Regulation of Hippo pathway by mitogenic growth factors via phosphoinositide 3-kinase and phosphoinositide-dependent kinase-1. Proc Natl Acad Sci U S A. 2013;110:2569-2574. [PMID: 23359693 DOI: 10.1073/pnas.1216462110]

VGLL fusions define a new class of intraparenchymal central nervous system schwannoma

BACKGROUND

Intracerebral schwannomas are rare tumors resembling their peripheral nerve sheath counterparts but localized in the central nervous system (CNS). They are not classified as a separate tumor type in the 2021 World Health Organization classification. This study aimed to compile and characterize these rare neoplasms morphologically and molecularly.

METHODS

We analyzed 20 tumor samples by histology, RNA next-generation sequencing, DNA-methylation profiling, copy number analyses, and single-nucleus RNA sequencing (snRNA-seq). Clinical data, including age, sex, and disease progression, were collected. Magnetic resonance imaging (MRI) series were included when available.

RESULTS

All cases with tissue available for histology review (n = 13) were morphologically consistent with intracerebral schwannoma, but differed in their extent of glial fibrillary acidic protein staining. All (n = 20) shared DNA-methylation profiles distinct from other CNS tumors, as well as from Vestigial-like family (VGLL)-altered peripheral nerve sheath tumors. Most cases (n = 14/17) harbored fusions of either Vestigial-like family member 3 (VGLL3) or Vestigial-like Family member 1 (VGLL1) (CHD7::VGLL3 [n = 9/17] and EWSR1::VGLL1 [n = 5/17]). In 2 cases, the presence of a VGLL3 fusion was also confirmed by copy number analyses (n = 2/17). MRI (n = 4) showed well-defined, nodular tumors with strong, homogeneous enhancement and no diffusion restriction. Tumors were located throughout the neuroaxis (supratentorial [n = 15], infratentorial [n = 4], and spinal [n = 1]). snRNA-seq of a VGLL1-fused tumor indicated VGLL1 upregulation in 28.6% of tumor cells (n = 1). During a median follow-up of 1.8 years (range 3 months-9 years), none of the tumors recurred (n = 10).

CONCLUSIONS

We identify and define a new benign tumor class, designated VGLL-altered intraparenchymal CNS schwannomas. These tumors feature VGLL alterations and a specific DNA-methylation profile, with schwannoma-like histopathology and CNS localization, akin to previously classified intracerebral schwannomas.

Pharmacological regulators of Hippo pathway: Advances and challenges of drug development

The Hippo signaling pathway is crucial in regulating organ size, tumor progression, tissue regeneration, and bone homeostasis. Inactivation of the Hippo pathway results in the nuclear translocation and activation of YAP/TAZ. This activation not only promotes tumor progression but also enhances tissue regeneration, wound healing, and maintenance of bone stability Although its discovery occurred over two decades ago, developing effective inhibitors or activators for the Hippo pathway remains challenging. Recently, however, the pace of advancements in developing Hippo signaling-related agonists and antagonists has accelerated, with some drugs that target TEAD advancing to clinical trials and showing promise for treating related diseases. This review summarizes the progress in research on Hippo signaling-related agonists and inhibitors, offering an in-depth analysis of their regulatory mechanisms, pharmacological properties, and potential in vivo applications.

Amphiregulin Downregulates E-cadherin Expression by Activating YAP/Egr-1/Slug Signaling in SKOV3 Human Ovarian Cancer Cells

Amphiregulin (AREG) stimulates human epithelial ovarian cancer (EOC) cell invasion by downregulating E-cadherin expression. YAP is a transcriptional cofactor that has been shown to regulate tumorigenesis. This study aimed to examine whether AREG activates YAP in EOC cells and explore the roles of YAP in AREG-induced downregulation of E-cadherin and cell invasion. Analysis of the Cancer Genome Atlas (TCGA) showed that upregulation of AREG and EGFR were associated with poor survival in human EOC. Treatment of SKOV3 human EOC cells with AREG induced the activation of YAP. In addition, AREG downregulated E-cadherin, upregulated Egr-1 and Slug, and stimulated cell invasion. Using gain- and loss-of-function approaches, we showed that YAP was required for the AREG-upregulated Egr-1 and Slug expression. Furthermore, YAP was also involved in AREG-induced downregulation of E-cadherin and cell invasion. This study provides evidence that AREG stimulates human EOC cell invasion by downregulating E-cadherin expression through the YAP/Egr-1/Slug signaling.

PI3K regulates TAZ/YAP and mTORC1 axes that can be synergistically targeted

Purpose

Sarcomas are a heterogeneous group of cancers with few shared therapeutic targets. PI3K signaling is activated in various subsets of sarcomas, representing a shared oncogenic signaling pathway. Oncogenic PI3K signaling has been challenging to target therapeutically. An integrated view of PI3K and Hippo pathway signaling is examined to determine if this could be leveraged therapeutically.

Experimental design

A tissue microarray containing sarcomas of various histological types was evaluated for PTEN loss and correlated with levels of activated TAZ and YAP. PI3K and Hippo pathways were dissected in sarcoma cell lines. The role of TAZ and YAP were evaluated in a PI3K-driven mouse model. The efficacy of mTORC1 inhibition and TEAD inhibition were evaluated in sarcoma cell lines and in vivo .

Results

PI3K signaling is frequently activated in sarcomas due to PTEN loss (in 30-60%), representing a common therapeutic target. TAZ and YAP are transcriptional co-activators regulated by PI3K and drive a transcriptome necessary for tumor growth in a PI3K-driven sarcoma mouse model. Combination therapy using IK-930 (TEAD inhibitor) and everolimus (mTORC1 inhibitor) synergistically diminished proliferation and anchorage independent growth of PI3K-activated sarcoma cell lines at low, physiologically achievable doses. Furthermore, this combination therapy showed a synergistic effect in vivo , reducing tumor proliferation and size.

Conclusions

TAZ and YAP are transcriptional co-activators downstream of PI3K signaling, a pathway that has lacked a well-defined oncogenic transcription factor. This PI3K-TAZ/YAP axis exists in parallel to the known PI3K-Akt-mTORC1 axis allowing for synergistic combination therapy targeting the TAZ/YAP-TEAD interaction and mTORC1 in sarcomas.

Development of a live cell assay for real-time monitoring the interactions between the Hippo pathway components 14-3-3 and TAZ

The Hippo pathway plays an important role in organ size control and tissue homeostasis. Dysregulation is involved in many pathologies, including cancer, which has attracted interest in targeting the Hippo pathway. Since the upstream components are bona fide tumor suppressors, it is feasible to target oncogenic downstream targets such as TAZ, a key downstream effector in the Hippo pathway. Its activity is regulated by phosphorylation on multiple sites, with Ser89 playing a critical role in regulation of TAZ activity. Phosphorylation of TAZ at Ser89 promotes binding to 14-3-3 scaffolding proteins, preventing nuclear translocation and abolishing target gene transcription. Here we describe the development of a cell-based assay suitable for high-throughput screening, based on a split NanoLuc luciferase, for monitoring interactions between 14 3-3 and TAZ in living cells. We have validated the assay by screening of a kinase-biased library. The assay can be quickly adapted for higher throughput and thus offers a valuable tool to study new signal inputs involved in regulation of TAZ activity as well as for identification of molecules that modulate the Hippo pathway.

ER stress-induced YAP upregulation leads to chondrocyte phenotype loss in age-related osteoarthritis

Background

Osteoarthritis (OA) is a common degenerative joint disease, leading to pain and restricted mobility. Age-related endoplasmic reticulum (ER) stress has been implicated in the pathogenesis of OA, but the underlying mechanisms remain unclear. This study aims to explore the relationship between age-related ER stress, YAP overexpression, and chondrocyte phenotype loss in the development of OA.

Methods

Cartilage samples were collected from patients undergoing amputation, and age-related ER stress markers and YAP expression were assessed using immunohistochemical staining and qPCR. Transgenic mice with cartilage-specific YAP overexpression (YAPOE) were created, and Pamrevlumab was administered to evaluate its therapeutic effects.

Results

Higher expression of ER stress markers and YAP were showed in aged tissues compared to younger tissues. YAP overexpression led to decreased levels of cartilage phenotype markers and increased osteogenesis-related proteins. In vivo, YAPOE mice exhibited OA-like cartilage degeneration, which was mitigated by Pamrevlumab treatment.

Conclusion

Age-related ER stress induces YAP overexpression, contributing to OA pathogenesis. Pamrevlumab effectively prevents this phenotype loss in YAPOE mice, suggesting its potential as a therapeutic agent for OA. These findings provide new insights into the molecular mechanisms of OA and highlight the importance of targeting the ER stress-YAP-CTGF signaling pathway in OA treatment and prevention.

EGF/EGFR-YAP1/TEAD2 signaling upregulates STIM1 in vemurafenib resistant melanoma cells

Stromal interaction molecule 1 (STIM1) is the endoplasmic reticulum Ca2+ sensor for store-operated calcium entry and is closely associated with carcinogenesis and tumor progression. Previously, we found that STIM1 is upregulated in melanoma cells resistant to the serine/threonine-protein kinase B-raf inhibitor vemurafenib, although the mechanism underlying this upregulation is unknown. Here, we show that vemurafenib resistance upregulates STIM1 through an epidermal growth factor (EGF)/epidermal growth factor receptor (EGFR)-Yes-associated protein 1 (YAP1)/TEA domain transcription factor 2 (TEAD2) signaling axis. Vemurafenib resistance can lead to an increase in EGF and EGFR levels, causing activation of the EGFR signaling pathway, which promotes YAP1 nuclear localization to increase the expression of STIM1. Our findings not only reveal the mechanism by which vemurafenib resistance promotes STIM1 upregulation, but also provide a rationale for combined targeting of the EGF/EGFR-YAP1/TEAD2-STIM1 axis to improve the therapeutic efficacy of BRAF inhibitor in melanoma patients.

Hippo Signaling Pathway in Colorectal Cancer: Modulation by Various Signals and Therapeutic Potential

Colorectal cancer (CRC) stands as a significant global health issue, marked by elevated occurrence and mortality statistics. Despite the availability of various treatments, including chemotherapy, radiotherapy, and targeted therapy, CRC cells often exhibit resistance to these interventions. As a result, it is imperative to identify the disease at an earlier stage and enhance the response to treatment by acquiring a deeper comprehension of the processes driving tumor formation, aggressiveness, metastasis, and resistance to therapy. The Hippo pathway plays a critical role in facilitating the initiation of tumorigenesis and frequently experiences disruption within CRC because of genetic mutations and modified expression in its fundamental constituents. Targeting upstream regulators or core Hippo pathway components may provide innovative therapeutic strategies for modulating Hippo signaling dysfunction in CRC. To advance novel therapeutic techniques for CRC, it is imperative to grasp the involvement of the Hippo pathway in CRC and its interaction with alternate signaling pathways, noncoding RNAs, gut microbiota, and the immune microenvironment. This review seeks to illuminate the function and control of the Hippo pathway in CRC, ultimately aiming to unearth innovative therapeutic methodologies for addressing this ailment.

A highly sensitive reporter system to monitor endogenous YAP1/TAZ activity and its application in various human cells

The activation of yes-associated protein 1 (YAP1) and transcriptional co-activator with PDZ-binding motif (TAZ) has been implicated in both regeneration and tumorigenesis, thus representing a double-edged sword in tissue homeostasis. However, how the activity of YAP1/TAZ is regulated or what leads to its dysregulation in these processes remains unknown. To explore the upstream stimuli modulating the cellular activity of YAP1/TAZ, we developed a highly sensitive YAP1/TAZ/TEAD-responsive DNA element (YRE) and incorporated it into a lentivirus-based reporter cell system to allow for sensitive and specific monitoring of the endogenous activity of YAP1/TAZ in terms of luciferase activity in vitro and Venus fluorescence in vivo. Furthermore, by replacing YRE with TCF- and NF-κB-binding DNA elements, we demonstrated the applicability of this reporter system to other pathways such as Wnt/β-catenin/TCF- and IL-1β/NF-κB-mediated signaling, respectively. The practicality of this system was evaluated by performing cell-based reporter screening of a chemical compound library consisting of 364 known inhibitors, using reporter-introduced cells capable of quantifying YAP1/TAZ- and β-catenin-mediated transcription activities, which led to the identification of multiple inhibitors, including previously known as well as novel modulators of these signaling pathways. We further confirmed that novel YAP1/TAZ modulators, such as potassium ionophores, Janus kinase inhibitors, platelet-derived growth factor receptor inhibitors, and genotoxic stress inducers, alter the protein level or phosphorylation of endogenous YAP1/TAZ and the expression of their target genes. Thus, this reporter system provides a powerful tool to monitor endogenous signaling activities of interest (even in living cells) and search for modulators in various cellular contexts.

Hippo signaling pathway regulates Ebola virus transcription and egress

Filovirus-host interactions play important roles in all stages of the virus lifecycle. Here, we identify LATS1/2 kinases and YAP, key components of the Hippo pathway, as critical regulators of EBOV transcription and egress. Specifically, we find that when YAP is phosphorylated by LATS1/2, it localizes to the cytoplasm (Hippo "ON") where it sequesters VP40 to prevent egress. In contrast, when the Hippo pathway is "OFF", unphosphorylated YAP translocates to the nucleus where it transcriptionally activates host genes and promotes viral egress. Our data reveal that LATS2 indirectly modulates filoviral VP40-mediated egress through phosphorylation of AMOTp130, a positive regulator of viral egress, but more surprisingly that LATS1/2 kinases directly modulate EBOV transcription by phosphorylating VP30, an essential regulator of viral transcription. In sum, our findings highlight the potential to exploit the Hippo pathway/filovirus axis for the development of host-oriented countermeasures targeting EBOV and related filoviruses.

YAP/TAZ enhances P-body formation to promote tumorigenesis

The role of processing bodies (P-bodies) in tumorigenesis and tumor progression is not well understood. Here, we showed that the oncogenes YAP/TAZ promote P-body formation in a series of cancer cell lines. Mechanistically, both transcriptional activation of the P-body-related genes SAMD4A, AJUBA, and WTIP and transcriptional suppression of the tumor suppressor gene PNRC1 are involved in enhancing the effects of YAP/TAZ on P-body formation in colorectal cancer (CRC) cells. By reexpression of PNRC1 or knockdown of P-body core genes (DDX6, DCP1A, and LSM14A), we determined that disruption of P-bodies attenuates cell proliferation, cell migration, and tumor growth induced by overexpression of YAP5SA in CRC. Analysis of a pancancer CRISPR screen database (DepMap) revealed co-dependencies between YAP/TEAD and the P-body core genes and correlations between the mRNA levels of SAMD4A, AJUBA, WTIP, PNRC1, and YAP target genes. Our study suggests that the P-body is a new downstream effector of YAP/TAZ, which implies that reexpression of PNRC1 or disruption of P-bodies is a potential therapeutic strategy for tumors with active YAP.

Ameliorative effect of Metformin / alpha-lipoic acid combination on diabetic nephropathy via modulation of YAP/ miR-29a/PTEN/p-AKT axis

Diabetic nephropathy (DN) is the most frequent and serious complication of type 2 diabetes (T2DM). Lack of a precise remedy and socio-economic burden of DN patients implements searching about alternative therapies. This study aims to evaluate the possible beneficial effect of alpha-lipoic acid (α-LA) alone or in combination with metformin (Met) in ameliorating STZ/High fat diet (HFD)-induced DN. T2DM was induced via HFD administration for 15 weeks and single ip injection of STZ (35 mg/kg) at week 7. Male Sprague-Dawley rats were randomly grouped as follows: control group, STZ/HFD-induced DN, Met/T; daily treated with 150 mg/kg Met, α-LA/T group; daily treated with 100 mg/kg α-LA, and Met/T + α-LA/T group; daily treated with Met and α-LA at same doses. Administration of Met and α-LA succeeded in attenuating STZ/HFD-induced DN as manifested by significant decrease in kidney weight as well as renal and cardiac hypertrophy index. Moreover, Met and α-LA improved glycemic control, kidney functions and lipid profile as well as restored redox balance. Additionally, Met and α-LA administration significantly upregulated PTEN level accompanied by significant downregulation in renal p-AKT and miR-29a levels. Histopathologically, Met and α-LA administration mitigated STZ/HFD-induced histopathological alterations in kidney and heart. Moreover, immunohistochemical examination revealed a significant decrease in renal YAP, collagen I and Ki-67. Taken together, these observations revealed that Met and α-LA administration could protect against STZ/HFD-induced DN.

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.

Nuclear phosphoinositide signaling promotes YAP/TAZ-TEAD transcriptional activity in breast cancer

The Hippo pathway effectors Yes-associated protein 1 (YAP) and its homolog TAZ are transcriptional coactivators that control gene expression by binding to TEA domain (TEAD) family transcription factors. The YAP/TAZ-TEAD complex is a key regulator of cancer-specific transcriptional programs, which promote tumor progression in diverse types of cancer, including breast cancer. Despite intensive efforts, the YAP/TAZ-TEAD complex in cancer has remained largely undruggable due to an incomplete mechanistic understanding. Here, we report that nuclear phosphoinositides function as cofactors that mediate the binding of YAP/TAZ to TEADs. The enzymatic products of phosphoinositide kinases PIPKIα and IPMK, including phosphatidylinositol 4,5-bisphosphate (PI(4,5)P2) and phosphatidylinositol 3,4,5-trisphosphate (P(I3,4,5)P3), bridge the binding of YAP/TAZ to TEAD. Inhibiting these kinases or the association of YAP/TAZ with PI(4,5)P2 and PI(3,4,5)P3 attenuates YAP/TAZ interaction with the TEADs, the expression of YAP/TAZ target genes, and breast cancer cell motility. Although we could not conclusively exclude the possibility that other enzymatic products of IPMK such as inositol phosphates play a role in the mechanism, our results point to a previously unrecognized role of nuclear phosphoinositide signaling in control of YAP/TAZ activity and implicate this pathway as a potential therapeutic target in YAP/TAZ-driven breast cancer.

Natural compounds targeting YAP/TAZ axis in cancer: Current state of art and challenges

Cancer has become a burgeoning global healthcare concern marked by its exponential growth and significant economic ramifications. Though advancements in the treatment modalities have increased the overall survival and quality of life, there are no definite treatments for the advanced stages of this malady. Hence, understanding the diseases etiologies and the underlying molecular complexities, will usher in the development of innovative therapeutics. Recently, YAP/TAZ transcriptional regulation has been of immense interest due to their role in development, tissue homeostasis and oncogenic transformations. YAP/TAZ axis functions as coactivators within the Hippo signaling cascade, exerting pivotal influence on processes such as proliferation, regeneration, development, and tissue renewal. In cancer, YAP is overexpressed in multiple tumor types and is associated with cancer stem cell attributes, chemoresistance, and metastasis. Activation of YAP/TAZ mirrors the cellular "social" behavior, encompassing factors such as cell adhesion and the mechanical signals transmitted to the cell from tissue structure and the surrounding extracellular matrix. Therefore, it presents a significant vulnerability in the clogs of tumors that could provide a wide window of therapeutic effectiveness. Natural compounds have been utilized extensively as successful interventions in the management of diverse chronic illnesses, including cancer. Owing to their capacity to influence multiple genes and pathways, natural compounds exhibit significant potential either as adjuvant therapy or in combination with conventional treatment options. In this review, we delineate the signaling nexus of YAP/TAZ axis, and present natural compounds as an alternate strategy to target cancer.

Insight into the differential toxicity of PFOA and PFBA based on a 3D-cultured MDA-MB-231 cell model

Perfluoroalkyl substances (PFASs) are a category of high-concerned emerging contaminants which are suspected to correlate with various human adverse health outcomes including tumors. It is also a question whether short-chain PFASs are qualified alternatives under the regulation of long-chain PFASs. In this study, a three-dimensional (3D) culture system based on Gelatin methacrylate (GelMA) hydrogel matrix was used to investigate the impacts of 120-h perfluorooctanoic acid (PFOA) and perfluorobutanoic acid (PFBA) exposure of MDA-MB-231 cells. The results showed that PFOA exposure promoted the proliferation, migration, and invasion of MDA-MB-231 cells in an environmentally relevant concentration range (0.1 to 10 μM), exhibiting a clear malignant-promoting risk. In contrast, PFBA only showed a trend to induce non-invasive cell migration. Hippo/YAP signaling pathway was identified as the contributor to the differences between the two PFASs. PFOA but PFBA reduced YAP phosphorylation and increased the nuclear content of YAP, which further facilitated abundant key factors of epithelial-mesenchymal transition (EMT) process. Our results provided a new idea for the carcinogenicity of PFOA using a 3D-based paradigm. Although the effects by PFBA were much milder than PFOA in the current test duration, the cell model suitable for longer exposure is still necessary to better assess the safety of alternative short-chain PFASs.

Hippo-YAP signaling activation and cross-talk with PI3K in oral cancer: A retrospective cohort study

OBJECTIVES

This study aimed to investigate the clinical and prognostic relevance of the Hippo-YAP transactivators YAP1 and TAZ in oral squamous cell carcinoma, and their possible relationship with PI3K/mTOR pathway activation.

MATERIALS AND METHODS

Immunohistochemical analysis of YAP1, TAZ, PIK3CA (p110α), p-AKT (Ser473), and p-S6 (Ser235) was performed in paraffin-embedded tissue specimens from 165 OSCC patients. Correlations between protein expression and clinical data were further assessed.

RESULTS

YAP1 expression was detected in both cytoplasm and nucleus of tumor cells, whereas TAZ expression was only found in the nucleus. Nuclear YAP1 was significantly associated with tumor size (p = 0.03), neck lymph node metastasis (p = 0.02), TNM stage (p = 0.02), and poor differentiation (p = 0.04). Nuclear TAZ was associated with tobacco (p = 0.03) and alcohol consumption (p = 0.04), and poor tumor differentiation (p = 0.04). There was a positive significant correlation between nuclear and cytoplasmic YAP1, nuclear TAZ, p110α expression, and mTORC1 activation p-S6 (S235). Combined expression of nuclear and cytoplasmic YAP1 was prognostic in both univariate and multivariate analyses. Active nuclear YAP1 was significantly and independently associated with poor disease-specific (p = 0.005, HR = 2.520; 95% CI = 1.319-4.816) and overall survival (p = 0.015, HR = 2.126; 95% CI = 1.155-3.916).

CONCLUSION

Nuclear YAP1 is an independent predictor of poor survival in oral squamous cell carcinoma.

The Role of Mechanotransduction in Contact Inhibition of Locomotion and Proliferation

Contact inhibition (CI) represents a crucial tumor-suppressive mechanism responsible for controlling the unbridled growth of cells, thus preventing the formation of cancerous tissues. CI can be further categorized into two distinct yet interrelated components: CI of locomotion (CIL) and CI of proliferation (CIP). These two components of CI have historically been viewed as separate processes, but emerging research suggests that they may be regulated by both distinct and shared pathways. Specifically, recent studies have indicated that both CIP and CIL utilize mechanotransduction pathways, a process that involves cells sensing and responding to mechanical forces. This review article describes the role of mechanotransduction in CI, shedding light on how mechanical forces regulate CIL and CIP. Emphasis is placed on filamin A (FLNA)-mediated mechanotransduction, elucidating how FLNA senses mechanical forces and translates them into crucial biochemical signals that regulate cell locomotion and proliferation. In addition to FLNA, trans-acting factors (TAFs), which are proteins or regulatory RNAs capable of directly or indirectly binding to specific DNA sequences in distant genes to regulate gene expression, emerge as sensitive players in both the mechanotransduction and signaling pathways of CI. This article presents methods for identifying these TAF proteins and profiling the associated changes in chromatin structure, offering valuable insights into CI and other biological functions mediated by mechanotransduction. Finally, it addresses unanswered research questions in these fields and delineates their possible future directions.

TAZ acting as a potential pathogenic biomarker to promote the development of lichen planus

BACKGROUND

Lichen planus is a chronic inflammatory disorder. Transcriptional coactivator with PDZ-binding motif (TAZ/WWTR1) is an important downstream effector of the Hippo pathway which regulates organ size and tissue homeostasis. But little is known about the role of TAZ in lichen planus so far.

OBJECTIVE

To explore the expression of TAZ in lichen planus and normal skin, and to discover the relationship between TAZ expression and the clinical characteristics of lichen planus patients.

METHODS

The method of immunohistochemistry was performed to quantify the expression of TAZ in 262 patients with lichen planus and 90 control tissues. Western blot and quantitative real-time reverse transcriptase-PCR (qRT-PCR) analysis were performed to examine and compare TAZ expression in 4 cases of fresh lichen planus lesions and normal skin tissues.

RESULTS

TAZ was weakly expressed in the basal layers of the epidermis in normal skin tissues with a positive rate of 52.22% (47/90). But in lichen planus, TAZ was strongly expressed in almost the entire epidermis with a positive rate of 81.30% (213/262), and the difference between the two groups was statistically significant (p<0.05). Additionally, TAZ expression was significantly related to the location of the lichen planus, clinical phenotype, smoking, and alcohol preference (p<0.05). Western blot and qRT-PCR showed that the expression of TAZ in protein and mRNA levels in four cases of lichen planus lesions was significantly higher than that in normal skin tissues.

CONCLUSION

TAZ may play a regulatory role in the occurrence and development of lichen planus, which might provide a new perspective for studying pathogenesis and theoretical treatment targets.

Environmental factor reversibly determines cellular identity through opposing Integrators that unify epigenetic and transcriptional pathways

Organisms must adapt to environmental stresses to ensure their survival and prosperity. Different types of stresses, including thermal, mechanical, and hypoxic stresses, can alter the cellular state that accompanies changes in gene expression but not the cellular identity determined by a chromatin state that remains stable throughout life. Some tissues, such as adipose tissue, demonstrate remarkable plasticity and adaptability in response to environmental cues, enabling reversible cellular identity changes; however, the mechanisms underlying these changes are not well understood. We hypothesized that positive and/or negative "Integrators" sense environmental cues and coordinate the epigenetic and transcriptional pathways required for changes in cellular identity. Adverse environmental factors such as pollution disrupt the coordinated control contributing to disease development. Further research based on this hypothesis will reveal how organisms adapt to fluctuating environmental conditions, such as temperature, extracellular matrix stiffness, oxygen, cytokines, and hormonal cues by changing their cellular identities.

Role of cell rearrangement and related signaling pathways in the dynamic process of tip cell selection

Angiogenesis is a complex, highly-coordinated and multi-step process of new blood vessel formation from pre-existing blood vessels. When initiated, the sprouting process is spearheaded by the specialized endothelial cells (ECs) known as tip cells, which guide the organization of accompanying stalk cells and determine the function and morphology of the finally-formed blood vessels. Recent studies indicate that the orchestration and coordination of angiogenesis involve dynamic tip cell selection, which is the competitive selection of cells to lead the angiogenic sprouts. Therefore, this review attempt to summarize the underlying mechanisms involved in tip cell specification in a dynamic manner to enable readers to gain a systemic and overall understanding of tip cell formation, involving cooperative interaction of cell rearrangement with Notch and YAP/TAZ signaling. Various mechanical and chemical signaling cues are integrated to ensure the right number of cells at the right place during angiogenesis, thereby precisely orchestrating morphogenic functions that ensure correct patterning of blood vessels. Video Abstract.

Role of the Hippo pathway in autoimmune diseases

The immune system is an important defense against diseases, and it is essential to maintain the homeostasis of the body's internal environment. Under normal physiological conditions, the steady state of the immune system should be sustained to play normal immune response and immune function. Exploring the molecular mechanism of maintaining immune homeostasis under physiological and pathological conditions will provides understanding of the pathogenesis of autoimmune diseases, infections, metabolic disorders, and tumors, as well as new ideas and molecular targets for the prevention and treatment of these diseases. Hippo signaling pathway can not only regulate immune cells such as macrophages, T cells and dendritic cells, but also interact with immune-related signaling pathways such as NF-kB signaling pathway, TGF-β signaling pathway and Toll-like receptor signaling pathway, so as to resist the internal environment disorder caused by the invasion of exogenous pathogenic microorganisms and maintain the internal environment stability and physiological balance of the body. Hippo signaling pathway is also involved in the pathological process of immune system-related diseases such as rheumatoid arthritis, inflammatory bowel disease and psoriasis. Hippo pathway is closely related to organ development, stem cell biology, regeneration, and tumor biology. It affects cell differentiation by participating in extracellular and intracellular physiological signal reactions, sensing cell environment, and coordinating cell reactions. This pathway is crucial in maintaining immune homeostasis. This review summarizes the mechanism of Hippo pathway in different immune cells and some autoimmune diseases and the interaction between different immune signaling pathways and Hippo signaling pathway. It aims to explore the role of Hippo in autoimmune diseases and provide theoretical and practical basis for the treatment of autoimmune diseases through Hippo signaling pathway.

YAP mediates resistance to EGF-induced apoptosis in EGFR-mutated non-small cell lung cancer cells

Mechanisms underlying the growth and survival of non-small cell lung cancer (NSCLC) cells positive for activating mutations of the epidermal growth factor receptor gene (EGFR) have remained unclear. We here examined the functional relation between such mutant forms of EGFR and Yes-associated protein (YAP), a transcriptional coactivator of the Hippo signaling pathway that regulates cell proliferation and survival. Under the condition of serum deprivation, epidermal growth factor (EGF) induced activation of YAP in NSCLC cell lines positive for mutated EGFR but not in those wild type (WT) for EGFR. Similar EGF-induced activation of YAP was apparent in A549 lung cancer cells forcibly expressing mutant EGFR but not in those overexpressing the WT receptor. Furthermore, EGF induced apoptotic cell death in serum-deprived A549 cells overexpressing the WT form of EGFR but not in those expressing mutant EGFR, and knockdown of YAP rendered the latter cells sensitive to this effect of EGF. Our results thus suggest that activation of YAP mediates resistance of EGFR-mutated NSCLC cells to EGF-induced apoptosis and thereby contributes specifically to the survival of such cells.

The TGFβ→TAK1→LATS→YAP1 Pathway Regulates the Spatiotemporal Dynamics of YAP1

The Hippo kinase cascade functions as a central hub that relays input from the "outside world" of the cell and translates it into specific cellular responses by regulating the activity of Yes-associated protein 1 (YAP1). How Hippo translates input from the extracellular signals into specific intracellular responses remains unclear. Here, we show that transforming growth factor β (TGFβ)-activated TAK1 activates LATS1/2, which then phosphorylates YAP1. Phosphorylated YAP1 (p-YAP1) associates with RUNX3, but not with TEAD4, to form a TGFβ-stimulated restriction (R)-point-associated complex which activates target chromatin loci in the nucleus. Soon after, p-YAP1 is exported to the cytoplasm. Attenuation of TGFβ signaling results in re-localization of unphosphorylated YAP1 to the nucleus, where it forms a YAP1/TEAD4/SMAD3/AP1/p300 complex. The TGFβ-stimulated spatiotemporal dynamics of YAP1 are abrogated in many cancer cells. These results identify a new pathway that integrates TGFβ signals and the Hippo pathway (TGFβ→TAK1→LATS1/2→YAP1 cascade) with a novel dynamic nuclear role for p-YAP1.

Targeting Hippo signaling in cancer: novel perspectives and therapeutic potential

As highly conserved among diverse species, Hippo signaling pathway regulates various biological processes, including development, cell proliferation, stem cell function, tissue regeneration, homeostasis, and organ size. Studies in the last two decades have provided a good framework for how these fundamental functions of Hippo signaling are tightly regulated by a network with numerous intracellular and extracellular factors. The Hippo signaling pathway, when dysregulated, may lead to a wide variety of diseases, especially cancer. There is growing evidence demonstrating that dysregulated Hippo signaling is closely associated with tumorigenesis, cancer cell invasion, and migration, as well as drug resistance. Therefore, the Hippo pathway is considered an appealing therapeutic target for the treatment of cancer. Promising novel agents targeting the Hippo signaling pathway for cancers have recently emerged. These novel agents have shown antitumor activity in multiple cancer models and demonstrated therapeutic potential for cancer treatment. However, the detailed molecular basis of the Hippo signaling-driven tumor biology remains undefined. Our review summarizes current advances in understanding the mechanisms by which Hippo signaling drives tumorigenesis and confers drug resistance. We also propose strategies for future preclinical and clinical development to target this pathway.

PIP5Kγ Mediates PI(4,5)P2/Merlin/LATS1 Signaling Activation and Interplays with Hsc70 in Hippo-YAP Pathway Regulation

The type I phosphatidylinositol 4-phosphate 5-kinase (PIP5K) family produces the critical lipid regulator phosphatidylinositol 4,5-bisphosphate (PI(4,5)P2) in the plasma membrane (PM). Here, we investigated the potential role of PIP5Kγ, a PIP5K isoform, in the Hippo pathway. The ectopic expression of PIP5Kγ87 or PIP5Kγ90, two major PIP5Kγ splice variants, activated large tumor suppressor kinase 1 (LATS1) and inhibited Yes-associated protein (YAP), whereas PIP5Kγ knockdown yielded opposite effects. The regulatory effects of PIP5Kγ were dependent on its catalytic activity and the presence of Merlin and LATS1. PIP5Kγ knockdown weakened the restoration of YAP phosphorylation upon stimulation with epidermal growth factor or lysophosphatidic acid. We further found that PIP5Kγ90 bound to the Merlin's band 4.1/ezrin/radixin/moesin (FERM) domain, forming a complex with PI(4,5)P2 and LATS1 at the PM. Notably, PIP5Kγ90, but not its kinase-deficient mutant, potentiated Merlin-LATS1 interaction and recruited LATS1 to the PM. Consistently, PIP5Kγ knockdown or inhibitor (UNC3230) enhanced colony formation in carcinoma cell lines YAP-dependently. In addition, PIP5Kγ90 interacted with heat shock cognate 71-kDa protein (Hsc70), which also contributed to Hippo pathway activation. Collectively, our results suggest that PIP5Kγ regulates the Hippo-YAP pathway by forming a functional complex with Merlin and LATS1 at the PI(4,5)P2-rich PM and via interplay with Hsc70.

Regulation of follicular activation signaling pathways by in vitro inhibition of YAP/TAZ activity in mouse ovaries

The Hippo pathway plays a crucial role in the regulation of follicular activation, which constitutes the first step of the folliculogenesis process. Disruption of this pathway occurs in several non-physiological contexts, after fragmentation for ovarian tissue cryopreservation procedures or chemotherapy exposure, leading to massive follicular growth and depletion. This study aimed to investigate the effect of controlling the Hippo pathway using verteporfin (VERT) during in vitro ovarian culture and to evaluate its potential preventive effects on chemotherapy-induced follicle activation using a mouse model. After exposure of cut ovaries to different concentrations of VERT for 3 h, a dose-dependent effect of VERT was observed that reached significant inhibition of YAP activity at 3 µmol/L. To assess the potential effect of controlling chemotherapy-induced Hippo pathway disruption, whole mouse ovaries were exposed to VERT alone or as a co-treatment with 4-hydroperoxycylophosphamide (4HC). VERT co-treatment prevented chemotherapy-induced YAP activation but had a limited impact on downstream effector gene, Ccn2. Surprisingly, VERT co-treatment also prevented mTOR and survival signaling pathway alterations following chemotherapy exposure. These results suggest an interaction between the two main signaling pathways regulating follicle activation and a protective effect of VERT on 4HC-induced DNA damage.

YAP/TAZ: Molecular pathway and disease therapy

The Yes-associated protein and its transcriptional coactivator with PDZ-binding motif (YAP/TAZ) are two homologous transcriptional coactivators that lie at the center of a key regulatory network of Hippo, Wnt, GPCR, estrogen, mechanical, and metabolism signaling. YAP/TAZ influences the expressions of downstream genes and proteins as well as enzyme activity in metabolic cycles, cell proliferation, inflammatory factor expression, and the transdifferentiation of fibroblasts into myofibroblasts. YAP/TAZ can also be regulated through epigenetic regulation and posttranslational modifications. Consequently, the regulatory function of these mechanisms implicates YAP/TAZ in the pathogenesis of metabolism-related diseases, atherosclerosis, fibrosis, and the delicate equilibrium between cancer progression and organ regeneration. As such, there arises a pressing need for thorough investigation of YAP/TAZ in clinical settings. In this paper, we aim to elucidate the signaling pathways that regulate YAP/TAZ and explore the mechanisms of YAP/TAZ-induce diseases and their potential therapeutic interventions. Furthermore, we summarize the current clinical studies investigating treatments targeting YAP/TAZ. We also address the limitations of existing research on YAP/TAZ and propose future directions for research. In conclusion, this review aims to provide fresh insights into the signaling mediated by YAP/TAZ and identify potential therapeutic targets to present innovative solutions to overcome the challenges associated with YAP/TAZ.

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

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

The Tumor Suppressor DAB2IP Is Regulated by Cell Contact and Contributes to YAP/TAZ Inhibition in Confluent Cells

External and internal mechanical forces modulate cell morphology, movement, proliferation and metabolism, and represent crucial inputs for tissue homeostasis. The transcriptional regulators YAP and TAZ are important effectors of mechanical signaling and are frequently activated in solid tumors, correlating with metastasis, chemoresistance, and shorter patient survival. YAP/TAZ activity is controlled by various pathways that sense cell shape, polarity, contacts, and mechanical tension. In tumors, aberrant YAP/TAZ activation may result from cancer-related alterations of such regulatory networks. The tumor suppressor DAB2IP is a Ras-GAP and scaffold protein that negatively modulates multiple oncogenic pathways and is frequently downregulated or inactivated in solid tumors. Here, we provide evidence that DAB2IP expression is sustained by cell confluency. We also find that DAB2IP depletion in confluent cells alters their morphology, reducing cell packing while increasing cell stiffness. Finally, we find that DAB2IP depletion in confluent cells favors YAP/TAZ nuclear localization and transcriptional activity, while its ectopic expression in subconfluent cells increases YAP/TAZ retention in the cytoplasm. Together, these data suggest that DAB2IP may function as a sensor of cell interactions, contributing to dampening cellular responses to oncogenic inputs in confluent cells and that DAB2IP loss-of-function would facilitate YAP/TAZ activation in intact epithelia, accelerating oncogenic transformation.

Lipid kinase PIP5Kα contributes to Hippo pathway activation via interaction with Merlin and by mediating plasma membrane targeting of LATS1

BACKGROUND

The Hippo pathway plays a critical role in controlled cell proliferation. The tumor suppressor Merlin and large tumor suppressor kinase 1 (LATS1) mediate activation of Hippo pathway, consequently inhibiting the primary effectors, Yes-associated protein (YAP) and transcriptional coactivator with PDZ-binding motif (TAZ). Phosphatidylinositol 4,5-bisphosphate (PIP2), a lipid present in the plasma membrane (PM), binds to and activates Merlin. Phosphatidylinositol 4-phosphate 5-kinase α (PIP5Kα) is an enzyme responsible for PIP2 production. However, the functional role of PIP5Kα in regulation of Merlin and LATS1 under Hippo signaling conditions remains unclear.

METHODS

PIP5Kα, Merlin, or LATS1 knockout or knockdown cells and transfected cells with them were used. LATS1, YAP, and TAZ activities were measured using biochemical methods and PIP2 levels were evaluated using cell imaging. Low/high cell density and serum starvation/stimulation conditions were tested. Colocalization of PIP5Kα and PIP2 with Merlin and LATS1, and their protein interactions were examined using transfection, confocal imaging, immunoprecipitation, western blotting, and/or pull-down experiments. Colony formation and adipocyte differentiation assays were performed.

RESULTS

We found that PIP5Kα induced LATS1 activation and YAP/TAZ inhibition in a kinase activity-dependent manner. Consistent with these findings, PIP5Kα suppressed cell proliferation and enhanced adipocyte differentiation of mesenchymal stem cells. Moreover, PIP5Kα protein stability and PIP2 levels were elevated at high cell density compared with those at low cell density, and both PIP2 and YAP phosphorylation levels initially declined, then recovered upon serum stimulation. Under these conditions, YAP/TAZ activity was aberrantly regulated by PIP5Kα deficiency. Mechanistically, either Merlin deficiency or LATS1 deficiency abrogated PIP5Kα-mediated YAP/TAZ inactivation. Additionally, the catalytic domain of PIP5Kα directly interacted with the band 4.1/ezrin/radixin/moesin domain of Merlin, and this interaction reinforced interaction of Merlin with LATS1. In accordance with these findings, PIP5Kα and PIP2 colocalized with Merlin and LATS1 in the PM. In PIP5Kα-deficient cells, Merlin colocalization with PIP2 was reduced, and LATS1 solubility increased.

CONCLUSIONS

Collectively, our results support that PIP5Kα serves as an activator of the Hippo pathway through interaction and colocalization with Merlin, which promotes PIP2-dependent Merlin activation and induces local recruitment of LATS1 to the PIP2-rich PM and its activation, thereby negatively regulating YAP/TAZ activity. Video Abstract.

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.

Phase separation of Hippo signalling complexes

The Hippo pathway was originally discovered to control tissue growth in Drosophila and includes the Hippo kinase (Hpo; MST1/2 in mammals), scaffold protein Salvador (Sav; SAV1 in mammals) and the Warts kinase (Wts; LATS1/2 in mammals). The Hpo kinase is activated by binding to Crumbs-Expanded (Crb-Ex) and/or Merlin-Kibra (Mer-Kib) proteins at the apical domain of epithelial cells. Here we show that activation of Hpo also involves the formation of supramolecular complexes with properties of a biomolecular condensate, including concentration dependence and sensitivity to starvation, macromolecular crowding, or 1,6-hexanediol treatment. Overexpressing Ex or Kib induces formation of micron-scale Hpo condensates in the cytoplasm, rather than at the apical membrane. Several Hippo pathway components contain unstructured low-complexity domains and purified Hpo-Sav complexes undergo phase separation in vitro. Formation of Hpo condensates is conserved in human cells. We propose that apical Hpo kinase activation occurs in phase separated "signalosomes" induced by clustering of upstream pathway components.

Non-hippo kinases: indispensable roles in YAP/TAZ signaling and implications in cancer therapy

The transcriptional co-activators Yes-associated protein (YAP) and PDZ-binding domain (TAZ) are the known downstream effectors of the Hippo kinase cascade. YAP/TAZ have been shown to play important roles in cellular growth and differentiation, tissue development and carcinogenesis. Recent studies have found that, in addition to the Hippo kinase cascade, multiple non-Hippo kinases also regulate the YAP/TAZ cellular signaling and produce important effects on cellular functions, particularly on tumorigenesis and progression. In this article, we will review the multifaceted regulation of the YAP/TAZ signaling by the non-Hippo kinases and discuss the potential application of the non-Hippo kinase-regulated YAP/TAZ signaling for cancer therapy.

Targeting Class I-II-III PI3Ks in Cancer Therapy: Recent Advances in Tumor Biology and Preclinical Research

Phosphatidylinositol-3-kinase (PI3K) enzymes, producing signaling phosphoinositides at plasma and intracellular membranes, are key in intracellular signaling and vesicular trafficking pathways. PI3K is a family of eight enzymes divided into three classes with various functions in physiology and largely deregulated in cancer. Here, we will review the recent evidence obtained during the last 5 years on the roles of PI3K class I, II and III isoforms in tumor biology and on the anti-tumoral action of PI3K inhibitors in preclinical cancer models. The dependency of tumors to PI3K isoforms is dictated by both genetics and context (e.g., the microenvironment). The understanding of class II/III isoforms in cancer development and progression remains scarce. Nonetheless, the limited available data are consistent and reveal that there is an interdependency between the pathways controlled by all PI3K class members in their role to promote cancer cell proliferation, survival, growth, migration and metabolism. It is unknown whether this feature contributes to partial treatment failure with isoform-selective PI3K inhibitors. Hence, a better understanding of class II/III functions to efficiently inhibit their positive and negative interactions with class I PI3Ks is needed. This research will provide the proof-of-concept to develop combination treatment strategies targeting several PI3K isoforms simultaneously.

Yes-Associated Protein Nuclear Translocation Is Regulated by Epidermal Growth Factor Receptor Activation Through Phosphatase and Tensin Homolog/AKT Axis in Glioblastomas

Gliomas are the most common and lethal primary brain tumors in adults. Glioblastomas, the most frequent and aggressive form of gliomas, represent a therapeutic challenge as no curative treatment exists to date, and the prognosis remains extremely poor. Recently, the transcriptional cofactors Yes-associated protein (YAP) and transcriptional co-activator with PDZ-binding motif (TAZ) belonging to the Hippo pathway have emerged as a major determinant of malignancy in solid tumors, including gliomas. However, the mechanisms involved in its regulation, particularly in brain tumors, remain ill-defined. In glioblastomas, EGFR represents one of the most altered oncogenes affected by chromosomal rearrangements, mutations, amplifications, and overexpression. In this study, we investigated the potential link between epidermal growth factor receptor (EGFR) and the transcriptional cofactors YAP and TAZ by in situ and in vitro approaches. We first studied their activation on tissue microarray, including 137 patients from different glioma molecular subtypes. We observed that YAP and TAZ nuclear location was highly associated with isocitrate dehydrogenase 1/2 (IDH1/2) wild-type glioblastomas and poor patient outcomes. Interestingly, we found an association between EGFR activation and YAP nuclear location in glioblastoma clinical samples, suggesting a link between these 2 markers contrary to its ortholog TAZ. We tested this hypothesis in patient-derived glioblastoma cultures by pharmacologic inhibition of EGFR using gefinitib. We showed an increase of S397-YAP phosphorylation associated with decreased AKT phosphorylation after EGFR inhibition in phosphatase and tensin homolog (PTEN) wild-type cultures, unlike PTEN-mutated cell lines. Finally, we used bpV(HOpic), a potent PTEN inhibitor, to mimic the effect of PTEN mutations. We found that the inhibition of PTEN was sufficient to revert back the effect induced by Gefitinib in PTEN-wild-type cultures. Altogether, to our knowledge, these results show for the first time the regulation of pS397-YAP by the EGFR-AKT axis in a PTEN-dependent manner.

The role of RAS oncogenes in controlling epithelial mechanics

Mutations in RAS are key oncogenic drivers and therapeutic targets. Oncogenic Ras proteins activate a network of downstream signalling pathways, including extracellular signal-regulated kinase (ERK) and phosphatidylinositol 3-kinase (PI3K), promoting cell proliferation and survival. However, there is increasing evidence that RAS oncogenes also alter the mechanical properties of both individual malignant cells and transformed tissues. Here we discuss the role of oncogenic RAS in controlling mechanical cell phenotypes and how these mechanical changes promote oncogenic transformation in single cells and tissues. RAS activation alters actin organisation and actomyosin contractility. These changes alter cell rheology and impact mechanosensing through changes in substrate adhesion and YAP/TAZ-dependent mechanotransduction. We then discuss how these changes play out in cell collectives and epithelial tissues by driving large-scale tissue deformations and the expansion of malignant cells. Uncovering how RAS oncogenes alter cell mechanics will lead to a better understanding of the morphogenetic processes that underlie tumour formation in RAS-mutant cancers.

TAZ/YAP fusion proteins: mechanistic insights and therapeutic opportunities

The Hippo pathway is dysregulated in many different cancers, but point mutations in the pathway are rare. Transcriptional co-activator with PDZ-binding motif (TAZ) and Yes-associated protein (YAP) fusion proteins have emerged in almost all major cancer types and represent the most common genetic mechanism by which the two transcriptional co-activators are activated. Given that the N termini of TAZ or YAP are fused to the C terminus of another transcriptional regulator, the resultant fusion proteins hyperactivate a TEAD transcription factor-based transcriptome. Recent advances show that the C-terminal fusion partners confer oncogenic properties to TAZ/YAP fusion proteins by recruiting epigenetic modifiers that promote a hybrid TEAD-based transcriptome. Elucidating these cooperating epigenetic complexes represents a strategy to identify new therapeutic approaches for a pathway that has been recalcitrant to medical therapy.

Hippo Signaling in the Ovary: Emerging Roles in Development, Fertility, and Disease

Emerging studies indicate that the Hippo pathway, a highly conserved pathway that regulates organ size control, plays an important role in governing ovarian physiology, fertility, and pathology. Specific to the ovary, the spatiotemporal expression of the major components of the Hippo signaling cascade are observed throughout the reproductive lifespan. Observations from multiple species begin to elucidate the functional diversity and molecular mechanisms of Hippo signaling in the ovary in addition to the identification of interactions with other signaling pathways and responses to various external stimuli. Hippo pathway components play important roles in follicle growth and activation, as well as steroidogenesis, by regulating several key biological processes through mechanisms of cell proliferation, migration, differentiation, and cell fate determination. Given the importance of these processes, dysregulation of the Hippo pathway contributes to loss of follicular homeostasis and reproductive disorders such as polycystic ovary syndrome (PCOS), premature ovarian insufficiency, and ovarian cancers. This review highlights what is currently known about the Hippo pathway core components in ovarian physiology, including ovarian development, follicle development, and oocyte maturation, while identifying areas for future research to better understand Hippo signaling as a multifunctional pathway in reproductive health and biology.

The critical role of the Hippo signaling pathway in kidney diseases

The Hippo signaling pathway is involved in cell growth, proliferation, and apoptosis, and it plays a key role in regulating organ size, tissue regeneration, and tumor development. The Hippo signaling pathway also participates in the occurrence and development of various human diseases. Recently, many studies have shown that the Hippo pathway is closely related to renal diseases, including renal cancer, cystic kidney disease, diabetic nephropathy, and renal fibrosis, and it promotes the transformation of acute kidney disease to chronic kidney disease (CKD). The present paper summarizes and analyzes the research status of the Hippo signaling pathway in different kidney diseases, and it also summarizes the expression of Hippo signaling pathway components in pathological tissues of kidney diseases. In addition, the present paper discusses the positive therapeutic significance of traditional Chinese medicine (TCM) in regulating the Hippo signaling pathway for treating kidney diseases. This article introduces new targets and ideas for drug development, clinical diagnosis, and treatment of kidney diseases.

Impact of SOX2 function and regulation on therapy resistance in bladder cancer

Bladder cancer (BC) is a malignant disease with high rates of recurrence and mortality. It is mainly classified as non-muscle-invasive BC and muscle-invasive BC (MIBC). Often, MIBC is chemoresistant, which, according to cancer stem cells (CSCs) theory, is linked to the presence of bladder cancer stem cells (BCSCs). Sex-determining region Y- (SRY) Box transcription factor 2 (SOX2), which is a molecular marker of BCSCs, is aberrantly over-expressed in chemoresistant BC cell lines. It is one of the standalone prognostic factors for BC, and it has an inherently significant function in the emergence and progression of the disease. This review first summarizes the role of SRY-related high-mobility group protein Box (SOX) family genes in BC, focusing on the SOX2 and its significance in BC. Second, it discusses the mechanisms relevant to the regulation of SOX2. Finally, it summarizes the signaling pathways related to SOX2 in BC, suggests current issues to be addressed, and proposes potential directions for future research to provide new insights for the treatment of BC.

Emerging Role of YAP and the Hippo Pathway in Prostate Cancer

The Hippo pathway regulates and contributes to several hallmarks of prostate cancer (PCa). Although the elucidation of YAP function in PCa is in its infancy, emerging studies have shed light on the role of aberrant Hippo pathway signaling in PCa development and progression. YAP overexpression and nuclear localization has been linked to poor prognosis and resistance to treatment, highlighting a therapeutic potential that may suggest innovative strategies to treat cancer. This review aimed to summarize available data on the biological function of the dysregulated Hippo pathway in PCa and identify knowledge gaps that need to be addressed for optimizing the development of YAP-targeted treatment strategies in patients likely to benefit.

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.

Integrating Genetic Alterations and the Hippo Pathway in Head and Neck Squamous Cell Carcinoma for Future Precision Medicine

Genetic alterations and dysregulation of signaling pathways are indispensable for the initiation and progression of cancer. Understanding the genetic, molecular, and signaling diversities in cancer patients has driven a dynamic change in cancer therapy. Patients can select a suitable molecularly targeted therapy or immune checkpoint inhibitor based on the driver gene alterations determined by sequencing of cancer tissue. This “precision medicine” approach requires detailed elucidation of the mechanisms connecting genetic alterations of driver genes and aberrant downstream signaling pathways. The regulatory mechanisms of the Hippo pathway and Yes-associated protein/transcriptional co-activator with PDZ binding motif (YAP/TAZ) that have central roles in cancer cell proliferation are not fully understood, reflecting their recent discovery. Nevertheless, emerging evidence has shown that various genetic alterations dysregulate the Hippo pathway and hyperactivate YAP/TAZ in cancers, including head and neck squamous cell carcinoma (HNSCC). Here, we summarize the latest evidence linking genetic alterations and the Hippo pathway in HNSCC, with the aim of contributing to the continued development of precision medicine.

IGF-1R/YAP signaling pathway is involved in collagen V-induced insulin biosynthesis and secretion in rat islet INS-1 cells

PURPOSE

Type V collagen (collagen V) is one of the important components of extracellular matrix (ECM) in pancreas. We previously reported that pre-coating collagen V on the culture dishes enhanced insulin production in INS-1 rat pancreatic β cells. In this study, we investigate the underlying mechanism.

RESULTS

Insulin biosynthesis and secretion are both increased in INS-1 cells cultured on collagen V-coated dishes, accompanied by the reduced nuclear translocation of Yes-associated protein (YAP), a transcriptional co-activator. YAP, the downstream effector of Hippo signaling pathway, plays an important role in the development and function of pancreas. Inhibition of YAP activation by verteporfin further up-regulates insulin biosynthesis and secretion. Silencing large tumor suppressor (LATS), a core component of Hippo pathway which inhibits activity of YAP by phosphorylation, by siRNA transfection inhibits both insulin biosynthesis and secretion. In the present study, the protein level of insulin-like growth factor 1 receptor (IGF-1 R), detected as the upstream molecule of YAP, is reduced in the INS-1 cells cultured on the dishes coated with collagen V. The silencing of IGF-1 R by siRNA transfection further enhances insulin biosynthesis and secretion. IGF-1 treatment reduces collagen V-induced up-regulation of insulin biosynthesis and secretion, accompanying the increased nuclear YAP.

CONCLUSION

Inhibition of IGF-1 R/YAP signal pathway is involved in collagen V-induced insulin biosynthesis and secretion in INS-1 cells.

Akt1-dependent expression of angiopoietin 1 and 2 in vascular smooth muscle cells leads to vascular stabilization

Retinal angiogenesis was delayed in VSMC-specific Akt1-deficient mice (Akt1^∆SMC) but not in Akt2^∆SMC mice. The proliferation of ECs, recruitment of pericytes, and coverage of VSMCs to the endothelium were defective in Akt1^∆SMC. The silencing of Akt1 in VSMCs led to the downregulation of angiopoietin 1 (Ang1) and the upregulation of Ang2. The activation of Notch3 in VSMCs was significantly reduced in the retinas of Akt1^∆SMC mice. Silencing Akt1 suppressed the activation of Notch3. Moreover, the silencing of Notch3 downregulated Ang1, whereas the overexpression of Notch3 intracellular domain (NICD3) enhanced Ang1 expression. The nuclear localization and transcriptional activity of yes-associated protein (YAP) were affected by the expression level of Akt1. Silencing YAP downregulated Ang2 expression, whereas overexpression of YAP showed the opposite results. Ang1 antibody and Ang2 suppressed endothelial sprouting of wild-type aortic tissues, whereas the Ang2 antibody and Ang1 facilitated the endothelial sprouting of aortic tissues from Akt1^∆SMC mice. Finally, severe hemorrhage was observed in Akt1^∆SMC mice, which was further facilitated under streptozotocin (STZ)-induced diabetic conditions. Therefore, the Akt1-Notch3/YAP-Ang1/2 signaling cascade in VSMCs might play an essential role in the paracrine regulation of endothelial function.

Loss of Arid1a and Pten in Pancreatic Ductal Cells Induces Intraductal Tubulopapillary Neoplasm via the YAP/TAZ Pathway

BACKGROUND & AIMS

Pancreatic ductal adenocarcinoma (PDAC) arises from several types of premalignant lesions, including intraductal tubulopapillary neoplasm (ITPN); however, the molecular pathogenesis of ITPN remains unknown.

METHODS

We performed studies with Hnf1b-CreERT2; Ptenf/f; Arid1af/f mice to investigate the consequence of genetic deletion of Arid1a in adult pancreatic ductal cells in the context of oncogenic PI3K/Akt pathway activation.

RESULTS

Simultaneous deletion of Arid1a and Pten in pancreatic ductal cells resulted in the development of ITPN, which progressed to PDAC, in mice. Simultaneous loss of Arid1a and Pten induced dedifferentiation of pancreatic ductal cells and Yes-associated protein 1/Transcriptional coactivator with PDZ-binding motif (YAP/TAZ) pathway activation. Consistent with the mouse data, TAZ expression was found elevated in human ITPNs and ITPN-derived PDACs but not in human intraductal papillary mucinous neoplasms, indicating that activation of the TAZ pathway is a distinctive feature of ITPN. Furthermore, pharmacological inhibition of the YAP/TAZ pathway suppressed the dedifferentiation of pancreatic ductal cells and development of ITPN in Arid1a and Pten double-knockout mice.

CONCLUSION

Concurrent loss of Arid1a and Pten in adult pancreatic ductal cells induced ITPN and ITPN-derived PDAC in mice through aberrant activation of the YAP/TAZ pathway, and inhibition of the YAP/TAZ pathway prevented the development of ITPN. These findings provide novel insights into the pathogenesis of ITPN-derived PDAC and highlight the YAP/TAZ pathway as a potential therapeutic target.

Hippo-TAZ signaling is the master regulator of the onset of triple-negative basal-like breast cancers

Breast cancer is the most frequent malignancy in women worldwide. Basal-like breast cancer (BLBC) is the most aggressive form of this disease, and patients have a poor prognosis. Here, we present data suggesting that the Hippo-transcriptional coactivator with PDZ-binding motif (TAZ) pathway is a key driver of BLBC onset and progression. Deletion of Mob1a/b in mouse mammary luminal epithelium induced rapid and highly reproducible mammary tumorigenesis that was dependent on TAZ but not yes-associated protein 1 (YAP1). In situ early-stage BLBC-like malignancies developed in mutant animals by 2 wk of age, and invasive BLBC appeared by 4 wk. In a human estrogen receptor⁺ luminal breast cancer cell line, TAZ hyperactivation skewed the features of these luminal cells to the basal phenotype, consistent with the aberrant TAZ activation frequently observed in human precancerous BLBC lesions. TP53 mutation is rare in human precancerous BLBC but frequent in invasive BLBC. Addition of Trp53 deficiency to our Mob1a/b-deficient mouse model enhanced tumor grade and accelerated cancer progression. Our work justifies targeting the Hippo-TAZ pathway as a therapy for human BLBC, and our mouse model represents a powerful tool for evaluating candidate agents.

Unraveling the Biology of Epithelioid Hemangioendothelioma, a TAZ-CAMTA1 Fusion Driven Sarcoma

Simple Summary

Epithelioid hemangioendothelioma (EHE) is a rare vascular cancer that involves a gain-of-function gene fusion involving TAZ, a transcriptional coactivator, and one of two end effectors of the Hippo pathway. Although the activity of TAZ and/or YAP, a paralog of TAZ, is consistently altered in many cancers, genetic alterations involving YAP/TAZ are rare, and the precise mechanisms by which YAP/TAZ are activated are not well understood in most cancers. Because WWTR1(TAZ)–CAMTA1 is the only genetic alteration in approximately half of EHE, EHE is a genetically clean and homogenous system for understanding how the dysregulation of TAZ promotes tumorigenesis. Therefore, by using EHE as a model system, we hope to elucidate the essential biological pathways mediated by TAZ and identify mechanisms to target them. The findings of EHE research can be applied to other cancers that are addicted to high YAP/TAZ activity.

Abstract

The activities of YAP and TAZ, the end effectors of the Hippo pathway, are consistently altered in cancer, and this dysregulation drives aggressive tumor phenotypes. While the actions of these two proteins aid in tumorigenesis in the majority of cancers, the dysregulation of these proteins is rarely sufficient for initial tumor development. Herein, we present a unique TAZ-driven cancer, epithelioid hemangioendothelioma (EHE), which harbors a WWTR1(TAZ)–CAMTA1 gene fusion in at least 90% of cases. Recent investigations have elucidated the mechanisms by which YAP/TAP-fusion oncoproteins function and drive tumorigenesis. This review presents a critical evaluation of this recent work, with a particular focus on how the oncoproteins alter the normal activity of TAZ and YAP, and, concurrently, we generate a framework for how we can target the gene fusions in patients. Since EHE represents a paradigm of YAP/TAZ dysregulation in cancer, targeted therapies for EHE may also be effective against other YAP/TAZ-dependent cancers.

Role of Yes-Associated Protein in Psoriasis and Skin Tumor Pathogenesis

Psoriasis and skin tumors (such as basal cell carcinoma, squamous cell carcinoma, and melanoma) are chronic diseases that endanger physical and mental health, and yet the causes are largely unknown and treatment options limited. The development of targeted drugs requires a better understanding of the exact pathogenesis of these diseases, and Yes-associated protein (YAP), a member of the Hippo signaling pathway, is believed to play an important role. Psoriasis and skin tumors are characterized by excessive cell proliferation, abnormal differentiation, vasodilation, and proliferation. Here, we review the literature related to YAP-associated disease mechanisms and discuss the latest research. YAP regulates cell apoptosis, proliferation, and differentiation; inhibits cell density and intercellular contacts and angiogenesis; and maintains the three-dimensional structure of the skin. These mechanisms may be associated with the occurrence and development of psoriasis and skin tumors. The results of recent studies have shown that YAP expression is increased in psoriasis and skin tumors. High expression of YAP in psoriasis and skin tumors may indicate its positive functions in skin inflammation and malignancies and may play an important role in disease pathogenesis. The study of new drugs targeting YAP can provide novel approaches for the treatment of skin diseases.