 breast cancer cell migration and arrests cell cycling in the S phase during cell division.

Pediatric Tumors-Mediated Inhibitory Effect on NK Cells: The Case of Neuroblastoma and Wilms' Tumors

Simple Summary

Neuroblastoma (NB) and Wilms’ tumor (WT) are the most common childhood solid extracranial tumors. The current treatments consist of a combination of surgery and chemotherapy or radiotherapy in high-risk patients. Such treatments are responsible for significant adverse events requiring long-term monitoring. Thus, a main challenge in NB and WT treatment is the development of novel therapeutic strategies to eliminate or minimize the adverse effects. The characterization of the immune environment could allow for the identification of new therapeutic targets. Herein, we described the interaction between these tumors and innate immune cells, in particular natural killer cells and monocytes. The detection of the immunosuppressive activity of specific NB and WT tumor cells on natural killer cells and on monocytes could offer novel cellular and molecular targets for an effective immunotherapy of NB and WT.

Abstract

Natural killer (NK) cells play a key role in the control of cancer development, progression and metastatic dissemination. However, tumor cells develop an array of strategies capable of impairing the activation and function of the immune system, including NK cells. In this context, a major event is represented by the establishment of an immunosuppressive tumor microenvironment (TME) composed of stromal cells, myeloid-derived suppressor cells, tumor-associated macrophages, regulatory T cells and cancer cells themselves. The different immunoregulatory cells infiltrating the TME, through the release of several immunosuppressive molecules or by cell-to-cell interactions, cause an impairment of the recruitment of NK cells and other lymphocytes with effector functions. The different mechanisms by which stromal and tumor cells impair NK cell function have been particularly explored in adult solid tumors and, in less depth, investigated and discussed in a pediatric setting. In this review, we will compare pediatric and adult solid malignancies concerning the respective mechanisms of NK cell inhibition, highlighting novel key data in neuroblastoma and Wilms’ tumor, two of the most frequent pediatric extracranial solid tumors. Indeed, both tumors are characterized by the presence of stromal cells acting through the release of immunosuppressive molecules. In addition, specific tumor cell subsets inhibit NK cell cytotoxic function by cell-to-cell contact mechanisms likely controlled by the transcriptional coactivator TAZ. These findings could lead to a more performant diagnostic approach and to the development of novel immunotherapeutic strategies targeting the identified cellular and molecular targets.

The association between the expression of nuclear Yes-associated protein 1 (YAP1) and p53 protein expression profile in breast cancer patients

Background

Yes-associated protein 1 (YAP1) is a key effector molecule regulated by the Hippo pathway and described as a poor prognostic factor in breast cancer. Tumor protein 53 (TP53) mutation is well known as a biomarker related to poor survival outcomes. So far clinical characteristics and survival outcome according to YAP1 and TP53 mutation have been poorly identified in breast cancer.

Patients and methods

Retrospectively, 533 breast tumor tissues were collected at the Seoul St Mary’s hospital and Gangnam Severance Hospital from 1992 to 2017. Immunohistochemistry with YAP1 and p53 specific antibodies were performed, and the clinical data were analyzed.

Results

Mutant p53 pattern was associated with aggressive tumor features and advanced anatomical stage. Inferior overall survival (OS) and recurrence free survival (RFS) were related with mutant p53 pattern cases with low nuclear YAP1 expression (P = 0.0009 and P = 0.0011, respectively). Multivariate analysis showed that mutant p53 pattern was an independent prognostic marker for OS [hazard ratios (HR): 2.938, 95% confidence intervals (CIs): 1.028–8.395, P = 0.044] and RFS (HR: 1.842, 95% CIs: 1.026–3.304). However, in cases with high nuclear YAP1 expression, there were no significantly difference in OS and RFS according to p53 staining pattern.

Conclusion

We found that mutant p53 pattern is a poor prognostic biomarker in breast tumor with low nuclear YAP1 expression. Our findings suggest that interaction between nuclear YAP1 and p53 expression pattern impact survival outcomes.

Long Non-Coding RNA XIST Promotes Wilms Tumor Progression Through the miR-194-5p/YAP Axis

Purpose

Although the long non-coding RNA (lncRNA) X inactive-specific transcript (XIST) has been reported to have an anti-tumor effect in multiple malignant tumors, its role in Wilms tumor (WT) progression has not been characterized. Thus, we investigated the underlying mechanism by which XIST regulates WT progression.

Patients and Methods

We performed microarray analysis and real-time quantitative PCR (RT-qPCR) to detect the expression levels of XIST lncRNA, microRNA-194-5p (miR-194-5p), and YAP (yes-associated protein in Hippo pathway) in tumor and matched adjacent normal tissues and blood collected from 49 WT patients. We also conducted bioinformatics analyses to identify differentially expressed genes. We measured the effects of XIST overexpression and knockdown on cell proliferation, apoptosis, migration, and invasion, and its association with the miR-194-5p/YAP pathway in the rhabdoid G401cell line using flow cytometry, transwell assays, immunohistochemistry, Western blot analysis, and the dual luciferase reporter gene assay.

Results

We found that XIST lncRNA levels were increased in blood and tissue samples of WT patients, and this upregulation was significantly correlated with TNM staging and shorter survival time. Notably, we found that XIST upregulation correlated with miR-194-5p downregulation and YAP upregulation in WT tissues, suggesting that XIST regulates the miR-194-5p/YAP pathway. Conversely, XIST downregulation inhibited WT cell proliferation, migration, and invasion and induced apoptosis. Our study revealed the oncogenic role of the lncRNA XIST in WT and demonstrated its role as a competitive endogenous RNA that regulates the miR-194-5p/YAP pathway.

Conclusion

Our study demonstrates XIST’s potential as a clinical prognostic biomarker and therapeutic target for WT.

Identification of neuroblastoma cell lines with uncommon TAZ+/mesenchymal stromal cell phenotype with strong suppressive activity on natural killer cells

Background

Neuroblastoma (NB) is the most common, extracranial childhood solid tumor arising from neural crest progenitor cells and is a primary cause of death in pediatric patients. In solid tumors, stromal elements recruited or generated by the cancer cells favor the development of an immune-suppressive microenvironment. Herein, we investigated in NB cell lines and in NB biopsies, the presence of cancer cells with mesenchymal phenotype and determined the immune-suppressive properties of these tumor cells on natural killer (NK) cells.

Methods

We assessed the mesenchymal stromal cell (MSC)-like phenotype and function of five human NB cell lines and the presence of this particular subset of neuroblasts in NB biopsies using flow-cytometry, immunohistochemistry, RT-qPCR, cytotoxicity assays, western blot and silencing strategy. We corroborated our data consulting a public gene-expression dataset.

Results

Two NB cell lines, SK-N-AS and SK-N-BE(2)C, exhibited an unprecedented MSC phenotype (CD105⁺/CD90⁺/CD73⁺/CD29⁺/CD146⁺/GD2⁺/TAZ⁺). In these NB-MSCs, the ectoenzyme CD73 and the oncogenic/immune-regulatory transcriptional coactivator TAZ were peculiar markers. Their MSC-like nature was confirmed by their adipogenic and osteogenic differentiation potential. Immunohistochemical analysis confirmed the presence of neuroblasts with MSC phenotype (CD105⁺/CD73⁺/TAZ⁺). Moreover, a public gene-expression dataset revealed that, in stage IV NB, a higher expression of TAZ and CD105 strongly correlated with a poorer outcome.

Among the NB-cell lines analyzed, only NB-MSCs exhibited multifactorial resistance to NK-mediated lysis, inhibition of activating NK receptors, signal adaptors and of NK-cell cytotoxicity through cell-cell contact mediated mechanisms. The latter property was controlled partially by TAZ, since its silencing in NB cells efficiently rescued NK-cell cytotoxic activity, while its overexpression induced opposite effects in non-NB-MSC cells.

Conclusions

We identified a novel NB immunoregulatory subset that: (i) displayed phenotypic and functional properties of MSC, (ii) mediated multifactorial resistance to NK-cell-induced killing and (iii) efficiently inhibited, in coculture, the cytotoxic activity of NK cells against target cells through a TAZ-dependent mechanism. These findings indicate that targeting novel cellular and molecular components may disrupt the immunomodulatory milieu of the NB microenvironment ameliorating the response to conventional treatments as well as to advanced immunotherapeutic approaches, including adoptive transfer of NK cells and chimeric antigen receptor T or NK cells.

ALKBH5 suppresses tumor progression via an m6A-dependent epigenetic silencing of pre-miR-181b-1/YAP signaling axis in osteosarcoma

ALKBH5 is the main enzyme for m⁶A-based demethylation of RNAs and it has been implicated in many biological and pathophysiological processes. Here, we aimed to explore the potential involvement of ALKBH5 in osteosarcoma and decipher the underlying cellular/molecular mechanisms. We discovered downregulated levels of demethylase ALKBH5 were correlated with increased m⁶A methylation in osteosarcoma cells/tissues compared with normal osteoblasts cells/tissues. ALKBH5 overexpression significantly suppressed osteosarcoma cell growth, migration, invasion, and trigged cell apoptosis. In contrast, inhibition of ALKBH5 produced the opposite effects. Whereas ALKBH5 silence enhanced m⁶A methylations of pre-miR-181b-1 and YAP-mRNA exerting oncogenic functions in osteosarcoma. Moreover, upregulation of YAP or downregulation of mature miR-181b-5p displayed a remarkable attenuation of anti-tumor activities caused by ALKBH5. Further results revealed that m⁶A methylated pre-miR-181b-1 was subsequently recognized by m⁶A-binding protein YTHDF2 to mediate RNA degradation. However, methylated YAP transcripts were recognized by YTHDF1 to promote its translation. Therefore, ALKBH5-based m⁶A demethylation suppressed osteosarcoma cancer progression through m⁶A-based direct/indirect regulation of YAP. Thus, ALKBH5 overexpression might be considered a new approach of replacement therapy for osteosarcoma treatment.

YAP-Mediated Repression of HRK Regulates Tumor Growth, Therapy Response, and Survival Under Tumor Environmental Stress in Neuroblastoma

Following chemotherapy and relapse, high-risk neuroblastoma tumors harbor more genomic alterations than at diagnosis, including increased transcriptional activity of the Yes-associated protein (YAP), a key downstream component of the Hippo signaling network. Although YAP has been implicated in many cancer types, its functional role in the aggressive pediatric cancer neuroblastoma is not well-characterized. In this study, we performed genetic manipulation of YAP in human-derived neuroblastoma cell lines to investigate YAP function in key aspects of the malignant phenotype, including mesenchymal properties, tumor growth, chemotherapy response, and MEK inhibitor response. Standard cytotoxic therapy induced YAP expression and transcriptional activity in patient-derived xenografts treated in vivo, which may contribute to neuroblastoma recurrence. Moreover, YAP promoted a mesenchymal phenotype in high-risk neuroblastoma that modulated tumor growth and therapy resistance in vivo. Finally, the BH3-only protein, Harakiri (HRK), was identified as a novel target inhibited by YAP, which, when suppressed, prevented apoptosis in response to nutrient deprivation in vitro and promoted tumor aggression, chemotherapy resistance, and MEK inhibitor resistance in vivo. Collectively, these findings suggest that YAP inhibition may improve chemotherapy response in patients with neuroblastoma via its regulation of HRK, thus providing a critical strategic complement to MEK inhibitor therapy. SIGNIFICANCE: This study identifies HRK as a novel tumor suppressor in neuroblastoma and suggests dual MEK and YAP inhibition as a potential therapeutic strategy in RAS-hyperactivated neuroblastomas.

Intrinsic and Extrinsic Modulators of the Epithelial to Mesenchymal Transition: Driving the Fate of Tumor Microenvironment

The epithelial to mesenchymal transition (EMT) is an evolutionarily conserved process. In cancer, EMT can activate biochemical changes in tumor cells that enable the destruction of the cellular polarity, leading to the acquisition of invasive capabilities. EMT regulation can be triggered by intrinsic and extrinsic signaling, allowing the tumor to adapt to the microenvironment demand in the different stages of tumor progression. In concomitance, tumor cells undergoing EMT actively interact with the surrounding tumor microenvironment (TME) constituted by cell components and extracellular matrix as well as cell secretome elements. As a result, the TME is in turn modulated by the EMT process toward an aggressive behavior. The current review presents the intrinsic and extrinsic modulators of EMT and their relationship with the TME, focusing on the non-cell-derived components, such as secreted metabolites, extracellular matrix, as well as extracellular vesicles. Moreover, we explore how these modulators can be suitable targets for anticancer therapy and personalized medicine.

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.

Minichromosome maintenance 6 complex component identified by bioinformatics analysis and experimental validation in esophageal squamous cell carcinoma

Esophageal squamous cell carcinoma (ESCC), the main subtype of esophageal cancer (EC), is a common lethal type of cancer with a high mortality rate. The aim of the present study was to select key relevant genes and identify potential mechanisms involved in the development of ESCC based on bioinformatics analysis. Minichromosome maintenance 6 complex component (MCM6) has been identified to be upregulated in multiple malignancies; however, its contributions to ESCC remain unclear. For the purposes of the present study, four datasets were downloaded from the Gene Expression Omnibus (GSE63941, GSE26886, GSE17351 and GSE77861), and the intersection of the differentially expressed genes was obtained using a Venn diagram. The protein‑protein interaction was then constructed, and the modules were verified by Cytoscape, in which the key genes have a high connectivity degree with other genes. Gene Ontology and Kyoto Encyclopedia of Genes and Genomes pathway were subsequently filtered out to analyze the development of ESCC. MCM6, an upregulated gene, was selected and connected with most of the other genes, for further research validation. The expression levels of MCM6 were then assessed using the Oncomine, GEPIA and UALCAN databases and validated in both ESCC tissues samples and cell lines by immunohistochemistry and RT‑qPCR. Cell counting kit‑8 (CCK‑8), flow cytometry, wound healing and Transwell assays were used to determine the proliferation, apoptosis, cell cycle, migration and invasion of ESCC cells. A total of 24 genes were identified by a series of bioinformatics analyses and the results revealed that the genes were associated with DNA replication and cell cycle. Experimental validation revealed that MCM6 expression was significantly elevated in both ESCC tissues and cell lines. The results were consistent with those of bioinformatics analysis. Furthermore, the knockdown of MCM6 inhibited cell proliferation, migration and invasion and promoted cell apoptosis, and made cells arrested in S stage. In summary, the findings of bioinformatics analysis provided a novel hypothesis for ESCC progression. In particular, the aberrantly elevated expression of MCM6 is a potential biomarker for ESCC diagnosis and treatment.

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 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.

YAP promotes the proliferation of neuroblastoma cells through decreasing the nuclear location of p27Kip1 mediated by Akt

Objective

We aimed to investigate the roles and underlying mechanisms of YAP in the proliferation of neuroblastoma cells.

Methods

The expression level of YAP was evaluated by Western blotting and immunocytochemistry. Cell viability, cell proliferation and growth were detected by CCK‐8, PH3 and Ki67 immunostaining, and the real‐time cell analyser system. The nuclear and cytoplasmic proteins of p27^Kip1 were dissociated by the nuclear‐cytosol extraction kit and were detected by Western blotting and immunocytochemistry. mRNA levels of Akt, CDK5 and CRM1 were determined by qRT‐PCR.

Results

YAP was enriched in SH‐SY5Y cells (a human neuroblastoma cell line). Knock‐down of YAP in SH‐SY5Y cells or SK‐N‐SH cell line (another human neuroblastoma cell line) significantly decreased cell viability, inhibited cell proliferation and growth. Mechanistically, knock‐down of YAP increased the nuclear location of p27^Kip1, whereas serum‐induced YAP activation decreased the nuclear location of p27^Kip1 and was required for cell proliferation. Meanwhile, overexpression of YAP in these serum‐starved SH‐SY5Y cells decreased the nuclear location of p27^Kip1, promoted cell proliferation and overexpression of p27^Kip1 in YAP‐activated cells inhibited cell proliferation. Furthermore, knock‐down of YAP reduced Akt mRNA and protein levels. Overexpression of Akt in YAP‐downregulated cells decreased the nuclear location of p27^Kip1 and accelerated the proliferation of SH‐SY5Y cells.

Conclusions

Our studies suggest that YAP promotes the proliferation of neuroblastoma cells through negatively controlling the nuclear location of p27^Kip1 mediated by Akt.

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.

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.

A New Regulatory Mechanism Between P53 And YAP Crosstalk By SIRT1 Mediated Deacetylation To Regulate Cell Cycle And Apoptosis In A549 Cell Lines

Background

Yes-associated protein (YAP) is downstream of the Hippo signaling pathway, which regulates several cellular processes. P53 is a key transcriptional regulator that responds to a variety of cellular stresses and regulates key cellular processes such as DNA repair, cell-cycle progression, angiogenesis, and apoptosis. Overexpression of YAP antagonizes P53 activity and targets its expression. However, the mechanism that underlies the post-transcriptional crosstalk between P53 and YAP has not been well dissected.

Methods

We performed an integrated analysis and found that SIRT1 is a key candidate that connects YAP and P53 by modulating their acetylation.

Results

We found that YAP promotes P53 deacetylation, promotes cell survival by inhibiting P53-induced G0/G1 arrest and apoptosis in A549 cells. Conversely, P53 enhances YAP acetylation, and decreases A549 cell survival by strengthening YAP acetylation-induced G0/G1 arrest and apoptosis both in vitro and in vivo.

Conclusion

Our results demonstrate that SIRT1 is responsible for YAP and P53 deacetylation of specific residues, and reveal for the first time, a new regulatory mechanism of P53 and YAP crosstalk by SIRT1-mediated deacetylation, which may be involved in lung tumorigenesis.

Intersectin 1 (ITSN1) identified by comprehensive bioinformatic analysis and experimental validation as a key candidate biological target in breast cancer

Background

As one of the most common cancers, breast carcinoma is the most common disease in women. Intersectin 1 (ITSN1) contributes to the actin cytoskeleton reconstruction in breast cancer.

Purpose

The objective of this study to explore the functions of ITSN1 in breast carcinoma.

Methods

We downloaded microarray datasets GSE8087, GSE50697, and GSE98238 from the Gene Expression Omnibus database. Differentially expressed genes (DEGs) were used to construct a protein–protein interaction (PPI) network using STRING database, and the modules from PPI network were verified by Cytoscape software. Gene ontology terms and Kyoto Encyclopedia of Gene and Genome pathway were used to analyze the biological functions using the DAVID database. ONCOMINE, GEPIA, UALCAN, and Human Protein Atlas databases were used to investigate the characteristics of ITSN1 for the prognosis of breast carcinoma. Cell counting kit-8, flow cytometry, and colony formation assays were used to detect cell viability, cell apoptosis, and cell proliferation. RT-PCR and Western blot assays were used to detect ITSN1, Ki67, and cleaved caspase-3 expressions.

Results

Low expressions of ITSN1 were significantly associated with clinical cancer stages. RT-PCR and Western blot analysis showed low expression of ITSN1 in breast cancer tissues and cell lines. ITSN1 inhibition could promote cell proliferation and inhibit cell apoptosis, while ITSN1 overexpression could inhibit cell proliferation and increase cell apoptosis by regulating the levels of expression of Ki67 and cleaved-caspase-3.

Conclusion

The results indicated that ITSN1 could be a prognostic biomarker for survivals of breast cancer patients.

Homeostatic and tumourigenic activity of SOX2+ pituitary stem cells is controlled by the LATS/YAP/TAZ cascade

SOX2 positive pituitary stem cells (PSCs) are specified embryonically and persist throughout life, giving rise to all pituitary endocrine lineages. We have previously shown the activation of the STK/LATS/YAP/TAZ signalling cascade in the developing and postnatal mammalian pituitary. Here, we investigate the function of this pathway during pituitary development and in the regulation of the SOX2 cell compartment. Through loss- and gain-of-function genetic approaches, we reveal that restricting YAP/TAZ activation during development is essential for normal organ size and specification from SOX2+ PSCs. Postnatal deletion of LATS kinases and subsequent upregulation of YAP/TAZ leads to uncontrolled clonal expansion of the SOX2+ PSCs and disruption of their differentiation, causing the formation of non-secreting, aggressive pituitary tumours. In contrast, sustained expression of YAP alone results in expansion of SOX2+ PSCs capable of differentiation and devoid of tumourigenic potential. Our findings identify the LATS/YAP/TAZ signalling cascade as an essential component of PSC regulation in normal pituitary physiology and tumourigenesis.

The pituitary is a gland inside the head that releases hormones that control major processes in the body including growth, fertility and stress. Diseases of the pituitary gland can prevent the body from producing the appropriate amounts of hormones, and also include tumours.

A population of stem cells in the pituitary known as SOX2 cells divide to make the specialist cells that produce the hormones. This population forms as the pituitary develops in the embryo and continues to contribute new hormone-producing cells throughout life. Signals from inside and outside the gland control how the pituitary develops and maintain the correct balance of different types of cells in the gland in adults.

In 2016, Lodge et al. reported that a cascade of signals known as the Hippo pathway is active in mouse and human pituitary glands, but its role remained unclear. Here, Lodge et al. use genetic approaches to study this signalling pathway in the pituitary of mice.

The results of the experiments show that the Hippo pathway is essential for the pituitary gland to develop normally in mouse embryos. Furthermore, in adult mice the Hippo pathway is required to maintain the population of SOX2 cells in the pituitary and to regulate their cell numbers. Increasing the level of Hippo signalling in mouse embryos and adult mice led to an expansion of SOX2 stem cells that could generate new specialist cell types, but a further increase generated aggressive tumours that originated from the uncontrolled growth of SOX2 cells.

These findings are the first step to understanding how the Hippo pathway works in the pituitary, which may eventually lead to new treatments for tumours and other diseases that affect this gland. The next step towards such treatments will be to carry out further experiments that use drugs to control this pathway and alter the fate of pituitary cells in mice and other animals.

Heat-shock protein B1 upholds the cytoplasm reduced state to inhibit activation of the Hippo pathway in H9c2 cells

Heat-shock protein B1 (HSPB1) is a multifunctional protein that protects against oxidative stress; however, its function in antioxidant pathways remains largely unknown. Here, we sought to determine the roles of HSPB1 in H9c2 cells subjected to oxidative stress. Using nonreducing sodium dodecyl sulfate polyacrylamide gel electrophoresis, we found that increased HSPB1 expression promoted the reduced states of glutathione reductase (GR), peroxiredoxin 1 (Prx1), and thioredoxin 1, whereas knockdown of HSPB1 attenuated these responses following oxidative stress. Increased HSPB1 expression promoted the activation of GR and thioredoxin reductase. Conversely, knockdown of HSPB1 attenuated these responses following oxidative stress. Importantly, overexpression of HSPB1 promoted the complex formation between HSPB1 and oxidized Prx1, leading to dephosphorylation of STE-mammalian STE20-like kinase 1 (MST1) in H9c2 cells exposed to H₂ O ₂ , whereas downregulation of HSPB1 induced the opposite results. Mechanistically, HSPB1 regulated the Hippo pathway by enhancing the dephosphorylation of MST1, resulting in reduced phosphorylation of LATS1 and Yes-associated protein (YAP). Moreover, HSPB1 regulated YAP-dependent gene expression. Thus, HSPB1 promoted the reduced state of endogenous antioxidant pathways following oxidative stress in H9c2 cells and improved the redox state of the cytoplasm via modulation of the Hippo signaling pathway.

Clinical implications of the Hippo-YAP pathway in multiple cancer contexts

The Hippo pathway plays prominent and widespread roles in various forms of human carcinogenesis. Specifically, the Yes-associated protein (YAP), a downstream effector of the Hippo pathway, can lead to excessive cell proliferation and the inhibition of apoptosis, resulting in tumorigenesis. It was reported that the YAP is strongly elevated in multiple types of human malignancies such as breast, lung, small intestine, colon, and liver cancers. Recent work indicates that, surprisingly, Hippo signaling components' (SAV1, MST1/2, Lats1/2) mutations are virtually absent in human cancer, rendering this signaling an unlikely candidate to explain the vigorous activation of the YAP in most, if not all human tumors and an activated YAP promotes the resistance to RAF-, MAPK/ERK Kinase (MEK)-, and Epidermal growth factor receptor (EGFR)-targeted inhibitor therapy. The analysis of YAP expressions can facilitate the identification of patients who respond better to an anti-cancer drug treatment comprising RAF-, MEK-, and EGFR-targeted inhibitors. The prominence of YAP for those aspects of cancer biology denotes that these factors are ideal targets for the development of anti-cancer medications. Therefore, our report strongly indicates that the YAP is of potential prognostic utility and druggability in various human cancers. [BMB Reports 2018; 51(3): 119-125].

Downregulation of YAP inhibits proliferation, invasion and increases cisplatin sensitivity in human hepatocellular carcinoma cells

Yes-associated protein (YAP) serves an essential role in tumorigenesis. However, the potential role and the molecular mechanism underlying the effect of YAP on hepatocellular carcinoma (HCC) cells have not been elucidated. In the current study, it was revealed that YAP expression was increased significantly in HCC cancer tissues and its overexpression was associated with tumor differentiation. The silencing of YAP by small interferring RNA led to the inhibition of HCC cell growth, which was associated with the promotion of apoptosis. The silencing of YAP also decreased the invasive potential of HCC cells and the activity of the phosphoinositide 3-kinase (PI3K)/AKT serine/threonine kinase (AKT) signaling pathway. Furthermore, silencing of YAP increased the chemosensitivity of HCC cells to cisplatin (CDDP) through inactivation of the PI3K/AKT signaling pathway. In vivo studies using PDTX model suggested a promotive role for YAP in the growth of HCC and knockdown of YAP increased the anti-tumor activity of CDDP. Taken together, these results revealed that YAP is overexpressed in HCC, and promotes proliferation, invasion and drug resistance of HCC cells. Inhibition of YAP, alone or in combination with traditional chemotherapy, may effectively combat HCC.

MST1 inhibits cell proliferation and invasion of non-small-cell lung cancer by regulating YAP phosphorylation and Hippo pathway

Mammalian ste20-like kinase 1 (MST1) is a Ser/Thr kinase involved in cell proliferation, apoptosis, and embryonic development. MST1 is also an important member of the Hippo pathway which can regulate organ size and cell proliferation. Growing evidence indicates that MST1 influences cell proliferation through different pathways including Wnt, Akt, JNK, and Hippo pathways in different cells respectively. However, little is known about the role and mechanism of MST1 in lung cancer. In this study, we aimed to assess the biological functions of MST1 in non-small-cell lung cancer (NSCLC). We investigated expression of MST1 in lung cancer cell lines and one human bronchial epithelium cell line (HBE) by Western blot. The results confirmed that MST1 expression was higher in HBE cells, but significantly lower in NSCLC cells. Moreover, MST1 was either overexpressed or depleted in NSCLC cell lines, and the results confirmed that MST1 could markedly inhibit cell proliferation and invasion through regulating the Hippo pathway and Yes-associated protein (YAP) phosphorylation. These results indicate that MST1 may play an important role in NSCLC and may serve as a potential therapeutic target for NSCLC.

Yap regulates gastric cancer survival and migration via SIRT1/Mfn2/mitophagy

Gastric cancer is the fifth most common cancer worldwide and Hippo-Yap is the novel signaling pathway which plays an important role in gastric cancer tumor development and progression. However, little insight is available to date regarding the specific role of Yes-associated protein (Yap) in gastric cancer. In the present study, we identified the mechanism through which Yap sustains gastric cancer viability and migration. Yap was greatly upregulated in gastric cancer cells and its expression promoted cellular migration and survival. Functional studies found that knockdown of Yap reduced the mitophagy activity, which subsequently caused mitochondrial apoptosis and cellular oxidative stress. The latter impaired adhesive protein expression, alleviated F-actin expression, blunted lamellipodium formation, leading to inhibition of cancer cell motility. Mechanistically, Yap preserved Sirtuin 1 (SIRT1) activity which manipulated mitofusin 2 (Mfn2) expression and subsequent mitophagy. Loss of Yap reduced SIRT1 expression and inhibited Mfn2-mediated mitophagy. Collectively, our results identified Hippo-Yap as a tumor promoter in gastric cancer that was mediated via activation of the SIRT1/Mfn2/mitophagy axis, with potential applications to gastric cancer therapy involving cancer survival and migration.

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.

Mst1 regulates colorectal cancer stress response via inhibiting Bnip3-related mitophagy by activation of JNK/p53 pathway

The Hippo-Mst1 pathway is associated with tumor development and progression. However, little evidence is available for its role in colorectal cancer (CRC) stress response via mitochondrial homeostasis. In this study, we conducted gain-of function assay about Mst1 in CRC via adenovirus transfection. Then, cellular viability and apoptosis were measured via MTT, TUNEL assay, and typan blue staining. Mitochondrial function was detected via JC1 staining, mPTP opening assay, and immunofluorescence of cyt-c. Mitophagy was observed via western blots and immunofluorescence. Cell migration and proliferation were evaluated via Transwell and BrdU assay. Western blots were used to analyze the signaling pathways with JNK inhibitors or p53 siRNA. We found that Mst1 was down-regulated in CRC. Overexpression of Mst1 induced CRC apoptosis and impaired cell proliferation and migration. Functional studies have illustrated that recovery of Mst1 could activate JNK pathway which upregulated the p53 expression. The latter repressed Bnip3 transcription and activity, leading to the mitophagy arrest. The defective mitophagy impaired mitochondrial homeostasis, evoked cellular oxidative stress, and initiated the mitochondrial apoptosis. Meanwhile, bad-structured mitophagy also hindered the cancer proliferation via CyclinD/E. Moreover, Mst1-suppressed mitophagy was associated with CRC migration inhibition via regulation of CXCR4/7 expression. Collectively, our data described the comprehensive role of Mst1 in colorectal cancer stress response involving apoptosis, mobilization, and growth via handling mitophagy by JNK/p53/Bnip3 pathways.