YAP1 increases organ size and expands undifferentiated progenitor cells

Hippo signaling effectors YAP and TAZ induce Epstein-Barr Virus (EBV) lytic reactivation through TEADs in epithelial cells

The Epstein-Barr virus (EBV) human herpesvirus is associated with B-cell and epithelial-cell malignancies, and both the latent and lytic forms of viral infection contribute to the development of EBV-associated tumors. Here we show that the Hippo signaling effectors, YAP and TAZ, promote lytic EBV reactivation in epithelial cells. The transcriptional co-activators YAP/TAZ (which are inhibited by Hippo signaling) interact with DNA-binding proteins, particularly TEADs, to induce transcription. We demonstrate that depletion of either YAP or TAZ inhibits the ability of phorbol ester (TPA) treatment, cellular differentiation or the EBV BRLF1 immediate-early (IE) protein to induce lytic EBV reactivation in oral keratinocytes, and show that over-expression of constitutively active forms of YAP and TAZ reactivate lytic EBV infection in conjunction with TEAD family members. Mechanistically, we find that YAP and TAZ interact with, and activate, the EBV BZLF1 immediate-early promoter. Furthermore, we demonstrate that YAP, TAZ, and TEAD family members are expressed at much higher levels in epithelial cell lines in comparison to B-cell lines, and find that EBV infection of oral keratinocytes increases the level of activated (dephosphorylated) YAP and TAZ. Finally, we have discovered that lysophosphatidic acid (LPA), a known YAP/TAZ activator that plays an important role in inflammation, induces EBV lytic reactivation in epithelial cells through a YAP/TAZ dependent mechanism. Together these results establish that YAP/TAZ are powerful inducers of the lytic form of EBV infection and suggest that the ability of EBV to enter latency in B cells at least partially reflects the extremely low levels of YAP/TAZ and TEADs in this cell type.

The hippo pathway: A master regulator of liver metabolism, regeneration, and disease

The liver is the only visceral organ in the body with a tremendous capacity to regenerate in response to insults that induce inflammation, cell death, and injury. Liver regeneration is a complicated process involving a well-orchestrated activation of non-parenchymal cells in the injured area and proliferation of undamaged hepatocytes. Furthermore, the liver has a Hepatostat, defined as adjustment of its volume to that required for homeostasis. Understanding the mechanisms that control different steps of liver regeneration is critical to informing therapies for liver repair, to help patients with liver disease. The Hippo signaling pathway is well known for playing an essential role in the control and regulation of liver size, regeneration, stem cell self-renewal, and liver cancer. Thus, the Hippo pathway regulates dynamic cell fates in liver, and in absence of its downstream effectors YAP and TAZ, liver regeneration is severely impaired, and the proliferative expansion of liver cells blocked. We will mainly review upstream mechanisms activating the Hippo signaling pathway following partial hepatectomy in mouse model and patients, its roles during different steps of liver regeneration, metabolism, and cancer. We will also discuss how targeting the Hippo signaling cascade might improve liver regeneration and suppress liver tumorigenesis.

Astrocytic YAP protects the optic nerve and retina in an experimental autoimmune encephalomyelitis model through TGF-β signaling

Rationale: Optic neuritis is one of main symptoms in multiple sclerosis (MS) that causes visual disability. Astrocytes are pivotal regulators of neuroinflammation in MS, and astrocytic yes-associated protein (YAP) plays a critical role in neuroinflammation. Meanwhile, YAP signaling is involved in visual impairment, including glaucoma, retinal choroidal atrophy and retinal detachment. However, the roles and underlying mechanisms of astrocytic YAP in neuroinflammation and demyelination of MS-related optic neuritis (MS-ON) remains unclear. Methods: To assess the functions of YAP in MS-ON, experimental autoimmune encephalomyelitis (EAE, a common model of MS) was established, and mice that conditional knockout (CKO) of YAP in astrocytes, YAPGFAP-CKO mice, were successfully generated. Behavior tests, immunostaining, Nissl staining, Hematoxylin-Eosin (HE) staining, TUNEL staining, Luxol Fast Blue (LFB) staining, electron microscopy (EM), quantitative real-time PCR (qPCR), gene set enrichment analysis (GSEA) and gene set variation analysis (GSVA) by RNA sequencing were used to examine the function and mechanism of YAP signaling based on these YAPGFAP-CKO mice and EAE model mice. To further explore the potential treatment of YAP signaling in EAE, EAE mice were treated with various drugs, including SRI-011381 that is an agonist of transforming growth factor-β (TGF-β) pathway, and XMU-MP-1 which inhibits Hippo kinase MST1/2 to activate YAP. Results: We found that YAP was significantly upregulated and activated in the astrocytes of optic nerve in EAE mice. Conditional knockout of YAP in astrocytes caused more severe inflammatory infiltration and demyelination in optic nerve, and damage of retinal ganglion cells (RGCs) in EAE mice. Moreover, YAP deletion in astrocytes promoted the activation of astrocytes and microglia, but inhibited the proliferation of astrocytes of optic nerve in EAE mice. Mechanically, TGF-β signaling pathway was significantly down-regulated after YAP deletion in astrocytes. Additionally, both qPCR and immunofluorescence assays confirmed the reduction of TGF-β signaling pathway in YAPGFAP-CKO EAE mice. Interestingly, SRI-011381 partially rescued the deficits in optic nerve and retina of YAPGFAP-CKO EAE mice. Finally, activation of YAP signaling by XMU-MP-1 relieved the neuroinflammation and demyelination in optic nerve of EAE mice. Conclusions: These results suggest astrocytic YAP may prevent the neuroinflammatory infiltration and demyelination through upregulation of TGF-β signaling and provide targets for the development of therapeutic strategies tailored for MS-ON.

Hippo-Yap Pathway Orchestrates Neural Crest Ontogenesis

Neural crest (NC) cells are a migratory stem cell population in vertebrate embryogenesis that can give rise to multiple cell types, including osteoblasts, chondrocytes, smooth muscle cells, neurons, glia, and melanocytes, greatly contributing to the development of different tissues and organs. Defects in NC development are implicated in many human diseases, such as numerous syndromes, craniofacial aberration and congenital heart defects. Research on NC development has gained intense interest and made significant progress. Recent studies showed that the Hippo-Yap pathway, a conserved fundamental pathway with key roles in regulation of cell proliferation, survival, and differentiation, is indispensable for normal NC development. However, the roles and mechanisms of the Hippo-Yap pathway in NC development remain largely unknown. In this review, we summarize the key functions of the Hippo-Yap pathway indicated in NC induction, migration, proliferation, survival, and differentiation, as well as the diseases caused by its dysfunction in NC cells. We also discuss emerging current and future studies in the investigation of the Hippo-Yap pathway in NC development.

Yes-associated protein expression is associated with poor prognosis in patients with colorectal cancer

Colorectal cancer (CRC) is the third leading cause of cancer-related death worldwide. The aim of the present study was to investigate the expression of yes-associated protein (YAP) in CRC tissues, and to determine the relationship between the expression levels of YAP and the clinicopathological characteristics and prognosis of patients with CRC. Bioinformatics analysis was conducted to examine the expression of YAP and its correlation with clinicopathological characteristics and key genes, using functional enrichment analysis. Immunohistochemistry was used to detect YAP expression in 181 CRC tissue samples and 30 normal colorectal mucosa samples. Western blotting and reverse transcription-quantitative PCR were performed to detect the expression of YAP and β-catenin in CRC cells, and cellular proliferation was assessed using a Cell Counting Kit-8 assay. Finally, apoptosis was analyzed using flow cytometry. Immunohistochemical staining indicated that the positive expression rate of YAP in CRC tissues was 73.5%, which was significantly higher than that in normal colorectal mucosa samples. The expression of YAP in CRC was associated with histological differentiation, lymph node metastasis and Duke's stage. However, no significant associations were observed between YAP expression and age, sex and T stage. Downregulation of YAP promoted the proliferation and the inhibited apoptosis of CRC cells, and YAP expression was positively correlated with that of β-catenin in both CRC tissues and cells. Furthermore, YAP expression was upregulated in CRC tissues, which was correlated with tumor progression and prognosis. Therefore, YAP expression may be used as an independent predictor of poor prognosis in patients with CRC, and the underling molecular mechanism may be associated with the combined effect of Hippo and Wnt/β-catenin signaling.

Extracellular matrix and Hippo signaling as therapeutic targets of antifibrotic compounds for uterine fibroids

BACKGROUND

Uterine fibroids are highly prevalent, collagen-rich, mechanically stiff, fibrotic tumors for which new therapeutic options are needed. Increased extracellular matrix (ECM) stiffness activates mechanical signaling and Hippo/YAP promoting fibroid growth, but no prior studies have tested either as a therapeutic target. We tested the hypothesis that injection of a purified form of collagenase Clostridium histolyticum (CCH) that selectively digests type I and type III collagens would alter ECM stiffness, Hippo signaling, and selectively reduce fibroid cell growth. We also used two FDA-approved drugs, verteporfin and nintedanib, to elucidate the role of Hippo/YAP signaling in uterine fibroid and myometrial cells.

METHODS

The clinical trial was registered (NCT02889848). Stiffness of samples was measured by rheometry. Protein expression in surgical samples was analyzed via immunofluorescence. Protein and gene expression in uterine fibroid or myometrial cell lines were measured by real time PCR and western blot, and immunofluorescence.

RESULTS

Injection of CCH at high doses (0.1-0.2 mg/cm3 ) into fibroids resulted in a 46% reduction in stiffness in injected fibroids compared to controls after 60 days. Levels of the cell proliferation marker proliferative cell nuclear antigen (PCNA) were decreased in fibroids 60 days after injection at high doses of CCH. Key Hippo signaling factors, specifically the transcriptionally inactive phosphorylated YAP (p-YAP), was increased at high CCH doses, supporting the role of YAP in fibroid growth. Furthermore, inhibition of YAP via verteporfin (YAP inhibitor) decreased cell proliferation, gene and protein expression of key factors promoting fibrosis and mechanotransduction in fibroid cells. Additionally, the anti-fibrotic drug, nintedanib, inhibited YAP and showed anti-fibrotic effects.

CONCLUSIONS

This is the first report that in vivo injection of collagenase into uterine fibroids led to a reduction in Hippo/YAP signaling and crucial genes and pathways involved in fibroid growth. These results indicate that targeting ECM stiffness and Hippo signaling might be an effective strategy for uterine fibroids.

Functional Genomic Screening During Somatic Cell Reprogramming Identifies DKK3 as a Roadblock of Organ Regeneration

Somatic cell reprogramming and tissue repair share relevant factors and molecular programs. Here, Dickkopf-3 (DKK3) is identified as novel factor for organ regeneration using combined transcription-factor-induced reprogramming and RNA-interference techniques. Loss of Dkk3 enhances the generation of induced pluripotent stem cells but does not affect de novo derivation of embryonic stem cells, three-germ-layer differentiation or colony formation capacity of liver and pancreatic organoids. However, DKK3 expression levels in wildtype animals and serum levels in human patients are elevated upon injury. Accordingly, Dkk3-null mice display less liver damage upon acute and chronic failure mediated by increased proliferation in hepatocytes and LGR5+ liver progenitor cell population, respectively. Similarly, recovery from experimental pancreatitis is accelerated. Regeneration onset occurs in the acinar compartment accompanied by virtually abolished canonical-Wnt-signaling in Dkk3-null animals. This results in reduced expression of the Hedgehog repressor Gli3 and increased Hedgehog-signaling activity upon Dkk3 loss. Collectively, these data reveal Dkk3 as a key regulator of organ regeneration via a direct, previously unacknowledged link between DKK3, canonical-Wnt-, and Hedgehog-signaling.

Concurrent YAP/TAZ and SMAD signaling mediate vocal fold fibrosis

Vocal fold (VF) fibrosis is a major cause of intractable voice-related disability and reduced quality of life. Excision of fibrotic regions is suboptimal and associated with scar recurrence and/or further iatrogenic damage. Non-surgical interventions are limited, putatively related to limited insight regarding biochemical events underlying fibrosis, and downstream, the lack of therapeutic targets. YAP/TAZ integrates diverse cell signaling events and interacts with signaling pathways related to fibrosis, including the TGF-β/SMAD pathway. We investigated the expression of YAP/TAZ following vocal fold injury in vivo as well as the effects of TGF-β1 on YAP/TAZ activity in human vocal fold fibroblasts, fibroblast-myofibroblast transition, and TGF-β/SMAD signaling. Iatrogenic injury increased nuclear localization of YAP and TAZ in fibrotic rat vocal folds. In vitro, TGF-β1 activated YAP and TAZ in human VF fibroblasts, and inhibition of YAP/TAZ reversed TGF-β1-stimulated fibroplastic gene upregulation. Additionally, TGF-β1 induced localization of YAP and TAZ in close proximity to SMAD2/3, and nuclear accumulation of SMAD2/3 was inhibited by a YAP/TAZ inhibitor. Collectively, YAP and TAZ were synergistically activated with the TGF-β/SMAD pathway, and likely essential for the fibroplastic phenotypic shift in VF fibroblasts. Based on these data, YAP/TAZ may evolve as an attractive therapeutic target for VF fibrosis.

Honokiol Affects Stem Cell Viability by Suppressing Oncogenic YAP1 Function to Inhibit Colon Tumorigenesis

Honokiol (HNK) is a biphenolic compound that has been used in traditional medicine for treating various ailments, including cancers. In this study, we determined the effect of HNK on colon cancer cells in culture and in a colitis-associated cancer model. HNK treatment inhibited proliferation and colony formation while inducing apoptosis. In addition, HNK suppressed colonosphere formation. Molecular docking suggests that HNK interacts with reserve stem cell marker protein DCLK1, with a binding energy of -7.0 Kcal/mol. In vitro kinase assays demonstrated that HNK suppressed the DCLK1 kinase activity. HNK also suppressed the expression of additional cancer stem cell marker proteins LGR5 and CD44. The Hippo signaling pathway is active in intestinal stem cells. In the canonical pathway, YAP1 is phosphorylated at Ser127 by upstream Mst1/2 and Lats1/2. This results in the sequestration of YAP1 in the cytoplasm, thereby not allowing YAP1 to translocate to the nucleus and interact with TEAD1-4 transcription factors to induce gene expression. However, HNK suppressed Ser127 phosphorylation in YAP1, but the protein remains sequestered in the cytoplasm. We further determined that this occurs by YAP1 interacting with PUMA. To determine if this also occurs in vivo, we performed studies in an AOM/DSS induced colitis-associated cancer model. HNK administered by oral gavage at a dose of 5mg/kg bw for 24 weeks demonstrated a significant reduction in the expression of YAP1 and TEAD1 and in the stem marker proteins. Together, these data suggest that HNK prevents colon tumorigenesis in part by inducing PUMA-YAP1 interaction and cytoplasmic sequestration, thereby suppressing the oncogenic YAP1 activity.

Fascin1 empowers YAP mechanotransduction and promotes cholangiocarcinoma development

Mechanical forces control cell behavior, including cancer progression. Cells sense forces through actomyosin to activate YAP. However, the regulators of F-actin dynamics playing relevant roles during mechanostransduction in vitro and in vivo remain poorly characterized. Here we identify the Fascin1 F-actin bundling protein as a factor that sustains YAP activation in response to ECM mechanical cues. This is conserved in the mouse liver, where Fascin1 regulates YAP-dependent phenotypes, and in human cholangiocarcinoma cell lines. Moreover, this is relevant for liver tumorigenesis, because Fascin1 is required in the AKT/NICD cholangiocarcinogenesis model and it is sufficient, together with AKT, to induce cholangiocellular lesions in mice, recapitulating genetic YAP requirements. In support of these findings, Fascin1 expression in human intrahepatic cholangiocarcinomas strongly correlates with poor patient prognosis. We propose that Fascin1 represents a pro-oncogenic mechanism that can be exploited during intrahepatic cholangiocarcinoma development to overcome a mechanical tumor-suppressive environment.

Utilizing the Hippo pathway as a therapeutic target for combating endocrine-resistant breast cancer

Drug resistance is always a great obstacle in any endocrine therapy of breast cancer. Although the combination of endocrine therapy and targeted therapy has been shown to significantly improve prognosis, refractory endocrine resistance is still common. Dysregulation of the Hippo pathway is often related to the occurrence and the development of many tumors. Targeted therapies of this pathway have played important roles in the study of triple negative breast cancer (TNBC). Targeting the Hippo pathway in combination with chemotherapy or other targeted therapies has been shown to significantly improve specific antitumor effects and reduce cancer antidrug resistance. Further exploration has shown that the Hippo pathway is closely related to endocrine resistance, and it plays a "co-correlation point" role in numerous pathways involving endocrine resistance, including related pathways in breast cancer stem cells (BCSCs). Agents and miRNAs targeting the components of the Hippo pathway are expected to significantly enhance the sensitivity of breast cancer cells to endocrine therapy. This review initially explains the possible mechanism of the Hippo pathway in combating endocrine resistance, and it concludes by recommending endocrine therapy in combination with therapies targeting the Hippo pathway in the study of endocrine-resistant breast cancers.

Hippo pathway: Regulation, deregulation and potential therapeutic targets in cancer

Hippo pathway is a master regulator of development, cell proliferation, stem cell function, tissue regeneration, homeostasis, and organ size control. Hippo pathway relays signals from different extracellular and intracellular events to regulate cell behavior and functions. Hippo pathway is conserved from Protista to eukaryotes. Deregulation of the Hippo pathway is associated with numerous cancers. Alteration of the Hippo pathway results in cell invasion, migration, disease progression, and therapy resistance in cancers. However, the function of the various components of the mammalian Hippo pathway is yet to be elucidated in detail especially concerning tumor biology. In the present review, we focused on the Hippo pathway in different model organisms, its regulation and deregulation, and possible therapeutic targets for cancer treatment.

High Yap and Mll1 promote a persistent regenerative cell state induced by Notch signaling and loss of p53

Specified intestinal epithelial cells reprogram and contribute to the regeneration and renewal of the epithelium upon injury. Mutations that deregulate such renewal processes may contribute to tumorigenesis. Using intestinal organoids, we show that concomitant activation of Notch signaling and ablation of p53 induce a highly proliferative and regenerative cell state, which is associated with increased levels of Yap and the histone methyltransferase Mll1. The induced signaling system orchestrates high proliferation, self-renewal, and niche-factor-independent growth, and elevates the trimethylation of histone 3 at lysine 4 (H3K4me3). We demonstrate that Yap and Mll1 are also elevated in patient-derived colorectal cancer (CRC) organoids and control growth and viability. Our data suggest that Notch activation and p53 ablation induce a signaling circuitry involving Yap and the epigenetic regulator Mll1, which locks cells in a proliferative and regenerative state that renders them susceptible for tumorigenesis.

Expression pattern of transcriptional enhanced associate domain family member 1 (Tead1) in developing mouse molar tooth

The Hippo pathway is essential for determining organ size by regulating cell proliferation. Previous reports have shown that impairing this pathway causes abnormal tooth development. However, the precise expression profile of the members of the transcriptional enhanced associate domain family (Tead), which are key transcription factors mediating Yap function, during tooth development is unclear. In this study, among the four isoforms of Tead (Tead1 - 4), only the expression of Tead1 mRNA was observed using semiquantitative RT- PCR in murine developing tooth germ at E16.5. The expression level of Tead1 mRNA in the excised murine mandibular molar tooth germ was significantly higher at E16.5 than at other developmental stages, as determined using quantitative PCR. We found that the mRNA expression of connective tissue growth factor (Ctgf), which is one of the Yap target genes directly controlling cell growth, changed consistently with that of Tead1 in developing molars. Fluorescent immunostaining revealed that Tead1 protein was expressed in both epithelial cells and mesenchymal cells of the dental lamina and dental epithelium, including the primary enamel knot during the cap stage. During the early bell stage (E16.5), Tead1 was expressed intensely in the inner and outer enamel epithelium, including the secondary enamel knot and the neighboring mesenchymal cells. Tead1 then specifically localized to the inner and outer enamel epithelium, which is responsible for enamel formation during the bell stage. These expression patterns were consistent with those of Yap, Taz, and Ctgf protein in developing molars. These results suggest that Tead1 acts as a mediator of the biological functions of Yap, such as the morphogenesis of cusp formation, during tooth development.

Expression levels and activation status of Yap splicing isoforms determine self-renewal and differentiation potential of embryonic stem cells

Yap is the key effector of Hippo signaling; however, its role in embryonic stem cells (ESCs) remains controversial. Here, we identify two Yap splicing isoforms (Yap472 and Yap488), which show equal expression levels but heterogeneous distribution in ESCs. Knockout (KO) of both isoforms reduces ESC self-renewal, accelerates pluripotency exit, but arrests terminal differentiation, while overexpression of each isoform leads to the reverse phenotype. The effect of both Yap isoforms on self-renewal is Teads-dependent and mediated by c-Myc. Nonetheless, different isoforms are found to affect overlapping yet distinct genes, and confer different developmental potential to Yap-KO cells, with Yap472 exerting a more pronounced biological effect and being more essential for neuroectoderm differentiation. Constitutive activation of Yaps, particularly Yap472, dramatically upregulates p53 and Cdx2, inducing trophectoderm trans-differentiation even under self-renewal conditions. These findings reveal the combined roles of different Yap splicing isoforms and mechanisms in regulating self-renewal efficiency and differentiation potential of ESCs.

Heterozygous Loss of Yap1 in Mice Causes Progressive Cataracts

Purpose

Yap1 encodes an evolutionarily conserved transcriptional coactivator and functions as a down-stream effector of the Hippo signaling pathway that controls tissue size and cell growth. Yap1 contributes to lens epithelial development. However, the effect of Yap1 haplodeficiency on the lens epithelium and its role in the development of cataracts has not been reported. The aim of the current study is to investigate Yap1 function and its regulatory mechanisms in lens epithelial cells (LECs).

Methods

Lens phenotypes were investigated in Yap1 heterozygous mutant mice by visual observation and histological and biochemical methods. Primary LEC cultures were used to study regulatory molecular mechanism.

Results

The heterozygous inactivation of Yap1 in mice caused cataracts during adulthood with defective LEC phenotypes. Despite a normal early development of the eye including the lens, the majority of Yap1 heterozygotes developed cataracts in the first six months of age. Cataract was preceded by multiple morphological defects in the lens epithelium, including decreased cell density and abnormal cell junctions. The low LEC density was coincident with reduced LEC proliferation. In addition, expression of the Yap1 target gene Crim1 was reduced in the Yap1^+/− LEC, and overexpression of Crim1 restored Yap1^+/− LEC cell proliferation in vitro.

Conclusions

Homozygosity of the Yap1 gene was critical for adequate Crim1 expression needed to maintain the constant proliferation of LEC and to maintain a normal-sized lens. Yap1 haplodeficiency leads to cataracts.

Yes-Associated Protein Is Crucial for Constitutive Androstane Receptor-Driven Hepatocyte Proliferation But Not for Induction of Drug Metabolism Genes in Mice

BACKGROUND AND AIMS

Constitutive androstane receptor (CAR) agonists, such as 1,4-bis [2-(3,5-dichloropyridyloxy)] benzene (TCPOBOP), are known to cause robust hepatocyte proliferation and hepatomegaly in mice along with induction of drug metabolism genes without any associated liver injury. Yes-associated protein (Yap) is a key transcription regulator that tightly controls organ size, including that of liver. Our and other previous studies suggested increased nuclear localization and activation of Yap after TCPOBOP treatment in mice and the potential role of Yap in CAR-driven proliferative response. Here, we investigated a direct role of Yap in CAR-driven hepatomegaly and hepatocyte proliferation using hepatocyte-specific Yap-knockout (KO) mice.

APPROACH AND RESULTS

Adeno-associated virus 8-thyroxine binding globulin promoter-Cre recombinase vector was injected to Yap-floxed mice for achieving hepatocyte-specific Yap deletion followed by TCPOBOP treatment. Yap deletion did not decrease protein expression of CAR or CAR-driven induction of drug metabolism genes (including cytochrome P450 [Cyp] 2b10, Cyp2c55, and UDP-glucuronosyltransferase 1a1 [Ugt1a1]). However, Yap deletion substantially reduced TCPOBOP-induced hepatocyte proliferation. TCPOBOP-driven cell cycle activation was disrupted in Yap-KO mice because of delayed (and decreased) induction of cyclin D1 and higher expression of p21, resulting in decreased phosphorylation of retinoblastoma protein. Furthermore, the induction of other cyclins, which are sequentially involved in progression through cell cycle (including cyclin E1, A2, and B1), and important mitotic regulators (such as Aurora B kinase and polo-like kinase 1) was remarkably reduced in Yap-KO mice. Microarray analysis revealed that 26% of TCPOBOP-responsive genes that were mainly related to proliferation, but not to drug metabolism, were altered by Yap deletion. Yap regulated these proliferation genes through alerting expression of Myc and forkhead box protein M1, two critical transcriptional regulators of CAR-mediated hepatocyte proliferation.

CONCLUSIONS

Our study revealed an important role of Yap signaling in CAR-driven hepatocyte proliferation; however, CAR-driven induction of drug metabolism genes was independent of Yap.

The ZMYND8-regulated mevalonate pathway endows YAP-high intestinal cancer with metabolic vulnerability

Cholesterol metabolism is tightly associated with colorectal cancer (CRC). Nevertheless, the clinical benefit of statins, the inhibitor of cholesterol biogenesis mevalonate (MVA) pathway, is inconclusive, possibly because of a lack of patient stratification criteria. Here, we describe that YAP-mediated zinc finger MYND-type containing 8 (ZMYND8) expression sensitizes intestinal tumors to the inhibition of the MVA pathway. We show that the oncogenic activity of YAP relies largely on ZMYND8 to enhance intracellular de novo cholesterol biogenesis. Disruption of the ZMYND8-dependent MVA pathway greatly restricts the self-renewal capacity of Lgr5⁺ intestinal stem cells (ISCs) and intestinal tumorigenesis. Mechanistically, ZMYND8 and SREBP2 drive the enhancer-promoter interaction to facilitate the recruitment of Mediator complex, thus upregulating MVA pathway genes. Together, our results establish that the epigenetic reader ZMYND8 endows YAP-high intestinal cancer with metabolic vulnerability.

The Act of Controlling Adult Stem Cell Dynamics: Insights from Animal Models

Adult stem cells (ASCs) are the undifferentiated cells that possess self-renewal and differentiation abilities. They are present in all major organ systems of the body and are uniquely reserved there during development for tissue maintenance during homeostasis, injury, and infection. They do so by promptly modulating the dynamics of proliferation, differentiation, survival, and migration. Any imbalance in these processes may result in regeneration failure or developing cancer. Hence, the dynamics of these various behaviors of ASCs need to always be precisely controlled. Several genetic and epigenetic factors have been demonstrated to be involved in tightly regulating the proliferation, differentiation, and self-renewal of ASCs. Understanding these mechanisms is of great importance, given the role of stem cells in regenerative medicine. Investigations on various animal models have played a significant part in enriching our knowledge and giving In Vivo in-sight into such ASCs regulatory mechanisms. In this review, we have discussed the recent In Vivo studies demonstrating the role of various genetic factors in regulating dynamics of different ASCs viz. intestinal stem cells (ISCs), neural stem cells (NSCs), hematopoietic stem cells (HSCs), and epidermal stem cells (Ep-SCs).

TAZ-CAMTA1 and YAP-TFE3 alter the TAZ/YAP transcriptome by recruiting the ATAC histone acetyltransferase complex

Epithelioid hemangioendothelioma (EHE) is a vascular sarcoma that metastasizes early in its clinical course and lacks an effective medical therapy. The TAZ-CAMTA1 and YAP-TFE3 fusion proteins are chimeric transcription factors and initiating oncogenic drivers of EHE. A combined proteomic/genetic screen in human cell lines identified YEATS2 and ZZZ3, components of the Ada2a-containing histone acetyltransferase (ATAC) complex, as key interactors of both fusion proteins despite the dissimilarity of the C terminal fusion partners CAMTA1 and TFE3. Integrative next-generation sequencing approaches in human and murine cell lines showed that the fusion proteins drive a unique transcriptome by simultaneously hyperactivating a TEAD-based transcriptional program and modulating the chromatin environment via interaction with the ATAC complex. Interaction of the ATAC complex with both fusion proteins indicates that it is a key oncogenic driver and unifying enzymatic therapeutic target for this sarcoma. This study presents an approach to mechanistically dissect how chimeric transcription factors drive the formation of human cancers.

The proliferation of human cells is tightly regulated to ensure that enough cells are made to build and repair organs and tissues, while at the same time stopping cells from dividing uncontrollably and damaging the body. To get the right balance, cells rely on physical and chemical cues from their environment that trigger the biochemical signals that regulate two proteins called TAZ and YAP. These proteins control gene activity by regulating the rate at which genes are copied to produce proteins. If this process becomes dysregulated, cells can grow uncontrollably, causing cancer.

In cancer cells, it is common to find TAZ and YAP fused to other proteins. In epithelioid hemangioendothelioma, a rare cancer that grows in the blood vessels, cancerous growth can be driven by a version of TAZ fused to the protein CAMTA1, or a version of YAP fused to the protein TFE3. While the role of TAZ and YAP in promoting gene activity is known, it is unclear how CAMTA1 and TFE3 contribute to cell growth becoming dysregulated.

Merritt, Garcia et al. studied sarcoma cell lines to show that these two fusion proteins, TAZ-CAMTA1 and YAP-TFE3, change the pattern of gene activity seen in the cells compared to TAZ or YAP alone. An analysis of molecules that interact with the two fusion proteins identified a complex called ATAC as the cause of these changes. This complex adds chemical markers to DNA-packaging proteins, which control which genes are available for activation. The fusion proteins combine the ability of TAZ and YAP to control gene activity and the ability of CAMTA1 and TFE3 to make DNA more accessible, allowing the fusion proteins to drive uncontrolled cancerous growth.

Similar TAZ and YAP fusion proteins have been found in other cancers, which can activate genes and potentially alter DNA packaging. Targeting drug development efforts at the proteins that complex with TAZ and YAP fusion proteins may lead to new therapies.

New Insights into YES-Associated Protein Signaling Pathways in Hematological Malignancies: Diagnostic and Therapeutic Challenges

Simple Summary

YES-associated protein (YAP) is a co-transcriptional activator that binds to transcriptional factors to increase the rate of transcription of a set of genes, and it can intervene in the onset and progression of different tumors. Most of the data in the literature refer to the effects of the YAP system in solid neoplasms. In this review, we analyze the possibility that YAP can also intervene in hematological neoplasms such as lymphomas, multiple myeloma, and acute and chronic leukemias, modifying the phenomena of cell proliferation and cell death. The possibilities of pharmacological intervention related to the YAP system in an attempt to use its modulation therapeutically are also discussed.

Abstract

The Hippo/YES-associated protein (YAP) signaling pathway is a cell survival and proliferation-control system with its main activity that of regulating cell growth and organ volume. YAP operates as a transcriptional coactivator in regulating the onset, progression, and treatment response in numerous human tumors. Moreover, there is evidence suggesting the involvement of YAP in the control of the hematopoietic system, in physiological conditions rather than in hematological diseases. Nevertheless, several reports have proposed that the effects of YAP in tumor cells are cell-dependent and cell-type-determined, even if YAP usually interrelates with extracellular signaling to stimulate the onset and progression of tumors. In the present review, we report the most recent findings in the literature on the relationship between the YAP system and hematological neoplasms. Moreover, we evaluate the possible therapeutic use of the modulation of the YAP system in the treatment of malignancies. Given the effects of the YAP system in immunosurveillance, tumorigenesis, and chemoresistance, further studies on interactions between the YAP system and hematological malignancies will offer very relevant information for the targeting of these diseases employing YAP modifiers alone or in combination with chemotherapy drugs.

A calcineurin-mediated scaling mechanism that controls a K+-leak channel to regulate morphogen and growth factor transcription

The increase in activity of the two-pore potassium-leak channel Kcnk5b maintains allometric juvenile growth of adult zebrafish appendages. However, it remains unknown how this channel maintains allometric growth and how its bioelectric activity is regulated to scale these anatomical structures. We show the activation of Kcnk5b is sufficient to activate several genes that are part of important development programs. We provide in vivo transplantation evidence that the activation of gene transcription is cell autonomous. We also show that Kcnk5b will induce the expression of different subsets of the tested developmental genes in different cultured mammalian cell lines, which may explain how one electrophysiological stimulus can coordinately regulate the allometric growth of diverse populations of cells in the fin that use different developmental signals. We also provide evidence that the post-translational modification of serine 345 in Kcnk5b by calcineurin regulates channel activity to scale the fin. Thus, we show how an endogenous bioelectric mechanism can be regulated to promote coordinated developmental signaling to generate and scale a vertebrate appendage.

Biomaterials Regulate Mechanosensors YAP/TAZ in Stem Cell Growth and Differentiation

Tissue-resident stem cells are surrounded by a microenvironment known as 'stem cell niche' which is specific for each stem cell type. This niche comprises of cell-intrinsic and -extrinsic factors like biochemical and biophysical signals, which regulate stem cell characteristics and differentiation. Biochemical signals have been thoroughly studied however, the effect of biophysical signals on stem cell regulation is yet to be completely understood. Biomaterials have aided in addressing this issue since they can provide a defined and tuneable microenvironment resembling in vivo conditions. We review various biomaterials used in many studies which have shown a connection between biomaterial-generated mechanical signals and alteration in stem cell behaviour. Researchers probed to understand the mechanism of mechanotransduction and reported that the signals from the extracellular matrix regulate a transcription factor yes-associated protein (YAP)/transcriptional coactivator with PDZ-binding motif (TAZ), which is a downstream-regulator of the Hippo pathway and it transduces the mechanical signals inside the nucleus. We highlight the role of the YAP/TAZ as mechanotransducers in stem cell self-renewal and differentiation in response to substrate stiffness, also the possibility of mechanobiology as the emerging field of regenerative medicines and three-dimensional tissue printing.

YAP-TEAD1 control of cytoskeleton dynamics and intracellular tension guides human pluripotent stem cell mesoderm specification

The tight regulation of cytoskeleton dynamics is required for a number of cellular processes, including migration, division and differentiation. YAP-TEAD respond to cell-cell interaction and to substrate mechanics and, among their downstream effects, prompt focal adhesion (FA) gene transcription, thus contributing to FA-cytoskeleton stability. This activity is key to the definition of adult cell mechanical properties and function. Its regulation and role in pluripotent stem cells are poorly understood. Human PSCs display a sustained basal YAP-driven transcriptional activity despite they grow in very dense colonies, indicating these cells are insensitive to contact inhibition. PSC inability to perceive cell-cell interactions can be restored by tampering with Tankyrase enzyme, thus favouring AMOT inhibition of YAP function. YAP-TEAD complex is promptly inactivated when germ layers are specified, and this event is needed to adjust PSC mechanical properties in response to physiological substrate stiffness. By providing evidence that YAP-TEAD1 complex targets key genes encoding for proteins involved in cytoskeleton dynamics, we suggest that substrate mechanics can direct PSC specification by influencing cytoskeleton arrangement and intracellular tension. We propose an aberrant activation of YAP-TEAD1 axis alters PSC potency by inhibiting cytoskeleton dynamics, thus paralyzing the changes in shape requested for the acquisition of the given phenotype.

Scaffolding Protein IQGAP1 Is Dispensable, but Its Overexpression Promotes Hepatocellular Carcinoma via YAP1 Signaling

IQ motif-containing GTPase-activating protein 1 (IQGAP1) is a ubiquitously expressed scaffolding protein that is overexpressed in a number of cancers, including liver cancer, and is associated with protumorigenic processes, such as cell proliferation, motility, and adhesion. IQGAP1 can integrate multiple signaling pathways and could be an effective antitumor target. Therefore, we examined the role of IQGAP1 in tumor initiation and promotion during liver carcinogenesis. We found that ectopic overexpression of IQGAP1 in the liver is not sufficient to initiate tumorigenesis. Moreover, we report that the tumor burden and cell proliferation in the diethylnitrosamine-induced liver carcinogenesis model in Iqgap1-/- mice may be driven by MET signaling. In contrast, IQGAP1 overexpression enhanced YAP activation and subsequent NUAK2 expression to accelerate and promote hepatocellular carcinoma (HCC) in a clinically relevant model expressing activated (S45Y) β-catenin and MET. Here, increasing IQGAP1 expression in vivo does not alter β-catenin or MET activation; instead, it promotes YAP activity. Overall, we demonstrate that although IQGAP1 expression is not required for HCC development, the gain of IQGAP1 function promotes the rapid onset and increased liver carcinogenesis. Our results show that an adequate amount of IQGAP1 scaffold is necessary to maintain the quiescent status of the liver.

Role of FAT1 in health and disease

FAT atypical cadherin 1 (FAT1), which encodes a protocadherin, is one of the most frequently mutated genes in human cancer. Over the past 20 years, the role of FAT1 in tissue growth and in the development of diseases has been extensively studied. There is definitive evidence that FAT1 serves a substantial role in the maintenance of organs and development, and its expression appears to be tissue-specific. FAT1 activates a variety of signaling pathways through protein-protein interactions, including the Wnt/β-catenin, Hippo and MAPK/ERK signaling pathways, which affect cell proliferation, migration and invasion. Abnormal FAT1 expression may lead to the development of tumors and may affect prognosis. Therefore, FAT1 may have potential in tumor therapy. The structural and functional changes mediated by FAT1, its tissue distribution and changes in FAT1 expression in human diseases are described in the present review, which provides further insight for understanding the role of FAT1 in development and disease.

Evidence for discrete modes of YAP1 signaling via mRNA splice isoforms in development and diseases

Yes-associated protein 1 (YAP1) is a transcriptional co-activator downstream of Hippo pathway. The pathway exerts crucial roles in organogenesis and its dysregulation is associated with the spreading of different cancer types. YAP1 gene encodes for multiple protein isoforms, whose specific functions are not well defined. We demonstrate the splicing of isoform-specific mRNAs is controlled in a stage- and tissue-specific fashion. We designed expression vectors encoding for the most-represented isoforms of YAP1 with either one or two WW domains and studied their specific signaling activities in YAP1 knock-out cell lines. YAP1 isoforms display both common and unique functions and activate distinct transcriptional programs, as the result of their unique protein interactomes. By generating TEAD-based transcriptional reporter cell lines, we demonstrate individual YAP1 isoforms display unique effects on cell proliferation and differentiation. Finally, we illustrate the complexity of the regulation of Hippo-YAP1 effector in physiological and in pathological conditions of the heart.

Glycyrrhizin Attenuates Carcinogenesis by Inhibiting the Inflammatory Response in a Murine Model of Colorectal Cancer

Glycyrrhizin (GL), an important active ingredient of licorice root, which weakens the proinflammatory effects of high-mobility group box 1 (HMGB1) by blocking HMGB1 signaling. In this study, we investigated whether GL could suppress inflammation and carcinogenesis in an azoxymethane (AOM)/dextran sodium sulfate (DSS)-induced murine model of colorectal cancer. ICR mice were divided into four groups (n = 5, each)—control group, GL group, colon cancer (CC) group, and GL-treated CC (CC + GL) group, and sacrificed after 20 weeks. Plasma levels of interleukin (IL)-6 and tumor necrosis factor (TNF)-α were measured using an enzyme-linked immunosorbent assay. The colonic tissue samples were immunohistochemically stained with DNA damage markers (8-nitroguanine and 8-oxo-7,8-dihydro-2′-deoxy-guanosine), inflammatory markers (COX-2 and HMGB1), and stem cell markers (YAP1 and SOX9). The average number of colonic tumors and the levels of IL-6 and TNF-α in the CC + GL group were significantly lower than those in the CC group. The levels of all inflammatory and cancer markers were significantly reduced in the CC + GL group. These results suggest that GL inhibits the inflammatory response by binding HMGB1, thereby inhibiting DNA damage and cancer stem cell proliferation and dedifferentiation. In conclusion, GL significantly attenuates the pathogenesis of AOM/DSS-induced colorectal cancer by inhibiting HMGB1-TLR4-NF-κB signaling.

Blockage of glioma cell survival by truncated TEAD-binding domain of YAP

BACKGROUND

Gliomas are highly aggressive and lack of efficient targeted therapy. YAP, as a Hippo pathway downstream effector, plays a key role in promoting tumor development through the interaction with transcription factor TEAD on the NH3-terminal proline-rich domain. Therefore, targeting TEAD-interacting domain of YAP may provide a novel approach for the treatment of gliomas.

MATERIALS AND METHODS

We generated a truncated YAP protein which includes the TEAD-binding domain (YAPBD), and supposed YAPBD can interact with endogenous TEAD but lost the function to activate YAP target gene expressions. The association of YAP expression with the malignant characters of glioma tissues were determined by immunohistochemistry. TEAD-binding capacity of YAPBD was determined by co-immunoprecipitation. The cell proliferation and migration were determined by MTT assay, xenograft assay, wound healing assay and transwell assay, respectively. YAP target genes were detected by Western blot.

RESULTS

YAP was highly expressed in glioma tissues and associated with tumor malignancy. YAPBD could block the TEAD-YAP complex formation by competing with YAP binding to TEAD. YAPBD could inhibit glioma cell growth both in vitro and in vivo, through the induction of cell cycle arrest and apoptosis. The cell cycle-related gene cyclin D1 and c-myc, and anti-apoptotic gene Bcl-2, Bcl-xL and survivin were inhibited after YAPBD overexpression. Furthermore, YAPBD also decreased cell migration and invasion, and repressed epithelial-mesenchymal transition.

CONCLUSION

YAPBD can block glioma cell survival and repress YAP-dependent gene expressions, indicating gene therapy which targets TEAD-YAP complex would be a potential and significant novel approach for human malignant gliomas.

Constitutive androstane receptor induced-hepatomegaly and liver regeneration is partially via yes-associated protein activation

The constitutive androstane receptor (CAR, NR3I1) belongs to nuclear receptor superfamily. It was reported that CAR agonist TCPOBOP induces hepatomegaly but the underlying mechanism remains largely unknown. Yes-associated protein (YAP) is a potent regulator of organ size. The aim of this study is to explore the role of YAP in CAR activation-induced hepatomegaly and liver regeneration. TCPOBOP-induced CAR activation on hepatomegaly and liver regeneration was evaluated in wild-type (WT) mice, liver-specific YAP-deficient mice, and partial hepatectomy (PHx) mice. The results demonstrate that TCPOBOP can increase the liver-to-body weight ratio in wild-type mice and PHx mice. Hepatocytes enlargement around central vein (CV) area was observed, meanwhile hepatocytes proliferation was promoted as evidenced by the increased number of KI67⁺ cells around portal vein (PV) area. The protein levels of YAP and its downstream targets were upregulated in TCPOBOP-treated mice and YAP translocation can be induced by CAR activation. Co-immunoprecipitation results suggested a potential protein–protein interaction of CAR and YAP. However, CAR activation-induced hepatomegaly can still be observed in liver-specific YAP-deficient (Yap^–/–) mice. In summary, CAR activation promotes hepatomegaly and liver regeneration partially by inducing YAP translocation and interaction with YAP signaling pathway, which provides new insights to further understand the physiological functions of CAR.

Liver Cancer: Therapeutic Challenges and the Importance of Experimental Models

Liver cancer is one of the main causes of death related to cancer worldwide; its etiology is related with infections by C or B hepatitis virus, alcohol consumption, smoking, obesity, nonalcoholic fatty liver disease, diabetes, and iron overload, among other causes. Several kinds of primary liver cancer occur, but we will focus on hepatocellular carcinoma (HCC). Numerous cellular signaling pathways are implicated in hepatocarcinogenesis, including YAP-HIPPO, Wnt-β-catenin, and nuclear factor-κB (NF-κB); these in turn are considered novel therapeutic targets. In this review, the role of lipid metabolism regulated by peroxisome proliferator-activated receptor gamma (PPARγ) in the development of HCC will also be discussed. Moreover, recent evidence has been obtained regarding the participation of epigenetic changes such as acetylation and methylation of histones and DNA methylation in the development of HCC. In this review, we provide detailed and current information about these topics. Experimental models represent useful tools for studying the different stages of liver cancer and help to develop new pharmacologic treatments. Each model in vivo and in vitro has several characteristics and advantages to offer for the study of this disease. Finally, the main therapies approved for the treatment of HCC patients, first- and second-line therapies, are described in this review. We also describe a novel option, pirfenidone, which due to its pharmacological properties could be considered in the future as a therapeutic option for HCC treatment.

Extracts of Perilla frutescens var. Acuta (Odash.) Kudo Leaves Have Antitumor Effects on Breast Cancer Cells by Suppressing YAP Activity

Yes-associated protein (YAP)/WW domain-containing transcription factor (TAZ) is critical for cell proliferation, survival, and self-renewal. It has been shown to play a crucial oncogenic role in many different types of tumors. In this study, we investigated the antitumor effect of the extracts of Perilla frutescens var. acuta (Odash.) Kudo leaves (PLE) on Hippo-YAP/TAZ signaling. PLE induced the phosphorylation of YAP/TAZ, thereby inhibiting their activity. In addition, the treatment suppresses YAP/TAZ transcriptional activity via the dissociation of the YAP/TAZ-TEAD complex. To elucidate the molecular mechanism of PLE in the regulation of YAP activity, we treated WT and cell lines with gene knockout (KO) for Hippo pathway components with PLE. The inhibitory effects of PLE on YAP-TEAD target genes were significantly attenuated in LATS1/2 KO cells. Moreover, we found the antitumor effect of PLE on MDA-MB-231 and BT549, both of which are triple-negative breast cancer (TNBC) cell lines. PLE reduced the viability of TNBC cells in a dose-dependent manner and induced cell apoptosis. Further, PLE inhibited the migration ability in MDA-MB-231 cells. This ability was weakened in YAP and TEAD-activated clones suggesting that the inhibition of migration by PLE is mainly achieved by regulating YAP activity. Taken together, the results of this study indicate that PLE suppressed cell growth and increased the apoptosis of breast cancer (BC) cells via inactivation of YAP activity in a LATS1/2-dependent manner.

Loss-of-Function Variants in the Tumor-Suppressor Gene PTPN14 Confer Increased Cancer Risk

The success of genome-wide association studies (GWAS) in identifying common, low-penetrance variant-cancer associations for the past decade is undisputed. However, discovering additional high-penetrance cancer mutations in unknown cancer predisposing genes requires detection of variant-cancer association of ultra-rare coding variants. Consequently, large-scale next-generation sequence data with associated phenotype information are needed. Here, we used genotype data on 166,281 Icelanders, of which, 49,708 were whole-genome sequenced and 408,595 individuals from the UK Biobank, of which, 41,147 were whole-exome sequenced, to test for association between loss-of-function burden in autosomal genes and basal cell carcinoma (BCC), the most common cancer in Caucasians. A total of 25,205 BCC cases and 683,058 controls were tested. Rare germline loss-of-function variants in PTPN14 conferred substantial risks of BCC (OR, 8.0; P = 1.9 × 10^-12), with a quarter of carriers getting BCC before age 70 and over half in their lifetime. Furthermore, common variants at the PTPN14 locus were associated with BCC, suggesting PTPN14 as a new, high-impact BCC predisposition gene. A follow-up investigation of 24 cancers and three benign tumor types showed that PTPN14 loss-of-function variants are associated with high risk of cervical cancer (OR, 12.7, P = 1.6 × 10^-4) and low age at diagnosis. Our findings, using power-increasing methods with high-quality rare variant genotypes, highlight future prospects for new discoveries on carcinogenesis. SIGNIFICANCE: This study identifies the tumor-suppressor gene PTPN14 as a high-impact BCC predisposition gene and indicates that inactivation of PTPN14 by germline sequence variants may also lead to increased risk of cervical cancer.

The Radiation-Induced Regenerative Response of Adult Tissue-Specific Stem Cells: Models and Signaling Pathways

Radiotherapy is involved in the treatment of many cancers, but damage induced to the surrounding normal tissue is often inevitable. Evidence suggests that the maintenance of homeostasis and regeneration of the normal tissue is driven by specific adult tissue stem/progenitor cells. These tasks involve the input from several signaling pathways. Irradiation also targets these stem/progenitor cells, triggering a cellular response aimed at achieving tissue regeneration. Here we discuss the currently used in vitro and in vivo models and the involved specific tissue stem/progenitor cell signaling pathways to study the response to irradiation. The combination of the use of complex in vitro models that offer high in vivo resemblance and lineage tracing models, which address organ complexity constitute potential tools for the study of the stem/progenitor cellular response post-irradiation. The Notch, Wnt, Hippo, Hedgehog, and autophagy signaling pathways have been found as crucial for driving stem/progenitor radiation-induced tissue regeneration. We review how these signaling pathways drive the response of solid tissue-specific stem/progenitor cells to radiotherapy and the used models to address this.

Oxygen regulates epithelial stem cell proliferation via RhoA-actomyosin-YAP/TAZ signal in mouse incisor

Stem cells are maintained in specific niches that strictly regulate their proliferation and differentiation for proper tissue regeneration and renewal. Molecular oxygen (O₂) is an important component of the niche microenvironment, but little is known about how O₂ governs epithelial stem cell (ESC) behavior. Here, we demonstrate that O₂ plays a crucial role in regulating the proliferation of ESCs using the continuously growing mouse incisors. We have revealed that slow-cycling cells in the niche are maintained under relatively hypoxic conditions compared with actively proliferating cells, based on the blood vessel distribution and metabolic status. Mechanistically, we have demonstrated that, during hypoxia, HIF1α upregulation activates the RhoA signal, thereby promoting cortical actomyosin and stabilizing the adherens junction complex, including merlin. This leads to the cytoplasmic retention of YAP/TAZ to attenuate cell proliferation. These results shed light on the biological significance of blood-vessel geometry and the signaling mechanism through microenvironmental O₂ to orchestrate ESC behavior, providing a novel molecular basis for the microenvironmental O₂-mediated stem cell regulation during tissue development and renewal.

"Biomechanical Signaling in Oocytes and Parthenogenetic Cells"

Oocyte-specific competence remains one of the major targets of current research in the field of reproduction. Several mechanisms are involved in meiotic maturation and the molecular signature of an oocyte is considered to reflect its quality and to predict its subsequent developmental and functional capabilities. In the present minireview, we focus on the possible role of mechanotransduction and mechanosensor signaling pathways, namely the Hippo and the RhoGTPase, in the maturing oocyte. Due to the limited access to female gametes, we propose the use of cells isolated from parthenogenetic embryos as a promising model to characterize and dissect the oocyte distinctive molecular signatures, given their exclusive maternal origin. The brief overview here reported suggests a role of the mechanosensing related pathways in oocyte quality and developmental competence and supports the use of uniparental cells as a useful tool for oocyte molecular signature characterization.

Role of the HIPPO pathway as potential key player in the cross talk between oncology and cardiology

The HIPPO pathway (HP) is a highly conserved kinase cascade that affects organ size by regulating proliferation, cell survival and differentiation. Discovered in Drosophila melanogaster to early 2000, it immediately opened wide frontiers in the field of research. Over the last years the field of knowledge on HP is quickly expanding and it is thought will offer many answers on complex pathologies. Here, we summarized the results of several studies that have investigated HP signaling both in oncology than in cardiology field, with an overview on future perspectives in cardiology research.

Myofibroblast contraction is essential for generating and regenerating the gas-exchange surface

A majority (~95%) of the gas-exchange surface area is generated through septa formation during alveologenesis. Disruption of this process leads to alveolar simplification and bronchopulmonary dysplasia (BPD), a prevalent disorder in premature infants. Although several models have been proposed, the mechanism of septa formation remains under debate. Here we show that inactivation of myosin light chain kinase (MLCK), a key factor required for myofibroblast contraction, disrupted septa formation, supporting the myofibroblast contraction model of alveologenesis. The alveoli simplification phenotype was accompanied by decreased yes-associated protein (YAP), a key effector in the Hippo mechanotransduction pathway. Expression of activated YAP in Mlck-mutant lungs led to partial reversal of alveolar simplification. In the adult, although Mlck inactivation did not lead to simplification, it prevented reseptation during compensatory regrowth in the pneumonectomy model. These findings revealed that myofibroblast reactivation and contraction are requisite steps toward regenerating the gas-exchange surface in diseases such as BPD and chronic obstructive pulmonary disease (COPD).

The protein phosphatase PPM1A dephosphorylates and activates YAP to govern mammalian intestinal and liver regeneration

The Hippo-YAP pathway responds to diverse environmental cues to manage tissue homeostasis, organ regeneration, tumorigenesis, and immunity. However, how phosphatase(s) directly target Yes-associated protein (YAP) and determine its physiological activity are still inconclusive. Here, we utilized an unbiased phosphatome screening and identified protein phosphatase magnesium-dependent 1A (PPM1A/PP2Cα) as the bona fide and physiological YAP phosphatase. We found that PPM1A was associated with YAP/TAZ in both the cytoplasm and the nucleus to directly eliminate phospho-S127 on YAP, which conferring YAP the nuclear distribution and transcription potency. Accordingly, genetic ablation or depletion of PPM1A in cells, organoids, and mice elicited an enhanced YAP/TAZ cytoplasmic retention and resulted in the diminished cell proliferation, severe gut regeneration defects in colitis, and impeded liver regeneration upon injury. These regeneration defects in murine model were largely rescued via a genetic large tumor suppressor kinase 1 (LATS1) deficiency or the pharmacological inhibition of Hippo-YAP signaling. Therefore, we identify a physiological phosphatase of YAP/TAZ, describe its critical effects in YAP/TAZ cellular distribution, and demonstrate its physiological roles in mammalian organ regeneration.

Inactivation of Lats1 and Lats2 highlights the role of hippo pathway effector YAP in larynx and vocal fold epithelium morphogenesis

Proliferation and differentiation of vocal fold epithelial cells during embryonic development is poorly understood. We examined the role of Hippo signaling, a vital pathway known for regulating organ size, in murine laryngeal development. Conditional inactivation of the Hippo kinase genes Lats1 and Lats2, specifically in vocal fold epithelial cells, resulted in severe morphogenetic defects. Deletion of Lats1 and Lats2 caused abnormalities in epithelial differentiation, epithelial lamina separation, cellular adhesion, basement membrane organization with secondary failed cartilage, and laryngeal muscle development. Further, Lats1 and Lats2 inactivation led to failure in differentiation of p63+ basal progenitors. Our results reveal novel roles of Hippo-Lats-YAP signaling in proper regulation of VF epithelial fate and larynx morphogenesis.

Dynamic patterns of YAP1 expression and cellular localization in the developing and injured utricle

The Hippo signaling pathway is a key regulator of tissue development and regeneration. Activation of the Hippo pathway leads to nuclear translocation of the YAP1 transcriptional coactivator, resulting in changes in gene expression and cell cycle entry. Recent studies have demonstrated the nuclear translocation of YAP1 during the development of the sensory organs of the inner ear, but the possible role of YAP1 in sensory regeneration of the inner ear is unclear. The present study characterized the cellular localization of YAP1 in the utricles of mice and chicks, both under normal conditions and after HC injury. During neonatal development, YAP1 expression was observed in the cytoplasm of supporting cells, and was transiently expressed in the cytoplasm of some differentiating hair cells. We also observed temporary nuclear translocation of YAP1 in supporting cells of the mouse utricle after short periods in organotypic culture. However, little or no nuclear translocation of YAP1 was observed in the utricles of neonatal or mature mice after ototoxic injury. In contrast, substantial YAP1 nuclear translocation was observed in the chicken utricle after streptomycin treatment in vitro and in vivo. Together, these data suggest that differences in YAP1 signaling may partially account for the differing regenerative abilities of the avian vs. mammalian inner ear.

Cross-talk between YAP and RAR-RXR Drives Expression of Stemness Genes to Promote 5-FU Resistance and Self-Renewal in Colorectal Cancer Cells

The mechanisms whereby the Hippo pathway effector YAP regulates cancer cell stemness, plasticity, and chemoresistance are not fully understood. We previously showed that in 5-fluorouracil (5-FU)-resistant colorectal cancer cells, the transcriptional coactivator YAP is differentially regulated at critical transitions connected with reversible quiescence/dormancy to promote metastasis. Here, we found that experimental YAP activation in 5-FU-sensitive and 5-FU-resistant HT29 colorectal cancer cells enhanced nuclear YAP localization and the transcript levels of the retinoic acid (RA) receptors RARα/γ and RAR target genes CYP26A1, ALDH1A3, and LGR5 through RA Response Elements (RARE). In these two cell models, constitutive YAP activation reinforced the expression of the stemness biomarkers and regulators ALDH1A3, LGR5, and OCT4. Conversely, YAP silencing, RAR/RXR inhibition by the pan-RAR antagonist BMS493, and vitamin A depletion downregulated stemness traits and self-renewal. Regarding the mechanisms engaged, proximity-dependent labeling, nuclear YAP pulldown coupled with mass spectrometry, and chromatin immunoprecipitation (ChIP)/re-ChIP experiments revealed: (i) the nuclear colocalization/interaction of YAP with RARγ and RXRs; and (ii) combined genomic co-occupancy of YAP, RARα/γ, and RXRα interactomes at proximal RAREs of LGR5 and ALDH1A3 promoters. Moreover, activation of the YAP/RAR-RXR cross-talk in colorectal cancer cells promoted RAR self-activation loops via vitamin A metabolism, RA, and active RAR ligands generated by ALDH1A3. Together, our data identify YAP as a bona fide RAR-RXR transcriptional coactivator that acts through RARE-activated stemness genes. IMPLICATIONS: Targeting the newly identified YAP/RAR-RXR cross-talk implicated in cancer cell stemness maintenance may lead to multitarget combination therapies for patients with colorectal cancer.

Hippo Signaling Pathway in Gliomas

The Hippo signaling pathway is a highly conserved pathway involved in tissue development and regeneration that controls organ size through the regulation of cell proliferation and apoptosis. The core Hippo pathway is composed of a block of kinases, MST1/2 (Mammalian STE20-like protein kinase 1/2) and LATS1/2 (Large tumor suppressor 1/2), which inhibits nuclear translocation of YAP/TAZ (Yes-Associated Protein 1/Transcriptional co-activator with PDZ-binding motif) and its downstream association with the TEAD (TEA domain) family of transcription factors. This pathway was recently shown to be involved in tumorigenesis and metastasis in several cancers such as lung, breast, or colorectal cancers but is still poorly investigated in brain tumors. Gliomas are the most common and the most lethal primary brain tumors representing about 80% of malignant central nervous system neoplasms. Despite intensive clinical protocol, the prognosis for patients remains very poor due to systematic relapse and treatment failure. Growing evidence demonstrating the role of Hippo signaling in cancer biology and the lack of efficient treatments for malignant gliomas support the idea that this pathway could represent a potential target paving the way for alternative therapeutics. Based on recent advances in the Hippo pathway deciphering, the main goal of this review is to highlight the role of this pathway in gliomas by a state-of-the-art synthesis.

The role of the Hippo pathway in the pathogenesis of inflammatory bowel disease

Inflammatory bowel disease (IBD) is a chronic and recurrent inflammatory disorder that primarily comprises Crohn's disease (CD) and ulcerative colitis (UC). Owing to its increasing prevalence in Eastern countries and the intractable challenges faced during IBD treatment, extensive research on IBD has been carried out over the last few years. Although the precise aetiology of IBD is undefined, the currently accepted hypothesis for IBD pathogenesis considers it to be a combination of environment, genetic predisposition, gut microbiota, and abnormal immunity. A recently emerged signalling pathway, the Hippo pathway, acts as a key regulator of cell growth, tissue homoeostasis, organ size, and has been implicated in several human cancers. In the past few years, studies have revealed the importance of the Hippo pathway in gastrointestinal tract physiology and gastrointestinal diseases, such as colorectal cancer and IBD. However, the role of the Hippo pathway and its exact impact in IBD remains to be elucidated. This review summarises the latest scientific literature on the involvement of this pathway in IBD from the following perspectives that account for the IBD pathogenesis: intestinal epithelial cell regeneration, immune regulation, gut microbiota, and angiogenesis. A comprehensive understanding of the specific role of the Hippo pathway in IBD will provide novel insights into future research directions and clinical implications of the Hippo pathway.

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

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

Implications of the specific localization of YAP signaling on the epithelial patterning of circumvallate papilla

Circumvallate papilla (CVP) is a distinctively structured with dome-shaped apex, and the surrounding trench which contains over two hundred taste buds on the lateral walls. Although CVP was extensively studied to determine the regulatory mechanisms during organogenesis, it still remains to be elucidated the principle mechanisms of signaling regulations on morphogenesis including taste buds formation. The key role of Yes-associated protein (YAP) in the regulation of organ size and cell proliferation in vertebrates is well understood, but little is known about the role of this signaling pathway in CVP development. We aimed to determine the putative roles of YAP signaling in the epithelial patterning during CVP morphogenesis. To evaluate the precise localization patterns of YAP and other related signaling molecules, including β-catenin, Ki67, cytokeratins, and PGP9.5, in CVP tissue, histology and immunohistochemistry were employed at E16 and adult mice. Our results suggested that there are specific localization patterns of YAP and Wnt signaling molecules in developing and adult CVP. These concrete localization patterns would provide putative involvements of YAP and Wnt signaling for proper epithelial cell differentiation including the formation and maintenance of taste buds.

Hippo signaling: bridging the gap between cancer and neurodegenerative disorders

During development, regulation of organ size requires a balance between cell proliferation, growth and cell death. Dysregulation of these fundamental processes can cause a variety of diseases. Excessive cell proliferation results in cancer whereas excessive cell death results in neurodegenerative disorders. Many signaling pathways known-to-date have a role in growth regulation. Among them, evolutionarily conserved Hippo signaling pathway is unique as it controls both cell proliferation and cell death by a variety of mechanisms during organ sculpture and development. Neurodegeneration, a complex process of progressive death of neuronal population, results in fatal disorders with no available cure to date. During normal development, cell death is required for sculpting of an organ. However, aberrant cell death in neuronal cell population can result in neurodegenerative disorders. Hippo pathway has gathered major attention for its role in growth regulation and cancer, however, other functions like its role in neurodegeneration are also emerging rapidly. This review highlights the role of Hippo signaling in cell death and neurodegenerative diseases and provide the information on the chemical inhibitors employed to block Hippo pathway. Understanding Hippo mediated cell death mechanisms will aid in development of reliable and effective therapeutic strategies in future.

The cellular niche for intestinal stem cells: a team effort

The rapidly self-renewing epithelium in the mammalian intestine is maintained by multipotent intestinal stem cells (ISCs) located at the bottom of the intestinal crypt that are interspersed with Paneth cells in the small intestine and Paneth-like cells in the colon. The ISC compartment is also closely associated with a sub-epithelial compartment that contains multiple types of mesenchymal stromal cells. With the advances in single cell and gene editing technologies, rapid progress has been made for the identification and characterization of the cellular components of the niche microenvironment that is essential for self-renewal and differentiation of ISCs. It has become increasingly clear that a heterogeneous population of mesenchymal cells as well as the Paneth cells collectively provide multiple secreted niche signals to promote ISC self-renewal. Here we review and summarize recent advances in the regulation of ISCs with a main focus on the definition of niche cells that sustain ISCs.

SOX13/TRIM11/YAP axis promotes the proliferation, migration and chemoresistance of anaplastic thyroid cancer

Anaplastic thyroid cancer (ATC) is one of the most aggressive and virulent solid tumors. The ubiquitin proteasome system presents in all eukaryotic cells and is essential for cellular homeostasis. While its underlying role in ATC remains largely unclear. TRIM11 is an E3 ubiquitin ligase and has been reported to act as an oncogene in several human cancers. The present study aims to reveal the oncogenic function of TRIM11 in ATC. Western blot was used to measure the protein expression of TRIM11 and YAP, while the YAP target genes were measured by real-time PCR. CCK8 assay was used to detect cell viability; wound-healing assay and transwell assay were used to measure the migration ability of ATC. The xeno-graft tumor model was used for in vivo study. Immuno-precipitation assay was used to detect the interaction domain between YAP and TRIM11. And the ubiquitin-based Immuno-precipitation assays were used to detect the specific ubiquitination manner happened on YAP. TRIM11 depletion significantly decreases cell proliferation and migration capabilities of ATC cells, and elevates cell sensitivity to chemotherapy, which effect could be further rescued by YAP overexpression. TRIM11 depletion decreases YAP protein level and YAP/TEAD target genes, such as CTGF, ANKRD1 and CYR61 in ATC. Indicating that TRIM11 is a regulator of Hippo signaling pathway. Immuno-precipitation assay shows that the RING domain of TRIM11 is essential for the interaction with WW domain of YAP. Further mechanistic analysis suggests that TRIM11 promotes the mono-ubiquitination of YAP, thus prolongs its protein half. Furthermore, TRIM11 promoter analysis revealed that SOX13 activates TRIM11 transcription by binding to the promoter of TRIM11. In summary, our study describes the oncogenic function of TRIM11 in ATC, which acts as a post-translational modulating factor of Hippo pathway. Targeting TRIM11 may be a potential therapeutic method for ATC treatment.