A Division of Labor between YAP and TAZ in Non-Small Cell Lung Cancer

YAP and TAZ differentially regulate postnatal cortical progenitor proliferation and astrocyte differentiation

WW domain-containing transcription regulator 1 (WWTR1, referred to here as TAZ) and Yes-associated protein (YAP, also known as YAP1) are transcriptional co-activators traditionally studied together as a part of the Hippo pathway, and are best known for their roles in stem cell proliferation and differentiation. Despite their similarities, TAZ and YAP can exert divergent cellular effects by differentially interacting with other signaling pathways that regulate stem cell maintenance or differentiation. In this study, we show in mouse neural stem and progenitor cells (NPCs) that TAZ regulates astrocytic differentiation and maturation, and that TAZ mediates some, but not all, of the effects of bone morphogenetic protein (BMP) signaling on astrocytic development. By contrast, both TAZ and YAP mediate the effects on NPC fate of β1-integrin (ITGB1) and integrin-linked kinase signaling, and these effects are dependent on extracellular matrix cues. These findings demonstrate that TAZ and YAP perform divergent functions in the regulation of astrocyte differentiation, where YAP regulates cell cycle states of astrocytic progenitors and TAZ regulates differentiation and maturation from astrocytic progenitors into astrocytes.

Dynamic YAP expression in the non-parenchymal liver cell compartment controls heterologous cell communication

INTRODUCTION

The Hippo pathway and its transcriptional effectors yes-associated protein (YAP) and transcriptional coactivator with PDZ-binding motif (TAZ) are targets for cancer therapy. It is important to determine if the activation of one factor compensates for the inhibition of the other. Moreover, it is unknown if YAP/TAZ-directed perturbation affects cell-cell communication of non-malignant liver cells.

MATERIALS AND METHODS

To investigate liver-specific phenotypes caused by YAP and TAZ inactivation, we generated mice with hepatocyte (HC) and biliary epithelial cell (BEC)-specific deletions for both factors (YAPKO, TAZKO and double knock-out (DKO)). Immunohistochemistry, single-cell sequencing, and proteomics were used to analyze liver tissues and serum.

RESULTS

The loss of BECs, liver fibrosis, and necrosis characterized livers from YAPKO and DKO mice. This phenotype was weakened in DKO tissues compared to specimens from YAPKO animals. After depletion of YAP in HCs and BECs, YAP expression was induced in non-parenchymal cells (NPCs) in a cholestasis-independent manner. YAP positivity was detected in subgroups of Kupffer cells (KCs) and endothelial cells (ECs). The secretion of pro-inflammatory chemokines and cytokines such as C-X-C motif chemokine ligand 11 (CXCL11), fms-related receptor tyrosine kinase 3 ligand (FLT3L), and soluble intercellular adhesion molecule-1 (ICAM1) was increased in the serum of YAPKO animals. YAP activation in NPCs could contribute to inflammation via TEA domain transcription factor (TEAD)-dependent transcriptional regulation of secreted factors.

CONCLUSION

YAP inactivation in HCs and BECs causes liver damage, and concomitant TAZ deletion does not enhance but reduces this phenotype. Additionally, we present a new mechanism by which YAP contributes to cell-cell communication originating from NPCs.

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.

The significance of Hippo pathway protein expression in oral squamous cell carcinoma

Introduction

The Hippo pathway consists of mammalian sterile 20-like kinase 1/2 (MST1/2), large tumor suppressor 1/2 (LATS1/2), and yes-associated protein (YAP)1. Herein, we present the first report on the significance of major Hippo pathway protein expression in oral squamous cell carcinoma (OSCC).

Methods

The analyses included oral epithelial dysplasia (OED, n = 7), carcinoma in situ (CIS, n = 14), and oral squamous cell carcinoma (OSCC, n = 109).

Results

Cytoplasmic expression of MST1, LATS1, and LATS2 was low in OED, CIS, and OSCC. The cytoplasmic expression of MST2 was high in OED (5/7 cases), CIS (9/14 cases), and poorly differentiated OSCC (8/8 cases) but was low/lost in a proportion of differentiated OSCC (60/101 cases). The expression of YAP1 was associated with differentiation; low YAP expression was significantly more frequent in well-differentiated OSCC (35/71 cases), compared to moderately and poorly differentiated OSCC (11/38 cases). An infiltrative invasion pattern was associated with a high expression of MST2 and high expression of YAP1. The high expression of YAP1 was associated with features of epithelial-to-mesenchymal transition (EMT), such as the loss of E-cadherin and high expression of vimentin, laminin 5, and Slug. High expression of protein arginine methyltransferase (PRMT) 1 or 5, which positively regulates YAP activity, was associated with the high expression of YAP1 (p < 0.0001).

Conclusion

Among the major Hippo pathway proteins, MST2 displayed a distinctive expression pattern in a significant proportion of differentiated OSCC, suggesting a possible differential role for MST2 depending on the course of OSCC progression. A high YAP1 expression may indicate aggressive OSCC with EMT via PRMTs at the invasive front.

Distinct and overlapping functions of YAP and TAZ in tooth development and periodontal homeostasis

Orthodontic tooth movement (OTM) involves mechanical-biochemical signal transduction, which results in tissue remodeling of the tooth-periodontium complex and the movement of orthodontic teeth. The dynamic regulation of osteogenesis and osteoclastogenesis serves as the biological basis for remodeling of the periodontium, and more importantly, the prerequisite for establishing periodontal homeostasis. Yes-associated protein (YAP) and transcriptional coactivator with PDZ-binding motif (TAZ) are key effectors of the Hippo signaling pathway, which actively respond to mechanical stimuli during tooth movement. Specifically, they participate in translating mechanical into biochemical signals, thereby regulating periodontal homeostasis, periodontal remodeling, and tooth development. YAP and TAZ have widely been considered as key factors to prevent dental dysplasia, accelerate orthodontic tooth movement, and shorten treatment time. In this review, we summarize the functions of YAP and TAZ in regulating tooth development and periodontal remodeling, with the aim to gain a better understanding of their mechanisms of action and provide insights into maintaining proper tooth development and establishing a healthy periodontal and alveolar bone environment. Our findings offer novel perspectives and directions for targeted clinical treatments. Moreover, considering the similarities and differences in the development, structure, and physiology between YAP and TAZ, these molecules may exhibit functional variations in specific regulatory processes. Hence, we pay special attention to their distinct roles in specific regulatory functions to gain a comprehensive and profound understanding of their contributions.

The long non-coding RNA TAZ-AS202 promotes lung cancer progression via regulation of the E2F1 transcription factor and activation of Ephrin signaling

Long non-coding RNAs (lncRNAs) are transcripts without coding potential that are pervasively expressed from the genome and have been increasingly reported to play crucial roles in all aspects of cell biology. They have been also heavily implicated in cancer development and progression, with both oncogenic and tumor suppressor functions. In this work, we identified and characterized a novel lncRNA, TAZ-AS202, expressed from the TAZ genomic locus and exerting pro-oncogenic functions in non-small cell lung cancer. TAZ-AS202 expression is under the control of YAP/TAZ-containing transcriptional complexes. We demonstrated that TAZ-AS202 is overexpressed in lung cancer tissue, compared with surrounding lung epithelium. In lung cancer cell lines TAZ-AS202 promotes cell migration and cell invasion. TAZ-AS202 regulates the expression of a set of genes belonging to cancer-associated pathways, including WNT and EPH-Ephrin signaling. The molecular mechanism underlying TAZ-AS202 function does not involve change of TAZ expression or activity, but increases the protein level of the transcription factor E2F1, which in turn regulates the expression of a large set of target genes, including the EPHB2 receptor. Notably, the silencing of both E2F1 and EPHB2 recapitulates TAZ-AS202 silencing cellular phenotype, indicating that they are essential mediators of its activity. Overall, this work unveiled a new regulatory mechanism that, by increasing E2F1 protein, modifies the non-small cell lung cancer cells transcriptional program, leading to enhanced aggressiveness features. The TAZ-AS202/E2F1/EPHB2 axis may be the target for new therapeutic strategies.

Multi-Functional Regulation by YAP/TAZ Signaling Networks in Tumor Progression and Metastasis

The Hippo pathway transcriptional co-activators, YES-associated protein (YAP) and Transcriptional Co-Activator with PDZ Binding Motif (TAZ), have both been linked to tumor progression and metastasis. These two proteins possess overlapping and distinct functions, and their activities lead to the expression of genes involved in multiple cellular processes, including cell proliferation, survival, and migration. The dysregulation of YAP/TAZ-dependent cellular processes can result in altered tumor growth and metastasis. In addition to their well-documented roles in the regulation of cancer cell growth, survival, migration, and invasion, the YAP/TAZ-dependent signaling pathways have been more recently implicated in cellular processes that promote metastasis and therapy resistance in several solid tumor types. This review highlights the role of YAP/TAZ signaling networks in the regulation of tumor cell plasticity mediated by hybrid and reversible epithelial-mesenchymal transition (EMT) states, and the promotion of cancer stem cell/progenitor phenotypes. Mechanistically, YAP and TAZ regulate these cellular processes by targeting transcriptional networks. In this review, we detail recently uncovered mechanisms whereby YAP and TAZ mediate tumor growth, metastasis, and therapy resistance, and discuss new therapeutic strategies to target YAP/TAZ function in various solid tumor types. Understanding the distinct and overlapping roles of YAP and TAZ in multiple cellular processes that promote tumor progression to metastasis is expected to enable the identification of effective therapies to treat solid tumors through the hyper-activation of YAP and TAZ.

Insights into recent findings and clinical application of YAP and TAZ in cancer

Decades of research have mapped out the basic mechanics of the Hippo pathway. The paralogues Yes-associated protein (YAP) and transcriptional co-activator with PDZ-binding motif (TAZ), as the central transcription control module of the Hippo pathway, have long been implicated in the progression of various human cancers. The current literature regarding oncogenic YAP and TAZ activities consists mostly of context-specific mechanisms and treatments of human cancers. Furthermore, a growing number of studies demonstrate tumour-suppressor functions of YAP and TAZ. In this Review we aim to synthesize an integrated perspective of the many disparate findings regarding YAP and TAZ in cancer. We then conclude with the various strategies for targeting and treating YAP- and TAZ-dependent cancers.

Anti-Cancer Activity of Verteporfin in Cholangiocarcinoma

Cholangiocarcinoma (CCA) is a heterogenous malignancy that arises from the biliary epithelium and has a poor clinical prognosis. The Hippo/yes-associated protein (YAP) pathway has been reported to affect various aspects of tumorigenesis, with high expression of YAP1 being negatively associated with survival in CCA patients. Thus, we investigated the antitumoral effect of verteporfin, a YAP1 pathway inhibitor, in YAP1/AKT hydrodynamic tail vein injected murine models. We also used flow cytometry and single-cell RNA sequencing (scRNA-seq) to analyze the change in the immune cell profile and malignant cell stemness following verteporfin treatment. Our results demonstrated reduced liver weight and tumor formation in verteporfin-treated groups compared to that of a vehicle-treated group. Immune cell profiling through flow cytometry showed that relative to the vehicle, verteporfin induced a higher ratio of tumor-associated macrophage (TAM) M1/M2 and increased the percentage of activated CD8 T cell population (CD8+CD25+ and CD8+CD69+). scRNA-seq analysis showed significantly increased TAM M1 populations following verteporfin treatment and decreased proportions of stem-like cells within the malignant cell population. In summary, this study indicates that in CCA YAP/AKT murine models, verteporfin reduces tumorigenesis by polarizing anti-tumoral TAM and activating CD8 T cells and decreasing stem-like malignant cell proportions in the tumor microenvironment.

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.

The role of selected non-coding RNAs in the biology of non-small cell lung cancer

Lung cancer is the second most frequently diagnosed cancer worldwide and a leading cause of cancer-related deaths. Non-small cell lung carcinoma (NSCLC) represents 85% of all cases. Accumulating evidence highlights the outstanding role of non-coding RNA (ncRNA) in regulating the tumorigenesis process by modulating crucial signaling pathways. Micro RNA (miRNA), long non-coding RNA (lncRNA) and circular RNA (circRNA) are either up- or downregulated in lung cancer patients and can promote or suppress the progression of the disease. These molecules interact with messenger RNA (mRNA) and with each other to regulate gene expression and stimulate proto-oncogenes or silence tumor suppressors. NcRNAs provide a new strategy to diagnose or treat lung cancer patients and multiple molecules have already been identified as potential biomarkers or therapeutic targets. The aim of this review is to summarize the current evidence on the roles of miRNA, lncRNA and circRNA in NSCLC biology and present their clinical potential.

An indispensable role of TAZ in anoikis resistance promoted by OTUB1 deubiquitinating enzyme in basal-like triple-negative breast cancer cells

Aggressive cancers, such as triple-negative breast cancer (TNBC), are mostly fatal because of their potential to metastasize to distant organs. Cancer cells acquire various abilities to metastasize, including resistance to anoikis, an apoptotic cell death induced by loss of anchorage to the extracellular matrix. Transcriptional coactivator with PDZ binding motif (TAZ) and Yes-associated protein (YAP), the downstream effectors of the Hippo pathway, regulate cell- and tissue-level architectures by responding to mechanical microenvironments of cells, including the cell-extracellular matrix interaction. The Hippo pathway is frequently disrupted in cancer cells, and TAZ and YAP are irrelevantly activated, potentially resulting in anchorage-independent survival/proliferation of cancer cells and metastatic progression. The study aims to investigate the roles of TAZ and YAP in anoikis resistance in basal-like (BL) TNBC cells, which comprise a major subtype (>70%) of TNBC. We found that TAZ and YAP had nonredundant roles in anchorage-independent cancer cell survival or anoikis resistance. Particularly, TAZ was indispensable for anoikis resistance in BL-TNBC cells but not for survival of non-transformed mammary epithelial cells (MECs). In contrast, YAP, a paralog of TAZ, was indispensable for survival of both non-transformed MECs and cancer cells. Therefore, TAZ might be a preferable therapeutic target against dissemination of aggressive cancer cells without killing normal cells. Interestingly, TAZ was abnormally stabilized in BL-TNBC cells under non-adherent conditions, which promoted anoikis resistance. Furthermore, OTUB1, a deubiquitinating enzyme, was responsible for the stabilization of TAZ in detached BL-TNBC cells. Importantly, simultaneous high expression of TAZ and OTUB1 was associated with poor prognosis in BC. Thus, OTUB1 has emerged as a potentially druggable target. Successful inhibition of OTUB1 enzymatic activity is expected to downregulate TAZ and eventually prevents metastasis of aggressive cancers, such as BL-TNBC.

Extracellular matrix remodeling in tumor progression and immune escape: from mechanisms to treatments

The malignant tumor is a multi-etiological, systemic and complex disease characterized by uncontrolled cell proliferation and distant metastasis. Anticancer treatments including adjuvant therapies and targeted therapies are effective in eliminating cancer cells but in a limited number of patients. Increasing evidence suggests that the extracellular matrix (ECM) plays an important role in tumor development through changes in macromolecule components, degradation enzymes and stiffness. These variations are under the control of cellular components in tumor tissue via the aberrant activation of signaling pathways, the interaction of the ECM components to multiple surface receptors, and mechanical impact. Additionally, the ECM shaped by cancer regulates immune cells which results in an immune suppressive microenvironment and hinders the efficacy of immunotherapies. Thus, the ECM acts as a barrier to protect cancer from treatments and supports tumor progression. Nevertheless, the profound regulatory network of the ECM remodeling hampers the design of individualized antitumor treatment. Here, we elaborate on the composition of the malignant ECM, and discuss the specific mechanisms of the ECM remodeling. Precisely, we highlight the impact of the ECM remodeling on tumor development, including proliferation, anoikis, metastasis, angiogenesis, lymphangiogenesis, and immune escape. Finally, we emphasize ECM "normalization" as a potential strategy for anti-malignant treatment.

Targeting YAP1/TAZ in nonsmall-cell lung carcinoma: From molecular mechanisms to precision medicine

Accumulating evidence has underscored the importance of the Hippo-YAP1 signaling in lung tissue homeostasis, whereas its deregulation induces tumorigenesis. YAP1 and its paralog TAZ are the key downstream effectors tightly controlled by the Hippo pathway. YAP1/TAZ exerts oncogenic activities by transcriptional regulation via physical interaction with TEAD transcription factors. In solid tumors, Hippo-YAP1 crosstalks with other signaling pathways such as Wnt/β-catenin, receptor tyrosine kinase cascade, Notch and TGF-β to synergistically drive tumorigenesis. As YAP1/TAZ expression is significantly correlated with unfavorable outcomes for the patients, small molecules have been developed for targeting YAP1/TAZ to get a therapeutic effect. In this review, we summarize the recent findings on the deregulation of Hippo-YAP1 pathway in nonsmall cell lung carcinoma, discuss the molecular mechanisms of its dysregulation in leading to tumorigenesis, explore the therapeutic strategies for targeting YAP1/TAZ, and provide the research directions for deep investigation. We believe that detailed delineation of Hippo-YAP1 regulation in tumorigenesis provides novel insight for accurate therapeutic intervention.

Targeting cancer stem cell pathways for lung cancer therapy

PURPOSE OF REVIEW

The unique properties of cancer stem cells (CSCs) make lung cancer untargetable for quite an extended period. The functional mechanism of this cell type has been illustrated step by step. However, the outcomes of lung cancer patients are still lower than expected clinically. The attempts made by scientists to make challenge history against stemness maintenance of lung cancer cells and their druggable targets are worth elucidating.

RECENT FINDINGS

Many agents, including the Bispecific T-cell engager (BiTE) and AMG 119 targeting DLL3-positive cells, are a tremendous breakthrough in the preclinical and clinical treatment of SCLC. More studies focus on targeting CSCs to overcome TKI resistance in NSCLC. The combo targeting of CSC and the immune microenvironment can favor the treatment of lung cancer patients.

SUMMARY

The current review elucidates the characteristics and related regulating pathways of lung CSCs from essential to preclinical research. We retrospectively introduce an update on the clinical development of therapeutics targeting CSC-associated developmental signaling pathways and discuss the opportunities to target CSC-immune interactions in lung cancer.

A self-amplifying USP14-TAZ loop drives the progression and liver metastasis of pancreatic ductal adenocarcinoma

With a 5-year survival rate of approximately 10%, pancreatic ductal adenocarcinoma (PDAC) is one of the most lethal solid malignancies in humans. A poor understanding of the underlying biology has resulted in a lack of effective targeted therapeutic strategies. Tissue microarray and bioinformatics analyses have revealed that the downstream transcriptional coactivator of the Hippo pathway, transcriptional coactivator with PDZ-binding motif (TAZ), might be a therapeutic target in PDAC. Since pharmacological inhibition of TAZ is challenging, we performed unbiased deubiquitinase (DUB) library screening to explore the pivotal regulators of TAZ ubiquitination as potential targets in PDAC models. We found that USP14 contributed to Yes-associated protein (YAP)/TAZ transcriptional activity and stabilized TAZ but not YAP. Mechanistically, USP14 catalyzed the K48-linked deubiquitination of TAZ to promote TAZ stabilization. Moreover, TAZ facilitated the transcription of USP14 by binding to the TEA domain transcription factor (TEAD) 1/4 response element in the promoter of USP14. USP14 was found to modulate the expression of TAZ downstream target genes through a feedback mechanism and ultimately promoted cancer progression and liver metastasis in PDAC models in vitro and in vivo. In addition, depletion of USP14 led to proteasome-dependent degradation of TAZ and ultimately arrested PDAC tumour growth and liver metastasis. A strong positive correlation between USP14 and TAZ expression was also detected in PDAC patients. The small molecule inhibitor of USP14 catalytic activity, IU1, inhibited the development of PDAC in subcutaneous xenograft and liver metastasis models. Overall, our data strongly suggested that the self-amplifying USP14-TAZ loop was a previously unrecognized mechanism causing upregulated TAZ expression, and identified USP14 as a viable therapeutic target in PDAC.

The Molecular and Cellular Strategies of Glioblastoma and Non-Small-Cell Lung Cancer Cells Conferring Radioresistance

Ionizing radiation (IR) has been shown to play a crucial role in the treatment of glioblastoma (GBM; grade IV) and non-small-cell lung cancer (NSCLC). Nevertheless, recent studies have indicated that radiotherapy can offer only palliation owing to the radioresistance of GBM and NSCLC. Therefore, delineating the major radioresistance mechanisms may provide novel therapeutic approaches to sensitize these diseases to IR and improve patient outcomes. This review provides insights into the molecular and cellular mechanisms underlying GBM and NSCLC radioresistance, where it sheds light on the role played by cancer stem cells (CSCs), as well as discusses comprehensively how the cellular dormancy/non-proliferating state and polyploidy impact on their survival and relapse post-IR exposure.

Substrate stiffness reduces particle uptake by epithelial cells and macrophages in a size-dependent manner through mechanoregulation

Cells continuously exert forces on their environment and respond to changes in mechanical forces by altering their behaviour. Many pathologies such as cancer and fibrosis are hallmarked by dysregulation in the extracellular matrix, driving aberrant behaviour through mechanotransduction pathways. We demonstrate that substrate stiffness can be used to regulate cellular endocytosis of particles in a size-dependent fashion. Culture of A549 epithelial cells and J774A.1 macrophages on polystyrene/glass (stiff) and polydimethylsiloxane (soft) substrates indicated that particle uptake is increased up to six times for A549 and two times for macrophages when cells are grown in softer environments. Furthermore, we altered surface characteristics through the attachment of submicron-sized particles as a method to locally engineer substrate stiffness and topography to investigate the biomechanical changes which occurred within adherent epithelial cells, i.e. characterization of A549 cell spreading and focal adhesion maturation. Consequently, decreasing substrate rigidity and particle-based topography led to a reduction of focal adhesion size. Moreover, expression levels of Yes-associated protein were found to correlate with the degree of particle endocytosis. A thorough appreciation of the mechanical cues may lead to improved solutions to optimize nanomedicine approaches for treatment of cancer and other diseases with abnormal mechanosignalling.

Targeting the Hippo/YAP/TAZ signalling pathway: Novel opportunities for therapeutic interventions into skin cancers

Skin cancers are by far the most frequently diagnosed human cancers. The closely related transcriptional co-regulator proteins YAP and TAZ (WWTR1) have emerged as important drivers of tumour initiation, progression and metastasis in melanoma and non-melanoma skin cancers. YAP/TAZ serve as an essential signalling hub by integrating signals from multiple upstream pathways. In this review, we summarize the roles of YAP/TAZ in skin physiology and tumorigenesis and discuss recent efforts of therapeutic interventions that target YAP/TAZ in in both preclinical and clinical settings, as well as their prospects for use as skin cancer treatments.

YAP and TAZ: Monocorial and bicorial transcriptional co-activators in human cancers

The transcriptional regulators YAP and TAZ are involved in numerous physiological processes including organ development, growth, immunity and tissue regeneration. YAP and TAZ dysregulation also contribute to tumorigenesis, thereby making them attractive cancer therapeutic targets. Arbitrarily, YAP and TAZ are often considered as a single protein, and are referred to as YAP/TAZ in most studies. However, increasing experimental evidences documented that YAP and TAZ perform both overlapping and distinct functions in several physiological and pathological processes. In addition to regulating distinct processes, YAP and TAZ are also regulated by distinct upstream cues. The aim of the review is to describe the distinct roles of YAP and TAZ focusing particularly on cancer. Therapeutic strategies targeting either YAP and TAZ proteins or only one of them should be carefully evaluated. Selective targeting of YAP or TAZ may in fact impair different pathways and determine diverse clinical outputs.

Cross-talk between mutant p53 and p62/SQSTM1 augments cancer cell migration by promoting the degradation of cell adhesion proteins

Missense mutations in the TP53 gene, encoding the p53 tumor suppressor, are very frequent in human cancer. Some of those mutations, particularly the more common (“hotspot”) ones, not only abrogate p53’s tumor suppressor activities but also endow the mutant protein with oncogenic gain of function (GOF). We report that p53^R273H, the most common p53 mutant in pancreatic cancer, interacts with the SQSTM1/p62 protein to accelerate the degradation of cell adhesion proteins. This enables pancreatic cancer cells to detach from the epithelial sheet and engage in individualized cell migration, probably augmenting metastatic spread. By providing insights into mechanisms that underpin mutant p53 GOF, this study may suggest ways to interfere with the progression of cancers bearing particular p53 mutants.

Missense mutations in the p53 tumor suppressor abound in human cancer. Common (“hotspot”) mutations endow mutant p53 (mutp53) proteins with oncogenic gain of function (GOF), including enhanced cell migration and invasiveness, favoring cancer progression. GOF is usually attributed to transcriptional effects of mutp53. To elucidate transcription-independent effects of mutp53, we characterized the protein interactome of the p53^R273H mutant in cells derived from pancreatic ductal adenocarcinoma (PDAC), where p53^R273H is the most frequent p53 mutant. We now report that p53^R273H, but not the p53^R175H hotspot mutant, interacts with SQSTM1/p62 and promotes cancer cell migration and invasion in a p62-dependent manner. Mechanistically, the p53^R273H-p62 axis drives the proteasomal degradation of several cell junction–associated proteins, including the gap junction protein Connexin 43, facilitating scattered cell migration. Concordantly, down-regulation of Connexin 43 augments PDAC cell migration, while its forced overexpression blunts the promigratory effect of the p53^R273H-p62 axis. These findings define a mechanism of mutp53 GOF.

TAZ is important for maintenance of the integrity of podocytes

The podocyte is an important component of the glomerular filtration barrier, and maintenance of the integrity of its highly specified structure and function is critical for normal kidney function. Yes-associated protein (YAP)/transcriptional coactivator with PDZ-binding motif (TAZ) are two crucial effectors of the Hippo signaling pathway, and recent studies have shown that podocyte-specific YAP deletion causes podocyte apoptosis and the development of focal segmental glomerulosclerosis followed by progressive renal failure. In the present study, we investigated a potential role of the YAP paralog TAZ in podocytes. TAZ was found to be constitutively active in podocytes, and mice with podocyte-specific deletion of TAZ (TazpodKO) developed proteinuria starting at 4 wk of age and had increased podocyte apoptosis. Using primary cultured podocytes or immortalized mouse podocytes from Tazflox/flox mice, we found that TAZ is a transcriptional activator for TEAD-dependent expression of synaptopodin, zonula occludens-1, and zonula occludens-2. This is the first study to determine that TAZ plays an important role in the maintenance of the structure and function of podocytes.NEW & NOTEWORTHY Podocytes play an important role in maintaining the integrity of the structure and function of the kidney. We observed that mice with selective deletion of transcriptional coactivator with PDZ-binding motif (TAZ) in podocytes developed proteinuria. TAZ is constitutively active and critical for expression of synaptopodin, zonula occludens-1, and zonula occludens-2 in podocytes. The findings of this study implicate TAZ as an important mediator of podocyte structural integrity and provide further insights into the role of Hippo-Yes-associated protein/TAZ in podocyte biology.

The Hippo Signaling Core Components YAP and TAZ as New Prognostic Factors in Lung Cancer

Background

The Hippo pathway is an essential signaling cascade that regulates cell and organ growth. However, there is no consensus about (i) the expression levels of the Hippo signaling core components yes-associated protein (YAP) and transcriptional co-activator with PDZ-binding motif (TAZ) in lung cancer, especially in small cell lung cancer (SCLC), or (ii) their association with the prognosis of patients with SCLC.

Methods

We screened relevant articles and identified eligible studies in the PubMed, EMBASE, COCHRANE, and WanFang databases. A combined analysis was performed to investigate (i) the expression levels of the major effectors, YAP and TAZ, in lung cancer and its subsets and (ii) their prognostic role in lung cancer, especially in SCLC.

Results

In total, 6 studies related to TAZ and 13 studies concerning YAP were enrolled in this meta-analysis. We found that high TAZ expression was significantly associated with poor overall survival (OS) of patients with non-small cell lung cancer (NSCLC) in the overall population [Ph &lt; 0.001, crude hazard ratio (HR) = 1.629, 95% CI = 1.199–2.214 for TAZ expression; Ph = 0.029, adjusted HR = 2.127, 95% CI = 1.307–3.460 for TAZ], the Caucasian population (Ph = 0.043, crude HR = 1.233, 95% CI = 1.030–1.477 for TAZ expression), and the Asian population (Ph = 0.551, adjusted HR = 2.676, 95% CI = 1.798–3.982 for TAZ). Moreover, there was a significant negative association between YAP expression and an unsatisfactory survival of patients with lung cancer (Ph = 0.327, crude HR = 1.652, 95% CI = 1.211–2.253 for YAP expression) and patients with NSCLC [disease-free survival (DFS): Ph = 0.693, crude HR = 2.562, 95% CI = 1.876–3.499 for YAP expression; Ph = 0.920, crude HR = 2.617, 95% CI = 1.690–4.052 for YAP-mRNA; OS: Ph = 0.878, crude HR = 1.777, 95% CI = 1.233–2.562 for YAP expression], especially in the Asian population (DFS: Ph = 0.414, crude HR = 2.515, 95% CI = 1.755–3.063; OS: Ph = 0.712, crude HR = 1.772, 95% CI = 1.214–2.587). However, no association was observed in the multivariate combined analysis. High YAP expression was significantly associated with short OS of patients with SCLC in our combined multivariate analysis in the Asian population (Ph = 0.289, crude HR = 4.482, 95% CI = 2.182–9.209), but not with crude data (Ph = 0.033, crude HR = 1.654, 95% CI = 0.434–6.300).

Conclusion

The Hippo pathway is involved in carcinogenesis and progression of NSCLC and SCLC, and high expression levels of YAP and TAZ are independent and novel prognostic factors for lung cancer.

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.

Combined control of the fibroblast contractile program by YAP and TAZ

Yes-associated protein (YAP) and transcriptional coactivator with PDZ-binding motif (TAZ) are transcription cofactors implicated in the contractile and profibrotic activation of fibroblasts. Fibroblast contractile function is important in alveologenesis and in lung wound healing and fibrosis. As paralogs, YAP and TAZ may have independent or redundant roles in regulating transcriptional programs and contractile function. Using IMR-90 lung fibroblasts, microarray analysis, and traction microscopy, we tested whether independent YAP or TAZ knockdown alone was sufficient to limit transcriptional activation and contraction in vitro. Our results demonstrate limited effects of knockdown of either YAP or TAZ alone, with more robust transcriptional and functional effects observed with combined knockdown, consistent with cooperation or redundancy of YAP and TAZ in transforming growth factor β1 (TGFβ1)-induced fibroblast activation and contractile force generation. The transcriptional responses to combined YAP/TAZ knockdown were focused on a relatively small subset of genes with prominent overrepresentation of genes implicated in contraction and migration. To explore potential disease relevance of our findings, we tested primary human lung fibroblasts isolated from patients with idiopathic pulmonary fibrosis and confirmed that YAP and TAZ combined knockdown reduced the expression of three cytoskeletal genes, ACTA2, CNN1, and TAGLN. We then compared the contribution of these genes, along with YAP and TAZ, to contractile function. Combined knockdown targeting YAP/TAZ was more effective than targeting any of the individual cytoskeletal genes in reducing contractile function. Together, our results demonstrate that YAP and TAZ combine to regulate a multigene program that is essential to fibroblast contractile function.

The YAP/TAZ Signaling Pathway in the Tumor Microenvironment and Carcinogenesis: Current Knowledge and Therapeutic Promises

The yes-associated protein (YAP) and the transcriptional coactivator with PDZ-binding motif (TAZ) are transcriptional coactivators, members of the Hippo signaling pathway, which play a critical role in cell growth regulation, embryonic development, regeneration, proliferation, and cancer origin and progression. The mechanism involves the nuclear binding of the un-phosphorylated YAP/TAZ complex to release the transcriptional enhanced associate domain (TEAD) from its repressors. The active ternary complex is responsible for the aforementioned biological effects. Overexpression of YAP/TAZ has been reported in cancer stem cells and tumor resistance. The resistance involves chemotherapy, targeted therapy, and immunotherapy. This review provides an overview of YAP/TAZ pathways’ role in carcinogenesis and tumor microenvironment. Potential therapeutic alternatives are also discussed.

YAP and TAZ are transcriptional co-activators of AP-1 proteins and STAT3 during breast cellular transformation

The YAP and TAZ paralogs are transcriptional co-activators recruited to target sites by TEAD proteins. Here, we show that YAP and TAZ are also recruited by JUNB (a member of the AP-1 family) and STAT3, key transcription factors that mediate an epigenetic switch linking inflammation to cellular transformation. YAP and TAZ directly interact with JUNB and STAT3 via a WW domain important for transformation, and they stimulate transcriptional activation by AP-1 proteins. JUNB, STAT3, and TEAD co-localize at virtually all YAP/TAZ target sites, yet many target sites only contain individual AP-1, TEAD, or STAT3 motifs. This observation and differences in relative crosslinking efficiencies of JUNB, TEAD, and STAT3 at YAP/TAZ target sites suggest that YAP/TAZ is recruited by different forms of an AP-1/STAT3/TEAD complex depending on the recruiting motif. The different classes of YAP/TAZ target sites are associated with largely non-overlapping genes with distinct functions. A small minority of target sites are YAP- or TAZ-specific, and they are associated with different sequence motifs and gene classes from shared YAP/TAZ target sites. Genes containing either the AP-1 or TEAD class of YAP/TAZ sites are associated with poor survival of breast cancer patients with the triple-negative form of the disease.

Context-dependent roles of YAP/TAZ in stem cell fates and cancer

Hippo effectors YAP and TAZ control cell fate and survival through various mechanisms, including transcriptional regulation of key genes. However, much of this research has been marked by conflicting results, as well as controversy over whether YAP and TAZ are redundant. A substantial portion of the discordance stems from their contradictory roles in stem cell self-renewal vs. differentiation and cancer cell survival vs. apoptosis. In this review, we present an overview of the multiple context-dependent functions of YAP and TAZ in regulating cell fate decisions in stem cells and organoids, as well as their mechanisms of controlling programmed cell death pathways in cancer.

CD43 (sialophorin) is involved in the induction of extracellular matrix remodeling and angiogenesis by lung cancer cells

Aberrant expression of CD43 in malignant tumors of nonhematopoietic origin such as those from lung, cervix, colon, and breast has been shown to correlate with poor prognosis, providing tumor cells with enhanced motility, anchorage-independent growth, and in vivo tumor size, while protecting the cells of NK lysis and apoptosis. To further characterize the role of CD43 in cell transformation, we tested whether interfering its expression modified the capacity of the A549 non-small cell lung cancer cells to secrete molecules contributing to malignancy. The proteomic analysis of the secretome of serum-starved A549 cells revealed that cells expressing normal levels of CD43 released significantly high levels of molecules involved in extracellular matrix organization, angiogenesis, platelet degranulation, collagen degradation, and inflammation, as compared to CD43 RNAi cells. This data reveals a novel and unexpected role for CD43 in lung cancer development, mainly in remodeling the tumor microenvironment.

YAP and endothelin-1 signaling: an emerging alliance in cancer

The rational making the G protein-coupled receptors (GPCR) the centerpiece of targeted therapies is fueled by the awareness that GPCR-initiated signaling acts as pivotal driver of the early stages of progression in a broad landscape of human malignancies. The endothelin-1 (ET-1) receptors (ET-1R), known as ET_A receptor (ET_AR) and ET_B receptor (ET_BR) that belong to the GPCR superfamily, affect both cancer initiation and progression in a variety of cancer types. By the cross-talking with multiple signaling pathways mainly through the scaffold protein β-arrestin1 (β-arr1), ET-1R axis cooperates with an array of molecular determinants, including transcription factors and co-factors, strongly affecting tumor cell fate and behavior. In this scenario, recent findings shed light on the interplay between ET-1 and the Hippo pathway. In ET_AR highly expressing tumors ET-1 axis induces the de-phosphorylation and nuclear accumulation of the Hippo pathway downstream effectors, the paralogous transcriptional cofactors Yes-associated protein (YAP) and Transcriptional coactivator with PDZ-binding motif (TAZ). Recent evidence have discovered that ET-1R/β-arr1 axis instigates a transcriptional interplay involving YAP and mutant p53 proteins, which share a common gene signature and cooperate in a oncogenic signaling network. Mechanistically, YAP and mutp53 are enrolled in nuclear complexes that turn on a highly selective YAP/mutp53-dependent transcriptional response. Notably, ET-1R blockade by the FDA approved dual ET-1 receptor antagonist macitentan interferes with ET-1R/YAP/mutp53 signaling interplay, through the simultaneous suppression of YAP and mutp53 functions, hampering metastasis and therapy resistance. Based on these evidences, we aim to review the recent findings linking the GPCR signaling, as for ET-1R, to YAP/TAZ signaling, underlining the clinical relevance of the blockade of such signaling network in the tumor and microenvironmental contexts. In particular, we debate the clinical implications regarding the use of dual ET-1R antagonists to blunt gain of function activity of mutant p53 proteins and thereby considering them as a potential therapeutic option for mutant p53 cancers. The identification of ET-1R/β-arr1-intertwined and bi-directional signaling pathways as targetable vulnerabilities, may open new therapeutic approaches able to disable the ET-1R-orchestrated YAP/mutp53 signaling network in both tumor and stromal cells and concurrently sensitizes to high-efficacy combined therapeutics.

2-Hydroxylation of Fatty Acids Represses Colorectal Tumorigenesis and Metastasis via the YAP Transcriptional Axis

Alteration in lipid composition is an important metabolic adaptation by cancer cells to support tumorigenesis and metastasis. Fatty acid 2-hydroxylase (FA2H) introduces a chiral hydroxyl group at the second carbon of fatty acid (FA) backbones and influences lipid structures and metabolic signaling. However, the underlying mechanisms through which FA 2-hydroxylation is coupled to metabolic adaptation and tumor growth remain elusive. Here, we show that FA2H regulates specific metabolic reprogramming and oncogenic signaling in the development of colorectal cancer. FA2H is highly expressed in normal colorectal tissues. Assessments through deciphering both published high-throughput data and curated human colorectal cancer samples revealed significant suppression of FA2H in tumors, which is correlated with unfavorable prognosis. Experiments with multiple models of genetic manipulation or treatment with an enzymatic product of FA2H, (R)-2-hydroxy palmitic acid, demonstrated that FA 2-hydroxylation inhibits colorectal cancer cell proliferation, migration, epithelial-to-mesenchymal transition progression, and tumor growth. Bioinformatics analysis suggested that FA2H functions through AMP-activated protein kinase/Yes-associated protein (AMPK/YAP) pathway, which was confirmed in colorectal cancer cells, as well as in tumors. Lipidomics analysis revealed an accumulation of polyunsaturated fatty acids in cells with FA2H overexpression, which may contribute to the observed nutrient deficiency and AMPK activation. Collectively, these data demonstrate that FA 2-hydroxylation initiates a metabolic signaling cascade to suppress colorectal tumor growth and metastasis via the YAP transcriptional axis and provides a strategy to improve colorectal cancer treatment. SIGNIFICANCE: These findings identify a novel metabolic mechanism regulating the tumor suppressor function of FA 2-hydroxylation in colorectal cancer.

YAP and TAZ Are Not Identical Twins

Yes-associated protein (YAP) and TAZ (WW domain containing transcription regulator 1, or WWTR1) are paralog transcriptional regulators, able to integrate mechanical, metabolic, and signaling inputs to regulate cell growth and differentiation during development and neoplastic progression. YAP and TAZ hold common and distinctive structural features, reflecting only partially overlapping regulatory mechanisms. The two paralogs interact with both shared and specific transcriptional partners and control nonidentical transcriptional programs. Although most of the available literature considers YAP and TAZ as functionally redundant, they play distinctive or even contrasting roles in different contexts. The issue of their divergent roles is currently underexplored but holds fundamental implications for mechanistic and translational studies. Here, we aim to review the available literature on the biological functions of YAP and TAZ, highlighting differential roles that distinguish these two paralogues.