Hippo Signaling Suppresses Cell Ploidy and Tumorigenesis through Skp2

Cellular feedback dynamics and multilevel regulation driven by the hippo pathway

The Hippo pathway is a dynamic cellular signalling nexus that regulates differentiation and controls cell proliferation and death. If the Hippo pathway is not precisely regulated, the functionality of the upstream kinase module is impaired, which increases nuclear localisation and activity of the central effectors, the transcriptional co-regulators YAP and TAZ. Pathological YAP and TAZ hyperactivity consequently cause cancer, fibrosis and developmental defects. The Hippo pathway controls an array of fundamental cellular processes, including adhesion, migration, mitosis, polarity and secretion of a range of biologically active components. Recent studies highlight that spatio-temporal regulation of Hippo pathway components are central to precisely controlling its context-dependent dynamic activity. Several levels of feedback are integrated into the Hippo pathway, which is further synergized with interactors outside of the pathway that directly regulate specific Hippo pathway components. Likewise, Hippo core kinases also ‘moonlight’ by phosphorylating multiple substrates beyond the Hippo pathway and thereby integrates further flexibility and robustness in the cellular decision-making process. This topic is still in its infancy but promises to reveal new fundamental insights into the cellular regulation of this therapeutically important pathway. We here highlight recent advances emphasising feedback dynamics and multilevel regulation of the Hippo pathway with a focus on mitosis and cell migration, as well as discuss potential productive future research avenues that might reveal novel insights into the overall dynamics of the pathway.

Coregulation of pathways in lung cancer patients with EGFR mutation: therapeutic opportunities

Epidermal growth factor receptor (EGFR) mutations in lung adenocarcinoma are a frequent class of driver mutations. Single EGFR tyrosine kinase inhibitor (TKI) provides substantial clinical benefit, but almost nil radiographic complete responses. Patients invariably progress, although survival can reach several years with post-treatment therapies, including EGFR TKIs, chemotherapy or other procedures. Endeavours have been clinically oriented to manage the acquisition of EGFR TKI-resistant mutations; however, basic principles on cancer evolution have not been considered in clinical trials. For years, evidence has displayed rapidly adaptive mechanisms of resistance to selective monotherapy, posing several dilemmas for the practitioner. Strict adherence to non-small cell lung cancer (NSCLC) guidelines is not always practical for addressing the clinical progression that EGFR-mutant lung adenocarcinoma patients suffer. The purpose of this review is to highlight regulatory mechanisms and signalling pathways that cause therapy-induced resistance to EGFR TKIs. It suggests combinatorial therapies that target EGFR, as well as potential mechanisms underlying EGFR-mutant NSCLC, alerting the reader to clinical opportunities that may lead to a deeper and more durable response. Molecular reprogramming contributes to EGFR TKI resistance, and the compiled information is relevant in understanding the development of new combined targeted strategies in EGFR-mutant NSCLC.

m6A Methyltransferase 3 Promotes the Proliferation and Migration of Gastric Cancer Cells through the m6A Modification of YAP1

Gastric cancer is the most common gastrointestinal tumor with an increasing incidence. Furthermore, advanced gastric cancer is more common, but the mechanism underlying the proliferation and metastasis of gastric cancer has not been thoroughly explored. N6-methyladenosine (m6A) methyltransferase 3 (METTL3) may be involved in the proliferation and metastasis of gastric cancer. Therefore, Yes-associated protein 1 (YAP1) in the Hippo pathway was selected as the target, and the relationship between METTL3 and the proliferation and metastasis of gastric cancer was proved through a series of experiments. This research showed that the expression of m6A and METTL3 was upregulated in human gastric cancer tissues and gastric cancer cell lines. After lentiviral transfection, METTL3 silencing in AGS (human gastric adenocarcinoma cell line AGS) and MKN-45 (human gastric cancer cell line MKN-45) gastric cancer cell lines directly inhibited the proliferation, aggressiveness, and migration of gastric cancer cells. Mechanically, the inhibition of the YAP1-TEAD signaling pathway by peptide 17 reduces m6A methylation and the total mRNA level of YAP1. It also eliminates the promoting effect of METTL3 on the proliferation and migration of gastric cancer cells. In turn, the overexpression of YAP1 eliminates the inhibitory effect of METTL3 silencing on the proliferation, migration, and invasion of gastric cancer cells. This article proved that m6A methyltransferase METTL3 promoted the proliferation and migration of gastric cancer cells through the m6A modification of YAP1.

Oncogenic PAX6 elicits CDK4/6 inhibitor resistance by epigenetically inactivating the LATS2-Hippo signaling pathway

Intrinsic resistance to CDK4/6 inhibitors hinders their clinical utility in cancer treatment. Furthermore, the predictive markers of CDK4/6 inhibitors in gastric cancer (GC) remain incompletely described. Here, we found that PAX6 expression was negatively correlated with the response to palbociclib in vitro and in vivo in GC. We observed that the PAX6 expression level was negatively correlated with the overall survival of GC patients and further showed that PAX6 can promote GC cell proliferation and the cell cycle. The cell cycle is regulated by the interaction of cyclins with their partner serine/threonine cyclin-dependent kinases (CDKs), and the G1/S-phase transition is the main target of CDK4/6 inhibitors. Therefore, we tested whether PAX6 expression was correlated with the GC response to palbociclib. We found that PAX6 hypermethylates the promoter of LATS2 and inactivates the Hippo pathway, which upregulates cyclin D1 (CCND1) expression. This results in a suppressed response to palbociclib in GC. Furthermore, we found that the induction of the Hippo signaling pathway or treatment with a DNA methylation inhibitor could overcome PAX6-induced palbociclib resistance in GC. These findings uncover a tumor promoter function of PAX6 in GC and establish overexpressed PAX6 as a mechanism of resistance to palbociclib.

Context-dependent effects of whole-genome duplication during mammary tumor recurrence

Whole-genome duplication (WGD) generates polyploid cells possessing more than two copies of the genome and is among the most common genetic abnormalities in cancer. The frequency of WGD increases in advanced and metastatic tumors, and WGD is associated with poor prognosis in diverse tumor types, suggesting a functional role for polyploidy in tumor progression. Experimental evidence suggests that polyploidy has both tumor-promoting and suppressing effects, but how polyploidy regulates tumor progression remains unclear. Using a genetically engineered mouse model of Her2-driven breast cancer, we explored the prevalence and consequences of whole-genome duplication during tumor growth and recurrence. While primary tumors in this model are invariably diploid, nearly 40% of recurrent tumors undergo WGD. WGD in recurrent tumors was associated with increased chromosomal instability, decreased proliferation and increased survival in stress conditions. The effects of WGD on tumor growth were dependent on tumor stage. Surprisingly, in recurrent tumor cells WGD slowed tumor formation, growth rate and opposed the process of recurrence, while WGD promoted the growth of primary tumors. These findings highlight the importance of identifying conditions that promote the growth of polyploid tumors, including the cooperating genetic mutations that allow cells to overcome the barriers to WGD tumor cell growth and proliferation.

Polyploid mitosis and depolyploidization promote chromosomal instability and tumor progression in a Notch-induced tumor model

Ploidy variation is a cancer hallmark and is frequently associated with poor prognosis in high-grade cancers. Using a Drosophila solid-tumor model where oncogenic Notch drives tumorigenesis in a transition-zone microenvironment in the salivary gland imaginal ring, we find that the tumor-initiating cells normally undergo endoreplication to become polyploid. Upregulation of Notch signaling, however, induces these polyploid transition-zone cells to re-enter mitosis and undergo tumorigenesis. Growth and progression of the transition-zone tumor are fueled by a combination of polyploid mitosis, endoreplication, and depolyploidization. Both polyploid mitosis and depolyploidization are error prone, resulting in chromosomal copy-number variation and polyaneuploidy. Comparative RNA-seq and epistasis analysis reveal that the DNA-damage response genes, also active during meiosis, are upregulated in these tumors and are required for the ploidy-reduction division. Together, these findings suggest that polyploidy and associated cell-cycle variants are critical for increased tumor-cell heterogeneity and genome instability during cancer progression.

Role of FGF15 in Hepatic Surgery in the Presence of Tumorigenesis: Dr. Jekyll or Mr. Hyde?

The pro-tumorigenic activity of fibroblast growth factor (FGF) 19 (FGF15 in its rodent orthologue) in hepatocellular carcinoma (HCC), as well as the unsolved problem that ischemia-reperfusion (IR) injury supposes in liver surgeries, are well known. However, it has been shown that FGF15 administration protects against liver damage and regenerative failure in liver transplantation (LT) from brain-dead donors without tumor signals, providing a benefit in avoiding IR injury. The protection provided by FGF15/19 is due to its anti-apoptotic and pro-regenerative properties, which make this molecule a potentially beneficial or harmful factor, depending on the disease. In the present review, we describe the preclinical models currently available to understand the signaling pathways responsible for the apparent controversial effects of FGF15/19 in the liver (to repair a damaged liver or to promote tumorigenesis). As well, we study the potential pharmacological use that has the activation or inhibition of FGF15/19 pathways depending on the disease to be treated. We also discuss whether FGF15/19 non-pro-tumorigenic variants, which have been developed for the treatment of liver diseases, might be promising approaches in the surgery of hepatic resections and LT using healthy livers and livers from extended-criteria donors.

Mutations and Copy Number Abnormalities of Hippo Pathway Components in Human Cancers

The Hippo pathway is highly conserved from Drosophila to mammals. As a key regulator of cell proliferation, the Hippo pathway controls tissue homeostasis and has a major impact on tumorigenesis. The originally defined core components of the Hippo pathway in mammals include STK3/4, LATS1/2, YAP1/TAZ, TEAD, VGLL4, and NF2. However, for most of these genes, mutations and copy number variations are relatively uncommon in human cancer. Several other recently identified upstream and downstream regulators of Hippo signaling, including FAT1, SHANK2, Gq/11, and SWI/SNF complex, are more commonly dysregulated in human cancer at the genomic level. This review will discuss major genomic events in human cancer that enable cancer cells to escape the tumor-suppressive effects of Hippo signaling.

Emerging Roles of SKP2 in Cancer Drug Resistance

More than half of all cancer patients receive chemotherapy, however, some of them easily acquire drug resistance. Resistance to chemotherapy has become a massive obstacle to achieve high rates of pathological complete response during cancer therapy. S-phase kinase-associated protein 2 (Skp2), as an E3 ligase, was found to be highly correlated with drug resistance and poor prognosis. In this review, we summarize the mechanisms that Skp2 confers to drug resistance, including the Akt-Skp2 feedback loop, Skp2-p27 pathway, cell cycle and mitosis regulation, EMT (epithelial-mesenchymal transition) property, enhanced DNA damage response and repair, etc. We also addressed novel molecules that either inhibit Skp2 expression or target Skp2-centered interactions, which might have vast potential for application in clinics and benefit cancer patients in the future.

SKP2-Promoted Ubiquitination of FOXO3 Promotes the Development of Asthma

Asthma is a respiratory disease with a dramatically increasing incidence globally. The present study explored the roles of S-phase kinase-associated protein 2 (SKP2) and forkhead box O3 (FOXO3) in asthma and their involvement in the Krüppel-like factor 15-lipoprotein receptor-related protein 5 (KLF15-LRP5) axis. SKP2 expression in patients with asthma and OVA-induced asthmatic Sprague Dawley rats was detected by reverse transcription quantitative PCR and Western blot assays. Alterations in SKP2 and LRP5 expression were evaluated in OVA-induced asthmatic rats, followed by measurement of inflammatory cytokines using ELISA and airway resistance using a methacholine challenge test. We applied TGF-β1 to establish the airway smooth muscle cell (ASMC) proliferation model of asthma. The FOXO3 ubiquitination and changes in cell biological behaviors were detected using immunoprecipitation, MTT, and Annexin V/propidium iodide assays. Flow cytometry was adopted to detect cell cycle, and ELISA was used to measure the concentrations of IL-4, IL-5, IL-13, and IgE in rat bronchoalveolar lavage fluid. SKP2 was highly expressed and FOXO3 was poorly expressed in patients with asthma and in OVA-induced asthmatic rats. SKP2 silencing decreased IL-4, IL-5, IL-13, and IgE expression in rat bronchoalveolar lavage fluid, whereas SKP2 enhanced FOXO3 ubiquitination to upregulate KLF15, which bound to the LRP5 promoter in TGF-β1-induced ASMCs and increased LRP5 expression. SKP2 enhanced airway hyperresponsiveness and inflammation in the OVA-induced rat model and augmented TGF-β1-induced ASMC proliferation by inhibiting the FOXO3/KLF15/LRP5 axis. Additionally, overexpressed SKP2 resulted in reduced numbers of ASMCs in the G1 phase but increased numbers in the G2/M phase. Collectively, we show that SKP2 promotes FOXO3 ubiquitination to suppress the KLF15-LRP5 axis, thereby exacerbating asthma.

The Hippo Pathway Effector YAP Promotes Ferroptosis via the E3 Ligase SKP2

Ferroptosis is a new form of regulated cell death resulting from the accumulation of lipid-reactive oxygen species. A growing number of studies indicate ferroptosis as an important tumor suppressor mechanism having therapeutic potential in cancers. Previously, we identified TAZ, a Hippo pathway effector, regulates ferroptosis in renal and ovarian cancer cells. Because YAP (Yes-associated protein 1) is the one and only paralog of TAZ, sharing high sequence similarity and functional redundancy with TAZ, we tested the potential roles of YAP in regulating ferroptosis. Here, we provide experimental evidence that YAP removal confers ferroptosis resistance, whereas overexpression of YAP sensitizes cancer cells to ferroptosis. Furthermore, integrative analysis of transcriptome reveals S-phase kinase-associated protein 2 (SKP2), an E3 ubiquitin ligase, as a YAP direct target gene that regulates ferroptosis. We found that the YAP knockdown represses the expression of SKP2. Importantly, the genetic and chemical inhibitions of SKP2 robustly protect cells from ferroptosis. In addition, knockdown of YAP or SKP2 abolishes the lipid peroxidation during erastin-induced ferroptosis. Collectively, our results indicate that YAP, similar to TAZ, is a determinant of ferroptosis through regulating the expression of SKP2. Therefore, our results support the connection between Hippo pathway effectors and ferroptosis with significant therapeutic implications. IMPLICATIONS: This study reveals that YAP promotes ferroptosis by regulating SKP2, suggesting novel therapeutic options for YAP-driven tumors.

Wound-induced polyploidization is dependent on Integrin-Yki signaling

A key step in tissue repair is to replace lost or damaged cells. This occurs via two strategies: restoring cell number through proliferation or increasing cell size through polyploidization. Studies in Drosophila and vertebrates have demonstrated that polyploid cells arise in adult tissues, at least in part, to promote tissue repair and restore tissue mass. However, the signals that cause polyploid cells to form in response to injury remain poorly understood. In the adult Drosophila epithelium, wound-induced polyploid cells are generated by both cell fusion and endoreplication, resulting in a giant polyploid syncytium. Here, we identify the integrin focal adhesion complex as an activator of wound-induced polyploidization. Both integrin and focal adhesion kinase are upregulated in the wound-induced polyploid cells and are required for Yorkie-induced endoreplication and cell fusion. As a result, wound healing is perturbed when focal adhesion genes are knocked down. These findings show that conserved focal adhesion signaling is required to initiate wound-induced polyploid cell growth.

The hepatic microenvironment promotes lung adenocarcinoma cell proliferation, metastasis, and epithelial-mesenchymal transition via METTL3-mediated N6-methyladenosine modification of YAP1

The inflammatory microenvironment plays an important role in the onset and progression of lung adenocarcinoma (LUAD), and the liver is a suitable site of metastasis for LUAD cells. However, whether the inflammatory microenvironment of the liver is conducive to the proliferation, invasion, and metastasis of LUAD cells remains unclear. In this study, we confirmed that the hepatic inflammatory microenvironment stimulated by IL-6 promoted the proliferation, migration, invasion, and epithelial–mesenchymal transition of LUAD cells, increased the m6A methylation of total RNA, and transcriptionally activated METTL3 expression. Additionally, METTL3 activated the YAP1/TEAD signaling pathway by increasing the m6A modification and expression of YAP1 mRNA. These results indicate that the hepatic inflammatory microenvironment plays a role in regulating the biological functions of LUAD cells. Further, our study identifies a molecular mechanism that may provide a new strategy for the early diagnosis, treatment, and prognosis of liver metastasis in LUAD patients.

Immuno-hippo: Research progress of the hippo pathway in autoimmune disease

Extensive research in Drosophila and mammals has identified the core components of Hippo signaling, which controls gene expression. Studies of Drosophila have demonstrated the highly conserved Hippo pathway controls tissue homeostasis and organ size by regulating the balance between cell proliferation and apoptosis. Recent work has indicated a potential role of the Hippo pathway in regulating the immune system, which is the key player in autoimmune disease (AID). Therefore, the Hippo pathway may become a novel target for curing AID. Although the pivotal role of both the Hippo pathway in tumorigenesis has been thoroughly investigated, the role of it in AID is still poorly understood. Elucidating the role of Hippo signaling pathways in the activation and expression of specific molecules involved in immune regulation is important for understanding the pathogenesis of AID and exploring novel therapeutic targets. To aid in further research, this review describes the relationship between the Hippo pathway and inflammatory signals such as NF-κB and JAK-STAT, the function of the Hippo pathway in the formation and differentiation of immune cells, and the regulatory role of the Hippo pathway in AID.

Centrosomal Localization of RXRα Promotes PLK1 Activation and Mitotic Progression and Constitutes a Tumor Vulnerability

Retinoid X receptor alpha (RXRα), a nuclear receptor of transcription factor, controls various physiological and pathological pathways including cellular growth, proliferation, differentiation, and apoptosis. Here, we report that RXRα is phosphorylated at its N-terminal A/B domain by cyclin-dependent kinase 1 (Cdk1) at the onset of mitosis, triggering its translocation to the centrosome, where phosphorylated-RXRα (p-RXRα) interacts with polo-like kinase 1 (PLK1) through its N-terminal A/B domain by a unique mechanism. The interaction promotes PLK1 activation, centrosome maturation, and mitotic progression. Levels of p-RXRα are abnormally elevated in cancer cell lines, during carcinogenesis in animals, and in clinical tumor tissues. An RXRα ligand XS060, which specifically inhibits p-RXRα/PLK1 interaction but not RXRα heterodimerization, promotes mitotic arrest and catastrophe in a tumor-specific manner. These findings unravel a transcription-independent action of RXRα at the centrosome during mitosis and identify p-RXRα as a tumor-specific vulnerability for developing mitotic drugs with improved therapeutic index.

Skp2 Deteriorates the Uterine Receptivity by Interacting with HOXA10 and Promoting its Degradation

Receptive endometrium plays a core role in successful embryo implantation, and about one-third of repeated embryo implantation failures are attributed to endometrial receptive defects. S-phase kinase-associated protein 2 (SKP2), a member of the F-box protein family, plays an important role in many cellular processes, including cell proliferation and apoptosis. However, its role in endometrial receptivity is still unclear. Here, we identified SKP2 was obviously upregulated in the patients with infertility. Functional study showed that SKP2 overexpression inhibited endometrial epithelial cell (EEC) proliferation, whereas SKP2 knockdown promoted the proliferation of EECs. In addition, the overexpression of SKP2 also repressed adhesion rate of embryonic cells to EECs. In vivo studies further suggested that the upregulation of SKP2 obviously suppressed endometrium receptivity formation and embryo implantation potential. Mechanistical study clarified that SKP2 directly interacted with HOXA10 and decreased protein stability through promoting the ubiquitin-mediated proteasome degradation of HOXA10. In conclusion, the current study documented that the high expression of SKP2 deteriorates endometrial receptivity formation by decreasing the HOXA10 expression and suggested that SKP2 may be defined as a marker of endometrial receptivity, and as a target for the diagnosis and treatment of infertility.

Emerging role of the Hippo pathway in autophagy

Autophagy is a dynamic circulatory system that occurs in all eukaryotic cells. Cytoplasmic material is transported to lysosomes for degradation and recovery through autophagy. This provides energy and macromolecular precursors for cell renewal and homeostasis. The Hippo-YAP pathway has significant biological properties in controlling organ size, tissue homeostasis, and regeneration. Recently, the Hippo-YAP axis has been extensively referred to as the pathophysiological processes regulating autophagy. Understanding the cellular and molecular basis of these processes is crucial for identifying disease pathogenesis and novel therapeutic targets. Here we review recent findings from Drosophila models to organisms. We particularly emphasize the regulation between Hippo core components and autophagy, which is involved in normal cellular regulation and the pathogenesis of human diseases, and its application to disease treatment.

Controversies Surrounding the Origin of Hepatocytes in Adult Livers and the in Vitro Generation or Propagation of Hepatocytes

Epithelial cells in the liver (known as hepatocytes) are high-performance engines of myriad metabolic functions and versatile responders to liver injury. As hepatocytes metabolize amino acids, alcohol, drugs, and other substrates, they produce and are exposed to a milieu of toxins and harmful byproducts that can damage themselves. In the healthy liver, hepatocytes generally divide slowly. However, after liver injury, hepatocytes can ramp up proliferation to regenerate the liver. Yet, on extensive injury, regeneration falters, and liver failure ensues. It is therefore critical to understand the mechanisms underlying liver regeneration and, in particular, which liver cells are mobilized during liver maintenance and repair. Controversies continue to surround the very existence of hepatic stem cells and, if they exist, their spatial location, multipotency, degree of contribution to regeneration, ploidy, and susceptibility to tumorigenesis. This review discusses these controversies. Finally, we highlight how insights into hepatocyte regeneration and biology in vivo can inform in vitro studies to propagate primary hepatocytes with liver regeneration-associated signals and to generate hepatocytes de novo from pluripotent stem cells.

Hepatic Hippo signaling inhibits development of hepatocellular carcinoma

Primary liver cancer is one of the most common cancer worldwide. Hepatocellular carcinoma (HCC) in particular, is the second leading cause of cancer deaths in the world. The Hippo signaling pathway has emerged as a major oncosuppressive pathway that plays critical roles inhibiting hepatocyte proliferation, survival, and HCC formation. A key component of the Hippo pathway is the inhibition of yes-associated protein (YAP)/transcriptional co-activator with PDZ-binding motif (TAZ) transcription factors by the Hippo kinase cascade. Aberrant activation of YAP or TAZ has been found in several human cancers including HCC. It is also well established that YAP/TAZ activation in hepatocytes causes HCC in mouse models, indicating that YAP/TAZ are potential therapeutic targets for human liver cancer. In this review, we summarize the recent findings regarding the multifarious roles of Hippo/YAP/TAZ in HCC development, and focus on their cell autonomous roles in controlling hepatocyte proliferation, differentiation, survival and metabolism as well as their non-cell autonomous in shaping the tumor microenvironment.

RASSF1A Suppresses Estrogen-Dependent Breast Cancer Cell Growth through Inhibition of the Yes-Associated Protein 1 (YAP1), Inhibition of the Forkhead Box Protein M1 (FOXM1), and Activation of Forkhead Box Transcription Factor 3A (FOXO3A)

The estrogen receptor alpha (ERα) is expressed by the majority of breast cancers and plays an important role in breast cancer development and tumor outgrowth. Although ERα is well known to be a specific and efficient therapeutic target, the molecular mechanisms that are responsible for the control of ERα expression and function in the context of breast cancer initiation and progression are complex and not completely elucidated. In previous work, we have demonstrated that the tumor suppressor RASSF1A inhibits ERα expression and function in ERα-positive breast cancer cells through an AKT-dependent mechanism. Transcriptional activators such as forkhead box protein M1 (FOXM1) and forkhead transcription factor 3A (FOXO3A) and signaling pathways such as the Hippo pathway are also known to modulate ERα expression and activity. Here we report that RASSF1A acts as an inhibitor of ERα-driven breast cancer cell growth through a complex, hierarchically organized network that initially involves suppression of the Hippo effector Yes-associated protein 1 (YAP1), which is followed by inhibition of AKT1 activity, increased FOXO3A activity as well as a blockade of FOXM1 and ERα expression. Together our findings provide important new mechanistic insights into how the loss of RASSF1A contributes to ERα+ breast cancer initiation and progression.

Polyploidy in liver development, homeostasis and disease

Polyploidy (or whole-genome duplication) is the condition of having more than two basic sets of chromosomes. Polyploidization is well tolerated in many species and can lead to specific biological functions. In mammals, programmed polyploidization takes place during development in certain tissues, such as the heart and placenta, and is considered a feature of differentiation. However, unscheduled polyploidization can cause genomic instability and has been observed in pathological conditions, such as cancer. Polyploidy of the liver parenchyma was first described more than 100 years ago. The liver is one of the few mammalian organs that display changes in polyploidy during homeostasis, regeneration and in response to damage. In the human liver, approximately 30% of hepatocytes are polyploid. The polyploidy of hepatocytes results from both nuclear polyploidy (an increase in the amount of DNA per nucleus) and cellular polyploidy (an increase in the number of nuclei per cell). In this Review, we discuss the regulation of polyploidy in liver development and pathophysiology. We also provide an overview of current knowledge about the mechanisms of hepatocyte polyploidization, its biological importance and the fate of polyploid hepatocytes during liver tumorigenesis.

Ectosomal PKM2 Promotes HCC by Inducing Macrophage Differentiation and Remodeling the Tumor Microenvironment

Tumor-derived extracellular vesicles are important mediators of cell-to-cell communication during tumorigenesis. Here, we demonstrated that hepatocellular carcinoma (HCC)-derived ectosomes remodel the tumor microenvironment to facilitate HCC progression in an ectosomal PKM2-dependent manner. HCC-derived ectosomal PKM2 induced not only metabolic reprogramming in monocytes but also STAT3 phosphorylation in the nucleus to upregulate differentiation-associated transcription factors, leading to monocyte-to-macrophage differentiation and tumor microenvironment remodeling. In HCC cells, sumoylation of PKM2 induced its plasma membrane targeting and subsequent ectosomal excretion via interactions with ARRDC1. The PKM2-ARRDC1 association in HCC was reinforced by macrophage-secreted cytokines/chemokines in a CCL1-CCR8 axis-dependent manner, further facilitating PKM2 excretion from HCC cells to form a feedforward regulatory loop for tumorigenesis. In the clinic, ectosomal PKM2 was clearly detected in the plasma of HCC patients. This study highlights a mechanism by which ectosomal PKM2 remodels the tumor microenvironment and reveals ectosomal PKM2 as a potential diagnostic marker for HCC.

The Impact of the Ubiquitin System in the Pathogenesis of Squamous Cell Carcinomas

The ubiquitin system is a dynamic regulatory pathway controlling the activity, subcellular localization and stability of a myriad of cellular proteins, which in turn affects cellular homeostasis through the regulation of a variety of signaling cascades. Aberrant activity of key components of the ubiquitin system has been functionally linked with numerous human diseases including the initiation and progression of human tumors. In this review, we will contextualize the importance of the two main components of the ubiquitin system, the E3 ubiquitin ligases (E3s) and deubiquitinating enzymes (DUBs), in the etiology of squamous cell carcinomas (SCCs). We will discuss the signaling pathways regulated by these enzymes, emphasizing the genetic and molecular determinants underlying their deregulation in SCCs.

The Hippo Pathway and YAP Signaling: Emerging Concepts in Regulation, Signaling, and Experimental Targeting Strategies With Implications for Hepatobiliary Malignancies

The Hippo pathway and its effector protein YAP (a transcriptional coactivator) have been identified as important in the biology of both hepatocellular carcinoma and cholangiocarcinoma. First identified as a tumor suppressor pathway in Drosophila, the understanding of the mammalian YAP signaling and its regulation continues to expand. In its "on" function, the canonical regulatory Hippo pathway, a well-described serine/threonine kinase module, regulates YAP function by restricting its subcellular localization to the cytoplasm. In contrast, when the Hippo pathway is "off," YAP translocates to the nucleus and drives cotranscriptional activity. Given the role of Hippo/YAP signaling in hepatic malignancies, investigators have sought to target these molecules; however, standard approaches have not been successful based on the pathways' negative regulatory role. More recently, additional regulatory mechanisms, such as tyrosine phosphorylation, of YAP have been described. These represent positive regulatory events that may be targetable. Additionally, several groups have identified potentiating feed-forward signaling for YAP in multiple contexts, suggesting other experimental therapeutic approaches to interrupt these signaling loops. Herein we explore the current data supporting alternative YAP regulatory pathways, review the described feed-forward signaling cascades that are YAP dependent, and explore targeting strategies that have been employed in preclinical models of hepatic malignancies.

Targeting Histone Deacetylase 6 Reprograms Interleukin-17-Producing Helper T Cell Pathogenicity and Facilitates Immunotherapies for Hepatocellular Carcinoma

BACKGROUND AND AIMS

Hepatocellular carcinoma (HCC) is often accompanied by resistance to immunotherapies despite the presence of tumor-infiltrating lymphocytes. We report that histone deacetylase 6 (HDAC6) represses interleukin-17 (IL-17)-producing helper T (TH 17) cell pathogenicity and the antitumor immune response, dependent on its deacetylase activity.

APPROACH AND RESULTS

Adoptive transfer of HDAC6-deficient TH 17 cells impedes HCC growth, dependent on elevated IL-17A, by enhancing the production of antitumor cytokine and cluster of differentiation 8-positive (CD8+) T cell-mediated antitumor responses. Intriguingly, HDAC6-depleted T cells trigger programmed cell death protein 1 (PD-1)-PD-1 ligand 1 expression to achieve a strong synergistic effect to sensitize advanced HCC to an immune checkpoint blocker, while blockade of IL-17A partially suppresses it. Mechanistically, HDAC6 limits TH 17 pathogenicity and the antitumor effect through regulating forkhead box protein O1 (FoxO1). HDAC6 binds and deacetylates cytosolic FoxO1 at K242, which is required for its nuclear translocation and stabilization to repress retinoic acid-related orphan receptor gamma (RoRγt), the transcription factor of TH 17 cell. This regulation of HDAC6 for murine and human TH 17 cell is highly conserved.

CONCLUSIONS

These results demonstrate that targeting the cytosolic HDAC6-FoxO1 axis reprograms the pathogenicity and antitumor response of TH 17 cells in HCC, with a pathogenicity-driven responsiveness to facilitate immunotherapies.

[Emerging roles of Hippo signaling pathway in gastrointestinal cancers and its molecular mechanisms]

Hippo signaling pathway is highly conservative in evolution. MST1/2, LATS1/2, and the effector protein YAP/TAZ are the core members of this signaling pathway in mammalian cells. There have been many studies on YAP/TAZ and its downstream, however, the upstream regulatory factors of the Hippo signaling pathway remain unclear, and become one of the hot research directions of this pathway at present. In addition, Hippo signaling pathway can cross-talk with other signaling pathways such as Wnt and Notch signaling pathways, and plays an important role in controlling organ size, maintaining tissue homeostasis, and promoting tissue repair and regeneration. Abnormal Hippo signaling pathway may lead to the occurrence of a variety of tumors, especially gastrointestinal cancers such as liver cancer, colorectal cancer and gastric cancer. The abnormal expression of its members in gastrointestinal cancers is related to cancer cell proliferation, apoptosis, invasion and migration. Hippo signaling pathway is vital for liver repair and regeneration. Its inactivation will lead to the occurrence of primary liver cancer. The mechanism of YAP in liver cancer mainly depends on TEAD-mediated gene transcription. Hippo signaling pathway is also important for maintaining intestinal homeostasis, and its imbalance can lead to the occurrence and recurrence of colorectal cancer. In primary and metastatic gastric cancer, the expression of YAP/TAZ is significantly up-regulated, but the specific molecular mechanism is unclear. This article summarizes the recent progress on Hippo signaling pathway and its upstream regulatory factors, its roles in the development of gastrointestinal cancers and related molecular mechanisms; and also discusses the future research directions of Hippo signaling pathway.

Correction of the tumor suppressor Salvador homolog-1 deficiency in tumors by lycorine as a new strategy in lung cancer therapy

Salvador homolog-1 (SAV1) is a tumor suppressor required for activation of the tumor-suppressive Hippo pathway and inhibition of tumorigenesis. SAV1 is defective in several cancer types. SAV1 deficiency in cells promotes tumorigenesis and cancer metastasis, and is closely associated with poor prognosis for cancer patients. However, investigation of therapeutic strategies to target SAV1 deficiency in cancer is lacking. Here we found that the small molecule lycorine notably increased SAV1 levels in lung cancer cells by inhibiting SAV1 degradation via a ubiquitin-lysosome system, and inducing phosphorylation and activation of the SAV1-interacting protein mammalian Ste20-like 1 (MST1). MST1 activation then caused phosphorylation, ubiquitination, and degradation of the oncogenic Yes-associated protein (YAP), therefore inhibiting YAP-activated transcription of oncogenic genes and tumorigenic AKT and NF-κB signal pathways. Strikingly, treating tumor-bearing xenograft mice with lycorine increased SAV1 levels, and strongly inhibited tumor growth, vasculogenic mimicry, and metastasis. This work indicates that correcting SAV1 deficiency in lung cancer cells is a new strategy for cancer therapy. Our findings provide a new platform for developing novel cancer therapeutics.

F-Box Proteins and Cancer

Controlled protein degradation is essential for the operation of a variety of cellular processes including cell division, growth, and differentiation. Identification of the relations between ubiquitin ligases and their substrates is key to understanding the molecular basis of cancer development and to the discovery of novel targets for cancer therapeutics. F-box proteins function as the substrate recognition subunits of S-phase kinase-associated protein 1 (SKP1)−Cullin1 (CUL1)−F-box protein (SCF) ubiquitin ligase complexes. Here, we summarize the roles of specific F-box proteins that have been shown to function as tumor promoters or suppressors. We also highlight proto-oncoproteins that are targeted for ubiquitylation by multiple F-box proteins, and discuss how these F-box proteins are deployed to regulate their cognate substrates in various situations.

Alternative Splicing in Hepatocellular Carcinoma

Hepatocellular carcinoma (HCC) accounts for the majority of primary liver cancer cases, with more than 850,000 new diagnoses per year globally. Recent trends in the United States have shown that liver cancer mortality has continued to increase in both men and women, while 5-year survival remains below 20%. Understanding key mechanisms that drive chronic liver disease progression to HCC can reveal new therapeutic targets and biomarkers for early detection of HCC. In that regard, many studies have underscored the importance of alternative splicing as a source of novel HCC prognostic markers and disease targets. Alternative splicing of pre-mRNA provides functional diversity to the genome, and endows cells with the ability to rapidly remodel the proteome. Genes that control fundamental processes, such as metabolism, cell proliferation, and apoptosis, are altered globally in HCC by alternative splicing. This review highlights the major splicing factors, RNA binding proteins, transcriptional targets, and signaling pathways that are of key relevance to HCC. We highlight primary research from the past 3-5 years involving functional interrogation of alternative splicing in rodent and human liver, using both large-scale transcriptomic and focused mechanistic approaches. Because this is a rapidly advancing field, we anticipate that it will be transformative for the future of basic liver biology, as well as HCC diagnosis and management.

LRPPRC sustains Yap-P27-mediated cell ploidy and P62-HDAC6-mediated autophagy maturation and suppresses genome instability and hepatocellular carcinomas

Mutants in the gene encoding mitochondrion-associated protein LRPPRC were found to be associated with French Canadian Type Leigh syndrome, a human disorder characterized with neurodegeneration and cytochrome c oxidase deficiency. LRPPRC interacts with one of microtubule-associated protein family MAP1S that promotes autophagy initiation and maturation to suppress genomic instability and tumorigenesis. Previously, although various studies have attributed LRPPRC nuclear acid-associated functions, we characterized that LRPPRC acted as an inhibitor of autophagy in human cancer cells. Here we show that liver-specific deletion of LRPPRC causes liver-specific increases of YAP and P27 and decreases of P62, leading to an increase of cell polyploidy and an impairment of autophagy maturation. The blockade of autophagy maturation and promotion of polyploidy caused by LRPPRC depletion synergistically enhances diethylnitrosamine-induced DNA damage, genome instability, and further tumorigenesis so that LRPPRC knockout mice develop more and larger hepatocellular carcinomas and survive a shorter lifespan. Therefore, LRPPRC suppresses genome instability and hepatocellular carcinomas and promotes survivals in mice by sustaining Yap-P27-mediated cell ploidy and P62-HDAC6-controlled autophagy maturation.

F-box proteins and cancer: an update from functional and regulatory mechanism to therapeutic clinical prospects

E3 ubiquitin ligases play a critical role in cellular mechanisms and cancer progression. F-box protein is the core component of the SKP1-cullin 1-F-box (SCF)-type E3 ubiquitin ligase and directly binds to substrates by various specific domains. According to the specific domains, F-box proteins are further classified into three sub-families: 1) F-box with leucine rich amino acid repeats (FBXL); 2) F-box with WD 40 amino acid repeats (FBXW); 3) F-box only with uncharacterized domains (FBXO). Here, we summarize the substrates of F-box proteins, discuss the important molecular mechanism and emerging role of F-box proteins especially from the perspective of cancer development and progression. These findings will shed new light on malignant tumor progression mechanisms, and suggest the potential role of F-box proteins as cancer biomarkers and therapeutic targets for future cancer treatment.

Paeoniflorin inhibits cell viability and invasion of liver cancer cells via inhibition of Skp2

Paeoniflorin (PF) has been demonstrated to exert tumor suppressive functions in various types of human cancer. However, the mechanisms of PF-mediated anti-tumor activity have not been fully elucidated. S-phase kinase associated protein 2 (Skp2) has been characterized as an oncoprotein that contributes to carcinogenesis. Therefore, the inhibition of Skp2 may be a useful approach for the treatment of various types of human cancer. The present study explored whether PF inhibited the expression of Skp2 in liver cancer cells, leading to cell viability inhibition, induction of apoptosis, and suppression of migration and invasion. PF treatment led to inhibition of Skp2 expression in liver cancer cells. The overexpression of Skp2 abolished PF-mediated anti-cancer activity, whereas the downregulation of Skp2 enhanced this type of activity. The data indicated that PF may be considered as a novel inhibitor of Skp2 in liver cancer cells.

Astrocytic YAP Promotes the Formation of Glia Scars and Neural Regeneration after Spinal Cord Injury

Yes-associated protein (YAP) transcriptional coactivator is negatively regulated by the Hippo pathway and functions in controlling the size of multiple organs, such as liver during development. However, it is not clear whether YAP signaling participates in the process of the formation of glia scars after spinal cord injury (SCI). In this study, we found that YAP was upregulated and activated in astrocytes of C57BL/6 male mice after SCI in a Hippo pathway-dependent manner. Conditional knockout (KO) of yap in astrocytes significantly inhibited astrocytic proliferation, impaired the formation of glial scars, inhibited the axonal regeneration, and impaired the behavioral recovery of C57BL/6 male mice after SCI. Mechanistically, the bFGF was upregulated after SCI and induced the activation of YAP through RhoA pathways, thereby promoting the formation of glial scars. Additionally, YAP promoted bFGF-induced proliferation by negatively controlling nuclear distribution of p27^Kip1 mediated by CRM1. Finally, bFGF or XMU-MP-1 (an inhibitor of Hippo kinase MST1/2 to activate YAP) injection indeed activated YAP signaling and promoted the formation of glial scars and the functional recovery of mice after SCI. These findings suggest that YAP promotes the formation of glial scars and neural regeneration of mice after SCI, and that the bFGF-RhoA-YAP-p27^Kip1 pathway positively regulates astrocytic proliferation after SCI.SIGNIFICANCE STATEMENT Glial scars play critical roles in neuronal regeneration of CNS injury diseases, such as spinal cord injury (SCI). Here, we provide evidence for the function of Yes-associated protein (YAP) in the formation of glial scars after SCI through regulation of astrocyte proliferation. As a downstream of bFGF (which is upregulated after SCI), YAP promotes the proliferation of astrocytes through negatively controlling nuclear distribution of p27^Kip1 mediated by CRM1. Activation of YAP by bFGF or XMU-MP-1 injection promotes the formation of glial scar and the functional recovery of mice after SCI. These results suggest that the bFGF-RhoA-YAP-p27^Kip1 axis for the formation of glial scars may be a potential therapeutic strategy for SCI patients.

The Skp2 Pathway: A Critical Target for Cancer Therapy

Strictly regulated protein degradation by ubiquitin-proteasome system (UPS) is essential for various cellular processes whose dysregulation is linked to serious diseases including cancer. Skp2, a well characterized component of Skp2-SCF E3 ligase complex, is able to conjugate both K48-linked ubiquitin chains and K63-linked ubiquitin chains on its diverse substrates, inducing proteasome mediated proteolysis or modulating the function of tagged substrates respectively. Overexpression of Skp2 is observed in various human cancers associated with poor survival and adverse therapeutic outcomes, which in turn suggests that Skp2 engages in tumorigenic activity. To that end, the oncogenic properties of Skp2 are demonstrated by various genetic mouse models, highlighting the potential of Skp2 as a target for tackling cancer. In this article, we will describe the downstream substrates of Skp2 as well as upstream regulators for Skp2-SCF complex activity. We will further summarize the comprehensive oncogenic functions of Skp2 while describing diverse strategies and therapeutic platforms currently available for developing Skp2 inhibitors.

Bile canaliculi remodeling activates YAP via the actin cytoskeleton during liver regeneration

The mechanisms of organ size control remain poorly understood. A key question is how cells collectively sense the overall status of a tissue. We addressed this problem focusing on mouse liver regeneration. Using digital tissue reconstruction and quantitative image analysis, we found that the apical surface of hepatocytes forming the bile canalicular network expands concomitant with an increase in F-actin and phospho-myosin, to compensate an overload of bile acids. These changes are sensed by the Hippo transcriptional co-activator YAP, which localizes to apical F-actin-rich regions and translocates to the nucleus in dependence of the integrity of the actin cytoskeleton. This mechanism tolerates moderate bile acid fluctuations under tissue homeostasis, but activates YAP in response to sustained bile acid overload. Using an integrated biophysical-biochemical model of bile pressure and Hippo signaling, we explained this behavior by the existence of a mechano-sensory mechanism that activates YAP in a switch-like manner. We propose that the apical surface of hepatocytes acts as a self-regulatory mechano-sensory system that responds to critical levels of bile acids as readout of tissue status.

Interaction of YAP1 and mTOR promotes bladder cancer progression

Yes‑associated protein 1 (YAP1) and mammalian target of rapamycin (mTOR) signaling pathways have been found to be deregulated in bladder cancer and accelerate the malignant progression of bladder cancer. However, the crosstalk between YAP1 and mTOR and its role in bladder cancer progression remains unclear. The aim of the present study was to investigate this crosstalk and the results revealed that the expression of YAP1 and mTOR was elevated in bladder cancer tissues compared with that in adjacent normal tissues. Knockdown of either mTOR or YAP1 with siRNA transfection significantly repressed the proliferation ability and induced apoptosis of HT‑1376 and J82 bladder cancer cells, particularly when YAP1 and mTOR were downregulated simultaneously. Upregulation of mTOR increased the mRNA and protein levels of YAP1 and enhanced its nuclear accumulation. In turn, YAP1 upregulation increased mTOR expression, reduced its protein degradation and increased its stability. In addition, immunofluorescence and Duolink assays demonstrated that YAP1 and mTOR were co‑localized in the nucleus. Immunoprecipitation assay demonstrated that the YAP1 protein was able to bind to the mTOR protein. Moreover, YAP1 combined with S‑phase kinase‑associated protein 2 (SKP2) and positively regulated its expression. Furthermore, the promotion of cell growth and inhibition of cell apoptosis induced by YAP1 overexpression were abolished when SKP2 was downregulated in HT‑1376 and J82 cells. Taken together, the findings of the present study indicated that the crosstalk between YAP1 and mTOR plays a pivotal role in accelerating the progression of bladder cancer, which may provide new insights into the role of the YAP1/mTOR axis in the occurrence and development of bladder cancer.

YAP promotes the proliferation of neuroblastoma cells through decreasing the nuclear location of p27Kip1 mediated by Akt

Objective

We aimed to investigate the roles and underlying mechanisms of YAP in the proliferation of neuroblastoma cells.

Methods

The expression level of YAP was evaluated by Western blotting and immunocytochemistry. Cell viability, cell proliferation and growth were detected by CCK‐8, PH3 and Ki67 immunostaining, and the real‐time cell analyser system. The nuclear and cytoplasmic proteins of p27^Kip1 were dissociated by the nuclear‐cytosol extraction kit and were detected by Western blotting and immunocytochemistry. mRNA levels of Akt, CDK5 and CRM1 were determined by qRT‐PCR.

Results

YAP was enriched in SH‐SY5Y cells (a human neuroblastoma cell line). Knock‐down of YAP in SH‐SY5Y cells or SK‐N‐SH cell line (another human neuroblastoma cell line) significantly decreased cell viability, inhibited cell proliferation and growth. Mechanistically, knock‐down of YAP increased the nuclear location of p27^Kip1, whereas serum‐induced YAP activation decreased the nuclear location of p27^Kip1 and was required for cell proliferation. Meanwhile, overexpression of YAP in these serum‐starved SH‐SY5Y cells decreased the nuclear location of p27^Kip1, promoted cell proliferation and overexpression of p27^Kip1 in YAP‐activated cells inhibited cell proliferation. Furthermore, knock‐down of YAP reduced Akt mRNA and protein levels. Overexpression of Akt in YAP‐downregulated cells decreased the nuclear location of p27^Kip1 and accelerated the proliferation of SH‐SY5Y cells.

Conclusions

Our studies suggest that YAP promotes the proliferation of neuroblastoma cells through negatively controlling the nuclear location of p27^Kip1 mediated by Akt.

The Hippo Pathway: Biology and Pathophysiology

The Hippo pathway was initially discovered in Drosophila melanogaster as a key regulator of tissue growth. It is an evolutionarily conserved signaling cascade regulating numerous biological processes, including cell growth and fate decision, organ size control, and regeneration. The core of the Hippo pathway in mammals consists of a kinase cascade, MST1/2 and LATS1/2, as well as downstream effectors, transcriptional coactivators YAP and TAZ. These core components of the Hippo pathway control transcriptional programs involved in cell proliferation, survival, mobility, stemness, and differentiation. The Hippo pathway is tightly regulated by both intrinsic and extrinsic signals, such as mechanical force, cell-cell contact, polarity, energy status, stress, and many diffusible hormonal factors, the majority of which act through G protein-coupled receptors. Here, we review the current understanding of molecular mechanisms by which signals regulate the Hippo pathway with an emphasis on mechanotransduction and the effects of this pathway on basic biology and human diseases.

HBX-induced miR-5188 impairs FOXO1 to stimulate β-catenin nuclear translocation and promotes tumor stemness in hepatocellular carcinoma

Cancer stem cells (CSCs) are the key factor in determining cancer recurrence, metastasis, chemoresistance and patient prognosis in hepatocellular carcinoma (HCC). The role of miR-5188 in cancer stemness has never been documented. In this study, we investigated the clinical and biological roles of miR-5188 in HCC. Methods: MiRNA expression in HCC was analyzed by bioinformatics analysis and in situ hybridization. The biological effect of miR-5188 was demonstrated in both in vitro and in vivo studies through the ectopic expression of miR-5188. The target gene and molecular pathway of miR-5188 were characterized using bioinformatics tools, dual-luciferase reporter assays, gene knockdown, and rescue experiments. Results: MiR-5188 was shown to be upregulated and confer poor prognosis in HCC patient data from TCGA database. MiR-5188 was subsequently identified as a significant inducer of cancer stemness that promotes HCC pathogenesis. Specifically, the targeting of miR-5188 by its antagomir markedly prolonged the survival time of HCC-bearing mice and improved HCC cell chemosensitivity in vivo. Mechanistic analysis indicated that miR-5188 directly targets FOXO1, which interacts with β-catenin in the cytoplasm to reduce the nuclear translocation of β-catenin and promotes the activation of Wnt signaling and downstream tumor stemness, EMT, and c-Jun. Moreover, c-Jun transcriptionally activates miR-5188 expression, forming a positive feedback loop. Interestingly, the miR-5188-FOXO1/β-catenin-c-Jun feedback loop was induced by hepatitis X protein (HBX) through Wnt signaling and participated in the HBX-induced pathogenesis of HCC. Finally, analyses of transcriptomics data and our clinical data supported the significance of the abnormal expression of the miR-5188 pathway in HCC pathogenesis. Conclusions: These findings present the inhibition of miR-5188 as a novel strategy for the efficient elimination of CSCs to prevent tumor metastasis, recurrence and chemoresistance in patients with hepatocellular carcinoma. Our study highlights the importance of miR-5188 as a tumor stemness inducer that acts as a potential target for HCC treatment.

Yorkie and JNK Control Tumorigenesis in Drosophila Cells with Cytokinesis Failure

Cytokinesis failure may result in the formation of polyploid cells, and subsequent mitosis can lead to aneuploidy and tumor formation. Tumor suppressor mechanisms limiting the oncogenic potential of these cells have been described. However, the universal applicability of these tumor-suppressive barriers remains controversial. Here, we use Drosophila epithelial cells to investigate the consequences of cytokinesis failure in vivo. We report that cleavage defects trigger the activation of the JNK pathway, leading to downregulation of the inhibitor of apoptosis DIAP1 and programmed cell death. Yorkie overcomes the tumor-suppressive role of JNK and induces neoplasia. Yorkie regulates the cell cycle phosphatase Cdc25/string, which drives tumorigenesis in a context of cytokinesis failure. These results highlight the functional significance of the JNK pathway in epithelial cells with defective cytokinesis and elucidate a mechanism used by emerging tumor cells to bypass this tumor-suppressive barrier and develop into tumors.

Non-canonical Hippo signaling regulates immune responses

The Hippo signaling pathway has been shown to play a pivotal role in controlling organ size and maintaining tissue homeostasis in multiple organisms ranging from Drosophila to mammals. Recently, we and others have demonstrated that Hippo signaling is also essential for maintaining the immune system homeostasis. Unlike the canonical Mst-Lats-Yap signal pathway, which controls tissue growth during development and regeneration, most studies regarding Hippo signaling in immune regulation is focusing in Mst1/2, the core kinases of Hippo signaling, cross-talking with other signaling pathways in various immune cells. In particular, patients bearing a loss-of-function mutation of Mst1 develop a complex immunodeficiency syndrome. Regarding the Hippo signaling in innate immunity, we have reported that Mst1/2 kinases are required for phagocytosis and efficient clearance of bacteria in phagocytes by regulating reactive oxygen species (ROS) production; and at the same time, by sensing the excessive ROS, Mst1/2 kinases maintain cellular redox homeostasis and prevent phagocytes aging and death through modulating the stability of the key antioxidant transcription factor Nrf2. In addition, we have revealed that the Mst1/2 kinases are critical in regulating T cells activation and Mst1/2-TAZ axis regulates the reciprocal differentiation of Treg cells and Th17 cells to modulate autoimmune inflammation by altering interactions between the transcription factors Foxp3 and RORγt. These results indicate that Hippo signaling maintains the balance between tolerance and inflammation of adaptive immunity.

Wound-induced polyploidization is driven by Myc and supports tissue repair in the presence of DNA damage

Tissue repair usually requires either polyploid cell growth or cell division, but the molecular mechanism promoting polyploidy and limiting cell division remains poorly understood. Here, we find that injury to the adult Drosophila epithelium causes cells to enter the endocycle through the activation of Yorkie-dependent genes (Myc and E2f1). Myc is even sufficient to induce the endocycle in the uninjured post-mitotic epithelium. As result, epithelial cells enter S phase but mitosis is blocked by inhibition of mitotic gene expression. The mitotic cell cycle program can be activated by simultaneously expressing the Cdc25-like phosphatase String (stg), while genetically depleting APC/C E3 ligase fizzy-related (fzr). However, forcing cells to undergo mitosis is detrimental to wound repair as the adult fly epithelium accumulates DNA damage, and mitotic errors ensue when cells are forced to proliferate. In conclusion, we find that wound-induced polyploidization enables tissue repair when cell division is not a viable option.

The Hippo Signaling Pathway in Regenerative Medicine

The major role of Hippo signaling is to inhibit their downstream effectors YAP/TAZ for organ size control during development and regeneration (Nat Rev Drug Discov 13(1):63-79, 2014; Dev Cell 19(4):491-505, 2010; Cell 163(4):811-828, 2015). We and others have demonstrated that the genetic disruption of kinases Mst1 and Mst2 (Mst1/2), the core components of Hippo signaling, results in YAP activation and sustained liver growth, thereby leading to an eight- to tenfold increase in liver size within 3 months and occurrence of liver cancer within 5 months (Curr Biol 17(23):2054-2060, 2007; Cancer Cell 16(5):425-438, 2009; Cell 130(6):1120-1133, 2007; Cancer Cell 31(5):669-684 e667, 2017; Nat Commun 6:6239, 2015; Cell Rep 3(5):1663-1677, 2013). XMU-MP-1, an Mst1/2 inhibitor, is able to augment mouse liver and intestinal repair and regeneration in both acute and chronic injury mouse models (Sci Transl Med 8:352ra108, 2016).In addition, YAP-deficient mice show an impaired intestinal regenerative response after DSS treatment or gamma irradiation (Proc Natl Acad Sci U S A 108(49):E1312-1320, 2011; Nature 493(7430):106-110, 2013; Genes Dev 24(21):2383-2388, 2010; J Vis Exp (111), 2010). IBS008738, a TAZ activator, facilitates muscle repair after cardiotoxin-induced muscle injury (Mol Cell Biol. 2014;34(9):1607-21). Deletion of Salvador (Sav) in mouse hearts enhances cardiomyocyte regeneration with reduced fibrosis and recovery of pumping function after myocardial infarction (MI) or resection of mouse cardiac apex (Development 140(23):4683-4690, 2013; Sci Signal 8(375):ra41, 2015; Nature 550(7675):260-264, 2017). This chapter provides a detailed description of procedures and important considerations when performing the protocols for the respective assays used to determine the effects of Hippo signaling on tissue repair and regeneration.

Aberrant methylation status of SPG20 promoter in hepatocellular carcinoma: A potential tumor metastasis biomarker

PURPOSE

The aim of this study is to analyze the methylation levels of SPG20 promotor region and explore the association between the methylation levels and clinical features in hepatocellular carcinoma (HCC).

MATERIALS AND METHODS

We collected paired of HCC and adjacent non-cancerous tissues (ANT) from 160 HCC patients and analyze the methylation levels through MassARRAY Analyzer 4. The statistical calculations were performed using SPSS version 22.0. Real-time-quantification PCR was performed to assess expression levels of SPG20 in HCC cell lines. Wound healing assay and transwell assay was used to measure cell migration capacity.

RESULT

We found that mean methylation level of SPG20 in tumor tissues was significantly higher than that in ANT (7.3% vs. 16.2%, P<0.0013). There was a significantly negative correlation between expression level and methylation level of SPG20 (P<0.01). In addition, the methylation levels in HCC were correlated with age and HBV infection. Meanwhile, micro-satellite tumors (P = 0.016) and tumor number (P = 0.018) was found significantly associated with increased methylation levels of several CpG sites and the mean levels of SPG20 promotor in ANT. In addtion, the capacity of cell migration was significantly enhanced in SPG20 knock-down HCC cells.

CONCLUSION

The hypermethylation status of SPG20 gene promoter is significantly associated with intra-hepatic metastasis and contribute to HCC metastasis.

Surviving Acute Organ Failure: Cell Polyploidization and Progenitor Proliferation

In acute organ failure, rapid compensation of function loss assures survival. Dedifferentiation and/or proliferation of surviving parenchymal cells could imply a transient (and potentially fatal) impairment of residual functional performance. However, evolution has selected two flexible life-saving mechanisms acting synergistically on organ function recovery. Sustaining residual performance is possible when the remnant differentiated parenchymal cells avoid cell division, but increase function by undergoing hypertrophy via endoreplication, leading to polyploid cells. In addition, tissue progenitors, representing a subset of less-differentiated and/or self-renewing parenchymal cells completing cytokinesis, proliferate and differentiate to regenerate lost parenchymal cells. Here, we review the evolving evidence on polyploidization and progenitor-driven regeneration in acute liver, heart, and kidney failure with evolutionary advantages and trade-offs in organ repair.

Oxidized low-density lipoprotein promotes vascular endothelial cell dysfunction by stimulating miR-496 expression and inhibiting the Hippo pathway effector YAP

Oxidized low‐density lipoprotein (ox‐LDL) can damage vascular endothelial cells and cause atherosclerosis, but its epigenetic regulatory mechanism has not been fully elucidated. We show that ox‐LDL induced significant apoptosis and loss of function in human umbilical vascular endothelial cells (HUVECs). At the same time, ox‐LDL significantly decreased the expression of Hippo–YAP/ZAP (Yes‐associated protein/YLP motif–containing 1) pathway proteins as compared to that of the control. The luciferase reporter system confirmed that microRNA (miR)‐496 silenced YAP gene expression by binding to its 3′ untranslated region (3′ UTR). Ox‐LDL–treated miR‐496 overexpression HUVECs had a higher apoptosis rate and more severe dysfunction compared to the control cells. This in‐depth study shows that ox‐LDL inhibits YAP protein expression by inducing miR‐496 expression, leading to its inability to enter the nucleus, thereby losing its function as a transcriptional cofactor for activating the downstream genes. Our findings reveal that, through epigenetic modification, ox‐LDL can inhibit the normal expression of Hippo–YAP/ZAP pathway proteins via miR‐496 expression and induce vascular endothelial cell dysfunction.

Yes-associated protein promotes cell migration via activating Wiskott-Aldrich syndrome protein family member 1 in oral squamous cell carcinoma

BACKGROUND

Yes-associated protein (YAP) is a candidate oncogene in various cancers including oral squamous cell carcinoma (OSCC). Our previous study demonstrated that TNF-alpha could inhibit cell proliferation and invasion by YAP phosphorylation in OSCC. However, the role of YAP in OSCC is not yet clear. The objective of the present study was to elucidate the function of YAP in promoting migration in OSCC and to explore the possible mechanism with a novel YAP inhibitor CA3.

METHODS

A total of 68 OSCC patients were enrolled, and the expression levels of YAP were investigated in tissue specimens by immunohistochemical staining. The inhibitory effects of CA3, a novel inhibitor of YAP, were demonstrated by immunofluorescence, Western blotting, and transwell assays. A human PCR motility array was performed to screen the changes in the gene expression profiles of the cells. In addition, shRNA interference, YAP re-expression, and WAVE1 overexpression plasmids were used to detect the regulatory mechanism of YAP and its relationship with cell migration.

RESULTS

Yes-associated protein nuclear expression levels were associated with metastasis and 5-year overall survival rate. CA3 exhibited potent inhibitory effects on OSCC migration. YAP knockdown significantly suppressed tumor cell migration in OSCC. These effects were rescued when YAP was re-expressed and during WAVE1 overexpression in YAP-shRNA stable cells.

CONCLUSIONS

The present study revealed that YAP was associated with cell migration and that this process was regulated by YAP/WAVE1. We also demonstrated that CA3 exhibited marked inhibitory effects on YAP expression and that it could be considered a potential therapeutic target for the treatment of OSCC.