Hippo signalling maintains ER expression and ER+ breast cancer growth

Strategies that regulate Hippo signaling pathway for novel anticancer therapeutics

As a highly conserved signaling network across different species, the Hippo pathway is involved in various biological processes. Dysregulation of the Hippo pathway could lead to a wide range of diseases, particularly cancers. Extensive researches have demonstrated the close association between dysregulated Hippo signaling and tumorigenesis as well as tumor progression. Consequently, targeting the Hippo pathway has emerged as a promising strategy for cancer treatment. In fact, there has been an increasing number of reports on small molecules that target the Hippo pathway, exhibiting therapeutic potential as anticancer agents. Importantly, some of Hippo signaling pathway inhibitors have been approved for the clinical trials. In this work, we try to provide an overview of the core components and signal transduction mechanisms of the Hippo signaling pathway. Furthermore, we also analyze the relationship between Hippo signaling pathway and cancers, as well as summarize the small molecules with proven anti-tumor effects in clinical trials or reported in literatures. Additionally, we discuss the anti-tumor potency and structure-activity relationship of the small molecule compounds, providing a valuable insight for further development of anticancer agents against this pathway.

YAP inhibits NF-κB signaling and ccRCC growth by opposing p65-ZHX2 cooperativity

Hippo pathway functions as a tumor suppressor pathway by inhibiting the oncogenic potential of pathway effectors YAP/TAZ. However, YAP can also function as a context-dependent tumor suppressor in several types of cancer including clear cell renal cell carcinomas (ccRCC). Here we show that YAP blocks NF-κB signaling in ccRCC to inhibit cancer cell growth. Mechanistically, YAP inhibits the expression of ZHX2, a critical p65 co-factor in ccRCC. Furthermore, YAP competes with ZHX2 for binding to p65. Consequently, elevated nuclear YAP blocks the cooperativity between ZHX2 and p65, leading to diminished NF-κB target gene expression. Pharmacological inhibition of Hippo/MST1/2 blocked NF-κB transcriptional program and suppressed ccRCC cancer cell growth, which can be rescued by ZHX2/p65 overexpression. Our study uncovers a novel crosstalk between the Hippo and NF-κB pathways and its involvement in ccRCC growth inhibition, suggesting that targeting the Hippo pathway may provide a therapeutical opportunity for ccRCC treatment.

Hippo pathway in non-small cell lung cancer: mechanisms, potential targets, and biomarkers

Lung cancer is the primary contributor to cancer-related deaths globally, and non-small cell lung cancer (NSCLC) constitutes around 85% of all lung cancer cases. Recently, the emergence of targeted therapy and immunotherapy revolutionized the treatment of NSCLC and greatly improved patients' survival. However, drug resistance is inevitable, and extensive research has demonstrated that the Hippo pathway plays a crucial role in the development of drug resistance in NSCLC. The Hippo pathway is a highly conserved signaling pathway that is essential for various biological processes, including organ development, maintenance of epithelial balance, tissue regeneration, wound healing, and immune regulation. This pathway exerts its effects through two key transcription factors, namely Yes-associated protein (YAP) and transcriptional co-activator PDZ-binding motif (TAZ). They regulate gene expression by interacting with the transcriptional-enhanced associate domain (TEAD) family. In recent years, this pathway has been extensively studied in NSCLC. The review summarizes a comprehensive overview of the involvement of this pathway in NSCLC, and discusses the mechanisms of drug resistance, potential targets, and biomarkers associated with this pathway in NSCLC.

A LATS2 and ALKBH5 positive feedback loop supports their oncogenic roles

N(6)-methyladenosine (m6A) critically regulates RNA dynamics in various biological processes. The m6A demethylase ALKBH5 promotes tumorigenesis of glioblastoma, while the intricate web that orchestrates its regulation remains enigmatic. Here, we discover that cell density affects ALKBH5 subcellular localization and m6A dynamics. Mechanistically, ALKBH5 is phosphorylated by the large tumor suppressor kinase 2 (LATS2), preventing its nuclear export and enhancing protein stability. Furthermore, phosphorylated ALKBH5 reciprocally erases m6A from LATS2 mRNA, thereby stabilizing this transcript. Unexpectedly, LATS2 depletion suppresses glioblastoma stem cell self-renewal independent of yes-associated protein activation. Additionally, deficiency in either LATS2 or ALKBH5 phosphorylation impedes tumor progression in mouse xenograft models. Moreover, high levels of LATS2 expression and ALKBH5 phosphorylation are associated with tumor malignancy in patients with gliomas. Collectively, our study unveils an oncogenic positive feedback loop between LATS2 and ALKBH5, revealing a non-canonical branch of the Hippo pathway for RNA processing and suggesting potential anti-cancer interventions.

Hippo pathway in cell-cell communication: emerging roles in development and regeneration

The Hippo pathway is a central regulator of tissue growth that has been widely studied in mammalian organ development, regeneration, and cancer biology. Although previous studies have convincingly revealed its cell-autonomous functions in controlling cell fate, such as cell proliferation, survival, and differentiation, accumulating evidence in recent years has revealed its non-cell-autonomous functions. This pathway regulates cell-cell communication through direct interactions, soluble factors, extracellular vesicles, and the extracellular matrix, providing a range of options for controlling diverse biological processes. Consequently, the Hippo pathway not only dictates the fate of individual cells but also triggers multicellular responses involving both tissue-resident cells and infiltrating immune cells. Here, we have highlighted the recent understanding of the molecular mechanisms by which the Hippo pathway controls cell-cell communication and discuss its importance in tissue homeostasis, especially in development and regeneration.

TMEM120B strengthens breast cancer cell stemness and accelerates chemotherapy resistance via β1-integrin/FAK-TAZ-mTOR signaling axis by binding to MYH9

BACKGROUND

Breast cancer stem cell (CSC) expansion results in tumor progression and chemoresistance; however, the modulation of CSC pluripotency remains unexplored. Transmembrane protein 120B (TMEM120B) is a newly discovered protein expressed in human tissues, especially in malignant tissues; however, its role in CSC expansion has not been studied. This study aimed to determine the role of TMEM120B in transcriptional coactivator with PDZ-binding motif (TAZ)-mediated CSC expansion and chemotherapy resistance.

METHODS

Both bioinformatics analysis and immunohistochemistry assays were performed to examine expression patterns of TMEM120B in lung, breast, gastric, colon, and ovarian cancers. Clinicopathological factors and overall survival were also evaluated. Next, colony formation assay, MTT assay, EdU assay, transwell assay, wound healing assay, flow cytometric analysis, sphere formation assay, western blotting analysis, mouse xenograft model analysis, RNA-sequencing assay, immunofluorescence assay, and reverse transcriptase-polymerase chain reaction were performed to investigate the effect of TMEM120B interaction on proliferation, invasion, stemness, chemotherapy sensitivity, and integrin/FAK/TAZ/mTOR activation. Further, liquid chromatography-tandem mass spectrometry analysis, GST pull-down assay, and immunoprecipitation assays were performed to evaluate the interactions between TMEM120B, myosin heavy chain 9 (MYH9), and CUL9.

RESULTS

TMEM120B expression was elevated in lung, breast, gastric, colon, and ovarian cancers. TMEM120B expression positively correlated with advanced TNM stage, lymph node metastasis, and poor prognosis. Overexpression of TMEM120B promoted breast cancer cell proliferation, invasion, and stemness by activating TAZ-mTOR signaling. TMEM120B directly bound to the coil-coil domain of MYH9, which accelerated the assembly of focal adhesions (FAs) and facilitated the translocation of TAZ. Furthermore, TMEM120B stabilized MYH9 by preventing its degradation by CUL9 in a ubiquitin-dependent manner. Overexpression of TMEM120B enhanced resistance to docetaxel and doxorubicin. Conversely, overexpression of TMEM120B-∆CCD delayed the formation of FAs, suppressed TAZ-mTOR signaling, and abrogated chemotherapy resistance. TMEM120B expression was elevated in breast cancer patients with poor treatment outcomes (Miller/Payne grades 1-2) than in those with better outcomes (Miller/Payne grades 3-5).

CONCLUSIONS

Our study reveals that TMEM120B bound to and stabilized MYH9 by preventing its degradation. This interaction activated the β1-integrin/FAK-TAZ-mTOR signaling axis, maintaining stemness and accelerating chemotherapy resistance.

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.

Cellular Impacts of Striatins and the STRIPAK Complex and Their Roles in the Development and Metastasis in Clinical Cancers (Review)

Striatins (STRNs) are generally considered to be cytoplasmic proteins, with lower expression observed in the nucleus and at cell-cell contact regions. Together with protein phosphatase 2A (PP2A), STRNs form the core region of striatin-interacting phosphatase and kinase (STRIPAK) complexes through the coiled-coil region of STRN proteins, which is crucial for substrate recruitment. Over the past two decades, there has been an increasing amount of research into the biological and cellular functions of STRIPAK members. STRNs and the constituent members of the STRIPAK complex have been found to regulate several cellular functions, such as cell cycle control, cell growth, and motility. Dysregulation of these cellular events is associated with cancer development. Importantly, their roles in cancer cells and clinical cancers are becoming recognised, with several STRIPAK components found to have elevated expression in cancerous tissues compared to healthy tissues. These molecules exhibit significant diagnostic and prognostic value across different cancer types and in metastatic progression. The present review comprehensively summarises and discusses the current knowledge of STRNs and core STRIPAK members, in cancer malignancy, from both cellular and clinical perspectives.

α-Catenin acetylation is essential for its stability and blocks its tumor suppressor effects in breast cancer through Yap1

α-Catenin plays a critical role in tissue integrity, repair, and embryonic development. However, the post-translational modifications of α-catenin and the correlative roles in regulating cancer progression remain unclear. Here, we report that α-catenin is acetylated by p300, and identify three acetylation sites, K45, K866, and K881. Conversely, α-catenin acetylation can be reversed by deacetylase HDAC6. Mechanistically, α-catenin acetylation releases the transcriptional coactivator Yes-associated protein 1 (Yap1) by blocking the interaction between α-catenin and Yap1, and promotes the accumulation of Yap1 in the nucleus. Through this mechanism, acetylation weakens the capacity of α-catenin to inhibit breast cancer cell proliferation and tumor growth in mice. Meanwhile, we show that CDDP induces acetylation of α-catenin, and acetylated α-catenin resists the apoptosis under CDDP conditions. Additionally, acetylation inhibits the proteasome-dependent degradation of α-catenin, thus enhancing the stability of α-catenin for storage. Taken together, our results demonstrate that α-catenin can be acetylated, an event that is key for the subcellular distribution of Yap1 and subsequent facilitation of breast tumorigenesis.

New Insights into YAP/TAZ-TEAD-Mediated Gene Regulation and Biological Processes in Cancer

The Hippo pathway is conserved across species. Key mammalian Hippo pathway kinases, including MST1/2 and LATS1/2, inhibit cellular growth by inactivating the TEAD coactivators, YAP, and TAZ. Extensive research has illuminated the roles of Hippo signaling in cancer, development, and regeneration. Notably, dysregulation of Hippo pathway components not only contributes to tumor growth and metastasis, but also renders tumors resistant to therapies. This review delves into recent research on YAP/TAZ-TEAD-mediated gene regulation and biological processes in cancer. We focus on several key areas: newly identified molecular patterns of YAP/TAZ activation, emerging mechanisms that contribute to metastasis and cancer therapy resistance, unexpected roles in tumor suppression, and advances in therapeutic strategies targeting this pathway. Moreover, we provide an updated view of YAP/TAZ's biological functions, discuss ongoing controversies, and offer perspectives on specific debated topics in this rapidly evolving field.

YAP1 Expression in HR+HER2- Breast Cancer: 21-Gene Recurrence Score Analysis and Public Dataset Validation

BACKGROUND

YAP1, an oncogene in numerous cancers, is a downstream transcription factor of the Hippo pathway. This study focuses on its relationship with the Oncotype Dx (ODX) test risk score (RS) in patients with hormone-receptor-positive, HER2-negative (HR+HER2-) breast cancer.

METHODS

We retrospectively analyzed 401 HR+HER2- breast cancer patients from Gangnam Severance Hospital who underwent ODX tests (May 2014-April 2020). YAP1 nuclear localization was evaluated via immunohistochemical staining and its clinical correlation with clinicopathological parameters, including RS, was analyzed. Public datasets TCGA-BRCA and METABRIC validated clinical outcomes.

RESULTS

YAP1 expression negatively correlated with ODX RS (OR 0.373, p = 0.002). Elevated YAP1 mRNA levels corresponded to better clinical outcomes, specifically in ER-positive patients, with significant results in METABRIC and TCGA-BRCA datasets (p < 0.0001 OS in METABRIC, p = 0.00085 RFS in METABRIC, p = 0.040 DFS in TCGA-BRCA). In subsets with varying ESR1 mRNA expression and pronounced YAP1 expression, superior survival outcomes were consistently observed.

CONCLUSION

YAP1 may be a valuable prognostic marker and potential therapeutic target in HR+HER2- breast cancer patients.

Value of negatively correlated miR-205-5p/HMGB3 and miR-96-5p/FOXO1 on the diagnosis of breast cancer and benign breast diseases

Background

MicroRNA (miRNA) and mRNA levels in matching specimens were used to identify miRNA-mRNA interactions. We aimed to integrate transcriptome, immunophenotype, methylation, mutation, and survival data analyses to examine the profiles of miRNAs and target mRNAs and their associations with breast cancer (BC) diagnosis.

Methods

Based on the Gene Expression Omnibus (GEO) database and The Cancer Genome Atlas (TCGA), differentially expressed miRNAs and targeted mRNAs were screened from experimentally verified miRNA-target interaction databases using Pearson's correlation analysis. We used real-time quantitative reverse transcription polymerase chain reaction to verify BC and benign disease samples, and logistic regression analysis was used to establish a diagnostic model based on miRNAs and target mRNAs. Receiver operating characteristic curve analysis was performed to test the ability to recognize the miRNA-mRNA pairs. Next, we investigated the complex interactions between miRNA-mRNA regulatory pairs and phenotypic hallmarks.

Results

We identified 27 and 359 dysregulated miRNAs and mRNAs, respectively, based on the GEO and TCGA databases. Using Pearson's correlation analysis, 10 negative miRNA-mRNA regulatory pairs were identified after screening both databases, and the related miRNA and target mRNA levels were assessed in 40 BC tissues and 40 benign breast disease tissues. Two key regulatory pairs (miR-205-5p/High mobility group box 3 (HMGB3) and miR-96-5p/Forkhead Box O1 (FOXO1)) were selected to establish the diagnostic model. They also had utility in survival and clinical analyses.

Conclusions

A diagnostic model including two miRNAs and their respective target mRNAs was established to distinguish between BC and benign breast diseases. These markers play essential roles in BC pathogenesis.

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.

The relationship between the Hippo signaling pathway and bone metastasis of breast cancer

Bone is the most common site of metastasis from breast cancer, which is the most prevalent cancer affecting women globally. Bone metastasis from breast cancer severely affects the quality of life of patients and increases mortality. The molecular mechanisms of metastasis, colonization, and proliferation of breast cancer cells in bone are complex and involve the interaction between breast cancer cells and the bone microenvironment. However, the precise mechanism is not clear at present. In recent years, the Hippo signaling pathway has attracted much attention due to its important role in regulating the expression of major effector molecules during tumor development. In particular, studies have found that the mutation and aberrant expression of the core components of the Hippo signaling pathway affect breast cancer cell migration and invasion, indicating that this pathway plays a role in bone metastasis, although the molecular mechanism of this pathway in breast cancer metastasis has not been fully elucidated. In this review, we discuss the function of the Hippo signaling pathway, introducing its role in breast cancer metastasis, especially bone metastasis of breast cancer, so as to lay a solid theoretical foundation for further research and for the development of effective targeted therapeutic agents.

KIAA1429-mediated m6A modification of CHST11 promotes progression of diffuse large B-cell lymphoma by regulating Hippo-YAP pathway

BACKGROUND

N⁶-methyladenosine (m6A) has been shown to participate in various essential biological processes by regulating the level of target genes. However, the function of m6A modification mediated by KIAA1429 [alias virus-like m6A methyltransferase-associated protein (VIRMA)] during the progression of diffuse large B-cell lymphoma (DLBCL) remains undefined.

METHODS

The expression and clinical significance of KIAA1429 were verified by our clinical data. CRISPR/Cas9 mediated KIAA1429 deletion, and CRISPR/dCas9-VP64 for activating endogenous KIAA1429 was used to evaluate its biological function. RNA sequencing (RNA-seq), methylated RNA immunoprecipitation sequencing (MeRIP-seq), RNA immunoprecipitation (RIP) assays, luciferase activity assay, RNA stability experiments, and co-immunoprecipitation were performed to investigate the regulatory mechanism of KIAA1429 in DLBCL. Tumor xenograft models were established for in vivo experiments.

RESULTS

Dysregulated expression of m6A regulators was observed, and a novel predictive model based on m6A score was established in DLBCL. Additionally, elevated KIAA1429 expression was associated with poor prognosis of patients with DLBCL. Knockout of KIAA1429 repressed DLBCL cell proliferation, facilitated cell cycle arrest in the G2/M phase, induced apoptosis in vitro, and inhibited tumor growth in vivo. Furthermore, carbohydrate sulfotransferase 11 (CHST11) was identified as a downstream target of KIAA1429, which mediated m6A modification of CHST11 mRNA and then recruited YTHDF2 for reducing CHST11 stability and expression. Inhibition of CHST11 diminished MOB1B expression, resulting in inactivation of Hippo-YAP signaling, reprogramming the expression of Hippo target genes.

CONCLUSIONS

Our results revealed a new mechanism by which the Hippo-YAP pathway in DLBCL is inactivated by KIAA1429/YTHDF2-coupled epitranscriptional repression of CHST11, highlighting the potential of KIAA1429 as a novel predictive biomarker and therapeutic target for DLBCL progression.

PHF6 recruits BPTF to promote HIF-dependent pathway and progression in YAP-high breast cancer

Background

Aberrant epigenetic remodeling events contribute to progression and metastasis of breast cancer (Bca). The specific mechanims that epigenetic factors rely on to mediate tumor aggressiveness remain unclear. We aimed to elucidate the roles of epigenetic protein PHF6 in breast tumorigenesis.

Methods

Published datasets and tissue samples with PHF6 staining were used to investigate the clinical relevance of PHF6 in Bca. CCK-8, clony formation assays were used to assess cell growth capacity. Cell migration and invasion abilities were measured by Transwell assay. The gene mRNA and protein levels were measured by quantitative real-time PCR and western blot. Chromatin immunoprecipitation (ChIP)-qPCR assays were used to investigate transcriptional relationships among genes. The Co-immunoprecipitation (Co-IP) assay was used to validate interactions between proteins. The CRISPR/Cas9 editing technology was used to construct double HIF knockout (HIF-DKO) cells. The subcutaneous xenograft model and orthotopic implantation tumor model were used to asess in vivo tumor growth.

Results

In this study, we utilized MTT assay to screen that PHF6 is required for Bca growth. PHF6 promotes Bca proliferation and migration. By analyzing The Cancer Genome Atlas breast cancer (TCGA-Bca) cohort, we found that PHF6 was significantly higher in tumor versus normal tissues. Mechanistically, PHF6 physically interacts with HIF-1α and HIF-2α to potentiate HIF-driven transcriptional events to initiate breast tumorigenesis. HIF-DKO abolished PHF6-mediated breast tumor growth, and PHF6 deficiency in turn impaired HIF transcriptional effects. Besides, hypoxia could also rely on YAP activation, but not HIF, to sustain PHF6 expressions in Bca cells. In addition, PHF6 recuits BPTF to mediate epigenetic remodeling to augment HIF transcriptional activity. Targeting PHF6 or BPTF inhibitor (AU1) is effective in mice models. Lastly, PHF6 correlated with HIF target gene expression in human breast tumors, which is an independent prognostic regulator.

Conclusions

Collectively, this study identified PHF6 as a prognostic epigenetic regulator for Bca, functioning as a HIF coactivator. The fundamental mechanisms underlying YAP/PHF6/HIF axis in breast tumors endowed novel epigenegtic targets for Bca treatment.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12967-023-04031-8.

YAP antagonizes TEAD-mediated AR signaling and prostate cancer growth

Hippo signaling restricts tumor growth by inhibiting the oncogenic potential of YAP/TAZ-TEAD transcriptional complex. Here, we uncover a context-dependent tumor suppressor function of YAP in androgen receptor (AR) positive prostate cancer (PCa) and show that YAP impedes AR+ PCa growth by antagonizing TEAD-mediated AR signaling. TEAD forms a complex with AR to enhance its promoter/enhancer occupancy and transcriptional activity. YAP and AR compete for TEAD binding and consequently, elevated YAP in the nucleus disrupts AR-TEAD interaction and prevents TEAD from promoting AR signaling. Pharmacological inhibition of MST1/2 or LATS1/2, or transgenic activation of YAP suppressed the growth of PCa expressing therapy resistant AR splicing variants. Our study uncovers an unanticipated crosstalk between Hippo and AR signaling pathways, reveals an antagonistic relationship between YAP and TEAD in AR+ PCa, and suggests that targeting the Hippo signaling pathway may provide a therapeutical opportunity to treat PCa driven by therapy resistant AR variants.

HERC3 promotes YAP/TAZ stability and tumorigenesis independently of its ubiquitin ligase activity

YAP/TAZ transcriptional co-activators play pivotal roles in tumorigenesis. In the Hippo pathway, diverse signals activate the MST-LATS kinase cascade that leads to YAP/TAZ phosphorylation, and subsequent ubiquitination and proteasomal degradation by SCFβ-TrCP . When the MST-LATS kinase cascade is inactive, unphosphorylated or dephosphorylated YAP/TAZ translocate into the nucleus to mediate TEAD-dependent gene transcription. Hippo signaling-independent YAP/TAZ activation in human malignancies has also been observed, yet the mechanism remains largely elusive. Here, we report that the ubiquitin E3 ligase HERC3 can promote YAP/TAZ activation independently of its enzymatic activity. HERC3 directly binds to β-TrCP, blocks its interaction with YAP/TAZ, and thus prevents YAP/TAZ ubiquitination and degradation. Expression levels of HERC3 correlate with YAP/TAZ protein levels and expression of YAP/TAZ target genes in breast tumor cells and tissues. Accordingly, knockdown of HERC3 expression ameliorates tumorigenesis of breast cancer cells. Our results establish HERC3 as a critical regulator of the YAP/TAZ stability and a potential therapeutic target for breast cancer.

The oncogenic roles and clinical implications of YAP/TAZ in breast cancer

Breast cancer (BC) is the most commonly diagnosed form of cancer and a leading cause of cancer-related deaths among women worldwide. Yes-associated protein (YAP) and transcriptional coactivator with PDZ-binding motif (TAZ) are homologous transcriptional coactivators and downstream effectors of Hippo signalling. YAP/TAZ activation has been revealed to play essential roles in multiple events of BC development, including tumour initiation, progression, metastasis, drug resistance and stemness regulations. In this review, we will first give an overview of YAP/TAZ-mediated oncogenesis in BC, and then systematically summarise the oncogenic roles of YAP/TAZ in various BC subtypes, BC stem cells (BCSCs) and tumour microenvironments (TMEs). Based on these findings, we will further discuss the clinical implications of YAP/TAZ-based targeted therapies in BC and the potential future direction.

Niche stiffness sustains cancer stemness via TAZ and NANOG phase separation

Emerging evidence shows that the biomechanical environment is required to support cancer stem cells (CSCs), which play a crucial role in drug resistance. However, how mechanotransduction signals regulate CSCs and its clinical significance has remained unclear. Using clinical-practice ultrasound elastography for patients' lesions and atomic force microscopy for surgical samples, we reveal that increased matrix stiffness is associated with poor responses to neoadjuvant chemotherapy, worse prognosis, and CSC enrichment in patients with breast cancer. Mechanically, TAZ activated by biomechanics enhances CSC properties via phase separation with NANOG. TAZ-NANOG phase separation, which is dependent on acidic residues in the N-terminal activation domain of NANOG, promotes the transcription of SOX2 and OCT4. Therapeutically, targeting NANOG or TAZ reduces CSCs and enhances the chemosensitivity in vivo. Collectively, this study demonstrated that the phase separation of a pluripotency transcription factor links mechanical cues in the niche to the fate of CSCs.

The Cancer/Testis Antigen CT45A1 Promotes Transcription of Oncogenic Sulfatase-2 Gene in Breast Cancer Cells and Is Sensible Targets for Cancer Therapy

PURPOSE

Invasive breast carcinomas (BRCAs) are highly lethal. The molecular mechanisms underlying progression of invasive BRCAs are unclear, and effective therapies are highly desired. The cancer-testis antigen CT45A1 promotes overexpression of pro-metastatic sulfatase-2 (SULF2) and breast cancer metastasis to the lungs, but its mechanisms are largely unknown. In this study, we aimed to elucidate the mechanism of CT45A1-induced SULF2 overexpression and provide evidence for targeting CT45A1 and SULF2 for breast cancer therapy.

METHODS

The effect of CT45A1 on SULF2 expression was assessed using reverse transcription polymerase chain reaction and western blot. The mechanism of CT45A1-induced SULF2 gene transcription was studied using protein-DNA binding assay and a luciferase activity reporter system. The interaction between CT45A1 and SP1 proteins was assessed using immunoprecipitation and western blot. Additionally, the suppression of breast cancer cell motility by SP1 and SULF2 inhibitors was measured using cell migration and invasion assays.

RESULTS

CT45A1 and SULF2 are aberrantly overexpressed in patients with BRCA; importantly, overexpression of CT45A1 is closely associated with poor prognosis. Mechanistically, gene promoter demethylation results in overexpression of both CT45A1 and SULF2. CT45A1 binds directly to the core sequence GCCCCC in the promoter region of SULF2 gene and activates the promoter. Additionally, CT45A1 interacts with the oncogenic master transcription factor SP1 to drive SULF2 gene transcription. Interestingly, SP1 and SULF2 inhibitors suppress breast cancer cell migration, invasion, and tumorigenicity.

CONCLUSION

Overexpression of CT45A1 is associated with poor prognosis in patients with BRCA. CT45A1 promotes SULF2 overexpression by activating the promoter and interacting with SP1. Additionally, SP1 and SULF2 inhibitors suppress breast cancer cell migration, invasion, and tumorigenesis. Our findings provide new insight into the mechanisms of breast cancer metastasis and highlight CT45A1 and SULF2 as sensible targets for developing novel therapeutics against metastatic breast cancer.

Expression of the Hippo Pathway Core Components in Endometrial Cancer and Its Association with Clinicopathologic Features

BACKGROUND

The Hippo signaling pathway has a key role in tumorigenesis. This study aimed to evaluate the relationship between the expression of core components of the Hippo signaling pathway and its association with clinicopathological features in endometrial cancer.

MATERIALS AND METHODS

We retrospectively collected endometrioid endometrial cancer specimens from 60 patients between January 2002 and December 2009 at Gyeongsang National University Hospital. Relevant clinicopathological data were obtained through electronic medical records of patients. The expression patterns of six core components (YAP, p-YAP, LATS1/2, MST1/2, KIBRA, and Merlin) were identified by immunohistochemistry on tissue microarray sections.

RESULTS

The positive expression ratio was 75.0% for YAP, 73.3% for p-YAP, 26.7% for MST1/2, 16.7% for KIBRA, 15.0% for Merlin, and 15.0% for LATS1/2. YAP expression was negatively correlated with MST 1/2 kinases (p = 0.045) and positively correlated with p-YAP (p = 0.012). Merlin, and MST 1/2 kinases (p = 0.043) showed a positive correlation. A subgroup of patients aged below 60 years (p = 0.004) and with myometrial invasion depth of less than 1/2 (p = 0.041) showed a positive association with YAP expression. p-YAP expression was negatively associated with a subset of patients with primary tumour size ≥4 cm (p = 0.03). Logistic regression analysis showed a significant association between age and YAP expression. The odds ratio of p-YAP expression was significantly lower in the group with tumour size ≥4 cm.

CONCLUSION

Two prognostic factors, age and tumour size, were significantly associated with the expression of YAP and p-YAP in endometrial cancer. Further research should focus on their expression as a marker for prediction of clinicopathological implications in endometrial cancer.

Breast cancer plasticity is restricted by a LATS1-NCOR1 repressive axis

Breast cancer, the most frequent cancer in women, is generally classified into several distinct histological and molecular subtypes. However, single-cell technologies have revealed remarkable cellular and functional heterogeneity across subtypes and even within individual breast tumors. Much of this heterogeneity is attributable to dynamic alterations in the epigenetic landscape of the cancer cells, which promote phenotypic plasticity. Such plasticity, including transition from luminal to basal-like cell identity, can promote disease aggressiveness. We now report that the tumor suppressor LATS1, whose expression is often downregulated in human breast cancer, helps maintain luminal breast cancer cell identity by reducing the chromatin accessibility of genes that are characteristic of a "basal-like" state, preventing their spurious activation. This is achieved via interaction of LATS1 with the NCOR1 nuclear corepressor and recruitment of HDAC1, driving histone H3K27 deacetylation near NCOR1-repressed "basal-like" genes. Consequently, decreased expression of LATS1 elevates the expression of such genes and facilitates slippage towards a more basal-like phenotypic identity. We propose that by enforcing rigorous silencing of repressed genes, the LATS1-NCOR1 axis maintains luminal cell identity and restricts breast cancer progression.

Inactivation of LATS1/2 drives luminal-basal plasticity to initiate basal-like mammary carcinomas

Basal-like breast cancers, an aggressive breast cancer subtype that has poor treatment options, are thought to arise from luminal mammary epithelial cells that undergo basal plasticity through poorly understood mechanisms. Using genetic mouse models and ex vivo primary organoid cultures, we show that conditional co-deletion of the LATS1 and LATS2 kinases, key effectors of Hippo pathway signaling, in mature mammary luminal epithelial cells promotes the development of Krt14 and Sox9-expressing basal-like carcinomas that metastasize over time. Genetic co-deletion experiments revealed that phenotypes resulting from the loss of LATS1/2 activity are dependent on the transcriptional regulators YAP/TAZ. Gene expression analyses of LATS1/2-deleted mammary epithelial cells notably revealed a transcriptional program that associates with human basal-like breast cancers. Our study demonstrates in vivo roles for the LATS1/2 kinases in mammary epithelial homeostasis and luminal-basal fate control and implicates signaling networks induced upon the loss of LATS1/2 activity in the development of basal-like breast cancer.

The Hippo signalling pathway and its implications in human health and diseases

As an evolutionarily conserved signalling network, the Hippo pathway plays a crucial role in the regulation of numerous biological processes. Thus, substantial efforts have been made to understand the upstream signals that influence the activity of the Hippo pathway, as well as its physiological functions, such as cell proliferation and differentiation, organ growth, embryogenesis, and tissue regeneration/wound healing. However, dysregulation of the Hippo pathway can cause a variety of diseases, including cancer, eye diseases, cardiac diseases, pulmonary diseases, renal diseases, hepatic diseases, and immune dysfunction. Therefore, therapeutic strategies that target dysregulated Hippo components might be promising approaches for the treatment of a wide spectrum of diseases. Here, we review the key components and upstream signals of the Hippo pathway, as well as the critical physiological functions controlled by the Hippo pathway. Additionally, diseases associated with alterations in the Hippo pathway and potential therapies targeting Hippo components will be discussed.

In Situ Transformable Supramolecular Nanomedicine Targeted Activating Hippo Pathway for Triple-Negative Breast Cancer Growth and Metastasis Inhibition

As it is closely associated with tumor proliferation, metastasis, and the immunosuppressive microenvironment, the dysfunctional Hippo pathway has become an extremely attractive target for treating multiple cancers. However, to date, the corresponding chemotherapeutic nanomedicines have not been developed. Herein, a supramolecular self-delivery nanomedicine with in situ transforming capacity was tailor-constructed for Hippo-pathway restoration, and its inhibitory effect against tumor growth and metastasis was investigated in a highly aggressive triple-negative breast cancer (TNBC) model. Stimulated by overexpressed glutathione (GSH) and esterase in cancer cells, the self-assembled nanomedicine transformed from inactive nanospheres to active nanofibers conjugating tyrosvaline and spatiotemporally synchronously released the covalently linked flufenamic acid in situ, together activating the maladjusted Hippo pathway by simultaneously acting on different targets upstream and downstream. The transcriptional expression of Yes-associated protein (YAP) and related growth-promoted genes were significantly reduced, finally significantly repressing the proliferation and metastasis of cancer cells. Additionally, the Hippo-pathway restoration showed an excellent radiosensitization effect, making the targeted therapy combined with radiotherapy display a prominent synergistic in vivo anticancer effect against TNBC. This work reports a specifically designed smart nanomedicine to restore the function of the Hippo pathway and sensitize radiotherapy, providing an attractive paradigm for targeted drug delivery and cancer combination therapy.

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.

Transcriptional Regulation of the Hippo Pathway: Current Understanding and Insights from Single-Cell Technologies

The Hippo pathway regulates tissue homeostasis in normal development and drives oncogenic processes. In this review, we extensively discuss how YAP/TAZ/TEAD cooperate with other master transcription factors and epigenetic cofactors to orchestrate a broad spectrum of transcriptional responses. Even though these responses are often context- and lineage-specific, we do not have a good understanding of how such precise and specific transcriptional control is achieved—whether they are driven by differences in TEAD paralogs, or recruitment of cofactors to tissue-specific enhancers. We believe that emerging single-cell technologies would enable a granular understanding of how the Hippo pathway influences cell fate and drives oncogenic processes, ultimately allowing us to design better pharmacological agents against TEADs and identify robust pharmacodynamics markers of Hippo pathway inhibition.

Identification of TAZ as the essential molecular switch in orchestrating SCLC phenotypic transition and metastasis

Small-cell lung cancer (SCLC) is a recalcitrant cancer characterized by high metastasis. However, the exact cell type contributing to metastasis remains elusive. Using a Rb1 L/L /Trp53 L/L mouse model, we identify the NCAMhiCD44lo/- subpopulation as the SCLC metastasizing cell (SMC), which is progressively transitioned from the non-metastasizing NCAMloCD44hi cell (non-SMC). Integrative chromatin accessibility and gene expression profiling studies reveal the important role of the SWI/SNF complex, and knockout of its central component, Brg1, significantly inhibits such phenotypic transition and metastasis. Mechanistically, TAZ is silenced by the SWI/SNF complex during SCLC malignant progression, and its knockdown promotes SMC transition and metastasis. Importantly, ectopic TAZ expression reversely drives SMC-to-non-SMC transition and alleviates metastasis. Single-cell RNA-sequencing analyses identify SMC as the dominant subpopulation in human SCLC metastasis, and immunostaining data show a positive correlation between TAZ and patient prognosis. These data uncover high SCLC plasticity and identify TAZ as the key molecular switch in orchestrating SCLC phenotypic transition and metastasis.

YAP inhibits ERα and ER+ breast cancer growth by disrupting a TEAD-ERα signaling axis

Hippo signaling restricts tissue growth by inhibiting the transcriptional effector YAP. Here we uncover a role of Hippo signaling and a tumor suppressor function of YAP in estrogen receptor positive (ER⁺) breast cancer. We find that inhibition of Hippo/MST1/2 or activation of YAP blocks the ERα transcriptional program and ER⁺ breast cancer growth. Mechanistically, the Hippo pathway transcription factor TEAD physically interacts with ERα to increase its promoter/enhancer occupancy whereas YAP inhibits ERα/TEAD interaction, decreases ERα occupancy on its target promoters/enhancers, and promotes ERα degradation by the proteasome. Furthermore, YAP inhibits hormone-independent transcription of ERα gene (ESR1). Consistently, high levels of YAP correlate with good prognosis of ER⁺ breast cancer patients. Finally, we find that pharmacological inhibition of Hippo/MST1/2 impeded tumor growth driven by hormone therapy resistant ERα mutants, suggesting that targeting the Hippo-YAP-TEAD signaling axis could be a potential therapeutical strategy to overcome endocrine therapy resistance conferred by ERα mutants.

YAP Dictates Mitochondrial Redox Homeostasis to Facilitate Obesity-Associated Breast Cancer Progression

Dysregulation of hormones is considered a risk factor for obesity-mediated breast tumorigenesis; however, obesity is associated with poor outcomes among women diagnosed with triple-negative breast cancer (TNBC), which is a hormone-independent breast cancer subtype. Thus, identifying the driving force behind the obesity-breast cancer relationship is an urgent need. Here it is identified that diet-induced obesity (DIO) facilitates tumorigenesis of TNBC cells. Mechanistically, DIO induces a metabolic addiction to fatty acid oxidation (FAO), accompanied by coordinated activation of Yes-associated protein (YAP) signaling. Specifically, YAP governs mitochondrial redox homeostasis via transcriptional regulation of antioxidant-related enzymes, which renders tumor cells capable of extenuating FAO-elicited mitochondrial oxidative stress. Moreover, adipocytes-derived fatty acids are identified to be responsible for enhancing the FAO-YAP axis and antioxidative capacity, and higher expression of an obesity signature in breast cancer patients is positively correlated with YAP signaling and antioxidant genes. The findings uncover the crucial role of YAP in dictating mitochondrial redox homeostasis for obesity-mediated metabolic adaptation and breast tumor progression.

Transcriptional repression of estrogen receptor alpha by YAP reveals the Hippo pathway as therapeutic target for ER+ breast cancer

Extensive knowledge has been gained on the transcription network controlled by ERα, however, the mechanism underlying ESR1 (encoding ERα) expression is less understood. We recently discovered that the Hippo pathway is required for the proper expression of ESR1. YAP/TAZ are transcription coactivators that are phosphorylated and inhibited by the Hippo pathway kinase LATS. Here we delineated the molecular mechanisms underlying ESR1 transcription repression by the Hippo pathway. Mechanistically, YAP binds to TEAD to increase local chromatin accessibility to stimulate transcription of nearby genes. Among the YAP target genes, Vestigial-Like Protein 3 (VGLL3) competes with YAP/TAZ for binding to TEAD transcription factor and recruits the NCOR2/SMRT repressor to the super-enhancer of ESR1 gene, leading to epigenetic alteration and transcriptional silencing. We developed a potent LATS inhibitor VT02956. Targeting the Hippo pathway by VT02956 represses ESR1 expression and inhibits the growth of ER⁺ breast cancer cells as well as patient-derived tumour organoids. Moreover, histone deacetylase inhibitors, such as Entinostat, induce VGLL3 expression to inhibit ER⁺ breast cancer cells. Our study suggests LATS as unexpected cancer therapeutic targets, especially for endocrine-resistant breast cancers.

ARSD, a novel ERα downstream target gene, inhibits proliferation and migration of breast cancer cells via activating Hippo/YAP pathway

Advanced breast cancer (BC), especially basal like triple-negative BC (TNBC), is a highly malignant tumor without viable treatment option, highlighting the urgent need to seek novel therapeutic targets. Arylsulfatase D (ARSD), localized at Xp22.3, is a female-biased gene due to its escaping from X chromosome inactivation (XCI). Unfortunately, no systematic investigation of ARSD on BC has been reported. In this study, we observed that ARSD expression was positively related to ERα status either in BC cells or tissue specimens, which were associated with good prognosis. Furthermore, we found a set of hormone-responsive lineage-specific transcription factors, FOXA1, GATA3, ERα, directly drove high expression of ARSD through chromatin looping in luminal subtype BC cells. Opposingly, ARSD still subjected to XCI in TNBC cells mediated by Xist, CpG islands methylation, and inhibitory histone modification. Unexpectedly, we also found that ectopic ARSD overexpression could inhibit proliferation and migration of TNBC cells by activating Hippo/YAP pathway, indicating that ARSD may be a molecule brake on ERα signaling pathway, which restricted ERα to be an uncontrolled active status. Combined with other peoples' researches that Hippo signaling maintained ER expression and ER + BC growth, we believed that there should exist a regulative feedback loop formation among ERα, ARSD, and Hippo/YAP pathway. Collectively, our findings will help filling the knowledge gap about the influence of ARSD on BC and providing evidence that ARSD may serve as a potential marker to predict prognosis and as a therapeutic target.

RASSF1A-Mediated Suppression of Estrogen Receptor Alpha (ERα)-Driven Breast Cancer Cell Growth Depends on the Hippo-Kinases LATS1 and 2

Around 70% of breast cancers express the estrogen receptor alpha (ERα). This receptor is of central importance for breast cancer development and estrogen-dependent tumor growth. However, the molecular mechanisms that are responsible for the control of ERα expression and function in the context of breast carcinogenesis are complex and not fully understood. In previous work, we have demonstrated that the tumor suppressor RASSF1A suppresses estrogen-dependent growth of breast cancer cells through a complex network that keeps ERα expression and function under control. We observed that RASSF1A mediates the suppression of ERα expression through modulation of the Hippo effector Yes-associated protein 1 (YAP1) activity. Here we report that RASSF1A-mediated alteration of YAP1 depends on the Hippo-kinases LATS1 and LATS2. Based on these results, we conclude that inactivation of RASSF1A causes changes in the function of the Hippo signaling pathway and altered activation of YAP1, and as a consequence, increased expression and function of ERα. Thus, the inactivation of RASSF1A might constitute a fundamental event that supports the initiation of ERα-dependent breast cancer. Furthermore, our results support the notion that the Hippo pathway is important for the suppression of luminal breast cancers, and that the tumor-suppressor function of RASSF1A depends on LATS1 and LATS2.

The two sides of Hippo pathway in cancer

The Hippo signaling pathway was originally characterized by genetic studies in Drosophila to regulate tissue growth and organ size, and the core components of this pathway are highly conserved in mammals. Studies over the past two decades have revealed critical physiological and pathological functions of the Hippo tumor-suppressor pathway, which is tightly regulated by a broad range of intracellular and extracellular signals. These properties enable the Hippo pathway to serve as an important controller in organismal development and adult tissue homeostasis. Dysregulation of the Hippo signaling has been observed in many cancer types, suggesting the possibility of cancer treatment by targeting the Hippo pathway. The general consensus is that Hippo has tumor suppressor function. However, growing evidence also suggests that the function of the Hippo pathway in malignancy is cancer context dependent as recent studies indicating tumor promoting function of LATS. This article surveys the Hippo pathway signaling mechanisms and then reviews both the tumor suppressing and promoting function of this pathway. A comprehensive understanding of the dual roles of the Hippo pathway in cancer will benefit future therapeutic targeting of the Hippo pathway for cancer treatment.

Identification of TAZ-Dependent Breast Cancer Vulnerabilities Using a Chemical Genomics Screening Approach

Breast cancer stem cells (BCSCs) represent a subpopulation of tumor cells that can self-renew and generate tumor heterogeneity. Targeting BCSCs may ameliorate therapy resistance, tumor growth, and metastatic progression. However, the origin and molecular mechanisms underlying their cellular properties are poorly understood. The transcriptional coactivator with PDZ-binding motif (TAZ) promotes mammary stem/progenitor cell (MaSC) expansion and maintenance but also confers stem-like traits to differentiated tumor cells. Here, we describe the rapid generation of experimentally induced BCSCs by TAZ-mediated reprogramming of human mammary epithelial cells, hence allowing for the direct analysis of BCSC phenotypes. Specifically, we establish genetically well-defined TAZ-dependent (TAZ_DEP) and -independent (TAZ_IND) cell lines with cancer stem cell (CSC) traits, such as self-renewal, variable resistance to chemotherapeutic agents, and tumor seeding potential. TAZ_DEP cells were associated with the epithelial to mesenchymal transition, embryonic, and MaSC signature genes. In contrast, TAZ_IND cells were characterized by a neuroendocrine transdifferentiation transcriptional program associated with Polycomb repressive complex 2 (PRC2). Mechanistically, we identify Cyclin D1 (CCND1) as a critical downstream effector for TAZ-driven tumorigenesis. Overall, our results reveal a critical TAZ-CCND1-CDK4/CDK6 signaling axis, suggesting novel therapeutic approaches to eliminate both BCSCs and therapy-resistant cancer cells.