The Hippo pathway promotes cell survival in response to chemical stress

The Hippo pathway terminal effector TAZ/WWTR1 mediates oxaliplatin sensitivity in p53 proficient colon cancer cells

YAP and TAZ, the Hippo pathway terminal transcriptional activators, are frequently upregulated in cancers. In tumor cells, they have been mainly associated with increased tumorigenesis controlling different aspects from cell cycle regulation, stemness, or resistance to chemotherapies. In fewer cases, they have also been shown to oppose cancer progression, including by promoting cell death through the action of the p73/YAP transcriptional complex, in particular after chemotherapeutic drug exposure. Using HCT116 cells, we show here that oxaliplatin treatment led to core Hippo pathway down-regulation and nuclear accumulation of TAZ. We further show that TAZ was required for the increased sensitivity of HCT116 cells to oxaliplatin, an effect that appeared independent of p73, but which required the nuclear relocalization of TAZ. Accordingly, Verteporfin and CA3, two drugs affecting the activity of YAP and TAZ, showed antagonistic effects with oxaliplatin in co-treatments. Importantly, using several colorectal cell lines, we show that the sensitizing action of TAZ to oxaliplatin is dependent on the p53 status of the cells. Our results support thus an early action of TAZ to sensitize cells to oxaliplatin, consistent with a model in which nuclear TAZ in the context of DNA damage and p53 activity pushes cells towards apoptosis.

From pixels to phenotypes: Integrating image-based profiling with cell health data as BioMorph features improves interpretability

Cell Painting assays generate morphological profiles that are versatile descriptors of biological systems and have been used to predict in vitro and in vivo drug effects. However, Cell Painting features extracted from classical software such as CellProfiler are based on statistical calculations and often not readily biologically interpretable. In this study, we propose a new feature space, which we call BioMorph, that maps these Cell Painting features with readouts from comprehensive Cell Health assays. We validated that the resulting BioMorph space effectively connected compounds not only with the morphological features associated with their bioactivity but with deeper insights into phenotypic characteristics and cellular processes associated with the given bioactivity. The BioMorph space revealed the mechanism of action for individual compounds, including dual-acting compounds such as emetine, an inhibitor of both protein synthesis and DNA replication. Overall, BioMorph space offers a biologically relevant way to interpret the cell morphological features derived using software such as CellProfiler and to generate hypotheses for experimental validation.

Hippo-YAP/TAZ signaling in breast cancer: Reciprocal regulation of microRNAs and implications in precision medicine

Breast cancer is a molecularly heterogeneous disease and the most common female malignancy. In recent years, therapy approaches have evolved to accommodate molecular diversity, with a focus on more biologically based therapies to minimize negative consequences. To regulate cell fate in human breast cells, the Hippo signaling pathway has been associated with the alpha subtype of estrogen receptors. This pathway regulates tissue size, regeneration, and healing, as well as the survival of tissue-specific stem cells, proliferation, and apoptosis in a variety of organs, allowing for cell differentiation. Hippo signaling is mediated by the kinases MST1, MST2, LATS1, and LATS2, as well as the adaptor proteins SAV1 and MOB. These kinases phosphorylate the downstream effectors of the Hippo pathway, yes-associated protein (YAP), and transcriptional coactivator with PDZ-binding motif (TAZ), suppressing the expression of their downstream target genes. The Hippo signaling pathway kinase cascade plays a significant role in all cancers. Understanding the principles of this kinase cascade would prevent the occurrence of breast cancer. In recent years, small noncoding RNAs, or microRNAs, have been implicated in the development of several malignancies, including breast cancer. The interconnections between miRNAs and Hippo signaling pathway core proteins in the breast, on the other hand, remain poorly understood. In this review, we focused on highlighting the Hippo signaling system, its key parts, its importance in breast cancer, and its regulation by miRNAs and other related pathways.

Proteomic analysis reveals oxidative stress-induced activation of Hippo signaling in thiamethoxam-exposed Drosophila

Thiamethoxam (THIA) is a widely used neonicotinoid insecticide. However, the toxicity and defense mechanisms activated in THIA-exposed insects are unclear. Here, we used isobaric tags for relative and absolute quantitation (iTRAQ) proteomics technology to identify changes in protein expression in THIA-exposed Drosophila. We found that the antioxidant proteins Cyp6a23 and Dys were upregulated, whereas vir-1 was downregulated, which may have been detoxification in response to THIA exposure. Prx5 downregulation promoted the generation of reactive oxygen species. Furthermore, the accumulation of reactive oxygen species led to the induction of antioxidant defenses in THIA-exposed Drosophila, thereby enhancing the levels of oxidative stress markers (e.g., superoxide dismutase, glutathione S-transferase, and glutathione) and reducing catalase expression. Furthermore, the Hippo signaling transcription coactivator Yki was inactivated by THIA. Our results suggesting that Hippo signaling may be necessary to promote insect survival in response to neonicotinoid insecticide toxicity.

TAZ upregulates MIR-224 to inhibit oxidative stress response in multiple myeloma

BACKGROUND

Oxidative stress within the bone marrow niche of multiple myeloma contributes to disease progression and drug resistance. Recent studies have associated the Hippo pathway with miRNA biogenesis and oxidative stress in solid tumors. Oxidative stress and miRNA pathway inter-relates in several cancers. Our group recently showed that TAZ functions as a tumor suppressor in MM. However, the role of TAZ in oxidative stress in MM is unknown.

AIMS

We sought to examine the role of TAZ in myeloma cells' response to BM oxidative stress. We postulated that TAZ might be associated with an oxidative stress phenotype and distinct miRNA signature in MM.

METHODS AND RESULTS

Using human myeloma cell lines and clinical samples, we demonstrate that TAZ promotes myeloma cells' sensitivity to oxidative stress and anticancer-induced cytotoxicity by inducing miR-224 to repress the NRF2 antioxidant program in MM. We show that low expression of TAZ protein confers an oxidative stress-resistant phenotype in MM. Furthermore, we provide evidence that overexpression of miR-224 in myeloma cells expressing low amounts of TAZ protein inhibits cell growth and enhances sensitivity to anti-myeloma therapeutics.

CONCLUSION

Our findings uncover a potential role for TAZ in oxidative stress response in MM via the miR-224-NRF2 molecular pathway. This provides the scientific ground to explore miR-224 as a potential molecular target to modify TAZ expression and enhance myeloma sensitivity to treatment.

Specific ablation of Hippo signalling component Yap1 in retinal progenitors and Müller cells results in late onset retinal degeneration

Yes-associated protein (YAP) is a major component of the Hippo pathway involved in development, growth, repair and homeostasis. Nonsense YAP1 mutations in humans result in autosomal dominant coloboma. Here, we generated a conditional knockout mouse model in which Yap1 was specifically deleted in embryonic retinal progenitor cells (RPCs) and in mature Müller cells using a Chx10-Cre driver. Our data demonstrated that the conditional ablation of Yap1 in embryonic RPCs does not prevent normal retinal development and caused no gross changes in retinal structure during embryonic and early postnatal life. Nevertheless, Yap1 deficient in retinal Müller cells in adult mice leads to impaired visual responses and extensive late-onset retinal degeneration, characterized by reduced cell number in all retinal layers. Immunofluorescence data further revealed the degeneration and death of rod and cone photoreceptors, bipolar cells, horizontal cells, amacrine cells and ganglion cells to varying degrees in aged knockout mice. Moreover, alteration of glial homeostasis and reactive gliosis were also observed. Finally, cell proliferation and TUNEL assay revealed that the broad retinal degeneration is mainly caused by enhanced apoptosis in late period. Together, this work uncovers that YAP is essential for the normal vision and retinal maintenance, highlighting the crucial role of YAP in retinal function and homeostasis.

Modulation of the cell membrane lipid milieu by peroxisomal β-oxidation induces Rho1 signaling to trigger inflammatory responses

Phagocytosis, signal transduction, and inflammatory responses require changes in lipid metabolism. Peroxisomes have key roles in fatty acid homeostasis and in regulating immune function. We find that Drosophila macrophages lacking peroxisomes have perturbed lipid profiles, which reduce host survival after infection. Using lipidomic, transcriptomic, and genetic screens, we determine that peroxisomes contribute to the cell membrane glycerophospholipid composition necessary to induce Rho1-dependent signals, which drive cytoskeletal remodeling during macrophage activation. Loss of peroxisome function increases membrane phosphatidic acid (PA) and recruits RhoGAPp190 during infection, inhibiting Rho1-mediated responses. Peroxisome-glycerophospholipid-Rho1 signaling also controls cytoskeleton remodeling in mouse immune cells. While high levels of PA in cells without peroxisomes inhibit inflammatory phenotypes, large numbers of peroxisomes and low amounts of cell membrane PA are features of immune cells from patients with inflammatory Kawasaki disease and juvenile idiopathic arthritis. Our findings reveal potential metabolic markers and therapeutic targets for immune diseases and metabolic disorders.

How do phosphodiesterase-5 inhibitors affect cancer? A focus on glioblastoma multiforme

Since the discovery of phosphodiesterase-5 (PDE5) enzyme overexpression in the central nervous system (CNS) malignancies, investigations have explored the potential capacity of current PDE5 inhibitor drugs for repositioning in the treatment of brain tumors, notably glioblastoma multiforme (GBM). It has now been recognized that these drugs increase brain tumors permeability and enhance standard chemotherapeutics effectiveness. More importantly, studies have highlighted the promising antitumor functions of PDE5 inhibitors, e.g., triggering apoptosis, suppressing tumor cell growth and invasion, and reversing tumor microenvironment (TME) immunosuppression in the brain. However, contradictory reports have suggested a pro-oncogenic role for neuronal cyclic guanosine monophosphate (cGMP), indicating the beneficial function of PDE5 in the brain of GBM patients. Unfortunately, due to the inconsistent preclinical findings, only a few clinical trials are evaluating the therapeutic value of PDE5 inhibitors in GBM treatment. Accordingly, additional studies should be conducted to shed light on the precise effect of PDE5 inhibitors in GBM biology regarding the existing molecular heterogeneities among individuals. Here, we highlighted and discussed the previously investigated mechanisms underlying the impacts of PDE5 inhibitors in cancers, focusing on GBM to provide an overview of current knowledge necessary for future studies.

Mechanosensing and the Hippo Pathway in Microglia: A Potential Link to Alzheimer's Disease Pathogenesis?

The activation of microglia, the inflammatory cells of the central nervous system (CNS), has been linked to the pathogenesis of Alzheimer’s disease and other neurodegenerative diseases. How microglia sense the changing brain environment, in order to respond appropriately, is still being elucidated. Microglia are able to sense and respond to the mechanical properties of their microenvironment, and the physical and molecular pathways underlying this mechanosensing/mechanotransduction in microglia have recently been investigated. The Hippo pathway functions through mechanosensing and subsequent protein kinase cascades, and is critical for neuronal development and many other cellular processes. In this review, we examine evidence for the potential involvement of Hippo pathway components specifically in microglia in the pathogenesis of Alzheimer’s disease. We suggest that the Hippo pathway is worth investigating as a mechanosensing pathway in microglia, and could be one potential therapeutic target pathway for preventing microglial-induced neurodegeneration in AD.

Genome-Wide Identification and Functional Prediction of Long Non-coding RNAs Involved in the Heat Stress Response in Metarhizium robertsii

Long non-coding RNAs (lncRNAs) play a significant role in stress responses. To date, only a few studies have reported the role of lncRNAs in insect-pathogenic fungi. Here, we report a genome-wide transcriptional analysis of lncRNAs produced in response to heat stress in Metarhizium robertsii, a model insect-pathogenic fungus, using strand-specific RNA sequencing. A total of 1655 lncRNAs with 1742 isoforms were identified, of which 1081 differentially expressed (DE) lncRNAs were characterized as being heat responsive. By characterizing their genomic structures and expression patterns, we found that the lncRNAs possessed shorter transcripts, fewer exons, and lower expression levels than the protein-coding genes in M. robertsii. Furthermore, target prediction analysis of the lncRNAs revealed thousands of potential DE lncRNA–messenger RNA (mRNA) pairs, among which 5381 pairs function in the cis-regulatory mode. Further pathway enrichment analysis of the corresponding cis-regulated target genes showed that the targets were significantly enriched in the following biological pathways: the Hippo signaling pathway and cell cycle. This finding suggested that these DE lncRNAs control the expression of their corresponding neighboring genes primarily through environmental information processing and cellular processes. Moreover, only 26 trans-regulated lncRNA–mRNA pairs were determined. In addition, among the targets of heat-responsive lncRNAs, two classic genes that may be involved in the response to heat stress were also identified, including hsp70 (XM_007821830 and XM_007825705). These findings expand our knowledge of lncRNAs as important regulators of the response to heat stress in filamentous fungi, including M. robertsii.

Effects of Spaceflight and Simulated Microgravity on YAP1 Expression in Cardiovascular Progenitors: Implications for Cell-Based Repair

Spaceflight alters many processes of the human body including cardiac function and cardiac progenitor cell behavior. The mechanism behind these changes remains largely unknown; however, simulated microgravity devices are making it easier for researchers to study the effects of microgravity. To study the changes that take place in cardiac progenitor cells in microgravity environments, adult cardiac progenitor cells were cultured aboard the International Space Station (ISS) as well as on a clinostat and examined for changes in Hippo signaling, a pathway known to regulate cardiac development. Cells cultured under microgravity conditions, spaceflight-induced or simulated, displayed upregulation of downstream genes involved in the Hippo pathway such as YAP1 and SOD2. YAP1 is known to play a role in cardiac regeneration which led us to investigate YAP1 expression in a sheep model of cardiovascular repair. Additionally, to mimic the effects of microgravity, drug treatment was used to induce Hippo related genes as well as a regulator of the Hippo pathway, miRNA-302a. These studies provide insight into the changes that occur in space and how the effects of these changes relate to cardiac regeneration studies.

On-Chip Cell Incubator for Simultaneous Observation of Culture with and without Periodic Hydrostatic Pressure

This paper proposes a microfluidic device which can perform simultaneous observation on cell growth with and without applying periodic hydrostatic pressure (Yokoyama et al. Sci. Rep.2017, 7, 427). The device is called on-chip cell incubator. It is known that culture with periodic hydrostatic pressure benefits the elasticity of a cultured cell sheet based on the results in previous studies, but how the cells respond to such a stimulus during the culture is not yet clear. In this work, we focused on cell behavior under periodic hydrostatic pressure from the moment of cell seeding. The key advantage of the proposed device is that we can compare the results with and without periodic hydrostatic pressure while all other conditions were kept the same. According to the results, we found that cell sizes under periodic hydrostatic pressure increase faster than those under atmospheric pressure, and furthermore, a frequency-dependent fluctuation of cell size was found using Fourier analysis.

Comprehensive Molecular Characterization of the Hippo Signaling Pathway in Cancer

Hippo signaling has been recognized as a key tumor suppressor pathway. Here, we perform a comprehensive molecular characterization of 19 Hippo core genes in 9,125 tumor samples across 33 cancer types using multidimensional "omic" data from The Cancer Genome Atlas. We identify somatic drivers among Hippo genes and the related microRNA (miRNA) regulators, and using functional genomic approaches, we experimentally characterize YAP and TAZ mutation effects and miR-590 and miR-200a regulation for TAZ. Hippo pathway activity is best characterized by a YAP/TAZ transcriptional target signature of 22 genes, which shows robust prognostic power across cancer types. Our elastic-net integrated modeling further reveals cancer-type-specific pathway regulators and associated cancer drivers. Our results highlight the importance of Hippo signaling in squamous cell cancers, characterized by frequent amplification of YAP/TAZ, high expression heterogeneity, and significant prognostic patterns. This study represents a systems-biology approach to characterizing key cancer signaling pathways in the post-genomic era.

Alternative Splicing in the Hippo Pathway-Implications for Disease and Potential Therapeutic Targets

Alternative splicing is a well-studied gene regulatory mechanism that produces biological diversity by allowing the production of multiple protein isoforms from a single gene. An involvement of alternative splicing in the key biological signalling Hippo pathway is emerging and offers new therapeutic avenues. This review discusses examples of alternative splicing in the Hippo pathway, how deregulation of these processes may contribute to disease and whether these processes offer new potential therapeutic targets.

p53 shades of Hippo

The three p53 family members, p53, p63 and p73, are structurally similar and share many biochemical activities. Yet, along with their common fundamental role in protecting genomic fidelity, each has acquired distinct functions related to diverse cell autonomous and non-autonomous processes. Similar to the p53 family, the Hippo signaling pathway impacts a multitude of cellular processes, spanning from cell cycle and metabolism to development and tumor suppression. The core Hippo module consists of the tumor-suppressive MST-LATS kinases and oncogenic transcriptional co-effectors YAP and TAZ. A wealth of accumulated data suggests a complex and delicate regulatory network connecting the p53 and Hippo pathways, in a highly context-specific manner. This generates multiple layers of interaction, ranging from interdependent and collaborative signaling to apparent antagonistic activity. Furthermore, genetic and epigenetic alterations can disrupt this homeostatic network, paving the way to genomic instability and cancer. This strengthens the need to better understand the nuances that control the molecular function of each component and the cross-talk between the different components. Here, we review interactions between the p53 and Hippo pathways within a subset of physiological contexts, focusing on normal stem cells and development, as well as regulation of apoptosis, senescence and metabolism in transformed cells.

Increased YAP Activation Is Associated With Hepatic Cyst Epithelial Cell Proliferation in ARPKD/CHF

Autosomal recessive polycystic kidney disease/congenital hepatic fibrosis (ARPKD/CHF) is a rare but fatal genetic disease characterized by progressive cyst development in the kidneys and liver. Liver cysts arise from aberrantly proliferative cholangiocytes accompanied by pericystic fibrosis and inflammation. Yes-associated protein (YAP), the downstream effector of the Hippo signaling pathway, is implicated in human hepatic malignancies such as hepatocellular carcinoma, cholangiocarcinoma, and hepatoblastoma, but its role in hepatic cystogenesis in ARPKD/CHF is unknown. We studied the role of the YAP in hepatic cyst development using polycystic kidney (PCK) rats, an orthologous model of ARPKD, and in human ARPKD/CHF patients. The liver cyst wall epithelial cells (CWECs) in PCK rats were highly proliferative and exhibited expression of YAP. There was increased expression of YAP target genes, Ccnd1 (cyclin D1) and Ctgf (connective tissue growth factor), in PCK rat livers. Extensive expression of YAP and its target genes was also detected in human ARPKD/CHF liver samples. Finally, pharmacological inhibition of YAP activity with verteporfin and short hairpin (sh) RNA-mediated knockdown of YAP expression in isolated liver CWECs significantly reduced their proliferation. These data indicate that increased YAP activity, possibly through dysregulation of the Hippo signaling pathway, is associated with hepatic cyst growth in ARPKD/CHF.

Retinal Degeneration Triggers the Activation of YAP/TEAD in Reactive Müller Cells

Purpose

During retinal degeneration, Müller glia cells respond to photoreceptor loss by undergoing reactive gliosis, with both detrimental and beneficial effects. Increasing our knowledge of the complex molecular response of Müller cells to retinal degeneration is thus essential for the development of new therapeutic strategies. The purpose of this work was to identify new factors involved in Müller cell response to photoreceptor cell death.

Methods

Whole transcriptome sequencing was performed from wild-type and degenerating rd10 mouse retinas at P30. The changes in mRNA abundance for several differentially expressed genes were assessed by quantitative RT-PCR (RT-qPCR). Protein expression level and retinal cellular localization were determined by western blot and immunohistochemistry, respectively.

Results

Pathway-level analysis from whole transcriptomic data revealed the Hippo/YAP pathway as one of the main signaling pathways altered in response to photoreceptor degeneration in rd10 retinas. We found that downstream effectors of this pathway, YAP and TEAD1, are specifically expressed in Müller cells and that their expression, at both the mRNA and protein levels, is increased in rd10 reactive Müller glia after the onset of photoreceptor degeneration. The expression of Ctgf and Cyr61, two target genes of the transcriptional YAP/TEAD complex, is also upregulated following photoreceptor loss.

Conclusions

This work reveals for the first time that YAP and TEAD1, key downstream effectors of the Hippo pathway, are specifically expressed in Müller cells. We also uncovered a deregulation of the expression and activity of Hippo/YAP pathway components in reactive Müller cells under pathologic conditions.