Yes-associated Protein Activation Research Articles

Senescent hepatic stellate cells promote liver regeneration through IL-6 and ligands of CXCR2.

Senescent cells have long been associated with deleterious effects in aging-related pathologies, although recent studies have uncovered their beneficial roles in certain contexts, such as wound healing. We have found that hepatic stellate cells (HSCs) underwent senescence within 2 days after 2/3 partial hepatectomy (PHx) in young (2–3 months old) mice, and the elimination of these senescent cells by using the senolytic drug ABT263 or by using a genetic mouse model impaired liver regeneration. Senescent HSCs secrete IL-6 and CXCR2 ligands as part of the senescence-associated secretory phenotype, which induces multiple signaling pathways to stimulate liver regeneration. IL-6 activates STAT3, induces Yes-associated protein (YAP) activation through SRC family kinases, and synergizes with CXCL2 to activate ERK1/2 to stimulate hepatocyte proliferation. The administration of either IL-6 or CXCL2 partially restored liver regeneration in mice with senescent cell elimination, and the combination of both fully restored liver weight recovery. Furthermore, the matricellular protein central communication network factor 1 (CCN1, previously called CYR61) was rapidly elevated in response to PHx and induced HSC senescence. Knockin mice expressing a mutant CCN1 unable to bind integrin α6β1 were deficient in senescent cells and liver regeneration after PHx. Thus, HSC senescence, largely induced by CCN1, is a programmed response to PHx and plays a critical role in liver regeneration through signaling pathways activated by IL-6 and ligands of CXCR2.

SUFU suppresses ferroptosis sensitivity in breast cancer cells via Hippo/YAP pathway

SummaryFerroptosis is a new kind of regulated cell death that is characterized by highly iron-dependent lipid peroxidation. Cancer cells differ in their sensitivity to ferroptosis. Here we showed that the Suppressor of fused homolog (SUFU), a critical component in Hedgehog signaling, regulates ferroptosis sensitivity of breast cancer cells. Ectopic SUFU expression suppressed, whereas depletion of SUFU enhanced the sensitivity of breast cancer cells to RSL3-triggered ferroptosis through deregulation of ACSL4. Moreover, SUFU depletion promoted the activation of Yes-associated protein (YAP), thereby increasing the expression of ACSL4. Mechanistically, SUFU is associated with LATS1. Deletion of a region comprising residues 174–385 in SUFU disrupted SUFU binding to LATS1, thus abrogating SUFU-mediated downregulation of the YAP-ACSL4 axis and sensitivity to ferroptosis. Noteworthy, we showed that vincristine downregulated SUFU, thus increasing breast cancer cell sensitivity to RSL3 in vitro and in vivo. Together, our findings uncover SUFU as a novel regulator in ferroptosis sensitivity.

3D Interfacial and Spatiotemporal Regulation of Human Neuroepithelial Organoids.

Neuroepithelial (NE) organoids with dorsal–ventral patterning provide a useful three‐dimensional (3D) in vitro model to interrogate neural tube formation during early development of the central nervous system. Understanding the fundamental processes behind the cellular self‐organization in NE organoids holds the key to the engineering of organoids with higher, more in vivo‐like complexity. However, little is known about the cellular regulation driving the NE development, especially in the presence of interfacial cues from the microenvironment. Here a simple 3D culture system that allows generation and manipulation of NE organoids from human‐induced pluripotent stem cells (hiPSCs), displaying developmental phases of hiPSC differentiation and self‐aggregation, first into NE cysts with lumen structure and then toward NE organoids with floor‐plate patterning, is established. Longitudinal inhibition reveals distinct and dynamic roles of actomyosin contractility and yes‐associated protein (YAP) signaling in governing these phases. By growing NE organoids on culture chips containing anisotropic surfaces or confining microniches, it is further demonstrated that interfacial cues can sensitively exert dimension‐dependent influence on luminal cyst and organoid morphology, successful floor‐plate patterning, as well as cytoskeletal regulation and YAP activity. This study therefore sheds new light on how organoid and tissue architecture can be steered through intracellular and extracellular means.

YAP1 activation is associated with the progression and response to immunotherapy of non-muscle invasive bladder cancer.

SummaryBackgroundDespite the availability of several treatments for non-muscle-invasive bladder cancer (NMIBC), many patients are still not responsive to treatments, and the disease progresses. A new prognostic classifier can differentiate between treatment response and progression, and it could be used as a very important tool in patient decision-making regarding treatment options. In this study, we focused on the activation of Yes-associated protein 1 (YAP1), which is known to play a pivotal role in tumour progression and serves as a factor contributing to the mechanism of resistance to various relevant therapeutic agents. We further evaluated its potential as a novel prognostic agent.MethodsWe identified YAP1-associated gene signatures based on UC3-siYAP1 cells (n=8) and NMIBC cohort (n=460). Cross-validation was performed using 5 independent bladder cancer patient cohorts (n=1006). We also experimentally validated the changes of gene expression levels representing each subgroup.FindingsThe 976-gene signature based on YAP1-activation redefined three subgroups and had the benefits of Bacillus Calmette-Guérin (BCG) treatment in patients with NMIBC (hazard ratio 3.32, 95% CI 1.29-8.56, p = 0.01). The integrated analysis revealed that YAP1 activation was associated with the characterization of patients with high-risk NMIBC and the response to immunotherapy.InterpretationThis study suggests that YAP1 activation has an important prognostic effect on bladder cancer progression and might be useful in the selection of immunotherapy.FundingA funding list that contributed to this research can be found in the Acknowledgements section.

PDE4D binds and interacts with YAP to cooperatively promote HCC progression

The role of cAMP in the development of hepatocellular carcinoma (HCC) is controversial and the biological function of cAMP-hydrolysing enzyme phosphodiesterase 4D (PDE4D) in HCC remains unclear. In this study, we observed markedly higher PDE4D expression in HCC patients with poor survival. PDE4D bound to yes-associated protein (YAP), and PDE4D expression positively correlated with YAP expression in HCC. Overexpression of PDE4D increased YAP dephosphorylation and activity and promoted HCC cell growth in vitro and in vivo, which was attenuated by the YAP inhibitor verteporfin. In contrast, silencing PDE4D reduced YAP expression and HCC cell growth. Notably, forced expression of YAP promoted PDE4D and YAP target gene expression and cell growth, which were abrogated by the PDE4D inhibitor roflumilast. Mechanistically, silencing of YAP caused PDE4D downregulation and HCC cell apoptosis via extracellular signal-regulated kinase (ERK) activation. Roflumilast activated cAMP-PKA signaling and induced cAMP-PKA-dependent YAP phosphorylation at serine 127, resulting in YAP degradation and suppression of HCC growth, which were reversed by the PKA inhibitor PKI. Additionally, transfection of the YAP-S127A mutant reversed roflumilast-mediated suppression of YAP and cell growth. Taken together, our findings indicate that PDE4D binds to and interacts with YAP to promote HCC progression. Targeting the PDE4D-YAP interaction with roflumilast may be an effective strategy for HCC treatment.

RGMa Participates in the Blood-Brain Barrier Dysfunction Through BMP/BMPR/YAP Signaling in Multiple Sclerosis.

The infiltration of inflammatory cells into the central nervous system (CNS) through the dysfunctional blood–brain barrier (BBB) was critical in the early stages of MS. However, the mechanisms underlying BBB dysfunction remain unknown. Repulsive guidance molecule-a (RGMa) is involved in the pathogenesis of multiple sclerosis (MS), but its role needs to be further explored. This study aimed to evaluate whether RMGa regulates BBB permeability in endothelial cells and MS, and if so, what mechanism may be involved. We created an experimental autoimmune encephalomyelitis (EAE) model in C57BL/6 mice and a human brain microvascular endothelial cell (HBMEC) culture. The permeability of the BBB is measured in response to various interventions. Our results showed that RGMa is expressed in the endothelial cells in HBMECs and EAE mice. RGMa and its signaling counterpart, bone morphogenetic protein 2 (BMP2)/bone morphogenetic protein receptor type II (BMPRII), were gradually increased as the disease progressed. Moreover, as EAE progressed and the BBB was disrupted, the downstream effector, yes-associated protein (YAP), as well as the tight junctional proteins zonula occludens 1 (ZO-1) and claudin-5, decreased significantly. The permeability assay revealed that lentivirus-induced RGMa overexpression in HBMECs caused a significant breakdown of the BBB, whereas RGMa knockdown significantly strengthens the integrity of the BBB. Furthermore, specifically activating BMPR II or inhibiting YAP based on RGMa knockdown results in a significant decrease of ZO-1 and claudin-5 in vitro. On the contrary, inhibition of BMPR II or activation of YAP after upregulating RGMa prevents the downregulation of ZO-1 and claudin-5 in HBMECs. In addition, serum-soluble RGMa (sRGMa) levels were significantly higher in MS patients, particularly in MS patients with Gd+ lesions, indicating that the BBB has been disrupted. In conclusion, this study shows that RGMa causes BBB dysfunction in endothelial cells via BMP2/BMPR II/YAP, resulting in BBB integrity disruption in MS and that it could be a novel therapeutic target for BBB permeability in MS.

Yes-associated protein promotes endothelial-to-mesenchymal transition of endothelial cells in choroidal neovascularization fibrosis.

To reveal whether and how Yes-associated protein (YAP) promotes the occurrence of subretinal fibrosis in age-related macular degeneration (AMD). Cobalt chloride (CoCl2) was used in primary human umbilical vein endothelial cells (HUVECs) to induce hypoxia in vitro. Eight-week-old male C57BL/6J mice weighing 19-25 g were used for a choroidal neovascularization (CNV) model induced by laser photocoagulation in vivo. Expression levels of YAP, phosphorylated YAP, mesenchymal markers [α smooth muscle actin (α-SMA), vimentin, and Snail], and endothelial cell markers (CD31 and zonula occludens 1) were measured by Western blotting, quantitative real-time PCR, and immunofluorescence microscopy. Small molecules YC-1 (Lificiguat, a specific inhibitor of hypoxia-inducible factor 1α), CA3 (CIL56, an inhibitor of YAP), and XMU-MP-1 (an inhibitor of Hippo kinase MST1/2, which activates YAP) were used to explore the underlying mechanism. CoCl2 increased expression of mesenchymal markers, decreased expression of endothelial cell markers, and enhanced the ability of primary HUVECs to proliferate and migrate. YC-1 suppressed hypoxia-induced endothelial-to-mesenchymal transition (EndMT). Moreover, hypoxia promoted total expression, inhibited phosphorylation, and enhanced the transcriptional activity of YAP. XMU-MP-1 enhanced hypoxia-induced EndMT, whereas CA3 elicited the opposite effect. Expression of YAP, α-SMA, and vimentin were upregulated in the laser-induced CNV model. However, silencing of YAP by vitreous injection of small interfering RNA targeting YAP could reverse these changes. The findings reveal a critical role of the hypoxia-inducible factor-1α (HIF-1α)/YAP signaling axis in EndMT and provide a new therapeutic target for treatment of subretinal fibrosis in AMD.

The Effect of Glucose Administration on Yes‐associated Protein (YAP) Activity in Healthy and Cachectic Mouse Muscles

Yes‐associated protein (YAP) is a downstream effector of Hippo signaling and regulates skeletal muscle size and homeostasis. The change of YAP activity has been reported in aging and dystrophic muscles. Our preliminary data showed that tumor burden alters the YAP activity in skeletal muscle. Recent studies showed that glucose metabolism also regulates YAP activity in cancer cells; however, it is unknown whether glucose administration stimulates YAP activity in skeletal muscle. The purpose of this study was to determine whether the YAP activity would change after acute glucose administration in healthy and cachectic mouse muscles. We hypothesized that glucose could stimulate YAP activity, at least in healthy muscle. Approximately 4‐month‐old wild‐type (WT, n=10) and ApcMin/+ mice (Min, n=10) were used in this study. Each group of mice was assigned to either control (Con, n=5 per group) or glucose administration (Glu n=5 per group) treatment. At first, all the mice fasted for four hours. Glucose dissolved in phosphate‐buffered saline (PBS, 2 mg/kg) was administered intraperitoneally to Glu groups. Con groups received PBS injections. Thirty minutes after glucose administration, the mice were euthanized, and plantaris muscles (PLAN) were removed. The time to sacrifice was based on the peak insulin secretion during a glucose tolerance test. To ensure injection accuracy, the glucose levels were measured using a handheld glucometer before glucose injection and at death. After total protein was extracted, routine Western blotting was performed using 50~100 µg of the total protein. Each phosphorylated protein was normalized to its respective total protein. Unpaired t‐test (WT vs. Min) and a two‐way ANOVA (genotype x glucose treatment) were used for statistical analysis. The levels of significance were set at 0.05. The body weight of Min mice was smaller than that of WT mice (19.8±1.2 mg vs. 17.3±0.5 mg for WT and Min, respectively, p=0.05). Likewise, the PLAN muscle mass of Min mice was smaller than that of WT mice (19.8±1.2 mg vs. 17.3±0.5 mg for WT and Min, respectively, p=0.05). There was no significant difference in fasting glucose levels between WT and Min mice, and glucose administration increased plasma glucose levels regardless of genotype (main effect of glucose administration, p<0.05). The activity levels of glycogen synthase kinase 3 beta (GSK3β) were comparable at the baseline (1.1±0.1 vs. 1.1±0.2 for WT and Min, respectively) and after glucose administration (1.1±0.2 vs. 1.1±0.4 for WT and Min, respectively). Min mice showed a reduction in total ribosomal protein S6 level after fasting (1.0±0.2 vs. 0.4±0.2 for WT and Min, respectively, p<0.05) and in response to glucose administration (2.7±1.5 vs. 0.6±0.4 for WT and Min, respectively, p<0.05). Interestingly, the basal YAP levels were comparable between WT and Min mice (1.0±0.1 vs. 1.1±0.1 for WT and Min, respectively), and the glucose administration did not alter the YAP levels (1.1±0.1 vs. 1.1±0.2 for WT and Min, respectively). These data suggest that YAP activity is independent of acute glucose administration in healthy and cachectic mouse skeletal muscles.

SIRT6 Protects Against Liver Fibrosis by Negatively Regulating YAP/TAZ

Hepatic fibrosis often occurs after chronic liver injury, and it is largely attributable to the activation of hepatic stellate cells (HSCs). It is a determining step in the pathophysiology of non‐alcoholic steatohepatitis (NASH), an advanced form of fatty liver disease. The Hippo pathway and its effectors Yes‐associated protein (YAP) and transcriptional coactivator with PDZ‐binding motif (TAZ), have been implicated in hepatic fibrogenesis. However, how YAP and TAZ are regulated in HSCs remains incompletely understood. Here in this work, we have identified Sirtuin 6 (SIRT6), a NAD+ dependent deacetylase, as a regulator of YAP and TAZ in HSCs. Using primary HSCs deficient in SIRT6 from mice fed a moderately‐high‐fat‐cholesterol‐cholate diet (HFCC) for one week as well as in vitro models using transforming growth factor‐β (TGF‐β) treated LX‐2 cells, we have revealed that YAP and TAZ were acetylated during the HSC activation. Moreover, expression of YAP and TAZ target genes including connective tissue growth factor (Ctgf), cysteine‐rich angiogenic inducer 61 (Cyr61) and ankyrin repeat domain 1 (Ankrd1) was increased in those HSCs. Immunofluorescence microscopy analysis of liver sections obtained from Sirt6 HSC‐specific knockout mice fed HFCC diet for six weeks showed elevated YAP nuclear localization in the HSCs, suggesting an activation of YAP during fibrosis. Further in vitroanalysis of YAP/TAZ activity upon gain‐ and loss‐of‐function of SIRT6 in TGF‐β treated LX‐2 cells showed a decrease or increase of Ctgf, Cyr61 and Col3a1gene expression,respectively. To understand how SIRT6 regulates YAP and TAZ, we performed immunoprecipitation and lysine acetylation analysis, and our data showed that SIRT6 indeed interacted with YAP and TAZ and deacetylated them. Taken together, our study has identified a key regulatory axis in which SIRT6 interacts with YAP/TAZ and deacetylates them at several lysine residues, thereby suppressing their transcriptional co‐activator activity during fibrosis.

Myeloid YAP Inhibition Improves Cardiac Phenotype During Pressure Overload Stress

Inflammation is an integral component of cardiovascular disease and is thought to contribute to cardiac dysfunction in ischemic and non‐ischemic models of heart failure. While ischemia‐induced inflammation has been extensively studied in the heart, relatively less is known regarding cardiac inflammation during non‐ischemic stress. Recent work has implicated a role for Yes‐associated protein (YAP), a transcription co‐factor, in modulating cardiac inflammation in response to ischemic injury; however, whether YAP influences inflammation in the heart during non‐ischemic stress is not described. We hypothesized that YAP mediates a pro‐inflammatory response during pressure overload (PO)‐induced non‐ischemic injury, and that targeted YAP inhibition in the myeloid compartment is cardioprotective. In mice, PO elicits an immune response characterized by infiltration of myeloid cells that precedes cardiac dysfunction. Myeloid cells isolated from the heart after 7 days PO showed evidence of increased YAP activity. Myeloid‐specific YAP knockout mice (YAPF/F;LysMCre) were subjected to PO stress. After 4 weeks, cardiac hypertrophy was similar between myeloid YAP KO mice and controls. However, systolic dysfunction, cardiac fibrosis, apoptosis, “fetal gene” induction, and additional indicators of pathological remodeling were attenuated in myeloid YAP KO mice compared to controls. Additionally, inflammatory gene expression and CCR2+ macrophage infiltration in the myocardium were significantly attenuated in myeloid YAP KO mice after PO, indicating reduced inflammation compared to controls. Conversely, angiogenic indicators and pro‐resolving genes were enhanced in myeloid YAP KO hearts. Experiments using primary bone marrow‐derived macrophages (BMDMs) from YAP KO and control mice demonstrated that YAP suppression attenuated “M1‐like” inflammatory gene expression, while “M2‐like” resolving genes were augmented following stimulation. The inflammasome is a multiprotein complex and important facilitator of cytokine processing that mediates inflammation in the injured heart. We observed attenuated inflammasome priming and function in YAP deficient BMDMs, as well as in myeloid YAP KO hearts following PO, indicating disruption of inflammasome induction. Finally, we leveraged nanoparticle‐mediated delivery of the YAP inhibitor verteporfin to test the translational potential of targeting YAP to prevent heart failure. An alternate‐day dosing regimen of drug‐loaded nanoparticles attenuated inflammation and fibrosis, and improved myocardial capillary density after 2 weeks PO compared to DMSO nanoparticle control treatment. Together these data implicate myeloid YAP as an important molecular nodal point that facilitates cardiac inflammation and pathology during PO stress and suggest that selective inhibition of YAP may prove a novel therapeutic target in non‐ischemic heart disease.

Inhibition of YAP signaling improves recovery in injured skeletal muscle

Skeletal muscle experiences mechanical forces that regulate its development, hypertrophy, and homeostasis. YAP (Yes‐associated protein) not only serves as an indicator of nuclear mechanical signals, but can also induce a wide range of downstream signaling cascades. We previously reported increased YAP signaling in healthy (wild type, WT) muscle following isometric contractile loading, and constitutively active YAP signaling in the muscles of mdxmice (dystrophin‐null, murine model of Duchenne muscular dystrophy, or DMD) and aged mice. We tested the hypothesis that increased YAP signaling contributes to the loss of muscle function following eccentric contraction‐induced injury in WT muscle. We also tested the hypothesis that pharmacological inhibition of YAP signaling (verteporfin, 100 mg/kg delivered via intraperitoneal injection every other day immediately following injury for 10 days) improves muscle function following injury. We found increased YAP signaling following eccentric contraction‐induced muscle injury in healthy muscles, indicated by increased gene expression of YAP and its downstream targets. Moreover, pharmacological inhibition of YAP activity resulted in hastened recovery following eccentric contraction injury. Following 50 eccentric contractions to the quadriceps muscles, vehicle (DMSO) treated muscles had a loss of force of 44.8 ± 14.1% and 42.9 ± 17.1% at days 2 and 4 following injury, while verteporfin treated muscles had a loss of force of 13.7 ± 24.7% and 9.05 ± 24.5% at days 2 and 4 following injury. Both groups were fully recovered at 6 days following injury. We conclude that reducing YAP signaling improves muscle function following injury to WT muscle, and could play a significant role in ameliorating muscle pathology in dystrophic and aged muscle.

Ha-RasV12-Induced Multilayer Cellular Aggregates Is Mediated by Rac1 Activation Rather Than YAP Activation.

We demonstrate that Ha-RasV12 overexpression induces the nuclear translocation of Hippo effector Yes-associated protein (YAP) in MDCK cells via the hippo-independent pathway at the confluent stage. Ha-RasV12 overexpression leads to the downregulation of Caveolin-1 (Cav1) and the disruption of junction integrity. It has been shown that the disruption of actin belt integrity causes YAP nuclear translocation in epithelial cells at high density. Therefore, we hypothesized that Ha-RasV12-decreased Cav1 leads to the disruption of cell junction integrity, which subsequently facilitates YAP nuclear retention. We revealed that Ha-RasV12 downregulated Cav1 through the ERK pathway. Furthermore, the distribution and expression of Cav1 mediated the cell junction integrity and YAP nuclear localization. This suggests that the downregulation of Cav1 induced by Ha-RasV12 disrupted the cell junction integrity and promoted YAP nuclear translocation. We further indicated the consequence of Ha-RasV12-induced YAP activation. Surprisingly, the activation of YAP is not required for Ha-RasV12-induced multilayer cellular aggregates. Instead, Ha-RasV12 triggered the ERK-Rac pathway to promote cellular aggregate formation. Moreover, the overexpression of constitutively active Rac is sufficient to trigger cellular aggregation in MDCK cells at the confluent stage. This highlights that Rac activity is essential for cellular aggregates.

Deletion of Trp53 and Rb1 in Ctsk-expressing cells drives osteosarcoma progression by activating glucose metabolism and YAP signaling.

Glucose metabolism reprogramming is a critical factor in the progression of multiple cancers and is directly regulated by many tumor suppressors. However, how glucose metabolism regulates osteosarcoma development and progression is largely unknown. Cathepsin K (Ctsk) has been reported to express in chondroprogenitor cells and stem cells besides osteoclasts. Moreover, mutations in the tumor suppressors transformation‐related protein 53 (Trp53) and retinoblastoma protein (Rb1) are evident in approximately 50%–70% of human osteosarcoma. To understand how deletion of Trp53 and Rb1 in Ctsk‐expressing cells drives tumorigenesis, we generated the Ctsk‐Cre;Trp53f/f/Rb1f/f mouse model. Our data revealed that those mice developed osteosarcoma without formation of tumor in osteoclast lineage. The level of cortical bone destruction was gradually increased in parallel to the osteosarcoma progression rate. Through mechanistic studies, we found that loss of Trp53/Rb1 in Ctsk‐expressing cells significantly elevated Yes‐associated protein (YAP) expression and activity. YAP/TEAD1 complex binds to the glucose transporter 1 (Glut1) promoter to upregulate Glut1 expression. Upregulated Glut1 expression led to overactive glucose metabolism, increasing osteosarcoma progression. Ablation of YAP signaling inhibited energy metabolism and delayed osteosarcoma progression in Ctsk‐Cre;Trp53f/f/Rb1f/f mice. Collectively, these findings provide proof of principle that inhibition of YAP activity may be a potential strategy for osteosarcoma treatment.

Activated TAZ induces liver cancer in collaboration with EGFR/HER2 signaling pathways

BackgroundLiver cancer is a major global health concern due to the steady increases in its incidence and mortality. Transcription factors, yes-associated protein (YAP) and WW domain-containing transcription regulator protein 1 (WWTR1, also known as TAZ) have emerged as critical regulators in human hepatocellular carcinoma (HCC) and cholangiocarcinoma (CC), the two major types of primary liver cancer. However, our study as well as other previous reports have shown that activation of YAP and TAZ (YAP/TAZ) in adult murine livers is insufficient for the development of liver cancer, suggesting a requirement for an additional oncogenic collaborator for liver carcinogenesis in adulthood. Therefore, we sought to identify the oncogenic partners of YAP/TAZ that promote hepatocarcinogenesis in adults.MethodsData analysis of the transcriptome of patients with liver cancer was performed using the national center for biotechnology information (NCBI) gene expression omnibus (GEO) database and the cancer genome atlas (TCGA). The cancer therapeutics response portal (CTRP) was used to investigate the correlation between sensitivity to chemicals and the copy number of TAZ in human cancer cell lines. Transposons encoding constitutively activated forms of TAZ (TAZS89A), BRAF (BRAFV600E), and PIK3CA (PI3KE545K) were used for hydrodynamic tail vein injection. Mice were monitored at least twice per week and sacrificed when moribund. Tumor-bearing livers were formalin fixed for hematoxylin–eosin staining and immunohistochemistry.ResultsThrough database analyses, we identified EGFR/HER2 signaling to be essential in human cancers with high TAZ activity. Furthermore, immunohistochemical analyses showed that human HCC and CC tissues with high YAP/TAZ activities exhibited concomitant activation of EGFR/HER2 signaling pathways. To demonstrate that EGFR/HER2 signaling promotes YAP/TAZ-mediated hepatocarcinogenesis, TAZS89A was simultaneously expressed in murine adult livers with BRAFV600E or PI3KE545K, activated forms of effector molecules downstream of EGFR/HER2 signaling pathways. Expression of TAZS89A plus BRAFV600E induced HCC, whereas TAZS89A and PI3KE545K led to the development of CC-like cancer.ConclusionsOur study demonstrates that TAZ collaborates with EGFR/HER2 signaling pathways to induce both HCC and CC.

Regulator of G protein signaling 2 inhibits Gαq-dependent uveal melanoma cell growth

Activating mutations in Gαq/11 are a major driver of uveal melanoma (UM), the most common intraocular cancer in adults. While progress has recently been made in targeting Gαq/11 for UM therapy, the crucial role for these proteins in normal physiology and their high structural similarity with many other important GTPase proteins renders this approach challenging. The aim of the current study was to validate whether a key regulator of Gq signaling, regulator of G protein signaling 2 (RGS2), can inhibit Gαq-mediated UM cell growth. We used two UM cell lines, 92.1 and Mel-202, which both contain the most common activating mutation GαqQ209L and developed stable cell lines with doxycycline-inducible RGS2 protein expression. Using cell viability assays, we showed that RGS2 could inhibit cell growth in both of these UM cell lines. We also found that this effect was independent of the canonical GTPase-activating protein activity of RGS2 but was dependent on the association between RGS2 and Gαq. Furthermore, RGS2 induction resulted in only partial reduction in cell growth as compared to siRNA-mediated Gαq knockdown, perhaps because RGS2 was only able to reduce mitogen-activated protein kinase signaling downstream of phospholipase Cβ, while leaving activation of the Hippo signaling mediators yes-associated protein 1/TAZ, the other major pathway downstream of Gαq, unaffected. Taken together, our data indicate that RGS2 can inhibit UM cancer cell growth by associating with GαqQ209L as a partial effector antagonist.

Fingolimod exerts in vitro anticancer activity against hepatocellular carcinoma cell lines via YAP/TAZ suppression.

Hepatocellular carcinoma (HCC) remains a notably global health challenge with high mortality rates and poor prognosis. The deregulation of the Hippo signalling pathway, especially the overexpression and activation of downstream effector Yes-associated protein (YAP), has been demonstrated to result in the rapid malignant evolution of HCC. In this context, multiple efforts have been dedicated to targeting YAP for HCC therapy, but effective YAP inhibitors are still lacking. In this study, through a YAP-TEAD (8×GTIIC) luciferase reporter assay, we identified fingolimod, an immunomodulatory drug approved for the treatment of multiple sclerosis, as a novel YAP inhibitor. Fingolimod suppressed the proliferation of HCC cell lines by downregulating the protein levels as well as the trans-activating function of YAP. Overall, our current study not only identifies fingolimod as a novel YAP-targeting in hibitor, but also indicates that this clinically-approved drug could be utilized as a potential and feasible therapeutic drug for HCC.

Activation of YAP1 by STK25 contributes to the progression of hepatocellular carcinoma

A pathogenic role of serine/threonine protein kinase 25 (STK25) has been observed in several chronic liver diseases. However, whether STK25 participates in hepatocellular carcinoma (HCC) remains unexplored. The current work aimed to explore the role and mechanism of STK25 in HCC. A high STK25 level was found in HCC tissue, which was associated with reduced overall survival. HCC cells with STK25 silencing displayed a marked decrease in proliferative and invasive ability, but were highly sensitive to apoptosis induced by the chemotherapy drug sorafenib. Reciprocally, HCC cells with forced expression of STK25 displayed the opposite effects. Further data unveiled that STK25 silencing restrained the activation of Yes-associated protein 1 (YAP1) associated with regulation of mammalian STE20-like protein kinase 1/2 (MST1/2). Forced expression of constitutively active YAP1 abolished STK25 silencing-induced antitumor effects, while repression of YAP1 reversed STK25 upregulation-induced protumor effects. Additionally, HCC cells with STK25 silencing exhibited reduced tumorigenic potential in vivo. Collectively, the results show that STK25 exerts a protumor function in HCC by enhancing YAP1 activation via regulation of MST1/2. These findings propose STK25 as a viable target for the development of anti-HCC therapy.

Regorafenib inhibits epithelial-mesenchymal transition and suppresses cholangiocarcinoma metastasis via YAP1-AREG axis

Cholangiocarcinoma (CCA) is a subtype of bile duct cancer usually diagnosed late with a low survival rate and no satisfactorily systemic treatment. Recently, regorafenib has been accepted as a second-line treatment for CCA patients. In this study, we investigated the potential signal transduction pathways mediated by regorafenib. We established a transcriptomic database for regorafenib-treated CCA cells using expression microarray chips. Our data indicate that regorafenib inhibits yes-associated protein 1 (YAP1) activity in various CCA cells. In addition, we demonstrated that YAP1 regulates epithelial-mesenchymal transition (EMT)-related genes, including E-cadherin and SNAI2. We further examined YAP1 activity, phosphorylation status, and expression levels of YAP1 downstream target genes in the regorafenib model. We found that regorafenib dramatically suppressed these events in CCA cells. Moreover, in vivo results revealed that regorafenib could significantly inhibit lung foci formation and tumorigenicity. Most importantly, regorafenib and amphiregulin (AREG) neutralize antibody exhibited synergistic effects against CCA cells. In a clinical setting, patients with high YAP1 and EMT expression had a worse survival rate than patients with low YAP1, and EMT expression did. In addition, we found that YAP1 upregulated the downstream target amphiregulin in CCA. Our findings suggest that AREG neutralizing antibody antibodies combined with regorafenib can reverse the CCA metastatic phenotype and EMT in vitro and in vivo. These findings provide novel therapeutic strategies to combat the metastasis of CCA.

Ablation of high-mobility group box-1 in the liver reduces hepatocellular carcinoma but causes hyperbilirubinemia in Hippo signaling-deficient mice.

Silencing the Hippo kinases mammalian sterile 20‐like 1 and 2 (MST1/2) activates the transcriptional coactivator yes‐associated protein (YAP) in human hepatocellular carcinoma (HCC). Hepatocyte‐derived high‐mobility group box‐1 (HMGB1) regulates YAP expression; however, its contribution to HCC in the context of deregulated Hippo signaling is unknown. Here, we hypothesized that HMGB1 is required for hepatocarcinogenesis by activating YAP in Hippo signaling‐deficient (Mst1/2 ΔHep) mice. Mst1/2 ΔHep mice developed HCC within 3.5 months of age and had increased hepatic expression of HMGB1 and elevated YAP activity compared to controls. To understand the contribution of HMGB1, we generated Mst1/2&Hmgb1 ΔHep mice. They exhibited decreased YAP activity, cell proliferation, inflammation, fibrosis, atypical ductal cell expansion, and HCC burden at 3.5 months compared to Mst1/2 ∆Hep mice. However, Mst1/2&Hmgb1 ΔHep mice were smaller, developed hyperbilirubinemia, had more liver injury with intrahepatic biliary defects, and had reduced hemoglobin compared to Mst1/2 ΔHep mice. Conclusion: Hepatic HMGB1 promotes hepatocarcinogenesis by regulation of YAP activity; nevertheless, it maintains intrahepatic bile duct physiology under Hippo signaling deficiency.

Yes-associated protein activation potentiates glycogen synthase kinase-3 inhibitor-induced proliferation of neonatal cardiomyocytes and iPS cell-derived cardiomyocytes.

Because mammalian cardiomyocytes largely cease to proliferate immediately after birth, the regenerative activity of the heart is limited. To date, much effort has been made to clarify the regulatory mechanism of cardiomyocyte proliferation because the amplification of cardiomyocytes could be a promising strategy for heart regenerative therapy. Recently, it was reported that the inhibition of glycogen synthase kinase (GSK)‐3 promotes the proliferation of neonatal rat cardiomyocytes (NRCMs) and human iPS cell‐derived cardiomyocytes (hiPSC‐CMs). Additionally, Yes‐associated protein (YAP) induces cardiomyocyte proliferation. The purpose of this study was to address the importance of YAP activity in cardiomyocyte proliferation induced by GSK‐3 inhibitors (GSK‐3Is) to develop a novel strategy for cardiomyocyte amplification. Immunofluorescent microscopic analysis using an anti‐Ki‐67 antibody demonstrated that the treatment of NRCMs with GSK‐3Is, such as BIO and CHIR99021, increased the ratio of proliferative cardiomyocytes. YAP was localized in the nuclei of more than 95% of cardiomyocytes, either in the presence or absence of GSK‐3Is, indicating that YAP was endogenously activated. GSK‐3Is increased the expression of β‐catenin and promoted its translocation into the nucleus without influencing YAP activity. The knockdown of YAP using siRNA or pharmacological inhibition of YAP using verteporfin or CIL56 dramatically reduced GSK‐3I‐induced cardiomyocyte proliferation without suppressing β‐catenin activation. Interestingly, the inhibition of GSK‐3 also induced the proliferation of hiPSC‐CMs under sparse culture conditions, where YAP was constitutively activated. In contrast, under dense culture conditions, in which YAP activity was suppressed, the proliferative effects of GSK‐3Is on hiPSC‐CMs were not detected. Importantly, the activation of YAP by the knockdown of α‐catenin restored the proproliferative activity of GSK‐3Is. Collectively, YAP activation potentiates the GSK‐3I‐induced proliferation of cardiomyocytes. The blockade of GSK‐3 in combination with YAP activation resulted in remarkable amplification of cardiomyocytes.