The YAP1 Signaling Inhibitors, Verteporfin and CA3, Suppress the Mesothelioma Cancer Stem Cell Phenotype

NF2: An underestimated player in cancer metabolic reprogramming and tumor immunity

Neurofibromatosis type 2 (NF2) is a tumor suppressor gene implicated in various tumors, including mesothelioma, schwannomas, and meningioma. As a member of the ezrin, radixin, and moesin (ERM) family of proteins, merlin, which is encoded by NF2, regulates diverse cellular events and signalling pathways, such as the Hippo, mTOR, RAS, and cGAS-STING pathways. However, the biological role of NF2 in tumorigenesis has not been fully elucidated. Furthermore, cross-cancer mutations may exert distinct biological effects on tumorigenesis and treatment response. In addition to the functional inactivation of NF2, the codeficiency of other genes, such as cyclin-dependent kinase inhibitor 2A/B (CDKN2A/B), BRCA1-associated protein-1 (BAP1), and large tumor suppressor 2 (LATS2), results in unique tumor characteristics that should be considered in clinical treatment decisions. Notably, several recent studies have explored the metabolic and immunological features associated with NF2, offering potential insights into tumor biology and the development of innovative therapeutic strategies. In this review, we consolidate the current knowledge on NF2 and examine the potential connection between cancer metabolism and tumor immunity in merlin-deficient malignancies. This review may provide a deeper understanding of the biological roles of NF2 and guide possible therapeutic avenues.

A review on decoding the roles of YAP/TAZ signaling pathway in cardiovascular diseases: Bridging molecular mechanisms to therapeutic insights

Yes-associated protein (YAP) and transcriptional coactivator with PDZ-binding motif (TAZ) serve as transcriptional co-activators that dynamically shuttle between the cytoplasm and nucleus, resulting in either the suppression or enhancement of their downstream gene expression. Recent emerging evidence demonstrates that YAP/TAZ is strongly implicated in the pathophysiological processes that contribute to cardiovascular diseases (CVDs). In the cardiovascular system, YAP/TAZ is involved in the orchestration of a range of biological processes such as oxidative stress, inflammation, proliferation, and autophagy. Furthermore, YAP/TAZ has been revealed to be closely associated with the initiation and development of various cardiovascular diseases, including atherosclerosis, pulmonary hypertension, myocardial fibrosis, cardiac hypertrophy, and cardiomyopathy. In this review, we delve into recent studies surrounding YAP and TAZ, along with delineating their roles in contributing to the pathogenesis of CVDs with a link to various physiological processes in the cardiovascular system. Additionally, we highlight the current potential drugs targeting YAP/TAZ for CVDs therapy and discuss their challenges for translational application. Overall, this review may offer novel insights for understanding and treating cardiovascular disorders.

Vascular mimicry as a facilitator of melanoma brain metastasis

Melanoma has the highest propensity among solid tumors to metastasize to the brain. Melanoma brain metastases (MBM) are a leading cause of death in melanoma and affect 40-60% of patients with late-stage disease. Therefore, uncovering the molecular mechanisms behind MBM is necessary to enhance therapeutic interventions. Vascular mimicry (VM) is a form of neovascularization linked to invasion, increased risk of metastasis, and poor prognosis in many tumor types, but its significance in MBM remains poorly understood. We found that VM density is elevated in MBM compared to paired extracranial specimens and is associated with tumor volume and CNS edema. In addition, our studies indicate a relevant role of YAP and TAZ, two transcriptional co-factors scarcely studied in melanoma, in tumor cell-vasculogenesis and in brain metastasis. We recently demonstrated activation of the Hippo tumor suppressor pathway and increased degradation of its downstream targets YAP and TAZ in a metastasis impaired cell line model. In the current study we establish the utility of anti-YAP/TAZ therapy in mouse models of metastatic melanoma whereby treatment effectively inhibits VM and prolongs survival of mice with MBM. The data presented herein suggest that VM may be an important and targetable mechanism in melanoma and that VM inhibition might be useful for treating MBM, an area of high unmet clinical need, thus having important implications for future treatment regimens for these patients.

YAP/TEAD-induced PRIM1 contributes to the progression and poor prognosis of gastric carcinoma

Gastric carcinoma has a poor prognosis and low survival rate. PRIM1 is closely associated with the origin of DNA replication and serves as a carcinogenic factor in multiple tumors. This study aimed to explore the functions of PRIM1 in the progression of gastric carcinoma. The luciferase reporter assay examined the regulatory effect of YAP1/TEAD4 on PRIM1. A xenograft tumor mouse model was constructed to observe cancer cell proliferation in vivo. The upregulation of PRIM1 was found in gastric carcinoma cells and tissues, and it was associated with poor prognosis. Silencing PRIM1 inhibited cell proliferation, arrested the cell cycle, and upregulated Cdc25, Cyclin B, and Cdc2 expression. In addition, apoptosis was increased upon PRIM1 knockdown, accompanied by increased protein levels of cleaved caspase-3 and caspase-8. In vivo, knockdown of PRIM1 suppressed the growth of xenograft tumors formed by gastric carcinoma cells. Moreover, PRIM1 silencing elevated the chemosensitivity of gastric carcinoma cells. By investigating molecular events downstream of the Hippo signaling pathway, we found that PRIM1 was a target gene of the YAP1/TEAD4 transcriptional regulatory complex. PRIM1 represents a novel target for gastric carcinoma therapeutic approaches.

Musculoskeletal defects associated with myosin heavy chain-embryonic loss of function are mediated by the YAP signaling pathway

Mutations in MYH3, the gene encoding the developmental myosin heavy chain-embryonic (MyHC-embryonic) skeletal muscle-specific contractile protein, cause several congenital contracture syndromes. Among these, recessive loss-of-function MYH3 mutations lead to spondylocarpotarsal synostosis (SCTS), characterized by vertebral fusions and scoliosis. We find that Myh3 germline knockout adult mice display SCTS phenotypes such as scoliosis and vertebral fusion, in addition to reduced body weight, muscle weight, myofiber size, and grip strength. Myh3 knockout mice also exhibit changes in muscle fiber type, altered satellite cell numbers and increased muscle fibrosis. A mass spectrometric analysis of embryonic skeletal muscle from Myh3 knockouts identified integrin signaling and cytoskeletal regulation as the most affected pathways. These pathways are closely connected to the mechanosensing Yes-associated protein (YAP) transcriptional regulator, which we found to be significantly activated in the skeletal muscle of Myh3 knockout mice. To test whether increased YAP signaling might underlie the musculoskeletal defects in Myh3 knockout mice, we treated these mice with CA3, a small molecule inhibitor of YAP signaling. This led to increased muscle fiber size, rescue of most muscle fiber type alterations, normalization of the satellite cell marker Pax7 levels, increased grip strength, reduced fibrosis, and decline in scoliosis in Myh3 knockout mice. Thus, increased YAP activation underlies the musculoskeletal defects seen in Myh3 knockout mice, indicating its significance as a key pathway to target in SCTS and other MYH3-related congenital syndromes.

Deciphering the involvement of the Hippo pathway co-regulators, YAP/TAZ in invadopodia formation and matrix degradation

Invadopodia are adhesive, actin-rich protrusions formed by metastatic cancer cells that degrade the extracellular matrix and facilitate invasion. They support the metastatic cascade by a spatially and temporally coordinated process whereby invading cells bind to the matrix, degrade it by specific metalloproteinases, and mechanically penetrate diverse tissue barriers by forming actin-rich extensions. However, despite the apparent involvement of invadopodia in the metastatic process, the molecular mechanisms that regulate invadopodia formation and function are still largely unclear. In this study, we have explored the involvement of the key Hippo pathway co-regulators, namely YAP, and TAZ, in invadopodia formation and matrix degradation. Toward that goal, we tested the effect of depletion of YAP, TAZ, or both on invadopodia formation and activity in multiple human cancer cell lines. We report that the knockdown of YAP and TAZ or their inhibition by verteporfin induces a significant elevation in matrix degradation and invadopodia formation in several cancer cell lines. Conversely, overexpression of these proteins strongly suppresses invadopodia formation and matrix degradation. Proteomic and transcriptomic profiling of MDA-MB-231 cells, following co-knockdown of YAP and TAZ, revealed a significant change in the levels of key invadopodia-associated proteins, including the crucial proteins Tks5 and MT1-MMP (MMP14). Collectively, our findings show that YAP and TAZ act as negative regulators of invadopodia formation in diverse cancer lines, most likely by reducing the levels of essential invadopodia components. Dissecting the molecular mechanisms of invadopodia formation in cancer invasion may eventually reveal novel targets for therapeutic applications against invasive cancer.

Mesothelioma cancer cells are glutamine addicted and glutamine restriction reduces YAP1 signaling to attenuate tumor formation

Glutamine addiction is an important phenotype displayed in some types of cancer. In these cells, glutamine depletion results in a marked reduction in the aggressive cancer phenotype. Mesothelioma is an extremely aggressive disease that lacks effective therapy. In this study, we show that mesothelioma tumors are glutamine addicted suggesting that glutamine depletion may be a potential therapeutic strategy. We show that glutamine restriction, by removing glutamine from the medium or treatment with inhibitors that attenuate glutamine uptake (V-9302) or conversion to glutamate (CB-839), markedly reduces mesothelioma cell proliferation, spheroid formation, invasion, and migration. Inhibition of the SLC1A5 glutamine importer, by knockout or treatment with V-9302, an SLC1A5 inhibitor, also markedly reduces mesothelioma cell tumor growth. A relationship between glutamine utilization and YAP1/TEAD signaling has been demonstrated in other tumor types, and the YAP1/TEAD signaling cascade is active in mesothelioma cells and drives cell survival and proliferation. We therefore assessed the impact of glutamine depletion on YAP1/TEAD signaling. We show that glutamine restriction, SLC1A5 knockdown/knockout, or treatment with V-9302 or CB-839, reduces YAP1 level, YAP1/TEAD-dependent transcription, and YAP1/TEAD target protein (e.g., CTGF, cyclin D1, COL1A2, COL3A1, etc.) levels. These changes are observed in both cells and tumors. These findings indicate that mesothelioma is a glutamine addicted cancer, show that glutamine depletion attenuates YAP1/TEAD signaling and tumor growth, and suggest that glutamine restriction may be useful as a mesothelioma treatment strategy.

Hypoxia-induced YAP activation and focal adhesion turnover to promote cell migration in mesenchymal TNBC cells

BACKGROUND

Hypoxia is commonly characterized by malignant tumors that promote the aggressiveness and metastatic potential of cancer. Triple-negative breast cancer (TNBC) is the most aggressive subtype of breast cancer, with approximately 46% capacity related to distant metastasis. Transcriptional factor yes-associated protein (YAP), a core component of the Hippo pathway, is associated with poor prognosis and outcome in cancer metastasis. Here, we explored the effect of hypoxia-mediated YAP activation and focal adhesions (FAs) turnover in mesenchymal TNBC cell migration.

METHODS

We characterized the effect of hypoxia on YAP in different breast cancer cell lines using a hypoxia chamber and CoCl₂ .

RESULTS

Hypoxia-induced YAP nuclear translocation is significantly observed in normal breast epithelial cells, non-TNBC cells, mesenchymal TNBC cells, but not in basal-like TNBC cells. Functionally, we demonstrated that YAP activation was required for hypoxia to promote mesenchymal TNBC cell migration. Furthermore, hypoxia induced the localization of FAs at the leading edge of mesenchymal TNBC cells. In contrast, verteporfin (VP), a YAP inhibitor, significantly reduced the migration and the recruitment of nascent FAs at the cell periphery under hypoxia conditions, which only showed in mesenchymal TNBC cells.

CONCLUSIONS

Our data support the hypothesis that YAP is novel factor and positively responsible for hypoxia-promoting mesenchymal TNBC cell migration. Our findings provide further evidence and outcomes to help prevent the progression of TNBC.

Repurposed Drugs in Gastric Cancer

Gastric cancer (GC) is one of the major causes of death worldwide, ranking as the fifth most incident cancer in 2020 and the fourth leading cause of cancer mortality. The majority of GC patients are in an advanced stage at the time of diagnosis, presenting a poor prognosis and outcome. Current GC treatment approaches involve endoscopic detection, gastrectomy and chemotherapy or chemoradiotherapy in an adjuvant or neoadjuvant setting. Drug development approaches demand extreme effort to identify molecular mechanisms of action of new drug candidates. Drug repurposing is based on the research of new therapeutic indications of drugs approved for other pathologies. In this review, we explore GC and the different drugs repurposed for this disease.

Ferroptosis Induction and YAP Inhibition as New Therapeutic Targets in Gastrointestinal Stromal Tumors (GISTs)

GISTs are sarcomas of the gastrointestinal tract often associated with gain-of-function mutations in KIT or PDGFRA receptor genes. While most GISTs initially respond to tyrosine kinase inhibitors, relapses due to acquired resistance frequently occur. The induction of ferroptosis, an iron-dependent form of non-apoptotic cell death, emerged as a novel therapeutic approach in cancers and remains poorly characterized in GISTs. We studied hallmarks of ferroptosis, i.e., lipid peroxidation, iron and glutathione content, and GPX4 protein expression in imatinib-sensitive (GIST882) and -resistant (GIST48) GIST cell lines. GIST cells were highly sensitive to the induction of ferroptosis by RSL3, which was reversed by liproxstatin and deferoxamine. Lipid peroxidation and ferroptosis were mediated by VP and CA3 in GIST cells through a significant decrease in antioxidant defenses. Moreover, VP, but surprisingly not CA3, inhibited a series of target genes downstream of YAP in GIST cells. The ferroptosis marker TFRC was also investigated by immunohistochemistry in GIST tissue arrays. TFRC expression was observed in all samples. High TFRC expression was positively correlated with high-risk GISTs, elevated mitotic count, and YAP nuclear localization, reflecting YAP activation. This study highlights ferroptosis as a novel cell death mechanism in GISTs, and a potential therapeutic target to overcome resistance to tyrosine kinase inhibitors.

Targeting the Hippo Pathway in Gastric Cancer and Other Malignancies in the Digestive System: From Bench to Bedside

The Hippo pathway is an evolutionally conserved signaling cascade that controls organ size and tissue regeneration under physiological conditions, and its aberrations have been well studied to promote tumor initiation and progression. Dysregulation of the Hippo tumor suppressor signaling frequently occurs in gastric cancer (GC) and other solid tumors and contributes to cancer development through modulating multiple aspects, including cell proliferation, survival, metastasis, and oncotherapy resistance. In the clinic, Hippo components also possess diagnostic and prognostic values for cancer patients. Considering its crucial role in driving tumorigenesis, targeting the Hippo pathway may greatly benefit developing novel cancer therapies. This review summarizes the current research progress regarding the core components and regulation of the Hippo pathway, as well as the mechanism and functional roles of their dysregulation in gastrointestinal malignancies, especially in GC, and discusses the therapeutic potential of targeting the Hippo pathway against cancers.

Tubular cell polyploidy protects from lethal acute kidney injury but promotes consequent chronic kidney disease

Acute kidney injury (AKI) is frequent, often fatal and, for lack of specific therapies, can leave survivors with chronic kidney disease (CKD). We characterize the distribution of tubular cells (TC) undergoing polyploidy along AKI by DNA content analysis and single cell RNA-sequencing. Furthermore, we study the functional roles of polyploidization using transgenic models and drug interventions. We identify YAP1-driven TC polyploidization outside the site of injury as a rapid way to sustain residual kidney function early during AKI. This survival mechanism comes at the cost of senescence of polyploid TC promoting interstitial fibrosis and CKD in AKI survivors. However, targeting TC polyploidization after the early AKI phase can prevent AKI-CKD transition without influencing AKI lethality. Senolytic treatment prevents CKD by blocking repeated TC polyploidization cycles. These results revise the current pathophysiological concept of how the kidney responds to acute injury and identify a novel druggable target to improve prognosis in AKI survivors.

Acute kidney injury is frequent, often fatal and can leave survivors with chronic kidney disease. Here the authors show that tubular cell polyploidy reduces early fatality sustaining residual function but promotes chronic kidney disease, which can be prevented by blocking YAP1

PAF1 cooperates with YAP1 in metaplastic ducts to promote pancreatic cancer

Acinar-to-ductal metaplasia (ADM) is a precursor lesion of pancreatic ductal adenocarcinoma (PDAC); however, the regulators of the ADM-mediated PDAC development and its targeting are poorly understood. RNA polymerase II-associated factor 1 (PAF1) maintains cancer stem cells leading to the aggressiveness of PDAC. In this study, we investigated whether PAF1 is required for the YAP1-mediated PDAC development and whether CA3 and verteporfin, small molecule inhibitors of YAP1/TEAD transcriptional activity, diminish pancreatic cancer (PC) cell growth by targeting the PAF1/YAP1 axis. Here, we demonstrated that PAF1 co-expresses and interacts with YAP1 specifically in metaplastic ducts of mouse cerulein- or KrasG12D-induced ADM and human PDAC but not in the normal pancreas. PAF1 knockdown (KD) reduced SOX9 in PC cells, and the PC cells showed elevated PAF1/YAP1 complex recruitment to the promoter of SOX9. The PAF1 KD reduced the 8xTEAD and SOX9 promoter-luciferase reporter activities in the mouse KC (KrasG12D; Pdx-1 Cre) cells and human PC cells, indicating that the PAF1 is required for the YAP1-mediated development of ADM and PC. Moreover, treatment with CA3 or verteporfin reduced the expressions of PAF1, YAP1, TEAD4, and SOX9 and decreased colony formation and stemness in KC and PC cells. CA3 treatment also reduced the viability and proliferation of PC cells and diminished the duct-like structures in KC acinar explants. CA3 or verteporfin treatment decreased the recruitment of the PAF1/YAP1 complex to the SOX9 promoter in PC cells and reduced the 8xTEAD and SOX9 promoter-luciferase reporter activities in KC and PC cells. Overall, PAF1 cooperates with YAP1 during ADM and PC development, and verteporfin and CA3 inhibit ADM and PC cell growth by targeting the PAF1/YAP1/SOX9 axis in vitro and ex vivo models. This study identified a regulatory axis of PDAC initiation and its targeting, paving the way for developing targeted therapeutic strategies for pancreatic cancer patients.

Recent insight into the role and therapeutic potential of YAP/TAZ in gastrointestinal cancers

With the rapid development of cancer treatment, gastrointestinal (GI) cancers are still the most prevalent malignancies with high morbidity and mortality worldwide. Dysregulation of the Hippo signaling pathway has been recognized to play a critical role during cancer development and adopted for monitoring disease progression and therapy response. Despite the well-documented tumor proliferation and metastasis, recent efforts in two core Hippo components, Yes-associated protein (YAP) and transcriptional coactivator with PDZ-binding motif (TAZ), have identified as the driving forces behind cancer metabolism, stemness, tumor immunity, and therapy resistance. Understanding the molecular mechanisms by which YAP/TAZ facilitates the tumorigenesis and progression of GI cancer, and identifying novel therapeutic strategies for targeting YAP/TAZ are crucial to GI cancer treatment and prevention. In this study, we summarize the latest findings on the function and regulatory mechanisms of YAP/TAZ in GI cancers, and highlight the translational significance of targeting YAP/TAZ for cancer therapies.

Role of O-GlcNAcylation on cancer stem cells: Connecting nutrient sensing to cell plasticity

Tumor growth and metastasis can be promoted by a small sub-population of cancer cells, termed cancer stem-like cells (CSCs). While CSCs possess capability in self-renewing and differentiating, the hierarchy of CSCs during tumor growth is highly plastic. This plasticity in CSCs fate and function can be regulated by signals from the tumor microenvironment. One emerging pathway in CSCs that connects the alteration in microenvironment and signaling network in cancer cells is the hexosamine biosynthetic pathway (HBP). The final product of HBP, UDP-N-acetylglucosamine (UDP-GlcNAc), is utilized for glycosylating of membrane and secreted proteins, but also nuclear and cytoplasmic proteins by the post-translational modification O-GlcNAcylation. O-GlcNAcylation and its enzyme, O-GlcNAc transferase (OGT), are upregulated in nearly all cancers and been linked to regulate many cancer cell phenotypes. Recent studies have begun to connect OGT and O-GlcNAcylation to regulation of CSCs. In this review, we will discuss the emerging role of OGT and O-GlcNAcylation in regulating fate and plasticity of CSCs, as well as the potential in targeting OGT/O-GlcNAcylation in CSCs.

YAP1 maintains active chromatin state in head and neck squamous cell carcinomas that promotes tumorigenesis through cooperation with BRD4

Analysis of The Cancer Genome Atlas and other published data of head and neck squamous cell carcinoma (HNSCC) reveals somatic alterations of the Hippo-YAP pathway in approximately 50% of HNSCC. Better strategies to target the YAP1 transcriptional complex are sought. Here, we show that FAT1, an upstream inhibitor of YAP1, is mutated either by missense or by truncating mutation in 29% of HNSCC. Comprehensive proteomic and drug-screening studies across pan-cancer models confirm that FAT1-mutant HNSCC exhibits selective and higher sensitivity to BRD4 inhibition by JQ1. Epigenomic analysis reveals an active chromatin state in FAT1-mutant HNSCC cells that is driven by the YAP/TAZ transcriptional complex through recruitment of BRD4 to deposit active histone marks, thereby maintaining an oncogenic transcriptional state. This study reveals a detailed cooperative mechanism between YAP1 and BRD4 in HNSCC and suggests a specific therapeutic opportunity for the treatment of this subset of head and neck cancer patients.

The application of cancer stem cell model in malignant mesothelioma

The high mortality rate of malignant pleural mesothelioma led to study the mechanisms for chemoresistance. The cancer stem cell (CSC) model has been proposed to explain chemoresistance. CSCs are characterized by self-renewal capacity, that is detected through tumor-initiating cell assays. As in other malignancies, many studies sought to identify surface markers to isolate CSCs from malignant mesothelioma. Other studies characterized malignant mesothelioma CSCs for the expression of specific genes involved in stemness and the expression of proteins involved in chemoresistance. However, the main methods to characterize isolated CSCs include sphere formation, invasiveness, tumor-initiating capacity and expression of specific surface markers. The better knowledge of malignant mesothelioma CSCs allowed exploring new potential targets to develop specific treatments.

Hybrid molecule between platanic acid and LCL-161 as a yes-associated protein (YAP) degrader

Dysregulated Yes-associated protein (YAP) is involved in several malignant cancers. However, discovering a druggable YAP inhibitor(s) is difficult because YAP itself does not have any enzymatic activity. In such cases, targeted protein degradation strategies based on hybrid molecules that bind to the target protein and an E3 ubiquitin ligase are useful for suppressing proteins that exhibit aberrant activation and/or excessive expression. Upon screening YAP-interacting small compounds, we identified HK13, a platanic acid, as a novel compound that interacts with YAP. Next, we synthesized hybrid compounds of platanic acid and LCL-161, which reportedly shows a high affinity to for cIAP, one of E3 ubiquitin ligases. Among these compounds, HK24 possessed the ability to inhibit the growth of YAP overexpressing NCI-H290 cells. This inhibitory activity may be mediated by YAP degradation, although HK24 exhibited weak YAP degradation. Furthermore, we confirmed involvement of proteasome pathway in HK24-dependent YAP degradation by culturing NCI-H290 cells in the presence of a proteasome inhibitor. Therefore, it is possible that platanic acid is a potential candidate for molecular medicine targeting YAP.

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.

Mesothelioma Malignancy and the Microenvironment: Molecular Mechanisms

Several studies have reported that cellular and soluble components of the tumor microenvironment (TME) play a key role in cancer-initiation and progression. Considering the relevance and the complexity of TME in cancer biology, recent research has focused on the investigation of the TME content, in terms of players and informational exchange. Understanding the crosstalk between tumor and non-tumor cells is crucial to design more beneficial anti-cancer therapeutic strategies. Malignant pleural mesothelioma (MPM) is a complex and heterogenous tumor mainly caused by asbestos exposure with few treatment options and low life expectancy after standard therapy. MPM leukocyte infiltration is rich in macrophages. Given the failure of macrophages to eliminate asbestos fibers, these immune cells accumulate in pleural cavity leading to the establishment of a unique inflammatory environment and to the malignant transformation of mesothelial cells. In this inflammatory landscape, stromal and immune cells play a driven role to support tumor development and progression via a bidirectional communication with tumor cells. Characterization of the MPM microenvironment (MPM-ME) may be useful to understand the complexity of mesothelioma biology, such as to identify new molecular druggable targets, with the aim to improve the outcome of the disease. In this review, we summarize the known evidence about the MPM-ME network, including its prognostic and therapeutic relevance.

NGF Signaling Interacts With the Hippo/YAP Pathway to Regulate Cervical Cancer Progression

Nerve growth factor (NGF) is increasingly implicated in cervical cancer progression, but its mechanism in cervical cancer is unclear. Here, studies demonstrate that NGF inhibits the Hippo signaling pathway and activates Yes-associated protein (YAP) to induce cervical cancer cell proliferation and migration. Our results suggested that stimulation of NGF promoted cell growth and migration and activated YAP in HeLa and C-33A cell lines. The expression of YAP target genes (CTGF and ANKRD1) was upregulated after NGF treatment. The NGF inhibitor Ro 08-2750 and siRNA-mediated NGF receptor gene silencing suppressed HeLa and C-33A cells proliferation and migration, activated large suppressor kinase 1 (LATS1) kinase activity, and suppressed YAP function. In addition, the expression of YAP target genes (CTGF and ANKRD1) was suppressed by Ro 08-2750 treatment in HeLa and C-33A cells. Interestingly, proliferation was significantly higher in NGF-treated cells than in control cells, and this effect was completely reversed by the YAP small molecule inhibitor-verteporfin. Furthermore, the mouse xenograft model shows that NGF regulates YAP oncogenic activity in vivo. Mechanistically, NGF stimulation inactivates LATS1 and activates YAP, and NGF inhibition was found to induce large suppressor kinase 1 (LATS1) phosphorylation. Taken together, these data provide the first direct evidence of crosstalk between the NGF signaling and Hippo cancer pathways, an interaction that affects cervical cancer progression. Our study indicates that combined targeting of the NGF signaling and the Hippo pathway represents a novel therapeutic strategy for treatment of cervical cancer.

ACTL6A suppresses p21Cip1 tumor suppressor expression to maintain an aggressive mesothelioma cancer cell phenotype

Mesothelioma is a poor prognosis cancer of the mesothelial lining that develops in response to exposure to various agents including asbestos. Actin-Like Protein 6A (ACTL6A, BAF53a) is a SWI/SNF regulatory complex protein that is elevated in cancer cells and has been implicated as a driver of cancer cell survival and tumor formation. In the present study, we show that ACTL6A drives mesothelioma cancer cell proliferation, spheroid formation, invasion, and migration, and that these activities are markedly attenuated by ACTL6A knockdown. ACTL6A expression reduces the levels of the p21^Cip1 cyclin-dependent kinase inhibitor and tumor suppressor protein. DNA binding studies show that ACTL6A interacts with Sp1 and p53 binding DNA response elements in the p21^Cip1 gene promoter and that this is associated with reduced p21^Cip1 promoter activity and p21^Cip1 mRNA and protein levels. Moreover, ACTL6A suppression of p21^Cip1 expression is required for maintenance of the aggressive mesothelioma cancer cell phenotype suggesting that p21^Cip1 is a mediator of ACTL6A action. p53, a known inducer of p21^Cip1 expression, is involved ACTL6A in regulation of p21^Cip1 in some but not all mesothelioma cells. In addition, ACTL6A knockout markedly reduces tumor formation and this is associated with elevated tumor levels of p21^Cip1. These findings suggest that ACTL6A suppresses p21^Cip1 promoter activity to reduce p21^Cip1 protein as a mechanism to maintain the aggressive mesothelioma cell phenotype.

Breast Cancer Stem Cell-Derived ANXA6-Containing Exosomes Sustain Paclitaxel Resistance and Cancer Aggressiveness in Breast Cancer

Continuous chemotherapy pressure-elicited annexin-A6 (ANXA6)-containing exosome (ANXA6-exo) secretion contributes to paclitaxel (PTX) resistance in breast cancer (BC), but the molecular mechanisms are not fully elucidated. The present study managed to investigate this issue and found that ANXA6-exo promoted PTX resistance and cancer progression in BC cells in a Yes-associated protein 1 (YAP1)-dependent manner. Specifically, the parental PTX-sensitive BC (PS-BC) cells were exposed to continuous low-dose PTX to generate PTX-resistant BC (PR-BC) cells, and we found that BC stem cells tended to be enriched in the descendent PR-BC cells in contrast with the PS-BC cells. In addition, PR-BC cell-derived exosomes were featured with highly expressed ANXA6, and ANXA6-exo delivered ANXA6 to promote cell migration, growth, autophagy, and stemness in PS-BC cells. Interestingly, ANXA6-exo increased PTX resistance in PS-BC cells via inducing autophagy, and the effects of ANXA6-exo on PTX resistance in PS-BC cells were abrogated by co-treating cells with the autophagy inhibitor 3-methyladenine. Moreover, the underlying mechanisms were uncovered, and we evidenced that ANXA6-exo up-regulated YAP1 to promote Hippo pathway dysregulation, and the promoting effects of ANXA6-exo on PTX resistance and cancer aggressiveness in BC cells were abrogated by silencing YAP1. Taken together, this study firstly elucidated the underlying mechanisms by which BCSC-derived ANXA6-exo facilitated BC progression and PTX resistance, which might help to develop novel treatment strategies for BC in clinic.

Integrated genomics point to immune vulnerabilities in pleural mesothelioma

Pleural mesothelioma is an aggressive malignancy with limited effective therapies. In order to identify therapeutic targets, we integrated SNP genotyping, sequencing and transcriptomics from tumours and low-passage patient-derived cells. Previously unrecognised deletions of SUFU locus (10q24.32), observed in 21% of 118 tumours, resulted in disordered expression of transcripts from Hedgehog pathways and the T-cell synapse including VISTA. Co-deletion of Interferon Type I genes and CDKN2A was present in half of tumours and was a predictor of poor survival. We also found previously unrecognised deletions in RB1 in 26% of cases and show sub-micromolar responses to downstream PLK1, CHEK1 and Aurora Kinase inhibitors in primary mesothelioma cells. Defects in Hippo pathways that included RASSF7 amplification and NF2 or LATS1/2 mutations were present in 50% of tumours and were accompanied by micromolar responses to the YAP1 inhibitor Verteporfin. Our results suggest new therapeutic avenues in mesothelioma and indicate targets and biomarkers for immunotherapy.

Transcriptomic Analyses Reveal B-Cell Translocation Gene 2 as a Potential Therapeutic Target in Ovarian Cancer

Ovarian cancer is the most common and aggressive type of tumor of the female reproductive system. Two factors account for this detrimental clinical presentation: (i) the lack of early detection methods and (ii) the inherently aggressive nature of this malignancy. Currently, transcriptomic analyses have become important tools to identify new targets in different cancer types. In this study, by measuring expression levels in ovarian cancer samples and stem cell samples, we identified 24 tumor suppressor genes consistently associated with poor prognosis. Combined results further revealed a potential therapeutic candidate, BTG2, which belongs to the antiproliferative gene family. Our results showed that BTG2 expression regulated ovarian cancer cell proliferation via G1/S phase cell cycle arrest by regulating Cyclin D1, CDK4, p-AKT, and p-ERK expression. BTG2 also inhibited cell migration by modulating MMP-2 and MMP-9 expression. Furthermore, xenograft models confirmed a growth inhibitory effect of BTG2 in ovarian cancer in vivo. BTG2 was significantly associated with ovarian cancer FIGO stage and grade in the clinic. Our findings indicated that BTG2 exerts a suppressive impact on ovarian cancer and could be a potential biomarker.

Multi-omics data integration reveals novel drug targets in hepatocellular carcinoma

BACKGROUND

Genetic aberrations in hepatocellular carcinoma (HCC) are well known, but the functional consequences of such aberrations remain poorly understood.

RESULTS

Here, we explored the effect of defined genetic changes on the transcriptome, proteome and phosphoproteome in twelve tumors from an mTOR-driven hepatocellular carcinoma mouse model. Using Network-based Integration of multi-omiCS data (NetICS), we detected 74 'mediators' that relay via molecular interactions the effects of genetic and miRNA expression changes. The detected mediators account for the effects of oncogenic mTOR signaling on the transcriptome, proteome and phosphoproteome. We confirmed the dysregulation of the mediators YAP1, GRB2, SIRT1, HDAC4 and LIS1 in human HCC.

CONCLUSIONS

This study suggests that targeting pathways such as YAP1 or GRB2 signaling and pathways regulating global histone acetylation could be beneficial in treating HCC with hyperactive mTOR signaling.

VGLL4 inhibits YAP1/TEAD signaling to suppress the epidermal squamous cell carcinoma cancer phenotype

Epidermal squamous cell carcinoma (SCC) develops in response to ultraviolet light exposure and is among the most common cancers. The transglutaminase 2 cancer cell survival protein stimulates the activity of the YAP1/TEAD transcription complex to drive the expression of genes that promote aggressive epidermal SCC cell invasion, migration, and tumor formation. Therefore, we are interested in mechanisms that may inhibit these events. Vestigial-like protein-4 (VGLL4) is a transcription cofactor/tumor suppressor that inhibits several pro-cancer pathways including YAP1 signaling. Our present studies show that VGLL4 inhibits YAP1/TEAD-dependent transcription to reduce the expression of YAP1 target genes (CCND1, CYR61, and CTGF) and pro-cancer collagen genes (COL1A2 and COL3A1). We further show that loss of these YAP1 regulated genes is required for VGLL4 suppression of the cancer cell phenotype, as forced CCND1 or COL1A2 expression partially restores the aggressive cancer phenotype in VGLL4 expressing cells. Consistent with these findings, VGLL4 expression reduces tumor formation, and this is associated with reduced CCND1, CYR61, CTGF, COL1A2, and COL1A3 mRNA and protein levels, and reduced EMT marker expression. These findings indicate that VGLL4 suppresses the malignant epidermal SCC cancer phenotype by inhibiting YAP1/TEAD-dependent pro-cancer signaling.

Anti-tumor effect of trametinib in bladder cancer organoid and the underlying mechanism

Bladder cancer (BC), a main neoplasm of urinary tract, is usually inoperable and unresponsive to chemotherapy. As a novel experimental model for muscle-invasive BC, we previously established a culture method of dog BC organoids. In the present study, the detailed in vitro and in vivo anti-tumor effects of trametinib were investigated by using this model. In each BC organoid strain, epidermal growth factor receptor (EGFR)/ERK signaling was upregulated compared with normal bladder cells. Trametinib even at a low concentration inhibited the cell viability of BC organoids and the activation of ERK through decreasing expression of c-Myc, ELK1, SIK1, and PLA2G4A. Trametinib arrested cell cycle of BC with few apoptosis. Dual treatment of BC organoids with trametinib and YAP inhibitor, verteporfin extremely inhibited the cell viability with apoptosis induction. Moreover, trametinib induced basal to luminal differentiation of BC organoids by upregulating luminal markers and downregulating basal ones. In vivo, trametinib decreased the tumor growth of BC organoids in mice and the xenograft-derived organoids from trametinib-administered mice showed enhanced sensitivity to carboplatin due to MSH2 upregulation. Our data suggested a new strategy of trametinib-YAP inhibitor or trametinib-carboplatin combination as a promising treatment of BC.

Role of Mechanotransduction in Periodontal Homeostasis and Disease

Novel findings broaden the concept of mechanotransduction (MT) in biophysically stimulated tissues such as the periodontium by considering nuclear MT, convergence of intracellular MT pathways, and mechanoresponsive cotranscription factors such as Yes-associated protein 1 (YAP1). Regarding periodontal disease, recent studies have elucidated the role of bacterial gingipain proteases in disturbing the barrier function of cadherins, thereby promoting periodontal inflammation. This leads to dysregulation of extracellular matrix homeostasis via proteases and changes the cell's biophysical environment, which leads to alterations in MT-induced cell behavior and loss of periodontal integrity. Newest experimental evidence from periodontal ligament cells suggests that the Hippo signaling protein YAP1, in addition to integrin-FAK (focal adhesion kinase) mechanosignaling, also regulates cell stemness. By addressing mechanosignaling-dependent transcription factors, YAP1 is involved in osteogenic and myofibroblast differentiation and influences core steps of autophagy. Recent in vivo evidence elucidates the decisive role of YAP1 in epithelial homeostasis and underlines its impact on oral pathologies, such as periodontitis-linked oral squamous cell carcinogenesis. Here, new insights reveal that YAP1 contributes to carcinogenesis via overexpression rather than mutation; promotes processes such as apoptosis resistance, epithelial-mesenchymal transition, or metastasis; and correlates with poor prognosis in oral squamous cell carcinoma. Furthermore, YAP1 has been shown to contribute to periodontitis-induced bone loss. Mechanistically, molecules identified to regulate YAP1-related periodontal homeostasis and disease include cellular key players such as MAPK (mitogen-activated protein kinase), JNK (c-Jun N-terminal kinase), Rho (Ras homologue) and ROCK (Rho kinase), Bcl-2 (B-cell lymphoma 2), AP-1 (activator protein 1), and c-myc (cellular myelocytomatosis). These findings qualify YAP1 as a master regulator of mechanobiology and cell behavior in human periodontal tissues. This review summarizes the most recent developments in MT-related periodontal research, thereby offering insights into outstanding research questions and potential applications of molecular or biophysical strategies aiming at periodontal disease mitigation or prevention.

Zinc-Dependent Regulation of ZEB1 and YAP1 Coactivation Promotes Epithelial-Mesenchymal Transition Plasticity and Metastasis in Pancreatic Cancer

BACKGROUND

Pancreatic cancer is characterized by extensive metastasis. Epithelial-mesenchymal transition (EMT) plasticity plays a critical role in tumor progression and metastasis by maintaining the transition between EMT and mesenchymal-epithelial transition states. Our aim is to understand the molecular events regulating metastasis and EMT plasticity in pancreatic cancer.

METHODS

The interactions between a cancer-promoting zinc transporter ZIP4, a zinc-dependent EMT transcriptional factor ZEB1, a coactivator YAP1, and integrin α3 (ITGA3) were examined in human pancreatic cancer cells, clinical specimens, spontaneous mouse models (KPC and KPCZ) and orthotopic xenografts, and 3-dimensional spheroid and organoid models. Correlations between ZIP4, miR-373, and its downstream targets were assessed by RNA in situ hybridization and immunohistochemical staining. The transcriptional regulation of ZEB1, YAP1, and ITGA3 by ZIP4 was determined by chromatin immunoprecipitation, co-immunoprecipitation, and luciferase reporter assays.

RESULTS

The Hippo pathway effector YAP1 is a potent transcriptional coactivator and forms a complex with ZEB1 to activate ITGA3 transcription through the YAP1/transcriptional enhanced associate domain (TEAD) binding sites in human pancreatic cancer cells and KPC-derived mouse cells. ZIP4 upregulated YAP1 expression via activation of miR-373 and inhibition of the YAP1 repressor large tumor suppressor 2 kinase (LATS2). Furthermore, upregulation of ZIP4 promoted EMT plasticity, cell adhesion, spheroid formation, and organogenesis both in human pancreatic cancer cells, 3-dimensional spheroid model, xenograft model, and spontaneous mouse models (KPC and KPCZ) through ZEB1/YAP1-ITGA3 signaling axis.

CONCLUSION

We demonstrated that ZIP4 activates ZEB1 and YAP1 through distinct mechanisms. The ZIP4-miR-373-LATS2-ZEB1/YAP1-ITGA3 signaling axis has a significant impact on pancreatic cancer metastasis and EMT plasticity.

Narciclasine is a novel YAP inhibitor that disturbs interaction between YAP and TEAD4

Yes-associated protein (YAP) is involved in development, cell growth, cell size, and homeostasis and plays a key role in the progression of various cancers. Among them, constitutive activation of YAP can often be observed in malignant mesothelioma, which arises in the pleura, peritoneum, and pericardium because of inactivation of the Hippo pathway. To date, however, only less-effective treatments such as chemotherapy, radiation therapy, and surgery are available for patients with malignant mesothelioma. In this study, we identified narciclasine as a novel YAP inhibitor that prevents YAP from interacting with TEAD4 because it competes with TEAD4 for binding to YAP. Furthermore, narciclasine could perturb the cell growth and colony formation of malignant mesothelioma NCI-H290 cells in addition to inhibiting their growth in nude mice. Therefore, narciclasine might be a potential seed for a novel antitumor drug against malignant mesothelioma and other cancers in which hyperactivation and/or overexpression of YAP are observed.

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.

Linc00475 promotes the progression of glioma by regulating the miR-141-3p/YAP1 axis

Glioma is the most prevalent and lethal primary brain tumour. Abundant long non‐coding RNAs ( lncRNAs) are aberrant and play crucial roles in the oncogenesis of glioma. The exact functions of linc00475 in glioma remain blurred. Here, we analysed the expression levels of linc00475 by qRT‐PCR and discovered that linc00475 was up‐regulated in glioma and predicted a poor prognosis in patients with glioma. Besides, inhibiting linc00475 restrained the progression of glioma in vitro and in vivo. Further experiments confirmed that linc00475 regulated the progression of glioma by acting as a sponge for miR‐141‐3p. Moreover, we detected the binding sites of linc00475 and miR‐141‐3p, the YAP1‐ 3′UTR and miR‐141‐3p by luciferase reporters. The rescue assays confirmed that inhibiting linc00475 restrained the progression of glioma through the miR‐141‐3p/YAP1 pathway. Collectively, our research demonstrates the key roles of linc00475 in glioma, which could be a promising therapeutic target.

The Role of Photoactivated and Non-Photoactivated Verteporfin on Tumor

Verteporfin (VP) has long been clinically used to treat age-related macular degeneration (AMD) through photodynamic therapy (PDT). Recent studies have reported a significant anti-tumor effect of VP as well. Yes-associated protein (YAP) is a pro-tumorigenic factor that is aberrantly expressed in various cancers and is a central effector of the Hippo signaling pathway that regulates organ size and tumorigenesis. VP can inhibit YAP without photoactivation, along with suppressing autophagy, and downregulating germinal center kinase-like kinase (GLK) and STE20/SPS1-related proline/alanine-rich kinase (SPAK). In addition, VP can induce mitochondrial damage and increase the production of reactive oxygen species (ROS) upon photoactivation, and is an effective photosensitizer (PS) in anti-tumor PDT. We have reviewed the direct and adjuvant therapeutic action of VP as a PS, and its YAP/TEA domain (TEAD)-dependent and independent pharmacological effects in the absence of light activation against cancer cells and solid tumors. Based on the present evidence, VP may be repositioned as a promising anti-cancer chemotherapeutic and adjuvant drug.

Mechanical Cues Affect Migration and Invasion of Cells From Three Different Directions

Cell migration and invasion is a key driving factor for providing essential cellular functions under physiological conditions or the malignant progression of tumors following downward the metastatic cascade. Although there has been plentiful of molecules identified to support the migration and invasion of cells, the mechanical aspects have not yet been explored in a combined and systematic manner. In addition, the cellular environment has been classically and frequently assumed to be homogeneous for reasons of simplicity. However, motility assays have led to various models for migration covering only some aspects and supporting factors that in some cases also include mechanical factors. Instead of specific models, in this review, a more or less holistic model for cell motility in 3D is envisioned covering all these different aspects with a special emphasis on the mechanical cues from a biophysical perspective. After introducing the mechanical aspects of cell migration and invasion and presenting the heterogeneity of extracellular matrices, the three distinct directions of cell motility focusing on the mechanical aspects are presented. These three different directions are as follows: firstly, the commonly used invasion tests using structural and structure-based mechanical environmental signals; secondly, the mechano-invasion assay, in which cells are studied by mechanical forces to migrate and invade; and thirdly, cell mechanics, including cytoskeletal and nuclear mechanics, to influence cell migration and invasion. Since the interaction between the cell and the microenvironment is bi-directional in these assays, these should be accounted in migration and invasion approaches focusing on the mechanical aspects. Beyond this, there is also the interaction between the cytoskeleton of the cell and its other compartments, such as the cell nucleus. In specific, a three-element approach is presented for addressing the effect of mechanics on cell migration and invasion by including the effect of the mechano-phenotype of the cytoskeleton, nucleus and the cell's microenvironment into the analysis. In precise terms, the combination of these three research approaches including experimental techniques seems to be promising for revealing bi-directional impacts of mechanical alterations of the cellular microenvironment on cells and internal mechanical fluctuations or changes of cells on the surroundings. Finally, different approaches are discussed and thereby a model for the broad impact of mechanics on cell migration and invasion is evolved.

Therapeutic Targeting of Signaling Pathways Related to Cancer Stemness

The theory of cancer stem cells (CSCs) proposes that the different cells within a tumor, as well as metastasis deriving from it, are originated from a single subpopulation of cells with self-renewal and differentiation capacities. These cancer stem cells are supposed to be critical for tumor expansion and metastasis, tumor relapse and resistance to conventional therapies, such as chemo- and radiotherapy. The acquisition of these abilities has been attributed to the activation of alternative pathways, for instance, WNT, NOTCH, SHH, PI3K, Hippo, or NF-κB pathways, that regulate detoxification mechanisms; increase the metabolic rate; induce resistance to apoptotic, autophagic, and senescence pathways; promote the overexpression of drug transporter proteins; and activate specific stem cell transcription factors. The elimination of CSCs is an important goal in cancer therapeutic approaches because it could decrease relapses and metastatic dissemination, which are main causes of mortality in oncology patients. In this work, we discuss the role of these signaling pathways in CSCs along with their therapeutic potential.

lncRNA MALAT1 modulates cancer stem cell properties of liver cancer cells by regulating YAP1 expression via miR‑375 sponging

Liver cancer stem cells (CSCs) are functionally defined by their ability to undergo self-renewal, and may contribute to metastasis, recurrence and drug resistance in liver cancer. The long non-coding RNA metastasis-associated lung adenocarcinoma transcript 1 (MALAT1) has been implicated in tumor formation and metastasis of liver cancer. However, the exact mechanism by which MALAT1 modulates liver CSC features remains largely unknown. In the present study, the expression level of MALAT1 was elevated in cancer spheroids compared with the corresponding levels noted in parental liver cancer cells, whereas the suppression of MALAT1 resulted in markedly reduced sphere formation and decreased expression of stemness factors in liver cancer cells. Dual-luciferase assay and RNA pull-down assays further indicated an interaction between MALAT1 and microRNA (miR)-375, and identified Yes-associated protein 1 (YAP1) as a direct target of miR-375 in liver cancer cells. In addition, YAP1 expression was correlated with MALAT1 in liver cancer. The reduced expression of YAP1 caused by knockdown of MALAT1 with MALAT1 small interfering RNA (si-MALAT1) could be partially abolished by miR-375 inhibition, suggesting that MALAT1 may regulate YAP1 expression by sponging miR-375. Furthermore, YAP1 overexpression rescued the decrease in CSC features of liver cancer cells caused by si-MALAT1, further supporting that MALAT1-mediated YAP1 signaling was required for the stem-like characteristics of liver CSCs. The present study revealed that MALAT1 may promote CSC properties of liver cancer cells by upregulating YAP1 expression via sponging miR-375. The MALAT1/miR-375/YAP1 axis may serve as a novel target for liver cancer therapy, particularly for the eradication of liver CSCs.