A YAP/TAZ-Regulated Molecular Signature Is Associated with Oral Squamous Cell Carcinoma

Peritoneal Microenvironment Promotes Appendiceal Adenocarcinoma Growth: A Multi-omics Approach Using Patient-Derived Xenografts

Appendiceal adenocarcinoma (AA) is unique from other gastrointestinal malignancies in that it almost exclusively metastasizes to the peritoneal cavity. However, few studies have investigated the molecular interaction of the peritoneal microenvironment and AA. Here, we use a multi-omics approach with orthotopic and flank-implanted patient-derived xenografts (PDX) to study the effect of the peritoneal microenvironment on AA. AA tumors implanted in the peritoneal microenvironment tended to grow faster and displayed greater nuclear expression of Ki-67 relative to the same tumors implanted in the flank. Comparing the tumor-specific transcriptome (excluding stromal transcription), the peritoneal microenvironment relatively upregulated genes related to proliferation, including MKI67 and EXO1. Peritoneal tumors were also enriched for proliferative gene sets, including E2F and Myc Targets. Proteomic studies found a 2.5-fold increased ratio of active-to-inactive phosphoforms of the YAP oncoprotein in peritoneal tumors, indicating downregulation of Hippo signaling.

IMPLICATIONS

The peritoneal microenvironment promotes growth of appendiceal tumors and expression of proliferative pathways in PDXs.

Identification of a Gene Signature That Predicts Dependence upon YAP/TAZ-TEAD

Targeted therapies are effective cancer treatments when accompanied by accurate diagnostic tests that can help identify patients that will respond to those therapies. The YAP/TAZ-TEAD axis is activated and plays a causal role in several cancer types, and TEAD inhibitors are currently in early-phase clinical trials in cancer patients. However, a lack of a reliable way to identify tumors with YAP/TAZ-TEAD activation for most cancer types makes it difficult to determine which tumors will be susceptible to TEAD inhibitors. Here, we used a combination of RNA-seq and bioinformatic analysis of metastatic melanoma cells to develop a YAP/TAZ gene signature. We found that the genes in this signature are TEAD-dependent in several melanoma cell lines, and that their expression strongly correlates with YAP/TAZ activation in human melanomas. Using DepMap dependency data, we found that this YAP/TAZ signature was predictive of melanoma cell dependence upon YAP/TAZ or TEADs. Importantly, this was not limited to melanoma because this signature was also predictive when tested on a panel of over 1000 cancer cell lines representing numerous distinct cancer types. Our results suggest that YAP/TAZ gene signatures like ours may be effective tools to predict tumor cell dependence upon YAP/TAZ-TEAD, and thus potentially provide a means to identify patients likely to benefit from TEAD inhibitors.

TM4SF19 controls GABP-dependent YAP transcription in head and neck cancer under oxidative stress conditions

Tobacco and alcohol are risk factors for human papillomavirus-negative head and neck squamous cell carcinoma (HPV- HNSCC), which arises from the mucosal epithelium of the upper aerodigestive tract. Notably, despite the mutagenic potential of smoking, HPV- HNSCC exhibits a low mutational load directly attributed to smoking, which implies an undefined role of smoking in HPV- HNSCC. Elevated YAP (Yes-associated protein) mRNA is prevalent in HPV- HNSCC, irrespective of the YAP gene amplification status, and the mechanism behind this upregulation remains elusive. Here, we report that oxidative stress, induced by major risk factors for HPV- HNSCC such as tobacco and alcohol, promotes YAP transcription via TM4SF19 (transmembrane 4 L six family member 19). TM4SF19 modulates YAP transcription by interacting with the GABP (Guanine and adenine-binding protein) transcription factor complex. Mechanistically, oxidative stress induces TM4SF19 dimerization and topology inversion in the endoplasmic reticulum membrane, which in turn protects the GABPβ1 subunit from proteasomal degradation. Conversely, depletion of TM4SF19 impairs the survival, proliferation, and migration of HPV- HNSCC cells, highlighting the potential therapeutic relevance of targeting TM4SF19. Our findings reveal the roles of the key risk factors of HPV- HNSCC in tumor development via oxidative stress, offering implications for upcoming therapeutic approaches in HPV- HNSCC.

Nuclear Import and Export of YAP and TAZ

Yes-associated Protein (YAP) and its paralog Transcriptional Coactivator with PDZ-binding Motif (TAZ) are major regulators of gene transcription/expression, primarily controlled by the Hippo pathway and the cytoskeleton. Integrating an array of chemical and mechanical signals, they impact growth, differentiation, and regeneration. Accordingly, they also play key roles in tumorigenesis and metastasis formation. Their activity is primarily regulated by their localization, that is, Hippo pathway- and/or cytoskeleton-controlled cytosolic or nuclear sequestration. While many details of such prevailing retention models have been elucidated, much less is known about their actual nuclear traffic: import and export. Although their size is not far from the cutoff for passive diffusion through the nuclear pore complex (NPC), and they do not contain any classic nuclear localization (NLS) or nuclear export signal (NES), evidence has been accumulating that their shuttling involves mediated and thus regulatable/targetable processes. The aim of this review is to summarize emerging information/concepts about their nucleocytoplasmic shuttling, encompassing the relevant structural requirements (NLS, NES), nuclear transport receptors (NTRs, karyophererins), and NPC components, along with the potential transport mechanisms and their regulation. While dissecting retention vs. transport is often challenging, the emerging picture suggests that YAP/TAZ shuttles across the NPC via multiple, non-exclusive, mediated mechanisms, constituting a novel and intriguing facet of YAP/TAZ biology.

Exploring the potential of dietary factors and plant extracts as chemopreventive agents in oral squamous cell carcinoma treatment

Oral cancer, particularly oral squamous cell carcinoma (OSCC), is a prevalent malignancy having a significant fatality rate worldwide. Despite advancements in conventional treatment modalities, the overall survival rate for OSCC remains low. Therefore, there is a critical need to explore alternative therapeutic approaches that can improve patient outcomes. This review focuses on the potential of dietary factors and plant extracts as chemopreventive agents in treating oral cancer. These compounds possess diverse biological functions encompassing a range of attributes, such as antioxidative, anti-inflammatory, and anticancer capabilities. By targeting multiple cellular pathways involved in carcinogenesis, they possess the capacity to hinder tumor growth and development, promote programmed cell death, and impede the progression of oral cancer. Signaling pathways targeted by natural compounds that have been included in this review include Akt/mTOR/NF-κB signaling, Hippo-Tafazzin signaling pathway, notch signaling pathway, mitochondrial pathway, and Sonic Hedgehog pathway.

Yes-associated protein-1 overexpression in ocular surface squamous neoplasia; a potential diagnostic marker and therapeutic target

Yes-associated protein-1 (YAP-1) is a Hippo system transcription factor, which serves as an oncogene in squamous cell carcinoma, and several solid tumors when the Hippo pathway is dysregulated. Yet, the activity of YAP-1 in ocular surface squamous neoplasia (OSSN) has not been determined. Here, we investigate the relationship between YAP-1 overexpression and OSSN. Using a cross-sectional study design, we recruited 227 OSSN patients from the University Teaching Hospitals in Lusaka, Zambia. Immunohistochemistry was used to assess YAP-1 protein overexpression in tumor tissue relative to surrounding benign squamous epithelium. OSSN patient samples (preinvasive, n = 62, 27% and invasive, n = 165, 73%) were studied. One hundred forty-nine invasive tumors contained adjacent preinvasive tissue, bringing the total number of preinvasive lesions examined to 211 (62 + 149). There was adjacent benign squamous epithelium in 50.2% (114/227) of OSSN samples. Nuclear YAP- 1 was significantly overexpressed in preinvasive (Fisher's (F): p <.0001, Monte Carlo (MC): p <.0001) and invasive (F: p <.0001, MC: p <.0001) OSSN in comparison to adjacent benign squamous epithelium when analyzed for basal keratinocyte positive count, staining intensity, expression pattern, and Immunostaining intensity-distribution index. YAP-1 expression did not differ between preinvasive and invasive OSSN (p >.05), keratinizing and non- keratinizing cancer (p >.05), or between T1/T2 and T3/T4 stages in invasive tumors (p >.05). However, grade 2 and 3 tumors had significantly stronger nucleus YAP-1 overexpression intensity than grade 1 tumors (F: p = .0078, MC: p = .0489). By immunohistochemistry, we identified significant overexpression (upregulation of YAP-1 protein expression) in preinvasive and invasive OSSN lesions compared to neighboring benign squamous epithelium. YAP-1 expression was significantly higher in poorly and moderately differentiated invasive squamous cancer than in well-differentiated carcinomas. Overexpression of YAP-1 within the margin of preinvasive and invasive OSSN, but not in the neighboring normal epithelium, indicates that it plays a role in the development and progression of OSSN.

Expression of miR-31-5p affects growth, migration and invasiveness of papillary thyroid cancer cells

PURPOSE

In this study, we evaluated the biological role of miRNA-31-5p in papillary thyroid cancer (PTC).

METHODS

By using the real-time PCR, we measured miRNA-31-5p expression levels in 25 PTC tissues and in two human PTC cell lines (K1 and TPC-1). Then, K1 cells were transiently transfected with mirVana inhibitor or mirVana mimic to miRNA-31-5-p. Cell proliferation was determined by MTT and colony formation assays. The in vitro metastatic ability of thyroid cancer cells was evaluated by adhesion, migration and invasion assays. Epithelial mesenchymal transition (EMT) and Hippo pathway related gene and protein levels were evaluated by using the TaqMan™ Gene Expression Assays and western blot analysis, respectively.

RESULTS

We found a significant increase of miR-31-5-p expression in tumor tissue and in K1 cells harboring the BRAF p.V600E mutation. Knockdown of miR-31-5p determined a reduction of cell proliferation, associated with a significant decrease in cell adhesion, migration and invasion properties. A downregulation of EMT markers and YAP/β-catenin axis was also observed.

CONCLUSIONS

Our findings suggest that miRNA-31-5p acts as oncogenic miRNA in human thyrocytes and its overexpression may be involved in the BRAF-related tumorigenesis in PTCs, providing new understanding into its pathological role in PTC progression and invasiveness.

Mechanosensitive Ion Channels and Their Role in Cancer Cells

Mechanical forces are an inherent element in the world around us. The effects of their action can be observed both on the macro and molecular levels. They can also play a prominent role in the tissues and cells of animals due to the presence of mechanosensitive ion channels (MIChs) such as the Piezo and TRP families. They are essential in many physiological processes in the human body. However, their role in pathology has also been observed. Recent discoveries have highlighted the relationship between these channels and the development of malignant tumors. Multiple studies have shown that MIChs mediate the proliferation, migration, and invasion of various cancer cells via various mechanisms. This could show MIChs as new potential biomarkers in cancer detection and prognosis and interesting therapeutic targets in modern oncology. Our paper is a review of the latest literature on the role of the Piezo1 and TRP families in the molecular mechanisms of carcinogenesis in different types of cancer.

Targeting Transcription Factors in Cancer: From "Undruggable" to "Druggable"

Deregulation of transcription factors is critical to hallmarks of cancer. Genetic mutations, gene fusions, amplifications or deletions, epigenetic alternations, and aberrant post-transcriptional modification of transcription factors are involved in the regulation of various stages of carcinogenesis, including cancer initiation, progression, and metastasis. Thus, targeting the dysfunctional transcription factors may lead to new cancer therapeutic strategies. However, transcription factors are conventionally considered as "undruggable." Here, we summarize the recent progresses in understanding the regulation of transcription factors in cancers and strategies to target transcription factors and co-factors for preclinical and clinical drug development, particularly focusing on c-Myc, YAP/TAZ, and β-catenin due to their significance and interplays in cancer.

The deubiquitinase USP7 promotes HNSCC progression via deubiquitinating and stabilizing TAZ

Dysregulated abundance, location and transcriptional output of Hippo signaling effector TAZ have been increasingly linked to human cancers including head neck squamous cell carcinoma (HNSCC). TAZ is subjected to ubiquitination and degradation mediated by E3 ligase β-TRCP. However, the deubiquitinating enzymes and mechanisms responsible for its protein stability remain underexplored. Here, we exploited customized deubiquitinases siRNA and cDNA library screen strategies and identified USP7 as a bona fide TAZ deubiquitinase in HNSCC. USP7 promoted cell proliferation, migration, invasion in vitro and tumor growth by stabilizing TAZ. Mechanistically, USP7 interacted with, deubiquitinated and stabilized TAZ by selectively removing its K48-linked ubiquitination chain independent of canonical Hippo kinase cascade. USP7 potently antagonized β-TRCP-mediated ubiquitin-proteasomal degradation of TAZ and enhanced its nuclear retention and transcriptional output. Importantly, overexpression of USP7 correlated with TAZ upregulation, tumor aggressiveness and unfavorable prognosis in HNSCC patients. Pharmacological inhibition of USP7 significantly suppressed tumor growth in both xenograft and PDX models. Collectively, these findings identify USP7 as an essential regulator of TAZ and define USP7-TAZ signaling axis as a novel biomarker and potential therapeutic target for HNSCC.

LATS kinases and SLUG regulate the transition to advanced stage in aggressive oral cancer cells

The epithelial-to-mesenchymal transition (EMT) is a critical process by which cancer cells acquire malignant features. However, the molecular mechanism and functional implications of EMT and the mesenchymal-to-epithelial transition (MET) in tumor progression remain elusive. In this study, we established two aggressive cancer cell lines from the human oral cancer cell line SAS, mesenchymal-like SAS-m4 and epithelial-like SAS-δ. SAS-δ is a revertant cell obtained by inducing MET in SAS-m4. SAS-δ, but not SAS-m4, exhibited abnormal cell growth, including piled-up overgrowth and invasive tumor formation in the tongues of nude mice, suggesting that SAS-δ represented more advanced cancer cells than the parental SAS cells. EMT-related transcriptional factor SLUG is phosphorylated at T208 and partly stabilized by the Hippo pathway kinases, LATS1 and LATS2. Depletion of SLUG promoted the invasive activity of SAS-δ by increasing the protein levels of LATS1/2 and the proportion of the phosphorylated form among total SLUG protein. Our results suggest that the LATS1/2-SLUG axis regulates the transition of SAS cells to the advanced stage via repeated switching between EMT and MET. Therefore, an anti-SLUG-pT208 antibody would be valuable not alone as a malignant tumor marker antibody but also as a prognostic tool for patients with malignant disease.

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.

YAP1 is essential for malignant mesothelioma tumor maintenance

Malignant pleural mesothelioma, a tumor arising from the membrane covering the lungs and the inner side of the ribs, is a cancer in which genetic alterations of genes encoding proteins that act on or are part of the Hippo-YAP1 signaling pathway are frequent. Dysfunctional Hippo signaling may result in aberrant activation of the transcriptional coactivator protein YAP1, which binds to and activates transcription factors of the TEAD family. Recent studies have associated elevated YAP1 protein activity with a poor prognosis of malignant mesothelioma and its resistance to current therapies, but its role in tumor maintenance is unclear. In this study, we investigate the dependence of malignant mesothelioma on YAP1 signaling to maintain fully established tumors in vivo. We show that downregulation of YAP1 in a dysfunctional Hippo genetic background results in the inhibition of YAP1/TEAD-dependent gene expression, the induction of apoptosis, and the inhibition of tumor cell growth in vitro. The conditional downregulation of YAP1 in established tumor xenografts leads to the inhibition of YAP1-dependent gene transcription and eventually tumor regression. This effect is only seen in the YAP1-activated MSTO-211H mesothelioma xenograft model, but not in the Hippo-independent HCT116 colon cancer xenograft model. Our data demonstrate that, in the context of a Hippo pathway mutated background, YAP1 activity alone is enough to maintain the growth of established tumors in vivo, thus validating the concept of inhibiting the activated YAP1-TEAD complex for the treatment of malignant pleural mesothelioma patients.

Induction of apoptosis using ATN as a novel Yes-associated protein inhibitor in human oral squamous cell carcinoma cells

Oral squamous cell carcinoma (OSCC) represents a clinical challenge due to the lack of effective therapy to improve prognosis. Hippo/Yes-associated protein (YAP) signaling has emerged as a promising therapeutic target for squamous cell carcinoma treatment. In this study, we investigated the antitumor activity and underlying mechanisms of {[N-(4-(5-(3-(3-(4-acetamido-3-(trifluoromethyl)phenyl)ureido)phenyl)-1,2,4-oxadiazol-3-yl)-3-chlorophenyl)-nicotinamide]} (ATN), a novel YAP inhibitor, in OSCC cells. ATN exhibited differential antiproliferative efficacy against OSCC cells (IC₅₀ as low as 0.29 μM) versus nontumorigenic human fibroblast cells (IC₅₀  = 1.9 μM). Moreover, ATN effectively suppressed the expression of YAP and YAP-related or downstream targets, including Akt, p-AMPK, c-Myc, and cyclin D1, which paralleled the antiproliferative efficacy of ATN. Supporting the roles of YAP in regulating cancer cell survival and migration, ATN not only induced caspase-dependent apoptosis, but also suppressed migration activity in OSCC. Mechanistically, the antitumor activity of ATN in OSCC was attributed, in part, to its ability to regulate Mcl-1 expression. Together, these findings suggest a translational potential of YAP inhibitors, represented by ATN as anticancer therapy for OSCC.

Genomic Hippo Pathway Alterations and Persistent YAP/TAZ Activation: New Hallmarks in Head and Neck Cancer

Head and neck squamous cell carcinoma (HNSCC) represents a highly prevalent and deadly malignancy worldwide. The prognosis for locoregionally advanced HNSCC has not appreciably improved over the past 30 years despite advances in surgical, radiation, and targeted therapies and less than 20% of HNSCC patients respond to recently approved immune checkpoint inhibitors. The Hippo signaling pathway, originally discovered as a mechanism regulating tissue growth and organ size, transduces intracellular and extracellular signals to regulate the transcriptional co-activators YAP and TAZ. Alterations in the Hippo pathway resulting in persistent YAP and TAZ activation have emerged as major oncogenic drivers. Our analysis of the human HNSCC oncogenome revealed multiple genomic alterations impairing Hippo signaling and activating YAP and TAZ, which in turn contribute to HNSCC development. This includes mutations and deletions of the FAT1 gene (29%) and amplification of the WWTR1 (encoding TAZ, 14%) and YAP1 genes (8%), together representing one of the most genetically altered signaling mechanisms in this malignancy. Here, we discuss key elements of the mammalian Hippo pathway, detail mechanisms by which perturbations in Hippo signaling promote HNSCC initiation and progression and outline emerging strategies to target Hippo signaling vulnerabilities as part of novel multimodal precision therapies for HNSCC.

Analysis of Yes-Associated Protein-1 (YAP1) Target Gene Signature to Predict Progressive Breast Cancer

Breast cancers are treated according to the ER/PR or HER2 expression and show better survival outcomes with targeted therapy. Triple-negative breast cancers (TNBCs) with a lack of expression of ER/PR and HER2 are treated with systemic therapy with unpredictable responses and outcomes. It is essential to investigate novel markers to identify targeted therapies for TNBC. One such marker is YAP1, a transcription co-activator protein that shows association with poor prognosis of breast cancer. YAP1 transcriptionally regulates the expression of genes that drive the oncogenic phenotypes. Here, we assess a potential YAP target gene signature to predict a progressive subset of breast tumors from METABRIC and TCGA datasets. YAP1 target genes were shortlisted based on expression correlation and concordance with YAP1 expression and significant association with survival outcomes of patients. Hierarchical clustering was performed for the shortlisted genes. The utility of the clustered genes was assessed by survival analysis to identify a recurring subset. Expression of the shortlisted target genes showed significant association with survival outcomes of HER2-positive and TNBC subset in both datasets. The shortlisted genes were verified using an independent dataset. Further validation using IHC can prove the utility of this potential prognostic signature to identify a recurrent subset of HER2-positive and TNBC subtypes.

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.

Inhibition of LSD1 attenuates oral cancer development and promotes therapeutic efficacy of immune checkpoint blockade and Yap/Taz inhibition

Lysine-specific demethylase 1 (LSD1) is a histone demethylase that contributes to the etiology of oral squamous cell carcinoma (OSCC) in part by promoting cancer stem cell phenotypes. The molecular signals regulated by LSD1, or acting with LSD1, are poorly understood, particularly in the development of OSSC. In this study, we show that conditional deletion of the Lsd1 gene or pharmacological inhibition of LSD1 in the tongue epithelium leads to reduced development of OSCC following exposure to the tobacco carcinogen 4NQO. LSD1 inhibition attenuated proliferation and clonogenic survival and showed an additive effect when combined with the YAP inhibitor Verteporfin. Interestingly, LSD1 inhibition upregulated the expression of PD-L1, leading to immune checkpoint inhibitor therapy responses. Implications: Collectively, our studies reveal a critical role for LSD1 in OSCC development and identification of tumor growth targeting strategies that can be combined with LSD1 inhibition for improved therapeutic application.

Desmoglein-3 induces YAP phosphorylation and inactivation during collective migration of oral carcinoma cells

Alterations of the Hippo-YAP pathway are potential targets for oral squamous cell carcinoma (OSCC) therapy, but heterogeneity in this pathway could be responsible for therapeutic resistance. We analysed the Hippo-YAP signatures in a cohort of characterised keratinocyte cell lines derived from the mouth floor and buccal mucosa from different stages of OSCC tumour progression and focused on the specific role of YAP on invasive and metastatic potential. We confirmed heterogeneity in the Hippo-YAP pathway in OSCC lines, including overexpression of YAP1, WWTR1 (often referred to as TAZ) and the major Hippo signalling components, as well as the variations in the genes encoding the intercellular anchoring junctional proteins, which could potentially regulate the Hippo pathway. Specifically, desmoglein-3 (DSG3) exhibits a unique and mutually exclusive regulation of YAP via YAP phosphorylation during the collective migration of OSCC cells. Mechanistically, such regulation is associated with inhibition of phosphorylation of epidermal growth factor receptor (EGFR) (S695/Y1086) and its downstream effectors heat shock protein beta-1 (Hsp27) (S78/S82) and transcription factor AP-1 (c-Jun) (S63), leading to YAP phosphorylation coupled with its cytoplasmic translocation and inactivation. Additionally, OSCC lines display distinct phenotypes of YAP dependency or a mixed YAP and TAZ dependency for cell migration, and present distinct patterns in YAP abundance and activity, with the latter being associated with YAP nuclear localisation. In conclusion, this study has provided evidence for a newly identified paradigm in the Hippo-YAP pathway and suggests a new regulation mechanism involved in the control of collective migration in OSCC cells.

YAP/TAZ and ATF4 drive resistance to Sorafenib in hepatocellular carcinoma by preventing ferroptosis

Understanding the mechanisms underlying evasive resistance in cancer is an unmet medical need to improve the efficacy of current therapies. In this study, a combination of shRNA-mediated synthetic lethality screening and transcriptomic analysis revealed the transcription factors YAP/TAZ as key drivers of Sorafenib resistance in hepatocellular carcinoma (HCC) by repressing Sorafenib-induced ferroptosis. Mechanistically, in a TEAD-dependent manner, YAP/TAZ induce the expression of SLC7A11, a key transporter maintaining intracellular glutathione homeostasis, thus enabling HCC cells to overcome Sorafenib-induced ferroptosis. At the same time, YAP/TAZ sustain the protein stability, nuclear localization, and transcriptional activity of ATF4 which in turn cooperates to induce SLC7A11 expression. Our study uncovers a critical role of YAP/TAZ in the repression of ferroptosis and thus in the establishment of Sorafenib resistance in HCC, highlighting YAP/TAZ-based rewiring strategies as potential approaches to overcome HCC therapy resistance.

Targeting Cancer Stem Cell Markers or Pathways: A Potential Therapeutic Strategy for Oral Cancer Treatment

Cancer stem cells (CSCs) are a small subset of cancer cells with stem cell-like properties, self-renewal potential, and differentiation capacity into multiple cell types. Critical genetic alterations or aberrantly activated signaling pathways associated with drug resistance and recurrence have been observed in multiple types of CSCs. In this context, CSCs are considered to be responsible for tumor initiation, growth, progression, therapeutic resistance, and metastasis. Therefore, to effectively eradicate CSCs, tremendous efforts have been devoted to identify specific target molecules that play a critical role in regulating their distinct functions and to develop novel therapeutics, such as proteins, monoclonal antibodies, selective small molecule inhibitors, and small antisense RNA (asRNA) drugs. Similar to other CSC types, oral CSCs can be characterized by certain pluripotency-associated markers, and oral CSCs can also survive and form 3D tumor spheres in suspension culture conditions. These oral CSC-targeting therapeutics selectively suppress specific surface markers or key signaling components and subsequently inhibit the stem-like properties of oral CSCs. A large number of new therapeutic candidates have been tested, and some products are currently in the pre-clinical or clinical development phase. In the present study, we review new oral CSC-targeted therapeutic strategies and discuss the various specific CSC surface markers and key signaling components involved in the stem-like properties, growth, drug resistance, and tumorigenicity of oral CSCs.

The Hippo pathway: a renewed insight in the craniofacial diseases and hard tissue remodeling

The Hippo pathway plays an important role in many pathophysiological processes, including cell proliferation and differentiation, cell death, cell migration and invasion. Because of its extensive functions, Hippo pathway is closely related to not only growth and development, but also many diseases, including inflammation and cancer. In this study, the role of Hippo pathway in craniofacial diseases and hard tissue remodeling was reviewed, in attempting to find new research directions.

The regulatory networks of the Hippo signaling pathway in cancer development

The Hippo signaling pathway is a relatively young tumor-related signaling pathway. Although it was discovered lately, research on it developed rapidly. The Hippo signaling pathway is closely relevant to the occurrence and development of tumors and the maintenance of organ size and other biological processes. This manuscript focuses on YAP, the core molecule of the Hippo signaling pathway, and discussion the upstream and downstream regulatory networks of the Hippo signaling pathway during tumorigenesis and development. It also summarizes the relevant drugs involved in this signaling pathway, which may be helpful to the development of targeted drugs for cancer therapy.

Bladder mesenchymal stromal cell-derived exosomal miRNA-217 modulates bladder cancer cell survival through Hippo-YAP pathway

BACKGROUND

Donor cell-derived exosomes regulate recipient cell functions. The aim of this study was to investigate the effect of human normal bladder stromal cell (hBSC) derived exosomal miR-217 on bladder cell cancer proliferation and migration.

METHODS

Human BSCs were transfected with miR-217 mimic or inhibitor and hBSC-derived exosomes were isolated. Human bladder cancer cell lines (T24 and 5367) were co-cultured with hBSC-derived exosomal miR-217 mimic or inhibitor. Proliferation, migration, and apoptosis of the bladder cancer cells were assessed by Edu assay, Transwell migration assay, and Annexin V assay.

RESULTS

Expression of miR-217 was significantly higher in the T24 and 5367 cell lines (P < 0.01). Exosomal miR-217 mimic enhanced proliferation and migration of T24 and 5367 cells, but inhibited apoptosis of the cells (P < 0.01); in contrast, exosomal miR-217 inhibitor suppressed proliferation and migration but stimulated apoptosis of the two cancer cell lines (P < 0.01). Moreover, exosomal miR-217 mimic stimulated YAP and its target proteins including Cyr61, CTGF, and ANKRD1 (P < 0.01), and in contrast, exosomal miR-217 inhibitor suppressed YAP and its target proteins (P < 0.01).

CONCLUSION

These findings suggested that hBSC-derived exosomal miR-217 may act as oncogene in bladder cancer cells, and that Hippo-YAP signaling pathway maybe the target for miR-217 in the bladder cancer cell lines.

Binary pan-cancer classes with distinct vulnerabilities defined by pro- or anti-cancer YAP/TEAD activity

Cancer heterogeneity impacts therapeutic response, driving efforts to discover over-arching rules that supersede variability. Here, we define pan-cancer binary classes based on distinct expression of YAP and YAP-responsive adhesion regulators. Combining informatics with in vivo and in vitro gain- and loss-of-function studies across multiple murine and human tumor types, we show that opposite pro- or anti-cancer YAP activity functionally defines binary YAP^on or YAP^off cancer classes that express or silence YAP, respectively. YAP^off solid cancers are neural/neuroendocrine and frequently RB1^-/-, such as retinoblastoma, small cell lung cancer, and neuroendocrine prostate cancer. YAP silencing is intrinsic to the cell of origin, or acquired with lineage switching and drug resistance. The binary cancer groups exhibit distinct YAP-dependent adhesive behavior and pharmaceutical vulnerabilities, underscoring clinical relevance. Mechanistically, distinct YAP/TEAD enhancers in YAP^off or YAP^on cancers deploy anti-cancer integrin or pro-cancer proliferative programs, respectively. YAP is thus pivotal across cancer, but in opposite ways, with therapeutic implications.

MYCN-induced nucleolar stress drives an early senescence-like transcriptional program in hTERT-immortalized RPE cells

MYCN is an oncogenic driver in neural crest-derived neuroblastoma and medulloblastoma. To better understand the early effects of MYCN activation in a neural-crest lineage context, we profiled the transcriptome of immortalized human retina pigment epithelial cells with inducible MYCN activation. Gene signatures associated with elevated MYC/MYCN activity were induced after 24 h of MYCN activation, which attenuated but sustained at later time points. Unexpectedly, MYCN activation was accompanied by reduced cell growth. Gene set enrichment analysis revealed a senescence-like signature with strong induction of p53 and p21 but in the absence of canonical hallmarks of senescence such as β-galactosidase positivity, suggesting incomplete cell fate commitment. When scrutinizing the putative drivers of this growth attenuation, differential gene expression analysis identified several regulators of nucleolar stress. This process was also reflected by phenotypic correlates such as cytoplasmic granule accrual and nucleolar coalescence. Hence, we propose that the induction of MYCN congests the translational machinery, causing nucleolar stress and driving cells into a transient pre-senescent state. Our findings shed new light on the early events induced by MYCN activation and may help unravelling which factors are required for cells to tolerate unscheduled MYCN overexpression during early malignant transformation.

Role of Yes-associated protein and transcriptional coactivator with PDZ-binding motif in the malignant transformation of oral submucous fibrosis

OBJECTIVE(S)

The objective of the present manuscript is to elucidate the role of matrix stiffness in the malignant transformation of oral submucous fibrosis.

DESIGN

The role of matrix stiffness in several cancers including oral cancer was reviewed with a tailored search strategy using relevant keywords as per the Medline format. The role of molecular mediators, Yes-associated protein 1 (YAP) and transcriptional coactivator with PDZ-binding motif (TAZ) was weighed in the context of OSF along two distinct pathways.

RESULTS

Increased matrix stiffness activates the transcriptional coactivators, YAP and TAZ shuttling between the nucleus and cytoplasm. YAP and TAZ, serve as mechanical transducers in promoting cell migration, invasion and epithelial-mesenchymal transition (EMT). The hypoxic microenvironment in the advanced stage of OSF promotes the migratory phenotype through mechanical memory.

CONCLUSIONS

Reprogramming of a stiff matrix has the potential to restore the Hippo-YAP/TAZ tumor suppressor pathway and reverse fibrosis-associated tumor development.

Aberrant epithelial polarity cues drive the development of precancerous airway lesions

Molecular events that drive the development of precancerous lesions in the bronchial epithelium, which are precursors of lung squamous cell carcinoma (LUSC), are poorly understood. We demonstrate that disruption of epithelial cellular polarity, via the conditional deletion of the apical determinant Crumbs3 (Crb3), initiates and sustains precancerous airway pathology. The loss of Crb3 in adult luminal airway epithelium promotes the uncontrolled activation of the transcriptional regulators YAP and TAZ, which stimulate intrinsic signals that promote epithelial cell plasticity and paracrine signals that induce basal-like cell growth. We show that aberrant polarity and YAP/TAZ-regulated gene expression associates with human bronchial precancer pathology and disease progression. Analyses of YAP/TAZ-regulated genes further identified the ERBB receptor ligand Neuregulin-1 (NRG1) as a key transcriptional target and therapeutic targeting of ERBB receptors as a means of preventing and treating precancerous cell growth. Our observations offer important molecular insight into the etiology of LUSC and provides directions for potential interception strategies of lung cancer.

Endothelial YAP/TAZ Signaling in Angiogenesis and Tumor Vasculature

Solid tumors are dependent on vascularization for their growth. The hypoxic, stiff, and pro-angiogenic tumor microenvironment induces angiogenesis, giving rise to an immature, proliferative, and permeable vasculature. The tumor vessels promote tumor metastasis and complicate delivery of anti-cancer therapies. In many types of tumors, YAP/TAZ activation is correlated with increased levels of angiogenesis. In addition, endothelial YAP/TAZ activation is important for the formation of new blood and lymphatic vessels during development. Oncogenic activation of YAP/TAZ in tumor cell growth and invasion has been studied in great detail, however the role of YAP/TAZ within the tumor endothelium remains insufficiently understood, which complicates therapeutic strategies aimed at targeting YAP/TAZ in cancer. Here, we overview the upstream signals from the tumor microenvironment that control endothelial YAP/TAZ activation and explore the role of their downstream targets in driving tumor angiogenesis. We further discuss the potential for anti-cancer treatments and vascular normalization strategies to improve tumor therapies.

YAP1 and its fusion proteins in cancer initiation, progression and therapeutic resistance

YAP1 is a transcriptional co-activator whose activity is controlled by the Hippo signaling pathway. In addition to important functions in normal tissue homeostasis and regeneration, YAP1 has also prominent functions in cancer initiation, aggressiveness, metastasis, and therapy resistance. In this review we are discussing the molecular functions of YAP1 and its roles in cancer, with a focus on the different mechanisms of de-regulation of YAP1 activity in human cancers, including inactivation of upstream Hippo pathway tumor suppressors, regulation by intersecting pathways, miRNAs, and viral oncogenes. We are also discussing new findings on the function and biology of the recently identified family of YAP1 gene fusions, that constitute a new type of activating mutation of YAP1 and that are the likely oncogenic drivers in several subtypes of human cancers. Lastly, we also discuss different strategies of therapeutic inhibition of YAP1 functions.

Inhibition of yes-associated protein dephosphorylation prevents aggravated periodontitis with occlusal trauma

BACKGROUND

Occlusal trauma can aggravate periodontitis, but the mechanism remains unclear. Yes-associated protein (YAP), a mechanical stressor protein, may play an important role in this process.

METHODS

Western blot and quantitative real-time polymerase chain reaction (qRT-PCR) were applied to detect the expression of YAP and inflammatory factors in patients with periodontitis accompanied with or without occlusal trauma. Through local administration of Porphyromonas gingivalis and composite resin bonding on maxillary molars in mice, we established periodontitis and occlusal trauma models. Treatment with or without XAV939, to inhibit YAP activation, was performed in these models. Micro-computed tomography, immunofluorescence (IF), and qRT-PCR were used to explore the YAP pathway in periodontitis with occlusal trauma. Cyclic stress and lipopolysaccharide (LPS) stimuli were applied to the L929 mouse fibroblast cell line with or without XAV939. Western blot, IF, and qRT-PCR were used to verify the in vivo results.

RESULTS

Activated dephosphorylated YAP and increased expression of inflammatory factors were observed in patients with periodontitis accompanied with occlusal trauma. In the mouse model of periodontitis with occlusal trauma, YAP transferred into the nucleus, resulting in Jun N-terminal kinases (JNK) related pro-inflammatory pathway up-regulation. L929 cell cyclic stress and LPS stimulation results confirmed the in vivo results. Application of XAV939 inhibited YAP protein dephosphorylation and reduced JNK pro-inflammatory pathway factor expression in vivo and in vitro.

CONCLUSIONS

Occlusal trauma can activate YAP nuclear transfer, resulting in the up-regulation of the JNK pro-inflammatory pathway. This can be inhibited by the XAV939 YAP inhibitor.

YAP signaling induces PIEZO1 to promote oral squamous cell carcinoma cell proliferation

Most cancer cells are exposed to altered extracellular environments, such as an increase in extracellular matrix (ECM) stiffness and soluble signals consisting of growth factors and cytokines. It is therefore conceivable that changes in tumor extracellular environments affect tumor cell behavior. The Hippo pathway reportedly responds to the extracellular environment and regulates the nuclear localization of the transcription co-activator, yes-associated protein (YAP)/transcriptional co-activator with PDZ-binding motif (TAZ). Inactivation of the Hippo pathway with nuclear translocation of YAP/TAZ stimulates cell proliferation. Its pathway also regulates gene expression, but the precise molecule(s) meditating the cell-proliferating effect of YAP signaling on oral squamous cell carcinoma (OSCC) is unclear. First, we examined the effects of YAP signaling on OSCC tumorigenesis. Loss-of-function experiments using siRNA or an inhibitor, and immunohistochemical analyses of tissue specimens obtained from OSCC patients demonstrated that YAP signaling was involved in OSCC cell proliferation. Second, we identified Piezo-type mechanosensitive ion channel component 1 (PIEZO1), a Ca²⁺ channel, as a transcriptional target of YAP signaling and showed that elevated PIEZO1 was required for PIEZO1 agonist-dependent Ca²⁺ entry and cell proliferation in OSCC cells. Experiments using three-dimensional and suspension culture revealed that PIEZO1 was involved in OSCC cellular growth. Finally, YAP overexpression in the nucleus and/or cytoplasm was immunohistochemically detected in tumor lesions with frequent expression of both PIEZO1 and Ki-67, but not in non-tumor regions of OSCC specimens. These results suggest that the YAP/PIEZO1 axis promotes OSCC cell growth. © 2020 The Pathological Society of Great Britain and Ireland. Published by John Wiley & Sons, Ltd.

Role of YAP1 gene in proliferation, osteogenic differentiation, and apoptosis of human periodontal ligament stem cells induced by TNF-α

BACKGROUND

Periodontitis is a chronic inflammatory disease that occurs in periodontal tissues and can cause tooth loosening and loss in severe cases. As the main effector of downstream of Hippo signaling pathway, yes-related protein 1 (YAP1) plays an important role in cell proliferation and differentiation. However, the role of YAP1 in periodontitis has not been reported.

METHODS

Cell activity was detected by Cell Counting Kit-8 (CCK-8). YAP1 was overexpressed by cell transfection, and then RT-qPCR and western blot were used to detect the expression of YAP1. The cell proliferation was determined by clone formation assay, and the expression of proliferation-related proteins was determined by western blot. The cell differentiation was detected by ELISA kit of alkaline phosphatase activity (ALP) and alizarin red staining. Finally, western blot was used to detect the expression of differentiation-related protein and Hippo signaling pathway-related proteins. Apoptosis was detected by flow cytometry.

RESULTS

With the increase of concentration induced by TNF-α, the cell survival rate of human periodontal ligament stem cells (HPDLSCs) decreased significantly. After the overexpression of YAP1, cell proliferation and proliferation-related protein expression increased. Overexpression of YAP1 can improve the differentiation and the formation of osteoblasts of HPDLSCs induced by TNF-α. The expression of Hippo signaling pathway-related proteins transcriptional coactivators with PDZ binding domains (TAZ), TEA domain family member (TRED) increased and proliferation-related protein P27 decreased, whereas there was no significant change in the expression of MST1.

CONCLUSION

TNF-α can inhibit proliferation and osteogenic differentiation of HPDLSCs, which can be ameliorated by the YAP1 gene through the Hippo signaling pathway. Our paper suggested that YAP1 may be a potential therapeutic target for periodontitis.

Genome-wide CRISPR screens of oral squamous cell carcinoma reveal fitness genes in the Hippo pathway

New therapeutic targets for oral squamous cell carcinoma (OSCC) are urgently needed. We conducted genome-wide CRISPR-Cas9 screens in 21 OSCC cell lines, primarily derived from Asians, to identify genetic vulnerabilities that can be explored as therapeutic targets. We identify known and novel fitness genes and demonstrate that many previously identified OSCC-related cancer genes are non-essential and could have limited therapeutic value, while other fitness genes warrant further investigation for their potential as therapeutic targets. We validate a distinctive dependency on YAP1 and WWTR1 of the Hippo pathway, where the lost-of-fitness effect of one paralog can be compensated only in a subset of lines. We also discover that OSCCs with WWTR1 dependency signature are significantly associated with biomarkers of favorable response toward immunotherapy. In summary, we have delineated the genetic vulnerabilities of OSCC, enabling the prioritization of therapeutic targets for further exploration, including the targeting of YAP1 and WWTR1.

The potential role of YAP in head and neck squamous cell carcinoma

The transcriptional cofactor YAP and its inhibitory regulators, Hippo kinases and adapter proteins, constitute an evolutionarily conserved signaling pathway that controls organ size and cell fate. The activity of the Hippo-YAP pathway is determined by a variety of intracellular and intercellular cues, such as cell polarity, junctions, density, mechanical stress, energy status, and growth factor signaling. Recent studies have demonstrated that YAP can induce the expression of a set of genes that allow cancer cells to gain a survival advantage and aggressive behavior. Comprehensive genomic studies have revealed frequent focal amplifications of the YAP locus in human carcinomas, including head and neck squamous cell carcinoma (HNSCC). Moreover, FAT1, which encodes an upstream component of Hippo signaling, is one of the most commonly altered genes in HNSCC. In this review, we discuss the causes and functional consequences of YAP dysregulation in HNSCC. We also address interactions between YAP and other oncogenic drivers of HNSCC.

Abnormal activity of a protein involved in cell proliferation may influence the progression of head and neck cancers. Head and neck squamous cell carcinoma (HNSCC) affects the skin, throat, mouth and nose tissues. Disruption to the Hippo-YAP signaling pathway, which plays a key role in cell proliferation and differentiation, is implicated in multiple cancers. Joon Kim and Eunbie Shin at the Korea Advanced Institute of Science and Technology, Daejeon, South Korea, reviewed recent research into the role of YAP in HNSCC. Abnormal YAP protein activity triggers the expression of genes that encourage cancer cell proliferation. Mice with over-expressed YAP showed tissue overgrowth and tumor formation. High YAP levels have been found at the invasive front of HNSCC tumors, suggesting a role in metastasis. Further research is needed to verify whether YAP is a potential therapeutic target.

Loss of oral mucosal stem cell markers in oral submucous fibrosis and their reactivation in malignant transformation

The integrity of the basal stem cell layer is critical for epithelial homoeostasis. In this paper, we review the expression of oral mucosal stem cell markers (OM-SCMs) in oral submucous fibrosis (OSF), oral potentially malignant disorders (OPMDs) and oral squamous cell carcinoma (OSCC) to understand the role of basal cells in potentiating cancer stem cell behaviour in OSF. While the loss of basal cell clonogenicity triggers epithelial atrophy in OSF, the transition of the epithelium from atrophic to hyperplastic and eventually neoplastic involves the reactivation of basal stemness. The vacillating expression patterns of OM-SCMs confirm the role of keratins 5, 14, 19, CD44, β1-integrin, p63, sex-determining region Y box (SOX2), octamer-binding transcription factor 4 (Oct-4), c-MYC, B-cell-specific Moloney murine leukaemia virus integration site 1 (Bmi-1) and aldehyde dehydrogenase 1 (ALDH1) in OSF, OPMDs and OSCC. The downregulation of OM-SCMs in the atrophic epithelium of OSF and their upregulation during malignant transformation are illustrated with relevant literature in this review.

Targeting the Hippo pathway in cancer, fibrosis, wound healing and regenerative medicine

The Hippo pathway is an evolutionarily conserved signalling pathway with key roles in organ development, epithelial homeostasis, tissue regeneration, wound healing and immune modulation. Many of these roles are mediated by the transcriptional effectors YAP and TAZ, which direct gene expression via control of the TEAD family of transcription factors. Dysregulated Hippo pathway and YAP/TAZ-TEAD activity is associated with various diseases, most notably cancer, making this pathway an attractive target for therapeutic intervention. This Review highlights the key findings from studies of Hippo pathway signalling across biological processes and diseases, and discusses new strategies and therapeutic implications of targeting this pathway.

YAP1 Promotes Tumor Invasion and Metastasis in Nasopharyngeal Carcinoma with Hepatitis B Virus Infection

INTRODUCTION

Nasopharyngeal carcinoma (NPC) patients with HBsAg (+) commonly present with high frequencies of distant metastasis and poor survival rate; however, the mechanism has not been elucidated.

MATERIALS AND METHODS

We analyzed the yes-associated protein 1 (YAP1) expression between HBsAg (+) and HBsAg (-) of NPC patients, then analyzed the relationship of YAP1 with survival. We further explored the anti-tumor role in NPC cell lines using YAP1 siRNA technique, and checked whether YAP1 regulatesepithelial-mesenchymal transition ( EMT). The relationship between HBV X protein (HBx) and YAP1 was also tested using Dual-Luciferase reporter assay. Finally, we explored anti-YAP1 to inhibit tumor metastasis using the xenograft mice model.

RESULTS

In the current study, we found that YAP1 expression was higher in HBsAg (+) samples than in the HBsAg (-) samples, as a clinical signature, suggesting that YAP1 could be used as a prognostic factor for NPC. Our results showed that the HBx could regulate YAP1, further promoting cellular invasiveness through EMT. Anti-YAP1 can also decrease metastasis in vivo.

CONCLUSION

Our findings suggest that YAP1 is a promising prognostic factor in NPC and could be used as a potential treatment target for NPC with HBV infection.

E3 ligase STUB1 attenuates stemness and tumorigenicity of oral carcinoma cells via transglutaminase 2 regulation

BACKGROUND/PURPOSE

Oral cancer is amongst the most prevalent cancers worldwide with rising incidence. Various attempts have been made to elucidate its pathogenesis, and we sought to examine the function of a ubiquitin E3 ligase that was encoded by STUB1.

METHODS

The mRNA expression of STUB1 in oral cancer samples and normal counterparts was determined by qRT-PCR. Numerous assays to assess the features of cancer cells, including self-renewal capacity, invasion and migration abilities were conducted following knockdown or overexpression of STUB1.

RESULTS

The expression level of STUB1 was reduced in oral cancer, which was associated with a reduced relapse-free survival. Two oral cancer cell lines with low expression of STUB1 (SAS and HSC3) were chosen for the overexpression of STUB1. We showed that ectopic expression of STUB1 led to the downregulation of TGM2, a multifunctional protein that contributed to cancer progression in several cancers. Our results demonstrated that overexpression of STUB1 suppressed the cancer aggressiveness, while restoration of TGM2 reverted the effects. Last, we showed that STUB1 silencing resulted in enhanced cancer features.

CONCLUSION

The abnormal downregulation of STUB1 may lessen its suppressive effect on TGM2, which induced the onset or exacerbated the progression of oral cancer. The therapeutic approach to enhance the expression of STUB1 could be a promising direction for cancer therapy.

Interplay between cancer cells and M2 macrophages is necessary for miR-550a-3-5p down-regulation-mediated HPV-positive OSCC progression

BACKGROUND

Human papillomavirus (HPV)-positive oral squamous cell carcinoma (OSCC) is increasing worldwide with typically higher grade and stage, while better prognosis. microRNAs (miRNAs) has been shown to play a critical role in cancer, however, their role in HPV-positive OSCC progression remains unclear.

METHODS

miRNA microarray was performed to identify differentially expressed miRNAs. qRT-PCR and FISH were performed to determine the relative expression of miR-550a-3-5p. CCK-8, Flow cytometry, Wound healing, Cell invasion assays and xenograft experiments were conducted to analyze the biological roles of miR-550a-3-5p. Tumor-associated macrophages (TAMs) generation, co-culturing of cancer cells with TAMs, Western blot, Dual-luciferase reporter gene assay, Immunohistochemistry and animal studies were performed to explore the mechanisms underlying the functions of miR-550a-3-5p.

RESULTS

We identified 19 miRNAs differentially expressed in HPV-positive OSCC specimens and miR-550a-3-5p was down-regulated. The low expression of miR-550a-3-5p correlated with higher tumor size and nodal metastasis of HPV-positive OSCC patients. Then, we found that miR-550a-3-5p suppressed the migration, invasion and EMT of HPV-positive OSCC cells dependent on decreasing M2 macrophages polarization. Moreover, miR-550a-3-5p, down-regulated by E6 oncoprotein, inhibited M2 macrophages polarization by YAP/CCL2 signaling, which in turn abrogating EMT program in HPV-positive OSCC cells. In addition, in both xenografts and clinical HPV-positive OSCC samples, miR-550a-3-5p levels were inversely associated with YAP, CCL2 expressions and the number of M2 macrophages.

CONCLUSIONS

E6/miR-550a-3-5p/YAP/CCL2 signaling induces M2 macrophages polarization to enhance EMT and progression, revealing a novel crosstalk between cancer cells and immune cells in HPV-positive OSCC microenvironment.

Expression and prognostic significance of YAP, TAZ, TEAD4 and p73 in human laryngeal cancer

OBJECTIVES

The Hippo signaling pathway plays a critical role in organ size control and tissue homeostasis and its perturbation is associated with tumorigenesis. YAP (Yes associated protein) and TAZ (transcriptional co-activator with PDZ- binding motif) are the major nuclear effectors of the Hippo pathway interacting with TEADs (TEA domain) and p73 transcriptional factors to regulate gene expression. Altered expression of the above proteins promotes tumor initiation, progression and metastasis in a variety of cancer types. This study addresses their expression and prognostic significance in human laryngeal carcinoma.

METHODS

Protein expression of YAP, TAZ, TEAD4 and p73 was examined by immunohistochemistry in 121 human laryngeal squamous cell carcinomas. Correlations with clinicopathological data and survival were evaluated.

RESULTS

All proteins were overexpressed in human laryngeal carcinomas compared to non-neoplastic adjacent epithelium. High expression of YAP, TAZ, TEAD4 and p73 correlated significantly with high grade, advanced stage, supraglottic location of tumor, nodal metastases and recurrence. Furthermore, high expression of all proteins was significantly associated with poor overall and disease- free survival. p73 expression proved to be an independent predictive factor of survival and YAP expression proved to be an independent predictive factor of disease recurrence.

CONCLUSIONS

Deregulation of the expression of the Hippo pathway proteins is implicated in human laryngeal carcinogenesis and YAP and p73 have prognostic significance in the outcome of the disease.

Targeted Disruption of Lats1 and Lats2 in Mice Impairs Adrenal Cortex Development and Alters Adrenocortical Cell Fate

It has recently been shown that the loss of the Hippo signaling effectors Yes-associated protein (YAP) and transcriptional coactivator with PDZ-binding motif (TAZ) in adrenocortical steroidogenic cells impairs the postnatal maintenance of the adrenal gland. To further explore the role of Hippo signaling in mouse adrenocortical cells, we conditionally deleted the key Hippo kinases large tumor suppressor homolog kinases 1 and -2 (Lats1 and Lats2, two kinases that antagonize YAP and TAZ transcriptional co-regulatory activity) in steroidogenic cells using an Nr5a1-cre strain (Lats1flox/flox;Lats2flox/flox;Nr5a1-cre). We report here that developing adrenocortical cells adopt characteristics of myofibroblasts in both male and female Lats1flox/flox;Lats2flox/flox;Nr5a1-cre mice, resulting in a loss of steroidogenic gene expression, adrenal failure and death by 2 to 3 weeks of age. A marked accumulation of YAP and TAZ in the nuclei of the myofibroblast-like cell population with an accompanying increase in the expression of their transcriptional target genes in the adrenal glands of Lats1flox/flox;Lats2flox/flox;Nr5a1-cre animals suggested that the myofibroblastic differentiation could be attributed in part to YAP and TAZ. Taken together, our results suggest that Hippo signaling is required to maintain proper adrenocortical cell differentiation and suppresses their differentiation into myofibroblast-like cells.

A robust six-miRNA prognostic signature for head and neck squamous cell carcinoma

Head and neck squamous cell carcinoma (HNSCC) remains a major health problem worldwide. We aimed to identify a robust microRNA (miRNA)-based signature for predicting HNSCC prognosis. The miRNA expression profiles of HNSCC were obtained from The Cancer Genome Atlas (TCGA) database. The TCGA HNSCC cohort was randomly divided into the discovery and validation cohort. A miRNA-based prognostic signature was built up based on TGCA discovery cohort, and then further validated. The downstream targets of prognostic miRNAs were subjected to functional enrichment analyses. The role of miR-1229-3p, a prognosis-related miRNA, in tumorigenesis of HNSCC was further evaluated. A total of 305 significantly differentially expressed miRNAs were found between HNSCC samples and normal tissues. A six-miRNA prognostic signature was constructed, which exhibited a strong association with overall survival (OS) in the TCGA discovery cohort. In addition, these findings were successfully confirmed in TCGA validation cohort and our own independent cohort. The miRNA-based signature was demonstrated as an independent prognostic indicator for HNSCC. A risk signature-based nomogram model was constructed and showed good performance for predicting the OS for HNSCC. The functional analyses revealed that the downstream targets of these prognostic miRNAs were closely linked to cancer progression. Mechanistically, in vitro analysis revealed that miR-1229-3p played a tumor promoting role in HNSCC. In conclusion, our study has developed a robust miRNA-based signature for predicting the prognosis of HNSCC with high accuracy, which will contribute to improve the therapeutic outcome.

GPR39 Overexpression in OSCC Promotes YAP-Sustained Malignant Progression

The clinical outcome of oral squamous cell carcinoma (OSCC) has not improved in recent years, mainly due to the limited effective targeted therapy that has been applied. Recently, a transcriptional coactivator, YAP, has been shown to have a key regulatory role in malignant progression in multiple cancers, including OSCC. But pharmacologically targeting YAP or the Hippo pathway, which is the main signaling pathway regulating YAP, has been proven to be challenging. Therefore, uncovering YAP upstream regulators in cancer would identify novel therapeutic targets for treatment of YAP-sustained cancers. Here, we showed that YAP was overactivated in OSCC and that high YAP activity in patients with OSCC was associated with malignant progression and poor survival. We uncovered that GPR39 (a G protein-coupled receptor) was overexpressed in OSCC, that the expression level of GPR39 was correlated with the activity level of YAP, and that the high GPR39 expression was associated with malignant progression and poor survival in patients with OSCC. Moreover, we found that GPR39 regulated YAP through a Gαq/11-RhoA-dependent signaling pathway. Importantly, inhibition of GPR39 resulted in YAP-sustained OSCC growth inhibition. Our findings suggest that GPR39 is a potential therapeutic target for OSCC treatment with itself as a biomarker.

YAP Activity is Not Associated with Survival of Uveal Melanoma Patients and Cell Lines

Recent experimental studies have demonstrated an essential role for the Hippo-Yes-associated protein (YAP) pathway in GNAQ/GNA11-induced tumorigenesis in uveal melanoma (UM). However, the association between YAP activity and clinical outcomes remains elusive. We investigated possible associations between YAP activity and clinicopathological features including survival outcomes in patients with UM using The Cancer Genome Atlas (TCGA) cohort and our local cohort. We estimated YAP activity by mRNA expression levels, Gene Set Variation Analysis (GSVA) for the TCGA cohort, and immunohistochemical YAP staining for the local cohort. In the TCGA cohort, most clinicopathological features including tumor stage, mitotic counts, mutation of genes, and tumor sizes did not significantly differ between low and high YAP activity groups. In the local cohort, YAP nuclear-positive staining was observed in 30 (42%) of 72 patients with primary UM. UM-specific survival was not significantly different between tumors with low and high YAP activities. Unlike mesothelioma cells harboring a mutation of negative regulators of YAP, the survival of multiple UM cell lines was not significantly reduced by YAP/TAZ depletion. Our results suggest that the effect of YAP on development, growth, and invasion of UM in actual patients is less than previously demonstrated in experimental studies.

YAP1 is a potent driver of the onset and progression of oral squamous cell carcinoma

Head-and-neck squamous cell carcinoma (HNSCC) is the sixth most common group of cancers in the world, and patients have a poor prognosis. Here, we present data indicating that YAP1 may be a strong driver of the onset and progression of oral SCC (OSCC), a major subtype of HNSCC. Mice with tongue-specific deletion of Mob1a/b and thus endogenous YAP1 hyperactivation underwent surprisingly rapid and highly reproducible tumorigenesis, developing tongue carcinoma in situ within 2 weeks and invasive SCC within 4 weeks. In humans, precancerous tongue dysplasia displays YAP1 activation correlating with reduced patient survival. Combinations of molecules mutated in OSCC may increase and sustain YAP1 activation to the point of oncogenicity. Strikingly, siRNA or pharmacological inhibition of YAP1 blocks murine OSCC onset in vitro and in vivo. Our work justifies targeting YAP1 as therapy for OSCC and perhaps HNSCC, and our mouse model represents a powerful tool for evaluating these agents.

STRIPAK directs PP2A activity toward MAP4K4 to promote oncogenic transformation of human cells

Alterations involving serine-threonine phosphatase PP2A subunits occur in a range of human cancers, and partial loss of PP2A function contributes to cell transformation. Displacement of regulatory B subunits by the SV40 Small T antigen (ST) or mutation/deletion of PP2A subunits alters the abundance and types of PP2A complexes in cells, leading to transformation. Here, we show that ST not only displaces common PP2A B subunits but also promotes A-C subunit interactions with alternative B subunits (B’’’, striatins) that are components of the Striatin-interacting phosphatase and kinase (STRIPAK) complex. We found that STRN4, a member of STRIPAK, is associated with ST and is required for ST-PP2A-induced cell transformation. ST recruitment of STRIPAK facilitates PP2A-mediated dephosphorylation of MAP4K4 and induces cell transformation through the activation of the Hippo pathway effector YAP1. These observations identify an unanticipated role of MAP4K4 in transformation and show that the STRIPAK complex regulates PP2A specificity and activity.

Cells maintain a fine balance of signals that promote or counter cell growth and division. Two sets of enzymes – called kinases and phosphatases – contribute to this balance. In general, kinases “switch on” other proteins by tagging them with a phosphate molecule. This process is called phosphorylation. Phosphatases, on the other hand, dephosphorylate these proteins, switching them off. Cancer cells often have mutations that activate kinases to drive cancer growth. The same cells can have mutations that inactivate the phosphatases or reduce their abundance. The roles of phosphatases in cancer are still being studied. One major hurdle in this research is that it is not always clear how they recognize the proteins they dephosphorylate.

Protein phosphatase 2A (or PP2A for short) is one of the phosphatases that is often mutated or deleted in human cancers. Even just reduced levels of PP2A can promote cancer. Kim, Berrios, Kim, Schade et al. used an experimental trick to decrease the phosphatase activity of PP2A in human cells growing in a dish. Biochemical analysis of these cells showed that, as expected, many proteins were now in their phosphorylated states. Unexpectedly, however, some proteins were dephosphorylated under these conditions. One of these proteins was called MAP4K4. In the case of MAP4K4, the dephosphorylated state contributes to the growth of the cancer cell. Kim et al. carried out further genetic and biochemical experiments to show that, in these cells, PP2A and MAP4K4 stay physically connected to one another. This connection was enabled by a group of proteins called the STRIPAK complex. The STRIPAK proteins directed the remaining PP2A towards MAP4K4. Low levels or activity of PP2A could, therefore, promote cancer in a different way.

Taken together, PP2A is not a single phosphatase that always turns proteins off, but rather is a dual switch that turns off some proteins while turning on others. Future experiments will explore to what extent these findings also apply in tumors. Information about how mutations in PP2A affect human cancers could suggest new targets for cancer drugs.

Anti-oral Squamous Cell Carcinoma Effects of a Potent TAZ Inhibitor AR-42

Oral squamous cell carcinoma (OSCC) is one of the most common malignancies worldwide. Although great progress has been made in diagnosis and treatment strategies in recent years, the 5-year survival rate of OSCC patients is still disappointingly low. Hence, there is still an unmet medical need for sufferers with OSCC. As a downstream effector of Hippo pathway, TAZ was up-regulated in multiple cancers including OSCC, and considered as an effective therapeutic target. In this study, we constructed a stable transfected cell line HEK293-TAZ to screen TAZ inhibitor using dual-luciferase reporter assay, and found a potential TAZ inhibitor AR-42. The results showed that AR-42 effectively suppressed the viability and proliferation of OSCC cells, and induced cellular apoptosis and cell cycle arrest in G2/M phase. Moreover, AR-42 potently inhibited cell invasion and the capacity of sphere-forming, as well as the expression of EMT and cancer stem cell related proteins in OSCC cells, exhibiting potential efficacy against OSCC metastasis and self-renewal of oral cancer stem cell. Further mechanism studies showed that AR-42 inhibited the total amount of TAZ and its paralog YAP mainly through blockade of TAZ/YAP transcription and promotion of TAZ/YAP protein degradation. Additionally, the inhibitory effect of AR-42 against TAZ, as well as its anti-OSCC activity could be also observed in SCC9 xenograft model. Taken together, AR-42 deserves to be further studied as a TAZ inhibitor, and is worthy to be further assessed as a potential drug candidate for OSCC treatment.