Expression Of YAP Target Genes Research Articles

Establishment of Anoxia/cytokine-induced Injury and Regeneration in Colonoids

Intestinal epithelial cells (IECs) play key roles in nutrient absorption and fluid secretion, providing a barrier to protect cells. IECs, derived from intestinal stem cells (ISCs), are crucial in maintaining intestinal homeostasis and regeneration, which is crucial in gastrointestinal diseases such as inflammatory bowel disease (IBD). To study epithelial injury/regeneration, primary cultured colonoids were utilized as a model system to mimic injury. They retain the composition and differentiation of the tissue, making it a suitable model for studying homeostasis and regeneration of ISCs in vitro. Anoxia and proinflammatory cytokines frequently coexist and exacerbate one another during intestinal injury. However, anoxic conditions have been mainly ignored in previous research. Thus, we developed a regeneration model using cytokines/anoxia injury to better recapitulate intestinal inflammation. Colonoids were treated with cytokines TNF-α and IFN-γ (5 ng/μL) in anoxic conditions for 24 hours to provoke an injury. After 24 hours of injury, the colonoids were exposed to normal oxygen and media conditions for regeneration. Regeneration was observed for 24, 48, and 72 hours and documented using photomicrographs. Morphological analysis detailed that injury was most severe 24 hours post-injury with the combined induction of cytokines and anoxia resulting in decreased colonoid area and number of buds compared to control groups. RT-PCR analysis detailed mRNA expression of stem cell markers ( Lgr5, Bmi1, and Hopx), Wnt ( Axin2, Myc2, and Ascl2), and YAP target genes ( Sca1 and Ctgf) were increased at peak injury and returned to pre-injury levels at 72 hours of recovery. Regeneration of the colonoids is consistent with in vivo observations, thus confirming the validity of the model. This versatile model can be used to study responses to injury and regeneration of intestinal epithelium and the function of ISCs with applications in intestinal disease therapeutics. University of Maryland College of Agriculture and Natural Resources and the Maryland Agricultural Experiment Station Undergraduate Research Grant Grant #4307572 from the Maryland Stem Cell Research Fund. This is the full abstract presented at the American Physiology Summit 2024 meeting and is only available in HTML format. There are no additional versions or additional content available for this abstract. Physiology was not involved in the peer review process.

Abstract 4585: Discovery of ETS-006, a highly potent YAP/TEADs PPI inhibitor with broad anti-tumor activity as a single agent

Abstract The transcription co-activators YAP, pairing with the TEAD family of transcription factors, serve as essential effectors of the conserved Hippo signaling pathway. Hippo kinase cascade controls YAP nuclear entry and binding with TEADs by modulating its phosphorylation and stability. Overexpression and activation of YAP/TAZ are frequently observed in a variety of cancers. It has been well established that YAP aberration contributes to cancer development, metastasis, immunosurveillance escape and drug resistance. Disruption of YAP/TEADs PPI is an effective approach to inhibit YAP transcriptional activity. We previously have reported the identification of YAP/TEADs PPI hit compound through the fragment-based screen and advanced the hit to lead compound ETS-003. Here we reported the preclinical candidate of YAP/TEADs PPI inhibitor ETS-006 with much more potent anti-tumor activity and favorable safety profile. Compared to TEAD palmitoylation inhibitor, ETS-006 could completely disrupt the interaction of YAP/TEADs, resulting in a more profound downregulation of YAP target gene expression. ETS-006 demonstrated more robust anti-tumor activity than the competitor’s YAP/TEADs PPI inhibitor in MPM CDX model with favorable ADME properties. Notably, ETS-006 showed promising efficacy across multiple solid tumor types, including head and neck squamous cell carcinoma, osteosarcoma, and triple-negative breast cancer with urgent unmet clinical needs. In conclusion, ETS-006 is a highly potent and orally available YAP/TEADs PPI inhibitor with broad anti-tumor activity as a single agent. Citation Format: Jiajun Lu, Ming Gao, Wenpei Du, Xiaofei Fan, Jinping Li, Mengya Wang, Lijian Feng, Yingjie Li, Jiaqi Yao, Jiting Lu, Wenqi Cui, Qiangang Zheng, Jidong Zhu. Discovery of ETS-006, a highly potent YAP/TEADs PPI inhibitor with broad anti-tumor activity as a single agent [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2024; Part 1 (Regular Abstracts); 2024 Apr 5-10; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2024;84(6_Suppl):Abstract nr 4585.

Blood Flow Directs Yap/Taz-Mediated Transcriptional Regulation of Self-Renewal Programs to Control Developmental HSPC Expansion By Mechanical Stimulation of Piezo1

Hematopoietic stem and progenitor cells (HSPCs) emerge from artery-derived hemogenic endothelium (HE) in the vertebrate embryo during development. This process entails a cellular reprogramming from endothelial to hematopoietic gene signatures driven by the Runx1 transcription factor (TF), which is referred to as the endothelial-to-hematopoietic transition (EHT). A major goal of cellular therapeutics is to derive patient-specific HSPCs from iPSCs for clinical use, yet current differentiation protocols largely fail to recapitulate EHT to produce or expand long-lived multi-potent HSPCs in vitro suggesting an incomplete understanding of the in vivo regulatory cues. Physical forces of wall shear stress (WSS) and cyclic stretch (CS) produced by hemodynamic blood flow in embryos are one such cue required during EHT to generate HSPCs from HE, however the mechanisms by which these forces are sensed and converted into a “stemness” regulatory module remain undefined. Our previous work implicated the Hippo pathway TF YAP as essential for the maintenance, but not initiation, of the hematopoietic program in newly specified HE. Here, using scRNA-sequencing of sorted zebrafish trunk endothelial cells to capture all stages of EHT progression, we find that overexpression of YAP drives lipid metabolism, cell cycling, and propagation of a hematopoietic gene regulatory network (GRN) in the earliest specified HE cells. By employing a heat shock-inducible dominant negative YAP zebrafish line, we unmask a latent role for the YAP paralogue TAZ in hematopoiesis, which can promote CD41 + and Flk +/Myb + HSPC production upon reduced YAP function. YAP and TAZ initiate transcriptional responses downstream of mechanical stimuli and require DNA binding cofactors to regulate target genes. Surprisingly, luciferase assays in HEK293 cells demonstrated a potent synergistic effect of TAZ/RUNX1, but not YAP/RUNX1, in transcriptional regulation at RUNX enhancers. Finally, by pharmacologic and genetic manipulation, we identify the stretch-gated membrane ion channel Piezo1 as a potent regulator of CS-induced YAP/TAZ mechanotransduction in HE. Stimulation of zebrafish embryos with the Piezo1 small molecule agonist Yoda1 significantly increases HSPC number and YAP target gene expression in a YAP-dependent fashion. A similar modulation of blood and YAP target genes in human iPSC-derived CD34+ HE cells is seen with Yoda1, suggesting that this stretch-Piezo1-YAP axis can be chemically tuned in vitro to enhance HSPC differentiation. These results illuminate molecular details of how YAP/TAZ directs the production of HSPCs from HE in response to mechanical cues, and have broader implications for alternate regulatory effects of mechanically-stimulated Hippo TFs depending on the transcriptional milieu in cell-type specific contexts.

AMPK-Dependent YAP Inhibition Mediates the Protective Effect of Metformin against Obesity-Associated Endothelial Dysfunction and Inflammation.

Hyperglycemia is a crucial risk factor for cardiovascular diseases. Chronic inflammation is a central characteristic of obesity, leading to many of its complications. Recent studies have shown that high glucose activates Yes-associated protein 1 (YAP) by suppressing AMPK activity in breast cancer cells. Metformin is a commonly prescribed anti-diabetic drug best known for its AMPK-activating effect. However, the role of YAP in the vasoprotective effect of metformin in diabetic endothelial cell dysfunction is still unknown. The present study aimed to investigate whether YAP activation plays a role in obesity-associated endothelial dysfunction and inflammation and examine whether the vasoprotective effect of metformin is related to YAP inhibition. Reanalysis of the clinical sequencing data revealed YAP signaling, and the YAP target genes CTGF and CYR61 were upregulated in aortic endothelial cells and retinal fibrovascular membranes from diabetic patients. YAP overexpression impaired endothelium-dependent relaxations (EDRs) in isolated mouse aortas and increased the expression of YAP target genes and inflammatory markers in human umbilical vein endothelial cells (HUVECs). High glucose-activated YAP in HUVECs and aortas was accompanied by increased production of oxygen-reactive species. AMPK inhibition was found to induce YAP activation, resulting in increased JNK activity. Metformin activated AMPK and promoted YAP phosphorylation, ultimately improving EDRs and suppressing the JNK activity. Targeting the AMPK-YAP-JNK axis could become a therapeutic strategy for alleviating vascular dysfunction in obesity and diabetes.

Chlamydia trachomatis induces the transcriptional activity of host YAP in a Hippo-independent fashion.

The obligate intracellular pathogen Chlamydia trachomatis is the causative agent of the most common bacterial sexually transmitted disease worldwide. While the host response to infection by this pathogen has been well characterized, it remains unclear to what extent host gene expression during infection is the product of Chlamydia-directed modulation of host transcription factors. To identify transcription factors potentially modulated by Chlamydia during infection, we infected immortalized endocervical epithelial cells (End1/E6E7) with the anogenital C. trachomatis serovar L2, harvesting polyadenylated RNA for bulk RNA-sequencing. Subsequent experiments elucidating the mechanism of infection-mediated YAP activation assayed YAP target gene expression via qRT-PCR, YAP nuclear translocation via quantitative immunofluorescence, and YAP phosphorylation via Western blotting. RNA sequencing of Chlamydia-infected endocervical epithelial cells revealed gene expression consistent with activity of YAP, a transcriptional coactivator implicated in cell proliferation, wound healing, and fibrosis. After confirming induction of YAP target genes during infection, we observed an infection-dependent increase in YAP nuclear translocation sensitive to inhibition of bacterial protein synthesis. While Hippo-mediated phosphoinhibition of YAP at S127 was unaffected by C. trachomatis infection, Hippo-independent phosphorylation at Y357 was increased. Infection did not enhance nuclear translocation of Y357F mutant YAP, illustrating a requirement for phosphorylation at this residue. Pharmacological inhibition of host Src-family kinase activity attenuated YAP Y357 phosphorylation, but not nuclear translocation - which was instead sensitive to inhibition of Abl. Our results define a transcriptome-altering mechanism of pathogen-directed YAP activation that bypasses canonical inhibition by the Hippo kinase cascade, with a potential link to chlamydial fibrosis and other advanced disease sequelae. Additional study is required to determine the specific role of infection-associated Y357 phosphorylation and Abl activity in chlamydial induction of YAP.

Structure-based discovery of a novel small-molecule inhibitor of TEAD palmitoylation with anticancer activity.

The paralogous oncogenic transcriptional coactivators YAP and TAZ are the distal effectors of the Hippo signaling pathway, which plays a critical role in cell proliferation, survival and cell fate specification. They are frequently deregulated in most human cancers, where they contribute to multiple aspects of tumorigenesis including growth, metabolism, metastasis and chemo/immunotherapy resistance. Thus, they provide a critical point for therapeutic intervention. However, due to their intrinsically disordered structure, they are challenging to target directly. Since YAP/TAZ exerts oncogenic activity by associating with the TEAD1-4 transcription factors, to regulate target gene expression, YAP activity can be controlled indirectly by regulating TEAD1-4. Interestingly, TEADs undergo autopalmitoylation, which is essential for their stability and function, and small-molecule inhibitors that prevent this posttranslational modification can render them unstable. In this article we report discovery of a novel small molecule inhibitor of YAP activity. We combined structure-based virtual ligand screening with biochemical and cell biological studies and identified JM7, which inhibits YAP transcriptional reporter activity with an IC50 of 972 nMoles/Ltr. Further, it inhibits YAP target gene expression, without affecting YAP/TEAD localization. Mechanistically, JM7 inhibits TEAD palmitoylation and renders them unstable. Cellular thermal shift assay revealed that JM7 directly binds to TEAD1-4 in cells. Consistent with the inhibitory effect of JM7 on YAP activity, it significantly impairs proliferation, colony-formation and migration of mesothelioma (NCI-H226), breast (MDA-MB-231) and ovarian (OVCAR-8) cancer cells that exhibit increased YAP activity. Collectively, these results establish JM7 as a novel lead compound for development of more potent inhibitors of TEAD palmitoylation for treating cancer.

Decellularized Spinach Biomaterials Support Physiologically Relevant Mechanical Cyclic Strain and Prompt a Stretch-Induced Cellular Response.

Recently, decellularized plant biomaterials have been explored for their use as tissue engineered substitutes. Herein, we expanded upon the investigation of the mechanical properties of these materials to explore their elasticity as many anatomical areas of the body require biomechanical dynamism. We first constructed a device to secure the scaffold and induce a strain within the physiological range of the normal human adult lung during breathing (12-20 movements/min; 10-20% elongation). Results showed that decellularized spinach leaves can support cyclic strain for 24 h and displayed heterogeneous local strain values (7.76-15.88%) as well as a Poisson's ratio (0.12) similar to that of mammalian lungs (10.67-19.67%; 0.01), as opposed to an incompressible homogeneous standard polymer (such as PDMS (10.85-12.71%; 0.4)). Imaging and mechanical testing showed that the vegetal scaffold exhibited strain hardening but maintained its structural architecture and water retention capacity, suggesting an unaltered porosity. Interestingly, we also showed that cells seeded on the scaffold can also sense the mechanical strain as demonstrated by a nuclear reorientation perpendicular to strain direction (63.3° compared to 41.2° for nonstretched cells), a nuclear location of YAP and increased expression of YAP target genes, a high cytoplasmic calcium level, and an elevated expression level of collagen genes (COL1A1, COL3A1, COL4A1, and COL6A) with an increased collagen secretion at the protein level. Taken together, these data demonstrated that decellularized plant leaf tissues have an inherent elastic property similar to that found in the mammalian system to which cells can sense and respond.

Abstract 12286: A Novel Yap Inhibitor Cbl0137 Protects Against Endothelial Inflammation and Atherosclerosis

Background: Endothelial activation is a critical hallmark in the initiation of atherosclerosis. Our previous study found that YAP activation plays a significant role in induction of endothelial inflammation and formation of atherosclerotic plaques, suggesting that targeting YAP signaling pathway might be effective for the treatment of atherosclerotic cardiovascular disease. We have recently set up a reporter gene assay-based drug screening platform and identified CBL0137 as an inhibitor of YAP activity in human endothelial cells. Methods: We used 8*GTIIC luciferase reporter gene assay to screen a drug library and other small molecule compounds. We validated the inhibitory effect of CBL0137 on YAP activity by detecting the expression of YAP target genes and phosphorylation of YAP, which were measured by quantitative real-time polymerase chain reaction and western blotting, respectively. Subsequently, we treated human endothelial cells with CBL0137 (1 μM) for 4 hrs, and then isolated the total RNA and performed transcriptome sequencing. We explored the anti-inflammatory effects and underlying mechanisms of CBL0137 in primary endothelial cells. Moreover, we assessed whether CBL0137 could retard formation of atherosclerotic plaques in ApoE-/- mice using carotid artery partial ligation-induced and chronic western diet-induced atherosclerosis models. Results: We identified CBL0137 as a novel YAP inhibitor through screening the drug library. In human endothelial cells, CBL0137 inhibited the phosphorylation of YAP at Y357 to suppress YAP activity, and therefore repressed the expression of YAP target genes. In addition, CBL0137 restrained endothelial inflammatory response in a YAP-dependent manner. Furthermore, CBL0137 inhibited YAP phosphorylation at Y357 via the tyrosine-protein kinase Src. In animal experiments, administration of low doses of CBL0137 attenuated endothelial inflammation and atherosclerosis induced by disturbed flow or atherogenic diets in both male and female ApoE-/- mice. Conclusions: CBL0137 is a novel YAP inhibitor that protects against endothelial inflammation and atherogenesis. CBL0137 might be a promising anti-atherosclerosis drug, but further investigations including clinical trials are required.

Endothelial cell activation by interleukin-1 and extracellular matrix laminin-10 occurs via the YAP signalling pathway

Laminin-10 (LM-10) is a key regulator of blood-brain barrier (BBB) repair after hypoxia and inflammation. Here we investigated the signalling mechanisms regulated by LM-10 in human brain endothelial cell line hCMEC/D3 in response to interleukin(IL)-1beta(β) in vitro. LM-10 promoted endothelial proliferation and repair of an endothelial monolayer after scratch injury, and upregulated IL-1β-induced ICAM-1 and VCAM-1 expression. IL-1β and LM-10 regulated YAP signalling pathway in endothelial cells leading to differential expression of YAP target genes, ctgf and serpine-1, providing evidence that the YAP signalling pathway could be a new therapeutic target for the treatment of BBB dysfunction in CNS diseases.

Bip-Yorkie interaction determines oncogenic and tumor-suppressive roles of Ire1/Xbp1s activation

Unfolded protein response (UPR) is the mechanism by which cells control endoplasmic reticulum (ER) protein homeostasis. ER proteostasis is essential to adapt to cell proliferation and regeneration in development and tumorigenesis, but mechanisms linking UPR, growth control, and cancer progression remain unclear. Here, we report that the Ire1/Xbp1s pathway has surprisingly oncogenic and tumor-suppressive roles in a context-dependent manner. Activation of Ire1/Xbp1s up-regulates their downstream target Bip, which sequesters Yorkie (Yki), a Hippo pathway transducer, in the cytoplasm to restrict Yki transcriptional output. This regulation provides an endogenous defensive mechanism in organ size control, intestinal homeostasis, and regeneration. Unexpectedly, Xbp1 ablation promotes tumor overgrowth but suppresses invasiveness in a Drosophila cancer model. Mechanistically, hyperactivated Ire1/Xbp1s signaling in turn induces JNK-dependent developmental and oncogenic cell migration and epithelial-mesenchymal transition (EMT) via repression of Yki. In humans, a negative correlation between XBP1 and YAP (Yki ortholog) target gene expression specifically exists in triple-negative breast cancers (TNBCs), and those with high XBP1 or HSPA5 (Bip ortholog) expression have better clinical outcomes. In human TNBC cell lines and xenograft models, ectopic XBP1s or HSPA5 expression alleviates tumor growth but aggravates cell migration and invasion. These findings uncover a conserved crosstalk between the Ire1/Xbp1s and Hippo signaling pathways under physiological settings, as well as a crucial role of Bip-Yki interaction in tumorigenesis that is shared from Drosophila to humans.

Optogenetic control of YAP cellular localisation andfunction.

YAP, an effector of the Hippo signalling pathway, promotes organ growth and regeneration. Prolonged YAP activation results in uncontrolled proliferation and cancer. Therefore, exogenous regulation of YAP activity has potential translational applications. We present a versatile optogenetic construct (optoYAP) for manipulating YAP localisation, and consequently its activity and function. We attach a LOV2 domain that photocages a nuclear localisation signal (NLS) to the N‐terminus of YAP. In 488 nm light, the LOV2 domain unfolds, exposing the NLS, which shuttles optoYAP into the nucleus. Nuclear import of optoYAP is reversible and tuneable by light intensity. In cell culture, activated optoYAP promotes YAP target gene expression and cell proliferation. Similarly, optofYap can be used in zebrafish embryos to modulate target genes. We demonstrate that optoYAP can override a cell's response to substrate stiffness to generate anchorage‐independent growth. OptoYAP is functional in both cell culture and in vivo, providing a powerful tool to address basic research questions and therapeutic applications in regeneration and disease.

MARK2 regulates chemotherapeutic responses through class IIa HDAC-YAP axis in pancreatic cancer.

Despite paclitaxel's wide use in cancer treatment, patient response rate is still low and drug resistance is a major clinical obstacle. Through a Phos-tag-based kinome-wide screen, we identified MARK2 as a critical regulator for paclitaxel chemosensitivity in PDAC. We show that MARK2 is phosphorylated by CDK1 in response to antitubulin chemotherapeutics and in unperturbed mitosis. Phosphorylation is essential for MARK2 in regulating mitotic progression and paclitaxel cytotoxicity in PDAC cells. Mechanistically, our findings also suggest that MARK2 controls paclitaxel chemosensitivity by regulating class IIa HDACs. MARK2 directly phosphorylates HDAC4 specifically during antitubulin treatment. Phosphorylated HDAC4 promotes YAP activation and controls expression of YAP target genes induced by paclitaxel. Importantly, combination of HDAC inhibition and paclitaxel overcomes chemoresistance in organoid culture and preclinical PDAC animal models. The expression levels of MARK2, HDACs, and YAP are upregulated and positively correlated in PDAC patients. Inhibition of MARK2 or class IIa HDACs potentiates paclitaxel cytotoxicity by inducing mitotic abnormalities in PDAC cells. Together, our findings identify the MARK2-HDAC axis as a druggable target for overcoming chemoresistance in PDAC.

RhoA enhances osteosarcoma resistance to MPPa-PDT via the Hippo/YAP signaling pathway

BackgroundOsteosarcoma (OS) is the most prevalent primary bone malignancy affecting adolescents, yet the emergence of chemoradiotherapeutic resistance has limited efforts to cure affected patients to date. Pyropheophorbide-α methyl ester-mediated photodynamic therapy (MPPa-PDT) is a recently developed, minimally invasive treatment for OS that is similarly constrained by such therapeutic resistance. This study sought to explore the mechanistic basis for RhoA-activated YAP1 (YAP)-mediated resistance in OS.MethodsThe relationship between YAP expression levels and patient prognosis was analyzed, and YAP levels in OS cell lines were quantified. Immunofluorescent staining was used to assess YAP nuclear translocation. OS cell lines (HOS and MG63) in which RhoA and YAP were knocked down or overexpressed were generated using lentiviral vectors. CCK-8 assays were used to examine OS cell viability, while the apoptotic death of these cells was monitored via Hoechst staining, Western blotting, and flow cytometry. Tumor-bearing nude mice were additionally used to assess the relationship between lentivirus-mediated alterations in RhoA expression and MPPa-PDT treatment outcomes. TUNEL and immunohistochemical staining approaches were leveraged to assess apoptotic cell death in tissue samples.ResultsOS patients exhibited higher levels of YAP expression, and these were correlated with a poor prognosis. MPPa-PDT induced apoptosis in OS cells, and such MPPa-PDT-induced apoptosis was enhanced following YAP knockdown whereas it was suppressed by YAP overexpression. RhoA and YAP expression levels were positively correlated in OS patients, and both active and total RhoA protein levels rose in OS cells following MPPa-PDT treatment. When RhoA was knocked down, levels of unphosphorylated YAP and downstream target genes were significantly reduced, while RhoA/ROCK2/LIMK2 pathway phosphorylation was suppressed, whereas RhoA overexpression resulted in the opposite phenotype. MPPa-PDT treatment was linked to an increase in HMGCR protein levels, and the inhibition of RhoA or HMGCR was sufficient to suppress RhoA activity and to decrease the protein levels of YAP and its downstream targets. Mevalonate administration partially reversed these reductions in the expression of YAP and YAP target genes. RhoA knockdown significantly enhanced the apoptotic death of OS cells in vitro and in vivo following MPPa-PDT treatment, whereas RhoA overexpression had the opposite effect.ConclusionsThese results suggest that the mevalonate pathway activates RhoA, which in turn activates YAP and promotes OS cell resistance to MPPa-PDT therapy. Targeting the RhoA/ROCK2/LIMK2/YAP pathway can significantly improve the efficacy of MPPa-PDT treatment for OS.

Abstract 2900: PRAMEF2 ubiquitylates and degrades LATS1 leading to enhanced nuclear accumulation of YAP and tumorigenesis

Abstract PRAMEF2 (PRAME Family Member 2) is a Cancer Testis Antigen belonging to the PRAME multi-gene family. All Cancer Testis Antigens are expressed in male testicular germ cells while remaining absent from other adult tissues. Conversely, they show aberrant re-expression in several human malignancies and also elicit immunogenic responses in cancer patients. This makes Cancer Testis Antigens and thereby PRAMEF2, effective and novel targets for cancer vaccine development. However, the physiological function of PRAMEF2 underlying tumorigenesis remains unspecified. Hence, we performed a proteomic screen to explore its unique interactome in the cell. Subsequent size exclusion chromatography and co-immunoprecipitation assays confirmed the role of PRAMEF2 as a BC-box containing substrate recognition subunit of a Cullin 2 based-E3 ubiquitin ligase complex. In the proteomic screen, several proteins were identified, however in-vivo assays revealed LATS1 to be a specific and novel interacting partner of PRAMEF2. LATS1 is a Ser/Thr Kinase of the Hippo Pathway, known to aid tumor suppression. We observed PRAMEF2 mediated ubiquitylation and subsequent proteasomal degradation of LATS1 through ubiquitylation assay. The site for ubiquitylation was mapped to the highly conserved Lysine 860 residue on LATS1. Upon activation of the Hippo Pathway, LATS1 results in phosphorylation of the transcriptional co-activator YAP, leading to its cytosolic translocation. Consequently, PRAMEF2 mediated LATS1 regulation resulted in decreased YAP phosphorylation and its increased accumulation in the nucleus. Furthermore, RTqPCR array and ChIP analysis showed the enhanced expression of YAP target genes implicated in proliferation and metastasis. Moreover, PRAMEF2 depletion also diminished the proliferative capacity, migration potential and invasiveness of tumor cells. Studies in mouse tumor models confirmed that PRAMEF2 abrogates the tumor suppressive function of LATS1 leading to ameliorated tumor growth and metastasis. Taken together, our findings help establish the role of PRAMEF2, an unique Cancer Testis Antigen, as a substrate recognition subunit of a Cullin 2- based E3 ubiquitin ligase complex which ubquitylates and degrades LATS1. Hence, PRAMEF2 realizes its oncogenic potential by increasing YAP nuclear accumulation and promoting tumor cell proliferation and metastasis. Citation Format: Madhurima Ghosh, Sanjeev Das. PRAMEF2 ubiquitylates and degrades LATS1 leading to enhanced nuclear accumulation of YAP and tumorigenesis [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2021; 2021 Apr 10-15 and May 17-21. Philadelphia (PA): AACR; Cancer Res 2021;81(13_Suppl):Abstract nr 2900.

YAP Regulates Hematopoietic Stem Cell Formation in Response to the Biophysical Forces of Blood Flow

Hematopoietic stem cells (HSCs) are first specified during embryonic development from hemogenic endothelial cells (HEC) in the ventral dorsal aorta (VDA). Prior studies from our lab and others demonstrated that HSC formation is coordinated with the onset of rigorous circulatory flow, which exposes the vascular endothelium to both wall shear stress (WSS) and circumferential stretch (CS). To better understand how these biomechanical forces drive HEC specification and HSC production, we engineered a microfluidics-based dorsal aorta-on-a-chip that recapitulates the biophysical features present in the vasculature. Using this biomimetic microsystem, human iPS-derived HEC exposed to WSS and CS through continuous media flow and cyclic stretching of the adherent cell layer showed an upregulation of RUNX1 (WSS, p<0.01; CS, p<0.05), the main transcription factor involved in HSC specification, by qPCR compared to cells in the static control. Interestingly, the YAP (Yes-associated protein) target genes CYR61, ANKRD1 and CTGF were also upregulated in human iPS-derived HEC after exposure to CS, suggesting a possible downstream mechanism for the effects of blood flow on HEC. YAP is the most downstream effector protein in the Hippo signaling pathway and is known to regulate stem cell dynamics and organ size. Prior work identified YAP as a mechanosensor, where it is activated in response to Rho GTPase activity and actomyosin filament rearrangement independent of the core Hippo pathway. To test whether YAP functions in response to mechanical force-activated Rho, iPS-derived HEC were exposed to circumferential stretch in the presence of a Rho inhibitor, which abolished CS-induced activation of YAP targets and RUNX1, indicating that Rho proteins are involved in mediating the effects of blood flow on HECs. Furthermore, treatment of iPS-derived HEC cultured under static conditions with either direct or indirect activators of the Rho GTPase family increased YAP activity and RUNX1 levels, demonstrating that biophysical forces from blood flow can be mimicked in vitro with Rho modulation. To investigate the implication of these findings in vivo, we utilized the zebrafish model: as in mammalian systems, HSCs are born in the VDA (24-36 hours post fertilization (hpf)) and migrate to the secondary sites of hematopoiesis to expand and differentiate before colonizing adult tissues. Heat-shock mediated overexpression of Yap at 12 hpf significantly increased runx1 + HEC specification at 36 hpf by both in situ hybridization and qPCR (p<0.01). This impact on HSC number was sustained throughout development, as Yap overexpression also significantly increased the number of Cd41+ HSCs present in the caudal hematopoietic tissue (CHT) at 72 hpf (p<0.05). In contrast, Yap knockout mutants exhibited a significant reduction in runx1 at 36 hpf (p<0.0001) despite normal Flk1+ vascular structure, indicative of a role for Yap in HSC specification. In line with the human in vitro data, activation of Rho GTPase increased expression of Yap target genes and runx1 at 36 hpf (p<0.05), suggesting a pathway in which Yap induces Runx1 downstream of Rho stimulation. Prior analysis of the silent heart mutant line as well as morpholino knockdown of cardiac troponin T type A (tnnt2a) revealed a significant deficiency in HEC specification and HSC production in the absence of heartbeat and blood flow. Importantly, compound-mediated activation of Rho GTPase (12-36 hpf) significantly increased runx1 expression in tnnt2a morphant embryos by in situ hybridization and qPCR (p<0.01), demonstrating that Rho activation can mimic the effects of blood flow on HSC production in vivo . Taken together, our findings point to a functional intersection between blood flow, Rho GTPase function and YAP activation in RUNX1-dependent HSC production; this mechanochemical mechanism may be exploited to improve in vitro human HSC differentiation protocols for the treatment for blood disorders. DisclosuresIngber:Emulate, Inc.: Equity Ownership, Membership on an entity's Board of Directors or advisory committees.

Vinculin Tension and YAP Activation are Altered in Dystrophic Muscle Cells

Duchenne muscular dystrophy is a lethal muscle wasting disease caused by the absence of dystrophin, a protein that links the actin cytoskeleton to the extracellular matrix. Cells generate, sense, and respond to forces via mechanosensitive protein complexes, and altered force transmission via these complexes such as focal adhesions (FAs) are known to contribute to the development and progression of muscular dystrophy. However, the interplay between loss of dystrophin and altered force transmission via FAs remains unknown. Here we show that FAs of dystrophin deficient muscle cells are under less mechanical load and have decreased activation of yes-associated protein 1 (YAP). Using a vinculin bioluminescent tension sensor, we measured FAs tension in transgenic muscle cells expressing wild type (WT) dystrophin, two patient derived dystrophin missense mutants (L172H and L54R), and a non-disease-causing mutation (I232M). We found that cells harboring WT dystrophin showed higher average tension across vinculin compared to the tension in dystrophic cells. I232M vinculin tension was the same as WT tension. YAP is a known FA mechano-target protein that functions in the nucleus as a transcriptional co-activator and regulates several cellular processes including cellular migration. Dystrophic cells had higher levels of cytoplasmic YAP when compared to nuclear YAP, increased YAP S127 inactivating phosphorylation and decreased migration rates, compared to WT and I23M. Our results suggest that the Hippo pathway may regulate YAP activation via LATS1/2 activity. LATS1/2 phosphorylates YAP in S172 sequestering it in the cytoplasm and preventing its translocation to the nucleus, decreasing the expression of YAP target genes in migration. Altogether, our results show that expression of disease-causing mutant dystrophins leads to decreased tension transmission and aberrant mechanotransduction via FAs. We propose that decreased vinculin tension leads to increased Hippo pathway signaling which causes decreased YAP activation that results in impaired migration. Therefore, our cell lines could be used as a platform to characterize the effectiveness of DMD therapies for patients with missense mutations by means of monitoring YAP and migration. Furthermore, they could also be used to explore novel therapeutic targets in the Hippo pathway.

A TNFR2-hnRNPK Axis Promotes Primary Liver Cancer Development via Activation of YAP Signaling in Hepatic Progenitor Cells.

Most primary liver cancer (PLC) cases progress mainly due to underlying chronic liver inflammation, yet the underlying mechanisms of inflammation-mediated PLC remain unclear. Here we uncover a TNF receptor II (TNFR2)-hnRNPK-YAP signaling axis in hepatic progenitor cells (HPC) essential for PLC development. TNFR2, but not TNF receptor I (TNFR1), was required for TNFα-induced activation of YAP during malignant transformation of HPCs and liver tumorigenesis. Mechanistically, heterogeneous nuclear ribonuclear protein K (hnRNPK) acted downstream of TNFα-TNFR2 signaling to directly interact with and stabilize YAP on target gene promoters genome-wide, therefore coregulating the expression of YAP target genes. Single-cell RNA sequencing confirmed the association of TNFR2-hnRNPK with YAP expression and the pathologic importance of HPC. Accordingly, expressions of TNFR2, hnRNPK, and YAP were all upregulated in PLC tissues and were strongly associated with poor prognosis of PLC including patient survival. Collectively, this study clarifies the differential roles of TNFRs in HPC-mediated tumorigenesis, uncovering a TNFR2-hnRNPK-centered mechanistic link between the TNFα-mediated inflammatory milieu and YAP activation in HPCs during PLC development. SIGNIFICANCE: This work defines how hnRNPK links TNFα signaling and Hippo pathway transcription coactivator YAP in hepatic progenitor cells during primary liver tumorigenesis.

Fatty Acids Activate the Transcriptional Coactivator YAP1 to Promote Liver Fibrosis via p38 Mitogen-Activated Protein Kinase.

Background & AimsPatients with simple steatosis (SS) and nonalcoholic steatohepatitis can develop progressive liver fibrosis, which is associated with liver-related mortality. The mechanisms contributing to liver fibrosis development in SS, however, are poorly understood. SS is characterized by hepatocellular free fatty acid (FFA) accumulation without lobular inflammation seen in nonalcoholic steatohepatitis. Because the Hippo signaling transcriptional coactivator YAP1 (YAP) has previously been linked with nonalcoholic fatty liver disease (NAFLD)–related fibrosis, we sought to explore how hepatocyte FFAs activate a YAP-mediated profibrogenic program.MethodsWe analyzed RNA sequencing data from a GEO DataSet (accession: GSE162694) consisting of 143 patients with NAFLD. We also performed immunohistochemical, immunofluorescence, immunoblot, and quantitative reverse-transcription polymerase chain reaction analyses (qRT-PCR) in liver specimens from NAFLD subjects, from a murine dietary NAFLD model, and in FFA-treated hepatic spheroids and hepatocytes.ResultsYAP-target gene expression correlated with increasing fibrosis stage in NAFLD patients and was associated with fibrosis in mice fed a NAFLD-inducing diet. Hepatocyte-specific YAP deletion in the murine NAFLD model attenuated diet-induced fibrosis, suggesting a causative role of YAP in NAFLD-related fibrosis. Likewise, in hepatic spheroids composed of Huh7 hepatoma cells and primary human hepatic stellate cells, Huh7 YAP silencing reduced FFA-induced fibrogenic gene expression. Notably, inhibition of p38 mitogen-activated protein kinase could block YAP activation in FFA-treated Huh7 cells.ConclusionsThese studies provide further evidence for the pathological role of YAP in NAFLD-associated fibrosis and that YAP activation in NAFLD may be driven by FFA-induced p38 MAPK activation.

YAP and AP-1 Cooperate to Initiate Pancreatic Cancer Development from Ductal Cells in Mice.

The development of pancreatic cancer is heavily dependent upon the aberrant activation of KRAS signaling. Among the downstream targets of KRAS, the effectors of the Hippo pathway YAP and TAZ (YAP/TAZ) are crucial during cancer initiation and progression. However, little is known about the cell type-specific effects of YAP/TAZ on the development of pancreatic cancer. Here we clarify the unique consequences of YAP/TAZ activation in the ductal cell population of the pancreas by generating mice with pancreatic duct cell-specific, inducible knockouts of Lats1 and Lats2, the main kinases upstream of YAP/TAZ. Oncogenic activation of YAP by deletion of Lats1/2 in ductal cells led to the rapid transformation of the pancreas, which was accompanied by a robust increase in the expression of YAP and AP-1 target genes. Pharmacologic inhibition of AP-1 activity induced death in Lats1/2 knockout organoids and attenuated YAP-dependent transformation of the pancreas in vivo. Both YAP and AP-1 were activated during the development of KRAS-dependent cancer in mice and human patients with pancreatic ductal adenocarcinoma, suggesting that this signaling hub represents an important mediator of pancreatic cancer development and progression. Collectively, these data define a YAP-dependent mechanism of pancreatic cancer cell development and suggest that inhibition of AP-1 can suppress this development. SIGNIFICANCE: A pancreatic ductal cell-specific knockout mouse model featuring constitutively active YAP allows for the study of YAP-dependent transformation of the pancreas and for screening pharmacologically active inhibitors.

Abstract 3691A: Targeting MARK2-HDAC-YAP signaling to overcome paclitaxel resistance in PDAC

Abstract Nanoparticle albumin-bound (Nab)-paclitaxel (taxol) combined with gemcitabine has been approved as a first-line chemotherapy for advanced pancreatic ductal adenocarcinoma (PDAC) patients. However, the response rate is still very low due to the occurrence of drug resistance and attempts in reversing the resistance have not been successful in the clinic. MARK (microtubule affinity-regulating kinase) proteins (MARK1-4) are critical for microtubule dynamics by modulating MAPs (microtubule-associated proteins). They are members of the AMPK/Snf1 family and control cell polarity and asymmetric cell division. Dysregulation of MARKs has also been associated with pathological conditions such as cancer and Alzheimer disease. Several recent studies showed that MARK family members are important regulators of Hippo-YAP (Yes-associated protein) signaling, which is critical in cancer development, drug resistance, and stem cell biology. Through Phos-tag-based kinome-wide screens, we identified MARK2 as a critical determinant for mitotic progression and paclitaxel chemosensitivity. MARK2 is phosphorylated by cyclin-dependent kinase 1 (CDK1) during paclitaxel-induced mitotic arrest and normal mitosis. MARK2 inhibition did not affect growth under normal conditions, but greatly sensitized PDAC cells to paclitaxel-induced apoptosis. Mechanistically, our findings also suggest that MARK2 controls paclitaxel chemosensitivity by regulating class IIa HDACs (histone deacetylase). MARK2 directly phosphorylates HDAC4 on multiple sites upon paclitaxel treatment. Inhibition (with knockdown or inhibitors) of HDACs significantly enhanced paclitaxel-induced cell death in a MARK2-phosphorylation dependent manner in PDAC cells. MARK2-phosphorylated HDAC4 positively regulates YAP (the transcriptional coactivator of the Hippo pathway) activity and controls expression of YAP target genes induced by paclitaxel. MARK2, class IIa HDACs, and YAP expression levels are upregulated and positively correlated in PDAC patients. Importantly, combination of HDAC inhibition (Vorinostat/SAHA, FDA-approved) and paclitaxel overcomes paclitaxel-resistance in preclinical PDAC animal models. Together, our findings reveal the MARK2-HDAC-YAP axis as a druggable target for overcoming paclitaxel resistance in PDAC. Citation Format: Yongji Zeng, Yuanhong Chen, Jixin Dong. Targeting MARK2-HDAC-YAP signaling to overcome paclitaxel resistance in PDAC [abstract]. In: Proceedings of the Annual Meeting of the American Association for Cancer Research 2020; 2020 Apr 27-28 and Jun 22-24. Philadelphia (PA): AACR; Cancer Res 2020;80(16 Suppl):Abstract nr 3691A.